Content Page

7.1 Introduction 1

7.2 Fibre Blend 1 7.2.1 General Principle 1 7.2.2 Type of Fibre Blends 2 7.2.3 Advantage of Fibre Blends 4

7.3 Yarn 6 7.3.1 Yarn Spinning 6 7.3.2 Fibre Spinning 12 7.3.3 Classification of Yarns 15 7.3.4 Novelty Yarns 16 7.3.5 Yarn Numbering Systems 19 7.3.6 Yarn Twisting 21

7.4 Fabric Construction 23 7.4.1 Fabric and Types 23 7.4.2 Woven Fabrics 25 7.4.3 Knit Fabrics 32 7.4.4 Non-woven Fabrics 38 7.4.5 Fabric Properties 39

7.5 Fabric Colouration 50 7.5.1 Colour Basics 50 7.5.2 Brief History of Dyes 51 7.5.3 Classification of Dyes 51 7.5.4 Dyeing 56 7.5.5 Dyeing Methods 57 7.5.6 Dyeing Machinery 59 7.5.7 Printing 62 7.5.8 Printing Methods 63 7.5.9 Printing Equipments 64 7.5.10 Fastness 67

7.6 Finishing 68 7.6.1 Pre-Treatments 68 7.6.2 After-Treatments 69

7.7 Fabric Quality 74 7.7.1 Strength 74 7.7.2 Pilling Resistance 77 7.7.3 Dimensional Stability 77 7.7.4 Colourfastness 78 7.7.5 Flammability 80 7.7.6 Toxicity 82 7.7.7 Rules and Regulations 83 7.7.8 Trademarks 87

7.8 Latest Development and Environmental Issues 89 7.8.1 Functional Textiles 89 7.8.2 Smart Fabrics 91 7.8.3 Plasma Technology 93 7.8.4 Environmental Protection 95

7.1 Introduction

Clothing (衣), then food (食), habitat (住) and transportation (行) are the four elements that are necessary to daily living. Fabrics which are made from a variety of fibres are the materials for making clothing and textile products. Each type of fibre or fabric has its own properties and can be made into a variety of end products with different functions Different ways to spin the fibre or to weave the yarn into fabric can change the properties and affect the appearance, colour, hand feel, style of the products. These properties should also be considered when designing fashion, developing textile materials and constructing garments in order to select or create the most suitable textile materials in meeting the needs of the wearers. Nowadays, the textile industry is able to produce functional textiles with extra functions such as UV protection and antibacterial.

7.2 Fibre Blend

Fibre blending is a common method to produce new textile materials by combining properties of individual fibre components together. There are many fibre blends available in the market. Some examples are cotton – polyester, nylon – spandex, wool – rayon, etc. They serve a wide range of properties to suit different applications.

7.2.1 General Principle

Blending is the mixing of two or more components together to form a new material. It can be done in several ways. Fibres can be blended in the fibre or yarn stages. The blending of staple fibre and staple fibre requires homogeneously mixing two together before yarn spinning. For the blending of filament fibre and staple fibre, filament is required to chop into short segments before blending. Another method is to spin staple fibre onto a filament core. The outcome of this would be that the core spun yarn maintains the strength of filament fibre but the appearance of the staple fibre. The blending of two synthetic fibres can form bi-component fibre. Fibre blends can also be done by weaving and knitting different yarns into a single fabric. The fabric produced will have properties of the two or more different textile fibres.

There are many combinations of blended materials. Some examples are natural – natural and natural – synthetic fibres. There are also many ways of blending. Some examples are staple – staple, core spun and bi-constituents. The properties of fibre

1 blends can be determined by the selection of component fibres and the fine tuning of blending ratio. Fibre blend composition is an important information for International trade. Many countries such as USA and Europe have imposed tariffs on different textile materials. It is rare to have fibre blend with 50% / 50% composition as there are no restrictions on the major components present in blended fabrics that would affect the tariff involved.

7.2.2 Types of Fibre Blends

Blending can be classified into different categories based on the textile fibre composition or way of blending used. The following are some common combinations of different fibre types:

Blending nature Type Examples A Natural– Natural Cellulosic – Cellulosic Cotton – Ramie Protein – Protein Wool – Cashmere B Natural – Regenerated Cellulosic - Cotton - Rayon Regenerated Protein - Regenerated Wool – Rayon C Natural – Synthetic Cellulosic - Synthetic Cotton – Polyester, Cotton – Spandex Protein - Synthetic Wool – Polyester, Wool – Acrylic D Synthetic – ― Polyester – Rayon Regenerated E Synthetic – Synthetic ― Nylon - Spandex

Apart from composition, classification of blended fabrics can be based on the way the fibres are blended.

Blending Nature Type Examples A Staple - Staple Yarn Cotton - Ramie B Core spun (Staple – Yarn Cotton – Polyester Core Filament Blends) Yarn C Bi-Constituent or Synthetic Filament Acrylic – Acrylic Tri-Constituent Filament D Blended Fabric Fabric Polyester Warp / Cotton Weft

2 Blending of various textile fibres gives new textile materials different merits.

(A) Cotton – Ramie Blends

This is an example of blending of two natural cellulosic fibres. The first advantage is cost reduction as cotton is cheaper than ramie. Second advantage is that ramie is stronger than cotton. Hence, the blended fabric has a better strength. Thirdly, Ramie is more water absorbent and dries quicker than cotton. This enhances the water absorption power and dry rate of the blended fabric. Fourthly, cotton can render the blend softer as ramie is a kind of stiffer and brittle fibre. The new fabric feels more comfortable. The degree of enhanced properties depends on the blending composition.

(B) Cotton – Polyester Blends

This is a popular fibre blend for all kinds of applications such as clothing, furniture, bedding items, etc. There are several types of blending. They are namely, T/C, CVC and CVS. T/C blend refers to polyester – cotton blend. “T” standard for a famous brand of polyester called Terylene produced by ICI. Polyester is the major component and polyester fibre content is higher than that of cotton in the finished blended fabric. Common ratios are 65/35, 80/20, etc. This kind of blended fabric demonstrates polyester properties such as wrinkle free, low shrinkage and it is compromised with better water absorption.

CVC stands for Chief Value Cotton in which cotton is the major component and such type of blended fabric demonstrates the advantages of cotton. CVS stands for Chief Value Synthetic with polyester is the major component and such type of blended fabric demonstrates the advantages of polyster.

(C) Wool – Polyester Blends

The major disadvantages of wool product are shrinkage and felting. The blending of polyester and wool makes the fabric resistant to shrinkage and felting. As polyester is low in moisture content, this will maintain wool’s quick dry property. Polyester is also easy to clean and this perfectly fits with wool’s soil resistant property. The blended fabric is commonly used for making suits and trousers.

3 (D) Nylon – Spandex Blends

This kind of blended fabric is a common fabric used for swimwear and sportswear as nylon provides good abrasion resistance and high strength. The incorporation of spandex renders the fabric highly stretchable. All these properties are basic requirements for fabrics used for swimwear and sportswear.

(E) Bi-Constituent Fibres

Man-made fibres can be blended together in the fibre spinning stage. Two different materials can be extruded together to form a single fibre. Two component materials are permanently joined together and cannot be separated. Fibre content analysis of such type of fibre is usually through the chemical approach.

Figure 7.1 Several types of bi-constituent or tri-component fibres with different textile materials A, B and C are fused together to form a single fibre

7.2.3 Advantages of Fibre Blending

Chemical synthesis is the major approach employed to create new materials. However, such process is time consuming and costly. This may also requires technological advancement, which is very likely to further increase the cost. The blending of different textile fibres in yarn or different yarns in fabric is a well known economic method to produce new textile materials. The development time can be kept to a minimum as all the technologies required are already well developed. This is why blending is a cheaper process. When fibres are blended, the weakness of one type of fibre may be complemented by the strength of the other. The following is the summary of the

4 advantages of fibre blending.

Low cost

Quick development time

Advantages of different fibre components can be combined and manifested

Enhancement of particular advantages of a fibre component

Minimise, reduce or compromise of demerits of a fibre component

Give a chance to fine tune various properties to suit different applications by changing fibre composition

5 7.3 Yarn

Yarn is a thread-like material with continuous length made from textile fibres being twisted together. The process is called yarn spinning. Staple fibre itself has limited length (ranging from an inch to few inches). Yarn spinning can produce threads with continuous length for fabric manufacturing. Filament fibres need fewer twisting to form stable threads. Man-made textile materials are thermoplastics and fibre extrusion (or fibre spinning) is required for the production of filament fibres. The thickness of the yarn and the number of twist will affect the thickness, weight, way of handling and end use of the fabric.

7.3.1 Yarn Spinning

The conversion of fibres into yarns is called yarn spinning. The principle of yarn spinning is twisting fibres together for coherence. There are two common processes for yarn production, viz ring and open end spinning.

(A) Preparation of Fibres for Yarn Spinning

Takes cotton as an example, Figure 7.2 illustrates the flow of the use of cotton from harvesting to shipment in the form of cotton fibre. Cotton seeds are harvested from plants and dried to reduce moisture. The dried seeds are then cleaned. Leaves, stems and other useless parts are removed. The next process is called ginning, which involves the use of machine to separate fibres from the seeds. Separated fibres are called lint. Cotton lint is then packed into standard package called bale. Bales are arranged into specific dimensions and weights. The bales are then graded depending on the fineness, staple length and colour of cotton lint. Graded cotton is then priced and shipped out. Remaining seeds are used for oil extraction.

6

Figure 7.2 Flowchart illustrating processes from harvesting cotton to shipping out for yarn spinning

Figure 7.3 Saw ginning machine is used to separate cotton seeds from lint

7

Figure 7.4 Universal density bales of cotton lint

Upon spinners receiving the bales, they will open the bales and further clean the lint. The lint is then being put through the following processes before yarn spinning.

(i) Carding

Each carding machine is set with hundreds of fine wires that separate the fibres and pull them into somewhat parallel form. A thin web of fibre is formed and passes through a funnel-shaped device that produces a ropelike strand of parallel fibres. Blending takes place by joining laps of fibres.

(ii) Combing

When a smoother, finer yarn is required, fibres are subject to a further paralleling method. A comb-like device arranges fibres into parallel form with short fibres falling out of the strand.

8

Carded yarn

Combed yarn

Figure 7.5 Carded and combed yarn

(iii) Drawing Out

After carding or combing, the fibre mass is referred to as the sliver. Several slivers are combined into one before the process of drawing out. The combined silver passes through a series of rollers rotating at different rates of speed. The process elongates the combined sliver into a single more uniform strand that is given a small amount of twist and fed into large cans. Carded slivers are drawn twice after carding. Combed slivers are drawn once before combing and twice more after combing.

(iv) Twisting

The slivers are fed through a machine called the roving frame where the strands of fibres are further elongated and given additional twist. These strands are called the roving.

(B) General Types of Yarn Spinning

(i) Ring Spinning

The roving is fed from the spool through rollers (drafting zone) where one roller turns slow and the next roller turns fast. This arrangement elongates the roving. It then passes through the eyelet, moving down and through the traveler. The traveler moves freely around the stationary ring at 4,000 to 12,000 rpm. The spindle turns the bobbin at a much faster speed (~25,000 rpm). Rotation of the bobbin and the movement of the traveler twist and wind the yarn in one operation.

9

Figure 7.6 Ring spinning

(ii) Open-end Spinning (Rotor Spinning)

The sliver is fed into the spinner by air jet. It is then delivered to a rotary beater that separates the fibres into a thin stream that is then carried into the rotor by a current of air through a duct and is deposited in a V-shaped groove along the sides of the rotor. As the rotor turns, twists are produced and the yarn is formed. The formed yarn is an one end yarn and is then packed tightly in rolls. The twisting of yarn is determined by the ratio of rotor speed and the linear speed of yarn transfer.

10

Figure 7.7 Open-end spinning

Open–end spinning produces twisting on the yarn surface and a more uniform yarn than ring spinning. The yarn produced with this technique is less strong, more extensible, bulkier, more abrasion resistant and absorbent. The technique brings to the yarn two advantages. It is fed by sliver instead of roving in ring spinning. This simplifies the process step and saves cost. It can also be modified to remove any remaining trash, thereby improving the quality of the yarn.

11

Figure 7.8 Comparison of ring spun and open-end yarn. Ring spun yarn has twisting throughout whole piece of yarn. Open-end yarn has twisting only on the outer surface and fibres in the centre are parallel to the yarn axis. Ring spun yarn is finer and stronger than open-end yarn.

7.3.2 Fibre Spinning

Fibre spinning is a similar process to yarn spinning but it refers to the formation of fibre from polymeric substances. It is a manufacturing process of synthetic fibre. There are three types of fibre spinning process, viz dry, melt and wet spinning. The fibres produced are in filament form and can be further processed to staple form for better imitation of natural fibres.

