Functional Finishes for Textiles: Improving Comfort, Performance and Protection 9780857098399, 9781782420323, 9781845691806, 9781845690731, 9780081012147, 9780081012505, 085709839X

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NANOFINISHING OF TEXTILE MATERIALS

THE TEXTILE INSTITUTE

AND

WOODHEAD PUBLISHING

The Textile Institute is a unique organisation in textiles, clothing and footwear. Incorporated in England by a Royal Charter granted in 1925, the Institute has individual and corporate members in over 90 countries. The aim of the Institute is to facilitate learning, recognise achievement, reward excellence and disseminate information within the global textiles, clothing and footwear industries. Historically, The Textile Institute has published books of interest to its members and the textile industry. To maintain this policy, the Institute has entered into partnership with Woodhead Publishing Limited to ensure that Institute members and the textile industry continue to have access to high calibre titles on textile science and technology. Most Woodhead titles on textiles are now published in collaboration with The Textile Institute. Through this arrangement, the Institute provides an Editorial Board which advises Woodhead on appropriate titles for future publication and suggests possible editors and authors for these books. Each book published under this arrangement carries the Institute’s logo. Woodhead books published in collaboration with The Textile Institute are offered to Textile Institute members at a substantial discount. These books, together with those published by The Textile Institute that are still in print, are offered on the Elsevier website at http://store.elsevier.com/. Textile Institute books still in print are also available directly from the Institute’s website at www.textileinstitutebooks.com. A list of Woodhead books on textile science and technology, most of which have been published in collaboration with The Textile Institute, can be found towards the end of the contents pages. Related Titles Functional Finishes for Textiles, 9780857098399 Protective Clothing, 9781782420323 High Performance Textiles and Their Applications, 9781845691806 Plasma technologies for textiles, 9781845690731

The Textile Institute Book Series

NANOFINISHING OF TEXTILE MATERIALS MAJID MONTAZER TINA HARIFI

An imprint of Elsevier

Woodhead Publishing is an imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom © 2018 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-08-101214-7 (print) ISBN: 978-0-08-101250-5 (online) For information on all Woodhead publications visit our website at https://www.elsevier.com/books-and-journals

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Introduction: Textile finishing 1.1 INTRODUCTION: TEXTILE FINISHING DEFINITION AND HISTORICAL OVERVIEW Through the literature review, we came up with two definitions of textile finishing both of which have been widely accepted and used. One of them is from narrow view, defining textile finishing as the final manufacturing step in the production of textile fabrics, where the final fabric properties are developed completing the fabric performance along with imparting special functional properties. The other definition is wide, referring to any operation for improving the appearance or value of a fabric after coming out of the loom or knitting machine. In this regard, pretreatments such as scouring and bleaching are also included in finishing step. Generally, it is necessary to carry out some preparatory treatments before the application of other finishing processes to achieve the enhanced finishing effect. Considering these two traditional definitions, we believe that finishing is any form of processing on the textile substrate to prepare the textile for further processing or for the customer. In this definition, textile substrate can be in any form ranging from fibers, flakes, webs, slivers, yarns, fabrics, garments, carpets to any other form of technical textiles. Regardless of any definition, the objective of finishing is to make the textile more acceptable to the consumer and to achieve several goals, including preparation through purification, activation and functionalization, increased added value, enhanced quality, repeatability, variety, improved attractiveness by modification of appearance, changed handle, increased comfort, dimensional stability, protection, and improved performance. The first efforts for textile finishing concerned with the application of finishes to natural fibers, including cotton and wool fibers to improve their resistance to creasing and their dimensional stability. Through the decades, although considerable interest was still being shown in modern developments of the former processes, introduction of man-made fabrics and their reputation over the years has encouraged the textile researchers to develop more modern methods. Undoubtedly, today’s sophisticated modern finishing methods are a development of former simple operations evolved over Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00001-7

© 2018 Elsevier Ltd. All rights reserved.

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the years from hand methods. In past, finishing procedures were mainly concerned with the traditional application of textiles, namely, dressing people. However, today textile finishing aims at converting a textile material into a technical textile with multifunctional properties, providing the wearer with comfort, enhanced performance, and protection. With today’s several functional finishes, the only challenge is selection of the appropriate finish depending on the fiber type and the desired end use. In addition to global awareness of environmental issues that have arose since 1990s affecting the direction of textile finishing, several other factors can be taken into account as driving force for the new trends. The need for higher-quality and higher value-added products, increased levels of automation and process control in machinery and equipment, and greater emphasis on cost reduction by minimizing the use of water and energy are among the effective parameters (Bajaj, 2002). Thus, new finishing methods have been developed as a solution to the environmental issues along with consumer and process demand satisfaction. In spite of wide progress during the history of textile finishing, there has been always a greater demand for novel finishes that confer enhanced appearance, handle, esthetics, and performance to appeal to the consumer. Historically, many references dealing with the subject of textile wet processing have been published ranging from the text books describing particular aspects of bleaching and dyeing to volumes describing chemical finishing and processes that were important at the time they were written. Lewin and Sello (1984) were among the first who tried to review the general area of finishing especially chemical finishing up to the early 1980s within a series of books named Handbook of fiber science and technology. Lack of single-volume reference book, which adequately covered the field of fabric preparation and finishing, urged Tomasino (1992) to gather the related information in a book entitled Chemistry and technology of fabric preparation and finishing. A book with the title Textile processing and properties, preparation, dyeing, finishing and performance was then written by Vigo (1994), dealing with all aspects of textile processing, modification, and performance. The fundamental aspects of chemistry, chemical technology, and machineries involved in the various pretreatment processes of textiles were also discussed by Karmakar (1999) in a book entitled Chemical technology in the pre-treatment processes of textiles, trying to keep the readers abreast of the latest advances in the field until 1999. Since 2000, there have been a number of books published within the area of textile finishing but with more specific information, for instance, based on the textile substrate, functionalities, or applications

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(Horrocks and Anand, 2000). A book entitled Advances in the dyeing and finishing of technical textiles edited by Gulrajani (2013) contained a section mainly dealing with advances in finishing techniques, the use of nanotechnology and specialty polymers in technical textiles. Last but not least was the book entitled Functional finishes for textiles edited by Paul (2015), focusing on the important finishes and finishing techniques to improve the textiles comfort and performance properties. In spite of extensive research on the nanofinishing of textile materials over the last years, comprehensive reference book pointing out different aspects of nanotechnology in textile finishing was lacking. The current book is particularly aimed at filling this gap by addressing different functionalities imparted into textiles through nanotechnology incorporation, from famous antibacterial activity to more complex properties including magnetism, conductivity, and wave protection. This book discusses not only the advantages but also the drawbacks of this fast-emerging technology, trying to propose solutions to tackle the involved limitations. The main focus of the book will be on recent nanofinishing developments categorized based on property. Development of new functionalities along with improvement in existing functions such as enhanced durability and less detrimental effect on hand feel will be dealt with, enabling to extend the application areas of textiles. Chapters will be organized based on different functional properties imparted into textiles through nanofinishing treatments, each containing the relevant nanomaterials, application methods, recent case studies, advantages, disadvantages, and challenges. A chapter will be also devoted to health, safety, and environmental aspects, which are of considerable importance not only to the manufacturers and operators, but also to the end users.

1.2 TEXTILE FINISHING CLASSIFICATION Textile finishing can be classified on different bases, which are briefly shown in Fig. 1.1. Based on the performance and functionality of the finished textiles, esthetic finishes modify the appearance, hand, or drape of the fabrics such as mercerizing, napping, shearing, softening, stiffening, while functional finishes improve the performance properties of the fabrics, including antibacterial, crease resistance, antistatic, water repellant, flame retardant, and soil release. The other classification is based on the finishing media, which comprise wet and dry methods. In wet methods, the chemical finish is a solution or

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Nature

Performance

Mechanical Physical Chemical Bio Nano Nanobio

Aesthetic Functional

Fig. 1.1 Textile finishing different classifications.

Permanence

Temporary Permanent - Durable - Semidurable - Nondurable

Functionality

Environmental concern

Media

Monofunctional Bifunctional Multifunctional

Friendly Unfriendly

Wet Dry

Nanofinishing of Textile Materials

Textile finishing classification

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emulsion of the finish in water or organic solvents, each of which has its own pros and cons. Although low cost, accessibility, safety, no toxicity, and neutrality made water a versatile media, it suffers from high boiling temperature, evaporation latent heat, and surface tension. On the other hand, use of organic solvents to apply chemical finishes is limited due to the high cost, possible toxicity, and flammability, though they benefit from lower boiling temperature, evaporation latent heat, and surface tension. In dry finishing, instead of immersing the fabric in water or solvent-based chemicals, gases and plasma are mainly used. Dry methods are more energyefficient and environment-friendly approaches compared with wet methods. Some finishing treatments are temporary, which are used when only temporary properties are required such as sizing the warp yarn to withstand the rigors of weaving. The warp size is then removed during the process called desizing. On the other hand, there are permanent finishes, which are grouped into durable, semidurable, and nondurable finishing. Durable finishes are those that undergo repeated launderings or dry cleanings without losing effectiveness. Semidurable finishes last through more than 5–10 washing cycles after which the properties diminish. Nondurable finishing in which the effect disappears after the first usage and wash is used when the finished textile typically is not washed or dry cleaned or in case of disposable technical textiles. Finishing can be also classified based on the number of functionalities imparted into the finished textile. Monofunctional finishing is when only one property is imparted into the textile substrate such as anticrease finishing of cotton. Through bifunctional finishes, two functionalities are simultaneously provided such as softening and anticrease. Moreover, finishing can be multifunctional bringing several features into the finished textile, mainly provided by nanotechnology. For instance, finishing of cotton fabric with TiO2 nanoparticles and silicone softener in presence of 1,2,3,4butanetetracarboxylic acid as a crosslinker provides simultaneous softness, anticrease, self-cleaning, UV protection, antibacterial, and flame-retardant properties (Harifi and Montazer, 2012). Besides, the synergistic effect of different finishing components will result in several enhanced properties. One of the important classifications of textile finishing came up after the global concerns about the environmental and human safety issues. In this regard, several attempts have been made to reduce the negative impacts of unfriendly finishes or to replace them with more environment-friendly finishing agents or techniques. For instance, N-methylol-based agents have long been used by the textile industry as durable press finishes producing

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wrinkle-resistant cotton fabrics. However, because they release formaldehyde either from treated fabrics or during finishing processes, their use in textile industries is limited. Formaldehyde has been identified to have impact on human health and the environment. For this purpose, many efforts have been done to reduce the formaldehyde released from the finished fabrics. These efforts range from after-washing the finished fabric and use of formaldehyde scavengers to developing nonformaldehyde reactants such as polycarboxylic acids (Harifi and Montazer, 2012). In addition to the introduction of more environment-friendly chemicals, physical finishing methods have been also developed to get over the environmental pollution problems associated with chemical methods. The most versatile physical methods include plasma, laser, ultrasonic irradiation, microwave (MW), radiofrequency (RF), and UV irradiation techniques. The most common textile finishing classification is based on the nature of finish as mechanical, physical, chemical, bio, nano, and nanobio finishing.

1.2.1 Mechanical finishing Mechanical finishing is mainly dealt with the application of mechanical treatments, including friction, tension, compression, temperature, and pressure to improve the appearance, performance, and hand properties of textile substrates imparting luster, smoothness, softness, and dimension change (Kumar and Sundaresan, 2013). The most common mechanical finishing methods are as follows. 1.2.1.1 Calendaring One of the mechanical finishing treatments is calendaring in which the fabric passes between heated rotating rollers (smooth or engraved) under controlled time, temperature, and pressure. The result will be soft handle, reduced thickness, reduced yarn slippage along with improved luster. 1.2.1.2 Raising The goal of raising is to remove individual fiber ends to the surface of fabric to produce soft and smooth handle, which is done with wire-covered rolls. If abrasive-covered rolls are used, the surface with short piles will result in shade change. 1.2.1.3 Decatizing Decatizing is done using a perforated roller immersed in hot water or blown with water vapor to improve the stability, luster, and hand of fabric.

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1.2.1.4 Fulling Application of heat along with friction and compression is usually done in fulling of wool to reduce the shrinkage. 1.2.1.5 Sanforizing Sanforizer, a machine with drums filled with water vapor, is used to control the shrinkage of the fabric. During the process, the fabric is under mechanical forces to achieve dimensional stability. In some cases mechanical and chemical finishing overlap with each other, as we need chemicals for some mechanical methods, while mechanical assistance is also required for chemical finishing.

1.2.2 Physical finishing 1.2.2.1 Plasma Plasma is a promising physical method, with alteration effects only limited to the surface of fabric, and is regarded as an environment-friendly approach. In definition, plasma is an electrically neutral ionized gas with electrically charged particles not bound to an atom or molecule. Due to thermal sensitivity of textile substrates, only nonthermal (cold) plasmas are attracted by textile researchers (Morent et al., 2008), which is further grouped into atmospheric pressure, vacuum, or low-pressure plasmas. Corona, dielectric barrier discharge, glow discharge, and plasma jet are four common types of atmospheric pressure plasma, which is famous for cost effectiveness. Chemistry of plasma gases, the nature of the substrate, and operating parameters are all effective on plasma-surface interactions. There have been vast number of studies about plasma application on different textile substrates to introduce hydrophilic functional groups such as dCOOH, dOH, and dNH2, thereby increasing the surface wettability (Hossain et al., 2006). Moreover, numerous studies were carried out by different plasma discharges to obtain hydrophobicity of various textile substrates such as polyester, polypropylene, and cotton (Molina et al., 2017). This was achieved by deposition of a polymer on fibers during the plasma treatment (plasma polymerization) or by creation of radicals on the fiber surface by plasma in inert gas and reaction of radicals with unsaturated monomers (Shishoo, 2007). To this end, polymerizing fluorocarbon gases such as hexafluoropropylene, fluorodecyl acrylate, hexafluoroethane, and tetrafluoromethane have been widely studied (Zille et al., 2015). Plasma has been also applied to increase the dyeing rates of textile substrates, the diffusion of dye molecules into the fibers, and washing fastness of several

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fabrics such as cotton, polyamide, polyester, polypropylene, silk, and wool (Ahmed and El-Shishtawy, 2010). Wool antifelting with plasma in noncontinuous vacuum and batch condition has been successfully introduced to replace chemical chlorine antifelting method (Zille et al., 2015). Plasma was also successful in enhanced interaction between fibers and finishing agents producing durable finishing (Zemljicˇ et al., 2009; Jazbec et al., 2015). 1.2.2.2 Laser Laser is short form of light amplification by stimulated emission of radiation and has four fundamental characteristics, namely, intensity, coherency, monochromaticity, and collimation, thereby differing from natural light. Laser has been widely used in textile industry in several applications such as cutting, fabric fault detection, denim fading by laser dye decomposition at specific points, and engraving making designs and patterns on buttons, leather, and denim. The most common lasers used in industrial applications include neodymium yttrium-aluminum-garnet (Nd:YAG), CO2, and excimer (UV) lasers (Bahners, 1995). There are also some cases of using laser as surface modification method resulting in enhanced dyeability (Wong et al., 2001). Most of the efforts in developing surface treatments have been made using UV lasers. As infrared (RF) radiation can cause thermal damages, selecting optimum laser parameters using RF lasers such as CO2 for surface modification is very important (Montazer et al., 2012, 2013). CO2 laser can be also used to reduce pilling of cotton/polyester fabric due to the melting effect (Hung et al., 2017). 1.2.2.3 Microwave Irradiation of textile material by MW will cause heating of the substrate in a very short time (Haggag et al., 2014). For the first time, MW was introduced to textile finishing for curing of durable press finished cotton fabrics (Englert and Berriman, 1974). Since that time, MW irradiation has been used in several processes such as dyeing, drying, desizing, scouring, bleaching, and silk degumming (Tarakc¸iog˘lu and Aniş, 1996). Moreover, there is a report on use of MW for eradication of insects from wool (Reagan, 1982). Use of MW irradiation to heat the dye bath was effective in increased dye uptake of cotton, wool, cotton/wool, silk, polyester, and polyamide fibers (Haggag et al., 2014). Furthermore, MW was used as a pretreatment in the presence of solvent to enhance dyeing adsorption of polyester fibers (Kale and Bhat, 2011). There have been some examples of using MW for waste water

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treatment through dye degradation (Garcı´a et al., 2017). Moreover, use of MW for synthesis of nanomaterials such as titania has been reported (Giesz et al., 2016). 1.2.2.4 Radiofrequency RF is used as a high-speed drying method and is famous for uniform drying due to the effect on the densest portion of the textile. 1.2.2.5 Infrared The main application of IR in textile finishing is in curing processes, where fabric is coated with the finishing resin, and run through the electric IR curing system. It can be also used to speed up the drying when applied in the entry of the Stenter. 1.2.2.6 Ultraviolet If the surface of fibers cannot absorb the ultraviolet (UV) light directly, photo initiators are required to produce reactive radicals. The main applications of UV irradiation in textile finishing are as follows: 1. As curing method where radicals are generated by the interaction of UV light with a suitable photoinitiator, making the low-temperature curing reaction of reactive monomers and oligomers possible (Ferrero et al., 2008). 2. As surface activation method where formation of hydroxyl, carbonyl, and/or carboxyl groups occurs by altering the contact angle and surface energy. There are some examples of pretreatment of textile substrates such as cotton to achieve higher dyeability. 3. As a posttreatment to excite UV-absorbing materials such as nano TiO2 particles for photocatalytic reactions. 1.2.2.7 Ultrasound The effects of ultrasound (US) arise from acoustic cavitation in liquid media with regard to the formation, growth, and violent collapse of bubbles in less than a microsecond, releasing extreme heat and forming short-lived hot spots. Degradation of organic compounds, oxidization, and/or reduction of inorganic compounds and sonolysis of water into reactive radicals •OH and H• are possible phenomena that occur by US irradiation. Accelerating chemical reactions, enhancing mass transfer, shortening reaction cycles, improving reaction yield, altering reaction pathway, increasing surface area between the reactants and accelerating dissolution are some of the US

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effects. US has been introduced to textile wet processing as a promising tool for reducing the operation time and energy consumption, and enhancing the quality of the products. Use of US in textile industry can be grouped into following categories (Harifi and Montazer, 2015): 1. Cleaning effect of US for textile machinery parts such as needles in knitting machines. 2. Dispersing action of US for preparation of pretreatment baths such as rapid preparation of starch sizing at low temperature, formation of long-time stable homogenous emulsions, dye dispersions and thickeners for print paste. 3. Use of US for removing impurities from surface of the fibers and enhancing diffusion of dyes or chemicals into the fabrics. 4. Application of US in textile wastewater remediation by the formation of oxidizing species. 5. Synthesis of nanomaterials and their deposition on different textile substrates.

1.2.3 Chemical finishing Addition of chemicals to textile substrates in order to achieve desired properties is generally regarded as chemical finishing, which can be done through batch processing, namely, exhaustion and continuous approaches such as pad-dry-cure. Coating, spraying, and foam solution are among other chemical finishing methods (Schindler and Hauser, 2004). Chemical finishing has been widely used due to its versatility to impart several functionalities into textile substrates such as being water repellent, water proof, moth proof, flame retardant, anticrease, and many others (Holme, 1993). However, the textile chemical finishing involves the use of large amounts of energy, chemicals, and water. Some chemical finishes may be harmful to human in the wastewater, and the presence of chemicals in the finished textiles may cause skin irritation in some people (Kan, 2015). Thus, there is an urge of everyday attempt to introduce more sustainable, greener, and cleaner chemical finishing generally termed as “green chemistry”. Safer chemicals with minimum or no toxicity to human health and the environment, safe solvents and auxiliaries, energy efficiency (reduced temperature and pressure), natural, biodegradable, and renewable chemicals are among the developed approaches.

1.2.4 Biofinishing Biofinishing is regarded as a suitable textile processing method that produces ecofriendly finished products with no detrimental effect on the environment

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in case of effluent discharge. Biofinishing is carried out using enzymes for desizing, biopolishing, bioscouring, and biobleaching; biopolymers such as chitosan and cyclodextrin for antibacterial, fragrance release, and wrinkle-free finishes; and aromatherapies such as Aloe vera and neem for antibacterial and moth-proofing properties. Some of the main hurdles for the industrial implementation of enzymes are their low stability, low compatibility with other chemical agents, longer processing time, and relatively high cost. On the other hand, enzyme treatment benefit from safety and low-energy consumption. Considering the versatility of enzymes in textile biofinishing, a brief overview of enzymes, their action mechanism, characteristics, and application is provided here. Enzymes are biocatalysts from natural proteins with the ability to catalyze specific chemical reactions. There are two mechanisms proposed for the specific action of enzyme. In the first one, which is called lock-and-key model, it is postulated that the geometric shapes of the enzyme and the substrate complete each other. This model was further developed by Koshland who found out that the enzyme active site is not rigid and is continuously reshaped by the interactions with the substrate. In this model, which is called induced fit model, the alteration of enzyme active sites will continue until the complete bounding to the substrate (Karmakar, 1999). General features of enzymes include (Paul and Genesca, 2013): – They are environment-friendly and their effluent is easy to treat and clean up – They increase the rate of chemical reactions by lowering the free energy barrier between the reactants and the products – They operate at mild conditions (enzymatic treatments can save energy as they operate at lower temperature and pH) – Their action is controllable – They act selectively at specific substrates – Their action is mainly limited to the surface Some of the important enzymes with their textile finishing applications are as follows. 1.2.4.1 Amylases Amylases, which are starch-degrading enzymes, are grouped into endoamylases, exoamylases, debranching enzymes, and transferases. α-Amylase is an endoamylase that catalyzes the hydrolysis of internal α-1,4-glycosidic linkages into glucose, maltose, and maltotriose units. The main application of amylases in textile finishing is desizing, which involves the removal of starch.

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These enzymes hydrolyze the starch molecules into small fragments that can be easily washed away or dissolved in hot water. There are three types of amylases regarding the temperature and pH condition. Regular amylases may be applied at pH 5.5–7.0 and 25–55°C. Medium-temperature amylases can be used above 50°C, while high-temperature amylases can be used at boil and in a padding process (Paul and Genesca, 2013). 1.2.4.2 Proteases Peptidases or proteases are the enzymes that catalyze the cleavage of peptide bonds in proteins. Depending on the nature of the functional group at the active site, they are divided into serine proteases, aspartic proteases, metalloproteases, cysteine proteases, and endopeptidases. In the textile industry, proteases are used in wool finishing and silk degumming (Freddi et al., 2003). Recently, proteases enzymatic hydrolysis together with the use of reducing agent was proposed for keratin extraction from wool and feather waste (Eslahi et al., 2013a). Moreover, protease biofinishing of wool followed by ultrasonic treatment was effective to produce wool nanoparticles (Eslahi et al., 2013b). Wool biofinishing with proteases is usually carried out to achieve higher shrink resistance (antifelting) and increased smoothness and softness together with improved dyeability (Parvinzadeh, 2007). Although the enzyme action is restricted to the surface of fibers, due to the open structure of wool fibers, proteases could penetrate into the interior of the fibers breaking down the cell membrane complex. Thus, wool enzymatic treatment with conventional proteases caused damage to fibers. One of the successful treatments to reduce the detrimental effects of proteases on wool strength is by the application of transglutaminase, which forms protein crosslinking (Montazer and Ramin, 2010). Controlled silk degumming (sericin removal) is possible using alkaline and neutral proteases with minimum changes in the fibroin structure and mechanical properties along with improved surface smoothness, handle, and luster (Teh et al., 2010). 1.2.4.3 Transglutaminases Transglutaminases are aminoacyltransferases that catalyze an acyl transfer between peptide-bound glutamine (acyl donors) and primary amines (acyl acceptors). Their application to wool fibers mainly results in increased protein stability and increased resistance to chemical and proteolytic degradation. It recovers the wool and silk from damage during chemical and

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enzymatic treatments. Improved shrink resistance and tensile strength of wool fibers are also some of the effective roles of transglutaminases. Through transglutaminases, grafting of amines or proteins to wool is possible. Microbial transglutaminase (mTGase) is the most common group of transglutaminases due to feasible preparation method (Cortez et al., 2005). 1.2.4.4 Pectinases Pectinolytic enzymes or pectinases are capable of hydrolyzing pectic substances and mainly are present in plants. Their main application in textile finishing is cotton bioscouring especially with alkaline pectinases. Improved properties have been achieved with combinations of pectinases with cellulases or proteases or lipases (Karapinar and Sariisik, 2004). Cotton bioscouring is further discussed in Chapter 3. 1.2.4.5 Lipases Lipasese are a member of carboxylic ester hydrolyzing enzymes capable of catalyzing the hydrolysis, synthesis, or transesterification of an ester bond. In the textile industry, their application includes the hydrolysis of synthetic fibers especially polyester and bioscouring in combination with pectinases. However due to the compact structure of polyester and the activity of enzymes limiting to the surface, only polyester surface activation is achieved via enzyme treatment and the process is not as efficient as alkaline hydrolysis to change the hand and weight loss. It is also used for lipid soil removal through washing and for desizing in combination with amylases to remove the residue of weaving lubricants (Djordjevic et al., 2005). 1.2.4.6 Cellulases Cellulases are hydrolyzing enzymes with the ability to act on cellulose (β-1,4-D-glucan linkages) to produce by-products such as glucose, cellobiose, and cello-oligosaccharides. Cellulose biopolishing and biostoning are the two main applications of cellulases in textile finishing. Besides, cellulases can be used to assist the production of nanocellulose (Ibrahim et al., 2011). Biopolishing is a process of using cellulases for surface modification of cellulosic fabrics to reduce the hairiness and increase the resistance to pilling. This is achieved by the hydrolysis of cellulose, eliminating the superficial microfibrils of the cotton fibers. Through this method, fabric softness and smoothness is also improved and the surface is less vulnerable to adsorb dirt. Biopolishing of cotton using cellulases also results in 3–6% weight loss and almost 10% decreased tensile strength, which is acceptable.

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Traditionally, the desired worn look of denim jeans was obtained by stone washing through which vat dye was eliminated by the rubbing effect of pumice stones soaked in sodium hypochlorite or potassium permanganate as oxidizing agents. However, due to the stone washing problems such as rapid wear and tear of washing machines, a large number of second-class garments, unsafe working conditions, environmental pollution, and the need for manual removal of pumice from pockets and folds of garments, biostoning using cellulases has been successfully introduced as an alternative method (Pazarlioglu et al., 2005). Cellulases together with mechanical agitation caused fiber surface abrasion along with dye release from yarns. Due to the detrimental effect of acid cellulases on cellulose degradation, neutral cellulases were used instead. In spite of the merits of biostoning with cellulases, redeposition of the released dye on the garments, also known as backstaining, was the major problem. In addition to antiredeposition chemicals or mild bleaching agents added during the enzyme washing or rinsing step, coapplication of cellulases with laccase as an oxidase enzyme was helpful to reduce backstaining (Sadeghian Maryan et al., 2013). 1.2.4.7 Laccases Laccases as oxidase enzymes are capable of catalyzing the oxidation of orthoand para-diphenols, aminophenols, polyphenols, polyamines, lignins, and aryl diamines as well as some inorganic ions coupled to the reduction of molecular dioxygen to water. Its main application in textile industry is the discoloration of dyeing effluent (Rodrı´guez Couto and Herrera, 2006). Laccase/mediator systems are also developed for biobleaching of cotton, which is further discussed in Chapter 4. Laccases are also used in combination with cellulases to achieve efficient biostoning with minimum backstaining and to decolorize the effluent from the dye as they have found acceptance for bleaching indigo in denim (Sadeghian Maryan et al., 2013). 1.2.4.8 Peroxidases Peroxidases are a member of oxidase enzymes with the ability to catalyze the oxidation of a wide variety of substrates especially H2O2. In textile finishing, post-treatment of hydrogen peroxide bleaching bath to remove the residue of H2O2 is assisted by peroxidases (Opwis et al., 2008).

1.2.5 Nanofinishing Imparting various specific characteristics to textiles is generally carried out during chemical finishing step. Since significant progress has been made

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in nanotechnology, nanofinishing has been introduced with potential applications ranging from water and stain repellent, wrinkle resistant, and flame retardant to high-tech applications such as microbe resistance and magnetic and conductive textiles. Different methods can be included in nanofinishing ranging from various deposition techniques such as electroless deposition and vapor deposition to layer-by-layer coating, sol-gel, ex situ and in situ synthesis, and fabrication of nanomaterials, which are thoroughly described in Chapter 2.

1.3 CONCLUSION Traditionally, textile finishing is a final step to change the quality of fabric in terms of appearance, handle, and functionally through mechanical and chemical routes. Over the years, textile finishing has been modernized to the process by which textile materials convert into technical textiles. Undoubtedly, the future trend in textile finishing is to develop multifunctional textiles, which are highly efficient, durable, cost effective, and manufactured in an environmentally sustainable manner. In this regard, nanofinishing will play a key role in the performance and properties of the finished products. Treatment methods with minimum use of chemicals requiring less capital-intensive machinery, few processing steps, and minimum effluent treatments are more preferred by fabric manufacturers. Besides, nanofinishing of textiles with no adverse effect on physical and mechanical properties of the fabrics will be more important.

REFERENCES Ahmed, N.S.E., El-Shishtawy, R.M., 2010. The use of new technologies in coloration of textile fibers. J. Mater. Sci. 45, 1143–1153. Bahners, T., 1995. Excimer laser irradiation of synthetic fibers as a new process for the surface modification of textiles–a review. Opt. Quant. Electron. 27, 1337–1348. Bajaj, P., 2002. Finishing of textile materials. J. Appl. Polym. Sci. 83, 631–659. Cortez, J., Bonner, P.L.R., Griffin, M., 2005. Transglutaminase treatment of wool fabrics leads to resistance to detergent damage. J. Biotechnol. 116, 379–386. Djordjevic, D.M., Petronijevic, Z.B., Cvetkovı´, D.M., 2005. Polyester fabric modification by some lipases. Chem. Ind. Chem. Eng. Q. 11, 183–188. Englert, R. D., Berriman, L.P. 1974. Curing chemically treated cellulosic fabrics, US Patent 3846845. Eslahi, N., Dadashian, F., Hemmati Nejad, N., 2013a. An investigation on keratin extraction from wool and feather waste by enzymatic hydrolysis. Prep. Biochem. Biotechnol. 43, 624–648.

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Eslahi, N., Dadashian, F., Hemmati Nejad, N., 2013b. Optimization of enzymatic hydrolysis of wool fibers for nanoparticles production using response surface methodology. Adv. Powder Technol. 24, 416–426. Ferrero, F., Periolatto, M., Sangermano, M., Bianchetto Songia, M., 2008. Water-repellent finishing of cotton fabrics by ultraviolet curing. J. Appl. Polym. Sci. 107, 810–818. Freddi, G., Mossotti, R., Innocenti, R., 2003. Degumming of silk fabric with several proteases. J. Biotechnol. 106, 101–112. Garcı´a, M.C., Mora, M., Esquivel, D., Foster, J.E., Roderod, A., Jimenez-Sanchidria´n, C., Romero-Salguero, F.J., 2017. Chemosphere 180, 239–246. Giesz, P., Celichowski, G., Puchowicz, D., Kami nska, I., Grobelny, J., Batory, D., Cieslak, M., 2016. Microwave-assisted TiO2: anatase formation on cotton and viscose fabric surfaces. Cellulose 23, 2143–2159. Gulrajani, M.L. (Ed.), 2013. Advances in the Dyeing and Finishing of Technical Textiles, first ed. USA, Elsevier. Haggag, K., Ragheb, A., Nassar, S.H., Hashem, M., El Sayed, H., Abd El-Thalouth, I., 2014. Microwave Irradiation and its Application in Textile Industries. Science Publishing Group, New York. Harifi, T., Montazer, M., 2012. Past, present and future prospect of cotton cross-linking: New insight into nano particles. Carbohydr. Polym. 88, 1125–1140. Harifi, T., Montazer, M., 2015. A review on textile sonoprocessing: a special focus on sonosynthesis of nanomaterials on textile substrates. Ultrason. Sonochem. 23, 1–10. Holme, I., 1993. New developments in the chemical finishing of textiles. J. Text. Inst. 84, 520–533. Horrocks, A.R., Anand, S.C. (Eds.), 2000. Handbook of Technical Textile. CRC Press, New York. Hossain, M.M., Herrmann, A.S., Hegemann, D., 2006. Plasma hydrophilization effect on different textile structures. Plasma Process. Polym. 3, 299–307. Hung, O., Chan, C.K., Kan, C.W., Yuen, C.W.M., 2017. Microscopic study of the surface morphology of CO2 laser-treated cotton and cotton/polyester blended fabric. Text. Res. J. 87, 1107–1120. Ibrahim, N.A., El-Badry, K., Eid, B.M., Hassan, T.M., 2011. A new approach for biofinishing of cellulose-containing fabrics using acid cellulases. Carbohydr. Polym. 102, 863–869. Jazbec, K., Sˇala, M., Mozeticˇ, M., Vesel, A., Gorjanc, M., 2015. Functionalization of cellulose fibers with oxygen plasma and ZnO nanoparticles for achieving UV protective properties. J. Nanomater. 2015, 1–9. Kale, M.J., Bhat, N.V., 2011. Effect of microwave pretreatment on the dyeing behavior of polyester fabric. Color. Technol. 127, 365–371. Kan, C.W., 2015. A novel green treatment for textiles plasma treatment as a sustainable technology. Text. Sci. Technol. 12, 418–440. Karapinar, E., Sariisik, M., 2004. Scouring of cotton with cellulases, pectinases and proteases. Fibres Text. East. Eur. 12, 79–82. Karmakar, S.R., 1999. Chemical Technology in Pretreatment Process of Textiles. Elsevier, USA. Kumar, R.S., Sundaresan, S., 2013. Mechanical finishing techniques for technical textiles. In: Gulrajani, M.L. (Ed.), Advances in the Dyeing and Finishing of Technical Textiles, first ed. Elsevier, USA. Lewin, M., Sello, S.B., 1984. Chemical Processing of Fibers and Fabrics - Fundamentals and Preparation. Handbook of Fiber Science and Technology, vol. 1. CRC Press, New York. Molina, R., Teixido´, J.M., Kan, C.W., Jovancˇic, P., 2017. Hydrophobic coatings on cotton obtained by in situ plasma polymerization of a fluorinated monomer in ethanol solutions. ACS Appl. Mater. Interfaces 9, 5513–5521.

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Montazer, M., Ramin, A., 2010. Influence of proteases and transglutaminases on wool. Fibres Text. East. Eur. 18, 98–102. Montazer, M., Taheri, S.J., Harifi, T., 2012. Effect of laser CO2 irradiation on various properties of polyester fabric: focus on dyeing. J. Appl. Polym. Sci. 124, 342–348. Montazer, M., Chizarifard, G., Harifi, T., 2013. CO2 laser irradiation of raw and bleached cotton fabrics, with focus on water and dye absorbency, coloration technology. Color. Technol. 130, 1–8. Morent, R., De Geyter, N., Verschuren, J., De Clerck, K., Kiekens, P., Leys, C., 2008. Nonthermal plasma treatment of textiles. Surf. Coat. Technol. 202, 3427–3449. Opwis, K., Knitter, D., Schollmeyer, E., Hoferichter, P., Cordes, A., 2008. Simultaneous application of glucose oxidases and peroxidases in bleaching processes. Eng. Life Sci. 8, 175–178. Parvinzadeh, M., 2007. Effect of proteolytic enzyme on dyeing of wool with madder. Enzym. Microb. Technol. 40, 1719–1722. Paul, R., 2015. Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing Limited, Cambridge. Paul, R., Genesca, E., 2013. The use of enzymatic techniques in the finishing of technical textiles. In: Gulrajani, M.L. (Ed.), Advances in the Dyeing and Finishing of Technical Textiles, (first ed). Elsevier, USA. Pazarlioglu, N.K., Sariisik, M., Telefoncu, A., 2005. Treating denim fabrics with immobilized commercial cellulases. Process Biochem. 40, 767–771. Reagan, B.M., 1982. Eradication of insects from wool textiles. J. Am. Inst. Conserv. 21, 1–34. Rodrı´guez Couto, S., Herrera, J.L., 2006. Lacasses in the textile industry. Biotechnol. Mol. Biol. Rev. 1, 115–120. Sadeghian Maryan, A., Montazer, M., Harifi, T., Mahmoudi Rad, M., 2013. Aged-look vat dyed cotton with anti-bacterial/anti-fungal properties by treatment with nano clay and enzymes. Carbohydr. Polym. 95, 338–347. Schindler, W.D., Hauser, P.J., 2004. Chemical Finishing of Textiles. Woodhead Publishing Limited, Cambridge. Shishoo, R., 2007. Plasma Technologies for Textiles. CRC Press, New York. Tarakc¸iog˘lu, I., Aniş, P., 1996. Microwave processes for the combined desizing, scouring, and bleaching of grey cotton fabrics. J. Text. Inst. 87, 602–608. Teh, T.K.H., Toh, S., Goh, J.C.H., 2010. Optimization of the silk scaffold sericin removal process for retention of silk fibroin protein structure and mechanical properties. Biomed. Mater. 5, 035008. Tomasino, C., 1992. Chemistry and Technology of Fabric Preparation and Finishing. Chemistry and Science College of Textiles North Calorina State University, USA. Vigo, T.L., 1994. Textile Processing and Properties, Preparation, Dyeing, Finishing and Performance. Elsevier, USA. Wong, W., Chan, K., Yeung, K.W., Lau, K.S., 2001. Chemical modification of poly(ethylene terephthalate) induced by laser treatment. Text. Res. J. 71, 117–120. Zemljicˇ, L.F., Persˇin, Z., Stenius, P., 2009. Improvement of chitosan adsorption onto cellulosic fabrics by plasma treatment. Biomacromolecules 10, 1181–1187. Zille, A., Oliveira, F.R., Souto, A.P., 2015. Plasma treatment in textile industry. Plasma Process. Polym. 12, 98–131.

2

Nanofinishing: Fundamental principles 2.1 INTRODUCTION When Richard Feynman was presenting a lecture at the American Physical Society meeting in 1959, he proposed a sentence “there is plenty of room at the bottom,” which was certainly the first step toward the introduction and creation of nanosized products using atoms as the building particles (Drexler, 1992). During the last years, his idea has been further developed by other scientists and today considerable researches are being underway in this area. Nanotechnology is the understanding and control of matter at nanoscale (1–100 nm, at least one dimension), through which unusual physical, chemical, and biological properties are imparted into materials differing from the bulk properties. The success of nanotechnology is due to the size-related properties and high surface area-to-volume ratio, which result in the enhanced characteristics compared with conventional macrometer-sized particles. In parallel with the advent of nanoscience and nanotechnology, a new category has been added to textile finishing called as “nanofinishing.” Nanofinishing has opened new paths to improve the existing processes or help to achieve new functional properties, which are not possible with conventional finishes. Due to the incorporation of nanotechnology in textile finishing, many novel and superior characteristics have been imparted into textiles providing multifunctional properties including antibacterial, self-cleaning, antistain, UV blocking, conductivity, magnetism and electromagnetic wave shielding. High-performance functional finishes have become possible by nanofinishing providing technical textiles with various end-uses such as agrotex (agriculture), buildtex (construction), geotex (geotextile and road construction), mobiltex (automotive, rail road), ecotex (environment protection), packtex (packaging), protex (people and property protection), pertex (perfumed textile), and sportex (sport and leisure). Nanofinishing also benefits from no adverse effect on fabric hand and breathability.

Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00002-9

© 2018 Elsevier Ltd. All rights reserved.

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Nanofinishing of Textile Materials

Undoubtedly, the first attempts in textile nanofinishing were made by Dr. David Soane, who tried to use nanotechnology for adding unusual properties to natural and synthetic textiles, without changing a fabric’s look or feel. He succeeded in establishing the first nanotechnology-based company, Nano-Tex, in 1998. Professor W. Barthlott, Dr. Walid Daoud, and Dr. John Xin also took pioneering steps to develop textile nanofinishing (Gulrajani, 2006). This was developed by Dr. Montazer and his colleagues and many other researchers around the globe. Today, application of organic and inorganic nanoparticles such as titanium dioxide, silver, zinc oxide, copper, gold, carbon nanotubes, nanolayered clay, and their nanocomposites to textile materials to impart various multifunctional properties is a broad area of research. New methods of nanocoating, electrospraying, layer-by-layer deposition, chemical vapor deposition, and sol-gel deposition are also being researched. Nanotechnology can be also used to provide surface activation and roughness in nanorange. A large number of functionalities can be imparted into textiles through nanofinishing, which is thoroughly discussed in various chapters.

2.2 NANOFINISHING CLASSIFICATION Nanotreatment of textile materials can be grouped into three main categories, namely, nanostructures, nanolayer, and nanoroughness, which are briefly described in the following sections (Fig. 2.1).

2.2.1 Nanostructures One of the wide areas of research in textile nanofinishing has been devoted to the application of nanomaterials on textile substrates. This includes nanoparticles with at least one dimension size in nanoscale or nanocomposites comprising two, three, or more components. Depending on many factors such as temperature, pH, precursor concentration, auxiliaries, and synthesis method, nanomaterials are formed in a variety of shapes such as nanorods, nanoneedles, nanowires, nanobars, nanoplates, nanospheres, nanocubes, nanopyramids, nanoprisms, nanostars, and many other shapes with different physical and chemical properties. Due to small size, nanoparticles have high surface-to-volume ratio, which gives them unique and potential features varying from the bulk material. Generally, there are two main approaches for the production of nanoparticles. In top-down methods, a pattern generated on a larger scale is

Metal

Ag, Au, Cu, Ni, ...

Metal oxide

TiO2, ZnO, Fe3O4, ..

Inorganic Nanoparticles

Chitosan, alginate, wool, cellulose, silk, .. Organic Nanostructures

Carbon based e.g. Carbon black, carbon nonotube Nanocomposites

Nanolayer

Inorganic

Organic

Nanoroughness

Fig. 2.1 Classification of textile nanofinishing.

Single rough Multi rough

Nanofinishing: Fundamental principles

Nanofinishing

Inorganic/inorganic Organic/organic Inorganic/organic

21

22

Nanofinishing of Textile Materials

changed into nanoscale. On the other hand, bottom-up methods begin with atoms or molecules and build up to nanostructures. Nanomaterials can be classified as organic and inorganic particles, which could be applied alone or in combination with each other as nanocomposites to provide multifunctional properties. Inorganic nanoparticles are further grouped into metals such as silver, gold, copper, nickel, and metal oxides, including titanium dioxide, zinc oxide, iron oxide, and copper oxide. Recently, semimetals have also been considered. On the other hand, there are inorganic nanoparticles as solid particles composed of organic compounds (mainly monomeric or polymeric) ranging in diameter from 10 nm to 1 μm such as nanochitosan, nanocellulose, nanowool, nanosilk, and denderimers. There are also some researches on the coapplication of organic and inorganic nanoparticles on textile substrates such as Ag/chitosan nanocomposite (Arif et al., 2015). Various nanomaterials used in textile nanofinishing have been summarized in Table 2.1 along with their related functional properties. Moreover, we tried to briefly introduce the most widely studied nanoparticles in textile nanofinishing. 2.2.1.1 Metal nanoparticles Silver (Ag)

Silver nanoparticles have a reputation for antibacterial activities and their therapeutic property has been proved against a broad range of diseasecausing microorganisms. They can be synthesized through a variety of methods ranging from simple chemical reduction processes to photochemical, biochemical, sonochemical, and Tollens’ reagent methods, which are further discussed in Chapter 10 along with specific studies (Dastjerdi and Montazer, 2010). The potentiating effect of silver nanoparticles in killing the microorganisms is generally related to silver metal ions and their small particle size and high specific surface area, which allow close interaction with microbial membranes. Attachment of silver ions or nanoparticles to the bacteria due to electrostatic interaction with negative charge of bacterial cell wall, damage to the lipids, proteins and DNA of the microorganisms are the main antibacterial mechanisms of silver nanoparticles, which are further discussed in Chapter 10 (Dastjerdi and Montazer, 2010). There are also some researches concerning the use of silver-based nanomaterials such as silver chloride nanocrystals to impart antibacterial efficiencies into textile substrates. Various attempts have been also made to provide silver-based antibacterial finishing of textiles with less toxicity and more

Nanofinishing: Fundamental principles

23

Table 2.1 Textile nanofinishing with various nanomaterials along with functional properties Nanomaterials Properties

Metal oxide nanoparticles

TiO2

ZnO CuO/Cu2O Fe3O4/Fe2O3

Metal nanoparticles

Carbon black nanoparticles Carbonyl iron Carbon nanotubes Clay nanoparticles Graphene Metal organic frameworks (MOFs)

Al2O3 ZrO2 Mn3O4, MnO2 MgO Ag Au Pd Pt Cu Ni

Photocatalytic, self-cleaning, antibacterial, UV-protection, flame retardant, reversible hydrophobic/hydrophilic properties, enhanced dyeing of polyester, photobleaching and photoscouring of wool and cotton, lower wool alkaline solubility, antifelting of wool, mothproofing of wool Similar properties as nano TiO2 Antibacterial Photocatalytic, antibacterial, magnetization Antibacterial, wool mordanting Photocatalytic, antibacterial Antibacterial Antibacterial Antibacterial, conductivity Antibacterial, conductivity Antibacterial Antibacterial Antibacterial, conductivity Magnetization, catalytic effect Abrasion and chemical resistance, electrical conductivity Conductivity, magnetization, hydrophobicity Thermal and electrical conductivity UV shielding, flame retardant, electrical and chemical resistance Electrical, application in energy conversion Antibacterial, chemical protection, anti-insect, application in energy conversion

biodegradability. This was achieved by using nontoxic and biodegradable protective (capping) agents such as poly(N-vinyl pyrrolidone) (PVP) forming Ag/PVP nanocomposites. There are also examples of silver-based nanocomposites with either organic or inorganic components such as Ag/SiO2, Ag/chitosan, Ag/sodium carboxy methyl cellulose, Ag/hydroxy

24

Nanofinishing of Textile Materials

apatite, Ag/sulfur, and many others to enhance the antibacterial activities and/or to provide multifunctional properties (Bozaci et al., 2015; Panwar et al., 2015; Ciobanu et al., 2013). Gold (Au)

Gold nanoparticles have been widely studied due to their unique optical and biological properties. They could be used for highly sensitive diagnostic assays, thermal ablation, and radiotherapy enhancement, as well as for drug and gene delivery. They are mainly prepared via chemical reduction method using gold salts such as hydrogen tetrachloroaurate (HAuCl4) as precursor and citrate as reducing agent. Interaction of light at specific wavelength causes collective oscillation of electrons on the gold nanoparticle surface known as surface plasmon resonance (SPR) resulting in strong extinction of light (absorption and scattering). The light wavelength is dependent on the gold nanoparticle size and shape. Hence, colloidal gold has red (for particles 9) or acidic (pH < 2.5) condition. Soap or nonionic detergents such as nonylphenol ethoxylated are also added to alkaline degumming process to lower the price, material usage, and process time. Three-step degumming using proteolytic enzymes such as proteases (e.g., carboxy peptidase A), serine proteases (chymotrypsin, trypsin, thrombin), and thiol proteases has been reported as successful silk biodegumming. Through silk degumming by enzymes, mechanical agitation enhances the enzyme penetration and results in complete sericin removal (Shen, 2010). Moreover, combining lipases with proteases for simultaneous sericin and wax removal has been successfully reported resulting in silk fibers with improved wettability and handle. Ultrasound was also successful in increased degumming efficiency using proteases due to the improved enzyme movement and increased sericin swelling (Mahmoodi et al., 2010). Silk pretreatment with sodium thiosulfate or sodium hydrosulfite was also effective in accelerated sericin removal, reduced enzyme consumption and time (Shen, 2010).

42

Nanofinishing of Textile Materials

Table 3.1 Common methods of synthetic fibers scouring Fiber type Method Remarks

Polyester

Nylon

Acrylic

Acetate

Viscose

Alkaline condition containing 2 g/L NaOH, soda-ash or ammonium hydroxide at 75–80°C for 30–60 min or anionic detergent at 80–95°C for 20–30 min Batch: Nonionic detergents under mild alkaline condition using 1–3 g/L soda ash at 70° C for 20–30 min Continuous: Nonionic detergents +3–6 g/L sodium pyrophosphate at 90°C for 10–20 min 1–2 g/L nonionic detergent +1 g/L trisodium phosphate +1 mL/L solvent-based detergent at boil for 30 min 3 g/L soap +1 g/L of a 25% solution of ammonia for 30–35 min at 70°C 0.3–0.5% soap solution + sodaash or trisodium phosphate at 80–90°C

Special care about polyester hydrolysis with strong alkali at high temperature

Scouring temperature for unset fabric should not exceed 60°C due to creasing in rope form scouring

No use of anionic detergent

Careful care for saponification under alkaline condition Scouring without tension due decrease in tensile strength under wet condition

3.2.4 Synthetic fibers scouring Unlike cotton and wool, synthetic fibers do not contain natural impurities. Thus, the scouring process is easier and only carried out with the aim of removing spin finishes, processing and coning oils, antistatic agents, size, dirt and sighting colors. Common methods for synthetic fibers scouring are summarized in Table 3.1 based on the report from Karmakar (1999).

3.3 NANOSCOURING In parallel with nano TiO2 application in water and air remediation fields (Shaham-Waldmann and Paz, 2016), use of titania nanoparticles on textile substrates has been also widely studied (Montazer and Pakdel, 2011). This led to the development of multifunctional textiles possessing various properties,

Nanoscouring

43

including self-cleaning, antibacterial, UV protection, hydrophilicity/ hydrophobicity, flame retardant, moth proofing, and others (Montazer and Seifollahzadeh, 2011; Montazer et al., 2011; Nazari et al., 2011; Hashemikiaa and Montazer, 2012). Montazer and Morshedi (2012) were the first who successfully utilized the photocatalytic activity of TiO2 nanoparticles for textile pretreatment, namely, scouring. Their approach was based on the capability of active oxygen species and hydroxyl radicals formed through TiO2 UV-light excitation, oxidizing organic compounds to carbon dioxide and water as shown in reaction (3.1): Cn Om Hð2n
2m + 2Þ + • OH + O2
! nCO2 + ðn
m + 1ÞH2 O

(3.1)

In fact, the photocatalytic activity of nano TiO2 was used to study the possible decomposition of hydrophobic impurities from desized cotton to obtain the hydrophilic cotton. Consequently, their proposed method was regarded as “nanophotoscouring.” In a typical nanophotoscouring method proposed by Montazer and Morshedi (2012) (Fig. 3.2), desized cotton fabrics were finished with Degussa P25 titanium dioxide nanoparticles through exhaustion or paddry-cure method. First, the aqueous TiO2 dispersion was prepared by adding 10% crosslinking agent (citric acid, CA), 6% sodium hypophosphite, 0.05% sodium dodecyl sulfate (SDS), and 0.5–10 g/L titanium dioxide nanoparticles in distilled water using ultrasonic bath for 15 min. Through the padding method, the desized cotton fabrics were impregnated in nano TiO2 dispersion for 1 min, padded with 80% wet pick-up, and then dried at 100°C and cured at 150°C for 4 min. Exhaustion was carried out by impregnating the fabrics in the prepared dispersion using ultrasonic bath for 10 min, following by drying at 100°C, and curing at 150°C for 4 min. The treated fabrics irradiated under UV-A lamps for 10 min or daylight for 7 days. Under the applied conditions, the crosslinking action of CA with cellulose and ionic interaction of nano TiO2 with free carboxylate groups of CA occurred. Nanocrosslinking phenomenon in presence of TiO2 nanoparticles and carboxylic acids has been comprehensively discussed in Chapter 8.

