Cotton Fabrics: Preparation, Synthesis and Applications

Table of contents :
Contents
Preface
Chapter 1
Recent Advances in Preparation, Modification and Functionalization of Cotton Fabric
Abstract
1. Introduction
2. Morphology and Classification of the Fiber
2.1. Morphology of the Fiber
2.2. Classification of the Fiber
3. Cotton Fabric: Preparation, Functionalization and Modification
3.1. Cotton Fiber Transformation
3.1.1. Cultivating, Harvesting and Ginning Processes
3.1.2. Yarn Manufacturing
3.2. Fabric Manufacturing and Preparation
3.2.1. Sizing and Desizing
3.2.2. Scouring
3.2.3. Bleaching
3.2.4. Mercerization
3.3. Standard Test Methods for the Evaluation of Cotton Fabric Quality Preparation
3.4. Cotton Fabric Modification and Functionalization
3.4.1. Flame Retardant Synthesis for Cotton Fabric
3.4.2. Antibacterial Synthesis for Cotton Fabric
3.4.3. Water Repellent Synthesis for Cotton Fabric
3.4.3.1. Synthesis of Multifunctional Cotton Fabric
Conclusion
References
Chapter 2
A New Method for Measuring Water Vapour Transfers through Fabrics
Abstract
1. Comfort Generality
1.1. Physical Comfort: Human-Clothing-Environment
1.1.1. Conduction
1.1.2. Convection
1.1.3. Radiation
1.1.4. Respiration Losses
1.1.5. Evaporative Skin Heat Loss
1.1.6. Metabolism
1.1.7. Stored Heat
1.1.8. Heat Balance of the Two-Node Model
1.2. Physiological Comfort: Thermoregulation
1.2.1. Thermoreceptors and Nociceptors
1.2.2. Hypothalamus
1.2.3. Thermogenesis
1.2.4. Thermolysis
1.3. Psychological Comfort
1.3.1. Integration and Evaluation of Sensory Stimuli
1.3.2. Formulation of the Feeling
1.4. Influence of Physical and Physiological Factors
2. Comfort and Textile
2.1. Moisture Transfer
2.1.1. Diffusion
2.1.2. Capillarity
2.1.3. Evaporation-Condensation
2.1.4. Liquid Water Flow
2.2. Impact of Fibers on Thermal and Hydric Transfers
2.2.1. Static Hydric and Thermal Transfers
2.2.2. Dynamic Hydric and Thermal Transfers
2.2.2.1. Min’s Model
2.2.2.2. Fenghzi’s Model
2.2.2.3. Xu’s Model
3. Cotton Fiber
3.1. Cotton Structure
3.2. Hydric Behaviour of Cotton Fiber
3.2.1. Water Bonds
3.2.2. Isotherm of Sorption
3.2.3. Hysteresis
3.2.4. Diffusion Phenomenon
3.2.5. Influence of the Crystallinity Degree
3.2.6. Influence of Porosity
3.2.7. Influence of the Surface Area
3.3. Impact of Cotton on Comfort
3.3.1. Thermal Conductivity
3.3.2. Thermal Resistance