(A) Dry Spinning

Dry spinning is based on the dissolution of polymer by volatile solvents. The polymer solution then passes through the filter for removing un-dissolved substances and extrudes through spinnerette. The extruded fibres then pass through a stream of hot air for evaporation of the solvent (drying) and solidifying.

12

Figure 7.9 Dry spinning

(B) Melt Spinning

Melt spinning is a technique that involves molten polymers. Melted polymers pass through a heated filter for removing solid trash. They are then extruded through the spinnerette. Afterwards, they pass through a stream of cool air. Extruded fibres solidify upon cooling.

13

Figure 7.10 Melt spinning

(C) Wet Spinning

This process is based on the modification of polymer. Modified polymers are soluble in a particular solvent. The polymer solution is then being extruded through the spinnerette, a technique similar to that involved in the dry spinning process. The extruded fibres then pass through a coagulating bath that converts the modified polymers back to insoluble form.

14

Figure 7.11 Wet spinning

7.3.3 Classification of Yarns

Based on fibre length, yarn can be classified as staple and filament. Staples refer to short fibres ranging from less than an inch to a few inches. Most of the natural fibres are staples. Filaments refer to long fibres with continuous length. Most of the man-made fibres are filaments. To imitate natural fibres, man-made filament fibres may be chopped into shorter lengths. The only natural filament is silk. The length of filament fibres extracted from silk cocoons is around a mile long. Yarn made from staple fibres needs twisting to hold fibres together to form a single thread. Yarn made from filaments does not need much twisting to hold filaments together. The twisting done in this way is not easily seen.

Figure 7.12 Staple and filament yarn

Furthermore, yarn can be classified into single and ply depending on the number of strands composing the yarn. Ply yarn is nomenclature with the number of strands in front of “ply yarn”. For example, a double strand yarn is called “two ply yarn”.

15

Figure 7.13 Z-twist ply yarn

7.3.4 Novelty Yarns (Fancy Yarns)

Yarn can also be texturised to give special effects. Such kind of yarn is called novelty yarn or fancy yarn. Novelty yarns (also called fancy yarns) are yarns with an interesting texture or other unusual features that distinguish them from ordinary yarns. Typically, these yarns involve at least one or two strands of regular yarns twisted together with something else to make an interesting texture and they are frequently made from synthetics such as nylon but can also be composed of natural fibres.

Very often, novelty yarns involve frequent colour change. Most often these will be obtained through the print process in which a fibre will be dyed in different colours through the dyeing process. Sometimes different colours and effects can be obtained by spinning yarns with different colours together. A series of colours or shades can be dyed in a part of the yarn. As the yarn is long enough, the dyeing sequence will be repeated for many times to enable a self-striping feature when knitted into fabric. If a proper number of stitches is cast, then stripes will appear as the yarn is knitted into a garment. Sock yarn companies have evidently taken a great interest in self-striping yarn. Such kind of yarn has a wide array of different effects that can be obtained by knitting the yarn in the round over the number of stitches normally cast for a sock.

(A) Bouclé

It appears as a length of loops of similar size and can range from tiny circlets to large curls.

16 (B) Eyelash Yarn

It appears as a thread base with several long strands spaced at even intervals that jut out at an angle from the main strand. The long strands or hair can be metallic, opalescent, matte or a combination of different types. The strands that jet out can be curly or straight and can sometimes be in two different lengths.

(C) Flammé

It is generally a loose or untwisted core wrapped by at least one other strand. The extra element can be a metallic thread or a much-thicker or much-narrower strand of yarn. It can also be yarn that varies between thick and thin.

(D) Ladder Yarn (Train Tracks Yarn)

It is constructed like ladders with a horizontal stripe of material suspended between two thinner threads, alternating with gaps.

(E) Ribbon Yarn (tape yarn)

It is made of ribbon but generally not the kind of ribbon used in sewing and millinery. They are in fact ribbons made especially for knitting or crocheting with some in a tubular form, some woven flat and some similar in appearance to bias tape. Ribbon yarn can be composed of many materials ranging from synthetics to silk, and to plant fibres.

(F) Slub Yarn

This a 2-ply yarn with a textured and lumpy surface. The yarn is made up of a smooth ply and one that is spun unevenly, which creates 'slubs' or lumps.

17 (1) Bouclé

(2) Eyelash

(3) Flammé

(4) Ladder

(5) Ribbon

(6) Slub yarns

Figure 7.14 Various types of novelty yarns

(G) Composite Twist Core-spun Yarn

This is a new type of yarn claimed to be no torque. The yarn has a hard core covers with dual spun. The dual spun layers are in opposite twist to counter balance torque.

Figure 7.15 Composite twist core spun yarn

18 7.3.5 Yarn Numbering Systems

The fineness of yarn (yarn size) is an important parameter to determine the quality of fabric properties. The way of describing yarn fineness is called yarn number. The finer the yarn, the thinner and softer the fabric will become and the clothes will fit better. Traditionally, there are many yarn number systems for different types of materials. However, these methods can generally be categorized into two main types, the direct and indirect systems. Most importantly, yarn size is defined by its length and mass.

(A) Direct Systems

“Direct” means the greater the yarn size, the greater the yarn number. It is based on the mass of the yarn segment per unit length. Common systems are denier and tex. Denier count (Td or D) is defined as weigh (in gram) of yarn per 9000 m of yarn segment. Tex count (tex) is defined as weigh (in gram) per 1000 m of yarn segment.

Examples:

Yarns Weigh per 1 m Length per 1 g (G) (m) 20 D yarn 0.002 450 20 tex yarn 0.02 50

Figure 7.16 A yarn size of 20 tex yarn

19 (B) Indirect Systems

“Indirect” means the greater the yarn size, the smaller the yarn number. It is based on the length of the yarn segment per unit mass. Cotton count (‘s) is a typical example. Cotton count is defined as the number of hanks of cotton yarn per 1 lb. traditionally, cotton yarn is traded in hanks and the length is 840 yards.

Examples:

Yarns Size Length per 1 lb Weigh per 1 yard (yard) (lb) 20 s’ cotton Thinner yarn 16800 0.00006 yarn 10 s’ cotton Thicker yarn 8400 0.0001 yarn

Figure 7.17 Yarns of size 20 s’ cotton count

In terms of SI unit, international metric count (Nm) is similar to cotton count and is defined as number of km of yarn per 1 kg. The figure below lists out the various conversions of different yarn number systems.

20

Yarn Type Conversion Equation Cotton to Denier 5315 / Cotton Count Denier to Cotton 5315 ÷ Denier Cotton to Metric Cotton Count x 1.69 Metric to Cotton Metric Count x 1.69 Denier to Metric 9000 ÷ Denier Metric to Denier 9000 ÷ Metric Count Cotton to Tex 590.5 ÷ Cotton Count Tex to Cotton 590.5 ÷ Tex Count Tex to Metric 1000 ÷ Tex Count Metric to Tex 1000 ÷ Metric Count Tex to Denier Tex Count x 9 Denier to Tex Denier ÷ 9 Denier to Decitex Denier ÷ 0.9 Metric to Decitex 10,000 ÷ Metric Count Cotton to Decitex 5905 ÷ Cotton Count

Figure 7.18 Various conversion factors for different yarn number systems

7.3.6 Yarn Twisting

Twisting is to hold fibres together in yarn. The more the twisting, the greater holding force imposed between fibres. As a result, a more compact yarn is produced (stiffer and finer) which is usually used as the warp yarn of woven fabric. On the contrary, the less the twisting, the softer the yarn will be. Also greater twisting gives greater yarn strength but also a greater tendency for fabric skewness. It is a parameter that determines the properties of fabrics. Twisting can be described by its direction and number of twisting per inch (TPI). Yarn twisting direction is classified as Z and S direction.

21

Figure 7.19 Various yarn directions (S and Z) and twist per inch

Although more twisting gives a stronger yarn, softness and absorbency will decrease. Fabrics made from high TPI yarns give a harsh hand feel and less efficient to keep warm. Furthermore, TPI cannot be increased continuously as over twisting will break the yarn. TPI needs to be balanced between strength and softness.

22 7.4 Fabric Construction

Fibre is the raw material in the textile industry. Yarn is produced from fibre. Yarns are then used for constructing fabrics. Fabrics are then applied for various kinds of final textile products such as garment, bedding items, bag, etc.

Figure 7.20 Different stages of textile production

7.4.1 Fabric and Types

Fabrics, which are also called piece goods, are basically constructed from yarns. The two processes used to convert yarns into fabrics are weaving and knitting. Fabrics produced from weaving are called woven fabric. Fabrics produced from knitting are called knit fabric. Besides, there is a third type of fabric that is produced directly from fibre without weaving and knitting. It is called non-woven fabric. The production cost of non-woven fabric is comparatively lower than that of woven and knit fabric. This kind of fabric is popularly used in one time use garment, reusable shopping bags, particle filter, etc. Fibres used to produce non-woven fabrics are held together by mechanical, adhesive or heat fusion.

Fabrics are usually traded in rolls. Some common terms for various parts of a fabric are as follows:

23

Figure 7.21 Various terms of fabric

(A) Face and Back

Each piece of fabric has its face and back, which may differ from each other. Face is usually the side with better appearance and more brilliantly coloured. Some fabrics types such as plain weave, rib, interlock, etc have identical sides and their face and back cannot always be distinguished.

(B) Length and Width

The long direction of fabric, which is the direction of machine producing the fabric, is called warpwise, lengthwise or machine direction in woven fabrics. Yarns that run along this direction are called warp or ends. The short direction of fabric is called weftwise, widthwise or cross-machine direction in woven fabrics. Yarns that run along this direction are called weft, filling or pick. For knit fabrics, the long direction is called wale or machine direction while the short direction is called course or cross-machine direction.

24 (C) Fabric Edge

The edge of fabrics is called selvedge, which usually has a different structure from the centre portion of the fabric. It is usually used for heat setting. Also, finishing or printing may not apply to selvedge.

7.4.2 Woven Fabric

Woven fabric is the kind of fabric formed from interweaving two sets of yarns at a right angle. Warp (or ends) yarns are parallel to the machine (lengthwise) direction. Weft (filling or picks) yarns are horizontal to the cross machine (widthwise) direction.

(A) Weaving

It is a process in which warp yarns and weft yarns are interlaced to form fabrics. The equipment for weaving is called weaving looms or simply weaving machine. Warp yarns are winded on a very big roll called the warp beam. Weft yarns are winded on a spindle shape apparatus called the shuttle. In the weaving process, warp yarns are separated into two groups and fed to two comb-like frames (harness) which can be raised and lowered alternately. This will produce an opening in the warp ends called shed. Weft yarn is passed through the shed and packed closely by a reed. The warp frames raise and lower alternately to complete a weaving action. A piece of fabric is produced by repeating the same action. The up and down patterns of warp beams determine the fabric construction.

25

Figure 7.22 Side view of a weaving machine. The filling yarn insertion is perpendicular to the page

Fill Insertion

Traditionally, filling yarn insertion is done by hand. Shuttle is thrown through the shed from left to right and right to left alternatively. It is for sure that modern weaving machines can do this in a more efficient and faster way. There are four main kinds of fill insertion.

(1) Shuttle

A modern from of shuttle machine that transfers shuttle mechanically. Usually, this is done by spring loaded projection.

(2) Projectile

This is a shuttleless loom that replaces shuttle with a bullet-shape projectile to carry the filling yarns.

(3) Rapier

It is a thin metallic shaft with a yarn gripping device. It includes a single or double rapier that carries filling through the shed.

(4) Water/Air Jet

This is a very fast weaving machine that employs either a jet of water or air to carry the

26 filling yarn through the shed.

(B) Types of Woven Fabric and their Properties

Different arrangements of up/down pattern of warp and weft yarns produce a wide variety of woven fabrics. According to the surface characteristics, there are woven fabrics with plain surface and woven fabrics with raised surface. There are three types of plain surface woven fabric. They are plain weaves, twills and, satins and sateens. Pile fabrics are woven fabric with raised surface as there are short fibres on the surface.

(i) Plain Weave

Fabric with yarn either warp or weft passes over only one yarn. Many kinds of plain weave fabric, e.g. canvas, poplin, chiffon, chambray, gingham, crepe, etc.

Figure 7.23 Plain weave z Poplin

Poplin is plain weave fabrics with high dense warp and low dense weft yarns. The count of weft yarn is usually half of the warp. This produces crosswise rib characteristics on the fabric.

27

Figure 7.24 Poplin z Chambray

A plain weave fabric mainly made of cotton or rayon with similar warp and weft density (~80 per inch). It is constructed with dyed warp beams and white weft yarns. The fabric is commonly applied to the production of child’s garments.

