High Performance Technical Textiles

Edited by

Roshan Paul University of Beira Interior, Portugal This edition first published 2019 © 2019 John Wiley & Sons Ltd All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of Roshan Paul to be identified as the author of the editorial material in this work has been asserted in accordance with law.

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Library of Congress Cataloging‐in‐Publication Data Names: Paul, Roshan. Title: High performance technical textiles / edited by Roshan Paul, University of Beira Interior, Portugal. Description: First edition. | Hoboken, NJ, USA : Wiley, [2019] | Includes bibliographical references and index. | Identifiers: LCCN 2018049413 (print) | LCCN 2018050917 (ebook) | ISBN 9781119325055 (AdobePDF) | ISBN 9781119325031 (ePub) | ISBN 9781119325017 (hardcover) Subjects: LCSH: Industrial fabrics. | Geotextiles. | Synthetic fabrics. Classification: LCC TS1770.I53 (ebook) | LCC TS1770.I53 H54 2019 (print) | DDC 677/.6–dc23 LC record available at https://lccn.loc.gov/2018049413

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Contents

List of Contributors xi

1 High Performance Technical Textiles: An Overview 1 Roshan Paul 1.1 Introduction 1 1.2 Application Areas of Technical Textiles 1 1.3 Technical Textiles by Functional Finishing 2 1.4 High Performance Technical Textiles 3 1.5 Conclusion 9

2 Household and Packaging Textiles 11 Pelagia Glampedaki 2.1 Introduction 11 2.2 Textile Materials, Properties, and Manufacturing 11 2.3 High Performance Applications 20 2.4 Testing Methods and Quality Control 23 2.5 Sustainability and Ecological Aspects 26 2.6 Conclusion 32 References 32

3 Sports Textiles and Comfort Aspects 37 Ali Harlin, Kirsi Jussila, and Elina Ilen 3.1 Introduction 37 3.2 Textile Fibres 37 3.3 Developments in Yarns 42 3.4 Developments in Fabric Structures 43 3.5 Special Finishes 45 3.6 High Performance Applications 46 3.7 Active Textiles 57 3.8 Smart Textiles and Garments 58 3.9 Testing Methods and Quality Control 61 3.10 Sustainability and Ecological Aspects 62 3.11 Conclusion 62 References 62 vi Contents

4 Medical and Healthcare Textiles 69 Nuno Belino, Raul Fangueiro, Sohel Rana, Pelagia Glampedaki, and Georgios Priniotakis 4.1 Introduction 69 4.2 Textile Materials, Structures, and Processes 70 4.3 High Performance Applications of Medical Textiles 72 4.4 Nanotechnology in Medicine and Healthcare 76 4.5 Thermo‐Physiological Comfort of Medical Textiles 81 4.6 Biocompatibility – Bioresorbability – Biostability 83 4.7 Intelligent Medical and Healthcare Textiles 85 4.8 Antimicrobial Textiles 93 4.9 Testing Methods and Quality Control 95 4.10 Sustainability and Ecological Aspects 98 4.11 Conclusion 100 References 100

5 Textile Materials for Protective Textiles 107 Ningtao Mao 5.1 Introduction 107 5.2 Performance Requirements of Protective Textiles 109 5.3 High Performance Fibres 110 5.4 High Performance Textile Materials 115 5.5 Thermal Burden and Thermo‐Physiological Comfort 131 5.6 Testing Methods and Standards 138 5.7 Sustainability and Ecological Issues 148 5.8 Conclusion 148 References 149

6 Personal Protective Textiles and Clothing 159 Sumit Mandal, Simon Annaheim, Martin Camenzind, and René M. Rossi 6.1 Introduction 159 6.2 General Aspects of Textile Based PPC 160 6.3 Fibres for PPC 162 6.4 Yarns for PPC 167 6.5 Fabrics for PPC 173 6.6 PPC Fabrication 183 6.7 Key Issues Related to PPC 187 6.8 Conclusion 189 References 189

7 Textiles for Military and Law Enforcement Personnel 197 Christopher Malbon and Debra Carr 7.1 Introduction 197 7.2 Ballistic and Sharp Weapon Protection 197 7.3 Protection from Heat and Flames 203 7.4 Chemical, Biological, Radiological, and Nuclear (CBRN) Protective Clothing 206 Contents vii

7.5 Functional Finishing 210 7.6 Conclusion 210 References 211

8 Industrial and Filtration Textiles 215 Tawfik A. Khattab and Hany Helmy 8.1 Introduction 215 8.2 Synthetic and Nanotechnical Fibres 216 8.3 Natural Fibres for Technical Applications 219 8.4 Manufacture of Technical Textiles 221 8.5 Functional Finishing 225 8.6 Textile Reinforced Composite Materials 227 8.7 High Performance Applications 228 8.8 Testing Methods and Quality Control 229 8.9 Sustainability and Ecological Aspects 232 8.10 Conclusion 233 References 234

9 Geotextiles and Environmental Protection Textiles 239 Jiří Militký, Rajesh Mishra, and Mohanapriya Venkataraman 9.1 Introduction 239 9.2 Structure and Performance 240 9.3 Fibres for Geotextiles 243 9.4 Geotextiles and Soil 254 9.5 Manufacturing Techniques 260 9.6 Sustainability and Ecological Aspects 272 9.7 Conclusion 274 References 275

10 Agrotextiles and Crop Protection Textiles 279 Adriana Restrepo‐Osorio, Catalina Álvarez‐López, Natalia Jaramillo‐Quiceno, and Patricia Fernández‐Morales 10.1 Introduction 279 10.2 Fibres for Agrotextiles 280 10.3 Textile Structures for Agrotextiles 284 10.4 High Performance Applications 285 10.5 Testing Standards Applicable to Agrotextiles 295 10.6 Sustainability and Ecological Aspects 311 10.7 Conclusion 312 References 313

11 Building and Construction Textiles 319 Jordan Tabor and Tushar Ghosh 11.1 Introduction 319 11.2 Architectural Textiles 320 11.3 House Wraps 327 11.4 Insulation 334 viii Contents

11.5 Textile Reinforced Concrete 341 11.6 Sustainability and Ecological Issues 347 11.7 Conclusion 349 References 349

12 Automotive Textiles and Composites 353 Bijoy K. Behera 12.1 Introduction 353 12.2 Mobiltech 354 12.3 Application Areas of Automotive Textiles 355 12.4 Textile Composites for Automobiles 369 12.5 3D Fabrics for Automotive Applications 372 12.6 Comfort Properties of Automotive Interior 376 12.7 Conclusion 379 References 380

13 Marine Textiles and Composites 385 Chi‐wai Kan and Change Zhou 13.1 Introduction 385 13.2 Textiles for Marine Applications 385 13.3 Properties of Textiles for Marine Applications 394 13.4 Marine Textiles and Quality Standards 397 13.5 Sustainability and Ecological Aspects 403 13.6 Conclusion 403 Acknowledgement 403 References 403

14 Aeronautical and Space Textiles 407 Sadaf A. Abbasi, Lijing Wang, Mazhar H. Peerzada, and Raj Ladani 14.1 Introduction 407 14.2 Synthetic and Nanotechnical Fibres 408 14.3 Natural and Bast Fibres for Technical Applications 413 14.4 Manufacture of Technical Textiles 415 14.5 Textile Reinforced Composite Materials 420 14.6 Textile Composite Material Finishing 425 14.7 High Performance Applications 426 14.8 Testing Methods and Quality Control 428 14.9 Self‐Healing of Composite Materials 431 14.10 Sustainability and Ecological Aspects 432 14.11 Conclusion 432 References 433

15 Wearable and Smart Responsive Textiles 439 Lihua Lou, Weijie Yu, and Seshadri Ramkumar 15.1 Introduction 439 15.2 Characterization of Smart Textiles 440 15.3 Smart Textiles Grouped by Function 440 Contents ix

15.4 Application of Smart Textiles 453 15.5 Sustainability and Ecological Aspects 462 15.6 Conclusion 464 Acknowledgements 464 References 464

Index 475

List of Contributors

Sadaf A. Abbasi Debra Carr School of Engineering Defense and Security RMIT University Accelerator, Dstl Melbourne Wiltshire Australia United Kingdom

Catalina Álvarez‐López Raul Fangueiro Universidad Pontificia Bolivariana University of Minho Medellín Guimarães Colombia Portugal

Simon Annaheim Patricia Fernández‐Morales Laboratory for Biomimetic Membranes Universidad Pontificia Bolivariana and Textiles Medellín Empa - Swiss Federal Laboratories Colombia for Materials Science and Technology St Gallen Tushar Ghosh Switzerland North Carolina State University Raleigh Bijoy K. Behera North Carolina Indian Institute of Technology Delhi USA New Delhi India Pelagia Glampedaki Social Fashion Factory – SOFFA Nuno Belino Athens University of Beira Interior Greece Covilhã Portugal Ali Harlin VTT Technical Research Centre Martin Camenzind of Finland Ltd Laboratory for Biomimetic Espoo Membranes and Textiles Finland Empa - Swiss Federal Laboratories for Materials Science and Technology St Gallen Switzerland xii List of Contributors

Hany Helmy Christopher Malbon Textile Research Division Centre for Defence Engineering National Research Centre Cranfield University Cairo Shrivenham Egypt United Kingdom

Elina Ilen Sumit Mandal School of Arts, Design and Architecture Laboratory for Biomimetic Membranes Aalto University and Textiles Espoo Empa - Swiss Federal Laboratories for Finland Materials Science and Technology St Gallen Natalia Jaramillo‐Quiceno Switzerland Universidad Pontificia Bolivariana Medellín Ningtao Mao Colombia School of Design University of Leeds Kirsi Jussila Leeds Finnish Institute of Occupational Health United Kingdom Oulu Finland Jiří Militký Department of Material Engineering Chi‐wai Kan Faculty of Textile Engineering Institute of Textiles and Clothing Technical University of Liberec The Hong Kong Polytechnic University Liberec Kowloon Czech Republic Hong Kong Rajesh Mishra Tawfik A. Khattab Department of Material Engineering Textile Research Division Faculty of Textile Engineering National Research Centre Technical University of Liberec Cairo Liberec Egypt Czech Republic

Raj Ladani Roshan Paul School of Engineering University of Beira Interior RMIT University Covilhã Melbourne Portugal Australia Mazhar H. Peerzada Lihua Lou Department of Textile Engineering Nonwovens & Advanced Materials Mehran University of Engineering & Laboratory Technology Texas Tech University Jamshoro Lubbock Pakistan USA List of Contributors xiii

Georgios Priniotakis Jordan Tabor Technological Education Institute North Carolina State University of Piraeus Raleigh Egaleo North Carolina Greece USA

Seshadri Ramkumar Mohanapriya Venkataraman Nonwovens & Advanced Materials Department of Material Engineering Laboratory Faculty of Textile Engineering Texas Tech University Technical University of Liberec Lubbock Liberec USA Czech Republic

Sohel Rana Lijing Wang University of Minho School of Fashion and Textiles Guimarães RMIT University Portugal Brunswick Australia Adriana Restrepo‐Osorio Universidad Pontificia Bolivariana Weijie Yu Medellín Nonwovens & Advanced Materials Colombia Laboratory Texas Tech University René M. Rossi Lubbock Laboratory for Biomimetic Membranes USA and Textiles Empa - Swiss Federal Laboratories for Change Zhou Materials Science and Technology College of Textile & Clothing St Gallen Jiangnan University Switzerland Wuxi China

High Performance Technical Textiles: An Overview Roshan Paul

University of Beira Interior, Covilhã, Portugal

1.1 Introduction

Technical textiles provide technical, functional, and performance properties, unlike textiles used in the fashion, artistic, or decorative sectors. These include textiles for households, packaging, sports, medical, protection, military, filtration, geotextiles, agriculture, construction, automotive, marine, aeronautic, and other smart applications. Synthetic as well as nanofibres – like aramid, polyolefin, polyamide, polyester (PES), viscose, glass, and ceramic fibres – are widely used for the manufacture of technical textiles. Nanofibre nonwovens can also improve the properties of textiles designed for technical applications. Natural and bast fibres like jute, flax, hemp, coir, ramie, kenaf, and abaca are also finding applications as technical textiles for environmental reasons. They are gaining increasing importance particularly as fibre reinforced composites in automotive, construction, aerospace, and packaging industries. This is mainly due to the fact that bast fibres offer good tensile strength and stiffness compared to synthetic fibres such as polyamide, carbon, and aramid. Besides, they originate from renewable natural resources and are environmentally friendly.

1.2 Application Areas of Technical Textiles

In general, application areas of technical textiles are classified as: ●● Hometech. Carpet components, furniture components, consumer and industrial wipes, air and water filtration, interior design, drapes, covers, ticking, composites, etc. ●● Packtech. Bulk packaging with a predefined three‐dimensional (3D) structure, scrap and disposable, spacer and tying, absorbent food pads, etc. ●● Sporttech. Luggage components, sports equipment, sportswear, wipes, covers, disposable, and camping equipment, etc. ●● Medtech. Drapes and gowns, sterile wrap, swabs and dressing, cleaning products, cover stock, wound care, protective apparel, bedding and sheets and masks, etc.

●● Protech. Chemical and biological protection, particulate protection, flame retardant, cut resistant, shields and gowns worn in emergency situations, chemical handling, hazardous waste control, cleaning, filtration, etc. ●● Clothtech. Cleanroom garments, shoe components, insulation and structure, sewing products, interlining, leather goods applications, etc. ●● Indutech. Electrical components, filtration and separation, satellite dishes, clothing surfacing tissues/veils, conveyor belts, reinforced plastics, polyvinyl chloride (PVC) substrates, flame barriers, noise absorbents, battery separators, antislip matting, lifting and pulling, etc. ●● Geotech. Asphalt overlay, soil stabilization, drainage, sedimentation and erosion control, pond liner, impregnation base, drainage channel liners, separation, reinforcement, filtration, offshore land reclamation, roadside, railside, river and canal banks, reservoirs, etc. ●● Oekotech. Environmental protection, exhaust air and waste water filtration, dust collection, oil and fuel absorbent, gas and odour removal, etc. ●● Agrotech. Crop covers, seed blankets, weed control fabrics, greenhouse shading, root bags, biodegradable plant pots, capillary matting cover, protection and collection, fishing, etc. ●● Buildtech. Roofing and tile underlay, underslating, thermal and noise insulation, house wrap, facings for plaster board, pipe wrap, concrete moulding layers, foundations and ground stabilization, vertical drainage, protection and display, textile construction, building components, reinforcements, high quality wallpapers, etc. ●● Mobiltech. Boot liners, parcel shelves, heat shields, shelf trim, moulded bonnet liners, boot floor covering, fuel/oil filters, headliners, rear parcel shelves, airbags, cabin air filters, engine intake and exhaust air filters, silencer pads, insulation materials, car covers, under padding, car mats, tapes, backing for tufted carpets, seat covers, door trim and insulation, floor coverings, protection, composites, etc.

1.3 Technical Textiles by Functional Finishing

It is a general concept that technical textiles are manufactured using technical fibres, with inherent technical properties. But innovative functional finishes are creating possibilities for developing functional technical textiles by a simple finish application at the end of the textile manufacturing process. The modification of commodity fibre and fabric properties by innovative finishes can be a cheaper route to high performance than by using high cost fibres with inherent built in performance properties. In a textile industry, finishing is usually done in the final stage of textile processing. A wide variety of functional properties can be created on textiles by means of chemical or bio finishing and also it is possible to develop multifunctional textiles. With the advent of nanotechnology, a new area has developed in the realm of textile finishing. Nanotechnology is opening new avenues in chemical finishing, resulting either in improved processes or in helping to achieve new functional properties, which were not possible with conventional finishes. Thus, the application of nanotechnology creates an expanded array of functional properties enabling textiles to be used in novel materials and products. Unlike in conventional finishing, the nanometric size of the coating will not affect negatively the hand and feel of the finished fabric. 1.4 High Performance Technical Textiles 3

The low temperature sol–gel techniques, as well as the new generation of polymeric resins, are offering new possibilities in textile chemical finishing. Another important development is the plasma enhanced chemical vapour deposition (PECVD) technique. It is a finishing process which can be used to deposit thin solid polymeric films from a gas state to a solid state on a textile substrate to achieve the desired properties. The advantage of such plasma treatments is that the modification turns out to be restricted to the uppermost layers of the substrate, thus not affecting the overall bulk properties. In general, plasma treatment can be considered as a dry alternative to the wet chemical treatments and so they are environmentally friendly. Layer by layer (LbL) assembly method is another new finishing technique by which ultrathin composite films can be developed on solid surfaces like textiles. It involves an LbL adsorption of polycations and polyanions to build a multilayer ultrathin polyelectrolyte coating on a textile substrate.

1.4 High Performance Technical Textiles

This book on high performance technical textiles covers almost all the important areas of technical textiles. The book starts with household and packaging textiles, hi‐tech sports textiles, and medical textiles. Further, it focuses on the protective aspects, with chapters on protective textiles, personal protective clothing, and military textiles. Industrial and filtration textiles, geotextiles, and agrotextiles are dealt with in the subsequent chapters. Important application areas like construction, automotive, marine, aeronautic, and space are covered in the following chapters. The last chapter talks exclusively about smart and responsive textiles.

1.4.1 Household and Packaging Textiles

Textiles have become an integral part of the home, both in daily use and in household installations. Household textiles include carpets, sheets, pillow cases, pillows, blankets and quilts, bedspreads, table linens, bathroom and kitchen towels, bathmats, shower curtains, readymade and custom made curtains, draperies, slipcovers, and other furniture protectors. They make life more comfortable and give home interiors a defined aesthetic characteristic. Technological innovations have converted conventional household textiles into high performance textiles by improving their durability and by adding multiple functionalities, thus allowing them to follow trends in line with e‐textiles, combining sustainable materials for easier disposal and reuse, and incorporating nanotechnology into everyday personal items. Hollow fibres with good insulation properties are broadly employed in bedding and sleeping bags. Other categories of fibre are increasingly being utilized to substitute foams in furniture because of the fear of fire and of health hazards created by such materials. Packaging textiles include all textile packing material for industrial, agricultural, and other goods. Lightweight nonwoven and knitted materials are widely used for various wrapping and protection purposes, particularly in foodstuff industries. Growing environmental concern over reusable packages and containers is opening new opportunities for textile products in this area. Textiles have helped high performance packaging 4 1 High Performance Technical Textiles: An Overview

to advance as they can be engineered to have very strong weaving structures while being lightweight and more sustainable than conventional packaging materials. High performance textiles along with modern materials handling methods have permitted the innovation of more proficient handling, storing, and distribution of various powdered and granular merchandise varying from fertilizers, sand, cement, sugar, and flour to dyes and pigments. Packaging textiles have also entered a new era of active and intelligent systems which interact with their content and inform the consumer about spoilage risks or products’ nonconformity.

1.4.2 Sports Textiles

Traditional applications of sports textiles are in high activity outdoor athletics, team sports, as well in less active games, for example golf. Further, they are also used in highly visible applications, including textiles for balloons, parachutes, paragliders, and sail- cloth. Sportswear has also become leisure and casual clothing. High performance sports textiles are widely used in shoes, sports equipment, winter and summer sports, flying and sailing sports, climbing, angling, and cycling. Functional sportswear has a new look as lifestyle wear, and accordingly sportswear is functionally modified and fashion elements are added to meet these new requirements. High performance sports textiles are manufactured using sophisticated raw materials and technology. The performance fibres, yarns, fabrics, and functional finishes developed for the sports sector are increasingly transferring the sportswear to the mass market in the high street. Sports textiles are also specially designed to take moisture away from the body, and attached with sensors to identify high impact stresses on joints, heart rate, temperature, and other physiological data. All these developments have made the choice of materials more pronounced and selection of them more complicated. This leads to balancing properties and functionalities with user and maintenance friendliness.

1.4.3 Medical Textiles

Medical textiles are one of the important areas within technical textiles and the use of textile materials for medical and healthcare products ranges from simple uniforms or gauze or bandage materials to scaffolds for tissue culturing and a large variety of pros- theses for permanent body implants. It should provide barrier properties, comfort and water vapour transmission, along with the required mechanical properties. Disposability is the main reason hospitals and operating rooms prefer nonwovens over woven fabrics. Generally, medical nonwovens offer unique antimicrobial solutions and provide increased protection for the user and have less potential for cross‐contamination. Nonwovens used in gauze swab should absorb exudates, protect from external contamination, cushion from further trauma and have good air permeability. High performance medical textiles are in constant demand, owing to their major expansion into fields like wound healing and controlled release, bandaging and pressure garments, implantable devices, as well as medical devices, and development of new intelligent textile products. Medical textiles are clearly driving the emergence of new and improved raw materials and processes, leading to new technological solutions specifically designed to tackle the problems medical professionals and patients are daily 1.4 High Performance Technical Textiles 5 faced with. At present, high performance medical textiles have the potential to substantially change the way patients receive medical assistance/services. Despite not being very common, the awareness of these intelligent textile systems is rising along with the number of marketed medical products.

1.4.4 Protective Textiles

Protective textiles are the technical textile materials used in the manufacturing of a wide variety of protective clothing (personal protective equipment [PPE]) for people working in hazardous situations. The diversity of protective textiles includes safety against cuts, impacts, abrasion, stabs, explosions, flame, foul weathering, severe high or low temperatures, high voltage, harmful dust and particles, and nuclear, biological, chemical, and hazardous materials. Natural fibres, specific synthetic fibres, high performance fibres, nanofibres, and other functional materials all demonstrate excellent performances in either protection or comfort of protective clothing in various environmental conditions. A combination of those high performance functional textile materials in engineered structures would help achieve desirable functionalities in specific applications. Protective textile products have been in constant demand and the main driving force is the increasing emphasis on the reduction of occupational hazards and assurance of the health, safety, and protection of the workforce. The constant revision of legislation, governmental policies, and standards has encouraged stakeholders to take initiatives to introduce accountable measures and equipment in the prevention of hazardous events and accidents at worksites.

1.4.5 Personal Protective Clothing

Protective clothing is generally designed to enhance the worker’s safety, by complying to the requirements stipulated by international regulatory bodies. Clothing plays an important role in protecting human beings from their surrounding environments. High performance PPE is widely used as advanced protective clothing – like coats, trousers, vests, etc. and body armour products like helmets, masks, aprons, gloves, socks, shoes, etc. – to protect the human body from environmental hazards. The hazards addressed by protective equipment include physical, electrical, heat, chemical, biohazards, and airborne particulate matter. PPE is also required to protect human beings from various natural hazards such as wind, cold air, rain, flash fire, etc. Protective equipment may be worn for job related occupational safety and health purposes, as well as for sports and other recreational activities. Thus, the main purpose of PPE is to reduce human exposure to hazards when engineering controls and administrative controls are not feasible or effective to reduce these risks to acceptable levels. PPE is expected to possess high thermal protective performance under a thermal or fire hazard. At the same time, it should effectively regulate the metabolic heat and sweat vapour from the wearer’s body to their surrounding environment, and this regulation will provide high thermo‐physiological comfort to the wearer. Along with this functional performance, it should also possess some aesthetic features like appropriate colours and printed designs. 6 1 High Performance Technical Textiles: An Overview

1.4.6 Military Textiles

Textiles for military uniforms face a complex set of challenges as they must provide protection, durability, and comfort in a wide range of hostile environments. Military and police forces are two sectors where protection and performance are paramount, as they are faced with diverse threats routinely in their employment. The main threats are ballistic, sharp weapon, flame, and chemical, biological, radiological, and nuclear (CBRN). Clothing and uniforms in these lines of work must offer a large variety of essential properties, from flexibility and breathability, to fire retardancy and body armour level protection. There is always a compromise between the protection offered by a clothing system and the ability to complete the task, i.e. between survivability and mobility. The optimum design of high performance protective clothing systems requires subject matter expert knowledge of the threats faced, the tasks to be completed, the anthropometric properties of the persons to be protected, the fabrics that might be used, integration with other fabrics and equipment, and knowledge of appropriate clothing manufacturing techniques and test methods.

1.4.7 Industrial and Filtration Textiles

Industrial textiles are widely used for chemical, mechanical, and electrical engineering purposes, such as filtration, plasma screens, lifting machines, transportation, sound proofing, roller covering, grinding equipment, insulation, and fuel cells. These textiles are generally strongly woven with high tenacity PES and/or polyamide yarns. This area of technical textiles offers solutions and products for different industries like paper, carbon, metal, ceramic, glass fibre, plastic, etc. High performance industrial textiles play a major role in filtration media and are widely employed to separate and clean industrial goods, gases, and effluents. A wide variety of fibres, DREF yarns, nonwoven fabrics, multifilament and monofilament woven fabrics, and in some cases blends or combinations of more than one of the above are used in filtration applications. Depending on the filtration purpose, several requirements and standards must be fulfilled for the production of filters. Sometimes it is required to merge different filtration media to better fit the application’s requirements, such as filter fabric and membrane.

1.4.8 Geotextiles and Environmental Protection Textiles

Geotextiles are permeable fabrics, and when used in association with soil have the ability to separate, filter, reinforce, protect, or drain. They are widely used in supporting embankments, bridges, and drainage systems. They are also employed for soil reinforcement, erosion control, and filters. Typically made from polypropylene (PP) or PES, geotextile fabrics come in three basic forms: woven, needle punched, or heat bonded. Geotextile composites have also been developed, and products such as geogrids and meshes are available commercially. A woven geotextile could be manufactured from monofilament, multifilament, or fibrillated fibres. A nonwoven geotextile could be fabricated from either continuous filaments or staple fibres. Nonwovens resistant to tear, soil chemicals, puncture, UV light exposure, mildew, rot, freeze/thaw conditions, etc. are an ideal choice for high performance geotextile applications. 1.4 High Performance Technical Textiles 7

Each configuration of geotextiles like geonets, geosynthetic clay liners, geogrids, geotextile tubes, etc. are able to yield benefits in geotechnical and environmental engineering design. The three main properties which are required and specified for geotextiles are mechanical responses, filtration ability, and chemical resistance. They should be able to withstand several high stress situations, be durable, and be able to soften an undesired fall. The environmental protection textiles are widely used for protection of environment and ecology. This is not a well‐defined sector yet, though it overlaps with numerous other application areas of technical textiles. They are also used for environmental protection such as floor sealing, erosion protection, oil spill management, air and water filters, and waste handling.

1.4.9 Agrotextiles

Agrotextiles offer advantages like flexibility, breathability, and greater ease of installation as compared to polymer films and are widely used for crop protection and for promoting crop development. The most important requirements of agrotextiles are weather resistance and resistance to microorganisms, in order to protect the plants against temperature extremes by day and by night. They are characterized by strength, elongation, stiffness, porosity, sunlight and toxic environment protection, and biodegradation. The use of agrotextiles to improve the conditions under which crops are grown or developed is increasing. They include all the woven, nonwoven, and knitted fabrics applied for agricultural and horticultural uses including livestock protection, shading, weed and insect control, and extension of the growing season. Lightweight spunbonded fleeces are employed for a range of products such as shading, thermal insulating, and weed suppression. Heavyweight nonwoven, knitted, and woven textiles are used for wind and hail shelters. Capillary nonwoven mats are employed for horticulture to spread moisture to rising plants. The type of fibre used in the development of high performance agrotextiles is important to ensure that the textile fulfils its protective functions efficiently and that it will withstand the environmental conditions. As the synthetic fibres such as PP, polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA) comply with these requirements, these fibres have been for many years the primary option for producing agrotextiles; however, these fibres are not biodegradable and have a significant impact on the environment once their useful life ends. New production techniques, the advancement of modern materials, and the use of ecological bast fibres have led to the development of sustainable high performance agrotextiles. These additional performance features can increase the productivity and quality of agricultural goods and thus help to effectively tackle the growing challenges currently experienced by the agricultural sector.

1.4.10 Building and Construction Textiles

Textiles in fibre, yarn, or fabric form combine excellent strength, resilience, and flexibility with low weight, resulting in desirable construction materials for multitudinous functions and appearances. They should offer mechanical properties such as lightness, strength, and resilience as well as resistance to many factors such as creep, degradation 8 1 High Performance Technical Textiles: An Overview

by chemicals and pollutants in the air or rain, and other construction material, as well as the effects of sunlight and acid. Construction textiles are widely employed in building construction, including textile reinforced concrete, house wrap, frontispiece, interior structures, sun protection, heat and noise insulation, water‐ and fireproofing, air conditioning, wall reinforcement, aesthetic, safety, sewer and pipe, and linings. They are also used for temporary constructions such as tents, marquees, and awnings. Such temporary use textile materials should be characterized by lightweight, strength, rot resistance, sunlight protective, flame retardant, and weatherproof. The application of new sustainable materials with high performance properties, together with a better understanding of textile structures and their mechanics, has led to new applications of these materials in construction. Architectural fabric structures are becoming an integral part of commercial construction, because of their energy efficiency and potential for creating a form of architecture. Similarly, insulation and house wraps are being improved to offer more efficient, comfortable, and sustainable structures.

1.4.11 Automotive Textiles

Automotive textiles are that area of technical textiles which are widely used in transportation vehicles and systems, including cars, trains, buses, ships, and aeroplanes. These textiles range from seats, carpets, belts, tyres, hose reinforcement, and air bags to reinforced composites for automotive and aircraft bodies, filters, battery separators, wings, and engine components, etc. Among all these applications, the major part constitutes seat upholstery and roof covering. They should not only cover isolation and safety aspects but also focus on comfort, style, and a wide range of functionalities. Other applications include solutions for engineering problems in the form of composites, tyre reinforcement, sound insulation, and vibration control. Textile reinforced composites and 3D woven solid structures are now widely used in the automotive sector replacing metallic parts, thus leading to weight reduction and fuel efficiency. Increasing complexity of product specifications and the requirement of high performance end uses have led to the adoption of sustainable, lightweight, durable, low cost, and more accurately engineered yarns, textiles, and nonwovens in the automotive sector.

1.4.12 Marine Textiles

As in other application areas, textiles are used in functional as well as decorative applications in the marine industry. Marine textiles play an integral role on every vessel, from protection to upholstery. They are the preferred choice for making hoods, tarpaulins, protective covers, rear closures, but also for decorating and boat furnishings. Textile reinforced composites are being increasingly used for navigational aids. Marine textiles are specialized technical textiles because of the high performance specifications and special properties required. Marine textiles have to withstand a much higher exposure to sunlight, seawater, and potential damage from ultraviolet radiation. In addition, safety features like flame retardant behaviour are crucial, and weight reduction and antifouling are also other important technical requirements. Owing to the 1.5 Conclusion 9 highly aggressive environment, marine textiles developed from natural and synthetic materials are then reinforced with different functional materials and techniques. In a marine environment, the comfort, design, and appearance of textiles are important for providing users with a relaxing atmosphere. In order to satisfy the high performance requirements, numerous advanced materials and technologies are being developed for marine applications.

1.4.13 Aeronautic and Space Textiles

From clothing to complicated aeroplane parts, textiles are found everywhere in aircraft. Aeronautic and space textiles include specially crafted lightweight structures as well as engineered textiles. The application of high performance textile composites in space shuttles and other aerospace products needs to be completely defect free. The use of textile reinforced composites reduces fuel consumption in aircraft and space shuttles, without any compromise on the strength. These products are mainly manufactured with high performance textile fibres, which require additional properties as compared to conventional fibres. Apart from aircraft applications, textile structures are widely used in the manufacturing of specialized space suits. Various new materials are used for making the space suit, including fabrics made from different functional polymers. Typically, the innermost layer of the suit is made up of a nylon tricot material, the second layer is manufactured with spandex which gives elasticity in the suit, and the next layer is made up of urethane coated nylon. Thermo‐physiological comfort aspects are also considered while designing the spacesuits.

1.4.14 Smart and Responsive Textiles

Active and responsive textile materials providing functional and high performance properties are generally termed smart textiles. Smart textiles are thus the textile materials or products that can discern and deduce changes in their surroundings and respond appropriately. Smart textiles act as both sensors and actuators and thus stand differently from the other existing multifunctional textiles that behave as mere passive materials with enhanced properties. Major end uses of high performance smart textiles include architecture, automotive, fashion, entertainment, military or protection, healthcare, sport or fitness, and others. Developments in smart and responsive textiles have made a great impact on human lives in recent years. They have a wide range of applications like wearable electronics, shape memory materials, barrier membranes, phase change materials, optical materials, and other functional textiles, which provide convenience and comfort required for a smart life.

1.5 Conclusion

A wide variety of high performance technical textiles can be developed either from technical fibres or through the functional finishing of conventional fibres. Technical textiles, textile reinforced composites, and 3D woven solid structures have a wide range of applications in different industrial sectors, offering multifunctional properties which 10 1 High Performance Technical Textiles: An Overview

are not possible to achieve by using conventional materials. On the other hand, smart and responsive textiles are contributing towards a smarter way of life. Sustainability and recyclability of technical textiles is becoming a significant concern in every area of its application. A major reason for reduced recyclability of technical textiles is the use of nonbiodegradable fibres. Hence, there is a great research focus to develop sustainable and biodegradable technical textile materials, which should be far simpler to recycle and reuse. 11

Household and Packaging Textiles Pelagia Glampedaki

Social Fashion Factory – SOFFA, Athens, Greece

2.1 Introduction

In a constantly technologically advancing world, homes are continuously turning ‘smarter’ and often ‘greener’, equipped with high performance household materials. Textiles are integral part of a household’s built and daily dynamics as they are sensed by the whole body and are related to every basic human need. Towels are used to dry the hands, cleansing wipes to clean the face, bed linen and duvets to cover the body, carpets to step on with the feet, food in textile packaging to alleviate the feeling of hunger, tents as a roof above the head to sleep in outdoors or as protective shades from excessive sun at home, and of course homewear clothing to shield oneself against weather conditions. As people worldwide become more educated and have access to opportunities for realizing a higher income, the information, knowledge, and financial independence that they have acquired drive their will to turn their houses into homes with high technology products which offer higher living standards and enhance performance, durability, comfort, hygienic conditions, and even aesthetics. Therefore, smart design solutions combined with high performance attributes are part of the package of modern‐day household and packaging textiles. This chapter offers an overview of the types of such textiles, as well as of their proper ties, engineering processes, testing methods, and applications. Sustainability aspects are also discussed before the chapter concludes.

2.2 Textile Materials, Properties, and Manufacturing

Like in any other category of high performance textiles, both natural and synthetic fibres are used in household and packaging textile‐based materials. Such fibres origi nate from the same sources used for common fabrics, such as wool (e.g. for carpets), cotton (e.g. for towels), jute (e.g. for food sacks), polyester (e.g. for curtains), and poly amide (e.g. for packaging bags). The key to their advanced properties is the type of fin ish and coating, the type of combination in composites, and even the structural

engineering of the textiles produced. Bast (i.e. woody, cellulosic, plant) fibres, for instance, have been used for decades in the manufacturing of wrapping and bagging materials from hemp, ramie, and flax. Nowadays, they are used in polymer matrix com posites which exhibit improved mechanical properties, such as tensile and flexural strength. Examples include the use of bamboo, kenaf, and sisal fibres combined with glass fibres in epoxy matrices to produce hybrid materials that are lighter with an increased impact energy [1]. Altering the layering sequence of bast fibre plies or varying the fibre content with different weight ratios are techniques to manufacture such high performance textile‐based composites. Lamination with various stacking sequences can be achieved by using regular vacuum bagging methods and post‐curing of compos ite laminates in an autoclave. A representative example of exploiting textile structures to achieve high performance is a recent study performed on woven polyester fabrics used to manufacture curtains as sound absorbers [2]. Four types of fabrics were investigated, all lightweight, contrary to the old practice of heavy velvet curtains used for sound absorption. Three to five differ ent types of yarns with various linear mass densities and different weaving patterns were employed to produce fabrics of increasing area density, specific airflow resistance, and cut‐off frequency. The fabrics were tested, both folded and unfolded, as well as with and without a rigid backing material (a wall), to distinguish among good or poor sound absorbance.

2.2.1 Household Textiles 2.2.1.1 Types and Properties In the global market of technical textiles, household textiles contribute with a share of 7% [3]. Examples include soft furnishings (carpets, rugs, upholstered furniture, cush ions, curtains, blinds, bed linen, blankets, duvets, and pillows); bath towels and kitchen cloths (oven gloves, tea towels, etc.); fibrefill (e.g. polyester staple fibres); nonwoven wipes for house cleaning and personal hygiene; and textile‐based filters for vacuum cleaners, heating, ventilation, and air‐conditioning systems, mosquito nets, even stuffed toys (Figure 2.1). Home products like impregnated fabric wipes have been developed decades ago [4] but technological progress has broadened the field of textile‐for‐house applications to uses beyond imagination. Knitted fabrics can be used to reinforce wall coverings, both outside and inside, as a lighter material than steel [5]. Solar textiles, inspired by biological archetypes such as polar bear fur, are used for the translucent thermal insulation of buildings. The sun shines through a transparent front sheet and warms up a dark absorber sheet lying behind. The absorber convects the heat to the brick wall and thus into the house. Insulation is achieved through a coated flexible spacer textile with smooth foils on both sides, the top one for self‐cleaning purposes functioning according to the lotus effect and the bottom one in the form of a black pigmented coating to absorb sunlight and transform it into heat [6]. Insulating textiles are becoming an integral part of wall constructions as they are flexible and lightweight. Novel systems, such as aerogel impregnated textiles that can act as the insulating core, can easily be installed in combination with suitable fabric finishes [7]. Even though such textiles (solar and wall covers) do not fall strictly under the category ‘household’ or ‘home’ but rather under ‘construction building’ textiles, it is evident that hundreds of square metres could be covered by textiles in a house. 2.2 Textile Materials, Properties, and Manufacturing 13

-Rugs - Insulating oor coverings Sleepwear - Homewear Carpets Robes/Slippers - & - Anti-slip substrates Cleansing wipes - Personal care - Roller blinds Curtains - Drapes - Window panels

- Sofa fabrics HOME TEXTILES Upholstery - Dining chairs - Wall covers

Ventilating - - Kitchen Mosquito nets - Towels - Bathroom Vacuum cleaning - - Cleaning wipes Bedding - Blankets/duvets (thermal) Filters - Bed linen - Mattresses

Figure 2.1 An overview of household or home textiles.

Owing to the large impact a home has on daily life, choosing household textiles is dictated by very concrete parameters, such as cost, durability, ease of cleaning, func tional properties, and of course colour and fashion style. For instance, curtains play an important multiple role in a house – they provide privacy, they retain warmth, they protect from the sun, and they add to the decoration – so choosing them is a matter not just of taste but also of functionality. Lined curtains have better drape, provide insula tion, and are less likely to fade with time and under the effect of sunlight so they may be preferred over nonlined ones. At the same time, it is good if they are also fire‐resistant. The same general attributes apply to upholstery fabrics, i.e. the outer fabrics which cover furniture. Duvets consist of an insulating material, such as down, feathers, or polyester wadding, to be warm but light. Carpets should be durable, fire‐resistant, moth proofed, and easy to clean, be able to absorb sound, and also add warmth. Therefore, the general properties of household textiles are mechanical strength, elasticity to avoid deformation, antistatic properties, hypoallergenic properties, soil releasing, flame retardancy, and insect repellence [8]. Particularly in the case of fire resistance and flame retardation, depending on the type of fibre used, each textile has different grades of flammability. Wool, for example, does not burn that easily, but synthetic fabrics like polyester could easily catch fire. To enhance their performance and safety features, flame‐retardant agents are used, especially for products like carpets and curtains. The new generation of such agents is halogen‐free, owing to environmental and health considerations. Silicon, nitrogen, and phosphorus based compounds are mainly employed with the ideal aim to produce only char and no toxic fumes while burning [9]. The burning behaviour of commercial polyester curtains treated with flame retardants has been reported in a study [10]. Fabrics had various weights in the range of 300–550 g m−2 and their flammability was investigated using cone 14 2 Household and Packaging Textiles

calorimetry. Apart from the efficiency of the flame retardant itself, the physical charac teristics of the fabrics, such as the weight per unit area, were found to be of importance influencing the rate of heat and smoke release, among other parameters [11]. Last but not least, fashion design and decoration are integral components of house hold textiles, particularly for furniture and drapes. Furnishing fabric designers use fancy yarns for decorative purposes but there are certain practical aspects to consider, such as formability and risk of deformation from daily usage, abrasion resistance, soft handle, insect repellence, etc. A material often used for furniture by designers is che nille yarn for its shiny appearance, reflection effect, and softness. A study on the per formance of chenille for upholstery fabrics showed that pile length is one of the properties of the chenille yarn which affects resistance to abrasion [12]. As the pile length increases, the pile loss decreases because it is harder to remove long fibres incorporated into the twists of the chenille yarns than short fibres. Also, the appear ance rate of chenille yarns on the surface of upholstery fabrics due to abrasion is related to weaving constructions [12].

2.2.1.2 Manufacturing One of the most modern types of high performance household textiles is that which offers protection from electromagnetic radiation. Such an attribute can be achieved by using electroconductive covers which can generate and transport free charges. There are two main paths for the production of such covers: (i) metallization of textile materials and (ii) coating textiles with conductive polymers. The most widely used metals are silver, copper, and stainless steel. However, conductive polymers, such as polypyrrole or polyaniline, and dispersed additives, such as carbon nanotubes or gra phene, can be also used to increase conductivity. Traditionally, sewing or stitching metallic yarns was used to create conductive patterns. More recent application tech niques include metal fibre staple spinning, vapour deposition, sputter deposition, plasma‐assisted coating, sol–gel processes, and even inkjet printing with conductive inks, which enable the production of stable coatings in the nanoscale [13–15]. Particularly for sample collections, inkjet printing is cost‐effective (very accurate usage of colour pastes) and time saving (production from two months down to two weeks) while it offers high pattern repeatability [8]. Another method is electroless metal plating which is a nonelectrolytic method of deposition of metal from solution and has some advantages such as coherent metal deposition, excellent conductivity, and shielding effectiveness [13]. In the case of coating with conductive polymers, there are various techniques, includ ing in situ chemical polymerization, in situ electrochemical polymerization in a one‐ compartment cell with two electrodes connected with an external power supply, in situ vapour phase polymerization, solution coating process, and in situ polymerization in a supercritical fluid. The conductive polymer coated composites manufactured by these methods function on the principle of absorption of electromagnetic rays rather than reflection [14]. A commercial example of conductive polymer coated yarn is the E‐glass/ polypropylene commingled yarn produced by the P‐D FibreGlass Group (Germany) and used for the production of poly(3,4‐ethylenedioxythiophene): poly(styrene sul fonate) (PEDOT: PSS)‐coated yarns as strain sensors [16]. Also, it has been reported that an increasing number of laminating layers increases the electromagnetic shielding effectiveness of woven polyester fabrics with stainless steel staple blended yarns and 2.2 Textile Materials, Properties, and Manufacturing 15 far‐infrared‐emissive polyester filaments produced with various structures, densities, lamination layers, and warp/weft arrangements [10]. The incorporation of small‐sized and lightweight electronic components, such as display screens and LED lights, into hidden parts of textiles is another easy way to pro duce e‐textiles for household applications. More advanced applications include GPS devices and antennas for wearable indoor location awareness systems [13]. Detachable functional elements, like electronic components, fastened onto or into home textile products can be in the form of buttons, zippers, ribbons, etc. for decorative purposes as well as for functional reasons, e.g. bearing a LED monitor or a light applied to bed linen, curtains, towels, even a textile cupboard [9]. Fire‐resistant textiles are manufactured to create a barrier preventing heat and flame from penetrating the substrate, whereas flame‐retardant textiles are designed to reduce the ease of ignition and the flame propagation rate [17]. As they are used for a number of household items such as sleepwear, bed linen, blankets, mattresses, upholstered fur niture covers, carpets, textile wallpapers, and curtains, it is crucial that they are engi neered to inhibit or suppress the combustion process during the heating, decomposition, ignition, or flame spreading stage. Organohalogen and inorganic compounds are nowa days the most predominant flame retardants used, although there are significant con cerns with their decomposition products (e.g. brominated and chlorinated furans and dioxins) as well as with their environmental impact in terms of safe disposal. Therefore, the focus has now shifted towards the development of halogen‐free additives, one group of which is inorganic aluminosilicates (clays). The most common application methods to impart flame retardation and fire resistance involve chemical finishing through the pad‐dry‐cure process which results in deposition, condensation, or polymerization of the additives on the textile surface. Compounds include ammonium polyphosphate and organophosphorus‐ and nitrogen‐containing monomers or oligomers. The back‐ coating treatment is another way to manufacture flame‐retardant textiles, particularly those used for upholstery furnishes. Antimony–halogen systems (e.g. decabromodi phenyl oxide, hexabromocyclododecane) are mainly used in this case and they are incorporated with a resin on the back of the fabric [17]. As in most functionalization cases, flame‐retardant additives can be either covalently bonded to the fibres during polymerization or fibre extrusion or physically incorporated, which is also the fastest and most cost‐effective way. In the former case, fibres and textiles are inherently fire resistant and flame retardant, whereas in the latter case they are rendered post‐produc tion as such. Commercial examples of flame‐retardant and fire‐resistant textiles and ® ® ® fibres include the Pyrovatex CP cotton, the Ultem 9011 polyimide, the Basofil mela ® ® mine, the Visil rayon fibres, and the Tes‐firESD series of fabrics which are both flame retardant and antistatic. For curtains, roller‐blinds, and even tents, fabrics with the ability to protect against ultraviolet (UV) radiation are essential. A fabric’s sun protection factor (SPF) is deter mined by the chemical structure of its constituent fibres, the substances present on and in them (additives, coatings), and by the fabric structure (porosity, thickness, surface roughness, etc.). Cotton, silk, polyamide, and polyamide/elastane fabrics with low delustrant content, particularly in pale shades, were found to be inefficient against intense UV radiation. Their performance can be markedly improved by treatment with UV absorbers, especially if the fabric porosity is low and its thickness high [18]. An example of UV blocking cotton fabrics are those developed by coating with ZnO and 16 2 Household and Packaging Textiles

TiO2 nanoparticles. The ZnO nanoparticles applied on cotton yarns were found to withstand the knitting operation. On the other hand, the TiO2 nanoparticles applied on bleached and dyed cotton fabrics by sol–gel and linking agent methods exhibited wash ing durability even after various cycles of domestic washing. Knitted fabrics treated with ZnO nanoparticles showed moderate to high values of ultraviolet protection factor (UPF), whereas 50+ UPF values were measured for the TiO2‐coated samples [19]. A very efficient technique to manufacture fabrics with antifouling and soil‐repellent properties, thus particularly relevant to upholstery and other household fabrics, is reported by Gotoh et al. [20]. Surface coating by atmospheric pressure plasma jet (APPJ) polymerization was employed, with hexamethyldisiloxane as a precursor, for depositing silicon oxide layers on the fibre surface of plain woven polyester and rayon filament fabrics. It was found that the APPJ polymerization remarkably prevented soil deposi tion of model particulate soils, carbon black and red clay, as compared to the treatment with two fluorochemical resins. In the spirit of novelty combined with sustainability, household linen manufacturers have turned to natural dyes for natural fibres, exploiting their lower toxicity and anti bacterial, antiallergic, even deodorizing properties which are quite rare for natural fab rics [21, 22]. Examples include the use of myrrh and gallnut extracts for cotton, silk, and wool, following common extraction and dyeing protocols, such as grinding and pro longed immersion in water at 90 °C for dye extraction, and exhaustion without auxilia ries at a specific liquor‐to‐goods ratio and 80 °C in a dye bath for fabric dyeing. Reported results show that the natural dyed fabrics have a good to excellent deodorizing function against ammonia, trimethyl amine, and acetaldehyde, and outstanding antibacterial activities (bacteriostatic reduction rate: 99.9%) against Staphylococcus aureus and Klebsiella pneumonia [21, 22]. Often, the high performance of household textiles can be achieved mechanically rather than chemically, especially when toxic emissions from, for example, coatings are consid ered on a daily basis in a home with possibly elderly people and children. An example where design and performance are paired in a more physical way is the reversible textile furnishing, a product that has no true inside out since either side can be used to give a different appearance or an alternative decorative surface [23]. A study was carried out to discover the existing reversible textile products and to explore the different ways of reversing a textile furnishing product. Reversible techniques were introduced to provide several possible looks within one item with a finished appearance. Apart from designing innovations, the possibility to reverse the faces of a furnishing fabric results in mitigating abrasion and weathering effects to both sides, prolonging the fabric’s life.

2.2.2 Packaging Textiles 2.2.2.1 Types and Properties Product packaging is part of the 4P marketing matrix: price, product, place, and promo tion. It is designed to give consumers awareness, product recognition, and helps build the manufacturer’s reputation. The factors taken into account in packaging decisions are the concept of product to structure the visual element of style, mood, and tone; the target group; the identity factor; the element of graphic design to strengthen product packaging; the aesthetic factor in terms of visual communication; the added value; the appeal to encourage consumers’ desire or need for consumption; the structure factor 2.2 Textile Materials, Properties, and Manufacturing 17 related to the product’s characteristics and product protection; the form of packaging matching the product type or environmental or legal issues that require consideration for sustainability, environmental responsibility, and applicable environmental and recy cling regulations; and of course the cost–profit relation [24]. It is not an easy task to produce packaging materials that fulfil all the above criteria, especially when the product to be contained is susceptible to spoilage, like food. Traditional food packaging was meant for protection, communication, convenience, and containment. The package was used to protect the product from the deteriorative effects of external conditions like heat, light, moisture, microorganisms, and gaseous emissions, so traditional packaging materials needed to be inert. A lot has changed in food packaging since the 1930s, when a fabric bag for fruits and vegetables was designed [25]. Not only chemically active and electronically intelligent systems are integrated into packaging but also the actual textile materials to build the packaging body have been reinvented. New types coated with antimicrobial agents have been developed, e.g. scoured jute fabrics treated with chitosan and chitosan–metal complexes [22]. It was actually found that the latter (i.e. jute fabrics treated with chi tosan–metal complexes) show better antimicrobial properties than fabrics treated only with chitosan or metal salts [26]. Nonwoven textiles are also rapidly developing as packaging materials that could replace plastic bags. As an example, a film based on gas‐permeable nonwoven fabric was engineered to prolong the shelf life of fresh fruits, vegetables, and vase flowers. The film has high permeability of oxygen and carbon dioxide providing a suitable atmos phere for the perishable products. At the same time, the reduced levels of oxygen inside the packaging decrease the respiration rate of the living item, leading to moisture loss and an increase in the metabolic heat while reducing ethylene levels [27]. Ethylene is a ripening agent, which is produced naturally in fresh fruits and vegetables as they respire. Reduced oxygen levels cause increased metabolic activity and hence reduction in shelf life, and increased carbon dioxide levels lead to tissue softening, fungal and bacterial growth. With 50% polyester‐50% rayon and a thin polymer layer, the nonwoven packag ing is both strong and permeable [27]. In the same aspect, a packaging material comprising a textile substrate impregnated with a solution of zeolite, a cross linker and a binder, has been developed to prolong the shelf life of fresh produce [28]. The packaging consists of a gas‐permeable container and an atmosphere‐modifying device within the container, with a carbon dioxide emitter, an oxygen scavenger, and an optional ethylene scavenger of CaO2, zeolite impregnated with permanganate, activated carbon, and combinations thereof. The packaging is suit able for home use (e.g. in a refrigerator), energy‐saving, cost‐effective, washable, reus able, simple in construction, and user friendly. The textile substrate could be woven, nonwoven, or knitted polyester, or blends of polyester with viscose, cotton, or acrylic fibres. To test its performance, fruits and vegetables were covered with the textile pack aging and were stored in uncontrolled atmosphere of 20–30 °C and 55–70% relative humidity. Mangoes covered with the engineered textile packaging were found to soften and blacken after eight days, while mangoes kept in a polyethylene bag for comparison under the same atmospheric conditions started softening and blackening in just three days. Similar experiments with other fruits and vegetables confirmed their shelf‐life extension (pomegranates six days, lemons seven days, tomatoes three days, and oranges four days) [28]. 18 2 Household and Packaging Textiles

Another invention relates to thermoplastic textile packaging with cyclodextrin as adsorbent in at least a monolayer coating and in combination with an effective amount of polyethylenimine [27]. Plastic fabrics with a metalized surface, which is also anti static, are another type of storage or transport container. Their development was based on the fact that fabrics for packaging need to be stronger and more durable than regular fabrics made of natural fibres. Also, when powder, granular, or liquid materials are poured into containers, static electric charge is developed through friction, and may lead to an explosion or fire if the container is not discharged [29]. In the group of bio‐based materials and, in particular, of fibrous cellulosic for packag ing, cellulose‐nanomaterial‐based foams are being studied for packaging applications in order to replace polystyrene based foams. Replacing a polymer produced from fossil fuel with a renewable material that decreases weight is an advantage of using webs of cellulose nanomaterials in packaging [30]. As most materials used today are nonde gradable and raise environmental and health concerns, the demand for exploring advanced and eco‐friendly packaging materials with superior physical, mechanical, and barrier properties is increasing. A study on totally green composites based on bamboo fabric and polypropylene and bamboo fabric and poly(lactic acid) was conducted to compare the performance of the green composites used for packaging as opposed to conventional thermoplastics. Results based on a number of analyses – such as drop weight impact tests, thermogravimetric analysis, differential scanning calorimetry, and heat deflection temperature analy sis – have shown that the addition of bamboo fabric improved the thermal resistance of the composites while providing mechanical reinforcement of the material. A shortcom ing of these packaging materials is that high humidity levels should be avoided [31]. It is self‐evident that there is a plethora of materials used for textile based packaging in combination with metals, glass, wood, paper, plastics, or composites. Most of these materials enter municipal waste streams at the end of their service life. Over 67 million tonnes of packaging waste are generated annually in the EU, comprising about one‐third of all municipal solid waste [32]. A large number of different types of polymers, each of which may contain different additives – such as fillers, colourants, and plasticizers – are used for packaging applications, and this complex composition makes recycling expen sive compared with disposal in landfill. These facts have given ground to the develop ment of biodegradable plastics for sustainable packaging applications, typically from renewable raw materials such as starch or cellulose, and with waste management by composting or anaerobic digestion.

2.2.2.2 Manufacturing Active packaging can be designed to modify the atmospheric concentration inside the package through selective absorbance of gaseous compounds, achieved by coating, lamination, microperforation, co‐extrusion, and polymer blending techniques. Depending on their protective mechanism, various active packaging can be categorized as oxygen scavengers; ethylene scavengers; carbon dioxide absorbers and emitters; anti microbial, moisture control systems; antioxidant release systems; and flavour or odour absorbers and releasers [33]. In the case of innovative packaging, materials have been produced from a mixture of textile dust fibre (i.e. waste from mechanical recycling of textiles) and paper fibre (recovered or virgin wood fibre) [34]. The technology required to produce this novel textile/paper material is of an existing infrastructure available in 2.2 Textile Materials, Properties, and Manufacturing 19 the paper making industry and at the same time it valorizes waste products as second ary raw materials. A third angle is that such a textile/paper material is further eco‐ designed to reduce its environmental impact and add to the category of sustainable packaging. Initially, the textile dust fibre needs to undergo the pulping process where the fibres are suspended in water. Then, this suspended dust fibre solution is refined with the fibres disintegrated into smaller ones (< 4 mm). Cotton fibres are separated from synthetic ones based on length and flexibility. The fine fraction of the textile dust solution is mixed with the paper fibre solution at different proportions based on the quality required for the application. Pressing and drying follows to produce the final textile/paper packaging material [34]. In the field of e‐textiles, artificial cilia have been introduced in the periphery of electronic devices as adhesive elements. The cilia also play an important role in con fining a small amount of glue and damping mechanical stress to maintain robust elec tronic performance under mechanical deformation, as it could happen in packaging applications. This example showcases how electronic functions can be imparted by transfer printing on unconventional complex surfaces, such as textiles [35]. The three‐dimensional (3D) woven structures made by multiple warp and weft systems are another path to multilayered textile based packaging and even carpets [36]. By using particular types of ties in advanced design, it is possible to produce solid orthogonal panels or solid panels with variable thickness to manufacture different types of containers. It is self‐evident that the basis of manufacturing techniques for high performance household and packaging textiles can coincide. The details that make the difference lie in specific requirements for the targeted technical performance, as well as in regulatory restrictions. For instance, textiles used in food packaging cannot contain dyes that could be harmful through ingestion but are safe for, for example, carpet production. Table 2.1 summarizes the main groups of manufacturing techniques applied to household and packaging textile materials.

Table 2.1 Summary of manufacturing techniques of household and packaging textiles.

Household textiles Packaging textiles

Metallization with stitched metal fibres Lamination Electroless metal plating Impregnation (e.g. with antioxidants) Conductive polymer coating Natural fibre/polymer composites Plasma surface treatment Metallization for antistatic properties Vapour deposition Biosensor integration Sputter deposition Chemical indicator integration Sol–gel processes (e.g. for UV absorbers) Microperforation Inkjet printing Co‐extrusion Pad‐dry‐cure treatment Polymer blending Back‐coating treatment for flame retardation Active atmosphere modifier incorporation Structure engineering (weaving, spacer Intelligent freshness indicator incorporation layering, etc.) 20 2 Household and Packaging Textiles

2.3 High Performance Applications

2.3.1 Household Textiles

Because of their prominent role in our daily lives, interior and household textiles rank second after apparel in textile production by volume and they are rapidly evolving in terms of high performance, much like technical textiles. For instance, e‐textiles have infiltrated the furniture and interior textiles sector. A typical example is thermal blan kets but home e‐textiles have been applied even to the production of carpet embedded guidance systems in buildings [13]. In fact, despite the technological, ergonomic, and financial barriers that textiles with embedded electronics face (e.g. washability, fashion able patterns, and price), the industry is turning to high tech home textiles such as curtains and carpets, owing to consumer demands. One way to impart or increase the electrical conductivity of textiles is the use of metallized yarns. They are produced by spinning or twisting metal wires with diameters of 1–8 μm. Blended conductive yarns consisting of regular textile and metallic fibres is another way, as well as coated textile fibres with a metallic layer, but they show lower conductivity than full‐metallic fibres. But even traditional textiles are being reinvented, like rayon, which is made from cel lulose pulp. Recently, scientists have developed a highly processed form of cellulose nanomaterial for stronger, lighter, and more durable textiles with a range of applications in homewear and personal care and hygiene products [11]. The super water absorbency of cellulose nanomaterials renders them ideal as biodegradable water retention fillers in incontinence pads and diapers, even underwear and wipes. In‐house water and air fil ters are another field of application for such novel nanomaterials, especially in the form of filters treated with aerogel particles which can absorb 130 times more pollutants than activated carbon [11]. Nanotechnology, as in any other scientific field, has induced great technological pro gress in the textile industry. An important application of this technology in this sector is self‐cleaning textiles for easy washing and maintenance, with lower energy and resources consumption than in the case of conventional textiles. Scientists have developed several methods and finishes to impart self‐cleaning properties. A typical example involves pho tocatalytic surface coatings or depositions using nanocrystalline TiO2, which is able to destroy organic material by solar irradiation [37]. The TiO2 photocatalytic effect is also self‐sterilizing (sanitizing) and, thus, odour‐reducing. Only a handful of commercial ® products exist in that category, including SUN‐ECO photocatalytic textiles and SHINE‐ ® UP deodorizing fibres with apatite coated TiO2 for interior building materials [38]. Self‐cleaning textile treatments reduce water and detergent consumption, as well as the temperature required for the removal of persistent stains, having a lower environmental impact according to lifecycle assessment (LCA) studies [37]. In the same spirit, soil release textiles have emerged. Fabric stains or smears due to dirt or grease are at times not easily removed by regular laundering procedures. For this purpose, soil release finishes have been developed to tackle mechanical and electro static adhesion of soil on textiles, or even its redeposition during washing. Depending on the type of fabric, soil can be repelled or, if not repelled, at least released through laundering. Natural fibres like cotton do not repel dirt but they are easily cleaned. Synthetic and particularly hydrophobic ones, like polyester, can often neither repel nor release soil, and are thus treated with chemical agents to achieve this result [12]. In the 2.3 High Performance Applications 21 case of household textiles, soil release systems are especially important when the item is light‐coloured and not easily removable for frequent washing (e.g. sofa fabrics). Apart from chemical treatments, exploiting the specific characteristics (e.g. fibre diameter, medullation, and bending rigidity) of individual fibres by placing them strate gically in yarn cross‐sections could result in enhanced properties. Such an approach has been applied to carpets produced with layered yarn structures rendering them more resistant to carpet pile decrease under dynamic loading and to fibre loss due to abra sion, and with improved overall performance [39]. Another application, where the physical structure of a household textile plays a func tional role, is insulation. In fact, advanced weaving or knitting structures can lead to the desired result. As an example, a knitted composite fabric made with alternating inter lock stitches at predetermined intervals can produce air pockets in a checkerboard pat tern on the inner layer of the fabric, while its outer surface is flat, thus exhibiting inherent thermo‐insulating properties [40]. Such an insulating fabric is a cost‐effective alternative to lined knit products produced by laminating or binding two separate fab rics for thermal regulation. A lesser‐known high tech category of household textiles is luminous embroidered fabrics. Compared with traditional embroidered ones, they present both a decorative and a luminous effect, after absorbing visible light, storing energy, and emitting it as light in the dark for more than 10 hours. In general, luminous fabrics are produced by weaving, knitting, or embroidering rare‐earth (e.g. europium ions, activated strontium aluminate phosphors) luminous fibres onto fabrics. For a more efficient production, a computer‐aided embroidery machine can be used to design patterns. Usually, lumi nous‐fibre embroidered fabrics emit yellow, yellow‐green, green, and blue light at night. They are nontoxic, nonradioactive, and can be recycled [41].

2.3.2 Packaging Textiles

Nowadays, the balance has shifted towards smart packaging systems which interact with their content to either act on changes of it and/or to inform consumers about them. Figure 2.2 presents a schematic overview of the main contemporary textile pack aging types. The two main categories of the new‐age packaging materials are active and intelligent. According to EC Regulation 1935/2004 and EC Regulation 450/2009, active materials and articles are intended to extend the shelf life or to maintain or improve the condition of packaged food [33]. Active packaging can be defined as a system in which the product, package, and environment interact in a positive way to extend the shelf life or to improve safety or sensory properties while maintaining the quality of the packaged food. They are designed with components that could release or absorb substances from the product’s environment to ensure the product’s safety and enhance its preservation. Prolonging shelf life can be achieved through various strategies, like temperature con trol, oxygen removal, moisture control, and addition of chemicals such as salt, sugar, carbon dioxide, or natural acids. Relative innovations include systems for delayed oxi dation, controlled respiration rate in horticultural products, moisture migration, and prevention of microbial growth in dried products. There are also self‐heating and self‐ventilating packaging materials in the category of active packaging for ready meals. According to EC Regulation 450/2009, self‐heating packaging has the ability to heat food contents without external heat sources or power, 22 2 Household and Packaging Textiles

• Metallised Traditional • Reinforced (inert) • Permeable

• Carbon dioxide Absorbers/emitters • Oxygen scavengers • Ethylene scavengers • Moisture control • Sensors PACKAGING • Antimicrobial • Indicators TEXTILES • Antioxidant release systems • Radiofrequency • Flavour/odour absorbents Identi cation

Active Intelligent

Figure 2.2 Main categories of packaging textiles in terms of consumer interaction.

while self‐venting packaging controls the steam or pressure in the pack, venting the steam when the required pressure/temperature level is reached. On the other hand, according to EC Regulation 450/2009, intelligent packaging mate rials and articles are those which monitor the condition of packaged food or the envi ronment surrounding the food and provide the user with information about temperature and pH levels. It is an extension of the communication function of traditional packaging based on the packaging’s ability to sense, detect, and record the changes in the product’s environment. Unlike active packaging, intelligent packaging is not designed to absorb or release any substances. However, it can contribute to improving and implementing hazard analysis and critical control points (HACCP) and quality analysis and critical control points (QACCP) systems, developed to identify potential health hazards and onsite unsafe products while establishing strategies to reduce or eliminate their occur rence. Intelligent packaging systems are categorized in three groups: sensors, indica tors, and radiofrequency identification (RFID) systems. Sensors include biosensors for biological reactions and gas sensors for detecting the presence of gases in the package. An emerging subgroup of intelligent sensor packaging in direct relationship to textiles is printed electronics on flexible substrates using elec trically functional inks. What makes them special is that they are lightweight, bendable, rollable, portable, and foldable. They have a chemical sensor (the receptor) which selec tively detects the presence, activity, composition, and concentration of a particular chemical or gas, and the information is converted into signals by a transducer. There are also sensors in the form of an electronic nose which mimics the mammalian olfactory system, allowing the identification and classification of aroma mixtures present in the odour. Electronic noses generate a unique response for every savour. In the group of intelligent indicator packaging, freshness indicators are more com mon. They provide visual information regarding the microbial quality of the product 2.4 Testing Methods and Quality Control 23 based on the reaction between the microbial growth metabolites of a product and the integrated indicators within the package. Time/temperature indicators are designed to inform about temperature increases above a certain threshold and about the amount of time a product has spent above the threshold temperature. In the form of labels, these systems provide visual indications of temperature history during product storage. Package integrity is monitored with leak indicators, while visual oxygen indicators impregnated with redox dyes change colour with changes in oxygen concentration. Last but not least, RFID is an automatic identification technology that uses wireless sensors to identify items and gather data without human intervention. An RFID is based on tags and readers [33]. Finally, energy absorbent materials are important in the packing of fragile goods. High performance composites capable of bearing plastic deformation while being light weight are highly regarded as packaging materials. Although the use of multilayer 2D reinforced composites has a long history, their production cost and the poor mechani cal properties of pre‐impregnated layers have restricted their use [42]. Instead, 3D com posites reinforced by weft knitted fabrics with engineered cell type, cell density, fabric structure, and loop density are increasingly attracting interest.

2.4 Testing Methods and Quality Control

2.4.1 Household Textiles

There are a number of tests and various standards to control the quality and perfor mance of household textiles. The main parameters determined are related to colour fastness, soiling, mechanical strength, abrasion, and flammability. More specifically: ●● Colour fastness to light is determined with a solar light weather chamber where sam ples are tested under specific conditions of temperature, time duration, and irradia tion power. Samples are evaluated under fluorescence based on the American Association of Textile Chemists and Colorists (AATCC) Gray Scale for Colour Change. Spectrophotometric analysis for the determination of the total colour differ ence based on International Commission on Illumination LAB (CIELAB) values can also be applied to confirm visual assessment. ●● Colour fastness to crocking (rubbing) according to AATCC Test Method 8 for uphol stery [43] rates samples according to the AATCC Chromatic Transference Scale. Grading is from 1 to 5, with 1 corresponding to high and 5 to negligible or no colour transfer. Number 4 is the minimum acceptable grade for dry tests and 3 for wet ones. Even the weaving structure of a fabric could affect its performance in such a test [43]. ●● Colourfastness to water (e.g. AATCC Test Method 130) where samples are immersed in water, passed afterwards through a wringer, stacked between plastic plates on a perspiration tester, and dried in an oven. During wetting and drying, multifibre (wool, silk, rayon, cotton, nylon, polyester) samples are attached to the sample and colour transfer is evaluated according to the Gray Scale for staining. ●● Tearing strength (e.g. American Society for Testing and Materials (ASTM) Test Method D2261 or D1424‐96), either of wet or of dry samples, can be determined with the falling‐pendulum type (Elmendorf) apparatus. It is suitable only for the warp direction testing of warp‐knit fabrics and it determines the force required to 24 2 Household and Packaging Textiles

propagate a single‐rip tear starting from a cut in a fabric, at a constant rate of exten sion. The minimum requirement for upholstery fabrics is 6 lbf. ●● Abrasion resistance (e.g. ASTM Test Method D3884) is determined based on the number of cycles required for yarn rupture and for a particular use. Pilling and frost ing (i.e. a noticeable colour change due to flat localized abrasion) can accompany abrasion tests for a complete picture of the fabric’s weathering. ●● Flammability test (e.g. ASTM Test Method D6413), which refers to the ease of igni tion and continuation of burning after ignition. The vertical flame test method is used to determine parameters such as the burn time, the afterglow time (i.e. the period of time that the fabric continued to glow after the flame removal), and the char length (no singular sample should exceed 25.4 cm. in order to pass the test), reflecting the flame resistance of the fabrics.

There are various standards to test all above parameters. For instance, the 16 CFR 1631 Standard for the Surface Flammability of Small Carpets and Rugs involves the exposure of each of eight conditioned, replicate specimens of a given carpet or rug to a standard igniting source in a draft‐protected environment and measurement of the proximity of the charred portion to the edge of the hole in the prescribed flattening frame. A speci men passes the test if the charred portion does not extend to within 2.54 cm (1.0 in.) of the edge of the hole in the flattening frame at any point. At least seven of the eight speci mens shall meet the test criterion in order to conform to the Standard. Flammability of Mattress Sets, Mattresses, and Mattress Pads, according to 16 CFR 1632 Standard for the Flammability of Mattresses and Mattress Pads, is tested to deter mine the ignition resistance of a mattress or a mattress pad when exposed to a lighted cigarette. Standard 16 CFR 1633 establishes flammability requirements that all proto type designs of mattress sets must meet before sale or introduction into commerce. The test method measures the flammability performance (fire test response characteristics) of a mattress (or mattress set) prototype by exposing the specimen to a specified flam ing ignition source and allowing it to burn freely under well‐ventilated, controlled envi ronmental conditions [44]. For cover fabrics, according to ASTM E1353‐08a ε1 test method, the first layer of filling materials located below the cover fabric shall also meet the test requirements which determine the tendency of upholstery cover fabrics to smoulder and contribute to fire propagation, when subjected to a smouldering ignition source. A material is con sidered to pass or fail based on the following criteria: (i) the mock‐up test specimen continues to smoulder after the 45 min test duration, (ii) a vertical char length of more than (4.5 cm) develops on the cover fabric, and (iii) the mock‐up test specimen transi tions to open flaming. On the other hand, the cover fabric passes the test if three initial mock‐up specimens pass the test, i.e. the cigarettes burn their full length and the mock‐ ups are no longer smouldering [44]. There is also the oily stain release test (e.g. AATCC Test Method 130) or the breaking strength test (e.g. ASTM Test Method D5034) that could complete the quality profile of household textiles. Of course, there are other tests that apply to household textiles but are not specific to them, i.e. they are more generic textile tests (e.g. washing fastness). Finally, there is a list of very specific procedures to test home textiles and it includes standards of: (e.g. ASTM standards list) Performance specification for woven uphol stery fabrics: plain, tufted, or flocked, performance specification for vinyl‐coated and 2.4 Testing Methods and Quality Control 25 urethane‐coated upholstery fabrics‐indoor (D3690 – 02(2009)), Performance specifica tion for woven, lace, and knit household curtain and drapery fabrics (D3691/ D3691M – 09), Performance specification for woven, knitted, or flocked bedspread fabrics (D4037 – 02(2013)), Performance specification for woven napery and tablecloth fabrics: household and institutional (D4111 – 12), Performance specification for woven slipcover fabrics (D4113 – 02(2013)), Performance specification for soft window cover ing fabrics for household use (D4720 – 08(2013)), Performance specification for knitted upholstery fabrics for indoor furniture (D4771/D4771M – 09), Performance specifica tion for woven and knitted shower curtains for institutional and household use (D5378 – 12), Performance specification for blanket products for institutional and household use (D5431 – 08(2013)), and others.

2.4.2 Packaging Textiles

For packaging textiles, there are many different regulations that guide their quality and performance aspects. Consumer packaging should bear a label specifying the identity of the commodity; the name and place of business of the manufacturer, packer, or distribu tor; and the net quantity of contents in terms of weight or mass measure, or numerical count in a uniform location upon the principal display panel. Toxic compounds in pack aging are a significant parameter to test with regard to the amount of heavy metals, such as mercury, lead, cadmium, and hexavalent chromium [44]. A very important quality test is also antimicrobial growth. Owing to their large sur face area and ability to retain moisture, textiles are known to be conducive to microor ganism growth, such as bacteria and fungi, which can be found almost everywhere and can quickly multiply, depending on moisture, temperature, and nutrients levels [45]. An antimicrobial treatment performed on textile packaging needs to satisfy different requirements, depending on the antimicrobial agent and the microbial target group. Also, specific harmful chemicals, such as fluorinated substances used in grease‐resistant food packaging, can leach into food and increase dietary exposure. Specific analytical techniques are needed in such cases to identify and quantify them when testing a textile packaging material, e.g. particle‐induced γ‐ray emission (PIGE) spectroscopy for total fluorine content or conventional solvent extractions followed by liquid chromatogra phy/high‐resolution mass spectrometry analysis [46]. Specific standards exist for specific type of packaging textiles, e.g. IS 6899‐1997 for high‐density polyethylene (HDPE) woven fabrics is a standard which specifies require ments of five varieties of HDPE woven fabrics generally used for wrapping, bale cover ing, and similar applications. Leakage tests include various types such as closure, air pressure, transport vibration, and vacuum leakage tests. Finally, permeability and bar rier tests required for packaging apply also to textile materials, along with bursting strength testing which measures the resistance of the packaging material to burst. It is common for paper packaging but it also applies to textiles and synthetic leather. Also, tests that determine the UPF and the UV resistance of textiles are significant in terms of material durability and product spoilage. Traditionally, the determination of the UPF of a fabric was analysed by placing a template with various samples next to human skin. UV radiation, 60 times stronger than the sun’s, was directed through the fabric and on the skin for various periods of time. The degree of sunburn of the exposed skin determined the fabric’s protection factor. Evidently, that method was potentially 26 2 Household and Packaging Textiles

unsafe for the exposed subjects and other methods have been developed. Standards such as AS/NZ 4399: 1996, AATCC 183: 2004, ASTM D6544 and D6603, and EN 13758‐1 describe UPF testing methods. In any case, to accurately assess the amount of protection provided by various fabrics requires measurement of the spectral transmit tance of each fabric across the wavelength range 280–390 nm, which includes the UVB (290–315 nm) and the UVA (315–380 nm). The UPF of fabric samples is determined after a defined incubation period of the samples using a UV transmittance analyser at a wavelength range from 450 to 250 nm. For each fabric sample, multiple spots are meas ured and the results are averaged [47]. UPF ratings include: Grade I, with values from 20 to 29 corresponding to fabrics that offer good protection; Grade II, with values from 30 to 40 corresponding to fabrics that offer very good protection; and Grade III, with values > 40 corresponding to fabrics that provide excellent protection [48]. For example, a UPF value of 50 means that only 1/50 (or 2%) of the biologically effective UV radiation will be able to pass through a piece of fabric. On the other hand, UV resistance is defined as the ability of a material to resist UV light or sunlight. UV irradiation will cause nonresistant materials and surfaces to fade or discolour. To be tested, fabric samples are conditioned and then exposed to UV rays for a defined period of time in an accelerated UV‐ageing tester. In fact, the UV acceler ated weathering tester reproduces the damage caused by sunlight over time. In other words, after exposure of a piece of textile to UV light for a few days or weeks, the tester can assess the effect that the sun will have on that textile in months or years of exposure. In practice, if a material after ageing has a UV resistance value of less than or equal to 2, it is considered UV‐resistant.

2.5 Sustainability and Ecological Aspects

2.5.1 Household Textiles

With petroleum resources rapidly depleting, the textile industry is shifting gradually from conventional processes to more sustainable solutions and raw materials. Con sidering, also, that synthetic fibre manufacturing is not a closed‐loop process, in that by‐products are not be fed back into the system, air and water pollution is another major issue, which makes way for the use of traditional fibres as sustainable alternatives. Such an example is reported in the study of Lambert et al. (2017) [43] for furniture applica tions, in which hemp fibres are compared with cotton in terms of performance, including colour fastness, resistance to abrasion, etc. It was found that hemp fabrics were compa rable to cotton with respect to mechanical properties meeting the minimum require ments for breaking and tearing strength of upholstery fabrics. Moreover, hemp fabrics performed somewhat better in colourfastness‐to‐water tests showing negligible resist ance to cleaning, i.e. very little dye loss and stain presence, particularly important if steam cleaners are used. However, hemp exhibited great colour changes upon exposure to light, limiting its use to indoor furniture, unless modified with suitable finishes [43]. In product manufacturing, planned obsolescence is a purposely implemented eco nomic and industrial strategy that ensures the current version of a given product will become obsolete or useless within a planned time period. This strategy guarantees that consumers will demand replacements sooner or later, supporting demand and sales. 2.5 Sustainability and Ecological Aspects 27

The phenomenon is evident especially in electronics, where new versions of products are launched every few months, but the textile industry has its own share of responsibility in that respect. In fact, ‘fast fashion’ was coined as a term to designate low‐cost clothing which imitates luxury fashion and feeds unscrupulous disposability. In much the same way, the term ‘fast furnishings’ has been introduced to describe the design and production of low‐cost home/soft furnishings in very short manufacturing and consuming cycles of residential textile products such as upholstery, carpets, curtains, bedding, and decorative pillows. As a result, fast furnishings contribute to the nonsustainability of the textile industry with respect to the overuse of natural resources, escalating pollution and waste production, the presence of harmful substances like toxins and carcinogens in fabrics, and the growing volume of textile goods that end up in landfills or incinerators [49]. The environmental impacts of textile consumption and use in the European Union are both supply and demand driven. Supply factors include agricultural practices, pro duction processes, product design and functionalities of washing/drying/ironing appli ances, and the existence of sorting and recycling schemes, while demand factors (which are mostly driven by social parameters) include choice of products/fibres, care practices (washing, drying, ironing), lifetime of product in a context of fast fashion, and disposal practices [50]. A study conducted to identify, map, and discuss LCA methodological issues in the textile sector focused on ranking three fabric types for a sofa – cotton, polyester, and wool/polyamide – and more specifically for a surface covering of a three‐seat sofa for private use during 10 years [51]. The results of the study revealed that with all assump tions and boundaries the polyester type of fabric has a lower environmental impact than the fabric made of natural fibres such as cotton. The significant issues addressed with respect to sustainability were: the production phase, yield (e.g. regarding cotton cultivation), air emissions of methane and ammonia from sheep or sheep manure, fossil energy extraction and use, type of electricity used, and system expansion/allocation choice. The system expansion/allocation choice in sheep farming, where oddments were assumed to replace first‐class wool, had most influence. Fuel replacement in the incinerator and recycling of packaging material had less influ ence. Less significant issues were: use phase, production of drinking water, freighter and truck transports, business trips, waste management of used fabrics or fibre waste, and type of heating value used. Issues not or not fully assessed were: the effects of chemicals discharged to water, inclusion of a wastewater treatment plant, eutrophying discharges to water, land use, human health impacts from the working environment, the effects of lubri cants, production of packaging materials, and production of chemicals [51]. Aspects of the negative impact of interior (home) textiles include contamination of indoor air quality, chemical usage, and energy and water consumption, calculated for the total lifecycle of the product. In fact, studies on interior spaces with a lot of furniture like schools and offices revealed that poor indoor air quality can cause ‘sick building syndrome’, which is a physical reaction expressed with fatigue and respiratory prob lems. Further to the emissions of harmful volatiles from home textiles, wall coverings and carpets can trap allergens such as mites and moulds and may contain trace amounts of formaldehyde, contributing to poor indoor air quality, especially in combination with poor ventilation. In the case of chemicals use, conventional cotton production, for example, involves the use of large amounts of pesticides and insecticides, some of which remain in the 28 2 Household and Packaging Textiles

finished textile product throughout its lifecycle. Chemical finishes such as soil repel lents and flame retardants may be released into the environment during the later stages of product use, maintenance, and disposal. For example, a common flame retardant such as decabromodiphenyl ether is a hazardous chemical used for interior furnishings and, if disposed in a landfill at its end of life, it can contaminate the ground during its slow decomposition affecting human health and wild life. Moreover, such chemicals may pose health risks to the workers who handle them, unload the shipment, and place the products for retail display. Also, the transportation of materials from one factory (or country) to another contributes to greenhouse gas emissions. The use of potentially harmful chemicals during the laundering process (e.g. softeners and dry cleaning sol vents) is another stage of environmental impact of household textiles post‐production. In a study about chemical toxicity [52], 14 commonly used household textile dyes and two colour removers were tested for their oral toxicity in mice and they were categorized as ‘moderately toxic’ compounds. Toxic symptoms appeared rapidly and consisted of marked respiratory difficulties and convulsions. Most deaths occurred within hours. The five most toxic dyes of the study and one colour remover were tested for oral toxicity also in dogs and, in this case, they were all characterized as ‘very toxic’. Symptoms resembled those seen in mice. In general, the dark dyes were more toxic than the pastel shades [52]. It is evident that sustainability aspects in the field of household and packaging textiles are not very different from those in the field of clothing textiles, and they reflect the deleterious impact of fast furnishings and single‐use packaging on the environment and on human health (Figure 2.3). Such a realization was the drive for some companies to embrace more holistic and sustainable approaches to interior textile design and manu facturing. Design for the environment (DfE) is such an approach. It is a process which

• Laundered • Planned micro-plastics obsolescence • E-textiles in • Fast fashion land ll • Fast furnishing • Sick building • Single use syndrome Product packaging Pollution Life Cycle Assessment

Circular Education Economy • Sustainable • Designers resources • Manufacturers • Waste/package • Policy makers valorisation • Consumers • Recycle/Reuse

Figure 2.3 Schematic summary of the key parameters that describe or influence the environmental impact of household and packaging textiles. 2.5 Sustainability and Ecological Aspects 29 takes into consideration the economic, health, and environmental impact associated with a product across its lifecycle, emphasizing the use of safe and sustainable materials, features, and processes, and with the understanding that environmental concerns need to be addressed during the initial design stage of the process [49]. Establishing long‐term relationships with various stakeholders – suppliers, govern ments, NGOs, consumers, and communities – can support efforts towards sustainabil ity. In the context of interior textile design, all levels of stakeholders may influence a product’s lifecycle and sustainability, including product designers and developers, mar keting managers, production experts, third‐party organizations (e.g. the Global Organic Textile Standard [GOTS] organization), government agencies, consumers, dry cleaners, and product recyclers [49, 53]. In that context, a product LCA model with respect to environmental design criteria specifically for interior textiles was developed (Environmental Design 2013). The model is based upon three propositions about environmentally responsible or ecologically sustainable organizations (ESOs). First, designers are given environmental objectives and goals for product design. Second, ESOs employ systems to assess environmental objectives or criteria at key points throughout the product design process. Third, ESOs integrate environmental considerations into the design process by measuring environ mental outcomes and incorporating outcomes into strategic planning. In a five‐step process of concept, product design, process design, package design, and product launch, sustainability can rise through product specifications, raw material selection, and end‐ of‐life planning (e.g. selecting materials that can easily be recycled), waste management during production, choosing a more ecological transportation manner, and evaluation of environmental outcomes using LCA, reports of regulatory experts, and cost analyses. Studies have shown that the application of sustainable design, development, and pro duction methods is limited in the textile industry for interior textiles, owing to indus trial standards and regulation, availability of products, production methods, and company size and resources. Furthermore, product performance and quality were per ceived to be more important to achieve than reduced impacts to human health and the environment [49]. However, in the framework of circular economy, choice of materials in product design plays an important role for sustainability, along with standardized parts, products designed to last, end‐of‐life sorting, product reuse, and closed‐loop manufacturing which valorizes by‐products and waste [34]. Taking into consideration that contemporary textile waste comes also in the form of e‐waste, three main concerns arise: (i) the e‐waste mountain piles, (ii) the toxic load from their constituents, and (iii) resource depletion for their manufacturing [13]. Even if e‐textiles enter municipal solid waste streams that lead to either landfill or incinera tion, they will be co‐processed with all other solid waste. Released pollutants would add to the overall environmental issues, plus no recovery of valuable materials would be expected. Upon dispersion within low‐grade wastes, valuable materials, such as metals, would be lost. However, if e‐textiles entered an e‐waste recycling scheme, the recycled fibres could be agglomerated to flocks or manufactured into nonwoven fabrics with applications in mattresses and upholstery (66%) or carpet underlay (11%), as well as in paper pulp (5%) and the automotive industry (8.7%). It is still not known whether it would be possible to maintain the ‘intelligence’ of e‐textiles for re‐use. It can be assumed that repairing e‐textiles would hardly be possible during textile recycling, either technically or 30 2 Household and Packaging Textiles

economically. However, old e‐textiles could provide classical textile functions. Therefore, a large part of them could be categorized as second‐hand clothes [13]. But it is not just solid waste that ends up in landfills. A new and more alarming source of marine contamination has been identified in micro‐ and nanosized plastic fragments. Microplastics are difficult to see with the naked eye and as they do not biodegrade in aquatic environments, they can be ingested by plankton or other marine organisms. Microplastics reach the sea through sewage contaminated by synthetic fibres from washing clothes and household textiles. In a relevant study [54], the highest release of microplastics was recorded for the wash of woven polyester and this phenomenon was correlated to the fabric characteristics. The number of microfibres released from a typi cal 5 kg wash load of polyester fabrics was estimated to be over 6 000 000 depending on the type of detergent used. The usage of a softener during washes reduces the amount of microfibres released by more than 35%. The amount and size of the released micro fibres confirm that they could not be totally retained by wastewater treatments plants, and potentially affect the aquatic environment [54]. A way to minimize or at least contain this environmentally unfriendly effect is to substitute synthetic components with natural ones, wherever possible. In this context, research has been conducted to substitute harsh chemical finishing agents with more benign and natural ones. For instance, vegetable oils from rapeseed, olive, coconut, saf flower, and linseed have been applied in the form of aqueous emulsions to investigate the wrinkle recovery of 100% cotton fabrics [55]. It was found that spraying such emul sions on cotton results in the formation of a thin microdroplet layer on the fibres, fila ments, and yarns, without any chemical bonding taking place. The performance and effectiveness of these natural antiwrinkling agents lie in the reduction of the friction coefficient which in turn promotes fibre relaxation after deformation. Another interesting approach is the use of bio‐binders for nonwovens. Researchers have tested soy‐protein‐based binders applied on viscose nonwoven textiles in the form of foam [56]. The same type of textiles treated with acrylic binders in a conventional pad‐dry‐cure method were used as a reference. The results of the study showed that foam‐applied biobinder‐treated nonwovens have comparable mechanical and thermal properties with conventional ones. Studies have also shown that the impregnation of personal care and household poly ester and cellulose wipes with solutions of natural components such as rosewater and olive oil, treated with sodium alginate and natural antibacterial agents of cinnamalde hyde and geraniol, can result in products with good liquid absorption and antibacterial performance [57]. Thus, they can substitute conventional commercial household wipes produced with synthetic means.

2.5.2 Packaging Textiles

In the case of packaging textiles, they emerged, among other materials, as sustainable alternative to bad practices of the past when storage life of perishable articles like fruit and vegetables was prolonged by spraying antibacterial and antifungal chemical agents (silver nitrate, sorbic acid anhydride, chlorinated hydrocarbon, potassium permanga nate) on the fruits and vegetables causing serious health hazards for the consumers [28]. Biodegradable textile based bioplastics are most suitable as sustainable packaging in such cases. Apart from their safer use, their end of life can take place by biological 2.5 Sustainability and Ecological Aspects 31 composting and potentially in anaerobic digestion systems. They should ideally be separated at the household level from other, nonbiodegradable materials and collected with organic waste, including food waste. By using biological waste treatments, the total waste sent to landfill would be reduced and the composts generated could be used as valuable soil improvers [32]. An example of creating a new value from the waste stream of textile recyclers in a sustainable way that promotes circular economy is the case of dust fibre valorization. Even though the quantity of dust fibre produced per tonne of discarded textile is still low, there is a high potential of around 60% to generate large amounts of dust fibre when the discarded textiles are diverted from incineration and landfill [34]. The dust fibre waste from textile recycling can find better use in packaging or other applications as a circular material. A textile paper bag has a lower environmental impact than virgin and recycled paper bags, and has lower operating costs, owing to the lower cost of the textile dust fibre [34]. ® Furthermore, even Tetra Pak packaging waste can be reused in combination with wool fibre waste or glass/jute woven fabrics to produce thermo‐insulating bio‐based composite materials [58], increasing also their sustainability features. In fact, the new materials exhibit improved thermal conductivity and thermal resistance compared to control samples made of plain Tetra Pak. Also, applications of composite plastic materials reinforced with natural fibres such as from flax, hemp, and various wood origins gain ground in many industries, including packaging boxes manufacturing. The main advantages are the low weight and the renewability of such fibres, while major disadvantages pertain to high water absorption, degradation in wet environments as well as under ultraviolet light, and high smoke emission in the presence of flame. Reportedly [59], the water absorbed by a flax/epoxy composite until saturation is more than 12 times greater than the water absorbed by a glass/epoxy composite. Also, accelerated UV weathering tests performed for 1500 hours led to decreased tensile and flexural strength of composite flax fabrics, according to the same report. But apart from traditional bast fibres from jute, flax, hemp, etc. that are combined with synthetic polymeric ones to increase biodegradability and induce sus tainability, lesser‐known natural sources have drawn attention owing to their valuable properties. Seaweeds are such a source, increasingly investigated for their use in medi cal and healthcare textiles thanks to their bioactive constituents [60], and they could find use also in naturally antimicrobial textile packaging. Pigments aside, which could be applied as natural dyes, seaweeds comprise a plethora of antioxidants and antimicro bial agents. In fact, most seaweeds contain carotenoids, phenolics, alkaloids, and orga nosulfur compounds, including a‐carotene, b‐carotene, lutein, and zeaxanthin, the antioxidant pigments of both red and green algae, as well as fucoxanthin and fucoidan found in brown seaweed. The analysis of possible improvement options in the sense of sustainability in house hold and packaging textiles indicates consumer education and awareness as fundamen tal to any change (Figure 2.4). In fact, some of these options would require small behavioural changes, such as reducing washing temperature, washing at full load, avoiding tumble drying when possible, purchasing eco‐friendly home textiles, donating textiles not being used any more, upcycling or downcycling clothes to create household textiles, and refusing to utilize single‐use packages. Education on ecolabels and promo tion of best practices could be used as tools for the overall improvement of 32 2 Household and Packaging Textiles

Choice of materials Design for the (sustainable, Environment biodegradable)

End-of-life Closed loop product manufacturing valorisation

Sustainability

Figure 2.4 Basic steps to sustainability in the household and packaging textile industry.

environmental performance. Consumers may exhibit greater support for sustainability if they consciously evaluate the consequences of their actions [61].

2.6 Conclusion

Household textiles are second after apparel in production volume worldwide and they comprise a large part of our living utilities. They are directly related to our basic func tions and needs (sleep, food, hygiene) in the form of soft furnishings, bed linen, carpets, towels, and even packaging. Technological developments have increased the perfor mance of home textiles in terms of durability and added functionalities, allowing them to follow trends in line with e‐textiles, combining sustainable materials for easier dis posal and reuse, embedding nanotechnology into everyday personal items. Packaging textiles, on the other hand, have entered a new era of active and intelligent systems which interact with their content and inform the consumer about spoilage risks or products’ nonconformity. Bio‐ and chemical sensors and indicators advert and at the same time educate the user about a product’s story, identity, and properties. Textiles have helped high performance packaging to advance, as they can be engineered to have very strong weaving structures while being lightweight and more sustainable than con ventional packaging materials. A lot needs to be done still to tackle environmental issues in this particular textile sector but there is preliminary evidence that textiles could be turned into circular materials in household textile and packaging production.

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Sports Textiles and Comfort Aspects Ali Harlin1, Kirsi Jussila 2, and Elina Ilen3

1 VTT Technical Research Centre of Finland Ltd, Espoo, Finland 2 Finnish Institute of Occupational Health, Oulu, Finland 3 Aalto University, School of Arts, Design and Architecture, Espoo, Finland

3.1 Introduction

During the last many years, sportswear has taken on a new look as lifestyle wear, and accordingly function required for sportswear on the whole has changed to meet these new requirements [1]. Textile materials are an essential part of all sports as sportswear, and in many games as sports equipment and sports footwear. The sports textiles sector includes specialist apparel for specific sports each with its own particular functions. The performance fibres, yarns, fabrics, and finishes developed for this specialist sector are increasingly transferring to the mass market in the high street. The increasing cultural importance of sportswear in fashion means that only 25% of sportswear finds use in active sports or during exercise [2]. Emerging sports like yoga and winter sports are changing sportswear tradition. This chapter emphasizes the requirements and applications of different sport textile materials in hi‐tech applications, with very good wear comfort properties. Comfort describes especially through thermal comfort and relates to moisture management.

3.2 Textile Fibres

The evolution of fibre developments has gone through the phases of conventional fibres, highly functional fibres, and high‐performance fibres. Polyester (PES) is the single most common fibre for sport and active wear. Other fibres suitable for activewear are polyamide, polypropylene, acrylic, and elastane. Wool and cotton fibres find application in leisurewear and in increasing comfort required, e.g. in yoga. Synthetic fibres can be modified, e.g. by producing hollow fibres and fibres with irregular cross‐sections, or optimally blended with natural fibres to improve their thermo‐physiological and sensory properties [3]. The performance space model of different materials is illustrated in Figure 3.1.

Thermal protection Comfort KillatN Lycra Dagron Feathers Lyocel

Kevlar Wool Mechanical Weight Casual protection Cotton

Polyester Nylon

Coolmax

Coretex

Breathability

Figure 3.1 Fibre materials enabling required performances.

3.2.1 Natural Fibres

Cotton was a traditional solution for sport clothes, but synthetic fibres have replaced it, because of its easier maintenance and faster drying, and because it is a lighter product, especially when wet. This does not mean cotton is replaced entirely. Cotton and polyamide blends find use in sports clothing because they perform better than cotton. Cotton can be blended with regenerated fibres like Tencel for performance wear and sports garments to achieve relatively less absorbent and ‐drying garments [4]. Bast fibres like hemp, jute, or kenaf are used as reinforcements in sport equipment. However, the soft hemp fibre is suitable for t‐shirts and underwear. In these applications, it replaces the cotton. Their particular benefits vis‐à‐vis sustainability include the absence of any genetic modification and the possibility of organic farming and hence they represent low to no risk to the environment. Hemp provides the same breathability as cotton but is more stain repellent and especially more wear resistant. Wool has good wicking ability, high moisture regain, and is a good insulator even when wet. However, wool is slow to dry. Superfine Merino wool possesses superior water vapour permeability and quick drying properties. Merino wool can be blended with a range of other fibres, including silk, viscose, Tencel, PES, and polyamide. In addition, very fine Merino wool is convenient as an inner face of the fabric with an outer face of polyamide. Sportswool, a trademark of the Woolmark Company, is an example of a fabric which has been engineered to manage moisture. It is a hybrid material composed of a fine Merino wool sublayer for insulation and a PES exterior, which draws moisture away from the wool layer to the outer surface. The wool fibre next to the skin attracts perspiration vapour molecules, before they have the chance to condense into liquid, and dis- perses them into the atmosphere. The fabric has attracted the attention of top Australian 3.2 Textile Fibres 39 athletes and the Manchester United football team. Its major drawback, however, is that it takes longer to dry because of its wool content. The Merino wool content is normally ® limited to 25% and the other 75% of the garment is CoolMax PES yarn. Silk is a luxurious material with the most versatile, breathable, durable, and exqui- sitely comfortable natural fibre. The material is very suitable for winter underwear and is also easy to care for. Benefit in use is also the low friction of the materials. Owing to its natural elastic properties, it can stretch up to 20%. In addition, its high tenacity allows lightweight clothes to be designed. Silk is able to absorb one‐third of weight moisture before it feels wet. It also enables regulation of body heat through its breathability and moisture balancing properties. It is a hypoallergenic and repels mould and mildew.

3.2.2 Regenerated Fibres

Regenerated fibres (man‐made cellulosic fibres) are derived from natural sources, and tend to be absorbent. Tencel is the registered trade name for a type of lyocell by Lenzing, made from wood pulp cellulose. It has a very high absorption capability, a unique nanofibril structure, and a very smooth surface. It is a soft fibre that is stronger than cotton, both wet and dry, which is resistant to wear and tear for clothing. As a result, all these physiological functions pronounce markedly more for Tencel than for other cellulosic fibres. Lyocell‐type fibres are textile fibres, which – both in 100% applications and as a part in textile blends – have a clearly positive influence on the comfort in wear of textiles. The nanofibrillary structure of lyocell, the resulting ability to perfect moisture management, its smooth surface, and the purity of the fibre, which is due to the environmentally friendly production process, result in superior properties regarding wearing physiology. Lyocell satisfies the requirements for the temperature regulation of the human body, for skin sensitivity, hygiene and electrostatic behaviour, because of its natural construction and the associated properties, when compared to other fibre materials [5]. Recently, researchers at Helsinki University and Aalto University were successful in developing a novel cellulose spinning solvent. This two component ionic liquid consisting of a super base/acid ion pair, revealed excellent, spin stability resulting in outstanding fibre properties. The optimum rheological properties of the cellulose dope for spinning are attained at moderate temperatures, thus reducing the risk of uncontrolled cellulose degradation that may compromise rheological properties. The mechanical properties of the resulting fibres are outstanding and reach the highest level known for commercial regenerated cellulose fibres (tensile strength 700–870 MPa, elastic modulus 25–35 GPa) [6]. Bamboo fabrics originate from pure bamboo fibre yarns, which have excellent wet permeability, moisture vapour transmission property, soft hand, better drape, easy dyeing, and splendid colours [7]. However, the fibre is simply just another type of viscose fibre, and suitable for underwear, tight T‐shirts, and socks [8]. The cellulosic fibre material should have antibacterial properties, especially viscose. Misleading statements have been published, for example that natural bamboo fibre has no natural antibacterial property. The shape could not affect the natural antibacterial property of natural bamboo fibre but the hygroscopic and extractives influence that [9]. However, the viscose‐ like fibres can be modified to possess antibacterial properties by means of adding silver, 40 3 Sports Textiles and Comfort Aspects

e.g. an in situ incorporation technique was used for coloration and acquiring excellent antibacterial properties for viscose fibres by silver nanoparticles (AgNPs) [10]. Recently antibacterial and antifungal materials based on cellulose carbamate have been invented [11]. The carbamate pathway provides a simple and environmentally friendly method, offering an alternative to the environmental drawbacks of the viscose process. The tenacity of the fibres was determined in the range of 1.7–2.4 cN/dtex, which was comparable with that of commercial viscose rayon. Furthermore, the regenerated cellulose carbamate fibres filaments showed improved dye properties compared with viscose rayon [12].

3.2.3 Synthetic Fibres

Synthetic fibres are a frequent choice for sportswear. PES has outstanding dimensional stability and offers excellent resistance to dirt and alkalis, and has a comfortable smooth feel. It is the fibre used most commonly in base fabrics for activewear because of its low moisture absorption, easy care properties, and low cost. PES is essentially hydrophobic and does not absorb moisture. However, most base layer are PES yarns chemically treated to wick moisture. High tenacity and good durability make PES the choice for high‐stress outdoors use too. PES is also a strong fibre that is hydrophobic in nature. It is thus ideal clothing for wet and damp environments. The water‐resistant finish of the fabric intensifies further its hydrophobic nature. By creating hollow fibre it is also possible to build insulation into the PES fibre. Air traps inside the fibre and insulates the body heat. This keeps the body warm in cold weather. Another method to build insulation is to use crimped PES in a fibrefill. The crimp helps keep the warm air in. PES is an ideal fabric for this kind of insulation because it retains its shape. Cotton and wool tend to flatten with use and lose their warming effect [13]. PES is also wrinkle resistant in everyday clothing, like trousers, shirts, tops, skirts, and suits. Used either by itself or as a blend, it is also stain resistant and hence very popular. Owing to its increasing consumption and nonbiodegradability, PES waste disposal has created serious environmental and economic concerns. Indeed, the management of PES waste has become an important social issue. In view of increasing environmental awareness in society, recycling remains the most viable option for the treatment of waste PES. Among the various methods of recycling (primary or ‘in‐plant’, secondary or mechanical, tertiary or chemical, quaternary involving energy recovery), only chemical recycling conforms to the principles of sustainable development because it leads to the formation of the raw materials from which PES is originally made [14]. Most synthetic fibres (approximately 70%) are made from PES, and the PES most often used in textiles is polyethylene terephthalate (PET). The majority of the world’s PET production – about 60% – is for textiles; and the rest makes bottles (30%) and other packaging materials (10%). Recycled PES (often written rPET) is a green option in textiles, for two main reasons: ●● The energy needed to make the rPET is less than for virgin PES in the first place, so we save energy. ●● Moreover, we are keeping bottles and other plastics out of landfill. 3.2 Textile Fibres 41

It is true that recycling PES uses less energy than creating virgin PES. Various studies agree that it takes from 33 to 53% less energy [15]. The rPET materials have been available since 1993 [16]. Recently, the chemical recycling of PES (as monomers back to polymeric fibres) has become a more prominent alternative, owing to improved yields and the ability to benefit lower quality of fractions. Teijin Eco Circle, a Japanese company, has developed a closed‐loop recycling system for used PES products that employs the world’s first chemical recycling technology. With this technology, chemically decomposed PES is first converted to monomers and then back to new PES [17]. Polypropylene (PP) fibres find increasing use in the sportswear market, although its market share is still small. The fibres have a very low moisture absorbency but excellent moisture vapour permeability and wicking capabilities. PP has the advantage of providing insulation when wet. Insensible and liquid perspiration transportation from the skin without being absorbed makes it an ideal fibre for sportswear. PP claims to be a proved performer in moisture management, owing to its hydrophobic nature, and it has very good thermal characteristics, keeping the wearer warm in cold weather and cold in warm weather [18]. Because PP does not absorb moisture into the fibre, drying time is minimal. The fabric will dry while you wear it. Therefore, the athlete stays drier longer and dries faster. Bacteria, mould, and mildew cannot grow on PP, and will not damage the fibre. A PP garment washed regularly will not retain body odours. However, PP is an olefin material: it has high oleic properties and so absorbs fat and grease, which makes it essential to wash PP clothes properly [19].

3.2.4 Special Fibres

Owing to recent inventions in design and production, today’s new sports textiles use both synthetic and natural fibres. Natural fibres are often unsuitable for high performance, while synthetics have been the top choice. However, natural fibres combined with synthetics give sophisticated finishing treatments to improve their performance. Customers like this new group of ‘techno‐naturals’ or ‘super naturals’, because of their familiar look and handle. The slow‐to‐dry and cold‐when‐wet characteristics of cotton make this an unsuitable fibre for use against the skin during strenuous activity. Table 3.1 lists some of the common types of sports textiles. Phase change materials (PCMs) take advantage of latent heat that can be stored or released from a material over a narrow temperature range. PCMs possess the ability to change their state within a certain temperature range. These materials absorb energy during the heating process as phase change takes place and release energy into the environment during a reverse cooling process. The insulation effect reached by the PCM depends on temperature and time. Recently, the incorporation of PCM in textiles by coating or encapsulation to make thermoregulated smart textiles has become an area of increasing research interest, to review the working principles of PCMs and their applications for smart, temperature‐regulated textiles. Different types of PCMs are available and have been incorporated into cooling textile structures. PCMs found in contemporary consumer products were originally used in spacesuits and gloves to protect astronauts from extreme temperature fluctuations in space. The use of innovative new materials and the integration of PCMs into garments requires, for example, the development of new types of testing methods and standards. Furthermore, 42 3 Sports Textiles and Comfort Aspects

Table 3.1 A comparison of sports textiles.

Name Type Method Property Use

Hygra™ Sheath‐core‐type Water‐absorbing Superior antistatic Apparel (unitika ltd.) filament yarn polymer and nylon properties even applications under low wet include conditions sportswear like athletic wear, skiwear, golfwear, etc. Killat N™ Hollow nylon Hollow portion is Good water Superior fabric, (kanebo ltd) filament about 33% of the absorbency and for wicking cross‐section warmth retentive action, drying property time, moisture absorption, and transport ® Lycra At least 85% Gives it stretch and Comfort and Swimwear, active segmented recovery fit‐to‐order sportswear, and polyurethane floor gymnastics Roica™ Polyether‐type Knitted with soft Knitted tricot Practical in (asahi chemical) spandex nylon 66 yarn fabric gives a soft swimwear (Leofeel™) touch and excellent stretch

the development of materials, such as their mechanical properties, durability, or functionality in various conditions, may take a long time. The main challenge in developing textile PCM structures concerns the method of their application. The encapsulation of PCMs in a polymeric shell is an obvious choice but it adds dead weight to the active material. Efficient encapsulation, yield of encapsulation, stability during use, and integration of capsules onto fabric structures are important technological issues to be considered. Another important challenge for this innovative textile in practical use concerns the durability of PCM‐incorporated textiles following repeated use [20].

3.3 Developments in Yarns

Fabrics made from staple fibre yarns absorb more than fabrics made from filament yarns of the same content and yarn size, owing to the looser packing of the yarn. A looser packing in the yarn increases the fibre surface area for absorption and by increasing the gaps between the yarns increases moisture vapour permeability. Staple fibre yarns also provide better thermal insulation, owing to the increased volume of air contained in the yarn. They may also improve the sensorial comfort through a warmer feeling to the touch and the yarns have slightly lower areas of contact with the skin. However, the strength of the continuous filament yarns is better. Crimping of synthetic yarns can improve their water vapour permeability by increasing the bulk of the fibres in yarns and yarns in fabrics, thus improving their thermo‐physiological comfort. However, staple fibre yarns do not shed soil as well as filament yarns and they have a greater tendency to pill or shed lint. Filament yarns are useful in windbreaker jackets 3.4 Developments in Fabric Structures 43 and in the shell and lining of skiwear, where a combination of dense weave and low surface coefficient of friction is desirable [21].

3.4 Developments in Fabric Structures

The performance of the fabric/garment is enhanced or achieved by a number of processes, like selection of fibres and blending of the performance fibres during spinning and weaving, along with other yarns like cotton, viscose, bamboo, PES, acrylic, nylon, and elastane, and also by processing and finishing with chemicals (also known as functional finishes) [22]. On the one hand, existing functionality can be improved using nanotechnology and, on the other, it could make possible the manufacture of textiles with entirely new properties or a combination of different functions in one textile material [23]. Knitted fabrics are preferred for sportswear, as these fabrics have greater elasticity and stretchability as compared to woven fabrics, which provide unrestricted freedom of movement and transmission of body vapours to the next textile layer in the clothing system [24]. For warmth and comfort in adverse conditions, brushed, bonded, padded, quilted, or wadded textile fabrics give lightweight volume with little excess bulk [25]. Liquid transporting and drying rate are two vital factors affecting the physiological comfort of sports garments. In a study, plated knitted fabrics produced with functional fibre yarns in the back of the knit (close to the body) combined with PP or PES in the face (outer surface) were tested in terms of their wicking behaviour and drying rate capacity. Functional knitted fabrics provide attractive properties in vertical and horizontal wicking tests. The drying capability was assessed by drying rate tests under two different conditions, namely at 20 ± 2 °C and 65 ± 3% relative humidity and, in an oven, at 33 ± 2 °C, in order to simulate the human body temperature [26]. The fabric structure is an important factor in the design of sportswear garments. A study on the effect of warp‐knitted structures on thermo‐physiological comfort properties showed that most open‐construction 3D Eyelet provided the best moisture vapour permeability but had poor thermal insulation. Micromesh structure, which has much smaller openings or holes than 3D Eyelet does, but is relatively more open than the Pique and Mock Rib structures, yielded the most favourable combination of comfort properties. Dense pile fabrics play a big part in sports clothing and clothes with a high pile trap air for insulation and are highly absorbing. Brushed surfaces apply as an inner lining where the wearer feels comfortable, as the brushed surface against the skin does not cling to the skin’s surface. Wadding of fabrics is for insulation. PES wadding or synthetic foam is sandwiched between fabrics. Some wadding originates from synthetic microfibres, making it waterproof and breathable. The real three‐dimensional (3D) cloth structures are still rare. One reason may be the cost to produce these multilayered structures. However, combinations of novel automation and 3D manufacturing technologies may provide adaptable insulation structures. Knitted fabrics with a foam backing can be very soft, and when blended with elastane have good stretch and recovery characteristics, making them suitable for extreme sports. Technical knitted fabrics that are moisture wicking tend to be more open in structure on the back than on the face. In such open structures, moisture from perspiration passes more quickly through them. Examples of this include Aertex, a traditional 44 3 Sports Textiles and Comfort Aspects

sports fabric, which is widely used. These specific fabric structures have been developed with the specific requirements of sports textiles in mind, including temperature regulation [27] and moisture management [28]. DuPont CoolMax is a high‐performance fabric that can help the performance of the athletes who wear it. CoolMax moves sweat away from the body to the outer layer of the fabric, where it dries faster than any other fabric. In moisture management tests, garments made with CoolMax dried almost completely in 30 minutes. Cotton, by comparison, remained wet nearly 50% longer. Better evaporation means you spend less energy to cool your body, which increases your performance and endurance. CoolMax fabrics are specially designed not only to provide superior moisture management but also to enhance the wearer’s comfort. All of the benefits of these fabrics are permanent and built into the fibre, requiring no chemical treatments. CoolMax fabric originally developed for clothing intended for use during extreme physical exertion – sweat can evaporate quickly so the wearer remains dry. Other useful properties include resistance to fading, shrinking, and wrinkling. The fibres are now ® often woven with other materials like cotton, wool, Spandex and Tencel. As a result, CoolMax is found in a wide variety of garments from mountain climbing gear to casual sportswear and underwear. The fibres are not round but oblong and in cross‐section with grooves running lengthwise along the threads. They are either tetra channel or hex channel style. The series of closely spaced channels creates capillary action that wicks moisture through the core and out to a wider area on the surface of the fabric. This increases evaporation. Toray Industries Inc. developed a series of waterproof/breathable fabrics. The ® Entrant fabrics series intended for active wear, and there are many variations that used advanced finishes. Entrant‐DT is a lightweight, waterproof, and breathable microporous coated fabric. It is soft, with a dry smooth texture, and is intended for cycling, running, and hiking. Entrant GII‐XT is a microporous coated fabric made of two polyurethane resin components that produce a ‘pumped‐up’ effect and rapidly wick away sweat. It is wind‐, rain‐, and snow‐proof and so suitable for many outdoor winter sports. Entrant Dermizax EV is a lightweight fabric having a feather smooth texture with excellent waterproof/moisture permeability and durable water repellence (i.e. 20 000 mm of water pressure resistance and moisture permeability of 30 000 g m−2 /24 h). It is an excellent and original active sportswear fabric with globally top class waterproof/ moisture permeability, as well as excellent durable water repellence. It has a water repellent membrane with improved moisture permeability, making it especially suitable for snow sports and climbing. Entrant HB is a new‐generation fabric with a hybrid structure that synergistically integrates the advantages offered by a coating (balanced moisture permeability) and lamination (high waterproofness). It has high resistance to water pressure and high durability against repeated washings (80 points or higher after 20 wash cycles). Its main application is outdoor wear. Toray has developed also H2OFF™ made up of PES microfibre fabric with a unique high‐density weave structure, comprising millions of microcrimped fibre loops. It also features superb and durable water repellence, superior breathability, wind‐chill resistance, and attractiveness with a soft hand. Unitika developed Naiva by combining Naiva yarn with a nylon microfibre. Naiva™ is an Eval/nylon bi‐component filament yarn and Eval is nothing but a copolymer resin 3.5 Special Finishes 45 of ethylene vinyl alcohol. Naiva yarn composition is 55% Eval (23% ethylene + 32% vinyl alcohol) and 45% nylon. In the Naiva fabrics there are many nylon microloops on the surface, which are formed by making use of the high thermal shrinkage property of Naiva yarn. Naiva fabric not only has good moisture permeability but also has some other positive features, such as being lightweight with a soft hand. It is successfully used in mountaineering wear and other active sportswear. Field Sensor™ is a very popular high‐performance fabric from Toray, which employs a multilayer structure that not only absorbs perspiration quickly but also transports it up to the outer layer of fabric very rapidly using the principle of capillary action. It is composed of coarser denier yarn on the inside surface (in direct contact with skin) and fine denier hydrophobic PES yarn in a mesh construction on the outer surface to accelerate the evaporation of sweat.

