Cut Protective Textiles (The Textile Institute Book Series) [1 ed.] 0128200391, 9780128200391

Table of contents :
Cover
The Textile Institute Book Series
Cut Protective Textiles
Copyright
Contents
Foreword
Foreword
Preface
1 Cut and slash hazards
2 Evaluate cut resistance
2.1 ISO13997
2.2 EN388:2016 and ISO23388:2018
2.3 ASTM F2992/F2992M-15
2.4 ISO13998
2.5 ISO13999
2.5.1 ISO13999-3
2.5.2 ISO13999-2
2.5.3 ISO13999-1
2.6 Cut resistance for protection against chainsaw
2.6.1 ISO and EN standards series for chainsaw protection
2.6.2 ASTM standards series for chainsaw protection
3 Fundamental of fibers
3.1 Basic forms of fibers
3.1.1 Staple and staple spun yarn
3.1.2 Filament yarn
3.1.3 Textured yarn
3.1.3.1 Air textured yarn
3.1.3.2 False twist textured yarn
3.1.3.3 Bicomponent textured yarn
3.1.4 Composite yarn: core-spun yarn and wrapped yarn
3.1.4.1 Core-spun yarn
3.1.4.2 Air-covered yarn
3.1.4.3 Wrap yarn
3.2 Basic properties of fibers
3.2.1 Linear density
3.2.2 Mechanical properties
3.2.3 Hairiness
3.2.4 Yarn evenness
3.2.5 Twist
4 Convert fiber to textile
4.1 Knitting
4.2 Weaving
4.3 Nonwoven
5 Choice of materials for cut protective textile
5.1 Spinning
5.1.1 Melt spinning
5.1.2 Solution spinning
5.2 Materials
5.2.1 para-Aramid
5.2.1.1 para-Aramid filament
5.2.1.2 Staple spun yarn
5.2.1.3 Textured yarn of para-aramid
5.2.2 High-strength polyethylene (ultrahigh molecular weight polyethylene)
5.2.3 Glass fiber
5.2.4 Steel wire
5.2.5 Nylon fiber
5.2.6 Polyester fiber
5.2.7 Wholly aromatic polyester fiber
5.2.8 Cotton fiber
5.2.9 Poly-p-phenylene benzobisoxazole fiber
5.2.10 High strength and high modulus polypropylene fiber
5.2.11 Polyvinyl alcohol fiber
5.2.12 Basalt fiber
5.2.13 Polyimide fiber
5.2.14 Tungsten wire
5.2.15 Other fibers
5.3 Dipping or coating materials for cut protective textile
5.3.1 Solvent-borne polyurethane
5.3.2 Water-borne polyurethane dispersion/emulsion
5.3.3 Natural rubber latex
5.3.4 Nitrile rubber latex
5.3.5 Chloroprene latex
5.3.6 Polyvinyl chloride dipping or dotting
5.3.7 Silicone rubber dotting
5.3.8 Other coating materials
6 Mechanism of cut and cut resistance, factors affecting cut resistance, and development trend of cut resistant products
6.1 Mechanism of cut
6.2 Factors affecting cut resistance
6.3 Development trend and measures to improve cut resistance
Appendix A Conversions between different units of tenacity and strength
Appendix B: Data in patents 242–258
Appendix C: Statistical analysis for data in patents
Appendix D: Physical properties of materials
Appendix E: Constructions of knit fabric with different fibers
References
Index
Back Cover

Citation preview

Cut Protective Textiles

The Textile Institute Book Series Incorporated by Royal Charter in 1925, The Textile Institute was established as the professional body for the textile industry to provide support to businesses, practitioners and academics involved with textiles and to provide routes to professional qualifications through which Institute Members can demonstrate their professional competence. The Institute’s aim is to encourage learning, recognise achievement, reward excellence and disseminate information about the textiles, clothing and footwear industries and the associated science, design and technology; it has a global reach with individual and corporate members in over 80 countries. The Textile Institute Book Series supersedes the former ‘Woodhead Publishing Series in Textiles’ and represents a collaboration between The Textile Institute and Elsevier aimed at ensuring that Institute Members and the textile industry continue to have access to high calibre titles on textile science and technology. Books published in The Textile Institute Book Series are offered on the Elsevier web site at: store.elsevier.com and are available to Textile Institute Members at a substantial discount. Textile Institute books still in print are also available directly from the Institute’s web site at: www.textileinstitute.org To place an order, or if you are interested in writing a book for this series, please contact Matthew Deans, Senior Publisher: [email protected]

Recently Published and Upcoming Titles in The Textile Institute Book Series: New Trends in Natural Dyes for Textiles, Padma Vankar Dhara Shukla, 978-0-08-102686-1 Smart Textile Coatings and Laminates, William C. Smith, 2nd Edition, 978-0-08-102428-7 Advanced Textiles for Wound Care, 2nd Edition, S. Rajendran, 978-0-08-102192-7 Manikins for Textile Evaluation, Rajkishore Nayak and Rajiv Padhye, 978-0-08-100909-3 Automation in Garment Manufacturing, Rajkishore Nayak and Rajiv Padhye, 978-0-08-101211-6 Sustainable Fibres and Textiles, Subramanian Senthilkannan Muthu, 978-0-08-102041-8 Sustainability in Denim, Subramanian Senthilkannan Muthu, 978-0-08-102043-2 Circular Economy in Textiles and Apparel, Subramanian Senthilkannan Muthu, 978-0-08-102630-4 Nanofinishing of Textile Materials, Majid Montazer Tina Harifi, 978-0-08-101214-7 Nanotechnology in Textiles, Rajesh Mishra Jiri Militky, 978-0-08-102609-0 Inorganic and Composite Fibers, Boris Mahltig Yordan Kyosev, 978-0-08-102228-3 Smart Textiles for In Situ Monitoring of Composites, Vladan Koncar, 978-0-08-102308-2 Handbook of Properties of Textile and Technical Fibres, 2nd Edition, A. R. Bunsell, 978-0-08-101272-7 Silk, 2nd Edition, K. Murugesh Babu, 978-0-08-102540-6

The Textile Institute Book Series

Cut Protective Textiles

Daniel (Xuedong) Li

Woodhead Publishing is an imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom Copyright © 2020 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-820039-1 (print) ISBN: 978-0-12-820391-0 (online) For information on all Woodhead Publishing publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans Acquisitions Editor: Brain Guerin Editorial Project Manager: John Leonard Production Project Manager: Debasish Ghosh Cover Designer: Christian Bilbow Typeset by MPS Limited, Chennai, India

Contents

Foreword by Alan E. Learned Foreword by Vlodek Gabara Preface

vii ix xi

1

Cut and slash hazards

1

2

Evaluate cut resistance 2.1 ISO13997 2.2 EN388:2016 and ISO23388:2018 2.3 ASTM F2992/F2992M-15 2.4 ISO13998 2.5 ISO13999 2.5.1 ISO13999-3 2.5.2 ISO13999-2 2.5.3 ISO13999-1 2.6 Cut resistance for protection against chainsaw 2.6.1 ISO and EN standards series for chainsaw protection 2.6.2 ASTM standards series for chainsaw protection

3

Fundamental of fibers 3.1 Basic forms of fibers 3.1.1 Staple and staple spun yarn 3.1.2 Filament yarn 3.1.3 Textured yarn 3.1.4 Composite yarn: core-spun yarn and wrapped yarn 3.2 Basic properties of fibers 3.2.1 Linear density 3.2.2 Mechanical properties 3.2.3 Hairiness 3.2.4 Yarn evenness 3.2.5 Twist

59 59 61 81 81 87 96 96 101 107 107 109

4

Convert fiber to textile 4.1 Knitting 4.2 Weaving 4.3 Nonwoven

111 111 121 125

15 15 21 34 40 44 45 48 49 50 50 53

vi

5

6

Contents

Choice of materials for cut protective textile 5.1 Spinning 5.1.1 Melt spinning 5.1.2 Solution spinning 5.2 Materials 5.2.1 para-Aramid 5.2.2 High-strength polyethylene (ultrahigh molecular weight polyethylene) 5.2.3 Glass fiber 5.2.4 Steel wire 5.2.5 Nylon fiber 5.2.6 Polyester fiber 5.2.7 Wholly aromatic polyester fiber 5.2.8 Cotton fiber 5.2.9 Poly-p-phenylene benzobisoxazole fiber 5.2.10 High strength and high modulus polypropylene fiber 5.2.11 Polyvinyl alcohol fiber 5.2.12 Basalt fiber 5.2.13 Polyimide fiber 5.2.14 Tungsten wire 5.2.15 Other fibers 5.3 Dipping or coating materials for cut protective textile 5.3.1 Solvent-borne polyurethane 5.3.2 Water-borne polyurethane dispersion/emulsion 5.3.3 Natural rubber latex 5.3.4 Nitrile rubber latex 5.3.5 Chloroprene latex 5.3.6 Polyvinyl chloride dipping or dotting 5.3.7 Silicone rubber dotting 5.3.8 Other coating materials

147 165 169 175 176 180 185 186 188 190 193 194 198 200 201 206 212 212 214 216 216 217 218

Mechanism of cut and cut resistance, factors affecting cut resistance, and development trend of cut resistant products 6.1 Mechanism of cut 6.2 Factors affecting cut resistance 6.3 Development trend and measures to improve cut resistance

219 219 224 228

Appendix A: Conversions between different units of tenacity and strength Appendix B: Data in patents Appendix C: Statistical analysis for data in patents Appendix D: Physical properties of materials Appendix E: Constructions of knit fabric with different fibers References Index

129 129 129 129 133 133

233 235 237 241 245 247 273

Foreword

Over 1 million workers in North America will be taken to the emergency room this year for the treatment of hand injuries. Seventy percent of those injuries occurred, while the workers were not wearing any protective gloves, and the remaining 30% were wearing the wrong type of gloves for the level of hazard they were experiencing. So YES!!!, cut protective gloves is an important topic from both a business cost perspective, with the average medical treatment cost ranging from $6000 to $10,000 for each injury, and from a personal pain and suffering perspective, where the impact is not only in the workplace, but also at home among families when a mother/father/ wife/husband/brother/sister/son/daughter returns from work injured. According to the Occupational Health and Safety Administration (OSHA is a federal agency in the United States responsible for assuring a safe and healthful environment for workers), more than 70% of those injuries could have been avoided with the appropriate training, design, and personal protective equipment, such as cut protective gloves. It was over a decade ago at a technology leadership conference that I first met Dr. Xuedong Li. My career in textiles and technology development has spanned over 40 years, and in that first meeting, I was impressed by Dr. Li’s passion for safety and protection. During the following years while Dr. Li worked in my global technology team, I learned to appreciate even more his strong intellectual curiosity that drove him to relentlessly pursue the fundamentals of his development projects, searching for better ways to provide higher performance and better protection. Dr. Li’s book on Cut Protective Gloves will provide you both a broad and deep look at this fascinating and complex topic, cut protection. He will introduce the basic building blocks of the protective materials, polymers, and fibers, how the fibers and fabrics are measured to understand their ability to protect the workers, and how the materials are constructed into their final protective form, gloves. Dr. Li will explore with you the fundamental mechanisms of cut protection and will even unpack for you several of the current mysteries that still exist in this field. Whether you are just beginning your journey to understand cut protection, or if you are an experienced professional in this area, I believe you will find new insights that will act as a catalyst to ultimately help workers return home safe and uninjured. Dr. Alan E. Learned Retired Global Technology Manager DuPont de Nemours, Inc.

Foreword

I have enjoyed writing this foreword for two reasons: I have spent most of my professional life doing research in the field of advanced fibers and I have known, the author, Dr. Daniel Li, for most of his professional life. R&D in advanced fiber field shares many elements with research on other fibers. In both cases, one needs to develop understanding of polymer chemistry and technology of polymer formation, in both one needs to develop understanding of engineering of fiber formation and many other technologies. What distinguishes the advanced fiber field is the necessity to understand how these fibers perform in final applications. This is as sophisticated and as fundamental science as science of polymerization chemistry or spinning solution rheology. This understanding is necessary to design final objects while maximizing the utilization of the unusual physical properties of these fibers. The unique anisotropy of properties of these fibers has to be considered in almost all applications. Dr. Li monograph covers cut protection, one the important applications of these fibers. The monograph covers a complete range of topics required to understand the problem. It includes basic science of fibers, yarns, composite yarn, and finally fabrics and their production. A very useful, brief description of fibers used in this application gives readers the necessary background information. Mechanism of cut protection and treatment of fabrics used in this application completes the monograph. In addition to its completeness, it is well written and I am convinced it will be useful for scientists and engineers with different levels of familiarity with the field. I do hope that Dr. Li will consider expanding his work into other applications of advanced fibers. Dr. Vlodek Gabara Retired Global Technology Manager, DuPont de Nemours, Inc. January 2019

Preface

The awareness of and demand for safety protection have been constantly increasing along with the ongoing development of our global economies. Worldwide, the developed countries are leading in the legislation and execution for labor protection as well as the development and use of personal protective equipment, which set examples for and can be used by the developing countries. I used to work in DuPont for many years on the applications of aramid fibers. In the manufacturing sector, the safety system and practices of DuPont have been well known across the world and have been viewed by many as setting the highest bar of safety performance in industry. DuPont has also participated in establishing many safety standards in the United States. I have experienced and learned tremendously both safety theory and practice during working in the laboratories in DuPont. In the DuPont manufacturing groups, safety contacts, auditing, and training were expected on each shift of every day. . .7 days per week. . .365 days per year. In nonmanufacturing group, safety is also a daily topic. In the R&D labs I worked, besides all the safety measures and information exchange done on a daily basis, a formal monthly safety training was mandatory for every employee. The training covered different contents each month, such as electric safety, hand safety, machinery safety, chemical safety, household safety, sports safety, motorcycle and bicycle safety, pedestrian safety, children safety, sometimes latest changes in laws and regulations such as new traffic laws. I always left my cell phones in office and sat in front of the training class in order for me to focus on the training. More than 10 years, such experience in training also benefits me tremendously. I had the opportunity to get hands-on and participate in upgrading many types of equipment and processes to improve the safety. As I handled lots of equipment, in DuPont’s machinery safety management standard and practice have tremendously benefited me at my job. The safety practices of DuPont not only cover on-the-job areas, but also extend to off-the-job, especially to the employees’ families, for instance, household safety, appliance safety, children safety. The strict policy of safety belt use and the penalty for not using also help to save lives of my colleagues who became involved in traffic accidents. I always remember a surprising moment in Shanghai, China that a taxi driver told me that I must be from DuPont when I got into his taxi and insisted on getting the seat belt to fasten. Influenced by the safety culture of DuPont, many employees equip fire extinguishers at home, which is not common in China. This did save one of my colleagues’ family in a home fire incident. In addition, aramid fibers are widely used in protective products. As my technical field was in aramid fibers, I did extensive research and development in cut

xii

Preface

protective products. A large portion of workplace injuries are hand injuries, with mechanical hazards, including cuts, being the most common. However, a search of the literature reveals that no definitive books have been written on this very important topic. Likewise there is also very limited academic research published on this subject. After having conducted extensive research and development in cut protective products during my career, I felt compelled to summarize the critical knowledge on this topic. I hope that readers of this book will be able to better understand the complexities of cut protection and continue to advance the technology in a way that helps to protect more people in their daily work for the decades to come. Originally, I intended to write a book on all major applications of aramid fiber, in which cut protection was supposed to be only one chapter. But during the writing of this chapter, the contents were gradually expanded and eventually became a standalone book. Some basic knowledge of textile and fiber materials is added, and thus this book can be used for all practitioners in this industry along the entire value chain. No confidential information from DuPont was used in writing this book. As I have a full-time busy job and also demanding family needs, I can only use part of the weekends and holidays to write this book to make sure this writing work does not conflict with the full-time job and family needs. It has been a difficult journey. I got up at 5:30 a.m. on every weekend day and holiday during the 2 years of writing, including in the coldest winter, and write until 8:30 or 9 a.m. when my daughters started to be active. Though this book is not long, it still took me more than 2 years to complete. I hereby would like to appreciate my family for their tolerance, especially my two daughters Esther and Joy. Though they really wanted to play with me, they knew I was rushing to complete this book and therefore behaved very well not to disturb my writing. Thank you Esther and Joy, you are my sunshine. And to my lovely wife, none of this would be possible without your love and support. You are my rock and my inspiration. I would like to extend my appreciation to Dr. Alan E. Learned and Dr. Vlodek Gabara. Dr. Learned used to lead the DuPont global personal protection technology team in aramid business and now has already retired. Dr. Learned helped me review the entire book and gave invaluable suggestions and also helped me on the language in this book. Dr. Gabara used to be a DuPont Fellow and had spent most of his career on aramid technology. He is a worldwide recognized high performance fiber expert and has played a critical role in commercial success of Kevlar and Nomx aramid fibers. He therefore earned a name of “Godfather of Kevlar Fiber.” He has retired from DuPont. Dr. Gabara has been a role model for me in my technical career and encouraged me to write something from application aspect. He helped me review the book. I would also like to extend my appreciation to Larry J. Prickett, a productive researcher in DuPont. Larry has worked on Kevlar aramid fiber for more than 40 years and developed many cut protective products containing Kevalr aramid fiber. He is a very kind coach and taught me a lot in cut protection and cut protective products. Daniel (Xuedong) Li Shanghai, China July 2019

1

Cut and slash hazards

According to the data released by the US Bureau of Labor Statistics, there were approximately 2.8 million nonfatal workplace injuries and illnesses reported by private industry in 2017, among which 882,730 occupational injuries and illnesses resulted in days away from work.1 Besides, there was a total of 89,180 injuries caused by cut, laceration or punctures (not only on hands), accounting for some 10% of the total injuries. While the top two categories are sprains, strains, tears, and soreness and pain, which are usually caused by overexertion of body, overstretch, and awkward body position, not by tools, as a contrast, the cut, lacerations, and punctures are usually caused by tools. Among these 882,730 injuries and illnesses, 201,910 (22.9%) occurred to hands, arms, and wrists. Hence, cut protection, especially for hand protection, is critically important to workplace safety. Table 1.1 shows the incident rate of different categories of injuries in the private industry of the United States in 2017. Cut hazards are everywhere. Cuts and lacerations occur at a rate of 8.1 incidents for every 10,000 workers. Some common workplaces with high cut hazards include the following: 1. Sheet metal handling such as metal forging and stamping, and sheet metal manual carrying. For instance, in stamping workshops of car manufacturing facilities, the workers need to transport thin steel sheets. It is often unavoidable to do manual handling of sheet metal on many occasions. Very thin sheet metal poses significant cut injury threats to Table 1.1 Incident rate in the private industry of the United States in 2017. Nature of injury or illness

Percentage of different categories

Sprains, strains, and tears Soreness and pain Cuts, lacerations, and punctures Fractures Bruise and contusions Multiple traumatic injuries Heat (thermal) burns Carpal tunnel syndrome Amputations Chemical burns and corrosions Tendonitis All others

35.3 16.2 10.1 9.5 9.0 2.0 1.6 0.6 0.5 0.3 0.3 14.6

Source: From Bureau of Labor Statistics, USA. ,bls.gov/iif/oshsum.htm#17Summary_News_Release.. Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00001-8 © 2020 Elsevier Ltd. All rights reserved.

2

Cut Protective Textiles

2.

3.

4.

5. 6.

7.

the workers. The sharp edge can easily cut through flesh and even bones especially when the sheet metal slips from hands if the workers do not grip it well. The author witnessed an injury when a worker in a stamping workshop of an automotive manufacturing factory carried a stainless steel sheet and it slipped from his hand and caused a thumb cut, even though he wore a pair of cut-resistant gloves. Handling sheet metal is shown in Fig. 1.1. Metal-processing factories where workers need to handle processed parts and offcuts. The workplaces are different from those in the metal forging and stamping process but the hazards are similar (Fig. 1.2). Glass manufacturing factories where workers need to handle glass sheets (see Fig. 1.3). The edges of finished glass-sheet products are usually not a problem as they are usually ground and, therefore, are smooth. The threat is posed by those semifinished sheets and broken sheets. Many workers suffer cut on hands and arms when they carry and move glass sheets. The author also witnessed many injuries caused by glass in glass-sheet factories. Some of those injuries are very serious and some workers lose some functions permanently. Slaughtering. Butchery is a very old occupation. The cutting hazard is very obvious to everyone. Slaughtering usually requires a high force for cutting; therefore the threat level is high (see Fig. 1.4). Steel chainmail gloves are commonly used in slaughtering houses to respond to this kind of high level of risk. Forestry (Fig. 1.5). In the forestry industry, logging usually requires full-body protection due to the use of chainsaw, and hand protection is the minimum requirement. Recycling and waste handling (Fig. 1.6). According to a study, garbage collection is ranked as one of the most dangerous jobs in the United States.2 There are many kinds of stuff that may cut the workers, such as broken glasses, knives, cans, porcelain, and so on and so forth. Fig. 1.5 shows the hazards of handling waste. Electronics assembling and handling exhibit cutting hazards too. For instance, the sharp edge of printed circuit board and the soldering point can easily cut hands when the hands

Figure 1.1 Sheet metal handling. Source: Courtesy MCR Safety.

Cut and slash hazards

3

Figure 1.2 Metal processing. Source: From Chevanon Photography on Pexels.com.

Figure 1.3 Glass-sheet handling. Source: Courtesy Kezzled Pakistan. slide on top of them. Fig. 1.7 shows such working environment. Certainly, the sharp soldering points also pose puncturing hazard which is different from cut hazard. The puncturing is not a subject of this book. 8. Food processing (Fig. 1.8). In food-processing factories and even in busy kitchens the workers do very frequent cutting with sharp tools; therefore the cutting hazard is very high. 9. Construction (Fig. 1.9). In construction work the workers need to handle construction materials with rough surfaces, such as cement blocks and bricks, and sharp-edged materials and tools, such as cut pipe ends and structure metal. 10. Pressurized glass bottle handling such as in beer brewery (Fig. 1.10). The pressurized glass bottles sometimes break or explode under pressure due to defects in the glass. The workers need to wear cut-resistant gloves when handling these bottles.

4

Figure 1.4 Slaughtering house. Source: Courtesy Birk Staal Denmark.

Figure 1.5 Use chainsaw. Source: Courtesy Irish Farmers Journal.

Cut Protective Textiles

Cut and slash hazards

5

Figure 1.6 Waste handling. Source: From ,https://www.epa.gov/sites/production/files/2017-10/recycling_from_above_0.jpg..

Figure 1.7 Handling electronics. Source: From ,denvergov.org.. 11. Pulp and paper industry. Pulp and paper manufacturing poses heavy hazards to the workers due to the massive weights and rolling and sliding pulpwood loads and fast-moving sharp paper. Many people have experience of being cut by copy paper in the office when a piece of paper slides on top of a finger. The moving speed of paper is much faster than that in the office and, therefore, is much more hazardous in terms of cut injury potential. Fig. 1.11 shows the personal protection from cutting by paper. 12. Leather and textile mills. Leather and textile industries exercise numerous cutting in their manufacturing, including cutting leather to desired shape, cutting yarn threads and

6

Figure 1.8 Food processing. Source: From chuttersnap on Unsplash.

Figure 1.9 Construction work. Source: Courtesy MCR Safety.

Cut Protective Textiles

Cut and slash hazards

Figure 1.10 Handling pressurized glass bottles. Source: Courtesy Myanmar Times.

Figure 1.11 Handling paper.

7

8

Cut Protective Textiles

fabrics to metered length or desired dimension, and so on. In textile mills the moving threads in spinning are also a type of cutting hazard to the operators. Fig. 1.12 shows the cutting hazard in fabric mill. 13. Sports. In hockey sports (Fig. 1.13) the skate blades are fairy sharp. Many players have full protection over the body but some skip the throat protection due to discomfort. However, throat cut accident did happen from time to time.3,4

Figure 1.12 Cut fabrics. Source: Courtesy Ordnur Textile and Finance.

Figure 1.13 Risk of skate blade slash injury. Source: Photo by Markus Spiske on Unsplash.

Cut and slash hazards

9

Last but not least, many office and household works are also hazardous, such as cutting with knives and scissors, cleaning glass fragments, scrap metals, and doing plumbing work. The top 30 nature of work which has the highest incident rates of cut and laceration in the United States are listed in Table 1.2.1 The entire personal protection equipment (PPE) market was valued at some US $48 billion in 2018, and expected to grow to some 70 billion by 2025 at an estimated compounded annual growth rate of 6.6%.5 There is no market size information available for the cut protection alone. Usually the protective products’ market Table 1.2 Incident rates of cut and laceration by the nature of work in 2017. Nature of work Marinas Framing contractors Flooring contractors Blind and shade manufacturing Electroplating anodizing and coloring metal Siding contractors Sign manufacturing Food product machinery manufacturing Bottled water manufacturing Roofing contractors Metal and mineral merchant wholesalers Meat markets Noncurrent-carrying wiring device manufacturing Concrete block and brick manufacturing Hog and pig farming5 Steel and precast concrete contractors Cut stock resawing lumber and planing Truss manufacturing Wood container and pallet manufacturing Other building equipment contractors Showcases partitions shelving and lockers Fabricated pipe and pipe fitting mfg Fabric coating mills Coating engraving and heat treating metals Commercial machinery repair and maintenance Support activities for printing Polystyrene foam product manufacturing Boat building Seafood product preparation and packaging Custom architectural woodwork and millwork

Total injury rate

Injury rate of cut and laceration

224.5 319.8 136.2 197.1 131.1 274.1 92.3 96 163.3 221.3 169.2 130 109.4

92.9 90.4 56.9 56.3 54.7 54.3 49.5 47.6 47 45.4 44.1 41 40.5

150.6 205.1 184.6 180.7 157.4 225.1 104.7 151 110.5 156.6 138.1 108.6 78.7 110.8 133.7 301.7 167.9

37.7 36.9 35.6 35.5 35.2 34.9 34.4 34.2 33.1 32.9 31.1 30.9 30.8 30.8 30.8 30.6 29.9

Source: From Bureau of Labor Statistics, USA. ,bls.gov/iif/oshsum.htm#17Summary_News_Release..

10

Figure 1.14 Textile gloves. Source: Courtesy MCR Safety.

Figure 1.15 Protective apron. Source: Courtesy MCR Safety.

Cut Protective Textiles

Cut and slash hazards

Figure 1.16 Protective sleeve. Source: Courtesy MCR Safety.

Figure 1.17 Protective gaiters. Source: From ,https://commons.wikimedia.org/wiki/File:Tourist_Gaiters.jpg..

11

12

Cut Protective Textiles

is categorized as hand protection, fall protection, head protection, respiratory protection, etc. However, most cut injuries occur to hands. Though hand protection also includes the chemical and other protections the majority is for cut protection or multifunction mechanical protection including cut protection. It is reasonable to use a discounted hand protection figure to estimate the cut protection market. The largest demand in PPE market is hand protection with a share of around 25% of the total. If the cut protection is estimated at 20% of the total PPE market, then the value is approximately US$10 billion. This is a huge market and it continues to grow; especially for that, the safety and protection for workers in the emerging markets around the world is rising. Cut injuries happen more to hands and forearms, hence cut-protective products are mainly gloves, arm guards, and sleeves. The substrates of cut-protective textiles

Figure 1.18 Neck guard for ice hockey sport: (A) neck guard and (B) an ice hockey player wears neck guard. Source: Courtesy Aegis Impact.

Cut and slash hazards

13

Figure 1.19 Chainmail glove.

are usually knitted, or cut and sewn with woven fabrics. Knitting is a highly productive process, good for mass production, but not suitable for products with complex structures. Cut and sewn manufacturing is suitable for products with complex structures but is very labor intensive; therefore the cost is high, as a result, it is not economical for very large-scale production. Regardless of the manufacturing process, usually cut-protective textiles are made of fibers as substrates. The examples of cut-protective equipment include textile gloves, sleeves and arm guards, aprons, gaiters, pants, neck guard, and chainmail glove. Figs. 1.14 1.19 show the photos of some of these equipment. The most critical factors influencing the cut protection performance of the textile are fiber materials and the weight per unit area. Commonly used fibers materials in cut protection include, in the order of cut resistance from low to high, leather, cotton, nylon and polyester fibers, high strength or high-performance polyethylene fiber (also called as ultrahigh molecular weight polyethylene), para-aramid, glass fiber, and steel wire. Generally, when the material is fixed, cut resistance of a knit or woven fabric is determined by the basis weight (or weight per unit area) of the fabric. More materials result in higher cut resistance when everything else is equal. However, it is necessary to start with how to evaluate cut resistance as a first step.

Evaluate cut resistance

2

In order to evaluate cut resistance of the protective products, one has to start by understanding how to test cut resistance, that is, testing standards first. The cutting and failure in cutting are very complex phenomenon, which lead to great difficulties in developing reliable methods to evaluate the cut resistance of materials. The earliest literature the author is able to retrieve is a description on defining a minimum requirement for cut resistance of firefighters’ glove.6 A static cut and a dynamic cut were specified in this old literature. The static cut described using a blade with an edge having a 60 degrees included angle and a 0.025 mm radius to swipe cut a glove surface under a load of 7.2 kg at a speed not higher than 2.5 cm/s. The glove material should resist such a single-swipe surface cut. The dynamic cut described a free-fall impaction of a blade onto the surface of the glove materials by a 0.20 kg penetrometer from a height of 7.6 cm. The blade specification is the same as that for the static cut. The impact velocity corresponding to this height is 1.2 m/s. Cut from drops at or less than this height would constitute insufficient resistance. The static and dynamic cut testings have evolved as of today to different testing standards. The static cut testing has evolved as of today to mainly three international testing standards for testing cut resistance of textile products, namely, ISO13997,7 EN388,8 and ASTM F2992,9 originating from different researches. ASTM F2992 is mainly recognized in North America. ISO13997 is mainly recognized in Japan and in some industries in Europe. EN388 is recognized in the rest of the world. They are discussed in details in the following sections. A few other standards, ISO13998, ASTM F1414, and ASTM F1790, which are used for smaller market or less used today, are also briefly covered. The dynamic cut testing has evolved to ISO13998 and ISO13999 series.

2.1

ISO13997

ISO13997’s full name is “ISO13997:1999 protective clothing
mechanical properties
determination of resistance to cutting by sharp objects.”7 It was issued in 1999. This standard was not widely used before 2016 when EN388 was revised. Though it was quoted in EN388:2003 which is an earlier version than EN388:2016, it was only used as an optional method. However, the industry has gradually recognized that it is a more reliable testing method, and as a result it is quoted in EN388:2016 as a mandatory method if the testing meets certain criteria, which will be explained later. Since the implementation of EN388:2016, the importance of ISO13997 has been widely recognized. Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00002-X © 2020 Elsevier Ltd. All rights reserved.

16

Cut Protective Textiles

The instrument for cut testing in ISO13997 is called the TDM-100, which is a product name from a Canadian company called RGI Industrial Products.10 TDM stands for Tomodynamometer. Tomo is from Ancient Greek language, meaning “cut, slice, section.” Dynamometer is a device for measuring force, torque, or power. Combination of Tomo and Dynamometer means a device for measuring cutting force. For many years, RGI Industrial was the only manufacturing source for a TDM-100 instrument. But now, Mesdan in Italy has also launched its cut tester for ISO13997, named the Linear Cut Resistance Tester 3394B cut resistance evaluator.11 Fig. 2.1 shows the photos of the TDM-100 and the 3394B. Satra Technology has also developed its own version of linear cut testing for ISO13997, but unfortunately the author did not get response from Satra to the permission request to use the picture in this book. The testing mechanism is schematically shown in Fig. 2.2. A sample swatch of 7 cm 3 7 cm is fixed onto the curve-surfaced sample holder with a radius of 38 mm. A straight (or linear) cutting blade (see the photo in Fig. 2.3) is applied on top of the sample. The blade is usually sold in boxes with 100 pieces/box. Each box of blades needs to be calibrated with a chloroprene rubber standard sample by sampling five pieces of blades in the box. During testing a normal (vertical) load is applied onto the blade which travels horizontally at a constant speed of 2.5 mm/s to cut the sample on the sample holder. The motion of the blade is automatically stopped when the sample is cut through after the blade travels to a certain distance, and this distance in the units of millimeters is recorded. In calibration runs on standard chloroprene samples, the vertical load applied on the blade is 500 g. The blades are supposed to cut through the chloroprene standard samples at a cut distance of 20 mm under 500 g load. During the cut runs for samples the vertical load can be changed each time. A different cut distance is obtained when a different normal load is applied. A higher load leads to a shorter distance to cut through the sample, and vice versa. Eventually, a set of load
distance data is obtained. As required by ISO13997, at least 15 pairs of such load
distance data are needed to be generated for each

Figure 2.1 Photos of cut testing instruments for ISO13997: (A) TDM-100; (B) Linear Cut Resistance Tester 3394B. TDM, Tomodynamometer. Source: Courtesy (A) Les Produits Industriels RGI Inc. and (B) Mesdan s.p.A.

Evaluate cut resistance

17

Figure 2.2 Schematic diagram of cut testing on TDM-100 instrument. TDM, Tomodynamometer.

Figure 2.3 Straight cut blade used for ISO13997 on TDM-100. TDM, Tomodynamometer.

sample, among which 5 pairs must be within a cut distance of 5
15 mm, 5 pairs within 15
30 mm, and 5 pairs within 30
50 mm. Each cut must be with a new unused blade or an unused section of a blade to ensure that the sample is cut with the same blade sharpness each time. An exemplary set of 15 pairs of raw data together with the blade calibration data are used in Table 2.1 to illustrate the calculation and regression process. After all raw data, that is, the cut-through distances versus different vertical load, are collected, the corrected cut-through distances need to be calculated first by using the following equation: dc 5

20 3d d0

(2.1)

where dc is the corrected cut-through distance; d0 is the calibration cut-through distance, which is the average cut-through distance of five blades on a chloroprene standard sample; and d is the cut distance of test sample.

18

Cut Protective Textiles

Table 2.1 An exemplary set of TDM-100 cut testing data. Calibration cut distance d0 (mm)

Range of cut distance (mm)

Run

Load (g)

Cutthrough distance d (mm)

Corrected cut-through distance dc (mm)

ln (corrected cutthrough distance dc)

23.5

30
50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1600 1600 1600 1600 1600 1800 1800 1800 1800 1800 2000 2000 2000 2000 2000

39.5 38.6 34.1 38.1 33.2 25.0 21.5 25.1 25.6 24.5 10.9 11.7 13.6 9.1 9.3

33.6 32.9 29.1 32.4 28.3 21.3 18.3 21.4 21.8 20.8 9.3 10.0 11.6 7.8 7.9

3.5 3.5 3.4 3.5 3.3 3.1 2.9 3.1 3.1 3.0 2.2 2.3 2.4 2.0 2.1

15
30

5
15

For example, the cut-through distance d of Run 1 is 39.5 mm, and d0 is 23.5 mm, therefore, dc 5

20 3 39:5 5 33:6 mm 23:5

These 15 pairs of data are plotted by using corrected cut-through distance as the Y-axis and the load as the X-axis, then a regression line is fitted for this plot (Fig. 2.4). It can be seen from Fig. 2.4 that the regression is nonlinear. The observation by Lara et al. in their research showed that the regression follows exponential behavior.12 Fig. 2.5 shows Lara’s work. The regression line shows that the blade displacement (cut-through distance) quickly decreased with increasing applied load when the load is low. With further increasing load the cut-through distance decreased more slowly. The results shown in Fig. 2.5 were obtained by cutting a Kevlar para-aramid fabric. Similar patterns were also observed in cotton fabric and neoprene rubber in this report. The load needed to cut through the sample at the 20 mm distance can be located on the plot or calculated from the fitting equation. This load is reported as the cutting force, which can be interpreted as the force needed to cut through a sample at a 20 mm travel distance. The higher this value, the higher the force that is needed to cut through a sample, therefore the sample is more cut resistant, and vice versa.

Evaluate cut resistance

19

Figure 2.4 Corrected cut-through distance versus load data and regression line.

Figure 2.5 Effect of applied load on blade displacement required to cut a Kevlar aramid material. Source: From Lara J, Turcot D, Daigle R, Payot F. Comparison of two methods to evaluate the resistance of protective gloves to cutting by sharp blades. In: Johnson JS, Mansdorf SZ, eds. Performance of Protective Clothing: Fifth Volume, ASTM STP 1237. American Society for Testing and Materials; 1996:32
42.

20

Cut Protective Textiles

In the current example an exponential fitting is used to get the curve and the final regression equation is as follows: y 5 4415:6e0:003x where y is the corrected cut-through distance and x is the load. x can be solved when y is 20 mm. In this example case, x is 1799 g. It needs to be pointed out that ISO13997 only provides a testing method but does not rate cut resistance levels, while ASTM F2992-15 and EN388:2016 do have cut resistance level rating. ISO13997 does not specify any fitting method and only mentions using best-fit curve but ASTM F2992-15 specifies logarithm regression as the fitting method which might be a result of the research of Lara et al. as shown in Fig. 2.5; hence many people use logarithm regression to fit ISO13997 data. In logarithm fitting, all cut distance data are transformed to their either common logarithm (log10) or natural logarithm (ln), then these data after logarithm transformation are plotted against the load data. Linear regression is conducted for the load data and the logarithm of cut data and the following equation is obtained: y 5 b0 1 b1 x

(2.2)

Ln (distance to cut-through) (ln mm)

where y 5 ln(dc); x is the load; b0 is the intercept of the straight regression line; and b1 is the slope of straight regression line. This linear regression for logarithm of cut distance and load is shown in Fig. 2.6. When dc is 20 mm, y is 2.9957 (which equals to ln 20), then x is solved to be 1799 g, the same result as solved from Fig. 2.4. When there is a new sample with unknown cut resistance, it is hard to know how much load is needed to allow the cut-through distance fall into the mentioned Load versus ln (corrected cut-through distance dc) 4.0 y = –0.003x + 8.3929 R² = 0.9283

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 1500

1700 1900 Load (gf)

Figure 2.6 Natural logarithm fit between cut distance and load.

2100

Evaluate cut resistance

21

three cut-through distance ranges before a cut is carried out; thus it requires the operator’s experience and a few trials in the beginning. If a first load is tried and the cut-through distance is lower than 5 mm, then a lower load is needed in next run. If the load leads to a cut-through distance higher than 50 mm, then a higher load should be tried in next run. It is interesting to notice that many people do the cut testing by getting five cut distance under the same load within one cut distance range, like the example given in Table 2.1, though a regression is better to be carried out with data uniformly spread across the data range. Some organizations do get data as exemplified in Fig. 2.6 which should be a better practice than getting five data points under the same load. One needs to note that the load is applied in the unit of grams (weight applied); however, the result is reported in Newton in ISO13997, therefore the results need to be converted from gram to Newton. After calculating the force required to cut through the material in a 20 mm cut distance, one needs to run five further cuts using the calculated force. The average value of these five cut distances under this calculated force needs to be between 18 and 22 mm. If the average value is outside this limit, include the latest 5 pairs of data into the earlier 15 pairs to do regression and calculation again to get a new calculated force. Then run another five cuts under this new calculated force to see whether the new five cuts will be within the limit of 18
22 mm or not. Repeat this cycle until the results are satisfactory. This is specified in 6.3.5e of ISO13997. As mentioned previously, ISO13997 only specifies testing method but does not rate the cut resistance levels. It must be repeatedly emphasized, though already mentioned earlier, that each cut must be on a new blade or a new section of a blade to ensure that each data is generated on the same blade sharpness. If a section of a blade is already used, then the unused section of the same blade can still be used as long as the unused section is long enough for the next cut run. ISO13997 linear blade cut resistance test method is likely a result of the research by Lara et al., which was published in 1996.12 In their research the similar method was called IRSST (Institut de recherche en sante´ et en se´curite´ du travail du Que´bec) method. This method was apparently converted to the first version of ASTM F1790 in 1997. Then ISO13997 was established in 1999. It is strongly believed that both standards are derived from the same research work.

2.2

EN388:2016 and ISO23388:2018

EN3888 is the most widely recognized standard in the world. Before EN388:2016 the last version was EN388:2003 which was updated in 2003. The first formal version of EN388 should be the 1994 version (and there was a preliminary version called prEN388 in 1992). The full name for EN388 version 2016 is called “DIN EN 388:2016: Protective gloves against mechanical risks.” Though it is a DIN EN

22

Cut Protective Textiles

standard, people usually call it EN388, therefore we use EN388 throughout this book. There are four testing items in version 2003, that is, abrasion, puncture, tear, and cut. One more testing method, impact, is added into the version 2016; thus now there are totally five testing items in this standard. We only cover cut testing in this book. Two methods for cut testing were mentioned in version 2003 of EN388, the circular blade rotatary blade cut testing and the ISO13997 straight (or linear) blade cut testing. The circular blade rotational cut is called the Coupe test, and the tester is also called a Coupe tester. Coupe originates from the French word “Coupe´,” meaning to cut or remove. The reason that this method has a French name may be that it originated from a research work by Payot of Institut Textile de France—Lyon in France.14 This method was called ITF method in Ref. [12] before it was converted to the EN388 Coupe testing standard. Though ISO13997 was mentioned in last version of EN388, EN388:2003, it was used as a reference method only, not a mandatory method, therefore its importance in the 2003 version was rather low. The circular blade cut (Coupe test) was mandatory in version 2003 and therefore the Coupe test has become widely known in the industry. The importance of ISO13997 in the new EN388:2016 becomes much higher than that in the old version and will be discussed later. A photo of the EN388 Coupe test is shown in Fig. 2.7, and the mechanism is schematically illustrated in Fig. 2.8. The photo of a circular blade used for this test method is shown in Fig. 2.9. As specified by EN388:2016, the blade material needs to be stainless steel with Vickers hardness of 700
720 which corresponds to HRC (Rockwell Hardness C) 60-61.

Figure 2.7 Cut distance
load data and regression line by having test conducted under load across the entire range.

Evaluate cut resistance

23

Figure 2.8 Coupe cut testing equipment. Source: Courtesy Mesdan s.p.A.

Figure 2.9 Schematic illustration of Coupe cut testing.

During Coupe cut testing a fixed vertical load of 5 N is applied on top of a rotational circular blade which rotates and travels horizontally back and forth on the sample (Fig. 2.10). Both the rotational and horizontal travels of the blade are reciprocating. When the blade travels horizontally to one direction, the blade rotates toward one direction too, for example, clockwise. When the blade travels to the end of its horizontal trip, its horizontal speed gradually decreases to zero. At the end of this trip the blade stops and starts to return. In the meantime the rotational speed also gradually decreases to zero, then the blade starts to rotate to the opposite direction, for example, counter-clockwise when it returns. Before the testing starts the initial sharpness of the blade is calibrated with standard cotton canvas samples. The blade needs to run on a standard cotton canvas

24

Cut Protective Textiles

Figure 2.10 Circular blade used for EN388 Coupe cut test.

sample to determine how many cycles it takes to cut through the canvas. The number of cycles has to be within a certain range to qualify this blade to be used. When the sample is cut through, the motion of the blade is automatically stopped and the total rotation cycles of the blade are recorded. Each specimen needs to be cut five times on different parts of the specimen by experiencing the following steps: 1. The blade needs to cut through a standard cotton canvas cloth to get a cutting cycle Cn. 2. Then the standard cotton canvas cloth is replaced with the testing specimen and is cut by the same blade to get a cutting cycle Tn. 3. The standard cotton canvas cloth is cut again to get a cutting cycle Cn11. 4. The relative cutting cycles of testing specimen in is calculated using the following equation:

in 5

C n 1 Tn Cn

(2.3)

where C n is the average cutting cycle of the two cut runs on the standard cotton canvas sample, that is, Cn 5

Cn 1 ðCn11 Þ 2

Its significance is the average sharpness of the blade during the testing.

(2.4)

Evaluate cut resistance

25

The same testing is repeated five times, resulting in five in for the same specimen. Then average of these five data is calculated as In . In 5

i1 1 i2 1 i3 1 i4 1 i5 5

(2.5)

Two specimens for one sample are tested. The lower In value of the two specimens is taken as the cut index of this testing sample. EN388 also specifies the standard way to record the experimental data as shown in Table 2.2. EN388 Coupe test rates five cut resistance levels: Cut level 1: In $ 1.2 Cut level 2: In $ 2.5 Cut level 3: In $ 5.0 Cut level 4: In $ 10.0 Cut level 5: In $ 20.0

The blade is used throughout the five-time testing for each specimen, meaning it is not replaced and the same blade is used throughout all these cycles. The blade is repeatedly applied on the sample. In other words, regardless of how cut resistant or how abrasive the sample is and therefore regardless of how the blade is dulled during the testing, the blade has to be used until the sample is cut through. An issue is thus presented to the testers. If a sample is very abrasive and dulls the blade very quickly and seriously, the Tn of testing specimen will be very high because it requires a large number of cycles to be cut through. The more abrasive the sample is, the more cycles it needs to be cut through. More cycles mean more dulling effect on the blade, which requires even more cycles to cut through the sample in next run. This generates a vicious cycle. Eventually, this kind of sample leads to a very high Tn, but this misleadingly high cut resistance value is mainly caused by the abrasive dulling effect on the blade by the test sample, not a typical hazard which will be experienced by a worker in the real-world reality. For instance, the glass fiber is a very abrasive

Table 2.2 EN388 Coupe cut testing record and calculation table. Sequence

1 2 3 4 5

Cn

Tn

Cn11

in

Standard cotton canvas

Testing specimen

Standard cotton canvas

Index

C1 C2 C3 C4 C5

T1 T2 T3 T4 T5

C2 C3 C4 C5 C6

i1 i2 i3 i4 i5

Source: Adapted from European Committee for Standardization. EN388:2016 Protective Gloves Against Mechanical Risks; 2016. Remark: it can be easily seen that Cn11 in previous cycle is used as Cn in the next cycle.

26

Cut Protective Textiles

material to the cutting blade. It is often observed that the blade edge is even broken during the testing, as the blade is repeatedly applied onto glass fiber. A glasscontaining sample can easily achieve cut level 5 in Coupe test. Lara et al. reported the dulling effect on the Coupe cutting blade in 1996.12 In this report a set of experiment was carried out by cutting a fiberglass-reinforced material with the same blade. The sample was cut through after 558 cutting cycles. During the testing the blade sharpness was checked with standard cotton canvas every 50 cycles of cut. The testing data are shown in Table 2.3. It was found that after first 50 cycles, the blade sharpness was dropped from 0.8 (Cn) to 25.5 (Cn11), meaning the blade was already degraded severely during the cutting process. In the following every 50 cycles the blade sharpness was checked and found being almost constant until the sample was cut through at 558 cycles. This means that the blade had been degraded (dulled) and a degraded blade was cutting the sample throughout almost the entire cutting process. As a result, a very high Tn was generated and a very high cut index was then concluded, but this was caused by the degradation (dulling) of the blade, not by the real cut resistance of the material. In the same report, Lara et al. also compared EN388 Coupe cut testing with the IRSST method (Table 2.4). Though overall a linear correlation was identified by Lara with a coefficient of correlation (r2) of 0.89 between these methods, there are many exceptions especially at high cut levels, for instance in Table 2.4, sample B1 versus D2, sample D1 versus D3, sample C2 versus D3, sample D1 versus E2, and so on. To enable a better reading, these pairs are compared from Tables 2.5
2.11. This study raised the concern over the dulling effect on the blade and proposed that it was more reasonable and scientific to use a straight blade cut under different loads to determine the cut resistance of materials. The high variability of Coupe cut test (ITF method) was also demonstrated by Lara in the same report.12 Five new blades, adjacent to each other in the blade box,

Table 2.3 Blade sharpness every 50 cut cycles in fiberglass containing fabric using the same blade with the ITF (Coupe) method. Number of cut cycles

Blade sharpness index before last cycles (Cn)

Blade sharpness index after last cycles (Cn11)

After 50 cycles After 100 cycles After 150 cycles After 200 cycles After 250 cycles After 300 cycles After 350 cycles After 400 cycles After 558 cycles (cut through)

0.8 25.5 24.2 27.3 24.4 23.4 29.3 27.4 27.2

25.5 24.2 27.3 24.4 23.4 29.3 27.4 27.2 28.1

Source: Modified from Lara J, Turcot D, Daigle R, Payot F. Comparison of two methods to evaluate the resistance of protective gloves to cutting by sharp blades. In: Johnson JS, Mansdorf SZ, eds. Performance of Protective Clothing: Fifth Volume, ASTM STP 1237. American Society for Testing and Materials; 1996:32
42.

Evaluate cut resistance

27

Table 2.4 Comparison between ITF and IRRST results (percentage data in the brackets are coefficient of variation). Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3 E1 E2 E3 F1 F2 F3

1.1 (0%) 1.1 (0%) 1.1 (1%) 2.0 (0%) 2.0 (0%
1%) 1.7 (4%) 2.8 (11%) 2.6 (0%
10%) 3.6 (12%
18%) 8.9 (20%
25%) 8.1 (15%
55%) 10.1 (24%
51%) 15.8 (8%
9%) 21.8 (16%
17%) 14.8 (9%
15%) 22.4 (19%
32%) 23.4 (25%
34%) 36.4 (9%)

2.2 2.1 4.4 5.9 4.1 2.6 7.4 8.6 5.8 16.3 5.6 8.4 10.0 14.8 17.8 19.1 29.8 27.3

Note: Wcal is the calculated load required to cut through the glove in a 10 mm blade displacement. IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec. Source: Modified from Lara J, Turcot D, Daigle R, Payot F. Comparison of two methods to evaluate the resistance of protective gloves to cutting by sharp blades. In: Johnson JS, Mansdorf SZ, eds. Performance of Protective Clothing: Fifth Volume, ASTM STP 1237. American Society for Testing and Materials; 1996:32
42.

