Surface modification of high-performance aramid and polyethylene fibres for improved adhesive bonding to epoxy resins Citation for published version (APA): Mercx, F. P. M. (1996). Surface modification of high-performance aramid and polyethylene fibres for improved adhesive bonding to epoxy resins. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR455550 DOI: 10.6100/IR455550 Document status and date: Published: 01/01/1996 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 04. Oct. 2021 SURFACE MODIFICATION OF HIGH-PERFORMANCE ARAMlD AND POLYETHYLENE FIBRES FOR IMPROVED ADHESIVE BONDING TO EPOXY RESINS Cover: Typical surface structure of air-plasma-treated PE tapes, showing many small pits (see chapter 5) Omslag: Karakteristieke oppervlaktestructuur van een met lucht-plasma behandelde PE film (zie hoofdstuk 5) SURFACE MODIFICATION OF HIGH-PERFORMANCE ARAMlD AND POL YETHYLENE FIBRES FOR IMPROVED ADHESIVE BONDING TO EPOXY RESINS Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof. dr. J.H. van Lint, voor een commissie aangewezen door het College van Dekanen in het openbaar te verdedigen op donderdag 7 maart 1996 om 16. 00 uur door Franciscus Petros Maria Mercx Geboren te Halsteren Dit proefschrift is goedgekeurd door de promotoren prof. dr. P.J. Lemstra prof. dr. ir. J. van Turnhout en de copromotor dr. ing. A.A.J.M. Peijs Contents Contents Chapter 1 Introduetion 1 1.1 Fibre-Reinforced Polymers 1 1.2 Adhesion 2 1.3 Developments in Aramid Fibre-Matrix and PE Fibre-Matrix Adhesion 4 1.3.1 Aramid Fibre-Matrix Adhesion 4 1.3.2 Polyethylene Fibre-Matrix Adhesion 7 1.4 Objective of the Present Investigation 8 1.5 Outline of the Thesis 9 1.6 References 10 Part A: Aramid Fibres Chapter 2 The Selective Introduetion of Specific Organic 15 Groups at the Surface of Aramid Fibres: A Model Compound Study 2.1 Introduetion 15 2.2 Experimental 15 2.2.1 Materials 15 2.2.2 Reactions 16 2.2.3 Characterization Methods 17 2.3 Results and Discussion 17 2.3.1 Chemica! Structure 17 2.3.2 Higher Homologues 23 2.3.3 Thermal Stability 24 2.3.4 Condusion 24 2.4 References 26 i i Contents Chapter 3 Surface Modification of Aramid Fibres 27 3.1 Introduetion 27 3.2 Experimental 27 3.2.1 Reactions 27 3.2.2 X -ray Photoelectron Spectroscopy 28 3.2.3 Scanning Electron Microscopy 28 3.2.4 Determination of Acthesion 28 3.2.5 Determination of Mechanical Properties 29 3.3 Results and Discussion 29 3.3.1 Chemical Structure 29 3.3.2 Acthesion and Mechanical Properties 33 3.4 References 35 Part B: Polyethylene Fibres Chapter 4 Oxidative Acid Etching 39 4.1 Introduetion 39 4.2 Experimental 40 4.2.1 Prepararlon of Tapes 40 4.2.2 Acid Treatment 41 4.2.3 Determination of Acthesion 41 4.2.4 Determination of Mechanica} Properties 42 4.2.5 X-ray Photoelectron Spectroscopy 42 4.2.6 Infrared Spectroscopy 42 4.2.7 Scanning Electron Microscopy 42 4.3 Results 43 4.3.1 Acthesion versus Mechanical Properties 43 4.3.2 Scanning Electron Microscopy 45 4.3.3 Weight Loss 47 4.3.4 Infrared Spectroscopy 47 4.3.5 X-ray Photoelectron Spectroscopy 48 4.4 Discussion 50 4.5 References 52 Contents iii Chapter 5 Air- and Ammonia-Plasma Treatment 55 5.1 Introduetion 55 5.2 Experimental 56 5.2.1 Polyethylene Tapes 56 5.2.2 Plasma Treatment 56 5.2.3 Adhesion, Mechanica! Properties and 57 Chemica! Characterization 5.2.4 Scanning Electron Microscopy 57 5.3 Influence of Process Parameters 58 5.4 Results and Discussion 59 5.4.1 Tape Charaterization 59 5.4.2 Acthesion and Failure Mode 65 5.4.3 Mechanism of Acthesion 67 5.5 Conclusions 71 5.6 References 72 Chapter 6 Corona Grafting of Acrylic Acid 75 6.1 Introduetion 75 6.2 Experimental 75 6.2.1 Polyethylene Tapes 75 6.2.2 Corona Grafting 76 6.2.3 Characterization 76 6.3 Results and Discussion 76 6.3.1 Tape Characterization 77 6.3.2 Acthesion and Mechanica! Properties 80 6.3.3 Surface Treatment and Shear Strength 80 6.4 References 81 Epilogue The Role of Fibre Anisotropy and Adhesion on 83 Composite Performance iiii Contents Summary 88 Samenvatting 92 