3.5 Special Finishes

Finishes can transform textiles and give them an array of sports applications. The latest finishes give textiles a new aesthetic, a ‘good to wear’ experience, and superior performance. A fabric could not be weatherproof and breathable before, but sophisticated membrane technologies in the form of new coatings and laminates have altered this. Both visible and invisible coatings make it possible for a fabric to carry sweat away from, and for air to circulate around, the body. Ultrafine and superlight treatments make textiles rain‐, wind‐, and fireproof, and breathable (Figure 3.2). An ultrafine treatment on the face of the fabric does not hide the underlying textile, and appearance, texture, and drape are less affected. Generally, there are two methods of creating breathable, waterproof textiles: by using either (i) microporous or (ii) hydrophilic technologies. The first work by means of very fine holes in the membrane that allow perspiration to escape as water vapour and move quickly from inside to outside but completely block the passage of water. The second

Rain Wind

Waterproof Drops of water (10 000–2 000 000 Å) are too big to penetrate the membrane

Moisture-permeable Perspiration vapour (3.5 Å) passes through membrane’s inter molecular openings

Figure 3.2 Semipermeable cloth structure. 46 3 Sports Textiles and Comfort Aspects

attracts water molecules and allows warmer water vapour to move through the membrane to the cooler temperature outside the garment [4].

3.6 High Performance Applications

3.6.1 Sportswear

Sports textile is one of the branches of technical textiles. Further, sophisticated technologies find ways for technical textiles to produce sportswear. Hi‐tech textiles in sports are nothing new. In recent years, fabrics have been designed to perform specific tasks – to take moisture away from the body; patches on all jerseys so that the players can dry their hands for better grip; fabrics that sense high‐impact stresses on the joints of players; and fabrics that can sense heart rate, temperature, and other physiological data. Sportswear (or active attire) is clothing, including footwear, worn for sport or exercise. Typical garments include shorts, tracksuits, t‐shirts, polo shirts, and trainers. Specialized garments include wetsuits and salopettes. It also includes some underwear, such as the jockstrap. Sportswear includes more often replacements of casual fashion clothing. The best athleticwear for some forms of exercise, for example cycling, should not create drag or be too bulky. On the other hand, it should be loose enough so as not to restrict movement [3]. Beyond the traditional sports, there are an increasing number of new sports and so novel requirements accordingly. Snow sports apparel plays a crucial role in comfort by ensuring that the wearer does not become cold or wet when spending many hours exposed to temperatures below freezing. However, consumers are now demanding garments which will not only keep them warm and dry but also have enhanced performance properties such as improved breathability, lightweight, softness, and stretch. Furthermore, consumers are demanding snow sports clothing for other outdoor sports and even for day‐to‐day wear [29].

3.6.2 Desirable Attributes of Functional Sportswear

PES is the single most common fibre material used in sportswear. Also, polyamide, PP, acrylics, and elastane are also used for active wears. The fabric used in sports jerseys must be both breathable and stretch. In active and endurance sports, the performance of a sportswear is synonymous with its comfort characteristics. It should be capable of maintaining the heat balance between the excess heat produced by the wearer due to increased metabolic rate, on the one hand, and the capacity of the clothing to dissipate body heat and perspiration, on the other. Today’s sports demand high‐performance equipment and apparel. The lightweight and safety features of sport‐tech have become important in their substitution for other materials. These high‐functional and smart textiles are increasingly adding value to the sports and leisure industry by combining utilitarian functions with wearing comfort that leads to achieving high levels of performance [30]. Technological developments have enabled the production of materials that are tougher than wood, which breathe like skin, are waterproof like rubber, and at the same 3.6 High Performance Applications 47

Function of clothing

Demands of Demands of the sport the body

Protection Duration of activity Anthropometry Safety/Survival Thermo-physiological regulation Range of sporting conditions Psychological considerations

Figure 3.3 Different factors involved in designing functional clothing. time are eco‐friendly and highly economical. The augmentations in the sports and leisure industry have resulted in the use of technical textiles in different sports. Figure 3.3 shows the different factors involved in the designing of a functional clothing, such as a sports jersey. ●● The fabric needs to be able to hold throughout the duration of the activity and support the safety of the user. For instance, cotton clothing does not have any elasticity. This leads to restrictions in movement and it cannot hold well against the harshness of the sports environment. ●● The fabric is good in hot climates, where the sweat transfers through capillary action to the fabric surface and evaporates. Nevertheless, the conditions for a sport are not always cold and the metabolic rate (the sweating rate) is not the same as normal conditions. ●● PES on the other hand wicks away the sweat from the surface faster in high metabolic rate sports and nowadays we see dry‐fit, which efficiently keeps the sports person dry. The literature gives several different listings of sport textiles requirements [31]. ●● Sports textile must have comfort ability, be easy to wear, and enjoy ease of handling. ●● Sports textiles fabrics have a very high electrical conductivity, so they can permit the effectual dissipation of electrical charge. ●● It should be as light as best as possible. ●● Highly effective in moisture management, wick the moisture from the body and keep it dry. ●● Sports textile should have good perspiration fastness. ●● It is well known that sports fabric must have a heat conductive property that makes the wearer feel cool in summer and warm in winter. ●● Garments manufactured from sports textiles fabrics keep the normal stability of body comfort, because these fabrics are ultra‐breathable, fast drying, and possess outstanding moisture managing properties, which rapidly wick moisture away from the body. ●● These garments are also lighter and feature elasticity properties, which provides immense comfort and independence of movement. ●● Keeping a normal level of bacteria on the skin offers a high level of comfort and personal hygiene, especially during athletic activities. 48 3 Sports Textiles and Comfort Aspects

●● Sports textiles fabrics remove UVA and UVB rays that are dangerous to the skin, and guarantees an improved level of defence compared to the majority of general natural and man‐made fibres. ●● It also provides superior strength and durability. It is not possible to achieve all of these properties in a simple structure of any single fibre or even a blend of them. Certain optimizations will be needed so that the sportswear can enhance the performance of the wearer. Thermal comfort is essential for body performance: low temperatures reduce muscular performance and accuracy, while high temperatures limit physiological resilience (see Figure 3.4).

3.6.3 Differentiation of Requirements

When sportswear is adapted to leisure and casual wear, the need to balance hi‐tech performance with comfort aspects becomes more pronounced. The spread of a desire for a healthy lifestyle and an understanding of sports versus leisurewear varies from country to country. Yet the general trend is for the incorporation of sports and technological components into nonsportswear clothing. The schematic view expressed in Figure 3.5 differentiates the requirements of sport textiles in different sports. The figure groups together available materials with their technologies.

3.6.4 Requirements for an Active Sportswear

Sportswear should support performance in an ambient condition and during an activity. The dependences between body performance and environment are complex and physiological aspects in respect of environment are not the only issues surrounding performance, but they may become limiting factors in certain cases. Ambient air may vary from mild and moist to dry and extremely cold and so thermal protective clothing has to vary accordingly. Environmental factors, such as wind, convey heat away from

36°C

34°C

32°C

30°C

28°C

Figure 3.4 Temperature distribution over the body at 20 °C and 35 °C ambient temperature. 3.6 High Performance Applications 49

Thermal protection Comfort Yoga Winter Extreme sports sports

Mechanical Weight Casual protection

Athletics Contact sports

Breathability

Figure 3.5 Schematic view for different requirements of sports textiles. the clothing and compress the air layers underneath outer garments, whereas water and dirt block fabric construction, increase thermal conductivity, and evaporate heat away from clothing. Figure 3.6 presents both environmental and human physiological factors influencing clothing properties and microclimatic conditions, which create a feeling of comfort and support the performance, health, and safety of the user.

Thermal comfort Performance Safety Health

Micro- Environment Clothing Human climate Coldness Thermal Temperature insulation Wind Dry heat loss

Air Humidity Rain permeability Evaporative heat Heat radiation Water vapour Air loss permeability movement Snow and sleet Clothing Behaviour and Skin contact Impurities design postures e Maintenanc

Figure 3.6 Effects of environmental and human physiological factors on textile properties and microclimatic conditions. 50 3 Sports Textiles and Comfort Aspects

Table 3.2 General requirements and standards for their valorization.

Property Requirements Reference

2 −1 Thermal insulation, Icler (m K W ) Long period at +10 °C, light activity 0.170 EN 14058 Short period cold exposure (−15 °C), light activity 0.310 EN 342 Long period cold exposure (−15 °C), light activity 0.470 EN 342 Protection against wind, air permeability (AP) (mm s−1) EN 342/ EN 14058 High activity 100 > AP Moderate activity 5 < AP ≤ 100 Low activity AP ≤ 5 Resistance to water penetration (WP) (Pa) EN342/EN343 Protection against foul weather 8000 ≤ WP < 13 000 Protection against rain and foul weather WP >13 000 2 −1 Water vapour resistance, Ret (m Pa W ) Ret < 55 EN 342 All clothing layers in cold climate

How humans sense is more than just a physical process; it can also be understood behaviourally. However, the valorization of textile properties is based not only on simply sensing but also on advanced measurements of microclimate, enabling a scientific approach to physiological studies. Table 3.2 lists the properties, requirements, and respective standards.

3.6.5 Moisture Management

Moisture management is one of the key performance criteria in today’s apparel industry. It is the ability of a garment to transport moisture away from the skin to the garment’s outer surface. This action prevents perspiration from remaining next to the skin. In hot conditions, trapped moisture may heat up and lead to fatigue or diminished performance. In cold conditions, trapped moisture will lead to a drop in body temperature, cause chilling, and finally even to hypothermia. Excessive moisture may also cause the garment to become heavy, increase friction of the material, as well as cause damage to the skin from chafing. The overall comfort of sportswear during sports activities is very much related to the moisture‐related comfort sensations and clothing properties [32]. And yet this does not hold true in all instances. For example, surface roughness and the water content of the textiles had no influence on sock comfort. Perceived comfort depended on the fibre content of sock fabrics and on the perceived dampness and temperature of the feet [33]. Moisture transportation in textiles takes place through capillary action or wicking. In textiles, the spaces between the fibres effectively form tubes, which act as capillaries, that transport the liquid away from the surface. Two fundamental properties define the capillary action: ●● The capillary diameter: the smaller the diameter or the greater the surface energy, the greater the tendency of a liquid to move up the capillary. ●● The surface energy: hydrophilic fibres have a high surface energy. 3.6 High Performance Applications 51

Consequently, they pick up moisture more readily than hydrophobic fibres do. For this reason, fabrics with many narrow capillaries, such as microfibres, are ideal for moisture transportation. Another factor which affects moisture management is absorbency. However, while greater absorbency increases the ability for moisture to be drawn into the fabric, the tendency of absorbent fibres to retain such moisture affects comfort levels, as the garment becomes saturated. The fabrics, which wick moisture rapidly through the fabric while absorbing little water, help to regulate body temperature, improve muscle performance, and delay exhaustion. Generally, the most effective moisture management fabrics are high‐tech synthetic fabrics, which are from polyamide or PES microfibres. These are lightweight, capable of transporting moisture efficiently, and dry relatively quickly. As the removal of moisture is an important criterion, so too is the repellence of the fabric to rainwater. For outdoor sports garments, it becomes a necessity. High barrier and controlled permeability efficiently limit water access in the systems but may also easily cause thermal and moisture discomfort during activity. Push‐pull fabrics – bi‐component materials composed of a nonabsorbent material on the inside and an absorbent material on the outside – have proved to be an effective construction for moisture management fabrics. This is because the absorbent material on the outside draws the moisture away from the skin while the nonabsorbent material keeps the skin dry. There are several factors which affect moisture transport in a fabric. The most important are: fibre type, cloth construction or weave, the weight or thickness of the material, and presence of chemical treatments. Compared to cotton, synthetics are preferred in clothing of active sports as they do not retain moisture and this has the advantage of keeping garments lighter than cotton when it is wet. In addition, synthetic fibres have the added advantages of quick‐dry and good shape‐retention properties.

3.6.6 Requirements of Cold Weather and Low Active Sports 3.6.6.1 Thermal Insulation Thermal transfer occurs through dry heat loss by convection, conduction, and radiation, while moisture transfer is due to moisture transportation [34–38]. Heat and moisture transfer occurs through the pores of textile, fibre interior, and surface; the capillaries between fibres and yarns; and the air between fabrics and yarns [39]. A fabric’s properties can significantly affect humidity and temperature distributions, as well as comfort [40]. In several studies [36, 38], the mechanisms of heat and moisture transfer from the skin to the environment have been modelled, and these are presented in Figure 3.7. Clothing prevents heat transfer between human and environment, which is determined by thermal insulation of the clothing. Thermal insulation is expressed in SI units by m2K W−1. It has been generalized that a warm business suit provides thermal insulation of approximately 0.155 m2K W−1 for the whole body, which was originally equal to 1 clo unit [41]. Fibres form on average about 5–20% of the efficient thermal insulation of the cold protective clothing system, whereas trapped dry and still air in the fabrics and between 52 3 Sports Textiles and Comfort Aspects

Air layers Boundary air layer Environment

Skin Wet conduction Conduction – Radiation − Convection Wicking Condensation Evaporation

Pores in fabric Conduction Radiation Convection

Evaporation Ventilation

Garment openings

Skin

Fabric layers

Figure 3.7 Heat and moisture transfer mechanisms from skin to environment.

garment layers forms on average about 80–95% [42], owing to the about eight times higher thermal resistance of the air than fibre materials [43]. The air volume underneath the clothing increases by adding clothing layers, but also fibre physical properties, such as diameter, crimp, length, and shape, as well as the yarn and the fabric structure. Garment fit and high air content in the clothing system increase the thermal insulation [44], but the insulation starts to drop beyond an optimum air layer thickness. Clothing size, and thus volume of the dry, still air in microclimate, is a significant factor when aiming for maximum thermal insulation of the cold protective clothing [37, 45, 46]. Air layers inside the clothing are not evenly distributed over the body and there is more small air gaps than large ones [47]. Air content in the clothing can be measured by pinching the fabric from different points of the body or by calculating from the difference between the clothing measure and manikin or test subject [48]. Recently, 3D body scanning methodology has been used to analyse garment fit and air gaps inside clothing. The method has been shown to give comparable results with manual measurements and to be a valuable tool for objective ratings and fit evaluation of garments [49–52].

3.6.6.2 Cold Protective Clothing The purpose of cold protective clothing is to prevent the effects of cold combined with wind and moisture. The base of the clothing is fibre material formed into yarns, which are finally produced into porous knitted or woven fabric constructions. The thermal resistance is shown to be higher when more air is trapped in the fibres and fabric structures [53]. Therefore, functional clothing consists of at least three separate layers: inner, 3.6 High Performance Applications 53 mid, and outer. The layered clothing enables the level of clothing insulation to be adjusted depending on the physical activities and ambient conditions. Thus, the materials for each layer have to be carefully selected [54–56]. The requirements of cold protective clothing are determined based on the ambient conditions (air temperature, wind, moisture, cold surfaces), cold exposure times, physical activity, and ergonomics during the activity as well as demands of the legislation and standards to maintain users’ thermal balance, comfort, and work ability in the cold [57]. Working postures and ergonomics have an effect on thermal insulation by compressing air layers inside the clothing. In addition, individual differences in body anthropomet- rics present challenges in clothing design and patterning, especially in protective clothing [58].

3.6.6.3 Inner Layer The inner layer is the functional part of the cold protective clothing and it is affected by mid‐ and outer garment layers [59]. The inner layer is exposed to heat, water vapour, and liquid exchange from the skin. The main function of the inner layer is to keep the wearer’s skin dry. In addition, it improves thermal and moisture sensations on the skin and, therefore, may significantly affect sensorial comfort [60]. Suitable inner layer material for a cold climate should provide good tactile properties and high wicking properties, and be lightweight and noncompressible [61–63]. It has been found that cotton with naturally absorbent fibre construction as an inner layer under winter clothing led to lower skin temperatures during recovery after walking and higher moisture content than a hydrophobic PP inner layer, whereas PP resulted in higher metabolic production than with cotton [64, 65]. Highly hydroscopic woollen fabrics have proven dryer perception and skin temperature when wet than weakly hydroscopic PES [66]. Wool is naturally flexible and breathable, owing to its fibre construction [67]. Itching of the woollen fabric is prevented by using Merino fibres thinner than 23 μm, because the fibre ends bend when touching the skin [68].

3.6.6.4 Layered Clothing The outer layer protects against cold, wind, and moisture and it has the most complex structure. The outer layer is often required for protection against wind and moisture from external sources as well as permeability of moisture vapour due to sweating [58]. The literature has discussed the use and benefit of semi‐permeable membranes in a cold climate, especially while and after sweating. It has been proposed [69] that permeable fabric constructions provide a clear benefit to wearers and breathable membranes have sufficient moisture transport at low temperatures as well (−20 °C). They showed that moisture accumulations were much lower with material combinations consisting of a breathable membrane than with nonbreathable systems. If a membrane was attached in four‐ and five‐layer fabric combinations, moisture accumulated mostly in the third and, secondly, in the fourth layers from the skin [70]. If an outer membrane is attached to the insulating layer of the multilayer clothing system, vapour permeability increases and moisture accumulations decrease in a cold climate after a period of sweating. It has also been reported that moisture accumulation in a multilayer clothing system affects layer arrays, such as air layers between the layers. 54 3 Sports Textiles and Comfort Aspects

It was found that the moisture accumulations were least when the fifth membrane layer was attached to the fourth fleece layer [71–73].

3.6.6.5 Comfort The importance of textile comfort has been studied widely [74]. Clothing comfort is a state of mind when it is at its lowest stress level. Comfort is defined as the absence of perceived pain and discomfort. Clothing comfort is a state of satisfaction indicating physiological, psychological, and physical balance in the person [75]. A balanced process of heat exchange between the human body, the clothing, and the environment can be defined as thermal comfort [76]. Types of clothing comfort depend on multiple variables [77]. ●● Thermal: heat and mass transfer. ●● Sensorial: tactile, touching, hand‐feel. ●● Movement: movement of body parts. ●● Social: status. ●● Psychological: aesthetic sense, design. ●● Functional: helpful for any function. Garment design is related to the aesthetic appeal of clothing, such as its colour, style, etc., as well as its functional properties. Garment design should also consider the aesthetic preferences of different age groups as well as the desired properties. Comfort can be divided into three main areas: aesthetic, sensorial, and thermo‐ physiological. As demonstrated in Figure 3.8, these can be viewed both as being separate influences and, when it comes to the wearer, as producing one sensation.

Thermo- Physiological

COMFORT

Aesthetic Sensorial

Figure 3.8 Various aspects of comfort. 3.6 High Performance Applications 55

3.6.7 Requirements for Hot Weather and High Activity

Hot weather clothing requires lightweight fabric, especially clothing made from very lightweight cotton fabric is comfortable to use. The moisture stability of the cloth has marked importance on comfort [78]. Garments design for extremely cold weather is very important. In such conditions, design of the clothing should be such that air cannot pass through or get in easily through the collar, cuff, ankle, front opening, and waist opening. Velcro is used instead of zips. It could be stated that the comfort ability of the clothing is related to the weight, thickness, heat resistant property, flexibility, softness and design of the clothing [79].

3.6.8 Techniques to Achieve the Requirements

The properties of clothing need to optimize several restricting variables achievable with different materials and constructions. Figure 3.9 illustrates some of the technical ena- blers necessary to meet these requirements, such as applying layered clothing to enhance thermal comfort, using body scanning to create the perfect fit, and introducing functional materials to improve textile performance. And in different environmental conditions, the same set of clothing will have different requirements. The optimization of clothing design and smart materials are discussed below.

3.6.9 Multiple Criteria Decision Making

MCDM and MCDA are well known acronyms for multiple criteria decision making and multiple criteria decision analysis. Stanley Zionts helped popularize the acronym with

Thermal protection Comfort Patterning Layered Functional structures Weaving Composites Mechanical Weight Casual protection

Knitted Body scan 3D Zoning

Active materials

Breathability

Figure 3.9 Enabling technologies for required performances. 56 3 Sports Textiles and Comfort Aspects

his 1979 article ‘MCDM – If not a Roman numeral, then What?’ intended for an entre- preneurial audience. MCDM is concerned with structuring and solving decision and planning problems involving multiple criteria. The purpose is to support decision makers facing such problems. Typically, there does not exist a unique solution for such problems and it is necessary to use a decision maker’s preferences to differentiate between solutions. ‘Solving’ can be interpreted in different ways. It could correspond to choosing the ‘best’ alternative from a set of available alternatives (where ‘best’ interpreters as ‘the most preferred alternative’ of a decision maker). Another interpretation of ‘solving’ could be choosing a small set of good alternatives, or grouping alternatives into different preference sets. An extreme interpretation could be to find all ‘efficient’ or ‘none dominated’ alternatives (which we will define shortly). When considering a simplified decision framework for a running suit, for example, a typical approach for whole dilemma solving is as follows: ●● Define the decision opportunity. ●● Identify stakeholder interests. ●● Build a decision framework. ●● Rate the alternatives. ●● Weight stakeholder interests. ●● Score the alternatives. ●● Discuss results, re‐score, discuss again, decide. In Figure 3.10 one hypothetical case for optimization is illustrated. Optimization criteria are essential for the result. However, one parameter may become limiting, and this may lead to trade‐offs with other requirements. The difficulty of the problem originates from the presence of more than one criterion. There is no longer a unique optimal solution to an MCDM problem that can be obtained without incorporating preference information. The concept of an optimal solution is often replaced by the set of nondominated solutions. A nondominated solution has the property that it is not possible to move away from it to any other solution without

Goal Interests Sub-criteria Alternatives

Stretch Knitted Comfort Lycra Sizing Select 3D modelled the best sport Thermal Breathable Polyester textile protection for Cooling running Cool max

Weight Ultralight Zone pattern

Figure 3.10 Layers of selecting features for optimized product. 3.7 Active Textiles 57 sacrificing in at least one criterion. Therefore, it makes sense for the decision maker to choose a solution from the nondominated set. Otherwise, they could do better in terms of some or all of the criteria, and not do worse in any of them. Generally, however, the set of no‐dominated solutions is too large to the decision maker for their final choice. Hence, tools that help the decision maker focus on their preferred solutions. Normally, one has to trade‐off certain criteria for others.

3.7 Active Textiles

3.7.1 Perception

Design has essential value for sport textile perception. A classic example is combat sports (e.g. boxing). Even though there is no scientific basis for the choice, red is favoured over blue by participants and spectators alike. However, it is predictable that colours and looks have an impact on individual and especially team performance. It has been shown scientifically that the perception of high functional sports/leisurewear can influence the wearer positively, such as boosting self‐confidence, affirmative thinking, or health consciousness [80].

3.7.2 Design

Strangwood [81] points out that the close interplay of design and sports materials brought about by engineering modelling is only as good as the data applied. Technological innovation, in both design and materials, has played a significant role in sport, achieving its current standing in both absolute performance and its aesthetics. In sports garments, two examples that clearly exemplify design and materials are graduated compression garments and swimming bodysuits. More technically speaking, design has a role in the physical performance. The use of textile materials in high‐performance sports can play a pivotal role in the outcome of the event and/or game. There is no doubt that an understanding of the aerodynamic effects of sports garments on sporting performance is becoming an important criterion of sports technology and product design. The demands on garment design associated with aerodynamics require a quantitative understanding of a material’s performance, textile, and surface texture. The body parts covered by textiles can influence aerodynamic behaviour by altering the transition from laminar to turbulent boundary layer of the flow without affecting body position [82].

3.7.3 Patterning

In sports like football and basketball, where there is intense multidirectional activity, loose‐fitting and comfortable clothes are required. In activities such as swimming and cycling, where speedy body movements are important, skintight or close‐fitting clothes are preferred. In addition, if the weather is cold, the clothing must exhibit a high level of thermal insulation, but when the wearer is hot the level of thermal insulation must be low [83]. However, outdoor activities demand good thermal balance, but this is difficult to maintain. For that reason, active sportswear should provide sufficient heat transfer for the skin temperature to remain within a comfortable range [84]. 58 3 Sports Textiles and Comfort Aspects

3.7.4 Active Materials

‘Biohacking’ is a general term for aiming to optimize the well‐being of a human. Biohackers are not necessarily interested in technology itself but rather a healthy lifestyle and well‐being followed by a deep understanding of them. In many cases, the deep understanding of the body requires exact body monitoring by measuring its vital signs – the bio‐signals of the body. Biohackers gather data about their bodies in everyday life, during training, working, and sleeping. By monitoring pulse, heart rate variability, muscle activity level, body movements, and breathing frequency, the wearer gets reliable, continuous information about their body, like body performance, sleep quality, and stress level. A wearable textile with integrated sensing applications is the most obvious solution for body monitoring.

3.8 Smart Textiles and Garments

Smart fabrics enable digital components (including small computers) and electronics to be embedded in them. Smart textiles are fabrics developed with new technologies that provide benefit to the wearer. Pailes‐Friedman of the Pratt Institute states that ‘what makes smart fabrics revolutionary is that they have the ability to do many things that traditional fabrics cannot, including communicate, transform, conduct energy and even grow’ [85]. Smart textiles can be broken into two different categories: aesthetic and performance enhancing. Aesthetic examples include fabrics that light up or change colour. Some of these fabrics gather energy from the environment by harnessing vibrations, sound, or heat and react to these inputs. Smart textiles are used to enhance performance in areas such as athletics, extreme sports, and the military. These include fabrics designed to regulate body temperature, reduce wind resistance, and control muscle vibration – all of which may improve athletic performance. Other fabrics form protective clothing, to guard against extreme environmental hazards, such as radiation and the effects of space travel [86].

3.8.1 Wearable Technology

The term ‘wearable technology’ covers all body monitoring devices for wearing or carrying. It can be divided into ‘wearable computing’, where a garment or textile does not exist, and ‘textile integrated wearable technology’ or ‘textile integrated sensing solutions’. Wearable computing requires only electronics, whereas smart textile solutions are realized on textiles using electronics, mechanical, or chemical technologies, or a combination of these approaches [87]. When a garment or a piece of clothing is involved as an integration platform, the combination becomes smart or intelligent clothing. The ‘intelligence’ of clothing does not have to be at the textile structure level and the textile can simply embed, cover, or protect electronics to form intelligent clothing. In these structures, commercial electronic devices attach to or laminate textile substrates [87]. Smart fabric or textiles can be defined as fibre based structures that can react to stimuli and are capable of interacting with the environment. The integration of 3.8 Smart Textiles and Garments 59 electronics with textiles provides new approaches for lighting, heating, cooling, energy harvesting, communicating, sensing, measuring, and monitoring. In addition to electronics, the smart fabric can also react to thermal, chemical, mechanical, or magnetic stimuli [88, 89]. Smart textile technology always includes a textile component that can change and adapt to changes, such as thermochromic materials, but such technology does not necessarily need to consist of electronics. Those smart textile applications that include electronics fit primarily to monitor the user or the environment based on output data that inform, support, take care of, and/or indirectly protect the user. Bekaert ® Textiles applied HeiQ’s Adaptive technology. Adaptive enables fabrics to respond dynamically to changes in temperature and moisture levels in order to achieve optimal comfort and performance [90]. A smart textile or garment is widely used for wearable applications in sports, medical and health care. For example, wearable textile electrodes can monitor vital functions. Wearable technology shows as beneficial for mHealth (mobile health) applications. Suunto has developed a versatile and a compact sensor system for sports called Movesense. It runs an open Movesense API (application program interface) for the development of unique motion‐sensing applications. In addition to the sensor, the system consists of a flat snap connector, enabling the smooth integration of the sensor to the garment, and a UI (user interface) device, e.g. smart phone and the cloud, for data storage (Figure 3.11). It uses Bluetooth technology in data transferring from sensor to UI. ® Movesense technology is being utilized in several applications. ReimaGO is an activity sensor for kids (Figure 3.12). It measures the duration and intensity of activity. The gathered data, the amount of energy used, are portrayed in a game app, which motivates the child to move. Kaunila has developed an activity collar for dogs. It again measures activity level and the app, allows the owner to follow their pet in real time. Suunto’s Smart sensor instead uses Movesense technology for heart rate monitoring and is able to store the data when the UI is not available (e.g. during swimming) [91]. In body‐monitoring, textile‐sensing solutions are applied [92, 93]: ●● Heart rate, heart rate variability, heart activity (ECG). ●● Stress level and sleep quality (ECG). ●● Brain function and vitality level (EEG). ●● Muscle rate and balance (EMG). ●● Body motions and postures (EMG). ●● Body composition – fat content and fluid balance (EBI). ●● Lung function (EIT).

Connector Sensor UI Devices Cloud

Figure 3.11 The operational components of Suunto Movesense. 60 3 Sports Textiles and Comfort Aspects

Figure 3.12 Movesense hardware technology: ReimaGO, Kaunila and Suunto Smart Sensor.

●● Respiration rate and frequency. ●● Skin conductivity. ●● Skin temperature. The term ‘textile electronics’ includes all of the applications in which textiles and electronics are involved. Textile applies only as a pure platform for covering and embedding existing commercial electronics [94] by using sophisticated textile and clothing technologies, such as lamination and welding; and textile‐related materials, such as foams; and trimmings, such as snaps, hooks, and zippers; alternatively, the textile can act as an electronic component within a system. The conductive textile instead performs as an electrode, antenna, signal, power, and heat transfer component, etc. These products are replacing conventional hard plastic solutions by providing better comfort to the user [95], which again enlarges the range of detecting based applications. The advantages of textile electronics are versatile: ●● Clothing‐embedded electrodes enable perfect electrode placement and shape. ●● The flexibility of electrodes guarantees proper skin contact. ●● Cables and wires can be integrated into textile invisibly. ●● System invisibility makes it acceptable for the user. ●● Comfortability and softness of electrodes enable long‐term measurement. Textile electronics is an interdisciplinary science of textile and clothing technology, electronics and information technology, as a system needs to have a certain architecture (Figure 3.13). The control‐processing unit (CPU) collects, processes, and transfers the data. The energy source embeds to the same package. Today, printable electronics integrate directly or indirectly with the textile substrate and has a flexible, garment‐like solution. The communication network can be wireless, but in many cases, visibly integrated conductive yarns implement the communication between the textile electrode and the electronic component (CPU). Smartphones seem to be the most useful devices for input and output interfaces of the system. Developed by Sensoria (formerly Heapsylon), based in Redmond, Washington, in the United States, a t‐shirt and bra carry out the real‐time monitoring of heart rate, burned calories, and respiration rate, among other parameters, by measuring ECG with textile 3.9 Testing Methods and Quality Control 61

Network Communication

Display Sensor Visual Sensing Feedback AND AND/OR Voice UI CPU INPUT Audio OUTPUT Input Data storage and processing Feedback AND/OR AND/OR Vibrator Antennae Tactile Positioning Feedback

Energy Source Power Supply

Figure 3.13 Smart clothing architecture. sensors and collecting data via Bluetooth technology [96]. Bluetooth is a dominant technology for wireless communication between the wearable textile electronic, the input device, and the output device display or smartphone. Runware, based in Sainte‐ Clotilde, France, is launching the Runalyzer chest strap for the iPhone, which provides access to more than one hundred activity applications for walking, running, cycling, and other activities [97]. The application areas for intelligent textile solutions are: ●● Professional and protective wear. ●● Fashion. ●● Sport and well‐being. ●● Home interiors. ●● Automotive. ●● Construction. ●● Gaming industries. ●● Medical and health care. It is expected that active and smart materials are increasingly present in high‐tech sport textile solutions. Developments in the field of the Internet of things (IoT) enable endless data access and computational capacity while artificial intelligence (AI) will improve the performance of adoptable systems.

3.9 Testing Methods and Quality Control

Testing methods of textile physiology provides us with the scientific means to evaluate real performance benefits of textile materials in extreme conditions. Ultimate performance is essential for professional competitors, but it is also important to hobby athletes. 62 3 Sports Textiles and Comfort Aspects

Sportswear textiles are becoming more like devices and technical compositions than simply garments. Garment development will take quality control to the next level, when the procedures used for testing in the electronics industry will be applied to sports textiles. Moreover, the increasing trend of personalization in fashion will create IoT solutions to define customers’ properties and desires.

3.10 Sustainability and Ecological Aspects

High‐performance materials have also environmental impact. The requirements of sustainability are increasing. Composite and mixed materials make the as yet rare textile recycling a challenge, especially smart and electrical devices which create totally new sustainability issues. At the same time, sport textiles are becoming increasingly casual, which increases the importance of ecological considerations. The use of natural materials should be promoted in all possible applications as it might contribute to sustainability and recyclability. In all products, however, the technical performance is most dominant and in the design focus should be on wear‐resistance and maintenance‐ friendly aspects.

3.11 Conclusion

The traditional application of sport textiles for high‐activity outdoor athletics, team sports, as well as less active games, e.g. golf, is changing. Sport textiles are now being designed for an ever‐increasing number of different sports, including so‐called well‐ being sports like yoga and outdoor pursuits like winter and extreme sports. Further, sportswear has become part of leisure and casual clothing. At the same time, high‐tech materials and wearable technologies have become more common and affordable, leading to the development of functional and high‐performance sports textiles. All these developments have led to a wide variety of materials, thus making their selection more complicated. This leads to a balancing of properties and functionalities with user and maintenance friendliness.

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Medical and Healthcare Textiles Nuno Belino1, Raul Fangueiro2, Sohel Rana2, Pelagia Glampedaki3, and Georgios Priniotakis4

1 University of Beira Interior, Covilhã, Portugal 2 University of Minho, Guimarães, Portugal 3 Social Fashion Factory ‐ Soffa, Athens, Greece 4 Technological Education Institute of Piraeus, Egaleo, Greece

4.1 Introduction

Medical textiles (medtech) are considered one of the key growth areas in the high tech textile and apparel industry. Medtech is clearly driving the emergence of new and improved raw materials and processes, leading to new technological solutions specifically designed to tackle the problems medical professionals and patients are daily faced with [1]. The manufacture of medical textiles involves many different polymers and production processes. Some of the technologies used are already consolidated, whereas others are at a more formative stage and will need more time before they become recognized, accepted, and widespread [2]. The continued and revolutionary advancement of materials science – notably in the fields of bionanotechnology, and tissue engineering – will likely reshape medicine as we know it, and will create a new world of opportunities for medical textiles in the forthcoming decade. The expectations in this field are very high and the aftermath of innumerable research efforts carried out by universities, laboratories, and companies around the world [3], undoubtedly at the forefront of science, will have a huge impact on the life expectancy, quality of life, and comfort of individuals.

4.1.1 Medtech Definition

There are a few known definitions that have been evolving over time. The most common one states that ‘medical textile’ is a general term which describes a textile structure which has been designed and produced for use in any of a variety of medical applications, including implantable applications. Other researchers look at medical textiles as fibre based products and structures used in first aid or in the clinical treatment of a wound or medical condition. It embraces all those technical textiles used in health and

hygiene applications. Ultimately, there is no universal definition for the term ‘medical textiles’. Typically, they are named by the type of their end use [4–6] and classified by their application, as follows: ●● nonimplantable materials. ●● implantable materials. ●● extracorporeal devices. ●● healthcare and hygiene products. Notwithstanding, different sorts of product families are complementary and expand the aforementioned categories. It can be clearly seen that the growing markets of functional clothing and smart textiles are amongst those technologies creating a new branch of, and boosting, medical textiles. Therefore, it is high time for a new and broader definition of medical textile products. In this new understanding, a manufactured good obtained or processed with textiles fibres and/or involving any textile transformation process which leads to a product that actively protects the human body from external hazards or environmental dangers, contributes to infection control, acts as body parts replacements, helps to maintain or assist human health, facilitates the administration of healthcare services, envisages patients’ and professionals’ comfort, or takes part in smart systems that provide health monitoring and telemedicine should be considered a medical textile product.

4.2 Textile Materials, Structures, and Processes

The use of fibrous materials in medical, healthcare, and hygiene products demand a great many specific attributes. Amidst others, fibres used in medical textiles must fulfil the following criteria. The fibres: ●● Must be nontoxic. ●● Must be nonallergenic. ●● Must be noncarcinogenic. ●● Must be able to be sterilized without impairing any change in their physical or chemical characteristics. ●● Where necessary are biodegradable. ●● Where necessary are nonbiodegradable ●● Are compatible with most living systems. ●● Are versatile in their physical form. ●● Allow drug transportation and delivery. ●● Possess good manipulability. ●● Have good wetting, wicking, and fluid control. A common classification of fibres used in health‐related applications [7, 8] is made in accordance to their origin and biological resistance, as seen in Figure 4.1. According to Source of Origin

●● Natural: cotton and silk most widely used. ●● Regenerated: Viscose. 4.2 Textile Materials, Structures, and Processes 71

FIBRE CATEGORIES

BY SOURCE OF BY BIOLOGICAL ORIGIN RESISTANCE

NATURAL REGENERATED SYNTHETIC SPECIALITY FIBRES BIODEGRADABLE NON-BIODEGRADABLE

Figure 4.1 Classification of fibres used in medical, healthcare, and hygiene products.

●● Synthetic: polyester, polyamide, polytetrafluoroethylene (PTFE), polypropylene, carbon, glass, and so on. ●● Speciality fibres: alginate, collagen, and chitin.

According to Biological Resistance

●● Biodegradable: fibres which are absorbed by the body within two to three months following implantation and include cotton, viscose rayon, polyamide, polyurethane, collagen, alginate, polycaprolactone, polypropiolactone. ●● Nonbiodegradable: fibres that are absorbed by the body slowly and take more than six months to degrade are considered as nonbiodegradable. Nonbiodegradable fibres include polyester (e.g. Dacron), polypropylene, PTFE, and carbon. The combination of the fibres’ features with the properties imparted by the production process will define the functional performance of the product [9]. Figure 4.2 depicts the relationship between all the key factors involved at different stages of the assembly of a health‐related product and the functional characteristics of the final product. Fibrous structures used in healthcare‐related applications are produced by one of the following technologies: woven, knitted, braided, nonwoven, and composite. The structure formed by the first three processes requires the use of yarns, whereas the nonwoven structures are, mainly, obtained directly from polymer extrusion. Composites structures are specifically designed and can be made using a combination of the previous processes.

MEDICAL, HEALTHCARE MOLECULAR FIBRE YARN FABRIC AND PROPERTIES PROPERTIES PROPERTIES PROPERTIES HYGIENE PRODUCT PERFORMANCE

FIBRE STRUCTURE YARN STRUCTURE FABRIC STRUCTURE TEXTILE PRODUCTION PROCESS

Figure 4.2 Variables involved in the overall performance of the medical textile product. 72 4 Medical and Healthcare Textiles

The production of this sort of product is largely dominated by the nonwoven process [10], because it permits the use of many different kinds of fibres in a wide variety of forming and consolidating possibilities and, thus, can manufacture a vast array of products in a very cost‐effective way.

4.3 High Performance Applications of Medical Textiles

The number, degree of complexity, and specificity of medical, healthcare, and hygiene applications are vast. Typically, this sort of product is classified into four main categories, as illustrated in Figure 4.3. The different medical applications are the result of the use of diverse textile fibres and production processes. All of them require specific attributes to attend to their end‐use functional properties. The most common applications are illustrated in Figures 4.4–4.7 in which used raw materials are represented by their standard name within a circle, whereas the production process is depicted by their initials inside a lozenge. Nonimplantable fibrous products. These products are meant to be used as external applications on the body and may or may not be in contact with the skin. Implantable fibrous products. Range of products that are used in the effective repairing of the body whether in wound closure or surgery replacement. Extracorporeal devices. Are synthetic organs designed to replace and support the function of vital organs such as the kidney, liver, and lung. They are mechanical devices, used for blood purification, that incorporate textile technology. Figure 4.8 shows the hollow fibres of a dialyzer, which is responsible for filtering the unwanted waste materials as a normal kidney will do. Healthcare and hygiene materials. Is one of the most important and widely spread sectors of health‐related products. The range of applications is vast and varies from care and safety of healthcare staff/patients to products used within the operating theatre. They can also be classified as reusable or disposable.

EXTERNAL USE

HEALTHCARE AND HYGIENE MATERIALS

IMPLANTABLE MEDICAL NON-IMPLANTABLE INTERNAL USE FIBROUS MATERIALS TEXTILES FIBROUS MATERIALS EXTERNAL USE

EXTRACORPOREAL DEVICES

EXTERNAL USE

Figure 4.3 Systematic classification of medical textiles. ABSORBENT NON-IMPLANTABLE NW CLY CV CV PLASTIC PAD FIBROUS PLASTERS CV FILMS CO PET GF KN PRODUCTS

WOUND NW WO WO PE CV PA SE CONTACT REQUIRED PRODUCT LAYER PROPERTIES WOUND CARE NW KN ANTIBACTERIAL BEHAVIOUR GAUZES CO CV WO NW KN HIGH WATER/VAPOUR PERMEABILITY

HIGH AIR PERMEABILITY PLASTIC NW WO CV BASE MATERIAL FILMS MOISTURE MANAGEMENT LINT CO WO DEGREE OF ADHERENCE

SIMPLE PHYSICAL BARRIER WO CV INELASTIC / ELASTIC ODOUR MANAGEMENT PLASTIC WADDING CV CO LINTERS FILMS THERMAL BARRIER

WO CV LIGHT SUPPORT DRUG LOAD PRODUCT DEFINING CLEANLINESS CHARACTERISTICS BANDAGES STERILE FIBRE TYPE FABRIC DESIGN WO CV COMPRESSION NON-TOXIC YARN BLEND FABRIC WEIGHT FIBRE LENGTH FABRIC STIFFNESS NON-ALLERGENIC FIBRE FINENESS FABRIC THICKNESS LIGHT SUPPORT FIBRE DIAMETER FABRIC RESILIENCY WO CV ORTHOPAEDIC THERMOPHYSIOLOGIAL FIBRE CROSS-SECTIONAL SHAPE FABRIC ABSORPTION CONFORT YARN LINEAR DENSITY FABRIC POROSITY DEBRIDMENT ABILITY YARN TWIST FABRIC SURFACE PROPERTIES YARN STRENGTH FINISHING OPERATIONS YARN ELASTICITY MATERIAL CONTAMINATION

Figure 4.4 Nonimplantable fibrous products. MONO COLLE- BIO- BR PGA PLA IMPLANTABLE ORTHOPAEDIC ARTIFICIAL JOINTS SILI- IMPLANT RGAN DEGRADABLE POM PE FIBROUS IMPLANTS AND BONES CONE PRODUCTS

NON- STEEL PP PTPE PET PA SUTURES REQUIRED PRODUCT VASCULAR BIODEGRADABLE CV PROPERTIES GRAFTS

MONO IMPLANT BR BIOCOMPATIBILTY CARDIO- VASCULAR BIODEGRADABLILITY IMPLANTS HEART CO WO KN WO CV ARTIFICIAL TENDOM NON-TERATOGENIC VALVES

BIOSTABILITY

WO CV ARTIFICIAL LIGAMENT NON-TOXIC

NON-ALLERGIC

NON-CARGINOGENIC POLYMER TYPE FLEXIBILITY SOFT WO ARTIFICIAL CARTILAGE POLYMER DENSITY RESILIENCE TISSUES BACTERIAL RESISTANT IMPLANTS POLYMER COUNT NUMBER TEAR STRENGTH WOUND CLOSURE POLYMER REACTIVITY CREEP BEHAVIOUR FIBRE TYPE FABRIC ABSORPTION HUMAN TISSUE GROWTH WO ARTIFICIAL SIGN FIBRE FITNESS FABRIC POROSITY FIBRE CROSS SECTINALSHAPE FABRIC SURFACE PROPERTIES FIBRE FRICTION FABRIC BULKINESS AND SOFTINESS PRODUCT DEFINING EYE CONTACT LENSES MATERIAL CONTAMINATION WO CV CHARACTERISTICS ARTIFICIAL CORNEA MATERIAL STRENGTH AND ELASTICITY

Figure 4.5 Implantable fibrous products. OTHER DIALYSES EXTRACORPOREAL ARTIFICIAL HOLLOW HOLLOW HOLLOW HOLLOW EXCRETION DEVICES KIDNEY PET CV CELULOSIC PSU ULTRAFILTRATION FIBRES

REQUIRED PRODUCT PROPERTIES

PRODUCT DEFINING CHARACTERISTICS NON-TERATOGENIC

FIBRE TYPE BIOCOMPATIBLE FIBRE LENGTH BLOOD/PLASMA BIOSTABLE FIBRE FINENESS ARTIFICIAL HOLLOW PURIFICATION FIBRE DENSITY LIVER CV NON-TOXIC FIBRE SURFACE CHARACTERISTICS TOXIN REMOVAL CROSS SECTION SHAPE NON-ALERGIC FIBRE CONTAMINATION NON-CARCINOGENIC MULTILAYER DENSITY GAS PERMEABILITY BACTERIAL RESISTANT FLUID PERMEABILITY STERILIZATION ABILITY POROSITY STRENGTH FLEXIBILITY

FLUID EXCHANGE ARTIFICIAL HOLLOW HOLLOW SILICONE BLOOD CARBON LUNG PP SILICONE MEMBRANE DIOXIDE REMOVAL

Figure 4.6 Extracorporeal devices. 76 4 Medical and Healthcare Textiles

Figure 4.7 Healthcare and hygiene materials.

4.4 Nanotechnology in Medicine and Healthcare

The scope of medical nanotextiles encompasses all the textile materials built in a nanoscale. These materials are used in the medical and healthcare sectors in many forms. The complexity and sophistication of their applications demand highly engineered products which can be produced through a variety of methods. Although the type of fibre and fibre structure varies with the specific end‐use, all this new medical nanofibre must be nontoxic, noncarcinogenic, nonallergic, mechanical‐ resistant, and capable of being sterilized without suffering physical damage or hinder their other features. Electrospinning is one of the most widely used methods to produce nanofibres for medical as well as many other technical applications. Different applications of electrospun nanofibres in the medical field are: ●● tissue engineering scaffolds. –– blood vessels –– bones –– muscles –– neural tissues ●● wound healing. ●● drug delivery. HEALTHCARE WO CO PILLOW CASES AND HYGIENE GOWNS CO PET PP NW WO MATERIALS

WO PET CO UNIFORMS CAPS CV NW REQUIRED PRODUCT PROPERTIES

NW PP PET PROTECTIVE MASKS CV PET GF NW CLOTHING CLEANLINESS MICROBIOLOGICAL ENDURANCE DIAPER/SHEET COMFORTABLE DRAPES PET PE NW WO NW CMC WOOO ABSORBENT LAYER ANTIBACTERIAL BEHAVIOUR MINIMUM CROSS-INFECTION

HIGH FILTER CAPACITY DIAPER/SHEET NW PE CLOTHS PET PE NW WO OUTER LAYER HIGH DURABILITY

HIGH WATER/VAPOUR

PERMEAABILITY BLANKETS NW CV CLOTHS/WIPES CO PET WO KN HIGH AIR PERMEABILITY

ERGONOMIC

PHYSICAL BARRIER SHEETS CO WO ICN EL CO PET PA SURGICAL HOSIERY

FIBRE TYPE FABRIC DESIGN FIBRE LENGTH FABRIC ENTANGLEMENT FIBRE FINENESS FABRIC WEIGHT PRODUCT DEFINING FIBRE DENSITY FABRIC ABSORPTION CHARACTERISTICS FIBRE SURFACE CHARACTERISTICS FABRIC POROSITY CROSS-SECTIONAL SHAPE FABRIC BULKINESS AND LOFTNESS FIBRE CONTAMINATION FABRIC SUPERFICIAL PROPERTIES

Figure 4.8 Close view of the dialyzer hollow fibres. 78 4 Medical and Healthcare Textiles

4.4.1 Blood Vessels

Blood vessels vary in size according to the location and their specific functions. It depends upon the mechanical biomechanical properties, cellular content, and structural organization of the blood vessels. The artificial vascular grafts designed should follow the requirements of blood vessels. The most challenging blood vessel replacement is that of the fine blood vessels below the diameter of 6 mm [20]. Some examples of blood vessel tissue engineering are discussed below. By comparing the cell growth on films and nanofibre mats, researchers have found that the cell grown on P(LLA‐CL) cast film has shown better function of vascular endothelial cells (ECs) as compared to the cell grown on the electrospun poly(l‐lactide‐ co‐ε‐caprolactone) (P(LLACL)) nanofibres [21]. According to Mo et al., the electrospun nanofibre mats could provide better support during the initial growth of the vascular muscle cells [22]. A 3D scaffold engineered by combining both smooth film and electrospun nanofibre mat would be more suitable for blood vessel tissue engineering. Bi‐layered electrospun fibres were studied to mimic the morphological and mechanical characteristics of native blood vessels. The small diameter vascular grafts, as shown in Figure 4.9, could be designed by using an external fibre reinforcing layer developed by deposition of electrospun nanofibres on the inner layer of a highly porous poly (ester urethane) urea [23]. The porosity difference between two layers has resulted in high cellular density in the inner layer along with better cell integration and growth. The mechanical properties of the bi‐layered scaffolds were comparable with that of the native vessels. The developed vascular graft has shown good integration of two polymeric layers without any delamination. The properties of ECs are also governed by the diameter of the electrospun fibres. The effect of diameter of cellulose acetate (CA) electrospun fibres on the EC culturing was examined for three different diameter ranges, (0.01–0.2, 0.2–1, and 2–5 μm) by Rubenstein et al. [24]. The ECs showed a growth preference towards larger fibres. Similar results were also seen by Balguid et al. using poly(ε‐ caprolactone) (PCL) nanofibres with five different diameters in the range of 3.4–12.1 μm [25]. Cell penetration was increased with the increase in fibre diameter and unobstructed cell delivery was observed only in the scaffold formed by fibres with a diameter of at least 12.1 μm.

(a) (b)

200 μm

Figure 4.9 The cross‐sectional view of a double‐layered PU vascular graft: (a) before cell culturing and (b) after cell culturing (blue, nuclei; green, F‐action; red, scaffold) [23]. 4.4 Nanotechnology in Medicine and Healthcare 79

4.4.2 Wound Healing

The wound healing process involves complex biochemical processes to repair the damage in a well‐coordinated manner. The process is categorized as haemostasis, inflammation, proliferation, angiogenesis, and re‐epithelialization synthesis. An ideal wound dressing process requires prevention of infection and simultaneously should accelerate the wound‐healing process [26]. Bioactive wound dressings are required for the wounds which are due to burns or deep ulcers since there are no source cells present for regeneration and the healing process requires more time than that for usual wounds. Electrospun nanofibres are recently gaining attention in wound dressing, owing to their extremely high surface area, high porosity, and relatively small pore size [27]. These properties are beneficial for allowing the wounded area to breathe properly, minimizing bacterial infection, and encouraging the proper release of bioactive molecules for a longer period of time. Electrospun fibres open the door to the utilization of a wide range of bioactive materials provided with greater mechanical support. Jannesari et al. has reported, electrospinning of bioactive drug (ciprofloxacin HCl [CipHCl]) with poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) (50: 50 composite blend) [28]. This technique could ensure the controlled release of the drug. The addition of poly(vinyl acetate) to PVA nanofibres decreased the drug‐release rate at earlier stages and supported the drug release for a much longer duration. Ultrafine biodegradable electrospun fibres (UFs) developed by using poly(lactic‐co‐glycolic acid) (PLGA) and fusidic acid have been studied for wound dressing [29]. It was noted that the loading of adequate concentrations of fusidic acid into the nanofibres prohibited bacterial biofilm formation. It was also observed that the pre‐exposure of the membrane to wound bacteria caused an accelerated release of drug. It also resulted in the deterioration of fibre as well as the reduction in pH of the incubation medium. As another example of the use of electrospun nanofibres for wound healing, the healing process of a skin wound using poly(d,l‐ lactic acid)‐poly(ethylene glycol) (PELA) nanofibrous mats is presented in Figure 4.10 [30].

a1 a2 a3 a4

1 wk 2 wk 3 wk 4 wk

b1 b2 b3 b4

Figure 4.10 The representative images of skin wounds after treatment with basic fibroblast growth factor (bFGF)/poly(d,l‐lactic acid)‐poly(ethylene glycol) (PELA) fibrous mats for one to four weeks (b1–b4), using untreated wound as control (a1–a4) [30]. 80 4 Medical and Healthcare Textiles

4.4.3 Drug Delivery

Electrospun fibres are a boon for the drug delivery process, owing to control over the fibre composition, porosity, and morphology. Electrospun nanofibres have the ability to deliver the bioactive substances in the targeted site, which avoids side effects caused by the drug during its systemic release. During drug release, controlled release of the drug is required to create a balance in the delivery kinetics, which will maintain the effective drug concentration at the impaired site. For drug delivery the preferred systems are mainly biodegradable and hydrophilic polymers. In most cases, an early‐stage release of drugs is required, since most of the infections occur in the first few hours. However, in some cases a longer‐lasting release of drugs is required; in these circumstances, it would be essential to maintain the release of drugs at a constant and stable rate. To maintain the controlled release of drugs, Chundler et al. performed a set of experiments to fabricate electrospun nanofibres with opposite charge weak polyelectrolytes, namely polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH), and a model drug (methylene blue) was used [31]. Release of methylene blue was controlled by the pH of a nonbuffered solution. To achieve the thermosensitive release of drugs, temperature‐sensitive PAA/poly(N‐isopropylacrylamide) (PNIPAAM) was deposited on the surface of electrospun fibres. Im et al. developed coated electrospun fibres loaded with Lactobacillus to study the target release of drugs in large intestine [32]. PVA electrospun fibres loaded with Lactobacillus were coated with alginate and chitosan. Alginate and chitosan got dissolved during passage through the stomach and large intestine, owing to the presence of acid and neutral pH leaving the Lactobacillus‐loaded PVA fibres. Figure 4.11 shows the mechanism of the procedure for the targeted release of the drug.

A In stomach

B In small intestine

C In large intestine

Figure 4.11 Drug release mechanism of chitosan/alginate/polyvinyl alcohol multilayered nanofibrous drug delivery system [32]. 4.5 Thermo‐Physiological Comfort of Medical Textiles 81

4.5 Thermo‐Physiological Comfort of Medical Textiles

Thermo‐physiological comfort of medical textiles refers to the type of comfort obtained due to proper levels of warmth and wetness, and this is achieved by the proper transport of heat and moisture through the textile fabrics [33]. A suitably designed medical textile should provide sufficient warmth in a cold atmosphere and coolness in hot conditions and also allow proper breathability and permeability. The thermo‐physiological comfort of textiles depends on the microclimate which exists in the microspace between human skin and a textile material. A schematic diagram explaining microclimate is provided in Figure 4.12. The microclimate decides the comfort of the medical textile and is influenced by the heat and moisture flow between the skin and clothing, which in turn is controlled by the atmospheric temperature and humidity as well as the heat and moisture transport properties of the medical textiles [33]. Conduction is a common mechanism by which heat transport occurs through a textile material. The thermal conductivity of the material decides its ability to transport heat by conduction [34]. Textile fibres, in general, have much lower thermal conductivity than other class of materials, such as water, glass, copper, diamond, etc. (see Table 4.1). Therefore, the textile fabrics are usually good insulators and can keep good warmth and comfort. Thermal insulation of textile material can be further improved to a considerable extent by entrapping air inside their structure, owing to the very low thermal conductivity of still air. Therefore, textiles with very good thermal insulation can be designed through using multilayered fabrics, in which a high volume of air remains trapped between the individual layers or using hollow fibres retaining air in the hollow structures and also by using a layer of loose fibrous structures (e.g. feather)s which can retain a high amount of trapped air [33].

Clothing Body Moist, Core Heat

Skin Micro- climate

Figure 4.12 Schematic of microclimate between skin and a textile fabric [33].

Table 4.1 Thermal conductivity of different materials [34].

Materials Diamond Copper Soda–lime glass Water Nylon fibre Still air

Thermal 900 401 1.4 0.58 0.25 0.024 conductivity (W m−1 K−1) 82 4 Medical and Healthcare Textiles

Besides conduction, heat can also be transported through a medical textile through convection, which occurs from the motion of a liquid or gas from a warmer region to a cooler region. A textile material with more porosity allows better heat transfer through convection. Radiation is also responsible for the heat transport through textiles and it does not need any intervening medium. Radiation is favoured by an open structure of fabrics, which allows more heat loss in the form of radiated waves [33]. Water or moisture transport through a medical textile occurs in two different steps: (i) water is transported from the microclimate region to the fabrics and (ii) water is transported from the fabric structure to the environment [33]. In the first step, water is transported through diffusion to the fabrics and can be absorbed or adsorbed or imbibed through capillary action (which is known as wicking). A hydrophilic fibre such as wool, cotton, etc. and fibres with micro‐/nanodiameters (consequently having a high surface area for better water adsorption) will improve the water diffusion to the fabrics, owing to higher absorption and adsorption [35]. Fabrics made of nanofibres and with a greater amount of capillary pores will improve the water diffusion, owing to better wicking behaviour. The transport of water from a fabric to the surrounding environment is referred as its ‘breathability’, which should be high for medical textiles to achieve greater patient comfort. Therefore, it can be clearly understood that the thermo‐physiological comfort of a medical textile is controlled by the fibre properties (thermal conductivity, diameter, shape, hydrophilicity, etc.), fabric properties (thickness, openness or porosity, number of layers, etc.), as well by the temperature and humidity conditions of the outer environ- ® ment. An example of enhancing the moisture transport through wicking is CoolMax fabrics, which use special shaped fibres such as kidney bean, tri‐lobal, and multi‐channel cross‐sections to improve the wicking behaviour of fabrics (Figure 4.13). An exam- ® ® ple of special fabric design to improve the breathability is Polartec Power Dry fabrics, in which a bi‐component knit structure has been used to provide a brushed inner surface and a porous outer surface. The inner fabric surface takes the moisture away from the skin, while it is drawn through the porous outer surface and spread over a wide area for quicker drying. The use of phase change materials (PCMs) is another approach to improve thermoregulation of fabrics. PCMs present in the fabrics are able to absorb excessive amounts of heat released by the body and release it again when required to maintain the body temperature at a particular level. PCMs can be applied to textile fabrics through a finishing or coating process [36] or, alternatively, PCMs can be integrated with the fibres during the fibre spinning process and, subsequently, fabrics are

Figure 4.13 Fibres with engineered cross‐sections used in CoolMax fabrics [33]. 4.6 Biocompatibility – Bioresorbability – Biostability 83

(a)

(b)

Figure 4.14 Fibres and fabrics with PCMs: (a) viscose rayon fibre containing PCMS and (b) a fabric finished with PCM [33].

® made using these PCM‐containing fibres (Figure 4.14). Outlast fabrics is the example of textiles developed using PCM technology for thermoregulation.

4.6 Biocompatibility – Bioresorbability – Biostability

Biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific application [37]. The biocompatibility of a medical textile represents the benign responses from the cells, tissues, and organs due to the implantation of the medical textile. When a medical textile is planted into the human body, the immune system intends to counteract the invasion of this foreign material in the same manner as it does for the other harmful agents, such as viruses, bacteria and parasites, etc. [38]. The host tissues interact with the implanted material and this strongly depends on the physical, mechanical, chemical, surface, and pharmacological properties of the implants [39]. The type of interactions between the implanted material and host tissues are [40]: ●● the blood–material interaction. ●● inflammation. ●● foreign body reaction. 84 4 Medical and Healthcare Textiles

Blood compatibility is an important property to define the success of a medical textile as implantable material [40]. It can be defined as the ability of a material to function properly when in contact with blood without causing adverse reactions. The negative effect of a blood incompatible material is the thrombus formation and inflammatory responses. Therefore, to determine biocompatibility of a medical device (for example a medical textile) can be tested by flushing the blood through a tube made of that material and, subsequently, evaluating the quantity of thrombi and the behaviour of the platelets [41]. The factors which influence the blood compatibility of medical materials include the nature of blood and blood flow, and the properties of the material’s surface. Inflammation is a type of nonspecific immune response of the body to react to the infections or injuries or artificial medical devices, resulting in different symptoms, including swelling, redness, and pain [40]. Owing to inflammation, chemicals such as enzymes are released that may degrade the implantable materials. The debris detached from an implantable device caused by wear, friction or degradation can cause a prolonged inflammatory response. Foreign body reaction [40] is the response of the host tissues to the implantable textile or other materials during their whole lifetime, and after the implantation. It occurs in the following steps (as shown in Figure 4.15): 1) Protein is adsorbed on the implanted material surface. 2) Different cells such as platelets, neutrophils, and macrophages attach to the material surface. 3) Coalescence of macrophages to form giant cells. 4) Fibrous encapsulation to segregate the implant from the host and its environment. The biostability of a medical material can be defined as the ability of the material to maintain its original dimensions and physical, mechanical, and chemical properties over a long period when it is in a hostile biological environment [42]. The bioresorbability, on the contrary, of a medical material is the ability of the material to be absorbed by the body after a certain period of time, which should be properly predicted or controlled for the proper development of host tissues. In a biological environment, an implantable polymeric material gets degraded (usually called biodegradation), owing to a hydrolysis reaction, oxidation, or enzymes and may result in complete digestion by the body [43]. Hydrolysis is the most common cause of degradation of a variety of polymers, including polyesters, polyamides, polysaccharides, polyacetals, etc. Owing to biodegradation, the mechanical properties of the implants reduce with time. The mechanical properties of medical textiles, which are important in their application as implants, are mechanical strength, elastic modulus, yield strength, creep, stress relaxation, etc. For some applications, like a nonabsorbable polyester vascular graft, it is necessary to maintain its mechanical properties during its life time. On the other hand, for other applications, the implant material is required for a particular period of time, after which it should be absorbed by the body so that it need not be surgically removed. For example, in tissue engineering, a scaffold is only required to support the proliferation of the cells until the complete regeneration of the tissue and then should be degraded and absorbed by the body. Therefore, medical textiles used for this purpose should have proper biodegradability. Although a number of polymers show biodegradability, not all of them could be used as medical implants, owing to poor biocompatibility. Not only the polymers but also their degradation products and their metabolites should 4.7 Intelligent Medical and Healthcare Textiles 85

Biomaterial

Figure 4.15 Reaction of host tissues to foreign bodies [33]. be biocompatible. Some examples of synthetic polymers with biodegradability are listed in Table 4.2 [33], along with some natural biodegradable polymers. In contrast to synthetic polymers, natural polymers have better biocompatibility and can be biodegraded by naturally occurring enzymes.

4.7 Intelligent Medical and Healthcare Textiles

The increased recognition by society that older and or disabled people and people with chronic disease need to have a comfortable, autonomous, and satisfactory life and, simultaneously, the growing awareness of concepts such as active ageing and healthy lifestyle have triggered the development of textile based e‐health systems. 86 4 Medical and Healthcare Textiles

Table 4.2 Properties and medical applications of selected biodegradable synthetic and natural polymers.

Polymers Properties Applications Problems

Synthetic Polymers Polyglycolic acid A highly crystalline Sutures, bone Most widely studied (PGA) polyester, high rate of fixation devices, degradable synthetic hydrolytic degradation scaffolds for tissue polymers Unresolved (loses mechanical strength engineering issues: poor substrate for in 2–4 wk), biocompatible in vitro cell growth; acidic degradation products, which may cause inflammatory response Polylactic acid Biocompatible, (PLA) hydrophobic, chiral molecule (i.e. a molecule not superimposable on its mirror image); see the following three stereoisomers D‐PLA (PDLA) Semicrystalline Less used L‐PLA (PLLA) Semicrystalline, low rate of Sutures, orthopaedic degradation devices, scaffolds for tissue engineering D, L‐PLA Amorphous, higher rate of Drug delivery Sutures, scaffolds for tissue degradation than PLLA engineering Copolymer of Reduced rate of PGA and PLA degradation than PGA, biocompatible Polydioxanone Degrade to low‐toxicity Sutures (PDS) monomers in vivo Polycaprolactone A semicrystalline polymer; Long‐term drug (PCL) degrades at a rate lower delivery, wound than PLA, remains stable closure for over 1 yr; nontoxic and biocompatible Polyanhydrides High degradation rate, Short‐term drug excellent in vivo delivery biocompatibility

Natural Polymers Collagen Biocompatible, degraded Wound closure, Lower mechanical strength by natural occurring artificial skin, than synthetic polymers enzymes, degradation rate vascular grafts, drug controllable by delivery, scaffolds for crosslinking tissue engineering Gelatin Biocompatible and Drug delivery, bioresorbable scaffolds for tissue engineering Hyaluronic acid Biocompatible and Scaffolds for tissue bioresorbable engineering 4.7 Intelligent Medical and Healthcare Textiles 87

Intelligent medical and healthcare textiles are an emerging and rapidly growing market, with a very broad range of applications which are expected to have a considerable impact on many aspects of the medical–patient relationship in the near future [11, 12]. The products lying under this category normally comprise some sort of textile fabric/ piece of clothing with some embedded electronic and digital components. They are primarily focused in health monitoring, data acquisition, disease management, diagnosis, autonomy, activity, and status‐tracking. Remote healthcare monitoring and ambient life assistance are vital not only for patients requiring continuous medical support but also to aid in the daily life of an increasingly ageing population [13]. These systems are meant to boost the activity and security, and prevent the potential crisis, of their wearers – in short expanding and enhancing their quality of life. Amidst many other possibilities the main end‐user applications are: ●● medical monitoring. ●● biofeedback. ●● diagnostic support. ●● rehabilitation. ●● infant monitoring. ●● disease monitoring. ●● obstetrics monitoring. ●● clinical trials monitoring. ●● athletics monitoring. ●● military uses. ●● healthcare prevention. ●● active ageing. ●● promotion of a healthy lifestyle. Electroactive or electrotextile systems are specifically designed to fulfil a purpose and demand the combination of different components categories to perform their task. Figure 4.16 depicts the working principle and major functions of a textile based e‐health system [14]. Biosignals, covering all the major body functions, can now be measured through different kinds of sensors. The most common medical measurands are listed in Table 4.3. To the exception of temperature, which normally varies slowly, all other vital signs have greater value dispersion and require sensors that are able to measure under dynamic conditions. Textile sensors for biophysiological assessment vary in their function, field of application, used materials, chosen technology solution, measurement units, and integration level into textile fabrics. A systematic approach can be made in accordance with their general working principles: either a physical approach, which would include optical transducers, or a chemical approach, which would entail counting with biochemical transducers. Another classify- ing method considers the integration level in the textile structure, namely: fibre based when the sensor is a single yarn, textile‐structured when all the components of the sensor are made of textile materials; textile‐based, when the textile materials are a substrate or become a nonsensitive but important part of the transducer; and textile‐ integrated, when textile materials play the function of the carrier. 88 4 Medical and Healthcare Textiles

Short range network Physiological signals (WLAN, PAN, Stimuli Sensoring Biomechanical variables Bluetooth, NFC) Kinesthesis Long range network (GPRS, 3G, 4G) Electrodes/Textrodes

Electroactive polymers Signal transmission

CONTROL Data unit UNIT Data processing Data gathering

Algorithms Data storage Pre-processing Processing Interpretation Response Actuators Controlling

Physical and/or chromatic and/or mechanical change Power supply Drug delivery Batteries and/or electric Alerts (Audio/Visual/Tactile re exes/Emergency call current

Figure 4.16 Schematic view of the working principle of an e‐health system.

Textile sensors are characterized as being flexible and having good connectivity for integration. Typically, they are used in a noninvasive way and embedded in the textile fabric and/or cloth. Despite the wide range of intelligent functions already developed for e‐textile products, sensing capabilities remain of paramount importance and there is still a wide scope of further improvement [15]. Table 4.4 provides a synoptic view of the most common textile sensors applied in biological signal monitoring. It is common knowledge that these sorts of medical textiles were initially derived from the Georgia Tech Wearable Motherboard (GTWM), a military project funded by the US Naval Department in 1996. This device was initially devised for military purposes, particularly for combat casu- alty care. It was built with an optical fibre sensing system which could detect and

Table 4.3 Biomedical measurand characteristic.

Measurement Range of parameter Frequency (Hz) Sensor or method

Blood flow 1–300 mL s−1 0–20 Flow meter Blood pressure 0–400 mmHg 0–50 Strain gauge or cuff Electrocardiography 0,5–5 mV 0,05–150 Skin electrodes Electroencephalography 5–300 μV 0,5–150 Scalp electrodes Electromyography 0,1–5 mV 0–10 000 Needle electrodes pH 3–13 0–1 pH electrode Respiratory rate 2–50 breaths min−1 0–10 Impedance Temperature 32–40 °C 0–0,1 Thermistor Source: Adapted from [44]. 4.7 Intelligent Medical and Healthcare Textiles 89

Table 4.4 Textile based sensors for biological signal monitoring.

Typical sensor Biosignal Sensor type Textile biosensor Signal source placement

Electrocardiogram Surface Woven/knitted Electrical Thoracic region electrodes metal electrodes activity of the heart Electromyogram Surface Woven/knitted Electrical Skin surface electrodes metal electrodes activity of the overlying relevant muscles muscles Respiration Piezoresistive Electroactive Expansion and Thoracic‐ sensor polymeric fibre contraction of abdominal region (EAP) the ribcage during breathing Blood oxygenation LED/Opto diode Woven/knitted Light absorption Regions with plastic optical of haemoglobin good blood fibres (POFs) in blood perfusion (e.g. fingertip, earlobe) Skin temperature Thermoelectrical Plastic optical Skin electrical Thoracic‐ sensors fibre or EAP conductivity abdominal region textiles Skin electrical Surface Woven/knitted Skin electrical Fingertips impedance electrodes metal electrodes conductivity Heart sound Piezoelectrical PVDF film or Sound waves Thoracic‐ microphone woven patch abdominal region Carotid and radial Piezoelectrical EAP Pressure and/or Neck and wrist artery pulse sensor noise variation Articulation Piezoelectric, EAP Body Joints, Depending segment position piezoresistive, Kinematics on the motion to and movements strain sensors, be analysed inertial sensors Composition of Electrochemical Woven/knitted Composition of Fluidic sampling body fluids sensors Chemosensitive sweat, saliva, system necessary Colourimetric pH patches urine Fabric Source: Adapted from [44, 45]. pinpoint bullet wounds and transmit the wearer vital signs to a centralized system in a matter of seconds. The commercial evolution of the GTWM, named Smart Shirt, was later produced by Sensatex, Inc. Described as the ‘the shirt that thinks’ or even as an ‘electronic shirt’, this piece of cloth, which could be worn under a normal vest, was capable to comfortably measure and real‐time monitor many physiological parameters, mainly: heart rate, respiration rate, body temperature, and caloric burn, and chemosensitive sensors warned of the presence of poisonous gases in the air. Additionally, it was built with a motion sensor, which provided feedback about the wearer’s posture and movements. This ability is particularly helpful for patient rehabilitation (or even in sport applications), where a set of movements are to be made in a 90 4 Medical and Healthcare Textiles

predefined sequence, repeatedly and in an accurate way, within a certain period. The fall/nonfall alarm is also a very important additional feature, notably for older people. In a similar way as its predecessor, the new technological solution resembles a t‐shirt. It was weaved by special technique with optical and conductive fibres and used embedded sensors to monitor and record more than 30 physiological parameters. It was the first attempt to bring textile based monitoring technology into daily life. The life‐shirt system, one of the first commercial garments developed by Vivometrics, comprised three components: the life‐shirt garment itself, which is a lightweight, machine‐washable, comfortable, and easy‐to‐use shirt with embedded sensors that measure the heart rate, breathing patterns, temperature, posture, and activity level of the wearer; the life‐shirt recorder, which includes an integrated personal data assistant to encrypt and store collected data into a compact flash memory card and manual inputs, by the patient, such as symptoms, moods, or any other relevant information, over time, in a personal digital diary named vivolog; and the vivologic software, which is responsible for decrypting and processing recorded data so as to be displayed and easily understood by professional staff. A different approach to health monitoring is taken by the Zoll Life Vest, which is a wearable defibrillator. This electronic garment is lightweight, shaped as the top of a bathing suit, comfortable, washable, and can be worn all day, except when bathing and showering. Specifically designed for high risk cardiac patients, it offers real‐time protection against sudden cardiac arrest. Worn outside the body, near to the skin, it monitors the heart rate through dry, nonadhesive electrodes so as to detect a life‐threatening abnor- mal heart rhythm. When a nonstandard situation is detected, the system promptly emits a warning alarm. If no action is taken to disengage the alarm, the device will trigger an electrical shock to restore normal heart rhythm. The Belgian company Verhaerth Design and Development and the University of Brussels developed a new type of pyjama aimed at the prevention of sudden infant death syndrome. This piece of cloth monitors babies during their sleep through five conventional sensors: three electrodes for the heart rate and two capacitive elongation sensors for the acquisition of respiratory data. Sensors are built in and placed over the chest and stomach of the infant. The pyjamas are made of nonallergic material which contacts directly with the skin and is machine washable, whereas the sensing system should be washed manually. The control unit is programmed with an alarm algorithm that continuously monitors the health status for any possible dangerous situations. The double sensing system guarantees redundancy and a high level of precision. With the continuous advance on miniaturization and integration of microelectronics, materials, optics, telecommunications, and biotechnologies, recently, a new generation of electronic textiles emerged along with a novel branch of science – fibertronics [16, 17]. These improved systems are smaller and embedded into the fabric, so that the end‐ user never feels its operation. The new e‐health platforms are also more complex, more resourceful, and far more interconnected, with a wide plethora of applications. The first ever e‐textile platform to address the clinical rehabilitation of cardiac patients was carried out during the framework of the EU‐funded project Wealthy [18]. The developed wearable‐integrated system aimed to be a comfortable garment capable 4.7 Intelligent Medical and Healthcare Textiles 91 of continuously monitoring the cardiac function, respiratory rate, temperature, posture, and activity level. The concern about assisting professional workers to assess their physical and health risks was also taken into consideration. For these purposes two types of textile sensors were developed: the first kind was made of an elastomeric‐coated fabric with carbon black and rubber and was intended for the measurement of the respiratory rate, whereas the second kind, textrode, was produced with metallic yarns in order to measure the heart rate. Two temperature transducers were also embedded along with an integrated connector for an SpO2 sensor. All textile sensors were integrated in a fully garment knitting process. The system was completed with a short‐range wireless system to transfer collected data from the garment to a computer and/or smartphone. Based upon the aforementioned project, a new proposal came out from the development of yet another EU‐funded project. Aiming to gain knowledge on the personal health status in large groups of individuals, the project My Heart focused on the monitoring of biophysiological signs for preventive healthcare, particularly for the prevention of cardiovascular risk factors and cardiac acute events [19]. The scope of this project is summarized in Figure 4.17. Belino et al. developed an electronic mattress with an integrated sensing layer that captures the anatomical position of the body over time and communicates with a PC to inform healthcare personnel about the necessity of changing a patient’s position in bed to encourage pressure relief [46]. This electrotextile tool is aimed primarily to combat bedsores prophylaxis in hospitals (Figure 4.18), rest homes, nursing homes, host institutions, and in patients subjected to ambulatory treatment. This technological solution integrated a piezoresistive sensor matrix, allowing for real‐time data acquisition, the storage and emission for a remote computer running the

HEART FAILURE MANAGEMENT - Improving the quality of life and life expectancy of cardiac patients by early prediction of decompensation and enhanced patient self-management.

NEURO REHAB − Remote support ACTIVITY CARE – Uses the for patients undergoing rehabilitation biofeedback data to help people to process. Dedicated to the post- MY HEART PROJECT become more active and healthy. intervention follow-up improving and Assessing and lowering risk factors shortening it. of cardiovascular diseases.

ACTIVITY COACH – Training platform to assist physical exercise. Biofeedback and professional aid are combined to maximize pleasure and health impact of the subject.

Figure 4.17 Schematic presentation of the disease management and prevention approach within the MyHeart project. Figure 4.18 Electronic mattress in use in the intensive care unit of CHCB. control algorithm, and patient‐specific parameters. Data transmission is available in real time or by request from a user. The sensor system has the ability to generate alarms (configurable and customized) that are sent to a remote platform (applications server, PDA, PC, or smartphone), so as to trigger preventive/corrective measures. Tavares et al. developed an electronic tool to study the relationship between anatomical position during sleep rest and some neurodegenerative diseases [47]. The system allows not only to assess sleep quality but also to establish a link between nocturnal movements (body area, number of movements, direction, intensity) of demented patients, their polysomnographic recorded data, and their disease stage/evolution. Seven sensors (tri‐axial accelerometers ADXL345 from Analog Devices) were sewed into predetermined areas, corresponding to the great anatomic zones of the human being: neck and head zone, torso zone, hip zone, right arm zone, left arm zone, right leg zone and left leg zone (Figure 4.19). These areas are activated or deactivated on a personalized basis.

Movement First layer

Sensing layer

7 Accelerometers

Third layer

Figure 4.19 Schematic view of the working principle. 4.8 Antimicrobial Textiles 93

Directly connected to the accelerometers (through the embroidered conductive yarns) an electronic data collection module reads the sensors status continuously and individually. The gathered information is passed to a collection and processing module which allows data acquisition, processing, and communication with the PC. The data transmission is performed in real time, through consultation, or upon request by an operator/user. Simultaneously to the development of the electronic modules, a software application has been built, guaranteeing the full management of the overall process and storage of the collected data, allowing the generation of information that will be presented as interactive charts, and tables or graphs, for both the body as a whole as well as particular areas of it. The new technological solution was devised to be applied as a biomedical device for the local/remote monitoring of patients with neurodegenerative diseases. A comparative study carried out in a clinical trial proved that this new e‐health system could provide the same data – regarding the movement detection – as the polysomnogra- phy study. Consequently, through its continued usage, a reduction of costs is expected, considering the avoidance of many expensive polysomnographic exams, the institutionalization of patients (in a hostile environment for them), and reductions in material consumption and the need for human resources. It is also very important to underline that patient comfort will improve as they will not need to leave their home as much.

4.8 Antimicrobial Textiles

Antimicrobial textiles have been a research topic of interest for decades and they cover a large area of textile products treated with biocides, i.e. agents that act against the growth of microorganisms. Triclosan, silane quaternary ammonium compounds, zinc pyrithione, and silver based compounds are the main antimicrobial agents used in textiles [48]. However, novel combinations are investigated for antimicrobial activity, such as silver or herbal nanoparticles, and biopolymers, such as polylactide and chitosan [49–51], and even antimicrobial peptides [52], on almost all common types of textiles, such as cotton, wool, polyester, nylon, and silk [50, 53–55]. According to a European Commission survey in 2009 of the use of biocidal substances in Europe for fibres, leather, rubber, and polymerized materials, as much as 1546 metric tonnes were used. The synthetic organic compounds dominate the textile market, with 1300–1400 metric tonnes in total for triclosan, silane quaternary ammonium compounds, and zinc pyrithione, as opposed to only 9–45 metric tonnes for silver based compounds [48]. The scope of antimicrobial textiles is dual: either to protect the textile product itself and enhance its durability against mould, decolouration, polymer fibre decomposition, bad odour etc. [56], and/or to protect the wearer from harmful microbes, either in everyday use or in clinical cases (e.g. in hospitals). Their application field is vast, ranging from mattresses, blinds, and bedsheets to wound patches, sportswear, and air/water/oil filters, even food packaging [48, 53, 57–61]. The most common antimicrobial agents used for textile treatment include metals (e.g. silver and copper), and their salts, metal‐organic complexes (e.g. zinc pyrithione), quaternary ammonium compounds, and halogenated phenols (e.g. triclosan) [48, 53]. 94 4 Medical and Healthcare Textiles

More specifically, triclosan is the 2,4,4′‐trichloro‐2′‐hydroxydiphenyl ether and is applied in a variety of products as an antimicrobial and preservative agent used in disinfectants, soaps, toothpastes, shampoos, and deodorants [62]. Quaternary ammonium compounds are cationic surfactants used as biocides and auxiliaries at different stages of textile manufacturing, as detergents, antistatic, and softening agents [63–65]. The term refers to linear alkyl ammonium compounds that are often composed of a long hydrophobic alkyl chain (12–18 carbon atoms) and a hydrophilic counterpart. Zinc pyrithione is a metal‐organic complex extensively used as a fungicide in antidandruff shampoos [64] and as an antifouling agent for ships [66]. Its consumption volume in textiles is lower than that of silane quaternary ammonium and triclosan but higher than that of silver. Particularly for silver, there are three main groups commercially available as antimicrobials: salts (silver chloride and its microcomposites with titanium dioxide), which are the most widely used form in textiles (79%), ion exchangers (e.g. silver zirconium phosphates and zeolites), and metal (e.g. silver filaments) [48]. Based on their nature and application, antimicrobials have various action mechanisms. Silver ions, for instance, have the ability to bind to disulfide bridges of proteins of microbe cell walls and to also replace metal ions such as calcium and zinc, causing cell death. Quaternary ammonium compounds, another common antimicrobial group of agents, have the ability to bind to basic structural elements of the cell membranes, such as phospholipids. They induce protein denaturation inhibiting membrane permeability and, thus, stop nutrients from entering the cell and eventually causing cell death [58, 67]. Potassium permanganate, which is a less common antimicrobial agent for textiles but is used also as an astringent, haemostatic agent and deodorant, acts as a strong oxidant for the active groups of bacteria, fungi, the hepatitis B virus, and spores leading effectively to their death, without forming toxic by‐products [55]. Antimicrobial peptides, another less common agent for textiles, are diverse in their sequence and structures, having the ability to effectively kill a plethora of microorganisms. They are produced in bacteria, insects, plants, and humans, with generally small sizes of 10–50 amino acids and at least two positive charges. The exact mechanism of their antimicrobial activity is yet unknown, but it is assumed that they interact electrostatically with the phospholipid head groups of the bacterial cell membrane, similarly to quaternary ammonium compounds, causing disruption and cell death [52]. One of the parameters which affect the selection for use of antimicrobial agents in textile finishes is the application rate required to impart certain antimicrobial functionality, in other words the level of dose required for effective and durable antimicrobial activity. It has been reported that bulk silver forms such as metal threads or silver‐ coated yarns require high application rates and so are not the agents of choice [48]. The lowest application rate (on a weight basis) has been reported for nanosilver forms with recommended concentrations between 10 and 100 mg kg−1, and the highest for bulk silver (e.g. silver‐coated fibres) with a maximum concentration of 40 000 mg kg−1 and a median of 12 990 mg kg−1. Application rates for organic compounds are reported higher for triclosan and lower for zinc pyrithione (median values of 6426 and 3263 mg kg−1, respectively), and lie in between those of nano‐ and bulk silver [48]. Another parameter affecting preference and extensive use of an antimicrobial agent over others is the ease and feasibility of incorporation of the agent into fibres, as opposed to, for example, surface coatings. The reason that this parameter is important relates to the durability of the finish as much as to the environmental impact of it. For instance, 4.9 Testing Methods and Quality Control 95 the durability of zinc pyrithione was reported lower than that of silver compounds. Moreover, atomic silver transforms rapidly into other forms in the environment, compared to, for example, triclosan, which does not degrade for long periods of time, but most leachable antimicrobials could be removed in waste‐water treatment plants [48]. Human toxicity is also important, particularly for special clothing applications with direct skin contact, but other properties as well, for example the photostability of the agent for outdoor textile products, such as tents, plays a role when choosing an antimicrobial compound for textile finishing. Functionalization modes of textiles with antimicrobial agents include in situ surface reactions, immersion, nebulization, pad‐dry‐cure techniques, plasma treatment, spraying, ultrasound‐assisted deposition, chemical/physical vapour deposition, encapsulation with thin film formation, and UV curing, among others [50, 51, 54, 55, 57, 59]. Often, antimicrobial agents are combined with drug delivery systems to prevent microbial growth, on the one hand, and achieve drug release, on the other. For example, Rehan et al. produced a modified cotton gauze by forming in situ silver nanoparticles with the help of trisodium citrate, which had a triple role: as a reducing agent for silver cations to silver atoms, as a stabilizing agent to prevent aggregation of silver nanoparticles, and as a linker for the nanoparticle fixation on the surface of the cotton gauze [68]. Then, oxytetracycline hydrochloride, an antibiotic drug, was loaded onto the silver‐treated cotton gauze by immersion. The results showed that the modified drug‐loaded cotton with silver nanoparticles completely inhibited the growth of Escherichia coli [68].

4.9 Testing Methods and Quality Control

Textiles in clinical settings, such as curtains and apparel, play an important role in the transmission of pathogens through cross‐contamination, and more specifically of both epidemic and endemic transmission of Clostridium difficile, vancomycin‐resistant enterococci, Acinetobacter baumannii, Pseudomonas aeruginosa, and norovirus [69]. Apparel worn in the healthcare sector moves around quickly, as opposed to, for example, curtains in a healthcare facility, and can easily carry and transmit harmful microorganisms. A relative study showed that up to 60% of hospital staff uniforms (out of more than a hundred) were tested positive for multidrug‐resistant organisms, based on samples taken from sleeves, waists, and pockets [69]. Such data underline that medical textiles have an important role as special technical materials, independent of their end‐use: to rapidly kill or inactivate a broad range of harmful microorganisms and pathogens, while being nontoxic and eco‐friendly. It is also essential for their performance to exhibit good washing durability and an ability to recharge with bioactive substances either during laundering or through another simple and user‐friendly technique. For these reasons, a major test for medical textiles is washing fastness, especially for those products that are re‐usable and wearable, like medical staff coats. Testing standards such as BS EN ISO 3175‐2: 2010 and AATCC 61‐2206 are recommended for professional dry and wet cleaning procedures to test the durability of the finish of medical textiles [70]. For textiles treated with silver nanoparticles, researchers have applied washing procedures typical for determining the colour fastness for home and commercial laundering, i.e. for 45 minutes at 50 °C using a nonionic detergent [71]. Instead of 96 4 Medical and Healthcare Textiles

usual colour fastness measurements, the concentration of silver in the effluent after multiple washing cycles was determined using atomic absorption spectroscopy (AAS), after digesting the textile samples for 20 min at 190 °C using concentrated HNO3 [71]. Apart from washing, another way to test the durability of a finish is to evaluate its resistance to biodegradation. The soil burial test offers such an evaluation and can be performed according to the SIST EN ISO11721‐2: 2003 standard method. Researchers have applied it to cotton, wool, and silk textile samples coated with 3‐(Trimethoxysilyl)‐ propyldimethyloctadecyl ammonium chloride (a silane‐quaternary ammonium compound with antimicrobial activity), which they buried in test soil for 6, 12, or 18 days under constant humidity of 60 ± 5% and a pH range between 4.0 and 7.5 [72]. After the studied samples were removed from the test soil, they were water rinsed and conditioned with 70% ethanol. Biodegradation was evaluated through reflectance spectroscopy [72]. Similarly, Alay et al. conducted extensive soil burial tests on knitted textiles manufactured with novel and ‘greener’ fibre combinations to assess their biodegradation behaviour over a period of up to 24 weeks without additional microorganisms using standard guidelines of DIN EN ISO 11721‐1 [73]. The soil burial tests were followed by ecotoxicological assessment of the soil used to bury the textile samples, with a plant‐ growth test according to OECD 208: 2006. In some cases, rubbing fastness tests may be applied according to standards EN ISO 12947‐2 and ASTM D4966 (e.g. for hospital bed‐sheets). Also, tribological tests that evaluate the friction between skin and medical textile (e.g. bedsheet) under both dry and wet conditions could be performed in vivo as a control test for the prevention of pressure ulcers on patients [74]. Particularly for their antimicrobial performance, medical textiles are tested using mainly two methods: a qualitative one according to standard AATCC 147‐2004 based on the agar diffusion test which rapidly evaluates the inhibition or not of bacterial growth on multiple textile samples, and a quantitative more laborious one based on a bacteria counting (or suspension) test according to standard AATCC 100‐2004 [70, 75] or AATCC 100‐1999 [76, 77]. In such tests, E. coli, a gram‐negative bacterium, is often selected as a test organism because of its resistance to common antimicrobials, and Staphylococcus aureus, a pathogenic gram‐positive bacterium, is usually selected as a major cause of cross‐infection in hospitals [76]. Standard ASTM E2149: 2013 is also used for testing antimicrobial activity in a similar way through colourimetric determination of the survivor organisms after incubation and against control samples [78]. Safety is another critical aspect to test for medical textiles, especially when there is skin or eye contact involved or finishes with nanoparticles that could leach out of the material. Safety is often reflected on the toxicity of the finishing agent used or on that of the whole final product. Cytotoxicity is tested based on the water‐soluble tetrazolium salt (WST‐1) assay, which is frequently used to assess cell proliferation. In brief, fibro- blasts are seeded onto well microplates and incubated in the absence or presence of test samples. Subsequently, a cell proliferation reagent (WST‐1) is added for 1–3 h, and the optical density of the reduced product (solubilized formazan product)is measured col- ourimetrically. The results are expressed as the percentage of cell survival (optical density of exposed vs. optical density of control nonexposed cells) [79]. Taking safety tests one step further, skin irritation development has been reportedly tested using albino mice, to which biofunctionalized polypropylene fabric swatches were attached for a period of two to three days. Histological analysis followed to observe pathological sections with optical microscopy [80]. 4.9 Testing Methods and Quality Control 97

Other common tests that assess more generic properties of textiles, such as mechanical strength, wettability, and wear comfort linked also to breathability, can be applied to medical textiles. In the case of nonwovens, for instance, which can be used as wound dressings, swabs, or instrument drapes in an operating theatre, tensile strength on strips according to standards EN ISO 29073‐3, ISO 9073‐3 and ASTM D5035 are performed to assess the strength of these products against tearing. Absorption capacity (EN ISO 9073‐6) is also important to test, especially in the case of wound dressings. More end‐ use‐specific tests include determination of the adhesive force (DIN EN 1939) applied on skin along with possible pain assessment upon application. For medical face masks, air permeability, splash resistance (ASTM F1862) against penetration of synthetic blood by visual inspection, and bacterial filtration efficiency (ASTM F 2101) are important to assess the mask’s performance as a piece of protective equipment. A hydrostatic pressure test for water resistance is another application‐specific test performed by subjecting one side of a textile sample to increasing hydrostatic pressure at a constant rate, until three points of leakage appear on the other side. For diapers and hygiene towels, the absorption capacity and rate, along with liquid retention and liquid strike‐through time (ISO 9073‐13: 2006), are critical parameters to be tested. The latter test is used as quality control for different types of nonwovens and it determines the time taken for a known volume of liquid (usually simulated urine) to pass through a nonwoven cover- stock which is in contact with an underlying dry absorbent pad. For gauze bandages, the yarn count and absorbency are significant parameters. For implantable products, biocompatibility tests are crucial, as are those for thermal resistance and mechanical strength. It is also to be noted that when medical textiles are loaded with pharmaceutical substances, either during the spinning process of fibres or in the finishing stage of the final product, the active ingredient must be quantified (assay control) and registered, even with different values depending on the different textile uses (e.g. clothing vs. mattress) (Figure 4.20). Moreover, in the case of long‐acting drug‐release systems, dissolution or release profiles should be controlled (e.g. chromatographically), because progressive

Ag+

Figure 4.20 Application of antimicrobial silver nanoparticles either on single fibres during spinning or in the finishing stage of the fabric. 98 4 Medical and Healthcare Textiles

loss or burst release of the active ingredient will cause inefficacy and will leave the user unprotected.

4.10 Sustainability and Ecological Aspects

It is becoming an increasing tendency in the textile industry to move towards so‐called greener practices in all manufacturing stages, from the selection of raw materials to the application of finishes. In the particular case of medical textiles, sustainability is introduced in similar ways as for the rest of textile classes (i.e. from the novel fibres used to the type of finishing agents applied, and from reducing harmful emissions during processing to producing easily disposable materials after use with low or no environmental impact). A study with respect to the environmental costs of different textile products, antimicrobial in particular, was first published in 2011 [48]. It presented a lifecycle assessment of a conventional t‐shirt compared to t‐shirts treated with common antimicrobial agents [81]. The authors showed that the contribution of the use of triclosan to the greenhouse gas emissions of producing a t‐shirt was insignificant, stressing the benefits that derive from using such agents because they help limit resource requirements for washing and override any additional resources consumed to apply an antimicrobial finish. Other studies of relative industries, such as the leather industry, support these conclusions, as they show that the use of certain agents, such as enzymes, in various process stages (soaking, dyeing, degreasing, etc.) can potentially save up to eight million gigajoules of energy and 0.7 million tonnes of CO2 per year [82]. A more recent study, the first of its kind on e‐textile eco‐design, focused on the lifecycle assessment of a wearable medical textile product named Vibe‐ing and its eco‐ redesign with a more environmentally friendly choice of materials and manufacturing practices [83]. The authors showed that the production phase had the biggest environmental impact in the product’s total lifecycle (74%) with the electronic systems used accounting for 71% of this impact largely because of its silver based wire composition. Also, the textile type itself, which was Merino wool, contributes another 57% to the product’s environmental impact. The electricity consumption of the final product was only a small percentage (5%) of the ecological impact. The authors suggested various strategies to redesign this medical wearable textile in a more sustainable manner, including a different choice of raw materials (copper instead of silver for wires and acryl textile instead of Merino wool) and even reduction of the amount of materials used, leading to cost reduction and an ecological benefit of at least 25% [83]. Among the new‐generation fibres, polylactic acid (PLA), chitosan, and lyocell are popular choices because they are eco‐friendly biopolymer based fibres [73]. Moreover, chitosan is used as a new antimicrobial agent for textiles, replacing, for example, silver nanoparticles, which in their turn had replaced synthetic organic compounds in the past [48, 73]. Other natural fibres, such as flax, are modified to produce more sustainable and more health‐beneficial materials (e.g. with higher bioactive content of phenolics and anti‐inflammatory compounds) for medical applications such as wound dressings [84]. A sustainable approach to textile manufacturing, including medical textiles, can be more holistic when valorizing vegetal resources, from which plant fibres can be derived, but also bio‐polysaccharides as thickeners and finishing agents, new natural pigments from suitable industrial crops using eco‐friendly extraction processes 4.10 Sustainability and Ecological Aspects 99 such as carbon dioxide, microwave and ultrasound techniques, herbal oils as deodorizing and aromatic finishes, linking in an innovative and profitable way the agricultural sector with the textile industry [85]. In the case of antimicrobial textiles, for instance, nanosilver and silver salts are prefer- able among the conventional antimicrobial agents because only low concentrations of them are required to achieve antimicrobial efficiency, and, thus, they can have a lower impact on nontarget organisms while at the same time reducing the intensity and frequency for textile care (e.g. laundering), which has high energy, water, and chemical demands [48]. For finishing agents, such as antimicrobials, their degradation speed and by‐products are also important with respect to ecology and sustainability. Silver forms cannot be considered biodegradable but they rapidly transform to other compounds (stable sulfide complexes) that are less toxic and more easily removed from aquatic environments [86]. Zinc pyrithione has a very rapid degradation process due to pho- tolysis with nontoxic by‐products [87], whereas triclosan causes concern, because of its degradation products which are potentially more toxic than the parent compound [48]. Risk assessment is, therefore, vital for the use of finishing agents in medical textiles but also for the finished products as well, which carry a noticeable amount of pathogens on them. Critical parameters such as the Measured Environmental, Predicted Environmental, and Predicted No Effect Concentrations of finishing agents are important to be taken into consideration as tools to assess the presence or absence of adverse effects on environmental organisms [48, 88]. Also, comparative studies for different finishing agents would be helpful in the selection of eco‐friendly steps for medical textile manufacturing, which would highlight important factors such as: (i) the minimum concentration required for effective functionalization, (ii) the durability of the functionalized material in terms of leaching but also of continuous high performance (i.e. does it emit harmful substances and does it continue to sufficiently protect the user and the environment?), (iii) persistence in the environment (does it degrade and how fast?), (iv) removal options with waste‐water treatment or air‐filtration, (v) bioaccumulation, and (vi) eco‐toxicity. A study on custom packs of healthcare facilities has revealed another aspect where there is room for improvement towards more sustainable and ecological practices: disposable products [89]. Cotton materials, in particular, have been identified as one area of concern, and suggestions were made to turn to reusable alternatives. According to the authors, a universal platform in the form of, for example, an online forum, where all hospitals compare their custom packs (e.g. towels for vaginal delivery of a child) could promote streamlining and sustainability of reusable products. Their recommendations were based on Design for Environment strategies which involved Design for Dematerialization (energy and material conservation, source reduction), Design for End of Life (recyclability and product recovery), and Design for Capital Protection and Renewal (human and economic capital) [89]. Sustainability, however, should be viewed in the light of not only the textile production processes but also the environmental knowledge of designers, managers, clients, and end‐users, as well. Only by bridging this gap on sustainable approaches can textile producers effectively apply financially viable eco‐friendly solutions by influencing the product architecture based on market insights but also environmental knowledge. Brockhaus et al. published a study in which they highlighted the motives which drive sustainability and concluded that the momentum for sustainability as a mainstream strategic priority for companies has diminished (possibly due to the financial crisis and 100 4 Medical and Healthcare Textiles

recession), but there can be two viable strategies: to leverage luxury (as sustainability aspects in products have often luxury and prosperity attributes embedded and can lead to an augmented value proposition) and to commoditize [90]. The latter strategy can be realized through technological evolution and innovation, making sustainability in product manufacturing a mainstream practice once more [90].

4.11 Conclusion

The scope of medtech encompasses all the textile based materials used in medical, healthcare and hygiene applications in both professional medical and consumer markets. Nowadays, innovative medical textiles have the potential to substantially change the way patients receive medical assistance/services. The continuous advancements of physics, chemistry, materials science, biotechnology, and nanotechnology along with highly engineered and improved fabrication processes/technologies has driven this sector to a new era, allowing not only a better life quality and life expectancy but, in some cases, also human survival. Owing to its highly beneficial cost‐effectiveness, market growth within this sector is expected to remain strong in the medium to long term. Amidst the e‐health textiles products, most of the recent research has focused on designing an ideal ambulatory wearable health monitoring system of longevity, and, simultaneously, being discreet and nonobtrusive. Despite the fact that these products are still relatively rare, there is a growing awareness of them and thus a rise in the number of marketable products.

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107

Textile Materials for Protective Textiles Ningtao Mao

School of Design, University of Leeds, Leeds, United Kingdom

5.1 Introduction

Textile materials are widely used in personal protective equipment (PPE) including advanced protective clothing like coats, trousers, vest, etc. and body armour products like helmet, masks, aprons, gloves, socks, shoes, etc. to protect human body from envi ronmental hazards. Protective textile products have been in constant and growing demand in the last few decades. The primary driving forces of this consistent growth are the increasing empha sis on the reduction of occupational hazards and the assurance of the health, safety, and protection of the workforce. The constant revision and development of legislation, gov ernmental policies, standards and industrial/organizational codes has encouraged cor porations and individuals to take initiatives to introduce accountable measures and equipment in the prevention of hazardous events and accidents at worksites. Various PPE and clothing are gradually becoming a part of the industry standard and norm. This demand leads to the consumption of great amounts of protective materials and the booming of innovations in protective textile products. On one hand, the strong demands of the protective clothing market pulls the development of high performance new tex tile materials and relevant technology; on the other hand, the rapid development of new technologies in emerging interdisciplinary fields, such as nanotechnology and biomi metics, also push the advancement of the protective clothing market. Fabrics made from traditional synthetic fibres such as polyethylene, polypropylene, polyester, polyamide, and polyurethane fibres are still widely used in protective cloth ing, especially specialist workwear for the purpose of balanced performance and cost effectiveness; for example, polyamide fibres (e.g. nylon) combined with a polyurethane coating are widely used as a durable layer in a great deal of protective clothing to com pensate the poor abrasion resistance of some high performance fibres (i.e. paramide fibres) to achieve superior abrasion resistance properties of the clothing. Microfibres, bicomponent fibres, hollow fibres, and fibres/filaments having noncir cular cross‐sections made from those conventional synthetic polymers are also fre quently used in the protective clothing system for protection, clothing comfort, and

durability purposes. Natural fibres such as cotton, wool, down, and fibres regenerated from natural polymers such as viscose rayon (including their special variants, e.g. flame‐retardant, FR, modified, nanoparticles coated) are also frequently employed to achieve protection (e.g. thermal and cold protection) and clothing comfort (both tac tile and thermo‐physiological comfort) properties. Fabrics made from those conven tional fibres are usually in a mixture form and additionally blended with other high performance fibres [1] for antistatic, bulletproof, stab‐proof, fire‐resistant and chemi cal‐resistant functions. Those fabrics usually require special treatment and finishing such as coating, lamination, and other special finishing (water/oil repellent, moisture permeable, softness, antibacterial, insecticide, etc.) to achieve multiple protection functions. High performance fibres are made from a wide source including organic polymers and inorganic materials such as ceramic fibres, carbon fibre, and stainless steel and aluminium fibres. High performance fibres are usually mixed or interwoven in the fab rics, or used as layered fabric structures to have a combination of multiple protection functions in protective clothing. However, most of those high performance fibres except those converted from natural fibre sources are stiff and do not have moisture manage ment properties, some of them have poor durability; therefore, the fabrics made from them are frequently used together with conventional fibres to achieve required durabil ity and clothing comfort properties. Woven and nonwoven fabrics made from synthetic filaments (e.g. polyester, polyam ide, polyethylene, and polypropylene) are frequently used in making reusable and dis posable protective workwear worn by people working in food, medical, pharmaceutical industries, and clean room environment of electronic industries. These fabrics not only protect people from many hazards such as biological and chemical substances, steam, temperature extremes, sharp‐edged tools, and harsh cleaning solutions they also pre vent contaminants both carried by workers (e.g. electrostatics, bacteria, hair, and skin flakes) and existed in workwear itself (e.g. monomer, filler, additives, dyestuff, lint, dust from polymer, fibre fabric, and coating materials of the garments) from entering the controlled environment and making contact with equipment or product. The materials used in those products are required to be both lint‐free and able to withstand the deg radation during harsh sterilization (either chemical or radiation) and laundering (for reusable clothing) process. Protective clothing has been remained as functionality‐driven products equipped with hybrid materials, smart technology, and nanotechnology. For example, novel energy absorption materials (e.g. shear‐thickening fluid, magnetic shear‐thickening materials, air inflatable structures) have been used in protective clothing to make flex ible and lightweight fabric without compromising protection and comfort properties; new materials and structure including nanoparticle‐fabric composites, phase change materials (PCMs), moisture/temperature responsive materials [2, 3], electric conduc tive yarns, and carbon nanotubes [4] are also used for thermal comfort; some of these materials are able to sense the wearer’s physiological condition [5], their posture and activity [6], and outside environment [7], as well as responsive action [8]. In this chapter, the effects of the functionalities of high performance textile materials on the overall performance of various protective clothing for the protection of the wearer from cold, thermal, fire, water, oil, radiation, acoustic, are microbial hazards are reviewed. 5.2 Performance Requirements of Protective Textiles 109

5.2 Performance Requirements of Protective Textiles

Textile materials used in protective clothing are determined by the requirements of the clothing performance in a specific human–clothing–environment system. While aes thetics of clothing were generic requirements for all types of garment, including fash ion, sportswear, casual wear, outdoor clothing, and protective clothing, the emphasis on the engineering design of protective clothing is laid on functional performance, includ ing protection, clothing thermal comfort, and human mobility. In protective clothing–human body–environment system, the interface between clothing and human body forms microenvironment which affects human comfort; and the interface between clothing and environment acts as a barrier to prevent human body from the exposure to harmful hazards. In a summary, the protective clothing per forms three functions: ●● Protection: protect wearer from environmental hazards, and this is the primary pur pose of protective clothing. ●● Clothing comfort: provide human comfort including tactile comfort and thermal comfort. ●● Mobility: maintain human mobility while the wearer carries out certain tasks. The clothing system is also required to maintain the three primary functions in cer tain conditions; therefore, a fourth requirement of protective clothing is the durability of the clothing: ●● Durability: the capability of the clothing system maintains the three primary func tions (protection, comfort, and mobility) under various environmental conditions after repeatedly external insults. Specific protective clothing is designed for use in defined environments to protect wearers from targeted environmental hazards. Environmental hazards are frequently grouped according to their physical forms (e.g. solid, particles, liquids, gases, mist) and properties. Some typical examples are shown below: ●● Mechanical hazards: abrasion, cut, puncture, slash, high speed bullet impact, low speed impact, explosion fragment, etc. ●● Thermal hazards: flame, fire, heat (infrared heat, radiation heat, hot gases, steam, hot liquid), ultraviolet (UV) exposure ,and cold (wind, ice, snow, deep sea water, exterri torial weather, liquid gases, cold surface, and solid materials) hazards. ●● Water: rain, snow, seawater, wastewater, ice, water vapour, etc. ●● Chemical hazards: oil, petrol, solvent, paint, alkali, acids, salt, heavy metals, toxic, flammable, explosive, and erosive chemicals. ●● Biochemical and biological hazards: bacterial, virus, blood, body fluid, drugs, etc. ●● Electrical hazards: high voltage, high current electricity, lightning, electrical spark, and arc. ●● Electromagnetic wave hazards: infrared, UV, laser, invisible light, sunlight, high inten sity light (SW, MW, LW, UH, UVW). ●● Acoustic hazards: low and high frequency noise, ultrasound, explosive waves, thunder. ●● Radioactive hazards: X‐ray, beta ray, gamma ray, protons, and neutrons, negative electron rays. ●● Industrial hazards: Hot metal liquids, welding arc and spark, saw, squeeze. 110 5 Textile Materials for Protective Textiles

5.3 High Performance Fibres

High performance textile materials having exceptional mechanical properties as well as fire‐resistant and chemical‐resistant properties are available in the form of fibre, film, membrane, and liquid and are frequently used in protective clothing. The high performance fibres are made from a wide source including organic polymers and inor ganic materials such as ceramic fibres, carbon fibre, and stainless steel and aluminium fibres [1]. High performance polymeric fibres having exceptional mechanical proper ties, fire‐resistant properties, chemical‐resistant properties and frequently being used in protective clothing are summarized in Table 5.1, and a comparison of pros and cons of some of those high performance fibres are shown in Table 5.2. High performance polymer fibres having ultrahigh mechanical properties, as shown above, were achieved mainly by orienting the chain molecules in fibres. There are two main routes for the preparation of high performance polymer fibres. One is based on flexible macromolecules, whereas the other route is based on rigid rod macromolecules. In the case of flexible chain polymers, such as polyethylene, solid‐state drawing (or gel spinning) is used to obtain the necessary level of chain extension to exploit the intrinsic properties of the polymer chain. In the case of rigid rod polymers, chain extension is already built in by the chemist and alignment in the extended chain configuration is achieved during fibre spinning. The properties of high performance fibres are significantly influenced by their chemi cal and physical structures. For example, the excellent thermal stability of p‐polyaramid ® ® (poly[p‐phenylene terephthalate]) fibres (e.g. Kevlar (DuPont) and Twaron (Akzo)) is due to their aramid ring, and aromatic/amide bonds have 20% higher dissociation ener gies than their aliphatic counterparts. These excellent physical properties are also due to their highly anisotropic (in comparison, graphite fibres are also anisotropic, while glass fibres are isotropic), crystalline, extended chain structure (i.e. there is no chain folding in the rod form of the para‐aramid molecules) [23]. The phenyl rings of adjacent molecule chains stack on top of each other very neatly to make the polymer highly crystalline after extrusion process, such structures make the fibre be an outstanding high strength, high modulus fibre, and relatively insensitive to temperatures up to Tg (–280 °C) and dimensionally stable. In practice, p‐polyaramid fibres could be designed progressively to have a higher orientation of polymer molecules and crystallinity to achieve the desired modulus and tenacity (e.g. Kevlar 29, Kevlar 49, and Kevlar 149) [24]. Any inherited problems in high performance fibres could also be due to their chemi cal compositions and microstructures. For instance, Kevlar fibre was found to be sensi tive to UV exposure and extreme freezing environmental temperature (less than 30 °F) [25], while poly(p‐phenylene‐2, 6‐benzobisoxazole), or poly(para‐phenylene benzo ® bisoxazole) (PBO) (Zylon ), fibre has high strength and a modulus almost double that of p‐aramid fibres (e.g. Kevlar, Twaron) and ultra‐high‐molecular‐weight polyethylene ® ® fibres (e.g. Dyneema , Spectra ), higher decomposition temperature (650 °C) than the p‐aramid fibres, as well as extremely high limiting oxygen index (LOI) of 68 [26]. PBO fibre is notorious for its susceptibility to moisture degradation. The strength of PBO fibre decreases under conditions of high temperature, high humidity, and exposure to UV and visible light [27], owing to the characteristics of the oxazole ring within the chemical structure of PBO [15]. The degradation of PBO fibre in bulletproof vests raised concerns and lawsuits in the commercial market [1, 28]. 5.3 High Performance Fibres 111

Table 5.1 Mechanical properties of high performance fibres [1, 8–15].

