Advanced functional textiles and polymers : fabrication, processing and applications [First edition] 9781119605843, 1119605849, 9781119605799, 9781119605829, 9781119605836

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Advanced Functional Textiles and Polymers

Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106 Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])

Advanced Functional Textiles and Polymers

Edited by

Shahid-ul-Islam and B.S. Butola

This edition first published 2019 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA © 2020 Scrivener Publishing LLC For more information about Scrivener publications please visit www.scrivenerpublishing.com. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. Wiley Global Headquarters 111 River Street, Hoboken, NJ 07030, USA For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials, or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Library of Congress Cataloging-in-Publication Data Names: Ul-Islam, Shahid, editor. | Butola, B. S. (Bhupendra Sing), editor. Title: Advanced functional textiles and polymers : fabrication, processing and applications / edited by Shahid-ul-Islam and B.S. Butola. Description: First edition. | Hoboken, New Jersey : John Wiley & Sons, Inc. ; Salem, Massachusetts : Scrivener Publishing LLC, 2019. | Includes bibliographical references and index. Identifiers: LCCN 2019033355 (print) | LCCN 2019033356 (ebook) | ISBN 9781119605799 (hardback) | ISBN 9781119605829 (adobe pdf) | ISBN 9781119605836 (epub) Subjects: LCSH: Textile fabrics--Technological innovations. | Textile fibers, Synthetic. | Polymers-Industrial applications. Classification: LCC TS1765 .A4234 2019 (print) | LCC TS1765 (ebook) | DDC 677/.028--dc23 LC record available at https://lccn.loc.gov/2019033355 LC ebook record available at https://lccn.loc.gov/2019033356 Cover image: Pixabay.Com Cover design by Russell Richardson Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines Printed in the USA 10 9 8 7 6 5 4 3 2 1

Contents Preface 1 Flame Retarded Cotton Fabrics: Current Achievements, Open Challenges, and Future Perspectives Giulio Malucelli 1.1 Introduction 1.2 Textile Finishing With Sol–Gel Treatments 1.2.1 Fully Inorganic Systems 1.2.2 Phosphorus-Doped Sol–Gel Coatings 1.2.3 Hybrid Organic–Inorganic Sol–Gel Coatings 1.3 Textile Finishing With Layer-by-Layer Assemblies 1.3.1 Fully Inorganic LbL Assemblies on Cotton 1.3.2 Intumescent LbL Assemblies on Cotton 1.3.3 Hybrid LbL Assemblies on Cotton 1.4 Current Limitations of Sol–Gel and Layer-by-Layer Treatments 1.5 Conclusions and Future Perspectives Acknowledgments References 2 UV Protective Clothing Anu Mishra and Bhupendra Singh Butola 2.1 Introduction 2.2 Harmful Effects of UV Radiations on Skin 2.2.1 Short-Term Effects 2.2.2 Long-Term Effects 2.3 Environmental Factors Influencing UV Level on Earth 2.3.1 Effect of Ozone Layer Depletion 2.3.2 Solar Elevation (Height of the Sun in the Sky) 2.3.3 Latitude and Altitude 2.3.4 Cloud Cover and Haze 2.3.5 Ground Reflection

xvii 1 2 8 10 13 14 17 18 19 23 25 26 27 27 33 33 34 37 38 39 40 40 40 41 41 v

vi

Contents 2.4 Effect of Physical and Chemical Characteristics of Textile Materials on UV Protection 2.4.1 Effect of Physical Parameters 2.4.1.1 Yarn Structural Parameters 2.4.1.2 Fabric Structural Parameters 2.4.2 Effect of Chemical Parameters 2.4.2.1 Effect of Fiber Chemistry 2.4.2.2 Effect of Chemical Processing (Bleaching, Dyeing, and Other Finishing Chemicals) 2.5 Type of UV Finishes, Their Working Mechanism, and Limitations 2.5.1 Organic UV Absorbers 2.5.2 Inorganic UV Blockers 2.6 Application Methods of UV Finish in Textiles 2.7 Test Methods for Quantitative Assessment of UV Protection of Textiles 2.7.1 In Vitro 2.7.2 In Vivo 2.8 Summary References

3 Potential of Textile Structure Reinforced Composites for Automotive Applications Vikas Khatkar, R. N. Manjunath, Sandeep Olhan and B. K. Behera 3.1 Introduction 3.2 Materials for Automotive 3.2.1 Metallic Materials in Automotive 3.2.1.1 Steel 3.2.1.2 Aluminum 3.2.1.3 Magnesium 3.2.2 Composite Materials for Automotives 3.2.2.1 Natural Fiber Reinforcement Polymer Composites 3.2.2.2 Advance Fiber-Based Composite 3.2.3 Advantage of Composite Over Conventional Materials 3.2.3.1 Lightweight 3.2.3.2 Crashworthiness 3.2.3.3 Joining 3.2.3.4 Recycling

42 43 43 43 44 44 45 46 46 49 50 54 56 57 57 58 65

66 68 68 68 68 69 70 71 73 75 75 78 79 79

Contents 3.3 Textile Materials for Automotive 3.3.1 Textile Structural Composites for Automotive 3.3.1.1 3D Fabrics as New Solutions for Transportation Applications 3.4 Potential Automotive Parts to be Replaced With Textile Structural Composites 3.4.1 Automotive Interiors 3.4.2 Exterior Body Panels 3.4.2.1 Car Hoods (Bonnet) 3.4.2.2 Bumpers 3.4.2.3 Door Panels 3.4.3 Structural Components 3.4.3.1 Leaf Spring 3.5 Lightweight Solution for Electric Car 3.6 Conclusion References 4 Biotechnology Applications in Textiles Lalit Jajpura 4.1 Introduction 4.2 Adverse Effects of Industrial Farm Practices in Cotton Cultivation 4.2.1 Adverse Effect of Synthetic Fertilizers 4.2.2 Adverse Effect of Synthetic Pesticides 4.2.3 Adverse Effect of Excessive Irrigation 4.3 Application of Biotechnology in Cotton Cultivation 4.3.1 Gene Construction and Transformation 4.3.2 Bt Cotton 4.4 Wet Processing of Cotton and Its Environmental Impact 4.5 Enzyme and Its Properties 4.6 Classification of Enzymes 4.7 Enzymatic Bioprocessing of Cotton 4.7.1 Desizing 4.7.2 Enzymatic Desizing 4.7.2.1 Amylase (E.C. 3.2.1.1) 4.7.2.2 Lipase (EC 3.1.1.3) 4.7.3 Scouring 4.7.4 Enzymatic Scouring 4.7.4.1 Pectinase (EC 3.2.1.15) 4.7.4.2 Lipase (EC 3.1.1.3) 4.7.4.3 Cellulase (EC 3.2.1.4)

vii 80 82 84 85 85 87 87 88 90 90 91 93 93 94 99 100 101 101 102 103 103 104 105 105 106 107 108 108 109 109 109 110 110 110 111 111

viii

Contents 4.7.4.4 Cutinase (EC 3.1.1.74) 4.7.4.5 Xylanase (EC 3.2.1.8) 4.7.5 Enzymatic Bleaching 4.7.5.1 Laccase (E.C. 1.10.3.2) Enzymatic Hydrogen Peroxide Removal by Catalase 4.8.1 Catalase (E.C. 1.11.1.6) Biopolishing of Cotton Enzymatic Fading of Denim Application of Biotechnology in Wool Production and its Wet Processing Enzymatic Bioprocessing of Wool 4.12.1 Enzymatic Carbonization of Wool 4.12.2 Enzymatic Scouring of Wool 4.12.2.1 Protease (EC 3.4.21.112) 4.12.3 Enzymatic Finishing of Wool Application of Biotechnology in Sericulture and Wet Processing of Silk Enzymatic Bioprocessing of Silk Application of Biotechnology in Sustainable Finishing Application of Enzyme Immobilization Techniques in Reuse of Enzymes Conclusion References

111 112 112 113 113 114 114 114

5 Environmental Issues in Textiles Rishabh Kumar Saran, Raj Kumar and Shashikant Yadav 5.1 Introduction 5.2 Textile Fiber 5.3 Processes in the Textile Industry 5.4 Key Environmental Issues 5.4.1 Supply Water 5.4.2 Chlorinated Solvents 5.4.3 Hydrocarbon Solvents—Aliphatic Hydrocarbons 5.4.4 Hydrocarbon Solvents—Aromatic Hydrocarbons 5.4.5 Oxygenated Solvents (Alcohols/Glycols/Ethers/ Esters/Ketones/Aldehydes) 5.4.6 Grease and Oil Impregnated Wastes 5.4.7 Used Oils 5.4.8 Dyestuffs and Pigments Containing Dangerous Substances

129

4.8 4.9 4.10 4.11 4.12

4.13 4.14 4.15 4.16 4.17

115 115 115 116 116 116 117 117 118 119 119 120

130 130 131 134 134 137 137 138 138 139 139 140

Contents 5.4.9 Heat and Energy Generation From Textile Industry Waste 5.4.10 Carbon Footprint of a Textile Product 5.5 Environmental Impact of Textile Industry Wastewater 5.6 Environmental Legislation References

ix

140 143 144 146 146

6 Water Saving Technologies for Textile Chemical Processing Nagender Singh 6.1 Introduction 6.1.1 Indian Textile Industry 6.1.2 Water Consumption in Textile Processing 6.2 Technologies for Water Saving in Textile Chemical Processing 6.2.1 Process Optimization Techniques 6.2.2 Emerging Water-Saving Wet Processing Technologies 6.2.3 Low Liquor Technologies 6.3 Conclusion References

153

7

171

Photocatalytic Dye Degradation Using Modified Titania Waseem Raza and Mohd Faraz 7.1 Introduction 7.1.1 Discovery of Photocatalysis: A Short Historical Overview 7.1.2 Photocatalytic Mechanism 7.1.3 Mechanism Under Visible Light Irradiation 7.1.4 Direct Mechanism for Dye Degradation 7.1.5 Our Research Focus 7.2 Photocatalytic Application 7.2.1 Degradation of Methylene Blue Using Fe-Doped TiO2 7.2.2 Degradation of Acid Yellow 29 Using La and Mo-Doped TiO2 Carbon Sphere (CS) 7.2.3 Degradation of Coomassie Brilliant Blue G250 Using La and Mo-Doped TiO2 Carbon Sphere 7.2.4 Degradation of Acid Green 25 Using La and Mo-Doped TiO2 Carbon Sphere 7.2.5 Degradation of Acid Yellow 29 Using Ce and Mn-Doped TiO2 Carbon Sphere 7.2.6 Degradation of Acid Green 25 Using Ce and Mn-Doped TiO2 Carbon Sphere

154 155 157 158 158 160 165 166 167

172 174 175 176 178 179 180 180 181 182 184 185 186

x

Contents 7.2.7 Degradation of Barbituric Acid and Matrinidazole in Using Undoped and Ni-Doped TiO2 7.3 Factors Affecting the Degradation of Organic Pollutants 7.3.1 Effect of pH 7.3.2 Effect of Photocatalyst Loading 7.3.3 Effect of Calcination Temperature 7.3.4 Effect of Reaction Temperature 7.3.5 Effect of Inorganic Ions 7.4 Conclusions References

8 Advanced Approaches for Remediation of Textile Wastewater: A Comparative Study Shumaila Kiran, Sofia Nosheen, Shazia Abrar, Fozia Anjum, Tahsin Gulzar and Saba Naz 8.1 Introduction 8.1.1 Textile Wastewater 8.1.2 Characteristics of Textile Wastewater 8.1.3 Damages Caused by Textile Effluent 8.1.4 Ecological Balance and Environmental Issue 8.1.5 Need for the Treatment 8.1.6 Standards of Textile Industry for Water Contaminants 8.2 Treatment Methods for Textile Effluent 8.2.1 Dealings to Control Water Contamination 8.2.2 Physical Methods 8.2.2.1 Screening 8.2.2.2 Coagulation–Flocculation Treatments 8.2.2.3 Sedimentation 8.2.2.4 Equalization or Homogenization 8.2.2.5 Floatation 8.2.2.6 Adsorption 8.2.2.7 Membrane Processes 8.2.3 Chemical Methods 8.2.3.1 Chemical Precipitation 8.2.3.2 Neutralization 8.2.3.3 Electro Chemical Process 8.2.3.4 Oxidation Methods 8.2.3.5 Ion Exchange Process 8.2.4 Biological Methods 8.2.4.1 Efficiency of Biological Methods

188 190 190 191 192 193 193 195 195 201

202 202 202 202 204 204 206 207 207 208 208 209 210 211 211 212 214 219 219 220 220 221 226 229 232

Contents 8.2.4.2 Bacterial Decolorization of Dyes 8.2.4.3 Dye Degradation by Fungal Cultures 8.2.4.4 Algae for Degradation of Dyes 8.2.4.5 Microbial Fuel Cell 8.3 Sequential Method for Textile Effluent Treatment 8.3.1 Levels of Textile Effluent Treatments 8.3.1.1 Preliminary Treatment 8.3.1.2 Primary Treatment 8.3.1.3 Secondary Treatment 8.3.1.4 Tertiary Treatment 8.4 Conclusion References 9 Polymer-Supported Nanocomposite-Based Nanomaterials for Removal and Recovery of Pollutants and Their Application in Bio-Electrochemical System Abdul Hakeem Anwer, Nishat Khan, Mohammad Shahadat, Mohammad Zain Khan, Ziauddin Ahammad Shaikh and Syed Wazed Ali 9.1 Introduction 9.1.1 Reason for Selection of Polyaniline-Based Nanocomposite Material 9.1.2 Synthesis of PANI Based Nanocomposite 9.1.2.1 Sol–Gel Methode 9.1.2.2 Hydrothermal Method 9.1.2.3 Chemical Reduction Method 9.1.2.4 Chemical In Situ Polymerization Method 9.1.3 Treatment of Wastewater Using Bioelectrochemical System 9.1.3.1 Microbial Fuel Cell 9.1.3.2 MEC System 9.1.3.3 Electrode Material 9.1.4 Polyaniline-Supported Electrodic Material for MFC/MEC 9.2 Conclusion Acknowledgments References

xi 232 234 236 238 240 241 241 242 243 245 247 247

265

266 268 269 274 274 274 275 275 276 279 279 281 282 283 283

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Contents

10 Reactive and Functional Polymers Tanvir Arfin 10.1 Introduction 10.2 Types of Textiles 10.3 Location of Textile Industries in India 10.4 Role of Polymer 10.4.1 Chitosan 10.4.2 Starch 10.4.3 Gelatin 10.4.4 Cellulose 10.4.5 Protein 10.4.6 MWCNT 10.4.7 Dendrimer 10.4.8 Polystyrene 10.4.9 Nylon-6,6 10.4.10 Polyaniline 10.4.11 Polyvinyl Alcohol 10.5 Conclusion References

291 291 293 293 294 294 295 296 297 298 298 299 299 300 300 301 301 302

11 Fabrication and Biomedical Applications of Polyvinyl-AlcoholBased Nanocomposites With Special Emphasis on the Anti-Bacterial Applications of Metal/Metal Oxide Polymer Nanocomposites 309 Shahnawaz Ahmad Bhat, Fahmina Zafar, Azar Ullah Mirza, Abdulrahman Mohammad, Paramjit Singh and Nahid Nishat 11.1 Introduction 310 11.2 Scope of the Chapter 312 11.3 Metal/Metal Oxide Nanoparticles 313 11.3.1 Preparation of Metal Oxide Nanoparticles 314 11.3.1.1 Co-Precipitation Method 314 11.3.1.2 Hydrothermal Technique 314 11.3.1.3 Micro-Emulsion Method 315 11.3.1.4 Sol–Gel Method 315 11.4 Nanocomposite 316 11.4.1 Preparation of Nanocomposite 318 11.4.1.1 Ex Situ Method 318 11.4.1.2 In Situ Method 318 11.5 Biomedical Applications of Nanocomposite 319 11.5.1 Anticancer Application 320

Contents 11.5.2 Antibacterial Application 11.6 Conclusions Acknowledgments References 12 Preparation, Classification, and Applications of Smart Hydrogels Ali Akbar Merati, Nahid Hemmatinejad, Mina Shakeri and Azadeh Bashari 12.1 Introduction 12.2 Preparation and Characterization of Smart Hydrogels 12.2.1 Preparation of Smart Hydrogels 12.2.2 Characterization of Smart Hydrogels 12.3 Classifications of Smart Hydrogels 12.3.1 Physical Stimuli-Responsive Hydrogels 12.3.2 Chemical Stimuli-Responsive Hydrogels 12.3.3 Biochemical Stimuli-Responsive Hydrogels 12.4 Applications of Smart Hydrogels 12.4.1 Drug Delivery Systems 12.4.2 Injectable Hydrogels 12.4.3 Tissue Engineering 12.4.4 Smart Hydrogels as Actuators 12.4.5 Sensors 12.4.6 Self-Healing 12.5 Smart Hydrogel-Functionalized Textile Systems 12.6 Electrospinning of Smart Hydrogels 12.7 Future Trends of Smart Hydrogels 12.8 Conclusions References 13 Potential Applications of Chitosan Nanocomposites: Recent Trends and Challenges Tara Chand Yadav, Pallavi Saxena, Amit Kumar Srivastava, Amit Kumar Singh, Ravi Kumar Yadav, Harish, R. Prasad and Vikas Pruthi 13.1 Introduction 13.2 Synthetic Routes for the Preparation of Nanocomposites of Chitosan 13.2.1 General Synthetic Routes 13.2.2 Physical Methods

xiii 320 325 326 326 337

337 339 339 341 344 345 346 347 348 349 350 351 351 351 352 353 355 356 357 357 365

366 368 368 369

xiv

Contents 13.2.2.1

Photochemical Methods (UV, Near-IR), Radiolysis, and Sonochemistry 370 13.2.3 Chemical Method 370 13.2.3.1 Borohydride Reduction 371 13.2.3.2 Citrate Reduction 372 13.2.4 Seeding-Growth Method 372 13.2.5 Biosynthesis Methods 372 13.3 Applications of Chitosan Nanocomposites 373 13.3.1 Chitosan Treatment of Textiles 373 13.3.1.1 Wool 374 13.3.1.2 Silk 375 13.3.1.3 Cotton 376 13.3.2 Textile Functionalities Achieved 376 13.3.2.1 Antimicrobial and Enriched Dyeing Properties 376 13.3.2.2 Wrinkle Proof Resistance 378 13.3.3 Effluent Treatment Applications 378 13.3.4 Bioremediation 379 13.4 Biomedical Application 380 13.4.1 Drug Delivery 380 13.4.2 Wound Healing 381 13.4.2.1 Scaffolds Ingrained With Chitosan/Natural/ Synthetic Graft for Wound Healing 381 13.4.2.2 Composite Chitosan Graft Scaffoldings for Wound Healing 382 13.4.2.3 Chitosan–Oil Ingrained Grafts for Wound Healing 384 13.4.2.4 Plant Extract Ingrained Chitosan Film Scaffoldings for Wound Healing 384 13.4.2.5 Modified Chitosan Products for Wound Healing 385 13.4.2.6 Toxicological Assessment of Tri-Methyl Chitosan 385 13.4.2.7 Effect of Trimethyl Chitosan in Wound Healing 385 13.4.2.8 Impact of Carboxymethyl Chitosan and Carboxymethyl-Trimethyl Chitosan 386 13.4.2.9 Peptides Conjugates-Chitosan/Derivatives for Wound Healing 386 13.4.2.10 Commercial Dressing Bandages of Chitosan Blend 387

Contents 13.5 Future Prospects References 14 Use of Polymer Nanocomposites in Asphalt Binder Modification Saqib Gulzar and Shane Underwood 14.1 Introduction 14.2 Background 14.2.1 Asphalt Binders 14.2.2 Asphalt Modification 14.2.3 Comparative Analysis 14.3 Polymer Nanocomposites 14.3.1 Polymers and Nanomaterials 14.3.2 Polymer Nanocomposites (PNC) 14.3.2.1 PNC Blended Systems 14.3.2.2 PNC Integrated Systems 14.4 Rheological Impacts 14.4.1 Measures for Polymer Modified and Nano Modified Asphalt Binder Systems 14.4.2 Measures With PNC Modified Asphalt 14.5 Suggested Evaluation Method for PNC Modified Asphalt Binders 14.6 Summary References

Index

xv 388 389 405 405 407 408 411 413 415 415 416 417 417 418 418 421 427 428 428

433

Preface Advanced functional textiles and polymers have assumed a prominent position in everyday life as well in industrial, and technological applications. Research on several functional materials is going on a war footing basis to explore effective finishing agents in order to produce materials with diverse functions. This book on advanced functional textiles and polymers contains 14 important chapters written by specialists to provide systematic and comprehensive coverage of the topics, from advanced fabrication methodologies, through novel materials, to current and potential application sectors. This book provides state-of-the art information to researchers on flame retardant textiles, antimicrobial textiles, medical-textiles, smart textiles, and nano-textiles etc. The book also introduces several advanced polymers and provides an overview of latest novel agents employed in the research and development of functional polymers. The book offers an excellent source for materials scientists, chemists, chemical engineers, textile engineers and especially for academicians working in the field of health care textiles, polymer processing, synthesis and modification, chemical processing of textiles, antimicrobial coatings, and nano finishing. We should acknowledge and thank all the authors who have contributed their informative and in-depth chapters, as well as Martin Scrivener for his patience and hard work, essential for the compilation of this book. Finally, we would like to thank our institute Indian Institute of Technology Delhi for providing infrastructure and allowing us to complete this edited book on time. Shahid-ul-Islam B.S. Butola Indian Institute of Technology Delhi (IITD), Hauz Khas, New Delhi, India August 2019

xvii

1 Flame Retarded Cotton Fabrics: Current Achievements, Open Challenges, and Future Perspectives Giulio Malucelli

*

Politecnico di Torino, Department of Applied Science and Technology, Alessandria, Italy

Abstract Among cellulosic textiles, cotton is the most utilized, thanks to its peculiar characteristics (including softness, hygroscopicity, excellent breathability, comfortableness, biodegradation, and good thermal conductivity, among a few to mention). However, cotton burns very easily when it comes in contact with a flame or is exposed to an irradiative heat flux: as a consequence, this negative effect remarkably confines the possible exploitation of this material, particularly referring to those application sectors where flame retardant fibers and fabrics are a prerequisite. In this context, the academic and industrial work has been extensively focused on improving the flame retardant behavior of this cellulosic material. Among the different possible solutions, the so-called surface engineering represents a suitable and efficient strategy for conferring flame retardant properties to cotton: in fact, this approach allows the deposition of fully inorganic, fully organic, or hybrid organic–inorganic protective coatings on the fiber/fabric surface. In doing so, the heat and mass transfer phenomena occurring during the fire stages can be remarkably limited: in particular, the structure and composition of the deposited coatings play a key role in the formation of a protective layer on the textile substrate, thus conferring the envisaged flame retardant properties to this latter. From an overall point of view, the surface engineering approaches mainly involve sol–gel processes and layer-by-layer architectures. In particular, the sol–gel technique, which is a very well consolidated approach for the fabrication of ceramics, has started to be exploited also in the textile field because of its advantageous characteristics: among them, it is easily applicable to even irregular substrates as fibers and fabrics, Email: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (1–32) © 2020 Scrivener Publishing LLC

1

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Advanced Functional Textiles and Polymers

it can be carried out using the already existing industrial finishing lines (such as impregnation/exhaustion units), and it is very efficient in providing the treated substrates with flame retardant features. Besides, the layer-by-layer approach, though it has been well established practically at a lab-scale only, shows some interesting potentialities in a view of a possible scale-up. In addition, very often, the aforementioned techniques allow providing the processed fibers/fabrics with more than one functionality: more specifically, the scientific literature well highlights the possibility of conferring antibacterial/antimicrobial features, low surface tension, and electrical conductivity, apart from the flame retardant properties. Finally, sol–gel and, sometimes, layer-by-layer architectures (the latter depending on the presence of reactive functional groups in the deposited assemblies, which can permanently link the layers to the fabric substrate) can ensure washing fastness to the treated fabrics, which is very often a requisite for a wide number of applications. This chapter aims to review the state of the art and the still open challenges related to the design of effective flame retarded cotton fabrics. In particular, the current achievements in flame retardancy, specifically involving nanotechnology and surface engineering, will be thoroughly described, highlighting the present limitations and some possible further improvements. Keywords: Cotton, flame retardancy, surface engineering, sol–gel processes, layer-by-layer architectures, intumescent coatings, superhydrophobicity, washing fastness

1.1 Introduction Cotton is the most well-known cellulosic material: it possesses such properties as strength, durability, flexibility and air permeability, as well as good biocompatibility, low cost and good mechanical behavior. About 60% of the world’s total cotton harvest is employed for clothings, the rest being utilized for home furnishings and industrial products (i.e., tents, car tire cord, fishnets, and book bindings). At variance, if not flame retarded, cotton, as most of the textile products, is easily flammable: in fact, it burns vigorously, leaving a negligible residue. The annual U.K. fire statistics document that a considerable percentage of the fire incidents occur in domestic environments and involve nightwear, bedding and upholstered furniture [1]. In order to overcome this limitation, since the 1950s, both academics and industrial companies have designed and developed efficient flame retardants (FRs), aiming at reducing the risk of fire: in fact, they are able to decrease the ease of flammability of textiles by lowering the propensity of the material to ignite or slowing down the flame spread rate when needed.

Flame Retarded Cotton Fabrics

3

From an overall point of view, flaming combustion, which occurs in the gas phase, is an oxidation reaction and requires oxygen (or air) supply from the surrounding atmosphere. Flaming combustion is a consequence of the degradation of the material with the formation of combustible gases; the latter mix together with atmospheric oxygen, hence promoting a selfsustaining combustion exothermic process, as depicted by Emmons’ fire triangle [2] (Figure 1.1). The combustion reactions can proceed as long as there is enough oxygen (air) and fuel and if the temperature is high enough; if one of these three conditions lacks, fire propagation stops. Besides, either an adequate fuel/oxidant ratio or enough energy to be provided to the system is necessary in order to reach and then overcome the activation energy of the combustion process. Very recently, a different approach, called “Fire loop”, which describes the polymer combustion, was proposed [3]. The loop (Figure 1.2) emphasizes the cyclic connection that takes place between the two sequential pyrolysis and oxidation reactions involved in the fire event, which determine the overall combustion process, highlighting a particular kinetic interdependence of the two reactions. Basic chemical kinetics states that the rate, at which a product deriving from two linearly connected consecutive reactions is produced, strictly corresponds to the rate of the slowest process. Conversely, in the Fire loop, the two sequential pyrolysis and oxidation reactions exert an effect on each

HEAT SOURCE

Return of heat To air

To fuel

Combustion AIR

FUEL Mixing

Figure 1.1 Emmons’ fire triangle.

4

Advanced Functional Textiles and Polymers OX (Combustion Products)

O2

kOX kG=overall specific rate of volatiles products formation by polymer pyrolysis

FUEL (Volatile pyrolysis products)

HEAT

kOX=overall specific oxidation rate of volatiles products

kG POLYMER

HEAT DISPERSION

Figure 1.2 “Fire loop”.

other: in particular, the rate of polymer pyrolysis affects the oxidation– combustion rate through the formation of volatile species, which in turn affects the pyrolysis through the feedback of the combustion heat. Flame retardants (FRs) are able to delay and even stop the selfsustaining combustion process of the textile materials; according to their structure and chemical composition, they can act either in condensed or gas phase. In addition, the overall effects on either burning rate reduction or on the extinction of the flame are also dependent on the chemical composition and on the thermal and fire characteristics of the textile materials [4–6]. Besides, any of the FRs available on the market or specifically designed for scientific purposes may contain such elements in their molecule, as halogens, metals, boron, phosphorus, sulfur, nitrogen, or a combination of them. The flame retardant can be embedded in the synthetic fibers during the spinning processes or can be covalently linked to the fibers, exploiting grafting or copolymerization reactions. Another possibility involves the application of FRs as surface treatments (i.e., the so-called surfaceengineering or surface-engineered approaches), which exploit either the impregnation of the textiles in solutions/stable suspensions containing the flame retardant additive (i.e., a standard finishing treatment), or the coating of the textile substrate with a continuous or discontinuous layer/film on both outer and back surfaces.

Flame Retarded Cotton Fabrics

5

In doing so, if these treatments are very effective in providing the textile material with flame retardant features, several outcomes should be attained: – the heat developed should be lower than that necessary for sustaining the combustion process; – the textile pyrolysis should be addressed toward the formation of a carbonaceous residue (i.e., char) in condensed phase, hence limiting the formation of flammable products that can fuel the combustion; – the flame should be separated from the oxygen/air source; – on the basis of the chemical composition of the flame retardants, chlorine or bromine atoms, which act as flame inhibitors in the gas phase, should be released as the textile material approaches its ignition temperature; – the heat flow back to the textile substrate should be lowered, hence limiting the occurrence of additional pyrolysis reactions, which can give rise to gaseous flammable products; – in the condensed phase, upon exposure to a heat flow or a flame, the formation of a barrier, generally made of a coherent char or an intumescent protective coating, should be preferred. Some halogenated flame retardants as polychlorinated biphenyls and pentabromodiphenyl or decabromodiphenyl ethers [7–9] were found toxic or even mutagenic and therefore they have been banned from the market (even some directives from the European Community have been made and shared with all the European countries); this issue stimulated the scientific and industrial world toward the seeking for less toxic products with low environmental impact. As a consequence, phosphorus-based (even in combination with nitrogen) flame retardants have been identified as suitable alternatives for replacing halogenated flame retardants [10, 11]. In parallel, the flame retardancy of cotton and of other cellulosicrich substrates has been significantly improved by either designing efficient halogen-free flame retardants for coatings and back-coated textiles (these efforts have been made from academics mainly), or by using N-methylolphosphonopropionamide derivatives (Pyrovatex ) or hydroxymethylphosphonium salts (Proban ).The latter are “standard” commercially available flame retardants that, apart a high FR efficiency, show significant drawbacks and limitations: in particular, the Proban process (schematically depicted in Figure 1.3) requires a specific plant for stabilizing

6

Advanced Functional Textiles and Polymers CH2OH 2 HOCH2

P+

CH3OH

+

H2NCONH2

CH2OH Cl CH2OH HOCH2

CH2OH P+

CH2NHCONHCH2

P+

CH2OH

CH2OH Cl-

CH2OH Cl-

+ NH3 P+

CH2NHCH2

P+

O

O + H2O2 P

CH2NHCH2

P

Figure 1.3 Scheme of the Proban process.

the treated fabrics; in addition, there may be the release of formaldehyde during the fabric use [12]. As far as Pyrovatex is considered, its process (schematically depicted in Figure 1.4) allows permanently anchoring just about 50% of the flame retardant product to cotton substrates: all the rest is lost during the first laundry occasion. At variance, from an overall point of view, replacing the commercially available flame retardants with performing alternatives is quite difficult for different reasons. First, apart from their effectiveness, the new products should be comparable to the commercially available counterparts as regard to the textile service-life (in particular, the new alternatives should exhibit acceptable comfort, mechanical properties and durability—washing fastness). Besides, the new FRs should not affect the fabric dyeability, aesthetics, and outward appearance; finally, their toxicity and environmental impact should be very limited or even negligible. All these requirements inspired the academic and industrial world toward the looking for possible alternative flame retardant treatments and related formulations. In doing so, some valuable surface engineered strategies have been designed, applied to textiles, and assessed [13]. In fact, these

Flame Retarded Cotton Fabrics HOCH2NH Cotton

NH CH2OH

N

+

N

N

+

7

O CH3O P CCH2CHONHCH2OH

CH3O NHCH2OH

H + (catalyst) O

- H2O

CH3O P CH3O

CH2CH2CONHCH2OCH2NH

NHCH2O Cotton

N

N

N

NHCH2OH

Figure 1.4 Scheme of the Pyrovatex process.

approaches demonstrate the key role played by the polymer surface during its exposure to a flame or a heat flux: the surface is the first to come in contact with the heat of the flame, and therefore, if properly flame retarded, it has the possibility to protect the underlying material during the exposure to a flame or an irradiative heat flux. In this context, the design of the new nanotechnologies for polymer surface engineering offers a promising outlook for polymer fire retardancy, especially for very irregular morphologies as those of textiles. Definitely, the textile surface, through which heat is conveyed to the degrading material and the combustible volatiles generated by the fabric degradation diffuse to the gas phase, plays a very important role, as it is able to control the fabric combustion process. Among the surface-engineered strategies, layer by layer assemblies and sol–gel treatments (the latter originating oxidic nanostructures on the fabric surface), represent the most common ways for conferring flame retardant features to any fabric substrate. As a consequence of these treatments, fabric combustion can be opportunely slowed down even to extinction, as a consequence of the creation of a surface barrier that successfully obstacles either heat or mass transfer across the fabric surface. Sol–gel treatments, which were first specifically designed for the fabrication of ceramic materials, began to be employed also in the textile field about 15 to 20 years ago, in order to obtain fabrics with different functional properties. Among the advantages of this strategy, it is worthy to mention that:

8

Advanced Functional Textiles and Polymers – it is possible to use the already existing industrial finishing lines for fabrics, hence avoiding further investments in new dedicated plants – it is possible to provide the fabrics with multifunctional features, not only including flame retardancy, but also (super) hydrophobicity and antimicrobial activity, among a few to mention – the irregular morphology of the fabrics does not affect the overall flame retardant properties achieved after sol–gel treatments – the sol–gel treated fabrics usually exhibit a high resistance to washing cycles, because of the occurrence of some reactions of the alkoxy functionalities of the precursors with the hydroxyls of cotton, hence making permanent the fire retardant treatments.

As far as layer-by-layer (LbL) assemblies are considered, their use for textile flame retardant applications is more recent than the sol–gel approach. The LbL strategy is a clear example of molecularly controlled fabrication of surface-confined nanostructured materials; in addition, these treatments allow specific modifications of the surface physico-chemical interactions. In particular, since any material is able to interact with the surrounding environment via its surface, the possibility of controlling the surface functionality allows tuning all the features that depend on these interactions. Similarly to sol–gel treatments, layer-by-layer architectures deposited on textiles can provide the latter with multifunctional features, including not only flame retardancy, but also electrical/thermal properties, hydrophobicity and antimicrobial activity, among a few to mention [14]. This chapter aims at summarizing the latest advances on the use of sol– gel and layer-by-layer approaches as efficient flame retardant systems for cotton fabrics; in particular, the recent scientific literature is discussed, highlighting the further potential progresses of these surface-engineered finishing strategies and their current limitations.

1.2 Textile Finishing With Sol–Gel Treatments Sol–gel treatments represent a synthetic bottom–up strategy that allows designing new materials with a high homogeneity degree at the molecular scale and with outstanding physico-chemical properties. Generally speaking, the sol–gel method exploits consecutive hydrolysis/condensation

Flame Retarded Cotton Fabrics

9

reactions of certain reactive precursors (namely, (semi)metal alkoxides). Among these latter, tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), aluminum isopropoxide, and titanium tetraisopropoxide are frequently employed. As a result, fully inorganic or hybrid organic–inorganic coatings at or near room temperature can be obtained, according to Figure 1.5, which schematizes the sol–gel reactions occurring in acidic conditions. Such parameters as pH and temperature, reaction time, water/precursor ratio, (semi)metal atom present in the sol–gel precursors and presence of co-solvents may affect the sol–gel processes and the structure and morphology of the obtained ceramic phases, either in form of coatings or particles [15]. These latter are undoubtedly responsible for the flame retardancy of cotton, as they create a thermal shield on the fabric surface, which protects the underlying material from the application of a flame or a heat source. In addition, the ceramic protective layer slows down the diffusion of the volatile combustible species derived from the degrading fabric toward the gas phase, as well as the diffusion of oxygen toward the burning area: these two actions are witnessed by the formation of a stable residue, made of char (usually aromatic) together with the formed oxidic phases [15, 16].

Hydrolysis of precursors (M = (semi)metal) OR 1)

RO

M

OR OR

+ H2O

H3O+

RO

OR

M

OH + ROH

OR

OR RO

M

OR OH + RO

OR

M

OR OR

H3O+

RO

OR

M

OR O

OR

2)

M

OR + ROH

OR

Possible condensation reactions OR RO

M OR

OR OH + HO

M OR

OR OR

H3O+

RO

M OR

OR O

M OR

Figure 1.5 Scheme of the sol–gel process occurring in acidic conditions.

OR + H2O

10

Advanced Functional Textiles and Polymers

It is worthy to note that, because of the limited thickness of the fabric substrate, the shielding effect provided by the formed oxidic phases is somehow limited: therefore, it is often necessary to favor the occurrence of additive or synergistic effects between the sol–gel oxidic phases and other concurrent present flame retardant additives. In particular, it has been found that FRs embedding phosphorus and/or nitrogen atoms are suitable and utilizable in combination with sol–gel treatments [17–19]. Table 1.1 collects the main advantages and drawbacks related to sol–gel treatments performed on textile substrates: among them, it is worthy to highlight the low process sustainability and high durability (i.e., washing fastness). The easiest way for classifying sol–gel systems is to divide them into the following sub-systems, namely: fully inorganic, phosphorus-doped, and hybrid O/I structures. These families will be thoroughly described in the following paragraphs.

1.2.1 Fully Inorganic Systems The first and pioneering sol–gel systems suitable as effective flame retardants for textiles involved the use of fully inorganic phases: in particular, sol–gel silica coatings (thickness: 350 nm) were applied to viscose fibers in order to provide them with flame retardant features; for the formation of the fully inorganic system, tetraethoxysilane (TEOS) was chosen [20]. Table 1.1 Key features of sol–gel finishing treatments carried out on fabrics. Main approach

- chemical process; usually, low MW by-products are formed

Multifunctionality of the treatment

- the tunability of the sol composition allows designing multifunctional sol–gel based finishing treatments

Durability (washing fastness)

- generally, very good

Comfort of the treated textiles (i.e., stiffness and soft touch of the sol–gel treated textiles)

- fair when fully inorganic sol–gel treatments are employed; it ameliorates when hybrid O/I systems are utilized

Sustainability (i.e., environmental impact)

- fair, because of the chemistry behind the sol–gel precursors

Flame Retarded Cotton Fabrics

11

The thermal stability and fire behavior of the sol–gel treated fibers were remarkably improved with respect to the untreated counterparts. More specifically, the former showed a 20°C increase of the first thermal degradation step, as well as 40°C temperature increase in the final residue after flammability tests: these findings are a clear indication of the protection exerted by the sol–gel coating deposited on the fibers, which is able to slow down the heat and mass transfer from and to the textile substrate, favoring, at the same time, the formation of a stable protective char.The same sol–gel approach was further employed for providing fire retardant features to cotton, polyester, and cotton/polyester-rich blends [21]. As clearly indicated by thermogravimetric analyses carried out either in nitrogen or in air, the deposited sol–gel coating was responsible for an increase of the thermal and thermo-oxidative stability of the fabrics, irrespective of their structure composition; besides, forced combustion tests (i.e., using a cone calorimeter operating at 35 kW/m2 heat flux) highlighted an increase of the time to ignition (TTI), as well as a decrease of the peak of the heat release rate (pkHRR), notwithstanding an increase of the final residue for the treated fabrics. Since, as previously mentioned, the sol–gel processes are driven by several parameters, which affect the overall fire behavior of the treated fabrics, it was worthy to focus on the effects of the structure of the sol– gel precursors, of the composition of the sols and of the adopted experimental conditions. For this purpose, different alkoxy precursors were selected, utilized for designing the sol–gel recipe and applied to cotton fabrics [22]. This way, it was possible to thoroughly investigate how temperature and time of the thermal treatment, and precursor:water molar ratio influence the morphology and fire behavior of the sol–gel derived coatings: in particular, carrying out the sol–gel reactions at 80°C for 15 h and using a 1:1 tetramethylortosilicate (TMOS):H2O molar ratio allowed optimizing the overall flame retardant behavior of the treated fabrics. These latter exhibited a decreased peak of heat release rate (pkHRR: −15%), which is a clear indication of the thermal insulation exerted by the oxidic phases formed on the fabric substrate. Furthermore, the sol–gel coating was able to favor the cotton dehydration, hence the formation of a stable aromatic protective char [16].The number and type of hydrolyzable groups in the alkoxy precursor play a key role in the flame retardant behavior of cotton: in particular, it was found that TMOS-based coatings (four methoxy groups) are more effective in providing cotton with flame retardant features than TEOS (bearing four ethoxy groups) and tetrabuthylorthosilicate (TBOS, four buthoxy groups), as confirmed by flame spread tests carried out in vertical configuration. More specifically, the

12

Advanced Functional Textiles and Polymers

shorter is the chain length of the utilized alkoxy precursor, the higher is the flame retardant performance. These findings were also supported by cone calorimetry tests [23]. Concerning the role of the number of hydrolysable groups of the alkoxy precursor and the burning behavior in forced combustion tests, cotton was treated with TEOS or 3-aminopropyl trimethoxysilane (APTES), triethoxy(ethyl)silane (TEES), 1,2-bis(triethoxysilyl)ethane (bTESE), diethoxy(methyl)phenylsilane (DEMPhS), and 1,4-bis(triethoxysilyl)benzene (bTESB) [24]. The overall fire behavior of the treated fabrics was strictly dependent on the presence of a different number of ethoxy units (from two to six) and/or of aromatic rings: in particular. It was found that: – two or three hydrolyzable units in the alkoxy precursor determine an overall fire behavior similar to that of TEOS, apart from a significant increase of smoke release; besides, the residue found at the end of cone calorimetry tests was very thin and incoherent; – replacing amino groups (APTES) with alkyl chains (TEES) favors the formation of a compact, coherent and thicker residue; – the use of bTESE or bTESB in the sol formulation considerably affects cotton flammability: in particular, treating the fabrics with the latter alkoxy precursor was very advantageous, as cotton did not burn, even when recurrently ignited (i.e., by 10 flame applications, for 5 s). It was, then, reasonable to compare the fire retardancy of sol–gel derived silica coatings (using TEOS as silica precursor) with those based on titania, alumina, or zirconia precursors and obtained from sols containing tetraethylortho-titanate, aluminum isopropylate, tetraethylortho-zirconate, respectively. This way, the influence of the structure and type of precursor of the oxidic phase on the overall flame retardant features of the sol–gel treated cotton was thoroughly evaluated. The comparison among the different oxidic phases deposited on cotton clearly indicated that the silica coating was the best, as revealed by the decrease of both time to ignition (−56%) and of the peak of heat release rate (−20%) in forced combustion tests; on the other hand, the treatments with aluminum isopropylate or tetraethylortho-zirconate sols conferred the highest abrasion resistance to the cellulosic fabrics.Then, the sol– gel silica coatings were embedded with pre-formed alumina micro- or nano-particles, aiming at investigating not only the effect of these latter

Flame Retarded Cotton Fabrics

13

on the overall fire behavior of cotton, but also to assess any improvement of its tribological properties. As expected, irrespective of the size of the utilized alumina particles, the abrasion resistance of the sol–gel treated fabrics was remarkably improved; besides, as highlighted by horizontal flame spread tests, the total burning time was lowered by 45%, notwithstanding the increase of the final residue (+46%) [25].

1.2.2 Phosphorus-Doped Sol–Gel Coatings Possible synergistic or additive interactions taking place between sol–gel derived coatings and other FR compounds bearing selected elements (in particular P and/or N) can be positively utilized for further improving the fire behavior of the treated cotton [18, 26–33]. In this context, it is possible to exploit three different methods. The first approach involves the selection of alkoxysilane precursors that contain both silane and phosphate groups within the same molecule: this strategy obviously implies that the selected alkoxy precursor should concurrently bear P and Si elements. When applied to cotton, the sol–gel derived coating is able to either form a mixed inorganic and carbonaceous residue (because of the activation of the phosphoric acid source, which favors the dehydration of the cellulosic substrate, instead of the formation of volatile combustible species), or create a ceramic protective layer on the fabric surface. The second method involves the mixing of alkoxysilane precursors with a source of phosphoric acid, hence giving rise to the formation of a hybrid phosphorus-doped ceramic coating on the fabric. The third and last method aims at incorporating alkoxysilane precursors bearing both silane and phosphate groups into phosphorus- and/or nitrogen-containing structures. Some examples will be discussed in the following. Diethylphosphatoethyltriethoxysilane (DPTES), an alkoxysilane precursor containing phosphate groups, was employed to form a P–Si hybrid organic/inorganic coating on the cellulosic fabric: to this aim, a multistep technique, involving the deposition of one, three, or six sol–gel layers on the substrate was utilized [30]. Forced combustion tests clearly indicated that the P–Si hybrid organic/inorganic coating determined a remarkable decrease (equal to −43%) of the combustion time for the flame retarded fabrics as compared with untreated cotton; besides, increasing the number of deposited layers significantly lowered the TSR values (i.e., total smoke release in cone calorimetry tests), achieving 20, 15, and 6 vs. 26 m2/m2 for one, three, and six layers and untreated cotton, respectively.

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Advanced Functional Textiles and Polymers

Encompassing a pre-hydrolysis step of the alkoxy precursor was the subsequent research step for optimizing the flame retardant properties of the hybrid P–Si organic/inorganic coatings [31]: as a result, the washing fastness of the flame retarded fabrics was significantly ameliorated, as they were able to resist to up to five washing cycles carried out according to the ISO 6330 standard. Synergism was then investigated by combining diethylphosphatoethyltriethoxysilane with aminopropyltriethoxysilane (APTES) or with APTES and a melamine-based resin (i.e., a nitrogen source) [32]. This strategy turned out to favor the char formation, as highlighted by the high residues (ranging from 38 to 42 wt.%) found after thermogravimetric analyses performed in oxidative-air-atmosphere. Finally, the replacement of the melamine-based resin with N,N,N ,N ,N ,N -hexakis-methoxymethyl-[1,3,5] triazine-2,4,6-triamine (HMT), together with their relative ratio optimization, highlighted a high char-forming character of the derived sol–gel coatings applied to cotton: in fact, the final residue after thermogravimetric analyses performed in air achieved about 70 wt.% [18]. In addition, in order to assess any possible synergistic effect, Lewin’s synergistic effectivity [34] was calculated: unlike hybrid N- and P-doped silica coatings, which showed additive effects only, the combination of the hybrid phosphorus-doped silica coatings with 1-hydroxyethane 1,1-diphosphonic acid displayed synergistic interactions taking place in between the two components. Furthermore, synergistic effects were also found when the silica coatings acted in combination with different sources of phosphoric acid comprising Aluminum phosphinate, Zirconium phosphate nanoplatelets, or a mixture of Aluminum phosphinate, Zinc and Boron oxide, and melamine poly(phosphate) [27]. Forced combustion tests proved a noteworthy TTI increase for the sol–gel treated cotton (40 s vs. 14—untreated cotton); besides, the limiting oxygen index—LOI—values increase from 19% (untreated fabric) to 30% (cotton treated with sol–gel precursor added of 5 wt.% of the selected P-containing compounds).

1.2.3 Hybrid Organic–Inorganic Sol–Gel Coatings The shift from fully inorganic to hybrid organic–inorganic sol–gel derived flame retardant treatments is mainly motivated by the need of getting flame retarded cotton fabrics with a “good hand” (i.e., acceptable mechanical properties, particularly referring to a limited stiffness), hence suitable for clothing purposes. Among the different available possibilities, the exploitation of dual-cure processes is very effective for obtaining hybrid flame

Flame Retarded Cotton Fabrics

15

retardant organic–inorganic coatings deposited on cotton: this way, it is possible to design flame retarded fabrics, with an acceptable washing fastness and flexibility. The dual-cure approach takes advantage from the combination of a photocuring step involving reactive groups (usually (meth) acrylic functionalities) embedded in selected monomers and/or oligomers with a successive thermal treatment: this latter promotes the sol–gel reactions [35–37]. This way, the formation of a hybrid durable co-continuous network, acting as thermal insulating coating, occurs. For this purpose, methacryloyloxypropyltrimethoxysilane (MEMO) was first exploited as a coupling agent within a UV-curable acrylic system comprising different concentrations of TMOS (from 30 to 80 wt.%) [38]. Cotton fabrics were treated with the dual-cure formulation, then UV-irradiated and finally thermally treated: the resulting hybrid coating turned out to increase the total burning time and final residue of the treated substrates, as assessed in horizontal flame spread tests. The thermal protective effect exerted by the coating was further confirmed by forced combustion tests carried out at 35 kW/m2, which highlighted a TTI increase, as well as a significant rise of the final residue. A sol comprising tri(acryloyloxyethyl)phosphate (used as sol–gel precursor) and triglycidylisocyanurate acrylate (as UV-curable component) was applied to cotton, in order to enhance the fire behavior of this latter [39]. In particular, when subjected to microscale combustion calorimetry, the treated fabrics showed a decrease of peak of heat release rate, heat release capacity and total heat of combustion, hence confirming the protection exerted by the deposited dual-cure coating. Recently, UV-photoinitiated thiol-ene click chemistry in combination with the sol–gel chemistry was utilized for the design of durable flame retardant cotton fabrics. In particular, dimethyl-[1,3,5-(3,5-triacryloylhexahydro)triazinyl]-3-oxopropylphosphonate, synthesized on purpose, was reacted with 3-Mercaptopropyltriethoxysilane, cotton fabrics were pre-treated with [40]. Different concentrations of the flame retardant treatment (namely, 2, 5, and 8 wt.%) were employed; the flame retardant features of the treated cellulosic substrates were clearly proven by the increase of LOI values and by the self-extinguishing character achieved during vertical flame spread tests. These performances were maintained even after 30 washing cycles in the presence of a surfactant. Very recently, flame retardant multilayer coatings were obtained, employing 1,2,3,4-butanetetracarboxylic acid for binding a carboxyl-functionalized organophosphorus oligomer to cotton fabrics; these latter were then recoated by using a sol made of three sol–gel precursors, namely 3-aminopropyltriethoxysilane, tetraethoxysilane, and 3-glycidyloxypropyltriethoxysilane

16

Advanced Functional Textiles and Polymers

[41]. The exploitation of the P-containing oligomer, together with the ceramic layer provided by the sol–gel reactions, allowed obtaining selfextinguishing fabrics; the main drawback of the designed systems referred to the poor washing resistance, with a partial leaching of the flame retardant layers from the cotton substrate, as indicated by vertical flame spread tests carried out on the washed fabrics. Despite this, the residues of these latter maintained the textile texture and were coherent and with mechanical strength. Another successful attempt was performed by designing hybrid organic/ inorganic sol–gel coatings through the combination of tetraethoxysilane/3aminopropyltriethoxysilane with gelatin [42]. As compared to untreated cotton, the LOI values of the treated fabrics increased (from 18% to 25%); furthermore, as observed in thermogravimetric analyses carried out in air, the flame retarded fabrics showed higher Tonset values, as well as a remarkable increase of the final residues. Several are the examples nicely reported in the scientific literature dealing with the design of sol–gel hybrid organic–inorganic coatings that, apart from the flame retardant properties, provided the cellulosic fabric with multifunctional features. In this context, a two-step strategy was exploited for conferring flame retardant and superhydrophobic features to cotton [43]. In particular, the fabric was treated with a sol–gel coating derived from 3-aminopropyltriethoxysilane and containing ammonium dihydrogen phosphate and/ or guanidine carbonate. Remarkable improvements of the flame retardant properties of the treated fabrics were obtained. Besides, a further addition to the sol recipe of a polysiloxane or a fluorofunctional silane allowed providing the flame retarded fabrics with superhydrophobicity. The occurrence of synergism between the P- and N-containing components of the sol and the organosilicon compounds was confirmed by the increase of the LOI values of the treated cotton, as well as by the remarkable decrease of its heat release rate values, obtained in microscale combustion calorimetry tests. Recently, waterproof and flame retarded cotton was designed through a one-pot sol–gel system, comprising tetraethoxysilane, ammonium polyphosphate, and a hydroxyl-terminated polydimethylsiloxane. The fabrics treated with the hybrid coating achieved self-extinction in vertical flame spread tests, notwithstanding superhydrophobic features, witnessed by the very high water contact angle values (beyond 160°) [44]. Very recently, sol–gel and self-assembly approaches were combined in a single stepcoating process, aiming at designing an intumescent flame retardant and hydrophobic coating for cotton fabrics [45]. For this purpose, sodium montmorillonite and ammonium dihydrogen phosphate

Flame Retarded Cotton Fabrics

17

were mixed with methyltrimethoxysilane (used as sol–gel precursor). The silica coating embedding the nanoclay and the phosphorus-containing compound provided cotton with interesting flame retardant features: in fact, the treated fabrics achieved self-extinction in vertical flame spread test; furthermore, microscale combustion calorimetry tests showed an outstanding reduction of the total heat release (more than 85%) and of peak of heat release rate as well (beyond 83%). Finally, the structure of the formed silica network in combination with the presence of methyl groups derived from the alkoxy precursor justified the high hydrophobicity achieved by the treated fabrics (the static water contact angles approached 120°).