Curriculum Vitae 96 Dankwoord 97 Introduetion 1 Chapter 1 Introduetion 1.1 Fibre-Reinforced Polymers The use of fibre-reinforced polymers has rapidly grown over the past few decades and there is every indication that this will continue. This growth has been achieved mainly by the reptacement of traditional construction materialsas metals, wood and concrete and was driven by the superior properties per unit weight (specific properties) of fibre-reinforced polymerie materials. The higher specific modulus and strength of fibre-reinforced polymers means that weight savings can be realized when constructing with these composite materials, which results in a greater efficiency and energy savings. Initially applied in military and aerospace applications, fibre-reinforced composites have now penetrated other segments of the market as well, including the automotive industry. Some examples of the various realized applications are given in table 1.1. Table 1.1 Applications offibre-reinforced polymeri·5 Industry Examples Aerospace Antennas, wings, radomes, helicopter blades, landing gears Marine Hulls, decks, masts Automobile Bumpers, drive shafts, seats, trailers Sport Tennis and squash rackets, fishing rods, skis, canoes, golf clubs Fumiture and equipment Chairs, tables, lamps, ladders Chemica! Pressure vessels, pipes 2 Chapter 1 Partienlady the inexpensive glass-fibre-reinforced polymers contributed much to the growth of polymerie composites in the last decade. The more actvaneed composites, based on carbon and/or aramid fibres, are stilllimited intheir commercial use because of high material costs. However, they are widely applied in the aerospace industry to satisfy requirements for enhanced performance and reduced maintenance. Moreover, since the sports industry discovered these advanced polymerie composites, the number of applications and consequently 2 3 their commercial importance is growing • .s. The reptacement of traditional materials as metals by polymerie composites was not achieved easily. It was in fact preceded by elaborate research to optimize the (mechanical) properties of fibre reinforeed polymers. The development of new high-performance fibres with improved strengthand stiffness to weight ratios was but one important step. Decisive for the evolution of fibre reinforeed polymers to its present accepted status as competitive construction material were, however, the developments in the area of fibre-matrix adhesion. 1.2 Adhesion The first applications of fibre reinforeed polymers can be traeed back to 1940s when glass fibres were first used as reinforcement in polyester resins. It soon became apparent that these polymerie composites may loose much of their strength in every day practice, resulting in 6 7 premature failures • • The in-depth investigations that foliowed traeed this back to the low initia! adhesion, that could not withstand the intrusion of water. Eventually this leads to the debonding of resin from the hydrophillic glass, causing the observed deterioration in properties. Following the recognition that the level of fibre-matrix adhesion was the key factor to composite performance, a search began for glass fibre sizings that could improve the adhesion between such dissimHar matenals as glass and polyester. To this end numerous compounds were evaluated. Not surprisingly, organofunctional silanes, which are hybrids of silica and organic matenals related to resins, were among the compounds tested. They proved to be highly effective in increasing both the dry- and wet-strengthof glass-fibre-reinforced 6 7 polyesters • • Moreover, by tailoring the organic part of these silanes, it proved to be relatively easy to optimize the adhesion of the glass fibres to other polymerie materials, 6 7 including epoxy resins, polyamides and even polyolefms • • It was these developments in the area of adhesion that increased the (long-term) performance and ensured the reliable use of glass-fibre-reinforced polymers in every day practice.