3.3.1 Nanophotoscouring of cellulosic fibers Raw cotton fibers include impurities such as pectin, protein, wax, hemicellulose, and natural pigments. Pectin is the methylated ester of poly galacturonic acid with 300–1000 units. Pentose, hexose, and uronic acids include the

44

Nanofinishing of Textile Materials

Cotton fabric

Desizing

Nano TiO2 dispersion 0.5–10 g/L nano TiO2, 6% SHP, 10% CA, 0.05% SDS Pad/dry/cure

Exhaustion

Impregnation, Padding (pick-up 80%), drying, curing at 150°C for 4 min

Treatment in ultrasonic bath for 10 min, drying, curing at 150°C for 4 min

Irradiation

UV-A (10 min)

Daylight (7 days)

Nano photo scoured cotton

Fig. 3.2 Typical cotton nanophotoscouring as proposed by Montazer and Morshedi (2012).

chemical structure of hemicellulose. Primary alcohols (CnH2n+1OH), normal fatty acids (CnH2nO2) from C24 to C34, some fatty acids such as palmitic acid, stearic acid, and oleic acid, compounds including glycerol, amyrin, resinous materials, and hydrocarbons can be found in cotton wax. Under UV light irradiation of TiO2 nanoparticles, negative electron and positive hole pairs are generated that react with oxygen and water molecules producing superoxide and hydroxyl radicals (reactions 3.2–3.6). The pectin and hemicellulose with polysaccharide structure will be depolymerized by the oxidizing radicals. Moreover, the generated anion radicals react with stearic and oleic acid causing fatty acids degradation. Through the applied nanophotoscouring procedure, the oxidizing radicals, including •OH, RO•, and RO•2, are also responsible for discoloration of natural pigments

Nanoscouring

45

existing in cotton (reactions 3.7–3.18). Thus, nano TiO2 can act as a bleaching agent, producing white cotton fabric. The nanophotobleaching effect of nano TiO2 particles is thoroughly discussed in Chapter 4. TiO2 + hν ! e
+ h +


•

e + O2 ! O2





•

(3.2)




(3.3)

e + O2 + 2H ! H2 O2

(3.4)

e
+ H2 O2 ! • OH + OH


(3.5)

h + + H2 Oads ! • OHads + H +

(3.6)

RCH2 COOH + h + ð• OHÞ ! RCH2 • + CO2 + H2 O

(3.7)

+

•

RCH2 + O2 ! RCH2 OO •

•

(3.8)

OH + H2 O2 ! H2 O + • OOH

(3.9)

RCH2 O2 • + • OOH ! RCH2 OOOOH

(3.10)

RCH2 OOOOH + RCH2 COOH ! RCH2 OH + RCHO + O2 + CO2 (3.11) RCOOCH3 + h + ð• OHÞ ! RCH3 • + CO2 + H2 O RCH2 OH + • OH ! RCHOH• + H2 O •

•

(3.12) (3.13)

RCHOH + H2 O ! RCHðOHÞ2 + H

(3.14)

RCHðOHÞ2 ! H2 O + RCHO

(3.15)

RCHO + • OH ! RCO + H2 O

(3.16)

•

RCO + H2 O ! RCOOH + H •

RCOOH + h ! R + CO2 + H +

(3.17) +

(3.18)

In addition to the simultaneous scouring and bleaching effects of the proposed method, the nano TiO2-treated fabrics benefit from multifunctional properties brought by nano TiO2, including self-cleaning, UV protection, and antibacterial. The only obstacle to the use of nanophotoscouring for cotton fabric through the proposed method was decreased tensile strength of the treated fabrics due to the acidic conditions of the process. According to the reports, in situ synthesis of nano TiO2 particles on cotton fabric instead of ex situ method can rise to the challenge. In a typical procedure, cotton fabrics were in situ treated in an ultrasonic bath containing titanium tetra isopropoxide and acetic acid (50 kHz, 50 W) (Akhavan and Montazer, 2014).

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Nanofinishing of Textile Materials

The process continued for 4 h at 75°C. Sonochemical method was effective in covalent bonding between the hydroxyl groups of cotton and TiO2 with no detrimental effect on the tensile strength of the treated fabric. Although Montazer and Morshedi (2012) suggested the nanophotoscouring of cotton fabrics treated with nano TiO2 using exhaustion or pad-dry-cure methods, any nanophotocatalysts with proper band gap capable of exciting under UV and visible lights can be applied on cotton fabrics as nanophotoscouring and nanophotobleaching agents producing hydrophilic white scoured cotton. The nanotreatment could be carried out through ex situ method or by using in situ synthesis and deposition of nanophotocatalysts.

3.3.2 Nanophotoscouring of protein fibers Nanophotoscouring technique is not limited to cellulosic fibers and can be broadened for scouring of all natural fibers due to the ability of nanophotocatalysts to decompose natural waxes and other hydrophobic impurities. The proposed nanophotoscouring technique is effective for decomposing the impurities of wool especially waxes consisting of esters of various long-chain fatty acids with long-chain alcohols and sterols (Sherrard et al., 1995), leaving a scoured bleached wool. As silk fibers are generally composed of 1.5–2% wax and fat, nanophotoscouring reactions could be also effective to decompose these impurities. Wool wax is rich in esters of 1- and 2-alkanols and 1,2-diols, sterol esters, triterpene alcohols, and free acids and sterols. A sterol component is mainly composed of lanosterol and the fatty acid components are saturated with isoand anteiso-methyl branched chains. As proved by Gauthier et al. (2006), photocatalysts such as nano TiO2 are capable of degrading esters into aldehyde and alcohols, which could be further decomposed by oxidizing radicals, including •OH, RO•, and RO•2 as discussed earlier. Similar to nanoscouring of cellulosic fibers, any nanophotocatalysts with proper band gap capable of exciting under UV and visible light can be applied for wool nanoscouring. For instance, nano ZnO particles have been in situ synthesized on wool fabric in one single-step method using alkaline medium. Zinc acetate was a precursor and the process was in water and water/ethanol media. After 7 days of sunlight irradiation, the wool samples were photocatalytically active to decompose natural waxes and hydrophobic impurities. Reactive oxygen species and hydroxyl radicals were formed, which were capable of impurities destruction by producing

Nanoscouring

47

scoured sample (Montazer et al., 2013). Photocatalytic reactions on wool are also effective to decompose wool natural pigments, namely, melanin producing wool fibers with less yellowness (Montazer and Morshedi, 2014). Nanophotobleaching of wool using photocatalysts is thoroughly discussed in Chapter 4.

3.3.3 Nanophotoscouring of synthetic fibers Nanophotoscouring can be also adapted to decompose the impurities of synthetic fibers generally oils. Sighting and tinting colors, which are added to identify different fiber grades, could be also effectively degraded through photocatalytic reactions using nanophotocatalysts. In Fig. 3.3, nanophotoscouring is schematically represented.

Fig. 3.3 Schematic representation of nanophotoscouring.

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Nanofinishing of Textile Materials

3.3.4 Nanobiophotoscouring It has been claimed that the photocatalytic activity of photocatalysts is enhanced by using hybrid photocatalysts composed of photocatalysts and redox enzymes. The favorable effect is derived from synergistic redox reaction occurring by photocatalysts as well as by the enzymes (Kamad and Sohb, 2015). Taking this into account, there is a possibility of enhancing the nanophotoscouring effect of photocatalysts by incorporating biocatalysts, namely, enzymes regarding as nanobiophotoscouring. Here, the enzyme specifically acts on the impurities, while further degradation occurs via photocatalytic reactions under light irradiation.

3.4 CONCLUSION Overviewing scouring history during the last decades shows considerable concern about complexity, effluent load, water, chemicals, and energy consumption. Researchers have made tremendous efforts to propose facial methods with less chemical usage that guarantees time and energy saving along with maximum scouring efficiency. In this contribution, nanotechnology provides the opportunity for simultaneous scouring and multifunctional finishing. The photocatalytic activity of nano TiO2 particles for decomposing organic materials under UV and/or sunlight irradiation has been beneficially used to introduce nanophotoscouring phenomenon on cotton fabric. Pectin, wax, and natural pigments of desized cotton fabric could be effectively decomposed through nano TiO2 treatment. Similar effect of photocatalytic scouring can be achieved on various natural and synthetic fibers using other nanophotocatalysts with proper band gap capable of exciting under UV and/or visible light. Nanophotoscoured fabrics possess multifunctional properties brought about by nanoparticles and are whiter due to the simultaneous nanophotobleaching effect of the photocatalyst. Special care toward the method of treating the fabrics with nanophotocatalysts is required in order to guarantee enhanced performance and higher durability with lower environmental toxicity. In this regard, in situ treatments may rise to the challenge. Moreover, nanobioscouring, which is the incorporation of photocatalysts together with enzymes, could be effective, as the enzyme is specifically acts on the impurities and further degradation occurs via photocatalytic reactions under light irradiation. This will end at increased scouring level and is ecologically more favorable.

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REFERENCES Agrawal, P.B., Nierstrasz, V.A., Warmoeskerken, M.M.C.G., 2008. Role of mechanical action in low-temperature cotton scouring with F. solani pisi cutinase and pectate lyase. Enzym. Microb. Technol. 42, 473–482. Akhavan, F., Montazer, M., 2014. In situ sonosynthesis of nano TiO2 on cotton fabric. Ultrason. Sonochem. 21, 681–691. Aksel Eren, H., Erismis, B., 2013. Ultrasound-assisted bioscouring of cotton. Color. Technol. 129, 360–366. Bahrum Prang Rocky, M.K., 2012. Comparison of effectiveness between conventional scouring and bio-scouring on cotton fabrics. Int. J. Sci. Eng. Res. 3, 1–5. Bahtiyari, M.I., Duran, K., 2013. A study on the usability of ultrasound in scouring of raw wool. J. Clean. Prod. 41, 283–290. Calafell, M., Garrig, P., 2004. Effect of some process parameters in the enzymatic scouring of cotton using an acid pectinase. Enzym. Microb. Technol. 34, 326–331. Choe, E.K., Nam, C.W., Kook, S.R., Chung, C., Cavaco-Paulo, A., 2004. Implementation of batchwise bioscouring of cotton knits. Biocatal. Biotransformation 22, 375–382. Degani, O., Gepstein, S., Dosoretz, C.G., 2002. Potential use of cutinase in enzymatic scouring of cotton fiber cuticle. Appl. Biochem. Biotechnol. 102, 277–289. Fong, W., Yeiser, A.S., Lundgre, H.P., 1951. A new method for raw-wool scouring and grease recovery. Text. Res. J. 21, 540–555. Freytag, R., Donze, J.J., 1983. Alkali treatment of cellulose fibers. In: Lewin, M., Sello, S.B. (Eds.), Chemical Processing of Fibers and Fabrics Fundamentals and Preparation, Part A. In: Handbook of Fiber Science and Technology, vol. 1. Marcel Dekker, New York. Gauthier, E., Boyer, C., Thivel, P.X., Delpech, F., Rou, J.C., 2006. Experimental study of odorous ester photocatalysis. Environ. Eng. Manag. J. 5, 1001–1010. Hasanbeigi, A., Price, L., 2015. A technical review of emerging technologies for energy and water efficiency and pollution reduction in the textile industry. J. Clean. Prod. 95, 30–44. Hashemikiaa, S., Montazer, M., 2012. Sodium hypophosphite and nano TiO2 inorganic catalysts along with citric acid on textile producing multi-functional properties. Appl. Catal. A Gen. 417-418, 200–208. Kamad, K., Sohb, N., 2015. Enhanced visible-light-induced photocatalytic activity of α-Fe2O3 adsorbing redox enzymes. J. Asian Ceramic Soc. 3, 18–21. Karapinar, E., Sariisik, M.O., 2004. Scouring of cotton with cellulases, pectinases and proteases. Fibres Text. East. Eur. 12, 79–82. Li, Q., Hurren, C.J., Wang, L.J., Lin, T., Yu, H.X., Ding, C.L., Wang, X.G., 2011. Frequency dependence of ultrasonic wool scouring. J. Textile Inst. 102, 505–513. Li, Q., Hurren, C.J., Yu, H., Ding, C., Wang, X., 2012a. Thermal and mechanical properties of ultrasonically treated wool. Text. Res. J. 82, 195–202. Li, Q., Lin, T., Wang, X., 2012b. Effects of ultrasonic treatment on wool fiber and fabric properties. J. Text. Inst. 103, 662–668. Li, Q., Ding, C., Yu, H., Hurren, C.J., Wang, X., 2014. Adapting ultrasonic assisted wool scouring for industrial application. Text. Res. J. 84, 1183–1190. Mahmoodi, N.M., Arami, M., Mazaheri, F., Rahimi, S., 2010. Degradation of sericin (degumming) of Persian silk by ultrasound and enzymes as a cleaner and environmentally friendly process. J. Clean. Prod. 18, 146–151. McNeil, S.J., McCall, R.A., 2011. Ultrasound for wool dyeing and finishing. Ultrason. Sonochem. 18, 401–406. Montazer, M., Morshedi, S., 2012. Nano photo scouring and nano photo bleaching of raw cellulosic fabric using nano TiO2. Int. J. Biol. Macromol. 50, 1018–1025. Montazer, M., Morshedi, S., 2014. Photo bleaching of wool using nano TiO2 under daylight irradiation. J. Ind. Eng. Chem. 20, 83–90.

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Montazer, M., Pakdel, E., 2011. Functionality of nano titanium dioxide on textiles with future aspects: Focus on wool. J. Photochem. Photobiol. C: Photochem. Rev. 12, 293–303. Montazer, M., Seifollahzadeh, S., 2011. Enhanced self-cleaning, antibacterial and UV protection properties of nano TiO2 treated textile through enzymatic pretreatment. Photochem. Photobiol. 87, 877–883. Montazer, M., Pakdel, E., Behzadnia, A., 2011. Novel feature of nano-titanium dioxide on textiles: antifelting and antibacterial wool. J. Appl. Polym. Sci. 121, 3407–3413. Montazer, M., Maali Amiri, M., Mohammad Ali Malek, R., 2013. In situ synthesis and characterization of nano ZnO on wool: influence of nano photo reactor on wool properties. Photochem. Photobiol. 89, 1057–1063. Nazari, A., Montazer, M., Moghadam, M.B., Anary-Abbasinejad, M., 2011. Self-cleaning properties of bleached and cationized cotton using nanoTiO2: a statistical approach. Carbohydr. Polym. 83, 1119–1127. Presa, P., Forte Tavcer, P., 2008. Bioscouring and bleaching of cotton with pectinase enzyme and peracetic acid in one bath. Color. Technol. 124, 36–42. Sedelnik, N., 2003. Biotechnology to improve the quality of wool. Res. J. Text. Appar. 7, 1–10. Shaham-Waldmann, N., Paz, Y., 2016. Away from TiO2: a critical mini review on the developing of new photocatalysts for degradation of contaminants in water. Mater. Sci. Semicond. Process. 42, 72–80. Shen, J., 2010. Enzymatic treatment of wool and silk fibers. In: Nierstrasz, V., CavacoPaulo, A. (Eds.), Advances in Textile Biotechnology. Woodhead Publishing, Cambridge. Sherrard, K.B., Marriott, P.J., Amiet, R.G., Colton, R., McCormick, M.J., Smith, G.C., 1995. Photocatalytic degradation of secondary alcohol ethoxylate: spectroscopic, chromatographic, and mass spectrometric studies. Environ. Sci. Technol. 29, 2235–2242. Thompson, T.E., 1940. The Scouring of Raw Wool in Theory and Practice. Emmott, Manchester (Textile manufacturer monographs). Tomasino, C., 1992. Chemistry and Technology of Fabric Preparation and Finishing. Chemistry and Science College of Textiles. North Carolina State University, NC, USA. Tzanov, T., Calafell, M., Guebitz, G.M., Cavaco-Paul, A., 2001. Bio-preparation of cotton fabrics. Enzym. Microb. Technol. 29, 357–362. Vouters, M., Rumeau, P., Tierce, P., Costes, S., 2004. Ultrasounds: an industrial solution to optimize costs, environmental requests and quality for textile finishing. Ultrason. Sonochem. 11, 33–38. Wang, Q., Fan, X., Hua, Z., Gao, W., Chen, J., 2007. Degradation kinetics of pectins by an alkaline pectinase in bioscouring of cotton fabrics. Carbohydr. Polym. 67, 572–575. WDS, 2016. Eco-efficient wool dry scouring with total by products recovery. Available at www.life-wds.eu.

SOURCES OF FURTHER INFORMATION Karmakar, S.R., 1999. Chemical Technology in Pretreatment Process of Textiles. Elsevier, USA. Marsh, J.T., 1946. In: Marsh, J.T. (Ed.), An Introduction to Textile Finishing. Chapman and Hall, London. Tomasino, C., 1992. Chemistry and Technology of Fabric Preparation and Finishing. Chemistry and Science College of Textiles North Carolina State University, USA.

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Nanobleaching 4.1 INTRODUCTION Although scouring is effective in removing the impurities of natural fibers, the coloring matters still remain in the fibers giving yellowish and brown look to the fibers. Thus, another preparatory step called bleaching is required to destroy the coloring matter, producing whiteness along with minimum detrimental effect on the fibers strength. Bleaching can be a separate preparatory process or may be combined with desizing and scouring depending on the applied procedures and economic factors (Xie et al., 2012). In addition to the necessity of bleaching for removing the coloring matters of cotton fabrics making them whiter, subsequent proper dyeing and finishing treatment of cotton fabric are dependent on satisfactory bleaching. Bleaching agents are generally categorized into oxidizing or reductive agents capable of oxidizing or reducing the coloring matter (Fig. 4.1). There are also some cases of combining reducing and oxidizing agents to achieve proper bleaching effect, for instance, in silk bleaching (Karmakar, 1999).

4.2 PROGRESS IN BLEACHING: A SHORT HISTORICAL OVERVIEW 4.2.1 Cotton bleaching There has been an intensive progress in bleaching of cellulosic fibers since 18th century when steeping of fibers in ashes of plants for several days following by soaking the fibers in sour milk was used by Egyptians to obtain a desired whiteness. Since that time, several progressive approaches have been introduced to impart maximum whiteness into cellulosic fibers with minimum fiber damage and reduced processing time. 1756 was the year of sour milk replacement by sulfuric acid, resulting in great bleaching time reduction from 2 months to 12–24 h. This advance was followed by the introduction of chlorine gas as a bleaching agent. However, this finding could never reach success due to toxic hazards. Real progress has been made when bleaching powder was produced by Tennant in 1799, which contained Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00004-2

© 2018 Elsevier Ltd. All rights reserved.

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Oxidizing Chlorines: Calcium/ sodium/ lithium hypochlorite, sodium chlorite chloramine, isocynual trichloride Peroxides: Hydrogen peroxide, sodium peroxide, sodium perborate, potassium permanganate, peracetic acid

Reductive

Sulphur dioxide, sodium hydrosulphite, sulphoxylates, acidic sodium sulphite, sodium bisulphites

Fig. 4.1 Bleaching agents classification.

calcium hypochlorite as the main component. Bleaching effect of calcium hypochlorite was based on oxidizing action of hypochlorous acid (Karmakar, 1999). In spite of strong bleaching activity of acidic hypochlorous, it caused cellulose degradation through oxycellulose formation. Thus, pH adjustment was a key factor for obtaining controlled bleaching. The substitution of sodium hypochlorite for bleaching powder was successfully brought about with several advantages. Sodium hypochlorite was easily handled due to water solubility. Bleaching with sodium hypochlorite could be carried out in shorter time due to penetration into the fabric. Sodium hypochlorite was free from calcium carbonate; thus, it did not suffer from lime deposition on the fiber during bleaching, as it occurred in bleaching powder. Bleaching with sodium hypochlorite could be achieved at milder pH, compared with high alkalinity required for calcium hypochlorite (Karmakar, 1999). The bleaching activity of sodium hypochlorite arises from hypochlorous acid formed in water based on reaction (4.1). NaOCl + H2 O ! Na + + OCl ! HOCl + HO

(4.1)

Posttreatment of bleached samples with HCl for neutralizing the alkali and with sodium thiosulfate or bisulfate for chlorine removal is also required following by fabric rising with water. The bleaching is carried out in batch equipment (1.5 g/L NaOCl and 5 g/L Na2CO3) due to prevention of chlorine liberation in to the atmosphere. The optimum pH for controlled bleaching is 9.5–11, providing less detrimental effect on fibers. The pH is adjusted using sodium carbonate as a buffer. More acidic conditions

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(pH < 5) produce large chlorine gas content with no bleaching effect, while 5 < pH < 8.5 causes severe damage to the fibers. Bleaching is carried out at 40°C for 1 h (Karmakar, 1999). Researchers have focused on introducing some methods to accelerate the bleaching effect of sodium hypochlorite at reduced bleaching time and lowered chlorine consumption. For instance, decreasing the pH value to 7, at which hypochlorous and hypochlorite ions are almost in the same level, was effective in achieving the enhanced bleaching within 10 min, however, at the expense of cellulose severe damage. In this regard, in order to minimize the negative effects on the fiber, use of sulfamic acid as a stabilizer was found effective. Another approach was the addition of bromides converting sodium hypochlorite into more active oxidant, namely, sodium hypobromite (Karmakar, 1999). In spite of advantages of sodium hypochlorite, it was only in wide usage until 1940 since peroxide bleaching was introduced, making continuous cotton bleaching possible using J-box or open-width steamers. Some of the disadvantages involved in sodium hypochlorite bleaching limiting its application are as follows: – Disability in achieving complete satisfactory whiteness – Demand for full prescouring of cotton fibers to remove any fats, oils, and waxes – Glucose linkage decomposition causing tensile strength loss – Equipment limitation due to corrosion effect – Unpleasant chlorine odor – Environmental harmful effect due to formation of chlorinated organic by-products Today most cotton fabrics are bleached with hydrogen peroxide, which decomposes into perhydroxyl ion in water acting as a bleaching agent. Contrary to sodium hypochlorite, hydrogen peroxide bleaching does not require complete prescouring of fabrics and can be done by continuous equipment. The harmful effect of hydrogen peroxide on cotton fibers is less than that of sodium hypochlorite. From environmental point of view, peroxide bleaching is free from all unpleasant odors or harmful materials liberation. Thus, hydrogen peroxide has been introduced as environmentally benign bleaching agent. Controlled bleaching is achieved by regulating the pH, at which sufficient perhydroxyl ions formed. Based on the literature, pH between 10.2 and 10.7 is the best condition, while higher pH resulted in oxygen gas formation with no bleaching effectiveness (Karmakar, 1999). Acidic condition also hindered the production of perhydroxyl ion due to the presence of unneutralized hydrogen ion according to reaction (4.2).

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H2 O2 + H2 O ! H + + HO2 

(4.2)

In spite of the only claim made by Dannacher and Schlenker in 1996 (Hashem et al., 2010) who proposed that the active superoxide radical formed from perhydroxyl ion is responsible for bleaching, there is a general agreement that perhydroxyl anion plays the key role in hydrogen peroxide bleaching. Based on reaction (4.2), bleaching is more effective in presence of alkali for neutralizing the H+ ion. Optimizing the peroxide bleaching was further achieved through the addition of materials called stabilizers into the bleaching bath. With the aid of stabilizers, peroxide is prevented from decomposition at high temperature; thus, bleaching activity is enhanced along with minimum fiber degradation. Stabilizers range from alkalis such as sodium hydroxide, sodium carbonate and silicates to phosphates, including tetrasodium pyrophosphate and hexametaphosphate, sequestering agents, namely, EDTA and gluconates, and inorganic stabilizers such as magnesium salts. Although there is no specific recipe for cotton bleaching with peroxide, and the bleaching condition is different depending on the fibers quality, bleaching equipment, and bleaching level, typical bleaching occurs at 90–100°C, with 2–4% o.w.f. (on weight of fiber) hydrogen peroxide for batch systems and 1–2% o.w.f. for continuous processes for 6–10 h. During the recent history, many of the research studies in the field of cotton bleaching have been devoted to activating the bleaching efficiency of hydrogen peroxide through facial methods. Decreased bleaching time and/ or temperature along with increased bleaching activity together with less cotton strength loss were among the researchers’ goals. Some of the studies are related to peroxide bleaching activators, which basically are peracid precursors that react with hydrogen peroxide in an aqueous solution leading to in situ formation of peracids (Xu et al., 20111), which are stronger bleaching agents at milder conditions. Peroxide activators are grouped into neutral, anionic, and cationic activators such as N,N,N0 ,N0 -tetra acetyl ethylene diamine (TAED) (Zhao et al., 2010; Long et al., 2013; Xu et al., 2013), nonanoyl benzene sulfonic acid (NOBS) and (N-[4-triethylammoniomethyl]-benzoyl) caprolactam chloride (TBCC) (Hou et al., 2010; Chen et al., 2016). Among various bleaching activators, cationic ones are more interesting due to the better water solubility providing satisfactory results. For instance, by use of N-[4-(triethylammoniomethyl) benzoyl] butyrolactam chloride (TBBC) in peroxide bleaching bath, high bleaching efficiency has been achieved at 40–60°C for 30 min at neutral pH (Xu et al., 2015). TBBC was more effective than TBCC due to the enhanced hydrolytic stability (Xu et al., 2015).

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Thiourea has been successfully introduced as an activator for hydrogen peroxide bleaching at reduced time, namely, 1 h. Formation of hydrogen peroxide-thiourea complex, following by hydroxyl free radicals were responsible for the improved whiteness of cotton fabrics (Abdel-Halim and Al-Deyab, 2013). Another type of enhanced peroxide bleaching systems are those obtained by cellulose fabric modification mainly through precationization providing improved whiteness at reduced time and temperature (Hashem et al., 2010; Xie et al., 2012). In some cases, precationized cellulose fabrics are bleached in presence of peroxide activators to achieve the maximum bleaching. Cellulose modification by triazine derivative, namely, 2,4,6-tri[(2-hydroxy-3-trimethylammonium)propyl]-1,3,5-triazine chloride (Tri-HTAC) resulted in enhanced low-temperature (60°C) bleaching in presence of tetra acetyl ethylene diamine (TAED), tetra acetyl glycineurea (TAGU), or TBCC as peroxide activators (Xie et al., 2012). Enzymatic cotton bleaching by peroxidases, laccases/mediator systems, and glucose oxidases has been widely researched as an environment-friendly approach. Although peroxidases are effective activators of oxidizing agents, their inclusion in peroxide bleaching of cotton fabrics was not as effective as expected. This was due to the reduced activity of the enzyme caused by hydrogen peroxide attack (Paul and Genesca, 2013). Laccases/mediator system was an effective pretreatment in enhancing the hydrogen peroxide bleaching efficiency on cotton fabrics, with the merits of lower hydrogen peroxide consumption along with reduced bleaching temperature and time (Tian et al., 2012). Based on the study carried out by Farooq et al., 2013, glucose oxidases were good candidates for hydrogen peroxide formation with the ability to replace conventional methods, providing satisfactory whiteness along with appropriate mechanical and enhanced comfort properties (Farooq et al., 2013). Moreover, gluconic acid, which formed during the conversion of glucose into hydrogen peroxide, is a chelating agent eliminating the need for any stabilizers in bleaching process. In spite of these merits, higher concentration of hydrogen peroxide formed by enzymatic treatment is required for comparable bleaching effect (Paul and Genesca, 2013). High cost and relatively slow reaction rate of enzyme bleaching encouraged the researchers to combine ultrasound and enzyme treatment for enhanced biobleaching efficiency. Efforts were made to enhance the enzymatic activity by incorporation of ultrasound energy, intensifying the enzyme diffusion into fibers. In spite of synergistic effects of ultrasound

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and enzymatic treatment on enhanced bleaching, the process condition (ultrasound power) should be controlled to reduce the possibility of enzyme inactivation under ultrasound energy, eliminating the demand for the use of stabilizers (Basto et al., 2007). Increased whiteness and reduced hydrogen peroxide consumption along with reduced bleaching temperature and time were reported using laccases/peroxide/ultrasound process (Gonc¸alves et al., 2014a). Following the great success in introduction of ultrasound to cotton biobleaching, a pilot reactor for laccases/hydrogen peroxide/ultrasound was scaled up by adding a piezoelectric ultrasonic device into a conventional dyeing machine (Gonc¸alves et al., 2014b). Another oxidative bleaching agent introduced for cotton was sodium chlorite, which benefits from excellent whiteness along with little cellulose degradation. This arises from the specific action of sodium chlorite with aldehyde groups rather than affecting on hydroxyl or glucosidic linkages. Chlorite ion (chlorine dioxide), which is formed from the acidified sodium chlorite solution, is responsible for the bleaching effect. Bleaching activity is only possible under acidic condition adjusted by buffers. In spite of the advantages, toxicity of chlorine dioxide gas and problem of corrosion restricted the cotton bleaching with sodium chlorite, although several approaches have been proposed to control the gas evolution and corrosiveness of chlorine dioxide. These include equipment enhancement such as use of fiber glass J-Box and surface coating with polyester resin, application of discontinuous processes, including closed jigger, addition of nitrogencontaining scavengers into the bleaching bath to adsorb chlorine, and use of activators such as magnesium dihydrogen phosphate to increase the pH condition. Although not successful in commercial range, cotton bleaching with peracetic acid has been also conducted and the mechanism is suggested to be similar to H2O2. Optimum bleaching condition is at 50–80°C for 20–60 min at pH ¼ 6–7. However, appropriate whiteness is achieved using a two-step bleaching procedure with peracetic acid in J-Box following by alkaline hydrogen peroxide bleaching (Karmakar, 1999).

4.2.2 Wool bleaching Contrary to cotton, the only well-known and effective oxidative bleaching agent for wool is hydrogen peroxide. Bleaching can be carried out under

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alkaline (pH ¼ 8–10) or acidic conditions (pH ¼ 4). However, acidic process is more desirable due to lower wool degradation and no requirement for post rising of the fibers. Similar to cotton bleaching with peroxide, activators have been added to the wool-bleaching bath to enhance the attained whiteness along with reduced time and temperature. Most activators include organic salts that form carboxylic acids. In addition to wool bleaching in aqueous solution, the emulsion of hydrogen peroxide in perchloroethylene has been found as an effective bleaching agent with the merits of reduced bleaching time and peroxide consumption, with more detrimental effect on wool mechanical properties (Karmakar, 1999). Traditionally, wool fibers were bleached with reductive bleaching agents, namely, sulfur dioxide and sodium bisulfite. However, due to many demerits of the process such as temporary whitening effect, the need for post oxidizing treatment and long time, these methods have been diminished. Next approach was use of sodium hydrosulfite named as hydro, which can be applied in nonstabilized form at lower temperature or along with stabilizers at higher temperature providing enhanced whiteness. The main drawback was fabric harsh hand, restricting its wide application. The most cost-effective approach was wool bleaching with thiourea dioxide as a reducing agent with less toxic effluents (Karmakar, 1999). 4.2.2.1 Wool photobleaching Considering the interest in more environment-friendly bleaching methods, photobleaching of wool has been introduced as a promising dry method, though not economically attractive for industrial application. Bleaching efficiency of light irradiation strongly depends on wavelength, as UV range lower than 310 nm results in yellowing effect and whiteness occurred under visible light exposure (Launer, 1965). Thus, sunlight irradiation of wool fibers may have contradictory whitening or yellowing effect depending on its spectral composition. Due to this fact, different whiteness or yellowness caused by sunlight irradiation of wool has been reported by researchers around the world. For instance, sunlight wool exposure in Melbourne, Australia, indicated yellowing effect, while the same procedure in Europe caused bleaching.

4.2.3 Silk bleaching As degumming is not effective in complete color elimination of silk, bleaching is a necessary step to degrade the organic coloring matters in silk, which can be

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done using both oxidative and reductive bleaching agents. The optimum bleaching effect is achieved using hydrogen peroxide under alkaline condition and the pH is adjusted using ammonia or tetrasodium pyrophosphate, as different types of silk fibers may be sensitive to alkali. Sulfur dioxide, sodium hydrosulfite, and sodium sulfoxylates are among the reducing agents that have been used for silk bleaching, however with half bleaching effect. In some special cases where high whiteness is demanded, combination of reductive and oxidative bleaching agents is performed via two-step method (Karmakar, 1999).

Table 4.1 Common methods of synthetic fibers bleaching. Fiber type Method Remarks

Polyester

Nylon

Acrylic

Acetate

Viscose

Sodium chlorite bleaching at pH ¼ 3 (formic acid) for 1–2 h at 95°C. – Sodium chlorite, pH ¼ 3.5–4 (acetic acid) for 1 h at 80–85°C – Bleaching with peracetic acid is also possible at milder condition (neutral pH) – Reductive bleaching at acidic condition Hydrogen peroxide, hydrosulfite, or peracetic acid bleaching –

Hydrogen peroxide bleaching for 1 h at 45°C with addition of 1–3 g/L sodium silicate. – Sodium chlorite bleaching in presence of mono ammonium phosphate produced much higher bleaching effect. – Peracetic acid is also suitable for obtaining whitening effect. Alkaline hypochlorite in jigger or hydrogen peroxide bleaching under alkaline condition at 70°C with the addition of sodium silicate or peracetic acid bleaching

Antichlorination with thiosulfate is required as a posttreatment No use of sodium chlorite or hydrogen peroxide due to great tensile strength loss

Yellowness and instability to light occur in case of chlorite bleaching Combined scouring and bleaching is possible adding a nonionic detergent.

Bleaching is essential for viscose in staple form

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4.2.4 Synthetic fibers bleaching Common methods of synthetic fibers bleaching based on fiber type are summarized in Table 4.1 based on Karmakar (1999).

4.3 NANOPHOTOBLEACHING In parallel with introduction of nanophotoscouring of cotton fabric with TiO2 nanoparticles as detailed in Chapter 3, positive effect of the treatment on increased whiteness of the samples was also directed toward developing nanophotobleaching technique. The typical procedure of cotton treatment with TiO2 nanoparticles proposed by Montazer and Morshedi (2012) was described in Chapter 3. According to the obtained result, whiteness index of the nano TiO2-treated cotton fabrics increased compared with the desized cotton, which could be owing to two mechanisms. Firstly, nanophotocatalysts such as TiO2 are white pigments and their deposition on the treated fabric surface provides a whitening effect. Secondly, nanophotobleaching arose from the ability of nano TiO2 photocatalyst to decompose the coloring matters of cotton fabric. It is generally known that the yellowish or brown color of cotton fiber is related to the protoplasmic residues of protein and the flavones pigments of cotton flowers. The discoloration of cotton natural pigments was achieved by the photogenerated oxidizing radicals, including •OH, RO•, and RO•2 formed on TiO2 surface under light irradiation. Moreover, the efficiency of nanophotobleaching method was further evaluated in comparison with conventional hydrogen peroxide bleaching. While nanophotobleached cotton treated with 7 g/L TiO2 possesses equivalent whiteness to the hydrogen peroxide bleached cotton (0.5 g/L H2O2), nano TiO2 treatment provides multifunctional properties, including UV protection, hydrophilicity, selfcleaning, antibacterial, and anticreasing. In situ synthesis of ZnO nanoparticles on starch-sized raw cotton fabric was also investigated by Khosravian et al. (2015) to produce white cotton fabric using nanophotobleaching technique. In the proposed method, starch size assisted the synthesis procedure and controlled the size of nanoparticles. The proposed approach takes advantage of the dual role of ZnO as a photocatalyst and white pigment providing simultaneous self-cleaning and whiteness. Based on the statistical analysis carried out by the authors, the alkaline condition of the preparation procedure was the most important factor, affecting the nucleation, synthesis, and adsorption of more ZnO nanoparticles on the cellulosic fabric, producing higher whiteness.

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Similar to cotton, nanophotobleaching of wool fabrics was also successfully achieved using TiO2 nanoparticles. In a typical nanophotobleaching method, desized and proteases pretreated wool fabrics were finished with different concentrations of Degussa P25 titanium dioxide nanoparticles suspension containing 6% sodium hypophosphite and 10% citric acid in an ultrasonic bath for 10 min (Montazer and Morshedi, 2014). Drying the samples at 80°C, curing at 120°C for 2 min, following by sunlight exposure for 7 days were the final steps. It is generally known that the cream to yellow color of wool fibers, which is dependent on the living condition of the animal, is due to melanin precursors derived from tyrosine. Thus, wool bleaching is mainly dealt with melanin decomposition. Reactive species formed from nano TiO2 excitation under light irradiation, namely, hydroxyl radicals, hydrated electrons, singlet oxygen, and superoxide anion are capable of forming reaction with melanin causing ring opening through nucleophilic attack (Fig. 4.2). Therefore, natural wool pigments are degraded creating whiteness effect. Another positive role of nano TiO2 on wool bleaching is due to the UV absorbing effect, diminishing the possible wool photoyellowing under UV irradiation (Montazer and Morshedi, 2014). As reported by Montazer and Morshedi (2014), the bleaching efficiency of nano TiO2-treated samples was superior to those of wool fabrics bleached with hydrogen peroxide under conventional bleaching procedure. Beside to this merit, the nanophotobleached samples benefit from multifunctional properties arises from nano TiO2, including self-cleaning, UV protection, antifelting, mothproofing, and antibacterial activities. In another study, Montazer and Maali Amiri (2014) studied the nanophotobleaching effect of in situ synthesis of ZnO nanoparticles on wool fabric. Zinc acetate was used as a precursor and the synthesis process was carried out in water and water/ethanol media. The treated wool fabrics were heated at 80°C for 10 h to dehydrate Zn (OH)2 obtaining ZnO nanoparticles. The fabric samples were then subjected to daylight for 7 days. The yellowness index of the fabrics indicated a decreasing trend with an increase in pH, zinc acetate concentration, ethanol, and heating. In situ sonosynthesis and sonofabrication of nano TiO2 particles on wool fabric was successfully achieved through hydrolysis of titanium isopropoxide or titanium butoxide in acidic media under ambient pressure at 60–65°C. In addition to antibacterial/antifungal, self-cleaning, low cytotoxicity, and decreased alkaline solubility, the treated samples possess lower yellowness due to the formation of TiO2 particles as white nanopigment and the photocatalytic activities of TiO2 capable of degrading wool natural pigments (Behzadnia et al., 2014).

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Fig. 4.2 Schematic representation of nanophotobleaching.

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Increased photocatalytic activities of photocatalysts were also studied to impart higher nanophotobleaching effect. Photocatalysts doping with nonmetallic elements such as nitrogen, doping with transition or noble metals, and coupling with other semiconductors were among the successful approaches. Wool fabric with multifunctional activities, including photocatalytic, antibacterial/antifungal against Staphylococcus aureus, Escherichia coli, and Candida albicans, and increased tensile strength was produced through in situ photosonochemical synthesis of N-doped Ag/TiO2 nanocomposites (Behzadnia et al., 2016). The fabric was treated with titanium isopropoxide, silver nitrate, and ammonia in a sonobath for 1 h at 75–80°C. Due to the positive role of nitrogen and silver in enhancing the photocatalytic activities of nano TiO2 particles, lower yellowness was obtained for samples treated with N-doped Ag/TiO2 nanocomposites compared with samples only treated with TiO2 nanoparticles. Thus, nanophotobleaching effect is boosted using modified photocatalysts with enhanced abilities to generate electron–hole pairs and subsequent radicals under light irradiation. Further discussions on semiconductors modification methods are provided in Chapter 9. Similarly, N doped Ag/ZnO honeycomb-like nanocomposites were successfully photosonosynthesized and sonoimmobilized on wool fabric through a facile one-step method under ambient pressure at low temperature to obtain superior photocatalytic activities, resulting in enhanced nanophotobleaching effect (Behzadnia et al., 2015a). In the other study, Behzadnia and Montazer were successful to propose a method of in-situ sonosynthesis and sonofabrication of N-doped ZnO/TiO2 nanocomposite on wool fabric (Behzadnia et al., 2015b). The generation of electron–hole pairs through N-ZnO/TiO2 core-shell nanocomposite UV irradiation was more than N-TiO2 and N-ZnO nanoparticles. These pairs react with oxygen and water molecules producing superior superoxide and hydroxyl radicals. Subsequently, active radicals destroy the pigments of wool producing white wool. In addition to whiteness, the treated wool samples benefited from decreased alkaline solubility, self-cleaning, antibacterial and antifungal activities with low cytotoxicity. Thus, nanophotobleaching effect can be obtained through in situ or ex situ synthesis of various nanophotocatalysts on cotton or wool fabric samples.

4.4 CONCLUSION Recorded history indicated major breakthroughs in the field of textile bleaching all of which associated with more friendly techniques with less harmful effects on human and the environment together with enhanced

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whiteness and reduced detrimental effect on fiber inherent properties including tensile strength. Nanophotobleaching can be regarded as a progressive approach equivalent to conventional bleaching methods, capable of imparting simultaneous multifunctional properties into the treated fabrics. With the introduction of in situ nanofinishing methods, durable treatment of fabrics with nanophotocatalysts is possible providing whiteness through safe method with even increased tensile strength properties. Moreover, there is a possibility of nanobiophotobleaching of textile substrates to benefit from both the specific action of enzymes and photocatalytic degradation of natural pigments under light irradiation.

REFERENCES Abdel-Halim, E.S., Al-Deyab, S.S., 2013. One-step bleaching process for cotton fabrics using activated hydrogen peroxide. Carbohydr. Polym. 92, 1844–1849. Basto, C., Tzanov, T., Cavaco-Paulo, A., 2007. Combined ultrasound-laccase assisted bleaching of cotton. Ultrason. Sonochem. 14, 350–354. Behzadnia, A., Montazer, M., Rashidi, A., Mahmoudi Rad, M., 2014. Sonosynthesis of nano TiO2 on wool using titanium isopropoxide or butoxide in acidic media producing multifunctional fabric. Ultrason. Sonochem. 21, 1815–1826. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015a. In situ photo sonosynthesis and characterize nonmetal/metal dual doped honeycomb-like ZnO nanocomposites on wool fabric. Ultrason. Sonochem. 27, 200–209. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015b. Simultaneous sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core–shell nanocomposite on wool fabric: Introducing various properties specially nano photo bleaching. Ultrason. Sonochem. 27, 10–21. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2016. In situ photo sonosynthesis of organic/inorganic nanocomposites on wool fabric introducing multifunctional properties. Photochem. Photobiol. 92, 76–86. Chen, W., Wang, L., Wang, D., Zhang, J., Sun, C., Xua, C., 2016. Recognizing a limitation of the TBLC-activated peroxide system on low-temperature cotton bleaching. Carbohydr. Polym. 140, 1–5. Farooq, A., Ali, S., Abbas, N., Fatima, G.A., Ashraf, M.A., 2013. Comparative performance evaluation of conventional bleaching and enzymatic bleaching with glucose oxidase on knitted cotton fabric. J. Clean. Prod. 42, 167–171. Gonc¸alves, I., Martins, M., Loureiro, A., Gomes, A., Cavaco-Paulo, A., Silva, C., 2014a. Sonochemical and hydrodynamic cavitation reactors for laccase/hydrogen peroxide cotton bleaching. Ultrason. Sonochem. 21, 774–781. Gonc¸alves, I., Herrero-Yniesta, V., Arce, I.P., Castan˜eda, M.E., Cavaco-Paulo, A., Silva, C., 2014b. Ultrasonic pilot-scale reactor for enzymatic bleaching of cotton fabrics. Ultrason. Sonochem. 21, 1535–1543. Hashem, M., El-Bisi, M., Sharaf, S., Refaie, R., 2010. Pre-cationization of cotton fabrics: an effective alternative tool for activation of hydrogen peroxide bleaching process. Carbohydr. Polym. 79, 533–540. Hou, A., Zhang, X., Zhou, Y., 2010. Low temperature bleaching of cellulose fabric with (N-[4-triethylammoniomethyl]-benzoyl) caprolactam chloride as novel cationic activator for H2O2 bleaching. Carbohydr. Polym. 82, 618–622.

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Khosravian, S., Montazer, M., Malek, R.M.A., Harifi, T., 2015. In situ synthesis of nano ZnO on starch sized cotton introducing nano photo active fabric optimized with response surface methodology. Carbohydr. Polym. 132 (2015), 126–133. Launer, H.F., 1965. Effect of light upon wool, part IV: Bleaching and yellowing by sunlight. Text. Res. J. 35, 395–400. Long, X., Xu, C., Du, J., Fu, S., 2013. The TAED/H2O2/NaHCO3 system as an approach to low-temperature and near-neutral pH bleaching of cotton. Carbohydr. Polym. 95, 107–113. Montazer, M., Morshedi, S., 2012. Nano photo scouring and nano photo bleaching of raw cellulosic fabric using nano TiO2. Int. J. Biol. Macromol. 50, 1018–1025. Montazer, M., Morshedi, S., 2014. Photo bleaching of wool using nano TiO2 under daylight irradiation. J. Ind. Eng. Chem. 20, 83–90. Montazer, M., Maali Amiri, M., 2014. ZnO nano reactor on textiles and polymers: ex situ and in situ synthesis, application, and characterization. J. Phys. Chem. B 118, 1453–1470. Paul, R., Genesca, E., 2013. The use of enzymatic techniques in the finishing of technical textiles. In: Gulrajani, M.L. (Ed.), Advances in the Dyeing and Finishing of Technical Textiles, first ed. Elsevier, USA. Tian, L., Branford-White, C., Wang, W., Nie, H., Zhu, L., 2012. Laccase-mediated system pretreatment to enhance the effect of hydrogen peroxide bleaching of cotton fabric. Int. J. Biol. Macromol. 50, 782–787. Xie, K., Hu, C., Zhang, X., 2012. Low temperature bleaching and dyeing properties of modified cellulose fabrics with triazine derivative. Carbohydr. Polym. 87, 1756–1762. Xu, C., Hinks, D., El-Shafei, A., Hauser, P., Li, M., Ankeny, M., Lee, K., 2011. Review of bleach activators for environmentally efficient bleaching of textiles. J. Fiber Bioeng. Inform. 4, 209–219. Xu, C., Long, X., Du, J., Fu, S., 2013. A critical reinvestigation of the TAED-activated peroxide system for low-temperature bleaching of cotton. Carbohydr. Polym. 92, 249–253. Xu, C., Hinks, D., Sun, C., Wei, Q., 2015. Establishment of an activated peroxide system for low-temperature cotton bleaching using N-[4-(triethylammoniomethyl)benzoyl]butyrolactam chloride. Carbohydr. Polym. 119, 71–77. Zhao, Q., Pu, J., Mao, S., Qi, G., 2010. Process optimization of tetra acetyl ethylene diamine activated hydrogen peroxide bleaching of Populus nigra CTMP. BioResources 5, 276–290.

FURTHER READING Karmakar, S.R., 1999. Chemical Technology in Pretreatment Process of Textiles. Elsevier, USA. Marsh, J.T., 1946. In: Marsh, J.T. (Ed.), An Introduction to Textile Finishing. Chapman and Hall, London.

5

Nanosurface activation 5.1 INTRODUCTION Surface properties of textile substrates are important factors governing the performance of the material. These are including wettability, adsorption, adhesion, friction, and biocompatibility that are critical to the textile substrate functionality, performance, and application. Manipulation of surface properties makes functional modification of textile substrate possible to meet specific requirements for a variety of applications. Surface activation can be defined similar to the other methods used to alter the chemistry of surface introducing chemical groups or charges on the surface or physical changes created on the surface through etching, removing impurities by ablation, roughening, wavy shapes, and voids formation. On these bases, surface activation methods can be grouped into additional methods in which functional groups or charges are added to the surface and subtractive methods through which chemicals are removed from the surface. Sometimes, it is difficult to segregate different activation methods as they may involve both additional and subtractive approaches. For instance, through aminolysis of polyester, the morphological modification occurred on the fiber surface and at the same time amino functional groups are introduced to the surface. While surface activation can be carried out using chemical methods by the addition of specific chemical species, nonchemical forces such as gas plasma, vaporization, and irradiation have been also developed as physical methods. Regardless of the applied method, surface activation is used to reach general objectives, including alteration in surface energy, introducing polar functional groups, alteration in surface wettability, namely, hydrophilicity, enhanced dyeability, durable finishing, increased reactivity, and creation of biocompatibility. Hence, surface activation is not limited to synthetic fibers such as polyester with low surface free energy as nonpolar fibers, and can be applied for natural fibers, including cotton with hydroxyl functional groups and high wettability to enhance the adsorption properties of surface for enhanced dyeing and finishing. Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00005-4

© 2018 Elsevier Ltd. All rights reserved.

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Traditionally, surface activation methods were regarded as pretreatments to increase the reactivity, adhesion, and adsorption properties of the surface for the subsequent treatment mainly dyeing, finishing, and using for technical purposes. However, advent of nanotechnology has brought about a new category regarding as nanosurface activation, which includes the use of nanotechnology to provide morphological and chemical changes on fiber surfaces individually or in combination with other physical and chemical surface activation methods as pre-, post-, or simultaneous treatment. Basically, surface activation (functional groups or charges) directly arose from nanoparticles or nanocomposites deposited on fiber surface (in situ or ex situ nanofinishing) or may be physical surface alteration in nanoscale such as nanolayer, nanoroughness, or nanovoids. Moreover in some cases, durable attachment of nanoparticles, nanocomposites, or nanocoatings is not completely achieved, unless pre- or simultaneous surface activation has been applied through various activation methods.

5.2 SURFACE ACTIVATION METHODS Based on traditional classification, surface activation is achieved through chemical, physical, and biochemical methods. In chemical methods, textile is treated with chemical reagents to generate reactive functional groups or charges on the surface. For instance, penetration of polypropylene fibers in chromic acid and potassium permanganate to introduce oxygen-containing moieties was a traditional chemical surface activation method. On the other hand, physical approaches involve the surface modification of fibers through dry processes without using chemicals. The most common physical surface activation methods are plasma, laser, UV (ultraviolet), gamma, microwave, and ultrasound. Biochemical surface activation methods are environment-friendly routes using enzymes (John and Anandjiwala, 2009).

5.2.1 Surface activation of cellulosic fibers One of the important surface activation methods of cotton fibers is changing the surface charge by introducing cationic groups to the surface through cationization (Ramasamy, 2005). Among various cationic agents with amino, ammonium, sulfonium, and phosphonium groups, reaction of cellulosic fiber with quaternary ammonium compounds is the most common approach for cellulose cationization (Hashem et al., 2010). Firstly, cellulose cationization with quaternary ammonium group (+ N(CH3)3) is effective in ionic bond formation with negatively charged dye anionic groups providing salt-free dyeing of cotton (Monatzer et al., 2008; Acharya et al., 2014).

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Secondly, it is possible for cotton to form ionic bonding with carboxylcontaining compounds forming ionic crosslinking rendering wrinkle recovery (Hashem et al., 2003). Thirdly, cationized groups could impart antibacterial activity to cotton. Fourthly, cationization of cotton was effective for enhanced metal nanoparticles adsorption. As a result of hydroxyl group ionization, cellulose fibers possess slightly negative charge in water. This is not favored in processes involving nanoparticles with negative surface charge such as silver nanoparticles dispersions in water, repulsing the anions on the surface of nanoparticles. This reduces the amount of nanoparticles deposition on the cellulosic surface. Hence, the cationized cotton with positive charge with lower zeta potential of the fiber surface is beneficial for deposition of colloidal silver nanoparticles. Therefore, precationization of cotton is favorable for appropriate deposition of metal nanoparticles (Khalil-Abad et al., 2009). Among various cationic agents for cotton, most studies have been carried out with 3-(chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC). Cationization of cotton with CHPTAC is schematically shown in Fig. 5.1.

Fig. 5.1 Thiol surface activation, cationization, and carboxymethylation of cotton fibers.