1.3 Textile Finishing With Layer-by-Layer Assemblies The layer-by-layer (LbL) surface approach is not new at all, as it was initially invented in 1966; however, it was abandoned until the early ‘90s, when it was rediscovered and new applications based on this strategy were successfully proposed. Thus, during the last two decades, this surface engineering method has become very important, mainly in the field of thin films and textiles, as it is capable for conferring different properties to the treated substrates, according to the structure and composition of the deposited layers: among a few to mention, it is possible to provide the treated substrates with barrier properties toward different gases, anti-reflection, antibacterial features, electrical and/or thermal conductivity [46]. Besides, the possibility of greatly improving the flame retardant features of the LbLtreated substrates [47, 48] has paved the way toward the development of new efficient strategies, not only from an academic point of view, but also stimulating the industrial research. The layer-by-layer approach, as it will be described later, is environmentally friendly and allows obtaining thin multilayered assemblies, even on such substrates that exhibit an irregular morphology as fabrics; therefore, it has been exploited for designing either natural or synthetic flame retarded fabrics [49]. A general scheme of the LbL approach is shown in Figure 1.6: the method exploits the alternate exposure (usually by dipping or spraying) of a fabric substrate to oppositely electrically charged aqueous solutions or micro- nano-particle suspensions that are consequently adsorbed as nanolayers on the fabric surface, which is always weakly negatively charged. This way, the oppositely charged pairing nanolayers that are assembled exploit electrostatic attraction in order to adhere each other [50]. Up to now, it was possible to utilize several different colloids, low molecular weight molecules, polymers as components of the assemblies deposited

18

Advanced Functional Textiles and Polymers First step - First deposited layer

Second step

positively charged solution/suspension

washing in deionized water

washing in deionized water

negatively charged solution/suspension

Fourth step

Third step - Second deposited layer

Figure 1.6 Scheme of the LbL process (one cycle corresponds to one deposited bilayer).

on the fabric surface: this means that the design of the LbL assemblies is very wide and tunable, leading to the creation of three main LbL assemblies: fully inorganic, intumescent, or hybrid organic/inorganic coatings. These three categories will be described in the following paragraphs.

1.3.1 Fully Inorganic LbL Assemblies on Cotton The first example of a flame retardant fully inorganic LbL coating on cotton dates back to 2011, when two oppositely charge nanoparticle suspensions, namely positive alumina-coated silica (size: 10 nm) and negative silica nanoparticles (size: 10 or 40 nm) were assembled on the cellulosic substrate, using a dipping method [51]. It was found that the coating consisting of 20 bilayers conferred self-extinction to the treated cotton as shown by flammability tests carried out in vertical configuration; besides, under

Flame Retarded Cotton Fabrics

19

the exposure to a 35 kW/m2 heat flux, time to ignition increased, hence highlighting the protection exerted by the fully inorganic assembly. Pursuing this research, the fire performances of cotton fabrics LbLtreated with the same silica nanoparticles suspensions were thoroughly assessed, specifically investigating the effect of the LbL deposition method (i.e., dipping vs. horizontal or vertical spraying): in particular, the best thermal shielding effect, as evaluated in forced combustion tests, was obtained when the LbL assembly was deposited by horizontal spraying [52]. Polyhedral Oligomeric Silsesquioxane (POSS ) salts, positively or negatively charged and water-soluble, were then employed as components in flame retardant LbL assemblies for cotton. In particular, OctaAmmonium POSS ((+)POSS) and OctaTetramethylammonium POSS ((−)POSS) were combined into a LbL assembly, giving rise to a 20 bilayered coating [53]. Microscale combustion calorimetry tests proved the char forming character of the designed assemblies deposited on cotton (final residue beyond 12 wt.%); in addition, vertical flame spread tests clearly indicated a significant decrease of the afterglow time, as well as the formation of coherent residues that kept the fabric texture and the shape of the single fibers.

1.3.2 Intumescent LbL Assemblies on Cotton The possibility of designing new LbL assemblies that combine the thermal shielding effect of inorganic layers with the char forming character of “intumescent” layers drove the research world in this field toward the development of intumescent layer-by-layer systems. From an overall point of view, intumescent additives are provided with: i) acid-generating species (that favor the dehydration of the cellulosic substrate, rather than the formation of combustible volatile species); ii) a carbon source (which further helps to form a stable char); iii) a blowing agent (that, upon exposure to a flame or a heat flux, generates gaseous products—like N2—in the degrading mass, thus contributing to the formation of a swollen protective char). One of the first examples of LbL intumescent coating consisted of alternate layers of poly(allylamine) (acting either as a carbon source or blowing agent) and sodium phosphates (utilized as acid source) [54]. Flammability tests performed in vertical configuration showed that the LbL-treated cotton easily reached self-extinction; these very good performances were further supported by forced combustion tests, as the treated substrate did not ignite under exposure to 35 kW/m2 irradiative heat flux. Ammonium polyphosphate (utilized as acid source/blowing agent) and chitosan (as carbon source) were then combined into a 20 layered coating on cotton–polyester blends [55]: horizontal flammability tests performed

20

Advanced Functional Textiles and Polymers

on the fabrics treated with 20 bilayered assemblies demonstrated a decreased combustion kinetics without the occurrence of afterglow phenomena; furthermore, the residues obtained after the tests were coherent and kept the fabric texture and the shape of the single fibers. Pursuing this research, intumescent bilayers were replaced by quadlayers consisting of poly(diallydimethylammonium chloride)/poly(acrylic acid)/poly(diallydimethylammonium chloride)/ammonium polyphosphate and applied to cotton. The self-extinguishing character of the LbLtreated fabrics was clearly proven by horizontal flame spread tests; besides, all the heat-related parameters in cone calorimetry tests were lowered, hence confirming the achieved good fire performances [56, 57]. An oligoallylamine and its phosphonated derivative were synthesized on purpose and applied to cotton in a LbL intumescent assembly [58, 59]. The overall effect of the deposited assembly on the flame retardant properties of the coated cellulosic substrate was thoroughly investigated, taking into account the molecular weight of the layer constituents and the pH of their LbL solutions. The high protective effect exerted by the deposited assemblies was first highlighted by the very high residues at 800°C obtained after thermogravimetric analyses carried out either in nitrogen or in air atmospheres (namely, 37 and 31%, respectively). Besides, the selected pH was found to remarkably affect the overall thickness of the deposited LbL coatings: more specifically, the lower the adopted pH, the higher was the obtained thickness. Then, the layers consisting of high molecular weight oligomers were more efficient in slowing down the total burning time and to increase the final residues obtained after horizontal flame spread tests. An intumescent polyacrylamide (obtained from the copolymerization of N1-(5,5-dimethyl-1,3,2-dioxaphosphinyl-2-yl)-acrylamide with acrylamide) was successfully combined with graphene oxide nanosheets in a layer-by-layer assembly deposited on cotton [60]. The designed coating was capable to enhance the thermal stability of the LbL-treated fabrics: these good results were further supported by forced combustion tests, which clearly highlighted a TTI increase, as well as a decrease of peak of heat release rate. An assembly consisting of trilayers of branched poly(ethylenimine), ammonium polyphosphate, and fluorinated-decyl polyhedral oligomeric silsesquioxane was employed for providing cotton fabrics with multifunctional features (namely, superhydrophobicity, flame retardancy, and self-healing capabilities) [61]. The deposited assemblies were very effective in conferring self-extinction to the cellulosic substrate, as indicated by flame spread tests performed in vertical configuration. Besides, the fluorinated POSS conferred either self-healing or superhydrophobic features to

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the treated fabrics. In particular, self-healing was demonstrated, as superhydrophobicity was easily restored by simply rinsing the LbL-treated substrates with water. Quite recently, the design of new and effective LbL assemblies has involved the use of “green” (i.e., low environmental impact) intumescent assemblies, which, apart from acceptable flame retardance, usually provide the treated fabrics with multifunctional properties. More specifically, it was possible to select different types of biomacromolecules for this purposes, as it will be discussed in the following. The first pioneering work dealt with the treatment of cotton fabrics with up to 30 bilayers made of phytic acid and chitosan. The former, which bears a negative charge, was used as an acid source; the latter, positively charged, was employed as a carbon source [62]. Two different pH values, namely 4 and 6, were chosen for preparing the aqueous solutions of the biomacromolecules: it was found that the pH significantly affects the morphology of the obtained LbL assemblies, as the coatings prepared at pH 4 were thinner than those obtained at pH 6. Furthermore, the thin and thick assemblies possessed a different phytic acid content (48 vs. 66 wt.% for thin and thick assemblies, respectively). The fabrics treated with the thick coatings (i.e., containing 66 wt.% of phytic acid) were self-extinguishing, as assessed in flammability tests performed in vertical configuration. In addition, microscale combustion calorimetry tests clearly revealed that the LbL assemblies deposited at pH 4 were capable to remarkably decrease either the total heat release or the peak of the heat release values (−76 and −60%, respectively). Another intumescent LbL assembly, made of chitosan (bearing a positive charge) and ammonium polyphosphate (negatively charged), was applied to cotton fabrics in a bilayered assembly [63]. 20 bilayers were sufficient to considerably lower the total burning time and to limit the burnt length of the treated cotton during flame spread tests carried out in horizontal configuration. Furthermore, the intumescent LbL assembly exerted a good protection on the underlying substrate that, even after burning, kept its texture and showed good mechanical properties. Lastly, microscale combustion calorimetry tests performed on the LbL-coated fabrics revealed decreased total heat release and peak of heat release rate values with respect to the untreated textile. Using a similar approach, chitosan was replaced with polyhexamethylene guanidine phosphate, in bilayered assemblies with ammonium polyphospate, able to provide flame retardant and antimicrobial features to cotton [64]. A decreased burning time, as well as increased residues and the absence of afterglow phenomena were obtained for the LbL-treated

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fabrics, by performing flammability tests in vertical configuration. In addition, apart from the enhanced fire behavior, the treated fabrics also showed antimicrobial properties against S. aureus and E. coli. Pursuing this research, polyhexamethylene guanidine phosphate was coupled with potassium alginate, isolated from seaweed and LbL-applied to cotton fabrics [65]. The treated substrates, as assessed in microscale combustion calorimetry tests, showed decreased total heat release and peak of heat release rate values, hence showing enhanced fire retardant properties promoted by the deposited coating. Besides, the LbL-treated fabrics revealed outstanding antibacterial features, witnessed by 100% inactivation of S. aureus and E. coli, which was completed in 30 and even 5 min, respectively.Another biomacromolecule that has gathered a great interest as green flame retardant is deoxyribonucleic acid (DNA): it is an intumescent-like species, as it contains all the three components required for intumescence, namely: i) acid-generating species (e.g., phosphate or carboxylate groups), ii) a carbon source, and iii) a blowing agent (particularly referring to nitrogenous bases that form, during the degradation of the biomacromolecule, gaseous products (usually N2)) [66, 67]. For these reasons, the suitability of DNA for the design of efficient layer-by-layer architectures has been assessed. The first pioneering work dates back to 2013 and describes the use of bilayered DNA (negatively charged)/chitosan (positively charged) architectures deposited on cotton fabrics [68]. In particular, 20 bilayers were capable to provide the cellulosic substrate with self-extinction in horizontal flame spread tests, highlighting the remarkable char forming tendency of the deposited assemblies. In addition, forced combustion tests, carried out at 35 kW/m2 irradiative heat flux, demonstrated that the coatings were responsible for 40% decrease of heat release rate, and for a significant increase of the residue at the end of the tests. Pursuing this research work, multifunctional DNA/chitosan assemblies were applied to cotton fabrics: in particular, regardless of the enhanced fire behavior (in fact, the treated fabrics showed self-extinction in horizontal flame spread tests), the UV-curable chitosan layers were exploited for improving the washing fastness of the deposited LbL architectures; besides, chitosan was also responsible for providing the cellulosic substrate with antimicrobial features against S. aureus [69]. Then, two biobased chitin derivatives, namely phosphorylated chitin and deacetylated chitin (i.e., chitosan), were layer-by-layer assembled on cotton [70]. The phosphorylated chitin content of the assembled LbL coatings was strictly related to either the number of deposited bilayers, or the concentration of phosphorylated chitin. As assessed in vertical flame

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spread tests, self-extinction was observed for the cellulosic fabrics treated with 20 bilayers based on 2 wt.% phosphorylated chitin content. In addition, microscale combustion calorimetry tests showed a clear decrease of peak of heat release rate and total heat release values with respect to untreated cotton. Recently, flame retardant and hydrophobic LbL assemblies based on polyethylenimine/melamine and phytic acid were applied to cotton; after the layer-by-layer process, the treated fabrics were impregnated with a diluted solution of poly(dimethylsiloxane) [71]. As shown by thermogravimetric analyses, the presence of the coating anticipated the fabric degradation: though it may be counterintuitive, this anticipation (that is very common for almost all the biomacromolecules utilized for flame retardant purposes) was necessary in order to activate the flame retardant assembly toward the formation of a protective char. This latter was further enhanced because of the presence of the poly(dimethylsiloxane) layer. Besides, vertical flame spread tests demonstrated that four bilayers of polyethylenimine/ melamine–phytic acid are sufficient for conferring self-extinguishing features to the treated fabrics. Then, forced combustion tests showed 50% decrease of the peak of heat release rate, as well as an increase of the residue at the end of the tests. Finally, the presence of poly(dimethylsiloxane) also provided the treated cotton with water repellency, as denoted by the high contact angles values with water found (beyond 130°). Very recently, 10 bilayered assemblies, consisting of polyethylenimine (positively charged) and hypophosphorous acid-modified chitosan (negatively charged) were applied to cotton fabrics [72]. Then genipin, a natural product extracted from gardenia fruit, was employed as a crosslinking agent: this way, it was possible to provide a good washing fastness to the flame retarded cellulosic substrates. The treated fabrics achieved selfextinction, as assessed in horizontal flame spread tests; furthermore, the results from microscale combustion calorimetry tests indicated a significant decrease of both peak of heat release rate (−73%) and total heat release (−80%), as compared with untreated cotton.

1.3.3 Hybrid LbL Assemblies on Cotton The third and last type of layer-by-layer assemblies involves the combination of intumescent organic layers with inorganic (based on nanoparticles) counterparts, hence giving rise to the formation of hybrid organic– inorganic assemblies. This combination is very effective for flame retardant purposes, as it exploits joint or even synergistic effects provided by the two types of constituents.

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One of the first example of hybrid assemblies refers to the coupling of poly(acrylic acid) and amino-functionalized montmorillonite nanoplatelets layers on cotton fabrics [73]. Vertical flame spread tests clearly indicated that the deposited coating was responsible for the decrease of the combustion kinetics, as well as for the increase of the residues after the tests. SEM analyses on the burnt LbL-treated fabrics showed the presence of a swollen charred morphology embedding montmorillonite nanoplatelets. The latter were then employed in combination with dimethyl diallyl ammonium chloride-allyl glycidyl ether, and coated on cotton [74]. In particular, the LbL dipping technique was slightly changed, as the dipping phase was followed by three consecutive steps, namely padding, drying, and final curing. Thermogravimetric analyses indicated an increase stability of the LbL-treated fabrics, with increased final residues; besides, flammability tests carried out in vertical configuration clearly showed a decrease of the combustion rate, as well as an increase of the residues at the end of the tests. Among different suitable nanofillers, MgAl–hydrotalcites (MgAl–LDHs) were exploited in combination with alginate in hybrid organic–inorganic assemblies deposited on cotton [75]. Forced combustion tests performed at 35 kW/m2 irradiative heat flux on the LbL-treated fabrics indicated a decrease of either peak of heat release rate or total heat release as compared with the untreated cellulosic substrate. These findings were ascribed to the thermal protection exerted by the hydrotalcite on the underlying fabric; besides, the ceramic phase was also responsible for hindering the release of CO from the degrading fabric substrate. The combination of up to 20 bilayers of potassium alginate–carbon nanotubes and polyhexamethylene guanidine phosphate on cotton fabrics provided these latter with such multifunctional features as flame retardancy, antimicrobial features and electrical conductivity [76]. The formation of a percolative network of carbon nanotubes justified the high electrical conductivity of the LbL-treated fabrics, which also exhibited enhanced thermal stability and flame retardancy with respect to untreated cotton. Finally, the deposited assemblies were responsible for inhibiting the growth of E. coli: this effect turned out to depend on the number of bilayers, the LbL coatings were made of. Recently, Chitosan was combined with sodium phytate and 3-aminopropyltriethoxysilane in a layer-by-layer assembly applied to cotton [77]: in particular, the odd numbers of deposited bilayers were made of 3-aminopropyltriethoxysilane and sodium phytate, while the even numbers comprised chitosan and sodium phytate. Up to 15 bilayered assemblies

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were deposited on the cellulosic substrate. The fabrics treated with the maximum number of bilayers achieved self-extinction in vertical flame spread tests (their limiting oxygen index value reached 29%). In addition, forced combustion tests (performed at 35 kW/m2 irradiative heat flux) showed a reduction of both thermal (heat release rate and total heat release) and smoke (total smoke release and smoke production rate) parameters, hence indicating the good fire performances of the proposed LbL architectures. Recently, superhydrophobic and flame-retardant LbL assemblies were designed on cotton fabrics by sequentially depositing branched poly(ethylenimine), ammonium polyphosphate, and a fluorinated silica@ polydimethylsiloxane composite [78]. The combination of these three components allowed obtaining multifunctional fabrics with acceptable flame retardant features (namely, self-extinction in vertical flame spread tests and a remarkable decrease of peak of heat release rate and total heat release values in microscale combustion calorimetry tests), superhydrophobicity (contact angle values with water of about 158°), as well as self-cleaning and antifouling features.

1.4 Current Limitations of Sol–Gel and Layer-by-Layer Treatments Notwithstanding the unquestionable benefits exhibited by the sol–gel and layer-by-layer techniques applied to cotton fabrics, these surfaceengineered finishing strategies have to fix some current limitations. In particular, as far as the sol–gel approach is considered, its most important drawback that at present limits its scaling-up and exploitation at an industrial level is related to the use of chemicals, mostly having quite an important environmental impact. This is the reason that is driving the academic and industrial research toward the seeking of less impacting sol–gel precursors, but still capable to provide acceptable flame retardant characteristics to cotton fabrics. At present, another substantial limitation refers to the “hand” (i.e., soft touch, comfort) of the sol–gel treated fabrics, especially when fully inorganic flame retardant coatings are applied to the cellulosic substrate: in fact, the fabrics, after the sol–gel treatment, increase their stiffness, so that they become suitable for upholstery applications, but not for clothing. It is worthy to note that this disadvantage is progressively reduced when fully inorganic recipes are replaced with hybrid organic–inorganic sol–gel coatings, as the organic constituents may exert a flexibilization effect.

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Despite the “unlimited” freedom in the design of the LbL architectures, the layer-by-layer is facing some limitations, mainly related to its scale-up at an industrial scale, notwithstanding some successful attempts to design and fabricate a roll-to-roll plant at a pilot scale [79]. To this aim, spray coating is obviously preferable to dipping for several reasons: spray coating is very quick and limits material waste; besides, it prevents the risk of contamination, each selected solution/suspension may undergo, because of the repetitive dipping of the textile into the solution/suspension baths. Surely, washing fastness represents another drawback of the layer-bylayer technique: in fact, the durability of the LbL treated fabrics is practically lost when they are subjected to standard washing cycles. This is due to two main reasons: LbL is almost always based on the use of waterborne systems and it exploits electrostatic interactions taking place in between the oppositely electrically charged layers. Therefore, this disadvantage considerably limits the life time of the flame retardant LbL treatments, though some attempts aiming at covalently linking the different layers have been made. In this context, there are few examples in the scientific literature that try to fix the problem through the exploitation of thermally or UV-curable organic layers [80, 81]during the deposition process. Unlike the sol–gel method that, as previously mentioned, suffers for the increased stiffness of the treated cotton after the creation of the ceramic coating, it is noteworthy that this is not usually an important issue when the layer-by-layer approach is utilized: ultrasonication during the rinse step, which does not impact on the overall fire performances, can be successfully employed [82].

1.5 Conclusions and Future Perspectives This chapter has clearly proven the importance, feasibility, and reliability of sol–gel processes and layer-by-layer methods as effective surface-engineered finishing treatments for cotton. In particular, by selecting proper precursors, polyelectrolytes, nanofillers, it is possible to easily find the best “recipes” for each strategy, thus optimizing the overall fire behavior of the treated fabrics. Another important issue refers to the multifunctional characteristics that can be conferred to the cellulosic substrates: in fact, it is possible to provide the fabrics not only with very high fire performances, but also with hydrophobicity, antibacterial, self-cleaning, self-healing, electrical features, on the basis of the design of the recipes of the two finishing approaches. All the drawbacks/limitations, described in the previous paragraph, still represent a challenge; however, it is expected that the further development

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and optimization of these surface engineered methods could solve these issues, leading to their industrial exploitation and valorization.

Acknowledgments H2020 DAFIA Project (Biomacromolecules from municipal solid biowaste fractions and fish waste for high added value applications—Grant no. 720770) is gratefully acknowledged for financial support.

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70. Pan, H., Wang, W., Pan, Y., Song, L., Hu, Y., Liew, K.M., Formation of self-extinguishing flame retardant biobased coating on cotton fabrics via Layer-by-Layer assembly of chitin derivatives. Carbohydr. Polym., 115, 516, 2015. 71. Liu, L., Huang, Z., Pan, Y., Wang, X., Song, L., Hu, Y., Finishing of cotton fabrics by multi-layered coatings to improve their flame retardancy and water repellency. Cellulose, 25, 4791, 2018. 72. Pan, Y., Liu, L., Zhang, Y., Song, L., Hu, Y., Jiang, S., Zhao, H., Effect of genipin crosslinked layer-by-layer self-assembled coating on the thermal stability, flammability and wash durability of cotton fabric. Carbohydr. Polym., 206, 396, 2019. 73. Huang, G., Liang, H., Wang, X., Gao, J., Poly(acrylic acid)/clay thin films assembled by layer-by-layer Deposition for improving the flame retardancy properties of cotton. Ind. Eng. Chem. Res., 51, 12299, 2012. 74. Gao, D., Li, R., Lv, B., Ma, J., Tian, F., Zhang, J., Flammability, thermal and physical–mechanical properties of cationic polymer/montmorillonite composite on cotton fabric. Compos. Part B-Eng., 77, 329, 2015. 75. Pan, H., Wang, W., Shen, Q., Pan, Y., Song, L., Hu, Y., Lu, Y., Fabrication of flame retardant coating on cotton fabric by alternate assembly of exfoliated layered double hydroxides and alginate. RSC Adv., 6, 111950, 2016. 76. Chen, X., Fang, F., Zhang, X., Ding, X., Wang, Y., Chen, L., Tian, X., Flameretardant, electrically conductive and antimicrobial multifunctional coating on cotton fabric via layer-by-layer assembly technique. RSC Adv., 6, 27669, 2016. 77. Liu, Y., Wang, Q.Q., Jiang, Z.M., Zhang, C.J., Li, Z.F., Chen, H.Q., Zhu, P., Effect of chitosan on the fire retardancy and thermal degradation properties of coated cotton fabrics with sodium phytate and APTES by LBL assembly. J Anal. Appl. Pyrolysis, 135, 289, 2018. 78. Lin, D., Zeng, X., Li, H., Lai, X., Facile fabrication of superhydrophobic and flame-retardant coatings on cotton fabrics via layer-by-layer assembly. Cellulose, 25, 3135, 2018. 79. Chang, S., Slopek, R.P., Condon, B., Grunlan, J.C., Surface coating for flame-retardant behavior of cotton fabric using a continuous layer-by-layer process. Ind. Eng. Chem. Res., 53, 3805, 2014. 80. Alongi, J., Di Blasio, A., Carosio, F., Malucelli, G., UV-cured hybrid organic– inorganic Layer by Layer assemblies: Effect on the flame retardancy of polycarbonate films. Polym. Degrad. Stab., 107, 74, 2014. 81. Carosio, F. and Alongi, J., Few durable layers suppress cotton combustion due to the joint combination of layer by layer assembly and UV-curing. RSC Adv., 5, 71482, 2015. 82. Guin, T., Krecker, M., Milhorn, A., Grunlan, J.C., Maintaining hand and improving fire resistance of cotton fabric through ultrasonication rinsing of multilayer nanocoating. Cellulose, 21, 3023, 2014.

2 UV Protective Clothing Anu Mishra1,* and Bhupendra Singh Butola2 1

Department of Textile Technology, Indian Institute of Carpet Technology, Bhadohi, Uttar Pradesh, India 2 Department of Textile Technology, Indian Institute of Technology, Delhi, India

Abstract UV radiation has harmful effects on the human body. Prolonged exposure to UV radiation may cause skin ageing, eye disorder, skin cancer, etc. Clothing is considered to be an excellent medium to mitigate the damaging effects of UV radiation on the human body. This chapter emphasizes the imminent need of protection of the human body against UV radiation. It discusses different environmental factors which play a vital role in deciding the extent of harmfulness of radiation. Various physical and chemical parameters of clothing affecting the UV protection property are also thoroughly discussed. The authors have tried to emphasize the recent developments in UV protective clothing based on application of various organic and inorganic finishes. Both qualitative as well as quantitative methods of measurement of UV protection property of clothing materials have also been included. Keywords: Clothing, ultraviolet protection, UV transmittance, UPF, TiO2, organic UV finishes, inorganic UV finishes

2.1 Introduction Solar radiations have an important contribution in existence of life on mother earth. These radiations are basically the outcome of various nuclear fusion reactions occurring in the solar atmosphere. Solar radiations are electromagnetic waves, which are in the form of radio waves, infrared, visible, ultraviolet, X-rays, and even gamma rays. Over 99% of the energy flux *Corresponding author: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (33–64) © 2020 Scrivener Publishing LLC

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of solar radiations is in the spectral region of 180 nm to 4000 nm. The solar radiations ranging below 180 nm are absorbed by the oxygen environment existing above the stratosphere (about 100 km above the earth surface). Similarly, radiations in between 180 nm to 280 nm are absorbed by the ozone layer of stratosphere (which exists at an altitude of about 15–30 km). As far as the wavelength of solar radiations reaching the earth’s surface is concerned, majority of them span in the range of 280 nm to 3000 nm [1–5]. UV radiation is one of the important components of solar radiations. In general, UV radiations are designated as a band of electromagnetic spectrum having wavelength ranging from 10 nm to 400 nm. These radiations have wavelengths shorter than visible light but longer than X-rays. The overall contribution of UV radiations in solar spectra is below 10%. The UV radiations have been classified as per ISO-21348. Table 2.1 demonstrates different types of UV radiations based on their wavelength [6]. UV radiations have both positive as well as negative effects on human life. One of the major positive impacts of solar UV radiation on human health is that it induces the production of vitamin D in the body. It is pertinent to mention that the low levels of vitamin D in human beings may lead to risk of development of rickets, osteoporosis, and osteomaloma, etc. [7]. The other important contribution of solar UV radiation with respect to human health is its disinfecting and sterilizing nature toward harmful bacteria and viruses. UV radiation is able to penetrate cell membranes of these microorganisms and thus destroy their DNA. Talking about the negative aspects, UVB radiations have been found to be a major cause of skin cancer, sun burn, and cataract. Excessive doses of UVB radiation may even destroy or modify the fundamental building element, i.e., DNA [8]. Sun is a natural source of UV radiations on earth. In addition to this, there are some artificial sources of UV radiations. These UV sources include different types of lamps for phototherapy, solariums, work place lightening, industrial arc welding, hardening plastics, resins and inks, sterilizations, authentication devices of bank currency and documents, advertising tools and medical care equipments, etc. While dealing with such types of tools or equipments, direct exposure to UV on human skin can be avoided with the aid of textile materials. Textile materials in the form of gloves, aprons, face masks, etc., find their application in this respect [9–11].

2.2 Harmful Effects of UV Radiations on Skin In a human body, skin is the largest organ. In an adult human being, the surface area of the skin is more than 1.5 m2 [12]. It acts as a barrier to

UV Protective Clothing 35 Table 2.1 Different types of UV radiations and their characteristic features [6]. Wavelength range (nm)

Type of light

Abbreviation

Features

Ultraviolet radiations

UVR

100 nm ≤ λ < 400 nm

This is the wavelength range of solar UV radiations, which may not be absorbed by earth atmosphere. The UVR is classified into UVC, UVB, and UVA.

Vacuum Ultraviolet

VUV

10 nm ≤ λ < 200 nm

VUV can be strongly absorbed by atmospheric oxygen, although wavelength in the range of 150–200 nm can penetrate through nitrogen atmosphere.

Extreme Ultraviolet

EUV

10 nm ≤ λ < 121 nm

These are basically ionizing radiations.EUV are completely absorbed by the atmosphere.

Hydrogen Lymanalpha

H Lyman-α

121 nm ≤ λ < 122 nm

Spectral line at 121.6 nm, 10.20 eV. Ionizing radiation at shorter wavelengths.

Ultraviolet C

UVC

100 nm ≤ λ < 280 nm

Short-wave, germicidal, completely absorbed by the ozone layer and atmosphere: hard UV

Ultraviolet B

UVB

280 nm ≤ λ < 315 nm

Medium-wave, mostly absorbed by the ozone layer: intermediate UV

Ultraviolet A

UVA

315 nm ≤ λ < 400 nm

Long-wave, black light, not absorbed by the ozone layer: soft UV

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protect the body against chemicals, radiations and various infections. Skin also acts as a good interface between the body and the outside exposed environment by preventing the evaporation of fluids from the body. The skin is constituted of three different layers namely: a) b) c)

epidermis, dermis and subcutaneous tissues.

The epidermis is the outermost layer of the skin, which includes dead cells (stratum corneum). These dead cells are continuously renewed. The epidermis is separated from the dermis by a membrane made of permanently dividing cells called Melanocytes and Keratinocytes. Melanocytes are responsible for the synthesis of the pigment melanin and its transfer to the neighboring Keratinocytes [13]. The dermis layer of skin contains collagen fibers, which provide elasticity and supportive strength to the skin. However, the collagen fibers break down on exposure to high levels of UV. This reduces the elasticity of the skin and results in premature ageing. Another type of cells known as Langerhans cells exist beneath the stratum corneum. These cells have ability to recognize the immunological changes and can easily identify the presence of any foreign substance in the body. The activity of these cells is very sensitive to UV radiations. The subcutaneous tissues constitute the innermost layer of the skin. This layer is also known as hypodermis. Hypodermis is made up of fat and connective tissues that house nerves and larger blood vessels. It acts as insulator and regulates the body temperature [14–16]. Health risks associated with UV exposure to skin depend on many factors. The type of UV light, duration of exposure, frequency of occurrence of exposure and the sensitivity level of the individuals are the important factors determining the risk level. Based on the sensitivity of the skin to UV light, human beings can be divided into three groups namely: • Lightly pigmented, • Intermediately pigmented and • Heavily pigmented group. In the group of lightly pigmented people, the UV exposure causes sunburn but tanning of the skin is little. People in this group can be distinguished by their fair complexion, red hair, and blue eyes. These people should take extra care in the sun because their skin is poorly protected and is prone to damage. In the other group containing intermediately

UV Protective Clothing 37 Harmful effects of UV radiations on Skin

Short term effects Sunbrun Tanning Photosensitivity

Long term effects Skin cancer Effects other than cancer Non-melanoma Dryness/Aging Freckles & solar Malignant brown spots melanoma Melanocytic naevi (moles) Solar keratosis

Figure 2.1 Harmful effects of UV radiations on human skin.

pigmented people, the UV exposure shall result in little sunburn. However, tanning is unavoidable. People in this group have dark black hair as well as eyes. These people exhibit better resistance toward damage of skin due to UV. To the group of heavily pigmented people, UV exposure rarely causes sunburn. The population in this group has very good natural protection against UV and has little risk of skin cancer. But there is a possibility of UV-induced eye damage. This group has reduced ability to combat infections when exposed to excessive UV levels [17, 18]. The harmful effects of UV radiations on human skin can be categorized in to short-term and long-term effects as shown in Figure 2.1.

2.2.1 Short-Term Effects The short term effects of UV radiations include sunburn, tanning and photosensitization of skin. Sunburn appears in the form of reddening of the skin (erythema), which persists in the body for some hours or few days. Exposure of UV to the skin may also result in tanning reactions. When melanin present in the skin darkens due to UV light exposure, immediate pigment darkening takes place. However, this skin darkening fades after few hours. In some cases, delayed tanning may also occur, which can persist for some weeks [19]. It is worth to mention that the human body has a natural defense system against UV radiation. On exposure to the UV radiation for a limited time, the skin tans itself. Tanning of the skin is an indication of release of melanin (a dark brown pigment) from the skin cells. Release of melanin plays a vital role in protecting the skin from harmful UV radiation. Melanin absorbs majority of UV radiation and blocks them from passing through the epidermis layer of the skin. Also, the presence of UV radiation in sun

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light stimulates the body to produce more melanin through a process called melanogenesis. Studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin, i.e., darker skin tone. Few people have photosensitivity toward the UV radiations and due to this, diseases like porphyria and lupus erythematosus can be triggered. The photosensitivity also reflects in the form of skin rashes and exaggerated sunburn [20, 21].

2.2.2 Long-Term Effects Long-term effects of UV radiations can be both cancerous and noncancerous in nature. Some of the long term effects of UV on skin include dryness, blemishing, or aging of the skin. However, they do not cause cancer. In the course of protecting the skin from sun, the outer layer of skin thickens and loses moisture. The effect of this is dryness of skin. Breakage of small blood vessels due to sun damage causes blotchy discoloration. This effect is known as blemishing. Another long term effect of UV radiations on skin is termed as ageing. Exposure of UVA radiations damages the elastin and collagen fibers of the skin. This results in loss of natural elasticity of the skin and becomes a cause of wrinkling of skin. Excessive wrinkling of skin due to sun exposure results ins kin aging [22]. In lightly pigmented people, freckles and solar brown spots (lentigines) are frequently formed on the portion of skin, which is exposed to sun. These spots generally appear in the form of flat pigmented surface, normally of the size below 0.5 cm. Mostly, the freckles occur in children, while the occurrence of solar lentigines is common in people of the age over 60 years. Melanocytic naevi (moles) are benign growth of pigmented skin cells, which start from the lower layer of the epidermis and later go into the dermis. Moles are common in the skin of lightly pigmented or white people and rarely exist in black populations. Among people with white complexion, the presence of moles is an indicative of increased risk of melanoma. Keratoses is a very common skin problem, which is caused due to high level of sunlight exposure on lightly pigmented people of relatively older age. Solar keratosis is a pre-cancerous growth of skin cells. As the number of these cells in the skin increases, there is a high risk of non-melanocytic skin cancer [23]. The long term effects of UV radiations may also result in skin cancer. Skin cancer is the most common cancer in the human beings. About 95% of these skin cancers are basal and squamous cell carcinomas, which are commonly referred to as ‘non-melanoma skin cancers’ (NMSC). The remaining 5% cells are ‘malignant melanoma’.

UV Protective Clothing 39 NMSC occurs predominantly on body sites, which get maximum sun exposure such as head, neck, and hands. In general, NMSCs are not fatal but it can be very disfiguring, if serious attention is not paid. The most common NMSCs are squamous and basal cell carcinomas. About 75% of basal cell carcinomas and more than 50% of all squamous cell carcinomas occur either on the head or on the neck. Lightly pigmented skin is more prone to develop NMSC as compared to the skin with higher pigmentation. An increased risk of non-melanoma skin cancer has been observed in people having prevalence of solar brown spots in their childhood [24, 25]. Malignant melanoma is the most dangerous type of skin cancer. It has been observed that among the diagnosed cases of melanomas, about 25% cases result into death. In comparison to other skin cancers, the number of cases of melanoma cancer is rising at an alarming rate. Unlike non-melanoma skin cancer, the incidence of melanoma can be observed on partially sun-exposed portions of the skin such as the lower legs (women) and the back (men). Therefore, UV exposure can be considered as one of the responsible factors, which leads to the development of melanoma in human skin. Studies have shown that melanoma is more common in lightly pigmented people than in heavily pigmented people. The harmful effects of UV are not limited up to the damage of skin. An extensive exposure of UV can suppress some of the immune responses in human beings. Exposure to UV may enhance the risk of infection, may decrease the effectiveness of vaccines, and may weaken the defensive system of the body against cancer cell growth. Several eye diseases are also caused by exposure to UV radiations. These diseases are related to damage of cornea (photokeratitis, Pterygium), retinal damage and loss of transparency of eye lens (cataract) [26].

2.3 Environmental Factors Influencing UV Level on Earth The effect of UV radiation on human health depends on type of radiation and its intensity reaching the earth’s surface. UV radiation falling on the earth’s surface and water bodies depends on many complicated absorption and scattering phenomenon, which occur in the atmosphere and on the surface of earth and water. The absolute intensity of UV irradiance at the earth’s surface depends on the intensity of solar spectrum. However, the intensity and angular distribution of UV irradiance on earth is affected by various geometrical and geophysical parameters. The geometrical parameters such as the distance

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between earth and sun, solar zenith angle at a specific time and location on the earth’s surface affect UV irradiance. Atmospheric constituents that allow the absorption or scattering of solar radiation come under geophysical parameters. UV radiations can be absorbed by various gases and absorbing aerosols present in the atmosphere. Similarly, scattering of UV can take place due to clouds, non-absorbing aerosols, snow, and sand, etc., present on the earth’s surface [27–29].

2.3.1 Effect of Ozone Layer Depletion Ozone layers existing in the stratosphere absorb the harmful UV radiation that would otherwise reach the earth’s surface. With depletion of the ozone layer, the protective filter provided by the atmosphere is progressively reduced. Consequently, human beings and the environment are exposed to higher UV radiation levels. Particularly the higher UVB levels have the greatest impact on human health, animals, marine organisms, and plant life. Computational models predict that a 10% decrease in stratospheric ozone can cause an additional 4500 melanoma and 300,000 non-melanoma skin cancers. It can also add up around 1.75 million more cases of cataracts worldwide every year [30]. The depletion in stratospheric ozone is basically a result of anthropogenic release of pollutants such as chlorofluorocarbons (CFCs) in the earth’s atmosphere. The active chlorine released by the photolysis of CFCs reacts catalytically to destroy stratospheric ozone. This eventually leads to increase in the level of UVB radiations on earth surface [31–33].

2.3.2 Solar Elevation (Height of the Sun in the Sky) The intensity of UV radiations received from sun depends on the distance between the sun and the earth. This distance varies depending upon the season, time of day and the latitude. Higher the sun elevation in the sky, higher is the UV radiation level. The intensity of UV radiations is found to be the highest during the summer season, specially a 4-h period around noon. The intensity of UVB varies more with the time of the day as compared to UVA. At noontime in summer season, UVB is two to three times more intense in equatorial areas than in northern Europe [34].

2.3.3 Latitude and Altitude The UV intensity at the earth’s surface is related to the angle at which the UV rays pass through the atmosphere. In the tropical regions near the

UV Protective Clothing 41 equator, solar UV is more intense. The reason why the intensity of UV is higher near the equator lies in the fact that it shall have to travel less distance through the atmosphere to reach the earth’s surface. At low latitudes closer to the equator, the solar UVR contains a greater proportion of shorter wavelengths. It is related to the low angle of incidence of the incoming radiation. In comparison to other parts of the world, Australia suffers from a very high level of UVR. With respect to geographical position, Australia is close to the equator. The earth’s elliptical orbit brings Australia closer to the sun especially during summer season. Due to this reason, Australia receives around 7% additional intensity compared to other countries. That is why; the occurrence of skin cancer disease is the highest in Australia, which is quite alarming [35]. The intensity of UV increases with the altitude. With increase in the value of altitude, the amount of atmosphere available to absorb UV is reduced. With every 1000 m increase in altitude value, UV radiation levels increase by 10% to 12%. Generally, shorter wavelength UV is able to reach higher altitude areas.

2.3.4 Cloud Cover and Haze One of the most important geophysical variables, which affect surface radiations, is cloud cover. There are different types of clouds having different impact on the intensity and angular distribution of surface UV radiation. The geometrical thickness, cloud height, its composition, and spatial homogeneity are the key variables affecting the surface UV irradiance. Under thin clouds, surface UV radiation is usually reduced provided the clouds are distributed uniformly. Under overcast conditions, clouds always reduce surface UV irradiance. Under broken cloud conditions, reduction is significant if the Sun is concealed. However, if the Sun is not concealed by the clouds, the reduction is small. Even, there is a possibility of enhancement of surface UV irradiance up to 25% if there is existence of bright clouds. In Hazy days, generally the amount of water vapor in the atmosphere is high. Due to this, scattering of UV in the atmosphere increases. Thus, even though haze or cloud cover can cause a feeling of cold, the UV irradiance can remain high [36].

2.3.5 Ground Reflection Depending upon the surface on which UV radiations are incident, the reflection or scattering behavior of UV radiations changes. The reflective

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properties of natural surfaces such as grass, soil and water are poor. These surfaces reflect less than 10% of the incident UV radiations. However, fresh snow reflects as much as 80% of UV radiations. During spring season at higher altitudes, the reflection from snow could increase UV exposure levels. Sand reflects 10–25% of UV and can significantly increase UV exposure at the beach. Reflected UV radiations have adverse effects on the eye. Snow-blindness while skiing or photokeratitis at the beach can be the result of prolonged exposure to reflected UV rays from snow or sand, respectively [37].

2.4 Effect of Physical and Chemical Characteristics of Textile Materials on UV Protection UV protection properties of a textile substrate depend upon the extent, to which the textile substrate transmits, absorbs, scatters, or reflects the UV radiations. Figure 2.2 is a schematic representation of behavior of solar UV radiations through unprotected human skin and the human skin, which has been protected using suitable clothing. The transmission, absorption and reflection properties of the fabric are dependent mainly upon the yarn/fabric constructional parameters and the finishing treatment applied. Parameters such as fiber type, weave construction, yarn number, thread density, cover factor, etc., have a determining role in imparting good UV protection property to the fabric. The type of dye used, shade

Solar UVR are absorbed/ transmitted/ diffuse transmitted through unproctected human skin

Solar UVR are absorbed/ reflected/ scattered through UV protected clothing (a)

(b)

Figure 2.2 Schematic representation of solar UV radiations through (a) unprotected human skin and (b) protected human skin using suitable clothing.

UV Protective Clothing 43 depth, presence of optical brightening agents, finishing agents (especially UV-absorbers), etc., also affect the UV protection property [38–40].

2.4.1 Effect of Physical Parameters 2.4.1.1

Yarn Structural Parameters

The amount of twist imparted during manufacture of a yarn has an important contribution in effective packing of fiber in the yarn structure. The effective packing of fiber in the yarn structure has a significant influence on UV protection properties of fabric. Twist affects both core and surface geometry of the yarn. The yarn surface characteristics are important factors in order to estimate fabric pore size distribution precisely. The yarn twist has a great influence on the UV protection properties of the knitted fabrics. The compactness of the yarn and its surface properties influence the porosity of the fabric [41].

2.4.1.2 Fabric Structural Parameters Fabric porosity or openness is a key parameter affecting the UV transmission behavior of textiles. Fabric porosity can be varied by varying cover factor, tightness of weave, fabric areal density, or thickness. Cover factor of a fabric is defined as the percentage area occupied by the constituent yarns in a given fabric area. Cover factor is related to UV transmission % as under:

UV transmission % = 100/Porosity = 100/(100 − cover factor%) UV protection property of the fabric can be improved by improving the cover factor of the fabric. The influence of cover factor on UV transmission property of the fabric can clearly be observed at higher values of cover factor [42]. Exceeding the value of cover factor percentage beyond 95% leads to considerable improvement in UV protection property of fabric (as shown in Figure 2.3). The tightness of the weave is determined by its fabric structure. The relationship between the fabric structure and its UV transmission behavior can be better understood by taking an ideal case. Imagine a hypothetical fabric is designed using its constituent yarns completely opaque to UV transmission. In this situation, UV radiations are allowed to transmit through inter yarn spaces. The closer the woven or the knitted structure, the less UV radiation shall be transmitted through the fabric. However,

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UV protection factor

200 150 100 50 10 99

95

90 Cover factor (%)

80

Figure 2.3 UV protection factor as a function of fabric cover factor (%), for details, refer to Ref. [42].

in practical situations the constituent yarns in the fabric are usually not opaque to UV radiation; thus, UPFs of actual fabrics are lower than that of an ideal fabric. In general, inter yarn space is lower in woven as compared to knitted fabrics. Researchers have shown that woven fabrics having sateen weave impart better UV protection in comparison to twill or plain weave structure. In fact, in case of sateen weave, the cover factor of the fabric is higher due to more grouping of constituent yarns in the fabric. This specific arrangement of fabric structure in sateen weave reduces the interlacing points and reduces the porosity of the fabric as compared to twill or plain weave [43]. Fabric porosity also depends on the areal density of the fabric. An increase in weight per unit area of fabric decreases its porosity. The inter yarn space is generally reduced in fabrics with high areal density, permitting transmission of less UV radiation. In most of the studies, the effect of fabric thickness on UV protection properties has not been reported. However, thickness is a useful variable in understanding differences in UV protection between fabrics. It has been established that thicker and denser fabrics transmit less UV radiation [43, 44].

2.4.2 Effect of Chemical Parameters 2.4.2.1

Effect of Fiber Chemistry

UV protection property of any textile material is strongly dependent on its fiber chemistry. On spectroscopic studies, it is evident that the gray cotton fabric shows moderate absorption of UV radiations over the entire UV range. It may be due to the presence of limited amount of impurities

UV Protective Clothing 45 such as pectins, waxes, and pigments in the gray cotton. Similarly, presence of lignin acts as a natural UV absorber in raw jute fiber. Among natural textile fibers, wool has a high absorption capacity for UV radiation over the full range of wavelengths. Synthetic fiber such as polyester with conjugated aromatic system is effective in blocking UV radiation [45, 46]. In addition to this, inorganic delusturing agents used during manufacture of synthetic fiber facilitates the absorption of UV-radiation in the fiber over the entire wavelength range. The UVR-blocking ability of polyester is further enhanced by the addition of a delusterant such as titanium dioxide. However, aliphatic polyamide, acrylic as well as acetate fibers are fairly permeable to UV radiation.

2.4.2.2 Effect of Chemical Processing (Bleaching, Dyeing, and Other Finishing Chemicals) Textile materials undergo various chemical processing stages such as scouring, bleaching, dyeing, printing, and finishing before converting into finished goods. After scouring and bleaching process, the UV protection property of cellulosic textile material is reduced. This is due to the removal of impurities like natural pigments, pectins, waxes, etc., in these processes, which otherwise act as natural UV absorbers. The dyestuff used for coloring a textile substrate can affect its UV protection property. Using UV absorption spectra of a dyestuff solution, the positioning of wavelength absorption bands and their UV absorption intensity is measured. Based on that, the UV absorbing ability of individual dyestuff can be evaluated. The response given by the individual dye after absorption of UV radiation is based on its chemical structure. However, in general the UV protection property of the textile material is improved after dyeing. Due to increased absorption of UV radiation, textile material dyed with darker shade gives better protection to the human body in comparison to the lighter shades. UV protection property of textile materials can also be improved by addition of UV absorbers during finishing stage. Ultraviolet absorbers for laundry detergents and rinse cycle application have been developed. Ultraviolet absorbers are colorless compounds having a tendency to absorb light in the wavelength range of 290 to 400 nm. UV absorbers can be applied suitably in lightweight fabrics of cotton and viscose, which offer a high level of wearing comfort in summer. For textile applications, these UV absorbers have been modified for specific substrates, allowing application in the batchwise and continuous dyeing processes with dyes [47].

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During processing and use, textile goods encounter various mechanical and thermal stresses. As a result of tension, shrinkage, felting, and hot pressing, etc., the porosity of both knitted and woven fabrics alter significantly. Due to the change of porosity, the UPF of the textile goods does not remain constant. After washing the textile goods, particularly cotton fabric, shrinkage occurs. Due to the shrinkage caused by washing, garments made up of cotton fabric exhibit a considerable increase in the UPF value. In contrast to this, when a textile material becomes wet due to air hydration, perspiration, or water, UV transmission through it changes significantly. The textiles made up of cotton and cotton blends witness a marked reduction in their UPF value on absorption of water. The presence of water in the interstices of a fabric reduces the optical scattering effects, which allows more transmission of UV through the fabric. Similarly, when the garments are stretched during wear, the UPF substantially decreases. In practical cases, the effect of stretch on the UPF is more prominent in garments having a UPF of less than 30 in their un-stretched conditions, particularly leggings, women’s stockings, and swimsuits [48–50].

2.5 Type of UV Finishes, Their Working Mechanism, and Limitations The UV protection property of textiles can be improved considerably by incorporating some chemical compounds into the textile structure, which either have tendency to absorb or to scatter UV radiations. These compounds should essentially remain stable against UVR for quite a long time. They should also have good thermal stability. In addition to this, these compounds should not have any tendency to degrade textiles or to destroy its color. It is also desirable to have very little or no absorbency by these compounds in visible or IR radiations. These compounds should have compatibility with other finishing chemicals used in textile processing. They should also remain non toxic and non-skin irritant. Compounds having UV absorbing or scattering property can be of organic or inorganic origin. In general, it is desired to have preferably colorless compounds, having strong tendency to absorb or scatter UV radiations.

2.5.1 Organic UV Absorbers Organic UV absorbers are mostly used as finishing agents. They are aromatic compounds with conjugated structure. After absorbing the UV radiations, these compounds reach their excited state. In this state, the absorbed

UV Protective Clothing 47 energy is transformed into vibration energy or heat, which eventually goes into the surrounding environment. Thus, UV absorbers incorporated in textile substrate convert electronic excitation energy in to thermal energy. In this way, UV absorbers protect textile materials from photooxidation and reduce the possibility of weathering under UV light [51]. As mentioned earlier, these UV absorbers should have a stable structure. After absorbing the UV light, these compounds should not permanently transform into any of their non-absorbing isomeric forms. On such transformation, these compounds shall no longer exhibit UV absorption property. Derivatives of hydroxyphenylbenzotriazoles, hydroxyphenyltriazines, and hydroxyphenylbenzophenones are some of the most common UV absorbing compounds (as shown in the Figure 2.4) [52]. However, due to their poor wash durability, these organic compounds cannot be applied on textile substrates directly. The fixation of these compounds in textile substrate has been improved by introducing some reactive groups in to their structure. In this regard, some reactive dye structures, such as chlorotriazine, vinylsulfone, and N-dihydroxy ethylene have been attempted [53–56]. As a result, the condensation products of aminohydroxyphenylsulfobenzotriazoles, cyanuric chloride, and p-aminophenyl-sulfa to ethylsulfone etc. have been investigated (as shown in Figure 2.5) [57]. These reactive UV absorbers form covalent bonds with the hydroxyl groups of cellulosic textile materials and thus significantly enhance their wash durability.