Protection from mechanical hazards Commercial (stab, ballistic, puncture, Types of fibres Composition products Density [10] chainsaw, etc.) Aramid fibres p‐aramid (poly(para‐ Kevlar (DuPont), 1.44–1.47 Tenacity: ca 3.0GPa, phenylene Twaron Modulus: 70‐110GPa terephthalamide)) (Acordis), and Tenacity: 194.3‐229.6 and its copolymer Technora cN/tex (Teijin) Modulus: 4061.8‐9713 Armos (Russia) cN/tex [16] Tenacity: 250–290 cN/ tex [16] Modulus: 145–160 GPa [16] m‐aramid Nomex, Kermel, 1.38 ++ (poly(meta‐phenylene and Corex Tenacity: 33.6–63.6 isophthalamide)) cN/tex Modulus: 106.0–123.6 cN/tex Polyamide‐ Polyimide (PI) Torlon (Solvay) 1.34 + ® imide (PAI) P‐84 (Evonik) Tenacity: 37.1 cN/tex and polyimide [17] fibres PBI fibres Polybenzimidazole PBI (Celanese) 1.43 ++ Tenacity: 23.8 cN/tex Modulus: 282.6 cN/tex PEN, PBO and PEN Zylon (Toyobo), 1.54–1.56 ++ (excellent abrasion) PIPD fibres (polyethylene‐2,6‐ M5 (Akzo Tenacity: 370.9 cN/tex naphthalate) Nobel) Modulus: 11479 cN/ PBO Novel yarn tex (p‐phenylene‐2,6‐ benzobisoxazole) UHMWPE Ultra‐high molecule Dyneema 0.97 ++ abrasion fibres [18, 19] weight polyethylene, (DSM), Spectra Tenacity: 264.9 cN/tex gel spun (Honeywell), Modulus: 12362 cN/ Tekmilon tex (Mitsui) LCP fibres [20] Polyarylate, liquid Vectran 1.41 ++ (excellent abrasion) crystal polymer fibre (Kuraray) Tenacity: 247.2–256.1 cN/tex modulus: 61.8–88.3 cN/tex ® PPS fibres Polyphenylene Ryton 1.37 + sulfide, Crystalline (Amoco), ® Tenacity: 30.9–39.7 thermoplastic fibre Procon cN/tex (Evonik), ® modulus: 61.8–88.3 Toray PPS cN/tex (Toray) (Continued) 112 5 Textile Materials for Protective Textiles

Table 5.1 (Continued)

Protection from mechanical hazards Commercial (stab, ballistic, puncture, Types of fibres Composition products Density [10] chainsaw, etc.) PEEK fibres Polyetheretherketone, ZYEX, ZEUS 1.30 ++ Semi‐Crystalline Tenacity: 17.7 cN/tex thermoplastic fibre modulus: 70.6 cN/tex Novoloid Cured Kynol 1.27 + (poor abrasion) fibres phenol‐aldehyde Tenacity: 11.5 cN/tex Modulus: 97.1 cN/tex ® Melamine Melamine Basofil (BASF) 1.44 + based fibres Tenacity: 17.7 cN/tex Modulus: 97.1 cN/tex Fire‐resistant Modified cellulosic Lenzing viscose 1.38 − natural and FR, DFG regenerated (Daiwabo), fibres Danufil CS (Kelheim) Modified wool Zirpro wool 1.32 − Inorganic Carbon fibre: Pitch / 2.0 ++ (poor abrasion) fibres Tenacity: 123.6–264.9 cN/tex Modulus: 8830– 51 656 cN/tex PAN / 1.40 ++ Tenacity: 158.9–618.1 cN/tex Modulus: 14481.2– 33 995.5 cN/tex Ceramic fibre Ceramic / ++ Metal (stainless steel, Stainless steel, 7.8 ++ aluminium) aluminium ++ means very good or excellent, + means mild or good, − means poor.

Heterocyclic copolymerized aramid fibres having different molecular architecture and phase morphology from homogeneous aramid fibre could lead to excellent proper ® ties [29–31]. For example, Armos fibres [32], a random copolyamide of poly(para‐ phenylene terephthalamide) (PPTA) and polybenzimidazole (PBI) (CP‐PTA/BI), not only have much greater tenacity and modulus than both p‐aramid and PBI fibres, but also exhibit excellent resistance to degradation of tensile properties in extreme weather conditions (80–100 °C in temperature and 100% relative humidity, or RH). After 34 days at the most extreme condition of 100 °C and 100% RH, aramid fibres showed a signifi cant loss of tensile strength (58% for KM2 and 34% for Twaron), while aramid copoly mer (Armos) fibres only showed a reduction in tensile strength of 13% [33]. It was 5.3 High Performance Fibres 113

Table 5.2 Comparison of high performance fibres [21, 22].

Material PROs CONs

Kevlar Aramid Strength comparable to Poor folding and abrasion ® Vectran , higher rigidity, and resistance better thermal properties Zylon PBO Higher tenacity, higher rigidity, Low flex resistance improved thermal properties [22] Poor resistance to moisture, visible light, and ultraviolet (UV) Poor adhesion to resins Expensive M5 PIPD Strong, excellent compressive Not commercially available properties, and excellent adhesion to resins [22] Excellent weatherability Vectran LCP Good strength and excellent cut Not as strong as Spectra or Zylon resistance Poor UV resistance Excellent durability and Poor thermal properties at higher mechanical properties at temperature extreme low temperature Spectra PE High strength and stiffness Low melting point, low LOI, poor Flexible and good weatherability creep resistance, and poor adhesion to resins [22] ® Kosa PET Tough, durable, inexpensive, Low strength fully evaluated LTA fibre believed that the ingress and egress of moisture in the highly ordered core structure in aramid fibres is the primary mechanism of degradation at temperatures between 80 and 100 °C. The presence of water in the intercrystalline regions of the fibre core enable seg mental chain motion that can relax tie molecules, alter crystal orientation, and change apparent crystallite size. It was evident that the moisture diffusion coefficient in the copol ® ymer Armos (D = 8.7 × 10–13 cm2 s−1) is much smaller than that in both Kevlar KM2 (D = 2.16 × 10–12 cm2 s−1) and Twaron homopolymers(D = 1.8 × 10–12 cm2 s−1) [33]. High performance polymers are also made into membranes, films and coated fabrics for liquid repellence, liquid and gas barrier to prevent gaseous, moisture and liquid vapour from permeation/penetration through protective clothing, especially chemical, biological, radiological and nuclear (CBRN) protective equipment. For those protective materials, their durability (weatherability, flex fatigue, low temperature flexibility, ozone resistance) and processing ability (adhesion to fabric/film and heat sealability) are also crucial for achieving the required performance. Table 5.3 summarizes some typical polymer materials, and the gas permeability is only an indication of the oxygen/nitrogen gas permeability of the polymer in specific temperature, RH, and atmospheric pressure, and their liquid vapour/water moisture permeation and diffusion properties could be found in relevant handbooks on polymers and protective clothing, which may depend on the polymer molecular structure, orientation, crystallinity and film/membrane thickness.

5.4 High Performance Textile Materials 115

5.4 High Performance Textile Materials

5.4.1 Protection Against Cold

People working in cold environments need to be provided with sufficient thermal insu lative products (e.g. clothing, footwear, gloves, and head protection equipment) to reduce risk of the wearer experiencing hypothermia or ‘cold stress’. Protective clothing against the cold usually consists of multiple layers, such as a base layer for wicking and moisture management, an interliner for thermal insulation, and a waterproof/windproof outer layer. The textile materials used in clothing against cold would depend the following eight properties: ●● Thermal resistance: the resistance against heat losses from the human body to envi ronments through heat conduction. The thermal insulation properties of fibre assem blies mainly depends on the thermal conductivity and specific heat capacity of the fibre (or polymer) materials, porosity (or still air contents), the thickness of fibrous materials, fibre diameter/fineness (e.g. fine fibres and microfibres), fibre geometry and morphology (e.g. crimped fibres, hollow fibres, and fibres with large surface areas), fibre orientation distribution within the fabrics, and the moisture/water con tent of the materials (e.g. wet fibres against dry fibres). Sometimes thermal resistance also relies on good compression recovery properties of textile materials, especially when thermal resistance under higher pressure is required. In this case, hollow fibres (such as natural hollow fibres like as Kapok, rabbit hair, and polar bear hair, as well as synthetic hollow fibres), down, and feather fibres are widely used. Other structures such as air pocket and baffle structures are also frequently used in thermal insulation materials. ●● Evaporative resistance: the resistance against the loss of moisture (either through evaporation or from human body metabolic activities) help maintains body tempera ture against cold weather. However, moisture can be condensed into liquid water inside clothing in cold weather and the human body can sweat to make skin wet, and these can promote heat loss through clothing in cold weather. Therefore, the evapora tive resistance of textile materials relies on the water vapour permeability of fabrics, moisture absorption/adsorption – desorption properties, exothermic and endother mic properties of polymeric fibre materials, air permeability of fibrous materials, thickness and wicking properties of textile materials, coated/laminated polymeric materials (e.g. monolithic polyurethane, porous polyester/polytetrafluoroethylene (PTFE) membrane). ●● Water resistance: the resistance of the outer shell of clothing against liquid water (mist, moisture condensation, rain, snow, ice, water, etc.) penetrating clothing materi als. Less water moisture and liquid water trapped inside clothing will help maintain the thermal insulation properties. ●● Wind resistance: the resistance of textile material against wind (or air flow) passing through textile materials; this airflow through textile materials will carry the body heat of the wearer away by convection. ●● Resistance to radiation: this resistance includes both the reflection of body radiative heat back towards the human body (e.g. aluminium sheet) and the absorption and storage of radiative heat into certain materials (e.g. carbon fibres and particles, 116 5 Textile Materials for Protective Textiles

certain ceramic particles) contained in textile fibres. It was found that the relationship between the effective thermal radiative conductivity and fibre fineness may be better fitted with a quadratic curve [35]. ●● Generation of exothermic heat: certain polymeric materials such as cellulosic fibres (e.g. cotton, ramie, hemp), keratin (wool, silk, feather, animal hairs), and some supera bsorbent materials will generate exothermic heat when they absorb moisture water from the environment. This will help prevent body heat losses from moist or wet weather. ●● Aerogel and nanoporous materials: aerogel and nanoporous materials are well known for their superior thermal resistance, such as silicon and silicone aerogel, carbon nanotube aerogel, flexible polymer aerogel, etc. ●● Storage of body heat: PCMs (e.g. candle wax) are widely used in clothing to store and release heat from the human body when needed. Many conventional natural textile materials – such as wool, animal hairs, silk, cotton, and their blends – are widely used as thermal insulation materials in protective clothing against cold, these materials also have good moisture management properties. Their structure and properties can be found in many textile books and will not be discussed here. Some special nature fibre materials – such as various downs, kapok, and milk weed, as well as synthetic textile materials – are discussed below.

5.4.1.1 Feather and Down Fibres Down is the undercoating fibres of waterfowl such as geese, ducks, swans, penguin, eider, and many other birds; it consists of light, fluffy filaments growing from a central quill point, thereby creating a three‐dimensional (3D) structure which traps air and gives down insulating ability [36]. Down and body feathers from waterfowl and other birds kept for meat or eggs (e.g. chicken) are used to stuff clothing, sleeping bags, pil lows, cushions, bedding products, and other such items to insulate against cold hazards. Down has the characteristics of lofty, lightweight, soft touch, and incredible warmth‐ to‐weight ratio. Its superior thermal insulation properties against cold climates are due to both its lofty configuration in fractional barb/barbule fibre structures and also its high buckling resistance; the lofty fractional configuration has unusually high effective ness in trapping still air to provide an outstanding thermal barrier, and its high com pression resilience enables the down to recover from any squeeze to its original configuration to retain the trapped air and thermal insulation properties (Figure 5.1). Goose and duck down are the most popular thermal insulative materials available for jackets and sleepbags against clod. Barbs and barbules in duck and goose down fibres have various irregular cross sections and their barbule branches have trilobal nodes; under compression, these nodes lock together to resist the stress. While barbs of duck down are found to be of irregular solid elliptical cross‐section, barbs of some goose down is found to be hollow and irregular triangular shape in cross section [37], which enable additional compression resistance in comparison with duck down (Figure 5.2). The warmth‐to‐weight ratio of down is quantified as ‘fill power’. European Union (EU) fill power and United States (US) fill power are defined and measured in cylinders of different diameters using different compression pressure after down fibres are steamed. EU fill power of 800 means that 30 g of down fibres occupies 800 cubic inches (13109.7 cubic centimetres) when exposed to a certain pressure, while US fill power of 5.4 High Performance Textile Materials 117

200 μm Mag = 101 X Signal A = InLens EHT = 3.00 kV WD = 3.1 mm Date : 2 May 2012

Figure 5.1 Duck down cluster.

2 µm2 µm

Figure 5.2 Cross‐section of goose and duck down fibres (1 – barb; 2 – barbule; 3 – possible hollow or medulla).

800 means that one ounce (23.8 g) of down fibres occupies 800 cubic inches when exposed to a different fixed pressure. Usually white goose down has better quality than duck down, and fill power of up to 1000 of white goose down is commercially available because of the progress in down categorizing selection technologies. Eiderdown is a type of scarce special down fibres and only four to five tonnes are produced each year in the world. Commercially available eiderdown comes from the breast feathers of female eider ducks in Iceland, Canada, and Greenland [38]. Eiderdown 118 5 Textile Materials for Protective Textiles

has unique characteristics, such as unique exceptional cohesiveness (or cling), is soft with no rigid quills, has extraordinary elasticity and resilience, as well as possesses excellent moisture management [39]. Eiderdown fibres have fill power varying from 400 to 900 in.3 oz−1 but still have excel lent thermal insulation properties. For example, pure true eiderdown has a relatively lower fill power (values around 500 in.3 oz−1) but could have the same insulating proper ties as the best‐quality commercial white goose down (from mature egg‐laying females) having the fill power of 800 in.3 oz−1 or more [39]. Therefore, it is claimed that fill power alone could not represent the quality of eiderdown [38]. This also means that eiderdown would have half the bulk of goose down plus enhanced dissipation of body moisture in corresponding insulation products. Penguin down and feathers are a special type of down fibres. On average, the barbules are 6 μm in diameter and 335 μm in length [40], and it is believed that both the optimum fibre diameter [35] and the number of layers of barb/barbule fibres contribute to shield ing radiative heat losses [40]. Penguin feathers are evenly packed to form a thin, smooth, and waterproof coat to include a thick and air‐filled porous down layer underneath (similar to an open‐cell foam covered with a windproof layer) that eliminates convec tion and reduces radiative and convective heat loss to a minimum. The thermal resist ance of the penguin coats (feather and skin assembly) are an average of 0.74 m2 kw−1 (or 7.4 tog) [41–43]. The thermal insulation of the down and feathers of penguin chicks has demonstrated unique thermal insulation properties in wind. The insulation of penguin feathers of pre‐fledged chicks increased with higher wind speeds, their insulation value in parallel airflow of 5 and 15 m s−1 are 87–112% and 136–179% of the insulation in still air, respec tively; and these penguin chicks can remain within their thermoneutral zones on windy days. Increasing insulative values of feathers or fur under increasing wind speeds have not been demonstrated previously in any bird or mammal [44]. However, down fibres are expensive (eiderdown is about 10 times more expensive than goose down and so can only be used in high end, luxury products) and feather fibres are usually heavy, the performance of their thermal insulation properties will be compromised when wet, and they can also trigger allergies. Often duck and goose downs are collected in a cruel way (e.g. live‐plucked [45]). Having said this, there has not been a better alternative insulation material that has a similar exceptional warmth‐ to‐weight ratio.

5.4.1.2 Kapok Kapok is a special type of plant fibre, being hollow, soft, hydrophobic, resistant to fungi and bacteria, and does not cause any allergies. Kapok fibre is a smooth, twistless, cylin drically shaped, hollow, unicellular fibre containing mostly alpha cellulose (35–65%), hemicelluloses (22–45%), pectin (15–23%), and lignin (13%) [46–51] and can contain about 10–11% of moisture. Because the fibre surface is covered with a thick layer of water repellent wax (2–3% wt), the fibre is hydrophobic. Kapok fibre is usually 10–35 mm in length and 20–43 μm in diameter, with the length‐to‐diameter aspect ratio being around 720, its tensile strength around 0.84 cN(dtex)−1 (93.3 MPa), and elongation around 1.2% to make the Young’s modulus of 4 GPa [52]. While the thin cell wall (1–3 μm in thickness) of kapok fibres has the absolute density of 1474 kg m−3, its lumen [53] is about 74% of fibre’s volume and filled with air to make 5.4 High Performance Textile Materials 119 the density of the fibres a mere 384 kg m−3, which provides excellent buoyancy of up to 20–36 times its own weight, the thermal conductivity of kapok fibrous assemblies ranges between 0.03 and 0.04 Wm−1 K−1 with a thermal diffusivity of around 17.1 × 10−7 m2 s−1 when their bulk density varies between 5 and 40 kg m−3 [46]. It has been used as insulation material to replace feathers, down, and synthetic materials in smaller refrigerating systems, lining in sleeping bags, gloves for dry ice handling, and the filling of insulative clothing linings [54]. However, it is flammable, and the lumen of kapok collapses gradually during multiple compressions, which compromises some of its performance aspects.

5.4.1.3 Milkweed Milkweed floss is another type of special plant fibre. It is produced by plants Asclepias, Ceropegia, and Calotropis and grows in abundance in North America, predominantly east of the Rocky Mountains. Similar to kapok, milkweed fibres are hollow, with a waxy, water‐repellent coating and are light enough to float away on the wind while carrying a big milkweed seed along for the ride. Those hollow fibres trap air and the waxy coating prevents them from absorbing water. Those properties lead milkweed work well in life jackets and thermal insulation products. The hand feel, loftiness and compressibility of 100% milkweed floss and its ability to retain loft and outright insulation is not as good compared to down and some tradi tional synthetic fibres. However, when blended with either down or synthetic fibres to form a mixture as an insulative fill material, milkweed floss performs at or near the top in every test [55]. Down is particularly useful in optimizing the performance properties of milkweed floss, and milkweed does not decrease the insulative properties of down [55]. Given that milkweed is about one‐half the price of goose down, the mixture of milkweed with down might be attractive for economic reasons.

5.4.1.4 Synthetic Insulative Materials Various man‐made and synthetic fibres are used in producing thermal insulative filling materials. They include cellulosic, protein, acrylic, nylon, polyester, and polyacrylate fibres of irregular cross‐sections. For example, they could be hollow fibres, microfibres, or a mixture of fibres having good compression recovery properties and surface areas. Some fibres have incorporated special active additives such as keratin and moisture absorption particles for heat generation; carbon particles, ceramic, and nanoclay parti cles for infrared absorptions; PCMs for heat storage and controllable release [56]; and shape memory materials and electroactive polymers used in smart fabric structures for intelligent heat and moisture management. Different fabric structures have been used in making thermal insulation materials, including pile fabrics; artificial fur; fleece fabrics; knitted fabrics; as well as nonwoven fabrics, such as Polarloft, PrimaLoft, and Thinsulate. While pile fabrics pill quickly, they have relatively lower density inner and greater density backing, and so have better capil lary wicking and moisture management properties to keep the wearer feeling dry. Fleece fabric is a softshell fabric and could be made waterproof and hydrophobic, it has supe rior moisture management properties. Nonwoven fabrics are widely used as wadding and padding materials and provide excellent warmth‐to‐weight ratio. Neoprene foams incorporating with textile fabrics are frequently used in wetsuits to protect people from a cold sea environment. 120 5 Textile Materials for Protective Textiles

5.4.1.5 Other Thermal Insulative Materials Water‐resistant coatings for down [57] are believed to increase its thermal insulation performance in wet conditions [58], and might lead to future hydrophobic downs [59]. An improved understanding of heat transfer mechanisms in fibrous structures and advance in fibre development might lead to artificial down fibre having fractal barb and barbule tertiary structures, which is hoped to improve thermal insulation properties to reduce radiative, convective, and conductive heat loss. Aerogels, especially flexible aerogels and nanoporous materials, are incredible syn thetic solids of extremely low density and have excellent thermal insulation properties. They are possible materials to revolutionize protective materials against the cold. However, commercially available silicone aerogels are still of limited uses in clothing, owing to its brittleness, cost, and health and safety concerns on its penetration of human skin and cell membranes. Flexible aerogels made from silicone and polymeric materials could overcome the shortcomings of brittleness while maintaining the lowest thermal conductivity in aerogels. They are a promising next generation of aerogels appropriate for clothing (Figure 5.3) [60]. Clothing equipped with active heating technologies has also been available for years but has been of limited use in protective clothing because of heavy, unreliable, and expensive batteries. More new fibres having heat generating and moisture management functions and infrared absorption properties such as polyacrylate fibres [61, 62] and biomimetic fibres mimicking penguins and polar bears are applicable to clothing. For example, the diam eter of penguin down is very close to the theoretical optimum fibre fineness for block ing radiation [35]. And the architecture structure of penguin feather coats could reduce

200 nm Mag = 120.00 K X Signal A = InLens EHT = 3.00 kV WD = 2.6 mm Date : 30 Aug 2013

Figure 5.3 Microstructure of aerogel. 5.4 High Performance Textile Materials 121 the turbulence of air flowing over the surface, thus having unique thermal insulation properties at higher wind speeds.

5.4.2 Protection Against Mechanical Cut Hazards

Textile polymeric materials, metal, and ceramics as well as their hybrid structures hav ing unique cut‐resistance properties are frequently employed in protective equip ment – including protective clothing. Different high performance fibres vary in cut resistance. Super‐strong, high per formance fibres (such as ultra‐high‐molecular‐weight polyethylene (UHMWPE) (UHMWPE) fibres) absorb the impact energy to stop damage inflicted by a knife and minimize trauma, while the metal wire blunts the sharp edge of knives and shrapnel. Results on stress–strain relationship and deformation characteristics during cutting are reported for three types of high strength yarns of Zylon, Kevlar, and Spectra [63]. It is found that Zylon fabric has the highest specific energy absorption in high speed frag ment impact test, and the specific energy absorption increases with the increase of the fabric tightness and fabric areal density. Different high performance fibres are frequently incorporated with conventional fibres in specially designed yarn and fabric structures for protective clothing to achieve targeted performance of durability, protection, and comfort in cut‐resistant products. For example, traditional protective clothing for chainsaw operators includes pants and chaps that generally have a nylon, polyester, or denim outer fabric and inner inserts comprising layers of ballistic nylon or high tenacity polyester fabric or, in higher‐quality clothing, layers of aramid fabric such as Kevlar or UHMWPE, such as Dyneema. Its cut‐resistant protective layers provide passive protection to the wearer and are designed to jam the chainsaw drive sprocket, thereby stopping the saw before it can cut through the trouser leg and cause injury. Strong polyester filament sheath‐ core composite yarns are also created for realizing both strength and comfort properties. Composite materials and hybrid structures are usually employed to provide multiple functions in addition to cut‐resistant requirement. Composite cord threads using metal filaments as core, and other high performance fibres as sheath are used in special fabrics to provide flexibility as well. Cut protection [64], ballistic‐proof and stab‐proof protec tions from gunshots, shrapnel and knives stabs have also been reported [65]. Composite cord threads using stainless steel filaments as core and other high performance fibres as sheath are used in cut‐resistance fabrics to provide both flexibility and cut protection [64]. Fabric weaves are also important. For example, basket weaves and rip‐stop struc tures are well known for their superior mechanical strength. A flexible body armour vest [65] made from a combination of Dyneema high performance polyethylene fibre from DSM and Steelskin steel cord material from Bekaert to offer both ballistic‐proof and stab‐proof protections from gunshots, shrapnel, and knives stabs are reported. The super‐strong high density polyethylene (HDPE) Dyneema fibre absorbs the impact energy to stop the damaged knife and minimize trauma while the steel wire blunts the sharp edge of knives and shrapnel. Rigorous requirements of abrasion resistance for protective clothing also make hybrid structure of protective textile materials desirable. For example, clothing and equipment used by motorcyclists are specified in a series of EU standards [66–74] and CE marks. 122 5 Textile Materials for Protective Textiles

In CE EN 13595, the material used in motorcycle protective clothing must have abra sion resistance of between four and seven seconds for use over the high impact areas of the body (Zones 1 and 2), as defined by Woods [75]. However, some high performance fibres (e.g. p‐aramid and m‐paramide fibres) has poor abrasion resistance. In this case, they usually blend with fibres having superior abrasion‐resistance properties, combined with polyurethane coating, or layered with nylon fabrics. Nylon fibre is famous for its durability, tensile strength, and tear‐ and abrasion‐resistance properties and thus is used in many other protective clothing rather than ballistics protection. The typical ® example of nylon fabrics used in protective clothing is Cordura Ballistic nylon fabrics [76, 77], which is a thick, tough, synthetic nylon fabric having a construction of 2 × 2 basket weaves. Cordura fabric consisting of 1000 denier and 500 denier nylon filaments are used in motorcycle jackets and workwear clothing for durability [78]. Fabrics con taining nylon filaments have also been widely used for the durable layer of military and civil personal protective equipment [79] to protect military personnel, chainsaw opera tors, and motorcyclists.

5.4.3 Protection Against Flame and Heat [80]

High performance fibres, having good thermal‐resistant properties, are employed in special uniform, workwear, and protective clothing to protect wearers from flame and heat hazards [81]. The mostly common fire‐resistant high performance polymeric fibres are shown in Table 5.4. For example, the outer shell and thermal liner of structural firefighters’ clothing [82, 83] are usually made from p‐polyaramid, m‐polyaramid, polybenzimidazole, or poly(melamine‐formaldehyde) fibres, and the composite structure of these fibres both resists fire and prevents water ingress, and cut, stab, tear, and abrasion hazards which may be present at the scene of a fire. ® Heat‐resistant m‐aramid fibres (e.g. Nomex ) can withstand exposure to extreme heat for over eight seconds and does not melt or drip, even at high temperatures. It offers excellent heat insulation, by absorbing heat energy when exposed to a heat source. It also boasts high UV resistance, abrasion resistance, and durability and is relatively soft to touch. So m‐aramid fibres have been the primary fibres for flame‐retardant and fire‐resistant textile products. While p‐aramid fibre (e.g. Kevlar) has good heat resistance as well as extremely high levels of tear and cut resistance, it absorbs hardly any heat energy when exposed to flames, so a large proportion of the energy can penetrate the fabric. In addition, it is less UV stable and abrasion‐resistant than a m‐aramid fibre, and tends to pill. Therefore, only a small proportion of p‐aramid fibres are used in flame‐retardant, for their high tensile strength and cut resistance. It was found that too high a content of p‐aramid may negatively impact on the performance of the flame‐ and heat‐resistant fabric [84]. In comparison with the fabrics with a 60% content of p‐aramid fibres, the fabrics with a p‐aramid content of between 5 and 23% achieved better values in terms of thermal protection (heat‐penetration resistance) as Nomex fibres absorb a large part of the heat energy when exposed to heat. It also has better abrasion resistance and UV resistance as well as washing behaviour. In contrast, the fabric containing 60% p‐aramid exhibited a significantly higher level of tear resistance in its original condition than the fabrics con taining less para‐aramid. 5.4 High Performance Textile Materials 123

Table 5.4 Flame‐retardant properties of high performance fibres [1, 8–15].

Protection from flame, Char fire and Onset residues Types of Commercial thermal decomposition at 850 °C fibres Composition products hazards in N2 (°C) (%) Aramid p‐aramid (poly(para‐ Kevlar ++ 530 / fibres phenylene terephthalamide)) (DuPont), LOI: 25–28 and its copolymer Twaron T*: 190 °C (Acordis), and Technora (Teijin) Armos ++ 450–550 (Russia) LOI: 39–42 [16] T*: 220–240 °C m‐aramid Nomex, + 400 35 (poly(meta‐ Kermel and LOI: 30 phenyleneisophthalamide) Corex T*: 205 °C Polyamide‐ Polyimide (PI) Torlon ++ 500 (PAI) 30 (PAI) imide (PAI) (Solvay) LOI: 38 fibre and P‐84 T*: 260 °C Polyimide (Evonik) [17] PBI fibres Polybenzimidazole PBI ++ 1000 59 (Celanese) LOI: 41 T*: 250 °C PEN, PBO PEN Zylon ++ 700(PBO) and PIPD (polyethylene‐2,6‐ (Toyobo), LOI: 68 fibres naphtalat) M5 (Akzo T*: PBO Nobel) 288–315 °C (p‐phenylene‐2,6— Novel yarn benzobisoxazole) LCP fibre Polyarylate, liquid crystal Vectran ++ / [20] polymer fibre (Kuraray) LOI 37 T*: > 392 °C PPS fibres Polyphenylene sulfide, Ryton + / Crystalline thermoplastic (Amoco), LOI: 34 fibre Procon T*: (Evonik) 288–315 °C Toray PPS (Toray) PEEK fibre Polyetheretherketone, ZYEX, ++ 580 semi‐crystalline ZEUS LOI: 95 thermoplastic fibre T*: 260 °C

(Continued) 124 5 Textile Materials for Protective Textiles

Table 5.4 (Continued)

Protection from flame, Char fire and Onset residues Types of Commercial thermal decomposition at 850 °C fibres Composition products hazards in N2 (°C) (%) Novoloid Cured phenol‐aldehyde Kynol ++ 450 45 fibre LOI: 33 T*: 96 °C Melamine Melamine Basofil ++ 400 based fibres (BASF) LOI: 32 T*: 204 °C PTFE PTFE PTFE LOI: 95 460 Fire‐ Modified cellulosic Lenzing ++ / resistant viscose FR natural and DFG regenerated (Daiwabo), fibre Avilon (Avilon) Modified wool Zirpro wool ++ Inorganic Carbon fibre: Pitch / ++ fibre T*: 300 – 538 °C PAN / T*: > 300 93 300 – 538 °C Ceramic fibre Ceramic ++ Metal (Stainless steel, Stainless ++ aluminium) steel, aluminium T* represents the temperature for the fibre to be frequently used for continuous operation. ++ means very good or excellent, + means mild or good, − means poor.

PBI (polybenzimidazole) fibre has excellent thermal resistant properties. It has one of the greatest LOI (limiting oxygen index; 41%), resistant to ignition and hydrolysis, nei ther burn in air nor melt or drip. PBI fabric can withstand dangers associated with firefighting, arc flash, and flash fire [85]. However, PBI has relatively low tensile strength, does not resist acids [86] or UV radiation exposure [87, 88], and degrades in moist environments. The PBI fibres used in firefighters’ clothing loses its mechanical proper ties in environments having a high RH [89]. It was reported that PBI fibres lost 30% tensile strength after exposure to the environment of 500 °C, RH 60% for 84 days, and 600 °C, RH 37% for 73 days [90]. Four forms of PBI fabrics (PBI Gold, PBI Matrix, PBI TriGuard, and PBI BaseGuard) are available on the market [91]. PBI Gold, which is available as PBI Gold knits, PBI Gold Ripstop, and PBI Gold Twill fabrics, has been widely used as an outer shell in firefighters’ clothing (e.g. Bristol Uniform) since 1978. It blends 40% thermal‐resistant PBI fibres with 60% p‐polyaramid fibres, resulting in a fabric which does not shrink, 5.4 High Performance Textile Materials 125 become brittle, or break open under extreme heat and flame exposure. PBI Matrix, which was introduced into the market in 2003, employs a durable matrix of high strength aramid filaments woven into the PBI Gold fabric to enhance and reinforce its resistance to wear and tear while retaining its superior flame and heat protection. PBI TriGuard fabric, a blend of three types of high performance fibres including PBI, Lenzing FR, and micro Twaron, is designed for flame protection, comfort, and durabil ity. It is certified for use in wildland firefighters’ clothing, special operations, and mot orsports applications, as well as petrochemical, gas utility, and electric utility industries. PBI TriGuard and PBI Gold knits are also in use at several major motorsport racetracks. PBI BaseGuard is a type of lightweight, soft, and flexible knitted fabric designed to be as a next‐to‐skin base layer in a firefighter’s clothing system to provide fire‐resistant pro tection with the consideration of moisture management and durability. PBI fibres is also used in military flame protection, automotive braking systems, and fire blocking layers in aircraft seats. A summary of some outer shell fabrics used in the turnout gear of structural firefighters’ clothing are shown in Table 5.5. The other reactive protective materials for flame and heat protection are also engi neered to provide minimal insulation during normal wear, and maximum insulation when the heat threat impinges. For example, intumescent treatments which normally are in the form of thin, low‐insulation coatings on a lining fabric: when activated by excessive heat or flames the formulation swells instantly to form an inert insulative char, protecting the wearer. Superior flame‐retardant PTFE or expandable polytetrafluoroethylene (ePTFE) membrane barrier is laminated to a thin polyaramid woven or nonwoven backing sub strate (Kevlar fabrics) to form waterproof and breathable moisture barrier fabrics that have superior mechanical properties [94]. The moisture barrier is typically the middle layer between the outer shell and thermal liner in firefighters’ clothing to prevent water, high temperature water vapour, chemicals, and other pathogens from the environment penetration into the firefighters’ clothing. One of the most significant fabrics is the Gore‐Tex based bi‐component polymeric membrane made of ePTFE porous structure embedded in a continuous polyurethane film to prevent the skin of the wearer to be burned by the hot‐water vapour to inversely penetrate through the moisture barrier. PTFE porous membrane could also be formed into 3D innovative functional bar rier materials (e.g. Gore‐Tex Airlock) to provide still air space between the moisture barrier and outer shell fabrics for firefighting clothing to make the clothing combine the functions of protection, comfort, and heat insulation [95]. The above high performance fire‐resistant fibres are also widely used in making ther mal insulation liners in firefighters’ clothing and flame‐retardant workwear (see Tables 5.6 and 5.7). The thermal liner layer provides primarily thermal protection and is usually engineered as a highly porous padding or nonwoven insulating structure fixed between an inner layer of woven fabric. The still air that remains in the nonwoven insu lating padding between the inner layer of woven fabric and the moisture barrier pro vides thermal protection. While a thicker thermal liner provides better heat protection, it might be heavier and less breathable and thus less thermal comfortable (Tables 5.6 and 5.7). In addition, other flame‐retardant treated natural and regenerated fibres such as wool and cellulosic fibres might also be used to produce thermal insulation liner materials. Wool is the only natural fibre having inherent flame‐retardant properties,

130 5 Textile Materials for Protective Textiles

and wool fabric has been used as a fire‐resistant layer in various products [99]. Owing to its relatively high nitrogen content (16%) and strong disulfide bond network in the microstructure of wool fibres, it has a high ignition temperature at 570–600 °C and an LOI [100] of 25–26% with low heat of combustion (4.9 kcal g−1) and low heat release [101]. There are durable flame‐retardant treatments [102, 103] based on different fire‐ retardant mechanisms developed for wool and its blend fabrics, including the treat ments based on phosphorous compounds [104–106] and intumescent agents [107]. The treatment based on phosphorous compounds tends to lower the thermal decomposi tion temperature of wool fabrics, allowing the volatile fuel to escape before the ignition temperature is reached, and the intumescent agent [107] combines the attributes of flame retardancy with the formation of a high thermal resistance insulating char layer and thus enhances the natural flame‐resistant and char formation properties of wool. However, wool fabrics treated by using both phosphorous compounds and intumescent agents have limited market size so far. The flame‐retardant treatments for wool fibres by introducing halogen donors [108] into wool treatment, although highly effective in interfering free radical process, have unavoidable associated environmental problems and their use is thus restricted. Zirpro wool (or wool with Zirpro treatment) [109–114] has been the most popular wool fabric used in firefighters’ clothing to date. It is developed by Benisek at the International Wool Secretariat and it involves a treatment with either hexafluorotitan ate or hexafluorozirconate. Zirpro treatments are based on the exhaustion of negatively charged zirconium or titanium salts onto positively charged wool, resulting in the depo sition of about 3% of flame‐retardant inside the fibre and causes the formation of intu mescent char during the burning process [115]. Zirpro wool has an LOI of 27–33% without decomposition temperature found. Benisek and Craven also showed that the combination of Zirpro and tetrabromophthalate has a synergistic effect in fire‐resist ance, although tetrabromophthalic acid or its salts are conducive to smoke on burning and are not durable to washing [116]. It has been claimed that Zirpro wool fabric assemblies show a relatively longer time to reach pain (first‐degree burn) and blister (second‐degree burn) thresholds, as well as the longer pain alarm time (the time available to the wearer to withdraw from the flame heat source before serious injuries occur) [117]. It is also claimed that, compared to other fibres including aramid and Novoloid fibres, Zirpro wool fabric assemblies have one of the lowest residual heat transfers after a limited flame exposure to the pain threshold and thus reduce the possibility of causing second‐ degree burns [20]. When used in firefighters’ clothing, it was found that a woven Zirpro wool fabric of high density over a bulky knitted Zirpro wool underwear fabric offered significantly better protection than a single layer of a woven or knitted fabric or a double layer of a woven fabric of the same total weight [20]. However, the Zirpro wool treatment process and Zirpro wool products have certain problems. First of all, both the zirconium and titanium hexafluorozirconate salts used in the Zirpro wool treatment have associated potential environmental problems and maybe affected by government legislations and directives, such as Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). In addition, Zirpro wool fibres tend to be brittle, which may lead to problems in yarn spinning and fabric 5.5 Thermal Burden and Thermo‐Physiological Comfort 131 weaving. However, research into developing new chemical treatments utilizing the syn ergic effects of phosphorous and nitrogen elements to achieve wool fibres of improved flame‐retardant properties are reported [118]. The use of a phosphorus additive [119] in viscose rayon (e.g. Clariant 5060) developed by Sandoz and Lenzing AG and silicic acid‐containing rayon fibres [120] developed in Finland by Sateri (formerly Kemira) are two typical fire‐resistant viscose rayon fibres potentially used as a blend in firefighters’ clothing. Remarkably, the phosphorus addi tives can be added to the highly alkaline cellulose xanthate ‘dope’ before fibre spinning. It survives the acidic coagulating bath and survives alkaline laundering. Visil [121] and other similar viscose fibres [122] are inherently flame‐retardant silicic acid‐containing viscose rayon fibres used as a blend component. Visil is made by wet spinning alkaline cellulose xanthate (viscose) containing a sodium silicate (equivalent to about 30–33% SiO2) with some aluminosilicate component [22]. During fire combus tion, flame retards by both endothermic water release and char formation. Halogen‐containing fibres such as modacrylic fibres [123] (e.g. Saran fibres [124]) are also used as a flame‐retardant component in blends of fire protection equipment [125, 126]. Modacrylic fibres are typically copolymers of vinyl chloride or vinylidene dichlo ride and acrylonitrile. However, while modacrylic fibres are nonflammable and do not melt‐flow or drip, they shrink rapidly when exposed to the fire and thus are rarely used in firefighters’ clothing. ™ ™ Polyphenylene sulfide (PPS) fibres (e.g. Torcon (Toray), Procon (Evonik) and ™ Diofort (Diolen)) have inherently fire‐resistant, chemical‐resistant, and high tenacity properties. They are widely used in high temperature filtration applications and chemi cal protective clothing. New materials and designs have been developed for improved thermal insulation. For example, nonwovens made with thin hollowed fibres can be made thermo‐adaptive with two‐way shape memory alloys like nickel‐titanium [127].

5.5 Thermal Burden and Thermo‐Physiological Comfort

Clothing comfort is a human feeling of satisfaction towards clothing when the clothing is seen, touched, or worn by the user. Thermal stress is an especial concern for all types of protective clothing [128]. The three characteristics of thermal stress in protective clothing are: ●● human body metabolic heat; ●● weight of protective clothing; ●● impermeability of the fabrics to water vapour.

5.5.1 Thermal Burden from Protective Clothing

The quantity of heat produced by a human being depends very much on their physical activity and can vary from 100 W while resting to over 1000 W during maximum physi cal performance [129]. Particularly during the cooler seasons (approx. 0 °C), the recom mended thermal insulation is defined to ensure that the body is sufficiently warm when resting. 132 5 Textile Materials for Protective Textiles

Some protective clothing is very heavy (e.g. body armour, CBRN clothing). Currently, the majority of available bulletproof vests are very heavy and bulky, the weight of such a bulletproof vest for US police uses ranges from 2.5 kg for US National Institute of Justice (NIJ) level III protection up to 10 kg when including ceramic plates for US NIJ level IV protections [130]. For some special military purposes, the weight of body armour could be up to 20 kg. It is found that weight of clothing is linearly related to metabolic energy consumed by the human body [131, 132], and the relationship between the metabolic energy consumed during loaded walking, Mw, and the load carried by the walker, L, is proposed by Givoni and Goldman as [133]:

Mw =+TW()LV(.23+−03.(22.)5016. 5 + GV()..20+−07(.25)

Mw =Metabolic energy consumed during walking (watts) W =Body mass (kg) L = Load mass (kg) T = Terrain factor V = Velocity or walking rate (m s−1) G = Slope or grade (%) Pandolf et al. expanded on the work of Givoni and Goldman to develop an equation to predict the energy cost of load carriage [134]:

  2 = ++L +++ 2 MWw 15..20()WL  TW()LV()15..035VG W

where T = Terrain Factor (1.0 = black top road; 1.1 = dirt road; 1.2 = light brush; 1.5 = heavy brush; 1.8 = swampy bog; 2.1 = loose sand; snow, dependent on depth of depression (T = 1.30 + 0.082*D, where D = depression depth in cm2)) [135]. As the thermal burden is proportional to the clothing weight, it thus requires more metabolic energy to be transported away from the human body within the microclimate of the heavier protective clothing in order to keep the wearer comfortable. Many differ ent technologies rarely used in traditional clothing systems have been invented to achieve thermo‐physiological comfort in protective clothing. One example technology is to place humidity‐absorbing modules containing hygroscopic endothermic salts within the protective clothing to reduce the RH, which increases the wearer’s comfort and allows more sweat to evaporate, leading to additional cooling [136]. In chemical protective clothing, especially for clothing against the penetration of haz ards in the forms of gas, liquid, and mist, the thermal burden usually comes from a lack of breathability of the clothing due to the impermeability of the fabrics to water vapour. A serious challenge associated with body armour and chemical protective clothing, apart from its excessive weight, is the heat caused by the lack of effective perspiration, eliminating the body’s natural ability to dissipate and dispose of metabolic heat. Increasing heat stress exhausts the human body within a short time, even under normal conditions, let alone the extreme heat encountered in the Middle East and Central Asia. Examples of individual protective clothing include body armour (e.g. bulletproof clothing, stab‐proof clothing, cut‐proof gloves, etc.); firefighters’ clothing; chemi cal, biological, radiological and nuclear (CBRN) protective clothing; and chemical 5.5 Thermal Burden and Thermo‐Physiological Comfort 133 protective clothing; etc. These garments usually need to bear certain labelling (e.g. the UL (Underwriters Laboratories) mark in the US or the CE mark and Wheel mark in the EU) to demonstrate compliance with legislative requirements (e.g. UL standards and 46 CFR US regulations in the US, EU Directive 89/686/EEC Protective Equipment Annex II Health & Safety Requirements (the new PPE Regulation [EU] 2016/425 shall apply from 21 April 2018 to replace Directive 89/686/EEC). Different types of protective clothing need to withstand the attack of specific environ mental hazards presented and thus require the constituent textile materials to have high performance in some specific properties. For example, body armour systems require the textile materials used to have superior mechanical properties; firefighters’ clothing requires its component materials to have exceptional fire‐resistant properties; and chemical protective clothing requires the materials to be resistant to the attacks of chemical agents. All of these clothing systems require the guarantee of clothing comfort in the envi ronment of their application. Clothing comfort includes tactile comfort and thermal comfort. Tactile comfort is one of the key requirements to the clothing/equipment next to the skin and the thermal comfort of clothing is required for all of these clothing sys tems. The thermal homeostasis of the body is a result of the balance between heat pro duction and heat dissipation. The primary factors influencing this thermal balance are energy metabolism, clothing thermal properties, and ambient climatic conditions. Several models or thermal indices – for example PMV (predicted mean vote), PPD (pre dicted percentage of dissatisfaction), DR (draught rate) – taking into account all of these factors have been developed to compute thermal interactions and their effect on the body. Protective clothing serves the purpose of eliminating or reducing the effects of environmental stress factors. High performance textiles, which include fibres, yarns, fabrics, and composite struc tures made from functional organic polymers and inorganic materials with remarkable functions and properties unmatched by conventional textile materials are widely used in protective clothing systems. The required special properties in protective clothing include mechanical properties (tensile strength and modulus, abrasion, puncture, and flex durability), thermal and electrical insulation properties, resistance to heat, flame and chemical agents, liquid absorption and diffusion properties, optical, and radioac tive absorption properties. Such exceptional properties are frequently integrated together in one protective clothing system to achieve both desirable protection and human comfort while wearing the clothing.

5.5.2 Materials for Improving Thermo‐Physiological Comfort

Both smart materials and structures can be used to achieve physiological comfort of protective clothing. In this chapter, three groups of typical examples of incorporating smart textile technologies into protective clothing to achieve clothing comfort are discussed. ●● The typical examples of using smart materials to achieve clothing comfort are heat storage and thermo‐regulating materials including PCMs [137, 138], temperature‐ sensitive materials [139] including shape memory polymer/alloy (SMP) [140]; smart polyurethane film for moisture transport and evaporative cooling technologies. 134 5 Textile Materials for Protective Textiles

●● The typical examples of using smart structure to achieve clothing comfort are ® Hainsworth TI‐TECHNOLOGY and clothing having forced ventilation system. ●● A range of active and proactive systems used in protective clothing to control the temperature and humidity of clothing microclimate such as active cooling system using ice, water, and Peltier plate are discussed.

5.5.3 Phase Change Materials (PCMs)

Better thermoregulation inside a garment is sought with using PCMs [141, 142], either encapsulated [143] or incorporated in a matrix [144]. PCMs are able to absorb, store, and release latent heat through undergoing one of the four types of phase transforma tions (solid–solid, solid–liquid, liquid–gas, and solid–gas phase transformations) in a nearly isothermal process within a certain range of environmental temperature. Solid– gas and liquid–gas transformations have relatively higher latent heat but can hardly be used in smart textiles, owing to the complex storing technique requirement with a pres surized container. Solid–liquid PCM is among the most favourable, owing to its rela tively large energy storage with acceptable volume change (≤ 10%) over small temperature variations. The latest development of solid–solid PCMs [145, 146], changing their crys talline structure from one lattice configuration to another, has some irreplaceable advantages, such as simple to use, small erosion, no leakage, no contaminant, longer lifespan, little change in appearance, no need of nucleation to prevent supercoiling, and their phase changing temperature remains between 25 °C (77 °F) and + 180 °C (356 °F). In general, PCMs can be grouped into three categories: organic, inorganic, and eutec tics materials. Organic materials used as PCMs include aliphatic compounds or poly mers with long chain molecules composed primarily of carbon and hydrogen (e.g. paraffin waxes (or n‐alkanes), oils, fatty acids, and polyglycols (polyethylene glycols, or PEGs)). They tend to exhibit high orders of crystallinity when freezing and mostly change phase above 0 °C (32 °F). Currently, crystalline alkyl hydrocarbons are used exclusively for textile applications, owing to their large latent heat, good thermal and chemical stability, low vapour pressure, and self‐nucleating behaviour [147]. Inorganic PCMs include salt hydrates, metallic, and ice. The typical inorganic PCMs are Glauber’s salt. Eutectic materials are a mixture of chemical compounds or elements (e.g. solutions of salts in water) that have a single chemical composition that solidifies at a lower tem perature (eutectic temperature) than any other composition made up of the same ingre dients. It is known that the phase change temperature of salt‐hydrates‐based eutectics could be below 0 °C (32 °F) or above 0 °C (32 °F) depending on the formula of the mix ture. Some of those water based eutectics can change phase at temperatures of up to 117 °C (242.6 °F) [148]. The PCMs having the most suitable phase change temperature for clothing are organic compounds such as paraffins or linear alkyl hydrocarbon and nonparaffinic materials (e.g. hydrocarbon alcohol, hydrocarbon acid, polyethylene or polytetramethylene glycol, and aliphatic polyester), and inorganic compounds such as hydrated inorganic salts, eutectics, or polyhydric alcohol‐water solution [136]. Table 5.8 shows the latent heat of selected waxes and stearates. Table 5.9 shows the latent heat and melting point of salt hydrates. PCM microcapsules were initially developed in textile structures and clothing in the early 1980s by NASA to provide improved thermal protection in textile and clothing, having smart acclimatizing properties for astronauts’ spacesuits against the extreme temperature fluctuations in outer space [155, 156]. PCM can be incorporated into 5.5 Thermal Burden and Thermo‐Physiological Comfort 135

Table 5.8 Latent heat of adsorption, emission, and crystallization temperature of selected waxes [141, 149] and stearates [150].

Latent heat of Latent heat Cystallization No of C adsorption (ΔH) of emission Melting temperature −1 −1 Hydrocarbons atoms in J g (−ΔH) in J g point (Tc, °C) Reference n‐Hexadecane 16 235.2 236.6 12.2 [151] n‐Heptadecane 17 176.4 182.6 16.5 [150] n‐Octadecane 18 244.8 246.4 22.0 [150] n‐Nonadecane 19 177.6 182.6 26.4 [150] n‐Eicosane 20 242 230 30.4 [152] Butyl stearate 120 19 21 [141] Vinyl stearate 122 27 29 [141] Isopropyl 142 14 18 [141] stearate

Table 5.9 Latent heat and melting point of selected salt hydrates [147, 153, 154].

Material Melting point (°C) Heat of fusion (kJ kg−1) Latent heat (MJ m−3)

MgCl2.6H2O 117 169 242

Mg(NO3)2.6H2O 89 163 252

CH3COONa.3H2O 58 226 287

MgCl2.6 H2O – Mg(NO3)2.6H2O 58 132 201 Urea – Acetamide [154] 53 224 263

Na2HPO4.12H2O 34 265 379

LiBr2.2H2O [153] 34 124 /

KFe(SO4)2.12H2O 33 173 /

Na2SO4.10H2O [154] 32 180 295

Na2CO3.10H2O 32 233 340

Urea – CH3COONa.3H2O [154] 30 200 266

LiNO3.2H2O [153] 30 296 /

CaCl2.6H2O [154] 30 127 230 Waxes 28 to 4 220 to 245 170 to 195 Polyethylene glycols 28 to 15 146 to 155 165 to 175 Glauber’s salt 24 to 4 wide range wide range (Na2SO4·10H2O) + additives

Mn(NO3)2.6H2O [153] 25.5 148 /

CaCl2.(H2O)6 – MgCl2.6H2O 25 127 205 (67 : 33) [154]

FeBr3.6H2O [153] 21.0 105 /

CaCl2.6H2O – CaBr2.6H2O 15 140 249

K2HPO4.6H2O [153] 14.0 109 / Water 0 335 335 136 5 Textile Materials for Protective Textiles

various fibres [157–159], nonwovens [10], polyurethane foams [160], and coated on fabrics [161] in original form, microcapsulated PCMs [11, 12] or nanocapsulated PCMs [162]. Fabrics [163] incorporating PCMs were used in protective clothing [164–166] to achieve the desired thermo‐regulating functions for clothing comfort. When the pro tective clothing is in use, PCMs absorb human body metabolic heat in clothing micro climate during its melting process to give a cooling effect to the wearer and release the stored energy to the environment during a reverse solidifying process to give the wearer a warming effect [167]. Outlast fibre is a bi‐component fibre, including both staple fibres and filaments, con taining patented tiny microcapsules (ca. 1–3 μm in diameter) of paraffin‐like PCMs, ™ Outlast Thermocules [168]. It is claimed that the new fibre with temperature manage ment can align particularly well with underwear and other products worn next to skin ,such as socks, t‐shirts, shirts, and trousers. Outlast technology used in firefighters’ ™ clothing was made from 60% MAC Protex and 40% CV Outlast [169]. In this bicom ponent yarn structure, the flame‐retardant Protex fibre stops the flame from spreading by producing minute amounts of inert noncombustible gases which ‘seal’ the fabric surface from oxygen. After the removal of the flame source, the flame is stopped from spreading. The Outlast fibre provides a high level of comfort, temperature regulation, and moisture management not normally associated with protective clothing. Beginn [170] reported an ultra‐high‐molecular‐weight polyethylene (UHMW‐PE) paraffin waxes (PW) composite gel structure having superior heat capacities (up to 200 J g−1 of enthalpies at the melting temperature of the paraffin waxes) to microencap sulated paraffin PCMs. Even with the cheap paraffin wax PW42, the melting enthalpies could be up to 120 J g−1, while commercial polyurethane PCM foams [171] only carry a latent heat of 60–65 J g−1. Another example of phase‐change technology used in protective clothing is utilizing evaporative cooling technology. Cooling fibres introduce water‐retaining fibres into the fabric structure [172], and these are sandwiched between breathable outer fabrics (e.g. cotton and Nomex). The inner layer containing cooling fibres conducts heat and moisture away from the body through the evaporation of water.

5.5.4 Smart Structure for Protection and Thermal Comfort

Outer shell textile materials for firefighting clothing have frequently been manufactured from 100% m‐aramid or polyamide‐imide, blends of m‐aramid, and p‐aramid fibres or by use of core spun yarns or staple mixtures with p‐aramid copolymer or fibres compris ing p‐aramid cores with m‐aramid or polyamide‐imide covers. However, m‐aramid and polyamide‐imide fibres shrink, consolidate, and thicken when exposed to a high tem perature heat source. The presence of p‐aramid or p‐aramid copolymer in either the fibre blend or as a core can be used to lessen fibre shrinkage and consequent breaking open of the garment. However, the inclusion of p‐aramid fibre in the blend has been found to be insufficient in tightly woven fabrics to prevent breaking open. ™ Hainsworth TI‐Technology [173–175] is a double‐layer spacer fabric construction that combines the high performance of Nomex and Kevlar fibres in an intelligent way by keeping them as separate layers to maximize the benefits of each fibre. Nomex is on the face of the fabric, with the high strength of Kevlar protected from the effects of UV degradation and abrasion on the back. When the fabric assembly is hit by extreme heat, 5.5 Thermal Burden and Thermo‐Physiological Comfort 137 the Nomex layer consolidates, while the Kevlar layer remains unchanged. The different thermal shrinkage of the two fibres means that the two layers move and react against each other. The dynamic nature of the fabric means that the open, breathable construc tion required for everyday activities moves to form air pockets between the two layers, thereby increasing thermal protection only when it is most needed. Temperature‐dependent permeability to moisture could be provided by polyurethane based shape memory polymer [176]. Better comfort is also provided by pulling humid ity and sweat away from the surface of the skin, either with hydrophilic linings [177] or by the use of channelled cross‐section fibres with reinforced wicking properties.

5.5.5 Active Cooling System for Clothing Comfort

Various smart textiles have been used to actively control clothing comfort for protective clothing. They include being able to sense the wearer’s physiological condition [5], their posture and activity [6], outside environment [7], as well as their responsive action [8]. Conductive yarns can be produced by coating with conductive polymers or by embed ded conductive fillers like carbon nanotubes [4]. Electrically active structures can then be formed, e.g. through specially patterned knitting [2] and ‐responsive materials for clothing [3]. However, numerous challenges remain, in particular with contactless sen sors, interconnects, electronic reliability, data and power transmission lines, and shield ing [178]. Other solutions use external power, e.g. for liquid coolant circulation [179] or with Peltier cells [180] embedded in the textiles. A personal cooling system sustains a microclimate circulating dry, fresh air, liquid, ice, or wax to draw and absorb heat from the wearer’s body. One example is a light weight ‘spacer vest’ for interceptor body armour (IBA), designed to assist the natural cooling through perspiration [181]. The spacer vest system could increase the evapora tive cooling potential by up to 20% in comparison with wearing standard IBA. Another example is a lightweight cooling system known as Breeze [182], which utilizes a light weight battery‐powered ventilation system that feeds fresh air beneath the body armour to re‐establish natural cooling through perspiration. The Breeze vest facilitates cooling by wicking moisture from the body and cooling through the natural phase change pro cess. A more advanced cooling system in the Future Force Warrior (FFW) project [183] was developed to provide microclimate control within the standard FFW suit or a full CBRN protected gear to support soldiers’ operation. The Body Ventilation System (BVS) [184] developed by Global Secure Safety Corporation uses a battery‐powered blower to circulate air through an air distribution device worn beneath the interceptor body armour and battledress uniform (BDU) to gain natural body cooling and improved physiological comfort. The Microclimate Cooling System (MCS) [185] is provided as part of the US Army’s Air Warrior program, for helicopter crews, operating in the hot climate of Southwest Asia. The microclimate cooling garment is connected to a con denser unit which chills water and pumps it through small tubes embedded in the vest. It is worn as an undergarment. Cooling can also be achieved by applying thermal regulation elements into the body armour [185]. This concept, eliminating the need for a liquid coolant or PCMs, uses high thermal‐conductivity channels embedded into the body armour itself. The heat conductors are applied over a moisture‐wicking layer pulling moisture from the body and dispersing the moisture to the outer surface, where it can evaporate. 138 5 Textile Materials for Protective Textiles

Protective suits for firefighters and others working in extremely hot conditions with a built‐in cooling system [186] is developed to provide a high quality thermal and mois ture management layer based on a 3D warp‐knitted fabric coated with a water‐binding polymer. Its structure will mimic the physical mechanisms for thermoregulation in the human body. A 3D textile structure is used for the thermal and moisture management layer with a cooling tubing system inserted into cavities in the 3D textile structure. The tubes have liquid circulating through them and remove heat in a similar manner to blood vessels in the body.

5.6 Testing Methods and Standards

Various EN ISO standards have been established for the rational assessment of protec tion requirements and subsequent selection of appropriate clothing suitable for vari ous environments. For example, protective clothing used in food, drink, pharmaceutical, cosmetics, medical, electronic manufacture, and healthcare industries is required to have further properties in order to protect not only the wearer from environmental hazards but also the product from contamination (e.g. linting, pilling, dissolved mono mer) or cross‐infection between the wearer and the protective clothing itself. In the engineering design of textile materials to meet those specific performance require ments of clothing set in the CE marking scheme together with other additional func tions, the composition of fibres, membrane, coating, and accessory materials (such as seals, tapes, and zips) used in the garment, together with the microstructure of fabrics, yarns, and fibres employed to construct the clothing, need to correspond to a hazard ous environment, physiological comfort, durability, and other special requirements (e.g. product hygiene) in order to reach the functions, properties, and performance of the clothing.

5.6.1 Protective Clothing and Gloves Against Cold

Major ISO standards for determining performance requirements and testing perfor mance of protective clothing and gloves are shown below. EN 340: 2003 – Protective clothing, general requirements specifies ergonomic requirements (comfort, weight, and design considerations), durability requirements (colour fastness and dimensional change after ageing), and sizing requirements (against wearer height, chest, and weight circumference). EN 342: 2004 – Protective clothing, ensembles, and garments against cold speci fies the requirements and test methods for performance of clothing ensembles (i.e. salopettes and jackets) to determine if adequate protection is provided by the protec tive clothing at temperatures lower than −5 °C. Performance of selected clothing ensemble can be tested by measuring the insulation value on a moveable, thermal manikin. BS EN 343:2003+A1: 2007 – Protective clothing. Protection against rain. This stand ard specifies protective clothings resistant to water penetration, including rain, precipi tation, fog, and ground humidity, as well as its level of breathability. 5.6 Testing Methods and Standards 139

BS EN 511: 2006 – Protective gloves against cold. Designed for testing any glove which claims protection against cold environments. The performance of protective gloves against cold are tested with a heated hand model. BS EN ISO 11079: 2007 – Ergonomics of the thermal environment. Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects. This standard specifies methods and strategies for assessing the thermal stress associated with exposure to cold environments, and will help determine required resultant clothing insulation for given conditions by using an IREQ index. These methods apply to continuous, intermittent, as well as occasional exposure and type of work (indoors and outdoors). BS EN 14058: 2004 – Protective clothing. Garments for protection against cool envi ronments. It specifies requirements and test methods for the performance of single garments (e.g. waistcoats, jackets, coats, or trousers and/or separable thermal linings) for protection against cooling of the body in cool environment. BS EN 13537: 2012 – Sleeping bag testing. A standard aiming to make sleeping bag testing and temperature rating more consistent. While this standard arguably still has flaws, it has largely achieved its objective. However, this standard does not apply to sleeping bags for use in extreme climates.

5.6.2 Protective Clothing Against Thermal and Fire Hazards

Protection against heat and flame EN ISO 11612 EN ISO 14116 | EN 1486 EN 407: 2004 – Protective gloves against thermal risks (heat and/or fire). EN 469: 2005 – Protective clothing for firefighters. Performance requirements for protective clothing for firefighting. EN 659: 2003 – Protective gloves for firefighters. BS EN ISO 6942: 2002 – Protective clothing – Protection against heat and fire. Method of test: evaluation of materials and material assemblies when exposed to a source of radiant heat. BS EN ISO 9151: 2016 – Protective clothing against heat and flame. Determination of heat transmission on exposure to flame. BS EN ISO 11612:2015 – Clothing for protection against heat and flame. Test meth ods and performance requirements for heat‐protective clothing. BS ISO 13506 part 1 and part 2 – 2008 Protective clothing against heat and flame. Test method for complete garments. Prediction of burn injury using an instrumented manikin. BS EN ISO 15025: 2016 – Protective clothing. Protection against flame. Method of test for limited flame spread. BS ISO 16073: 2011 – Wildland firefighting personal protective equip ment. Requirements and test methods. ISO 17492: 2003 – Clothing for protection against heat and flame. Determination of heat transmission on exposure to both flame and radiant heat.

5.6.3 Protective Clothing Against Radiation

X‐ray protection clothing for the individual using radiation is governed by a new EU directive regarding PPE 2016/425. X‐ray protection clothing for patients is governed by 140 5 Textile Materials for Protective Textiles

the EU directive for medical devices (MDD) 93/42/EWG. In order to comply with PPE, the article must be marked with a CE logo and a four‐digit number that correlates to the notified certification office. In the US, some radiative protective clothing must meet the burn safety criteria of OSHA Rule 29CFR Part 1910.269 and be compliant with National Fire Protection Association (NFPA) standards 2112 and NFPA 70E. EN 421: 2010 – Protective gloves against ionizing radiation and radioactive contamination. BS EN 1073‐1: 2016 – Protective clothing against solid airborne particles including radioactive contamination. BS EN 1073‐2: 2002 – Protective clothing against radioactive contamination.

5.6.4 Protective Clothing Against Microbial Hazards

BS EN 14126: 2003 – Protective clothing. Performance requirements and tests meth ods for protective clothing against infective agents. ISO 16603: 2004 – Clothing for protection against contact with blood and body fluids. Determination of the resistance of protective clothing materials to penetration by blood and body fluids. Test method using synthetic blood. ISO 16604 – Clothing for protection against contact with blood and body flu ids. Determination of resistance of protective clothing materials to penetration by blood‐borne pathogens. Test method using Phi‐X 174 bacteriophage (‘virus’ penetra tion simulation). ISO 22610: 2006 – Surgical drapes, gowns and clean air suits, used as medical devices, for patients, clinical staff, and equipment. Test method to determine the resistance to wet bacterial penetration (wet bacterial penetration). ISO/DIS 22611 – Resistance to penetration by biologically contaminated liquid aerosols. ISO 22612: 2005 – Clothing for protection against infectious agents. Test method for resistance to dry microbial penetration.

5.6.5 Protection Against Chemicals

Protection against chemicals EN 943‐1 | EN 943‐2 | EN 13034 EN 14605 | EN 13982‐1 EN ISO 5630 – Penetration test results at one minute of exposure to the hazardous substance. EN ISO 6529 – Permeation test assesses long‐term response, up to eight hours.

5.6.6 Protective Clothing Against Mechanical Hazards

EN 381: 1999 – Protection against chainsaws. EN 388: 2003 – Protective gloves against mechanical risks. BS EN 510: 1993 – Specification for protective clothing for use where there is a risk of entanglement with moving parts. EN 1082‐1: 1997 – Protective clothing. Gloves and arm guards protecting against cuts and stabs by hand knives. Chainmail gloves and arm guards. 5.6 Testing Methods and Standards 141

BS EN ISO 13998: 2003 – Protective clothing. Aprons, trousers, and vests protecting against cuts and stabs by hand knives. EN 14328: 2005 – Gloves and armguards protecting against cuts by powered knives. BS EN ISO 14877: 2002 – Protective clothing for abrasive blasting operations using granular abrasives. BS EN 1522: 1999 – Windows, doors, shutters, and blinds. Bullet resistance. Requirements and classification. BS EN 1523: 1999 – Windows, doors, shutters, and blinds. Bullet resistance. Test method.

5.6.7 Ballistic Resistance and Stab/Cut Resistance

NIJ Standard 0101.06 – Ballistic Resistance of Body Armour. NIJ Standard 0115.00 – Stab Resistance of Personal Body Armour. NIJ Standard 0104.02 – Riot Helmets and Face Shields. NIJ Standard 0106.01 – Ballistic Helmets. NIJ Standard 0117.00 – Public Safety Bomb Suit Standard. NIJ Standard 0108.01 – Ballistic Protective Materials. FBI Body Armour Test Protocol 2008. HP White 401‐01B Bullet Resistant Helmet Testing Procedure. HOSDB Body Armour Standards for UK Police (2007) Part 1: General Requirements (39/07/A). HOSDB Body Armour Standards for UK Police (2007) Part 2: Ballistic Resistance (39/07/B). HOSDB Body Armour Standards for UK Police (2007) Part 3: Knife and Spike Resistance (39/07/C).

5.6.8 Other Standards

EN 50237: 2000 – Gloves and mitts with mechanical protection for electrical purposes. EN ISO 11611 – Protective clothing used during welding operations. BS EN 1149‐1‐8: 2006 – Protective clothing. Electrostatic properties. EN ISO 20471 – High visibility protective clothing (equipment)

Some typical examples of the performance of protective clothing set in the CE mark ing scheme and defined by various associated BS EN ISO standards were summarized in Table 5.10. All the standards for CE marking clothing are based on the other EN and ISO standards for the examination of the fabric properties, which are decisive for the clothing functions including protection (e.g. heat, cold, electricity, cut, stab, etc), com fort (thermal and tactile comfort properties such as moisture transport resistance, smoothness, and softness), mobility (heaviness, flexibility, and conformability), durabil ity (protection properties and strength properties after washing, flex cracking, and age ing), and others (environmental impact, toxicity, etc.).

148 5 Textile Materials for Protective Textiles

5.7 Sustainability and Ecological Issues

Single‐use items of protective equipment – such as gloves, aprons, and masks – are usually disposed of after each procedure or activity to prevent cross‐transmission of microorganisms. Manufacture of most of the high performance fibres could be harmful to environ ment. For example, one of the main solvents used in the process of spinning Kevlar fibres is sulphuric acid, which is very toxic to animals and plants if disposed of or used incorrectly and is dangerous to workers when used in operation, thus the production process could be a problem in sustainability. Most high performance fibres used in protective textile products are not biodegrad able. They barely decompose in a landfill, even over a very long period. Currently, the only way to reduce the environmental impact of these products is to reuse and recy cle them. When recycling, the disposed product made from filament could be made into yarns and nonwovens after being chopped into staple fibres and pulps. Lifecycle assessment of the environmental impact of three types of protective cloth ing – including emergency operations under extreme weather conditions (floods, hail, etc.), firefighters’ clothing for fighting wild land fires, and medical protective clothing for first aid – has been conducted [188]. As most protective clothing for emergency operations, which is mainly made from conventional fibres (e.g. nylon, polyester and cotton) and membranes, can be either reused or recycled, it was found that its major environmental impact came from its uses and maintenance processes (e.g. laundry and disinfections, etc). However, for protective clothing for firefighters and medical first aid ® which are mainly made from flame‐retardant materials (e.g. chemicals used in Proban flame‐retardant agents) and high performance fibres (e.g. Kevlar and Nomex), the manufacturing process is more polluting than its maintenance and use phase. Apparently, the disposal of contaminated protective clothing is still a challenge in terms of sustainability, although the reuse and recycling of used protective textiles is currently common practice.

5.8 Conclusion

Textile materials are employed in various protective textile products for the protection of wearers from cold, thermal, fire, water, oil, radiation, acoustic, and microbial hazards while maintaining comfort. Natural fibres, specific synthetic fibres, high performance fibres, and other functional materials all demonstrate excellent performances in either protection or comfort of protective clothing in various environmental conditions; engi neering design of their microstructures, hierarchy architectures, and properties play a great role in achieving the required performance. A combination of those functional textile materials in engineered structures would help achieve desirable functionalities in specific applications. The disposal of contaminated protective clothing is still a chal lenge in terms of sustainability, although the reuse and recycling of used protective textiles is currently common practice. References 149

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159

Personal Protective Textiles and Clothing Sumit Mandal, Simon Annaheim, Martin Camenzind, and René M. Rossi

Empa - Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Biomimetic Membranes and Textiles, St Gallen, Switzerland

6.1 Introduction

Clothing plays an important role in protecting human beings from their surrounding environments [1–3]. For centuries, human beings have used regular clothing (jacket, windcheater) to protect themselves from light rain, cold, and/or windy environments. In recent times, specialized clothing is considered significantly important for the per‑ sonal protection of working human beings from their occupational hazards [4]. In some occupations, workers are exposed to various hazards, namely chilled air, extreme cold air/water, heavy rain, high heat (e.g. flash fires, hot liquids splash, steam, electric arc), bullets or knives, chemical substances (e.g. flammable materials, acids), biological matters (e.g. bacteria, viruses), radiological threatening agents, and/or nuclear elements [5–8]. For example, food processing unit operators, pilots of capsized vessels, navy personnel, police officers, and flood rescuers can occasionally be exposed to chilled air, cold water, and/or heavy rain; cooks/chefs, firefighters, and industry (forg‑ ing, oil, and gas) workers can often be exposed to high heat; police officers and military personnel can be exposed to bullets or knives; and, laboratory technicians, healthcare staff, and military personnel can be exposed to chemical, biological, radiological, and/ or nuclear hazards. In order to get protection from the hazardous working environments, employees (e.g. police officers, military personnel, firefighters, healthcare staff) need to wear textile based personal protective clothing (PPC) [9, 10]. PPC acts as a barrier between hazard‑ ous environments and wearers, which actually provides them with protection and safety [11]. It is also required that PPC should effectively regulate the metabolic heat and sweat vapour generated by wearers’ bodies [12, 13]. This effective regulation of meta‑ bolic heat and sweat vapour should provide thermo‐physiological comfort to wearers. Along with functional performance (hazards protective performance and thermo‐ physiological comfort performance), PPC should also possess some aesthetic features like appropriate colour (e.g. dark blue or tan coloured PPC is mainly worn by police officers) and printed design (e.g. camouflage designs are generally printed on military PPC). These aesthetic features are especially required to ensure the visual presence of

the on‐duty employees. However, PPC should have both functional performance (pro‑ tection and comfort) as well as aesthetic features (colour and printed design) for its effective use by a wearer. To achieve the desired functional performance and aesthetic features, it is necessary to thoroughly understand the various aspects of textile based PPC (e.g., textile materials, manufacturing processes). Considering this, various aspects of textile based PPC are discussed in the following section. Furthermore, some key issues related to various aspects of PPC are indicated before concluding this chapter. By resolving these key issues, high quality PPC could be manufactured in future which could provide more effective functional performance and aesthetic features for the wearers.

6.2 General Aspects of Textile Based PPC

Generally, PPC is commercially manufactured through different stages, as shown in Figure 6.1. As per Figure 6.1, the basic raw material for manufacturing the PPC is textile fibre. After the selection of suitable fibres (e.g. natural, synthetic, or a blend of natural and/or synthetic fibres), they are spun into different types of yarns (e.g. ring‐spun, other‐spun) using various spinning techniques (e.g. ring spinning, rotor spinning) [14]. Then, these spun yarns are used in the weaving or knitting process to produce the woven or knitted fabrics, respectively [15, 16]. Sometimes, the fibres or filaments of the synthetic fibres are directly used in the nonwoven process (e.g. chemical bonding, mechanical bonding, electrospinning) to produce nonwoven fabrics [17]. Finally, the fabrics (woven, knitted, and/or nonwoven) are used in the garmenting process (cutting, sewing) to fabricate the PPC. Depending upon the requirements, the intermediate materials (fibres, yarns, and fab‑ rics) for PPC can be processed through different dyeing, printing, and/or finishing techniques (Figure 6.1) [18, 19]. For example: colours can be imparted on these materi‑ als using different dyes into the dyeing processes such as loose stock fibre dyeing, high temperature high pressure (HTHP) fibre, yarn dyeing, and continuous fabric dyeing. These dyes can also be used to print a design on fabrics by applying different printing techniques such as roller printing and screen printing. Furthermore, fabrics can be mechanically (by sanforizing with moisture and dryer) and/or chemically (by padding with finishing agents) finished in order to enhance their properties, such as dimensional stability, flame retardancy, water repellency, etc. The above discussion shows how different processing techniques (spinning, weaving, knitting, nonwoven, dyeing, finishing, garmenting) can help to manufacture PPC with the required functional performance and aesthetic features. It is further notable that these techniques can generate a huge amount of waste materials (fibres, yarns, fabrics), chemicals (dyes, finishing agents), energy (thermal, electrical), and water (during wet processing, namely dyeing and finishing) [20, 21]. There is an estimate that nearly 200 l of waste water can be generated during wet processing of 1 kg material [22]. This indi‑ cates that water is the largest waste product during the manufacturing of PPC. All this waste can affect the ecology by polluting the environment of the inhabitants of this earth. Hence, it is necessary to use ecologically sustainable approaches for PPC manu‑ facturing through proper waste management (e.g. waste water recycling, workers train‑ ing and awareness, monitoring waste generation and disposal) (Figure 6.1). Additionally, 6.2 General Aspects of Textile Based PPC 161

Dyeing Textile Fibre Dyed Fibre (e.g. natural, synthetic) ) g Spinning Spinning (e.g. ring, rotor) Dyeing Spun Yarn Dyed Yarn (e.g. ring-spun, other-spun) , electrospinnin g (e.g. chemical bonding, mechanical (e.g. chemical bonding, mechanical bondin bonding, electrospinning) Knitting Knitting Weaving/ Weaving/

Fabric Finishing, Dyeing, Printing Finished, dyed, printed fabrics Nonwoven process Nonwoven process (e.g. woven, nonwoven) Garmenting Garmenting Personal Protective Clothing (e.g. for hazards like extreme cold, high heat)

Figure 6.1 Manufacturing of PPC.

PPC should not contain any harmful substances (e.g. textiles, finishes) that can affect the wearer’s health and damage the environment; so, the materials used for PPC should also be ecologically sustainable. According to Figure 6.1, PPC can be manufactured through the technical processing of different materials. Eventually, the types (e.g. natural fibres, ring‐spun yarns, woven fabrics) and processing techniques (e.g. spinning, weaving, dyeing) of these materials can significantly affect the manufacturing of the PPC [23]. It is recommended to sys‑ tematically and intermittently monitor the properties (e.g. tenacity, strength, colour fastness) of these materials to effectively achieve the desired quality of the manufac‑ tured PPC, especially in terms of its required functional performance and aesthetic features [24]. Notably, this continuous monitoring of the properties can also help to minimize the re‐processing of any material, which ultimately makes the textile busi‑ ness profitable (by reducing the extra cost of purchasing and re‐processing of materi‑ als) and ecologically sustainable (by reducing the textile waste). For this monitoring, the properties of materials can be measured using different test methods developed by standard organizations, namely the International Organization for Standardization 162 6 Personal Protective Textiles and Clothing

(ISO), American Society for Testing Materials (ASTM), American Association of Textile Chemists and Colorists (AATCC), European Committee for Standardization (CEN), and National Fire Protection Association (NFPA). This suggests that a thorough understanding of materials is essential in order to manufacture PPC with proper quality (i.e. functional performance and aesthetic fea‑ tures). Therefore, the following sections discuss each of the materials (fibres, yarns, fabrics) used in PPC manufacturing. In these sections, the types, processing techniques, ecological sustainability, and/or testing of the materials are scientifically explained. Thereafter, the fabrication process of the PPC from fabrics is highlighted.

6.3 Fibres for PPC

Two different types of fibres – natural and/or synthetic – are usually selected for the industrial manufacturing of PPC [11, 25, 26]. Commonly, it is expected that the tenacity (i.e. the ratio of the load required to break a fibre and the linear density of that fibre) and elasticity (i.e. the ability of a fibre to return to its original length after the removal of stress) of the selected fibres should be adequate enough to maintain the integrity of the PPC under any hazardous environment. Depending upon the type of hazardous envi‑ ronment, moisture regain (MR; i.e. the weight of water in a fibre as a percentage of its oven dry weight), ignition, or glass transition temperature (i.e. the temperature at which a natural fibre ignites or a hard synthetic fibre is transferred to a soft rubbery fibre), and limiting oxygen index (LOI, i.e. the minimum amount of oxygen required to support the combustion of the fibres) of the fibres could be substantially important to achieve the required quality of the PPC. Although the MR and ignition/glass transition temperature mainly depend upon the polymer composition of the fibres, it is notable that LOI values of the artificially produced fibres (e.g. regenerated natural fibre viscose, synthetic fibre polyester) could be enhanced by doping the phosphorous based flame‐retardant (FR) chemicals (e.g. bis(2‐thiono‐5,5‐dimethyl‐l,3,2‐dioxaphosphorinayl)oxide, n‐propoxyphosphazene, n‐methylol‐3‐dimethylphosphonopropionamide, red phosphorous) within their poly‑ mer compositions. The enhancement of LOI could help to convert an originally unsuitable non‐FR fibre (viscose, polyester) for PPC into a suitable FR fibre (FR vis‑ cose, FR polyester). Furthermore, fibre structure (e.g. surface topography, cross‐section) can substantially control some of its properties (e.g. colour fastness at fabric stage, tenacity, elasticity). Hence, fibre structure is important to consider for the manufacture of good‐quality PPC.

6.3.1 Natural Fibres

Considering the properties (tenacity, elasticity, MR, combustion temperature, and LOI), two natural fibres – ‘plant/cellulosic fibre cotton’ and ‘animal/protein fibre wool’ – are commonly used for PPC (Table 6.1). Recently, some other natural fibres (such as ‘plant fibre flax’ and ‘animal fibre silk’) have also been introduced for the manufacture of PPC (Figure 6.2). Contextually, it is notable that these natural fibres are relatively expensive. Hence, cost‐efficient regenerated natural (cellulosic) fibre ‘viscose’ is preferred nowadays for the manufacture of PPC. Along with natural or 6.3 Fibres for PPC 163

Table 6.1 Properties of natural fibres used in PPC.

Tenacity Elasticity MR Ignition Temperature LOI Fibres Polymer composition (gm/denier) (%) (%) (°C) (%)

Cotton Cellulose 4 52 7.5 ~400 15 (burn freely) Wool Protein 1.6 69 13.6 ~600 25 (do not burn freely) Flax Cellulose 4–5 Very low 12 ~400 18 (burn freely) Silk Protein 4 52 11 ~600 20 (do not burn freely) Viscose Regenerated cellulose Varies, as Varies, as 11 ~100 19 artificially artificially produced produced Glass, A compound of silica, Varies, as Varies, as 0 ~1500 70 Ceramic sodium, potassium, artificially artificially magnesium, calcium, produced produced strontium, barium regenerated organic fibres (cotton, wool, flax, silk, viscose), a few regenerated natural inorganic fibres (eco‐friendly glass, ceramic fibres) have also been used for PPC manu‑ facturing [27–29]. According to Table 6.1, the properties of these fibres (cotton, wool, flax, silk, viscose, glass, ceramic) can vary in a certain range at a standard atmospheric condition (21 °C temperature and 65% relative humidity). Additionally, their tenacity could change in wet conditions, such as at high relative humidity (e.g. wet tenacity of cotton and flax is higher and lower, respectively). It is further notable from Figure 6.2 that the surface topographic views of these fibres are different in scanning electron microscopy (SEM). As a result, the uptake of dyes and finishing agents of these fibres is different, which ultimately varies the colour fastness of fabrics. Altogether, it reflects that PPC with varied quality can be manufactured by using different types of natural fibres. Finally, as any type of natural fibre is ecologically sustainable (because they are bio‑ degradable and require less industrial processing to produce), it is required to investi‑ gate the usability of other natural organic fibres (e.g. jute, hemp, ramie) for PPC manufacturing apart from the existing cotton, wool, flax, silk, and viscose [30]. Notably, it is very difficult to consistently achieve the required properties of natural organic fibres from one lot to the other lot even though they are cultivated at the same place. Therefore, commercial markets nowadays are more interested in synthetic‐fibres‐ based PPC [27].

6.3.2 Synthetic Fibres

A set of synthetic fibres (e.g. polyester, nylon, acrylic, aramid, polyimide, polybenzi‑ midazole, polybenzoxazoles, melamine formaldehyde, chlorinated, fluorinated, poly‑ phenylene sulfide, semi‐carbon) are widely used for manufacturing PPC (Table 6.2) Gossypium hirsutum Cotton

Ginning SEM View

Ovis aries Wool Scouring and Bleaching SEM View

Linum usitatissimum Flax Retting SEM View

Bombyx mori Silk Boiling and Demineralizing SEM View

Figure 6.2 Natural fibres for PPC (cotton, wool, flax, silk). Source: Ms. Mary Ankeny (Vice President – Product Development and Implementation Operations, Cotton Incorporated, USA), Mr. Andy Cooper (Science Impact Leader − Wool Products & Supply, AgResearch Limited, New Zealand), Ms. Patty Grossman (President, Two Sisters Ecotextiles, USA), Prof. (Dr) Ryszard Kozłowski (Deputy Director, Institute of Natural Fibres and Medicinal Plants, Poland), Dr Hariraj Gopal (Scientist, Central Silk Technological Research Institute, India). 6.3 Fibres for PPC 165

Table 6.2 Properties of the synthetic fibres used in PPC.

Glass transition Spinning MR temperature LOI Fibres Polymer composition techniques (%) (%) (%)

Polyester Terephthalic acid and Melt 0.4 250 20 ethylene glycol Nylon Adipic acid and Melt 4.5 250 20 hexamythelenediamine Acrylic Acrylonitrile Wet‐solution 1.5 100 18 Aramid Aromatic diamines and Wet‐solution 5–7 300 45 diacids or diacids chlorides Polyimide Aromatic Wet‐solution 3.5 380 45 tetracarboxylic dianhydride and aromatic diamine Polybenzimidazole Tetra‐aminobiphenyl Dry‐solution 13 420 40 and diphenylisophthalate Polybenzoxazoles Benzoxazoles Wet/ 1.5 500 65 Dry‐solution Melamine formaldehyde Melamine and Dry‐solution 5 315 32 formaldehyde Chlorinated (polyvinyl Chloride Melt 0 80 40 chloride) Fluorinated Fluoride Melt 0 115 95 (polytetrafluoroethylene) Polyphenylene sulfide Phenylene sulfide Melt 0.1 80 40 Semi‑carbon Acrylonitrile Wet‐solution 0 300 55

[11, 27]. These fibres are artificially manufactured from a group of polymers using different spinning techniques, namely melt spinning, dry‐solution spinning, or wet‐ solution spinning (Figure 6.3). By adjusting the drawing or stretching process in these spinning techniques, it is possible to control the tenacity and elasticity of these fibres as per the requirements of further use. Depending upon the polymeric compositions, the MR, melting temperature, and LOI of these fibres can be varied in a wide range to achieve the required quality of PPC. Nevertheless, the cross‐sectional view of con‑ ventional synthetic fibres is usually solid‐circular with very high diameter (≥ 5 μm). Therefore, they possess some properties (e.g. tenacity, elasticity, dye uptake) in a limited range. In order to overcome this limitation, some fibres have been recently developed with different cross‐sectional views (e.g. hexalobular, scalloped oval, hol‑ low‐circular) and/or lower diameters (50–500 nm). The latest development in this context is a hollow nanofibre, such as carbon nano tube (CNT), which can be used in PPC [31, 32]. 166 6 Personal Protective Textiles and Clothing

Polymer Hopper Polymer Container

Molted Polymer Polymer Solution

Spinning Pump Spinning Pump

Spinning Nozzle Spinning Nozzle

Blade Blade Warm Air Cold Air

Fibre Fibre Drawing Roller Drawing Roller Filament Stretching Filament Stretching

Melt Spinning Dry-solution Spinning

Polymer Container

Polymer Solution

Spinning Pump

Spinning Nozzle

Blade Chemical Bath

Fibre Drawing Roller Stretching Filament

Wet-solution Spinning

Figure 6.3 Fibre spinning techniques.

6.3.3 Dyed Fibres

Natural and synthetic fibres are generally dyed using the loose stock and HTHP fibre dyeing machines, respectively (Figure 6.4) [33]. The working principles of the loose stock and HTHP machines are similar; however, as the name suggests, the HTHP machine can be operated at high temperature and high pressure depending upon the types of synthetic fibres being used for the dyeing. In this machine, a carrier with a removable perforated lid and base is loaded with fibres and its lid is closed with two screws. Through its base, dye liquor is circulated within the carrier from a storage tank for a certain duration (depending upon the type of fibre, e.g. natural wool or synthetic aramid, and dye, e.g. direct, disperse, sulfur, pigment, mordant, vat, reactive, macromo‑ lecular, metalized, azo, aniline, anthraquinonoid). And, the temperature of the dye liq‑ uor is adjusted depending upon the types of fibres and dyes. After the circulation, the dye liquor is drained from the carrier and fibres are taken out of the carrier (by opening 6.4 Yarns for PPC 167

Lid Lid Closing Screw Fibre inside the carrier

Dye-liquor Storage

Fibre Carrier Reversible Pump and Valve

Dye-liquor circulation system Draining

Figure 6.4 Working principle of loose stock or HTHP fibre dyeing machine.

Table 6.3 Test standards for measuring fibre properties.

Fibre properties Test standards

Tenacity ISO 5079:1995; ASTM D 3217 M:2015 Elasticity ISO 5079:1995; ASTM D 1774:1994 MR ISO 6741‐4:1987; ASTM D629:2015 Combustion/Melting temperature ISO 11357‐1:2016; ASTM D 7138:2016 LOI ISO 4589‐2:1996; ASTM D 2863:2013 Structures ISO 11827:2012; ASTM D 276:2012 the lid). The advantage of this technique is that the colour fastness of the dyed fibres is very high. However, it is very difficult to achieve the required colour of the PPC from the dyed/coloured fibres because they need further processing to manufacture the PPC.

6.3.4 Fibre Testing

The above discussion indicates that some fibre properties are very important for manufacturing the PPC with quality. These properties are mainly tenacity, elasticity, MR, combustion/melting temperature, LOI, and structure. In order to measure these properties, standard test methods developed by ISO and ASTM are used. Specific test standards along with corresponding fibre properties are presented in Table 6.3 [34–44].

6.4 Yarns for PPC

It is notable that the filament can be directly used as a yarn, by removing the blading process of converting filament into fibre (Figure 6.3) [45]. The direct use of filament yarns escapes all the processing stages involved in converting fibres into yarns, and thus makes it a cost‐effective (less production cost) and ecologically sustainable approach (it generates less soft fibres, hard yarns, and energy waste). However, the 168 6 Personal Protective Textiles and Clothing

surface of filament yarns is very smooth, which makes it difficult to use them during the weaving/knitting/garmenting process to manufacture the fabrics and PPC with quality. Owing to the smooth surface topography, the uptake of dyes and finishing agents of these filament‐yarns‐based fabrics is very low, which also ultimately affects the quality of PPC. Owing to this limitation, the use of spun yarns in PPC manufactur‑ ing has gained popularity over filaments yarns [14, 46]. Broadly, spun yarns are pro‑ duced from fibres and can be categorized into ‘ring‐spun’ and ‘other‐spun’ (e.g. rotor, air‐jet, friction) yarns. In general, ring‐spun yarns are produced through numerous stages, whereas fewer stages are involved in the production of other‐spun yarns. Therefore, the production of the ring‐spun yarn and its production cost are very high and low, respectively. Nevertheless, any type of fibres can be used in the production of ring‐spun yarns and their properties (e.g. breaking strength, evenness) are much better controlled than the other‐spun yarns. Because of the versatility of ring‐spun yarns, they are generally used for the manufacture of PPC. Notably, by using a suitable yarn dyeing machine and dyes, both ring‐ and other‐spun yarns can be coloured as per the con‑ sumer’s requirements. And, the properties of the undyed or dyed yarns can be meas‑ ured by various ISO and ASTM standard methods.

6.4.1 Ring‐Spun Yarns

Ring‐spun yarns are generally produced through different processing stages, as indi‑ cated in Figure 6.5 [14]. At first, the fibres supplied in the bale form (Figure 6.6a) are opened and cleaned by a bale opening machine (Figure 6.7a) in the blow room process. Then, these opened fibres are individualized to produce sliver (Figure 6.6b) in the

Opened Blowroom Carding Carded Combing Combed Fibre Bale and Cleaned Sliver Sliver Fibres

Winding Drawing Ring-spun Ring-spun Ring Spinning Roving Roving Draw-framed Yarn Package Yarn Bobbin Yarn Sliver

Figure 6.5 Processing of ring‐spun yarns.

(a) (b) (c) (d) (e)

Figure 6.6 Materials used for producing yarn: (a) fibre bale, (b) sliver, (c) roving yarn package, (d) yarn bobbin, and (e) yarn package. Source: Mr Nityanada Kundu (Manager, Vardhaman Spinning Mills, India). 6.4 Yarns for PPC 169 carding process by a carding machine (Figure 6.7b). Next, the carded sliver is passed through a lap former (Figure 6.7c) and short fibres are subsequently removed from the formed lap (as the presence of only long fibres enhances the strength of produced yarns) in the combing process by a combing machine (Figure 6.7d). And then, the combed slivers are drawn in the drawing process by a draw frame machine (Figure 6.7e) to make the parallel orientation of the long fibres within the slivers (as the parallel orientation of fibres enhances the strength and evenness of the yarns). Thereafter, draw‐framed slivers are processed by a speed frame machine (Figure 6.7f) for drawing and twisting them to produce the package of roving yarns (Figure 6.6c). Finally, roving yarns are re‐drawn and re‐twisted by a ring spinning machine (Figure 6.7g and h) to produce the ring‐spun yarns and to wrap them onto small bobbins (Figure 6.6d). The ring‐spun yarns from these bobbins are re‐winded on plastic cones in the winding process by a winding machine (Figure 6.7i) to produce the yarn packages (Figure 6.6e). The evenness of the conventional ring‐spun yarns is generally low, owing to their high hairiness. However, the more even (i.e. less hairiness) and compact ring‐spun yarns can also be produced

(a) (b) (c)

(d) (e) (f)

(g)

Figure 6.7 Machinery for producing yarn packages: (a) bale opening, (b) carding, (c) combing, (d) draw frame, (e) speed frame, (f) ring spinning, and (g) winding. Source: Mr Nityanada Kundu (Manager, Vardhaman Spinning Mills, India). 170 6 Personal Protective Textiles and Clothing

nowadays in the ring‐spinning machine by condensing (e.g. aerodynamic condensing, mechanical condensing, and magnetic condensing) the drawn roving yarns before twisting them to produce ring‐spun yarns.

6.4.2 Other‐Spun Yarns

Apart from ring‐spun yarns, some other‐spun yarns are also widely used in PPC manu‑ facturing. As other‐spun yarns are directly produced from fibres/slivers, their produc‑ tion is cost‐effective and ecologically sustainable. Depending upon the processing technique, the other‐spun yarns can be primarily categorized into rotor‐spun, friction‐ spun, and air‐jet‐spun [47–50].

6.4.2.1 Rotor‐Spun Yarn Rotor‐spun yarn technology was developed in 1963 by Cotton Research Institute, Czechoslovakia [47]. This technology involves direct feeding of a draw‐framed fibre sliver (Figure 6.8) into a rotor‐spinning machine to produce the yarn packages (Figure 6.9). These yarns comprise looped, hooked, and/or disoriented fibres in their structures; eventually, the breaking extension, hairiness, and abrasion resistance of these yarns are much higher than the ring‐spun yarns. Nowadays, rotor‐spun yarns are widely used after ring‐spun yarns.

Opened Blowroom Carding Carded Combing Combed Fibre Bale and Cleaned Sliver Sliver Fibres

Rotor Spinning Drawing Rotor-spun Draw-framed Yarns Sliver

Figure 6.8 Processing of rotor‐spun yarns.

Trash Feed Plate Yarn to Transport Channel Package Sliver Opening Roller Dof ng Tube Feed Roller

Rotor

Figure 6.9 Working principle of rotor‐spinning machine. 6.4 Yarns for PPC 171

Opened Blowroom Carding Carded Combing Combed Fibre Bale and Cleaned Sliver Sliver Fibres

Friction Spinning Drawing Friction-spun Draw-framed Yarns Sliver

Figure 6.10 Processing of friction‐spun yarns.

Drafting Rollers Air Flow Device Yarn to Package Fibre Opening

Slivers Rollers

Friction Rollers Drafting Rollers

Figure 6.11 Working principle of friction spinning machine.

6.4.2.2 Friction‐Spun Yarn The technique to produce friction‐spun yarn was developed by Dr Ernst Fehrer in 1975 and is called DREF friction spinning technology [50]. This technology was further improved by Dr Fehrer and is called DREF‐II and DREF‐III friction spinning technolo‑ gies. These technologies involve feeding a draw‐framed fibre sliver into a DREF friction spinning machine (Figure 6.10). This machine first drafts the sliver and then opens it by an opening roller (Figure 6.11). The opened fibres are thereafter passed through friction rollers with the help of air flow. Owing to the friction in the friction rollers, the yarns are formed and winded on a package. The friction‐spun yarns are bulky and thermally insu‑ lative in nature, which makes them suitable for the production of PPC. However, the low strength of the friction‐spun yarns could be one of the concerns about their suita‑ bility to use in PPC.

6.4.2.3 Air‐Jet‐Spun Yarn The technology to produce air‐jet‐spun yarns was commercially introduced in the mar‑ ket by Murata Machinery Limited, Japan in 1990 [48, 49]. In 2003, Rieter Group of Switzerland introduced its own spinning technology to produce the air‐jet‐spun yarns. As Rieter’s air‐jet spinning machine has high productivity, flexibility, simple settings, ease of operation, and low downtimes for maintenance, this technology quickly gained popularity in the market for producing air‐jet‐spun yarns. As per this technology, a strand of draw‐framed fibre sliver is directly fed into the air‐jet spinning machine (Figure 6.12). Next, the sliver is drafted by drafting rollers and then passed through air nozzles to produce the yarn (Figure 6.13). The core of this yarn has parallel fibre strands 172 6 Personal Protective Textiles and Clothing

Opened Blowroom Carding Carded Combing Combed Fibre Bale and Cleaned Sliver Sliver Fibres

Air-jet Spinning Drawing Air-jet-spun Draw-framed Yarns Sliver

Figure 6.12 Processing of air‐jet‐spun yarns.

Drafting Rollers Air Sheath with Nozzles s Twisted Fibres Yarn Sliver Core with Parallel Fibres Drafting Rollers

Figure 6.13 Working principle of air‐jet spinning machine.

and its sheath is wrapped by fibres. The air‐jet‐spun yarns possess the least hairiness and abrasion resistance in comparison to the rotor‐spun and friction‐spun yarns, which makes air‐jet‐spun yarns more suitable for the production of a knitted fabric.

6.4.3 Dyed Yarn

An undyed yarn package can be dyed using the loose stock or HTHP yarn dyeing machine, depending upon the types of fibres used in the yarn (Figure 6.14) [51]. In this machine, yarn packages are loaded onto a perforated spool within a carrier having removable perforated lid and base. Next, the lid of the carrier is closed by closing screws,

Lid Lid Closing Screw Perforated Spool

Dye-liquor Storage Packages Yarn Package Carrier Reversible Pump and Valve

Dye-liquor Circulation System Draining

Figure 6.14 Working principle of a yarn dyeing machine. 6.5 Fabrics for PPC 173

Table 6.4 Test standards for measuring yarn properties.

Yarn Properties Test Standards

Breaking strength and extension ISO 2062:2009; ASTM D 2256M:2010 Evenness ISO 16549:2004; ASTM D 1425M:2014 Hairiness ASTM D 5647: 2007 Abrasion resistance ASTM D 6611:2007 and dye liquor from a storage tank is circulated within the carrier through its base. The temperature of the dye liquor can be adjusted depending upon the types of fibres, yarns, and dyes. After dyeing, the dye liquor is drained off from the carrier and yarn packages are taken out of the carrier (after opening the lid). This technique has the advantage that the customized colour and shade matching of the small lot yarns packages is possible. However, the poor colour uniformity and fastness of the dyed yarns ultimately affect the quality of the PPC.

6.4.4 Yarn Testing

Based on the above discussion, it is clear that some yarn properties – such as breaking strength, breaking extension, evenness, hairiness, and abrasion resistance – are impor‑ tant in order to produce a suitable fabric for PPC [52]. To measure these properties, the standard test methods developed by ISO and ASTM can be used (Table 6.4) [53–58].

6.5 Fabrics for PPC

In general, four types of fabrics are used for the PPC: woven fabrics, knitted fabrics, nonwoven fabrics, and composite fabrics [59–62]. Considering different fabric proper‑ ties (weight, thickness, air permeability, thermal resistance, evaporative resistance, and/ or colour fastness), the selection of a particular type of fabric depends upon the end use of the PPC. For example, as underwear is always in close contact with a wearer’s skin, it is necessary that the fabric used for it should have good extensibility and strength. Considering this, knitted fabrics are preferred for the manufacturing of underwear to be worn by wearers under their PPC. Also, as strength and thermal insulation are the key fabric properties to consider, an assembly of woven, nonwoven, and/or composite fab‑ rics is generally preferred for the manufacturing of PPC for firefighters/military person‑ nel. Sometimes, the electrostatic propensity (EP) of the fabric becomes very important for the manufacturing of PPC, and the EP is primarily dependent on the MR, polymer composition, and electrical resistance of the fibres. The EP of a natural‐fibre‐based fab‑ ric is very low as it has high MR and low electrical resistance (e.g. electrical resistance of cotton is 6.8 Ω), whereas the EP of a synthetic‐fibre‐based fabric is very high, owing to its low MR and high electrical resistance (e.g. electrical resistance of polyester/acrylic is 14 Ω). A fabric with high EP could make a cling PPC, and also makes it difficult to remove soil from the PPC during its washing and dry cleaning. Notably, by using a suit‑ able fabric dyeing machine and dyes, all types of fabrics can be coloured as per the 174 6 Personal Protective Textiles and Clothing

Reed Heddle Weft Insertion Device Cloth Fell

Front Rest Back Rest Fabric Warp Warp Beam Cloth Beam

Figure 6.15 Working principle of a power loom weaving machine.

Weft Warp

Figure 6.16 Plain weave fabric.

consumer’s requirements. And, the properties of the fabrics can be measured by various ISO and ASTM standard methods.

6.5.1 Woven Fabrics

Woven fabrics for PPC are generally produced on a power loom (shuttle loom, projec‑ tile loom, rapier loom, air‐/water‐jet loom) machine by proper interlacement of warp and weft yarns (Figure 6.15) [63]. This loom involves dividing a set of warp yarn (on a warp beam) lengthwise into two sets (upper positions and lower positions) by using two heddles, and the up and down movement of these heddles can help to interchange the positions of these two sets of warp yarns. Then, a weft yarn is cross‐wisely inserted in between the two sets of warp yarns by a device/technique (shuttle, projectile, rapier, air jet, or water jet) and a traverse‐motioned reed helps to securely push the weft yarn into the cloth fell to produce the fabric. Then, this fabric is winded onto a cloth beam. By varying the movements of the two sets of warp yarns at different time intervals, it is possible to produce the woven fabric with different interlacement of warp and weft yarns. These fabrics can be categorized into plain weave fabrics (1 warp up and 1 weft down), twill weave fabrics (2 warp up and 1 weft down), etc. (Figures 6.16 and 6.17).

6.5.2 Knitted Fabrics

Although woven fabrics are produced by interlacing two different yarns (lengthwise warp yarns and crosswise weft yarns), knitted fabrics are produced by interlacing only one yarn [64]. The yarn in the knitted fabric follows a meandering path and forms 6.5 Fabrics for PPC 175

Weft Warp

Figure 6.17 Twill weave fabric.

Figure 6.18 Working principle of a Yarn Guide circular knitting machine. Yarn

Yarn Package

YarnTensioner

Feeder Yarn Guide Needle Fabric Take Down Roller Cloth Beam

symmetric loops above and below the mean path of the yarn. If these loops run across the length and width of the fabric, this is called warp and weft‐knitted fabrics, respec‑ tively. In general, weft‐knitted fabrics are used in the garment manufacturing. The weft‐ knitted fabric can be manufactured by a circular knitting machine or flatbed knitting machine. The cost of the circular knitting machine is lower than the flatbed knitting machine; therefore, circular knitting machines are widely used in the production of knitted fabrics (Figure 6.18). In the circular knitting machine, the yarns from the pack‑ ages are passed through a tensioner and feeder before reaching the needle. These nee‑ dles help to form loops in the knitted fabric and then the knitted fabric is passed through the take down roller and winded onto a cloth beam.

6.5.3 Nonwoven Fabrics

As indicated earlier, nonwoven fabrics are produced directly from a filament or bunch of fibres [65]. The filaments or fibres are laid together in the form of a sheet or web, and then they are bonded in the sheet or web form mechanically (by interlocking the fibres with serrated needle), chemically (by applying the adhesives to interlock the fibres), and/or thermally (by applying and heating the binder on the sheet or web). Based on the filament or fibres laying techniques (by laying the melt spun filament of Figure 6.3 onto a solid collector or by blowing the melt spun filament of Figure 6.3 through the spin‑ neret and then laying onto a solid collector, or by laying the dry fibres from carding to a solid collector, or by laying the mixture of fibres and water onto a wire mesh), the 176 6 Personal Protective Textiles and Clothing

Nonwoven Fabrics

Filament Web Fibre Web

Spun-Laid Web Melt Blown Web Dry Laid Web Wet Laid Web

Parallel-Laid Cross-Laid Random-Laid

Figure 6.19 Classification of nonwoven fabrics.

nonwoven fabrics can be classified as per Figure 6.19. Among these classifications, the production of spun‐laid nonwoven fabrics is most economical; therefore, it is widely used commercially for the manufacturing of PPC. Recently, nanofilament based spun‐ laid nonwoven fabrics have also been commercially used especially for the manufac‑ turing of PPC. For these fabrics, filaments are generally manufactured by an electrospinning machine and laid onto an electric field supported collector (Figure 6.20). As nanofibres based nonwoven fabrics are lightweight, these fabrics are becoming more popular in the production of PPC; this lightweight PPC can be used for providing chemical, biological, and thermal protection to wearers.

Syringe Pump

Polymer Solution in Syringe

Voltage Needle Needle Tip

Bended or Whipped Jet Nano Filament Splaying

Collector Voltage

Figure 6.20 Working principle of an electrospinning machine to produce nanofilament based nonwoven fabrics. 6.5 Fabrics for PPC 177

6.5.4 Composite Fabrics

The fabrics produced by the above methods can be reinforced with different high strength fibres (glass, carbon, aramid) in order to produce composite fabrics [66]. This fibre reinforcement can add strength to the fabric even though the fabric remains light‑ weight. For example, aramid‐fibre‐based woven fabric can be reinforced with glass and carbon fibres in order to enhance its ballistic and stab protective performance. Many researchers compared the ballistic and/or stab protective performance of fibre rein‑ forced fabrics with ordinary fabrics. They found that fibre reinforced fabrics possess much higher strength and protective performance than the ordinary woven/knitted/ nonwoven fabrics.

6.5.5 Dyed and Printed Fabrics

A fabric can be dyed in a batch or continuous process. In the batch process, a certain length of fabric can be dyed by different dyeing machines (e.g. beck, jet, jig) [18]. These machines mainly move the fabric through the dye liquor or move the dye liquor through the fabric or both (fabric as well as dye liquor). As the exhaustion of dyes within the fabric materials is very high in the batch‐dyeing process, the colour fastness of the batch‐dyed fabrics is very high. However, the production rate of dyed fabrics by these machines is very low, whereas the production rate of continuous dyeing machine is high. Therefore, the continuous dyeing process is preferred for industrial use (Figure 6.21). Nevertheless, the colour variation across the length and width of the continuous dyed fabric may occur, owing to its high production speeds and large num‑ ber of process variables (e.g. dye padding time, steaming time). By applying suitable dyes, a fabric can be printed using different processes: (i) block printing (by transferring a design engraved on a wooden block to the fabrics using dyes), (ii) roller/cylinder printing (by passing the fabrics over an engraved dye containing roller), (iii) stencil printing (by passing the dyes through the interstices of a designed stout paper sheet onto the fabric), (iv) screen printing (by squeezing the printing paste through the opening of a screen onto the fabric). Among all these processes, screen printing is widely used because of its high productivity and print quality. This type of printing is usually carried out by flatbed screen printing machines (Figure 6.22) or rotary screen printing machines (Figure 6.23).

Guide Roller Undyed Fabric Drying Steaming Roll Dyed Fabric Roll

Washing Padding of Padding of Fabrics Fabrics with with Chemical Dye (e.g. salt, alkali)

Figure 6.21 Working principle of continuous fabric dyeing machine. 178 6 Personal Protective Textiles and Clothing

Squeezer

Dyes Designed Screen Printed Design on Fabrics

Fabric Moving Fabric Holder

Figure 6.22 Working principle of flatbed screen printing machine.

Figure 6.23 Working principle of rotary screen printing machine. Printed Fabrics Rotating Screen

Squeezer Impression Dyes Cylinder

Unprinted Fabrics

6.5.6 Finished Fabrics

After dyeing and printing, a fabric is mechanically and/or chemically finished to improve its properties, such as dimensional stability, fire retardancy, water repellency, antimicrobial, ballistic and stab protection, and thermo‐regulation (i.e. total heat loss (THL) from the body through proper metabolic heat and sweat vapour dissipation) [67–69]. Notably, both mechanical and chemical processing techniques can comple‑ ment each other to improve a property. To improve dimensional stability of a fabric by mechanical finishing, the fabric is passed through a sanforizing machine (Figure 6.24). In this machine, the fabric is first wetted in a moistening device to shrink and then pressed against a heated rubber band to relax and re‐shrink. Next, the fabric is passed through a dryer to stabilize the shrinkage by removing the moisture from it. After pro‑ ducing the antishrink fabric, it is generally finished through chemical processing. During this processing, chemical substances are generally finished on the fabric surface through padding, exhaustion, coating, spraying, and foam formation. For example, phosphorous and fluorinated based chemical substance are finished on the fabric sur‑ face by a padding machine to improve its flame retardancy and water repellency, respectively (Figure 6.25). Similarly, a coating of shear thickening agents may improve the ballistic and stab‐protection properties of the fabric. During this stage, it is 6.5 Fabrics for PPC 179

Dimensionally Stable Anti-shrink Fabric Roll

Dimensionally Unstable Fabric Roll Dryer

Moistening Heated Rubber Device Band Assembly

Figure 6.24 Working principle of sanforizing machine for improving the dimensional stability (antishrink) of a fabric.

Un nished Guide Roller Fabric Drying Roll

Finished Fabric Roll Padding of Fabrics with Chemicals (Phosphorous, Fluorine)

Figure 6.25 Working principle of padding machine for improving the flame retardancy and water repellency of a fabric. necessary to remember that the finishing agents should not contain any harmful chemi‑ cal substances that could affect the wearer’s health. For example, the halogen based chemical substances could also improve the flame retardancy of a fabric, but these halo‑ gen substances are carcinogenic and are illegal to use for imparting flame retardancy to the fabric.

6.5.7 Fabric Testing

The above discussion shows that many fabric properties are substantially important to measure before fabrication of the PPC [70, 71]. These properties are: weight, thick‑ ness, air permeability, thermal resistance, evaporative resistance, EP, colour fastness, shrinkage, fire retardancy, water repellency, antimicrobial, ballistic and stab‐protection, and thermo‐regulatory. These properties can be measured by various test standards developed by ISO, ASTM, and the National Institute of Justice (NIJ) (Table 6.5) [72–95]. Contextually, some bench‐scale tests are available to evaluate the protective per formance of fabrics under different hazards. For example, ISO 9151:2016 and ISO 12127‐1:2015 test standards are available for evaluating the protective performance of fabrics under flame and hot surface contact hazards, respectively [96, 97]. Never theless, these bench‐scale tests for fabrics may not holistically/accurately represent 180 6 Personal Protective Textiles and Clothing

Table 6.5 Test standards for measuring fabric properties.