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Alkaline treatment of cotton during which fiber structure converts from α-cellulose to β-cellulose provides the fabric with lustrous appearance. It has prominent effect on physical and chemical properties of cellulose fibers, including crystallinity, dyeability, and reactivity. It has been reported that through alkaline treatment of cellulosic fibers, a surface with more active sites for metallic ions adsorption is prepared (Yazdanshenas and ShateriKhalilabad, 2012). Direct immersion of alkali-treated cotton fabrics (immediately after alkaline treatment without neutralizing and drying) into silver salt solution is beneficial for silver ions adsorption on the cellulose fiber surface due to exchange that occurred from salt of Cell.O– to silver salt of Cell. O
Ag+. Moreover, oxycellulose can be produced through oxidation of cellulose in presence of alkali and oxygen. Thus, reduction of Ag+ ions to metallic silver is possible by the generated electrons. This occurred due to the possible conversion of cellulose hydroxyl groups into ketone, aldehyde, and carboxylate compounds (Yazdanshenas and Shateri-Khalilabad, 2012). Anionic groups such as carboxymethyl, phosphate, and sulfate groups have been also introduced into cotton cellulose producing anionic cotton. Sulfomethyl, sulfoethyl, and tartrate have been also used to alter the surface charge of cotton (Baugh et al., 1970). The main purpose of producing anionic cotton was to increase the wet soiling resistance. Moreover, it has been reported that phosphate groups impart flame-retarding properties. Carboxymethylation has been also reported as a method of stiffening cotton fabric. Among various anionic modifiers of cotton, carboxymethylation has been widely studied using monochloroacetic acid and sodium hydroxide as shown in Fig. 5.1 (Wang et al., 2015). Thiol modification of cellulosic fabric has been reported by fabric immersion in acidic solution containing thiol functional group, namely, mercaptoacetic acid. Thiol surface activation of cotton was effective for covalent attachment of metal nanoparticles such as silver and palladium to cotton based on thiol chemistry according to which soft acids such as noble metals with a relatively high electronegativity and large ionic radius bind covalently with soft bases such as thiol, sulfide, and phosphorus compounds with low electronegativity and radius (Park et al., 2012). Thiol surface activation of cotton is schematically shown in Fig. 5.1. Another surface activation method is called grafting in which radicals are formed on surface to initiate copolymerization reactions with different monomers. Although grafting is a chemical method of surface activation, it can be also grouped as physicochemical method as the source of radical generation could be UV light, plasma, and gamma or electron

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beam irradiation. Alteration in surface roughness has been also reported through graft copolymerization (Walo et al., 2015). Cellulose grafting with monomers containing hydroxyl and carboxylate has been proposed to enhance the adsorption of metal ions. Cotton fabric modification with cyclodextrin polyacrylic acid copolymer for in situ preparation of nanosilver particles (Hebeish et al., 2014), cotton fibers grafted by glycidyl methacrylate-iminodiacetic acid immersed in silver salt solution forming grafted-cotton-fiber-Ag+ complexes irradiated with ultraviolet resulted in silver nanoparticles synthesis (Chen and Li Chiang, 2008). Also grafting of cotton fabric with a poly (acrylamide-co-itaconic acid) copolymer followed by Ag nanoparticles entrapment is the other recent related study (Gupta et al., 2008). Covalent bonding of macromolecular chains such as chitosan to cellulose fibers is another successful surface activation for strong bonding of nanoparticles to cellulosic substrate. Chitosan is a biocompatible polysaccharide capable of adsorbing some metal ions such as silver through amino (dNH2) and hydroxyl (dOH) groups. Thus, metal nanoparticles bind to (dNH2) and hydroxyl (dOH) groups of chitosan forming durable antibacterial coatings (Thomas et al., 2011). Simultaneous polymerization and metal nanoparticles synthesis can be also concerned through redox reaction process, with the oxidization of monomer and reduction of metal ions producing polymer-metal nanocomposites on cellulose substrates (Firoz Babu et al., 2012). In situ chemical oxidative polymerization using pyrrole and silver nitrate was proposed to prepare antibacterial conductive polymercoated textile. Silver nanoparticles were deposited on/into the polypyrrole/ cotton matrix layer by adsorption or electrostatic interaction (Firoz Babu et al., 2012). Plasma has been introduced as an efficient physical method for cellulosic fiber activation with low environmental impact (Tourrette et al., 2009). Through interaction of cellulosic textile with plasma, active sites such as radicals, hydroxyl, carboxyl, and carbonyl groups may be formed on the fiber surface, which can initiate chemical reactions (Cho et al., 2009). There have been a number of studies on surface modification of cellulosic fibers via plasma treatment. According to our literature review, most cases were related to the use of low-pressure plasma rather than atmospheric plasma. Surface activation of cellulosic substrates by plasma technology was searched to gain various goals ranging from increased hydrophylicity and capillarity of the treated cotton, viscose, modal, and lyocell fibers, to improve dyeing and finishing (Prysiazhnyi et al., 2013).

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The use of plasma in the finishing process proves to be effective with a great variety of effects and durability (Jazbec et al., 2015). Atmospheric plasmas especially DBD plasmas were applied as pretreatment to enhance € the effectiveness of finishing of cotton fabric (Karahan and Ozdo, 2008). For instance, an improvement in wrinkle recovery angle of a cotton fabric pretreated with a DBD plasma discharge has been reported using a crosslinking resin of low-formaldehyde content. Oxygen plasma was also effective in enhanced wrinkle-resistant finishing of cotton with polycarboxylic acid due to surface activation of cotton resulting in improved hydrophylicity. Cotton surface activation with corona prior to antibacterial finishing with silver nanoparticles was effective to improve the stability of antibacterial activities even after 20 washes. Linen-based fabrics were activated by oxygen or nitrogen plasma following by nanofinishing with Ag, TiO2, or ZnO (Gulrajani and Gupta, 2011). CO2 laser was used to enhance antibacterial activity of cotton fabric treated with silver nanoparticles. The authors claimed that due to carboxylic acid functional groups formation, positive ions of metals such as silver were attracted to the surface, resulting in durable antibacterial properties after repeated laundering (Nourbakhsh and Ashjaran, 2012). The effect of CO2 laser irradiation on raw and bleached cotton fabrics indicated different morphological structures for raw and bleached samples after laser irradiation providing different physical and comfort properties. Laser increased the air permeability of raw cotton fabric. On the other hand, the air permeability of laser-irradiated bleached cotton fabric decreased owing to opening of the yarn structure and the production of discontinuous pores on the fiber surface after laser irradiation. Laser irradiation led to an increase in wettability of bleached fabric in comparison with the more hydrophobic property obtained on raw cotton fabric. Furthermore, the results revealed that the dyeability of raw cotton fabric irradiated before and after dyeing was negatively affected in comparison with the higher dye adsorption observed on bleached cotton fabric irradiated after dyeing (Montazer et al., 2014).

5.2.2 Surface activation of protein fibers The covalently bound fatty acids and the high number of disulfide bridges make the outer wool surface highly hydrophobic rendering wool dyeing and finishing difficult. Thus, wool surface activation to increase hydrophilicity is of high importance.

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Oxidative treatments of wool and wool biofinishing with protease are the common chemical surface activation methods. Oxidation of wool fabrics with potassium permanganate created more negative groups such as dCOO– on the fabric surface. Aminoacids of cystine, tyrosine, and tryptophan are greatly affected by potassium permanganate treatment. The sharp edges of wool scales are removed through potassium permanganate oxidation, which leads to increased water adsorption (Barr and Edgar, 1941). On the other hand, hydrolysis of peptide bonds through protease enzyme pretreatment resulted in wool surface with more hydrophilicity and amine-carboxyl groups (Freddi et al., 2003). Plasma treatment with N2, O2/N2, and O2 gases as a physical surface activation method was effective in increased wettability of wool fibers due to the creation of chemical groups and elimination of the fatty layer on the wool surface. There have been vast number of studies concerning with plasma surface activation of wool fibers using glow discharge, DBD, corona, and lowpressure plasma to improve wool dyeability. For instance, DBD plasma discharge using N2 gas resulted in the creation of NH2 groups on wool surface, improving wettability, increased acid dye exhaustion, increased initial dyeing rate, and decreased equilibrium time (El-Zawahry et al., 2006). Moreover, silk fibers were activated by oxygen and argon plasma, resulting in improved dye adsorption especially for the argon plasma treatment (Boonla and Saikrasun, 2013). Plasma discharge was applied on wool fabrics with gaseous oxygen, nitrogen, and air in order to improve fiber accessibility to transglutaminases, to increase wool yarns and fabrics tensile strength. Activation of wool with RF low-temperature plasma enhanced the effectiveness of wool biofinishing with protease to achieve shrink resistance properties (Zille et al., 2014). Atmospheric plasma treatment enhanced the adhesion of chitosan to the surface and improves the hydrophilicity, dyeing efficiency, and shrink resistance properties (Demir, 2010). Also, plasma activation has been used to enhance the reactivity of wool fabric to silicone polymers to achieve soft handle. Although atmospheric plasma treatment could be a suitable method for wool antifelting, it has adverse effect on hand feel. Thus, plasma treatment is usually followed by silicone polymer deposition to obtain acceptable hand feel (Demir, 2010).

5.2.3 Surface activation of synthetic fibers In spite of widespread application of polyester as synthetic fiber, poor wettability, lack of functional groups, and low moisture permeation make

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polyester dyeing, finishing, and functionalization difficult. Thus, polyester surface activation through which functional groups are introduced to the surface is of high importance. The most common chemical activation methods of polyester fibers are alkaline hydrolysis and aminolysis. In general definition, alkaline hydrolysis is the cleavage of ester linkages on the polyester surface due to reaction with strong base creating terminal hydroxyl and carboxyl groups. Through alkaline hydrolysis, the low molecular segment of the chains are removed causing weight and fiber diameter loss. Alkaline hydrolysis of polyester makes the surface more porous with lots of small size voids. There are different types of polyester hydrolysis depending on the number of hydroxide ions reacting with polyester, namely, unimolecular (one hydroxide ion) and bimolecular (two hydroxide ions) or by use of alcohols or glycols. In the latter one, polyester hydrolysis is called glycolysis (reactions 1–3) (Dave et al., 1986; Wang and Liu, 2009). The extent of polyester alkaline hydrolysis can be further enhanced using alcoholic alkali or additives such as quaternary ammonium salts and water-soluble cationic surfactants with short-chain length, namely, CTAB (cetyltrimethylammonium bromide) (Allahyarzadeh et al., 2013). It has been reported that alkaline hydrolysis occurred through two stages. In the first step, polymer chains are randomly cleaved at the surface forming hydrophilic groups on the surface. The second step involves the pitting of the fiber surface increasing the surface roughness. PET
COO
PET + NaOH ! PET
COO
+ HO
PET

(1)

PET
COO
PET + ROH ! PET
COOR + HO
PET

(2)

PET
COO
PET + RðOHÞ2 ! PET
COOROH + HO
PET (3) In alkaline hydrolysis, one of the hydroxyl groups is consumed while using glycols in the chain scission reaction, and the other one is incorporated into the polyester structure (reaction 3). This provides the possibility of further crosslinking between polyester chains. In this regard, even enhanced tensile strength properties are achievable, which is contrary to common alkaline hydrolysis using NaOH or monoalcohols causing reduced mechanical properties (Natarajan and Moses, 2012). Polyester aminolysis is generally defined as a reaction of amines with ester groups of polyethylene terephthalate, creating amide groups on polyester surface (Avny and Rebenfeld, 1986). There are several types of aminolysis depending on the functionality of amines, namely, monofunctional amines (R-NH2), multifunctional amines (NH2-R-NH2), amino alcohols and

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highly branched amines, namely, dendrimers such as poly(amidoamine) and polypropylenimine. In multifunctional amines, one of the amine groups takes part in the chain scission reaction, while other amines are incorporated into the polyester structure. Amino alcohols containing both amine and alcohol groups form a new amide bond and introduce free amino and alcohol groups on the polyester surface. Here, the attack to the polyester chain may be from nitrogen or hydroxyl sides depending on the number of hydroxyl groups. Monoethanolamine attacks on polyester from the nitrogen due to the higher electronegativity of two nucleophilic nitrogen centers. On the other hand, steric hindrance around the amine group in triethanolamine causes the attack from hydroxyl groups producing hydroxylamine functional groups on the polyester surface. Compared with alkaline hydrolysis, fewer cracks with larger size and depth are created through aminolysis (Avadanei et al., 2010; Bech et al., 2007; Zhong et al., 2012; Heidari and Tahvildari, 2013; Martin and Twyman, 2001). Various polyester aminolysis reactions are as follows: PET
COO
PET + RNH2 ! PET
CONHR + HO
PET

(4)

PET
COO
PET + NH2 RNH2 ! PET
CONHRNH2 + HO
PET (5) PET
CONHRNH2 + PET
COO
PET ! PET
CONHRCONH
PET + HO
PET

(6)

PET
COO
PET + NH2 ROH ! PET
CONHROH + HO
PET (7) PET
COO
PET + NðROHÞ3 ! PET
COORNðROHÞ2 + HO
PET (8) PET
COO
PET + D ðdendrimerÞ ! PET
CONHD + HO
PET (9)

Although polyester aminolysis is mainly involved with tensile strength reduction, aminolysis with aminoalcohols with different number of hydroxyl groups, multifunctional amines such as NH2-R-NH2, and highly branched amines provide the possibility of further reaction between the free amine or hydroxyl groups and another polyester chain. The crosslinking effect results in enhanced tensile properties as proved by Poortavasoly et al. (2014), which is thoroughly discussed in Chapter 8. UV graft copolymerization of dextran-methacrylate on polyester fabric was found to be effective in providing reactive dyeability of treated polyester

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fibers (Arslan and Lu, 2008). The silicone polymers containing cationic groups were grafted on polyester microfibers forming thin films having excellent shade-darkening effect on dyed polyester microfiber fabric (Yahaya et al., 2001; Xie et al., 2007). Surface activation of polyester has been also carried out using biofinishing to replace alkaline hydrolysis or aminolysis, obtaining more hydrophilic fibers. Compared with other chemical surface activation methods due to the disability of enzyme bulky macromolecules to penetrate the inner of fibers, surface modification is superficial. Cutinase, lipase, and esterase are hydrolytic enzymes applied to polyester to impart better wettability. Hydroxyl and carboxylic groups are formed due to hydrolysis of ester linkages in polyester using hydrolyzing enzymes. This method also benefits from mechanical properties stability. Use of polyester biotreatment to enhance acrylic acid grafting yield has been also reported. Pretreatment of polyester fibers with enzymes was also effective in increased color depth of samples dyed with cationic dye due to the carboxylic end groups on the modified polymeric chain (Kato et al., 2000; Bruckner et al., 2008; Wavhal and Balasubramanya, 2011). Plasma, UV, gamma, microwave, laser, and ultrasound are common physical methods for polyester surface activation. It has been reported that through these physical treatments, the amorphous portion of the fibers is degraded and etched away, and the effect on the amorphous zone is more predominant than the crystalline area (Parvinzadeh Gashti et al., 2011). Among physical surface activation methods, plasma treatment has been widely applied to impart hydrophilicity and enhanced dyeability to polyester. Formation of oxygen-containing polar groups such as dCOO– and dOH on the polyester macromolecular backbone and morphological changes, including generation of micropits during etching due to some degradation reactions occurring in the bombardment of the exited species and electrons as well as the oxidative reactions, are considered as determined factors for improving the wettability of polyester fibers (Wolf and Sparavigna, 2010; Dave et al., 2012). Depending on the type of plasma gas, treatment time and input power different extent of activation is achieved. For instance, corona treatment gives a higher surface roughness than atmospheric plasma glow discharge or DBD (Zeronian and Collins, 1989). Gases or mixtures of gases have been used for plasma treatment of polyester, including nitrogen, argon, oxygen, helium, nitrous oxide, water vapor, carbon dioxide, methane, and ammonia, each of which produces a unique plasma composition and results in different surface properties (Wolf and Sparavigna, 2010).

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The effect of plasma with oxygen, argon, and air for the modification of polyester and polypropylene resulted in considerable increase in surface energy of substrates increasing hydrophilicity (Jasso et al., 2006). Carboxylic acid groups were introduced on the surface of polyamide and polyester fabrics by a low-pressure plasma discharge and then dyed with cationic dyes. The results showed a significant increase in the color strength for both substrates (Wang et al., 2005). Nitrogen groups have also been introduced into polyester fibers by irradiating with argon plasma in combination with solid-phase monomer deposition such as allylbiguanide hydrochloric acid salt, N-methylol acrylamide, and N-isopropyl acrylamide. Some researchers introduced plasma-induced polymerization of maleic acid and polyethylene glycol as grafting chemicals on polyester fibers to improve wettability. Polyester was treated with argon plasma discharge and grafted by different molecular polyethylene glycols to reduce water contact angle. Researchers claimed that plasma process can improve adhesion strength between polyester fibers and various polymers, biomaterials, and nanoparticles, including styrene-butadiene rubber, silicone resins, fluorocarbon, conductive polypyrrole, cells, bacterial cellulose, silver and nickel nanoparticles (Charpentier et al., 2006). The possibility of using dielectric barrier discharge air plasma, corona, low-temperature radiofrequency and nitrogen/argon plasma for fiber surface activation to facilitate deposition of aluminum oxide, nanosilver, ZnO nanorods, and nanotitanium dioxide onto polyester fabric was investigated (Raslan et al., 2011). Simor et al. (2003), used nitrogen plasma to impart hydrophilicity to polyester fibers to facilitate the absorption of a palladium catalyst, which was used as a seed catalytic surface for further electroless deposition of nickel. Besides, low-temperature plasma with oxygen gas created a hydrophilic polyester surface facilitating the nickel deposition through an electroless plating process (Yuen et al., 2007). Polyester fabric was coated with carbon nanotube via plasma treatment to improve microwave-shielding behavior (Haji et al., 2014). Plasma surface activation at different process parameters, including power and etching time, has been combined with natural montmorillonite adsorption to improve the thermal stability and flame retardancy of polyester fabrics (Carosio et al., 2011). The effect of excimer UV laser surface activation on polyester was extensively investigated by Kan (2008). Morphological study of the untreated and treated polyester fibers revealed a ripple-like structure on the treated fibers, which resulted in enhanced wettability and air permeability while fiber

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weight and diameter, tensile strength, yarn abrasion, and bending properties were adversely affected. KrF excimer laser working at 248 nm was used to develop a periodic roughness or ripple structure on polyester surface. Laser treatment was also effective in improved initial rate of dyeing and equilibrium exhaustion. An increase in surface area and dye adsorption was found after CO2 pulsed laser irradiation of polyester and polyamide fabrics as a result of certain roughness created on the fiber surface. The effect of CO2 laser on dyeing property of polyester fibers has been studied in two different conditions, namely, laser irradiation before dyeing and after dyeing. Although low-intensity laser had no significant influence on color fastness, high-intensity laser irradiation increased the light and rubbing fastness. Laser irradiation before dyeing resulted in surface morphological modification; however, laser treatment after dyeing led to changes in molecular structure of the dyes (Montazer et al., 2011). Sonochemistry has been also applied for surface modification of various substrates causing weight loss, increased roughness, and decreased contact angle. In a recent study, ultrasound cavitation as a means of concentrating the diffuse energy of sound into unique intense localized hot spots with high pressure was successfully used for the surface modification of polyester fibers, enhancing their wettability and reactivity for TiO2 nanoparticles adsorption. It is well known that water molecules sonolyzed to hydrogen radicals (H•) and hydroxyl radicals (•OH) during ultrasonic process. Hence, hydroxylation of terephthalate can be possibly promoted by •OH radical, forming functional groups on polyester surface improving the wettability (Harifi and Montazer, 2015). The possible terephthalate hydroxylation under ultrasound irradiation is schematically shown in Fig. 5.2.

5.3 NANOSURFACE ACTIVATION As proposed by several research studies physical, chemical, and biochemical surface activation methods provide opportunity to obtain durable finishing especially nanofinishing of various textile substrates. In this regard, activation methods are pretreatments carried out prior to ex situ nanofinishing methods or they can occur in parallel with in situ nanofinishing. In both cases, the result is strong adherence of nanomaterials on the surface providing durability. On the other hand, nanotreatment of various textile substrates can be regarded as nanosurface activation method beneficial for simultaneous surface activation and creation of several functional properties to the fibers.

Nanosurface activation

Fig. 5.2 Surface activation of polyester under ultrasound irradiation. (Reprinted with permission from Harifi, T., Montazer, M., 2015. A review on textile sonoprocessing: A special focus on sonosynthesis of nanomaterials on textile substrates. Ultrason. Sonochem. 23, 1–10. Copyright 2015, Elsevier).

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Materials at nanoscale possess totally different behavior than those of bulk. Since nanoparticles have large surface-area-to-volume ratio and high surface energy, they impart valuable properties into the treated textiles with no adverse effect on original handle and breathability. One of the successful studies on nanosurface activation was reported in 2013, through which nano TiO2 treatment of polyester fibers was found beneficial to replace carrier dyeing. The polyester fabric was first thermally treated with nano TiO2 and then dyed with two different disperse dyes at the boil without a carrier. The dyeing efficiency was compared to the common carrier dyeing of the polyester. Based on the results, dyeing adsorption was positively affected by nano TiO2 pretreatment and an increase in nano TiO2 content led to higher color strength. While nano TiO2-treated samples adsorb the dye almost equally in comparison to the fabric dyed by carrier, they simultaneously benefited from multiproperties obtained by nano TiO2 application, including self-cleaning, hydrophilicity, and UV protection and they were free from the disadvantages involved in carrier dyeing such as toxicity and bad odor. Also, the proposed method proved to have no adverse effects on fastness properties. In the proposed research, nano TiO2 pretreated fabrics were irradiated under sunlight prior to dyeing. Due to irradiation, an electron-hole pair is produced between the valence and conduction band of TiO2. The generated photoinduced electrons and holes can play a prominent role in imparting higher wettability to TiO2-treated fabrics. The oxygen radical anions produced in the reduction process of Ti4+ to Ti3+ can be changed into oxygen molecules, which then are ejected, resulting in oxygen vacancies remaining on surface of the TiO2 leading to increase in wettability. In higher concentrations of nano TiO2, the oxygen vacancies are more accessible, resulting in higher capacity for water adsorption. The higher wettability of the polyester fabrics pretreated by nano TiO2 improved the dyeability (Harifi and Montazer, 2013). In the other study, wool fabrics were treated with nano TiO2 particles prior to the application of multiwall and functionalized (carboxylated) multiwall carbon nanotubes. Photoinduced wettability of nano TiO2 pretreated fabrics was effective in improving the surface adsorption and subsequent electrical conductivity of the treated samples (Nafeie et al., 2016). There is also a study claiming that cotton surface activation was carried out by deposition of silver nanoparticles on the surface through in situ method. The synthesized silver nanoparticles were used as seeds for the formation and deposition of ZnO nanoparticles on the surface. The authors claimed that loading ZnO nanoparticles into the unactivated cotton fibers

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led to formation of agglomerated nanoparticles, while preactivated surface with silver nanoparticles prevented nanoparticles agglomeration (Barani, 2014). Recently, Norouzi and Montazer had studied the preactivation of surface with in situ synthesis of ZnO nanoparticles to achieve super hydrophobic fabric using fluorocarbon and silicone-based compounds. In addition to the simultaneous self-cleaning activities, successful results of the study could be applicable to swimsuits (Norouzi et al., 2018).

5.4 CONCLUSION Numerous physical, chemical, and biochemical methods have been proposed for introducing functional chemical groups or charges to the surface of textile substrates, obtaining hydrophilicity, enhanced dyeability, and durable finishing. Despite the extensive research studies, there is still a challenge to select the appropriate surface activation method with high efficiency, low chemical consumption with ecological acceptability, and longlasting properties. The minimum detrimental effect of surface modification methods on inherent mechanical properties is another important factor. In this regard, creation of multifeatures in combination with the surface activation could be of significant importance. Nanosurface activation is a new insight into textile surface activation methods that bring valuable properties. In this regard, in situ sonochemical synthesis and deposition of nanoparticles could be a possible solution to meet the involved challenges of surface activation approaches.

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Baugh, P.J., Lawton, J.B., Phillips, G.O., 1970. Modification of the surface characteristics of cotton by the introduction of anionic groups, and the mechanism of ion binding. In: Symposium of Surface Active Agents in the Textile Industry, New Orleans. Bech, L., Meylheuc, T., Lepoittevin, B., 2007. Chemical surface modification of poly(ethylene terephthalate) fibers by aminolysis and grafting of carbohydrates. J. Polym. Sci. 45, 2172–2183. Boonla, K., Saikrasun, S., 2013. Influence of silk surface modification via plasma treatments on adsorption kinetics of lac dyeing on silk. Text. Res. J. 83, 288–297. Bruckner, T., Eberl, A., Heumann, S., 2008. Enzymatic and chemical hydrolysis of poly(ethylene terephthalate) fabrics. J. Polym. Sci. A 46, 6435–6443. Carosio, F., Alongi, J., Frache, A., 2011. Influence of surface activation by plasma and nanoparticle adsorption on the morphology, thermal stability and combustion behavior of PET fabrics. Eur. Polym. J. 247, 893–902. Charpentier, P.A., Maguire, A., Wan, W.K., 2006. Surface modification of polyester to produce a bacterial cellulose-based vascular prosthetic device. Appl. Surf. Sci. 252, 6360–6367. Chen, C.Y., Li Chiang, C., 2008. Preparation of cotton fibers with antibacterial silver nanoparticles. Mater. Lett. 62, 3607–3609. Cho, S.C., Hong, Y.C., Cho, S.G., Ji, Y.Y., Han, C.S., Uhm, H.S., 2009. Surface modification of polyimide films, filter papers, and cotton clothes by HMDSO/toluene plasma at low pressure and its wettability. Curr. Appl. Phys. 9, 1223–1226. Dave, J., Kumar, R., Srivastava, H.C., 1986. Studies on modification of polyester fabrics I: Alkaline hydrolysis. J. Appl. Polym. Sci. 33, 455–477. Dave, H., Ledwani, L., Chandwani, N., 2012. Use of dielectric barrier discharge in air for surface modification of polyester substrate to confer durable wettability and enhance dye uptake with natural dye eco-alizarin. Compos. Interfaces 19, 219–229. Demir, A., 2010. Atmospheric plasma advantages for mohair fibers in textile applications. Fibers Polym. 11, 580–585. El-Zawahry, M.M., Ibrahim, N.A., Eid, M.A., 2006. The impact of nitrogen plasma treatment upon the physical-chemical and dyeing properties of wool fabric. Polym.-Plast. Technol. Eng. 45, 1123–1132. Firoz Babu, K., Dhandapani, P., Maruthamuthu, S., Anbu Kulandainathan, M., 2012. One pot synthesis of polypyrrole silver nanocomposite on cotton fabrics for multifunctional property. Carbohydr. Polym. 90, 1557–1563. Freddi, G., Mossotti, R., Innocenti, R., 2003. Degumming of silk fabric with several proteases. J. Biotechnol. 106, 101–112. Gulrajani, M.L., Gupta, D., 2011. Emerging techniques for functional finishing of textiles. Indian J. Fibre Text. Res. 36, 388–397. Gupta, P., Bajpai, M., Bajpai, S.K., 2008. Investigation of antibacterial properties of silver nanoparticle-loaded poly (acrylamide-co-itaconic acid)-grafted cotton fabric. J. Cotton Sci. 12, 280–286. Haji, A., Rahbar, R.S., Shoushtari, A.M., 2014. Improved microwave shielding behavior of carbon nanotube-coated PET fabric using plasma technology. Appl. Surf. Sci. 311, 593–601. Harifi, T., Montazer, M., 2013. Free carrier dyeing of polyester fabric using nano TiO2. Dyes Pigments 97, 440–445. Harifi, T., Montazer, M., 2015. A review on textile sonoprocessing: A special focus on sonosynthesis of nanomaterials on textile substrates. Ultrason. Sonochem. 23, 1–10. Hashem, M., Hauser, P., Smith, B., 2003. Wrinkle recovery for cellulosic fabric by means of ionic crosslinking. Text. Res. J. 73, 762–766. Hashem, M., El-Bisi, M., Sharaf, S., Refaie, R., 2010. Pre-cationization of cotton fabrics: An effective alternative tool for activation of hydrogen peroxide bleaching process. Carbohydr. Polym. 79, 533–540.

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Hebeish, A., El-Shafei, A., Sharaf, S., Zaghloul, S., 2014. Development of improved nanosilver-based antibacterial textiles via synthesis of versatile chemically modified cotton fabrics. Carbohydr. Polym. 113, 455–462. Heidari, S., Tahvildari, K., 2013. Preparation and characterization of diols and polyols based on aminolysis of poly (ethylene terephthalate) wastes with alkanolamines. J. Appl. Chem. Res. 7, 33–42. Jasso, M., Hudeca, I., Alexya, P., 2006. Grafting of maleic acid on the polyester fibers initiated by plasma at atmospheric pressure. Int. J. Adhes. Adhes. 26, 274–284. Jazbec, K., Sˇala, M., Mozeticˇ, M., Vesel, A., Gorjanc, M., 2015. Functionalization of cellulose fibers with oxygen plasma and ZnO nanoparticles for achieving UV protective properties. J. Nanomater. 2015, 1–9. John, M.J., Anandjiwala, R.D., 2009. Surface modification and preparation techniques for textile materials. In: Wei, Q. (Ed.), Surface Modification of Textiles. Woodhead Publishing, UK. Kan, C.W., 2008. Impact on textile properties of polyester with laser. Opt. Laser Technol. 40, 113–119. € Karahan, H.A., Ozdo, E., 2008. Improvements of surface functionality of cotton fibers by atmospheric plasma treatment. Fibers Polym. 9, 21–26. Kato, K., Kikumura, Y., Yamamoto, M., 2000. Collagen immobilization onto the surface of artificial hair for improving the tissue adhesion. J. Adhes. Sci. Technol. 14, 635–650. Khalil-Abad, M.S., Yazdanshenas, M.E., Nateghi, M.R., 2009. Effect of cationization on adsoprtion of silver nanoparticles on cotton surfaces and its antibacterial activity. Cellulose 16, 1147–1157. Martin, I.K., Twyman, L.J., 2001. Acceleration of an aminolysis reaction using a PAMAM dendrimer with 64 terminal amine groups. Tetrahedron Lett. 42, 1123–1126. Monatzer, M., Malek, R.M.A., Rahimi, A., 2008. Salt free reactive dyeing of cationaized cotton. Fibers Polym. 8, 608–612. Montazer, M., Taheri, S.J., Harifi, T., 2011. Effect of laser CO2 irradiation on various properties of polyester fabric: focus on dyeing. J. Appl. Polym. Sci. 124, 342–348. Montazer, M., Chizarifard, G., Harifi, T., 2014. CO2 laser irradiation of raw and bleached cotton fabrics, with focus on water and dye absorbency. Color. Technol. 130, 13–20. Nafeie, N., Montazer, M., Nejad, N.H., Harifi, T., 2016. Electrical conductivity of different carbon nanotubes on wool fabric: an investigation on the effects of different dispersing agents and pretreatments. Colloids Surf. A Physicochem. Eng. Asp. 497, 81–89. Natarajan, S., Moses, J.J., 2012. Surface modification of polyester fabric using polyvinyl alcohol in alkaline medium. Indian J. Fibre Text. Res. 37, 287–291. Norouzi, N., Gharehaghaji, A.A., Montazer, M., 2018. Reducing drag force on polyester fabric through superhydrophobic surface via nano-pretreatment and water repellent finishing. J. Text. Inst. 109, 92–97. Nourbakhsh, S., Ashjaran, A., 2012. Laser treatment of cotton fabric for durable antibacterial properties of silver nanoparticles. Materials 5, 1247–1257. Park, S.Y., Chung, J.W., Priestley, R.D., Kwak, S., 2012. Covalent assembly of metal nanoparticles on cellulose fabric and its antimicrobial activity. Cellulose 19, 2141–2151. Parvinzadeh Gashti, M., Willoughby, J., Agrawal, P., 2011. Surface and bulk modification of synthetic textiles to improve dyeability. In: Hauser, P. (Ed.), Textile Dyeing. InTech. Poortavasoly, H., Montazer, M., Harifi, T., 2014. Simultaneous synthesis of nano silver and activation of polyester producing higher tensile strength aminohydroxylated fiber with antibacterial and hydrophilic properties. RSC Adv. 4, 46250. Prysiazhnyi, V., Kramar, A., Dojcinovic, B., Zekic, A.B., Obradovic, M., Kuraica, M.M., Kostic, M., 2013. Silver incorporation on viscose and cotton fibers after air, nitrogen and oxygen DBD plasma pretreatment. Cellulose 20, 315–325. Ramasamy, M., 2005. Effect of cationization of cotton on its dyeability. J. Text. Inst. 30, 315–323.

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Raslan, W.M., Rashed, U.S., El-Sayad, H., 2011. Ultraviolet protection, flame retardancy and antibacterial properties of treated polyester fabric using plasma-nano technology. Mater. Sci. Appl. 2, 1432–1442.  ´ k, M., 2003. Atmospheric-pressure plasma treatment of polyester Simor, M., Ra´hel, J., Cerna nonwoven fabrics for electroless plating. Surf. Coat. Technol. 172, 1–6. Thomas, V., Bajpai, M., Bajpai, S.K., 2011. In situ formation of silver nanoparticles within chitosan attached cotton fabric for antibacterial property. J. Ind. Text. 40, 229–245. Tourrette, A., De Geyter, N., Jocic, D., Morent, R., Warmoeskerken, M.M.C.G., Leys, C., 2009. Incorporation of poly(N-isopropylacrylamide)/chitosan microgel onto plasma functionalized cotton fiber surface. Colloids Surf. A Physicochem. Eng. Asp. 352, 126–135. Walo, M., Przybytniak, G., Męczy nska-Wielgosz, S., 2015. Improvement of poly(esterurethane) surface properties by RAFT mediated grafting initiated by gamma radiation. Eur. Polym. J. 68, 398–408. Wang, J., Liu, J., 2009. Surface modification of textiles by aqueous solutions. In: Wei, Q. (Ed.), Surface Modifications of Textiles. Woodhead Publishing, UK. Wang, J., Pan, C.J., Huang, N., 2005. Surface characterization and blood compatibility of poly(ethylene terephthalate) modified by plasma surface grafting. Surf. Coat. Technol. 196, 307–311. Wang, Z., Hauser, P.J., Rojas, O.J., 2015. Study on charge distribution of carboxymethylated cotton fabric by streaming potential/current measurements. AATCC J. Res. 2, 13–19. Wavhal, S.D., Balasubramanya, R.H., 2011. Role of biotechnology in the treatment of polyester fabric. Indian J. Microbiol. 51, 117–123. Wolf, R., Sparavigna, A.C., 2010. Role of plasma surface treatments on wetting and adhesion. Engineering 2, 397–402. Xie, K., Yu, J., Jiang, D., 2007. Shade darkening effect of polyorganosiloxane modified with amino and hydroxy groups on dyed polyester microfiber fabric. J. Appl. Polym. Sci. 106, 1256–1262. Yahaya, G.O., Brisdon, B.J., Maxwell, M., 2001. Preparation and properties of functionalized polyorganosiloxanes. J. Appl. Polym. Sci. 82, 808–817. Yazdanshenas, M.E., Shateri-Khalilabad, M., 2012. The effect of alkali pre-treatment on formation and adsorption of silver nanoparticles on cotton surface. Fibers Polym. 13, 1170–1178. Yuen, C.W.M., Jiang, S.Q., Kan, C.W., 2007. Effect of low temperature plasma treatment on the electroless nickel plating of polyester fabric. J. Appl. Polym. Sci. 105, 2046–2053. Zeronian, S.H., Collins, M., 1989. Surface modification of polyester by alkaline treatments. Text. Prog. 20, 1–26. Zhong, X., Lu, Z., Valtchev, P., Wei, H., 2012. Surface modification of poly(propylene carbonate) by aminolysis and layer-by-layer assembly for enhanced cytocompatibility. Colloids Surf. B Biointerfaces 93, 75–84. Zille, A., Oliveira, F.R., Souto, A.P., 2014. Plasma treatment in textile industry. Plasma Process. Polym., 1–38.

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Nanosoftening 6.1 INTRODUCTION: DEFINITION AND MECHANISM OF SOFTENING Softness is one of the most important properties of clothing with direct impact on customer’s purchase decision, which is also in close relation with comfort feeling of wearer. Although household softeners have been developed as ingredients of synthetic detergent or soaping agents to be employed at the end of washing cycle, the demand for durable softness makes softening finishing a crucial finishing procedure. During the last decades, there has been increasing progress in softening agents and application technologies. The recorded history indicated the manufacturers’ trend toward costeffective softening chemicals, which are easy to handle, compatible with other finishing agents, resistant to high temperatures and nonyellowing with no detrimental effect on shade and fastness properties of dyed textiles. Researchers have put more effort into introducing green multifunctional softeners together with ecofriendly application technologies, as fabric softness is felt by touch. Based on a definition proposed by Mallinson (2001), softeners are chemicals with the ability to change the handle of textile materials to a more “pleasing to touch state.” Moreover, it is expected that softening finishes provide other desirable properties more than just soft handle and smoothness—e.g., antistatic, hydrophilic and moisture regulation, elasticity, soil release, sewability, and abrasion resistance. Softening finishing can be obtained through three main routes, namely, mechanical, biochemical, and chemical methods. There have been some reports concerning mechanical methods such as raising, napping, emerising, and calendering for softening the textile substrates through increasing the loft or compressibility of the fabric. Controlled lyocell fibrillation makes it possible to achieve special surface effect such as peach skin effect. Biochemical methods using enzymes have been also successful in improving the surface smoothness by removing the surface fibers and reducing fabric hairiness. However, softening finishing is mainly obtained by

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© 2018 Elsevier Ltd. All rights reserved.

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chemical softening agents reducing the interyarn and interfiber forces of friction at the fiber surface. The generally accepted mechanism for softening properties is based on orientation of chemical softener molecules on textile surface, which is dependent on nature of softener and fabric substrate. In this regard, electrostatic attraction and hydrophobic model are the two main involved mechanisms. Moreover, based on the size of softening agents, it is possible for the smaller molecules to penetrate inside the fibers, causing a plasticizing action on the fibrous polymer, reducing its glass transition temperature. In general, softeners are surfactants with a hydrophobic (or fatty) part, which does not mix with water, and a hydrophilic part enabling to disperse in water. Depending on the surfactant charge and fiber zeta potential in water (generally negative), different orientation of softeners takes place on the surface (Fig. 6.1). Cationic softeners are generally attracted toward negatively charged fabric surface, creating a new hydrophobic chain surface with excellent lubricity. However, the hydrophobic attraction is the more acceptable mechanism for softener loading on the textile materials. On the other hand, anionic softeners orient themselves with the negatively charged ends repelled away from the negatively charged fiber surface, leaving a more hydrophilic surface with reduced softness comparing with cationic softeners. In comparison, the hydrophilic portion of the nonionic softeners is attracted to hydrophilic surfaces and the hydrophobic portion is attracted to hydrophobic surfaces, thus imparting hydrophilicity or hydrophobicity. It is believed that a group of mechanisms, including hydrophobic and ionic interactions, are responsible for softening properties of silicone-based softeners (Roy Choudhury et al., 2012). It is generally accepted that silicone’s softening potential comes from the flexibility of siloxane backbone to freely rotate along the SidO bonds. Thus, R groups are arranged away from the fiber surface causing reduced fiber-to-fiber interaction making the fabric softer (Nostadt and Zysch, 1997).

Fig. 6.1 Orientation of cationic and anionic softeners on fiber surface with negative zeta potential based on ionic interaction theory.

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6.2 SOFTENING AGENT CLASSIFICATION Three types of softener classifications can be found through various literatures. The first category belonged to Mahapatro et al. (1991) who divided textile softeners into substantive, nonsubstantive, and reactive softeners. Next classification was based on the durability of softening properties and grouped into permanent and temporary softeners. The most popular classification, which is widely used today, is the one proposed by Bajaj in 2002, based on ionic nature and polarity of softeners, including anionic, cationic, nonionic, amphoteric, pseudoionic, and silicone-based softeners. A brief overview of softening agents based on ionic nature has been provided in Table 6.1, and silicone-based softeners as the most common ones are discussed in detail. Silicones are classified as a separate class of synthetic softeners, which are mainly in polymeric forms such as polydialkylsiloxanes, and supplied as aqueous emulsions through dispersing silicone oil in water using an appropriate emulsifier. They have excellent properties, including high stability against chemicals, heat, microorganisms, low surface tension, freedom of rotation, high glass transition temperature over 200°C, low refractive index, good flexibility, environment friendly, and many others. The surface of silicone-treated fabrics is mostly nonpolar and hydrophobic, and they are used to enhance the water repellency effects. The extent of hydrophobicity of textiles depends on the silicone chain length (Berthiaume and Baum, 1997). Silicone-based softeners are chemically formulated as poly R2SiO, in which different substituents are attached to the silicon (Schindler and Hauser, 2004). The most common silicone-based softeners are chemically shown in Fig. 6.2. The first silicone softeners were dimethyl polysiloxanes, which were nonreactive and less durable and mainly used in synthetic fibers. Over the years, silicone-based softeners have been modified with several chemical compounds to obtain desirable properties along with softness. For instance, dimethylpolysiloxanes were modified using methyl hydrogen siloxane, silanol, or ester functional groups. Moreover, functional amino mercapto and epoxy groups capable of reacting with fibers have been used for modifying dimethylpolysiloxanes preparing organoreactive silicone softeners. Thus, softeners of this type containing reactive groups could effectively react with natural fibers such as cellulosic fabrics. Modification of silicone-based softeners with amino ethyl or propyl groups has been also developed resulting in super softness properties (Lacasse and Baumann, 2004).

Amine salts, imidazolines, amino esters, fatty alcohol based, dicyanadiamide and stearylamine, polyamine-based difatty amino imidazoline, diethanolamine

Anionic

Soaps, sodium salt of fatty acids, sulfosuccinates of fatty acid, sulfate and sulfonate of fatty acids

Nonionic

Wax and polyethylene emulsions, glycerol monostearate, ethoxylates of fatty acids,

Best softness High exhaustion due to ionic interaction with negatively charged fibers. Improved tear strength, abrasion resistance and sewability, antistatic property Stability in high temperature and alkaline condition, compatibility with bleach and dye bath additives, Hydrophilicity and antistatic properties, resistance to yellowing compatibility with other ionic formulations, no yellowing, ecofriendly

Disadvantages

Application method

Ref

Low compatibility with other auxiliaries, Slight yellowing, environmental effects

Exhaustion or padding

Goyal and Prabhu (2008)

Sensitive to metal ions imparting hardness to water and electrolytes in the finishing bath

Padding

Wahle and Falkowski (2002)

Lack of distinctive substantivity to the fiber substrates

Padding

Mooney (2003)

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Table 6.1 Classification of common textile softeners. Ionic nature Example Advantages

Amphoteric

Pseudoionic

Silicone based

ethoxylates of fatty amines, castor oil, ethoxylated fatty alcohol, ethoxylated fatty esters Substituted amino acids, amine oxide, betaine and sulfobetaines, amphoteric imidazoline Pseudoionic softeners are formed by combining nonionic and cationic or anionic softeners.

Average level of softness

Padding

Teli (2015)

Pseudocationic softeners are used on white fabrics with good affinity and almost same softness as cationic softeners along with lower drying temperature Efficient softness, temperature resistance

–

Padding

Nostadt and Zysch (1997)

Yellowing, darker shades in case of amino functional silicones, environmental effects

Padding

O’Lenick (2000); Somasundaran et al. (2010) Nanosoftening

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Polydimethyl siloxane (PDMS), polymethyl hydrogen siloxane (PMHS), aminofunctional silicone, epoxysilicone, amidosilicones, hydrophilic silicones,

good compatibility with another finishing, antistatic and hydrophilic properties

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R R R R R Si O Si O Si O Si R R R R1 R x O R:CH3 R1:H , CH3 , R’ NH2 , R’ HC CH2 , NH C R’ O

Fig. 6.2 Chemical formula of common silicone-based softeners.

In addition, silicone-based softeners usually provide durable softness together with additional properties, including improved crease resistance and wear comfort. This arises from the ability of silicone polymer to form elastic network entrapping fibers within the matrix, making the fibers capable of recovery from deformation. Moreover, due to the high-temperature resistance of silicone-based softeners, they impart flame-retardant properties through the silica ash acting as insulating blanket (Jang and Yeh, 1993; Butts and Shaffer, 2006). In spite of efficient softness, amino silicone-based softeners may suffer from yellowing effect during curing. In this regard, polysiloxanes modified with primary amines showed increased thermal yellowing due to oxidative decomposition of amino groups and the formation of chromophoric groups, whereas this effect was negligible for polysiloxanes containing tertiary amines (Lacasse and Baumann, 2004). Moreover, it has been reported that fabric pilling tendency is increased after softening finishing. Considering the appropriate softness brings about by silicone-based softeners, researchers have made tremendous efforts to resolve their limitations. To this end, hydrophilic silicones have been introduced to provide both softness and comfort properties through hydrophilicity. These include organosilicone terpolymers containing a number of reactive epoxy groups and polyoxyalkylene groups, silylated organic polymers obtained by reacting polymeric organic acids with silylated amino functional polyethers, hydrophilic organosilicone, including a trialkoxysilyl pendant group, and a polyoxyethylene/polyoxypropylene chain terminated with a hydrogen or acyl group. Silicones carrying hindered amino functional groups with good hydrophilicity without yellowing, organopolysiloxanes comprising carboxyl groups offering good softening with little yellowing and modified alkyl epoxy silicone compositions capable of curing at ambient conditions are some of the advanced silicone based softeners (Chardon and Olier, 2011; Gupta, 2013; Teli, 2015).

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Coapplication of the polyurethane resin along with silicone-based softener and citric acid has been reported as a successful method to reduce fabric pilling along with improved crease resistance properties (Montazer and Hashemikia, 2012). There have been also some patents concerning with encapsulated softeners to allow their slow release. Softeners mixed with aroma chemicals to impart simultaneous fragrance and softness is also reported (Ibrahim et al., 2013). Encapsulation methods will be discussed in more detail in Chapter 19. In addition to softening effect of polysiloxanes, they have been successfully introduced as stabilizing agents for nanofinishing of textiles (Dastjerdi et al., 2010). For instance, durable antibacterial properties have been achieved on polyester fibers using Ag/TiO2 nanoparticles along with polysiloxane as stabilizer. Moreover, by controlling the concentration of nanoparticles and polysiloxane softener, it is possible to achieve adjustable hydrophilicity/hydrophobicity. This is due to the alteration in polysiloxane functional groups orientation on the surface and multiple size roughness created by two nanoparticles with different size (Dastjerdi et al., 2012). Multiple size surface roughness has been thoroughly discussed in Chapter 2. Crosslinkable polysiloxane softener, which is resistant to oxygen radicals, mechanical, thermal, and chemical attacks, is also effective as a photocatalyst assistant of TiO2 nanoparticles. This arises from the ability of polysiloxaneshield nanoreactor to trap more dye molecules for further degradation by photocatalytic activity of TiO2 (Dastjerdi et al., 2013).

6.3 NANOSOFTENING Similar to positive effect of nanotechnology on several textile finishing sectors, softening finishing has been also substantially affected by nanotechnology. Firstly, softening agents in nanosize range could easily penetrate into fibers, causing a plasticizing action on the fibrous polymer, reducing glass transition temperature. In this regard, nanoemulsions of silicone-based softeners have been successfully introduced providing high levels of softness. Secondly, as softness can be achieved by reduced friction, application of nanoplatelets such as nanolayers of silicate (nanoclay) or nanographene platelets that are delaminated and form nanolayers could be effective to hinder forces of friction at the fiber surface.

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6.3.1 Nanoclay Natural phyllosilicates, known as clays, such as montmorillonite (MMT) with a chemical structure of (Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2nH2O is a 2:1 type layered silicates consisting of packets of two tetrahedral silicate layers and an octahedral with adjacent margins. These sheets retain a negative charge, which is neutralized by exchangeable cations such as Na+ or Ca2+ located in the interlayer spacing (gallery) and on the surface. The replacement of the natural inorganic cations in the clays with other organic cations has been widely studied to alter the surface properties of clays in order to improve their adsorption capacity. Ion exchange with surfactant cations such as quaternary ammonium salts has been extensively investigated. The modification process may induce an enormous change in the surface and pore structure of clays and mediate the practical applications of clays as adsorbents or catalysts. They are also famous as antimicrobial agents due to their nontoxic and environment-friendly characteristics. Incorporating nanoclays into textiles by melt spinning or by producing polymer/nanoclay composite as a coating to finished textiles to impart flame-retardant properties has been widely studied (Asadi and Montazer, 2013). During the last 5 years, efforts to use nanoclays as nanofinishing agent to impart old-look, flame-retardant, UV protection, and antibacterial properties to denim garments without backstaining and clear effluent have been made. Studies revealed the positive effect of nanoclay on soft handle of the treated garments (Sadeghian Maryan et al., 2013a, b, 2015).

6.3.2 Nanosilicones Depending upon the particle size, silicone emulsions are categorized into macro (milky, particle size: 150–300 nm), semimicro (hazy, particle size: 80–120 nm) or micro (transparent, particle size below 40 nm) forms. Microemulsions, which are obtained only through the introduction of hydrophilic amino groups into the silicone basic chain, have higher shear stability. The most advanced in this series are nanoforms of silicone, with particle sizes of lower than 10 nm, which offer improved penetrability in textile substrates, providing excellent softness (Roy Choudhury et al., 2012). The smallersized silicone softeners show better performance and improved softness to a remarkable extent due to deep penetration and lubrication at the fiber level. Moreover, pilling resistance of fabrics is increased after treatment with nanosilicone-based softeners due to the increased slipperiness of fiber surface making fiber ends entangling difficult (C ¸ elik et al., 2010).

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A comparative study of various silicone softeners indicates that macrosilicones are less flexible and less hydrophilic compared to microsilicones, whereas nanosilicones offer the best hydrophobicity and pilling resistance without affecting fastness properties, due to the increase in slipperiness (Gulrajani, 2006). It has been reported that macrosilicones remain on the surface, nanosilicones penetrate deep inside the matrix, and microsilicones remain at the intermediate stage (Teli, 2015). Thus, the durability of finishing with nanosilicones is higher than the other sizes. However, there have been reports considering the adverse effects of nanosilicones on physical properties such as tensile strength and abrasion resistance. The first published literature concerning with nanoemulsion silicone softeners dated back to the year 2008 where polyester fabrics were treated with nano- and microemulsion silicone softeners. More decrease in bending length was observed for nanoemulsion silicone-treated samples compared to microemulsions. Moisture regain was decreased for samples treated with nano- and microsoftener solutions. Nanosilicone particles may create a stronger barrier due to reducing water transmission (Parvinzadeh and Hajiraissi, 2008). In the next study researchers aimed at investigating the effect of nanosilicone softener application on color fastness, abrasion, and pilling resistance properties of knitted fabrics. The abrasion resistance of sample fabrics deteriorates by application of nanosilicone softener. It is the possible result of fiber mobility inside the fabric, which is increased by nanosilicone softener. Pills on the fabric are formed by entangled fiber ends; however, nanosilicone softener increases the slipperiness of fiber surface and entangling of fiber ends becomes difficult. Therefore, nanosilicone treatment improves the pilling resistance of the fabrics. In the case of color fastness, it is evident that nanosilicone softener treatment has no deterioration effect on color fastness (C ¸ elik et al., 2010). In 2015 bleached cotton fabrics were dyed with CI Reactive Black 5 and then treated with known concentrations of silicone softeners by the pad-dry method. The silicone nanoemulsion was combined with micro- and macroemulsion softeners using blending ratios of nano:micro (1:1) and nano: macro (1:1). Treated fabrics were compared in terms of physical properties such as fabric handling, wrinkle recovery angle, bending length, abrasion resistance, and tensile strength. The fabric handling performance results show that the silicone nanoemulsions outperform the micro- and macroemulsions in terms of fabric softness, smoothness, cooler feel, and thinness. The silicone nanoemulsion showed a significantly increased WRA in

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comparison to neat micro-, neat nano-, and other combinations. Results of fabric bending length showed that increasing the concentration of softeners from 10 to 40 g/L decreased the bending length of the fabric. The silicone nanoemulsion deteriorated the tensile strength of the fabric to a greater extent in comparison to neat micro, macro, and combinations; however, combining nano- with macroemulsion softener improved the tensile strength. In comparison to nano- and microemulsion softeners, the macroemulsions showed enhanced color yield. Scanning electron microscope (SEM) analysis suggests that the fiber morphology of the treated fabrics was very smooth and uniform. Silicone nanoemulsion softener indicated an advantage over many physical properties except for the tensile strength; however, this can be compensated by use of the macroemulsion softener in combination (Jatoi et al., 2015).

6.4 CONCLUSION Softening finishing is also dealt with today’s challenge of health and environmental issues. In this regard, application methods with less environmental effects have been extensively attracted researchers. This ranges from use of ultrasound in the treatment of textile substrates with softeners to microwave application replacing conventional thermal condensation methods. Considering the effectiveness in bringing high level of softness, siliconebased softeners have been modified by ester groups to impart biodegradability to them. There is an urge to search for new softening agents or choosing the appropriate blends of softeners to provide multifunctional properties together with durable softness and limited adverse effect on other fiber inherent properties and environmental impact. It seems that application of nanoplatelets such as nanoclays would be effective to provide durable softness with simultaneous antibacterial and flame-retardant properties.