3.3.3. Thermal Absorptivity (or Effusivity)
3.3.4. Water Vapor Permeability
3.3.5. Moisture Management Propreties (MMT)
4. Measures of Water Vapour and Liquid Transfer on Textiles
4.1. Water Vapour Transfer
4.1.1. Dynamic Vapour Sorption Test
4.1.1.1. Description
4.1.1.2. Modelisation
4.1.1.3. DVS Results
4.1.2. Frame Test
4.1.2.1. Sweating Guarded Hot Plate (Skin Model)
4.1.2.2. Frame Design
4.1.2.3. Frame Instrumentation
4.1.2.4. Test Protocol
4.1.2.5. Frame Results
4.2. Liquid Transfer
4.2.1. Description
4.2.2. MMT Results
4.3. Conclusion
Conclusion
Acknowledgments
References
Chapter 3
Advances in Phosphorus-Based Flame Retardant Cotton Fabrics
Abstract
1. Introduction
2. Cotton as a Cellulose-Based Polymer
3. Mechanism of Combustion
3.1. Flammability of Cellulosic Textiles
3.2. Char Formation and Intumescence Behavior
4. Mechanism of Flame Retardancy
5. Chemistry of Flame Retardant Additives
5.1. Flame Retardants Based on Durability
5.2. Phosphorous-Based Flame Retardants
5.3. Inorganic Phosphorus
5.4. Organic Phosphorus
5.5. P-N Synergism
5.6. Other Flame Retardants Compounds
6. Novel Approaches
6.1. Sol-Gel Technique
6.2. Layer by Layer Assembly
Conclusion
Acknowledgment
References
Chapter 4
Functionalization of Cotton Fabrics by Cathechol Bound PCM-Microcapsules
Abstract
1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Preparation of Microcapsules
2.3. Textile Functionalization
2.3.1. Exhaustion Method for Fabric Functionalization with L-DOPA
2.3.2. Exhaustion Method for L-DOPA Fabric Functionalization with Microcapsules
2.3.3. Padding Method for Fabric Functionalization with L-DOPA
2.4. Analytical Methods
2.4.1. Microscopic Examinations
2.4.2. Surface Characterization of Fabrics
2.4.3. Color Measurement of Fabrics
2.4.4. Color Measurement of Aqueous Solutions
2.4.5. Durability/Fastness Tests
2.4.6. Durability/Fastness Tests
3. Results and Discussion
3.1. Poly(DOPA) Formation
3.1.1. Poly(DOPA) Formation in Solutions
3.1.2. Poly(DOPA) Formation on Cotton Fabric Surface
3.2. Influence of Temperature and Time on L-DOPA Fabric Functionalization
3.3. Stability of the L-DOPA Treatment
3.4. Functionalization of Textile with Microcapsules by Bath Exhaustion Process
3.5. Functionalization of Textile with Microcapsules by Pad-Dry-Cure Process
Conclusion
References
Editor Contact Information
Index
Blank Page