Table 2.5 Comparison between samples B1 and D2. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

A1 A3

1.1 (0%) 1.1 (1%)

2.2 4.4

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Table 2.6 Comparison between samples B1 and D2. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

B1 D2

2.0 8.1

5.9 5.6

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

28

Cut Protective Textiles

Table 2.7 Comparison between samples D1 and D3. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

D1 D3

8.9 10.1

16.3 8.4

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Table 2.8 Comparison between samples C2 and D3. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

C2 D3

2.6 10.1

8.6 8.4

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Table 2.9 Comparison between samples D1 and E2. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

D1 E2

8.9 21.8

16.3 14.8

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Table 2.10 Comparison between samples E2 and E3. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

E2 E3

21.8 14.8

14.8 17.8

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Table 2.11 Comparison between samples F1, F2, and F3. Glove sample

Average cut index by ITF method

Cut resistance by IRSST method Wcal (N)

F1 F2 F3

22.4 23.4 36.4

19.1 29.8 27.3

IRSST, Institut de recherche en sante´ et en se´curite´ du travail du Que´bec.

Evaluate cut resistance

29

Table 2.12 Test results of a steel-reinforced fiber glove material using the ITF method with different new blades. Blade no. 94 95 96 97 98

Cn 1.4 1.2 0.8 0.8 0.8

Tn 12.0 70.6 29.9 54.8 40.2

Cn11 3.4 5.4 5.9 5.5 5.2

in 6.0 22.4 10.1 19.7 14.6

Index In 5 14.4 Standard deviation of In 5 6.73 Coefficient of variation 5 46.7% Source: Modified from Lara J, Turcot D, Daigle R, Payot F. Comparison of two methods to evaluate the resistance of protective gloves to cutting by sharp blades. In: Johnson JS, Mansdorf SZ, eds. Performance of Protective Clothing: Fifth Volume, ASTM STP 1237. American Society for Testing and Materials; 1996:32
42.

were taken to cut specimens from the same glove material sample. Each blade was used only once for one specimen. The results were shown in Table 2.12. Rebouillat and Steffenino studied the effect of blade dulling on the cut resistance of material by replacing blades during the course of five times cut testing on one specimen.15 Table 2.13 shows the results reported in this study. The cut study was conducted on a “stop-and-go” basis, that is, changing the blade during the test every 1, 2, 3, and 5 cycles as illustrated in Table 2.6 and compared with no blade replacement. These results clearly demonstrated that the blade was degraded and dulled seriously during cutting high cut resistance materials. The dulling was negligible if the blade was replaced after every three or less cycles; therefore their cutting index were not much different. But the cutting index result was significantly higher if the blade was not replaced before the fifth cycle. In a different report, Rebouillat et al. also studied different materials with different levels of cut resistance by using two different cutting methods, that is, Coupe cut and ISO13997 straight blade cut. These samples included para-aramid gloves, steel/para-aramid blend gloves, glass fiber/para-aramid blend gloves, and glass fiber gloves without para-aramid fiber.16 The results were tabulated in Table 2.14. In Table 2.14, one can clearly see that the EN388 Coupe cut index of the glasscontaining glove is almost three times of that of steel/para-aramid-containing glove, but its cutting force tested per ISO13997 is only approximately one-half of the latter. These results strongly prove the dulling effect of glass in Coupe test in which the blade is not replaced. A similar pattern is also observed in other comparisons. Therefore these two methods do not have correlation at all for high cut resistance materials. Furthermore, the variation of EN388 Coupe cut index data is also higher than that for ISO13997 cut data. The higher the cut index, the higher variation, meaning EN388 Coupe test is more variable than ISO13997, which is supported by the report by Lara et al.12 The dulling effect of blade during testing of abrasive materials was also discussed by Iramanska and Stefka.17

30

Cut Protective Textiles

Table 2.13 Dulling effect on cutting blade in Coupe cut testing. Blade replacement (every cycle)

Cn: Control specimen before (cycles)

Tn: Sample tested (cycles)

Cn11: Control specimen after (cycles)

In : Cut index

No blade replacement 5 3 2 1

1

44.4

4.7

16.5

0.9 1 0.9 0.9

23.5 16.2 17.9 16.7

4.4 3.4 4.1 2.9

9.8 8.3 8.1 9.8

Source: From Rebouillat S, Steffenino B. High performance fibres and the mechanical attributes of cut resistant structures made therewith, WIT Trans Built Environ. 2006;85(High Performance Structures and Materials III):279
299. doi:10.2495/HPSM06028.

Table 2.14 Comparison between cut resistance tested with Coupe and ISO13997 for different materials (percentage data in the brackets are coefficient of variation).

p-Aramid-containing glove Steel/p-aramid containing glove Glass/p-aramid containing glove Glass-containing glove

EN388 Coupe cut (index)

ISO13997 TDM cut [normalized force (N)]

8.5 (9.5%) 24.2 (12.1%) 21.2 (8.2%) 92.1 (62.1%)

9.4 (5.1%) 22.9 (3.5%) 12.8 (3.3%) 11.4 (2.1%)

TDM, Tomodynamometer. Source: Modified from Rebouillat S, Steffenino B. Aramid, steel and glass: characterization via cut performance testing, of composite knitted fabrics and their constituent yarns, with a review of the art. J Mater Sci. 2010;45 (19):5378
5392. doi:10.1007/s10853-010-4590-5.

The blade-dulling effect was not mentioned in EN388:2003. For materials of low cut resistances, the Coupe cut testing method has demonstrated strong value. But with the advancement in product development, more and more products with much higher cut resistance have been developed around the world; the limitation of Coupe cut testing has become more critical than before. Now this issue has been widely recognized by the industry, and as a result EN388:2016 specifically mentions how to deal with blade dulling in Coupe test and specifies the rules as follows: 1. The Coupe test should be automatically stopped and the result considered invalid at Tn . 60, then ISO13997 must be employed and those ISO13997 results should be used as the best indication of cut resistance performance. Version 2003 did not specify this. 2. ISO13997 must be employed and the data are used as cut resistance performance when Cn11 . 3Cn. Version 2003 did not specify this. 3. The Coupe test blade should no longer be used and should be replaced when Cn11 . 2. Version 2003 specified that blade should be replaced when Cn11 . 3. 4. Initial Cn, that is, C1, the indicator of sharpness of a new blade, must be between 0.8 and 1.4, applicable to all scenarios. But in the old version 2003, C1 needs to be between 1 and 4

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31

when sample’s cut level is lower than level 3 (not including level 3); while C1 needs to be between 1 and 2 when cut level is or higher than cut level 3. This creates complexity and confusion for the testing, because the sample’s cut level is unknown before the testing is started. The change to the 2016 version eliminates this complexity.

EN388:2016 clearly mentions the word “dulling.” It is clear that the new version attempts to minimize or eliminate the artificially high cut index caused by dulling effect of abrasive test samples. For any dulling that meets any criteria of the abovementioned four scenarios, the version 2016 specifies that only ISO13997 can be used as the determination of cut resistance and the Coupe cut index is no longer valid, while in version 2003, ISO13997 was quoted but was only mentioned as a reference and not a mandatory requirement. In addition to the existing five cut levels based on Coupe test, six cut resistance levels based on cut forces by ISO13997 test are added into EN388:2016, as shown in Table 2.15. The changes associated with cut testing in EN388:2016 against the old version 2003 are summarized in Table 2.16. But actually there are also some other changes, such as abrasion testing, which are not discussed in this book. The major differences between Coupe circular blade cut testing in old version EN388:2003 and the TDM straight blade cut testing are as follows: 1. Coupe cut is conducted under fixed load of 5 N; TDM cut testing is done at variable load. 2. Coupe cut is conducted with a combination of circular rotation of blade and horizontal motion of blade; TDM uses horizontal motion of blade only. 3. In five-time test for each specimen in Coupe test in version 2003, the circular blade is not replaced, regardless of how the blade is degraded and dulled. Even for a used blade, if the sharpness can meet the criteria, it can still be used. But in TDM, a brand new blade or new section of a used blade must be used. 4. Coupe test result is the rotation cycles to cut through the sample (relative to standard cotton canvas), while TDM result is the cut force fitted from the load
cut distance regression line.

It was already mentioned earlier that the correlation between Coupe test and TDM cut test is very weak. In Table 2.14 the glass fiber’s Coupe cut index is higher than that of steel wire, but its TDM cut force (ISO13997) is lower than that of steel wire, which is caused by the dulling effect of glass fiber on the repeatedly used

Table 2.15 Cut levels rating by ISO13997 method in EN388:2016. EN388:2016 cut resistance levels based on ISO13997 test

Cut force (N)

A B C D E F

$2 $5 $ 10 $ 15 $ 22 $ 30

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Cut Protective Textiles

Table 2.16 Changes in EN388:2016 versus EN388:2003 version. Item

EN388:2003

EN388:2016

For ISO13997 TDM cut test

6.2.6, Table 3 mentioned Not mandatory, can be neglected The wording is easily misunderstood as there was correlation between Coupe and TDM cut testing data

Coupe: when to stop Coupe: initial blade sharpness (C1) Coupe: material choice to adjust blade’s sharpness Coupe: blade replacement

No statement

4.1 Table 2 6.2.6, when Cn11 . 3Cn, Coupe data cannot be used and TDM must be used. And TDM cut results are used as cut resistance performance Clearly states that there is no correlation between Coupe test and TDM test Six levels are added based on ISO13997 TDM cut test (A
F) A: $ 2 N B: $ 5 N C: $ 10 N D: $ 15 N E: $ 22 N F: $ 30 N Automatically stops when cycles .60 (6.2.6) C0 5 0.8
1.4 (6.2.6)

Coupe: number of specimens per sample

Two (did not specify whether two specimens are from one sample or not)

C0 5 1
4 (when cut level ,3) C0 5 1
2 (when cut level $ 3) Three layers of standard cotton canvas or other suitable materials

Three layers of standard cotton canvas (6.2.6)

Must replace blade when Cn . 3

Must replace when Cn . 2 Initial C1: 0.8
1.4, and sharpness during testing: 0.8
2.0 (6.2.6) Two: specifies that two specimens must be from two different samples (6.2.3)

TDM, Tomodynamometer.

circular blade. This dulling effect has gradually been recognized by the industry in the past years, and as a result this pushed the upgrading of EN388. However, an unreasonable practice has arisen after the implementation of EN388:2106. Though EN388:2106 clearly mentions and defines the blade dulling and that the cut rating based on TDM should be used when there is blade dulling, many users have become comfortable with the old Coupe cut rating and unfortunately they have not fully understood the significant flaw of the Coupe cut method for highly abrasive materials and this flaw method leads to misleading cut level

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rating, so they still request to have Coupe cut rating regardless of whether the cut cycles exceed 60 cycles or the blade’s sharpness is out of range. The new EN388:2016 also states, “However, the test method corresponding to 6.2 could be done on request” (section 6.2 in EN388:2016 is the Coupe cut testing), therefore even the authoritative third party testing labs continue to report the Coupe cut rating by request though there is obvious dulling effect. According to the 2016 version of EN388, the test stops when the cut cycles reach 60 regardless of whether the sample is cut through or not, therefore the maximum cut cycles can be obtained in Coupe test according to the 2016 version standard is 60. Many people use this 60 cut cycles as Tn to calculate the Coupe cut index no matter whether the sample would be eventually cut through at 65 or 150 cycles if the test would be continued without stop. The calculation is in 5

C n 1 Tn Tn Tn 60 511 511 511 ðCn 1 Cn11 Þ=2 ðCn 1 Cn11 Þ=2 Cn Cn

(2.6)

In this calculation, as already said, 60 is used as Tn to do the calculation regardless of how the sample really performs as long as the cut exceeds 60 cycles. This will lead to a weird phenomenon as illustrated in Table 2.17. If there are two samples A and B, A has a TDM cut force of 1800 gf and B 3150 gf, therefore B is more cut resistant than A in TDM cut testing. When they are tested on Coupe cut, sample A is cut until 60 cycles and the test is manually stopped, and 60 is used as Tn for calculating A’s Coupe cut index. Sample B is more cut resistant than A, but it is also cut until 60 cycles and the test is also manually stopped at this cycles, and 60 is also used as Tn. Because B is more cut resistant than A, its Cn11 is also higher than that for A. The initial sharpness Cn for both should be the same, thus ðCn 1 ðCn11 ÞÞ=2 for B is larger than that for A, as a result the cut index of B is lower than that of A. Therefore this practice leads to an unreasonable conclusion, that is, a higher TDM cut rating will get a lower Coupe cut rating. The same logic applies to sample C. Sample C has the highest TDM cut resistance but the lowest Coupe cut level rating among these three samples. The cause responsible for this kind of unreasonable result is that the number 60 is used for all Tns of samples with high cut resistance regardless of their actual cut resistance. As a matter of fact, the cut-through cycles of a sample may exceed 60 marginally, for example, 65, but may also exceed significantly such as 150 if the test could be continued until the sample is cut through. Then for the calculation of Coupe cut index for highly cut resistant material, there is only one variable Cn11 in this calculation: in 5 1 1

60 : ðCn 1 Cn11 Þ=2

The sample with higher cut resistance will get larger Cn11 and thus lower in. This certainly conflicts with the spirit of the new EN388:2016 standard, which tries

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Cut Protective Textiles

Table 2.17 An example with higher TDM cut force but lower Coupe cut index.

TDM cut result TDM cut force (gf) TDM cut rating by EN388:2016 Coupe cut result Cn Tn Cn11 In Coupe cut rating

Sample A

Sample B

Sample C

1800 D

2850 E

4900 F

1 60 4.5 22.8 5

1 60 6.8 16.4 4

1 60 13.6 9.2 3

TDM, Tomodynamometer.

to correct that there was no correlation between Coupe cut and TDM cut due to blade dulling effect in many cases. But now, it looks like this flaw in the original Coupe test method is overcorrected and an opposite phenomenon arises, that is, higher TDM cut force but lower Coupe cut index. It is unlikely this situation would be improved unless the statement “the test method corresponding to 6.2 could be done on request” is removed from the 2016 version of EN388 and a new statement “it is not allowed to use method corresponding to 6.2 when the cut cycles exceed 60” because the practitioners around the world have been so used to the cut level rating by Coupe cut testing in the past decades. It is recommended that Coupe cut index should not be calculated and not be reported when there is dulling effect or when the cut cycle exceeds 60, otherwise the abovementioned wrong conclusion will be drawn. If someone insists on requesting Coupe cut index for a product with high cut resistance, the testing party can use the old version to test and report, making a clear remark in the report, instead of using 60 universally for all different samples. In end of 2018 a new standard, ISO23388,13 was released. ISO23388 is the same as EN388:2016, with very minor revision in the standard cotton canvas specification. It was developed to meet the needs of non-EU countries. As this standard is same as EN388:2016, it is not necessary to discuss its details.

2.3

ASTM F2992/F2992M-15

ASTM F2992/F2992M-15 is a new standard, completed in 2015.9 Its current full name is “ASTM F2992/F2992M-15: standard test method for measuring cut resistance of materials used in protective clothing with tomodynamometer (TDM-100) test equipment.” To be simple, ASTM F2992-15 is used in the following discussions. This standard’s name already specifies the testing to be done on TDM-100. This standard’s testing is almost exactly the same as ISO13997 except a few minor details. Table 2.18 compares these small differences.

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Table 2.18 Comparison between ASTM F2992-15 and ISO13997:1999.

Load used for calibration with standard chloroprene sample Acceptable cut distance in calibration with standard chloroprene sample 15 pairs of load
cut distance data

Data fitting

ASTM F2992-15

ISO13997:1999

500 g

5 N (510 g)

15
25 mm

20
30 mm

All data must be between 5 and 50.8 mm, in which Five pairs within 5
20 mm Five pairs within 20
33 mm Five pairs within 33
50.8 mm Does not specify

All data must be within 5
50 mm, in which Five pairs within 5
15 mm Five pairs within 15
30 mm Five pairs within 30
50 mm Specifies logarithm fitting (lg y 5 b0 1 b1x)

Table 2.19 Cut level rating by ANSI/ISEA 105-2016. ANSI/ISEA 105-2016 cut level

Cut force (g)

A1 A2 A3 A4 A5 A6 A7 A8 A9

$ 200 $ 500 $ 1000 $ 1500 $ 2200 $ 3000 $ 4000 $ 5000 $ 6000

Similar to ISO13997, ASTM F2992-15 only specifies the testing method but does not specify the cut rating levels. ANSI/ISEA 105-2016,18 a newly revised standard in 2016, rates the cut levels by quoting testing standard ASTM F2992-15. The full name of ANSI/ISEA 105-16 is “American National Standard for Hand Protection Selection Criteria.” This standard also includes other protection performance such as abrasion, puncture, chemical penetration, heat resistance, and heat aging stability. The cut level rating is tabulated in Table 2.19. The last version of ANSI/ISEA 105 is version 2011 (ANSI/ISEA 105-2011), in which there were only 6 cut levels, including level 0. They were as follows: Level 0 (,200 g) Level 1 ($200 g)

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Cut Protective Textiles

Level 2 ($500 g) Level 3 ($1000 g) Level 4 ($1500 g) Level 5 ($3500 g)

Comparison for cut levels between the old version (2011) and the new version (2016) in ANSI/ISEA 105 is shown in Fig. 2.11. One can see that the gap between cut level 4 and level 5 in the old version ANSI/ISEA 05-11 is very large, which is not good for differentiating products with great difference in cut forces within the range of 1500
3500 g. For example, one product has a cut force of 1600 g and another one 3200 g. The latter’s cut resistance is 2 times of the former, but they are both rated as level 4; therefore customers will not be willing to pay more for the latter, and in turn the manufacturers do not have motivation to develop a high level 4. However, the higher cut resistance does provide extra cut protection value; hence the changes to 2016 version recognize this and shall motivate the manufacturers to develop such products.

Figure 2.11 Comparison in cut level rating between ANSI/ISEA 105-11 and ANSI/ISEA 105-16.

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Table 2.20 Cut levels rating based on TDM cut test per EN388:2016 and ANSI/ISEA 105-2016. EN388:2016 cut levels (TDM method per ISO13997)

EN388:2016 cut forces (TDM method per ISO13997)

ANSI/ISEA 105-16 cut levels (TDM per ASTM F2992-15)

ANSI/ISEA 105-16 cut forces (TDM per ASTM F2992-15)

A B C D E F None None None

$2 N $5 N $ 10 N $ 15 N $ 22 N $ 30 N None None None

A1 A2 A3 A4 A5 A6 A7 A8 A9

$ 200 g $ 500 g $ 1000 g $ 1500 g $ 2200 g $ 3000 g $ 4000 g $ 5000 g $ 6000 g

TDM, Tomodynamometer.

There are similarities as well as differences between TDM cut levels classified in EN388:2016 according to ISO13997 method and TDM cut levels in ANSI/ISEA 105-16 according to ASTM F2992-15 method. The comparison between them is tabulated in Table 2.20. It is worthy of mentioning that ASTM F2992-15 is not really a brand new testing method. As a matter of fact, it is carved out from ASTM F1790-05. ASTM F179005 is a cut resistance testing method as told by its full name of “Standard test method for measuring cut resistance of materials used in protective clothing.” But there are two individual methods coexisting in this ASTM F1790-05, one being TDM-100 cut test, the other CPPT (full name is “cut protective performance test”). TDM-100 cut test is done in horizontal direction, while CPPT is done in vertical direction but with a very similar mechanism to that of TDM-100. A picture of CPPT’s instrument is shown in Fig. 2.12, and its mechanism is shown in Fig. 2.13. In 2015 the TDM cut method was carved out from ASTM F1790-05 to form a stand-alone standard ASTM F2992-15, and new ASTM F1790-15 version only keeps CPPT cut test method. ANSI/ISEA 105-2016 only quotes ASTM F2992-15, that is, TDM cut results, but does not refer to CPPT at all. This change is illustrated in Fig. 2.14. Therefore the cut testing methods and cut levels rating are united between North America and Europe to a great extent, but not exactly the same yet. Now they both use the TDM cut method, and there are only very minor differences in testing details. In cut level ratings the first 6 levels of both of them are almost the same. Table 2.21 summarizes the different testing standards, cut testing methods quoted by different standards and the corresponding testing instruments. Because of the complexity of cut level ratings by different standards and different testing methods, the standard must be specified if a cut level is given. In reality, many users do not understand the standard and cut level ratings (and likely they are

38

Cut Protective Textiles

Figure 2.12 Picture of ASTM F1790-05 CPPT instrument.

Balde moving

Balde holder

Balde

Load Sample Holder

Figure 2.13 Schematic illustration of CPPT cut testing.

not interested in knowing), including many HSE (health, safety, environment) responsible people. Due to the historic dominance of Coupe testing method by EN388 in the world, many people simply mention a cut level, for example, level 5, without mentioning the standard, but actually they refer to EN388 Coupe testing standard. Now with the changes and the enforcement of standards, this situation should be improved.

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Figure 2.14 Changes of ASTM F1790-05. Table 2.21 Comparison between different cut resistance testing standards. Performance rating standards

Cut levels rating

Quoted testing standard

Instrument

ISO13997 EN388:2016

No rating Five levels with Coupe method: Level 1 . 5 1.2 Level 2 . 5 2.5 Level 3 . 5 5.0 Level 4 . 5 10.0 Level 5 . 5 20.0 6 levels with TDM-100 method: Level A .2 N Level B .5 N Level C .10 N Level D .15 N Level E .22 N Level F .30 N 9 levels A1: 200 g A2: 500 g A3: 1000 g A4: 1500 g A5: 2200 g A6: 3000 g A7: 4000 g A8: 5000 g A9: 6000 g

ISO13997 EN388 ISO13997

TDM-100 Coupe TDM-100

ASTM F2992-16

TDM-100

ANSI/ISEA 105-2016

TDM, Tomodynamometer.

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Cut Protective Textiles

From the results consistency perspective, Table 2.14 already mentioned that TDM cut method exhibits much better consistency, while Coupe exhibits higher variability. With the implementation of EN388:2016, the TDM cut method is becoming more broadly accepted by the industry.

2.4

ISO13998

ISO13998’s full name is “Protective clothing
aprons, trousers and vests protecting against cuts and stabs by hand knives.”19 Its latest revision was in 2003. This is a standard for both testing and performance requirements. There are two different testing which are related to cut resistance in this standard, cut testing according to ISO13997 and knife penetration testing. ISO13997 is already discussed in details in Section 2.1. The knife impact penetration testing is discussed here. The setup of knife impact penetration testing is shown in Fig. 2.15. The test sample is tested by repeated impact of standard knife blades held in a guided falling block. After release of the block, it falls in a free-falling mode and penetrates the sample placed underneath. The blade holding block holds the blade so that the blade protrudes by 40 mm, and the center of gravity of the block and blade assembly is 65 mm above the blade tip. The total mass of the block and blade assembly is 1000 g. The blade holding block and key parameters are shown in Fig. 2.16. There are two standard distances from the blade tip to the test specimen, 250 mm for performance level 1 testing or 500 mm for performance level 2 testing, so that the free-falling block and blade assembly can generate 2.45 or 4.9 J impact energy, respectively, when the blade impacts the specimen. The energy is calculated as follows: Ei 5 mhg

(2.7)

where Ei—impact energy, m—mass of free-falling object, g—gravitational acceleration constant, 9.81 m/s2, and h—height of free fall.

Therefore when m 5 1000 g (1 kg), h 5 250 mm (0.25 m), Ei 5 2.45 J; while when h 5 500 mm (0.5 m), Ei 5 4.90 J. The profile and dimensions of test blade are shown in Fig. 2.17. The blade material shall be made of cold-forged stainless steel with a degree of hardness of higher than 47 HRC (while ISO13997 cutting blade is higher than 45 HRC). One more critical specification in this standard is the material of the sample support on which the test sample is put for testing. The sample support is a material to simulate human flesh. It is recommended to be a mixture of fine white maize flour and liquid paraffin with a mixing ratio of approximately 1 kg flour to 170 mL of a paraffin of specific gravity of 0.84
0.86 g/cm3. The density and rheological

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Figure 2.15 Schematic diagram of ISO13998 impact cut test. 1—Table; 2—base plate; 3—support; 4—bracket; 5—fixing block for the upper end of the guide rods; 6—electromagnetic release mechanism; 7—falling block and test blade; 8—guide rods; 9—fixing block for the lower end of the guide rods; 10—test specimen; 11—tilting mechanism. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). From ISO13998:2003. Protective Clothing
Aprons, Trousers and Vests Protecting Against Cuts and Stabs by Hand Knives. International Organization for Standardization; 2003. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https://shop. bsigroup.com/..

properties of this kind of mixture are temperature dependent thus conditioning prior to testing is extremely important. This material has to meet two specification items as illustrated next 1. The specific gravity of the material shall be between 1.0 and 1.5 g/cm3. 2. A steel ball dropping indentation testing (as illustrated in Fig. 2.16) should be carried out on the mixture, and the mean depth of indentation after 10 times dropping testing should be 20 6 2 mm.

Key facts of the setup in Fig. 2.18 are listed as follows: Steel ball size: 63.5 mm in diameter; Steel ball weight: 1043 g; Distance from steel ball lower surface to surface of plastic mass: 2000 mm.

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Cut Protective Textiles

Figure 2.16 Blade holding block for ISO13998. 1—Guide rod; 2—wheel or bearing; 3—block; 4—cut out space to achieve correct mass distribution; 5—center of gravity of block plus test blade; 6—test blade; l1 5 100 mm, l2 5 65 mm; l3 5 40 mm; l4 5 5 mm, l5 5 75 mm. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). From ISO13998:2003. Protective Clothing
Aprons, Trousers and Vests Protecting Against Cuts and Stabs by Hand Knives. International Organization for Standardization; 2003. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https://shop. bsigroup.com/..

If the depth of indentation does not meet the 20 6 2 mm requirement, the plastic mass material should be reconditioned at a different temperature, or the material should be remixed with more paraffin oil or flour, or the material should be disposed and a new mixture should be made. After the plastic mass is verified meeting the requirement, the blade impact testing can be carried out. The first set of 10 tests is carried out by having the test specimen and the plastic mass support material horizontal. After each blade impact, rotate the specimen 35 degrees with respect to the blade to provide 10 different orientations of impact. The second set of 10 tests is carried out by having the test specimen and the plastic mass support material inclined at 30 degrees to the horizontal as shown in Fig. 2.19. Five tests should be conducted by aligning the vertical axis of the test specimen along the inclined plane of the plastic mass and the other five tests by

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43

Figure 2.17 Profile and dimensions of test blade. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). Modified from ISO13998:2003. Protective Clothing
Aprons, Trousers and Vests Protecting Against Cuts and Stabs by Hand Knives. International Organization for Standardization; 2003. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https://shop.bsigroup.com/..

aligning it transversely across the plane of the tray. After each test the specimen should be rotated approximately 60 degrees with respect to the test blade. For garments of performance level the average penetration shall not exceed 10 mm and no single penetration shall exceed 17 mm. For garments of performance level 2 the average penetration shall not exceed 12 mm and no single penetration shall exceed 15 mm. The cut relevant performance requirements according to ISO13998 are summarized in Table 2.22. It is worth pointing out that ISO13998 does not have a blade calibration procedure.

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Figure 2.18 Verification of the rheological properties of the plastic mass by steel ball indentation.

2.5

ISO13999

ISO13999 is a family of standards for gloves and arm guards protecting against cuts and stabs by hand knives. This family consists of three parts. Its part 1, ISO13999-1,20 defines the specification for chain-mail gloves and metal or plastic arm guards, which are not considered as textile products, and also defines the testing methods. ISO13999-221 specifies requirements for the gloves, arm guards, and protective sleeves made of materials other than chain mail and rigid metal and plastics. Therefore ISO13999-2 is a specification standard, not including test method. Part 3, ISO13999-3,22 specifies an impact cut test for use on fabric, leather, and other materials. The part 3 is a pure testing standard, not a product performance specification standard. ISO13999 series are equal to EN1082 series, which also have three parts, with each part corresponding to ISO13999-1, -2 and -3, respectively. Instead of starting from the part 1, we start from part 3 first. The readers will understand why they are introduced in reverse order when they continue reading to the end. As this book only covers cut resistance, only the cut testing in these standards are discussed.

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45

Figure 2.19 Blade impact penetration test on inclined specimen.

Table 2.22 Cut and impact penetration performance requirements per ISO13998.

Cut resistance (ISO13997) Knife impact penetration resistance

Performance level 1

Performance level 2

$ 50 N

$ 50 N

Average penetration # 10 mm Single penetration # 17 mm (impact energy 2.45 J)

Average penetration # 12 mm Single penetration # 15 mm (impact energy 4.90 J)

2.5.1 ISO13999-3 ISO13999-3’s full name is “Protective clothing—gloves and arm guards protecting against cuts and stabs by hand knives—Part 3: Impact cut test for fabric, leather and other materials.”22 It is a testing standard only, not performance specification. Its latest version is the version of 2002. The test setup is shown in Fig. 2.20. One can see that the principle of this testing is very similar to the ISO13998 testing

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Cut Protective Textiles

Figure 2.20 Setup for ISO13999-3 impact cut test. 1—Table; 2—base plate; 3—support; 4—bracket; 5—fixing block for the upper end of the guide rods; 6—electromagnetic release mechanism; 7—falling block and test blade; 8— guide rods; 9—fixing block for the lower end of the guide rods; 10—test specimen support; 11—clip; 12—weigh piece. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). From ISO13999
3:2002. Protective Clothing
Gloves and Arm Guards Protecting Against Cuts and Stabs by Hand Knives
Part 3: Impact Cut Test for Fabric, Leather and Other Materials. International Organization for Standardization; 2003. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https://shop.bsigroup.com/..

method. The major difference is that the test specimen or glove is supported on a horizontal arm which ends in a circular anvil with a hole in which the knife enters after free-falling during the test, while ISO13998 is carried out on test specimens put on plastic mass that can be inclined. What is measured in ISO13999-3 is the penetration depth of the blade, same as that in ISO13998. The circular anvil has a domed top surface that supports the test specimen and a rectangular slot cut in the center to allow the blade to penetrate through the specimen.

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Table 2.23 Differences in test blade and holding block between ISO13999-3 and ISO13998. Item

ISO13999-3

ISO13998

Blade drop height

600 mm

Blade impact energy

0.65 J

Mass of holding block and blade Protruding length of blade from the block Distance from center of gravity of the block and blade to the blade tip Offset distance from blade tip to center line of block Blade material

1000 g 40 mm 100 mm

250 mm (performance level 1) and 500 mm (performance level 2) 2.45 J (performance level 1) and 4.90 J (performance level 2) 110 g 55 mm 65 mm

8 mm

5 mm

Stainless steel . 45 HRC 20 mm $ 65 mm 1.5 mm 30 degrees

Stainless steel . 47 HRC 20 mm $ 65 mm 1.5 mm 30 degrees

30 degrees

30 degrees

Blade width Blade length Blade thickness Angle from blade sharp edge to blade back Inclined angle of blade sharp edge

Besides the major difference in the test specimen support between ISO13999-3 and ISO13998, there are many other differences in the blade and blade holding block as well as commonalities. These differences and commonalities are compared in Table 2.23. The test blades are almost the same in these two standards. Another major difference is that there is a 1000 g standard weight loaded to the clip that clips the bottom part of the test specimen along the center line of the anvil to ensure that the tension on the specimens is the same during impact, otherwise the results’ variation will be very high. The penetration through a specimen under lower tension will be much lower than that under higher tension. Before tests are conducted on test specimens, the blade calibration test should be carried out on reference material. The reference material is the same as the cotton canvas used in EN388. The calibration procedure is as follows: 1. Make tubes of cotton canvas by aligning warps in the two layers in the same direction. Staple or sew the open edges together. 2. Put the tube onto the sample support and apply the clip and weight piece. 3. Conduct six impact cuts for tube samples, by having two along the warp, two along the weft, and two at 45 degrees. Each cut should be at least 10 mm apart. The impact energy is 0.65 J (600 mm blade drop height). Measure penetration length of each impact cut test. 4. Calculate the average of the six penetration depth hrf. The reference penetration depth should be 14 mm.

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Cut Protective Textiles

If the average penetration depth deviates from the reference value too far, then either blade resharpening or blade blunting (or dulling) is needed. Unfortunately, ISO13999-3 does not prescribe the tolerance of the reference value href. After resharpening or blunting the blade sharpness needs to be tested again. While cutting the test specimens, each impact cut should be apart in at least 10 mm distance, same as in testing the reference material, and two cuts along the warp, two along the weft, and two at 45 degrees. Measure the penetration depth of the blade. Please note that the specimen thickness should be subtracted if the depth is measured from the top surface of the specimen to the blade tip. For samples made of normal fibers and leathers, the knife sharpness should be calibrated every 50 cuts or less, depending upon the test materials. If there are highly cut resistant and dulling materials such as metal or ceramic fibers in the test sample, the knife sharpness needs to be checked more frequently, or even after every cut if the blade is only dulled. If the blade is damaged, even just partially, it should be replaced with a brand new one. Calculate the average impact cut penetration depth of the test specimen hs then calculate the relative impact cut penetration depth hrel using the next equation. hrel 5

14 3 hs hrf

(2.8)

The principle of calculating the relative impact cut penetration depth is similar to the blade sharpness calibration in ISO13997, in which the reference cut length 20 mm is divided by the cut length on standard neoprene sample as shown in Eq. (2.1). hrel is not the final result in ISO13999-3 yet. It is interesting to point out that ISO13999-3 describes a measurement uncertainty and the final result hfin needs to be expressed by adding or subtracting the measurement uncertainty as hfin ðupper limitÞ 5 hrel 1 Um

(2.9)

hfin ðlower limitÞ 5 hrel 2 Um

(2.10)

or

where Um stands for the measurement uncertainty. The higher the value, the lower the protective performance because of more blade penetration. If hfin exceeds the product standard, then the test sample is considered failing the test. Unfortunately, ISO13999-3 does not define how to calculate the measurement uncertainty nor quotes a standard with regard to doing this calculation. Some ISO standards can be referred to determine and use the measurement uncertainty.23
30

2.5.2 ISO13999-2 ISO13999-2’s full name is “ISO13999-2: protective clothing
gloves and arm guards protecting against cuts and stabs by hand knives
Part 2: gloves and

Evaluate cut resistance

49

arm guards made of material other than chain mail.”21 Its latest version is in 2003. This is a performance standard. There are two performance requirements associated with cut resistance, one being the knife penetration resistance according to ISO13999-3, and the other being the regular cut resistance according to ISO13997. ISO13999-2 standard requires that the protective products shall not exceed 8 mm in average knife penetration depth and no single knife penetration shall exceed 14 mm according to ISO13999-3 with impact energy of 0.65 J and requires that the ISO13997 cut resistance shall exceed 20 N of cutting force, which does not correspond to any cut resistance level rating in EN388:2016.

2.5.3 ISO13999-1 ISO13999-1’s full name is “ISO13999-1: protective clothing
gloves and arm guards protecting against cuts and stabs by hand knives
Part 1: chain-mail gloves and arm guards.”20 Its latest version is in 1999. The name is a little bit confusing as many people believe this standard is for chain-mail gloves and chain-mail arm guards, but actually it is for gloves made of chain-mail and arm guards made of any hard materials, such as plastic, not just chain-mail. ISO13999-1’s testing setup is very similar to what is described in ISO13998 as schematically shown in Fig. 2.14 but has major differences in parameters. For regular chain-mail materials and combinations of chain-mail and metal plate, the testing is only conducted with 250 mm dropping height, that is, 2.45 J impact energy. The standard requires that such products shall not exceed 10 mm in average penetration depth and no single penetration shall exceed 17 mm, which corresponds to performance level 1 in ISO13998. For rigid arm guards made of such as rigid plastic, the test sample needs to be supported by a package filled with rice and conditioned first, then is secured onto the sample support made of flesh stimulant as shown in Fig. 2.21. The blade dropping height for rigid plastic arm guards is 500 mm (4.90 J impact energy), while for metal arm guards the dropping height is 250 mm (2.45 J impact energy). The standard requires that such products shall not exceed 12 mm in average penetration depth and no single penetration shall exceed 15 mm, which corresponds to performance level 2 in ISO13998. ISO13999-1 does not have requirement of cut resistance based on ISO13997. It is necessary to make a summary for ISO13998 and ISO13999 to allow a clearer overview of them. This summary is tabulated in Table 2.24. Strictly speaking, the blade impact cut or penetration test is not considered as a cut resistance test, instead it is considered as a stab resistance test. Stab has very different mechanism from cut/slash. Many regular cut resistance gloves are not stab resistant or only have very limited stab resistance. All these testing standards covered in from Sections 2.1
2.5 differ significantly from one another, but it is of interest to compare the blade materials. This comparison is summarized in Table 2.25.

50

Cut Protective Textiles

Figure 2.21 Rigid arm guard sample prepared for knife impact penetration testing. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). From ISO13999-1:1999. Protective Clothing
Gloves and Arm Guards Protecting Against Cuts and Stabs by Hand Knives
Part 1: Chain-Mail Gloves and Arm Guards. International Organization for Standardization; 1999. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https://shop.bsigroup.com/..

2.6

Cut resistance for protection against chainsaw

The use of chainsaw poses serious risk to the users. Improper chainsaw use can lead to serious injury and even death. Each year in the United States there are more than 30,000 injuries related to chainsaw use, some of which are catastrophic.31 The Pro golfer Greg Norman nearly lost his left hand in a chainsaw accident.32 The saw chains can run at a speed of more than 20 m/s, meaning faster than 72 km/h. This high speed can cause very serious injury, sometimes fatal if a kickback occurs toward the direction of neck.33 The most frequent chainsaw injuries occur to the left leg and the back of the left hand of the user. The average injury required 110 stitches, and the medical cost for these injuries amount to over US $350 million each year. Because of the high speed of the chainsaw, the user is unable to rely on his/her reaction time to prevent the injury, therefore appropriate personal protective equipment is critically important to save the user’s life.

2.6.1 ISO and EN standards series for chainsaw protection ISO11393-1 through ISO11393-6 are a series of standards specifying the chainsaw cut test rig (ISO11393-134), test methods, and performance requirements for protective equipment, including leg protectors (ISO11393-235), footwear (ISO11393-336), gloves (ISO11393-437), gaiters (11393-538), and upper body protectors (ISO11393-639).

Table 2.24 Overview of ISO13998 and ISO13999. ISO13998

ISO13999-1

ISO13999-2

ISO13999-3

Content

Testing and performance specification

Performance specification only

Testing only

Testing object

All materials

Testing and performance specification Chain-mail gloves and rigid arm guards

Non-chain-mail materials

Cut-related testing

Blade impact penetration and ISO13997 TDM cut

Blade impact penetration ISO13998

Fabric, leather, and other materials Blade impact penetration

Impact cut energy

2.45 J for performance level 1 and 4.90 J for level 2

Performance rating or specification

Level 1 (2.45 J impact): average penetration # 10 mm, single # 17 mm Level 2 (4.90 J impact): average penetration # 12 mm, single # 15 mm TDM cut force $ 50 N for all

2.45 J for chain-mail and metal plates 4.90 J for rigid arm guards Chain-mail and metal plates: level 1 of ISO13998 Rigid arm guards: level 2 of ISO13998

TDM, Tomodynamometer.

No TDM cut

Blade impact penetration ISO13999-3 and ISO13997 TDM cut 0.65 J (ISO13999-3)

Average penetration # 8 mm, single # 14 mm TDM cut force .20 N

0.65 J

NA

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Cut Protective Textiles

Table 2.25 Blade material and hardness comparison for cut testing. Standard

Blade material and hardness

EN388:2016 (ISO23388:2018)

Stainless steel, Vickers hardness of 700
720 (60-61 HRC) Stainless steel .45 HRC Stainless steel .45 HRC Stainless steel .45 HRC Stainless steel .47 HRC Stainless steel .45 HRC

ISO13997:1999 ASTM F2992/F2992M-15 ASTM F1790F1790M-15 ISO13998:2003 impact penetration blade ISO13999
3:2002

Figure 2.22 Test rig for chainsaw cut resistance. Source: From Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). ISO11393
1:2018. Protective Clothing for Users of Hand-Held Chainsaws
Part 1: Test Rig for Testing Resistance to Cutting by a Chainsaw. International Organization for Standardization; 2018. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https:// shop.bsigroup.com/..

ISO11393-1 describes a test rig illustrated in Fig. 2.22. A chainsaw is placed on top of a test sample under a normal load 15 N and is able to run at a speed up to 28 m/s during testing. The profile of the chain is shown in Fig. 2.23. Before actual testing for sample a calibration procedure needs to be carried out by checking the chain stopping time and calibrating chain sharpness by cutting standard clogging material. The chain stopping time has to be within the range of 4 6 0.2 seconds, otherwise the chain tension needs to be adjusted. The clogging material for chain sharpness calibration is a pad consisting of 12 layers fabrics. The bottom layer is one layer of 58 6 2 gsm 100% polyester warp knit fabric. On top of this knit fabric, there are 10 layers of 105 6 3 gsm woven fabrics made of 940 dtex polyamide fiber as weft and two different polyester yarns, 50 and 167 dtex, as warps. The top layer of the calibration pad is one layer of 225 6 5 gsm 100% polyester warp knit fabric.

Evaluate cut resistance

53

25 degrees ± 2 degrees

X

Y

Z

Figure 2.23 Profile of saw chain. Source: Permission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). From ISO11393
1:2018. Protective Clothing for Users of Hand-Held Chainsaws
Part 1: Test Rig for Testing Resistance to Cutting by a Chainsaw. International Organization for Standardization; 2018. No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop ,https:// shop.bsigroup.com/..

The calibration pad, under a standard tension, is mounted on top of the standard foam which is mounted on the sample mount. Then the chain saw is run at 19 and 21 m/s speeds to cut the calibration pad. The chain sharpness should allow the pad to be cut through at 21 m/s speed and the length of cut shall be between 10 and 50 mm in the bottom layer, while cannot cut through at the speed of 19 m/s. There are other details to be taken care in the testing procedure but they will not be covered here. ISO11393-2
ISO11393-6 standards are the testing standards and performance requirements for different chainsaw cut protective equipment. These standards use the same test rig as described in ISO11393-1 and the general procedures are the same but differ in sampling and positioning of testing specimens specific to different forms of products such as leg protectors, footwear, gloves, gaiters, and upper body protectors. Most of them share the same rated levels of cut resistance except ISO11393-4 for the gloves. They are summarized in Table 2.26. ISO11393-4 and -6 define four classes of cut resistance, while others define three classes. The family of EN381 standards40
50 is similar to ISO11393 family but there are some differences. These two families of standards are tabulated in Table 2.27. The chainsaw cut resistance ratings for EN381 family are the same as those for ISO11393 family.

2.6.2 ASTM standards series for chainsaw protection ASTM also has a family of standards for chainsaw cut resistance testing and performance requirements. They are listed in Table 2.28. There are only standards for lower body and foot protection, no standards for upper body and gloves protection, but they may be evaluated using the same standards. ASTM F1897 specifies the performance requirement for lower body protectors and uses ASTM F1414 as test method. ASTM F1818 uses ASTM F1458 as test

54

Cut Protective Textiles

Table 2.26 Summary of ISO11393 standards for chain saw cut testing and performance requirements. Standard

Scope

Cut resistance rating

ISO11393-1 ISO11393-2

Test rig and calibration procedure for chain saw Performance requirements and test method for leg protectors

ISO11393-3

Performance requirements and test method for footwear

ISO11393-4

Performance requirements and test method for protective gloves

ISO11393-5

Performance requirements and test method for protective gaiters

ISO11393-6

Performance requirements and test method for upper body protectors

NA 3 classes: Class 1: 20 m/s Class 2: 24 m/s Class 3: 28 m/s 3 levels: Level 1: 20 m/s Level 2: 24 m/s Class 3: 28 m/s 4 classes: Class 0: 16 m/s Class 1: 20 m/s Class 2: 24 m/s Class 3: 28 m/s 3 classes: Class 1: 20 m/s Class 2: 24 m/s Class 3: 28 m/s 4 classes: Class 0: 16 m/s Class 1: 20 m/s Class 2: 24 m/s Class 3: 28 m/s

Note: For cut resistance rating, ISO11393-3 uses the term of “level” while others use “class,” but they mean the same thing.

method. Interestingly, ASTM F3325-19, the latest version of this standard, does not specify testing method. The readers can only guess that ASTM F3324 may be its test method. The principle and test rig of ASTM standards F3324, F1414, and F1458 are almost the same as those of ISO11393, but the calibration procedure, calibration materials, and performance criteria are very different. The technical details are listed in Table 2.29. The Chain Speed (CS) 50 (CS50) in ASTM F1414 and ASTM F1458 is the mean speed that the cut-through occurs. It also means the speed at which there is 50% probability of cut-through. In the test a sufficient number of attempts should be made in order to obtain minimum three results that are failures and minimum three results which are passes, and the range between them should be limited as much as possible. The failures should yield cut-through distance up to 25 mm long on the bottom layer, and the passes should show a cut through of all layers except

Evaluate cut resistance

55

Table 2.27 ISO11393 and EN381 standards for chainsaw cut testing and performance requirement. Scope

ISO standards

EN standards

Major difference

Test rig

ISO11393-1

EN381-140

Leg protectors

ISO11393-2

Footwear

ISO11393-3

Gloves

ISO11393-4

Gaiters

ISO11393-5

Upper body protectors

ISO11393-6

EN381-241 for test method EN381-544 for performance requirements EN381-342 for test method EN381-645 for performance requirements EN381-443 for test method EN381-746 for performance requirements EN381-847 for test method EN381-948 for performance requirements EN381-1049 for test method EN381-1150 for performance requirements

ISO11393-1 adds measuring chain tension, adds calibration pads at 19 m/s, adds checking the moment of inertia around pivot, and deletes calibration using a plastic bar Only minor differences

ISO11393-3 increases the total number of cuts by 2 ISO11393-4 defines two different glove types and adds gripping test Only minor differences

Only minor differences

Table 2.28 ASTM standards for chainsaw cut testing and performance requirements. Scope

Test method

Performance requirements

Lower body (leg) protectors

ASTM F332451 ASTM F141453

Foot protectors

ASTM F145855 (use the same calibration method in ASTM F1414)

ASTM F332552 ASTM F189754 (quote ASTM F1414 as test method) ASTM F181856 (quote ASTM F1458 as test method)

the last layer of the pad. Then the mean (average) value of these six speeds is calculated and taken as CS50. The performance requirements defined in ASTM F1897, F3325, and F1818 are also different. These differences are tabulated in Table 2.30.

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Cut Protective Textiles

Table 2.29 Testing key facts of chainsaw cutting in ASTM standards. Standard

Items

Key facts

ASTM F3324 for leg protectors

Calibration pad

Top cover: minimum 400 D nylon fabric One layer plain woven Kevlar 49 fabric, Lincoln fabric style 30316.0580.2000 One layer greige fabric with 13 ends warp and 12 ends picks One layer of Albarrie Canada felt style 5101 One layer of Lincoln woven Kevlar 49 fabric, Lincoln fabric style 30316.0580.2000 One layer of Albarrie Canada felt style 5101 Bottom layer: minimum 70 D tricot (knit fabric) Threshold chain speed: chain speed that results in a 6 mm cut in the bottom layer 15 6 1 m/s

Determination of cutthrough chain speed

Calibration test chain speed Calibration pass criteria Test cut failure criteria

ASTM F1414 for lower body protectors

Calibration pad

Determination of cutthrough chain speed

Calibration test chain speed Calibration pass criteria Test cut failure criteria

Threshold chain speed meets 15 6 1 m/s Cut through time ,1.5 s, or cut-through of bottom layer .25 mm Top cover: minimum 400 D nylon fabric Six layers of Lincoln fabric ID 1060.071.02.000 fabric Bottom layer: minimum 70 D tricot (knit fabric) CS50: chain speed that has 50% probability to cut through the sample, or the mean speed at which the cut-through occurs Variable to obtain CS50 CS50 5 13.9 6 1 m/s .25 mm cut-through (Continued)

Evaluate cut resistance

57

Table 2.29 (Continued) Standard

Items

Key facts

ASTM F1458 for foot protectors

Calibration pad Determination of cutthrough chain speed Calibration test chain speed Calibration pass criteria Test cut failure criteria

Same as ASTM F1414

Note: It is worthy of pointing out that the materials for calibration pad are not very well specified. For instance, ( ) top cover minimum 400 D nylon fabric. Basis weight is a very critical parameter to cut resistance. This fabric does not specify basis weight at all. People may be able to manipulate it. In addition, nylon 66 and nylon 6 also differ in properties. (  ) One layer greige fabric with 13 ends warp and 12 ends picks. No basis weight and no material type are specified. (  ) Minimum 70 D tricot. Again, no basis weight for this fabric is specified. The author suggests to better specify these materials. The author also suggests to add “or equivalent” to those materials specified such as “Albarrie Canada felt style 5101.” It is better to use “Albarrie Canada felt style 5101 or equivalent.” CS50, Chain speed 50.

