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Textiles and clothing : environmental concerns and solutions
 9781119526599, 1119526590, 9781119526629, 1119526620, 9781119526667, 1119526663, 9781119526315

Table of contents :
Content: Introduction to textiles and the environment --
Synthetic dyes : a threat to the environment and water ecosystem --
In search of natural dyes towards sustainability from the regions of Africa --
Revitalization of carotenoid-based natural colorants in applied field : a short review --
Environmentally sound dyeing of cellulose-based textiles --
Environment-friendly textile finishing --
Functional finishes for cotton-based textiles:current situation and future trends --
Remediation of textile effluents via physical and chemical methods for a safe environment --
Advanced oxidation process for the remediation of textile dyes : an experimental study --
Recent advances in the processing of modern methods and techniques for textile effluent remediation : a review --
Removal of heavy metal ions from wastewater using micellar-enhanced ultrafiltration technique (MEUF) : a brief review.

Citation preview

Textiles and Clothing

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

Textiles and Clothing Environmental Concerns and Solutions

Edited by

Mohd Shabbir

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 © 2019 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: Shabbir, Mohd (Chemist), editor. Title: Textiles and clothing : environmental concerns and solutions / edited by Mohd Shabbir. Description: Hoboken, New Jersey : John Wiley & Sons, Inc. ; Salem, Massachusetts : Scrivener Publishing, LLC, [2019] | Includes bibliographical references and index. | Identifiers: LCCN 2019009264 (print) | LCCN 2019012287 (ebook) | ISBN 9781119526667 (ePDF) | ISBN 9781119526629 (ePub) | ISBN 9781119526315 (hardback) Subjects: LCSH: Textile industry--Waste disposal. | Textile industry--Environmental aspects. | Textile chemicals--Environmental aspects. | Dyes and Dyeing--Environmental aspects. | Textile fabrics. | Factory and trade waste--Environmental aspects. | Heavy metals--Environmental aspects. Classification: LCC TD899.T4 (ebook) | LCC TD899.T4 T49275 2019 (print) | DDC 677.0028/6--dc23 LC record available at https://lccn.loc.gov/2019009264 Cover image: Pixabay.Com Cover design by Russel 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

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1 Introduction to Textiles and the Environment Mohd Shabbir and Masoom Naim 1.1 Introduction 1.2 Textile Fiber Manufacturing/Processing and the Environment 1.3 Textile Finishing and the Environment 1.4 Dyeing and the Environment 1.5 Technologies and Methods to Cure the Textile-Infected Environment 1.6 Reuse of Wastewater from the Textile Industry 1.7 Conclusion and Perspectives References 2 Synthetic Dyes: A Threat to the Environment and Water Ecosystem Mohd Yusuf 2.1 Introduction 2.2 Environmental Hazards Parallel to Dye Applications 2.2.1 Impact on Human Health 2.2.2 Impact on Growth of Crops and Plants 2.2.3 Impact on Water Ecosystem 2.3 Regulations and Toxicological Prospects of Synthetic Dyes 2.4 Conclusion and Future Prospects References 3 In Search of Natural Dyes Towards Sustainability from the Regions of Africa (Akebu-Lan) S. Anuradha Jabasingh 3.1 Role of Natural Dyes in the Tradition of the African Continent 3.2 Indigenous Sources of Natural Dyes 3.3 Dyeing and Processing Techniques

1 1 3 4 4 5 7 7 8 11 11 12 13 15 16 18 23 24 27 28 30 34 v

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Contents 3.4 Fashion Fabric with Natural Colors 3.5 Natural Shades for Environmental Sustainability: Application Aspects 3.6 Conclusions References

4 Revitalization of Carotenoid-Based Natural Colorants in Applied Field: A Short Review Fazal-ur-Rehman, Shahid Adeel, Kaleem Khan Khosa, Mahwish Salman, Atta-ul-Haq and Sana Rafi 4.1 Introduction of Natural Dyes 4.2 Carotenoids as Natural Colorant 4.3 Classification of Carotenoids 4.3.1 Structure-Based Carotenoids 4.3.1.1 Carotene 4.3.1.2 Xanthophylls 4.3.2 Color 4.3.2.1 Red 4.3.2.2 Yellow 4.3.2.3 Orange 4.4 Sources of Carotenoids as Natural Pigment 4.4.1 Plants 4.4.2 Microorganisms 4.5 Functional Assets of Carotenoids 4.5.1 Antioxidant Activity 4.5.2 Antimicrobial Activity 4.5.3 Photoprotection Property 4.6 Extraction Phenomenon of Carotenoids 4.6.1 Conventional Methods 4.6.1.1 Solvent Method 4.6.1.2 Soxhlet Method 4.6.2 Advanced Methods 4.6.2.1 Supercritical Fluid Method 4.6.2.2 Pressurized Liquid Extraction (PLE) 4.6.2.3 Ultrasound Method 4.6.2.4 Microwave Radiation 4.6.2.5 Ultraviolet Radiation 4.6.2.6 Gamma Radiation 4.7 Potential Resurgence of Carotenoids in Textile 4.7.1 Marigold 4.7.2 Saffron

36 41 42 42 45

46 46 48 48 48 50 53 53 53 54 54 54 56 57 58 59 60 60 60 61 61 61 62 63 63 64 64 64 65 65 66

Contents vii 4.7.3 Pepper 4.7.4 Annatto 4.7.5 Tomato 4.7.6 Delonix regia 4.7.7 Sweet Potato 4.8 Conclusion Acknowledgments References

67 67 68 68 68 68 69 69

Environmentally Sound Dyeing of Cellulose-Based Textiles Nabil A. Ibrahim, Basma M. Eid and Tawfik A. Khattab 5.1 Introduction 5.2 Cellulose-Based Textiles 5.3 Common Preparation Processes and Environmental Impacts 5.4 Dyeing of Cellulosic Substrates 5.5 Environmental Impacts of Conventional Dyeing 5.6 Cleaner Production Opportunities 5.7 Future Trends References

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6 Environmentally-Friendly Textile Finishing Mohammad Tajul Islam and Syed Asaduzzaman 6.1 Use of Enzymes in Textile Finishing 6.1.1 Bio-Polish 6.1.2 Anti-Felting 6.1.3 Denim Washing 6.1.4 Hydrophilic Finishing 6.2 Easy Care 6.2.1 Finish Containing Low “Free Formaldehyde” 6.2.2 Non-Formaldehyde Finish 6.3 Softening Finishes 6.4 Repellent Finishes 6.4.1 Short-Chain Fluorocarbon 6.5 Flame-Retardant (FR) Finish 6.5.1 Replacing Bromine 6.5.2 Replacing Formaldehyde Chemistry 6.5.3 Novel Surface Chemistries 6.6 Ultraviolet (UV) Protection Finish 6.7 Plasma Treatment 6.7.1 Plasma Application on the Finishing of Natural Fibers 6.7.2 Plasma Application on the Finishing of Synthetic Fibers

101

5

79 80 81 82 84 88 89 95

101 102 104 105 107 107 108 108 110 113 114 115 117 118 119 119 120 121 121

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Contents 6.8 Energy-Efficient and Water-Saving Finishing Processes 6.8.1 Low Wet Pickup Methods 6.8.2 Hotmelt Polymers/Adhesives 6.8.3 Minimization of Energy Consumption of Stenter Frames 6.8.4 Emerging Processes References

7 Functional Finishes for Cotton-Based Textiles: Current Situation and Future Trends Nabil A. Ibrahim, Basma M. Eid and Samar M. Sharaf 7.1 Introduction 7.2 Easy Care Finishing 7.2.1 Essential Properties of Finishing Agent 7.2.2 Current Easy Care Finishing Agent 7.2.3 Cross-Linking of Cellulose Structure 7.2.4 Test Method 7.3 Softening Finishes 7.3.1 Desirable Properties 7.3.2 Classification 7.3.3 Chemical Structures 7.3.4 Silicone Softeners 7.3.4.1 Molecular Size 7.3.4.2 Reactivity 7.3.4.3 Chemical Structure 7.3.5 Mode of Interaction 7.3.6 Evaluation of the Performance of the Soft Finish 7.4 Hydrophobic and Oleophobic Functional Finishes 7.4.1 Mode of Actions 7.4.2 Water- and Oil-Repellent Finishing Agents 7.4.3 Test Methods 7.5 Flame-Retardant Functional Finish 7.5.1 Factors Affecting Functionalization 7.5.2 Major Requirements 7.5.3 Mode of Action 7.5.4 Flame-Retardant Types 7.5.5 Test Methods 7.6 Antimicrobial Finish 7.6.1 Mode of Action 7.6.2 Requirement of Antimicrobial Finishes 7.6.3 Antimicrobial Agents

122 122 123 123 124 124 131 131 133 134 134 134 140 140 141 142 142 142 142 147 147 147 147 150 150 151 151 151 155 155 155 157 160 160 160 161 161

Contents ix 7.6.4 Methods of Application 7.6.5 Test Methods 7.7 UV Protection Functional Finishes 7.7.1 Factors Affecting UV-Blocking Ability 7.7.2 UV-Protection Mechanisms 7.7.3 Application Methods 7.7.4 Evaluation of UV-Protection Textiles 7.8 Recent Developments in Functional Finishes 7.9 Future Trends References 8 Remediation of Textile Effluents via Physical and Chemical Methods for a Safe Environment Shumaila Kiran, Sofia Nosheen, Shazia Abrar, Sadia Javed, Nosheen Aslam, Gulnaz Afzal, Ikram Ahmad and Farhat Ijaz 8.1 Physical Methods for the Wastewater Treatment Processes 8.1.1 Screening Removal System 8.1.1.1 Types of Screens 8.1.1.2 Coarse Screens 8.1.1.3 Cleaned Screens through Hand 8.1.1.4 Cleaned Screens through Mechanical Process 8.1.1.5 Fine Screens 8.1.1.6 Micro Screens 8.1.2 Grit Chamber 8.1.3 Skimming Tank 8.1.4 Solids Separation through Sedimentation 8.1.4.1 Parameters Influencing Sedimentation 8.1.4.2 Types of Sedimentation Tank 8.1.5 Filtration 8.1.5.1 Membrane Technology 8.1.5.2 Microfiltration 8.1.5.3 Ultrafiltration (UF) 8.1.5.4 Nanofiltration 8.1.6 Reverse Osmosis 8.1.7 Adsorption 8.1.7.1 Adsorption by Activated Carbon (AC) 8.1.7.2 Adsorption by Peat 8.1.7.3 Absorption by Wood Chips 8.1.7.4 Adsorption by Fly Ash and Coal (Mixture) 8.1.7.5 Adsorption by Silica Gel

161 161 168 168 168 168 171 171 171 179 191

192 192 192 193 193 193 194 195 195 196 197 197 197 198 199 200 200 201 202 203 204 205 205 206 207

x

Contents 8.1.8 Electro-Kinetic Coagulation 8.1.9 Coagulation and Flocculation 8.1.10 Ion Exchangers 8.2 Chemical Methods for Wastewater Treatment 8.2.1 Precipitation 8.2.2 Flotation 8.2.3 Neutralization 8.2.4 Oxidation/Reduction 8.2.5 Advanced Oxidation Process 8.2.6 Cucurbituril 8.2.7 Ozonation 8.2.8 Photochemical Process 8.2.9 Chlorination 8.3 Conclusion Acknowledgments References

9 Fenton and Photo-Fenton Oxidation for the Remediation of Textile Effluents: An Experimental Study Zubera Naseem, Haq Nawaz Bhatti, Munawar Iqbal, Saima Noreen and Muhammad Zahid 9.1 Introduction 9.2 Materials and Methods 9.3 Results and Discussion 9.3.1 Effect of pH 9.3.2 Effect of Contact Time 9.3.3 Effect of Fe+2 Concentrations 9.3.4 Effect of H2O2 Dose 9.3.5 Effect of Initial Dye Concentration 9.3.6 Effect of Temperature 9.3.7 Effect of UV Radiation 9.4 Kinetic Modeling 9.4.1 Comparison of First-Order, Second-Order, and Behnajady–Modirshahla–Ghanbery Kinetic Models for AO3 9.4.2 Comparison of First-Order, Second-Order, and Behnajady–Modirshahla–Ghanbery (BMG) Kinetic Models for AY 216 at Different Intensities of UV Radiation at a Wavelength of 365 nm 9.5 Conclusions References

207 208 209 211 211 211 212 212 213 213 216 218 220 221 222 222 235

236 237 237 237 239 240 241 242 243 244 245

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247 247 249

Contents xi 10 Recent Advances in the Processing of Modern Methods and Techniques for Textile Effluent Remediation—A Review Sabiyah Akhter, Luqman Jameel Rather, Showkat Ali Ganie, Ovas Ahmad Dar and Qazi Parvaiz Hassan 10.1 Introduction 10.2 Pollution Problems with Associated Human Health and Environmental Risks 10.3 Types of Textile Effluents 10.4 Effluent Treatment 10.5 Traditional/Conventional Physicochemical Methods for Effluent Removal 10.5.1 Physical Methods 10.5.1.1 Adsorption Process 10.5.1.2 Irradiation 10.5.1.3 Electro-Kinetic Coagulation 10.5.1.4 Membrane Filtration/Separation 10.5.2 Chemical Methods (Advanced Oxidative Processes) 10.5.2.1 H2O2–Fe (II) Salts (Fenton’s Reagent) 10.5.2.2 Ozonation 10.5.2.3 Photochemical Oxidation 10.5.2.4 Sodium Hypochlorite 10.5.2.5 Electrochemical Oxidation 10.6 Biopolymers as Potential Wastewater Management Alternative 10.7 Conclusion Acknowledgment References

253

254 254 260 261 262 262 262 265 266 266 267 268 269 270 271 271 272 276 277 278

11 Removal of Heavy Metal Ions from Wastewater Using MicellarEnhanced Ultrafiltration Technique (MEUF): A Brief Review 289 Amnah Yusaf, Shahid Adeel, Muhammad Usman, Asim Mansha and Matloob Ahmad 11.1 Introduction 290 11.2 Removal of Single Metals by MEUF 291 11.2.1 Removal of Arsenic 291 11.2.2 Removal of Cadmium 292 11.2.3 Removal of Copper 294 11.2.4 Removal of Chromium 295 11.2.5 Removal of Uranium 295 11.2.6 Removal of Gold 295 11.2.7 Removal of Iron 296

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11.3

11.4 11.5 11.6 Index

11.2.8 Removal of Lead 11.2.9 Removal of Nickel 11.2.10 Removal of Manganese 11.2.11 Removal of the Platinum Group 11.2.12 Removal of Americium 11.2.13 Removal of Aluminum 11.2.14 Removal of Palladium 11.2.15 Removal of Zinc 11.2.16 Removal of Metals in the Presence of Other Metals Factors Affecting the Efficiency of MEUF 11.3.1 Effects of Surfactant Concentrations 11.3.2 The Effect of Ratio of Concentration of Surfactant to Metal Ion (S/M) 11.3.3 The Effect of Mixed Micellization 11.3.4 Effect of pH Value 11.3.5 Effects of Electrolytes 11.3.6 Effects of Transmembrane Pressure 11.3.7 Effect of Temperature 11.3.8 Effect of Nature of Membrane 11.3.9 The Effect of Concentration of Metal Ion in Feed 11.3.10 The Effect of Operating Time 11.3.11 The Effect of Rate of Feed Flow 11.3.12 Effect of Applied Pressure 11.3.13 Effect of Initial Concentration of Metal Ions Surfactant Recovery from Retentate Summary (in Tabulated Form) Conclusions References

296 297 298 298 298 298 298 299 299 301 301 302 302 302 303 303 304 304 304 305 305 305 306 306 306 310 310 317

Preface Counted among mankind’s other basic needs, the fascination with textiles and clothing has resulted in a great amount of attention being invested in their evolution, which in turn has had a direct effect on environmental ecosystems. Due to current worldwide concern for these ecosystems, the impact that the manufacturing, finishing, and utilization of textile fibers has on the environment needs to be addressed. Since it is imperative that environmental rehabilitation occur, there is a demand for more sustainable green processes in the textile and clothing industry. Therefore, greater emphasis needs to be placed on research into eco-friendly processes particularly suited for this industry. With this goal in mind, all environmental aspects relating to the textile and clothing industry are discussed in this book. Included in the 11 informative chapters herein are topics covering the correlation between the environment and the processing and utilization of textiles and clothing. Chapter 1 discusses the direct impact that the textile industry has on the environment. The hazardous environmental consequences that synthetic dyes used to color textiles have on the environment are highlighted in Chapter 2. Greener alternatives to dyeing are discussed in Chapters 3 through 5, and eco-friendly ways of finishing textiles are discussed in Chapters 6 and 7. Finally, solutions to address the environmental hazards associated with the textile industry are presented in Chapters 8 through 11. Textiles and Clothing: Environmental Concerns and Solutions is a book that will definitely be helpful in achieving a more sustainable textile industry, and researchers from both textile and environmental domains can benefit from reading it. In conclusion, this is the perfect opportunity for me to thank all the eminent authors for their contributions to this book. I am very sure that the readers will benefit from their insights. I also wish to express my appreciation to my

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colleagues for their invaluable suggestions and to my family for their moral support. In particular, I would like to express my gratitude and appreciation to Scrivener Publishing for agreeing to the compilation of this book. Dr. Mohd Shabbir March 2019

1 Introduction to Textiles and the Environment Mohd Shabbir1* and Masoom Naim2 1

2

Department of Chemistry, Sanskriti University, Mathura, UP, India Department of Applied Sciences, Satya Group of Institutions, Palwal, India

Abstract The textile industry highly influences the environment, whether it is due to dyeing or manufacturing of the textiles, and it is considered as the number one pollutant after agriculture. Clothing is a basic need for everyone, and a lot of choices are there when it comes to clothing. Huge consumption of water and discharging of effluents from textile manufacturing and dyeing units lead to environmental hazards. Recent past evidences of increased awareness about ecofriendly techniques and products for textiles industry, supplement the research motivation towards ecofriendly textiles. This chapter is about the relationship of textiles and the environment and describes the various aspects of industrial effects on the environment. Keywords: Textiles, environment, effluents, dyeing, water

1.1 Introduction Textiles play an important role in human life and are considered as a basic need along with food and shelter. With the population explosion and varied choices of human beings, the textile industry is pressured to produce more to meet the current demands. The textile industry is known for its high effluent production and for creating environmental pollution. Textile production starts from fiber manufacturing and processing and ends with finishing them to make them wearable to humans. All the steps involve

*Corresponding author: [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (1–10) © 2019 Scrivener Publishing LLC

1

2

Textiles and Clothing Textiles and clothing

Environmental concerns

Environmental solutions

Textile manufacturing Textile processing and dyeing Textile finishing Effluents discharge

Natural fibers for textiles Natural dyeing and functionalization Effluents remediation

Figure 1.1 Processes responsible for environmental concerns and solutions in the textile industry.

utilization of water and other chemicals that may be hazardous to the environment and mankind. This direct relation of the textile industry and environment is a great concern to textile chemists as well as to environmental chemists. Environmental protection nowadays is being implemented as an administrative philosophy. Rapid degradation in environmental conditions has made industrial managers to consider ecology a significant factor while taking decisions related to industrial management. Chemicals discharged into air, water, and soil are the parameters responsible for environmental pollution (Figure 1.1). Companies are now well aware of the relationship between environmental quality and prospects within the framework of economic development, and this environmental quality and responsibility factor highly affects the success of companies. Consumer demands guide companies to include certain environmental issues in addition to quality, cost, and production flexibility. Demand for environmentally friendly products manufactured under natural conditions from food products to clothes has made companies more sensitive to the environment [1]. New ecolabels for textile products and tighter restrictions on wastewater discharges force textile wet processors to reuse process water and chemicals. This challenge has prompted intensive research in new advanced treatment technologies, some of which are currently making their way to full‐scale installations [2]. Eco textiles include products that are manufactured using materials and methods that do not pose any harm to people and nature from textile fiber production to the makeup of the finished textile (textile fiber production, dyeing, chemicals, energy and water consumption) and that can be disposed of (decomposition, recycling) without harming human health and nature [1].

Introduction to Textiles and the Environment

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1.2 Textile Fiber Manufacturing/Processing and the Environment The textile industry is shared between natural fibers, such as wool, silk, linen, cotton, and hemp, and man-made ones, such as polyamide and acrylic made from petrochemicals. Textile fibers are classified into three categories on the basis of their origin: natural, synthetic, and semisynthetic fibers (Figure 1.2). Natural fibers are considered as ecofriendly relatively but their production also leads to some environmental disturbance. Cotton is considered as an environment friendly, renewable, and biodegradable cellulosic fiber. However, cotton also has other environment issues, such as this crop needs higher use of pesticides and insecticides, as it is prone to insects and diseases. Scouring (removal of the waxy outer layer on cotton), mercerization, press finishing, and bleaching need aqueous sodium hydroxide, formaldehyde, and other chemicals associated with health hazards. Such hazards are tried to be overcome by using some alternatives such as citric acid, chitosan, etc. on cotton to improve characteristics [3–5]. Wool is another fiber produced naturally and is considered an ecofriendly textile substrate, but it also requires some alkaline or chemical processing that may lead to a slight negative impact on the environment. Naturally produced textile substrates (wool, silk, cotton, etc.) are expected to be superior to synthetic ones in terms of environmental impacts [6]. Regenerated cellulosic fibers (Rayon, Tencel), also known as semisynthetic fibers, produced from cellulosic materials utilize a large amount of waste but use of harsh chemicals in production leads to environmental imbalance. A lot of developments have been carried out in the past for the production of regenerated cellulosic fibers that are sustainable

Synthetic fibers Semisynthetic fibers

Natural fibers

Textile fibers

Figure 1.2 Classes of textile fibers on the basis of their origin.

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and ecofriendly, and the use of environment-incompatible chemicals is restricted to some extent [7]. Nowadays, most of the clothes in our wardrobes contain polyester, elastane, or Lycra of synthetic origin. These cheap and easy-care fibers are becoming the textile industry’s miracle solution. However, their manufacture creates pollution and they are hard to recycle [8]. There are concerns about the use and disposal of hazardous chemicals in the production of synthetic textile fibers. Recycling, reuse of synthetic fibers, and use of natural fibers over synthetic ones are essential to restrict the hazardous impact on the environment.

1.3 Textile Finishing and the Environment Textile finishing is an important step in textile manufacturing before making them usable. Many of the steps such as scouring, bleaching, and mercerization are being carried out as finishing of textiles or textile fibers and have important roles to enhance the characteristics of textiles. Scouring removes substances that have adhered to the fibers during production of the yarn or fabric, such as dirt, oils, and any sizing or lint applied to warp yarns to facilitate weaving. Bleaching, a process of whitening fabric, is usually carried out by means of chemicals selected according to the chemical composition of the fibers. Chemical bleaching is usually accomplished by oxidation, destroying color by the application of oxygen, or by reduction, removing color by hydrogenation. Cotton and other cellulosic fibers are usually treated with heated alkaline hydrogen peroxide; wool and other animal fibers are subjected to such acidic reducing agents as gaseous sulfur dioxide or to such mildly alkaline oxidizing agents as hydrogen peroxide. Synthetic fibers may be treated with either oxidizing or reducing agents, depending on their chemical composition. Mercerization is a process applied to cotton and sometimes to cotton blends to increase luster, to improve strength, and to improve affinity for dyes to them. The process involves immersion of fiber or textile under tension in sodium hydroxide solution, which is later neutralized in acid [9, 10]. All these finishing steps involve use of chemicals with high content of water, and all chemicals discarded to water bodies lead to environmental (water) pollution.

1.4 Dyeing and the Environment The color of textiles always fascinates mankind, and a long range of textile colors are available to people. This step of textile processing is very crucial

Introduction to Textiles and the Environment

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with respect to environmental concerns, as a large amount of unadsorbed dyes is discarded into water bodies. Dyes are also classified as natural and synthetic on the basis of their origin. Natural dyes have been used to color textiles in ancient times, but in the 19th century, synthetic dyes replaced natural dyes after discovery of mauve colorant [11]. The expansion of the use of synthetic dyes overburdened the pressure on environment and consequently increased pollution. Some azo dyes, a class of synthetic dyes, are banned for their carcinogenic effects on human health. Synthetic dyes are nonbiodegradable and nonbiocompatible and disturb the water ecosystem with high impacts. Minimum use of synthetic dyes or replacement of these dyes with natural dyes, which are known for their biodegradability and biocompatibility, can be of great help to minimize the negative impact on the environment. Natural dyes also have less substantivity towards textile fibers or textiles and require use of metals as mordants for the fixation of dyes on textile surfaces, and these metals are responsible for the contaminated water bodies [12]. The dyeing process, whether it is by natural or synthetic dyes, has an impact on the environment to some extent as a result of spilling out of nondegradable dye compounds or hazardous metal ions used as mordants to fix dye molecules on textile surfaces. Methods used for dyeing textiles are quite important to decide the extent of polluting the environment. Microwave and sonicator dyeing and the application of compounds with pad-dry cure method are considered as effective dyeing processes that lead to high adsorption of dyes and to ultimately protecting the environment [13]. The use of ecofriendly or natural compounds such as chitosan and biomordants to enhance the substantivity of dyes towards textiles in place of toxic metals may be a great step towards a safe environment and ecofriendly dyeing [14]. The use of ecofriendly chemicals, dyes, and suitable techniques for maximum output without simultaneous generation of waste would be important aspects to establish a safe relationship between the textile industry and the environment today and in the future.

1.5 Technologies and Methods to Cure the Textile-Infected Environment Textile production/manufacturing, processing, dyeing/finishing, and discarding after use as waste lead to infecting the environment as discussed earlier in this chapter. It would be better to take care of the environment during the processing steps as well as in later stages for the things left out

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particularly in water bodies. Even if care is taken to minimize waste, there will still be waste to treat. Textile manufacturing, dyeing, and finishing processes produce waste containing both organic and inorganic compounds. Removal of these substances from wastewater is expensive and difficult to achieve [15]. Today, almost everywhere in the world, there is ongoing research on treatment of wastewater to meet the demands of mankind. Almost 70% of Earth is covered with water, but only a small fraction of it is utilized for drinking. A large number of methods and techniques are used to cure wastewater, classified mainly into three categories: chemical, physical, and biological (Figure 1.3). The coagulation and flocculation technique can be used for the removal of various hazardous components from wastewater from textile industry effluents. Colloidal or suspended particles are charged and stable in water. Coagulation destabilizes these charged particles in wastewater, leading to aggregation and formation of floccules. The addition of a specific coagulant (with a charge opposite of the particles) is required to stabilize the colloidal particles, and the efficiency is estimated by the factors in the wastewater such as type and concentration of flocculant and coagulant, final pH, intensity, and duration of mixing [15]. The use of membranes and nanofiltration is one of the methods to cure wastewater. It removes most of the organic molecules, viruses, and the natural organic matter as well as some salts. Nanofiltration does not remove dissolved compounds. Chemical oxidation aims at oxidizing organic pollutants or even some inorganic components into less dangerous or harmless components. Complete oxidation sometimes results in the production of CO2 and H2O. Chemical oxidation processes use different reacting systems involving oxidants such as ozone, hydrogen peroxide, sodium hypochlorite, peroxyacetic acid, and oxygen. These are all characterized by the same chemical

Chemical methods

Biological methods

Physical methods

Figure 1.3 Various methods to treat textile industry effluents.

Introduction to Textiles and the Environment

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feature of production of OH radicals. OH radicals are extraordinarily reactive species and they attack the most part of organic molecules with high rate constants. Fenton’s process, photocatalysis, electrochemical oxidation, and ozone systems are other advanced chemical oxidation processes for the treatment of wastewater from the textile industry [16]. Degradation (aerobic and anaerobic) of pollutants or discoloration of effluents can also be achieved via the application of bacteria, fungi, and algae, which is a form of biological treatment [17].

1.6 Reuse of Wastewater from the Textile Industry Reusing rinse water from one process to another cleaning process is an example of on-site recycling or reuse. It involves collecting waste and reusing it in the same or different parts of the production. Nonpreventable wastes can be recycled or vend as an offshoot [18]. The textile industry uses large amounts of water and is highly responsible for wastewater production. The textile industry’s wastewater contains various nondegradable dyes and finishing chemicals. It is quite necessary to reuse the wastewater after treatment, and there are various methods discussed earlier to treat wastewater. It is important to install the textile industry near water to fulfill the requirements of water, and simultaneously, there should be a wastewater treatment plant installed. This parallel treatment of wastewater leads to an increase in the cost of production, but as per the freshwater resources are shrinking, this is the demand of the current scenario and we need to compromise on increased costs. If not all, at least some of the steps of manufacturing can use the treated water in place of freshwater.

1.7 Conclusion and Perspectives The textile industry and the water ecosystem used to have a strong bond. It is well known that the textile industry needs a lot of water in all steps of manufacturing and finishing of textiles and a large amount of effluents are discarded into water bodies. Today, human beings have a wide range of choices of clothing and also the number of products to be used. To maintain balance between textile processes and the environment, sustainable approaches and the use of ecofriendly techniques are needed. Optimum use of natural fibers such as wool, silk, cotton, jute, flex, etc. (produced without or with minimum pesticides or insecticides) and natural dyes in place of synthetic ones can overcome the load on petrochemical products

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Textiles and Clothing

and on environmental disturbance. There is a lot to do for the remediation of textile effluents and protection of contamination of water bodies. Development of wastewater treatment techniques of high efficiency and maximum recovery of the pollutants are the main concerns for the future, and researchers all over the globe are looking seriously into it.

References 1. Guner, M. and Yucel, O., Environmental protection and waste management in textile and apparel sectors. J. Appl. Sci., 5, 10, 1843–1849, 2005. 2. Vandevivere, P.C., Bianchi, R., Verstraete, W., Treatment and reuse of wastewater from the textile wet-processing industry: Review of emerging technologies. J. Chem. Technol. Biotechnol., 72, 4, 289–302, 1998. 3. Chen, H.L. and Burns, L.D., Environmental analysis of textile products. Clothing Text. Res. J., 24, 3, 248–261, 2006. 4. Wei, W. and Yang, C.Q., Polymeric carboxylic acid and citric acid as a nonformaldehyde DP finish. Text. Chem. Color. Am. Dyest. Rep., 32, 2, 53–57, 2000. 5. Shabbir, M., Rather, L.J., Mohammad, F., Chitosan: Sustainable and environmental-friendly resource for textile industry, in: Chitosan : derivatives, composites and applications, 233–252, 2017. 6. Shabbir, M. and Mohammad, F., Natural textile fibers: Polymeric base materials for textile industry, in: Natural Polymers: Derivatives, Blends and Composites—Volume 2, pp. 89–102, 2017. 7. Shabbir, M. and Mohammad, F., Sustainable production of regenerated cellulosic fibres, in: Sustainable Fibres and Textiles, pp. 171–189, 2017. 8. Challa, Lakshmi, Impact of textiles and clothing industry on environment: Approach  towards eco-friendly textiles, https://www.fibre2fashion.com/ industry-article/1709/impact-of-textiles-and-clothing-industry-on - environment?page= 1. 2018. 9. Textile Finishing Processes, https://www.britannica.com/topic/textile/Textilefinishing-processes. Retreived on 26-11-2018. 10. Saik Al Maruf. Textile Finishing Processes. http://textilelearner.blogspot. com/2013/07/textile-finishing-processes.html. 2018. 11. Yusuf, M., Shabbir, M., Mohammad, F., Natural colorants: Historical, processing and sustainable prospects. Nat. Prod. Bioprospect., 7, 1, 123–145, 2017. 12. Shabbir, M., Rather, L.J., Mohammad, F., Economically viable UV-protective and antioxidant finishing of wool fabric dyed with Tagetes erecta flower extract: Valorization of marigold. Ind. Crops Prods., 119, 277–282, 2018. 13. Vankar, P.S., Shanker, R., Mahanta, D., Tiwari, S.C., Ecofriendly sonicator dyeing of cotton with Rubia cordifolia Linn. using biomordant. Dyes Pigm., 76, 1, 207–212, 2008.

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14. Shabbir, M., Rather, L.J., Bukhari, M.N., Shahid-ul-Islam, Khan, M.A. and Mohammad, F., First-time application of biomordants in conjunction with the Alkanna tinctoria root extract for eco-friendly wool dyeing. J. Nat. Fibers, 1–9, 2018. https://doi.org/10.1080/15440478.2018.1441085 15. Weydts, D., De Smet, D., Vanneste, M., Processes for reducing the environmental impact of fabric finishing, in: Sustainable Apparel, pp. 35–48, 2016. 16. Andreozzi, R., Caprio, V., Insola, A., Marotta, R., Advanced oxidation processes (AOP) for water purification and recovery. Catal. Today, 53, 1, 51–59, 1999. 17. Sarayu, K. and Sandhya, S., Current technologies for biological treatment of textile wastewater—A review. Appl. Biochem. Biotechnol., 167, 3, 645–661, 2012. 18. Toprak, T. and Anis, P., Textile industry environmental effects and approaching cleaner production and sustainability: An overview. J. Textile Eng. Fashion Technol., 2, 1–16, 2017.

2 Synthetic Dyes: A Threat to the Environment and Water Ecosystem Mohd Yusuf Department of Chemistry, YMD College, M.D. University, Nuh, Haryana, India

Abstract The textile industry is among the most complex and oldest industries. Dyeing is the process in textiles that highly influences the choice of people for their clothing. Synthetic dyes are highly used for textile coloration since these are expected to have a wide range of colors with high substantivity to textiles. Along with these beneficial characteristics, dyes are associated with environmental hazards, particularly that concerning the water ecosystem. Effluents generated during the synthesis of dyes and application on textiles cause adverse effects on biological life in water bodies. This chapter aims to summarize the relationship between synthetic dyes and the environment or the water ecosystem, the impact on biological life in water, and advanced approaches to deal with these associated hazards. Keywords: Textile industry, dyeing, environment, effluents, synthetic dyes

2.1 Introduction To make things look aesthetic and colorful, colored additives (mainly dye molecules) are added from ancient human civilizations. Early dyes were obtained from mineral, animal, and vegetable sources, with no to very little processing. By far, the greatest source of dyes has been from the plant kingdom, notably, roots, berries, leaves, and wood/bark. The documentation of past civilizations had been investigated by several research groups through various archaeological periods for the dyestuffs used as coloring materials. Studies revealed that in the Ancient Stone Age, many antiquity documents Email: [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (11–26) © 2019 Scrivener Publishing LLC

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Textiles and Clothing

and descriptions showed that people used various colored nature-derived minerals and dyes that were applied to their hair, body parts, occasional dressings, items of clothings, their house paintings, etc. [1–3]. In the ancient and medieval world, Tyrian purple and crimson kermes dyes were highly prized luxury items with brilliant and permanent fixation. Other plantorigin dyes such as madder, henna, indigo, woad, saffron, etc. were economically important. The first synthetic dye, Mauveine or Mauve, was discovered serendipitously by Sir William Henry Perkin in 1856 when he synthesized quinine medication to treat malaria fever, which exists in a wider color range with brighter shades [2, 4]. However, the commercial role of synthetic dyes day by day has been increasing thoroughly. At present, they possess diversified angles of coloration such as textiles and clothings, leather, fur, photography, refined petroleum products, food, paper, printing, plastic, fashion and design, body art, paint, etc. Many industries globally discharge a million volumes of effluents containing dyes, heavy metals, acids, bases, and other inorganic and organic chemicals. All of these discarded substances make effluents toxic and highly hazardous to the aquatic as well as aerial ecosystems. Nowadays, more than 3600 individual textile dyes are being manufactured worldwide that use approximately 8000 chemicals in various processes [4]. Synthetic dyes are utilized as coloring agent in numerous industrial sectors such as textile, food and beverage, leather, paper, cosmetics, pharmaceuticals, etc. It is assumed that about 10–15% of synthetic dyes are suspended during different processes of the textile industry as effluent. United Nations Statistics Division (UNSD), New York, estimated that the global import and export market for acid dyes containing the azo (-N=N-) group chiefly was found to be 680,000 tons in 2011 [5]. Various dyes and chemicals used in several textile industries in huge quantities possess environmental risks [3, 6]. Therefore, the effluent carries dyes and other additives in large amounts, which can be transported easily through sewers and rivers especially because of their high water solubility and are difficult to remove from the environment. After the degradation process, these pollutants form unpleasant as well as undesirous products that are highly toxic, hazardous, and even carcinogenic [7]. Thus, they are associated with potential hazards to living organisms. An overview is presented in this chapter towards the impact of synthetic dyes on environmental ecosystems.

2.2

Environmental Hazards Parallel to Dye Applications

Almost every industrial dye process involves a solution of a dye in water/ solvent during the dyeing process and generates large volumes of effluents

Synthetic Dyes: A Threat to the Environment

13

that are complex mixtures of many pollutants, ranging from original colors lost during the dyeing processes associated with mordants/metals including: • Auxiliaries and basic chemicals (e.g., alkalis, metals and acid salts, reducing/oxidizing agents, etc.) • Dyes (excessive and unused) • Other contaminants (e.g., residues of finishing agents and fibers used) In general, when one’s body is warm and skin pores have opened to allow perspiration, textiles and clothing come into direct contact with our skin, and therefore some sensitive and toxic chemicals are often absorbed by the skin epithelial tissues. The symptoms of sensitivity and toxicity of dyes as well other chemicals from wearing range from skin rashes, dizziness, difficulty breathing, irregular heartbeat, to seizures, to name a few. Indeed, textile and the relevant dye industry produce high levels of dyes and floating solid materials. These sensitive and toxic substances are dumped in the form of effluent merged into rivers/canals/canalizations, and when not properly treated, they can cause serious contamination of the water sources. Thus, the materials that are dumped into the water ecosystems are effluents containing high organic pollutants with a strong/dark color, low visibility, high biochemical oxygen demand, low dissolved oxygen concentrations, and low biodegradability [8, 9].

2.2.1 Impact on Human Health Although synthetic dyes have brilliant technical characteristics, they are found to have several adverse effects on working people in the industry. Also, it is noteworthy that there are numerous adverse responses to dyes because of the large number of chemicals associated with them. Human health concerns fall under two categories: acute toxicity and genotoxicity. Acute toxicity caused by reactive dyes involves oral ingestion and inhalation and the chief negative responses are skin sensitization and irritation, for example, contact dermatitis, allergic conjunctivitis, rhinitis, asthma, or other allergic reactions. ETAD (Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers) had published the directives on the list of reactive dyes that have caused respiratory or skin sensitization in associated dye industry workers on occupational exposure, out of which immediate allergic reactions are less common (Table 2.1). For textile fibers, the symptoms of immediate allergy to textile products

14

Textiles and Clothing Table 2.1 Synthetic dyes (reactive and disperse) classified as respiratory/ skin sensitizers based on ETAD directives [11]. Color index number (reactive)

Color index number (disperse)

Yellow dyes

Reactive Yellow 25 Reactive Yellow 39 Reactive Yellow 175

Disperse Yellow 1 Disperse Yellow 9 Disperse Yellow 3 Disperse Yellow 39 Disperse Yellow 49

Red dyes

Reactive Red 29 Reactive Red 65 Reactive Red 66 Reactive Red 123 Reactive Red 219 Reactive Red 225

Disperse Red 1 Disperse Red 17 Disperse Red 15

Orange dyes

Reactive Orange 4 Reactive Orange 12 Reactive Orange 14 Reactive Orange 16 Reactive Orange 64 Reactive Orange 67 Reactive Orange 86 Reactive Orange 91

Disperse Orange 1 Disperse Orange 3 Disperse Orange 37

Blue dyes

Reactive Blue 114 Reactive Blue 205

Disperse Blue 1 Disperse Blue 3 Disperse Blue 7 Disperse Blue 35 Disperse Blue 106 Disperse Blue 124

Violet dyes

Reactive Violet 33

NA

Black dyes

Reactive Black 5

NA

Dye color

include redness, rash, wheals, respiratory and circulatory problems, and even anaphylactic shock [10]. Genotoxicity is defined in genetics as a destructive effect on a cell’s genetic material (i.e., DNA, RNA) that affects its integrity either whole or partially. In other words, genotoxins are mutagens that can cause mutations including both radiation and chemical agents. Certain dyes are proven to

Synthetic Dyes: A Threat to the Environment

15

be genotoxic [1, 10]. Particularly, in the mid-20th century, a high incidence of bladder cancer was observed in plant workers involved in the manufacture of particular dyes. Azo dyes and other relevant dyes have shown carcinogenic properties due to the release of aromatic amines after the degradation process. In July 2002, ETAD published the 19th amendment of the restrictions on the marketing and use of certain azo-based colorants (see “Directive 2002/61/EC of the EP and of the EC”) [12]. According to this directive, azo dyes, which by reductive cleavage of one or more azo groups, may release one or more of the 22 aromatic amines in detectable concentrations (i.e., above 30 ppm) in the finished articles or in the dyed parts thereof. Azo dyes are the most important chemical class of dyes, representing 60–70% of all dyes used. Only about 5% of azo dye structures are affected by the 19th amendment, which is already largely phased out for consumer goods in the EU. It is suggested that the dyes from the fabric that release the carcinogenic amines when they come in close contact with the human body are leached/absorbed out from the fabric due to human perspiration. The absorbed dye contents alter the skin’s metabolic reactions, which may lead to allergic and carcinogenic responses [2, 10]. When metabolized by liver enzymes, azo and aromatic amine-based dyes are found to be dangerous. Aromatic amines can be mobilized by water or skin’s sweat pores absorbed through the skin and other exposed areas. Absorption by ingestion is also faster and even potentially more dangerous, as more dye can be absorbed in a smaller time frame [13].