REFERENCES Asadi, M., Montazer, M., 2013. Multi-functional polyester hollow fiber nonwoven fabric with using nano clay/nano TiO2/polysiloxane composites. J. Inorg. Organomet. Polym. Mater. 23, 1358–1367. Bajaj, P., 2002. Finishing of textile hand assessment in the United States and Japan. Text. Res. J. 56, 227–240. Berthiaume, M.D., Baum, A.D., 1997. Organofunctionalized silicone resins for personal care applications. J. Soc. Cosmet. Chem. 48, 1–21. Butts, M.D., Shaffer, K.A., 2006. Silicone based flame retardant systems for textiles. US Patent 7,147,671 B2.

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C ¸ elik, N., Deg˘irmenci, Z., Kaynak, H.K., 2010. Effect of nano-silicone softener on abrasion and pilling resistance and color fastness of knitted fabrics. Teksti˙l ve Konfeksi˙yon 1, 41–47. Chardon, J., Olier, P., 2011. Treating textile materials with polyorganosiloxanes. US Patent 8,038,727. Dastjerdi, R., Montazer, M., Shahsavan, S., 2010. A novel technique for producing durable multifunctional textiles using nanocomposite coating. Colloids Surf. B. Biointerfaces 81, 32–41. Dastjerdi, R., Montazer, M., Stegmaier, T., Moghadam, M.B., 2012. A smart dynamic selfinduced orientable multiple size nano-roughness with amphiphilic feature as a stainrepellent hydrophilic surface. Colloids Surf. B. Biointerfaces 91, 280–290. Dastjerdi, R., Montazer, M., Shahsavan, S., B€ ottcher, H., Moghadam, M.B., 2013. Novel durable bio-photocatalyst purifiers, a non-heterogeneous mechanism: Accelerated entrapped dye degradation into structural polysiloxane-shield nano-reactors. Colloids Surf. B. Biointerfaces 101, 457–464. Goyal, R., Prabhu, C.N., 2008. Cationic softener concentrates. Courage 55 (10), 95–96. Gulrajani, M.L., 2006. Nano finishes. Indian J. Fibre Text. Res. 31, 187–201. Gupta, D., 2013. Softening treatments for technical textiles. In: Gulrajani, M.L. (Ed.), Advances in the Dyeing and Finishing of Technical Textiles, first ed. Elsevier, USA. Ibrahim, N.A., El-Sayed, Z.M., Fahmy, H.M., Hassabo, A.G., Abo-Shosha, M.H., 2013. Perfume finishing of cotton/polyester fabric cross-linked with DMDHEU in presence of softeners. Res. J. Text. Appar., 58–63. Jang, K., Yeh, K., 1993. Effect of silicone softeners and silane coupling agents on the performance properties of cotton fabrics. Text. Res. J. 63, 557–565. Jatoi, A.W., Khatri, Z., Ahmed, F., Memon, M.H., 2015. Effect of silicone nano, nano/ micro and nano/macro-emulsion softeners on color yield and physical characteristics of dyed cotton fabric. Journal of Surfactants and Detergents 18, 205–211. Lacasse, K., Baumann, W., 2004. Textile Chemicals-Environmental Data and Facts. Springer, Heidelberg, pp. 381–393. Mahapatro, B., Shenai, V.A., Saraf, N.M., 1991. Chemistry and applications of softening agents for textiles. Colourage 38, XII-XXIII. Mallinson, P., 2001. Soft sell. Int. Dyer 186, 36–40. Montazer, M., Hashemikia, S., 2012. Application of polyurethane/citric acid/silicone softener composite on cotton/polyester knitted fabric producing durable soft and smooth surface. J. Appl. Polym. Sci. 124, 4141–4148. Mooney, W., 2003. Chemical softening. In: Heywood, D. (Ed.), Textile Finishing. Society of Dyers and Colorists. Nostadt, K., Zysch, R., 1997. Softeners in the textile finishing industry. Colourage, 53–57. O’Lenick, J., 2000. Silicone emulsions and surfactants. J. Surfactant Deterg. 3, 387–393. Parvinzadeh, M., Hajiraissi, R., 2008. Effect of nano and micro emulsion silicone softeners on properties of polyester fibers. Tenside Surfactant Deterg. 45, 254–257. Roy Choudhury, A.K., Chatterjee, B., Saha, S., Shaw, K., 2012. Comparison of performances of macro, micro and nano silicone softeners. J. Text. Inst. 103, 1012–1023. Sadeghian Maryan, A., Montazer, M., Harifi, T., Mahmoudi Rad, M., 2013a. Aged-look vat dyed cotton with anti-bacterial/anti-fungal properties by treatment with nano clay and enzymes. Carbohydr. Polym. 95, 338–347. Sadeghian Maryan, A., Montazer, M., Rashidi, A., 2013b. Introducing old-look, soft handle, flame-retardant, and anti-bacterial properties to denim garments using nano clay. J. Eng. Fibers Fabr. 8, 68–77. Sadeghian Maryan, A., Montazer, M., Damerchely, R., 2015. Discoloration of denim garment with color free effluent using montmorillonite based nano clay and enzymes: nano bio-treatment on denim garment. J. Clean. Prod. 91, 208–215.

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Schindler, W.D., Hauser, P.J., 2004. Chemical Finishing of Textiles. Woodhead Publishing, Cambridge. Somasundaran, P., Purohit, P., Gokarn, N., Kulkarni, R.D., 2010. Silicone emulsions— interfacial aspects and applications. Househ. Personal Care Today 3, 35–42. Teli, M.D., 2015. Softening finishes for textiles and clothing. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge. Wahle, B., Falkowski, J., 2002. Softeners in textile processing. Part 1: An overview. Rev. Prog. Color. 32, 118–124.

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Nanocoating and lamination 7.1 INTRODUCTION: DEFINITION AND GENERAL CONCEPTS 7.1.1 Coating Coating is generally defined as forming a layer of chemical formula on one or both sides of fabric substrate usually woven, knitted or nonwoven, creating a composite structure consisting of at least two components. The final properties of the coated fabric are function of both the fabric and the coating. Conventionally, coating material includes natural or synthetic polymers and the coating procedure follows by heating and curing for polymerization. Coating thickness, weight, chemical formula, and number of layers are dependent on the end use of the coated fabric. In some cases, coating may be sandwiched between two fabric layers. Various polymers have been applied as coating compounds to obtain desired functionalities. The most applicable polymer coatings for textile substrates are natural rubber (polyisoprene), styrene-butadiene rubber, nitrile rubber (acrylonitrile-butadiene copolymers), neoprene (polychloroprene), butyl rubber (isobutene-isoprene copolymers), hypalon (chlorosulfonated polyethylene), polyvinyl chloride (PVC), polyvinylidene chloride, polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, fluororubbers, polyurethanes (PUs), and silicone rubbers (polysiloxanes) (Wilkinson, 1996). Biocompatibility, higher thermal, mechanical and chemical stability, increased wear protection, and lower friction or corrosion are some of the properties that can be brought up by coating. Various functionalities such as soil release, water and oil repellent, water proof, thermal resistance and insulation, chemical and solvent resistance, corrosive resistance, abrasion resistance, aging resistance, and stiffness have been imparted into coated fabric depending on the chemical formula of coating. Coated fabrics have been used in many industrial applications such as architecture, construction, transportation, safety, and protective systems (Joshi and Butola, 2013).

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7.1.2 Lamination When two or more layers, one of which is a fabric, are closely bonded together via added adhesive, heat and pressure, or inherent adhesion properties of one of the components, the process is called lamination. The added layers could be polymers or in some cases metal particles. Selection of appropriate adhesive system is the important factor in lamination processes. There are several parameters that need to be taken into account, including (Joshi and Butola, 2013): – Strong bonding durable to washing – Less effect on fabric esthetics – Less stiffening – Less effect on flexibility and drape – Less effect on comfort – Small amount of adhesive with maximum bonding effect – Environmental concerns

7.2 COATING METHODS Based on our literature review, the first general classification of coating was proposed in 1996 by Martin Wilkinson who grouped the coating process into direct and indirect methods. Direct coating (knife coating or spread coating) was regarded as the oldest and easiest method of coating that consists of placing a sharp blade or knife at a fixed distance from the substrate surface to uniformly spread the coating across the fabric, leaving a thin wet film. In this method, the fabric is stretched flat to form an even uniform surface and is transported under a stationary doctor blade. As the fiber moves forward, it is scraped by the knife and the polymer resin compound is spread evenly over the surface. Different blade angle positions and blade profiles have been developed affecting the coating add-on. During the years, direct coating has progressed based on the knife arrangement, typically known as knife on air, knife on blanket, and knife over roll (Wilkinson, 1996). While direct coating was the direct application of coating compound to the fabric, indirect coating consisted of polymer film formation on release paper following by the indirect transfer to the textile. The indirect method is also called transfer coating and was developed for delicate and stretchable fabrics, which could not be coated via direct method due to the distortion under the tension (Wilkinson, 1996). During the recorded history, several coating methods have been developed, which can be applied depending on the fabric nature, coating material,

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end use, and economic considerations. An important class of coating method is roll coating, which further expands into Mayer rod coating, direct roll coating, kiss coating, gravure coating, reverse roll coating, and dip coating. Among various roll coating methods, reverse roll coating, gravure coating, and Myer rod are the most versatile and important techniques. In spite of low cost and precise coating weight of gravure and Myer rod methods, reverse roll coating is beneficial due to its compatibility with a wide range of coating viscosities and coating weights independent of substrate thickness. Reverse roll coating consists of following steps (Joshi and Butola, 2013): 1. Coating on the transfer paper following by solvent evaporation 2. Coating on the second layer as a base layer to join the top layer to the fabric 3. Laying the fabric on top of the coating, nipping, solvent evaporation, and crosslinking the two layers 4. Peeling off the coated fabric from release paper The schematic representation of various coating methods is shown in Fig. 7.1. Dip coating (immersion or saturation coating) is also very popular due to simplicity and minimum detrimental effect on fabric strength. In this method, the substrate is dipped into coating bath, normally with low viscosity, following by squeezing the excess material by passing through nip rolls or a set of flexible doctor blades (Joshi and Butola, 2013). Next approach was foam coating as a more environment-friendly alternative to impregnation. Foam coating consists of direct coating of foams onto one side of the fabric at the appropriate concentration. This method benefits from low water to dry off and subsequent lower energy consumption. However, the foam may be instable and the reproducibility of the coating was not proper. Based on the form of coating compound, textile coating can be further classified into liquid coating (solutions and pastes) and dry coating (powder, granules, chips and films). Liquid coating can be applied by knife coating, roll coating, dip coating, and spray coating (Wilkinson, 1996). Hot melt extrusion and calendar coating are the main methods used for dry coating. Hot melt extrusion coating is used for solid thermoplastic polymers such as PU, polyolefins, and PVC. The polymer granules are fed into the nip between moving heated rollers. Zimmer machine with two melt rollers and Bema machine consisting of three rollers are the two popular hot melt coating equipment (Singha, 2012).

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Direct coating

Knife over air

Knife over blanket

Knife over roll

Indirect coating

Transfer coating

Roll coating

Direct roll coating

Kiss coating

Nip-fed

Pan-fed

Dip coating

Mayor rod

Gravure coating

Reverse roll coating

Fig. 7.1 Schematic representation of various coating methods.

Calendar is a number of five to more massive rollers with various configurations that rotate to crush the “dough” and smooth it into films of uniform thickness. The greater the number of rollers, the more accurate and uniform is the produced film. In addition to the heat generated from the friction of moving rollers, some of the rollers are heated to melt the polymer. In this method, the melted polymer is fabricated into a continuous sheet and adheres to the fabric substrate (Joshi and Butola, 2013). Scatter coating and dot coating are included in dry powder coating method in which fusible polymer powders such as polyethylene, polyamide, and polyester are coated into textiles with main application in carpet back coating. In scatter coating process, polymer powder of 20–200 μm is spread uniformly onto a moving textile substrate. The web is then passed through a fusion oven and calendared. Scattering can be done using a vibrating screen or a more precise method of hopper with a rotating brush arrangement. The coating weight is dependent on feed rate and web speed.

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In dot coating process, a heated web with surface temperature slightly less than the melting point of the polymer is brought in contact with an engraved roller, embedded with dry powder. The web is then coated with a tacky polymer powder, in a pattern dependent on the engraving. The engraved roller is kept cool to prevent the polymer from sticking to the roll (Joshi and Butola, 2013).

7.3 LAMINATION METHODS The first lamination method was flame laminating through which PU foam is melted over a gas flame at around 950°C and bonds the textile substrate. Harmful gaseous emission hindered the wide application of this method as the device should be equipped with carbon filter absorbers making the process high cost (Stephen et al., 2005). An effective method of laminating is known as hot melt lamination through which hot melt adhesives (thermoplastic polymers) are melted by heat and spread on the fabric in the hot state. Slot die extrusion, nip roller, and calendaring are the main techniques used for hot melt laminating (Joshi and Butola, 2013). Film lamination can be also used in which preformed polymer film is applied to the textile with the aid of an adhesive under light pressure passing through ovens or heated rollers. Adhesive systems could be aqueous based benefiting from safety, soft handle with high breathability however at the expense of high-energy consumption or solvent based with easier surface wetting, easier drying but environmental impacts. Kiss coating, transfer coating, or rotary screen printing are mainly used for aqueous or solvent-based adhesive laminating (Singha, 2012).

7.4 NANOCOATING With the advent of coating technologies from direct knife coating to roll coatings, foam coating, calendar coating, extrusion, and others, some of the application limitations of coating methods have been resolved. However, conventional coating methods still suffer from drawbacks, including strength loss, improper adhesion, poor abrasion resistance, and low durability. Minimizing the coat-to-weight ratio was an effective solution to overcome the involved problems, and this has been brought thanks to

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nanotechnology. Hence, the process of covering a material with a layer with thickness on a nanometer scale (50–100 nm) or covering a surface with a nanoscale entity has been introduced and defined as nanocoating. Nanocoating provides higher coating reactivity, strength, and durability. Nanocoatings are developed during the coating process using innovative methods or formed using nanocoating formula. Vapor deposition, plasma-assisted/ion-beam-assisted techniques, pulsed laser deposition, mechanical milling, magnetron sputtering, self-assembly, layer-by-layer (LBL) coating, dip coating, sol-gel coating, and electrochemical deposition are among the widely used nanocoating methods. In the following sections, we try to focus on each of these techniques along with their advantages and limitations (Parvinzadeh Gashti et al., 2016).

7.4.1 Nanocoating techniques 7.4.1.1 Electroless deposition Electroless deposition or plating of metals such as silver, aluminum, copper, nickel, and iron is a uniform coating of metallic layer on the surface of fibers through chemical reduction of metal ions in an aqueous solution and the subsequent deposition of metal without the use of electrical energy. The electroplated fibers benefit from electrical conductivity and electromagnetic interference (EMI) shielding effectiveness depending on the applied metal. In most cases, prior or simultaneous surface modification of fibers through physical or chemical methods is required for good adherence of the electroplated layer on the surface. For instance, Lu et al. (2010) formed a silica-like layer on polyester fabric using acetone solution of (3-aminopropyl) trimethoxysilane following by anhydrous toluene solution containing 3-mercaptopropyltriethoxysilane to produce silver-plated polyester fabric with good conductivity and strong adherence using ultrasonic-assisted electroless plating. Moreover, Wang et al. (2012) carried out the electroless plating of silver on polydopaminefunctionalized polyester fabric. In addition to these methods requiring preactivation of surface for durable electroless plating, Montazer and Allahyarzadeh (2013) proposed a novel route to introduce compact nanolayer of silver nanoparticles on polyester surface. In this method, silver was directly plated onto the polyester fabric using simple, low-cost conventional exhaustion process without the need for sensitization and activation processes. The polyester fabric was hydrolyzed with sodium hydroxide to introduce carboxylate and hydroxyl functional groups onto the polyester

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Fig. 7.2 FESEM image of polyester fiber silver plated using the method proposed by Montazer and Allahyarzadeh (2013). Reprinted with permission from Montazer, M., Allahyarzadeh, V., 2013. Electroless plating of silver nanoparticles/nanolayer on polyester fabric using AgNO3/NaOH and ammonia. Ind. Eng. Chem. Res. 52, 8436–8444. Copyright 2013, American Chemical Society.

fabric surface and also to produce terephthalic acid, ethylene glycol, and other forms of water-soluble low-molecular-weight polyester structures as reducing agents, as a result of polyester alkali hydrolysis. Silver ions were then absorbed onto the polyester fabric surface through binding to the carboxylate and hydroxyl functional groups and then reduced to silver metal. This step was followed by the formation of a condensed nanolayer of silver nanoparticles on the polyester fabric surface by posttreatment with ammonia. Field emission scanning electron microscope (FESEM) image of the silver-plated polyester fibers using the proposed method is shown in Fig. 7.2 indicating a uniform and condensed silver nanolayer coated on the polyester. 7.4.1.2 Vapor deposition Vapor deposition technique is coating processes in which materials in a vapor state are condensed through condensation, chemical reaction, or conversion to deposit thin films on different substrates, and classified as physical (PVD) and chemical (CVD) vapor deposition methods. PVD is vaporization process through which atom-by-atom or molecule-by molecule transfer of material occurs from the solid phase to the vapor phase resulting in deposition on the surfaces of textile substrates. PVD is a process in which a thin layer of coating is deposited on the substrate through a vaporization process. A solid material is used as the source of vapor, which is transferred to the surface of substrate, forming a uniform coating layer. Through PVD

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method, the vapor atoms or molecules generated from a solid material are placed next to each other on the substrate. Vacuum evaporation, ion implantation, and sputtering are the most important techniques used in PVD. In vacuum evaporation, the evaporation and deposition of film on substrate is carried out in the vacuum condition. This allows vapor molecules to condense directly on the substrate surface, creating a solid film, and prevents a reaction with the free space. Vacuum evaporation has been used to produce EMI shielding textiles. Thermal vacuum evaporation of silver was used to deposit a conductive layer on polyester woven fabric. The main principle of ion implantation as an environment-friendly technique is to bombard the surface of a solid material with known metallic ions to implant into the near surface of textiles (Wei, 2009). Among PVD methods, magnetron sputter systems have been widely used to deposit coatings such as metallic, oxide, polymer, and composite coatings. During sputter coating, reactive gas molecules strike a target and cause atoms from the target to travel toward the substrate. Nanostructured thin films containing metals and metal oxides such as zinc oxide (ZnO), copper (Cu), silver (Ag), tin-doped indium oxide, iron oxide, and aluminumdoped zinc oxide have been sputter deposited on different fabrics providing different properties, including antibacterial, conductivity, and UV-shielding features. The most important advantage of sputter deposition is that materials with high melting point can be easily sputtered on textile substrates at low temperature. Nanocomposite coatings can be also easily obtained by the cosputtering of various materials. Sputter coating also affects the surface roughness of treated substrates—for instance, the effect of copper sputter coating on surface roughness and dynamic contact angle of polyester fibers. The increase in surface roughness was caused by the growth of copper clusters on the polyester fiber surface as evidenced by atomic force microscopy (AFM) and increased dynamic contact angle hysteresis (Wei et al., 2004). Wei et al. (2007) investigated the functionalization of spun-bonded polypropylene nonwovens by sputter coating of copper and silver to reduce the ultraviolet and visible light transmittance of the samples due to light shielding effect. Surface electrical resistance of the nonwovens was also significantly reduced. There are also successful reports concerning EMI shielding efficiency of polyester nonwovens sputtered with silver. Recently, aluminum sputter coating was applied on polyester fabrics previously padded with layers of nanocarbon black and carbonyl iron powders to produce textile with the ability to absorb physical waves, namely, X-band microwave (Simayee and Montazer, 2016).

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Xu et al. (2007) used magnetron sputter coating to deposit nano TiO2 film on the surface of cotton woven fabric and polyester knitted fabric at room temperature providing self-cleaning properties. On the other hand, CVD is using a chemical reaction to form a coating from a vapor, with the reaction by-products leaving as volatile species. CVD mainly requires high temperature to start the chemical reaction. However, modified forms of CVD, namely, plasma-enhanced CVD and photo-CVD have been introduced, enabling the chemical reaction formation at low temperature. The most famous application of CVD in textile finishing is electroconductive composites made of polypyrrole that can be used in microwave attenuation, static charge dissipation, EMI shielding, and sensors (Malinauskas, 2001). Production of superhydrophobic surfaces with self-cleaning properties has been also achieved by thermal CVD of polymethylsiloxane coating on cotton cellulose. The proposed method involved the reaction of cotton with trichloromethylsilane following by reaction with pyridine solution at room temperature and drying at 150°C for 10 min to polymerize Si–OH to form a nanoscale silicone coating (Li et al., 2007). Recently, a progressive method has been introduced to form semiconductor compounds and very thin inorganic coating onto textile by atomic layer deposition. The procedure involves exposing a substrate to a vapor that contains one of the related elements. The vapor is then removed from the process chamber, and a second vapor is admitted, to react with the first atomic layer, forming a second coat. The capability of the method was proved by Hyde et al. (2007) who deposited aluminum oxide films on cotton at 100°C from sequential 1 or 2 s exposure to low-pressure trimethyl aluminum in argon and water vapor. The subsequent reaction with water forms an oxide layer, with the carbonaceous by-products removed as volatiles. 7.4.1.3 Layer by layer LBL technique is another method for fabricating a thin layer film on textile substrates. Generally, LBL is based on electrostatic interaction and was first introduced through the alternate deposition of polyelectrolytes with opposite charge on various substrates. The LBL technique is not limited to polyelectrolytes and can be used for nanoparticles and nanowires as well. It has been used to create nanoscale multilayer films on various substrates. Applying a thin nanocomposite layer on the fabric surface could be also achieved by LBL technique. Although formation of uniform multilayer films on

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textile substrates is difficult due to 3D nonplanar surface structure, controlled deposition conditions, including concentration and number of layers, ionic strength, and pH is important to optimize LBL process on fibers. First examples of LBL technique on textile substrates were deposition of various materials, including polyelectrolytes and nonreactive dyes onto textile fibers. Formation of multilayer thin film of poly(allylamine) and poly(styrenesulfonate) (PSS) on cotton fibers, and deposition of laccase and urease on cotton fibers using poly(diallyldimethylammonium chloride) (PDDA) as an electrostatic glue between the proteins are some of the recent studies (Wei, 2009). Chitosan and PSS were used as cationic and anionic polyelectrolytes to obtain uniform deposition of bilayers with antibacterial activities on cotton fibers. In 2014, chitosan and pentasodium tripolyphosphate-based bilayers were fabricated on cationized woven cotton fabric via LBL technique, producing novel antibacterial textiles with the highly attractive feature in the medical and hygienic products (Rouhani Shirvan et al., 2014). Various nanoparticles have been also incorporated into textile substrates via LBL technique. For instance, chitosan nanoparticles and silver-modified chitosan nanoparticles were applied on cotton and polyester fibers to impart antibacterial properties by LBL method. Nylon and silk fibers were sequentially dip coated with PDDA and silver nanoparticles capped with poly(methacrylic acid) to produce antibacterial thin film through LBL method. Antibacterial, UV blocking, and self-cleaning efficiencies have been imparted into precationized cotton fabric by nano ZnO and TiO2 incorporation via LBL method. Flame-retardant cotton fabric was developed using polyethylenimine/nano clay layers. Increased thermal stability of polyester fibers treated with LBL deposition technique using α–zirconium phosphate nanoplates with cationic PDDA has been also reported. Similar results have been achieved via LBL deposition of silica nanoparticles on polyester fibers (Gulrajani and Gupta, 2011). 7.4.1.4 Plasma polymerization Plasma polymerization provides the deposition of nanocoatings on fibers via gas phase activation and plasma substrate interactions. This environmentfriendly durable nanocoating method overweighs conventional coating methods as it needs a very low material and energy input, without interference to the bulk properties of textiles such as feel, handle, optical properties, and mechanical strength. Plasma polymerization is performed using different types of plasma polymerizable gases (monomers) such as hydrocarbons

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(i.e., methane, ethylene, or acetylene) or organosilicon monomers to obtain various properties. For instance, plasma polymerization of organosilicon compounds is reported to impart good dielectric properties, thermal stability, flame retardant as well as adjusting the wettability of textiles (Joshi, 2008). Multifunctional acrylic-like coating on fibers such as polyester or polyamide has been obtained by low-pressure plasma polymerization using acrylic acid as monomer. Acrylic coatings were found to improve their wettability, dyeability (using acid dyes), and also the cell adhesion for tissue engineering (Detomasa et al., 2005). 7.4.1.5 Sol gel Sol gel is a chemical method based on hydrolysis and condensation reactions producing nanoparticles or nanocoatings. Sol-gel derived solutions can be applied on textile materials using a simple pad-dry-cure or dip coating for preparing self-cleaning, antibacterial, UV protection, and flame-retardant properties. Sol-gel coating of titanium dioxide nanocrystals and silica nanoparticles has been widely studied (Parvinzadeh Gashti et al., 2016). There are many publications regarding the application of metal oxide nanoparticles such as TiO2 through sol gel method. Daoud and his research group have done a vast number of studies concerning the nano TiO2 sol gel coating of cotton and wool fabrics. In their studies, TiO2 nanosols were synthesized through a low-temperature sol gel method from the precursor of TTIP in presence of ethanol, acetic acid, and nitric acid. The coating process of fabrics was conducted based on the conventional method of dip-pad-drycure. An efficient antibacterial property and UV protection have been imparted into the coated fabrics via sol gel coating method (Daoud and Xin, 2005). Modification of TiO2 by metal, including Ag, Au, and Pt, was also carried out and the nanocomposite prepared by sol-gel was applied on cotton and wool fabric, indicating enhanced photocatalytic activity by continuous coating layer of composite nanoparticles on fibers (Pakdel et al., 2014).

7.5 SMART NANOCOATINGS Together with the advent of nanocoating, the term “smart and active coating” has been introduced versus “common coating.” Smart coatings are those that respond to an environmental stimulus such as temperature, pH, light, moisture, pressure, sound, and magnetic and electric field. Memory polymer coatings, durable self-cleaning coatings, durable self-healing

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coatings, breathable coatings, and conductive coatings are among the various types of smart coatings that have been developed. Coating using phase change materials (PCM) and conductive coatings will be thoroughly discussed in Chapters 19 and 17 concerning nanoencapsulation and conductive nanofinishes.

7.6 CONCLUSION During the last years, new coating and laminating methods have been developed to introduce more flexible coated/laminated textile substrates with multifunctional properties and minimum detrimental effect on the environment. Substitution of solvent-based methods due to environmental dangers and water-based methods because of high energy and water consumption are some of the new trends. In this regard, plasma technology is a good response to the involved challenges. Nanocoating technologies, including electroless deposition, PVD, CVD, LBL, and sol-gel, are successful candidates to form nanolayers of metal, metal oxides, or polymers on various textile surfaces. Further to the application methods, eco-friendly coating materials such as biodegradable polymers are also widely investigated to replace harmful coating formulas.

REFERENCES Daoud, W.A., Xin, J.H., 2005. Synthesis of single-phase anatase nanocrystallites at near room temperatures. Chem. Commun. 3, 2110–2112. Detomasa, L., Gristina, R., Senesi, G.S., Agostinno, R.D., Favia, P., 2005. Stable plasmadeposited acrylic acid surfaces for cell culture applications. Biomaterials 26, 3831. Gulrajani, M.L., Gupta, D., 2011. Emerging techniques for functional finishing of textiles. Indian J. Fibre Text. Res. 36, 388–397. Hyde, G.K., Park, K.J., Stewart, S.M., Hinestroza, J.P., Parsons, G.N., 2007. Atomic layer deposition of conformal inorganic nanoscale coatings on three-dimensional natural fiber systems: Effect of surface topology on film growth characteristics. Langmuir 23, 9844–9849. Joshi, M., 2008. The impact of nanotechnolgy on polyesters, polyamides and other textiles. In: Deopura, B.L., Alagirusamy, R., Joshi, M., Gupta, B. (Eds.), Polyesters and Polyamides. Woodhead Publishing, Cambridge, UK. Joshi, M., Butola, B.S., 2013. Application technologies for coating, lamination and finishing of technical textiles. In: Gulrajani, M.L. (Ed.), Advances in the Dyeing and Finishing of Technical Textiles. Woodhead Publishing, Cambridge, UK. Li, S., Xie, H., Zhang, S., Wang, X., 2007. Facile transformation of hydrophilic cellulose into superhydrophobic cellulose. Chem. Commun. 5, 4857–4859. Lu, Y., Jiang, S., Huang, Y., 2010. Ultrasonic-assisted electroless deposition of Ag on pet fabric with low silver content for EMI shielding. Surf. Coat. Technol. 204, 2829–2834.

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Malinauskas, A., 2001. Chemical deposition of conducting polymers. Polymer 42, 3957–3962. Montazer, M., Allahyarzadeh, V., 2013. Electroless plating of silver nanoparticles/nanolayer on polyester fabric using AgNO3/NaOH and ammonia. Ind. Eng. Chem. Res. 52, 8436–8444. Pakdel, E., Daoud, W.A., Afrin, T., Sun, L., Wang, X., 2014. Self-cleaning wool: effect of noble metals and silica on visible-light-induced functionalities of nano TiO2 colloid. J. Text. Inst. 106, 1348–1361. Parvinzadeh Gashti, M., Pakdel, E., Alimohammadi, F., 2016. Nanotechnology-based coating techniques for smart textiles. In: Hu, J. (Ed.), Active Coatings for Smart Textiles. Woodhead Publishing, Cambridge, UK. Rouhani Shirvan, A., Hemmati Nejad, N., Bashari, A., 2014. Antibacterial finishing of cotton fabric via the chitosan/TPP self-assembled nano layers. Fibers Polym. 15, 1908–1914. M. Simayee, M. Montazer. 2016. A protective polyester fabric with magnetic properties using mixture of carbonyl iron and nano carbon black along with aluminium sputtering, J. Ind. Text. DOI: https://doi.org/10.1177/1528083716667261. Wilkinson, M., 1996. A review of industrial coated fabric substrates. J. Coated Fabr. 26, 87–106. Singha, K., 2012. A review on coating & lamination in textiles: processes and applications. Am. J. Polym. Sci. 2, 39–49. Stephen, G., Serge, B., Meryline, R., Isabelle, V., Lan, T., Rene, D., Frank, P., 2005. Flame retarded polyurea with microencapsulated ammonium phosphate. Polym. Degrad. Stab. 88, 106–113. Wang, W., Cheng, W., Tian, M., Zou, H., Li, L., Zhang, L., 2012. Preparation of PET/Ag hybrid fibers via a biomimetic surface functionalization method. Electrochim. Acta 79, 37–41. Wei, Q.F., Wang, X.Q., Gao, W.D., 2004. AFM and ESEM characterization of functionally nanostructured fibres. Appl. Surf. Sci. 236, 456–460. Wei, Q.F., Yu, L.Y., Hou, D.Y., Wang, Y.Y., 2007. Comparative studies of functional nanostructures sputtered on polypropylene nonwovens. e-Polymers 039. Wei, Q., 2009. Surface Modification of Textiles. Woodhead Publishing, Cambridge, UK. Xu, Y., Wei, Q.F., Wang, Y.Y., Huang, F.L., 2007. Preparation of TiO2 coated on fabrics and their photocatalytic reactivity. J. Donghua Univ. 24, 333–336.

FURTHER READING Makhlouf, A.S.H., 2014. Handbook of Smart Coatings for Materials Protection. Woodhead Publishing, UK.

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Nanocrosslinking 8.1 INTRODUCTION: GENERAL DEFINITION AND HISTORY OF CELLULOSE CROSSLINKING In general, crosslinking is a covalent or ionic bonding that links one polymer chain to another; thus, the polymer chains are bridged across. From the textile manufacturers’ point of view, crosslinking is the term generally associated with cellulose stabilization with certain compounds to improve the crease recovery properties. This includes the self-polymerize crosslinkers that form three-dimensional polymers, and cellulose reactants forming covalent bonds by reacting with cellulose hydroxyl groups (Harifi and Montazer, 2012). However, today we know that crosslinking has been expanded to other forms of textiles, including wool, silk, and synthetic fibers, including polyester and nylon. Within the history of cotton crosslinking, several chemical compounds have been introduced to achieve enhanced crease recovery properties with less practical limitations. This begins with phenol/formaldehyde and urea/ formaldehyde resins that form crosslinks between adjacent cellulose molecules; however, they suffered from chlorine retention problem. Although methylolmelamines were resistant to rendering by chlorine, they were not very successful due to their yellowing effect (Bajaj, 2002; Harifi and Montazer, 2012). Attempts were then made to introduce crosslinking reactant with no free NH groups. This resulted in the production of tetramethylol acetylenediurea and dimethylol ethyleneurea with very effective crease resistance properties, however with decreased light fastness of direct or reactive dyes (Harifi and Montazer, 2012). Dimethyl ether of dimethyloluron (DMEU), triazone resins, and dimethylol dihydroxyethyleneurea (DMDHEU) were the next generation of cellulose crosslinkers, and the latter one was very effective for durable press garments (Huang, 2000). Dimethyol carbamates were then introduced to replace DMDHEU due to chlorine retentive and yellowing effect. However, application of methyl and ethyl carbamates was diminished as they were carcinogenic (Bajaj, 2002). A vast number of studies in cotton crosslinking history were related to methods of reducing the formaldehyde release of N-methylol durable Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00008-X

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press finishes and introduction of chemical compounds with lower formaldehyde content or formaldehyde-free crosslinking systems. To this end, α-hydroxyalkyl amides, polymers from urea and glutaraldehyde, diamido dihydroxyethane, 1,3-dimethylurea and glyoxal (4,5-dihydroxy-1,3dimethylimidazolidinone, DHDMI), systems based on glyoxal with coreactive additives and several polycarboxylic acids have been developed (Harifi and Montazer, 2012). With the advent of polycarboxylic acids as cellulose durable press finish agents, the term “esterification crosslinking” has been introduced as the formation of a cyclic anhydride intermediate by the dehydration of two carboxyl groups, and the reaction between cellulose and the anhydride intermediate to form an ester. It is believed that polycarboxylic acids with three or more carboxyl groups bonded to the adjacent carbons of their molecular backbone with small molecular size for easier mobility of anhydride intermediate are effective crosslinking agents for cellulose (Harifi and Montazer, 2012). The popular polycarboxylic acids include citric acid (CA), 1,2,3,4-butanetetracarboxylic acid (BTCA), poly(maleic acid), and itaconic acid (ITA). In some cases, a combination of polycarboxylic acids have been applied to impart crease recovery properties such as maleic acid and ITA or CA/BTCA/malic acid or 1,2,3,4-butanetricarboxylic acid (BTA) and 1,2,3-propanetricarboxylic acid (PCA). 2-Hydroxy-4-6di-thiosuccinyl-s-triazine and novel anionic aqueous polyurethane modified with silane coupling agent and maleic anhydride were among the next generation of cotton crosslinking agents introduced to replace BTCA due to its high cost (Harifi and Montazer, 2012). In parallel with considerable effort made for new and more effective cotton crosslinking agents, two new terms, namely, “ionic crosslinking” and “ester and ionic crosslinking” have been also introduced. For ionic crosslinking, both anionic and cationic groups are introduced into two adjacent cellulose chains. As indicated in Fig. 8.1, carboxymethylated cotton and quaternized (cationized) cotton could form ionic crosslinked cellulose. Ester and ionic crosslinking include the precationization of cellulose with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride and esterification of cationized cotton with CA or BTCA in presence of sodium hypophosphite (SHP) as a catalyst. The involved reactions proposed by Hebeish et al. (2006) are shown in Fig. 8.2. Comprehensive review paper written by Harifi and Montazer (2012) is recommended for further detailed information on the cotton crosslinking. Apart from the type of cellulose crosslinking agents, decreased tensile strength, tearing strength and abrasion resistance of the treated cotton fabric

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Fig. 8.1 Ionic crosslinking.

are the major deficiency of crosslinking agents. The use of both N-methylol compounds, such as DMDHEU and polyfunctional carboxylic acids, has been shown to cause reduction in the properties of finished fabric. This may be caused by the cellulose acid degradation or cellulose crosslinking.

8.2 CROSSLINKING AS STABILIZATION AGENT In addition to cotton crosslinking for crease recovery properties, crosslinking chemicals have been applied as fixation agents to stabilize other finishing agents into fabrics. For instance, covalent crosslinking of chitosan into cellulose using GA, CA, and BTCA was successful to obtain durable antibacterial properties (El-tahlawy et al., 2005). Combination of crosslinking agents with flame-retardant finishing has been also reported. It was shown that dimethylphosphonopropionamide was covalently bound to cellulose by the reaction between N-methylol group and trimethylol melamine (TMM) used as a coreactant. TMM and DHDMEU were used to form a covalent linkage between hydroxy-functional organophosphorus oligomer as a flame retardant and cotton. In addition to crosslinking, they enhanced flameretardant properties due to nitrogen-phosphorus synergism (Cheng and Yang, 2009). To improve the washing durability of water repellency, some crosslinking agents have been used along with the water-repellent agents. Montazer (1996) applied BTCA, with the optimum concentration of 5 g/L, and

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Cell O CH2 CH CH2 N (CH3)3 + C6H8O7

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H

OO C H

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H

OO C H

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SHP Δ Cell-OH H OH

(CH3)3 CellOOC H

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OCC OH

CellOOC H H

Fig. 8.2 Ester and ionic crosslinking as proposed by Hebeish et al. (2006).

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different concentrations of fluorocarbon agent for water repellent finishing of cotton fabrics. It has been reported that the water repellency of the cotton treated with fluorocarbon resin and BTCA was much higher than the sample treated only with fluorocarbon resin (Xu and Shyr, 2001). In 2008, a novel per-fluorinated acrylate copolymer was prepared by emulsion polymerization and applied on cotton fabric, resulting in good and durable water repellency and increased crease recovery angle (Li et al., 2008). The stabilization of β-cyclodextrins (β-CDs) on textiles with polycarboxylic acids as binding and crosslinking agents has been also proposed. Through application of three different crosslinking agents, including two nonformaldehyde crosslinking agents (CA and BTCA) and one formaldehyde-based crosslinking agent (DMDHEU), Montazer and Jolaei (2010) stabilized β-CD on the spacer polyester fabric, indicating higher efficiencies of BTCA.

8.3 NANOCROSSLINKING Chemical crosslinking agents have been progressed during the past century as illustrated in Fig. 8.3 and nanocrosslinking has been introduced as a new era. In this chapter, the term nanocrosslinking is devoted to two categories of (1) crosslinking agents for fixation of nanoparticles on textile substrates and (2) nanoparticles as crosslinking agents, which are thoroughly discussed.

–Triazones –Dimethyloldihydroxyethyleneurea –Phenol/formaldehyde (DMDHEU) –Urea/formaldehyde –Carbamate

1928-2000

–Methylolmelamines (Melamine/formaldehyde) –Tetramethylolacetylenediurea –Dimethylol ethylenurea (DMEU)

Polycarboxylic acids –Citric acid (CA) –1, 2, 3, 4 butanetetracarboxylic acid (BTCA) Nanocrosslinking –Poly (maleic acid) (PMA) –Itaconic acid (ITA)

2000-Now

New era

–α-Hydroxyalkylamides –Polymers from urea and glutaraldehyde –Diamidodihydroxyethane –4,5-Dihydroxy-1,3-dimethylimidazolidinone (DHDMI) –Glyoxal with coreactive additives

Fig. 8.3 Crosslinking agents’ timeline.

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8.3.1 Crosslinking agents for fixation of nanoparticles on textile substrates As mentioned earlier in Chapter 2, one of the methods of nanoparticles application on textile substrates is through ex situ approach, which includes the presynthesis of nanoparticles along with preparation of stable dispersions following by textile application. In this technique, final fixation step is usually required for obtaining durable properties. In addition to durability, stabilization of nanoparticles on fabrics is of prominent importance mostly because of potential health and environmental concerns. Hence, crosslinking agents can be applied to fix the nanoparticles on textile substrates, providing durable ex situ nanofinishing. In these cases, the term “nanocrosslinking” is used as a combination of nanotechnology and crosslinking treatments. Meilert et al. attached TiO2 nanoparticles on the cotton fabric surface by using carboxylic acids as the linking spacers. They used succinic acid, PCA, and BTCA and established stable linkage between the particles and substrate. The coating process consisted of two main steps, including fabrics pretreatment with the chemical spacers and coating with TiO2 nanoparticles. Montazer and Pakdel in a series of publications examined different characteristics of wool fabrics coated with TiO2 nanoparticles (Montazer and Pakdel, 2011). They used BTCA and CA as two crosslinking agents in the presence of SHP to anchor the TiO2 nanoparticles onto the wool surface. In addition, surface oxidation of wool fabrics by potassium permanganate solution was employed as a pretreatment to increase the uptake of nanoparticles on the fabric surface. The reaction between crosslinking agents and the wool was related to the established bonds between the carboxyl groups of linking agents with functional groups of wool such as –NH2, –SH, and –OH during the curing step (Montazer and Pakdel, 2011). Nazari et al. (2009) utilized CA and BTCA to treat bleached cotton fabric in the presence of nano TiO2 and SHP under three different curing conditions, including ultraviolet (UV) irradiation, high temperature (High temp), and a combination of UV and high temperature (UV/High temp). According to their findings, the crosslinking process was more effective under UV-High temp condition than those obtained by UV or High temp alone. Under UV-Temp curing method, both crosslinking mechanisms of cotton fabric based on UV and Temp occurred. Irradiation of nano TiO2 with UV light in the wet carboxylic acid led to the formation of positive holes on TiO2 surface and proton, which may act as a Lewis acid catalyst and activate

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the carbonyl group of acid toward the addition of hydroxyl group of cotton fibers, leading to ester bond formation. Their proposed mechanism is shown in Fig. 8.4. Based on the findings, nano TiO2 acts as a cocatalyst to enhance the anticreasing properties of polycarboxylic/SHP treated cotton. Durable antibacterial and crosslinking finishing of cotton fabrics has been proposed with colloidal silver nanoparticles and BTCA without yellowing effect. It was found that BTCA as a crosslinking agent plays a prominent role in stabilizing the antimicrobial properties of the treated cotton fabric. It has been shown that in the presence of BTCA as a crosslinker silver nanoparticles entrapped physically on the cellulose structure and firmly attached to the fabric in comparison with the fabric without crosslinking agent. Different concentrations of commercial SiO2 nanoparticles along with BTCA and SHP were used and linkages between the BTCA and hydroxyl and carbonyl groups of cotton were confirmed (Parvinzadeh Gashti et al., 2016). Moreover, the same group reported that the surface coating of wool fabrics with nanozirconia imparts some novel features such as flameretardant and electromagnetic reflection wool. The wool fabrics were treated with different concentrations of ZrO2 nanoparticles in an ultrasonic bath containing CA and SHP followed by padding and UV illumination. Crosslinks between the nanoparticles and substrate were established during the UV illumination process (Parvinzadeh Gashti et al., 2016).

Fig. 8.4 Proton attraction mechanism for cotton crosslinking using carboxylic acids and nanophotocatalysts based on Nazari et al. (2009) research.

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The effective role of CA as stabilizing and protective agent against aggregation and oxidation of Cu nanoparticles on cotton fabric has been proved. Moreover, CA as a crosslinking agent crosslinks the hydroxyl groups of cellulosic chains, forming ester linkages (Sedighi et al., 2014).

8.3.2 Nanoparticles as crosslinking agents Another approach in nanocrosslinking is the use of nanoparticles as fillers or crosslinking agents may be able to enter in between the polymer chains because of their small size. In this way, we benefit from both nanoproperties and crosslinking, obtaining durable multifunctional textiles. Besides, unlike chemical crosslinking that has the disadvantage of imparting rigidity to the treated fabrics and decreased mechanical properties, nanoparticles as crosslinkers seem not to interfere much to the polymer, even resulting in improved tensile strength. In comparison to the use of crosslinking agents for fixation of nanoparticles ex situ applied on textile substrates, nanoparticles are usually acted as crosslinking agents during the in situ method. Here, while there is no need for further fixation of nanoparticles, they are responsible for imparting durable multifunctional features along with enhanced mechanical properties in most cases. Nanocrosslinking can occur during the in situ synthesis of various nanoparticles and nanocomposites. Here, some of the recent studies concerning with nanocrosslinking have been explained. In a study carried out by Poortavasoly et al. (2014) aminohydroxylated polyester fabric with durable antibacterial activity, enhanced hydrophilicity, and improved mechanical properties was prepared in one single-step process. In the proposed method, synthesis of silver nanoparticles was carried out along with the aminohydrolysis of polyester fabric using triethanolamine (TEA), acting as reducing and stabilizing agent. Findings suggest the potential of TEA in the simultaneous aminohydrolysis of polyester fabric and reduction of silver ions into silver nanoparticles, preparing a fabric with excellent antibacterial efficiency against Staphylococcus aureus and Escherichia coli, higher tensile strength, and improved hydrophilicity. Interestingly, the introduction of silver nanoparticles into the structure of polyester fibers improved the tensile strength of the treated fabric to about 25%, possibly due to the crosslinking of the nanoparticles between the polymer chains of polyester fibers, as shown schematically in Fig. 8.5. The same research group conducted a study concerning the simultaneous polyester surface modification and synthesis of zinc oxide nanoreactors

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Fig. 8.5 Polyester aminohydrolysis and in situ synthesis of silver nanoparticles as proposed by Poortavasoly et al. (2014). (Reproduced with permission from Poortavasoly, H., Montazer, M., Harifi, T., 2014. Simultaneous synthesis of nano silver and activation of polyester producing higher tensile strength aminohydroxylated fiber with antibacterial and hydrophilic properties. RSC Adv. 446250. Copyright 2014, The Royal Society of Chemistry).

to develop durable photobioactive fabric with variable hydrophobicity/ hydrophilicity under sunlight. For this purpose, TEA was applied as a stabilizer and pH adjusting chemical for the aminolysis of polyester surface and enhancing the surface reactivity along with synthesis and deposition of ZnO nanoparticles on the fabric. Therefore, TEA played a crucial role in

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providing the alkaline condition for the preparation of zinc oxide nanoparticles and acting as stabilizer controlling the size of the prepared nanoparticles. As indicated in Fig. 8.6, the authors claimed that crosslinking could occur between polyester chains due to the simultaneous aminolysis and ZnO nanoparticle synthesis. Thus, the strong adherence of the nanoparticles to the fibers was achieved through the proposed single-step method (Poortavasoly et al., 2016). In situ synthesis of ZnO nanorods on cellulosic chains of cotton fabric was accomplished using natural plant source, namely, Keliab and zinc acetate. The interaction between ZnO and functional groups of cellulosic chains of cotton fabric was found beneficial to enhance crease recovery angle and tensile strength of samples. The crease recovery angle of different fabrics showed the higher value for the treated sample due to nanocrosslinking of functional groups in cellulosic chains through in situ synthesis of nanoparticles. In situ synthesis of nano ZnO linked the hydroxyl groups of cellulosic chains leading to reduced free hydroxyl groups, in addition to the role of nanoparticles as fillers.

Fig. 8.6 Polyester aminolysis and in situ synthesis of ZnO nanoparticles as proposed by Poortavasoly et al. (2016). (Reprinted with permission from Poortavasoly, H., Montazer, M., Harifi, T., 2016. Aminolysis of polyethylene terephthalate surfacealong with in situ synthesis and stabilizing ZnO nanoparticles using triethanolamine optimized with response surface methodology. Mater. Sci. Eng. C 58, 495–503. Copyright 2016, Elsevier).

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A new method of in situ synthesis of nanosilver within protein chains of wool fibers using sulfur-based reducing agent along with the extension of wool yarn to obtain fine wool fibers has been proposed by Hosseinkhani et al. (2012). Two different reducing agents as weak and strong ones compared and confirmed the applicability of both in this processing. Interestingly, higher tensile strength was obtained, which was related to the ionic crosslinking of synthesized nanosilver within protein chains of wool. Crosslinking of nanosilver with imine and thiol groups of protein chains is schematically shown in Fig. 8.7. The authors claimed that although the strong reducing agent broke more disulfide bonds within the wool structure and caused decreased tenacity, in situ synthesis of nanosilver formed ionic linkages between the protein chains of wool (thiol groups and imine, amide, and carbonyl), compensating the tenacity loss. The possibility of nanoparticles crosslinking with protein chains of wool has been also confirmed by Montazer et al. (2013) who studied the in situ synthesis of ZnO nanoparticles on wool fabric. Zinc acetate was used as a precursor and the synthesis process was done in water and water/ethanol media. The treated wool fabric was heated at 80°C for 10 h to dehydrate Zn(OH)2 obtaining ZnO nanoparticles. Higher tensile strength was

Fig. 8.7 Crosslinking of nanosilver with imine and thiol groups of wool protein chains as proposed by Hosseinkhani et al. (2012). (Reprinted with permission from Hosseinkhani, M., Montazer, M., Eskandarnejad, S., Rahimi, M.K., 2012. Simultaneous in situ synthesis of nano silver and wool fiber fineness enhancement using sulphur based reducing agents. Colloids Surf. A Physicochem. Eng. Asp. 415, 431–438. Copyright 2012, Elsevier).

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obtained due to the interaction of ZnO with protein chains of wool. The crosslinking effect also resulted in lower alkaline solubility of the treated fabric. Behzadnia and Montazer have done vast number of studies regarding the in situ sonosynthesis of nanophotocatalysts on wool fabric (Behzadnia et al., 2014a, b, 2015a, b, 2016). Sonosynthesis of nano TiO2 using titanium isopropoxide or butoxide in acidic media was the first approach resulting in antibacterial/antifungal and self-cleaning properties along without low cytotoxicity. The treatment was also effective in reduced alkaline solubility and photoyellowing. Loading of nano TiO2 particles into the structure of the wool fiber improved the tensile strength of the fabric due to the crosslinking action of nanoparticles between protein chains of wool fibers (Behzadnia et al., 2014a). In situ photosonochemical synthesis of N-doped Ag-TiO2 nanocomposite was further investigated by treating the wool sample with titanium isopropoxide, silver nitrate, and ammonia in a sonobath for 1 h at 75–80°C. Functional groups of wool acted as reactive sites for linkages between photosonosynthesized N-Ag/TiO2 nanocomposites and protein chains of wool. The reaction between photosonosynthesized N-Ag/TiO2 nanocomposites and functional groups of wool led to crosslinking of the protein chains of wool fibers increasing the tensile strength (Behzadnia et al., 2016). In another study, honeycomb-like N-Ag/ZnO nanocomposites were successfully photosonosynthesized and sonoimmobilized on wool fabric introducing superior photocatalytic activity due to the presence of nitrogen and silver on the nano ZnO particles (Behzadnia et al., 2015a). Similar crosslinking effect between the nanocomposites and protein chains of wool has occurred, resulting in increased tensile strength. Superior multifunctional properties have been achieved via sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core-shell nanocomposite on wool fabric. Creation of crosslinked structure between the protein chains of wool fibers increasing the tensile strength is schematically shown in Fig. 8.8 (Behzadnia et al., 2015c). Polyester hydrolysis and formation of PVA-tragacanth hydrogel along with in situ synthesis of nanosilver particles has been reported by Montazer and Kahali (2016). They used CA as a crosslinker and speculated that silver nanoparticles crosslinking between chains of various polymers, including PVA, taragacanth, and hydrolyzed polyester, has occurred producing a three-dimensional network and stabilizing the PVA-targacanth on the fabric surface (Fig. 8.9).

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Fig. 8.8 Creation of crosslinked structure between the protein chains of wool and N-doped ZnO/TiO2 core-shell nanocomposite as proposed by (Behzadnia et al., 2015c). (Reprinted with permission from Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015c. Simultaneous sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core–shell nanocomposite on wool fabric: introducing various properties specially nano photo bleaching. Ultrason. Sonochem. 27, 10–21. Copyright 2015, Elsevier).

In a recent study carried out by Bashiri Rezaie and Montazer (2017), polyester fabric was in situ treated with Cu/Cu2O nanoparticles using TEA for polyester aminolysis. The authors claimed that each hydroxyl end group of TEA nucleophilically attacked the ester bonds of the polyester chains linking the separated polyester oligomers causing ester crosslinks between the various polyester chains as shown in Fig. 8.10.

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Fig. 8.9 Alkaline hydrolysis and synthesis of PVA-tragacanth/Ag hydrogel on polyester fabric proposed by Montazer and Kahali (2016).