As for CS50, as a matter of fact, there is a more statistically sound method to obtain this kind of data by using logistic regression (also called logit regression). By doing a number of testing starting from low speed and gradually increasing to higher speed, one can get a set of data, CS versus pass or fail (recorded as 1 or 0). At some CSs the sample sometimes passes and sometimes fails, therefore testing needs to be repeated multiple times at these speeds. At speeds lower than this speed range, the test samples definitely pass, and at speed higher than this range, the test samples definitely fail. Eventually, these data can be plot as shown in Fig. 2.24, in which the diamond markers are those actual testing points and the solid-lined curve is the binary logistic regression curve. Find the CS on the curve corresponding to 50% probability. This regression method to find 50% probability of pass has been used in some standards such as testing the bullet resistance in ballistic armor testing. MIL-STD-662 (MIL_STD-662: V50 ballistic test for armor, Department of Defense, the United States) and ASTM F1959/F1959M (ASTM F1959/F1959M14e1, Standard Test Method for Determining the Arc Rating of Materials for Clothing, ASTM International, West Conshohocken, PA, 2014, www.astm.org). But this method needs larger number of testing. The logistic regression is also more difficult for people than the calculation of mean is. But nonetheless, ASTM F1414 and ASTM F1458 may be able to leverage the knowledge from those standards such as ASTM F1958 to use logistic regression to obtain more statistically sound results. ASTM F3324 and F3325 are very new standards. Their first versions were published in 2018 and were soon revised in 2019, while ASTM F1414, F1897, F1818, and F1458 all have had more than 20 years history. They were first published in the 1990s. The research on developing an appropriate standard has started in the 1980s and there have been some research results published.57,58 Feasibility of a performance criterion for protective leggings worn by chainsaw operators was also studied and reported.59 These works were also mainly carried out by IRSST, the institute that spent extensive efforts on developing TDM method. The repeatability

58

Cut Protective Textiles

Table 2.30 Performance requirements by ASTM chainsaw cutting resistance standards. Standard

Test method and scope

Performance criteria

ASTM F1897

ASTM F1414 for lower body protectors

ASTM F1818

ASTM F1458 for foot protectors

ASTM F3325

ASTM F3324 (however, not referenced in ASTM F3325) for lower body protectors

CS50 $ 14 m/s, and cut-through time $ 1.5 s at both 45 and 90 degrees cut testing CS50 $ 13.9 m/s, or no cut through at 1.5 s (or cut through time .1.5, not $ ) Threshold chain stopping speed $ 15 m/s, or the cut-through time $ 1.5 s at 90 degrees

100

Probability of cut-through (%)

90 80 70 60 50 40 30 20 10 0 10

11

12

13

14

15

16

17

18

Chain speed (m/s)

Figure 2.24 Logistic regression for chain speed versus pass/fail.

and reproducibility of these rough-looking chainsaw cut testing were proved fairly good. The same IRSST research group also evaluated a method of using flywheeldriven chainsaw to cut the test pad and of using the total cut-through energy as the performance criterion.60 It was mentioned that this method was independent of the drive system and consequently the motor driving the flywheel could be replaced or underwent maintenance without affecting the results. However, apparently this method was eventually not adopted as a testing standard.

Fundamental of fibers

3

Textile is basically made of fibers of various forms. To understand the cut protective textile, it is necessary for one to understand the basic forms of fibers, basic terminologies and the properties of fibers and yarns.

3.1

Basic forms of fibers

The majority of cut protective equipment is fundamentally are textile products made of fibers. When talking about the difference among cut resistance of different materials, one has to bear in mind that different materials have different ranking by different testing methods, as there is no correlation between the tomodynamometer (TDM) and coupe test methods. For instance, steel performs better than glass fiber in TDM test, but the results are generally just opposite in the coupe test, as aforementioned. With the implementation of EN388:2016, TDM cut testing is becoming more popular now. The TDM cut method (ISO13997 and ASTM F2992-15) is more reliable, and the results are more consistent. The general order of cut resistance of different materials is leather , cotton , nylon
polyester , HPPE (UHMWPE) ,
para-aramid , glass fiber , steel, by the TDM cut method. Certainly, the amount of materials, that is, the basis weight (weight per unit area), is also a determining factor on cut resistance. Therefore all general comparisons in cut resistance between materials should be based on the same weight. Basic forms of fibers used in cut protective textile are discussed in this section. But some basic concepts and terminologies need to be introduced and explained before the fiber forms are discussed. Fiber is a natural or synthetic substance that is significantly longer than it is wide. Continuous fiber is called filament yarn, and discontinuous fiber is called short fiber. The short fiber is further divided into staple and floc, defined by the length and the shape. Different people in the industry use different fiber lengths when they distinguish between staple and floc. Some people define short fibers longer than 12 mm as staple and shorter ones as floc, and some define 6 mm or above as staple and shorter as floc. Besides length, the most critical difference is that the staple is added with crimps that allow lumps of staple to be spun into yarn, called staple yarn or spun yarn, while the floc does not have crimps and keeps straight. Figs. 3.1 and 3.2 show the pictures of filament yarn and different short fibers, and Fig. 3.3 schematically shows their difference in shape. The floc cannot be converted to fabrics and is usually not used in cut protective textile, therefore it is not discussed further in this book. Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00003-1 © 2020 Elsevier Ltd. All rights reserved.

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Cut Protective Textiles

Figure 3.1 Picture of filament yarn.

Figure 3.2 Pictures of different short fibers: (A) floc (no crimp) and (B) staple (with crimp).

Fundamental of fibers

61

Figure 3.3 Schematic representation of different fibers: (A) floc, (B) staple, and (C) filament yarn.

3.1.1 Staple and staple spun yarn Staple cannot be directly used to form fabrics by weaving or knitting, instead it must be spun into yarn which can afterward be used for weaving or knitting. For instance, a well-known staple product is the cotton fiber. Cotton fiber cannot be directly made into cloth without being spun into yarn. The staples used in cut protective textile must be spun to yarn first then further converted to fabrics. The staples are usually 38 mm (1.5 in.) for cotton spinning system, or 51 mm (2 in.) for synthetic fiber spinning system, or 75102 mm (34 in.) for woolen spinning system. The short fiber for spinning must be crimped. The crimps allow adequate friction forces among fibers after spun into yarn form so that the yarn has enough strength and cohesion between fibers. Before the crimps are added the short fibers are straight in shape and become zigzag shaped after crimped. The critical properties of crimp include number of crimps per unit length, height of crimp, and elastic recovery of crimp. Fig. 3.2A shows the picture of floc without crimp, and Fig. 3.2B of the crimped staple. There are different technologies to add crimps onto fiber. First of all, the crimps are added onto filament yarn first then the crimped filament yarn is cut to defined length to form staple. Fig. 3.4 shows two common crimping technologies.61 What is shown in Fig. 3.4A is called stuffer box crimping in which the yarn is overfed into a heated stuffer box and crimps form in the box due to the overfeeding and heating. The process shown in Fig. 3.4B is called gear crimping in which the yarn passes a pair of heated gears which crimp the yarn. The continuous yarn formed with staple fibers bundled together with spinning process is called spun yarn, staple yarn, or staple spun yarn. The single short fiber in spun yarn is still discontinuous, but all the short fibers are bundled together and constrain each other by friction forces. Fig. 3.5 shows a picture of spun yarn sample. The characteristics of crimps of staples are determining factors on the spinning process and properties of spun yarn. The number of crimps, percentage crimp, elastic recovery of crimp, and elasticity of crimp are critical characteristics of crimp, which can be tested according to standard GB/T 14338 (Chinese standard),62 which is similar to the Japanese Industrial Standards L1015.63 The number of crimps is also called crimp frequency, which means the total number of crimps in a unit length. It is measured by counting the number of crimps

62

Cut Protective Textiles

Figure 3.4 Two common fiber crimping processes: (A) stuffer box and (B) gear. Source: From Lord, PR. Textile products and fiber production. In: Handbook of Yarn Production: Technology, Science and Economics. Cambridge, England: Woodhead Publishing; 2003 [Chapter 2].

Figure 3.5 Spun yarn.

Fundamental of fibers

63

Figure 3.6 Measurement of percentage crimp: (A) curved form under a lighter load and (B) straight form under a heavier load.

after the short fiber is loaded with a standard light weight. The crimps enable the short fibers to have cohesion by friction forces to impart strength to the spun yarn. But the opening and drawing of the short fibers before spinning would be difficult if the number of crimps is too high. On the contrary, if the number of crimps is too low, the short fibers can easily get straightened during the multistep drawing process, and the friction force between fibers is too low, resulting in a spun yarn with very low strength. Hence, in order to get good spinning processability and spun yarn quality, the number of crimps (crimp frequency) must be optimized to strike a balance between processability and yarn strength. Percentage crimp is also called crimp contraction. It is expressed as the percentage of the original length of crimped short fiber to the straightened length. Fig. 3.6 shows the principle of measuring the percentage crimp. During testing the straightened length L1 is measured under a relatively heavier load, while the original length L0 is measured under a lighter load. Then the percent crimp is calculated with the following equation: Percentagecrimp 5

L1 2 L0 3 100% L1

(3.1)

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Cut Protective Textiles

The light and heavy loads are specified in the standard. For all staple fibers the light load is 0.002 cN/dtex (refer to Sections 3.2.1 and 3.2.2 for the meaning of cN and dtex). If a staple fiber is 2 dtex, then the load is 0.004 cN, which is a very light load. The high load is 0.075 or 0.05 cN/dtex, depending upon the material type. These loads can only be realized on precision instrument; therefore it is nearly impossible to be measured by manually adding weight onto the staple. Higher percentage crimp can improve the cohesion between the fibers in spun yarn and therefore improve the yarn quality. But higher percentage crimp can also create higher friction among fibers and therefore makes spinning difficult. The crimp recovery rate is measured by the following steps: 1. 2. 3. 4.

Apply a heavier load first onto the staple and measure the staple length L2. Remove the heavier load and wait for 2 minutes. Apply a lighter load onto the staple and measure the staple length L1. Calculate the crimp recovery rate using the following equation:

Crimp recovery rate 5

L1 2 L2 3 100% L1

(3.2)

where L1 is the staple length measured after it is applied with the heavier load and L2is the staple length measured under the lighter load after 2 minutes after the heavier load is removed. The lighter and heavier loads are the same as those used in percentage crimp measurement. From Eq. (3.2), one shall easily understand that the crimp recovery rate is an index of how well the fiber can recover its crimps after being tensioned. From Eq. (3.2), one shall easily understand that the crimp recovery rate reflects how well the staple’s crimps can recover after tensioned. This is fairly critical in spinning process as the staples frequently experience tension throughout the entire spinning process. If the crimp recovery rate is poor, then the yarn strength will be low in the end. The crimp elasticity rate is measured by the following steps: 1. The staple is applied with the lighter load for the first time, and the length is measured and recorded as L0. 2. Remove the lighter load and add the heavier load, measure the length L1, keep for 30 seconds, then remove the heavier load, and wait for 2 minutes. 3. Add the lighter load onto the staple for the second time, and measure the length L2. 4. Calculate the crimp elasticity rate using the following equations:

Crimp elasticity rate 5

L1 2 L2 3 100% L1 2 L0

(3.3)

Crimp elasticity rate 5

Crimp recovery rate 3 100% Percentage crimp

(3.4)

Fundamental of fibers

65

where L0, L1, and L2 have the same meanings as in Eqs. (3.1) and (3.2) explained earlier. This calculation clearly explains that the crimp elasticity rate is an index of how well the fiber can recover itself after being tensioned. This rate is 100% if the short fiber length under the lighter load for the second time is equal to its original length when the lighter load was applied for the first time, that is, L2 5 L0. The staples are frequently under tension during the spinning process. The higher crimp recovery rate and higher elasticity rate of the staples the better capability of recovery, then the staples are more tolerant to the spinning process; therefore the spinning process window can be broader and a more consistent yarn quality can be ensured. Typical testing standards for these staple properties are ASTM D3937-1264 and GB/T 14338-200862 in China. Fig. 3.7 schematically shows several different crimp status. Staple is usually supplied in compressed bale. Spinning staple to spun yarn usually takes several steps as described in Fig. 3.8.65 Please note that this process scheme is very basic. In some cases, there are also some additional steps such as combing, which is not included here.

Figure 3.7 Schematic diagram of staples with different number of crimps and percentage crimp.

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Cut Protective Textiles

Bale opening and cleaning

Carding

Drawing

Roving

Twisting

Doubling

Winding

Spining

Figure 3.8 Process steps to spin staple to spun yarn. The steps represented by the dashed rectangles and dashed arrows mean that they are optional unless for producing plied yarns. The whole process for single yarn is finished at the winding step.

Opening and cleaning: A step to separate or break up bales of fibers. The compressed bale is opened to loosen fiber bundles while minimizing damage to the staple fibers and to effectively clean impurities and dirt. If the target spun yarn is a mixture of different types of materials, this step can also serve the purpose of staple mixing in designed ratios. The product of this step is a roll of a thin layer or batt of fibers in which staple fibers are loosely entangled with a certain level of alignment. This roll is called a picker lap. Fig. 3.9A shows a picture of bale opener and cleaner system, and Fig. 3.9B is the schematic diagram of the bale opening and cleaning mechanism. Carding: A mechanical process that breaks up entanglement and unorganized clumps of staple fibers and then aligns the individual fibers to be parallel with one another. Also, mixing is further improved if different fibers are used. Continuous web or sliver is produced at this step for a subsequent step of processing. Fig. 3.10A shows a picture of carding workshop, and Fig. 3.10B schematically shows the principle of carding. Drawing: It is a process of passing multiple ends of slivers through a series of rollers, which spin at different speeds with the later ones spinning faster than the previous ones; thus the individual fibers are straightened and made more parallel. Drawing reduces a soft mass of fiber to a firm uniform strand of usable size. This step allows different fibers to be further mixed more uniformly. Usually, there are multiple repetitions of this step, with a minimum of twice, but usually three to four times, or even more. Fig. 3.11A and B shows the photo of drawing and the schematic diagram. Roving: It is a process after drawing that further slightly draws the sliver and adds slight twist to the sliver to form the proper thickness and lengths suitable for spinning. The product of this step is also called roving. Fig. 3.12A shows the picture of a roving process and Fig. 3.12B shows its principle in a schematic diagram. Spinning: A step of high ratio stretch and twisting of roving to form yarn. The direction of twisting at the spinning step and the roving step is the same, usually Z direction. Fig. 3.13A shows a photo of a spinning frame, Fig. 3.13B shows a closer

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Figure 3.9 Bale opening and cleaning: (A) photo of bale opening and cleaning machine. (B) Schematic diagram of bale opening and cleaning process. [(1) Feed table; (2) internal feed lattice; (3) light barriers, (4) baffle plate; (5) brush rolls; (6) spiked lattice; (7) cleaner roller; (8) evener roller; (9) stripper roller.] Source: (A) Courtesy Rieter AG; (B) From Lawrence CA. Materials preparation stage II: fundamentals of the carding process. In: Fundamentals of Spun Yarn Technology. Boca Raton, FL: CRC Press; 2003 [Chapter 2].

view of the ring spinning, and Fig. 3.13C shows a schematic diagram of the ringspinning process. The photo shown here is for ring spinning. Other spinning technologies such as open-end spinning, and air-jet spinning are not discussed here but can be read in

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Figure 3.10 Carding process: (A) photo of carding machine and (B) schematic diagram of carding process. Source: (A) Courtesy Rieter AG; (B) From Lawrence CA. Materials preparation stage II: fundamentals of the carding process. In: Fundamentals of Spun Yarn Technology. Boca Raton, FL: CRC Press; 2003 [Chapter 3].

literatures.66 Fig. 3.14 shows the comparison among yarns spun by different spinning technologies. The sliver/yarn linear density (or yarn count) continuously decrease from carding step to spinning step. That means the sliver/yarn becomes thinner and thinner along the consecutive process steps. This is achieved by a mechanism called drafting in each step. Drafting is the process of attenuating the mass of a sliver/yarn by using a combination of pairs of rollers which run with speed differential. The mechanism is

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Figure 3.11 Drawing process: (A) photo of a drawing machine and (B) schematic diagram of drawing process. Source: (A) Courtesy Rieter AG; (B) From Lord PR. Sliver preparation. In: Handbook of Yarn Production: Technology, Science and Economics. Woodhead Publishing; 2003 [Chapter 6].

shown in Fig. 3.15.67 The front rollers run faster than the back rollers; therefore a speed differential is created and the staple fibers in the sliver/yarn are pulled apart along the running direction and the sliver/yarn becomes thinner after coming out. This figure only shows a single-zone drafting. There are usually consecutive multiple zones of drafting at one step. After spinning step the yarn linear density (or yarn count) is fixed and will no longer decrease in the next process steps. Winding: It is a process step to wind up the spun yarn onto standard packages, either cones or straight tubes (bobbins), with metered length. The defects on the yarn can be detected and removed at this step. Splicing is needed at this step to make the package large enough after winding. Fig. 3.16A shows the photo of a winding machine and Fig. 3.16B shows the principle of winding.

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Figure 3.12 Roving process: (A) photo of a roving machine and (B) schematic diagram of roving process.

Doubling: Also called combining or assembly winding. When plied yarn is needed, two or more ends of single end spun yarn are combined together. The different ends are parallel to each other at this step after doubling process. Fig. 3.17A shows the photo of a doubling machine. Fig. 3.17B shows the mechanism of doubling. Though the term is doubling, it does not necessarily mean only two ends are combined together. As a matter of fact, combining more than two ends together is not uncommon, though two ends are the most common configuration. Twisting: There are actions of twisting in both roving and spinning steps, but the twisting discussed in this section is the twisting of combined ends. The combined

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Figure 3.13 Ring spinning: (A) photo of a ring spinning machine, (B) a closer view of the ring spinning, and (C) schematic diagram of ring-spinning process. Source: (A) Courtesy Rieter AG; (C) From Tang ZX, Fraser WB, Wang X. Modeling yarn balloon motion in ring spinning. Appl Math Model. 2007;31(7):13971410. doi:10.1016/j. apm.2006.03.031.

ends of yarns are twisted together, adding cohesiveness and strength. The principle of twisting at this step is the same as the twisting added to yarn at the roving step and spinning step. The tenacity of ply yarn formed by twisting is higher than the single end yarn before plying twist, and the ply yarn is more uniform and more abrasion resistant than the single end yarn. Twisting can also twist together different yarns of different materials which perform different functions. Doubling and twisting not only can be done at two separate steps but can also be done in one single step for instance by using a two-for-one twister. The direction of twisting is

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Figure 3.14 Staple yarn spun from different spinning technologies. Source: From Course ‘New Spinning System’. ,https://nptel.ac.in/courses/116102038/45..

Figure 3.15 Mechanism of drafting. Source: From Lawrence CA. Materials preparation stage III: drawing, combing, tow-top conversion, roving production. In: Fundamentals of Spun Yarn Technology. Boca Raton, FL: CRC Press; 2003 [Chapter 5].

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Figure 3.16 Yarn winding: (A) photo of a winding machine and (B) principle of winding. Source: (A) Courtesy Muratec Co.

Figure 3.17 Yarn doubling: (A) photo of a doubling machine (assembly winder) and (B) principle of doubling (assembly winding). Source: (A) Courtesy SSM AG.

usually in the S direction, which is opposite to the direction of the twist added at spinning and roving steps. Fig. 3.18A shows the photo of a twisting machine. What is shown here is a two-for-one twister. Productivity of two-for-one twisters is higher than for ring twisters, but ring twisters are more flexible in doing different twisting. Twists are added to yarn at steps of roving, spinning, and twisting to different extents. Twist is necessary to form short fiber into yarn by holding the short fibers together and generates friction among short fibers. Twisting is acted by the rotation of the yarn around its own axis along length direction, by which the fibers spirally wrap around the axis from the original state of being parallel to the axis. The performance of the yarn and the textile made of the yarn is heavily affected by the twisting direction and the amount of twist.

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Figure 3.18 Two-for-one twisting: (A) photo of a two-for-one twister, (B) a closer view of the two-for-one twisting, and (C) principle of the two-for-one twisting. Source: From Course 6.2 ‘Two-For-One Twisters’. Modified from: ,https://nptel.ac.in/ courses/116102038/40..

The direction of twist is the tilting direction of the fiber in the spiral, usually denoted as Z or S. It is called Z direction if the fibers tilt from lower left to the upper right like the middle section of letter Z as illustrated in Fig. 3.19B, and S direction if the fibers tilt from lower right to the upper left like the middle section of letter S as illustrated in Fig. 3.19B.

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Figure 3.19 S twist direction and Z twist direction of yarn. (A) Z direction: alignment of fibers is like the middle section of letter Z. (B) S direction: alignment of fibers is like the middle section of letter S). Source: From McLoughlin J, Paul R. Future textiles for high-performance apparels. In: Mcloughlin J, Sabir T, eds. High-Performance Apparel: Materials, Development, and Applications. 1st ed. Cambridge, England: Woodhead Publishing; 2017 [Chapter 11].

Usually, as an industry common practice, a single end yarn is twisted in direction Z, and a plied yarn in direction S. The twist direction of a plied yarn is denoted as the sequence of twisting, for example, ZS stands for the twist of single yarn is Z direction, then the followed plying is in direction of S. This kind of construction is illustrated in Fig. 3.20. The twist direction of ply heavily affects the appearance and hepatic feeling of the fabric. The combination of yarns of different twist directions with different weaving patterns can create fabrics with very different styles. Fig. 3.21 illustrates how the twisting directions of warp and weft can be the same or different in the woven fabrics. When the twisting directions of warp and weft yarns are the same (Fig. 3.21A), the directions of them in the fabric surface are actually opposite to each other as illustrated in the diagram; as a result, the optical reflections of the fibers of warp and of weft are different. However, the fibers are at the same direction at the contact points and they tend to interlock with each other, creating a fabric that tends to be tight and stable. When the twisting directions of the weft yarn and warp yarn are opposite to each other (Fig. 3.21B), actually the fibers on the fabric surfaces have the same alignment direction; therefore the optical reflection is the same, and as a result, the fabric is more luminous than the fabric in which the twist directions of warp and weft are the same. But at the contact points, the fibers alignment is opposite to each other, therefore the fabric tends to be loose and soft.

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Figure 3.20 Twist directions in plied yarn. Source: From Jorgensen LB. Textiles and textile trade in the first millennium AD. In: Mattingly DJ, Leitch V, Duckworth CN, et al., eds. Trade in the Ancient Sahara and Beyond. Cambridge University Press; 2017 [Chapter 9]. doi:10.1017/9781108161091.

Figure 3.21 Effect of twist directions of warp and weft yarns on the fabric. [(A) Same twist direction Z of both warp and weft yarns. Opposite direction of fiber alignment on the fabric surface but the same direction of fiber alignment at the contact point; (B) opposite twist directions of warp (Z) and weft (S) yarns. Same direction of fiber alignment on the fabric surface but opposite direction of fiber alignment at the contact point.]

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Figure 3.22 Different twist levels caused by different thickness at same twist level.

The total number of turns formed by the twisting in a unit length is called the number of twist or twist level. There are a couple of ways to express twist level: number of twists per meter (TPM), or per inch (TPI), or twist per 10 cm (twist per decimeter). Apparently, the tilting angle (or spiral angle) of the fiber in a thinner yarn appears to be different from that in a thicker yarn, when their twist levels are identical as illustrated in Fig. 3.22. A different term, twist factor, is introduced to describe the level of tilting angle in a yarn. Twist factor is the value obtained by multiplying the twist with the square root of the linear density of the yarn as shown by Eq. (3.5). With the introduction of square root of linear density into the equation, the difference in mass is normalized, therefore the twist factor can be used to compare the degree of tilting of the fibers in yarns of different linear density (or yarn count). Having the same twist factor means having the same tilting angle of fibers regardless of the linear density of the yarn. The definition and description of linear density can be found in Section 3.2.1. The equations for calculating twist factor are in Tex system: Twist factor 5 twist percentimeter 3

pffiffiffiffiffiffiffiffi Tex

(3.5)

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in cotton (English) count system: twist per inch Twist factor 5 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi cotton countðNeÞ

(3.6)

in metric count system: twist per meter Twist factor 5 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi metric countðNmÞ

(3.7)

If two different yarns have the same linear density (or yarn count) and the same twist level, then they will have the same twist factor according to Eqs. (3.5), (3.6), or (3.7). However, if these two different yarns are made of two different materials with different specific gravities, then their thickness is different from each other, though they have the same linear density. At the same linear density, the material of higher specific gravity will get a thinner yarn and vice versa. The difference in thickness (diameter) illustrated in Fig. 3.22 may be simply caused by the difference in specific gravity. Therefore Eqs. (3.5)(3.7) do not resolve the problem of comparing the twist levels of yarns with different specific gravities. A correction factor associated with specific gravity should be introduced into these equations as follows to address this issue68 Correctedtwist factor 5 sffiffiffiffiffiffiffiffi Tex （twist per centimeter） 3 ρ

(3.8)

where ρ is the specific gravity. Generally, it is believed that increasing twist level increases the yarn strength. This is true when the twist level increases from 0 to an optimum level. After an optimum level the yarn strength starts to decrease as shown in Fig. 3.23.69 The cohesiveness is improved by adding twist to the yarn; as a result, the break strength and break elongation are improved, and the wrinkle resistance and abrasion resistance of the fabrics are also improved. But with further increased twist, the yarn and the fabric made with the higher twist will become more rigid and more difficult for dyestuff to penetrate. Different applications require different twist levels. Generally, lower twist is better for softer haptic and more elastic feeling. Filament needs a low level of twist; fleece products also need low twist yarn to allow them to be easily brushed to generate fleece. Yarn for the warp needs slightly higher twist to allow it to undertake the tension and abrasion during weaving. For a shirt application, which needs wrinkle resistance and a stiff and smooth feeling, higher twist is needed. The twist factor for cut resistance fabric is usually 3.13.2 for single end yarn and 1.52.3 for plied yarn.70 Too high twist level causes liveliness of yarn. The liveliness of yarn is referred to that a twisted yarn has the tendency to twist around itself under an untensioned

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Figure 3.23 Effect of twist level on yarn tenacity.

Figure 3.24 Liveliness of twisted yarn: (A) under tension and (B) relaxed. Source: From Lord PR. Common principles. In: Handbook of Yarn Production: Technology, Science and Economics. Woodhead Publishing Ltd.; 2003 [Chapter 3].

state as illustrated in Fig. 3.24. This phenomenon should not be new to the readers. During twisting the yarn is forced by a torsional force to form twists. When the yarn is not tensioned, the yarn tends to untwist to release the residual torque. The higher twist level, the higher liveliness. High liveness causes difficulties in handling, including fabric weaving and knitting, as the yarn tends to snarl if there is no or inadequate tension on the yarn. High liveliness of yarn also causes distortion of fabric after it is knitted or woven because the yarn attempts to untwist to release the residual torque. The liveliness of yarn with low twist level is generally not an issue. Plying yarn in a twist direction opposite to the original twist direction of single yarn can reduce

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Figure 3.25 Photo of a steaming vessel.

liveliness. Another common technology to reduce the liveliness is a process called steaming by conditioning the yarn packages in a sealed vessel filled with oversaturated steam. The residual torque is reduced at the high temperature with the assistance of steam. Fig. 3.25 shows a photo of steaming equipment. This process is actually used to condition the yarn to equilibrium moisture level. The liveliness reduction is just a side effect. The twist level also affects the diameter and linear density of the yarn. After being twisted the yarn contracts along the length; thus the mass of equal length of the yarn increases, then the linear density increases. Higher twist reduces the yarn diameter and increases the tightness. As a result, the basis weight of the fabric increases when the distance between yarns in the fabric is the same. The free space inside the yarn is reduced when the twist level increases and then the air in this space is squeezed out, which reduces the thermal insulation capability of the fabric because the thermal insulation of the fabric is heavily dependent upon the stationary air inside the fabric. The more stationary air is in the fabric, the better the thermal insulation is. The free space inside the fabric also affects the air permeability. The more free space there is, the higher air permeability the fabric has. As aforementioned, the twist directions of the warp and weft yarns in the fabric affect the style of the fabrics. When the twist directions of warp and weft are the same, the fibers at the contact points of warp and weft are spiraling in the same direction so that they can penetrate into each other, therefore the cohesiveness is improved. This penetration makes the fabric thinner than the fabric with warp and weft yarns having opposite twist directions. If a thick, soft, and fluffy fabric product is desired, it is better to use warp and weft yarns with opposite twist directions, but this will create operation management complexity.

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The type of staple spinning system used also depends on the staple length. Cotton spinning system uses staple with length of 38 mm (1.5 in.), synthetic staple fiber spinning system for 51 mm staple (2 in.), and woolen spinning system for 75102 mm (34 in.). Para-aramid staples are often available in 48 and 51 mm, suitable for synthetic staple fiber spinning system.

3.1.2 Filament yarn Filament yarn is the yarn consisting of fibers with each end being endless. The continuous and endless fiber is called filament. In spun yarn, though the whole yarn is continuous, each staple fiber is discontinuous. Fig. 3.1 already showed the picture of filament yarn. Filament yarn is often, though not always, twisted before use. The twist level of filament yarn is usually expressed as TPM or TPI. Twist factor, also called twist multiplier, is similar to that used for spun yarn. In DuPont’s product technical guide the twist multiplier for Kevlar para-aramid fiber is defined as71 pffiffiffiffiffiffiffiffiffi TPM 3 dtex Twistmultiplier 5 3000

(3.9)

It remains unknown that why the constant is 3000 in this equation. DuPont company did not explain why. It is worth mentioning again that twist multipliers are different for yarn materials with different specific gravities even when the twist level and linear density are the same. For instance, para-aramid’s specific gravity is 1.44, while Nylon6 1.06; therefore para-aramid’s diameter is smaller than Nylon6 at equal linear density. The previous equation is only applicable to para-aramid or to fibers with the same specific gravity of para-aramid. The effect of twist on the filament yarn properties, such as yarn strength, diameter, and abrasion resistance, is similar to the one on the staple spun yarn. For instance, Kevlar aramid filament yarn has an optimum twist level to achieve the highest strength. The twist level is twist multiplier of 1.1 as reported by DuPont.72 By using Eq. (3.9), one can easily get that the highest strength of an 1100 dtex Kevlar aramid yarn is when the twist level is around 95 TPM. Please bear in mind that this optimum twist level applies to Kevlar aramid filament yarn only. It does not apply to other filament yarns. One has to experiment by him/herself to find out the optimum twist level for a specific yarn.

3.1.3 Textured yarn Textured yarn is very common in cut protective gloves. Textured yarn is made of filament yarn that has been passed through a texturing process. Texturing is a process that changes the parallel alignment of fibers in filament yarn by mechanical or physical measures to make the yarn possess actual or latent crimps, coils or loops, with or without twist liveliness by which the yarn has or can develop bulk and/or stretch properties by posttreatment. There are different texturing processes, such as

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Draw Textured Yarn (DTY), False Twist Textured Yarn, Air Textured Yarn (ATY), and Bulked Continuous Filament. ATY and DTY are discussed here as two most commonly used textured yarns in cut protective textile products.

3.1.3.1 Air textured yarn ATY73 was invented by DuPont.74 It was made by overfeeding filament yarn into a turbulent stream of compressed air. The filament yarn is interlaced in the action of compressed air and irregular loops are formed; as a result, the yarn has increased bulk. The most important element of this process is the texturing nozzle. The filament yarn is overfed at a certain overfeeding ratio into the nozzle, and the high pressure compressed air blows on the yarn along the running direction of the yarn and texturizes the yarn. This process is schematically illustrated in Fig. 3.26. DuPont branded the air jet as Taslan when the company invented it. This textured yarn possesses some properties of both filament and spun yarn, for instance, continuous in form, fluffy, and soft. The linear density of textured yarn is higher by 10%15% than its precursor filament yarn. The textured yarn is more cohesive than the filament yarn but also softer, therefore is good for the knitting process and generates good haptic feeling. Fig. 3.27 schematically shows the appearance of ATY. It needs to be stressed here that one needs to distinguish the air-interlaced yarn from the ATY. The air-interlaced yarn is interlaced with filament yarn by compressed air, therefore it shares some similarities with ATY, but they do have several critical differences. The interlacing process is illustrated in Fig. 3.28, from which one can see that there is strong similarity to the air-texturizing jet. But the compressed air applied to the ATY is continuous throughout the process, while the compressed air applied to the interlaced yarn is discontinuous with a regular onoff mode. The compressed air applied to the interlaced yarn lasts very short therefore it

Figure 3.26 Principle of the air texturing. Source: From Mankodi HR. Developments in hybrid yarns. In: Gong RH, ed. Specialist Yarn and Fabrics: Development and Applications. Cambridge, England: Woodhead Publishing; 2011 [Chapter 2].

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Figure 3.27 Picture of an air textured yarn. Source: From Demir A, Acar M, Wray GR. Air-jet textured yarns: the effects of process and supply yarn parameters on the properties of textured yarns. Textile Res J. 1988;58 (6):318328.

Figure 3.28 Interlacing process. Source: Courtesy Textile Study Center. ,https://textilestudycenter.com/man-made-fibreproduction/..

Figure 3.29 Schematic illustration of interlaced yarn: (A) interlaced point and (B) open area. Source: From Hearle JWS, Hollick L, Wilson DK. False-twist textured yarns. In: Yarn Texturing Technology. Cambridge, England: Woodhead Publishing; 2000 [Chapter 5].

acts just like a pinch on a point of the yarn. Only the points where the compressed air is applied form interlace while other areas—actually majority of the yarn—are generally unaffected. Therefore the difference in the process leads to a critical difference in appearance of these two yarns: the ATY forms lots of loops on the surface, while the interlaced yarn does not have (see Fig. 3.29). From properties point of view the ATY is elastic and retains low strength, while the interlaced yarn is not elastic and retains good strength. The details can be further understood in references.73 Usually, what is commonly seen in the cut protective textile products is ATY.

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3.1.3.2 False twist textured yarn False twist texturing is a process that introduces bulkiness and elasticity to filament yarn by leveraging the thermoplasticity of thermoplastic yarn.75 The continuous filament yarn is first twisted to one direction, heat set to form permanent twist, followed by being twisted to opposite direction to remove the twist. Bulky and elastictextured yarn is formed after this step of twist removal. This process is illustrated in Fig. 3.30. There is a false twist device between the feed rollers and the delivery rollers which both hold the yarn. Between the two pair of rollers there is a false twist device which rotates at a high speed. The yarn is twisted to one direction between the feed rollers and the false twist device before entering the false twist device, followed by twisted to the opposite direction at exactly the same twist level between the false twist device and the delivery rollers after exiting the false twist device. The yarn is heat set between the feed rollers and the false twist device. The distortion of the yarn is generated in first twist and preserved by the heat setting.

Figure 3.30 Mechanism of false twist texturing.

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The high elastic and low elastic yarns can be both made with false twist process. What is shown in Fig. 3.30 is the basic mechanism of false twist and usually the high elastic yarn is made with this process. The high elastic yarn not only possesses high elasticity and high bulkiness but also possesses high residual torque and high inconsistency of elasticity. To overcome these weaknesses a false twist process with two-step heat setting chambers was developed, also called modified or improved false twist process. In the process shown in Fig. 3.30 the heat setting chamber is between the feed rollers and the false twist device, before the yarn enters the false twist device (also shown in Fig. 3.31A). While in the modified false twist process, one more heat setting chamber is added between the false twist device and delivery rollers, and there is an overfeed roller added between the false twist device and this second heat setting chamber, as illustrated in Fig. 3.31B. The overfeed roller overfeeds the twisted and heat set yarn into the second heat setting chamber, therefore a relaxed status of heat set twisted yarn is created, then the high distortion part in the yarn is reduced to low distortion, and the resultant yarn is less elastic than the yarn without this second heat setting. Another commonly seen textured yarn is DTY. DTY is actually a type of false twist yarn but uses partially oriented yarn as precursor yarn of which the mechanical properties are not optimized by drawing yet. Usually, the yarn needs adequate drawing to achieve optimal mechanical properties after spinning. Historically, yarn is fully drawn then goes to false twist texturing in two separate processes, or even in two separate factories, which had very low productivity and thus was not cost-effective to

Figure 3.31 Processes for (A) high elastic and (B) low elastic yarns.

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improve the productivity, a two-step process was developed on one continuous line to draw the yarn first followed by false twist texturing. This intended to improve the productivity but it was realized that the strength of this kind of yarn was low and the texture was not stable and was difficult to be preserved. The manufacturing machine was also complex and the cost effectiveness was not really improved much. To resolve these problems a one-step process was developed by having the drawing and false twisting in one zone, which produces the currently widely used false twist textured yarn. Another broadly used texturing technology is the friction false twisting.76 It falls into the category of false twisting but is different from what was described previously. Fig. 3.32 shows the mechanism of texturizing by friction false twisting. The yarn is twisted through friction contact with totally nine rotating friction disks, which are located on a three-spindle unit by passing through a helical path along the central axis of the spindles. Twisting torque is applied to the yarn through friction contact with each rotating disk. As the yarn, continuously passes through the disk stacking, twist is added to the yarn and remains until it exits the stack of disks. Fig. 3.33 shows a set of friction false twist disk unit.

Figure 3.32 Principle of friction false twist texturing.

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Figure 3.33 Friction false twist disk unit. Source: Courtesy SSM AG.

3.1.3.3 Bicomponent textured yarn Bicomponent textured yarn is made by leveraging the difference in heat shrinkage of two different fiber materials which are spun together then heat treated. Because of the differential heat shrinkage, the yarn forms three-dimensional coils after treatment at elevated temperature and therefore creates elasticity. As early as in the 1950s, DuPont had already filed patents disclosing yarn with crimps formed with two components.7779 There are different types of bicomponent fibers, defined based on morphology, including side-by-side, sheath-core, splittable-pie, and seaisland types. Fig. 3.34 illustrates the cross-sectional morphologies of these different bicomponent fibers. Side-by-side is spun in spinners with two melts or solutions of two different materials which are individually fed to the spinneret and form a composite melt or solution and are spun through the spinneret. The differential shrinkage forces between the two different materials generate bending and torsional forces which act together to make the yarn form crimps and coils. These crimps and coils impart elasticity to the yarn. A typical example of such yarn is T400 from Invista which is spun with polyethylene terephthalate and polytrimethylene terephthalate fiber materials.80 Other types of textured yarns are not discussed here. Interested readers can do further reading in the references.73

3.1.4 Composite yarn: core-spun yarn and wrapped yarn Composite yarn refers to yarn which consists of different types of fibers and therefore different properties of different materials are combined into one yarn. Core-spun

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Figure 3.34 Schematic diagram of the morphologies of bicomponent fibers.

yarn and wrap yarn are two common composite yarns. Both core-spun yarn and wrap yarn are yarns with one type of yarn covered by another type, but with a large difference in structures. As a matter of fact, the bicomponent yarn mentioned in Section 3.1.3.3 is also one type of composite yarn because there are two different materials in one yarn.

3.1.4.1 Core-spun yarn Core-spun yarn81 is made in the process of staple spun yarn spinning. In the spinning step (the step after roving), the core is inserted into the roving and the roving is further drawn and twisted around the core. Eventually, the staple yarn forms a sheath that covers the core. Theoretically, the core can be either spun yarn or filament yarn, but in reality, the core is usually filament yarn, such as steel, glass, spandex, or monofilament of organic fiber such as polyester. But, nonetheless, the sheath must be staple spun yarn. Usually, the sheath made of staple spun yarn covers the core fairly well and the core can hardly be seen from outside. Fig. 3.35 shows the schematic diagram of core-spun process. Fig. 3.36 illustrates how the core yarn is inserted into the sheath roving in ring-spinning process by entering into a triangle area formed by the sheath roving after a pair of drafting rollers. After entering into this triangle area, the core yarn and sheath roving continue to move together and the roving sheath starts to wrap around the core yarn due to the twisting action of the spinning. Fig. 3.37 schematically shows how a core-spun yarn looks like.

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Figure 3.35 Schematic diagram of core-spun process. Source: Chen T. Compound yarn. In: Gong RH, ed. Specialist Yarn and Fabric Structures. Cambridge, England: Woodhead Publishing; 2011 [Chapter 1].

Another spinning technology that has attracted much attention worldwide to make core-spun yarn is DREF spinning. DREF spinning is an open-end spinning technology, invented by Dr. Ernst Fehrer, an Austrian inventor, with patents filed in 1973,8284 and named after Dr. Ernst Fehrer, using his salute “Dr.” and the two initial letters E and F of his name. It is worth mentioning that Dr. Ernst Fehrer started inventing things when he was only 14 years old and filed his first patent at 18. He filed in total more than 1000 patents before he passed away in 2000. DREF spinning leverages friction between rollers and fiber to twist the yarn after the staple fibers are condensed by the air. In DREF spinning the opened staple fibers are transported by air flow to a moving perforated surface with negative pressure which sucks and secures the staple fibers onto the surface to form a web. While moving forward, the staple web is twisted around itself to form yarn by friction force generated by the two corotating friction rollers, which rotates in a direction perpendicular to the moving direction of web. The formed yarn is delivered along the direction perpendicular to the staple-feeding and web-moving direction. Fig. 3.38 shows the very basic mechanism of friction spinning. Input staple fibers are opened, drafted, and fed onto perforated suction rolls. The two suction rolls

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Figure 3.36 Core entering into triangle area of core-spun in ring-spinning process.

Figure 3.37 Schematic diagram of core-spun yarn: (A) monofilament as core and (B) multifilament yarn as core. Source: Modified from Chen T. Compound yarn. In: Gong RH, ed. Specialist Yarn and Fabric Structures. Cambridge, England: Woodhead Publishing; 2011 [Chapter 1].

rotate at the same direction and twist the web into yarn between the two rolls by friction force, and the yarn is delivered in the direction perpendicular to the web-feeding direction. The mechanism is shown in a different ways in Figs. 3.39 and 3.40. The spinning drums of a DREF facility can rotate at very high speed, while the yarn tension is practically independent of speed and hence very high production rates (up to 300 m/min) can be achieved. But the tension during spinning is low,

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Figure 3.38 Basic mechanism of friction spinning. Source: From Lord PR. Short staple spinning. In: Handbook of Yarn Production: Technology, Science and Economics. Cambridge, England: Woodhead Publishing; 2003 [Chapter 7].

Figure 3.39 Basic mechanism of friction spinning. 1—Perforated suction rolls (drums); 2—delivery rolls; 3—suction; 4—staple; 5—yarn. Source: Modified from National Institute of Research on Jute and Allied Fibre Technology. Friction spinning for technical textile: an overview. Indian Text J. 2012. Available in http:// www.indiantextilejournal.com/articles/FAdetails.asp?id 5 4636

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Figure 3.40 Basic mechanism of friction spinning. 1—Drawing zone; 2—combing roll; 3—air flow; 4—perforated suction rolls; 5—suction; 6—yarn. Source: Modified from National Institute of Research on Jute and Allied Fibre Technology. Friction spinning for technical textile: an overview. Indian Text J. 2012. Available in http:// www.indiantextilejournal.com/articles/FAdetails.asp?id 5 4636

the alignment of staple fibers is low and hairiness is high. The friction among staple fibers in the yarn is not strong, therefore the yarn strength is weaker than the yarn spun from ring spinning. DREF yarns have been seen to be inferior in terms of unevenness, imperfections, strength variability, and hairiness to yarns spun from other traditional technologies such as ring spinning and rotor spinning. The author believes that the concept of friction spinning by Dr. Ernst Fehrer is actually already emerged in earlier patents by him in 1968.85,86 In these patents, Dr. Ernst Fehrer disclosed a method to spin yarn with frictional forces by using counter-rotating belts, instead of suction drums in later invention. DREF spinning is a very good method to produce core-spun yarn by introducing a second yarn as core yarn such as glass fiber, steel wire or organic filament, or staple spun yarn. This process is demonstrated in Fig. 3.41. The core yarn 1 is fed by rollers 1 and 2 into the nipping zone of the spinning drums 4 and wrapped by the web 5 from the conveyor. Then the two materials are rotated and twisted by the friction force, and the formed core-spun yarn is delivered and wound up. The core yarn is false twisted by the spinning drum. The sheath staples are deposited on the false twisted core surface and are wrapped helically over the core with varying helix angles. It is believed that the false twist in the core gets removed once the yarn has emerged from the spinning drums, so that this yarn has a virtually

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Figure 3.41 Schematic illustration of core-spun yarn spun on friction spinning system. Source: Modified from National Institute of Research on Jute and Allied Fibre Technology. Friction spinning for technical textile: an overview. Indian Text J. 2012.

twist-less core. However, it is quite possible that the false twists are not fully removed and some amount of the twists is still retained in the finished core-spun yarn because of the fact that the sheath has entrapped the core during yarn formation in the spinning zone. Friction spinning is very good for heavy yarn spinning such as yarn with linear density (or yarn count) is heavier than 600 dtex (B10 cc). If yarn is lighter than 300 dtex (yarn count .20 cc), then ring spinning or other technologies are better. The major strength of DREF spinning is its high production speed. It can produce yarn at a speed up to 300 m/min, 1020 times of ring spinning speed and 35 times of rotor spinning. DREF spinning system is also much more tolerant with the staple quality than other spinning technologies do. It can spin recycled staples very well. Staples with different length can be spun on one DREF spinning machine. The development of DREF spinning has experienced multiple generations, including the first generation of DREF-I, the second DREF-II, the third DREF-III, followed by DREF2000 and DREF3000.87 It is worth mentioning the life of Dr. Ernest Fehrer, the inventor of DREF spinning system, who had made tremendous contribution to the development of textile industry.88 He had dedicated his entire career to inventing new textile machineries to either make products with better quality or improve the production efficiency. After finishing his doctoral (PhD) study in theoretical physics from Graz University of Technology in 1947, he joined his father’s spinning machinery company and started his contribution to the textile industry. In 1953 he founded Fehrer AG and started his own business. In 1965 his first modular design needle felting machine was put into market and this technology contributed to secure Fehrer AG’s reputation in the global textile industry. In 1973 Dr. Ernest Fehrer started his attempt to develop a more productive spinning system which was expected to operate at a much lower cost. This development effort led to the invention of the DREF spinning system. The DREF-I system was developed in 1974 and the DREF-II in 1977

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followed by the DREI-III in 1979. By 1979 his company owned more than 400 patents and by 1988, 700 patents around the world. In 1999 the DREF2000 was launched into the market. Dr. Ernest Fehrer passed away in December 2000. Right after his death, DREF3000 started testing in the market in 2001. In 1988 Dr. Ernest Fehrer received the Technical Association of the Pulp and Paper Industry Nonwovens Division Award. To recognize his contribution to the textile industry, Textile World presented him the first Lifetime Achievement Award in 1994. Fehrer AG’s nonwoven machinery business was acquired by Saurer AG in 2005,89 and its DREF spinning machinery business, called DREF Corp, was acquired by Nordin Technologies in 2007.90

3.1.4.2 Air-covered yarn Air-covered yarn (ACY) is also a core-sheath type yarn, but the sheath is wrapped onto the core, not by staple-spinning process. The sheath in the wrapped yarn is a well-formed yarn, which can be a continuous filament or a staple spun yarn but cannot be a roving. The difference in structure between core-spun yarn and covered yarn will be shown at the end of this section. So far the air-covering process is mainly used for covering highly elastic yarn such as spandex. In the air-covering process the sheath yarn and the tensioned and elongated spandex core yarns are cofed into an air nozzle, the high pressure compressed air is applied onto the cofed yarns in a regular pattern to form interlaced spots regularly on the composite yarn product without any twist. Fig. 3.42 shows an example of the air-covering process. Practically, ACY is a special type of interlaced yarn, with an elastic yarn (such as spandex) as the core. Fig. 3.28 already illustrates how the interlace is formed. Fig. 3.43 shows a picture of ACY. The core yarn is under tension during the air-covering process, due to the high elasticity of the core yarn, then the core retracts when the tension is removed but the cover yarn does not retract, therefore the yarn exhibits a pattern as shown in Fig. 3.43. DTY is the most commonly used cover yarn in ACY. In many elastic apparel products, such as swimming suits, running suits, and gym suits, wrapped yarn of DTY on spandex is the most popular construction.

3.1.4.3 Wrap yarn Wrap yarn is also called spin-covered yarn. It is made by continuously wrapping (twisting) a continuous yarn around a core yarn which can be a mono- or multifilament yarn or a staple spun yarn. Fig. 3.44 shows the schematic diagram of two wrap yarns. One can see that the sheath cover yarn is wrapped onto the core, like the vines twining around a tree. If spandex is used as the core, it undergoes tension during wrapping process then retracts when the tension is removed. When the spandex retracts, the cover yarn does not retract together, therefore a highly covered surface is formed. Fig. 3.45 shows the process diagram of wrapping. In Fig. 3.45A a single layer of cover yarn is wrapped onto the core. In Fig. 3.45B, two layers of cover yarns are wrapped onto the core yarn one by one but in opposite directions.

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Figure 3.42 Air-covering process.

Figure 3.43 Picture of air-covered yarns.

Due to the wrapping structure of wrapped yarn, it is not good to make wrapped yarn with a slippery core yarn. For instance, steel wire is slippery, resulting in that the cover yarn easily slips on the core yarn’s surface. If the cover yarn is a staple spun yarn, it slips less than a filament yarn does. If the cover yarn is also slippery

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Figure 3.44 Structures of wrapped yarns: (A) single- and (B) double-layer wrap.

for instance HPPE yarn, then HPPE cannot really wrap steel wire very well because it slips on steel’s surface very easily. It is very rare to see steel wire wrapped with HPPE yarn in the market. Both core-spun and wrapping can be used to make elastic-covered yarn with spandex as the core. Prestretch ratio is a very critical parameter to product design parameter for spandex-covered yarn. If the prestretch ratio is too low, then the yarn’s elasticity is inadequate. If the prestretch ratio is too high, then spandex easily breaks in the process and easily creeps during storage which makes elasticity downgrade with time. A good range of prestretch ratio for spandex is between 1.5 and 3.5, with the optimum to be around 2 to 2.5.70 Fig. 3.46 shows different structures of composite yarns.

3.2

Basic properties of fibers

3.2.1 Linear density Linear density is the measure of fiber’s mass per unit length or length per unit mass.91 Commonly seen units of linear density include denier (D), decitex (dtex), cotton count (cc or Ne), and metric count (Nm). They are explained one by one as follows: Denier (D): Denier is usually used for continuous filament yarn, defined as the mass in gram per 9000 m yarn. For instance, 400 D means the mass of 9000 m of the yarn is

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Figure 3.45 Schematic diagram of yarn wrapping process: (A) single and (B) double wrap process. 1—Feeding roller; 2—core yarn package; 3—pretension device; 4,4ʹ—cover yarn; 5—pigtail guide; 6—delivery roller; 7—winding roller.