OH

HO N

O

R

OH

C

N X1

X2

N

RO

OR

(a)

(b) OH R1

N N N

X

R2 (c)

Figure 2.4 Chemical structures of derivatives of (a) hydroxyphenylbenzotriazoles, (b) hydroxyphenylbenzophenones, and (c) hydroxyphenyltriazines [52].

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Advanced Functional Textiles and Polymers OH N N NaO3S

N

N

NH

NH

SO2CH2CH2OSO3Na

UV-I

NH

SO2CH2CH2OSO3Na

UV-II

NH

SO2CH2CH2OSO3Na

UV-III

N

N C1

OH N

N

NH

N NaO3S

N SO3Na N

C1

OCH3

N NaO3S

N

N

N

N

NH N

N C1

N N NaO3S

CH2CH3

N

N

N

NH

SO2CH2CH2OSO3Na

UV-IV

NH

SO2CH2CH2OSO3Na

UV-V

N

N C1

OH N N N

N

NH N

N C1

Figure 2.5 Some organic UV absorbers, for details of synthesis refer to Ref. [57].

However, their photo stability shall depend upon their ability to disperse the absorbed energy. The dispersion of energy can occur in the form of heat through slight transformation in the chemical bonding of the UV absorber. This transformation should ideally be regenerative and should remain long lasting. For example, the formation of hydrogen bonding between phenolic hydroxyl group and triazine ring in a reversible manner imparts photostability in the structure of UV absorbers containing 2-hydroxyphenyl group (as shown in Figure 2.6) [57]. On the other hand, the organic UV absorbers can also be incorporated as fillers during the manufacturing of manmade fibers. However, these UV absorbers can cause discoloration to the textile substrate, if used in higher concentrations.

UV Protective Clothing 49 H

O

N N X

N Y

Figure 2.6 Formation of hydrogen bond between phenolic hydroxyl group and triazine ring [57].

The synthesis of an organic UV absorber involves multi step processes. Each step of synthesis possesses risk of generation of toxic side products. The after use disposal of these compounds may also add up different level of toxicity in the environment. Therefore, in recent years, considerable efforts have been paid to identify bioactive substances having ability to absorb UV radiations. Various plant extracts have been attempted to act as source of mordants and/or natural colorants. Few of them have been found to have very good UV-absorbing property due to the presence of phenols, flavonoids, and tannins. Emblica officinalis G., Rheum, Lithospermum erythrorhizon, and galls of Quercus infectoria are some of the examples of plant based natural extracts, which have shown improvement in the UV protection properties of textiles [58–60].

2.5.2 Inorganic UV Blockers As discussed earlier, there are several means by which human beings protect themselves against UV radiations. Sun protection creams, hats, sun glasses, and textile materials etc are the obvious means for this purpose. It has been observed that UV radiations are harmful not only to the human beings, but their long term exposure also degrades textile substrates. Therefore, many UV blocking agents are being developed to add or improve the UV protection property of textiles based on inorganic origin. These inorganic based UV blockers efficiently scatter both UVA and UVB radiations. As compared to organic UV absorbers, inorganic UV blockers are biocompatible and much cheaper. They also have higher thermal and chemical stability, better durability, and excellent UV blocking properties over a broad range of UV wavelengths. With respect to organic UV absorbers, inorganic blockers are preferred due to their non toxicity on disposal. Inorganic UV blockers based on transition metal oxides are popular nowadays because they impart some additional properties like antibacterial, self-cleaning ability, etc., to textiles. Nanoparticles (NPs) of TiO2, ZnO, and Ag2O can impart UV protection and antibacterial activity to the textiles at very low concentrations [61].

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The mechanism of working of these inorganic materials as UV blocking agent is different in comparison to that of organic UV absorbers. There are differences in views, while understanding the UV blocking mechanism exhibited by inorganic materials. Among scientific community, one school of thought suggests the high refractive index of inorganic materials to be responsible for exhibiting high reflection and scattering behavior of UV light from its surface. In this way, good UV protection property in inorganic materials can be achieved. The other group stands in favor of basic semi-conducting nature of these metal oxides, which allow them to absorb UV radiations. The extent of UV blocking tendency with these inorganic materials depend upon the particle size of deposition and its distribution on the substrate surface. In general, inorganic UV blockers in the form of NPs can be more effective as compared to their bulk form. This is due to their large surface area to volume ratio. Furthermore, NPs with a crystal form are characterized by high refractive indices in the UV and visible wavelength ranges, which is why their UV blocking function is attributed to refraction and/or scattering of UV rays [62]. Many researchers have systematically investigated the mechanisms of UV blocking tendency of TiO2 on textiles. In one such study, researchers used four different types of TiO2 powders with respect to crystal phase and size. It has been found that nano TiO2 powder of rutile phase exhibited the strongest absorption of UV light. The nano scale TiO2 also represented good affinity with textiles due to its large specific surface area and high surface energy [62]. However, when using semiconductors as UV protection finishes, their inherent photocatalytic property is perceived as a major disadvantage, since photodegradation of dyes and textile fibers leads to color fading and deterioration of the mechanical properties of textile substrates.

2.6 Application Methods of UV Finish in Textiles Organic UV absorbers are generally applied on textile substrates by normal padding or exhaustion methods. It has been found that derivatives of orthohydroxyphenyl and diphenyltriazine have excellent sublimation fastness and self dispersing formulation. Therefore, they can be applied in textile materials using pad-thermosol process. They can also be included in printing paste composition. Generally, UV absorbers are not applied on textiles during dyeing. Application of UV absorbers during dyeing may decrease the dye uptake. Therefore they are applied in a separate step. A number of water soluble colorless organic UV absorbers based on

UV Protective Clothing 51 derivatives of symmetrical triazine have also been used during commercial laundering process [63]. Depending upon the type of textile substrate, its construction and the level of UV protection required, UV absorbers are applied in the concentration range of 10–40 g/L. Inorganic UV blocking compounds lack functional groups to react with textile materials and to form chemical bonding. Therefore, they are generally applied using adhesives, binders, cross-linking agents, etc. But use of such agents not only affects the touch and feel of the fabric, but also results in poor wash durability. By decreasing the particle size in the nano range, the interaction between these compounds and textile surface can be improved. Due to the large surface-to-volume ratio of the NPs, a greater extent of vander Waal forces of interaction between these compounds and textile surface is possible [64]. Stability of inorganic NPs in various dispersion media and ease of their application on textile substrate have been studied in detail. Colloidal sols of silica, chitosan and acrylic binders have been used to incorporate inorganic UV blockers on textile substrates [65–67]. The deposition of inorganic NPs on textile substrates has many challenges. There are requirements of good compatibility between textile substrate and the chemicals used during deposition of these NPs on the surface. Essentially, the original color of the fabric should not be changed during the treatment. Also, the mechanical properties of the fabric must remain intact after the treatment. Wash durability is also one of the major concerns to which very few researchers have paid serious attention to. Several studies have reported that coating of inorganic UV blockers on textiles could be performed using different pretreatments and techniques [68–70]. Figure 2.7 classifies various methods of application of Inorganic UV blockers on textiles. Some of the pretreatments that have been done on textile substrates to develop affinity with inorganic UV blockers include: RF-plasma, MW-plasma, and UV-irradiation, etc. [71–73]. Apart from this, use of cross linking agents, development of good electrostatic interactions and incorporation of reactive functional groups onto textiles have been some of the techniques to strengthen the binding between these UV blockers and textile substrate. Inorganic UV blockers can be applied at different textile production stages, among which the finishing of fabrics by the sol–gel technique is of great technological importance [74]. There are several other issues related to application of inorganic UV blockers on textile substrates. Researchers have faced issues related to the agglomeration of NPs, low adsorption ability of textile fibers for NPs and low durability of the coating. To resolve these problems, new routes of synthesis of NPs have been introduced to improve the dispersion of NPs, such as the in situ growth of NPs on textile fibers in the presence of stabilizing

52

Advanced Functional Textiles and Polymers From readymade powder of inorganic UV blockers

Application of inorganic UV blockers on textiles

Application during Fiber manufacture Application on textiles without binder/ cross linking agent Application on textiles using binder/ cross linking agent

In-situ preparation on textiles

Application of inorganic precursor on textiles followed by heat treatment Application of mixture of precursor on textiles followed by heat treatment

Layer by layer method of deposition

Application on textiles after functionalization of UV blocking agent Application of UV blocking agent after functionalization of textiles using RF-plasma, MW-plasma or vacuum-UV irradiation

Figure 2.7 Application of inorganic UV blockers on textiles.

agents [75, 76] and the use of hydrothermal, solvothermal, microwave, and sputtering deposition methods [77, 78]. To enhance the adsorption ability of textile fibers and consequently the washing durability of the coatings, polyester fibers have been pre-treated with sodium hydroxide to improve their wettability [79]. Similarly, cellulose fibers have been pre-modified with chloroacetic acid to create new active carboxylic groups [52]. Cotton is a polysaccharide with many free hydroxyl groups on its surface. One way to graft inorganic UV blockers like nano TiO2 on cotton is the use of cross-linking agents [80, 81]. The cross-linking agent needs to have at least two free carboxylic groups to make a bridge between cotton and TiO2. The cross-linking agent can be introduced by the formation of a covalent ester bond. This implies esterification of one carboxylic group of the cross-link agent by a hydroxyl group of cellulose. The second carboxylic group is supposed to bind TiO2 by an electrostatic interaction. Previous studies have shown that TiO2 forms strong electrostatic interaction with carboxylic group as shown in Figure 2.8 [82, 83]. Some studies have also been conducted using succinic acid and citric acid as linking agent between cotton and TiO2NPs [84]. In another study, a novel technique was adopted to improve the durability of TiO2NPs on cotton. The surface of TiO2NPs was first functionalized with maleic anhydride and subsequently co-grafted. The modified TiO2 along with 2-hydroxyethyl acrylate was treated with cotton using -irradiation. The grafted TiO2NPs showed much better durability on cotton during accelerated washing test [85].

UV Protective Clothing 53 O

Strong ester bond

O 2C

succinic acid HO O

O HO

O

O HO

OH

Strong electrostatic inrteraction

CO2H

CO2H

HO2C

O

O

O

O

OH

Ti4+O2

O n

n

Figure 2.8 Bonding of succinic acid with cotton and TiO2 using cross-link method.

In a different study, cotton surface was modified by mono-chloro acetic acid (MCAA) via carboxy-methylation as shown in Figure 2.9. Modified cotton was grafted with TiO2 nano particles using ultra-sonication at 20 KHz for 20 min. TiO2 (P-25) grafted cotton was evaluated for stain removal of methyl orange, under UV-A and UV-B. Results indicated that the number of surface carboxylic acid groups increase with the increase in concentration of sodium mono-chloro acetate used in surface modification reaction. Higher degree of surface modification increased the loading of TiO2 NPs on cotton fabrics thereby increasing the stain removal activity [86]. Besides these, other poly-carboxylic acids such as 1, 2, 3 propane tri carboxylic acid and 1, 2, 3, 4-butane tetra carboxylic acid have also been used for cross-linking the TiO2 with cotton [87]. The layer by layer deposition method has also been used for application of inorganic UV blockers onto textile substrates. This method comprises of immersion of substrate in two solutions of opposite polarity in an TiO2 nanoparticle

TiO2 nanoparticle Ti O H

O

O

OH

O

H O

O

CH2 C

CH2 C

-H2O

O HO

HO O

O O

OH

O HO

HO O

O

O

HO OH

OH OH

O OH

O OH

n

H O

O

O

O OH

OH

O

O H

Ti

O

O

Ti

TiO2 nanoparticle

O H

CH2 C

Ti O H

CH2 C

TiO2 nanoparticle

HO O

O

O

HO

O OH

OH HO O

O O

OH n

OH

Figure 2.9 Mechanism of TiO2 nanoparticles with surface carboxylic acid groups.

n

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Advanced Functional Textiles and Polymers

alternate manner. In this case, a multi-layer film is obtained, based on electrostatic interactions between layers. The step can be repeated many times, depending on the desired level of UV protection. Layer-by-layer molecular self-assembly technique has been used for multilayered film deposition of ZnO nanoparticle on cationized woven cotton fabric. Cationic charge on cotton fabric was developed with 2,3-epoxypropyltrimethylammonium chloride (EP3MAC) by pad-batch method. Layer by layer deposition on the positively charged cotton fabric was carried out in four sequential steps. The fabric was immersed sequentially in solutions of (a) anionic ZnO solution at pH 11, (b) deionized water, (c) cationic ZnO colloid solution at pH 3, (d) deionized water. Multilayer film deposited on cotton fabric in this way, was dried at 60°C and cured at 130°C for 3 min. The nano-ZnO films deposited on cotton fabrics exhibited enhanced protection from UV radiation along with excellent antimicrobial activity [88]. Attempts have also been made to functionalize the textile surface using radio frequency, microwave plasma or UV irradiation for better interaction between inorganic NPs and textile substrate. This process of surface functionalization takes place at low pressure in presence of air. In this case, exposed surface can be transformed up to a depth of 1–20 nm. Due to these radiations, functional groups like –COO– and –O–O can be formed on the textile surface, which subsequently attract the positively charged nano particles by electrostatic forces. In case of microwave plasma, the field is significantly shorter and ranges in between 5 and 45 seconds. On the other hand, the RF field goes up to 30 min. The activation of the textile surface by vacuum UV radiation takes place at relatively lower energy, which results in formation of only atomic and excited oxygen species. It has been realized that the vacuum UV radiation results in better uniformity in surface modification. However, the limitation of such surface functionalization is that TiO2 can bind only to the textile surfaces which get charged due to radiations. It is necessary to apply TiO2 immediately after the surface activation because the active oxygen species undergo quick reaction with air to get deactivated. This reduces the overall effectiveness of the process [72].

2.7 Test Methods for Quantitative Assessment of UV Protection of Textiles The safety of skin from solar UV radiations can be ensured by limiting the exposure time to sun. The other possible solutions to minimize deleterious effects of UV radiation include the use of protective garments and accessories (such as hats, shoes, umbrellas, etc.) or use of sunscreens lotion.

UV Protective Clothing 55 The rating system used for sun protection products like sunscreens is based on a value known as Sun Protection Factor (SPF). SPF is understood in terms of a factor of time for the protection of skin using a protecting agent as compared to without use of the same. For example, suppose a person shows visible erythema (sunburn) after a time duration of 5 min of exposure. After application of a sunscreen having SPF value 8, the same person shall extend this time duration to 40 min [89, 90]. Scientific methods of evaluating the SPF have been developed and specified. One such standard method is as per Australia/New Zealand (AS/NZ) 2604:1998. The standard is based on diffuse transmittance measurement. Using a UV-Visible spectrophotometer equipped with a diffuse reflectance accessory, the measurement is carried out. To measure the degree of protection offered by textile materials against UV radiation, the term Ultraviolet Protection Factor (UPF) is used. The textile materials are generally rated according to their UPF value. Unlike SPF, UPF rating gives an idea about protection against both UVA and UVB. Based on recorded data, UV protection rating of the fabric is calculated as per AATCC 183:2010 standards. UV protection textiles include various apparels, and accessories, such as hats, shoes, shade structures such as umbrellas, etc. [49]. UPF is the ratio of average effective UV irradiance transmitted through air to the average effective UV irradiance transmitted through the fabric. It is calculated based on following expression:

UPF

400 290

400 290

E( ). ( ). Δ( ) E( ). ( ). T( ). Δ( )

where, E(λ) = relative erythemal spectral effectiveness; ε(λ) = solar spectral irradiance (W m−2 nm−1); T(λ) = average of measured spectral transmittance of the sample (%); Δ(λ) is the measured wavelength interval (nm); As per the standard, E(λ) spectra is taken in the wavelength range of 290 to 400 nm. The value of UPF theoretically ranges from 1 to infinity. UPF value of 20 means that 1/20th or 5% of effective UV radiation striking the surface of the fabric actually passes through it. Higher the value of UPF of a fabric, the better is its skin protection ability. UPF value above 50 is considered as a desirable value to ensure UV protection.

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2.7.1 In Vitro UPF is based on a vitro test method, which gives a ranking to the textiles on the basis of their sun protective abilities. It is the ratio of an average effective ultraviolet radiation (UVR) irradiance calculated for unprotected skin to the average effective UVR irradiance calculated for skin protected by the test fabric. It is the quotient of the permitted radiation exposure relative to a minimum reddening of the skin in the protected area. The calculation is based on a UV transmission spectrum, which is recorded using a spectrophotometer. In this case, both of the relevant components, UV-A (wave lengths from 315 to 400 nm) and UV-B (280–315 nm) are included. Solar irradiance is the quantity of energy emitted by the sun, which is received at the surface of the earth per unit wavelength and per unit area. Suitable UV sources, such as xenon arc lamps, deuterium lamps, and solar simulators are used to provide UV radiation in the wavelength range of 280 to 400 nm. The total spectral transmittance is measured by irradiating the sample with monochromatic or polychromatic UV radiation and collecting the total (diffuse and direct) transmitted radiation. UPF is the measure of UV radiation (UVA and UVB) blocked by the textile material. The testing laboratory procedure using in vitro measurements and UPF ratings were first described in 1996 with AS/NZS standard 4399 and later with ASTM D 6603 (2000), as well as EN standard 13758-2 (2003). Radiometric UV transmission test uses a broadband UV light to illuminate a fabric sample. This UV light is filtered into UVB or a combination of UVA and UVB spectral regions. The accuracy of the test method is based on the UV source that closely matches the solar spectrum. Similarly, the detectors used should be able to mimic the response of human skin to the UV radiation closely. Nevertheless, this technique is more useful, if relative variation in UPF needs to be measured [49]. Spectroradiometer or spectrophotometer has an integrating sphere positioned behind the textile specimen, which collects transmitted and scattered radiation. Although spectrophotometer fitted with a double monochromator has a large dynamic range and good accuracy, the regular scans of the UV source (deuterium or xenon arc lamp) are always required to provide reference data. For UPF determination, at least four samples must be taken from different portions of a garment. Out of this, two samples must be in the machine direction and two in the cross-machine direction. The results of inter-laboratory comparison among different testing laboratories have shown that the spectrophotometry is the most accurate and reproducible test method for determining UPF. It has been observed that

UV Protective Clothing 57 the actual UV protection rendered by a particular fabric is generally higher than its measured value using spectrophotometry.

2.7.2 In Vivo Measurement of UV protection property of textiles using direct sun light as the source of UV radiation has practical limitations. Reproducibility as well as repeatability of such measurement is a challenge. Besides this, to arrange human volunteer as subject to carry out such measurement is also not easy. Therefore, a control source of UV radiation is produced using xenon arc solar simulator. This control source has provision to absorb light of wavelengths below 290 nm using filters. It also has filters to reduce the effect of visible and infrared radiation. Many researchers have described in vivo test methods based on minimal erythema dose (MED) [91, 92]. MED is the amount of UV radiation that produces minimal erythema (sunburn or redness) on an individual’s skin. Depending upon the skin phototype, MED is determined. In this case, an incremental dose of UVB is exposed on the upper back portion of a subject and its effect is measured after 24 h. These measurements of MED are carried out for both uncovered and covered skin with textile material. The in vivo and in vitro methods are considered in good agreement, if the ratio of the MED of skin covered with textile material to the MED of uncovered skin matches with UPF value obtained using in vitro method. In real life situations, it has been found that UPF determined using the in vivo “on skin” method is significantly lower than the UPFs obtained in vitro [93–95]. In general, the actual UV protection provided by clothings worn in sunlight is about 50% higher than that measured by conventional in vitro testing using collimated radiation beams [96].

2.8 Summary The idea of writing this chapter was to make the readers aware about the harmful effects of UV radiations on human health. Therefore, the ill effects of these radiations especially on human skin have been thoroughly discussed. The harmfulness of solar UV radiations depends upon various environmental factors such as solar elevation, latitude and altitude of UV rays, ozone layer depletion, cloud cover etc. The effect of these environmental factors on changing the UV levels at earth surface has also been documented. Textile materials have the ability to protect human body against heat, cold, and other environmental hazards. The write up includes the role of

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various physical and chemical parameters of textiles in imparting UV protection property. The available literature establishes that UV protection property of textile materials considerably depends upon fabric construction, structure of the constituent yarns, chemical structure of dyes used, and various finishing processes carried out. In the later part of the write up, the mechanisms of working of various organic and inorganic UV finishes and the method of application of these finishes on textile substrates have been thoroughly discussed. A large number of studies have proven that textile substrates treated with inorganic materials such as TiO2 and ZnONPs showed outstanding UV protection with good wash durability. The qualitative and quantitative methods of measurement of UV protection property of clothing have also been described.

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UV Protective Clothing 61 49. Hoffmann, K., Laperre, J., Avermaete, A., Altmeyer, P., Gambichler, T., Defined UV protection by apparel textiles. Arch. Dermatol., 137, 8, 1089–1094, 2001. 50. Akgun, M., Becerir, B., Alpay, H.R., Ultraviolet (UV) protection of textiles: A review. International Scientific Conference-UNITECH, vol. 10, 2010. 51. Bodur, M.S., Bakkal, M., Sonmez, H.E., A study on the photostabilizer additives on the textile fiber reinforced polymer composites: Mechanical, thermal, and physical analysis. Polym. Eng. Sci., 58, 7, 1082–1090, 2018. 52. Mavrić, Z., Tomšič, B., Simončič, B., Recent Advances in the Ultraviolet Protection Finishing of Textiles. Tekstilec, 61, 3, 201–220, 2018. 53. Chakraborty, J.N., Enhancing UV protection of cotton through application of novel UV absorbers. J. Text. Apparel Technol. Manage., 9, 1, 1–17, 2014. 54. Czajkowski, W., Mamnicka, J., Lota, W., Lewartowska, J., Application of reactive UV-absorbers for increasing protective properties of cellulose fabrics during standard laundering process. Fiber Polym., 13, 7, 948–953, 2012. 55. Shen, Y., Zhen, L., Huang, D., Xue, J., Improving anti-UV performances of cotton fabrics via graft modification using a reactive UV-absorber. Cellulose, 21, 5, 3745–3754, 2014. 56. Feng, Y., Li, D., Zhang, F., Zhang, G., A novel reactive anti-ultraviolet finishing of cotton fabric based on N-dihydroxy ethylene cyanoguanidine. Text. Res. J., 87, 14, 1722–1729, 2017. 57. Akrman, J. and Přikryl, J., Application of benzotriazole reactive UV absorbers to cellulose and determining sun protection of treated fabric spectrophotometrically. J. Appl. Polym. Sci., 108, 1, 334–341, 2008. 58. Chao, Y.C., Ho, T.H., Cheng, Z.J., Kao, L.H., Tsai, P.S., A study on combining natural dyes and environmentally-friendly mordant to improve color strength and ultraviolet protection of textiles. Fiber Polym., 18, 8, 1523–1530, 2017. 59. Grifoni, D., Bacci, L., Zipoli, G., Albanese, L., Sabatini, F., The role of natural dyes in the UV protection of fabrics made of vegetable fibers. Dyes. Pigm., 91, 3, 279–285, 2011. 60. Feng, X.X., Zhang, L.L., Chen, J.Y., Zhang, J.C., New insights into solar UV-protective properties of natural dye. J. Clean Prod., 15, 4, 366–372, 2007. 61. Paul, R., Bautista, L., De la Varga, M., Botet, J.M., Casals, E., Puntes, V., Marsal, F., Nano-cotton fabrics with high ultraviolet protection. Text. Res. J., 80, 5, 454–462, 2010. 62. Yang, H., Zhu, S., Pan, N., Studying the mechanisms of titanium dioxide as ultraviolet-blocking additive for films and fabrics by an improved scheme. J. Appl. Polym. Sci., 92, 5, 3201–3210, 2004. 63. Czajkowski, W., Mamnicka, J., Lota, W., Lewartowska, J., Application of reactive UV-absorbers for increasing protective properties of cellulose fabrics during standard laundering process. Fiber Polym., 13, 7, 948–953, (2012).

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64. Khandual, A., Luximon, A., Sachdeva, A., Rout, N., Sahoo, P.K., Enhancement of functional properties of cotton by conventional dyeing with TiO2 nanoparticles. Mater. Today Proc., 2, 4–5, 3674–3683, 2015. 65. Zhang, Y., Yu, L., Ke, S., Shen, B., Meng, X., Huang, H., Chan, H.L.W., TiO2/ SiO2 hybrid nanomaterials: Synthesis and variable UV-blocking properties. J. Solgel. Sci. Technol., 58, 1, 326–329, 2011. 66. Arik, B. and Seventekin, N., Evaluation of antibacterial and structural properties of cotton fabric coated by chitosan/titania and chitosan/silica hybrid sol–gel coatings. J. Text. Apparel/TekstilveKonfeksiyon, 21, 2, 107–115, 2011. 67. Gupta, K.K., Jassal, M., Agrawal, A.K., Sol–gel derived titanium dioxide finishing of cotton fabric for self-cleaning. IJFTR, 33, 4, 443–450, 2008. 68. Gowri, S., Almeida, L., Amorim, T., Carneiro, N., Pedro Souto, A., Fátima Esteves, M., Polymer nanocomposites for multifunctional finishing of textiles–a review. Text. Res. J., 80, 13, 1290–1306, 2010. 69. Qi, K., Wang, X., Xin, J.H., Photocatalytic self-cleaning textiles based on nanocrystalline titanium dioxide. Text. Res. J., 81, 1, 101–110, 2011. 70. Radetić, M., Functionalization of textile materials with TiO2 nanoparticles. J. Photoch. Photobio. C., 16, 62–76, 2013. 71. Yuranova, T., Mosteo, R., Bandara, J., Laub, D., Kiwi, J., Self-cleaning cotton textiles surfaces modified by photoactive SiO2/TiO2 coating. J. Mol. Catal. A Chem., 244, 1–2, 160–167, 2006. 72. Bozzi, A., Yuranova, T., Guasaquillo, I., Laub, D., Kiwi, J., Self-cleaning of modified cotton textiles by TiO2 at low temperatures under daylight irradiation. J. Photochem. Photobiol. A, Chem., 174, 2, 156–164, 2005. 73. Qi, K., Daoud, W.A., Xin, J.H., Mak, C.L., Tang, W., Cheung, W.P., Selfcleaning cotton. J. Mater. Chem., 16, 47, 4567–4574, 2006. 74. Farouk, A., Textor, T., Schollmeyer, E., Tarbuk, A., Grancacic, A.M., Sol– gel–derived inorganic–organic hybrid polymers filled with ZnO nanoparticles as an ultraviolet protection finish for textiles. Autex. Res. J., 10, 3, 58–63, 2010. 75. El-Naggar, M.E., Shaheen, T.I., Zaghloul, S., El-Rafie, M.H., Hebeish, A., Antibacterial activities and UV protection of the in situ synthesized titanium oxide nanoparticles on cotton fabrics. Ind. Eng. Chem. Res., 55, 10, 2661– 2668, 2016. 76. Montazer, M. and Maali Amiri, M., ZnOnano reactor on textiles and polymers: Ex situ and in situ synthesis, application, and characterization. J. Phys. Chem. B, 118, 6, 1453–1470, 2014. 77. Mishra, A. and Butola, B.S., Development of Cotton Fabrics with Durable UV Protective and Self-cleaning Property by Deposition of Low TiO2 Levels through Sol–gel Process. Photochem. Photobiol., 94, 3, 503–511, 2018. 78. Li, S., Zhu, T., Huang, J., Guo, Q., Chen, G., Lai, Y., Durable antibacterial and UV-protective Ag/TiO2@ fabrics for sustainable biomedical application. Int. J. Nanomed., 12, 2593, 2017.

UV Protective Clothing 63 79. Zhu, T., Li, S., Huang, J., Mihailiasa, M., Lai, Y., Rational design of multi-layered superhydrophobic coating on cotton fabrics for UV shielding, self-cleaning and oil–water separation. Mater. Des., 134, 342–351, 2017. 80. Chen, C.C. and Wang, C.C., Crosslinking of cotton cellulose with succinic acid in the presence of titanium dioxide nano-catalyst under UV irradiation. J. Solgel. Sci. Technol., 40, 1, 31–38, 2006. 81. Wang, C.C. and Chen, C.C., Physical properties of the crosslinked cellulose catalyzed with nanotitanium dioxide under UV irradiation and electronic field. Appl. Catal. A Gen., 293, 171–179, 2005. 82. Meilert, K.T., Laub, D., Kiwi, J., Photocatalytic self-cleaning of modified cotton textiles by TiO2 clusters attached by chemical spacers. J. Mol. Catal. A Chem., 237, 1–2, 101–108, 2005. 83. Yuranova, T., Laub, D., Kiwi, J., Synthesis, activity and characterization of textiles showing self-cleaning activity under daylight irradiation. Catal. Today, 122, 1–2, 109–117, 2007. 84. Nazari, A., Montazer, M., Rashidi, A., Yazdanshenas, M., Anary-Abbasinejad, M., Nano TiO2 photocatalyst and sodium hypophosphite for cross-linking cotton with poly carboxylic acids under UV and high temperature. Appl. Catal. A Gen., 371, 1–2, 10–16, 2009. 85. Yu, M., Wang, Z., Liu, H., Xie, S., Wu, J., Jiang, H., Li, J., Laundering durability of photocatalyzed self-cleaning cotton fabric with TiO2 nanoparticles covalently immobilized. ACS Appl. Mater. Interface, 5, 9, 3697–3703, 2013. 86. Wijesena, R.N., Tissera, N.D., Perera, R., de Silva, K.N., Amaratunga, G.A., Slightly carbomethylated cotton supported TiO2 nanoparticles as selfcleaning fabrics. J. Mol. Catal. A Chem., 398, 107–114, 2015. 87. Senić, Ž., Bauk, S., Vitorović-Todorović, M., Pajić, N., Samolov, A., Rajić, D., Application of TiO2 nanoparticles for obtaining self-decontaminating smart textiles. Sci. Tech. Rev., 61, 3–4, 63–72, 2011. 88. Uğur, Ş.S., Sarıışık, M., Aktaş, A.H., Uçar, M.Ç., Erden, E., Modifying of cotton fabric surface with nano-ZnO multilayer films by layer-by-layer deposition method. Nanoscale. Res. Lett., 5, 7, 1204, 2010. 89. Dutra, E.A., Oliveira, D.A.G.D.C., Kedor-Hackmann, E.R.M., Santoro, M.I.R.M., Determination of sun protection factor (SPF) of sunscreens by ultraviolet spectrophotometry. RevistaBrasileira de CiênciasFarmacêuticas, 40, 3, 381–385, 2004. 90. Stenberg, C. and Larkö, O., Sunscreen application and its importance for the sun protection factor. Arch. Dermatol., 121, 11, 1400–1402, 1985. 91. Stanford, D.G., Georgouras, K.E., Pailthorpe, M.T., Rating clothing for sun protection: Current status in Australia. J. Eur. Acad. Dermatol. Venereol., 8, 1, 12–17, 1997. 92. Gies, H.P., Roy, C.R., Holmes, G., Ultraviolet radiation protection by clothing: Comparison of in vivo and in vitro measurements. Radiat. Prot. Dosimetry, 91, 1–3, 247–250, 2000.

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93. Menzies, S.W., Lukins, P.B., Greenoak, G.E., Walker, P.J., Pailthorpe, M.T., Martin, J.M., Georgouras, K.E., A comparative study of fabric protection against ultraviolet-induced erythema determined by spectrophotometric and human skin measurements. Photodermatol. Photoimmunol. Photomed., 8, 4, 157–163, 1991. 94. Gambichler, T., Avermaete, A., Bader, A., Altmeyer, P., Hoffmann, K., Ultraviolet protection by summer textiles. Ultraviolet transmission measurements verified by determination of the minimal erythema dose with solar-simulated radiation. Br. J. Dermatol., 144, 3, 484–489, 2001. 95. Greenoak, G.E. and Pailthorp, M.T., Skin protection by clothing from the damaging effects of sunlight. Australas. Text., 16, 61–61, 1996. 96. Ravishankar, J. and Diffey, B., Laboratory testing of UV transmission through fabrics may underestimate protection. Photodermatol. Photoimmunol. Photomed., 13, 5–6, 202–203, 1997.

3 Potential of Textile Structure Reinforced Composites for Automotive Applications Vikas Khatkar*, R. N. Manjunath, Sandeep Olhan and B. K. Behera Department of Textile Technology Indian Institute of Technology Delhi, New Delhi, India

Abstract Since 1950, Composites have been tried in automobiles due to their added advantages of being lightweight, corrosion resistant and better fatigue behavior. However, no significant changeover from metal to composite is observed in automotive industries barring selective applications (like electric vehicles and formula one car) due to various technical issues associated with use of composite materials. There exists a continuing demand over the industry’s ability to hold a breakthrough research in materials and processing technologies. Today, automobile manufacturers are seeking aggressive weight reduction of materials and ready to compromise with the cost even if it is several times higher than steel or aluminum. Use of FRP composites is limited to semi structural components like bumper, dashboard, instruments panels, and door trims. Potential of composites for structural components like doors, suspension system, chassis, body shell etc, need to be explored. Use of advanced textile structural composites in producing mass consumption utility cars is in its infancy. There are potential economic and functional benefits for both consumers and manufacturers that can be derived by using composites in automobile construction. Therefore, this chapter envisages the potential application of 3D woven structures in automotive sectors along with use of advanced textile structural composites. Keywords: Automotive structures, composites, light-weight, 3D woven, fatigue behavior, durability, leaf spring, crashworthiness, textile structures

*Corresponding author: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (65–98) © 2020 Scrivener Publishing LLC

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3.1 Introduction Over past few decades, growths of transportation sector and vehicular emissions have increased exponentially leading to severe consequences on human health. It is reported that 95% of the global transport energy derived from fossil fuels gasoline and diesel [1]. As result of this government bodies have come up with strict regulations on transportation sectors. Therefore, automotive industries are in search of advance lightweight materials which can be a substitute to conventional steel and its alloy to reduce overall vehicle weight. It is reported that the reduction of vehicle weight by 10% would reduce the fuel consumption by 6% to 7% [2–3]. In lieu with this, researchers came up with Al (aluminum) and Mg (Magnesium) to replace the conventional steel [4, 5]. But with the growing stringent pollution norms to keep carbon footprints on check, scientific community came up with fiber reinforced polymer composite (FRP). The efficacy of such advanced fiber reinforced polymers and their manufacturing aspects for automotive applications were collectively studied [6, 7]. Natural fibers based composites is being used in automobile sector for various semi structural (Non load bearing) component in interiors of vehicle like dashboard, bumper, door trims, body panels etc. since last two decades. Various investigations were carried out on natural fiber based composites by different researchers [8–14] Kumar and Das [8] have investigated the suitability of bio composites made from nettle and PLA fibers for automotive dashboard application. Belingardi et al. [9] studied about alternative lightweight materials for vehicle frontal bumper beam. Wood plastic bio-based composites can enhance mechanical strength and acoustic performance, with substantial weight reduction and improve biodegradability for the auto interior parts [10]. G Marsh reported that natural fibers have potential to reduce weight, up to 40% compared to glass fibers, which is majorly used in automotive application [11]. Koronis et al. conducted an extensive review on application of green composites for automotive body panels [12]. John A. and Alex S. conducted review on the composite materials used for automotive bumper in passenger vehicles [13]. Khalfallah et al. investigated the thermal stability of flax tapes reinforced Acrodur bio composites for their applicability to automotive application [14]. Poor mechanical and interfacial properties of natural fiber based FRP’s restrict their usages in structural and load bearing components of automobile like chassis, suspension system etc. Several research were conducted for the use of advance fiber based (Glass/carbon) composites

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for load bearing components of automobile [15–18]. Study conducted by Feraboli and Masini [15] dealt with development of carbon/epoxy composites for high performance vehicles. Zhang et al. [16] investigated the static mechanical behavior of hybrid composite laminates reinforced with glass/carbon woven fabrics for lightweight load bearing structures for automotive applications. Obradovic et al. [17] designed and analyzed carbon fiber composites lightweight frontal impact attenuators for their use in nose cone of formula SAE cars. Adam [18] presented different automotive components like axel, spring road, chassis, drive shaft made from advance carbon fiber composite and discussed their applicability chances and risk in automotive applications. Apart from availability of high performance fibers (glass/carbon/aramid), textile manufacturing technology has witnessed invent of large number of complex textile structures using existing process such as weaving, knitting, nonwoven, and braiding. Development of a wide range of 3D woven structures as potential preform has created ample opportunity to produce high performance structural composite materials to be used not only in automotive sector but also all other transport sectors such as aerospace, marine and high speed bullet trains. Advanced textile structures like 3D woven solid structures, spacer fabrics, woven honeycomb structures and woven auxetic fabrics are being developed using traditional weaving principles incorporating certain modifications in the existing machines for making composite preforms. Greenhalgh and Hiley [19] reviewed the various materials concept, plain matrix, 2D and 3D woven structures, stitching, through thickness pinning and hybrid laminates, for improving the damage tolerance of aerospace stiffened structures. 3D woven structures found to be a potential material for impact tolerance design. Manjunath and Behera [20] carried out modeling of unit cell geometry of 3D woven fabric with integrated stiffener section for their applicability navel and aerospace application as a remedial solution to delamination problem at stiffener section due to lack of reinforcement. Kim et al. [21] manufactured a carbon epoxy sandwich composite structure for a train car body and carried out its structural safety evaluation and found its stiffness were matching the specific design. In the light of above discussion this chapter will give a brief outline of various textile structures as preforms, their corresponding composite materials and their properties from automotive application point of view. The discussion also covers the limitations of currently used materials and the potential benefits of the use of textile structural composites in automotive industry in terms of fuel efficiency, clean environment, durability, and safety aspects.

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3.2 Materials for Automotive 3.2.1 Metallic Materials in Automotive 3.2.1.1 Steel Steel and its alloys are accounted for more than 65% of the transport family; weight reduction is possible through constant innovation in iron and steel. Steel is the predominantly used materials in automotive industry and its application not only includes vehicle bodies but also engine, chassis, wheels and various other structural components (load bearing). The usage commonly results in weight reduction and simultaneous improvements in strength, stiffness, and other structural performance characteristics, thus it has a huge potential to make vehicles lighter and safer at the same time. However vehicle chassis, engine and various other components like power train are made up off ferrous materials contribute to the maximum part of vehicle weight, so lightweight steel and iron has a competitive edge with various other potentials substitute like, mg, aluminum, composite, etc., in all such application. They offer improved energy absorption capacity during impact and crash situation so these materials are preferred in body structure of automobiles [22]. These materials also have a good joining and formability, so they are the materials of choice for body in white structure (BIW) for automotive experts and manufacturer [23]. High strength steel (HSS) and its alloys founds an extensive usages in automotive applications. With use of these materials, new designs and manufacturing technique formed ultra-light steel body (ULSAB), and these car body (ULSAB) resulted in 20% weight reduction in body structure and superior strength and structural performance (including crashworthiness) along with a reduced part count and net manufacturing cost saving compared to a conventional steel body [24].

3.2.1.2 Aluminum Aluminum is being used since late 19 century in automotive sector and there are various example of its use in automobile but steel is the most desirable for most automobile manufacturers. However changing regulations related to pollution, fuel efficiency and recycling have focused on weight reduction by most of the automobile manufacturer. Aluminum has many advantages over steel. It has lower density than steel almost one third of steel and also meets structural requirement like strength and torsional stiffnesslike properties for an automotive materials, however its

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cost is almost five times the steel. Despite of being expensive the average total weight of 140 kg aluminum is used in passenger cars in various parts like power train, chassis, suspension system, body in white, hoods, door, etc. [25]. Use of aluminum is still limited to few components without changing the main design, e.g., transmission systems, engine blocks, and wheels majorly as casting with some forging and extrusions, whereas use of wrought aluminum is limited to AC units and Closure panels of car body. Recently researchers are exploring the manufacturing technology and mechanical properties of newer aluminum alloys for automotive applications [26, 27]. Shin et al. [27] explored the castability and mechanical behavior of 7xxx aluminum alloy for automotive body and chassis applications. In simple words aluminum can be used an alternative to steel, iron and copper in some selected components of the car and this will definitely help in achieving weight reduction to some extent and increase in performance of the car. The increase in performance may be in terms of improvement in vehicle fuel economy, loading extra safety and comfort features and increased vehicle life cycle. New alloys and advanced fabrication and manufacturing techniques have been tried with interest of testing suitable joining methods. The Honda NS-X and AudiA8 used aluminum vehicle made in a limited production run. However aluminum can replace steel with any significance is when only aluminum sheet replaces steel as the main material in the vehicle chassis [28].

3.2.1.3 Magnesium Top automotive manufacturers have shown a great interest for the use of magnesium in automobile parts due its low density and high strength, so magnesium is seen as a potential material for use its use in automotive applications. It is about 35% lighter than aluminum, which is used as structural parts of automobile and aerospace application. However its poor strength at elevated temperature and a poor corrosion resistance (due to impurities of iron copper and nickel) of magnesium alloys restricts their use in structural automotive application [29]. Prime objective for its use in automotive is to achieve weight reduction and better fuel economy by decreasing the rolling resistance and acceleration resistance. It is believed by most of the car manufacturers that use of magnesium will be 40 to 100 kg in a car in future [30]. German company Büssing introduced magnesium casted parts in trucks. The Adlerwerke in Germany were producing an automobile using magnesium cast and pressed parts since 1927. Parts like disk wheels, gear box cases, gear box covers, rear suspension gear box

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cases, chain locker, chain locker cover, crank cases, fly wheel cases, and various bearings, slide guiding, and covers. In 1931 Cheverlair by GM used sand casted magnesium crank case [31]. Besides the conventional automobile sector magnesium parts were also introduced in motor sport racing cars. Magnesium has been used since 1940 by top car manufactures in various parts like gears, ignition system, wheels and car body shell even some of the top racing cars from Mercedes and Porsche found its use in their frame and skin. Commercial use of sand casted magnesium was also reported in city buses and tractors transmission housing in England in 1930 [32]. Volkswagen beetle used magnesium in its transmission system housing and crank case with almost 17 kg weight. Although magnesium offers a high strength to weight ratio and motivate for its use in lightweight construction, but with growth of material science and newer material it has to competes with other alloys and polymers composite. Nowadays its use is being limited to few parts in automotive applications due to more stringent pollution norms and research development in newer materials [33]. Figure 3.1 shows the various automotive components made from magnesium alloys. Table 3.1 summarizes the basic mechanical properties of Al, Mg, and Fe.

3.2.2 Composite Materials for Automotives In general, composite materials are lighter in weight than steel or aluminium, which provides engineers with a lightweight alternative for use in a wide range of automotive structures and components. High strength and

Figure 3.1 Different magnesium casted automotive components (images modified and recreated from Refs. [29] and [34]).

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Table 3.1 Mechanical properties of Al, Mg, and Fe [30].

Material

Density (g/cc)

Young’s modulus (GPa)

Tensile strength (MPa)

Melting point (0C)

Mg

1.70

45

240

650

Al

2.74

48

320

660

Iron

7.86

206

350

1536

lighter weight leading to better fuel efficiency are the key benefits that composites offer the automotive sector; greater design flexibility, enhanced aesthetics, and improved durability are other advantages. But there are several reasons why advanced composites have not been more widely adopted by the automotive industry. The key stumbling block is price, while the availability and future supply of carbon fibers is another issue that is being addressed by fiber producers. Many companies, from carbon fiber suppliers through to original equipment manufacturers are now entering the market, with a wave of partnerships and joint ventures announced over recent years. Meanwhile, there are ongoing attempts to replace glass fiber with natural fibers, such as flax, sisal, and hemp.

3.2.2.1 Natural Fiber Reinforcement Polymer Composites Use of natural fibers reinforced composite for greening of automotive industry is the top priority of car companies. Natural fibers have advantage of being lightweight (low density), high specific strength and stiffness, and renewable resources. Natural fibers also have low hazard manufacturing processes and less abrasive damage to processing machineries and equipment compared to synthetic fibers. Table 3.2 summarizes the mechanical properties of natural fibers [35]. Since most of the natural fibers have lower density compared to the advance fibers like glass, carbon, etc., so natural fiber reinforced composites are the materials of choice for automotive applications. However their use is limited to semi structural and non-structural components in automotive industry due to low load bearing strength compared to advance fibers. In recent past various investigations were carried out to investigate the mechanical behavior of natural fiber based composites to check their applicability in automotive applications. Research carried out by Al-Oqla, and Sapuan [36] dealt with applicability of date palm fiber in automotive

Density (g/cc)

1.5

1.5

1.5

1.3–1.5

1.3

1.3–1.5

1.4

1.5–1.6

1.2

1.3

0.9

1.3

Material

Ramie

Flex

Hemp

Jute

Harakeke

Sisal

Alfa

Cotton

Coir

Silk

Feather

Wool

2.3–5

3–10

5–24

4–6

6–13

18–25

9–28

14–33

10–55

60–70

27–80

44–128

Young’s modulus (GPa)

50–320

100–200

100–1500

130–220

285–800

180–300

505–855

440–990

390–800

550–1100

350–1830

400–940

Tensile strength (MPa)

Table 3.2 Mechanical properties of natural fibers [35, 36].

1.8–3.8

3.4–11

4–20

3–5

3.8–8.4

13–18

7–20

11–25

7–39

40–47

18–52

29–80

Specific Young’s modulus (GPa/g cm3)

40–240

110–220

100–1500

110–180

190–530

130–220

360–610

340–760

300–610

370–740

230–1200

270–620

Specific strength (MPa/g cm3)

13–35

6–7

15–60

15–31

3.0–10

1.5–2.4

2.0–2.5

4.2–5.8

1.5–1.8

1.4–1.6

1.2–3.0

2.0–3.7

Failure strain (%)

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application. It was found with competitive properties suitable for automotive application. They were found best regarding the specific modulus to cost criteria and the cheapest among other natural fiber composites. Alves et al. [37] investigated the potential of jute fiber based composite for frontal bonnet of an off road automotive buggy, and compared its performance with glass fiber based composite. Jute fiber composites found to be more economical while safe for environment with suitable mechanical properties for automotive applications. Ashori [38] work dealt with wood plastic composite. These could be promising materials for automobile applications, because of the advantages compared to the fibrous materials like high strength and stiffness, low cost, low density, low CO2 emission, also fibers like flex and hemp are up to 40% less costly than glass fibers also studied from technical point of view like improvement in mechanical strength, reduce material weight, acoustic performance, energy/fuel consumption, lower production cost, improvement in passenger safety etc. and most importantly biodegradability of auto interior parts, use of bast fiber in automotive industry include weight saving between 10% to 30%. The use of natural fiber (such as flax, jute, hemp, sisal offer weight reduction, cost, and CO2 emission) with thermoplastic and thermoset matrices have been used doors panel, seat backs, headliners, package tray, dashboards and interiors parts to improve recyclability of vehicle parts. Table 3.3 shows the various composite based automotive parts which are being used by various automotive, manufacturers [39]. Also natural fiber based composites overcome shortcomings of glass reinforced plastic such as their high fiber density. Density of majority of advance fibers is approximately 40% higher than natural fibers, they are difficult to machine and their poor recyclability are still the challenge. However use of natural fibers composites is limited to the nonstructural or semi structural component in the vehicle interior and exteriors. Natural fiber based composites also have limitation of achieving class A surface finish and cannot be used in structural elements (load bearing) of automobile application due to their low strength. But from recyclability point of view these have advantage over the glass fiber reinforced polymers [40].

3.2.2.2 Advance Fiber-Based Composite Advance fiber- (carbon/glass/aramid) based composites are the material of choice for aerospace application since 1950. Due to their improved mechanical properties they are sought to be desirable materials for automotive application. Composite have many advantage over metals because of their unique properties like lightweight, better fatigue resistance and

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Table 3.3 Application of natural fibers composites in vehicle by different manufacturers [39]. Manufacturer

Model

NFC composite parts

Audi

A2, A3, A4, Avant, A6

Seat back, side and back door panel, boot lining, hat track, and spare tire lining

BMW

3, 5, 7 series and others

Door panels, headliner panels, noise insulation panels, molded foot, and well linings

Daimler/ Chrysler

A, C, E, and S class Evo bus (Exterior)

Door panels, windshield, Dash Board, Business Table, and Pillar cover panels

FORD

Mondeo CD 162, FOCUS

Door panels, B-Pillars, and Boot liner

Mercedes-Benz

Trucks

Internal engine cover, engine insulation, sun visor, interior insulation, bumper, wheel box, and roof cover

Toyota

Brevis, Harrier, Celsior, RAUM

Door panels, seat back, and spare tire cover

Volkswagen

Golf, Passat, variant, Bora, Fox, Polo

Door panels, seat back, boot liner, and boot lid finish panels

Volvo

C70, V 70

Seat padding, natural foams, and cargo floor tray

easily molded to shape. However various technical issues related to the composite materials including accurate material characterization manufacturing and joining needs to be addressed. Apart from material characterization and joining issues like repair potential, design, and structural simulations, crashworthiness, manufacturing, lightweighting, joining, recycling, modeling, fire safety, new materials concepts needs a detailed investigation [41]. Use of fiber reinforced composite in automobile in structural parts (load bearing), body structure was very limited and the possible reason for this the material cost, proof of structural integrality and durability, development of new and innovative fabrication procedures for optimization of manufacturing economics [42]. Various investigations were carried for use of advance fiber composites for structural elements

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in automotive. Use of carbon fiber reinforced composite (monolithic 2 x 2 twill laminate) in the design of high performance vehicle body and chassis were explored to achieve weight saving and manufacturing flexibility [43]. Potential of short fiber reinforced CRP composites for various non-structural automotive components like bending axle, FRP spring road (using compression mounding methods), cradon shaft, etc., have been explored in past. Beside the lightweight construction aspects, high energy absorption capacity of material can contribute to improved crash management [18]. In a study potential of carbon/epoxy structural composite for body panels of Lamborghini were explored and influence of fiber architecture on strength of composite panel with same fiber resin system is discussed and focused on the two major failure mode in designing of polymer composite, delaminating, and flexural failure. Resin impregnated carbon fiber shows a great deal of weight saving with respect to their predecessor in high performance cars but high grade steel and aluminum shows a perfect surface finish, alloy can withstand with weathering agents during the vehicle lifespan and very reliable joining methods. So a constant evaluation and research need to be carried out in order to get performance equal if not greater than the metallic counterparts [44]. All OEM trying to bring downs the vehicle weight to the suggested limit to match the global environment norms for reduction of Green House Gas emission (GHG) [45]. However, the main restriction to the use of advance composite in structural parts of automotive is high volume production technology for reinforcement architecture and faster composite manufacturing techniques. Resin transfer molding (RTM) offer a great economic balance as hand layup molding (wet), hand layup molding (prepreg) and tape winding (prepreg) that cannot meet the requirement of high production.

3.2.3 Advantage of Composite Over Conventional Materials 3.2.3.1 Lightweight It is one of the major motivations for use of composite compare to conventional metallic materials. However weight reduction helps in different way for different category of vehicle like in trucks lightweight allows to increase payload with maintaining the same overall mass, in sports utility vehicle it helps in increasing performance but in mass production vehicle reduction in weight helps in reduction of fuel consumption. So one has to go for optimum balance between weight saving and additional cost for that. Not only payload and performance but passenger comfort can be achieved by addition of extra features to the cars, so the textile structural composite

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can fulfill this demand and suitable material for this is glass fiber which is having least cost compared to the other fibers like carbon/aramid fibers.

3.2.3.1.1 Physics of Vehicle Weight Reduction This is a well-known fact the reducing vehicle weight will improve vehicle efficiency by reducing fuel consumption because as the vehicle weight reduced, the engine has to overcome less inertial forces during acceleration, so a result of this work required to move the vehicle is reduced. Figure 3.2 shows the schematic view of physics of vehicle weight reduction. The key parameters that contribute to vehicle fuel consumption can be examined from the following relationship given below [1]:

be

be P dt

Ft v

dt

FC v dt

v dt

where FC: Vehicle fuel consumption (L/km) be: Engine Specific fuel consumption (L/kWh) P: Engine power output (kW)

FC

POWER

Ft

FROLL

FDRAG FACC

Figure 3.2 Physics of vehicle weight reduction.