Fabric properties Test standards

Weight ASTM D 3776:2013 Thickness ASTM D 1777:2015 Air permeability ASTM D 737:2016 Thermal resistance ISO 11092:2014; ASTM F 1868:2014; ASTM D 1518:2014 Evaporative resistance ISO 11092:2014; ASTM F 1868:2014 Electrostatic propensity ISO 18080‐1:2015; ASTM D 4238:1990 (withdrawn in 1996) Colour fastness ISO 105:2013; AATCC TM6:2016; AATCC TM23:2015; AATCC TM61:2013; AATCC TM125:2009 Dimensional stability ISO 3005:1978; ASTM D 6207:2015 Fire retardancy ISO 15025:2016; ASTM E 1321:2013 Rainwater repellency ISO 9865:1991; ASTM D 7017:2014 Antimicrobial ISO 20743:2013; ASTM E 2149:2013 Ballistic and stab protection NIJ 0108.00:1985; NIJ 0115.0:2000 Thermo‐regulatory ISO 18640‐1:2018; ASTM F 1868:2014

the protective performance of whole PPC (made from the same fabrics) under these hazards. Hence, it is recommended to use the full‐scale instrumented manikin tests for evaluating the hazard protective performance of whole PPC (which discussed in the next section). According to Table 6.5, ASTM F 1868:2014 standard can be used for evaluating three fabric properties: thermal resistance, evaporative resistance, and thermo‐regulatory. Actually, thermal and evaporative resistance values are used for evaluating the thermo‐ regulatory property of the fabric in terms of THL (i.e. equivalent to the total amount of heat transferred through a fabric by the combined dry metabolic heat and sweat vapour evaporative heat exchanges). Eventually, this THL can explain the thermo‐regulatory property of the fabric. Historically, ISO 11092 standard was developed by the Hohenstein Institute of Germany for evaluating thermal and evaporative resistances. Thereafter, the NFPA developed a method to determine the THL of thermal protective fabrics using the ISO 11092 standard, and this THL method was included in several standards (e.g. NFPA 1971, NFPA 1977, NFPA 1951, NFPA 1999). Later, the members of the ASTM F23 committee decided to compile the evaluation procedures for measuring thermal resistance, evaporative resistance, and THL in one document, which resulted in the ASTM F 1868:2014 standard. The ASTM F 1868:2014 standard uses the sweating guarded hot plate device for evaluating thermal and evaporative resistances (Figure 6.26); and then, a mathematical equation is used for predicting the THL from the thermal and evaporative resistances. As per the ASTM F 1868:2014 standard, a fabric specimen is placed on a sweating guarded hot (35 °C) plate (to simulate human skin); and, the ambient air temperature, relative humidity, and ambient air velocity are controlled at 25 °C, 65%, and 0.5–1 m s−1, respectively. When the specimen and hot plate reach the steady‐state condition, the amount of heat flow per unit area of the specimen is measured. By using the 6.5 Fabrics for PPC 181

Figure 6.26 Sweating guarded hot plate tester at Empa, Switzerland.

temperature difference between the hot plate surface (Ts) and ambient air (Ta), heat flow (Hc) per unit area (A), and the thermal resistance of the boundary air layer of the 2 hot plate (Rcb), the thermal resistance of the fabric (Rcf) is calculated in m K/W (Eq. 6.1). In order to evaluate the evaporative resistance, the temperatures of the sweating guarded hot plate and ambient air are set at 35 °C (please note: this isother‑ mal condition can prevent the dry heat exchange between the hot plate and ambient air, but the evaluation of evaporative resistance is also possible under nonisothermal conditions). And the relative humidity and velocity of the ambient air are set at 40% and 0.5–1 m s−1, respectively. Then, water is fed to the surface of the plate‐guard sec‑ tion (to simulate the sweating on wearers’ bodies) and covered with a liquid barrier having a permeability index greater than 0.7. Thereafter, the fabric specimen is placed on the liquid barrier covered plate. When the fabric specimen reaches the steady‐state condition, water vapour pressure on the plate (at 35 °C temperature and 100% relative humidity) and fabric surface (at 25 °C temperature and 40% relative humidity) are cal‑ culated by using the internationally recognized water vapour saturation tables. By using the vapour pressure difference between the hot plate surface (Ps) and ambient air (Pa), heat flow (He) per unit area (A) and the evaporative resistance of the boundary air layer of the hot plate (Reb), the evaporative resistance of the fabric (Ref) is calculated 2 in m Pa/W (Eq. [6.2]). Rcf and Ref values obtained from Eqs. (6.1) and (6.2) are used to calculate the THL through the fabric using Eq. (6.3). Many organizations also used this method to standardize the THL requirement of a fabric used in PPC. For example: NFPA 1971:2007 recommends that the THL of multi‐layered fabrics used in firefight‑ ers’ PPC should be at least 205 W m−2; the fulfilment of this requirement could provide better thermo‐regulation to on‐duty firefighters. 182 6 Personal Protective Textiles and Clothing

RTcf =−()SaTA/ HRcc − b (6.1)

RPet = ()Sa− PA/ HRee − b (6.2) ° 10 C 35. 7kPa THL = + (6.3) RRcf + 00. 4 ef + 0.0035

Although the ASTM F 1868:2014 standard procedure possesses high reproducibility and repeatability for evaluating thermo‐regulatory property in terms of THL, it does have some shortcomings and limitations. For example, reaching the steady‐state con‑ dition of the thick fabric specimen and hot plate is often quite difficult while evaluating thermal and evaporative resistances. At the high ambient air velocity, the fabric speci‑ men may also lift off from the hot plate; this situation could result in high thermal resistance, high evaporative resistance, and low THL. The calculation procedure of the THL is also tedious and time‐consuming. Finally, many researchers found that the individual evaluation of thermal and evaporative resistances could be unrealistic because dry and evaporative heat losses occur simultaneously from the human body to the ambient environment. Therefore, this method of THL calculation could not realis‑ tically represent the thermo‐regulatory property of the fabric. Considering this, a group of researchers from Empa in Switzerland have contributed to the development of a torso test device that can realistically evaluate the thermo‐regulatory property of the fabric, by considering the combined heat and vapour/moisture transfer through fabric [98–100]. Presently, this torso test method has been approved by the ISO and documented in ISO 18640‐1:2018 standard. Although the torso method of this stand‑ ard is presently applicable for evaluating the thermo‐regulatory property of fabrics used in firefighters’ PPC, this method could also be used for developing the standard for fabrics used in other types of PPC (e.g. chemical protective clothing or rain protec‑ tive clothing). The sweating torso device mentioned in ISO 18640‐1:2018 standard has an upright standing heated cylinder, representing the surface of a human trunk, with the ability for perspiration through nozzles (Figure 6.27). As per this standard, a fabric specimen is wrapped around the torso (surface temperature of the torso is 35 °C) that is placed in a climatic chamber at controlled air temperature (20 °C), relative humidity (50%), and air velocity (1 m s−1). Then, the torso device is run through three consecutive phases of 60 minutes each (Phase 1 condition: at constant torso surface temperature of 35 °C without sweating; Phase 2 condition: apply constant heating power of 125 W to torso with a sweat rate of 100 g h−1; Phase 3 condition: apply constant heating power of 25 W to torso without any sweating) to measure dry thermal insulation, dry and wet heat transfer, and the drying properties of the fabrics. These measurements together could holistically explain the thermo‐regulatory property of a fabric in a complete simulated situation where firefighters first wear the dry clothing (Phase 1 of the torso test), then they start sweating while performing activities (Phase 2 of the torso test), and finally no sweating after their activities (Phase 3 of the torso test). As an air gap (microclimate region) always exists between the PPC and firefighters, the torso test can be conducted by considering the air gap between the torso surface and tested fabric. This test can also 6.6 PPC Fabrication 183

Figure 6.27 Sweating torso tester at Empa, Switzerland. be conducted in combination with underwear to more realistically analyse the thermo‐ regulatory property of the fabric.

6.6 PPC Fabrication

PPC is usually fabricated through the cut‐and‐sew garmenting process [101, 102]. First, fabrics (single‐layered or multilayered) are cut into the pattern of different body parts (e.g. sleeve, back body panel, front body panel). And then, these patterned parts are sewn together by different types of stitches (e.g. chain‐stitch, lock‐stitch, zigzag‐stitch) and seams (e.g. plain‐seam, flat‐seam, lapped‐seam) using an industrial sewing machine. For the stitching, a thread is inserted via needle to seam the fabric parts together for fabricating the PPC. After fabricating the PPC, various trims and accessories (e.g. front panel closing fasteners, flaps, reflective tape) are attached to it. In some cases, a single coloured PPC can be dyed using a paddle garment dyeing machine. In this machine, the PPC is first immersed in dye liquor within a steam‐heated dye bath and then moved through the padding roller within the dye liquor (Figure 6.28). If required, PPC can also be printed using a newly developed digital inkjet printing machine. Overall, PPC can be fabricated in a similar way as regular clothing; however, the fabricator of the PPC should follow some guidelines (related to innocuousness, size des‑ ignation, ageing, compatibility, marking, and ergonomics) provided by ISO 13688:2013 (Protective clothing – general requirements). These guidelines should be applied in combination (strictly not on a stand‐alone basis) with other standards that can measure the specific functional performance. Notably, the functional performance (hazard pro‑ tective and thermo‐physiological comfort) of PPC can be measured against different hazards/environments using various standards, as indicated in Table 6.6 [103–121]. The standards mentioned in Table 6.6 for evaluating the protective performance of PPC mainly use instrumented manikins to simulate an adult‐sized human body. The PPC that needs to be tested is donned on the manikin (with or without underwear) and the clothed manikin is exposed to the hazards to predict the protective performance of 184 6 Personal Protective Textiles and Clothing

Rotating Padding PPC Roller

Dye Bath Dye Liquor

Dye Liquor Draining

Figure 6.28 Working principle of PPC dyeing machine.

Table 6.6 Test standards for measuring functional performance of PPC.

Clothing functional performance Hazard/Environment Test standard

Protective Cool/Chilled air CEN 14058:2004 Cold water ISO 15027‐3:2012 Cold air CEN 342:2004 Rain CEN 14360:2004 Flash fire ISO 13506:2008; ASTM F 1930:2017 Arc and flame ASTM F 1891:2012 Hot liquid splash NFPA 1992 Steam vapour NFPA 1991 Knife stab ISO 13998:2003 Chemical substances ISO 16602:2007; ASTM F 1296:2008; NFPA 1994 Radioactive agents CEN 1073‐1:2016; CEN 1073‐2:2016 Biological matters CEN 14126:2003; NFPA 1994 Thermo‐physiological Ambient temperature is similar ISO 9920:2007; ASTM F comfort to or lower (12 °c) than human skin 1291:2010; ASTM F 2370:2010 temperature of 35 °C

the PPC. For example, as per Figure 6.29, the clothed manikin is exposed to flash fire (at 84 kW m−2) in a fire chamber according to ISO 13506:2008 standard. Thereafter, the time and percentage of burn injury generated on the human body is predicted by more than 100 heat flux sensors that are instrumented on the manikin. PPC that takes a long time or generates a low percentage of burn injury is considered high performance fire pro tective clothing. Similarly, as per Figure 6.30, the clothed manikin is exposed to the rain (cloudburst rain: 450 l (m2 h)−1; drizzle rain: 40 l (m2 h)−1; persistent rain: 100 l (m2 h)−1) 6.6 PPC Fabrication 185

(a) (b) (c)

Figure 6.29 Flash fire manikin ‘Henry’ at Empa, Switzerland: (a) nude instrumented manikin; (b) clothed manikin; (c) clothed manikin engulfed in flash fire.

(a) (b) (c)

Figure 6.30 Rain manikin ‘James’ at Empa, Switzerland: (a) nude instrumented manikin; (b) clothed manikin under a rain tower; (c) wet zones on the underwear. under a rain tower according to CEN 14360:2004 standard. Thereafter, the presence of wet zones on the underwear is detected by 22 conductance sensors that are instrumented on the manikin, and the size of the wet zone is calculated manually by the experimenter. PPC that generates smaller size wet zones is considered high performance rain protective clothing. According to Table 6.6, there exist individual test standards for evaluating the protec‑ tive performance of PPC depending upon the hazard. But, the ISO has also recom‑ mended one single test (ISO 9920:2007) to evaluate the thermo‐physiological comfort performance of all types of PPC. As per the ISO 9920:2007 standard, the thermal and 186 6 Personal Protective Textiles and Clothing

Figure 6.31 Clothed sweating thermal manikin ‘Sam’ at Empa, Switzerland.

evaporative resistances of the clothing are measured to explain its thermo‐physiological comfort performance. In order to evaluate the thermal resistance, a sweating thermal manikin (skin tem‑ perature of the manikin is set at 35 °C) is housed in a climatic chamber having ambient air temperature: 23 °C, relative humidity: 50%, and air velocity: 0.4 m s−1 (Figure 6.31). To evaluate evaporative resistance, the temperatures of both manikin skin and ambient air are kept at 35 °C (please note: the evaluation of evaporative resistance can also be possible under nonisothermal conditions). The PPC that needs to be tested is donned on the manikin (with or without underwear) and the skin temperature of the clothed manikin is further stabilized to reach the steady‐state (i.e. the mean skin temperature and electrical heating power input remain constant ±3%). After reaching the steady‐ state, the manikin’s skin temperature and the ambient air temperature are recorded at every one‐minute interval. The average of these records is taken over a period of 30 minutes in order to determine the thermal or evaporative resistance value. Over the test period of 30 minutes, the power input to heat the manikin is also continuously measured at every one‐minute interval. Then, the thermal resistance of the clothing with the manikin’s surface (boundary) air layer is calculated according to Eq. (6.4), where, Rt = total thermal resistance of the clothing and surface air layer around the 2 −1 manikin (°C m W ); Ts = temperature at the manikin’s skin surface (°C); Ta = tempera‑ ture of the ambient air flowing over the clothing (°C); A = area of the manikin’s surface (m2); and, H = power required to heat the manikin (W). Here, it seems that a significant amount of trapped air on the boundary of the manikin’s surface (or around the mani‑ kin) contributes to Rt. Thus, the intrinsic thermal resistance (Rcl) of the clothing can be determined by subtracting the thermal resistance (Ra) of the nude manikin from the Rt 6.7 Key Issues Related to PPC 187

2 −1 based on Eq. (6.5), where, Rcl = intrinsic thermal resistance of the clothing (°C m W ); 2 −1 Ra = thermal resistance of the air layer on the surface of the nude manikin (°C m W ); and, fcl = clothing area factor (dimensionless) that can be estimated using the ISO 9920 standard, or a photographic method described by [122]. The evaporative resistance (Ret) of the clothing with the manikin’s surface (boundary) air layer can be determined by Eq. (6.6), where, Ret = total evaporative resistance provided by the clothing with a surface air layer around the manikin (kPa m2 W−1); A = area of the manikin’s sweating 2 surface (m ); Ps = the water vapour pressure at the manikin’s sweating surface (kPa); Pa = the water vapour pressure of the air flowing over the clothing (kPa); He = electrical heating power required for the sweating area (W); Ts = temperature at the manikin’s skin surface (°C); Ta = temperature of the air flowing over the clothing (°C); and Rt = total thermal resistance of the clothing with manikin’s surface air layer measured by Eq. (6.4) 2 −1 (°C m W ). Similar to intrinsic thermal resistance (Rcl), the intrinsic evaporative resistance (Recl) of clothing is also determined by subtracting the evaporative resistance of the air layer on the surface of the nude manikin’s sweating surface (Rea) from the Ret 2 −1 [Eq. (6.7), where Recl = intrinsic evaporative resistance of the clothing (kPa m W ); Rea = the evaporative resistance of the air layer on the surface of the nude manikin’s sweating surface (kPa m2 W−1)].

RTts=−()TAa / H (6.4)

=−Ra RRcl t (6.5) fcl

=− −− RPet [( saPA)] ]/[(HTesTAat)/R ] (6.6)

=−Rea RReclet (6.7) fcl

6.7 Key Issues Related to PPC

Although PPC has been successfully manufactured over decades, a few key issues still remain that need to be addressed in future. These issues are mainly related to (i) devel‑ oping new high performance fabric materials and (ii) ecologically sustainable process‑ ing techniques and materials. In the following sections, these issues are discussed.

6.7.1 Development of New High Performance Fabric Materials

PPC generally employs heavyweight, thick, and/or air‐impermeable fabrics/membrane [11, 23, 123]. This type of fabric is required mainly to provide effective protection to the wearer. However, this type of fabric lowers the thermo‐physiological comfort perfor‑ mance of the PPC by exerting weight on the wearer’s body, restricting the metabolic heat and sweat vapour transmission through the fabric. Considering this, many research‑ ers have put great effort into developing new materials or implementing smart tech nologies (e.g. foamed silicone on vapour permeable membrane, macro‐encapsulated nanoporous gels or aerogels, or nanoclay‐reinforced resin coating on woven/nonwoven 188 6 Personal Protective Textiles and Clothing

fabrics, nanofibres in nonwoven fabrics, nano finishes or phase change materials (PCMs), or shape memory alloy in woven/nonwoven fabrics, sensors, gas detectors, safety alarm, cooling devices) in PPC that can give better protection and comfort to wearers [124–129]. Nevertheless, these new materials and smart technologies are not yet very cost‐effective and are confined to laboratory settings and/or are only applied in highly specialized circumstances like aerospace, military, and defence. In future, it will be required to use different cost‐effective technologies (nanotechnology, smart textiles) to manufacture a fabric that can be lightweight and thin, and effectively transmit the metabolic heat and sweat vapour from wearers’ bodies. For example, nanofibre based nonwoven fabrics are lightweight and have good thermal insulation capacity. This type of fabric can be used for the manufacturing of firefighters’ PPC. This will ultimately provide better thermo‐physiological comfort to the wearers. Furthermore, biological and chemical protective clothing mainly comprises a membrane fabric that is air‐imper‑ meable. This air‐impermeable fabric impedes the transfer of sweat vapour from the wearer’s body and thus lowers the thermo‐physiological comfort of the PPC. Instead of using the membrane, some finishing could be applied to the woven fabrics to make them biological and chemical protective. This can also enhance the comfort performance of the fabrics. By incorporating the PCM and moisture management finishes within the fabrics, it is also possible to absorb the metabolic heat and sweat vapour generated from the wearers’ bodies, and provides them better thermo‐physiological comfort. Additionally, some new test methods needs to be developed to realistically evaluate the functional performance (hazards protective performance and thermo‐physiological comfort performance) of PPC by properly simulating the hazards and environments faced by wearers.

6.7.2 Ecologically Sustainable Processing Techniques and Materials

The PPC is generally manufactured using wide range of processing techniques. All of these techniques cause a significant amount of air and water pollution. Also, most of the waste textile materials (fibres, yarns, fabrics) generated during the manufactur‑ ing and disposal stage of PPC also involves synthetic petrochemical based materials and such materials do not decompose easily. In fact, an estimate indicates that such materials may take 40 years to degrade naturally [130]. Overall, the air/water pollu‑ tion and nonbiodegradable materials can significantly affect our ecological system. This makes it necessary to focus on different ecologically sustainable processing techniques and materials that can lower the waste and save the environment. For example: use of digital colouring or printing techniques can significantly reduce the water consumption during the manufacturing of PPC. Proper maintenance (wash and care) of PPC can lower its ageing and thus wearers can use it for long time. Additionally, this will considerably reduce the dumping of nonbiodegradable materi‑ als in environment. In this context, it is notable that Hohenstein Institute of Germany has introduced standard certifications (Oeko‐Tex Standard 100/1000) for textile products. These standard certifications mainly control the harmful substances in a textile product (e.g. formaldehyde, pesticides, heavy metals, carcinogenic amines) and/or promote environmental friendly textile productions (e.g. prohibit the uses of harmful technologies, control the wastage of water and energy, reduce the noise and air pollutions). Eventually, the implementation of these certifications in PPC could References 189 help to make it more ecologically sustainable and can protect the global people and environment.

6.8 Conclusion

PPC is required to protect the human beings from various hazards such as wind, cold air, rain, flash fire. In general, it is necessary that PPC should possess high thermal protective performance under a particular hazard. At the same time, the PPC should effectively regulate the metabolic heat and sweat vapour from wearers’ bodies to their surrounding environment; this regulation will provide high thermo‐physiological com‑ fort to the wearers. Along with these functional performance (hazards protective per‑ formance and thermo‐physiological comfort performance), PPC should also possess some aesthetic features like appropriate colours and printed designs. Notably, various aspects (e.g. materials used, manufacturing process employed) associated with the tex‑ tile based PPC can help to achieve the desired functional performance and aesthetic features. There are different processing techniques (spinning, weaving, knitting, nonwoven, dyeing, finishing, garmenting) to manufacture the PPC from various materials (fibres, yarns, fabrics). Generally, fibres are used as basic raw materials for manufacturing the PPC. These fibres are processed into the spinning process to produce filament‐ or spun‐ yarns. Then, these yarns are used in the weaving/knitting/nonwoven process to produce the fabrics. These fabrics are further dyed and finished in order to impart some proper‑ ties. Finally, these dyed and finished fabrics are used in the garmenting process to fabri‑ cate PPC. There are different standard testing methods available for evaluating the properties of various materials used for the manufacture of PPC. Additionally, the functional per‑ formance (hazard protective performance and thermo‐physiological comfort perfor‑ mance) of whole PPC can also be measured by using various standard methods. In general, sensor instrumented manikins are used for evaluating the protective perfor‑ mance of PPC under various hazards. Additionally, sweating thermal manikins are used for evaluating the thermo‐physiological comfort performance of PPC. Although PPC has been manufactured and tested successfully over the decades, some key issues (development of new high performance materials, ecologically sustainable processing techniques and materials) related to the PPC still remain unaddressed. In future, it will be necessary to resolve these key issues in order to manufacture a high performance PPC that can provide better protection and comfort to the wearers.

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105 CEN 342: 2004. Protective clothing – garments and clothing combinations for protection against cold air. 106 CEN 14360:2004. Protective clothing against rain test method for readymade garments impact from above with high energy droplets. 107 ISO 13506:2008. Protective clothing against heat and flame – test method for complete garments – prediction of burn injury using an instrumented manikin. 108 ASTM F 1930:2017. Standard test method for evaluation of flame resistant clothing for protection against fire simulations using an instrumented manikin. 109 ASTM F 1891:2012. Standard specification for arc and flame resistant rainwear. 110 NFPA 1992. Standard on liquid splash‐protective ensemble and clothing. 111 NFPA 1991. Standard on vapor‐protective ensemble and clothing. 112 ISO 13998:2003. Protective clothing – aprons, trousers and vests protecting against cuts and stabs by hand knives. 113 ISO 16602:2007. Protective clothing for protection against chemicals – classification, labelling and performance requirements. 114 ASTM F 1296:2008. Standard guide for evaluating chemical protective clothing. 115 NFPA 1994. Standard on protective ensemble for chemical/biological terrorism incidents. 116 CEN 1073‐1:2016. Protective clothing against radioactive contamination – requirements and test methods for ventilated protective clothing against particulate radioactive contamination. 117 CEN 1073‐2:2016. Protective clothing against radioactive contamination – requirements and test methods for non‐ventilated protective clothing against particulate radioactive contamination. 118 CEN 14126:2003. Protective clothing – performance requirements and tests methods for protective clothing against infective agents. 119 ISO 9920:2007. Ergonomics of the thermal environment – estimation of thermal insulation and water vapour resistance of a clothing ensemble. 120 ASTM F 1291:2010. Standard test method for measuring the thermal insulation of clothing using a heated manikin. 121 ASTM F 2370:2010. Standard test method for measuring the evaporative resistance of clothing using a sweating manikin). 122 McCullough, E.A., Jones, B.W., and Huck, J. (1985). A comprehensive data base for estimating clothing insulation. ASHRAE Transactions 91: 29–47. 123 Bajaj, P. and Sengupta, A.K. (1992). Protective clothing. Textile Progress 22 (2): 1–110. 124 Dadi, H.H. 2010. Literature Overview of Smart Textiles. MSc thesis. University of Borås, Borås, Sweden. 125 Donnelly, M.K., Davis, W.D., Lawson, J.R., Selepak, M.J. 2006. Thermal Environment for Electronic Equipment Used by First Responders, National Institute of Standards and Technology. Technical Note 1474. National Institute of Standards and Technology, USA, 1–36. 126 Hocke, M., Strauss, L., and Nocker, W. (2000). Firefighter garment with non textile insulation. In: Proceedings of NOKOBETEF 6 and 1st European Conference on Protective Clothing, Stockholm, Sweden (ed. K. Kuklane and I. Holmer), 293–295. Denmark: European Society for Protective Clothing. 127 Holme, I. (2004). Innovations in performance clothing and microporous film. Technical Textiles International 13 (4): 26–30. References 195

128 Jin, L., Hong, K.A., Nam, H.D., and Yoon, K.J. (2011). Effect of the thermal barrier on the thermal protective performance of firefighter garment. In: Proceedings of TBIS2011, Beijing, China (ed. Y. Li, X.N. Luo and Y.F. Liu), 1010–1014. Hong Kong: Textile Bioengineering and Informatics Symposium Society. 129 Song, G. and Lu, Y. (2013). Structural and proximity firefighting protective clothing: textiles and issues. In: Handbook of Fire Resistant Textiles (ed. F.S. Kilinc), 520–548. Cambridge: Woodhead Publishing. 130 Wool and Biodegradability. (n.d.). Retrieved from: http://www.iwto.org/sites/default/ files/files/iwto_resource/file/Wool%20and%20Biodegradability_IWTO%20Fact %20Sheet_update.pdf. Accessed 21 April 2017.

197

Textiles for Military and Law Enforcement Personnel Christopher Malbon1 and Debra Carr 2

1 Centre for Defence Engineering, Cranfield University, Shrivenham, United Kingdom 2 Defense and Security Accelerator, Dstl, Wiltshire, United Kingdom

7.1 Introduction

Military and law enforcement personnel are faced by diverse threats routinely in their employment. Examples of these threats include ballistic, chemical, flame, and environmental threats (e.g. extremes of temperature, precipitation, wind). There is always a compromise between the protection offered by a clothing system and the ability to complete the task (i.e. survivability vs. mobility). The optimum design of protective clothing systems requires expert knowledge of the threats faced, the tasks to be completed, the anthropometric properties of the persons to be protected, the fabrics that might be used, integration with other fabrics and equipment, and knowledge of appropriate clothing and textile sciences manufacturing techniques and test methods. Amongst the threats considered in such an analysis are those that require specialized fabrics and clothing systems to provide protection (e.g. ballistic and sharp weapon; flame retardant; and chemical, biological, radiological, and nuclear). These threats are considered in this chapter and the fabrics and test methods used are summarized.

7.2 Ballistic and Sharp Weapon Protection

The primary cause of injury to military personnel in modern warfare is fragmentation, e.g. [1–3]. Fragments originate from traditional munitions such as grenades and artil- lery shells and from improvised explosive devices (IEDs). Fragments vary in size, shape (preformed cubes, ball bearings, random), and velocity (Figure 7.1) [1, 4, 5]. Military personnel are also injured by bullets: gunshot wounds were the second highest injury suffered by UK personnel in recent conflicts [3]. The rifle ammunition typically of concern is 5.45, 5.56, and 7.62 mm calibre (Figure 7.2). For civilian law enforcement personnel the threat could be both sharp weapon and ballistic albeit of a lower calibre typically than the military. For example, in the UK a police officer is most likely to be threatened by a sharp weapon such as a knife (Figure 7.3) [6]. Sharp weapons vary from weapons

High Performance Technical Textiles, First Edition. Edited by Roshan Paul. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 198 7 Textiles for Military and Law Enforcement Personnel

Figure 7.1 Typical fragmentation from traditional munition.

Figure 7.2 Rifle ammunition: 5.45 × 39 mm, 7.62 × 39 mm, 5.56 mm NATO and 7.62 mm NATO. 7.2 Ballistic and Sharp Weapon Protection 199

Figure 7.3 Sharp weapons used for testing law enforcement stab‐resistant armour in the UK.

Figure 7.4 Pistol ammunition: 9 mm Luger FMJ, 9 mm Luger HP and .357 Magnum. of opportunity such as a kitchen knife to a weapon that may be carried by an expert user, e.g. [7–10]. Pistol ammunition is also considered a threat to routine patrol police officers (Figure 7.4), e.g. [11, 12]. Authorised firearms officers (AFOs) and specialist firearms officers (SFOs) can face greater threats than beat officers that may include rifle and carbine ammunition similar to that faced by military personnel.

7.2.1 Protective Materials

The materials used in protective equipment are briefly discussed in this section; a more descriptive description of fibres and materials can be found in textbooks such as that edited by Bhatnagar [13]. Protection from the threats summarized in Figures 7.1–7.4 are typically achieved by the use of protective systems such as body armour and helmets [11, 14]. Body armour is usually a waistcoat or tabard style garment that provides protection to the critical organs of the torso (Figures 7.5 and 7.6). Body armour that protects the wearer from 200 7 Textiles for Military and Law Enforcement Personnel

Figure 7.5 Typical military body armour.

Figure 7.6 Typical police body armour. 7.2 Ballistic and Sharp Weapon Protection 201 fragments, sharp weapons, and low velocity pistol ammunition typically comprises multiple layers of fabrics; if protection from high velocity rifle ammunition is required then hard plates are added to the body armour (Figure 7.7) [14]. Body armour increases the thermo‐physiological loading on the user because of an increase in mass and thickness (bulk) [15]. Helmets usually have a composite shell and provide protection to the brain and brainstem (Figure 7.8) [16, 17]. The fibre types that are used in modern body armour and helmets are synthetic polymer high performance fibres; two main types are ® ® used (i) para‐aramids (e.g. Kevlar and Twaron ) and (ii) ultra‐high‐molecular‐weight ® ® polyethylene (UHMWPE) (e.g. Dyneema and Spectra ). These fibres are high tenacity and high stiffness products. Military body armour typically provides protection from fragments using plain woven para‐aramid fabrics; the amount of layers in the armour will be adjusted as required by the user with respect to mass and protection offered. Some countries use a cross‐ply UHMWPE multilayered solution, i.e. the fibres are arranged perpendicularly in layers with a low‐molecular‐weight layer of polymer between them. High velocity rifle protection for both military and specialized law enforcement personnel is provided by the use of plates which are usually ceramic faced (alumina, silicon carbide, boron carbide)

Figure 7.7 Typical hard armour plates (rifle protection). 202 7 Textiles for Military and Law Enforcement Personnel

Figure 7.8 Typical ballistic helmet.

and composite backed (para‐aramid or UHMWPE); in some cases a 100% cross‐ply UHMWPE plate is used [11, 14]. Law enforcement body armour provides protection from sharp weapons by the use of chainmail or ‘laminated’ fabrics, i.e. single layers of (usually) plain woven para‐aramid fabrics impregnated with a polymer [18]. Protection from pistol ammunition can be provided by a wide range of fabrics, including plain woven para‐aramid, noncrimp para‐aramid, and cross‐ply UHMWPE [18].

7.2.2 Test Methods

Most countries have their own requirements in terms of protection offered by body armour. For example, in the UK, military armour is tested according to NATO STANNAG AEP‐2920 and law enforcement armour is tested according to a Home Office Standard [12, 19]. Protection from fragments for military armour is usually 7.3 Protection from Heat and Flames 203 assessed using standardized steel fragment simulating projectiles (FSPs) because real fragmentation varies in size, shape, and material. The FSP used commonly in the UK is the 1.1 g chisel nosed FSP, but other shapes and masses are defined in AEP‐2920. AEP‐2920 also describes test methods for bullet‐resistant armour. UK police sharp‐ weapon‐resistant armour is typically tested using a standard knife; again, real knives vary in size and shape (including sharpness) (Figure 7.3). Spike‐resistant armour is also available and this is tested using the standard spike (Figure 7.3). Most police officers in the UK wear a sharp‐weapon‐ and ballistic‐resistant armour, the ballistic protection provided is typically from pistol ammunition (e.g. Figure 7.4). Some specialized police officers (e.g. AFOs, SFOs) wear body armour plates that are tested using rifle ammunition (e.g. Figure 7.2).

7.3 Protection from Heat and Flames

7.3.1 Background

Both military personnel and police officers can also be faced with the threat of fire, primarily from petrol bombs, more commonly known as a Molotov cocktail. Over the past decade there have been several cases highlighted in the press. There were reports of an attack on a UK patrol in Basra, Iraq by anti‐British protestors, which resulted in an armoured vehicle being hit by a petrol bomb. Images show one of the soldiers jumping from the vehicle on fire [20]. There were similar incidents of police officers involved in public order policing in Northern Ireland, including one where an officer was struck by a petrol bomb resulting in burning fluid covering his overalls [21]. All these incidents point out the importance of donning flame‐retardant garments by the security personnel.

7.3.2 Mechanisms of Injury

The human body is covered in skin, which is susceptible to heat, leading to various degrees of damage. The prediction of the response of the skin to burns has been modelled and shown to be exponential [22]. A first‐degree, or superficial, burn is classed as reddening of the skin, and typically happens with a 12 °C rise in surface skin temperature. A second‐degree, or mixed depth, burn is deeper and generally results in blistering of the skin. A third‐degree, or full thickness, burn generally extends through the entire skin layers [23]. Fire can cause injury to the body in three ways: ●● Direct burning of the skin due to the flames coming into contact with the flesh, generally having burnt through or melted any clothing layers. ●● Heat transfer via either conducted or radiant heat passing through the clothing layers, necessarily holing the clothing. ●● Steam burns, which although caused predominantly by heat transfer through clothing are exacerbated by moisture speeding up the transfer of heat. 204 7 Textiles for Military and Law Enforcement Personnel

7.3.3 Protective Clothing

UK police have been using protective clothing for use in public disorder situations since the 1980s. This clothing was generally a wool barathea overall that had been treated with a flame‐retardant finish. This would have been worn over the officer’s standard beat duty uniform, which consisted of wool trousers and a cotton shirt. The selection of wool was mainly due to the inherent flame‐retardant properties of wool, including a high ignition temperature, a high limiting oxygen index (LOI) of 25–28%, and a tendency for slow burning and self‐extinguishing [24]. In addition, wool has natural insulating properties which when combined with the wool trousers and cotton shirt help reduce the risk of burns due to heat transfer. The main drawback with this type of garment is the requirement to ensure the flame‐retardant treatment applied to the fabric is maintained as it degrades following washing and from wear and tear. In addition, these treatments generally had to be reactivated after washing by heat, either by tumble drying or ironing with a hot iron. In more recent years, wool barathea overalls have been replaced by overalls made from synthetic inherently flame‐retardant materials (Figure 7.9). The most common of ® ® these in the UK are Nomex and Kermel viscose. Nomex is a flame‐retardant polyamide (meta‐aramid) product produced by DuPont, which has an LOI of 29–30%, making it ideal for flame retardant clothing [24]. It also has benefits over other materials such as glass fibre, which can be woven to produce a garment that has significant issues with skin irritation. Nomex does not burn or melt, but chars, meaning that the flames cannot spread rapidly; however, Nomex can become very brittle, almost paper like, when exposed to high temperatures. Kermel is a polyamide‐imide part of the meta‐aramid family and is designed to withstand very high temperatures (1000 °C) for a few seconds. An alternative version is ® Kermel Tech polyimide‐amide fibre which is designed to withstand high temperature for extended periods of time [25]. The combination of Kermel with viscose, commonly at a ratio of 50/50, is done to improve comfort and flexibility of the finished product. The basic requirement for public order overalls in the UK is to provide a minimum of four seconds of protection, before the rise in heat behind the overalls when tested exceeds 12 °C. In addition to providing flame retardancy, another requirement is that these overalls provide a level of resistance to liquids, with the aim being that the majority of any liquid runs off the material and is not absorbed. This is typically done using a chemical treatment which, as with the treatment for wool barathea, has a limited lifespan and needs to be reactivated after washing. The repellency of these overalls to liquids includes hydrocarbons (petrol), chemicals, both alkaline and acids, and water. Current treatments use C8 fluorocarbons, which are being phased out as part of the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) [26] regulations. Alternatives that are as effective are currently being investigated [27]. Guidance for UK police officers wearing public order overalls is that they should wear them as the outer‐most layer to reduce the risk of creating flammable liquid traps. In addition, they are designed to be loose fitting as this provides an additional air gap between the outer layer of the overall and the body, reducing the rate of heat transfer to the skin, as air is a natural insulator. 7.3 Protection from Heat and Flames 205

Figure 7.9 Flame‐retardant clothing used by police officers.

Within the UK military sphere, the majority of the Multi‐Terrain Pattern (MTP) combat clothing is not inherently flame retardant, with the main emphasis being on environmental comfort. These uniforms are made from a cotton/polyester blend (typically 65/35 mix). UK military personnel deployed during operations in Afghanistan starting in 2001 were provided with clothing commonly known as The Black Bag [28]. Certain roles within the UK armed forces do use flame‐retardant clothing, e.g. Royal Navy personnel for whom it is mandatory to wear flame‐retardant clothing when at sea. The decision on whether to use flame‐retardant clothing within the armed forces is based on a risk assessment of individual roles. The level of protection in this clothing 206 7 Textiles for Military and Law Enforcement Personnel

will be dependent on the role, but may have different requirements in general to that used in public order. It should also be noted that many other civil responders and industries use and deploy flame‐retardant clothing, much of which is based on the same technology and materials used for the police and military.

7.3.4 Test Standards

There are multiple standards for flame‐retardant material and clothing. Some are bespoke to applications, whereas others are related to test methods and are generally referenced from other standards. A list of some of the British, European, international, and American standards for flame‐retardant material and clothing that are extant at the time of publishing are shown in Table 7.1. In addition to these standards, more exist which relate to materials used in the home or office, such as curtains and flooring materials, which are not detailed in the table.

7.4 Chemical, Biological, Radiological, and Nuclear (CBRN) Protective Clothing

Details on the exact protection required for the testing of chemical, biological, radiological, and nuclear (CBRN) clothing worn by law enforcement and military personal are briefly discussed here. A characterization of chemical, biological, and nuclear agents is presented by Turaga, who provides a background understanding of potential threats [29]. The use of CBRN clothing by law enforcement and the military comes with its own issues. The very nature of the role requires the clothing to enable personnel to still perform their required roles, and be operationally effective, e.g. use a firearm or detection equipment. This adds extra challenges when considering the clothing. The challenge of protecting a user from the risk of contamination by liquids or gases chemical, biological, or nuclear in form requires the combination of different types of material properties. An example of where this has been done is with the UK civilian law enforcement CBRN suit, the Civil Responder 1 (CR1). This consists of a multilayer garment, the base layer is known as the Cooler layer, which is designed to help maintain body temperature and encourage the movement of sweat away from the body. The second layer is a one‐piece carbon‐loaded suit with a butyl rubber seal around the neck, wrists, and ankles to provide a tight seal. This second layer is known as the ‘Britannia’. The final and outer layer is another one‐piece permeable layer which is designed to provide a high level of cut, tear, abrasion, and fire resistance. This third layer provides chemical resistance and some vapour protection. It is known as the Peeler [30]. To work as a CBRN protective ensemble, protective boots and gloves are also required, typically made of butyl rubber which forms a seal with the clothing layer. The ensemble is completed with the addition of a suitable respirator, and the whole system is tested to ensure it meets the necessary protection levels (Figure 7.10). The main issues with the CR1 (and all CBRN clothing) are thermo‐physiological loading of the wearer and the time taken to don the suit [31–33]. A newer version of the suit has been developed which is the Swift Responder 3, or ‘quick don’, which is a single‐garment double‐layer fabric which combines the attributes of the CR1 with a decrease in weight and time taken to put on. 7.4 Chemical, Biological, Radiological, and Nuclear (CBRN) Protective Clothing 207

Table 7.1 Standards for flame‐retardant clothing and materials for various applications.

Document Number Description Publisher Publication Date

BS EN 61482‐1‐1:2009 Live working. Protective clothing against BSI 31/07/2010 the thermal hazards of an electric arc. Test methods. Method 1. Determination of the arc rating (ATPV or EBT50) of flame resistant materials for clothing BS 4569:1983 Method of test for ignitability (surface BSI 28/02/1983 flash) of pile fabrics and assemblies having pile on the surface BS 5438:1976 Methods of test for flammability of BSI 30/11/1976 vertically oriented textile fabrics and fabric assemblies subjected to a small igniting flame BS 7175:1989 Methods of test for the ignitability of BSI 31/07/1989 bedcovers and pillows by smouldering and flaming ignition sources BS EN ISO 14116:2015 Protective clothing. Protection against BSI 31/07/2015 flame. Limited flame spread materials, material assemblies and clothing BS EN ISO 15025:2016 Protective clothing. Protection against BSI 31/12/2016 flame. Method of test for limited flame spread ASTM F1506‐15 Standard performance specification for ASTM 01/11/2015 flame resistant and arc rated textile materials for wearing apparel for use by electrical workers exposed to momentary electric arc and related thermal hazards ASTM E2573‐12 Standard practice for specimen ASTM 02/01/2012 preparation and mounting of site‐ fabricated stretch systems to assess surface burning characteristics ASTM E2404‐15A Standard practice for specimen ASTM 06/01/2015 preparation and mounting of textile, paper or polymeric (including vinyl) and wood wall or ceiling coverings, facings and veneers, to assess surface burning characteristics ASTM F1930‐15 Standard test method for evaluation of ASTM 02/01/2015 flame resistant clothing for protection against fire simulations using an instrumented manikin ASTM D6413/ Standard test method for flame ASTM 01/06/2015 D6413M‐15 resistance of textiles (Vertical Test) ASTM D6545‐10 Standard test method for flammability of ASTM 23/08/2010 textiles used in children’s sleepwear

(Continued ) 208 7 Textiles for Military and Law Enforcement Personnel

Table 7.1 (Continued)

Document Number Description Publisher Publication Date

BS EN ISO 6941:2003 Textile fabrics. Burning behaviour. BSI 08/01/2004 Measurement of flame spread properties of vertically oriented specimens BS EN 1624:1999 Textiles and textile products. Burning BSI 15/11/1999 behaviour of industrial and technical textiles. Procedure to determine the flame spread of vertically oriented specimens BS EN 16806‐1:2016 Textiles and textile products. Textiles BSI 31/03/2016 containing phase change materials (PCM). Determination of the heat storage and release capacity BS EN 14878:2007 Textiles. Burning behaviour of children’s BSI 31/07/2007 nightwear. Specification BS EN ISO Textiles. Determination of certain flame BSI 31/03/2016 17881‐1:2016 retardants. Brominated flame retardants BS EN ISO Textiles. Determination of certain flame BSI 31/03/2016 17881‐2:2016 retardants. Phosphorus flame retardants BS EN 1103:2005 Textiles. Fabrics for apparel. Detailed BSI 14/02/2006 procedure to determine the burning behaviour 16/30318704 DC BS EN ISO 18640‐1. Protective clothing BSI 01/07/2016 for fire fighters physiological impact. Part 1. Measurement of coupled heat and mass transfer with the sweating TORSO 16/30318707 DC BS EN ISO 18640‐2. Protective clothing BSI 01/07/2016 for fire fighters physiological impact. Part 2. Determination of physiological heat load caused by protective clothing worn by firefighters ISO 15384:2003 Protective clothing for fire fighters. ISO 15/04/2003 Laboratory test methods and performance requirements for wildland fire fighting BS EN 1486:2007 Protective clothing for fire fighters. Test BSI 31/03/2008 methods and requirements for reflective clothing for specialized fire‐fighting BS ISO 22488:2011 Ships and marine technology. Shipboard BSI 31/07/2011 fire fighters’ outfits (protective clothing, gloves, boots and helmet) BS 7971‐10:2014 Protective clothing and equipment for BSI 28/02/2014 use in violent situations and in training. Coveralls. Requirements and test methods 89/08 HOSDB flame retardant overalls Home 2008 standard for UK police (2008) Office 7.4 Chemical, Biological, Radiological, and Nuclear (CBRN) Protective Clothing 209

Figure 7.10 Police officers working in CR1 (training exercise).

The materials used for chemical and biological clothing typically fall into one of four categories: permeable, semi permeable, selectively permeable, or impermeable [34]. Permeable material allows liquid through at low hydrostatic pressures and is usually treated with a liquid repellent finish and is combined with a sorptive material, such as activated carbon‐impregnated foam or felt to absorb harmful chemical vapours. However, because of its permeability, convective air flow helps with the thermo‐ physiological burden of the wearer. Semi‐permeable materials can be classed as porous or nonporous (solution diffusion membranes). Porous membranes allow for the flow of air and vapours through, but vary depending upon the type of porous membrane: macroporous, microporous, or ultrapor- ous. Nonporous membranes do allow gas vapours to diffuse across it, dependent upon concentration gradient, time, and thickness. An example of a nonporous membrane is ® Gore‐Tex (W.L. Gore & Associates). Impermeable materials include butyl and neoprene, which are in common use in CBRN protective clothing. They provide a barrier to liquids and gases and vapours entering the body. However, their being impermeable means convective airflow cannot occur and the thermo‐physiological burden is high. Selectively permeable materials have the combined properties of impermeable and semipermeable materials, providing a high level of protection, allowing sweat to evaporate without the need for the heavy sorptive layer [34]. 210 7 Textiles for Military and Law Enforcement Personnel

7.5 Functional Finishing

Finishing chemicals can be used to convert a textile material into a technical textile with functional properties. The modification of commodity fibre and fabric properties by innovative finishes could be a cheaper route to high performance than using a high cost fibre with inherent performance properties. There are different types of functional finishes and the right type of finish should be selected, depending on the fibre type of the textile substrate and the desired end use. It is possible to change the performance of the materials used for ballistic and impact protection by the use of additional treatments. Several technological solutions to protect the persons against impacts by chemical finishing exist. At present, the most promising technology is based on the use of shear thickening fluids, which consist mainly of highly concentrated nanoparticles dispersed in liquids. A shear‐ thickening fluid can harden in a few milliseconds, when it encounters mechanical stress or shear and will start behaving like a solid. Their viscosity and surface tension can be regulated in order to adapt the chemical formulation to conventional finishing technologies available in the textile industry. Some other very interesting alternatives to shear‐thickening fluids include ceramic or metallic spray coatings and silicone based dilatant powders. The future of flame retardancy is hindered greatly by environmental and eco‐toxicological considerations, both of the flame‐retardant chemicals and the toxic nature of the by‐products released upon combustion of textile fabrics. Thus, the new flame‐retardant chemistry is based on phosphorus, silicone, and nitrogen compounds. Flame‐retardant overalls used by police in public order situations are also treated with a liquid‐repellent coating to reduce the probability of liquids being absorbed by the material. There is a great interest to develop multifunctional protective textile materials by finishing techniques to counter CBRN threats. Liquid‐repellent coatings are also applied on CBRN protective materials. Aramids can be coated with a water‐repellent finish to help preserve the longevity of the materials if they come into contact with moisture [35].

7.6 Conclusion

Clothing worn by military and law enforcement personnel has to protect the wearer from a wide range of threats faced during their duties. The threats considered in this chapter are ballistic and sharp‐weapon, flame, and CBRN. There is always a compromise between the protection offered to wearers of such personal protective equipment (PPE) and the ability to complete their duties. Optimum design of protective clothing systems requires knowledge of the threats faced, the tasks to be completed, the anthropometric properties of the persons to be protected, the fabrics that might be used, integration with other fabrics and equipment, and knowledge of appropriate clothing and textile sciences manufacturing techniques and test methods. References 211

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18 Horsfall, I. ((2012). Key issues in body armour: threats, materials and design. In: Advances in Military Textiles and Equipment (ed. E. Sparks). Cambridge: Woodhead Publishing / The Textile Institute. 19 The NATO Standardization Office (2015). NATO Standard AEP‐2920: Procedures for the evaluating and classification of personal armour bullet and fragmentation threats Edition A Version 1. Brussels: NATO. 20 BBC. BBC news website 2005. http://news.bbc.co.uk/1/hi/4269672.stm. Accessed 11 October 2018. 21 BBC. BBC news website 2013. http://www.bbc.co.uk/news/uk‐northern‐ ireland‐23378221. Accessed 11 October 2018. 22 Henriques, F.C. and Moritz, A.R. (1946). Studies of thermal injury. The American Journal of Pathology https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1934298/pdf/ amjpathol00501‐0024.pdf. Accessed 11 October 2018. 23 Lee, K.C., Joory, K., and Moiemen, N. (2014). History of burns: The past, present and the future. Burns Trauma 2 (4): 169–180. https://doi.org/10.4103/ 2321‐3868.143620. 24 Cardamone, J. (2013). Flame resistant wool and wool blends. In: Handbook of Fire Resistant Textiles (ed. F. Selcen Kilinic), 245–271. Cambridge: Woodhead Publishing. 25 Kermel (2018). Polyamide‐imide fibres protecting against fire: Kermel. Available at: http://www.kermel.com/fr/Production‐of‐High‐Tech‐non‐flammables‐Fibres‐640. html. Accessed 11 October 2018. 26 HSE (2018). REACH : Registration, Evaluation, Authorisation & Restriction of Chemicals. Available at: http://www.hse.gov.uk/reach/. Accessed 11 October 2018. 27 Blackburn, R. (2015). Sustainable Apparel: Production, Processing and Recycling. https://doi.org/10.1016/C2014‐0‐02597‐X. Accessed 11 October 2018. 28 Defence Clothing Team (DCT) (2018). Clothing for Operations: ‘The Black Bag’. London: Ministry of Defence. Available at: http://anyflip.com/tjtz/klri. Accessed 11 October 2018. 29 Turaga, U., Kendall, R., Singh, V. et al. (2012). Advances in materials for chemical, biological, radiological and nuclear (CBRN) protective clothing. In: Advances in Military Textiles and Personal Equipment (ed. E. Sparks), 260–287. Cambridge: Woodhead Publishing. 30 Remploy (n.d.) Frontliner CBRN Suit. Available at: http://ampsys.com.my/frontliner. pdf. Accessed 11 October 2018. 31 Blacker, S.D. et al. (2013). Physiological responses of police officers during job simulations wearing chemical, biological, radiological and nuclear personal protective equipment. Ergonomics 56 (1): 137–147. https://doi.org/10.1080/00140139.2012. 734335. 32 Ormond, R.B. and Barker, R.L. (2014). Chemical, biological, radiological and nuclear (CBRN) protective clothing. In: Protective Clothing: Managing Thermal Stress (ed. F. Wang and C. Gao), 112–145. Cambridge: Woodhead Publishing / The Textile Institute. References 213

33 Potter, A. et al. (2015). Biophysical characteristics of chemical protective ensembles with and without body armour. Natick, MA: United States Army Medical Research & Materiel Command. 34 Truong, Q. and Wilusz, E. (2008). Chemical and biological protection. In: Military textiles (ed. E. Wilusz), 242–280. Cambridge: Woodhead Publishing. 35 Paul, R. (ed.) (2015). Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Cambridge: Woodhead Publishing.

215

Industrial and Filtration Textiles Tawfik A. Khattab and Hany Helmy

Textile Research Division, National Research Centre, Cairo, Egypt

8.1 Introduction

Technical textiles have been used as filter media. Depending on the filtration purpose, several requirements and standards must be fulfilled for the production of filters. Sometimes it is required to merge different filtration media to better fit the application’s requirements, such as filter fabric and membrane. In addition to such requirements and standards, the environmental impacts and structural design of textile filters and their production technologies are also discussed [1, 2]. High performance textiles are usually employed in filtration to separate and clean industrial goods, gases, and effluents. Therefore, textile filters represent a growing global market, as manufacturing and environmental demands increase. There are five major classes of filtration, which can be best classified as solid–gas, solid–liquid, solid–solid, liquid–liquid, and gas–gas separation. Textile permeability can be defined as the degree to which a fabric allows the flow of specific materials through it. This requires engineering precise characteristics into a functional fabric according to a specific desired outcome and the properties of the solids being filtered. The selection of the fibre and textile materials and their assembly properties are critical to the performance of a specified filter cloth and its processing abilities with a specified slurry composition, the properties of which must be obviously identified and understood to reduce any expected problem, such as filter plugging leading to low durability due to the accumulation of the solids being separated [3]. The different chemical, thermal, and pressure circumstances that are usually available in the various applications of filters have profound effects on the type of polymer used, as well as the target product. The solids being separated also have major effects on the sort of fabric structure in use. When selecting the suitable filter for an application, the properties of the fluid surrounding the filter must be considered, such as their chemical composition, temperature, humidity, and mass flow. Also, the particle properties such as particle size and their size distribution must be taken into consideration [4–7].

8.2 Synthetic and Nanotechnical Fibres

8.2.1 High Performance Synthetic Fibres

A synthetic fibre is a man‐made fibre developed to improve on animal and plant natural fibres. However, all man‐made fibres are not synthetic fibres. For example, nylon and polyester are synthetic fibres, while rayon and cellulose acetate are man‐made fibres but cannot be considered as synthetic fibres. Nylon, modacrylic, olefin, acrylic, and polyester fibres are classified as ‘common synthetic fibres’, while ‘speciality synthetic fibres’ include rayon artificial silk, acrylonitrile rubber, vinyon, vinalon, aramids, Dyneema, polybenzimidazole, polylactic acid, metallic, Zylon, glass, and Derclon. Synthetic fibres are chemically produced by joining monomers into polymers, through a process called polymerization (Figure 8.1). The majority of synthetic and cellulosic based fibres are generated by ‘extrusion’ via forcing such thick, viscous polymer fluid through tiny holes of the spinneret, while cooling, to afford continuous solid thread [8]. In their preliminary state, such fibre forming polymeric materials are in their solid state and therefore must be first transformed into the liquid phase for extrusion. This is generally done by melting, in the case of thermoplastic synthetic polymers, or by applying an appropriate solubilizing solvent to dissolve the polymer, in the case of nonther- moplastic cellulose. If they are not soluble or melted, they have to be chemically functionalized to produce soluble or thermoplastic modified polymer. In the case of polymeric materials that do not melt, dissolve, or afford suitable derivatives, small liquid monomers and additives are mixed in to react to produce these otherwise intracta- ble polymeric materials during the extrusion course. Depending on the synthetic merchandise functional properties, a variety of chemicals can be added to introduce softer, stain‐resistant, wrinkle‐free, flame‐retardant, hydrophobic, or moth‐repellent garments. The above synthetic fibres have been modified and customized for extremely specific end‐users by blending and/or changing specific properties, such as tenacity, length, decitex, surface morphology, finish, etc., to make new hybrid product systems. However, it is the development of the so‐called technical fibres since the early 1980s that has introduced some of the most important and spectacular impulses to the evolution of high performance textiles [9].

Figure 8.1 Structural formula of cellulose acetate. O CH3 O OCH3 O HO O O O HO O CH O 3 O CH3 O n 8.2 Synthetic and Nanotechnical Fibres 217

8.2.2 Nanotechnical Fibres

Nanofibres have received significant attention in different filtration applications. There are a variety of techniques to develop nanofibres, such as conjugate spinning (sea‐island method), chemical vapour deposition, phase separation, self‐assembly, melt‐blowing, and electrospinning. Among those techniques, the electrospinning method is a versatile and broadly accepted process to manufacture textile filters. Nanofibrous materials created from synthetic polymers are favoured to prepare textile filters, although a number of biopolymers have also been considered. Recently, nanofibres have been functionalized with a number of additives to separate gaseous contaminants [10, 11].

8.2.2.1 Filters for Air Pollutants Gaseous pollutants and particulate matter vary in their size and chemical composition. According to inhalable particle diameter, particulate matter is categorized as coarse (between 2.5 and 10 mm), fine (between 0.1 and 2.5 mm), and ultrafine (less than 0.1 mm). A particulate matter filter is thin, light, and highly porous compared to a gas filter, which are usually manufactured from granules of activated carbon with an extremely large surface area. Air filters are typically characterized in terms of their filtration effectiveness, penetration pressure drop, highly penetrating particle size, filter resistance, and quality factor. ‘Filter resistance’ indicates the filter breathability and is mostly related to pressure drop [11].

8.2.2.2 Pollutant Capture Mechanism of Fibrous Filters The air filtration mechanism describes the mode by which contaminants are adsorbed, attached, and captured by the filter medium. It mainly depends on the properties of the filter medium and the nature of contaminants. The filtration mechanisms of particulate matter and gaseous pollutants can be similar physically to some degree but chemically completely different. Filtration by micro‐ or nanofibres is usually controlled by physical factors, including contaminant size, filter geometry, and rate of air flow. The micro‐ and nanofibrous materials can hold the particles physically much smaller than its pore size, which is beyond simply sieving [12]. The filtration mechanisms include diffusion, interception, intermolecular interaction, straining, inertial impaction, gravitation, and electrostatic interaction of particles on the filter surface. Both diffusion and interception are the most significant particle capture mechanisms of nanofibrous filters. Diffusion holds fine particles below 0.5 mm diameter that move randomly, owing to Brownian movement. A particle interception with a nanofibre occurs when the distance between the nanofibre surface and the particle centre is equal to or less than the particle radius. The small fibrous diameter enhances the particle interception efficiency. Particle capture by nanofibrous filter depends on Peclet and Knudsen numbers and the nanofibre packing density. The Peclet number stands for the relative strength between interception and diffusion mechanisms, while the Knudsen number is the ratio of mean free path of air molecules to the particle size. Strong diffusion is accompanied by a decreased Peclet number and an increased Knudsen number. However, such strong diffusion results in high air flow (Figure 8.2) [13]. Therefore, the aerosol retention time on nanofibres gets decreased, leading to inefficient diffusion mechanism. Nanofibre packing density is known as the accumulative mass of nanofibres per unit length. It depends on fibre density and filter thickness. High 218 8 Industrial and Filtration Textiles

Electrostatic attraction

Interception Diffusion

Intertial impact Air Fiber cross section Stream

van der Waal Gravitation interaction Straining

Aerosol particle

Figure 8.2 Particle collection mechanism of fibres.

packing density is a sign of efficient particle capture. Straining takes place in a filter when the particles go through passages between two or more fibres that have dimensions lower than the particle diameter. Straining is a significant capture mechanism. However, in the case of a nanofibrous medium, straining along with intertial impact and gravitation may be less efficient than diffusion and interception. The intermolecular attraction mechanism, also known as Van der Waals forces, holds uncharged particles with a diameter of less than 0.5 mm that move with speeds of less than 0.01 m s−1. The electrostatic interaction mechanism separates particulate particles according to Coulomb’s law. This mechanism is favoured for particulate particles with a diameter range of 0.1 to 1 mm [12]. Physisorption and chemisorption are the two essential separation mechanisms of gaseous contaminants. Physisorption refers to separation at the surface pores of the nanofibrous structure as a result of Van der Waals forces. Nanofibres can have strong intermolecular attraction forces with the gaseous units, owing to a higher surface area, which raises the physisorption ability. Therefore, the nanofibrous filter with a large surface area should be aimed to separate gaseous contaminants. Chemisorption converts contaminants into simple materials via catalytic or noncatalytic reduction. Chemisorption is a highly selective technique compared to physisorption. Such selec- tivity can be enhanced via surface active functionalization of the fibre structure [13].

8.2.2.3 Synthetic Polymers for Technical Nanofibres Synthetic polymers are ideal for the formation of nanofibres via electrospinning towards filter membranes. This is due to the outstanding chemical and thermal stability of synthetic polymers along with controllable fluid properties and simplicity of spinning. Filter membranes can be created from polyamide and polyacrylonitrile (formation). Polyamide is easy to spin because of its short length of di‐acid and di‐amine monomer units. Its fibres are characterized as being suitable for air filtration because of their small diameter, narrow diameter distribution, large surface area, and enhanced dirt‐loading capability along with their high electrostatic charge. Polyamide electrospun nanofibres demonstrated outstanding filtration efficiency that was 250% higher than pristine 8.3 Natural Fibres for Technical Applications 219 clothing, with five times less areal density, and about three times less pressure drop than the marketable glass filter media [14]. Polyacrylonitrile nanomembranes more effectively separated particulate matter and gaseous pollutants than other polymers such as polyamide, polyvinyl pyrrolidine, polystyrene, polyvinyl alcohol, and polypropylene. Its nanofibrous membranes separated pollutants 10 times its own mass, owing to better surface properties, higher single nanofibre separation capacity, and higher dipole moments. Polyacrylonitrile nanofibres are also characterized by high quality tensile strength and moisture vapour transport properties. For other synthetic polymers, the filtration effectiveness and pressure drop of polyvinyl alcohol nanofibrous membranes displayed better characteristics than conventional cotton. Polyurethane based polymers were electrospun to create nanofibres for absorption of volatile organic compounds (VOCs) in air, and were also prepared as protective technical garments against chemical and biological threats [15].

8.2.2.4 Biopolymers for Technical Nanofibres Recently, biopolymers gained attention as matrix materials to produce nanofibrous membranes for textile filters. There are some polymers, such as wool keratin, chitosan, and polylactic acid, that have been electrospun to prepare filter membranes. A limited number of biopolymers have been electrospun for textile filters, because of the difficulty in electrospinning biopolymers. Therefore, biopolymers are usually blended, typically with synthetic polymers, such as keratin/polylactic acid and chitosan/ poly(ethylene oxide) blends to get a uniform nanofibrous diameter with a bead‐free structure [16]. Keratin biopolymer absorbs and removes toxic materials in fluids such as formaldehyde in air and other hazardous VOCs, owing to its unique molecular structure and chemical properties. Electrostatic wool based microfibrous filters remove particulate matter via columbic attraction. Nanofibrous membranes made from chitosan biopolymer possess excellent antimicrobial properties. Chitosan can also afford positive charge on filter fibrous surface and can efficiently neutralize air pollutants by unique physical and chemical methods. Polylactic acid can introduce promising applications such as a respiratory filters, owing to its sustainable and carbon‐neutral nature. An optimized nanostructure composition, made up of 5% of polylactic acid in a 10% solvent, provided the highest quality factor. Biopolymer blended from polylactic acid/polyhydroxybutyrate displayed good mechanical strength, high filtration efficiency, low pressure drop, high dust loading, and dust purification regeneration capacity [17].

8.3 Natural Fibres for Technical Applications

Natural fibres are produced by plants, animals, and geological processes as follows: ●● Plant fibres such as cotton are the cell walls that are located in stem and leaf elements and are composed of cellulose, hemicellulose, lignin, aromatic substances, waxes, lipids, ash, and other water‐soluble materials. The chemistry and structural properties of fibres determine their functionalities and processing efficiencies. ●● Animal fibres include catgut, mohair, silk, wool, angora, and alpaca textile fibres. They normally comprise proteins such as collagen, keratin, and fibroin. 220 8 Industrial and Filtration Textiles

●● Mineral fibres are produced from mineral resources. They could be used in their natural structure or after slight modification. Mineral fibres include metallic fibres, such as aluminium fibres; asbestos that can be modified into serpentine and amphi- boles; or ceramics, such as glass fibres prepared from aluminium oxide, boron carbide, glass wool, quartz, and silicon carbide. Natural fibres can be employed as a constituent of a composite, where the orientation of fibres influences the properties. They can also be matted into sheets to construct goods such as paper, felt, and fabric. The most primitive proof of humans using fibres is the finding of wool and dyed flax fibres. Natural fibres are used for high tech purposes, such as composites for automobiles. Compared to reinforcement of composites with glass fibres, composites with natural fibres are characterized by having less density, improved thermal isolation, and decreased skin irritation. Furthermore, in contrast to glass fibres, natural fibres are biodegradable by bacteria once they are no longer in use [18].

8.3.1 Bast Fibres

Bast fibres – such as ramie, flax, hemp, jute, kenaf, and abaca – are soft wooded fibres, which are produced from the stems or stalks of dicotyledonous natural plants. The fibres are located in bundles or aggregates. The bundles are of 10–25 elementary fibres, 2–5 mm length, and 10–50 μm diameter. The bundles are linked by lateral ramification, creating three‐dimensional (3D) networks. The basic fibrils and bundles are reinforced by lignin and pectin intercellular matter, which have to be eliminated during the processing of fibre extraction. Bast fibres have been used not only in the textile industry but also for modern eco‐friendly composites for building supplies, insulation panels, geotextiles, foodstuff, cosmetics, medicine, and as a resource for other biopolymers [19].

8.3.2 Technical Applications of Natural Fibres

The most common textile fibres available that have been used for technical and industrial applications are cotton and a range of coarser vegetable fibres, such as flax, jute, and sisal. They have been typically used to produce heavy canvas‐type goods, ropes, and twines. They are characterized by comparatively high weight, low resistance to water, microbial, and fungal attack as well as weak flame retardance. Natural fibres are gaining increasing significance in automotive, aerospace, packaging, fibre reinforced composites, and other high performance textiles applications. Natural fibres present excellent specific tensile strength and stiffness, in some cases even better than glass fibres but somewhat similar to synthetic fibres. In addition, they present other advantages including enhanced energy recovery, carbon dioxide sequestration, production simplicity, and production flexibility, and are eco‐friendly and come from renewable natural resources. However, the market demand for natural fibres is also changing, owing to the availability of newer biodegradable polymers, such as polylactic acid prepared from corn. Currently, some other biopolymers have characteristics comparable to their petroleum origin counterparts. To strike a balance between price, quality, performance, ecological regulations, and supply of natural fibres, a number of composites and high performance fabric producers are developing novel facilities for using alternative 8.4 Manufacture of Technical Textiles 221 fibres. The automotive division requires rationally durable materials which must be biodegradable at the ending of their service life [3]. In order to explore value‐added products, it is necessary to understand the value addition during each stage of manufacturing. Usually, very little value addition is achieved in the early stage of the processing chain, for example cultivation, harvesting, fibre extraction, and fibre preparation. The value addition increases further up the chain, particularly in the production of products with functional attributes which can satisfy demanding technical specifications, for example woven fabrics for soil erosion and preforms for reinforced composites or nonwoven fabrics for insulation and filtration. Even still, higher levels of value addition can be achieved when producing products with multifunctional attributes, for example composite panels with thermal and acoustic barriers and roofing products with built‐in photovoltaic cells. Semi‐finished and finished components can provide still higher levels of value addition, for example automotive parts and panels, such as parcel trays and door panels. With the increasing added value across the value‐addition chain, obviously, the technical complexity increases, and this requires careful research interventions and investment in the development process [20]. It is often mentioned that the tensile properties of natural fibres are much lower than that of E‐glass, Kevlar, and carbon fibres. However, the advantage of natural fibres lies in their comparatively lower densities. Therefore, an effective comparison of mechanical properties should be in terms of their specific mechanical properties according to which it is apparent that certain tensile strength of some of the natural fibres, such as flax, kenaf, hemp, and Caraua is quite comparable to that of E‐glass fibres. Therefore, natural‐fibre‐based products clearly provide an opportunity to reduce component weight and are therefore widely used in technical textiles and as reinforcements in composite products for the transportation sector [20].

8.4 Manufacture of Technical Textiles

8.4.1 Electrospinning for Technical Textiles

Principally, electrospinning is a method to manufacture synthetic textile nanofilaments by applying an electric force on a polymer fluid. The electrospinning process was originally patented by Formhals. Taylor mathematically modelled the electrospinning approach to illustrate the effect of electric force on the fluid droplet creating a cone profile, known as the Taylor cone. Electrospinning received real momentum in 1990s mostly due to knowledge progression in nanoscience. Electrospinning is characterized by simplicity and versatility to afford nanofibres and control their shape [21, 22]. In a typical electrospinning system (Figure 8.3), a capillary tube located on a syringe pump containing viscoelastic polymer fluid which could be a polymer dissolved in a solvent or molten form. A high voltage is applied to the polymer fluid enclosed in the capillary tube. Electrically charged polymer fluid overcomes its surface tension, producing a Taylor cone at the needle tip, which elongates in a jet shape towards the grounded collector. The concurrent effect of the jet stretching and solvent evaporation during the jet travel produces nanofibres characterized by a small pore size and high specific surface area with higher ability to capture dust particles on its surface, and 222 8 Industrial and Filtration Textiles

Syringe pump

Syringe containing polymer solution

High voltage power supply Fiber

Grounded collector

Figure 8.3 Diagram displaying an electrospinning setup.

eventually this enhances filtration efficiency compared to microfibrous membranes. Air filtration is the earliest commercial application of electrospun nanofibres such as pulse filters, turbine air filters, and vacuum bag filters. A thin layer of nanofibrous membrane is appropriate for the preparation of filter media for antimicrobial air filters, cabin air filters, and filters for individual protective textiles. Owing to their efficient ability to capture air contaminants, technical textiles from electrospun nanofibres have strong potential in the clean energy, healthcare, and ecological sectors [22, 23].

8.4.2 Effect of Nanofibre Parameters on Air Filtration

The fibre diameter, pore size, surface area, thickness, mass coverage, and structure of the membrane of an air filter can generally be manipulated.

8.4.2.1 Fibre Diameter The fibre diameter has a deep effect on the filtration efficiency. The nanofibre diameter up to 300 nm can be appropriate to achieve more than 99% filtration effectiveness of sodium chloride particles up to 300 nm in size. Reducing the fibre diameter from 300 to 120 nm considerably increases the filtration effectiveness at all levels of mass coverage of nanofibres. For instance, the filtration performance of a polyacrylonitrile based nanofibrous filter increased from 48.21 to 98.11% as the fibre diameter decreased from 1000 to 200 nm. Compared to wider distribution of the same fibre diameter, the lower distribution of fibre diameters can affect the filtration efficiency because it may lead to less pressure drop and normalized thickness. It has been reported that the small diameter nanofibres (less than 100 nm) offer improved aerodynamic slip, where air molecules do not collide with the nanofibres. This slip flow decreases the friction effect, and pressure drop was not increased significantly. The small fibre diameter enhances the filtration performance but with a large pressure drop. The small fibre diameter decreases the 8.4 Manufacture of Technical Textiles 223 pore size by reducing the pore aperture and improves the direct interception effect for particle capture [24].

8.4.2.2 Pore Size Nanofibres can form closed, blind, and through pores in their 3D structure. The closed pores are not accessible, while the blind pores terminate within the intertwined structure itself. Through pores are open and therefore significant for air filtration media. The smaller through pore size can accomplish high filtration performance but adversely affects air permeability and pressure drop of the filter media. The nanofibrous membrane containing both high and small through pore size exhibited more efficient air filtration than the one with only a small pore size of the same thickness. This can be attributed to the less twisting path of air flow compared to less porous membrane, and consequently, highly porous membranes can result in a smaller pressure drop [24].

8.4.2.3 Membrane Thickness and Mass Coverage Membrane thickness is linearly correlated to the electrospinning time. It is directly proportional to pressure drop and reversely proportional to air permeability. A very thin nanofibrous layer of a few microns’ thickness restricts the air flow of the membrane to a large degree. Nanofibrous membrane of comparable thickness and multilayer system increases the filtration efficiency [24].

8.4.3 Yarn Types and Fabric Constructions

There are different types of manufactured yarns to select from when designing a filter fabric, as described below.

8.4.3.1 Monofilaments Being produced from thermoplastic polymeric materials, monofilament based yarns are prepared by the extrusion of molten polymer through a precision engineered die nozzle. On emergence from the extruding point, the polymer melt is cooled, generally in a water bath, and drawn over a series of rollers to orient the molecules and to afford the monofilament with the requested stress strain properties. The bath through which the monofilament passes may also include additives such as lubricants to help in weaving and antistatic agents to prevent shocks during high rapidity warping. The diameters of the monofilaments employed range from 0.1 to 1.0 mm, the small diameters being employed mostly in applications related to candle filters, rotary vacuum disc, filter presses, pressure leaf, and rotary vacuum drum filtration systems. On the other hand, the higher diameters are used largely for coarse filtration purposes, including heavy duty vacuum belt filtration systems and multiroll filter presses [25]. Although usually extruded in circular cross‐section, for particular applications they may also be obtained in flat or oval shapes. The major properties of monofilament cloths (Figure 8.4) involves resistance to blinding, elevated filtrate throughput, and effective cake discharge at the end of the filtration cycle. These properties are ascribed to the smooth surface of the yarn and, in the case of cake discharge, weaving in a satin building can further improve this. On the downside, the spaces that are shaped between adjacent threads and at the interweaving points may prove to be extremely large for the capture of very fine particles, such as colourants, even though the warp threads may be 224 8 Industrial and Filtration Textiles

Figure 8.4 Diagram representing monofilament fabric.

highly dense. For most filtration purposes employing monofilaments, the mostly employed diameters range from 0.15 to 0.35 mm. Heavy‐duty filter belt applications typically use diameters of between 0.3 and 1.0 mm [25].

8.4.3.2 Multifilaments Similar to monofilaments, multifilaments are also extruded throughout a precision engineered die nozzle. However, the die in this case involves many nozzles of much smaller sizes. Furthermore, the substance to be extruded may also be in the shape of a molten polymer or dissolved in a solvent which can be evaporated upon extrusion to be recycled for further use. The threads are drawn so as to orient the molecules and develop suitable tenacity. Producers of multifilament yarns introduce several standard linear densities that, for industrial filtration applications, may range in fineness from 120 to 2200 decitex, with single filaments ranging from 6 to 10 decitex. Multifilament garments are distinguished by their high strength and resistance to stretch, these characteristics being improved as the tenacity of the yarn raises. Multifilament yarns are more flexible compared to monofilaments, leading to easier weaving of the tightest and most effective of all woven garments [26]. In regard of the textiles tightness into which they are often woven, multifilament garments are usually substandard to monofilaments for the sake of throughput, and their resistance against blinding will be also decreased. This is due to the reality that, in addition to the filtration which occurs between adjacent threads, particles are also separated and probably permanently trapped and accumulated in the threads leading to swelling of yarns. The light fabrics may necessitate extra support via fabric backing to prevent damage from abrasive filter plates or possibly to prevent the fabric deformation to the indentations of the plate surface where it would hinder escape of the filtrate. Heavier garments will be employed mostly without support for harder and higher stress‐related purposes, such as filtration belts on vertical automatic filtration presses [26].

8.4.3.3 Fibrillated Tape Yarns These yarns are manufactured from a narrow width polypropylene film split into some components then given a twist to bind the fibres. They could be seen as rather coarse multifilaments, however, as fibrillated tape yarns are much stiffer than the multifilament yarns. They are not usually employed in filter cloths as such but rather in higher 8.5 Functional Finishing 225 open‐weave backing textiles. Therefore, their purpose is to afford protection for the more fragile primary filter fabrics from damaging surfaces, while allowing the free flow of filtrate from the filtration compartment as displayed by mock leno weave [27].

8.4.3.4 Staple‐Fibre Yarns These yarns are manufactured by a continuous extrusion method, then converted into a short staple length. Cotton affords yarns that are rather lean in nature, whereas those from the wool based textiles are more bulky. In addition to their excellent ability to collect particles, fabrics obtained from wool based spun staple‐fibre yarns are distinguished by their resistance to abrasive forces. For filtration applications, the yarns are typically spun with 3.3 decitex fibres in moderately coarse linear densities from 1.3 to 2.5 decitex. Yarn combinations can be presented in different ways, such as multifilament warp/staple based weft yarns and monofilament warp/multifilament fibre weft yarns to result in an enhancement in filtration efficiency, particularly if it is correctly textured. For fabric constructions, plain weave is the basic weave of all woven assemblies and provides the skeleton for the tightest and most rigid single layer filtration fabric. Other woven structures include twill weaves, satin weaves, needlefelts, duplex and semiduplex weaves, and link fabrics [28].

8.5 Functional Finishing

Functional finishing treatments are designed mainly to enhance fabric dimensional stability during use, filtration collection effectiveness, better dust discharge, and resistance to damage due to moisture or chemical agents. A variety of finishing methods are employed to accomplish these objectives, for instance heat setting, singing, raising, calendering, and chemical and plasma treatments. Fabric finishes are designed mainly to guarantee the filtration fabric will exhibit specific characteristics as follows: ●● Stable dimensions during usage. ●● Afford efficient cake release during the cleaning cycle. ●● Convene the fabric’s designed air permeability. ●● Being protected from any chemicals or environmental circumstances.

8.5.1 Heat‐Setting Process

Synthetic fibres and continuous filament yarns usually shrink when subjected to high temperatures. In addition, because of tensions imposed on fibres and yarns during processing or use, additional shrinking is predictable as a result of relaxation effects. Fabric shrinking may lead to too tight filter sleeves on filter cages to result in ineffective cleaning, and in severe cases can yet produce such force as to lift the cages out of the cell plates into which they have been positioned. In order to decrease these effects, textiles are commonly exposed to thermal relaxation or heat‐setting. Enhanced dimensional stability is necessary in order to avoid shrinkage during usage [4]. Fabric shrinking may be caused by the relaxation of tensions applied on fibres and/or yarns during the production process, or could be due to the inherent shrinking properties of the fabric’s raw materials. The thermal circumstances that are frequently found in a dust collector will 226 8 Industrial and Filtration Textiles

encourage fabric relaxation and, if not effectively addressed during fabric production, could result in severe shrinkage problems during use. For instance, in a pulse collector, lateral shrinking could lead to high fabric tightness on the supporting cage, resulting in ineffective cleaning and eventually an undesirable pressure drop. As heat is the major reason of shrinking, it is reasonable that fabric stability should be accomplished by thermal methods. Such a process is generally referred to as ‘heat setting’, and may be performed by surface contact methods via air equipment or stentering. The latter two are favoured because they enable better penetration of heat. This is especially relevant in the needlefelts fabric construction because the scrim is to some degree insulated by the batt fibres. The heat setting technique also increases the density of the structure via increasing the fibre consolidation, which assists in accomplishing a better level of filtration efficiency [29].

8.5.2 Singeing Process

Filter fabrics, particularly needlefelts, which are manufactured from short staple fibres, usually have a surface with protruding fibre ends. Since such protrusions may reduce cake release efficiency by clinging to the dust, it is ordinary practice to eliminate them. This is accomplished by singeing at relatively high speed on a direct gas flame or on a copper plate heater. The direct flame causes the fibres to contract to the fabric surface, forming, in the case of thermoplastic fibres, small hard polymer beads. Singeing speed and gas pressure are usually set depending on polymer category and end‐use preference [30].

8.5.3 Raising Finishing Process

While the singeing approach is intended to denude the fabric of its protruding fibres, the raising technique is considered to generate a fibrous surface, usually on the outlet side of the filter sleeve, to improve the fabric’s dust collection efficiency. Hence, the raising method is intended fundamentally for woven garments containing staple‐fibre yarns. In the raising technique, the fabric is drawn over a sequence of rotating rollers known as pile and counter‐pile covered by card wire and located concentrically on a cylinder of about 1.5 m diameter. Raised fabrics may contain 100% staple‐fibre yarns or a combination of multifilaments/staple‐fibre yarns. The smooth surface introduced by the multifilaments will assist cake discharge, while the raised staple yarns on the reverse surface will improve particle collection capability [31].

8.5.4 Calendering Technique

The calendering process is used to enhance the fabric’s surface smoothness assisting dust release, and to increase the fabric’s filtration capability by controlling its density and permeability, which leads to higher tightness of yarns and fabrics, making it harder for particles to pass through or even into the fabric. Calenders in industry are mainly composed of at least two bowls, one made from chrome plated steel and another from a more flexible matter such as nylon or highly packed cotton or wool fibres. The steel bowl is set with a heat supply such as gas, electric power components, superheated steam, or circulating hot oil. Thus, by changing the processing temperature, pressure, and speed, the required density and level of surface polish can be achieved [32]. 8.6 Textile Reinforced Composite Materials 227

8.5.5 Chemical Treatments

Chemical treatments are usually applied to aid in dust release, particularly where moist sticky dusts, probably containing oil or water vapour, are encountered. Chemical treatments are also used to offer protection from chemically harmful gases. Other chemical treatments are used for more specific applications. For instance, proprietary treatments used to improve yarn‐to‐yarn or fibre‐to‐fibre lubricity during pulse or flex cleaning and likewise, where flammability is a possible risk, padding through commercially available flame‐retardant materials is necessary [33].

8.5.6 Plasma Treatment

Plasma textiles are an innovative category of compressed filters which offer improved submicron particle filtration for particle diameters in the range of 30–300 nm. Unlike conventional inactive respiratory filters, plasma textiles are active filters which can be produced from woven, nonwoven, or knitted garments. Both woven and nonwoven plasma garments offer filtration effectiveness close to 100% for ultrafine particles. Textiles are exposed to plasma in the range from several seconds to a few minutes to afford effective fabrics. Plasma flexible fabrics with embedded electrically conductive wires have been employed as wearable sterile textiles or antiseptic filters. These fabric embedded high voltage electrodes are able to generate in situ room temperature plasma. Well‐designed textiles produce plasma, thus offering reactive species such as free radicals, ions, and excited molecules that are potentially destructive for bacteria [34].

8.6 Textile Reinforced Composite Materials

Fibre reinforced composites for high performance textile filters are increasingly utilized in our daily life. Composites are structurally engineered materials with a high modulus of elasticity able to offer materials with stiffness, high strength, and low weight properties. Technical textile fibres with superior mechanical, thermal, and chemical characteristics have presented a novel generation of composite materials. Given increasing pollution, particularly air and water pollution, and its effects on humans, filtration processes have become more significant. Filtration introduces surface adjustment for better healthcare and a cleaner environment [3, 7]. Air and water filters are very significant, and high performance textile structures are broadly employed for the filtration processes of fluids. Technical textile engineering affords 3D networks of fibres for efficient filtration. The surfaces of such textile fibres capture particles, and consequently fibre surface features are critical to filtration efficiency. A technical fibre owes its efficiency to a composite through the boundary between the matrix and the fibre surface [35]. The most commonly utilized technical fibres for filtration are polyester fibres. They illustrate moderately good strength, are inexpensive, and possess high temperature resistance. However, polyester fibres possess weak resistance to alkalis, acids, and steam. On the other hand, polyester fibres of diverse linear densities and cross‐sectional forms can be manufactured easily. Teflon and glass fibres are utilized for 228 8 Industrial and Filtration Textiles

high‐temperature filtration. Glass fibres are characterized by a strong particle capture capacity, while ceramic fibres are appropriate for hot glass filtration. After polyester, polypropylene is the most broadly used fibre for filtration. It is characterized as a hydrophobic with strong acid, alkali, and abrasion resistance. It is highly appropriate for melt‐ blown and spunbond nonwovens. However, it has a comparatively low melting point [36]. Both Teflon and polypropylene are hydrophobic and possess a nonwettable surface Therefore, they have been used in the filtration of liquid aerosols. These hydrophobic fibres enforce the liquid particles to produce droplets that can be drained and collected. When these droplets reach a critical size they start to oscillate, then break free and pass through the filter. This self‐cleaning feature of the hydrophobic filter surface has significant applications in filtering liquid aerosols because, in the case of wettable surfaces, liquid aerosols adhere to a wettable surface, producing liquid layers around the fibres [36].

8.7 High Performance Applications

In air filtration fabrics, there is a growing interest in combating air pollution. Enhanced media filtration efficiency will be needed in order to meet the current demands, and in traditional dust collection, it is anticipated to see greater use of finer fibres, and fibres of irregular cross‐sectional form, used in the form of surface layers. There is also a growing demand for the use of cartridge filter elements which can be installed either in novel filtration tools or as retrofit units in existing filters. There are three essential types of structures found in fabric dust filters involving woven fabrics, needlefelts, and knitted structures. Both woven fabrics and needlefelts are manufactured in flat form and will necessitate slitting to a suitable width and converting into tubular sleeves, while knitted fabrics may be manufactured directly into a tubular shape [4–7].

8.7.1 Woven Fabrics

Woven fabrics are used mainly in shaking mechanism based filters cloths which may consist of twisted continuous filament yarns, short staple‐fibre yarns, or possibly a combination of both. Weave models may be in the shape of elementary twills or possibly simple satin designs, the latter affording higher flexibility and therefore excellent resistance to flex fatigue and a smoother surface for excellent cake release. The area densities of woven fabric are usually between 200 and 500 gsm [37].

8.7.2 Needlefelts

This category of construction is by far the most common in dust filtration processes, affording an infinitely larger number of pores and facilitating significantly higher filtration velocities than woven filter cloths. On the whole, they are manufactured by needle punching a batt of fibre onto both sides of a woven cloth or scrim. This may be performed in a continuous procedure or by attachment of a pre‐needled batt formed in a separate process [38]. 8.8 Testing Methods and Quality Control 229

8.7.3 Nonwoven Fabrics 8.7.3.1 Spunbonded Fabrics As in synthetic yarn manufacture, spunbonded garments are also formed by extruding molten polymer chip through a spinneret, the difference being that the spinning head or die includes a much larger number of holes. The filaments that come out from the extruder first pass through a quenching region, where they are hardened by jets of cold air. This is followed by high velocity air leading to the orientation of polymer chains and increasing the filament strength [39].

8.7.3.2 Melt‐blown Fabrics In parallel vein to spunbonded garments, melt‐blown textiles are also manufactured by extruding molten polymer chip through a die. The distinction being that in this case the emerging filaments are fibrillated and fractured by a jet of high velocity hot air to afford much finer fibres, ideally 0.5–5 μm. The airflow guides the fibres to a vacuum‐supported mandrel where they produce a fibrous batt, being cooled and solidified followed by secondary air that is drawn into the procedure [40, 41].

8.7.4 Knitted Fabrics

Because of their capability of being manufactured in a seamless tubular structure, weft‐ knitted garments afford an attractive and economic substitute to both woven and needled fabrics. By inlaying suitable yarns into the knitted fabric, the elasticity which is usually coupled to such fabrics can also be controlled and the same may be employed to improve the particle filtration ability [42].

8.8 Testing Methods and Quality Control

8.8.1 General Quality Control Tests

General quality control measurements are usually performed in normal textile laboratories to guarantee that the materials under examination have been made in accordance with design requirements, and to supervise any short‐, medium‐, or long‐term trends. Such examinations are concerned mainly with area and linear densities, fabric structure and type, air permeability, thickness, tensile properties, fabric set, and dimensional stability. Fabric resistance to stretch is of great significance with respect to tensile properties. Although filtration textiles are rarely exposed to forces that will lead to tensile failure, they may undergo a degree of stretch that could have severe consequences [4–7]. Resistance to stretch at low loads (i.e. less than 100 N per 5 cm) is consequently of particular significance from a control point of view. In addition, since shrinkage is temperature dependent, the capability to perform such tests at high temperatures is also useful [43]. Shrinking tests possess a number of forms depending on whether the end‐use is wet or dry. For dust collection purposes, testing fabric’s free shrinkage in an air circulating oven is the standard technique, the time of exposure and temperature changes being dependent on the particular test procedure. By comparison, since it is familiar in liquid 230 8 Industrial and Filtration Textiles

filters for cloths to be removed from the filter and exposed to a laundering process, a laboratory examination has to be devised that will reproduce the mechanically stimu- lated shrinking produced by an industrial tumble washing machine. Such action, by virtue of the weight of cloths included, is unavoidably more severe than a domestic machine. Although examination procedures are available to evaluate the liquid permeability of fabrics (e.g. by calculating the time for a particular volume of water to pass through the fabric), either under gravity (falling column) or at a certain vacuum, it is usually more suitable to quantify the permeability of fabrics by air methods [43, 44].

8.8.2 Performance Related Tests

While the above testing techniques are ideal for regular quality control purposes, they offer very little assistance about the aperture size and consequently the real efficiency of the filter fabric in dealing with particles of identified size. In the case of large mesh monofilament screening cloths, it is likely to determine the aperture size easily via thread diameters and thread spacing. Alternative approaches must be taken with tighter structures. The test of ‘equivalent pore size’ by a bubble point practice is possibly the most popular approach and includes soaking the fabric in an appropriate wetting liquid and then reporting the air pressure that is essential to generate a bubble on the surface. The pore size can be determined from the relationship r = 2 T ¥ 105/sPg, where r is the pore radius (mm), T is the surface tension of the liquid (mNm−1), s is the density of −3 water at the testing temperature (g.cm ), P is the bubble pressure (mm H2O), and g = 981 cm.s−2 [43, 44].

8.8.3 Characterization of the Filtration Efficiency of Nonwovens

Nonwoven filters have not completely uniform structures as screens. The filtration effectiveness of an ideal filter should be the same at each point of its active surface. It is significant to evaluate uniformity of filtration fabric, particularly in the case of nanofibrous filtration systems. Uniformity of a filter depends on mechanical properties, uniformity of fibres, layer thickness, and uniformity of a fibre deposition. In other words, the filter uniformity is the quality gauge of the filtration material. The examination technique investigates filtration material in processing by artificial seeding particles [4–7].

8.8.4 Characterization of Electrospun Nanofibres

It is required to characterize the properties of nanofibres – such as fibre diameter, pore size, surface area, and surface chemistry – to evaluate their effects on air filtration. Generally, nanofibres can be studied according to their geometrical, chemical, and mechanical properties.

8.8.4.1 Geometrical Characterization Both fibre diameter and pore size are significant geometrical properties of nanomembranes that can considerably influence air filtration. The fibre diameter, distribution, orientation, cross‐sectional shape, and surface roughness can be measured using electronic microscopes, such as the scanning electron microscope (SEM) as shown in 8.8 Testing Methods and Quality Control 231

Figure 8.5 Scanning electron microscope image showing the porous structure of random orientation.

Figure 8.5, transmission electron microscopy (TEM), and atomic force microscopy (AFM) followed by image analytical techniques. TEM is most valuable when the nanofibre’s diameter is lower than 300 nm. AFM is a little difficult to be used in the determination of the nanofibre’s diameter precisely, but it is a multipurpose system used to study the surface morphology precisely. Several studies report nanofibre thickness employing SEM images. However, it is hard to prepare a uniform cross‐section of a model from delicate polymer based nanofibrous membrane, unlike microfibres. Therefore, the thickness preciseness determined by SEM is suspicious. Pore size, pore distribution, and porosity can be determined by microscopy and porosimetry techniques. In microscopic systems, SEM, TEM, and AFM images can be employed to determine the pore size on nanofibrous surface. Porosimetric systems involves intrusion (mercury), extrusion (capillary flow), and molecular resolution (known as the Brunauer–Emmett–Teller (BET) analytical technique. The benefit of BET analysis is that it can determine surface area, porosity, pore size, and distribution [45].

8.8.4.2 Chemical Characterization Chemical characterization of nanomaterials can recognize the chemical character of such materials before and after being electrospun. Nuclear magnetic resonance (NMR) and Fourier‐transform infrared (FTIR) spectroscopies can identify the molecular structure of polymers, their reaction with other materials, and the existence of specific additives. The identification of macromolecules and crystalline character of nanomaterials can be considered using X‐ray diffraction (XRD). The dissimilarity in the diffraction peaks can chemically determine different materials exist in the nanofibre membrane. Surface chemistry of nanofibrous membrane can be studied using X‐ray photoelectron spectroscopy (XPS) and water contact angle evaluation. X‐ray photoelectron spectroscopy can quantitatively measure the atomic concentration of elements that exist on the surface of the nanofibrous membrane. The water contact angle investigation of the nanofibrous membrane gives details of the hydrophilic/hydrophobic character 232 8 Industrial and Filtration Textiles

alongside its surface chemistry. The elevated water contact angle of a nanofibrous membrane surface signifies hydrophobic activity which may be valuable in enhancing the antifouling nature of the filter [46].

8.8.4.3 Mechanical Characterization For air fabric filters, elevated tensile strength, and elongation of nanofibrous membranes are enviable to guarantee dimensional stability and durability. In general, nanofibrous membranes, unaccompanied by microfibrous substrate support, have poor mechanical properties and fail to resist the macroscopic effects of air flow. Nanofibrous membranes can be mechanically described employing tensile examination and other approaches such as AFM and dynamic mechanical analysis (DMA). The tensile examination investigates the mechanical properties such as mechanical strength and elongation. The elastic modulus is studied using AFM, while dynamic mechanical analysis identifies the different dynamic moduli of polymers. The tensile strength of nanomembranes can be adjusted by changing their polymer concentration and solvent nature. Sometimes, additives used during the electrospinning process can also enhance the tensile stress, Young’s modulus, elongation, and elastic modulus of the nanofibrous membrane [47].

8.8.5 Standard Testing Methods

There are different standard testing methods for filtration systems [48–51]. Testing appliances can be divided into three major categories: Filtration of combustion appliances

●● Filtration of hot combustion merchandise via filtration materials and self‐cleaning power of filtration elements testing (Standard Methods: ISO 11057, ASTM D6830‐02, VDI/DIN 3926). ●● Testing of hot combustion filtration systems in real circumstances of hot combustion merchandise with no solid particles. Filtration of air

●● Small‐grained filters for atmospheric air via highly efficient filtration elements (Standard Method: EN 1822). ●● Small‐grained filters for atmospheric air via respirators (Standard Method: EN 143). ●● Coarse‐grained filters for atmospheric air (Standard Method: EN 779). ●● Air permeability (Standard Method: EN ISO 9237). Filtration of liquids

●● Porous size determination through the bubble method (according to the Standard ASTM F316‐A3). ●● Dynamic water permeability.

8.9 Sustainability and Ecological Aspects

In the area of air pollution control, there are numerous choices that over the years have become available, such as textile filters whose use has become more significant, owing 8.10 Conclusion 233 to increasing pollution emission. Textile filtration efficiently controls environmental contaminants in either gaseous or liquid streams. In air pollution control systems, fabric filters remove dry particles from gaseous pollution emissions. In water pollution control, fabric filters remove suspended solid contaminants. In solid‐waste disposal, fabric filters concentrate solids, decreasing the landfill area needed [4–6]. Filtration techniques usually decrease air, water, and solid‐waste pollution concurrently. In an air pollution control system, for instance, a fabric filter can remove particles and/or gases from a pollution emission source and may be composed of a rubbing device that removes particulates by impaction and the gases by chemical absorption. The reaction products of gases and chemical materials can create a crystalline sludge. Textile filters may also be employed to remove solids from liquids so that such liquids can be recycled. As a result, sewage slurry does not represent a water pollution crisis. The efficient optimization of a fabric filter would reduce filter problems with waste disposal. Although textile filters are appropriate to remove solids from both gases and liquids, it is important that the filter stays dry when gases are filtered and, similarly, it is advisable to prevent the filter from drying out in liquid filtration. In gaseous systems, numerous solid materials are deliquescent (i.e. they tend to pick up moisture and dissolve in it to some extent), leading to a mudded filter fabric. It is usually not possible to remove this mudded sludge without washing or scraping the filter fabric. If the cake on the fabric filter is allowed to dry during liquid filtration, a decrease in the porosity of the cake as well as a fractional blinding of the filter could result, which could then decrease the rate of consequent filtration [52, 53]. Although technical textile filtration is very significant for pollution reduction, the textile industry itself causes ecological harm, contamination, and resources exhaustion. Production, finishing, and circulation of fibres, yarns, or fabrics are made with the assistance of huge, complicated, expensive machines, and chemicals. Therefore, there is a high probability that materials such as fibre components or chemicals used in processing will escape, during processing, leading to ecological pollution. In addition, efforts to produce finished goods result in spreading impurities into the air, water, and soil, as well as in undesirable noise or visual ugliness. Both air and water pollution influences human health, machines, and even the final product. There is an increased occurrence of harmful health effects, particularly byssinosis, tuberculosis, and asthma due to air pollution. This may be due to harmful gases such as formaldehyde, warfare nerve agents, or other volatile organic materials. Noise pollution arises in, for instance, twisting, spinning, and weaving machinery and transportation systems, while visual pollution is due to waste accumulation at landfill sites or that which is illegally dumped to become an eyesore [54, 55].

8.10 Conclusion

Fabric filters are one of the highly expanding industrial sectors in the technical textile market. The rapid growth of technical textile filtration systems and of their application has generated various opportunities for diverse innovations. Industrial textile filtration processes are found in the manufacture of limitless items that we use in our daily lives, and yet further processes and techniques are emerging which enhance environment protection. This chapter attempts to offer a concise overview of the textile filtration 234 8 Industrial and Filtration Textiles

techniques that are included in industrial separation processes. The chapter also illustrates the nature of textile filter media that are used in diverse operations, their strengths and weaknesses, and the applied finishes used to improve their efficiency.

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Geotextiles and Environmental Protection Textiles Jiří Militký, Rajesh Mishra, and Mohanapriya Venkataraman

Department of Material Engineering, Faculty of Textile Engineering, Technical University of Liberec, Liberec, Czech Republic

9.1 Introduction

Textile use is no longer restricted to apparel and upholstery. Textiles were used in road- way construction in the days of the pharaohs to stabilize roadways and their edges. These early textiles were made of natural fibres, fabrics, or vegetation mixed with soil and used to improve road quality, particularly when roads were made on unstable soil [1]. Geotextiles are one of the fastest‐growing sectors and have proven to be among the most versatile and cost‐effective ground modification materials. Their use has expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal, and hydraulic engineering. They form the major component in the area of geosynthetics, the others being geogrids, geofoams, etc. Geotextiles are permeable fabrics, which are used to filter, reinforce, and separate when working in association with soil. The term ‘geotextile’ comes from ‘geo‐’ meaning earth and ‘textile’ meaning fabric. The American Society for Testing Materials (ASTM), defines geotextile as a permeable geosynthetic comprised solely of textiles. Geotextiles are used with foundation, soil, rock, earth, or any other geotechnical engineering‐related material as an integral part of human‐made projects, structures, or systems, or more simply a permeable textile materials used in contact with soil, rock, earth, or any other geotechnical‐related material that is an integral part of a civil engineering project, structure, or system. Examples of the use of natural fibre for reinforcement can be traced back 3000 years, when Babylonians constructed the ziggurat in Dur‐Kurigalzu (present‐day Aqar‐Quf), and the Great Wall of China, completed around 200 BC, used tamarisk branches mixed with clay. The earliest materials which were used as geotextiles are based on natural fibre. The use of synthetic‐fibre‐based geotextiles in the twentieth century was a revolutionary change. One of the earliest documented cases was a waterfront structure built in Florida in 1958. Then, the first nonwoven (needle‐punched) geotextile was developed in 1968 by the Rhône‐Poulenc company in France and was used in dam construction in France in 1970 [2]. Talking about the serious work in this direction vis‐à‐vis geotextiles, in 1977 Rankilor produced the first ‘design manual’ for geotextiles. It was the first manual for the commercial use of geotextiles [3]. In the 1980s, a significant book was

High Performance Technical Textiles, First Edition. Edited by Roshan Paul. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 240 9 Geotextiles and Environmental Protection Textiles

published by Koerner and Welsh, which was about the work conducted up till then in the United States at an advanced level [3]. This was the time when engineers started doing serious work on geotextiles in their own respective countries. In 1978, the International Geotextile Society was established for the development of geotextile design and its utilization. The society provided a platform for publications, providing exposure of developments to all interested engineers. Once a textile was recognized as a good material for reinforcement, engineers started developing new types of textiles and composites to solve more difficult problems. In 1984–1985, researchers developed the design and use of warp‐knitted fabrics for civil engineering [4]. During the last 20 years, the use of geotextiles increased across the world and advanced developments were made in design for their better performance. The development and usage of geotextiles will only increasing in the coming years.

9.2 Structure and Performance

Different types of textile structures are available for a broad range of geotechnical applications. For such applications, an understanding of the dynamic interaction between the textile structure and the geotechnical environment is very important. Two‐ and three‐dimensional (2D and 3D) fabric structures, methods to weave, multiaxial warp‐ knit structures, and braided structures are some important parameters for developing multifunctional structural geotextiles. A novel method of joining geotextiles by robotic one‐side stitching technology is also interesting. The application of emerging nanofibre technologies is leading to the development of the next generation of geotextiles [5]. The main processes used for technical textiles are weaving, nonwoven, braiding, knitting, tufting, etc. Traditional as well as contemporary fabric structures are increasingly gaining acceptance in industries such as defence, transportation, automobile manufacture, energy, and marine, owing to their attractive specific performances and low cost in use for the technical textiles [6, 7]. Biaxial, triaxial, and more sophisticated multiaxial 3D fabric structures are used as structural elements in these areas [8] (Figure 9.1). Geotextiles are a subset of industrial/technical textiles. There are three types of industrial categories (see Table 9.1). Geotextiles fall into the first and the third categories. For many years, industrial textiles were known as mechanical fabrics as described

Figure 9.1 Geotextiles in use. 9.2 Structure and Performance 241

Table 9.1 Categories of industrial textiles [9].

Composite industrial textiles Textiles prepared by coating, impregnating, laminating, or other processes not normally undertaken within the textile industry Examples of products in this category include reinforced rubber; reinforced plastics, metal, ceramics and carbon matrices; abrasive fabrics; asphalt impregnates; etc. Processing industrial textiles Textile structures used as a component in a manufacturing process Examples include filtration fabrics such as paper‐making felts; polishing fabrics; laundry machine aprons; etc. Direct use industrial textiles Textile structures that are manufactured or incorporated directly into the finished products Examples include awnings, tarpaulins, marine equipment, outdoor furniture, sporting goods, canvas bags, shoe linings, etc. focusing on tyre fabrics, balloon fabrics, and wing fabrics using woven cotton cord as the primary material [10]. Many industrial textiles have traditionally been produced by members of the Canvas Product Association (CPA) in the United States. The diversification of fibre materials and the expansion of applications from awning to geotechnical and other industrial applications, as well as the trend in market globalization in the 1970s, led to the reorganization of the CPA to the Industrial Fabrics Association International (IFAI), which has played an important role in promoting geotextiles [11]. Industrial fibre manufacturers – such as Owens Corning Fiberglas, DuPont, Celanese, Allied, Union Carbide and Dow Corning – played an important role in developing materials and processing technology that supported the growth of the industrial textiles market. According to SANS ISO 10318:2013, geosynthetics are products with several components made from raw material derived from synthetic or natural origins. Components may be in the form of a sheet, a strip, or three‐dimensional structure employed in contact with soil and/or other materials for geotechnical and civil engineering applications. The major members of geosynthetic family are geomats, geonets, geogrids, geocells, geostrips, geoliners, geospacers, geomembranes, geotapes, geotextiles, geocomposites, etc. (see Figure 9.2).

WOVEN, NON_WOVEN, KNITTED GEOMEMBRANES GEOTEXTILES

GEOGRIDS

GEOSYNTHETICS it is a general term, involves a broad range of products

GEONETS, GEOMATS, GEOCELLS GEOCOMPOSITES

Figure 9.2 Geosynthetics family [12]. 242 9 Geotextiles and Environmental Protection Textiles

Main functions of geotextiles are separation, filtration, drainage, and reinforcements. ●● Separation: defined as the introduction of a flexible porous textile placed between dissimilar materials so that the integrity and the functioning of both the materials can remain intact or be improved [12, 13]. It actually acts as a separator between fine soil and crushed stone. The geotextile prevents mixing of the two materials. ●● Filtration: defined as the equilibrium geotextile‐to‐soil system that allows for adequate liquid flow with limited soil loss across the plane of the geotextile over a service lifetime compatible with the application under consideration. Filtration applications are drainage systems beneath highways, retaining wall drainage, landfill leachate collection systems, as silt fences and curtains, and as flexible forms for bags and tubes. ●● Drainage: a geotextile acts as a drain when it acts as a conduit for the movement of liquids or gases in the plane of the geotextile. Geotextile materials which have good filtration and permittivity characteristics can be used for this purpose. ●● Reinforcements: a geotextile can be used as reinforcement material when the stability of the road is not good. To reinforce embankments and retaining structures, a woven geotextile is recommended because it can provide great strength at small strains. Although there are numerous textile structures suitable for geotechnical applications, a textile structure is not a geotextile until the interaction of the fabric with soil or the geotechnical environment is considered a total system [12]. Observing the lack of understanding at the time on the importance of soil–fabric interaction, it was pointed out that almost every geotextile application is multifunctional, involving separation, reinforcement, and drainage; and that fabric forming deals with water and its proper dissipation [14, 15]. This feature underscores the necessity of determining a given fabric’s hydraulic properties – more specifically, its flow rate, permeability, or permittivity (permeability divided by thickness). Towards this end, many organizations have recommended test methods and specifications for the laboratory determination of these fabric properties. It should be noted, however, that these procedures are generally for the fabric alone, e.g. ASTM’s Standard Method for Testing the Water Permeability of Geotextiles – Permittivity Method, as proposed by the Subcommittee D13.61 on Geotextiles. While of interest in comparing one fabric to another, these tests have no indication of the hydraulic behaviour of the combined soil–fabric system. Researchers went on to explain that, as soon as soil is placed adjacent to the fabric, it is seen that the soil’s hydraulic properties dominate the initial behaviour of the system [12, 16, 17]. Only after a period of time does the fabric begin to play a role and, ideally, not at all in the long‐term, e.g. when a properly designed configuration exists. In this latter instance, the flow passing through the soil/fabric system becomes constant and an equilibrium situation exists thereafter. To verify and quantify these long‐term hydraulic behaviours, a simple test for various soil/fabric systems was established. This system consists of water at a constant head, flowed downward through the soil, then through the fabric and out of the system where it is collected and a flow rate is calculated [2]. Design of geotextiles is described in many publications [18–24]. The porosity of geotextiles is here one of most important parameters. Fabric performance characteristics are a result of the interaction between fibre (material properties), yarn and fabric geometry, and finishing treatment. Textile structures in fabric form (produced by yarn‐to‐fabric such as woven and knitted fabrics or 9.3 Fibres for Geotextiles 243 fibre‐to‐fabric processes such as nonwoven fabrics) can be characterized in terms of geometric and performance properties. Performance maps provide an overview of the range of behaviours of various fabrics as a function of four geometric parameters and four performance parameters [25]. The geometric parameters include: ●● Porosity: the amount of open space in a unit volume of the fabric. As the fibre diameter and yarn diameter increase, the structure tends to be porous. The porosity of a fabric is inversely proportional to the areal coverage or cover factor of a fabric. A porous fabric tends to be lighter and more permeable. The permeability k of nonwoven geotextiles is nonlinear function of their porosity P, k ≈ P3/(1 ‐ P)2 [18]. Woven and knitted structures are generally worse in comparison with nonwovens because some pores are larger, which leads to the unwanted increase of air permeability. Nonwoven structures can be tailor‐made by simple modification of fabrication process. Especially perpendicularly laid structures of the ROTIS (rotary instrument) type can be prepared in huge variation of porosities, owing to the changing density of waves. ●● Surface texture: the surface geometry of a fabric is characterized by the smoothness of the surface, which in turn is governed by fibre and yarn diameter. Modular length of fibre or yarn is the essential geometric repeating unit in fabrics. ●● Voluminosity: a reflection of the bulkiness of a fabric for a given areal density (mass per unit area). A fabric tends to be more voluminous if the fibre/yarn diameter is larger and the freedom of fibre mobility in the geometric repeating unit is high. Voluminosity is directly related to fibre thickness in that a voluminous fabric tends to be thick. ●● Thickness of the fabric: similar to voluminosity, fabric thickness is related to fibre and yarn diameter. The larger the fibre and yarn diameter, the thicker and bulkier the fabric [18].

9.3 Fibres for Geotextiles

Polymeric fibres have a typical fibrous structure characterized by the hierarchy of bundles of a long thin element (molecular chains, microfibrils, macrofibrils) oriented pref- erably in the fibre axis direction and having more or less ordered 3D arrangements (semicrystalline state). Owing to these special structural arrangements, fibres have strong anisotropy of physical and mechanical properties and extraordinary good mechanical/physical properties in fibrous axis direction in comparison with plastics of the same chemical composition. A typical feature of fibres is the cooperative character of deformation where the deformation process acts on the group of molecular chains (elements) together. Textile fibres have special organoleptic properties (lustre, hand), technological properties (length, strength, crimp, surface roughness, etc.), and utility properties (sorption, ability to stabilize form, abrasion resistance, etc.). The majority of these properties are changed, because of ageing, weathering, or environmental degradation, which is important especially when these processes are long term and intensive, as in the case of geotextiles. Here, the soil itself is responsible for the combined chemical, physical, and microbial 244 9 Geotextiles and Environmental Protection Textiles

degradation (see Section 9.4). The textile fibres can be divided according to their preparation and source of raw polymers into four groups: ●● Natural fibres: prepared by nature from natural polymers. ●● Man‐made fibres: prepared artificially from natural polymers. ●● Synthetic fibres: prepared artificially from synthetic polymers. ●● Nonpolymeric fibres: prepared from nonpolymeric materials. The internal structure of a fibre is determined by the orientation of polymeric chains along the fibre axis. Orientation in natural fibres is caused by biological requirements during their growth. The molecular alignment is an inherent characteristic of fibre (it is often significantly different in different morphological parts of natural fibres) and is commonly stable. Within the groups of cellulosic fibres, ramie and jute both have an extremely high degree of fibrils orientation, whereas that of cotton is much lower. In cotton the chains are helically oriented. The orientation of synthetic fibres is started during the spinning stage. After spinning, fibres are progressively elongated in the fibre axis direction during fibre drawing. Polymeric chains are oriented and partial crystallization occurs, resulting in drawn fibre. Drawing ratio, i.e. ratio between length of drawn and undrawn fibre, is usually 3–5 (standard fibres) or in special cases as much as 10. Spinning ability can be characterized by natural draw ratio λp, which is dependent on temperature and rate of deformation.

●● Stiff polymers (polystyrene, aramids) have λp = 1.5–2.5 (as for viscose). ●● Semicrystalline polymers with lower stiffness, for example polyamide (PA) and polyester (PES), have λp = 3–5. ●● High crystalline, flexible polymers (polypropylene [PP], polyethylene [PE]) have λp = 5–10. ●● For gel spinning of PE is λp = 50 and more.

Polymeric chains in undrawn fibres are randomly oriented, i.e. only 33% lie in the fibre axis direction. Polymeric chains in drawn fibre are mainly oriented to the fibre axis (around 80–90% of chains are oriented in the fibre axis direction). Drawing is therefore responsible for increasing fibre strength, decreasing deformation at break, and formation of proper fibre structure (fibrillar) structure. For geotextiles the cheaper fibres are commonly used. Durability and degradation in soil aspects are usually not the main issues.