Figure 7.25 Chambray fabric

(ii) Twill

This a kind of woven fabric with the weft yarn passes over more than one warp yarn. Such construction will produce different slanted patterns on the fabric surface. If the pattern slants to right hand side, the fabric is called S twill. Fabric with pattern slants to left hand side is called Z twill. Common examples are 2/1, 2/2, 3/1 twill, herringbone, etc.

28

(A) 2/1 S-twill (B) 2/2 Z-twill

Figure 7.26 Twill fabrics z Denim

This is a very popular type of twill fabric for making jeans, jackets, shirts, bags, etc. The warp beam is dyed with indigo and weft yarns are usually not dyed. It is usually made of cotton, rayon or cotton/polyester blends. The fabric is comfortable, very durable with a wash look.

Figure 7.27 Denim fabric (Z twill)

(iii) Satin and Sateen

Similar to twill, fabrics with a weft yarn pass over five to eight warp yarns are classified as satin or sateen. As one yarn floats over so many yarns, the face will mainly show the float yarns. For warp on the face, this kind of fabric is called satin. For weft on the face, this kind of fabric is called sateen.

29

(A) satin (B) sateen

Figure 7.28 Satin and sateen fabric

(iv) Pile Fabrics

Pile fabrics are fabrics with short fibres (pile) on the surface. Usually, pile is produced from cutting floating yarns on the surface of fabrics and having them brushed. Corduroy and velvet are two popular examples.

30

(A) corduroy

(B) velvet

Figure 7.29 Fabric construction of corduroy and velvet

31 7.4.3 Knit Fabrics

Knit fabrics are fabrics produced by interlocking loops of yarn.

Figure 7.30 Single jersey

(A) Knitting

Unlike weaving, knitting is done based on a single yarn. Knit fabrics are composed of continuous interlocking loops. The major part of the machine is (latched) needles which have hooks with flipping latches. Those needles will move up and down according to a rotating metal cam at the base. The flipping latch will open and close during the knitting action cycle to grab new yarn segment through the yarn loop. A new yarn loop is called a stitch. A knit fabric is formed from repeating these actions.

32

Figure 7.31 Knitting action for constructing a weft knit fabric. Step 1: Needle in ground position and it is closed and holding a yarn loop. Step 2: Needle moving up according to the clearing cam and the yarn loop flip open the latch. Step 3: Needle continues to move up and the open hook passes over a new yarn segment. Step 4: Needle hooks the new yarn segment and moves downward. The old loop flips up the latch and closes the hook. Step 5: Needle moves downward and draws the yarn through the old loop to form a new loop. The process repeats.

33

Figure 7.32 Basic design of a latched needle. Various parts of the needle serve different functions. The hook is for collecting yarn and drawing the yarn through the yarn loop. The latch enables the hook to close and open. The roundout is for holding the loop. The butt is to translate the needle motion according to the clearing cam.

There are two types of stitches depending on either the next stitch passes through the previous loop from above or below. If the stitch passes from above, it is called a purl stitch. If it goes below, it is called a knit stitch.

Figure 7.33 Purl and knit stitch

(B) Types of Knit Fabric and their Properties

According to the orientation of loops, there are two types of knit fabrics, viz weft and warp knit. Traditionally, weft knit fabrics are used more for clothing. Warp knit fabrics are for special applications.

34 (i) Weft Knit

Weft knit is a fabric formed from parallel courses of yarn running horizontally. This direction is called course. The loop is aligned parallel to the fabric axis and called wale. Basically, the fabric can be produced from a single yarn. Most of the knit fabrics commonly used are weft knit. z Single Jersey

This is the most common and simplest kind of weft knit fabric. The fabric is formed from continuous knit stitches. The face and back of this kind of fabric are completely different. Rows of “V” shape can be seen on the face side and on the back side are rows of “half circle” shape.

(A) Face side (sketch) (B) Back side (sketch)

(C) Face side (photo) (D) Back side (photo)

Figure 7.34 Single jersey fabric

35 z Rib

Knit fabrics are constructed with alternate purl and knit stitches form the rib. The fabric formed by one purl stitch alternates one knit stitch is called 1 x1 rib fabric. Similarly, the fabric formed by two purl loops with one knit loop is called 2 x1 rib fabric. Rib fabrics have twice the thickness of single jersey fabrics and they are more extensive along the course direction.

(A) 1x1 rib (B) 2x2 rib

Figure 7.35 Rib fabric z Interlock

This is a double knitted fabric with two identical layers that interlace together. Both sides of the fabric are identical. It is a stable knit fabric with less shrinkage.

Figure 7.36 Interlock fabric.

36 z French Terry

Knit fabrics with extra yarn inserts that contain hanging loops form a raised surface. Those fabrics are mainly applied to towel and infant clothing production as the loosely twisted loop yarn renders the fabrics greater water absorbency and softness.

Figure 7.37 French terry fabric

(ii) Warp Knit

Fabric formed from many yarns that run vertically. Loops interlock each other horizontally. Warp knit is a technique commonly used to construct lace, mesh, elastic knit, etc, for lingerie and swimwear.

Figure 7.38 Warp knit fabric

37 z Lace

An openwork fabric patterned with open holes in the work made by machine or by hand. The formation of these holes is done via the removal of threads from a woven fabric but many kinds of lace are made by the warp knit technique.

Figure 7.39 Lace fabric (Source: http://www.asyoulikeitbridal.com)

7.4.4 Non-woven Fabrics

The cost for producing non-woven fabrics is usually cheaper than that of woven and knit fabrics as no yarn is required in the production process. Non-woven fabrics are formed directly through fibre compression. The interlocking of fibres can be done by mechanical (friction), adhesive and heat fusing. Mechanical bonding is done by piercing the fibres with saw-like needles which will roughen the surface of fibres as the friction between fibres locks each other.

Figure 7.40 Non-woven fabric

38 7.4.5 Fabric Properties

Different fabrics possess various kinds of properties. These properties can basically be classified into different categories based on their physical characteristics, chemical composition, etc.

(A) Physical Properties

Fabrics can be specified by several fundamental physical properties, viz fabric weight, fabric count and yarn count.

(i) General Fabric Specifications

Fabric weight is the measurement of the weight of fabric per unit area. It is an indication of fabric density and it relates to other fabric properties such as strength, etc. Fabric weight is an important specification that is usually included in buying contracts. Traditionally, it will express as ounce per square yard (oz/yd2) or simply called ounce. It is still commonly used for woven fabric specification. SI unit version is gram per square meter (g/m2). This is commonly used in knit fabric.

Another property for fabric specification is fabric count. It is the number of yarns per unit distance of fabric. The common practice is to express the number of yarn per one inch. Woven fabric construction can be specified as number of warp yarn per inch and weft per inch. For knit fabrics, it can be specified as the number of wale per inch and the number of course per inch.

Yarn count is another specification for fabric that has been explained in the previous section.

Different fabric constructions give different properties. Woven fabrics are generally more dimensionally stable to laundering, more abrasion resistant, less extensible and not elastic, except with spandex yarn. On the contrary, knit fabrics are a more delicate construction; knit fabrics are better in terms of drape, more flexible, softer, with greater extensibility and certain amount of elasticity. However, knit fabrics are less strong, less abrasive resistant and less dimensionally stable to laundering.

(ii) Abrasion Resistance

Abrasion resistance refers to the fabrics’ resistance to rubbing until defects appear.

39 Common defects are yarn breakage, fabric rupture, removal of coating, removal of pile, etc. This is one of the measures to test fabric durability. Products with higher abrasion resistance are ensured to be more durable. Abrasion resistance is a complex property. The performance of abrasion resistance depends on the material used, its smoothness, yarn size, yarn twisting, fabric construction, fabric thickness, etc. Polyamide (or Nylon) and polyester are well known as materials with good abrasion resistance. They are the major fibres used for sportswear. High amount of rubbing is expected during their usage. Furthermore, a high twisted yarn has a greater holding force between fibres and gives better abrasion resistance.

(iii) Dimensional Stability

Dimensional stability refers to the dimensional change, change in length and width and fabric skewness after repeating laundering. Fabrics made from interlacing or interlocking of yarns are not rigid materials. They can extend or shrink upon usage and processing. Generally, fabrics tend to shrink rather than grow. The main reason is that tension set in textile processing such as spinning, weaving, colouration, etc may release upon un-tension wet process, i.e. washing.

(iv) Shrinkage in Cellulosic Fabrics

The shape of cellulosic fibres is hold by weak hydrogen bonding. Hydrogen bonding between molecular chains can be destroyed by water. Water will swell the fibre and release the stress set in previous processing. As a result, fibres shrink. Upon drying, water molecules evaporate and new inter-molecular chain hydrogen bondings form and set the shape of fibres that have shrunk.

40

Figure 7.41 Cellulosic shrinkage and wrinkle formation through the wet–dry state such as laundering

(v) Strength

Strength can be measured in many ways depend on the type of material being tested. These ways include tensile, compression, shearing, etc. Commonly, textile material strength can be measured in three ways.

Fabrics Strength Woven fabrics Tensile strength Tearing strength Knit fabrics Bursting strength z Tensile Strength

Tensile strength for textile materials is defined as the maximum pulling force (Fbreaking) that a material can stand before rupture per width of specimen under tension. The tensile strength of warp and weft are usually different. As warpwise direction is always under tension in weaving and processing, warp requires a higher tensile strength than weft yarn.

41

Fbreaking Tensile Strength = —————————— Specimen

z Tearing Strength

Tearing strength for textile materials is the force required to tear off a certain length of a fabric sample. Similar to tensile strength, tearing strength of warp yarn is stronger than that of weft yarn. Tearing strength parallel to weft is stronger than that of warp direction.

(A) Tearing along warp direction and . (B) Tearing along weft direction and weft yarns breaks the fabric. warp yarns breaks the fabric

Figure 7.42 Tearing strength z Bursting Strength

Knit fabric strength is expressed by its bursting strength. It is similar to inflating a balloon until it burst. With the help of highly elastic rubber membrane, knit can be inflated to burst. The pressure required is called bursting strength.

(vi) Extensibility

Another important property for fabric is extensibility. This relates to garment fitting. Fabric construction allows certain degree of extensibility. Generally speaking, knit fabrics are more extensible than woven fabrics as the interlocking loops of knit fabrics can extend under stress. Extensibility of a fabric also depends on the material used. Synthetic fibres are mainly made of thermoplastic materials and these materials can be extended more than natural cellulosic fibres. Regenerated cellulosic fibres can also be

42 considered as a kind of plastic material and they give greater extension then natural cellulosic fibres.

(vii) Elasticity

Elasticity is very similar to extensibility; however, elasticity refers to the retention of the original dimension after the removal of stress or simply the fabric’s recovery ability. This can also be called the memory of the material. Rubber is a well known elastic substance. Textile fibres are inelastic, except spandex. Spandex or elastane fibre is made from segmented polyurethane polymer. Besides, elasticity partly comes from the material itself. It can partly come from fabric construction. The interlocking of loops in knit fabrics renders the fabric greater elasticity. Woven fabric construction is generally inelastic but elasticity can be imposed by incorporating elastic yarn in the production of woven fabrics. In the market, it is not difficult to find elastic denim jeans that such production principle is applied to it.

(viii) Thermal Insulation

This is one of the functions of textiles. Irrespective of the textile materials involved, some specific fabric constructions are able to increase the fabrics’ ability to keep warm. For example, raised fabrics can trap more air, which is a poor thermal conductor, to allow more heat to be trapped within the clothing. Apart from that, a more compact construction can prevent air flow and minimise heat loss by convection.

(ix) Air Permeability

This property refers to the restriction of air flow through the fabric, it is an opposite property to the thermal insulation; however, good air permeability allows fabrics to breathe. This means that sweat can evaporate and freely pass through clothing. This is one of the measures used to evaluate clothing of their comfortability. It is an important parameter for sportswear application.

(x) Water Proofing

Without specific finishing done, most of the textile materials are not water proofing. Water proofing is generally achieved by applying hydrophobic reagents on fabrics.

(xi) Water Absorbency

Most of the textile materials are able to absorb water and moisture. Wet textiles usually demonstrate strength loss after being wet, except natural cellulosic fibres. Water

43 absorbency is important in some applications such as towel, sportswear, underwear, etc.

(xii) Comfortability

Whenever consumers select clothing, comfortability is a very important factor to them. It is not a property that stands on its own. It most certainly relates to a number of physical and chemical properties such as softness, smoothness, breathability, water absorbency, absence of skin irritant, compatible pH level, etc. Some of the factors can be collectively called hand feel. Comfortability is a subjective property and it varies from user to user.