2.2.2 Impact on Growth of Crops and Plants Among many types that are industrially discharged as wastes, the textile industry effluents raise great concern because of their acute as well as diverse environmental hazards, for example, those that are mutagenic and carcinogenic in nature [1, 4, 12]. The contribution of each toxic component to toxicity varies with its dilution and dispersion into groundwater and, therefore, affects the diversity of the living environment [14]. Living organisms are almost always exposed to possibly genotoxic environmental agents both at the cellular and the molecular level. Genotoxic potential studies are important to predict the impact of certain agents on animals, vegetables, and, consequently, human beings [15, 16]. Wang and Keturi reported that % seed germination and root–shoot ratio tests have been used as a rapid, reliable, simple, and reproducible technique in order to investigate the damage caused by toxic compounds present in various polluted wastewater reservoirs [17, 18]. Umesh et al. performed a study to evaluate the toxicity of synthetic textile effluent on germination and root/shoot

16

Textiles and Clothing

elongation of five plant seeds [19]. In this study, it was suggested that the phytotoxicity bioassay can be used as an efficient toxicity test for synthetic textile dye effluent and also as a monitor of environmental contamination. The toxic effect of dyes reported in this study also suggests the need for remediation of textile dyes in industry effluents before discharging them into the environment. Studies revealed that crop plants grown on the heavy-metal-contaminated medium can accumulate high concentrations of trace elements that may lead to specific health risks to consumers [1, 16–20]. The mineral uptake process and accumulation by crops and plants depend on factors including concentrations of available metals in the soil, their solubility index, and the plant species itself [21]. Leafy vegetables contain high mineral sources and therefore need higher uptake and accumulation of heavy metals compared to other ones. This capability has been ascribed to the increased rates of transpiration and translocation in leafy vegetables compared with non-leafy vegetables in which transfer of metals from root to stem and then to fruit is longer and results in lower accumulation than leafy vegetables [22, 23]. Oguntade et al. studied the growth, dry matter, and heavy metal uptake of potted Amaranthus cruentus L. as influenced by dye-laden wastewater [24]. It is concluded from the study that at lower dyestuff concentration, the nutrient elements therein impacted Amaranthus growth and yield positively but the heavy metal contents and their degraded products accumulated in edible shoots and high concentration of dyestuff solution retarded the growth and yield. Bioaccumulation of heavy metals and organic dye molecules were found to have a higher value in edible shoots than in roots, with high concentrations of Mn, Fe, and Zn in edible shoots that are higher than permissible limits for human consumption by WHO/FEPA/FAO. This observation points to the health risk of consuming dye effluent-infected vegetables in the daily diet. In addition, Savin and Butnaru observed in a study that the toxic nature of reactive dyes causes death to the soil microorganisms, which directly affects the agricultural productivity to a significant extent [25]. Thus, pretreatment/ detoxification of industrial effluent is required when nutrients are taken from wastewater directly for crop and vegetable production.

2.2.3 Impact on Water Ecosystem Undoubtedly, wastes from textile-related industries are one of the most important sources of water pollution and are recognized as one of the chief causes of environmental misbalance. These effluents have shown acute disorders such as various physiological disorders (i.e., hypertension, sporadic fever, renal damage, cramps) in aquatic organisms, which uptake them

Synthetic Dyes: A Threat to the Environment

17

through the food chain in aquatic organisms [26]. Further, the bioaccumulation of organic and inorganic toxicants depends on the availability and persistence in the water ecosystem, food chain type, and physiological properties. Consequently, aquatic vertebrates such as fishes, tadpoles, etc. live in an intimate contact with the aquatic ecosystem through the gills, the primary organs for respiration, acid–base balance, and iono and osmoregulation, making them susceptible to aquatic pollutants. If pollution reached high levels, the function of these organs may cause homeostatic disorders that result to poor overall life performance of aquatic animals due to the breakdown of some physiological functions [27]. The pollutants present in the water ecosystem have an inhibitory effect to the aquatic biota and particularly affected the rate of photosynthesis for green biome species. Nevertheless, being nondegradable in nature, synthetic dyes are broken down anaerobically in the sediment, as toxic amines are often produced [1, 10, 27]. Karthikeyan et al. studied the impact of textile effluents on a proteinous edible freshwater fish, Mastacembelus armatus, by examining the changes in the ionic regulations of some selected tissues (liver, kidney, and muscles) before and after exposure to Acid Blue 92 (C.I. No. 13390) (exposed to sublethal concentrations of Acid Blue 92 for a period of 35 days), a reactive dye [28]. In this study, a decrease in the concentration of Na+ and Cl− ions and an increase in the concentration of K+, Ca++, and Mg++ ions were observed. The magnesium ion concentration increased, but only slightly, when compared to the fluctuations of the other ions. The cationic concentrations of the test individuals indicated that the impact of textile effluents has an adverse effect on the ionic regulations. A comparative toxicological study on textile dye wastewater with respect to treatment/nontreatment of a freshwater fish (Gambusia affinis) has been performed by Soni et al. [29]. A marked reduction in mortality and cytotoxic effects on RBCs was observed in the study, and a reduction in their counts and percent changes in their shape (poikilocytosis) and variation in their size were also found. Consequently, Selvaraj et al. aimed to determine the toxicological and histopathological impacts of textile dyeing industry effluents on teleost fish (Poecilia reticulata) in their study [30]. The effluents cause abnormal behavior including rapid opercular movement, erratic swimming, hyperexcitation, and thick mucus covering. Also, histopathological changes were noticed in the study, including enlargement of the primary gill bar, detachment of the secondary gill bar, the disintegration of intestinal villi, and infiltration of hemocytes into the lumen. Spirulina platensis is a filamentous cyanobacterium that is an important food diet in some countries due to its high nutritional value. However, measuring pollution by toxicological tests in aquatic environments, algae

18

Textiles and Clothing

are more sensitive to contaminants compared to other common organisms. In the context of algae, the presence of dyes in the water ecosystem affects significantly many biochemical parameters such as growth; protein, mineral, and pigment contents; and other nutrients. It is noteworthy that various types of dyes have different potential effects on algae based on the toxicity, reactivity, and functional moiety of dyes. Also, few dyes create a film on the water surface, resulting in low sunlight penetration for aquatic organisms. In a study, de Sousa et al. evaluated the effect of a simulated textile effluent (Remazol Red Brilliant) on phytoplankton by Winogradsky columns with a micro-ecosystem in a glass container composed of soil (taken from the river bottom), water, and necessary nutrients [31]. This assessment concluded that the presence of Remazol Red Brilliant dye would affect the decrease in photosynthesis and ecological imbalance in the food chain. Therefore, the contaminated water containing high concentrations of industrial dyes has an adverse impact on phytoplankton as well as other organisms of the aquatic ecosystem.

2.3 Regulations and Toxicological Prospects of Synthetic Dyes The toxic nature and various adverse effects of synthetic origin dyes and pigments, chiefly azo-based ones, have been revived by the scientific community worldwide, with the belief that these responses are not only due to the dye’s toxicity but also due to certain mordants that have to be used with them [1, 14]. In fact, there is no legal hard prohibition on these dyes in any country but some organizations, such as The International Association for Research and Testing in the Field of Textile and Leather Ecology (OEKOTEX®), which is a union of 18 independent textile research and testing institutes in Europe and Japan and their worldwide representative offices [32]. The association is composed of (1) AITEX, Instituto Tecnológico Textil, Spain; (2) CENTEXBEL, Belgian Textile Research Centre, Belgium; (3) CENTROCOT, Centro Tessile Cotoniero e Abbigliamento S.p.A., Italy; (4) CITEVE, Centro Tecnológico das Indústrias Têxtil e do Vestuário de Portugal; (5) DTI, Danish Technological Institute, Denmark; (6) FILK, Research Institute for Leather and Plastic Sheeting, Germany; (7) Hohenstein Institute, Germany; (8) IFTH, Institut Français du Textile et del'Habillement, France; (9) INNOVATEXT, Textile Engineering and Testing Institute, Hungary; (10) Instytut Wlokiennictwa, Textile Research Institute, Poland; (11) MIRTEC, Materials Industrial Research & Technology Center, Greece; (12) Nissenken, Nissenken Quality

Synthetic Dyes: A Threat to the Environment

19

Evaluation Center, Kuramae Taito-ku Tokyo, Japan; (13) ÖTI, Institut für Ökologie, Technik und Innovation GmbH, Austria; (14) PFI, Testing and Research Institute Pirmasens, Germany; (15) Shirley Technologies Limited, United Kingdom; (16) SWEREA, Swedish Research Institute for Industrial Renewal and Sustainable Growth, Sweden; (17) Testex AG, Swiss Textile Testing Institute, Switzerland; (18) and Vutch-Chemitex, Slovakia. Other scientific authorities responsible for defining and maintaining specifications and for the assessment of the safety in different applications are the European Commission (EC) in the European Union (EU), the Food and Drug Administration (FDA) in the United States, as well as Ministry of Health, Labour and Welfare in Japan and Government of Canada in similar to the U.S. regulations [32]. The European Commission has circulated a working document relating to the restrictions on the preparation and marketing and use of dangerous substances (mainly azo dyes). From the consideration of the European Parliament and the Council, there are 22 banned amine substances according to the Commission of the European Communities: Directive 2002/61/EC mentioned by ETAD (Table 2.2) [12, 33]. In continuation, the other European Commission directive, “European Commission directive— Regulation (EC) No 1907/2006 (REACH)”, gives detailed explanatory notes in the dyed parts thereof, on the basis of several reports to the specified testing methods [34]. In this context, the following usable articles made up of textile and leather come into direct and prolonged contact with the human skin, causing serious negative responses: • yarn and fabrics, clothing, bedding, towels, sleeping bags, hair pieces, wigs, hats, nappies, and other sanitary items; • gloves, handbags, purses/wallets, briefcases, footwear, wristwatch straps, chair covers; • toys and toy covers or garments for use by the final consumer. The EIPPCB (European Integrated Pollution Prevention and Control Bureau) estimated that the textile industry releases more than 0.2 million tons of salts in the environment every year [35]. Nevertheless, genotoxicity and carcinogenicity are critical human health impacts for characterization of risk assessment for certain azo- and benzidine-based dyes. Several azo dyes and dye intermediates have been investigated by the International Agency for Research on Cancer (IARC), categorized under Group 1, 2A or 2B, referring to known, probable, and possible human carcinogens, respectively [36, 37]. In 1993, the Government of India prohibited the handling of 42 benzidinebased dyes. Further, in 1997, the Ministry of Environment and Forests

20

Textiles and Clothing

Table 2.2 List of ETAD banned aromatic amines due to their carcinogenic effects [1, 33]. Sr. no.

Names of aromatic amines

CAS numbers

1.

4-Aminoazobenzene

60-09-3

Chemical structure N

NH2

N

2.

o-Anisidine

90-04-0

NH2 OCH3

3.

2-Naphthylamine

91-59-8 H2N

4.

Benzidine

92-87-5

5.

3,3 -Dichlorobenzidine

91-94-1

NH2

H2N Cl

NH2

H2N Cl

6.

3,3 -Dimethoxybenzidine

119-90-4

H3CO NH2

H2N

OCH3

7.

3,3 -Dimethylbenzidine

119-93-7

H3C H2N

NH2 CH3

8.

4-Aminodiphenyl

92-67-1

9.

o-Toluedine

95-53-4

NH2 NH2 CH3

(Continued)

Synthetic Dyes: A Threat to the Environment

21

Table 2.2 List of ETAD banned aromatic amines due to their carcinogenic effects [1, 33]. (Continued) Sr. no.

Names of aromatic amines

CAS numbers

10.

4-Chloro-o-toluedine

95-69-2

Chemical structure NH2 CH3

Cl

11.

4-Methyl-1,3phenylenediamine

95-80-7

NH2

CH3

12.

o-Aminoazotoluene

97-56-3

NH2

CH3

CH3 N

NH2

N

13.

5-Nitro-o-toluedine

99-55-8

NH2 CH3

NO2

14.

15.

16.

4,4 -Methylene-bis-(2chloraniline)

4,4 -Methylenedianiline

4,4 -Oxydianiline

101-14-4

Cl

Cl

H2N

NH2

H2N

NH2

101-77-9

101-80-4

O H2N

17.

p-Chloraniline

106-47-8

NH2 NH2

Cl

(Continued)

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Textiles and Clothing

Table 2.2 List of ETAD banned aromatic amines due to their carcinogenic effects [1, 33]. (Continued) Sr. no.

Names of aromatic amines

CAS numbers

18.

p-Cresidine

120-71-8

Chemical structure NH2 OCH3 H 3C

19.

2,4,5-Trimethylaniline

137-17-7

NH2 CH3 H3 C CH3

20.

4,4 -Thiodianiline

139-65-1

S H2N

21.

4-methoxy-mphenylenediamine

615-05-4

NH2 NH2

NH2 OCH2

22.

4,4 -Methylenedi-otoluedine

838-88-0

H3C

CH3

H2N

NH2

(MOEF) prohibited the handling of an additional 70 azo dyes under the provisions of the Environment Protection Act, 1986 [38, 39]. Azo colorants are the most important textile colorants, which are divided broadly on the basis of their solubility, for instance, soluble azo dyes and insoluble pigments. In fact, upon breakdown, azo dyes produce their constituent aromatic amines and/or their amino counterparts. It is well observed that soluble azo dyes, when incorporated into the body context, split into corresponding aromatic amines by the azo-bond cleavage with enzymes of inner organs and the intestinal microbes [40, 41]. It was previously mentioned that several azo-based dyes can liberate arylamines, which are suspected of having carcinogenic potential. Markedly, three types of the cleavage of azo-bond through the metabolic activation

Synthetic Dyes: A Threat to the Environment

23

Pathway-I: formation of aromatic amines followed by nitrenium ion

N

R

R'

Azo Cleavage

R

N

+

NH2

R' H2N

Hydoxylation

Degradation

R' HN

O O

O-acylation

R'

HO

N H

R' N H

Nitrenium ion DNA/RNA Binder Pathway-II: formation of reactive electrophilic species through oxidation of a free aromatic amine group that is part of the azo dye structure NH2 R

N

NH

Oxidation N

R

N

N

DNA/RNA Binder

Pathway-III: Activation of the azo dyes via direct oxidation of the azo linkage to highly reactive electrophilic diazonium salts OH N

N

Oxidation N

N

Diazonium ion

Scheme 2.1 Representation of the cleavage of the azo-bond through the metabolic activation of azo dyes.

of azo dyes are identified: (i) Pathway-I: formation of aromatic amines followed by nitrenium ion, (ii) Pathway-II: formation of reactive electrophilic species through oxidation of a free aromatic amine group that is part of the azo dye structure, and (iii) Pathway-III: activation of the azo dyes via direct oxidation of the azo linkage to highly reactive electrophilic diazonium salts represented in Scheme 2.1. These activated species were found to have sufficient capacity to bind covalently to deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) and respond to mutagenicity and acute toxicity [42, 43].

2.4 Conclusion and Future Prospects It can be concluded from the above facts that the synthetic textile dyes represent a large group of organic compounds and possess undesirable effects on the environment. In practice, assessment factors vary in magnitude

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Textiles and Clothing

and are used to account for such factors as an extrapolation from acute to chronic effects, extrapolation from single-species laboratory tests to ecosystem impacts, and variations in sensitivity between species and/or between individuals within a species. Additionally, some of them proved to pose serious risks to human health as well as the aquatic ecosystem. The increasing complexity and difficulty in treating textile wastes have led to a new search for curing methods that would be effective and economically viable. Thus, there is a pressing requirement for alternatives to dyes to minimize the problems related to the environment. Due to the emotive nature of the debate and greater consumer concerns, it should be prescribed as high priorities for action globally to make environmentally safe dyes and pigments and auxiliaries.

References 1. Yusuf, M., Shabbir, M., Mohammad, F., Natural colorants: Historical, processing and sustainable prospects. Nat. Prod. Bioprospect., 7, 123–145, 2017. 2. Yusuf, M., Shahid, M., Khan, M.I., Khan, S.A., Khan, M.A., Mohammad, F., Dyeing studies with henna and madder: A research on effect of tin (II) chloride mordant. J. Saudi. Chem. Soc., 19, 64–72, 2015. 3. Yusuf, M., Ahmad, A., Shahid, M., Khan, M.I., Khan, S.A., Manzoor, N., Mohammad, F., Assessment of colorimetric, antibacterial and antifungal properties of woollen yarn dyed with the extract of the leaves of henna (Lawsonia inermis). J. Cleaner Prod., 27, 42–50, 2012. 4. Kant, R., Textile dyeing industry an environmental hazard. Nat. Sci., 4, 1, 22–26, 2012. 5. United Nations Statistics Division (UNSD), 2013. https://unstats.un.org/ unsd/contactus.htm 6. Kestioglu, K., Yonar, T., Azbar, N., Feasibility of physico-chemical treatment and advanced oxidation processes (AOPs) as a means of pretreatment of olive mill effluent (OME). Proc. Biochem., 40, 2409–2416, 2005. 7. Kaushik, P. and Malik, A., Fungal dye decolourisation: Recent advances and future potential. Environ. Int., 35, 127–141, 2009. 8. Seesuriyachan, P., Takenaka, S., Kuntiya, A., Klayraung, S., Murakami, S., Aoki, K., Metabolism of azo dyes by Lactobacillus casei TISTR 1500 and effects of various factors on decolorization. Water Res., 41, 5, 985–992, 2007. 9. Hao, O.J., Kim, H., Chiang, P.C., Decolorization of wastewater. Crit. Rev. Environ. Sci. Technol., 30, 4, 449–505, 2000. 10. VRM11.8088-Final Report, European Commission (Draft no.7). Study on the Link between Allergic Reactions and Chemicals in Textile Products (January 7, 2013). 11. Working together for safer colorants, https://etad.com/en/

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12. ETAD Information on the 19th Amendment of the Restrictions on the Marketing and Use of Certain Azocolourants (Directive 2002/61/EC of the EP and of the EC of 19 July 2002). 13. Puvaneswari, N., Muthukrishnan, J., Gunasekaran, P., Toxicity assessment and microbial degradation of azo dyes. Indian J. Exp. Biol., 44, 8, 618–626, 2006. 14. Reemtsma, T., Prospects of toxicity-directed wastewater analysis. Anal. Chem. Acta, 426, 279–287, 2001. 15. Kim, H., Rakwal, R., Shibato, J., Iwahashi, H., Choi, J., Kim, D., Effect of textile wastewaters on Saccharomyces cerevisiae using DNA microarray as a tool for genome-wide transcriptomics analysis. Water Res., 40, 1773–1782, 2006. 16. Jadhav, J.P., Kalyani, D.C., Telke, A.A., Phugare, S.S., Govindwar, S.P., Evaluation of the efficacy of a bacterial consortium for the removal of color, reduction of heavy metals, and toxicity from textile dye effluent. Biores. Technol., 101, 1, 165–173, 2010. 17. Wang, W. and Keturi, P., Comparative seed germination tests using ten plants species for toxicity assessment of a metal engraving effluent samples. Water Air Soil Pollut., 52, 369–376, 1990. 18. Chang, L.W., Meier, J.R., Smith, M.K., Application of plant and earthworm bioassays to evaluate remediation of a lead-contaminated soil. Arch. Environ. Cont. Toxicol., 32, 2, 166–171, 1997. 19. Umesh, J.U., Rhushikesh, D.N., Vishal, D.V., Ashok, C.D., Manohar, P.V., Phytotoxic effect of synthetic textile dye effluent on growth of five plant species. Trends Biotechnol. Res., 5, 2, 2–6, 2016. 20. Khan, S., Farooq, R., Shahbaz, S., Khan, M.A., Sadique, M., Health risk assessment of heavy metals for population via consumption of vegetables. World Appl. Sci. J., 6, 12, 1602–1606, 2009. 21. Gupta, A.K. and Sinha, S., Chemical fractionation and heavy metals accumulation in the plants of Sesamum indicum (L.) var. T55 grown on soil amended with tannery sludge: Selection of single extractants. Chemosphere, 64, 161– 173, 2006. 22. Islam, E.U., Yang, X.E., He, Z.L., Mahmood, Q., Assessing potential dietary toxicity of heavy metals in selected vegetables and food crops. J. Zhejiang Univ. Sci. B, 8, 1, 1–13, 2007. 23. Itanna, F., Metals in leafy vegetables grown in Addis Ababa and toxicological implications. Ethiopian J. Health Dev., 16, 3, 295–302, 2002. 24. Oguntade, O.A., Adetunji, M.T., Salako, F.K., Arowolo, T.A., Azeez, J.O., Growth, dry matter and heavy metal uptake of potted Amaranthus cruentus L. as influenced by dye-laden wastewater. Trop. Agric., 41, 3216, 020132– 020145, 2018. 25. Savin, I. and Butnaru, R., Wastewater characteristics in textile finishing mills. Environ. Eng. Manag. J., 7, 6, 859–864, 2008. 26. Gita, S., Hussan, A., Choudhury, T.G., Impact of textile dyes waste on aquatic environments and its treatment. Environ. Ecol., 35, 3C, 2349–2353, 2017.

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27. Pereira, L. and Alves, M., Dyes—Environmental impact and remediation, in: Environmental Protection Strategies for Sustainable Development, A. Malik and E. Grohmann (Eds.), pp. 111–162, Springer, Dordrecht, 2012. 28. Karthikeyan, S., Jambulingam, M., Sivakumar, P., Shekhar, A.P., Krithika, J., Impact of textile effluents on fresh water fish Mastacembelus armatus (Cuv. & Val). J. Chem., 3, 4, 303–306, 2006. 29. Soni, P., Sharma, S., Sharma, S., Kumar, S., Sharma, K.P., A comparative study on the toxic effects of textile dye waste waters (untreated and treated) on mortality and RBC of fresh water fish Gambusia affinis (Baird and Gerard). J. Environ. Biol., 27, 623–628, 2006. 30. Selvaraj, D., Leena, R., Kamal, D.C., Toxicological and histopathological impacts of textile dyeing industry effluent on a selected teleost fish Poecilia reticulata. J. Pharmacol. Toxicol., 3, 26–30, 2015. 31. De Sousa, M.L., de Moraes, P.B., Lopes, P.R.M., Montagnolli, R.N., de Angelis, D.F., Bidoia, E.D., Contamination by Remazol Red Brilliant dye and its impact in aquatic photosynthetic microbiota. Environ. Manag. Sust. Dev., 1, 2, 129–138, 2012. 32. https://www.oeko-tex.com/en/business/certifications_and_services/ots_100/ ots_100_start.xhtml 33. Yusuf, M., Shahid, M., Khan, S.A., Khan, M.I., Islam, S.U., Mohammad, F., Khan, M.A., Eco-dyeing of wool using aqueous extract of the roots of Indian madder (Rubia cordifolia) as natural dye. J. Nat. Fibers, 10, 1, 14–28, 2013. 34. EU-Directive 2002/61/EC [Regulation (EC) No 552/2009 of 22 June 2009 amending Regulation (EC) No 1907/2006 (REACH)]. 35. http://eippcb.jrc.ec.europa.eu/ 36. Hessel, C., Allegre, C., Maisseu, M., Charbit, F., Moulin, P., Guidelines and legislation for dye house effluents. J. Environ. Manag., 83, 2, 171–180, 2007. 37. https://www.iarc.fr/ 38. Sengupta, A., Environmental regulation and industry dynamics. B.E. J. Eco. Anal. Policy, 10, 1, 1–27, 2010. 39. hktdc research. https://hkmb.hktdc.com/en/1X09YJMT/hktdc-research/ India-Azo-Requirement-on-Imported-Apparel-and-Textile-Products 40. Pinheiro, H.M., Touraud, E., Thomas, O., Aromatic amines from azo dye reduction: Status review with emphasis on direct UV spectrophotometric detection in textile industry wastewaters. Dyes Pigments, 61, 2, 121–139, 2004. 41. Platzek, T., Lang, C., Grohmann, G., Gi, U.S., Baltes, W., Formation of a carcinogenic aromatic amine from an azo dye by human skin bacteria in vitro. Hum. Exp. Toxicol., 18, 9, 552–559, 1999. 42. Brown, M.A. and DeVito, S.C., Predicting azo dye toxicity. Crit. Rev. Environ. Sci. Technol., 23, 3, 249–324, 1993. 43. Snyderwine, E.G., Sinha, R., Felton, J.S., Ferguson, L.R., Highlights of the eighth international conference on carcinogenic/mutagenic N-substituted aryl compounds. Mut. Res./Fundament. Mol. Mech. Mutagen., 506–507, 1–8, 2002.

3 In Search of Natural Dyes Towards Sustainability from the Regions of Africa (Akebu-Lan) S. Anuradha Jabasingh Process Engineering Division, School of Chemical and Bio Engineering, Addis Ababa Institute of Technology, Addis Ababa University, Ethiopia

Abstract This chapter “In Search of Natural Dyes Towards Sustainability from the Regions of Africa (Akebu-Lan)”, features the dyes, colors, and shades of the African continent, historically known as “Akebu-Lan”, which means the “Mother of Mankind”. The expedition is made to disclose the deliberate role played by the natural dyes in the culture and festivities of the Akebu-Lan continent. An assortment of the indigenous sources of natural dyes, their colors, and shades is identified in this hunt. The dye synthesizing methods adopted by different communities and ethnic varsities of the continent are brought to the limelight. The natural dyes possess various properties, which includes shade, fastness, dusting, simplicity in application, durability, and resistance in addition to a variety of medicinal and healing properties, all of which are explored herein. Attention is drawn to provide an inclusive depiction of the fashion drive possessed by the growing communities of the world towards fabric dyed with natural colors. To wrap up, the aspect of environmental sustainability is argued in relation to its emphasis on the natural dyes. Keywords: Natural dyes, sustainability, Africa, indigenous, properties, environment

Email: [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (27–44) © 2019 Scrivener Publishing LLC

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3.1 Role of Natural Dyes in the Tradition of the African Continent Dye refers to the colored substance, known for its affinity towards any substrate on which it is applied, in the presence of a mordant. Dyeing is an ancient art and could be traced back to the Bronze Age era, during which the dyeing technique is based on sticking the colored substance to fabric followed by vigorously rubbing the crushed pigments onto the clothes [1]. The dyes used in the tradition of the African continent were mostly of animal, vegetable, or mineral origin, with no or little processing. Undoubtedly, the greatest sources of natural dyes have been the bark, berries, leaves, roots, wood, fungi, and lichens. The majority of natural dyes are from plant source roots, berries, bark, leaves, and wood. Textile dyeing dates back to the Neolithic period, whereby the people have applied the dyes on their textiles using the potential locally available sources. Scarce dyestuffs, producing brilliant, enduring colors were highly esteemed extravagant items in the early medieval times. The advantages of natural dyes are accountable for their wide application in the continent of Akebu-Lan [2]. This includes their softness on fabric, lustrous shine, soothing effect on the fibers, mix-match coordination with the capability of producing a wide range of colors, eco-friendly apt dyeing techniques, wide shift in color ranges, exceptional color ideas, habitual harmonization, renewable, sustainable, biodegradability, and nil disposal problems. The other advantages include the potential of these plants to grow in the wastelands, or as host in gardens, with less cost and effort involved. The natural dye industry is highly labor intensive; hence, job opportunities are available in abundance during the cultivation, extraction, and application processes. They are an apt alternative to the synthetic dyes, which rely on the fossil fuel. In addition, they are anti-allergens and are nonhazardous. Natural dyes are augmented with age, and although they discharge the color after their application on the fabric and longer usage, they do not stain other fabrics and are completely moth proof. Natural dyes and fabrics dyed with them are the preferred brand on the textile market since the phytoconstituents, coumarins, polyphenols, flavonoids, and sterols are powerful antioxidants and act as anti-mutagenic agents with antimicrobial properties. Hence, their application as coloring agents in combination with other natural products makes them sustainable with biodegradable properties and health and environmental benefits [2]. Despite their several advantages, they have limitations, which hinder their application and development. This includes the difficulties that are

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incurred during the reproduction of shades and standardization; requirement of skilled workmanship; expensive and nonaffordability; low color yield; requirement of mordants and their extra cost; lack of sufficient scientific backup; lack of precise technical knowledge on their extraction processes; color discharge during the exposure to the sun, sweat, and air; lack of adequate color fastness; and inadequate performance ratings for the modern textile industry practice. These disadvantages lead to the discovery of man-made synthetic dyes in the late 19th century and wrecked the large-scale budding market for natural dyes [3, 4]. The rich cultural environment with which the continent is endowed has been a channel to the riches of visual, creative, imaginative, and artistic expressions emanating from this region. This is the reason why the people of the continent have greatly impacted the world artistic civilization in textile art, sculpture, printmaking, and painting. There are scores of artistic traditions that embody the most decorative patterns. The application of the natural dyes and their creation, acceptance, and their standardization are pinched from the myths, proverbs, legends, history, folktales, religion, and tradition of various communities in the continent. The techniques are taught and inherited from the fore parents to the future generations [3]. However, external influences and internal developments have led to the fading of the traditional methods adopted. The cloth produced and dyed bestow in their origin, culture, language, script, tradition, design, and style to the specific ethnic group, or cultural background of the weavers and dyers, producing these clothes. Dyeing dates back since ancient times, to the development of the textile industry. Woven clothes manufactured from cotton and vegetable dyes are an ancient African art form in West Africa and date back to the 10th century. The dyed clothes have a special impact on the African people as they are used in some of the very important rituals and ceremonies. In Ghana, clothes are dyed using specific plant dyes from the Kuntunkuni and Badie trees and are used during important traditional sacred ceremonies and funerals. Traditionally, the plants in Uganda have been utilized as colorant sources for rope and mat making. They were also employed in home-based craft materials. Some extracts of the dye-yielding plants were used in traditional medicine. This shows the massive reservoir of novel molecules, still waiting to be learned towards prospective dye yielding activities. The Garra dyed textiles acquire a distinct strong scent during their synthesis and have therapeutic properties for pregnancy-related morning sickness. This also improves the health of the newborn babies wrapped around with Garra dyed fabrics. The natural dyes from the Garrisa region of the continent are used for wood carvings and wooden utensils used for storage.

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In some specific communities, men and women used Lawsonia inermis for hair coloring and skin decoration. It is also used since antiquity to dye leather and wool. The natural dyes have played a major role in people’s economic growth and cultural values. Their usage and involvement could be distinctly found in leather, textiles, cosmetics, and food industries [4]. The deep crimson dyes extracted from beetroot are used as an upper surface dyestuff for indoor applications, toys, inks, and leather garments. Vibrant colors have been used for the scripts in ancient handwritten religious books and traditional garments of monks in monasteries. Anthocyanin from Hibiscus has been used in folk medicines and in the beverage industry. This is a good colorant and potent source of antioxidants. It is also used for fabric dyeing. Extracts from the bark of whistling pine and the root of African peach in the Abraka, Nigeria region have been used for textile dyeings and drink and food colorings.

3.2 Indigenous Sources of Natural Dyes The African continent is loaded with different plant species capable of yielding natural dyes. This section has tried to identify the natural sources of dyes used in the African fabric industry. Most of the dyes are extracted locally from the inner and/or outer bark of the dyeing plant. Madder, containing over 20 individual chemical substances, is used to produce turkey reds, orange-red, terracotta, mulberry, and in permutation with other dyes and procedures yield crimson, browns, rust, purple, and black shades. It grows wild all through the parts of Akebu-Lan. Log wood, a bushy, thorny tree grown in parts of Africa, concentrates a purple dye in the heartwood. Locust bean pod is another source of natural dyes and contain 12–14%, and the pod husks, when boiled in water, produces a reddish brown color that is used for coloring the clay tiles for local floor construction and finishing. The possibility of using them as natural dyes on natural cotton and silk is underway. Reseda luteola is the oldest and most widely used flavonoid dye source known by the African tribes still in the Neolithic period. It was cultivated in the Mediterranean area during Hellenistic times, and in the Roman Empire, it was used by Egyptians in Coptic textiles [5]. Hibiscus sabdariffa is widely grown in Central and West Africa. Hibiscus anthocyanins are phenolic natural pigments extracted from its dried flowers. The bark of the plant whistling pine (Casuarina equisetifolia) and the root of African Peach (Nauclea latifolia) were collected, chopped, dried, and pulverized. The dye extracts were obtained using ethanol (absolute) as extracting solvent. Whistling pine bark yielded a reddish brown color

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while the root of African peach yielded a brown color. Nauclea latifolia (African peach) is mainly used for medicinal purposes, is native to tropical Africa, and has been utilized for the extraction of dye for the cotton fabrics. In Ghana, great potential exists for natural dyes from dye-yielding plants. Over 40 plant species in Ghana are reported as primary sources of natural dyes. Fourteen of these are tree species with tremendous potential in the textile industries of Ghana. Ghana owns some of the moist semideciduous forest in the savanna transitional zone, which abodes some of the potential dye-yielding plants for the cottage textile industry [6, 7]. The natural dyes are obtained from Rhodognaphalon brevicuspe (Sprague) and Bridelia micrantha (Hochst). The black dye is obtained from the root of the Kuntunkuni tree, and the bark of the Badie tree produces a dark-browncolored dye. Some of the potential dye-yielding species of the continent includes Acacia nilotica whose pods and bark are used to produce gray, black, and light yellow shades. They are distributed throughout the tropics and seasonally flooded areas. The leaves of Anogeissus leiocarpa are used to obtain the yellow and ochre red shades. It is a deciduous tree found in the savanna and dry forests, and often grows gregariously in moist fertile soil. The heartwood, roots, and leaves of Baphia nitida are used to give a red color. It is an ornamental shade tree that is grown as fence and hedge in abandoned farmlands [6]. Caesalpinia coriaria gives black and blue shades from its pods. The plant grows on the clay and poor sandy soils and thrives in dry (warm) temperate climates to wet tropical climates. The leaves, stems, and root bark of Combretum glutinosum are used to give a yellow to brownish yellow shade. These plants are seen all over in west Akebu-Lan in the savanna and in the open woodlands. The other sources are Craterispermum, whose barks and leaves provide the yellow shades. The barks of Craterispermum schweinfurthii give out yellowish brown shades, and the barks of Ficus glumosa give out a brick red shade. Lannea barteri barks give red shades; Lannea microcarpa and Lannea velutina barks give out a more brighter red shade. Morinda lucida root barks offer scarlet red shades, and Syzygium rowlandii barks give out black shades. The barks of Terminalia scutifera give out yellow shades and the Khaya senegalensis barks give out brown shades. The heartwood of Milicia excels and Pterocarpus erinaceus gives out red shades, whereas Rhodognaphalon brevicuspe bark and roots give out reddish brown shades. The leaves of Tectona grandis give out reddish shades, and the bark of Vitex doniana provides gray shades. The fruits, roots, and barks of Senna singueana and Phyllanthus reticulatus give out red and black shades. The twigs of Bridelia micrantha and Azadirachta indica give out reddish dark brown shades [7].

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Figure 3.1 shows some of the natural dyes derived from the African continent. Uganda has over 5000 dye-yielding plant species, and most of them have not been identified, named, or documented. While investigating the color production and yield of indigenous plants in Uganda, as potential sources of textile dyes, the roots of Morinda lucida and the barks of Azadirachta indica have been found to be a good source with good color absorption onto cotton fabrics. These natural dyes have been found to be excellent in terms of fastness to light, washing, and rubbing. Other potential sources of colorants include Tectona grandis, which remains largely in the wild, being unexploited. Indigofera arrecta, Harungana madagascariensis, Syzygium cordatum, Bixa orellana Linn, Albizia coriaria, Curcuma longa, and Justicia betonica were among the other plants most commonly used in dyeing. Dyes produced by Vitex doniana, Lawsonia inermis, Morinda lucida, and Indigofera arrecta have the capability of dyeing the craft items and materials [9]. The Ethnobotanical literature survey indicates that Bixa orellana, Lawsone inermis, Curcuma longa, Rubia cordifolia, and Morinda lucida possess high comparative dye-yielding properties, though not much of them were systematically investigated for color production and performance on

Alkanet

Black Oak

Brazil wood

Chamomile

Cochineal

Cutch extract

Fustic extract

Henna

Indigo

Lac extract

Log wood

Madder

Marigold

Myrobalan

Pomegranate

Safflower

Weld

Woad

Osage orange sawdust

Figure 3.1 The eco-friendly natural dyes [8].