9.3.1 Natural Fibres

The commercially important natural fibres for geotextiles are based on cellulose (vegetable fibres) extracted from different part of plants. Typical vegetable fibres are: ●● Seed fibres (fibres cover seeds): cotton. ●● Fruit fibres (nuts are covered by fibres): kapok, coir. ●● Bast fibres (fibre bundles lie between the outer bark and the woody core of the stem): flax, hemp, jute, ramie, kenaf, nettle, sugar cane, bamboo. ●● Leaf fibres (fibre bundles are located in the leaf’s tissue): sisal, abaca (Manila hemp), agave, pineapple, aloe, cabuya. 9.3 Fibres for Geotextiles 245

A major part of these fibres is cellulose, one of the most abundant materials in nature. It is a renewable and biodegradable material, available widely and at low cost, with a low‐energy consumption profile and good mechanical properties, such as high modulus. Another advantage of cellulose is the creation of long fibrous cells, which can be aligned and oriented easily [19, 20]. Cellulose is polyalcohol, having one primary and two secondary −OH groups. In backbone are ether bonds (glycoside link) −C−O−C−. − − − Contracted notation is cel OH or cel (OH)3. The OH groups are the sites for creation of hydrogen bonds and some chemical reactions, such as esterification. Cellulose chains are connected by various systems of hydrogen bonds, which have a significant influence on properties (see Figure 9.3). These bonds are responsible for the limited solubility of cellulose in most solvents, the swelling in water, the reactivity of the hydroxyl groups, and morphological features (crystallinity). Cellulose also contains hydrophobic areas (around the C atoms) that have partial influence on the overall solubility. Intermolecular hydrogen bonds are responsible for the strong interaction between cellulose chains. These bonds are produced between adjacent cellulose macromolecules located along the (002) plane in the crystal lattice of cellulose I (native cellulose), mainly between the oxygen atom in C3 and − the OH at C6 [21]. Together, the hydrogen bonding, weak C–H–O bonds, and hydrophobic interactions are responsible for the assembly of cellulose in layers [22]. The density of α‐cellulose is about 1560 kg m−3. Well‐aligned bundles of cellulose chains are creating crystalline nanofibrils [23]. The main building element of vegetable fibres is the cellulose microfibrils aligned mainly along the fibre axis, which ensure maximum tensile and flexural strengths, in addition to improved rigidity (high initial modulus) [24]. The main components of vegetable fibres are cellulose (α‐cellulose), hemicellulose, lignin, pectin, and waxes. These fibres can be considered to be composites of cellulose fibrils held together by a lignin and hemicellulose matrix. The amorphous matrix phase in a cell wall is very complex and consists of hemicellulose, lignin, and in some cases pectin [26]. Schematic structure of these constituents are shown in Figure 9.4. The typical content of these constituents in typical fibres used commonly for geotextiles is shown in Table 9.2. Lignin is a complex thermoplastic hydrocarbon based, 3D copolymer with both aliphatic and aromatic constituents, and is shown in Figure 9.5. Hydroxyl, methoxy, and carbonyl groups have been identified. The density of lignin is about 1260 kg m−3 and the initial modulus is 5.9 GPa [27]. Lignin is fully insoluble in most solvents and cannot be broken down to monomeric units. Lignin is totally amorphous and hydrophobic in nature. It has a glass transition temperature of around 90 °C and a melting point of around 170 °C. It is the compound

H H H O H O 6 O H O 5 H H O H O 4 O O O O 1 O O O O O O O O 3 2 O O O H O H O H O H O H H H

Figure 9.3 Cellulosic chain with hydrogen bonds [21]. 246 9 Geotextiles and Environmental Protection Textiles

CH OH OH CH2OH 2 O HO O O O O O HO O HO OH CH2OH OH Cellulose

OH O HO O O O O O HO O HO OH OH Hemicellulose

O O OH COOH OH HO O HO

O O COOCH3 HO OH COOCH O O 3 Pectin

O CH=CH—CH2OH

H3CO H H OCH3 C O O

OCH3 Lignin

Figure 9.4 Schematic structure of vegetable fibres constituents.

Table 9.2 Typical composition of selected vegetable fibres.

Fibre type Cellulose (wt. %) Hemi cellulose (wt. %) Lignin (wt. %) Pectin (wt. %)

Bamboo 26–43 15–26 21–31 — Flax 60–81 14–19 2–3 0.9 Hemp 70–92 18–22 3–5 0.9 Sisal 43–78 10–13 4–12 0.8–2 Jute 51–84 12–20 5–13 0.2 9.3 Fibres for Geotextiles 247

OH O

O OH HC OH HO O O CH3 OH

H3C O O O OH O O OH

HO O OH

Figure 9.5 Structure of lignin.

that gives rigidity to the plants. One of the basic units of lignin is 3‐(4‐hydroxyphenyl) prop‐2‐methoxy‐eneol group in the ortho position of the phenol ring (Figure 9.6). Lignin can be used also as a replacement for phenol in the preparation of phenol‐ formaldehyde resins. It is not hydrolysed by acids, but soluble in hot alkali, readily oxi- dized, and easily condensable with phenol. Lignin can be removed from fibres by chlorination forming a complex chloro‐lignin, which is soluble, like hemicellulose in dilute alkalis. In some vegetable fibres there is degradation or removal of lignin accompanied by evolving of very short ultimate fibres in the form of ‘dust’ (e.g. in the case of jute). Lignin is a macromolecular framework that is difficult to degrade, even by microorganisms. Only ligninolytic microorganisms can do it. It is beneficial, especially for geotextiles, because of its durability in soil is longer. Pectin (see Figure 9.7) consisting of polysaccharides is characterized by a high content of glucuronic acid and the corresponding methyl ester, and partially also the acetyl ester. Component D‐galacturonic acid is combined with D‐galactose and L‐arabinose. They give plants flexibility. Pectin can be removed readily in alkalis and it is sensitive to microbial attack and enzymes (pectinases). Soil degradation is easy.

Figure 9.6 Basic unit of lignin. OH

R1 R2 R1, R2 : OMe, H OH

3-(4-hydroxy phenyl) prop-2-eneol 248 9 Geotextiles and Environmental Protection Textiles

Plant Cell Wall Middle Structure Lamella

Primary Pectin Cell Wall

Cross-Linking Glycan Plasma Cellulose Membrane Micro brils

Figure 9.7 Schematic arrangement of primary wall [28].

Hemicelluloses (see Figure 9.7) are characterized by irregularities in the chains. They consist mainly of low molecular chains composed of hexoses, pentoses, and parts of uronic acids. Single chains contain D‐xylose portions as well. Branched portions consist of both a D‐xylose component as well as components of glucuronic acid and the corresponding methyl ester. Density of hemicelluloses is about 1450 kg m−3 and the initial modulus is 8.4 GPa [29]. Hemicelluloses differ from cellulose in three aspects: ●● They contain several different sugar units, whereas cellulose contains only 1,4–β‐d‐ glucopyranose units. ●● They exhibit a considerable degree of chain branching containing pendant side groups giving rise to its noncrystalline nature, whereas cellulose is a linear polymer. ●● The degree of polymerization (DP) of hemicellulose is around 50–200 [30]. This is 10–100 times lower than native cellulose. Hemicelluloses are very hydrophilic, soluble in alkali, and easily hydrolysed in acids. Waxes make up the last part of fibres and they consist of different types of alcohols. Cotton fibres are in fact single‐cell, while other fibres are multi‐cell connected by natural glues (pectin and lignin). The majority of natural fibres can be then considered as naturally occurring composites of cellulose microfibrils in a matrix of intertwined hemicellulose and lignin or pectin [31]. Hemicellulose and lignin matrix is called lignin–carbohydrate complex (LCC) and cellulose glued by pectin mainly is called pecto‐cellulose complex (PCC). The density of LCC is about 1340 kg m−3 and initial modulus is 6.93 GPa [32]. The average electrostatic energies between cellulose microfibril faces and hemicellulose, LCC and lignin are 38, 57, and 58 mJ m−2, respectively, and the average van der Waals energies between cellulose microfibril faces hemicellulose, LCC, and lignin are 44, 76, and 95 mJ m−2, respectively. Lignin van der Waals energy is therefore around 116% higher than that of hemicellulose, whereas the electrostatic energy is higher by about 50%. The superiority of lignin adhesion energies to cellulose comes from the relatively higher van der Waals energies [33]. 9.3 Fibres for Geotextiles 249

Many plant cells have a primary cell wall, which accommodates the cell as it grows, and a secondary cell wall they develop inside the primary wall after the cell has stopped growing. The main chemical components of the primary plant cell wall are cellulose in the form of organized microfibrils (see Figure 9.7). The cell wall contains two groups of branched polysaccharides, the pectins, and cross‐linking glycans (derivatives of polysaccharides [34]). Cellulose microfibrils cross‐linked by glycans increase the tensile strength of the cellulose, and a network of pectins provides the cell wall with the ability to resist compression. In addition to these networks, a small amount of protein can be found in all plant primary cell walls [35]. In the secondary cell wall additional substances, especially lignin, are often found. Lignin also makes plant cell walls less vulnerable to attack by fungi or bacteria. Bast fibre (e.g. flax, jute, and hemp) bundles are located in the outer layer of the stem. Their cross‐sections consist of 10–40 elementary fibres glued together with pectin and/ or lignin. The length of the elementary fibres varies between 5 and 55 mm and the thickness is about 20 μm. Bast fibres have a thicker cell wall and a smaller lumen. Common features of bast and other vegetable fibres are:

●● Technical fibres are multi‐cell, consisting of a series of elementary (ultimate) fibres bonded by pectins or lignin. ●● The fibres have a similar chemical composition: cellulose 65–85%; waxes, 2–4%; pectins, hemicelluloses from 2 to 10%; lignin from 1 to 20%; humidity 10%. ●● The fibres have a similar microscopic appearance. ●● The fibres have similar properties. They are strong enough (wet strength is higher), have low deformation at break, and are resistant to both freshwater and saltwater.

The plants, technical fibres bundles and surface structure of fibres for selected vegetable fibres are shown in Figure 9.8. The selected vegetable fibre crystallinity and an average polymerization degree of cellulose of different origin are given in the Table 9.3. Lowest polymerization degree is in case of bamboo fibre. Polymerization degree is directly connected with strength and resistance to external influences. The selected physical parameters of some vegetable fibres are given in Table 9.4. Low fibre density compared with the density of the cellulose 1560 kg m−3 indicates their porosity and the presence of lignin.

(P) (B) (P) (B) (P) (B)

(S) (S) (S)

(a) (b) (c)

Figure 9.8 Plant (P); a bundle (B), and SEM surface (S) for the sisal (a), jute (b), and bamboo (c) fibres [36]. 250 9 Geotextiles and Environmental Protection Textiles

Table 9.3 Crystallinity and cellulose polymerization degree of selected vegetable fibres.

Fibre Hemp Sisal Jute Flax Bamboo

Crystallinity (%) 88 71 72 91 70–75 Polymerization degree of 1170 4500 1123 2801 891 cellulose

Table 9.4 Selected physical parameters of some vegetable fibres.

Fibre Density (kg m−3) Moisture regain at 65% RH (%) Porosity (%)

Flax 1540 12 10 Jute 1500 13.8 14–15 Hemp 1480 12 11 Sisal 1200–1450 14 17 Bamboo 850–1100 6–8 High

It is evident that the highest porosity and content of lignin is to be found in bamboo fibre. The density of fibre without pores ρ composed from weight fraction wC of α‐cellulose (density ρC), weight fraction wH of hemicelluloses (density ρH), weight fraction wL of lignin (density ρL), and weight fraction wP of pectin (density ρP) is in fact weighted harmonic mean, i.e.

1 wwC H wwL P (9.1) C H L P

If the density of fibre with pores is equal to ρf, it is simple to calculate the fibre poros- −3 ity Pf (neglecting the air density around 1 kg m ) from Eq. (9.1). In the majority of vegetable fibres, technical fibres are composed from many ultimate (elementary) fibres. Especially the bast fibres, where ultimate fibres are glued by pectin mainly and are relatively strong (wet strength is higher) with low deformation at break and better degradation resistance to the normal water and seawater. Ultimate (elementary) vegetable fibres form long elongated cells, sealed at the ends, and have typically lumen, i.e. a central channel. It can be seen that only for flax and hemp are ultimate fibres sufficiently long and soft for textile processing. For other fibres, it is necessary for textile processing (spinning) to use technical fibres (bundles of ultimate fibres glued by pectin or lignin). Lignin (particularly in bamboo and jute) causes an increased stiffness of technical fibres, which limits their use for textile purposes but can be beneficial for some geotextiles. The most abundantly used multicellular cellulose fibre is flax (3–6 cells constitute a fibre cross‐section). Each fibre consists of cells cemented together by wax, pectin, and hemicelluloses (see Figure 9.9). Dimensions of elementary (ultimate) bast fibres are given in Table 9.5. It can be clearly seen from this table that these dimensions are too small for spinning some bast fibres. The elementary flax fibre dimensions are comparable with cotton and therefore can be 9.3 Fibres for Geotextiles 251

(a) (b)

Figure 9.9 Bundle of ultimate flax fibres (a) glued by pectin, (b) after removal of pectin.

Table 9.5 Ultimate fibre dimensions of some vegetable fibres.

Average length Range of lengths Average width Range of widths Fibre (mm) (mm) (μm) (μm)

Flax 33 9–70 19 5–38 Jute 2 1–5 20 10–25 Hemp 25 5–55 25 10–51 Sisal 3 1–8 20 8–41 Bamboo 2.7 1.5–4.4 14 7–27 used for direct spinning. The process of preparing elementary flax fibres is called cottonization. The geometrical characteristics of selected technical vegetable fibres are shown in Table 9.6. Mechanical properties of selected vegetable fibres are summarized in Table 9.7. It can be clearly seen from the table that the flax fibres have the best tensile properties. Their application in geotextiles is often limited, owing to relatively quick degradation in soils. Most common fibres in geotextiles are jute, flax, coconut matting, and straw. Every fibre is used with reference to its specific properties. Jute is easily degradable when it absorbs moisture so this is mostly used on seashores to give wind shield to small trees till they are mature. By the time trees grow larger, jute shielding is degraded and the cover of jute is removed automatically to give way to the growing tree. In general, natural fibres are used in geotextiles for short‐term applications only (see Section 9.4).

9.3.2 Synthetic Fibres

Geotextiles are commonly made from PP, polyester, polyethylene, polyamide (nylon), polyvinylidene chloride. PP is the most used fibre because its water sorption is approximately equal to zero and its degradation in soil is very slow. For the production of PP fibres, only isotactic PP is suitable. The space helix of polymer chains is here due to − presence of voluminous side CH3 group. Helix unit is composed from three monomer 252 9 Geotextiles and Environmental Protection Textiles

Table 9.6 Geometrical characteristics of selected technical vegetable fibres.

Fibre Length (mm) Diameter (mm) Fineness (tex)

Flax 200–1400 0.04–0.62 0.18–2 Jute 1500–3600 0.03–0.14 1.4–3 Hemp 1000–3000 0.16 0.34–2.2 Sisal 600–1000 0.1–0.46 2–40 Bamboo 60–80 0.5–0.6 3.5

Table 9.7 Mechanical properties of selected vegetable fibres [37].

Deformation at Fibre Strength (MPa) break (%) Modulus (GPa)

Flax 345–2000 1.6–3 27.5–85 Jute 393–773 1.7 10–30 Hemp 368–800 1.6 17–70 Sisal 350–700 2–7 9–22 Bamboo 140–230 2.8–4 11–17

−3 units (gauche). Glass transition temperature is Tg = −10 to 0 °C, density is 900 kg m , and melting temperature is Tm = 165 °C. The moisture content is only 0.05%. Preparation of isotactic PP was first described in 1954 (Natta). The principle involves the coordina- tion stereospecific polymerization of propylene with special catalyst TiCl3, Al(C2 H5)3 (Ziegler – Natta catalyst). Polymerization at 100 °C and pressure 3 MPa leads to highly crystalline isotactic PP. Molecular mass of polymer before spinning Mn = 100 000– 600 000 and the molecular mass of fibre is 50 000–250 000. Industrial production of PP fibre Meraklon IT (Montecatini) started in 1960. Standard process of PP fibres preparation consists of three steps:

●● Melt spinning in inert atmosphere (PP melt is sensitive to O2). ●● Cooling in the long cooling tube, owing to low temperature conductivity of polypropylene (PP). Undrawn fibre contains about 70% of crystalline phase. ●● Cold drawing (with neck) to draw ratio 3–5. Crystallinity degree of drawn fibres is about 70–80%. Microvoids may appear depending on the drawing temperature. Drawn fibre is characterized by high orientation of crystalline phase fc = 0.98 but very low orientation of amorphous phase fa = 0.2–0.4. Structural features are microvoids (20%), tie chains (3%), crystalline phase (70%), and amorphous phase (7%). Setting (stabilization) at 130 °C in free‐state (shrinkage till 40%) leads to the improvement of recovery properties. The properties of PP fibres differ substantially from common synthetic fibres. They are hydrophobic and practically do not have any group capable to water bonding. PP fibres show excellent chemical resistance. A low glass transition temperature and melting point is not essential for geotextiles. Bacterial resistance is also excellent for 9.3 Fibres for Geotextiles 253

PP fibres. PP fibres show brittleness, low mechanical performance, and low impact because of their high crystallinity. Sewing thread for geotextiles is made from Kevlar or any of the above polymers. The physical properties of these materials can be varied by changing the condition of drawing and heat setting or by the use of additives. Yarns may be composed of very long fibres (filaments) or relatively short pieces cut from filaments (i.e. staple fibre).

9.3.3 Nonpolymeric Fibres

Some geotextiles are made from fibreglass or basalt mainly, or these materials are used in preparation of hybrid structures in combination with natural fibres (see Section 9.4). Mineral fibres from basalt are not new, but their suitability as reinforcement in composites or in hybrid woven structures is a relatively new issue. Basalt fibres have good physical and chemical properties, as well as good adhesion to metals, epoxies, and glues. Basalts also exhibit excellent thermal, electrical, and acoustic insulation properties. Owing to all these favourable properties, basalt fibre can be used in several applications in technical textiles. Basalt fibre density is 2733 kg m−3 and has a softening temperature of about 960 °C. The diameter of standard fibres is around 9–12 μm. Glass transition temperature from thermomechanical curves is Tg = 596 °C. Axial thermal expansion under Tg is −6 −1 −6 −1 a1 = 4.9·10 deg and above Tg is a2 = 19.1·10 deg . The shear modulus of basalt fibres is about 21.76 GPa. The modulus of elasticity in the axial compression is 112 GPa [38]. From the cross‐section of broken fibres (see Figure 9.10), the brittle fracture caused by structure heterogeneities is evident. Basalt has excellent stability in soil and it is not attacked by microorganisms. Basic physical and mechanical properties of basalt fibres and a comparison with different other commercial fibres are depicted in Table 9.3, which shows that basalt has an excellent tensile strength and also a good modulus. Regarding mechanical properties, basalt fibres are positioned between E‐glass fibres and S2‐glass fibres. Researchers investigated the mechanical properties of glass fibre, short basalt fibre, and continuous basalt fibre from different manufacturers [39]. They concluded that all tested fibres

Figure 9.10 Cross‐section of broken basalt fibre. 254 9 Geotextiles and Environmental Protection Textiles

Table 9.8 Physical and tensile properties of basalt, glass, and carbon fibres.

Properties Basalt E‐Glass S2‐Glass Carbon

Density (kg m−3) 2630–2800 2540–2570 2540 1780–1950 Filament diameter (μm) 6–21 6–21 6–21 5–15 Single filament tensile strength (MPa) 3000–4840 3100–3800 4020–4650 3500–6000 Initial modulus (GPa) 93–110 72.5–75.5 83–97/86 230–600 Elongation at break (%) 3.1–6 4.7 5.3 1.5–2.0

have a rigid behaviour, without plastic deformation. The tensile modulus and strength of continuous basalt fibres and glass fibres are quite similar, while short basalt fibres are considerably less stiff. The joint SiO2 and Al2O3 content (denominated as ceramic‐like materials) of basalt fibres shows correlation with the tensile properties of fibres. It was noted that continuous basalt fibres were competitive with glass fibres and short basalt fibres were weaker in terms of mechanical properties. Physical and tensile properties of basalt, glass, and carbon fibres are summarized in Table 9.8. It is known that the fibrous fragments with a diameter of 1.5 μm or less and a length of 8 μm or greater should be handled and disposed of using the widely accepted procedures for asbestos. The experimental data of basalt particle dimensions created by the abrasion of basalt weaves showed that, because the mean value of fibre fragment diameter is the same as the diameter of the fibres, no splitting during fracture occurs [40]. Basalt fibres and fabrics are labelled as safe according to both US and European occupational safety guidelines. Its particles or fibrous fragments due to abrasion are too thick to be inhaled and deposited in the lungs, but care in handling is recommended. Basalt filaments can be used as one component of hybrid fabrics containing natural fibres for the creation of geotextiles with enhanced resistance in soil burial conditions. Influence of fibre type on selected properties of hybrid plain woven fabrics with basalt filaments in the warp and basalt or jute yarns in the weft are shown in Table 9.9. All fabrics were made on the CCI sample loom under the same technological conditions with the same density for all fabrics. The sett was 12 threads cm−1 in warp and 8 threads cm−1 in weft [41]. The presence of basalt yarns is enhancing tensile mechanical properties of fabric and this fabric portion is not degraded in soil.

9.4 Geotextiles and Soil

Geotextiles are during their whole service time buried in soil. The majority of soils have a solid phase including inorganic solids and organic solids, a liquid phase including dilute aqueous solution of inorganic and organic compounds, and a gas phase as a mixture of some major (e.g. nitrogen, oxygen) and trace (e.g. carbon dioxide, methane, nitrous oxide) gases (see Figure 9.11) [42]. 9.4 Geotextiles and Soil 255

Table 9.9 Influence of weft and warp composition on mechanical properties of plain fabrics.

Material Basalt/basalt Basalt/jute Jute/jute

Fabric composition

Tensile 3912.9 926 369.95 modulus (MPa) warp Tensile 3839.7 466.1 77.41 modulus (MPa) weft Shear rigidity 0.05 0.372 0.095 (MPa) Strength (MPa) 1154.9 192.9 153.7 weft Strength warp 1403.5 535.1 101.9 (MPa)

Under optimal conditions for the growth of upland plants, the solid components (inorganic and organic) constitute about 50% of the total volume, while liquids and gases comprise 25% each. Particles that constitute the soil are called sand (2–0.02 mm), silt (0.02–0.002 mm), and clay (< 0.002 mm). Sand grains comprise mostly quartz but also contain fragments of feldspar and mica, and traces of heavy minerals. There is practically no cohesion between sand particles. Silt is an intermediate size fraction, and

Figure 9.11 Basic phase of soils [42]. Water/liquid

Solid Air/gas 256 9 Geotextiles and Environmental Protection Textiles

also constitutes the skeleton of the soil. The mineralogical composition of silt is similar to that of sand, but silt has a greater surface area. Clay is the fine fraction, and constitutes the reactive fraction of the soil. Because of its very fine size, the clay fraction is colloidal, highly reactive, has a large surface area, and a high charge density. The clay particles are plate‐like or needle‐like. The clay particles comprise a group of clay minerals, called aluminosilicates. These are secondary clay minerals, and also contain fine particles of iron oxide (Fe2O3), aluminium oxide (Al2O3), calcium carbonate (CaCO3), and other salts. Because of its larger surface area, the clay fraction has the most influence on many soil properties [43]. Immediately after rain or irrigation, the entire pore space or the voids in between the particles are completely filled with water, and the soil is saturated. In a dry state the pores are filled by air or gases. Under optimal conditions for the foundation for buildings and roads or runways, the pore space is minimized by compaction or compression. The solid components are 80–90% of the total soil volume. Some industrial functions may require anaerobic conditions. Owing to the transformation of organic matter by methanogenesis, the emissions of methane (CH4) to the atmosphere occurs. The mechanism of degradation under anaerobic conditions is shown in Figure 9.12. In aerobic conditions the oxidation and mineralization of organic matter may cause the release of carbon dioxide (CO2) to the atmosphere [44]. The mechanism of degradation under aerobic conditions is shown in Figure 9.13. The particle size of the soil could affect the process of decomposition. Decomposition can be decreased in soil of a coarse texture, owing to the diffusion of gases through the soil matrix. On the other hand, fine‐textured (clay) soil has a lower rate of gas diffusion than coarse‐textured soil. Therefore, oxygen–CO2 exchange might not be sufficient to produce aerobic microbes, and these conditions cause domination of anaerobes which are less efficient decomposers [45]. Soil liquid phase properties are one of the main factors influencing the behaviour of geotextiles in soil. The soil liquid phase may be explained by the diversity of water forms in soil and the characteristics of water. Basic water forms in soil are chemically hard bonded, crystallizational water, physically bonded (hygroscopic), slightly bonded (at interface between water and solid particles), capillary, gravitational, etc. [46]. Capillary water, also called free or pore moisture, is a major part of the soil liquid phase. It is readily available to interact with geotextiles. Capillary water composition and properties are not constant. The soil liquid phase is heterogeneous as a result of nonequilibrium processes of mass transport from soil particles, diffusion transport in liquid phase, possible emissions of substances by plants or microorganisms, and leaching of substances from geotextiles as well. The soil solution contains the following ions

PolymerCO2 + CH4 + H2O + biomass + residues

Figure 9.12 Degradation under anaerobic conditions.

Polymer + O2 CO2 + H2O + biomass + residues

Figure 9.13 Degradation under aerobic conditions. 9.4 Geotextiles and Soil 257

− − 2− 2+ 2+ mainly: HCO3 , CI , SO4 , Ca , Mg . Most soils are slightly acidic (pH = 5–6.5). For podzolic virgin soil has a pH of around 3 and for some soils pH is slightly over 7 [46]. Acid soils are degradation prone for buried cellulose based textiles. Alkali soil has the opposite effect (i.e. degradation is slightly slower). Under the majority of soil conditions, textile materials based on the natural polymers do not survive long‐term burial. Natural fibres are readily degraded by the action of soil‐resident microorganisms, often in combination with degradation promoted by components of soil water or gases presented in the soil. Degradation occurs over a comparatively short period of time unless the burial conditions inhibit biodegradation. Soil burial biodegradability depends on polymer type and structure. Polymers of lower molecular weight, lower crystallinity or orientation, and higher hydrophilicity have shown greater biodegradability [47]. Biodegradation can occur by two different mechanisms: hydro‐biodegradation and oxo‐biodegradation [48]. The hydro‐biodegradation is much more important in the case of hydrolysable natural polymers such as cellulose. Oxo‐biodegradation predominates in the case of other natural polymers, such as rubber and lignin. Lignin normally requires the presence of enzymes that initiate peroxidation [49]. The synthetic hydrocarbon polymers (e.g. polyethylene, PP) do not hydrolyse under normal environmental conditions, but it was found that, after transition metal catalysed thermal peroxidation, they biodegrade readily in the presence of a variety of thermophilic microorganisms [37]. Figure 9.14 shows the microscopic photographs of cellulose based fabric specimens after the soil burial test [51]. Linen fabric developed more fungi than other samples and exhibited the most serious shape deformation caused by fibre damage. The thickness of yarns is not significantly

untreated 4 days 20 days

Linen

Cotton

Viscose

Acetate

Figure 9.14 Biodegradation of cellulose based textiles during soil burial test (cotton, linen, viscose, and cellulose acetate) [50]. 258 9 Geotextiles and Environmental Protection Textiles

changed in comparison with cotton and viscose materials. Some fungi developed on cotton and viscose samples, and their shape changed and damaged as the burial time increased. Acetate showed the least amount of fungi formation and the least shape deformation over time because of its high hydrophobicity and slow rate of degradation. These results are valid for fabrics after textile pre‐treatment which can partly attack the pectins in flax fibres. Desiccation, freezing, and the presence of metal ions such as chromium or copper will considerably retard microbial action. Waterlogged soils with anoxic or low oxygen concentrations will exclude aerobic fungi, although anaerobic bacteria may still flour- ish. Under these conditions, soil pH is a major factor in the differential preservation of textiles. In acid conditions, protein fibres (wool and silk) are partially protected, but cellulosic materials (cotton, vegetable fibres) degrade more rapidly. Under anaerobic alkaline conditions, cellulose based materials are more protected. Cellulose is readily attacked by the cellulolytic enzymes of microorganisms. The enzymatic cleavage of cellulose is catalysed by cellulase, which in fungi consists of at least three enzymes. Some fungi can only degrade modified cellulose, which has already been subjected to chain scission by other microorganisms or acid hydrolysis. In well‐ aerated soils, cellulose is degraded by fungi, myxobacteria, and eubacteria, while under anaerobic conditions it is bacteria of the genus Clostridia that predominate. Figures 9.15–9.17 show the appearance and morphological changes of various cellulose based fabric that has been buried in soil from one to four weeks [50]. The cotton fabric (planar mass = 182 g m−2) was partially degraded after one week and totally degraded after only three weeks (see Figure 9.15). The jute fabric (planar mass = 263 g m−2) was slightly degraded after two weeks and totally degraded after four weeks (see Figure 9.16). Jute fabric is heavier and has a more compact structure. The presence of lignin hinders degradation. The linen fabric (planar mass = 211 g m−2) was partly destroyed after one week and totally degraded after only two weeks (see Figure 9.17). In fact, the pectin parts in flax fibres in linen fabric are partially damaged during chemical pre‐treatment. Synthetic polymers are generally resistant to biodegradation. The only important exceptions are polymers with aliphatic esters in the main chain and polyurethanes based on polyester diols [52]. It was found that polyolefin polymers (polyethylene, PP) do not support the growth of microorganisms. Oligomers present originally in these polymers augmented by those produced by, for example, photooxidation support growth if separated from the polymer matrix [52]. Pre‐treatment, such as weathering, UV irradiation, and thermal treatment, was employed to raise the hydrophilicity of

Before 1 Week degradation 3 Weeks degradation

Figure 9.15 Cotton samples [50]. 9.4 Geotextiles and Soil 259

Before 2 Weeks degradation 4 Weeks degradation

Figure 9.16 Jute samples [50].

Before 1 Week degradation 2 Weeks degradation

Figure 9.17 Linen samples [50]. polyolefin polymers by introducing carbonyl groups −C=O to the backbone chains, which enables their microbial metabolization [52, 53]. A few microbes capable of degradation of the pre‐treated polyolefin polymers have so far been isolated. The isolation of a strain capable of polyethylene degradation from a crude‐oil‐contaminated soil at room temperature is described in [53]. The morphology of low‐molecular‐weight polyethylene (LMWPE) after biodegradation in a sterilized compost inoculated with the isolated bacterium Pseudomonas sp. E4 for 80 days at 37 °C is shown in Figure 9.18 [53].

Molecular weight SEM before biodegradation SEM after biodegradation

9700

16 900

Figure 9.18 SEM images of the LMWPE sheets before and after 80 days of composting (5000× magnification) [53]. 260 9 Geotextiles and Environmental Protection Textiles

It can be seen that the smooth surface of the LMWPE sheets was eroded as a result of biodegradation. Many of the bacterial cells adhering to the surface of the LMWPE sheets can be seen. The degree of surface erosion is more pronounced for LMWPE with a lower molecular weight. The degradability/biodegradability of PP films for packing applications after 11 months’ burial in the São Giácomo landfill in Caxias do Sul (Brazil) were investigated by researchers [54]. Comparing the buried PP film to a sample of virgin PP, two peaks of degrading activity appeared at the thermogravimetry (TG) curve as well as structure modification typified by the occurrence of new absorption bands at Fourier‐transform infrared (FTIR), which can be due to changes in crystallinity. Thermal analysis carried out on the buried PP showed decreases in the percentage of crystallinity due to chain scission. The scanning electron microscopy (SEM) revealed the start of degradation/biodegradation processes of the polymeric film in the landfill typified by microorganism colonies on the polymer surface, chromatic alteration, and the formation of cracks [54]. The stability of geotextiles is generally dependent on their nature and type of soil or microorganisms presented. For geotextiles from natural fibres it is relatively simple to partially enhance durability in soil burial conditions by increasing their surface hydrophobicity [55, 56] or using an antimicrobial treatment [57]. Recent possibilities of the different natural fibre treatments used to reduce the moisture absorption and fibre degradation has been reviewed by researchers [56]. A wide range of various pre‐ treatments is available, such as acetylation, silanization, benzoylation, fluorocarbon, isocyanate, methacrylate treatment, etc. Plasma‐mediated surface modification, pre‐ activation, and grafting is very efficient. Cold plasma of high frequency can be produced by microwave energy, whereas alternating current of a lower frequency discharge at atmospheric pressure produces corona plasma. Plasma effects on the fibre surfaces can be tuned by the distance of samples to the plasma source, treatment time, intensity of plasma treatment, and by the type of gas mainly [58]. For the surface hydrophobization, gaseous forms of fluorocarbons, like CF4, C2F6, and SF6, are commonly used. In the case of the plasma treatment of fibres, particular surface modification does not affect bulk substrate properties since the depth of surface penetration, which is approximately a function of plasma power and treatment time, is typically < 100 nm (0.1 μm). The mean free path of plasma particles in atmospheric plasma is nearly 0.1 μm, and in thicker geotextiles, plasma radicals do not come into contact with the fibre bulk.

9.5 Manufacturing Techniques

Of the large family of textile structures, woven and nonwoven fabrics have found extensive applications as geotextiles because of their broad availability and low cost. Two traditional but less widely known technologies are braiding and warp knitting. These technologies have been rediscovered recently and have many geotechnical applications. Taking advantage of its multidirectional reinforcement capability, multiaxial warp knits (MWK) have been adopted extensively for large area coverage/reinforcement applications. There is a large family of textile structures available for geotextiles. Figure 9.19 illustrates examples of these structures. In the past two decades, aside from traditional woven fabrics, a diversification into various forms including knits and speciality 9.5 Manufacturing Techniques 261

BIAXIAL HIGH MODULUS MULTILAYER TRIAXIAL TUBULAR TUBULAR FLAT BRAID FLAT BRAID WOVEN WOVEN WOVEN WOVEN BRAID BRAID LAID LAID IN WARP IN WARP

WEFT KNIT WEFT KNIT WEFT KNIT WEFT KNIT LAID SQUARE SQUARE BRAID 3–D BRAID 3–D BRAID LAID IN WEFT LAID IN WARP IN WEFT LAID BRAID LAID IN WARP LAID IN WARP IN WARP

WARP KNIT WARP KNIT WEFT INSERTED WEFT INSERTED FIBER MAT STICHBONDED BIAXIAL XYZ LAID IN LAID IN WARP WARP KNIT WARP KNIT LAID LAID IN WARP BONDED SYSTEM IN WARP

Figure 9.19 Textile structures for geo‐applications [59]. nonwovens has occurred. A particular class of textile structure that has been rediscovered and undergone extensive development for advanced geocomposites and many other industrial applications is the 3D textile structure [60]. Selected methods available to manufacture these geo‐based technical textiles are described here.

9.5.1 Two‐Dimensional Woven Fabric

Two‐dimensional woven fabric is the most popular material in the geocomposite industry, with nearly 70% of production. Typically, 2D woven fabric has two yarn sets as warp (0°) and filling (90°) interlaced to each other to form the surface. Using traditional weaving, plain, twill, and satin weaves are produced (Figure 9.20). Two‐dimensional woven fabric in rigid form suffers from poor impact resistance because of crimp, low delamination strength because of the lack of binder fibres (Z‐fibres) to the thickness direction, and low in‐plane shear properties because it has no off‐axis fibre orientation other than the material principal direction [51]. Although through‐the‐thickness reinforcement eliminates the delamination weakness, it reduces the in‐plane properties [61, 62]. On the other hand, uni‐weave structure with one yarn set as warp (0°) and multiple warp yarns locked by the stitching yarns has been developed [63]. Bi‐axial noncrimp fabric was developed to replace the unidirectional cross‐ply lamina structure [64]. Fabric has basically two sets of fibres as filling and warp and locking fibres. Warp positioned to 0° direction and filling by down on the warp layer to the cross‐direction (90°) and two sets of fibres are locked by two sets of stitching yarns, one directed to 0° and the other to 90°. Traditional weaving loom was modified to produce such fabrics. Additional warp beam and filling insertions are mounted on the loom. 262 9 Geotextiles and Environmental Protection Textiles

1 6 2 5 3 4 4 3 5 2 6 1 1 2 3 4 5 6 1 2 3 4 5 6 1 (a) (b) (d)

(c)

Figure 9.20 Two‐dimensional woven fabric (a) interlacement, (b) scheme, (c) longitudinal cross‐ section, and (d) transverse cross‐section.

Also, it has been shown that 3D shell shapes with high modulus fibres can be knitted by weft knitting machine with a fabric control sinker device, as shown in Figure 9.21. The influence of weave type on selected properties of hybrid woven fabrics with basalt filaments in the warp and jute yarns in the weft are shown in Table 9.10. All fabrics were made on the CCI sample loom under the same technological conditions and with the same density for all fabrics. The sett was 12 threads cm−1 in warp and 8 threads cm−1 in weft [67]. The number of pores was deduced from the number of interlacing points given by the warp and weft yarn density, i.e. as the product of measured warp and weft densities. The pore volume and shape of these fabrics woven with identical yarn diameter and yarn spacing will vary depending on the manner of the interlacing of the threads. The pore walls are not flat and their cross‐section changes with the fabric thickness with respect to the type of pores, type of yarns, and their characteristics. It can be seen that the plain weave develops the most compact structure with the best mechanical properties. Plain weave has relatively lower porosity parameters, i.e. fewer numbers of pores and a lower portion of open area as compared to matt and twill weaves. Both matt and twill weaves have higher thicknesses, owing to longer float lengths of yarn and lower area, thus more fluids can be trapped in the structure. In fact, plain weave is composed from regularly interlaced weft and warp yarns with highest density (see Figure 9.22).

(a) (b)

Figure 9.21 Biaxial noninterlaced (a) woven fabrics and (b) knitted fabric [65]. 9.5 Manufacturing Techniques 263

Table 9.10 Influence of weave on selected properties of basalt/jute woven fabrics [66].

Weave Plain Matt 1/3 Twill

Type

Cover factor (%) 79.3 78.6 74.9 Thickness 1.77 1.82 1.80 (mm) Areal mass 658 678 698 (g m−2) No. of pores 88.3 97.6 106.9 (/100 cm2) Open area (%) 20.7 21.4 25.1 Tensile 926 838.48 478.44 modulus (MPa) warp Tensile 256.5 467.75 466.1 modulus (MPa) weft Shear rigidity 0.37 0.32 0.25 (MPa) Strength (MPa) 192.9 290.43 170.75 weft Strength (MPa) 535.1 247.2 469 warp

Figure 9.22 Structure of plain weave binding point.

F Fo o

Leno fabrics comprise a warp and weft thread system just the same as normal plain fabrics. The warp system is split into straight and looping warp threads. Straight warp threads are always under the weft threads and represent the lower shed during weaving. Looping warp threads are always above the filling threads and represent the upper shed 264 9 Geotextiles and Environmental Protection Textiles

Figure 9.23 Structure of leno weave binding point [68].

Fo/2 Fo/2

~ B

during weaving. The number of crossings threads within a binding point is higher and the wrapping angle of thread crossings is larger (see Figure 9.23). The binding point for plain weave is planar but for leno is spatially arranged. Warp threads are crossing in the plane having some angle γ, from plane ‘weft–warp’. The cross‐sections for leno threads are elliptical. The length lM is the solution of four biquad- ratic equations [69]. The slip force in the fabric element FP is generally defined as the force in thread which leads to imbalance at the binding point. For plain weave the FP depends on the thread axial force F0, friction coefficient f, and wrap angle θP, according to the relation:

FFPP0 exp( f ) (9.2)

For leno fabrics FL (in the warp direction) is defined as: (9.3) FFLL0 exp( f ()L )

where θL is the wrap angle of weft–warp and σL is the wrap angle warp–warp. For the Pierce model and symmetric angles θL = σL is valid

FFLL0 exp(2 f ) (9.4)

The ratio between slip forces is then [69].

FFLp/exp f 2 LP (9.5) The ratio between slip forces as a function of yarn spacing for f = 0.5 is shown in Figure 9.24

9.5.2 Triaxial Fabrics

Triaxial weave has basically three sets of yarns as ±bias, ±warp, and filling [70]. They interlace with each other at about a 60° angle to form fabric, as shown in Figure 9.25. The interlacement is similar to traditional fabric, which means one set of yarns is above and another one below and this repeats through the length and width of the fabric. Normally, the fabric has large open areas between the interlacements. While dense fabrics can be produced, it may not be woven in a very dense structure compared to traditional fabrics. This process has mainly open reed. Triaxial fabrics have two variants: (i) loose weave and (ii) tight weave. The open‐weave triaxial fabric has a certain stability and shear stiffness to ±45° direction compared to the biaxial fabrics and has more isotropy [70]. 9.5 Manufacturing Techniques 265

500

450 weft 10 tex

400 weft 50 tex

350 weft 100 tex

300 weft 200 tex

250 weft 500 tex

200 Ration FL / FP[%] 150

100

0 01234 5678910 Weft spacing [mm]

Figure 9.24 Slip forces ratio for various weft spacing [69].

Figure 9.25 Triaxial woven fabrics. 266 9 Geotextiles and Environmental Protection Textiles

9.5.3 Three‐Dimensional Woven Fabrics

Three‐dimensional orthogonal woven preforms have three yarn sets: warp yarn, filling yarn, and z‐yarn [71]. These sets of yarns are all interlaced to form the structure wherein warp yarns were longitudinal and the others orthogonal. Filling yarns are inserted between the war players and double picks were formed. The z‐yarns are used for binding the other yarn sets to provide the structural integrity. The unit cell of the structure is given in Figure 9.26. A state‐of‐the‐art weaving loom can be modified to produce 3D orthogonal woven fabric [71–75]. Three‐dimensional angle interlock fabrics can be fabricated by a 3D weaving loom [76]. They are considered layer‐to‐layer and through‐the‐thickness fabrics, as shown in Figure 9.27. Layer‐to‐layer fabric has four sets of yarns as filling, ±bias, and stuffer yarns (warp). ±Bias yarns are oriented along thickness direction and are interlaced with several filling yarns. Bias yarns make zigzag movement at the thickness direction of the structure and change course in the structure to the machine direction.

9.5.4 Nonwovens

Nonwoven geotextile is produced by bonding or interlocking fibres, or both, through mechanical, thermal, or chemical means. It has captured more than 75% of the market in a very short span of time. It is extensively used for drainage, filtration, and

Figure 9.26 Three‐dimensional orthogonal woven fabric. 9.5 Manufacturing Techniques 267

Figure 9.27 Three‐dimensional angle interlock fabrics. stabilization. Constructed from a felt‐like fabric, geotextiles are light in weight and act as filters and reinforcements. These fabrics are typically classified into lightweight, medium weight, or heavyweight, details of which are given in Table 9.11 [77]. Nonwoven geotextile is generally manufactured by placing and orienting the filaments or fibres onto a conveyor belt, to be subsequently bonded by needle punching or melt bonding.

9.5.4.1 Standard Nonwovens There are two main methods for the manufacture of nonwoven geotextiles: thermal bonding and needle‐punching. Heat‐bonded nonwoven textiles are made from continuous filament fine fibres that are laid randomly onto a moving belt and passed between heated rollers. These fabrics can have different melting points, and so get their coherence and strength from the partial melting of fibres between the hot rollers, or resins can be used on a fibre matt for bonding. Needle‐punched nonwoven fabrics are made from blended webs of continuous or staple filaments that are passed through banks of multiple needles. The fabric derives mechanical coherence from the entangling of fibres caused by the needles [78].

Table 9.11 Types of nonwoven geotextiles [77].

Type kg/m2 Applications

Light weight 0.088–0.119 High drainage areas, landscaping, asphalt overlay Medium weight 0.170–0.227 Drain filtration, erosion control, aggregate separation Heavy weight 0.283–0.455 Aggregate separation, high filtration areas 268 9 Geotextiles and Environmental Protection Textiles

9.5.4.2 Thick Nonwovens The thickness of nonwoven structures is made by the stratification of ‘semi‐products’: fibres, carded webs, or 2D nonwovens. The directions of this stratification can be different; the predominate directions are horizontal (Figure 9.28a) and vertical (Figure 9.28b). The direction of stratification determines the orientation of structural elements in the structure of a product and significantly influences the choice of fixation principle. Three‐dimensional products with a horizontal orientation of structural elements, for example, cannot be fixed on the surfaces of the product only. Decomposition of the product in this case is evident.

9.5.4.2.1 Mechanical Fixation of Surfaces of Nonwoven Structures The industrial application of a web ‘wave’ as the basic ‘construction’ element of a 3D nonwoven fabric inspired designers to look for a mechanical method of fixation of these web (or nonwovens) waves in products that would not significantly change the fixed structure (as happens, for example, in the case of needle‐punching) [78]. For 3D textiles manufactured through vertical folding of a web into ‘waves’, the main characteristic fact is that the folded formation (fibres, nonwoven) goes ‘through’ the product from one side to the other (Figure 9.29). The basic relation between the product parameters and the technology parameters are known to researchers and are derived in [78]. Today, there are two main methods of mechanical surface fixation of nonwoven structures that can be applied onto 3D structures. The first is splicing by means of fibre bundles using the MULTIKNIT machine. The second is the method developed at TUL, in the Czech Republic, which is based on twisting the fibre ends protruding from the web wave peaks into so‐called quasi‐yarns [79]. The machine for implementation of this method includes no parts performing oscillatory motion. The appearance and properties of the products of course conform to different fixation principles. A big advantage of this method is, in contrast to the first method, that it makes it possible to add and to bond

Layers of web

(a) Horizontal strati cation (b) Vertical strati cation

Figure 9.28 Basic types of stratification.

Figure 9.29 MULTIKNIT structure. 9.5 Manufacturing Techniques 269 reinforcing nets to the surface of fixed structures. The basic idea of this method is to splice the waves of web into a cohesive whole just on their peaks [80]. Such a method uses less energy than conventional methods like heat fixation, and neither the structure nor the shape of the product will be significantly changed. During this time it has been verified experimentally. It is only now, following the development of corrugated 3D textile fabrics [81], that efforts have been directed towards developing mechanical fixation, and its application using technologies such as spunbond and spunlace nonwoven techniques.

9.5.4.2.2 Principle of Quasi‐Yarn Formation Both classic and quasi‐yarns belong to fibre formations that are made by fibre twisting. Unlike classic yarns, quasi‐yarns are formed by twisting of ends or, as the case may be, of loose segments of fibres situated on the surface of a structure – fleece or some other sort of textile product. A model of a quasi‐yarn structure is shown in Figure 9.30. It can be compared to the body of a centipede: the twisted fibres lie on the surface of the structure, forming its body, while its ‘legs’ penetrate the structure. According to the principle of quasi‐yarn, the rotating cylinder or cone‐shaped body moves on the fibrous web surface, as shown in (Figure 9.31). The rotating element leaves behind a track or the twisted quasi‐yarn. The shape of this ‘track’ is similar to the classical yarn and therefore it is called quasi‐yarn. Quasi‐yarns are formed from protruding fibres on the web surface. They are parallel to each other with variable spacing as per requirement. By suitable mutual layout of the rotating body and the textile fabric surface, for example according to Figure 9.32, it is possible to bond textile fabrics together by ‘surface‐ broad’ lamination. By repeated lamination it is possible to produce textile fabrics of the required thickness (e.g. 10–200 mm).

α 2

Figure 9.30 Characteristics of quasi‐yarns.

n n v β v

Figure 9.31 Principle of quasi‐yarn creation. 270 9 Geotextiles and Environmental Protection Textiles

Rotating elements

Product 2 Product 1

Laminated product

Figure 9.32 Principle of lamination.

9.5.4.2.3 ROTIS Principle of Nonwoven Structures Production The main characteristics of ‘conventional’ nonwoven products are their constant parameters (constant height and density); ‘nonconventional’ products are characterized by locally different parameters of products. One possibility of how to create a 3D product based on conventional 2D nonwoven web is shown in Figure 9.33. For forming of 3D textile structures with prescribed thickness in the range of 4–10 mm based on conventional planar web with a thickness of 0.2–2 mm, the ROTIS device was invented and designed. Principle is preparation of perpendicularly laid structures by deformation between toothed gears. A combination of the ROTIS principle with quasi‐ yarns formation is shown in Figure 9.34. ROTIS type 3D structures can be prepared in a huge variation of porosities due to the changing density of ‘waves’. Provided that a ‘wave’ made of a semi‐finished article (web, nonwoven) is the basic building block of the product, one can easily deduce the basic relations between the parameters of technology and the geometric dimensions of the product [82]. The product thickness H (m) is expressed as:

Av1 H (9.6) 2v3

3D 2D H t

Figure 9.33 Creation of a 3D product.

Waves maker Fixing ROTIS

Quasi-yarns maker Input Output

Figure 9.34 Combination of ROTIS and quasi‐yarns. 9.5 Manufacturing Techniques 271

−1 −1 where v1 (m s ) is the web input rate, v3 (m s ) is the rate of the working roller 3, and A (m) is the tooth pitch of the working roller 3. The wave number of a ROTIS structure (number of waves per 1 m) wn is equal to

2 − = t 1 wn 2 (9.7) 4H and the required thickening of the starting web t is equal to

22 tH=+41wn (9.8) −1 The output rate of the conveyor 2 v2 (m s ) and rate v3 are interrelated with product characteristics by

v1 wAn v1 v2 ==andv3 (9.9) t t The wave number of the ROTIS structure is dependent on rates by relation

zn3 ==v3 wn (9.10) v2 Av2

−1 where n3 (1 s ) is the revolutions of the working roller 3 and z is the teeth count of the working roller. Using these relations between the product parameters H, wn, and technological parameters v1, v2, and v3, it is possible to project and produce nonwoven products of the required macro‐geometrical structures. Using, for example, the assumption that v1, v2, and v3 velocities are constant, the machine produces conventional (plane) product (Figure 9.35). Using, for example, the assumption that v1 is constant and v2 and v3 velocities are changing, the ROTIS machine produces various nonconventional products.

Laminated Products By means of mutual laminating of these mentioned types of textiles it is possible to obtain other types of nonconventional products, like ‘hollow’ products or products of structured surface, for instance according to the scheme in Figure 9.36 [83]. Three layer ROTIS nonwovens: outer layers, middle layer spunbond with nanofibrous net, inner layer – FIBERTEX type Fiberback 80 CB is shown in Figure 9.37. Before creating the final product, these layers were joined by needle punching.

α H n Hn

ρ α

Figure 9.35 Conventional of 2D structure with quasi‐yarns. 272 9 Geotextiles and Environmental Protection Textiles

Figure 9.36 Product created by lamination.

Figure 9.37 Three‐layer ROTIS structure with nanofibrous net.

Figure 9.38 Some 3D structures prepared by ROTIS technology.

Some other examples of 3D structures prepared by ROTIS technology are shown in Figure 9.38.

9.6 Sustainability and Ecological Aspects

Sustainability is defined by Brundtland as the ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’ [84]. This section deals with the key parameters of sustainability with a special 9.6 Sustainability and Ecological Aspects 273 focus on CO2 emissions. It provides scenarios where geotextiles can improve the sustainability credentials of an engineered solution.

9.6.1 Geotextiles and Sustainable Development

With the increasing adoption of geotextiles, it is imperative to study the environmental impact of its usage. Various studies have been carried out in this regard, with one being of particular prominence [84]. In this study, embodied carbon data for two geotextile product ranges produced by two different manufacturers was calculated. The manufacturers producing, on the one hand, a needle‐punched product and, on the other, thermal‐bonded geotextiles had used different manufacturing processes. This study provided data for a range of products with varying masses. This allowed the overall energy consumption per kg of products to be calculated. The small difference in EC (embodied carbon) values (Table 9.12) may be attributed to different manufacturing processes and fuel sources. In this research, the mean value for nonwoven geotextiles −1 was 2.35 tCO2e t . While broad conclusions as to thermally bonded material being more sustainable than a needle‐punched material cannot be inferred, these results can be used to build a database of the EC footprint of geotextiles. Such a database will increase the accessibility, transparency, repeatability, and rigour of sustainability assessment.

9.6.2 Environmental Impacts of Geotextiles

The environment impact of geotextiles, throughout their lifecycle, can be assessed using a technique called lifecycle analysis (LCA) [85]. During LCA, clearly defined boundary conditions in material production, manufacture, and deployment are considered. The stages and system boundaries are given in Figure 9.39. Rigorous LCA requires a clear definition of boundaries which are fit for purpose for the intended comparison. The most commonly used LCA conditions are given in Table 9.13. A research by the Waste and Resources Action Program (WRAP) highlighted lower transportation emissions as a key advantage of geotextiles, owing to their comparatively low weight and volume compared to carrying soil or aggregate to site [86]. Plastics are typically high in EC materials [87]; however, when used correctly and efficiently, a geotextile based solution can have significantly lower EC than alternative solutions. With

Table 9.12 Embodied carbon values for geotextiles [84].

Conversion of Manufacturing Polymer embodied granules to fibres carbon emissions Total embodied e e e e Geotextile type carbon (tCO2 /t) (tCO2 /t) (tCO2 /t) carbon (tCO2 /t)

Nonwoven 1.983 0.241 0.053 2.28 needle‐punched Nonwoven 0.189 2.42 thermally bonded/ needle‐punched 274 9 Geotextiles and Environmental Protection Textiles

EXTRACTION CRADLE MANUFACTURE TO GAT E CRADLE TO SITE TRANSPORTATION CRADLE TO END OF CONST. CRADLE TO GRAVE CONSTRUCTION

DISPOSAL

Figure 9.39 Stages and system boundaries of LCA [85].

Table 9.13 Common LCA conditions [85].

Boundary conditions Description

Cradle–gate Includes all emissions in the extraction and manufacture of a product, including all transport‐related emissions associated with interim stages of manufacture (such as moving of polymer fibres and granules) Cradle–site Includes transportation of material to the site This must include the cumulative emissions from all transportation types (e.g. road, rail, ship) Cradle–end of construction Includes all of the emissions associated with the manufacturing process. For geotextiles this may include items such as the preparation of the subgrade by rollers, excavators used to lift rolls of material, excavation, and filling Items such as provision of cabins and welfare facilities should also be considered as these have an associated embodied carbon for the construction phase Cradle–grave Includes demolition and disposal emissions associated with the end of life of a structure

increasing research on the sustainability of geotextiles, there are encouraging indicators that the use of geotextiles can bring both cost and EC savings.

9.7 Conclusion

In general, geotextiles are made from some natural (jute mainly) and synthetic fibres such as PP, polyester (PES), and polyethylene (PE), in either woven or nonwoven forms. A woven geotextile could be manufactured from monofilament, multifilament, and slit‐film or fibrillated fibres. A nonwoven geotextile could be fabricated from either References 275 continuous filaments or staple fibres. Woven geotextiles have pore sizes within a relatively narrow range than nonwovens because of the limitations in the manufacturing process, including the number of warp and weft yarns used and the types of weave. Three‐dimensional corrugated ROTIS structures provide a higher potential for several applications. A large amount of research has concentrated on testing and the experimental characterization of structures and/or their hydraulic behaviour, including pore size and pore size distributions, permeability, and the soil transport process in geotextiles. Some of the frequently adopted approaches have been standardized, mainly by the ASTM. Theoretical work is obviously less available than experimental studies. A comprehensive research in this area is needed to meet future requirements.

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Agrotextiles and Crop Protection Textiles Adriana Restrepo‐Osorio, Catalina Álvarez‐López, Natalia Jaramillo‐Quiceno, and Patricia Fernández‐Morales

Universidad Pontificia Bolivariana Medellín, Colombia

10.1 Introduction

For decades, traditional textiles have been used in agriculture. However, new produc tion techniques and the advancement of modern materials have led to the development of technical textiles used not only for agriculture but also for applications in different industries, ranging from aerospace to fashion. Agrotextiles, under the concept of tech nical textiles, are materials with higher durability and performance than traditional materials that are expanding to new application areas in the field of agriculture. These features increase the productivity and quality of agricultural goods, which helps allevi ate the growing challenges currently experienced in the agro‐industrial field caused by the continuous increase of the world population. Agrotextiles are woven and nonwoven materials that are used for agricultural and horticultural applications, including livestock protection, shading, and weed and insect control [1]. Agrotextiles are also used as crop covers for the protection of plants, as seed blankets, as shade providers in greenhouses, as pots for the control of roots, and as lawn covers [2]. They can be classified by area of application, such as crop production, horti culture, floriculture, forestry, livestock, aquaculture, and agro‐engineering [3]. In any case, the use of agrotextiles will depend on economic feasibility with regard to their material cost, installation, operation, and maintenance. This means that the investment made should be reflected in a reduction of production costs and in the amount of agri cultural work done, which will result in greater productivity and quality of the agricul tural goods [2]. The increase in crop productivity when agrotextiles are used is due to an artificial improvement of weather conditions. The use of agrotextiles contributes to better plant development [4], protects crops against weed growth, and prevents insect attacks, all without affecting the air and water interaction required for the spread of new roots in the parent plant. Thus, fruit storage times are improved, crops are protected from excessive sunlight or frosts [3], and excessive loss of soil moisture is avoided, resulting in the optimization of water use and reduced fertilizer, pesticide, and herbicide require ments [1].

10.2 Fibres for Agrotextiles

Agrotextiles are manufactured from textile fibres from two categories: natural fibres and artificial fibres. Typical reasons for using fibrous materials are their flexibility, high surface area, and that they can easily be transformed into woven and nonwoven textile structures [2]. Agrotextiles, as well as the fibres used to manufacture them, must com ply with a number of basic requirements; consequently, agrotextiles must have one or more of the following properties [2, 5]: ●● Resistance to solar radiation and ultraviolet light. Prolonged exposure to the weather makes certain agrotextile products, such as shade nets, antibird nets, or crop covers, more vulnerable to solar or UV radiation. In general, agrotextile fibres can be treated with different additives that impart UV radiation stability. ●● Resistance to constant thermal changes, weather changes, and winds because agro textiles are typically outdoors and are therefore exposed to different environmental conditions while in use. ●● Ability to create a microclimate between the ground and the nonwoven textile, to provide a balance between temperature and moisture of the crop and an optimum temperature for the roots. ●● Resistance to microorganisms, to protect against fungi and other diseases caused by constant moisture. ●● Biodegradability; the degradation of the agrotextile, once it has fulfilled its function in the crop, may be desirable to not cause pollution or harm to the environment. ●● High water retention potential is desirable for applications such as capillary mats or covers for water retention. Depending on the application, a large number of fibres can potentially be used to develop agrotextiles: natural or synthetic fibres, biodegradable or nonbiodegradable.

10.2.1 Natural Fibres

Currently, the use of natural fibres for the development of new materials is one of the priorities of global organizations such as the Food and Agriculture Organization (FAO) because it is expected that their use will increase the effectiveness and sustainability of agricultural industries worldwide [6]. This type of initiative in part has led to an increase in the consumption of natural fibres in recent years, which, coupled with their charac teristics, have made these materials favourable candidates to replace synthetic materials in some applications. Natural fibres are biodegradable and renewable and have neutral CO2 emission; high mechanical strength, modulus, and moisture absorption; low elon gation and elasticity; low density; and, generally, low cost, making them an important economic focus for developing countries [7]. In addition, natural fibres have high mois ture retention capacity, help reduce evaporation, and prevent the soil from drying out. The disadvantage of these fibres is their short useful life relative to that of synthetic materials [2]. Owing to the above mentioned characteristics, natural fibres are used in different technical textile sectors, one of which is agriculture. As technology and development of textiles advances, the use of natural fibres that can meet different specifications and respond to technical requirements of woven and nonwoven agrotextiles is continuously 10.2 Fibres for Agrotextiles 281 being studied and selected [4]. While natural fibres can be produced or grown with the express purpose of developing technical materials, such as agrotextiles, these fibres are often obtained from other transformation processes that consider them by‐products. The characteristic of being readily available by‐products favours their use when faced with the challenge of increasing the effectiveness and sustainability of agricultural industries worldwide. The characteristics of natural fibres, either of plant or of animal origin, enable them to perform under different applications. In this regard, animal fibres in general have lower resistance and modulus and greater elongation than that of vegetable fibres [7]. Vegetable fibres are most commonly used for their superior engineering properties; vegetable fibres can withstand much more heat and sunlight than most synthetic fibres, and some can even withstand the harsh conditions of the marine environment. Some of the natural fibres used in agrotextiles are jute [8], coconut, sisal [9], flax, hemp [10] and wool [11]. In particular, coconut fibre is characterized by its high lignin content (40– 50%); consequently, it has a lower degradation rate relative to that of other natural fibres, which makes it more resistant and durable in high‐humidity conditions. Other characteristics of these fibres are their flexibility, high resistance relative to that of other natural fibres, and high availability [9]. Agrotextiles made with coconut fibres can reduce the swelling of expansive soils, at the same time helping to maintain the mois ture of the land and supporting vegetation growth. It has been reported that coconut fibre can maintain up to 19% of its original tensile strength after nine months of using it for watershed protection. In addition, after a year of exposure to wet soils, this fibre was found to maintain 20% of its strength, while fibres such as jute and cotton degraded in eight and six weeks, respectively [9]. Agrotextiles made of flax or hemp fibres can replace the plastic covers that are used for the protection of young plantations or as a base layer of greenhouse crops. It has been reported that the plants reach marketing age faster when these agrotextiles are used than when a conventional substratum is used; in addition, agrotextiles do not require additional fertilizers. However, for aqueous or muddy environment applica tions, agrotextiles are unsuitable, owing to their low lignin content (~4%), which makes them susceptible to microorganism attacks [10]. Jute is the lignocellulosic natural fibre most used in industrial and engineering appli cations in the textile sector; one of these applications is the development of technical textiles. Ropes, twines, sacks, and hessian cloths made with this material are used as agrotextiles [12]. Jute agrotextiles, when used as blankets, have been found to be effec tive at minimizing weed growth. Jute has also been used to produce nonwoven agrotex tiles that promote plant rooting, reduce soil erosion, and control nutrient loss. Furthermore, jute has been used as a sustainable agrotextile for agricultural soil applica tions, specifically in the development of agricultural covers, riverbank protection, and channel liners [8]. Wool is still the only natural fibre of animal origin used in the development of agro textiles. It is used to produce mulch mats for crop protection. This fibre degrades over a period of one to five years; during this process, it is incorporated into the soil as a fertilizer, and because it is a protein fibre, it provides significant amounts of nitrogen. Unlike certain plastics used in this application, wool mulch allows water to penetrate the soil and prevents its desiccation during dry periods. Wool also helps prevent frost damage to plants and keeps soil temperatures constant [11]. 282 10 Agrotextiles and Crop Protection Textiles

10.2.2 Synthetic Fibres

Synthetic fibres are typically used more than natural fibres in agricultural applications, mainly owing to their price, ease of transport and storage, and longer service life [5]. These fibres have high mechanical strength, modulus, and elongation; a reasonable amount of elasticity; and relatively low moisture absorption [7]. The most commonly used synthetic fibres in agrotextiles are polyamides (PA) such as nylon, polyester (PET), polyethylene (PE), and polypropylene (PP); polyolefins are most often used in agrotex tiles [5]. An adequate balance of its physical properties characterizes PE, but it is easy to hydrolyse and has low wear resistance. Nylon has robust toughness and wear resistance, low modulus, and adequate distortion recovery; however, it yellows easily, it is one of the more expensive conventional fibres, and its production requires high energy con sumption. PP has excellent chemical resistance and low specific weight, and its produc tion requires low energy consumption; however, it is not suitable for colouring processes, has low heat resistance, and high creep resistance and stress relaxation [13]. PP is the most widely used polymer to produce shading fabrics. When it is used in materials such as curtains for chicken coops, pigpens, and barns, it protects them from the weather and at the same time provides beneficial ventilation. Additives and pig ments added during its manufacture impart resistance to sunlight and weather. PE is used in greenhouses for insect control [3].

10.2.3 Biopolymers

The degradation of synthetic fibres takes many years, owing to their chemical composi tion; consequently, they remain unchanged for a long time. This stability has created a problem in landfills and thus environmental problems related to their final disposal. One of the alternatives for managing synthetic fibres after the conclusion of their useful life has been recycling, but this approach applies to only a small number of polymers and thus cannot be the solution to the final disposal issue [14]. This problem has led to a new alternative, which is the use of biodegradable or compostable materials in the development of agrotextiles. In this process, polylactic acid (PLA) is mainly used; to a lesser amount, polyhydroxybutyrate (PHB), polybutylene succinate (PBS), cellulose esters, soy based, starch, cellulose derivatives, zein, chitosan, sodium alginate, polycap rolactone (PCL), gelatin, among others, are also used [15, 16]. These materials must ensure that no ecotoxic effects occur within the soil during their degradation process and that their biodegradability and compostability do not produce fragments of poly meric material over long periods of time [16]. In agrotextiles, PLA fibre has proven to be an alternative to PP, PET, or PE because its properties are similar to those of these nonbiodegradable synthetic fibres in terms of controlled crimp, smooth surface, and low moisture absorption. PLA fibre has better weather resistance and flame retardancy relative to that of PET, and it degrades quickly in activated sludge. Its specific gravity, glass transition temperature and modulus are within the values reported for nylon and PET. PLA is characterized by low energy con sumption and carbon dioxide (CO2) gas exhaust during its production relative to that of other synthetic fibres, and it is usually carbon‐neutral [13, 16]. The use of polymers such as PLA in agriculture has been reported for the development of soil retention products [14, 17]. 10.2 Fibres for Agrotextiles 283

There are also agrotextile developments that use biopolymers, some of them on a commercial scale, such as woven and nonwoven PLA ground covers for horticulture [16]; nonwoven mulches of polylactic acid/polyhydroxyalkanoates (PLA/PHAs) [2]; seed blankets, root covers, and biodegradable copolyester mulches; polyvinyl alcohol ® (PVA) root covers; PCL covers [18]; mulch mats made of PBS, PLA, and Mater‐Bi [19]; and crop covers made of PLA and PBS [16]. In the case of aquaculture applications, biopolymers such as PBS and poly(butylene adipate‐co‐terephthalate) (PBAT) have been used to replace the synthetic fibres used in the manufacture of nets [20].

10.2.4 Nanofibres

Nanofibres are one of the most developed topics regarding nanodimensional textiles; their importance is due to certain unique properties, namely their high surface area, high porosity, and high safety relative to that of other nanomaterials [15]. Electrospinning is the most studied technique for the development of nanofibres and nanometric textile membranes because it is a simple, low‐cost method with strong performance and ver satility. However, its application in the manufacture of agrotextiles is still in its infancy because it faces the following challenges: (i) many biodegradable and nonbiodegradable polymers transformed by electrospinning dissolve into potentially toxic solvents; (ii) the electrospinning of polymers in an aqueous solution results in processing difficulties; (iii) some water‐soluble or biodegradable polymers cannot be electrospun, owing to their high viscosity; and (iv) large‐scale production of nanofibres or membranes with this technique is still limited [15, 21]. To overcome these limitations, researchers have sought alternatives using biodegradable polymers, water‐soluble polymers, and mix tures of non‐electrospinnable polymers with other highly electrospinnable polymers, such as polyoxyethylene (PEO) or PVA, or using alternative techniques, such as coaxial electrospinning [15]. Among the applications of nanofibres in the development of agrotextiles, use as a technique for insect control has been studied. This technique is based on the encapsula tion and immobilization of pheromones in electrospun porous nanofibres, which are released in a controlled manner over a long period. Polymers such as polyamides (PA), cellulose acetate (CA), polycaprolactone (PCL), polyoxyethylene (PEO), ethyl cellulose (EC), polyvinyl acetate (PVA), and blends such as: polyethylene glycol/ polycaprolac tone (PEG/PCL) and polyvinyl acetate/polyvinylpyrrolidone (PVA/PVP) [15, 21] – have been used for this purpose. The encapsulation of biological agents to control pathogens is implemented on nanofibres [22] to apply them to the seeds, leaves, or roots of the plants. This approach includes the use of microorganisms such as Trichoderma, Bacillus subtilis, and Rhizobia, which, once incorporated in the textile nanostructures, protect the plants from environmental factors and improve their viability during storage and processing. PVA and formulations of chitosan‐poly(ethylene oxide) (PEO) and chitosan‐ polyacrylamide (PAAm) have been used to encapsulate microorganisms; these elements allow a controlled release of biological agents [15]. Another application of electrospun fibres is the encapsulation of agrochemicals through mixing different materials or using coaxial electrospinning, which consists of a special spinneret with two concentric capillaries that allow the simultaneous electro spinning of two polymers into a single fibre and encapsulate the agrochemicals in the internal fibre or core. Thus, the mechanisms for the release of substances occur through 284 10 Agrotextiles and Crop Protection Textiles

the pores of the nanofibres, by the degradation of the polymer matrix, or by a combina tion of both mechanisms. Pesticides are encapsulated in CA, PLA [15], EC [23], mix tures of zein/polyurethane crosslinking with glutaraldehyde [24], fertilizers in wheat gluten, or mixtures of PHB and PLA [15].

10.3 Textile Structures for Agrotextiles

The textile structures used in the production of agrotextiles include woven, nonwoven, and knitted fabrics [3]. These structures are flexible, resistant, porous, and permeable to air and water, among other properties [25]. This feature enables them to compete with other structures traditionally used in agriculture, such as polymeric films or glass covers [2]. Depending upon their final use and its requirements, different kinds of tex tile structures are used, for example: ●● Woven fabrics and nonwovens, for ground covers, mulch mats, shade cloths, and fruit bags. ●● Woven fabrics, for sapling bags; insect‐proof, antibird, and hail protection nets. ●● Knitted and knotting, for screens, packaging materials, antibird nets, fishing nets [26, 27]. The woven agrotextiles are produced using special projectile weaving machines as they meet large widths and can be employed for a wide variety of fibres, natural or synthetic, as well as for different kinds of yarns [1]. The use of woven fabrics as shade cloth allows different degrees of shade controlling the thread count, according to the individual plant’s requirements, and they are relatively stiff and resistant to deforma tions. Also it is possible to use leno weave structures when higher stability of agrotextile is required, e.g. for crops during strong hailstorms. Or to use fine denier yarns for insect screening in greenhouses with woven agrotextiles [3, 28]. A large proportion of the agrotextiles structures are knitted, in particular the warp‐ knitted fabrics, because they have versatile properties, such as: elasticity or dimensional stability and may be fabricated with high or low density of construction, and fine or coarse structures. It is possible to produce these textiles in flat, tubular, or three‐ dimensional shapes, with a width of 6 m or more, also warp‐knitted technology permits a variety of different designs to suit specific requirements, which makes these agrotex tiles useful in a wide range of applications [29, 30]. Among warp‐knitted technologies, Raschel machinery produces fabrics and nets with longitudinal loops and transversal knitted threads, which link the threads strongly and provide enough resistance against strong wind or hailstorms [28]. Finally, the use of nonwovens as agrotextiles has increased in the past years, spun bonding and needle‐punching being the mainly used techniques. Spunbonded struc tures have high tensile strength and good tear strength, which permits its use as direct cover on plants to protect cultivations from rain, frost, or wind. Moreover, spunbonded agrotextiles are used for covering fruits, for bird and insect control. Nonwoven bags have an advantage over plastics bags, because these agrotextiles are ventilated, may pre vent fruit from rotting in the summer, and protect fruit from freezing in the winter, the former may also provide better light penetration and promote a better appearance to the fruits [25, 28, 31]. The needle‐punched nonwovens have been used as greenhouses 10.4 High Performance Applications 285 covering, because these structures can be easily saturated by capillary action, and help to keep the required moisture and humidity level for the crops [3]. In general, nonwo vens have a relatively low structural resistance and cannot be used as covers for struc tural frames [28]

10.4 High Performance Applications

Agrotextiles are used to promote the growth, protection, and storage of crops and ani mals [2]. For these purposes, there are various types of agrotextiles, and some of the most important are nets or barriers for the protection of crops, fishing nets, ground, or root covers. Depending on their use, agrotextiles have certain characteristics that allow them to perform specific functions, as discussed below.

10.4.1 Nets and Protection Barriers for Crops

Nets and barriers for crops, or permeable covers, are characterized by structural factors such as fibre type, threads, or yarns; textile structure; and the shape and dimensions of these structures. These factors define the properties of agrotextiles, such as weight, shading factor (SF), radiometric properties, porosity, air permeability, mechanical properties, durability, and biodegradability [32]. One of the most widely used fibres for the manufacture of nets and barriers is high density polyethylene (HDPE), owing to its outstanding mechanical properties, such as its high modulus and high mechanical strength, low density, and robust tear and cut resistance [33]. Another frequently used polymer is PP; to a lesser extent, low density polyethylene (LDPE), poly(ethylene‐vinyl acetate) (PEVA), and polyvinyl chloride (PVC) are also used. For this type of application, UV stabilizers are typically used in the fibres, owing to the specific expected operating conditions [34]. The threads or yarns used in the manufacture of nets and barriers are monofilament, fibrillated, or ribbon‐ type yarns [11]. The structure of nets and barriers are primarily constructed using Raschel knit and plain or leno weaves [33]. In special applications, nonwovens can be used, e.g. nonwo vens made using spray as a flexible obstructive barrier [35]. Raschel knitting produces nets that combine longitudinal chains with transversal knitted fabrics, which allows for joints in all threads and prevents unweaving caused by mechanical actions. Nets made with plain weaves are characterized by perpendicular intertwining of warp and weft threads, which gives them shape stability with some degree of stiffness but does not allow them to withstand large deformations. In contrast, nets made with leno weave have double‐thread interweaving in the direction of the warp that tie each end of the weave, which prevents large deformations, maintains the pore consistency, and pro vides high stiffness [33]. Nets and barriers for crops can be classified into basic categories, as shown in Table 10.1. However, it is possible for a net or barrier to fulfil more than one function at a time, e.g. antihail nets also provide shade to crops, and crop‐shading nets protect against hail [36]. Nets for crops can be used as protection screens, either as structures that cover the planting site with the help of poles or structures, as low tunnels, or by directly covering plants in planting rows. In any case, these permeable covers modify the microclimate 286 10 Agrotextiles and Crop Protection Textiles

Table 10.1 Classification and characteristic features of nets or barriers for crops [11, 33, 36].

Characteristic features Net type Structure Net mesh size Colour

Anti‐insect Plain or leno From 0.2 to 3.1 mm Transparent or white Antibird Raschel From 20 to 40 mm Green, white, or beige Antihail, snow, or Leno or Raschel From 1.5 to 4 mm Transparent or green heavy rain Windbreak Raschel or plain From 1 to 7 mm Dark colours Shade netting Raschel or plain From 0.6 to 7 mm Black or green

that surrounds the plants by decreasing wind speeds by up to 50%, decreasing the tem perature by 1–3 °C and increasing the relative humidity by 2–6% during the day. These changes lead to a reduction in atmospheric water demand and less leaf transpiration [37], which increases soil humidity and fruit and vegetable quality and improves pro ductivity [38]. Antibird nets are a physical and visual barrier that keep pests away from growing plants or from fruits at harvest time [39]. Consequently, this type of agrotextile is con sidered an alternative to the intensive use of pesticides; because it is potentially recycla ble, it is classified as an eco‐friendly alternative and as a strategy of integrated pest management based on passive methods of sustainable crop protection [40]. These nets are mostly made of PE and PP, which makes them much lighter and more economical than metallic nets. Antibird nets can be divided into knotted nets, knitted nets, and extruded nets. The flexibility of the net depends on the shape of the mesh; a diamond shape allows for vertical and horizontal deformation of the net, while a square shape limits such deformation and is therefore commonly used in custom applications [2]. In addition to its function of keeping insects, birds, and even snails away, these nets help protect crops from heavy rains, and in sunny and arid areas they contribute to the sta bilization of the air temperature underneath them [38]. Similarly, antihail nets are used to prevent crop damage due to leaves damaged by hail, which reduces the photosynthesis processes and can damage the fruit during its growth process [41]. These covers are also used to protect glass panels used for crop protection. When these panels break, it results in crop damage, risks to workers, and high replacement or repair costs. Antihail nets are used frequently in orchards and con tribute to improving the appearance of the fruit skin by reducing fruit defects such as sunburn, cracked skin, and friction due to wind [42]. However, such nets have been associated with the reduction of solar radiation, which sometimes adversely affects fruit quality [36]. Nets and windbreakers are used to prevent wind damage; the type of damage can be mechanical, such as detachment of leaves, flowers, fruits or branches, or biological, such as difficulties in the pollination process or excessive evaporation/transpiration. Nets can be panels that block wind flow, or crop covers, which must have sufficient mechanical strength and UV radiation stability [34, 36]. Shade nets are used for protecting plants from excessive solar radiation and elevated temperatures. These nets can be made using plain or knit weaves of PP, PE, and PET. The key property of these nets is the SF, which corresponds to the relative amount of 10.4 High Performance Applications 287 radiation that is absorbed and reflected in the visible range of solar radiation [43]. This factor indicates the amount of light lost through the net, and its values can vary between 20% and 70% [33]. The SF depends primarily on the type of weave and its density. Studies indicate that the type of colour used has no detectable impact on the SF [44], although a correlation between net colour and repellence to certain insect species has been reported [45], which results in an additional positive effect for the crops. Shade nets are also made with aluminium‐coated threads or fibres, which increases reflectiv ity and keeps the plants cooler during sunny days [46]. These nets can also be used as thermal covers, particularly during winter nights, to increase the reflection of distant infrared radiation emitted towards the inside of the cover and to keep the environment of the plants warmer during the night [28]. Tables 10.2 and 10.3 show selected commercial examples of antibird and shade nets, respectively, the type of structure and fibre used to manufacture them, and their main characteristics and applications.

10.4.2 Fishing Nets

Fishing nets have been in use for more than 4000 years and are one of the oldest agro textiles; these nets are associated with the evolution of human culture and the search for Table 10.2 Commercial examples of bird protection nets.

Type of Commercial Main product name Producer Material characteristics Main applications ® Knitted bird AviGard Plantraa HDPE Knitted, rip‐stop, Vineyard bird netting netting b high‐density PE Antibird net FILMAR Blueberry netting with UV Figure 10.1a,b Temporary netting of inhibitors structures to protect Diamond or cherries, raspberries, square mesh net and other fruit crops Netting individual fruit trees Pond netting to prevent herons from eating the fish Knotted Knotted bird Boegger Knotted high Pigeon netting, bat bird netting netting Industrial density PE with netting, and pond c Figure 10.1c Limited UV inhibitors netting Diamond or square mesh net The knotted structure supplies more tensile strength than the knitted and extruded bird netting a) http://www.plantra.com/BirdNetting.aspx. b) http://www.filmar.qc.ca/index.php?filet=materiaux&lang=en. c) http://www.plasticscreenmesh.com/product/bird‐netting.html. 288 10 Agrotextiles and Crop Protection Textiles

(a) (b)

(c)

Figure 10.1 Images of bird protection nets: (a) diamond knitted; (b) square knitted (Source: Reproduced by permission of Filmar Inc.); (c) diamond knotted (Source: Reproduced by permission Bird‐X Inc.).

food [47]. Fishing nets are used in various systems for fishing gear and fishing cages. Different types of fishing nets have been developed, such as circular nets, elongated nets for river mouths, traps, purse seines, nets used in boats for capturing fish shoals, and drag nets for marine species [48]. Nets are also used in fish farming cages; here, the structure of these cages can be classified as fixed, floating, or submersible, depending on their operation [47]. In all cases, fishing nets are knit fabrics (knotless net) or threads connected by knots (knotted net) manufactured using mono‐ or multifilaments [49]. Historically, these nets were made with natural fibres such as cotton and hemp [20], which have been progressively replaced by PA, more recently by PP and ultra‐high‐ molecular‐weight polyethylene (UHMWPE) [50], with successive improvement in mechanical strength and stability against environmental conditions. The requirements for a fishing net include its transparency in the water and its strength to ensure fish capture and prevent fish escape. These nets require materials with high breaking strength and extensibility [51] that are also resistant to loading and constant deformation processes, which requires knowledge of their creep behaviour at the different temperatures of the fishing zone [52]. Fishing nets are affected by envi ronmental factors such as wind, river or seawater, sand, chemical waste, and

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(a) (b)

Figure 10.2 Images of commercial shading nets: (a) TenCate Nicolon® shade cloth fabrics and (b) TenCate Nicolon knit cloth fabrics. Source: Reproduced by permission of TenCate Geosynthetics.

contamination; the dry nets are even subject to radiation once the fishing activity ends. These factors all adversely affect the strength of the nets and their durability [53]. To improve the performance of fishing nets against environmental factors, an alternative is to reduce the thickness of the mono‐ or multifilaments used to make them, thus reducing the surface and thickness of UV radiation penetration [54]. Another option is to incorporate additives in the manufacturing of synthetic fibres, including radiation absorbers, or coatings, such as catechu and coal tar, that provide colour to the nets. These coatings, in addition to improving the resistance to solar radiation, also increase the stiffness, sinking speed, abrasion resistance, and thus the durability of the nets; however, disadvantages also exist, such as net weight increase and the severe environmental consequences if the coating detaches in a body of water [53]. There are deep environmental concerns regarding the use of fishing nets and their final disposal because they are made of high mechanical strength synthetic fibres with degradation rates requiring hundreds of years. Their final disposal is a complex issue, particularly when many of them, after being used, are abandoned accidentally or inten tionally in oceans and rivers. It is estimated that, in the North Pacific, for every kilo of plankton, there are approximately 6 kg of plastic and that 70% of marine pollution cor responds to plastic waste, of which one of the main elements is discarded fishing nets. To mitigate the growing contamination of plastics in oceans, alternatives for their col lection, sorting, and recycling strategies have been sought for decades [57]; for example, PA are recycled to produce garments [55], mixtures of HDPE, PA 6, and PA 66 are used to develop plastic wood, and concrete and polymer matrices are reinforced with the fibre from the nets for the manufacture of composites [56]. The other major environmental issue associated with the use of fishing nets is ghost fishing, which occurs when abandoned or discarded nets continue to catch fish or other marine species. A potential alternative solution to this problem is the development of fishing nets from biodegradable polymers that have a breakdown rate of approximately two years in marine environments; this period of time matches the average life of tradi tional fishing nets. This initiative reports the development of fishing nets made with a blend of biopolymers PBS and PBAT [20] that have resulted in a sustainable alternative to the ghost fishing problem. 10.4 High Performance Applications 291

10.4.3 Mulch Mats or Ground Covers

Mulch mats or ground covers are materials used to cover the ground, usually around the base of a plant, to prevent the growth of unwanted species that compete with the crops of interest [57], maintain soil hydration, control frost effects, stabilize and help the sepa ration of soils, and contribute to the germination and growth of plants [25]. Agrotextiles used for this application include: needle‐punched nonwoven natural fibres [58], spun bond nonwovens of synthetic or biodegradable polymers [19], and plain weaves made of natural or synthetic fibres [25]. Textile covers compete with film covers and have supe rior permeability and flexibility properties; these covers are suitable for temperate or warm climates but are not as effective in protecting against ground freezing [19]. Synthetic mulch mats made with fibres such as LDPE, HDPE, PP, and PET [59] are considered agro‐ecological alternatives for weed control, as they minimize the use of chemical herbicides [60] and, in particular, are recyclable. However, these agrotextiles have a high environmental impact on planting sites because they contain nonbiode gradable synthetic polymers; thus, at the end of their useful life, either owing to their deterioration or because the activities of the crop require their removal, they are removed from the crop and sent to landfills, incinerated, or buried at the cultivation site, which causes great harm to the environment [61]. However, mulch mats are one of the agrotextiles that have the most applications using natural fibre [61] and compostable and biodegradable polymers [19]. In the case of natural fibre mulch, various fibres are used, such as jute, flax, hemp, and coconut, with the advantage that the mat will provide nutrients to the soil during the decomposition process and thus contribute to the growth and survival of plants [58]. Similarly, wool mulch mats contribute to crop growth, increase biomass, and are effective in weed elimination [62]. In addition, there are reports regarding the production of mulch mats using biodegradable polymers, predominantly PLA, but also PHA, PLA/PHA [2], PBS, and Mater‐Bi. Some of these, owing to their higher mechanical strength, exhibit a greater durability during the cultivation period relative to that of biodegradable films [19]. Table 10.4 shows selected commercial examples of mulch mats and ground covers.

10.4.4 Root Protection

This group of agrotextiles includes nonwoven materials for controlling root growth [63] and nets used to avoid root damage that can occur when young plants are dug out, transported, or transplanted. Generally, the nets are knitted fabrics made of PET and rubber fibres, while nonwovens are made from PP using the spunbond technique. Nets are a preferred alternative to plastic films because their removal is not required after use because their structure allows the roots to penetrate it and continue growing [5, 11]. Table 10.5 shows a list of selected commercial examples of this type of agrotextile.

10.4.5 Crop Covers, Floating Row Covers, Row Covers

These agrotextiles differ from mulch mats in that they cover the plants and not the planting ground, providing protection near the plant by creating a microclimate close to it and protecting it against environmental and biological factors, such as hail and insects, respectively [64]. Crop covers can be installed either directly over the plant,

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(a) (b)

Figure 10.3 Images of commercial mulch mats or ground covers: (a) CovertexTM, woven groundcover (Source: Reproduced by permission of Hy Tex (UK) Ltd.) and (b) Nonwoven/Mesh biodegradable groundcover (Source: Reproduced by permission of Compañía de Empaques S.A.)

provided that it is sufficiently flexible to allow the plant to grow, or supported by some type of structure, known as a low tunnel [65]. In the past, crops were covered with cotton fabric, which was replaced by transparent, semi‐transparent, or white woven and nonwoven PP or PE spunbond fabric [66]. The main functions of these agrotextiles are to protect plants from frost, heavy rains, and strong winds; decrease the evaporation of soil moisture [67]; and help control pests and viruses. In addition, by modifying the microclimate near the plant, these agrotextiles

Table 10.5 Commercial examples of root protectors.

Type of Commercial Main product name Producer Material characteristics Main applications

Knitted root Root Ball TruNet Rubber Knitted net Holds the soil ball net Netting (Vietnam) Co. and PET together and a Net sizes: Ltd 200–550 mm protects plant roots in diameter from damage during transportation or storage Provides a natural way to transplant trees and shrubs Nonwoven Nonwoven Shenzhen PP Spunbonded Horticulture, root bag Root Control Lifeng Zend nonwoven, floriculture, garden Bags Technologyb diamond and forest design nurseries, Fastest to drain disposable supplies Stops the root tips from spreading a) http://furniweb.com.my/product‐applications/agriculture/root‐ball‐netting/. b) http://www.nonwovenfabric.in/non‐woven‐root‐control‐bags.htm. 10.5 Testing Standards Applicable to Agrotextiles 295 can create a low‐stress environment during the development of the plant [68] that pro duces greater consistency in the quality of the fruits grown and extends the harvest season [64]. In countries with seasons, crop covers are often used in horticulture a week before the frosts begin and until plants are finished flowering; subsequently, they need to be removed [3]. The lighter covers are used primarily as an insect barrier during the warmer months, while the heavier ones are preferred for protection against wind, hail, and frost [2]. Crop covers have a relatively short usage, but their reuse for several crop cycles after removal from the crop is possible, provided that there is no significant deterioration from UV radiation and no mechanical damage and that they have been stored properly and are free of contaminants [65]. The economic and ecological impacts of using these covers is reduced by reusing them [3]. To further reduce the environmental impact of these agrotextiles, the use of biodegradable polymers as substitutes for synthetic poly ® mers has increased and includes PLA, Bionelle (PBS), and Institute of Biopolymers and Chemical Fibers (IBWCh) biodegradable PET in nonwovens manufactured with the melt‐blown technique [66]. The results of using these biodegradable polymers are comparable or superior to that of crop covers made with synthetic polymers. Table 10.6 shows selected commercial examples of crop covers.

10.4.6 Capillary Mats

Capillary mats are a resistant and absorbent type of nonwoven mat that has been used in greenhouses for decades to ensure uniform water distribution to growing plants [69]. These mats use the principle of capillarity to hydrate the plants from the bottom up, allowing water to reach the roots and avoiding foliage damage caused by watering from above (Figure 10.5). Capillary mats are an option for the uniform and healthy growth of flowers and vegetables in greenhouses and even hydroponics [70]. Punching or spun bond techniques are used to produce these agrotextiles, using rayon, PP, recycled acrylic and blends of wool, fibres, and latex. In particular, PP mats have certain advantages over other materials, such as rayon: they are lightweight; resistant to degradation, mould, and chemical substances; easy to cut; and resistant to crushing [2]. Table 10.7 shows selected commercial examples of capillary mats.

10.4.7 Growing Medium

A growing medium is a porous agrotextile mostly used for growing small plants in hydroponic systems and green roofs. These felts are manufactured from different mate rial mixtures: mixtures of biopolymers and natural fibres; viscose and PET; and PP, jute, and cotton [71]. Table 10.8 shows a list of selected commercial examples of this type of agrotextile.

10.5 Testing Standards Applicable to Agrotextiles

Agrotextiles, similar to other technical textiles, are used because their specific proper ties suit the application for which they are designed. In the case of textiles used in agri culture, the selection of the product and its durability and performance during its use

298 10 Agrotextiles and Crop Protection Textiles

(a) (b)

Figure 10.4 Commercial examples of crop covers: (a) Typar®, nonwoven row cover (Source: Reproduced by permission of Johnny’s Selected Seeds) and (b) knitted crop cover.

Terracotta Pot (with sealed drainage hole)

Capillary Mat Soil 3 Water

1 2

Plastic Tray

Figure 10.5 Capillary mats: operating diagram. Source: Reproduced by permission of Angelo Eliades, author of Deep Green Permaculture blog.

are influenced by its mechanical and optical properties, biodegradability, water reten tion, air permeability properties, and weight per unit area. These properties, their importance for the agriculture, the standards governing the tests designed to establish them, and some of their typical values associated with their use are described below.

10.5.1 Mechanical Properties

The mechanical properties of agrotextiles, whether films or nets, play an important role in terms of their performance, durability, and functionality [2, 72]. It is common for polymeric covers or agricultural nets to undergo high mechanical stresses during their installation and use in the field. Agrotextiles are progressively degraded by the applica tion of loads and the exposure to environmental factors such as wind, hail, rain, solar radiation, air temperature, and relative humidity; this degradation is evidenced mainly

10.5 Testing Standards Applicable to Agrotextiles 301

Figure 10.6 Image of a biobased growing medium. Source: Reproduced by permission of FibreDust LLC. by the weakening of mechanical properties [73, 74]. In general, the mechanical proper ties of agrotextiles depend on aspects such as the type of material, processing condi tions, use of additives, and film thickness. Among the most important mechanical properties for this type of application are tensile strength, tearing resistance, and impact resistance. Tensile strength evaluates the ability of the material to withstand primarily tensile forces. Tearing resistance is important, particularly in films, for preventing acci dental cuts or tearing. The impact resistance is required to withstand strong winds and hailstorms [2, 72]. Table 10.9 shows the ISO, ASTM, and UNI standards used for the mechanical characterization of different types of agrotextiles and applications.

10.5.1.1 Tensile Strength The mechanical behaviour of agrotextiles is based on the ratio between the load and the deformation, and indicates the robustness against mechanical stress caused by external loads and installation conditions. Depending on the application, agrotextiles must have the capacity to withstand loads or deformation. The load will cause a deformation, and that deformation will lead to stress in the agrotextile. To avoid premature failures, it is important to determine the type of load the agrotextile will be subject to in terms of its direction and whether there are any concentrations of stress. In general, it is ideal to have a uniform distribution of the loads applied to the material, which is not always possible [8]. By characterizing the mechanical properties of agrotextiles, in addition to the tensile strength corresponding to the maximum stress, it is possible to determine properties such as stiffness, creep resistance, breaking stress, and the deformation performance under load. Specifically, the stiffness of the material is characterized by the modulus of elasticity and is indicated by the slope of the straight section of the stress–strain curve [8, 49].

304 10 Agrotextiles and Crop Protection Textiles

Similarly, the tenacity can be determined based on the breaking load value, as calculated by Eq. (10.1) [8]: Breaking load N Fabric tenacity(/cN tex) 100 Specimen widthm ( m) (10.1) Fabrica rea density (gm/ 2 )

The mechanical properties of agrotextiles, particularly nets, depend on the mechanical properties of the fibres and fibre structure, the structure of the thread, and the structure (knitted and woven) of the agrotextile. Specifically, in fabrics it is standard practice to dif ferentiate between the warp and weft directions, and in nonwovens between the machine and cross directions. Such characterization of mechanical behaviour tends to be aniso tropic. In that regard, it is important to assess the mechanical strength of agrotextiles in either the longitudinal and transverse directions, which are relative to the roll or the extru sion direction of the film. In addition, it is important to establish the elongation at break, which must be sufficient to prevent the agrotextile from deforming during installation [73].

10.5.1.2 Tear Resistance Although the European standards EN 13655 and 13206 set the basic requirements for the physical and mechanical characteristics of various types of films and thermoplastic covers for use in agriculture and horticulture [73, 75], these standards do not include the property of tear resistance. However, this property is relevant in agricultural plastic films and proves to be a complex function of their final breaking resistance. In that regard, there are two different values to determine: the force to initiate tearing and the force required to propagate a tear. The test specifications to measure tear resistance, for both initiation and propagation, can be found in ASTM D1004‐90 (ISO 34‐1). This property can also be measured by the method established by ISO 6383/1 and ASTM D4533 [75].

10.5.1.3 Impact Resistance The resistance to hail of the plastic films used in agriculture and horticulture is closely related to their impact resistance. According to a new standard, EN 13206, the impact resistance of plastic films should be measured per the specifications listed in ASTM D1709 (ISO 7765‐1); this standard is the most appropriate for estimating the energy absorption capacity when external elements impact the cover or net. The energy is expressed in terms of the weight of a missile mass dropped from a specified height that would result in a 50% failure of the sample tested. Under this standard, there are two test methods that can be used; the difference between them is the size of the dart used and the height from which it falls on the sample, differentiated as methods A and B [33, 75]. Method B has been found to be the best suited for the impact testing of nets for agriculture [33].

10.5.2 Optical and Radiative Properties

The shading factor (SF) is one of the parameters used by manufacturers and users of agrotextiles to define the relative amount of radiation that is absorbed and reflected. Specifically, the SF represents a quantitative estimate of the loss of light due to using the agrotextile, but it does not report the qualitative changes (at a spectrum level) [43]. 10.5 Testing Standards Applicable to Agrotextiles 305

Notably, specific bands of the solar spectrum can affect the behaviour of plants. This influence can be either positive, causing plant growth and quality improvement, or negative, causing adverse effects such as fungi growth or reduction in the quality of fruit and flowers [76]. Thus, the shading effect is not limited to the reduction of solar radia tion intensity, because it may also help modify the environmental conditions (tempera ture and relative humidity) to improve plant growth and agricultural production [77]. The transmission of solar radiation through plastic shade nets is one of the key factors to determine regarding their radiometric properties. However, the diffusion character istics of solar radiation through the nets are difficult to determine because this type of material is not homogeneous. Net parameters such as colour, porosity, and texture have an important impact on how the net responds to radiation and therefore on its perfor mance. In general, no specific technical data are available on the radiometric properties of nets or covers used as agrotextiles [78]. In agriculture applications, the radiation spectrum can be divided into two bands: (i) shortwave (SW), which includes the photosynthetically active radiation (PAR, 400– 700 nm), which is needed for photosynthesis and whose absorption is therefore essen tial for plants, and (ii) longwave (LW), which is primarily thermal radiation and includes the near infrared (NIR, 700–1500 nm) [43, 76]. Thermal radiation is the electromag netic radiation emitted by a body based on its temperature. Theoretically, incident radiation can be classified into three types: (i) reflected, (ii) absorbed (which increases the temperature of the material), and (iii) transmitted (which passes through without producing heat). For any given wavelength, the sum of the three previous coefficients must be equal to 1 or 100% [72, 76]. A material is considered transparent when it allows a substantial part of the radiation to pass through it, whereas an opaque material blocks radiation. When radiation passes through a semi‐transparent or translucent material, it is dispersed in all directions and creates shadows. The perfect material for shading should allow 100% transmission in the PAR range, which is impossible. To obtain the optimal greenhouse effect, a favourable material for shading must be transparent to solar NIR radiation and as opaque as possible to IR wavelengths [72]. In terms of use, the photodegradation generated in agrotextiles by solar rays occurs as a surface reaction, caused by UV radiation, that causes both physical and chemical changes and deteriorates the mechanical properties of the material [53, 54, 74]. UV additives and antioxidants used for stabilizing covers and nets prevent premature deg radation of the material [2, 5, 34]. It has been determined that not only age but also dust and condensation influence the transmissivity of agrotextiles covers. These factors result in radiation losses [72]. To improve the response of agrotextiles to radiation, aluminized PET fabrics resistant to UV rays that are highly reflective and protect against strong solar radiation and increase the internal temperature of greenhouses [27] are used, as are reflective alumin ized shade nets made with PP for photosynthetic use in lemon crops [79]. Transparent agrotextiles allow optimal light transmission of the appropriate waves of the spectrum (i.e. PAR) [1], while coloured nets and mulches modify the spectral composition of the light transmitted and the light reflected, which makes them attractive for use with fruit crops and ornamental plants [34]. Nets in colours such as white [37], yellow, green‐yel low, black, pearl, and silver have different effects on the levels of protection against insects and pests, thus influencing the productivity and quality of crops [73, 80]. The amount of shade and colour used affects the quantity and quality of the light that plants 306 10 Agrotextiles and Crop Protection Textiles

receive, which directly influences their branching; spread of roots; productivity; and quality of the fruits, flowers, and vegetables [81]. There are reports that the use of blue and grey nets has negative effects on fruit crops; however, it has also been proposed to use nets made with blue fibre to protect maize crops from bird attacks [35]. The use of coloured or photoselective nets produces significant changes in reproduc tive behaviour and certain ripeness parameters [80]. Nets and photoselective polymeric films can be made with translucent threads and additives, respectively, that act as a shade that selects the bands of the light spectrum transmitted through them [72]. Over the past decades, the use of agrotextiles with optical and radiative properties has been increasing because these materials can generate economic benefits in terms of saving energy and increasing crop quantity and quality [82]. It is possible to find metallized woven and nonwoven materials for applications in greenhouses, nurseries, and orchards that are used to prevent heat losses or, alternatively, to protect from excessive solar radiation [3]. There are several standards that, although not specific for measuring radiometric properties of the material, establish the performance and durability of the material through accelerated degradation under test parameters and light sources that simulate weather and radiation conditions, respectively. The standards available for testing agro textile materials under accelerated conditions and to evaluate deterioration are ASTM D5970, ASTM D4355, ASTM G151/ASTM G152/ASTM G153/ASTM G154/ASTM G155, EN 12224/EN 12226, ISO 4892‐1994, ASTM D4355, and EN 12226 [74]. There are reports of a simple method to determine total hemispherical longwave radiative properties [82]. Similarly, global radiation has been characterized using poly mer nets for shade and measuring each of the parameters that make up such radiation [76]. The integrating sphere method is a laboratory technique considered the most reli able for measuring the radiometric properties of agrotextile materials; it has been adopted by most of the existing international standards. A variation of the integrating sphere method is the double‐beam spectrophotometer technique, which is used to measure the direct spectral transmittance of films in the solar range [73, 81]. The spec tral refractive index of thin films and sheets can be determined using the spectroscopic ellipsometry technique [77]. The SF of the plastic nets has been measured using the Italian standard UNI10335, which outlines a specific methodology to assess this param eter [78]. To anticipate the durability of plastic covers used in agriculture and horticul ture, the standard UNE‐EN‐13206 defines three climatic areas as a function of solar radiation and establishes a correlation between natural and artificial ageing through the artificial accelerated ageing test [72]. In general, the need to establish standards and specifications for the radiometric and optical characterization of agrotextile nets and films is evident [76, 82].

10.5.3 Biodegradability

Polymer based agrotextiles are commonly used in agro‐industrial mass production, which is a growing problem, because of their final disposal. This challenge has led to the search for sustainable alternatives, among which is the potential use of biodegradable plastics that are compostable and can degrade in the ground or water after a short or pre‐determined period of time, as shown in Figure 10.7 [20]. 10.5 Testing Standards Applicable to Agrotextiles 307

0 month 6 months 12 months 18 months

24 months 30 months 36 months 42 months

Figure 10.7 The degradation process of the immersed biodegradable monofilament observed with scanning electron microscope. Pictures show the degradation states at 6‐month intervals up to 42 months. Source: Reproduced from [20], with permission of John Wiley & Sons.

To avoid waste accumulation of plastics used in agriculture, it is necessary to control the degradation of the material using polymers with light‐sensitive pro‐oxidant addi tives. However, this practice causes controversy because greater and irreversible pollu tion of agricultural land can result from the accumulation of fragments produced by the photodegradation of the material [34, 83]. This issue has prompted many researchers to search for agrotextiles that are properly biodegradable or compostable. In general, agro textiles based on biodegradable materials have poorer mechanical properties than com monly used nonbiodegradable polymers, which is one of the main disadvantages of using this type of material. Ideally, these materials would maintain their physical and mechanical properties while in use; subsequently, their biodegradable nature would allow microorganisms to degrade them into methane or CO2, water, and biomass [84, 85]. Another important practice applied in agrotextiles is the use of natural fibres such as jute, coconut, and cotton, among others. In addition, fully biodegradable polymers have been used; these materials have the advantage of biodegradation but have less service time than that of synthetic fibres [5, 59]. Other materials used include 100% composta ble fabrics composed of PLA fibre for positioning plants on the ground, coconut fibre mats for the accelerated growth of roots and to support plants, and nonwovens made of bagasse fibre in pots [2]. There are no reports of regulations for testing biodegradable agrotextiles. Therefore, to test the compostability of a biodegradable material in accordance with international regulations, biodegradable plastic products may be tested under ASTM D5338 or European standards EN 13432 or EN 14995 [86–88], which define the technical speci fications for the compostability of plastics products. According to these standards, agrotextiles must be biodegradable and disintegrate in a composting system within a certain timeframe, and the compost produced must meet the quality criteria set by the standards. In countries such as Germany, the United States, Belgium, and Australia, among others, programmes and certifications exist for biodegradable products, which must comply with standards relating to compostability, such as EN 13432, or to plastics in general, such as ASTM D6400 [89]. 308 10 Agrotextiles and Crop Protection Textiles

Biodegradable materials to produce agrotextiles for agricultural and aquacultural applications are an environmentally friendly alternative. Studies have been performed on bioplastics and nonwoven bio‐fabrics in tomato and bell pepper crops [19]; biode gradable nonwoven fabrics in onion production [90]; biopolymers based on mixtures of 82–95% PBS and 5–12% PBAT for nets used in ponds and fishing nets to prevent the phenomenon called ghost fishing [20, 91]; biodegradable films for mulching for crop ® improvement; and compounds of PLA, ECOFLEX , and cellulose fibres, among others [14, 34].

10.5.4 Water Retention

Favourable water retention and transfer properties are required for both woven and non woven agrotextiles that are designed for applications such as filtration, separation, and drainage or for use as covers for agro‐plantations, weed control, humidity control, soil stabilization, and erosion control [8]. Agrotextiles used in this last application must have a high potential for water retention and must reduce evaporation to avoid soil dryness [2]. The water absorption capacity of agrotextiles can be determined using ISO standard 9073‐6 or ASTM D4491. In general, the test consists of subjecting samples that have been previously weighed to normal weather conditions. These samples are soaked in distilled water for 24–48 hours and then hung in the open air to allow excess absorbed water to drip away. Finally, the samples are placed on blotting paper for five minutes to finish absorbing excess water present on their surface. Equation (10.2) [92] is used to determine water absorption capacity as a percentage:

WWwetdry Wabs % 100 (10.2) Wwet

where Wdry is the mass in grams of the dry test sample and Wwet is the mass in grams of the wet test sample at the end of the test. A recent use of nonwoven agrotextiles is aimed at increasing the humidity in green houses and distribution of moisture of the growing plants [2, 5]. Mat type covers made with mixtures of synthetic and natural fibres that serve as a water reservoir for plants have also been used [25]. Recent studies report the use of mats made with jute blended with PP, as a replacement for rayon products in horticulture. These jute blends are more efficient because of their rapid water absorption, and they are lighter and more resistant in wet environments. The use of nonwoven coconut fabrics for the retention of moisture for long periods of time and for filtering excess water in other cases is increasing. In activities such as fish farming, the retention of water in ponds is essential. For that rea son, geotextiles are perfect for creating a waterproof layer for fishing ponds and limiting filtration in highly permeable soil regions [2]. Another use for agrotextiles is wrapping PE pipes in agricultural drainage systems to improve permeability and control the level of water in the soil [25]. Hydrogel based agrotextiles have the characteristics mentioned above and can therefore fulfil some of the applications of the nonwoven fabrics [34].

10.5.5 Measurement of Air Permeability

Plastic nets are widely used as agrotextiles to protect crops against insects and birds and to protect crops of fruit and ornamental plants against snow, wind, or strong rain; these 10.5 Testing Standards Applicable to Agrotextiles 309 nets are also used to provide shade to greenhouses or modify their microenviron ments [32]. The flow of air through the net depends on different geometric parameters, such as the thread diameter, wet perimeter, mesh size, type of fabric, and porosity. The main parameter for defining the flow characteristics of air passing through the net per unit of area is porosity. It is important to note that the pressure drop is a function of the poros ity and the Reynolds number (Re). For laminar flow, Re will be low, and the air pressure drop will increase; for turbulent flow, Re will be high, and the air pressure drop will be independent of Re. The basic property that characterizes the flow through porous media is the permeability [32]. In a steady state of incompressible flow of fluid through a highly porous medium, the permeability can be obtained using the unidirectional momentum equation for fluids in homogeneous and isotropic porous media that was established by Darcy and extended by Forchheimer (Eq. (10.3) [33]).

dp F v v2 (10.3) dx K K where −dp/dx is the pressure drop in the x direction, μ is the dynamic viscosity, v is the Darcy velocity of the fluid (ms−1), K is the permeability (m2), ρ is the relative density (kg m−3), and F is the inertial coefficient. In particular, K represents the ability of the medium to transmit the fluid through it, and F represents an empirical function that depends on the microstructure of the porous medium [32]. Equation (10.3) expresses the pressure drop gradient perpendicular to the direction of flow as a function of the speed of the fluid. In a practical sense, it describes the ease with which a fluid moves through a porous structure [93]. For slow flow rates, the quadratic term of Eq. (10.3) can be ignored, which leads to Darcy’s law, as shown in Eq. (10.4):

dp v (10.4) dx K Standard ASTM D737 is typically used for testing the air permeability of fabrics, both woven and nonwoven. In general, the test involves placing the agrotextile sample in the measuring equipment (i.e. an air permeability tester), and setting an input pressure. Once the test starts, air is passed through the sample and measured by a pressure gauge; the result is reported in units of volume of air (cm3) that pass per second through 1 cm2 of fabric at a given pressure difference [8, 94]. The air permeability value can be calcu lated by dividing the flow speed, measured in cm3/s, at a known pressure (usually 1 cm) by the test area. Equation (10.5) shows how to calculate the sectional air permeability (SAP) [8]:

cm33/ cm SAPair permeability value mean thicknesscm (10.5) s

Additionally, studies have been performed on air permeability for nets made with round HDPE monofilaments and flat woven materials based on the standard UNI EN ISO 9237, and the standard PN‐EN ISO 9073 has been used for the air permeability characterization of nonwoven materials [32]. 310 10 Agrotextiles and Crop Protection Textiles

10.5.6 Fabric Weight

Fabric weight is the weight per unit area, and it is expressed in g m−2. The standard used for this test is ASTM D3776 [95], which is relatively simple and consists of carefully cutting samples of the agrotextile (woven or nonwoven) to subsequently weigh them on a precision scale. A significant number of measurements are necessary to obtain a reli able average result [94]. Table 10.10 shows the weights per unit area for agrotextiles in different applications. The data vary according to the application, material used, yarn, and fabric structure. Nonwovens are gaining acceptance as agrotextiles in applications such as ground and crop covers [2]. Among those applications are uses in greenhouses, gardens, orchards, vineyards, and other areas, where their purpose includes humidity control, weed control, frost protection, shade, soil separation, soil stabilization and erosion control, and promotion of germination and plant growth. Spunbond nonwovens are commonly used in such applications, with weights per unit area between 20 and 100 g m−2 [25]. Nonwoven fleece covers have been reported to typically weigh between

Table 10.10 Fabric weight of some agrotextiles.

Area of application Fabric weight [g/m2] References

Pest control fabric 17 [11] Winter covering system 30 Nets for protecting grassy area 30–40 Bird protection/shading net/windscreen Plant net Bird protection 40–80 Shading net Harvesting net 40–90 Windscreen Packaging material for agricultural products 50–60 Mulching and shading 60 Windbreak net 40–445 [27] Harvest net 33–110 Insect‐proof netting 80–135 34–130 [96] Shading net 40–240 Hail protection netting 40 45–65 Antibird netting 110–135 13–50 Meant for the covering of plants 15–60 [97] Embankments and slopes 100–500 10.6 Sustainability and Ecological Aspects 311

17 and 20 g m−2 [34]. Below are the weights per unit area for nonwoven agrotextiles reported in [2].