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POLYMER SCIENCE AND TECHNOLOGY

COTTON FABRICS PREPARATION, SYNTHESIS AND APPLICATIONS

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POLYMER SCIENCE AND TECHNOLOGY Additional books and e-books in this series can be found on Nova’s website under the Series tab.

POLYMER SCIENCE AND TECHNOLOGY

COTTON FABRICS PREPARATION, SYNTHESIS AND APPLICATIONS

FABIEN SALAÜN EDITOR

Copyright © 2019 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected]. NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the Publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

Library of Congress Cataloging-in-Publication Data ISBN: H%RRN

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

vii Recent Advances in Preparation, Modification and Functionalization of Cotton Fabric Aziz Bentis, Aicha Boukhriss, Mehdi El Bouchti and Said Gmouh A New Method for Measuring Water Vapour Transfers through Fabrics Adeline Marolleau, Fabien Salaün, Daniel Dupont, Hayriye Gidik and Sylvie Ducept Advances in Phosphorus-Based Flame Retardant Cotton Fabrics Giulio Malucelli and Giuseppe Rosace Functionalization of Cotton Fabrics by Cathechol Bound PCM-Microcapsules Wajdi Abdel-Haq, Rolf-Dieter Hund, Chokri Cherif and Fabien Salaün

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37

107

167

Editor Contact Information

207

Index

209

PREFACE In recent years, improvements in production technology for cotton yarn have led to great increases in production rates. Cotton fiber is the most important natural fiber in the world and the essential cellulosic source. Cotton fibers represent one of the most widely used textile resources on the world market, with a market share of around 50%, mainly for clothing and textile products. The quality and therefore the origin of the fibers significantly influence its market value and the quality grade of the products obtained. In this context, where competition with other fibers is affected by innovations and the marketing of other fibers, in particular, synthetic fibers (polyesters and nylons), elastomers (spandex) and artificial fibers (lyocell), the research conducted in this field have significantly increased the functional potential of these supports. Fundamental understanding of fibers (structural formation during development, chemistry, physics), significant improvement in fiber quality as well as process innovation and product differentiation are essential to maintaining the inter-fiber competitiveness of cotton fibers and the share of cotton fibers in world clothing and other textile markets. In order to develop effective strategies for improving fiber quality and textile finishing treatments for the development of higher value-added products in this competitive sector, research is focused on identifying the chemical and physical properties and particular qualities of fibers. The

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Fabien Salaün

relationship between the development of fiber chemistry and fiber structure and properties has only recently attracted attention. The objective of « Cotton Fabrics: Preparation, Synthesis and Applications” book is to present readers with updated information on existing cotton fabric uses and functionalization treatments, highlighting detailed inventory, description, characterization and utilization as well as challenges and perspectives. In the present book, renowned experts and researchers from academia provide a concise and ut-to-date overview of different issues regarding the application of cotton and its derivatives for the development and optimization of textile products. This book is divided in four different chapters. The first chapter discusses general aspects of cotton and traditonnal finishing treatments, with particular emphasis on issues related to the development of new products, comprising an useful background for the following chapters. Chapter two deals with the wearerenvironment interactions interms of thermal comfort, with a focuss on new thermal models and more specialy for the mass transfer. Further, chapter three continues and icomplements the previous ones by discussing in detail specific applications of cotton fabrics in flame retardant field. The last chapter is devoted to a new explorating way to fnctionnalize cotton susbtarte by chemical grafting. This book should be a comprehensive reading source for textile research community and students to gather important information on worldwide cotton functionalization processes.

In: Cotton Fabrics Editor: Fabien Salaün

ISBN: 978-1-53615-006-3 © 2019 Nova Science Publishers, Inc.

Chapter 1

RECENT ADVANCES IN PREPARATION, MODIFICATION AND FUNCTIONALIZATION OF COTTON FABRIC Aziz Bentis1,2, Aicha Boukhriss2,*, Mehdi El Bouchti2 and Said Gmouh1 1

Laboratory (LIMAT), Ben M'sik Faculty of Sciences, Hassan II University of Casablanca, Morocco 2 Laboratory (REMTEX), School of Textile and Clothing Industries, ESITH-Casablanca, Morocco

ABSTRACT This chapter reviews the most important processes and steps for the preparation and synthesis of cotton fabric, from the fiber to the final product. Firstlty, in order to remove natural and other impurities, and improve cotton fabric performance in the subsequent finishing stages, this chapter discussed the objectives and basic principles of preparatory process consisting on desizing, scouring, bleaching, and mercerization. Then, *

Corresponding Author Email: [email protected].

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Aziz Bentis, Aicha Boukhriss, Mehdi El Bouchti et al. several methods of testing and control of cotton fabric quality preparation process are mentioned. Finally, the evolution from traditional to multifunctional cotton fabric, using different synthesis processes based on the interaction of cotton surface and the active agent responsible of the desired properties with high level of quality are reviewed, as well as their applications and end uses.