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V: Vehicle instantaneous speed (m/s, km/hr) Ft: Tractive force (KN) η: Drive Train Efficiency T: Time (s or h) For a vehicle given speed time trace, and assuming that the engine specific fuel consumption and efficiency as a function of speed and load are known, the main parameter that affects the amount of energy output needed from engine is the amount of tractive forces vehicle has to overcome. The tractive forces is the sum of • Tire rolling resistance • Acceleration or braking resistance • Aerodynamics drag and climbing resistance. For an accelerating vehicle on road, total tractive forces is given by

Ft

FROLL

FACC

FDRAG

( f mg ) (ma)

FROLL: Rolling Resistance [N] FACC: Acceleration resistance [N] FDRAG: Aerodynamic drag [N] f: Rolling resistance Coefficient m: Vehicle plus payload masses [kg] v: Instantaneous Vehicle Speed [m/s]

1 CD 2

AIR

v2 A

g: Gravitational Acceleration [m/s2] a: Vehicle Acceleration [M/s2] Cd: Drag Coefficient : Air Density [kg/m3] A: Vehicle frontal area [m2]

From this equation we can see how vehicle weight has a direct impact on reducing the total tractive force and thus the fuel consumption, since mass appears in rolling and acceleration components of total resistive forces so reduction in rolling and acceleration mass component will help in improving fuel consumption. Aerodynamic drag does not affect vehicle energy requirement much except when travelling at high speed. The national research council report that a 10% reduction in weight can improve fuel consumption by 6–7%. In a study by P. Beardmore, C.F. Johnson [42] major weight saving in carbon fiber reinforced plastic in place of steel in various automotive parts as shown in Table 3.4 below, the CRPF vehicle having weight 2500 lbs compared to steel 3750 lbs, but during testing of vehicle no significant difference found in ride quality and vehicle dynamics between

78

Advanced Functional Textiles and Polymers Table 3.4 Comparison of weight reduction between metal and composite automobile components [42]. Weight (lb) Component

Metal

Composite

Reduction (lb)

Body in white

423

160

253

Frame

95

30

65

Wheel

91.7

49

42.7

Hood

49

17.2

32.2

Decklid

42.8

14.3

28.5

Doors

141

55.5

85.5

Bumpers

123

44

79

Drive Shaft

21.1

14.9

6.2

Total

3750

2504

1246

both the materials cars so a vehicle with totally FRP structure proved to be as good as steel vehicle with weight saving of up to 67%. This study reveals that high cost fibers and high cost fabrication techniques can provide a perfectly acceptable vehicle but the real challenge to convert the performance onto reality.

3.2.3.2 Crashworthiness It has become very important now a days so now people are trying to produce stiff and quasi non deformable cars chassis which are not deformable and dissipate energy definitely will receive a very hard impact so now target has been for producing the vehicle which includes various zone of high deformation and energy absorption specially at the front and rear ends of the vehicle. Car interiors also plays important role in developments of crashworthiness using energy absorbing materials for components like pillar trims. Many other technical issues are under the development including energy absorbing bonnet materials, concept of active bonnet i.e. which rise during impact to create space for energy absorption. So textile structural composite is an opportunities in such area or is a material of choice while designing crashworthiness as it will offer excellent crash performance and having high specific energy absorption compared to those of metals.

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3.2.3.3 Joining It is a critical aspect of vehicle assembly, design and manufacturing. Each joint will disturb the structural integrity and creating the discontinuity in material, problem of stress concentration load transfer will occur, and this will lead to NVH (Noise, Vibration and harshness) characteristics. Also use of mechanical fastening i.e. nut bolt, rivets, welding leads to increase in weight of the component to be joined so purpose of weight reduction lost. These issues can be overcome using textile structural composite, as these structure can be produced to near net shape and no hole, no joining, i.e., welding, mechanical fastening, etc., not required. In terms of Mechanical joints there is a major shift toward integral attachments like snap fits. Composite is receiving attention in automotive industry as a major structural constituent for various automotive parts and this is justified by its various advantages over its metal counterparts • • • • • • • • •

High specific strength and stiffness Have high fatigue resistance and creep resistance God corrosion resistance and chemical stability Better NVH noise vibration and harshness characteristics Anisotropicity and structural integrity Low coefficient of friction and wear Proven thermal stability Energy efficient raw material and manufacturing processes Electrical and thermal properties may be designed as per requirement

Only deficiency is there in availability of database on composite design. Also mode of failure can be different from those of steel counterparts. Due to the isotropic nature of steel strength and stiffness steel parts can be designed to take major static as well as dynamic loads in automobile. While composite properties are direction dependent so it is important to know the magnitude and direction of all minor and major loads. So it is very important to develop database prior to the use of composites in load bearing application.

3.2.3.4 Recycling Recycling of glass, carbon, aramid fiber reinforced with polyester epoxy are difficult so use of thermoplastic can provide some solution to the above issue as these resin can be recycled to produce new components. So these

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recyclable resins like pp, polyethylene polyamide polyurethane can be reinforced with natural fibers which are biodegradable. Natural fiber has a potential to reduce weight up to 40% compared with glass fiber which is now used in various automobile parts. Also production cost and energy is comparatively lesser than that of glass fiber and production of glass lead to emission. Emits comparatively less CO2 also these do not cause many problems to manufacturing tools and processing machines so this is one on the alternatives in the countries where agriculture is well developed. Now mostly automotive manufacturer is looking for sustainable and environment friendly vehicle components at economical cost. According to European guideline issued by European commission, 85% of the weight of the vehicle has to be recycled by 2002, and 95% by 2015 [46]. New renewable materials are now being used in various interior and exterior automotive components like door, seat cushions, dash boards, cabin linings, in recent time an interest has been grown to various natural fibers like jute, for mass usages. Many material scientist from various automotive companies estimated that composite body for a vehicle could be 50–65% lighter compare to the steel counterparts [47]. Prenatally even people trying to reduce the use of costly fiber like glass carbon, aramid with the natural fiber having low density only for interior parts of vehicle. Mercedes Benz used jute with epoxy matrix for its door panels in E class vehicle in 1996 [48]. In 2000 Audi used in door trim panels made up of flax/sisal fiber with polyurethane matrix. Toyota used 100% bioplastic. Mitsubishi used floor mats made of PLA and nylon fibers. In 2010 Ford used wheat straw used as reinforcement in storage bin and inner lid. And Toyota developed an Eco plastic for the interiors of the car using sugar cane. But their limitation to the usages of load bearing element and temperature application like hoods of car become unstable [49]. Major advantage of composites in automotive is the weight reduction are up to 35% less weight than aluminum and 60% less weight than steel and overall weight can be reduced up to 10% [50]. In addition to this tooling cost can be reduced up to 50 to 70% [51]. As of now composite materials made of both thermoset and thermoplastic materials is used including SMC, BMC, GMT, and FLRT (long fiber reinforced composites) is used for glass fiber.

3.3 Textile Materials for Automotive The automotive industry is one of the fastest growing industries in the world and the most global of all industries, because of product distribution. The term automobile textile means all types of textile components like fibers, filaments,

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yarns, and the fabrics of various structures used in automotives. Automobile textiles are non-apparel textiles widely used in vehicles like cars, trains, buses, aircraft, and marine vehicles. Textiles which constitute approximately 20–25 kg in a car are not only used for enhanced aesthetic of automotives but also for sensual comfort and safety. Additionally, few textile products found their applications as design solutions to engineering problems in the form of composites, tire reinforcement, sound insulation, and vibration control. Apart from woven and knitted constructions, nonwovens also find applications in transport textiles due to certain advantages served by them. Normally, the percentage of textile in a motor car amount to 2% of overall weight of the car. Car seats are the most important part of the interior from aesthetic appeal and customer satisfaction point of view. Almost 50–55 square yards of textile material is used in an average car. Nearly two third of the automobile textiles are for interior trim. The major parts of automotive textiles constitutes of the Seat—Upholstery and Roof Covering. The hidden textiles weigh almost 10–12 kg. Textiles for automobiles must satisfy very strong requirements for both security and competing demands. Automotive textiles can be classified into four major groups based on their functions. The main functions identified are comfort, aesthetics, safety, and specialty in material characteristics. Comfort includes both physical and physiological aspects of textiles used in seats and interiors of the vehicle whereas aesthetics of textiles used in a car include interior design of carpets, roof covers, and side walls for decoration purpose. Textiles used for safety purposes are safety belts, air bags, and helmets. These products are manufactured using stringent specifications. Several technical textiles are being used in modern cars to enhance functional requirements such as noise controllers, filters, battery separators, composite materials, etc. All textiles used in automotives in the form of fibers, filaments, yarns, and fabrics can also be classified into two different types such as visible components and concealed components. Components like upholstery, carpet, seat belt, roof liner, etc., which have significant role in aesthetic appeal of the car are classified under visible components and components like tire cord, composite materials, air bag, etc., which have significant functional attributes but do not appear from outside are called concealed components. Although there are more than 30 components from textile material origin are being used in a modern car, only a few items which have perceptible effect on function, comfort, aesthetic appearance, and economics of the vehicle are described briefly here in this chapter. Composite materials have been used for non-structural car parts since the 1950s. In recent decades, automotive interiors have been increasingly produced from thermoplastics, with semi-structural parts now widely made from thermoset composites. In the aircraft, boat building and racing/sports car sectors, the use of carbon fiber composites, in particular, has

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grown rapidly in recent years. In the aerospace industry, for example, carbon fiber-based composite parts in the aircraft body now account for more than 50% of the total weight of the latest models, such as the Airbus A380 and Boeing 787 Dreamliner.

3.3.1 Textile Structural Composites for Automotive Textile structural composites are the composite in which textile material is used as reinforcement phase. Typically textile materials are available in the form of fiber, yarns, and fabrics. Fabric can be produced by various techniques like non-woven, woven, and knitting. Weaving is the most commonly used technique to produce fabric. 3D weaving fabric is the recent development in making woven preform for advance composite application. It is different from conventional 2D weaving in a sense that yarn is inserted in through thickness direction. Figure 3.3 shows the principle of 2D weaving and 3D weaving. Basic difference between bidirectional (2D) and three dimensional (3D) weaving is summarized in Table 3.5. 3D woven structures overcomes the disadvantages of 2D, i.e., low strength and stiffness in thickness direction. 3D could be hollow, solid,

Shedding

Picking

2D Interlaced fabric

2D Weaving

Reed

Healed frame

shed

Filler Yarn

3D Weaving

Figure 3.3 2D and 3D weaving principle.

Binder warp

Main warp

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Table 3.5 Difference in 2D and 3D weaving. 2D Weaving

3D Weaving

Low thickness

High thickness

High crimp

Zero crimp or very low crimp

Low production speed

High production speed

Single pick in one cycle

Multiple pick in one cycle

profiled depending upon requirement [52]. In this chapter our discussion is limited to the use of 3D solid woven structure for automotive applications. Figure 3.4 shows the classification of 3D solid structures. 3D fabric can be defined as the fabric in which yarns are disposed in 3D mutually perpendicular direction. It is a multilayer structure, substantially thick and an integrated structure could be a potential replacement for conventionally used laminated composite structures. 3D woven reinforced structures could be used as a potential material for automotive application as it offers near net shape structure without any joining, machining, pinning, and welding. Behera and Das [53] reported 3D shows negligible delamination compared to unidirectional (UD) and bidirectional (2D) laminated composite, possible reason was mentioned through thickness reinforcement. 3D composites also offers better in plane shear and almost no delamination

Orthogonal

Warp Interlock

Angle Interlock

Figure 3.4 3D woven solid structures.

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because of through thickness reinforcement. Apart from these advantage textile structural composites offer the following advantages • • • • •

Light in weight (Energy efficient) High specific strength and stiffness (Durability) Anisotropy (arrangement of fibers in preferential direction) Structural integrity (interconnectivity between x, y, z yarns) Corrosion free

3D woven solid textile structures offers us a unique advantage of structural maneuverability, i.e., position of fibers inside a woven structure is manipulated depending on the type of structures we wish to use for a given application.

3.3.1.1 3D Fabrics as New Solutions for Transportation Applications Transportation industries are willing to replace metallic materials by composites materials on structural parts subjected to severe mechanical solicitations with equal mechanical performances. Composite materials are proposed because they are able to provide credible answers to the optimization of large and thick structural parts. Their good strength/weight ratio and especially their anisotropy which can be adapted to the mechanical solicitation of the structure are particularly interesting. 3D warp interlock fabrics can be used as fibrous reinforcement in composite material. Composite materials made with commingled E-glass/Polypropylene yarns inserted in 3D warp interlock fabric has been one of the studied solution to cope with fast and low cost production requirements of the EU-research program MAPICC3D. To obtain 3D final shape of the composite part, the forming of the 3D warp interlock preforms made with commingled yarns can be performed at room temperature on dedicated mold. Then a thermocompressing step is applied to the 3D formed fabric in order to melt the polypropylene filaments all around the E-glass filaments to ensure a complete consolidation of the composite material [54, 55]. Research work carried out in IIT Delhi confirms [56] the formability behavior of the 3D warp interlock reinforcements make the fabric a suitable preform for complex shaped automobile components. Different solutions have been developed according to the different transportation areas requirements, as: an oil container for the automotive application (AUTO-MAPICC), a seat reinforcement for the truck application (TRUCK-MAPICC), a tubular cross for the rail application (RAIL-MAPICC), and an F-preform for the aeronautic application (AERO-MAPPIC). All of these solutions tend to

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replace existing metallic parts by lightweight composite materials, including fibrous reinforcement as a 3D warp interlock fabric. In recent past study on mechanical performance of 3D woven reinforced composite proved these materials could be the future materials for automotive applications [57–59]. The study carried by Dai et al. [57] dealt with 3D woven carbon epoxy composites prepared with a sample loom and vacuum assisted resin transfer molding (VARTM) process. Effect of fiber architecture (orthogonal and angle interlock fabric) on tensile, flexural and compressive properties of composites were investigated. Mechanical performance was found to be effected by resin rich regions (binding points) and crimp (waviness) in the loading direction fibers. Clark and Mouritz [58] investigated 3D orthogonal woven composites for the tensile fatigue behavior. Effect of varying binder percentage on tensile fatigue were investigated. Fatigue performance degraded with increase in binder percentage due to resin rich regions near binder configuration. Zhang et al. [59] investigated the low velocity impact behavior of polyethylene reinforced unidirectional, 2D and 3D woven composites. Composite reinforced with single ply 3D woven structures found to be superior energy absorption and impact damage resistance. Investigation of Behera and Das [53] dealt with 2D and 3D woven (orthogonal, angle interlock) reinforced composites. 3D woven composites found to be superior in knife penetration, Impact damage resistance and dynamic mechanical behavior. It has been proved from several basic research that 3D structural composite have superiors mechanical properties in terms of tensile, flexural, impact damage, dynamic mechanical analysis, and others which make these composites as a potential materials for automotive application. These structures can be explored for various automotive components depending upon load requirement and possible is emerging as one of the futuristic materials for automotive applications. It is also evident from several basic research that textile reinforcement can contribute to the extent of almost 90% of total load bearing capacity of a structural composite provided the internal geometry of the architecture of the textile material is property designed and preserved.

3.4 Potential Automotive Parts to be Replaced With Textile Structural Composites 3.4.1 Automotive Interiors Recyclability is the one of the major concern for automotive industry as almost every household has at least one or more vehicle. In a study by

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regulatory bodies it was purposed that 95% of any car interiors as well as exteriors should be recycled [60]. Most common automotive interiors are instrument carrier panel, seat structures, door trims and dashboard, etc., as shown in Figure 3.5 conventionally reinforced polymers were used for such parts due their increased strength compared to virgin plastic. Glass fiber is most commonly used reinforcement material due to its high strength and low cost compared to other advance fiber like carbon, aramid etc. Now a day’s hemp fiber and clay Nano composite were seen as an alternative to glass being lightweight and ecofriendly at the same time they offer similar mechanical properties to glass. Composites for automotive interiors parts application should have simple manufacturing process and must be able to withstand impact forces in the event of collision. Apart from this, interior requirement like acoustic insulation, aesthetics, life cycle odor/fogging, etc., should also be fulfilled [61]. Resin volatility is the main reason for fogging which may cause fog on front windshield. Most common used resins are epoxy, polyurethane, polypropylene, and polyethylene. The choice of resin depends on particular application for which it is intended to use also its compatibility with the reinforcement material used. Polypropylene is the highly compatible with majority of the fibers due to its excellent capability of blending at molecular level as well as offer excellent mechanical and physical properties [62]. BMW used door trims made of Epoxy/flex, various other car manufacturers explored composites for interior application, e.g., are front end carrier of Volkswagen Passat, Instrument Panel carrier (Mercedes E class) and seat structures. A study by [ACC] automotive composite consortium [63] showed that a 23% of weight saving can be done by replacing a steel seat structure with a composite made structure. Table 3.6 shows the weight saving from of individual seat parts in kilograms.

Figure 3.5 Automotive interiors (images modified and recreated from Refs. [11] and [40]).

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Table 3.6 Seat parts made of steel and composites [63]. Seat parts

Steel weight in kg

Composite weight in kg

Back

3.56 kg

3.16 kg

Cushion

3.88 kg

2.59 kg

Total

7.44 kg

5.75 kg

3.4.2 Exterior Body Panels Automotive exteriors are generally made up of metallic material. They are accounted for a significant weight portion of the total vehicle weight and offers a possibility of weight saving id replaced with composite structures. Doors, bonnet, deck lid, bumper, fenders, and rocker panels are the main exterior panels of the automotive body structure. In this study only few parts like hoods, bumpers etc. are discussed.

3.4.2.1 Car Hoods (Bonnet) Figure 3.6 shows a typical bonnet of a passenger car. Car Hood is a part of body that borders to the front fenders, front light, bumper, and plenum cover. Car hood plays a very important role during the vehicle accidents; it

Figure 3.6 Automotive hood.

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should have high stiffness and better crash performance during accident. It also provide environmental protection to the engine and various other parts inside the hoods, also it should have a good dent resistance. A suitable composite materials with similar properties to the conventional materials and also provide reduction in weight of the vehicle needs to be used for such parts. Composite parts may not provide very good surface quality but it can provide at pedestrian safety and high energy absorption during impact can safeguard the passenger. Generally hood weight is around 10 kg so a huge potential is there to reduce it weight by substituting a suitable composite materials.

3.4.2.2 Bumpers Figure 3.7 shows a typical bumper of racing and passenger car. It is a structure attached with a vehicle at its front and rear ends in order to absorb impact stresses developed during minor collision and basically serves the purpose to minimize the repair cost of vehicle, various automotive company have started use of composite bumpers compared to plastic one as composite have potential of high energy absorption in the event of impact, and hence improve its crashworthiness. Impact strength (Frontal impact, side impact, pedestrian impact) is the main requirement of bumper of a vehicle as during vehicle collision it has to absorb the impact energy.

Figure 3.7 Bumper panels (images modified and recreated from Refs. [11] and [15]).

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Conventional steel bumper are five time heavier and aluminum bumpers are double the wright of the composite made bumper now our objective is to develop and replace the conventional materials bumpers with the composite bumpers which are satisfying the conditions of suitable manufacturing process, low cost, achieving the weight reduction compared to steel and aluminum and improved impact behavior in a similar manner to the conventional materials. It was reported by researcher that bumper beam made by carbon fiber composites absorb nearly same kinetic energy and the maximum deformation of the carbon fiber composite bumper beam is lower than that of steel bumper beam, so by using carbon fiber composite, the impact performance of the bumper beam is found to be improved. Also the impact force between the impactor and fascia and the acceleration of the impactor are decreased slightly [64].

3.4.2.2.1 Design Criteria of Bumper In bumper design, commonly used design criteria are damage and protection analysis, for damage analysis relative displacement and stiffness are examined. Crash test is done to know how car will behave during front and rear end collision. Important parameter to be designed to improve impact performance, Maximum conversion of kinetic energy into internal energy Deformation of the bumper beam should be lower, Lightweight, Maximum stress should not exceed the yield stress.

Figure 3.8 Door systems of an automobile.

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3.4.2.3 Door Panels Figure 3.8 shows the typical door system of a passenger car. After vehicle chassis door system of a car carry a huge portion of the total weight of a car. Total door system consists of almost 135 kg in a passenger car. In a study by Sakthi Vijayalakhsmi [65] replacing metallic door system (all four doors) with textile structural composite may reduce the weight up to 40% of the door system alone. Table 3.7 shows the comparative analysis of weight of metallic body panels with textile structural composites. It can be seen that a total of 7% to 8% weight reduction is possible if door panels, bumper, and frontal hood are replaced with textile structural composites.

3.4.3 Structural Components Structural component of vehicle are the components which are load bearing, chassis, suspension system (leaf spring), floor pan, alloy wheel, drive shaft, bending axel, etc., in this chapter leaf spring is considered for further discussion. Leaf spring (shown in Figure 3.9(e)) shares a major portion of unsprung weight (weight of chassis, suspension system, axles, wheels, etc.) of a vehicle. It is about 15% to 20% of the total unsprung weight. Leaf spring can be a potential part for weight saving in automobile.

Table 3.7 Comparative analysis of metallic body panels vs. TSC panels [65]. Weight (Kg) Components

Steel

TSC

Reduction

Weight reduction (%)

Doors

Door Frames (Steel alone)

68.04

13.922

–

–

Total Door System

135.68

81.56

54.118

39.88

Bumper beams (Steel alone)

14.62

2.99

–

–

Total bumper system

33.6

21.97

11.63

34.61

Front hood

8

1.64

6.36

79.5

177.28

105.17

72.11

40.68

Bumper

Bonnet Total

Textile Structure Reinforced Composites (b)

(a)

(d)

(e)

91

(c)

(f)

Figure 3.9 Structural (Load bearing) components of automobile: (a) spring rod, (b) Chassis, (c) Leaf spring (composite), (d) brake disc, (e) leaf spring (metallic), (f) bending axel (images modified and recreated from Refs. [15] and [18]).

3.4.3.1 Leaf Spring Leaf spring absorb and store energy and release when vehicles come across road irregularities and act as a vibration damper. Leaf spring is used in light truck, SUV, and heavy duty vehicles at front and rear axles. Figure 3.10 shows a common configuration of leaf spring. Major function of leaf spring to absorb the jerk coming to vehicle body when vehicle is moving on bumpy roads and come across some uneven surface or obstacle, support the chassis weight, control axel damping and breaking force, regulates wheel base length under acceleration and breaking. First ever fiber reinforced plastic (FRP) mono leaf spring was used in Chevrolet Corvette in 1981. Composite transverse mono leaf spring weight 3.7 kg compared to steel leaf spring with 10 leaf weighing 18.6 kg. Weight reduction of almost Eye

Camber

Central Clamp

Master Leaf Graduated Leaves

Figure 3.10 Semi elliptic Leaf Spring.

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15 kg from the corvette [66]. The new Volvo XC90 (from 2016 year model and forward) has come up with a transverse composite leaf spring a solution that is similar to the latest Chevrolet Corvette. This results weight saving of almost 4.5 kg compared to the conventional concept [67]. It may be in the great interest of automobile industry in replacing of steel leaf spring with composite leaf spring as composite have high strength to weight ratio, good corrosion resistance and better design flexibility. Fatigue behavior and deflection of composite leaf spring should be high compared to the metal counterpart. High performance composite shows a linear stress strain curve and shows a similar behavior of brittle materials like ceramics compared to the metals which shows a high degree of plasticity as shown in Figure 3.11. Table 3.8 summarizes the relative energy absorption

70000 60000 50000 Load (N)

composites 40000 Metals

30000 20000 10000 0 0

10

20 30 Extension (mm)

40

50

Figure 3.11 Typical load vs. elongation curve for composite and metals.

Table 3.8 Energy absorption per unit weight of various materials [42]. S. No.

Material

Relative energy absorption (per unit weigh)

1

High Performance composite

100

2

Commercial composite

60–75

3

Mild steel

40

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of composites and metal. From stress stain behavior it can be concluded that materials like composite and ceramics are elastic to failure and hence do not have much energy absorption as they do not shows plastic deformation for such requirement. But elastic materials can be very effective energy absorber because the failure mechanism is fracture surface energy rather than plastic deformation. It has shown by P. Beardmore, C.F. Johnson [42] that fracture mechanism of glass fiber composite is dependent on weight as shown in table given below. Also composite which use fiber like Kevlar fails like metals using plastic deformation as energy absorbing mechanism. Stiffness is also one of the important parameter for a leaf spring, since loss in stiffness under fatigue loading could result in loss of stiffness related functions like NVH, with no loss in any mechanical function. From the above in can be concluded that automobile component should be designed in such a way that continuous fiber take the major loads and chopped fiber to provide some degree of orthotropic behavior. This is clear that glass fiber reinforced composite can be designed to withstand under severe fatigue loading one such example is leaf spring design.

3.5 Lightweight Solution for Electric Car Environmental impact can be reduced further with lightweight electric vehicles. Textile reinforced composite can be potential materials for the successful lightweight electric cars designs. Because lightweight electrics cars is an advanced step toward achieving the goal of lower vehicular emission. Successful implementation of electric vehicles worldwide is possible only with the development of advance battery system and the lightweight composite materials. Textile reinforced structural composites are the composites dedicated for load bearing applications, so it may be a material of choice for lightweight solar powered and electric vehicle in future.

3.6 Conclusion Government bodies came up with stringent pollution norms for automotive sectors due to increased vehicular emission. Almost all top automotive industries are striving to achieve vehicle weight reduction, so that improved fuel efficiency with low carbon footprints can be achieved. It is said that every 10% reduction in vehicle weight can improve fuel efficiency up to 7%. Initially alloys, magnesium and aluminum were tried by various manufacturers in different parts of automobile from engines frames to

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body panels. In recent time composite opens up a completely new skyline for sectors like aerospace, automotive, railways, sports, defense etc. So far, use of composite in automobile sector is limited to some semi structural components like dashboard panels, bumper, etc. Composite offers lightweight solution to the automotive sector and offers a high specific strength and stiffness, corrosion free low maintenance compared to metallic materials. 3D woven structure reinforced composite is the new development in the field of textile structural composite which could be a potential solution for the automotive sector. 3D solid woven preforms could be used in different load bearing structures, as they offer high strength compared to laminated composite without any delamination issues. Companies like BMW, Mercedes have already came up with the concept of using full body in white (BIW) structures made up of composites. The success of development of electric cars world over is purely dependent on use of advanced textile structural composites. Use of advance fiber (carbon/glass) based 3D solid woven structural composites can be a potential solution for load bearing component like suspension system and vehicle chassis. Despite various advantages over conventional materials no significant changeover from metals to composite is noticed in automotive industry despite few sports utility vehicles and formula racing cars. Various issues associated with composites like reparability, crashworthiness, fire safety, recycling, joining, manufacturing are still needs to be explored for their applicability in various automotive components.

References 1. Boden, T.A., Marland, G., Andres, R.G., Global, Regional, and National Fossil-Fuel CO2 Emissions, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, 2010. 2. Cheah, L.W., Cars on a diet: The material and energy impacts of passenger vehicle weight reduction in the US, Doctoral dissertation, Massachusetts Institute of Technology, 2010. 3. Joost, W.J., Reducing vehicle weight and improving US energy efficiency using integrated computational materials engineering. Jom., 64, 9, 1032– 1038, 2012. 4. Cole, G.S. and Sherman, A.M., Lightweight materials for automotive applications. Mater. Charact., 35, 1, 3–9, 1995. 5. Kulekci, M.K., Magnesium and its alloys applications in automotive industry. Int. J. Adv. Manuf. Technol., 39, 9–10, 851–865, 2008.

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6. Elmarakbi, A., Advanced Composite Materials for Automotive Applications: Structural Integrity and Crashworthiness, John Wiley & Sons, New Jersey, USA, 2013. 7. Friedrich, K. and Almajid, A.A., Manufacturing aspects of advanced polymer composites for automotive applications. Appl. Compos. Mater., 20, 2, 107–128, 2013. 8. Kumar, N. and Das, D., Fibrous biocomposites from nettle (Girardinia diversifolia) and poly (lactic acid) fibers for automotive dashboard panel application. Compos. Part B-Eng., 130, 54–63, 2017. 9. Belingardi, G., Beyene, A.T., Koricho, E.G., Martorana, B., Alternative lightweight materials and component manufacturing technologies for vehicle frontal bumper beam. Compos. Struct., 120, 483–495, 2015. 10. Ashori, A., Wood–plastic composites as promising green-composites for automotive industries. Bioresour. Technol., 99, 11, 4661–4667, 2008. 11. Marsh, G., Next step for automotive materials. Mater. Today, 4, 6, 36–43, 2003. 12. Koronis, G., Silva, A., Fontul, M., Green composites: A review of adequate materials for automotive applications. Compos. Part B-Eng, 44, 1, 120–127, 2013. 13. John, A. and Alex, S., A Review on the Composite Materials used for  Automotive Bumper in Passenger Vehicles. Int. J. Eng. Manag. Res., 2, 98–101, 2014. 14. Khalfallah, M., Abbès, B., Abbès, F., Guo, Y.Q., Marcel, V., Duval, A., Rousseau, F., Innovative flax tapes reinforced Acrodur bio composites: A new alternative for automotive applications. Mater. Des., 64, 116–126, 2014. 15. Feraboli, P. and Masini, A., Development of carbon/epoxy structural components for a high performance vehicle. Compos. Part B-Eng., 35, 4, 323–330, 2004. 16. Zhang, J., Chaisombat, K., He, S., Wang, C.H., Hybrid composite laminates reinforced with glass/carbon woven fabrics for lightweight load bearing structures. Mater. Des. (1980–2015), 36, 75–80, 2012. 17. Obradovic, J., Boria, S., Belingardi, G., Lightweight design and crash analysis of composite frontal impact energy absorbing structures. Compos. Struct., 94, 2, 423–430, 2012. 18. Adam, H., Carbon fiber in automotive applications. Mater. Des., 18, 4–6, 349–355, 1997. 19. Greenhalgh, E. and Hiley, M., The assessment of novel materials and processes for the impact tolerant design of stiffened composite aerospace structures. Compos. Part A Appl. Sci. Manuf., 34, 2, 151–161, 2003. 20. Manjunath, R.N. and Behera, B.K., Modelling the geometry of the unit cell of woven fabrics with integrated stiffener sections. J. Text. Inst., 108, 11, 2006– 2012, 2017. 21. Kim, J.S., Lee, S.J., Shin, K.B., Manufacturing and structural safety evaluation of a composite train car body. Compos. Struct., 78, 4, 468–476, 2007.

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22. Marsh., M., Development of auto body sheet materials for crash performance. Proc. Of Conference of Materials and structures for energy Absorption, IMech, London, 2000. 23. Magnusson, C. and Andersson, R., Stainless Steel as Light Weight Automotive  Material, R&D-Forming & Materials, Swedish Tools & Die Technology, Lulea, Sweden, 2001, https://www.bssa.org.uk/cms/File/Conf%20 03%20SS%20as%20a%20Lightweight%20Automotive%20Material.pdf. 24. Ghassemieh, E., in: Materials in Automotive Application, State of the Art and Prospects, University of Sheffield, U.K., 2011. 25. Hirsch, J., Recent development in aluminium for automotive applications. T. Nonferr. Metal. Soc., 24, 7, 1995–2002, 2014. 26. Zhou, J., Wan, X., Li, Y., Advanced aluminium products and manufacturing technologies applied on vehicles presented at the EuroCarBody conference. Mater. Today Proc., 2, 10, 5015–5022, 2015. 27. Shin, J., Kim, T., Kim, D., Kim, D., Kim, K., Castability and mechanical properties of new 7xxx aluminum alloys for automotive chassis/body applications. J. Alloys Compd., 698, 577–590, 2017. 28. Roth, R., Clark, J., & Kelkar, A., Automotive Bodies: Can aluminum be an Economical Alternative to Steel. JOM, 53, 8, 28–32, 2001. 29. Luo, A.A., Magnesium casting technology for structural applications. J. Magnesium Alloys, 1, 1, 2–22, 2013. 30. Aghion, E., Bronfin, B., Eliezer, D., The role of the magnesium industry in protecting the environment. J. Mater. Process. Technol., 117, 3, 381–385, 2001. 31. Powell, B.R., Krajewski, P.E., Luo, A.A., Chapter 4: Magnesium Alloys, in: Materials Design and Manufacturing for Lightweight Vehicles, pp.  114–168, Woodhead Publishing Ltd, Cambridge, UK, 2010. 32. Emley, E.F., Principles of Magnesium Technology, Pergamon Press, London, 1966. 33. Blawert, Hort, N., Kainer, K.U., Automotive application of magnesium and its alloy. Trans. Indian Inst. Met., 57, 4, 397–408, 2004. 34. Kulekci, M.K., Magnesium and its alloys applications in automotive industry. Int. J. Adv. Manuf. Technol., 39, 9–10, 851–865, 2008. 35. Pickering, K.L., Efendy, M.A., Le, T.M., A review of recent developments in natural fiber composites and their mechanical performance. Compos. Part A Appl. Sci. Manuf., 83, 98–112, 2016. 36. Al-Oqla, F.M. and Sapuan, S.M., Natural fiber reinforced polymer composites in industrial applications: feasibility of date palm fibers for sustainable automotive industry. J. Clean. Prod., 66, 347–354, 2014. 37. Alves, C., Silva, A.J., Reis, L.G., Freitas, M., Rodrigues, L.B., Alves, D.E., Ecodesign of automotive components making use of natural jute fiber composites. J. Clean. Prod., 18, 4, 313–327, 2010. 38. Ashori, A., Wood-plastic composite as promising green composites for automotive Industry. Bioresour. Technol., 99, 4661–4667, 2008.

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39. Ahmad, F., Choi, H.S., Park, M.K., A Review: Natural fiber composites selection in view of Mechanical, Light Weight and Economic Properties. Macromol. Mater. Eng., 300, 10–24, 2015. 40. Holbery, J. and Houston, D., Natural-Fiber-Reinforced polymer composites in automotive Applications. JOM, 58(11), 80–86, 2006. 41. Mangino, E. The future use of structural composite materials in the automotive industry. et al., Int. J. Vehicle Des., 44, 3/4, 211–232, 2007. 42. Beardmore, P. and Johnson, C.F., The potential for composites in structural automotive applications. Compos. Sci. Technol., 26, 4, 251–281, 1986. 43. Feraboli, P.A. and Bonafatti, A., Advanced composites for the body and chassis of a production high performance car. Int. J. Vehicle Des., 44, 3/4, 233–246, 2007. 44. Feraboli, P. and Maisini, A., Development of carbon/epoxy structural components for a high performance vehicle. Compos. Part B, 35, 323–330, 2004. 45. Prvaiz, M., Panthapulakkal, S., Birat, K.C., Sain, M., Tjong, J., Emerging Trend In Automotive Light-weighting through Noval Composite Materials. Mater. Sci. Appl., 7, 26–38, 2016. 46. Greening transport, European commission, European Parliament and the council, SEC/2008/2206 FIN [08/.07.08]. 47. Davies, G., Materials for Automobile Bodies, Repika Press Pvt. Ltd., Oxford, 2003. 48. Suddell, B. and Evnas, W., Natural fiber composite in automotive application, in: Natural Fibers, Biopolyners, and Biocomposites, A.K. Mohanti, M. Mishra, T.L. Drzal (Eds.) CRC Press, Florida,USA, 2005. 49. Koronis, G., Silva, A., Fontul, M., Green composites: A review of adequate materials for automotive application. Compos. Part B, 44, 120–127, 2013. 50. Das, S., Life cycle assessment of carbon fiber-reinforced polymer composites. Int. J. Life Cycle Assess., 16, 268–282, 2011. 51. Jacob, A. Car makers increase their use of composites. Reinforced Plastics, 48(2), 26–32, 2004. 52. Behera, B.K. and Mishra, R., 3-Dimensional weaving. Indian J. Fiber Text. Res., Vol. 33, 33, 2008. 53. Behera, B.A. and Dash, B.P., Mechanical behavior of 3D woven composites. Mater. Des., 67, 261–271, 2015. 54. Dufour, C., Jerkovic, I., Wang, P., Boussu, F., Koncar, V., Soulat, D., Pineau, P., Innovative monitoring of 3D warp interlock fabric during forming process. IOP Conference Series: Materials Science and Engineering, vol. 254, IOP Publishing, p. 042010, 2017. 55. Dufour, C., Jerkovic, I., Boussu, F., Wang, P., Soulat, D., Grancaric, A.M., Pineau, P., Global and local observations of 3D warp interlock fabric behaviour during forming process. AIP Conference Proceedings, vol. 1769, AIP Publishing, p. 170017, 2016. 56. Das, A., Mechanical performance of 3D woven solid structures and their composites, Ph.D. thesis, IIT Delhi. New Delhi, 2019.

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57. Dai, S., Cunningham, P.R., Marshall, S., Silva, C., Influence of fiber architecture on the tensile, compressive and flexural behaviour of 3D woven composites. Compos. Part A Appl. Sci. Manuf., 69, 195–207, 2015. 58. Rudov-Clark, S.A. and Mouritz, A.P., Tensile fatigue properties of a 3D orthogonal woven composite. Compos. Part A Appl. Sci. Manuf., 39, 6, 1018– 1024, 2008. 59. Zhang, D., Sun, Y., Chen, L., Pan, N., A comparative study on low-velocity impact response of fabric composite laminates. Mater. Des., 50, 750–756, 2013. 60. Mann, D., Van den Bos, J.C., Way, A., Automotive Plastics and Composites: Worldwide Markets and Trends to 2007, 2nd ed., Elsevier, U.S., 2007. 61. Magurno, A., Vegetable fibers in automotive interior components. Die. Angewandte. Makromolekulare Chemie, 272, 1, 99–107, 2000. 62. Overview of materials for polypropylene with 30% glass fiber filler. [Online material data] [2008 Mar 25], Available at http://www.matweb.com/search/ datasheet.aspx?matguid=e2a28c79390342e4904502d582e69c62&ckck=1. 63. Berger, L. et al., Structural Automotive Components from Composite Materials, Automotive Composites Consortium May 2012, https://www. energy.gov/sites/prod/files/2014/03/f10/lm049_berger_2012_o_0.pdf. 64. Wang, T. and Li, Y., Design and analysis of automotive carbon fiber bumper beam based on finite element analysis. Adv. Mech. Eng., 7, 6, 1–12, 2015. 65. Vijaylakshami, S., Textile structural composite for automotive application, M. Tech thesis, IIT Delhi. New Delhi, 2018. 66. Wood, K., Composite leaf springs: Saving weight in production suspension systems. Compos. Technol., 19, 1, 2014. 67. Kerstan, F., Henkel enabling weight savings on heavy SUV’s. Reinforced Plastics, 60, 1, 56–58, 2016.

4 Biotechnology Applications in Textiles Lalit Jajpura

*

Department of Textile Technology, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar, India

Abstract Biotechnological applications in textiles play a vital role from fiber cultivation/ production to apparel production in sustainable way. Biotechnological applications help in fulfilling the increasing demand of the cotton and other natural fibers along with it paved the road towards the cultivation of sustainable organic cotton, gene modified cotton or Bt Cotton and other natural plant based fibers; sericulture of silk and wool production with the better traits of fiber quality and yield by the help of gene and clone technology. Biotechnology has great prospects in textile wet processing from pretreatment to finishing operations also. Amylase, pectinase, lipase, hemicellulase, cellulase, catalase, protease, sericinase, cutinase, laccase, xylanase, etc are extensively used enzymes in textiles. These enzymes have tremendous scope in replacing toxic chemicals being used in various textile wet processing operations such as desizing, scouring of cotton, retting of bast fibers, bio-bleaching, fading of denim, dye decolorization in effluent, biopolishing of cellulosic textile materials, fading of denim; bio carbonization, scouring, antishrinking and softening of wool; degumming of silk and removal of hydrogen peroxide, etc. The present chapter emphasizes the biotechnological applications in abatement of use of toxic chemicals and processes from fiber cultivation to waste disposal for sustaining the environment and biodiversity. Keywords: Cotton cultivation, Bt cotton, sericulture, wool production, enzyme applications, textile wet processing, biopolymers, immobilization

Email: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (99–128) © 2020 Scrivener Publishing LLC

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4.1 Introduction In the past century numerous developments took place in textile sector from fiber cultivation to finished apparel to cope with the growing demand of exploding population of the globe. These developments took place at the cost of environment and biodiversity as most of the manmade fiber production need non renewable petroleum based raw materials, chemicals along with high amount of energy and water. Even agricultural based cotton and other renewable fibers which seem sustainable are found to be associated with use of huge amount of toxic pesticides, synthetic fertilizers and water [1, 2] and affecting the ecology at large. Produced textile materials are further pretreated, dyed, printed, and finished in wet processing operations to fulfill the aesthetic, comfort and other pre-requisite properties of the final textile products. These textile wet processing operations from pretreatment to finishing are associated with use of numerous toxic chemicals and auxiliaries. The residual liquor of processing industries contains high amount of BOD, COD, TDS, TSS, and non biodegradable contaminants, i.e., dyes, finishes, and auxiliaries which pollute the environment and has lethal effects on biodiversity if drained without effluent treatment [3]. Especially trace of employed color and pigment in small amount even in ppm prohibit the transmission of visible sunlight in water and interfere in photosynthesis reaction of aquatic plants leading to oxygen depletion and devastate whole aqua biological system [1, 4]. Further industrial generated textile fiber waste as well as consumer used textile waste is causing severe disposing problems due to non biodegradability of most of the synthetic fibers. Therefore, there is dire need to replace these toxic chemicals, processes and products with eco friendly sustainable alternatives. Biotechnology plays a vital role in replacing toxic chemicals and processes from fiber cultivation/production to dyeing and finishing stage and till disposal at the last stage of product cycle. There is surge of developments in sustainable biotechnology based natural fiber cultivation to production of biodegradable manmade fiber; sustainable pretreatment, dyeing and finishing operation. These biotechnological developments give better prospects for symbiotic ecofriendly textile production from fiber to apparel stage to end product disposal needed for survival of human being as well as for maintaining ecology and biodiversity for future generation. In the same context various biotechnological developments are discussed in the following contents of the chapter.

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4.2 Adverse Effects of Industrial Farm Practices in Cotton Cultivation Cotton is the most extensively used natural fiber and known for its soothing aesthetic appearance, softness, and comfort [5]. It shares approximately one third of global requirement of textiles and apparels. Cotton cultivation has commercial significance as not only it fulfills the requirement of clothing but also contributes in cotton seed production. The increased demand of food and fiber was fulfilled by expanding area of cultivation by converting tropical forest into farms with devastation of biodiversity. Further, green revolution made it feasible to feed more than 7.5 billion people with increase in crop yield without significant increase in area of cultivated land by the help of automation in agricultural sector, use of fertilizers, pesticides, appropriate irrigation technologies, and nevertheless advancement in biotechnology. The population of the world is exploding rapidly and it is estimated that agricultural production has to be almost doubled in next 50 years, although, since 1974 land area for cotton cultivation has been limited to 30–35 million hectares and is unlikely to increase significantly to address this demand [6]. The use of pesticides, fertilizers and water resources are already exploiting the environment excessively thus doubling of agricultural production further will be very difficult task as even lesser land will be available for cotton and other fibers cultivation in future due to prioritization toward the food crops [7]. The effect due to excessive use of synthetic fertilizers, toxic pesticides, and water resources in mass cultivation technologies for cotton and other agricultural production are as follows [8].

4.2.1 Adverse Effect of Synthetic Fertilizers The application of synthetic fertilizers increased across the globe due to employment of mass production technology in agricultural sector. In India only the fertilizer consumption increased from mere 0.3 million tonnes in 1959–1960 to more than 20 million tonnes in 2005–2006 [9]. The synthetic fertilizers contain high amount of nitrogen, phosphorous, potassium, calcium and other micronutrients which increase crops’ yield but contrary their excessive use impact soil, water, and air quality. The nitrogen based fertilizers are responsible for acidification by conversion of ammonia in to nitrate by nitrification reaction. Beside that excessively used fertilizers and other nutrients causes accumulation of heavy metals. The abundant amount of metallic salt and nutrients are responsible

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for oxygen depletion leading to stage of eutrophication. The depletion of oxygen due to eutrophication destroys the aquatic life and develops dead zones in surface water and in sea [10]. Besides water pollution, use of synthetic fertilizers leads to formation of fog and acid rain.

4.2.2 Adverse Effect of Synthetic Pesticides Pesticides are toxic substances used for preventing, destroying and controlling the insects, weeds, mould along with rodents. It is estimated that only 0.1% to 5% of pesticides applied to crops actually reach and control the pest. Cotton accounts only around 5–7% of the total cultivation area but consumes more than 50% of the total pesticides used. The excess used toxic pesticides leach into soil, water and even in clouds as shown in Figure 4.1 and create lethal environmental impact related to biodiversity [11, 12]. They not only harm humans and aquatic life but are also lethal to ecofriendly arthropods, earthworms, fungi, bacteria and other organisms which are essential for symbiotic ecosystem [13, 14]. The effect of toxic pesticides will be for decades as number of pesticide such as DDT are not biodegradable and they remain in environment for more than decade [15]. The pesticides cause temporary to permanent health

Transportation of toxic substances of pesticides reaching to atmospheric layers and contamination of clouds

Dry deposition

Water bodies like ponds, rivers, sea

Rain with contaminants

Pesticides used for pest control, fungi, weeds, moulds, etc pollute the farm land and nearby environment

Contamination to ground water

Figure 4.1 Pesticide in the atmosphere and water [11, 12].

Evaporation

Seepage to water bodies

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effect such as asthma, birth defect, neurological effects, and cancer. Even prolong exposure of small amount of pesticide can kill humans and animals.

4.2.3 Adverse Effect of Excessive Irrigation Cotton cultivation needs huge amount of water ranging from 7 to 29 tonnes/ kg [16]. In past century, number of dams, canals and artificial water supply systems have been constructed to cope with the increased demand of agricultural sector and drinking water. It is surprising to know that Aral Sea in central Asia has been reduced to small percentage of its original size due to irrigation of agricultural crops like cotton and resulting aquatic life and biodiversity in the region is at danger [8]. The overall impact of employed synthetic fertilizer, pesticide, and mass scale irrigation on ecosystem is tabulated in Table 4.1.

4.3 Application of Biotechnology in Cotton Cultivation There is need to improve cotton fiber yield by developing cotton variety that can be grown with lesser consumption of water, more resistant to pest, drought, and adverse climate conditions. Beside these, it is required that crop yields best quality of cotton fiber consisting long fiber length, higher strength, fineness, etc., prerequisite properties to get best price of the crop as these fibers attributes are essential for better yarn quality as well as high productivity in high speed spinning operations. The conventional breeding techniques improve the fiber qualities to some extent but major threat of pests and insects remains as it is. Beside these, indiscriminate use of chemical pesticide harms the farmers and consumers health with affecting the environment and biodiversity at large. Therefore biotechnological approaches including genetic engineering were opted to alter the plant characteristics for better pest resistance, productivity and other chemical and physical properties of cotton fiber and its seed [17, 18]. With advancements in biotechnology and genetic engineering these aforesaid prerequisite quality of cotton is being significantly improved in gene modified cotton. Transgenesis or genetic engineering is an ideal solution to these challenges with its ability to introduce diverse agronomical important genes from various biological species. The gene technology made it feasible to cultivate gossypol free cottonseed which produces oil and proteins suitable for human consumption. Thus, more than 80 % cotton is grown currently by gene modified technology due to significant improvement in cotton variety

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Table 4.1 Adverse effect of excessive use of fertilizers, pesticide, and water irrigation. Adverse effect of synthetic fertilizers

Adverse effect of synthetic pesticides

Adverse effect of excessive irrigation

Acidification by nitrification reaction

Increases toxic substances in farm and vicinity of pesticide used

Excess used water increases water table of land

Accumulation of heavy metals in soil and water

Kill the symbiotic pest and living organism

Increasing salinity of water bodies

Eutrophication in water bodies

Pesticide such as DDT are not biodegradable

Diminishing soil fertility

Affecting aquatic life

Leaching pesticide into soil, water and transfer even in to clouds

Drying of ponds, dams and sea

Development of dead zones in water

Affecting human health, i.e., Asthma, birth defect, allergy, cancer or even death

Non replenishment of natural water resources, i.e., ponds, river, sea by fresh water addition

Acid rain and formation of fog

Rain with toxic substances

Causing devastation in aquatic life in water bodies and deforestation

[5, 19]. Further, adoption of biotechnology in cotton cultivation gives good prospective for contributing global needs of oil and food [6].

4.3.1 Gene Construction and Transformation In genetic modification, genes of an organism, i.e., plant, bacteria, fungi, animal is altered as per the requirement. In genetic modification Recombinant DNA technique, DNA of one gene is recombined with other host gene thus the modified resultant gene has characteristics of both the gene, i.e., better productivity as well as pest resistance. The foreign gene

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also known as transgene can be transferred from a plant to another plant, from a plant to an animal, or from a microorganism to a plant [20]. The modified gene based organism is known as genetically modified organism (GMO) i.e. genetically modified cotton [21].

4.3.2 Bt Cotton Many genes code of protein containing the insecticidal properties are identified but few of them were commercially used for production of insecticidal transgenic cotton such as proteinase inhibitors [22], lectins [23], B. thuringiensis Insecticidal Proteins [24, 25], etc. Most of the gene based protein inhibits either digestion system of the pest by hampering their catalytic activity or hampering other biological activity leading to their growth and death [17]. B. thuringiensis has been used as biopesticide since long as alternative to toxic synthetic pesticides [26]. This property of B. thuringiensis leads to development of transgenic cotton, known as Bt cotton containing the gene information of B. thuringiensis in cotton seed [17]. China commercialized cultivation of Bt cotton in 1997 and leads in cultivating major share in GMO cotton [27]. In India Bt cotton is the only genetically engineered (GE) crop approved for commercial cultivation in 2002 and it is observed that Bt cotton hybrids give 80% more average yield than non Bt cotton hybrids [28]. As per estimate, it accounts over 95% share of India’s total production of about 29.7 million bales (480 lb bales) in MY 2017/18 (August–July). With adoption of Bt cotton, India became the world’s largest producer and second largest exporter of cotton [29].

4.4 Wet Processing of Cotton and Its Environmental Impact Fabric is made clean and absorbent in preparatory wet processing operations by removal of various impurities before dyeing and printing to insure better dye penetration inside the fiber for achieving better color yield. These operations need various toxic chemicals which not only pollute the environment but some of them damage the equipment as well as fabric being corrosive in nature [30]. The sequence of operation and contents of effluent discharge is shown in Table 4.2 [3]. The effect of employed colorants in textile wet processing is tremendous on water, ecology, and biodiversity as over 7 million tons of more than 10000 dyes are annually produced and out of which most of the unexhausted dyes

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Table 4.2 Textile wet processing operations and their effluent contents. Process

Effluent contents

Sizing

Starches, PVA, CMC, etc

Desizing

Hydrolyzed product of starches, PVA, CMC, etc., acids

Scouring

Caustic soda, soda ash, wetting agent, etc.

Bleaching

Absorbable chlorine, hydrogen peroxide and degraded oxidized cellulosic products

Mercerization

Concentrated Caustic soda and wetting agents

Dyeing

Unexhausted different types of biodegradable and non biodegradable dyes, pigments along with salts, surfactants, and other auxiliaries

Printing

Wash out exhausted printing paste consisting concentrated dyes, pigments, thickeners, auxiliaries, and other residual of printing paste constituents

Finishing

Exhaust liquor consisting traces of employed finishes such as Urea formaldehyde resins, stiffeners, softeners, water, and flame retardants, etc.