(xiii) Heat Stability

Textile products may form wrinkles upon daily use and laundering, particularly cellulosic materials. Ironing is usually applied to remove wrinkles. Heat stability is an important factor that affects the ironing temperature that the fabrics can afford.

Materials Recommended Ironing Setting Temperature Cellulosic fibre Hot ~200°C Protein fibre Warn ~150°C Synthetic fibre Cool ~110°C

Cellulosic fibres are very heat stable. They will char and do not melt at high temperature. They can be used as a thermal insulated material such as thermal gloves. Animal fibres are mainly protein fibres and their heat stability is of medium level. Similar to cellulosic fibres, animal fibres will not melt but high heat may damage the fibres. Most of the synthetic fibres such as polyester, nylon and acrylic are thermoplastics. They get softened upon heating. This temperature that transforms the physical formation of fabrics is called the glass transition temperature. It is important to note that synthetic fibres do melt at certain high temperature. Specific types of synthetic fibres made of highly crystalline polymers such as aramid or thermal setting materials such as melamine are with high heat stability. They are usually used for the production of firemen’s clothing.

(xiv) Static Electricity

Static electricity is the local accumulation of either positive or negative charges. Static electricity is caused by the transfer of electrons from one object to another and during rubbing. As charges are built up and accumulated, they may discharge to any substances that are nearby. This is why there is sparking when clothe are taken off at

44 night, particular in dry weather. Most of the textile materials are electrical insulators and can build up charges readily when rubbing. Static electricity may create different problems:

z Skin irritation

z Sticking dusts

z Sparking

z Damage electronic device

Figure 7.43 Static electricity

Measurement of Static Electricity

Static electricity is usually considered as the reverse of conductivity and it is defined as the resistivity per unit length of material. The unit is m-1.

(B) Chemical Properties

(i) Light Fading and Degradation

Light is electromagnetic radiations that can be classified into various types according to their different wavelengths. Electromagnetic radiation spectrum contains low energy radio waves, very high energy X-ray and cosmic ray. Sunlight (or daylight) is one of the light sources that contains infrared, visible and ultraviolet radiations. Different types of light interact with materials differently. Infrared radiation (IR) is related to heating effect. Visible light is what naked human eye can see. Ultraviolet (UV) radiation is contains a higher level of energy in terms of chemical bonding. It is well known that textile colour

45 fades under light. UV is the main cause. UV can gradually degrade almost all colourants. Apart from that, UV can also induce photo-degradation on finishing and textile materials. In time, finishing and textile materials rupture and turn yellow.

(ii) Photo-degradation

Photo-reactions are very complex sets of reactions mainly caused by free radicals which cause the aging of materials.

(iii) Thermal Degradation

Heat can degrade textile materials through various kinds of chemical reactions that are known as thermal degradations. Heat generally accelerates most of the chemical reactions. For example, high temperature may degrade resin finishing and release formaldehyde. This is one of the common problems that emerges during product shipment. In the past, there were many overseas buyers complaining about the bad smell that released from shipped products when opening up the carton boxes. Usually, heat is not the only factor that contributes to this phenomenon. Moisture may support and accelerate the degradation process.

(iv) pH Value

Acid or alkaline is commonly employed in textile processing. Different textile materials demonstrate different effects. Cellulosic materials can damage or degrade under acidic media but resistant to strong alkaline. Alkaline processes such as mercerization can enhance tensile strength of cotton. On the contrary, alkaline can damage protein fibres such as wool. So wool products are better handwashed with non-ionic detergent. Residual acid or alkaline may induce skin irritation. Environmentally friendly garments should have pH compatible to slightly acidic skin pH.

(v) Bleaching

Bleaching is a process to make textiles white. Many natural fibres have their own natural colour, which will hinder later colouration and subject to removal. The bleaching mechanism destroys colour stains through either oxidation or reduction. Chemically, these processes are called the redox reactions. Oxidation is a well known process in which substances react with oxygen. Reduction can be simply referred as reactions reversing the oxidised materials back to its original state. Generally, the textile industry employs oxidative bleaching as the effect is more persistent. The main disadvantage of reductive bleaching is that stains may form upon air oxidation.

46 Commercially, there are two main types of bleaching agents, viz chlorine and non-chlorine. Chlorine bleach is a strong bleaching agent that can oxidise most colourants. High chlorine concentration can stripe colours from dyed textiles. Non-chlorine bleaches are mild bleaching agents and colour safe. They only remove colour stains and are popular bleaching agents for home laundering.

Redox Reactions

Redox reactions refer to the pairing of two chemical reactions, oxidation and reduction, that take place simultaneously. One reactant is being oxidised and another reagent is being reduced. Chemically speaking, this will be described with “oxidation number” of an element or molecule. The oxidation number of the oxidised reagent is raised while the reduced reagent is lowered. Specifically, redox reactions are based on the transfer of electrons.

Figure 7.44 Redox reactions

(vi) Yellowing

White and denim fabrics are subject to yellowing which may be caused by various chemicals such as acid, softener, polluted gases, antioxidant, etc or environmental factors such as temperature, light, etc. Yellowing may be due to oxidative degradation of textile materials or finishing, destruction of optical brightener, formation of yellowing species, etc.

47 (C) Flammability

Most of the textile materials can be burnt. Flammability is an important safety factor that can be evaluated in different ways. They are:

z Ease of ignition

z Burn time

z Burn rate

z Burnt area

z Burnt length

Different textile materials burn differently. Cellulosic materials burn most easily and demonstrate afterglow. Afterglow is a very dangerous phenomenon which refers to the recurrence of burning after the fire is extinguished. Animal hairs such as wool burn with material charred. Animal hairs are flame resistant materials as flame removed fire will extinguish. When synthetic fibres are being burnt, their component materials will melt and drip. They are flame resistant and similar to animal hairs.

Apart from the material involved, fabric construction can also affect flammability of fabrics. Plain surface fabrics are less vulnerable to burning than raised surface fabrics. The reason is that raised surface is known to trap more air and have protruded parts for easy ignition. With the similar reason, fabrics with loose construction may burn more readily than fabrics with compact construction.

Essential Factors for Burning

There are three essential factors for burning to be present. They are fuel, oxygen and ignition. Fuel is the substance that is flammable. Oxygen must be present to support burning. Ignition is the temperature where substance will ignite (start burning). For example, a match is a fuel. Simply a match will not burn until it rubs on a rough surface. The rubbing action increases the surface temperature of the match through friction. The match will not burn in the absent of air even with rubbing done repeatedly.

48

Figure7.45 Essential factors for burning

49 7.5 Colouration

7.5.1 Colour Basics

Red, blue, green, yellow, etc. are the usual ways to describe the colours of an item. There are three basic elements for colour, viz light, object and observer, Without any one of these elements, you cannot see the colour of any given object. The study of colour is called colour physics. In order to describe colour more precisely, many colour order systems such as RGB, CMYK, pantone, CIE Lab, etc have been developed for different industries. The basic principle is to arrange different colours systemically in a space called colour order space. CIE Lab is one of the common systems used in the textile industry. CIE stands for La Commission Internationale de l'Eclairage (English: International Commission on Illumination) which is an international authority on light, illumination, colour and colour spaces.

Figure 7.46 Basic elements of colour

50 CIE Lab Colour Space

The colour vision of human can be described by a set of primary colours called the tristimulus values (XYZ). Colours can be systemically arranged with tristimulus values in a three-dimensional space. This is one kind of colour order space. The major drawback of XYZ colour space is nonlinearity and it is hard to apply. Based on the tristimulus values, CIE has developed a linear colour space called Lab system. This space arranges colours in accordance to their lightness (L), a and b (hue and intensity).

Figure 7.47 CIE Lab colour order space

7.5.2 Brief History of Dyes

The earliest record of people using dyestuffs is from China in 2600 B.C. Rome people in 715 B.C. had already established their set of wool dyeing technique. At 700 A.D., Chinese had documented their dyeing process that involved wax resist technique (batik). In 1856, William Henry Perkin discovered the first synthetic dye stuff called “Mauve”, which is a basic dye and it started the modern synthetic dye industry.

7.5.3 Classification of Dyes

Dyestuffs are water soluble coloured chemicals with affinity to fibres. Water insoluble colourants are called pigment. Basically, dye molecules are composed of chromophore and auxochrome. Chromophore is a chemical structure that is able to absorb certain visible radiations and reflect the unabsorbed light energy. For example, a red dye reflects red light and absorbs other radiations such as green, blue, etc.

51

Dyes Pigments

Soluble in its application medium, Insoluble in its application medium usually water.

With affinity (substantivity) to fibres No affinity to fibres

Smaller particle size Large particle size

Adhere to substrate by physical or Adhere to substrate by binder chemical linkage

Figure 6.48 Comparison between dyes and pigments

(A) Chromophore

Chromophores are chemical structures with alternate single and double carbon–carbon bonding and the system is called the conjugated system. Commonly, structures are in shapes such as aromatic ring, azo bond, etc. Electrons within the conjugated system can transfer from carbon–carbon double bond to single bond. This shifting is called electronic resonance and able to absorb visible light energy. Unabsorbed light energy is reflected and this is the colour of the dye molecule.

Figure 7.49 Electronic resonance within a conjugated system

52 (B) Auxochrome

Auxochromes are chemical structures that can assist chromophores to intensify the colour, enabling dye water solubility and affinity. Colourants without auxochrome are pigments. Common auxochrome structures are hydroxyl, carboxyl, sulfonic, amino groups, etc.

(C) Interactions of Dyes and Textile Fibres

Dye has affinity to fibres. Affinity comes from dye molecules when they are having specific interactions with certain structures of fibres. There are four types of interaction.

(i) Van der Waal Forces

It is a weak attractive force depending on molecular mass. The greater the molecular mass, the stronger the attraction force. Furthermore, the bigger the molecule, the bigger the attraction force.

(ii) Hydrogen Bonding

It is a specific bonding between the OH (hydroxyl) group. As oxygen atoms attract electrons more strongly than hydrogen atoms, electrons in hydrogen–oxygen bonds will shift to the oxygen side. Hence, the polar of the hydroxyl group with O is slightly negative and H is slightly positive. Dyes and fibres with the hydroxyl group that cellulosic fibres contain will attract each other. Such bonding is called the hydrogen bonding.

(iii) Ionic Bonding

It is the attraction between the positive ions (cation) and the negative ions (anion). Some of the chemical structures are able to ionise in water. For example, acid dye + - ionizes to give hydrogen ions (H ) and anions (R ). Wool fibres contain amino (-NH2) group that will form cations under acidic condition and it will attract dye anions.

(iv) Covalent Bonding

It refers to true bonding between the dye and the fibre. Dye with reactive group is able to react with certain structures of a textile fibre. This can be considered as the strongest bonding.

53 Dye – Fibre Example Interactions Van der Waal Direct Dye Forces Hydrogen Bonding Direct Dye Ionic Bonding Acid Dye Covalent Bonding Reactive Dye

Apart from these interactions, some dye molecules attach to the textile fibre based on their own solubility. For example, vat dye can be reduced into soluble form during the dyeing process and oxidised to become insoluble form after dyeing. This change in solubility renders vat dye goods wet fastness. Disperse dye employs another principle. It has differential solubility in aqueous medium and fibre phase. Disperse dyes are fairly water soluble but highly soluble in fibre phase, so dye tends to stay in fibre rather than in the aqueous dyebath. This can be considered as a solid solution.

(D) Dye and Toxicity

Congo Red is well known a carcinogenic dyestuff that has been banned long ago. It is a kind of azo dye. The toxicity comes from the reduced amino products. The European Union (EU) has already banned textile products that contain azo dyestuff with restricted amines. EU has also complete restriction on textiles with sensitiwed and carcinogenic dyes. They are disperse dyes. Dye toxicity is particular concerned in infant and children products as they may put textiles into their mouths. Saliva resistance is an important test in infant and children products.

Figure 7.50 Reaction scheme for the release of restricted amine from Congo Red

54 Dyestuffs can be classified according to their chemical class or applications.

Figure7.51 Basic construction of a dye molecule

Although there are many dye classes, only a few types are popularly used. The following table indicates the major colourfastness of popular various kinds of dyestuff.