Keywords: cotton fabric, preparation, synthesis and modification

1. INTRODUCTION Cotton fabric have been found dating back to 3500 BC [3] and since ancient times, textile in general, and cotton more particularly has traced and contributed to the social, politic and economic history of many countries worldwide [4]. It’s still the natural fiber, composed of a high cellulosic part of α-cellulose (88.0–96.5%) and noncellulosics omponents include proteins (1.0–1.9%), waxes (0.4–1.2%), pectins (0.4–1.2%), inorganics (0.7–1.6%), and other (0.5–8.0%) substances [5-6]. Cotton fabric is a manufacturing biomaterial, based on the conversion of fiber into yarn, yarn into fabric, it’s one of the most important material in the textile industry. World cotton fiber production is 19 million tonnes from 33.4 million hectares [7]. It’s one of the most important source of employment for many families. Among the main producers of cotton are Russia, China, the United States, India, Pakistan, Turkey, Brazil, Egypt and Uzbekistan. Cotton fabric is widely used and applied in daily life to various fields such as in military, industry and civilisation. This is due to its excellent intrinsic characteristics including softness, breathability, warmth, mechanical properties, comfort, renewability, flexibility, hydrophilic, and biodegradability. However, Cotton fabric has relatively low microbial resistance versus cellulolytic bacteria and fungi [8], inflammable due to its low Limiting Oxygen Index (LOI) and combustion temperature [9], etc., which considerably limits and restrict their uses in some application area.

Recent Advances in Preparation, Modification …

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Within this context, this chapter discusses the key stages in cotton preparation and production from cultivation and harvesting to spinning, knitting and weaving. Various synthesis for the functionnalization of cotton fabric have been summarized. Also, different applications of cotton fabric synthesized have been mentioned in this chapter.

2. MORPHOLOGY AND CLASSIFICATION OF THE FIBER 2.1. Morphology of the Fiber As it is noticeable from the Figure 1, cotton fiber consists of primary and secondary layers, while lumen is present in the centre. Primary layer holds up to 30% cellulose and non-cellulosic materials. This cellulose is of lower molecular weight with the degree of polymerization (DP) between 2,000 and 6,000. Secondary wall is rich in cellulose of higher weight with DP of 14,000 [10].

Figure 1. Schematic structure of a mature cotton fibre, identifying its six parts. Reprinted by permission from (Springer), ref: Mohamed AL, Hassabo AG Flame retardant of cellulosic materials and their composites. In: Flame retardants, 2015.

2.2. Classification of the Fiber Cotton fibers may be classified roughly into three large groups based on staple length (average length of the fibres making up a sample or bale of cotton) and appearance [11].

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



Long-staple cotton is a fine, lustrous fibre with typical staple length ranging from about 30 to 40mm, and includes types of the highest quality, such as Sea Island, Egyptian, and Pima cottons. Due to the difficulty in its cultivation and its limited production, long-staple cottons are costly and are used mainly for fine fabrics, yarns, and hosiery. Medium-staple cotton is plentiful and standard, such as American Upland, with staple length from about 25 to 33mm. Medium-staple cotton provides about 90% of the current world production of raw cotton fibre. This fibre is widely used for apparel, home furnishings, and industrial products. Short-staple is coarse cotton, ranging from about 10 to 25mm in length, which makes textile processing very difficult and consequently it is not commonly used in textiles, except for very low-grade products. The colour of cotton fibre varies from almost pure white to a dirty grey. However, the standard cotton grades classify colour as white, light spotted, spotted, tinged, yellow stained, and light grey. High quality cotton is usually very light or almost white.

3. COTTON FABRIC: PREPARATION, FUNCTIONALIZATION AND MODIFICATION 3.1. Cotton Fiber Transformation Cotton fiber transformation started by cultivation and harvesting of cotton plant and ended by finishing step, the following figure summarize the principal stages of cotton fiber transformation.

Cotton fiber transformation started by cultivation and harvesting of cotton plant and ended by finishing step, the following figure summarize the principal stages of cotton fiber transformation. Recent Advances in Preparation, Modification …

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Figure 2. Cotton fabric preparation stages Figure 2. Cotton fabric preparation stages.