Boilers

High dissolved solids ranges from 3500 to 60000 mg/lt

are drained as it is without treating in effluent treatment plant [4]. Beside these, various carcinogenic employed dyes and pigments, surfactants, thickeners, finishes, etc are polluting the environment at great extent. There is dire need to substitute these used toxic chemical sustainably so effluent load and adverse effect can be minimized. Biotechnology based enzymatic applications give best opportunity to replace toxic chemicals as well reduce effluent load. The following section discusses enzymatic applications in cellulosic textiles as follows.

4.5 Enzyme and Its Properties Enzymes are precious gift of nature to all living entities and without them life cannot be thought of. Enzymes are high molecular weight protein molecules in specific three dimensional globular structures [31]. All catalytic reactions of bioorganisms are performed by enzymes thus they are also known as biocatalyst [32, 33]. They have active site in form of holes, cavities or a fissure

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by which they make complex with substrate in lock and key principle. This principle of enzyme working was proposed long back in 1980 by E. Fisher and helpful in understanding various enzymatic properties [34]. The properties of enzymes beneficial for sustainable textile wet processing are as follows [34]: • Accelerate the chemical reactions by minimizing the activation energy without taking direct part in the reaction. • Work under optimum condition such as temperature and pH [35]. • Acts on specific substrate as work on lock and key mechanism. • Sustainable being capacity to replace synthetic chemicals reaction such as hydrolysis, oxidation, reduction, coagulation, decomposition, etc. • Handling and storage is easier without any significant hazard. • Renewable and biodegradable in nature.

4.6 Classification of Enzymes The enzymes are very complex molecule and human being are not capable to synthesize them in the laboratory. The only way of producing enzymes is growing the enzymes producing living organism, i.e., bacteria, fungi, etc. in bioreactors at mass scale and then extraction of enzymes from these organisms. Enzymes are classified as bacterial, animal, yeast or fungal based on the basis of their origin. They are also categorized as intra or extracellular based on mode of enzyme working in bacterial cell. If enzyme is produced by bacteria or fungi to work inside their confined cell structure then it is known as intracellular and if they secrete the enzyme outside their cellular structure for performing the required catalytic reaction then enzyme is known as extracellular enzyme. The International Union of Biochemistry and Molecular Biology (NC-IUBMB) classified the enzymes into main six classes and further subclasses as per the type of reaction catalyzed [36]. These six classes of enzymes are as follows: 1. Oxidoreductases: peroxidase, oxidases, dehydrogenases, etc. 2. Transferases: ATP glucose phosphotransferease, glucokinase, etc. 3. Hydrolases: amylase, pectinase, lipase, protease, etc.

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Advanced Functional Textiles and Polymers 4. Lyases: pyruvatelyase, decarboxylase, aldolase, etc. 5. Isomerases: maleate isomerase, glucose isomerase, etc. 6. Ligases: pyruvate carboxyligase

Enzymes are extensively used in various industries such as baking, beverage, dairy, pharmaceutical, polymer, paper and pulp, leather, textile at mass scale. The application of enzyme in textiles is discussed below [30, 37].

4.7 Enzymatic Bioprocessing of Cotton 4.7.1 Desizing Size consisting natural and synthetic materials is applied to most of the yarns to facilitate the high speed weaving operation. The applied size coating facilitates the weaving operation by providing appropriate strength and lubricity to yarn to sustain against high mechanical forces and friction. Although this size coating needs to be removed before dyeing operation as it hinders the penetration of water during wet processing. Size paste consists of thickening agents along with lubricating agents (i.e., lipids, tallow, fats, etc), antistatic agents, antibacterial, or anti mildewing agents. Extensively used thickeners are natural based polymeric materials, i.e., starches, British gum, or other modified starches or its derivatives, cellulose derivatives, etc. Although application of synthetic sizing agents i.e. poly vinyl alcohol, poly vinyl acetate, polyacrylate, polyurethane are also extensively used for synthetic yarns and their blends [38]. In desizing operation these size materials are removed from fabric surface. The major component of size is starch which needs solubilization in desizing operation. In conventional desizing operation size is removed by any one of the desizing method such as acid desizing, rot steeping or oxidative desizing. The objective in all these desizing methods is to hydrolyze the starch macro insoluble polymeric molecules in to smaller water soluble starch molecules such as dextrin or glucose [39]. The employed mineral acid in acidic type of desizing not only increases the effluent load but also hydrolyzes the cellulosic polymer and deteriorates the fabric strength. Similarly uncontrolled explosion of different types of enzymes may deteriorate the fabric itself in rot steeping. The oxidative chemicals such as sodium hypochlorite, sodium chlorite, sodium bromite, etc., being used not only damage the textile material but also pollute the environment and affect the human health and biodiversity.

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Removal of size by aforesaid methods consumes large amounts of water, surfactants, acids/oxidizing agents, manpower, and energy. The enzymatic desizing has great prospects in replacing the toxic chemicals used in traditional desizing methods in ecofriendly manner.

4.7.2 Enzymatic Desizing Enzymatic desizing is carried out sustainably by mixture of amylase and lipase.

4.7.2.1 Amylase (E.C. 3.2.1.1) Amylases are one of the extensively used enzymes which are obtained from plants, animals, and microorganisms [40, 41]. The amylases are essential biocatalyst for conversion of starch in to oligosaccharide and play a major role in digestion of human being. Bacterial diastase was first produced commercially in 1919 under the trade name Rapidase. Microbial source of amylase is extensively applicable in industries due to its production in mass scale at low cost with higher activity and stability at extreme pH, temperature, and pressure. Crude amylases broadly consists α-amylase, β-amylase, glucoamylase, and α-glucosidase. Alpha amylases (E.C.3.2.1.1) hydrolyze the internal α-1,4 and α-1,6-glycosidic linkages of starch molecule rapidly at random and produces dextrin and soluble sugars of low molecular weight where as beta amylase producing the maltose units by hydrolyzing the straight starch chains at end groups gradually [42–44]. Thus higher alpha proportion in amylase is preferred for rapid desizing operation [45].

4.7.2.2 Lipase (EC 3.1.1.3) Lipase is extensively used valuable enzyme [46]. It is used in removal of triglyceride from textile material in various wet processing operations such as desizing, scouring, and laundering. Lipase enzyme is used along with amylase in desizing operation to assist the removal of lubricants, fats and other lipid hydrophobic impurities present in size to improve absorbency of the fabric. Lipase hydrolyzes the ester bonds in triglycerides which are major constituents of oils and fats. Lipase is used in many industrial applications such as textiles, detergent, food, biodiesel, cosmetics, in synthesis of fine chemicals, agrochemicals, etc. [47, 48]. Besides desizing other prospect application areas of Lipase is scouring of cotton, wool, detergent, etc. [49–51].

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The enzymatic desizing with amylase is specific to starch hydrolysis thus there is no adverse effect on strength of cellulosic textile material. Although shelf life and cost are the issues which have to be addressed to further enhance enzyme applications.

4.7.3 Scouring Cotton is monocellular fiber consisting 88% to 96.5% alpha cellulose along with 3.5% to 12% impurities. The major constituents of impurities are proteins (1.0–1.9%); waxes (0.4–1.2%); pectins (0.4–1.2%); ash or inorganic salts (0.7–1.6%) and other hemicelluloses, sugars, etc. (0.5– 8.0%) [39]. It is prerequisite to remove these hydrophobic impurities in preparatory scouring or kier boiling operation to improve the absorbency of cotton textile material. In traditional scouring operation fabric is boiled in caustic soda (3–6% owf) at 120–130°C for 8–10 h. Oily and waxy impurities are removed in alkali boiling via saponification and emulsification, respectively. The process is not ecofriendly as it involves high amount of alkali, wetting agent, etc., with large amount of energy and water consumption. This process generates waste water consisting high COD, BOD, TDS, and alkalinity [52].

4.7.4 Enzymatic Scouring The aforesaid impurities can be removed sustainably by combination of enzymes in bioscouring operation. In bioscouring, fabric is treated with pectinase, cellulase, lipase, cutinase, and other enzymes [53]. Being specific in nature these enzymes such as pectinase [54], cellulase [55], lipase [49], cutinase [56], and xylanase [57] hydrolyze the pectin, cellulose, lipid, cutin, xylan, respectively, in their water soluble decomposed products. The employed enzymes in scouring are as follows.

4.7.4.1 Pectinase (EC 3.2.1.15) Pectins are polysaccharides presents in plant cells consisting mainly of galactoronic acid [56, 58]. The pectinase are basically mixture of esterases and depolymerases, polygalacturonases, and polygalacturonate lyases which depolymerize the insoluble pectin molecules into water soluble oligomers by hydrolysis and deesterification reactions [59–62]. The resulting textile material has increased absorbency and whiteness without affecting the cellulose polymeric structure and its strength [63–64]. Pectinases

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also have good potential in removal of pectins in bast fiber wet processing operations and pulp processing industries.

4.7.4.2 Lipase (EC 3.1.1.3) The lipase enzyme is taken with other enzymes in bioscouring to remove naturally imbedded fatty acid, alcohol and their triglyceride molecules present on cuticle and inner cell walls of the fiber. Details of lipase are already discussed in desizing operation.

4.7.4.3 Cellulase (EC 3.2.1.4) Cellulase is produced by different microorganisms but only a few produces cellulase in bulk amount significantly required for hydrolyzing the crystalline cellulose [65]. Trichoderma reesei and Humicola insolens fungi are extensively used for producing commercial cellulases that are crude mixture of multiple enzyme system mainly consisting following three major types of cellulases [66, 67]: • 1,4-ß-D-glucan 4-glucanohydrolases simply known as endoglucanases which randomly hydrolyzes the polymeric cellulose chain. • 1,4-ß-D-glucan cellobiohydrolases also known as exocellulase or cellobiohydrolases. It split cellobiose from the cellulose chain end. • ß-D-glucanohydrolases known as cellobiases or ß-glucosidases splits cellobiose to glucose. The impurities, i.e., pectins, lipids, cutins, xylans, proteins, etc., are imbedded in outer cuticle as well as inner cellulosic structure. It has been observed that the application of cellulase hydrolyzes superficial cellulosic chains and loosen up the imbedded impurities for better interaction with lipase, pectinase and other enzymes. Thus cellulase enzyme improves the effect of bioscouring operation with added softness by removing the protruding fibers.

4.7.4.4 Cutinase (EC 3.1.1.74) Cutinase is also esterase type of enzyme like lipase but it is more specific for cutin removal from waxy layer present on cotton fiber. The cutinases are capable to hydrolyze cotton waxes at low temperature [56].

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4.7.4.5 Xylanase (EC 3.2.1.8) Xylanase has great applications in pulp and paper, food and in ethanol production industries [57]. Xylanase in combination with cellulose remove hemicelluloses by cleaving β-1, 4 linked xylosyl sequences present in cotton and improve the efficiency of bioscouring [68]. Most of the hydrophobic impurities in cotton are present in outer cuticle layer to provide natural protection to the fiber against external environment. These impurities are also imbedded in interior primary cell walls, secondary cell walls and in lumen [39, 69]. Alkali used in traditional scouring penetrates interior cellulosic structure due to its smaller size and remove the impurities efficiently from interiors, whereas, enzymes have lesser penetration in interiors due to larger size limiting their efficiency in bioscouring, although, some surfactants improve the enzyme penetration and enhance the efficiency of bioscoring. The bioscouring operation reduces the effluent load significantly by decreasing the BOD, COD, and TDS values to 20–50% as compared to alkaline scouring. The Life Cycle Analysis (LCA) shows that bioscouring limits appreciably consumption of water, chemicals, and energy [70]. Few of the observed advantages of bioscouring are: • Suitable for alkali sensitive fibers and their blends. • Removal of fuzz with added softness, suppleness, and luster. • Safer working condition, corrosion free chemical recipe for equipment, and no pollution load on environment. • Considerable savings in time, energy, water, and use of chemicals.

4.7.5 Enzymatic Bleaching In convention bleaching operation textile materials are treated with chemicals such as sodium/calcium hypochlorite in alkaline media; sodium chlorite in presence of sodium nitrate and formic acid; peroxides, etc. These chemicals especially halogen based chemicals are very toxic and produce pungent fumes containing absorbable organic halides affecting the environment and human health to great extent. The use of hydrogen peroxide bleaching is increased as it is comparatively environment friendly and produces permanent whiteness in fabric at low cost. Although this process requires high temperature up to boil in presence of concentrated alkali and consumes high amount of energy and water. Beside these, employed alkali leads to fiber damage especially to alkali sensitive fibers like wool, silk, and bast fibers [71].

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In place of chemical oxidative agents, oxydoreductase enzymes such as Peroxidase, laccase, glucose oxidase in conjunction with cellulase and hemi-cellulase can be employed in biobleaching of textile material and pulp of paper making industries.

4.7.5.1 Laccase (E.C. 1.10.3.2) Laccase is an oxidoreductase enzyme. It works on substrate by the laccase mediator system (LMS) [72]. It is an important enzyme due to its broad substrate specificity in various important oxidoreductive reactions in bioorganism at milder pH and temperature [73]. The high molecular weight complex substrates cannot penetrate the active site of enzyme directly. Small organic compounds such as azine 2,2´azino-bis-(3-ethylbenzothiazoline-6 sulfonic acid) (ABTS), benzo triazole (BT) and 1-hydroxybenzotriazole (HBT) known as mediators having high redox potentials can interact at ease with enzyme and convert in to oxidizing intermediate form (co-mediator) [74]. Though, laccase oxidizes the mediator but it simultaneously reduces oxygen (co-substrate). So in other word laccase consumes oxygen for oxidation of mediator and further oxidized mediator move in nearby vicinity of substrate and resulting degradation of the large molecular substrate by oxidation reaction. A large number of natural and synthetic mediators can be efficiently used for biobleaching of textiles, wood pulp, and decolorization of synthetic dyes, toxic phenols, etc. [75–77]. Besides bleaching, laccase can be applied for fading of denim, bast fiber processing, paper and pulp industries as well as in dye degradation and bioremediation.

4.8 Enzymatic Hydrogen Peroxide Removal by Catalase The toxic residual hydrogen peroxide after completion of bleaching in spent liquor must be decomposed otherwise it may deteriorate the textile material, affect the subsequent dyeing operation and can cause environmental problems if disposed untreated [78]. Traditionally employed neutralization techniques of hydrogen peroxide are rinsing multiple times by water or reduction with inorganic salts. The multiple rinsing and washing requires huge amount of water whereas chemical dosing is also not sustainable as inappropriate dosing of reducing agent may adversely affect the subsequent dyeing operation [78]. Alternatively, the residual hydrogen peroxide can be removed sustainably by addition of small amount of catalase after the bleaching operation.

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4.8.1 Catalase (E.C. 1.11.1.6) Catalase is heme containing oxidoreductase enzyme also known as peroxide killer [79, 80]. It has very high catalytical activity as one molecule of catalase can decompose five million molecules of hydrogen peroxide in to water and oxygen in one minute. The catalase removes residual hydrogen peroxide at economical cost with saving water, energy, and time.

4.9 Biopolishing of Cotton Protruding fibers subdue the luster of fabric surface as well as give fuzzy appearance. Beside these, protruding fibers lead pills formation and soiling on the fabric surface. These protruding fibers are being removed in singeing operation. But singeing has certain limitations as flame can reach only to fabric surface and in its interstices of warp and weft. Whereas cellulase enzyme not only remove the protruding fibers but also smoothen the fiber surface resulting cleaner surface, improved suppleness and drapability of textile material [81] and give brighter fabric surface [82]. Uncontrolled biopolishing may affect the fabric strength tremendously thus weight loss must be controlled with appropriate enzyme exposure of textile material [83].

4.10 Enzymatic Fading of Denim Denim is known for its vintage faded effect. In the same concern warp sheet of cotton is indigo dyed in such a way that indigo dye penetrates maximally in outer surface of fibers or yarn so getting faded effect in subsequent process become easier. Traditionally enzyme is faded by either mechanical or chemical action. In case of mechanical action, the superficial loosely attached dye on fabric surface leaches out due to friction exerted by pumice stone, ceramics, sand paper, etc. The exerted friction give requisite fading effect but there is significant loss in fabric strength. The fading operation increases tear and wear in apparels, its accessories and machine in which fading operation is employed. Whereas hypochlorite, hypochlorate, potassium dichromate, potassium permanganate, etc., chemical oxidative agents are toxic in nature and deteriorate the denim fabric by formation of oxycellulose. Fading of denim can be performed safely in sustainable enzymatic operation instead of harmful chemical and mechanical action mentioned

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above [84]. The enzymatic fading can be performed either by cellulase or oxidative Laccase. The cellulase enzyme removes superficially attached cellulosic chains from fiber surface leading to facilitate releasing of loosely attached indigo dye from the fiber surface, whereas laccase converts indigo dye into colorless products via oxidation by the help of mediator [85, 86].

4.11 Application of Biotechnology in Wool Production and its Wet Processing Wool is protein fiber obtained from animal hairs and known for its warmth and moisture regain. Wool fiber comprises three layers such as cuticle which is outer most scaly layer surrounding the cortex fibrous layer whereas medulla is innermost layer. Biotechnology has great prospects in improving the wool quality, production yield, and subsequent wool wet processing. The developed cross-breeding in sheep by the help of gene modification or clone technology improves wool quantity and quality. The raw wool consists around 50% of impurities in terms of dirt, dust, fat and suint, and vegetable matter. It is essential to remove all these impurities for at least satisfactory cleanliness and to make the fiber absorbent in preparatory wet processing for subsequent dyeing, printing and finishing operation [87].

4.12 Enzymatic Bioprocessing of Wool Traditional chemical methods are very toxic as cellulosic impurities are removed by acid hydrolyzation at high temperature in strong mineral acids which not only cause local damage to wool fiber itself but also pollute the environment. After aforesaid carbonization operation oil, wax, suint, dirt, and dust are removed in subsequent scouring by alkaline solution, solvent, or emulsion. The alkalis increase the effluent load as well as deteriorate the wool fibers whereas solvents employed in solvent scouring are also toxic. Enzymes offer good sustainable prospective in replacing these harsh chemicals and processes in ecofriendly way.

4.12.1

Enzymatic Carbonization of Wool

The cellulosic impurities can be removed sustainably by the help of cellulase, pectinase, hemicellulase enzymes in appropriate formulation. Being specific toward the substrate, cellulase enzyme only hydrolyzes the

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cellulosic impurities without harming wool at all with saving of chemicals, water, and energy. Thus instead of acid, these cellulosic impurities can be efficiently removed by cellulases enzyme alone or in combination with the other enzymes without any chemical and physical loss to wool fibers [88].

4.12.2

Enzymatic Scouring of Wool

The concept of bioscouring of wool is similar to cotton. Although present impurities, i.e., oil, wax, dirt, and dust in wool are in more proportion than cotton. These oily and waxy impurities are removed by lipase in conjunction with protease enzymes. The protease enzyme hydrolyzes the scaly surface of wool fiber which facilitates loosening of imbedded impurities from the interior of the fiber. It has been observed that protease scoured wool fabric gives improved whiteness index and dye ability in subsequent bleaching and dyeing operations.

4.12.2.1

Protease (EC 3.4.21.112)

It catalyzes the hydrolysis reaction in peptide bonds of proteinaceous polymer [89]. It is second largest used industrial enzyme after the amylase and it has great application in wet processing of wool, silk and laundering operations. In wool it is extensively used in bioscouring, biopolishing, and descaling or shrink proofing applications [90].

4.12.3

Enzymatic Finishing of Wool

Cuticle protects wool fiber being the outer most layer but its scaly surface causes etching sensation to wearer. Beside this, wool scales exert directional frictional effect which causes uneven shrinkage in wool during washing or laundering treatment. Therefore, wool needs surface modification for improvement in comfort and shrink prevention properties. In conventional method scales are smoothened by oxidative chemicals such as hypochlorite [91], Potassium permanganate [92], etc., and further rough surface of fiber is coated with polymeric resins, i.e., polyamide epichlorohydrin in chlorine–Hercosett process [93]. Although hypochlorite treatment is associated with absorbable organic halides [94] where as resin coating affects the stiffness and deteriorate fabric handle [95]. The protease based shrink resistance, antifelting, and antipilling treatment give prospects of ecofriendly wet processing of wool [96].

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The  protease has potential to remove proteinaceous polymer on wool scales by hydrolytic reaction resulting in smoother, softer wool having less tendency to shrink and felt. In case of enhanced protease exposure the whole protruding fibers are removed imparting extraordinary softness along with reduction in pilling tendency in subsequent use. It has been reported that prior chemical modification by plasma and UV/ Ozone treatments break disulphide cross links and remove some lipids from wool fiber surface which improves enzyme access in to fiber interiors in subsequent enzymatic treatment [97–99]. It has been reported that lipases [100] and cutinase [101] in conjunction with protease improves the wettability, shrinkage resistance along with improvement in dyeability of wool fabric in subsequent dyeing operation. It has been observed that oxidoreducatase based laccase in presence of appropriate mediator can also facilitate the anti-shrinkage treatment of wool [102], although uncontrolled enzymatic treatment may cause unacceptable fiber damages [103].

4.13 Application of Biotechnology in Sericulture and Wet Processing of Silk The silk filament is spun by silkworm in form of cocoon. The secreted silk consists of two proteinaceous fibroin filaments surrounded by gummy layer of sericin. Biotechnology has good prospects in improving the silk production from sericulture to degumming operations sustainably. The DNA marker assisted breeding helps in getting disease resistant silk worm with other required traits resulting in more weight of cocoon and more efficiency in getting longer silk filament with higher strength.

4.14 Enzymatic Bioprocessing of Silk Silk consists of around 25–30% sericin content which needs to be removed in degumming operation as it subdue the silk luster, provide sticky or gummy characteristics as well as hinder the subsequent bleaching and dyeing operation. In traditional techniques sericin is removed by alkali, acid or soap type of degumming operations [104, 105] but these chemical methods of degumming deteriorate the fibroin composition of fiber resulting loss in aesthetic and physical properties of silk filament. These degumming operations not only consume huge amount of water and energy but also increase BOD and COD load of the effluent.

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Sericin can be removed sustainably by the help of protease from raw silk in enzymatic degumming operation. Enzymatic degumming improves the luster, softness, and handle properties of silk effectively with controlled strength loss [106, 107].

4.15 Application of Biotechnology in Sustainable Finishing Most of the synthetic finishes and auxiliaries being used in textiles such as anticreasing cross linking agents, flame retardants, soil release, antibacterial finishes, amine based quaternary finishes, chelating agents, etc., are known for their toxicity and associated with adverse effect on human health and environment. Biopolymers and natural renewable alternatives have great potential in substituting these aforesaid harmful chemicals in textile finishes. Biotechnology gives better understanding of biopolymers such as amino acids, proteins and their derivatives, albumin, alginate, sericin, chitosan, carbohydrates, and derivatives, and other plant, animal, etc., to extract them from their respective bioorganism at the highest yield and required traits [108, 109]. Biopolymers have novel applications as finishing agents in textiles due to biocompatibility, biodegradability and other valuable properties. The sericin and PLA etc biopolymers have been already discussed. Certain biopolymers have capability to impart various functional properties such as moisture regain, antibacterial properties, antioxidant properties, softness, UV protection, etc., to textile material. Chitin is abundantly available biopolymer in nature, obtained from waste of sea food, i.e., crab, lobster, etc. Chitin is inert in nature but its deacytylated product by alkali hydrolysis give chitosan which is natural polyelectrolyte. Chitosan is produced commercially by heating the chitin with concentrated sodium hydroxide solution (40–50% w/v) at high temperature and pressure. Chitin is deacetylated to chitosan in this alkaline condition at high temperature [110, 111]. The conversion of chitin to chitosan need huge amount of alkali, energy, time, and water, although alternative enzymatic deacetylation of chitin to chitosan gives better sustainable perspective in the same concern [112]. Having ecofriendly antibacterial and cationic properties, chitosan is applied to textile material alone or in conjunction with cross linking agents [113–115]. Sustainable dyeing and finishing has been also attempted by the help of natural dyeing in conjunction with chitosan [116–118]. Chitosan has been also applied excessively

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in biomedical and pharmaceutical, food, cosmetic industries along with waste water treatment plants [119].

4.16 Application of Enzyme Immobilization Techniques in Reuse of Enzymes The immobilization technology made it feasible to use the enzyme repeatedly in batch reactors or continuously in continuous feed reactors. In immobilization procedure, enzymes are basically adsorbed, bound, or entrapped in suitable inert support material in such a way that they sustain catalytic activity even in restricted condition for repeated or continuous use [30]. The immobilization techniques improve enzyme stability against pH, temperature or other chemicals in reaction bath as well as it provide storage stability and improve shelf life of enzymes. The immobilized enzymes and microbial cells have extensive applications in foods, pharmaceuticals, biosensors, synthesis of biochemicals, and effluent treatment. In textiles, immobilized enzymes give good prospects in bioremediation by removal of hydrogen peroxide, several toxic dyes and pigments, phenolic and aromatic compounds from effluent [42, 120].

4.17 Conclusion Biotechnological developments are playing an important role in textiles from fiber cultivation/production to their disposal after completion of the product cycle. Advancements in biotechnology gives sustainable approach in cultivation of plant based fiber without excessive use of synthetic fertilizers, pesticides, and water. Similarly their role cannot be ignored in improvement of quality and productivity of silk and wool production. The improvement in enzyme production with aid of recombinant deoxyribonucleic acid (RDNA) technology, employment of sustainable raw material in microbial growth, improved fermentation and down streaming operations as well as immobilization techniques offer numerous advantages and give perspective to produce enzyme at mass scale with improved stability. The improved enzymes at lesser cost make it feasible to employ them in textile wet processing and effluent treatment plant for bioremediation. Thus application of biotechnology is paving the road

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toward environmental friendly textile production for better tomorrow by replacing the toxic chemicals and conserving bioresources, water, and energy symbiotically.

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28. Quaim, M. and Zolberman, D., Yield effects of genetically modified crops in developing countries. Science, 299, 5608, 900, 2003. 29. https://gain.fas.usda.gov/Recent%20GAIN%20Publications/Agricultural %20Biotechnology%20Annual_New%20Delhi_India_11-30-2018.pdf, 2018. 30. Shukla, S.R., Jajpura, L., Damle, A.J., Enzyme: The biocatalyst for textile processes. Colorage. Special issue on TEXTINDIA FAIR Club Melange, 7–9, 41, 2003. 31. Palmer, T., Understanding Enzymes, p. 17, Ellis Horwood Ltd., New York, 1981. 32. Sumner, J.B., The isolation and crystallization of the enzyme urease: Preliminary paper. J. Biol. Chem., 69, 435, 1926. 33. Michaelis, L. and Menten, M.L., Die Kinetik der Invertinwirkung. Biochemische Zeitschrift., 49, 333, 1913. 34. Rodwell, V.W. and Kennelly, P.J., Enzymes kinetics, Harper’s biochemistry, in: A Lange Medical Book, 25th Edn, pp. 86–102, Appleton & Lange, Stamford, Connecticut, 1999. 35. Jenkins, R.O., Enzymes, in: Textile Processing with Enzymes, 1st Edn, A. Cavaco-Paulo and G. Gubitz (Eds.), pp. 1–41, Woodhead Publishing Limited, Cambridge, 2003. 36. Nomenclature Committee of The International Union of Biochemistry and Molecular Biology (NC-IUBMB), Enzyme Nomenclature, Academic Press, San Diego, 1992. 37. Singh, R., Kumar, M., Mittal, A., Mehta, P.K., Microbial enzymes: Industrial progress in 21st century. 3. Biotech., 6, 174, 2016. 38. Khandual, A., Jajpura, L., Pai, R.S., Sizing processes and its application. Colorage, 11, 33, 2004. 39. Karmakar, S.R., Textile Science and Technology 12: Chemical Technology in the Pre-Treatment Processes of Textiles, pp. 69–84, Elsevier, Amsterdam, 1999. 40. Saxena, R. and Singh, R., Amylase production by solid-state fermentation of agro-industrial wastes using Bacillus sp. Braz. J. Microbiol., 42, 4, 1334, 2011. 41. Shukla, S.R. and Jajpura, L., Estimating amylase activity for desizing by DNSA. Text. Asia, 35, 11, 15, 2004. 42. Jajpura, L., Enzyme: A bio catalyst for cleaning up textile and apparel sector, in: Detox Fashion, Sustainable Chemistry and Wet Processing, S.S. Muthu (Ed.), pp. 95–137, Springer Nature Singapore pte Ltd, Singapore, 2018. 43. Chiba, S., Molecular mechanism in (X-glucosidase and glucoamylase). Biosci. Biotech. Bioc/zell., 61, 8, 1233, 1997. 44. Ajgaonkar, D.B., Talukdar, M.K., Wadewkar, V.R., Sizing Materials and Methods Machines, p. 5, Textile Trade Press, Ahmedabad, 1982. 45. Rana, N., Walia, A., Gaur, A., α–Amylases from microbial sources and its potential applications in various industries. Natl. Acad. Sci. Lett., 36, 1, 9, 2013.

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46. Cherif, S., Mnif, S., Hadrich, F., Abdelkafi, S., Sayadi, S., A newly high alkaline lipase: An ideal choice for application in detergent formulations. Lipids Health Dis., 10, 221, 2011. http://www.lipidworld.com/content/10/1/221. 47. Svendsen, A., Lipase protein engineering. Biochim. Biophys. Acta., 1543, 223, 2000. 48. Hasan, F., Shah, A.A., Javed, S., Hameed, A., Enzymes used in detergents: Lipases. Afr. J. Biotechnol., 9, 31, 4836, 2010. 49. Xia, J., Chen, X., Nnanna, I.A., Activity and stability of penicillium cyclopium lipase in surfactant and detergent solutions. J. Am. Oil. Chem. Soc., 73, 115, 1996. 50. Varanasi, A., Obendorf, S.K., Pedersen, L.S., Mejldal, R., Lipid distribution on textiles in relation to washing with lipases. J. Surfactants. Deterg., 4, 135, 1997. 51. Sangwatanaroj, U. and Choonukulpong, K., Cotton scouring with pectinase and lipase/protease/cellulase. AATCC Rev., 3, 17, 2003. 52. Holkar, C.R., Jadhav, A.J., Pinjari, D.V., Mahamuni, N.M., Pandit, A.B., A critical review on textile wastewater treatments: Possible approaches. J. Environ. Manage., 182, 351, 2016. 53. Agrawal, P.B., The performance of cutinase and pectinase in cotton scouring, dissertation, University of Twente, the Netherlands, Wohrmann Print Service, the Netherlands, 2005. 54. Tyndall, R.M., Improving the softness and surface appearance of cotton fabrics and garments by treatment with cellulase enzymes. Text. Chem. Col., 24, 6, 23, 1992. 55. Li, Y. and Hardin, I.R., Enzymatic scouring of cotton-surfactants, agitation and selection of enzymes. Text. Chem. Col., 30, 23, 1998. 56. Sakai, T., Sakamoto, T., Hallaert, J., Vandamme, E.J., Pectin, pectinase and protopectinase: Production, properties and applications. Adv. Appl. Microbiol., 39, 213, 1993. 57. Dhillon, A., Gupta, J.K., Jauhari, B.M., Khanna, S., A cellulase-poor, thermostable, alkalitolerante xylanase produced by Bacillus circulans AB 16 grown on rice straw and its application in biobleaching of eucalyptus pulp. Bioresour. Technol., 73, 273, 2000. 58. Araujo, R., Casal, M., Cavaco-Paulo, A., Application of enzymes for textile fibers processing. Biocatal. Biotransform., 6, 5, 332, 2008. 59. Kalantzi, S., Kekos, D., Mamma, D., Bioscouring of cotton fabrics by multienzyme combinations: Application of Box–Behnken design and desirability function. Cellulose, 26, 2771, 2019. 60. Gandhi, N.N., Applications of lipase. J. Am. Oil Chem. Soc., 74, 6, 621, 1997. 61. Hartzell, M.M. and Hsieh, Y.L., Enzymatic scouring to improve cotton fabric wettability. Text. Res. J., 68, 4, 233, 1998. 62. Buchert, J., Pere, J., Puolakka, A., Nousiainen, P., Scouring of cotton with pectinases, proteases and lipases. Text. Chem. Color. Am. D., 32, 5, 48, 2000.

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63. McNeil, M., Darvill, A.G., Fry, S.C., Albertsheim, P., Structure and function of the primary cell walls of plants. Ann. Rev. Biochem., 53, 625, 1984. 64. Mousa, A.H.N., Optimisation of rope-range bleaching of cellulostic fabrics. Text. Res. J., 46, 493, 1976. 65. Mojsov, K., Enzyme scouring of cotton fabrics: A review. Int. J. Market. Technol., 2, 9, 256, 2012. 66. Sarkar, A.K. and Etters, J.N., International conference and exhibition. AATCC, 12–15 Oct 1999, p. 274, 1999. 67. Etters, J.N., Advances in indigo dyeing: Implication for the dyer, apparel manufacturer and environment. Text. Chem. Color, 27, 2, 17, 1995. 68. Dhiman, S.S., Sharma, J., Bindu, B., Industrial applications and future prospects of microbial xylanases: A review. Bioresources, 3, 4, 1377, 2008. 69. Traore, M.K. and Buschle-Dilleer, G., Environmentally friendly scouring processes. Text. Chem.Color. Am. Dyest Rep., 32, 12, 40, 2000. 70. Nielsen, P.H., Kuilderd, H., Zhou, W., Lu, X., Enzyme biotechnology for sustainable textiles, in: Sustainable Textiles, R.S. Blackburn (Ed.), pp. 113–138, Woodhead Publishing, Cambridge, 2009. 71. Gürsoy, N.Ç., Lim, S.H., Hinks, D., Hauser, P., Evaluating hydrogen peroxide bleaching with cationic bleach activators in a cold pad batch process. Text. Res. J., 74, 11, 970, 2004. 72. Banci, L., Ciofi-Baffoni, S., Tien, M., Lignin and Mn peroxidase-catalyzed oxidation of phenolic lignin oligomers. Biochemistry, 38, 3205, 1999. 73. Rodriguez-Couto, S., Laccases for denim bleaching: An eco-friendly alternative. Open Text. J., 5, 1, 2012. 74. Claus, H., Laccases and their occurrence in prokaryotes. Arch. Microbiol., 179, 145, 2003. 75. Kunamneni, A., Plou, F.J., Ballesteros, A., Alcalde, M., Laccases and their applications: A patent review. Recent Pat. Biotechnol., 2, 10, 2008. 76. Canas, A.I. and Camarero, S., Laccases and their natural mediators: Biotechnological tools for sustainable eco-friendly processes. Biotechnol. Adv., 28, 694, 2010. 77. Jajpura, L., Decolorisation of textile effluent by laccase—A review. Conference Proceeding of International conference—Emerging trends in traditional and technical textiles (ICETT) organised by Department of Textile Technology, NIT Jalandhar-144011 on 11–12 April 14, pp. 191–196, 2014. 78. Shukla, S.R. and Maheshwari, K.C., Use of standing bath technique in peroxide bleaching of cotton. Color. Technol., 118, 2, 75, 2002. 79. Maehly, A.C. and Chance, B., The Assay of Catalase Peroxidase, in: Methods of Biochemical Analysis, D. Glick (Ed.), p. 357, Vol 1, Interscience Publishers Inc., New York, 1954. 80. Chance, B., Sies, H., Boveris, A., Hydroperoxide metabolism in mammalian organs. Physiol. Rev., 59, 3, 527, 1979.

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81. Schimper, C.B., Constanta, I., Bechtold, T., Effect of alkali pre-treatment on hydrolysis of regenerated cellulose fibers by cellulases (part 1: viscose). Cellulose, 16, 6, 1057, 2009. 82. Morgado, J., Cavaco-Paulo, A., Rousselle, M., Enzymatic treatment of Lyocell-clarification of depilling mechanisms. Text. Res. J., 70, 8, 696, 2000. 83. Rau, M., Heidemann, C., Pascoalin, A.M., Filho, E.X.F., Camassola, M., Dillon, A., José, P., Fernandes, D., Chagas, C., Andreaus, J., Application of cellulases from Acrophialophora nainiana and Penicillium echinulatum in textile processing of cellulosic fibers. Biocatal. Biotransform., 26, 5, 383, 2008. 84. Shahbaz, B., Farooq, A., Asgher, M., Hassan, K., Performance evaluation of exotic and indigenous neutral cellulolytic enzymes as denim stone wash substitute. J. Chem. Soc. Pakistan, 27, 662, 2005. 85. Tzanov, T., Basto, C., Gübitz, G.M., Cavaco-Paulo, A., Laccases to improve the whiteness in a conventional bleaching of cotton. Macromol. Mater. Eng., 288, 807, 2003. 86. Campos, R., Kandelbauer, A., Robra, K.H., Cavaco-Paulo, A., Gübitz, G.M., Indigo degradation with purified laccases from Trametes hirsute and Sclerotium rolfsii. J. Biotechnol., 89, 131, 2001. 87. Karmakar, S.R., Textile Science and Technology 12: Chemical Technology in the Pre-Treatment Processes of Textiles, pp. 344–359, Elsevier, Amsterdam, 1999. 88. Heine, E., Ruers, A., Hocker, H., Enzymatic degradation of vegetable residues in wool. DWI Rep., 123, 475–479, 2000. 89. Yoon, M.Y., Kellis, J., Poulose, A.J., Enzymatic modification of polyester. AATCC Rev., 2, 6, 33, 2002. 90. Rinsey, J.V.A. and Karpagam, C.S., Degumming of silk using protease enzyme from bacillus species. Inter. J. Sci. and Nat., 3, 1, 51, 2012. 91. Van Rensburg, N.J.J. and Barkhuysen, F.A., Continuous shrink-resist treatment of wool tops using chlorine gas in a conventional suction-drum backwash. SAWTRI Tech. Rep., 539, 22, 1983. 92. Bahi, A., Jones, J.T., Carr, C.M., Ulijn, R.V., Shao, J., Surface characterization of chemically modified wool. Text. Res. J., 77, 12, 937, 2007. 93. Udakhe, J., Honade, S., Shrivastava, N., Recent advances in shrink proofing of wool. J. Text. Assoc., 72, 171, 2011. 94. Dominguez, J.G., Erra, P., De La Maza, A., Julia, M.R., Barella, A., Shaw, T., The application of the Hercosett-anionic-surfactant process to impart shrink resistance to wool. J. Text. Inst., 71, 165, 1980. 95. Chen, Q.H., Au, K.F., Yuen, C.W.M., Yeung, K.W., Development of wool shrink proofing, 1969–99. Text. Asia, 31, 38, 2000. 96. Schumacher, K., Heine, E., Höcker, H., Extremozymes for improving wool properties. J. Biotechnol., 89, 281, 2001.

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97. Shao, J., Hawkyard, C.J., Carr, C.M., Investigation into the effect of UV/ozone treatments on the dyeability and printability of wool. J. Soc. Dyers Color., 113, 4, 126, 1997. 98. Ceria, A., Rovero, G., Sicardi, S., Ferrero, F., Atmospheric continuous cold plasma treatment: Thermal and hydrodynamical diagnostics of a plasma jet pilot unit. Chem. Eng. Process., 49, 1, 65, 2010. 99. Kan, C.W. and Yuen, C.W.M., Surface characterisation of low temperature plasma treated wool fiber. J. Mater. Process. Technol., 178, 52, 2006. 100. El-Sayed, H., Kantouch, A., Heine, E., Hocker, H., Developing a zero-AOX shrink-resist process for wool, Part 1, Preliminary results. Color. Technol., 117, 234, 2001. 101. Silva, C., Araújo, R., Casal, M., Gubitz, G.M., Cavaco-Paulo, A., Influence of mechanical agitation on cutinases and protease activity towards polyamide substrates. Enzyme Microb. Technol., 40, 1678, 2007. 102. Lantto, R., Schänberg, C., Buchert, J., Effects of laccase-mediator combination on wool. Text. Res. J., 74, 713, 2004. 103. Negri, A.P., Cornell, H.J., Rivett, D.E., A model for the surface of keratin fibers. Text. Res. J., 63, 109, 1993. 104. Freddi, G., Mossotti, R., Innocenti, R., Degumming of silk fabric with several proteases. J. Biotechnol., 106, 101, 2003. 105. Rangi, A. and Jajpura, L., The biopolymer sericin: Extraction and applications. J. Texti. Sci. Eng., 5, 1, 1, 2015. 106. Gulrajani, M.L., Agarwal, R., Chand, S., Degumming of silk with fungal protease. Indian J. Fiber Text. Res., 25, 138, 2000. 107. Gulrajani, M.L., Agarwal, R., Grover, A., Suri, M., Degumming of silk with lipase and protease. Indian J. Fiber Text. Res., 25, 69, 2000. 108. Rangi, A. and Jajpura, L., Guggul gum a biopolymer finishing agent for textiles. International Conference on Textile and Clothing—Present and Future Trends (TCPFT-2017) at “Department of Jute And Fiber Technology, University of Calcutta, Calcutta, India, pp. 91–94, 2017. 109. Rani, N., Jajpura, L., Butola, B.S., Antimicrobial and antioxidant behavior of natural dye extracted from Kalanchoe pinnata. International Conference on Textile and Clothing—Present and Future Trends (TCPFT-2017) at “Department of Jute And Fiber Technology, University of Calcutta, Calcutta, India., pp. 94–99, 2017. 110. Mima, S., Miya, M., Iwamoto, M., Yoshikawa, S., Highly deacetylated chitosan and its properties. J. Appl. Polym. Sci., 28, 1909, 1983. 111. Lalit, J., Chitin & Chitosan: An Ecological Biopolymer. National Seminar on Recent innovations and Advances in Textiles (RIAT-2014) 2014, organized by Department of Textile Engineering, J. N. Govt. College, Sundernagar, Mandi, Himachal Pradesh, pp. 24–28, 2014. 112. Martinou, A., Kafetzopoulos, D., Bouriotis, V., Chitin deacetylation by enzymatic means: Monitoring of deacetylation processes. Carbohydr. Res., 273, 235, 1995.

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5 Environmental Issues in Textiles Rishabh Kumar Saran1, Raj Kumar2 and Shashikant Yadav3* 1

Department of Civil Engineering, Indian Institute of Technology Bombay, India 2 National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, India 3 Department of Chemical Engineering, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar, India

Abstract The textile sector is experiencing several environmental issues, such as emission of greenhouse gases, excessive use of water, and generation of hazardous chemicals and effluents. The major problem arising from the wet processes of textile manufacturing, such as dyeing, printing, and finishing is the release of toxigenic gases into the atmosphere. On the other hand, in the case of dry processes, yarn spinning and textile knitting and weaving result in the emission of carbon dioxide and release of particulate matter. The wastewater disposed from the industry is contaminated to alarming levels and is detrimental to the environment because it consists of chemicals, such as dyes, acids, alkalis, starch, H2O2, dispersing agents, surfactants, and soaps of metals. When the effluents from the textile industry are dumped into the water bodies, they pose a threat to the aquatic organisms owing to decreased light penetration and lowered utilization of oxygen. Therefore, the textile wastewaters should be subjected to appropriate treatment processes before discharging into the environment. The current chapter focuses on the various environmental hazards that result from the textiles segment and also suggests appropriate treatment measures to combat these environmental issues. Keywords: Hazards in textile processes, textile pollutants, wastewater treatment

*Corresponding author: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (129–152) © 2020 Scrivener Publishing LLC

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5.1 Introduction In recent times increasing industrialization and globalization coupled with ever-increasing population numbers has led to excessive discharge of industrial effluents into surrounding water bodies and as a result led to exacerbated contamination of freshwater resources [1]. One of the most significant sources of industrial effluents are textile wastewaters which are often characterized by high color, organic loads, and toxicity levels, all of which are known to cause serious detrimental effects on the surrounding environment as well as human health [2]. Textile wastewaters are often high in both organic and inorganic compounds such as biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS) [3, 4]. The mixture of such compounds at varying concentrations as well as the non-biodegradable nature of organic dyes further complicates any ordinary treatment processes that may be applied and hinders overall effective removal and decolorization [5]. While the literature has reported extensively on various biological and physico-chemical treatment processes, most of these methods are neither economically nor technologically suitable for large scale use. Furthermore, in order for suitable treatment thresholds to be reached, much of these treatments require the combined action of two or three methods which can, at times, be costly. To reduce such exorbitant costs, much of this effluent tends to be released into surrounding rivers, thereby creating extensive environmental imbalances and serve impacts on various processes such as plant photosynthesis, sunlight penetration, and oxygen consumption which ultimately impacts aquatic life. Much of this effluent contains suspended particles, metallic components and various chemicals which may further exhibit harmful effects on certain forms of aquatic life [6].

5.2 Textile Fiber Textile fibers are defined as any kind of flexible material consisting of a network of natural or artificial fibers (Figure 5.1), either yarn or thread and are often produced by spinning of raw fibers to produce longer strands which is then converted into a textile by various processes such as weaving, knitting, crocheting, knotting, tatting, felting, or braiding [7, 8]. While these textiles are used for various purposes, their most common use is for clothing, bags, and baskets. Domestic uses include the use of textiles in

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Classification of fibers

Natural fibers

Animal origin Raw wool Silk fiber Hair

Chemical fibers

Vegetable origin Raw cotton fiber Flax Jute

Natural polymers fiber

Synthetic polymer fiber

Viscose, cupro, lyocell Cellulose acetate Triacetate Organic polymer Inorganic polymer Polyester Glass for fiber glass Polyamide Metal of metal fiber Polyacrylonitrile Polypropylene Elastane

Figure 5.1 Classification of fibers. 

carpeting, upholstered furnishings, window shades, towels, coverings for tables, beds, and other flat surfaces, as well as in aesthetic uses such as art tapestries. They are also used in various industrial and scientific processes to provide strength of composite materials as well as in the creation of flags, backpacks, tents, nets, handkerchiefs, cleaning rags and transportation devices such as balloons, kites, sails, and parachutes. They are also used in various other industries for the structure they provide in automotive applications, medical implants, reinforcement of embankments, crop protection as well as protection against heat and radiation in certain clothing [9–11].

5.3 Processes in the Textile Industry Conventional wet processing techniques usually involve a multitude of stages such as various pretreatments, dyeing, printing, and finishing processes (Figure 5.2). Pretreatments involve a desizing step of untreated grey textile materials to remove sizable components using various desizing agents [12, 13]. Common sizable constituents include fat, wax, starch, and enzymes, most of which tend to hinder the fixation of dye molecules during the dyeing process [14–16]. Much of the natural starch is removed through hydrolysis or oxidation reactions using acidic or oxidative desizing agents. Once broken down, the water-soluble products of degraded starch subsequently tend to increase the biological oxygen demand (BOD) of wastewater to levels that render the water body useless for agricultural and human use [15, 17]. The scouring step allows the removal of

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Process

Wax, starch, wetting agent, carboxymethyl cellulose

Sizing

Fat, wax, starch, enzyme

Desizing

Sodium hypochlorite, hydrogen peroxide, chlorine, sodium phosphate, sudium silicate, acid, surfactant

Bleaching

Effluent Characteristics

High BOD, COD

High BOD, COD, dissolved solids, suspended solids

High pH, suspended solids

High pH, low BOD, high dissolved solids

Sodium hydroxide, cotton wax

Mercerizing

Color, reducing agent, oxidizing agent, acetic acid

Dyeing

High BOD, dissolved solids, heavy metal

Urea, oil, blinder, reducing agent

Printing

High BOD, suspended solids, slightly alkaline

Resin, catalyst, softener, fluorocarbon, inorganic salt

Finishing

Low BOD, slightly alkaline

Figure 5.2 Components of major pollutants involved in various stages of a textile manufacturing industry [26].

impurities such as lubricants, dirt, gums, and waxes and the conversion of these impurities into water-soluble compounds. These processes are often enhanced through the addition of emulsifiers, sequestering agents, surfactants, wetting agents, and reducing agents; all of which generate wastewater with high TDS, BOD, and COD [15, 18]. In addition, colored substances are removed via bleaching processes which increases the overall whiteness level. Common examples of bleaching agents include sodium hypochlorite, hydrogen peroxide, chlorine, sodium phosphate, and so on.

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Many of these bleaching agents tend to degrade the color generating chromophores via reductive, oxidative, or enzymatic mechanisms. Oxidative agents decompose in alkaline medium to produce active oxygen which as a result, decomposes various coloring substances [19–21]. Bleaching is subsequently followed by mercerizing which uses a strong alkali to induce dimensional stability, smoothness, and luster for better dye absorption profiles. The excessive alkali is then removed with water thereby pushing up the pH of the effluent which negatively affects aquatic life. Such preparatory treatments are used to pre-prep textiles for the subsequent dyeing process [19, 22]. Colorants used in the dying process could be watersoluble dyestuffs or water-insoluble pigments and are usually prepared under acidic or basic conditions using various dye solutions mixed in water. Dye solutions are commonly prepared in aqueous media using additives such as auxiliary chemicals. These chemicals are used to prevent foaming and obtain a leveling effect. Water-insoluble pigments are applied using various binding agents while synthetic dyes used for textiles are often produced from a variety of toxic chemicals [23–25]. Dyes can be categorized into various groups based on how they react. The first category of reactive dyes includes mordants as well as direct, acidic, and basic dyes; all of which react via covalent bonding with functional groups present in the fabric itself. A second group includes sulfur and vat dyes which require chemical reactions for the dyeing process to take place. The third group consists of the disperse dyes. Various reducing agents, solubilizing agents, and alkalis are used to enhance the efficiency of the dyeing process while various other methods are used to apply water-insoluble pigments to textiles [27]. These include discharge methods, resist methods and direct printing methods. Each of these different methods may require different kinds of chemical to carry out the dyeing process. For example, carcinogenic chemicals like formaldehyde are widely used for pigment applications that use the discharge printing process. Such effluents being discharged contain substantial amounts of salts, alkali, unfixed dyes, and several toxic chemicals which can be harmful to the surrounding environment and make the dyeing process a nonsustainable one [24, 27]. Once the dying process has been completed, a finishing step must be carried out; often either through mechanical or chemical methods to yield softness and durability in the finished textile. Much of the finishing agents used tend to be produced from formaldehyde-based products. In addition, various antimicrobial agents are used to convey disinfectant properties in textiles while halogenated compounds are used as stain, oil, and waterresistant finishes. Much of these finishes can be toxic and therefore

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inefficient removal of excess and unused finishes may contaminate wastewater effluents and ultimately become dangerous for human health and ecosystem [23, 24, 28].

5.4 Key Environmental Issues Wastewater effluent generated from the textile industry tends to be quite alkaline and contains a high concentration of various chemicals as well as high biological oxygen demand (BOD), chemical oxygen demand (COD) and total dissolved solids (TDS) (see Table 5.1). This often leads to a vast amount of environmental problems if the wastewater is not appropriately treated before discharge in the environment [29–31]. The presence of sulfur, naphthol, vat dyes, nitrates, acetic acid, soaps, chromium compounds, and heavy metals like copper, arsenic, lead, cadmium, mercury, nickel, and cobalt, and certain auxiliary chemicals further increase the toxicity of the effluent [32]. In addition, the presence of other harmful chemicals such as formaldehyde-based dye fixing agents, hydrocarbon-based softeners, and nonbiodegradable dyeing chemicals further compound the problem. Mill effluent is also of high temperature and pH, both of which can be extremely damaging. Organic materials present may react with other chemicals tend to evaporate into the air we breathe or are absorbed through the skin and show up as allergic reactions which in turn can cause harm to human life [33–35]. Apart from water pollution, the textile industry also generates large amounts of air pollution through the processing of textile fibers before and during the spinning and weaving process. This creates large amounts of dust and lint which may lead to respiratory diseases among the workers. Previous literature has reported on the chronic lung disease known as byssinosis which is frequently experienced by workers exposed to cotton, flax, and hemp dust. Apart from water and air pollution; noise pollution forms another environmental issue due to the vast number of process operations in the textile industry that produce extremely loud sounds [32].