Dye class Characteristic Washing Crocking Disadvantage fastness Reactive A kind of dyestuff that is able Very good Very good Cannot attain dyes to react with fibres to form dark colours chemical bonding; all round fastness Acid dyes Major dyestuff for animal Moderate Excellent Easy wash off (protein) and polyamide to poor Disperse Major dye for man-made Good Good Some can cause dyes fibres skin irritation Direct dyes Dye cellulose with big Poor Good Easy wash off molecular size Vat dye Water soluble only in dyeing Excellent Good Careful dyeing is stage required Sulfur Black Used to dye for the black Poor to Poor Stain problem colour good from rubbing

Figure 7.52 General characteristics and fastness properties of some common dye

55

(E) Colour Index

This is the technical reference published by the Society of Dyers and Colourists (SDC) that collects details of all available commercial colourants, including both dyes and pigments. Each colourant is assigned a name with the following name system:

[Application class] + [base colour] + [number]

C. I. name Trivial name Acid Red 66 Biebrich Scarlet Basic Red 9 Sulphonated Pararosanilin Acid Yellow 24 Martius Yellow Direct Red 28 Congo Red Solvent Red 23 Sudan III

Figure 7.53 Examples of the SDC colour index

7.5.4 Dyeing

Dyeing is a process where dye molecules migrate from aqueous phase to fibre phase. Dye molecules have a tendency to diffuse from aqueous medium towards textile fibres. In the dyeing process, dye molecules are absorbed by the fibre and then they further diffuse into the fibre interior. This is the dye absorption process. The dye finally will attach to a particular location of the textile fibre called dye site. Different types of dye have different dye sites on different fibres. The interaction between the textile fibre and the dye determines the persistence of the final colour. This level of persistence is called colourfastness. The process in which the dye is absorbed into the fibre is called exhaustion. The total amount of dye exhausted includes both the amount of the absorbed dye molecules and fixed dye molecules. It is what is referred as the shade or how deep is the dyeing. The dye molecules being absorbed or fixed still have chance to go back to the aqueous medium. This phenomenon is referred to as desorption. When exhaustion rate is equal to desorption rate during the dyeing process, this state is called equilibrium exhaustion. Further dyeing after this state will result in no change in shade and the dyeing process is considered to be finished.

56

Figure 7.54. Dyeing process

7.5.5 Dyeing Methods

Dyeing can be carried out in different stages of textile manufacturing. Colouration that is applied to polymeric solution or melt before fibre extrusion is called dope dyeing. Colouration that is applied to yarn stage are called cone dyeing and beam dyeing. Dyeing in the fabric stage is the most common practice. It can be a batch or continuous process. Besides, dyeing can be carried out in the product stage such as garment dyeing. However, dyeing in the yarn stage or garment stage is not common practice. Yarn dyeing may produce colour variation in fabrics. Another drawback is that the later wet processing on fabrics may affect the final colour. Garment dyeing is a complex process when trims such as lining and buttons are present. Various dyeing methods are discussed as follows:-

57 (A) Batik Dyeing

Batik dyeing is a traditional dyeing method and is a kind of resist dyeing process that is used to produce patterned fabrics. Part of the fabric is coated with wax and dyed. Dye can only penetrate fabric area without wax. The waxed area is left blank. After dyeing, the wax is removed. The process can be repeated to obtain patterns with multiple colours.

(B) Lap Dip

It is a small scale of dyeing usually performed in laboratory. This is normally a preparatory stage of the dyeing recipe that matches as much as possible the colour reference of customers.

(C) Dope Dyeing (Pigmentation)

Dope dyeing refers to the colouration of man-made fibres that takes place in polymer either in the solution or melting (dope) state before fibre extrusion. This is not a dyeing process. It is simply a process of mixing colourants into the dope. The colourants employed are usually pigments. As colourants disperse in fibres, very good fastness properties are shared. The drawbacks of such technique are the difficulties in colour matching and possibilities of colour variation in fabrics.

(D) Cone Dyeing

Cone dyeing is a kind of yarn dyeing. Cones of yarn are placed in a perforated stand which dye liquor can pass through. Dyeing evenness depends on the penetration of dye liquor through the yarn cones. The rate if dye penetration is affected by the pressure of the pump and the duration of dyeing time.

Similar to dope dyeing, difficulties in colour matching and colour variation in fabrics are the drawbacks. Cone dyeing is commonly applied to yarn dye fabrics to produce stripe or check pattern.

(E) Beam Dyeing

This is another yarn dyeing process. Warp yarns are winded on a big roller for dyeing and the roller is called the warp beam. Beam dyeing shares the similar principles with

58 cone dyes but the size of the beam used is much bigger than that of yarn cone. The beam is placed on a perforated shaft and dye liquor is being pumped through the beam. Denim and chambray are beam dyed fabrics with dyed warps and blank wefts.

(F) Batch Dyeing

Batch dyeing refers to the process of dyeing fabrics in a batch of a few tens of yards to a few hundred yards. It is a common dyeing process done before the development of continuous dyeing range. One of the disadvantages is the colour variation between batches, so it is suitable for dyeing fabrics in small amount. Many small dye houses are still using such method and the machinery used is simpler than that needed for continuous dye range. It can also be used as a top dyeing process for modifying the shade of fabrics to fit specific colour standard of customers.

(G) Continuous Dyeing

It is a complete dyeing process that may include fabric preparation, dyeing and after-treatment. Contemporary automatic dyeing range may incorporate dye dispensing, exhaustion, fixation, rinsing and drying together. This is a fast and large scale of production involving fabrics that are in the size of a few thousands to over ten thousand yards.

7.5.6 Dyeing Machinery

The basic design of dyeing equipments is a tough to hold dyeing solution and textile. This is a dyebath. It should have facility for circulating either the dye solution or the fabric to produce even dyeing. Heating facility is also important for dye exhaustion.

(A) Jig Dyeing Machine

With the jig dyeing machine, fabrics are being operated in an open width form. Fabrics are being held in two rollers with only a part of the piece of fabric being dyed being dipped in the dye bath. Fabrics are either being circulated or transferred repeatedly from one roller to another roller for agitation.

59

Figure 7.55 Jig dyeing machine

(B) Jet Dyeing Machine

The machine is a close system. The ends of fabrics are joined together to form a loop and they are being circulated and moved around the dyeing chamber through a Venturi jet. Given that the machine is a closed system, pressure can be applied to perform high temperature dyeing.

Figure 7.56 Jet dyeing machine

60 (C) Cone Dyeing Machine

All cone dye machines contain a platform with several perforated posts connected to a pump. Dye liquor circulates through the posts to arrive at the dye chamber and then back to the pump. Yarn cones are placed on the posts.

Figure 7.57 Cone dyeing machine

(D) Beam Dyeing Machine

The design principle of beam dyeing machines is similar to that of the cone dye machines but in bigger size. Usually one dye chamber handles one warp beam. A perforated shaft is connected to a pump that handles the circulation of dye liquor.

Figure 7.58 Beam dyeing machine

61 (E) Continuous Dyeing Range

Each of this type of dyeing range usually contains a number of chambers for various purposes. This type of machines is well equipped to complete the entire dyeing process on its own, including the processes of dyeing, rinsing and drying. After dyeing, the range can be connected to later after-treatment ranges. Advanced continuous dyeing range are usually computerised and co-controlled by colour monitoring devices to ensure the accuracy of the colours aimed. The running cost is usually higher than that of the batchwise machine as the continuous dyeing range occupies more space, consumes more water and electricity. Nonetheless, it is more efficient. The production cost per yardage can be lower than that of batchwise dyeing. The following diagram illustrates the arrangement of a continuous dyeing line.

Figure .59 Continuous dyeing range

7.5.7 Printing

This is a colouration process that produces patterns. Unlike dyeing, printing is a localised colouration process. Print paste is employed to prevent lateral dye migration and maintain the sharpness of patterns being produced. Paste is a concentrated dye solution with thickening agents such as starch. Print fixation is usually done in high temperature, for instance, by means of steaming, to ensure a quick dye fixation which can prevent dye migration.

62 7.5.8 Printing Methods

Textile industries nowadays employ major methods that concern the following aspects: direct, resist, discharge and transfer.

(A) Direct Printing

A process of printing dyes directly on fabrics to create print patterns. This technique creates coloured patterns on white fabrics.

(B) Resist Printing

Resist printing refers to the application of a resisting agent such as wax or colourants to specific patterns to prevent the penetration of another dye. This technique produces different coloured patterns on fabrics. The print paste used as a protection layer contains a substance resistant to a second dye, which assist the development of colours in specifically aimed areas of fabrics.

(C) Discharge Printing

Instead of dye, a discharging agent is printed on fabrics. The function of discharging agents is to remove colours from fabrics. This technique creates blanks on dyed fabrics. This technique can be combined with direct printing to produce fabrics with colour print patterns on dyed fabrics.

(D) Transfer Printing

The printing is done on another media. For instance, paper. The printing is then transferred to textile fabrics through ironing. Disperse dyes are usually employed as they sublime during ironing and migrate to the fabrics. This technique produces very fancy patterns.

63 7.5.9 Printing Equipment

Screen printing is the major printing method being used nowadays. Print patterns are transferred to nylon or metallic screens with pattern areas that are open and other areas being blocked.

(A) Flatbed Screen Printing Machine

This method uses a screen spread over a frame. The portions of the design to be printed are made of porous nylon fabric that allows the dyestuff to pass through the screen. Print patterns with colour separations done are transferred on a series of flat nylon screens. The areas that are not to be printed are covered or coated. Fabrics are being fed intermittently for each individual colour printing. Dyestuff is poured into the frame shell and is forced through the nylon by means of a squeegee moved back and forth. Flatbed screen printing is versatile but expensive. Sometimes, a design pattern may require as many as 40 - 50 silk screens with separate colours to be applied.

(B) Hot Press Machine

Steam or electrically heated press machines are used for heat transfer printing. The machines are usually composed of two pressing flatbeds. These two flatbeds are either heated both at the same time or just alone.

The rotary screens or rollers first print dyestuffs onto paper. The paper can then be kept for use at any time. To print on fabric, the paper and fabric are put through hot rollers. The dyestuffs sublimate into gas, which transfers from the paper base onto the fabric. The advantages of this method are that it gives a clean, fine line on knitted fabric and paper is inexpensive investment. However, this method can cause stiff hand feel of the fabric and the dyestuff transfers only to the fabric surface without thorough penetration, causing potential grin-through (fabric showing through) problems.

Heat-transfer printing has become more popular than before in recent years because of the development in low-sublimation dyes and deeper-penetrating dyes as well as relatively less waste water and fewer harmful discharges in dry dyeing. Dry printing is considered as a more environmentally friendly dyeing method.

64 (C) Roller Printing Machine

This is a kind of printing machine that is very efficient in producing stripe patterns. This method requires separate roller engravings to be used for each colour in the pattern of design.The patterns are engraved in a copper roller. Print paste then fills the engraved area and transfers the patterns to the fabric as it passes through the printing machine.

Figure 7.60 Roller printing machine

(D) Rotary Printing Machine

Rotary printing is a quicker version of screen printing and is continuous without breaks between screens, Print patterns with colour separations done are transferred to a series of metallic rotary screen which are porous in the areas to be printed. Fabrics are being fed continuously. Dye is forced into the roller cylinder and through its porous screen as it rolls over the fabric. The repetition frequency of print patterns is limited by the circumference of the rotary screens.

65

Figure 7.61 Rotary printing machine

(E) Digital Printer

This is a new development of the textile printing technology. This technique applies digital printing to textiles. The process requires no print screens and the patterns are stored electronically as a computer-aid design (CAD) file in computers. This printing technique can produce very fancy and complicated patterns. It is even possible to modify a print design according to the shape of garment pieces. Digital printing is a flexible process that provides the opportunity for quick response to changes in colour or design of customers. This method is increasingly used for sample development under environment of short lead time and increasing demand for customisation.

66

Figure 7.62 Structure of a printer head. Piezoceramic material changes shape according to electronic signal and pressurises the pressure chamber and send out dye droplets

7.5.10 Fastness

Fastness (or colourfastness) refers to the colour resistance of a product upon various effects such as light, washing, etc. There are two aspects concerned, viz colour change and colour staining. Colour change refers to the amount of colour loses when a material is being exposed to various effects. It is a colour fading phenomenon as dye loss takes place gradually. Colour staining refers to the migration of colours from a product to other textile materials when in contact.

67 7.6. Finishing

Finishing is an extensive term that refers to all kinds of pre-treatments and after-treatments applied to textiles. Pre-treatments are referring to treatments prior to dyeing which prepare fabrics for colouration. After-treatments are treatments applied to fabrics after colouration, which enhance and add further properties to fabrics.

Figure 7.63 Pre-treatments and after-treatments

7.6.1 Pre-treatments

They are preparatory treatments to prepare fabrics for dyeing.

(A) Singeing

The process of burning off loose fibres on protruding fabric surfaces which may produce “frosting” during colouration. During the process, fabrics are being passed through a row of gas flame and then immediately through a quenching bath which may contain desizing agent.

(B) Desizing

Size such as starch and PVA is commonly added to warp yarns during weaving to strengthen the yarns and prevent yarn breakage. Below are the common desizing methods.