●● Jute‐PP‐blended needle‐punched nonwovens as mulching material (30–70 g m−2). ●● Plant cover with nonwoven PP for protecting horticultural crops (46 g m−2). ●● PP, PE, or polyamide nonwovens meant for the covering of plants (15–60 g m−2). ●● Fabrics for insect control and for frost protection: (10–50 g m−2). ●● Agrotextile row covers (42 g m−2). ●● Cabbage and cauliflower. High protection from the attack of insects/pests, porous enough to allow water/pesticides if required, recommended for cold climate (17–19 g m−2). ●● Floating row covers have been shown to provide pest control in several regions with a variety of crops (10–17 g m−2). ●● Protection from frosts of crops (strawberry, lettuce, flowers, melons, watermelons, pumpkins, tomatoes, peppers, summer squash, green chilly) (17–30 g m−2). ●● UV stabilized PP needle‐punched nonwoven fabric the outdoor storage of straw bales and sugar beets (140 g m−2). ●● Use of fruit cover for grapes, guava, pomegranate, Alphonso mango, vanilla, jackfruit (17–25 g m−2). ●● Spunbonded nonwoven fabric for banana bunch, cover bag (18–25 g m−2). ●● Landscaping fabrics or weed barriers: for most domestic applications (60–70 g m−2).

10.6 Sustainability and Ecological Aspects

As previously mentioned, agrotextiles’ characteristics allow the increase of the pro ductivity and the quality of agricultural goods. This will help us meet the increasing demand for food, which currently is been threatened by limited land availability, declining soil fertility, and weather variability and climate change. Increasing sus tainable crop production should also seek to preserve and enhance the natural resource base and environment to reduce the impact of climate change [2]. Agrotextiles present different functional benefits in the agricultural field that can contribute to this sustainability intensification; for example, they reduce the need for chemicals such as fertilizers, pesticides, and herbicides, because such textiles protect crops against weed growth and prevent insect attacks [29]. Owing to this, the use of these materials results in the optimization of water use because they avoid loss of soil moisture. Other features that agrotextiles materials present to intensify crop production sus tainably are: (i) they do not affect the crops or the soils; (ii) they lead to low moisture conditions, reducing the risk of fungi contamination because they give very good venti lation and permeability of soil; (iii) nets do not affect the growth of both crops and fruit trees; (iv) they are not toxic to birds or other animals; (v) waste is diminished or elimi nated, owing to the protective properties for crops against weather and pests; (vi) exhibit resistance to solar radiation and ultraviolet light, to frequent thermal, weather, and wind changes, and to mildew and degradation; (vii) they can be reused several seasons; and (viii) they can be biodegradable once they have fulfilled their function in the crop [2, 5, 29]. 312 10 Agrotextiles and Crop Protection Textiles

Biodegradable agrotextiles can be made by using natural fibres or biodegradable syn thetic fibres. In economic terms, natural fibres have the advantage to be less expensive than synthetic fibres. Besides, they are biodegradable and renewable, have neutral CO2 emission, a high moisture retention capacity which prevents the soil from drying out, and play an important economic roll for developing countries in the preservation and understanding of cultural heritage [7, 10]. According to the FAO [6], the use of natural fibres is a priority of global organizations because they increase the effectiveness and sustainability of agricultural industries worldwide. Owing to these issues, there is a global trend towards sustainable development focused on the use of renewable raw materials such as natural fibres, which are nowadays increasingly used for the prepara tion of woven and nonwoven textile structures [94]. Some examples can be find in sci entific literature [8, 29, 31, 98].

10.7 Conclusion

The agrotextile industry is one of the best‐placed industries to meet the demands of an increasing global population and the challenge of finding suitable soils for producing sufficient food to feed it. Other reasons are the changing climatic conditions encoun tered by crops and challenges in controlling pests and other threats in the development of agricultural products. The use of textiles to improve the conditions under which crops are established or developed has gained importance. Similarly, the use of textiles in aquaculture has been, for years, one of the most important tools in fish farming and catching, particularly for food purposes. In this regard, agrotextiles are produced to fulfil a technical function such as crop protection, promoting crop development and allowing fish reproduction, or catching. Agrotextiles offer advantages in flexibility and breathability, and have greater ease of installation relative to polymer films. Each type of application has a series of requirements to which the agrotextile is sub jected. Therefore, a series of tests and standards are required to determine properties according to the function and environment to which the agrotextile will be subjected and to help establish degradability properties to help predict how and under what con ditions the final decomposition process will occur. The type of fibre used in the development of agrotextiles is important to ensure that the textile fulfils its protective functions efficiently and that it will withstand the envi ronmental conditions. Because synthetic fibres such as PP, PE, PET, and PA comply with these requirements, these fibres have been for many years the primary option for producing agrotextiles; however, these fibres are not biodegradable and have a signifi cant impact on the environment once their useful life ends. In response to this situation, recycling or the use of recycled materials is sought in certain applications, such as fishing nets and certain types of agricultural nets and cov ers. Although this approach reduces the negative effects of using nonbiodegradable synthetic materials, in the end it is still insufficient. Therefore, the use of biodegradable and compostable polymers and of natural fibres in applications that allow it is gaining importance in the agrotextiles market. Producers and consumers are increasingly aware of the environmental impact of using this type of textile and are therefore seeking more sustainable alternatives. References 313

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Building and Construction Textiles Jordan Tabor and Tushar Ghosh

North Carolina State University, Raleigh, North Carolina, USA

11.1 Introduction

From the dawn of civilization, humankind has sought shelter from the elements. Early nomads used tent‐like structures made of furs and fabrics that were lightweight and easy to carry. As more permanent human settlements emerged, more durable building materials were introduced. Fibre reinforced composites were in use as early as 1500 bce, when early Egyptians and Mesopotamians used straw‐reinforced mud to create strong and durable buildings [1]. Use of fibrous materials as insulation dates back to ancient civilizations [2]. Over the thousands of years, use of new materials and technologies turned human ‘shelters’ from caves to current ‘smart’ homes. It is uncertain exactly when textiles were introduced as a construction material. However, today textile materials are used extensively in the construction of large and small public spaces (temporary or permanent) as well as other civil engineering structures, such as roads, bridges, and tunnels. Textiles, in fibre, yarn, or fabric form, combine excellent strength, resilience, and flexibility with low weight, resulting in desirable construction materials for multitudinous functions and appearances. The discovery of new fibre forming polymers and processing technologies used in textiles together with a better understanding of textile structures and their mechanics have led to new applications of these materials in construction. Relevant knowledge of fibrous materials is even more important today in light of ongoing climate change and its potential future impact on human ecological systems, population distributions, and migration. In this chapter, the state of the art of textiles used in construction of buildings is discussed. The use of textiles in temporary and permanent structures for buildings and other civil engineering structures, such as highways and bridges, is well documented [3]. The primary focus of this chapter is on the various textile products utilized in building/construction applications including architectural textiles, house wraps, insulation, and textile reinforced concrete (TRC).

11.2 Architectural Textiles

Architectural textiles are fabrics (or fabric reinforced membranes) that are used in the construction of relatively static enclosed environments. Fabrics may be used either as load bearing structural members or as membranes separating the enclosed environment from the outdoors. The earliest use of textile fabrics in portable, temporary structures is often associated with nomads. By most accounts, textiles were not widely accepted as ‘engineered’ architectural applications until the mid‐twentieth century. At this time, manufactured fibres and fabric treatments were developed which improved the mechanical, physical, and chemical properties of fabrics – allowing them to be more successfully integrated into architectural applications [2]. The genesis of today’s architectural textiles likely began with the development of radar domes by Walter Bird [4]. Today, fabrics are not simply used in speciality structures or as auxiliary components but rather as integral structural units. In some architectural applications, textiles comprise entire structures, determining the shape and functionality of the building [2] (see Figure 11.1). The Elrey Jeppesen terminal within the Denver International Airport, shown in Figure 11.1a and b, is one of the most recognized tension fabric structures in the world. This structure incorporates two layers of fabric membrane to provide sound and thermal insulation. The terminal was completed in 1994 and is composed of 375 000 square feet of polytetrafluoroethylene (PTFE)/glass fabric membrane. Figure 11.1c and d shows the Estádio Nacional which is a stadium located in Brasilia. In 2014, a tensile roof structure was installed on the stadium which was constructed of 920 000 ft2 (85470.7968 cm2) of double‐layer PTFE/glass fabric as an outer layer. Finally, a soccer dome in Chicago, shown in Figure 11.1e and f, is an air‐supported two‐layer fabric structure which was manufactured using vinyl coated polyester fabric as the outer membrane. These figures provide a few examples of the capabilities of architectural textiles. Traditionally, fabric based structures conjure the image of a limp fabric supported at the top by a pole and anchored to the ground, i.e. tents. Today’s architectural textile structures are very different from tents. In tents, fabrics flap and billow in the wind and can only support forces using gravity. Comparatively, in architectural fabric structures, the skin remains taut, preserving the static equilibrium of the system under most environmental conditions. There are many obvious advantages in using textile fabrics for enclosures rather than traditional materials. These include: ●● Fabrics are much lighter than conventional building materials. This allows significantly larger span lengths (i.e. longer distance between supporting structures, like columns). ●● Fibrous materials can be transported easily, owing to low mass packing volume. This is ideal for tactical structures. ●● In the case of failure, the low mass of fibrous materials poses little risk. ●● Seismic forces are proportional to a structure’s mass, so heavy steel and concrete structures experience large forces. Alternatively, fabrics have high strength‐to‐weight ratios. As a result, properly designed fabric based structures perform well during seismic activity. ●● Fabric systems can be designed with the desired level of translucency and UV‐blocking agents specific to a location’s climate. This allows natural light to enter the structure which reduces the need for artificial lighting, thereby lowering energy costs. 11.2 Architectural Textiles 321

(a) (b)

(e) (f)

Figure 11.1 Examples of architectural fabric structures. (a) the Elrey Jeppesen Terminal at the Denver International Airport; (b) the interior view of the Elrey Jeppesen Terminal; (c) Estádio Nacional in Brasilia; (d) close‐up of the roof structure of Estádio Nacional in Brasilia during installation; (e) a soccer dome in Chicago; (f) interior of the soccer dome shown in (e). Source: Images 11.1a–d, courtesy of Birdair, Inc. Images 11.1e–f, courtesy of The Farley Group.

●● The reflectivity of the fabric exterior surface can be modified to reduce heat gain, resulting in energy efficient buildings in warm climates. ●● Potential fabric based architectural shapes are unique. The principal structural forms are doubly curved surfaces, shapes that are difficult to achieve using conventional materials. This provides organic designs which are drastically different from traditional buildings. The two most important materials used to build a fabric based structure are fabrics and cables. These materials do not have any stiffness in bending or in‐plane 322 11 Building and Construction Textiles

compression, and can only support tension. Therefore, the fundamental principle for designing stable fabric structures is ensuring that fabrics and cables remain under tension. As a result, the fabric is always pre‐tensioned or post‐tensioned by some means to develop stability. Accordingly, architectural textile structures are generally classified into two categories based on the method of applying tension: air structures and tension structures.

11.2.1 Air Structures

In air structures, air pressure is used to pre‐strain the fabric such that the material is capable of resisting external forces. The air pressure acts outward and normal to the fabric membrane surface. The structure remains in equilibrium and stable by maintaining a pressure differential within the enclosure. Pressure differentials (from inside to outside) result in structures that are doubly curved and concave or convex all over or synclastic (e.g. domes); see Figure 11.2a. There are two principal air structures: air supported and air inflated structures.

11.2.1.1 Air Supported Structure In air supported structures, an external force acting outward and normal to the membrane surface is generated using a small pressure differential over atmospheric pressure to apply and maintain tension in the fabric membrane and in turn to support the weight of the structure and external loads. The textile membranes (or fabrics) in this application serve primarily as protective barriers that separate the outside environment from the inside, while the pressurized air is primarily responsible for resisting loads applied to the structures [5]. The study of soap bubbles helps to better understand how air supported structures ideally work. Soap bubbles possess equal stress in every direction and are well suited to resist the primary state of stress. Therefore, designers have developed soap‐bubble‐ shaped structures that help air supported structures achieve their ideal behaviour [6]. Air supported structures are generally sections of spherical membranes. Hemispheres are suitable for buildings of greater heights and can withstand large pressure differences. Three‐quarter spheres are generally used as hulls for radar stations. The fundamental difference between air supported structures and other conventional structures is that for air supported structures there is no theoretical maximum span length as determined by material properties. In conventional structures, higher span length may

(a) (b) (c)

Figure 11.2 Examples of potential architectural fabric structures. (a) Basic hemisphere, example of a synclastic structure; (b) basic saddle point, example of an anticlastic structure; (c) hyperbolic paraboloid, another example of an anticlastic structure. 11.2 Architectural Textiles 323 cause buckling of the structure because of its own weight. Therefore, air supported structures are the most efficient structural systems available to achieve long spans [7]. Air supported structures are often accessible through air locks or pressure balanced doors, like revolving doors, to minimize escaping air [7]. Additionally, these structures may comprise a single membrane material or a reinforced membrane. Single membrane structures require strong envelope materials that provide uniform properties throughout. This can be achieved with materials like films or coated fabrics. Reinforced wall structures possess double or triple walls to ensure safety, reshape the building, stabilize the envelope under loads, as well as provide additional thermal insulation [8].

11.2.1.2 Air Inflated Structure Air inflated structures are quite different from air supported structures. In air inflated structures, the space between the inner and outer skins of the structure, or the structural elements, is inflated to relatively high pressures to achieve the level of pre‐stress required to resist compressive loads. The occupied space in this instance remains at atmospheric pressure and no airlocks or revolving doors are necessary. In these types of systems, inflated components such as arches, beams, or columns are utilized. These elements must be inflated to high pressures to provide the necessary pre‐stress to resist compressive loads [7]. Structurally, inflated elements act more as shell structures compared to the membrane‐like behaviour in the air supported structures. Air inflated structures are relatively less efficient than other structures (which possess steel/wooden column, truss, etc.) in supporting transverse forces. However, they are easy to construct and dismantle. Other advantages include the materials’ low weightiness, portability, compact packaging, and the elimination of airlocks which are required in air supported structures.

11.2.2 Tensioned Fabric Structures

Tensioned fabric structures are considered self‐supported; therefore, no externally applied force, such as air pressure, is necessary. The pre‐tension in the structure is developed using negative Gaussian curvature or anticlastic shapes with opposite curvature in two principal planes, (Figure 11.2b and c). Stability is provided by the opposing curvatures which enable the surface to be tensioned without losing its form. A hyperbolic paraboloid, or saddle, is an example of an anticlastic surface, where the tension along one arc is resisted by tension in the opposing curved element. These structures are used more widely for permanent architectural solutions. Structural membranes are required to withstand a larger amount of stress compared to air supported structures. The membrane material is particularly important for tensioned structures. Tensioned fabric structures are unique because the fabric membrane must have strength and curvature appropriate to resist applied loads. The success of the textile structure largely depends on the performance and serviceability of the selected material. It is particularly important that the materials provide high strength, modulus, and elasticity such that stability is maintained during loading [7].

11.2.3 Material Requirements

Membrane materials used for architectural applications should generally be flexible and lightweight, with adequate strength and durability. Other properties of interest include 324 11 Building and Construction Textiles

flame retardancy, thermal conductance/mass, and opacity. For air structures the membrane should ideally be impermeable to air. Two types of membrane structures are used for architectural structures: first, coated or laminated fabrics, which consist of a textile substrate (woven or nonwoven) with a protective polymer coating, and second, single layer polymeric films (or foils). The functional behaviours – particularly mechanical and optical properties – of coated fabrics and films are very different and their use is determined by application requirements. In general, films (or foils) are considered suitable for transparent cladding or roofing applications. The current discussion will be limited to coated fabrics. A sectional view of a typical coated fabric membrane used in architectural applications is shown in Figure 11.3a. Each component of the multilayered structure serves a specific function: ●● The fabric (referred to as ‘base fabric’ in Figure 11.3a) provides the material’s mechanical strength, stiffness, etc. ●● The coating portion of the fabric (referred to as ‘main coat’ in Figure 11.3a) provides the membrane stability, weatherproofing, UV protection, abrasion resistance, as well as fire resistance. ●● The top coat is used to seal the material from dirt and other pollutants in order to improve the material’s durability [2]. Typically, the fabric layer of the coated fabric is woven from polyester, glass, or aramid yarns [9]. The fabric layer of the structure provides the multilayered structure with the

top coat primer main coat adhesion layer base fabric adhesion layer main coat primer top coat (a)

(b) (c)

Figure 11.3 (a) Coated fabric multilayer structure (Source: Photo provided by MEHGIES® by Low & Bonar); (b) plain weave configuration; (c) 2 × 2 basket weave configuration. 11.2 Architectural Textiles 325 necessary mechanical properties – stiffness, tensile strength, and tear resistance – to withstand pre‐stressing processes as well as external loads during use. Two weave designs are commonly utilized for the fabric base layer: plain and basket weaves (see Figure 11.3b and Figure 11.3c [2]). The weave design and other structural parameters (yarn mass linear density, etc.) influence almost all mechanical properties of the ultimate architectural membrane. Commonly applied coatings include polyvinylchloride (PVC), PTFE, expanded polytetrafluoroethylene (ePTFE), polyvinylidene difluoride (PVDF), and silicone [9]. The most commonly used coated fabrics in architectural textiles are: first, PTFE coated glass fibre fabrics and, second, PVC coated polyester fabrics. PTFE or ePTFE coated glass substrates have excellent mechanical properties as well as environmental stability. These fabrics are generally used for long life (~30+ years), permanent structures. Structurally, PTFE and ePTFE fibreglass fabric membranes are waterproof, UV resistant, and chemically inert, with exceptional stain and mildew resistance. PTFE/glass fabrics provide better resistance to soiling than ePTFE coated glass substrates [10]. ePTFE is an improved variation of PTFE with a microporous structure which provides superior thermal and creep behaviour [11]. Glass fibre fabrics may also be coated with silicone. Silicone coatings may be used on glass fibres rather than PTFE because they provide better flexibility and translucency. However, silicone attracts more dirt compared to the ‘self‐cleaning’ PTFE. PVC coated polyester fabrics offer optimal cost‐durability ratio [12] compared to PTFE coated fabrics. PVC membranes are commonly coated with a protective layer of PVDF for improved durability. Functional finishes are often applied to these fabrics as a part of the coating to enhance performance. The functional finish utilized can have a large effect on the ultimate properties of the substrate [13]. The precise properties necessary for architectural textiles are dependent on the location of the installation as well as its intended application. However, the most common and critical properties required for architectural textile materials are discussed in the following sections.

11.2.3.1 Mechanical Properties The most important feature that architectural textiles must provide is adequate mechanical behaviour. The membrane material must be able to withstand applied stresses and strains under extreme environmental exposure. Over its lifetime, an architectural textile membrane must be able to withstand static loading. In the case of tension structures, the membrane must be able to withstand static loading during pre‐tension application. Air structure membranes must be able to withstand inflation pressure. Regardless of structure type (air structure or tension) the material must be resistant to live loads due to snow and wind. In general, high tensile strength, high modulus, and low creep deformation are desired for architectural materials. For most applications, high tear strength and puncture resistance as well as resistance to tear propagation are important. Shear stiffness of coated fabrics is generally in orders of magnitude greater than that of an equivalent woven substrate [8]. It is easier to create shaped surfaces with membrane materials having low in‐ plane shear stiffness. A critical consideration in choosing the appropriate material for architectural applications is the long term environmental stability of the material. The membrane must retain its critical properties upon exposure to environmental conditions, such as moisture, temperature, ultraviolet radiation, oxidation, dusts, and salts 326 11 Building and Construction Textiles

within the air, as well as potential corrosive gases that may be present in the environment. Over time, there may be significant changes in the material behaviour [14].

11.2.3.2 Fire Resistance An ideal architectural membrane must have superior fire resistance to ensure sufficient time to evacuate the building in the event of a fire. When considering textile structures, it is important to examine the material’s behaviour when ignited, its flammability, and the characteristics of the smoke generated by the fabric as well as the burning drops produced by the fabric [2].

11.2.3.3 Thermal Behaviour Energy expended in the heating and cooling of buildings accounts for a significant part of the world’s total energy use and greenhouse gas emissions. Thermal behaviour of structural materials is one of the key parameters in the design and construction of energy efficient buildings. In choosing appropriate thermal characteristics for building envelopes, designers try to maintain the internal environmental conditions at a comfortable level under varying external environments, using the minimum resources in terms of materials and energy. Desired thermal properties are often complex because of the significant changes in the external environment over seasons and over the 24 hours of a day. Depending on the location and time, the building envelope may be required to absorb heat, store heat (high thermal mass), or reject heat (high thermal insulation). In general, comfortable spaces are created using traditional materials of appropriate thermal mass and thermal insulation. High thermal mass helps minimize variations in internal environment as the external conditions change, while high insulation isolates the inside from the outside. Unfortunately, most architectural membranes possess low thermal mass and high thermal conductivity. Therefore, changes in external environment can quickly change the internal temperature and comfort of a textile structure. For example, a 1500 gsm PVC coated polyester fabric, which is one of the heaviest fibrous materials used as architectural fabric, provides a global thermal conductivity of 6.4 W/m2/°C. Extruded polystyrene insulation, a common material used in traditional buildings, possesses a thermal conductivity of 0.5–3 W/m2/°C [2].

Figure 11.4 Haj Airport in Jeddah, Saudi Arabia. Source: Image courtesy Birdair Inc. 11.3 House Wraps 327

There are potential solutions to alleviate this problem. In cold climates, designers can incorporate double or triple layer external envelopes to provide stationary air spaces to improve the thermal behaviour of the structure. The textile structure can incorporate a suitable translucent fabric to take advantage of the greenhouse effect which can harness both direct and diffused solar energy. Additionally, using low emissivity or ‘low‐e’ fabrics can drastically reduce the heat transfer. By contrast, in warm climates, utilizing the ‘parasol effect’ is advantageous. In this case, less‐translucent fabrics should be incorporated into the structure, and drafts should be generated to reduce the ambient temperature of the structure. This concept is employed in the Haj Airport in Jeddah, Saudi Arabia (see Figure 11.4), where indoor temperatures of 25 °C have naturally been attained, despite its desert location [2].

11.3 House Wraps

House wraps have significantly changed the way the construction industry manages moisture within buildings. House wraps are highly engineered textile materials which provide air infiltration resistance, a barrier to water penetration, and water vapour permeability. House wraps, also referred to as ‘weather‐resistive barriers’, are installed outside of sheathing [15] and under cladding materials such as stucco (cement plaster) wood, or wood derived products, vinyl (PVC), and masonry veneer [16]. When installed properly, house wraps can provide energy savings exceeding 25%, lower the cost to construct buildings, and reduce the potential for moisture related issues such as rotting and moulding [17]. Some methods of installing house wraps into wall systems are shown in Figure 11.5a and the actual application of house wrap material is shown in Figure 11.5b1. House wraps are considered a second layer defence for homes. As shown in Figure 11.6, house wraps fulfil three essential functions.

Timber Frame Timber Frame Traditional (Reversed construction Horizontal Weatherboarding)

(a) (b)

Figure 11.5 (a) Two possible wall construction incorporating DuPont™ Tyvek®; (b) installation of Tyvek by DuPont. Source: Photos provided by DuPont.

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Figure 11.6 Schematic of house wrap responsibilities. Water Vapor

Water

Air

Housewrap

●● House wraps allow water vapour to pass freely. House wraps are vapour permeable membranes which permit moisture transfer [18]. This is possibly the most important function of house wraps. House wraps are designed to allow the passage of water vapour to prevent moisture accumulation. This reduces the risk of mould growth on wooden framing/walls and eventual rotting of the structure [15, 19]. This concept is shown in Figure 11.7 which compares the state of oriented sheet boards (OSBs), one of which was protected by a low vapour permeable house wrap while the other was protected by a high vapour permeable house wrap. ●● House wraps serve as a backup layer, secondary to siding, responsible for protecting sheathing. If siding is properly installed there should be no water leakage [19]. However, siding may expand and contract, which creates gaps behind the exterior. Additionally, wind driven rain and snow can move through siding or between intersections and

OSB after Low vapor permeable housewrap is cut away (OSB is visibly wet)

OSB after High Vapor Permeable housewrap is cut away (OSB is visibly dry)

Figure 11.7 Low vapour permeable house wrap versus high vapour permeable house wrap. Source: Photo provided by DuPont. 11.3 House Wraps 329

joints [16]. When necessary, house wraps help keep water off the structural sheathing and framing of a building by redirecting water away from the building’s wall assembly. ●● House wraps, such as the one shown in Figure 11.8 2, serve as a barrier layer to prevent the movement of hot and cold air through walls [15]. Assuming joints are sealed properly, house wraps should reduce air infiltration and potential drafts, therefore improving the comfort of those in the building and reducing utility costs [19].

11.3.1 Property Requirements

Fundamentally, house wraps should provide water resistance, water vapour permeability, air resistance [20], durability, and compatibility with other building materials [16]. House wraps may be compared utilizing the performance criteria recognized by the International Code Council Evaluation Service (ICC‐ES). ICC‐ES criteria are used to evaluate the code compliance of building products, including house wraps. Table 11.1 provides an overview of ICC‐ES criteria, test methods used to evaluate the materials, as well as the minimum requirements of house wraps [18]. The ICC‐ES evaluates the following characteristics of house wrap materials: water resistance, durability, vapour permeability, drainage, and air permeability.

11.3.1.1 Water Resistance At the most basic level, house wraps must prevent water infiltration. Water infiltration most often originates in the form of precipitation [16]. The water resistance of a house wrap material may be evaluated using one of three different standards: the Boat test (ASTM 779), the Water Ponding test (CCMC 07102, Section 6.4.5), and the Hydrostatic Pressure test (American Association of Textile Chemists and Colorists [AATCC] Test

Figure 11.8 DuPont AirGuard® reflective vapour control layer which prevents convective heat loss. Source: Photo provided by DuPont.

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Table 11.1 International Code Council Evaluation Service (ICC‐ES) house wrap performance criteria [18].

Minimum performance Characteristic evaluated Test method requirement

Durability Strength ASTM D5034: Standard Test > 40 lbf MD, 35 lbf CD Method for Breaking Strength > 20 lbf MD, 20 lbf CD and Elongation of Textile Fabrics (Grab Method) ASTM D882: Standard Test Method for Tensile Properties of Thin Plastic Sheeting Weathering UV Exposure/ Weathered samples Accelerated‐Aging pass strength and water resistance Cold resistance AC38 Section 3.3.4: Cold No cracking Mandrel Bend Test Water resistance Boat test ASTM D779: Standard Test 10 min – no water Method for Water Resistance passage of Paper, Paperboard and Other Sheet Materials by the Dry Indicator Method Water ponding CCMC 07102 (Section 6.4.5): 2 h – no water passage test Water Ponding Test Static and dynamic AATCC Test Method 127: 5 h – no water passage water pressure Water Resistance Hydrostatic resistance Pressure Test Permeability Water vapour ASTM E96: Test Method for > 5 US perms transmission Water Vapour Transmission of Materials Air resistance Air barrier ASTM E2178: Standard Test < 0.02 L/SM2@75 psi (optional) resistance Method for Air Permeability [0.004 CFM/ of Building Materials [email protected] psi] Drainage Drainage ASTM E2273: Test Method > 90% drainage (optional) efficiency for Determining the Drainage efficiency Efficiency of Exterior Insulation and Finish Systems (EIFS) Clad Wall Assemblies Fire resistance Flame spread ASTM E84: Test Method for Class A (optional) index and smoke Surface Burning development Characteristics of Building Materials

Method 127) [16, 18]. The Boat test and the Hydrostatic Pressure test are most commonly utilized in the US building codes to evaluate house wrap materials [16].

11.3.1.2 Durability House wrap materials must be able to withstand the stresses and strains applied during installation without compromising the properties of the material. Weather resistive barriers must be able to withstand potential exposure to harsh UV rays, wind, and 11.3 House Wraps 331 precipitation for long periods of time prior to cladding installation [16]. Tear resistance is particularly important during installation when the material may be exposed to strong winds [21]. Other important physical properties that should be considered are breaking strength, elongation, shrinkage, and puncture resistance [15]. Durability of a house wrap is generally evaluated by analysing the material’s resistance to UV radiation and cold temperatures as well as its strength in tear and tensile loading. Many house wraps advertise a tolerable 90‐ to 180‐day gap for siding installation, However, it is generally recommended that house wraps are covered within 30 days [18]. House wrap material is not accessible unless the cladding material is removed. Therefore, it is expected that the house wrap remains functional during the entire service life of the wall system [16].

11.3.1.3 Vapour Permeability Vapour permeability is a measure of the amount of water vapour transmitted through the barrier membrane per unit time [19]. The presence of water within a wall cavity can be due to many sources, including initial construction moisture, condensation of water vapour within the wall, and weak spots in the house wrap material. Therefore, it is important that the weather resistive material allows drying from the interior of the wall and moves the wetness to the exterior wall [16]. The moisture vapour transmission rate [19], also denoted as the water vapour transmission rate [16], is usually determined through a standard test protocol (e.g. ASTM E96) [16, 19]. This test indicates how much water vapour can pass through a barrier in a 24‐hour period. In Table 11.2, this criterion is indicated as the ‘perm rating’. A higher perm rating indicates a material which possesses higher permeability. Materials with greater perm ratings allow moisture to escape more quickly, resulting in a lower chance of moisture vapour accumulation. However, higher perm ratings do not necessarily indicate a better house wrap. Low tech house wraps often achieve high air perm values with mechanically punched perforations. While these perforations do facilitate vapour transport, they also create a material more susceptible to water leakage. Well‐designed house wraps, such as the HomeWrap and R‐Wrap, discussed in Table 11.2, offer high vapour transmission while preventing the movement of liquid water. Current building codes require a house wrap to meet or exceed grade‐D building paper, meaning house wraps must possess a perm rating of five or higher [19]. Some consider a perm rating of 10–20 to be ideal for house wraps [18].

11.3.1.4 Drainage This parameter is widely accepted as one of the best ways to evaluate a house wrap’s ability to reduce moisture, keep walls dry, and minimize structural damage due to rain penetration [18]. House wrap materials are designed to drain water, which can enter through exterior cracks, or accumulate because of condensation or evaporation out of the wall cavity. However, if the siding is applied too tightly to the house wrap, there is insufficient space to allow drainage. To overcome this issue, some house wraps incorporate channels in the barrier material [22] via creping, embossing, weaving, or filament spacers to provide suitable paths for drainage [18]. Additionally, many builders incorporate a 1/4–3/8 in. (0.64–1.9 cm) drainage separation between siding and house wrap material via vertical furring strips. This gap provides adequate space for moisture to dissipate naturally [19]. 332 11 Building and Construction Textiles

Table 11.2 Common house wrap materials [19].

Name Type Perm rating Notes

HomeWrap Nonwoven 58.0 30+ years ago, this was the first house (DuPont) polyolefin wrap on the market It accounts for more than 70% of the total house wrap sales PinkWrap Woven perforated 14.0 This incorporates a translucent (Owens Corning) polyolefin membrane which makes it simple to see where to nail siding material Typar Nonwoven 11.7 Provides excellent protection against (Typar) polyolefin surfactants Ideal for use with stucco siding (which is porous) Guaranteed tear resistance StuccoWrap Nonwoven 50.0 Designed for use under traditional and (DuPont) polyolefin synthetic stucco Does not absorb water, expand or contract thus reducing cracking Surface texture allows for channelling of water. Weathermate Nonwoven N/A Translucent and perforated (The Dow polyolefin Perforated products are less protective Chemical against water intrusion Company) Weathermate Plus Woven perforated 6.7 Texture is comparatively more foam like (The Dow polyolefin and substantial Chemical Company) Barricade Woven perforated N/A Perforated products are less protective (Barricade Building polyolefin against water intrusion Products) UV resistant for 12 mo R‐Wrap Nonwoven 59.0 Provides the highest perm rating (Barricade Building polyolefin Products) GreenGuard Ultra Nonwoven 48.0 Incorporates a reinforcing scrim which (Kingspan) polyolefin provides high tear resistance Translucent membrane facilitates seeing where to nail siding Weather Trek Perforated 6.5 Possesses distinct texture that ensures (Barricade Building polyethylene water drains easily regardless of Products) orientation Raindrop Woven polyolefin 10.0 Drainage channels are woven into the (Kingspan) surface which directs water down and out; therefore, channels must run vertically 11.3 House Wraps 333

11.3.1.5 Air Permeability Air permeability indicates how well a house wrap prevents unwanted air from moving across a building enclosure. This property is comparatively less critical than other requirements discussed in this section [18]. However, most house wraps provide an air leakage value of between 0.03 and 0.08 CFM/ft2 with higher values indicating greater airflow through the material [21].

11.3.2 House Wrap Materials

Fibrous materials are ideal house wrap materials because they are breathable and capable of preventing moisture infiltration [23]. Early materials utilized for house wraps included asphalt saturated felts and papers (also called kraft papers) [16]. Asphalt saturated felts and papers are two distinct products. ‘Kraft paper’ broadly refers to various types of sulfate paper but the term is most often used to describe basic grades of unbleached sulfate papers. Asphalt saturated felts are made in processes similar to papermaking in order to create fibrous, felt materials. Felts and kraft papers are made waterproof via asphalt saturation [16]. In the 1980s, plastic, polymeric house wraps were developed and gained popularity because of their ease of installation, durability, and ability to block water [16, 18]. The advantages and disadvantages of traditional asphalt based products and polymeric house wrap materials are compared in Table 11.3. As previously mentioned, house wraps are incorporated into buildings to provide a barrier to external environments while also allowing air to pass through the structure. How this is achieved is dependent on the fabric design and the specific wall assembly [17]. Table 11.2 includes some of the available house wrap materials as well as important design characteristics. Most house wraps consist of either woven or nonwoven polyolefin (usually either polyethylene or polypropylene fibres) [18]. Each house wrap product is designed to provide specific, unique properties such as tear or UV resistance. Regardless of the unique characteristics provided, every house wrap must provide a means of moisture management. Some house wrap materials have microperforations to allow moisture vapour to pass through while others are designed to transport water vapour through the fabric itself (microporous). When considering the microperforated approach (which is used in many woven house wrap fabrics), vapour transport is facilitated while water resistance is reduced. On the other hand, microporous materials provide sufficient vapour movement while also providing excellent resistance to water [18]. House wrap materials can potentially come into contact with surface active agents, called surfactants [20]. This is problematic because surfactants reduce the surface tension of water such that a liquid can penetrate deeper into the microscopic openings of a fibrous material. As a result, water may eventually interact with a building’s sheathing. House wrap designers can overcome this issue by applying surfactant‐resistant coatings or primers to the house wrap or by creating drainable house wraps [18, 19]. For exam- ® ple, Typar , which is described in Table 11.2, possesses superior resistance to surfactants when compared to other house wraps [19]. 334 11 Building and Construction Textiles

Table 11.3 Advantages and disadvantages of asphalt based and polymeric based house wrap materials [16].

Asphalt saturated kraft Material Asphalt saturated felt paper Polymeric products

Potential Successful applications Successful Highly resistant to advantages throughout history under applications tearing and breaking normal exposure throughout history Large sheet products Conforms to many model under normal meaning joints are codes exposure minimized Material costs are low Conforms to many Not susceptible to Long‐term durability, possibly model codes deterioration upon better than paper based Material costs are low water exposure products Better bending Can act as a barrier properties than felt to air movement based Possess high water Lower permeance vapour permeance than felt based, less potential for condensation build up Potential Not much performance data Tear resistance is low Relatively expensive disadvantages supporting use as house wrap Highly susceptible to compared to other Relatively high permeance may deterioration upon available materials lead to condensation build up exposure to water, air, Susceptible to Minimal resistance to tears, and/or UV deterioration upon breaks, and bending long‐term exposure Susceptible to deterioration to UV when exposed to water, air, Water resistance can and/or UV be negatively Surfactant exposure reduces impacted by water penetration resistance surfactants Does not conform to some Can slow down building codes for application evaporation of excess with plaster over wood based water sheathing

11.4 Insulation

Energy use in commercial and residential buildings accounts for a significant part of the world’s total energy use and greenhouse gas emissions. According to the Department of Energy in the United States, an average American home consumes 50–70% of its total energy during heating and cooling [24]. Similarly, the European Union (EU) estimates that 79% of the energy consumed in EU households is utilized for heating alone, while cooling accounts for a much smaller percentage. However, energy requirements for cooling increase as the effects of climate change progress and temperatures rise. The EU has progressive strategies in place to improve both energy efficiency and decrease greenhouse gas emissions 20% by 2020. Part of the EU’s strategy to meet these goals is utilizing high performance insulation materials in new and existing buildings to reduce energy consumption and harmful emissions [25]. 11.4 Insulation 335

Insulation is a thermal barrier layer which reduces heat flow through building components and enhances a building’s energy efficiency. To understand how insulation works, it is beneficial to understand heat flow. Heat flow is achieved via conduction, convection, and/or radiation. Conduction is the manner in which heat moves through materials, convection describes the way heat circulates, while radiation is the movement of heat in the form of electromagnetic waves. Fibrous insulating materials discussed within this section work primarily by minimizing conductive heat flow, and to a lesser extent by reducing convective heat flow [26]. Thermal insulating materials are porous and contain microscopic pockets of stationary or dead air, which suppress heat flow. Inherently, stagnant air is one of the best thermal insulators. Therefore, air trapped within the insulating material is responsible for thermal resistance rather than the fibrous material itself [27]. Insulation materials are incorporated within various building components, including interior or exterior walls, roofs, garages, foundations, unheated garages, band joists, and around windows, doors, and heating systems [2]. The benefits of utilizing thermal insulation include: ●● Energy cost savings: With little capital expenditure (insulation only accounts for approximately 5% of building costs), dependence on heating/cooling systems can be reduced, which in turn provides energy cost savings. ●● Environmental footprint: Reducing the use of heating/cooling systems, which lowers emitted pollutants and helps to preserve natural resources. ●● Building structural integrity: Insulation helps to minimize temperature fluctuations that could compromise a building’s structural integrity and shorten its lifetime. ●● Acoustic insulation: Thermal insulation can also reduce disturbing noises from outside environments, providing improved acoustical comfort. ●● Vapour condensation prevention: Insulation that is properly designed and installed can help to prevent vapour collection on building surfaces. ●● Fire protection: Some insulations incorporate means to retard heat and prevent flame immigration [27].

11.4.1 Types of Insulating Materials

Building insulation materials can be categorized by their form and packaging. The insulation market is dominated by two basic groups of materials: inorganic fibres and organic foams. These could be packaged or installed in the form of blown‐in/loose‐fill insulation, batts, rolls, foam boards/panels, and spray foam. Blanket insulation, as shown Figure 11.9,3 which encompasses batts and rolls, is the most commonly used and widely available type of insulation. It is made with 6 in. (15.24 cm) uninsulated flaps that allow all horizontal and vertical seams to be installed in a shingled fashion. Batts and rolls are available in a variety of widths which are designed to fit the standard spacing of wall studs, attic rafters, and floor joists. Alternatively, continuous rolls are available that can be trimmed to custom fit desired structures [28].

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Figure 11.9 DuPont Tyvek ThermaWrap® R5.0 – an insulated house wrap that provides air and water protection. Source: photo provided by DuPont.

11.4.2 Property Requirements

Thermally insulting materials must prevent heat flow. To achieve this, insulating materials should possess high thermal resistance to reduce heat transmission. The key parameter related to this is thermal conductivity. The thermal conductivity of a material is the rate of steady state heat flow through a unit area of the material of unit thickness in a direction perpendicular to the isothermal planes, induced by a unit temperature difference across the sample [29]. Thermal conductivity, indicated by a material’s k‐value, is expressed in units of W m−1 K−1. When considering insulation materials, a low thermal conductivity is desired. A low thermal conductivity allows a relatively thin building envelope to obtain a high thermal resistance [30]. Insulation materials are objectively compared and rated according to their thermal resistance or R‐value. The R‐value is an indicator of a material’s ability to resist heat flow through a given thickness and is expressed in units of (m2K)/W . The higher the R‐value, the better a material is at preventing heat flow. R‐values are dependent on the type of insulation, its thickness, as well as the material’s density. The degree of insulation needed depends on several factors, including climate, location within the building, type of heating/cooling system, and building construction type [2]. The US Department of Energy recommends R‐values based on geographic region and location of installation within a building. As an example, the United States’ geographic zone distinction is shown in Figure 11.10 and the respective R‐value requirements are shown in Table 11.4. This information is specific to new wood framed houses. It is important to note that R‐value requirements vary if the structure is pre‐existing.

11.4.3 Fibrous Insulating Materials

Most insulation materials are either fibrous or foam based. Polyurethane and polystyrene foams are common foam based solutions. However, this discussion will focus on fibrous insulation materials, which are the most widely utilized insulating materials today [2]. 11.4 Insulation 337

Figure 11.10 U.S. Department of Energy R‐value zones. Source: Image courtesy of the US Department of Energy.

Table 11.4 US Department of Energy recommended total R‐values for new wood framed houses [26].

Wall Heating Cathedral Insulation Zone system Attic ceiling Cavity sheathing Floor

1 All R30–R49 R22–R38 R13–R15 None R13 2 Gas, heat R30–R60 R22–R38 R13–R15 None R13 pump, fuel oil Electric R30–R60 R22–R38 R13–R15 None R19–R25 3 Gas, heat R30–R60 R22–R38 R13–R15 None R25 pump, fuel oil Electric R30–R60 R30–R38 R13–R15 R2.5–R5 R25 4 Gas, heat R38–R60 R30–R38 R13–R15 R2.5–R6 R25–R30 pump, fuel oil Electric R38–R60 R30–R38 R13–R15 R5–R6 R25–R30 5 Gas, heat R38–R60 R30–R38 R13–R15 R2.5–R6 R25–R30 pump, fuel oil Electric R38–R60 R30–R60 R13–R21 R5–R6 R25–R30 6 All R49–R60 R30–R60 R13–R21 R5–R6 R25–R30 7 All R49–R60 R30–R60 R13–R21 R5–R6 R25–R30 8 All R49–R60 R30–R60 R13–R21 R5–R6 R25–R30 338 11 Building and Construction Textiles

Glass wool Inorganic Fibers Mineral wool

Insulating PET Materials Cellulose Organic Cotton Fibers Sheep wool

Bast

Figure 11.11 Insulating material types.

As shown in Figure 11.11, fibrous insulation materials can be divided into two categories: inorganic fibre based products and organic fibre based products. Regardless of whether the insulation comprises inorganic or organic fibres, manufacturers typically attach a ‘face’ layer, such as kraft paper, foil‐kraft paper, or vinyl, to act as a vapour and/ or air barrier layer. The ‘facing’ material may also possess flame‐resistant properties and facilitate the installation process [28].

11.4.3.1 Inorganic Fibres Fibre based insulation materials are typically produced with inorganic fibres. Over time, inorganic fibres have been developed to provide higher performance compared to organic fibres. Specifically, inorganic fibres provide increased product lifetime and better thermal stability [2].

11.4.3.1.1 Fibreglass Fibreglass (glass wool), a material made up of very fine glass fibres, is one of the most dominant insulation materials. It is most often used in blanket (batt and roll) or loose‐ fill form but it can also be found in the form of rigid boards and duct insulation. Fibreglass products are available in various densities and thicknesses to achieve the desired R‐values, as shown in Table 11.5. Lofty glass wool products are applied inside the structural cavities of walls and floors of buildings. When used as loose‐fill insulation, fibreglass is made from molten glass spun or blown into fibres. Glass wool is produced from borosilicate glass heated around 1400 °C, and pulled through rotating nozzles [30]. Loose‐fill fibreglass insulation usually consists of 20–30% recycled glass fibres. In loose‐fill form, fibreglass must be applied using an insulation blowing machine within spaces appropriate for open blowing, such as attics or in closed cavities of inner walls and attic floors [31]. A well‐documented issue regarding fibreglass insulation is the tendency for glass fibres to break. When inhaled, the glass fibres can cause lung damage. Additionally, many fibreglass insulation materials contain carcinogenic substances. So, most manufacturers have developed new processes which eliminate the use of carcinogenic chemicals. 11.4 Insulation 339

Table 11.5 Fibreglass batt R‐value comparison [28].

Thickness (cm) R‐value

8.89 11 9.21 13 8.89 (high density) 15 15.24–15.88 19 13.34 (high density) 21 20.32–21.59 25 20.32 (high density) 30 24.13 (standard) 30 30.48 38

11.4.3.1.2 Mineral Wool The term ‘mineral wool’ can apply generally to two distinct types of insulation: ●● Rock wool, which is a manufactured material containing natural minerals like basalt or diabase. ●● Slag wool, also a manufactured material, which contains material from blast furnace slag. Rock wool is produced from melted stone at approximately 1500 °C, using a wheel centrifuge process wherein the heated mass is hurled out from a wheel or disk, thus creating discontinuous fibres [30]. Mineral wool insulation is typically available as a blanket (batt or roll) as well as loose‐fill insulation. Generally, mineral wool insulation contains approximately 75% post‐industrial recycled content [31].

11.4.3.2 Organic Fibres Organic fibrous materials are historically significant in the development of insulation. In ancient times, natural fibres like cotton, sheep wool, straw, hemp, and asbestos were used as building insulation. However, the issues associated with organic fibres, such as their low resistance to elevated temperatures and environmental extremes, limit their use in the insulation field [2]. PET (polyethylene terephthalate) based insulation is less readily available when compared to other types of insulation. Insulation containing PET primarily consists of fibres produced from recycled plastic bottles. PET fibres are generally used to form batt insulation products similar to high density fibreglass materials. One positive aspect of this type of insulation is that it is relatively nonirritating to work with and does not cause the health problems associated with glass fibre materials. The R‐values provided by PET based insulation varies based on density. A 1.0 lb ft−3 material reportedly provides an R‐value of 3.8 per in., while a 3.0 lb ft−3 insulation provides an R‐value of 4.3 per in. value [31]. Cellulose insulation is produced from recycled paper products, most often news- papers. This form of insulation generally contains 80–90% recycled material. To produce this material, recycled paper is first shredded to small pieces and then converted to a fibre form. Cellulose insulation may be installed in attics as well as densely 340 11 Building and Construction Textiles

packed in to building cavities in loose‐fill form. Cellulose based fibrous material is capable of tightly packing into cavities, efficiently inhibiting airflow, and provides an R‐value of 3.6–3.8 per in. More recent methods of application include damp‐spraying. In damp‐spraying, the spray nozzle tip provides the cellulose with a small amount of moisture which activates natural starches and causes the cellulose to adhere to cavities. Dry cellulose fibres may also be applied when dry as loose‐fill insulation within attics [31]. Cotton insulation is available as a loose‐fill material or in batt form. Cotton insulation comes in a few varieties. Some cotton insulation is produced from approximately 85% recycled cotton and 15% plastic fibres treated with borate. Other cotton insulation products are produced from denim scraps and thus require minimal energy to manufacture. Cotton insulation can be nontoxic. Therefore, it can be installed without concern for respiratory issues or skin contact. However, cotton insulation typically costs 15–20% more than fibreglass batt insulation. Cotton insulation can provide an R‐value of approximately 3.4 per in. [31]. Sheep wool may also be used as insulation. Similar to cotton and cellulose, sheep wool requires borate treatment. Wool is capable of high moisture regain which can be problematic because boric acid may leach after repeated wetting and drying cycles. The R‐value provided by sheep wool is approximately 3.5 per in., which is similar to other insulation materials [31]. Recently, the use of bast fibres for insulation has gained interest. The bast fibre group includes natural fibres such as hemp, linseed, and flax. Although flax and hemp have a long history in insulation application, they are often considered new materials in this area, owing to their recent gain in popularity. Hemp and flax are plants which grow on an annual basis and thus are considered renewable materials. As ecological issues become of greater concern in the industry, materials which are recyclable and renewable, and require relatively few resources for production will become increasingly popular. Traditionally, tows of hemp and flax fibres have been utilized in timber houses in the form of tapes. More recently, bast fibre mats and loose‐fill bast insulation have become more commercialized with different thicknesses available for modern structures. The thermal conductivity of bast fibres is comparable to conventionally used insulation

Table 11.6 R‐values of fibre assemblies, per centimetre of thickness [24, 31].

Insulation type R‐value per 2.54 cm of thickness

Fibre glass blanket or batt 2.9–3.8 High performance fibre glass blanket 3.7–4.3 or batt Loose fill fibre glass 2.3–2.7 Loose fill rock wool 2.7–3.0 PET 3.8–4.3 Loose fill cellulose 3.4–3.7 Cotton (type not specified) 3.4 Sheep wool (type not specified) 3.5 Bast fibre (specifically, Hemp) 3.5 11.5 Textile Reinforced Concrete 341 materials, owing to the porous nature of bast fibres and their low bulk density, which allows the fibres to trap a large amount of air. However, bast fibres make up a very small portion of the market, which may be explained by the twofold price increase when compared to other insulation materials like mineral wool [32]. The R‐values of the materials discussed in this section are shown in Table 11.6.

11.5 Textile Reinforced Concrete

Textile reinforcements for concrete can be described as fibrous arrangements which are incorporated within concrete to improve the lifetime and performance of concrete structures. Concrete reinforced with fibres randomly distributed throughout the concrete matrix is termed fibre reinforced concrete (FRC); on the other hand those reinforced with mesh‐like textile arrangements are called textile reinforced concrete (TRC). These concepts are shown schematically in Figure 11.12. While there is extensive literature pertaining to FRCs, this discussion will primarily focus on TRCs. Concrete, or ‘artificial rock’ [33], is one of the most commonly used materials in the construction industry [34]. The components of concrete include cement, stone aggregates, and water. Pure concrete is a material characterized by high compressive strength (about 60 N mm−2), but also very low tensile strength [33]. The low tensile strength of pure concrete can lead to crack propagation and crack growth, which ultimately causes material failure. The concept of TRC is relatively new with research initiatives beginning in the mid‐ 1990s [35] . Historically, the low tensile strength of concrete was mitigated utilizing steel bar reinforcements [33], as shown in Figures 11.12 and 11.13. While steel bar reinforcements do provide advantageous properties like high load capacity, straightforward processing [37], durability, and versatility [36], they are also highly prone to corrosion. Within the reinforced concrete structure, steel bars are protected from corrosion by concrete encapsulation. However, over time, substances can penetrate concrete such that the steel bars are no longer protected and begin to corrode. As the reinforcement corrodes, the concrete begins to break up into smaller components ultimately leading to structural failure [37].

Concrete

Reinforcement

(a) (b) (c)

Figure 11.12 Schematic of different reinforcement systems: (a) steel reinforced concrete; (b) fibre reinforced concrete; (c) textile reinforced concrete. Source: Redrawn with permission from SGL, German Centre for Textile Reinforced Concrete and JEC Composites Magazine. 342 11 Building and Construction Textiles

(a) (b)

Figure 11.13 (a) Carbon fibre roving used for concrete reinforcement; (b) carbon fibre textile structure and its incorporation into concrete. Source: Images from [36] courtesy of SGL, German Centre for Textile Reinforced Concrete and JEC Composites Magazine.

There are many advantages to utilizing textile arrays for concrete reinforcement. Most importantly, textile concrete reinforcements are noncorrosive; however, there are many other advantages, including: ●● TRC requires far less concrete encapsulation than steel bars. To prevent steel bar degradation, building standards require that steel bars are protected by concrete layers with a minimum thickness of 35 mm, which leads to an overall material thickness of at least 100 mm. This can be compared to TRC products which are typically 20–30 mm thick as they only require 10–15 mm layers of concrete encapsulation. Therefore, TRCs are thinner, lighter, and require less material than steel reinforced materials. Compared to steel reinforced concretes, TRCs require up to 80% less concrete to produce, allowing for significant cost savings [37]. ●● TRC has high specific strength (strength‐to‐weight ratio) [38]. ●● TRC materials are lighter and therefore can be transported at lower costs. ●● Textile reinforcement layers possess much greater surface area when compared to steel bar reinforcements. This creates high bonding forces between the textile reinforcement and the surrounding matrix [36]. ●● TRCs can achieve high tensile strengths, up to 3000 N mm−2 [35]. Their strength properties can be five to six times greater than traditional steel reinforced concrete [37]. ●● TRCs are applicable to structures exposed to high chloride stresses, such as bridges, parking decks, and maritime structures [35]. ●● TRCs can be used as very thin strengthening layers and repair layers. Strengthening layers have been shown to reduce subsequent concrete cracking.

11.5.1 Requirements for Textile Reinforcement Materials

Textile materials used in TRCs must carry the tensile forces which occur when concrete cracks [34]. Most continuous fibres are well suited for use as concrete reinforcement materials. However, it is imperative that the fibre type utilized is noncorrosive and that the selected reinforcing material creates a strong bond with the concrete. This means 11.5 Textile Reinforced Concrete 343 that the fibres should be permanently compatible with the concrete matrix, both chemically and physically. Additionally, it is important that reinforcing fibres are high strength and possess low fracture elongation. More specifically, it is necessary that the Young’s modulus of the reinforcing fibre is sufficiently larger than the concrete matrix to avoid significant strength reduction upon crack development [33].

11.5.2 Types of Reinforcing Fibrous Materials

The fibre types that are most often utilized for TRCs are alkali‐resistant (AR) glass fibres, and carbon fibres. AR glass fibres and carbon fibres are not susceptible to corrosion and also possess high strength [37]. AR glass and carbon fibres are used in the form of filament yarns or rovings, as shown in Figure 11.13. These materials typically provide low material strain under tensile load, which is desirable for reinforced concrete structures. While most TRCs are produced with AR glass or carbon fibres, other fibre types have also been explored, such as polypropylene, polyvinyl alcohol, polyacrylonitrile [33], polyethylene, aramids, and basalt. Recently, basalt fibres have gained significant attention in the area of TRCs, owing to their low cost and environmental friendliness [38]. Table 11.7 provides qualitative comparison of the different reinforcement materials based on corrosion resistance, temperature resistance, bond quality, demand, and production costs. Corrosion resistance indicates a material’s ability to withstand alkaline, neutral, and acidic conditions. Temperature resistance is compared based on the reinforcements’ thermal conductivity and coefficient of thermal expansion. Bond quality comparisons depend heavily on the geometrical properties and surface finishes utilized; therefore, bond quality can significantly vary with design. Demand analysis indicates how easily the reinforcement material can be obtained, while production cost involves the monetary requirements which vary with demand, availability, and production method [39]. A quantitative comparison of the common reinforcement materials can be found in Table 11.8. For the sake of comparison, and owing to the current available data, the yield stress and strain are recorded as the tensile strength and ultimate strain of steel reinforcements. However, the tensile strength and ultimate strain of the AR glass, carbon, and basalt fibres is provided. Using these data, the values were normalized with respect to steel as the reference material. The normalized results are shown in Figure 11.14 [39]. The qualitative and quantitative data provided show that in some areas the common reinforcement materials are comparable in performance. However, steel reinforcements prove insufficient when considering corrosion resistance in realistic environmental settings. In terms of tensile strength, carbon fibres may be the optimal fibre reinforcement material, although carbon fibres can be expensive, difficult to obtain, and possess a comparatively low ultimate strain. AR glass fibres present some issues, such as their poor temperature behaviour and low strength performance but impressive corrosion resistance. Basalt fibres provide greater tensile strength properties than AR‐glass fibres. Overall, the performance of AR glass fibres and basalt fibres is relatively similar [39]. When incorporated into TRCs, fibrous materials are used in the form of yarns or rovings and processed into planar textile structures like those shown in Figure 11.13, with optimal fibre alignment. The fibre alignment achieved in textile materials provides TRCs’ higher load bearing performances when compared to FRCs with equivalent or 344 11 Building and Construction Textiles

Table 11.7 Qualitative comparison of TRC reinforcement materials.

Reinforcement Temperature Demand/ material Corrosion resistance resistance Bond quality production cost

Conventional High resistance to Average Low to high High/average, steel high alkaline High thermal based on commonly used reinforcement solutions expansion and mechanical Low resistance to low conductivity deformations alkaline, neutral, or realistic acidic outdoor conditions AR‐Glass Average resistance to Low Average, depends Average, high alkali attack Average thermal on density of yarn particularly High resistance to expansion Improve with produced for neutral or realistic Low thermal coating alkaline acidic outdoor conductivity environments conditions Carbon High resistance to High Low to average Low/high, acid, alkaline and Low thermal Smaller filament compared with all organic solvents expansion, diameter leads to other (inert) shortens when weaker adhesion reinforcement heated Improve with materials Average thermal coating conductivity Basalt Comparable to High Unsized filament Low/average, unsized E‐glass and Low thermal Low friction easily extractable AR‐glass in high expansion coefficient, natural resource alkaline solutions Geometrically improve with High resistance to stable coatings neutral or realistic Low thermal and alkaline outdoor conductivity conditions Source: Reformatted with permissions from [39] Copyright © 2014, ASCE.

Table 11.8 Comparison of mechanical properties of TRC reinforcement materials.

Modulus of Reinforcement material Tensile strength (MPa) elasticity (GPa) Ultimate strain

Conventional steel 560 (±30) 205 2.0 (±0.2) reinforcement (B500B) AR‐glass 1870 (±127) 70 (±1) 2.7 (±0.2) Carbon 4348 (±385) 238 (±9) 1.8 (±0.2) Basalt 2809 (±964) 86 (±8) 3.2 (±0.7) Source: Reformatted with permissions from [39] Copyright © 2014, ASCE.

reduced fibre content [36]. The textile materials utilized for TRCs are typically open structure configurations, which provide extensive surface contact area for the matrix material. This allows for optimal bonding between the concrete and reinforcing textile material [34]. 11.5 Textile Reinforced Concrete 345

Tensile Strength Modulus of Elasticity Ultimate Strain

Basalt

7.8

Carbon

AR-glass

Steel

0123456 Normalized Value

Figure 11.14 Comparison of normalized mechanical properties (tensile strength of steel considered yield stress and ultimate elongation of steel is considered yield strain). Source: Image reprinted with permissions from [39] Copyright © 2014, ASCE. All rights reserved.

Considering the large variety of textile manufacturing methods available, textile reinforcement materials can be configured in a wide range of manners. Fibres may be configured with no specific orientation utilizing nonwoven fabric techniques. Alternatively, yarns in the fabric may be oriented in predetermined manners with unidirectional, biaxial, and multiaxial orientations. Unidirectional reinforcements are typically in the form of pre‐pregs. Similarly, a unidirectional nature can be achieved with woven fabrics containing one yarn set which is significantly weaker than the other such that one direction of the fabric does not significantly contribute to the reinforcement properties. Multiaxial textile materials can be made manufacturing techniques such as weaving, multilayer knitting, multiaxial warp knitting, or braiding. Reinforcing yarn materials can be interlaced with each other in different orientations via woven and braiding methods. Additionally, the textile reinforcement layer can contain many stacked yarn layers in different orientations held together by a binding yarn. This can be achieved with multiaxial warp knitting, multilayer knitting, and multilayer woven fabrics. Alternatively, the reinforcement layer can provide reinforcement in all three axes. With 3D weaving, multilayer weaving, or multiply knitting, z‐axis reinforcements provide additional resistance to impact. In these manners, the properties of the TRC can vary from strongly anisotropic to quasi‐isotropic [33]. TRCs can be manufactured in a number of ways. Textile materials may be incorporated into concrete via processes such as hand lay‐up (shown in Figure 11.15), casting, or laminating. Alternatively, FRC can be manufactured through processes like spraying, 346 11 Building and Construction Textiles

Figure 11.15 Hand lay‐up of TRC. Source: Images from [36] courtesy of SGL, German Centre for Textile Reinforced Concrete and JEC Composites Magazine.

spinning, and extrusion [40]. The processing method utilized for TRCs will determine the specific materials which can be incorporated and the final properties of the material.

11.5.3 Applications of Textile Reinforced Concrete

TRCs are a relatively new class of materials which are noncorrosive, lightweight, thin, and durable. As these materials have developed and emerged, designers have been able to create new and unique structural designs utilizing TRC materials. TRC has been used in a variety of applications, including facades, roofs, balconies, noise barriers, furniture, tanks, bridges, pipes, etc. Examples of structures produced with TRC are shown in Figure 11.16. The Albstadt‐ Ebingen Bridge in Germany was the first bridge in the world to be made entirely from carbon reinforced concrete. The bridge is frost resistant, requires no surface coating, and is capable of supporting a 10‐tonne vehicle [41]. Also shown in Figure 11.16 is the Eastsite VIII building located in Mannheim, Germany, which is the largest textile‐reinforced sandwich facade in the world. The facade is quite thin, thus achieving significant reduction in concrete usage [42]. Another emerging application of TRC is the strengthening and repairing of existing concrete structures. As structures reinforced with steel age and degrade because of corrosion, structural damage, increased loading, design faults, or construction faults, repairing and strengthening methods may be required to maintain the integrity of the structure [36]. By virtue of the noncorrosive nature of textile materials, thin TRC layers can be utilized as additional reinforcement layers while only slightly increasing the overall weight of the structure. TRC materials are easily shaped, thus allowing the layers to easily adapt to most component geometries [33]. For example, textile reinforced composite materials have been used to strengthen masonry structures in the event of seismic activity. TRCs can help to increase the shear and flexural resistance, the in‐ plane and out‐of‐plane strength, and deformation capacity of existing reinforced concrete structures [43]. 11.6 Sustainability and Ecological Issues 347

(a) (b)

Figure 11.16 Applications of textile reinforced concrete: (a, b) the Albstadt‐Ebingen bridge which is made entirely from carbon reinforced concrete; (c, d) the Eastsite VIII sandwich facade in Mannheim, Germany. Source: Images courtesy of solidian® at www.solidian.com.

11.6 Sustainability and Ecological Issues

Sustainability in this context means being good stewards of our natural resources to ensure a long‐term ecological balance. The US Environmental Protection Agency describes sustainability as a pursuit ‘to create and maintain the conditions under which humans and nature can exist in productive harmony to support present and future generations’ [44]. The construction industry has a significant impact on both problems as well as potential solutions regarding issues related to sustainability. While the industry is a major consumer of natural resources and energy as well as a producer of solid waste during construction, it also has a long‐term lasting influence on the lifetime carbon footprint of its products through the entire process of design, engineering, and construction. In the United States, the construction industry is reported to be the third‐largest contributor to greenhouse gas emissions [45]. It is estimated that the building/construction sector accounts for 40% of the natural resources utilized in industrialized countries, 70% of electricity, as well as 12% of the portable water available. Additionally, researchers estimate that 45–65% of the construction/building sector’s material waste is disposed in landfills [46, 47]. The United Nations estimates that the global population will reach 8.5 billion by 2030, 9.7 billion by 2050, and 11.2 billion in 2100 [48]. While the 348 11 Building and Construction Textiles

growth in global population and issues related to climate change are likely to increase demands for resources (materials, energy, etc.) these problems can be mitigated through sustainable practices. Perhaps the most compelling reason to pursue sustainable practices for the industry and society at large is the financial incentives derived from delivering buildings and services at a low cost and with great energy efficiency over their lifetimes. Textiles can play an essential role in realizing these efforts. The EU has initiated various actions to overcome issues related to textiles and sustainability. Reportedly, approximately 5.8 million tonnes of textile products are discarded each year in the EU. About 25% of this waste, or 1.5 million tonnes, is recycled via chari- ties or industrial enterprises. The remaining 4.3 million tonnes of textile waste is sent to landfills or municipal waste incinerators [49]. In order to combat the issues related to excessive waste, the EU has taken action through legislation. One such regulation is called the Waste Framework Directive (Directive 2008/98/EC), which specifically con- fronts textile related waste issues. In the directive, the EU defines waste, recycling, and recovery while also encouraging adaptation of waste management and waste prevention programs. The EU has set aggressive goals to reduce household related waste by 50% and construction and demolition waste by 70% before 2020 [50, 51]. Similarly, the EU has implemented Regulation (EC) No 1907/2006, also known as REACH (Registration, Evaluation, Authorization, and Restriction of Chemical Substances). This regulation requires that the chemical substances used to produce textiles in Europe are registered and reported. In order to improve transparency and better inform consumers, companies are required to report textile products which contain harmful chemical products in a concentration greater than 0.1% [51, 52]. Further, the EU has developed a voluntary scheme called Ecolabel, in which sustainable products are clearly designated with a particular logo. Businesses are only allowed to place the distinct logo on their product when an independent body recognizes the good as complying with strict ecological criteria. Ecolabel products meet environmental standards throughout their lifecycles from raw material extraction, through production, distribution, and disposal. The labels allow consumers to easily choose sustainable products and provides opportunities for companies to gain recognition for adhering to environmentally friendly standards [52, 53]. While countries like the United States and China are not taking as aggressive a stance on such issues, it is likely that in the near future such policies will be ubiquitous. The construction industry has been slowly embracing the new paradigms of environmental sustainability, including efforts to reduce energy consumption, decrease waste, and lower greenhouse gas emissions. This is being accomplished by methods such as utilizing more environmentally friendly materials, reusing material waste, as well as rehabilitating existing buildings to prevent further waste [49]. Textile materials that are currently used in construction and those that can be potentially designed from improved materials and structural design practices offer many opportunities to advance sustainability. Possibly the most important example is architectural textiles. The fabric membranes used in tension and air structures offer superior area‐to‐weight ratio, specific strength, and environmental and mechanical stability and therefore are suitable for lightweight, long‐span structures that can function under a variety of loading conditions including seismic. Designs with tunable optical transparency of fabric membranes offer savings in energy. The low thermal mass of fabric membranes can be advantageous in certain climatic conditions, including hot and humid tropical climates. References 349

Natural fibres – such as flax, hemp, jute, kenaf, and sheep wool – are being examined for their potential as sustainable, natural, and renewable insulation materials. These types of fibres could serve their regional or niche markets. In addition to fibre based insulation, other textile structural components, such as house wraps, do have significant roles to play in energy management and environmental impact in the design and lifecycle of buildings. There is significant untapped potential for reducing the environmental ‘footprint’ of buildings by reusing and recycling these materials. Textiles offer many alternatives to construct lightweight, energy efficient, long‐span structures that are compatible with a sustainable future while maintaining high quality living standards for future generations. Architectural textiles with integrated sensors and actuators are likely to play an integral role in this. In the future, smart and responsive textile materials and structures will offer opportunities to design active structures for safe and comfortable environmental conditions. The construction industry as well as the regulators need to adapt and drive the necessary cultural shift such that the construction industry incorporates new sustainable concepts. Relevant research and regulatory reform (i.e. building codes) could lead the way to a more sustainable efficient future for all.

11.7 Conclusion

Textiles used in construction span a wide variety of applications, including architectural membranes, weather‐resistant house wraps, thermal insulation layers, as well as TRC. The use of specific polymer types, fabric structures, or fabric finishes depends on the application environment. Additionally, the material requirements vary depending upon the location of construction, surrounding building components, and regional building codes. Textile based construction solutions offer promising prospects for the future. Architectural fabric structures will become a larger part of commercial construction by virtue of their energy efficiency, and potential in creating a form of architecture that is more organic, natural, and aesthetically pleasing. Similarly, insulation and house wraps are being improved to offer more efficient and comfortable structures. The use of textile materials in construction will evolve with the development of new sustainable materials with improved properties, manufacturing technologies, and analytical techniques as well as design paradigms.

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Automotive Textiles and Composites Bijoy K. Behera

Indian Institute of Technology Delhi, New Delhi, India

12.1 Introduction

The textile industry stemmed from the need of human beings to protect themselves from the changing climatic conditions. Humans first learnt to cover their bodies with leaves and the bark of trees to get protection against adverse environmental conditions. With progress in civilization, various natural fibres from plant and animal sources were discovered and used as the basic raw materials to produce fabric. Textile fabric gradually became a symbol of tradition and culture of various parts of the globe. In subsequent years, textile became the mainstream product dominating the fashion industry all over the world. Today, the trend of textile development is dominated by functionality in addition to the basic need of protection, culture, and fashion. The textile industry is as old as human civilization. Cloth is one of the basic needs of human beings. In ancient times, cloth was made only from cotton, flax, and hemp. At present, cloth is made from silk, rayon, nylon, acrylic, viscose, polyester (PES) staple, and filament yarns. Besides this, cloth is prepared by weaving, knitting, nonwoven, braiding, etc. not only for apparel purpose but also for numerous technical, industrial, and functional applications. Textiles are broadly applied in three different fields: apparel, home textiles, and technical textiles. Among these three categories of applications, technical textiles are an expanding area of textile industries. New yarn and fibre development is one of the driving forces of the modern technical textile industry. Technical textiles are the textile applications in nonconventional areas, such as medicine, agriculture, packaging, civil engineering, automotive design, and many other fields. Technical textiles are gaining fast becoming one of the most dynamic and promising areas for the future of the textile industry for high performance applications. Automotive textiles happen to be one rewarding sector, which extensively uses technical textiles, namely for interior trims, safety devices like seatbelts and airbags, carpets, filters, battery separators, hood liners, hoses, and belt reinforcement. The potential for the growth of the automotive textile business is considered one of the most progressive sectors in over the world, as car production is exponentially increasing in almost all developing countries [1].

12.2 Mobiltech

Among other sectors, the automotive industry is one of the largest single market for technical textiles and one of the most diverse as well. This market comprises automobiles, trains, marine vehicles, and aeroplanes. Technical textiles that are used in this automotive or transport sector are called Mobiltech. Mobiltech today covers not only isolation and safety aspect but also focuses on comfort, style, and a wide range of functionality. The customers look for aesthetically pleasing interiors, great comfort, and fuel economy. Mobiltech is also known as Mobiltex in some literature. Truck covers like polyvinyl chloride (PVC) coated PES fabrics and restraints are significant textile end‐ uses in the transportation sector. They can range from simple ropes and tarpaulins to highly engineered flexible curtain systems and webbing tie‐downs. Other examples include seat covers (both knitted and woven), denim, pile fabrics, floor coverings, tubes and tapes, tyre cord, filter, seatbelts, nonwovens for cabin air filtration, airbags, parachutes, car boot coverings (often needle felts), lashing belts for cargo tiedowns, seatbelts, nonwovens for cabin air filtration (also covered in Indutech), airbags, parachutes, boats (inflatable), air balloons, aerostats, and airships [2, 3].

12.2.1 Textile and Automotive Industry

The automotive industry is one of the fastest growing industries in the world and the most global of all industries, because of product distribution. The term ‘automobile textile’ means all type of textile components like fibres, filaments, yarns, and the fabrics of various structures used in automotive production. Automobile textiles are nonap- parel textiles widely used in vehicles like cars, trains, buses, aircraft, and marine vehicles. Textiles which constitute approximately 20–25 kg in a car are used not only for their enhanced aesthetic value in automotive design but also for sensual comfort and safety. Additionally, few textile products found their applications as design solutions to engineering problems in the form of composites, tyre reinforcement, sound insulation, and vibration control. Apart from woven and knitted constructions, nonwovens also find applications in transport textiles, owing to certain advantages served by them. Normally, the percentage of textile in a motor car amounts to 2% of the overall weight of the car. Car seats are the most important part of the interior, from an aesthetic appeal and customer satisfaction point of view. Almost 45–50 m2 of textile material is used in an average car. Nearly two‐thirds of automobile textiles are for interior trim. The majority of automotive textiles are used for the upholstery and roof covering. The hidden textiles weigh almost 10–12 kg. Textiles for automobiles must satisfy very strong requirements for both security and competing demands [4].

12.2.2 Classification of Automotive Textiles

Automotive textiles can be classified into four major groups based on their functions. The main functions identified are comfort, aesthetics, safety, and speciality in material characteristics. Comfort includes both the physical and the physiological aspects of textiles used in seats and interiors of the vehicle, whereas aesthetics of textiles used in a car include the interior design of carpets, roof liners, and side walls for decoration purpose. Textiles used for safety purposes are seatbelts, airbags, and helmets. These 12.3 Application Areas of Automotive Textiles 355 products are manufactured using stringent specifications. Several technical textiles are used in modern cars to enhance functional requirements such as noise controllers, filters, battery separators, composite materials, etc. All textiles used in automotive design in the form of fibres, filaments, yarns, and fabrics can also be classified into two different types: visible components and concealed components. Components like upholstery, carpet, seatbelt, roof liner, etc. which have a significant role in the aesthetic appeal of the car are classified under visible components. Components like tyre cord, composite materials, airbag, etc., which have significant functional attributes but do not appear from outside are called concealed components. Although there are more than 30 components made from textiles in a modern car, only the items which have a perceptible effect on the function, comfort, aesthetic appearance, and economics of the vehicle are described in this chapter [5]. Some major technical textile products covered under Mobiltech are listed below: ●● Automotive upholstery and other textile fabrics used inside the vehicle. ●● Airbag fabrics. ●● Fabric used as a basis for reduction in weight of body parts. ●● Tyre cord fabrics (including hose and drive belt reinforcements). ●● Tyres (for cord reinforcement material, side and thread walls, carcass piles, etc.). ●● Engine (radiator hoses, power steering, hydraulic lines, filters, etc.). ●● Composites for body and suspension parts (bumpers, wheel covers, door han- dles, etc.). ●● Comfort and decoration (seating, carpets, interior decoration). ●● Safety (seatbelts, airbags, seat fire barriers, etc.). ●● Car body covers. ●● Headliners. ●● Insulation felts (noise, vibration, and harshness [NVH] components). ●● Sun visors/sun blinds. ●● Helmets. ●● Airline disposables. ●● Webbings for aircrafts. ●● Aircraft upholstery. ●● Railways seating fabrics. ●● Cargo fastening belt. ●● Lifting straps. ●● Composite preforms.

12.3 Application Areas of Automotive Textiles

12.3.1 Seat Covers and Upholstery

The car seat constitutes the primary part of the interior decoration. The car seat is perhaps the most important part of the interior, because it is the first element that the customer appreciates when they open the door to look inside and it is the main interface between human and machine in a passenger vehicle. The volume of upholstery varies by region since manufacturers from different regions may prefer different styles of vehicle interiors. An average of 5–6 m2 of fabric is used in cars for upholstery. PES is 356 12 Automotive Textiles and Composites

the most widely used material in car seat coverings all over the world. Fabrics produced by weaving and circular and warp knitting are commonly used depending on colour, design, pattern, surface properties, and comfort characteristics demanded by customers. Modern designers try to give a sporty or elegant look to fabric structures by introducing innovative patterns and colour combinations. Computer aided design system supported by electronic dobby and jacquard has brought a spectacular change in introducing innovative designs in seat covers and upholstery. The very initial types of seat cover were made of leather or leather imitation material. As leather was relatively scarce and of limited comfort, it was gradually replaced by copolymers of vinyl and vinylidene chloride in which the pigment was dyed directly into the melt and had high light fastness. These were very easy to clean but still lacked many of the necessary attributes related to mechanical wear and tear, acoustic absorption, and other utility performance aspects. Then PVC coated fabrics were used and subsequently the fabrics made from the threads that were generated from PVC were used that pos- sessed increased mechanical stability but lacked comfort. Modern seat covers started with the use of cotton and viscose, which have lower abrasion resistance than nylon, PES, and acrylic as they are comfort giving, easy to clean, and environment friendly. Acrylics then came along, as they have a very high UV light resistance, which is a major requirement for automobiles as the colour and properties get majorly affected by the action of UV radiations. PES is stronger than acrylics and thus is preferred from a durability point of view. The properties of PES are enhanced through various chemical processes such as mixing a UV light absorbing chemical in the dye bath of the fabric. PES is also cost efficient and has very high abrasion resistance and could be spun dyed. Some people use denim and pile fabrics to upholster their cars [6]. Figure 12.1 shows a typical textile based car seat cover.

12.3.1.1 Types of Seat Covers Some major seat covers used in the industry are: camo seat covers, canvas seat covers, mesh seat covers, neoprene seat covers, leather seat covers, pet seat covers, and denim seat covers.

12.3.1.2 Properties Seat cover fabrics are generally woven and engineered to give mechanical and physiological comfort along with having an aesthetic appeal. The major mechanical requirements of the fabric used are durability, UV light resistance, wear and tear resistance, flexibility, stretch ability, waterproofing, and wrinkle resistance. The comfortability and safety attributes are studied by automobile manufacturers, fabric production houses, seat makers, and research centres like universities or independent organizations and the same are followed by automobile industries with the utmost care because of stiff competition amongst the manufacturers. To overcome the two major tribulations of soiling and steam rupturing, the upholstery fabric once fixed in place must last the life of the car without being put in a washing machine. The fabric should have desired wear properties (abrasion and pilling resistance) and seam strength. Functional properties such as wet ability, water repellency, oil and stain resistance, and flammability must meet specific standards [4, 7–11]. One of the most traditional forms of automobile upholstery is plain woven fabric manufactured from air‐jet textured and spun PES yarns. The textured yarns have good 12.3 Application Areas of Automotive Textiles 357

Figure 12.1 Textile based car seat cover. abrasion resistance because of their tight loop structure. The yarn contrived from core and effect components can produce fabric covers of very good quality. These types of yarns are based on a central yarn called the core, which gives strength and stability to the yarn structure.

12.3.1.3 Test Methods Test methods and quality measurement attributes for seat covers are internationally standardized by several institutions like ASTM, SAE, etc. Many different companies have their own testing methods and assessment checks and the results of those tests vary at a certain level. Many attempts are made to harmonize those results. To achieve this, each testing house uses different methodology to do the same property testing. Different abrasion tests, like the Martindale, Schopper, and transversal, are performed and the general trend could be that the results obtained by two methods coincide and differ from the third one or all three results have variation to a certain degree.

12.3.1.4 Utility Performance of Seats All these aspects relate to the technical characteristics of textiles. Automotive textiles have to fulfil certain technical requirements, which strongly depend on the application. One can divide them into the following groups: [12] Processing Properties ●● sewability. ●● sewing strength. ●● seam slippage resistance. ●● stiffness. ●● elongation. ●● tensile strength. 358 12 Automotive Textiles and Composites

Service Properties ●● mechanical behaviour (strength, elongation, bending and folding, tear propagation strength, dimension stability, pressure resistance). ●● ageing behaviour (heat/cold, temperature, humidity, light). ●● colour fastness (friction, light, chemicals, sweating). ●● friction behaviour (brushing‐up, abrasion, pilling, fibre migration). ●● bio‐physiological demands (air permeability, heat and humidity transport in upholstery). ●● emission behaviour (toxic elements, smelling, fogging, total emission). ●● contamination and cleaning behaviour. ●● electrostatic behaviour. ●● flammability. ●● optical, haptic, and design. Depending on the application, some additional specific requirements may have to be considered. The diversity in textiles for automotive end‐uses offers plenty of opportunities for growth in the automotive textile industry because of the ever‐increasing demand on aesthetics, comfort, and safety of passengers as well as environmental issues such as low weight, lower energy consumption, and recycling at the end of a vehicle’s lifecycle. New designs in automotive construction are increasingly influenced by the legal regulations on emissions and those on the waste from old vehicles, which require the use of materials that can be recycled. These influence nearly all textile developments in the automotive sector. It was required for automobile manufacturers to greatly increase the recyclable products used in vehicles with a target rate of 95% recyclability. The textiles for interior furnishing are primarily made of woven, weft knitted, warp knitted, tufted, and laminated fabrics and nonwovens. Design, aesthetics, feel, and comfort are important considerations for automotive textiles. One future trend for car seats is to replace the foam by a textile material able to match various constraints such as resilience and resistance to fatigue. As a result, the chemical agents used in foam production and the different solvents used during the production process will be avoided, which may lead to a more easily recycled material. The seats of some models used to be stuffed with hair. But, with mass production, it soon became clear that hair fibres require treatment to avoid disintegration or loosening. For that purpose, animal fibres were impregnated and bonded with natural or synthetic rubber latex. More recently, coconut fibres have been used, along or in combination with animal fibres. Today, small volumes with coconut fibres agglomerated with a latex mixture are still produced in Europe. Latex was replaced by polyurethane foam for two main reasons: the production process of polyurethane foam is easier to master and provides a more consistent product, and its cost is lower than that of the latex foam production process. This is why the technology was relatively quickly replaced by polyurethane foam when it came onto the market. Polyurethanes, one of the most versatile group of plastics, are used in a wide range of applications. They are made from two basic raw materials: polyols and polyisocy- anates, which are measured and mixed to form solid polyurethanes or various types of foams. 12.3 Application Areas of Automotive Textiles 359

Polyurethanes combine lightweight and flexibility with strength and durability. Their versatility is instrumental in achieving the precise mechanical properties required for specific applications. Polyurethane foam is commonly used as padding in car seats despite some problems concerning comfort and recycling. In addition, their thermo‐ physiological comfort properties are poor because they are not breathable. Because of these problems, much research has been carried out and many developments are being made to improve the thermal comfort of car seats. Investigations into the use of textiles as substitutes for polyurethane foam in car seats have been carried out by several European car manufacturers. Today, the three‐ dimensional (3D), stitch‐bonded nonwovens, Multiknit/Caliweb® are used in several types of car [13]. Three‐dimensional spacer fabrics to improve breathability and hence thermal comfort of the seating materials are becoming more popular. There has been a continuous improvement of both the technology and the fabric quality for both the warp and weft knitting sectors over the last two decades. As a result, machines are now capable of producing spacer fabrics to a very high standard for a wide range of applications [12, 14, 15].

12.3.2 Carpets

Carpet is an important part of the automotive interior. Carpets must withstand temperature extremes. Major car producers are using tufted cut‐pile carpets in their cars. Carpets usually have a rubberized backing. The important quality parameters of a carpet used in car include light fastness, mouldability, and soil and abrasion resistance. Carpets are manufactured either by tufting or needle felting. Carpets made by tufting are based upon a supportive backing which is used as a base for the pile yarns which becomes the upper most surface. Carpet backing is usually spunbonded and is made by an integrated process in which polymer chips are melted and filaments are extracted through a die. Mainly PES is used in making this carpet backing where as a blend of nylon and PES is used on some occasions. The process of needling has got the advantage of more productivity at relatively low cost. But carpets produced by needling have the advantage of greater productivity at a relatively low cost. But carpets produced by needling cannot be used to cover sharp‐edged surfaces, especially foot areas and transmission tunnels. Superior needled material has a good filling which is determined by the amount of vertically oriented fibres at a given stitch density.

12.3.2.1 Interior Carpet It is also placed on the vehicle floor, on top of which is then placed a rubber mat to provide compression resistance to the fabric. Usually, nonwoven textile fibres using polypropylene are used in flooring carpet. Figure 12.2 shows typical flooring carpets. The thickness of the fabric used is around 3 mm and areal density around 500 gsm. The desired characteristics of interior carpets are: ●● high durability. ●● high abrasion resistance. ●● tensile strength. ●● low inflammability. ●● good compression recovery. 360 12 Automotive Textiles and Composites

Figure 12.2 Flooring carpet for automotive applications.

12.3.3 Roof Headliner

The hood part comprises almost 18% of the total textile used in an automobile. In the earlier stages of the automobile manufacturing the headliner just consisted of a fabric that was a mere covering to the metal roof. Some basic requirements of the hood covering are lightweight, flexibility, acoustic insulation, antiflex, antivibrational, soft feel, and aesthetically presentable. The evolved version of the headliner consists of multiple layers which may vary from three to eight, depending on the requirements. Each layer serves a defined purpose, such as rigidity, aesthetics, etc. Figure 12.3 shows a nonwoven textile based car roof headliner.

Figure 12.3 Typical nonwoven car roof headliner. 12.3 Application Areas of Automotive Textiles 361

12.3.3.1 Structure and Properties The layers used are produced by needle‐punched nonwoven PES bonded with phenolic resins, and are soft and thermoplastic. The face fabric is made up of tricot knit fabric covered by melted polyurethane foam. The areal density varies from 185 to 220 gsm. A layer is formed by PSF (polyester staple fibre) sprayed between two reinforced sheets. The central layer of the multilayer structure is a semi‐rigid polyurethane NVH foam guarded by two layers of chapped fibre glass sheet, each on either side, which imparts stability and rigidity to the structure and helps with acoustic damping and absorption. The next layers are decorative ones and are nonwoven scrimp attached on both sides of the structure, and provide heat insulation and aesthetic properties. The layers are joined by melted adhesives in a plain laminator, and precaution should be taken to ensure the central layers do not become too compressed and thin; otherwise, the decorative aspect of the outer most layers will be adversely affected. Some major types of headliners are brushed nylon, union cloth, perforated vinyl, moonstone, and perforated moonstone‐ type headliners.

12.3.4 Seatbelts

The seatbelt, also known as a safety belt, is a vehicle safety device designed to secure the occupant of a vehicle against harmful movement that may result during a collision or a sudden stop. A seatbelt functions to reduce the likelihood of death or serious injury in a traffic collision by reducing the force of secondary impacts with interior strike hazards, by keeping occupants positioned correctly for maximum effectiveness of the airbag (if equipped), and by preventing occupants from being ejected from the vehicle in a crash or if the vehicle rolls over. When in motion, the driver and passengers are travel- ling at the same speed as the car. If the driver makes the car suddenly stop or crashes it, the driver and passengers continue at the same speed the car was going before it stopped. A seatbelt applies an opposing force to the driver and passengers to prevent them from falling out or making contact with the interior of the car. Seatbelts are known as primary restraint systems (PRSs), because of their vital role in occupant safety. Seatbelts are arguably the single most important safety feature in a vehicle and when properly designed and utilized save countless lives. However, when they fail to perform as intended or malfunction thanks to a defect in their design or manufacturing, tragic results can occur. Figure 12.4 shows typical seatbelts used in automotive industry.

12.3.4.1 Manufacturing Process In seatbelt manufacture, the yarn specification is a frequently debated issue, especially the linear density of the yarn and its constituent filaments. The debate primarily concerns the threads whose strength is most critical in the event of a crash. The weft yarns have less influence on the mechanical performance of the belt than the finer filaments do, and are more prone to contamination and the incidence of yarn impurities tends to be greater. In comparison, coarser filaments produces webbing with superior abrasion resistance and improved lateral tear strength. Moreover, when the linear density of individual filaments rises, the translational efficiency also rises. The choice between twisted and untwisted yarn is another debatable issue and also equally unsettled. Untwisted yarns yield product and cost advantages over their twisted rivals. The untwisted yarns give softer and more flexible webbing as they are thinner 362 12 Automotive Textiles and Composites

Figure 12.4 Typical seatbelts used in automotive industry.

and smoother, because the untwisted filaments pack themselves closer together. Original seatbelt webbing was woven on shuttle looms, around 1959. These looms were capable of delivering up to 200 weft insertions per minute from small weft supplies, which frequently needed replenishing. Since 1975, most seatbelt webbing has been made on needle looms which run at considerably higher speeds. The needle loom is shuttle less and is capable of delivering over 1000 picks per minute or even more. In the needle loom, weft is inserted from one side of the warp sheet and here a selvedge is formed. The other side of the webbing is held by an auxiliary needle which manipulates a binder and a lock thread. Once these threads are combined with the weft yarn, a run‐proof selvedge is created. Special care must be taken when constructing the selvedge to ensure it is abrasion‐resistant. It is equally important to ensure that the selvedge is soft and comfortable to wear.

12.3.4.2 Seatbelt Material Properties Seatbelt webbing material is normally made of nylon or PES and woven from about 300 warp strands and one weft strand. The width of the webbing is about 48 mm and has a tensile strength sufficient to support approximately three tonnes. Most seatbelt webbing is made from PES because it is a high quality material that has high strength (tenacity almost 10 g/den). They are more than just a strap that passengers wrap on their bodies. The following are some of the qualities that webbing made of PES has: ●● Very high strength tenacity: up to 10 g/den. ●● Elongation: up to 25% at break. ●● Abrasion: excellent resistance to abrasion. ●● Moisture: has a very low regain of 0.4%, making it feel damp very quickly. ●● Temperature: the melting point is around 260 °C and will withstand temperatures above 180 °C for some time. It will lose some strength if kept at high temperature for extended periods. ●● PES is very good in low temperatures, increasing in strength and reducing elongation. ●● PES webbing is difficult to ignite, and tightly woven structures do not burn quickly. ●● PES has excellent resistance to sunlight (one of the best for outdoor use). ●● PES is resistant to most common chemicals. 12.3 Application Areas of Automotive Textiles 363

After the belt is made and finished, it should have certain properties to meet safety standards. These properties are: ●● Good retraction behaviour. ●● High load bearing capacity (up to 1500 kg). ●● Abrasion resistance. ●● Resistance to heat. ●● Capable of being removed and put back in place. ●● UV resistance. ●● Lightweight. ●● Flexibility and extensibility.

12.3.5 Airbags

In an automobile, in addition to comfort, aesthetics, speed, mileage, durability and efficiency, safety is a priority for the passengers. Airbags work as a supplementary safety device for an occupant who is correctly restrained with a seatbelt. In the event of a collision, seatbelts hold the occupant securely in place and the airbags inflate instantly to cushion the passenger with a gas filled pillow. The airbag is a part of an inflatable restraint system known as an air cushion restraint system (ACRS) or airbag supplemen- tal restraint system (ASRS). All modern vehicles incorporate a wide variety of airbags in the form of driver, front passenger, side impact, and rollover airbags in various side and frontal locations. The airbags work as a supplement to other active restraints (i.e. seatbelts). Airbags are passive devices, as no action by the vehicle occupant is required to activate or use them. On the other hand, seatbelts are considered active devices, as the vehicle occupant must act to enable them. Figure 12.5 shows some examples of airbags used in the automotive industry. Airbags constitute about 3.7% of the textiles used in a car. It is made from nylon 6,6 of lighter linear density and is normally coated with silicone. The amount of fabric used per

Figure 12.5 Airbags used in automotive industry. 364 12 Automotive Textiles and Composites

airbag is approximately 1.8 m2. It is usually located in both the front and the back side of the vehicle and can be classified into three categories based on positioning: ●● roof mounted airbags. ●● door mounted airbags. ●● seat mounted airbags. Nowadays, all airbags (driver, passenger, side, and others) remain either coated or uncoated, like their predecessors. However, the performance criteria are gradually becoming more stringent. The coated or uncoated airbags developed in the last two decades are significantly superior compared to earlier designs, as they are lighter in weight, have improved performance and ageing characteristics, and have better packability. However, the market share of coated airbags is gradually reducing, owing to cost and environmental issues. The cost reduction of uncoated fabrics has been realized by the reduced material content and reduced cost of manufacture. In the industry, the coating process is well known for being extremely cost sensitive, for which reason the traditional coated fabrics are not preferred against alternative materials. Another reason for this can be attributed to technical developments, which enable the specification requirements to be obtained without any coating. In addition, today’s uncoated airbag fabrics are better engineered with respect to the construction and yard utilization, which overcomes the problems of poor seam strength, bulkiness, gas leakage, and variation of permeability [16–23]. One type of airbag material may not be practical for all applications, owing to the associated factors such as steering wheel design (pan size), inflator type (azide, gas assist, or liquid), inflator aggressiveness, and bag type (driver, passenger, side, knee‐bolster, or others). Hence, several airbag designs exist with different automobile manufacturers.

12.3.5.1 Fabrics for Airbags Almost all the airbags manufactured world‐ide are from woven fabrics of nylon 6,6 yarns. The other structures used are knitted and nonwoven. The airbag fabric is required to have the following properties: ●● High tensile strength. ●● High tear and bursting strength. ●● Good heat stability. ●● Good ageing characteristics. ●● High energy absorption features. ●● Good coating adhesion. ●● Functionality at extreme hot and cold conditions. ●● Good packability. The early stage airbag fabrics were coarse and heavy. The surface of the airbag made from this fabric was coated by relatively heavy neoprene coating [17]. In addition, the coated surface was heavily covered with talc to facilitate handling and packaging as well as to prevent the possibility of blocking between fabric layers during folded storage of the airbag. The coated airbag fabric was heavy with a weight as high as 500 gsm. Therefore, the early airbags needed a large module for storage and deployment. The subsequent fabrics were modified to be lighter weight, cheaper, and with improved performance [24–30]. 12.3 Application Areas of Automotive Textiles 365

12.3.5.2 Future Trends The future of airbags is promising, as there are a wide range of applications ranging from motorcycle helmets to aircraft seating. The airbags in future will be more economical, owing to developments in the technology and availability of advanced materials. The focus of the airbags from the very early stage of development is longer service life, smaller package size, cost reduction, and improved occupant safety. Owing to the sharp increases in the prices of new automobiles, car owners try to keep their vehicles longer before trading them in. As per the legislation, the legal ramifications of failed safety devices can be ruinous. Hence, the safety restraint systems should perform longer even under more adverse conditions. The airbags in most recent cars use and in future will be using a range of intelligent sensing elements to ensure the severity of a crash before the deployment. This reduces the likelihood of airbags deploying in the case of minor crashes. The first‐generation airbags were of a larger size. The design of smaller cars provided a lower amount of interior space to accommodate these airbags. However, technological developments helped to reduce the size of the airbags, while ensuring the same level of protection for the reduced interior. It is an established fact that airbag deployment causes minor injuries, such as bruises, abrasions, scratches, contusions, and burns. However, modern airbags are designed with lighter, softer, and smoother fabrics with a lower surface friction to reduce bruises and abrasions. The main focus is to reduce secondary injury risks while improving primary injury protection. The airbag triggering algorithms used in recent vehicles are becoming much more precise and complex. They try to reduce unnecessary deployments and to adapt the deployment speed to the crash conditions. The algorithms are considered valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine whether a baby seat is present. In future airbags, fuzzy logic controllers should be used to address the complexity of restraint system. The system should include occupant detection sensors, weight sensors both for driver and passenger, a distributed crash sensor arrangement, a dual stage airbag for both the driver and passenger, and a micro‐ controller implementing a fuzzy logic algorithm. Crash sensors can be fitted in several positions on the front and rear of the vehicle, which can monitor the airbag deployment. Future airbags will be smaller and lighter in weight, with more integrated systems and improved sensors. Tomorrow’s airbag systems will be smart adaptive restraint systems that can detect the size and position of the occupant, out‐of‐position conditions, distance between the occupant and the airbag module, as well as the severity of the crash [31]. Depending on these conditions, the airbag deployment (i.e. the height and velocity) can be tailored or the airbag can be completely disabled. The future airbags will focus on the following parameters:

●● Lighter fabrics with good packability and use of cold inflator technology. ●● New coating polymers. ●● New application for airbags: such as side curtain, rollover protection. external pedes- trian protection, and other special areas. ●● Consolidation/integration of supply chain. ●● Combinations of nonwovens and film. 366 12 Automotive Textiles and Composites

Newer designs of airbags need to hold the air for longer with a reduced level of coating material. Hence, the coating should provide effective air retention as well as prevent edge combing in order to sufficiently protect the driver and the passenger.

12.3.6 Insulating Felts

It is used for acoustic and thermal insulation in automobiles and is often known as an NVH product. It is the main constituent of bonnet lines, outer dash, wheelhouse, and outer floor under shield. It functions as noise reduction both inside and outside the car. Fabric used in this case is made of 100% PES using nonwoven technical textiles. Based on the nonwoven technique used for PES, insulating felts are of three types: ●● needle‐punched. ●● phenolic resin bonded. ●● thermoplastic.

12.3.7 Sun Visor

These are located just above the windscreen in the interior of four‐wheelers. Their main function is to block the sunlight that enters through the windscreen. There are generally two sun visors in a car: one for the driver and the other for the passenger. It is made up of three components: ●● Synthetic backbone made of polypropylene/kenaf fibres. ●● Scrim composed of coarse woven reinforcement fabric. ●● Upholstery typically made of artificial leather.

12.3.8 Helmet

Helmets are used to prevent the shock of a crash. Usually, a motorbike helmet’s internal layer is made up of polystyrene or polypropylene foam with a cushion and the external layer of plastic glass and other synthetic fibres like acrylonitrile butadiene styrene (ABS), which is very hard in nature. The function of the helmet is to absorb the shock of a crash and thus put a stop to major injury to the brain, rather than preventing head and facial injuries.

12.3.9 Car Outer Body Covers

The outer body cover is used to cover the whole car, or any kind of vehicle, to protect it from dust and rain, etc. Generally, covers are made from HDPE (high density polyethylene), PVC, reinforced cotton material, nylon and canvas covers.

12.3.10 Tyre Cord Fabric

Tyre cord fabric is used to provide strength and support to a tyre. It is prepared from fabric of high tenacity and continuous filament yarn. The fabric is made by twisting and plying the filaments. Both nylon 6 and nylon 6,6 are used to produce tyre cord fabric. 12.3 Application Areas of Automotive Textiles 367

Some typical denier and ply types of nylon 6 used for this fabric are 840/2, 1260/2, 1260/3, 1680/2, and 1890/2 with a 6 denier per filament (dpf of 6). Typical tyre cord fabric is shown in Figure 12.6. The properties required for fabric of nylon tyre cord are: ●● high strength. ●● fatigue‐resistant. ●● impact‐resistant. ●● high adhesion.

12.3.11 Tyres

Textile materials such as viscose, glass, and steel cords are used as reinforcement materials in the manufacture of tyre cord. They provide dimensional stability as well as reinforcement. Dimensional stability is an essential requirement for tyres. There are many textile components in a tyre such as casting belt breaker fabric, bead wrapping fabric, chafer fabric, filler fabric, tyre cord fabric, etc. The fibres generally used for tyre cords are high tenacity filament yarns of nylon 6, nylon 6,6, PES, and viscose. Nylon 6 is most commonly used in tyre cord manufacturing. Plied cotton yarn was originally used for the manufacture of tyre cord fabric. It was preferred as it had natural compatibility towards rubber. Kevlar, glass, or steel are used in the manufacture of cords for the breaker or belt layer. They are preferred because of their high modulus. Viscose is the commonly used fibre in radial ply tyre casing. Carbon fires are also finding application in the form of reinforcing material.

12.3.12 Filters and Engine Compartment Items

The important components of a car engine are its hoses, belts, and linens. They are reinforced with textile materials. Automotive filters are largely made of textiles. The air filter and oil filter are two examples of the types of filters to be found. The function of these filters is to filter the fluid before it enters the engine because certain delicate machine components may be destroyed if dust particles enter the engine.

Figure 12.6 Typical tyre cord fabric. 368 12 Automotive Textiles and Composites

Paper is used in many applications, such as the oil filter and carburettor air filter. Nowadays, nonwovens are used in some cars for their filter application. The latest advanced filters combine mechanical filtering through polypropylene nonwoven elec- tret fabric with adsorption by activated carbon. Filter fabric is arranged in a pleated form to maximize the surface area with minimum airflow resistance. The nonwoven filter fabric must be strong. When it is wet, it has to be odour‐free, resistant to microorganisms, and resistant to extremes of temperature. A woven fabric structure is also used in some of the applications, but nonwoven textile fabrics are the most widely used textile filtration media, and they have good filtration efficiency. This is mainly due to their complex structures, which are as a result of a 3D network of fibres and their considerable thickness. Different types of finishing – like calendaring, raising, chemical treatments, and special surface treatments – are used to improve the filter efficiency of the fabric.

Type of Filter Media and Applications ●● Carburettor air filters: wet, dry, needled, or spunbonded. ●● Engine oil filters: resin impregnated wet laid nonwovens. ●● Fuel tank filters: activated carbon. ●● Cabin interior filters: electrostatically charged fibre media, nonwoven, activated carbon. ●● Diesel/soot filters: ceramic materials. ●● ABS wheel/brake filters: metal or fibre woven screens. ●● Power steering filters: mainly screen fabrics. ●● Transmission filters: woven fabrics or needle felts. ●● Wiper washer screen filters: woven fabrics. ●● Air conditioning recirculation filters: nonwoven/activated carbon. ●● Crank case breather filters: nonwovens. The filtration efficiency of a particular filter depends upon the fibre structure, yarn structure, fabric structure, weight per unit area, porosity, and surface characteristics of the fibre. By making necessary changes in the fibre, yarn, or fabric level, one can alter the filtration efficiency and the properties of the filter fabric.

12.3.13 Acoustic Textiles

The use of acoustic textiles in the transportation industry currently represents the most important application of textiles in the world. In general, acoustic textiles are used in the transportation industry to reduce interior noise and vibration and improve the sensation of ride comfort for passengers. Interior noise is currently a competitive quality characteristic of every mode of transport facility, and in particular for automobiles. Although interior noise lowers the comfort feeling inside a vehicle, it also induces fatigue and may reduce driving safety. In the case of automobiles, sound is propagated through the air and by vibration of the car body. There are three basic mechanisms for reducing it: by absorption, by claim- ing, and by isolation or insulation. In general, a thick piece of material will absorb more sound than a thinner piece of the same material. And various permutations of the 12.4 Textile Composites for Automobiles 369 number of layers and the type of materials used can be employed to reduce noise and dampen vibrations experienced inside the vehicle. These layers are: ●● Top decorative layer: tufted bulked continuous filament (BCF) nylon or needle‐ punched PES or polypropylene‐back acrylic. ●● Thermoforming layer: polythene powder. Mouldable fibre ethylene‐vinyl acetate (EVA) or a further thick layer of compounded styrene‐butadiene rubber (SBR) later. ●● Acoustic layers: heavy layers of EPDM (ethylene propylene diene monomer) rubber, shoddy fibres, or polyurethane foam. These layers are generally made up by being filled with lots of small pieces of material, which is a time consuming process and it produces an inferior insulation performance than a continuous layer. In some vehicles this insulation layer is formed directly on the back of the pre‐formed carpet itself by back injection moulding using polyurethane foam. Eliminating unwanted noise in the passenger compartments of vehicles is important to automobile manufacturers. Several methods are presently employed to reduce noise and its sources. One of the most popular methods uses sound absorbing materials attached to various components such as floor coverings, package trays, door panels, headliners, and trunk liners. Natural fibres are also considered noise absorbing materials that are renewable and biodegradable, making them an attractive choice for the automobile industry. Control of the interior frequency response of a car can be achieved by modifying the cabin geometry so that high acoustic resonance peaks are reduced and the interior frequency response tends to be linear. However, the new design of automobile cabin shapes is usually limited, and the acoustic resonances are often damped through the use of sound absorption. The addition of acoustic damping in the form of a sound absorbing material on the surfaces greatly affects the acoustic character of the passenger space. Research work reveals that the addition of a thick nonwoven textile lining significantly reduces the resonant response peaks of the acoustic modes at mid‐ and high frequencies. The number of cars exceeds by many times the total number of other means of transport produced every year in the world. The need to reduce noise in the passenger cabin of a car is of paramount importance resulting in the widespread use of acoustic textiles. A variety of sources contribute to the interior noise of a vehicle, which can be structure‐ borne or airborne sound. Acoustic textiles used to control noise in vehicles must provide airborne transmission reduction, damping, and sound absorption. However, the use of acoustic textiles in vehicles is not only dependent on their acoustic properties but also on additional characteristics. The selection of a particular material is also determined by its ratio between performance and cost. Acoustic textiles employed to reduce noise and vibrations are used either individually or as components of complex composite materials, which is an interesting area of research [1, 4, 32–36].

12.4 Textile Composites for Automobiles

Composite materials have been used for nonstructural car parts since the 1950s. In recent decades, automotive interiors have been increasingly produced from thermoplastics, with semi‐structural parts now widely made from thermoset composites. In 370 12 Automotive Textiles and Composites

the aircraft, boat building, and racing/sports car sectors, the use of carbon fibre composites, in particular, has grown rapidly in recent years. In the aerospace industry, for example, carbon fibre based composite parts in the aircraft body now account for more than 50% of the total weight of the latest models, such as the Airbus A380 and Boeing 787 Dreamliner. In general, composite materials are lighter in weight than steel or aluminium, which provides engineers with a lightweight alternative for use in a wide range of automotive structures and components. High strength and lighter weight leading to better fuel efficiency are the key benefits that composites offer the automotive sector; greater design flexibility, enhanced aesthetics, and improved durability are other advantages. Amongst all materials, composite materials have the potential to replace widely used steel and aluminium, and often this will mean better performance. Replacing steel components with composite components can save 60–80% in component weight, and 20–50% weight by replacing aluminium parts. There are many other advantages of using composites over metals in the advanced transport sector, such as in aerospace applications. Monolithic metals and their alloys cannot always meet the demands of today’s advanced technologies. For example, trusses and benches used in satellites need to be dimensionally stable in space during temperature changes between −160 and 93.3 °C.

12.4.1 Textile Structural Composites

Textile structural composites (TSCs) are composites reinforced by textile structures dedicated for load bearing applications. These composites must have textile as well as resin, metal, or ceramic components and must be capable of withstanding the primary and secondary load to the basic framework. The primary work in TSCs was initiated in the 1970s and subsequently composite materials became common engineering materials. Today, composites are the materials of choice for many engineering applications, including automobiles, aerospace, marine, and many other advanced fields. The principal objective of structural composites envisages the utilization of textile structures in composite manufacturing in order to achieve: ●● lightweight composites. ●● load bearing composites. ●● advanced composites. And the main advantage of TSCs is utilization of advantages of textile structure in addition to textile materials in composites so as to obtain: ●● High strength (strength/weight ratio). ●● Structural anisotropy. ●● Endless textile structures, such as woven, knitted, braided, etc. ●● Numerous shapes and geometry. ●● Using existing textile manufacturing technologies. ‘Advanced composite materials’ refers to those composite materials developed and used in the aerospace industries. They usually consist of high performance fibres as reinforcing phases and polymers or metals as matrices. But there are several reasons why advanced composites have not been more widely adopted by the automotive industry. The key stumbling block is price, while the availability and future supply of carbon 12.4 Textile Composites for Automobiles 371 fibres is another issue that is being addressed by fibre producers. Many companies, from carbon fibre suppliers through to original equipment manufacturers (OEMs), are now entering the market, with a wave of partnerships and joint ventures announced recently. Meanwhile, there are ongoing attempts to replace glass fibre with natural fibres, such as flax and hemp.

12.4.2 Application of Structural Composites

In the automotive industry, there is an increasing demand for higher quality exterior panels with better functional properties and reduced weight. The weight of an automobile is directly related to fuel efficiency and emissions. Weight reduction is one of the main problems of new vehicle design. In modern daily life, composites are used because they have less weight and more strength than conventional metals. Therefore, TSCs are a good substitute for advanced automotive structural applications, owing to their high specific mechanical properties and other properties like corrosion‐free low maintenance, especially fatigue resistance. Textile composites are widely used in many different areas of transportation applications, such as aircraft, marine, and automotive, and are available in various structures. The most important factor in fabricating these composites is to achieve better structure in automotive design, where aesthetics and weight play an important role. In one study, theoretical analysis was done to examine the advantage of TSCs over conventional metals in terms of their mechanical, weight reduction, and fuel saving properties. A comparative analysis was also done between the mechanical properties of composites with different textile reinforcing structures like chopped fibres, unidirectional (UD) fabric, 2D fabric, and 3D orthogonal fabric. From these analysis, it could be concluded that TSCs have good potential to replace metals in automobile body panels. A comparison has been done between composites with a 3D orthogonal structure preform of various stuffer‐to‐binder ratios. The tensile properties of composite and metal are compared to ensure the potential of TSCs to replace conventional metal [37].

12.4.3 An Engineered Alternative

Recent analysis of the automotive industry has identified that the textile industry is becoming an increasingly important part of the global automotive supply chain, because textile products are now used so widely for interior, exterior, and even suspension parts and components of automobiles. The automotive industry is increasingly demanding higher quality exterior panels with better functional properties and reduced weight. One of the main reasons for this demand is based on the fact that 3D woven composites technology innovations have the potential to replace the existing technology. Light vehicles represent an important market for plastic resins and composites. The new role of the textile industry could make important changes in the automotive supply chain industry, such as changes in the size of the supply chain, the time to market, and the position of the textile industry in the automotive supply chain structure. Textile composites are widely used in many different areas of transportation applications – such as aircraft, marine, and automotive – and are available in various structures. The process of manufacturing thick 3D orthogonal woven composites is capable of weaving thick (up to 7.6 cm) preforms from practically any fibre. The 3D woven preforms are 372 12 Automotive Textiles and Composites

conformable and can be easily moulded to complex shapes and made into high performance composite materials. Typically, composites are up to 40% lighter than steel parts of equal strength. Structural composites were first used in a mass‐produced vehicle on the closure panels of the 1953 Corvette, and their use has grown significantly during last decades. The average light vehicle contains 171 kg of plastics and composites (9.4% of total vehicle weight). Lightweight, fibre‐reinforced composites made primarily of polypropylene and fibreglass are steadily being adopted by the automotive market, based on their performance properties, and their lightweight and cost savings characteristics. High performance textiles for automotive applications usually consist of high performance fibres, yarns, or rovings. Typical materials are carbon, glass, and aramid. In most cases, twisted and untwisted multifilaments, the so‐called rovings, are used. Twisting the roving slightly improves its processability significantly and decreases the risk of filament damage. For the use of textile structures as reinforcement in composites, it is often important to realize a yarn position that is as straight as possible, because noncrimped fibres can bear the highest loads and induce the highest stiffness. In other applications fibre crimp is needed, for example to achieve high damage tolerance or high energy absorption. Therefore, each application requires its own textile structure.

12.4.4 Advantages of Composites

Composites have many advantages over traditional materials, such as their relatively high strength and low weight, excellent corrosion resistance, thermal properties and dimensional stability, and their greater resistance to impact, fatigue, and other static and dynamic loads that car structures are subjected to. These advantages increase the performance of cars and lead to greater safety and less energy consumption. It should be noted that car performance is affected not only by engine horsepower but also by other important parameters such as the weight‐to‐ horsepower ratio and the good distribution of weight. Moreover, reducing the weight of vehicles reduces their fuel consumption. It has been estimated that fuel economy improves by 7% for every 10% of weight reduction from a vehicle’s total weight. It is reported that using carbon fibre composites instead of traditional materials in the body and chassis car parts could reduce a car’s weight by up to 50%. In addition, it means for every kilogram of weight reduced in a vehicle, there is about 20 kg of carbon dioxide reduction [37].