5.4.1 Supply Water Water is used in many process steps within the textile industry making it an extensively water-intensive industry [37]. Water is used for cleaning raw materials as well as for flushing steps during the whole production process. Various processes such as desizing, scouring or kiering, bleaching, mercerizing, dyeing, washing, and neutralization utilize water (refer to Table 5.2); however the amount of water used varies greatly depending on

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Table 5.1 Characteristic range of various parameters and heavy metals in textile wastewater [36]. S. No.

Parameters

Typical range

NEQS limit

1

pH

5.5–10.5

6–9

2

COD (mg/L)

350–700

Up to 150

3

BOD (mg/L)

150–350

Up to 80

4

TDS (mg/L)

1500–2200

Up to 3500

5

TSS (mg/L)

200–1100

Up to 200

6

Sulfides (mg/L)

5–20

1.0

7

Chlorides (mg/L)

200–500

1000

8

Chromium (mg/L)

2–5

1.0

9

Zinc (mg/L)

3–6

5.0

10

Copper (mg/L)

2–6

1.0

11

Sulfates (mg/L)

500–700

600

12

Sodium (mg/L)

400–600

–

13

Potassium (mg/L)

30–50

–

14

Cadmium (mg/L)

0.07–2

0.1

15

Iron (mg/L)

0.03–2.0

2.0

16

Nickel (mg/L)

0.5–3

1.5

the operation and textile [38, 39]. Wooland felted fabrics and related processes tend to be more water intensive than processes related to woven textiles, knits, stocks, and carpets. Natural fibers tend to have the highest water use while synthetic fibers require lower water volumes per unit of the product due to the lower cleaning and scouring needs. An abundant supply of clean water is needed to ensure a textile processing plant operates to suitably. Dye houses are usually located in areas where natural water supply is sufficient and clean, often close to rivers, lakes, and wells [40]. Almost all dyes are applied to textile substrates from water baths while most fabric-preparation steps (such as desizing, scouring, bleaching, and mercerizing) tend to use aqueous systems as well. The amount of water used varies depending on the specific processes, the equipment used as

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Table 5.2 Average water supply for different textile wet processes [40]. Material

Process

Water usage (l kg−1)

Cotton

Desizing

3–9

Scouring or kiering

26–43

Bleaching

3–124

Mercerizing

232–308

Dyeing

8–300

Scouring

46–100

Dyeing

16–22

Washing

334–835

Neutralization

104–131

Bleaching

3–22

Scouring

50–67

Dyeing

17–33

Scouring

50–67

Dyeing

17–33

Final scour

67–83

Scouring

25–42

Dyeing

17–33

Final scour

17–33

Scouring and dyeing

17–33

Salt bath

4–13

Scouring and dyeing

33–50

Wool

Nylon

Acrylic

Polyester

Viscose

Acetate

well as overall management philosophy where the environment and water use is concerned. In addition, different types of processing machinery use different amounts of water and this is influenced by the bath ratio in dyeing processes; better known as the ratio of the mass of water in an exhaust dye bath to the mass of fabric to be dyed [23, 41].

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Washing processes often use more significant quantities of water than dyeing and various mechanical factors such as agitation, mixing, bath, and fabric turnover rate, turbulence, and other mechanical considerations all influence the amount of water used and overall washing efficiency (Table 5.2). The quantity of water used for a particular process also depends on the state of the equipment and overall development process in relation to technological advancements. Heating of dye baths constitutes a significant portion of the energy consumed in dyeing. Low bath-ratio dyeing equipment tends to conserve water but also saves energy while also reducing steam use and air pollution from boilers. These machines conserve chemicals as well as water and also achieve higher fixation efficiency rates [25, 40].

5.4.2 Chlorinated Solvents Chlorinated solvents are used for various operations in the textile manufacturing industry such as scouring, desizing, dyeing, and cleaning [42]. These solvents form a large family of chemical compounds that contain chlorine. Commonly used chlorinated solvents include carbon tetrachloride (CCl4), chloroform (CHCl3), methylene chloride or dichloromethane (CH2Cl2), tetrachloroethylene (C2Cl4), trichloroethane (C2H3Cl3), and trichloroethylene (C2HCl3) [43]. Much of these chlorinated solvents tend to be harmful to human and ecological health and are often suspected of causing cancer and other harmful effects on aquatic organisms. These contaminants are often present in the subsurface as non-aqueous phase liquids or as dissolved contaminants in groundwater and as vapors in the unsaturated zone; all of which are known to cause widespread sub-surface contamination in the environment. These contaminants tend to sink in groundwater systems due to their density being greater than water and often results in a complex dispersal and plume patterns making them difficult to cleanup [32, 42].

5.4.3 Hydrocarbon Solvents—Aliphatic Hydrocarbons Aliphatic compounds are hydrocarbon compounds containing carbon and hydrogen elements joined together in straight chains, branched trains, or non-aromatic rings. These compounds may be saturated (hexane and other alkanes) or unsaturated (hexene, other alkenes and alkynes) and are present in the effluent of the textile industry are cyclohexene (C6H10), cyclohexane (C6H12), n-hexane (C6H14), n-heptane (C7H16), pentane (C5H12), and petroleum ether [16, 44]. The majority of these compounds tend to be flammable thereby allowing these

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hydrocarbons to be used as fuel. These aliphatic hydrocarbons can also act as asphyxiants and central nervous system depressants while also exhibiting certain toxic effects such as asphyxia and chemical pneumonitis for certain paraffins, axonal neuropathy for n-hexane, and cancer for 1,3-butadiene [32].

5.4.4 Hydrocarbon Solvents—Aromatic Hydrocarbons Polycyclic aromatic hydrocarbons (PAHs) are commonly present in high concentrations of the effluents of textile dyeing plants making these effluents challenging to treat. Common aromatic hydrocarbons found in the textile effluent are benzene (C6H6), naphthalene (C10H8), toluene (C7H8), and xylenes or dimethylbenzene (C8H10) [45]. Most PAHs do not dissolve easily in water but instead, tend to stick to solid particles and settle to the bottom of lakes or rivers or tightly to particles in soils. Certain PAHs can further move through soil particles and contaminate underground water [32].

5.4.5 Oxygenated Solvents (Alcohols/Glycols/Ethers/Esters/ Ketones/Aldehydes) An oxygenated solvent contains oxygen molecules and is known to have high solvency and low toxicity. These solvents are widely used in the textile processing sector. Common examples include methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), butanol (C4H9OH), ethylene glycol (C2H6O2), diethyl ether ((C2H5)2O), ethyl acetate (C4H8O2), acetone (C3H6O), methyl ethyl ketone or butanone (C4H8O), methyl isobutyl ketone (C6H12O), and methyl n-butyl ketone or 2-hexanone (C6H12O) [46]. These solvents tend to be volatile and reactive to sunlight as well as reaching “ground-level ozone” which is known to be harmful to human health and surrounding flora and fauna. Prolonged exposure to oxygenated solvents is known to cause blindness, irregular heartbeat, and damage to the kidneys, liver, lungs, and the overall central nervous system while some are listed as human carcinogens and are known to cause cancer. Regular exposure to such oxygenated solvents may cause memory and hearing loss, mental illness, depression, fatigue, confusion, dizziness, feeling drunk or “high,” lack of coordination, headache, nausea, stomach pains, skin rashes, cracking or bleeding skin, and irritated eyes, nose, and throat. Exposure to oxygenated solvent vapors can cause hoarseness, coughing, lung congestion, chest tightness, and shortness of breath as well as asthma in children if exposed to high levels [32].

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5.4.6 Grease and Oil Impregnated Wastes Grease is better known as a thick and oily lubricant consisting of inedible fat rendered from waste animal parts, or petroleum-derived, synthetic oils containing a thickening agent. White grease is made from inedible fat and has a low content of free fatty acids. These wastes are known to be harmful to aquatic life with long-lasting adverse effects. Waste cloths soaked with grease and oil when burnt emit the toxic gases such as carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons, nitrous gases (NOX), and sulfurous gases (SOX). Common side effects may include eye damage and eye irritation [32, 47].

5.4.7 Used Oils The oils used during textile processing and often oils present in the textile effluent may lead to potential acute health effects if ingested and or if humans or animals come into physical contact with it. The oils may exhibit severe carcinogenic effects on humans. Highly refined mineral oils are not classified as human carcinogens however, related forms such as untreated and mildly treated oils used in metal machining, mule spinning, and jute processing are listed as human carcinogens by the International Agency for Research on Cancer (Group 1) while oils are not expected to cause any skin irritation upon direct single, repeated and/or prolonged contact; similar products with similar chemical composition applied to the skin of lab animals may result in minimal to slight dermal irritation. Mild irritation of the eyes may occur while respiratory tract irritation with coughing and shortness of breath may also occur. Aspiration may lead to chemical pneumonitis which is characterized by pulmonary edema and hemorrhage and may be fatal. Increased respiratory rate, increased heart rate, and bluish discoloration of the skin as well as coughing, choking, and gagging are often noted at the time of aspiration and may also occur [47, 48]. Ingestion of such components is relatively non-toxic unless aspiration occurs. It has laxative properties and may cause gastrointestinal tract discomfort, abdominal cramps, vomiting, and diarrhea. Exposure to a large single dose or repeated small doses by inhalation, aspiration, or ingestion (which subsequently may lead to aspiration) can lead to lipid pneumonia or lipid granuloma. These, however, are low-grade, chronic localized tissue reactions which are not fatal. The oils may also be combustible at high temperature and indicate the presence of a fire hazard due to them being slightly flammable in the presence of open flames [32].

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5.4.8 Dyestuffs and Pigments Containing Dangerous Substances The presence of color in wastewater is one of the main problems in the textile industry [49]. Colors are easily visible to human eyes even at extremely low concentrations. Most of the dyes are stable and have no known effect in the presence of light or oxidizing agents. They are also not easily degradable by conventional treatment methods [50]. Removal of dyes from the effluent can be a major problem in most of the textile industries [52–54]. Organo-halogens, better known as a pigment containing a covalent fluorocarbon, chlorocarbon, bromocarbon, or iodocarbon bond as well as toxic elements such as lead, cadmium, mercury, vanadium, chromium, cobalt, nickel, arsenic, antimony, or selenium containing pigments are known to have potential toxic and hazardous risks associated with them (see Tables 5.3 and 5.4). Organic compounds such as benzene, methane, and paraffin are made of two elements—namely carbon and hydrogen and can be found in coal, crude oil, natural gas, and plant life. Hydrocarbons are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics; petroleum is a mixture of several hydrocarbons [20, 32].

5.4.9 Heat and Energy Generation From Textile Industry Waste When wastewater effluent is treated using microbial fuel cells (MFCs), this often leads to the generation of heat and energy. In textile industry natural gas, coal, and oil are consumed as energy sources with the energy being mainly used for heating and cooling purposes, steam generation in boilers, lighting, and mechanical operations [32]. Most of the thermal energy is consumed for heating the dye bath during the wet dyeing process (see Table 5.5). This process requires a tremendous amount of water at each step of every process starting from preparatory treatments till final finished goods. The water is generally used as a washing and cleaning agent, for steam generation, and as a medium for the solution of chemicals. At the end of the textile wet processing steps, the wastewater effluents contain unfixed dyes, washing agents, finishing agents, and other organic or inorganic auxiliary salts which are discharged into the open land thereby putting plants, human health, and ecosystems at risk. Much of these pollutants tend to bioaccumulate and further exhibit adverse effects on the environment. Common water treatment techniques such as membrane filtration, aeration, clarification, flocculation, and filtration are often applied to recover water quality before disposing it off [55].

Main application

Used for all cellulosic goods (knitted fabric), wool, silk, and nylon

Cellulosic fibers, rayon, silk, and wool

Polyester, acetate, nylon, and acrylic

Wool, silk, paper ink, nylon, and leather

Acrylic, polyester, wool, and leather

Cotton, wool, and rayon

Used for heavy cellulose goods in dark shades, and rayon

Dye class

Reactive

Direct

Disperse

Acid

Basic

Vat

Sulfur

Difficult to apply, cheap, poor fastness, and insoluble in water

Difficult to apply, expensive, good fastness except indigo and sulfurized vat species, and insoluble in water

Careful application required to prevent unlevel dyeing and adverse effect in hand feel, cationic, and highly water-soluble

Easy application, poor fastness, anionic compounds, and highly water-soluble

Require skill in application (by carrier or high temperature), good fastness, and limited solubility in water

Simple application, cheap, moderate color fastness, anionic compounds, and highly water-soluble

Easy application; moderate price, good fastness, anionic compounds, and highly water-soluble

General description

Table 5.3 Classification of dyes based on application methods [51].

Indeterminate structures

Anthraquinone (including polycyclic quinones) and indigoids

Cyanine, azo, azine, hemicyanine, diazahemicyanine, triarylmethane, xanthen, acridine, oxazine, and anthraquinone

Azo (including premetallized), anthraquinone, azine, triphenylmethane, xanthene, nitro, and nitroso

Azo, anthraquinone, nitro, and benzodifuranone

Azo, phthalocyanine, stilbene, nitro, and benzodifuranone

Azo, anthraquinone, phthalocyanine, formazan, oxazine, and basic

Chemical type

Environmental Issues in Textiles 141

pH

5–10

4.8–8

–

1.5–3.7

–

Fibers

Cotton Linen Viscose

Wool

Polyamide

Acrylic

Polyester

480–27 000

175–2000

–

380–2200

11–1800

BOD (mg l−1)

–

833–1968

–

3855–8315

500–14 100

TSS (mg l−1) Organic substances Naphtol, acetate, amides of naphtoic acid, anionic dispersing agents, anionic surfactants, cationic fixing agents, chloro amines, formaldehyde, formate, nitro amines, nonionic surfactants, residual dyes, soaps, soluble oils, sulfated oils, tannic acid, tartrate, urea Acetate, dispersing agents, formate, lactate, residual dyes, sulfated oils, tartrate Acetate, formate, polyamide oligeines, residual dyes, sulfonated oils Acetate, aromatic amines, formate, leveling agents, phenolic compounds, residual dyes, retardants, surfactants, thiourea dioxide Acetate, anionic surfactants, antistatic agents, dispersing agents, dye carriers, EDTA, ethylene oxide condensates, formate, mineral oils, nonionic surfactants, residual dyes, soaps, solvents

Inorganic substances Na+, Cr3+, Cu2+, Sb3+, K+, NH4+, Cl−, CO32−, CO42−, F−, NO2−, O22−, S2−, S2O32−, SO32−, SO42−

Na+, Cr3+, Cu2+, Sb3+, K+, NH4+, Al3+, Cl−, CO32−, S2O4−, SO32−, SO42− Na+, Cl−, CO32− Na+, NH4+, Cu2+, SO42−

Na+, NH4+, Cl−, S4O62−, ClO−, SO32−, NO3−

Table 5.4 Possible pollutants and characteristics of effluents from dyeing [40].

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Table 5.5 Approximate consumption of energy for 1 kg of textile material [55]. S. No.

Process

Energy (MJ/kg)

1.

Finishing

6–12

2.

Dyeing, finishing, and drying

8–18

3.

Bleaching, dyeing, and drying

10–35

4.

Bleaching and drying

8–33

5.

Scouring without drying

5–18

5.4.10

Carbon Footprint of a Textile Product

The textile industry forms one of the largest contributors to greenhouse gas emissions. Such emissions occur at all stages of the process, starting with the raw material extraction steps, through to the supply chain and throughout various life cycle phases. The fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC) pointed out that global warming caused by the rapidly increasing global emissions of greenhouse gases is resulting in sea level rise and increasing the frequency and intensity of extreme climate-related events; all of which severely threaten global food production, human life, and the natural environment as a whole [27, 56–59]. The textile industry is the second largest contributor and accounts for approximately 10% of greenhouse gas (GHG) emissions. In the developing world, where the textile industry represents a large percentage of GDP and plants are often antiquated, the GHG emissions can be even more significant. GHG emissions from the textile industry can be divided into two parts–direct emissions and indirect emissions. Direct emissions include that which occurs from sources that are owned or controlled by textile companies while indirection emissions are defined as those emissions from the generation of purchased electricity, heat, steam and so on, which are subsequently consumed by these textile companies [60]. Numerous studies have shown that the consumer use phase is the most significant contributor to GHG emissions in a typical product life cycle. Aggregated GHG emissions of a typical textile product across different life cycle phases are presented in Table 5.6. The main processes in a product life cycle include yarn spinning, weaving or knitting while in wet processes these include bleaching, dyeing, printing, finishing (mechanical and chemical); and finally clothing manufacturing. Most of these

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Table 5.6 Total aggregated GHG emissions of multiple clothing types [60]. Life cycle phase

% Total GHG emissions (for multiple clothing types)

Fiber production

18

Yarn production

16

Preparation and blending

5

Knitting

7

Dyeing and finishing

3

Other raw materials

5

Garment manufacture (making-up)

2

Packaging

4

Transportation

1

Use phase

39

processes are energy intensive and hence are responsible for a significant amount of greenhouse gas emissions in addition to a large amount of consumables required which further contribute to the GHG emission levels [61, 62]. A large amount of raw materials are used to manufacture textile products in the clothing sector. These include conventional cotton, organic cotton, flax, acrylic, viscose, polyester, polypropylene, nylon, silk, and wool. Much of these require enormous levels of energy and are manufactured by different processes, producing varying levels of greenhouse gas emissions. In addition, the same type of fiber produced in different countries will have different carbon footprints (Table 5.7) [60]. Muthu et al. used GHG emissions from cradle to gate stages for different fibers in their unique model developed to quantify the environmental impact and ecological sustainability indices of textile raw materials [62].

5.5 Environmental Impact of Textile Industry Wastewater Any industrial activity can cause pollution in one form or the other. Wastewater from textile plants is classified as one of the most polluting

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Table 5.7 GHG emissions of various textile fibers [60]. Fiber

CO2 emissions – kg CO2 per kg of fiber

Nylon 6

5.5

Nylon 66

6.5

Viscose

9 (−3.5 for bio-mass credit)

Acrylic

5

Polyester

2.8

Organic cotton

2.5

Conventional cotton

6

Wool

2.2

Flax

3.8

Polypropylene

1.7

industrial sectors due to the large volume generated as well as its complex composition. Such dye wastewater generated from textile industries are known to have a direct effect on surface and groundwater. The amount of dye loss can vary from 2% for basic dyes to as high as 50% for reactive dyes, leading to severe contamination of surface and groundwater [28]. This coupled with reducing light penetration through water decreases photosynthetic activity, leading to oxygen deficiencies and deregulation of biological cycles of aquatic biota. Many dyes are also highly toxic to the ecosystem and can serve as mutagens depending on the exposure time and dye concentration. Numerous dyes have been associated with growth reduction, metabolic stress and death in fish, and growth and productivity hindrance in plants. The wastewater from the textile industry also has an indirect effect on the soil through erosion. The bacteria and fungi which maintain the soil fertility will be affected by the highly toxic chemicals being released [51]. There is a large and immediate oxygen demand by these effluents which in turn tends to cause rapid depletion of dissolved oxygen. Such conditions result in a foul odor and in the production of hydrogen sulfide gas, which precipitates iron as a black sulfide that has an unsightly appearance. The chemicals evaporated into the air may then be inhaled or absorbed through the skin further resulting in toxic effects [63].

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The long-term effects on human, animal, and plant health are well known. These synthetic dyes are known to cause skin diseases and allergies during processing. Normal functioning of cells become distressed, which in turn may cause alteration in the physiology and biochemical mechanisms, resulting in impairment of important function like respiration, osmoregulation, reproduction, and mortality [64].

5.6 Environmental Legislation To date, there is international consensus concerning the discharge of textile effluents. In addition, no official documents listing the different effluent limits applied in different countries. Many developed countries, such as the United States of America, Canada, Australia, and the nations of the EU have enforced environmental legislation, which establishes limits. Other countries, such as Thailand, have copied the US system, whereas others, such as Turkey and Morocco, have copied the EU model. In other nations, including India, Pakistan, and Malaysia, the effluent contamination limits are recommended, but not mandatory while in many developing countries, dye limitations are not specified as a separate category from that of other chemical or biological groupings such as total dissolved solids [51].

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48. Speight, J.G. and Exall, D.I., Refining used lubricating oils, CRC Press, 2014. 49. Núñez, J., Yeber, M., Cisternas, N., Thibaut, R., Medina, P., Carrasco, C., Application of electrocoagulation for the efficient pollutants removal to reuse the treated wastewater in the dyeing process of the textile industry. J. Hazard. Mater., 371, 705–711, 2019. 50. Jönsson, C., Posner, S., Roos, S., Sustainable chemicals: A model for practical substitution, in: Detox Fash., S. Muthu (Ed.), pp. 1–36, Springer, Singapore, 2017. 51. Sahu, O. and Singh, N., Significance of bioadsorption process on textile industry wastewater, Elsevier Ltd, 2018. 52. Sharma, A., Syed, Z., Brighu, U., Gupta, A.B., Ram, C., Adsorption of textile wastewater on alkali-activated sand. J. Clean. Prod., 220, 23–32, 2019. 53. Nippatla, N. and Philip, L., Electrocoagulation-floatation assisted pulsed power plasma technology for the complete mineralization of potentially toxic dyes and real textile wastewater. Process Saf. Environ. Prot., 125, 143– 156, 2019. 54. Liang, J., Ning, X.A., Sun, J., Song, J., Hong, Y., Cai, H., An integrated permanganate and ozone process for the treatment of textile dyeing wastewater: Efficiency and mechanism. J. Clean. Prod., 204, 12–19, 2018. 55. Gulzar, T., Ahmad, I., Kiran, S., Hameed, A., Farooq, T., Green chemistry in the wet processing of textiles, in: Impact Prospect. Green Chem. Text. Technol., pp. 1–20, Elsevier Ltd., 2018. 56. Yadav, S. and Mehra, A., Dissolution of steel slags in aqueous media. Environ. Sci. Pollut. Res., 24, 16305–16315, 2017. 57. Yadav, S. and Mehra, A., Mathematical modelling and experimental study of carbonation of wollastonite in the aqueous media. J. CO2 Util., 31, 181–191, 2019. 58. Yadav, S. and Mehra, A., Experimental study of dissolution of minerals and CO2 sequestration in steel slag. Waste Manag., 64, 348–357, 2017. 59. Saran, R.K., Arora, V., Yadav, S., CO2 sequestration by mineral carbonation: A review. Glob. NEST J., 20, 497–503, 2018. 60. Muthu, S.S., Amsterdam, Assessing the Environmental Impact of Textiles and the Clothing Supply Chain, Woodhead P, Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge, CB22 3HJ, UK, n.d. 61. Zamani, B., Svanström, M., Peters, G., Rydberg, T., A carbon footprint of textile recycling: A case study in Sweden. J. Ind. Ecol., 19, 676–687, 2015. 62. Muthu, S.S.K., Li, Y., Hu, J.Y., Ze, L., Carbon footprint reduction in the textile process chain: Recycling of textile materials. Fibers Polym., 13, 1065–1070, 2012. 63. Jayanthy, V., Geetha, R., Rajendran, R., Prabhavathi, P., Karthik Sundaram, S., Dinesh Kumar, S., Santhanam, P., Phytoremediation of dye contaminated soil by Leucaena leucocephala (subabul) seed and growth

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assessment of Vigna radiata in the remediated soil. Saudi J. Biol. Sci., 21, 324–33, 2014. 64. Parisi, M.L., Fatarella, E., Spinelli, D., Pogni, R., Basosi, R., Environmental impact assessment of an eco-efficient production for colored textiles. J. Clean. Prod., 108, 514–524, 2015.

6 Water Saving Technologies for Textile Chemical Processing Nagender Singh

*

Department of Textile Technology, Indian Institute of Technology (I.I.T.), Delhi, India

Abstract Textile chemical processing industries require a large amount of water for textile processing and discharge a massive quantity of wastewater, which can unavoidably lead to scarcity of water shortly. This chapter focuses on the importance of water saving technologies in textile chemical processing, and discuss the innovative technologies involved in water saving process. The primary reason for the conservation of water is the less availability of clean water due to the declining of earth water level and reduction of clean water resources. Keeping this in mind there is an acute requirement to implement water saving technologies in the textile processing sector. The conservation of water in textile processing sector can be achieved through various techniques such as reuse/recycle of washing/rinsing water, or by optimizing the water softening unit, or by recovery and reuse of regenerated wastewater. These practices demand the setting up of environmental management system, preventive maintenance and repair programs, applications of control and monitoring techniques. Apart from these technologies, one can adopt some unique technologies for processing sector like low add-on techniques, waterless dyeing technologies, foam technologies, and digital printing. The textile processing sector could conserve tremendous amounts of water by adopting conventional and innovative technologies. Keywords: Water saving, textile processing, preparatory processes, optimization techniques

Email: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (153–170) © 2020 Scrivener Publishing LLC

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6.1 Introduction Currently, many industrial activities are continuously polluting natural water resources. Based on average economic growth data, the demand for water in the world is expected to be around 1500 billion m3 in 2030. Today water has become an object of taxation for state authorities because of industrial discharges account for 16% of global demand [1]. Hence, to avoid a water crisis in the future, protection of water against contamination and conservation of water resources is vital issues around the globe [2]. The textile processing industry is one of the most fragmented industrial sectors which are mainly dominated by small and medium enterprises. Recently, industries are obliged to work in more sustainable manner due to the limitation of natural resources such as water [1, 3]. In the last three decades, different approaches have been developed to support the sustainable manufacturing processes and sustainable use of natural resources [4, 5]. One of these approaches is the use of water saving technology in textile processing. Textile processing industries discharge the wastewater which contains auxiliaries such as surfactants, dispersing agents, chelating agents, inorganic salts, metallic ions, dyes, and pigments [6]. The characteristics of textile processing wastewater can vary significantly, e.g., conductivity 0.1‒120 mS/cm, pH 2‒13, turbidity 0–200 NTU, suspended solids 5‒9000 g/cm3, absorbance up to 200, total COD 0.3‒60.000 g/m3 [7]. Moreover, improper treatment of textile wastewater creates significant environmental problems [8‒10]. Typically, the textile industry is likely to use a high quality/quantity of fresh water in all wet processes and mostly discharges the wastewater without any pre-treatment, because effluent treatment facilities are unaffordable for small and medium scale textile industries [1]. According to reports, China is the biggest textile exporter in the world, which released 2 million tons of chemical oxygen in 2014 and use 4  billion  m3/year of water [11, 12]. For the textile industry in European Union, which is the second biggest textile exporter in the world [11], annual water use is 600 million m3 [1]. Cleaner production is defined by United Nations Environment Programme (UNEP) as “The continuous application of an integrated environmental strategy to processes, products, and services to increase efficiency and reduce risks to humans and the environment” [9, 13]. The application of cleaner production methods can increase the economic, environmental, and technical performances of industries. Furthermore, cleaner production strategies are providing benefits regarding legal discharge limits and standards. In 1996, an article published on The Integrated

Water Saving Technologies for Textile Chemical Processing 155 Pollution Prevention and Control Directive (IPPC, 96/61/EC) which represents an important piece of European Union (EU) legislation directed to minimize and to reduce harmful wastes from various industries [14]. Two fundamental principles are the foundation pillars of this directive: using Best Available Techniques (BAT) and the application of the integrated approach. BATs are the appropriate techniques to protect the environment through the balance between environmental welfare and the cost [15, 16]. Indian textile industry is leading exporter for EU and thus, according to IPPC legislation, Indian textile industry has to fulfill conditions on discharge standards/limits. According to a report of USEPA, a unit generated 20,000 lb/day of fabric on the cost of 36000 L of water. Mostly water is used in the processing sector for the fulfillment of two purposes, one in the form of solvent for solutes like chemicals and dyes and another for washing/ringing purposes. Steam drying and cleaning, ion exchange, and boiler are some other uses of water in the textile processing sector [17]. The demand for water is varied from one mill to another mill, depending on fabric type which has to be produced, processing method and machinery used. The saving fresh water is necessary due to the various reasons like very fast decline in water table, reduction in the source of clean water, increased demand from industry and residences area. So due to these reasons, water price is increasing day by day. This puts a lot of pressure on the manufacturer to develop cost-effective production using less water. For solving these issues, it is necessary for the the manufacturer to install several techniques which are considered as water saving technologies [18, 19]. A literature review has been conducted to understand the current status of the Indian textile industry. Furthermore, water consumption in textile processing has been discussed. In this chapter, the best available techniques for water saving have been studied. In short, the water saving techniques to achieve sustainable chemical processing of textiles were reviewed.

6.1.1 Indian Textile Industry The textile industry is the most important and the oldest industry in the Indian economy. It accounts for around 2% of GDP, 8% of excise and customs revenue collections. The earning from industrial production and export is 14% and 12%, respectively. The textile industry provides employment to nearly 35 million people, and is the second-largest employment-generating industry [20]. Since the textile industry is highly water intensive and India had been identified as a highly water-scarce region, the long-term viability of the Indian textile industry hinges heavily

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INPUTS

PROCESS

OUTPUTS

Fabric storage

*Raw fabric (cotton, viskon, PES, polyamid)

Fabric opening

*Raw fabric (cotton, viskon, PES, polyamid)

*Auxiliary chemicals (sodium hydroxide, soap) *Wetting agent *Water

Scouring

*Semi-finished fabric *Wastewater

*Auxiliary chemicals (hydrogen peroxide, soap) *Wetting agent *Water

Bleaching

*Semi-finished fabric *Wastewater

*Caustic *Water

Mercerizing

*Semi-finished fabric *Wastewater

*Semi-finished fabric *Auxiliary chemicals *Dyestuffs *Water

Dyeing

*Dyed fabric *Wastewater

*Semi-finished fabric *Water

Finishing

*Semi-finished fabric *Wastewater

*Raw or semi-finished fabric *Auxiliary chemicals *Dyestuffs *Semi-finished fabric *Auxiliary chemicals *Dyestuffs *Water *Printed fabric *Caustic, hydrogen sulphide *Acetic acid and soap *Water *Printed fabric *Auxiliary chemicals (Softeners, stabilizers) *Water

Printing

*Printed fabric

Fixing

*Printed fabric *Wastewater

Washing

*Printed fabric *Wastewater

Finishing

*Printed fabric *Wastewater

Quality Control

Delivery

Figure 6.1 Process flow diagram of the textile processing.

Water Saving Technologies for Textile Chemical Processing 157 on sustainable water management practices. Several factors such as cheap raw material, low-cost labor, skilled workforce, vast fiber varieties, potential domestic and global marketplace, and independent textile industry make India a favorable place for textile industry [21]. Nevertheless, its environmental and social sustainability constitute critical challenges for the industry. A significant amount of wastewater is generated primarily in the dyeing and bleaching processes resulting in polluted effluents that often end up in water bodies.

6.1.2 Water Consumption in Textile Processing The study estimated that the water consumption by Indian textile industry alone is about 200–250 m3/ton of cotton cloth in comparison to the global consumption of less than 100 m3/ton of cotton cloth [22, 23]. The textile industry exhausts a large quantity of water in various processing operations such as pretreatments, dyeing, printing, and finishing. Water baths are used mostly for the application of all chemical, dyes and finishing chemicals onto textile substrates. Additionally, aqueous systems are used for almost all fabric pretreatments such as de-sizing, scouring, bleaching, and mercerizing as shown in Figure 6.1 [24]. The water consumption for various operations in a conventional cotton textile industry and synthetic textile industry and the consumption of water during wet processing are given in Tables 6.1 and Table 6.2, respectively [17, 25]. The variation of water consumption is mainly due to the use of various technologies and machines in different processing steps. Table 6.1 Water consumption in a textile factory. Water use % Purpose

Cotton textile

Synthetic textile

Steam Generation

5.3

8.2

Cooling Water

6.4

–

Demineralized water for special use

7.8

30.6

Process Water

72.3

28.3

Sanitary use

7.6

4.9

Miscellaneous

0.6

28.0

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Table 6.2 Total water consumption during wet processing. Process

Water consumption %

Bleaching

38%

Dyeing

16%

Printing

8%

Boiler

14%

Other use

24%

6.2 Technologies for Water Saving in Textile Chemical Processing 6.2.1 Process Optimization Techniques • Pad-Batch Countercurrent Washing Gokce Tezcanlı Güyer and co-worker found that large quantity of wastewater can be saved based on countercurrent washing strategies in the textile processing. The countercurrent washing is generally practiced by introducing fresh water into the last wash of washing series. The wastewater flows from the last step to the previous step and so on up the line. The cleanest water is used to wash the cleanest product and the dirtiest water is used to wash the most contaminated product. Through this system huge savings of water is possible. The washer comprises of eight boxes: first four boxes contain a solution of water and soap, whereas only rinse water is contained in last four boxes. Initially, through the first four boxes containing soap solution where fabric is fed while rinse water is inserted into the last four boxes. The wastewater from last four rinse basins wastewater can be loaded to other basin directly after filtration with a smart filter. In the process, the demand for hot water temperature is around 70°C and the fresh water (groundwater) has a temperature of 20°C. The rate of water flow is 17 L/min for the last three boxes. The countercurrent washing can save 26,414m3 freshwater at a single washer [26]. • Use of Standing Bath This method is mostly used in H2O2 bleaching of cotton. This is performed by replenishing the bath with equivalent peroxide concentration and maintaining the pH. The replenishment level of the stabilizer is varied up to 70% of the initial value. This method is also adopted for the reuse of polyester and nylon dye bath [27].

Water Saving Technologies for Textile Chemical Processing 159 • Reuse of Final Rinse Water From Dyeing for Dye Bath Make-up This method is employed for the batch dyeing process. The water is clean to a large extent and can be utilized directly for further rinsing or to make up subsequent dye baths. This practice is usually followed in some fabric and carpet industry [28]. • Reuse of Soaping Wastewater Such wastewater can become reusable in the washing of gray fabric, where very high-quality water is not desirable. In another way, this can be used in cleaning floor and equipment [17]. • Reuse of Scouring Rinse for De-sizing In the de-sizing process, very high quality of water is not required so the rinse water could be used. It may also be used in the cleaning of equipment and floor. • Reuse of Mercerizing or Bleach-wash Water for Scouring or De-sizing Mercerizing and bleaching wastewater can be used in de-sizing and scouring processess because the bleach stream and caustic may degrade many size compounds. Scouring of cotton requires caustic soda which is also present in the wastewater originating from mercerization and bleaching. Thus reuse of such caustic-rich wastewater can be done with added advantage. • Use of Automatic Shut-Off Valves In a unit process, the flow of water can be controlled by an automatic shut-off valve set to time, temperature, and level. Due to the use of a thermally controlled shut-off valve, the reduction up to 20% in water usage can be achieved. • Use of Pressure-Reduction Control Valves The amount of water used in a clean-up or washing step can significantly reduced by using pressure-reduction control valves. These valves are particularly useful in cleaning areas where operators are not always worried about the requirement for water conservation [17]. • Waterless Processing or Solvent Processing The most commonly preferred solvent is perchloroethylene. This medium is used instead of water in a closed equipment, like a dry-cleaning machine where the solvent can be recovered from the fabric by suction or by hydro-extraction. The solvent is reused again and again [29]. • Use of a Single Stage of Processing In knitting industries, yarn without any size is used for making the fabric. The carded yarn is mostly used for such purpose. The considerable amount of water can be saved by adopting combined bleaching/scouring and dyeing process for the knitted fabric. The scouring and bleaching process is carried out for 10–20 min followed by dyeing without any drainage

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of bath without any significant depth loss. Also, both finishing and dyeing processess can also be carried out together [29]. • Best Water Management Practices i. Water audit can be carried out to identify how and where water is used in the plant. ii. Track weekly reports and determine the water cost for each production line. iii. All of the production line costs can be calculated to find the possible level of saving and to justify and recommend the modifications with reimbursement. iv. Establish a water-saving team to assess saving methods, thoughts, and equipment. v. Water saving information should be obtained from a trade association, suppliers, consultants, and state agencies. vi. Train the employees involved in the processing sector, to give details about the importance of water conservation and ask for employee suggestions on efficient water savings [18].

6.2.2 Emerging Water-Saving Wet Processing Technologies • Enzymatic Treatments in Textile Wet Processing In the textile processing, enzymes are widely used in wet processing especially for natural fibers. Various enzymes are available for desizing (amylase), bio-scouring (pectinase), biowashing (cellulase), bio-bleaching of denim (laccase) etc. Enzymatic scouring, in which enzymes are used with a combination of surfactants, e.g., wetting agents as well as an emulsifier with complexing agents, can be an eco-friendly alternative of traditional alkaline scouring process. There is less consumption of auxiliaries and chemicals in the bleaching of textiles with the use of enzymes with a better result in comparison to other methods. Enzymes for wool scouring, cotton scouring, cotton bleaching, flax softening, and silk degumming are in development phase till now [30]. Lower water consumption and lower processing temperature are the benefits of enzymatic processes over conventional processes [31]. Advantages of enzymatic scouring as compared to alkaline scouring: i. Reduction in water consumption is up to 20–50% ii. Sodium hydroxide, generally used in conventional scouring, is not required, iii. Reduction of BOD and COD up to 20–40%. iv. Reduction in processing time

Water Saving Technologies for Textile Chemical Processing 161 • Ultrasonic Treatments The applicable frequency of ultrasonic waves in this particular treatment is higher than 16 kHz which is greater than the human audible range of frequency. Transducers either mechanical, magnetic, or piezo-electric ones are excellent sources of producing ultrasonic waves. Ultrasonic equipment is composed of the two-component system, which is a generator or a converter or cleaning bath, respectively. The generator can generate the electric energy and high frequency by the conversion of 50–60 Hz alternating current which is fed to the transducer to create mechanical vibration by the transformation of electrical energy into vibrational energy. The transducer vibrations are longitudinal which transmits waves in the fluid. With the propagation of these waves, the occurrence of cavitation happens [32]. The application of the ultrasonic waves in the dyeing of cotton, nylon, and polyamide has been reported in various studies. The studies show that washing process can speed up upto two to three times by ultrasonic treatment and this is drastically enhanced for wool, cotton, and polyester fabrics [33]. Sonotronic Nagel GmbHcompany has adapted the technology of washing and developed innovative ultrasonic washing units. Advantages of ultrasonic treatment in wet processing [31]: i.

Shorter cycle times and lower process temperatures result in energy savings. ii. 20–30% reduction in effluent load on reducing the consumption of dyes and chemicals. iii. Water saving can be around 20%. iv. Due to the shorter cycle times productivity can be increased • Ozone Bleaching for Cotton Fabrics A considerable quantity of water and chemicals are being consumed in conventional bleaching of cotton which contaminate the water with solid particles and chemical components. Environmental concerns have provoked for a suitable solution to reduce the wastewater generated from the bleaching process. The use of ozone (O3) for the preparation of cotton is the one way for a decrease in discharged wastewater. The oxidation potential of ozone in bleaching is 2.07 electron-volts (eV), that is more than the commonly used bleaching agent, H2O2 (1.77 eV). The availability of ozone on the earth is in the molecular form of acidic pH [34]. The equipment used in ozone-bleaching is divided into three components which are ozone generator, ozone applicator, and ozone destroyer. In

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this equipment, oxygen is supplied from a pressurized cylinder as an input. Supply of significant concentrated amount of ozone-oxygen mixture by the generator to an applicator which is a cylindrical glass tube consists of a diffuser in its bottom [35]. Production of ozone is carried out by feeding 20% oxygen, which is present in the air, for pressurized swing adsorption for raising ozone concentration 90% which further applied by plasma method for generating ozone [31]. Benefits of O3 for cotton bleaching as compared to conventional bleaching are summarized as follows [31]: O3 bleaching is done at room temperature resulting in energy savings ii. 50% reduction in CO2 emissions iii. Significant water savings iv. Short cycle time bleaching resulting in increased the productivity of the process i.

• Electrochemical Dyeing Sulfur and vat dyes are widely used for coloration of cellulosic fibers. Despite all the advantages, these dyes have certain disadvantages including the complicated application method and requirement of reduction and oxidization steps [31, 35]. Non-regenerable oxidized by-product present in the bath is obtained on the use of reducing agents for the reduction of dyestuffs. When these dye baths' wastewater will be discarded in rivers and water-bodies, which may generate many environmental issues. The electrochemical technique is an attractive, appropriate technique which can be used for the reduction of these dyes. While performing the direct electrolysis, the dye reduces at the surface of the cathode. Practically, dye stuff can be partially reduced by applying a reductive process carried out by a reducing agent, and then a complete reduction of dyes is achieved by the electrochemical process. These improve the stability of the reduced dye [36]. On another hand, indirect electrochemical dyeing, dye reduction is not taken place directly on the cathode. Here dye reduction takes place through the action of the conventional reducing agent, e.g., Fe2+/Fe3+ (regenerable). After reduction of the dye, this agent oxidizes and reduce subsequently at cathode surface so that this reducing agent is available, again and again, for dye reduction. During the dyeing process, this cycle continuously repeats again and again in acyclic manner. An agent used in electrochemistry either undergoes oxidation or reduction or both process (redox system) [37].

Water Saving Technologies for Textile Chemical Processing 163 Benefits of electrochemical dyeing as compared to conventional dyeing are listed as follows: i.

Reductions of water and chemical consumption due to the recycling of the mediator system and dyeing liquors. ii. No significant effect on aquatic life iii. Reduction of wastewater discharges • Plasma Treatment Plasma is a hot ionized gas which is a mixture of ions, molecules, electrons, and neutral atoms. In textile processing, for the modification of textile substrates, cold plasma is used. Furthermore, plasma treatment requires water and chemical and acknowledged as a dry, environment-friendly process in the textile industry. The plasma treatment can be used in the field of  apparel and textiles for various processes like pre-treatment of wool fabric, modification in hydrophobic and hydrophilic properties, pretreatment for printing and dyeing, anti-felt finishing and shrinkage for wool fabric, etc. [38]. Openair Plasma pretreatment undoubtedly improves the wettability of fibers and yarns; this opens a new route for solvent-free dyes to bond well and remain durable. The hydrophobic and dirt-repellent surface finishes are applied with the help of plasma treatment. Openair Plasma jets can compete with the standard requirements of the new high-performance spinning equipment [39]. Benefits of plasma treatment as compared to conventional treatment: i. Low-temperature process results in energy savings ii. Almost no or a small quantity of solvents and water is needed iii. Appropriate savings of the dyestuff and finishing auxiliaries • Supercritical CO2 Dyeing A supercritical fluid is a fluid state that is just above to the critical temperature and critical pressure. In this supercritical state, the fluid has the density and dissolving capacity (mass carrying capacity) of that of liquid, while viscosity and diffusion characteristics to that of a gas. Thus, in a supercritical state, it is easy to diffuse the dissolved dye in the textile material leading to the increased penetration and reduction in dyeing time. The supercritical state could be rapidly aborted by changing pressure and temperature, and thus drying of the fabric is very fast, saving time and energy. Leftover dyes could be reused, and the gas could be recycled

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again. Since no water is used in the whole process, no water-related pollution originates. The supercritical state of CO2 is easily achieved as compared to that of other gases (critical condition is 31°C and 74 bar pressure). Moreover, it is nonflammable, non-corrosive, non-hazardous and is suitable for environment and industry. It is produced commercially and can be transported easily [40]. Although, supercritical CO2 (ScCO2) dyeing for polyester and polypropylene has already been developed on a commercial scale. Application of such dyeing technique for wool, acrylic fiber as well as cotton is still facing some problems due to the polarity of dyestuff which is used for coloring the fibers. The optimum conditions for polyester dyeing with the help of ScCO2 are pressure higher than 180 bar and temperature should be above 70°C [41]. DyeCoo utilized industrially proven and patented technology based on ScCO2. In this technology, CO2 has been treated as the dyeing medium in a closed loop process. In the pressurized condition, CO2 changes into supercritical CO2. In that condition, the solvation power of CO2 is much higher, and it enhances the dissolution of dye. Thus dyes can penetrate very quickly and deeply into fibers, creating vibrant colors. The benefits of ScCO2 dyeing over conventional dyeing are summarized as follows: i. Zero water used for dyeing. ii. The reduction in energy consumption by 50–60%. iii. Exhaustion of dye is nearly 100% compared to the traditional value of 80–90%. iv. Production cost decreases by 30–50%. v. Chemical consumption decreases by 50%. vi. Zero discharge of hazardous dyes and chemicals in water streams. vii. The CO2 gas is recycled up to 90% efficiency. No off-gas emission. viii. Drying step is not required. • Digital Printing Digital textile printing has also became a new fashion trend where the complicated designs can be easily printed on textiles. It is required for mills to invest heavily in digital printing machines and to train the manpower. With the continuous developments in specialized inks, cost effective digital prints can now be obtained. Digital printing has allowed mills to print an almost unlimited array of colors and intricate patterns in short runs. Digital printing is also an immaculate process that minimizes waste and

Water Saving Technologies for Textile Chemical Processing 165 substantially reduces water and energy consumption. These innovations are a range of reactive dyes for cotton and cellulosic fibers using technology that assists in them getting absorbed by textile fibers more rapidly, using less salt during dyeing and less water during the wash-off process. These unique set of properties ensure high-quality results at much lower costs along with improved environment acceptability [29]. This process also required post-treatment for completion of the whole printing process. It includes steaming for fixation of dyes. For weak colors, a short period (10 min, 102°C) steaming is needed and for vibrant, durable printing color period is more substantial in comparison to the past (17 min). After steaming, washing is also carried out as there is always some unfixed reactive dye present on the fabric. This printing method is generally employed for small batches. Sample transformation on the substrate is taken place through several ink drops which pressed out to from the nozzles. The drops of single color produce each “dots” for dot/inch which is typically expressed as (d.p.i) and responsible for the image formation. The rectangular formation of parallel scanning lines that guides the electron beam on a screen is known as raster program. With the help of this program, these drops can be managed either one upon another or side by side for the image formation in which one primarily considers about base shade, tinctorial power, and patterns [42]. Following are benefits of digital textile printing: i. Energy savings ii. Considerable water savings iii. Printing screens are not required due to the use of an indirect printing method

6.2.3 Low Liquor Technologies • Foam technology for textile finishing In foam finishing, the surfactants are diluted by air, and it is an alternative technique which is generally used to apply finishing chemicals on the textile substrates. The 90% water is being replaced by air which results in substantial reduction in water consumption and requirements of energy in the drying operations [33]. Foams are micro heterogeneous colloidal systems in which gases are distributed within a liquid or reliable dispersing agent. They can be produced chemically (foaming agents), mechanically (air blowing) and by a combination of both methods. Blow ratio is used to design the relative

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(b)

Doctor coater

Roller coater

Flow coater

(d)

(c)

Vacuum Pressure

Transfer rollers

Figure 6.2 Methods of foam application (a) horizontal padder (b) doctor coating, roller coating and flow coating (c) pressure or vacuum application (d) transfer double sided.

proportions of liquid and air phases in the foam. The constant attention is needed for critical parameters such as foam density, stability, and diameter. There are numerous applications of foam technology in textile chemical processing processes like as preparatory, printing, and dyeing. Foam technology can be used in durable press finishing, soil release finishing, softening, water repellent, oil repellent and flame-retardant finishes. Foam application on fabric can be done either on one side or the both [33]. Systems commonly used in application of foam finishing are kissed roller coating, knife on air, horizontal padders, slot applicators, and knifeover-roller coating as shown in Figure 6.2. After application of foam on to textile, the foams can be busted by vacuum application and conventional padding [43, 44].

6.3 Conclusion The water shortage and contamination issues generated by industries are becoming dangerous; the industries are forced to utilize water-saving

Water Saving Technologies for Textile Chemical Processing 167 techniques, especially in a textile wet processing industry which is one of the highest water consuming industry in the world. This paper reviewed the current status of the Indian textile industry and water consumption in textile processing. The different emerging water-saving technologies are available which needs to be adopted by textile industries. Less waterintensive processes must be invented by the researchers. By this, one can conclude that there is no best and only solution available for water saving. Therefore, the portfolio of water-saving technologies should be developed and deployed to address issues raised in the textile industry. Textile industry should remain receptive to the emerging techniques to ensure efficient water savings.

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11. World Trade Organization, World Trade Organization (WTO) International Trade Statistics Form 2000–2014. Available from: https://www.wto.org/ english/res_e/statis_e/its_e.htm/, 2016. 12. National Bureau of Statistics of the People’s Republic of China, China’s Environmental Statistics Report from 2000–2014. Available from: http:// www.stats. gov.cn/ztjc/ztsj/hjtjzl/, 2015. 13. Unep, I.E., Cleaner Production: A Training Resource Package, United Nation Publication, Paris, 1996. 14. Laforest, V., Assessment of emerging and innovative techniques considering best available technique performances. Resour. Conserv. Recy., 92, 11–24, 2014. 15. Derden, A. and Huybrechts, D., Brominated flame retardants in textile wastewater: Reducing Deca-BDE using best available techniques. J. Clean. Prod., 53, 167–175, 2013. 16. Cikankowitz, A. and Laforest, V., Using BAT performance as an evaluation method of techniques. J. Clean. Prod., 42, 141–158, 2013. 17. Shaikh, M.A., Water conservation in the textile industry. Pak. Text. J., 58(11), 48–51, 2009. 18. Chougule, M.B. and Sonaje, N.P., Novel techniques of water recycling in textile wet processing through best management practices (BMP’s). Int. J. Appl. Sci. Adv. Technol., 1, 29–33, 2012. 19. Wang, R., Jin, X., Wang, Z., Gu, W., Wei, Z., Huang, Y., Qiu, Z., Jin, P., A multilevel reuse system with source separation process for printing and dyeing wastewater treatment: A case study. Bioresour. Technol., 247, 1233–1241, 2018. 20. Ministry of Textiles. Strategic Plan, 2012–2016, 1–52. Accessed: http:// texmin.nic.in/sites/default/files/strategic_plan_2011_2016.pdfm, 2011. 21. Restiani, P. and Khabdelwal, A., Water governance mapping report: Textile industry water use in India, 1–56. Accessed: https://www.siwi.org/wp-content/ uploads/2017/06/Water-Governance-Mapping-Report-INDIA.pdf, 2016. 22. Outlook, S., Zero liquid discharge: Outlook for Indian industry. Market Brief. Available from: http://www.sustainabilityoutlook.in/content/marketoutlook-zero-liquid-discharge-zld-indian-industry-755285, 2015. 23. Cosgrove, W.J. and Rijsberman, F.R., World Water Vision: Making Water EveryBody’s Business, Routledge, https://repository.tudelft.nl/islandora/ object/uuid:f52abf06-e53b-4bbf-9626-2e2a2c5e8f2e, 2014. 24. Dilaver, M., Hocaoğlu, S.M., Soydemir, G., Dursun, M., Keskinler, B., Koyuncu, İ., Ağtaş, M., Hot wastewater recovery by using ceramic membrane ultrafiltration and its reusability in textile industry. J. Clean. Prod., 171, 220–233, 2018. 25. Board, N.I.I.R., The Complete Technology Book on Textile Processing with Effluent Treatment, 2003. 26. Güyer, G.T., Nadeem, K., Dizge, N., Recycling of pad-batch washing textile wastewater through advanced oxidation processes and its reusability assessment for Turkish textile industry. J. Clean. Prod., 139, 488–494, 2016.