8.4 CONCLUSION In situ synthesis of nanostructures on textile substrates was not only beneficial for the multifunctional nanofinishing of textiles with less complicated procedure, but also provides the possibility to crosslink textile polymeric chains via nanostructures acting as crosslinkers. This is an added advantage resulting in durable multifunctional activities along with enhanced mechanical properties. This is a feasible approach, which can be obtained by in situ synthesis of various nanoparticles and nanocomposites on different textile substrates. Moreover, nanocrosslinking is in good accordance with human health and environmental concerns, as it provides durable attachment of nanoparticles with minimum release and less toxicity.

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Fig. 8.10 Polyester treatment via in situ synthesis of Cu/Cu2O nanoparticles proposed by Bashiri Rezaie and Montazer, 2017. (Reprinted with permission from Bashiri Rezaie, A., Montazer, M., 2017. Polyester modification through synthesis of copper nanoparticles in presence of triethanolamine optimized with response surface methodology. Fibers Polym. 18, 434–444. Copyright 2017, Springer Nature).

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REFERENCES Bajaj, P., 2002. Finishing of textile material. J. Appl. Polym. Sci. 83, 631–659. Bashiri Rezaie, A., Montazer, M., 2017. Polyester modification through synthesis of copper nanoparticles in presence of triethanolamine optimized with response surface methodology. Fibers Polym. 18, 434–444. Behzadnia, A., Montazer, M., Rashidi, A., Mahmoudi Rad, M., 2014a. Sonosynthesis of nano TiO2 on wool using titanium isopropoxide or butoxide in acidic media producing multifunctional fabric. Ultrason. Sonochem. 21, 1815–1826. Behzadnia, A., Montazer, M., Rashidi, A., Mahmoudi Rad, M., 2014b. Rapid sonosynthesis of N-doped nano TiO2 on wool fabric at low temperature: introducing self-cleaning, hydrophilicity, antibacterial/antifungal properties with low alkali solubility, yellowness and cytotoxicity. Photochem. Photobiol. 90, 1224–1233. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015a. In situ photo sonosynthesis and characterize nonmetal/metal dual doped honeycomb-like ZnO nanocomposites on wool fabric. Ultrason. Sonochem. 27, 200–209. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015b. In-situ sonosynthesis of nano N-doped ZnO on wool producing fabric with photo and bio activities, cell viability and enhanced mechanical properties. J. Photochem. Photobiol., B 149, 103–115. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015c. Simultaneous sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core–shell nanocomposite on wool fabric: introducing various properties specially nano photo bleaching. Ultrason. Sonochem. 27, 10–21. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2016. In situ photo sonosynthesis of organic/inorganic nanocomposites on wool fabric introducing multifunctional properties. Photochem. Photobiol. 92, 76–86. Cheng, X., Yang, C.Q., 2009. Flame retardant finishing of cotton fleece fabric. Part IV. Bifunctional carboxylic acids. J. Fire Sci. 27, 431–446. El-tahlawy, K.d.F., El-bendary, M.A., Elhendawy, A.G., Hudson, S.M., 2005. The antimicrobial activity of cotton fabrics treated with different cross-linking agents and chitosan. Carbohydr. Polym. 60, 421–430. Harifi, T., Montazer, M., 2012. Past, present and future prospects of cotton cross-linking: new insight into nano particles. Carbohydr. Polym. 88, 1125–1140. Hebeish, A., Hashem, M., Abdel-Rahman, A., El-Hil, Z.H., 2006. Improving easy care nonformaldehyde finishing performance using polycarboxylic acids via precationization of cotton fabric. J. Appl. Polym. Sci. 100, 2697–2704. Hosseinkhani, M., Montazer, M., Eskandarnejad, S., Rahimi, M.K., 2012. Simultaneous in situ synthesis of nano silver and wool fiber fineness enhancement using sulphur based reducing agents. Colloids Surf. A Physicochem. Eng. Asp. 415, 431–438. Huang, K., 2000. Physical properties of cotton fabrics and free CH2O content in creaseresistant finish with DMEU/MMEU prepolymer mixture. J. Appl. Polym. Sci. 75, 390–395. Li, Z.R., Fub, K.J., Wang, L.J., Liuc, F., 2008. Synthesis of a novel perfluorinated acrylate copolymer containing hydroxyethyl sulfone as cross-linking group and its application on cotton fabrics. J. Mater. Process. Technol. 205, 243–248. Montazer, M., 1996. Water Repellent Finishing of Cotton Fabrics (Ph.D. Thesis). Leeds University. Montazer, M., Jolaei, M.M., 2010. β-Cyclodextrin stabilized on three-dimensional polyester fabric with different cross-linking agents. J. Appl. Polym. Sci. 116, 210–217. Montazer, M., Kahali, P., 2016. A novel polyvinyl alcohol–tragacanth/nano silver hydrogel on polyester fabric through in situ synthesis method. J. Ind. Text. 45, 1635–1651.

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Montazer, M., Pakdel, E., 2011. Functionality of nano titanium dioxide on textiles with future aspects: focus on wool. J. Photochem. Photobiol. C, 293–303. Montazer, M., Amiri, M.M., Malek, R.M.A., 2013. In situ synthesis and characterization of nano ZnO on wool: influence of nano photo reactor on wool properties. Photochem. Photobiol. 89, 1057–1063. Nazari, A., Montazer, M., Rashidi, A., Yazdanshenas, M., Anary-Abbasinejad, M., 2009. Nano TiO2 photo-catalyst and sodium hypophosphite for cross-linking cotton with poly carboxylic acids under UV and high temperature. Appl. Catal. A Gen. 371, 10–16. Parvinzadeh Gashti, M., Pakdel, E., Alimohammadi, F., 2016. Nanotechnology-based coating techniques for smart textiles. In: Hu, J. (Ed.), Active Coatings for Smart Textiles. Woodhead Publishing, Cambridge, UK. Poortavasoly, H., Montazer, M., Harifi, T., 2014. Simultaneous synthesis of nano silver and activation of polyester producing higher tensile strength aminohydroxylated fiber with antibacterial and hydrophilic properties. RSC Adv. 4, 46250. Poortavasoly, H., Montazer, M., Harifi, T., 2016. Aminolysis of polyethylene terephthalate surface along with in situ synthesis and stabilizing ZnO nanoparticles using triethanolamine optimized with response surface methodology. Mater. Sci. Eng. C 58, 495–503. Sedighi, A., Montazer, M., Hemmatinejad, N., 2014. Copper nanoparticles on bleached cotton fabric: in situ synthesis and characterization. Cellulose 21, 2119–2132. Xu, W., Shyr, T., 2001. Applying a non-formaldehyde cross-linking agent to improve the washing durability of fabric water repellency. Text. Res. J. 71, 751–754.

9

Nanofinishes for self-cleaning textiles 9.1 INTRODUCTION: DEFINITION AND HISTORICAL OVERVIEW Self-cleaning clothes with the ability to clean themselves are dreams come true thanks to great efforts made by researchers during the last decades. A path to achieve self-cleaning clothes was actually paved with the aid of living nature. As the first hints to achieve self-cleaning surfaces have been brought by mimicking nature, self-cleaning surfaces are also famous as bioinspired surfaces. In addition to legs of water strider and wings of butterflies, self-cleaning was mainly inspired by leaves of plants, namely, lotus, making it known as lotus effect. Neinhuis and Barthlott were the first who introduced the idea of lotus effect in 1997, arising from the micropapillae structures with the ability to trap a large amount of air, and low surface energy of epicuticular wax crystalloids coating the leaf surface (Sas et al., 2012). Their idea was further developed by Feng et al. (2002) who found out that the surface of leaves has branchlike nanostructures with 124 nm diameter, causing contact angles greater than 160 degrees. Scientific analysis of lotus leaf revealed that a water droplet on the leaf is almost spherical in shape and can roll off easily. This resulted from the combination of a hierarchical surface structure that traps air beneath a water droplet and the hydrophobicity of the surface wax. Moreover, the surface has low adhesion force and low coefficient of friction. Thus, the interfacial area between contamination particles and the surface is very small, resulting in reduced adhesion (Fig. 9.1). On such a surface, water droplets from rainfall can pick up the contamination particles and carry them away when the droplets roll off the surface, leading to self-cleaning properties also known as lotus effect. Both surface morphology and hydrophobic wax material are necessary to create such a superhydrophobic surface on lotus leaves. Moreover, superhydrophobic surfaces with contact angles of more than 150 degrees possess self-cleaning properties only if their contact angle hysteresis and sliding angle are low (Nishimoto and Bhush, 2013). Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00009-1

© 2018 Elsevier Ltd. All rights reserved.

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Water

Water

Leaf

Microstructured surface

Dirt

Fig. 9.1 Lotus effect.

Similar superhydrophobicity and self-cleaning properties have been found in plant leaves such as rice and taro leaves with hierarchical surface structures. Moreover, plant leaves with unitary surface structure such as Ramee leaf and Chinese watermelon indicate superhydrophobicity and self-cleaning properties (Sun et al., 2005). Inspired by lotus effect, researchers have developed self-cleaning textiles by combining low surface energy materials and creating surface roughness. The common low surface energy materials include organic silanes, fluorinated silanes, alkyl amines, and silicates. Popular surface modification methods include wet chemical reactions, self-assembly and sol-gel, layerby-layer (LBL) deposition, polymerization reactions, colloidal template techniques, chemical vapor deposition, plasma treatment, and electrospinning (Gupta and Gulrajani, 2015). Further to lotus effect, self-cleaning has been also achieved by the opposite surface wettability, namely, superhydrophilicity in which water completely covers the surface with a continuous film and washes away the contaminants. This is usually achieved via photocatalysts also benefiting from generating active radicals under light irradiation capable of decomposing organic contaminants (Wang et al., 2015). Semiconductor photocatalysts such as nano TiO2 and ZnO have been mainly used on various textile substrates in the form of nanocoatings or by ex situ or in situ synthetic methods to produce self-cleaning textiles. The treated textiles also benefit from multifunctional activities, including UV protection and antibacterial properties (Montazer and Maali Amiri, 2014). Moreover, there have been numerous efforts to improve the photocatalytic activities of semiconductors using different surface modification methods to produce semiconductors with enhanced activities under solar light irradiation (Zaleska, 2008). After a brief overview of different surface wetting theories, this chapter mainly deals with nanofinishes for producing self-cleaning textiles and we tried to provide the most recent case studies.

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9.2 SURFACE WETTABILITY Depending on surface smoothness or roughness, three theories have been proposed for surface wettability (Callies and Qu
er
e, 2005). 1. Young model, which is only valid for smooth surfaces and is based on the correlation between the three interfacial energies per unit area, which are in equilibrium at the droplet (Eq. 9.1) γ sv¼ γ sl + γ lv cos θ (9.1) where θ is contact angle, γ sv and γ sl, γ lv and are the interfacial energies per unit area of the solid-vapor, solid-liquid, and liquid-vapor interfaces, respectively. 2. Wenzel theory, which is based on complete wetting of a rough surface where the liquid penetrates into the grooves of the rough surface (Eq. 9.2). cos θa¼ r cos θs (9.2) where apparent contact angle θa is the true contact angle of the droplet on a plain surface θs multiplied by roughness factor (r), and r is the ratio between the actual rough surface area and the geometric surface area (r¼ Ageometric/ Areal). 3. Cassie and Baxter theory, which describes the nonwetted contact between the liquid and rough surface arising from vapor pockets trapped underneath the liquid in the grooves. Based on this theory when a liquid spreads over a rough porous surface, the solid-vapor interface converted into two new interfaces, solid-liquid and liquid-vapor interfaces (Eq. 9.3). cos θa¼ fs cos θs + fv cos θv

(9.3)

where fs and fv are the fractions of the solid and vapor on the surface. The theories are schematically shown in Fig. 9.2. g1v gsv

(A)

q

gs1

(B)

(C)

Fig. 9.2 (A) Young, (B) Wenzel, and (C) Cassie and Baxter theories for wetting behavior of smooth and roughened surfaces.

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9.3 NANOFINISHES FOR SELF-CLEANING TEXTILES 9.3.1 Self-cleaning textiles based on lotus effect Inspired by lotus effect, self-cleaning textiles could be prepared via two basic approaches (Stegmaier et al., 2008): 1. Introducing nanoscale roughness on textile surface using nanoparticles such as silver, rod arrays such as ZnO nanorods and carbon nanotubes, or by physical surface modification methods such as laser or plasma along with application of low surface energy materials to impart hydrophobicity (Liu et al., 2007; Xu and Cai, 2008; Dastjerdi et al., 2010). 2. Treatment of fabrics having micro- or nanostructure with low surface energy materials. For instance, silicone was coated on microfiber polyester fabric to produce superhydrophobic polyester with self-cleaning properties (Gao and McCarthy, 2006). Some of the recent studies concerning with these two approaches are as follows: Superhydrophobic self-cleaning cotton fabrics were prepared by hydrothermal synthesis of ZnO nanorods followed by coating with dodecyltrimethoxysilane to impart surface roughness and hydrophobicity. Cotton fabric treatment with silver nitrate in presence of potassium hydroxide following by surface hydrophobization with octyltriethoxysilane has been also reported (Xu and Cai, 2008). In situ synthesis of silver nanoparticles on cotton fabric along with treating the fabric with hexadecyltrimethoxysilane was also successful to provide superhydrophobic fabric with self-cleaning properties (Xue et al., 2012). Similar researches have been carried out using carbon nanotubes to create nanoscale roughness on various textile substrates (Liu et al., 2007). Silica nanoparticles have been extensively used to impart superhydrophobic properties into textiles. For instance, polydimethylsiloxane filled with fluorinated alkylsilane functionalized silica nanoparticles and fluorinated alkylsilane were successful to prepare superhydrophobic coating on fabrics (Zhou et al., 2012). Chemical vapor deposition and LBL techniques are among the widely applied methods to produce superhydrophobic textiles. Nanocoating of silicone was deposited on cotton fabric via chemical vapor deposition followed by hydroxylation and polymerization (Li et al., 2007). Polyelectrolyte/silica nanoparticle multilayers were deposited on cotton fabric using LBL method. The process was followed by fluoroalkylsilane treatment to impart superhydrophobicity (Zhao et al., 2010). Modified silica nanoparticles with epoxy functional groups were applied on

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cotton fabric to produce dual-size hierarchical surface structure following by treatment with stearic acid or 1H,1H,2H,2H-perfluorodecyltrichlorosilane or their combination to impart hydrophobicity (Xue et al., 2008). In all cases, durability of the treatment is important and the other involved challenge is the tendency of the treated surfaces to adsorb oily contaminants. These obstacles restricted the feasibility of these methods.

9.3.2 Photoinduced hydrophilicity and self-cleaning: Definition and mechanism As thoroughly discussed in Chapter 2, photocatalysis is based on the irradiation of semiconductors by light with energy equal or greater than the band gap, during which electrons are excited from the valence band to the conduction band and then migrate to the semiconductor surface to produce radicals for contaminants degradation. Accidental finding of a research group in TOTO laboratory revealed that TiO2 films possess superhydrophylic properties under UV light illumination. This phenomenon, which is called photoinduced hydrophilicity, is reversible and the surface becomes hydrophobic in the absence of light. This effect, which was found in 1995, was a pioneering step to achieve self-cleaning surfaces and was first applied to develop selfcleaning glass. Since the introduction of this effect, three different mechanisms have been proposed to support the photoinduced hydrophylicity properties. These include the generation of surface vacancies developed by Wang et al., photoinduced reconstruction of Ti-OH bonds, and photocatalytic decomposition of organic adsorbents (Zhang et al., 2012). However, as none of the proposed mechanisms could completely explain all experimental instances, a combined theory has been developed. Based on the combined theory, which is schematically shown in Fig. 9.3, first step in the photoinduced hydrophilicity is decomposition of organic contaminants by photocatalytic UV-irradiation of semiconductor to obtain a clean surface. This step is followed by electron-hole pair consumption to form oxygen vacancies at which new OH groups are formed causing increased surface energy. In a review written by Zhang et al. (2012) the photoinduced hydrophilicity combined mechanism is shown as Fig. 9.3. 9.3.2.1 Enhanced photocatalytic self-cleaning properties Due to the limitations involved in application of photocatalysts to impart self-cleaning properties, several approaches have been employed to enhance the photocatalytic efficiencies of semiconductors such as TiO2. Nanophotocatalysts with a wide bang gap were only excited via UV light irradiation.

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Fig. 9.3 Mechanism of photoinduced hydrophilicity provided by Zhang et al. (2012). Reproduced with permission from Zhang, L., Dillert, R., Bahnemann, D.W., Vormoor, M., 2012. Photo-induced hydrophilicity and self-cleaning: models and reality. Energy Environ. Sci. 5, 7491–7507. Copyright 2012, The Royal Society of Chemistry.

Moreover, there is a strong tendency for electron-hole pairs to recombine with each other dissipating the energy into heat. Thus, the modification methods have been proposed to develop visible light active semiconductors (Zaleska, 2008). The most versatile procedures are as follows: 1. Doping of photocatalysts such as TiO2 with metal species: Transition metal ions, including Cu, Ni, Mn, Mo, Fe …, and noble metal nanoparticles, such as Ag, Au …, have been successfully applied to enhance the photocatalytic activities of semiconductors such as TiO2 by reducing the recombination rate of charge carriers and producing visible light active photocatalysts. This can be achieved through introducing a new energy level in the band gap of semiconductor or surface Plasmon absorption of electrons in metals such as silver. Moreover, during the visible light irradiation of modified semiconductors, the dye molecules or colored satins such as coffee can be excited by absorbing the light irradiation in the visible region (mostly at maximum absorption wavelength), injecting an electron into the conduction band (and/or surface states) of semiconductor, which was captured by surfaceadsorbed oxygen to generate superoxide radical. Subsequently, stain degradation is facilitated by the generated oxygen radicals. Thus, in visible light photocatalytic reactions, the stain itself helps the degradation process (Montazer et al., 2012; Harifi and Montazer, 2014a). 2. Doping of photocatalysts such as TiO2 with nonmetal species: Doping with nonmetals such as N, C, S enhances the visible light photocatalytic efficiencies of semiconductors due to three different main

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O2

O2·-

e-

e-

CB

hn

Noble metal e.g. Ag VB

h+

(A)

Semiconductor

H2O

OH·

O2·-

CB

O2

Fe3+ + hn → Fe4+ + e-

Fe3+/Fe4+ VB

OH·

hn

H2O

Semiconductor

(B)

Energy level of doped agent such as Fe ions

O2

O2·-

hn (visible) e-

CB

Dye

VB

(C)

Semiconductor

hn

Semiconductor

CB

e-

CB

O2

O2·-

VB

OH·

h+

H2O

VB Semiconductor

(D) hn

CB e- Semiconductor CB VB

OH·

h+

VB

H2O Semiconductor

(E) Fig. 9.4 Enhanced photocatalytic properties by (A) and (B) doping, (C) dye sensitization, (D) coupled dual semiconductors, and (E) capped dual semiconductors.

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reasons, namely, narrowing the band gap, impurity energy levels, and oxygen vacancies (Behzadnia et al., 2015). 3. Sensitization with dyes: Semiconductor sensitization with organic and organometallic dyes is another approach to enhance the visible light photocatalytic activities. For instance, self-assembling of meso-tetra (4-carboxyphenyl) porphyrin (TCPP) monolayers on anatase-coated-cotton fabric with superior visible-light self-cleaning performance in the degradation of Methylene Blue and coffee stains as compared to bare TiO2-coated cotton (Afzal et al., 2012). Based on a recent study carried out by Gaminian and Montazer (2017), polyester fabric treated with sensitized Madder/TiO2 nanoparticles had superior self-cleaning activities under visible light irradiation due to the positive effect of Madder as a natural safe sensitizer for nano TiO2. Through the visible light illumination of dye-sensitized semiconductors, dye molecules are excited generating electron from their ground state (HOMO) to the excited state (LUMO). Subsequently the generated electron was transferred to the conduction band of semiconductor. Formation of superoxide and hydroxyl radicals is the next step to decompose organic contaminants. Therefore, dye molecules on the surface possibly alter the photoresponse from UV to the visible region (Gaminian and Montazer, 2017). 4. Dual semiconductors: Semiconductor combinations could be also beneficial to improve the photocatalytic activities through separation of charge carriers and enhancing the visible light absorption by combining with short band gap semiconductor. These dual systems could be in form of coupled or capped semiconductor combinations, which are different in case of interfacial charge carrier transfer to the surface. SiO2/TiO2, WO3/ TiO2, CdS-TiO2, CdS-ZnO … are some of the combined semiconductors (Pakdel et al., 2013; Harifi and Montazer, 2014b; Gaminian and Montazer, 2015). We tried to schematically summarize the approaches applied for enhancing the photocatalytic activities of semiconductors in Fig. 9.4.

9.3.2.2 TiO2 nanoparticles for self-cleaning textiles Searching through literature, we came up with a vast number of studies dealing with application of TiO2 nanoparticles on various textile substrates mostly cotton, wool, and polyester or cotton/polyester blends to obtain

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self-cleaning activities. These include the nanocoatings and ex situ or in situ synthesis approaches. During the recent years, most studies have been aimed at enhancing the self-cleaning properties of the treated textile substrates by proposing new application methods or synthesis procedures. Moreover, there have been some efforts to increase the durability and attachment of nanoparticles to fibers. This ranges from using spacers, crosslinking agents, physical preactivation methods to in situ sonosynthesis and sonofabrication of nanoparticles. Application of modified TiO2 nanoparticles such as doped photocatalysts and dual semiconductor nanocomposites has been also concerned to intensify the photocatalytic activities. As it was difficult to discuss about all the reported studies, here we tried to provide some examples of case studies. First efforts to prepare self-cleaning cotton fibers with TiO2 nanoparticles dated back to the year 2004 when TiO2 nanocoatings with anatase crystalline structure were prepared on cotton fabrics from tetraisopropoxide using a low-temperature sol-gel process under ambient pressure. Crystallization of titania nanoparticles was obtained during boiling the treated fabric in water for 180 min. Strong acidity of the prepared sols was the main drawback of the applied methods causing tensile strength loss of cotton fibers. To reduce this detrimental effect, Qi et al. (2011) prepared nanocrystalline TiO2 sols with high TiO2 concentration and a very low amount of acid by sol-gel process in an acidic aqueous solution at a low temperature of 60°C under mechanical stirring. TiO2 thin films were produced on cotton fabrics from a colloidal sol by a simple dip-pad-dry-cure process in a short process time. The treated samples had significant self-cleaning performance toward the colorant decomposition and degradation of coffee and curry stains under 4-h UV irradiation. There were many studies reporting the treatment of cotton fabrics in both bleached and mercerized forms with dispersions of commercial TiO2 Degussa P25 or nanocolloidal TiO2 prepared from titanium alkoxides. These methods mainly involved preactivation of fiber surface to provide durable attachment of nanoparticles. For instance, RF-plasma, MW-plasma, and UV-irradiation were applied to introduce negative functional groups to anchor TiO2 on treated cotton fabrics (Bozzi et al., 2005). In other studies, polycarboxylic acids, namely, succinic acid, 1,2,3propanetricarboxylic acid and 1,2,3,4-butanetetracarboxylic acid (BTCA) have been used to form ester bonds acting as spacers to attach TiO2 nanoparticles on cotton fibers. Thus, the carboxylic acids provide the opportunity to form ester bond with hydroxyl groups of cellulose and to anchor TiO2 by

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electrostatic interaction (Harifi and Montazer, 2012). Nazari et al. (2011) treated, bleached, and cationized cotton fabrics with nanotitanium dioxide particles in presence of BTCA. Precationization of fibers with 3-chloro-2-hydroxypropyl was found effective to obtain enhanced selfcleaning properties toward Methylene Blue dye discoloration. Statistical analysis showed that higher amount of TiO2 is not necessarily effective for improved photocatalytic activities, as in higher concentration of nanoparticles the chance for nanoparticles agglomeration is more. Nano TiO2 Degussa P 25 was immobilized on cotton/polyester knitted fabric by citric acid under sonication and discoloration of CI Reactive Black 5 in aqueous solution was successfully achieved by the treated samples. The treated fabrics could be repeatedly used for the dye discoloration due to formation of covalent ester bond in presence of citric acid (Hashemikia and Montazer, 2011). There have been some studies claiming that the oxidative degradation of cellulose and successive cleavage polymer chain occurred under light exposure of cotton fabrics treated with TiO2 due to the generated radical species, causing fabric yellowing. Cotton surface coating with amorphous SiO2 layers prepared from the hydrolysis of tetraethoxysilane (TEOS) following the LBL deposition of previously synthesized TiO2 nanoparticles and use of trialkoxysilanes (OTMS, octyltrimethoxysilane; PTMS, phenyltrimethoxysilane) as interface coupling agents between the cellulose fibers and the deposited TiO2 nanoparticles have been claimed to enhance the chemical resistance of cellulosic chains during the photocatalytic activity of TiO2 nanoparticles (Goncalves et al., 2009). In recent years, sonochemistry has gained wide attraction for ultrasonic polycondensation of Ti–OH or Ti–OR treating textile substrates with TiO2 nanoparticles without requiring subsequent heating of the textile. Perelshtein et al. (2012) were first who used this method for deposition of titanium dioxide nanoparticles with anatase and rutile crystalline structures on cotton fabrics with self-cleaning activities in photodegradation of methylene blue. Their proposed method involved the in situ generation of TiO2 nanoparticles and their simultaneous deposition onto the fabric in a one-step reaction by using ultrasound irradiation promoting the crystallization process of titania due to the high local temperature and pressure generated during the collapse of the acoustic bubble under sonochemical irradiation. Fast migration of the synthesized nanoparticles onto the fabric caused local melting of the fibers at the contact sites and resulted in strong adherence of the nanoparticles to the fabric surface. Akhavan Sadr and Montazer (2014) developed

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the in situ sonosynthesis of nano TiO2 particles on cotton fabric using titanium tetra isopropoxide as a precursor and ultrasonic bath (50 kHz, 50 W). The treated fabric showed excellent self-cleaning properties with no negative effect on the fabric mechanical strength. The best self-cleaning property was obtained by using 9 mL precursor for 4 h sonication at low temperature (75°C). Au/TiO2/SiO2 nanocomposites were used to improve the visible light self-cleaning performance of cotton. Although the prepared nanocomposite was successful, its application was limited due to high cost of gold (Wang et al., 2012). Many research studies have been carried out on the use of Ag/TiO2 nanocomposites on cotton fabrics providing higher stain photodegradation due to the role of silver in trapping the excited electrons reducing charge carrier recombination rate and enhancing the visible light absorption arisen from silver plasmon resonance. Platinum (IV) chloride modified TiO2 (Pt-TiO2) and N-TiO2 (Pt-N-TiO2) nanosols have been synthesized through a low-temperature precipitation-peptization method. The visible light activity was attributed to the surface strongly attached PtCl6 anions, which enable visible light activity of TiO2 through a mechanism of charge transfer from ligand to metal excitation. However, the modification of Pt does not notably improve the performance of N-TiO2 coatings because the surface-adsorbed species on N-TiO2 block the adsorption of PtCl6 anions (Long et al., 2016). Nano TiO2 has been also applied on wool to produce self-cleaning textile, although the application has some difficulties due to low thermal resistance of wool fibers. Montazer and his research group have done many researches to treat wool fabrics with nano TiO2 Degussa. Incorporation of carboxylic acids as crosslinking agents and preactivation of surface with potassium permanganate has been also done to enhance the adsorption of nanoparticles. Self-cleaning efficiencies of the treated samples were assessed toward the discoloration of coffee, fruit juice, concentrated tea, and Methylene Blue dye (Montazer and Pakdel, 2011). Enzymatic pretreatment was also beneficial for enhanced nanoparticles adsorption and subsequent improved self-cleaning properties of wool/polyester fabrics treated with TiO2 Montazer and Seifollahzadeh, 2011). A uniform coating of TiO2/ SiO2 (50:50 and 30:70) nanocomposites was formed on wool to produce self-cleaning and superhydrophilicity. A higher concentration of silica resulted in enhanced self-cleaning (Pakdel et al., 2013). Sonochemistry was also successful to prepare wool fabrics with superior self-cleaning activities. Behzadnia et al. (2014a) presented a novel idea to

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prepare nanocrystalline TiO2 on wool fabric under ambient pressure at 60–65°C using in situ sonosynthesis method. They suggested the higher photocatalytic efficiency of TiO2 nanoparticles prepared by titanium tetra isopoxide in comparison to titanium butoxide as a precursor. The same group also studied the sonosynthesis of N-doped nano TiO2 on wool fabric at low temperature using ammonia (Behzadnia et al., 2014b). Due to lack of functional groups and hydrophobicity of polyester fibers, their successful nanofinishing with TiO2 is dependent on preactivation of surface using chemical or physical surface modification methods. For instance, RF-plasma, MW-plasma, and vacuum-UV light irradiation have been applied as pretreatment allowing the loading of TiO2 by wet chemical techniques in the form of transparent coatings constituted of nanoparticles of diverse sizes. The treated samples possessed significant ability to degrade coffee stains. Recently, simultaneous surface modification of polyester fibers and in situ sonosynthesis of TiO2 nanoparticles have been carried out using ultrasound bath. Hydroxylation of terephthalate occurred by hydroxyl radicals formed during water sonolysis, forming functional groups on polyester surface enhancing nanoparticles adsorption. Self-cleaning activity of sonosynthesized nano TiO2-treated polyester samples toward degradation of Methylene Blue stain was superior to coating of fabric with commercial nano TiO2 (Harifi and Montazer, 2017). 9.3.2.3 ZnO nanoparticles for self-cleaning textiles Up to now, ZnO nanoparticles have been used parallel with TiO2 as ideal photocatalysts. However, incorporation of ZnO nanoparticles into textile materials has been recently gained interest, and the number of studies concerning synthesis and application of nano ZnO particles is not to the level of textiles treated with nano TiO2 particles. Kathirvelu et al. (2010) synthesized nano ZnO by homogeneous phase reaction and then applied on the cotton fabric to obtain the stain-eliminating function. The authors reported that a long time was required to remove stains from the substrate due to large band gap of ZnO making it inefficient to be excited by sunlight. In situ synthesis of ZnO nanoparticles on starch-sized cotton fibers was successful to produce excellent self-cleaning properties against Methylene Blue stain by 2% zinc nitrate and 15% sodium hydroxide using the reducing and stabilizing effect of starch (Khosravian et al., 2015). In situ biosynthesis of zinc oxide nanoparticles on cotton fibers was also reported beneficial to achieve Methylene Blue dye stain self-cleaning properties. In the proposed

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method, Keliab with 15% (v/v) was used as a natural agent to produce ZnO nanoparticles (Aladpoosh and Montazer, 2015). Using triethanol amine as a reducing agent and simultaneous surface modification of polyester fibers resulted in textiles with superior self-cleaning properties due to the photocatalytic activities of ZnO nanoparticles (Poortavasoly et al., 2016). N-doped ZnO/TiO2 nanocomposite was sonosynthesized on wool fabric in ultrasonic bath through hydrolysis of zinc acetate and titanium isopropoxide. Presence of optimal nitrogen and TiO2 on ZnO led to enhanced photocatalytic properties under sunlight light irradiation due to separation of photogenerated electron and holes, reducing the recombination rate. Moreover, sonochemistry created smaller nanoparticles with higher crystallinity resulting in superior self-cleaning properties than conventional sol-gel treatments (Behzadnia et al., 2015). 9.3.2.4 Other nanosemiconductors ZrO2 nanocrystals were successfully synthesized and deposited onto wool fibers using the sol-gel technique at low temperature. Although the treated samples possessed photocatalytic activities toward Methylene Blue and Eosin Yellow dyes, the self-cleaning properties were lower than samples treated with TiO2 nanoparticles in a similar manner. This was attributed to the lower band-gap energy of titania (3.2 eV) comparing with zirconia (4.5 eV) and anatase crystalline structure of TiO2 (Moafi et al., 2010). Nano Cu2O particles were synthesized on cotton fabric using CuSO4 as a precursor and glucose as reducing and capping agent in alkali. The treated fabrics showed photocatalytic activity toward the degradation of Methylene Blue under daylight (Sedighi et al., 2014). Recently, cotton fabric was in situ treated with nanocupric oxide using nanobio method to impart self-cleaning activities (Bashiri Rezaie et al., 2017). 9.3.2.5 Methods for evaluating photocatalytic self-cleaning properties In most studies, self-cleaning properties are assessed by staining the treated samples with organic dirt such as coffee, make up, or dye. Methylene Blue, Methyl Orange, Rhodamine B, and reactive black 5 are the most common model dye compounds. After exposure of samples to light irradiation, the degree of discoloration is evaluated by colorimetric measurements before and after light illumination and is reported as ΔE (Eq. 9.4).  1=2 ΔE ¼ ðΔL ∗ Þ2 + ðΔa∗ Þ2 + ðΔb∗ Þ2 (9.4)

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where ΔL*, Δa*, and Δb* are color coordinates of samples in Lab* color space before and after light exposure. Self-cleaning efficiencies of treated textiles are also evaluated by scanning the samples and measuring the color coordinates in RGB color space using Matlab software (Eq. 9.5). 
4 RGB ¼ ðR2  R1 Þ2 + ðB2  B1 Þ2 + ðG2  G1 Þ2  1=2 (9.5) where R1G1B1 and R2G2B2 are color coordinates of samples before and after light illumination, respectively (Harifi and Montazer, 2014a, b). Staining gray scale can be also used to evaluate the self-cleaning effectiveness of the treated samples. In this regard, 5 and 1 refers to maximum and minimum stain degradation, respectively. In some studies, treated textiles are dipped in dye solutions and light irradiated for a definite time duration. Prior to irradiation, the system should be kept in dark for some hours, e.g., 24 h to reach adsorption-desorption equilibrium between treated fabric and dye. Here, photocatalytic efficiencies of the treated samples are evaluated by measuring dye absorbance at maximum wavelength before and after light irradiation (Eq. 9.6). Conversion% ¼ ðA0  At Þ=A0  100 (9.6) where A0 and At are dye absorbance at maximum wavelength before and after t (h) light irradiation, respectively (Harifi and Montazer, 2014a, b).

9.4 CONCLUSION In addition to the published studies concerning with two common approaches for preparing self-cleaning textiles, which have been thoroughly discussed in this chapter, production of surfaces with adjustable hydrophilic and hydrophobic properties for other applications such as separation of oil from water will be a focus of future researches. New photocatalysts such as metal organic frameworks (MOFs) will be also applied on various textile substrates to impart self-cleaning properties. These materials with versatile structures have recently attracted researchers for their photocatalytic efficiencies, although research to enhance their properties together with their stability under photocatalytic reactions needs to be further developed. Graphitic carbon nitride (g-C3N4) is also an attractive low-cost sustainable metal-free photocatalyst with the potential to absorb visible light. Although still not applied on textile substrates, we will see more studies in future using these new photocatalysts. Research will also focus on nanocomposite structures of the new photocatalysts to achieve enhanced properties.

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REFERENCES Afzal, S., Daoud, W.A., Langford, S.J., 2012. Self-cleaning cotton by porphyrin-sensitized visible-light photocatalysis. J. Mater. Chem. 22, 4083–4088. Akhavan Sadr, F., Montazer, M., 2014. In situ sonosynthesis of nano TiO2 on cotton fabric. Ultrason. Sonochem. 21, 681–691. Aladpoosh, R., Montazer, M., 2015. The role of cellulosic chains of cotton in biosynthesis of ZnO nanorods producing multifunctional properties: mechanism, characterizations and features. Carbohydr. Polym. 126, 122–129. Bashiri Rezaie, A., Montazer, M., Mahmoudi Rad, M., 2017. Biosynthesis of nano cupric oxide on cotton using Seidlitzia rosmarinus ashes utilizing bio, photo, acid sensing and leaching properties. Carbohydr. Polym. 177, 1–12. Behzadnia, A., Montazer, M., Rashidi, A., Mahmoudi Rad, M., 2014a. Sonosynthesis of nano TiO2 on wool using titanium isopropoxide or butoxide in acidic media producing multifunctional fabric. Ultrason. Sonochem. 21, 1815–1826. Behzadnia, A., Montazer, M., Rashidi, A., Mahmoudi Rad, M., 2014b. Rapid sonosynthesis of n-doped nano TiO2 on wool fabric at low temperature: introducing self-cleaning, hydrophilicity, antibacterial/antifungal properties with low alkali solubility, yellowness and cytotoxicity. Photochem. Photobiol. 90, 1224–1233. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015. Simultaneous sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core-shell nanocomposite on wool fabric: Introducing various properties specially nano photo bleaching. Ultrason. Sonochem. 27, 10–21. Bozzi, A., Yuranova, T., Guasaquillo, I., Laubb, D., Kiwi, J., 2005. Self-cleaning of modified cotton textiles by TiO2 at low temperatures under daylight irradiation. J. Photochem. Photobiol. A Chem. 174, 156–164. Callies, M., Qu
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e, D., 2005. On water repellency. Soft Mater. 1, 55–61. Dastjerdi, R., Montazer, M., Shahsavan, S., 2010. A novel technique for producing durable multifunctional textiles using nanocomposite coating. Colloids Surf. B: Biointerfaces 81, 32–41. Feng, L., Li, S., Li, Y., Li, H., Zhang, L., Zhai, J., Song, Y., Liu, B., Jiang, L., Zhu, D., 2002. Super-hydrophobic surfaces: From natural to artificial. Adv. Mater. 14, 1857–1860. Gaminian, H., Montazer, M., 2015. Enhanced self-cleaning properties on polyester fabric under visible light through single-step synthesis of cuprous oxide doped nano-TiO2. Photochem. Photobiol. 91, 1078–1087. Gaminian, H., Montazer, M., 2017. Simultaneous nano TiO2 sensitization, application and stabilization on polyester fabric using madder and NaOH producing enhanced selfcleaning with hydrophilic properties under visible light. J. Photochem. Photobiol. A Chem. 332, 158–166. Gao, L., McCarthy, T.J., 2006. Artificial lotus leaf prepared using a 1945 patent and a commercial textile. Langmuir 22, 5969–5973. Goncalves, G., Marques, P.A.A.P., Pinto, R.J.B., Trindade, T., Neto, C.P., 2009. Surface modification of cellulosic fibers for multi-purpose TiO2 based nanocomposites. Compos. Sci. Technol. 69, 1051–1056. Gupta, D., Gulrajani, M.L., 2015. Self-cleaning finishes for textiles. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge, UK. Harifi, T., Montazer, M., 2012. Past, present and future prospects of cotton cross-linking: new insight into nano particles. Carbohydr. Polym. 88, 1125–1140. Harifi, T., Montazer, M., 2014a. Fe3+:Ag/TiO2 nanocomposite: synthesis, characterization and photocatalytic activity under UV and visible light irradiation. Appl. Catal. A Gen. 473 (2014), 104–115.

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Harifi, T., Montazer, M., 2014b. A novel magnetic reusable nanocomposite with enhanced photocatalytic activities for dye degradation. Sep. Purif. Technol. 134, 210–219. Harifi, T., Montazer, M., 2017. Application of sonochemical technique for sustainable surface modification of polyester fibers resulting in durable nano-sonofinishing. Ultrason. Sonochem. 37, 158–168. Hashemikia, S., Montazer, M., 2011. Stabilization of nanosized TiO2 particles on knitted cotton/polyester fabric by citric acid for self-cleaning and discoloration of reactive black 5 from waste water. Iran. J. Polym Sci. Technol. 24, 33–42. Kathirvelu, S., D’Souza, L., Dhurai, B., 2010. Study of stain-eliminating textiles using ZnO nanoparticles. J. Text. Inst. 101, 520–526. Khosravian, S., Montazer, M., Malek, R.M.A., Harifi, T., 2015. In situ synthesis of nano ZnO on starch sized cotton introducing nano photo active fabric optimized with response surface methodology. Carbohydr. Polym. 132 (2015), 126–133. Li, S., Xie, H., Zhang, S., Wang, X., 2007. Facile transformation of hydrophilic cellulose into super hydrophobic cellulose. Chem. Commun. (46), 4857–4859. Liu, Y., Tang, J., Wang, R., Lu, H., Li, L., Kong, Y., Qia, K., Xin, J.H., 2007. Artificial lotus leaf structures from assembling carbon nanotubes and their applications in hydrophobic textiles. J. Mater. Chem. 17, 1071–1078. Long, M., Zheng, L., Tana, B., Shu, H., 2016. Photocatalytic self-cleaning cotton fabrics with platinum (IV) chloride modified TiO2 and N-TiO2 coatings. Appl. Surf. Sci. 386, 434–441. Nazari, A., Montazer, M., Moghadam, M.B., Anary-Abbasinejad, M., 2011. Self-cleaning properties of bleached and cationized cotton using nanoTiO2: a statistical approach. Carbohydr. Polym. 83, 1119–1127. Nishimoto, S., Bhush, B., 2013. Bioinspired self-cleaning surfaces with superhydrophobicity, superoleophobicity, and superhydrophilicity. RSC Adv. 3, 671–690. Moafi, H.F., Shojaie, A.F., Zanjanchi, M.A., 2010. The comparison of photocatalytic activity of synthesized TiO2 and ZrO2 nanosize onto wool fibers. Appl. Surf. Sci. 256, 4310–4316. Montazer, M., Behzadnia, A., Bameni Moghadam, M., 2012. Superior self-cleaning features on wool fabric using TiO2/Ag nanocomposite optimized by response surface methodology. J. Appl. Polym. Sci. 125, E356–E363. Montazer, M., Maali Amiri, M., 2014. ZnO nano reactor on textiles and polymers: ex situ and in situ synthesis, application, and characterization. J. Phys. Chem. B 118, 1453–1470. Montazer, M., Pakdel, E., 2011. Functionality of nano titanium dioxide on textiles with future aspects: focus on wool. J. Photochem. Photobiol. C, 293–303. Montazer, M., Seifollahzadeh, S., 2011. Pretreatment of wool/polyester blended fabrics to enhance titanium dioxide nanoparticle adsorption and self-cleaning properties. Color. Technol. 127, 322–327. Pakdel, E., Daoud, W.A., Wang, X., 2013. Self-cleaning and superhydrophilic wool by TiO2/SiO2 nanocomposite. Appl. Surf. Sci. 275, 397–402. Perelshtein, I., Applerot, G., Perkas, N., Grinblat, J., Gedanken, A., 2012. A one-step process for the antimicrobial finishing of textiles with crystalline TiO2 nanoparticles. Chem. Eur. J. 18, 4575–4582. Poortavasoly, H., Montazer, M., Harifi, T., 2016. Aminolysis of polyethylene terephthalate surface along with in situ synthesis and stabilizing ZnO nanoparticles using triethanolamine optimized with response surface methodology. Mater. Sci. Eng. C 58, 495–503. Qi, K., Wang, X., Xin, J.H., 2011. Photocatalytic self-cleaning textiles based on nanocrystalline titanium dioxide. Text. Res. J. 81, 101–110. Sas, I., Gorga, R.E., Joines, J.A., Thone, A.K., 2012. Review on superhydrophobic selfcleaning surfaces produced by electrospinning. J. Polym. Sci. B Polym. Phys. 50, 824–845.

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Sedighi, A., Montazer, M., Samadi, N., 2014. Synthesis of nano Cu2O on cotton: morphological, physical, biological and optical sensing characterizations. Carbohydr. Polym. 110, 489–498. Stegmaier, T., Arnim, V.V., Scherrieble, A., Planc, H., 2008. Self-cleaning textiles using the Lotus effect. In: Abbott, A., Ellison, M. (Eds.), Biologically Inspired Textiles. Woodhead Publishing, Cambridge, UK. Sun, T.L., Feng, L., Gao, X.F., Jiang, L., 2005. Bioinspired surfaces with special wettability. Acc. Chem. Res. 38, 644–652. Wang, R.H., Wang, X.W., Xin, J.H., 2012. Advanced visible-light-driven self-cleaning cotton by Au/TiO2/SiO2 photocatalysts. ACS Appl. Mater. Interfaces 2, 82–85. Wang, J., Zhao, J., Sun, L., Wang, X., 2015. A review on the application of photocatalytic materials on textiles. Text. Res. J. 85, 1104–1118. Xu, B., Cai, Z., 2008. Fabrication of a superhydrophobic ZnO nanorod array film on cotton fabrics via a wet chemical route and hydrophobic modification. Appl. Surf. Sci. 254, 5899–5904. Xue, C.H., Jia, S.T., Zhang, J., Tian, L., Chen, H.Z., Wang, M., 2008. Preparation of superhydrophobic surfaces on cotton textiles. Sci. Technol. Adv. Mater. 9, 1–7. Xue, C.H., Chen, J., Yin, W., Jia, S.T., Ma, J.Z., 2012. Superhydrophobic conductive textiles with antibacterial property by coating fibers with silver nanoparticles. Appl. Surf. Sci. 258, 2468–2472. Zaleska, A., 2008. Doped-TiO2: a review. Recent Pat. Eng. 2, 157–164. Zhang, L., Dillert, R., Bahnemann, D.W., Vormoor, M., 2012. Photo-induced hydrophilicity and self-cleaning: models and reality. Energy Environ. Sci. 5, 7491–7507. Zhao, Y., Tang, Y., Wang, X., Lin, T., 2010. Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy. Appl. Surf. Sci. 256, 6736–6742. Zhou, H., Wang, H., Niu, H., Gestos, A., Wang, X., Lin, T., 2012. Fluoroalkyl silane modified silicone rubber/nanoparticle composite: a super durable, robust superhydrophobic fabric coating. Adv. Mater. 24 (18), 2409–2412.

FURTHER READING Ganesh, V.A., Raut, H.K., Naira, A.S., Ramakrishna, S., 2011. A review on self-cleaning coatings. J. Mater. Chem. A 21, 16304–16322. Ragesh, P., Ganesh, V.A., Naira, S.V., Nai, A.S., 2014. A review on ‘self-cleaning and multifunctional materials’. J. Mater. Chem. A 2, 14773–14797. Schneider, J., Matsuoka, M., Takeuchi, M., Zhang, J., Horiuchi, Y., Anpo, M., Bahnemann, D.W., 2014. Understanding TiO2 photocatalysis: mechanisms and materials. Chem. Rev. 114 (19), 9919–9986.

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Antimicrobial textile nanofinishes 10.1 INTRODUCTION Since the increased public health awareness during the recent years, consumers’ demand for antimicrobial textiles has been widely growing. The importance of minimizing or eliminating microbial growth on textiles is also of high importance due to the susceptibility of textiles to microorganisms such as bacteria and fungi intensifying based on moisture, nutrients, and temperature. In this regard, hydrophilic natural and regenerated textile fibers are more vulnerable to microorganism’s growth. The demand for antimicrobial textiles has gained weight not only for apparel goods and medical textiles but also for sport clothing, food packaging, home furnishings, automotive textiles, air filters, water purification systems, and others (Gao and Cranston, 2008; Morais et al., 2016; Montazer and Harifi, 2017). Moreover, antimicrobial treatment of textiles also acts as anti-odors controlling the growth of odor-causing bacteria arising in everyday use of apparel and home textiles. Thus, more than 10,000 scientific papers have been published proposing new antimicrobial agents and approaches or modifying the existing methods. The antimicrobial agents can be incorporated into the polymers prior to extrusion or blended into synthetic fibers during their formation. Such processing provides the best durability as the active agent is physically embedded in the structure of the fiber and released slowly during use. Exhaustion, pad-dry-cure, spraying, and foaming are also common finishing methods to apply antimicrobial agents on various textile substrates. In this regard, major steps have been taken thanks to nanotechnology. This ranges from textile nanofinishing with nanoclays, carbon nanotubes, natural polymers such as chitosan to metal, metal oxide nanoparticles, and nanoencapsulated agents. In this chapter after a brief overview of common textile bacteria and fungus, we provide a comprehensive discussion on antimicrobial mechanism and common antimicrobial agents. Here we also focus on evaluating antimicrobial activities of textiles based on standard methods. An insight has been also put into antimicrobial textiles market and the necessity of nontoxicity.

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10.2 COMMON TEXTILE BACTERIA AND FUNGUS Bacteria with three main shapes of coccus (spheres), bacillus (rods), and spirillum (spirals) have an outer, rigid cell wall that provides their shape and support. The inside of the cell wall is a plasma membrane forming both a boundary for the contents of the cell and a barrier to substances entering and leaving. Cell cytoplasm contains ribosomes (for protein synthesis), the nucleoid (concentrated genetic material), and plasmids (small, circular pieces of DNA). Hans Christian Gram was a scientist who categorized the bacteria into Gram positive and Gram negative based on their structural differences in the cell wall. Bacteria that retain the crystal violet dye due to thick multilayer of peptidoglycan are called Gram-positive, while Gram-negative bacteria do not retain the violet dye and are colored red or pink due to thin singlelayered peptidoglycan. Gram-positive bacteria have a single lipid membrane surrounded by a cell wall composed of a thick layer of peptidoglycan and lipoteichoic acid, which is anchored to the cell membrane by diacylglycerol. In comparison, the cell wall of Gram-negative bacteria consists of a thin layer of peptidoglycan in the periplasmic space between the inner and outer lipid membranes. Almost all antibacterial textiles possess antibacterial efficiencies against Gram-positive bacteria Staphylococcus shortly known as S. aureus. Although S. aureus is not always pathogenic, it is a common cause of skin infections such as abscesses, respiratory infections such as sinusitis, and food poisoning. The cell wall of S. aureus is composed of peptidoglycan, teichoic acids, and proteins. It has thick electron-dense layer of the cell wall, as has been seen in many Gram-positive bacteria. Chemical analysis of the cell wall indicated that more than 70% of the weight of the cell wall is peptidoglycan and that the teichoic acid is covalently bound to the peptidoglycan through a phosphodiester bond. The surface of the cell wall is covered with a fuzzy coat mostly of a complex of teichoic acids and proteins (Umeda et al., 1987). On the other hand, Escherichia coli shortly called E. coli is a common rodshaped Gram-negative bacteria that has been widely studied in antibacterial textile field. There are many instances of the bacteria in food, water, and even person-to-person contact. It possesses adhesive fimbriae and a cell wall that consists of an outer membrane containing lipopolysaccharides, a periplasmic space with a peptidoglycan layer, and an inner, cytoplasmic membrane. Even though it has extremely simple cell structure, with only one chromosomal DNA and a plasmid, it can perform complicated metabolism to maintain its cell growth and cell division (Brown et al., 2015).

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Cell wall

DNA Peptidoglycan Ribosome

Protein Cell wall

Flagella

Cell membrane DNA

Peptidoglycan

Cytoplasm

Cytoplasm

Ribosome

Capsule

Staph (Gram positive) bacteria

Capsule

E. coli (Gram negative) bacteria

Fig. 10.1 Schematic representation of cell structure of S. aureus as a Gram-positive and E. coli as a Gram-negative bacteria.

Simple schematic representation of cell structure of S. aureus as a Grampositive and E. coli as a Gram-negative bacteria has been shown in Fig. 10.1.

10.3 ANTIMICROBIAL MECHANISM Negative effect on vitality of microorganisms is called antimicrobial, which, depending on type of microorganism, is called antibacterial or antifungal. There are also two keywords commonly used in antimicrobial field, namely, “static” and “cidal.” These expressions show the degree of activity as a substance that inhibits multiplying of bacteria without destroying them is called bacteriostat, while bacteriocide agents kill the bacteria. Antimicrobial activities are generally carried out based on two mechanisms (Bajaj, 2001): 1. Controlled-release mechanism in which antimicrobial agents diffuse to kill the microbes. Thus, here the durability of antibacterial agents is not strong and mostly there is no chemical bonding between the agent and textile fibers. In this regard, leaching rate of the antimicrobial agent is an important factor affecting the efficiency. 2. Direct contact mechanism in which the antimicrobial agent is strongly attached to the textile fibers and acts when it is in contact with microorganisms. Thus, possible hazardous effects of antimicrobial agents are minimum through this mechanism, and they are more compatible with toxicological and ecological principles.

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Intruption of transformation Nanoparticles adhesion to cell membrane

DNA interaction Inhibition of DNA replication

Cell wall disruption Protein denaturation

Enzyme disruption

Penetration inside cell

ROS

Fig. 10.2 Different antibacterial mechanisms.