400 g; 200 D means the weight of 9000 m of the yarn is 200 g; 1500 D, 1500 g per 9000 m. Denier is usually abbreviated as D, such as 400, 200, and 1500 D. It is very straightforward that higher denier means thicker (or heavier) yarn for the same material. The word “denier” originates from the French Denier, a medial coin which took its name from the Frankish coin first issued in the late 7th century.91 Decitex (dtex) is a metric unit, also mainly used for continuous filament yarn, defined as the mass in gram per 10,000 m. For instance, 440 dtex means 440 g per 10,000 m fiber/ yarn; 220 dtex, 220 g per 10,000 m fiber/yarn; 1670 dtex, 1670 g per 10,000 m. Therefore denier and decitex are different but very similar and can be converted to each other very easily. Multiplying denier by 1.11 gets the decitex value. 400 D is 444 dtex (usually simplified as 440 dtex), 200 D is 222 dtex (usually simplified as 220 dtex), 1500 D is 1667 dtex (usually simplified as 1670 dtex). Many times, tex is also used, defined as the mass in grams per 1000 m fiber or yarn. By this definition, 1670 dtex is 167 tex. One can divide dtex by 10 then gets the value for tex.

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Figure 3.46 Comparison in structures for different composite fibers/yarns: (A) core-sheath fiber, (B) core-spun yarn, (C) air-covered yarn, and (D) wrap yarn (spin-covered yarn).

Cotton count (cc, Ne), an English unit, is mainly used for staple spun yarn and is defined as how many 840 yards (1 yard 5 0.91 m) per pound of yarn (1 lb 5 0.454 kg). For instance, if 1 lb yarn has twenty 840 yards (total 16,800 yards), then it is called 20 cc (or Ne). If 1 lb yarn has thirty 840 yards, then it is called 30 cc (or Ne). If one yarn consists of two plies of yarn with each end being 20 cc, then it is usually written and called 20 cc/2, and its total yarn count is 10 cc. If a yarn consists of two plies with different yarn count, for instance, one being 20 cc and the other 30 cc, then it can be written as 20 cc/30 cc, and its total yarn count is 12 cc. English cotton count unit is still commonly used now for staple spun yarn. If not specified, usually it refers to English cotton count when people say yarn count. Unlike denier or decitex, higher yarn count means lighter (thinner) yarn. Plied yarn can be further combined and twisted to form further plied yarn. For instance, two ends of 20 cc/2 yarn can be further combined and twisted to form 20 cc/2/2 yarn, but this is not common because the additional production step increases cost. Many people also like to use “s” to replace cc, such as 20 s/2 instead of 20 cc/2, where “s” stands for single. Metric count (Nm): A metric unit, also used for staple spun yarn, defined as the number of meters per gram of fiber or yarn. For instance, 50.8 Nm mean 50.8 m per gram of yarn; 33.8 Nm mean 33.8 m per gram of yarn. Cotton count and metric count are directly convertible, 1 cc 5 0.591 Nm, 1 Nm 5 1.692 cc. 30 cc equals to 50.8 Nm, and 20 cc equals to 33.8 Nm.

One may immediately realize that cotton count and metric count can only be used for spun yarn or filament yarn which both have continuous length, while decitex and denier can be used for both short fibers and yarn.

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All the units for linear density are convertible to one another according to their definitions. Decitex, cotton count, and metric count are used around the world, while denier is used in the United States and American companies. As the definitions of linear density and yarn count are fairly straight forward, their measurements are also easy to understand. Generally, a fixed length of fiber or yarn is taken and its mass is measured, then the linear density or yarn count can be determined. There are many ways to determine the linear density of yarns and fibers. ASTM D190792 and ISO206093 define the test methods for measuring the linear density of yarn by the skein method. A standard reel with 1 m perimeter (Fig. 3.47) is recommended to wind up a prescribed number of wraps followed by being cut from the reel then by weighing. A strand of yarn wound up on the reel is called a skein. The number of wraps is dependent upon the linear density of the yarn. Table 3.1 shows the number of wraps specified by ASTM D1907 and ISO2060 for yarns of different linear density to measure linear density. If the purpose of measurement is only for estimation which does not require good accuracy, one can use a number of wraps different from those in the table, especially when the amount of sample is not enough. ASTM D1907 and ISO2060 are skein methods for determining linear density of yarn; thus they cannot be used for the staples or other short fibers. To determine the

Figure 3.47 Reel for winding up yarn. Table 3.1 Number of wraps and length of skeins on a reel of 1 m perimeter. Yarn

ASTM D1907

ISO2060

,12.5 tex (125 dtex) ,100 tex (1000 dtex)

NA 100 wraps 5 100 m

Spun yarn .100 tex Filament yarn .100 tex

50 wraps 5 50 m 10 wraps 5 10 m

200 wraps 5 200 m 100 wraps 5 100 m (between 12.5 and 100 tex) 10 wraps 5 10 m

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linear density of staples and other short fibers, one need to refer to ISO1973,94 ASTM D1577,95 and ASTM D105996 are the test standards for the linear density determination of short fibers. ASTM D1577 describes three options based on two natures of methods: gravimetric method which shares the same logic as the ISO 2060 or ASTM D1907 does for yarn, and vibroscopic method. Vibroscopic method measures fiber linear density by subjecting an individual fiber of a given length to vibration at resonance frequency under specified tension and calculating the linear density using Mersenne’s law as shown in the following equation: 1 f5 2L

sffiffiffiffi T μ

(3.10)

where f is the resonance frequency of vibration in Hz, L is the length of the vibrating fiber in km, T is the tension applied to the string in N, and μ is the linear density of the fiber in tex (g/km). Knowing f, L, and T, one can easily solve μ using the following equation: μ5

T 4f 2 L2

(3.11)

Measuring linear density with vibroscope is schematically shown in Fig. 3.48. ISO1973 also describes the gravimetric method and vibroscopic method. Because ASTM D1059 and the gravimetric method of ISO1973 are based on the short length fiber specimens, the results should only be considered as approximation of fiber linear density. The vibroscopic method is considered more accurate for single short fiber linear density measurement. As a matter of fact, ASTM also has an equivalent method. ASTM D1577 is another method for fiber linear density measurement, including fiber bundle weighing, single fiber weighing, and vibroscopic methods. Table 3.2 summarizes the international standards for measuring linear density.

Figure 3.48 Measurement of linear density with vibroscope. L—Fiber length; T—tension; f—vibration frequency.

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Table 3.2 International standards for measuring linear density. Standard

Skein weighing method for yarn

Short fiber— bundle weighing

Short fiber— single fiber weighing

Vibroscopic method

ASTM D1907 ISO2060 ASTM D1059 ASTM D1577 ISO1973

Yes Yes No No No

No No Yes Yes (option A) Yes

No No No Yes (option B) No

No No No Yes (option C) Yes

3.2.2 Mechanical properties Tenacity: Or breaking tenacity, in the fiber industry, is defined as break force per unit linear density of fiber.97 It is obtained in tensile testing and calculated with the following equation: BT 5

F LD

(3.12)

where BT stands for break tenacity, F for break force, and LD for linear density. The break force can be in unit of gram force (g or gf), Newton (N), centi-Newton (cN), or milli-Newton (mN). Usually commonly used unit of tenacity are as follows: N/tex: Force (in Newton) required to break 1 tex fiber; cN/tex: Force (in centi-Newton) required to break 1 tex fiber; mN/dtex: Force (in milli-Newton) required to break 1 tex fiber; cN/dtex: Force (in centi-Newton) required to break 1 dtex fiber; gpd (or g/d, or gf/d): Force (in gram) required to break 1 D fiber;

Gpd (or g/d, gf/d) is commonly used in the United States and American companies, while other units are used in the rest of the world. The conversions among them can be found in the Appendix A. The conversions between them and GPa (or MPa) are also listed in Appendix A. Elongation is defined as the percentage of change in length relative to the original length. The percentage of length change when fiber breaks in tensile mode is the break elongation, or elongation at break. This property means how much displacement the fiber/yarn has before break. Elongation is also often called strain in the discipline of material mechanics. It is calculated with the following equation: εb 5

lb 2 l0 3 100% l0

(3.13)

where εb is the elongation at break, lb is the length of fiber at break; and l0 is the original length of fiber before tensile.

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Figure 3.49 Stressstrain (tenacityelongation) curves of some common fibers.

During tensile testing the stress changes with the displacement (strain), the stressstrain (or tenacityelongation) data are acquired by the tensile instrument, and a stressstrain curve is plotted. Typical stressstrain curves for some commonly used fibers are shown in Fig. 3.49. Modulus,98 if not specified, refers to the tensile modulus of yarn or fiber. Tensile modulus is defined as the ratio of tensile stress to strain, that is, the ratio of tenacity to elongation for fiber. It is a measurement of material’s capability to resist deformation under tension. As the tenacityelongation curve of a fiber is usually not linear as shown in Fig. 3.49, the more strict definition for the modulus is the ratio of initial tenacity to the corresponding elongation, and this modulus is called initial modulus. In material mechanics the initial modulus is usually called Young’s modulus or elastic modulus. It is defined as the slope of the initial straight-line portion of the curve which corresponds to the elastic deformation of the material. Fig. 3.50 shows the tangent line on the tenacityelongation curve to calculate the initial modulus. In fiber testing, what is obtained as illustrated in Fig. 3.50 is called tangent modulus. There are also chord modulus and secant modulus which can be further understood in the reference.98 Due to the small diameter of the single filament, it is not an easy task to carry out a good tensile testing for fiber. Though flat-faced jaws are allowed for fiber and yarn tensile testing in some standards, the fiber or yarn either easily slips between the flat jaw surfaces if the clamping pressure is not enough or easily gets pinched between the jaw surfaces and breaks prematurely between the jaw surfaces if the clamping pressure is high. It is nearly impossible to define a proper clamping

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Figure 3.50 Determination of initial tensile modulus for fiber.

pressure to test the tensile of fiber of high tenacity. The circular jaw surfaces are better choices to address this issue. Fig. 3.51 shows the picture of a bollard-type jaws for light denier yarns and Fig. 3.52 shows that of jaws for wire and heavy cord. Fig. 3.53 shows the picture of capstan-type jaws. These types of jaws allow the load during testing to be shared on the circular surfaces therefore there is much lower load at the grips than on the flat-faced jaws. These types of jaws require adequate length of the testing sample therefore are usually used for testing yarns. It is impossible to test short fibers on the jaws shown in Figs. 3.49 and 3.50 but may be able to be tested on the jaws shown in Fig. 3.48 if the short fiber is long enough and the jaws are small enough, otherwise they still have to be tested on flat-faced jaws. There are a number of international testing standards for yarn and fiber tensile testing: G

G

G

G

G

G

ASTM D88599: Skein method for organic filament yarn (including Rayon), excluding high tenacity aramid yarn. ASTM D7269/D7269M100: Skein method for high tenacity aramid yarn. Though this method’s name is for aramid yarn, it is actually intended for high tenacity aramid such as para-aramid yarn. ASTM D1578101: Skein method for spun yarn. ASTM D2256102: For single strand fiber (or monofilament). ASTM D2343103: For glass fiber, impregnated method. ASTM D3822104: For yarn and staple of nature fiber and man-made fibers with enough length.

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Figure 3.51 Bollard-type jaws for light denier yarn tensile testing. Source: Courtesy Instron.

Figure 3.52 Bollard-type jaws for wire and heavy denier yarn tensile testing. Source: Courtesy Instron.

G

G

G

G

G

G

G

G

ASTM D2969105: For steel wire. ASTM D2970106: For glass filament yarn. ISO2062107: For single strand (monofilament) method. ISO6939108: Skein method for yarn. EN12562109: Skein method for para-aramid filament yarn. ISO3341110: Skein method for glass yarn. ISO 22034-1111: For steel wire. Single filament method. ISO 6892-1112: For all metallic materials with all different cross sections.

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Figure 3.53 Capstan-type jaws for yarn and cord testing. Source: Courtesy Instron.

These testing methods are compared in Table 3.3. The term of modulus and its determination are mentioned in ASTM D7269 and D885 methods but are not in the ISO methods. Besides the initial modulus (Young’s modulus), a different modulus, called chord modulus, and its determination are also mentioned in ASTM D7269 and D885. The chord modulus is calculated with the following equation: Mc 5

F2 2 F1 3 100 ε2 2 ε1

(3.14)

where Mc stands for the chord modulus, F2 and F1 are the forces per linear density at specified upper and lower points, and ε2 and ε1 are the strains at specified upper and lower forces as illustrated in Fig. 3.54. For instance, F1 and F2 for aramid are 3.0 and 4.0 cN/dtex, respectively. Tensile testing is conducted, then ε1 and ε2 are determined on the stressstrain curve as shown in Fig. 3.54, and Mc can be calculated by using these data. The upper and lower force limits for different fibers are tabulated in Table 3.4.

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Table 3.3 International tensile testing standards for fiber and yarn. Material

Filament yarn

Staple spun yarn

Single strand (monofilament)

Short fiber

Single end fiber (long or short)

Aramid

ASTM D7269 (skein) ISO6939 (skein) EN 12562 (skein) ASTM D2970 (skein) ISO3341 (skein) ASTM D2969 (for tire cord) ISO22034-1 ISO6892-1 ASTM D885 (skein method) ISO6939 (skein)

ASTM D1578 ISO6939 (skein)

NA

ASTM D3822

ASTM D3822

NA

NA

NA

NA

NA

NA

NA

NA

ASTM D1578 (skein) ISO6939 (skein) NA

ASTM D2256

ISO 2062

ASTM D3822

ISO2062

ASTM D3822 NA

Glass

Steel wire

Other natural and manmade organic fibers Other metallic wire

ISO6892-1

NA

Figure 3.54 Illustration for determining chord modulus on stressstrain curve.

NA

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Table 3.4 Lower and upper limits of the chord modulus for different types of fibers.

Lower limit F1 (cN/dtex) Upper limit F2 (cN/dtex)

Rayon

Nylon

Polyester

Aramid

0.3 0.4

0.2 0.4

0.3 0.6

3.0 4.0

Table 3.5 Tensile testing standards for carbon and glass fibers—impregnation methods. Carbon fiber Yarn Short fiber

ASTM D4018 ISO10618114 ISO11566116

Glass fiber 113

ASTM D2343103 ISO9163115 NA

For those fragile fibers, such as glass fiber and carbon fiber, even the circularsurfaced jaw may not be able to grip these fibers properly. There are testing standards designed specifically for these kinds of fibers by using resin to impregnate the yarn or short fiber prior to testing. Table 3.5 summarizes these testing standards.

3.2.3 Hairiness Hairiness is a property which indicates the amount and length of fiber ends and loops protruding from the body of the yarn. The hairiness imparts a fuzzy appearance to the yarn product. It is desired in some situations such as for thermal insulation and not desired in some other situations such as where clean operation is needed because the fiber ends often break and drop from the hairy yarns by abrasion. Fig. 3.55 shows a picture of a hairy yarn. In metal processing factories, when the metal sheets need spray coating, the surface cleanness is very important; therefore the yarn hairiness is undesired as the yarn may leave lots of broken fiber ends on the metal surface to be sprayed. Another circumstance is the food processing. Nobody wants to discover fiber ends in his/her food. ASTM D5647 is an international testing standard for measuring yarn hairiness.117 It specifies a photoelectric method which counts the protruding fiber ends or broken filament ends from the yarn by passing the yarn through a photoelectric device and using a digital volt meter or computer interface. The number of protruding ends less than 10 mm length per unit length of the yarn is reported as the hairiness. The average length of the protruding ends can also be calculated as a reference.

3.2.4 Yarn evenness Yarn unevenness means the variability of yarn in its properties along its length, such as diameter, linear density, tenacity, hairiness, and twist. These properties are also associated with one another, for instance, diameter unevenness affects the

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Figure 3.55 Yarn hairiness. Source: From Gandhi K, ed. Yarn preparation for weaving: sizing. In: Woven Textiles: Principles, Developments and Applications. Cambridge, England: Woodhead Publishing; 2012 [Chapter 4].

linear density and tenacity unevenness. Generally, unevenness is referred to the linear density unevenness. The unevenness is also called irregularity. There are two common expressions of yarn unevenness of linear density. One is the coefficient of variation (CV) and the other is the mean deviation unevenness (U). The simplest way to measure the unevenness of linear density is the direct method by cutting and weighing a number of segments of the same length from the yarn. The mass of each segment is weighed and the CV% is calculated with the following equation: CV% 5

σm 3 100 m

(3.15)

n P where m 5 mi which is the mean value of the measured mass of each segment i51 sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi n P 2 ðmi 2mÞ

miσm 5 i51 n The mean deviation unevenness U% is calculated with the following equation:  U% 5

n P

i51

 jmi 2 m j =n m

(3.16)

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In Eq. (3.16) the denominator is the mean value of the measured mass of each segment, and the numerator is the mean value of the absolute values of the deviations. One who is familiar with the modern statistics shall know that the CV% receives more recognition than the mean deviation unevenness U%. The most obvious consequence of yarn unevenness is the variation of strength along the yarn. Another obvious consequence is the visible defects of the yarn and fabric. ISO16549 specifies a capacitance method to determine the unevenness of linear density by measuring the changes in the electrical current caused by the changes in the thickness of yarn placed inside a capacitor.118 ASTM D1425 also specifies the same capacitance testing method.119

3.2.5 Twist Twist has significant effect on the properties of yarn, for both filament yarn and staple spun yarn. Fig. 3.23 already showed the effect of twist level on the tenacity of yarns. There are two main methods to measure the twist level: one being the untwistretwist method, the other direct-counting method. The yarn contracts in length when it is twisted and it recovers its length when the twist is removed. The untwistretwist method leverages this characteristic of yarn. During the test, one end of yarn is secured with two clamps, one of which is fixed, and the other is movable under a tension. The fixed end is revolved to the direction opposite to the yarn twist. For instance, if the yarn’s twist is Z direction, then rotate the fixed end to S direction to remove the twist. The yarn will become longer when the twist is removed, and as a result the movable clamp will move toward the farther end under tension to accommodate the longer yarn. When the twist level is reduced to zero, the yarn is the longest. Now the first step untwist part is completed. The fixed end continues to be rotated to the same direction then the yarn is twisted to the opposite direction therefore the yarn will become shorter than its zero twist status. The movable clamp will move back until it returns to its original starting point. At this point the second step retwist is completed. The total twist number read from the counter divided by 2 is the twist number of the yarn. Fig. 3.56 shows the principle of untwistretwist method. Typically, this method is used for single yarn and high twist yarns.

Figure 3.56 Principle of untwistretwist method for measuring twist number.

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Figure 3.57 Principle of direct-counting method for measuring twist number: (A) clamp and untwist yarn, and (B) pass cleanly through and separate the yarn with a tool to ensure zero twist.

The direct-counting method is more accurate but slower than the untwistretwist method. It also uses the untwist but does not have the retwist step. A single end of yarn is fixed onto two clamps separated apart with a known distance. The yarn is untwisted by rotating one clamp until the yarn’s twist level becomes zero, which is judged by using a tool such as a pick to separate the yarn and pass cleanly from one end to the other. The reading of number of rotations is the twist number. Fig. 3.57 shows the principle of the direction-counting method. It is better for plied yarns and low twist level yarns. ISO17202120 and ASTM D1422121 describe untwistretwist method. ISO 2061122 and ASTM D1423123 describe the direct-counting method. ISO 1890 is a direct-counting method for determining the twist level of reinforcement yarn, such as carbon fiber yarn, glass yarn, and aramid yarn. This chapter does not intend to explain everything about fibers and yarns. For other basic terminologies, such as moisture regain, the reader can refer to ASTM D4849.124

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Fiber or yarn has to undergo a fabric-forming process to form fabric product. Cut protective fabric products are mainly made with these three technologies, that is, knitting,125,126 weaving,133,134 and nonwoven,140 142 among which knitting and weaving are used more than nonwoven in cut protective products. Other typical textile fabric formation technologies, such as braiding, netting, and lacing, are not common in cut protective products and not discussed in this book.

4.1

Knitting

In our tradition, the sweaters, gloves, socks and sometimes even shoes were knitted manually with hand tools (you might have seen your grandmother’s hand knitting work). The hand pin knitting was first recorded in religious paintings in 1350 in northern Italy. The principles of hand knitting with two pins (hand pin knitting) are illustrated in Fig. 4.1. In Fig. 4.1A, pin a, held in left hand, is retaining the previously formed row of loops (termed as course). The right-hand pin b is used to draw through and retain the next course of loops, one at a time. In Fig. 4.1B, pin b has drawn the newly formed loop 2 through loop 1 of the previous course. Pin a then withdraws and releases loop 1, which hangs from loop 2, which itself is held and retained by pin b. The same action is repeated, and the fabric is then knitted. The majority of cut protective textile is made by knitting. Fig. 4.2 shows the picture of a pair of knit mittens. Knitting can be carried out on a high-speed knitting machine, and therefore the productivity is high and the unit production cost is low. In the knitting process the knitting needles create multiple yarn loops and pull the next row of loops through the prior row of loops to make the loops intertwined. Knitting can be basically categorized as weft knitting and warp knitting. Knitted textile has good drape, elasticity, and air permeability; therefore knitted products can offer great comfort and good dexterity. 1. The needle moves up from its rest position, then the old loop (a) forces the latch to open, and the loop is therefore cleared from the needle hook to a lower position on the needle stem. This is called clearing [Fig. 4.3(1) and (2)]. 2. The needle continues to move further up and reaches its highest position as shown in Fig. 4.3(3). A new yarn (b) is fed to the needle hook at a higher position than the previous old loop (a). 3. The need starts to descend, and the hook catches the yarn and carries it to descend. The yarn (b) bends and forms a new loop as shown in Fig. 4.3(4). This step is called carrying. Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00004-3 © 2020 Elsevier Ltd. All rights reserved.

Figure 4.1 Principle of hand pin knitting. A and B are two pins; 1 and 2 are two different ends of yarns. (A) Left-hand pin A is retaining the previously formed row of loops (course). The right-hand pin B is drawing through and retaining the next course, one at a time. (B) Pin B has drawn the newly formed loop 2 through loop 2 of the previous course. Pin A then releases loop 1, which hangs from loop 2, which itself is hanging from pin B. Source: From Spencer DJ. Chapter 2: Comparison of weft and warp knitting. In: Knitting Technology A Comprehensive Handbook and Practical Guide. 3rd ed. Cambridge, England: Woodhead Publishing; 2001.

Figure 4.2 Knit mittens. The basic process of knitting is shown in Fig. 4.3, including steps of “clearing (push back)— carrying—closing—landing (cast on)—cast off (knocked over)—pulling through (drawn through).” Source: By Petritap—Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index. php?curid 5 7787272.

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Figure 4.3 Mechanism of forming knitting loop. Source: From https://nptel.ac.in/courses/116102005/m1-introduction/l2-knitting.htm. Course “Introduction to Fabric Manufacturing.” 4. While the needle and the carried yarn continue to descend, the old loop (a) now helps to close the latch by pushing it in upward direction. This step is called closing. Fig. 4.3(5) shows that the latch is fully closed, and the new yarn (b) is enclosed inside the hook by the latch and is formed a U-shaped loop. This is called cast-on. The old loop (a) is excluded from the hook, which is called landing. 5. The new loop formed of yarn (b) is drawn through the head of the old loop (a) by the closed hook (or the hook pulls the new loop through the old loop) as shown in Fig. 4.3(6). Simultaneously, the old loop slides off the closed hoop, which is called cast-off or knocked-over.

Now the old loop (a) hangs from the feet of the fully formed new loop of yarn (b), and the knitting cycle starts again. In cut protective textiles, usually yarns (b) and (a) are the same end of yarn but are just different sections of same yarn. But, yarn (b) can be different yarn from (a). As aforementioned, there are two major varieties of knitting: weft knitting and warp knitting. In weft knitting the yarn is fed from the weft direction to the knitting needle, and the feeding direction, or yarn path, is perpendicular to the loop formation and knitting direction (Fig. 4.4). In weft knit fabric the entire fabric can be produced from a single end of yarn. Then if the fabric is cut, or the yarn end is pulled, the fabric can be unraveled very easily; whereas in warp knitting the yarn is fed from the warp direction, and the feeding direction, or yarn path, is roughly parallel to the loop formation and knitting direction (Fig. 4.5). Every wale requires one end of yarn; therefore it is not as easy as in weft knit to unravel the warp knit. Figs. 4.6 and 4.7 show the structures of weft knitting and warp knitting.

Figure 4.4 Weft knitting. Source: From Anand SC. Chapter 5: Technical fabric structures 2. Knitted fabrics. In: Horrocks AR, Anand SC, eds. Handbook of Technical Textiles Volume 1: Technical Textile Processes. 2nd ed. Cambridge, England: Woodhead Publishing; 2016.

Figure 4.5 Warp knitting. Source: From Spencer DJ. Chapter 6: Comparison of weft and warp knitting. In: Knitting Technology A Comprehensive Handbook and Practical Guide. 3rd ed. Cambridge, England: Woodhead Publishing; 2001.

Figure 4.6 Weft knitting structure. Source: From en.wikipedia.org/wiki/knitting.

Figure 4.7 Warp knitting structure. Source: From en.wikipedia.org/wiki/knitting.

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Now it is good timing to understand some knitting terminologies from Figs. 4.5 4.7. A course is a predominantly horizontal row of needle loops (in an upright fabric as knitted) produced by adjacent needles during the same knitting cycle. A wale is a predominantly vertical column of intermeshed needle loops generally produced by the same needle knitting at successive knitting cycles. Warp knitting is a technique of making flat fabric with a straight edge. The speed of warp knitting can be fairly high; therefore the productivity is very high. Warp knit fabric still possesses some elasticity but much lower than the weft knit. The characteristics of weft knit fabric include elasticity, edge curling, and unraveling. Warp knit’s elasticity is lower than weft knit; therefore its dimensional stability is better than weft knit. Warp knit does not have problems of edge curling and unraveling, hence it is a better solution to make cut-and-sewn fabric than weft knit. The differences between warp knitting and weft knitting are summarized in Table 4.1. The material type and fabric basis weight are determining factors for cut resistance performance. The basis weight is defined as the weight (or more scientifically, mass) per unit area, generally with a unit of ounce/yard2 (oz/yd2) in the United States and a unit of g/m2 in the rest of the world. The basis weight of knit fabric is mainly determined by (1) gauge, number of needles per inch width; (2) yarn thickness (or linear density); and (3) course spacing, defined by the number of courses per unit distance. Course spacing can also be understood as the height of loop.

Table 4.1 Differences between warp knitting and weft knitting. Characteristics

Warp knitting

Weft knitting

Knitting direction

The loops are knitted to the length (warp) direction of fabric Elastic along the length (warp) direction

The loops are knitted to the width (weft) direction of fabric

Elasticity of knit fabric

Shrinkage of knit fabric Feeding Number of yarns Tendency to unravel Edge curling

Elastic along with both directions but more elastic along the width (weft) direction Elasticity higher than warp knit

Elasticity lower than weft knit Lower shrinkage than weft knit Yarns are usually supplied from the beam At least one end of yarn for each needle Not easy to unravel

Yarns are usually supplied from the cones Can be one single end yarn for the entire fabric Easily unravels

Limited edge curling

More edge curling than warp knit

Higher shrinkage than warp knit

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Figure 4.8 Course spacing. Course spacing of (A) is larger than that of (B).

Knitting gauge means how many needles per inch width on the knitting machine do the knitting at the same time. For instance, 7-ga means there are 7 needles per inch of width, and 13-ga means 13 needles per inch. It is not difficult to envision that there are fewer needles on a lower gauge knitting machine; therefore the size of needle can be larger (or thicker). A larger (or thicker) needle allows heavier yarn to be knitted; hence a heavier and thicker fabric can be made. Vice versa, higher gauge means shorter distance between needles; therefore needles have to be smaller (thinner), which can only accommodate thinner (lighter) yarn, as a result lighter and thinner fabrics can be made. One may question why not to use a lower gauge machine to knit lighter yarn so that the fabric can be light and thin too. Yes, it is true, light yarn can still be knit on a low-gauge knitting machine with large needles, but then the distance between the loops is long and the fabric is very loose. Each gauge has an optimal range of yarn counts to knit. When the yarn is too heavy (thick), exceeding the upper limit of the optimal range, the needle’s size is not large enough to take the yarn, and the needle can easily be broken. When the yarn is too light (thin), below the lower limit of the optimal range, the knit fabric is too loose and the coverage is very low. There is an overlap of the optimal range of yarn count between two gauges if the difference between the two gauges is not too large, meaning that the lower range of the optimal range for a lower gauge overlaps with the upper range of the optimal range for a higher gauge, provided that these two gauges’ difference is not large. In this overlapped range, if two different gauges knit yarns of same yarn count and the only difference is the gauge, then the higher gauge will knit a heavier fabric because the distance between loops is shorter and the fabric is denser. When the difference in two gauges is large enough, then there is no overlap between them. As for the effect of yarn thickness, it is apparent that thicker yarn leads to heavier and denser fabric on the same gauge machine. Gauge (number of needles per inch) is a measure along the wale direction, determining the density along this direction. It is apparent that another dimension is the density along course direction, which is determined by the course spacing. Fig. 4.8 shows two different course spacings. The course spacing in Fig. 4.8A is larger than that in Fig. 4.8B; therefore the former is more loose than the latter. This figure also

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Table 4.2 Relationship between gauge and basis weight. Gauge 7 10 13 15 18 20

Basis weight (gsm) 500 430 350 250 200 150

700 550 450 370 270 230

indicates that the course spacing is proportional to the height of loop. The larger the course spacing is, the higher the loop height, and the looser fabric, and therefore the lighter fabric, and vice versa. Course spacing also has an optimal range for a given fabric. Too low small spacing leads to too dense and rigid fabrics, and too large course spacing leads to too loose fabrics. Cut protective textile usually uses 7-, 10-, 13-, 15-, 18-, and 20-ga knitting for products of different basis weights, and the industry is trending toward even higher gauge (even lighter fabric). 7-ga knits rather heavy and thick fabrics, with basis weights from 500 to 700 gsm (grams per square meter) and normally does not knit elastic yarn. 10-ga normally knits fabric with basis weights of 400 550 gsm, 13-ga for 350 450 gsm, 15-ga for 250 370 gsm, 18-ga for 200 270 gsm, and 20-ga for 150 230 gsm. Table 4.2 summarizes these figures. It is worth noting that the abovementioned figures are just approximate estimation. Different materials with different specific gravities will produce different basis weights on the same gauge knitting machine. As a matter of fact, yarn diameter, not the yarn count, is the determining factor for whether the yarn is suitable for a certain needle. At equal yarn thickness (diameter), a material of higher specific gravity is heavier than that of lower specific gravity, then will yield a heavier fabric knitted on the same gauge machine, and vice versa. The specific gravities of some typical materials used in cut protective products are tabulated in Appendix D. In knitting, it is practical to feed either one end or cofeed multiple ends together to one needle at the same time, or cofeed combinations of different ends of yarns, as long as the total yarn counts are in the optimal range of the needle’s capacity. For instance, 7-ga can knit three ends of 10 s/2 per needle, or knit six ends of 20 s/2 per needle. Three ends 10 s/2 and six ends 20 s/2 have same total yarn counts; 13-ga: cofeed total three ends, one end 20 s/2 para-aramid yarn, one end wrapped glass fiber in which glass fiber is 100 D and the wrap yarn consists of two layers of 70 D nylon 66 DTY, and one end wrapped or covered spandex in which spandex is 70 D covered or wrapped with one end 70 D nylon 66 DTY. They are listed as follows: 1. End 1: 20 s/2 para-aramid staple yarn, 2. End 2: 100 D glass fiber wrapped with two layers of 70 D nylon DTY yarns, and 3. End 3: 70 D spandex covered or wrapped with one end 70 D nylon 66 DTY.

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This kind of cofeeding is schematically illustrated in Fig. 4.9. Or these three different types of yarns are wrapped together by making wrapped glass fiber first, followed by using this wrapped glass fiber as wrapping yarn to wrap spandex, then using this double wrapped yarn to wrap para-aramid yarn. This is actually not a cofeeding because only one single end yarn with complex wrapping structure is fed. This is illustrated in Fig. 4.10. Or these three ends of yarns are made into two ends: for instance, making a wrapped spandex by using spandex as core and one end already wrapped glass fiber yarn as wrapping yarn, then cofeeding this double wrapped yarn with para-aramid yarn. This kind of cofeeding is illustrated in Fig. 4.11. The above examples are for knitting and can also be done three-dimensionally (3D) to form 3D-knitted fabrics.127 Fig. 4.12 shows a cross-sectional picture of a 3D-knitted fabric with spacer, and Fig. 4.13 shows a schematic diagram of a 3Dknitted structure with spacer. International brands for knitting machines include ShimaSeiki,128 Karl Meyer,129 Santoni,130 Stoll,131 and Fukuhara.132

Figure 4.9 Cofeed three ends to knit.

Figure 4.10 “Cofeed” multilayer wrapped yarn.

Figure 4.11 Cofeed two ends to knit.

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Figure 4.12 3D-knitted fabric. 3D, Three-dimensional. Source: From Fangueiro R, Soutinho F. Chapter 3: Textile structures. In: Fangueiro R, ed. Fibrous and Composite Materials for Civil Engineering Applications. Cambridge, England: Woodhead Publishing; 2011.

Figure 4.13 Schematic diagram of a 3D-knitted fabric with spacer. 3D, Three-dimensional. Source: From Liu Y, Hu H. Chapter 6: Three-dimensional knitted textiles. In: Chen X, ed. Advanced in 3D Textiles. Cambridge, England: Woodhead Publishing; 2015.

4.2

Weaving

Traditionally, weaving is conducted on shuttle looms, but modern weaving machines no longer have shuttles. During weaving, traditionally, two distinct sets of yarns are interwoven at right angles to form a fabric with a preset pattern. The longitudinal yarns are called the warp, and the lateral yarns are called the weft or filling yarns, and the resultant fabric is called a woven fabric. Fig. 4.14 shows the

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Figure 4.14 Cut-and-sewn gloves with woven fabric. Source: By Daderot—Own work, CC0, https://commons.wikimedia.org/w/index.php? curid 5 19740887.

Figure 4.15 Mechanism of primitive weaving. Source: From Bali Woman at Her Loom. From Nieuwenhuis AW. Nieuwenhuis. In: Nederlandsch Indie, Oud & Nieuw. Amsterdam; 1916.

picture of an ancient woven fabric. Though the work shown in this picture was very old, it clearly shows the woven structure. The development of weaving technology can be dated back to more than 5000 years ago. Its history has witnessed the development of ancient weaving, manual looms, automated looms, shuttle-less looms, and so on. The weaving in early cultures, for example, was practiced completely manually as illustrated in Fig. 4.15.

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Figure 4.16 Principle of weaving. Source: From Gandhi KL. Chapter 5: The fundamentals of weaving technology. In: Gandhi KL, ed. Woven Textiles: Principles, Developments and Applications. Cambridge, England: Woodhead Publishing; 2012.

One end of all yarn threads is tied onto one wooden stick and the other end onto another wooden stick as warp. Then these threads are manually separated by hands or with a separating stick to two layers, followed by that the weft is inserted into the spacing between the two separated layers of warp threads. Fig. 4.16 shows the basic mechanism of loom weaving. Warp yarns are arranged and fed into the heald frame where the warp yarns are split up alternately and pass through eyes in the middle of the healds which are held on frames. The heald frames can be lowered or lifted, and as a result the alternate ends are separated to produce the shed opening. The weft yarn is then inserted into the opening. Immediately after that, the reed is swung forward and pushes forward the newly inserted weft yarn against previously inserted weft yarn. Such a cycle of actions is repeated over and over, then a woven fabric is formed. The yarn parallel to the fabric edge is called warp, and the perpendicular one called weft or pick. There are many alternative constructions, such as plain, twill, and Satin. Weaving fabrics are much more rigid and less elastic than knit fabric, suitable for making shirt, jacket, etc. Fig. 4.17 shows some common weaving constructions. The patterns of the examples shown in Fig. 4.17 are in two directions, that is, warp and weft. Weaving can also be done in more than two directions, such as triaxial weaving. Fig. 4.18 shows two pictures of two triaxial weaving patterns. Looking at Fig. 4.19, one may realize that multiaxial weaving is nothing new, instead it is a very traditional practice. Fig. 4.19A shows a household basket. The earliest triaxial weaving was likely very common in basketry practices in many cultures, very possibly dated back some millenniums. What is shown in Fig. 4.19B is a Sepak Takraw ball.135 Sepak Takraw, meaning kick volleyball, is a game popular

Figure 4.17 Common weaving constructions. Source: Modified from Bilisik K, Karaduman NS, Bilisik NE. Chapter 3: Fiber architectures for composite applications. In: Rana S, Fangueiro R, eds. Fibrous and Textile Materials for Composite Applications. Singapore: Springer Science 1 Business Media; 2016:78. https://doi. org/10.1007/978-981-10-0234-2.

Figure 4.18 Triaxial woven fabric: (A) basic triaxial weave and (B) basic triaxial basket weave. Source: From Gandhi KL, Sondhelm WS. Chapter 4: Technical fabric structures 1. Woven fabrics. In: Horrocks AR, Anand SC, eds. Handbook of Technical Textiles Volume 1: Technical Textile Processes. 2nd ed. Cambridge, England: Woodhead Publishing; 2016.

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Figure 4.19 Goods made by triaxial weaving: (A) woven basket and (B) Speak Takraw basket. Source: From Tyler T. Chapter 7: Developments in triaxial woven fabrics. In: Gong RH, ed. Specialist Yarn and Fabric Structures, Cambridge, England: Woodhead Publishing; 2011.

in Southeast Asia countries such as Thailand and Myanmar. Its older version is called Chinlone that means “cane ball” in Burmese. It has been already played in Myanmar for more than 1500 years, indicating that this kind of triaxial weaving has a long history. Like knitting, weaving can also be done 3D. Fig. 4.20 shows two 3D woven structures. Knitting and weaving can also be combined to form hybrid structures. The weft insertion by shuttle is very slow in speed and generates significant vibration and noise. Modern weaving has phased out shuttle by introducing shuttleless weaving, such as air-jet looms, water-jet looms, rapier looms, and projectile looms. Shuttle-less looms are much faster than the shuttle looms and generate lower noise and vibration, and can weave wider fabrics. Famous brands of weaving machines include but are not limited to Dornier,136 Picanol,137 Toyota Textile Machinery,138 Tsudakoma,139 and so on.

4.3

Nonwoven

Nonwoven is a fabric-like material made from staple or long fibers, bonded together by chemical, mechanical, or heat treatment.140 142 Generally, the manufacturing of nonwoven fabric comprises four major steps, fiber preparation, web formation, bonding, and finishing, among which web formation and bonding are the most critical steps. Technologies of web formation include dry laying, wet laying, spun web forming. Wet laying is a process in which short fibers (staples) are dispersed

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Figure 4.20 Three-dimensional woven fabric: (A) orthogonal, (B) through-the-thickness angle interlock, (C) layer-to-layer angle interlock, and (D) fully interlaced. Source: From Karaduman NS, Karaduman Y, Ozemir H, et al. Chapter 4: Textile reinforced structural composites for advanced applications. In: Kumar B, Thakur S, eds. Textiles for Advanced Applications. London: Intechopen; 2017. https://doi.org/10.5772/intechopen.68245.

and suspended in water then form web-like in the papermaking process. Dry laying is opposite to wet laying in which short fibers are laid in dry form to form web. The fibers are still loose and do not entangle with one another to form a secure fabric. The web does not have strength. Therefore the web needs to be bonded to form a stable and strong enough fabric. The bonding can be achieved by mechanical, heat, and chemical treatment as mentioned earlier. Mechanical treatment includes needle punching, hydroentanglement, and stitching; Heat treatment includes melt blown, spunbond, flashing spinning, thermoplastic powder bonding; Chemical treatment includes dipping, foam, printing, and spraying bonding. Needle punching is also called needle felting. Fig. 4.21 shows a scheme of a typical needle punching loom. The principle of water-jet bonding is very similar to that of needle punching, but the metal needles are replaced with many streams of high-pressure water jet. Water-jet bonding is also called spunlace or hydroentanglement.

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Figure 4.21 Schematic diagram of needle punching loom. 1—Needle plate, 2—needles, 3—batt, 4—bed plate, 5—stripper plate, 6—drawing rollers, 7—needle felt (nonwoven).

Thermal bonding uses thermoplastic adhesive powder to bind the fiber web by melting the adhesive powder above its melting temperature followed by solidifying upon cooling down. Chemical bonding uses dispersions or solutions of adhesive to bind the fiber web. Dispersions or solutions are applied to fiber web by various methods, then the water or solvents are evaporated at elevated temperature, then the fiber web is bonded by the dried adhesive.

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5

Textiles, regardless of manufacturing technologies and constructions, eventually need fiber as the basic materials to construct. The processes of manufacturing fibers are introduced first in this chapter.

5.1

Spinning

Spinning is the process in which the raw materials are formed into continuous fiber shape from solution or molten state.143,144 Viscose fiber, polyester fiber, nylon fiber, glass fiber, carbon fiber are all spun into fiber form. There are usually two major categories of spinning: solution spinning and melt spinning. This spinning is different from the spinning introduced in Chapter 3, Fundamental of fibers, which is the process of converting staples to spun yarn. Spinning in this chapter means the process of converting nonfiber materials into fiber forms.

5.1.1 Melt spinning Thermoplastic fibers are mainly produced with melt spinning. Nylon, polyester, and liquid crystalline aromatic polyester are all manufactured with melt spinning. They are first heated above their melting temperatures, then extruded through spinneret to form continuous fiber, followed by drawing, cooling, and winding. This process is schematically illustrated in Fig. 5.1. Fig. 5.2 shows a picture of spinneret that is spinning a strand of filament yarn. Fig. 5.3A shows a picture of a conjugate spinneret that is designed for melt spinning island sea-type bicomponent fiber, and Fig. 5.3B shows a regular melt spinning spinneret. Circular shape is the most common design for the spinneret hole, but different shapes of the spinneret holes have also been designed to spin fibers of different cross-sectional profiles. Fig. 5.4 shows some common profiles of spinneret. Spinning glass fiber is a special type of melt spinning. Glass is melted at high temperature, then it is drawn through spinneret by its own gravity to form continuous fiber as shown in Fig. 5.5.

5.1.2 Solution spinning Solution spinning is used when a material does not melt but can dissolve in an appropriate solvent. The material is dissolved in the solvent first and defoamed then extruded through a spinneret followed by coagulation in a nonsolvent or drying in Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00005-5 © 2020 Elsevier Ltd. All rights reserved.

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Figure 5.1 Schematic illustration of melt spinning process. Source: From Mather RR, Wardman RH. The Chemistry of Textile Fibres. 2nd ed. Royal Society of Chemistry; 2011:7 [Chapter 1].

hot air. If the extruded solution is extruded into a nonsolvent to coagulate the solution and get the fiber, this process is called wet spinning. If the extruded solution is dried in hot air to evaporate the solvent, this process is called dry spinning. Figs. 5.6 and 5.7 demonstrate the wet spinning and dry spinning processes, respectively. Viscose fiber (or rayon), meta-aramid, etc. are spun with wet spinning process. Acetate fiber, spandex fiber, etc. are spun with dry spinning. Acrylonitrile fiber, vinylon fiber, spandex, etc. can actually be spun by both spinning processes. Dry spinning is faster than wet spinning. Usually, filament is spun more often with dry spinning than with wet spinning. The spinning process for para-aramid fiber is unique, combining both dry and wet spinning. para-Aramid polymer is dissolved in fume sulfuric acid first followed by spinning through a spinneret. After passing through the spinneret the spinning solution experiences a very short distance of air (roughly 0.5 3 cm), which is called an air gap, followed by going into the coagulation bath. This process looks like dry first, then wet spinning. It is called dry wet spinning or air-gap spinning, also called dry jet wet spinning because the spinneret (jet) itself is dry.

Figure 5.2 A spinneret is spinning fiber. Source: Courtesy Wacker AG.

Figure 5.3 Spinnerets: (A) a conjugate spinneret for spinning bicomponent fiber and (B) melt spinning spinneret. Source: Courtesy (A) Kasen Nozzle Co. and (B) Nippon Nozzle Co.

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Figure 5.4 Common spinneret profile designs. Source: From Module 7, high performance and specialty fibres. Textile Eng. ,https://nptel. ac.in/courses/116/102/116102006/..

Figure 5.5 Schematic diagram of glass fiber spinning. Source: From Jones FR. Glass fibres. In: Hearle JWS ed. High Performance Fibres. Cambridge: Woodhead Publishing; 2001 [Chapter 6].

This process was invented by Herbert Blades in the 1970s.145 Fig. 5.8 illustrates this spinning process. After the fiber is spun from melt or solution, it is typically wound up to form continuous fiber or cut into short fibers (staple or floc). If crimps are added to the filaments before cutting, then staple fiber can be obtained after cutting.

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Figure 5.6 Schematic diagram of wet spinning process. Source: Modified from Mather RR, Wardman RH. The Chemistry of Textile Fibres. 2nd ed. Royal Society of Chemistry; 2011:232 [Chapter 6].

There is a very special type of solution spinning to make high-performance fibers, especially ultrahigh molecular-weight polyethylene (PE) (UHMWPE) fiber, called gel spinning. PE is dissolved in a solvent at elevated temperature, followed by being spun into a cooler medium, such as a nonsolvent or air, then is drawn with a very high ratio at elevated temperature and is removed of the residual solvent. This process will be further covered in Section 5.2.2.

5.2

Materials

5.2.1 para-Aramid para-Aramid fiber146 is one of the most commonly used materials in cut protective textiles.146 para-Aramid was invented by DuPont in 1965,147 149 and was commercialized and branded as Kevlar in 1972 after the breakthrough invention of dry wet spinning (air-gap spinning).145 There are mainly three categories of para-aramid, as defined by their chemical structures. The first and most popular one is poly(para-phenylene terephthalamide) (PPTA) fiber, represented by the abovementioned DuPont Kevlar fiber. A picture of DuPont Kevlar fiber is shown in Fig. 5.9. Its chemical structure is shown in

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Figure 5.7 Schematic diagram of dry spinning process. Source: From Mather RR, Wardman RH. The Chemistry of Textile Fibres. 2nd ed. Royal Society of Chemistry; 2011:149 [Chapter 5].

Fig. 5.10A. It is a polymerized product of two monomers, p-phenylenediamine and terephthaloyl chloride. Its polymerization is shown in Fig. 5.11. The main manufacturers of PPTA include DuPont in the United States (brand Kevlar)150 and Teijin in Japan (brand Twaron).151 The capacity and production of these two companies share more than 80% of the total para-aramid manufactured in the world. Japanese Teijin’s Twaron para-aramid fiber was acquired from the Dutch company Akzo Nobel, and this product is still manufactured in The Netherlands, with all R&D continuing there as well. There are also some other Asian para-aramid manufacturers, such as Kolon in Korea (brand Heracron),152 Hyosung in Korea (brand Alkex),153 Huvis in Korea,154 Tayho Advanced Materials (brand Taparan) in China,155 Yizheng Chemical Fiber of Sinopec in China,156 and Bluestar New Chemical Materials in China.157 There are some other Chinese companies that used to participate in this industry, including Shenma, Guigu, and Zhaoda but seemingly already

Figure 5.8 Dry wet spinning of para-aramid fiber. Source: From Mather RR, Wardman RH. The Chemistry of Textile Fibres. 2nd ed. Royal Society of Chemistry; 2011:232 [Chapter 6].

Figure 5.9 Picture of DuPont Kevlar PPTA fiber. PPTA, Poly(para-phenylene terephthalamide). Source: Courtesy DuPont de Nemours.

Figure 5.10 Chemical structures of different para-aramids. (A) Molecular structure of PPTA aramid, (B) molecular structure of Technora aramid, and (C) molecular structure of Armos aramid. PPTA, Poly(para-phenylene terephthalamide).

Figure 5.11 Polymerization of PPTA. PPTA, Poly(para-phenylene terephthalamide).

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stopped. A Korean company Taekwang also claims to have successfully commercialized para-aramid fiber product.158 In China, recently there is a new para-aramid fiber manufacturer called AFChina (meaning Aramid Fiber of China) who uses technology from Tsinghua University,159 which is worthy of attention due to its high performance to cost ratio and its consistent quality. Different from the semicontinuous polymerization process that most para-aramid manufacturers use, AFChina uses fully continuous polymerization160,161 that produces highly consistent intrinsic viscosity of polymer. Disclosed by AFChina, the monthly coefficient of variation of the viscosity is below 5% now, and first pass yield is almost 90%, which are leading figures in China. The good consistency of intrinsic viscosity of polymer is a precondition for consistent quality of fiber. Currently, the tenacity of AFChina’s regular para-aramid fiber type (equivalent to DuPont Kevlar 29) can consistently achieve a 20 cN/dtex strength level. In a very short time, AFChina’s production has ramped up to almost 800 t/annum based on its asset of 1000 tons/ annum capacity, and the first pass yield of fiber has achieved 95%. It has been reported in the market that AFChina is building a 2000 t/annum line. With higher output the cost is expected to be further driven down at same performance. The industry should pay attention to this rising star. Reportedly, this company is developing high modulus grade and will be commercialized shortly. The second chemical type of para-aramid is represented by Technora fiber of Teijin in Japan.162 Its chemical structure is shown in Fig. 5.10B. Technora is also a high tenacity, high modulus, and heat-resistant fiber, with better abrasion resistance and flex fatigue resistance than PPTA, mainly used in cables and composites now. Though under the same Teijin Company, Technora fiber has different history than Twaron. Technora was independently developed by Teijin in Japan in the 1970s,163 not like Twaron fiber that was acquired from Akzo Nobel. Chemically Technora has a third unit, an aromatic amine with ether bond, in its main molecular chain in addition to PPTA’s two-monomer structure. This ether bond imparts flexibility to the molecule chain, which is a hypothesized cause responsible for its better flex fatigue resistance than PPTA fiber. Fig. 5.12 shows a picture of Technora fiber. The third chemical type of para-aramid is PPTA with added third monomer of heterocyclic aromatic ring unit, represented by Armos or Rusar from Russia.164 This family of products is often called aramid III, meaning there is a third monomer in the structure. China Bluestar Chengrand also developed and is manufacturing similar products and branded as Stararamid (as shown in Fig. 5.13).165 Different monomers with different heterocyclic aromatic rings can be used as the third monomers to get different products with different properties. Fig. 5.10C shows the chemical structure of one typical type, Armos, but in reality, Technora and Armos type fibers are rarely used in cut protective textiles. It needs to be pointed out that para-aramid fiber is referred to as PPTA in this book if otherwise not specified though there are other types of para-aramid fibers as aforementioned. PPTA para-aramid fibers are categorized into different types by their mechanical properties, such as basic type represented by DuPont’s Kevlar 29 (K29) and Teijin’s Twaron D1000; high tenacity type represented by DuPont’s Kevlar 129 (K129) and Teijin’s Twaron D2000; high modulus type represented by

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Figure 5.12 Photo of Teijin Technora fiber. Source: Courtesy Teijin Aramid Co.