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any textiles. M. indica, R. cordifolia, M. lucida, V. paradoxa, S. cordatum, and A. coriaria are some of the indigenous plants that have been evaluated with good colorfastness performance values with potential marketability as dyestuffs. The bark was found to have a more predominance of dye than other plant parts. The bark and roots of V. paradoxa, M. lucida, and A. cordifolia produce color of more or less similar intensity. The leaves of Indigofera arrecta and Justicia betonica show high accumulation of dye-yielding molecules. R. cordifolia and C. longa showed more dye-yielding molecules in their roots than in other parts. The roots of Curcuma longa, Acacia seyal, Alchornia cordifolia, Prosposis african, Rubia cordifolia, and Morinda lucida showed good dye-yielding abilities. The barks of Albizia coriaria, Syzygium cordatum, Erythrina abyssinica, Harungana madagascariensis, and Terminalia brownie have dye-yielding abilities. The leaves of Justicia betonica and Indigofera arrecta possess excellent dye-yielding capabilities. The seeds of B. orellana possess good dye yielding molecules. The bark of Syzygium cuminii, Albizia zygia, Vitellaria paradoxa, Kigelia africana, Psidium guajava, Syzygium guineense, Entanda abyssinica, and Azadirachta indica produced average to moderately darker shades [10]. Tagetes erecta, the African marigold, serving as a major source of a carotenoids and lutein, produces yellow to orange red colors. Lonchocarpus cyanescens leaves of Ghana have been found to possess functional groups similar to those associated with synthetic indigo dyes. Lonchocarpus cyanescens known as the west African wild indigo, Wulim, Garra, or Yuroba indigo is one of the regularly used vegetable dyes in the cottage industry in Ghana. Garra is widely used because it is fast to wash and light. Parkia biglobosa is another species from which the colors can be extracted by the addition of water. Osyris quadripartita (Qerete) is found in abundance in the Garissa region. The region also hosts other plant species that are a source of natural dyes and tannins. The main plant sources of dyes and tannins in this region are Commiphora holtiziana (Haggar), Acacia bussei L. inermis (Elan), and Commiphora campestris. Some of the natural mordants found abundantly in this region are the ashes from Salsola dendroides and Var Africana Brenan (Durte). In Kenya, the most common species used by the local communities for textile dyeing are Albizia amara, Azanza gackeana, Euclea divinorum, Ekebergia capensis, Erythrina abyssinica, and Syzygium cuminii. Kenya exports dyes and tannins from Acacia mearnsii and Bixa orellana (annatto). Some communities use extracts from wild leek (Allium burdickii) to dye the cotton fabric. In this case, the mango tree bark is used as a mordant. Beetroot (Beta vulgaris) has been widely used to dye wood with vinegar as the mordant. The dye was found to be capable of dyeing

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oriental beech (Fagus orientalis), walnut (Juglans regia), scots pine (Pinus sylvestris), and oak (Quercus petraea) wood. Environmentally friendly stains have been derived from laurel (Laurus nobilis), oleander (Nerium oleander), madder root (Rubia tinctorium), and acorn (Quercus ithaburensis), which have a pleasing aesthetic appearance, when used in coloring [9, 11]. Nigeria has copious resources in terms of plants containing dyes. Guinea corn (Sorghum bicolor) leaf is a good source for dye extraction. This study was based on using the guinea corn leaves for dye extraction that is environmentally friendly. Rubia is a genus of the madder family Rubiaceae, and is the source of red dyes known as rose madder and Turkey red. It has been used since ancient times as a vegetable red dye for leather, silk, wool, and cotton. Galls or cecidia, outgrowths on the surface of life forms caused by invasion of parasites, fungi, or bacteria, are other well-known sources of natural dyes. They are rich resources of resins and tannic acid and have been used in the manufacture of permanent inks [3, 6, 12]. Ethiopia has a rich custom of using natural sources for textile coloring. The apparels are decorated with dyes obtained from a wide range of flora found in various regions of the country. Qerte (Osyris quadripartita) plant found in the Tigray and Oromia is locally used for dyeing of baby clothes (Ankelba). Sumac or sumach found in the subtropical and temperate regions of Africa produces fruits of reddish dense clusters and a dye is extracted from the same. Combretum collinum leaves; barks of Ficus sycamores, Syzygium guineense, Eriobotrya japonica, and Ficus sycamores; flowers of Tagets minuta and Scadoxus multiflorus; and leaves of Rhamnus prinoides, Zana Stereospermum, and Zembaba Stereospermum are widely used for the extraction of natural dyes in Ethiopia, Kenya, Sudan, Egypt, Eritrea, South Africa, Madagascar, Zambia, the Democratic Republic of Congo, and Senegal [13].

3.3 Dyeing and Processing Techniques African fabrics are dyed by adopting various dyeing techniques. Dye application adds color to yarns, fibers, and fabrics. In the process when the fabric is exposed to the dye bath, the fabric absorbs the dye molecules and the excess dye remains on the exterior surface of the fabric with the aid of additives or mordants, which assist the absorption of the dye onto the cotton fiber. With the advent of technical developments and contemporary mechanized methods of extraction, improvements have been made for the design creation [14].

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Maceration and extraction are other important techniques used. Maceration is a cold or hot technique used in extracting dye from plants and involves soaking the pulverized plant part in a closed container with some solvents and occasionally shaking or stirring the contents. The process is completed by straining the dye extract from the plant parts. Extraction is carried out by a suitable soxhlet extraction technique, where the plant part from which the dye is to be extracted is placed in a thimble in between a flask and a condenser and the solvent is refluxed such that it repeatedly washes the solid, extracting the desired compounds into the flask. Extraction is also performed with distilled water in a ultrasonic bath at an optimum mass ratio of plant matter to the liquid volume for a specified time and temperature. Nowadays, the ultrasound-assisted extraction is employed as an alternative technique to the conventional extraction methods. It has enhanced extraction yield and more rapid kinetics and also allows reduced operating temperature for the extraction of more thermolabile compounds of the dye. Grape vinegar is normally used for the color stabilization and to increase the retention amount of dyes when they are applied to the fibers [10, 11]. Across Africa, most of the patterned cloths were produced using a resist dyeing technique to manage the absorption of color. The art of batik (wax painting) is another antique craft used in Africa for decorating fabrics. The batik images or effects are achieved with the help of wax. The artistic appearance on the fabric is totally based on the artistic desire. Some artists paint, brush, or pour the wax onto the fabric, and later apply the dye on the fabric in between the wax. The procedure occurs in a sequence of dyeing, followed by drying and waxing steps. After final application, the fabric is hung up to dry. The final process is to iron the fabric by placing it in between the papers. This enables the wax to be absorbed and thus the vibrant colors and fine crinkle outlines are revealed in the final batik [15]. Tie-dyeing (resist dyeing) is applied to knitted, woven cotton fabric. It typically uses bright colors. The name signifies the resulting pattern or any item that features the patterns. The process is carried out by fabric folded by patterns and binded with strings. This is then followed by the application of dyes. Designs form during the application of different colors to the wet fabric sections. The ties produces beautiful elegant patterns by preventing the whole material from being dyed. The resisting agents used are mostly cassava starch. Pad-batch dyeing or the exhaustion method is one of the most consistent and environment-friendly methods used for cotton. In this process, the fabric is dyed followed by the squeezing out of the excess dye and storage of fabric. The fabric is then washed after 2 to 12 hours,

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thus ensuring waste reduction, simplicity, and speed. This also allows the elimination of salt, reduction of water consumption, and energy consumption. Furthermore, the quantity of dyes, chemicals, labor, and floor are adequately reduced. Automatic dispensing is an enhancement that reduces wastage by precisely calculating the amount of dye to be used in the dyeing process. The exhaustion method is excellent to be used on smaller lots of fabric [3, 16].

3.4 Fashion Fabric with Natural Colors Fashion, fabric, along with style are closely linked together. They should give the impression of being precise on the wearer, when combined together. The fashion industry is a multi-trillion-dollar trade in the world, and involves and encompasses cultural and social history. African people have urbanized wealthy textile traditions and distinguishing forms of dress to converse and augment the meaning of various cultures. African people love to wear clothing and outfits that represent their country, known as the national dress. Either walking casually on a street or attending a special ceremony or occasion, the person with the African fabric soon is the focal point of fashion. Throughout Africa, men wear pre-shaped shirts and garments, along with trousers or sometimes wrappers. Decorations make a distinction between the garments and show their association with the ethnic group. Wearing gowns made of African fabric is the height of African trend. The everlasting exquisiteness and eminence of the fabric is perceptible with or without the awareness of textiles [3, 7, 14]. The petite minutiae bring out the splendor of the larger pattern and is enhanced by the brilliant colors. African clothing is available in many diverse designs, patterns, and colors. Traditional African cloth may feature dazzling colors and geometric patterns. Traditional African fabric that dates back thousands of years is handmade and many cultures produce the traditional African fabrics and hand over the patterns, techniques, and colors to the following generations. But some of them have changed after exposure to other world cultures. Frequently, women are responsible for spinning and dyeing the thread and the men do the weaving of the fabric. Tradition dictates that the different stages of fabric-making had different spiritual or religious significance. Many people are unaware of the cultural importance of traditional African clothes. The approach echoes fabulous years of cultural change and the influence of the other cultures on the tribes of the continent. Customarily, the fabrics are depicted as forms of wearable art [17].

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The techniques for spinning thread and weaving of the fabric are similar, but the patterns and colors and gradient vary from one region to another, Today, the people of this African continent are identified with brightness, vivacity, fun, and life, which are brought about by these brilliant colors. There are different types of fabric in Africa, which are used to design different garments like the Kente, Adire, Ankara, woodin, Aso-oke, and George. These fabrics are made by the different ethnic groups of the continent like the Barkcloth, Mudcloth, Kanga, and Kitenge. The traditional fauna and flora motifs noticed in alabere, Adire, and eleko designs are deeply rooted in Yoruba culture. Each brand of cloth is designed traditionally with its own special and specific trade names derived from dyeing or designing methods. Adire, the patterned textile fabric, still remains the most decorative of all the fashion trends. The symbols of Adire are created, accepted, and standardized through the aspect of the people’s culture. Adire identifies the culture, the language, and an artistic tradition of the people and is a facilitator of the spoken or written word. It is made from cotton fabric and has a traditional color for wrapped skirt, loosely layered blouse, and blue indigo colored head tiles. The beautiful patterns and small spherical designs are produced by pinching up the clothes and tying them with raffia (thread) before the actual dyeing process. Patterns produced in this way have different names [8, 16]. Nigeria produces a hand-dyed Abeokuta cloth by the textile artisans of Itoku, in the western Nigerian city. Gore designs depict the long history and play a major role in the economy and culture of West African countries. It uses a combination of anthropological, archaeological, historical, and artistic approaches. The cloth design is carried out by stamping dye or weaving design into the textiles. Kente is an additional popular African fabric, made by the people of the Gold Coast, the tribes of Ghana. Kente is also known as Nwentoma, or the woven cloths worn only in times of tremendous importance by the royal class. It is a type of silk fabric made of interwoven cloth strips and is native to the Akan people of Ghana and the Ivory Coast, including the Asante, Bono, Fante, and Nzema. It is the best known of all the African textiles, identified by its dazzling, bright multicolored patterns, incredible shapes, and bold designs. The weft designs woven into every available block of plain weave are known as adweneasa. Kente cloths come in various colors and are associated with different occasions. Black specifies maturation and intensified spiritual energy. Blue indicates peace, harmony, and love; green signifies spiritual renewal; and gold signifies royalty, wealth, and spiritual purity. Gray shows cleansing rituals, and maroon is associated with healing. Pink and purple relate with the female essence of life; red shows the

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bloodshed, sacrificial rites, and death; and silver shows the serenity and purity. White signifies festive occasions, and yellow pictures the preciousness and fertility [10, 18]. Akwete are clothes produced in Akwete of Abia state, in eastern Nigeria. They are produced in a broad range of patterns from plain striped ones to an abundantly charming category based on geometrical motifs of domesticated animals. Other patterns include symbolic objects floating or grounded with weaves using extra wafting. Weavers receive a source of their pattern motifs from inspiration, imagination, or original drawings and weave them. Ankara, also known as wax prints, has been produced in Holland and imported to Africa since 1846. Woodin from the Ivory Coast is another artistic feature to be adorned and admired. Different types of woodin designs exist, including Ethnic, Batik, Safari, Afric, and Bassam. Of these, the batiks are the most expensive. African batiks are unique pieces of art, handcrafted by talented artisans. The West African communities have perfected this art of dyeing. Bogolan techniques adopted in Mali are responsible for the high global demand for these products. The rich cultural environment with which the Yoruba of Southwestern Nigeria is endowed has been a catalyst to the wealth of visual artistic expressions emanating from this region, and for which the people have greatly impacted world artistic culture. The Yoruba of Southwestern Nigeria are renowned for their pulsating cultural environment. Aso-oke is a fabric made of strips and then later joined together as a single fabric. The traditional Yoruba women’s Aso-oke outfit consists of a blouse like shirt, a wrapper, the head tie, and a shawl (shoulder slash). This is handloomed and has beautiful geometric patterns worked into the fabric. Also-oak comes in styles of fashion and allows people to be widely choosy on these fabrics. Among the Yoruba, Anaphase, the wild silk, is treasured and woven into a strip of cloth called Sanya, a clothing for some important occasions. The wild silk is used for warp and yarns. In places like Ilorin, cotton fiber is used for warp and the indigenous silk is used for weft. Alari is a silk fiber dyed deep red and woven into narrow band strips, used as wrappers. Agbada is used for wedding as well as other important occasions. Etu is an extraordinary, narrow band, finely woven fabric from indigo-dyed cotton, deep, blue-black in hue. It is special, as it is dyed over a period of 3 years, before its final finishing. Etu is mostly used in funerals and grave happenings [8, 19]. George, a type of fabric originated in the Indian subcontinent, is used for the saris, the traditional outfit of Indian women. This is embraced by some Africans and Nigerians in the eastern region (Ibos and Ijaws), as part of their traditional attire. Some tribes use different colors of Bogolan,

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a  mud-dyed cloth, from Mali, gaining ground internationally. Sequins are enjoyable to wear and offers instant glamour. The solution is wearing a sequin dress elegantly in moderation. The Ariya, the African wedding dress for a woman, is a four-piece gorgeous outfit. The traditional men’s wedding outfit is the Agbada. It is made up of a very long shirt, trousers, and a robe, worn over the shirt, finished off with a hat or head covering. Strip weaving is another textile technique in which large numbers of thin strips of clothes are sewn together to produce a finished fabric. They are produced in West Africa using the handwoven fabric made out of cotton, silk, and rayon fibers. Traditionally, these clothes are hand-spun, even though machine spun types are coming increasingly into use. Wool is also used for weaving the strip weave blankets by the Fulani people in Mali. The khanga comes from the old Bantu (Kiswahili) and is a colorful garment similar to Kitenge, worn by women and occasionally by men throughout Eastern Africa. It is a piece of printed cotton fabric, with a border along all four sides (called Pindo in Swahili). Khangas are very colorful, indeed. There have been a traditional type of dress among women in Central/East Africa. In the East African countries, the fabric adorns some phrases in Kiswahili, and in Central Africa, phrases both in Kiswahili and Lingala are fashionable. Accordingly, the Aso-oke fabric is woven by the Yoruba people and another Adire is a tie-dye fabric produced by the Yoruba people. Kente cloth is woven by the Ashanti and Ewe people and the Bark cloth is fashioned by the Buganda tribe. Mud cloth is created by the Bambara tribe and Kitenge is formed in Kenya and other regions of East Africa. The mud cloth and batik prints continue to be part of some of the world’s most famous silk, linen, and cotton textile mills. Early evidences of dress are depicted in the rock art of Northern, Southern, and Eastern Africa, indicating items of dress and showing association with European, Asian, and Middle Eastern people. Tellem caves in Mali show cloth fragments providing evidence of handwoven apparel prior to Saharan or coastal trade [5, 11]. During the 21st century, African fabrics are fashioned from local resources and tools, such as wrappers. They are handwoven from the handspun cotton threads on handmade looms in the West African countries of Mali, Sierra Leone, and Nigeria. In Ghana, Asante men wear handwoven Kente togas; in Ethiopia, women wear handwoven shawls of sheer, which are white cotton; in Nigeria, Yoruba women garb themselves in indigo resist-dyed wrappers; in Zaire, the Kuba dress in raffia skirts are adorable. In southern Africa, the Ndebele and Xhosa women wrap commercially made blankets around themselves, and Zulu men wrap aprons made of

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skin and dyed. The Baganda in Uganda, the Masai of Kenya, and Somalis from the Horn of Africa traditionally wore bark-cloth wrappers. Masai warriors wear a wrapper, which is either below the knee or very short. They wrap it around the waist and also across one shoulder. The Masai women wear a skirt or cloth wrapped around their waist as well as a blanket or cloth wrapped over their shoulders. Somali people initially wore leather garments, which were of their own making before the 1800s. But very soon, imported cotton textiles influenced the way people dress in the region. The cotton fabrics then dominated the fabric industry, depending on the occasion and the climatic conditions [12, 13]. For festive, ritual, or ceremonial occasions, Ghanaian men wear African wraparound garment similar to the Roman toga. They take a large rectangle of cloth, from time to time as large as six yards square, and wrap it full length around the body with one shoulder uncovered. This is similar to the traditional outfit of the Masai men. This style became internationally visible in the 1960s, as the first president of Ghana was wearing it for ceremonial occasions. Pre-shaped dress involves cutting and sewing lengths of cloth to make a garment fit the body. Common styles among the Ghanian people were the shirts, blouses, robes, and pants, or the Hausa men’s Baba Riga. Cross-cultural contacts influence the design of many of these garments [10, 18]. The colonial impact and trade contacts of the late 19th and early 20th centuries are influenced in several costumes. The long gown (Boubou) made popular by Wolof women in Senegal indicates their origin in the Middle Eastern regions. The gowns of Herero women in Namibia and Efik women in Nigeria and the gown of women in Egypt show their origin in the 19th century. The fabrics also show dominance and variation in their shapes during their weaving process. Along with the Western fashions found across the continent, indigenous fashions also flourish, quite remarkably. In Nigeria, Hausa men wear extremely large drawstring breeches with a Baba Riga over the top. Yoruba men wear wide or narrow trousers, along with a robe (Agbada) and shirt (Dansiki). The men’s collection is tailored from colored, wax-printed cotton, and is interpreted as informal. Sanyan, made from damask, eyelet, brocade, lace, or the handwoven native silk, is considered as the formal wardrobe. In the Republic of Benin, men’s ensemble comprises a heavily embroidered, sleeveless tunic pleated at the neckline and flared at the hipline, and this is combined with embroidered trousers and a cap. In Cote D’Ivoire, Mandinka and Akan men dress in garments known as war shirts or sometimes known as hunter’s shirts. A printed textile used for wrappers in Tanzania and Kenya is known as khanga. It has  a distinct pattern, with bright yellow, green, orange, and

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red colors. The cloth is printed in repeat motifs that include a motto. They communicate political or social viewpoints [5, 7]. A particular type of cloth or dress, worn across the regions, is a visible sign, gesturing the gender, social status, or political system. The impact of fashion trends in the improvement of African clothing relates to the acceptance of new materials and dyes. Many designers in Africa attempt to give their craft a continental touch by utilizing the varying traditions and textile designs in fashionable style. The African fabric is eco-friendly, incredibly beautiful, amazingly attractive, and astonishingly unique; nevertheless, some of them are really very expensive.

3.5 Natural Shades for Environmental Sustainability: Application Aspects The color of natural dyes, from either plant or animal sources, provides substitute to synthetic and complex chemical dyes. These natural shades are environmentally sound, could be grown organically, and are intrinsically carbon neutral. Natural dyeing methods should be supported and highlighted to bring out the high-quality experience of using them. The most important classic natural dyestuffs, weld, cutch, madder, cochineal, and indigo, yield strong colors, are tough to fading, and are relatively fast [12, 14]. The vibrant colors of the natural dyes can be used to proffer real social benefits, provide sustainable livelihoods, make the textile industry more competitive, reduce production costs, and boost the financial system of developing nations. By-products of these dye-yielding crops could be used as an organic compost, as they could provide eco-friendly sound alternatives to other products. They also have the potential to regenerate the natural environment, increase permanent forest cover, and preserve biodiversity. One of the drawbacks is that the use of natural dyes makes the garment more expensive, due to the use of more land area and raw material. Another concern is the production and application of natural dyes. The dyeing process seems to be very time-consuming and expensive. The most important drawback is the nonavailability or less availability of natural dyes. This is not a concern, in case of the small dye run, but for a larger-scale company, it is extremely due to the insufficient supply. Hence, improvisation should be made towards the performance and impacts of natural dyes. Other advantages include the powerful antiseptic property of tannin used as a mordant, in dyeing. The focus should be made for using and planning the dyeing process better and employing more yarn in a single dye bath, avoiding the usage of the full dye bath for a small lot of yarn.

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Furthermore, darker dyes could be added to the previous dye baths so as to enable the reuse of water or colors [6, 20]. It is always preferable to add the color at the yarn stage, as this aids the environment, taking care of the impact the process may have on it. Also, the aesthetic look is improved by adopting this strategy. Dyeing at the fiber stage requires extensive use of water and leads to an uneven absorption of color. The effluent after the dyeing with natural dyes could be cleaned using the natural polymers, which includes the guar gum, locust bean gum, and cassia gum.

3.6 Conclusions Natural dyes present us with innumerable benefits but have many drawbacks in the form of availability, water usage, and the application processes. Nevertheless, it is essential to be aware of the tree species used by the local community members and groups for dyeing their fabrics, the process of extraction, the use of dyes and tannins, the time for dyeing, the influence of these dyes on the livelihood of the people, the current preservation status of the dye, the tannin-producing tree species, the challenges faced by the community members in the species conservation, and the utilization of these species. Fieldwork studies, with the emphasis on the origin of the vivacious cultural environment, are key to understanding the significant contribution and artistic traditions of various communities in the continent, whether it be the application of the natural dyes to the fabric, wood carvings, stones, terracotta, metal sculptures, pottery, bead making, blacksmithing, mat weaving, gourd decoration, cloth weaving, leather work, or pattern cloth dyeing. The level of acceptability, durability, and quality of the fabrics should also be given priority and hence investigated in detail.

References 1. Ali, N.F., EL-Mohamedy, R.S.R., El-Khatibl, E.M., Antimicrobial activity of wool fabric dyed with natural dyes. Res. J. Textile Appeal., 15, 1–10, 2011. 2. Calis, A., Celik, G.Y., Katircioglu, H., Antimicrobial effect of natural dyes on some pathogenic bacteria. Afr. J. Biotechnol., 8, 291–293, 2009. 3. Anuradha Jabasingh, S., Sahu, P., Yimam, A., Enviro-friendly biofinishing of cotton fibers using Aspergillus nidulans AJSU04 cellulases for enhanced uptake of Myrobalan dye from Terminalia chebula. Dyes Pigm., 129, 129– 140, 2016.

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4. Ali, S., Hussain, T., Nawaz, R., Optimization of alkaline extraction of natural dye from Henna leaves and its dyeing on cotton by exhaust method. J. Cleaner Prod., 17, 61–66, 2009. 5. Bechtold, T., Turcanu, A., Ganglberger, E., Natural dyes in modern textile dye houses—How to combine experiences of two centuries to meet the demands of the future? J. Cleaner Prod., 11, 499–509, 2003. 6. Cristea, D. and Vilarem, G., Improving light fastness of natural dyes on cotton yarn. Dyes Pigm., 70, 238–245, 2006. 7. Polakoff, C., African Textiles and Dyeing Techniques, p. 24, Routledge and Kegan Paul Ltd. London and Henley, United Kingdom, 1982. 8. Anuradha Jabasingh, S., Ecofriendly bio-finishing and dyeing of natural fibers, in: Handbook of Textile Coloration and Finishing, M. Shahid, G. Chen, R.-C. Tang (Eds.), pp. 37–53, Studium Press LLC, USA, 2018. 9. Areo, M.O., Adire: The dynamics of yoruba resist-dyed cloths. Afr. J. Contemp. Issue, 2, 3, 313–332, 2004. 10. Wanyama, P.A.G., Kiremire, B.T., Ogwok, P., Murumu, J.S., Indigenous plants in Uganda as potential sources of textile dyes. Afr. J. Plant Sci., 5, 1, 28–39, 2011. 11. Anna, H. and Christian, R.V., The potential use of organically grown dye plants in the organic textile industry. Experiences and results on the cultivation and yields of dyers chamomile (Anhemis tinctoria L.), Dyers Knotweed (Polygonum tinctoria it) and Weld (Reseda luteola L). J. Sustain. Agric., 23, 2, 17–40, 2003. 12. Guinot, P., Annick, G., Gilles, V., Alain, F., Claude, A., Primary flavonoids in Marigold dye: Extraction, structure and involvement in the dyeing process. Phytochem. Anal., 19, 46–51, 2007. 13. Jansen, P.C.M. and Cardon, D., Dyes and Tannins: Plant Resources of Tropical Africa, Backhuys Publishers, Netherlands, 2005. 14. Kriger, C., Cloth in West African History, AltaMira Press, Lanham, MD, 2006. 15. Prideaux, V., A Handbook of Indigo Dyeing, Turnbridge Wells, Search Press Limited, Kent, 2003. 16. Schaedler, K.-F., Weaving in Africa South of the Sahara, Panterra Verlag, Munchen, 1987, Translated by Leonid Prince Lieven and Judy Howell. 17. Murmann, J.P. and Homburg, E., Comparing evolutionary dynamics across different national settings: The case of the synthetic dye industry. J. Evol. Econ., 11, 2, 177–205, 2001. 18. Ado, A., Yahaya, H., Kwalli, A.A., Abdulkadir, R.S., Dyeing of textiles with ecofriendly natural dyes: A review. Int. J. Environ. Monit. Assess., 1, 5, 76–81, 2014. 19. Kechi, A., Chavan, R., Moeckel, R., Ethiopian dye plants as a source of natural dyes for cotton dyeing. Univ. J. Environ. Res. Technol., 3, 4, 501–510, 2013. 20. Murmu, J.S., Characterization of color from some dye-yielding plants in Uganda. Afr. J. Pure App. Chem., 4, 10, 233–239, 2010.

4 Revitalization of Carotenoid-Based Natural Colorants in Applied Field: A Short Review Fazal-ur-Rehman1, Shahid Adeel2*, Kaleem Khan Khosa2, Mahwish Salman3, Atta-ul-Haq2 and Sana Rafi1 1

1

Department of Applied Chemistry, Government College University, Faisalabad, Pakistan 2 Department of Chemistry, Government College University, Faisalabad, Pakistan 3 Department of Biochemistry, Government College University, Faisalabad, Pakistan

Abstract Sustainable products from plants, animals, and minerals being eco-friendly in nature have been welcomed in different applied fields due to the legislative restriction imposed on synthetic colors by many agencies. Natural pigments are found abundantly in nature, where almost 750 species of carotenoids as natural colorants have been found. Carotenoids are the largest group of natural colorants with brilliant colors, i.e., yellow, red, and orange, which have widespread use in different fields. The extraction of carotenoids from different sources needs highly efficient methods that give not only good color yield but also acceptable color characteristics in applied fields. This chapter will deal with the existence, chemistry of carotenoids, extraction methodology using cost-, time-, and labor-efficient tools and their possible application in textiles, food flavors and colors, cosmetics, pharmaceuticals, etc. Hopefully, this chapter will be useful for the research community, traders, and consumers around the world who urge to see the resurgence of carotenoids as natural colorants in applied fields. Keywords: Carotenoids, cosmetics, food and flavors, extraction, natural dye, sustainability, textiles

*Corresponding author: [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (45–78) © 2019 Scrivener Publishing LLC

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4.1 Introduction of Natural Dyes The world is enriched with attractive colors that make life impossible to imagine as a black and white picture. Without color, life is weary, and people from ancient times applied color in their life in different fields such as cloth dyeing, printing, food coloring, cosmetics, and pharmaceuticals [1, 2]. At that time, color was obtained from natural sources such as plants, insects, and microorganisms known as natural colorants [3, 4]. However, the usage of natural colorant had declined in the 19th century due to accidental discovery of synthetic dyes “mauviene” by W.H. Perkin. Synthetic dyes become prominent over time due to their good fastness properties, reproducibility, having brilliant colors, ease in application, and inexpensive nature [5, 6]. Now, eco-consciousness researchers, traders, and consumers are now aware of the hyperallergenicity, carcinogenicity, and noxious effects of preparative colorants [7, 8]. The toxic effects of colorant products especially colorants and their manufacturing process and wastes skewed the global community to reuse natural colorants and to make possible the use of eco-friendly products [9]. Natural dyes not only are biodegradable and biocompatible colorants but also give enormous functional properties to the material that is to be consumed [10, 11]. Due to these properties, researchers and manufacturers are trying their best to explore natural dyes by knowing their chemical composition [12]. Different plants, animals, and microorganisms are producing various chemical constituents such as anthraquinone, indigoid, flavonoids, chlorophyll, and carotenoids (see Scheme 4.1), which are responsible for producing different hues on different substrates such as natural and synthetic fabrics [13, 14] (Scheme 4.1). In this chapter, carotenoid-based natural colorants will be discussed as a short review. This information will help researchers and readers to find possible ways of obtaining carotenoid-based natural colorants from unique plant sources for their use in applied fields.

4.2 Carotenoids as Natural Colorant Carotenoids are one of the complex molecules that impart yellow to red coloration onto materials. Its name was derived from the Latin word Carota, meaning “carrot” (Daucus carota), which is a major source of carotenoid. Carotenoids are tetraterpenoids that have 40 carbons in their backbone. In general, they are C-20 geranylgeranyl diphosphates that are joined together and give C-40, which produces a number of derivatives [15]. In nature, around the globe, more than 750 carotenoid derivatives

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Classification of natural dyes

Structure

Color

Yellow Red Blue Black Brown Purple

Indigoid

Quinones

Source

Tetraterpenoids Tetrapyrrols

Indigo Tyrian purple

Plants Insects Microorganisms

Carotenoid Tannin

Chlorophyll

Anthraquinone Napthaquinone Condensed tannin

Hydrolysed tannin

Flavonoids

Ellagic acid Gallic acid

Anthocyanin Catechin Flavones

Scheme 4.1 Classification of natural dyes on color, structure, and source basis.

are being discovered as natural pigment. However, some of them, such as β-carotene acts to metabolize the eye’s macula and retina in humans. Carotenoids are synthesized by plants, fungi, algae, and bacteria, while animals including humans are unable to synthesize them and are dependent to take from their diet. In plants, these are present in plastids like chlorophyll and take part in photosynthesis as an accessory pigment [16]. Carotenoids not only act as natural colorants but are also applied in food, pharmaceuticals, cosmetics, textiles, and biotechnology. Literature had demonstrated that different sources of carotenoids are being used for commercial production. Cryptococcus (a fungus) was the first source of carotenoid that was used on commercial sale in 1954. Extraction of carotenoid from Rhodotorula glutinis was started in 1963. Astaxanthin as carotenoid was obtained from Phaffia rhodozyma in 1970.  In 1980, -carotene was isolated from Dunaliella salina and was cultivated by Betatine Limited Corporation for large-scale production [17]. After the pathway of carotenoids, isolation has explored new sources and they have been employed for their practical application in daily life.

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4.3 Classification of Carotenoids Carotenoids are classified based on structure, color, and source. The overview of carotenoids given in Scheme 4.2 shows its various types.

4.3.1 Structure-Based Carotenoids Carotenoids are polyene molecules that have alternating double and single bonds and have 40 carbons per molecule. All carotenoids synthesize from C40H56 by process of cyclization, hydrogenation, oxidation, dehydrogenation, chain elongation, and double bond migration [18]. However, chemically, carotenoids are basically present in two types such as carotene and xanthophylls.

4.3.1.1 Carotene Carotenes are a very important class of carotenoids. Oxygen is absent in its molecule and is based merely on carbon and hydrogen. It is nonpolar and highly lipophilic in nature and generally extracted using organic solvents. Due to the presence of a large number of alternative double bonds, it absorbs light at a higher wavelength, i.e., 400–500 nm, and yields orange-red pigments onto substrates. It has various isomers such as alpha-, Classification of Carotenoids

Structure

Source

Color

Yellow Red Orange

Deoxygenated carotenoids (Carotene)

Oxygenated carotenoids (Xanthophylls)

Alpha-carotene, beta-carotene Lycopene Beta-Cryptoxanthin

Zeaxanthin Astaxanthin Lutein Violaxanthin Neoxanthin Bixin Capsanthin

Scheme 4.2 Classification of carotenoids based on color, structure, and source.

Plants Microorganisms

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beta-, gamma-, delta-, epsilon-, and zeta-carotene. However - and carotene are more important constituents for pigmentation (Figure 4.1a to  f). Different carotenes along with their chemical structure and origin are given below. H3C CH3

CH3

CH3

CH3

CH3

CH3

Present in spinach, mangoes, cantaloupe, kale, carrots, sweet potato, broccoli etc.

H3C CH3

CH3

Figure 4.1a α-Carotene.

H3C

CH3

CH3

H3C

CH3

Found in Carrot, Pumpkin, potato etc.

CH3

CH3

CH3

H3C

CH3

Figure 4.1b β-Carotene.

H3C CH3

CH3

Mainly present in tomato, Pink guava and water melon.

CH3

CH3 H3C

CH3

CH3

Figure 4.1c Lycopene.

Intermediate in the biosynthesis of lycopene

Figure 4.1d Neorosporene.

Present in tomato

Figure 4.1e Phytofluene.

CH3

CH3

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Present in tomato

Figure 4.1f Phytoene.

4.3.1.2 Xanthophylls Xanthophylls are the class of carotenoids that have oxygen-containing functional groups such as hydroxyl, keto, epoxy, methoxy, carboxylic acid, etc. Xanthophylls are pigments that are mostly located in the green parts of the plants and impart yellow color. These are more polar in nature than carotenes. Zeaxanthin, astaxanthin, lutein, violaxanthin, neoxanthin, echinenone, isocryptoxanthin, isozeaxanthin, tunaxanthin, fucoxanthin, xeinoxanthin, bixin, crocin, crocetin, capsorubin, and capsanthin are examples of xanthophylls (Figure 4.2a to n). Lutein, bixin, capsorubin, capsanthin, crocin, and crocetin are derived from food sources while others come from microorganisms such as algae, fungi, bacteria, or marine organisms.

H3C

H3C

CH3

CH3

CH3

Mainly found in Spice i.e., Paprika

CH3

CH3

HO

CH3

H3C

CH3

Figure 4.2a β-Cryptoxanthin.

H3C

CH3

CH3

H3C

CH3

CH3

CH3

CH3

H3C

CH3

OH

Figure 4.2b Isocryptoxanthin.

H3C

CH3

CH3

H3C

CH3

H 3C HO

CH3

Figure 4.2c Zeaxanthin.

CH3

CH3

OH

CH3

Commonly found in green leafy vegetables such as spinach

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51

OH

H3C

CH3

CH3

H3C

CH3

H3C CH3

CH3

CH3

OH

Figure 4.2d Iso-zeaxanthin. O CH3

H3C CH3

OH

CH3 H3C

CH3

CH3

HO

H3C

CH3

Producer of astaxanthin are microbes and marine organisms

CH3

O

Figure 4.2e Astaxanthin.

H3C

CH3

CH3

OH Marigold

CH3

CH3

HO

H 3C

CH3

CH3

H3C

CH3

Figure 4.2f Lutein. CH3 H3C

CH3

CH3

CH3

HO

CH3

OH

O CH3

CH3

H3C

Pansies CH3

Figure 4.2g Violaxanthin. OH

O

OH

Figure 4.2h Neoxanthin.

OH

Green leafy vegetables i.e. spinach

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COOH

Annatto

H3COOC

Figure 4.2i Bixin. OH CH3

H3C CH3

CH3

H3C

CH3 O

CH3

CH3

HO

Spice i.e. Paprika

CH3

CH3

Figure 4.2j Capsanthin. OCOCH3

HO

Found in seaweed, pomegranate and brown algae as brown pigment

C O HO

O

Figure 4.2k Fucoxanthin. OH

HO

Present in marine organism such as salmon fish, crab, trout, shrimp etc.

Figure 4.2l Tunaxanthin. H3C

CH3

CH3

CH3

CH3

CH3

CH3

H3C

CH3

Produced by cyanobacteria and sea urchin

O

Figure 4.2m Echinenone. CH3 H3C

HO

H3C

CH3

CH3

CH3

Figure 4.2n Zeinoxanthin.

CH3

CH3

H3C

CH3

Carotenoid-Based Natural Colorants

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4.3.2 Color Carotenoids have three different colors, i.e., red, orange, and yellow. Carotenoids and chlorophyll in plants are not present independently, and their ratio provides a variety of colors to different parts of the plants [19]. Carotenoids absorb light in the range of 400–500 nm and thus produce yellow, orange, and red colors.

4.3.2.1 Red The red pigment is mainly produced by lycopene, astaxanthin, tunaxanthin, delta-carotene, and bixin [20, 21]. These have conjugated double bonds that help to impart red coloration onto materials. Lycopene is basically found in fruits and vegetables, i.e., papaya (Carica papaya), pink grapefruit (Citrus paradise), tomato (Lycopersicon esculentum), red cabbage (Brassica oleracea), asparagus (Asparagus officinalis), dry persimmon (Diospyros kaki), pink guava (Psidium guajava), watermelon (Citrullus lanatus), etc. [22]. The famous annatto seeds (Bixa orellana) contain bixin, which, upon hydrolysis, is converted into norbixin, which acts as a natural red colorant. It has significant applications in food, cosmetics, and the textile industry. Similarly, marine animals such as salmon, trout, shrimp, lobster, and crab are also enriched with red pigment based on astaxanthin and tunaxanthin.

4.3.2.2 Yellow Carotenes such as lutein, violaxanthin, crocin, neoxanthin, zeaxanthin, -cryptoxanthin, and -carotene impart yellow coloration to substrates. Lutein gives a yellow coloration absorbed as blue light. It is mainly found in fruits and vegetables and is very common example of the xanthophyll group. Lutein is commonly found in fruits and green leafy vegetables. Marigold (Tagetes erecta) is the best example of a plant containing lutein that imparts yellow color onto the matrix abundantly. However, marigold also comprises zeaxanthin. Crocin and crocetin are xanthophyll carotenoids that are obtained from saffron (Crocus sativus) as yellow pigment (Figure 4.3a and b). Other examples of lutein-containing sources are wild cabbage (Brassica oleracea), lettuce (Lactuca sativa), hummingbird tree (Serbania grandiflora), spinach (Spinacia oleracea), katuk (Sauropus androgynous), eggplant (Solanum melongena), paprika (Capsicum annuum), ivy gourd (Coccinia grandis) and pumpkin (Cucurbita maxima). Similarly, -cryptoxanthin and -carotene produce yellow color, while in the presence of zeaxanthin, they give an orange-yellow color.

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CH3

O

O O

O

O

HO

OH

O

O

OH O

OH

O O

CH3

CH3

OH

OH HO

HO

OH OH HO

OH

Figure 4.3a Crocin.

COOH HOOC

Figure 4.3b Crocetin.

4.3.2.3 Orange β-Carotene is the best source of orange coloration. β-Carotene is mainly found in carrot, sweet potato, and tomato [23]. Other sources of β-carotene are yellow maize (Zea mays), black nightshade (Solanum nigrum), and mulla thotakura (Amaranthus spinosus). Similarly, β-cryptoxanthin is also a big source of orange color and is mainly found in pepper (Capsicum annuum), starfruit (Averrhoa carambola), persimmon (Diospyrus kaki), and papaya (Carica papaya). It has also been noted that pigment color also depends on its concentration. The higher the concentration of the pigment, the color tone moves from yellow to red such as the palm fruit giving yellow coloration of -carotene at lower concentrations and red at higher concentrations.

4.4 Sources of Carotenoids as Natural Pigment The major sources of carotenoids are plants and microorganisms. Animals are unable to synthesize carotenoids and take them from diet. Details on plant-derived carotenoids are as follows.

4.4.1 Plants In plants, carotenoids are located in plastids as a complex carotene protein. They are present along with chlorophyll as carotene-chlorophyll or

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xanthophyll carotene. Therefore, the concentration of carotenoids is higher in vegetables or green leaves as compared to fruits, flower petals, or the wood part of the plant. However, papaya (Carica papaya) and persimmon (Diospyros kaki) have higher contents of lutein and zeaxanthin (Table 4.1). Most of the petals have xanthophylls and are responsible for the yellow coloration. Oakwood (Quercus robur), chestnut (Cartanea sativa), and beech (Fagus sylvatica) also have carotenoids in the form of lutein and β-carotene. Annatto (Bixa orellana) is one of the historical natural red colorants for food, cosmetics, etc. and is also known as achiote or lipstick tree. Other constituents present in the seeds of annatto are lutein, cryptoxanthin, β-carotene, zeaxanthin, and methylbixin at minimum amount. Paprika (Capsicum annuum), which originated from the Latin word pepper, is a familiar spice that contains capsanthin and capsorubin (shown in Figure 4.4) as the main coloring component and produces orange-red coloration [24]. Other carotenoids that are also present in paprika are lutein, β-carotene, β-cryptoxanthin, zeaxanthin, and violaxanthin. Table 4.1 Plant-derived carotenoids. Source

Chemical constituents

Avocado (Persea americana)

Lutein, α-carotene, β-carotene, neoxanthin, violaxanthin, zeaxanthin, antheraxanthin

Cantaloupe (Cucumis melo var. cantalupensis)

β-Carotene

Dandelion greens (Taxacum officinale)

Lutein, β-carotene

Papaya (Carica papaya)

β-Carotene, β-cryptoxanthin, lycopene

Pumpkin (Cucurbita pepo)

β-Carotene, lutein, lycopene, α-carotene

Spinach (Spinacia oleracea)

β-Carotene, violaxanthin, neoxanthin

Sweet potato (Ipomoea batatas)

β-Carotene

Tangerine (Citrus reticulate)

β-Carotene, cryptoxanthin

Turnip greens (Brassica rapa)

β-Carotene, lutein, zeaxanthin

Watermelon (Citrullus lanatus)

Lycopene, β-carotene, neoxanthin

Winter squash (Cucurbita maxima)

Lutein, zeaxanthin, β-carotene

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O OH

HO O

Figure 4.4 Capsorubin.