Based on other classification, antimicrobial textiles are grouped into active and passive substrates. Compared with active textiles finishing with active antimicrobial agents, the ability of passive substrates to have detrimental effect on microorganism’s viability is due to their surface or structure through antiadhesive effect (Boryo, 2013). Considering the chemical and structural nature of antimicrobial agents, the following mechanisms lead to reduced microbial growth and cell death as summarized in Fig. 10.2. – Inhibition of cell wall synthesis – Inhibition of protein synthesis – Inhibition of enzyme action – Inhibition of nucleic acid synthesis – DNA damage – Inhibition of metabolic pathways – Interference with cell membrane integrity – Interference with cell membrane permeability – Cell wall damage (Dastjerdi and Montazer, 2010).

10.4 COMMON TEXTILE ANTIMICROBIAL AGENTS Here we tried to briefly summarize the most common antimicrobial agents have been applied on various textile substrates with special focus on metal and metal oxide nanoparticles. – Quaternary ammonium compounds with linear alkyl ammonium compounds composed of a hydrophobic alkyl chain and a hydrophilic part such as 3-(trihydroxysilyl) propy (dimethyl-octdecyl ammonium chloride have been mainly applied in natural fibers such as wool forming covalent bonds with the substrate or in synthetic fibers such as nylon through ionic interactions. Alkyl chain length, presence of the

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perfluorinated group, and number of cationic ammonium groups affect the antibacterial efficiencies. Interaction of surface positive charges and cell membrane negative charges, interfering cell membrane permeability and leakage are among the possible antimicrobial mechanism, which causes cell damage, denaturation of proteins, and inhibition of DNA production avoiding multiplication (Kim and Sun, 2001; Jiang et al., 2017). – Polybiguanides (polycationic amines composed of cationic biguanide repeat units separated by aliphatic chains) such as polyhexamethylene biguanide shortly named as PHMB are promising antibacterial agents for natural and synthetic fibers and mainly act via electrostatic attraction with the negatively charged bacterial cell interfering membrane permeability (Ahani et al., 2017). – Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) (C12H7Cl3O2) has been also used as antibacterial and antifungal agent for finishing of textile substrates through blocking lipid-biosynthesis such as phospholipids, lipopolysaccharides, and lipoproteins affecting the integrity of cell membranes and acting as a barrier to bacteria (Iyigundogdu et al., 2017). – Chitosan has a reputation for natural antibacterial agent, which overweighs other chemicals due to biodegradable and biocompatible properties. It has been applied to textile fibers via various methods, including encapsulation and bonding or crosslinking with the substrate. Interaction between the primary amine group’s positive charges and the negative charges on the microbes’ surface, penetration into the cell wall, combining with DNA and inhibiting the synthesis of mRNA, preventing protein synthesis. Some modifications have been also carried out on chitosan to produce enhanced antibacterial activities. For instance, Wang et al. (2005) produced chitosan-metal complexes with bivalent metal ions, including Cu(II), Zn(II), and Fe(II) indicating superior antimicrobial activities against Gram-positive, Gram-negative, and fungus due to stronger positive charge after complexion. Nanocapsules of polypeptide-grafted chitosan with excellent antibacterial efficacies have been also reported (Zhou et al., 2013). The main advantages of chitosan as an antimicrobial agent for textiles, either as a finishing or to be incorporated in synthetic fibers, are its biocompatibility. However, poor handling and pH and temperature activity dependence of chitosan make its application with some limitations (Nayak and Padhye, 2015). – Natural herbal products such as neem oil and neem derivatives, which are mainly applied through encapsulation. There have been also some

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natural plant-based antibacterial agents such as quinones, lectins, polypeptides, and flavonoid benefiting from no antimicrobial resistance (Ghayempour and Montazer, 2017). – N-halamines are heterocyclic organic compounds containing one or two covalent bonds between nitrogen and a halogen mainly Cl. Nitrogen can be in form of amine, amide, or imide having the highest antibacterial activities. N-halamines act by bonding between Cl and microorganisms interfering the cell enzymatic and metabolic processes, causing the consequent microorganism destruction. Recently, there have been some efforts to produce nano N-halamines with superior antibacterial activities due to larger surface area (Islam et al., 2016). – Natural dyes, including alizarine and pupurine and some of synthetic dyes such as basic dyes, are also capable of acting as antimicrobial agents. Protein-binding ability of tannin existed in natural dyes and cationic structure of basic dyes interrupting the negative bacterial cell life are the main antibacterial mechanisms (Saranya et al., 2017). – Enzymes: Alkaline pectinase, amylase, and laccase have been immobilized onto cotton fibers and reported to have antibacterial efficiencies. The antibacterial activity depends on the type of immobilized enzyme as well as nature and structure of microorganism (Ibrahim et al., 2007). – Metal nanoparticles: Metal nanoparticles such as Ag, Au, Pt, Cu are among the most important class of antibacterial species. In vitro studies revealed that metal nanoparticles inhibited several microbial species. Precursors used for the synthesis of metal nanoparticles, preparation methods, nanoparticles size and shape are the main parameters affecting the antimicrobial effectiveness. Although still under investigation, there are two more popular possibilities for the mechanism of antibacterial activities, namely, metal ion toxicity arising from dissolution of the metals from surface of the nanoparticles and generation of reactive oxygen species (ROS) on surfaces of the nanoparticles (Fig. 10.2) (Dastjerdi and Montazer, 2010). The positive surface charge of the metal nanoparticles facilitates their binding to the negatively charged surface of the bacteria, which may result in an enhancement of the bactericidal effect (Maleki Dizaj et al., 2014). According to the literature, Ag nanoparticles are the widely studied inorganic nanoparticles used as antimicrobial agents and their antibacterial action is due to damage of the bacterial outer membrane producing pits and gaps in the bacterial membrane and Ag ions interacting with disulfide or sulfhydryl groups of enzymes leading to disruption of metabolic processes, which, in

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turn, cause the cell death. Various methods employed for nanosilver synthesis, including photocatalytic reduction, chemical reduction, photochemical or radiation-chemical reduction, metallic wire explosion, sonochemical, polyols, reverse micelle-based methods, and biological methods. There have been a vast number of studies concerning application of silver nanoparticles on various textile substrates producing antibacterial and antifungal properties. These range from embedding particles on the fiber polymeric matrix such as bulk modification of filament yarns via melt mixing of silver nanoparticles as filler, ex situ application of nanosilver colloids via exhaustion, or pad-dry-cure methods to in situ synthesis and fabrication of fabrics. First studies were mainly devoted to the use of nanosilver colloids in which exhaustion of nanoparticles has been carried out on various textile substrates. In this regard due to the functional negative groups of wool, it provides the opportunity to adsorb silver by ionic interaction. There are some examples of using silver as mordant in wool dyeing too. Moreover, application of silver nanocolloid on wool is durable as nanoparticles can be deposited between wool fiber chains. In comparison, exhaustion of nanocolloidal silver is difficult on polyester fibers due to their compact structure and lack of functional groups for nanoparticles adsorption. Alkaline hydrolysis of fibers or physical surface modification of fibers prior to nanofinishing is necessary to achieve the optimum adsorption (Dastjerdi and Montazer, 2011). Dastjerdi et al. (2010) reported the successful preparation of antibacterial polyester fabrics using crosslinkable polysiloxane as simultaneous or after treatment with different concentrations of nanosized colloidal silver. Treated fabrics showed very good antibacterial activity against S. aureus even using 10 ppm nanosilver particles, but they were less active against Klebsiella pneumoniae. Simultaneous application of nanosized silver solution and polysiloxane emulsion on the fabric surfaces showed improved antibacterial efficiencies. In situ synthesis of silver nanoparticles is another approach that recently has attracted researchers (Allahyarzadeh et al., 2013). In this regard, chemical reduction of silver salts, mainly silver nitrate, is a common method, in which inorganic and organic chemical reducing agents are used to prepare silver nanoparticles (Sadeghian Maryan et al., 2013). Moreover, there have been some reports confirming the effective role of textile substrates such as cellulose and wool to act as reducing agents for silver nanoparticles formation (Jiang et al., 2011; Aladpoosh et al., 2014). In situ synthesis of metal nanoparticles within cellulosic materials has been reported as an efficient

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approach for imparting antibacterial activity to the treated fabrics. This method normally involves the adsorption of metal ions onto fiber surfaces by electrostatic or Van der Waals forces, followed by reduction of ions into metal nanoparticles using various reducing agents. Cellulose is a linear chain polymer with three hydroxyl groups per anhydroglucose unit, possessing hydrophilicity and chemical reactivity due to functional hydroxyl groups (O’Connell et al., 2008). It is well known that cellulose has heavy metal adsorption capacity. The capability of cellulosic substrates to reduce various metal ions has been reported in several studies. For example, the Ag nanoparticles were in situ synthesized on cotton fabric using cellulose as reducer and stabilizer. High-temperature reaction at 90°C was effective for enhancing the reactivity of hydroxyl groups and reducing ends of cellulose molecules (Jiang et al., 2011). According to the study carried out by Pinto et al. (2009) if reducing ends of cellulose are removed, silver nanoparticles are not synthesized through UV irradiation of silver nitrate solution. Tollen’s reagent method was applied for in situ synthesis of silver nanoparticles on cotton fabric by transforming AgNO3 to [Ag(NH3)2]+ complex using ammonia and the nanosilver particles formation on the surface of the cotton using the reducing and stabilizing properties of cellulosic chains of the cotton fabric (Montazer et al., 2012). The silver nanoparticles imparted an efficient antibacterial property to the treated cotton fabrics with an excellent washing durability. The reduction in antibacterial properties of the nanosilver-treated cotton fabrics after 30 cycles of washing was negligible. Some reagents have been also added to the silver nanoparticles preparation bath to intensify the reduction reactions (Hosseinkhani et al., 2017). In some cases, these reagents play multiple roles, such as reducing agent, dispersing agent, and stabilizer. For example, Sadeghian Maryan et al. (2013) proposed a simple green route for producing worn-look denim garments with antibacterial property through in situ synthesis of silver nanoparticles by reducing silver nitrate using cellulosic chains of cotton, starch and/or glucose in alkali media. Glucose served as a reducing agent to reduce indigo dye and resulted in better control of particle size and stability. Butylamine was used as a weak organic reducing agent to reduce silver ions bounded to the anionic oxygen sites of cotton fabrics, and the potential of the functionalized fabric as an antiseptic bandage was confirmed by evaluating the bactericidal effect on both Gram-positive and Gram-negative bacteria, and on an antibiotic-resistant strain (Hyang et al., 2007). Simultaneous in situ synthesis of silver nanoparticles and slenderizing of wool fibers was carried out in one single-step process in presence or absence

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of external reducing agent. It has been reported that functional groups of wool fibers such as thiol created under heat and moisture had the potential to reduce silver ions preparing silver nanoparticles (Hosseinkhani et al., 2012). According to reactions (10.1)–(10.4), silver ions, which are formed through silver nitrate ionization, substitute the H+ of thiol groups due to the higher positive chemical potential, forming –S–Ag bond. Moisture

Wool
S
S
Wool ! Wool
SH + Wool
SOH Heat

Wool
SH ! Wool
S
+ H + AgNO3 ! Ag + NO3 +




Wool
SH ! Wool
SAg

(10.1) (10.2) (10.3) (10.4)

In spite of the successful synthesis of Ag nanoparticles, due to the crosslinking of nanoparticles within protein chains, the synthesized silver nanoparticles were not accessible enough to be released and act as antibacterial agent killing the bacteria. Therefore, the antibacterial activity of the treated samples was not very high (Hosseinkhani et al., 2012). Simultaneous aminohydroxylation of polyester fibers along with in situ synthesis of silver nanoparticles has been also carried out to prepare polyester fabrics with excellent antibacterial efficiency against S. aureus and E. coli (Poortavasoly et al., 2014). Triethanolamine with three –CH2OH groups acted as reducing agent and silver ions were reduced to silver metal during the oxidation of the CH2CH2OH groups in TEA to –CH2CHO. Consequently, Ag nanoparticles coordinated with hydroxyl groups on polyester fabric and were substituted with hydrogen. Aminolysis of polyester fabric along with in situ synthesis of silver nanoparticles was developed using dopamine hydrochloride as a friendly reducing and stabilizing agent (Rastegar et al., 2016). Photochemical reduction of silver ions is another method for the treatment of textile substrates with silver nanoparticles providing antibacterial properties. In 2012, silver nanoparticles were synthesized on the surface of cotton fibers by direct reduction of AgNO3 with electron beam irradiation and the treated fabrics indicated good antibacterial efficiency against both Gram-negative and Gram-positive bacteria (Chmielewska and Sartowska, 2012). The in situ synthesis of silver nanoparticles on cotton fabric was achieved by photoreduction of AgNO3 to silver nanoparticles producing a fabric with strong durable antimicrobial property. The in situ method was more successful in producing a fabric with no significant adverse effect on physical properties and less leaching out of

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silver compared to ex situ approach (Perera et al., 2013). UV-C irradiation was also used for in situ synthesis of silver nanoparticles on cotton fabric via digital printing (Kozicki et al., 2013). A more controllable version of the photochemical method is a combined chemical-photochemical reduction of metal precursor, where active reducing and stabilizing agents are also present in reaction solution. For instance, in 2014 water radiolysis under γ-irradiation created hydrated electron (eaq
) and hydrogen radical, which were effective in silver nitrate reduction producing Ag nanoparticles/cotton fabrics. The process was carried out in chitosan solution as a stabilizer and chemical bonding of silver nanoparticles with hydroxyl groups of cotton along with physical adsorption were effective factors in durable nanofinishing (Thi Hanh et al., 2014). In the last decade, biosynthesis of silver nanoparticles has been introduced as an ecofriendly procedure to avoid use of toxic chemicals and to achieve biological compatibility. Application of biosynthesis methods through the use of microorganisms, yeasts, plants, or plant extracts is known as green synthesis. For example, Keliab (ashes of burnt leaves and stems of Seidlitzia rosmarinus plant) was used as a natural source with simultaneous reducing and stabilizing action for in situ synthesis of silver nanoparticles on cotton. The role of cellulosic fiber acting as a reducing agent and presence of Keliab providing an alkali medium were considered as possible mechanisms for silver nanoparticles preparation (Aladpoosh et al., 2014). The reducing ability of hydroxyl radicals formed through water sonolysis has been beneficially used for the sonosynthesis of silver nanoparticles based on reactions (10.5)–(10.7) (He et al., 2014; Harifi and Montazer, 2015a). H2 O

Sonication

!

H• +• OH,

HO• +• OH ! H2 O2 ,

H• + Ag + ! H + + Ag° H2 O2 ! H2 O + ½ O2

2 Ag + + H2 O ! 2 Ag° + ½ O2 + 2 H +

(10.5) (10.6) (10.7)

For instance, cotton fabrics with antibacterial properties were prepared by silver coating using ultrasound irradiation in a one-step procedure. The authors claimed that there is no relation between the amount of deposited silver and the nature of the substrate due to the only physical adsorption of the nanoparticles on the surface. They rejected any chance of chemical bonding between the silver and functional groups of the substrate (Perelshtein et al., 2008). However, we believe that chemical bonding of silver nanoparticles and cellulosic substrate is also possible considering cellulose

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with abundant hydroxyl groups acting as a reducing agent for silver nanoparticles synthesis (Aladpoosh et al., 2014). The in situ synthesis of copper nanoparticles on cotton fabric using citric acid as a stabilizing and protective agent against aggregation and oxidation of nanoparticles, and sodium hypophosphite as a reducing agent has been also reported (Sedighi et al., 2014a, b). The in situ synthesis of other metal nanoparticles such as Au, Pd, and Pt was also reported by some research groups on cellulosic substrates mainly by immersion of cationic cellulosic material into metal salt solution followed by immersion in NaBH4 solution to reduce the metal ions to zero-valence metal. In situ synthesis of nanocupric oxide has been reported through bio method using Seidlitzia rosmarinus ashes as reducing and stabilizing agents (Bashiri Rezaie et al., 2017). Polyester fabric was in situ treated with Cu/Cu2O nanoparticles in one single step using diethanolamine, introducing amide and hydroxyl active groups on the polyester surface, improving the surface reactivity (Bashiri Rezaie and Montazer, 2017). – Metal oxide nanoparticles: TiO2 and ZnO nanoparticles are among the widely known metal oxides used for antibacterial finishing of textile materials. Antimicrobial property of metal oxide nanoparticles, which is related to its crystal structure, shape, and size, is mainly due to the generation of ROS causing specific DNA damage (Dastjerdi and Montazer, 2010). Photocatalytic properties of metal oxide nanoparticles are also effective in antibacterial activities. However, use of UV light for photocatalytic activation is restricted because of genetic damage in human cells and tissues. Thus, several modification methods that have been proposed for visible lightenhanced photocatalytic activities of semiconductors (thoroughly discussed in Chapter 9) are beneficial to solve this problem. There have been a vast number of studies focusing on textile substrates finishing with TiO2 and ZnO nanoparticles or their modified nanocomposites such as TiO2/Ag, TiO2/SiO2, ZnO/Ag, TiO2/ZnO/Ag, TiO2/Ag/ Fe3O4 to produce antibacterial properties. In most of the reported studies, the antibacterial activities of the treated samples are evaluated against S. aureus and E. coli as Gram-positive and Gram-negative bacteria (Harifi and Montazer, 2015b; Behzadnia et al., 2015; Aladpoosh and Montazer, 2016). In some cases, the antifungal efficiencies have been also assessed against diploid fungus, namely, Candida albicans. Nanofinishing of textile substrates with TiO2 is mainly carried out through two routes, namely, ex situ application of commercial TiO2 nanoparticles mainly Degussa P25 via exhaustion or pad-dry-cure methods or in

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situ synthesis and deposition of nanoparticles. As thoroughly discussed in previous chapters, crosslinking agents such as carboxylic acids or preactivation of textile substrates by bio, chemical, or physical methods is essential to achieve strong adsorption of nanoparticles on the textile fibers (Montazer and Pakdel, 2011). Titanium dioxide nanoparticles are generally formed according to hydrolysis and polycondensation reactions. Regarding the need for the crystallization process of TiO2 nanoparticles, sonochemical route was the only successful method for the in situ synthesis of anatase titania nanoparticles without requiring subsequent heating of the coated textile (Harifi and Montazer, 2017). Precipitation process is a widely used method for in situ one-pot synthesis of zinc oxide nanoparticles on textile materials. The simple precipitation process for the synthesis of zinc oxide nanoparticles involves the low-cost precursors such as zinc salts, and synthesis can be achieved under alkaline condition. Zn (OH)2, ZnðOHÞ4 2
or ZnðNH3 Þ4 2 + are the intermediate products converting to ZnO nanoparticles through dehydration and crystallization. The alkaline condition can be prepared using bases such as NaOH or compounds that are source of alkali (Khosravian et al., 2015). For instance, biomediated methods using biomaterials producing alkaline condition has been focused as ecofriendly procedures (Aladpoosh and Montazer, 2015).

10.5 TOXICITY AND HEALTH ISSUES In spite of beneficial effects of antibacterial nanomaterials producing antibacterial textiles with variety of applications, inhibiting the bacteria growth or killing the microorganisms may have harmful effect on other living species, including human being. Antimicrobial present in clothing, healthcare fibrous product, or home textile may contact an individual’s skin or it may affect any living species found in the surrounding environment. Therefore, an appreciation of environmental concerns is obviously important to produce antimicrobial fibrous products with an acceptable ecological performance. Searching through the literature we came up with many instances of antibacterial textiles with focus on finish composition, application methods, and subsequent antibacterial activities evaluation. However, global awareness about human and environmental risks of antibacterial nanomaterials needs careful control of the toxicity problems they may cause. It is crucial to assess the human and environment-friendly character of antimicrobial finishes and develop antimicrobial effects using natural antimicrobials of plant

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and animal origin such as chitosan. In this regard, use of green synthesis procedures together with application of biocompatible nontoxic agents is of high importance. Introducing methods to provide durable attachment of antibacterial nanoparticles to textiles also guarantees the minimum leaching of the nanoparticles to the human and environment. In this regard, in situ nano/bio finishing approaches will be useful. For instance, cotton fabrics with excellent antibacterial activities have been prepared via nanobiofinishing with quaternary modified montmorillonite and common enzymes such as cellulase, laccase, and their mixture. The nano/biofinishing was effective to impart antibacterial and antifungal activities, while cell toxicity investigations showed no adverse effects on human dermal fibroblasts.

10.6 EVALUATION OF ANTIMICROBIAL ACTIVITIES For evaluating the antimicrobial activities of antibacterial textiles, there are mainly two basic approaches depending on controlled-release or direct contact mechanism of antibacterial agents. The ability of treated textiles to reduce the bacteria colonies in contact with an agar culture medium inoculated with the test bacteria is one of the common approaches. On the other hand, if a diffusible, or leaching, antibacterial activity is present, it will be possible to observe a clear zone around the treated sample compared to the zone of bacterial growth around the untreated control sample after the same contact time (Sedighi et al., 2014b). AATCC 100 is a quantitative antimicrobial standard method used to test the antimicrobial activity of the textiles/fabrics over the contact period of 24 h against common bacteria, including S.aureus, K. pneumonia, and E.coli. It determines both bacteriostatic activity (inhibition of multiplication) and bactericidal activity (killing of bacteria) of the antimicrobial test agent. In a typical procedure, microbial culture is prepared in growth enrichment broth for 24 h of incubation to obtain high concentration of the test organisms. High counts of test organism are inoculated onto the antimicrobial test fabric swatches and untreated control fabric. Bacteria counts on the fabrics are monitored at the initial stage (0 h) by standard microbiological microorganisms monitoring techniques. Organism-inoculated fabrics are then incubated for 24 h under favorable conditions of nutrients and temperature. Bacteria will multiply and will increase in number if fabric is not antimicrobial. Untreated control used in the test will assure the increase in microbial growth. Surviving microbial counts are then monitored after neutralization

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and extraction and percent reduction is calculated by using initial count and surviving count data. Percentage of antibacterial reduction is calculated based on Eq. (10.8) (Rastgooa et al., 2017): %R ¼ A
B=A  100

(10.8)

where A and B are the number of bacteria colonies recovered from control and treated fabric samples, respectively. AATCC 147 is a qualitative antimicrobial test used to detect bacteriostatic activity on textile materials. This test determines antibacterial activity of diffusible antimicrobial agents on treated textile materials. It provides a qualitative zone of inhibition around the treated fabric. The size of the zone of inhibition and the narrowing of the streaks caused by the presence of the antibacterial agent permit an estimate of the residual antibacterial activity after multiple washings. Specimens of the test material, including corresponding untreated controls of the same material, are placed in intimate contact with growth agar, which has been previously streaked with test organism. After incubation, a clear area of interrupted growth underneath and along the sides of the test material indicates antibacterial activity of the specimen (Nayak and Padhye, 2015).

10.7 CONCLUSION Thanks to the introduction of antibacterial agents into textile materials, significant achievements have been represented in clothing, medical, and industrial application fields. However, in addition to the antibacterial potentials against microorganisms, special concern should be paid to nontoxicity of the antibacterial textiles to human and environment. Although valuable, proposing vast number of studies about new antibacterial finishes or application methods without a focus on the possible detrimental effects on consumers and environment is not sufficient. Considering the global awareness and regulations, future studies should be concentrated on antibacterial agents with natural and biocompatible bases along with green synthesis approaches. In situ finishing of textile materials via sonochemical methods along with incorporation of biomaterials seems to be effective to provide durable antibacterial activities with minimum harmful effects to human and environment.

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REFERENCES Ahani, E., Montazer, M., Toliyat, T., Mahmoudi Rad, M., Harifi, T., 2017. Preparation of nano cationic liposome as carrier membrane for polyhexamethylene biguanide chloride through various methods utilizing higher antibacterial activities with low cell toxicity. J. Microencapsul. 34, 121–131. Aladpoosh, R., Montazer, M., 2015. The role of cellulosic chains of cotton in biosynthesis of ZnO nanorods producing multifunctional properties: Mechanism, characterizations and features. Carbohydr. Polym. 126, 122–129. Aladpoosh, R., Montazer, M., 2016. Nano-photo active cellulosic fabric through in situ phytosynthesis of star-like Ag/ZnO nanocomposites: Investigation and optimization of attributes associated with photocatalytic activity. Carbohydr. Polym. 141, 116–125. Aladpoosh, R., Montazer, M., Samadi, N., 2014. In situ green synthesis of silver nanoparticles on cotton fabric using Seidlitzia rosmarinus ashes. Cellulose 21, 3755–3766. Allahyarzadeh, V., Montazer, M., Hemmati Nejad, N., Samadi, N., 2013. In situ synthesis of Nano silver on polyester using NaOH/Nano TiO2. J. Appl. Polym. Sci. 5, 892–900. Bajaj, P., 2001. Finishing of textile materials. J. Appl. Polym. Sci. 83, 631–659. Bashiri Rezaie, A., Montazer, M., 2017. Amidohydroxylated polyester with biophotoactivity along with retarding alkali hydrolysis through in situ synthesis of Cu/Cu2O nanoparticles using diethanolamine. J. Appl. Polym. Sci. 134 (21). Bashiri Rezaie, A., Montazer, M., Mahmoudi Rad, M., 2017. Biosynthesis of nano cupric oxide on cotton using Seidlitzia rosmarinus ashes utilizing bio, photo, acid sensing and leaching properties. Carbohydr. Polym. 177, 1–12. Behzadnia, A., Montazer, M., Mahmoudi Rad, M., 2015. Simultaneous sonosynthesis and sonofabrication of N-doped ZnO/TiO2 core–shell nanocomposite on wool fabric: introducing various properties specially nano photo bleaching. Ultrason. Sonochem. 27, 10–21. Boryo, D.E.A., 2013. The effect of microbes on textile material: a review on the way out sofar. Int. J. Eng. Sci. 2, 9–13. Brown, L., Wolf, J.M., Prados-Rosales, R., Casadevall, A., 2015. Through the wall: extracellular vesicles in gram-positive bacteria, mycobacteria and fungi. Nat. Rev. Microbiol. 13, 620–630. Chmielewska, D., Sartowska, B., 2012. Radiation synthesis of silver nanostructures in cotton matrix. Radiat. Phys. Chem. 81, 1244–1248. Dastjerdi, R., Montazer, M., 2010. A review on the application of inorganic nano-structured materials in the modification of textiles: focus on anti-microbial properties. Colloids Surf. B: Biointerfaces 79, 5–18. Dastjerdi, R., Montazer, M., 2011. Nano-colloidal functionalization of textiles based on polysiloxane as a novel photo-catalyst assistant: processing design. Colloids Surf. B: Biointerfaces 88, 381–388. Dastjerdi, R., Montazer, M., Shahsavan, S., 2010. A novel technique for producing durable multifunctional textiles using nanocomposite coating. Colloids Surf. B: Biointerfaces 81, 32. Gao, Y., Cranston, R., 2008. Recent advances in antimicrobial treatments of textiles. Text. Res. J. 78, 60–72. Ghayempour, S., Montazer, M., 2017. Herbal products on cellulosic fabric with controlled release: comparison of in situ encapsulation and UV curing of the prepared nanocapsules. Cellulose 24, 4033–4404. Harifi, T., Montazer, M., 2015a. A review on textile sonoprocessing: A special focus on sonosynthesis of nanomaterials on textile substrates. Ultrason. Sonochem. 23, 1–10.

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Harifi, T., Montazer, M., 2015b. A robust super-paramagnetic TiO2:Fe3O4:Ag nanocomposite with enhanced photo and bio activities on polyester fabric via one step sonosynthesis. Ultrason. Sonochem. 27, 543–551. Harifi, T., Montazer, M., 2017. Application of sonochemical technique for sustainable surface modification of polyester fibers resulting in durable nano-sonofinishing. Ultrason. Sonochem. 37, 158–168. He, C., Liu, L., Fang, Z., Li, J., Guo, J., Wei, J., 2014. Formation and characterization of silver nanoparticles in aqueous solution via ultrasonic irradiation. Ultrason. Sonochem. 21, 542–548. Hosseinkhani, M., Montazer, M., Eskandarnejad, S., Rahimi, M.K., 2012. Simultaneous in situ synthesis of nano silver and wool fiber fineness enhancement using sulphur based reducing agents. Colloids Surf. A Physicochem. Eng. Asp. 415, 431–438. Hosseinkhani, M., Montazer, M., Eskandarnejad, S., Harifi, T., 2017. Optimization of wool slenderizing along with in-situ synthesis of silver nanoparticles using box–behnken design. J. Nat. Fibers 14, 175–184. Hyang, G., Lee, Y., Kun Park, H., Mi Lee, Y., Kim, K., Bum Park, S., 2007. A practical procedure for producing silver nanocoated fabric and its antibacterial evaluation for biomedical applications. Chem. Commun. 2007, 2959–2961. Ibrahim, N., Gouda, M., El-shafei, A.M., Abdel-Fatah, O.M., 2007. Antimicrobial activity of cotton fabrics containing immobilized enzymes. J. Appl. Polym. Sci. 104, 1754–1761. Islam, S., Shabbir, M., Mohammad, F., 2016. Insights into the functional finishing of textile materials using nanotechnology. Text. Cloth. Sustain., 97–115. Iyigundogdu, Z.U., Demir, O., Asutay, A.B., Sahin, F., 2017. Developing novel antimicrobial and antiviral textile products. Appl. Biochem. Biotechnol. 181, 1155–1166. Jiang, T., Liu, L., Yao, J., 2011. In situ deposition of silver nanoparticles on the cotton fabrics. Fibers Polym. 12, 620–625. Jiang, Z., Qiao, M., Ren, X., Zhu, P., Huang, T., 2017. Preparation of antibacterial cellulose with s-triazine-based quaternarized N-halamine. J. Appl. Polym. Sci. 134. https://doi. org/10.1002/app.44998. Khosravian, S., Montazer, M., Malek, R.M.A., Harifi, T., 2015. In situ synthesis of nano ZnO on starch sized cotton introducing nano photo active fabric optimized with response surface methodology. Carbohydr. Polym. 132 (2015), 126–133. Kim, Y.H., Sun, G., 2001. Durable antimicrobial finishing of nylon fabrics with acid dyes and a quaternary ammonium salt. Text. Res. J. 71, 318–323. Kozicki, M., Sasiadek, E., Kołodziejczyk, M., Komasa, J., Adamus, A., Maniukiewicz, W., Pawlaczyke, A., Szynkowska, M., Rogowski, J., Rybicki, E., 2013. Facile and durable antimicrobial finishing of cotton textiles using a silver salt and UV light. Carbohydr. Polym. 91, 115–127. Maleki Dizaj, S., Lotfipour, F., Barzegar-Jalali, M., Zarrintan, M.H., Adibkia, K., 2014. Antimicrobial activity of the metals and metal oxide nanoparticles. Mater. Sci. Eng. C 44, 278–284. Montazer, M., Harifi, T., 2017. New approaches and future aspects of antibacterial food packaging: from nanoparticles coating to nanofibers and nanocomposites, with foresight to address the regulatory uncertainty. In: Grumezescu, A.M. (Ed.), Food Packaging. Elsevier, USA. Montazer, M., Pakdel, E., 2011. Functionality of nano titanium dioxide on textiles with future aspects: Focus on wool. J. Photochem. Photobiol. C, 293–303. Montazer, M., Alimohammadi, F., Shamei, A., Rahimi, M.K., 2012. In situ synthesis of nano silver on cotton using Tollen’s reagent. Carbohydr. Polym. 87, 1706–1712. Morais, D.S., Guedes, R.M., Lopes, M.A., 2016. Antimicrobial approaches for textiles: from research to market. Materials 9, 498–510. Nayak, R., Padhye, R., 2015. Antimicrobial finishes for textiles. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge, UK.

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O’Connell, D.W., Birkinshaw, C., O’Dwyer, T.F., 2008. Heavy metal adsorbents prepared from the modification of cellulose: a review. Bioresour. Technol. 99, 6709–6724. Perelshtein, I., Applerot, G., Perkas, N., Guibert, G., Mikhailov, S., Gedanken, A., 2008. Sonochemical coating of silver nanoparticles on textile fabrics (nylon, polyester and cotton) and their antibacterial activity. Nanotechnology 19, 245705–245711. Perera, S., Bhushan, B., Bandara, R., Rajapakse, G., Rajapakse, S., Bandar, C., 2013. Morphological, antimicrobial, durability, and physical properties of untreated and treated textiles using silver-nanoparticles. Colloids Surf. A Physicochem. Eng. Asp. 436, 975–989. Pinto, R.J.B., Marques, P.A.A.P., Neto, C.P., Trindade, Y., Daina, S., Sadocco, P., 2009. Antibacterial activity of nanocomposites of silver and bacterial or vegetable cellulosic fibers. Acta Biomater. 5, 2279–2289. Poortavasoly, H., Montazer, M., Harifi, T., 2014. Simultaneous synthesis of nano silver and activation of polyester producing higher tensile strength aminohydroxylated fiber with antibacterial and hydrophilic properties. RSC Adv. 4, 46250. Rastegar, L., Montazer, M., Gaminian, H., 2016. Clean low-temperature in situ synthesis of durable silver nanoparticles along with aminolysis of polyester fabric using dopamine hydrochloride. Clean Techn. Environ. Policy 18, 2019–2026. Rastgooa, M., Montazer, M., Harifi, T., Mahmoudi Rad, M., 2017. In-situ sonosynthesis of cobblestone-like ZnO nanoparticles on cotton/polyester fabric improving photo, bio and sonocatalytic activities along with low toxicity and enhanced mechanical properties. Mater. Sci. Semicond. Process. 66, 92–98. Sadeghian Maryan, A., Montazer, M., Harifi, T., 2013. One step synthesis of silver nanoparticles and discoloration of blue cotton denim garment in alkali media. J. Polym. Res. 20, 189–198. Saranya, D.K., Sruthy, P.B., Anjana, J.C., Rathinamal, J., Jayashree, S., 2017. Study on antibacterial activity of natural dye from the bark of Araucaria columnaris and its application in textile cotton fabrics. J. Microbiol. Biotechnol. Res. 4. Sedighi, A., Montazer, M., Hemmatinejad, N., 2014a. Copper nanoparticles on bleached cotton fabric: in situ synthesis and characterization. Cellulose 21, 2119–2132. Sedighi, A., Montazer, M., Samadi, N., 2014b. Synthesis of nano Cu2O on cotton: morphological, physical, biological and optical sensing characterizations. Carbohydr. Polym. 110, 489–498. Thi Hanh, T., Van Phu, D., Thi Thu, N., Anh Quoc, L., Bich Duyen, D.N., Quoc Hien, N., 2014. Research gamma irradiation of cotton fabrics in AgNO3 solution for preparation of antibacterial fabrics. Carbohydr. Polym. 101, 1243–1248. Umeda, A., Ueki, Y., Amako, K., 1987. Structure of the staphylococcus aureus cell wall determined by the freeze-substitution method. J. Bacteriol. 169, 2482–2487. Wang, X., Du, Y., Fan, L., Liu, H., Hu, Y., 2005. Chitosan-metal complexes as antimicrobial agent: synthesis, characterization and structure-activity study. Polym. Bull. 55, 105–113. Zhou, C., Wang, M., Zou, K., Chen, J., Zhu, Y., Du, J., 2013. Antibacterial polypeptidegrafted chitosan-based nanocapsules as an “armed” carrier of anticancer and antiepileptic drugs. ACS Macro Lett. 2, 1021–1025.

FURTHER READING Sadeghian Maryan, A., Montazer, M., Harifi, T., 2015. Synthesis of nano silver on cellulosic denim fabric producing yellow colored garment with antibacterial properties. Carbohydr. Polym. 115, 568–574.

11

Flame-retardant textile nanofinishes 11.1 INTRODUCTION The desire for textiles with reduced flammability has a long recorded history beginning from production of high-performance fibers with intrinsic flameretardant properties such as asbestos, ceramic fibers, kevlar, nomex, and polybenzimidazole to the application of chemicals with the ability to retard the tendency to ignite and burning. This provides many application areas, including home and office applications such as floor coverings, curtains, furniture, workers and firefighter’s uniforms, transportation, and military applications. Textiles with flame-retardant properties belong to a group of protective technical textiles that protect the wearers and textiles material from flame and heat. Over the past years, researchers have been looking for flame-retardant materials with higher efficiencies, minimum effect on fibers inherent properties producing through simple and cost-effective processes, and retaining the property for long time resulting in durable properties. Another important factor is the safety of the material to the environment, limiting the application of some of the introduced materials. In addition to the common halogen, phosphorous, and nitrogen-containing materials with flame-retardant properties, the field has widely progressed by recent development of nanoparticles, nanocomposites, and nanocoating. In this chapter after a brief overview of common flame-retardant compounds, their classification, and general mechanisms, we will focus on the nanoparticles currently applied to impart flame-retardant properties into textiles. Nanocoating methods, namely, layer-by-layer (LBL) assembly and sol-gel methods will also be discussed.

11.2 GENERAL CLASSIFICATION AND MECHANISM Looking up into literature, we have come up with different classification of flame-retardant materials. Most of the classifications are based on the theory of fiber combustion shown in Fig. 11.1 based on the report by Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00011-X

© 2018 Elsevier Ltd. All rights reserved.

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Gas phase Thermal oxidation (flame)

O2

Products

Dispersion

Volatile products

Heat

Thermal degradation

Char

Condensed phase

Heat from ignition

Heat

Dispersion

Thermal oxidation

Fig. 11.1 Fiber combustion theory. Reprinted with permission from Camino, G., Costa, L., Luda di Cortemiglia, M.P., 1991. Overview of fire retardant mechanisms. Polym. Degrad. Stab. 33, 131–154. Copyright 1991, Elsevier.

Camino et al. (1991). According to the classification proposed by Horrocks (1986), flame retardants can be categorized into six groups based on the mechanism of retarding the flammability as: 1. Heat removal 2. Increased decomposition temperature (pyrolysis temperature, Tp) 3. Inhibition from oxygen as a necessary compound for combustion 4. Reducing the volatile and combustible gases 5. Increased combustion temperature (Tc) 6. Interfering the flame chemistry Another classification as proposed by Schindler and Hauser (2004) is three groups of primary flame retardants based on halogens and phosphorous materials, synergistic compounds that their combination with the first group flame retardants possess sufficient flame-retardant properties such as nitrogen and antimony, and adjunctive materials working based on physical barrier. Another classification, which is currently more acceptable, has grouped the flame retardants into four categories based on their action as gas phase, condensed phase, intumescent, and heat sink flame retardants. Gas phase action of flame retardants regarded the evolution of reactive species capable of scavenging free radicals formed during combustion in

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the vapor phase. The widely known compounds working based on this mechanism are halogen-based flame retardants that produce hydrogen halides reacting with hydroxyl and hydrogen radicals interfering with the burning cycle. Phosphorous compounds with constituent of PO, HPO2, and PO2 can also work based on gas phase action. Phosphorous compounds with the ability to form acidic intermediates such as phosphoric acid are also in this group. Forming a barrier between the fibers and flame for instance by forming chars, affecting the pyrolysis reaction causing less flammable volatiles, preventing further degradation of material, and inhibiting the production of flammable degradation products is regarded as condensed phase action of flame retardants. Phosphorous compounds with the ability to form phosphorous acids can also act based on condensed phase, and one of the widely known applications is in cellulose as hydroxyl-containing polymer. Here cotton crosslinking by the produced phosphoric acid or catalyzed dehydration of cellulose as shown in Fig. 11.2 (reactions 11.1 and 11.2) prevented the production of flammable levoglucosan (reaction 11.3) (Neisius et al., 2015). Synergistic systems based on incorporation of nitrogen based

Fig. 11.2 Possible reactions for condensed phase flame-retardant phosphorous compounds on cellulose.

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materials with phosphorous compounds have been also reported as condensed phase mechanism enhancing the flame retardant properties. Nitrogen-based flame retardants can be efficient in both gas and condensed phase action, releasing ammonia diluting combustible gases. Formation of insulating barrier around fibers below the Tp, by applying boric acid and its hydrated salts is also grouped in this method, producing foam-like surface insulating the fibers from heat and oxygen. Intumescent flame retardants, which can be also grouped as condensed phase materials, are a combination of a char-forming agent (polyol, sorbitol, resorcinol, polyhydtrophenol, sugar, glucose, maltose, dextrin, and starch), dehydrating compound capable of forming acid (mono and di ammonium phosphate, melamine phosphate), foam-forming material to release nonflammable gases under combustion (urea, melamin, guanidine, chloroparaffin, dicyandiamide) and stabilizers, crosslinkers, or binders. It has been proved that the intumescent materials work based on formation of foamed char layer preventing the combustion of fibers by inhibition of oxygen and heat (Vandersall, 1971). Heat sink materials work based on heat removal by endothermic reactions, releasing nonflammable gases such as H2O and CO2. The famous flame retardants work based on this mechanism are Al2O3, Mg (OH)2, and CaCO3. Flame retardants can be also categorized based on their durability to laundry as durable, semidurable, and nondurable flame retardants. UV graft polymerization has been applied to produce durable flame-retardant properties on fibers. This includes the application of monomer with flame-retardant properties such as phosphorous-containing materials and their polymerization under UV light exposure forming graft polymerized on the surface (Neisius et al., 2015). Chemical bonding of flame-retardant monomers by crosslinking with the textile substrate has been also developed to produce durable properties. Common crosslinker that has been used in flameretardant finishing is formaldehyde and its derivatives, although many attempts have been made to replace formaldehyde due to environmental problems. In this regard, dimethylol dihydroxy ethylene urea (DMDHEU) was also developed to crosslink a hydroxyl functionalized oligomeric phosphorous compound (HFPO) on cotton fabric (Yang and Qiu, 2007). Another attempt was the application of maleic anhydride with sodium hypophosphite (SHP) forming ester crosslinking with cotton (Wu and Yang, 2008). Application of carboxylic acids such as 1,2,3,4-butane tetracarboxylic acid (BTCA) and triethanolamine as formaldehyde-free crosslinkers has been also

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reported to provide durable flame-retardant properties. In these studies, the flame-retardant material was HFPO (Yang et al., 2009; Guan et al., 2009) and the protection properties were imparted to cotton, silk, and nylon fabrics. In Table 11.1, we tried to summarize most of the reported flame retardant agents for cotton, wool, polyester, and nylon fabrics based on reports from Vandersall (1971), Schindler and Hauser (2004), and Neisius et al. (2015). As indicated in Table 11.1, most of the researches have been done to impart flame-retardant properties into cotton. Wool fibers are inherently less flammable compared with cotton, and synthetic fibers such as polyester show melt-drip behavior thus indicating vertical flame resistance due to melting away from the flame (Schindler and Hauser, 2004). In spite of many progresses in introduction of new halogen, phosphorous, and nitrogencontaining flame retardants, environmental limitations involved in halogen-based materials producing toxic gases and smoke, negative effects of some flame retardants on fabric handle and reduced tensile strength, and formaldehyde release during the application urged the researchers to propose new materials and application processes with more environmentfriendly manners. In this regard, first step was the development of silicone-based materials. Synergistic combination of phosphonate and silicone has been reported as shown in Fig. 11.3, producing durable flameretardant properties on cotton, while siloxane forms crosslinking with cotton hydroxyl groups (Zhao, 2010). The superior properties of siloxane-based agents directed researchers to the introduction of sol-gel method using hydrolysis and condensation of tetraethyl orthosilicate (Totolin et al., 2010). It has been reported that siliconcontaining flame retardants form thermal stable and protective coatings on the surface (Norouzi et al., 2015). Within the development of nanotechnology and its outstanding effects in textile finishing, use of nanoparticles, nanocomposites, and nanocoating methods have brought many advantages to the progressive trend of textile flame-retardant finishing. Combining nanoparticles with traditional flame-retardant materials has been also reported to enhance the thermal stability and mechanical strength while reducing the environmental effects. Flame-retardant nanomaterials can be applied into textiles through conventional exhaustion, pad-dry-cure, backcoating, laminating, sol-gel, and LBL self-assembly methods. Incorporation of nanoparticles and nanocoatings for flame-retardant finishing benefits from no adverse effect on color, comfort, handle, and tensile strength of the treated fabrics (Alongi et al., 2014a).

Table 11.1 Common flame retardant agents based on fiber type Fiber type Flame retardant

Maleic acid + sodium hypophosphite Phosphate acrylate monomer polymerized by UV (TGMAP) UV curable phosphate monomers Vinyl phosphonic acid + triallyl cyanurate (crosslinker) (Opwis et al., 2011) Novel compound named as PDHA with chemical structure of

Nondurable/condensed phase P/N synergism/nondurable/condensed phase Nondurable/gas phase/harsh handle/high cost Nondurable Semidurable/improved whiteness Semidurable Semidurable Stiffness/formaldehyde release/reduced tensile strength Improved handle and tensile strength (difficult reactive and direct dyeing) Eliminate the production of bis(chloromethyl) Reduced acidic tendering Final washing to phosphoric acid removal/unpleasant odor/anticrease/P-N synergism/harsh handle Anticrease and flame retardant/cellulose crosslinking

UV graft polymerization UV graft polymerization Enhanced char formation due to phenolic moiety/UV graft polymerization/Durable (Yuan et al., 2012)

Nanofinishing of Textile Materials

Ammonium sulfamate Diammonium phosphate Ammonium bromide Acid boric/borax Aluminumhydroxy phosphate (AHP) Halogen + Sb2O3/Sb2O5 Hexa bromo cyclo dedecane Tetrakis (hydroxymethyl)phosphonium chloride) (THPC) + urea Precondensated of THPC + urea +ammonia + hydrogen peroxide THPC + sulfate THPC + hydroxyl salts N-methylol dimethylphosphonopropionamide

168

Cotton

Remarks

2-acryloyloxydroxyethyl diethyl phosphate (Siriviriyanun et al., 2008)

Wool

Silk

Nylon

Covalent bonding resulting in durable properties Durable/nucleophilic substitution of chlorine by cotton hydroxyl groups Flame retardant and oil repellency Char formation/combined dyeing and finishing Yellow effect on fibers Toxic polybrominated dioxin formation Nondurable

Carcinogen

Flame retardant and antidrip, intumescent char forming/10 % tensile strength loss Lowering nylon Tm/nylon crosslinking

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Polyester

169

Copolymerization of phosphoramide monomers with acrylic acid and acrylic acid (Huang et al., 2012a,b) Dimethyl-[1,3,5-triacrylol hexahydro)triazinyl]3-oxopropyl phosphonate (Yoshioka-Tarver et al., 2012) Dimethyl phosphite + paraformaldehyde + cyanuric chloride (Nguyen et al., 2012) Fluorinated derivatives of cyclophosphazene (Zhanxiong and Liping, 2010). Hexafluoro zirconate Hexafluoro titanate salts Tetrabromophthalic anhydride (TBPA) Urea + phosphoric acid N-methyloldimethylphosphonpropionamide Hydroxyfunctional organophosphorous (HFPO) + BTCA Diethyl-2-(methacryloyloxyethyl) phosphate Tridibromopropylphosphate (Tris) Cyclic phosphate/phosphonate Hexabromocyclododecane (HBCD) Mixture of bis-phosphonic acid and ammonium sulfamate (Feng et al., 2012) 2-hydroxy propylene spirocyclic pentaerythritolbisphosphonate) (PPPBP) Condensation product of thiourea + formaldehyde + urea Back-coating with antimony trioxide + bromine donator and binder

Admicellar polymerization by sodium dodecyl sulfonate as surfactant and azobis isobutyro nitrile as radical initiator/soft handle

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Fig. 11.3 An example of phosphonate and silicon-based flame retardant.

11.3 NANOCLAY Nanoparticles of hydrous aluminum silicates with sheet structure (layer) also known as natural phyllosilicates such as montmorillonite (MMT), bentonite, kaolinite, hectorite, and halloysite that are usually organically modified to alter the surface properties improving their adsorption capacity have high surface area, high cation exchange capacity, and high modulus. Chemical structure of MMT consists of (Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2nH2O forming 2:1 type layered silicates of packets of two tetrahedral silicate layers and an octahedral with adjacent margins. Ion exchange of MMT with surfactant cations such as quaternary ammonium salts has been extensively investigated and the potential of such compounds as adsorbents and antibacterial agents has been widely reported (Sadeghian Maryan et al., 2013). Most of the research studies devoted to addition of clay nanoparticles into polymer matrix producing nanocomposite fibers through melt spinning possessing higher mechanical properties along with flame-retardant properties (Norouzi et al., 2015). Textile finishing with clay nanoparticles is mainly done by producing polymer/nanoclay composite and its application as a coating material on fabrics (Ghosh, 2011). Polyurethane resins have been combined with MMT and applied on polyester fabric through coating to develop flame-retardant properties (Devaux et al., 2002). The exact mechanism of flame-retardant properties of clay nanoparticles has not been recognized yet. Although scientists reported that while the polymer matrix is burned and gasified during combustion, the incorporated nanoclays accumulate at the surface and form a barrier for oxygen diffusion, thereby slowing down the burning process (Ghosh, 2011). It has been also speculated that clay nanoparticles act by enhanced char formation. However, thermal stability may be restricted due to nanoclay or degradation products of organic modifier, which catalyzes the degradation of polymer (Asadi and Montazer, 2013). In spite of these merits, there are no complete flame-retardant properties when clay nanoparticles are applied alone, and always combination of clay with other traditional organophosphorous compounds results in better activities (Ghosh, 2011). Incorporation of clay dispersions on textile substrates has been also developed in recent years. For this approach, surface modification of textile

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is necessary for attachment of nanoclays into surface (Carosio et al., 2011a). For instance, cotton fabrics with flame-retardant properties have been prepared by prenitrogen gas plasma treatment followed by nanoclay treatment (Shahidi and Ghoranneviss, 2014). The char yield of the treated samples increased by 12% due to the synergistic effect of N2 plasma and clay nanoparticles inhibiting the transmission of heat, energy, and O2 between flame and cotton fabrics. Synergistic effects of clay and intumescent flame retardants have also focused on the ability to provide enhanced flame-retardant properties through protective barrier, which swells and forms a stable char at the surface of the material acting as a thermal shield (Wu et al., 2014). This was achieved by preparation of electrospun nylon 6 nanocomposite nanofibers containing MMT and intumescent nonhalogenated flame-retardant additives. The ability of hollow polyester nonwoven fabric treated with nanoclay/ TiO2/polysiloxane to provide thermal stability above 400°C has been also reported (Asadi and Montazer, 2013). TG–DTA analysis showed more residual ash in presence of nanoclay and the degradation of polyester delayed at high temperatures. Layered double hydroxide (LDH), known as brucite-like compound, which is a class of anionic materials with general formulation of M1
x 2 + Mx 3 + ðOHÞ2 x + Az x
H2 O, where M is metallic cation (Mg2+, Ca2+, Zn2+, Al3+, Cr3+, Fe3+, Co3+) and A (Cl
, CO3 2
, NO3
) refers to the interlayer anion, has been also regarded with potential flame-retardant properties due to the increased thermal degradation temperature of fibers, insulating barrier formation over the surface and endothermic heat sink action of LDH releasing water and carbon dioxide diluting the combustible gases. The potential of LDH to suppress the smoke production rate has been also reported (Pan et al., 2016). In addition to preparation of LDH/polymer nanocomposite fibers, incorporation of LDH on textile fabrics through finishing is mainly reported by LBL assembly, which will be focused in Section 11.8. We found a recent study on the application of LDH combined with dyeing (vinyl sulfone reactive dye) providing fabrics with UV resistance and flame-retardant properties (Barik et al., 2017).