DuPont’s Kevlar 49 (K49) and Teijin’s Twaron D2200; low modulus, high elongation type represented by DuPont’s Kevlar 119 (K119) and Teijin’s Twaron D2100; high tenacity, high elongation type represented by DuPont’s KM2; and so on. In cut protection the basic type is generally used, for instance, DuPont’s Kevlar 29 type. Table 5.1 compares the properties of different Kevlar fibers, Technora fiber, and Bluestar’s aramid III fibers in twisted form.71,166 169 Only yarn tensile properties are listed here. There are no data available about the differences in their cut resistance. The development of para-aramid fiber in cut protection can be dated back to 1974,170 shortly after the commercialization of DuPont Kevlar fiber. The features of PPTA para-aramid include high specific strength (tenacity), high specific modulus, flame resistance, high heat resistance, cut resistance, and so on. It does not melt at elevated temperature but directly decomposes starting at around 450 C. The tenacity of the basic type is about 23 gf/den (or B20.4 cN/dtex) in a twisted form, with an elongation at break of 3% 4%. Its color is bright yellow as shown in Fig. 5.9, but it discolors after exposure to light.146,171 Filament, staple spun yarn, and textured yarn of para-aramid can all be used in cut protection.

5.2.1.1 para-Aramid filament Filament is the most commonly seen product of para-aramid in the industry market. para-Armid filament yarn is widely used in ballistic protective products, tire cord

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Figure 5.13 Bluestar’s Staramid aramid III.

fabric, rubber hose and belt reinforcement, optical cable reinforcement, composites, etc. The filament yarn does not have twist after spinning, sometimes called flat yarn or flat filament, and therefore is quite loose. What is shown in Fig. 5.9 is filament yarn. Usually, the filament yarn is twisted more or less in most industrial applications (except a few applications such as optical fiber reinforcement and some composite applications). The filament yarn is not popular in cut protective textiles because of its rigid feeling and looseness, which makes it difficult to knit. Even twisted filament is not easy to knit. However, twisting together with elastic yarn or used in wrapped yarn makes it easier for para-aramid filament to be used in knitting. Some embodiment examples are described as follows. Example 5.2.1-1: Spandex is wrapped with nylon or polyester denier textured yarn (DTY) yarn, then twisted with 600 D para-aramid filament together to form 800 900 D yarn. This yarn can be knit to a 13-gauge knit fabric. The details are as follows:

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Table 5.1 Tensile properties of different aramid fibers.71, 166 Fiber

Kevlar 29 (general type) Kevlar 49 (high modulus type) Kevlar 129 (high tenacity type) Kevlar 119 (low modulus and high elongation type) Twaron D1000 (general type) Twaron D2000 (high tenacity type) Twaron D2100 (low modulus and high elongation type) Twaron D2200 (high modulus type) Technora T200 Bluestar F-3 aramid III fiber (impregnation method) Bluestar F-3A aramid III fiber (impregnation method)

169

Tenacity (GPa)

Chord modulus (GPa)

Elongation at break (%)

GPa

cN/dtex

GPa

cN/dtex

2.9 2.8 3.3 3.0

20 19.5 23 21

72 110 94 54

500 760 135 375

3.4 2.4 3.2 4.2

2.8 3.3

19.5 23

70 90

490 625

3.5 3.5

3.0

21

55

380

4.3

2.9

20

110

760

2.7

3.4 $ 4.2

23.6 $ 29

63 $ 125

440 870

4.7 3.2 4.1

$ 4.4

$ 30.5

$ 145

1000

$ 2.5

Wrap one end of 70 D spandex with two ends of 70 D or one end of 140 DTY (nylon or polyester). Spandex is stretched to a ratio of 2.0 4.0.70,172 This wrapped yarn is then twisted together with 600 D para-aramid filament yarn, with a twist level of B200 twists per meter, in a twisting direction opposite to the last wrapping direction in the above wrapped yarn. The composite yarn has a linear density of B900 D. This twisted composite yarn product can be used in a 13-gauge knit fabric. Example 5.2.1-2: Spandex is wrapped with nylon or polyester DTY yarn, then twisted with 400 D paraaramid filament together to form 800 900 D yarn. This yarn can be knit to a 13-gauge knit fabric. The details are as follows: Wrap one end of 70 D spandex with two ends of 70 D or one end of 140 DTY (nylon or polyester). Spandex is stretched to a ratio of 2.4 4.0. This wrapped yarn is then twisted together with 400 D para-aramid filament yarn and 210 DTY (or three ends of 70 D), with a twist of B200 twist per meters, in a twisting direction opposite to the last wrapping direction in the above wrapped yarn. Alternatively, the para-aramid filament yarn and textured yarn can be further wrapped onto the wrapped yarn of spandex and textured yarn to form a fully wrapped yarn. The composite yarn has a linear density of B900 D. This twisted composite yarn product can be used in a 13-gauge knit fabric. Example 5.2.1-3: Spandex is wrapped with nylon or polyester DTY yarn then twisted with 400 D paraaramid filament together to form 500 to 600 D yarn. This yarn can be knit to a 15-gauge knit fabric. The details are as follows

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Wrap one end of 40 D spandex with two ends of 70 D or one end of 140 DTY (nylon or polyester). Spandex is stretched to a ratio of 2.0 3.0. This wrapped yarn is then twisted together with 400 D para-aramid filament yarn, with a twist level of B200 twists per meters, in a twisting direction opposite to the last wrapping direction in the above wrapped yarn. Alternatively, the para-aramid filament yarn and textured yarn can be further wrapped onto the wrapped yarn of spandex and textured yarn to form a fully wrapped yarn. The composite yarn has a linear density of B600 D. This twisted composite yarn product can be used in a 15-gauge knit fabric. These examples are tabulated in Table 5.2.

5.2.1.2 Staple spun yarn Fig. 5.14 shows a picture of PPTA staple spun yarn. The staple spun yarn possesses good cohesiveness caused by the high twist level and thus is easier to knit or weave as compared to filament yarns. For example, in knitting, 100% staple spun yarn can be directly knit for a 7 or 10-gauge fabric: yarn together with wrapped spandex can be knit for fabric higher than 10-gauge, and an 18-gauge fabric can be knit with spun yarn and textured yarn without spandex. The detailed examples are given as follows. Example 5.2.1-4: 7-gauge: 7-gauge gloves are usually thick and heavy with poor elasticity (or do not need much elasticity). The needle for 7-gauge can accommodate yarn with linear density from 2000 to 3000 D (1.8 2.6 cc), with the optimal being 2500 D (2.1 cc). Five ends 20 cc/2 yarn together meet this range and can be cofed to knit. The resultant fabric has a basis weight of 580 600 gsm. Its cut resistance rating by EN388 Coupe cut test is level 3. The cut force per ISO13997 (or ASTM F2992-16) is around 1000 gf (or 10 N), therefore level B (by EN388:2016) or A2 (by ANSI/ISEA-15). If higher resistance to cut is needed, then six ends of 20 cc/2 yarn can be cofed to knit, and a fabric of 680 700 gsm can be obtained. This fabric’s EN388 Coupe cut resistance rating is still level 3 and may sometimes reach a level 4 due to lab-to-lab variation. However, it can robustly achieve 1000 gf (or 10 N) in cut force per ISO13997 or ASTM F2992 and therefore can achieve a robust level C (EN388:2016) or A3 (ANSI/ISEA 105-16). Ansell GoldKnit 70-225 glove is a typical 7-gauge knit with 100% para-aramid.173 Example 5.2.1-5: 10-gauge: 10-gauge fabric is lighter than 7-gauge. The needle for 10-gauge can accommodate yarn in the range of linear density from 1000 to 1500 D, with the optimal being around 1300 D. Two or three ends of 20 cc/2, or two ends 20 cc/1 plus one end 20 cc/1 can be used to knit. If three ends 20 cc/2 are cofed, the basis weight of the resultant fabric is about 480 520 gsm. EN388 Coupe test rating is level 2 or 3. ISO13997 or ASTM F2992 cut force is 700 800 gf (7 8 N), level B (EN388:2016) or A2 (ANSI/ISEA 10516). PowerGrab KEV4 by PIP, an American PPE company, is a 10-gauge knit glove product with para-aramid.174 If two ends 20 cc/2 are cofed to knit, then the basis weight is about 350 450 gsm. If two ends 20 cc/2 plus one end 20 cc/1 are cofed to knit, then the basis weight is between that knit with two ends 20 cc/2 and that with three ends 20 cc/2. Example 5.2.1-6 13-gauge: 13-gauge is very popular for knitting light and thin protective gloves, and usually these constructions will use spandex to get elasticity. 13-gauge needle can

Table 5.2 Constructions of knit fabrics with poly(para-phenylene terephthalamide) para-aramid fiber. Example

Fiber material

Gauge

Construction

Basis weight (gsm)

Estimated TDM cut force (gf)

5.2.1-1

para-Aramid filament

13

400 450

500 550

5.2.1-2

para-Aramid filament

13

400 450

340 380

5.2.1-3

para-Aramid filament

15

300 350

380 410

5.2.1-4

para-Aramid spun yarn

7

5.2.1-5

para-Aramid spun yarn

10

A: 580 B: 680 A: 350 B: 400

A: 980 1050 B: 1100 1200 A: 600 700 B: 700 850

5.2.1-6

para-Aramid spun yarn

13

(70 D spandex wrapped with 2 3 70 D DTY) twisted with 600 D para-aramid filament (70 D spandex wrapped with 2 3 70 D DTY) 1 400 D para-aramid filament 1 3 3 70 D DTY (40 D spandex wrapped with 2 3 70 D DTY) 1 400 D para-aramid filament A: 5 3 20 cc/2 para-aramid spun yarn B: 6 3 20 cc/2 para-aramid spun yarn A: 2 3 20 cc/2 para-aramid spun yarn B: 2 3 20 cc/2 para-aramid spun yarn 1 1 3 20 cc/1 paraaramid spun yarn C: 3 3 20 cc/2 para-aramid spun yarn A: 1 3 20 cc/2 para-aramid spun yarn 1 (70 D spandex wrapped with 2 3 70 D DTY) B: 1 3 24 cc/2 para-aramid spun yarn 1 (70 D spandex wrapped with 2 3 70 D DTY) A: 1 3 24 cc/2 para-aramid spun yarn 1 (70 D spandex wrapped with 2 3 70 D DTY) B: 1 3 24 cc/2 para-aramid spun yarn 1 (2 3 70 D DTY wrapped 40 D spandex) A: 1 3 40 cc/2 para-aramid spun yarn 1 1 3 40 D DTY B: 1 3 40 cc/2 para-aramid spun yarn 1 1 3 40 D DTY wrapped 20 D spandex

5.2.1-7

5.2.1-8

para-Aramid spun yarn

para-Aramid spun yarn

15

18

DTY, Denier textured yarn; TDM, Tomodynamometer.

600 700 400 500

C: 480 520 A: 400

C: 800 930 A: 500 550

B:

370

B: 450 500

A: 300 350

A: 360 400

B: 300 350

B: 360 400

A: 200 250 B: 200 250

A: 320 400 B: 320 400

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Figure 5.14 Picture of PPTA staple spun yarn. PPTA, Poly(para-phenylene terephthalamide). accommodate yarn of linear density from 700 to 1000 D, with the optimal being around 800 900 D. Because spandex needs to be used and wrapped, the staple spun yarn has to be lighter than 800 900 D for knitting. Two examples are given next. Example 5.2.1-6A: 70 D spandex is wrapped with two ends of 70 DTY (nylon or polyester), with stretch ratio for spandex between 2.4 and 2.5, then used together with one end 20 cc/2 spun yarn (around 530 D). Total denier of this yarn is about 700 D. The knit fabric has a basis weight of B400 gsm. If gloves are knit, each pair is around 45 50 g. 20 cc/2 para-aramid spun yarn can be cofed with the wrapped spandex to knit or can also be used to further wrap the wrapped spandex to form a single end yarn to knit. Example 5.2.1-6B: 70 D spandex is wrapped with two ends of 70 DTY (nylon or polyester), with stretch ratio for spandex between 2.4 and 2.5, then used together with one end 24 cc/2 spun yarn (around 440 D). Total linear density of this yarn is about 610 D. The knit fabric has a basis weight of B370 gsm. If gloves are knit, each pair has around 40 43 g. 24 cc/2 para-aramid spun yarn can be cofed with the wrapped spandex to knit or can also be used to further wrap the wrapped spandex to form a single end yarn to knit. Example 5.2.1-7 15-gauge: 15-gauge knit fabric is lighter than 13-gauge. The needle of a 15-gauge knitting head can accommodate yarn of linear density from 400 to 800 D, with the optimal being around 600 D. 15-gauge can use exactly the same example with 24 cc/2 yarn

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example mentioned earlier and get a fabric heavier than the 13-gauge with same yarn, at a basis weight of around 380 gsm. Example 5.2.1-8 18-gauge: 18-gauge knit fabric is very light and thin. The needle of 18-gauge can accommodate 200 and 400 D, optimal 250 400 D. A 40 cc/2 yarn (around 265 D) can be knit together with one end of 40 DTY without spandex. Or one end 20 D spandex is wrapped with 40 DTY with a stretch ratio of spandex of 2.4 2.5, then further wrapped one end 40 cc/2 spun yarn to form a single yarn to knit. The resultant knit fabric has a basis weight of 200 250 gsm. To make these descriptive statements clearer, these constructions are tabulated in Table 5.2.

5.2.1.3 Textured yarn of para-aramid Textured yarn can be knit like spun yarn, and the linear density range is the same as for spun yarn introduced earlier, that is, 2000 3000 D for 7-gauge, 1000 1500 D for 10-gauge, 700 1000 D for 13-gauge, 400 800 D for 15-gauge, and 200 400 D for 18-gauge. para-Aramid filament, spun yarn, and textured yarn differ greatly in tenacity. Spun yarn’s tenacity is only about 30% 40% as compared to the filament yarn, and a textured yarn’s tenacity is even slightly lower. It is always an interesting question to ask whether there is any large difference in their cut resistance. Generally speaking, they do not have much difference in cut resistance although the difference in their tenacity is large. The tenacity is a longitude property, while cut resistance is a transverse property. As a general rule, every gsm of fabric made of para-aramid fiber contributes 1.7 1.9 gf in ISO13997 (or ASTM F2992-15) testing, with an average of around 1.8 gf. In other words, if a fabric has a basis weight of 1 gsm, then its cut force is around 1.7 1.9 gf. If a fabric has a basis weight of 100 gsm, then its cut force by ISO13997 or ASTM F2992-15 is around 170 190 gf. A 600 gsm of para-aramid fabric would exhibit a cut force of 1050 gf by ISO13997 or ASTM F2992-15.16 para-Aramid fiber is widely recognized in the cut protection market, and many people equate yellow fiber and cut protection due to its yellow color. As a result, there are many yellow fiber products that look similar to their para-aramid counterparts in color only. Their actual cut performance can be far worse, putting workers who use these products at a high risk. para-Aramid is not resistant to acid or alkaline, and thus the applications that use strong acid or alkaline environments, or laundering solutions that use these conditions, such as hypochlorite, should be avoided. Perborate bleach can be used for para-aramid.175 DuPont’s laundering data show that Kevlar fiber strength decreased by 88% (in other words, retained only 12%) after six cycles of sodium hypochlorite laundering. While laundered in sodium perborate, Kevlar fiber retained 94%, only losing 6% of its strength. DuPont’s research data showed that the cut resistance of a glove knit with Kevlar yarn was not affected after 10 cycles of cleaning, though the yarn strength was slightly decreased (either water laundry or dry cleaning). Fig. 5.15 shows these results.175

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para-Aramid fiber discolors when exposed to light and becomes darker and darker, accompanied by the decrease in its tenacity. DuPont’s research data showed that obvious discoloration can be observed after 3 days of outdoor exposure of a glove knit with Kevlar fiber and became heavier after 5 days exposure (Fig. 5.16) (12 hours exposure per day). But nonetheless, the cut resistance of these gloves was not decreased as shown in Fig. 5.17.176 In most cases these kinds of gloves are used indoor where the light intensity is much weaker than the outdoor sunlight, or used outdoor only for a limited duration of time; therefore it is safe to assume that the

Average cut force (kgf)

1.4 1.2 1 0.8 Laundering Dry Cleaning

0.6 0.4 0.2 0 0

1

2

3

4

5

6

7

8

9

10

11

Number of cleaning cycles

Figure 5.15 Cut resistance of gloves of DuPont Kevlar fiber after cleaning. Source: Courtesy DuPont de Nemours Co. DuPont. DuPontt Kevlars Laundering Guide for Cut Resistant Apparel. K17038; 2007.

Figure 5.16 Glove of DuPont Kevlar fiber (from left to right: before exposure, exposed for 3 days and for 5 days). Source: Courtesy DuPont de Nemours Co. DuPont de Nemours Co. DuPontt Kevlars: Guide to UV Stability for Cut-Resistant Gloves. K-27461; 2013.

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Figure 5.17 Cut resistance of gloves with DuPont Kevlar fiber after outdoor exposure. (Gloves were tested in accordance with ASTM F1790-97 using the CPPT instrument. Gloves were not used prior to or after exposure to UV sunlight. UV, Ultraviolet.) Source: Courtesy DuPont de Nemours. DuPont de Nemours Co. DuPontt Kevlars: Guide to UV Stability for Cut-Resistant Gloves. K-27461; 2013.

cut resistance of para-aramid gloves is not significantly affected in a most typical work environment. para-Aramid fiber absorbs a certain amount of moisture and achieves equilibrium in a given environment. Kevlar 29 fiber, as an example, equilibrates at a moisture regain of 6% 7% in an environment of 60% 70% RH.177 A common but less noted phenomenon is that the cut resistance of para-aramid decreases with increasing moisture content in fiber.178 In order to improve the comfort, especially the dexterity and sweat absorption, para-aramid fiber can be blended with other fibers such as cotton and nylon that are good for apparel can be blended to make cut protective textile.179,180 para-Aramid fiber possesses outstanding heat resistance. It does not melt at high temperature, instead it decomposes when it is heated up to 450 C, and thus fabrics made of para-aramid fiber are also used in thermal protection, for instance, industrial thermal protective gloves and oven gloves. The industrial standard for heat protection usually referred to is EN407. Thermal protection mainly relies on materials, design of gloves, thickness and weight, and so on, which are not illustrated here. para-Aramid fiber also possesses excellent flame resistance and therefore is a choice of material for flame resistance gloves and apparel. Certainly, there is also heat in a fire event, and thus the design of flame-resistant gloves and fabrics also need to take thermal protection into account.181 184 para-Aramid fiber exhibits moderate abrasion resistance. 7-gauge with 600 gsm knitted 100% para-aramid fabric can only achieve abrasion level 1 according to

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C=O C=O

C=O

O=C O=C

O=C

N–H

N–H

N–H

H–N H–N

H–N

C=O C=O

C=O

O=C O=C O=C

Figure 5.18 Intermolecular hydrogen bonding in PPTA para-aramid fiber. PPTA, Poly (para-phenylene terephthalamide). Source: Courtesy DuPont de Nemours Co. DuPont de Nemours Co. Kevlars Aramid Fiber Technical Guide; 2017.

EN388 (250 500 cycles), while 13-gauge nylon 66 can achieve abrasion level 2 3 (500 2000 cycles or 2000 8000 cycles), and 13-gauge high-performance PE (HPPE) can achieve abrasion level 4 ( . 8000 cycles). para-Aramid fiber becomes hairy very easily under abrasion, which is determined by the microstructure of para-aramid. The molecular chains of para-aramid fiber orient along the fiber axial direction and form intermolecular hydrogen bonding (as shown in Fig. 5.18).177,185 The hydrogen-bonded sheets stack along radial direction to form a pleated crystal structure (Fig. 5.19).177,186 The fiber is actually not uniform along the radial direction. There are a skin layer and a core layer along the radial direction. The core layer has a higher degree of crystallization and is denser, whereas the skin layer is less dense and has a lower degree of crystallization (Fig. 5.20).146,187,188 And therefore the skin is vulnerable to abrasion and prone to form fibrils on the skin.187,189 The surface morphologies of para-aramid fiber before and after abrasion are shown in Fig. 5.21.190 With continued abrasion, these fibrils eventually break and fall off from the fiber. That is why the gloves of para-aramid fiber easily generate dusts.

5.2.2 High-strength polyethylene (ultrahigh molecular weight polyethylene) In the material industry, high-strength PE is usually called UHMWPE191, but in the PPE industry, it is called high-performance polyethylene, or HPPE as abbreviation.

Figure 5.19 Skin-core morphology of PPTA para-aramid fiber. PPTA, Poly(para-phenylene terephthalamide). Source: From Northolt MG. X-ray diffraction study of poly(p-phenylene terephthalamide) fibres. Eur Polym J. 1974;10(9):799 804. doi:10.1016/0014-3057(74)90131-1.

Figure 5.20 Radial stacking of hydrogen-bonded sheets in PPTA para-aramid fiber. PPTA, Poly(para-phenylene terephthalamide). Source: Courtesy DuPont de Nemours Co. DuPont de Nemours Co. Kevlars Aramid Fiber Technical Guide; 2017:3.

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Figure 5.21 Microphotos of para-aramid fibers. (A)—Smooth surface of fiber without abrasion and (B)—fibrillated surface of fiber after abrasion. Source: Courtesy DuPont de Nemours Co. Tsimpris CW, Jacob JP, Vercesi GP. Kevlars engineered elastomer for tire reinforcement. In: Paper 14C, Presented at the International Tire Exhibition and Conference. Akron, Ohio, September 10 12, 2002. DuPont Publication H-89939.

Figure 5.22 Molecular structure of polyethylene.

Hereafter, UHMWPE is used when referred to the resin, while HPPE is used when referred to the fiber. PE is a very common thermoplastic material, with a very simple chemical structure (Fig. 5.22). PE is defined with four major categories by molecular weight (or molecular mass): (1) medium molecular weight below 110,000 Da; (2) high molecular weight between 110,000 and 250,000 Da; (3) superhigh molecular weight between 250,000 and 1,500,000 Da; and (4) and ultrahigh molecular weight higher than 1,500,000 Da. Normal PE fiber is melt spun with medium or high molecular weight PE, with resultant tenacity of 4 8 cN/dtex. It is relatively easy to melt and spin fiber from PE with not superhigh molecular weight, but it is very hard to melt and spin UHMWPE due to very high melt viscosity. It was first believed that the UHMWPE could not be spun. But in 1979 the Dutch company DSM (DSM stands for Dutch State Mines) invented a method that made it possible to spin UHMWPE from its solution.192,193 These invention patents were assigned to its subsidiary Stamicarbon that is DSM’s intellectual property managing center in the past. In this invention the prototype of gel spinning was developed. This process includes the steps191 195: 1. Dissolve UHMWPE in a hydrocarbon solvent such as decalin or xylene at a low concentration, for instance, B2% 5%. Because UHMWPE does not dissolve in solvent at room temperature, the solution has to be at elevated temperature such as above 140 C. The low

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Figure 5.23 Comparison between orientation of HPPE and regular PE. HPPE, Highperformance polyethylene; PE, polyethylene. Source: Courtesy DSM. DSM. Technical Brochure: Dyneemas in Marine and Industrial Applications. concentration of the solution allows the reduction or even elimination of entanglement of the very long PE molecular chains. The low concentration also makes the solution not too viscous to be processed in next steps. In the earliest DSM patent the concentration was 2%. 2. Spin (extrude) the solution through a spinneret with nozzles of large enough holes, for instance, 0.5 mm, into a quenching medium, such as air or water. The solution is quickly quenched to below the solution temperature of UHMWPE in the solvent, leading to the solidification of the mixture and to keep the disentangled state of UHMWPE molecules. The cooling medium has to minimize either the evaporation of the hydrocarbon solvent in the case of gaseous cooling medium or the extraction of hydrocarbon solvent in the case of liquid medium. If the quenching medium is a gas, then this process is like the dry spinning. If the quenching medium is a liquid, then this process is like the wet spinning. In the quenching medium, UHMWPE molecules start to form crystals. In the earliest DSM patent, water was used as the quenching medium. After quenching the mixture becomes like a gel in the medium. This is why this method is called gel spinning. 3. Draw (stretch) the gel fiber a temperatures close to but below the melting point of UHMWPE with multistep drawing of very high drawing ratio in the presence of solvent. At this step the long molecules of UHMWPE form highly oriented structure, and the crystallinity grows significantly. In the meantime the solvent gradually evaporates due to the high temperature. This step is called superdrawing due to the very high drawing ratio. The drawing temperature in DSM’s earliest patent was 120 C 130 C. After super drawing the high orientation of UHMWPE molecules is schematically shown together with that of normal PE in Fig. 5.23.

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Figure 5.24 Gel spinning process disclosed in DSM patent. (A—Polyethylene solution, B—Cooling bath, C—Filament, D—Roller, E—Oven, M— Heated jacket or oven, N—Spinneret, O—Plunger, P—guidance roller.) DSM, Dutch State Mines. Source: From Smith P, Lemstra PJ. Process for Making Polymer Filaments Which Have a High Tensile Strength and a High Modulus, US Patent 4,344,908; 1980.

Fig. 5.24 shows the process scheme described in this DSM’s patent. One shall realize from this drawing that there is also an air gap before the solution enters the quenching water. This configuration of gap may be inspired from the air gap developed in the PPTA fiber spinning. The products developed by DSM were commercialized under the brand name of Dyneema, a well-recognized brand worldwide today. As a matter of fact, though there was only one stretching step shown in Fig. 5.24 taken from the US patent 4,344,908, there are multiple steps of stretching (drawing) in later real production. The superdrawing significantly increases the fiber tenacity and modulus. Fig. 5.25 shows what was disclosed by DSM in its first patent on this subject. With superdrawn to a ratio of 25, the fiber tenacity increased to nearly 3 GPa, while modulus to 70 GPa. Afterward DSM has made extensive studies on the effect of gel spinning process on the properties of HPPE fiber,196 200 and nowadays the commercial grades can achieve tenacity of close to 4 GPa and modulus close to 120 GPa by processed at draw ratios up to 50 100.191 The superhigh tenacity and modulus are attributed to the almost perfectly oriented structure of UHMWPE molecular chains. In the 1980s Allied Corp201 in the United States also spent a significant amount of efforts on researching spinning polyolefin and developed a gel spinning process by changing the solvent from decalin to mineral oil202 205 and commercialized the product with the brand name of Spectra.206,207 Toyobo in Japan also made efforts in developing HPPE fiber after DSM’s development. However, it might judge that it was impossible to get around the basis patent covered by DSM, it entered into a collaboration with DSM. Toyobo and

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Figure 5.25 Effect of draw ratio on tensile properties of HPPE fiber. (A) Tenacity versus draw ratio of gel-spun polyethylene. (B) Modulus versus draw ratio of gel-spun polyethylene. HPPE, High-performance polyethylene. Source: From Smith P, Lemstra PJ. Process for Making Polymer Filaments Which Have a High Tensile Strength and a High Modulus, US Patent 4,344,908; 1980.

DSM set up a joint venture company in The Netherlands in 1986. Toyobo itself set up a research plant in Japan. In Japan market, Toyobo sells the fiber product manufactured with DSM technology under the brand name of Dyneema. However, Toyobo also owns its own HPPE fiber product branded as Tsunooga. It is reported that Toyobo uses a melt spinning process,208 different from the gel spinning. The tenacity of melt spun Tsunooga HPPE fiber, around 14 cN/dtex only, is much lower than that of the gel-spun Dyneema and Spectra HPPE fiber, which is around 35 38 cN/dtex. Reportedly Tsunooga fiber is also marketed at a much lower price than Dyneema fiber. Huvis in Korea has also commercialized HPPE fiber and branded it as Duraron.209 In China, there are more than 20 manufacturers of HPPE fiber, represented by Tong Yi Zhong,210 Sinopec Yizheng Chemical Fiber,211 Surrey,212 Jonnyma,213 JJJ,214 ICD Fiber,215 etc. ICD Fiber was acquired by DSM in 2011.216 Their products are all spun from gel spinning technology mostly sourced from Donghua University, formerly known as China Textile University. These Chinese HPPE fibers are nicknamed Chineema marketed at prices of ranging from 1/4 to 1/3 of Dyneema’s equivalent grades, but cut performance has been well accepted by the market. Fig. 5.26 shows a picture of HPPE, yarn and Table 5.3 summarizes the tensile properties of different grades of HPPE yarn. HPPE fiber possesses some exceptional features illustrated as follows:

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Figure 5.26 Gel-spun HPPE yarn. HPPE, High-performance polyethylene.

Table 5.3 Tensile properties of different grades of high-performance polyethylene (HPPE) yarn. HPPE grade

Dyneema SK60 Dyneema SK65 Dyneema SK71 Dyneema SK75 Dyneema SK76 Spectra 900 Spectra 1000 Spectra 2000

Tenacity

Modulus

Elongation at break (%)

GPa

cN/dtex

GPa

cN/dtex

2.7 3.0 3.4 3.4 3.6 2.5 3.1 3.3

28 31 35 35 37 26 32 34

88 94 118 107 116 73 107 116

910 970 1220 1100 1200 750 1100 1200

3.5 3.6 3.7 3.8 3.8 3.6 3.3 2.9

Source: From Dingenen JLJ. Gel-spun high-performance polyethylene fibres. In: Hearle JWS, ed. High Performance Fibres. Cambridge, England: Woodhead Publishing; 2001:69 [Chapter 3].

1. Superhigh tenacity: tenacity of most HPPE fiber grades is higher than 30 cN/dtex (higher than basic grade of PPTA para-aramid fiber by 50%). Tenacity of DSM’s SK76 fiber is even close to 40 cN/dtex, which is nearly twofold of the tenacity of general para-aramid fiber. This is a result of very high degree of orientation, crystallization and very low number of defects in the HPPE fiber. 2. Outstanding abrasion resistance: HPPE fiber can easily achieve the highest EN388 abrasion resistance level (level 4) in a 13-gauge glove even without coating. In contrast, nylon 66 fiber usually achieves level 3 in 13-gauge gloves, and polyester level 3, poorer than nylon 66. PPTA para-aramid fiber can only achieve up to level 2 in 13-gauge gloves without coating. Credited to its superior abrasion resistance, HPPE fiber generates little dust during use, not like PPTA fiber. This is very desired at dust-free workplaces.

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Figure 5.27 Strength retention of different fibers after outdoor exposure. Source: From Dingenen JLJ. Gel-spun high-performance polyethylene fibres. In: Hearle JWS, ed. High Performance Fibres. Cambridge, England: Woodhead Publishing; 2001:77 [Chapter 3]. 3. Excellent ultraviolet (UV) resistance and weathering resistance: even after long-term outdoor exposure, HPPE still retains very good strength and also exhibits little discoloration, thus it is a fiber of choice for outdoor applications. The strength retention of some different high-performance fibers after outdoor exposure is shown in Fig. 5.27.191 4. High thermal conductivity: HPPE fiber’s thermal conductivity coefficient is as high as 4 20 W/(m K),217 221 which is about 100 500 times of that of para-aramid fiber; therefore the textile made of HPPE is felt fairly cool and comfortable in normal and warm environments when worn in direct contact with the body. Gloves made of HPPE fiber are more suitable for wearing in summer or in warm environments, while para-aramid is more suitable for wearing in winter or in cold environments (such as meat processing factories). 5. Superior chemical resistance: HPPE fiber is very resistant to chemicals, especially strong acid, alkali, and polar solvents. Fig. 5.28 illustrates how HPPE and para-aramid fibers behave differently after being exposed to acid and alkali.191 More chemical resistance data can be found in Refs. [191,221]. Therefore there are more choices for laundering HPPE fabrics. 6. Low-specific gravity: HPPE fiber’s specific gravity is 0.97 0.99 g/cc, lower than paraaramid fiber by around 30% and lower than nylon fiber by around 15%. 7. HPPE fiber is very hydrophobic. It does not absorb moisture, and its properties are not affected by water. 8. The melting point of HPPE fiber is between 135 C and 145 C; therefore HPPE fiber’s heat resistance is much poorer than para-aramid fiber. HPPE fiber starts to soften even

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100

HPPE in alkali HPPE in acid

Strength retention (%)

80

Alkali = 10% NaOH/95°C Acid = 40% H2SO4/95°C

60

Aramid in alkali

40

20 Aramid in acid 0 0

50

100

150

200

Time (hours)

Figure 5.28 Acid and alkaline resistance of HPPE and para-aramid fibers. HPPE, Highperformance polyethylene. Source: From Dingenen JLJ. Gel-spun high-performance polyethylene fibres. In: Hearle JWS, ed. High Performance Fibres. Cambridge: Woodhead Publishing; 2001:77 [Chapter 3]. below its melting point, and also it conducts heat fairly quickly. The heat will be quickly transferred from HPPE fabric to the other side when it is in contact with a hot object; therefore it is not recommended to wear HPPE glove for operations that involve the handling of objects above 80 C. Because of its melting characteristic, HPPE fabric is not suitable for working environment where there are sparks. HPPE easily melts and forms holes after contacting sparks. Moreover, it is not flame resistant; therefore it is not a selection for textile or gloves at places where there is fire such as firefighting.

In cut protective textiles, especially in gloves, usually HPPE is used in filament yarn formation. Due to HPPE’s low friction and therefore slippery characteristic, gloves made of HPPE fiber usually need palm coating (or called dipping) to enhance grip. Palm coating is more suitable for 13-gauge or lighter gloves than the heavier 7 or 10-gauge gloves. 7- and 10-gauge gloves are thick and relatively loose. The coating material can penetrate heavily into the gloves and thus makes the gloves heavy and rigid. This is the reason that coating is usually applied to 13gauge or lighter gloves. For these high-gauge gloves, light denier yarns are more appropriate. 600 D yarn is suitable for 13-gauge, 400 D for 15-gauge, and 200 D for 18-gauge. If glass fiber is added, then 400 D HPPE can be used for 13-gauge. Some practical examples are demonstrated as follows Example 5.2.2-1 A 600 D filament HPPE knit to a 13-gauge fabric together with 70 D spandex wrapped with two ends of 70 DTY in which spandex is stretched to a stretch ratio of 2.4 2.5.

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Total denier of this yarn is about 770 D, and the fabric (or glove) has a basis weight of B400 gsm. If gloves are knit, the weight is 43 48 g per pair. A 600 D HPPE yarn can be cofed with the wrapped spandex, or HPPE can be used to further wrap the wrapped spandex then a single end of yarn is used for knitting. Example 5.2.2-2 A 100 D glass fiber is wrapped with two ends of 70 DTY in two layers, respectively (one end DTY for each layer), and a 70 D spandex is also wrapped with two ends of 70 DTY with a stretch ratio of 2.4 2.5 for spandex. Then one end of 400 D HPPE yarn and the wrapped glass fiber are used to further wrap the wrapped spandex in sequence to form a single end yarn of B810 D. This yarn is knit into a 13-gauge fabric with a basis weight of 380 450 gsm. If gloves are knit, the weight per pair is 45 50 g. Example 5.2.2-3 One end 70 D spandex is wrapped with two ends of 70 D DTY in two layers (one end DTY per layer) with a stretch ratio of 2.4 2.5 for spandex, then one end of 400 D HPPE is used to further wrap this wrapped spandex to get a B580 D yarn. This yarn is used to knit a 15-gauge fabric or glove. The basis weight of the resultant fabric is 350 400 gsm. If gloves are knit, the weight per pair is 40 45 g. Example 5.2.2-4 One end 200 D HPPE yarn is cofed together with one end 70 D DTY to knit 18-gauge fabric or glove. The basis weight of the resultant fabric is 200 250 gsm. If gloves are knit, the weight per pair is 27 30 g. Example 5.2.2-5 One end 20 D spandex is wrapped with one end 40 D DTY, then the wrapped yarn is further wrapped with one end 200 D HPPE. The resultant singe end of yarn is about 280 D. This yarn is knit to a 18-gauge fabric or glove. These constructions are summarized in Table 5.4.

One may be curious why HPPE staple spun yarn is not introduced here. As a matter of fact, HPPE staples are rarely seen in the market. The main reason is that HPPE can hardly retain its crimp overtime after being crimped, and also the staple fibers tend to slip away from one another due to their low-friction characteristics. The presence of crimp is critical to the cohesiveness and strength of staple spun yarn. If staple of HPPE needs to be used, it can be blended with other staple fibers, such as nylon and aramid. HPPE yarn has a very smooth surface, a very low-friction coefficient, and is very abrasion resistant. The low friction on the one hand causes poor grip but on the other hand imparts good abrasion resistance. Greige (noncoated) 13-gauge glove of HPPE can easily pass EN388 level 4 in abrasion testing (level 4 is the highest level for abrasion in EN388). In contrast, para-aramid can only achieve level 1 or maximum level 2 in 13-gauge fabric without coating. Due to the inertness of HPPE’s surface, the adhesion between coating layer and HPPE yarn is usually not good enough. The adhesion mainly relies on the penetration of coating material into the space between yarns. This penetration is often called strike-through. The textured yarn can help enhance the adhesion while offering elasticity to the fabric. As aforementioned, HPPE is felt cool when worn next to the skin because of its high thermal conductivity. Its thermal conductivity coefficient along the fiber axis

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Table 5.4 Constructions of knit fabrics with high-performance polyethylene (HPPE) fiber. Example

Fiber material

Gauge

Construction

Basis weight (gsm)

Estimated TDM cut force (gf)

5.2.2-1

HPPE filament

13

350 400

390 460

5.2.2-2

HPPE filament

13

380 450

500 600

5.2.2-3

HPPE filament

15

350 400

350 420

5.2.2-4

HPPE filament

18

200 250

250 300

5.2.2-5

HPPE filament

18

(70 D spandex wrapped with 2 3 70 D DTY) 1 600 D HPPE filament (70 D spandex wrapped with 2 3 70 D DTY) 1 (100 D glass wrapped with 2 3 70 D DTY) 1 400 D HPPE filament (70 D spandex wrapped with 2 3 70 D DTY) 1 400 D HPPE filament 1 3 70 D DTY 1 200 D HPPE filament (20 D spandex wrapped with 1 3 40 D) 1 200 D HPPE filament

210 260

270 340

DTY, Denier textured yarn; TDM, Tomodynamometer.

is as high as 15 W/(m K), while that of para-aramid fiber is 0.04 W/(m K) as a contrast. The heat can be conducted away more quickly by HPPE fiber, and therefore the fiber is felt cool, while para-aramid is felt warm, therefore HPPE is better suited for summer wearing, and para-aramid is better for winter or in freezing environments (such as in meat cutting process workshop where low temperature is needed to keep meat fresh). The melting point of HPPE fiber is 135 C 145 C, which makes its heat resistance much poorer than para-aramid fiber. Though HPPE starts to melt above its melting point, its softening already starts before that. HPPE gloves are not recommended to be used for handling objects with a temperature higher than 80 C. Also due to its melting, it is not recommended to use HPPE in an environment where there are sparks such as welding. The sparks can easily melt the spot on HPPE fabric where the sparks hit. HPPE is not flame resistant. Excellent chemical resistance of HPPE fibers allows broad selection for detergent and bleaching agent for laundering, which is not the case for para-aramid fiber. HPPE fiber is very hydrophobic, and therefore its moisture absorption is extremely low, and its performance is not affected by water.

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Change in color and strength of HPPE fiber after being exposed to light is much lower than that of para-aramid fiber; therefore HPPE fiber is very good for outdoor application. Interestingly, some studies reported that the cut resistance of HPPE is not influenced by its tenacity and modulus.222 Cut resistance of HPPE fiber according to ISO13997 (or ASTM F2992-15) is generally lower than para-aramid fiber by 10% 20%. The cut force of HPPE fiber per gsm is about 1.4 1.6 gf per ISO13997 (or ASTM F2992-15), as a contrast to para-aramid’s 1.7 1.9 g cut force per gsm as mentioned earlier. That means, a 100 gsm pure HPPE fabric will show a cut force of 140 160 g. In a fabric with HPPE and other fibers, such as DTY and/or spandex, the cut force depends upon the weight percentages of different fibers. Usually, a commercially available fabric in the market with HPPE fiber and without other high cut resistance fibers contributes B1.0 1.1 g cut force per gsm because of the presence of other materials of lower cut resistance, such as spandex and DTY. As mentioned previously, the Coupe test in EN388 used to be widely accepted worldwide and still retains strong influence today. Glass fiber performs very well in Coupe testing due to its abrasiveness. If a 13-gauge glove contains one end of 100 D glass fiber, it easily achieves level 5 in the Coupe test. The main reason is that glass fiber dulls the cutting blade very quickly then the dulling makes it difficult to cut through the fabric. But before the fabric is cut through, the testing continues and the blade becomes duller, in turn it is even more difficult for the increasingly duller blade to cut through the fabric. This kind of vicious cycle artificially boosts the cut resistance performance test result. This is the main reason for the vast majority of 13-gauge fabrics with cut resistance of Coupe level 5 containing glass fiber in conjunction with its very low cost. Most people claim HPPE fiber gloves with level 5 cut resistance, but actually it is because of the glass fiber. An English company called PPSS claims its high cut-resistant garment CutPRO is made of a composite of HPPE fiber223 but should be more clearly communicated as a composite of HPPE and glass fibers. After revision of EN388 in 2016 the testing results of glass fiber containing fabrics easily meet the criteria of blade dulling defined in the new EN388:2016 standard; therefore the cut levels of these kinds of fabrics will very likely need to be redefined. There are a number of HPPE fiber manufacturers in China. The cut resistance of these Chinese HPPE fibers is very close to DSM’s Dyneema fiber, but their prices are much lower than Dyneema fiber. In order to improve differentiation, DSM developed the Dyneema Diamond Technology in 2006. Dyneema Diamond Technology is actually HPPE filled with a micro-sized, cut-resistant hard inorganic filler; therefore it can be viewed as a composite instead of pure HPPE. The morphology of the fiber by Dyneema Diamond Technology is schematically shown in Fig. 5.29.224 According to the patents filed by DSM, the filler should be RB215-Roxul-1000 or a filler of the same material but with a different length,225 227 a mineral fiber produced by Lapinus, an Italian company.228 The average fiber length of RB215 is 150 μm. There are shorter products in Lapinus portfolio, RB250, RB271, and RB295, with an average length of 125 μm.

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Cut-resistant microparticles protect the fiber

Unique polymer providing high strength, cool-touch comfort, and maximum durability

Figure 5.29 Illustration of microscopic structure of fiber based on the Dyneema Diamond Technology. Source: Courtesy DSM. Dyneemas Diamond Technology. Technical Brochure of DSM. Table 5.5 Cut resistance performance of protective products with Dyneema Diamond Technology. Manufacturer

Product

Gauge

Cut level rating (ANSI/ISEA105-16)

MCR Safety MCR Safety MCR Safety MCR Safety MCR Safety Ansell Juba Radians Safety

Cut Pro 9672 glove Cut Pro 9672 glove Ninja N9676DT glove Cut Pro 9318DT10 sleeve Cut Pro 97080 glove Hyflex 11-518 glove DY008B RWGD104

13 13 15 10 18 18 15 13

A4 A3 A3 A4 A2 A2 A3 A4

Because of the presence of the inorganic cut resistance filler, the cut resistance of fiber with Dyneema Diamond Technology is improved significantly versus regular HPPE fiber. According to DSM’s public information the cut resistance of Dyeema Diamond Technology offers a 200% improvement in cut resistance versus regular Dyneema fiber.229 If evaluated by EN388 Coupe test, a 13-gauge glove made of yarn of Dyneema Diamond Technology can achieve a level 4, and sometimes even a level 5 by some external testing parties, while similar constructions of knit fabric with regular HPPE fiber can only achieve Coupe level 2 or 3. Some companies have already started to use HPPE fiber of Dyneema Diamond Technology to make cut-resistant gloves, such as Cut Pro 9672 glove,230 Ninja N9676DT glove,231 and Cut Pro 10-gauge 9318DT10 sleeve by MCR Safety,232 Hyflex 11-518 by Ansell,233 DY008B by JUBA,234 and Axis D2 RWGD104 by Radians.235 The cut resistance performance of these products is summarized in Table 5.5. These gloves are all palm coated (dipped) with acrylonitrile-butadiene rubber (NBR) or polyurethane (PU). But usually the palm coating does not offer step change in cut resistance level.

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Adding filler makes the fiber spinning more difficult. Superdrawing is critical to achieving a very high degree of orientation and high crystallinity, which enable the high modulus and high tenacity of HPPE fiber. But after inorganic fiber is added, the superdrawing is much more difficult, and the spinnability is detrimentally affected. The fiber’s tenacity is reduced by more than 50%.225 A couple of other HPPE manufacturers have been developing their own versions of diamond yarn. A company in China called Jonnyma213 published a patent on HPPE yarn filled with silicone carbide (SiC).236,237 Another company in China called Tong Yi Zhong (TYZ)210 also published some patents on the similar subject.238 240 As a matter of fact, it is not a new idea to use hard filler to fill thermoplastic fiber to improve cut resistance. In the 1990s Hoechst Celanese241 filed patents on using inorganic fillers or fibers to fill fiber to improve cut resistance.242 248 In these patents, tungsten and aluminum oxide were specifically mentioned, which improved the cut resistance by up to more than 300% based on a specific cut testing. Some of the data are shown in Table 5.6 and more can be found in Appendix B. These data are based on polyester fiber matrix. In these patents filed by Sandor and his coworkers, a set of data was also disclosed about alumina filled aramid fiber (see Table 5.7). The cut resistance was improved by 110% in the presence of alumina in para-aramid fiber based on a specific cut testing. Another patent also disclosed the addition of alumina into para-aramid fiber to improve cut resistance.249 With 0.5% by weight of alumina in the fiber, the cut resistance was improved by 15% without sacrificing the tenacity. In some cases, para-aramid and HPPE fibers are blended in use. A preferred practice is double-layer knitting by knitting HPPE fiber as the inside layer and para-aramid fiber as the outside layer. Having HPPE fiber as the inside layer allows it to contact body to create a cool feeling, while having para-aramid fiber as the outside layer allows the fabric to insulate the worker from an external thermal threat and offers flame resistance and spark resistance as well as good grip.250 Besides gel and melt spinning, there is another type of HPPE fiber manufacturing technology called solid-state extrusion (SSE). This technology was developed by a few academic researchers in the 1970s.251 256 In 1986 Nippon Oil Company (NOC) started developing SSE technology257 260 and set up a pilot line after 8 years of development effort. Afterward NOC sold this product under the brand name of Milite through its subsidiary Nippon Petrochemicals for a very short time. In 1999 Nippon Petrochemicals licensed this technology to Synthetic Industries in the United States; Synthetic Industries and Integrated Textile Systems (ITS) jointly used this technology to manufacture products that were branded as Tensylon to the market. Afterward, Synthetic Industries withdrew completely from this joint venture, and ITS owned this company. In 2006 Armor Holdings in the United States acquired ITS261 followed by that Armor Holdings was acquired by BAE Systems in 2007.262 In 2012 DuPont acquired Tensylon from BAE Systems.263,264 Now Tensylon is a brand owned by DuPont, and the products are manufactured and sold by DuPont.265

Table 5.6 Selected cut resistance data reported in patents.242 Example

Filler type

2 3 5 16 25 37 55

None None Tungsten Alumina Tungsten Tungsten Alumina

Filler size (µm) 0 0 1 1 0.6 0.6 0.6

248

(The fiber matrix is polyester.)

Filler weight percentage

Fiber linear density (D)

Basis weight (OSY)

CPP (gf)

CPP /Basis weight (gf/OSY)

Improvement (vs similar basis weight) (%)

0 0 1 1.9 11.03 11.03 6.82

5 5 5.6 5.6 10 1.4 4

6.8 13 7.3 6.7 6.8 7 13

384 589 565 478 621 580 818

56.5 45.3 77.4 71.3 91.3 82.9 62.9

37 26 61 47 39

CPP, Cut protective performance; OSY, ounce/yard2.

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Table 5.7 Cut resistance data for aramid fiber filled with alumina. Example

Basis weight (OSY)

CPP (gf)

CPP/basis weight (gf/OSY)

Improvement (%)

Unfilled aramid Aramid filled with alumina

3.7 4.6

379 951

102 205

101

CPP, Cut protective performance. Source: Sandor RB, Carter MC et al. Cut-Resistant Fiber Containing a Hard Filler, US Patent 5,851,668. Hoechst Celanese Corp; 1996. Table 8.

Figure 5.30 Schematic diagram of HPPE solid-state extrusion process. HPPE, Highperformance polyethylene. Source: Modified from Mather RR, Wardman RH. The Chemistry of Textile Fibres. 2nd ed. Cambridge: Royal Society of Chemistry; 2015:203.

SSE technology is completely different from gel spinning. SSE does not use solvent or any other processing additives but compresses UHMWPE powder below its melting point to form film that is afterward superdrawn below its melting point. The superdrawn film is then split to appropriate width to form tape or even fiber. Dingnen,191 Mather et al.,266 and Wedon267 described this process as schematically shown in Fig. 5.30. UHMWPE powder is first compressed below its melting point between a pair of moving steel belts followed by passing through a pair of heated rolls to further compress to form a film. The film thickness after these two steps is about one-seventh of the original powder layer. The compressed film is then superdrawn below UHMWPE’s melting point. However, in this description, there is no extrusion but only compression, it is not a full description of this SSE process.