H3C

CH3

CH3

H 3C

CH3

H3C HO

CH3

CH3

CH3

CH3

Figure 4.5 Rubioxanthin.

Flame plant (Delonix regia) is also considered as a major source of carotenoids. Previous studies revealed that petals of Delonix regia have 29 carotenoids that are responsible for the yellow coloration onto stuff, including -carotene, lycopene, rubiaxanthin (Figure 4.5), lutein, zeaxanthin, phytoene, phytofluene, etc. The dried stigma of saffron (Crocus sativus) is used (instead of the whole flower) as a natural yellow colorant. The main coloring component responsible for the yellow color is water-soluble crocin. Other constituents are also present such as apocarotenoids, crocetin glycosides, picrocrocin, and safranal that are obtained after degradation of zeaxanthin. Carrot is also one of the major natural sources of carotenoids that give orange pigment due to the presence of β-carotene moiety. β-Carotene is mostly accumulated in the root part of the carrot. Carrot contains 80% β-carotene along with α-carotene and lutein with minimum concentration. The flower of marigold also contains lutein as a major colorant and yields yellow coloration.

4.4.2 Microorganisms Microbes such as algae, fungi, and bacteria are also prominent sources of carotenoid due to their easy production, easy cultivation, isolation, no climate issue, higher stability to pH, mineral and temperature, economic value, and time-conserving property. There is an increase in the detrimental effects of synthetic colorants, and the production of natural colorants such as carotenoids from natural sources especially from microbes has been dramatically increased. Many industries cultivated microbes in liquid or

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solid media through fermentation, producing carotenoids. The fish industry uses carotenoid as a feed to enhance the pink coloration of salmon. Food, cosmetics, and textile industries use microbial carotenoid for coloration purposes. The pharmaceutical industry uses carotenoids due to their antioxidant, anti-pathogenic, anti-inflammatory, and anti-cancer properties. Photosynthetic bacteria can synthesize 80% of carotenoids. Various microbial families such as Myxococcus streptomyces, Mycobacterium kansasii, Agrobacterium tumefaciens, Sulfolobus shibatae, Agromyces ramosus, Microbacterium arborescens, and Leifsonia sensulato and members of Microbacteriaceae are key producers of carotenoids. Astaxanthin is an important class of carotenoids that is rarely produced by plants. The main sources of astaxanthin are bacteria, fungi, algae, and aquatic animals such as shrimp, crab, salmon, etc. that give an orange-red color. It has higher antioxidant and photoprotective activity than β-carotene and lutein. Due to increase in the demand of astaxanthin as a natural red colorant, it can be produced from different microbes at the commercial level. Different species such as Phaffia rhodozoa, Haematococcus pluvialis, red basidiomycetous (yeast), Agrobacterium aurantiacum, Xanthophyllomyces dendrorhous, and Bradyrhizobium [21, 25, 26]. Astaxanthin from marine bacteria such as Paracoccus sp., Brevundimonas, Erythrobacter sp., Halobacterium sp., Altererythrobacter ishigakiensis, Sphingo microbium astaxanthinifaciens, and Sphingomonas faeni [27]. Another source of carotenoid is β-carotene, which is obtained by cultivation of Phycomyces in solid or liquid and Mucor circinelloides in blue light. Similarly, β-carotene from Blakeslea trispora is produced by fermentation process [28]. Other sources such as Dunaliella salina and red algae Rhodophyta also produce β-carotene along with -carotene, lutein, zeaxanthin, and β-cryptoxanthin [29]. The major source of canthaxanthin as orange pigment is produced by photosynthetic bacteria such as Bradyrhizobium japonicum and Dietzia natronolimnaea, whereas the fungal species Fusarium sporotrichioides, which is genetically modified, produces lycopene colorant [30]. However, the concentration of microbial carotenoids depends on some factors such as culture media, fermentation process, and time of incubation [31].

4.5 Functional Assets of Carotenoids In addition to carotenoids being a great source of natural pigment, they also have some biological functions that are valuable for human health and the global ecosystem. Various derivatives of carotenoids have antioxidant,

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antibacterial, anti-inflammatory, and anticancer properties, as well as the ability to regulate immune response [32].

4.5.1 Antioxidant Activity Antioxidants are those moieties that have the capability to reduce the formation of free radicals or singlet oxygen that cause various chronic diseases such as cancer, heart-related diseases, diabetes, etc. Singlet oxygen are highly unstable and reactive species that react with DNA, protein, and other metabolites in the body and disturb the human immune system. Carotenoids are enriched with various natural bioactive components that have the capability to quench the singlet reactive oxygen and protect from oxidative stress. Literature has shown the antioxidant properties of various plants and microbes that have natural carotenoid pigment. Naguib examined the antioxidant properties of oxygenated and de-oxygenated carotenoids such as astaxanthin, lutein, β-carotene, α-carotene, lycopene, and ketocarotenoid [33]. They found that, among all carotenoids, astaxanthin has the best antioxidant property. The antioxidant properties of carotenoids such as β-carotene are mainly due to the presence of the number of double bonds that have high reducing ability and help to scavenge free radicals [34]. Previously, it has also been found that saffron is an excellent source of antioxidants, it is used in the cure of Alzheimer’s disease [35]. They also found that saffron has the ability to reduce the aggregation of β-peptide (Aβ) fibrils in human brain, which is the main cause of Alzheimer’s disease. Prommuak et al. examined the antioxidant activity of Thai silk with carotenoid pigment and without carotenoid pigment [36]. They found that pigmented silk has a higher capability to scavenge free radicals than Sericin silk alone. Another carotenoid, i.e., staphyloxanthin, is a yellow pigment that has been produced by Staphylococcus aureus and has high antioxidant potential [37]. Pepper (Capsicum annuum) is commonly known as a traditional spice food and has medicinal value as well. The principal constituents present in pepper are capsanthin, capsaicinoids, and phenolic components, which make it a great antioxidant source [38]. Yuan et al. examined the antioxidant activity and stability of astaxanthin and proved that astaxanthin has high radical scavenging property [39]. Kasperczyk et al. have reported that β-carotene has the ability to minimize oxidative stress in vivo [40]. Prabhakara Rao et al. used annatto seeds and examined their antioxidant and stability power. They found that annatto seeds have highly antioxidant properties and have high stability on exposure to UV radiation [41]. Kehili et al. observed the quenching ability of lycopene and β-carotene that were extracted from

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tomato and they found good antioxidant activity [42]. Roehrs et al. examined the effect of annatto dye on oxidative stress and the immune system. They found that norbixin in annatto dye has coped with oxidative stress and regulates the human immune response to great extent [43]. Pogorzelska et al. also investigated the antioxidant activity of astaxanthin component that has been derived from algae Haematococcus pluvialis and found outstanding results [44].

4.5.2 Antimicrobial Activity In antimicrobial activity, a bioactive component must play the role of inhibiting the growth of pathogenic bacteria or even killing them. In the textile industry, various functional finishing processes are being employed in which toxic antimicrobial reagents are used. However, with the passage of time, pathogenic bacteria became resistant to the antibiotic agents or chemicals and can cause very harmful or infectious diseases. For such reason, scientists and researchers try to find a way to overcome such problems by developing potent antimicrobial agents. Previous studies also revealed that similar to other bioactive constituents such as flavonoids, tannin, and anthraquinone, carotenoids also exhibit antimicrobial potential. Venugopalan and Giridhar extracted annatto in different solvent media and observed its antimicrobial activity against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Bacillus subtilis. They found that annatto inhibits the growth of all bacterial species and thus has potent antimicrobial properties [45]. Teli et al. described the antimicrobial activity of soybean protein fabric that has been dyed with marigold flower as temple waste [46]. Yolmeh et al. observed the antimicrobial activity of annatto against the highly pathogenic bacteria Salmonella enteritidis. They concluded that annatto seeds have minimized the population of S. enteritidis and increased the storage capacity of substrate that is to be treated with annatto [47]. Similarly, Yolmeh et al. did the same experiment on annatto dye sample against Escherichia coli and found the same results [48]. dos Santos et al. have found the antifungal properties of Capsicum annuum that inhibit the formation of phytopathogenic bacteria (Fusarium lateritium) [49]. Nathan et al. also reported the antimicrobial property of annatto seeds that were mainly subjected to bixin and norbixin components present in the dye [50]. In another study, red sweet pepper (Capsicum annuum) has been extracted in aqueous and organic media, and its biological activity has been determined. They found that pepper has high cytotoxic, antimicrobial, and antioxidant activity [51].

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4.5.3 Photoprotection Property The rays from sunlight is the biggest source of UV radiation, which has shorter wavelength and high penetration power, making it dangerous to skin and eye cataracts and causing various diseases such as genetic disorder, erythema, skin cancer, vision loss, etc. However, carotenoids have the ability to absorb such shorter wavelength and protect the human and plant’s DNA from damage and prevent genetic variation. Cesarini et al. described the effect of -carotene on skin as photoprotection against UV light [52]. Aust et al. observed that lycopene obtained from tomato has the ability to act as a photoprotective agent [53]. Unsaturation present in the lutein and zeaxanthin structure protects the eyes from vision loss as it absorbs dangerous blue light that causes macular degeneration [54]. The photoprotective properties of silk fabric dyed with Delonix regia as carotenoid source have been proven by Teli and Pandit [55]. Astaxanthin and zeaxanthin that yield red and yellow color have the ability to protect skin from photodamage [56]. Hence, overall, carotenoids have a great potential to exhibit antimicrobial, UV-protective, and antioxidant activity. Thus, the use of natural carotenoid as a natural colorant and functional agent can be recommended to reduce the consumption of synthetic functional finishing material that is toxic to the ecosystem.

4.6 Extraction Phenomenon of Carotenoids Extraction is the process in which the desired component is transferred from raw material to the solvent. The demand for natural dyes has increased due to its eco-friendly, biodegradable, and hygienic properties compared to synthetic dyes. Carotenoid is one of the natural colorant sources that has been demanded by the global community to be a part of the food, textile, cosmetics, and pharmaceutical industries. To improve the extraction methodology, various conventional and advanced methods are being employed by researchers to increase the yield of carotenoids and their existence in applied fields.

4.6.1 Conventional Methods Different researchers use different conventional methods to extract carotenoids in organic solvents, namely, the soxhlet method, maceration process, boiling method, etc.

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4.6.1.1 Solvent Method Because most of the carotenoids are lipophilic or less polar, they are mostly solubilized in organic solvents such as alcohol, acetone, hexane, etc. For example, Daood et al. used organic media to extract carotenoids from red pepper and tomato [57]. Fikselova et al. employed different extraction conditions such as temperature, time, and solvent to extract carotenoid from carrot [58]. In the study of Wu et al., a great concentration of capsanthin from seed containing chili was observed in acetone media [59]. Rebecca et al. extracted carotenoid from red and yellow capsicum (Capsicum annuum), red spinach (Amaranthus dubius), carrot (Daucus carota), and broccoli (Brassica oleracea) in organic solvent [60]. Derrien et al. extracted lutein from spinach using water and methanol as solvent media. They observed that methanol is a better solvent than water to extract lutein efficiently [61]. Vargas et al. extracted carotenoid from peach (Prunus persica) using ethanol as solvent media [62]. All the examples demonstrated that carotenoids are best dissolved in organic media due to its less polar nature.

4.6.1.2 Soxhlet Method Soxhlet extraction method is another conventional method that has been employed by various researchers to increase extraction efficiency. For example, Chen and Wu used the soxhlet method for extraction of coloring pigment from capsanthin using organic solvents and gained reasonable yield [63]. Ismail used the soxhlet method to extract -carotene from carrot in acetone and alcohol solvent. He found that acetone was the best solvent to extract -carotene, yielding a greater amount [64]. RaybaudiMassilia et al. observed the biological activity of red sweet pepper in aqueous and organic media by employing maceration and the soxhlet method for extraction [51].

4.6.2 Advanced Methods Conventional methods are observed to be less advantageous as these tools consume a lot of solvents, time, energy, and labor but provide less color yield. For such reason, researchers have developed and employed a novel method of extraction that can isolate the carotenoids with higher yield. These methods include the following: 1. Supercritical fluid method (SFC) 2. Pressurized liquid extraction

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Microwave radiation Ultrasonic radiation Gamma radiation Ultraviolet radiation

The utilizations of such methods in the extraction of carotenoids are discussed below in detail.

4.6.2.1 Supercritical Fluid Method Extraction of coloring component with the supercritical fluid method is one of the revolutionary methods in which less solvent is being consumed. It is a greener process that uses compressed carbon dioxide as solvent. Various studies reveal that extraction of natural colorant using the supercritical fluid method is higher than that using the conventional method. Lycopene is water insoluble and fairly soluble in toxic and expensive organic solvents such as alcohol, acetone, and hexane. However, to tackle such problems, various researchers have used the supercritical fluid extraction method that not only reduces the consumption of toxic solvent but also increases the color yield. A study of Beltrame et al. demonstrated that dyeing of cotton fabric with natural lycopene dye using the supercritical fluid method has increased the dye uptake ability [65]. To increase the extraction yield, Cadoni et al. employed the supercritical fluid method to isolate lycopene and -carotene from ripe tomatoes [66]. Vasapollo et al. extracted lycopene from tomato using the supercritical fluid extraction method in conjunction with vegetable oil as co-solvent and found significant yield [67]. Vági et al. extracted lycopene and -carotene from tomato waste using the supercritical fluid method and found an increase in yield [68]. Macías-Sánchez et al. (2009) extracted carotenoid from Dunaliella salina using ultrasound and the supercritical fluid method and compared the results. They noticed that the supercritical fluid method is the best option to achieve higher yield [69]. Nobre et al. also employed the supercritical fluid method to extract lycopene from tomato waste and found excellent yield [70]. Wu et al. obtained crimson red coloration on milk protein fiber dyed with capsanthin using the supercritical fluid method [71]. Guo et al. dyed kenaf fiber with capsanthin using the supercritical fluid method and found good K/S on dyed fabric [72]. Taham et al. also employed the supercritical fluid method to efficiently extract colorant (bixin) from annatto seeds [73]. Hence, the supercritical fluid method, being a clean and eco-friendly tool, is gaining popularity in the extraction of carotenoids from plant sources.

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4.6.2.2 Pressurized Liquid Extraction (PLE) The pressurized liquid extraction (PLE) method is a greener process that uses less solvent and energy and gives higher yield with minimum time consumption. Pressurized liquid extraction was implemented by Santos et al. to extract the coloring component from annatto seeds and jabuticaba skins effectively [74]. Similarly, Mustafa et al. extracted -carotene from tomato using the PLE method and found that this method helps to upsurge the yield to a great extent [75].

4.6.2.3 Ultrasound Method The sonication technique is the cavitation phenomenon in which the formation and burst of bubbles increases the kinetic energy that ultimately increases the temperature, reaction rate, extraction of colorant, and dye uptake ability. Literature review showed the application of ultrasound technique in carotenoid extraction and dyeing phenomenon. Lianfu and Zelong found the extraction efficiency of lycopene from tomato using microwave/ultrasonic and ultrasonic methods and compared the results. They found that the microwave/ultrasonic extraction method was best to achieve higher colorant yield [76]. Wang et al. and Jiang and Wu have employed the ultrasonic method for extraction of capsanthin from capsicum and lycopene from fresh tomato. The result indicated that ultrasound has increased the colorant yield from good to excellent [77, 78]. Kamel et al. extracted colorant from Crocus sativus using the ultrasound technique and dyed cotton fabric and compared the results with the traditional extraction method. The result indicated that the traditional method has produced lower yields as compared to the ultrasonic method and low color character is found [79]. Zhang et al. extracted capsanthin using ultrasonic treatment as green process and noticed that extraction yield was increased with the sonication process [80]. Ali et al. used the sonication process to effectively extract carotene from Daucus carota. The extracted carotene pigment was then used to dye silk fabric that showed excellent color fastness properties [81]. For the effective extraction of lycopene colorant from tomato waste, Kumcuoglu et al. have adopted the ultrasound method. They found that ultrasonic-assisted extraction has minimized the consumption of energy, time, and toxic organic solvents [82]. Srivastava and Vankar explored a new source of carotenoid that was extracted from petals of Canna flower using the ultrasonic method. They also investigated the antioxidant properties with improved extraction efficiency [83]. Yan et al. extracted carotenoid as coloring component from rapeseed meal using ultrasonic

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treatment in organic solvents. The results found that the ultrasonic method has increased the isolation of coloring component to a great extent [84]. Yolmeh et al. found that ultrasonic-assisted extraction has helped to increase the color yield from annatto (Bixa orellana) compared to the conventional method [85]. Goula et al. also used the sonication method for extraction of carotenoid content from pomegranate peel [86]. Nguyen and Dang extracted bixin pigment from annatto seeds using the ultrasonic method as a green process and found excellent yield [87]. Thus, US treatment being a clean heating source is also found to be a good method for extraction of carotenoids.

4.6.2.4 Microwave Radiation Microwave energy has played an important role in the extraction process. It increases the reaction rate and transferability of colorant to the solvent with minimum consumption of time, energy, and cost. It also ruptures the cell wall and isolates the color from hard stuff via mass transfer kinetics. When electromagnetic radiation propagates, the molecules of solvent change their orientation and cause friction. This friction is responsible for heat energy that is used to transfer the coloring component from plant material to the solvent. Sinha et al. showed the use of microwave energy for the extraction of bixin colorant from annatto. Studies revealed that microwave has improved the extraction process and produced colorant with maximum yield [88]. Chumnanpaisont et al. as well as Hiranvarachat and Devahastin extracted -carotene from carrot peels using microwave radiation and observed excellent results [89, 90].

4.6.2.5 Ultraviolet Radiation UV radiation also has an integral role in the extraction of carotenoids and dyeing onto natural fabrics to increase the dye uptake ability and color strength. Rehman et al. examined the effect of UV radiation on lutein dye powder and cotton fabric. Examination of the color strength and fastness properties of dyed fabric revealed that UV radiation has helped to increase the dye uptake ability without affecting any of the physiochemical properties of dyed fabric [91].

4.6.2.6 Gamma Radiation Gamma radiations are a powerful energy source that has the ability to extract the coloring matter from the source with minimum time loss,

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energy, and water. It also increases the wettability, dye uptake ability, and morphological changes of fabric surface. Carotenoids are complex lipophilic molecules that have less solubility in water and need toxic organic solvents to be extracted. However, gamma radiation is an effective tool in the extraction of carotenoid pigment from plant material without use of any harmful solvents and is thus implemented as a green process. They remarked that 32 kGy was an optimum absorbed dose that enables the effective removal of desired component from plant material. Hence, these modern tools not only have made the natural dyeing process more viable but also enhance their color characteristics.

4.7 Potential Resurgence of Carotenoids in Textile Dyeing and printing of fabric with natural colorant is as old as human civilization. However, the emergence of synthetic dyes in 1856 has limited the use of natural dyes. But recently, evidence of serious health effects caused by synthetic colorants drastically forced global textile industrialists to use eco-friendly products. Natural dyes not only are noncarcinogenic and nontoxic but also provide functional and hygienic characteristics to the fabric; thus, their applied resurgence has been revised in many fields. Carotenoids are one of the natural dye classes that have been blessed with various functional properties like antioxidant, antipathogenic, and UV-protective properties. They also have a strong aroma and a pleasant taste that help to keep the fabric fresh. The natural orange, yellow, and red coloration obtained from carotenoids also provides a cool and soothing sensation to the eye. Literature studies have proven the useful application of different sources of carotenoids in textile coloration. The following are the plant-derived sources of carotenoids that are being used in textile.

4.7.1 Marigold Marigold is a major source of lutein as yellow pigment and has been used by various researchers to extract coloring component for textile coloration. They observed various shades on cotton depending on the mordant used. Montazer and Parvinzadeh have dyed wool fabric with marigold in the presence of alum mordant and ammonia treatment [92]. Jothi has used marigold as natural yellow color and dyed silk and cotton fabric in the presence of a different mordant. He observed that lutein after making

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coordination complex with mordant exhibits good fastness characteristics [93]. Vankar et al. and Jain have collected the waste of marigold and utilized it as a source of natural yellow color and dyed cotton, wool, and silk fabric. They also applied different mordants to observe the different hue production after making a complex of mordant and dye [94, 95]. Teli et al. employed the waste of marigold flower as an eco-friendly natural dye and dyed soyabean protein fabric. Effective dyeing has been achieved by using different chemicals and biomordants that helped to fix the dye components onto fabric [46]. Khattak et al. dyed cotton fabric with marigold flower using the pad steam method in the presence of different metal mordants. They found that light yellow, deep yellow, and other shades depend on the mordants used and observed remarkable fastness properties [96]. Teli et al. pretreated cotton fabric with chitosan as biomordants and dyed with catechu and marigold. They also found antipathogenic activity against gram-positive and gram-negative bacteria [97]. Chavan and Ghosh collected African marigold flower and used it to dye cotton and silk fabric in the presence of different chemical mordants. The results demonstrated good fastness properties due to the strong coordination between dye, mordant, and fabric [98]. Ali et al. have adopted the central composite design method to extract the coloring component from marigold and applied it on cotton fabric. They determined that extraction at pH 4 resulted in maximum shades and fastness properties on dyed fabric [99]. Morshed et al. also extracted coloring material from marigold along with other natural dye sources and applied them on cotton fabric. They found that these natural dyes could be effectively used in place of toxic synthetic dyes [100]. Adeel et al. have employed the marigold flower to dye cotton fabric using gamma radiation. They noticed that dyeing with an optimum absorbed dose of 30 kGy of gamma radiation has remarkably increased the color depth and fastness characteristics of the dyed fabric [101].

4.7.2 Saffron Saffron (carotenoid pigment) is another major source of yellow coloration for textile. The stigmas of saffron contain crocin as the main yellow carotenoid pigment. Tsatsaroni et al. pretreated wool and cotton fabric with enzyme and proteins and dyed them with saffron colorant. They examined the effect of pretreatment on dyeing ability [102]. Gui-zhen has also employed saffron petals as natural yellow coloration to dye silk fabric [103]. Raja et al. observed the dyeing capability of waste saffron petals on wool fabric. They observed that wastes of the saffron flower have retained dye contents and have the ability to produce yellow coloration on pashmina

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wool fabric [104]. Dyeing of wool fabric with saffron petals in the presence of different mordants have been adopted by Mortazavi et al. [105]. They found that mordants have aided to improve color depth and fastness properties. Ghaheh et al. extracted natural colorant from green tea, madder, turmeric, saffron petals, and henna to color wool fabric in the presence of different mordants. They also observed their biological activities as well. They found that all sources of natural colorant have effective bioactive properties against various pathogenic microbes [106]. El-Khatib et al. have also employed saffron dye as a source of natural yellow color to dye silk and silk fabric. Before dyeing, the fabrics were pretreated with neem oil to cause swelling action in fabric to achieve easy penetration of dye into the fabric. The results also evaluated high color depth, fastness properties, and functional properties on dyed fabric [107].

4.7.3 Pepper Pepper not only is used as a spice but also has coloring and medicinal properties. Kulkarni et al. reported the use of chili skin as a source of carotenoid for dyeing of cotton fabric followed by pre-, post-, and simultaneous mordanting. They remarked that mordants not only help to make a firm bond between dye and fabric but also give different shades of yellow color [108]. Similarly, El Ksibi et al. used chili for coloration of wool fabric and investigated their antimicrobial ability against human pathogens [109].

4.7.4 Annatto They found fair to good fastness properties with the application of mordants. Savvidis et al. have printed cotton fabric with annatto seeds along with 10 other natural dyes using chemical mordants. Using Spectraflash, they evaluated that color fastness properties to light and rubbing and washing of dyed fabric were excellent [110–112]. Chattopadhyay et al. used annatto seeds as natural red color to dye jute fabric in the presence of chemicals and biomordants. They found that mordants helped to improve the fixation of the dye component onto the fabric and thus enhanced color strength properties [113]. Islam et al. have also reported the use of annatto seeds as natural red coloration for dyeing of wool fabric followed by different mordants and ammonia treatment [114, 115]. Chattopadhyay et al. dyed jute fabric with annatto dye in combination with other natural dyes. They also evaluated the fastness properties and functional properties on dyed fabric [116]. Similarly, Moses and Venkataraman also used annatto seeds in dyeing of cotton fabric and examined the functional properties of dyed fabric [117].

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4.7.5 Tomato Carvalho and Santos dyed polyester fabric with lycopene as natural red color that was obtained from Solanum lycopersium fruit [118]. Similarly, Baaka et al. have extracted lycopene colorant from tomato as a source of red coloration and used to dye wool, silk, and polyamide fabric. They also investigated the antioxidant and fastness properties of dyed fabric. The results showed that tomato is a greener source of natural colorant that provides functional property to the fabric [119].

4.7.6 Delonix regia It has been found that the flame tree could be used as an alternative to red synthetic dye for coloration of silk fabric using eco-friendly biomordants and enzymes [120]. Teli and Pandit also used Delonix regia as a source of natural carotenoid pigment source and dyed mulberry silk fabric followed by a pre- and post-mordanting method. The results demonstrated high color strength, color fastness properties, and multifunctional properties on dyed fabric [55].

4.7.7 Sweet Potato Sweet potatoes are enriched with bioactive coloring components such as -carotene, which has the ability to fight pathogenic microbes. Due to such coloring and biological properties, Velmurugan et al. extracted sweet potato using the ultrasonic-assisted extraction method and dyed with cotton, leather, and silk. They found that after dyeing, the fabric has not only showed depth of color but also reduced the population of disease-causing bacteria [121]. Thus, carotenoids are a major alternative source of toxic synthetic dyes that produce large amounts of pollutants in the environment during production and through wastes. Carotenoid-based natural dyes not only are safe to use but also provide various functional properties to the fabric.

4.8 Conclusion Carotenoids are one of the biggest class of natural colorants that have numerous applications such as in textiles, pharmaceuticals, foods, flavors, cosmetics, solar cell industry, etc. Various techniques have been developed in order to obtain maximum carotenoid-based colorants from sources with improved applied characteristics. However, there remains a dire need to explore more

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plants that contain carotenoid as a basic functional moiety, and for its extraction, cost-, time-, and energy-efficient methods should be used, such as radiation. This chapter contains in-depth information on carotenoids, including their detailed characteristics, which might be helpful for readers, industrialists, and researchers who plan to use them in various fields.

Acknowledgments The authors are thankful to American Association of Textile Chemists and Colorist (AATCC), Society of Dyers and Colourists (SDC), UK, which helped to gather related materials and scientific information. We are also thankful to students of AATCC-GCUF Chapter, Mr. Zafar Iqbal (Manager), Noor Fatima Fabrics, Faisalabad, Pakistan, and Mr. Muhammad Abbas (Chief Executive), Harris Dyes and Chemicals, Faisalabad, Pakistan, for technical and scientific guidance in preparation of this chapter.

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Textiles and Clothing compound from plant material: Extraction of β-carotene from carrot peels. Chem. Eng. Sci., 116, 442–451, 2014. Hiranvarachat, B. and Devahastin, S., Enhancement of microwave-assisted extraction via intermittent radiation: Extraction of carotenoids from carrot peels. J. Food Eng., 126, 17–26, 2014. Rehman, F., Adeel, S., Hanif, R., Muneer, M., Zia, K.M., Zuber, M., Khosa, M.K., Modulation of marigold based lutein dye and its dyeing behaviour using UV radiation. J. Nat. Fib., 14, 1, 63–70, 2017. Montazer, M. and Parvinzadeh, M., Dyeing of wool with marigold and its properties. Fibers Polym., 8, 2, 181–185, 2007. Jothi, D., Extraction of natural dyes from African marigold flower (Tagetes erecta L) for textile coloration. Autex Res. J., 8.2, 49–53, 2008. Vanker, P.S., Utilization of temple weste flower Tageteserecta for dyeing of cotton, wool and silk in industrial scale. J. Text. Apparel Technol. Manage., 6, 1, 1–15, 2009. Jain, N., Extraction and application of natural dye by utilizing temple floral waste Tageteerecta L. Int. J. Eng. Technol. Sci. Res., 4, 3, 144–150, 2017. Khattak, S.P., Rafique, S., Hussain, T., Ahmad, B., Optimization of fastness and tensile properties of cotton fabric dyed with natural extracts of Marigold flower (Tagetes erecta) by pad-steam method. Life Sci. J., 11, 7s, 52–60, 2014. Teli, M.D., Sheikh, J., Pradhan, C., Simultaneous natural dyeing and antibacterial finishing using chitosan from bio-waste. Melliand Int., 20, 3, 171–172, 2014. Chavan, S. and Ghosh, E., Cotton and silk dyeing with natural dye extracted from floral parts of African marigold (Tagetes erecta), in: National Conference ACGT, vol. 2015, pp. 13–14, 2015. Ali, S., Noor, S., Siddiqua, U.H., Jabeen, S., Hussain, T., Central composite design approach for optimization of extraction and dyeing conditions of marigold colorant. Nat. Prod. Chem. Res., 4, 4, 1–5, 2016. Morshed, M.N., Deb, H., Al Azad, S., Aqueous and solvent extraction of natural colorants from Tagetes erecta L., Lawsonia inermis, Rosa L for coloration of cellulosic substrates. Am. J. Polym. Sci. Technol., 2, 2, 34–39, 2016. Adeel, S., Gulzar, T., Azeem, M., Saeed, M., Hanif, I., Iqbal, N., Appraisal of marigold flower based lutein as natural colourant for textile dyeing under the influence of gamma radiations. Radiat. Phys. Chem., 130, 35–39, 2017. Tsatsaroni, E., Liakopoulou-Kyriakides, M., Eleftheriadis, I., Comparative study of dyeing properties of two yellow natural pigments—Effect of enzymes and proteins. Dyes Pigm., 37, 4, 307–315, 1998. Gui-zhen, K.E., Dyeing of silk fabric with natural plant dye saffron. Silk, 12, 003, 2010. Raja, A.S.M., Pareek, P.K., Shakyawar, D.B., Wani, S.A., Nehvi, F.A., Sofi, A.H., Extraction of natural dye from saffron flower waste and its application on pashmina fabric. Adv. Appl. Sci. Res., 3, 1, 156–161, 2012.

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105. Mortazavi, S.M., Kamali Moghaddam, M., Safi, S., Salehi, R., Saffron petals, a by-product for dyeing of wool fibers. Prog. Color Colorants Coat., 5, 75–84, 2012. 106. Ghaheh, F.S., Mortazavi, S.M., Alihosseini, F., Fassihi, A., Nateri, A.S., Abedi, D., Assessment of antibacterial activity of wool fabrics dyed with natural dyes. J. Cleaner Prod., 72, 139–145, 2014. 107. El-Khatib, E.M., Ali, N.F., El-Mohamedy, R.S.R., Influence of neen oil pretreatment on the dyeing and antimicrobial properties of wool and silk fibers with some natural dyes. Arabian J. Chem., 2017. (In Press) https://doi. org/10.1016/j.arabjc.2017.09.012 108. Kulkarni, S.S., Bodake, U.M., Pathede, G.R., Extraction of natural dye from chili (Capsicum annuum) for textile coloration. Univ. J. Environ. Res. Technol., 1(1), 58–63, 2011. 109. El Ksibi, I., Slama, R.B., Faidi, K., Ticha, M.B., M’henni, M.F., Mixture approach for optimizing the recovery of colored phenolics from red pepper (Capsicum annuum L.) by-products as potential source of natural dye and assessment of its antimicrobial activity. Ind. Crops Prod., 70, 34–40, 2015. 110. Savvidis, G., Zarkogianni, M., Karanikas, E., Lazaridis, N., Nikolaidis, N., Tsatsaroni, E., Digital and conventional printing and dyeing with the natural dye annatto: Optimisation and standardisation processes to meet future demands. Color. Technol., 129, 1, 55–63, 2013. 111. Savvidis, G., Karanikas, E., Nikolaidis, N., Eleftheriadis, I., Tsatsaroni, E., Ink-jet printing of cotton with natural dyes. Color. Technol., 130, 3, 200–204, 2014. 112. Savvidis, G., Karanikas, V., Zarkogianni, M., Eleftheriadis, I., Nikolaidis, N., Tsatsaroni, E., Screen-printing of cotton with natural pigments: Evaluation of color and fastness properties of the prints. J. Nat. Fib., 14, 3, 326–334, 2017. 113. Chattopadhyay, S.N., Pan, N.C., Roy, A.K., Khan, A., Dyeing of jute fabric with natural dye extracted from annato. Indian J. Nat. Fib., 1, 1, 65–76, 2014. 114. Islam, S., Rather, L.J., Shahid, M., Khan, M.A., Mohammad, F., Study the effect of ammonia post-treatment on color characteristics of annatto-dyed textile substrate using reflectance spectrophotometery. Ind. Crops Prod., 59, 337–342, 2014. 115. Islam, S., Rather, L.J., Shabbir, M., Bukhari, M.N., Khan, M.A., Mohammad, F., First application on mix metallic salt mordant combinations to develop newer shades on wool with Bixa orellana natural dye using reflectance spectroscopy. J. Nat. Fib., 15, 30, 1–10, 2017. 116. Chattopadhyay, S.N., Pan, N.C., Roy, A.K., Khan, A., Sustainable coloration of jute fabric using natural dyes with improved color yield and functional properties. AATCC J. Res., 2, 2, 28–36, 2015. 117. Moses, J. and Venkataraman, Study of the chemical treatment on cotton fabrics to increase the UV protection and anti-odour retention properties. J. Text. Apparel, 26, 4, 400–406, 2016.

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5 Environmentally Sound Dyeing of Cellulose-Based Textiles Nabil A. Ibrahim*, Basma M. Eid and Tawfik A. Khattab 1

Textile Research Division, National Research Centre, Giza, Egypt

Abstract In this chapter, the most commonly used dye classes, dyeing auxiliaries, and application methods for dyeing cellulose-based textiles as well as their negative impacts on the product and environment quality are discussed. This chapter also demonstrates the current research and development efforts for producing more eco-friendly dyestuffs and greener chemical auxiliaries along with upgrading the available dyeing techniques to be sustainable and environmentally sound. Finally, future trends aiming at reduction of chemicals/water/energy consumptions, the enhancement in extent of dye exhaustion and fixation, potential waste minimization, minimal ecology and safety adverse effects, better use of natural resources along with high quality and productivity of cellulose-based textile dyeings are considered. Keywords: Cellulosic textiles, dyeing, environmental impacts, pollution prevention, waste minimization, sustainable dyeing

5.1 Introduction Due to intensive consumption of various processing chemicals, e.g., synthetic dyes, auxiliaries, etc., water and energy in conventional pretreatment and dyeing of cellulosic substrates, subsequent generation of large volumes of dyehouse effluent with high pollution load, along with increasing environmental concerns and the rapid changes in the consumer demands [1–3], there have been serious efforts on improving sustainability and *Corresponding author: [email protected]; [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (79–100) © 2019 Scrivener Publishing LLC

79

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eco-friendliness of dyeing processes. Hence, this chapter is devoted to (i) analyze conventional pretreatments and post-conventional cellulosic dyeing and their negative impacts, (ii) discuss recent developments and alternative possibilities for upgrading both the product and environmental quality, and (iii) highlight future trends and the key emerging technologies to achieve eco-friendly dyeings with high-performance properties in environmentally benign, effectively and economically feasible manufacturing processes.

5.2 Cellulose-Based Textiles Cellulose is the most abundant and sustainable natural polymer. The cellulose chemical structure may be described as a 1,4-β-glucan (Figure  5.1). The abundant hydroxyl groups, namely, -CH2OH (at C-6) and -CHOH (at C-2 and C-3) on each anhydroglucose unit, are responsible hydrophilic active sites for further chemical modifications, dyeing, as well as chemical finishing. Cellulose-based textiles include natural fibers, e.g., cotton, flax, jute etc., and regenerated ones, e.g., viscose, modal, lyocell, etc. The differences among natural and regenerated cellulosic substrates arise from differences in degree of polymerization, i.e., chain length, cellulose content, amount of noncellulosic impurities, amorphous/crystalline region ratio, as well as availability and accessibility of active sites in cellulose structure. Cotton is by far the most popular choice, among the natural fibers, in apparel industry due to its unique properties like hydrophilicity, softness, as well as comfortability in wear [4–6].

2

3 CH2OH

HO

O

OH

HO O

HO OH

CH2OH O O

CH2OH 6

Figure 5.1 Cellulose chemical structure.

O

OH

HO OH N-2

Dyeing of Cellulose-Based Textiles 81

5.3 Common Preparation Processes and Environmental Impacts Figure 5.2 shows several dry, e.g., spinning, weaving, and knitting etc., and wet chemical processing, e.g., pretreatments, dyeing, and finishing of cotton fabric as the most important natural fiber. Preparation of a cotton fabric includes desizing, scouring, bleaching, and mercerization in some cases. Pretreatments are essential for efficient removal of

Natural Cotton Linen Jute Ramie

Regenerated Viscose Modal Lyocell

Fiber preparation Thread Fabric Knitted

Woven

Pretreatment Desizing (woven) Scouring Bleaching

Mercerizing

Dyeing Direct

Vat

Reactive

Sulphur Finishing

Finished fabric

Clothings

Home textiles

Commercial use

Figure 5.2 Flow diagram for common steps of cotton fabric preparation processes.

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size ingredients, noncellulosic and hydrophobic impurities, and natural color matters, which in turn lead to a remarkable improvement in hydrophilicity, wettability, uniformity, accessibility, and affinity of cellulose active sites to the subsequent dyeing and/or finishing treatments [7, 8]. Pretreatment sequence, active ingredient type and concentration, kind of auxiliary, stabilizing chemicals (e.g., wetting, desizing, emulsifying, sequestering, oxidizing agent, etc.), and treatment conditions are governed by type and fabric construction, available production line, subsequent dyeing, and/or finishing treatments as well as the demanded final properties. Conventional preparatory processing of natural cellulosic fibers, e.g., cotton, flax, jute, etc. consumes large amounts of chemicals, water, and energy and generates effluents that exhibit high COD, BOD and TDS and that are alkaline in nature [9, 10].

5.4 Dyeing of Cellulosic Substrates Dyeing of cellulosic substrates is one of the most important steps in the textile wet processing chain. The main task of the dyeing is to impart the desired color with high fastness properties. Most of the industrially used dyestuffs for cellulosic fibers such as reactive, direct, vat, indigo, sulfur, etc. are synthetic [4, 5]. The dye structure comprises both chromophore groups like azo (-N=N-), carbonyl (-C=O), nitro (-NO2), methine (-CH=), quinoid groups, etc., which are responsible for the color and also coloration and contamination of wastewater, as well as auxochrome groups such as amine (-NH2), hydroxyl (-OH), carboxyl (-COOH), and sulfonate (-SO3H) groups that cause or intensify the color of chromophore components. Moreover, the presence of acidic groups, e.g., -SO3H, -COOH, etc., in the dye structure significantly enhances their aqueous solubility [1, 11]. There are two ways to classify dye classes, namely, (i) chemical structure, e.g., azo dyes, anthraquinone, indigo dyes, etc. (Figure 5.3), and (ii) application method, e.g., reactive, direct, acid, basic, vat, etc. [4, 11]. The main steps involved in dyeing cellulosic substrates are [4, 5]: i.