68 (C) Scouring

The process refers to the washing off of impurities in fabrics, also called kier boiling. For cellulosic fibres, scouring refers to the treating of fabrics with strong alkaline such as caustic soda or soda ash. The process removes most of the impurities such as natural grease and wax and pectin which will hinder colouration and further finishing.

(D) Mercerisation (An optional finishing process)

Mercerisation is a process that applies caustic soda (NaOH) to fabrics to produce silk-like appearance for cotton. Ribbon-like cotton fibres will swell and produce a smooth shinny surface. In addition, treated cotton fibres will have greater strength and better dye exhaustion.

(E) Bleaching

Bleaching is the process that removes natural colours present in textile fibres. The process is important for producing white fabrics for later colouration. This is usually done by oxidative type of bleaching. Hydrogen peroxide (H2O2), sodium hypochlorite

(NaClO) and sodium chlorite (NaClO2) are the common chemicals employed. The advantage of oxidative bleaching is that the effects are permanent.

(F) Caustic Reduction

The surface of the polyester fibres is eroded away in a caustic bath which reduces the weight of the fabrics and gives them a silk-like feel.

7.6.2 After-treatments

These treatments are used to add extra effects and finishes to fabrics. The process can be mechanical or chemical in nature. The advancement in technology of after-treatments is entering a new era with the application of nanotechnology in the production process. Nanotechnology marks the beginning of the second industrial revolution of the new millennium.

69

Figure 7.64 Evolution of textile materials

(A) Mechanical Treatments

Mechanical treatments refer to all the treatments that are employed to modify textile appearance mechanically.

(i) Calendaring

Calendaring is a mechanical pressing process that uses heated metal calendars to produce high luster fabrics. Fabric is passed between heavy rollers by applying heat and pressure. The process produces different effects such as glaze, watermark or moire. It is usually done on synthetic fabrics because the effects done cannot be kept permanently on natural fibres.

(ii) Embossing

A patterned calendaring process for producing raised or projected figures or designs in relief on fabric surface.

(iii) Brushing (Raising or Napping)

A process employed to raise the fibres on the surface by rotating brushes. Short fibres will loosen from the yarns upon brushing. It produces a soft, comfortable and raised surface on fabrics. Brushing can be applied to either side or both sides of fabrics.

70 (iv) Sanding and Peaching

Sanding is a process employed to treat fabric surface with abrasive sand. This can produce a raised surface similar to suede on fabrics. When the size of sanding particle reduces, a peach effect will be created on sanded fabric surface. This process is called micro-sanding or peaching.

(v) Shrinkage control (sanforizing process)

This process preshrinks cotton fabric so that it will not shrink during laundering

(vi) Pleating

Pleats refer to the folds in fabrics done by doubling the material upon itself and then being pressed or stitched in place. Pleating is a pressing process usually done along with heat to fix folding permanently.

(vii) Felting

It is the process of compacting masses of wool fibre under heat, moisture and mechanical pressing to form mats as wool fibres possess scales on their surface and they tend to entangle together under such situation. This process is carried out in fulling mills.

(viii) Decatizing

This process uses heat and moisture to stabilise wool fabrics.

(ix) Heat setting

This process stabilises the fabric so that there will be no further changes in its dimension or shape and thus improves the fabric's resilience. The effect is achieved by heating thermoplastic (synthetic) fabrics to just below their melting point.

(x) Laser Trimming

Traditionally, burn out effect requires the application of printing techniques that print sulphuric acid paste on fabrics. Sulphuric acid will etch fabrics to form holes. With the advancement of laser technology, laser trimming can produce any shapes of hole on fabrics with accurate and sophisticated computer control.

71 (B) Chemical Treatments

(i) Shrinkage Resistance and Wrinkle Free

These properties are achieved on fabrics with the application of resin finish to fix the fabric construction and prevent both shrinkage and wrinkle formation. Some of the resins used are formaldehyde based, which may lead to formaldehyde related problems. This is particular important for infant and children products. Wrinkle free finish also increases tearing strength of products, in which case garment seams may need enhancement.

(ii) Water Repellency and Resistance

Water repellency refers to the resistance of textile materials to wetting and water penetration. Usually, this process is done based on hydrophobic agent or plastic coating such as PVC, silicone, etc.

(iii) Soil Release (Stain Release)

Treatment of textile materials with waxy or hydrophobic agent can alter the surface condition of textiles and produce a less sticky surface. Stain can be washed off easily during laundering.

(iv) Easy Care

Easy care refers to the finishes that render textile products the durability to laundering, a smooth appearance with no ironing is needed and a minimised shrinkage. Sometimes it is called “durable press” or “wash-and-wear” finishes. This can be achieved by special resin finish on cellulosic / thermoplastic fibre blends. Cellulosic part is permanently set by heat setting the resin and thermoplastic fibre part.

(v) Flame Resistance

Flame resistance can be enhanced through the application of flame retardants, which are chemicals that can reduce, minimise burning or self-extinguish. The major drawbacks of flame resistance are its toxicity and durability. Some of the flame retardants have been found toxic to human body and banned by the European Union.

(vi) Durable press (permanent press)

The application of resins to cotton or cellulosic fabrics for eliminating future ironing.

72 (vii) Antistatic Finishes

Antistatic finishes are particularly important in work clothes of the electronic and petroleum industry. Antistatic finishes are done with the incorporation of conducting substances on the fabric.

(viii) Antibacterial and Antifungal Finishes

Antibacterial and antifungal are finishes that resist bacterial or fungal growth on textile materials. This can be achieved by incorporating germicides on fabrics to prevent odors formed by bacterial decomposition of perspiration and mildew growth. A new technique of applying a biocide called tributyl tin (TBT), which is commonly used in paint, for the purpose has been put into practice. However, TBT is found to be highly toxic to human and has been banned form being applied to textile products in European countries.

(ix) Moothproofing Finishes

This is a particular finish applied to wool products. Wool is susceptible to moth attack. Mothproofing chemicals are incorporated with wool fibres to prevent moth and beetle attack. These chemicals have a certain degree of resistance to laundering. Some of these finishes are able to react with wool fibres to form linkage that enhances the washing fastness of wool products.

(x) Antipilling Finishes

Pilling resistance can be enhanced by reducing the surface friction of yarn surface. Antipilling agents are polymers with low friction that can be coated on yarns to give a smooth surface. An example of such antipilling agents is polyethylene.

(xi) Nano Finishes

Nanotechnology refers to the manipulation substances in very small scale. Atomic size is 1 x 10-10m and nanometre is 1 x 10-9m. Unlike traditional technology, nanotechnology handles substances in molecular level. There are stain resistant garments available in the market based on nano-finish. These products have good resistance to aqueous and oily dirt.

73 7.7 Fabric Quality

7.7.1 Strength

This is a factor for selecting suitable materials for specific applications. For example, textiles used for casual wear and work wear are different. Work wear should use strong materials as workers may carry heavy tools. On the contrary, strong materials are not necessary to casual wear.

(A) Tensile Strength

This is a measurement of the maximum pulling a textile material can stand before it breaks. The test is mainly done on woven fabrics. Tensile strength of textiles is defined as the maximum breaking force per unit cross-section area. The common units are N/m (m=metre) or lbf/in (in=inch). N stands for Newton, which is a SI (Systema International) unit for force. lbf stands for pound-force and it is a non-SI unit for force. One Newton equals to 0.225 pound-force. The test is conducted under tensile strength testers which consist of two clamps. One is fixed and another is movable. The testers are equipped with electronic load cells to record the force applied.

The greater the tensile strength means the stronger the material. Depending on applications, different strengths are required. For example, bag requires a greater strength rather than a shirt. Tensile strength depends on many factors. These factors include materials, yarn twisting, fabric construction, finishing, etc.

Tensile Property

Tensile strength of textile materials is the breaking force per width of specimen. It is important to note that this is only a simplified expression. For bulk materials such as metal and plastic, tensile strength is defined as the breaking force per cross-sectional area of the specimen.

Fbreaking Tensile strength = —————————— Width / Cross-section

74 The following illustrates the difference between tensile strength for bulk materials and textile fabrics. Furthermore, the unit for tensile strength of bulk materials is the equivalent to pressure. N/m2, Pa (Pascal), lb/in2 (pound per square inch, psi) are the common units used.

(A) bulk materials (B) bulk fabrics

Figure 7.65 Tensile strength of various materials

Engineering studies tensile property of materials through tensile modulus (E) which is defined as the ratio of stress and strain.

Stress Tensile modulus (E) = —————— Strain

Stress is defined as the ratio of tension over cross-sectional area. Strain is defined as the ratio of original length of specimen to the strained length. When the increase of stress is directly proportional to the increase of strain, a series of data concerning the tensile modulus are collected which is called the elastic region. The modulus within this region is called elastic modulus or Young’s modulus. If there is a continue increase in stress but not in strain, the modulus will then go beyond the elastic region and finally reach the yield point. When the materials are further stressed, they will reach the work harden state where the materials will break. For textile materials, work harden is a state

75 where polymer chains straighten and form better alignment, i.e. crystallinity increase, therefore strength increases. As materials are further stressed, they will break. The breakage stress is referred to as the tensile strength of materials.

Figure 7.66 Tensile modulus. (a) Tough substances such as steel (b) soft substances such as textiles

As it is shown in the diagram, a tough material such as steel has a steep curve. Steel behaves almost elastically before breakage. A soft material such as textile only has a small elastic region. Furthermore, the curve is less steep than that of steel, which means textiles can be stretched easily with small force when compared to steel.

(B) Tearing Strength

Tearing strength is another strength property for woven fabrics and it measures the resistance of textiles in terms of tearing. Generally, the test is conducted with falling pendulum testers (or Elmendorf testers). Test specimens are pre-cut a slit. Tearing is done by the pendulums’ swinging motion. The tearing force or energy is recorded.

Tearing strength may drop dramatically after resin treatments such as wrinkle free finish. The reason is that fabric constructions have been fixed and yarns cannot move to counter balance the tearing force. Tearing strength is higher for loosely packed fabrics as yarns can move to counter balance the tearing action.

76 (C) Bursting Strength

Bursting strength measures the strength property of knit fabrics. It is the maximum pressure required to burst a fabric. Pneumatic or hydraulic testers are employed for such testing.

7.7.2 Pilling Resistance

Pilling refers to the entanglement of short fibre during textile material rubbing with other surfaces and the subsequent spherical change of shape.

Figure 7.67 The development of pills

7.7.3 Dimensional Stability

Dimensional stability refers to the stability of various dimensions of textile materials against home laundering process. For fabrics, such testing is based on the change in length of the pairs of benchmarks put on the sample before and after washing. Both lengthwise and widthwise dimensions are measured and changes are expressed in percentage.

77 (A) Shrinkage and Growth

Decrease in length between benchmarks after washing is shrinkage and increase in length is growth. The amount of change depends on the textile material, fabric construction and finish. Cellulosic materials always demonstrate shrinkage upon washing. Shrinkage for woven fabrics is usually smaller when compared to knit fabrics. Commercial requirements for growth are quite strict as they are related to the puckering of products, which greatly affects their appearance.

(B) Skewness

Skeweness refers to the tilting appearance of fabrics after laundering. Skewness is also called torque or spirality. Skewed fabrics affect the pattern marking process and waste more fabric.

7.7.4 Colourfastness

Colourfastness means the resistance of colour of a product against various conditions when using or during manufacturing. There are two effects, colour change and colour staining. Colour change refers to the change in colour of the product before and after a process. Basically, the change is fading. Which colour is getting less. Colour staining refers to the migration of colour from product to neighborhood during a process.

(A) Light

Colourfastness to light refers to the resistance of colour when exposed to light, daylight, store lighting in particular. Colour will fade under light when dyes or colourants are destroyed. Normal daylight is a mixture of radiations of mainly infrared (IR), visible and ultraviolet (UV). IR radiation is related to thermal energy. Visible radiation is the light human eyes can detect. UV radiation has energy in the range of chemical bonding that is able to break dye or colourant molecules.

78

Figure 7.68 Colour fade away when dyed textiles are exposed to light

(B) Crocking

Crocking fastness measures the colour migration of products to adjacent materials through rubbing.

(C) Washing

This particular fastness refers to the resistance of colour against various kinds of washing including hand wash, machine wash, commercial laundering, etc. It is used to develop garment care label. Colour change and staining are evaluated. Colour change is an indication of the durability of colour against washing. Colour staining indicates the migration of colour to other product including the colour migration caused by washing.

(D) Perspiration

The colour of textile products may be affected by sweat when in contact with skin. This fastness measures the colour change and staining property of textile products under contact of artificial human sweat. There are two types of sweat solution, viz acidic and alkaline. Depending on the standard testing method, one type or both types of solution are applied to products under controlled condition.