Water Saving Technologies for Textile Chemical Processing 169 27. Hashem, M., El-Bisi, M., Sharaf, S., Refaie, R., Pre-cationization of cotton fabrics: An effective alternative tool for activation of the hydrogen peroxide bleaching process. Carbohydr. Polym., 79, 533–540, 2010. 28. Sonaje, N.P. and Chougule, M.B., Recycling of wastewater in textile wet processing. Intr. J. Contemp. Res. India, 2, 7–12, 2012. 29. Bhatia, S.C., Pollution Control in Textile Industry, WPI Publishing, Accessed: https://books.google.co.in/books?id=fmQ-DwAAQBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false, 2017. 30. Nieminen, E., Linke, M., Tobler, M., Vander Beke, B., EU COST Action 628: Life cycle assessment (LCA) of textile products, eco-efficiency and definition of best available technology (BAT) of textile processing. J. Clean. Prod., 15, 1259–1270, 2007. 31. Hasanbeigi, A., Alternative and Emerging Technologies for an Energy-Efficient, Water-Efficient, and Low-Pollution Textile Industry, No. LBNL-6510E. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States), 2013. 32. Guglani, R., Recent developments in textile dyeing techniques, 2008. 33. Ramachandran, T., Karthik, T., Saravanan, D., Novel trends in textile wet processing. J. Inst. Eng., 89, 3, 2008. 34. Eren, H.A. and Ozturk, D., The evaluation of ozonation as an environmentally friendly alternative for cotton preparation. Text. Res. J., 81, 512–519, 2011. 35. Hasanbeigi, A. and Price, L., A technical review of emerging technologies for energy and water efficiency and pollution reduction in the textile industry. J. Clean. Prod., 95, 30–44, 2015. 36. Božič, M. and Kokol, V., Ecological alternatives to the reduction and oxidation processes in dyeing with vat and sulphur dyes. Dyes Pigm., 76, 299–309, 2008. 37. Kariyajjanavar, P., Jogttappa, N., Nayaka, Y.A., Studies on the degradation of reactive textile dyes solution by electrochemical method. J. Hazard. Mater., 190, 952–961, 2011. 38. Zille, A., Oliveira, F.R., Souto, A.P., Plasma treatment in textile industry. Plasma Process Polym., 12, 98–131, 2015. 39. https://www.plasmatreat.com/industrial-applications/plasma-treatmentin-textile-manufacturing.html. 40. Atav, R., The use of new technologies in dyeing of proteinous fibers, in: EcoFriendly Textile Dyeing and Finishing, IntechOpen. Accessed: https://www. intechopen.com/books/eco-friendly-textile-dyeing-and-finishing/the-useof-new-technologies-in-dyeing-of-proteinous-fibers, 2013. 41. Tušek, L., Golob, V., Knez, Ž., The effect of pressure and temperature on supercritical CO2 dyeing of PET-dyeing with mixtures of dyes. Int. J. Polym. Mater., 47, 657–665, 2000. 42. Matsuo, T., Innovations in textile machine and instrument, IJFTR, 33(3), 288–303, 2008.

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43. Kapar, B.Ç. and Güneşoğlu, C., Crease Recovery Treatment Via Pad and Chemical Foam System with Different pH Values. Journal of Textiles and Engineer, 20, 90, 2013. 44. Hasanbeigi, A., and Price, L. A technical review of emerging technologies for energy and water efficiency and pollution reduction in the textile industry. JJ. Clean. Prod., 95, 30–44, 2015.

7 Photocatalytic Dye Degradation Using Modified Titania Waseem Raza1* and Mohd Faraz2† *

1

Department of Chemistry, Indian Institute of Technology, Delhi, India 2 Department of Physics, Indian Institute of Technology, Delhi, India

Abstract Water is one of the most fundamental requirements of life. The addition of any chemical substance may lead to contamination of water, which makes it unfit for use. A wide variety of organic and inorganic pollutants are continuously discharged into water bodies from various sources. Synthetic dyes are the major pollutants in textile industry wastewaters, with an annual production of more than 7 × 105 tons. These dyes are environmentally hazardous materials, attributed to their toxicity and non-biodegradability. In present scenario, there is an urgent need to treat the textile industry wastewater for removal of dyes with a cost effective technology. In this regard, photocatalysis is one of the most appealing and attractive technology which is considered as an efficient cure for dye pollution. Among the various materials, TiO2 is one of the most widely used benchmark photocatalyst in the field of environmental remediation. TiO2 is considered as both supplementary as well as complementary through the destruction or transformation of hazardous chemical wastes to innocuous end-products such as CO2 and H2O. This chapter therefore explores and summarizes the recent efforts in the area of photo catalysis using TiO2. All aspects of TiO2 material synthesis, modifications, and application for dye removal have been thoroughly discussed. Keywords: Wastewater, photocatalysis, dyes and TiO2

*Corresponding author: [email protected] † Corresponding author: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (171–200) © 2020 Scrivener Publishing LLC

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7.1 Introduction Water is one of the most fundamental requirements of life. The availability of water is of great importance for the development of economic activities and mainly for human health. The addition of any chemical substance may lead to contamination of water and make it unfit for use. However, the fast development of the global economy and rapid increase in industrialization in the past century are the major cause of the water pollution [1, 2]. Different organic and inorganic pollutants are continuously disposed into the water system from various sources such as agricultural runoffs, chemical industries, power plants, and chemical spills [3]. Therefore, environmental pollution and lack of sufficient clean water are some of the most serious problems presently faced on a global scale. Dyes are the major class of organic compounds, which makes our world beautiful. Dyes play a vital role in our daily life, such as clothing, leather, plastic, cosmetic, paint, brightener, sprinting, and drugs. The modern textile industries consume about 80% synthetic dyes and large amount of other chemicals for their manufacture and processing [4]. It is estimated that typically dyeing of 1  kg of cloth consume around 120–280 L water. The dye industries dispose a huge amount of inorganic salts, dyes, and other chemicals directly into water bodies. These dyes contain different chromophoric groups such hydroxyl group (–OH), sulfonate group (–SO3) and also azo (–N=N–) as well as high degree of aromaticity resulting low biodegradability property. These dyes upon mixing with water bodies cause serious environmental problems such as reduce the penetration of light, increase the chemical oxygen demand (COD) [4, 5]. These textile dyes not only polluted water as well as hazardous for health. It is estimated that there is little or no clean water supply to about 4 billion people worldwide. Approximately millions of people were dying annually due to water borne diseases because of unsafe water, poor sanitation, and inadequate hygiene [6]. The estimate figures are expected to increase in the near future because an increase in the water pollution due mismanagement of effluents. In the modern age, water pollution becomes a hot topic to discuss because the quality of water directly affects the life of human and animals as well as the depleting of underground water resources. Therefore, it is necessary to treat these hazardous effluents to avoid the accumulation in the environment, damaging the life and decrease the availability of clean water. Therefore, different methods have been established for purification of water, such as physical (coagulation, filtration, adsorption and flocculation), biological, chemical and advanced oxidation processes (AOPS) [4, 7, 8]. The physical methods

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are not so effective that can degradate pollutant completely, whereas transfer them one phase to another [9]. It is reported that most of the synthetic organic dyes/compounds are resistant to biological treatment [10]. Among chemical processes, advanced oxidation processes (AOPs) have been proven as an efficient method for wastewater treatment, because they completely degrade the pollutants into CO2, H2O and mineral acid [11]. The application of AOPs are based on the highly reactive species such as hydroxyl radical, •OOH radical and superoxide radical anion in water for mineralization of a wide range of organic and inorganic pollutants [12]. Among various AOPs, semiconductor mediated heterogeneous photocatalysis has proven to be widely applicable for degradation of the hazardous waste and toxic chemicals/dyes directly mineralize into CO2 and H2O [3, 9]. Heterogeneous photocatalysis is advantageous over traditional methods because its use sunlight to initiate the chemical reaction, work at ambient temperature and pressure as well as completely mineralized the pollutant. Different metal oxide semiconductors have been reported for the degradation of various pollutants such as TiO2, ZnO, MoO3, WO3, Fe2O3, Bi2O3, SnO2, CdS, ZnS, etc. [13]. Among various heterogeneous photocatalysts, TiO2 has proven to be the most promising semiconductor photocatalyst widely used for wastewater treatment owing to its enormous advantages, including its strong chemical stability in a large pH range, relatively inexpensive, nontoxicity, excellent photocatalytic property and easy to handle as evidence by the number of publication [14, 15]. There are three main crystal phases of TiO2 such as anatase, rutile, and brookite. The anatase and rutile are tetragonal in structure and brookite is orthorhombic. The rutile is most stable phase among three phases, whereas anatase and brookite are metastable phases. The photocatalytic activity of anatase is high among all forms of TiO2. Anatase and brookite can convert into rutile phase upon calcination. However, the practical application of pristine TiO2 is limited due to its wide band gaps 3.0–3.2 eV and fast recombination rate of photogenerated electron–hole pairs [16–18]. The wide band gap allows the absorption only in ultraviolet (UV) region, which is a small part of (3–5%) solar spectrum. During the past few decades, an enormous amount of work has been devoted to extending the spectral response of TiO2 in the visible region including doping with metals and non-metals. It has been reported that metals can replace Ti4+ ions and non-metals elements can replace O2− ions of TiO2 lattice to bring about visible-light absorption [19–22]. Hence, doping is a necessary strategy for the development of visible light TiO2. The electrical and optical properties of semiconductor can be changed by the doping. However, the photocatalytic activity of anion-doped titania is

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limited due to massive charge carrier recombination. On the other hand, doping of TiO2 with metals has attracted much attention. Because this method not only extends the photoresponse toward visible region, but also improves the efficiency of charge separation [23]. Despite greater efforts to improve the photocatalytic performance of TiO2, carbon sphere offer unique advantages such as high surface area, chemical inertness, porous structure, stability, and electrical properties. The carbonaceous material to act as a support for metal oxide due to large surface area, highly adsorptive active sites and high mobility of charge carriers. The carbonaceous material increases the adsorption of the pollutants on the surface and provides good contact between the pollutants and the photocatalyst. The carbon spheres play an important role in improving the photocatalytic activity of TiO2 by yielding synergistic effects between the TiO2 and the carbonaceous material. This chapter therefore explores and summarizes the recent efforts in the area of photocatalysis using TiO2. All aspects of TiO2 material synthesis, modifications, and application for dye removal have been thoroughly discussed.

7.1.1 Discovery of Photocatalysis: A Short Historical Overview From the ancient times TiO2 powder has been used due to its low cost, chemical stability and harmless property. TiO2 is active under UV light irradiation, therefore, it has a white color. However, some reports on TiO2 in sun, sunlight also reported such as flaking of paints, degradation of fabrics and photobleaching of dyes [24, 25]. However, “photocatalyst’’ terminology was not used for TiO2 that time, but called a photosensitizer. After that a series of experiments was done by Mashio et al. using TiO2 entitled “Autoxidation of solvents” [26]. Perhaps, this article can be considered as the first article on TiO2 as photocatalyst under UV light irradiation. Fujishima and Honda discovered the photocatalytic water splitting on TiO2 electrode using a Pt metal electrode as cathode and a TiO2 anode irradiated with UV light [27]. This was the beginning of a new era in the field of heterogeneous photocatalysis. However, firstly this discovery was not accepted by electrochemist because oxygen cannot be generated at such a low voltage. Therefore, extensive research was carried out by chemists, physicists, and chemical engineers for understanding the fundamental process. This inspired that TiO2-based photocatalyst are considered as an attractive approach and growing rapidly for the total destruction of organic compounds in polluted air and wastewater [27–29].

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7.1.2 Photocatalytic Mechanism The word “photocatalsis” is derived from the Greek language and made up of two parts: “Photo” energy in the form of light and “catalysis” any substance which change the speed of the reaction without using it [30–32]. Catalysts speed up the rate of reaction by decreasing the activation energy of a reaction. The catalyst can be classified in two categories: “homogenous” in which catalyst and reactant present in the same phase and “heterogenous” in which reactant and catalyst present in a different phase. Heterogeneous catalyst always upper hand to homogenous catalyst because is easy to support, provide high surface area and highly active site for reaction and easy reusable. The properties of heterogenous photocatalyst semiconductor like TiO2 can be explained in terms of band gap theory. According to the band theory, at absolute zero temperature (0 K) a perfect crystal of semiconductor will act as an insulator [33]. According to the band theory, each semiconductor consists of fully filled valence band which possesses lower energy and unfilled conduction band with higher energy. The energetic distance between the two bands known as forbidden band or band gap. The certain amount of energy is required to excite the electrons from the valence to the conduction band. In the TiO2 photocatalyts, the conduction band is made up by 3d orbitals of Ti4+, while the valence band is made up by overlapping of the oxygen 2p orbitals. It is very important that if there is no light, than there is no reaction even we have 100% photo efficient material [34]. The mechanism involved in the degradation of organic pollutants employing irradiated. TiO2 could be visualized as follows. On absorption of photons of energy equal to or greater than its band gap of TiO2 photocatalyst, an electron may be promoted from the valence band (VB) to the conduction band (CB) leaving behind an electron vacancy or “hole” in the valence band [35]. If charge separation is maintained, the electron and hole may migrate to the catalyst surface where they participate in redox reactions with sorbed species. If we do the reaction in the presence of water and oxygen. Specially, hole generated at the valence band (h+VB) may react with surface bound H2O to produce the hydroxyl radical and electron present at conduction band (e−CB) is picked up by oxygen to generate superoxide radical anion. The general mechanism of photocatalysis given in Figure 7.1. A scheme of possible mechanism for the degradation of dyes or organic pollutants given in following equations under UV light irradiation. Charge carrier generation:

TiO2

hv(UV)

TiO2 (ecb

h vb )

(7.1)

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CB

e-

O2

e-

hv

O2 Ti02 3.2 eV Recombination h+

H2O OH/O2

VB

h+

OH

+ Organic pollutants

CO2 + H2O

Figure 7.1 Mechanism for photodegradation of organic pollutants using pristine TiO2 semiconductor photocatalyst.

Recombination of charge carrier:

ecb

h vb

energy

(7.2)

O•2

(7.3)

Reaction of electron with Oxygen

eCB

O2

Reaction of hole with hydroxyl group/water

h vb h vb

H 2O OH

•

H •

OH

OH

(7.4) (7.5)

These active species are responsible for the degradation of dyes. The superoxide anion acts as strong a reducing agent and hydroxyls radical acts as a strong oxidizing agent to degrade the organic pollutants/dyes into H2O and CO2. •

OH / O•2

organic pollutants / Dyes

degraded products (7.6)

7.1.3 Mechanism Under Visible Light Irradiation Doping techniques have been applied in photocatalysis to overcome the limitations of pristine TiO2, such as a wide band gap, ineffectiveness of

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photocatalysis under sunlight, and thermal instability. The metal doped TiO2 increases the light absorption range in the visible region and enhance the quantum efficiency by inhibiting the recombination rate of the photogenerated electrons and holes. The doping of semiconductor with metal decrease the band gap through the generation of an impurity band between VB and CB thereby extend the spectral response toward visible region [36]. On the other hand, doping of TiO2 with rare earth metals has attracted much attention. Rare earth metals having incompletely occupied 4f and empty 5d orbital, could be used as catalysts or to promote photocatalysis. The higher photocatalytic activity of rare earth metals may be due to the transition of 4f electrons. Rare earth metals are able to retard the development of the grain size of TiO2 to decrease its crystallite size (increase the specific surface area), hence improving the photocatalytic activity. Besides the redox pair, rare earth metals can act as an electron scavenger if dispersed on the surface of TiO2. The trapping of electron can inhibit electron hole recombination during irradiation thereby increasing the lifetime of charge carriers, leads to an increase in the performance of the photocatalytic activity as shown in Figure 7.2 [37]. A possible mechanism for decomposition of dyes over doped-TiO2 under visible light illumination as given in the following equations.

Doped TiO2

Visible Light Mn

ecb M( n

e

e-

eImpurity Band

CB

e-

H2O

VB

h+

1)

(7.7) (7.8)

Dopant e-

O2 h+

h vb

O2

OH Organic pollutants

CO2 + H2O

Figure 7.2 Mechanism for photodegradation of Organic pollutants using doped TiO2 semiconductor.

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_

N H3C

Cl +

S

N

N

COOH

CH3

CH3

CH3

N

Methylene Blue

O

Cl− + N

CI N

Rhodamine B

N

N N C2H5 NaO3S

N

H

OH N

N

SO3Na

SO3Na

Reactive Red 214

Scheme 7.1 Chemical Structure of some selected dyes.

M(n

1)

ecb O•2

•

OH / O•2

e

e

h VB

•

H

organic pollutants/Dyes

(7.9)

(7.10)

H 2O 2

(7.11)

OH

(7.12)

OH OH

H 2O

Mn O•2

O2 2H

H 2O 2

h VB

O•2

O2

OH •

(7.13)

OH

(7.14)

degraded produccts (7.15)

7.1.4 Direct Mechanism for Dye Degradation On the other hand another mechanism of photocatalytic dye degradation is also possible under visible illumination due to dye-sensitized

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mechanism. This mechanism involves the excitation of dye takes place from the ground state (Dye) to the triplet state (Dye*) under visible light illumination. The excited (Dye*) is further converted into semi-oxidized radical cation (Dye+) after transferring electron to the conduction band of TiO2. The trapped electrons may subsequently be transferred to adsorbed oxygen to generate the superoxide radical anion(O2¯•) due to a reaction between (O2¯•) and electron proton finally turns into hydroxyl radicals (•OH). These reactive species are mainly responsible for the degradation of organic compounds represented by the equations and Figure 7.2 [34].

Dye Dye

visible light TiO2

Dye Dye

(7.16)

TiO 2

(7.17)

7.1.5 Our Research Focus We have studied the photocatalytic degradation of different variety of organic pollutants under visible light illumination to understanding the detailed degradation kinetics for better understanding the mechanism. The different class of organic pollutants studied by our research group is shown below in Table 7.1. Table 7.1 Photocatalytic degradation of different organic pollutants under visible light illumination. S. No.

Organic Compound Studied

References

1

Methylene Blue (MB)

Ali et al., 2017

[34]

2

Acid Yellow 29 (AY-29)

Raza et al., 2015

[35]

3

Coomassie Brilliant Blue G250 (CCBG250)

Raza et al., 2015

[35]

4

Acid Green 25 (AG-25)

Raza et al., 2015

[35]

5

Acid Yellow 29 (AY-29)

Raza et al., 2015

[36]

6

Acid Green 25 (AG-25)

Raza et al., 2015

[36]

7

Barbituric Acid

Haque et al., 2014

[38]

8

Matrinidazole

Haque et al., 2014

[38]

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7.2 Photocatalytic Application 7.2.1 Degradation of Methylene Blue Using Fe-Doped TiO2 The photocatalytic efficiency of the Fe-doped TiO2 was investigated by degradation of MB (Figure 7.3(e)) dye in aqueous solution under visible light illumination. The controlled experiment displays that photodegradation of MB was resistant under visible-light irradiation without photocatalyst. Therefore, both light and catalyst are needed for efficient degradation of MB dye. However, some degradation of dye was observed in dark in the presence of Fe-doped TiO2 due to adsorption of dye on the surface of catalysts. Figure 7.3(f) indicates that 75% decolorization of dye takes place after 90 min [34]. It could be seen from the figure that main peak of MB dye (664) decreases gradually with irradiation time. This may be attributed due to breaking of chromophoric group present in which dye is responsible for the color of MB dye [36]. The photocatalytic activities of Fe-doped TiO2 with different % of Fe loading are also carried out and shown in Figure 7.3(g). The results indicate a beneficial effect of Fe doping for degradation of MB. The best result in degradation of MB dye was observed for 3% Fe–TiO2 after 90 min. The pristine TiO2 also indicates some degradation of MB dye under visible light illumination due to dye sensitized mechanism. A drastically enhancement of degradation of MB dye was observed after the (b)

1.0

H 3C

N

CH3

S (e)

_

Cl + CH3

N CH3

Absorbance (a.u.)

N

(d)

(c)

0.8

0.6

(f)

00 min 15 min 30 min 45 min 60 min 90 min

(g)

1.0 0.8

C/C0

(a) (a)

0.4

0.6 Blank Pure TiO2 3% Fe-doped TiO2

0.4

0.2

0.2

0.0 450

0.0 500

550

600 650 700 wavelength (nm)

750

800

5% Fe-doped TiO2 7% Fe-doped TiO2 10% Fe-doped TiO2 0

20

60 80 40 Irradiation time (min)

100

Figure 7.3 (a) SEM images of pristine TiO2, (b) 3% Fe-doped TiO2, (c) TEM images of pristine TiO2, (d) 3% Fe-doped TiO2, (e) chemical structure of MB dye, (f) change in the absorbance of MB dye in the presence of the 3% Fe-doped TiO2, and (g) change in the concentration of MB dye in the presence of pristine and different percentage of Fe-doped TiO2 under visible-light illumination (500 W tungsten lamp) as a function of irradiation time 90 min.

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addition of a small amount of 3% Fe metal ion. However, further increase in Fe loading lowered the photocatalytic activity [34]. The increase in the photocatalytic activity by doping of 3% Fe may be due to the shortening of the band gap. Another reason for the increase in the photocatalytic activity by 3% Fe doping could be attributed to the fact that the doping introduces new trapping sites which affects the lifetime of charge carriers by splitting the arrival time of photogenerated electrons and holes resulting reduction of electron−hole recombination. However, at a higher dopant concentration there was occurrence of multiple trapping of charge carriers and hence increase the possibility of electron–hole recombination therefore fewer charge carriers will reach the surface to initiate the degradation of the dye. In addition, at high dopant percentage blocking of light rays or shadowing effect was observed. The turbidity of powder takes place due to aggregation of the catalyst particles, which decreases the penetration depth of light. The aggregation of TiO2 powder covers the part of the photosensitive surface, thereby, decrease the number of surface active sites [34].

7.2.2 Degradation of Acid Yellow 29 Using La and Mo-Doped TiO2 Carbon Sphere (CS) An aqueous solution of AY-29 (Figure 7.4(d)) was irradiated with a visible light halogen lamp in the presence of La and Mo-doped TiO2 (1 g L−1) (b)

N N HO (d)

O NaO S O

2.0

H3C

(e)

N N Cl

1.0

00 min

1.6

Absurbance (a.u)

O S N H O

(c)

05 min

(f)

0.8

10 min

1.2

C/C0

(a)

30 min

0.8

0.6 0.4

Pure TiO2 CS 0.5% La-TiO2 CS 1.0% La-TiO2 CS

0.2

1.5% La-TiO2 CS 2.0% La-TiO2 CS 2.5% La-TiO2 CS

60 min

0.4

120 min 0.0

0.0 320

360

440 400 Wavelength (nm)

480

520

0

20

100 40 80 60 Irradiation time (mn)

120

Figure 7.4 SEM images of (a) carbon sphere, (b) undoped TiO2 CS, (c) La-doped TiO2 CS. (d) Chemical structure of acid yellow 29. (e) Change in absorbance on irradiation of an aqueous solution AY-29 in the presence of (2.0%) La-doped TiO2 CS at different time intervals. (f) Change in concentration as a function of time on irradiation of an aqueous solution of AY-29 in the presence of undoped and Mo-doped TiO2 CS.

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(a)

1.8

(b)

1.0

00 min

0.8 10 min

1.2

C/C0

Absurbance (a.u)

(c)

05 min

1.5

30 min

0.9

0.4

60 min

0.6

Pure TiO2 CS 0.5 Mo-doped TiO2 CS

120 min

0.3

0.6

1.0 Mo-doped TiO2 CS

0.2

1.5 Mo-doped TiO2 CS 2.0 Mo-doped TiO2 CS

0.0 300

350

400

450

Wavelength (nm)

500

550

0

20

40

60

80

100

120

Irradiation time (min)

Figure 7.5 (a) SEM image of Mo-doped TiO2 CS. (b) Change in absorbance on irradiation of an aqueous solution AY-29 in the presence of (1.5%) Mo-doped TiO2 CS at different time intervals. (c) Change in concentration as a function of time on irradiation of an aqueous solution of AY-29 in the presence of undoped and Mo-doped TiO2 CS.

under constant stirring and bubbling of atmospheric oxygen. The degradation of dye was monitored by measuring the change in the absorbance as a function of irradiation time. Figures 7.4(e) and 7.5(b) exhibit the change in absorbance of dye as a function of irradiation time in the presence of 2.0% La and 1.5% Mo-doped TiO2 carbon sphere, respectively. The results indicate that 88% and 71% degradation of AY-29 take place after 120 min of irradiation time in the presence of 2.0% La-doped TiO2 and 1.5% Mo-doped TiO2 carbon sphere, respectively [35]. For better understanding, we also did the experiment using pristine and different percentage of La and Mo doped TiO2 carbon sphere as shown in Figures 7.4(f) and 7.5(c). It is clearly seen from the figures that the degradation of AY-29 increases with increasing the dopant concentration up to 2.0% in the case of La-doped and 1.5% in case of Mo-doped TiO2 carbon sphere. Further increases in dopant concentration lead to decrease in degradation of AY-29 dye. On the other hand, there is no observable decrease in the dye concentration can be seen employing the undoped TiO2 [35].

7.2.3 Degradation of Coomassie Brilliant Blue G250 Using La and Mo-Doped TiO2 Carbon Sphere An aqueous solution of CBBG-250 (Figure 7.6(a)) was irradiated in the presence desired amount of La doped TiO2 CS with a visible light source in the presence of atmospheric oxygen under analogous condition. Figure 7.6(b) shows the change in absorbance as a function of time of irradiation of an aqueous solution of CBBG-250 in the presence of 2.0% La-doped TiO2 CS. It could be seen from the figure that the absorption intensity decreases with increase in irradiation time. Figure 7.6(c) shows the change in concentration of dye as a function of irradiation time in the presence of undoped and at varying concentration of La-doped TiO2 CS. The results

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_

(a)

CH3

O

O ONa S O

N

N H H3C

2.0

Absorbance (a.u)

(d) 1.5

1.5

(b)

1.0 0.8

10 min

60 min

-2.0 560 640 720 Wavelength (nm)

480

100 40 60 80 Irradiation time (min)

120

(e)

0.6 0.4

0.0 750

20

0.8

Pure TiO2CN S 0.5 Mo-doped TiO2 CN S 1.0 Mo-doped TiO2 CN S 1.5 Mo-doped TiO2 CN S 2.0 Mo-doped TiO2 CN S

0.2

550 600 650 700 Wavelength (nm)

0

800

1.0

00 min 05 min 10 min 30 min 60 min 120 min

0.5

500

Pure TiO2CS 0.5 La-doped TiO2 CS 1.0 La-doped TiO2 CS 1.5 La-doped TiO2 CS 1.0 La-doped TiO2 CS 2.5 La-doped TiO2 CS

0.0

120 min 0.0 400

0.4 0.2

30 min 0.5

(c)

0.6

1.0

1.0

0.0 450

00 min 05 min

C/C0

H3C

2.0

C/C0

CH3

O O S O

+

N

Absorbance (a.u)

H3C

800

0

20

100 40 80 60 Irradiation time (min)

120

Figure 7.6 (a) Chemical structure of CBBG-250. (b) Change in absorbance on irradiation of an aqueous solution CBBG-250 in the presence of (2.0%) La-doped TiO2 CS at different time intervals. (c) Change in concentration as a function of time on irradiation of an aqueous solution of CBBG-250 in the presence of undoped and different % of La-doped TiO2 CS. (d) Change in absorbance on irradiation of an aqueous solution CBBG-250 in the presence of (1.5%) Mo-doped TiO2 CS at different time interval. (e) Change in concentration as a function of time on irradiation of an aqueous solution of CBBG-250 in the presence of undoped and Mo-doped TiO2 CS.

indicate that there is no change in concentration of dye is observed in the presence of undoped TiO2 CS, whereas highest degradation efficiency was observed by 2.0% La-doped TiO2 CS. The results also indicate that the degradation of CBBG-250 increases with the increase in dopant concentration from 0.5% to 2.0% and a further increase in dopant concentration (2.5%) lead to decrease in degradation efficiency of the catalyst. The degradation of CBBG-250 was also investigated with Mo (different loading) doped TiO2 CS by irradiating of an aqueous solution of the dye under analogous conditions. Figure 7.6(d) shows the change in absorbance as a function of time in the presence of Mo (1.5%) doped TiO2 CS [35]. Figure 7.6(e) exhibits the change in concentration as a function of time on irradiation of an aqueous solution of CBBG-250 in the presence of different loadings of Mo doped TiO2 CS. Results indicate that the degradation of dye increases with the increase in dopant concentration from 0.5 to 1.5% in case of Mo dopants. Further increases in dopant concentration lead to decrease in degradation efficiency of the catalyst. The results indicate that 91% and 38% degradation of dye takes place over 120 min in the presence of 2.0% La and 1.5% Mo doped TiO2 CS, respectively [35].

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7.2.4 Degradation of Acid Green 25 Using La and Mo-Doped TiO2 Carbon Sphere The irradiation of an aqueous solution of AG-25 (Figure 7.7(a)) in the presence of the desired amount of La doped TiO2 CS under analogous conditions also leads to degradation of the dye. Figure 7.7(b) shows the change in absorbance as a function of time of irradiation of an aqueous solution of AG-25 in the presence of 2.0% La-doped TiO2 CS. It could be seen from the figure that the absorption intensity decreases with irradiation time. Figure 7.7(c) displays the change in concentration of dye as a function of irradiation time in the presence of undoped and varying concentration of La-doped TiO2 CS. The results indicate that there is no change in concentration of dye was observed in the presence of pure TiO2 CS, whereas highest degradation efficiency was observed with a 2.0% La-doped TiO2 CS [35]. The results also indicate that the degradation of AG-25 increases with the increase in dopant concentration from 0.5% to 2.0% and further increase in dopant concentration (2.5%) lead to decrease in efficiency of the catalyst. The degradation of AG-25 was also investigated with Mo (different loading) doped TiO2 CS by irradiating of an O

(a) O

HN O S NaO O

2.0

Absorbance (a.u.)

NaO O HN

(b)

1.0 00 min

1.5

05 min

0.6

10 min

1.0

Pristine TiO2 C S 0.5 La-doped TiO2 C S 1.0 La-doped TiO2 C S 1.5 La-doped TiO2 C S 2.0 La-doped TiO2 C S 2.5 La-doped TiO2 C S

(c)

0.8

C/C0

CH3

S

0.4

30 min

0.5

60 min

0.2

120 min

0.0

CH3

0.0 400

480

2.0

(d) Absorbance (a.u.)

560

640

Wavelength (nm)

1.5

1.0 0.8

600

650

700

750

40

60

80

100

120

Pristine TiO2 C S 0.5 Mo-doped TiO2 C S 1.0 Mo-doped TiO2 C S 1.5 Mo-doped TiO2 C S 2.0 Mo-doped TiO2 C S

0.2 0.0

Wavelength (nm)

20

0.6 0.4

550

0

(e)

0.5

500

800

Irradiation time (min)

10 min 30 min 60 min 120 min

1.0

720

00 min 05 min

C/C0

O

800

0.0 0

20

40

60

80

100

120

Irradiation time (min)

Figure 7.7 (a) Chemical structure of AG-25. (b) Change in absorbance on irradiation of an aqueous solution AG-25 in the presence of (2.0%) La-doped TiO2 CS at different time intervals. (c) Change in concentration as a function of time on irradiation of an aqueous solution of AG-25 in the presence of undoped and different % of La-doped TiO2 CS. (d) Change in absorbance on irradiation of an aqueous solution AG-25 in the presence of (1.5%) Mo-doped TiO2 CS at different time intervals. (e) Change in concentration as a function of time on irradiation of an aqueous solution of AG-25 in the presence of undoped and Mo-doped TiO2 CS.

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aqueous solution of the dye under analogous conditions. Figure 7.8(d) shows the change in absorbance as a function of time in the presence of Mo (1.5%) doped TiO2 CS. Figure 7.7(e) exhibits the change in concentration as a function of time of irradiation of an aqueous solution of AG-25 in the presence of different loadings of Mo doped TiO2 CS. Results indicate that the degradation of dye increases with the increase in dopant concentration from 0.5% to 1.5% in case of Mo dopants. Further increases in dopant concentration lead to decrease in degradation efficiency of the catalyst. The result indicates that 94% and 44% degradation of AG-25 dye takes place over 120 min in the presence of 2.0% La, 1.5% Mo doped TiO2 CS, respectively [35].

7.2.5 Degradation of Acid Yellow 29 Using Ce and Mn-Doped TiO2 Carbon Sphere The phototcatalytic activity of the as prepared Ce and Mn-doped TiO2 CS were evaluated by the monitoring the degradation of aqueous suspension of AY-29 (Figure 7.4(d)) under visible light irradiation. The degradation of dye was investigated by measuring the change in the absorbance as a function of irradiation time. Control experiments exhibit that there is almost 2.0

(a)

(b)

00 min

1.0 Pristine TiO2C S

05 min

0.8

10 min

0.6

C/C0

Absorbance (a.u.)

1.5

1.0 30 min

4% Ce doped TiO2 C S

0.4

(c)

0.2

120 min 0.0 300

350

400

500

450

550

0.0

Wavelength (nm)

(d) 1.2 0.8

20

40

60

80

100

120

Irradiation time (min)

00 min

1.0

05 min

0.8

10 min

0.6

(e)

0

Pristine TiO2C S 0.5% Mn doped TiO2 C S 1.0% Mn doped TiO2 C S 1.5% Mn doped TiO2 C S 2.0% Mn doped TiO2 C S

C/C0

Absorbance (a.u.)

3% Ce doped TiO2 C S

60 min

0.5

1.6

1% Ce doped TiO2 C S 2% Ce doped TiO2 C S

30 min

(f)

0.4

60 min 0.4

0.2

120 min

0.0

0.0 350

400

450

500

550

Wavelength (nm)

600

0

20

40

60

80

100

12 0

Irradiation time (min)

Figure 7.8 (a) SEM image of Ce-doped TiO2 CS. (b) Change in absorbance on irradiation of an aqueous solution AY-29 in the presence of (3.0%) Ce-doped TiO2 CS at different time intervals. (c) Change in concentration as a function of time on irradiation of an aqueous solution of AY-29 in the presence of undoped and different % of Ce-doped TiO2 CS. (d) SEM image of Mn-doped TiO2 CS. (e) Change in absorbance on irradiation of an aqueous solution AY-29 in the presence of (1.5%) Mn-doped TiO2 CS at different time intervals. (f) Change in concentration as a function of time on irradiation of an aqueous solution of AY-29 in the presence of undoped and different % of Mn-doped TiO2 CS.

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no change in the absorbance of AY-29 under visible light illumination without photocatalyst. Therefore, AY-29 was stable and do not reveal self photodegradation under visible light irradiation without catalyst. Hence, AY-29 can only be decomposed under the joint function of light and catalyst. Figure 7.8(b) shows the change in the absorbance at different time interval on irradiation of AY-29 in the presence of 3.0% Ce doped TiO2 CS [36]. Figure 7.8(c) exhibits the change in the concentration as a function of irradiation time in the presence of different concentration (0 to 4.0%) of Ce-doped TiO2 CS. The results indicate that 89% of AY-29 dye takes place after 120 min irradiation time in the presence of Ce (3.0%) doped TiO2 coated CS. It could be seen from the figure that the disappearance of the main absorption peak of dye takes place with irradiation time. To compare the results, we also performed the experiments for decomposition of AY-29 in the presence of Mn-doped TiO2 CS under visible light illumination with the continuous purging of atmospheric oxygen. Figure 7.8(e) shows the degradation of AY-29 in the presence of 1.5% Mn-doped TiO2 CS as confirmed by a change in the absorbance at different time interval on irradiation. Figure 7.8(f) exhibits the change in the concentration as a function of irradiation time in the presence of different concentration (0% to 2.0%) of Mn-doped TiO2 CS. The results indicate that 71% of AY-29 dye takes place after 120 min irradiation time in the presence of 1.5% Mn-doped TiO2 coated CS. The results indicate that the degradation rate of dye derivative was found to increase with increase in dopant concentration up to a certain limit and then decrease in degradation rate was observed. Whereas in the presence of pristine TiO2CS no observable degradation of the dye could be seen under visible light illumination [36].

7.2.6 Degradation of Acid Green 25 Using Ce and Mn-Doped TiO2 Carbon Sphere The irradiation of AG-25 in the presence of Ce-doped TiO2 CS under analogous conditions also leads to degradation of the dye. Figure 7.9(a) exhibits the change in the absorbance as a function of time in the presence 3.0% Ce-doped at different time intervals under visible light illumination. Figure 7.9(b) shows the change in the concentration of AG-25 dye as a function of irradiation time in the presence of pristine and 0–3.0% Ce-doped TiO2 CS. We also study the degradation of AG-25 in the presence of different concentration of Mn-doped TiO2 CS under visible light illumination. Figure 7.9(c) shows the degradation of AG-25 in the presence of 1.5% Mn-doped TiO2 CS. It could be seen from the Figure 7.9(c) that degradation of AG-25 confirmed by a change in the absorbance at different time interval

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2.0 1.0

00 min

1.5

Pristine TiO2CN S 1.0% Ce-doped TiO2 C S

0.8

05 min

2.0% Ce-doped TiO2 C S

10 min

1.0

C/C0

Absorbance (a.u.)

(a)

30 min

3.0% Ce-doped TiO2 C S

0.6

4.0% Ce-doped TiO2 C S

0.4

(b)

60 min

0.5

0.2 120 min

0.0

0.0 500

550

600

650

700

750

0

800

20

2.0 00 min

1.5

80

100

120

05 min

0.6

10 min

1.0

30 min

(d)

0.8

C/C0

Absorbance (a.u.)

60

1.0

(c)

0.4

Pristine TiO2 C S 0.5% Mn doped TiO2 C S 1.0% Mn doped TiO2 C S

60 min

0.5

0.2

1.5% Mn doped TiO2 C S 2.0% Mn doped TiO2 C S

120 min

0.0

0.0 490

40

Irradiation time (min)

Wavelength (nm)

560

630

700

Wavelength (nm)

770

0

20

40

60

80

100

120

Irradiation time (min)

Figure 7.9 (a) Change in absorbance on irradiation of an aqueous solution AG-25 in the presence of (3.0%) Ce-doped TiO2 CS at different time interval, (b) Change in concentration as a function of time on irradiation of an aqueous solution of AG-25 in the presence of undoped and different % of Ce-doped TiO2 CS, (c) Change in absorbance on irradiation of an aqueous solution AG-25 in the presence of (1.5%) Mn-doped TiO2 CS at different time interval and (d) Change in concentration as a function of time on irradiation of an aqueous solution of AG-25 in the presence of undoped and different % of Mn-doped TiO2 CS.

on irradiation. Figure 7.9(d) exhibits the change in the concentration as a function of irradiation time in the presence of pristine and 0 to 2.0% Mn-doped TiO2 CS. The results indicate that 86% and 77% of AG-25 dye takes place after 120 min irradiation time in the presence of 3.0% Ce and 1.5% Mn-doped TiO2 CS. The results indicate that the degradation rate of dye derivative was found to increase with increase in dopant concentration up to a certain limit and then decrease in degradation rate was observed. Whereas in the presence of pristine TiO2 CS no observable degradation of the dye could be seen under visible light illumination [36]. The increase in the photocatalytic activity by increasing the dopant concentration in the case of La, Ce, Mn, and Mo may be due to the shortening of band gap by introducing a new energy level also known as an impurity

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band between the conduction band and valence band of TiO2. Therefore, TiO2 has been activated under visible illumination. This impurity band can either accept electrons from the valence band or donate electrons to the conduction band. After formation of new bands between VB and CB the band gap energy decreases, therefore, longer wavelength, i.e., visible light enough energetically to facilitate the electron transition. Another reason for the increase in the photocatalytic activity by increasing the dopant concentration could be attributed to the fact that the doping of TiO2 with La, Ce, Mn, and Mo, introduces new trapping sites which affects the lifetime of charge carrier by splitting the arrival time of photogenerated electrons and holes to reach the surface of photocatalyst and thus electron–hole recombination is reduced. It can be explained on the basis of the results that the dopant can act as electron–hole separation centers. Nevertheless, further increase in the concentration of dopant lead to decrease in degradation of dyes. At higher dopant concentration there was occurrence of multiple trapping of charge carriers and hence the possibility of electron–hole recombination increases and fewer charge carriers will reach the surface to initiate the degradation of the dye. Therefore, decrease in decomposition of dyes was observed [39, 40]. In addition, at high dopant percentage the blocking of light rays or shadowing effect was observed. The turbidity of powder also takes place due to aggregation of the catalyst particles, which decreases the penetration depth of light. The aggregation of TiO2 CS powder covers the part of photosensitive surface, thereby decreasing the number of surface active sites. Only appropriate amounts of dopant can improve photcatalytic activity.

7.2.7 Degradation of Barbituric Acid and Matrinidazole in Using Undoped and Ni-Doped TiO2 An aqueous solution of a model pollutant Barbituric acid was irradiated in the presence of Ni-doped TiO2 with a visible light halogen lamp in an immersion well photochemical photoreactor at different time interval with continuous bubbling of atmospheric oxygen and the reaction was followed by measuring the change in absorbance and depletion in TOC content. Figure 7.10(a) shows a decrease in absorbance as a function of irradiation time for an aqueous suspension of Barbituric acid (0.5 mM) in the presence of 0.5% Ni-doped TiO2 (1 g L−1) under visible light halogen linear lamp. Figure 7.10(b) shows the change in concentration and depletion in TOC as a function of time on irradiation of an aqueous solution of Barbituric acid in the presence and absence of 0.5% Ni-doped TiO2 under analogous conditions. It could be seen from the figure that there is no change in concentration when irradiation is carried out in the presence of pristine TiO2

Visible light/TiO2

2.0 1.1

t= 15 min t= 30 min

1.0

t= 90 min t= 120 min

1.0

Visible light/0.5% Ni-TiO2 (Mineralization) Visible light/0.5% Ni-TiO2 (Degradation)

0.9

(a)

t= 60 min

1.0

C/C0 TOC/TOC0

Absorbance

1.5

t= 0 min

(b)

0.8 0.7 0.6 0.5 0.4 0.3

0.0

0.2 200

250

300

350

Wavelength (nm)

400

Degradation rate (mol L−1 min−1, 10−3)

Photocatalytic Dye Degradation Using Titania Barbituric Acid (Mineralization) Barbituric Acid (Degradation) Matrinidazole (Mineralization) Matrinidazole (Degradation)

0.12 0.10 0.08

189

(c)

0.06 0.04 0.02 0.00

0

20

40

60

80

100

Irradiation time (min)

120

0.0

0.2

0.4

0.6

0.8

Dopant concentration (Ni, w/v)

Figure 7.10 (a) Change in absorption on irradiation of aqueous solution of Barbituric acid in the presence of 0.5% Ni-doped TiO2 under visible light halogen linear lamp (500 W, 9500 Lumens). (b) Depletion in TOC and change in concentration as a function of irradiation time for an aqueous solution of Barbituric acid in the presence of pristine and 0.5% Ni-doped TiO2. (c) Influence of dopant concentration on the mineralization and degradation of barbituric acid and Matrinidazole.

whereas in the presence of 0.5% Ni-doped TiO2 68% mineralization and 86% degradation was observed after 120 min [33]. The photocatalytic activity of different concentration of Ni doped TiO2 (0–0.8%) was investigated by studying degradation and mineralization of barbituric acid and matrinidazole compounds. Figure 7.10(c) shows the degradation and mineralization rate of barbituric acid and matrinidazole in the presence of Ni-doped TiO2 (Ni varying from 0% to 0.8%). It could be seen from the figure that the degradation rate of barbituric acid and matrinidazole increases with increase in dopant concentration up to 0.5% and on further increases in concentration leads to a slight decrease in the degradation rate. The photocatalytic degradation rate of 0.5% Ni–TiO2 was found to be better as compared to other percentage of Ni doped TiO2 particles [33]. The increase in the photocatalytic activity by increasing the dopant concentration may be due to the shortening of the band gap, thereby effectively absorbing the light of longer wavelength. Another reason for the increase in the photocatalytic activity by increasing the dopant concentration could be attributed to the fact that the doping of TiO2 with dopant introduces new trapping sites which affect the lifetime of charge carriers by splitting the arrival time of photogenerated electrons and holes to reach the surface of photocatalyst and thus electron–hole recombination is reduced. In the case of Ni-doped TiO2 the degradation rate of both the compounds studied increases with the increase in dopant concentration from 0.1% to 0.5%, which on further increase in the dopant concentration lead to decrease in the rate. The decrease in the rate at a higher dopant concentration (0.8% in the case of Ni) may be due to the occurrence of multiple trapping of charge carriers and hence the possibility of electron–hole recombination increases and fewer charge carriers will reach the surface to initiate the degradation

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of compounds, hence decrease in degradation efficiency at higher dopant concentration was observed [41, 42].

7.3 Factors Affecting the Degradation of Organic Pollutants 7.3.1 Effect of pH In photocatalytic reaction, the pH of the solution plays a vital role as it can influence the reaction rates in multiple ways. The pH of reaction controlled surface charge of the catalyst resulting affect the adsorption of dyes/ pollutants on the surface of semiconductor photocatalyst. It has been reported that the effect of pH van be easily explained on the basis of the zero point (ZPC) [43]. The ZPC for the TiO2 is reported pHZPC = 6.8 [44]. In our case the ZPC of doped TiO2 CS is found to be pHZPC = 6.6 to 6.8 [45]. Hence, the surface of TiO2 gets to positively charged with respect to acidic medium pH < 6.8 and negatively charged in alkaline medium pH > 6.8 respectively. Under acidic or alkaline condition the surface of TiO2 can be protonated or deprotonated respectively according to the following equations [46]:

TiOH TiOH

H OH

TiOH 2 TiO

(7.18)

H 2O

(7.19)

Therefore, if the pH of the solution is lower than the ZPC value the surface of photocatalyst will be positively charged and attract the negatively charged dyes/pollutants. On the other hand, if the pH of the solution is higher that the ZPC value the surface of photocatalyst will be negatively charged and attract the positively charged dyes/pollutants. In order to see the effect of pH on the degradation kinetics we also investigated the degradation rate of two different organic dyes at different pH values using Ce and Mn-doped TiO2 CS. Figure 7.11(a) shows the degradation rate of AY-29 dye as a function of pH using Ce-doped TiO2 CS and Figure 7.11(b) exhibit the degradation rate of AG-25 dye as a function of pH using Mn-doped TiO2 CS under the visible light illumination. The results indicate that the degradation rate of both dyes was found better at lower pH and highest efficiency was observed at pH 4.2 for AY-29 and 3.5 for AG-25. The both dyes contain sulfonate group which upon hydrolyzed in aqueous solution gives negatively charged surface, therefore at lower pH

(a)

AY-29

0.00464

0.00406

0.00348

0.00290 1.8

3.6

5.4

Degradation rate [mol L−1 min−1 * 10−3]

Degradation rate [mol L−1 min−1 * 10−3]

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191

(b)

AG-25

0.00304

0.00266

0.00228

7.2

pH

1.8

3.6

5.4

7.2

pH

Figure 7.11 (a) Effect of pH on the degradation rate of AY-29 and (b) AG-25 in the presence of Ce/Mn-doped TiO2 CS, respectively.

(acidic pH) both dyes would absorb more efficiently onto the surface of positively charged TiO2. So the degradation rate of both the dyes was found to better at acidic pH. In contrast, at a high pH value negatively charged on the surface of TiO2 would repel the negatively charged sulfonate group of dyes resulting reduction in degradation rate of both dyes [36].

7.3.2 Effect of Photocatalyst Loading Photocatalyst loading also plays a crucial role for efficient removal of dye, in order to avoid the excess use of the photocatalyst. The number of active sites on the surface of semiconductor would increase with the quantity of catalyst loading resulting enhancement in the photocatalytic degradation rate. It has been found that the degradation rate would decrease beyond an optimum loading of catalysts. The effect of catalyst loading was examined for getting the optimum amount of catalyst for the degradation of two different organic dyes in order to avoid excess catalyst loading. Figure 7.12(a) and (b) show the degradation rate of AY-29 and AG-25 as a function of catalyst dose in the presence of Ce and Mn doped TiO2 CS respectively under the visible light illumination. The degradation rate of AY-29 was found to increase with increase in catalyst loading from 0.5 to 1.5 g L−1 and the rate of AG-25 was found to increase with increase in catalyst loading from 0.5 to 2 g L−1. It is evident that initially photodegradation rate increases with an increase in the amount of photocatalyst and then decrease with increase in catalyst concentration. This may be due to several reasons. As the catalyst loading increases the degradation efficiency, increase due to higher availability of surface active sites for the dye derivatives. The further increase in the catalyst loading may increase the opacity of the suspension, which may retard the degradation rate as well as at the excessive amount of catalysts

Advanced Functional Textiles and Polymers

0.0045

AY-29

(a)

0.0044

0.0043

0.0042

0.0041

0.0040 0.5

1.0

1.5

2.0

Degradation rate [mol L−1 min−1 * 10−3]

Degradation rate [mol L−1 min−1 * 10−3]

192

0.003393 0.003354

AG-25

(b)

0.003315 0.003276 0.003237 0.003198 0.003159 0.003120

0.61

2.5

1.83

1.22

Catalyst loading (gL−1)

2.44

Catalyst loading (gL−1)

Figure 7.12 (a) Effect of catalyst loading on the degradation rate of AY-29 and (b) AG-25 in the presence of Ce/Mn-doped TiO2 CS, respectively.

block the light penetration resulting decrease in the photocatalytic degradation rate. After the adsorption on dye molecules on photocatalyst surface, the addition of higher quantities of photocatalyst would have no further enhancing effect on the degradation efficiency [36].

7.3.3 Effect of Calcination Temperature

0.004512

(a)

AY-29

0.004488

0.004464

0.004440

0.004416

300

400

500

Calcination temperature

600

Degradation rate [mol L−1 min−1 * 10−3]

Degradation rate [mol L−1 min−1 * 10−3]

In order to evaluate the optimum calcination temperature for degradation kinetics we tested the degradation of two different organic dyes at different calcination temperature using Ce and Mn-doped TiO2 CS. Figure 7.13(a) and (B) exhibit the degradation rate of AY-29 and AG-25 as a function of calcination temperature in the presence of Ce and Mn doped TiO2 CS, respectively, under the visible light illumination. The 3.0% Ce and 1.5% Mn doped TiO2 CS was calcinated at 400°C shows the better photocatalytic

0.003375

(b)

AG-25

0.003330

0.003285

0.003240

268

335

402

469

536

603

Calcination temperature

Figure 7.13 (a) Effect of calcination temperature on the degradation rate of AY-29 and (b) AG-25 in the presence of Ce/Mn-doped TiO2 CS.

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activity compared to other calcined temperature. As the calcination temperature increases, the anatase diffraction peaks become sharper, which indicates an increase in crystallite size of TiO2 therefore decrease in the surface area available for light adsorption hence a drop in the photocatalytic degradation rate was observed at higher calcined temperature [36].

7.3.4 Effect of Reaction Temperature Different researchers have been investigating the study the dependence of photocatalytic activity on reaction temperature. Generally, an increase in temperature leads to increase the photocatalytic activity. However increase in reaction temperature above 80°C promotes the recombination rate of charge carrier as well as favor the desorption process of organic compounds/dyes on the titania surface, resulting in the decrease of photocatalytic activity [47]. As evident from the name photocatalytic activity activated by photons so heat is not required for the system can operate at room temperature. Therefore, the optimum reaction temperature for photocatalytic activity lies below the 80°C as well as favors the adsorption whereas further decrease in reaction temperature to 0°C results in an increase in the apparent activation energy [48, 49].

7.3.5 Effect of Inorganic Ions The presence of various mineral ions such as magnesium, iron, zinc, copper, bicarbonate, phosphate, nitrate, sulfate, and chloride in dye contents of waste water is common. It has been reported that calcium, magnesium and zinc have very little effect on photodegradation of dyes due to that these cations are present in their highest oxidation states causing little or no inhibitory effect in wastewater. However, cations such as copper, phosphate and iron have been reported to have the greatest ability to decrease the photodegradation efficiency than above one. It may be due to that these cations may compete with dyes for the active sites on the TiO2 surface and thus deactivate the photocatalyst resulting in decrease in dye degradation rate. Waste water from textile industries conations a considerable amount of inorganic salts such as carbonates, bicarbonates, nitrates, sulfates, and chlorides. The presence of these salts diminishes the stability of colloidal stability, decreases the surface contact between photocatalyst and dye and enhances the mass transfer. These inorganic scavenge the active species in photocatalysis such as hole and hydroxyl radical as given below [50, 51].