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Figure 5.31 Illustration of solid-state extrusion process. Source: From Mark HF, ed. Solid state extrusion. In: Encyclopedia of Polymer Science and Technology. 3rd ed. Vol 11. Wiley-Interscience; 2004:852.

The SSE actually includes an essential step of extrusion of polymer powder below its melting point.268 273 This SSE is performed by extruding the polymer under pressure through a conical die just below the polymer’s melting point followed by ultradrawing. The extrusion process is illustrated in Fig. 5.31. In this extrusion process the draw ratio plays a very critical role to increasing the material’s strength and modulus in addition to the molecular weight of the polymer. With high-density PE, the modulus could go up close to 230 GPa and the tensile strength close to 6 GPa as shown in Fig. 5.32.271 However, how the SSE process became a compression process? Nippon Oil’s patent revealed the answer. After studying the real SSE process and having filed some patents,257 259 Kobayashi et al. discovered a new process by applying compression pressure on UHMWPE powder followed by ultradrawing.260 This process is illustrated in Fig. 5.33. The example in this patent achieved a tensile modulus of 130 GPa and a tensile strength of 3.4 GPa from a UHMWPE of about 2,000,000 pressed at 130 C 140 C and drawn at a ratio of 20 at 135 C. I would rather call this process as solid-state compression instead of SSE. The cut resistance of UHMWPE tape product appeared having much higher than aramid and gel-spun UHMWPE fiber. Table 5.8 shows the comparison of

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Figure 5.32 Effect of molecular weight and draw ratio on the tensile properties of HDPE film. HDPE, High-density polyethylene. Source: From Porter RS, Wang LH. Uniaxial extension and order development in flexible chain polymers. J Macro Sci, C: Rev Macromol Chem Phys. 1995;C35(1):63 115. doi:10.1080/15321799508014590.

cut resistance between Kevlar and Tensylon.274 The improvement of Tensylon versus Kevlar KM2 is more than 200%. Kevlar KM2 is a ballistic grade PPTA fiber from DuPont, but its mechanical properties are not available in the public. Besides DuPont, another aramid manufacturer called Teijin Aramid also manufactures this kind of UHMWPE tape with SSE technology. Teijin Aramid commercialized its UHMWPE tape product branded as Endumax in 2012.275 Its tenacity is between 23 and 25 gf/den (2.2 2.4 GPa) and modulus between 1947 gf/den, and 2129 gf/den (189 207 GPa).276 Its tenacity is at the same level of PPTA fiber, but the modulus is significantly higher. DSM also offers similar product called Dyneema tape, but there are no data available in the public.277

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Figure 5.33 Process disclosed by Nippon Oil. (1 4—Rollers, 5 and 6—Endless belts, 7—Platens, 8—Rollers, 9—Chains, 10—Sprockets; 12—Preheater; 14—Feeder.) Source: Modified from Kobayashi S, Mizoe T, Iwanami Y. Continuous Production Process of High Strength and High Modulus Polyolefin Material, Patent US5,091,133. Nippon Oil; 1989.

Table 5.8 Cut resistance of Tensylon compared with Kevlar KM2. Material

Basis weight (gsm)

Cutting force per CPPT method (gf)

Cutting force/basis weight (gf/gsm)

Kevlar KM2 woven fabric Kevlar KM2 woven fabric Tensylon SSE UHMWPE, woven fabric

129 159 146

329 325 702

2.55 2.04 4.81

CPPT, Cut protective performance test; SSE, Solid-state extrusion; UHMWPE, ultrahigh molecular weight polyethylene. Source: Modified from Singletary J, Lauke B. Structure of SSE-PE. In: Chen X, ed. Advanced Fibrous Composite Materials for Ballistic Protection. Cambridge: Woodhead Publishing; 2016:403 [Chapter 13.2.6].

5.2.3 Glass fiber Glass fiber is also often called fiberglass, and they mean the same.278 Glass fiber has been widely used, mainly in the composite industry, for its cost-effectiveness and good performance. As early as the 18th century, Europeans already realized that glass could be spun into fibers that can be woven. There were already decorative fabrics made of glass fiber in the coffin of the French Emperor Napoleon. There are both filament and staple or floc of glass fiber. The glass filaments are usually used in the composites, rubber goods, conveyor belts, tarpaulin, etc. Short fiber is mainly used in nonwoven felt, engineering plastics, and composites. The spinning of glass filament is shown in Fig. 5.34, including steps of weighing, melting, spinning, finishing, and winding. Usually, light denier glass fibers, from 50 to 200 D in multifilament form, are used in cut-resistant textiles, especially cut protective gloves. The multifilament

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Figure 5.34 Schematic diagram of glass fiber spinning.

consists of many ends of very fine single end filaments. Glass fiber cannot be used for gloves alone because of its abrasiveness and irritation against the skin. Glass fiber often creates strong irritation against and generates severe rashes on skin, which sometimes can lead to wide festering wounds. Therefore glass fiber usually needs to be well wrapped in other nonirritating fibers, such as nylon or polyester DTY.279 286 The most commonly seen wrap construction for glass fiber is double-layer wrapping by two ends of DTY, one end for each layer wrapped in sequence in the opposite direction. For instance, one end of 100 D glass fiber is wrapped with one end 70 D nylon DTY in the Z direction first, then wrapped with another 70 D nylon DTY in the S direction, as a result the glass fiber can be almost fully covered in two-layer wrapping yarns so that it does not get exposed and contact the skin. The wrapped yarn is then wrapped again with or cofed together with other fiber such as para-aramid yarn.287 But even done like this, sometimes there are still not well covered yarns that are not well covered, and therefore exposed the glass fiber gets exposed in the yarn. Sometimes the glass fiber breaks in use due to its brittleness, and the broken end protrudes through the wrapping layer and contacts with skin. Some people have made attempts to coextrude glass fiber with thermoplastic polymer. The coextruded fiber has a core sheath structure in which glass fiber is the core. This glass core sheath fiber is further wrapped with a wrap yarn in order to fully cover the glass fiber. By doing this the exposure of glass fiber may be eliminated.288 But this technology is seemingly not commercialized.

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Figure 5.35 New fiberglass containing cut-resistant sleeve: photomicrographs showing glass fiber protruding. (A) Wrist seam of a new sleeve and (B) body of a new sleeve. Source: From Tapp L, Ceballos D, Wiegand D. Evaluation of cut-resistant sleeves and fiber glass fiber shedding at a steel mill. In: Health Hazard Evaluation Program. Report No. 20110113-3179. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health; 2013. ,https://www.cdc. gov/niosh/hhe/reports/pdfs/2011-0113-3179.pdf..

An investigation by Occupational Safety and Health Administration showed that the glass fiber protruded from both the outside and inside of the sleeve as shown in Fig. 5.35.289 In laundered sleeve, similar phenomenon was also observed (Fig. 5.36). In the same investigation, lots of broken glass ends were identified on

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Figure 5.36 Laundered fiberglass containing cut-resistant sleeve: photomicrographs showing glass fiber protruding. (A) Wrist seam of a laundered sleeve and (B) body of a laundered sleeve. Source: From Tapp L, Ceballos D, Wiegand D. Evaluation of cut-resistant sleeves and fiber glass fiber shedding at a steel mill. In: Health Hazard Evaluation Program. Report No. 20110113-3179. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health; 2013. ,https://www.cdc. gov/niosh/hhe/reports/pdfs/2011-0113-3179.pdf..

the surfaces of the sleeves and on some surfaces that contacted with the sleeve. This investigation proves that glass fiber can still easily get out of the wrapped composite yarn. This does pose irritation risk to the wearers; therefore the use of glass fiber has to be seriously evaluated.

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There is no doubt that glass fiber improves cut resistance versus organic fibers. It has been repeatedly stated that a 13-gauge glove knit with one end wrapped 100 D glass fiber together with other fiber, such as one end 400 D HPPE can undoubtedly achieve Coupe cut level 5 per the old EN388:2003 method. Tested according to ISO13997 (or ASTM F2992-15), the cut force of 100% glass fiber is higher than that of para-aramid fiber of equal weight by about 200% (in other words, is three times of that of para-aramid fiber). The cut force generally follows the rule of addition when materials are blended for use. For instance, if one end of 400 D para-aramid fiber and one end of 100 D glass fiber are used together, then the cut force of the fabric per gsm can be estimated as follows. Total linear density of yarn: 400 1 100 5 500 D Glass fiber’s weight percentage 5 400/500 5 80% para-Aramid’s weight percentage 5 100/500 5 20% Cut force 5 80% 3 1.75 gf/gsm 1 20% 3 (1.75 3 3) gf/gsm 5 2.45 gf/gsm

Therefore the cut force of the composite fabric is around 2.45 gf/gsm. However, a report revealed that there was a synergistic effect in fabric of glass fiber blended with other fiber.287 In other words the cut force of a blend fabric is higher than that from the rule of addition. Because of its high cut resistance and the dulling effect on the cutting blade, glass fiber easily enables a fabric to achieve Coupe cut level 5 according to the old version of EN388 (version 2003). HPPE fiber is very often used together with glass fiber in cut protective fabrics to achieve high cut levels, but this kind of composite fabric is often called HPPE fabric (or glove) without mentioning the glass fiber; therefore a misunderstanding has been created that HPPE can achieve Coupe cut level 5, which is, as a matter of fact, contributed by the glass fiber. Pure HPPE fiber alone is unable to achieve this level unless in a very heavy fabric. Because the glass fiber heavily dulls the cutting blades, it usually meets the criteria for dulling effect according to EN388:2016. With implementation of the new EN388:2016, the use of glass fiber might be affected. There is a large number of manufacturers of glass fiber, but the volumes are concentrated with a few giants, including AGY (Advanced Glass Yarn Co.),290 Nippon Electric Glass Co.,291 CPIC (Chongqing Polycomp International Co., China),292 Jushi Group,293 and Taishan Fiberglass Inc.294

5.2.4 Steel wire The steel manufacturing has had a very long history. Steel is an inorganic material. The steel wire is not made with the spinning process for organic fibers and for glass fiber, while it is made with a cold drawing process in which a steel ingot or a thick rod is drawn through a circular-shaped die of a high hardness mold that is thinner than the ingot.295 The steel deforms to smaller diameter under the pressure from the mold. By multiple steps of such cold drawing, the diameter of the wire is gradually reduced to desired level. This process is illustrated in Fig. 5.37.

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Figure 5.37 Steel wire cold drawing process. Source: Modified from Tucker KH. Wire drawing. In: Byers JP, ed. Metalworking Fluids. 3rd ed. Boca Raton, FL: CRC Press; 2017:115 [Chapter 5.3.5].

Steel wire exhibits very high cut resistance. A thicker steel wire exhibits higher cut resistance than a thinner steel wire of same quality even at equal basis weight. In some scenarios where the cut hazard is very high, such as butchery or meat processing factories, full steel wire mesh gloves, or called chainmail gloves, are required. The testing standard (ISO13998) and performance requirements (ISO13999-1) for chainmail products are discussed in Chapter 2, Evaluate cut resistance, Fig. 5.38 illustrates the use of chain mail glove. The steel chainmail gloves are not comfortable and not flexible and make hands too cold in cold weather or cold factories. Steel wire reinforced fiber can be used in textiles in work conditions where cut risk is not too high but glass fiber reinforced para-aramid or HPPE fiber or pure para-aramid or HPPE fiber is not protective enough. Usually steel wire is wrapped as core yarn with organic fiber as wrapping yarn, and the wrapped composite yarn is knit to form fabric, or steel wire wrapped yarn (steel wire as core) is knit together with spandex wrapped yarn.180,296 298 The earliest patent filed on the use of steel wire in cut protective textiles actually did not specify any wrapping on or core-spun with steel wire, but just mentioned the combination of steel with other fiber.299 Steel wire can also be used as wrapping yarn, not just core yarn. An example was disclosed that one end of steel wire wrapped onto an organic fiber (steel as wrap, organic fiber as core) first, then another end of organic fiber further wrapped onto the former wrapped yarn.300 This kind of construction is shown in Fig. 5.39. In cut protection application the steel wire is usually used in the form of single filament, not like the multifilaments of glass fiber and organic fibers. Most steel wires used in cut protection are in the diameter range of 20 60 μm, preferably in the range of 30 50 μm. The cut resistance force is highly dependent upon the wire diameter. Even with same weight of steel, the cut force of thicker wire (larger in diameter) is higher than that of thinner wire (smaller in diameter).

Figure 5.38 Cut protection with steel chainmail glove and apron. Source: Courtesy Birk Staal Denmark.

Figure 5.39 Steel wire as wrapping yarn. Source: Modified from Hummel J. Knittable Yarn and Safety Apparel, Patent US 6,279,305. Wells Lamont Industry Group; 1995.

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Steel wire can be covered by other fibers with core-spun or wrap structure. Steel wire surface is slippery; therefore the wrapping layer may slip on the surface, and then the wire is exposed if covering is achieved by wrapping. Steel does not irritate skin as seriously as the multifilament glass fiber so usually it does not affect the wearer if it gets exposed. However, if it is broken and the broken end protrudes to outside, the broken end may hurt the wearer or at least make the wearer uncomfortable. It is very rare to use HPPE fiber to wrap steel because HPPE fiber is also slippery and therefore can hardly hold onto the steel wire. A better practice is to use staple to cover steel wire with core-spun structure. Steel wire must possess a certain level of elasticity with break elongation higher than 10% for use in these composite yarns. Without adequate elasticity (or ductility), the steel wire will break during wrapping, core-spun spinning, knitting, or weaving, as well as wearing. A steel wire can achieve a relatively high elongation via an appropriate annealing process after cold drawing. Some examples of steel wire in cut protective gloves are listed as follows: Example 5.2.4-1: Use a 12 s/1 cotton staple spun yarn (Example 5.2.4-1 A) or a 400 D nylon textured yarn (Example 5.2.4-1B) to wrap a 50 μm steel wire, then knit a 13-gauge fabric together with a 70 D spandex wrapped with two ends 70 D nylon or polyester DTY. This fabric has a basis weight of about 400 gsm. Example 5.2.4-2: Use staple fiber (such as polyester, cotton, and para-aramid) to do core-spun to cover 50 μm steel wire to form a core-spun yarn with total yarn count of 12 s, then cofeed together with two ends of 20 s/2 to knit a 10-gauge fabric or glove. This knit fabric has a basis weight of about 450 550 gsm. Example 5.2.4-3: Use staple fiber (such as polyester, cotton, and para-aramid) to do core-spun to cover 50 μm steel wire to form a 12 s/1 core-spun yarn, then this yarn is twisted together with one end of 12 s/1 spun yarn without steel. Knit a 10-gauge fabric or fabric with this twisted yarn. The knit product has a basis weight of about 420 500 gsm. Example 5.2.4-4: Use staple fiber (such as polyester, cotton, para-aramid) to do core-spun to cover 50 μm steel to form a 12 s/1 core-spun yarn, then knit 13-gauge glove together with a 70 D spandex wrapped with two ends 70 D nylon or polyester DTY. The knit product has a basis weight of about 360 450 gsm. Example 5.2.4-5: Use staple fiber (such as polyester, cotton, and para-aramid) to do core-spun to cover 30 35 μm steel to form a 20 s/1 core-spun yarn, then knit 18-gauge glove together with a 40 D spandex wrapped with one end 70 D nylon or polyester DTY. The product has a basis weight of 270 300 gsm.301 These examples are summarized in Table 5.9.

Both the Coupe cut test and the Tomodynamometer (TDM) cut test use the conductivity of cutting blades to detect when the blade cuts through the fabric, and then the instruments automatically stop the cut. Because the steel wire is electrically conductive, if the cutting blade contacts the steel wire during testing while the fabric is not insulated, then the test will be automatically stopped and a false

Table 5.9 Constructions of knit fabrics with steel wire. Example

Fiber material

Gauge

Construction

Basis weight (gsm)

Estimated TDM cut force (gf)

5.2.4-1

Steel wire

13

A: 50 μm steel wrapped with 12 s/1 cotton spun yarn) 1 (70 D spandex wrapped with 2 3 70 D DTY B: 50 μm steel wrapped with 400 D nylon textured yarn) 1 (70 D spandex wrapped with 2 3 70 D DTY [12 s/1 core-spun (50 μm steel with para-aramid staple)] 1 (2 3 20 s/2 para-aramid spun yarn) [12 s/1 core-spun (50 μm steel with para-aramid staple)] 1 (1 3 12 s/2 para-aramid spun yarn) [12 s/1 core-spun (50 μm steel with para-aramid staple)] 1 (70 D spandex wrapped with 2 3 70 D DTY) [20 s/1 core-spun (35 μm steel with para-aramid staple)] 1 (40 D spandex wrapped with 1 3 70 D DTY)

A: 450 500

A: 1800 2500

B: 420 470

B: 1700 2400

450 550

2200 3000

420 500

2000 2700

360 450

1800 2400

270 300

1200 1700

5.2.2-2

Steel wire

10

5.2.2-3

Steel wire

10

5.2.2-4

Steel wire

13

5.2.2-5

Steel wire

18

DTY, Denier textured yarn; TDM, Tomodynamometer.

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cut-through is recorded, and wrong data are generated. Therefore great care must be exercised during cut testing on steel wire containing fabrics. An insulating layer needs to be added underneath the sample fabric, but the insulating layer should have minimal contribution to cut force, otherwise the cut resistance will be incorrectly higher than it ought to be. According to the descriptions in the testing standards EN388 and ISO13997, an insulating thin filter paper or plastic film can be used. Or a thin weighing paper, commonly available in many labs, can also be used. It is of great interest to take a deeper look into steel wire’s performance tested according to the EN388 Coupe test. Steel wire also dulls cutting blades. Because the cut index is calculated with the following equation (same as Eq. 2.3): in 5

C n 1 Tn Tn 511 Cn Cn

(5.1)

A change in either Tn or ̅C n will change the result in . When the dulling effect is very significant, the increase in ̅C n is possibly higher than that in Tn, as a result in decreases. But with the implementation of EN388-2016, in such event of heavy dulling, ISO13997 TDM cutting should be used as a reference method. However, the new standard EN388:2016 also states that the Coupe cut testing could still be done on request, this makes situation complicated. In the new standard the Coupe cut only lasts until 60 cycles, then it should be manually stopped though the fabric is not cut through yet. If the Coupe cut index is still needed, then this number 60 is used as Tn to do calculation. But in the spirit of Coupe cut testing, Tn should be the number of cycles when the sample is cut through, not a number at which the fabric is NOT cut through. In other words, Tn should be .60, but as the test is manually stopped, and no data are available for calculation, then 60 is taken to do the calculation. This is not scientific at all. The test is stopped at 60 cycles, then the cut-through number of cycles is unknown, may be slightly higher than 60, may be a few folds of 60; therefore the real in may be very different. Using 60 to replace an unknown number as Tn to do calculation is totally wrong. But nonetheless, this is still a good news for steel wire, because steel wire performs better than glass fiber in the TDM cut testing per ISO13997 or ANSI/ISEA 105-16 but usually performs poorer than glass in the Coupe cut testing as discussed in Section 2.16. Some people have also attempted to develop products containing both steel wire and glass fiber.297,302 Popular steel wires used in cut protective products are AISI/ASTM 304, 304L, 316, and 316L grades stainless steel. Not all wire properties are readily available in public. The wire properties heavily depend upon the drawing process conditions. Steel manufacturing has been a very classical industry, and therefore there are a large number of suppliers in the market. Some spinning factories even do steel wire cold drawing and annealing by themselves.

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5.2.5 Nylon fiber Nylon is also called polyamide. The most commonly used nylon fiber in cut protective textiles is nylon 66, followed by nylon 6.303,304 The overall performance of nylon 66 fiber is better than nylon 6 fiber. Nylon 66’s melting point is B260 C, versus B215 C for nylon 6. The specific gravity of nylon 6 is 1.13, while it is 1.14 for nylon 66. Nylon fibers are spun with melt spinning process. Nylon fiber was invented by the research group led by the famous scientist Dr. Wallace Carothers in DuPont in 1930. This research group spun the historic world’s first nylon 6 fiber with high molecular weight in 1934.305 In the next year, this group succeeded in spinning nylon 66 fiber.306 Fig. 5.40 shows the different chemical structures of nylon 66 and 6. The cut resistance force of nylon fiber is not high. Nylon 66’s average cut force per gsm is 1.0 1.2 gf (ISO13997 or ASTM F2992-15). If a 7-gauge glove of nylon 66 fiber has a basis weight of 600 gsm, then its cut force is 600 700 gf, rated as level A2 per ANSI/ISEA 105-2016, or level B per ISO13997. Fabrics with 100% pure nylon fiber can only be used at places where cut risk is not high. Nylon fibers are often used as the wrapping yarns in the form of textured yarn or sheath in corespun yarns on other cut-resistant fibers, or simply cofed with other fibers to knit. Both nylon staple spun yarn and filament yarn are used in cut protective application. Filament yarn is usually used in the form of textured yarn. Some practical examples are given below. Example 5.2.5-1: 100% nylon 66 textured yarn for knitting A percentage of 100 pure nylon 66 DTY is usually used in knitting 13 18-gauge fabric. The use of pure textured yarn can replace spandex in many cases, but good elasticity can still be achieved. The fabrics knit with pure nylon 66 textured yarn are very soft, smooth, and therefore comfortable and can be used in low cut risk scenarios. A typical example: two ends of 420 D nylon 66 DTY are knit to 13-gauge (Example 5.2.5-1A), or two ends of 300 D nylon DTY are knit to 15-gauge (Example 5.2.5-1B), or one end 300 D is knit to 18-gauge (Example 5.2.5C). Example 5.2.5-2: Wrap yarn with nylon 66 textured yarn Nylon textured yarn can be used to wrap other core yarn such as spandex or glass fiber. The textured yarn is smooth and easily slips on steel wire surface and can leave

Figure 5.40 Chemical structures of nylon 66 and nylon 6.

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steel wire exposed; therefore nylon/steel wrap yarn is not an ideal structure. Spandex or glass fiber wrapped with nylon textured yarn is very commonly seen in the market. For instance, one end 70 D spandex is wrapped with one or two ends of 70 DTY with a stretch ratio of 2.4 2.5 for spandex. The wrapped yarn can be directly used in knitting. If glass fiber is wrapped with the textured yarn, then the wrapped yarn will lose elasticity, so the wrapped yarn needs to be knit together with elastic yarn, such as textured yarn or spandex, if elasticity is needed for the textile product. A practical example: one end of 100 D glass fiber is wrapped with one end 70 D nylon 66 textured yarn in Z direction first, then wrapped with another end of 70 D nylon in S direction. The double-layer wrapped glass fiber is knit to a 13-gauge fabric together with one end of 400 D HPPE yarn, and one end of 70 D spandex is wrapped with two ends of 70 D nylon 66 textured yarn. There are two common technologies to make wrapped spandex with textured yarn. One is the abovementioned wrapping on ring twisters. The other technology is wrapping during the air-texturing process, also called air-covering process and the product is called air covered yarn. Example 5.2.5-3: Cofeed nylon DTY with other yarn Nylon textured yarn can be used to replace spandex and cofed with other fiber in knitting. But the elasticity of textured yarn is not as good as spandex; therefore replacing spandex with nylon textured yarn is limited to some cases only. When the elasticity requirement is not very high, for example, a10-gauge glove can be knit with two ends of 600 D HPPE filament yarn and one end of 210 D (or three ends of 70 D) textured yarn together (Example 5.2.5-3A), or an 18-gauge glove can be knit together with one end of 200 D HPPE filament yarn and one end of 70 D nylon 66 textured yarn. Nylon textured yarn can also be used as filler yarn to knit together with other yarn when the total linear density is not sufficient for effective knitting. For instance, the total linear density of one end of 70 D spandex wrapped with two ends of 70 DTY, and one end of 400 D para-aramid fiber is not heavy enough for 13-gauge knitting, then one end of 210 D (or three ends of 70 D) nylon 66 textured yarn can be used as filler yarn to help improve the efficiency of the knitting process. Example 5.2.5-4: Nylon staple spun yarn 51 mm (2 in.) nylon staple can be spun into spun yarn of various yarn counts, or nylon staple can be blended with other types of staple fibers to make a blended spun yarn. These constructions are tabulated in Table 5.10.

Nylon fibers possess outstanding abrasion resistance, and nylon 66 is better than nylon 6 in abrasion resistance. A 13-gauge glove with nylon 66 without palm coating (or dipping) can get close to the abrasion resistance level 4 according to EN388 and easily achieves level 4 with additional coating. Nylon fiber can be blended with para-aramid fiber, and the resultant blend fiber exhibits much better abrasion resistance than pure 100% para-aramid fiber.307 Nylon fiber absorbs a certain level of moisture, and its commercial moisture regain is 4.5%.308

5.2.6 Polyester fiber Polyester is a family of materials.309,310 Dr. Wallace Carothers in DuPont spun the world’s first polyester fiber in his lab in 1930.311 But his initial fiber’s melting point

Table 5.10 Constructions of knit fabrics with nylon yarn. Example

Fiber material

Gauge

Construction

Basis weight (gsm)

Estimated TDM cut force (gf)

5.2.5-1

Nylon 66 textured yarn

5.2.5-2

Nylon 66 textured yarn

A: 13 B: 15 C: 18 13

300 250 200 380

300 250 220 500

5.2.5-3

Nylon 66 textured yarn

A: 2 3 420 D DTY B: 2 3 300 D DTY C: 1 3 300 D DTY Cofeed: End 1: 100 D glass wrapped with 2 3 70 D nylon 66 End 2: 400 D HPPE End 3: 70 D spandex wrapped with 2 3 70 D nylon 66 A. Cofeed: End 1: 2 3 600 D HPPE filament End 2: 3 3 70 D nylon 66 B. Cofeed: End 1: 200 D HPPE filament End 2: 70 D nylon 66

A: 10 B: 18

DTY, Denier textured yarn; HPPE, high-performance polyethylene; TDM, Tomodynamometer.

350 300 250 450

A: 450 550 B: 200 250

400 320 270 600

A: 580 750 B: 250 300

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was low, and its mechanical properties were not good enough and not durable enough for practical use, then it was abandoned. In 1941 two British researchers Whinfield and Dickson developed polyester material based on terephthalate ester.312 This discovery covered today’s commonly used polyesters, including PE terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT). The terephthalate-type polyesters possess higher melting point and better mechanical properties and exhibited more practical value. PET fiber was put into mass production in 1946 by Imperial Chemical Industries (ICI)313 and branded as Teleron. Later DuPont purchased one of ICI’s patents in 1949. DuPont started to manufacture PET fiber and put it into market under the famous brand name of Dacron in 1951. In textiles field, PET is the most commonly used in the family of polyesters. Usually people refer to PET when they mention polyester fiber without mentioning the specific name. PET’s chemical structure is shown in Fig. 5.41A. Its melting point is about 260 C, and its specific gravity 1.38 g/cc. PET fiber is spun with melt spinning. The use of polyester fiber is almost exactly same as that of nylon fiber. It can be made to textured yarn, and the textured yarn can be used alone and can also be used as wrapping yarn to wrap other fiber, or its staple can be spun to spun yarn

Figure 5.41 Chemical structures of different polyesters: (A) PET, (B) PTT, and (C) PBT. PBT, Polybutylene terephthalate; PET, polyethylene terephthalate; PTT, polytrimethylene terephthalate.

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(spun alone or blended with other fibers). PET fiber’s abrasion resistance is much lower than nylon 66 but is still much better than para-aramid fiber. Greige 13gauge gloves with pure PET fiber can achieve abrasion resistance level 3 according to EN388. The cost of PET fiber is much lower than nylon 66. Though their prices fluctuate every day, usually PET fiber’s price is only half, or even only one-third of nylon 66 fiber. Among different textured yarns, nylon 66 is the most commonly used fiber used in cut protective textiles, but since PET fiber is much cheaper, it is also commonly used in areas where the overall performance requirement is not very high. The cut resistance of PET fiber is similar to that of nylon, also in the range of 1.0 1.2 gf/gsm. Polyester hardly absorbs moisture. Its commercial moisture regain is only 0.4%.308 Similar to nylon, PET fiber is also melt spun. Another polyester fiber, PTT fiber, has attracted much attention in the past decades. PTT’s full name is polytrimethylene terephthalate. Its chemical structure is shown in Fig. 5.41B. From the structure, one can immediately identify that PTT has one more CH2 group than PET. First, synthesis of PTT was reported in the patent by Whinfield and Dickson in the patent disclosing terephthalic ester based polyester in 1941.312 Historically, the manufacturing and use of PTT was restricted due to its very high cost caused by the very expensive process of making trimethylene glycol (HO (CH2)3 OH). But with discovered more cost-effective process, PTT’s cost was gradually reduced. It was not commercially available until 1998 after Shell Oil Co. developed a cost-effective process and commercialized the product under the brand name Corterra. DuPont invented a fermentation process to make trimethylene glycol out of corn starch and has then manufactured PTT polymer branded as Sorona.314 PTT fiber is also melt spun. Although the difference in chemical structure between PTT and PET is only one that PTT has one more CH2 group, this one additional CH2 creates large differences in properties between them. PTT crystallizes much faster than PET, and its melting point is 227 C, lower than that of PET. Its specific gravity is 1.35 g/cc, also slightly lower than that of PET. PTT is very soft and comfortable, much softer than PET, good for clothing-type applications. Research of Ward et al results showed that PTT exhibits much better elastic recovery after being strained than both PET and PBT,315 and this is supported by a recent research by Chen et al.316 and DuPont’s statement.317 PTT’s elastic recovery is even much better than nylon 66. PTT also exhibits better UV and chlorine resistance than nylon 66. PTT is a very good candidate for making elastic bicomponent yarn with a different component, such as PET, by leveraging the differential thermal shrinkage between them. Lycra T400 is a typical bicomponent yarn of PTT/PET that forms coils due to the thermal shrinkage.318 The industry also calls this a kind of self-crimped yarn.319 322 DuPont sells PTT resin to downstream spinner and licenses Sorona brand to its downstream value partner to use in the fiber. Shell Oil used to manufacture and sell PTT fiber with the brand name Corterra but has stopped since 2010. PBT is also a result of the invention by Whinfield and Dickson.312 Its chemical structure is shown in Fig. 5.41C. It has one more CH2 group than PTT.

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Table 5.11 Typical properties of polyester fibers and nylon 66 fiber used in apparel textile.304,309,315,316

Melting point ( C) Specific gravity (g/cc) Tenaciy (cN/dtex) Modulus (cN/dtex) Break elongation (%) Instantaneous elastic recovery at 20% strain (%)

PET (2GT)

PTT (3GT)

PBT (4GT)

Nylon 66

260 1.38 B5.5 B65 B25 B38

227 1.35 B3 B20 B40 B87

223 1.34 B3 B27 26 B75

265C 1.14 B6 B35 B30 B60

PBT, Polybutylene terephthalate; PET, polyethylene terephthalate; PTT, polytrimethylene terephthalate.

Figure 5.42 Molecular structure of Vectra polymer.

Because PET, PTT, and PTT are all based on terephthalates of different glycols, with PET having two methylene groups ( CH2 group) in its glycol, PTT having three, and PBT having four, they are also called 2GT, 3GT, and 4GT, respectively. PBT’s melting point is 223 C. PBT fiber is also melt spun. Its mechanical properties are close to PTT but are cheaper than PTT. Its elastic recovery is better than PET but poorer than PTT. It is also commonly used in making bicomponent yarn with PET.323,324 The basic properties of these polyester fibers are listed in Table 5.11 together with nylon 66 fiber. There is no publicly available cut resistance data for PBT and PTT as they are not broadly used yet, but one would expect a similar cut resistance performance to that of PET. The way to use polyester fibers in cut protective application is generally very similar to that of nylon fibers. The wholly aromatic polyester is also an important polyester material. It is discussed in the next section.

5.2.7 Wholly aromatic polyester fiber The wholly aromatic polyester is also called polyarylate.325 The most representative example, if not the only, of the polyarylate fiber is Vectran fiber manufactured by Kuraray326 in Japan. Its chemical structure is shown in Fig. 5.42. It possesses the

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characteristic of thermotropic liquid crystalline and is a member of the liquid crystalline polymer (LCP) family. Vectran fiber was originally developed by Celanese in the 1970s.327,328 Later, Celanese licensed this technology to Kuraray to further develop, and the manufacturing by Kuraray was started in 1990. Kuraray acquired all the rights of Vectran from Celanese in 2005.329 Celanese still keeps manufacturing and selling the resin, not the fiber, and has marketed the resin under the brand name of Vectra in its LCP product portfolio.330 Vectran fiber possesses high tenacity, high heat resistance, high abrasion resistance, and high cut resistance. Its tenacity is even slightly higher than general grades of para-aramid fiber. Its modulus is at the same level as that of para-aramid. Its highly oriented molecular structure and high crystallization contribute to its high tenacity and modulus. Its thermotropic liquid crystalline characteristic allows the molecules to achieve almost completely extended structure within a proper temperature range during spinning, and this highly extended structure is retained after spinning; therefore a very high tenacity and high modulus are achieved. Though normal polyesters such as PET can also form oriented structures, their molecular chains are still folded, and thus they cannot achieve similar high tenacity levels. These two different orientation configurations are shown in Fig. 5.43. The physical properties of this kind of fibers are listed in Table 5.12. Thanks to its excellent properties, Vectran fiber was used in the airbag fabric used in rover landings on Mars.331 The single filament form of Vectran is usually thick, B5.5 dtex (B5.0 D) per filament332 that makes the fiber felt stiff and not very comfortable. As a comparison, usually para-aramid fiber’s single filament product is 1.5 D per filament. A research revealed that this kind of LCP fiber also shows skin-core morphology as shown in Fig. 5.44 and fibrillates under abrasion.333 However, it exhibits superior abrasion resistance to para-aramid and poly-p-phenylene benzobisoxazole (PBO) fibers by at least one order of magnitude. Table 5.13 summarizes the comparison in abrasion resistance among liquid crystalline polyester fiber, para-aramid, and HPPE fibers per testing standard CI-1503,334 a standard developed by the Cordage Institute. These data clearly show that Vectran fiber is the best among these materials in dry abrasion, even better than HPPE fiber.335 In general, the abrasion resistance of organic fibers is in the order of Vectran .HPPE . nylon 66 . PET . para-aramid . cotton. Though it fibrillates, Vectran fibrillation is much slower than para-aramid, and the number of fibrils is much less, attributed to its superior abrasion resistance. Its heavy denier per single filament may play a role in this good abrasion resistance as demonstrated in Fig. 5.45.336 Its excellent abrasion resistance may also be attributed to its special finish336 and high finish level on the surface, generally .4.0%.325 Vectran fiber’s cut resistance is claimed to be higher than para-aramid.336,337 In a test developed by Kuraray, Vectran fiber exhibited a cut resistance higher than para-aramid fiber by 35%.336 In another Kuraray test named Sintech cut testing, a regular type of Vectran fiber exhibited higher cut resistance than para-aramid fiber by 100%, and a high tenacity Vectran fiber higher than para-aramid fiber by more than 200%.336 But these in-house testing methods are not used by others, and it is

Figure 5.43 Schematic diagram of microorientation structures of liquid crystalline polyester and normal polyester fibers. Source: From Beers D. Melt-spun wholly aromatic polyester. In: Hearle JWS, ed. HighPerformance Fibres. Cambridge, England: Woodhead Publishing; 2001:94 [Chapter 4].

Table 5.12 Physical properties of high-strength liquid crystalline wholly aromatic polyester fibers. Vectran HT Specific gravity (g/cc) Tenacity (gf/D) Tensile strength (GPa) Tensile modulus (cN/dtex) (GPa) Elongation at break (%) Moisture regain (%) Melting point ( C) Limited oxygen index

1.40 23 28 2.85 3.47 525 700 65 87 $ 3.3 ,0.1 330 30

Source: Beers D. Melt-spun wholly aromatic polyester. In: Hearle JWS, ed. High-Performance Fibres. Cambridge, England: Woodhead Publishing; 2001 [Chapter 4].

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Figure 5.44 Skin-core and fibrillar texture of liquid crystalline polyester fiber. Source: From Sawyer LC, Chen RT, Jamieson MG, et al. The fibrillar hierarchy in liquid crystalline polymers. J Mater Sci. 1993;28(1):225 238. doi:10.1007/BF00349055.

Table 5.13 Comparative testing of fiber-to-fiber abrasion resistance. Fiber

LCP wholly aromatic polyester fiber Aramid (lowest CTF dry) Aramid (highest CTF dry) HPPE (lowest CTF dry) HPPE (highest CTF dry)

Average cycles-tofailure Dry

Wet

16,672 718 1773 8518 17,761

21,924 258 758 23,619 78,369

CTF, Cycle-to-Failure; HPPE, High-performance polyethylene; LCP, liquid crystalline polymer. Source: Beers D. Melt-spun wholly aromatic polyester. In: Hearle JWS ed. HighPerformance Fibres. Cambridge, England: Woodhead Publishing; 2001 [Chapter 4].

not clear how these methods correlate to the cut testing standards described in Chapter 2, Evaluate cut resistance. Kuraray also reported that Vectran fiber performed better than para-aramid fiber and close to HPPE fiber especially in low basis weight fabrics in a slash testing with the UK Home Office testing standard.338,339 One also needs to note that the diameter of the single filament of LCP

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Figure 5.45 Effect of LCP filament diameter on yarn-on-yarn abrasion performance. LCP, Liquid crystalline polymer. Source: From Sloan F. Liquid crystal aromatic polyester-arylate (LCP) fibers: structure, properties, and applications. In: Bhat G, ed. Structure and Properties of High-Performance Fibers. Cambridge, England: Woodhead Publishing; 2017:137 [Chapter 5].

polyester fiber is much larger than the regular types of PPTA and HPPE fibers, which may also cause higher cut resistance of LCP polyester fiber. Meat and food processing have a high hygiene requirement. All the reusable cutresistant gloves need to be sterilized. It is claimed that strength retention of Vectran fiber is much higher than that of para-aramid fiber after bleaching.336,337,340,341 Though a decrease in tenacity may not necessarily mean a decrease in cut resistance, too much decrease in the tenacity may make the cut protective product lose its protective property. LCP polyester fiber does not show good light stability due to its molecular structure. In the worst case, it will not retain acceptable performance after long-term exposure to UV. LCP polyester’s UV resistance is poorer than PPTA aramid. Tests showed that a 1500 D LCP fiber only retained 20% of its original strength after 500 hours exposure to a simulated sunlight (carbon arc light), while PPTA aramid retained more than 50% and HPPE more than 60% at equal linear density. LCP polyester fiber is usually used after processing such as coating with colored resin in applications where the UV influence is concerned. Recently, Sumitomo Chemical also launched its LCP fiber trademarked as Sumikasuper. Fig. 5.46 shows the picture of this new LCP fiber, and Fig. 5.47 shows its chemical structure. The disclosed information tells it is a high strength and high heat resistance fiber, but the exact technical data are not available in the public yet.342

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Figure 5.46 Sumikasuper LCP fiber. LCP, Liquid crystalline polymer.

Figure 5.47 Chemical structure of Sumikasuper LCP. LCP, Liquid crystalline polymer.

5.2.8 Cotton fiber Cotton should be well known to almost everyone. Cotton fiber is a natural fiber, with an equilibrium moisture regain of B10%. It exhibits very soft haptics; therefore it makes the wearer feel very comfortable and also thanks to its moisture absorption capability. Cotton grows only as staple fiber, so it must be converted into spun yarn. The cotton staple spinning process is generally the same as that for the synthetic staple fibers, with a difference in staple length. Cotton spinning usually uses 38 mm cotton staple, while synthetic fiber often uses either 38 or 51 mm. Cotton’s cut resistance is low. It contributes to B0.9 gf cut force per gsm cotton fiber, about half of that of PPTA para-aramid fiber. Its abrasion resistance is not very good either, and therefore its durability is not good. Moreover, cotton easily gets rotten and degrades in very humid environment, thus additional care must be exercised for the storage of cotton fiber and cotton fabrics. Cotton fiber can be used alone and can also be used together with other fibers in blended form. Pure cotton products are only used for light duty work that requires very low level of cut protection. Polyester is more often used than other fibers to

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blend with. Cotton fiber can also be blended with para-aramid fiber and certainly can also be blended with nylon fiber etc. For instance, MCR Safety’s Cut Pro 9430KM is a glove made of blended Kevlar and cotton fibers.343 Another MCR Safety’s product Cut Pro 7-gauge glove style 9362 is also made of a blend of DuPont Kevlar para-aramid fiber and cotton fiber344 but by double-layer knitting of pure Kevlar PPTA yarn and pure cotton yarn. Kevlar yarn and cotton yarn are knit into a two-layer construction, with cotton being the interior and Kevlar yarn as the exterior. The cotton layer is in direct contact with the wear’s skin; therefore it offers a very good contact feeling, while Kevlar yarn as the exterior provides good cut protection. When cotton is used in a product of high cut resistance, it is usually used to cover steel wire in core-spun process to make cotton/steel core-spun yarn. When cotton/steel core-spun yarn is made, its cut resistance is mainly attributed to the steel wire.

5.2.9 Poly-p-phenylene benzobisoxazole fiber PBO is based on azole chemistry. PBO is a superhigh tenacity organic fiber,345 represented by Zylon fiber manufactured by Toyobo Co. in Japan. Zylon’s chemical structure is shown in Fig. 5.48, and the fiber’s picture is shown in Fig. 5.49. Academic research on azole-based polymers was started in the 1960s.346 349 The US Air Force started research by working with Stanford Research Institute in the 1980s to develop more practically useable polyazoles.350 352 Celanese also participated in this project.353 Eventually, almost all patents were licensed to the US Air Force.354 357 Basic physical properties of Zylon PBO fiber is summarized in Table 5.14.358 Zylon PBO fiber exhibits very high tenacity and very high modulus. Its tenacity is higher than normal para-aramid fiber by as much as B80%. Zylon AS’s modulus is about 2.5 times of normal para-aramid fiber and is about 1.6 times of high modulus para-aramid. Zylon HM’s modulus is even higher than T300 type carbon fiber. Its moisture regain is lower than para-aramid, and its thermal decomposition temperature is higher than para-aramid by B100 C. Its flame resistance is also much higher than para-aramid. PBO’s limited oxygen index (LOI) is 68, while PPTA para-aramid’s is 30 31.

Figure 5.48 Molecular structure of Zylon PBO. PBO, Poly-p-phenylene benzobisoxazole.

Figure 5.49 Zylon PBO fiber. PBO, Poly-p-phenylene benzobisoxazole. Source: Courtesy Toyobo Co.

Table 5.14 Physical properties of poly-p-phenylene benzobisoxazole fiber.

Linear density of single filament (dtex) Specific gravity (g/cc) Tenacity (cN/dtex) Tensile strength (GPa) Tensile modulus (cN/dtex) (GPa) Elongation at break (%) Moisture regain (%) Decomposition temperature ( C) LOI CTE (m K/m)

Zylon AS

Zylon HM

1.70 1.54 37 5.8 1150 180 3.5 2.0 650 68

1.70 1.56 37 5.8 1720 270 2.5 0.6 650 68 26 3 1026

CTE, Coefficient of thermal expansion; LOI, Limited oxygen index. Source: Courtesy Toyobo Co. PBO fiber Zylons technical information. Toyobo Co. Document 0739K; 2005.

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Because of its very high tenacity, PBO fiber is taken for granted that its cut resistance should be very high. But due to its very high price, it is not really seen in cut protective products. Very limited literature stated that its cut resistance is more than three times of para-aramid at equal basis weight.359 The development of PBO in protective products is mainly seen for ballistic and thermal protection.

5.2.10 High strength and high modulus polypropylene fiber Tenacity of normal polypropylene (PP) fiber is about 4 8 gf/den (3.5 7 cN/dtex). There have been attempts to develop high tenacity, high modulus PP fiber since the 1960s.360,361 A patent filed in 1957 by Heumann in Esso362 disclosed a technology of making high tenacity PP.361 In the description of this patent, isotactic PP was used as the raw material for melt spinning PP fiber followed by hot drawing in the temperature range of 80 C 110 C to improve molecular chains’ orientation. The tenacity of this fiber was above 7 gf/den (6.2 cN/dtex) that was rather high at that time, though is considered fairly moderate nowadays when compared to other highperformance fibers. Another patent filed in 1959 by Munt also disclosed similar process of melt spinning isotactic PP followed by hot drawing before cooling down, then a PP fiber with tenacity higher than 7.2 cN/dtex (100,000 lb/in.2 used in the patent) was obtained.363 In 1960 Noether et al. in Celanese developed a continuous process of a threestage hot drawing after melt spinning of isotactic PP and got a PP fiber product with tenacity exceeding 10 gf/den (8.85 cN/dtex).364 Sheehan et al. developed PP fiber with tenacity above 13 gf/den (11.5 cN/dtex) in a research published in 1964.365 Described in a patent filed by Haruto in Uniroyal Canada in 1968,366 high molecular weight isotactic PP was melt spun and kept at a temperature above melting point for a certain time, then cooled down at room temperature, followed by reheated up to 130 C 160 C then hot drawn. The fiber tenacity was above 12 gf/den (10.6 cN/dtex), which is considered of high tenacity even nowadays. While doing research and development for gel spinning of polyolefin fiber in the 1980s, Kavesh et al. in Allied Corp201 also attempted to develop both UHMWPE fiber (see Section 5.2.2) and ultrahigh molecular weight PP fiber367 and achieved tenacity of 13 gf/den and modulus of 370 gf/den with this PP fiber.202,367,368 Pinoca et al. in Montell Co.369 filed a series of patents in 1990 for melt spinning high molecular weight PP fiber, but the obtained tenacity was only about 6.2 cN/dtex.370 372 An American company Innegrity disclosed in 2006 that they invented a process to develop high tenacity propylene fiber.373,374 They achieved maximum 11.6 gf/den tenacity and 207 gf/den modulus. Donghua University in China filed a Chinese patent in 2007 and disclosed a method of gel spinning to spin high tenacity PP fiber375. The raw material is isotactic PP with 99% isotacticity and a molecular weight of 500,000 1,500,000. Paraffin oil is used as solvent to dissolve PP. 1,3:2,4-Bi(3-methyl-4-benzlidene)sorbitol, a nucleating agent, under the brand name of Hyperfom by Milliken, was used

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Table 5.15 Tenacity and modulus of high tenacity, high modulus polypropylene fibers obtained in historical researches and developments. Researcher(s)

Year

Maximum tenacity (strength) cN/dtex

385

Heumann Munt363 Noether and Singletone364 Sheehan and Cole365 Haruto366 Williams377 Cansfield et al.379 Taylor WN, Clark ES378 Kamezawa et al.380 Kavesh and Prevorsek367,368 Kanamoto et al.382 Pinoca et al.370 372 Suzuki et al.381 Morin373,374 Wang et al.375 Chen et al.384 Kitagawa et al.386

1957 1959 1960 1964 1968 1973 1976 1978 1979 1983, 1984 1984 1996, 1998 1997 2006 2007 2007 2011

6.63 .7.2 11.8 11.8 11.3

9.8 11.5 16.0 6.2 11.5 10.2 14.4 13.4 18.1

Maximum modulus

GPa

0.62 .0.68 1.1 1.1 1.10 No data No data 0.93 No data 1.08 1.5 0.58 1.08 0.96 1.35 1.3 1.7

cN/dtex

GPa

No data No data 157 14 10.8 10 No data 186 17.0 196 20.0 235 22 160 15.0 326 30.6 351 33.0 No data 156 14.7 183 17.2 352 33.1 278 27.0 No data

Note: When only either GPa or cN/dtex data are available, the specific gravity 0.94 is used to estimate the other one by the conversion equations in Appendix A.

to accelerate crystallization of PP. The fiber was gel spun followed by coagulation, deoiling, predrawn, extraction of paraffin oil by gasoline, drying, three-stage hot drawing, and eventually heat setting and winding. The resultant PP fiber was reported having a tenacity of 14.4 cN/dtex (1.35 GPa) and a modulus of 352 cN/dtex (33.1 GPa). The first draw ratio in this process was 5:1 at a temperature of B135 C; the second draw ratio was 2.5:1 at a temperature of B150 C; and the third draw ratio was 2:1 at a temperature of B160 C. There have also been a number of academic researches on high tenacity PP fibers.376 384 The maximum tenacity and modulus of PP fiber obtained in all these developments are summarized in Table 5.15. Among these results the highest tenacity was achieved by Kitagawa et al. using SSE that is used in making Tensylon explained in Section 5.2.2. But this has stayed in the research lab and seems never getting to commercial success. Belgian Fibers produces superhigh tenacity PP staple with tenacity higher than 5.2 cN/dtex.387 IFG Exelto also claims to have high tenacity PP fibers for geo- and agro-textiles, but the highest tenacity is only 5.4 cN/dtex.388 Innegrity in the United States has also marketed its Innegra high tenacity fiber after they have successfully

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secured the patent rights.373,374 The Innegra S grade PP fiber has a tenacity of 7.95 cN/dtex, and the highest modulus in this family is 176.6 cN/dtex.389 Literatures on PP fiber used in cut protective textiles are very limited. In most cases PP fiber is only listed as possible options in many cut protective textile patents. PP fiber gloves can be found on some shopping websites but are not for cut protection purpose. Usually in gloves, hollow PP fibers are used for thermal management390 or sweat management purposes.391,392 Based on internet searches, there are very limited offers of PP gloves listed on the websites of Ansell, PIP, and Superior Glove.