Reduction of insoluble dyes, e.g., vat, sulfur, indigo, to the soluble leuco form ii. Impregnation of the cellulosic fibers with the dye solution iii. Dye adsorption and penetration within the cellulosic structure

Dyeing of Cellulose-Based Textiles 83 Cl N SO3H

O

NH2 SO3H

N

OH HN

N

NH2

O

N N

O

HN

O

S O

HO3S

O OH

S O

SO3H C.I. Reactive Blue 19 Vinylsulfone (Monofunctional) Dye

C.I. Reactive Red 12 Monochlorotriazine (Monofunctional) Dye Cl N

Cl N

N

N

SO3H

HO3S N

OH HN

HN

N

NH

NH

OH

N N

N N

HO3S

SO3H

HO3S

SO3H

C.I. Reactive Red 120 Bis-monochlorotriazine Dye Cl SO3H N N

HN

N

H N

N

OH HN

N H3C SO3H

N

SO3H

Cl

Cl HO3S

C.I. Reactive Yellow 4 Dichlorotriazine Dye H O H N C N

NaO3S

SO2CH2CH2OSO3H

N N

N N

SO3H

C.I. Reactive Red 194 Heterobifunctional Reactive Dye

SO3Na

N N

H N

NO2

N N OH

COONa

NH2

C.I. Sulfur Black 11

HO

C.I. Direct Red 250

O

OH

OH

O

O N

Br

O C.I. Vat Red 10 Leuco form of anthraquinoid dye

Br

N N

O O

H

Br

H

Br O

C.I. Vat Blue 5 Indigoid Vat dye

Figure 5.3 Representative examples for reactive dyes.

iv. Fixation of the dye on/within the cellulose (Cell.OH) structure via chemical bonds with its –OH groups, i.e., dyeing sites (reactive dyeing; Figure 5.4), hydrogen bonds, and van der Waals forces, as in the case of direct dyeing, respectively, as well as via oxidation of pre-dissolved vat, sulfur, or indigo dyes to the insoluble form [12–14], and v. After washing to remove unfixed dyestuffs and auxiliary chemicals.

84

Textiles and Clothing Cell.OH + –OH

Cell.O– + H2O O

Cl (a) [Dye]

Cellulose

N

N N

+

Cell.O–

[Dye]

N N

N

R

R Dyed fiber Hydrolysis OH N [Dye]

N N

R Hydrolysed, none recative dye

(b) [Dye]-SO2CH2CH2OSO3H

–OH

[Dye]-SO2CH=CH2 + Cell.O–

[Dye]-SO2CH=CH2 [Dye]-SO2CH2CH2.O.Cell

Figure 5.4 Reactive dyeing mechanism.

5.5 Environmental Impacts of Conventional Dyeing There are many factors affecting the unsustainability of conventional dyeing of cellulose-based textiles such as use of persistent and hazardous chemicals, nonbiodegradable organic chemicals, non-eco-friendly dyestuffs, high water and energy consumption, generation of liquid wastes in an environmentally disposal way, as well as both generation of volatile organic compounds (VOCs) and air emissions from boiler, e.g., NOx, SO2, etc. [15–17], which in turn negatively affects the human health. Wastewater contaminants associated with conventional dyeing include unfixed dye, non-exhausting textile auxiliaries, alkali or acid, salts, reducing and oxidizing agents, metals, and spent solvents, which in turn lead to high levels of BOD, COD, TSS, TDS, heavy metals, and pH. The variation in dyehouse effluent volume and pollution load is determined by type of cellulosic substrate, class and chemistry of the used dye, dyeing formulation constituents, available production line, dyeing regime and scale of dyeing, i.e., continuous or batch process, as well as the demanded performance and coloration properties of the produced dyeings. Table 5.1 demonstrates the most common dyestuffs used in dyeing cellulosic substrates, dyeing formulations, mode of interaction, as well as environmental impacts.

i. Monofunctional • Monochlorotriazine • Dichlorotriazine • Monofluorotriazine • Trichloropyrimidine • Difluoropyrimidine • Dichloroquinoxaline • Vinylsulfone

Reactive

iii. Heterobifunctional • Monochlorotriazine/ vinylsulfone • Monofluorotriazine/ vinylsulfone • Difluoropyrimidine/ vinylsulfone

ii. Homobifunctional • Bis(monochlorotriazine) • Bis(monofluorotriazine) • Bis(vinylsulfone)

Subclass

Class Covalent bond with cellulose under alkaline conditions.

Dye–fiber bond Common salt Soda ash Urea Anti-creasing agent Leveling agent Temperature: 60°C–80°C Time: 60 min Liquor ratio 1:20

Dye-bath contents pH COD BOD Release of chemicals Increase salinity Color pollution

Wastewater contaminants

(Continued)

[18–22]

Ref.

Table 5.1 Common dyestuffs used in dyeing cellulosic substrates, dye–fiber bond, dyeing formulations, as well as environmental impacts.

Dyeing of Cellulose-Based Textiles 85

Mechanical entrapment of insoluble oxidized dye.

i. Indigoid vat dyestuffs ii. Leuco form of anthraquinoid dyestuffs

Vat

Dye–fiber bond Through hydrogen bond and van der Waals forces.

Subclass

Direct

Class

Water-insoluble dyestuff dissolved by reducing with sodium hydrogensulfite, then exhausted on cotton fibers and reoxidized.

Salt Soda ash Wetting agent Sequestering agent Leveling agent Temperature: 90–100°C Time: 50–60 min pH: neutral to slight alkaline Liquor ratio 1:10

Applied from neutral or slightly alkaline dye-bath containing an electrolyte.

Dye-bath contents – – – – – –

pH COD BOD Color pollution Chemical residues

pH COD BOD TOC Increase salinity Color

Wastewater contaminants

(Continued)

[27–29]

[23–26]

Ref.

Table 5.1 Common dyestuffs used in dyeing cellulosic substrates, dye–fiber bond, dyeing formulations, as well as environmental impacts. (Continued)

86 Textiles and Clothing

Subclass

i. Sulfur dyestuffs ii. Leuco sulfur dyestuffs iii. Water-soluble sulfur dyestuffs

Class

Sulfur

Mechanical entrapment of insoluble oxidized dye.

Dye–fiber bond

Sodium sulfide (reducing agent) Salt Soda ash Chelating agent (EDTA) Temperature: 100°C Time: 90 min Liquor ratio 1:20

Wetting agent Sodium hydrogensulfite Sequestering agent Dispersing agent Caustic soda Hydrogen peroxide Temperature: 25–60°C Time: 50–60 min

Dye-bath contents

pH COD BOD Chemical residues Increase salinity Color pollution EDTA

Wastewater contaminants

[30–32]

Ref.

Table 5.1 Common dyestuffs used in dyeing cellulosic substrates, dye–fiber bond, dyeing formulations, as well as environmental impacts. (Continued)

Dyeing of Cellulose-Based Textiles 87

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5.6 Cleaner Production Opportunities The textile industry, especially textile wet processing, is the second highest consumer and polluter of freshwater and is one the most ecologically harmful industry with a huge environmental footprint. Production ecology, user ecology, as well as disposal ecology should be taken into consideration to ensure successful application and adoption of cleaner production strategy and practices. Utilization of environmentally sound chemical materials, implementation of emerging green technology, as well as processes rationalization, optimization, and modification are required to upgrade both the product and environment quality taken into mind both the economic concerns and social responsibilities. Most of the environmental problems or concerns associated with preparation and dyeing of cellulosic substrate can be solved successfully by the implementation of cleaner production approaches (at the source before it is generated). Cleaner production strategy aims to cut the resources consumption along with pollution generation as a direct consequence of inefficient production processes. Cleaner production can be achieved by the following approaches: i.

Water, energy, and chemical savings as well as waste minimization

The recommended practices for chemicals, dyes, auxiliaries, freshwater and energy savings, and waste minimization [17, 33–35] are as follows: • Promote good housekeeping • Reusing: the non-contact cooling water, steam condensate, as well as processing water from H2O2- bleaching and mercerization • Recovering: the synthetic size, e.g., PVOH, caustic soda, and heat • Ensuring: efficient and uniform pretreatments for subsequent uniform post-dyeing • Combining: pretreatment steps, i.e., desizing, scouring, and bleaching, in one stage • Using: counter-flow washing to ensure improved washing efficiency

Dyeing of Cellulose-Based Textiles 89 • Process optimization, rationalization, and modification to ensure high efficiency with minimum environmental impacts • Maximizing: exhaustion and dye fixation as well as minimizing washoff • Using ultra-low liquor dyeing systems • Applying: Right first time (RFT) dyeing approach to ensure high productivity as well as more efficient use of resources and fixed capital • Automation of pretreatment and dyeing machines and dispensing systems • Dyebath reuse specially in case of direct dyeing of cellulosic substrate ii.

Eco-friendly substitution of environmentally harmful chemicals (Table 5.2) iii. Implementation of emerging green technologies (Table 5.3)

5.7 Future Trends In the future, more consideration and efforts will have to be given to: • Development of new generation of environmentally sound dyestuffs, textile auxiliaries, and specialty chemicals with significantly improved fixation and performance properties using green technologies that are easily applicable on automated equipment and machineries. • Development of green functional dyes for simultaneous coloration and functionalization of cellulosic substrates. • Ensure success adoption and implementation of the emerging clean wet processing technologies on full commercially successful application scales for sustainable water, energy, and materials savings along with minimal environmental negative impacts. • Potential applications of the bio-, water-free, and chemicalfree green technologies in future wet processing operations of cellulosic substrates for environmental and economical reasons, i.e., for sustainable development.

Application process

Sizing

Desizing of starch size

Scouring

Bleaching

H2O2 stabilizer

Mercerization

Wet processing

Neutralization

Dyeing

Dyeing

Harmful chemicals

Starch

Mineral acid, e.g., HCl

Alkalis, e.g., NaOH, Na2CO3, etc.

NaOCl

Silicate or phosphate-based compounds

Highly concentrated caustic soda

Synthetic nonbiodegradable textile auxiliaries

CH3COOH

Metal-containing direct or reactive dyes

CH2O-containing fixing agents

Cationic fixing agent to enhance reactive or direct dye fixation

Metal free vat dyes

HCOOH

Sustainable–biodegradable auxiliaries

Water-less mercerization using liquid ammonia

Gluconic acid, citric acid, or nitrogenous stabilizers

H2O2 or gaseous bleaching (ozone in cold water)

Acid or alkaline pectinase (enzymatic scouring)

Alpha amylase (enzymatic desizing)

Water-soluble recoverable sizing agent, e.g., PVOH

Proposed eco-friendly alternative

Table 5.2 Some environmentally harmful chemicals and their eco-friendly alternatives.

(Continued)

[40]

[17]

[39]

[40]

[39]

[40]

[39]

[38]

[37]

[36]

Ref.

90 Textiles and Clothing

Application process

Reactive dyeing

Sulfur dyeing

Sulfur dye reduction

Vat dyes reduction

Oxidation of solubilized sulfur dyes

Oxidation of solubilized vat dyes

Dyeing

Dyeing

H2O2 killer

Indigo dyeing

Harmful chemicals

Monofunctional reactive dyes

Sulfur dyes in powder forms

Na2S

Na2S2O4

K2Cr2O7

H2O2, Na-perborate or K2Cr2O7

Banned benzidine dyestuffs, e.g., some direct dyes

Synthetic dyes

NaHSO3 or Na2S2O3

Na-dithionate

α-Hydroxycarbonyls

Catalases enzyme

Natural dyestuffs

Non-benzidine dyestuffs

Expose to air oxygen

H2O2 as preferred oxidant

By electrochemical means for the reduction and oxidation

Glucose-based reductant

Pre-reduced form

Low salt bifunctional (homo or hetero) or tri-anchors counterparts to enhance the extent of dye fixation

Proposed eco-friendly alternative

Table 5.2 Some environmentally harmful chemicals and their eco-friendly alternatives. (Continued)

[52]

[51]

[50]

[49]

[15]

[39, 45, 46]

[47, 48]

[39, 45, 46]

[43, 44]

[19, 41, 42]

Ref.

Dyeing of Cellulose-Based Textiles 91

Bio-treatment of cellulosic substrates, e.g. Amylases: for desizing of starch size, Pectinases: for bioscuring, Laccases: for enzymatic bleaching Catalases: for H2O2 removal before reactive dyeing, etc.

Electrochemical reduction of numerous dyes like vat, indigo, and sulfur dyes

Cotton bleaching

Electrochemical dyeing technology

Ozone technology

Application field

Bio-technology

Emerging technology

– Substantial energy and water savings – Stop using harmful chemicals – Remarkable decrease in CO2 emissions – Short time process, so increased productivity

– Environmentally friendly technology – Nonhazardous reducing agents contain sulfur – Recyclability of both mediators system and dye liquors – Increase productivity – Nontoxic contaminants in effluent, so no negative impacts on aquatic life

– Eco-friendly wet processes – Carried out at mild conditions – Less water and energy consumption in comparison with the traditional counterparts

Positive impacts

Table 5.3 Some emerging clean technology for green preparation and dyeing of cellulosic substrates.

(Continued)

[56, 57]

[54, 55]

[33, 53]

Ref.

92 Textiles and Clothing

• Facilitate size removal, e.g., PVOH • Enhance surface hydrophilicity, wettability and dyeability of cellulosic substrates

Plasma technology

– Energy, water, and chemicals consumption is negligible – Considerable improvements in surface properties of treated substrates – Does not affect the bulk properties of treated textiles – Shorter treatment time compared with the conventional methods – A wide array of textile applications

– Energy, water, and chemicals savings – Reduction in the amount and pollution load of effluent – Improve both the productivity and product quality

– Bleach down effects without adversely affecting the strength properties – Cleanup of pockets, and upgrade the white–blue contrast

Fade down denim jeans and to eliminate indigo back-staining

• Clean technology for textile wet processing, e.g., pretreatment, dyeing, etc. • Enzymatic desizing for cotton • Enhancing the whiteness degree of bleached linen fabric • An efficient technique for natural dyeing

Positive impacts

Application field

Ultrasound technology

Emerging technology

Table 5.3 Some emerging clean technology for green preparation and dyeing of cellulosic substrates. (Continued)

(Continued)

[61–63]

[58–60]

Ref.

Dyeing of Cellulose-Based Textiles 93

Supercritical CO2 dyeing technology (scCO2)

Emerging technology

• Extraction of natural products • As a dye medium for PET • Application of this technique in wet processing of natural fibers, e.g., cellulosic fibers, is still under development, e.g., developing new dyes for scCO2 reactive dyeing of cellulosic fibers • Removing the hydrophobic/noncellulosic impurities, e.g., fats, oils, waxes

Application field

– Water-free process – No wastewater, i.e., minimized environmental impacts – Environmentally friendly process – Easy solute recovery and solvent reuse

Positive impacts

Table 5.3 Some emerging clean technology for green preparation and dyeing of cellulosic substrates. (Continued)

[53, 64, 65]

Ref.

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Dyeing of Cellulose-Based Textiles 95 • Adoption of eco-friendly surface modification methods of plant fibers to stop the use of conventional non-eco-friendly counterparts. • The ever-increasing demands for eco-friendly textile wet processes and product in the future. • Exploring novel and environmentally benign plant-based natural products for various potential applications in textile wet processing to cope with the ever-growing consumer awareness of eco-safety and to take part in developing highly value-added textile products. • The application of cleaner strategy, best available techniques, life cycle assessment, eco-label criteria and other aspects of clean technology as well as green chemistry principles to minimize resources consumption, prevent pollutants generation, cut production costs, improve competitiveness, and meet the requirements of existing and future legislations, and eco-labeling criteria, i.e., taking into consideration production, human, and disposal ecology.

References 1. Sarayu, K. and Sandhya, S., Current technologies for biological treatment of textile wastewater—A review. Appl. Biochem. Biotechnol., 167, 645–661, 2012. 2. Dasgupta, J., Sikder, J., Chakraborty, S., Curcio, S., Drioli, E., Remediation of textile effluents by membrane based treatment techniques: A state of the art review. J. Environ. Manage., 147, 55, 2015. 3. Kant, R., Textile dyeing industry: An environmental hazard. Nat. Sci., 4, 22, 2012. 4. Ibrahim, N.A., Dyeing of textile fibre blends, in: Handbook of Textile and Industrial Dyeing, M. Clark (Ed.), pp. 148–149, Woodhead Publishing, UK, 2011. 5. Koh, J., Dyeing of cellulosic fibres, in: Handbook of Textile and Industrial Dyeing, M. Clark (Ed.), pp. 129–132, Woodhead Publishing, UK, 2011. 6. Bide, M., Fiber sustainability: Green is not black + white. AATCC Rev., 9, 34, 2009. 7. John, M.J. and Anandjiwala, R.D., Surface modification and preparation techniques for textile materials, in: Surface Modification of Textiles, Q. Wei (Ed.), pp. 1–25, Woodhead Publishing Cambridge, UK, 2009. 8. Harane, R.S. and Adivarekar, R.V., Sustainable processes for pre-treatment of cotton fabric. Text. Cloth. Sustain., 2, 2, 2016.

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9. Babu, B.R., Parande, A.K., Raghu, S., Kumar, T.P., Cotton textile processing: Waste generation and effluent treatment. J. Cotton Sci., 11, 141, 2007. 10. Ozturk, E., Karaboyacı, M., Yetis, U., Yigit, N.O., Kitis, M., Evaluation of integrated pollution prevention control in a textile fiber production and dyeing mill. J. Clean. Prod., 88, 116, 2015. 11. Waring, D.R. and Hallas, G.E., The Chemistry and Application of Dyes, Springer, Boston, 1990. 12. Rippon, J.A. and Evans, D.J., Improving the properties of natural fibres by chemical treatments, in: Handbook of Natural Fibres, R.M. Kozłowski (Ed.), pp. 63–140, Woodhead Publishing, Cambridge, UK, 2012. 13. Shore, J., Dyeing with reactive dyes, in: Cellulosics Dyeing, J. Shore (Ed.), pp. 237–240, Society of Dyers and Colourists, Bradford, 1995. 14. Roy Choudhury, A.K., Textile Preparation and Dyeing, pp. 777–789, Science Pub Inc, Enfield, NH, USA, 2006. 15. Bide, M., Environmentally responsible dye application, in: Environmental Aspects of Textile Dyeing, R.M. Christie (Ed.), pp. 74–85, Woodhead Publishing, Cambridge, UK, 2007. 16. Schlaeppi, F., Optimizing textile wet processes to reduce environmental impact. Text. Chem. Color., 30, 19, 1998. 17. Shukla, S.R., Pollution abatement and waste minimisation in textile dyeing, in: Environmental Aspects of Textile Dyeing, R.M. Christie (Ed.), pp. 116–148, Woodhead Publishing, Cambridge, UK, 2007. 18. Khatri, Z., Ahmed, F., Jhatial, A.K., Abro, M.I., Mayakrishnan, G., Kim, I.-S., Cold pad-batch dyeing of cellulose nanofibers with reactive dyes. Cellulose, 21, 3089, 2014. 19. Khatri, A., Peerzada, M.H., Mohsin, M., White, M., A review on developments in dyeing cotton fabrics with reactive dyes for reducing effluent pollution. J. Clean. Prod., 87, 50, 2015. 20. Farouk, R. and Gaffer, H.E., Simultaneous dyeing and antibacterial finishing for cotton cellulose using a new reactive dye. Carbohydr. Polym., 97, 138, 2013. 21. Hunger, K., Industrial Dyes: Chemistry, Properties, Applications, Wiley-VCH Verlag GmbH & Co, Germany, 2004. 22. Clark, M.E., Handbook of Textile and Industrial Dyeing, Woodhead Publishing, Cambridge, UK, 2011. 23. Luo, M., Zhang, X., Chen, S., Enhancing the wash fastness of dyeings by a sol–gel process. Part 1; Direct dyes on cotton. Color. Technol., 119, 297, 2003. 24. Chrastil, J., Adsorption of direct dyes on cotton: Kinetics of dyeing from finite baths based on new information. Text. Res. J., 60, 413, 1990. 25. Kan, C.-W. and Au, C.-H., Effect of direct dyes on the UV protection property of 100% cotton knitted fabric. Fiber. Polym., 16, 1262, 2015. 26. Porter, J.J., Understanding the sorption of direct dyes on cellulose substrates. AATCC Rev., 3, 20, 2003.

Dyeing of Cellulose-Based Textiles 97 27. Zhuo, J. and Sun, G., Antimicrobial functions on cellulose materials introduced by anthraquinone vat dyes. ACS Appl. Mater. Interfaces, 5, 10830, 2013. 28. Hihara, T., Okada, Y., Morita, Z., Photo-oxidation and-reduction of vat dyes on water-swollen cellulose and their lightfastness on dry cellulose. Dyes Pigm., 53, 153, 2002. 29. Khatri, M., Ahmed, F., Shaikh, I., Phan, D.-N., Khan, Q., Khatri, Z. et al., Dyeing and characterization of regenerated cellulose nanofibers with vat dyes. Carbohydr. Polym., 174, 443, 2017. 30. Aspland, J., Dyeing cotton or regenerated cellulose using sulfur dyes oxidized with aqueous sodium bromite solution. US Patent 3716325A, assigned to Martin Marietta Corp, 1973. 31. Chadwick, A.F. and Terhune, H.D., Oxidation of sulfur dyes on cotton using hydrogen peroxide solutions. US Patent 3278254A, assigned to EI du Pont de Nemours and Co, 1966. 32. Jaruhar, P. and Chakraborty, J., Dyeing of cotton with sulfur dyes using alkaline protease. Text. Res. J., 83, 1345, 2013. 33. Roy Choudhury, A.K., Green chemistry and the textile industry. Text. Prog., 45, 3–143, 2013. 34. European Integrated Pollution Prevention and control (IPPC). Reference Document on Best Available Techniques for the Textiles Industry, Directive 96/61/EC. Seville, Spain, July 2003. 35. Babu, B.R., Parande, A.K., Raghu, S., Prem, K.T., Cotton textile processing: Waste generation and effluent treatment. J. Cotton Sci., 11, 141, 2007. 36. Ibrahim, N.A. and Trauter, J., Optimization of the desizing process by application of water-soluble sizing agents. Melliand Textilber., 71, 199, 1990. 37. Shahid, M., Mohammad, F., Chen, G., Tang, R.-C., Xing, T., Enzymatic processing of natural fibres: White biotechnology for sustainable development. Green Chem., 18, 2256, 2016. 38. Ibrahim, N.A., El-Hossamy, M., Morsy, M.S., Eid, B.M., Development of new eco-friendly options for cotton wet processing. J. Appl. Polym. Sci., 93, 1825, 2004. 39. Arputharaj, A., Raja, A.S.M., Saxena, S., Developments in sustainable chemical processing of textiles, in: Green Fashion, vol. 1, S.S. Muthu and M.A. Gardetti (Eds.), pp. 217–252, Springer, Singapore, 2016. 40. Roy Choudhury, A.K., Environmental impacts of the textile industry and its assessment through life cycle assessment, in: Roadmap to Sustainable Textiles and Clothing: Environmental and Social Aspects of Textiles and Clothing Supply Chain, S.S. Muthu (Ed.), pp. 1–39, Springer, Singapore, 2014. 41. Girod, K. and Galafassi, P., The genuine low salt reactive days. Colourage, 51, 100, 2004. 42. Kitamura, S., Washimi, T., Yamamoto, K., Low salt dyeing using fiber reactive dyes on cotton. Book of Papers. AATCC International Conference & Exhibition, Philadelphia, USA, p. 406, 1998.

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43. Ozturk, E., Yetis, U., Dilek, F.B., Demirer, G.N., A chemical substitution study for a wet processing textile mill in Turkey. J. Clean. Prod., 17, 239, 2009. 44. Chavan, R.B. and Vhanbatte, S., Alternative reducing system for dyeing of cotton with sulphur dyes. Indian J. Fibre Text. Res., 27, 179, 2002. 45. Ibrahim, N.A., El-Gamal, A.R., Mahrous, F., Eco-friendly sulfur dyeing of cellulosic woven fabrics. Polym. Plast. Technol. Eng., 44, 1059, 2005. 46. Ibrahim, N.A., El-Gamal, A.R., Mahrous, F., Improving the environmental aspects of sulphur dyeing of cotton knitted fabrics. J. Nat. Fib., 5, 238, 2008. 47. Bechtold, T. and Turcanu, A., Electrochemical reduction in vat dyeing: Greener chemistry replaces traditional processes. J. Clean. Prod., 17, 1669, 2009. 48. Roessler, A. and Jin, X., State of the art technologies and new electrochemical methods for the reduction of vat dyes. Dyes Pigm., 59, 223, 2003. 49. Gregory, P., Toxicology of textile dyes, in: Environmental Aspects of Textile Dyeing, R.M. Christie (Ed.), pp. 53–61, Woodhead Publishing, Cambridge, UK, 2007. 50. Samanta, A.K. and Agarwal, P., Application of natural dyes on textiles. Indian J. Fibre Text. Res., 34, 384, 2009. 51. Isobe, K., Inoue, N., Takamatsu, Y., Kamada, K., Wakao, N., Production of catalase by fungi growing at low pH and high temperature. J. Biosci. Bioeng., 101, 73, 2006. 52. Meksi, N., Ben, Ticha, M., Kechida, M., Mhenni, M.F., Using of ecofriendly α-hydroxycarbonyls as reducing agents to replace sodium dithionite in indigo dyeing processes. J. Clean. Prod., 24, 149, 2012. 53. 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, 2015. 54. Das, D., Chatterjee, K.N., Arora, S., Electrochemical dyeing of cellulosics: A novel method. Indian J. Text., February, 2012. http://www.indiantextilejournal.com/articles/FAdetails.asp?id=4246. 55. Božič, M. and Kokol, V., Ecological alternatives to the reduction and oxidation processes in dyeing with vat and sulphur dyes. Dyes Pigm., 76, 299, 2008. 56. Eren, H.A. and Ozturk, D., The evaluation of ozonation as an environmentally friendly alternative for cotton preparation. Text. Res. J., 81, 512, 2011. 57. Özdemir, D., Duran, K., Bahtiyari, M.İ., Perincek, S., Körlü, A.E., Ozone bleaching of denim fabrics. AATCC Rev., 8, 40, 2008. 58. Wang, W.-M., Yu, B., Zhong, C.-J., Use of ultrasonic energy in the enzymatic desizing of cotton fabric. J. Clean. Prod., 33, 179, 2012. 59. Abou-Okeil, A., El-Shafie, A., El Zawahry, M.M., Ecofriendly laccase– hydrogen peroxide/ultrasound-assisted bleaching of linen fabrics and its influence on dyeing efficiency. Ultrason. Sonochem., 17, 383, 2010. 60. Shahid, M., Shahid-ul-Islam, Mohammad, F., Recent advancements in natural dye applications: A review. J. Clean. Prod., 53, 310, 2013.

Dyeing of Cellulose-Based Textiles 99 61. Bhat, N., Netravali, A., Gore, A., Sathianarayanan, M., Arolkar, G., Deshmukh, R., Surface modification of cotton fabrics using plasma technology. Text. Res. J., 81, 1014, 2011. 62. Sun, D. and Stylios, G.K., Effect of low temperature plasma treatment on the scouring and dyeing of natural fabrics. Text. Res. J., 74, 751, 2004. 63. Ibrahim, N.A., El-Hossamy, M., Hashem, M.M., Refai, R., Eid, B.M., Novel pre-treatment processes to promote linen-containing fabrics properties. Carbohydr. Polym., 74, 880, 2008. 64. Ahmed, N.S.E. and El-Shishtawy, R.M., The use of new technologies in coloration of textile fibers. J. Mater. Sci., 45, 1143, 2010. 65. Dyecoo. Textile Machinery, Dyecoo: Waterless dyeing, http://www.dyecoo. com/pdfs/colourist.pdf, issue 3, 2010.

6 Environmentally-Friendly Textile Finishing Mohammad Tajul Islam1* and Syed Asaduzzaman2 1

Department of Textile Engineering, Ahsanullah University of Science and Technology, Dhaka, Bangladesh 2 Department of Textile and Clothing Technology, Niederrhein University of Applied Sciences, Mönchengladbach, Germany

Abstract Textile finishing units use a large volume of water and huge amounts of numerous chemicals with various complexities. Energy consumptions of conventional textile finishing processes are very high. Finishing processes generate wastewaters of great chemical complexity, waste (i.e., waste of textiles and chemicals), odors, and noise. Therefore, textile finishing can create an impact on the environment substantially. To limit the impact on environment, environment-friendly finishing processes are being researched and developed using almost without water, minimizing the consumption of chemicals and energy considerably, and replacing toxic chemicals with nontoxic substances. In this chapter, environment-friendly textile finishing chemistries, processes, and techniques are overviewed. Keywords: Textile pollution, textiles finishing, eco-friendly, water-saving, green finishing, energy efficient, chemical substitution

6.1 Use of Enzymes in Textile Finishing Enzymes are normally biodegradable proteins; for some specific chemical reactions, it can act as biological catalysts and work in relatively mild conditions [1]. An enzyme’s exact reaction specificity can be used for precise or targeted textile finishing without inflicting undesirable effects [2]. The enzyme usage in the textile industry has become an example of green chemistry, which allows improving the final product quality by the development and application *Corresponding author: [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (101–130) © 2019 Scrivener Publishing LLC

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of eco-friendly technologies in fiber processing and strategies [3]. Microbial enzymes are considered environmentally friendly as naturally occurring, nonpathogenic microorganisms usually produce them. In addition, the fermentation biomass that is also known as the principal waste product can generally be recycled to the environment as organic manure. The microbial enzymes are biodegradable and do not increase the waste accumulations [4]. Among the recognized 7000 enzymes, only 75 are normally used in textile industry processes [5]. According to the Enzyme Commission of the International Union of Biochemistry, enzymes can be categorized into six groups such as oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases [6]. Out of these six groups, hydrolases and oxidoreductases are mainly used in the textile industry. Amylases, cellulases, proteases, pectinases, and lipases/esterases are some examples of hydrolasetype enzymes. The first enzyme used in textile processing was amylase, and in fact, no other enzyme made into the textile industry until the 1980s. After that, cellulases were introduced as these enzymes are capable of de-pilling and de-fuzzing of cellulose-based fabrics [7]. Since then, the use of enzymes in textile processing started growing. Figure 6.1 exhibits the recent state of the art of natural fiber processing using enzymes. Use of enzymes for the pretreatment of cellulosic and protein fibers is emerging such as degumming of silk, scouring of bast fibers and wool fibers, and bleaching of cotton. Moreover, scouring of cotton with enzyme is already available. However, since this chapter is dedicated to textile finishing, only bio-polishing, anti-felting, and denim washing are discussed here.

6.1.1 Bio-Polish Bio-polishing of cotton knit fabrics has been practiced widely in the textile industry. It is the removal of micro, fuzzy fibrils from the fabric surfaces Cotton

Desizing (state of art)

Bioscouring (available)

Bast fibers

Retting (emerging)

Scouring (emerging)

Wool

Scouring (emerging)

Carbonizing (emerging)

Silk

Degumming (emerging)

Bleaching (emerging)

Denim washing (available)

Biopolishing (available)

Antifelting/shrink proofing (emerging)

Figure 6.1 Current advancement in enzymatic processes in natural fiber processing. Reproduced from [8] with permission of the Royal Society of Chemistry.

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by using the appropriate enzyme. Bio-polishing not only improves appearance, color brightness, water absorbance property of fibers, and hand feel, but also minimizes the tendency for pill formation. As a result, fabric with a cleaner surface without fuzz can be obtained [9]. Bio-polishing can be achieved by cellulose enzyme, one of the most commonly used enzymes in clothing and textiles. Natural total crude cellulases that are normally excreted by various fungi and bacteria consist of the mixtures of cellobiohydrolases (CBH), endoglucanases (EG), and β-glucosidase [1]. β-Glucosidases can deteriorate small cellulose oligomers and cellobiose, in the most accessible part of the cellulose polymers (amorphous region), to glucose by catalyzing the hydrolysis of cellulose by deteriorating β-(1-4) glycosidic linkages (Figure 6.2). Therefore, cellulase enzyme has been widely used as bio-polishing agent for cellulosic fibers. Process conditions and category of cellulase enzyme can play a major role in achieving good-quality bio-polishing treatment. Many research groups tried to optimize bio-polishing of cellulosic textiles using various commercial cellulases. However, different research groups had obtained different optimized conditions such as concentration of cellulases. In general, the acid cellulases augmented with endoglucanase were found suitable for bio-polishing of cellulosic materials [10, 11]. Bio-polishing of polyester fiber has also been extensively studied and reported. Mccloskey et al. [13] showed that cutinase can be used as a suitable enzyme to impart a bio-polished finish on 100% polyester fabric. Furthermore, a combination of cellulase and cutinase was found effective in the bio-polishing of polyester/cotton blend fabric. Two different types of cutinase were studied on 100% polyester woven fabric. Polyester/ cotton (50%/50%) blend knit fabric was treated with cutinase and cellulase

CBH CBH

Amorphous zone

Crystalline zone

EG

Crystalline zone

Figure 6.2 Action of cellulases on cotton. Reproduced from [12] with permission of Elsevier.

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enzymes in a single bath. In order to understand the effect of enzymes on treated textiles, several characterizations were carried out including weight loss, high-performance liquid chromatography (HPLC) of the treatment liquor, and pilling note. For both polyester and polyester blends, a reduction in pilling note was gained. HPLC analysis of the treatment liquors indicated that the polyester hydrolysis was a result of the cutinase action, which was reflected in the pilling note results. This study claimed that the inclusion of this technology to polyester finishes and the bio-polishing area offers an eco-friendly finishing process as an alternative to the conventional textile finishes currently being used in the clothing sector [13].

6.1.2 Anti-Felting Laundering of wool fabric can lead to the progressive entanglement causing irreversible shrinkage and felting of the wool fabric. The cuticle scales on the surface of the wool fiber are mainly responsible for felting shrinkage of wool fibers (Figure 6.3). Lowering the abrasion among the fibers can hinder shrinkage of wool to achieve machine wash ability. Smoothing or eliminating the cuticle scales on the surface of the wool fibers can reduce the

10 μm EHT=12.00 kV 3 μm

WD = 10mm Mag= 1.75 K X Photo no. = 1147 Detector= SE1

Figure 6.3 Scanning electron micrograph of wool fiber. Reproduced from [17] with permission of Elsevier.

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friction between the fibers. Chlorine–Hercosett is a chemical process conventionally used to make wool fiber shrink-resistant. Chlorine–Hercosett consists of a chlorination step where cuticle scale is degraded. Afterwards, a sulfuric acid treatment in the presence of cationic polymer resin is given to cover the scales. One of the main disadvantages of the chlorination step is the release of absorbable organic halogens to the wastewater discharge, which contaminates the effluent. Strict environmental legislation and awareness among the consumers demand the replacement of the conventional Chlorine–Hercosett process by green ones for anti-pilling finishing. Therefore, many researchers have been engaged to establish an alternative eco-friendly shrink-proofing process, which is an enzyme-based anti-shrink finishing treatment of wool. Since protease has the ability to promote hydrolysis of protein compounds, it can be employed to hydrolyze the cuticle scales on the wool fiber surface. Therefore, protease enzyme has gained much attention in wool treatment enzymatically. For an example, Silva et al. [14], in an attempt to replace the traditional chlorine treatment, demonstrated that protease enzyme can smooth out the outermost layer of wool and provide the fabric with anti-shrinking behavior. However, proteolytic action can extend beyond the fiber surface and attack inner fiber structure, causing substantial loss of weight and tensile strength. Proteolytic attack can be confined to the cuticle scales by enlarging the molecular size of the protease. Increase of molecular size involves the covalent coupling of protease enzyme with a polymer, but the high expense involved in the coupling process does not make it suitable for textile application. Genetic engineering can also enlarge the size of protease, which only targets the cuticle layer of wool, but the cost of genetically modified enzyme production is too high [15]. Recently, Smith and Shen [16] cross-linked protein resin onto wool fiber of knitted wool fabric to modify the surface of wool fiber. Protein resin was extracted from the low-quality wool fiber. Modified wool showed a higher level of shrink resistance along with machine wash ability. Moreover, hand feel and tensile strength of the wool fabric were not compromised.

6.1.3 Denim Washing Washed jeans have gained popularity as casuals especially among the young generation for their special faded and aged look. Denims are twill woven 100% cotton fabrics dyed with indigo used for making jeans. Traditionally, jeans are washed with pumice stones along with bleaching chemicals to obtain a desirable outlook and enhanced softness and flexibility. Nonetheless, natural pumice stones may cause some problems

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including removal difficulties of residual pumice from garments that are already processed, physical damage of garments and machines, and clogging of the draining pipes of machine and sewer lines from pumice dust [18]. Moreover, permanganate treatment or chlorine-based bleaching used to obtain a faded effect involves chemicals, which are normally considered as harsh with regard to the environmental pollution and safe work environment. Novozymes first developed cellulase enzymes as an alternative for pumice stones in 1987 and has been used in the industry since the 1990s. Cellulase enzyme was first applied in textile processing with denim washing in the late 1980s. Cellulase treatment on denim is commonly known as bio-washing. Nowadays, bio-washing has emerged as an eco-friendly alternative to obtain “stone-washed” effects with better quality. Cellulase enzyme makes an uneven removal of surface fiber dyed with indigo dye leading to a fade and worn look [9]. Actually, partial hydrolysis of the fiber surface by cellulase in combination with mechanical agitation during washing releases indigo dye from the fiber. As a result, the lightly dyed core of the yarns is exposed and makes a contrast with the nonhydrolyzed dyed fiber surface. To achieve a particular look, many cellulases with their own distinguished properties are available, which can be used either alone or in combination. Cellulases are classified into three groups based on the application pH such as acidic (pH 4.5–5.5), neutral (pH 6.6–7), or alkaline (pH 9–10) cellulase [9]. This enzyme can be used at a wide range of washing temperatures between 30°C and 60°C [5]. The stripped indigo dyes can re-deposit back onto the white portion of denim garments. This problem is also known as back-staining. An ideal bio-washing should be free from such problems. The back-staining is mainly caused by the high affinity between indigo and cellulase enzyme and the strong binding of cellulases to cotton cellulose. Neutral cellulases show lower affinity towards indigo dyes compared to acid cellulases. Therefore, neutral including endoglucanase-rich cellulases are preferable for removing indigo dyes from denims [19]. Currently, laccase and peroxidase are receiving more interest from textile processors and researchers. These two enzymes are oxidoreductases and are capable of catalyzing the oxidation of phenolic and related compounds, for example, indigo dyes. Therefore, laccase becomes another environmentally friendly alternative to conventional fading process of denim with chemicals. Laccases are already available in the market and used in the presence of a mediator to get a color faded vintage look (stonewashed effect) without using pumice stone [20].

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6.1.4 Hydrophilic Finishing Another research area of textile finishing using enzymes is enhancing the hydrophilicity of synthetic polymer by hydrolyzing its surface. Synthetic fibers are generally hydrophobic in nature. For example, polyester and polyamide are two main synthetic fibers that do not allow evaporation of perspiration, making them not very comfortable to wear. Traditionally, an alkaline hydrophilization technique, usually sodium hydroxide treatment, is used to improve the wettability of synthetic fibers. Care needs to be taken for such chemical treatment; otherwise, fiber damage is inevitable with a substantial loss of weight of 10–30%. Enzymes have been used to hydrolyze polyester, including cutinases, lipases, and esterases. Proteases, amidases, and cutinases have been applied to hydrolyze polyamide. However, environmental gain is somewhat compromised if high temperature is required for deactivation of the enzyme [21].