12.5 3D Fabrics for Automotive Applications

Using new possibilities and improved machine technology, spacer fabrics have already become an established feature of many areas. Unlike regular 2D fabrics, spacer uses two separate fabrics, joined by microfilament yarn, to create a breathable, 3D free space between layers. Spacer textiles in upholstery are made from warp knitted (double‐ Raschel machine) or (circular knitting machine) fabrics. Spacers are also made from two separate textile layers which are connected by stiff spacer yarns so as to achieve the desired resilience. Figure 12.7 shows the 3D spacer knitted fabric production. 12.5 3D Fabrics for Automotive Applications 373

Figure 12.7 3D spacer knitted fabric production.

Monofilaments are mainly used for spacer yarns, also called pile threads. The height of the structure is governed by the distance of the two needle bars of the Raschel machine and by the distance between the cylinder and rib discs in the circular knitting machine. The force that is necessary to keep the two textile layers apart depends on the material, thickness, and structural integration of the spacer yarns (monofilaments) into the basic layers. Spacer structures have an elastic pressure behaviour: by pressing on the surface, they are compressed. When the pressure is released, they relax in an elastic way. The space between the two layers is an air‐filled cavity from which the air is removed during compression, and into which air is sucked during decompression. Unlike foam constructions, these textile constructions are able to breath. Figure 12.8 shows some examples of 3D stitch bonded nonwovens.

12.5.1 Applications Areas

Transportation industries are willing to replace metallic materials by composites materials on structural parts subjected to severe mechanical solicitations with equal mechanical performances. Composite materials are proposed because they are able to provide credible answers to the optimization of large and thick structural parts. Their good strength‐to‐weight ratio and especially their anisotropy, which can be adapted to the mechanical solicitation of the structure, are particularly interesting. Three‐dimensional warp interlock fabrics can be used as fibrous reinforcement in composite material.

6 2 5 3 1

4 7

Figure 12.8 3D stitch bonded nonwovens. 1. Stitching needle, 2. Closing wire, 3. Knock over bit, 4. Support, 5. Oscillating, stuffing unit, 6. Nonwoven, 7. Fibre loop, 8. Pole fibre fold. 374 12 Automotive Textiles and Composites

Recently, a general definition of the 3D warp interlock fabric was proposed for the scientific community in order to take into account all the main parameters of this 3D woven fabric architecture. Thus, the complexity of the 3D warp interlock fabric geometry could be better described and this definition could help designers understand the influence of product parameters on residual mechanical properties. Composite materials made with commingled E‐glass/polypropylene yarns inserted in 3D warp interlock fabric have been one of the studied solutions to cope with fast and low cost production requirements of the European Union (EU) research project MAPICC 3D. To obtain a final 3D shape of the composite part, the forming of the 3D warp interlock preforms made with commingled yarns can be performed at room temperature on dedicated mould. Then a thermo‐compressing step is applied to the 3D formed fabric in order to melt the polypropylene filaments all around the E‐glass filaments to ensure a complete consolidation of the composite material. Different solutions have been developed according to the different transportation area requirements: an oil container for the automotive application (Auto‐Mapicc), a seat reinforcement for the truck application (Truck‐Mapicc), a tubular cross for the rail application (Rail‐Mapicc), and an F‐preform for the aeronautic application (Aero‐Mapicc). All of these solutions tend to replace existing metallic parts by lightweight composite materials, including fibrous reinforcement as a 3D warp interlock fabric. The three ground transportation applications are using commingled E‐glass; polypropylene yarns and aeronautic application is based on qualified carbon yarns and epoxy resin.

12.5.2 3D Woven Structures for Reinforcements

Processes for the production of 3D textile structures often allow the realization of textile preforms in one production step. Many production processes to create 3D textiles have been invented over the last two decades and development has not ceased yet. The most relevant technologies are described below [4, 38–44]. Different types of 3D woven solid structures are developed during last decade. Among the solid structures, orthogonal, warp interlock, and angle interlock are most prominent weave architecture, as shown in Figure 12.9a–c, respectively. Table 12.1 gives an overview of some common types of 3D structures with the type of weaving machine and process used to produce them.One kind of 3D fabric structure is the so‐called multi‐layer woven fabric. This is manufactured by the composition of several fabric layers without any spacing between. The layers are fixed by interlocking or warp knitting. The yarns are oriented in a 0° and 90° direction, and yarns in a z‐direction are variable. Multilayer fabrics can be draped well, having very good elongation behaviour and good tensile, compression, and bending stability. True 3D woven fabrics are manufactured by inserting two picks with double shed opening, being perpendicular to each other. The yarns are fed in a 0° and 90° direction and an additional yarn is positioned orthogonally towards the two others in a z‐direction. Three‐dimensional fabrics feature quasi‐isotropic properties, a high tensile and compression strength, as well as a good bending stability and a very good impact behaviour. The distribution of the reinforcement fibres is very uniform in all three dimensions. The drapability and the elongation behaviour of 3D fabrics, however, is very poor. Three‐dimensional fabrics are applied in fibre‐reinforced composites with high thermal impacts as well as for structural parts for cars and aircraft. 12.5 3D Fabrics for Automotive Applications 375

(a) (b) (c)

Figure 12.9 3D solid structures: (a) orthogonal; (b) warp interlock; and (c) angle interlock.

Table 12.1 Overview of 3D structures with the type of weaving machine and process.

S. No Name Weaving device Set of yarns involved Weaving process 1 Multilayer Conventional Multilayer warp yarns (Z) Two orthogonal set of interlaced 3D 2D waving Weft yarns (X) yarns interlaced fabric device together Ex: angle and warp interlock 2 Multilayer Modified 2D Multilayer warp yarns (Z) Three sets of noninterlaced weaving Weft yarns (X) orthogonal yarns bound 3D fabric machine Binder warp yarns (Y) together but not interlaced 3 Fully interlaced Specifically Multilayer warp yarns (Z) Three orthogonal sets 3D fabric designed 3D Weft yarns in row (X) of yarn are completely weaving Weft yarns in column (Y) interlaced together machine 4 Nonwoven, Specially Multilayer warp yarns (Z) Three orthogonal sets noninterlaced designed Weft yarns in row (X) of yarns together with 3D fabric device Weft yarns in column (Y) no interlacing Noobing (weaving), interloping (knitting), or intertwining (braiding) The fabric is held together by a special binding process

Woven spacer fabrics also have a 3D structure. They are manufactured by weaving in upright pile warps, and their properties are comparable to those of multilayer fabrics, but their drapability is poor. The distance between the two layers can be adjusted individually. These textiles show a high resistance to perforation. They are applied in sandwich structures, for example in composite lightweight design applications [45, 46].

12.5.3 Advantages of 3D Woven Preforms

In the automotive industry, various kinds of composites have many advantages in comparison with heavy metal materials. The actual material cost of a composite is higher than the cost for a comparable metal material, but lifetime analysis shows that savings in fuel over the life time of the vehicle significantly exceed the extra cost of manufacturing. [4]. There are 376 12 Automotive Textiles and Composites

several significant benefits from composites’ use in automotive industry. The main benefits are: less bulk (this creates more useful space), anticorrosion, dent resistance, high rigidity, and strength. Composites also allow more moulding freedom, which is very important in creating aerodynamic shapes and in the integration of many different components (a single composite can replace several individual metal parts which have to be joined together). To perform effectively in the case of a car crash, vehicle components have to have high energy absorption properties. While energy absorption in metal structures is achieved by plastic deformation, in composites it relies on a material’s diffuse fracture. For that reason, composites have a better capacity to absorb kinetic energy compared to metal parts [38]. Three‐dimensional woven composites have many advantages in comparison with different composites technologies. First of all, the thickness of 3D woven preform eliminates multiple plies of 2D woven preforms and at the same time dramatically reduces labour time and decreases the costs associated with building up the desired thickness for constructing a given part. One or a handful of 3D woven thick fabric plies replaces dozens or hundreds of 2D woven fabric plies needed to achieve the required thickness of the material and eliminates every layer’s resin pre‐impregnation process and lamination process. Compared with 2D woven laminated composites, 3D woven composites demonstrate higher through‐ thickness and interlaminar properties because of their integrated structure in the presence of orthogonal constituents. Unlike very thick laminates from multiple 2D woven fabric reinforcements, 3D woven composites can be easily machined into components in the same fashion as aluminium or steel. A thick composite based on a single ply fabric preform will not delaminate and will provide exceptional mechanical performance [39]. The unique reinforcement geometry of 3D orthogonally woven fabric‐reinforced composites (z‐yarns act as capillary channels to transfer resin into the preform interior from the outer surface) creates significantly improved resin infusion and resin transfer moulding methods with much higher resin penetration speeds during composite processing. They wet out faster in both open and closed moulding, improving quality, reducing moulding times, and facilitating migration to vacuum resin infusion. Two‐dimensional woven fabrics have an inherent crimp in the interlaced yarns that is undesirable for maximum composite properties. The absence of interlacing between warp and pick yarns allows 3D orthogonal woven panels to bend and internally shear easily without jamming and buckling within in‐plain reinforcement that allows an easier moulding process for different shaped parts and also leads to stronger and lighter structures. Even 2D woven fabric composites are characterized by superior impact resistance and damage tolerance characteristics and high fracture toughness. However, 3D orthogonal woven composites have an advantage in impact tolerance compared with 2D woven laminates. Z‐yarns, connecting different layers of warps and picks, create higher interlaminar shear strength, and in this way dramatically improve impact damage tolerance. Connected layers eliminate the risk of composite delamination as a failure mode, so a more effective load transfer can be achieved [47, 48].

12.6 Comfort Properties of Automotive Interior

Most of the developments of components, parts, pieces, and materials used in a car are primarily governed by comfort, functionality, safety, economy, and ecology. Comfort is the first criterion that values the customer. In the case of a car’s upholstery, both 12.6 Comfort Properties of Automotive Interior 377 psychological comfort (the aesthetic aspects) and thermo‐physiological comfort (captured by the touch and feel of the fabric) are considered. Thermal comfort while sitting is evaluated by the ‘cold–hot’ sensation. Functionality and material safety criteria are captured during use of the vehicle, by means of wear, seat ventilation, the internal environment, ease of care, etc. In fact, comfort in a car is a complex phenomenon and comprises different aspects, such as noise, driving behaviour, and ease of handling, as well as the most important factor influencing passenger convenience: thermal comfort. A particularly important aspect of vehicle comfort is the seats. Seats do not only have to have an attractive design or meet specific design criteria for safety reasons; they must also have optimum comfort properties. But seat comfort is much more than just passenger convenience. Scientific findings show that the performance of a driver over long distances significantly decreases if the car seats do not support posture and heat balance as required. This leads to exhaustion and loss of concentration, which, in extreme cases, could result in serious accidents. In addition to the ergonomic considerations of comfort, the climatic or thermo‐physiological comfort of the seat is of particular importance. This indicates whether the seat is able to support the thermoregulation of the body via heat and moisture transport [49–52].

12.6.1 Parameters of Seating Comfort

From the thermo‐physiological point of view, seat comfort comprises four parameters: ●● The initial heat flow following the first contact with the seat, i.e. the sensation of warmth or cold in the first few minutes or even seconds after entering the car. ●● The dry heat flow on long journeys, i.e. the amount of body heat transferred by the seat. ●● The ability, known as breathability, to transfer sweat away from the body. In so‐called normal sitting situations, there is no perceptible perspiration, but, nevertheless, the human body constantly releases moisture (so‐called insensible perspiration), which has to be taken away from the body. ●● In the event of heavy perspiration (a car in summer heat, stressful traffic situations) the ability to absorb perspiration without the seat feeling damp [49].

12.6.2 Warmth Sensation

About 25% of human body remains in contact with the car seat and the car seat acts as an extra layer of clothing, thus the parameter of clothing comfort is the same for car seat thermal comfort as well. The passenger has their first thermal impression of a car seat upon entering the vehicle. This initial perception of warmth after sitting depends on the thermal absorptivity of the car seat. It is affected by the heat capacity of the car seat material. Heat capacity is the amount of heat required to raise its temperature by 1 °C. Heat capacity varies with the mass of the cushion and the type of material. Thermal conductivity is also another parameter of thermal absorptivity and it should be as low as possible; otherwise, a car seat feels too cold in winter or too hot in summer. Although this initial feeling may last only a few minutes, it is nevertheless very important for the user’s acceptance, as it is repeated frequently. If a car is used every day during the winter time and each morning the driver is dissatisfied when entering the 378 12 Automotive Textiles and Composites

car, acceptance can be significantly decreased. During long journeys, it is favourable if the seat offers a high steady state heat flow, to minimize the tendency to sweat, whereas for the initial perception a low heat flux is required. Hence, a conflict arises between these two scenarios. This conflict can be overcome, because the cover, which determines the initial perception, has only a minor influence over the steady state heat flux, which is mainly determined by the thermal insulation of the seat. Owing to its greater thickness and, hence, higher thermal insulation in comparison to the cover, the cushion becomes the dominant factor. On the other hand, the heat flux is also dependent on the ventilation in the seat and between the seat and the passenger. Ventilation itself is determined by the design of the seat (side supports, surface grooves), the elasticity and air permeability of the cushion, and, if present, a fan to enforce ventilation. For car seats with heating, the dominant seat component is the cover. Other than the thermal properties of the car seat cover, heating power and its position are of great importance. As a common material used in car seats, foams are poor conductors of heat and have a low heat capacity. A thin layer of foam (plus cover) warms up to skin temperature when the driver sits on it but does not draw much heat from the body’s tissues. In warm environments, or during physical exercise, the body attempts to lose heat but is prevented from doing so in the buttocks area and back rest, owing to the insulating foam of the cushion. This region may therefore begin to heat, resulting in uncomfortable dampness. A car seat with an impermeable foam can increase the skin temperature by 10 °C in two hours. And this increase will cause sweating [49, 51–56].

12.6.3 Moisture Sensation

The moisture sensation of the passenger is very important for perceived overall seat comfort. In order to achieve a dry microclimate, the ability, known as breathability, of the seat to transport any perspiration formed away from the body is crucial. Not only under warm summer conditions is good water vapour transport necessary but even when there is no perceptible perspiration. The human body constantly releases moisture, the so‐called insensible perspiration. As the skin is not totally water vapour tight, our body loses at least 30 g of moisture per hour. Because a car seat covers large areas of the body, the seat has to manage a large part of the perspiration formed, and, hence, a considerable amount of moisture. Moisture accumulation results in discomfort and, in some cases, an increased risk of soft tissue damage. Many factors determine the causes and prevention of moisture accumulation. The generation of excessive quantities of heat can cause sweating. Sweat is normally generated to assist in the thermoregulation of the body by the evaporation of moisture to cool the surface of the skin. Normally, sweating is suppressed locally by pressure. However, sweating can occur in an uncontrolled manner, independent of thermoregulation, as in insensible perspiration. Poor air exchange is one of the reasons for moisture accumulation If there is a poor exchange of air in the supported area and the supported area is thermally insulated by the cushion, the interface temperature can exceed 38 °C, whereupon sweating increases rapidly with increasing temperature. So, use of impermeable covers for car seats can increase this moisture accumulation. If materials in close contact with the skin are not breathable, the sweat on the body will not be evaporated so that natural environmental cooling cannot occur, which will result in more heat build‐up and more sweating. 12.7 Conclusion 379

Methods for preventing moisture build‐up include the use of cushion and cover materials that encourage air exchange between the cushion and the skin. Any impermeable layer of a car seat will be the barrier for moisture transport and will make the complete structure impermeable and so uncomfortable. Cushions with good heat dissipation characteristics help to reduce moisture build‐up; if they include absorbent materials like wool or cotton, it helps to reduce moisture build‐up. Some cushions naturally pump air that is trapped in their structure when compressed. This effect can contribute to maintaining comfortable moisture level at the cushion/skin interface, if the cushion is fitted with an air permeable cover [49]. One solution to reduce passenger discomfort is to improve the ventilation properties of the car seat. This can go a long way towards reducing the problems of uncom- fortably high temperatures and levels of moisture. But it is important that the car seat has sufficient air permeability, and air distribution within the car should also be optimized at the design stage. Another important parameter for ventilation is to do with the suction or blowing of air. The insertion of a component blocking the transport of moisture (e.g. polyurethane foam of a thickness greater than 5 mm leather and artificial leather products, flame, and the other adhesive lamination of the layers) inside a package disqualifies the whole package, irrespective of the quality of the remaining components. This is an unwanted situation for seats, be they with or without ventilation systems. In this case the water vapour absorbency is the car seat cover layer is the only source to remove the moisture from microclimate in between human body and the car seat [49, 51, 52, 57–59].

12.7 Conclusion

Textiles for automobiles must satisfy very stringent requirements for both security and competing demands. High performance textile materials are widely used in automobiles for interior trim and for ensuring comfort (seat covers, carpets, roof liners, and door liners) as well as for reinforcement (tyre) and filters. Textiles also offer weight reduction, which in turn results in fuel economy. Airbags help to save lives, but at times they can also be a source of serious injury. The search for a uniform smart airbag, which can perceive the size of the passenger or whether the seat is empty and react in that manner, is underway. Such a smart airbag will incorporate sensors to judge the weight, size, and location of the car’s passengers and hence be deployed more appropriately. The trend towards uncoated fabrics is anticipated to continue and so is the improved trend towards more airbags per car and full size bags. The use of acoustic textiles in the transportation industry currently represents the most important application of textiles in the world. In general, acoustic textiles are used in the transportation industry to reduce interior noise and vibration and improve the sensation of ride comfort for passengers. Although interior noise lowers the comfort feeling inside a vehicle, it also induces fatigue and may reduce driving safety. Many factors affect the automotive industry. Government policies, competitive rival- ries, safety requirements, and environmental regulations influence the research, design innovations, and changes in the manufacturing processes. The style, reliability, and performance requirements and at a lower cost are driven by consumer requirements and 380 12 Automotive Textiles and Composites

preferences. Changes in technology are also very important drivers in the automotive industry. The demand for lighter vehicles leads to replacing metal body parts with lighter composite materials. The body of the vehicle makes up to 28% of its total mass and gives the biggest opportunity to reduce the weight by substituting current materials with lighter weight composites. Replacing a car’s metal body parts with lighter composites will lead to improved fuel efficiently, reduced emissions, and decreased processing time, increased performance, and improved corrosion resistance. The properly selected fibre and resin, and the architecture of the composite will not only reduce automobile weight but also maintain safety standards as their performance characteristics, such as impact resistance and flexural characteristics, will stay the same or even be improved. In addition, tooling for composites parts can be 80% lower than comparable steel parts. The role of the textile industry is significantly increasing in the global automotive supply chain, as new textile composites are aggressively penetrating this market. High performance textile products nowadays can be used not only for interior and exterior components but even for suspension parts of automobiles. The incorporation of 3D woven composites is changing automotive design and the development process; instead of one level, the textile industry will be engaged at all stages of the automotive development process.

References

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385

Marine Textiles and Composites Chi‐wai Kan1 and Change Zhou2

1 Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Kowloon, Hong Kong 2 College of Textile & Clothing, Jiangnan University, Wuxi, China

13.1 Introduction

Textiles can be used for decoration and for providing a warm soft touch to surfaces, thus enhancing human wellbeing and comfort. In this respect, textiles are extensively used in transportation with different technical functions [1]. Fibres are used in several functional applications and most commonly have decorative and technical applications in the marine industry [2]. Textile products in the form of clothing, furniture, carpets, canvas, burlap, ropes, and bedding, etc. are used extensively in the marine environment; others are carried as cargo, besides use as technical textiles for water–oil separation [3, 4]. Textiles in marine applications can be classified as technical because of the very high performance specifications and special properties required [1]. For instance, tex‑ tiles for marine usage have to withstand a much higher exposure to daylight, seawater, and potential damage from ultraviolet (UV) radiation. In addition, safety features like flame‐retardant behaviour are crucial and weight saving and antifouling are also other important technical requirements, especially in racing craft [5–7]. In marine environments, the comfort, design, and appearance of textiles are impor‑ tant for providing users with a relaxing atmosphere [1, 2]. In order to satisfy the high requirements, numerous advanced materials and technologies are being developed for marine applications. For example, reinforcement composites are used to replace tradi‑ tional materials for ship construction and nanotechnology can be used for antifouling of materials in marine environment [2, 8]. This chapter aims to summarize characteris‑ tics of some raw materials and fabrics which can be used for marine textiles. Besides this, certain marine products and manufacturers of marine products are also introduced.

13.2 Textiles for Marine Applications

In the very beginning, all textile materials used in marine applications were natural materials, such as fish nets and ropes. These are heavy in weight, absorb water easily, and can be damaged by rot. With the development of material technology, synthetic

fibres/plastic composites are being used for replacing metallic components and more traditional materials with considerable benefits, especially savings in weight [1]. Materials used in marine products are generally classified into three groups, namely: (i) reinforcement materials, (ii) resin materials, and (iii) core materials [2]. A very good review of materials used in marine applications is provided by [2] and the key issues are summarized in Sections 13.2.1–13.2.3.

13.2.1 Reinforcement Materials 13.2.1.1 Tough Cotton Normal cotton fabric can be made into tough cotton by coating with carbon nano‑ tubes. The coated fabric will have improved mechanical behaviour, flame retardancy, UV blocking, and water‐repellent properties, etc. when compared with original cotton fabric [9, 10]. Nanotubes, acting as a reinforcement and protective shell, are used for making tough cotton that forms a cross‐linking network with a thickness of about 500 nm surrounding the cotton fibres. The cross‐linking network in the tough cotton is nanoscale and hydrophobic in nature, which can help the original hydrophilic cot‑ ton to repel water win the same way as the lotus leaf [11]. In addition, these cotton fabrics with nanotube networking are stronger and more resistant to tear than the original untreated cotton fabrics. A concentration of nanotubes over 2% in the applied emulsion may make the cotton fabric more difficult to catch fire and can prevent treated fabric from burning by forming a carbonaceous char on the surface of the cot‑ ton. This carbonaceous char can serve as a heat shield to prevent burning. In the case of UV protection, more that 90% of harmful UV radiation can be blocked with just 0.25% addition of nanotubes to the cotton fabric [9]. Fabrics with UV resistance and water‐repellent properties can offer new opportunities for textile products in marine applications [9].

13.2.1.2 Glass Fibre Glass fibre generally consists of more than 90% of fibres used in reinforced plastics because they are not expensive to produce but have very good strength properties. Generally speaking, glass fibre can exhibit very good chemical resistance and process‑ ability [12]. Owing to its highly competitive cost and relatively good mechanical proper‑ ties, glass fibre can be widely applied in making reinforced composites in the marine field, such as canoes and fishing trawlers, etc. Glass fibre can also be found in the rein‑ forcement of making the composites for offshore drilling platforms and liquid conduct‑ ing pipes, etc. [13, 14]. Continuous glass fibre can be produced by the extrusion of molten glass into filaments with a diameter of between 5 and 25 μm. For practical use, the individual glass fibre filaments are then coated with a sizing material (serving as a coupling agent during the resin impregnation) to minimize and reduce abrasion and they can be combined into a strand with either 102 or 204 filaments. There are two types of glass fibres: (i) E‐glass and (ii) S‐glass. The E‐glass (lime aluminium borosili‑ cate) is the most commonly used for reinforcing marine laminates, owing to its good strength and resistance to water degradation [2]. The S‐glass (silicon dioxide, alumin‑ ium, and magnesium oxides) can exhibit about a one‐third higher tensile strength, and demonstrates better fatigue resistance than E‐glass. The comparison of E‐glass and S‐glass is shown in Table 13.1 [2]. 13.2 Textiles for Marine Applications 387

Table 13.1 Glass fibre composition [2].

E‐glass (%) S‐glass (%)

Silicon dioxide 52–56 64–66 Calcium oxide 16–25 0–3 Aluminium oxide 12–16 24–26 Boron oxide 5–10 — Sodium and potassium oxide 0–2 0–3 Magnesium oxide 0–5 9–11 Iron oxide 0.05–4 0–3 Titanium oxide 0–8 — Fluorides 0–1 —

13.2.1.3 Spectra A high strength/modulus extended chain polyethylene fibre called Spectra was devel‑ oped by Allied Corporation and introduced in the market in 1985. At room tempera‑ ture, Spectra has a better specific mechanical properties better than Kevlar, but its performance falls off at elevated temperatures. The chemical and wear resistance per‑ formance of Spectra is superior to the aramid fibres. The comparison between Kevlar and Spectra fibres is also shown in Table 13.1 [2].

13.2.1.4 Polyester and Nylon Polyester and polyamide (nylon) are commonly used for making ropes because of their good strength and resistance to corrosion in marine environment [15–18]. Polyester and nylon thermoplastic fibres are used in the marine industry as primary reinforce‑ ments and in a hybrid arrangement with fibreglass [5]. A product called COMPET was developed by Allied Corporation which is based on a finish application on polyester fibres that enhances matrix adhesion properties [2]. Some properties of COMPET are listed in Table 13.1 [2].

13.2.1.5 Trevira Trevira is a hi‐tech polyester fibre which is designed as a bulking material and as a gel coat barrier to reduce print‐through [2]. Although original polyester fibres have high strength, their stiffness is considerably below that of glass. This brings the attractive features of Trevira, other than original polyester fibres, which include low density, rea‑ sonable cost, good impact, and fatigue resistance, and potential for vibration damping and blister resistance [2].

13.2.1.6 Carbon Fibre All continuous carbon fibre is being produced recently from organic precursors, which in addition to PAN (polyacrylonitrile), include rayon and pitches, with the latter two generally used for low modulus fibres. Carbon fibres can provide the highest strength and stiffness among all commonly used reinforcement fibres. Carbon fibres are not subjected to stress rupture or stress corrosion, and high temperature performance is 388 13 Marine Textiles and Composites

Table 13.2 Comparison of different fibre properties [2].

Density Tensile strength Tensile modulus Ultimate Fibre (lb./in.3) (psi ×103) (psi ×103) elongation (%) Cost ($/lb.)

E‐glass 0.094 500 10.5 4.8 0.8–1.2 S‐glass 0.090 665 12.6 5.7 4 Aramid‐Kevlar 49 0.052 525 18.0 2.9 16 Spectra 900 0.035 375 17.0 3.5 22 Polyester‐COMPET 0.049 150 1.4 22.0 1.75 Carbon‐PAN 0.062–0.065 350–700 33–57 0.38–2.0 17–450

particularly outstanding. The major drawback of carbon fibre is due to the cost of PAN based fibres, which is based on the high cost of precursors and an energy intensive manufacturing process [2]. Some properties of carbon fibre (Carbon‐PAN) are shown in Table 13.2 [2].

13.2.2 Resin 13.2.2.1 Polyester Resin Polyester resin is the simplest, most economical resin system that is easiest to use and shows good chemical resistance. Unsaturated polyester consists of unsaturated materi‑ als, such as maleic anhydride, which is dissolved in a reactive monomer, e.g. styrene. Most polyesters are air inhibited and do not cure when exposed to air. Typically, in the formulation of resin, paraffin is added for the effect of sealing the surface during the curing process. Moreover, wax film on the surface presents a practical problem for resin bonding or finishing and so the wax film must be completely removed during the appli‑ cation of polyester resin. Non‐air‐inhibited resins do not present this problem and are, therefore, more widely accepted in the marine industry [2]. There are two basic polyester resins that are commonly used in the marine industry: (i) orthophthalic and (ii) isophthalic. Orthophthalic resins are widely used but they have relatively lower thermal stability, chemical resistance, and processability charac‑ teristics when compared with isophthalic resins. Isophthalic resins have generally better mechanical properties and show better chemical resistance when compared with orthophthalic resins. Their increased resistance to water permeation has prompted many builders to apply this resin as a coating in marine laminates [2].

13.2.2.2 Vinyl Ester Resin Vinyl ester resin is unsaturated resin prepared by the reaction of a monofunctional unsaturated acid, e.g. methacrylic or acrylic, to a bisphenol diepoxide. The resulting polymer is mixed with an unsaturated monomer, e.g. styrene. Thus, the handling and performance characteristics of vinyl esters are similar to those of polyesters. Some advantages of vinyl ester, other than its higher cost, include good corrosion resistance, superior hydrolytic stability, and excellent physical properties, e.g. impact and fatigue resistance. The vinyl ester resin matrix can provide an excellent permeation barrier that resists blistering in marine laminates [2]. 13.2 Textiles for Marine Applications 389

13.2.2.3 Epoxy Resin Epoxy resin is a family of materials which contains a reactive functional group in its molecular structure. Epoxy resin has the best performance characteristics among all resins used for marine applications. Other than marine applications, epoxy resin is used exclusively in aerospace applications. However, its high cost of application and handling difficulties limit its usage for large marine structures [2].

13.2.2.4 Thermoplastic Resin Thermoplastic resin has two structures: (i) one‐dimensional (1D) or (ii) two‐dimensional (2D) molecular structures, as opposed to three‐dimensional (3D) structures for ther‑ mosets. The thermoplastic resin is generally in the form of moulding compounds that soften at high temperatures. Examples of thermoplastic include polyethylene, polysty‑ rene, polypropylene (PP), polyamide, and nylon. Their marine applications are gener‑ ally limited to small boats and recreational items. Owing to the development of reinforcement technology and the need for advanced materials for marine applica‑ tions [2], reinforced thermoplastic materials have recently been investigated for the possibility of use in the large scale production of structural components. Thermoplastic resin has some attractive features, such as (i) no exothermal reaction upon cure and (ii) enhanced damage tolerance. Figure 13.1 shows a comparison chart of different resin systems used in the marine industry [2].

13.2.3 Core Materials 13.2.3.1 Balsa Balsa has a closed‐cell structure which consists of elongated, prismatic cells with a length (grain direction) approximately 16 times the diameter. Material with balsa structure generally exhibits excellent stiffness and bond strength. The stiffness and strength characteristics of balsa are similar to aerospace honeycomb cores. When

0% 10% 20% 30% 40% 50% Orthopolyester for Hulls Orthopolyester for Decks Orthopolyester for Parts Isopolyester for Hulls Isopolyester for Decks Isopolyester for Parts Vinyl Ester for Hulls Vinyl Ester for Decks Vinyl Ester for Parts Epoxy for Hulls Epoxy for Decks Epoxy for Parts

Figure 13.1 Marine industry resin systems [2]. 390 13 Marine Textiles and Composites

compared with PVC (polyvinyl chloride), a balsa panel has a higher static strength than PVC foam but its impact energy absorption is lower. However, the local impact resist‑ ance of balsa is very good because stress is efficiently transmitted between its sandwich skins. In the market, end‐grain balsa in sheet form is available for constructing flat panels or for conforming complex curves [2].

13.2.3.2 Thermoset Foams Foamed plastics – such as cellular cellulose acetate (CCA), polystyrene, and polyure‑ thane – are very light. They can resist water and fungi formation. These materials have very low mechanical properties and so they cannot conform to complex curves. Their uses are generally limited to buoyancy instead of structural applications. Polyurethane is usually a foam material in‐place when used as a buoyancy material [2, 19].

13.2.3.3 Cross‐Linked PVC Foam Polyvinyl foam core is manufactured by combining a polyvinyl copolymer with stabiliz‑ ers, plasticisers, cross‐linking compounds, and blowing agents. The mixture is heated under pressure to initiate the cross‐linking reaction and is then submerged in hot water to expand to the desired density with cell diameters ranging from 0.025 to 0.25 cm. The resulting material is thermoplastic, conforming to the compound curves of a hull. PVC foam has almost exclusively replaced urethane foam as a structural core material, except in configurations where the foam is ‘blown’ in place [2].

13.2.3.4 Linear PVC Foam In marine applications, linear PVC foam is used because it has good and unique mechanical properties, owing to its nonconnected molecular structure allowing signifi‑ cant displacement before failure happens. When compared with cross‐linked (nonlin‑ ear) PVC foam, the static properties of linear PVC foam are less favourable, but it does have better impact resistance [2].

13.2.3.5 Honeycomb Honeycomb cores are used extensively in the aerospace industry which can be fabri‑ cated by different materials such as PP, aluminium, or phenolic resin impregnated fibreglass. Although honeycomb core can be used for fabricating extremely lightweight panels, its applications in the marine environment are limited because of the difficulty of making complex face geometries and its potential to absorb significant amounts of water [2].

13.2.3.6 PMI Foam ® Polymethacrylimide (PMI) foam, for example Rohacell , is used for composite con‑ struction which requires minimum laminating pressure to develop good peel strength. The most important feature of PMI foam is its ability to withstand curing temperatures in excess of 176 °C, which makes it attractive for use with reinforcements [2, 19].

13.2.3.7 FRP Planking FRP (fibreglass reinforced plastic) planking consists of rigid fibreglass rods held together with unsaturated strands of continuous fibreglass rovings and a light fibre‑ glass cloth which can be used to build a cost effective one‐off hull. The self‐supporting 13.2 Textiles for Marine Applications 391 material conforms to compound curves and a typical application involves a set of male frames as a mould [20, 21]. The planking has more rigidity than PVC foam sheets, which eliminates the need for extensive longitudinal stringers on the male mould [2].

13.2.4 Fabrics for Marine Applications 13.2.4.1 Core Fabric Various natural and synthetic materials can be used for manufacturing products to build laminate thickness economically [2, 22]. Plywood is a structural core material, although fibreglass is generally viewed as sheathing when used in conjunction with ply‑ wood. Plywood can be used as a core, because of its low density, to improve the com‑ pressive properties of the laminate. Plywood can sometimes be used as a form for longitudinal, but its continuous exposure to water leads to concerns of moisture absorp‑ tion in a maritime environment. The absorption of moisture will make the wood swell and cause delamination. Thus, there is a decline in the use of plywood and the uneven surface of plywood can make it a poor bonding surface. In addition, the low strength and low strain characteristics of plywood can lead to failures when they are used as a core [2].

13.2.4.2 Reinforcement Fabric Reinforcement materials are combined with resin systems in a variety of forms to cre‑ ate structural laminates. Different forms of reinforcement material are graphically shown in Figure 13.2 [2]. Owing to processing and economic considerations, some of the lower strength noncontinuous configurations are limited to fibreglass [2]. Because of their light weight, high strength, stiffness and resistance to high temperature, fabric reinforced composites have been used widely in marine applications [23]. The two

Biaxial High Modulus Multilayer Triaxial Tubular Tubular Flat Braid Flat Braid Woven Woven Woven Woven Braid Braid Laid Laid in Warp in Warp

Weft Knit Weft Knit Weft Knit Weft Knit Laid Square Square Braid 3-D Braid 3-D Braid Laid in Weft Laid in Warp in Warp Laid Braid Laid in Warp Laid in Warp in Weft

Warp Knit Warp Knit Weft inserted Weft inserted Fiber Mat Stichbonded Biaxial XYZ Laid in Laid in Warp Warp Knit Warp Knit Laid Laid in Warp Bonded System in Warp

Figure 13.2 Different forms of reinforcement [2]. 392 13 Marine Textiles and Composites

main advantages of fibre‐reinforced plastics over metals are (i) resistance to the marine environment and (ii) ease of tailoring structures by moulding processes. Glass‐fibre‐reinforced polymer (GRP) composites are generally used in marine craft such as canoes and fishing trawlers, etc. [14]. Fibreglass composites can also be used in offshore drilling platforms for deck grates, low‐pressure pipes, and storage tanks [24–26]. The polymer matrix in almost all GRP composites for seawater applications is based on isophthalic polyester or vinyl ester resin [1]. In marine applications, glass/ polyester and glass/vinyl ester composites must retain their mechanical properties and should not degrade even after remaining immersed in seawater for many years [25]. One disadvantage of using polyester based composites in seawater is that the polymer matrix and fibre/matrix interphase can be degraded by a hydrolysis reaction of unsatu‑ rated groups within the resin. Seawater degradation can cause swelling and plasticiza‑ tion of the polyester matrix and debonding at the fibre–matrix interface, which may weaken the mechanical properties [26–30]. This problem can be alleviated by using vinyl ester based composites that generally have superior chemical stability in seawater [5, 7]. Another disadvantage of using GRP composites in marine structures is the rela‑ tively low Young’s modulus, which makes it difficult to build ultralight marine struc‑ tures with adequate stiffness. For this reason, marine composite structures requiring high stiffness are often built using carbon fibre composites. Carbon/epoxy laminate is occasionally used [31], but the high cost of epoxy resin has led to the increased use of carbon/polyester and carbon/vinyl ester composites in racing yachts and naval patrol vessels [25].

13.2.4.2.1 Woven Reinforcement Structure Cloth or woven roving used in marine applications is normally considered woven com‑ posite reinforcements. Such cloths of woven composite reinforcement are light in weight but their usage in the marine sector is limited to the construction of small parts and repairs. The weave patterns used in marine application include (i) plain weave, which is highly interlaced; (ii) basket weave, which has warp and fill yarns that are paired up; and (iii) satin weaves, which exhibit a minimum of interlacing. Some com‑ mercially available weave patterns are summarized and illustrated in Figure 13.3 [2].

Plain weave Basket weave Twill

Crowfoot satin 8 harness satin 5 harness satin

Figure 13.3 Commercially available weave patterns [2]. 13.2 Textiles for Marine Applications 393

Other than woven cloth, woven roving reinforcements consist of flattened bundles of continuous strands in a plain weave pattern. This is the most commonly used type of reinforcement for building large marine structures, owing to its heavyweight, which enables the rapid build‐up of thickness. Woven reinforcement structures also have good directional strength properties and the impact resistance is enhanced because the fibres are continuously woven [2].

13.2.4.2.2 Knitted Reinforcement Structure When compared with woven reinforcement structures, knitted fabrics for reinforce‑ ment can provide greater strength and stiffness per unit thickness than woven struc‑ ture. The knitted reinforcement structure is constructed by using a combination of unidirectional reinforcements that are stitched together with a nonstructural synthetic, such as polyester, to form a layer of mat in the structure [2]. The manufacturing process provides an advantage that the reinforcing fibre is lying flat when compared with the crimped orientation of fibre in woven reinforcement structures. In addition, knitted reinforcement structures can be oriented along any combination of axes. A comparison of woven roving and knitted constructions is shown in Figure 13.4 [2].

13.2.4.2.3 Omnidirectional Reinforcement Structure Omnidirectional reinforcement is generally in the form of a chopped strand mat which can be applied during hand lay‐up as a prefabricated mat or via the spray‐up process. The chopped strand mat contains randomly oriented glass fibre strands which are bonded together with a soluble resin binder. Other than chopped strand mats, continu‑ ous strand mats are also available. They are similar to chopped strand mats, except the fibre is continuous and laid down in a swirl pattern. Both hand lay‐up and spray‐up methods can produce plies with equal properties along the x and y axes with good interlaminar shear strength [32]. The omnidirectional reinforcement structure is an economical way to build up thickness but its mechanical properties are not as good as other reinforcements [2].

End View

Woven Roving

End View

Knitted Biaxial

Figure 13.4 Comparison of woven roving and knitted construction [2]. 394 13 Marine Textiles and Composites

13.2.4.2.4 Unidirectional Reinforcement Structure Pure unidirectional reinforcement means no structural reinforcement in the fill direc‑ tion. For example, carbon fibre, an ultra‐high‐strength/modulus material, is sometimes used for making pure unidirectional reinforcement structure, owing to its specificity of application. The width of material with unidirectional reinforcement structures is gen‑ erally limited because of the difficulty of handling and wet‐out. In order to produce material with a unidirectional reinforcement structure, the structure is held together with a thermoplastic web binder compatible with thermoset resin systems. A typical application of unidirectional reinforcement structure includes stem and centreline stiff‑ ening. Entire hulls are fabricated from unidirectional reinforcements when an ultra‐ high‐performance laminate is desired [2].

13.2.4.2.5 Three‐dimensional (3D) Textile Structure Polymer materials reinforced with a 2D layered fibre structure have been used with outstanding success in maritime applications. Despite the widespread use of 2D mate‑ rials over a long period, their use in many structural applications has been limited because of manufacturing problems and because of some inferior mechanical proper‑ ties. Reinforcement materials with 3D fibre architectures can overcome many of the problems with manufacturing and mechanical properties of materials [33]. Three‐ dimensional textile structural composites possess superior mechanical performance, for example improved structural integrity, enhanced fracture toughness, and through‐ the‐thickness strength against delamination [34, 35]. Three‐dimensional textile com‑ posites can be made by weaving, braiding, stitching, and knitting. Three‐dimensional textile composites include 3D braided composites, 3D woven composites, 3D stitched composites, 3D knitted composites, as well as 3D auxetic textile structures consisting of weft, warp, and stitch yarn systems. The potential of 3D materials is impressive and they have been used in items such as inlet ducts and rotor blades, etc. [33]. Three‐ dimensional textile composites have a vast range of properties that are superior to traditional 2D laminates and, therefore, it is advantageous to exploit them for many applications.

13.3 Properties of Textiles for Marine Applications

13.3.1 Antifouling

Marine structures such as platforms and ship hulls are subject to the problem of bio‑ fouling. The inhibition methods for both organic and inorganic growth on wet sub‑ strates are varied but most antifouling systems use the form of protective coatings. Biofouling can negatively affect the hydrodynamics of a hull by increasing its required propulsive power and fuel consumption. Therefore, fouling is also a concern in the case of surfaces exposed to aquatic environments where marine microorganisms can bind to a surface and form a conditioning layer, which then provides an easily accessible plat‑ form for other aquatic species, such as diatoms and algae, to attach and proliferate [36–38]. The critical issues associated with biofouling include increased operational and maintenance cost due to fouling of water conduits and ship hulls and the degradation of abiotic materials [39, 40]. Recently, different strategies for antifouling, antimicrobial as 13.3 Properties of Textiles for Marine Applications 395

Table 13.3 Requirements for an optimal antifouling finishing [39].

Must be Must not be

Anticorrosive Toxic to the environment Antifouling Persistent in the environment Environmentally acceptable Expensive Economically viable Chemically unstable Long life A target for nonspecific species Compatible with underlying system Resistant to abrasion/biodegradation/erosion Capable of protecting regardless of operational profile Smooth well as marine antifouling, applications have been developed. One of the most common approaches to prevent the surface from adhesion of microbes involves the treatment of polyethylene glycol (PEG) or oligo (ethylene glycol) groups. This treatment will induce surfaces with a low surface energy and give the optimized surface topography with promising results. This promotes the development of new approaches for the func‑ tionalization of surfaces with PEG and the development of alternatives to PEG for resisting microbial adhesion. Other important approaches for killing or degrading bac‑ teria include the design of surfaces that release antibiotics or silver, surfaces functional‑ ized with polycations or antimicrobial peptides (AMPs), etc. Their widespread use, however, results in the emergence of antibiotic‐ or silver‐resistant bacteria. Moreover, antibiotic‐ and silver‐containing coatings act through a release based mechanism and are therefore exhausted over time. Approaches involving the generation of microbicidal coatings based on AMPs and polycationic polymers have gained significant attention and are promising. Meanwhile, activity of these biomolecules upon incorporation into coatings need to be improved by using appropriate linkers and nanomaterials as immo‑ bilization supports [7]. The requirements for an optimal antifouling coating are listed in Table 13.3 [39]. As shown in Table 13.3, most of these strategies are helpful in combating the problem of fouling but several of them are also associated with shortcomings related to stability, toxicity, or the method of fabrication. A comprehensive review about marine antifoul‑ ing coating is provided by [39].

13.3.2 Flame‐Retardant Nature

Conventional polyester and epoxy type organic matrix materials are currently used in shipboard applications but they support combustion and generate large quantities of smoke while burning. Therefore, methods to inhibit fire growth in composites rely on using either (i) a fire‐retardant ingredient in the matrix resin or (ii) resins that can func‑ tion under high temperatures, such as polyimides. Fire resistance and reduced smoke and toxicity can also be achieved by the use of fire barriers, which include ceramic fabric, ceramic coating, intumescent coating, or other high temperature foam insulation 396 13 Marine Textiles and Composites

barriers [5]. An abridged version of fire characteristics to be investigated and the test methods and requirements for qualifying composite materials for use on‐board a naval submarine are presented in Table 13.4 [5]. A comprehensive review of fire safety require‑ ments of products for marine (naval) application is given by [5].

Table 13.4 Some fire performance acceptance criteria [5].

Fire test/characteristics Requirement Test method

Oxygen‐ Oxygen at 25 °C 35 ASTM D‐2863 temperature Oxygen at 75 °C Minimum 30 index (%) (modified) Oxygen at 300 °C 21 100 kW m−2 irradiance 60 75 kW m−2 irradiance 90 Ignitability (s) Minimum ASTM E‐1354 50 kW m−2 irradiance 150 25 kW m−2 irradiance 300 Flame spread 20 Maximum ASTM E‐162 index 100 kW m−2 irradiance, 150 peak Average for 300 s 120 75 kWm−2 irradiance, 100 peak Heat release Average for 300 s 100 −2 Maximum ASTM E‐1354 (kW m ) 500 kW m−2 irradiance, 65 peak Average for 300 s 50 25 kW m−2 irradiance, 50 peak Average for 300 s 50

Ds during 300 s 100 ASTM E‐662 Dmax 200 Combustion gas CO = 200 ppm generation (25 kW m−2) CO2 = 4%v ASTM E‐1354 HCN = 30 ppm

Smoke HCL = 100 ppm Maximum obscuration N‐gas model smoke No deaths Modified toxicity Screening test Pass NBSTTM Quarter‐scale fire test No flashover in DTRC Quarter‐ 10 min scale test Burn‐through fire test No burn‐through Burn‐through fire in 30 min test (DTRC) 13.4 Marine Textiles and Quality Standards 397

13.3.3 Mechanical Behaviour

Marine textiles are exposed to moisture and hydrostatic pressure in the deep sea envi‑ ronment, which may affect its mechanical properties. For example, the moisture absorption of polymer would cause a reduction of the glass transition temperature of the matrix, leading to a loss of stiffness and strength, which causes fibre microbuckling and premature fracturing. Accordingly, the effect of moisture absorption on the com‑ pressive, tensile, and shear behaviours of marine textiles has been investigated by many researchers [13, 24, 31, 41]. The mechanical behaviour of specimens can be tested according to the ASTM E1922, ASTM D2344, ASTM D256, for an edge notched tensile test, a short beam bend test, and impact tests, respectively [24].

13.4 Marine Textiles and Quality Standards

The development of textile technology means that hull structures can be produced to meet the demands of higher loads [42] while at the same time using lighter struc‑ tures. And the materials used for this are steadily replacing the natural materials traditionally used for ship construction. Fibre composites of glass reinforced plastic are used extensively in small vessels, patrol boats, and pleasure craft [14]. Polyester fibre is being used to replace some of the heavier and costly glass fibres in compos‑ ites. The advantages are: easy handling, corrosion resistance, and low maintenance. Kevlar (DuPont) is also used, sometimes in combination with glass fibre. Examples of specific cases where metal cannot be used are minesweepers, sonar domes, and cor‑ rosive cargo carriers. Composites are being increasingly used for navigational aids, such as buoys, so that no damage results to the craft in the event of an accidental collision. A very good summary about the textiles for marine application and their quality standard is provided by [2], and the key issues are summarized in the follow‑ ing sections.

13.4.1 Furnishing Fabrics

Carpets are necessities for the furnishing of passenger vessels because of their noise and vibration absorbing properties. Meanwhile, carpets should be more pleasant to walk upon than on a hard surface in order to reduce physical stress against hard ground surface. Owing to the special characteristics of passenger vessels (i.e. escape restrictions at sea, narrow corridors, and low ceilings in many vessels, etc.), there is a particular requirement a high degree of flame retardancy for the carpets that are used. In pas‑ senger vessels, fires are frequently caused by careless smokers. Flame retardancy is important and wool carpets are generally treated with flame‐retardant materials, for example Zirpro (IWS). Because of the special service environment, dyes used for marine textiles in passenger vessels must possess good fastness properties to light, rubbing, and saltwater, and durability is also an important consideration for marine textiles [1, 2]. Besides the high requirements of the carpets, furnishing fabrics must also pass rigorous evaluation standards set by the International Maritime Organization (IMO). Such standards of flame retardancy include IMO Resolution A471 (XII), DIN 4102 class B, and BS476 paragraph 6 [1]. 398 13 Marine Textiles and Composites

13.4.2 Sails

Nylon and polyester are commonly used for making sails because of their good prop‑ erties of lightweight, rot‐resistant, low water absorption, and high sunlight resistance. When polyester and nylon materials are compared, polyester is generally better than nylon. However, in the case of spinnaker sails, nylon material shows a better perfor‑ mance than polyester in terms of stretch and elasticity. Recently, some modern racing sails have been produced from polyester film laminated to woven polyester or nylon fabric. The development of sails has progressed to lighter laminated types where film is bonded to the fabric. Thus, the fabric does not form the surface of the sail but acts as the reinforcing structure. For racing yachts in which fabric weight is a crucial factor in affecting the performance, aramid is used in the reinforcement structure because of its high strength and light weight. However, aramid degrades in sunlight; ultra‐high‐ modulus polyethylene yarns and carbon fibres are now used as an alternative aramid. The polyethylene yarn has also found application in heavy duty ropes [2]. The main requirements for sail cloth are: (i) lightweight, (ii) dimensional stability, (iii) puncture resistance, (iv) high tear strength, (v) high seam strength, (vi) low porosity to wind, (vii) low water absorbency, (viii) good resistance to microbes and UV degradation, and (ix) smoothness [2]. Sails which absorb water will increase the overall weight of the vessel and reduce its efficiency. Also, a sail with a rough surface can increase the frictional drag. The fabric bias stretch will limit the usage of sail cloths, which can be eliminated by calendering with or without a resin coating. In making the sail, the seam will be a source of weak‑ ness and under high stress the sewing holes in the seam may be enlarged, which may affect the porosity of the sail. Under prolonged high stress, the sail fabrics will be dis‑ torted and their shape will change subsequently. In order to retain the sail shape, most sails are laminated with polyester film (has high modulus of elasticity in all directions) and the final sails will have excellent shape retention properties with very little distor‑ tion or stretch. Moreover, the laminated sail must be bonded with an adhesive that can withstand seawater and UV degradation during normal marine application conditions [2, 19, 21, 22]. For modern racing sails, they comprise film laminated to threads of yarn laid on the bias of the sail to produce an article of high dimensional stability that is very lightweight [2]. Spectra, Vectran, and carbon fibre – which all have good UV degradation resistance when compared with nylons, polyesters, and aramids – can be used for making racing sails [2]. As a coin has two sides, laminated sails do not last as long as normal fabric sails, but laminated sails are highly important in terms of speed and performance. When sails are cleaned, any detergent or cleaning agent must be rinsed away because it may affect the laminated bond strength or contribute to UV degradation of the materials. Hot melt adhesive films are generally used, and these factors must be taken into consideration when the adhesive is selected [2].

13.4.3 Hovercrafts Skirts

The skirt material is a nylon fabric coated with a polychloroprene/natural rubber blend or natural rubber/polybutadiene and compounded for oil resistance. PVC blended with nitrile rubber was evaluated but was not found to be as satisfactory. The nylon cords are 13.4 Marine Textiles and Quality Standards 399 highly twisted in the fabrics (woven) in order to impart fatigue resistance to withstand the rapid and continual flexing during use. The adhesion used for bonding the fibre to the rubber must be of the best standard so that a suitable priming coat can be formed. Nylon is the best overall fibre for this application. Other than nylon, polyester yarns can be used because they are less affected by water. However, coated polyester fabrics do not last as long as nylon. This may be due to the poorer polyester/rubber bonding com‑ pared with nylon/rubber. Cotton and rayon absorb too much water and are not gener‑ ally strong enough and recommended for this application. And although aramids are stronger than both nylon and polyester, they break down quite rapidly because of their low fatigue resistance [2].

13.4.4 Inflatable Craft

Inflatable craft have many advantages over rigid boats and have become widely used since around 1960 [43]. They are used as lifeboats and rescue craft, as freight carrying vessels and as pleasure craft, besides having several military applications. When they are not in use or when they are transported to different locations, they can be deflated, folded, and packed into a relatively small capacity. They are made from individual buoy‑ ancy tubes or several different compartments, so that even if a particular section is damaged the whole craft is still able to float and be capable of supporting weight. There are national standards and minimum performance specifications for the coated fabric and the craft itself but these standards do not actually specify which materials should be used. Different coatings, polychloroprene, polyurethane and PVC, and nylon woven fabric are used. Good tear strength is a required property to prevent propagation of any damage. Although polyester with a higher yarn modulus can be used as an alternative to nylon, it is usually more difficult to bond rubber coatings to polyester, and polyester can be degraded by certain compounding ingredients. In addition, polyester is heavier than nylon. If cost allows, aramid fibre may be used, thus saving a significant amount of weight [2].

13.4.5 Naval Ships and Submarines

A wide range of naval structures are being developed using fibre reinforced polymer composites. Their special structures, such as sandwich composite, provide savings in hull weight for the design of patrol boats. This development is driven by the need to enhance the operational performance (e.g. increased range, stealth, stability, payload) and at the same time reduce the ownership cost (e.g. reduced maintenance, fuel con‑ sumption cost) of warships and submarines. Other new or potential uses for compos‑ ites are in the superstructures, advanced mast systems, bulkheads, decks, propellers, propulsion shafts, and rudders for large surface combatants [44]. They were built with a sandwich composite consisting of glass‐ and carbon‐fibre laminate skins with a PVC core. Use of the sandwich composites simplified the construction of the hull and superstructure and provides a high strength‐to‐weight ratio; good impact prop‑ erties; and low infrared, magnetic, and radar cross‐sectional signatures. The sand‑ wich composites are also used to build mine countermeasure vessels, corvettes, hydrofoils, and hovercrafts to reduce weight, improve damage tolerance, and reduce maintenance [14]. 400 13 Marine Textiles and Composites

13.4.6 Marine Safety Apparatus

Coated fabrics are used for life raft buoyancy tubes, canopies, and lifejackets. The base fabric for life rafts is generally woven polyamide with butyl or natural rubber, polychlo‑ roprene, or thermoplastic polyurethane coatings. Natural rubber, polyurethane, or SBR (styrene‐butadiene rubber) coated on woven polyamide fabric is much lighter and suit‑ able for canopies used on life rafts. Lifejackets are generally made from woven polyam‑ ide coated with butyl or polychloroprene rubber. Performance standards for the coated fabrics used for life rafts and lifejackets are usually subject to government controls and specifications. Quality tests of fabrics used for life rafts include air porosity, coating adhesion, and breaking and tear strength both in the warp and weft direction, flexing, antifouling, and waterproofness measured by hydrostatic head test methods. Performance specifications of fabrics used for lifejackets include polymer adhesion, tensile strength, flex cracking, antifouling and elongation‐at‐ break, including testing after immersion in water for 24 hours [1, 2, 7, 8, 36, 45]. The specifications and performance standards for lifejackets and life rafts are subject to dif‑ ferent regulations, such as (i) UL 1123, Marine Buoyant Devices and (ii) UL 1180, Recreational Inflatables. Specifications are also issued by the military in different coun‑ tries. Aircraft survival equipment such as lifejackets, life rafts, and escape chutes are generally made from woven nylon coated with polyurethane or synthetic rubber, but PVC is avoided. This is because PVC may generate toxic gases in the event of fire [18].

13.4.7 Oil–Water Separation

Many textiles can be used for oil–water separation, such as cotton fibre, woven and nonwoven PP, as well as polyethylene terephthalate (PET) [46, 47]. However, the oil containment capacities of samples are inversely proportional to their porosity [4]. Electrospun nanofibrous materials with tunable surface wettability have shown great promise for oil–water separation applications. Based on the different types of separa‑ tion materials, these nanofibrous materials can be divided into three parts (Figure 13.5): nanofibrous sorbents for oil spill clean‐up, nanofibrous membranes for oil–water sepa‑ ration. and nanofibrous aerogels (NFAs) for emulsified oil–water separation. A variety of different nanofibrous materials with tunable surface wettability for oil–water separa‑ tion applications have been developed (Table 13.5). As sorbents, the oil sorption capacity of nanofibrous materials has been proven to be further enhanced because the nanofibrous sorbent can drive the oil not only into the voids between fibres but also into its multi‐pores. Three major categories of nanofi‑ brous sorbents – hydrophobic‐oleophilic polymer nanofibres, composite nanofibres, and carbon nanofibres – have been developed for oil sorption. Nanofibrous membranes used to treat oily wastewater are attributed with high separation efficiency and rela‑ tively simple operational processes. The fabrication of fibrous membranes with selec‑ tive superwetting property can be achieved through manipulating both the surface geometrical structure and the chemical composition. Generally speaking, these separation membranes are classified into three types: oil‐ removing, water‐removing, and smart separation membranes, including superhydro‑ phobic and superoleophilic nanofibrous membranes, superhydrophilic and underwater superoleophobic nanofibrous membranes, nanofibrous ultrafiltration membranes, and smart special wettable nanofibrous membranes. Three‐dimensional functional aerogels 13.4 Marine Textiles and Quality Standards 401

Figure 13.5 Electrospun nanofibrous materials for oil–water separation [45].

Table 13.5 Electrospun nanofibrous materials for oil–water separation applications [45].

Water contact angle/oil Type Materials contact angle Oil–water separation performancea)

Nanofibrous PS nanoporous 147.6°/0° 113.87 (motor oil), 111.80 (bean oil), 96.89 sorbents fibres (sunflower seed oil) PS nanoporous 151.3 ± 1.6°/0° 131.63 (motor oil), 112.30 (peanut oil), 81.40 fibres (silicone oil), 7.13 (diesel oil) PVC/PS composite — 146 (motor oil), 119 (peanut oil), 81 (ethylene nanofibres glycol), 38 (diesel oil) PU/PS composite 118–138°/0° 30.81 (motor oil), 24.36 (sunflower seed oil) nanofibres

PVDF/Fe3O4@PS ~126°/0° 35–45 (sunflower oil, soybean oil, motor oil, composite diesel oil) nanofibres PU‐PS core–shell ~140°/0° 64.40 (motor oil), 47.48 (sunflower seed oil) fibres Carbon nanofibres 155.3°/0° 138.4 (silicone oil), 94.0 (corn oil), 73.8 (pump oil), 64.0 (mineral oil)

(Continued ) 402 13 Marine Textiles and Composites

Table 13.5 (Continued)

Water contact angle/oil Type Materials contact angle Oil–water separation performancea)

Nanofibrous F‐PBZ/SiO2 161°/3° Fast separation for a 200 g oil–water (50% membranes NPs‐CA v/v) mixture −2 −1 F‐PBZ/SiO2 161°/0° Oil flux of 3311 l m h for oil NPs‐PMIA (dichloromethane) and water (50% v/v) mixtures −2 −1 F‐PBZ/Al2O3 161°/0° Oil flux of 892 l m h for a surfactant‐ NPs‐SNM stabilized (span 80) water‐in‐oil (petroleum ether) emulsion Aminated PAN‐Ag 162.4 ± 1.9°/0° Oil flux of 4774.6 ± 45.6 l m−2 h−1 for a 200 ml mixture of oil (1,2‐dibromoethane, 50% v/v) and water Flexible 144.2 ± 1.2°/0° Oil flux of 3032.4 ± 234.6 l m−2 h−1 (petroleum −2 −1 SiO2‑carbon spirit), oil flux of 2648.8 ± 89.7 l m h composite (hexane) nanofibres PS nanofibres/steel 155 ± 3°/0° Easily separating diesel oil from water mesh

CaCO3 mineralised 0°/157 ± 2.4° Can separate oil–water mixtures with high PAA‐grafted PP separation efficiency (> 99%) and high water flux (> 2000 l m−2 h−1)

SiO2 NPs‐SNM 0°/161° Can separate oil‐in‐water emulsions by gravity, with an extremely high water flux of 2237 l m−2 h−1 −2 −1 NiFe2O4 NPs‐SNM 0°/145° High water flux of 1580 ± 106 l m h for a surfactant‐stabilized (span 80) water‐in‐oil emulsion PVA hydrogel‐ — High water flux (up to 330 l m−2 h−1 at the MWNT/PVA/ feed pressure of 100 psi) for an oil/–water Nonwoven emulsion Chitosan/PAN/ — High water flux (~170 l m−2 h−1 at the feed Nonwoven pressure of 130 psi) and good filtration efficiency (> 99.9%) PVA/PAN — High water flux (210 l m−2 h−1 at the feeding composite pressure of 0.3 MPa) with high rejection rate membranes (99.5%) in oil–water emulsion separation −2 −1 PMMA‐co‐ 147°/36° – N2 Oil flux of 17 000 l m h (before CO2 −2 −1 PDEAEMA 36°/155° – CO2 bubbling), water flux of 9554 l m h (after CO2 treatment) for oil–water mixture separation Nanofibrous FIBRE NFAs 145°/0° High water flux of 8100 ± 160 l m−2 h−1 for a aerogel surfactant‐stabilized water‐in‐oil emulsion −2 −1 SiO2 NPs‐FIBRE 162°/0° High water flux of 8140 ± 220 l m h for a NFAs surfactant‐stabilized water‐in‐oil emulsion

a) Sorbent capacity (g oil/g sorbent); Membrane and aerogel permeate flux (l m−2 h−1). References 403 with special wettability – including silica colloid aerogels, carbon nanotube aerogels, graphene monoliths, porous boron nitride, and polymer sponges as demulsification – can be used to realize oil–water separation. This is because they possess versatile poros‑ ity, low density, and high internal surface area properties [45].

13.5 Sustainability and Ecological Aspects

Sustainability and ecological aspects are now important issues in the field of material development. Based on the analysis of different information obtained, composite mate‑ rials would be a trend for developing sustainable marine textiles. Owing to the forma‑ bility of the composite materials, we can design them for suiting different purposes, according to their end use.

13.6 Conclusion

Because of the aggressive environment, textiles used in marine applications are devel‑ oped from natural and synthetic materials, and are then reinforced with different mate‑ rials and techniques because synergistic interaction between the environment and the applied loads accelerates fatigue damage of materials. The reinforcement materials are designed to resist primary loads that act on the laminate and the resin serves to transmit loads between the plies, primarily via shear. For the purpose of protecting humans against injuries from marine environment and disasters, materials for marine applica‑ tions are finished with advanced technologies and evaluated against strict standards. The use of reinforcement materials enables the building of bigger, lighter, and stronger ships, making it safer for people to work at sea. Another advantage is that the applica‑ tion of reinforcement materials alleviates marine pollution, owing to its long service life. This is beneficial for the sustainable development of the marine industry.

Acknowledgement

The authors would like to thank the financial support from The Hong Kong Polytechnic University for this work.

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Aeronautical and Space Textiles Sadaf A. Abbasi1, Lijing Wang2, Mazhar H. Peerzada3, and Raj Ladani1

1 School of Engineering, RMIT University, Melbourne, Australia 2 School of Fashion and Textiles, RMIT University, Brunswick, Australia 3 Department of Textile Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan

14.1 Introduction

The history of textiles started when human beings began using textiles to cover their bodies and protect them from the environment. Today’s innovations in the textile industry go far beyond what early humans could have conceived of. Amongst many textile applications, one area is space and aeronautical textiles. These days, the design, manufacturing, and application of textile composites in space and aerospace have become a very important and challenging industry. The phrase ‘composite material’ refers to material combining two or more different constituents together in order to get desired properties in an end product. The application of composite techniques in the making of space shuttles and other aerospace products needs to be defect free. Composites help in improving reduction of fuel consumption in aircraft and space shuttles. These products are mainly manufactured with high performance textile fibres, which require additional properties compared to the conventional fibres. High specific modulus and high specific strength are the basic requirements for aerospace structural parts. Good fatigue and stress resistance, good dimensional stability, and conformability are some additional properties. Along with fibres, the preform manufacturing process also requires attention. Fibres – such as carbon, glass, aramid, Kevlar, and many others – are commonly used as composite reinforcement in the manufacture of structural parts of commercial and military aircraft. Recent advances in the composite industry show the use of some natural fibres in the construction of aircraft parts following sustainability concerns. Apart from aircraft applications, textile fibres are used in the manufacture of spacesuits. Various raw materials are used for tailoring the spacesuit, including fabrics made from different synthetic fibres. For example, the innermost layer of a suit is made up of a nylon tricot material; the second layer is manufactured with spandex, which gives elasticity in the suit; and the next layer is made up of urethane coated nylon. Many other materials are also used in the manufacturing process, such as Dacron (a type of

polyester fibre used as a pressure restraining layer), Neoprene (a type of rubber), aluminized Mylar, Gore‐Tex, Kevlar, and Nomex. Manufacturing processes of composites play a significant part in the aerospace industry. It is necessary to choose cost effective, economical, and sustainable processes for the manufacture of composites. Advances in weaving, knitting, braiding, and nonwoven techniques opened new ideas for getting near net shape preforms, which can reduce the manufacturing time, material wastage, and production cost. This chapter deals with the typical synthetic and natural fibres used in the manufacture of aerospace materials, their characterization, manufacturing techniques, and testing methods. It also covers sustainability issues regarding textiles in the aerospace industry.

14.2 Synthetic and Nanotechnical Fibres

Generally, fibres are classified as natural or manufactured (including nanofibres), as shown in Figure 14.1. The raw material for manufactured fibres may be derived from natural sources, like nonfibrous material such as glass fibres, natural polymers such as rubber fibre from latex, synthesized polymers such as polyamides and polyesters, and other manufactured fibres which have undergone further processing and modifications, for example carbon fibres manufactured from acrylic and pitch fibres. Nanofibres are fibre with diameters of less than 100 nm [1]. They are classified as manufactured fibres.

Textile Fibre

Natural Manufactured

Vegetable Animal Synthetic Mineral Re-Generated Synthetic

Cotton Silk Asbestos Viscose Rayon Nylon Jute Wool Cupramonium Rayon Polyester Hemp Acetate Rayon Acrylic Rample Ramie Carbon Linen Linen Aramid Vectran Nano bres

Figure 14.1 Classification of textile fibres. 14.2 Synthetic and Nanotechnical Fibres 409

Technical fibres are widely used in various high‐tech applications, owing to their superior properties. They are capable of offering special characteristics to end products (technical textiles), such as mechanical, thermal, conduction, durability, resistance to flame, heat, smoke and chemical, etc. Technical textiles have been defined as ‘textile materials and products manufactured primarily for their technical and performance properties rather than their aesthetic or decorative characteristics’ [1]. The properties of material made by technical fibres can be tailored according to the needs of users by applying a manufacturer’s knowledge. New material characteristics can be developed by employing technical fibres and suitable technologies together. In the last few decades, the aerospace industry has focused on fibrous material to replace conventional material, and to manufacture various parts with fabrics, such as the fuselage, wings, landing gears, tail boom, rotor blades, skin, and thermal insulation tiles of spacecraft and space shuttles [2–7]. Among the fibrous material, natural fibres are irrelevant; however, manufactured fibres have huge potential. During polymerization, the characteristics of manufactured fibres can be modified easily according to a user’s needs.

14.2.1 Carbon Fibre

Carbon fibre contains a minimum of 90% carbon which is attained from a controlled pyrolysis process. Carbon fibre is known for its high specific strength in the aerospace industry. Carbon fibre was discovered in 1879 by Edison when he placed a patent for the manufacture of electric lamps from carbon filaments [8]. However, the commercial production of carbon fibre started in the early 1960s. At that time, carbon fibre was used mainly in military aircraft, taking the advantage of its lightweight characteristics [9]. Carbon fibre is manufactured with the help of the controlled pyrolysis of organic precursors in the form of fibrous material by removing the oxygen, nitrogen, and hydrogen from the precursor. The mechanical properties of carbon fibre mainly depend on the polymer orientation in precursor fibre. Therefore, it is important to use highly oriented precursor fibre to manufacture strong and defect‐free carbon fibre. In recent decades, carbon fibre has become prominent in many industries, including aerospace, defence, sports and leisure, automobile, construction and infrastructure, etc. Carbon fibre is mainly used where lightweight property is of primary importance. Along with its lightweight property, carbon fibre composites are used in applications where strength, stiffness, and outstanding fatigue characteristics are required. Occasionally, carbon fibre is used where high temperature, chemical inertness, and high damping are important. There are a wide range of structural applications of carbon fibre in the aerospace industry, such as floor beams, stabilizers, flight controls, primary fuselage, and wing structure [10–16]. Along with its many advantages, there is a disadvantage: lower conductivity than aluminium. This is why lightning protection mesh or coating is essential to improve the conductivity of carbon fibre based materials for the aerospace industry. Advances in carbon fibre manufacturing techniques harness its flexibility and introduce novel types of carbon fibre in terms of improved modulus and strength for the aerospace industry. Research and development of carbon fibre is in two directions: one is to increase the strength (>5 GPa) with concurrent increase of modulus to a moderate level (>300 GPa) and this is for aircraft applications. Another is aimed at high modulus 410 14 Aeronautical and Space Textiles

(> 500 GPa) with moderate strength (3.5 GPa) for space applications. The higher failure strain for carbon fibre is assumed to be the outcome of composites with improved damage resistance [17, 18].

14.2.2 Aramid/Kevlar Fibre

Aramid fibre was first introduced in the early 1970s, produced by DuPont under the tradename of Kevlar [19]. At the time of its first commercial introduction, aramid fibre had the highest strength‐to‐weight ratio among reinforced fibres. At that time aramid fibre was mainly used as a reinforcement in tyres and plastics, but now there are many applications of aramid fibre in different industries, and especially in the aerospace industry [20]. Aramid fibre is manufactured from the condensation reaction of para- phenylenediamine and terephthaloyl chloride. The structure of aramid fibre is an aromatic ring which contributes high thermal stability, whereas the para position gives stiff, rigid molecules, giving the fibre great strength and a high modulus. Aramid fibre is light in weight, strong, and tough. Kevlar 49 and Kevlar 29 are types of aramid fibres. Kevlar 49 is known in the aerospace industry for its high modulus, high resistance, and high impact resistance. Similarly, Kevlar 29 has a low modulus, is lightweight, and nonflammable. However, Kevlar fibre has disadvantages in compression and hygroscopy. Nevertheless, the remarkable performance of aramid fibre is used to increase fuel efficiency and decrease operating and maintenance costs. The interior parts of aircraft – such as cabin floors, overhead bins, and bulkheads – are manufactured with Kevlar honeycomb cores, which can help to reduce the weight of aircraft [21]. In spite of the weight reduction, a honeycomb structure is known for its low electrical conductivity and high fire resistivity, which are very demanding characteristics for meeting the safety standards. Kevlar fibre is strong enough to last in the extreme forces and temperature variations of space travel. Kevlar is used in communication satellites and also in space shuttles to protect against impact from orbital debris. Some more application examples are given in Table 14.1.

14.2.3 Glass Fibre

Glass fibre is the oldest and most common reinforcement material used in the aerospace industry to replace heavier metal parts. Its density is higher than carbon fibre. Glass fibre is not as stiff as carbon fibre but has high impact resistivity and high elongation at break. Continuous glass fibre was manufactured by Owens Corning Textile Products in 1930s for high temperature electrical applications. Raw material for glass fibre involves silicates, soda, clay, limestone, boric acid, fluorspar, or various metallic oxides. These raw materials are mixed thoroughly to form a glass batch which is then melted in a furnace and also refined. The molten glass passes through various heating treatments and then is quickly quenched and attenuated in air into fine fibres ranging from 3 to 35 μm. Finally, winders are used to pass the fibres over the applicator which is used to apply chemical sizing to aid additional processing and performance. Glass fibre is stronger than any other inorganic fibre but it lacks in rigidity in account of its molecular structure [23]. E‐glass, also called borosilicate glass, is mainly used as the composite reinforcement material. Glass fibre has a low density, high resistance to chemicals, and excellent insulation capacity, which makes the fibre fit for the aerospace 14.2 Synthetic and Nanotechnical Fibres 411

Table 14.1 Applications of aramid fibre in aerospace [22].

Aircraft: exterior Wing‐to‐body fairing Landing gear doors Leading and trailing edges of wings and control panels Engine nacelles Crash‐proof helicopter structures Helicopter blades Propellers Aircraft central fuselage (Super Puma MK2)

Aircraft: interior Window reveals Overhead and side panels Cargo liner panels Armoured seats on military helicopters Partitions, lavatories, galleys, and bulkheads Pressure bottles for escape slides Air ducting Passenger seat pedestals

Missiles and space Filament‐wound rocket engine cases Pressure bottles Launch tube reinforcement Air ducting industry. The disadvantages of glass fibre are its low tensile strength when subjected to high tensile stress for long periods, and its brittle nature, which gives little warning before catastrophic failure. Regardless of this, glass fibre can still be used in break resistance parts at higher stress levels but for short timeframes. Secondary parts of aircraft – such as the fairing, radomes, wing tips, and helicopter rotor blades – are manufactured with glass fibre.

14.2.4 Vectran Fibre

Vectran is the brand name of a high performance thermoplastic multifilament spun yarn having light crystal polymers (LCPs). It is manufactured with the help of a melt spinning process and also found as a melt spun LCP fibre. Chemically, it is an aromatic polyester produced by the polycondensation of 4‐hydroxybenzoic acid and 6‐hydroxynaphthalene‐2‐carboxylic acid. Vectran fibre possesses extraordinary strength and rigidity and is five times stronger than steel and ten times stronger than aluminium [24]. It has two variants: Vectran HS (high strength reinforcement fibre) and Vectran M (high performance matrix fibre). Vectran fibre was first produced in 1990 by Celanese scientists [25]. At the time of this fibre invention, the usage was limited to specialized military applications. But its unique properties opened new doors to the aerospace industry. In July 1997, airbags made from Vectran fibre were used to cushion the Pathfinder’s successful landing on the surface of Mars [26]. 412 14 Aeronautical and Space Textiles

14.2.5 Carbon Nanotubes

The composite manufacturing industry always works to improve mechanical properties and this leads to research in carbon nanofibres. Improvement in crack propagation and fibre defects called for alternative solutions for obtaining ultra‐high‐modulus fibres. In the late 1950s, Roger Bacon found straight, hollow tubes of carbon which consist of graphite layers [27]. In the 1970s, Morinobu Endo produced tubes by gas‐phase and observed that some tubes contain single layer of rolled‐up graphite. Furthermore, in 1991, Sumio Iijima discovered multiwall nanotubes [28]. Carbon nanotubes (CNTs) can be produced with the help of a catalytic chemical vapour deposition technique. This low cost technique is simple and can deposit CNTs at a specific place on a substrate [29]. CNTs have unique nanostructures with remarkable electronic and mechanical properties, which are of prime importance for the aviation industry [30]. CNTs are employed in many scientific applications, including electrical energy management, sensing, conductive textiles, electronics, composite materials, mechanical systems, etc. It is evident that aerospace technology is an emerging discipline for CNTs. The introduction of new commercial aircraft, such as the Boeing 787 and the Airbus A380, opened new doors for CNTs in the aeronautical and space industry [31, 32]. Basic applications of CNTs in the aerospace sector consist of reduction of mass, improvement in functionality, self‐healing and durability, and enhancement in damage tolerance, thermal protection, and control.

14.2.6 Graphene

Graphene is a revolutionary material for aerospace technology. It consists of a single atom thick sheet and an allotrope of carbon. Graphene is a flat monolayer of carbon atoms which are compactly packed into a two‐dimensional (2D) honeycomb lattice and is a main component for graphitic materials of all other dimensionalities. Graphene can be wrapped up into 0D fullerenes, rolled into 1D nanotube, or arranged into 2D and 3D graphite. Various efforts were made to synthesize monolayer graphene but were unsuc- cessful until 2004, when Andre Geim and Konstantin Novoselov used a method to isolate graphene [33]. Since then, a new era of graphene has begun. The graphene has attracted significant attention, owing to its high specific area and novel properties, including thermal, electrical, and mechanical properties. Following recent advances it has become possible to manufacture graphene polymer composites when a graphene sheet was exfoliated from graphite for bulk production. Several methods of preparing ordered graphene fibres were developed, for example hydrothermal and wet spinning of graphite oxide liquid crystal solution. The thermal and mechanical properties of graphene fibres are still unsatisfactory. Attempts have been made to overcome such problems by size selection of graphene oxide and the thermal treatment of graphene fibres. However, these approaches are complex and costly. Nevertheless, graphene is continually finding new applications within the aerospace industry; some recent applications include graphene/epoxy coating as multifunctional material (anticorrosion/hydrophobicity) for aerospace structures, electrically conductive epoxy resins, and aviation electronics. 14.3 Natural and Bast Fibres for Technical Applications 413

14.3 Natural and Bast Fibres for Technical Applications

Nowadays, customers demand more environmentally friendly products and more sustainable technologies to reduce the global waste. This has led to greater attention being given to green products using renewable resources in the polymer industry. It is well accepted that natural fibres are renewable, hence more sustainable and environmental friendly, than synthetic fibres. Therefore, interest in research and development using natural fillers to reinforce polymers is growing in the field of composite materials [34]. Natural fibres offer several advantages over conventional reinforced fibres, such as lower cost, low density, toughness, and biodegradability. Hence, the use of natural fibres in the production of composite materials is well developed. Natural fibres are obtained from plants (such as cotton, flax, ramie, and hemp) and from animals (such as silk and wool). Table 14.2 shows the physical and mechanical properties of different natural fibres in comparison with manufactured fibres that may be used in the aerospace industry. It is obvious that the tensile strength of natural fibres is lower than that of synthetic fibres, but natural fibre reinforced materials still receives research attention because of its low cost and low environmental impact. On a ‘per weight’ basis, flax, jute, and hemp fibres have higher tensile moduli than E‐glass fibres, owing to the low density of natural fibres compared to E‐glass [38]. This is particularly important in applications where weight reduction is a priority. Therefore, it is not surprising that natural fibres are used as reinforcement for polymer matrices to replace conventional glass fibres.

14.3.1 Flax

Flax is better known as linen. It is obtained from the stalk of Linum usitatissimum plant, which is 80–120 cm high. Flax was used in ancient Egyptian for mummy wraps, clothing, bed linen, and ships’ sails. Flax is two to three times stronger than cotton fibre but it is not very elastic in nature. Flax fibre is more resistant to wear and abrasion.

Table 14.2 Density and tensile properties of different fibres [35–37].

Density Tensile strength Young’s modulus Elongation at break Fibre (g/cm3) (MPa) (GPa) (%)

Flax 1.50 345–1500 27.6 2.7–3 Hemp 1.48 690 70.0 1.6 Jute 1.3–1.49 393–800 13–26.5 1.2–1.5 Ramie 1.55 400–938 61.4–128 1.2–3.8 Sisal 1.45 468–700 9.4–22 3–7 Cotton 1.5–1.6 287–800 5.5–12.6 7–8 E‐glass 2.55 3400 73 2.5 Kevlar 1.44 3000 70.5–112.4 2.5–3.7 Carbon 1.78 3400–4800 240–425 1.4–1.8 414 14 Aeronautical and Space Textiles

Materials made from flax do not tend to lose their shape easily. Flax fibre absorbs humidity well, and is also hypoallergenic; hence, it is an excellent choice of fibre for home textiles. In 1941, flax and hemp fibres were used in the manufacture of the bodywork of a new car, nicknamed the Soybean Car, which was claimed to have 10 times more impact strength than a car made with traditional steel [39]. Flax is finding its place in thermoplastic matrix composite panels for the internal structures of aircraft, but because of the high standards of the aviation industry, testing and research are still necessary before the commercial use of flax fibres becomes acceptable in the aviation industry.

14.3.2 Hemp

Hemp fibre is obtained from Cannabis sativa L. plant, which is native to central Asia and was grown in China over 4500 years ago [39]. The plant can grow up to 4 m in 12 weeks. It does not require any fertilizer, herbicides, or pesticide to grow, which is why this fibre garnered interest regarding sustainability. Hemp fibre is a fine, lustrous, light‐ coloured, and strong bast fibre. There are grades of hemp fibre. Lower grade fibres are dark cream and have less fibrous material. Higher grade fibres are found in the skin/ stalk of the plant, which contain approximately 70% of the fibres and are long, high in cellulose, and low in lignin. Primary bast fibres are the most valuable part of the stalk, and are generally considered among the strongest part, and are mainly used in aviation applications. Similar to other natural fibres, hemp fibre is also finding its place in thermoplastic matrix composites for internal structures in automotive and aviation applications. Airbus and the South African Council for Scientific and Industrial Research launched a joint project into the research and application of natural and recyclable fibre based materials, including hemp fibre, for the manufacture of internal structures of aircraft, such as sidewall and ceiling panels, insulation blankets, and other less load bearing parts [40]. Hemp fibre is also used to make hybrid sustainable composite materials [41, 42].

14.3.3 Jute

Jute is native to the Asian subcontinent. It is bast fibre and obtained from Corchorus capsularis (white jute) and Corchorus olitorius (dark jute). Jute fibre was spun mechanically in the early 1800s. After cotton, jute is the second most common natural fibre. The plant grows to 2.5–4.5 m. It is mostly grown in Bangladesh, Brazil, China, India, and Indonesia. Jute fibre is for applications where low cost is more important than durability. Jute based thermoplastic matrix composites find a substantial market in the German automotive door panel industry. Jute fibre is being used in fibre reinforced composite materials because of its adequate tensile strength and good specific modulus. Jute composites can thus ensure a very effective and value‐added application avenue for the natural fibre. Ongoing research focuses on using natural fibres in reinforced polymer matrices and as a replacement of glass fibre, but still proper research and development using jute fibre is necessary for finding proper applications of jute fibre in the aerospace industry [43]. 14.4 Manufacture of Technical Textiles 415

14.3.4 Kenaf

Kenaf is bast fibre and obtained from Hibiscus cannabinus, a warm seasoned and wild plant, which is native to Africa and Asia. This plant has been cultivated since around 4000 bce, for food and fibre [39]. The plant consists of different lengths of fibres, both long bast and short core fibres with a hollow core. The plant grows to up to 4–6 m in about five months. The properties of kenaf fibre are similar to jute fibre. Kenaf fibre may be used as an alternative of jute fibre. Beyond cordage, bast fibres are beginning to enter the markets of mouldable nonwoven fabrics, reinforced composite materials, and packaging and other industrial fibres. Past research on kenaf fibre includes proper moulding condition for kenaf fibres, mechanical properties of heat treated kenaf fibres, and also the biodegradability of composite material using kenaf fibre [44].

14.4 Manufacture of Technical Textiles

Textile fabrics for composite materials are designed and fabricated for load bearing functions. Since textile engineered with the same fibre orientation exhibits maximum tensile properties in the fibre length direction, often fibres are engaged in multiple orientations in a composite material to achieve optimum mechanical properties. In this context, biaxial woven fabrics and knitted fabrics with yarn interlacing and interlooping respectively exhibit high strength in both fabric width and length directions [45], but poor in radial direction. Nonwoven fabrics can be laminated at randomly oriented technical fibres for a degree of quasi‐isotropic properties. Below are most common technical textile fabric manufacturing techniques for composites.

14.4.1 Spinning

Technical yarns are used to manufacture technical products to fulfil the requirements of their intended end use. There are many spinning techniques to convert fibres into yarns, as shown in Table 14.3, but this chapter deals with aeronautics and space textiles and most of the yarns used in this industry are synthetic fibres such as carbon, glass, Kevlar, etc. Synthetic fibres are extruded through the melt, dry, or wet spinning process. Apart from these techniques, many other techniques – such as reaction spinning, gel spinning, dispersion spinning, and electrospinning – are also used but only in particular situations. Melt spinning is the process in which a molten polymer is forced through a spinneret to form filaments. The filaments pass from the stretching zone in winding which facilitates orientation in the polymer chains along the fibre axis. Different cross‐sectional shapes of spinneret can be used in the melt spinning process depending on the end‐use application. After leaving the winding zone, a drawing process is used to give strength in the filament and make it suitable for technical applications. Normally, drawing is done with the help of two pairs of rollers, the second of which forwards the filaments at a faster speed than the first. According to their intended use, the filaments are then wound onto a package with or without twist. The untwisted filaments at this stage can form filament tow flat tape. Figure 14.2 shows the melt spinning process and drawing process. 416 14 Aeronautical and Space Textiles

Table 14.3 Techniques of converting fibres into yarn.

Short staple yarn Ring spinning Rotor spinning Friction spinning Self‐twist spinning Electro‐static spinning Vortex spinning Air‐jet spinning Twistless spinning

Synthetic filament yarn Melt spinning Dry spinning Wet spinning Reaction spinning Gel spinning Dispersion spinning

Nanofibre yarn Electrospinning Bicomponent spinning Melt‐blowing Flash spinning

14.4.2 Electrospinning

Nanofibres for textile applications are fibres having diameters of less than 1000 nm. There are a number of techniques for nanofibre production such as drawing, template synthesis, phase separation, self‐assembly, and electrospinning. Amongst all these techniques, electrospinning has become popular and is proven to be the simplest, most convenient, and a relatively cheap method of producing nanofibres. Electrospinning is the spinning technique in which ultrafine polymeric fibres are produced. Such ultrafine fibres are difficult to produce in any other normal spinning technique. Electrospinning was invented in the 1930s, but it was not popular; following the growth in interest in nanotechnology and nanoscience, researchers realized the importance of this spinning technique [46]. Nanofibres with a large surface area and small pore size can be used for nanocomposite and nanocatalytic applications. Development of electrospinning is mainly divided into three sections: the investigation of electrospinnable polymers, alignment control of electrospun nanofibres, and development of nanofibre yarns. Today, many synthetic and natural polymers have been electrospun, including polylactic acid (PLA), polyurethane (PU), polycaprolactone (PCL), polylactic‐co‐glycolic acid, polyethylene‐co‐vinyl acetate, and polylactide‐co‐caprolactone (PLLA‐CL). Amongst natural polymers, collagen, chitosan, hyaluronic acid, and silk fibroin have been successfully electrospun into nanofibres, thus opening up a whole range of application potentials for these fibres [47–50]. More recently, electrospinning has been systematically combined with melt‐blowing technology or flash spinning to mass produce nanofibres. To date, only nonwoven nanofibre materials have been commercially viable to produce. Despite considerable recent progress in electrospinning, fabrication of yarns with controlled nanofibre orientation remains one of the most serious challenges. 14.4 Manufacture of Technical Textiles 417

Hopper for polymer granulate Drawing

Extruder for cladding material Spinning extruder Feed rollers Blow box for cooling

Drawing Stretching and rollers take-up

Package

Figure 14.2 Melt spinning process and drawing process.

14.4.3 Weaving

Weaving, a fabric manufacturing technique, is most widely used to produce woven fabrics. This technique is very suitable for flat panel and 2D laminated composites. In weaving, a set of warp yarns is interlaced with a set of weft yarns at right angles. Warp yarns are oriented at 0° and weft yarns at 90° directions respectively. Plain, twill and satin are common designs for 2D woven preforms, as shown in Figure 14.3. Composites having 2D woven preform exhibit tensile strength and in‐plane shear characteristics. The plain weave has the ability to resist shear deformation at some point because it is the most highly interlaced and tightest woven, though the tight weave can be problematic to saturate with normally used resins in the composite manufacturing process. On the other hand, satin weave contains the least interlacing and as such has less resistance to shear distortion as compared to plain and twill. Hence, satin increases the ability to conform to complex contour shapes (drapeability). Other advantages that make satin weaves important for applications such as in aerospace include their high tensile and flexural strengths and minimum thickness.

14.4.4 Three‐Dimensional Weaving

Three‐dimensional weaving is a promising and advanced preform manufacturing technique for engineering materials used in niche applications, such as stiffeners, aircraft wing joints, rocket nose cones, etc. [51]. This technique is similar to 2D woven preform structures except for the addition of a number of layers and binder yarns. During the manufacture of 3D woven preforms, three sets of yarns are interlaced, i.e. warp yarns in 0° direction, weft yarns in 90° direction, and binder yarns (also known as z‐yarns) in the through thickness direction. Three types of preforms can be manufactured: orthogonal, angle interlock, and layer to layer 3D weave designs. Three‐dimensional fabric 418 14 Aeronautical and Space Textiles

Figure 14.3 Plain, twill, and satin 2D weave constructions.

designs with their shape description are shown in Table 14.4. Composite materials from 3D woven preforms have some impact resistance and damage tolerance [52–54] and are delamination free [52, 55–57].

14.4.5 Knitting

Knitting is a fabric manufacturing process by intermeshing loops of yarns. Generally, two types of knitted preforms are used in composite, i.e. warp knitted and weft knitted preforms. Weft knitted preforms is the utmost designed for their ease and manufacturability. It is considered to offer the most potential and versatile 3D shapes, which is required in the aerospace industry. Warp knitted structures are used to produce elastic or stable, open or closed, or flat or tubular structures. Composites having knitted preforms possess low mechanical properties [58, 59]. Despite the compromised mechanical properties and damage of fibre in preform due to knitting needles, knitted preforms are suited for rapid production of composite components with complex and near‐net 14.4 Manufacture of Technical Textiles 419

Table 14.4 Three‐dimensional textile structures and weave architectures [52].

Structure Architecture Shape

Solid Multilayer Compound structure with regular or tapered Orthogonal geometry Angle interlock Hollow Multilayer Uneven surfaces, even surfaces, and tunnels on different level in multi‐directions Shell Single layer Spherical shells and open box shells Multilayer Nodal Multilayer Tubular nodes and solid nodes Orthogonal Angle interlock shapes, with minimum material wastage. Knitted ceramic composite jet engine vanes impregnated with silicon carbide by chemical vapour deposition [60], rudder tip fairing for mid‐sized jet engine crafts [61], and electrically conductive composites [62] are worth a mention for the application of composite material.

14.4.6 Braiding

Braiding is a composite preform manufacturing technique where three (minimum) or more yarns are intertwined to create a desired architecture. During braiding, each yarn crosses over the other yarns at an angle of between 0° and 90°. Tri‐axial braid with axial yarn added along the length of braided preform increases stiffness, tension, and bending strength of composite materials [63–65]. In addition, it also resists shrinkage in radial and in width (during tensile loads) in flat tri‐axial braids. The most common composite applications of braiding preforms are over‐braided fuel lines, rocket launch tubes, braided air ducts, and aircraft structures [66]. Dry and pre‐preg yarns can be used to manufacture braided preforms. The braiding preform manufacturing technique com- petes well with tape lay‐up, pultrusion, and tape winding, owing to design flexibility, damage tolerance, and low manufacturing cost. Figure 14.4 shows a braided structure.

14.4.7 Nonwoven/Stitching

A nonwoven preform is produced by laying up multiaxial layers. The most significant advantage of multiaxial layers is that the end material may have different fibre properties, and the ability to optimize the thickness, weight, and strength at particular load paths. To make a multilayer preform, the layers may be stitched to improve the through thickness strength and damage tolerance of the materials. Stitching can be carried out by high performance fibres such as Kevlar, carbon, or glass. On one hand, stitching is a simple way of fabricating multiaxial layers but, on the other hand, it leads to significant in‐plane fibre damage that can compromise in‐plane mechanical properties. Three‐dimensional nonwoven composites have been largely successful in structural applications, including ceramic based and C based structures. Three‐dimensional 420 14 Aeronautical and Space Textiles

Figure 14.4 Braided structure.

needle‐punched carbon/carbon (C/C) and carbon/silicon carbide (C/SiC) composites, for instance, have been widely used in Airbus aircraft C/C brakes, automobile brake discs, solid rocket motors, nozzle throats, exit cones, etc. [67].

14.5 Textile Reinforced Composite Materials

Textile reinforced composite material is replacing conventional material in several engineering applications, owing to its useful properties such as being lightweight, and having high stiffness, good fatigue resistance, and corrosion resistance. It can be used to manufacture engineering parts with complicated geometries and designs at a low cost compared with conventional manufacturing techniques. The composite material combines two or more different constituents in order to get the desired properties in the end product. There are three main types of composites materials: ●● metal matrix composites (MMCs). ●● ceramic matrix composites (CMCs). ●● polymer (textile) matrix composites. Fibre reinforced polymer composites consist of two main components: reinforcement (textile material) and matrix (resin), as shown in Figure 14.5. There are several composite material manufacturing techniques that are widely used for high performance aerospace products. In this chapter, five of the most important techniques are introduced.

14.5.1 Hand Lay‐Up Technique

The hand lay‐up technique is the simplest and easiest method of composite manufacturing particularly suitable for making low cost large parts, such as yacht hulls. The infrastructural requirement and processing steps are quite simple and suitable for flat 14.5 Textile Reinforced Composite Materials 421

Reinforcement Composite Matrix

Figure 14.5 Polymer reinforced composite structure. or curvy shapes. Most aeroplane parts – such as flaps, ailerons, rudder, radomes, etc. – are usually made by the hand lay‐up technique. In the first step of the hand lay‐up composite manufacturing technique, release gel is sprayed on the mould surface, which is necessary to avoid sticking the polymer melt to the surface of mould. Reinforcement such as woven/knitted fabric or chopped fibre mat is cut in the same size of mould and carefully placed on the surface of the mould. Resin (liquid form of thermosetting material) that was mixed carefully in appropriate amount with a prescribed hardener (i.e. curing agent) is applied to the surface of the reinforcement already placed in the mould by pouring, brushing, or spraying. A mild pressure roller or squeegee is used on the reinforcement layers to remove trapped air bubbles. The process is repeated for each layer of reinforcement until the desired thickness is reached. Typically, this lay‐up technique is suitable to manufacture wide variety of composite parts using an open moulding method. Stacked layers are usually cured at room temperature without a vacuum bag. Although using vacuum bags increases costs, the vacuum bag offers better consolidation, uniform thickness, and better surface finishes. Curing time of hand lay‐up depends upon the type of polymers for composite manufacturing, e.g. epoxy based polymers take 24–48 hours curing time at room temperature. The hand lay‐up technique is suitable for thermosetting polymer based composites. This technique requires low capital and infrastructure compared with other techniques. However, the production is low and it is difficult to produce a high volume fraction of reinforcement. The hand lay‐up technique has many applications in the aerospace industry. Table 14.5 shows the raw materials to fabricate composites with the hand lay‐up technique.

14.5.2 Vacuum Bagging Technique

A vacuum bagging technique has been developed for fabricating composite material by applying atmospheric pressure to adhere prepregs until the composite is consolidated

Table 14.5 Raw materials used in the hand lay‐up technique.

Matrix Epoxy, polyvinyl ester, polyester, phenolic resin, unsaturated polyester, polyurethane resin Reinforcement Glass fibre, carbon fibre, aramid fibre, natural plant fibres (sisal, banana, nettle, hemp, flax, etc.) 422 14 Aeronautical and Space Textiles

through curing. It has been developed for manufacturing various components but mostly for low cost complex shapes, double contours, and large structural parts. This technique involves a sealed bag in which a vacuum is created and an even amount of pressure of up to 1 atm (14 psi) is applied to the laminated material in the mould. This assembly is then placed in an oven for curing. This technique uses low cost equipment and tooling and is able to produce good quality composite components. Manufactured fibres – such as glass, carbon (graphite), and Kevlar – can be used in the vacuum bagging process. This method produces high quality mouldings with minimum or no air bubbles and can also improve the inner surface of the moulding. The controlled curing temperature helps to improve quality and consistency and gives time to allow resin to be used properly, while opening the way to additional quick cure with a quicker turnaround of moulds.

14.5.3 Advantages of Vacuum Bagging

Vacuum bagging offers a suitable clamping method for very small to large scale applications, such as aerospace parts, wind turbines, race car components, musical instru- ments, model boats, etc. It has the following advantages: ●● The method is simple and produces high quality mouldings with minimum or no air bubbles. ●● A variety of moulds can be used. ●● A variety of fibres can be combined in a single laminate. ●● Materials/polymers can be carefully chosen precisely to match the structural requirements of an end product. ●● Vacuum bagging gives firm and evenly disturbed pressure over an entire surface, whereas mechanical clamping applies pressure only to concentrated areas and may damage fragile core material. ●● The method can achieve optimum amount of adhesive in laminating, resulting in higher fibre volume fraction.

14.5.4 Injection Moulding

Injection moulding is similar to metal die casting and is one of most important manufacturing techniques for plastic and plastic composite parts. It can produce fibre reinforced composite parts, especially glass fibre. It is based on Darcy’s law of flow through porous media. This law calculates that the flow rate per unit area (Q/A) is proportional to the preform permeability (k) and pressure gradient (ΔP) and inversely proportional to the viscosity (μ) of the resin and the flow length (L), i.e.:

Q/Ak=∆P/µL In this method, a special reciprocating single screw extrusion machine is used. The fibre filled matrix is fed into a machine, where it is melted within the barrel. This is followed by injection, where it is forced into the cavity of the mould, where it freezes and is ultimately ejected as the finished part, as shown in Figure 14.6. The injection moulding process permits finer part details and can be easily computerized. The 14.5 Textile Reinforced Composite Materials 423

Mould Injection moulding screw Gas water

Temperature Pressure regulator controller High pressure Injection unit

Figure 14.6 Setup for the injection moulding process. portion and mould can produce near‐net shape parts. There is a limit to the amount and types of fibre reinforcement that can be included in an injection moulding part. The injection moulding process of thermoplastic is slightly different from thermosets. In the thermoplastic injection moulding process, a melted thermoplastic material is enforced on an orifice into a cold mould, where it solidifies. In thermoset injection moulding, a liquid state material is forced into a warm/hot mould, where the material polymerizes/cross‐links to a solid part. Injection moulding is widely used in the aerospace industry, automotive industry (air intake manifolds, rocker covers, etc.), electronic industries, medical and dental products (heart pump parts, orthopaedic devices, electrocardiograph, and oxygen parts), and household appliances (washing machine cylinders), etc.

14.5.5 Autoclave

Autoclave processing is a popular method to manufacture fibre reinforced composites for high performance applications, typically for large complex engineering parts. Autoclave is the technique to manufacture large aircraft components like wings and fuselages. It is also used to produce a wide variety of materials, such as thermoplastics and thermoset composite materials. The aircraft industry has very strict quality standards. Apart from ensuring reliable and consistent processing methods, the industry also focuses on the improvement in the efficiency and cost effectiveness of aircraft structural systems. It is necessary and challenging for the designer to propose a proper autoclave system with controlled heated atmosphere, which produces satisfactory results and fulfils the requirements of the aircraft. An autoclave system is multidisciplinary in nature; it involves mechanical, electrical, electronic, and instrumental engineering and process controls in order to make it a completely automated system with reliable computerized control. In autoclave, pressure bag, moulding, heat and pressure are applied on the lay‐up from pre‐preg materials. The autoclave operating parameters such as temperature and pressure are based on the resin systems used. A vacuum may be applied in the early stages to remove trapped air. Air can be used for pressure, and forced hot air is used for stream heat‐up. The service temperature of these epoxy resin based structural components is restricted to about 120 °C [68]. A typical layout of autoclave is 424 14 Aeronautical and Space Textiles

Insulated Air distribution Heating shell shroud elements

Bagged composites on moulds Quick Circulating air opening door

Figure 14.7 Schematic diagram of autoclave.

shown in Figure 14.7. In an autoclave process, a number of thin sheets of high modulus fibres are impregnated with moderately cured resin then cut and stacked in sequence to the required shape. Then various layers of different materials (such as breather, bleeder, etc.) are covered to absorb excess resin and remove air and unwanted volatile gases from the stacked layers during the curing process. For a smooth surface, both sides of the laminate are usually covered with a fine polyester fabric which is peeled off after curing. For curing, certain pressures and temperatures are provided to laminate in a determined curing cycle for polymerization reaction. Autoclave technology is considered one of the mature technologies to produce composite materials that have quality, high performance, and the desired fibre volume fraction for high‐end applications.

14.5.6 Pultrusion

The pultrusion process is a mature process for manufacturing fibre reinforced composite products. It produces profile shapes of continuous length of fibre reinforced polymer. The word ‘pultrusion’ is generally a combination of the two words ‘pull’ and ‘extrusion’. The pultrusion process involves pulling and drawing high performance fibres and pushing them into a resin liquid which is used to saturate the fibre reinforcement. The most preferred fibre is glass fibre (owing to its cheap price). The fibre and resin mixture allows for multidirectional reinforcement, resulting in the formation of strong material. Types of resins which can be used in pultrusion include polyester resin, vinyl ester resin, polyurethane resin, and epoxy resin. In this method, a surface veil may be used to avoid corrosion and erosion, and resist ultraviolet (UV) radiation. The resin and glass fibre combination is pulled together through a special heating die for a process of polymerization. After that, the mass of reinforced material in the shape of the die leaves to harden and to heat set into a desired shape. Finally, the consolidated composite material is cut into length and is ready for use. Through the pushing process a fixed 14.6 Textile Composite Material Finishing 425

Ventilation

Resin injection

Pulling device Saw Heating & curing

Reinforcement

Figure 14.8 Schematic diagram of the pultrusion process. cross‐sectional shape may also be obtained. A schematic diagram of pultrusion is given in Figure 14.8. The pultrusion process is one of the low production cost processes because of minimum scrappage, simple machine, and low cost for the raw material. It is restricted to constant cross‐section, continuous reinforcement, and low viscosity resin. It is often used for high volume production runs of parts for the automotive and transportation industries.

14.6 Textile Composite Material Finishing

The term ‘finishing’ refers to improving the serviceability and functionality of the material. Although there are several techniques to improve the aesthetic properties of composite material, there are no such standard finishing methods to finish or polish the material. Over the last couple of decades, a lot of effort has been made to improve durable cosmetic finishes such as smooth and high gloss finishes, etc. The following materials are mostly preferred for finishing the textile composite material, especially for aerospace application: ●● finishing and covering material. ●● paints. Finishing to airframe structures (internal as well as external) is done for several reasons including identity, protection from corrosion (where metal parts are used), solar and UV radiation, moisture, and biological attack. Although textile composite parts are free from corrosion, it is very necessary to provide an impermeable surface coating to block moisture from penetrating the laminates. The moisture may lead to delamination or weaken the part. Spraying is the most common method of applying a quality finish. There must be a suitable source of compressed air, a feed tank to hold a finishing material, and a device (like a nozzle) for controlling the combination of the air and finishing material ejected in spray form against the surface to be treated. Paint finishes 426 14 Aeronautical and Space Textiles

always require time, patience, and a lot of skill. Paint finish involves mostly three ingredients, i.e. binder, pigment, and solvent. After mixing these ingredients, the paint may be applied by brush, roller, or spray.

14.7 High Performance Applications

Advances in material engineering facilitated the need of customized engineered materials. Textile composite material is replacing the conventional materials in several fields such as aerospace, automobiles, transportation, sports, and other niche applications, owing to its light weight, superior corrosion resistance, and high strength and stiffness.

14.7.1 Spacesuit

Textile composites have extended their boundaries from regular use to aerospace applications. The spacesuit is one such example, and is used for launch and space walks. It has zero tolerance for defects. On earth, nature provides humans with the correct mixture of gases in the environment necessary for our survival, including oxygen, nitrogen, carbon dioxide, and water vapour. However, in space there is no such natural environment, and astronauts encounter harmful radiation, low pressure, and high temperatures. Hence, a spacesuit is made from nonflammable, high performance textile fibre. The spacesuit is designed to protect the astronaut and keep them comfortable by providing cooling, clean air, and pressurizing systems inside the suit. The spacesuit should be lightweight, flexible, strong, thermally insulated, and thermal‐resistant. The suit consists of several layers, and each layer has different functions. The inner layer is manufactured by knitting technique for the comfort of the astronaut. The second and third layers are primarily made of polyurethane elastic fabric and urethane coated nylon fabric for pressure balancing (internal and external). Above these layers, seven layers are placed for thermal insulation. The outer layers are made of Kevlar and Nomex fibres for protection against electrical charges, particles, UV radiation, and meteoroids, which are the main threats that astronauts will encounter in space. Meteoroids are very small pieces of metal and rock. They travel at high velocity and can easily penetrate the body. Therefore, the spacesuit must be able to resist the impact and stress caused by these fragments and particles.

14.7.2 Textile Composites in the Aerospace Industry

Excellent specific strength, stiffness properties, and lightweight structures are always the primary material requirements for aerospace and defence applications. The selection of high performance fibres and orientating the fibre in the required direction enable material engineers to tailor fibre reinforced composites with optimum mechanical properties. In addition, compound shapes and excellent fatigue and corrosion resistance have made composite material more significant and favourable through an 14.7 High Performance Applications 427 appropriate textile composite manufacturing technique. Therefore, commercial aircraft, such as the Boeing 787, Dreamliner, and Airbus A350 XWB, contain large proportions (by weight as well as by volume) of composite parts [60]. In addition, compound shapes and excellent fatigue and corrosion resistance have made composite material more significant and favourable through an appropriate textile composite manufacturing technique.

14.7.2.1 Structural Requirement of Aircraft According to material definition, any structural component whose failure could endan- ger the aircraft is known as primary structure. The other structural parts are referred to as secondary structure. Fibre reinforced composites have a very wide variety of usage in different applications such as from air gondolas and gliders to passenger aeroplanes and military aircraft. Every application has a different need of mechanical properties and different area of usage. For example, carbon fibre has different mechanical characteristics (like high modulus) than glass fibre. It has a unique fatigue property, but on the other hand it is brittle. Boeing used 1500 composite components successfully in its helicopter to replace the metal with carbon composites. The aviation industry is increasing the use of composite parts and replacing metal parts to reduce weight and therefore fuel consumption, and carbon products are most widely used reinforced composite in aviation applications for both primary and secondary structures.

14.7.2.2 Fuselage The fuselage is based on a semi‐monocoque structure containing longitudinal stringers. Conventionally, the fuselage was manufactured by different materials, such as wood and aluminium. However, these days only textile material, for example glass fibre or carbon fibre impregnated with epoxy resin, is preferred, owing to its low weight and superior mechanical properties. There are three areas in a fuselage: the crown, sides, and bottom. The skin of the fuselage holds the pressure and shear loads, while stringers carry longitudinal tension and compression loads. During flight, the fuselage bends because of the loading of the wings. This causes tension in front, shear in the sides, and compression in the bottom.

14.7.2.3 Wing The wing is an important part of the aircraft and acts like a beam used to transmit the applied air load to the fuselage. Generally, various materials (wood, metals, and textile composites) are used to meet specific properties, such as strength, elasticity, specific weight, and corrosion resistance. The wings consist of wing box, spars, and ribs. The wing box contains top and bottom covers (skin and stringers) and carries the torsion load during flight. The spars work like a beam. The wing materials are designed according to their specific structural function and the right materials should be used for the appropriate parts of the wing. Replacing aluminium alloys, advanced composite materials can be tailored to meet specific design loads, strengths, and tensions for different wings and aircraft models. In past years, the use of nanomaterials has increased in the manufacture of wings. For example, electric conductive nanoparticles were introduced into structural components like wings to protect them against lightning strikes and also to increase damage resistance of the outer wing laminate [69]. 428 14 Aeronautical and Space Textiles

14.7.2.4 Empennage The tail of an aeroplane is known as the empennage. It is composed of rudders, elevators, a vertical stabilizer, and a horizontal stabilizer. Structural designs of both stabilizers (horizontal and vertical) are as important as the design of the wing. Owing to bending, the upper and lower surfaces of the horizontal stabilizer are usually important in compression. Textile fibre benefits the empennage in different aspects. For example, different textile fibres may be blended in order to make the laminate lighter as well as lower in cost, such as a combination of carbon/glass fibres. In addition, carbon and glass fibres possess excellent fatigue resistance and are free of corrosion, and thus there will be no significant deterioration seen in the material, even after years of continual use. In addition to composites for structural parts, composite materials are also used for interior parts, such as overhead luggage compartments, sidewalls, ceilings, floor, galleys, lavatories, partitions, cargo liners, etc. Interior parts are usually made of fibre reinforced epoxy or phenolic resin. The composite parts include the wing box, forward fuselage, horizontal stabilizer, elevators, rudder, over‐wing surfaces, etc. There are many military aircrafts in which composites are used, such as the B‐B1 Lancer, F‐14A, F16, and the Navy’s V‐22. Almost 90% of the Voyager, which travelled around the world without refuelling, was made up of graphite fibre composites [70].

14.7.3 Textiles in Space Industry

Composite materials also play an important role in manufacturing space structures such as missiles, rockets, and satellites. Space structures require low weight, high stiffness, a low coefficient of thermal expansion, and dimensional stability. These properties are offered by composites. The application areas of composites in missile systems include rocket motor case, nozzle, skirts, and inter‐stage structures, control surfaces, and guidance structural components. E‐glass, S‐glass, aramid, and carbon graphite fibres are widely used in space and missile composite structures.

14.8 Testing Methods and Quality Control

The applications of textile composite material increase as more and more industries realize what this material can offer. Aerospace structures made by composite materials requires wide range testing because composite products must face incredibly severe conditions, and it is a prime requirement to test them thoroughly to ensure the safety and reliability of the final product. Composite materials are anisotropic and nonhomo- geneous, and a full classification of the material properties must be conducted if they are to be used in structural aerospace situations. The determination of bulk properties requires tension, compression, and shear tests. During qualification and material development, other test types – such as open‐hole tension/compression, interlaminar fracture toughness, compression after impact, and fatigue tests – are used to explore more complex properties. These tests should be conducted according to a test standard set by organizations such as: ●● International Composites Testing Standards: the American Society for Testing Materials (ASTM), International Organization for Standardization (ISO), and European Committee for Standardization (CEN). 14.8 Testing Methods and Quality Control 429

●● Manufacturer Proprietary Standards: Boeing safety standards (BSS) Series and Airbus Industries Test Method (AITM) Series. ●● Obsolete Standards (rarely used): Suppliers of Advanced Composite Materials Association (SACMA), Composites Research Advisory Group (CRAG), and European Association of Aerospace Industries (AECMA). In most cases, the test procedure is similar in different standards; they only differ in specimen size. The following lists some important and common tests.