5.2.11 Polyvinyl alcohol fiber Polyvinyl alcohol (PVA) fiber is also widely known and called Vinylon that is actually a brand.393,394 What is used in the technical textile products with good durability is not PVA but should be acetalized PVA. PVA possesses very high water solubility and therefore is usually not a choice for technical textiles unless water solubility is desired. Most commonly seen acetalized PVA is polyvinyl formal. Molecular structures of PVA and polyvinyl formal (Vinylon) are shown in Fig. 5.50. Spinning of PVA fiber can be dated back to the 1920s and 1930s in the research work of Hermann et al.395 397 In 1930 Wacker AG in Germany started to produce PVA fiber but did not find much commercial success due to its high water solubility. During 1939 40 the research group of Ichiro Sakurada398 in Japan discovered a process to make PVA fiber with good hot water resistance.399 Japan started to produce this kind of fiber in mass scale and branded it as Vinylon in the 1950s. PVA fiber can be spun with either a dry spinning process, a wet spinning process, or a dry wet spinning process. Normal PVA fibers have tenacity of 4 7 cN/dtex in dry state and retain 70% 80% of its original tenacity in wet state. As mentioned previously, PVA fiber’s resistance to hot water is poor, but acetalization improves it. Although PVA fiber was originally invented in Germany, most of the later researches and development have been concentrated in Japan and China, especially by Kuraray in Japan that has carried out the development of PVA fiber for many years.400 404 Kuraray is now the world technology and business leader for high tenacity and high modulus PVA fiber. In 1970 researchers in Kuraray developed a process to get a PVA fiber with a tenacity of 10.2 cN/dtex and a modulus of 256 cN/dtex.400 The development of high tenacity, high modulus PVA fiber has started to take off since then. In 1985

CH2

CH

CH2–CH–CH2–CH

n

n

O OH Polyvinyl alcohol

O

CH2 Polyvinyl formal

Figure 5.50 Molecular structures of polyvinyl alcohol and polyvinyl formal.

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the PVA fiber tenacity was improved to 11.9 cN/dtex.402 In 1989 the tenacity was dramatically improved to 18.8 cN/dtex and the modulus improved to 483 cN/dtex,403 already close to the level of PPTA para-aramid fiber. In the next year the tenacity was further improved to 22.8 cN/dtex and modulus to 564 cN/ dtex.405 In the late 1990s Kuraray commercialized PVA fiber with the trade name Kuralon K-II, with highest tenacity of 15 cN/dtex and modulus of 330 cN/dtex achieved with gel spinning process.406 Allied Corp in the United States filed two patents in 1982 on gel spinning of PVA fiber when they attempted to develop gel-spun polyolefin fibers as mentioned in UHMWPE and high tenacity PP fibers sections (see Sections 5.2.2, and 5.2.10).407,408 In these patents the tenacity of such fiber achieved 17 cN/dtex tenacity and 340 cN/dtex modulus. But apparently Allied did not commercialize this product. Toray company in Japan also did development on high tenacity PVA fiber409 411 and disclosed achieving a tenacity of 17.8 cN/dtex and a modulus of 423 cN/dtex.409 Noteworthy is that a Japanese company Unitika412 played an important role in developing and commercializing high tenacity, high modulus PVA fiber. As early as in 1971, at almost the same time of Kuraray’s first high tenacity PVA fiber patent, Unitika disclosed a process to make high tenacity fiber, and a tenacity of 15.2 cN/dtex was achieved with an estimated modulus of 380 cN/dtex.413,414 This tenacity and modulus were considered very high at that time. In next decades, Unitika made significant progress in further improving the mechanical properties of PVA fiber.415 418 In 1987 a tenacity of 26.6 cN/dtex and a modulus of 547 cN/dtex were achieved by Unitika. These properties are equivalent or even slightly higher than commercial grades of high tenacity PTPA para-aramid fibers. Unitika manufactured, commercialized, and sold PVA fiber for more than 50 years, but this business was unfortunately discontinued in March 2016.419 The Another Japanese company called Nitivy420 also makes PVA fiber but does not make high tenacity grades. The highest tenacity available from Nitivy is only 5.7 cN/dtex. Recently, a few Chinese patents disclosed melt spinning process to get high tenacity PVA fibers surprisingly with melt spinning process.421 424 A Chinese company called Tianyi Engineering Fiber Co. produces and sells PVA filament yarn with tenacity of higher than 11 cN/dtex and modulus higher than 290 cN/dtex.425 The tensile properties of high tenacity, high modulus PVA fibers disclosed by different sources are summarized in Table 5.16. It needs to be mentioned that North Korea has a strong PVA fiber industry, as a result of the efforts by a Korean scientist Lee Sung-ki, who was in Ichiro Sakurada’s research group in Kyoto University and played a critical role in successfully developing PVA fiber in 1939. Lee returned to Korea after World War II and defected to the North and led the PVA fiber development in the North. There are two PVA fiber production sites in the North, but no product information is available.426

Table 5.16 Representative tenacity and modulus of high tenacity high modulus polyvinyl alcohol fibers from the disclosures. Company/organization

Country

Year

Maximum tenacity (cN/dtex)

Maximum modulus (cN/dtex)

Process

Kuraray400 Unitika413 Allied Corp407 Toray409 Unitika415 Kuraray405 Hunan Xiangwei421 Shanghai Luoyang422 Jiangsu Liujia424 Kuraray Kuralon K-II EQ5-R short cut fiber406 Kuraray Kuralon K-II RECS15406 Kuraray Kuralon K-II EQ2 staple fiber406 Tianyi Engineering Fiber425

Japan Japan Japan Japan Japan Japan China China China Japan Japan Japan China

1970 1971 1982 1984 1987 1990 2008 2012 2014 Commercial grade Commercial grade Commercial grade Commercial grade

10.2 15.2 17.0 17.8 26.6 22.8 17.5 B13.1 13.3 15 12 11 .11

256 380 340 423 547 564 No data B250 320 330 320 120 .290

Wet spinning Wet spinning Gel spinning Dry wet spinning Dry wet spinning Dry wet spinning Wet spinning Melt spinning Melt spinning No information No information No information No information

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The use of high tenacity and high modulus PVA fiber has not been seen in cut-resistant textiles yet regardless of its high tenacity and modulus, supposedly because of its water solubility, which makes it a challenge for PVA fibers to go through the wash and sterilization process, especially some such products are sterilized at elevated temperature. Though one US patent mentioned the use of PVA fiber in cut-resistant gloves, there is no actual example in this patent.427 A couple of other patents also describe the use of PVA fiber in the gloves, but the mentioned purpose of using PVA fiber is not for cut resistance but for allowing the gloves to be dissolved in water after use in order to reclaim the PVA material.428,429

5.2.12 Basalt fiber Basalt fiber is produced with a melt spinning process similar to glass fiber spinning with basalt rock as the raw material.430 Basalt fiber’s modulus and tenacity are at the same level of glass fiber. Similar to glass fiber, basalt fiber also possesses electrical insulating properties, corrosion resistance, and high temperature resistance. It is also fragile and easily breaks like glass fiber; therefore processing basalt fiber such as twisting and weaving requires great care. Basalt fiber is also irritating to skin like glass fiber. A patent on basalt fiber was filed as early as in 1921.431 Some researches were carried out later in the United States and in the former USSR, and currently the commercialized basalt fiber products are mainly used in Russia and China, for instance, Kamenny Vek in Russia,432 Technobasalt in Ukraine.433 Sichuan Aerospace Tuoxin Industries in Sichuan Province China,434 Shanghai Russia & Gold Basalt Fiber Co. in China,435 and Jiangsu Tianlong Continuous Basalt Fiber Co.436 in China. European companies include Basaltex in Belgium 437 and Mafic in Ireland.438 Sudaglass Fiber Technology in the United States also manufactures and sells basalt fiber in various forms.439 Fig. 5.51 shows the pictures of basalt continuous filament and short fiber.

Figure 5.51 Pictures of basalt fiber: (A) basalt filament yarn and (B) basalt short fiber. Source: Courtesy Kamenny Vek.

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Following are the typical properties of basalt fiber: Specific gravity: B2.70 g/cc Tensile strength: 2.7 3.2 GPa Tensile modulus: 85B95 GPa Elongation at break: 2% 3%

There are only a few publications on use of basalt fiber in cut protective textiles,440,441 but the cut-resistant performance is not reported. However, based on its mineral characteristic, and similar physical properties to the glass fiber, its cut resistance may be also close to the glass fiber.

5.2.13 Polyimide fiber Polyimide is often abbreviated as PI.442,443 The general structure of PI is shown in Fig. 5.52. The general structure indicates that PI can have many varieties that lead to very different properties in fiber form. The PIs we usually refer to are aromatic types, which can be more practically used due to their high heat resistance and flame resistance. Even among aromatic PIs, a large variety of products can be made with different monomers. In the literatures the earliest PI development was disclosed by P. J. Flory, the famous polymer scientist and Nobel Prize laureate.444,445 The PI structures reported by Flory in his patent are shown in Fig. 5.53.

Figure 5.52 General molecular structure of polyimide.

Figure 5.53 Structures of polyimides disclosed by P. J. Flory. Source: From Flory PJ. N-Acyl Polyimides of Polycarboxylic Acids, Patent US2,558,675. Wingfoot Corp; 1950.

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O

195

O

N

N

O n

O

O

Figure 5.54 Molecular structure of DuPont Kapton.

O

O CH3

N

N

O

O

O

Figure 5.55 Molecular structure of P84 polyimide.

Afterward DuPont also disclosed its research in this field in its patents.446,447 The world’s first patent on PI fiber was also disclosed by DuPont,448 but DuPont eventually commercialized PI polymers into films (branded as Kapton) and engineering plastic products (branded as Vespel), not into fiber. The chemical structure of Kapton is shown in Fig. 5.54. The conventional PIs are heat-resistant products, not high tenacity products, for instance, P84 fiber by Evonik (chemical structure shown in Fig. 5.55)449 or Kurakisss fiber by Kuraray.450 In China, manufacturers of heat-resistant PI fibers include Shino New Materials Technology in Jiangsu Province,451 Aoshen Hi-tech Materials in Jiangsu Province,452 and Changchun Hipolyking in Jilin Province.453 The tenacity of heat-resistant grade PI fiber is usually around 4 cN/dtex. These low tenacity but heat-resistant PI fibers are often used in thermal and fire protective apparels and flue gas filtration. Fig. 5.56 shows the chemical structures of some different PIs. In recent years, high tenacity fibers have been developed and commercialized in China by the two aforementioned Chinese companies, Shino and Aoshen, both in Jiangsu Province, China. Shino was founded by a research group from Beijing University of Chemical Technology. This group has been granted a number of patents in PI synthesis and fiber spinning454 458 and has commercialized the high tenacity PI fiber products. These high tenacity, high-performance products have been used in some very demanding niche applications. Fig. 5.57A shows a picture of Shino’s high tenacity filament yarn and Fig. 5.57B the staple fiber. The filament yarn exhibits a shining metallic appearance. This kind of appearance lasts much longer than aramid that discolors fast under light. Shino’s high tenacity PI fibers possess the advantages as follows:

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O

O

N

CH2

N

n O

O

O

O

N

O

O

N

R n

O

O

Figure 5.56 Molecular structures of some other aromatic polyimides.

Figure 5.57 Photos of polyimide filament and staple from Shino New Materials: (A) filament yarn and (B) staple fiber. Source: Courtesy Shino New Materials Co. 1. High tenacity. Different monomers can be used to regulate the tenacity. The highest tenacity grade has 4.0 GPa (27.5 cN/dtex) among all commercialized products. Shino is also developing a grade with even higher tenacity. 2. Excellent UV resistance. A 1670 dtex high tenacity PI filament yarn from Shino retained 95% of its original tenacity after exposure to UV for 192 hours, which is much better than the PPTA para-aramid fiber. 3. Much better abrasion resistance than the PPTA para-aramid fiber. At same basis weight, the fabric of high tenacity PI fiber from Shino was more than 10 times better than para-aramid in abrasion testing according to both EN388-2016 and ASTM D3884 Taber abrasion.459 The weight loss after Taber abrasion is at least 30% lower than PPTA para-aramid fiber. 4. Better flame resistance than PPTA para-aramid fiber. LOI of Shino’s high tenacity PI fiber is .40, while para-aramid is 29 30.

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Table 5.17 Physical properties of Shino high-tenacity polyimide fiber versus para-aramid fiber. Properties

High tenacity polyimide fiber

Basic grade of PPTApara-aramid fiber

Specific gravity (g/cc) Tenacity (cN/dtex) Tensile strength (GPa) Tensile modulus (cN/dtex) (GPa)

1.45 17 24 2.5 3.5 B1030 B150

1.44 19 2.8 500 72

Elongation at break (%) Moisture regain (%) Initial decomposition temperature ( C) LOI

1.5 2.8 B1 550

3.5 7 480

.40

29 30

LOI, Limited oxygen index; PPTA, poly(para-phenylene terephthalamide). Source: Courtesy Shino New Materials. Shino New Materials.

Table 5.18 Physical properties of Shino high tenacity polyimide fibers. Product grade

Tensile strength (GPa)

Tensile modulus (GPa)

Break elongation (%)

Moisture regain (%)

S25M S30 S30M S35

2.4 2.9 2.9 3.4

130 110 130 110

.1.5 .2.8 .1.5 .2.8

,1 ,1 ,1 ,1

2.9 3.4 3.4 3.9

160 130 160 130

5. Excellent heat resistance. The lowest decomposition temperature among the different grades is 550 C, and some are even up to 610 C, much higher than 480 C of PPTA paraaramid fiber. 6. Very low moisture absorption, less than 1%, while basic grade of para-aramid fiber’s moisture absorption is up to 7%. 7. Low dielectric constant, B3.5. 8. Good chemical resistance especially against strong acid. Shino’s high tenacity PI fiber almost retains its full strength after being immersed in a 10% sulfuric acid at 93 C for 24 hours.

The comparison of properties between high tenacity PI fibers and para-aramid fiber is tabulated in Table 5.17. Table 5.18 lists the physical properties of different grades of high tenacity PI fibers of Shino. Source: Courtesy Shino New Materials Co. ,http://www.jsshino.com/gaoxingnengjuluyaan/640.htm.. Shino and Aoshen are the only two manufacturers in the world, which produce and sell high tenacity PI fibers, and Shino is the only one in the world producing high tenacity PI filament yarn.

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According to Shino the cut resistance of high tenacity PI fibers is at same level as para-aramid fiber. There is no public report on the cut resistance of high tenacity PI fiber used in cut protective textile products yet.

5.2.14 Tungsten wire A few patent disclosures in the past decade or so has attracted the author’s attention on the use of tungsten wire in cut protective textiles. Tungsten, denoted as W (taken from Wolfram), is a precious metal.460,461 It has the highest melting point, 3422 C, among all metals. Its hardness is very high, rated at Mohs scale 7.5 (the diamond’s Mohs hardness is rated at 10). It is a very good candidate to alloy with steel to improve steel’s hardness. For instance, high-speed tool steel is made by adding tungsten and some other element additives into steel. Different compositions lead to different properties therefore to different grades of high-speed tool steel. Tungsten possesses very high hardness and stiffness. Typical properties of pure tungsten, tungsten tool steel and stainless steels are listed in Table 5.19. In a Great Britain patent filed in 2007,462 it was claimed that a core yarn such as steel wire is wrapped with an additional metallic yarn with tungsten as a choice, but there was not any cut resistance data in this patent. In a patent filed by Panasonic in Japan in 2016,463,464 it was disclosed that tungsten wire with a preferred diameter of 13 μm was used as a wrap yarn wrapped onto an organic core such as aramid or nylon yarn (as shown in Fig. 5.58A), or that tungsten wire was twisted together with an organic yarn (as shown in Fig. 5.58B). The hybrid yarn formed was then knit to gloves. The surface of tungsten wire was chemically roughened but still retained good smoothness. But again, this patent did not report any cut resistance performance. There were some Chinese patents disclosing tungsten wire used as core yarn in core-spun yarn to make cut-resistant yarn for cut protective products in recent years.465,466 CN108,505,174A disclosed a multiple layer wrapped structure with tungsten wire as the core. The tungsten wire’s diameters of this patent are from 6 to 25 μm in all the examples. A typical example given in this patent is a φ10 μm tungsten wire was wrapped with one end of 55 D polyester yarn in Z direction followed by another end of 55 D polyester yarn in S direction. This double-layer wrapped Table 5.19 Properties of tungsten, tungsten tool steel, and stainless steels.

Specific gravity (g/cc) Hardness (Rockwell C) Young’s modulus (GPa)

Tungsten

Tungsten-based high-speed tool steel

Stainless steel 304

Stainless steel 316

19.3 31 400

7.9 8.2 60 65 205

7.9 11.5 193

8.0 15.5 193

Note: These properties are based on bulk materials, not based on wire form. Source: ,www.worldsteelgrades.com., ,www.azom.com., and ,www.matweb.com..

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Figure 5.58 Hybrid yarn with tungsten wire disclosed by Panasonic: (A) wrap structure and (B) twist structure. (1—Tungsten wire, 2—Organic yarn, 3—Roughened surface of tungsten wire.) Source: From Terada T, Sugita K, Kanazawa T, et al. Hybrid Fiber, Patent US2018135211. Panasonic IP; 2017.

yarn was combined in parallel with one end of 60 D spandex, then was wrapped with a 70 D nylon 6 yarn. Finally this composite yarn was wrapped with one end of 100 D HPPE yarn. This structure is schematically shown in Fig. 5.59. The cut resistance for the examples in this patent was tested in accordance with EN388 Coupe testing, and unfortunately no TDM cut data were available; therefore it is hard to know the real cut resistance of Tungsten wire. In another patent CN107,541,830 A, although 18 40 μm tungsten wire was mentioned and cut forces between 1000 and 2200 gf were also mentioned, there was no information about basis weight, no information on specific grade of tungsten wire and on type and percentage of cover yarn, there is no way to understand the cut resistance of tungsten wire from these patents. But tungsten has good physical properties, such as strength and hardness, it is supposed to have good cut resistance. However, due to its very high cost, its application would be expected to be limited.

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Figure 5.59 Tungsten wire-containing composite yarn disclosed in CN108,505,174 A. (A)

(B)

CH2

CH n C≡N

CH2

CH C≡N

m CH2

CH n

X

Figure 5.60 Typical molecular structures of (A) acrylic and (B) modacrylic fibers (X stands for halogen such as Cl or Br.)

5.2.15 Other fibers There are a number of other fibers that can also be used in textile products. Some examples include cellulose fibers,467 acrylic or modacrylic fiber,468 carbon fiber,469,470 and ceramic fibers.471,472 Cellulose fiber, sourced from plants, especially trees, can be dissolved in solvent, then solvent spun to form fiber, also referred to as regenerated cellulose fiber. Commercially available cellulose fiber products include viscose (or rayon), cuprammonium rayon, modal, lyocell. Cellulose fiber is also called artificial silk, with similar properties to cotton. Cellulose fiber is very soft. Its tenacity is relative low. It possesses very good moisture absorption. Its cut resistance remains unknown but should be similar to that of cotton. Internationally well-known cellulose fibers include Viscose, Modal, Tencel from Lenzing in Austria.473 Acrylic fiber is a synthetic fiber, which is sometime called artificial wool because its touch is close to wool. Acrylic fiber is soft. Modacrylic is the term used to refer to flame resistant modified acrylic fiber that has good flame resistance and is often used in fire protective or arc protective textiles. Its cut resistance performance remains unknown, but supposedly being between cotton and nylon fibers. Fig. 5.60 shows the molecular structures of acrylic and modacrylic. Carbon fiber exhibits very high tenacity and modulus and is mainly used in the composites. But it is brittle and very expensive. One of its most common applications in textile is as an antistatic additive fiber in the textile products. Its cut resistance performance is unknown. But limited reports have shared that its cut

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Table 5.20 Typical properties of carbon fibers and ceramic fibers.

Torayca T300 Torayca T700S 3M Nextel 720 3M Nextel 610 Ube Tyranno ZMI Ube Tyranno 5A Tashika Type F Nicalon CG

Material

Specific gravity (g/cc)

Tensile strength (GPa)

Tensile modulus (GPa)

Carbon fiber Carbon fiber Aluminosilicate Alumina Si/metal/C/O Si/metal/C/O Alumina Silicon carbide

1.76 1.80 3.4 3.9 2.48 3.10 2.90 2.50

3.53 4.9 1.9 2.80 3.4 2.4 2.0 3.2

230 230 250 370 195 380 170 200

resistance is not high,474 assumed to be the reason for its limited use in cut protective textiles. Ceramics include aluminum oxide (alumina), zirconium oxide, aluminum silicate, boron nitride, and so on. Ceramic fibers are very resistant and insulating to heat, of high hardness, but also rather brittle. There are not many ceramic continuous filament products available in the market, mainly only Nextel by 3M in the United States,475, Tyranno by Ube Industries in Japan,476 Nicalon by Nippon Carbon,477 and Tashika’s product with unknown brand.478 The typical properties of these carbon fiber and ceramic fiber products are summarized in Table 5.20.

5.3

Dipping or coating materials for cut protective textile

Though many cut protective textile products are pure textile without dipping, many gloves need palm dipping (or coating) in order to improve abrasion resistance, oil resistance, grip, cut resistance, and puncture resistance. Main categories of dipping or coating materials include solvent-borne PU, NBR latex, natural rubber (NR) latex, polyvinyl chloride (PVC), and silicone rubber. Recently, the water-borne PU has attracted much attention. By coverage area on the glove, dipping or coating is divided into three different categories, half coating, full coating, and three-quarter coating which mean coating coverage is between half and full. Half dipping/coating refers to coverage only on the palm side, as shown in Fig. 5.61. Full dipping/coating means the palm side and back side are all dipped/coated such as what are shown in Fig. 5.62. Fig. 5.63 shows the coating coverage between half and full, which is often called threequarter dipping. Some gloves have more than one layer of dipping/coatings when one single layer cannot meet the requirement of use, with each layer performing different functions. The dipping coverage of each layer can be different, and usually, the inner layer’s coverage is higher than the outer layer (see Fig. 5.64).

Figure 5.61 Palm dipped gloves (half dipping). Source: Courtesy MCR Safety. ,https://www.mcrsafety.com/safety-equipment/gloves/ 9687#..

Figure 5.62 Fully dipped gloves. Source: Courtesy Pearl Glove (Malaysia). ,http://www.pearlglove.com.my/index.php/ products/nitrile-coated-gloves/fully-coated..

Figure 5.63 Partially dipped gloves (three-quarters dipping). Source: Courtesy MCR Safety. ,https://www.mcrsafety.com/safety-equipment/gloves/ 9750..

Figure 5.64 Multilayer dipped gloves. (A) Double-layer dipping. The first layer (bottom layer) is full dipping, and the second layer is half dipping. (B) Double-layer dipping. The first layer is three-quarter dipping, and the second layer dipping is on fingers only.

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Figure 5.65 Palm dotted gloves. Source: Courtesy by MCR Safety. ,https://www.mcrsafety.com/safety-equipment/gloves/ 9390pdf..

Some gloves are dotted by printing (see Fig. 5.65), not by dipping or coating, in order to enhance grip. Some gloves are dotted after dipping or coating, in other words, dots are printed on first dipping/coating layer (Fig. 5.66). Different postdipping treatment processes offer different surface texture or effects. Fig. 5.67 shows the effect of sandy surface, called sandy gloves. Fig. 5.68 shows the crinkling effect on coating, called crinkled gloves. Some gloves are printed with special cut-resistant materials by screen printing on high-risk areas in order to enhance protective performance on these areas. For examples, as shown in Fig. 5.69, cut- and abrasion-resistant materials are printed on thumbs, index finger, and partially on middle finger areas. On some gloves, soft materials such as thermoplastic elastomer are hot laminated or injected onto the glove liner to impart impact and vibration-resistant function, as shown in Fig. 5.70. There is one type of glove made by sewing one genuine leather layer on the liner. This kind of construction with leather on surface provides protection in welding environment, because genuine leather is resistant to the sparks or hot drops generated by welding. The picture of this kind of glove is shown in Fig. 5.71. The leather layer is stitched onto the textile liner. In order to be able to be dipped, the gloves must be put on hand molds. The hand molds for the textile gloves are usually made of aluminum alloy. As a

Figure 5.66 Dipped and dotted gloves.

Figure 5.67 Sandy gloves. Source: Courtesy Pearl Glove (Malaysia). ,http://www.pearlglove.com.my/index.php/ products/cut-resistant-gloves/hppe-cut-5-nitrile..

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Figure 5.68 Crinkled gloves.

contrast, the hand molds for pure latex gloves, such as the latex examination gloves, are made of porcelain. Fig. 5.72 shows a picture of a pair of aluminum alloy hand molds. Different sizes of hand molds are designed for different sizes of gloves. Different dipping materials are dipped with different processes, which will be covered later. Fig. 5.73 shows some pictures of a glove dipping line and process.

5.3.1 Solvent-borne polyurethane Solvent-borne PU refers to PU resin dissolved in organic solvents. The solventborne PU used for gloves dipping is almost the same as that used for synthetic leather (also called artificial leather in some countries). PU is dissolved in dimethylforamide (DMF) then coated onto a substrate followed by coagulating from the solvent and forming microporous coating on the substrate. Usually, PU solution with 30% solid content in DMF is obtained by the glove or synthetic leather manufacturers. This solution is first further diluted with DMF to an appropriate concentration, usually around 20%, then added with other additives. The gloves dipped with solvent-borne PU are usually half dipped. Full dipping with solvent-borne PU is not commonly seen in the market.

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Figure 5.69 Specialty screen printed gloves.

The textile glove liners are first manually put onto the hand molds. The gloves loaded onto the hand molds are moved to on top of the dipping tank filled with the PU solution. The gloves’ palm sides facedown toward the dipping tank, then they are dipped into the PU solution by having the palm slightly immersed underneath the liquid level so that only the palm side is dipped and the back side is not. In some designs what moves is the dipping tank instead of the glove. After dipping the hand molds continue to move forward with the gloves and rotate downward to allow the excessive solution to be automatically removed by gravity. But if the hand molds only rotate downward, then the dipping may not be uniform. Some manufacturers make designs to allow the hand molds to rotate upward after being downward so that the solution can be uniformly distributed on the palm. This dipping process is shown in Fig. 5.73B and C. After palm surface dipping the gloves on the hand molds are dipped into water or solution of DMF in water. The concentration of solution of DMF in water is usually 10% 30%. Water and DMF are completely soluble in each other, but PU does

Figure 5.70 Impact- and vibration-resistant gloves. Source: Courtesy MCR Safety. ,https://www.mcrsafety.com/safety-equipment/gloves/ t100#..

Figure 5.71 Leather palm stitched gloves. Source: Courtesy MCR Safety. ,https://www.mcrsafety.com/safety-equipment/gloves/ 9686..

Figure 5.72 Aluminum hand molds for textile gloves dipping: (A) gloves are dipped in solution or dispersion/emulsion, (B) gloves are rotated to face up after dipping, and (C) gloves are dried and are ready to be taken from the hand molds.

Figure 5.73 Pictures of glove dipping. Source: Courtesy Sishui Spark Hardware Factory, China. ,www.sparkdip.com..

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Figure 5.74 Bilateral diffusion between DMF and water. DMF, Dimethylforamide.

not dissolve in water; therefore water starts to diffuse into the PU solution on the glove, and DMF in the PU solution diffuses in the opposite direction, that is, from the PU resin solution to water. When there is enough water diffusing into the resin solution, PU starts to coagulate from the solution due to its insolubility in water. In a DMF/water solution the lower the DMF concentration, the slower the speed of coagulation, and the more DMF coming out of resin solution, thus lowering DMF residue in the final dipping layer, and vice versa. Usually, there are multiple coagulation baths of DMF/water solution, with gradually reducing DMF concentration. The coagulation bath of DMF/water can also be heated to accelerate the bilateral diffusion between DMF and water, and the temperature can be controlled between 50 C and 60 C. Eventually, a fully coagulated PU layer is formed on the glove surface. Fig. 5.74 illustrates the bilateral diffusion process. There is more or less residual DMF in the coagulated layer. DMF is harmful to human health; therefore many manufacturers wash the gloves in water or warm water, and then dry these washed gloves at elevated temperature. Multiple washes may be needed if the residual DMF needs to be very low. During the course of bilateral diffusion of DMF and water, water replaces DMF in the resin solution and PU shrinks due to the reduction of DMF in the solution, as a result many micropores are created and multilayer microporous structures are formed. A typical structure is a finger-like (or column-like) microporous structure as schematically shown in Fig. 5.75. The top layer of this structure is a dense film with many pores. The middle of this structure is long hollow columns, which look like fingers from the cut section. The walls of these holes extend to the bottom of this structure, and there are also channels on the walls to connect the columns. This kind of structure exhibits very high moisture permeability. Solvent-borne PU is a uniform system in which PU resin dissolves uniformly in the solvent DMF, and therefore it exhibits a good capability of penetration into substrates. Usually, solvent-borne PU can penetrate into the inner side of the glove during dipping; therefore there is PU resin on both sides of the substrate, inner and

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Figure 5.75 Finger-like channels formed after bilateral diffusion between DMF and water. DMF, Dimethylforamide.

outer sides. It is not difficult to identify whether a glove is dipped with solventborne PU or not by looking at the inner layer to see whether there is resin penetration. As a contrast, water-borne dispersion or latex is not a uniform system. The resin exists as very fine particles dispersed in water, not uniform dissolution, which makes the water-borne dispersion’s penetration capability not as good as solventborne system. Moreover, the substrate is usually dipped with coagulant before dipped in water-borne dispersion or latex to accelerate coagulation of the resin. This coagulant dipping makes penetration even more difficult. Nowadays, the DMF is almost fully recovered via a rectification process after dipping. If one has some knowledge of synthetic leather manufacturing and process technology, he(she) may quickly realize that the process of solvent-borne PU dipping for gloves is almost the same as the wet process for making synthetic leather.479 PU is very soft but also very abrasion resistant. It offers very good grip and permeability to air and moisture vapor. The formulation and process are very mature, and cost is low. These benefits have made PU-dipped gloves own a considerable percentage of the global glove market.

5.3.2 Water-borne polyurethane dispersion/emulsion Solvent-borne PU for dipping uses a very large amount of DMF solvent. Although almost all the DMF is recovered and reused, the workers in the factories are still exposed to the DMF. The finished products also contain more or less residual

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DMF. Using water-borne PU can address this health and environmental concern. Water-borne PU refers to the emulsion or dispersion of PU in water.480 482 The substrate needs to be dipped in coagulant before dipping in water-borne PU. A typical recipe of coagulant solution is as follows,483,484 Calcium chloride or calcium nitrite: Water: Ethanol or methanol:

2 5 B25 B70

The purpose of applying the coagulant is to coagulate the PU resin from the dispersion or emulsion onto the substrate surface so that the liquid resin does not penetrate too much into the substrate. Too much penetration of resin into the substrate cause three major problems: too much coating consumption which increases the cost, too stiff feeling of the coated product, and too heavy coated product. A typical recipe of water-borne PU is as follows484: Water-borne polyurethane: Foaming agent: Foam stabilizer: Thickener: Water:

45 55 Depends Depends Varies 45 55

The PU resin dispersion/emulsion can be directly used for dipping or used after mechanical foaming with a foam generator.

5.3.3 Natural rubber latex The name of NR latex is self-explanatory, a latex of NR. NR possesses good mechanical properties and grip and is resistant to polar solvent, but it is not resistant to nonpolar solvent such as oil and fat.485 A typical recipe of NR latex for dipping is as follows486: 60% NR latex 50% zinc oxide (ZnO) dispersion 50% Antioxidant D dispersion 10% Casein solution 25% potassium hydroxide (KOH) solution 20% Sodium hexametaphosphate 20% Lanum emulsion 50% accelerator TMTD dispersion 25% Carbon black dispersion 50% Sulfur dispersion 8% Polyvinyl alcohol solution (added later)a Water a

100 0.6 1.2 0.9 1.5 0.36 0.96 0.3 0.6 1.5 1.4 12 1.2 10.8 10.5

Polyvinyl alcohol solution: polyvinyl alcohol 8, water 92, glycerol 42.

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The substrate needs to be treated with coagulant first. A typical recipe of a coagulant is as follows: Calcium chloride or calcium nitrite Ethanol or methanol

4 5 95 96

Gloves are put on the hand molds and preheated to 50 C 80 C, then dipped in the coagulant followed by dried at 70 80 C. After drying the gloves are dipped in the latex then dried and prevulcanized at 70 C 80 C for 20 30 minutes, then washed in warm water to remove the coagulant salt. After the salt removal by wash, the gloves are finally put at 90 C 110 C for 40 60 minutes to fully vulcanize the rubber The surface of the glove dipping made from above process is flat. The flat surface in many cases does not have sufficient grip. In order to improve the grip, the surface is better to have higher roughness. One way is to create wrinkles on the rubber surface. The glove industry has widely used a method to create wrinkles on the glove surface made of NR latex, and this kind of product is called crinkled glove, and the surface is called crinkled surface. A picture of crinkled gloves is shown in Fig. 5.68. The crinkled gloves offer much better grip than the flat surfaced glove. The crinkling is created by immersing the wet coated surface before drying in a swelling agent to allow the wet coating surface to swell.487,488 The swelling agent is a mixture of a coagulant acid, such as acetic acid, a nonpolar solvent, such as toluene or xylene, and optionally a water soluble solvent such as methanol or ethanol. The swelling is caused by the affinity of NR to the nonpolar solvent, which is xylene in this example. The function of alcohol is to allow xylene to get into the aqueous or semisolid phase of the latex. The swelling of rubber creates wrinkles of the latex. The wrinkled coated product is then dried and vulcanized to get crinkled product. This process is described in further details as follows: Step 1: Heat up the hand molders to 50 80 C. Step 2: Put textile glove liners on the hand molders and dip in a coagulant such as 5% calcium nitrate in methanol. Step 3: Exit from the coagulant dipping then dip in the latex. Step 4: Exit from the latex dipping and stay for 2 5 minutes to allow the dipping to uniformly spread on the glove liners’ surface. Step 5: Dip the coated glove into the swelling agent, for instance, an acetic acid/ methanol/xylene solution (2/18/80 by weight) for 2 5 seconds. Step 6: Exit from the swelling tank and dry at 70 C for 40 minutes followed by vulcanized at 120 C for 60 minutes. Step 7: Exit from the vulcanization oven and take off the finished gloves.

Creating crinkles on the rubber surface with swelling agent is actually not something new. Patents as early as in the 1930s already disclosed the techniques to create swelling on partially vulcanized rubber surface by using swelling agent such as naphtha, a nonpolar solvent.489,490

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5.3.4 Nitrile rubber latex Nitrile rubber latex is the latex of NBR. NBR is very resistant to nonpolar solvent, especially oil and fat, but less resistant to polar solvent. The content level of acrylonitrile in the NBR is a critical factor to the properties of NBR. The higher the acrylonitrile content, the better the resistance to nonpolar solvent. But higher acrylonitrile content leads to higher glass transition temperature of NBR and thus makes the rubber more rigid and less resistance to cold. NBR possesses good mechanical properties and abrasion resistance.491,492 The coagulant dipping on the hand formers is also needed before NBR latex dipping. The coagulant recipe can be the same as that used in NR latex dipping. Zinc chloride was also reported as a coagulant salt.493,494 A typical NBR latex dipping recipe is as follows495: NBR latex or carboxylated NBR latex Dispersing agent Vulcanization package Water

80 1 10 100

The vulcanization package comprises the following additives for vulcanization, which are ball milled to form a stable dispersion in water. Water Colloidal sulfur ZnO Pigment Accelerator zinc dibutyldithiocarbamate Surfactant sodium dodecylbenzenesulfonate

100 20 40 Depends 10 10

The pH value of latex dispersion with the vulcanization package needs to be adjusted to a proper range by adding KOH aqueous solution (0.5% concentration) into the NBR latex. The textile glove liners are put on hand mold the hand molds and preheated to 50 C 80 C, then dipped in the coagulant followed by drying at 70 C 80 C. After drying the gloves are dipped in the NBR latex, then dried and prevulcanized at 70 80 C for 20 30 minutes, then washed in warm water to remove the coagulant salt, and finally vulcanized at 90 110 C for 40 60 minutes. In many cases NBR latex is added with water-borne PU (10 20 parts by weight) to improve flexibility and sometimes squeaky noise observed during use.494 496 Some reports also disclosed the use of NR latex or chloroprene latex to blend with NBR latex.495 NBR latex can be foamed before dipping to make a foam coating on the glove, then a foaming agent and foam stabilizer are needed. It is difficult to crinkle the NBR latex coating like NR latex coating. In order to improve the grip of NBR latex coating surface, a process to make sandy NBR coating surface has been used. After dipping in NBR latex and coagulation of the latex

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Figure 5.76 Crinkling effect of NBR coating by process described in patent CN108,384,079A. Source: From Zhou X, Sun Y. A Preparation Method for Crinkled Nitrile Rubber Latex Coated Glove, Patent CN108,384,079A. Shandong Xingyu Glove; 2014.

on the substrate, salt particles, such as sodium chloride or sodium sulfate, are sprayed onto the wet surface, followed by drying and curing. After being cured the coated product is washed in water therefore the salt dissolves in water and is removed. The sandy surface is therefore formed. Fig. 5.67 shows the sandy surface. However, Chinese patent CN108,384,079A claims a method to make crinkled surface from NBR latex coating.497 The crinkling process described in this patent is very similar to that used for NR latex coating except that the swelling solution consists of three components: the first component is an organic solvent that can swell NBR, the second component is an alcohol and the third component is an organic acid. A process example is briefly described as follows: Step 1: Prepare NBR latex dipping recipe. Step 2: Heat the hand mold to 50 C, and dip into 2% Ca(NO3)2 solution in methanol. Step 3: Dip into NBR latex. Step 4: Dip the NBR latex dipped glove into a swelling agent with 100 parts by weight xylene, 30 parts by weight methanol, and 2 parts by weight acetic acid, then exit. Step 5: Vulcanize the dipped glove at 75 C for 40 minutes, then at 110 120 C for 70 minutes.

Fig. 5.76 shows the crinkling effect of the coating surface by this process.

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5.3.5 Chloroprene latex Chloroprene is resistant to nonpolar solvent, weathering, abrasion, heat and flame but not very resistant to polar solvent.491,498 Similar to other latex dipping, the substrate needs coagulant dipping prior to chloroprene latex dipping. The coagulant is a solution of high-concentration calcium salt such as calcium nitrate in water. A typical dipping recipe of chloroprene latex is as follows499: Chloroprene latex ZnO dispersion Antioxidant dispersion KOH solution Wetting agent CaCO3 Carbon black dispersion Plasticizer Accelerator TMTD dispersion Sulfur dispersion

100 (dry substance) 5 (dry substance) 2 (dry substance) 0.8 (dry substance) 0.2 (dry substance) 1 (dry substance) 2 (dry substance) 7 (dry substance) 2 (dry substance) 1 (dry substance)

The dipping process is similar to that for NBR latex dipping.

5.3.6 Polyvinyl chloride dipping or dotting PVC exhibits excellent mechanical properties, good resistance to abrasion, to nonpolar solvent and has good flame resistance.500 PVC is also fairly costeffectiveness. But PVC becomes stiff and turns brittle at low temperature; therefore usually PVC is more used for dotting than for whole palm dipping. PVC plastisol is used instead of PVC dispersion. A typical recipe of PVC plastisol is as follows495: PVC powder resin for plastisol Plasticizer Heat stabilizer Filler

100 100 3 Varies

The PVC plastisol resin suspends in the plasticizer first after mixing. After dipping or dot printing, the gloves pass through high temperature heating, for instance, 5 minutes at 190 C. At high temperature the plasticizer quickly penetrates into the PVC powder to plasticize it, and the mixture starts phase inversion from liquid suspension/plastisol to solid. The dot printing is similar to the screen printing process. A screen with holes is put on top of the glove or substrate, and the plastisol is spread on top of the screen and scraped. The plastisol passes through the holes and adheres to the substrate, then the glove is conveyed into an oven to cure. The plastisol needs to be used up quickly after mixing because the plasticizer starts to penetrate into the PVC powder once they are mixed together even at room temperature, and as a result, the viscosity of the suspension continues to rise. The phase inversion can be completed at room temperature given enough time. The mixing speed should be low enough to prevent temperature rise in the mixture.

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Properly formulated plastisols can be heated at lower temperatures than regular PVC plastisol compounds to complete liquid solid inversion to reduce thermal degradation of PVC and reduce energy consumption.501

5.3.7 Silicone rubber dotting Silicone rubber (or silicone elastomer)502 is very soft and very resistant to chemicals. It possesses excellent resistance to both cold and heat, and to slipping. Silicone rubber is often used in dotting on gloves or socks. A typical recipe is as follows: Two-component liquid silicone elastomer 100 (total of A and B components) Thickener Varies Polymerization inhibitor Depends

High temperature vulcanization grades should be used instead of the room temperature vulcanization grades. After dot printing the printed substrate can be vulcanized at elevated temperature, for example, 130 160 C for 3 5 minutes. After mixing of components A and B, the system starts to polymerize slowly even at room temperature; therefore the mixture should be used up shortly after mixing, or a polymerization inhibitor can be used to slowdown the vulcanization.

5.3.8 Other coating materials Other materials, including epoxy, can also be used as coating or dotting materials on cut protective textile substrates. Epoxy is rather stiff, thus not suitable for full surface coverage coating, but can be printed with discontinuous coverage on the substrates, as shown in Fig. 5.77, to achieve good cut and puncture resistance.503 There can be a large varieties of this kind of printing layout. A Chinese company also applied for a similar patent in China.504 A picture of such a printed product is shown earlier in Fig. 5.78.

Figure 5.77 A pattern example of printed surface disclosed in patent US6,962,739.

Figure 5.78 Cut protective shoes with specialty printing of a hard material.

Mechanism of cut and cut resistance, factors affecting cut resistance, and development trend of cut resistant products

6.1

6

Mechanism of cut

There is a very limited number of publications on how the intrinsic properties of materials affect their cut resistance, in other words, what the mechanism of cut resistance is. A brief overview is made here to discuss these publications. Gent and Wang reported that the energy required to cut through polymers consisted of two parts, one being the energy to cut the molecular chains, the other the energy contributed to the viscoelastic and plastic deformation of materials.505 The percentage of each energy varies from material to material. Shin et al. developed a single yarn (not single filament) cut testing method506,507 and tested PPTA para-aramid yarn, HPPE yarn, and Zylon PBO yarn. This testing method is schematically shown in Fig. 6.1. Tests were carried out with different inclined angles of the blade, different pretension on the yarn, and different blade sharpness. The stress
strain curves were recorded during the cutting. These curves showed a linear pattern in the early stage of cutting, indicating a tensile manner of the yarns. After the fibers began to fail, the yarns immediately transitioned to a nonlinear pattern. When the inclined angle of the blade was 90 degrees, that is, the blade simply pushed the yarn, the yarn failed with severe

Figure 6.1 Schematic diagram of cut testing setup by Shin et al. Cut Protective Textiles. DOI: https://doi.org/10.1016/B978-0-12-820039-1.00006-7 © 2020 Elsevier Ltd. All rights reserved.

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plastic deformation. While when the inclined angle decreased, the fiber ends showed much less deformation. The results produced with 60 and 45 degrees inclined angle showed little plastic deformation. The scanning electron microscope (SEM) results revealed that the fiber sections underneath the blade contact point were actually pushed and extruded from the opposite side of the blade when the test was carried out at a high inclined degree, which means more compression. The SEM photos also revealed that the cut sections of the fiber ends were more bulbous at a high inclined angle of the blade, while the cut sections were less bulbous and cleaner at a low inclined angle of the blade. These results imply that the fiber fails with different mechanisms when the forces are exerted differently. When there are less slicing action and more pushing (or compression) of the blade, the failure is mainly by compression-shear that creates an extrusion force. When there is more slicing, the failure is mainly by tension-shear. In these studies, Zylon PBO yarn demonstrated much higher cut resistance than both PPTA para-aramid and HPPE yarns. Mayo and Wetzel used a method similar to Shin’s method to evaluate the cut resistance of single filament.508 Mayo et al. proposed that the filament experienced different mechanisms throughout the cut. In the very beginning the transverse compressive stress is dominant, then local flaws such as cracks and kink bands are induced. As the blade travels through the fiber, the effective cross-sectional area of the fiber is reduced and the stress is more concentrated; therefore the tension in the fiber increases. Eventually, the remaining fiber area is overwhelmed by the level of fiber tension and the fiber rails catastrophically. In this study, it was also discovered that the organic fibers and inorganic fibers failed differently. For instance, the Sglass fiber showed localized failure with little evidence of deformation, attributed to its brittleness, while the organic fibers exhibited evident deformation. In the high strength organic fibers, interfibril fiber splitting was discovered in this single filament cut study while no such phenomenon was reported in Shin’s yarn cut study. This indicates that the failure mechanism is different between a state of constrained filament and a state of free filament. In single filament the filament is free and the fibril splitting is not constrained. In the yarn testing as a contrast the filaments are compacted and constrained by many neighboring filaments. But nonetheless, the interfibril splitting in single filament cutting presents an evidence of lateral shear force in the organic fiber in the slicing action. However, the single filament study exhibited an inherently high noise. No significant difference in cut resistance was concluded for all the studied organic fibers, including Zylon PBO, Vectran, Dyneema HPPE yarn, Kevlar, and Twaron PTPA para-aramid fiber. But inorganic fibers S-glass and carbon fibers showed much higher cut resistance and less cutting angle dependence than those organic fibers. Research by Knoff from DuPont concluded that cutting para-aramid fiber was actually a process of wear178; thus the cut resistance is associated with the transverse toughness of materials. He conducted a series of transverse compression studies on para-aramid fiber and observed that the transverse deformation work is proportional to the fiber’s cut resistance, and is inversely proportional to the moisture content of fiber. A Kawabata transverse compression instrument509 was used

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for the study in Knoff’s work. In this study the fiber was supported on a surface; therefore there was no tension-shear on the fiber. In Knoff’s work the cut process was carried out by pushing the cutting blade against the fiber, that is, pure compression and compression-shear under a normal load, without any sliding of the blade on the fiber, that is, slashing or slicing. Though compression and shear are part of the cutting action, they are still different from the slashing or slicing. Slashing is more often encountered in real life while pure compression is rare. All the above studies are either based on single filament or single yarn. While in the fabrics, the situation is more complex as there are more constraints such as interlocking between the warp and weft ends, or loops in the knit structure, or the entangled fiber in the nonwovens. Vu Thi et al. used the ISO13997 TDM cutting method to do a study on the cut mechanism.510 This research concluded that the cut resistance was attributed to two factors, one being the intrinsic strength of material, the other being the friction of the material. The friction is further attributed to two different frictional forces, the first being the friction between the blade tip and the material, the second being that between the sides of the blade and the contacting material (see Fig. 6.2). The second friction is further attributed to two factors: gripping force between blade and material, which should be a result of van der Waals force, and the classical friction determined by normal load and coefficient of friction. The friction between blade tip and material is negligible compared with that between the blade side and material; therefore the frictional force mainly comes from the sides of the blade. Vu Thi et al. proposed that the different frictions have different contributions to the cut resistance. According to this proposal, the friction between the blade tip and the material reduces cut resistance, while the friction between sides of blade and material, especially the contribution from the gripping force, increases the cut resistance. They found that the friction between Spectra HPPE fabric and the blade is much lower than that between Kevlar para-aramid fabric and the blade, while the FN a a

1/2 μ1Fload

α α

1/2 Fload

1/2 μ1Fload

X

1/2 Fload

Y

Figure 6.2 Schematic distribution of the forces resulted from the applied normal load on the blade. Source: From Vu Thi BN, Vu-Khanh T, Lara J. Mechanics and mechanism of cut resistance of protective materials. Theor Appl Fract Mech. 2009;52(1):7
13. https://doi.org/10.1016/j. tafmec.2009.06.008.

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Hor. friction force (N)

6

y = 0.42x + 1.77

Kelvar t = 0.64 mm Kelvar t = 0.34 mm Spectra t = 0.54 mm

5

C.V = 5%

4

y = 0.35x + 1.74 3 2 y = 0.26x + 0.27 1 0 2

0

4

6

8

10

Applied normal load (N) Figure 6.3 Horizontal frictional force versus applied normal load for woven Kevlar and Spectra fabrics. Source: From Vu Thi BN, Vu-Khanh T, Lara J. Mechanics and mechanism of cut resistance of protective materials. Theor Appl Fract Mech. 2009;52(1):7
13. https://doi.org/10.1016/j. tafmec.2009.06.008.