6.2 Easy Care Cotton fabrics have the disadvantage of retaining creases acquired in washing and in use. A very important chemical finish known as easy care overcomes this problem. Easy-care finishing provides resistance against swelling and shrinkage and improves wet and dry wrinkle recovery. The development of easy-care finishes was based on the finding of the effect of formaldehyde reacting with cellulose [22]. At the end of the 1920s, formaldehyde condensation products were brought into market for the easy-care finishing of cellulosic fabrics including viscose, linen, or cotton fabrics. Melamine–formaldehyde compounds came into the market soon after the initial introduction of urea–formaldehyde products. Afterwards, in 1947, products based on dimethylolethylene urea started to appear in the market. However, although formaldehyde is an inexpensive chemical, concerns arose about the usage of formaldehyde during the 1960s and 1970s, particularly regarding health and safety. Formaldehyde is an organic compound, which is volatile. People can mainly be affected by formaldehyde through inhalation, but absorption through the skin is also possible. Workers are prone to exposure during direct formaldehyde production, materials treatment with formaldehyde, and resins production. Consumers may also be exposed to formaldehyde during the use of easy-care textiles. Concern about formaldehyde inspired the development of cross-linking finishes without formaldehyde or low level of formaldehyde for cellulosic fibers. The main focus was to find environment-friendly easy-care finishing

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processes that limit the impact on health and environment. Continued research has resulted into products of both low “free formaldehyde” content and completely formaldehyde free. OEKO-TEX set limits to formaldehyde for textile clothing and the acceptable limiting ranges are much less for baby cloth (>16 mg/kg) and direct skin contact cloth (75 mg/kg) compared to no direct skin contact cloth (300 mg/kg) and decoration material (300 mg/kg).

6.2.1 Finish Containing Low “Free Formaldehyde” N,N -Dimethylol-4,5-dihydroxyethylene urea (DMDHEU) is the chemical foundation of about 90% of the easy-care finish products available on the market [23]. DMDHEU is synthesized from three chemicals, namely, urea, glyoxal, and formaldehyde, as shown in Figure 6.4. A typical DMDHEU commercial product contains 45% DMDHEU, 9% diethylene glycol, and 2% methanol. “Free formaldehyde” level in DMDHEU can be as low as 0.3%. The main reaction of DMDHEU products is the cross-linking of adjacent cellulose molecules, as shown in Figure 6.5. When stress is applied to DMDHEU-treated textile substrate, this cross-linking confines the movement of the fiber molecules and prevents shrinkage and wrinkle formation.

6.2.2 Non-Formaldehyde Finish N,N -Dimethyl-4,5-dihydroxyethylene urea (DMeDHEU) is completely free from formaldehyde. Synthesis of DMeDHEU requires relatively expensive

O O C H2N

O O C C

+ NH2

Urea

H

H Glyoxal

O C

N H H N + C OH HO C H H 4,5 - Dihydroxyethylene urea

O 2 C H H Formaldehyde

C N H H N HO C C OH H H 4,5 - Dihydroxyethylene urea

O C

HOCH2 N N CH2OH HO C C OH H H 1,3 -Dimethylol - 4,5 - Dihydroxyethylene urea (DMDHEU)

Figure 6.4 Synthesis of DMDHEU. Reproduced from [23] with permission of Elsevier.

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O CH2OH

+

C

N

CH2O R

HO C

C

OH

H

H

OCH2

R

N

+2 ROH

HOCH2

+

–2 ROH R = H, CH3, CH2CH2OCH2CH2OH O

OCH2

CH2

N

C

N

CH2O

HO C

C

OH

H

H

CH2

Figure 6.5 Cross-linking of cellulose with DMDHEU products. Reproduced from [23] with permission of Elsevier.

N,N -dimethyl urea and gloxal (Figure 6.6). DMeDHEU is less reactive compared to DMDHEU as the two hydroxyl groups in the 4,5-position of DMeDHEU are not as responsive as the N,N -methylol groups of DMDHEU [24]. As a result, successful cross-linking requires stronger catalysts or harsher reaction conditions. The price of DMeDHEU is about twice that of DMDHEU. Moreover, a comparable easy-care effect requires nearly twice the amount of DMeDHEU. This poor cost performance ratio does not allow the DMeDHEU to penetrate the easy-care finish market. Another reason for which total zero formaldehyde finish is not becoming successful is that ultralow formaldehyde products can fulfill the requirement limit set by regulating authorities or standardization bodies such as OEKO-TEX . However, a 1:1 mixture of DMDHEU and DMeDHEU is gaining popularity in the

O O O O

C H3CN H

NCH3 H

N, N’-Dimethyl urea

+

C H

H3CN

C H

Glyoxal

C

NCH3

HO C

C

H

H

OH

N, N’- Dimethyl-4,5-dihydroxyethylene urea (DMeDHEU or DMUG)

Figure 6.6 Synthesis of DMeDHEU. Reproduced from [23] with permission of Elsevier.

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processing industry due to its minimal formaldehyde levels with slightly poor physical properties at an affordable cost. 1,2,3,4-Butanetetracarboxylic acid (BTCA) could be an alternative possibility for a formaldehyde-free easy-care finish [25]. Although BTCA provides good crease recovery, one of the disadvantages of BTCA is poor durability to laundering due to the hydrolysis of the ester bonds to cellulose. Another drawback of BTCA is its high cost; it is comparable in cost to DMeDHEU. Similar polycarboxylic acids such as citric acid have been an interest for textile researchers as it is less expensive. Citric acid was used as an esterifying agent in the presence of sodium hypophosphite as a catalyst to develop easy-care properties in cellulose-containing fabrics [26]. Recently, formic acid was also tried in combination with citric acid to improve the wool fabric easy care and shrinkage [27, 28]. However, a large amount of catalyst such as sodium hypophosphite is necessary for cross-linking reaction between acid and fiber molecules. Being a reducing agent, sodium hypophosphite can discolor specific dyestuffs, such as some reactive and sulfur dyes. Moreover, sodium hypophosphite is also expensive. Less expensive polyacrylic acid-based products, such as maleic acid anhydride copolymers, have also been reported in literature, and comparable properties to BTCA were obtained [29]. New cellulosic cross-linking agents were developed by modifying the BTCA structure. Phosphorus catalyst was incorporated in the BTCA structure. These formaldehyde-free phosphonoand phosphinocarboxylic acids have several advantages including better cross-linking properties with minimum loss of strength, without any change of shade and good durability for up to 20 washing cycles [23]. Other chemical cross-linking agents that have been applied to impart easy-care properties to cellulosic materials include diglyoxal urea, triazons, dimethylol ethylene or propylene urea, urons, carbamates, diepoxides, and diisocyanates. However, very few actually gained commercial success due to their high cost or limited technical advantages. Sometimes, they are applied in a small amount in combination with DMDHEU for special effects. Environmentally safe silicone softeners have been studied for improving wrinkle properties of cellulosic fibers and suggested as an alternative to formaldehyde easy-care finish by several researchers including Mohamed Hashem et al. [30] and Mohsin et al. [31].

6.3 Softening Finishes Softening finishes are one of the most important of textile chemical finishes. The use of soft finishes is now universal as the cost of such a simple

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final treatment is low, and the result is a dramatic improvement in perceived fabric quality. Textiles can become harsh after pretreatment processes as natural oils and waxes are removed. Finishing with softeners at the end can overcome this problem and restore or even improve on the original suppleness. Softener mainly acts as a lubricant. Reduction of the coefficient of friction between the fibers and yarn is the key to soften the textile fabric. However, softeners may also have some role as plasticizers. Small softener molecules can provide an internal plasticization of the fiber-forming polymer after penetrating into the fiber and by reducing glass transition temperature Tg. Softeners are surface active agents with a long hydrophobic chain and a short hydrophilic polar water solubilizing group. Softeners can be categorized into six groups according to the ionic nature and polarity [32]: 1. Cationic softeners: mainly quaternary ammonium and other cationic products 2. Anionic softeners: soaps, sulfated oils, sulfated alcohols and tallows, oil emulsions 3. Non-ionic softeners: derivatives of polyoxyethylene (ethoxylates), wax emulsions polyethylene emulsion 4. Amphoteric softeners: carboxylate salts, imidazoline, amine oxides 5. Reactive softeners: contains reactive groups in the longchain softening group 6. Special softeners: silicones A soft finish remains in the finished goods and will, in many cases, be worn next to the skin, which means that special care needs to be taken to avoid physiological effects. From the classification, it is clear that chemical soft finishes are greatly diverse in chemical types. Therefore, it is difficult to categorize in terms of health and environmental behavior. However, most of the softening chemicals are benign, including hydrocarbon waxes, fatty esters, and sorbitan ethoxylates. Starting materials used by softener manufacturers such as fatty acids, fatty alcohols, triglycerides, and long-chain fatty amines are considered as low-risk components. Nitrogen compound-based softeners are problematic as they have a higher tendency to be physiologically active. For an example, alkyl amines are not only strong bases but also often volatile and foul smelling and are difficult to handle. Alkyl amines have the potential to form nitrosamines, which are carcinogens. Moreover, they can be explosive, combustible, and irritant. To prepare a cationic softener, nitrogen atoms need to be quaternized

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by alkylating agents such as dimethyl sulfate and epichlorohydrin. These alkylating agents represent an even greater risk since they are carcinogens, toxic, capable of absorption through the skin, mutagenic, explosive, combustible, and strongly basic. Luckily, the final soft finishes made from the alkylating agents are usually amine salts or quaternary ammonium compounds, which are relatively benign compared to the starting materials. However, these softeners are still more hazardous than other types of softeners. The amine salts are surface-active and responsible for foaming and increasing the chemical oxygen demand and biological oxygen demand of the effluent. The quaternary ammonium compounds, however, have a degree of fish toxicity and retard biological effluent treating systems. One of the most effective quaternary ammonium softener is distearyl dimethyl ammonium chloride. However, only low concentrations of free distearyl dimethyl ammonium chloride actually reach the effluent system and have not caused adverse effects over many years of use. The newer esterquats are nonetheless far safer in the aquatic environment. Di-tallow ester of 2,3-dihydroxypropanetrimethyl ammonium chloride (Figure 6.7) is a commercially available esterquat. The chemical compound shown in Figure 6.7 hydrolyzes easily in the environment via the 3-monoester to the very soluble diol quaternary ammonium compound, which is readily biodegradable [33]. The DEQ has a low solubility of 2.8  μg/L and hence low bioavailability and low toxicity to sewage bacteria and aquatic organisms. Polydimethyl siloxane is ecologically inert and does not have any effect on aerobic or anaerobic bacteria. Their molecular sizes do not allow them to pass through the biological membranes of aquatic animals such as fish. Silicones from padding and exhaust treatments, and repeated domestic laundering may reach a high level. Silicones can easily be combined with particulate matter, and accumulated and treated as a part of sludge. However, even high levels of silicone in wastewater will not pose any adverse effects on activated sludge processes [34]. Treated water contains silicones to an undetectable level. Silicone is slowly mineralized if disposed CH3 H3C

N

R=C17H35

+

O CH3

O O

R

Figure 6.7 A diester quaternary (DEQ).

O R

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of as landfill by, initially, nonbiological catalysis and finally by biological degradation. Incineration simply results in finely divided silica, which is no more innocuous than fine sand [33].

6.4 Repellent Finishes Water-repelling finishes (water repellent), oil (oil repellent), and dirt (stain repellent) are necessary for clothing, home, and technical textiles. Many chemistries are available on the market currently to impart repellent properties to textiles and can be categorized as hydrocarbons, silicones, fluorocarbons, and other chemistries (dendrimers and inorganic nanoparticles). Hydrocarbons, such as paraffin, based on crystallized linear n-alkyl chains [–(CH2)n–CH3], show repellency towards water but do not repel oil. Physically bound waxes do not perform well against laundering or dry cleaning, which has inspired researchers to synthesize more stable resins based on melamine. The silicone-based polymeric repellents, based on the polydimethylsiloxane (PDMS) backbone [–Si (CH3)2O–], have high repellency to water and treated fabrics obtain a soft hand feel [35]. The durability of modern silicone finishes to normal laundering and dry-cleaning treatments is fair. Unlike hydrocarbon- and silicone-based finishes, which confer only water repellency on textile fiber and fabric surfaces, fluorocarbon finishes can provide outstanding water and oil repellency simultaneously. Leaves of the lotus plant have inherent water repellency owing to leaves’ nanostructure. Repellents based on dendrimers and nanoparticles after modification with fatty acids, per- or polyfluoroalkyl groups, or polyalkylsiloxanes can mimic the nanostructures of the lotus plant’s leaves and obtain properties of repellency [35]. Out of these four types of repellent finishes, fluorocarbon is the most attractive to textile finishers as it repels both water and oil and durability of treated fabric is excellent. Previously, C8 fluorocarbons, which have eight carbon atoms in their structure, were mainly applied for textile finishing. Nonetheless, these fluorocarbons can release harmful materials into the environment, for example: perfluoroalkyl carboxylates (PFOA) or perfluoroalkyl sulfonates (PFOS). These materials have been recognized as very high concern substances as they stay in the environment and ecosystem (persistent and bioaccumulative) and have other nondesirable properties including mutagenic, carcinogenic, or toxic for reproduction properties [22, 36]. Fluorocarbon finishes can be mainly synthesized by two major routes, namely, telomerization of tetrafluoroethylene (Teflon, Du Pont) and

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electrofluorination of hydrocarbons (Scotchgard, 3M). While production using the telomerization route continues, in 2003, 3M voluntarily phased out the manufacturing of Scotchgard Protector based on responsible environmental management and sound business reasons [37]. Accordingly, commercial and scientific interest increased to find nonbioaccumulative fluorinated materials with shorter carbon perfluoroalkyl chain (four to six) or nonfluorinated products that can avoid environmental and health concerns.

6.4.1 Short-Chain Fluorocarbon RUCO-GUARD and RUCOSTAR from Rudolf are two of the examples of finishing products with C6 fluorocarbon. Rudolf and HeiQ jointly developed the BARRIER series, which offers water, oil, and stain repellency to clothing wear for outdoor activities. This product range is based on three chemical compounds: C6- and C8-based fluorine, fluorinefree dendrimer, coral-like 3D hyperbranched polymer technologies, and clean C6- and C8-based fluorine. 3M developed new fluorocarbons based on C4, which are free of PFOA and PFOS. 3M later introduced two products under Scotchgard brand, namely, Stain Release PM 490 and PM 492 based on fluorochemical urethanes, which showed good stain release and lower repellency compared to fluorocarbons. C4 fluorocarbonbased dual action (repel and release) resin solutions such as PM 900 and PM 930 (Scotchgard brand) are developed for improved water and oil repellency of textile fabrics. CHT marketed TUBIGUARD 42-AT as a water-repellent finish based on fluorocarbon for polyamide (nylon) raincoats. Another CHT product based on fluorocarbon was introduced (TUBIGUARD SRO) as soil release finish. Archroma introduced various water- and oil-repellent products under the NUVA series consisting of different C6 [22]. However, shortening fluorinated chain may decrease many of the major performances of fluoropolymers. Moreover, short-chain fluorinated products do not degrade readily. Their longer chain homologues can continue to exist in nature and could remain as a threat to health and the environment. It is required to have non-fluorinated chemistry in order to solve the abovementioned concerns. In one attempt to generate non-fluorinated silicone-based material, tris-trimethylsilyl was incorporated into the side chain of the polyacrylate as the functional group for the treatment of fabrics to get better anti-stain property [36]. Recently, another work of fluorocarbon-free water repellent has been reported by modification of silicone [38]. In another attempt, silica nanoparticles were used as an alternative

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to fluorocarbon. Surface of the silica nanoparticles was modified with (3-aminopropyl) triethoxysilane and hexadecyltrimethoxysilane in order to prepare the coating material [39]. Grozea et al. [40] reported a cheap, simple, eco-friendly aqueous method using non-fluorinated graft copolymers to impart water repellency in cotton fabrics. In order to obtain water repellency, a series of graft copolymers including poly[(oligo (ethylene glycol) methacrylate)-co-(2-hydroxyethyl methacrylate)-co-(n-butyl methacrylate)-co-(methyl methacrylate)]-graft-poly(dimethylsiloxane) was synthesized. Mohsin et al. [41] presented an environment-friendly method where a combination of fluorocarbons was used. In the study, fluorocarbon was also tried in combination with the formaldehyde-free cross-linker. This finishing provided not only a cost-efficient alternative but also better repellency to oil and water by notably minimizing the amount of fluorocarbon as good repellency rating was at lower dosage. Another group researched on cotton fabrics to make it water-repellent using radical ultraviolet. Cotton fabric coated with silicone and urethane acrylates was cured by ultraviolet. The advantages highlighted by authors include energy savings (without drying and a low-temperature process), less impact on environment (zero emission of solvents), simple, cost-effective, and less time-consuming [42].

6.5 Flame-Retardant (FR) Finish The necessity for FR materials in the workplace has increased rapidly nowadays with the use of plastics. Fire-retardant finishes provide safety and protection to the people from unsafe conditions, especially from fire. In addition, firefighters or other emergency personnel need to be protected from unsafe apparels, which can cause injury or even death. FR textiles can be manufactured either by using inherently FR fibers or by finishing or coating. Inherently, FR fibers are obtained from inherently FR polymers, which include aramids, polyimide, melamine, glass, basalt, halogen-containing olefins, oxidized polyacrylonitrile, and polyphenylene sulfide [43]. By introducing FR co-monomers in the polymer system, FR fiber is also possible to develop such as Trevira CS and modacrylics. Another way to obtain FR fibers is to incorporate special nonreactive FR additives in the fibers. Viscose FR and Visil are two FR viscose fibers composed of FR additives at a high concentration (~30%). On the other hand, FR textiles via finishing or coating are obtained by the application of FRs in fabric form using finishing followed by fixation.

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Horrocks et al. [44] have developed a simple model to measure the environmental effect of the commonly used FR fibers including finished and inherently FR types. In brief, each step of the processing and end-use stage of each fiber was identified and ranked from 0 to 5, for zero to maximum environmental impact, respectively. The score for each fiber type was then mathematically summed and expressed as a percentage of environmental impact index (Figure 6.8). Interestingly, despite the very different fiber types and process histories, the environmental index has not varied substantially (39–51%). FR finishes are prepared based on the following types of chemical compounds [43]: i. ii. iii. iv. v. vi. vii.

Phosphorus in their various inorganic and organic forms, Halogens (fluorides of zirconium, brominated, chlorinated organics), Inorganic or organic forms of silicon, Boron, Metals (hydroxides of Al, Ca, Mg, phosphinates of Zn, Al, and Ca and Zinc borates, fluorides of zirconium), Organic or inorganic nitrogen, or nitrogen combined with phosphorus (organic or inorganic), Antimony oxides in combination with halogens.

Environmental index, % 60 50 40 30 20 10 0

D

I LO VO

NO

NE

E I YL PB OP PR LY PO E OS SC IC VI YL CR YA OX ON TT CO ID AM AR DC PV C/ PV R TE ES LY PO L OO LIC W RY AC OD M

Figure 6.8 Environmental indices. Reproduced from [44] with permission of Wiley.

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The U.S. Environmental Protection Agency states that polymers are relatively nontoxic, as living body present in the environment does not easily assimilate them. Therefore, polymeric FRs do not need to be enlisted to Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). On the other hand, FR finishes require close monitoring as these compounds are increasingly found in slit, building dusts, microorganisms, fish, and animals including polar bears, seals, raptors and their eggs, and even in human blood, tissues, and breast milk [43]. As a result, these products have received more focus in scientific and political discussions and special attention of national or international environmental committees (such as REACH). Horrocks et al. [45] outlined the current challenges of wellestablished FR processes as (i) replacing bromine, particularly in coating and back-coating formulations, and (ii) replacing formaldehyde chemistry, notably in case of cotton and blended fabrics.

6.5.1 Replacing Bromine Brominated FRs, often used in combination with synergists such as Sb2O3, have been used as FR finish for more than 50 years. In 2008, the European Commission had restricted the following halogenated FRs for fireproofing garments: • tris(2,3-dibromo-1-propyl)-phosphate • polybrominated biphenyls • tris-(aziridinyl)-phosphinoxide Tetrabromobisphenol A, decabromodiphenyl ether (DecaBDE), and hexabromocyclododecane (HBCD) are some commonly used brominated FRs worldwide. DecaBDE and HBCD are used as FR for furniture and textiles, and in the electrical and electronic equipment (plastic casing) [46]. Both HBCD, deca-BDE is being replaced by less toxic alternatives as they are recognized as highly concerned substances. The phase out of antimony trioxide, synergist of halogenated-based FR, is also ongoing. The aforementioned disadvantages stimulated the development of phosphorus-based compounds, which appear to have low toxicity and might be a suitable option to replace bromine-based counterparts. Although generally not all phosphorus compounds are nontoxic, FRs based on phosphorus compounds have lower toxicity profiles [47]. Commercially available phosphorus-containing co-monomer-based FR (in the form of propionylmethylphosphinate), in particular, Trevira CS , has been utilized

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for imparting FR properties to polyester fibers and fabrics. For the treatment of cotton and cellulosic materials, the well-recognized processes are the Proban and Pyrovatex processes based on hydroxymethylphosphonium salts and N-methylol phosphonopropionamide derivatives, respectively. The chemistry of the Proban process involves the application of tetrakis (hydroxymethyl) phosphonium–urea condensate (THPX) by padding, followed by cross-linking with ammonia gas using special equipment. Proban does not make any link with the fibers but mechanically retains within the fiber interstices by a polymer network formed through cross-linking of the deposited chemicals. The result is a durable FR finished textile. However, one of its major demerits is the probable release of formaldehyde at the time of the fabric use. On the other hand, Pyrovatex is capable of forming covalent bonds with the hydroxyl groups of the cellulose molecules in the presence of an appropriate cross-linking agent such as methylolated chemical compound. Nonetheless, first laundry may remove about 50% of Pyrovatex , although it remains linked thereafter in a stable way. This high removal of Pyrovatex is associated with the extraction of unreacted products. However, the use of ammonia during the curing process produces formaldehyde, and VOC emissions present another environmental challenge.

6.5.2 Replacing Formaldehyde Chemistry The abovementioned issue due to formaldehyde is mainly caused by durable THPX and dialkyl phosphonopropionamide-type FR treatments prompted considerable research works leading to the development of formaldehyde-free FR alternatives. Salmeia et al. [48] have recently reviewed the research on phosphorus-based FRs developed for cotton, polyester, and nylon in which environmental sustainability was a main focus. Polycarboxylated BTCA along with other functional species can chemically react with cellulose to produce acceptable levels of flame retardancy. However, washing durability is only moderate; therefore, suitable textile application is limited to upholstery, which requires washing durability of moderate level such as carpets. This is because the formed BTCA-cellulose ester linkages are prone to hydrolysis [49]. A novel commercial formaldehyde-free FR, Noflan , was introduced about a decade earlier by Firestop Chemicals Ltd. (Holmes Chapel, UK). Noflan was based on a phosphorus- and nitrogen-containing molecule in which an alkyl phosphoramidate was stabilized as a salt adduct with ammonium chloride. It performs more effectively on cotton and cotton– polyester blends with acceptable levels of durability.

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6.5.3 Novel Surface Chemistries El-Shafei et al. [50] presented environmentally friendly finishing agents for cotton fabrics to enhance FR using TiO2 nanoparticles and chitosan phosphate (chit-P). The presence of BTCA, TiO2, and chit-P play a key role to make the cotton fabric thermally stable. In this research, cotton fabric was padded, followed by drying with chitosan phosphate in the presence of BTCA and sodium hypophosphite as catalysts. Then, dried fabric was treated with nano-TiO2 followed by drying and curing. Favorable limited oxygen indices of the treated cotton fabrics were obtained. Another approach to provide eco-friendly FR finish is the use of biomacromolecules specifically hydrophobins and whey proteins, proteins like caseins, and deoxyribonucleic acid (DNA). Some of these products contain phosphorus and other elements such as nitrogen and/or sulfur, which can provide FR properties to different fibers and fabrics [48]. Whey protein was applied on cotton fabric and FR properties were checked. Coating seems to partially protect cotton possibly by preventing the oxygen diffusion and absorbing the heat at the time of combustion [51]. El-Tahlawy [52] showed that chitosan could be included to the phosphorylation bath to confer flame retardancy on the cotton fabric in an environmentally friendly manner. Chitosan being a natural nitrogen source can give a synergistic effect with phosphorus. By increasing 1–2% chitosan concentration, a substantial improvement in the performance properties and flame retardancy of the finished fabric was obtained. The finished fabric showed good endurance against successive washing. The recent results achieved using biomacromolecules are presented in a review compiled by Malucelli et al. [53]. That review clearly concluded that novel, eco-friendly, and efficient FRs for different fabrics are possible to develop, at least at the laboratory scale.

6.6 Ultraviolet (UV) Protection Finish Nowadays, consumers have become concerned of skin problems caused by sunray and its relationship with increased exposure to UV light. Skin aging and sunburn are two main chronic damages caused by UV radiation. Protection against UV radiation type of finishing is attracting more and more attention, specifically green techniques that can give protection without any harm to the environment. Nattadon Rungruangkitkrai et al. [54] examined the possibility of a naturally extracted dye from eucalyptus leaves to be used as a UV protection

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finish. A wool fabric was dyed with eucalyptus extract solution to a pale yellowish brown shade. Dyed fabric showed very good ultraviolet protection factor (UPF) values. Additionally, when FeSO4 was used as mordant, darker color was obtained. Dark color can absorb more UV radiation and better UV protection was achieved. Therefore, UV-proof wool fabric can be successfully developed by dyeing with eucalyptus extract with or without metal mordants. Another group took a similar type of approach to prepare UV-proof silk fabric by dyeing with extraction from eucalyptus leaves. Conventional pad-batch and pad-dry techniques were used for such application under various conditions. Good to excellent UPF values were possible to obtain by increasing dye concentration [55]. Chengyu Pan et al. [56] showed inexpensive and ordinary Al (NO3)3 and sodium stearate can be applied to produce eco-friendly UV-protected surfaces for various materials. Industrially available and inexpensive longchain monocarboxylic acids (CH3–(CH2)n–COOH, n = 8–22) or salts, such as stearic acid or stearates, are safe and eco-friendly. Superhydrophobic surfaces on cotton substrates were formed by dip-coating the nano-Al sol with Al (NO3)3 followed by surface modification with sodium stearate (C17H35COONa) to get a thin film through self-assembly. Very good hydrophobic properties coupled with UV protection efficiency with a larger water contact angle (146.27°) and higher UPF value (164.06) were achieved. Durable UV resistance was developed on cotton fabric by Chunxia Wang et al. [57] using plasma treatment. To get durable UV resistance and antibacterial activity for cotton fabric, ZnO/CMCS composite finishing was applied on plasma pretreated cotton fabric. Cold oxygen plasma was used for the pretreatment of the cotton fabric and pad-dry-cure method was employed to apply the ZnO/CMCS composite finishing. The UV-resistant finished cotton fabric showed an excellent durability to laundering.

6.7 Plasma Treatment The deposition of functionalities as a nanolayer on textiles using atmospheric plasma, low-pressure plasma, or plasma sputtering is known as plasma coating. Nowadays, plasma has become one of the popular environment-friendly textile finishing techniques as various functionalities can be incorporated into the textile easily [58, 59]. Nevertheless, the whole process should be controlled carefully as it can damage the surface of the substrate. Samanta et al. [60] cover the eco-friendly application of plasma for textile processing in their recent review.

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6.7.1 Plasma Application on the Finishing of Natural Fibers In Section 6.1.3, enzymatic washing of denims has been discussed. However, denim washing with enzymes uses more water, making the process less environmentally friendly. Recently, low-pressure plasma and corona treatments to develop the faded look on denim fabrics have gained industrial attention. Radetic et al. [61] calculated color differences using CIE L a b colorimetric values of untreated and plasma-treated denim fabrics. They found that lightness of the faded portion is proportional to the higher power and higher number of passes in the corona treatment. Atmospheric pressure plasma technique is used to apply silicone dioxide‐ based compounds as a coating on cotton fibers [62]. Plasma treatment was found useful in enhancing the flame retardancy of cotton fabric [63]. In another study, cotton was chemically finished with fluorocarbon in combination with atmospheric pressure plasma in order to confer hydrophobicity in cotton [64]. Although eco-friendly plasma treatment was involved in the finishing, use of fluorocarbon did not make the finishing process entirely environment-friendly. Plasma treatment was successfully applied for developing antimicrobial activity on cotton dyed fabric along with fastness enhancement. Cotton fabric dyed with direct, vat and reactive dyes were sputtered by silver and copper using plasma sputtering system for 15 s. Antimicrobial property and improvement of color fastness were obtained by the deposition of silver or copper nanoparticle layer on the cotton fabric surfaces [65]. The modification of the surface of the cotton fiber is necessary to enhance the BTCA treatment with TiO2. However, surface of the cotton fiber is generally modified by using various types of chemicals, which increase the risk of environment pollution. Nowadays, the modification of the fabric surface is performed vastly with the help of atmospheric pressure plasma jets in the textile factory, which leads to less consumption of chemicals and energy [62].

6.7.2 Plasma Application on the Finishing of Synthetic Fibers Polyester fabric was treated with plasma for different periods under optimized plasma emitting conditions followed by dipping in dichlorodimethylsilane (DCDMS). Fabric treated with DCDMS without any plasma modification was used as a control in the study. A control fabric surface modification through plasma treatment prior to dipping in DCDMS solution resulted into deposition of more silane groups. As a result, better water repellency was obtained compared to the control [66].

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A series of silicone-modified surfactants were cleaved after treatment with plasma, resulting in water-insoluble silanol moieties. When applied to nylon fiber, the hydrophobic silanol moiety readily underwent polymerization through silanol condensation and deposited a hydrophilic film onto the fiber. The resulting fiber showed very good water repellency with a contact angle of 130° [67]. Plasma treatment was found to be useful for enhancing the antibacterial property of nylon fiber. Tseng et al. [68] grafted chitosan on nylon by open-air plasma treatment and found that the antimicrobial property was improved. Moreover, nylon became more hydrophilic as plasma treatment allowed more grafting of chitosan polymer onto the surface of nylon.

6.8 Energy-Efficient and Water-Saving Finishing Processes High amounts of water and energy are required for conventional fabric finishing processes. For many years, researchers are trying to develop finishing processes that would be water-saving and energy-efficient. The advantage of these processes would include absence or less amount of water, elimination of the energy-intensive oven, and minimizing the floor space required for the machines. While some of them are about to be used at industrial scale, others are still on a laboratory level [58].

6.8.1 Low Wet Pickup Methods Typically, wet pickups are in the range of 70–100% for pad applications of chemical finishes. Consequently, the elimination of huge amounts of water is necessary during drying. Various techniques have been introduced to minimize the pickup in finish applications in order to reduce the energy costs associated with drying large amounts of water. There are two main types of low wet pickup applicators available. One is the saturation-removal type where the normal method is applied to saturate the fabric completely with the finish liquor followed by the elimination of extra liquid mechanically or using vacuum technique prior to drying. An effective lower pickup is achieved by returning extracted liquid to the pad. In another type, an exact amount of finish liquid is applied uniformly to the fabric using lickroller (kiss-roll), spray, or foam application technique [69]. Both types of low wet pickup application method can save 30–40% energy in subsequent thermal drying. Machnozzle system (Figure 6.9), based on the similar principle of air-jet ejectors, is another comparatively easy method of

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High speed steam injection B

Fabric +

+

+

A

+

A

+ +

Figure 6.9 Machnozzle system from [69] with permission of Elsevier.

minimizing wet pickup. This device is suitable for synthetic fabric where high pressure steam is applied to bring the extra liquid out of the fabric. Sarwar et al. [70] developed a water- and energy-efficient finishing of DHEU by foam coating on stretch denim fabric. Stable foam resin application to the cotton lycra stretch denim fabric drastically reduced the pickup % of the DHEU, which is significantly less when compared with the conventional padding. Consequently, times for drying and curing of the fabric were less.

6.8.2 Hotmelt Polymers/Adhesives Hotmelt polymers/adhesives are completely water-free finishing processes. The advantage of water-free finishing formulations is that no material is wasted or unused in the finishing process, and no water emissions occur, as there is no water involved. Initially, the hotmelt process for textiles was developed for lamination applications (e.g., fusible interlining for cuffs and collars of shirts) [71]. Later, it was realized that coating can also be carried out using the hotmelt process. Normally, in a hotmelt process, a polymer is used as a material, which is molten by applying heat, and then molten polymer is transferred onto the textile as a coating layer. By using functionalized hotmelt, the textiles can be made FR, antimicrobial, hydrophobic, and more. Polymer with high viscosity is applied by an extrusion coating method where an extruder is coupled [72].

6.8.3 Minimization of Energy Consumption of Stenter Frames Textiles are mainly heat set, dried, thermosol processed, and chemically finished using a stenter machine. Roughly, each textile product is subjected to a stenter machine for the abovementioned treatments on an average

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of 2.5 times. According to best available techniques documented by the European Commission [73], a stenter can be made more energy efficient by applying the following techniques: i.

Optimizing exhaust air flow using variable-speed fan can save 57% energy consumption ii. Recovery of exhaust heat using air-to-water heat exchanger iii. Proper insulation of stenter encasement can save about 20% energy consumption iv. Using a gas heating system v. Regular maintenance of burner to reduce methane emission

6.8.4 Emerging Processes Radiation curing is an alternative to heat curing, which can save energy in water-based and water-free coating finishing. Ultraviolet, light-emitting diode, or electron beam is used for the radiation curing process. One of the important benefits of this technique is that it is space-saving. Other benefits of radiation curing include the integration of the radiation curing machinery into the existing coating line and minimized run lengths [58]. Digital finishing is gaining popularity day by day. Digital printers normally designed for printing of the textile materials have now been tried for textile finishing. The cost-effectiveness of such technique mainly comes from the probability of localized application with a reduction of chemicals, less amount of solvents, and using energy as less as possible than the conventional finishing of an entire textile [58].

References 1. Shen, J. and Smith, E., Enzymatic treatments for sustainable textile processing, in: Sustainable Apparel, pp. 119–133, 2015. 2. Yuan, M., Wang, Q., Shen, J., Smith, E., Bai, R., Fan, X., Enzymatic coloration and finishing of wool with laccase and polyethylenimine. Text. Res. J., 88, 16, 1834–1846, 2018. 3. Singh, R., Kumar, M., Mittal, A., Mehta, P.K., Microbial enzymes: Industrial progress in 21st century. 3. Biotech, 6, 2, 174–174, 2016. 4. Wadham, M., Bio-polishing of cellulosic fabrics. Color. Technol., 110, 11, 367–368, 1994.

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5. Araújo, R., Casal, M., Cavaco-Paulo, A., Application of enzymes for textile fibres processing. Biocatal. Biotransfor., 26, 5, 332–349, 2008. 6. Shen, J., Enzymatic treatment of wool and silk fibres, in: Advances in Textile Biotechnology, V.A. Nierstrasz and A. Cavaco-Paulo (Eds.), pp. 171–192, Woodhead Publishing, Cambridge, UK, 2010. 7. Kristina, Š., Ivo, S., Tanja, P., Application of cellulases in the process of finishing. Tekstilec, 58, 1, 47–56, 2015. 8. Shahid, M., Mohammad, F., Chen, G., Tang, R.-C., Xing, T., Enzymatic processing of natural fibres: White biotechnology for sustainable development. Green Chem., 18, 8, 2256–2281, 2016. 9. Madhu, A. and Chakraborty, J.N., Developments in application of enzymes for textile processing. J. Clean. Prod., 145, 114–133, 2017. 10. Bai, G., Fu, K.L., Jin, N.Y., Zhu, L.L., Chai, H.M., Lu, D.N., Bio-polishing of cotton fabric with cellulase. Adv. Mater. Res., 468–471, 46–49, 2012. 11. Liu, J., Otto, E., Lange, N., Husain, P., Condon, B., Lund, H., Selecting cellulases for bio-polishing based on enzyme selectivity and process conditions. Text. Chem. Color. Am. Dyest. Rep., 32, 5, 30–36, 2000. 12. Saravanan, D., Vasanthi, N.S., Ramachandran, T., A review on influential behaviour of biopolishing on dyeability and certain physico-mechanical properties of cotton fabrics. Carbohydr. Polym., 76, 1, 1–7, 2009. 13. Mccloskey, S.G. and Jump, J.M., Bio-polishing of polyester and polyester/ cotton fabric. Text. Res. J., 75, 6, 480–484, 2015. 14. Silva, C.J.S.M., Prabaharan, M., Gübitz, G., Cavaco-Pauloa, A., Treatment of wool fibres with subtilisin and subtilisin-PEG. Enzyme Microb. Technol., 36, 7, 917–922, 2005. 15. Araújo, R., Silva, C., Machado, R., Casal, M., Cunha, A.M., RodriguezCabello, J.C., Cavaco-Paulo, A., Proteolytic enzyme engineering: A tool for wool. Biomacromolecules, 10, 6, 1655–1661, 2009. 16. Smith, E. and Shen, J., Surface modification of wool with protease extracted polypeptides. J. Biotechnol., 156, 2, 134–140, 2011. 17. Shen, J., Wool finishing and the development of novel finishes, in: Advances in Wool Technology, N.A.G. Johnson and I.M. Russell (Eds.), pp. 147–182, Woodhead Publishing, Cambridge, UK, 2009. 18. Pazarlioğlu, N.K., Sariişik, M., Telefoncu, A., Treating denim fabrics with immobilized commercial cellulases. Process Biochem., 40, 2, 767–771, 2005. 19. Mojsov, K., Biopolishing enzymes and their applications in textiles: A review. Tekstilna Ind., 61, 2, 20–24, 2014. 20. Rodríguez-Couto, S., Laccases for denim bleaching: An eco-friendly alternative. Open Text. J., 5, 1–7, 2012. 21. Pasquet, V., Behary, N., Perwuelz, A., Environmental impacts of chemical/ ecotechnological/biotechnological hydrophilisation of polyester fabrics. J. Clean. Prod., 65, 551–560, 2014. 22. De Smet, D., Weydts, D., Vanneste, M., Environmentally friendly fabric finishes, in: Sustainable Apparel, pp. 3–33, 2015.

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23. Schindler, W.D. and Hauser, P.J., Easy-care and durable press finishes of cellulosics, in: Chemical Finishing of Textiles, W.D. Schindler and P.J. Hauser (Eds.), pp. 51–73, Woodhead Publishing, Cambridge, UK, 2004. 24. Roy Choudhury, A.K., Easy-care finishing, in: Principles of Textile Finishing, A.K. Roy Choudhury (Ed.), pp. 245–284, Woodhead Publishing, Cambridge, UK, 2017. 25. Welch, C.M., Formaldehyde-free durable-press finishes. Rev. Progr. Color. Relat. Top., 22, 1, 32–41, 1992. 26. Ibrahim, N.A., M.H.A.-S., Elnagdy, E.I., Gaffar, M.A., Eco-friendly durable press finishing of cellulose containing fabrics. J. Appl. Polym. Sci., 84, 12, 2243–2253, 2002. 27. Mohsin, M., Farooq, U., Raza, Z.A., Ahsan, M., Afzal, A., Nazir, A., Performance enhancement of wool fabric with environmentally-friendly bio-cross-linker. J. Clean. Prod., 68, 130–134, 2014. 28. Raza, Z.A., Siddque, A., Mohsin, M., Multi-performance enhancement of knitted wool fabric with citric acid: An eco-compatible cross-linker. J. Nat. Fib., 14, 6, 887–896, 2017. 29. Shank, D., Non-formaldehyde wrinkle-free finishing: A commercial update. AATCC Rev., 2, 3, 29–32, 2002. 30. Mohamed Hashem, N.A.I. and El-Shafei, A., Refaie, R., Hauser, P., An ecofriendly–novel approach for attaining wrinkle-free/soft-hand cotton fabric. Carbohydr. Polym., 78, 690–703, 2009. 31. Mohsin, M., Farooq, U., Naveed, R., Rasheed, A., Ahmad, S., Ahsan, M., Softener impact on environment friendly low and zero formaldehyde crosslinker performance for cotton. Ind. Textila, 65, 3, 134–139, 2014. 32. Bajaj, P., Finishing of textile materials. J. Appl. Polym. Sci., 83, 3, 631–659, 2002. 33. Mooney, W., Chemical softening, in: Textile Finishing, D. Heywood (Ed.), pp. 251–307, Society of Dyers and Colourists, Hampshire, UK, 2003. 34. Chandra, G., A review of the environmental fate and effects of silicone materials in textile applications. Text. Chem. Color., 27, 4, 21–24, 1995. 35. Holmquist, H., Schellenberger, S., van der Veen, I., Peters, G.M., Leonards, P.E., Cousins, I.T., Properties, performance and associated hazards of stateof-the-art durable water repellent (DWR) chemistry for textile finishing. Environ. Int., 91, 251–264, 2016. 36. Lei, H., Xiong, M., Xiao, J., Zheng, L., Zhu, Y., Li, X., Zhuang, Q., Han, Z., Fluorine-free low surface energy organic coating for anti-stain applications. Progr. Org. Coat., 103, 182–192, 2017. 37. Roy Choudhury, A.K., Repellent finishes, in: Principles of Textile Finishing, A.K. Roy Choudhury (Ed.), pp. 149–194, Woodhead Publishing, Cambridge, UK, 2017. 38. Ma, Y., Zhu, D., Si, Y., Sun, G., Fabricating durable, fluoride-free, water repellency cotton fabrics with CPDMS. J. Appl. Polym. Sci., 135, 25, 46396, 2018.