3.1.1. Cultivating, Harvesting and Ginning Processes Cotton is a natural fiber of vegetal origin, it’s seed hairs from plants of the order Malvales, family Malvaceae, tribe Gossypieae, and genus Gossypium [12-14]. Cotton (Gossypium) is a shrub that blooms annually, a closed pod succeeding the flower; it contains the seeds covered with white fibers called cotton. When the seeds are ripe, the husk burst and the fibers escape into a down called “capsule”. The capsules left on the plant for 2 to 3 months mature and the husk dries, which facilitates manual or Mechanical harvesting by removing the entire capsule from the plant. The cotton capsules are harvested and followed by ginning procedure to separate the fibers from all the rest. They are then compressed to the press to form balls of 225Kg [15]. These processes, which represent the first steps in the conversion of fiber to fabric, have a significant influence on the quality of the fiber realized from a crop. A number of studies have focused on Cotton cultivating and harvesting in order to improve its quality and productivity [16-17].

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3.1.2. Yarn Manufacturing The preparation of the yarn present the first step for Cotton fabric manufacturing, after the cotton ginning processes, yarns manufactured in the spinning process are used to make woven or knitted fabrics, it’s consist on opening, blending, carding, drawing, combing, if necessary, roving, spinning into yarn and winding [6, 18].

3.2. Fabric Manufacturing and Preparation Cotton yarn manufactured in the spinning process was used to make woven or knitted fabrics, while going through a set of steps and treatments of fabric preparation, based on desized, scoured, bleached, and mercerized, in the objective to remove natural non-cellulosic constituents, and impurities. Also, to increase the affinity of cellulose for dyes and finishes by ensuring uniform absorption of water.

3.2.1. Sizing and Desizing Before proceeding to the weaving process, it requires to coat cotton yarn with starch or some other ‘size’ in order to protect him from excessive abrasion during the weaving operation and subsequently to increase its efficiency. A large number of classes of chemical substances are used as sizing agents, the most common warp sizes used for cotton are Starches and carboxymethyl cellulose [19-21]. The warp sizes a temporary treatment that must be removed during “desizing process”, prior to dyeing and finishing, in order to facilitate the penetration of dyes and chemicals in the subsequent wet processing operations. For instance, the presence of starch can hinder the penetration of the dye into the fiber. Depending on the size that has been used;enzymes and oxidising agents were made to break down and remove it. For desizing starch, enzymes and or dilute mineral acids are used for the hydrolysis of starch and to remove or converted it into simple water-soluble products. For example, α and β-amylase enzymes as a traditional desizing method was used at temperature around 40-70°C and pH values of 4.6-7.0

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to catalyse the hydrolysis of the starch molecules into water-soluble pieces [22-24]. Several studies are focused on another alternative starch desizing procedure based on the oxidization reaction in order to solubilize the starch warp size by sodium bromide, sodium chlorite, etc. [25-26]. The recycling of starch size is not possible and it must be handled to avoid environmental problems, more particularly water pollution. For desizing carboxymethyl cellulose, the elimination of the carboxymethyl cellulose warp sizes can be carried out by a simple rinsing with hot water at neutral pH [27-28]. And regards recycling carboxymethylcellulose chain size, theoretically is feasible from the concentration of the desizing solution, but so far their recycling is limited due to microbial growth in the size of the recycled chain.

3.2.2. Scouring The objective of scouring is to remove impurities from the cotton, because it contain from 4-12% by weight impurities in the form of waxes, proteins, pectins, ash, and miscellaneous substances such as pigments, hemicelluloses and reducing sugars. Sodium hydroxide or Calcium hydroxide or Sodium carbonate are commonly used in scouring as a purifying treatment agents. 3.2.3. Bleaching After scouring processes, the natural fabric still contain naturally occurring colouring matter may be related to flavones pigments of the cotton flower, it is necessary to decolorize the raw cotton fabric via bleaching process, in order to remove residual impurities and change the fabric colour to clear white rather than the off white it was before bleaching. Bleaching is carried out by oxidative chemistry, most often with hydrogen peroxide as the active bleaching agent but without optical whiteners, and under alkaline conditions to activate the bleaching agent and a stabilizer (often sodium silicate) to control the reaction rate and to avoid excessive fiber damage. The temperature must be over 60 °C, which increases energy consumption [29-31]. Moreover, a large amounts of water

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are used during the bleaching process, which increases also water consumption, to overcome this problem, there is a new technique “photolysis technique” as a suitable method for raw cotton bleaching, combining ultraviolet (UV) light and H2O2 in acidic pH to promote raw cotton fabric bleaching, without adding heat and stabilizers [32]. Reductive chemistry for bleaching cotton can be used as an alternative procedure using to remove colour is available [33].