(E) Water

This colourfastness measures colour change and staining of textile products under prolonged contact with water. It is particularly important for the development of the drying instructions for colour blocks products with light and dark colours after laundering. If there is colour staining observed, such product is recommended to dry promptly after

79 laundering, otherwise self staining may take place.

(F) Bleaching

Bleaching is one of the processes in care. Colourfastness to bleaching measures the colour resistance of textiles in respect of commercial bleaches. There are two main types of commercial bleaches, viz chlorine and non-chlorine bleach. Chlorine bleach is liquid bleach which reacts vigorously. Not all colours are safe for this bleach. Non-chlorine bleaches are mild bleach and colour safe. They are available in both powder and liquid form.

Commercial Bleaches

Commercial chlorine bleach is composed of hypochlorite, which is a strong bleaching agent. High concentration of such solvent may strip colours. Chlorine bleach may react vigorously with other reagents such as washing powder, other bleaching agents and generate toxic gas, so it is not recommended to be used together with other reagents. Commercial non-chlorine bleaches are mainly composed of two types of chemicals, sodium perborate and hydrogen peroxide. They are mild bleaching agents which are colour safe. They are usually applied together with other reagents. Sodium perborate bleach is in powder form and hydrogen peroxide type bleach is a viscous liquid. All commercial bleaches are oxidative chemical and decompose gradually upon storage. They are recommended to be placed in dark and cold environment.

7.7.5 Flammability

Flammability is a safety requirement for textile clothing in USA. Textile clothing is separated in two groups, which are general wearing apparel and children’s sleepwear. Testing and requirements on these two groups of clothing are not the same.

(A) General Wearing Apparel

This group covers all sorts of commercial textile fabrics and wearing apparel except for children’s sleepwear. The regulation exempts footwear, glove and hat. Those products must pass a 45°C burning test. The test measures the time requires to burn a definite size of fabric swatch. This time of burning is referred as the burn time. Based on the burn time, products are classified into three classes, I, II and III. Class I is the best result. The criteria for fulfilling Class I is that the burn time of a product should be longer than

80 3.5 seconds for plain surface fabrics. Stricter requirements are imposed on raised surface fabrics; the burn time of a given product should be more 7.0 seconds as this kind of fabric burns more easily.

(B) Children’s Sleepwear

This is a particular item that special attention is required to be paid to in USA. Children’s sleepwear refers to the garment worn for sleeping and in the size of 0 to 14. As children may wear sleepwear and play around. Loose fitting sleepwear may catch fire easily when there is open flame such as candle. Given that children are not able to strip off the burning garment supposedly on their own, stricter burning test standards have been imposed on such kind of product. Fabric samples are tested in vertical manner and the test measures only the char length. Burning time or rate is not important in that item. Textile materials used for children’s sleepwear must be able to self-extinguish. The general requirement is that the average char length of five specimens cannot exist 7.0 inch. The following illustration shows the styles that the USA Consumer Products Safety Commission (CPSC) may consider as children’s sleepwear.

Figure 7.69 Typical styles considered by CPSC as children’s sleepwear (Source: US Consumer Products Safety Commission)

81 7.7.6 Toxicity

(A) Formaldehyde

It is a common chemical that may be present in textile materials, particularly resin treated materials such as wrinkle free finish. Common resins employed include formaldehyde base resins such as urea-formaldehyde resin, melamine-formaldehyde, etc. Formaldehyde has two problems, viz smell and health. Excessive presence of formaldehyde on textiles will give a fishy smell. As the resin technology begun, the chemistry of resin has not been very stable and was subject easily to degradation in damp environment. Therefore, many shipped textile products in the past might have a fishy smell. Nowadays, smell problem is not encountered very often given the change in resin chemistry and very stable resins are available. In respect of health related issues, formaldehyde may cause skin irritation and cancer when entering human body. This is particularly important for infant and children’s garment as they usually put things into their mouths.

Formaldehyde is soluble in water. The amount of formaldehyde present in textile products is calculated by the amount of formaldehyde extracted by water from textile products. The extracted formaldehyde is used to react with chemicals to make it coloured. The coloured solution is then subject to spectrophotometric analysis to quantify the formaldehyde amount present. The concentration of formaldehyde present in textile materials is usually expressed in part per million (ppm). 1 ppm means 1 gram of textile material containing 10-6 g (0.000001 g) of formaldehyde.

(B) Lead and Heavy Metals

Lead and heavy metals may present in paint coating and plastic materials as stabilizer and catalyst. Lead is a well known heavy metal toxic to human. As lead level in the blood builds up, it will poison and damage the central nervous system. Consumer product safety regulations of USA restrict the total amount of lead permitted in paint and coating of consumer products to be not greater than 600 ppm (0.06%). Besides, many other heavy metals such as mercury, chromium, arsenic, etc are highly toxic, too. The European Union has restrictions on the extractable level of eight different heavy metals present in consumer products. These metals are mercury, lead, chromium, arsenic, antimony, barium, cupper and selenium.

82 (C) Azo Dyes

“Azo” is a chemical structure referring to a double bonded nitrogen bridge (–N=N–). This is a common structure for dye molecules and may cleave to give out amines (-NH2). Some of the amines are carcinogen (cancer inducing chemical) or suspected carcinogen. The European Union has listed 20 restricted amines that no more than 30 ppm of any of these restricted amines is allowed to be present in textile materials.

7.7.7 Rules and Labelling

Many countries have law and regulations on textile products. There are two forms of control imposed on the regulations, product safety and labelling of textile products. Product safety involves flammability, mechanical and chemical hazards. The purpose of labelling is to inform consumers of what materials a given textile product contains and its basic caring method.

(A) Fibre labelling

Fibre labelling is a mandatory requirement for textile articles in major markets such as USA, Europe, etc. It requires all the textile products to have labels that contain information in respect of fibre content of products, manufacturer or importer identification and country of origin at the point of sale. The disclosure of fibre content needs to be in the form of generic names defined in correspondence to different countries’ regulations. Fibre generic names accepted in USA are different than those of Europe. The figure below compares some common fibre generic names used in USA and Europe. The languages used for the labels are also monitored according to the importing countries. For example, English should be used in USA. However, Canada requires labels to be printed in both the language of English and French.

USA Europe* Cotton Cotton Wool Wool Silk Silk Rayon / Viscose Viscose Spandex / Elastane Elastane Nylon Polyamide / Nylon

Figure 7.70 Comparison between fibre generic names using in USA and Europe

83

Figure 7.71 Fibre label

(B) Care Labelling

Care labelling is another mandatory requirement for wearing apparel in USA. In Europe, there is no particular care labelling regulation. However, there are product liability directives to prevent consumer loss and these directives require wearing apparel to have care label. Care labels provide consumer with care instruction information in laundering the apparel. Care labels in USA can be in the form of pure text, symbols or symbols with text. For European countries, care symbols based on ISO standards are preferred. The following diagram shows the care symbols used in USA.

84

Figure 7.72 USA care symbols based on ASTM standard. As a minimum, laundering instructions include, in order, four symbols: washing, bleaching, drying and ironing. Dry cleaning instructions include one symbol. Additional symbols or words or both may be used to clarify the instructions.

(i) Labelling in Hong Kong

Hong Kong SAR government did not have a particular rule and regulation for labelling textile garments. According to consumer rights, it is required to have garment label to indicate care and fibre content, Hong Kong accepts all worldwide labelling system, but language should be in Chinese, English or both.

(ii) Children Products

Children’s garments or products require additional safety considerations similar to toys. There are two major aspects concern, mechanical and chemical hazard. In USA, additional flammability regulation is required for children’s sleepwear.

85 z Mechanical Hazards

This type of hazard involves three sub-categories, viz small parts, sharp point and sharp edge. Small parts are lethal and can cause potential choking hazards. Any products for infants of the age of year three or below should not carry any small parts. Warning labels are required for products having small parts for infants aged above year three. Sharp points and sharp edges are potential to the piercing and cutting of the skin. All children’s products are regulated to prevent such hazards from taking place. z Chemical Hazards

Another safety concern is toxicity. Harmful chemicals present on children’s products may lead to serious health problems as children’s may put clothing items or accessories in their mouths. This is a direct intake of harmful substances. Children’s products usually are required to be toxic-free. One of the harmful chemicals is lead (Pb), which can poison the central nervous system upon accumulation. USA has regulations in controlling the total amount of lead present in coating in children’s products. Apart from lead, European countries restrict seven more heavy metals in children’s products. These metals are mercury (Hg), chromium (Cr), cadmium (Cd), arsenic (As), antimony (Sb), barium (Ba) and selenium (Se). z Drawstrings

Drawstrings refer to strings that go through a channel to control the size of openings. Drawstrings are particularly dangerous when they are present in the neck area of children’s wear, which may cause strangulation hazards. Drawstrings present in the waist area may also cause dragging hazards. Therefore, it is highly recommended to remove or replace such design from children garments.

Figure 7.73 USA care symbols based on the ASTM standard (Source: US Consumer Products Safety Commission)

86 7.7.8 Trademark

(A) Woolmark

Woolmark is a globally reconginsed textile fibre brand and is the guarantee of fibre content and quality specification. A unique quality endorsement will be given to products that meet the standard and specifications determined by the Woolmark Programme. Through the licensing of Woolmark, the products can be allowed to use the related brand name: Woolmark, Woolmark Blend and Wool Blend. These brand names are mainly used in the clothing, interior textile and home laundry sector.

(B) GORE-TEX

GORE-TEX is a technology in high-performance windproof, waterproof and breathable clothing. GORE-TEX® fabrics are created by laminating GORE-TEX® membrane to high-performance textiles. The membrane gives durable waterproofing properties with breathability to the treated fabrics.

(A) GORE-TEX fabrics. (B) GORE-TEX membrane

Figure 7.74 GORE-TEX (Source: www.gore-tex.com)

(C) Lycra

LYCRA® is a brand name for spandex / elastane. Spandex can enhance the quality and improve the appearance of clothing.. It is widely used in swimwear, underwear, jeans, casual wear, tops, socks and hosiery.

87 (D) Oeko-Tex 1000

A number of prominent textile testing institutions have already recognised the trend to non-harmful fabrics in the 90s. They have jointly defined the standards that a textile product has to fulfill in order to qualify as safe in every respect. They have also set out guidelines that have documented these relevant requirements. Manufacturing plants that have undergone the comprehensive examination and have achieved the prescribed standard can attach the “Confidence in textiles – Eco-friendly factory according to Oeko-Tex Standard 1000 label” to their production site. The former and still valid Oeko-Tex Standard 100 provided the basis. Unfortunately, the Oeko-Tex Standard 1000 certificate is not yet widely known in the marketplace.

To obtain the label, the plants’ compliance with environmentally relevant legislation and regulations must be verified. This is primarily a matter of analyzing exhaust air and wastewater values as well as noise emissions. The dyestuffs and chemicals in use are also required to be reviewed in terms of their compliance with Oeko-Tex Standard 1000 and in some cases replaced, which, for sure, in turn results in adjustments to formulations and processes.

(A) Oeko-tex 100 (B) Woolmark (C) Gore-tex (D) Lycra

Figure 7.75 Trademarks

88 7.8 Latest Development and Environmental Issues

7.8.1 Functional Textiles

The very beginning functions of textile fabrics are for keeping warm and protecting the body. Upon development, the additional functions such as water proof, wind blocking, antibacterial, antistatic, etc are incorporated in fabrics.

(A) Moisture Management (Quick Dry)

This is an advanced development for textile material which can manage the moisture together with air permeability. Traditional water proofing textile is simultaneously air impermeable, which makes the wearers feel uncomfortable. Moisture managing textiles usually have good wickability and low water absorbency. Another characteristic of this kind of textile is its water vapor permeability.

Figure 7.76 Moisture management

(B) Stain Proof

Stain proof refers to a textile’s resistance to both aqueous and oily based stains. This can be achieved with the advancement of fluoropolymer chemistry and nanotechnology. Textile can be incorporated with a very thin (molecular layer) fluoropolymer layer which 89 renders the fabric surface a very low surface tension to resist aqueous and oily based stains.

(C) Wind Blocking

This is one of the thermal insulation requirements. Wind is the major contribution to convection heat loss. Wind blocking finishes are able to prevent air flow through fabrics under certain pressure.

(D) UV Protection

As there is a massive use of inflammable fluorocarbon gases as propellant in spray products, the ozonosphere gets holes. Ozonosphere is a particular gas layer of atmosphere that contains ozone that blocks and prevents harmful UV (ultra violet) radiation from reaching the ground. High energy UV can produce damage in human deoxyribose nucleic acid (DNA) and cause skin cancer. There is a need for developing UV protective clothing. UV protection of garment can be indicated by the UV Protection Factor (UPF), which measures the blocking ability of fabrics to UV. For example, a UPF 30 fabric allows 1/30 of the UV radiation pass through the fabric and blocks 96.7% of the radiation. The maximum UPF rating is 50+, which means the fabric can block over 98% of the UV radiation.