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39. Zhao, Q., Wu, L.Y.L., Huang, H., Liu, Y., Ambient-curable superhydrophobic fabric coating prepared by water-based non-fluorinated formulation. Mater. Des., 92, 541–545, 2016. 40. Grozea, C.M., Huang, S., Liu, G., Water-based, heat-assisted preparation of water-repellent cotton fabrics using graft copolymers. RSC Adv., 6, 24, 20135–20144, 2016. 41. Mohsin, M., Farooq, A., Abbas, N., Unsa, N., Sarwar, N., Khan, A., Environment friendly finishing for the development of oil and water repellent cotton fabric. J. Nat. Fib., 13, 3, 261–267, 2016. 42. Ferrero, F., Periolatto, M., Sangermano, M., Bianchetto Songia, M., Waterrepellent finishing of cotton fabrics by ultraviolet curing. J. Appl. Polym. Sci., 107, 2, 810–818, 2007. 43. Gaan, S., Salimova, V., Rupper, P., Ritter, A., Schmid, H., Flame retardant functional textiles, in: Functional Textiles for Improved Performance, Protection and Health, N. Pan and G. Sun (Eds.), pp. 98–130, Woodhead Publishing, Cambridge, UK, 2011. 44. Horrocks, A.R., Hall, M.E., Roberts, D., Environmental consequences of using flame-retardant textiles—A simple life cycle analytical model. Fire Mater., 21, 5, 229–234, 1997. 45. Horrocks, A.R., Flame retardant textile finishes, in: Textile Finishing: Recent Developments and Future Trends, K.L. Mittal and T. Bahners (Eds.), pp. 69–127, 2017. 46. Umweltbundesamt, Brominated Flame Retardants: Guardian Angels with a Bad Streak?, pp. 1–26, Umweltbundesamt Dessau-Roßlau, Germany, 2008. 47. Hirsch, C., Striegl, B., Mathes, S., Adlhart, C., Edelmann, M., Bono, E., Gaan, S., Salmeia, K.A., Hoelting, L., Krebs, A., Nyffeler, J., Pape, R., Bürkle, A., Leist, M., Wick, P., Schildknecht, S., Multiparameter toxicity assessment of novel DOPO-derived organophosphorus flame retardants. Arch. Toxicol., 91, 1, 407–425, 2017. 48. Salmeia, A.K., Gaan, S., Malucelli, G., Recent advances for flame retardancy of textiles based on phosphorus chemistry. Polymers, 8, 9, 319, 2016. 49. Horrocks, A.R., Flame retardant challenges for textiles and fibres: New chemistry versus innovatory solutions. Polym. Degrad. Stab., 96, 3, 377–392, 2011. 50. El-Shafei, A., ElShemy, M., Abou-Okeil, A., Eco-friendly finishing agent for cotton fabrics to improve flameretardant and antibacterial properties. Carbohydr. Polym., 118, 83–90, 2015. 51. Bosco, F., Carletto, R.A., Alongi, J., Marmo, L., Di Blasio, A., Malucelli, G., Thermal stability and flame resistance of cotton fabrics treated with whey proteins. Carbohydr. Polym., 94, 1, 372–377, 2013. 52. El-Tahlawy, K., Chitosan phosphate: A new way for production of ecofriendly flame-retardant cotton textiles. J. Text. Inst., 99, 3, 185–191, 2008. 53. Malucelli, G., Bosco, F., Alongi, J., Carosio, F., Di Blasio, A., Mollea, C., Cuttica, F., Casale, A., Biomacromolecules as novel green flame retardant systems for textiles: An overview. RSC Adv., 4, 86, 46024–46039, 2014.

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7 Functional Finishes for Cotton-Based Textiles: Current Situation and Future Trends Nabil A. Ibrahim*, Basma M. Eid and Samar M. Sharaf Textile Research Division, National Research Centre, Giza, Egypt

Abstract This chapter focuses on functional finishes for cotton-based textiles that are carried out individually or in combination to enhance or create novel performance functionalities for diverse potential applications. A wide range of currently used functional finishes such as antimicrobial, UV protection, self-cleaning, anti-crease, soft finish, soil release, flame-retardant, water/oil-repellent, etc. are discussed, taking into consideration the finishing chemicals, application technologies, imparted functionality, as well as environmental and safety concerns. The positive impacts of application of new and emerging technologies on developing an eco-friendly multifunctional cotton textile products in an environmentally sustainable way to meet the ever-growing consumer demands, and environmental concerns, as well as to promote materials and energy saving are discussed. New and future trends within the realm of functional finishes for cellulose-based textiles and how they should positively affect development of multifunctional cotton products in an environmentally sustainable manner are highlighted. Keywords: Cotton-based textiles, functional finishes, environmental impacts, pollution prevention, eco-friendly processes and products, future prospective

7.1 Introduction Nowadays, natural cellulosic fibers are widely used in the textile industry for many reasons like availability, biodegradability, and biocompatibility, in addition to the ever-growing consumer demands to eco-friendly and green *Corresponding author: [email protected]; [email protected] Mohd Shabbir (ed.) Textiles and Clothing: Environmental Concerns and Solutions, (131–190) © 2019 Scrivener Publishing LLC

131

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textile products based on renewable resources [1, 2]. Production of cellulosebased textiles comprises the following steps: yarn formation, fabric (woven or knit) formation, wet chemical processing whether continuous or batch preparation, dyeing or printing, chemical finishing, and textile fabrication (apparel or non-apparel textile products) (Figure 7.1) [3, 4]. The main task of textile wet processing is to upgrade both comfort and aesthetic properties as well as to impart value-added functionalities to fulfill the consumer demand [1–3]. Moreover, a variety of functional finishes have been developed for (i) imparting new and desirable functional properties to the final textile product to meet the ever-growing consumer Natural Cotton Linen Jute Ramie

Regenerated Fiber preparation

Viscose Modal Lyocell

Thread Fabric Knitted

Woven

Pretreatment Desizing (woven) Scouring Bleaching

Mercerizing

Coloration Antimicrobial UV-protection

Easy care Finishing

Flame retardant

Soft finishing Water/oil repellent

Finished fabric

Clothings

Home textiles

Figure 7.1 Wet processes of cellulosic fabrics.

Commercial use

Functional Finishes for Cotton-Based Textiles 133 requirements; (ii) cutting water, energy, and chemical consumption, thereby minimizing production costs and maintaining high competitive edge; (iii) developing innovative and value-added functionalized textile products using emerging green technologies and environmentally sound finishing agents and textile auxiliaries; and (iv) avoiding or preventing the potential negative impacts on both the human health and the environment [4–6]. In addition, the key factors affecting functional finish effectiveness include [7]: i. ii. iii. iv. v.

Type of substrate being treated The demanded performance and functional properties Existing finishing techniques and available production lines Compatibility of finishing formulation ingredients, as well as Economical and ecological concerns

The most common application methods for functional finishes for cotton textiles include pad-dry-cure, by exhaustion, encapsulation, coating, by low add-on technique, e.g., foaming spraying, etc. and layer-by-layer assembly method of deposition [8]. Additionally, the use of environmentally benign raw materials and implementation of innovative green technologies in textile finishing are highly demanded to achieve textile production ecology, human ecology, as well as disposal ecology. Environmental and economic aspects along with social responsibility should be taken into consideration to achieve sustainability in the textile industry [9–12]. This chapter demonstrates some of the main functional finishes for cotton-based textiles to resolve their drawbacks and/or to impart new and desirable functional properties, highlights the positive role of emerging green technologies in upgrading both the functionalized products and environment quality, and intends to provide an overview of the new and future trends in functionalization of cotton textiles to cope with several requirements.

7.2 Easy Care Finishing Easy care finishing of cotton cellulose is carried out to overcome the inherent drawback of easy wrinkling via formation of ether, ester, and/or ionic cross-links between the adjacent chains especially in the amorphous area of cellulose structure to impart anticrease functionality [13, 14, 17–19].

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7.2.1 Essential Properties of Finishing Agent – Impart significant anticrease properties in both the dry and wet states as well as dimensional stability without adversely affecting the mechanical properties. – Compatible with other finishing ingredients in the finishing formulation. – Has no negative impacts on handling and whiteness properties of the finished substrate. – Has no or minimal impact on coloration properties. – Low or zero CH2O release. – Eco-friendly with no negative impacts on working conditions, product, and consumer health. – Working under mild conditions for energy cost savings. – High durability to wash.

7.2.2 Current Easy Care Finishing Agent Table 7.1 demonstrates some of the current finishing agents used in easy care finishing, which can be classified into (i) formaldehyde-based finishing agents and (ii) formaldehyde-free finishing agents, taking into consideration application conditions as well as their negative or positive impacts on products and environment quality.

7.2.3 Cross-Linking of Cellulose Structure The mechanisms of formation of various cross-links in cellulose structure upon using different types of easy care finishing agents are presented in Scheme 7.1: i.

Formation of ether cross-links [13, 22] O C

Cell.OH

+ ROH2CN

Cotton cellulose

HO

NCH2OR

+

H+

HO.Cell

O

OH

C Cell.O.H2CN HO

NCH2OCell + 2ROH OH

(7.1)

I. CH2O-containing finishing agent (the CH2O content follows the decreasing order: DMDHEU > DMeDHEU > Alkylates DMDHEU

Type of finishing agent

C

OH

NCH2OH

C

OCH3

H3CO

Alkylates DMDHEU

N-CH3

OH

N-CH3

H3C-N

C

O

DMeDHEU

HO

H3C-N

O

N,N -dimethylol-4,5dihydroxyethylene urea (DMDHEU)

HO

HOH2CN

O

Cross-linking agent Ether cross-links

Type of cross-linker - Using the pad-drythermofixation method. - Inclusion of the recommended catalyst along with proper finishing auxiliaries in the finishing formulation.

Highlights - Finished products with low or zero CH2O release levels. - Remarkable permanent press performance, durability to wash as well as chlorine retention and resistance. - Does not affect lightness of colored substrates. - Some decrease in light fastness of reactive and direct dyeings.

Remarks

(Continued)

[7, 13, 14, 20–22]

Refs.

Table 7.1 Some of the most currently used finishing agents, mode of interactions and their positive and negative impacts.

Functional Finishes for Cotton-Based Textiles 135

ii. Ionic crosslinking agents

II. CH2O-free finishing agent. i. Polycarboxylic acids

Type of finishing agent

COOH COOH

COOH

CH

CH2

COOH

COOH

COOH

CH2

C

CH2

- Pre-cationization of cotton with 3-chloro2-hydroxypropyl trimethyl ammonium chloride (CHTAC) followed by esterification with citric acid or BTCA.

Citric acid (CA)

HO

1,2,3,4-Butanetetra carboxylic acid (BTCA)

CH

COOH

CH2

Cross-linking agent

Ester/Ionic cross-links

Ester cross-links

Type of cross-linker

- By exhaustion and/or thermofixation in the presence of recommended catalysts.

- Pad-dry-thermoor microwave fixation technique - Using sodium hypophosphite (NaH2PO2) as the proper catalyst.

Highlights

- Improvement in easy care properties with or without loss in strength properties.

- Zero CH2O finish - Highest level of DP rating and easy care properties. - High cost, loss in tensile strength.

Remarks

(Continued)

[13, 14, 17, 25, 26]

[7, 13–15, 23, 24]

Refs.

Table 7.1 Some of the most currently used finishing agents, mode of interactions and their positive and negative impacts. (Continued)

136 Textiles and Clothing

Type of finishing agent Ionic cross-links

Ionic cross-links

- Inclusion of amine silicone softener in the ionically crosslinked cellulose structure

Type of cross-linker

- Carboxymethylation of cotton cellulose to impart anionic character followed by treatment with CHTAC as a reactive cationic agent.

Cross-linking agent

Highlights

Results in an improvement in dry and wet crease recovery angle along with a remarkable softness.

Remarks

Refs.

(Continued)

Table 7.1 Some of the most currently used finishing agents, mode of interactions and their positive and negative impacts. (Continued)

Functional Finishes for Cotton-Based Textiles 137

iii. Non-CH2O easy care finish

Type of finishing agent

CHO

CH2

Glutaraldehyde

CHO

CH2

Cross-linking agent Hemiacetal and acetal links

Type of cross-linker - Incorporation of aluminum sulfate Al2(SO4)3 as a catalyst along with Na-perborate and borax as additives in the finishing formulation. - Using pad-drycure method.

Highlights - Finished fabric with improved wrinkle recovery angle, degree of whiteness, and retained tensile strength.

Remarks

[13, 27, 28]

Refs.

Table 7.1 Some of the most currently used finishing agents, mode of interactions and their positive and negative impacts. (Continued)

138 Textiles and Clothing

Functional Finishes for Cotton-Based Textiles 139 ii.

Formation of ester cross-links [14, 16] COOH

CH2 HO

COOH

C

SHP Δ

HO

C

CO

CH2

COOH

CH2

CO

CH2

O

Δ

+ Cell.OH

HO

COOH

CH2

COOCell

C

COOH

CH2

COOH

Δ

CA

HO

CH2

COOCell

C

CO

CH2

CO

Δ

+ Cell.OH

HO

O

CH2

COOCell

C

COOH COOCell

CH2

(7.2) iii. Formation of ionic cross-links [13, 17, 25, 26] CH3

OH

CH2

HOOC

Cell.O.CH2.CH CH2 N+ CH3-CI−

+

HOOC HOOC

CH3

Δ OH

C CH2

CA

Precationized cellulose

+ − Cell.O.CH2.CH CH2 N (CH3)3 OOC OH

CH2

HOOC HOOC

C

OH

HCI

+

CH2

(I)

(7.3)

(I)

SHP Δ

+ − Cell.O.CH2.CH CH2 N (CH3)3 OOC OH

OH

+ Cell.OH

CH2 C

CO

H2C

CO

O

+ − Cell.O.CH2.CH CH2 N (CH3)3 OOC OH

Δ

OH

CH2 C

COOH

CH2.COO.Cell

(7.4)

140

Textiles and Clothing iv. Formation of hemiacetal and acetal links [28] O−Cell CH2

CHO +

CH2 CH2

2Cell.OH

Al2(SO4)3

CHO

Δ

CH2

CH

2Cell.OH OH OH

CH2 CH2

Δ

CH O Cell

Glutaraldehyde

Hemiacetals O Cell CH2

CH O Cell O Cell

CH2 CH2

CH O Cell

Acetal links

(7.5)

7.2.4 Test Method Several standard methods have been developed to assess the easy care properties of finished fabrics as well as the presence of formaldehyde, such as: – AATCC 66-2008 (wrinkle recover angle of woven fabrics) – AATCC 88C-2011 (retention of creases after repeated home launderings) – AATCC 124-2011 (appearance of fabric after repeated home launderings) – ISO-1418-1:2011 or Japanese law 112 (for determination of free formaldehyde and formaldehyde extracted thorough water extraction) – ISO-1418-2:2011 (for determination of the amount of formaldehyde released under the conditions of accelerated storage by means of a vapor absorption method)

7.3 Softening Finishes Softening treatment for cotton textiles, especially apparel and home textiles, is carried out to compensate the removal of natural oil and waxes

Functional Finishes for Cotton-Based Textiles 141 during the pretreatment steps, thereby restoring their original suppleness and/or upgrading their surface softness and smoothness to a higher extent as well as to improve some technical properties like sewability, tear strength, abrasion resistance, fullness, etc. [29, 30].

7.3.1 Desirable Properties Desirable properties of textile softeners are as follows [29–31]: – Easy handling – Compatible with common textile auxiliaries and specialty chemicals – Non-yellowing and should not negatively impact the coloration properties of colored textile materials – Eco-friendly and biodegradable – Low foaming and good exhaustion properties The softening effect is governed by the physical arrangement and the orientation of the exhausted softener molecules on textile surface and is determined by the ionic nature of the softener as well as the hydrophobicity of the treated fiber surface (Figure 7.2). On the other hand, the smaller molecules have the ability to penetrate the fiber structure, thereby causing an internal plasticization on the fiber polymer along with reducing its glass transition temperature [29–31].

Anionic hydrophilic group

hydrophobic part







Hydrophobic part

hydrophobic part

Cationic hydrophilic group

+



Nonionic hydrophilic group

+

+

+

δ–

δ–

δ–

Cellulosic fabric

Cellulosic fabric

Cellulosic fabric

Cationic softener

Anionic softener

Non-ionic softener

Figure 7.2 Orientation of textile softeners on cellulose fiber surface.

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7.3.2 Classification The textile softeners are classified according to their [32–35]: i. Ionic nature, i.e., anionic, nonionic, amphoteric ii. Chemical composition, as well as iii. Permanent or non-permanent softeners

7.3.3 Chemical Structures The chemical structures of some of the used textile softeners are presented in Table 7.2.

7.3.4 Silicone Softeners Soft finishing of cellulosic textiles with silicone softeners brings about a significant soft handle along with an enhancement in other desired properties like smoothness, anticrease, tear strength, sewability, thermal stability, durability, etc. The extent of improvement in the aforementioned properties is governed by the type of silicone softener, particle size, as well as its reactivity. Silicone softeners are marked as aqueous dispersion (10–50% active ingredients) along with other additives, e.g., emulsifiers, dispersants, antifoamers, etc.

7.3.4.1 Molecular Size The silicone emulsion forms comprise the following types: (i)

Macroemulsion (milky; particle size range, 150–300 nm), (ii) Semi micro (hazy; particle size range, 80–120 nm), (iii) Micro (transparent; particle size, 150 ) cotton surfaces can be classified into (i) fabricating a rough surface from a low surface energy material and (ii) post-modification of a rough surface, to micro- or nanostructure, with a material of extremely low surface energies, e.g., fluorocarbon (FCs), etc. [41–45].

7.4.1 Mode of Actions • The created repellence functional properties are attributed to the remarkable decrease in surface free energy of finished textile fibers [42, 45]. • Polysiloxanes, [R2SiO]n where R = an organic group, have the ability to form hydrogen bonds with cellulose hydroxyl groups as well as to form a hydrophobic sheath around the fiber, thereby imparting water repellency as follows: CH3 HO

Si

O Si

CH3

CH3

CH3 CH3n

Silanol

O

Si CH3

CH3 OH +

H3C

Si

CH3 O Si

CH3

CH3 O Si

CH3 CH3

CH3

m

O

Si CH3

CH3 + Cell.OH Cotton

Silane Tin octane catalyst Three-dimensional cross-linked hydrophobic sheath around cellulosic fibres

(7.6) where silanol, silane, and tin octoane are components of the siliconewater-repellent agent [44]. • On the other hand, highly ordered fluoro alkyl chains are required to lower the surface free energy to the highest extent, thereby achieving outstanding water- and oil-repellent

Functional Finishes for Cotton-Based Textiles 151 functions as a direct consequence of the orientation of fluorinated component to the air. The extent of creating both the water and oil repellence functions as well as the durability of imparted functions to laundering and dry cleaning are determined by the fluorocarbon chemistry, length of perfluorinated alkyl chains, incorporated anchor groups, e.g., epoxy, hydroxyl groups, etc., additional chemicals application method, as well as mode and extent of loading onto fabric surface [42, 43]

7.4.2 Water- and Oil-Repellent Finishing Agents Some of the most common repellent agents, application methods, imparted functional properties, as well as their advantages and disadvantages are summarized in Table 7.4.

7.4.3 Test Methods Some of the more common test methods are given below: – – – –

AATCC TM 22-2017: Water repellency: spray test AATCC TM 42-2017: Water resistance: impact penetration test AATCC TM 35-2017: Water resistance: rain test AATCC TM 118-2013 or ISO 14 419: Oil repellency: hydrocarbon resistance test

7.5 Flame-Retardant Functional Finish Cotton and cellulosic-rich textile materials are not inherently flameretardant. When cellulosic substrate is heated in air, several thermal degradation and decomposition steps may occur, thereby affecting its ultimate flammability (Figure 7.3). To impart flame retardancy to the cellulosic substrates, they have to be treated with proper flame retardants (FRs) that have the ability to inhibit or delay the appearance of a flame and/or hinder the flame spread rate, i.e., inhibit or resist fire spreading, thereby offering protection to the textile user and avoiding fire hazards [54, 55]. Both padding and coating application methods can be applied to create a protective layer/coating on the treated fabric surfaces using FR additives. Flame-retardant functional textile products have many diverse potential applications such as protective clothing, nightwear, bedding, upholstered furnishings, etc.

1. Repellent agent based on stearic acid

Repellent agent

By both padding and exhaustion

- By padding technique. - Some derivatives can be applied by exhaustion.

Al or Zr salts of stearic acid (emulsion)

Stearic acid/ melamine derivatives.

Application method

Durable water repellency due to the positive role of N-methylol groups on forming ether links with the cellulose active sites, i.e., OH groups.

Water repellency

Imparted functional properties

Table 7.4 Some of the commonly used water- and oil-repellency agents.

Advantages: - Durable water repellency. - Full hand. Disadvantages: - No oil repellency. - CH2O release. - Loss in mechanical properties of finished cotton fabrics. - Negative impacts on the shade of treated dyeings.

Advantages: - Compatible with most type of finishes. - Low cost. - Generate waterproof effect. Disadvantages: - No oil repellency. - Lack of durability. - Negative impacts on air and vapor permeability. - Increase flammability.

Advantages and disadvantages

(Continued)

[42–44]

Refs.

152 Textiles and Clothing

R

(Polysiloxanes copolymer)

R

Si O Si CH3

CH3

R

CH3

H3C Si O

CH3

2. Silicone-based finishing agents

Repellent agent

- By pad-dry-cure technique. - Polysiloxane emulsion (by exhaust method).

Application method - High degree of water repellency. - Very soft fabric hand.

Imparted functional properties Advantages: - Improved sewability, shape retentions, appearance and feel of pile fabric. - Enhanced durability can be achieved by including suitable reactant resin in the pad bath. - Reasonable cost. Disadvantages: - Increased pilling and seam slippage. - Attraction of hydrophobic contaminants. - Negative impacts on aquatic life. - Some deterioration in performance properties of cellulosic substrates due to swelling in water.

Advantages and disadvantages

Table 7.4 Some of the commonly used water- and oil-repellency agents. (Continued)

(Continued)

[42–44, 46]

Refs.

Functional Finishes for Cotton-Based Textiles 153

n

iii. F3C(CF2)7SO3H Perflouroctansulfonic acid (PFOS)

ii. F3C(CF2)7-COOH Perfluorooctanoic acid (PFOA)

C2F5

CH2

O

CO

CH2 CH

3. Fluorocarbon-based repellents (FCs) such as i. Perfluorinated polyacrylate polymer

Repellent agent

- Most of FC repellents are applied by pad-dry-cure method. - Some of new FCs can be applied effectively by exhaustion.

Application method

Advantages and disadvantages Advantages: - Low active ingredients add-on. - More rapid drying. Disadvantages: - High cost. - Ecological disadvantages, e.g., persistent of FCs (nonbiodegradable).

Imparted functional properties Imparted both hydrophobic and oleophobic properties.

Table 7.4 Some of the commonly used water- and oil-repellency agents. (Continued)

[42, 43, 47–51]

Refs.

154 Textiles and Clothing

Functional Finishes for Cotton-Based Textiles 155 Cotton cellulose

Dehydration (up to 120°C)

Depolymerization (beyond 150°C heating)

Char (at 450°C)

Volatiles, i.e. levoglucosan (220°C - 300°C)

Figure 7.3 Thermal degradation of cotton cellulose by heating [52, 53].

7.5.1 Factors Affecting Functionalization For imparting durable flame-retardant functionalities to cotton textiles, the following factors should be taken into consideration: fabric construction, finishing formulation components, compatibility with the selected RF additive with other ingredients, application methods, cost-to-benefit ratio, performance requirements, as well as ecological and environmental awareness [56].

7.5.2 Major Requirements The major requirements for an efficient FR finish to suppress the flame and/or minimizing the burn rate, are [52, 57]: – It should be effective in lowering the developed heat to suppress the combustion process. – It should modify the pyrolysis process to minimize the amount of generated flammable volatiles and enhance the char creation. – It should have the ability to release flame inhibitors. – It should be compatible with other textile finishes. – It should be durable and cost-effective. – It should not negatively impact the product quality as well as the environment.

7.5.3 Mode of Action Classification of FRs by their mode of action is as follows: i.

Gas-phase inhibition action: via generation of reactive species during the burning stage, which in turn act as free radical scavengers in the vapor phase, i.e., halogen and phosphorus-based FRs, and interfere with burning cycle according to the following reactions [58–61]:

156

Textiles and Clothing

HX +H• OH• + HX

H2 + X•

(7.7)

H2O + X•

(7.8)

where HX: hydrogen halide: X• halogen radical H• and OH•: generated radicals from decomposition of flame retardant (RX) or the polymer (PH) or

PO• + H• HPO + H•

HPO

(7.9)

H2 + PO•

(7.10)

where PO and HPO are phosphorus species ii.

Condensed phase action: via the formation of a protective barrier/char between the pyrolyzing polymer and heat source during the thermal decomposition of the polymer, thereby producing less flammable volatiles and more residual char. Incorporation of nitrogen additives along with phosphorus flame retardant (P-N synergism) results in an enhanced phase action, most probably due to the formation of a protective coating on the char surface according to the following reactions [55, 56, 58]: O

O

Cell.O.P-O.Cell + 2H2O

Cell.OH + HO -P-OH + HO-Cell Cotton cellulose O produced phosphoric acid

O Less flammable by products

(7.11)

CH2OH O -O

O H

OH

dehydrated Cellulose + 3H2O

OH

Cell.OH

CH2 O

O

-O OH

OH

(7.12)

Functional Finishes for Cotton-Based Textiles 157 i.e., catalyze the dehydration of cellulose (Equation 7.12) as well as inhibit the formation of undesirable Levoglucosan (precursor of flammable volatiles) OH O O

OH OH

iii. Intumescent and heat sink effects are characterized by the ability to form a foam-like thermal insulation barrier when exposed to flame, thereby providing a heat sink on and/or within the cellulosic fiber, which in turn negatively impacts both the pyrolysis temperature and combustion process. The heat sink effect could be discussed in terms of endothermic decomposition reactions, e.g.,

Al2O3 .H 2O   CaCO3  

Δ

Δ

  Al2O3   H 2O  

CaO  CO2  

(7.13) (7.14)

heat absorption by water formed as well as dilution of gases generated due to pyrolysis of cellulosic polymer [56, 62]. On the other hand, using a phosphorus–nitrogen-based intumescent system contains a blowing agent (urea, melamine, etc.), acid source (to generate H3PO4 during thermal decomposition), and char former (e.g., pentaerythritol, etc.) and is accompanied by the formation of foam of char on the surface of textile materials [56, 63].

7.5.4 Flame-Retardant Types As far as types of flame retardants are considered, FRs may be classified into four groups, namely, halogenated organic, organophosphorus, inorganic, and nitrogen-based FR materials [64]. An overview of the most common FRs for cotton functionalization is demonstrated in Table 7.5.

Mode of action

- Act principally in vapor phase by a radical trap mechanism.

Group

1. Halogenated FRs

- Repressing combustion and disrupting exothermic processes, low cost, miscibility, low negative impact on physicomechanical properties. - Br-based FR is the most efficient agent due to its bonding to carbon and its H-Br accessibility at high concentration in the flame zone enabling it to hinder the combustion process. - The enhancement in FR efficiency follow the decreasing order I > Br > Cl > F. - Possible ecological and environmental hazards.

Highlights

Br Br

Br O Br

Br

Br

Br

Poly-brominated diphenylether

Br

Br

FR agent

Table 7.5 Some halogen- and phosphorus-based FRs for cotton functionalization.

Br

(Continued)

[53, 64, 65]

Refs.

158 Textiles and Clothing

Mode of action

- Act in cellulose by a condensed phase mechanism via reduction of volatile and flammable products as well as by increasing the residual carbonaceous chars. - Lightweight and open fabrics require higher add-ons as compared with their counterparts.

Group

2. Phosphoruscontaining FRs

- Very effective for cellulosic substrate. - Compatible with many textile chemicals. - Acceptable from both environmental and toxicological perspectives. - Halogen free. - Inorganic phosphorus FRs agents are mostly non- or semidurable. - THPC [tetrakis(hydroxymethyl) phosphonium chloride (HOCH2)4PCl] finishes are applied by the paddry-cure process and impart a remarkable durable flame retardancy. CH2OH

O

THPC (Pyrovatex CP) =

O

Cl

2X

O

O

O

O(CH2)2-O-P

O O(CH2)2-O-P

=

X

O(CH2)2OH

(HFPO) Hydroxy functional organophosphorus oligomer

H

(DMPMP) N-methyloldimethylphosphonopropionamide (Pyrocatex CP)

(CH3O)2-P-CH2CH2-C-NHCH2OH

=

CH2OH

HOCH2-P-CH2OH

FR agent

=

Highlights

Table 7.5 Some halogen- and phosphorus-based FRs for cotton functionalization. (Continued)

[53, 56, 58, 64, 65]

Refs.

Functional Finishes for Cotton-Based Textiles 159

160

Textiles and Clothing

7.5.5 Test Methods Some of the commonly used flammability tests are: • (LOI, ASTM D-2863 or ISO4589-2): The Limiting Oxygen Index • IEC 60695-11-10, ASTM D6413, or EN ISO15025: Vertical/ horizontal burning tests • ASTM E162: The Radiant Panel Flame Spread Test

7.6 Antimicrobial Finish Cellulose-based textiles are more easily attacked by harmful microorganisms, e.g., bacteria, fungi, yeast, etc. Microbial growth and subsequent attack on cellulosic substrate bring about multiple negative impacts on both the textile itself and the textile user such as fiber damage, stains, discoloration, and generation of unpleasant odor as well as cross transmission of infectious diseases [3, 66, 67]. Owing to the ever-growing demand for high-added-value, longlasting, and eco-friendly antimicrobial textile products to protect textile users from pathogenic and/or odor-generating microorganisms, a variety of antimicrobial finishing agents and functional methods of application have been developed to cope with the consumer needs for comfortablehygienic clothing and active wear [66–69].

7.6.1 Mode of Action Antimicrobial finishes imparted their functional properties via (i) inhibiting the enzyme activity and destroying the cell wall, thereby killing the microorganisms, i.e., biocides, and/or (ii) inhibiting the growth of harmful microorganism, i.e., biostats, through reaction with the cell membrane, blocking the enzyme and/or the cell reduction [67, 68, 70, 71]. Antimicrobial mechanisms are broadly classified into the following: (i) controlled release mechanism where the active ingredients are slowly leached from the textile into the surrounding environment whereupon pathogenic microbes are killed in the presence of moisture, (ii) regenerable mechanism where N-halamine biocides are used, which are usually regenerated during laundering with NaOCl and can kill the pathogenic microorganisms without the release of free chlorine, and (iii) bound-type, non-leached finishes that act as barrier-forming agents or having blocking mechanisms against the deposited pathogenic microorganisms onto the fabric surface and without leaching [5, 66–68, 72].

Functional Finishes for Cotton-Based Textiles 161

7.6.2 Requirement of Antimicrobial Finishes The major requirements for eco-friendly and efficient anti-microbial finishes include [3, 66–68]: – Be effective against a broad range of pathogenic microorganisms – Be safe to the textile user as well as to nonpathogenic bacteria on the skin – Be eco-friendly, cost-effective, and durable to laundering and dry cleaning – Be compliant with the government regulations as well as with the quality requirements – Be compatible with other textile wet processes without adversely affecting the final product quality.

7.6.3 Antimicrobial Agents In order to impart antimicrobial functionality to cotton fabrics, different types of antimicrobial agents have been developed. Some of the most important and commonly used antimicrobial agents are demonstrated in Table 7.6.

7.6.4 Methods of Application The most common antimicrobial finishing of cotton fabrics include padding, exhausting, and spraying techniques, as well as sol-gel process.

7.6.5 Test Methods – AATCC TM30-2017: Antifungal Activity Assessment on Textile Materials—Mildew and Rot Resistance of Textile Materials (determination the susceptibility of the textile materials to mildew and rot and to evaluate the efficacy of fungicides on textile materials) – AATCC TM90-2016: Antibacterial Activity Assessment of Textile Materials—Agar Plate Method (qualitative detection of bacteriostatic activity for textile products that are treated with antimicrobials that are capable of producing a zone of inhibition) – AATCC TM100-2012: Assessment of Antibacterial Finishes on Textile Materials (quantitative procedure for the evaluation

Regenerable N-halamines

O

Cl

Cl

H3C H 3C

Cl

N

O H3C C C O CH2

CH3

CH3

2,4,4 -trichloro-2 hydroxy-diphenyl ether

Cl

OH

H3C‒ (CH2)n‒N+(CH3)3Br‒ Alkytrimethylammonium bromide

QACs (quaternary ammonium compound)

Triclosan (chlorinated bisphenol)

Chemical structure (prominent examples)

Antimicrobial agent

(Continued)

[67, 72, 80–83]

[67, 72, 74–79]

- The imparted antimicrobial activity is attributed to its ability to block lipid biosynthesis as well as negatively affect the integrity of cell membranes. - Posttreatment of triclosan-treated cellulosic substrates with polycarboxylic acid enhances its durability to wash. - The imparted antibacterial functionality is a direct consequence of the ability of generated Cl, in the presence of water, to bind with the acceptor sites on microorganism, thereby hindering enzymatic and metabolic processes and causing the destruction of the pathogenic microorganisms.

[66, 68, 72, 73]

Refs.

- Attractive interaction between the cationic nitrogen and negatively charged cell membrane of microbe, thereby leading to the formation of a complex. - This in turn results in damaging of cell membrane, denaturing protein, inhibiting DNA as well as avoiding multiplication.

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles.

162 Textiles and Clothing

Sustainable polymers

Polybiguanides

Antimicrobial agent

+

NH2Cl



Chitosan

O

HO

NH2

O

OH

n

OH

Polyhexamethylene biguanide (PHMP)

x (CH2)3 N C N C N (CH2)3 H H H

NH n

y

Chemical structure (prominent examples)

- The antimicrobial function of chitosan is attributed to its polycationic nature especially in acidic media. - Its positively charged free amino groups can bind to the negatively charged residues at the cell surface of microorganism, thereby leading to disruption of cell membrane, an increase in its permeability, interruption of cell function, and finally the death of these cells.

- The antimicrobial effect is a direct consequence of interaction of its cationic sites with anionic phospholipids in the cell wall of microorganism, which in turn results in cell membrane disruption and subsequent lethal leakage of cytoplasmic components. - Presence of –COOH groups in the cotton cellulose as well as pre-dyeing of cotton cellulose with anionic reactive dyes enhance the extent of adsorption and fixation of PHMP onto cellulose structure.

- To enhance both the antimicrobial effectiveness and sustainability of the imparted functionality, the proper N-halamine compounds must be used.

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles. (Continued)

(Continued)

[4, 66, 67, 72, 79, 85–90]

[67, 72, 74, 84]

Refs.

Functional Finishes for Cotton-Based Textiles 163

Antimicrobial agent

Chemical structure (prominent examples)

H

C

N   H 2O]

(7.15)

- Low molecular weight soluble chitosan has the ability to penetrate the cell wall, combine with DNA, and inhibit mRNA synthesis thereby preventing protein synthesis. - High molecular weight soluble chitosan may cause the leakage of intracellular substances and/or block the transport of essential solution to the cell. - Chitosan-bivalent metal complexes, e.g., Cu2+, Zn2+, etc., exhibit a wide antimicrobial activity against Gram-positive and Gram-negative bacteria.

[ CHO H 2 N  

- Enhancing both the antimicrobial durability and antiseptic effects can be achieved by ester cross-linking or by peroxidation of cellulose structure to create aldehyde groups that have the ability to interact with their amino groups and to form a Schiff base

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles. (Continued)

(Continued)

Refs.

164 Textiles and Clothing

Plant-based compounds

Antimicrobial agent O

Coumarins

Quinones

O

R

Flavonoids

R

HO

Terpenoids

CH3

R

O

O

R

R

O

O

O O

R

OR

H2C=C (CH2)2 O P O P O

O

Chemical structure (prominent examples) [1, 67, 91–98]

- No side effects, easy availability, environmentally friendly. - Wide activity against different pathogens. - No antimicrobial resistance (most probably due to their multiple action mechanism).

(Continued)

Refs.

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles. (Continued)

Functional Finishes for Cotton-Based Textiles 165

Ag-NPs or Au-NPs

Nano-sized metals and metal oxides

ZnO- or TiO2-NPs

Chemical structure (prominent examples)

Antimicrobial agent

H 2O  

O2  

Ag

 O2  (aq ) 4 H 3O

  H 2O [O]

ZnO  or  TiO2 h  (

UV /vis  

388nm) 

 h

(7.18)

 e

(7.17)

(7.16)

  Ag (aq ) 6 H 2O

- Antimicrobial functionality is attributed to their photocatalytic action as follows:

4 Ag

- The imparted antimicrobial functional property is ascribed to both the release of Ag+ ions from nanoparticles as well as generation of oxidative species that can attack the microbe cell wall, disrupt adenosine phosphate (ATP) production DNA, replication, and finally lead to death as follows:

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles. (Continued)

(Continued)

[3, 20, 66, 68, 72, 99–103]

Refs.

166 Textiles and Clothing

Antimicrobial agent

Chemical structure (prominent examples)

  HO2•



2 HO2•  

 O2   H 2O2

(7.22)

(7.21)

(7.20)

  •O2

O2   e O2   h

(7.19)

OH h

H 2O h

The generated reactive oxygen species (ROS), e.g., HO•, O2•‒, H2O2, etc. can inhibit the normal metabolism and oxidize organic components in the bacteria cell that lead to cell death.

Highlights

Table 7.6 Some of the main antimicrobial agents used in functional finishing of cotton textiles. (Continued) Refs.

Functional Finishes for Cotton-Based Textiles 167

168

Textiles and Clothing of the degree of antibacterial activity when bactericidal agent is applied) – AATCC TM147-2016: Antibacterial Activity Assessment of Textile Materials—Parallel Streak Method (quick and easily executed qualitative method to determine antibacterial activity of diffusible antimicrobial agents on treated textile materials)

7.7 UV Protection Functional Finishes Due to the negative impacts of long-term exposure to harmful UV radiation, especially UV-A (315–400 nm) and UV-B (290–315 nm), on human health such as sunburns, photo-aging, and skin cancer, intensive R&D efforts have been promoted to impart anti-UV functionality to lightweight summer clothes without adversely affecting their comfortability [104, 105].

7.7.1 Factors Affecting UV-Blocking Ability Table 7.7 demonstrates some of the main factors affecting the UV rays reflection and/or absorption and subsequent transmission, i.e., UV-protection degree (Figure 7.4).