11.4 CARBON NANOTUBE Carbon nanotubes (CNTs) are also regarded as flame-retardant materials due to the formation of char layers acting as a heat barrier and thermal insulator re-emitting the radiation back to gas phase retarding the polymer

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degradation, increased thermal conductivity, and radical scavenging effect. It has been reported that due to the fibrous morphology of CNTs, their effect as a barrier needs high level of concentration compared with nanoclays. Most of the researches are focused on the application of CNTs in polymer matrix, while several studies have been also focused on addition of other fillers such as clay, graphite, or intumescent compositions into CNT/ polymer mixture. CNTs were stabilized on cotton fabrics using vinylphosphonic acid monomer as a crosslinking agent introducing UV curable flame retardants improving the thermal properties and flammability of the coated samples due to heat insulation effect and the mass transport barrier of CNTs embedded in the coating (Parvinzadeh Gashti and Almasian, 2013). Backcoating of cotton fabrics with polyurethane nanocomposite of CNTs/conventional phosphorus flame retardants such as melamine polyphosphate and ammonium polyphosphates (APPs) has been carried out indicating the synergistic effect between CNTs and phosphorous compounds reducing the flammability and improving thermal stability of the fabric (Wesolekand and Giepard, 2014). Combination of CNT with clay nanoparticles has been also developed to enhance the flame-retardant properties due to the synergistic sealing effect of CNTs between clay platelets, creating a compact protective surface layer. Electrospun nylon 6 nanofiber consisting of multiwall CNTs, nanoclay particles, and intumescent flame retardants was an example (Yin et al., 2015). CNT was coated by an exhaustion method and stabilized on cotton using BTCA as crosslinking agent and SHP as catalyst, increasing the thermal stability (Liu et al., 2008). In a very recent study, carboxylated single-walled CNTs were stabilized on cotton fabrics in presence of citric acid as a crosslinker and SHP as a catalyst. Fine dispersion of CNTs was prepared using sodium dodecyl sulfonate as a dispersing agent. The result indicated high char yield of treated fabric with durable properties (Motaghi and Shahidi, 2017). The positive effect of SHP as a phosphorous compound in enhancing the char yield and flame-retardant properties has been proved by researchers (Yazhinia and Prab, 2015).

11.5 NANO-ORGANIC-INORGANIC HYBRID Polyhedral oligomeric silsesquioxane (POSS) with general structure of silicon-oxygen cage surrounding by organic R groups, shown in Fig. 11.4,

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Fig. 11.4 POSS general structure.

has been recently developed as a promising flame-retardant material forming thermally stable silica layer under degradation reaching to the surface acting as a protective layer. It has been found that POSS treatment of cotton fabric using DMDHEU as a binder favored the carbonization of the cellulose and slow down the kinetics of thermo-oxidation in air. The main result is the formation of a carbonaceous surface char that acts as a physical barrier toward the heat and oxygen transfer to the polymer. The authors compared the potential of the treated fabrics with samples finished with conventional phosphorus-based flame retardant and indicated that the performance of nanoparticles is higher than traditional flame retardant during the combustion tests by cone calorimetry. It was speculated that nanoparticles are able to induce the carbonization of cellulose, but through a physical mechanism due to the formation of a ceramic barrier on the textile surface. However, formation of phosphoric and polyphosphoric acid at high temperatures modifies the combustion mechanism of the cellulose chemically in condensed phase (Alongi et al., 2012a). In 2015, branched polyethyleneimine (BPEI), APP, and fluorinateddecyl polyhedral silsesquioxane on cotton fabric was developed to produce multifunctional flame retardant, self-healing, self-cleaning, and superhydrophobicity (Chen et al., 2015).

11.6 SiO2 In situ formation of silica nanoparticles or silica coatings onto polyester, cotton, and their blends has shown promising thermal stability and flameretardant properties. Silica nanoparticles were prepared from waste agriculture products such as rice husk (RH-SNP), and their combination with organic borate as back coating on linen fabrics indicated the synergistic effect (Attia et al., 2017).

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Nanofinishing of Textile Materials

Most of the reported researches concern the application of sol-gel method to promote the formation of a surface silica insulating barrier capable of enhancing the thermo-oxidative stability and flame-retardant properties. Several studies showed that the structure of precursors used in sol-gel method, namely, number and type of hydrolysable groups and presence of aromatic rings has direct effect on the obtained result. Independent from the structure of the precursors, the mechanism of flame-retardant properties is through char formation (Alongi et al., 2012b). It is reported that the thickness of the shielding layer through sol-gel treatment of textiles is very limited. Thus, combination of sol-gel treatment with other conventional flame retardants has been investigated. For instance, addition of 5 wt% phosphorous-containing materials resulted in enhanced flame-retardant properties of cotton (Alongi et al., 2012a). In addition to mixing alkoxysilane precursor with phosphoric acid compounds, it is possible to use precursors with concurrent presence of Si and P components such as diethylphosphatoethyltriethoxysilane as a monomer to prepare a hybrid phosphorous/silicon organic-inorganic flame retardant (Brancatelli et al., 2011). A comprehensive review has been published by Alongi et al. (2014a) concerning recent sol-gel treatment of textile substrates for achieving flame-retardant properties.

11.7 METAL (OXIDE/HYDROXIDE) NANOPARTICLES Aluminum oxide hydroxide nanoparticles (bohemite) act as a heat sink flame retardant through endothermic decomposition releasing water, resulting in cooling and dilution effects (Alongi et al., 2012a). Nano TiO2 particles have been also incorporated into textiles to impart flame-retardant properties. It has been reported that TiO2 promotes the dehydration of cellulose in high temperature forming a char barrier (Lam et al., 2011). Wall effect theory based on the potential of TiO2 to act as a wall absorbing heat and dissipating it in the combustion zone has been also speculated by researchers. Most of the researches concerning with the application of TiO2 are in combination with a crosslinker such as BTCA and a catalyst, namely, SHP with phosphor source being advantageous to the obtained flame-retardant properties (Hashemikia and Montazer, 2012). TiO2 nanoparticles prepared by sol-gel method were applied on cotton fabric using pad-dry-cure method in presence of BTCA/SHP and chitosan phosphate (El-Shafei et al., 2015). Flame-retardant cotton fabrics based on pad-dry-cure treatment of fabrics with SHP, maleic acid, triethanolamine, and nano TiO2 have been

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prepared by Lessan et al. (2011). The results revealed the importance of SHP in enhancing the flame-retardant properties. Triethanolamine prevented the fabric yellowing during the process. Similar to TiO2, ZnO nanoparticles have been also investigated in combination with other flame-retardant materials to provide enhanced properties (Abd El-Hady et al., 2013). N-Methylol dimethyl phosphonopropionamide in combination with melamine resin, phosphoric acid, and nano ZnO was applied on cotton fabrics (Lam et al., 2011). The authors regarded ZnO as a cocatalyst imparting higher durable flame-retardant properties with lower mechanical strength loss and formaldehyde release.

11.8 NANOCOATINGS BASED ON LBL TECHNIQUE LBL assembly, which is done through immersing the substrate into positively and negatively charged polyelectrolyte and/or nanoparticle solutions to prepare multilayer coatings, has been developed as a novel flame-retardant technology in textile nanofinishing. This method mainly contains coating deposition of textile material by positive and negative dispersions of particles, alternately. Some of the LBL coatings based on positive and negative counterparts have been summarized in Table 11.2. Creation of surface barrier and thermal insulator system promoting char formation and inhibiting the production of volatile species, thereby preventing the transmission of heat and oxygen are the general mechanisms of inorganic LBL flame-retardant properties. Intumescent coatings based on the organic or hybrid organic-inorganic LBL coatings have been also developed as more efficient flame-retardant finishing of textiles. In these systems, acid source and gas source are the layers, while in most cases cotton substrate acts as a carbon source. The mechanism is based on the action of the acid source promoting the thermal degradation of the carbon source forming a thermal insulation layer, while inert gases are produced under degradation of gas source promoting the char foam to form a porous and swollen carbon layer, improving the flame-retardant properties (Qiu et al., 2018). Poly(diallydimethylammonium chloride), poly(allylamine), poly (diallydimethylammonium chloride), and APP were LBL deposited on cotton, polyester, and their blends showing potential to create thermally stable char forming capacity not only in cotton as a carbon source substrate but also in polyester (Alongi et al., 2012a).

176

Cotton

Sodium MTT Silica Anionic Al2O3 Silica 1,3,5,7,9,11,13,15-octakis(cyloxide) hydrate POSS Ammonium polyphosphate (APP) Ammonium polyphosphate (APP) Poly(sodium phosphate) (PSP) Sodium MTT Graphene oxide Phytic acid Titanate nanotube Mg-Al layered double hydroxides (Mg-AlLDH) Laponite clay Sodium polyborate

Ramie

Poly(vinylphosphonic caid) (PVPA) Ammonium polyphosphate (APP)

Polyester

Silica α-zirconium phosphate nanoplateles

Positive counterpart

Ref.

Polyethyleneimine (PEI) Ammonium coated silica Cationic Al2O3 Branched Polyethyleneimine (BPEI) Octa-3ammoniumpropyl chloride POSS

Li et al., 2010 Laufer et al., 2011 Ug˘ur et al., 2011 Alongi et al., 2014a,b Li et al., 2011a

Ammonium coated silica Chitosan Poly(allylamine) (PAA) Amino derivative of poly (acrylic acid) Derivative of polyacrylamide Chitosan Chitosan Alginate

Carosio et al., 2012 Carosio et al., 2012 Li et al., 2011b Huang et al., 2012a Huang et al., 2012b Laufer et al., 2012 Pan et al., 2015 Pan et al., 2016

Branched Polyethyleneimine (BPEI) Polyhexamethylene guanidine phosphate (PHMGP) Branched Polyethyleneimine (BPEI) Amino functionalized multi wall carbon nanotube Ammonium coated silica Octa-3ammoniumpropyl chloride POSS

Li et al., 2009 Fang et al., 2016 Wang et al., 2014 Zhang et al., 2013 Carosio et al., 2011a,b Carosio et al., 2011b

Nanofinishing of Textile Materials

Table 11.2 Nanocoatings based on layer by layer technique Fiber type Negative counterpart

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Chitosan provides multiactions in LBL systems, thus has attracted researchers as a positive counterpart. The promising features of chitosan include (1) acting as a char-forming agent due to the polyhydroxy structure, (2) production of nitrogen under degradation acting as a gas source, and (3) acting as a binder providing durable properties. Moreover, chitosan is regarded as a biocompatible agent, thus providing the opportunity to produce biobased intumescent LBL coatings. In this regard, one of the examples is application of chitosan and DNA from herring sperm that contains phosphate acid source, deoxyribose (char former), and many nitrogencontaining bases (Carosio et al., 2013). A comprehensive review published by Qiu et al., 2018 provided detailed information on LBL method for achieving flame-retardant properties.

11.9 FLAME-RETARDANT EVALUATION METHODS Among various standard methods of evaluating flame-retardant properties of textiles, limiting oxygen index (LOI) and cone calorimetry have been widely used. LOI is limiting oxygen index determined according to ASTM D 2863, which is defined as the content of oxygen in an oxygen/nitrogen mixture. In this regard, fabrics with LOI index of higher than 20 will not get burnt. Cone calorimetry is based on the measurement of heat release rate during textile combustion using an oxygen consumption calorimeter. Mass loss rate, ignition time, and CO2/CO production can be also measured by this method (ASTM E 135, ISO 56.60-1). Another recent approach is development of microscale combustion calorimeter working based on pyrolysis combustion method (Neisius et al., 2015).

11.10 CONCLUSION In spite of the vast number of studies concerning with the introduction of newly emerging nanobased technologies to impart flame-retardant properties into textiles as proposed in this chapter, the efforts to commercializing these materials for replacing the common flame retardants is in the initial steps. Research on developing more durable flame-retardant properties using nanoparticles and nanocoating methods is still demanded. Reviewing the literature shows the possible focus of the future research on use of bio-nanobased materials to produce sustainable green systems inhibiting harmful effect on the environment. For instance, use of proteins such as

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casein and hydrophobins containing phosphate and disulfide groups has been regarded as potential flame retardants with char-forming effect. Introduction of flame-retardant materials with multifunctional properties imparting multifeatures such as antibacterial, superhydrophobicity, and self-healing would be of high importance directing the future studies.

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Nguyen, T.M.D., Chang, S.C., Condon, B., Uchimiya, M., Graves, E., Smith, J., Easson, M., Wakelyn, P., 2012. Synthesis and characterization of a novel phosphorus–nitrogen containing flame retardant and its application for textile. Polym. Adv. Technol. 23, 9–13. Norouzi, M., Zarea, Y., Kiany, P., 2015. Nanoparticles as effective flame retardants for natural and synthetic textile polymers: application, mechanism, and optimization. Polym. Rev. 55, 531–560. Opwis, K., Wego, A., Bahners, T., Schollmeyer, E., 2011. Permanent flame retardant fi nishing of textile materials by a photochemical immobilization of vinyl phosphonic acid. Polym. Degrad. Stab. 96, 393–395. Pan, H., Wang, W., Pan, Y., Zeng, W., Zhan, J., Song, L., Hu, Y., Liew, K.M., 2015. Construction of layer-by-layer assembled chitosan/titanate nanotubes based nanocoating on cotton fabrics: flame retardant performance and combustion behavior. Cellulose 22, 911–923. Pan, H., Wang, W., Shen, Q., Pan, Y., Song, L., Hu, Y., Lu, Y., 2016. Fabrication of flame retardant coating on cotton fabric by alternate assembly of exfoliated layered double hydroxides and alginate. RSC Adv. 6, 111950–111958. Parvinzadeh Gashti, M., Almasian, A., 2013. UV radiation induced flame retardant cellulose fiber by using polyvinylphosphonic acid/carbon nanotube composite coating. Compos. Part B Eng. 45, 282–289. Qiu, X., Li, Z., Li, X., Zhan, Z., 2018. Flame retardant coatings prepared using layer by layer assembly: a review. Chem. Eng. J. 34, 108–122. Sadeghian Maryan, A., Montazer, M., Harifi, T., Mahmoudi Rad, M., 2013. Aged-look vat dyed cotton with anti-bacterial/anti-fungal properties by treatment with nano clay and enzymes. Carbohydr. Polym. 95, 338–347. Schindler, W.D., Hauser, P.J., 2004. Chemical Finishing of Textiles. Woodhead Publishing, Cambridge, UK. Shahidi, S., Ghoranneviss, M., 2014. Effect of plasma pretreatment followed by nanoclay loading on flame retardant properties of cotton fabric. J. Fusion Energ. 33, 88–95. Siriviriyanun, A., Rear, E.A.O.’., Yanumet, N., 2008. Improvement in the flame retardancy of cotton fabric by admicellar polymerization of 2-acryloyloxyethyl diethyl phosphate using an anionic surfactant. J. Appl. Polym. Sci. 109, 8–16. Totolin, V., Sarmadi, M., Manolache, S.O., Denes, F.S., 2010. Atmospheric pressure plasma enhanced synthesis of flame retardant cellulosic materials. J. Appl. Polym. Sci. 117, 281–289. Ug˘ur, Ş.S., Sarıışık, M., Aktaş, A.H., 2011. Nano-Al2O3 multilayer film deposition on cotton fabrics by layer-by-layer deposition method. Mater. Res. Bull 46, 1202–1206. Vandersall, H.L., 1971. Intumescent coating systems, their development and chemistry. J. Fire Flammability 2, 97–140. Wang, L.L., Zhang, T., Yan, H.Q., Peng, M., Fang, Z.P., Li, Y., Hao, W., 2014. Flame-retardant coating by alternate assembly of poly(vinylphosphonic acid) and polyethylenimine for ramie fabrics. Chin. J. Polym. Sci. 32, 305–314. Wesolekand, D., Giepard, W., 2014. Single- and multiwalled carbon nanotubes with phosphorus based flame retardants for textiles. J. Nanomater. 2014, 1–6. Wu, X., Yang, C.Q., 2008. Flame retardant finishing of cotton fleece fabric. II. Inorganic phosphorus-containing compounds. J. Appl. Polym. Sci. 108, 9–15. Wu, H., Krifa, M., Koo, J.H., 2014. Flame retardant polyamide 6/nanoclay/intumescent nanocomposite fibers through electrospinning. Text. Res. J. 84, 1106–1118. Yang, C.Q., Qiu, X., 2007. Flame-retardant finishing of cotton fleece fabric: Part I. The use of a hydroxy-functional organophosphorus oligomer and dimethylol dihydroxyl ethyleneurea. Fire Mater. 31, 15–22.

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Yang, H., Yang, C.Q., He, G., 2009. The bonding of a hydroxy-functional organophosphorus oligomer to nylon fabric using the formaldehyde derivatives of urea and melamine as the bonding agents. Polym. Degrad. Stab. 94, 9–12. Yazhinia, K.B., Prab, H.G., 2015. Study on flame retardant and UV protection properties of cotton fabric functionalized with ppy-ZnO-CNT nanocomposite. RSC Adv. 5, 49062–49069. Yin, X., Krifa, M., ScD, J.H.K., 2015. Flame-retardant polyamide 6/carbon nanotube nanofibers: Processing and characterization. J. Eng. Fibers Fabr. 10, 1–11. Yoshioka-Tarver, M., Condon, B.D., Cintro´n, M.S., Chang, S., Easson, M.W., Fortier, C.A., Madison, C.A., Bland, J.M., Nguyen, T.-M.D., 2012. Enhanced flame retardant property of fiber reactive halogen-free organophosphonate. Ind. Eng. Chem. Res. 51, 7–15. Yuan, H., Xing, W., Zhang, P., Song, L., Hu, Y., 2012. Functionalization of cotton with UV-cured flame retardant coatings. Ind. Eng. Chem. Res. 51, 8–14. Zhang, T., Yan, H., Peng, M., Wang, L., Ding, H., Fang, Z., 2013. Construction of flame retardant nanocoating on ramie fabric via layer-by-layer assembly of carbon nanotube and ammonium polyphosphate. Nano 5, 3013–3021. Zhanxiong, L., Liping, D., 2010. Synthesis of fluorocyclotriphosphazene derivatives and their fi re-retardant finishing on cotton fabrics. Int. J. Polym. Sci. 2010, 1–8. Zhao, X., 2010. Synthesis and application of a durable phosphorus/silicon flame-retardant for cotton. J. Text. Inst. 101, 9–12.

FURTHER READING Alongi, J., Colleoni, C., Rosace, G., Camino, L.C., Dicortemiglia, M.P.L., 1991. Overview of fire retardant mechanisms. Polym. Degrad. Stab. 33, 131–154. Li, Y.C., Mannen, S., Morgan, A.B., Chang, S., Yang, Y.H., Condon, B., Grunlan, J.C., 2011c. Intumescent all-polymer multilayer nanocoating capable of extinguishing flame on fabric. Adv. Mater. 23, 3926–3931.

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Water-repellent textile nanofinishes 12.1 INTRODUCTION: DEFINITION AND HISTORICAL OVERVIEW There have been generally three types of repel textile finishing, including water, oil, and soil repellency, among which first attempts have been made to produce water-repellent fabrics. Water repellency is a term related to the ability of a fabric to resist wetting. Here, due to the fabric pores and permeability to air and water vapor, protection against water is not complete under high hydrostatic pressure and the wearer will become wet in downpour when the hydrostatic pressure is high enough. There is also other term called waterproof fabrics with less or even no pores with complete resistance to the penetration of water at any hydrostatic pressure. Recently, focus has been turned into waterproof breathable fabrics satisfying the waterproof requirements as well as being able to allow air and water vapor penetration to provide wearers with high comfort. The distinction between waterproof and water-repellent textiles becomes important when considering the end use of the textile. Water-repellent finishing of textile materials has been focused in this chapter. An insight into oil-repellent finishes has been also provided. Waterproof textiles and soil-repellent finishing will be discussed in Chapters 13 and 14. Some finishes will provide both water and oil repellency, which will be also discussed here. The contact angle of a liquid on the surface of a material is a measurement of the wettability, which relates to the interactions of the solid, liquid, and gas phases. Thus, the differences between the surface energies of the solidvapor and solid-liquid phases strongly affect the resultant contact angle formed between the solid and liquid. Depending on the surface smoothness or roughness different contact angle equations were proposed, which have been thoroughly discussed in Chapter 9. Surfaces with contact angles of 90 degrees or higher are usually considered hydrophobic. This degree can

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be reached to 120 degrees for plain surfaces, such as glass, and to more than 150 degrees for rough surfaces, including textiles. Reducing free surface energy of fibers (lower than water surface tension) is the key step in achieving water-repellent textiles. Except the use of special fabric construction such as stretched polytetrafluoroethylene films (GoreTex), which is not our goal in this chapter, fiber surface with low tendency to interact with water droplets is obtained by using water-repellent finishes such as paraffin emulsions, fatty acid resins, and film-forming products, including silicone and fluorocarbon (FC)-based materials. Through our literature review, we found out that in addition to the water repellency of metallic salts and soaps, the first chemicals used to obtain water-repellent textiles were paraffin waxes in three forms of solvent, molten, and emulsions among which emulsions containing aluminum or zirconium salts of fatty acids were more famous forming hydrophobic chains away from the fiber. Although effective at the time of introduction, these finishes could not continue their application due to poor durability. Modification methods such as formulation with poly(vinyl alcohol), polyethylene, and copolymers of stearyl acrylate-acrylic or methacrylic acids were not successful to widen their usage. Higher fabrics flammability, low air, and water vapor penetration were also reported as other disadvantages of paraffin wax emulsions (Schindler and Hauser, 2004). Next effort was introducing compounds that can react with cellulose to provide permanent water-repellent properties. This was achieved by reacting stearic acid, formaldehyde, and melamine in which the hydrophobic stearic acid groups provide the water repellency, while the remaining N-methylol groups react with cellulose or with each other (crosslinking). Some drawbacks such as formaldehyde release and tear and abrasion resistance loss restricted the application of this type of water-repellent finishes as well. Similar approach has been used to introduce pyridinium compounds as famous water-repellent finishes although with toxicological considerations during production (Schindler and Hauser, 2004; Mahltig, 2015). Significant progress has been made by DuPont introducing Quilon as water-repellent finish made from reacting stearic acid with basic chrome chloride in isopropanol solution. Bonding of the compound with fiber surface occurred during drying and curing steps forming polymerized complex with hydrophobic tails standing away from the surface. Undoubtedly real progress has been achieved by the introduction of silicone-based water-repellent finishes that form hydrogen bonds with fibers while providing hydrophobic outer surface. Silicone is a generic term that

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refers to a class of man-made polymers based on a framework of alternating silicon and oxygen bonds, with organic substituents attached to the silicon. Methyl groups are the most important organic substituents used in silicones mainly polydimethylsiloxanes (PDMSs). Due to the difficulties in the application of PDMS requiring high curing temperature, methyl hydrogen silicones have been introduced. More durable polysiloxane (POS) water repellents contain three main components, namely, silanol, silane, and a catalyst such as tin octoate. Silanol and silane components react to form a threedimensional crosslink around the fiber during curing step. Moreover, functional amino mercapto and epoxy groups capable of reacting with fibers have been used for modifying PDMSs preparing organoreactive silicone-based water-repellent finishes (Schindler and Hauser, 2004; Mahltig, 2015). In addition to the suitable water repellency brought about by relatively low amount of PDMSs, soft hand, improved sewability and appearance are among other advantages of silicone-based water-repellent finishes. Softness properties of silicone-based compounds have been thoroughly discussed in Chapter 6. Fig. 12.1 indicates the possible orientation of PDMSs on fiber surface with methyl groups standing outwards producing water-repellent properties. However, using higher dosage of PDMSs will result in second layer decreasing the hydrophobicity with outward orientation of polar groups (Fig. 12.1). Thus, careful attention is required in the amount of usage. Moreover, there are some reports that silicone-based repellents increase pilling and seam slippage, attraction of hydrophobic dirt, and has moderate durability to laundering and dry cleaning. These drawbacks made researchers investigate another form of waterrepellent finishing agents. These efforts led to the development of FC polymers with both water- and oil-repellent properties due to their lowest O

O Si

CH3

Si

CH3

CH3

Si

CH3

CH3 CH3

Si O

CH3 CH3

CH3

CH3 CH3

Si O

Second layer decreasing hydrophobicity

Si

CH3 CH3

CH3 CH3

Si O

O

O Si

CH3 CH3 CH3 CH3

CH3 Si

O

O

O

Si O

Fig. 12.1 Possible orientation of PDMSs on fiber surface.

O

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surface energy. Fluoropolymers consist of a polymeric backbone such as acrylate or polyurethane, with fluorinated side chains. Their effectiveness for each application varies with chain length, the shape of the chain, and the type of end groups of the fluorinated side chains. Conventional fluoropolymers, including esters and amides of polyacrylic acids although imparting good water-repellent properties, had weak durability to laundering. Thus, efforts have been made to modify fluoropolymers with higher laundry and dry cleaning durability. Fluorosurfactants with the ability to withstand more washing cycles have been proposed based on perfluoroalkyl hydroxyalkyl siloxane or fluorosilicone compounds (Schindler and Hauser, 2004; Mahltig, 2015). Investigating the surface tension of polymers showed that the content of fluorinated alkyl groups is necessary for oil-repellent properties. In this regard, trifluorinated methyl groups (–CF3) with the lowest surface tension were found to be the best choice to impart oil-repellent properties into textiles. It should be also noted that more than the inclusion of perfluorinated alkyl chains, high density of these groups through high chains orientation on the surface is also required for enhanced repellent properties (Duschek, 2001). Scientists revealed that length of eight perfluorinated carbon atoms is the minimum requirement to achieve oil repellency. However, ecological concerns limited their application, making the researchers to look for alternatives. One of the solutions was introduction of flexible methylene groups or stiff phenyl groups as spacers between the polymer backbone and perfluorinated chains, making the application of perfluorinated carbon atoms with shorter chain length possible (Wang et al., 2010). Another attempt to produce more safe oil-repellent material is the introduction of perfluorinated alkylsilane modified with different anchor groups such as epoxy (Qing et al., 2002). Some efforts have been also made regarding the feasibility of the finishing procedure such as use of UV curing instead of high temperature, resulting in enhanced superior oil-repellent properties (Ferrero et al., 2012). Another important factor in water- and oil-repellent properties is the durability of finish to washing cycles. This has been achieved through introduction of crosslinkers and boosters. Isocyanate block copolymers, aziridine compounds, formaldehyde-free crosslinking agents, and carboxylic acids are among the studied cases (Sato et al., 1994; Yildiz et al., 2012). Washing durability of repellent finish can be regarded from two aspects, namely, total removal of finish from the surface after laundering or change in the orientation of the repellent material on the surface, which could be recovered by heat treatment. Crosslinking of the repellent finish will stabilize the agents

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on the surface, decreasing the possibility of disorientation of FC chains during washing (W€ unsche, 2008).

12.2 WATER-REPELLENT NANOFINISHES 12.2.1 Plasma In addition to the use of plasma as a surface modification method enhancing the attachment of water- and oil-repellent finishing materials on the surface (Mahltig, 2015), monomers with the required properties can be used in plasma polymerization and sputtering for producing water- and oil-repellent fabrics. This includes low-pressure plasma with a vacuum device and energy source such as a microwave source and atmospheric plasma with a corona discharge. During sputtering, instead of a gaseous source a solid substrate is used as source for the hydrophobic groups. Monomers with hydrophobic/oleophobic properties and sufficient high vapor pressure are required for plasma polymerization. In this regard, silane compounds with alkyl groups can be used such as hexamethyldisiloxane and vinyltrimethylsilane (Hegemann and Fischer, 2004). Fluorinated monomers such as perfluorinated alkanes, including tetrafluoromethane, have been also used in order to obtain water- and oil-repellent properties. Larger molecules such as 2-(perfluorohexyl) ethyl acrylate with six FC chains can also be used in plasma polymerization processes (Malshe et al., 2013).

12.2.2 Nanostructured materials and nanosurface roughness While evaluating the surface wettability by contact angle, a term can be also studied named as contact angle hysteresis, which is the difference between the advancing and the receding contact angles on the fabric surface. One of the reasons of contact angle hysteresis is the surface roughness. Inspired by lotus effect, which has been thoroughly discussed in Chapter 9, incorporation of nanostructure materials along with hydrophobic properties has been proposed to produce water-repellent textile substrates with fibers of micrometer diameter scale. Smart adopted dual or multisize surface roughness of leaves and insect wings inspired the researchers to develop superhydrophobic and oleophobic properties by nanosurface roughness. The hierarchical multisize surface roughness allows air chamber to form between the water droplet and surface texture, facilitating water droplet to roll off easily (Xing et al., 2018). As included in Chapter 5, deposition of fibers with nanostructure materials or physical modification of fiber surface is a common approach to provide

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nanosurface roughness. Common nanofinishing methods such as in situ and ex situ synthesis, nanocoatings, including sol-gel, layer-by-layer (LBL) deposition, chemical vapor deposition (CVD), and graft polymerization can be applied to impart the repellent properties (Li et al., 2017). Gold nanoparticles were incorporated into cotton fabrics through reduction of HAuCl4 by trisodium citrate to develop a micro- and nanosize surface roughness (Wang et al., 2007). The authors speculated that due to the presence of cooperative binary structures at micro- and nanometer scales, superhydrophobic properties have been achieved. Four different surface roughnesses have been proposed on the surface of gold-treated fabrics apart from the microdiameter scale of woven fabric, the distance between the gold particles on the surface (100 nm to tens of micrometers in size), the size of gold particles, and the roughness of gold nanoparticles. Nanoscaled linear structures were formed on cotton fibers by precipitation of chitosan structures followed by hydrophobic modification with alkylsilanes creating water-repellent fabrics (Liu et al., 2007). Incorporation of calcium carbonate nanoparticles with polymers of poly(glycidyl methacrylate) and poly(styrene-b-ethylene-co-butylene-b-styrene) as hydrophobic component has been also reported (Yu et al., 2007). Silicone and FC-based hydrophobic finishes have been also combined with in situ synthesis of ZnO nanoparticles on polyester fabrics to produce water- and oil-repellent textiles. Incorporation of ZnO nanoparticles with perfluoroalkyl methacrylic copolymer and subsequent fabric treatment by spraying has been also reported. Flower-like hierarchically structured cotton fabric surface was prepared by in situ synthesis of TiO2 nanoparticles on the surface following by treatment with fluoroalkylsilane, resulting in superhydrophobic properties (Li et al., 2015). LBL self-assembly has been also conducted to prepare a superhydrophobic fabric by polyelectrolyte/silica nanoparticles multilayer and postfluorinating treatment (Li et al., 2017). Use of sol-gel process is one of the other methods to increase surface roughness through the introduction of nanoparticles. Sol-gel processing of organofunctional trialkoxysilane precursors in which the organic moiety, including alkyl or perfluoroalkyl groups, is hydrophobic or oleophobic has been widely investigated (Vasiljevic et al., 2017). It has been reported that the water- and oil-repellent properties are due to the low surface energy of alkyl and perfluoroalkyl-functionalized polysilsesquioxane coatings along with surface roughness properties. Nanosilica sols modified with perfluorinated monomers, nonfluorinated silanes such as alkyl trialkoxy silanes, and silicon-based hydrophobically

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modified polymers have been used to create water- and oil-repellent properties (Takenori et al., 2009). A dual-size surface roughness was prepared by incorporation of titania sols on cotton fibers followed by hydrophobization with stearic acid, 1H,1H,2H,2H-perfluorodecyltrichlorosilane or their combination (Xue et al., 2008). One-step sonochemical method has been applied to produce superhydrophobic and superoleophilic cotton fabric by in situ incorporation of SiO2 nanoparticles functionalized with octadecyltrimethoxysilane. SiO2 nanoparticles were synthesized based on sol-gel method using tetraethylorthosilicate (Li et al., 2015). Silica nanoparticles were in situ synthesized on cotton fibers followed by surface treatment with monoepoxy-functionalized PDMS or perfluoralkyl silane to produce water-repellent and oil-repellent properties, respectively (Hoefnagels et al., 2007). The treatment was durable due to the amine functionalization of silica nanoparticles making the covalent bonding possible. The authors speculated the dual-size surface roughness as important factor to achieve superior repellent properties. The raspberry-like, triple-size surface roughness structure has been developed by Leng et al. (2009) by in situ covalent bonding of big silica particles of 800 nm on cotton fibers, followed by treatment with 3-aminopropyl-triethoxysiloxane and hydrochloric acid to change the surface charge to make the attachment of negatively charged silica nanoparticles on the fiber surface possible. The treatment was stabilized by SiCl4 crosslinking, followed by surface modification with a perfluoroalkyl silane. The process is schematically shown in Fig. 12.2.

Fig. 12.2 Creation of dual-size structure on the surface of woven cotton fibers, as proposed by Leng et al. (2009). (Reprinted with permission from Leng, B., Zhengzhong, S., de With G., Ming, W., 2009. Superoleophobic cotton textiles. Langmuir 25, 2456–2460. Copyright 2009, American Chemical Society).

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In a very recent study hierarchical morphology of micro/nanosized roughness has been developed on cotton fabric treating with hydrophobized silica nanoparticles. Trichlorododecylsilane was used to render lower surface tension on silica nanoparticles (Jeong and Kang, 2017). Carbon nanotubes contain linear structures with diameters in the nanometer range that produces nanoscopic structure on textile fibers similar to surface of rice leaf. In some cases, hydrophobic modification of carbon nanotubes for instance with butylacrylate has been reported to produce strong water-repellent properties. Carbon nanotubes with poly(butylacrylate) shells were prepared and applied on cotton textiles to produce a durable artificial lotus-leaf effect possessing super water-repellent properties (Liu et al., 2007). Although still not applied on textile substrates, there have been some reports on the POS-modified multiwalled carbon nanotubes (Zhang et al., 2017) with potential water- and oil-repellent properties. UV excimer laser has been applied to synthetic fibers followed by treatment with fluorinated agents creating water-repellent properties. Plasma etching has been also applied before sol-gel treatment enabling the creation of a dual micro- to nanostructured roughness producing super hydrophobicity and high oleophobicity (Vasiljevic et al., 2017). Another recent approach to enhance the surface roughness is through electrospining. For instance, superamphiphobic alumina nanofiber mats were prepared using trimethoxysilane with a short perfluoroalkyl chain (Gao et al., 2017).

12.2.3 Dendrimers Dendrimer FCs, which contain fluorinated alkyl groups and combination of nonfluorinated dendrimers with conventional FC finishing, have been also reported as successful approaches to provide water- and oil-repellent properties. In this way, water-repellent properties have been achieved using lower amount of finishing agents along with low condensation temperature (80–130°C), high abrasion resistance, high washing durability, and soft hand (Atav and Bariş, 2016). Based on the literature, the ability of polymeric dendrimer-containing FC to produce water- and oil-repellent properties was superior to nanosized FC polymer, nanosilica acid, and conventional agents such as paraffin emulsion containing zirconium salt and conventional FC compound (Namligoz et al., 2009). Although still not applied on textile substrates, dendrimer-like porous silica particles with center-radial pores and interconnected nanowrinkles on particle surface have shown

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superhydrophobic properties (Xing et al., 2018). The authors speculated that the nanoroughness effect allowing the air pockets to center-radial porous channels enhanced the hydrophobicity.

12.2.4 Biomaterials Hydrophobins are spherical proteins with diameters of few nanometers, which can bring water-repellent properties to hydrophilic textile substrates such as cotton through attachment of hydrophilic textile fiber groups with the hydrophilic part of the hydrophobin, leaving the hydrophobic part outwards of the surface. In addition to hydrophobic effect, antistatic properties have been also reported using hydrophobin (Opwis and Gutmann, 2011). Another approach is application of bioinspired materials based on catechol structures, which are aromatic molecules with two o-hydroxyl groups (Garcı´a et al., 2014). A series of catechol derivatives with a different number of linear alkyl chain substituents and different lengths were polymerized in the presence of aqueous ammonia and air forming water-repellent coatings on cotton and polyester fabrics.

12.3 SELF-HEALING PROPERTIES Efforts to improve the durability of water- and oil-repellent finishing of textiles against laundering, mechanical abrasion, and chemical attack have directed the researchers toward introduction of bioinspired self-healing ability, idea of which arises from the plants maintaining their superhydrophobicity by regenerating the epicuticular wax layer after they are damaged (Wang et al., 2011b). The idea is based on the ability of surface coating material to be supplied consecutively after damage, which can be achieved through the micro/nanomultiscale morphology serving as the nanoreserviors for trapping the low surface tension materials, which will be transported to the surface (Wang et al., 2011a). Thus, the reported selfhealing finishing includes embedding an excess amount of low-surface energy species into rough matrices with micro- and nanoscaled multistructures, which can migrate to the surface under an external stimulus to repair the surface with a layer of low-surface-energy species and restore the original superhydrophobicity (Wu et al., 2016). First study was done by Li et al. (2010) in which CVD of porous polymer coatings based on fluoroalkylsilane with micro- and nanoscaled hierarchical structures was concerned. A large number of reacted fluoroalkylsilane moieties acted as healing agents, migrating to the coating surface under a slightly humid environment to heal the superhydrophobicity.

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Fabrics with a self-healing superhydrophobic and superoleophobic surface properties were prepared by coating with a hydrolysis product from fluorinated decyl polyhedral oligomeric silsesquioxane (FD-POSS) and a fluorinated alkyl silane (Wang et al., 2011a, b). Solution-dipping method based on the sequential deposition of cotton fabrics in branched poly(ethylenimine) (PEI), silver nanoparticles, and FD-POSS has been found effective as a self-healing superhydrophobic approach (Wu et al., 2016). Co-deposition of dopamine with an alkyl silane, namely, hexadecyltrimethoxysilane has been recently investigated with potential to produce durable superhydrophobic properties with self-healing ability against chemical damages such as plasma treatment and etching in acid or alkali (Fig. 12.3) (Wang et al., 2017).

Fig. 12.3 Schematic production of cotton fabrics with self-healing superhydrophobic properties as proposed by Wang et al. (2017). (Reprinted with permission from Wang, H., Zhou, H., Liu, S., Shao, H., Fu, S., Rutledgec, G.C., Lin, T., 2017. Durable, selfhealing, superhydrophobic fabrics from fluorine-free, waterborne, polydopamine/alkyl silane coatings. RSC Adv. 7, 33986–33993. Copyright 2017, The Royal Society of Chemistry).

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12.4 EVALUATION TEST METHODS As water-repellent finishing of textiles means the resistance of fabric to absorption, adsorption, and penetration of water, measuring the fabric contact angle is not sufficient to achieve reliable judgment for consumer-related situations such as exposure to rain. One of the most common methods to evaluate water-repellent properties is drop test according to which a drop of liquid is placed on the fabric and observed for liquid sinking during a definite time to rate the textile repellency. Water/isopropanol mixtures are usually used according to the AATCC Test Method 193-2007. The amount of isopropanol increases from 2% (lowest rating 1) to 60% (highest rating 8). Spray test according to AATCC TM 22 is also used in which fabric is stretched, held at a 45 degrees, and sprayed with 250 mL of water from above. The resulting wetting pattern, if any, is rated using photographic standards. Hydrostatic pressure test can be also applied. One surface of fabric is subjected to increasing hydrostatic pressure until three points of leakage appear on the opposite surface. The pressure at the third point of leakage is recorded in centimeters or meters on a water gauge (AATCC TM 127, ISO 811, or EN 20811). For fabrics that require durable repellency performance, the test methods can be applied to fabrics that have been laundered or dry cleaned by standard methods (as AATCC TM 124 and TM 86) in order to determine the durability of the repellency properties (Mahltig, 2015).

12.5 CONCLUSION Although successful in providing water- and oil-repellent properties, perfluorocarbon products are in black list of environmental associations due to their toxicity. Thus, new trends of water- and oil-repellent finishes with minimum side effects on human and environment are more demanded. In this regard, nanotechnology has brought valuable achievements and further investigations will be a focus of future. Finishing methods based on nanostructured surface roughness will be of high importance to provide both fluorine-free repellent finishes along with durability in terms of self-healing properties. Nanoparticles and application methods resulting in water-/oilrepellent properties along with other multifunctionalities such as selfcleaning, antibacterial, flame retardant, and UV protection will be also concerned in future.

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REFERENCES Atav, R., Bariş, B., 2016. Dendrimer technology for water and oil repellent cotton textiles. AATCC J. Res. 3, 16–24. Duschek, G., 2001. Emissionsarme und APEO-freie Fluorcarbon-Ausr€ ustung. Melliand Textilber. 82, 604–608. Ferrero, F., Periolatto, M., Udrescu, C., 2012. Water and oil-repellent coatings of perfluoropolyacrylate resins on cotton fibers: UV curing in comparison with thermal polymerization. Fibers and Polym. 13, 191–198. Gao, S., Nakane, K., Ohgoshi, A., Isaji, T., Ozawa, M., 2017. Development of superamphiphobic alumina nanofiber mats using trimethoxysilane with a short perfluoroalkyl chain. Text. Res. J. https://doi.org/10.1177/0040517517712093. Garcı´a, B., Saiz-Poseu, J., Gras-Charles, R., Hernando, J., Alibes, R., Novio, F., Sedo´, J., Busque, F., Ruiz-Molin, D., 2014. Mussel-inspired hydrophobic coatings for waterrepellent textiles and oil removal. ACS Appl. Mater. Interfaces 6, 17616–17625. Hegemann, D., Fischer, A., 2004. Plasma functionalization of textiles and fibers. Vak. Forsch. Prax. 16, 240–244. Hoefnagels, H.F., Wu, D., de With, G., Ming, W., 2007. Biomimetic superhydrophobic and highly oleophobic cotton textiles. Langmuir 23, 13158–13163. Jeong, S.A., Kang, T.J., 2017. Superhydrophobic and transparent surfaces on cotton fabrics coated with silica nanoparticles for hierarchical roughness. Text. Res. J. 87, 552–560. Leng, B., Zhengzhong, S., de With, G., Ming, W., 2009. Superoleophobic cotton textiles. Langmuir 25, 2456–2460. Li, Y., Li, L., Sun, J., 2010. Bioinspired self-healing superhydrophobic coatings. Angew. Chem. 122, 6265–6269. Li, J., Yan, L., Zhao, Y., Zha, F., Wang, Q., Le, Z., 2015. One-step fabrication of robust fabrics with both-faced superhydrophobicity for the separation and capture of oil from water. Phys. Chem. Chem. Phys. 17, 6451–6457. Li, S., Huang, J., Chen, Z., Chen, G., Lai, Y., 2017. Review on special wettability textiles: theoretical models, fabrication technologies and multifunctional applications. J. Mater. Chem. A 5, 31–55. Liu, Y., Tang, J., Wang, R., Lu, H., Li, L., Kong, Y., Qia, K., Xin, J.H., 2007. Artificial lotus leaf structures from assembling carbon nanotubes and their applications in hydrophobic textiles. J. Mater. Chem. 17, 1071–1078. Mahltig, B., 2015. Hydrophobic and oleophobic finishes for textiles. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge, UK. Malshe, P., Mazloumpour, M., El-Shafei, A., Hauser, P., 2013. Multi-functional military textile: plasma-induced graft polymerization of a C6 fluorocarbon for repellent treatment on nylon–cotton blend fabric. Surf. Coat. Technol. 217, 112–118. Namligoz, S., Bahtiyari, M.I., Hosaf, E., Coba, S., 2009. Performance comparison of new (dendrimer, nanoproduct) and conventional water, oil and stain repellents. Fibres Text. East. Eur. 17, 76–81. Opwis, K., Gutmann, J.S., 2011. Surface modification of textile materials with hydrophobins. Text. Res. J. 81, 1594–1602. Qing, F.-L., Ji, M., Lu, R., Yan, K., Mao, Z., 2002. Synthesis of perfluoroalkyl-containing multifunctional groups compounds for textile finishing. J. Fluor. Chem. 113, 139–141. Sato, Y., Wakida, T., Tokino, S., Niu, S., Takekoshi, S., 1994. Effect of crosslinking agents on water repellency of cotton fabrics treated with fluorocarbon resin. Text. Res. J. 64, 316–320. Schindler, W.D., Hauser, P.J., 2004. Chemical Finishing of Textiles. Woodhead Publishing, Cambridge, UK.

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Takenori, T., Hiroyuki, N., Yoshie, K., Yuji, O., Kazufumi, O., 2009. Development of a water- and oil-repellent treatment for silk and cotton fabrics with fluoroalkyltrimethoxysilane. J. Text. Eng. 55, 13–21. Vasiljevic, J., Tomsˇicˇ, B., Jerman, I., Simoncˇicˇ, B., 2017. Organofunctional trialkoxysilane sol-gel precursors for chemical modification of textile fibres. Tekstilec 60, 198–213. Wang, T., Hu, X., Dong, S., 2007. A general route to transform normal hydrophilic cloths into superhydrophobic surfaces. Chem. Commun., 1849–1851. Wang, Q., Zhang, Q., Zhan, X., Chen, F., 2010. Structure and surface properties of polyacrylates with short fluorocarbon side chain: role of the main chain and spacer group. J. Polym. Sci. A 48, 2584–2593. Wang, X., Liu, X., Zhou, F., Liua, W., 2011a. Self-healing superamphiphobicity. Chem. Commun. 47, 2324–2326. Wang, H., Xue, Y., Ding, J., Feng, L., Wang, X., Lin, T., 2011b. Durable, self-healing superhydrophobic and superoleophobic surfaces from fluorinated-decyl polyhedral oligomeric silsesquioxane and hydrolyzed fluorinated alkyl silane. Angew. Chem. 123, 11635–11638. Wang, H., Zhou, H., Liu, S., Shao, H., Fu, S., Rutledgec, G.C., Lin, T., 2017. Durable, selfhealing, superhydrophobic fabrics from fluorine-free, waterborne, polydopamine/alkyl silane coatings. RSC Adv. 7, 33986–33993. Wu, M., Ma, B., Pan, T., Chen, S., Su, J., 2016. Silver-nanoparticle-colored cotton fabrics with tunable colors and durable antibacterial and self-healing superhydrophobic properties. Adv. Funct. Mater. 2016 (26), 569, 557. W€ unsche, H., 2008. Neue fluorcarbon-generation mit LAD-effekt. Textilveredlung 43, 5–6. Xing, Y., Du, X., Li, X., Huang, H., Li, J., Wen, Y., Zhang, X., 2018. Tunable dendrimerlike porous silica nanospheres: effects of structures and stacking manners on surface wettability. J. Alloys Compd. 732, 70–79. Xue, C., Jia, S., Chen, H., Wang, M., 2008. Superhydrophobic cotton fabrics prepared by sol–gel coating of TiO2 and surface hydrophobization. Sci. Technol. Adv. Mater. 9, 1–5. € € Yildiz, U.Y., Aslan, C., Ureyen, M.E., Koparal, A.S., Dogan, A., 2012. Properties of textile fabrics treated with antibacterial and repellent finishes. In: Proceeding of 12th World Textile Conference AUTEX, 13–15 June, Zadar, Croatia, pp. 735–740. Yu, M., Gu, G., Meng, W., Qing, F.L., 2007. Superhydrophobic cotton fabric coating based on a complex layer of silica nanoparticles and perfluorooctylated quaternary ammonium silane coupling agent. Appl. Surf. Sci. 253, 3669–3673. Zhang, J., Yu, B., Gao, Z., Li, B., Zhao, X., 2017. Durable, transparent and hot liquid repelling superamphiphobic coatings from polysiloxane-modified multiwalled carbon nanotubes. Langmuir 2017 (33), 510–518.

FURTHER READING AATCC Test Method 193-2007, 2009. AATCC Technical Manual., pp. 362–364. AATCC Test Method 22-2005, 2009. AATCC Technical Manual., pp. 67–69.

13

Waterproof nanofinishes for textiles 13.1 INTRODUCTION: DEFINITION AND HISTORICAL APPROACHES Waterproof and breathable fabrics, which can not only prevent water droplets permeation but also allow water vapor transmission, are of high importance for textile researchers providing the ability to protect rain and snow water while allowing sweat vapor to evaporate from inside to outside. These fabrics have many practical applications such as protective clothing, sportswear, medical equipment, military, construction, and aerospace. Moisture control management and breathability are the ability of textiles to transport moisture and water vapor away from skin, and directly affect comfort feeling of the wearers. This is especially important for sportswear when athlete’s perspiration needs to escape from the wearer’s skin to the surrounding, providing comfort (Harifi and Montazer, 2017). Moisture management systems are mainly based on wicking (capillary movement) of the moisture away, evaporation, and final drying of skin (Pavlidou and Paul, 2015). Traditionally, there are four main approaches to produce waterproof breathable textiles as shown in Fig. 13.1. Apart from breathable woven fabrics developed by tight and dense weaving construction, laminating and coating of porous membranes on textile substrates was the first successful approach for waterproof breathable fabrics. This was achieved by application of polyurethanes (PU), polytetrafluoroethylene (PTFE), acrylics, and polyamino acids. Famous Gore-Tex garments were developed through this method. Common method involved the microporous layers containing PU, a water-repellent agent to cover the inner wall of cavities, polyisocyanate, and nonionic surfactant (Mukhopadhyay and Kumar Midha, 2008). Systems based on the absorption of moisture vapor, migrating it to the opposite surface due to concentration gradient were the ideas to develop hydrophilic nonporous membranes for breathable properties. In this method, hydrophilic segments have been added to the hydrophobic polymer structure, in which chemical adsorption of moisture Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00013-3

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Traditional approaches for waterproof breathable textiles

Closely woven fabrics

Hydrophobic microporous membranes

Hydrophilic nonporous membranes

Combined microporous and hydrophilic membranes

Fig. 13.1 Traditional approaches for waterproof breathable textiles.

occurred in the hydrophilic backbone and water is repelled by the hydrophobic segments. Incorporation of hydrophilic groups, including hydroxyl and amine in a block copolymer, and use of polyethylene oxide are among the applied reports (Lomax, 1990). Polyacrylamide coatings were applied to cotton fabrics along with citric acid and sodium hypophosphite as crosslinker and catalyst to form crosslinking between polymer chains and polymer cellulose, rendering the fabric good water vapor permeability and water penetration resistance (Save et al., 2002). Bicomponent systems comprising microporous membranes and hydrophilic polymer coating have been also developed with several advantages brought about by each of the components (Mayer et al., 1989).

13.2 NEW APPROACHES AND MATERIALS Within the development of nanotechnology, microporous membranes with holes of 2–3 μm size that are smaller than the size of raindrops and larger than water vapor molecule have been replaced by nanoporous hydrophilic membranes allowing water vapor to pass through a chemical adsorption process forming amorphous regions in the main polymer system of the hydrophilic part acting as intermolecular pores allowing water vapor molecules to pass (Kim and Par. 2013). For instance, polyester fabrics were laminated by different layers of (PTFE) microporous hydrophobic membrane and PU nanoporous hydrophilic membrane indicating water resistance and vapor breathability (Razzaque et al., 2017). In next sections, some of the new materials and approaches for preparing waterproof breathable textiles have been described.

13.2.1 Waterborne polyurethane After the synthesis of waterborne PU (WPU), textile waterproof finishing has significantly progressed. WPU is an active branch of PU produced from

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reaction of PU prepolymer with water. This involves the structural modification of hydrophobic PU backbone with built-in hydrophilic groups, followed by addition of deionized water to emulsify and disperse the hydrophilic WPU prepolymer, with the process of chain extension (Zhou et al., 2015). WPU has been modified with fluorinated compound and used for fabrication of waterproof-breathable membranes with significant superhydrophobic performance. Modification of polyacrylonitrile (PAN) nanofibrous membranes with fluorinated-WPU such as short perfluorohexyl (-C6F13) chains has been reported as a promising method to prepare good waterproofness and high moisture vapor permeability (Wang et al., 2014). WPU has been also modified by nonfluorine compounds such as polydimethylsiloxane to fabricate waterproof breathable membranes (Sheng et al., 2017). Recently, novel waterproof and moisture permeable coating was prepared by modifying a WPU agent with silk fibroin and polyvinylpyrrolidone. The prepared material was applied on polyester fabric through coating providing desirable waterproof and breathable effect (Shao et al., 2017).

13.2.2 Electrospinning Electrospinning with the ability to form nanofibrous porous membranes with small pore size, high porosity, good mechanical strength, fine flexibility has opened a promising route to develop waterproof breathable fabrics. PU electrospun fibrous membranes with different diameters were effective to produce waterproof and breathable properties. However, hydrophobic properties of the prepared membranes were low, thus directing the researchers to develop fluorinated PU electrospun nanofibrous membranes with good water resistance and moisture vapor permeability. Another attempt was reducing the pore size of the nanofibrous material by application of carbon nanotubes, which benefit from electrical conductivity boosting the stretching effect of jet stream, forming thin fibers with small pore size (Li et al., 2015). In the applied method, carbon nanotubes were modified with fluorinated compounds. In a very recent study, one-step electrospinning of fluorinated PU (C6FPU) containing short perfluorohexyl (-C6F13) chains has been developed as a fibrous membrane with good hydrophobicity, high porosity, and small pore size, which also involved less environmental harmful effects

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Fig. 13.2 Schematic illustration of fabrication process of PU/C6FPU/MgCl2 waterproof and breathable membrane as proposed by Zhao et al. (2017). (Reprinted with permission from Zhao, J., Li, Y., Sheng, J., Wang, X., Liu, L., Yu, J., Ding, B., 2017. Environmental friendly and breathable fluorinated polyurethane fibrous membranes exhibiting robust waterproof performance. ACS Appl. Mater. Interfaces 9, 29302–29310. Copyright 2017, American Chemical Society).