CO32

•

OH

CO3 •

OH

(7.20)

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HCO3

•

CO3 •

•

Cl •

CO3 •

OH OH h

OH

Cl

HOCl•

(7.21)

H CO3

(7.22)

Cl•

(7.23)

HOCl•

(7.24)

Cl•

H

H 2O

H 2O

(7.25)

We also performed experiments to examine the main reactive species— hydroxyl radical, superoxide radical anion and hole—using different scavengers. Therefore, different scavengers were added to the aqueous solution of dyes to investigate the inhibitory effects of scavengers. Figure 7.14 displays the change in degradation rates in the presence of different scavengers. In order to examine the role of •OH, we use isopropyl alcohol (IPA) and the photodegradation of AY-29 strongly depressed. When potassium dichromate (PD {quencher for electron}) was added, slight decrease in the degradation of dyes takes place as compare to IPA. Furthermore, the role of hole in the photodegradation of dye was No Scavenger AO PD IPA

1.0 0.8

C/C0

0.6 0.4 0.2 0.0 0

20

40

60

80

100

120

Irradiation time (min)

Figure 7.14 The effect of different scavenger on degradation of AY-29 in the presence of 3.0% Ce doped TiO2 CS under visible light illumination.

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determined by the addition of ammonium oxalate (AO) there was a significant reduction in decomposition process of AY-29. These results reveal that hydroxyl radicals, electron, and holes play an important role in the photodegradation of AY-29.

7.4 Conclusions In this chapter, a comprehensive series of doped TiO2 photocatalyst, basic theory of photocatalysis, mechanism and effect of parameters are discussed. Photocatalysis is simply powerful emerging and promising technology due to its advantage of degradation on pollutants. TiO2 is a better catalytic material for degradation of various contaminants and sustainable environmental remediation technology due to its many advantages. The literature survey indicates that doping technique is simple procedure used to enhance photocatalysis by TiO2. Doping technique easily provides small crystallite size, high surface area and anatase phase. Therefore, an ideal photocatalyst should be inexpensive, nontoxic, long-term stabile, and easily reproducible on separation. Overall, this chapter brings to attention the advancements of TiO2 for water treatment. Due to theses advancements, TiO2 can degrade organic pollutants, it serves as a cheap dual process that can be further explored to realize the potential of TiO2 in water-treatment processes. Moreover, titania provides a cheaper alternative that can be used in conjunction with the already existing water-treatment technologies. Furthermore, the use of titania based systems is a better alternative for the use since it harnesses the green solar energy and thus reduces the environmental waste due to the use of chemicals. Therefore, the ability of TiO2 to completely deal with organic pollutants without producing recalcitrant by-products has thus opened new research avenues to be pursued.

References 1. Hu, J.S., Ren, L.L., Guo, Y.G., Liang, H.P., Cao, A.M., Wan, L.J. et al., Mass production and high photocatalytic activity of ZnS nanoporous nanoparticles. Angew. Chemie – Int. Ed., 44, 1269–73, 2005. 2. Li, Y.-F., Xu, D., Oh, J Il, Shen, W., Li, X., Yu, Y., Mechanistic Study of Co doped Titania with Nonmetal and Metal Ions: A Case of C + Mo Codoped TiO2. ACS Catal., 2, 391–8, 2012. 3. Rasalingam, S., Wu, C.M., Koodali, R.T., Modulation of pore sizes of titanium dioxide photocatalysts by a facile template free hydrothermal synthesis

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20. Inturi, S.N.R., Boningari, T., Suidan, M., Smirniotis, P.G., Flame aerosol synthesized Cr incorporated TiO2 for visible light photodegradation of gas phase acetonitrile. J. Phys. Chem. C., 118, 231–42, 2014. 21. Hamilton, J.W.J., Byrne, J.A., Dunlop, P.S.M., Dionysiou, D.D., Pelaez, M., O’Shea, K. et al., Evaluating the mechanism of visible light activity for N,FTiO2 using photoelectrochemistry. J. Phys. Chem. C., 118, 12206–15, 2014. 22. Liu, G., Han, C., Pelaez, M., Zhu, D., Liao, S., Likodimos, V. et al., Enhanced visible light photocatalytic activity of CN-codoped TiO2 films for the degradation of microcystin-LR. J. Mol. Catal. A Chem., 372, 58–65, 2013. 23. Wang, C., Ao, Y., Wang, P., Hou, J., Qian, J., A facile method for the preparation of titania-coated magnetic porous silica and its photocatalytic activity under UV or visible light. Colloids Surf. A Physicochem. Eng. Asp., 360, 184–9, 2010. 24. Keidel, E., Die Beeinflussung der Lichtechtheit von Teerfarblacken durch Titanweiss. Farben. Ztg., 34, 1242, 1929. 25. Goodeve, C. F., Kitchene, J. A., The mechanism of photosensitisation by solids. Trans. Faraday Soc., 34, 902, 1938. 26. Kato, S. and Mashio, F., Autooxidation by TiO2 as a photocatalyst. Abstract B Annu. Meet. Chem. Soc. Japan, 223, 1956. 27. Fujishima, A. and Honda, K., Electrochemical photolysis of water at a semiconductor electrode. Nature, 238, 37–8, 1972. 28. Rajeshwar, K., Osugi, M.E., Chanmanee, W., Chenthamarakshan, C.R., Zanoni, M.V.B., Kajitvichyanukul, P. et al., Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media. J. Photochem. Photobiol. C Photochem. Rev., 9, 171–92, 2008. 29. Fujishima, A., Rao T.N., D.T., Titanium dioxide photocatalysis. Photochem. Photobiol., 1, 1–21, 2000. 30. Fujishima, A., Rao, T.N., Tryk, D.A., Titanium dioxide photocatalysis. J. Photochem. Photobiol. C Photochem. Rev., 1, 1–21, 2000. 31. Li, X., Xiong, Y., Li, Z., Xie, Y., Large-scale fabrication of TiO2 hierarchical hollow spheres. Inorg. Chem., 45, 3493–5, 2006. 32. Subramanian, V., Wolf, E.E., Kamat, P.V., Catalysis with TiO2/Gold Nanocomposites. Effect of Metal Particle Size on the Fermi Level Equilibration. J. Am. Chem. Soc., 126, 154943–4950, 2004. 33. Xu, A.W., Gao, Y., Liu, H.Q., The preparation, characterization, and their photocatalytic activities of rare-earth-doped TiO2 nanoparticles. J. Catal., 207, 151–7, 2002. 34. Ali, T., Tripathi, P., Azam, A., Raza, W., Ahmed, A.S., Ahmed, A. et al., Photocatalytic performance of Fe-doped TiO2 nanoparticles under visible-light irradiation. Mater. Res. Express, 4, 015022, 2017. 35. Raza, W., Haque, M.M., Muneer, M., Fleisch, M., Hakki, A., Bahnemann, D., Photocatalytic degradation of different chromophoric dyes in aqueous phase using La and Mo doped TiO2 hybrid carbon spheres. J. Alloys Compd., 632, 837–44, 2015.

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8 Advanced Approaches for Remediation of Textile Wastewater: A Comparative Study Shumaila Kiran1*, Sofia Nosheen2, Shazia Abrar1, Fozia Anjum3, Tahsin Gulzar1 and Saba Naz1 1

Department of Applied Chemistry, Government College University, Faisalabad, Pakistan 2 Department of Environmental Science, Lahore College for Women University, Lahore, Pakistan 3 Department of Chemistry, Government College University, Faisalabad, Pakistan

Abstract Textile dyes by fabrication are used in numerous kinds of products such as leather and paper. Textile industrial effluents contain synthetic dyes that are released into the environment. These effluents enhance poisonousness to human beings and other living things. Nowadays, the removal of textile dyes from industrial wastewater has become an environmental issue worldwide. Water contamination causes some chronic diseases to humans and it is one of the great threats for the environment. As textile dyes contain several lethal chemicals, it is essential to discharge industrial effluents through an appropriate treatment as rapidly as possible. The effluent discharged from textile industries experiences several physio-chemical treatments like coagulation, flocculation, ozonation, etc., which is followed by biological processes for the elimination of metals, organics, nitrogen and phosphorous. The complete remediation method of textile effluent comprises of primary, secondary and tertiary treatments. The purpose of this chapter is to demonstrate the technical and economic feasibility of an integrated process or processes for treatment of textile effluents. This chapter covers the detail and comparison among all possible approaches to treat textile wastewater and recent developments in textile wastewater treatments. Keywords: Textile wastewater, primary treatment, secondary treatment, tertiary treatment, comparison, COD, TOC *Corresponding author: [email protected]; [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (201–264) © 2020 Scrivener Publishing LLC

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8.1 Introduction According to the statistics, 100,000 dyes known worldwide, are available at commercial level and amount of world annual production of dyestuffs is more than 71,000,000 tons of which azo dyes are mostly used because of their many advantages ranging from wide variety of color shades and ease of application, etc. [1]. Also, it is estimated that the dyestuff of 10–15% is used in dye manufacturing is released into the environment throughout the synthesis and dyeing process.

8.1.1 Textile Wastewater Textile wet processing is a major part in the manufacturing process of textile product. It includes series of processes from singeing to finishing using water as a media. The spent liquor in all these processes is harmful to the environment. These enormous amounts of chemicals pose a danger and threat to the environment due to their non-biodegradable nature as they contain dyes and pigments. The whole textile processing uses various chemicals based on the nature of raw material and product. Hence the effluents resulting from these processes also vary largely in their composition, chemicals present, etc. The major problem comes from the dyeing and finishing processes employ a large amount of organic chemicals and dyestuffs which create a disposal problem [2].

8.1.2 Characteristics of Textile Wastewater Textile effluent contains considerable quantities of unfixed dyes (about 20%). Treatment of finishing and dyeing process effluent represents significant environmental problems in textile sector [3]. Textile wastewaters have color and contain high COD, BOD values, extreme pH, and they have different contents of heavy metals, surfactants, salts, mineral oils besides organic dyes, chemicals, and others [4, 5]. Synthetic dyes and dye intermediates are major areas of concern. In the textile industry, the dyeing and finishing units consume a wide-ranging of dyestuffs which pose a potential threat to the environment (Table 8.1).

8.1.3 Damages Caused by Textile Effluent The wastewater generated throughout this whole textile procedure comprises huge quantity of chemicals having trace metals (Cr, As, Cu, and Zn) and dyes

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Table 8.1 Specific pollutants from textile wet processing [6]. Process

Composition of Effluent

Nature of Pollutant

Sizing

Carboxymethyl cellulose (CMC), starch, waxes, wetting agents, polyvinyl alcohol (PVA)

High in COD, BOD

Desizing

CMC, starch, waxes, fats, PVA, pectins

High in COD, BOD, dissolved solids (DS), SS

Bleaching

NaOH, Cl2, acids, H2O2, NaSiO3, sodium phosphate, surfactants, sodium hypochlorite, short cotton fiber

High SS, highly alkaline

Mercerizing

Cotton wax, sodium hydroxide

High pH, high DS, less BOD

Dyeing

Oxidizing agents, reducing agents, Dyestuffs urea, acetic acid, wetting agents, detergents

Heavy metals, highly colored, low SS, high DS, BOD

Printing

Starch, urea, oils, gums, binders, acids, thickeners, reducing agents, alkali, cross-likers

Strongly colored, high BOD, SS, oily look, little alkaline

which are able to harm the human health and environment. The wastewater can cause typhoid, diarrhea, cancer, liver damage, kidney damage, gastroenteritis, nausea, cholera, ulceration of skin, hemorrhage, skin irritation dermatitis [7]. Synthetic dyes give a vast range of colorfastness and bright shades. Though their poisonous nature became the reason of high concern to ecologists. The utilization of synthetic dyes influence in bad ways on all living organisms [8]. The presence of nitrates, sulfur, chromium compounds, naphthol, vat dyes, acetic acid, soaps, enzymes and heavy metals such as arsenic, copper, lead, cadmium, nickel, cobalt, and mercury as well as certain secondary chemicals, mutually form the textile wastewater extremely contaminated [9]. The other detrimental chemicals in the effluent can be dye fixing agents based on formaldehyde, removers of chlorinated stain, softeners based on hydro carbon, non-biodegradable dyeing compounds. These organic matters react with numerous disinfectants particularly chlorine and make byproducts

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(DBP’S) that are carcinogenic and hence objectionable [10]. Mostly they show allergic reactions. The colloidal material present with colors and oily layer enhances the turbidity, contributes in the bad appearance of water and bad smell as well as inhibits the sunlight penetration that is vital for the photosynthesis process. This as a result interferes with the oxygen transfer mechanism at air water boundary which in consequences affects the marine life [11] and self-purification operation of water [12]. This wastewater if permitted to run in the fields, blocks the soil pores causing in loss of soil efficiency. If permitted to flow in drains and rivers it influences the excellence of drinking water in hand pumps making it unhealthy for human health.

8.1.4 Ecological Balance and Environmental Issue Ecological imbalance is increasing due to various aspects like ozone layer depletion, carbon monoxide percentage increase etc. The time has come for the technologies, researchers, academia, and industries to consider the environmental issues seriously and plan for strategies accordingly to address various issues [13]. The major problem facing textile industry is to amend the fabrication processes which are highly environment friendly at a reasonable cost by consuming safe chemicals and dyes and also decreasing the expense of wastewater treatment methods [14]. With reference to the green environment, it is necessary for a common man to know the various processes of the textile manufacture like spinning, weaving, chemical processing, and garment production. These textiles wet processing accounts for major environmental issues as the spent liquor is released outside by the wet processing units [6]. However some of the process as in weaving (preparatory process like sizing) is not free from the environmental problems. Especially sizing process uses starch which is a feed material for micro-organisms. Unused material is released to the outside streams that are dangerous for the environment [15]. Today the sizing ingredients are recommended with pollutant free atmosphere. Efforts have been made to install or practice green process in textile wet processing by using either natural resources or eco-friendly materials [16, 17].

8.1.5 Need for the Treatment Textile industry wastewater contains non-degradable substances. Textile wastewater causes a big environmental problem due to the huge amounts of effluent generated from textile and dyeing processes as mentioned in Fig. 8.1 [18]. So wastewater treatment and reuses of treated effluent in textile industry is must, especially in countries that suffer from water scarcity

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Textile industry wastewater

Desizing effluent

Bleaching of fluents

Biological treatment

dyeing or printing of effluents

Mercerization effluent

Partial oxidation of dyeing printing of fluents by H2O2

NaoH recovered by Multi effect evaporation

Water quality COD, TOC, BOP etc Biodegradable BOD, COD Non biodegradable BOP, COD less than 0.3 greater than 0.3

Biological treatment Discharge COD permisible limit range

Biodegredation

Non toxic Toxic intermediate intermediate Post treatment by AOP

AOP process

Biodegrability analysis during AOP treatment

Figure 8.1 Damages of wastewater.

[19]. Even though modern technologies suggest for a low liquor concept in textile wet processing, environmental issues remain unanswered. Due to the rapid industrialization there is an increase in the toxic pollutants in the industrial effluents and this is a major environmental issue [20, 21]. A comprehensive view of different pollutants discharged during different textile operations and their possible effects on human health is given in Table 8.2.

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Table 8.2 Effluent discharge from textile industry [23]. Pollutants effects on health

S. No.

Process

Chemical

Discharge

1.

Sizing

Benzene

Fats, resins, waxes, glucose, and starch

Mutagenic, Carcinogenic, and disturbs central nervous system

2.

Bleaching

Cyanide

Grease, wax, sodium silicate, soda ash

Prolonged experience will upset liver and kidney and cause death

3.

Dyeing

Sulfate

Acetic acid, sulfides, mordant

Respiratory and eye problem

4.

Printing

Phosphate, nitrate

Gums, starch, acids, mordant

Detrimental health threats

5.

Finishing

Lead

Finishing agents, salts, starch

Suppression of hematological system

The today’s interest is not only in techniques of color elimination but in techniques as well, that can harvest water which is reusable, recover the salt, recover the dyes, mineralize aromatic compounds, remove toxicity, and do not generate toxic sludge or sludge at all as shown in Table 8.2 [22]. The tools for color elimination were significant before 30 years, are famous now. Therefore, effluent remediation practices for the dyes mineralization are discussed in the consequent portions instead of color elimination.

8.1.6 Standards of Textile Industry for Water Contaminants There are strict restrictions for the discharge of the textile effluent because of its toxicity and harms to the environment and humanities. The standards of the effluent discharge [21] have so many parameters because of the different raw materials used, various kinds of dyes and tools (Table 8.3). The textile effluent have dyes, metal ions and its color are of the main concern due to their unsafe and dangerous nature to environment and society.

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Table 8.3 Textile industry standards for water pollutants. Sr. #

Parameters

Standards

1

pH

6.9

2

BOD

30 ppm

3

COD

250 ppm

4

TDS

2000 ppm

5

Sulfide

2 ppm

6

Chloride

500 ppm

7

Calcium

75 ppm

8

Magnesium

50 ppm

In recent years, the wastewater recovery and reuse has gained remarkable attention due to the water shortage.

8.2 Treatment Methods for Textile Effluent The effluent of textile industry has intense color, salt (Total Dissolved Solids (TDS)), and high BOD/COD load [24]. The effluent produced from dyeing industry of cotton fabric is highly contaminated because of the reactive dyes presence that are actually not ready to biological remediation [25]. The effluent having color causes scarceness in light that is vital for the growth of aquatic life. As a consequence, it causes in the loss of natural balance of environment [26]. Hence many treatment methods counting physical, chemical, biological and combine treatment operations have been established to treat wastewater in an effectual manner, economically before its discharge into river (Figure 8.2). These treatments are proved to be extremely powerful for the remediation of effluent [27].

8.2.1 Dealings to Control Water Contamination Some measurements should be taken in order to lessen water contamination for betterment of life. It will be easy to carry over preliminary steps for eliminating hazards before moving into major treatment procedures. The preliminary stages involve the deletion of waste material and extra

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Physical Methods

Screening Coagulation-Flocculation

Sedimentation

Chemical Methods Chemical Precipitation Neutralization Electro Chemical Process Oxidation

Biological Method Bacterial Decolorization Fungal Degradation Algae Degradation Microbial fuel cell

Homogenization Ion Exchange Process

Floatation Adsorption Membrane Processes

Figure 8.2 Various remediation methods for the treatment of textile effluent.

solid substances followed by neutralization of acids and other intermediate components that can be attained properly by pH test or aeration or chemical oxidation methods [28, 29].

8.2.2 Physical Methods 8.2.2.1 Screening Screening is the very first operation used at effluent treatment plants. It is a mechanical procedure which separates the particles on the basis of their size. It eliminates things such as paper, plastics, rags, and metals to avoid damage and blockage of downstream instrument, piping, and appurtenances. There are numerous categories, which have static, vibrating or rotating screens. Screen surfaces have openings size range dependent upon the nature of waste. They must be small enough to hold pieces of cloth in textile dyeing industries, which can damage process instrument, lessen the efficiency of the effluent treatment plant or contaminate waterways. Many latest effluent treatment plants use both coarse screens and fine screens

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together (Fig. 8.3). Bar screens and fine screens that are mechanically cleaned eliminate most of fibers from wastewater. The effluent moving from the textile industry, streams to a collecting pit where a pumping system lifts the wastewater to screen, generally separates solids and the textile fiber by automatic self-cleaning type which fray throughout the various working stages. The effluent flows over the surface of screening though the separated solids are taken by the brushes into a collecting hopper automatically.

8.2.2.2 Coagulation–Flocculation Treatments Coagulation is a chemical rapid mixing technique which is directed toward the destabilization of the charged colloidal particles. It means the process in which agglomeration of dispersed colloidal particles take place. Various coagulants are used in this method. Coagulants may be polymers or metallic salts (such as alum). Polymers are anionic, cationic or nonionic. Coagulants having charges that are opposite to the suspended solids added in effluent to neutralize the negative charges on non-settable dispersed solids like color-producing organic matters and clay. This permits the particles to forms larger clumps by coming together. Cationic coagulants are mostly used for this purpose. By the addition of coagulants, the mixture is quickly mixed to disperse coagulants through the liquid [30]. Flocculation is the gentle mixing technique. Its aim is to carry the colloidal and particulate material into an aggregated term by the agglomeration of the stabilized particles so they can be separated from the process stream with further treatment (Fig. 8.4). Moreover flocculation also permits the suspended particles and dissolved organic substances having high molecular weight to become trapped in the growing floc. Flocculants ease the agglomeration and consequently make bigger floccules. Because of the gravitational oversize

feed

medium

Fine undersize

Figure 8.3 Screening of effluent.

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Advanced Functional Textiles and Polymers +

+ -

+ -

+ (a)

Flocullation Polymer

Suspended particle

+

Agglomerated Particles

(b)

Figure 8.4 (a) Coagulation and (b) Flocculation.

forces, they tend to settle down. Flocculants try to link the molecules establishing clumps. For example an anionic flocculants will react with a positively charge polymer and adsorbs those particles. Both coagulation and flocculation are used for the degradation of disperse dyes from effluent. They actually have less efficiency of degradation for the vat and reactive dyes from the effluent. These methods also restrict their use because of the low degradation proficiency and large sludge production [31, 32]. These techniques are not efficient for deletion of soluble dyestuffs.

8.2.2.3 Sedimentation The fine suspended substance passed over the screens can be eliminated by sedimentation effectively and economically. This is attained in a tank known as the sedimentation tank, clarifier or settling tank. The settling tanks are designed in such a way that the smaller particles are allowed to settle under the effect of gravity. This method is mainly beneficial to treat wastes holding large amount of settlable solids. The stable sludge is taken out from clarifier by mechanical scrapping into hoppers and pumping it out later. Sometimes the sedimentation is collectively used with equalization process. After that, the

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flocs and water flow slowly through the large basins recognized as sedimentation or settling basins. The water moves in very slow manner through these basins, this permits the flocs of large size to settle at bottom of the basin. The large rotating scrapers are used to collect flocs into a hopper where it is taken out numerous times by the plant operators in a day. The clear water streams out of the settling basin and to the filters that are above the floc layer (known as process residuals). The particles in the settling basin are removed, improves the procedure of filters that comprises the next process stages. A comparison of coagulation, flocculation and sedimentation is given in Fig. 8.5.

8.2.2.4 Equalization or Homogenization The various process of the textile dyeing method like pre-treatment, dyeing, and finishing means the effluent quality and quantity changes substantially with time, though wastewater treatment plants are typically designed to treat effluent that has a more or less constant flow and a quality that only varies within a limited range. The wastewater of textile is greatly variable in extent of impurities and sense of pH. The effluents from such individual processes will harshly upset the secondary processes of wastewater treatments. Therefore it is essential to combine the discharges of different operations. The equalization tank does this by gathering and storing the wastewater, permitting it to mix well to make sure that it becomes less variable in composition before it is propelled to the treatment plants at a constant rate [33].

8.2.2.5 Floatation A large quantity of tiny bubbles is generated by floatation to make the three-phase constituents of solid, gas, and water. The pressurized dissolved air can be used to produce the micro-bubbles which combine to particles.

Coagulation

Flocculation

Sedimentation

Figure 8.5 Comparison of coagulation, flocculation, and sedimentation.

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The micro-bubbles, under the influence of interfacial tension, hydrostatic pressure, tendency of bubble rising and different other forces, adhere to the little fibers. The wastes float on the surface because of its less density so the oil particles are removed from the effluent. So this operation can efficiently eliminate the fibers from effluent [33].

8.2.2.6 Adsorption In the physiochemical treatments, adsorption is one of the key operation of filthy solutions. It is a separating tool through which components of liquefied phase are moved to the solid adsorbent’s surface. When a solid is interacting with liquefied phase, the molecules present in the liquid phase are able to accumulate at surface of solid material. Separation happens because of the polarity, variations in molecular mass or shape of certain molecules causes them to be attached more strongly on the surface of adsorbent than remaining or because the pores that are so small to hold the bigger particles [34].

8.2.2.6.1 Mechanism of Adsorption The main steps involves in adsorption of pollutants on adsorbent’s surface are following: 1. Metal ions are transferred from the bulk of liquid to the external side of adsorbent’s surface. 2. Transmission of inner mass through pore diffusion from outer side of adsorbent’s surface to inner surface of the porous structure (Fig. 8.6). 3. Adsorbate adsorb, through the active sites, onto the pores of adsorbent. 4. The overall adsorption rate is directed either by film development or intra particle diffusion. The last two steps are highly faster than other [35].

8.2.2.6.2 Types of Adsorption There are two types of adsorption which are given below. Adsorption at the molecular level arises due to the chemical attractions between a solid surface of adsorbent and adsorbate. 1)

Physical adsorption It occurs by the attractive forces between adsorbent’s molecules and adsorbate surface. The attractive forces present

Remediation of Textile Wastewater Adsorbate

Adsorbent

Figure 8.6 Mechanism of adsorption.

in molecules that grasp the adsorbent on the adsorbate are of physical nature, called vander walls forces (Fig. 8.7). It is reversible operation. The order of magnitudes of interaction energy in between the adsorbent and adsorbate are similar but actually higher as compare to condensation energy of adsorptive. So, activation energy is not required [36].

Physical Adsorption (a)

Chemical Adsorption (b)

Figure 8.7 (a) Physical adsorption. (b) Chemical adsorption.

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Chemical adsorption It occurs due to the chemical bonding between solid and adsorbed matter called activated adsorption as well. It can be exothermic/endothermic procedures ranging from very less to very higher magnitudes. The main step of chemisorption mostly involves large amount of activation energy [37].

8.2.2.6.3 Advantages of Adsorption • • • • • •

Simple design Less cost Highly effective Very less chemical and biochemical sludge production Additional chemical is not required Bio-sorbent regenerate at the end [38, 39]

8.2.2.6.4 Significance of Adsorption Adsorption methods have gained great attention because of their better efficiency of decolorization for effluent comprising multiple dyes. The higher affinity, regeneration ability of the adsorbent and compounds are the key features which must be taken in to account during the selection of adsorbents [40].

8.2.2.6.5 Adsorbents The Activated carbon (AC) is one of the efficient adsorbent adsorb a vast range of dyes. But difficulty in its regeneration and high cost limit its use for degradation [41]. For the economic utilization of the adsorption process, many researchers applied inexpensive adsorbent matter like fly ash, bentonite clay, peat and polymeric resins for the deletion of color from effluent. Different adsorbents with the dye removal efficiency are briefed in Table 8.4 [42]. Adsorbents must be used to practices which have less amounts of contaminants or can be easily regenerated or when the adsorbent is inexpensive [43].

8.2.2.7 Membrane Processes A membrane is acting as an interphase in between two joint phases and as a selective barrier, maintaining the transfer of materials in between two sections. The major advantage of membrane process as compared to other technologies in chemical engineering that are relevant to this unique principle of separation is the transfer selectivity of the membrane. The

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Table 8.4 Different adsorbent and their dye adsorption. Sr. #

Adsorbent

Dye

Reference

1

Coco-peat

Effectively remove methylene blue

[44]

2

Coconut coir dust

Effectively remove methylene blue

[45]

3

Coconut shell charcoal

Efficiently remove basic yellow13 (BY13) and basic red14 (BR14)

[46]

4

Sawdust materials

Efficiently remove Pb2+ and methylene blue

[47]

5

Activated carbon formed from textile sludge

Efficiently remove Reactive Black 5 (RB5) and methylene blue

[48]

6

Powdered eggshell

Effectively remove the congo red dye

[49]

separation with membrane does not need any additives, and they can be carried out at low temperatures isothermally and compared to other thermal filtration procedures consuming low energy (Table 8.4). The up scaling and downscaling of membrane technologies as well as their integration into other reaction or separation techniques are simple [50]. Separation processes like microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are applied to reuse and recover water.

8.2.2.7.1 Mechanism of Membrane Process Membrane technology or treatment operation primarily depends upon three basic principles named as adsorption, sieving and electrostatic phenomena [51]. The mechanism in the membrane separation unit is on the basis of hydrophobic interactions between membrane and analyte (solute). These connections usually prone to more rejection just because it becomes the cause of reduction in the membrane’s pore size [52].

8.2.2.7.2 Types of Membrane Process The material’s separation through the membrane depends upon molecule and pore size [53]. So that, different membrane processes with different mechanism of separation have been established. These are:

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The different membrane processes are:

8.2.2.7.2.1

Microfiltration

Microfiltration (MF) is a pressure driven technique which separate out compounds having sizes in range of 0.1–0.2 μm [54]. Dye baths containing pigment dyes and rinsing baths can be treated using microfiltration. This process may be applied as a pre-treatment to reverse osmosis or nanafiltration to lessen the fouling potential [55]. The central disadvantages of this tool are that it cannot eradicate pollutants (such as dissolved solids) that are less than 1 mm in size. Moreover, it is not a perfect barrier to viruses. Though when applied together with disinfection, it seems to control these microbes in water [55].

8.2.2.7.2.2

Ultrafiltration

Ultrafiltration (UF) membrane technology can separate compounds between the range of 0.005 ≈ 10 μm in size that is in between MF and RO [56]. These membranes are very prominent filters in deletion of pathogenic microbes, suspended maters and macro molecules with less energy consumption as compare to others [57]. Therefore this process has some restrictions including its incapability to eliminate any dissolved inorganic matters from effluent and cleaning on daily basis is to regulate the high pressure flow of water [58]. Mocanu and some other researchers established a synthetic method for hybrid ultrafiltration membrane for wastewater treatment. They applied inversion method in wet-phase with polysulfone and graphene nanoplatelets modified by using poly (styrene) to achieve their membranes. ZnO with polymers which are water soluble was placed on one side of membrane’s surface [59]. In another study described by Igbinigun and other researchers, the modified ultrafiltration membrane showed 2.6 times better flux recovery as compare to the unmodified membrane and this illustrates that it is better to modify membrane to enhance the flux recovery [60]. Therefore water treated by ultra-filtration may be used for minor operations like rinsing and washing where salinity is not a problem. This is a pre-treatment process is applied for reverse osmosis or by combining with biological reactor.

8.2.2.7.2.3

Nanofiltration

Nanofiltration (NF) technique in combination with adsorption can be adopted and the adsorption step proceeds. In terms of environmental

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regulation and an alternative treatment technique nano-filtration is favorable. It has ability of eliminating ions which contribute significantly to osmotic pressure hence permits the operation pressures that are lesser than that reverse osmosis. For nanofiltration to be an effective pre-treatment is required for some heavily contaminated waters. Membranes are actually sensitive to free chlorine. The soluble substances cannot be separated out from water [61, 62]. Xu and other researchers informed NF membrane for treatment of textile effluent, the synthesized membrane exhibited good elimination of heavy metal ions, dyes and common salts presenting high deletion efficiency toward cationic dyes and metal ions [63]. Lin and others reported nanofiltration membranes are for dye (Direct red and Congo red) and salt rejection, the outcomes exhibited high dye rejection and less salt rejection that illustrates the chance to reuse salt in Forward osmosis [64].

8.2.2.7.2.4

Reverse Osmosis

Reverse osmosis (RO) is pressure driven technology applied to eliminate smaller particles and dissolved solids. It is only permeate water molecules. The pressure applied on RO should be sufficient so that water can be able to overcome the osmotic pressure (Fig. 8.8). The RO membrane’s pore structure is much tighter than UF, they transform hard water into soft water and

Pressure

SO4–

Na+

Fe+2

H2 O HCO3–

Feed Flow

H2O

Mg+2 +2

Ca

H2O H2O

H2O H2O H2O

Permeate

Figure 8.8 Mechanism of reverse osmosis.

Concentrated salts

Cl–

H2O

Membrane

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they have ability to remove all particles, bacteria, and organics practically, it needs low maintenance [65, 66]. RO has very small pores size and are able to eliminate components less than 0.1 nm [67]. Huang and some other researchers informed that RO membranes coated with azide functionalized graphene oxide hence formed smooth, hydrophilic and antibacterial membrane that lowered BSA fouling and eliminated Escherichia Coli [68]. This process, for mostly ionic compounds, has a retention rate of 90% and produces excellent permeate quality. In a single step removal of chemical auxiliaries and decoloration, it also removes the hydrolyzed reactive dyes, mineral salts and chemical auxiliaries. Osmotic pressure depends on the concentration of the dissolved salts. Higher the concentration, higher amount of energy is vital for separation operation [69]. 8.2.2.7.2.4.1 Advantages and Disadvantages The membrane processes are advantageous over conventional tools because of its modular design, simple maintenance, no requirement of chemical addition, ease of adaptation to present facilities, less or no accumulation occur in this operation [70]. The disadvantages of membrane process are membrane fouling, use of high pressure and continuous backwashing (that induce greater process costs), and investment costs, high level of pretreatment is required in some cases [71]. A brief comparison of all types of membranes along with their efficiencies is given below in Fig. 8.9.

MF (0.1-1μm)

Suspended solids Bacteria Virus Proteins (Mw > 10k)

UF(0.01-0.1μm) Trace Organics (Mw > 200 Divalent ions NF(1-10nm) Trace Organics (Mw >100 Monovalent ions RO (nonporous)

H2O Charge neutral organics Mw chitosan > O-carboxymethylated chitosan [201]. Enhanced proliferation of fibroblast and keloid formation was observed to intensify the cytocompatibility. Treatment of TMC with CH3COOH and NMP at pH 10.0 results in formation of O-carboxymethyl-N, N, N-trimethyl chitosan [202]. Precise and accurate monitoring of each and every step of reaction is required because chitosan encompasses C3 and C6 as carboxymethylation sites which may get hindered by O-methylation posing hindrance for additional substitutions [203].

13.4.2.9

Peptides Conjugates-Chitosan/Derivatives for Wound Healing

Wound healing can be speed up by using an exclusive method. In this method other than soaking with biochemical factors, functionalizing of the scaffolds with peptides takes place. Dressing material attachment with extracellular components of skin could be improved by peptide-conjugated scaffold material. Fast and complete healing of traumatic wounds is results of increasing quick migration cell differentiation with enriched

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proliferation observed in L929 fibroblast (mouse). Conjugation of extracellular matrix with RGD (arginine/glycine/aspartate) signaling peptides enhances cell adhesion and activates Rho GTPase pathway leads to activation of integrin resulting in enhanced cell adhesion [204, 205]. The impregnated chitosan scaffolds with RGD sequence elevates cell adhesion and biocompatibility and was recognized by the receptors [206]. Therefore, the functionalized 3-D scaffold of chitosan aids as an ancillary to the ECM [207]. Tryptophan impregnated with carboxymethyl-trimethyl chitosan has been employed in delivery of genetic material, conjugation of two or more peptides and site-specific drug delivery [208]. To obtain a more optimized and stable product TMC complexed with CMC by using succeeding derivatization [209]. PEC (polyelectrolyte complex) was a product obtained by the conjugation of GRGDS (Gly–Arg–Gly–Asp–Ser) peptide with CMTMC (carboxymethyl-trimethyl-chitosan) it enhances cell adhesion and migration. Ionic complexation method was used for production of nanoparticles with wound healing efficacy impregnated with chondroitin sulfate [210]. Enhanced adhesion of fibroblast and dermal fibroblast was found to be dispersed three-fold with the application of active peptide functionalized scaffolds. These afore mentioned reports supports important and favorable use of modified and biologically active chitosan and its derivatives facilitated tissue engineering.

13.4.2.10

Commercial Dressing Bandages of Chitosan Blend

Chitosan along with its derivatives appeared as an outstanding biopolymer of natural origin to be fabricated in form of commercial dressing bandage. Chitipack P (Eisai Co.) (Bloated chitin fortified over poly (ethylene terephthalate) and ChitipackS are very popular for their efficacy as commercial dressing bandage. ChitipackS has ability to promote early granulation, therefore it is used to treat traumatic wound and surgical tissue defects, while Chitipack P was mainly used to cover open cut wounds affecting a wider area. Syvek–Patch (reinforced chitin fibrils) developed and owned by Marine Polymer technologies, was used to speed up hemostatic processes [211]. HemCon (freeze dried chitosan salt) capable of producing hemostatic effect as well as prevents supra-infection, was used enormously during civil medical emergency [212–214]. It is effectively used as an anti-infective dressing patch on in burns wound management and maintains the structural integrity and mucosal adhesiveness of chitosan at the injury site. Improvement in structural rearrangement of tissues, reepithelialization and accelerated healing of wounds has been markedly shown by

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meshed chitosan membrane [215]. Kratz et al. developed a reinforced heparin–chitosan membrane to evaluate the wound healing efficacy in skin of donors [216]. Damour et al. developed a novel approach to substitute dermis of skin using a dermal substrate [217], which aims at promoting neovascularization as well as precise and measured colonization of fibroblast manifolds [218].

13.5 Future Prospects Chitosan nanocomposites not only possess unique properties to be used for various applications but also safe for environment after their disposal. Being a natural biopolymer chitosan nanocomposites are biocompatible, hydrophilic, biodegradable, non-toxic, cost effective and efficient in basic as well as neutral pH due to which versatile applications are possible. The abundance and the renewability along with the ease in modification as per the requirement geared up the research in the direction of biopolymers. With the arrival of benign synthesis methods of chitosan nanocomposites along with the efficient functionalization develops the curiosity of further exploration of this biomolecule for further advancement in the technology. The promising potential of chitosan based nanocomposites can be further improved by improving their coagulation–flocculation efficacy and absorbance to improve waste water treatment, bioremediation and biosensor development. We could develop cost effective methods for various contaminants and deal with the pollution efficiently. Furthermore, the antibacterial strength of the fabric could be improved further after more exploration by changing different functional groups of the molecule. The scope of betterment is still present regarding the various applications without posing any serious threat to the environment. State-of-the-art technologies and innovative solutions implemented at industrial processing centers to introduce commercial feasibility of sustainable biopolymer in real market is still an economical challenge. However, fabrication and manufacturing of these biopolymers into bioactive functional textile is a promising prospect. Further insightful investigation is required to render biopolymer potential into industrial realism. These encouraging investigation leads to improvement in studies oriented toward procurement of novel sources, low cost intensive extraction process, and implementation of innovative method which could provide alternatives to harmful synthetic antimicrobial mediators. Hence, functional textiles of bioactive origin may accomplish the need of consumers and

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fulfill their demand of safe, healthier, and ecofriendly product capable of promoting well-being in near future.

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162. Gonzalez, J.S., Maiolo, A.S., Ponce, A.G., Alvarez, V.A., Composites based on poly(vinyl alcohol) hydrogels for wound dressing. XVIII. The Argentine Congress of Bioengineering and Clinical Engineering Conference VII, SABI, pp. 1–4, 2011. 163. Kweon, D.K., Song, S.B., Park, Y.Y., Preparation of water-soluble chitosan/heparin complex and its application as wound healing accelerator. Biomaterials, 24, 1595, 2003. 164. Rui, Z., Xiang, L., Bolun, S., Ying, Z., Dawei, Z., Zhaohui, T., Xuesi, C., Ce, W., Electrospun chitosan/sericin composite nanofibers with antibacterial property as potential wound dressings. Int. J. Biol. Macromol., 68, 92, 2014. 165. Nishimura, S., Kai, H., Shinada, K., Yoshida, T., Tokura, S., Kurita, K., Regioselective syntheses of sulfated polysaccharides: Specific anti-HIV-1 activity of novel chitin sulfates. Carbohydr. Res., 306, 427, 1998. 166. Fwu, L.M., Yu, B.W., Shin, S.S., Chao, A.C., Juin, Y.L., Chia, C.S., Asymmetric chitosan membranes prepared by dry/wet phase separation: A new type of wound dressing for controlled antibacterial release. J. Membr. Sci., 212, 237, 2003. 167. Meng, X., Tian, F., Yang, J., He, C.N., Xing, N., Li, F., Chitosan and alginate polyelectrolyte complex membranes and their properties for wound dressing application. J. Mater. Sci. Mater. Med., 21, 1751, 2010. 168. Wang, L.S., Khor, E., Wee, A., Lim, L.Y., Chitosan-alginate PEC membrane as a wound dressing: assessment of incisional wound healing. J. Biomed. Mater. Res., 63, 610, 2002. 169. Mi, F.L., Wu, Y.B., Shyu, S.S., Schoung, J.Y., Huang, Y.B., Tsai, Y.H., Hao, J.Y., Control of wound infections using a bilayer chitosan wound dressing with sustainable antibiotic delivery. J. Biomed. Mater. Res., 59, 438, 2002. 170. Pang, H.T., Chen, X.G., Ji, Q.X., de Zhong, Y., Preparation and function of composite asymmetric chitosan/CM-chitosan membrane. J. Mater. Sci. Mater. Med., 19, 1413, 2008. 171. Radhakumary, C., Antonty, M., Sreenivasan, K., Drug loaded thermoresponsive and cytocompatible chitosan based hydrogel as a potential wound dressing. Carbohydr. Polym., 83, 705, 2011. 172. Yajing, Y., Xuejiao, Z., Caixia, L., Yong, H., Qiongqiong, D., Xiaofeng, P., Preparation and characterization of chitosan-silver/hydroxyapatite composite coatings on TiO2 nanotube for biomedical applications. Appl. Surf. Sci., 332, 62, 2015. 173. Madhumathi, K., Sudheesh Kumar, P.T., Abilash, S., Sreeja, V., Tamura, H., Manzoor, K., Nair, S.V., Jayakumar, R., Development of novel chitin/ nanosilver composite scaffolds for wound dressing applications. J. Mater. Sci. Mater. Med., 21, 807, 2010. 174. Chen, M., Yang, Z., Wu, H., Pan, X., Xie, X., Wu, C., Antimicrobial activity and the mechanism of silver nanoparticle thermosensitive gel. Int. J. Nanomedicine, 6, 2873, 2011.

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14 Use of Polymer Nanocomposites in Asphalt Binder Modification Saqib Gulzar* and Shane Underwood Department of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, USA

Abstract Polymer nanocomposites (PNCs) are a class of innovative modifiers used to improve the performance and rheological properties of asphalt binders. PNCmodified binders are intended for use in the construction of high quality pavements which can durably withstand increasing vehicular loads under changing climatic conditions. Such pavements are subject to very high stresses and strains as such the response of such binders under high stresses/strains needs to be evaluated. In this chapter, a concise overview of PNC-modified binders is given, followed by their preparation methods and diverse applications in improving asphalt rheology are highlighted. Further, a large amplitude oscillatory shear protocol is presented to evaluate nonlinear response of PNC-modified binders under high stresses/strains. It has been seen that PNC-modified binders show better rheological characteristics, temperature susceptibility, and performance over conventional unmodified binders. Keywords: Polymer nanocomposites, asphalt, SARA, rutting, preparation, LAOS testing

14.1 Introduction Asphalt binders have been extensively used in road construction industry for many decades [1]. The amount of asphalt binders in a mix is relatively small, around 7% by weight, yet their effect on pavement performance is

*Corresponding author: [email protected] Shahid-ul-Islam and B.S. Butola (eds.) Advanced Functional Textiles and Polymers, (405–432) © 2020 Scrivener Publishing LLC

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huge. This is attributed to the higher dependence of asphalt binder properties on traffic and climatic variations such as temperature and moisture changes over aggregates which form the skeleton of asphalt concrete mix. Conventional asphalt binders, also referred to as unmodified binders have been used in the construction of pavements under normal traffic and environmental conditions [2]. In the USA, these binders have been used in the base, intermediate, and surface courses of a pavement structure. However, their performance has not been satisfactory under high traffic and changing climatic conditions. Many pavements constructed using unmodified binders have been reported to fail prematurely due to rutting, fatigue, and/ or thermal cracking. In order to enhance the resistance of the pavement to these distresses, modification of asphalt binders is done to reduce rutting, fatigue damage, thermal cracking, stripping, and other major distresses. The modified asphalt concrete mixes have been extensively used in the construction of airport runways, national highways, high freight traffic routes, intersections, vehicle stations, etc. Further, these modified systems are used in surface and wearing courses of a pavement structure to enhance durability and provide seamless ride quality. Apart from improving the performance characteristics of the asphalt concrete, other additives are also added based on different requirements such as antistripping agents like hydrated lime and amine based liquids, and workability enhancers like waxes and surfactants. Among the performance enhancers, the most common modifiers are polymers and crumb rubber. These impart elasticity to the mix, improve its durability and temperature susceptibility, besides improving the performance under high and repeated traffic loads, as well as under extreme weather conditions. Polymer modified asphalt binders have a proven record of improving the pavement performance [3]. Polymer nanocomposites (PNCs) are an additional class of enhanced polymers used in the modification of asphalt binders very recently [4]. These are reported to influence the rheological properties of asphalt binders. The focus of this chapter to present an overview of PNC modified asphalt binders along with the preparation methods, characterization techniques, and rheological measures used. Section 14.2 provides a background on asphalt binders and their chemical composition. Sections 14.3 and 14.4 explain the modification process of asphalt binders, in general and with respect to PNCs in particular, respectively. Section 14.5 describes the rheological measures used for PNC-modified asphalt binders and argues for the need to investigate mechanical response of such binders under high stresses/ strains. Section 14.6 gives an overview of nonlinear rheological protocol and Section 14.7 outlines a framework for evaluating the properties of PNC-modified asphalt binders. These binders are still a matter of academic

Polymer Nanocomposites in Asphalt Binder Modification 407 discussion and come under a class of innovative asphalt binders which may be used in practice in the future.

14.2 Background Asphalt is a petroleum by-product and is commonly referred to as asphalt binder in the field of pavement engineering, since it binds the aggregate particles together in an asphalt concrete mixture. These mixtures form the surface, intermediate, and in some cases base layers of a flexible pavement. Asphalt is a temperature sensitive material and is semisolid or solid at ambient temperature while liquid at high temperatures. Asphalt binders vary based on source and refining processes, and are graded using rheological based characterization tests. Since the properties of asphalt are influenced by temperature and rate of loading, these tests must capture the effects of variation in temperature and rate of loading on the mechanistic and/or index properties of these binders. These properties are essential from the manufacturing (construction and mix design), but also the long-term performance of asphalt concrete mixtures. In the construction process, the asphalt binder is first transported from the petroleum refinery followed by mixing and storing at the plant. Depending upon the type of construction, the binder is pumped through pipes and mixed with aggregates at the plant or on site. In the former case, the mix is transported to the construction site to be laid down and compacted by the rollers. The mixing and compaction temperatures are specific to the binder and should be such that each step is done in an optimal and efficient manner. In the mix design process, asphalt binder is required to blend well with the aggregates to produce a design mix, which when it is laid on the road is capable of withstanding the design traffic under varied climatic conditions during the design life of a pavement. Thus, an asphalt binder must be characterized properly at varied temperatures and loading rates to ensure that both construction process and mix design process produce the best possible results. In other words, the asphalt binder has to be sufficiently fluid-like at high temperatures to be pumpable and workable in order to ensure complete coating of aggregates with asphalt binders during the mixing process. These should also be stiff enough to resist permanent deformation (rutting) at the highest in-service pavement temperatures, as well as soft enough to resist cracking at intermediate and low in-service pavement temperatures. As a result, there are different paving grades of asphalt binders suitable for different regions, where stiffer binders are used for hotter climates and softer binders are used for colder climatic regions. Asphalt binders are graded

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by using different grading systems such as penetration grading system, viscosity grading system, and the most recent superpave grading system. In the Superpave grading system, the binders are graded based on performance at high, intermediate, and low temperatures. A binder is grades as PG HT-LT where HT is the highest temperature and LT is the lowest temperature. Depending on geographical and climatic conditions, the high temperature and low temperature grades vary. In the case of the US, the high and low temperature grade requirement spatial variations at 98% reliability are shown in Figures 14.1 and 14.2, respectively.

14.2.1

Asphalt Binders

Asphalt binders are a class of complex viscoelastic materials, whose rheological behavior plays a deterministic role in their pavement performance [5–8]. Asphalt binders are mainly composed of carbon and hydrogen atoms, typically by 81–89% by weight and 7–12% by weight respectively. As a results, asphalt binders are predominantly composed of hydrocarbons, with a H/C molar ratio of around 1.5, which is in between that of aromatics(H/C~1) and saturates(H/C~2) [9–11]. Further, these also consist of other elements such as sulfur, nitrogen, oxygen, along with traces of some metals such as vanadium, nickel, manganese, etc. The complexity of asphalt binders comes from it chemical composition and viscoelastic nature. The asphalt binders used in the Strategic Highway Research Program (SHRP) in the USA came from different sources and had different

High Pav. Temp. (98% Reliability)

76 70 64 58 52 46 40

Figure 14.1 High temperature binder grade requirement across USA (Source: LTTPBind).

Polymer Nanocomposites in Asphalt Binder Modification 409

Low Pav. Temp. (98% Reliability) –52 –46 –40 –34 –28 –22 –16 –10

Figure 14.2 Low temperature binder grade requirement across USA (Source: LTTPBind).

C

H

O

N

S

100% 80% 60% 40% 20% 0% Canada

USA

Canada

USA

USA

USA

Venezuela

USA

AAA-1

AAB-1

AAC-1

AAD-1

AAF-1

AAG-1

AAK-1

AAM

Figure 14.3 Elemental composition of SHRP asphalt binders (Data from [12]).

elemental composition. Figure 14.3 shows the basic elemental composition of the asphalt binders used in SHRP in terms of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). As can be seen, all binders are mostly composed of carbon and hydrogen with traces of other elements. These chemical elements constitute the molecular structures which are affected by the aging phenomena, temperature conditioning, and when put

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in place, by loading and climatic conditions [13, 14]. The internal structure of asphalt binder keeps on changing from its source extraction, to the refinery, storage, and transportation to the mixing plant, and final mixing to produce hot mix asphalt concrete. This is due to repeated cooling and heating cycles at different stages in the entire process. So, identifying these complex molecular forms is very difficult, and attempts to establish correlations between chemical elements and performance have not been very successful [14]. Rather correlating chemical composition and asphalt binder properties based on polar fractions has gained wide spread acceptance in pavement engineering community [15, 16]. The chemical fraction method for deciphering asphalt binder chemical composition is called SARA fractionalization method. According to this method, asphalt binder is composed of four fractions, Saturates (S), Aromatics (A), Resins (R), and Asphaltenes (A). Saturates have a very low glass transition temperature of around −70°C and are mainly composed of linear alkanes and branched long chain aliphatic chains. However, these may contain very few polar rings as well. Saturates are almost colorless and maintain a liquid state at room temperature. Aromatics are denser than saturates and carry a yellowish to reddish tint in liquid state at room temperature. These are mainly composed of aromatic chains, and comparatively are usually the most abundant fraction in an asphalt binder. Resins are moderately polar and solid like with a blackish tint at room temperature. These are mainly composed of fused aromatic rings, and act as a stablizers for asphaltenes. Hence, resins play a vital role in overall stability of an asphalt binder. Finally, asphaltenes are n-heptane insoluble part of asphalt binder which are thermally stable dark black powder over the normally investigated temperature range. Asphaltenes

Saturates

Aromatics

Resins

Asphaltenes

Figure 14.4 SARA fractions dissolved in different solvents (Image taken from [16]).

Polymer Nanocomposites in Asphalt Binder Modification 411 are polar in nature. Figure 14.4 shows the image of all the four SARA fractions [11]. It can be seen that each fraction can be distinguished by its color and form. These SARA fractions are obtained by exploiting their solubility in different solvents. Zhang et al. [16] extracted thee SARA fractions from asphalt binder using an experimental scheme shown in Figure 14.5. The functional SARA components of SHRP asphalt binders are shown in Figure 14.6. It can be seen that all of the binders are mostly composed of aromatics and resins, followed by asphaltenes, while saturates occur in the least [12]. These fractions are interconvertible and undergo physical and chemical transformation upon temperature changes and oxidative aging processes. Saturates have the least while asphaltenes have the highest molecular weights, however, physiochemical properties vary from fraction to fraction. Resins contain the least saturated hydrocarbons while thermal stability follows the order: Saturates