3.2.4. Mercerization The principal function of mercerization treatment is to increase cotton fabric luster, reactivity and affinity for dyes. Moreover, fabric appearance and strength are greatly enhanced by this treatment [6]. Essentially, mercerization is done by treating cotton fabric with a strong aqueous solution of sodium hydroxide (about 18–24%) at various temperature and washing-off the caustic after 1 to 3 min, while holding the material under tension [34-36]. During this treatment, the internal fibrous structure of the cotton may undergo irreversible physical modifications related to polymorphic change in the cellulose (known as cellulose II) due to the swell of cotton fibers by the concentrated alkali. Besides mercerization with sodium hydroxide, liquid ammonia can be used as another approach for cotton treatment, with a polymorphic change in the fiber structure (currently denoted as Cellulose III) [37-39].

3.3. Standard Test Methods for the Evaluation of Cotton Fabric Quality Preparation After the treatment and preparation of cotton fabric through all of the processes mentioned above, the quality of the textile fabric must be controlled to assess the desired properties during the preparation process. For this, there are several methods of testing and control of cotton fabric quality have been developed, for instance. The American Association of Textile Chemists and Colorists (AATCC) and the American Society for Testing and Materials (ASTM), AATCC provides performance test

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methods, while ASTM provides not only test methods but also suggested specifications for different product end uses [40]. Table 1 shows a list of cotton fabric quality-control methods after the preparation process. Table 1. Useful test methods for preparation process quality control [1-2] Test method

Number

Method title

Comment

79

Absorbency of bleached pH of wet processed textiles Fluidity of cellulose

Water drop absorbency

81 82 AATCC test method

89 97

110 D1424 ASTM

D5035 D3786

Mercerization in cotton Extractable content with enzyme, solvent, and water Whiteness of textiles Tearing strength of fabrics Breaking strength of fabric Breaking strength of knitted fabrics

Measurement of fabric pH Determines fiber damage from preparation Measures extent of mercerization Measure of extractable material Measure of bleaching efficiency Determines woven fabric damage from preparation Determines woven fabric damage from preparation Determines knitted fabric damage from preparation

After the mercerisation step, cotton fabric can be dyed, printed and finished. Finishing, as the term implies, is the final step in fabric production, it can be change the look and feel of the cotton fabric and be add special characteristics and properties using different synthesis processes based on the interaction of cotton surface and the active agent responsible of the

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desired properties such as, flame resistance, antimicrobial activity water repellency, multifunctional properties etc…

3.4. Cotton Fabric Modification and Functionalization Generally, cotton can be functionalized at different stages such as: 1. On the cotton fiber before its transformation into a textile fabric (fiber finishing). 2. By structuring during the manufacturing operations (multidimensional architecture:2D or 3D). 3. On the surface of cotton fabric. Cotton fabric functionalisation stage, will be the subject of this chapter, in which it can be done through two methods kind, in the one hand, by traditional methods such as calendering, Flocking, Sanforisage, scraping, exhaustion and pad-dry-cure techniques. On the other hand, it can be done by emerging methods such as grafting by polymerization, coating techniques, plasma processing, nanotechnology, microencapsulation and sol-gel process. In order to improve the intrinsic properties of cotton and to give it new functionalities, the synthesis and functionalization of cotton fabric remains an essential finishing process. Because, the cotton fabric is highly combustible and poorly resistant to microorganisms. Then, currently, cotton fabric is largely soughtin terms of water resistance as an important property for certain applications and it has been extensively investigated, hence the need to use finishing agents able to synthesis flame retardancy, antimicrobial and water repellent cotton fabric. In the present chapter, we have tried to put together an overview of all synthesis discovered for cotton fabric, their properties and their applications.