(Zhao et al., 2017). The authors reported the positive effect of MgCl2 on the decreased pore size. The proposed synthesis approach is shown in Fig. 13.2. Waterproof breathable membranes with porous structures were prepared by treating elctrospun PAN with amino-silicone oil/n-hexane solutions through dip coating followed by blade coating of SiO2 nanoparticle in acetone solution. The proposed method took the advantages of using nanoparticles as nanoroughness structures. Moreover, SiO2 nanoparticles were fillers covering the spaces among the adjacent nanofibers to minimize the pore size (Sheng et al., 2017). In addition to the superhydrophobic waterproof breathable properties, this method is regarded as an environment-friendly fluorine-free technique. Achieving waterproof, moisture permeable, and moisture unidirectional transport functions was another strategy reported, based on the surface coating of textiles by composite material composed of at least two heterogeneous layers with different performances. A double-layer membrane composed of a hydrophilic thermoplastic PU (TPU) tree-like nanofiber electrospun membrane/tetrabutylammonium chloride and a hydrophobic pure TPU nanofiber membrane was prepared with superior waterproof, moisture permeability, and moisture unidirectional transport performance (Ju et al., 2017).

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13.2.3 Smart polymers Waterproof fabrics with tuneable breathability can be produced using smart polymers such as shape memory polymers (SMPs). In these systems, transmission of water vapor is smartly controlled with low heat and vapor transfer at low temperatures and higher transfer at high temperatures. One of the widely applied SMPs is PU, in which at lower temperatures the coating absorb water and is in swollen state, while at temperatures more than transition temperature the coating has opening microcracks due to the collapsed state, resulting in high diffusion flux of water molecules (Mukhopadhyay and Kumar Midha, 2008). Detailed description of SMPs and temperature responsive polymers can be found in Chapter 15. In addition to SMPs, temperature-sensitive polymers such as poly (N-tert-butylacrylamide-ran-acrylamide) can be applied to textile substrates working based on the swelling/deswelling effect resulting in smaller and larger pore size for water vapor transmission (Save et al., 2002; Mondal, 2008). Phase change materials (PCMs) are another group of smart polymers with the ability to produce moisture/thermal management properties. Vapor-permeable water-repellent fabrics treated with PCMs benefit from temperature-regulating properties to protect the wearer against heat or water. Incorporation of PCMs into textiles is mainly based on encapsulation methods. Microencapsulated core/shell octadecane/melamin formaldehyde was deposited on nylon fabric producing vapor-permeable water-repellent properties with comfortable thermoregulating effect (Chung and Cho, 2004). Detailed information on the PCMs and microencapsulation technology has been provided in Chapter 19.

13.3 CONCLUSION Promising potential of electrospun membranes with nanoporous structures, small pore size, good mechanical strength, and flexibility will highlight the future of waterproof breathable textiles. Toward this approach, incorporation of nanoparticles with nanofibrous electrospun materials will add to the properties through formation of nanostructured rough surfaces. More attention to propose environment-friendly fluorine-free methods will be also concerned. Efforts to apply nanoparticles achieving waterproof properties will also attract the researchers, as surface nanotreatments are preferred since they do not have detrimental effect on original inherent properties of fibers, including breathability.

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REFERENCES Chung, H., Cho, G., 2004. Thermal properties and physiological responses of vaporpermeable water-repellent fabrics treated with microcapsule-containing PCMs. Text. Res. J. 74, 571–575. Harifi, T., Montazer, M., 2017. Application of nanotechnology in sports clothing and flooring for enhanced sport activities, performance, efficiency and comfort: a review. J. Ind. Text. 46, 1147–1169. Ju, J., Shi, Z., Deng, N., Liang, Y., Kang, W., Cheng, B., 2017. Designing waterproof breathable material with moisture unidirectional transport characteristics based on a TPU/TBAC tree-like and TPU nanofiber double-layer membrane fabricated by electrospinning. RSC Adv 7, 32155–321633. Kim, K.S., Par, C.H., 2013. Thermal comfort and waterproof breathable performance of aluminum-coated polyurethane nanowebs. Text. Res. J. 83, 1808–1820. Li, Y., Zhu, Z., Yu, J., Ding, B., 2015. Carbon nanotubes enhanced fluorinated polyurethane macroporous membranes for waterproof and breathable application. ACS Appl. Mater. Interfaces 7, 13538–13546. Lomax, G.R., 1990. Hydrophilic polyurethane coatings. J. Coated Fabrics 20, 88–107. Mayer, W., Mohr, U., Schrierer, M., 1989. High-tech Textiles: Contribution made by finishing, in an example of functional sports and leisurewear. Int. Text. Bull. 35, 16–32. Mondal, S., 2008. Phase change materials for smart textiles—an overview. Appl. Therm. Eng. 28, 1536–1550. Mukhopadhyay, A., Kumar Midha, V., 2008. Fundamental principles and designing aspects of breathable fabrics a review on designing the waterproof breathable fabrics part I. J. Ind. Text. 37, 228–262. Pavlidou, S., Paul, R., 2015. Moisture management and soil release finishes for textiles. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge, UK. Razzaque, A., Tesinova, P., Hes, L., Salacova, J., Affan Abid, H., 2017. Investigation on hydrostatic resistance and thermal performance of layered waterproof breathable fabrics. Fibers Polym. 18, 1924–1930. Save, N.S., Jassal, M., Agrawal, A.K., 2002. Polyacrylamide based breathable coating for cotton fabric. J. Ind. Text. 32, 119–138. Shao, J., Wang, C., Zhou, J., Wan, L., 2017. Waterproof and moisture permeable coating of polyester fabrics using a novel waterborne polyurethane agent modified with silk fibroin and polyvinylpyrrolidone. J. Text. Inst. 108, 864–869. Sheng, J., Xu, Y., Yu, J., Din, B., 2017. Robust fluorine-free superhydrophobic aminosilicone oil/SiO2 modification of electrospun polyacrylonitrile membranes for waterproof-breathable application. ACS Appl. Mater. Interfaces 9, 15139–15147. Wang, J.Q., Li, Y., Tian, H.Y., Sheng, J.L., Yu, J.Y., Ding, B., 2014. Waterproof and breathable membranes of waterborne fluorinated polyurethane modified electrospun polyacrylonitrile fibers. RSC Adv. 4, 61068–61076. Zhao, J., Li, Y., Sheng, J., Wang, X., Liu, L., Yu, J., Ding, B., 2017. Environmental friendly and breathable fluorinated polyurethane fibrous membranes exhibiting robust waterproof performance. ACS Appl. Mater. Interfaces 9, 29302–29310. Zhou, X., Li, Y., Fang, C., Li, S., Cheng, Y., Lei, W., Meng, X., 2015. Recent advances in synthesis of waterborne polyurethane and their application in water-based ink: a review. J. Mater. Sci. Technol. 31, 708–722.

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Antifouling and soil-repellent nanofinishes 14.1 INTRODUCTION Fouling is a term generally used to describe the contamination and encrusting of a surface by materials from the surrounding environment (Magin et al., 2010). Although looking into literature fouling is a word usually used in building materials, marine, and household, it can be generalized to any surface in which contaminants harm the esthetic, hygienic, or technical operation. Antifouling techniques, although mostly specified to marine vessels biofouling, can refer to all systems that prevent an unwanted substance from attaching to a surface. In addition to biofouling, which is the accumulation of undesired microorganisms on surfaces, there exists inorganic fouling, including the deposition of dirt, suspended particles, and oil on the surface. Self-cleaning can be also regarded as a technique for the removal of deposited fouling on the surface, which has been thoroughly discussed in Chapter 9. Antifouling properties have been developed, based on increasing the hydrophilicity and/or bioinspired from microstructured surfaces such as shark skin, rice leaves, and butterfly wings (Bixler et al., 2014; Zinadini et al., 2017). There are some examples of antifouling treatment of fibrous membranes especially designed for filtration applications. For instance, multiwalled carbon nanotubes coated by zinc oxide nanoparticle were blended in polyethersulfone membrane to impart antibiofouling properties by increased hydrophilicity (Zinadini et al., 2017). Application of antibacterial coatings and nanoparticles for antibiofouling of fibrous membranes has been developed. The investigated materials include silver nanoparticles or polymeric biocide polyhexamethylene guanidine (Rahimi et al., 2016; Protasov et al., 2017). All the reported literature designed strategies to increase the hydrophilicity of membranes or adding antibacterial efficiencies to resist against biofouling. In spite of these studies, very rare research studies have been found in the literature concerning the specific use of “antifouling” word as a textile finishing treatment. However, regarding soil as an unwanted substance at the Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00014-5

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surface of textile clothing with main classification of dry particulates, oily soils and/or combination of both, soil-repellent textile finishing can be grouped into antifouling treatment. Textile clothing during its lifetime can be soiled with the mentioned soils through mechanical adhesion, direct contact or rubbing, electrostatic attraction of dust from the air, or by soil redeposition during laundering. Textile with anti-decontamination properties are not easily wetted by oily soils, or do not adsorb dust or particulates on the surface. More than the term soil repellent finishing of textiles, which refers to the soil guard efficiency of surface, soil-release finishes are also concerned to enhance the washability of soiled clothing during laundering. Most of the researches devoted to soil-repellent textiles focus on imparting hydrophobic properties into surface, developing soil protection effect according to the work of adhesion by reducing the surface energy (Gotoh et al., 2017). Water- and oil-repellent textile finishing methods have been described in Chapter 11. On the other hand, hydrophobization of fiber surface decreases the soilrelease property during laundering. Soil-release finishes should make the fabric more hydrophilic for better wettability in soil removal. However, due to the high surface energy of hydrophilic surfaces, oil and organic matters can easily contaminate the surface. Thus, research studies are focusing on methods and materials, which can not only resist the surface from soil but also enhance the soil-release activities during laundering. Endowing hydrophilic/oil repellent properties into textile substrates is an approach to achieve this goal. In this chapter, we will review the methods and finishes developed for soil-release treatment of textiles based on physical, chemical, bio-, and nanotechniques. An insight into bioinspired micro/nanostructured surfaces for preparing hydrophilic/oleophobic properties capable of soil-repellent and soil-release efficiencies will be also provided.

14.2 CHEMICAL METHODS For the first time in history, the necessity of soil-release finishing of textiles was recognized after the introduction and application of resin-treated durable press cotton fabrics. The main mechanism of soil-release finishing agents is based on the reduced adhesion of the soil on the surface and increased diffusion of water and detergent into fiber-particles interface. Although some factors such as solubilization and emulsification of soils, or hydrodynamic flow for carrying the soil away from the surface are also important, detergent

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General soil release mechanisms

Roll-up

Penetration of soil/fiber interface by wash liquid

Physical soil removal by surface abrasion

Finishing agent swelling

Fig. 14.1 General soil-release mechanisms.

composition and washing machine parameters are responsible for them. Thus, in view of textile expertise, four main mechanisms should be concerned and controlled to impart soil-release properties as shown in Fig. 14.1 (Schindler and Hauser, 2004). Roll-up mechanism is special for oily soils based on the high fiber/oil interfacial energy, low fiber/wash liquid interfacial energy, and low oily soil/wash liquid interfacial energy. This mechanism brought the idea of using hydrophilic/oleophobic finishes on textiles to impart efficient oily soil-release properties (Schindler and Hauser, 2004). Other mechanisms, including penetration of soil/fiber interface by wash liquid, physical soil removal by surface abrasion (materials such as carboxymethyl cellulose and starch), and finishing agent swelling are applicable for both particulate and oily soils (Pavlidou and Paul, 2015). Common soil-release finishing agents are summarized in Table 14.1, based on their chemical structure (Schindler and Hauser, 2004; Pavlidou and Paul, 2015). Most of the soil-release finishing agents are based on the balance between hydrophilicity and oleophobicity named as hydrophilic-lipophilic balance (HLB). Finishes with HLB ¼ 15 provide good soil-release efficiencies (Griffin, 1950). Silicone/polyalkylene oxide copolymers with hydrophobic dimethylsiloxane segments and hydrophilic silicone modifications by ethoxylated or amino groups are among the examples providing enhanced soil-release properties and softness (Holme, 2003). Fig.14.2 shows the dual action of hybrid fluorocarbons in water and air caused by different orientation of hydrophobic/hydrophilic segments, producing prominent soil-release properties. In these systems, in dry state, fluorocarbon segments block the hydrophilic groups, which will be swollen in wash liquor condition. In addition to these chemicals, any chemical methods bringing hydrophilicity into fibers such as polyester alkaline hydrolysis (Schindler and

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Table 14.1 General chemical soil-release finishing agents Chemical group Example Remarks

Carboxy based

Acrylic, methacrylic acid and ester copolymers, styrene-maleic anhydride copolymers and carboxymethyl cellulose Starch, methyl cellulose, ethyl cellulose, hydroxyl ethyl cellulose, hydroxyl propyl starch, hydrolyzed cellulose acetate Condensation copolymers of terephthalic acid and ethylene glycol Hybrid fluorocarbons containing perfluoroalkyl and hydrophilic segments

Hydroxy based

Ethoxy based

Fluorine based

Finish swelling mechanism Combination with crosslinkers such as dimethyloldihydroxyethyleneurea (DMDHEU) Combination with crosslinkers

Durable soil release of polyester through exhaustion and pad-dry-cure Hydrophobicity/oleophobicity in air Hydrophilicity and oil releasing in water

Hydrophobic fluorocarbon segments

Hydrophilic segments Air

Water

Fig. 14.2 Dual orientation of hybrid fluorocarbon-based materials with soil-release properties in water.

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Hauser, 2004) and cellulose carboxylation (Obendorf, 2004) also result in soil-release properties. These methods basically work by electrostatic repulsion of soils. Soil-release effect can be recognized by eye, comparing the photographic standards, reflectance measurements, and microscopy. AATCC has developed two standard methods, one focuses on oily soils placed on the fabric following by pressing, washing, drying, and comparison with standard photographs rating from 1 to 5 (AATCC 130), and the other is soil redeposition evaluation measured by change in fabric reflectance (AATCC 151).

14.3 PHYSICAL METHODS One of the approaches to physically impart soil-repellent properties into textiles is application of plasma. Surface coating by atmospheric pressure plasma jet polymerization using hexamethyldisiloxane as a precursor for depositing silicon oxide layers on the poly (ethylene terephthalate) and rayon fiber surface has shown promising water-repellent soil deposition resistance (Gotoh et al., 2017). Potential of plasma for soil-release treatment of textiles has been also proved through imparting hydrophilic- and oil-repellent properties. A recent approach for promising anticontamination and easy decontamination properties has been made by treating hydrophilic PEGylated surface with CF4 plasma (Peng and Yongcun, 2017).

14.4 BIOFINISHING It has been reported that treatment of cotton surface by cellulase enzyme is beneficial for soil-release properties, through surface polishing effect. Cleaning cellulase enzyme (CCE) has been developed to impart soil release under washing with specific action on beta-glucan stains and the ability to protect cotton from soil redeposition. Modification of CCE with carboxymethyl cellulose has been also reported to produce soil-release properties (Calvimontes et al., 2011). Lipase and cutinase are also effective to produce hydrophilicy on the surface of polyester resulting in soil-release properties.

14.5 NANOFINISHING All nanoparticles, nanocomposites, and nanocoating methods with photocatalytic activities as described in Chapter 9 can be grouped as antifouling

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agents for photodegradation of organic soils. Moreover, creation of surface nanostructured roughness based on lotus effect will result in soil-repellent and soil-release properties as discussed in next section.

14.6 NEW ANTIFOULING/SOIL-RELEASE APPROACHES Although not applied on textile substrates yet, some research groups have tried to develop stimuli-responsive surfaces with hydrophilic and oleophobic intercalated constituents that simultaneously have hydrophilicity and oleophobicity based on interaction with polar/nonpolar liquids (Lampitt et al., 2000). In these systems, hydrophilic moieties locate at the interface endowing the penetration of water molecules due to water-induced molecular rearrangement, while in the presence of oil low-surface energy component is located in the interface, resulting in oleophobicity (Howarter et al., 2011). Although not published yet, textiles with switchable hydrophobic (soilrepellent) to hydrophilic (soil-release) properties have been recently developed. In dry state, the surface is completely resistant to water, while immersion in water makes the surface hydrophilic by swelling, producing soilrelease properties. This property is recovered as soon as the textile is dried. These systems are based on the covering of silica nanoparticles by hydrophilic and hydrophobic organic chains. Highly branched polyalkoxysiloxane was used as a silica precursor, which is partially end group modified by either hexadecyl or polyethylenglycol chains (Houben et al., https://www.dwi. rwth-aachen.de/index.php?id¼1372). Combination of hydrophilic/hydrophobic properties of polymers with nanoparticles producing micro-nanoscaled hierarchical structures is a novel recent approach to prepare superhydrophilicity/superoleophobicity providing oil-fouling properties. In specific research poly (diallyldimethylammonium chloride) (PDDA) with sodium perfluorooctanoate (PFO) (PDDA-PFO) was combined with SiO2 nanoparticles preparing nanocomposite coatings benefiting from nanostructured roughness (Yang et al., 2012). Detailed information on the nanostructured surface roughness is provided in Chapters 5, 9, and 11. Multiple scale nanoroughness covered by different weight ratio of oppositely charged inorganic nanoparticles (silver and nano TiO2) and amino-functionalized polysiloxane system has been developed as a novel hydrophilic soil-repellent finishing of polyester fabric with amphiphilic hybrid block copolymer-like feature depending on the orientation of resin

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layers on the surface (Dastjerdi et al., 2012). The applied aminofunctionalized polysiloxane contained hydrophobic dimethylsiloxane interspersed with hydrophilic amino-modified side groups. Hydrophilic surface covered by inorganic nanoparticles attracts the hydrophilic groups of resin allowing the hydrophobic regions to be arranged on the surface. This is the proposed orientation in one layer of resin. Double layer of the resin will be oriented in the opposite manner due to the hydrophobic interaction of the hydrophobic regions, forming hydrophilic segments on the top of roughness on the particles. The authors claimed that the proposed orientation of the resin layer will be opposite on fabric surface areas not covered by the particles. Thus, amphiphilic hybrid block copolymer structure is similar to the soil-release agent based on fluorocarbons in the air and water, here showed by droplet absorption by time. Moreover, nanoscale roughness boosted the swelling effect of hydrophilic groups on the surface.

14.7 CONCLUSION Special wetting surface with hydrophilic/oil-repellent features to impart antifouling and soil-release properties based on bioinspired nanoscale surface roughness will be more researched in future resulting in outstanding superior properties, which cannot be achieved by traditional compounds. These systems will be also beneficial for soft handle and durability. Besides, the applied methods could result in multifunctional properties brought about by incorporation of nanoparticles.

REFERENCES Bixler, G.D., Theiss, A., Bhushan, B., Lee, S.C., 2014. Anti-fouling properties of microstructured surfaces bio-inspired by rice leaves and butterfly wings. J. Colloid Interface Sci. 419, 114–133. Calvimontes, A., Lant, N.J., Dutschk, V., 2011. Cooperative action of cellulase enzyme and carboxymethyl cellulose on cotton fabric cleanability from a topographical standpoint. J. Surfactant Deterg. 14, 307–316. Dastjerdi, R., Montazer, M., Stegmaier, T., Moghadam, M.B., 2012. A smart dynamic selfinduced orientable multiple size nano-roughness with amphiphilic feature as a stainrepellent hydrophilic surface. Colloids Surf. B. Biointerfaces 91, 280–290. Gotoh, K., Shohbuke, E., Ry, G., 2017. Application of atmospheric pressure plasma polymerization for soil guard finishing of textiles. Text. Res. J.. https://doi.org/ 10.1177/0040517517698988. Griffin, W.C., 1950. Classification of surface-active agents by HLB. J. Soc. Cosmet. Chem. 1, 311–320. Holme, I., 2003. Water repellency and waterproofing. In: Heywood, D. (Ed.), Textile Finishing. Society of Dyers and Colourists, Bradford, pp. 185–186.

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Howarter, J.A., Genson, K.L., Youngblood, J.P., 2011. Wetting behavior of oleophobic polymer coatings synthesized from fluorosurfactant-macromers. ACS Appl. Mater. Interfaces 3, 2022–2030. Lampitt, R.A., Crowther, J.M., Badyal, J.P.S., 2000. Switching liquid repellent surfaces. J. Phys. Chem. B 104, 10329–10331. Magin, C.M., Cooper, S.P., Brennan, A.B., 2010. Non-toxic antifouling strategies. Mater. Today 13, 36–44. Obendorf, S.K., 2004. Microscopy to define soil, fabric and detergent formulation characteristics that affect detergency: A review. AATCC Rev. 4, 17–23. Pavlidou, S., Paul, R., 2015. Moisture management and soil release finishes for textiles. In: Paul, R. (Ed.), Functional Finishes for Textiles: Improving Comfort, Performance and Protection. Woodhead Publishing, Cambridge, UK. Peng, S., Yongcun, M., 2017. Fabrication of hydrophilic and oil-repellent surface via CF4 plasma treatment. Mater. Des. 139, 293–297. Protasov, A., Bardeau, J.F., Morozovskaya, I., Boretska, M., Cherniavska, T., Petrus, L., Tarasyuk, O., Metelytsia, L., Kopernyk, I., Kalashnikova, L., Dzhuzha, O., Rogalsky, S., 2017. New promising antifouling agent based on polymeric biocide polyhexamethylene guanidine molybdate. Environ. Toxicol. Chem. 36, 2543–2551. Rahimi, M., Zinadini, S., Zinatizadeh, A.A., Vatanpour, V., Rajabi, L., Rahimi, Z., 2016. Hydrophilic goethite nanoparticle as a novel antifouling agent in fabrication of nanocomposite polyethersulfone membrane. J. Appl. Polym. Sci. 133, 1–13. Schindler, W.D., Hauser, P.J., 2004. Chemical Finishing of Textiles. Woodhead Publishing, Cambridge, UK. Yang, J., Zhang, Z., Xu, X., Zhu, X., Men, X., Zhou, X., 2012. Superhydrophilic– superoleophobic coatings. J. Mater. Chem. 22, 2834–2837. Zinadini, S., Rostami, S., Vatanpour, V., Jalilian, E., 2017. Preparation of antibiofouling polyethersulfone mixed matrix NF membrane using photocatalytic activity of ZnO/ MWCNTs nanocomposite. J. Membr. Sci. 529, 133–141.

FURTHER READING AATCC Test Method 130, 1999. Soil Release: Oily Soil Method, AATCC Technical Manual. American Association of Textile Chemists and Colorists, Research Triangle Park, NC, pp. 217–219. AATCC Test Method 151, 1999. Soil Redeposition, Resistance to: Launder-Omeler Method, AATCC Technical Manual. American Association of Textile Chemists and Colorists, Research Triangle Park, NC, pp. 267–268.

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Sensing nanofinishes for textiles 15.1 INTRODUCTION Human senses, which give the body the ability to receive signals from the environment and react to them, were the inspiration for creation of smart textile sensors to detect and respond to environmental stimulus. This is achieved by incorporation of stimulus-responsive materials with textile substrates and/or electronic textiles capable of electronically transduced interactions with the local environment (Smith and Mirica, 2017). Thus, textile-based sensors are capable of receiving the signals and stimulus from the environment and respond to them. Textile-based sensors have the advantage of flexibility and have recently attracted the researchers to replace conventional rigid sensors. They can be easily attached to various surfaces to provide real-time detection in wearable and portable electronics, wearable health-monitoring systems, and sportswear to monitor athlete’s performance. Wearable sensor systems were historically based on direct attachment or swing of the circuit chips, resistors, and capacitors into textiles such as garments or furniture known as adapted electronics (Castano and Flatau, 2014). However, integrated textile sensors have been developed in recent years using fibers made of sensing materials by electrospinning method or textile finishing and coating methods treating the textile surface with stimuli-responsive materials. In this chapter, we will focus on the methods and materials used for preparing stimuli-responsive textile sensors based on chemical and physical classification of stimuli. In each subcategory, we will provide different methods applied to recognize the output response of the textile-based sensors. Sensors can be sensitive to chemical stimuli such as humidity, pH, organic and inorganic compounds, and physical stimuli, including temperature, light, electricity, force, pressure, and strain (Fig. 15.1). In general, the sensor response is in the form of electrical or optical signal, and regarded as electrical, electrochemical, and optical sensors (Buengera et al., 2012). In electrical sensors, the response to the stimuli is correlated to a change in electrical current, resistance, or capacitance. Electrochemical sensors are mainly designed for chemical detection where oxidizing or reducing the target Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00015-7

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Temperature

Light Physical Mechanical

Electrical Stimuli pH

Moisture Chemical Chemical compounds Biochemical compounds

Fig. 15.1 Physical and chemical classification of stimuli.

chemical is related to current. On the other hand, optical sensors are mainly worked based on the change in the absorbance and transmittance of light intensity. A change in color upon external stimuli can be also grouped in optical sensors.

15.2 PHYSICAL STIMULUS 15.2.1 Temperature-sensitive textiles Hydrogels are three-dimensional networks of hydrophilic polymers, which swell and absorb water; however, they do not solubilize in water due to crosslinks between network chains. They can be classified into different groups based on source (natural, synthetic), charge (nonionic, cationic, anionic), structure (amorphous, semicrystalline, crystalline), preparation method (homopolymeric, copolymeric, multipolymer interpenetrating), and environmental stimuli response (temperature, pH, electrical, mechanical, photo, and magnetic responsive) (Ahmed, 2015). Recently, functionalization of textiles with micro- and nanostimuli responsive hydrogels has been concerned owing to the high response rate along with no detrimental effect on inherent properties of the textiles

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(Bashari et al., 2013). Hydrogels undergo changes in contact with stimuli and the changes are reversible, returning to the original state in the absence of stimuli. Overall, obtaining a durable stimuli-responsive polymer finishing on textiles along with effective functionality is a major challenge that can be resolved by activation of fabrics prior to hydrogel finishing or use of crosslinking agents to produce three-dimensional networks between the hydrogels and the fibers. For instance, low-temperature plasma has been applied to functionalize the surface forming covalent bonding between the textile substrate and stimuli-responsive hydrogels (Tourrette et al., 2009) or carboxylic acids such as 1,2,3,4-butanetetracarboxylic acid (BTCA) as crosslinkers in covalent bonding of poly(N-isopropyl acrylamide)/chitosan hydrogel on cotton fabric (Liu et al., 2009). One of the approaches to prepare temperature-sensitive textiles is application of temperature-responsive hydrogels, which are grouped into negative and positive temperature-sensitive hydrogels. Here two terms of lower (LCST) and upper (UCST) critical solution temperatures are defined, which determine the swelling and shrinkage of negative and positive temperature-sensitive hydrogels. Shrinkage occurs below UCST of positive temperature hydrogels such as poly(acrylic acid) (PAA), polyacrylamide, and poly(acrylamide-co-butyl methacrylate)), while poly (N-methylacrylamide), poly(N,N-dimethylacrylamide) or poly(N-isopropylacrylamide) (PNIPAAm), poly(N-vinyl isobutyramide), and poly (N-vinylcaprolactam) are negative temperature-sensitive hydrogels, which swell below their LCST (Buengera et al., 2012). As temperature-sensitive textiles treated with hydrogels are generally applied in contact with human body, hydrogels with critical temperature of around physiological body temperature are more interesting, although the critical temperature of hydrogel can be tuned based on addition of hydrophobic and hydrophilic structure (Buengera et al., 2012; Bashari et al., 2013). Another temperature-responsive polymer applied in textiles is shape memory polymers (SMPs). SMPs are polymers that respond to a specific stimulus with a change in the shape. The reason is capability to memorize the original shape and reform to the prior shape after deformation with no need for mechanical force. The mechanism of shape recovery in SMPs is due to the inclusion of partially crystalline hard segments and soft amorphous parts at the transition temperature (Tg) (Stylios and Wan, 2007). Most of the SMPs are sensitive to temperature change, under which they rapidly alter their shape from a temporary to the original shape. Moreover, there are some SMPs, which are sensitive to moisture, pH, light, and stress

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(Chakraborty et al., 2017). For temperature-sensitive SMPs, the thermal transition temperature should be above the temperature of the environment. Due to the application of SMPs-treated textiles in contact with body, the switching temperature of SMPs can be tuned around body temperature (Hu et al., 2012). A widely studied SMP is polyurethane (Tg ¼ 25°C), which is directly applied to textile fabrics through finishing and coating methods or electrospinning to form shape memory nanofibers (Zhuo et al., 2008; Chakraborty et al., 2017). Most of the related literature about textile finishing with SMPs is associated to wrinkle-free, anticrease, and antishrink properties (Stylios and Wan, 2007). In wrinkle-resistance treatment of cotton fabric with SMPs of polyurethane, the fabrics can recover to their original flat shape within a minute upon blowing steam. Achieving a crease pattern design on cotton fabric is also possible using SMPs based on polyurethane (Hu et al., 2008). Another strategy to produce temperature-responsive textile-based sensors is application of conductive materials such as conductive polymers and carbon-based materials that are sensitive to temperature change. Here the stimulus is temperature alteration and the sensor response is detected by a change in the resistivity of the conductive material. Thus, these sensors are called resistive sensors. Detailed information on the methods and materials used to prepare conductive textiles is provided in Chapter 17. In a specific research, nylon fabrics were impregnated in an aqueous dispersion of poly (3,4-ethylenedioxythiophene-poly(4-styrenesulfonate) (PEDOT-PSS). The conductive fibers were sensitive to temperature between 15°C and 45°C and relative humidity between 25% and 90%, as monitored by change in the specific resistance. This is due to the sensitivity of polythiophenes conductivity to temperature and humidity changes. For temperature-sensing studies, the opposite sides of the coated fabrics were pressed between two copper plates for measuring the change in resistivity using multimeter (Daoud et al., 2005).

15.2.2 Light-sensitive textiles Hydrogels containing 3D polymeric network and photochromic chromophores such as poly(N,N-dimethylacrylamide-4-phenylazophenyl acrylate), poly(NIPAAm-triphenylmethaneleuconitrite), and partially esterified poly (N-isopropyl acrylamide-hydroxyethyamide) are grouped into lightresponsive hydrogels (Hu et al., 2012).

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Photochromic organic and inorganic compounds can be also applied on textiles creating color change in response to light stimuli through isomerization of molecules, ionization of molecules, and redox reaction of molecules depending on the structure (Hu et al., 2012). Azobenzenes, spiropyrans, spirooxazines, viologens, fulgides, 1,4-dihydroxy anthraquinone, and diarylethenes are some of the common photochromic compounds. Optical fibers have been also developed with the function of accurately monitoring body and environmental conditions, with photoluminescence properties (Crano and Guglielmetti, 2002).

15.2.3 Mechanical-sensitive textiles For describing the mechanical-sensitive textiles, some terms of piezoelectric, piezoresistive, and piezocapacitive should be defined. In piezoelectric sensors, a change due to the applied mechanical force in form of pressure, stress, or strain is responded by an electrical charge. In piezoresistive sensors, the electrical resistivity of the material is changed in response to mechanical force, while in piezocapacitance sensors mechanical force created the dielectric constant change. Conductive polymers and nanoparticles making conductive fibers and fabrics are used to prepare mechanical-sensitive textile sensors based on piezo effect. The advantage of conductive polymer-based sensors is flexibility that is compatible with textile structures. The variation of electrical conductivity of these materials under mechanical force can be measured (Cochrane et al., 2007). Cu-Ni electroless plated polyester fabrics were prepared to form sensor suits capable of sensing pressure response by change in electrical resistivity (Inaba et al., 1996). Suspensions of conductive PEDOT-PSS were prepared and inkjet printed on cotton fabrics to form strain sensors by measuring a change in fabric electrical resistivity by multimeter when tensile strength using Instron is applied. The authors claimed the capability of these sensors to monitor human joint motion (Sawhney et al., 2006). A piezoelectric sensor based on the voltage difference in response to mechanical signal from periodic expansion and contraction of heartbeat was prepared using polyvinylidine fluoride (Kim, 2009). In a very recent study, pressure-sensitive textile sensor was developed by a bottom interdigitated textile electrode comprising laser scribing masking and electroless deposition of Ni on polyester fabric, and a top bridge of carbon nanotube (CNT)-coated cotton fabric. The prepared textile-based

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sensor was applicable to detect various forces and vibrations while attached to human skin and directly incorporated into fabric (Liu et al., 2017a,b). Some information on laser scribing method producing conductive patterns on fabric is provided in Chapter 17. The authors speculated that the hierarchical porous nanostructure of the prepared textile sensor was responsible to provide sufficient roughness and elasticity to feel the variation of contact resistance when pressure is applied. Under external pressure, the porous structure of the sensor is deformed increasing the contact area between the top CNT fabric bridge and the bottom Ni textile electrodes, causing an increase in the current (Liu et al., 2017a,b). Graphene has been also applied to produce pressure-sensitive textilebased sensors. For instance, silk textiles were dipped into the graphene oxide (GO), following by heating at 255°C for 6 h, forming rGO (reduced GO)/silk network structures showing resistance-pressure correlation (Liu et al., 2017b). The mechanical-sensitive textile-based sensors based on piezocapacitance mechanism is mainly prepared by using two conductive textiles as electrode plates, separated by flexible dielectric spacers such as foams, fabric spacers, and soft polymers. In a specific research, the conductive fibers were fabricated by coating poly(styrene-block-butadienstyrene) on the surface of poly(p-phenylene terephthalamide) (Kevlar) fiber, followed by silver nanoparticles coating. By coating poly(dimethylsiloxane) (PDMS) as dielectric layers on the surface of the conductive fibers and stacking the two PDMS-coated fibers perpendicular to each other, a capacitive-textile pressure sensor was achieved (Lee et al., 2015).

15.3 CHEMICAL STIMULUS 15.3.1 pH-sensitive textiles As many processes in nature are affected by pH alteration, sensors with the ability to detect pH changes are of particular importance. pH-sensitive wound dressings based on the variation of pH of the skin during healing is one of the interesting application areas (Van der Schueren and De Clerck, 2011). Another application of pH-sensitive textile based sensors is sportswear, where monitoring of the wearer’s sweat pH is important (Coyle et al., 2009). First and widely used approach to prepare pH-sensitive textiles is dyeing of fabrics with pH-indicator dyes using conventional dyeing methods, regarding as halochromic dyes (Coyle et al., 2009). In these systems the

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stimulus is alteration of pH and the treated fabric works as a sensor responding to the stimuli by color change. In recent years, production of electrospun pH-sensitive fibers prepared by direct incorporation of the dyes in the polymer solution before the electrospinning has been also investigated (Van der Schueren and De Clerck, 2011). Another approach is the development of pH-sensitive textiles treated with hydrogels. A change in environmental pH causes pH-induced volume-phase transitions (Buengera et al., 2012). This mainly comes from the acidic or basic pendant groups on the polymer network of hydrogels. Swelling/deswelling response to pH changes occurred depending on the anionic and cationic network of the hydrogel. For instance, when pKa of the anionic pendant groups is lower than the environmental pH, hydrophilic properties of the network increase, and the hydrogel starts to swell (Buengera et al., 2012). On the other hand, when lowering the acidity of the solution, the network becomes hydrophobic causing deswelling. Cationic networks also work on the same basis but in the opposite manner. PAA, poly(methacrylic acid), poly(carboxyacrylanilide-MMa), poly(sulfoxyethyl methacrylate), poly(aminoethyl methacrylate), poly [(N,N-dimethylamino)ethyl methacrylate], chitosan, polyvinylpyridine, poly[(vinylbenzyl)trimethylammonium chloride], poly(acrylic acidmethacrylamidopropyl trimethylammonium chloride), poly[sodium 2-acrylamido-2-methylpropylsulfonate-N-3-(dimethylamino)propylacrylamide], chitosan (poly(n-acetyl-D-glucosamine-co-D-glucosamine), and collagen are some of the widely studied pH-responsive polymers (Hu et al., 2012). pH-responsive textiles treated with polyvinyl acetate crosslinked with PAA hydrogels were capable of monitoring the stage of the wound-healing process. The response to pH changes was detected based on optical sensing probing refractive index changes (Pasche et al., 2008).

15.3.2 Humidity-sensitive textiles Due to the plasticizing effect of water molecules enhancing the flexibility of macromolecule chains, a change in SMPs can occur under water or moisture. This provides fabric with temperature and moisture management properties. Shape memory polyurethane can be converted into moistureresponsive shape memory polyurethane through addition of pyridine into polyurethane via N-bis-(2-hydroxyethyl) isonicotinamine (Yvonne and Chan, 2007).

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Conductive polymers can be also applied to textile to produce sensors in which the resistive signal is proportional to the actual moisture. The electrical properties (specific resistance) of PEDOT:PSS coated fabrics changed, based on variation in surrounding humidity and temperature, where the resistance decreases with increasing humidity (Daoud et al., 2005). It has been known that water molecules affected the electronic feature of polythiophene-based transistors due to the adsorption on the polymer layer (Hoshino et al., 2004). It is claimed that the change in resistivity of treated nylon fabrics in contact with moisture is due to the adsorption of water molecules on the surface of polymer increasing the charge carrier density due to the relatively large dipole momentum (Daoud et al., 2005).

15.3.3 Chemical-sensitive textiles Chemical sensors can be categorized into gas molecule sensors such as NH3, NO, H2, CO, CO2, NO2, liquid sensors such as alcohols, metal ion sensors such as Fe3+ and Hg2+, and biocomponent sensors such as glucose. Independent from the target compound, the response can be color change in presence of the chemical, change in electrical resistance or electrochemical reactions. One of the important factors in chemical sensors is the high surface area increasing the interaction with target molecules. Thus, most of the recent approaches are dealt with introducing more porous structure with increased surface area to develop high sensitive chemical sensors. 15.3.3.1 Chemical sensors based on color change Fluorescent agents capable of color change in presence of ions have been widely used as chemical sensors that are working based on optic. The pyrene derivative, pyrene methanol (PM), was used and electrospun PM-PAA nanofibers with high surface area were prepared for detection of metal ions Fe3+ and Hg2+ ions by showing a change in fluorescence spectra as a function of different concentrations of metal ions (Wang et al., 2002). One of the widely studied chemical target molecules is ammonia, which has been sensed and detected by optical mechanism through color changes in copper-containing compounds. Copper-based materials are of interest due to the broad range of colors they may indicate through various reactions. Color change of carbon fibers impregnated with copper hydroxy nitrate, following by heating to prepare carbon fiber/CuO, was detected against dimethyl chlorophosphate (DMCP), simulating chemical warfare agents. A visible color change from blue-green to yellow-orange through reaction with DMCP was reported (Florent et al., 2017).

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Cotton fabrics in situ treated with Cu2O nanoparticles have been regarded as ammonia and hydrogen peroxide sensor through color change from green to blue. This is due to the formation of [Cu(NH3)2]+ complex which undergoes oxidation creating [Cu(NH3)4]2+. After sometime under the air, the color gradually returns to the original color of the fabrics. The authors claimed that exposure of the fabrics to acetic acid could result in the reverse action forming Cu2O particles. The original green color of cotton/ nano Cu2O-treated fabric also changed into brown in presence of hydrogen peroxide due to formation of CuO. The same reverse reaction and color change from brown to green was reported in presence of acetic acid (Sedighi et al., 2014). A recent study again supported the color-sensing effect of cuprous oxide nanoparticles in situ synthesized on polyester fabric using copper sulfate (CuSO4), sodium hypophosphite, polyvinylpyrrolidone, and monoethanolamine (MEA) as precursor, reducing agent, stabilizer, and surface modifier. The color of the treated fabric wetted with ammonia solution was significantly changed from dark brown to white blue after 2 min (Bashiri Rezaie et al., 2017). 15.3.3.2 Chemiresistive and electrochemical sensors Chemiresistor sensors work based on the change in electrical resistance of the sensing material in presence of target chemical. For instance, CNTcotton yarn ammonia sensors were prepared using CNT as both electrode and sensing material. The authors speculated that the signal response was not changed after bending the sensor and the hydrogen bonding between the CNT and cotton leads to high adhesion, flexibility without losing resistance and chemical response (Han et al., 2013). Conductive polymers have been widely investigated in chemical sensors due to the high sensitivity on electrical changes when exposed to diverse types of gases or liquids such as alcohols, ethers, halocarbons, ammonia, NO2, and CO2 with low detection limit and potential to operate at or near room temperature (Hong et al., 2004). This is mainly attributed to the π-conjugated structure of conducting polymer chains. Increase/decrease of polaron and/or bipolaron densities inside the band gap of the polymer through interaction with chemical target molecules results in electrical changes. Thin films of conductive polymers, including polypyrrole or polyaniline, were coated on polyester or nylon threads, followed by weaving into fabric mesh. The prepared samples were capable of sensing NH3 and NO2 in accordance with the change in electrical resistivity. NH3 as a strong reducing

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agent resulted in lower conductivity due to the elimination of free hole charge carriers, while NO2 increased the conductivity due to the formation of additional free hole charge carriers (Collins and Buckley, 1996). Ammonia gas sensor was prepared by polymerization of aniline on the surface of nylon 6 fabrics and doped with various acids such as formic acid, acrylic acid, and trichloroacetic acid, indicating high sensitivity and fast response (Hong et al., 2004). Oxidative in situ chemical polymerization of polypyrrole and polyaniline on cotton fabrics resulted in sensors for detecting ammonia gas and ethanol vapors based on change in current (Deogaonkar and Bhat, 2015). Graphene has been also introduced as an effective material to prepare flexible gas sensors for the detection of various chemicals such as NO2, NH3, H2, H2S, CO2, SO2, ions including Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag, and volatile organic compounds comprising nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A, chemical warfare agents, and environmental pollutants. This is mainly due to the oxygenated functional groups in GO imparting amphiphilic property, which facilitates the reactivity toward different types of molecules on the graphene surface. A change in electrical resistance of graphene occurred through formation of a charge-transfer complex by interaction with chemical target acting as electron donor or acceptor (Singh et al., 2017). Yun et al. (2017) developed a wearable, washable, and bendable gas sensor by depositing rGO on polyester and cotton yarns, capable of detecting NO2. Composite graphene materials were prepared by graphene doping with metal nanoparticles of Pt, Pd, Au, polymers such as polyaniline and polypyrrole and metal oxides such as ZnO, TiO2, SnO2 as an effective method to produce more selectivity toward chemical compounds (Singh et al., 2017). For instance, Feng et al. (2016) reported the efficiency of electrospun rGO and Co3O4 nanofibers as ammonia sensors and selectivity over methanol, ethanol, formaldehyde, acetone, benzene, and methylbenzene. One of the newly emerging materials used as electrochemical sensor for chemicals detection is based on metal-organic frameworks (MOFs), due to the porous, d-π conjugated, crystalline frameworks providing electronic response to stimuli and high surface area (Smith and Mirica, 2017). Incorporation of MOFs to textile for preparing textile-based sensors is a very new topic and has not been investigated widely. This is due to the fact that most MOF structures previously incorporated into textiles were nonconductive. The only study we have come up with is the report of Smith and Mirica

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(2017), in which cotton and polyester fabrics were treated with one-step direct self-assembly of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) or 2,3,6,7,10,11-hexaaminotriphenylene (HATP) organic ligands with metallic nickel(II) nodes from solution, forming Ni3HHTP2- and Ni3HITP2-treated fabrics. The resultant fabrics provided enhanced porosity by combining mesoporosity of the textile and microporosity of the conductive MOF capable of detection and capture of gases (NO and H2S) based on chemiresistive sensor, while their property is durable to heat and washing. More information on MOF structures as newly emerging materials integrated with textiles for energy storage and conversion applications has been provided in Chapter 17. One of the categories of electrochemical sensors is biosensors, which work on enzymatic and nonenzymatic approaches. Developing reliable methods to monitor blood glucose in diabetes disease is one of the applications of electrochemical sensors in health issues. In this regard, electrocatalytic oxidation of glucose on the surface of electrodes has been proposed as an alternative to enzymatic glucose sensors. In addition to use of metal electrodes such as Pt and Au, production of electrodes based on transition metal oxide and hydroxides has been successful to provide highly sensitive, longterm stable sensors. Recently, application of textile-based electrodes such as Ni(OH)2 nanoplates/electrospun carbon nanofibers was reported as hierarchical nanostructured electrodes with enhanced rapid glucose detection with high reproducibility (Chen et al., 2017).

15.4 CONCLUSION Following the increased interest in producing smart textiles sensitive to stimuli, producing textile-based sensors with higher sensitivity, wider detection range, as well as quicker response and shorter recovery times will be further researched in future. Development of textile-based sensors with multisensitivity properties capable of detecting various stimuli will be of high importance. Current researches are mainly focusing on simultaneous pH, temperature, and moisture responsive polymers. More attention has been also concerned on using electronic-based textiles with stimuli-responsive properties acting both as detector and transducer, eliminating the need for using external attenuation, which is more compatible for wearable sensors.

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Magnetic nanofinishes for textiles 16.1 INTRODUCTION: GENERAL DEFINITIONS AND APPLICATIONS In spite of vast number of studies focusing on functional finishing of textiles, including antibacterial, self-cleaning, water repellent, conductive and others, our literature review showed lack of sufficient investigations and knowledge about textiles with magnetic properties. Although there have been a number studies concerning with magnetic nanoparticles such as iron, iron oxides, nickel and others, textile finishing with these nanoparticles still lacks and only some pioneering researches have been done during the last five years. This also raised a question when we reached to a patent published in 1999 reporting textile coating with iron oxide nanoparticles, however with no indication of magnetic properties (Kuhn and Kang, 1999). Recent research studies have shown the potential of magnetic textiles to be used in variety of applications such as magnetic filters, invisible water marks, magnetic coils for sensors and actuators, shielding of static magnetic fields, magnetic stimulus in shape memory polymers, textile whiteboards, textile antennae with artificial magnetic conductor planes, bioseparation, magnetographic printing, and magnetic screens. Magnetorheological fluids have been integrated in spacer fabrics to produce composites, which an external magnetic field can harden (Mistik et al., 2012). The optical properties of a textile can be modified by an external magnetic field if structural colors are formed by magnetic nanostructures, for utilization as pixels in a color-changing pattern (Kim et al., 2013). Measuring magnetic properties of textiles can be used, for magnetic ink in order to overcome the low efficiency of artificial eyes or for brand protection (Blachowicz and Ehrman, 2016). Here, after brief description of different types of magnetic materials, we try to provide all case studies related to magnetic textiles. A section has been also provided focusing on methods of assessing magnetic properties.

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16.2 DIFFERENT TYPES OF MAGNETIC MATERIALS The origin of magnetism lies in the orbital and spin motions of electrons and how the electrons interact with each other. Based on materials’ response to magnetic field, there are different magnetic types. Diamagnetism, paramagnetism, ferromagnetism, ferrimagnetism, and antiferromagnetism are five common magnetic behavior of materials. Since the introduction of nanomagnetic materials a new class has been also proposed called superparamagnetism. Depending on the ordering of the materials’ spin, there is a term called magnetic susceptibility (χ), which is magnetization (M) divided by applied magnetic field (H, Henry). Magnetization is the magnetic moment within a material in the presence of an external field (Kumari, 2015). Another important term in describing magnetic properties is Curie temperature, which is the temperature at which a material loses its magnetism due to the effect of heating on exciting the atoms so that they cannot remained aligned in one direction (Kumari, 2015). Diamagnetic materials have a weak negative susceptibility (χ < 0). In a diamagnetic material, the atoms have no net magnetic moment in the absence of magnetic field. Under applied field, the spinning electrons motion produces magnetization in the opposite direction to the applied field (Fig. 16.1). On the other hand, there are paramagnetic, ferromagnetic, ferrimagnetic, and antiferromagnetic materials with positive magnetic susceptibility, but the magnitudes of χ depend on ordering of the materials spin and temperature (Kumari, 2015). In paramagnetic materials, atoms have a permanent nonzero net magnetic moment due to the sum of orbital and spin magnetic moments. However at room temperature, in paramagnetic materials, thermal energy causes random distribution of magnetic moments; hence, net magnetization appears to be zero for the whole material. Upon application of a field, the moments tend to align up in the direction of the field overcoming the thermal barrier and giving a net positive magnetic moment in the direction of the applied field. The susceptibilities of these materials are usually very small, 10
3–10
6. Thus, paramagnetic materials with a small, positive susceptibility to magnetic fields are slightly attracted by a magnet; however, they cannot retain the magnetic properties when the external field is removed (Fig. 16.1). Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum (Kumari, 2015). In comparison, ferromagnetic materials with a large, positive susceptibility to external magnetic field have strong attraction to magnet, which is permeant if the external field is removed. Ferromagnetic materials consist of

Magnetic nanofinishes for textiles

H=0

H=0

H

Diamagnetic H=0

227

H

Paramagnetic

H

H=0

Ferromagnetic

H

Ferrimagnetic H=0

H

Antiferromagnetic

Fig. 16.1 Different types of magnetic materials.

ordered regions or domains of single orientation giving rise to large finite magnetization in the absence of a magnetic field. This phenomenon is observed below the Curie temperature, above which the material behaves like a paramagnetic material. They get their strong magnetic properties due to the presence of magnetic domains. In these domains, large numbers of atoms’ moments are aligned parallel so that the magnetic force within the domain is strong. In the absence of magnetic field, the domains are nearly randomly organized and the net magnetism is zero (Kumari, 2015). When a magnetizing force is applied, the domains become aligned to produce a strong magnetic field within the part (Fig. 16.1). Iron, nickel, and cobalt are examples of ferromagnetic materials (Kumari, 2015). Thus, ferromagnetism is only possible when atoms are arranged in a lattice and the atomic magnetic moments can interact to align parallel to each other. When a varying magnetic field is applied to a ferromagnetic material, the material exhibits a hysteresis loop between magnetization and the magnetic field. Upon application of magnetic field, these domains start aligning in the direction of applied field and when completely aligned, reach to saturation magnetization, Ms. When the field is reduced to zero, the domains do not adopt a

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configuration, so there is a net magnetization in the absence of field called as remnant magnetization, Mr. To bring the magnetization of the material back to zero, one needs to apply an extra field in the opposite direction, which is called coercive field Hc (Fig. 16.2). A ferromagnetic material is a hard magnet when it has large coercivity or soft magnet when coercivity is small (Kumari, 2015). These are materials, which show antiparallel alignment of moments at particular atomic sites, for instance, magnetic moment of one crystal sublattice is antiparallel to the other. But since most of these materials consist of cations of two or more types, sublattices contain two different types of ions with different magnetic moment for two types of atoms and, as a result, net magnetization is not equal to zero (Fig. 16.1). NiFe2O4, CoFe2O4, Fe3O4 (or FeOFe2O3), CuFe2O4 are some of the examples of ferromagnetic materials (Kumari, 2015). In antiferromagnetc materials such as MnO, FeO, CoO, NiO, Cr, Mn, the magnetic moments are aligned in opposite directions and are equal in magnitude. Thus, when antiferromagnetic material is unmagnetized, its net magnetization is zero (Kumari, 2015). In the presence of the strong magnetic field, antiferromagnetic materials are weakly magnetized in the direction of the field (Fig. 16.1). Since the introduction of materials in nanoscale, their properties have widely changed leading to valuable new properties. One of these size-dependent properties is superparamagnetism. As discussed here, within magnetic materials there are different regions or domains. With a decrease in

Magnetization (emu/g) Ferromagnetic Paramagnetic Superparamagnetic

Ms

Mr

Ms HC

Magnetic field (Oe)

Fig. 16.2 Hysteresis curve magnetization of ferromagnetic, paramagnetic, and superparamagnetic particles.

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size of a material, these domains are gathered together and form only one single domain (Kumari et al., 2015). In these single-domain materials, all magnetic moments are aligned in the same direction, so applying an external magnetic field will cause very large magnetization, which is called superparamagnetic behavior. In fact, superparamagnetic materials share both paramagnetism and ferromagnetism as in the absence of external magnetic field they do not retain their magnetic properties and under the influence of a low magnetic field they show high levels of magnetization (Fig. 16.2). There is a transition temperature between superparamagnetism and ferromagnetism, which increases with increasing size. Superparamagnetic properties can also be suppressed by shape effects, most notably in needles (Kumari et al., 2015). Superparamagnetism is mainly found in particles