14.8.1 Tensile Testing

Tensile testing is one of most common mechanical tests used for textile composite materials. A key purpose of this test is to determine the ultimate tensile stress and strain, tensile modulus (E), and maybe Poisson’s ratio with addition instrumentation attached while testing. Details and failure behaviour may be closely observed under controlled conditions. Testing metal is not difficult, owing to its isotropic homogeneous nature, whereas textile composites are anisotropic and complex, owing to fibre direction, diameter irregularity along the length, voids (air gaps), and resin rich area within the structure, etc. Textile composites will show optimum tensile properties if fibres are aligned in load direction; however, they will be weaker if fibres are perpendicular to the load. There are three types of specimen used for tensile testing: dog‐bone, waisted, and bow‐tie. Examples of common standards for the tensile testing of laminates made from high performance textile fibres are: ●● Standard test method for tensile properties of polymer matrix composite materials (ASTM D 3039). ●● Carbon fibre reinforced plastics. Undirectional laminates. Tensile test parallel to the fibre direction (EN 2561). ●● Carbon fibre reinforced plastics. Unidirectional laminates. Tensile test perpendicular to the fibre direction (EN 2597). ●● Determination of tensile properties. Test conditions for isotropic and orthotropic fibre‐reinforced plastic composite (ISO 527‐4). ●● Determination of tensile properties. Test conditions for unidirectional fibre‐reinforced plastic composites (ISO 527‐5). The specimens are parallel sided with bonded tabs to prevent the grip jaws from damaging the material and causing premature failures. Gripping mechanisms include manual and hydraulic wedge grips.

14.8.2 Compression Testing

Textile composite materials are mainly manufactured in the form of laminates of mono, double, and sometimes several layers. Compression testing introduces compressive load into a material while preventing it from buckling. Textile composite materials are mostly good in tensile strength. However, some composites have low compressive strength, because their constituent fibre possesses low strain at break. During loading, specimen surfaces must be as flat and parallel as possible. If required, a specimen may be rubbed manually with different grades of emery paper or it may be 430 14 Aeronautical and Space Textiles

grinded by machine to achieve the desired results. The strain gauges should be affixed on both sides of the specimen in order to measure macro‐buckling. Compressive loads are introduced into a test specimen (often thin and flat) by following the standard methods. Common compression test standards for textile composite materials are: ●● Standard test method for compressive properties of rigid plastics/composites (ASTM D695). ●● Standard test method for compressive properties of polymer matrix composite materials with unsupported gage section by shear loading (ASTM D3410). ●● Standard test method for compressive properties of polymer matrix composite materials using a combined loading compression (CLC) test fixture (ASTM D6641). ●● Fibre reinforced plastic composites. Determination of compressive properties in the in‐plane direction (ISO 14126). Carbon fibre thermosetting resin unidirectional laminates. Compression test parallel to fibre direction (EN 2850). The standards can be used for: ●● End loading: the load is introduced into the flat end of the test specimen. ●● Shear loading: the load is introduced into the wide faces of the test specimen. ●● Combined loading: a combination of shear and end loading is used.

14.8.3 Shear Testing

Textile composites are often compromised because of their low shear stiffness and poor strength. Thus, a laminate stacking sequence is arranged in order to increase shear resistance, though this would compromise other properties. Ideally, a test specimen should provide quantitative shear measurements during the linear and nonlinear response regimes. Unfortunately, this is not possible, because of the material’s anisotropic and inhomogeneous nature. This is why there are several national and international test standards. However, no universal method is suitable for the accurate evaluation of a wide range of textile composites that have a variety of architectures. The following test methods are those commonly used for the determination of shear properties. ●● Uniaxial tension of a ±45° laminate (ASTM D3518/D3518M‐94). ●● Two‐rail and three‐rail shear tests (ASTM D 4255). ●● The V‐notched beam shear specimen (ASTM D7078/D7078M‐05). ●● In‐plane shear test (ASTM D3518 and ISO 14129). Furthermore, there are other ways to determine shear properties: ●● In‐plane shear: standard method for in‐plane shear response of polymer matrix composite materials by tensile test of ±45° laminate (ASTM D3518/D3518M‐13 and ISO 14129). ●● Interlaminar shear: standard method for short‐beam strength of polymer matrix composite materials and their laminates (ASTM D2344, EN2563 and ISO 14130). ●● Rail shear: standard method for in‐plane shear properties of polymer matrix composite materials by the rail shear method (ASTM D4255 and ASTM D7078). ●● V‐notched beam: standard method for shear properties of composite materials by the V‐notched beam method (ASTM D5379). 14.9 Self‐Healing of Composite Materials 431

14.8.4 Fatigue Testing

Failure of engineering material due to cyclic loading is known as material fatigue. Compared to metallic materials, textile materials possess excellent fatigue properties, owing to their anisotropic and inhomogeneous natures. Hence, it has been adopted by industries such as the aerospace and automotive industries. The following important variables affect fatigue properties. ●● Textile fibre type. ●● Resin type. ●● Design structure of reinforcement (unidirectional, woven, knitting, braiding, etc.). ●● Laminate stacking sequence. ●● Environmental conditions (temperature and moisture absorption). ●● Loading condition. Any test method for static testing may be used for the fatigue testing of textile composite material. Correct gripping and alignment are very important for better results. Failure must occur within gauge length. Generally uniaxial tension–tension cycling is done on composite material. However, tension–compression and compression– compression cycling is rarely used. High cyclic frequency in fatigue testing on polymer composites can cause temperature rises in the specimen being tested. The maximum temperature rise recommended by the ISO 13003 fatigue standard is 10 °C.

14.9 Self‐Healing of Composite Materials

Engineering material has always benefited from the latest technological advancements in various applications. Today, it is no longer fanciful to speak of developing material which could repair itself and restore its structural integrity in the event of failure. For example, such material may recover its original shiny body surface, even after being scratched. An example of this would be Scratch Guard Coat, a Nissan product [71]. The original concept is taken from living species whose cuts and wounds heal naturally. In engineering, long‐term degradation can lead to microcracks and ultimately the failure of the material, and so ongoing self‐repair would be indispensable when designers look to increase the lifetime of the material. High performance textile based reinforced composites are the leading contenders for component materials to enhance reliability, efficiency, and the long‐term service life in various applications such as transport, aerospace, building, and many more. They offer immense scope for incorporating multifunctionality, owing to their hierarchical internal architecture. However, their relatively poor performance under impact loading leads to a significant reduction in strength, stiffness, and stability [72], and creates defects and damage by absorbing energy. As a result, the damage often manifests itself internally as matrix cracks and delamination, but it is very difficult to detect visually. Thus, textile fibre reinforced composites could directly benefit from incorporating an added functionality, such as self‐healing. Self‐healing techniques may be categorized into three groups: capsule based, vascular, and intrinsic [73]. In capsule based techniques, small capsules contain a liquid able to heal the crack. When a crack causes capsule damaged, the liquid inside the capsules is released and fills in the gap. In vascular type techniques, the self‐healing material is a 432 14 Aeronautical and Space Textiles

vascular structure which is similar to a tunnel network. These tunnels are filled with liquid and when the rupture takes place the damaged tunnels break the vascular network and the liquid closes the gap. Conversely, intrinsic self‐healing techniques heal through inherent reversibility of chemical or physical bonding instead of through structural design [74]. Thermally remendable, highly cross‐linked polymeric materials like shape memory polymers are used in this type of self‐repair.

14.10 Sustainability and Ecological Aspects

Demand for air transport is continually growing day by day. To meet the demand, society must also accept the costs. With the increase of air transportation, people can also be facing problems of noise, air pollution, climate change, greenhouse gases, etc. It is highly unlikely to achieve 100% sustainability in the aviation industry, but sustainability can be improved. It is believed that the aviation industry is one of the most polluting industries. In a report released by Air Transport Action Group (ATAG) [75], it is estimated that aircraft transport accounts for 12% of the total emission of carbon dioxide globally. The Intergovernmental Panel on Climate Change stated that 2% of global anthropogenic carbon dioxide emission is because of the aviation industry [76]. Increasing awareness of sustainability issues promoted the industry to research not only into the sustainability of biofuels but also into changing manufacturing practices by using natural fibres in composite manufacturing. Future aircraft are supposed to include new and environmentally friendly materials like natural fibres, and use more composite materials instead of metals. For example, Boeing is working on using parts manufactured with composite material in its beta versions of the new 767 in the hope that they will improve lift and reduce the aeroplane’s environmental impact.

14.11 Conclusion

Textile material is a promising engineering material that has proved its worth in numerous applications such as aerospace, civil, transportation, medical, and many more. Some high performance textile fibres, such as carbon, possess high specific strength and modulus, good fatigue, and stress resistance, as well as being corrosion free. They are a highly desirable material for aerospace structural parts. Textile fibres may be divided into two categories: natural and manufactured fibres. Nanofibres became popular manufactured fibres because of their high surface area and functional properties. Synthetic fibres are widely used in the aerospace industry as compared to natural fibres because, during polymerization, the characteristics of synthetic fibre can be modified easily according to user needs. Carbon, glass, Kevlar, polyester, and Vectran fibres are some examples of such synthetic fibres with aerospace applications. It is well accepted that natural fibres are renewable, and hence more sustainable and environmentally friendly, than synthetic fibres. Natural fibres are increasingly used, in part because of customer demand for more environmentally friendly products and more sustainable technology to reduce global waste and greenhouse gases. References 433

Textile fibres are generally converted into fabrics that can carry out load bearing functions. Fibres and polymers are first of all converted into yarns or filaments through spinning. They can also be used to produce nonwovens directly. The yarns/filaments are then used to manufacture woven, knitted, or braided fabrics through weaving, knitting, and braiding manufacturing techniques. Among all these techniques, weaving is the most widely used to produce fabrics, particularly 3D woven fabrics, for textile reinforced composite material for niche applications such as stiffeners, aircraft wings, joints, and rocket nose cones. Textile reinforced composite materials are replacing conventional metal materials in several engineering applications including aerospace, owing to their desired properties such as lightweight, high strength and stiffness, good fatigue resistance, and good corrosion resistance. In order to test their properties, different testing standards can be used for different structural materials of an aircraft. Fibre reinforced composites consist of two main components, textile reinforcement as core and matrix (resin) for shap- ing. Textile reinforcement is impregnated with resin to make composite parts and then consolidated according to a suitable composite manufacturing technique such as vacuum infusion, autoclave, pultrusion, etc. The selection for an appropriate technique relies on manufacturing cost, shape complexity, fibre volume fraction, and intended application. Generally, vacuum infusion is widely used for composite parts manufacturing, while autoclave processing is a popular method to manufacture fibre reinforced composites for high performance applications, typically for large complex engineering parts such as aircraft components like wings and fuselages. Autoclave is also used to produce a wide variety of materials such as thermoplastics and thermoset composite materials. Textile composite materials are replacing conventional material in several fields, such as aerospace, transportation, sports, and other niche applications, because of its lightweight, superior corrosion resistance, higher strength, and stiffness properties. The wide deployment of composite materials in commercial aircraft, such as the Boeing 787 Dreamliner, and the Airbus A350 XWB, is an example of the current application of textile composite materials. Today, all major parts of an aircraft – such as the fuselage, wings, empennage, and interior parts – are made using textile composite materials. Space and aeronautical textiles have a bright future.

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439

Wearable and Smart Responsive Textiles Lihua Lou, Weijie Yu and Seshadri Ramkumar

Nonwovens & Advanced Materials Laboratory, Texas Tech University, Lubbock, USA

15.1 Introduction

Textile materials that provide functional and high performance properties, which make them active, are generally termed smart textiles. Smart textiles, as indicated by their name, suggest materials that do not have the normal characteristics and functions of commodity textiles. In other words, materials when made into some shape or form, could somehow function as a textile material with enhanced functionalities can be con- veniently grouped as smart textiles [1]. For example, smart textile is a subcategory within textiles and refers to textiles that can be worn and have electronic components. However, wearable smart textiles are not confined to electronic materials. In the past, wearables were bulky and not very aesthetically pleasing. Since consumers demand comfort and fashion, wearables have become smaller, lighter, and more stylish. Not only do consumers want comfort, they also want a product that is the most technically advanced for their individual lifestyle needs. Electronic components in wearables vary tremendously and include simple monitoring of footsteps to more complicated capabilities, such as monitoring heart rate and body temperature and detecting dangerous levels of air polluting substances, such as carbon dioxide [1]. Smart textiles have been around for about 1000 years, with the earliest wearable eye- glasses dating back to 1282. [2, 3] Throughout history, pioneers in wearables have attempted to create wearable accessories, to enhance the functionality of clothing. A wearable computer in 1962, George, another wearable computer, in 1972, the Pulsar ‘Calculator’ wristwatch in 1975, a wired computer backpack in 1981, digital hearing aids in 1987, the Bluetooth headset in 2000, a full digital pacemaker in 2003, the Fitbit in 2007, and Google Glass in 2013 [2, 3]. The development of smart textiles requires a multidisciplinary approach in which knowledge of circuit design, smart materials, micro‐electronics, and chemistry are fundamentally integrated with a deep understanding of textile fabrication [4]. Smart textiles provide unlimited opportunities to satisfy human imagined and dreamed smart life. Currently, there are more than 100 million wearable devices on the market, with a projected estimate of 600 million by 2020. Thanks to these smart textiles,

healthcare, medical, fashion, lifestyle, sport, security, and other aspects of future human life can be smarter and simpler than today [3–6]. This chapter provides an overview of the development of smart textiles over the past 20 years, their current status, and future prospects in smart textiles. In particular, this chapter intends to highlight future directions of smart textiles in the market, including challenges and competitiveness.

15.2 Characterization of Smart Textiles

Smart textiles can be characterized by function and application. There are seven categories of characterizing smart textiles by function. They are: (i) shape memory textiles/ polymers [7–12], (ii) optical textiles (solar cells, light emitting, photovoltaic textiles) [5, 13–17], (iii) wearable electronics (electrotextile interfaces, textile based sensors, textile based actuators) [18–84], (iv) barrier membranes (waterproof garments, medical textiles, warfare protection) [85–96], (v) phase change materials (PCMs) (thermal energy storage) [97–102], (vi) chromic materials (colour change, photochromic, thermochromic, electrochromic, piezochromic, solvatochromic) [103–107], and (vii) other functional textiles (waterproof textiles, emitting scents textiles, breathable textiles, etc.) [108–115]. Characterizing smart textiles by application can be done as follows: (i) medical and healthcare [6, 12, 116–120], (ii) sport and wellness [121–126], (iii) fashion electronics [12, 124, 127], (iv) defence textiles (military, security) [128, 129], and (v) conductive ink textiles [130–134]. In addition to function and application, a general and broader categorization method has also been proposed by Md. Syduzzaman: (i) aesthetic and (ii) performance enhancing [19]. Matteo Stoppa and Alessandro Chiolerio categorized smart textiles into four groups by their sense and response to external stimuli: passive smart materials, active smart materials, very smart materials, and materials with even higher level of intelligence [18]. Lastly, smart textiles can also be characterized by fibre type, for example metal fibres, nanoparticles, polymers, composites, etc.

15.3 Smart Textiles Grouped by Function

15.3.1 Shape Memory Materials

Shape memory materials are one kind of smart material that can change their shapes to temporarily deformed shapes induced by external stimuli (pressure, pH, temperature, electric, magnetic, chemical, ultraviolet light, etc.). [7] Based on the adjustment and control of the material parameters, the shape, permeability, surface tension, and tensile properties of shape memory materials can be controlled. This control has been applied to biomedical and microelectromechanical systems (MEMSs), and the aerospace, automobile, and telecommunication industries, etc. [8]. Shape memory materials are categorized based on the type of material: alloys and polymers. Polymer application seems to have great development prospects compared to relatively developed alloys because polymers are cheap, easily controllable, and have 15.3 Smart Textiles Grouped by Function 441 a large deformation range. The shape recoverable mechanism of shape memory polymers is due to their ability to transfer energy from thermal energy to mechanical energy, as an example. The extremely extensibility ability (about 400%) is derived from polymer networks’ intrinsic elasticity, viscoelastic, mechanical, and optical properties [9]. Temperature is the major and most commonly used external stimuli for polymers. The temperature at which a polymer shape change occurs is known as the transformation temperature (Ttrans) [9]. If the deformation occurs within the polymer recovery range, the shape of the polymer will return. However, once the unrecoverable deformation has occurred, the shape of polymers cannot be reinstated. Shape memory polymers can be categorized into four groups by transformation temperature: physically cross‐linked noncrystalline thermoplastic polymers, physically cross‐linked semi‐crystalline block copolymers, chemically cross‐linked glassy thermosetting materials, and chemically cross‐linked semi‐crystalline rubbers [11]. In fact, the intrinsic properties and the structural design are two major factors that affect polymer shape recovery behaviours. Many polymers have an increased shape retention performance and high recovery rate, thanks largely to these two factors. One of the parameters to measure the shape recovery behaviours of polymers is the shape memory cycle (strain recovery rate and strain fixity rate) [9]. Commonly used shape memory polymers include cross‐linked poly(cyclooctene), polyurethanes, poly(ester urethane), poly(D,l‐lactide), poly(1,4‐butylene adipate), poly(hexamethylene adipate), poly(ε‐caprolactone), poly(ethylene adipate), poly(ethylene glycol), poly(l‐lactide), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), poly(ethylene glycol) dimethacrylate, poly(ethylene oxide), poly(methyl methacrylate), poly(cyclooctene), poly(1,4‐butylene succinate‐co‐1,3‐propylene succinate), etc. [7–12]. Research has shown that 50–70% of patents for shape memory material target medical applications. Commercial polymers, for example New Ortho Polymers, MedShape, and MnemoScience, have been used in custom‐fitted perforated medical casts [12]. As polymers allow for minimum surgery and reduce rejection responses with imbedded drugs, shape memory materials have great potential in future medical applications. Furthermore, there has been an increase in interest for the application of shape memory material in smart textiles (nonwoven materials) in recent years. The material could be used as window treatments, room partitions, smart clothing, and wall hangings, which are triggered by temperature, electric, sunlight, etc., as shown in Figure 15.1 [7–12].

15.3.2 Optical Textiles

Wearable optical textiles produced from optical fibres or electronic wires blended with textiles have been used as electronics, sensors, and optics [13]. Optical textiles are able to carry light and are immune to electromagnetic fields. Park and Jayaraman invented the smart optical shirt, which is flexible, comfortable, wearable, and able to sense a variety of vital signs, such as body temperature, electrocardiogram, heart rate, and pulse oximetry [5]. Optical smart textiles can easily connect to optical devices, for example a photo detector, light source, and connector. The structure of optical fibres consists of the cladding and the core, in which the light is kept in the core and is satisfied with the internal reflection condition: n (core) > n (cladding), where n reflects the refractive indices [14]. Commonly used material for the 442 15 Wearable and Smart Responsive Textiles

(a)

Weaving Deformation

Shape-memory device Traditional Yarn Smart energy storage shape memory fabrics Healing

Shape recovered

Fabrics with original shape Shape recovering

(b) Smart energy storage Automatic cloths transformation Easy to deform

Normal temperature Over 35°C Cooling down

Figure 15.1 The application of shape memory materials [10]. Source: Thakur S. Shape Memory Polymers for Smart Textile Applications[M]//Textiles for Advanced Applications. InTech, 2017.) under CC BY 3.0 license. Available from: http: //dx.doi.org/10.5772/intechopen.69742.

core is polystyrene. Polymethyl methacrylate (PMMA), styrene‐methylmethacrylate copolymers, polyethylene, polyvinyl chloride, and polyamide are commonly used materials for the cladding. The major optical fibre polymer suppliers are Toray, AGE, Inc., Asahi Kasei Corporation, and Mitsubishi Rayon [12]. As optical materials are brittle, and may break during textile processing, weaving, and knitting, processing methods need to be carefully selected to prevent breakage and thereby ensure light transmitting over a long distance. Optical fibres can be integrated into either warp or weft directions [15]. During the fabrication process, the fibre bending ratio and radius must be properly designed. Mikwang Dyetech has developed different weaving processes for optical smart textiles production [15]. As yarns in knitted fabric are exposed to severe bending, optical fibre is usually integrated in a straight line during the production process. The application of plasma for optical fabrics surface treatment greatly improves the surface wettability and chemical composition of the surface. Optical smart fabrics are categorized into two classes: smart shirts and photonic textiles [16]. Smart shirts have been designed for soldiers, athletes, and patients for medical monitoring, biofeedback, and clinical trials monitoring. Smart shirts that have been designed for fashion costumes, clothing, curtains, and handbags are called light 15.3 Smart Textiles Grouped by Function 443 illuminating textiles. Light illuminating textiles are irradiated by light emitting diodes (LEDs) and are battery operated. Photonic textiles consist of flexible displays and light therapy. Flexible displays are capable of displaying graphics and videos on the wearer and portable electronic devices. Light therapy has its application in medicine and can be used to treat skin diseases and nonseasonal depression. The mechanism of light therapy is based on the wavelength of light, 600–900 nm, emitted by the textiles [15]. Optical textile sensors are designed to measure the light transmitted intensity change applied to the textiles. The performance of optical smart fabrics can be enhanced if improved optics and electronics technology are embedded into fabrics and garments. However, signals remain relatively weak, which results in optical smart fabrics with weak durability and poor reliability [17]. Moreover, the bending of optical textiles is unavoidable during the production process, which also weakens the optical signal. It is believed that optical smart fabrics will become competitive in the medical and fashion industries once a new method for weaving optical smart fabrics without fibre breakage is designed. Without breakage, fabric with optimized light emission performance can be produced.

15.3.3 Wearable Electronics

Wearable electronic textiles are fabrics interconnected with electronics, which provide flexibility, integration, and low power consumption to electronics. Wearable electronics are further categorized into three subgroups: passive smart textiles, active smart textiles, and highly active smart textiles [18]. All three subgroups need sensors to sense stimuli and react based on the signal’s outcome. Most passive wearable electronics have been used in biomedical fields, such as sensing of biophonic, electroencephalography, electromyography, electrocardiogram, and human muscle movement [19]. For active wearable electronics, they have been used in assistive technology, radio frequency (RF) functionality, human interface elements, and power storage or generation. The power of active wearable electronics is derived from motion or is photovoltaic. One of the materials used for wearable electronics is conductive fibre. Fabrics with conductive fibres could be applied to infrared absorption, protective clothing, electromagnetic interference (EMI) shielding, and antistatic fields. There are several conductive fibres production processes, one of which is wire drawing. Wire drawing, including metal monofilaments and blended fibres, could be directly used in fabric production process (weaving and kitting). Common products include copper clad aluminium (CCA) filaments, silver plated brass (Ms/Ag), aluminium (Al) filaments, silver plated copper (Cu/Ag) filaments, and metal filaments/yarns (cotton, aramids, polyesters, polyamides) [18]. Another method to produce conductive fibres is coating. Coating is relatively easier than fabrication, as metals are sprayed onto the surface of fabrics, yarns, or fibres. Coating technologies used include sputtering, evaporative deposition, and electroless plating [20]. A major advantage of coating is high yield. However, it also has disadvantages, for example poor durability and mechanical properties. Wearable electronics textiles are also produced with conductive inks [21]. The ingredients of conductive ink are highly conductive metal (copper, gold, and silver nanoparticles) and pure water. The technology to produce electronic textiles is called screen‐printing, 444 15 Wearable and Smart Responsive Textiles

which is versatile and provides high durability and flexibility. The possible disadvantages include low resolution and nozzle clogging caused by high viscosity particles. Wearable antennas are an essential part of the development of autonomous garments, which have controllable electric monitors [22]. The permittivity and mechanical properties of antennas are influenced by the bandwidth and efficiency of the materials used. The major issue facing wearable antennas is shape change due to body movements: bending, or deforming. Designers need to consider this influencing factor during the design process. Wearable electronics textiles can be used as sensors, which react to the environmental stimuli, for example pressure, electrochemical, and stretch [23]. Pressure sensors are mainly used as switches for electronic devices. The operational mechanism of pressure sensors is sensing the planar pressure or capacitance variations. Electrochemical sensors can convert chemical signals into physical measurements. Stretch sensors can sense body temperature, heart rate, blood pressure, respiration, muscle movement, and other body parameters. For example, a comfortable knitted fabric produced by Shu Yang and Randall Kamien’s groups was made which incorporated nano yarn structure [24]. The colour of the knitted fabric would change with the sweat increasing from the wearer, which indicates the health condition of the wearer. Smart textiles also could get energy from sunlight or body motion. A woven solar cell with triboelectric fibrous nanogenerators made by polymeric fibre has been produced by Zhonglin Wang’s team. This smart product could be used to charge cell phones and watches [25]. Qing Wang’s team has produced a wearable cooling vest with nanoarrays made from ferroelectric barium strontium titanite that can run for two hours on a 500 g battery [26]. A flexible and wearable battery has been invented by Yong‐Hee Lee et al., which is made by coating nickel on woven polymer and electroless deposition method. This solar‐charged textile battery can illuminate nine LED bulbs [27]. Nowadays, research is mainly focused on the development of intelligent textiles rather than passive or active electrical textiles. Figure 15.2 shows the basic structure of electric textiles. Interdisciplinary cooperation breaks the barriers between disciplines and

Pressure

Shield Electrode Array

Spacer (foam, textile)

Back Electrode Shield

Figure 15.2 Electronic textiles. 15.3 Smart Textiles Grouped by Function 445 promotes the improved development of smart and intelligent electrical textiles. For example, a group of scientists from Austria, Germany, and Israel incorporated glucose moieties into upland cotton in vitro [28]. Glucose moieties incorporated with magnetic complexes enable cotton fabric to be magnetic. Ultimately, the market and consumer demand are the driving forces.

15.3.3.1 Piezoelectric Sensors ‘Piezoelectricity’ means electric charge that accumulates on materials in response to mechanical pressure or latent heat, and the interaction between the mechanical and electrical state of a material is linear and reversible [29]. Piezoelectricity has been applied to several application fields, such as the generation of high voltages, sound production and detection, microbalances, and electronic frequency generation [30]. The piezoelectric phenomenon was discovered by the Curie brothers in 1880 [31]. At the beginning of the twentieth century, macro‐scale piezoelectric transducers were produced for military application, which were called MEMSs [32]. Inorganic materials are commonly used for MEMS, for example silicon‐ and lead‐containing materials [33]. Since the 1990s, polymeric materials have created great interest, owing to the advantages of flexibility, low cost, and having additional properties [34]. Recently, nanostructured piezoelectric materials have been produced, which are called nanogenerators [35–40]. Ali Gheibi fabricated a one‐step nanogenerator using polyvinylidene fluoride (PVDF) with electrodes, which has an electric output as high as 1 V [35]. Polymer piezoelectric materials can be divided into two types of bulk polymers: (i) voided charged polymers and (ii) composite polymers [41]. Bulk polymers’ molecular structures need to be arranged to have piezoelectric mechanism [36, 37]. Voided charged polymers are polymers with gas voids and internal dipoles to form charges. Composite polymers are polymers integrated with piezoelectric ceramics [42]. Conductive textiles with zinc oxide have excellent piezoelectrical properties, which have proved to be alternative substrates to conventional substrates [43]. There are two common type of bulk polymers: amorphous and semi‐crystalline polymers. Amorphous polymers including polyimide [29] and polyvinylidene chloride [44, 45]. Commonly used semi‐crystalline polymers include polyamides [46], PVDF [47, 48], Parylene C™, and liquid crystal polymers [49, 50]. The mechanism of semi‐crystalline polymers piezoelectric materials is similar with inorganic materials. The negative and positive ions or polar groups of polymers are arranged in crystalline structures which cause polarization change depending on the stress [31]. The structure of voided charged polymers was invented by Gerhard Sessler [31]. The charged voids rather than ion displacement are the reason for the piezoelectric effect. There are several factors affecting charges of voided charged polymers, for example density/shape of voids and type/pressure of gas [31]. Composite polymers with piezoelectric ceramics have several advantages, for example flexibility, higher coupling, low acoustic impedance, few spurious modes, and dielectric constant [51]. Smart Material produces randomly or arranged scattered rods in polymer films. Microscale or nanoscale particles incorporated into a polymer matrix are another way to produce composite polymers piezoelectric materials [52, 53]. There are several applications of piezoelectric materials, including piezoelectric tactile sensors [54, 55], vibration energy harvesters [56, 57], acoustic transducers [58], and inertial sensors [36, 59]. Piezoelectric tactile sensors can be used to measure shape, 446 15 Wearable and Smart Responsive Textiles

tactile temperature, pressure, softness, and force. Ceramic/PVDF composites and PVDF‐TrFE with improved piezoelectricity flexibility [60] and softness have been designed. Nanograss PVDF sensor with a sensitivity of 0.56 V at 98 mN force is produced, which is 2.8 times higher than regular thin films [60]. Some researchers are using cellular polypropylene (PP) to analyse and identify touch location. [55] Other research has incorporated carbon black and high density polyethylene with PVDF and piezoelectric bicomponent fibre to detect the human heartbeat [61]. Piezoelectric materials with a high voltage of 20 V have also been applied to muscle driven applications [29]. There are many novel products designed using piezoelectric materials for energy harvesting, which could replace batteries [62, 63]. Usually inorganic materials are used because of their high power output [64]; however, polymeric piezoelectric materials provide flexibility and decrease stiffness, which could improve the lifetime of the device [65]. PEDOT/PSS polymer electrodes with PVDF [45], PZT‐epoxy composite harvesters [66, 67] and PMN‐PT nanowire based/PDMS composite are proving to be more robust than indium tin oxide (ITO) or platinum (Pt) electrodes. Polymers could effectively compensate high coupling and flexibility [68]. And, there is already continuous production technology for piezoelectric PVDF electronical textiles [69]. All fibre and environmentally friendly piezoelectric fabrics of ‘3D spacer’ technology have been produced by researchers, which have a power density of 1.10–5.10 μW cm−2 at applied pressure of 0.02–0.10 MPa [70], for an energy harvester and power generator. Besides that, a wearable piezoelectric fibre composite microsystem with a voltage output about 6 V is produced by Swallow et al. [71]. Another application of piezoelectric materials is for acoustic transducers, which are operated within audio, infrasonic, and ultrasonic ranges and could be used for loud- speakers and microphones [31]. It could also be used for medical applications, such as medical automated machinery or medical imaging. Inertial sensors produced by piezoelectric materials can be used to detect material orientation or acceleration and velocity. Edmison et al. applied piezoelectric materials for glove based electronic textiles that could sense hand movement [72]. Seyedin’s group used stretchable conductive knitted textile sensor, which can detect up to 200% strains and up to 500 cyclic stretching compared to the initial sample size [73]. Other research conducted by his group using polyurethane/poly(3,4‐ethylenedioxythiophene)polystyrene sulfonate (PEDOT: PSS) composite fibres showed excellent electrotechnical properties [74]. There is growing interest in making piezoelectric smart textiles, because they do not need to consume power to operate [75]. The polylactic acid (PLLA) piezoelectric braided cord sensor has also been used for fashionable clothes by a group of scientists [76]. More interdisciplinary research and funding focus on this field and its adaptation for consumers can accelerate the practical potential of piezoelectric smart textiles with further advances in their performances [76, 77].

15.3.3.2 Diapers and Incontinence Products with Sensors Urinary tract infections are common and usually affect children and the elderly [78]. However, conventional testing methods use urine culture, microscopic examination, and dipsticks [79]. These methods take a long time, and samples may be contaminated and a large number of samples are necessary. Diapers are commonly used for patients with urinary tract infections, thus the detection of urinary discharges on diapers will be a low‐cost and easier method for disease diagnosis. 15.3 Smart Textiles Grouped by Function 447

There are many existing technologies incorporating wireless and self‐power biosensors [80, 81] in diapers [82]. The power comes from the urine activated battery, which enables free movement and does not interfere with the wearer’s comfort. The connected transmitter will transmit an ID signal over a distance of 5 m at a voltage of 1 V [82]. A paper based device has been invented by Couto and Dong, which is used to analyse biomarkers from urine on diapers. The thickness of the device is 5.3 mm, which is important as it means comfort is guaranteed. Besides that, the results could be obtained within eight hours [84]. A smart diaper with integrated dipsticks is designed for colorimetric analysis of urinary tract infections, which can be used for the elderly and pets [83].

15.3.4 Barrier Membranes

Barrier smart textiles can be used as military protective clothing; medical garments with antibacterial and antifungal properties; or sportswear with protection against water, bacteria, viruses, blood, particulate matter particles, etc. The major advantage of barrier textiles is their breathability, which makes these textiles more comfortable than traditional barrier materials. Barrier smart textiles are categorized as waterproof garments, medical textiles, and warfare protective clothing.

15.3.5 Waterproof Garments

Although waterproof garments guard against liquids, they are breathable porous textiles. The pore size and fibre diameter are major factors that determine their performance. Besides that, affinity (chemistry) and surface roughness (morphology) also have an influence on the wetting processes. There are three models to describe the behaviour of waterproof garments: the Wenzel model, the Cassie–Baxter model, and the Young– Laplace Equation [85].

15.3.6 Medical Textiles

Medical textiles are usually single‐use products, for example surgical clothing and medical antibacterial masks or caps. The apparel may also be covered with fluoro compounds or fluoropolymer based coatings and are used to prevent strike through by organic solvents with contaminants [86]. Additionally, multiple layer membranes are used, with each membrane having a different function. The inner layer is typically designed for comfort, while the barrier layer faces the outside. Metal oxides, activated carbon, and small particles have been imbedded into polymers to make composite membranes and provide biomimetic activity to the barrier layer.

15.3.7 Warfare Protective Clothing

Warfare protection is the major application of barrier smart textiles. Protective armours have been used for almost five millennia and have gradually evolved from the use of animal skins and furs to metals and fibres [87]. Fibre materials belong to the class of soft body armours that are lightweight and more comfortable than ancient protective armours [88]. 448 15 Wearable and Smart Responsive Textiles

Some of the earlier designs of soft body armours use silk woven fabric, which was later replaced by other fibres, such as aromatic polyamides and nylon 66 [89]. Nowadays, there are newer high performance fibres that are being used for ballistic protection. This includes Zylon [90], Kevlar [91], Technora [92], Spectra [93], and Nomex [94]. The ballistic‐proof ability depends on the absorbing energy performance of the materials, and the ability to distribute energy across the whole structure [89]. Thus, sonic velocity [95], tenacity, modulus, and extension at the break of the materials are important parameters determining the protection level. The detail properties of the materials listed above are described in Table 15.1. Zylon, or poly(p‐phenylene‐2,6‐benzobisoxazole), PBO, trademarked name, is a synthetic fibre manufactured by the Toyobo Corporation and was developed by DRI International in the 1980s [90]. Zylon has a tensile strength of 5.8 GPa, which is about 1.6 times higher than Kevlar [90]. Moreover, Zylon has excellent thermal stability. The modulus of Zylon is twice that of p‐aramid fibres and its decomposition occurs about 100 °C hotter than them [90]. These properties contributed to Zylon gaining wide application in body armour in 1998. However, recently some issues with Zylon have arisen, such as the degradation of the tensile strength under high ultraviolet (UV) radiation [90]. Kevlar, a para‐aramid synthetic fibre, was developed by DuPont in 1965. It is produced from poly‐paraphenylene terephthalamide and consists of long molecular chains [91]. Its high alignment of Kevlar molecular chains results in a high tensile strength (about 3620 MPa), low extension, high modulus/toughness, high chemical resistance, high thermal stability, and low flexibility [90]. The high tensile‐strength‐to‐weight ratio makes Kevlar five times stronger than steel [90]. Kevlar is a well‐known component for ballistic vests and face masks.

Table 15.1 Ballistic protection materials.

Tensile Chemical name/ strength Extension Density Fibre name Type Company formula (MPa) (%) (g/cc) Zylon [90] PBO Toyobo poly(p‐ 1800 3.5 0.97 phenylene‐2,6‐ benzobisoxazole) Kevlar 29 [91] Paramid DuPont Poly(p‐phenylene 3900 3.5 1.44 terephthalamide) Technora [92] Paramid Teijin Diaminodiphenyl 3100 4.4 1.39 ether‐para‐ phenylenediamine‐ terephthaloyl dichloride Spectra [93] HPPE Honeywell High performance 3000 3.5 0.97 polyethylene Nomex [94] Ballistic DuPont Poly‐meta‐ 485 35 1.38 protection phenylene materials isophthalamide Meta‐aramid 15.3 Smart Textiles Grouped by Function 449

Technora is a para‐aramid fibre developed by Teijin. Its high strength and resistance properties make it useful in a number of applications, such as ballistic protection, cables, and ropes. Additionally, this fibre has good fatigue resistance, dimensional stability, and high thermal resistance [91]. Technora is produced by condensation polymerization of terephthaloyl chloride (TCI), p‐Phenylenediamine (PPD), and 3,4‐diaminodiphenyl ether (ODA) [91]. Spectra, a product of Honeywell, is an ultra‐high‐molecular‐weight polyethylene (UHMWPE) fibre, synthesized from the monomer ethylene [92]. Spectra is a thermoplastic polyethylene fibre. This material has a high strength (2.4 GPa) and is abrasion‐ resistant because of its extremely long chains and high molecular mass (3.5 and 7.5 million amu) [92]. Moreover, Spectra has a lower coefficient of friction than nylon, and its strength‐to‐weight ratio is about 8–15 times higher than steel [89]. Spectra is developed to provide arm and leg protection. Nomex is a meta‐aramid polymer developed by DuPont in the 1960s [93]. The aromatic backbones makes this polymer rigid and durable. Nomex is produced by a condensation reaction of m‐Phenylenediamine and isophthaloyl chloride [92]. Moreover, it has excellent thermal, chemical, and radiation resistance. Nomex is a commonly used polymer for protection against fire [92, 93]. The mechanisms of the ballistic proof ability of materials are the absorption of impact energy and redistribution of impact energy [89]. A protective material should absorb the energy before the bullet completely penetrates the material by either stretching, compressing, or destroying the material [92]. The energy spread speed should be quick, as the bullet’s speed is about 900 m s−1 [92]. The protection performance of ballistic materials is attributed to the rapid conversion and dispersion of the kinetic energy to strain energy. The absorption and redistribution of energy can be achieved when: (i) the protective materials decelerate and finally stop the high speed bullet by dissipating the kinetic

Cross-section of the Composite

Leather Layer

Nylon

Nonwoven

Anti-ballistic Layer

U.S. Patent # 686127

Figure 15.3 Ballistic protection materials [88]. Source: Texas Tech University. 450 15 Wearable and Smart Responsive Textiles

energy along the plane of the protective material impacted [89], (ii) the protective materials bounce the high speed bullet [96], or (iii) a combination of 1 and 2. The transverse and longitudinal structure of ballistic fabric can be seen in Figure 15.3 [92]. The transverse wave propagates perpendicular to a material, while the longitudinal wave travels in the plane of the material [89]. The major parameters affecting the dissipation of kinetic energy are the tensile strength of the fibre, the number of layers, and the fabric structure. In conclusion, to be considered a ballistic material, the material should completely absorb the kinetic energy of the high speed bullet, to prevent injuries to the body.

15.3.8 Phase Change Materials

PCMs are substances capable of storing and releasing energy during the phase change process, for example solid to liquid during the melting process. The NASA research programme was the first to incorporate PCMs in textiles (fibres, yarns, fabrics) in an effort to improve thermal protection for astronauts [97]. Textiles with PCMs react with the change of the body’s microclimate to provide thermal comfort. The mechanism of PCM materials is illustrated in Figure 15.4. For the past 30 years, PCMs have been widely applied in wallboards, walls, floors, and ceilings for active or passive solar heating, shutters, underfloor electric heating systems, night cooling, and textiles [98]. PCMs are essential for reducing dependency on nonre- newable resources and contribute towards an increase in the use of efficient and

Heat absorbed

PCM solid PCM liquid

Heat emitted

PCM fabric

Figure 15.4 Schematic energy exchange process of phase change materials. 15.3 Smart Textiles Grouped by Function 451 environmentally friendly solar energy. Thermal energy storage of shape change materials can be accomplished by either sensible or latent heat storage processes [98]. Sensible storage processes are a traditional process, which needs a larger volume of material for energy storage than latent storage process. There are two kinds of PCMs: organic and inorganic. The most commonly used organic PCMs are polyethylene glycol (PEG), fatty acids, and paraffins [99]. The use of organic PCMs is advantageous in that they are recyclable, chemically stable, nonreac- tive, safe, compatible, not segregated, easily cooled, and have a wide temperature range. The possible disadvantages of organic PCMs include flammability, low energy storage capacity, and low thermal conductivity [98]. The commonly used inorganic PCMs are salt hydrates and metallics. The advantages of inorganic PCMs include nonflammability, high thermal conductivity, sharp phase change, low cost, and high energy storage capacity. The possible disadvantages of inorganic PCMs include segregation, super‐cooling, and high volume change [98]. There are three commonly used methods to measure the thermal properties of PCMs: differential scanning calorimetry (DSC), differential thermal analysis (DTA), and T‐history method. DSC measures the difference of heat capacity, melting temperature, solidification temperature, and heat of fusion between the samples and reference during the same heating process [100]. DTA uses the same heat applied to the samples and reference to measure the temperature difference between them. On the other hand, the T‐history method was used to measure thermal conductivity, heat of fusion, degree of super‐cooling, and the melting temperature [100]. For a PCM to be used in textiles, it has to satisfy several demands, including low price, ease of availability, large and effective thermal conductivity, stability for repetition of melting and solidification, be nonflammable, have a low toxicity level, be harmless to the environment, have temperature difference between the melting point and the solidification point, large heat of fusion, and a melting point between 15 and 35 °C [99, 100]. The materials that have satisfied these demands include hydrated inorganic salts, linear long chain hydrocarbons, and PEGs [101]. Hydrated inorganic salt incorporated textiles usually have an absorbing and releasing temperature range of 20–40 °C, for example Glauber’s salts have a melting temperature of 32.4 °C. Hydrophilic linear hydrocarbons absorbing and releasing temperature range depends on the number of n of CnH2n+2 [101]. PEG is one of the most important PCMs for textile applications. Commercial paraffin waxes have a wide melting temperature range and are cheap. Others include fatty acids (stearic acids, palmitic, lauric, and capric) and butyl stearate [101]. PCMs are incorporated into textiles during the liquid state; the diameter of these microcapsules is about 1–30 μm. When the temperature rises, the microcapsule melts and the heat is transferred and stored. When the temperature decreases, the stored heat is released and the microcapsules are solidified [102]. There are many individual differences amongst PCMs. As far as comfort goes, about 80% of the occupants have deemed the comfort of phase change textiles acceptable. The methods used to incorporate PCMs into textiles include fibre technology, coating, and lamination [104]. The fibre technology method involves adding the PCM microcapsules into the liquid polymer solution. The drying of wet spinning methods forms the PCM/fibre composites. Coating composition for textiles – such as PCM microcapsules, a dispersant, a surfactant, a thickening agent, and an antifoam agent – are 452 15 Wearable and Smart Responsive Textiles

applied directly to the textile substrate. Lastly, the lamination method incorporates PCMs as a thin polymer layer [101]. Although there are many applications of phase change textiles (shoes, accessories, bedding, sportswear, spacesuits, and medical applications), there are many challenges facing this textile. First, no standard testing method currently exists. Second, the mechanical properties of phase change textiles are bad.

15.3.9 Chromic Textiles

Chromic materials or chameleon textiles are materials that show a colour change due to the external stimulus [103]. The external stimuli include light (photochromic), temperature (thermochromic), electricity (electrochromic), pressure (piezochromic), and pH (halochromic) [103]. Photochromic materials are materials, which change colour when exposed to UV light or electromagnetic radiation. In the 1960s, there were two significant applications of photochromic materials: photochromic glasses and photochromic micro‐ images [104]. An application in the optical industry is that photochromic glasses change tint, while photochromic micro‐images use an innovate method that allows the storing of images. The mechanism of action from photochromic materials comes from the electronic configuration change under excitation, which induces the change of the absorption spectrum in the visible range [103]. Most compounds switch from a colourless or light colour state to a darker colour state. The thermal activated reaction is called type T, while a photo activated reaction is called type P [104]. Photochromic materials can be organic and inorganic compounds [104]. Inorganic compounds are incorporated into glass, while organic compounds are incorporated into polymer matrices, microcapsules, stabilizers, or barrier polymers. Inorganic compounds have a long life and good resistance to fatigue. Commonly used inorganic compounds are silver salts. The commonly used organic compound comes from the spiropyran family of organic chemical compounds. These compounds can be degraded by UV radiation, oxygen, and free radicals. Some applications of inorganic/organic hybrid composite compounds are also used, for example polyoxometalates [105]. Thermochromic materials when induced by temperature will produce a colour change. The mechanisms of change include physical and chemical (phase transition, decompositions, and thermal dilation), modification of chemical structure, crystalline field, and charge transfer [105]. Thermochromic materials are classified as continuous and discontinuous. Continuous thermochromic materials undergo a gradual temperature change process. Discontinuous thermochromic materials undergo an abrupt change of colour at specific temperatures. There are two main families of thermochromic compounds: irreversible and reversible systems [106]. Electrochromic materials change colour when induced by an electrical current. The change of colour is dependent upon redox reactions, for example Fe+2 is yellow, while Fe+3 is orange [105]. Generally, electrochromic textiles need to have a sandwich structure to carry out the reaction: a support layer that allows for mechanical holding, a conducting layer to supply the system with electricity, an electrolyte layer, an ionic storage layer, a transparent conductive layer, an electrolyte layer, and an upper support layer [106]. 15.4 Application of Smart Textiles 453

There are two families of thermochromic compounds: inorganic and organic. Inorganic compounds include metal oxides and Prussian blue. The commonly used organic compounds include conductive polymers and viologens [107]. Most chromic materials applied in textiles are in the field of fashion and technical and smart textiles. There are also some other possible application areas, for example in wound dressing to indicate the healing process.

15.3.10 Other Textile Products

There are also some other types of functional smart textiles, for example waterproof textiles, scent emitting textiles, breathable textiles, etc. Waterproof fabrics could provide protection against rain and wind [108]. Scent emitting textiles can emit scent which could alter the wearer’s memory and mood [109]. Breathable textiles allow water vapour diffusion and prevent the penetration of water [108]. There are two types of waterproof fabrics: hydrophilic fabrics and microporous fabrics [110]. Hydrophilic polymers – for example modified polyurethane, polypropylene, nylon and polyester – are used for the production of hydrophilic fabrics. Microporous fabrics have tiny holes which are smaller than waterdrops and larger than water vapour molecules [111]. The commonly used polymer for the production of microporous fabrics include PVDF and polytetrafluoroethylene (PTFE). Waterproof fabrics can be applied for functional leisurewear and sportswear [110]. Emitting scents textiles are designed for human health regulation. For example, a herbal scented pillow has been designed for revitalizing and soothing the user with herbal aromas. Perfume emitting clothes are also designed for changing human moods and fighting diseases (e.g. Alzheimer’s disease) [113]. Breathable textiles have been used in medical and military fields, because breathability is associated with the comfort of the body in different environmental conditions [114]. One of the important developing trends for breathable textiles is the production of smart waterproof and breathable fabrics. Materials explored are shape memory polymer, such as shape memory polyurethane, cotton/poly(N‐tert‐butylacrylamide‐ran‐ acrylamide: 27: 73), etc. [108, 115].

15.4 Application of Smart Textiles

Smart textiles are serving in various fields nowadays since they offer versatile functions for information, assistance, communication, aesthetics, etc. As Figure 15.5 shows, the application of wearable technology is mainly in the sectors of safety and security, medical and wellness, sport and fitness, communication, computing and entertainment [12]. Of these, the most widely used that are related to our daily life are the fields of medicine and sport. Apart from these applications in military and environmental fields, wearables also find applications in fashion sectors. Although, developments in smart clothing technology are highly innovative and advanced, application is only in its starting phase. Some products are on the market, but most of the new products are not in the market yet, which suggests that their potential use is enormous. So is the potential of integration with the electronic and fashion industries [12]. Figure 15.5 World of wearable technology applications. Source: Beecham Research, UK. 15.4 Application of Smart Textiles 455

15.4.1 Medical and Healthcare

Smart and high performance textiles are widely applied in the medical field, owing to their specific chemical and physical characteristics, quick production, and multiple functionality. Importantly, these textiles can serve as a platform to carry and deliver drugs. Therefore, the research and development of medical textiles is experiencing rapid growth because of their high potential in the world of technology and because of their potentially huge monetary value. Functional nonwoven materials in the medical sector can be classified according to where they are applied: (i) near the patient, (ii) on the patient, or (iii) in the patient. Medical textiles ‘near the patient’ are protective garments and articles that the surgeons need to wear and use while doing the surgery, ‘on the patient’ products are used to treat the wounds on the surface of the patient’s body, and ‘in the patient’ products could be planted inside the patient’s body for medical purposes.

15.4.1.1 Near the Patient ‘Near the patient’ textiles include surgery gowns, hats, and masks that the surgeons wear and the towels, sheets, and covers used in surgeries. Their purpose is to prevent cross‐infection between the surgeon and the patient, and to provide a sanitary environment during surgery. Therefore, the requirements for these materials are that they should have proper barrier capabilities against microbes such as bacteria, viruses, and microparticles; be comfortable to wear; be resistant to abrasion; be able to undergo disinfection treatment; and have a good balance between cost and performance, etc. [116]. Different nonwoven technologies and different new finishing technologies can give the material properties that meet these requirements. The material produced by a single nonwoven method has its limitations in the property and cannot meet all the requirements in medical practice, and hence the combination of two or three types of methods or raw materials is the way forward. For example, the composite fabric of SMS (spunbond melt‐blown spunbond) technology has a good balance of protection and comfort and is widely used in medical clothing. A comparison of the properties of different nonwoven technologies for the production of surgical gowns (spunbond, thermalbond, SMS, and spunlace) has shown that the comfort of spunbond and barrier quality of thermalbond are not good enough for them to serve as surgery gowns. Although spunlace materials have the best comfort and barrier qualities, its cost is the highest. Therefore, SMS technology can achieve a good barrier property and lower cost at the same time [117]. The finishing of surgical gowns usually includes water‐repellency, oil‐repellency, and alcohol‐repellency treatments that ensure the material’s barrier functions by enforcing its leakage‐proof property and sterilizing treatment like steaming process, ethylene oxide gas processing, and radiation sterilization [117].

15.4.1.2 On the Patient ‘On the patient’ medical materials are those that are used to treat patient wounds, like surgical dressings, bandages, gauzes, suture lines, etc. They should have no toxicity, good absorbency of blood, and good affinity for the wound so that they can facilitate haemostasis and wound healing. They should also provide comfort for the patient, such 456 15 Wearable and Smart Responsive Textiles

as gas permeability, and no adhesion to the wound so that they will not cause trauma at removal [118]. More advanced requirements include odour management, microbial control, scar reduction, debridement of necrotic tissue, and other properties that accelerate the wound healing process [6, 116]. More and more new materials and technologies have been developed and introduced in the market for the use of dressings and bandages since the 1990s. In addition to maintaining the good absorbency of traditional cotton gauzes, new smart wound care materials have more advanced functions that better meet the requirements of the healing process. For example, bandages made of chitin fibres can accelerate the healing process because the glucosamine structure in the molecules of chitin has good biocompatibility with human tissue and chitin can enter bacteria cells and disturb their metabolism, also the hydrophilic groups in its molecules can retain moisture and make patients feel comfortable. Alginate fibres are ideal materials for wound dressings as their unique ion exchange property can swell the fibres in aqueous conditions. After cellulosic fibres are carboxymethylated, they become high absorbent fibres that absorb fluid near the wound directly into the fibre body instead of holding, which creates an environment of fewer microorganisms and makes dressing changes less painful [117]. In order to achieve multiple functions, modern wound care products adopt different composite structures with different materials in each part according to their uses. As Figure 15.6 shows, the most generally used structure is composed of three layers: the contact layer, the functional layer, and the retention layer. The contact layer provides a nonadherent interface with the wound which allows exudate to pass into the functional layer, and it can be made of polyamide nonwoven, polyurethane foam, etc. The functional layer absorbs and contains wound exudate and controls microbial growth, so it is made of superabsorbent and antimicrobial material. The retention layer secures the dressing onto the wound edge and provides both physical protection and a breathable path for oxygen in and moisture out. Therefore, it is often made of polyurethane films and hydroentangled nonwoven materials [6, 116, 135].

15.4.1.3 In the Patient ‘In the patient’ textiles are those applications such as artificial skin, artificial blood vessels, and artificial organs that are implanted into the patient’s body. These applications have higher requirements for the materials and technologies. Functional

Retention Layer Functional Layer

Contact Layer

Figure 15.6 Structure of modern composite wound care products. 15.4 Application of Smart Textiles 457 nonwoven materials combined with modern chemistries have played a significant role in human tissue engineering and have become an important component in medical smart textiles [116]. One classical example of in the patient medical textile is the artificial blood vessel. It should be biologically safe to the human body and physically stable during application, which means it should have proper porosity, stiffness, and flexibility so that it can be resistant to pressure. Also, it should be easy for suture at implanting surgery. Silk, polyester filament, and PTFE have been used to develop artificial blood vessels. Large artificial blood vessels with an inner diameter of more than 10 mm are usually made by weaving or knitting material and should have good stability and flexibility. The requirements of artificial blood vessels with small diameters (< 6 mm) are better satisfied by nonwoven technology and coating with biocompatible materials [119]. The fabrication of multifunctional blood vessels by electrospinning is currently enjoying a period of rapid development. Artificial organs and tissues include the kidney, pancreas, bones, soft tissues, etc. The textile materials to be implanted into the human body should be biocompatible, nontoxic, and have good strength and chemical stability. The porosity and surface roughness of materials as cell growth media also influence the growth of tissue cells nearby. Hollow fibres from regenerated cellulose, acetate cellulose, polyacrylonitrile (PAN), polysulfone, etc. are used to make artificial kidneys. The substitute materials for soft tissues include ossein, silk protein, cellulose, chitin, hydrogel, carbon fibre, etc. The hard tissue implanting materials for bones are high strength and high modulus composite materials made from carbon fibre, polyester fibre, ceramic fibre, etc. [116]. These days, in‐plant materials are made using micro‐ and nanofibres produced using electrospinning and other techniques. Electrospinning technology produces ultrafine and solid fibres with diameters at the nanometre level which have large surface areas, and so the biochemical characteristics of nanofibre mats are similar to the features of natural tissue. This has resulted in the wide application of polymer nanofibres produced by electrospinning in the field of biomedicine. For example, biocompatible and biodegradable polymers, such as polyglycolic acid (PGA) and polylactic acid (PLA) are often used as the base materials for implant devices and they can provide high efficiency in drug loading [120]. Figures 15.7 and 15.8 show the process of electrospinning and the diameter of nanofibres produced using electrospinning.

Polymer solution Nano bres Collector

Syringe Pump

High Voltage + –

Figure 15.7 Electrospinning set‐up. 458 15 Wearable and Smart Responsive Textiles

S4800 3.0 kV 9.7 mm × 10.0k SE(M) 4/12/2013 5.00 μm S4800 3.0 kV 9.7 mm × 10.0k SE(M) 4/12/2013 5.00 μm (a) (b) 90 84 120 80 100 68 100 70 62 80 60

80 y y 67 50 60 40 36 Frequenc Frequenc 40 30 29 22 20 17 20 10 10 10 8 1 3 2 1 0 0 0 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 1 0 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 1 Fiber Diameter Fiber Diameter microns microns (c) (d)

Figure 15.8 SEM images of untreated and treated nanowebs (a) and (b). Fibre diameter distribution histograms of untreated and treated nanowebs (c) and (d). Source: Reprinted with permission from Uday Turaga, Vinitkumar Singh, Rachel Behrens, Carol Korzeniewski, Sudheer Jinka, Ernest Smith, Ronald J. Kendall, and Seshadri Ramkumar. Breathability of Standalone Poly(vinyl alcohol) Nanofiber Webs. Industrial & Engineering Chemistry Research 2014 53 (17), 6951–6958 [121]. Copyright 2014 American Chemical Society.

15.4.2 Healthcare Applications

The application of smart textiles for healthcare and hygiene purposes is also very wide as they are necessities in our daily life. As elaborated earlier, there is a large market and huge space for the development of sustainable materials used to make baby or adult diapers, female hygiene products, and personal care wipers. With the development of economies and technology, and also the improvement of life quality, healthcare and hygiene products will not only grow in volume but also become more sophisticated and smart, with diverse functions, even built‐in performance indicators and warnings for disposal or change [118]. The common fibres used for healthcare products like incontinence diaper or wipes are: polyester, polypropylene, wood fluff, and viscose [122]. 15.4 Application of Smart Textiles 459

15.4.3 Sports and Fitness

Using smart textiles for sports and fitness involves more than just the fabrication of textile materials. It also means combining woven, knitted, or nonwoven materials with electronic technologies so that the device‐cum‐garment can monitor various aspects of the wearer’s body, such as body temperature, heart rate, blood pressure, or detect various activities, such as sweating, skin pH, moisture levels, etc. Wearable clothes for sports and fitness share some of the goals of healthcare appliances in the hospital, such as the result of the indicator points that reflect a person’s health condition, while the difference is smart textiles are more ‘smart’ and easy to use, which only require the wearer’s simple interaction, like a voice or gesture, instead of the complicated data doctors input in the hospital. Wearable devices also offer the possibility to monitor physiological signals continuously over long periods instead of a brief check only on visits to hospital [124]. Fibres and fabrics with a significant and reproducible change of properties according to specific environmental factor changes have been created using textile materials and processes, so they can be used as sensors or actuators [123]. Strain sensors in wearable outfits may be used in biomechanical analysis to provide interaction of posture detection, movement performance improvement, and injury reduction. For example, the Canadian company Heddoko has designed a set of smart compression clothing with textile embedded sensors that track the movement of body joints and provide live coaching feedback [125]. Chemical sensors could be used to detect the amount of sweat in athletic performance. Modified foams coated with conducting polymer or modified stretch knit fabrics can be incorporated into a garment to measure the breathing rate [126]. Figure 15.9 shows the functions of wearable sensors in sports.

Figure 15.9 Smart textiles system with monitoring functions in sports. 460 15 Wearable and Smart Responsive Textiles

The application of wearable textile technology in electronics partially overlaps with applications in other areas, such as healthcare, sports, defence, etc. In the medical field, long‐term monitoring and recording of the physiological signals of patients with chronic diseases requires electronic devices. In sports, smart clothes with sensors attached detect the activities of wearers to improve training regimens. For the military, wearable electronic systems can collect, process, and, crucially, give feedback on data pertaining to potential threats to soldiers on operations [124]. With the development of information technology, smart clothes not only serve basic functions like health and safety but also allow personal expression to satisfy the wearer’s fashion requirements. Clothes and other wearable products like handbags integrated with LED electronic parts show different dazzling colours in a dramatic way. For example, Luminex® is a fabric that can be illuminated by LEDs, as it is integrated with fibreoptic strands during the weaving process [124]. Clothes that have an ‘emotional effect’ can interact with their wearer ‘emotionally’. The electronic parts can detect the wearer’s bodily signals and reflect these back, thus ‘reflecting their emotional state’ [12]. Diverse innovative designs of textile based electronics can not only offer people aesthetic value but also provide different new functions by integrating sensors and electronics with numerous types of textile products to improve a person’s lifestyle. The integration of textile technology and electronic technology can greatly facilitate people’s lives and in many different ways. For example, a light and easily portable fabric key- board that can be rolled up was invented years ago [124]. Smart gloves, socks, and footwear with electronic sensors can control factors like temperature. Curtains or car seats can alert people to environmental changes [127].

15.4.4 Defence Applications

Smart textiles are applied in the military field for the protection of soldiers from chemical, biological, thermal, and additional external threats, such as high velocity projectiles [128]. Figure 15.10 shows the structure of a nonparticulate pad that can be used for chemical warfare decontamination. It is manufactured by needle‐punch technology, bonding three layers of viscose, activated carbon, and polyester fibres together. This dry decontamination pad can absorb a wide range of both liquid and gaseous chemicals, and can be applied to both the human body and a soldier’s equipment [129].

15.4.5 Conductive Ink on Textiles

Smart textiles with electronic parts that have a sensor or communication function to work with the wearer’s body have one major design issue. The hard electronic parts or stiff metallic fibres that have been developed to form the fabrics can compromise a garment’s comfort and/or breathability[130, 131]. One solution is to print functional conductive inks onto the surface of the textiles [130]. The printing of conductive inks on textiles has enjoyed rapid developmental break- throughs in recent years. The key determiner of this technology’s adoption and growth is ensuring the conducting property of the ink material and the flexibility of both ink and base materials, and to ensure that the ink will maintain a good durability after wearing or washing. 15.4 Application of Smart Textiles 461

Top absorbent layer Activated carbon fabric Bottom fabric layer

Cross section of the three-layered wipe

Figure 15.10 Nonwoven decontamination fabric and its structure [129].

Insulating upper cover layer Conductive wire Insulating lower cover layer

Fabric substrate

Figure 15.11 Structure of textiles printed with conductive ink.

Two printing methods are used in the production of a whole conductive patch: screen printing and stencil printing. As Figure 15.11 shows, the structure of conductive inks is printed on the textiles in the sequence such as first a lower insulated cover layer is printed, then the conductive layer is printed on top of it, and finally an upper insulated cover layer on top of the conductive wire is printed. Stencil printing is only for the printing of an encapsulation layer with an increased thickness around the electrodes [132]. The textile materials used as the substrate vary from fabrics made of natural or synthetic fibres such as cotton, viscose, polyester, and polyamide to blended fibres like cotton/polyester. Silver, gold, and copper have been used to make conductive wires [133, 134]. 462 15 Wearable and Smart Responsive Textiles

15.5 Sustainability and Ecological Aspects

In contrast to the positive and useful aspects smart textiles bring to human beings, they are now facing a critical challenge. There is growing concern about the ecological effects and sustainability of smart textiles [136–137]. Nanomaterials have been applied in smart textiles in different fields, because of their special properties: antibacterial (silver), UV protective (TiO2), electrically conductive (gold, carbon), etc. [140–141]. Some materials are not toxic when they are in their usual bulk state but they become toxic when they have nanostructures like nanoparticles or nanofibres. The small size of nanoparticles allows them to go through the exposure pathways and cross barriers easily, enter the inner organs and tissues, and damage the health of organisms. All aspects of their toxicity should be studied and settled into a series of related standards: mass, diameter, shape, and difference when taken through different pathways [138, 143]. The problems of what to do with the waste generated by manufacturing smart textiles, as well as the excessive energy consumed and the environmental hazards potentially produced during this process, not to mention the various demands of washing and maintaining smart clothes all highlight the sustainability challenge of textiles. Smart textiles promote a new marketing model called fast fashion, whose quick product turnover brings with it an environmental and economic burden [144]. Meadows et al. came up with the idea of holistic sustainability, which considers economic, soci- etal, and environmental sustainability together. Right now, it seems economy wins over the other two [138]. However, in order to reach holistic sustainability, a redefined con- sumerist culture and economy should be propounded. Moreover, a qualitative risk assessment of nano‐bio‐info‐cogno‐ (NBIC) smart technology has been conducted by Claudia Som and Lorenz M. Hilty [145]. The results assume the NBIC has great impact on traffic, housing, work, and health. Wearable sensors may impact the traffic situation by modifying the individual’s short‐term decision‐ making. The possible impact on housing involves human occupants focusing more on virtual environments than on the actual environment. The possible impact in the world of work is individuals who are not smart tech savvy being treated as though they were disabled. The possible impact on human health is the increased risk of privacy intrusion and ethical dilemmas [145]. Toxic and scarce materials in the electronic smart textiles also will lead to e‐waste, which has a severe environmental burden [141, 146–148]. This e‐waste is normally treated as normal waste right now, which is even worse for the environment. Besides e‐waste, chemical waste during textile production and use is a widespread problem. Most chemicals are not immediately toxic but have chronic effects on human health [149–151]. Researchers are increasingly focusing on monitoring and measuring smart textiles’ environmental impact [152, 153]. They believe the technology embedded in clothes – for example electronic textiles, phase change textiles, chromic textiles, shape memory textiles, and conductive textiles – can be used to encourage those activities that are environmentally sustainable. Fic et al. published a paper about future materials for electrochemical capacitors that suggested using by‐products from the food industry as a carbon precursor, for example coconut shells, various seeds, shells, coffee grounds, etc. [153]. Some other work has already been done to combine wearable technologies and environmental sustainability with textiles, for example clothes responsive to noise, light, and air pollution [154–156]. 15.5 Sustainability and Ecological Aspects 463

Before the issues surrounding sustainability can be tackled, researchers must understand that smart textiles are first and foremost user‐centric. And because of their high energy and raw material consumption, lack of long‐term functional durability (i.e. they become less waterproof, weatherproof, comfortable, easily stored, heat‐resistant, etc., over time) and the difficulty in recycling them, their impact on public health and the environment can be quite significant [136–139]. Niu has suggested several methods of recharging wearable electronics that are convenient for wearers and could elongate battery life: generating power from the wearer’s body movement, using human food as a power source, especially for soldiers, and recovering power from the sun and radio transmissions [157]. Genuinely sustainable smart textiles can have a positive impact on both society and human beings [137]. Many users abandon smart textiles after wearing them only a few times. The main reason for this seems to be designers’ lack of understanding of the requirements of long‐ term usability. Sustainable smart textiles, as the name indicates, means designing smart textiles and applications that have a positive effect on humans, public health, and society at large without causing environmental hazards [137]. The idea of increasing the service life of textiles by creating enriching stories is promoted based on the definition above [137]. Electronics textiles with sensors can contact skin and response with environmental data, which could promote data visualization and experience surrounding environment. Shape memory textiles could sense data and express either positive or negative responses, which would enhance and stimulate the relationship between textile and wearer [137]. The major considerations for sustainability are material selection, possible waste production, and waste treatment. Possible waste production and waste treatment can be improved by changing consumer consumption habits and modifying production processes [136]. Marilyn Waite mentioned using bamboo as a raw materials because it is more environmentally friendly than common polymers and natural fibres, because of its biodegradability and renewability [158]. Moreover, designers should also consider experience based design from the perspective of customers. Usually, five elements should be considered when designing sustainable smart textiles: (i) comfort, (ii) interaction and communication between smart textiles and their surroundings, (iii) to sense change in both the wearer and their surroundings, (iv) respond effectively to visible signals, and (v) functionality [137]. Kristi Kuusk [136] conducted research into sustainable smart textiles. He concluded sustainable smart textiles have eight issues: controlling energy and chemical use, minimizing consumption, caring for longevity, developing constantly, updating the product, supporting meaningful creation, building relationships, and empowering positive emotions. Reducing energy and chemical use means reducing toxins during production and use. Caring for longevity means paying attention to a product’s durability. Supporting meaningful creation is about inspiring consumers’ creativity. Developing constantly means using the same products for different purposes to improve their service life. Building relationships is about creating relationships between consumers and smart textiles. Empowering positive emotions is about enhancing a garment’s use and its wearer’s comfort. Besides that, economy and market sustainability are also important. Irene Pasqualotto’s thesis talked about the circular economy and textile recycling market opportunities. 464 15 Wearable and Smart Responsive Textiles

‘Circular economy’ means integrating and managing the different aspects of sustainability, for example utilizing renewable energy and waste and avoiding waste generation and clean production [159]. Aparna Sharma conducted a study about eco‐friendly textiles and sustainable textile production processes [160]. It concluded that smart textiles need to be kept in use as long as possible to maximize their value by providing an emotional connection between products and the humans who use them.

15.6 Conclusion

Developments in smart and wearable textiles have had a great impact on daily life in recent years. These textiles have a large range of applications, for example wearable electronics, barrier membranes, PCMs, shape memory materials, optical materials, and other functional textiles, which provide convenience, comfort, and sense of technology to satisfy humans’ imagined and dreamed smart life. Areas that use smart textiles include architecture, automotive design, fashion and entertainment, military, healthcare, sport and fitness, among others. From a research point of view, this field has attracted a wide array of groups and funding. Some of the major challenges facing this field are cost, logistics, durability and textile‐like feel and hand. These challenges need to be tackled to make smart textile products a mainstay of the textiles sector. This chapter has analysed the definitions, categories, functions, applications, and sustainability of smart textiles. The topics covered here show that interdisciplinary research is necessary for designing smart textiles, including computer and sensor technology, material research, engineering, fashion design, marketing analysis, etc. To avoid possible waster production, chemical pollution, energy consumption caused by design defects of wearable textiles, an eco‐friendly and sustainable design method should be proposed. In future, new technologies – such as advanced nanotechnologies, electronic technologies, computer technologies, etc. – will play an important role in determining the next generation of smart textiles. In the meantime, empowering positive emotional interactions between smart textiles and their consumers will encourage the longevity of smart textiles and decrease the pollution they cause. Therefore, user‐oriented technology development, ecological design, and fashion design should be integrated for future smart textile design.

Acknowledgements

The authors would like to acknowledge Abdul‐Hamid Cherissa at TTU Health Sciences Center for her help with some discussions on the chapter.

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Index a Air permeability 4, 50, 97, 115, 144, 173, Abrasion resistance 14, 24, 107, 113, 121, 179, 180, 223, 225, 229, 232, 243, 122, 126, 128, 145, 170, 172, 173, 285, 298, 308–309, 329, 333, 358, 228, 243, 290, 324, 356, 357, 359, 378, 379 361, 363 Air pollutants 217, 219 Absorbents 1, 2, 23, 38, 39, 51, 53, 97, 116, Air structures 322–325, 348 295, 299, 379, 456 Air supported structure 322–323 Accidents 5, 107, 290, 301, 377, 397 Ammunition 197–202 Acoustic textiles 368–369, 379 Antennas 15, 60, 444 Activated carbon 17, 20, 217, 368, Antifouling 8, 16, 94, 232, 385, 447, 460 394–395, 400 Active cooling system 134, 137–138 Antimicrobial textiles 31, 93–95, 99 Active materials 21, 42, 58 Antistatic properties 13, 19, 42 Active sportswear 42, 44, 45, 48–50, 57 Application areas 1–3, 7, 8, 61, 279, Active textiles 57–58 355–369, 428, 453 Aerogel 12, 20, 116, 120, 187, 400, Applications 2, 4, 8, 9, 14, 15, 20–23, 29, 402, 403 31, 39, 46–57, 59–61, 69, 70, 72–76, Aeronautic textiles 1, 9, 407–433 84, 86, 87, 90, 93, 94, 125, 133, Aeroplanes 8, 9, 354, 421, 427, 428, 432 206–208, 215, 219–221, 227–229, Aerospace industry 370, 390, 408–414, 240–242, 251, 253, 260, 279–295, 418, 421, 423, 426, 432 305, 306, 308, 310, 320, 322–325, Agrotech 2 346–347, 353–376, 385–403, 407, Agrotextiles 3, 7, 279–312 409–417, 419–428, 431, 440–443, Airbags 2, 353–355, 361, 363–366, 445–449, 452–461, 463 379, 411 Aprons 5, 107, 140, 141, 147, 241 Airborne particulate matter 5 Aramid fibre 111–113, 123, 177, 387, 399, Aircrafts 8, 9, 125, 354, 355, 370, 371, 374, 410, 411, 421 400, 407, 409–412, 414, 417, 419, Architectural fabric structures 8, 320–322, 420, 423, 426–428, 432, 433 349 Air filtration 99, 217, 218, 222–223, 228, Architectural textiles 319–326, 348, 349 230, 354 Atmospheric pressure plasma jet Air inflated structure 322, 323 (APPJ) 16 Air‐jet‐spun yarns 171–172 Autoclave 12, 423–424, 433

Automotive industry 29, 354, 361–363, Carbon fibre 108, 110, 112, 115, 124, 127, 370, 371, 375, 376, 379, 380, 423 177, 221, 254, 342, 343, 370–372, Automotive interior 359, 369, 376–379 387–388, 392, 394, 398, 399, Automotive textiles 8, 353–380 408–410, 421, 427, 429, 430, 457 Awnings 8, 241 Carbon nanotubes (CNTs) 14, 108, 116, 137, 165, 386, 403, 412 b Car covers 2 Ballistic protection 202, 448, 449 Carpets 1–3, 8, 11–13, 15, 19–21, 24, 27, Ballistic resistance 141 29, 32, 353–355, 359, 360, 369, 379, Balsa 389–390 385, 397 Barrier membranes 9, 331, 440, 447, Cellulose 18, 20, 30, 39, 40, 78, 118, 131, 464 163, 216, 219, 244–246, 248–250, Basalt fibres 253, 254, 343 257, 258, 282, 283, 293, 308, 339, Bast fibres 1, 7, 12, 31, 38, 220, 244, 249, 340, 414, 457 250, 340, 341, 413–415 Characterization 206, 230–232, 275, 301, Binders 30 302, 304, 306, 309, 408, 440 Biocompatibility 83–86, 97, 456 Chemical, biological, radiological and Biodegradability 31, 40, 84, 85, 257, 260, nuclear (CBRN) 6, 13, 132, 137, 280, 282, 285, 298, 306–308, 413, 146, 197, 206–211 415, 463 Chemicals Biodegradable plastics 18, 306, 307 characterization 231–232 Biohazards 5 resistance 7, 209, 252, 282, 386, 388, Biopolymers 93, 98, 217, 219, 220, 448 282–283, 290, 295, 300, 308 treatments 3, 21, 44, 51, 131, 206, 227, Bioresorbability 83–85 368 Biostability 83–85 Chemical vapour deposition 3, 217, 412, Blood vessels 76, 78, 138, 456, 457 439 Boats 8, 288, 329, 330, 354, 370, 389, 397, Chenille yarns 14 399, 422 Chitosan 17, 80, 93, 98, 219, 282, Body armour 5, 6, 107, 121, 132, 133, 137, 402, 416 141, 199–202, 447, 448 Chromic textiles 452–453, 462 Braiding 240, 260, 345, 353, 375, 394, 408, Classification 22, 70–72, 141, 176, 286, 419, 431, 433 354–355, 408, 428 Breathability 6, 7, 38, 39, 44, 46, 81, 82, 87, Clothing 128, 132, 138, 217, 312, 359, 377, cold protective 51–53 378, 447, 453, 458, 460 comfort 54, 107–109, 131, 133, 134, Bridges 6, 94, 319, 342, 346, 347 136–138, 377 Building textiles 12 Clothtech 2 Buildtech 2 CNTs see Carbon nanotubes (CNTs) Bulletproof vests 110, 132 Cold weather sports 51–54 Burn 13, 24, 60, 79, 89, 124, 125, 130, 139, Comfort 4–6, 8, 9, 11, 37–62, 69, 70, 140, 163, 184, 204, 207, 208, 326, 81–83, 97, 107–109, 121, 125, 362, 365, 386, 395 131–138, 141, 148, 159, 160, 183–189, 205, 206, 326, 329, 335, c 354–356, 358, 359, 363, 368, Calendering technique 226 376–379, 385, 426, 439, 447, 450, Capillary mats 2, 280, 295, 298, 299 451, 453, 455, 460, 463, 464 Index 477

Composites Development 3, 4, 7, 9, 15, 18, 29, 32, 37, fabrics 21, 173, 177, 455 40–46, 59, 61, 62, 84, 85, 90, 91, 93, material finishing 425–426 96, 107, 120, 134, 165, 182, 187–188, materials 373, 420, 432, 433, 457 212, 221, 240, 261, 269, 272, 273, Compression testing 429–430 279–283, 290, 295, 312, 320, 339, Conductive inks 14, 440, 443, 460–461 343, 349, 353, 358, 359, 364, 365, Conductive polymers 14, 19, 137, 453 374, 376, 380, 385, 389, 395, Construction textiles 7–8, 319–349 397–399, 403, 409, 413, 414, 416, Controlled release 4, 79, 283 428, 439, 440, 444, 445, 453, 455, Core fabric 391 457, 458, 460, 464 Core materials 386, 389–391, 422 Diapers 20, 97, 446–447, 458 Cotton 11, 15–17, 19, 20, 23, 26, 27, 30, Down fibres 116–118, 120 37–41, 43, 44, 47, 51, 53, 55, 70, 71, Drainage 2, 6, 242, 266, 267, 308, 329, 332 82, 93, 95, 96, 99, 108, 116, 136, 148, Drug delivery 76, 80, 86, 95 162–164, 173, 204, 206, 219, 220, Durability 3, 6, 11, 13, 16, 25, 32, 40, 42, 225, 226, 241, 244, 248, 250, 257, 44, 48, 93–96, 99, 108, 109, 113, 121, 258, 281, 288, 294, 295, 300, 307, 122, 125, 127, 128, 133, 138, 141, 339–341, 353, 356, 366, 367, 379, 215, 232, 244, 247, 260, 279, 285, 386, 399, 400, 413, 414, 443, 445, 290, 291, 295, 298, 306, 323–325, 453, 456, 461 329–331, 333, 341, 356, 359, 363, Crops 370, 397, 409, 412, 414, 443, 444, covers 2, 279, 280, 283, 286, 291, 460, 463, 464 294–298, 310 Duvets 11–13 protection textiles 279–312 Dyed fabrics 16, 177 Cross‐linked PVC foam 390 Dyed fibres 166–167 Curtains 3, 11–13, 15, 20, 25, 27, 95, 206, Dyed yarns 168, 172–173 242, 282, 354, 365, 442, 460 Cut hazards 121–122 e Cut resistance 113, 121, 122, 141, 147, 285 Ecological aspects 26–32, 62, 98–100, Cyclodextrin 18 232–233, 272–274, 311–312, 403, 432, 462–464 d Ecological issues 141, 148, 340, 347–349 Decision making 55–57 e‐health system 85, 87, 88, 93 Defence applications 426, 460 Electromagnetic radiation 14, 305, 452 Degradation 7–8, 31, 39, 84, 86, 99, 108, Electromagnetic shielding 14 110, 112, 113, 136, 243, 244, 247, Electrospinning 76, 79, 217–219, 221– 250, 251, 256–260, 280–282, 284, 223, 232, 283, 415–417, 457 290, 295, 298, 305–307, 311, 342, Electrospun nanofibrous 400, 401 386, 392, 394, 398, 431, 448 Embankments 6, 242, 310 Design 6, 7, 9, 14, 16, 19, 27, 29, 41, 54, 55, Emergency situations 2 57, 82, 109, 131, 138, 159, 160, 177, Empennage 428, 433 197, 215, 229, 240, 284, 325, 326, Energy efficiency 8, 334, 335, 348, 349 333, 343, 346–349, 353–356, 358, Engine compartment items 367–368 364, 365, 369–371, 377–379, 385, Engineered structures 5, 148 395, 399, 403, 407, 417–420, 427, Environmental impacts 15, 19, 20, 27–29, 428, 431, 432, 439, 441, 444, 448, 31, 62, 94, 98, 141, 148, 215, 273–274, 460, 463 291, 295, 312, 349, 413, 432, 462 478 Index

Environmental protection textiles 6–7, Fitness 9, 453, 459–460, 464 239–275 Flame protection 125 Epoxy resin 374, 389, 392, 412, 423, 424, Flame‐retardant (FR) 2, 8, 13–15, 28, 108, 427 122, 123, 125, 130, 131, 136, 148, Erosion control 2, 6, 267, 292, 308, 310 162, 197, 204–208, 210, 211, 216, e‐textiles 3, 15, 19, 20, 29–30, 32, 88, 227, 385 90, 98 Flax 1, 12, 31, 98, 162–164, 220, 221, 244, 246, 249–252, 258, 281, 291, 340, f 349, 353, 371, 413–414, 421 Fabrication 162, 179, 183–187, 243, 395, Floating row covers 291–295, 311 400, 416, 439, 442, 443, 457, 459 Fluorochemical resins 16 Fabrics Food packaging 17, 19, 25, 93 constructions 49, 52, 53, 136, 223–226 Friction‐spun yarns 171, 172 structures 8, 15, 23, 42–45, 52, 82, 108, Fuel efficiency 8, 370, 371, 410 119, 121, 136, 215, 229, 240, 310, Functional finishing 2–4, 9, 43, 210–211, 320–323, 349, 356, 368, 374, 450 225–227, 325 weight 126, 127, 296, 310–311, 398 Functional materials 5, 9, 55, 148, 412 Fatigue testing 431 Functional performance 5, 71, 109, Feather fibres 115, 118 159–162, 183, 184, 188, 189 Fibreglass 253, 325, 338–340, 372, 387, Functional sportswear 4, 46–48 390–392 Furnishing fabrics 14, 16, 397 Fibreglass reinforced plastic (FRP) Fuselage 409, 411, 423, 427, 428, 433 planking 390–391 Fibres g diameter 21, 78, 115, 118, 222–223, Geogrids 6, 7, 239, 241 230, 243, 429, 447, 458 Geometrical characterization 230–231 reinforced composites 1, 220, 227, 319, Geonets 7, 241 372, 374, 414, 422–424, 426, 427, Geotech 2 431, 433 Geotextile composites 6 Fibrillated tape yarns 224–225 Geotextiles 1, 3, 6–7, 220, 239–275, 302, Fibrous filters 217–219, 222 303, 308 Fibrous insulating materials 335–340 Glass fibres 6, 12, 110, 204, 220, 227, 228, Fibrous materials 70, 115, 280, 319, 320, 253, 254, 325, 338, 339, 343, 371, 326, 333, 335, 339, 340, 343–346, 386–387, 393, 397, 408, 410–411, 409, 414 413, 414, 421, 422, 424, 427, 428 Filters 2, 6, 8, 72, 215, 217–219, 222–228, Gloves 5, 12, 41, 107, 115, 119, 132, 230, 232–234, 239, 267, 308, 138–141, 208, 209, 446, 460 353–355, 367–368, 379 Graphene 14, 403, 412 Filtration efficiency 97, 218, 219, 222, 223, Ground covers 283, 284, 291, 292, 294 225–228, 230, 368, 402 Growing medium 295, 300, 301 Filtration media 6, 215, 223, 368 Filtration textiles 3, 6, 215–234 h Finished fabrics 2, 178–179, 189 Hand lay‐up technique 420–421 Fire hazards 5, 139 Hazardous situations 5 Fire resistance 13, 15, 130, 209, 324, 326, Hazardous waste control 2 330, 395 Healthcare textiles 31, 69–100 Fishing nets 284, 285, 287–290, 303, Heat bonding 6, 267 308, 312 Heat protection 125 Index 479

Heat‐setting process 225–226 Insulative materials 116, 119–121 Helmet 5, 107, 141, 199, 200, 203, 208, Intelligent textiles 4, 5, 61, 444 354, 355, 365, 366 Interior carpet 359–360 Hemp 1, 12, 26, 31, 38, 116, 163, 220, 221, International regulatory bodies 5 244, 246, 249–252, 281, 288, 291, Internet of things (IoT) 61, 62 339–341, 349, 353, 371, 408, 413, 414, 421 j High activity 4, 50, 55, 62 Jackets 42, 116, 119, 122, 138, 139, High performance applications 20–23, 159, 400 46–57, 72–76, 228–229, 285–295, Jerseys 46, 47 353, 423, 426–428, 433 Jute 1, 11, 17, 31, 38, 163, 220, 244, 246, High performance textiles 3, 4, 9, 11, 12, 247, 249–252, 254, 255, 258, 259, 108, 110, 115–131, 133, 215, 216, 262, 263, 274, 281, 291, 292, 295, 220, 227, 372, 379, 380, 407, 426, 300, 307, 308, 311, 349, 413–415 429, 431, 432, 455 k Hometech 1 Honeycomb core 389, 390, 410 Kapok 115, 116, 118–119, 244 Horticulture 7, 279, 283, 294, 295, 302, Kenaf 1, 12, 38, 220, 221, 244, 349, 304, 306, 308 366, 415 Hot weather 55 Key issues 160, 187–189, 386, 397 Household textiles 3, 12–16, 19–21, 23–32 Knife 121, 141, 184, 197, 199, 202 House wraps 2, 8, 319, 326–334, 336, 349 Knitted fabrics 7, 12, 16, 23, 43, 119, 125, materials 327, 330–334 130, 160, 172–175, 228, 229, 240, Hovercrafts skirts 398–399 242, 262, 284, 285, 289, 291, 297, 372, 373, 393, 415, 421, 442, 444 i Knitted reinforcement structures 393 Impact resistance 261, 301–304, 376, 380, Knitting 16, 21, 91, 137, 160, 168, 175, 390, 393, 410, 418 189, 240, 260, 262, 285, 345, 353, Incontinence products 446–447 356, 359, 372–375, 394, 408, Industrial textiles 6, 233, 240, 241 418–419, 426, 431, 433, 442, 457 Indutech 2, 354 Inflatable craft 399 l Injection moulding 369, 422–423 Lamination 12, 15, 18, 19, 44, 60, 78, 108, Injury 121, 139, 184, 197, 204, 361, 365, 269, 270, 272, 376, 379, 451, 452 366, 379, 459 Land reclamation 2 Inkjet printing 14, 19, 183 Law enforcement personnel 197–211 Inner layer 21, 53, 78, 125, 136, 271, 426, 447 Layered clothing 53–55 Inorganic fibres 112, 124, 163, 335, Lifecycle assessment (LCA) 20, 27, 29, 338–339, 410 98, 148 Insect repellence 13, 14 Lightweight 3, 4, 7–9, 12, 15, 22, 23, 32, Insulating felts 366 39, 43–46, 51, 53, 55, 90, 108, 116, Insulating materials 13, 335–340 125, 127, 129, 137, 176, 177, 188, Insulation 2, 3, 6, 8, 12, 13, 21, 38, 40–43, 267, 295, 319, 323, 346, 348, 349, 51–53, 57, 81, 115, 116, 118–122, 359, 360, 363, 370, 372, 374, 375, 125, 131, 133, 138, 139, 173, 182, 188, 390, 398, 409, 410, 420, 426, 433, 447 220, 221, 253, 319, 320, 323, 326, Linear PVC foam 390 334–341, 349, 354, 355, 360, 361, 366, Linen 11, 12, 15, 16, 32, 257–259, 413 368, 369, 378, 395, 409, 410, 414, 427 Low active sports 51–54 480 Index

m Membrane 6, 9, 44–46, 53, 54, 79, 94, 110, Manikin 52, 138, 139, 180, 183–187, 189, 113, 115, 120, 125, 127, 138, 148, 187, 207 188, 210, 215, 218, 219, 222, 223, Manufacture/manufacturing 230–232, 283, 292, 320, 322–327, processes 2, 148, 160, 189, 241, 331, 332, 348, 400, 402, 440, 447, 464 273–275, 361–362, 379, 388, 393, Meshes 6 407, 408, 417, 418 Microbial hazards 108, 140, 148 techniques 6, 19, 197, 211, 260–272, Microclimate 50, 52, 81, 82, 132, 134, 136, 345, 408, 409, 415, 417, 419–422, 137, 182, 280, 285, 291, 294, 378, 426, 433 379, 450 Marine applications 9, 385–403 Microorganisms 7, 17, 25, 93–96, 141, Marine composites 392 247, 253, 256–258, 260, 280, 281, Marine safety apparatus 400 283, 307, 368, 394, 456 Marine textiles 8–9, 385–403 Mildew 6, 39, 41, 289, 311, 325 Masks 1, 5, 97, 107, 141, 447, 448, 455 Military Mass coverage 222, 223 textiles 3, 6 Material properties 209, 242, 322, uniforms 6 362–363, 428, 455 Milkweed 116, 119 Material requirements 323–326, 349, 426 Mineral fibres 220, 253 Mattress 15, 24, 29, 91–93, 97 Mobility 6, 109, 141, 197, 243 Measurement 24, 26, 50, 52, 60, 87, 88, 91, Mobiltech 2, 354, 355 96, 182, 208, 229, 308–310, 357, 430, Moisture management 37, 39, 41, 44, 47, 444 50–51, 108, 115, 116, 118–120, 125, Mechanical behaviour 301, 304, 325, 358, 136, 138, 188, 333 386, 397 Moisture sensation 53, 378–379 Mechanical characterization 232, 301, 302 Monofilaments 6, 223–225, 230, 274, 285, Mechanical fixation 268–269 307, 309, 373, 443 Mechanical hazards 109, 111, 112, Mulch mats 281, 283, 284, 291, 292, 294 140–141 Multifilaments 6, 224–226, 274, 288, 290, Mechanical properties 4, 7, 12, 23, 26, 39, 372, 411 42, 78, 84, 110, 111, 113, 124, 125, Multiple criteria 55–57 133, 221, 230, 232, 243, 245, 251–255, 262, 285, 298–305, 307, n 325, 344, 345, 359, 371, 374, Nanofibres 1, 5, 76, 78–80, 82, 165, 176, 386–388, 390, 392–394, 397, 409, 188, 217–223, 230–232, 240, 412, 413, 415, 418, 419, 426, 427, 283–284, 400–402, 408, 412, 416, 443, 444, 452 432, 457, 462 Mechanism 18, 51, 52, 80, 81, 94, 113, Nanotechnical fibres 216–219, 408–412 120, 130, 138, 204, 217–218, 228, Nanotechnology 2, 3, 20, 32, 43, 76–80, 256, 257, 283, 284, 368, 395, 429, 100, 107, 108, 188, 385, 416 441, 443–445, 449, 450, 452 Natural fibres 5, 16, 18–20, 27, 31, 37–39, Medical textiles 3–5, 69–100, 440, 447, 41, 98, 108, 125, 148, 161–164, 173, 455, 457 216, 219–221, 239, 244–251, 253, Medicine 69, 76–80, 220, 353, 443, 453 254, 257, 260, 280–282, 288, 291, 295, Medtech 1, 69–70, 100 300, 307, 308, 312, 339, 340, 349, 353, Melt‐blown fabrics 229 369, 371, 407–409, 413, 414, 432, 463 Index 481

Naval ships 399 Performance 1, 2, 4–7, 9, 11, 17, 19, 23, Needlefelts 225, 226, 228 24, 26, 29, 30, 37, 38, 43, 44, 46, 48, Needle punching 6, 228, 239, 267, 268, 50, 55, 58, 59, 71, 95, 97, 99, 109– 271, 273, 284, 291, 292, 311, 361, 111, 113, 118–122, 125, 131, 133, 366, 420, 460 136, 138–141, 148, 159, 160, 162, Nets 12, 269, 280, 283–291, 298, 303–306, 180, 183–186, 188, 200, 210, 215, 308–312, 385, 408 220, 222, 223, 240–243, 253, 279, Nonpolymeric fibres 244, 253–254 283, 290, 295, 298, 305, 306, 323, Nonwovens 325, 329, 330, 338, 340, 343, fabrics 6, 17, 29, 108, 119, 160, 173, 356–359, 364, 369, 370, 372, 373, 175–177, 188, 221, 229, 243, 260, 377, 385, 387–389, 396, 398–400, 267, 268, 308, 311, 345, 415 409, 410, 420, 424, 426, 429, 431, structures 71, 243, 268–272 441, 443, 446–449, 455, 459 Nylon 9, 23, 42–45, 81, 93, 107, 114, 119, Performance tests 230 121, 122, 148, 163, 165, 216, 226, Perishable products 17 251, 282, 353, 356, 359, 361–364, Permeable fabrics 6, 53, 239 366, 367, 369, 387, 389, 398–400, Personal protective clothing (PPC) 3, 5, 407, 426, 448, 449, 453 159–189 Phase change materials (PCMs) 9, 41, 42, o 82, 83, 108, 116, 119, 133–137, 188, Occupational hazards 5, 107, 208, 440, 450–452, 464 159 Photocatalysis 20 Occupational safety 5, 254 Piezoelectric sensors 445–446 Oekotech 2 Plasma treatment 3, 95, 225, Oil spill management 7 227, 260 Oil‐water separation 400–403 Police 6, 132, 141, 159, 197, 199, 201–206, Omnidirectional reinforcement 208, 209, 211 structures 393 Pollutant capture 217–218 Optical properties 298, 324, 441 Polyamide (PA) 1, 6, 7, 11, 15, 27, 37, 38, Optical textiles 440–443 46, 51, 71, 84, 107, 108, 204, 218, Organic fibres 163, 338–340 219, 244, 251, 282, 283, 311, 387, 389, 400, 408, 442, 443, 445, 448, p 456, 461 Packaging textiles 3–4, 11–32 Polyester 1, 11–17, 20, 23, 27, 30, 37, 71, Packtech 1 84, 93, 107, 108, 114, 115, 119, 121, Parameters 13, 14, 23–25, 27, 28, 56, 60, 134, 148, 162, 163, 165, 173, 206, 88, 89, 92, 94, 97, 99, 222–223, 240, 216, 227, 228, 244, 251, 258, 274, 242, 243, 249, 250, 262, 268, 282, 320, 324–326, 353, 361, 387, 270–272, 304–306, 309, 325, 326, 388, 392, 393, 395, 397–399, 407, 331, 336, 359, 365, 372, 374, 377, 408, 411, 421, 424, 432, 443, 453, 379, 423, 440, 441, 444, 448, 450 457, 458, 460, 461 Patients 4, 5, 69, 70, 72, 82, 87, 89–93, 96, Polyester resin 388, 424 100, 139, 140, 442, 446, 455–458, Polyethylene (PE) 7, 17, 25, 40, 107, 108, 460 110, 111, 114, 121, 134, 135, 244, Patterning 53, 57 251, 257–259, 274, 282, 283, 332, Perception 53, 57, 377, 378 333, 343, 387, 389, 398, 442 482 Index

Polymers 9, 14, 18, 69, 80, 84–86, 107, 108, Property requirements 329–333, 336 110, 113, 119, 133, 134, 137, 165, Protech 2 216–220, 231, 232, 244, 253, 257–259, Protection 6–8, 14, 16, 17, 26, 53, 90, 282, 283, 290, 291, 293, 295, 307, 312, 107–141, 160, 188, 197–206, 209, 319, 365, 370, 395, 407, 408, 413, 416, 210, 225, 227, 239–275, 279–312, 421, 422, 432, 433, 440–442, 445–447, 353, 425, 427, 440, 447–450, 453, 452, 453, 457, 463 455, 456, 460 Polymethacrylimide (PMI) foam 390 Protection barriers 285–287 Polypropylene (PP) 6, 14, 18, 37, 41, 71, Protective materials 107, 113, 120, 125, 96, 107, 108, 219, 224, 228, 244, 252, 141, 199–201, 211, 449, 450 282, 333, 343, 359, 366, 368, 369, Protective textiles 3, 5, 107–148, 159–189, 372, 374, 389, 446, 453, 458 211, 222 Polystyrene 18, 219, 244, 326, 336, 366, Pultrusion 419, 424–425, 433 389, 390 Puncture 6, 109, 111, 112, 128, 133, 145, Pore size 79, 217, 221–223, 230, 231, 275, 302, 325, 331, 398 416, 447 q Porosity 7, 15, 78–80, 82, 115, 231, 233, Quality control 23–26, 61–62, 95–98, 242, 243, 249, 250, 262, 283, 285, 229–232, 428–431 305, 309, 368, 398, 400, 403, 457 Quality standards 397–403, 423 Principle 14, 40, 41, 45, 87, 88, 92, 166, Quasi‐yarn formation 269–270 167, 170–172, 174–179, 184, 252, 268–272, 295, 322 r Printed electronics 22 Radiation 8, 14, 15, 25, 26, 51, 58, 82, 108, Printed fabrics 177–178 109, 115, 120, 124, 139–140, 142, 144, Production 6, 7, 14, 19–21, 23, 27–29, 168, 280, 286, 287, 289, 290, 295, 298, 39–41, 46, 53, 69, 71, 72, 98, 99, 133, 304, 306, 311, 325, 331, 335, 356, 385, 148, 167, 168, 170–172, 175–177, 386, 424–427, 448, 449, 452, 455 215, 220, 221, 225, 226, 233, 251, 252, Radiative properties 304–306 261, 270–273, 279, 282–284, 291, Radiofrequency identification (RFID) 305, 306, 311, 340, 343, 344, 348, 353, systems 22, 23 354, 356, 358, 372–374, 389, 408, Raising finishing process 226 409, 412, 413, 416, 418, 421, 425, 442, Recyclability 10, 62, 99, 358 443, 445, 446, 453, 455, 461–464 Regenerated fibres 38–40, 112, 124 Properties 1, 2, 7, 9, 11–19, 30, 31, 38–41, 43, Reinforcement fabrics 366, 391–394 46, 49, 50, 52–55, 71, 78, 79, 81–84, Reinforcement materials 242, 342–345, 86, 95, 97, 108, 110, 111, 115, 116, 355, 367, 386–388, 391, 394, 403, 410 118–121, 124–126, 130, 131, 133, 134, Reinforcing fibrous materials 343–346 137, 138, 141–147, 161–163, 165, 167, Renewable natural resources 1, 220 168, 173, 174, 178–180, 182, 197, 204, Requirements 4–9, 19, 24–26, 37, 39, 44, 209, 210, 215–221, 223, 230, 232, 242, 46–56, 62, 78, 98, 109, 121, 126–128, 245, 251–254, 256, 260–263, 268, 133, 134, 138–142, 144, 145, 160, 165, 282–285, 291–306, 311, 322–325, 331, 168, 174, 181, 183, 201, 204–206, 208, 333, 341, 343–346, 356–359, 361–364, 215, 229, 244, 269, 275, 279, 280, 284, 367–369, 371, 372, 375–379, 385, 386, 288, 304, 312, 323–326, 329–334, 336, 388, 390–403, 407, 409, 412, 413, 415, 342–343, 349, 354–360, 364, 367, 374, 418–420, 425–433, 440, 441, 443–449, 379, 385, 395–398, 407, 415, 420, 422, 451, 452, 455, 456, 459, 462 423, 426–428, 455–457, 460, 463 Index 483

Resin 15, 44–45, 187, 366, 368, 370, 374, repellent 16, 28 376, 380, 386, 388–395, 398, 403, Space industry 412, 428 420–425, 427–431, 433 Spacesuit 9, 41, 134, 407, 426–428, Responsive textiles 3, 9, 10, 349, 452 439–464 Space textiles 9, 407–433 Ring‐spun yarns 168–170 Spandex 9, 42, 44, 407 Roof headliner 360–361 Special fibres 41–42 Root protection 291 Special finishes 45–46, 108 ROTIS technology 272 Spectra fibre 387 Rotor‐spun yarns 170, 172 Spinning 14, 20, 39, 43, 82, 97, 110, 130, Row covers 291, 296, 298, 311 131, 141, 160, 161, 165, 166, 168, R‐value 336–341 169, 171, 172, 189, 217, 218, 229, 233, 244, 250–252, 346, 411, 412, s 415–417, 433, 451 Sails 398, 413 Sports 1, 3–5, 9, 37–62, 89, 370, 409, 426, Seatbelts 353–355, 361–363, 365 433, 440, 453, 459–460, 464 Seat covers 3, 354–359, 378, 379 Sports textiles 3, 4, 37–62 Seating comfort 377 Sporttech 1 Seawater 8, 109, 250, 288, 385, Spunbonded fabrics 229 392, 398 Stab resistance 141 Self‐cleaning 12, 20, 228, 232, Standard nonwovens 267 325 Standards 5, 6, 11, 23–26, 29, 41, 50, 53, Self‐healing 412, 431–432 95–97, 107, 121, 133, 138–147, 167, Sensors 4, 9, 14, 22, 23, 32, 45, 59–61, 173, 179, 180, 183–185, 206, 207, 87–93, 137, 184, 185, 188, 349, 365, 215, 295–312, 329, 342, 348, 349, 379, 440, 441, 443–447, 459, 460, 356, 363, 380, 397–403, 410, 414, 462–464 423, 429, 430, 433, 462 Shading 2, 7, 279, 282, 289, 290, 297, 305, Staple‐fibre yarns 42, 225, 226, 228 310 Stiffness 1, 7, 113, 200, 220, 227, 244, 250, Shape memory materials 9, 119, 440–442, 264, 285, 290, 301, 321, 324, 325, 464 357, 372, 387, 389, 391–393, 397, Sharp weapon protection 197–203 409, 419, 420, 426, 428, 430, 431, Shear testing 430 433, 446, 457 Ships 8, 94, 208, 274, 385, 394, 397, 399, Stitching 14, 183, 240, 261, 373, 394, 403, 413 419–420 Shoes 2, 4, 5, 107, 241, 452 Strength 1, 7–9, 12, 23, 24, 42, 110, 121, Silicone 116, 120, 127, 187, 210, 211, 325, 125, 136, 141, 169, 173, 177, 217, 363, 401 219, 220, 224, 227, 232, 249, 250, Singeing 226 254, 267, 281, 282, 284, 286, 288, Skiwear 42, 43 290, 291, 301, 304, 319, 323, 325, Smart garments 58–61 331, 341, 343, 348, 356, 357, 359, Smart structures 134, 136–137 361, 362, 364, 366, 370–372, 374, Smart textiles 9, 41, 46, 58–61, 70, 133, 134, 376, 386, 387, 391, 393, 398–400, 137, 188, 439–464 407, 409–411, 413–415, 417, 419, Socks 5, 39, 50, 107, 136, 460 426, 427, 429–431, 433, Soil 448–450, 457 reinforcement 6 Structural requirements 420, 422, 427 484 Index

Structure 15, 16, 21, 39, 43–45, 48, 52, 53, Techniques 3, 6, 7, 9, 12, 14, 16, 18, 19, 25, 58, 69–72, 82, 108, 110, 115, 116, 55, 95, 99, 160–162, 165, 166, 175, 119, 121, 125, 126, 133, 134, 136, 178, 187–189, 197, 211, 230, 231, 167, 170, 222, 226, 230, 231, 233, 234, 260–272, 279, 283, 284, 239–247, 249, 253, 260–264, 266, 295, 345, 349, 403, 407–409, 415, 268–272, 280, 284–285, 287, 288, 416, 420–422, 425, 431–433, 457 294, 304, 319–326, 328, 333, Tensile strength 1, 39, 97, 112, 118, 122, 340–344, 346–349, 357, 361, 362, 124, 126, 133, 142–145, 147, 364, 368–376, 379, 389, 390, 219–221, 232, 249, 253, 254, 281, 392–394, 397–400, 409, 410, 412, 284, 287, 301–304, 325, 341–345, 414, 417–421, 425–432, 441, 444, 357, 359, 362, 364, 386, 388, 400, 445, 448, 450, 452, 456, 460, 461 411, 413, 414, 417, 429, 448, 450 Submarines 396, 399 Tensile testing 429 Sunlight 7, 8, 12, 13, 26, 109, 279, 281, Tensioned fabric structures 323 282, 315, 362, 366, 398, 441, 444 Tents 8, 11, 15, 95, 320 Sun protection factor (SPF) 15 Testing methods 11, 23–26, 41, 61–62, Sun visor 355, 366 95–98, 138–147, 209, 249–232, 302, Surfaces 3, 19, 26, 43, 53, 225, 227, 228, 357, 408, 428–431, 446, 452 260, 268–269, 321, 325, 335, 359, Testing standards 95, 295–311, 428, 433 369, 385, 394, 395, 419, 428, 429 Textile reinforced composite Sustainability 10, 11, 16, 17, 26–32, 62, materials 227–228, 346, 420–425, 98–100, 141–148, 162, 232–233, 433 272–274, 280, 281, 311–312, Textile reinforced concrete (TRC) 8, 319, 347–349, 403, 407, 408, 414, 432, 340–349 462–464 Textile reinforcement materials 342–343, Sustainable development 40, 273, 312, 403 345 Sustainable processing 187–189, 408 Textiles Sweat 5, 44, 45, 47, 53, 89, 115, 132, 137, composites 9, 369–372, 380, 394, 407, 159, 178, 180–183, 186–189, 425–431, 433 208–210, 358, 377, 378, 444, 459 electronics 60, 61 Synthetic fibres 1, 5, 7, 11, 26, 30, 37, 38, fibres 9, 20, 37–42, 72, 81, 116, 160, 40–41, 51, 107, 119, 148, 160, 219, 220, 227, 243, 244, 280, 359, 162–166, 173, 216, 220, 225, 239, 407, 408, 426, 428, 429, 431–433 244, 251–253, 274, 280–283, 290, manufacturing 2, 94, 98, 99, 345, 370 291, 307, 312, 366, 413, 415, 432, materials 4, 5, 8–19, 25, 37, 43, 57, 61, 448, 461 70–72, 76, 81, 82, 87, 107–148, 160, 188, 207, 210, 211, 215, 239, 242, t 257, 319, 325, 326, 342–346, 348, Tarpaulins 8, 241, 354 349, 354, 358, 367, 370, 379, 385, Tear resistance 122, 128, 142, 145, 409, 420, 427, 431, 432, 439, 457, 302–304, 325, 331, 332, 334, 356 459, 461 Technical applications 1, 76, 219–221, processes 2, 250, 442 240, 385, 413–415 products 3–5, 15, 16, 20, 27, 28, 70, 71, Technical textiles 1–10, 12, 20, 46, 47, 69, 88, 93, 95, 98, 99, 107, 122, 148, 188, 208, 210, 221–225, 227, 233, 240, 208, 269, 319, 348, 354, 355, 371, 253, 261, 279–281, 293, 295, 380, 385, 386, 410, 453, 460, 462, 464 353–355, 366, 385, 409, 415–420 properties 49, 50 Index 485

structures 8, 9, 12, 41, 58, 69, 87, 134, u 138, 227, 240–242, 260, 261, 270, Ultraviolet protection factor 16 280, 284–285, 312, 319, 320, 322, Unidirectional reinforcement 323, 326, 342, 343, 370, 372, 374, structures 394 394, 419 Uniforms 4, 6, 25, 95, 122, 124, 204, 206, Textile structural composites (TSCs) 219, 230, 231, 295, 301, 325, 374, 370–371, 394 379, 421 Thermal behaviour 326 Upholstery 8, 13–16, 23–27, 29, 239, Thermal burden 131–138 354–359, 366, 372, 376 Thermal comfort 37, 48, 54, 55, 108, 109, Utility performance 356–359 125, 133, 136–137, 359, 377, 450 UV light 26, 31, 142, 280, 311, 356, 440, Thermal insulation 12, 42, 43, 50–53, 57, 452 81, 115, 116, 118–121, 125, 131, 143, 144, 173, 182, 188, 320, 323, 326, v 335, 349, 366, 378, 409, 427 Vacuum bagging technique 421–422 Thermo‐physiological comfort 5, 9, 42, Vapour permeability 38, 41–43, 53, 115, 43, 81–83, 108, 131–138, 159, 327, 329, 331 183–189, 359, 377 Vectran fibre 411, 432 Thermoplastic resin 389 Vehicles 8, 203, 346, 354, 355, 358, 359, Thermoset foams 390 361, 363–366, 368, 369, 371, 372, Thickness 15, 19, 51, 52, 55, 82, 113, 115, 375–377, 379, 380 118, 173, 179, 180, 200, 204, 210, Vinyl ester resin 388, 392, 424 217, 222, 223, 229–231, 242, 243, Viscose 1, 17, 30, 38–40, 43, 70, 71, 83, 249, 257, 261–263, 266, 268–270, 108, 112, 124, 131, 162, 163, 204, 290, 301, 309, 336, 338–342, 359, 205, 244, 257, 258, 295, 300, 353, 368, 373, 376, 378, 379, 386, 391, 356, 367, 458, 460, 461 393, 394, 417, 419, 421, 447, 461 Thick nonwovens 268–273, 369 w Three‐dimensional textile structures 394, Warfare protective clothing 447–450 419 Warmth sensation 377–378 Three‐dimensional weaving 417–418 Waterproof garments 440, 447 Three‐dimensional woven fabrics 266, Water resistance 97, 115, 329–330, 376 333, 334 Tough cotton 386 Water retention 20, 280, 298, 300, 308 Toxicity 16, 28, 95, 96, 141, 395, 396, 451, Wearable electronics 9, 440, 443–447, 455, 462 460, 463, 464 Trains 8, 354 Wearable technology 58–61, 453, 454 Transportation 6, 8, 28, 29, 41, 50, 51, 70, Weather resistance 7, 282 221, 233, 240, 273, 274, 294, 354, Weaving 4, 12, 14, 19, 21, 23, 32, 43, 131, 368, 371, 373, 374, 379, 385, 425, 160, 161, 168, 174, 189, 223, 224, 426, 432, 433 233, 240, 261, 263, 264, 266, 284, Trevira 387 285, 331, 345, 353, 356, 371, 374, Triaxial fabrics 264–265 375, 394, 408, 417–418, 433, 442, Two‐dimensional woven fabric 261–264, 443, 457, 460 376 Weed suppression 7 Tyre cord fabric 355, 366–367 Weight reduction 8, 371, 372, 379, 410, Tyres 8, 241, 354, 355, 366, 367, 379, 410 413 486 Index

Wings 8, 241, 409, 411, 417, 423, 427, 428, x 433 Xanthate 131 Wool 11, 13, 16, 23, 27, 31, 37–39, 44, 53, X‐rays 109, 231 82, 93, 96, 98, 108, 112, 116, 124, protection 139 125, 129–131, 162–164, 166, 204, 206, 219, 220, 225, 226, 258, 281, y 291, 292, 295, 299, 338–341, 349, Yarns 4, 6, 7, 12, 14, 21, 30, 37, 40, 42–43, 379, 397, 413 45, 51, 52, 71, 91, 121, 133, 148, 160, Wound healing 4, 76, 79, 455, 456 167–175, 188, 223–229, 242, 253, Woven fabrics 4, 6, 25, 31, 43, 52, 125, 254, 261, 262, 264, 266, 284, 285, 130, 136, 161, 173–175, 177, 188, 310, 319, 324, 343, 345, 353, 354, 221, 228, 254, 260–263, 265, 266, 357, 361, 372–374, 376, 398, 284, 289, 303, 345, 356, 364, 368, 415–419, 442, 443, 450 374, 376, 399, 415, 417, 433, 448 types 223–225 Woven preforms 266, 371, 375–376, 417–419 z Woven reinforcement structures 392–393 Zeolite 17, 94 Woven structures 19, 225, 253, 362, Zippers 15, 60 374–375, 393 Zirpro wool 112, 124, 130 WILEY END USER LICENSE AGREEMENT Go to www.wiley.com/go/eula to access Wiley’s ebook EULA.