7.7.2 UV-Protection Mechanisms The imparted UV-protection functionality to cotton fabrics could be discussed in terms of the ability of the used organic attenuators, UV absorbers, to function as radical scavengers as well as single oxygen quenchers, and the ability of the loaded inorganic blockers, e.g., ZnO, TiO2 nanomaterials, to reflect, absorb, and scatter the incident solar radiation, thereby preventing it from reaching the skin and avoiding its subsequent negative impacts on human body [104, 134].

7.7.3 Application Methods The commonly used application methods for imparting anti-UV functionality to cotton fabrics, depending on kind of active ingredients and fiber type, include pad-dry-cure, by exhaustion, by coating, pre-surface modification using plasma or enzymes followed by subsequent loading of nanomaterials, in situ deposition of nanomaterials, and layer-by-layer deposition method as promising application methods [100, 104, 124, 135, 136].

Functional Finishes for Cotton-Based Textiles 169 Table 7.7 Factors affecting the extent of UV-protection ability. Factor

Highlights

Refs.

Fiber chemistry

The protection degree follows the decreasing order: synthetic fibers > natural ones.

[106, 107]

Yarn structure

The UV protection of knitted fabrics is governed by the yarn twist and its impact on yarn compactness, surface properties, and fabric porosity.

[104, 108]

Fabric construction

High fabric tightness gives higher UV-protection ability. Higher cover factor and lower volume porosity results in higher extent of UV-blocking.

[109–111]

Pretreatment

Bleaching of cotton fabrics results in a remarkable decrease in UV-protection ability due to the removal of natural coloring agents which act as natural UV-absorbers.

[112, 113]

Coloration, i.e., dyeing and/or printing

The UV-blocking ability of woven or knitted cotton fabrics follows the decreasing order: colored cotton > uncolored cotton. The darker in the depth of shade, the higher the UV-blocking ability, taking into consideration the type of coloring agent, its concentration as well as the type of fabric.

[114–118]

Finishing using conventional UV-absorbers and UV-blocking nanomaterials

- Optical brightening of bleached cotton fabrics enhances their UV-blocking ability

[104, 119, 120]

(Continued)

170

Textiles and Clothing

Table 7.7 Factors affecting the extent of UV-protection ability. (Continued) Factor

Dry or wet state

Highlights

Refs.

- Finishing of cotton textiles using conventional organic UV-absorbers, e.g., 2-hydroxybenzo-phenone, O-hydroxyphenyl-hydrazines, etc. results in a significant improvement in UV-protection degree. The main drawbacks of using conventional UV-absorbers include weak durability to wash, poor activity, as well as toxicity.

[121, 122]

- Using nanoparticles, e.g., ZnO and/or TiO2 nanoparticles can impart multifunctional properties to the treated cotton textiles such as UV protection, antimicrobial, as well as self-cleaning properties in one step.

[123–133]

The degree of UV protection follows the decreasing orders: dry > wet state.

[104]

UV light Scattering

Reflection

Fabric Absorption

Transmission

Figure 7.4 UV-transmittance characteristics of a textile material.

Functional Finishes for Cotton-Based Textiles 171 Table 7.8 UPF rating and protective grade. UPF

Grade

Cd2+. By using sodium dodecyl sulfate (SDS), copper (Cu2+) and cobalt (Co2+) separation has been studied from the aqueous phase. A number of factors like the operating time (10–120 min), the crossing rate (100–250 ml/min), pH (2.8–5.6), and S/M ratio of 5–8 were also studied [45, 46]. pH is another important factor to play a role in removing heavy metals. The removal was examined using anionic surfactant i.e., SDS, and hydrophilic membranes (polyether sulfone, PES). The corresponding heavy metal removal efficiency decreases with an increase in concentration of metal ions in media of 1–12 pH. In addition, the removal efficiency of ions of heavy metal (with an initial concentration of 50 ppm) is given as follows: Pb2+ > Cd2+ > Zn2+ > Cu2+ [47]. Ni2+ and Co2+ have been removed simultaneously from water by the method of cross-flow MEUF along with polysulfone membrane, and removal of 99% has been observed. The presence of salt in water feed leads to a decline in rejection from 99% to 88% [48]. It has been observed that with the S/M ratio (using SDS) being greater than 10, more than 95% metal removal was attained. The order of removal was Cd2+ > Cu2+ > Co2+ = Ni2+ [49, 50]. The removal efficiency was 90.3% for Cd2+ and 89.6% for Zn2+. In the SDS system, an increase in Cd2+ removal was observed with an increase in the concentration of SDS, which reached 97% at 8.0 mM SDS solution [33]. In another study, aqueous solutions of sodium dodecyl sulfate (SDS) and linear alkylbenzene sulfonate (LAS) were used for removing Cd2+, Cu2+, Ni2+, Pb2+, and Zn2+, and the effect of concentration of surfactant, conductivity, and pH was examined. Removal of more than 90% was observed [51]. It was found that MEUF removes divalent metal ions, i.e., Cd2+, Cu2+, Ca2+, and Zn2+, and their mixtures with a removal efficiency of at least 96%. In another study, Co2+, Cr3+, Ni2+, and Zn2+ ions of cobalt, nickel, zinc, and chromium were removed from wastewater by MEUF using an ultrafiltration (UF) membrane (210 kDa monotubular ceramics) with anionic surfactant, i.e., sodium dodecyl sulfate (SDS) [52]. In some studies, nonionic surfactant TX-100 has also been applied for the removal mechanism of various metals like Co2+, Cu2+, Ni2+, Mn2+, and Zn2+ simultaneously from the wastewater at pH 6 and removal percentage greater than 96.0% was achieved using a mixture of anionic and nonionic surfactants. Cd2+ and Zn2+ were effectively removed, and it was observed that at a metal ion concentration of 50 ppm and that of SDS greater than 2.15 g L−1, 92–96% removal was witnessed. Rhamnolipid (a biosurfactant) has also been used for metal removal at an

Removal of Heavy Metal Ions Using MEUF

301

S/M ratio of about 2:1, temperature of 25 C, pressure of 69 kPa, and pH 6.9. More than 99.0% removal was obtained in a mixture of metal ions, i.e., Cd2+, Cu2+, Pb2+, and Zn2+ [13].

11.3 Factors Affecting the Efficiency of MEUF 11.3.1

Effects of Surfactant Concentrations

The removal of metal ions increases with the concentration of surfactant because at pre-micellar concentration of surfactants, the unimers of surfactants form complexes with metals and can easily pass through membrane pores. However, at higher concentration of surfactant, i.e., at or above critical micellar concentration (CMC), surfactant micelles are formed, which provides more surface area or reacting sites to metal ions for binding. In this way, binding of metal ions with micelles occurs and hence their removal is enhanced [13]. Even at lower surfactant concentration, pollutants from wastewater can be easily removed using the MEUF method [7]. Samper and his coworkers developed a system to remove heavy metal ions using linear alkyl sulfonate (LAS) and SDS with a % removal of about 90%. In the presence of low concentration of LAS, almost 100% metal ion removal was obtained. A decreased rate of metal ion transfer from aqueous to surfactant solutions was observed in the post-micellar concentration of surfactant [53]. It has been noticed that the molar ratio of 1:5 causes 98% chromium removal. When the concentration of CPC was 5–10 mM, the CPC showed excellent result for arsenate removal (removal efficiency = 86% to 94%). The removal of Zn and Cd was explained by MEUF and it was found that this process is dependent on the nature and concentration of surfactant, i.e., SDS, and that of heavy metal in the feed solution. Effective removal of arsenic (V) was achieved, when the concentration of CPC was 1 to 3 mM and the efficiency of removal was found to be 98%. It has been found that the removal efficiency of Cr+3 was enhanced from 33% to 99% by increasing SDS concentration from pre-micellar to post-micellar concentration. Removal of Zn was only 46% and 53% at 1 mM SDS and 3.4 mM SDS. Gold removal efficiency was found to be 100%, 99.9%, and 89% by CPC, POESA, and PONPE10. At lower SDS concentration, there was greater reduction in permeate flow than at high CMC [44].

302

Textiles and Clothing

It has been noticed that at very high concentration of surfactant, the micelles break up into smaller aggregates, which can attach metal ions to their surface and cause them to be removed just as micelles do [13].

11.3.2

The Effect of Ratio of Concentration of Surfactant to Metal Ion (S/M)

The removal of the metal ions increases with the S/M ratio because of the increased number of micelles available for binding of metal ions [13, 24].

11.3.3

The Effect of Mixed Micellization

The lower is the critical micellar concentration (CMC) of surfactant, the lesser will be its amount used in MEUF. One way to reduce CMC is by using a mixed solution of nonionic and ionic surfactant. In such mixture, the hydrophilic portions of the nonionic surfactant decrease the repulsions between the identically charged hydrophilic moieties of ionic surfactants. The charge density on the surface of the micelle is thus reduced, which results in a reduction in the electrical potential. The permeate flux, however, decreases in the presence of nonionic surfactants due to high viscosity and change in the shape of the micelle from spherical to cylindrical or laminar [13]. Better reduction in CMC can be obtained by using the mixed system of nonionic–ionic surfactants rather than using the anionic–cationic mixed system [18, 54] because in the mixture of surfactant, the hydrophilic portions of the nonionic surfactant balance the charge of the ionic hydrophilic groups [37, 43]. It has also been observed that CPC removal efficiency increased from 91% to 99% using Tween 80 to produce more micelles. Li et al. reported that in the presence of nonionic surfactants, Cu2+ is removed with greater %, i.e., from 15% to 70% than in the absence of surfactant [55]. Similar results were observed in the case of Zn2+ ions by Fillipi et al. [56]. Using Triton X-100 concentration of less than 0.1 mM, no significant change in copper removal was observed with SDS. Also, permeate flux is lowered during the MEUF process when nonionic surfactants are used in the above said process [43, 54].

11.3.4

Effect of pH Value

pH is a very important factor affecting the efficiency of surfactants to remove metal ions. In strong acidic media, the metal ions (like Cd2+, Cu2+, As3+, Cr3+, Fe2+, Pt2+, Al3+, and Sc3+) are replaced by H+ ions on the surface of micelles and reduce the separation efficiency of micellar media at low

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pH. At low (acidic) pH, removal was minimum due to the replacement of H+ ions with heavy metal ions entrapped in the micelles of surfactant molecules. Therefore, it is not appropriate to use MEUF to remove heavy metals under acidic conditions [44]. Bade et al. reported that metal removal was greater than 80% in SDS solutions at basic pH. At lower pH, the removal efficiency of metal ions suffers from reduction due to the replacement of H+ ions and positively charged metal ions that adsorb on the surface of the SDS micelle having a negative charge on their surface. Removal of certain metal ions like Sr+2 and Cr+3 is not affected by pH. In the pH range of 3–11, the removal of Cd2+ ions increased from 83% to 99% [18, 44]. Viera et al. explained that the efficiency of removal was 55%, 53%, and 74% for Ca2+, Mg2+, and Fe2+, respectively, with the PEI membrane within a pH range of 4–5. But it has also been noticed that the efficiency of removal decreased by approximately 10% when pH changes above or below this range [57].

11.3.5

Effects of Electrolytes

Investigation about the effect of electrolytes in the MEUF process is very important as electrolytes are necessarily present in aqueous medium. This is because CMC decreases in the presence of electrolyte due to neutralization of charges. The higher salt concentration in the feed solution decreases the CMC of ionic surfactants because when salt is added, the electrical double layer is compressed and then it is quite possible to reduce the electrostatic attraction in micelles and ions. It is also due to the increase in concentration of salt; the competition of metal ion also increased, which enables it to reduce the binding of metal ions with the micelles in the presence of salts [13]. The addition of electrolytes not only reduces flow rate but only makes the gel layer of micelles on the surface of the membrane more compact. The said phenomenon results in the increase in surface resistance of the membrane. The addition of electrolytes also results in an increase in the viscosity and hydraulic resistance [53].

11.3.6

Effects of Transmembrane Pressure

The transmembrane pressure is a key factor in controlling the efficiency of MEUF in terms of removal rate and concentration of heavy metal ion being removed. In general, the removal efficiency of the MEUF process is increased with increasing membrane pressure. This is because high pressure minimizes the resistance between the membrane and the permeation pressure. Consequently, the flow of contaminated solutions across the membrane is facilitated [32]. Besides these benefits, high membrane

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pressure also allows the growth of the gel layer at the membrane surface; as a result, flow rate becomes lowest as explained by Purkait et al. [58]. Further studies carried out by Juang et al. showed that pressure has no significant effect on the MEUF process [59].

11.3.7

Effect of Temperature

Temperature has a key role in controlling the efficiency of MEUF because CMC depends on temperature. At higher temperature, CMC increases and micellization is not favored. Hence, the dissociation of surfactant ions from the bulk of micelles takes place. The increase in temperature thus causes a decrease in aggregation number and size of micelle as well as expansion of membrane. Both aforementioned phenomena facilitate the passage of surfactant unimers in the permeate [27]. At 298.15 K, 323.15 K and 328.15 K, the CMC values of SDS were recorded as 2.257, 2.445, and 2.706 ppm, respectively [60]. Krafft temperature is the temperature when solubilization of ionic surfactants becomes equal to their critical micellar concentration [61]. The anionic surfactants are more resistant to temperature than cationic surfactants [62]. This can be explained on the basis of adsorption of hydrophobic and hydrophilic groups of surfactants on the membrane surface leading to separation of micelles from the membrane being used for removal process as observed from the study of Zeng et al. [63]. Due to this, some CPC monomers pass through the permeate. The same phenomenon occurs due to the thermal increase of the membrane [13].

11.3.8

Effect of Nature of Membrane

Kim et al. reported that the polyethylene glycol (PEG) membrane has allowed the greater removal of ions due to high hydrophobicity [49, 64]. Byhlin and Jonsson reported that rejection of metals remains constant using nonionic surfactant, namely, Triton X-100, when the concentration is below the critical micellar concentration with hydrophobic and hydrophilic membranes. However, above CMC, removal percentage was the same for the hydrophilic membrane (regenerated cellulose) and increased for the hydrophobic membrane (polyether sulfone) [65].

11.3.9

The Effect of Concentration of Metal Ion in Feed

When the concentration of metal cations increases, forces of repulsion among anionic hydrophilic groups decrease, and micelle formation is highly favored. The aforesaid phenomenon causes greater number of

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surfactant molecules to be accommodated in micelles, and thus, their size and removal efficiency increase. However, a very high metal ion concentration leads to micellar saturation and causes decrease in the efficiency of MEUF. The high concentration of metal ion in feed solution causes equilibrium to be established between free and adsorbed metal ions. Consequently, retention of metal ions is increased. Increase in the concentration of heavy metal in feed produces an increase in the micellar zeta potential and a decrease in the charge density of surface. The aforementioned phenomena result in the decrease in retention due to the unavailability of binding sites [66].

11.3.10

The Effect of Operating Time

Besides the abovementioned parameters, time is also a very important factor that affects the efficiency of MEUF. With passage of time, gel formation on micellar surface is observed, which results in the blockage of micellar surface, and a decrease in % removal of metal ions is observed. After further time passage, the thickness of the gel layer at the membrane surface no longer increases and hence permeate flux becomes almost constant [13].

11.3.11

Effect of Rate of Feed Flow

The increase in the rate of feed flow shows an initial rise in the removal efficiency until maxima and then decreases subsequently. The rate of feed flow where maximum removal is achieved is called the rate of optimal flow. Higher flow rate allows the maximum pumping of surfactant micelles across the membrane [38]. The increase in the rate of flow increases instability due to turbulence, and thus, the transfer of mass across the surface of membrane also increases. All aforementioned factors result in an increase in permeate flux and removal ability [13].

11.3.12

Effect of Applied Pressure

The applied pressure between retentate and permeate is actually a very effective and wonderful driving force for the process. An increase in pressure causes a decrease in resistance between membrane and permeate pressure. Consequently, the rate of filtration increases, causing greater permeate flux across the membrane. At critical micellar concentration of surfactant, greater number of surfactant molecules are present in the form of micelles at membrane surfaces than in monomeric forms, which

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provides more available sites for interactions with metal ions. Applied pressure must be maintained at a suitable limit where the membrane could bear it [13].

11.3.13

Effect of Initial Concentration of Metal Ions

It has been observed that percentage removal decreases with the increase in initial concentration of metals at constant concentration of surfactant. The reason behind the said phenomenon is decrease in availability of sites for metal ions [27].

11.4 Surfactant Recovery from Retentate The most notable drawback of MEUF is secondary contamination due to the presence of surfactant molecules in the retentate [8, 14, 44]. The reusability of surfactant once used in MEUF is thus highly appreciated. Canizares et al. explored the use of polymeric material at various pH of solution to recover the surfactant from bulk solution, which could be reused subsequently. The pH change causes protonation or dissociation in micellar structure by developing interactions with polymeric material [67]. Hiraide and Itoh performed the same experiment for SDS and recovered 84% surfactant to be used for the removal of Cu+2 ions multiple times [68]. Juang et al. reported the use of NaOH to recover the surfactant until a slight precipitate appeared. The precipitates were removed by repeated centrifugation at 5000 rpm, and the remaining solution was used [59]. Liu and Li explored the use of Ca2+ in excess to increase the precipitation of SDS. After removing precipitated material by centrifugation, SDS molecules remaining in the solution were again used for metal removal. The removal of metals like Sr2+, Mn2+, Cu2+, Cu+, Zn2+, and Cr3+ may be achieved up to 50–58% using recovered SDS [20].

11.5 Summary (in Tabulated Form) Removal of a variety of metal ions by MEUF has been studied, and the effects of various factors like the type of surfactant, the effect of pH, temperature, pressure, type of membrane, etc. have been reviewed. The removal efficiency is summarized in Table 11.1.

Surfactant used

SDS

SDS and mixed SDS/ Triton X-100

SDS

SDS and LAS

Oleylethoxycarboxylate

Metals removed

Cd, Zn [54]

Cd [33]

Cu [55]

Cd, Cu, Zn [51]

Fe, Cu, Cd, Zn, Ni, Mg [56]

Presence of membrane

Effect of surfactant concentration on metal retention, pH, and conductance on metal retention

Effect of current density, surfactant concentration, hydraulic residence time (HRT), and pH

Effect of pure and mixed surfactant on removal of Cd ions

Effect of pH, nature of chelating agent and type of acid used

Parameters studied

Table 11.1 Effects of various parameters on the removal of heavy metal ions by MEUF.

(Continued)

Using a pore size of ≤10 kDa of membrane, 95% removal is obtained in the following order: Fe+2 ≈ Cu+2 > Cd+2 > Zn+2 > Ni+2  > Mg+2

Using LAS = 1 mM and SDS = 5.31 mM, % removal of metal ions = 90%

90.4% removal at HRT of 15 min, pH = 6, current density = 30 A/m2, SDS = 8.5 mM

With SDS, Cd removal = 97.0%

With EDTA at pH = 9 Cd+2 = 95.8% Zn+2 = 96.8%

% Removal

Removal of Heavy Metal Ions Using MEUF 307

Surfactant used

CTAB

SDS

SDS

SDS

CPC

Metals removed

As [7]

Cd [8]

Cd [16]

Cu [57]

Cr (VI) [27]

Effect of chromate and surfactant concentration, and effect of pressure

Effect of flux on Cu removal, retentate pressure, molar ratio of Cu to SDS, initial concentration of Cu, pH

Effect of pH

Effect of retentate pressure, membrane pore size, and pH

Effect of concentration of surfactant and metal ions and pH

Parameters studied

(Continued)

Maximum removal at CPC conc. = 30 mM and initial conc. of Cr = 99.2%

Initial permeate flux = 1.05 m3/ m2/day, Cu/SDS ratio = 1:30, operating pressure = 1.4 bar, % removal = 98%

At pH = 0.5, % removal = 70%

At pH = 8.6, MWCO = 100,000 = 47.4%, 0.28 MPa = 39.6%

At pH = 6.73, CTAB = 2.83 mM, As = 29.44 μg/L, % removal = 93.30%

% Removal

Table 11.1 Effects of various parameters on the removal of heavy metal ions by MEUF. (Continued)

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Surfactant used

Rhamnolipid (JBR 425)

Rhamnolipid

SDS and its mixture with Brij 35, Tween 80, and Triton X-100

SDS and mixed surfactants of SDS and Triton X-100

Oleylethoxycarboxylate

Metals removed

Cr (III) [2]

Cr (III) and Cr (IV) [25]

Cu [24]

Cu [22]

Cu [21]

Effect of pH and ionic character of surfactant

Effects of composition and concentration of mixed anionic/nonionic surfactants

Effect of pH, molar ratio of SDS/Brij 35, SDS/TW80 and SDS/TX100

Effect of pH, conc. of rhamnolipid, initial conc. of Cr (VI), and temperature

Effect of transmembrane pressure, temperature, rhamnolipid concentration, and pH

Parameters studied

Maximum removal is 90%

85% Cu removal was obtained at maximum mole fraction of SDS in a mixed surfactant system

Maximum removal of 98.3% when molar ratio of Brij 35 and TW80 to SDS was 0.3

Maximum removal was obtained at pH = 6, initial conc. of Cr(VI) = 10 mg/L and rhamnolipid = 2%

At pH = 6, conc. of Cr (III) = 2.6 mg/L, rhamnolipid conc. = 0.1%, % removal = 96.2%

% Removal

Table 11.1 Effects of various parameters on the removal of heavy metal ions by MEUF. (Continued)

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11.6 Conclusions There is an extreme shortage of safe and clean drinking water, and among the toxic pollutants, heavy metals occupy a significant toxic profile. Heavy metals are conventionally removed by different chemical and physical methods. MEUF proved itself as an excellent choice for heavy metal removal. When the surfactant is at or above its critical micellar concentration (CMC), the process of MEUF is used to separate organics and metal ions like copper, chromium, zinc, nickel, cadmium, and arsenic. Various factors affecting the efficiency of removal of metals have been studied. Pressure, pH, temperature, the concentration of the surfactant, the presence of the nonionic nature of surfactant and salt, the type of membrane, the size of pores, and some inhibitors like citric acid and EDTA affect the efficiency of the process. By increasing the pressure of the ionic surfactant, the removal percentage of heavy metal increases. Addition of a nonionic surfactant in a micellar solution reduces the CMC of the surfactant and, thus, enhances the removal efficiency. However, sometimes the presence of a nonionic surfactant reduces metal removal because of the increase in viscosity of solution. In comparison with other techniques, MEUF has the advantages of high efficiency, low power consumption, and easy operation, and a wide variety of metals may be removed from wastewater. The surfactant is selected on the basis of its charge and according to the nature of the particular metal to be removed. The nature and pore size of membrane also affect the efficiency of the process. The removal of metal usually does not depend on the initial concentration of that surfactant; rather, it is dependent on the concentration above CMC and the surfactant concentration in the neighborhood of the membrane surface. In MEUF, the important factors for removing heavy metals are the nature of the surfactant, the pressure that is applied, the concentration of the surfactant (above CMC), operating time, and pH. MEUF is used in synthetic streams, and it has also been observed that this process can be used in combination with some other processes that are equally useful for both aqueous and nonaqueous streams. The specialty of MEUF is to remove the metals efficiently in the presence of each other and in the presence of organic matters as the surfactant solution acts as a supersolvent. The use of a mixed micellar solution provides even better and economic removal compared to that of a single surfactant.

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60. Kowalska, I., Majewska-Nowak, K., Ksch-Korbutowicz, M., Influence of temperature on anionic surface active agent removal from a water solution by ultrafiltration. Desalination, 198, 124131, 2006. 61. Rosen, M.J., Surfactants and Interfacial Phenomena, John Wiley and Sons, New York, USA, 2012. 62. Urbanski, R., Goralska, E., Bart, H.J., Szymanowski, J., Ultrafiltration of surfactant solutions. J. Colloid Interface Sci., 253, 2, 419–426, 2002. 63. Zeng, G.M., Xu, K., Huang, J.H., Li, X., Fang, Y.Y., Qu, Y.H., Micellar enhanced ultrafiltration of phenol in synthetic waste water using polysulfone membrane. J. Membr. Sci., 310, 149–160, 2007. 64. Kim, H., Baek, K., Kim, B.K., Shin, H.J., Yang, J.W., Removal characteristics of metal cations and their mixtures using micellar-enhanced ultrafiltration. Korean J. Chem. Eng., 25, 253, 2008. 65. Byhlin, H. and Jonsson, A.S., Influence of adsorption and concentration polarization on membrane performance during ultrafiltration of a non-ionic surfactant. Desalination, 151, 21–31, 2002. 66. Mungray, A.A., Kulkarni, S.V., Mungray, A.K., Removal of heavy metals from wastewater using micellar enhanced ultrafiltration technique: A review. Cent. Eur. J. Chem., 10, 1, 27–46, 2012. 67. Canizares, P., Prez, A., Camarillo, R., Recovery of heavy metals by means of ultrafiltration with water-soluble polymers: Calculation of design parameters. Desalination, 144, 279–285, 2002. 68. Hiraide, M. and Itoh, T., Ultrafiltration and alumina adsorption of micelles for the preconcentration of copper (II) in water. Anal. Sci., 20, 231–233, 2004.

Index Abeokuta, 37 Acid orange 3, 235 Acidic functional groups, 205 Action of gravity, 197 Activated carbon, 204 Activation time, 205 Adire, 36 Adsorbants, 204, 205, 206 Adsorption, 203, 289 Adsorption capacity, 206 Advanced oxidation process, 213, 218, 236 Aesthetic, 34, 42 African continent, 28 Aggregation number, 290 Agrobacterium aurantiacum, 57 Agrobacterium tumefaciens, 57 Agromyces ramosus, 57 Akebu-Lan, 27–28, 30–31 Alari, 38 Algae control, 217 Alkaline hydrophilization technique, 107 Alkalinity, 209 Altererythrobacter ishigakiensis, 57 Aluminum, 298 Alzheimer’s disease, 58 Amaranthus spinosus, 54 Americium, 298 Amine form, 206 Ammonia persulfate solution, 205 Amphoteric softeners, 145 Anionic, 208 Anionic softener, 141, 144 Ankara, 38

Anthocyanin, 30 Anthraquinone, 46 Anti-allergens, 28 Anti-bacterial, 58 Anti-cancer, 58 Anti-crease, 133, 134, 142, 145, 148 Anti-inflammatory, 58 Anti-microbial finish, 160, 172, 176 Antioxidant, 57 Antiseptic, 41 Apocarotenoids, 56 Applied pressure, 305 Arsenic, 291 Asparagus officinalis, 53 Astaxanthin, 47 Automatic dispensing, 35 Auxiliaries, 79, 84, 88, 89, 90 Averrhoa carambola, 54 Bacillus subtilis, 59 Backwashing, 194, 195 Baganda, 40 Bar screen, 193 Basic resins, 210 Behnajady–Modirshahla–Ghanbery (BMG), 237 Biocides, 160, 176 Biocompatible, 46 Biodegradable, 46 Biological treatment, 211 Bio-polishing, 102–104 Biopolymers as potential wastewater management alternative, 272 Biostats, 160

317

318

Index

Bio-technology, 92 Bio-washing, 106 Bixa orellana, 53 Bixin, 50 Blakeslea trispora, 57 Bleaching, 4, 81, 88, 90, 92, 98 BOD, 82, 84–87 Bradyrhizobium, 57 Bradyrhizobium japonicum, 57 Brassica oleracea, 53 Brassica rapa, 55 Brevundimonas, 57 Cadmium, 292 Capsanthin, 50 Capsicum annuum, 53 Capsorubin, 50, 56 Carbonaceous materials, 204 Carbonization temperature, 205 Carcinogenic effects, 19, 20, 21 Carcinogenic nitrogenous aromatics, 218 Carcinogenicity, 46 Carica papaya, 53 Carota, 46 Carotene, 48 Carotenoids, 46 Cartanea sativa, 55 Catalytic reaction, 212 Catalyzed, 240 Cationic pollutants, 208 Cationic resins, 210 Cationic softener, 141, 143, 147 Cationic surfactants, 207 Cellulosic fibers, 3 Cellulosic substrates, 79, 80, 82, 84, 85, 87, 89, 92–94, 147, 151, 153, 162 Chain elongation, 48 Chain reaction mechanism, 217 Chalcogenides, 213 Channel, 194 Charge interaction, 202 Chemical oxidants, 218 Chemical oxidation, 6 Chemical precipitation, 211, 289

Chitosan, 163, 164, 175 Chloric acid, 220 Chlorine–Hercosett, 105 Chlorophyll, 46 Chromium, 291 Chromium plating industries, 211 Citrullus lanatus, 53 Citrus paradise, 53 Citrus reticulate, 55 Cleaner production, 88 Coagulant dose, 208, 209 Coagulants, 208, 209 Coagulation, 6, 207, 209, 212, 217 Coccinia grandis, 53 COD, 82, 84–87 Color pollution, 85–87 Combined ozone, 213 Complex chemistry, 217 Composite adsorption, 207 Compressed air, 211 Contaminants, 211, 193, 203 Copper, 294 Cotton, 3 Coumarins, 28 CPC, 301 Critical micellar concentration (CMC), 290 Crocetin, 50 Crocetin glycosides, 56 Crocin, 50 Crocus sativus, 53 Cross linkage, 210 Crystallites, 219 Cryptococcus, 47 Cucumis melo var. cantalupensis, 55 Cucurbita maxima, 53, 55 Cucurbita pepo, 55 Cucurbiturils, 213 Cyclization, 48 Cyclodextrins, 215 Deactivation of maximum microbes, 220 Decolorization efficiency, 244 Decontaminator, 220, 221

Index 319 Degradation, 243 Dehydrogenation, 48 Delonix regia, 56 Desilanation, 203 Desizing, 81, 88, 90, 92, 93 Dietzia natronolimnaea, 57 Diffusion, 208 Digital finishing, 124 Diospyros kaki, 53 Direct dyes, 82, 83, 86, 90, 91 Disinfection, 212 Dissolved contaminats, 211 Double bond migration, 48 Dunaliella salina, 47 Dye photo-degradation, 218 Dyehouse effluent, 79, 84, Dyeing, 4, 5, 28–29 Easy care, 132, 133, 134, 136, 138, 140, 171, 172 Echinenone, 50 Eco-textiles, 2 Eco-friendly, 79, 80, 89–92, 95, 131, 134, 141, 160, 161, 171 Effluent, 41 Effluent load, 202 Effluent treatment, 261 Electro-migration, 208 Electro-osmosis, 208 Electro-phoresis, 208 Electrochemical dyeing technology, 92 Electro-floctants, 211 Electrolyte, 303 Electrophilic agents, 217 Environmental hazard, 11, 12, 15 Environmental Impacts, 81, 84–86, 89, 94 Environmental risks, 12 Enzymes cellulases, 102–103, 106 cutinase, 103–104, 107 hydrolases, 102 microbial, 102 oxidoreductases, 102 proteases, 102, 107

Equilibrium, 239 Erythrobacter sp., 57 Escherichia coli, 59 Ester cross-links, 134–136, 139 Ether cross-links, 134, 135 Ethiopia, 34 Etu, 38 Exchange resin, 210 Excitation of photon, 218 Extraction, 35 Fagus sylvatica, 55 Fashion, 36 Feed flow, 305 Fenton, 236 Fenton’s oxidation, 213 Fiber, 2 Filtration, 209, 211 First-order, 245 Flame-retardant, 145, 151, 155, 157, 171, 175 Flavonoids, 28, 46 Floatation, 209, 212 Floculants, 209 Floculation, 208, 210 Fluoro alkyl, 150 Fluorocarbon, 150, 151, 154, 173, 174 Formaldehyde, 107–110, 115, 117–118 Fucoxanthin, 50 Fulani, 39 Fusarium sporotrichioides, 57 Gamma radiation, 62 Garrisa, 29 Genotoxicity, 13, 14, 19 Geometric patterns, 36 Geranylgeranyl diphospahtes, 46 Ghana, 29–31 Glycoluriluntis, 214 Gold, 295 Gravitational force, 195 Grit chamber, 195 Gritty matter, 195 Guest molecule, 215

320

Index

Haematococcus pluvialis, 57 Halobacterium sp., 57 Halogenated FRs, 158 Heavy metals, 205, 289 Hotmelt process, 123 Human health, 13, 19, 24 Hydrogen peroxide, 241 Hydrogenation, 48 Hydrolysis, 241 Hydroxy free redical, 220 Hydroxyl radicals, 217, 241 Hyperallergenicity, 46 Hypochloric acid, 207, 220 Hypochlorite ion, 220 Immobilization, 206 Impregnation ratio, 205 Indigo dyeing, 91 Indigoid, 46 Industrial wastewater, 212 Inorganic flocculants, 209 Interfacial tension, 294 Internal periphery, 198 Ion-exchange resins, 210 Ion-exchange, 289 Ionic cross-links, 133, 136, 137, 139 Ipomoea batatas, 55 Iron, 296 Isocryptoxanthin, 50 Isozeaxanthin, 50 Kente, 37 Kenya, 33–40 Kinetic modeling, 245 Klebsiella pneumoniae, 59 Lactuca sativa, 53 Lead, 296 Leifsonia sensulato, 57 Lickroller (kiss-roll), spray, or foam application technique, 122 Low-cost neutralization techniques, 205 Low-level direct current, 207 Lutein, 50

Lycopene, 48 Lycopersicon esculentum, 53 Maceration, 35 Macro-pollutants, 217 Madder, 30 Maganese, 298 Mali, 39 Masai, 40 Mauve, 12 Mauviene, 46 Mechanical screening, 193 Mechanization, 201 Membrane filtration, 289 Mercerization, 4 MEUF, 291 Microfiltration techniques, 200 Microbacterium arborescens, 57 Microfiltration, 200 Microwave radiation, 62 Mixed micellization, 302 Mono-oxygenation, 212 Mordant, 28–29 Mycobacterium kansasii, 57 Myxococcus streptomyces, 57 Namibia, 40 Nanomaterials, 168, 169, 179 Nanoparticles, 174, 175, 177, 205, 220 Nano-sized metals, 166 Natural dyes, 27 Natural organic pollutant, 219 Natural sorbent, 205 Natural zeolite, 206 Nature of membrane, 304 Neolithic period, 28–30 Neorosporene, 49 Neoxanthin, 50 Neutralization, 212 N-halamines, 162 Nickel, 297 Nigeria, 30–34 Non-ionic softener, 141 Noxious effects, 46

Index 321 Oleophobic, 150, 154, 171, 173 Operating Time, 305 Organic compound, 197 Organic contaminants, 207 Organic matter, 195, 212 Organic toxins, 213 Outer feed circulation, 198 Oxidation, 48, 245 Oxidation/reduction, 212 Oxidizing agents, 236 Ozonation, 216, 218 Ozone, 216 Ozone technology, 92 Palladium, 298 Paracoccus sp., 57 Persea americana, 55 PH, 302 Phaffia rhodozoa, 57 Phaffia rhodozyma, 47 Phosphorus-containing FRs, 155, 158, 159, 175 Photo-catalysis, 213, 214 Photo-catalytic mixture, 219 Photo-chemical process, 218 Photo-electric energy, 219 Photo-Fenton, 213, 236 Physical chemical interaction, 203 Physical techniques, 203 Phytoconstituents, 28 Phytofluene, 49 Picrocrocin, 56 Pigments, 28 Plant-based compounds, 165 Plasma coating, 120 Plasma technology, 93 Platinum, 298 Pollutants, 211 Polluted water, 210 Pollution, 289 Pollution load, 79, 84, 93 Pollution problems with associated human health and environmental risks, 254

Polybiguanides, 163 Polyene, 48 Polymeric adsorbent, 204 Polyphenols, 28 Polysiloxanes, 150, 153 Precipitates, 208 Precipitation, 209, 212 Pressure driven process, 202 Proban process, 118 Pseudomonas aeruginosa, 59 Psidium guajava, 53 Pyrovatex process, 118 QACs, 162 Quercus robur, 55 Radiation curing, 124 Rake, 193 Reaction intermediates, 219 Reaction kinetics, 245 Reactive dyeing, 83, 84, 91, 92, 94 Reactive dyes, 83, 85, 90, 91 Rectangular basin, 197, 202, 203 Red basidiomycetous, 57 Reduction, 212 Repellency dirt/stain, 114 oil, 113–114 water, 113, 115, 121–122 Resins, 209 Rhodotorula glutinis, 47 Rubioxanthin, 56 Safranal, 56 Saturation-removal, 122 Sauropus androgynous, 53 Sawdust, 206 Sawdust activated carbon, 206 Scale water treatment plants, 197 Scouring, 81, 88, 90 Screening, 194 SDS, 293 Second-order, 245 Sedimentation, 195, 197, 211

322

Index

Sediments, 197 Self-cleaning, 131, 170–172, 178 Semi permeable membrane, 203 Semiconductor, 218 Serbania grandiflora, 53 Silica gel waste, 207 Silicone softeners, 142, 147–149, 173 Silk, 3 Size exclusion, 202 Sizing, 81, 82, 88, 90 Skimmed off, 211 Skimming tank, 196 Sludge, 211 Sludge exclusion, 198 Sodium hydroxide treatment, 107 Soft finish, 131, 142, 147, 172 Soft finishes, 110–112 Solanum melongena, 53 Solanum nigrum, 54 Sorption capacity, 204 Sphingo microbium astaxanthinifaciens, 57 Sphingomonas faeni, 57 Spinacia oleracea, 53 Stabilization, 35 Staphylococcus aureus, 58 Stearic acid, 152 Steril-contaminants, 218 Sterols, 28 Sulfolobus shibatae, 57 Sulfonic acid group, 210 Sulfur, 82, 83, 87, 91, 92 Supercritical CO2 dyeing technology, 94 Surface area, 205 Surfactant, 289 Surfactant concentration, 301 Surfactant recovery, 306 Suspended particles, 192 Suspended solids, 212 Sustainability, 27–41 Sustainable polymers, 163 Swimming pool, 220 Synthetic dyes, 11, 12, 13, 14, 17, 18

Synthetic organic pollutants, 220 Synthetic resins, 209 Tagetes erecta, 53 Tanzania, 40 Taxacum officinale, 55 Temperature, 243, 304 Tetraterpenoids, 46 Textile bleaching, 220 Textile operation, 221 Textile wastewater, 207, 221 Toxic dyes, 204 Toxin, 211 Tradition, 36 Traditional/Conventional Physicochemical Methods for Effluent Removal physical methods, 262 adsorption process, 262 activated carbon and peat, 262 fly ash and coal, 264 ion exchange, 264 silica gel, 265 wood chips, 263 electro-kinetic coagulation, 266 irradiation, 265 membrane filtration/separation, 266 chemical methods (advanced oxidative processes), 267 electrochemical oxidation, 271 H2O2–Fe (II) salts (Fenton’s Reagent), 268 ozonation, 269 photochemical oxidation, 270 sodium hypochlorite, 271 Transmembrane pressure, 303 Triclosan, 162 Tunaxanthin, 50 Types of textile effluents, 260 Uganda, 29–32 Ultrasonic radiation, 62 Ultrasound technology, 93

Index 323 Ultraviolet photolysis, 213 Ultraviolet radiation, 62 Unit operation, 195 Uranium, 295 UV absorbers, 168–170, 177 UV intensity, 236 UV protection, 168–171, 177 UV radiation, 245 UV/Fenton, 213 UV/ozone, 213 UV-blocking, 168, 169, 172

Water ecosystem, 11, 13, 16, 17, 18 Water treatment, 202 Wavelength, 247 Wet processing, 82, 88–90, 93–95 William Henry Perkin, 12 Wooden material, 205 Wool, 3

Vat, 86, 90–92 Violaxanthin, 50 VOCs, 84

Yoruba, 36–38

Wastewater, 82, 84–87, 94, 207, 218, 220, 249, 289 Wastewater plants, 191 Water- and oil-repellent, 150, 151, 173 Water decontamination, 191

Xanthophyllomyces dendrorhous, 57 Xanthophylls, 50 Xeinoxanthin, 50

Zea mays, 54 Zeaxanthin, 50 Zeinoxanthin, 51 Zeolitized fly ash, 206 Zinc, 299 α-carotene, 48 β-carotene, 47

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