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3.4.1. Flame Retardant Synthesis for Cotton Fabric The synthesis of a flame retardant cotton fabric still a major challenge to protect consumers from unsafe apparels and expand several areas of application, among others: Firefighters and emergency personnel require protection from flames, as do floor coverings, upholstery and drapery, especially when used in public buildings. The military and airline industries also have multiple needs with regards to fire retardancy [41] For that several types of compounds and polymers are used as flame retardant (FR) for cotton fabric to render it resistant to fire, their main objective is to minimize the risk of fire in case of contact with a small source of heat (cigarette, candle or electrical fault). If the material is ignited, the flame retardant will slow down combustion and prevent the fire from spreading to other items. Flame retardant (FR) may be classified into three categories [42]: 



Primary FR based on phosphorous and/or halogen—the phosphorous derivatives act usually in solid or condensed phase, while halogen (chlorine or bromine) is active in gaseous phase. FR using synergists such as nitrogen and antimony for phosphorous and halogen-based FRs respectively. Synergists themselves are not flame retardants. FRs exhibiting P/N and/ or Sb/X synergism are durable in nature.

Adjunctive or physical FRs includes alumina trihydrate, boron compounds, silicates, and carbonates. Their activity is mainly physical, although recently some evidence of a chemical effect has been cited. They are non durable and used only if durability in laundering is not important. Several works have been reported the detailed flame retardancy treatment of cotton fabrics and different techniques used to impart its flame resistance [43-47]. An important recent development in flame retardancy of cotton fabric, is the use of a Flame retardants (FRs) chemicals based on Phosphore, Nitrogen and Silicon that are added to combustible textile material to make it fire resistant.

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For example Pengshuang He et al. [48] synthesised a flame retardant cotton fabric by the reaction of cellulose fiber with monochlorotriazine aminopropylsilanol phosphate (MCASP) (Figure 3), their results showed that the cotton fabric treated with 300 g/l MCASP obtained the best flame retardancy with a LOI value of 31.0%, and the char length decreased to 4.5 cm. It was observed that the ignition time increased, and the values of total heat release, heat release rate, mass loss decreased. Their results showed also that MCASP played a protective role on the degradation of cotton fabric, hindered the formation of volatile species and favored the formation of char and the tear force test and washing durability test show the treated cotton fabric has good strength and wash ability.

Figure 3. Schematic illustration of Cotton fabric reaction with monochlorotriazine aminopropylsilanol phosphate flame retardant.

Bin Zhao et al. [49] treated cotton fabric by phosphoramidate named 2,2-dimethyl-1,3-propanediol-N,N-bis(2-hydroxyethyl) (DPDA) (Figure 4), their results showed that the introduction of DPDA greatly improved the char yields of cotton cellulose during heating. Meanwhile, fabrics treated with DPDA passed the vertical burning tests and obtained high LOI values (27.0 to 29.3%) at the add-ons from 16.4 to 25.2 wt%. SEM-EDX results for

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the char layers after burning indicated that DPDA promoted cotton to form phosphorus-rich and compact char residue. They found that, according to cone calorimetric results, DPDA revealed good inhabitation of fire and heat for cottons due to promote generating more non-combustible volatiles in the gaseous phase. In addition to the TG-FTIR tests, the incorporation of DPDA for cotton fabric led to less flammable gases (CO, ether and carbonyl) released in the gaseous phase during heating due to the phosphorylation.

Figure 4. Chemical structure of 2, 2-dimethyl-1, 3-propanediol-N, N-bis(2hydroxyethyl).