Kelvar t = 0.64 mm Cotton t = 1.09 mm Kelvar t = 0.34 mm Spectra t = 0.53 mm

Blade displacement (mm)

70 60 50

C.V = 6 %

40 30 20 10 0 0

2

4

6

8

10

Applied normal load (N) Figure 6.4 Blade displacement to cut through fabric samples versus normal load for different fabrics. Source: From Vu Thi BN, Vu-Khanh T, Lara J. Mechanics and mechanism of cut resistance of protective materials. Theor Appl Fract Mech. 2009;52(1):7
13. https://doi.org/10.1016/j. tafmec.2009.06.008.

gripping force exerted by Spectra fabric on the blade is also much lower (see Fig. 6.3). As a result, the tested cutting force per unit weight of Spectra HPPE is much lower than that of Kevlar para-aramid fabric (see Fig. 6.4). The effect of

Mechanism of cut and cut resistance, factors affecting cut resistance, and development

223

friction was also discussed by Vu Thi et al. in another publication.511 A similar mechanism was discussed. Although Vu Thi studied and discussed the contribution of frictional forces, another contribution, that is, the intrinsic material strength, remains unclear. What does this intrinsic strength mean? It seems that the authors referred to the tensile strength because HPPE and para-aramid fibers used in these studies are typical representatives of materials of high tensile strength. But glass fiber has higher cut resistance than HPPE and para-aramid fibers though its tensile strength is lower. In both ISO13997 and EN388 cut testing the glass fiber exhibits significantly higher resistance to cut than the HPPE and para-aramid fibers at equal basis weight. Moreland’s research proved that there was no correlation between para-aramid’s tenacity and cut resistance.512 Moreland spun para-aramid fiber under different process conditions and got fibers with different transverse properties and longitude properties. An experimental fiber with a tenacity of only 4.2 cN/dtex showed higher cut resistance than commercial Kevlar fiber (page 156 of Ref. [512]). The contribution of friction to the cut resistance was also observed by the author in some cases where the glove manufacturers use thick rubber coating. The rubber itself is rather weak and is easily cut through. But the contact surface area between the rubber and the blade was large due to the high coating thickness, in some cases observed by the author especially in the Coupe cut, the blade was even unable to reach the textile substrate due to the high frictional force and therefore the cut resistance rating was high. Rebouillat et al. proposed a mechanism of densification
compression
cut
relaxation in the cutting of textile substrates. This mechanism is illustrated in Fig. 6.5.15 Rebouillat et al. also proposed that friction was the primary contributor to the cut resistance.16 These abovementioned researches were all conducted at a slow speed of cutting, that is, quasistatic cutting. In real life the cutting speed may be very variable. It was proved that the cut resistance is also cutting speed dependent.513 The testing methods for impact cut and slash resistance19,22,339 are conducted at a much higher speed which can be considered as dynamic cuttings. The response of a material to a quasistatic stress may be different from that to a dynamic stress especially for viscoelastic materials,514,515 among which polymers are representative. There are very few reports discussing the failure mechanism of slash. In summary, there is no completely satisfactory theory system for explaining the cut failure and the effect of materials properties on the cut resistance. In real life, the situation is much more complex. The cutting speed can be very different from the testing speed in the standards; the cutting angle may also vary; the pretension on the yarn can be very different. The blade sharpness and the load can be very different. Thus even the same cut level rated protective product may perform very differently in different scenarios. This area is worthy of more research. As for the mechanism in the stab testing, the failure model is very different. The stab testing is carried out with a very sharp pointed knife, not blade. The stab protection is mainly in military and law enforcement sector and is out of the scope in this edition of this book. The readers can refer to the references about the testing standards and research results.516
523

224

Cut Protective Textiles

Figure 6.5 Cut mechanism proposed by Rebouillat et al. Source: Modified from Rebouillat S, Steffenino B. High performance fibres and the mechanical attributes of cut resistant structures made there with. WIT Trans Built Environ. 2006;85 (High Performance Structures and Materials III):279
299. https://doi.org/10.2495/HPSM06028.

6.2

Factors affecting cut resistance

Understanding the factors that affect the cut resistance enables one to develop products with higher cut resistance. Vu Thi et al. mentioned the intrinsic material properties but did not make it very clear what it refers to. However, the work by other people inferred that one of the intrinsic properties be the transverse compression resistance. Knoff’s research demonstrated that the transverse compressive property such as modulus is at least one critical factor to the cut resistance of fiber. Besides the intrinsic properties of materials, other structural factors of the substrate may also contribute to the cut resistance. Rebouillat et al. proposed below factors16: 1. Deformability of materials: the ability of retaining specific gravity and toughness by the material. 2. Dulling effect of material on cutting blade: already illustrated in EN388 cut testing.

Mechanism of cut and cut resistance, factors affecting cut resistance, and development

225

3. Toughness and impact resistance of materials: ductile material has higher cut resistance than brittle material. 4. Skin-core type material is better than uniform material in cut resistance. The thicker the skin, the better the cut resistance. The authors did not explain why, and this author is somewhat skeptical of that conclusion If a thicker skin improves the cut resistance, then in an extreme case if the skin is 100% of the material, that is, uniform structure, then the cut resistance should be the highest, which is contradictory to the conclusion of the skincore being better than uniform structure. Or, there is an optimal percentage of skin at which the cut resistance is maximized, but where is this optimal point? If there is such an optimal point, then the statement of skin-core being better than a uniform structure without any condition is not correct. 5. Mobility of materials in the structure: if the structure is loose, the fiber in the structure may easily slip and move during cut, the cut resistance may be higher than substrates with a tight structure.

With regard to the mobility, some research results indicated that it is a contributing factor, but the results supported an opposite conclusion. The results by Kothari and Sreedevi showed that the plain-woven structure exhibited higher cut resistance than the twill woven structure.524 Twill woven has less tightness and more mobility than the plain woven, but in this study, it showed lower cut resistance, contrary to Rebouillat’s theory. Memon et al. discovered that the woven structure had a higher cut resistance than the knit structure.525 Fig. 6.6 shows this comparison. It is a common sense that woven structure is more stable and tighter than the knit structure and therefore the yarn in a woven structure has less mobility than that in a knit structure at equal basis weight. But Memon’s results were based on the Coupe cut. It is not clear whether the same could happen in TDM cut. Fangueiro et al. tested cut resistance of different knitted structures and found that the tuck stitch structure showed the highest cut resistance than the other structures.526 Tuck stitch reduces (A)

(B) 14

14 100% Kevlar 100% PE 50% Kevlar/50% PE

12 10

10 Cut index

Cut index

100% Kevlar 100% PE 50% Kevlar/50% PE

12

8 6

8 6

4

4

2

2

0

0 Knitted samples

Woven samples

Knitted samples

Woven samples

Figure 6.6 Comparison of knitted and woven samples [(A) cut at 145 degrees; (B) cut at 245 degrees]. Source: From Memon AA, Peerzada MH, Sahito IA, et al. Facile fabrication and comparative exploration of high cut resistant woven and knitted composite fabrics using Kevlar and polyethylene. Fashion Text. 2018;5:5. https://doi.org/10.1186/s40691-017-0122-0.

226

Cut Protective Textiles

the yarn mobility; therefore this result does not support the mobility hypothesis. Furthermore, Alpyildiz et al. compared the cut resistance of knitted structure with inlay yarns and without inlay yarns. Their results showed that adding inlay yarns increased the cut resistance.527 Again, inlay yarn certainly adds more locking into the structure and reduces the mobility. All these results support an opposite conclusion to what Rebouillat hypothesized. Though not everything is completely clear to us, it is still possible to give a list of factors: 1. Material type: some materials are more resistant to cut than the others, though some behave differently in different types of testing. This is easy to understand. Generally, inorganic materials are more cut resistant to organic materials. Some materials have more dulling effect than the others and increase the cut resistance in Coupe cut testing. 2. Amount (quantity) of material: a higher amount of material in the same volume then the product is more resistant to cut. In the textile product, generally the amount of material. This is very straightforward. 3. Structural effects mentioned by Rebouillat. In the above-discussed section, different structures such as woven versus knit and different knitting structures affect the cut resistance. Govarthanam et al. did lots of experiments and also reported that different structures with same yarn exhibited very different slash resistance.528,529 4. Size of the material: Kothari and Sreedevi’s research results revealed that a monofilament (large diameter of single filament as a contrast to the small diameter of multifilament yarn) nylon fabric exhibited much higher cut resistance than PPTA para-aramid even at same basis weight.524 Fig. 6.7 showed the comparison among fabrics of different yarn construction. HP5 is a fabric made of nylon monofilament; therefore it should be made clear that the comparison is based on the same basis weight and the same size of filament when one says nylon’s cut resistance is much lower than PPTA para-aramid fiber or HPPE fiber.

Figure 6.7 Cut resistance of fabrics made of multifilaments and monofilaments. (Sample specifications are listed in Table 6.1.) Source: From Kothari VK, Sreedevi R. Cut resistance of textile fabrics
a theoretical and an experimental approach. Indian J Fiber Text Res. 2007;32:306
311.

Mechanism of cut and cut resistance, factors affecting cut resistance, and development

227

Table 6.1 Specifications of fabrics tested by Kothari and Sreedevi.524 Sample no.

HP1 HP2 HP3 HP4 HP5

Material

Nylon multifilament Nylon camouflage HPPE para-Aramid 100% Nylon monofilament

Weave

Plain Plain 3/3 Twill Plain 3/3 Twill

Thread count (ends/ cm) Warp

Weft

13 12 51 9 41

16 14 21 9 13

Fabric thickness (mm)

Fabric weight (g/ m2)

0.41 0.44 0.70 0.30 1.1

200 250 330 200 400

Source: Kothari VK, Sreedevi R. Cut resistance of textile fabrics
a theoretical and an experimental approach. Indian J Fiber Text Res. 2007;32:306
311. Table 2.

5. Tensile strength: this mainly applies to chainsaw cutting. In the resistance to chainsaw cutting, clogging the chain by the fiber is a major contribution to stopping the chain. When the yarn is pulled into the chain from the protective cloth, it clogs the chain. The yarn is under high tensile load while clogging the chain; therefore higher tensile strength provides better clogging capability in addition to the cut resistance. However, in TDM cut or Coupe cut, the tensile strength seems not a determining a factor because the tensile properties are along the longitude direction while cutting is a transverse load, though higher tenacity fibers exhibit higher cut resistance in general. 6. Young’s (elastic) modulus: Messiry and El-Tarfawy proposed that the cut resistance is proportional to the fiber’s Young’s modulus.530 An equation was developed in their research as shown in the following equation: K ðcutting resistance coefficientÞ 5

7. 8.

9. 10.

ðP 3 W 3 EÞ V

(6.1)

where P is the critical cut-through normal force (N), V the cutting speed (mm/min), W the fabric basis weight (g/cm2), and E Young’s modulus. However, the number of materials examined in this research was very limited and no inorganic materials were studied. It is fairly doubtful whether this can be broadly applied to all materials, for which many researches proved that the transverse properties instead of longitude properties are the governing factors. Mode of cutting: sliding leads to lower energy to cut through the textile than pushing under normal load. Cutting speed: besides Wang et al.’s study which proved that a higher cutting speed leads to a lower energy to cut through the textile.513 The results of Messiry et al. also supported the same conclusion.530 Cutting angle: more inclined blade edge on the fiber leads to lower energy to cut through. Pretension on yarn: higher pretension on yarn leads to lower energy to cut through.506,507

The quantitative contribution of materials to cut resistance is hard to be determined due to very limited available literature and limited research. The cut resistance data disclosed in patents may be of interest to study, but most of them are

228

Cut Protective Textiles

hard to analyze due to inconsistent testing methods and not very systematic data. However, one family of patents is highly worthy of investigation.242
248 This patent family disclosed more than 70 sets of data about the cut resistant of PET fiber with different fillers. Five factors were studied in these patents: (1) type of filler, tungsten powder or alumina powder; (2) filler’s particle size; (3) weight percentage of filler; (4) linear density of fiber; (5) basis weight of fabric. Among all the examples, one was coated; therefore the basis weight was not based on pure textile and the coating weight was unknown, so this example is excluded in our analysis. There are 72 sets of data are leftover; thus there are adequate degrees of freedom to try different fitting models. Among a number of attempts of fitting, many models showed good fitting. Among all these attempts, a linear model after natural log transformation of cut protection performance (CPP) showed acceptable R2 [R2(adjusted) 5 0.807 and R2(prediction) 5 0.789]. It was selected as the final model to fit these data and is shown in the following equations: For tungsten, lnðCPPÞ 5 5:6030 1 0:1746A 1 0:01759B 1 0:00:01781C 1 0:04664D

(6.2)

For alumina, lnðCPPÞ 5 5:7524 1 0:1746A 1 0:01759B 1 0:00:01781C 1 0:04664D

(6.3)

where A is the filler size, B is the weight percentage of filler, C is the linear density of fiber, and D is the basis weight. Fig. 6.8 shows the effect of all factors on CPP. As seen in this figure, the most significant factor is basis weight (D), followed by filler size (A) which even exceeds the effect of the weight percentage of filler. The larger the filler size, the higher the CPP. Furthermore, the linear density of fiber (C) also has influence to certain extent. The thicker the fiber, the higher the CPP, which is consistent with the result of Kothari and Sreedevi.524 The analysis shows that the alumina has slightly better cut resistance than tungsten. The linear relationship between basis weight and cut resistance is supported by the research results by LaNieve and Williams.531 Fig. 6.9 shows this relationship developed by LaNieve et al. As a matter of factor, the models presented in Eqs. (6.2) and (6.3) are not the ones that showed best R2s. As to why a model with lower R2 is selected, the reader can proceed to Appendix B.

6.3

Development trend and measures to improve cut resistance

The major development trend for cut protective textile has two directions. 1. Lighter weight, better comfort, more dexterity, and higher cut resistance. Lighter weight usually offers the wearer better dexterity and comfort. Higher cut resistance imparts better protection for the wearer. However, these two are conflicting against each other. Lighter

Mechanism of cut and cut resistance, factors affecting cut resistance, and development

229

Figure 6.8 Effects of factors on CPP when filler is (A) tungsten and (B) alumina. (Reference point: A: filler size 5 1.5 µm; B: filler wt.% 5 8.5%; C: fiber linear density 5 7 D; D: basis weight 5 20 oz/yard2.) CPP, Cut protection performance.

weight means less material and then usually lower cut resistance. Innovative ways have to be created to meet this market demand. For instance, as introduced in Chapter 5, Choice of materials for cut protective textile, some companies have developed 18-ga products than can meet A4 cut level in accordance with ANSI/ISEA105-16. Imagine an extreme case that if a very thin medical latex glove could have good cut resistance so that the surgeons handle with very sharp surgery blades with much better protection than current latex gloves that do not have any cut protective performance. 2. Multifunction textile for multipurpose protection, such as two-in-one for both chemical resistant and cut resistant gloves. Many jobs face different risks in one task therefore multipurpose protection is often necessary. Imagine someone is handling broken glasses that are contaminated with chemicals.

Many attempts have been made to improve materials’ cut resistance. They are summarized as follows and some proposals are also made based on the author’s observation on the results.

230

Cut Protective Textiles

Figure 6.9 Cut resistance of generic materials measured by ASTM F1790-97. Source: From LaNieve L, Williams R. Cut resistant fiber and textiles for enhanced safety and performance in industrial and commercial applications. Mater Technol. 1999;14(1):7
9. https://doi.org/10.1080/10667857.1999.11752803. 1. Continuous endeavor of searching new materials. Since the first use of HPPE yarn in the cut protective textiles, the materials used have not had many changes. Fiberglass, steel wire, para-aramid, HPPE, nylon, polyester, and cotton have been used for many years. But the industry has never stopped searching for new material such as the recent effort in evaluating tungsten (see Section 5.2.14). 2. Selection of materials. Proper selection and careful experimentation can help one maximize the cut resistance. Everyone wants to use materials of higher cut resistance This seems very straightforward and easy, but one has to experiment on his/her own to explore even among existing materials because often people found contradictory results between different. For instance, some reports report that Vectran fiber has higher cut resistance than PPTA para-aramid fiber,336 while Messiry et al. reported that PPTA para-aramid showed much higher cut resistance than Vectran fiber in both yarn form and fabric form. The normalized cut-through energy of PPTA para-aramid fabric in their studies was three times of the fabric made of Vectran fiber. However, the testing methods used in these two researches were different. These contradictory results further prove that the cut resistance of materials is highly dependent upon the real cutting mode, therefore developing a cut protective product is not an easy task at all due to the complexity of different cutting

Mechanism of cut and cut resistance, factors affecting cut resistance, and development

231

situation in real life. Another example is that Shin et al. reported that Zylon fiber exhibited multiple times higher cut resistance than PPTA para-aramid fiber in yarn form,507 but Mayo and Wetzel’s result did not support it with a similar testing method on single filament.508 These results indicate that different product forms may get different cut resistance. Thus one needs to experiment on his/her own in his/her own product form to screen materials regardless of the published research results. 3. Hybrid/composite fibers with materials of high cut resistance. Hybrid/composite fibers can be divided into two categories: macroscopic and microscopic hybrids/composites. The macroscopic hybrid/composite fibers include the examples of wrapped yarn and core-spun yarn. The typical examples of macroscopic hybrids/composites are wrapped or core-spun fiberglass or metallic wire with organic cover fiber. Many such examples can be found in the references cited in earlier chapters. Some academic research is also of high interest.528,529 The microscopic hybrid/composite fibers include the examples of bi-component fiber, filler filled fiber. The typical examples of microscopic hybrids/composite fibers include the alumina filler or tungsten powder-filled thermoplastic yarn as analyzed earlier for Hoechst Celanese’s patents which resulted in the CRF technology,531 and the Dyneema Diamond Technology. 4. Hybrid/composite textile. This is different from the hybrid/composite fiber/yarn. In hybrid/composite textile, different yarns of different materials are made into one textile product. Or even different structures are integrated into one product. Govarthanam et al. developed a unique two-layer structure by using different pure PPTA para-aramid fiber and HPPE fiber in different layers of a textile fabric that showed synergistic effect and the slash resistance of the composite fabric is higher than either pure PPTA para-aramid or HPPE at equal basis weight.529 Memon et al. reported that a 50% PPTA/50% HPPE fabric knit with two different yarns had higher cut resistance than either 100% PPTA fabric and 100% HPPE as shown in Fig. 6.10. Similar conclusion was also supported by Kirtay and Ertekin.532 5. Use material of larger size. The results analyzed from the Hoechst’s patent family and from Kothari’s study clearly show that larger size (or diameter) of filament has higher cut

(A) 14 12

(B) 14

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5

12 10

Cut index

Cut index

10

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5

8 6

8 6

4

4

2

2

0

0

100% PPTA

100% HPPE

50%/50% PPTA/HPPE

100% PPTA

100% HPPE

50%/50% PPTA/HPPE

Figure 6.10 Cut index of PPTA, HPPE, and hybrid fabrics [(A) cut at 145 degrees; (B) cut at 245 degrees]. Source: From Memon AA, Peerzada MH, Sahito IA, et al. Facile fabrication and comparative exploration of high cut resistant woven and knitted composite fabrics using Kevlar and polyethylene. Fashion Text. 2018;5:5. https://doi.org/10.1186/s40691-017-0122-0.

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Cut Protective Textiles

Table 6.2 Cut resistance of alumina filled PVC coating containing alumina filler. Example

Filler concentration (wt.%)

Basis weight (oz/ yard2)

Cut protective performance (ASTM F1790)

CPP/ BW

Improvement (%)

A 3 5

0 5 15

10 12 13

35 97 142

3.5 8.1 10.9


131 211

BW, basis weight; CPP, Cut protection performance. Source: Modified from Oakley EO, Johnson GJ, Lanieve HL. Polymeric Articles Having Improved Cut-Resistance, Hoechst Celanese, Patent US6,080,474; 1997.

resistance than smaller ones at equal basis weight. Therefore there are multiple ways to improve cut resistance such as using yarns with thicker filaments, using monofilament as core in core-spun or wrapped yarn or using thicker filler in the filled yarn. 6. Surface treatment/modification. Surface treatment includes treatment on filament, on yarn and on the textile product. Atanasov et al. reported cut resistance of PPTA fiber could be improved by an ultrathin layer deposition of inorganic materials.533 But it seems the improvement was marginal as the coating was very thin. Coating can also be applied to the surface of the textile as discussed in Section 5.3. The pure elastomeric coatings, such as NBR, NR, and PU, do not have good cut resistance and their contribution to the cut resistance of the coated product is limited unless they are coated with high thickness, which in turn will sacrifice weight and comfort. Adding cut resistant filler into the coating is a way to tackle this. Ansell disclosed a latex coating composition which contains hard fillers such as silicon carbide, aluminum oxide, or boron carbide to improve cut resistance.534,535 But unfortunately no cut resistance data were reported. Hoechst Celanese Corp disclosed the similar concept much earlier and reported the cut resistance results based on PVC as the coating matrix.536 Table 6.2 summarized the data reported in this patent. The cut resistance was dramatically improved by adding alumina into PVC. Hoechst Celanese also filed a patent to protect the articles made of this kind of composition based on this invention.537 7. Cross-sectional shape of the material. The effect of cross-sectional shape on the cut resistance was not studied much. However, Moreland’s research showed that the circular shape was better than other shapes in cut resistance.512 If possible, one should explore this possible factor and find out the optimal cross-sectional shape.

The cut protection is a very niche area where the research is limited. The understanding on the mechanism is incomplete. The reports on the effect of different factors on cut resistance sometimes are contrary to each other. The real-life situation is much more complex than what one gets from a standard test. However, the cut protection is very important to the job safety. Therefore there is still a lot of room and opportunities for the researchers to further understand the mechanism and for the developers to develop better products.

Appendix A: Conversions between different units of tenacity and strength

1 N/tex 5 100 cN/tex 1 cN/dtex 5 10 cN/dtex 1 cN/dtex 5 0.1 N/tex 1 gf/day 5 0.882 cN/dtex 1 GPa 5 1000 MPa 1 cN/dtex 5 0.1ρ GPa (ρ is the specific gravity)

For instance, if a fiber has a tenacity of 10 cN/dtex and its specific gravity is 1.38 g/cm3, then its tenacity is 1.38 GPa.

Appendix B: Data in patents242

258

Ex.

Filler type

Filler size (µm)

Filler weight percentage

Fiber linear density (D)

Basis weight (oz/yard2)

CPP (gf)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

None None None Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten Tungsten

0 0 0 1 1 1 1 1 1 1 1 1 0.05 0.05 1 1 0.05 0.05 0.6 0.8 1.4 1.6 1 0.8 0.6 0.8 0.6 1.5 0.6 1 0.6 0.6 0.6 0.6 0.6 0.6

0 0 0 1 1 4 4 10 10 10 0.21 0.21 0.86 0.86 1.9 1.9 2.1 2.1 5.52 16.55 5.52 16.55 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03 11.03

3.1 5 5 6 5.6 6 5.9 11.6 7.4 6 11.4 5.6 5.6 5.7 11.8 5.6 5.4 5.9 10 10 10 10 10 10 10 10 10 12 2.4

7.1 6.8 13 9.1 7.3 7 7.3 7.5 8.5 7.6 7.2 7.5 7.3 6.7 8.2 6.7 6.7 6.2 8 9.5 8.2 8.2 8 7 6.8 7 7.9 7.6 13.6 7.5 28 19 26 20 12 16

421 384 589 540 565 643 620 697 759 670 547 463 501 497 683 478 496 431 562 557 714 821 708 724 621 596 703 644 656 503 1226 964 1225 900 628 685

2.4 2.4 2.4 10 2.4 1.4

(Continued)

236

Appendix B: Data in patents

(Continued) Ex.

Filler type

Filler size (µm)

Filler weight percentage

Fiber linear density (D)

Basis weight (oz/yard2)

CPP (gf)

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65a 66 67 68 69 70 71 72 73

Tungsten Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina Alumina

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 3 3 0.5 0.5 3 0.5 0.5 0.6 0.6 0.5 0.6 3 3 2 2 2 2 2 2 2 2 2 2 3 0.6 0.6 3 3 1

11.03 6.82 2.27 4.54 6.82 9.09 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82

1.4 3 10 10 10 10 3 3 3.6 3.6 1.4 1.4 3.1 5.5 5.5 6.4 5.5 6.7 4 3.1 3.1 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 10 6.4 6.4 4.2 4.2 12.9

7 22 10 12 10 10 19 9 16 11 15 13 18 23 21 23 19 8 13 15 15 18 9 5 5 11 17 17 36 18 9 23 18 21 14 11 7.3

580 1285 990 912 823 852 1074 487 1234 981 810 623 1555 1197 1082 1242 1505 597 818 1370 1283 1562 905 611 615 785 1593 1506 1022 1573 956 1414 1084 996 1079 883 943

CPP, Cut protection performance. a Coated fabric.

Appendix C: Statistical analysis for data in patents

The data for statistical analysis are taken from references.242
248 There are many fitting models to select in data analysis. The principles for the author to work on the data and select the best model among all possible models are 1. 2. 3. 4. 5.

the highest R2 (adjusted); the highest R2 (prediction); the difference between R2 (adjusted) and R2 (prediction) is small; insignificant lack of fit; and high signal-to-noise ratio.

As there are 72 sets of data and only 5 factors, there are adequate degrees of freedom to explore different models even with high orders. After several attempts, it was discovered that third order is significant among all the possible high order models, therefore the cubic model is selected as the starting point and stepwise factor screening was carried out to remove those insignificant factors (by using 90% confidence level). Below model in Eq. (C.1) is then obtained. CPP 5

1 1595:11 1 494:13  A 1 818:27  D 1 449:83  A  B 2 462:58  A2 2 163:36  B2 2 665:05  D2 1 267:06  A  C  D 2 114:13  C  D  E 2 312:11  A2  D 2 565:17  A  D2 1 344:21  B  D2 1 73:66  C 2  E 2 579:89  D3

(C.1)

where A is the filler size; B is the weight percentage of filler; C is the linear density of fiber; D is the basis weight; and E is the type of filler (tungsten or alumina. Tungsten is coded as 21 and alumina is coded as 11). The parameters to judge the goodness of model are listed in Table C.1

238

Appendix C: Statistical analysis for data in patents

Table C.1 Parameters for goodness of model for the cubic model. Parameter

Value

Significance of model Lack of fit R2 R2 (adjusted) R2 (prediction) Signal-to-noise ratio

P , .0001 P 5 .0777 0.9381 0.9249 0.9156 31.3

Figure C.1 Normal probability of standardized residuals with cubic model.

These data show excellent goodness of fit [P , .0001 R2 (adjusted) 5 92.49%], and insignificant lack of fit (P 5 .0777). The accuracy of prediction is also high [R2 (prediction) 5 91.56%]. This R2 (prediction) is the highest value among all tested models. The signal-to-noise ratio 31.3 is also outstanding. The normality of standardized residuals is fairly good, except very limited number of data points as seen in Fig. C.1. The high R2 (adjusted) indicates the chance of under-fitting is very low, and high R2 (prediction) indicates the chance of over-fitting is also very low. The predicted values and actual values shown in Fig. C.2 have very high degree of consistency. All these indicate that this model is satisfactory. However, looking at Eq. C.2, one shall realize that the model is fairly complicated and is hard to explain. Though it is not necessary to explain everything from

Appendix C: Statistical analysis for data in patents

239

Figure C.2 Correlation between CPP’s predicted values and actual values based on cubic model. CPP, Cut protection performance.

machine learning perspective, our purpose is to understand what factors contribute to the cut resistance and why, not only to do prediction. Now we change the modeling strategy by compromising the R2s. We would like to have a simpler model with acceptable R2s. A linear model was attempted with natural log transformation of cut protection performance (CPP) data and the model in Eq. C.2 is obtained. lnðCPPÞ 5 5:684 1 0:153 3 filler size 1 0:139 3 tungsten % 1 0:111 3 alumina % 1 0:021 3 linear density 1 0:044 3 basis weight (C.2) Eq. (C.2) is equivalent to the two Eqs. (6.2) and (6.3). It has a R2 (adjusted) of 0.81, R2 (prediction) of 0.79, P value ,.000, and signal-to-noise ratio of 33.7. It shows a significant lack of fit with P value of .0165 for lack of fit. We take a compromise to accept this model. The normal plot of residuals based on this model is shown in Fig. C.3. This plot supports that the model is acceptable as the residuals follow very normal distribution. Fig. C.4 shows the correlation between predicted ln(CPP) and actual ln(CPP). The predication power of this model looks not bad. The P values of hypothesis test for all significant factors are tabulated in Table C.2. Those insignificant ones are not listed.

Figure C.3 Normal plot of residuals based on linear model.

Figure C.4 Correlation between ln(CPP) predicted values and actual values based on linear model. CPP, Cut protection performance. Table C.2 P Values of all significant factors. Factor

P Value

Filler size Tungsten% Alumina% Linear density Basis weight

, .0001 .0481 , .0001 .001 , .0001

Appendix D: Physical properties of materials

Specific gravity

Tenacity

Tensile modulus

cN/dtex GPa

cN/dtex

GPa

Break elongation (%)

Moisture LOI Melting regain (%) point* ( C)

Chemical resistance

Unit cut index (gf/gsm fiber)

Abrasion resistance

Diameter dependent B2.5 3.0, diameter dependent

1111

Steel wire

7.85

4

2.8

290

200

1.4

0

100

1510

2

E glass fiber

2.60

13

2.3.4

277

72

3.1

0

100

1050

1

S glass fiber PPTA paraaramid

2.55 1.44

16.1 20

4.1 2.8

341 500

87 72

3.1 3.5

0 7

1000 1100 29 480*

HPPE

0.97 0.98 35

3.5

1200

120

3.0

0

17

135 150

PBO HS PP Nylon 6

1.55 0.91 1.13

37 15 4 7

5.8 1.3 0.5 0.8

1150 350 25 35

180 32 2.8 4

3.5 6.0 20 50

2 0 3.5

68 17 20

650* 175 210

Nylon 66

1.14

5 8

0.6 0.9

30 40

3.4 4

20 40

4.5

20

250

PET

1.38

4 8

0.55 1.1 30 70

3.5 7

10 50

0.4

20

255

11

B1.65 2.0, diameter dependent 1111 1 1.5 1.7, diameter dependent 1 No data 11 1 No data 11 B1 1.2, diameter dependent 11 B1 1.2 diameter dependent 11 1 B1 1.2, diameter dependent

2

1 1111 1 1 11 11 1 1111 11

11

1450

1

2

60

1000*

0.006 500 700 2.8 7.1 20 55

1.3 1.5

19 18

250 310

75

0.05

29

350

5.3 7.7 15

12

20

300

0.45 0.8 60 80

9 12

3 7

10

20

340

15

1.4

330

42

6

4

20

2.70

6 12

16 3.2

320 360 85 95

2 3

0

100

1.45

17 28

2.5 4.0

1030

2 3.6

,1

. 40 . 550

1.79

Spandex Acrylic fiber

1.30 0.5 1.5 0.06 0.2 0.05 1.14 1.19 2 3.5 0.2 0.4 25 60

TLCP polyarylate Viscose

1.40

23

3.2

1.53

2 2.5

0.3 0.38 35 50

Cotton

1.54

3 5

High strength polyvinyl formal Basalt fiber

1.30

High tenacity polyimide fiber

80

1111 1 B2 2.5, diameter dependent 1 No data 11 B1, diameter dependent 11 1 B2 3, diameter dependent 11 B0.8 1, diameter dependent 0 B0.8 1, diameter dependent 0 No data

0

(T300) Carbon fiber

21

3.8

12.8

530

230

150

1.6

3.8

11 1

B2.5 3, diameter dependent B1.65 2.0

2 11 1 11 1111 1 1

11

HPPE, high performance polyethylene; HS PP, high strength polypropylene; PBO, poly-p-phenylene benzobisoxazole; PET, polyethylene terephthalate; PPTA, poly(para-phenylene terephthalamide); TLCP, thermotropic liquid crystalline polymer. Note: *means degradation temperature.

Appendix E: Constructions of knit fabric with different fibers

Fiber material

Gauge

Construction

Basis weight (gsm)

p-Aramid filament (incl. textured yarn)

13

400 450

p-Aramid filament (incl. textured yarn) p-Aramid spun yarn p-Aramid spun yarn

15

1. (2 3 70D DTY wrapped 70D spandex) 1 600D p-Aramid filament 2. (2 3 70D DTY wrapped 70D spandex) 1 400D p-Aramid filament 1 3 3 70D DTY (2 3 70D DTY wrapped 40D spandex) 1 400D p-Aramid filament

7 10

p-Aramid spun yarn

13

p-Aramid spun yarn

15

p-Aramid spun yarn

18

HPPE

13

HPPE

15

1. 5 3 20cc/2 p-Aramid spun yarn 2. 6 3 20cc/2 p-Aramid spun yarn 1. 2 3 20cc/2 p-Aramid spun yarn 2. 2 3 20cc/2 p-Aramid spun yarn 1 1 3 20cc/1 p-Aramid spun yarn 3. 3 3 20cc/2 p-Aramid spun yarn 1. 1 3 20cc/2 p-Aramid spun yarn 1 (2 3 70D DTY wrapped 70D spandex) 2. 1 3 24cc/2 p-Aramid spun yarn 1 (2 3 70D DTY wrapped 70D spandex) 1. 1 3 24cc/2 p-Aramid spun yarn 1 (2 3 70D DTY wrapped 70D spandex) 2. 1 3 24cc/2 p-Aramid spun yarn 1 (2 3 70D DTY wrapped 40D spandex) 1. 1 3 40cc/2 p-Aramid spun yarn 1 1 3 40D DTY 2. 1 3 40cc/2 p-Aramid spun yarn 1 1 3 40D DTY wrapped 20D spandex 1. (2 3 70D DTY wrapped 70D spandex) 1 600D HPPE filament 2. (2 3 70D DTY wrapped 70D spandex) 1 (2 3 70D DTY wrapped 100D glass) 1 400D HPPE filament 1. (2 3 70D DTY wrapped 70D spandex) 1 400D HPPE filament

300 350

1. 580 2. 680 1. 350 2. 400 3. 480

600 700 400 500 520

1. B400 2. B370

300 350

200 250

1. 350 400 2. 380 450

350 400 (Continued)

246

Appendix E: Constructions of knit fabric with different fibers

(Continued) Fiber material

Gauge

Construction

Basis weight (gsm)

HPPE

18

200 250

Steel wire

10

Steel wire

13

Steel wire

18

Nylon or PET DTY Nylon or PET DTY Nylon or PET DTY

13 15 18

1. 1 3 70D DTY 1 200D HPPE filament 2. (1 3 40D wrapped 20D spandex) 1 200D HPPE filament 1. 12s/1 spun yarn wrapped 50 mm steel 1 2 3 20s/2 spun yarn 2. 12s/1 staple/50 mm steel core-spun yarn 1 12s/1 spun yarn 1. 12s/1 spun yarn wrapped 50 mm steel 1 (2 3 70D DTY wrapped 70D spandex) 2. 12s/1 staple/50mm steel core-spun yarn 1 (2 3 70D DTY wrapped 70D spandex) 20s/1 staple/30 35 mm steel core-spun yarn 1 (1 3 70D DTY wrapped 40D spandex) 2 3 420D DTY 2 3 300D DTY 1 3 300D DTY

cc, Cotton count; DTY, draw textured yarn; PET, polyethylene terephthalate.

1. 450 500 2. 420 470

1. 350 400 2. 330 380

270 300

300 350 250 300 200 250

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Index

Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively. A Acetate fiber, 129 130 Acrylic fiber, 200 Acrylonitrile-butadiene rubber (NBR), 159, 214 216 Acrylonitrile fiber, 129 130 AFChina, 133 137 Air-covered yarn (ACY), 94, 95f Air-gap spinning dry jet wet spinning, 130 132 Air textured yarn (ATY), 82 83, 82f, 83f interlacing process, 83f Akzo Nobel, 133 137 Allied Corp, 151 ANSI/ISEA 105-2016, 35t, 36f, 37t Aoshen, 197 Aramid III, 137 para-Aramid fiber, 130 147, 220 221 filament, 138 141 staple spun yarn, 141 144 textured yarn of, 144 147 Artificial wool, 200 Asian para-aramid manufacturers, 133 137 ASTM D1907, 99 100 ASTM D5647, 107 ASTM F1790-05 CPPT instrument, 38f ASTM F2992/F2992M-15, 34 40, 35t ASTM standards series for chainsaw protection, 53 58, 55t B Bale opening and cleaning, 67f Basalt fiber, 193 194 Bicomponent textured yarn, 87, 88f Blade displacement, 222f Bluestar New Chemical Materials, 133 137 Bluestar’s Staramid aramid III, 139f

C Carbon fiber, 129, 200 201 and ceramic fibers, 201t Cellulose fiber, 200 Ceramics, 201 Chainsaw, protection against cut resistance for, 50 58 ASTM standards series for chainsaw protection, 53 58 ISO and EN standards series for chainsaw protection, 50 53 Chainsaw cut resistance, 52f Chainsaw protection ASTM standards series for, 53 58, 55t ISO and EN standards series for, 50 53 Chain Speed (CS) 50 (CS50), 54 55 Chemical bonding, 127 Chinlone, 123 125 Chloroprene latex, 216 Composite fibers/yarns comparison in structures for, 98f Composite yarn, 87 96 Construction work, 3 Continuous fiber, 59 Core-spun yarn, 87 94, 89f, 90f Cotton count, 98 Cotton fiber, 61, 185 186 Coupe cut testing, 23f, 26 29 Coupe test, 22, 30, 30t, 158 CPPT (cut protective performance test) cut testing, 38f Crimp contraction, 63 64 Crimp elasticity rate, 64 65 Crimp frequency, 61 63 Crimping technologies, 61 Crimp recovery rate, 64 Crinkled gloves, 206f Cut

274

Cut (Continued) mechanism of, 219 223 and slash hazards, 1 Cut protection performance (CPP), 227 228 Cut resistance development trend and measures to improve, 228 232 factors affecting, 224 228 Cut resistance, evaluating, 15 ASTM F2992/F2992M-15, 34 40 EN388:2016, 21 34 for protection against chainsaw, 50 58 ASTM standards series for chainsaw protection, 53 58 ISO and EN standards series for chainsaw protection, 50 53 ISO13997, 15 21 ISO13998, 40 43 ISO13999, 44 49 ISO13999-1, 49 ISO13999-2, 48 49 ISO13999-3, 45 48 ISO23388:2018, 21 34 Cut resistance data reported in patents242 248, 161t, 235 236 D Decitex, 97 Deformability of materials, 224 Denier, 96 97 Dimethylforamide (DMF), 206 211 Dipped and dotted gloves, 205f Dipping/coating materials for cut protective textile, 201 218 chloroprene latex, 216 epoxy, 218 natural rubber latex, 212 214 nitrile rubber latex, 214 216 polyvinyl chloride (PVC) dipping or dotting, 216 217 silicone rubber dotting, 217 218 solvent-borne polyurethane, 206 212 water-borne polyurethane dispersion/ emulsion, 212 Direct-counting method, 110 Discontinuous fiber, 59 Draw Textured Yarn (DTY), 66f, 81 82, 85 86 DREF spinning, 89 93

Index

Dry jet wet spinning, 130 132 Dry spinning process, 134f Dry wet spinning, 130 132, 135f DSM, 149 152, 151f DuPontt, 160, 195 DuPontt Kaptons, molecular structure of, 195f DuPontt Kevlars fiber, 133 137, 145f, 146f DuPont’s Kevlars 49 (K49), 137 138 DuPont’s Kevlars 119 (K119), 137 138 Dynamometer, 16 Dyneemas Diamond Technology, 158 159, 159f, 159t E Electronics, handling, 5f Electronics assembling and handling, 2 3 Elongation, defined, 101 EN388:2016, 21 34, 31t, 32t, 37t EN388 Coupe test, 174 F False twist textured yarn, 84 86, 84f Fibers, basic forms of, 59 96 air-covered yarn (ACY), 94, 95f core-spun yarn, 88 94, 89f, 90f filament yarn, 81 staple and staple spun yarn, 61 81 textured yarn, 81 87 air textured yarn, 82 83, 82f, 83f bicomponent textured yarn, 87, 88f false twist textured yarn, 84 86, 84f wrap yarn, 94 96, 96f, 97f Fibers, basic properties of, 96 110 bollard-type jaws for light denier yarn tensile testing, 104f bollard-type jaws for wire and heavy denier yarn tensile testing, 104f capstan-type jaws for yarn and cord testing, 105f hairiness, 107 international testing standards for yarn and fiber tensile testing, 103 105 linear density, 96 100 mechanical properties, 101 107 stress strain (tenacity elongation) curves, 102f twist, 109 110

Index

yarn evenness, 107 109 Fibers, constructions of knit fabric with, 245 246 Fiber to textile conversion, 111 knitting, 111 120 nonwoven, 125 127 weaving, 121 125 Filament yarn, 59, 60f, 81 Floc, 59, 60f Food processing, 3, 6f Forestry, 2 Friction false twisting, 86, 86f, 87f Friction spinning, basic mechanism of, 89 90, 91f, 93, 93f Fully dipped gloves, 202f G Gear crimping, 61, 62f Gel-spun HPPE yarn, 153f Glass fiber, 129, 132f, 165 169 Glass fiber spinning, 166f Glass manufacturing factories, 2 Glove dipping, 209f Gloves crinkled, 206f dipped and dotted, 205f dipping, 209f fully dipped, 202f impact- and vibration-resistant, 208f leather palm stitched, 208f palm dipped, 202f palm dotted, 204f partially dipped, 203f sandy, 205f specialty screen printed, 207f steel chainmail, 170, 171f Guigu, 133 137 H Hand pin knitting, 111, 112f High-performance polyethylene (HPPE), 146 149, 150f, 151 156, 152f, 153f, 153t, 169 High strength and high modulus polypropylene fiber, 188 190 Hoechst Celanese filed patents, 160 HPPE yarn, 95 96 Huvis, 133 137 Hybrid/composite fibers, 231

275

Hybrid/composite textile, 231 Hydroentanglement, 126 Hyosung, 133 137 I Ice hockey sport, 12f Impact- and vibration-resistant gloves, 208f Imperial Chemical Industries (ICI), 176 178 Integrated Textile Systems (ITS), 160 International tensile testing standards for fiber and yarn, 106t International testing standards for yarn and fiber tensile testing, 103 105 ISO and EN standards series for chainsaw protection, 50 53 ISO13997, 15 21 cut testing instruments for, 16f straight cut blade used for, 17f ISO13997 TDM cutting, 174 ISO13998, 40 43, 51t blade holding block for, 42f, 47t impact cut test, 46f penetration performance requirements per, 45t ISO13999, 44 49, 51t ISO13999-1, 49 ISO13999-2, 48 49 ISO13999-3, 45 48 ISO2060, 99 100 ISO23388:2018, 21 34 K Kawabata transverse compression instrument, 220 221 Kevlars 29 (K29), 137 138 Kevlars 49 (K49), 137 138 Kevlars 119 (K119), 137 138 Kevlar para-aramid fiber, 81 Kevlar yarn, 185 186 Knife impact penetration testing, 40, 50f Knit fabric, constructions of with different fibers, 245 246 with nylon yarn, 177t with steel wire, 173t Knitting, 12 13, 111 120 course spacing, 117 118, 117f knit mittens, 112f mechanism of forming knitting loop, 113f

276

Kolon, 133 137 Kuralons, 190 191 Kuraray, 180 184, 190 191, 195 L Laundered fiberglass containing cut-resistant sleeve, 168f Leather and textile mills, 5 8 Leather palm stitched gloves, 208f Liquid crystalline polyester, microorientation structures of, 182f Liquid crystalline polymer (LCP), 180 181 Liveliness of yarn, 79 80 Logit regression, 57 M Macroscopic and microscopic hybrids/ composites, 231 Materials, choice of, 129 para-Aramid, 133 147 para-Aramid filament, 138 141 staple spun yarn, 141 144 textured yarn of para-aramid, 144 147 basalt fiber, 193 194 cotton fiber, 185 186 dipping/coating materials for cut protective textile, 201 218 chloroprene latex, 216 epoxy, 218 natural rubber latex, 212 214 nitrile rubber latex, 214 216 polyvinyl chloride (PVC) dipping or dotting, 216 217 silicone rubber dotting, 217 218 solvent-borne polyurethane, 206 212 water-borne polyurethane dispersion/ emulsion, 212 glass fiber, 132f, 165 169 high strength and high modulus polypropylene fiber, 188 190 high-strength polyethylene (ultrahigh molecular weight polyethylene), 147 164 nylon fiber, 175 176 other fibers, 200 201 polyester fiber, 176 180 polyimide fiber, 194 198 poly-p-phenylene benzobisoxazole fiber, 186 188

Index

polyvinyl alcohol (PVA) fiber, 190 193 spinning, 129 133 melt spinning, 129, 130f solution spinning, 129 133 steel wire, 169 174 tungsten wire, 198 199 wholly aromatic polyester fiber, 180 184 Melt spinning, 129, 130f Mersenne’s law, 99 100 Metal-processing factories, 2 Metric count, 98 Modacrylic, 200 Modified/improved false twist process, 85 N Natural rubber latex, 212 214 Needle punching loom, 126, 127f New fiberglass containing cut-resistant sleeve, 167f Nextels, 201 Nippon Oil Company (NOC), 160 process disclosed by, 165f Nippon Petrochemicals, 160 Nitivy, 191 Nitrile rubber latex, 214 216 Nonwoven, 125 127 Nylon 6, chemical structures of, 175f Nylon 66, chemical structures of, 175f Nylon 66 fiber, typical properties of, 180t Nylon fiber, 129, 175 176 Nylon yarn, knit fabrics constructions with, 177t P P84 polyimide, molecular structure of, 195f Palm dipped gloves, 202f Palm dotted gloves, 204f Paper, handling, 7f Partially dipped gloves, 203f Percentage crimp, 63 64 measurement of, 63f Personal protection equipment (PPE) market, 9 12 p-Phenylenediamine, 133 137 Physical properties of materials, 241 244 Plied yarn, 98 Poly(para-phenylene terephthalamide) (PPTA) para-aramid fiber, 133 138, 136f, 142t, 143f, 147f

Index

DuPontt Kevlars PPTA fiber, 135f intermolecular hydrogen bonding in, 147f radial stacking of hydrogen-bonded sheets in, 148f skin-core morphology of, 148f Polyamide, 175 Polybutylene terephthalate (PBT), 176 180 Polyester, 129, 176 180, 185 186 chemical structures of, 178f microorientation structures of, 182f typical properties of, 180t Polyethylene (PE), 149 151 high-strength, 147 164 molecular structure of, 149f Polyethylene terephthalate (PET), 176 178 Polyimide fiber, 194 198 Polyimide filament, 196f poly-p-phenylene benzobisoxazole (PBO) fiber, 181, 186 188 physical properties of, 187t Polypropylene (PP) fiber, 188 Polytrimethylene terephthalate (PTT), 176 179 Polyurethane (PU), 159, 206 212 Polyvinyl alcohol (PVA) fiber, 190 193 Polyvinyl chloride (PVC) dipping or dotting, 216 217 Pressurized glass bottle handling, 3 4, 7f Protective gaiters, 11f Protective sleeve, 11f Pulp and paper industry, 5 R Recycling and waste handling, 2 Regenerated cellulose fiber, 200 S Sandy gloves, 205f Saw chain, profile of, 53f Scanning electron microscope (SEM), 219 220 Sheet metal handling, 1 2, 2f Shenma, 133 137 Shino, 197 Shino high tenacity polyimide fibers, physical properties of, 197t Shin’s method, 220 Short fiber, 59, 60f Silicone elastomer, 217 218

277

Silicone rubber dotting, 217 218 Sintech cut testing, 181 184 Skate blade slash injury, risk of, 8f Skin-core type material, 225 Slaughtering, 2, 4f Solid-state extrusion (SSE) process, 160, 162 163, 163f Solution spinning, 129 133 Solvent-borne polyurethane, 206 212 Soronas, 179 Spandex, 129 130 Spandex fiber, 129 130 Specialty screen printed gloves, 207f Spinneret, 130 132 Spinning, 129 133 melt spinning, 129, 130f solution spinning, 129 133 Spinning glass fiber, 129 Sports, 8 Spun yarn, 61 81, 62f Staple and staple spun yarn, 59, 60f, 61 81 carding, 66, 68f doubling, 70, 73f drafting, 68 69, 72f drawing, 66, 69f opening and cleaning, 66, 67f process steps to spin staple to spun yarn, 66f roving, 66, 70f spinning, 66 68, 71f, 81 spun from different spinning technologies, 72f twisting, 70 75, 74f, 75f, 76f, 77 79, 77f winding, 69, 73f with different number of crimps and percentage crimp, 65f Staple spun yarn, 141 144 Staramid aramid III, 139f Statistical analysis for data in patents, 237 240 Steel chainmail glove and apron, cut protection with, 171f Steel chainmail gloves, 170 Steel wire, 169 174 as wrapping yarn, 171f cold drawing process, 170f knit fabrics constructions with, 173t Stuffer box crimping, 61, 62f Sumikasuper LCP fiber, 185f

278

Sumikasuper LCP fiber (Continued) chemical structure of, 185f Surface treatment/modification, 232 Synthetic Industries, 160 T Tayho Advanced Materials, 133 137 TDM-100, 16 cut testing on TDM-100 instrument, 17f Technoras fiber, 137, 138f Teijin, 133 137 Twarons, 133 137 Teijin Aramid, 164 Tenacity, 101 Tenacity and strength conversions between different units of, 233 234 Tensile modulus, 102 Tensylons, 160, 163 164, 165t, 189 Terephthalate-type polyesters, 176 178 Terephthaloyl chloride, 133 137 Textile gloves, 10f Textured yarn, 81 87 air textured yarn, 82 83, 82f, 83f bicomponent textured yarn, 87, 88f false twist textured yarn, 84 86, 84f of para-aramid, 144 147 Thermoplastic fibers, 129 3D-knitted fabric, 121f with spacer, 121f Three-dimensional woven fabric, 126f 3M, 201 Tianyi Engineering Fiber Co., 191 Tomodynamometer (TDM), 16, 59, 172 174 Toyobo, 151 152 Triaxial weaving, goods made by, 125f Triaxial woven fabric, 124f Tsunoogat, 151 152 Tungsten wire, 198 199 Twarons D1000, 137 138 Twarons D2100, 137 138 Twarons D2200, 137 138 Twaron para-aramid fiber, 133 137 Twist factor, 81 U Ultrahigh molecular-weight (PE) (UHMWPE) fiber, 133, 147 149, 162 163

Index

Ultrahigh molecular weight polyethylene, 13, 147 164 Untwist retwist method, 109 V Vectrant fiber, 180 184, 230 231 Vectrat polymer, molecular structure of, 180f Vinylon fiber, 129 130 Viscose fiber, 129 130 W Warp knitting, 113, 114f, 116 structure, 115f versus weft knitting, 116t Warp yarn, 123 Water-borne polyurethane dispersion/ emulsion, 212 Water-jet bonding, 126 Weaving, 121 125 common weaving constructions, 124f mechanism of primitive weaving, 122f principle of, 123f Web formation, technologies of, 125 126 Weft knitting, 113, 114f structure, 115f versus warp knitting, 116t Wet spinning, 129 130, 133f Wholly aromatic polyester fiber, 180 184 Woven fabric, 121 122, 122f three-dimensional woven fabric, 126f triaxial woven fabric, 124f Wrapping yarn, steel wire as, 171f Wrap yarn, 87 88, 94 96, 96f, 97f Y Yarn evenness, 107 109 Yarn hairiness, 107, 108f Yarn tenacity, 79f Yizheng Chemical Fiber of Sinopec, 133 137 Young’s (elastic) modulus, 227 Z Zhaoda, 133 137 Zylons PBO fiber, 187f molecular structure of, 186f