Terrestrial UV Radiations

With the protection of the ozonosphere, high energy UV radiations cannot reach terrestrial. There are two types of UV radiation that can reach the ground, UVA and UVB. UVA radiation has a wavelength from 315 to 400 nm and UVB ranges from 280 to 315 nm. UVA causes premature skin aging. UVB causes sun burn and DNA damage, which may lead to skin cancer.

90

u Chromophore UVB filter

HOy or singlet O 2 Chromophore UVB filter

Figure 7.77 Interaction of UVB and DNA

(E) Germ Killing

Pure silver is well known for its germ killing property. With the introduction of nanotechnology to the textile industry, nano-silver can be applied to textile materials to provide such function.

(F) Skin Care and Fragrance

With the introduction of nanotechnology, textile materials can be able to release fragrance, skin care chemical or even medicine gradually. Useful chemicals can be trapped in a coating layer with micro-capsule. Rubbing and touch rupture the capsule and release the chemical.

7.8.2 Smart Fabrics

With the incorporation of other technologies such as electronics, textile products nowadays are equipped with extra new functions such as shape memory, television, etc.

(A) Shape Memory Fabric

With the discovery of shape memory polymers (SMP), shape memory clothing is feasible. Triggered by heat, shape memory polymers can retain previous shape. When

91 these shape memory materials in garments are activated, the air gaps between adjacent layers of clothing are increased in order to give better heat insulation. The incorporation of shape memory materials into garments confers greater versatility in the protection that the garment provides against extreme heat or cold.

(B) Garment Integrated with Electronic Devices

This is a combination of miniaturized electronic components and textile materials and clothing. The product has an artificial intelligence but looks like an ordinary clothing equipped with different functions, such as using conductive thread to embroider an audible keypad on the jacket, integrating electronic products with clothing as ‘wearable electronics”, using optical and electrical fibres that are woven to fabric to monitor the health condition of wearer, sealing light-emitting diode (LED) on fabric to produce patterns of light, etc.

(C) Temperature Sensitive Fabrics

The fundamental job of clothes is to keep us warm or cool, so it's no surprise that many of the smart textiles that enters the market nowadays look to regulate body temperature. Paraffin has been applied on fabrics. Paraffin changes its phase according to air temperature. When the body is hot, paraffin liquefies and heat can pass out the garment. As the body gets cold, paraffin solidifies and blocks heat loss from the garment. This kind of fabric is called phase-change fabric.

(D) Touch Sensitive Fabrics

Consoles and hard plastic switches can be replaced by soft fabric controls. The controls on the car dashboards may be an integral part of the interior upholstery and the laptop could be part of a bag.

(E) Autoclean Fabrics

With the advancement of nanotechnology, many specific compounds can be applied to textile materials. Incorporating minute size of titanium oxide (TiO2) in textiles can render the textiles the auto-clean property. TiO2 is a good photo-oxidation catalyst which can destroy stain and dirt under sunlight. Normally speaking, odor is formed on bacterial action with perspiration. With such kind of garment, perspiration can be disintegrated

92 under light and no smell is produced during the process.

(F) Medicinal Application

Many diseases require the use of medication in a long term and gradual period. Microcapsule fabric can incorporate medicine in the capsule and have it released gradually to wearers.

7.8.3 Plasma Technology

Plasma is basically a collection of ionic gases. Plasma can be generated through heating of gases or electrical bombardment. Plasma is a reactive gas that only reacts on superficial level of textile fibres. It can modify the fibre surface through either etching or addition of polymer. This is a versatile technology which may increase the wetability of fibres but at the same time increases water repellency. Advantages of plasma treatments to conventional wet processes are water saving and that plasma treatments do not affect the central structure of fibres.

Figure 7.78 Plasma treatments in textiles

93 For example, the plasma treatment for antipilling of wool is a much safer treatment than chlorination. Plasma treatment can etch away surface scales without damaging the inner part of wool fibres.

What can Plasma do?

Plasma is a complex gas mixture with ions (cations and anions), electrons and free radicals. Certain amount of electronically excited molecules may also be present. Generally, plasma has three effects on textiles and they are shown as follows:-

Etching

This refers to the taking away of some substances from the surface of fabrics. This will increase the surface roughness and wetability.

Surface chemical group modification

This refers to the change in surface chemical groups depending on the nature of the plasma applied. The newly formed chemical groups can induce further surface chemical reactions.

Plasma polymerisation or plasma that controls vapour deposition

This refers to the deposition of very thin films of polymers onto textile fibres. The properties of deposited polymer change the surface properties such as water repellency of textile materials.

Below are common types of plasma employed and their effects.

Plasma Effect Argon Increase surface roughness Oxygen Modification of surface chemical groups – Increase hydrophilicity Fluorocarbon Polymerisation – Increase hydrophobicity Ammonia, Modification of surface chemical groups Carbon Dioxide

The following chart, summarises the effects of plasma on textile materials. Plasma is a versatile technology that reduces water consumption, which suits the current trend of

94 environmental protection. Furthermore, plasma only deals with surface (only a few nanometers at stick) and will not affect the inner part of the fibre and retain the material strength.

Figure 7.79 Effects of plasma on textiles

7.8.4 Environmental Protection

Textile production from the stage of fibre to garment and textile products creates a lot of environmental impacts. Synthetic fibre production generates chemical wastes. Textile processing such as bleaching, washing, dyeing, rinsing, etc uses up tremendous amount of water and produce high volume of waste water. In addition, the industry consumes large amount of petroleum for energy generation, synthetic fibre production, colourant and auxiliary chemical production. Environmental protection is an unavoidable aspect for the future development of the industry.

(A) Waste Water Treatment

Textile processing uses great amount of water, particularly in the dyeing and finishing processes. Waste water is highly polluted with acid, base, starch and other chemicals. Many countries have waste water discharge regulations that require the textile industry to pre-treat waste before discharging it to the sewage system.

The measurement of the amount of pollutant present in waste water is indicated by the amount of oxygen consumption for biological system or chemical.

95 (i) Biological Oxygen Demand (BOD)

This measurement measures how fast biological organisms use up the oxygen in polluted water. It is usually performed over a 5-day period at 20° Celsius. It is used in water quality management and assessment.

(ii) Chemical Oxygen Demand (COD)

This measurement measures the amount of organic compounds in water. Most of the applications of COD determine the amount of organic pollutants found in surface water such as lakes and rivers, making COD a useful measurement of water quality. It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per litre of solution.

(iii) Activated Sludge

Many dyeing plants are installed with waste water treatment and employ activated sludge treatment as the major water purification process. Activated sludge is a process in which air or oxygen is forced into sewage liquor to develop a biological floc that reduces the organic content of the sewage. The biological floc mainly contains bacteria and protozoa fed on the dissolved organisms in the water. The purified water can be drain down the sewage or recycle for further use.

(B) Biodegradable versus Recycling

Waste accumulation is one of the environmental concerns for many cities. Two major approaches to reduce waste are “biodegradable” and “recycling”

Biodegradability refers to the degradability of materials by living organisms, mainly bacteria, in the soil. Reclamation is one kind of waste treatment that applies the method of waste biodegradation. Bacteria decompose waste to simpler forms and the degraded substances may provide nutrient to the plantation on top. Non-biodegradable wastes are stable in the soil for decades and the pace of their recycling circle is slow. They are being accumulated on a daily basis and occupy enormous space. One way to reduce waste is to have them produced biodegradable in the first place.

Recycling refers to the extract of materials from waste and re-use them for new products. Many cities are practicing the classification of waste disposal which is a practice that facilitates the gathering and handling of re-useable materials. It is obvious nowadays that many daily products can be made from recycled materials such as tissue paper,

96 writing pads, glass container, packaging material, etc. There are three common recycling marks present in daily products.

Recycle mark for Green Dot which Recycle mark, which introduced by battery which used in the paper Society of Plastic Industry for needs special industry. It means plastics (SPI), indicates the product treatment before the company has is made from recycled plastic. The disposal. contribution to center digit indicates the types of recycling. recycled plastic and sometime the plastic abbreviation will write below. PE-HD stands for high density polyethylene.

Figure 7.80 Various recycling marks on daily products

(i) Biodegradability

Biodegradability reduces waste by breaking down materials through bacterial actions. z Advantages

- Natural process - Breakdown products may re-entre nature as plant nutrients - Lower cost as soil contain many bacteria z Disadvantages

- Slow process and take long time to complete - The process may release toxic substances and further harm the environment - Not all materials can be degraded completely. Plastic, glass and metal are some examples of non-degradable materials. - Biodegradable products have limited shelf life

97 (ii) Recycle

Recycle uses material repetitively, its advantages are: z Advantages

- Reduce the need for new materials - Minimal waste - Functionally, recycled products may not be very different from new products z Disadvantages

- Recycling requires energy and water - High cost given that advanced technology may be required - Education, regulation and government administration are required to practice the classification of waste disposal - Recycled products usually are not attractive and they are usually in dark colours as they are being recycled from coloured products - Not all materials are able to recycle. Thermosetting materials are an example of non-recyclable material.

Biodegradation

Biodegradation is the process during which organic substances are broken down by living organisms. The term is often used in relation to ecology, waste management, environmental remediation (bioremediation) and plastic materials due to their long life span. Organic materials can be degraded aerobically with oxygen or anaerobically without oxygen. A term related to biodegradation is biomineralisation, which refers to the process of organic matter being converted into minerals.

Biodegradable matters are generally organic materials such as plant and animal matters and any other substances originating from living organisms. They can also be artificial materials that are similar enough to plant and animal matters that can be put to use by microorganisms. Some microorganisms have the astonishing, naturally occurring and microbial catabolic capacity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, metals, etc.

98 (C) Lyocell and Tencel®

Generally speaking, lyocell is a kind of rayon. Viscose is a popular rayon production method. The process is based on toxic carbon disulfide (CS2) as the solvent. The environmental impact of such process is the discharge of CS2 and xanthate (cellulose - carbon disulfide solution). Lyocell is a green process that employs non-toxic amine oxide as the solvent. Used amine oxides will be purified and recycled back to the production system, which enables further reduction of chemical waste. Tencel® is the trademark of lyocell which is produced by Lenzing Inc.

Figure 7.81 The lyocell process

(D) Organic Cotton

Conventional cotton plantation very much depends on chemicals. It takes up 10% of all agricultural chemicals and 25% of the insecticides applied. According to certain studies, a Tee-shirt made of cotton requires an average of 17 teaspoons of synthetic fertilisers plus 3/4 teaspoons of active ingredients such as insecticides, pesticide and herbicides. According to the information provided by the World Health Organization (WHO), around 20,000 deaths occur annually due to pesticide poisoning in developing countries. Organic cotton refers to the cotton that is grown naturally without the usage of artificial fertilisers, herbicides and pesticides. It is a kind of natural and clean cotton, which is very suitable for infant and children’s products.

99 (E) Bamboo Rayon

Viscose rayon is made by using wood pulps as raw material. Although wood pulps are industrial waste of the wood industry, wood is still considered as a non-renewable resource. Trees need many years to grow. Bamboo is an alternative source of cellulose that in fact grows much faster than other plants. Making rayon out of bamboo reduces the use of tree.

(F) Synthetic Fibres made from Resources other than Petroleum

Polylactic acid (PLA) fibre is a synthetic fibre made from fermented sugar extracted from corn or sugar beet. Chemists have been able to successfully convert natural sugar obtained from plants such as sugar cane and corn into ethanol, a substance that can be used as fuel for automobiles. This is one of the substitutions of petroleum.

(G) Polyester Recycling

Given the negative environmental impact of the PVC material, the selection of packaging material in the industry has been shifted to polyester. Polyethylene terephthalate (PET) is the most commonly used polyester and it is also the polyester fibre that we wear. PET has been being recycled from shot drink bottles and bubble packaging materials for clothing. PET packaging material is cleaned and crashed before the process of re-melting and being extruded to form new fibres. One of the major limitations of PET recycling is its colour. The colour of PET can only be dark.

Figure 7.82 Recycling of polyester packaging materials

100

(H) Water and Energy Saving

Same as any other industries or business operations, the textile industry is the course of adopting many energy saving operations in the production process to reduce energy consumption. Furthermore, the implementation of waterless production processes such as plasma treatment reduces water consumption. Many organisations are operating under worldwide environmental protection standards such as ISO 14000 to reduce energy or water consumption, save resources and reduce and recycle waste.

101

Not for Sale

The copyright of the materials in this booklet belongs to the Education Bureau. The materials can be used by schools only for educational purpose. Prior written permission of the Education Bureau must be sought for other commercial uses.

102 103

104