Figure 5. Routes during the fabric treatment.

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Li Zhou et al. [50] investigated the flame retardancy properties of cotton fabric treated by environmentally friendly flame-retardant compound, diethyl 3-(triethoxysilanepropyl) phosphoramidate (DTP), the synthesized compound was coated onto cotton fabrics via covalent bond (Figure 5), with different levels of add-ons (5–17 mass %) using the traditional pad-dry-cure method. They demonstrated that the cotton fabric treated with DTP became less flammable due to the lower HRR, THR and CO2/CO ratio and it exhibited efficient flame retardancy, which was evidenced by limiting oxygen index (LOI) and vertical flammability test. Their results showed that the modified cotton fabric had high LOI values of 23–32% and thermogravimetric analysis results show that the usage of DTP promotes degradation of the cotton fabrics and catalyzes its char formation. Chaohong Dong et al. [51], synthesized a novel formaldehyde-free flame retardant containing phosphorus and dichlorotriazine components 2(2-aminoethyl hydrogen phosphite)4,6-dichloro-1, 3,5-triazine (CTAP) and then treated cotton fabric by (CTAP) via covalent reaction (Figure 6). Their results showed that the addition of 20.7wt% CTAP into the cotton fabric obtained a high limiting oxygen index value of 31.5%, which was 13.5% higher than the pure cotton fabric and the cone calorimetry test also reveals a superior flame resistant performance, according to the lower HRR and THR values. Furthermore, the TG curves have shown lower decomposition temperature and higher char residues of 46.4% at 700°C, due to the mechanism of phosphorous- and triazine-containing components and the synergistic effect of P and N elements. They found that compared to the untreated cotton fabrics, CTAP performed an effective role in flame retardancy for treated cotton fabrics. Meanwhile, it stimulated the formation of char and promoted the thermal stability of treated cotton fabrics during combustion. Giuseppe Rosace et al. [52] immobilized carboxyl-functionalized organophosphorus oligomer onto cotton fabrics using 1,2,3,4butanetetracarboxylic acid as an environmentally-friendly binder, in the presence of sodium hypophosphite, used as a catalyst, and triethanolamine, which contributes to phosphorous-nitrogen synergism.

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Figure 6. Substitution reaction between CTAP and cotton fiber.

It’s an eco-friendliness flame retardant agent, since it does not contain halogen-based molecules and does not release formaldehyde. Moreover, with the aim of reducing the formation of insoluble calcium salt during home laundering, due to the free carboxylic acid groups bound to the cotton fabric, they recoated the treated samples employing three sol-gel precursors, namely 3-aminopropyltriethoxysilane, tetraethoxysilane and 3glycidyloxypropyl-triethoxysilane. Their results showed that with respect to the untreated cotton, an increase in flame retardant performances of the treated fabrics was observed, with a reduction of both the total burning time and rate, as well as with a higher char amount left at the end of combustion. Their results suggest that the proposed FR multilayer coatings could effectively control the combustion process and favour the achievement of self-extinction for the treated fabrics. In our previous study [53], we developed flame retardant cotton fabric by the sol-gel method, in order to enhance their flame retardant properties. We synthesized seven sols using tetraethylorthosilicate (TEOS) and different ionic liquids (ILs) consist on pyridinium and Methylimidazolium cations with different anions such as: PF6-, CH3COO-, and Br-. We grafted them separately onto cotton fabrics by a pad-dry-cure process (Figure 7). We determined the flame retardant properties of functionalized cotton fabrics before and after washing by the vertical flame tests according to ISO6940:2004(F) standard, also we investigated the effects of anions, aiming at the optimization of the targeted properties. We studied the

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thermogravimetric and mechanical properties according to NF EN ISO 13934-1:2013standard. Our results showed that flame retardancy, thermal stability and mechanical properties of treated fabrics were enhanced by using ionic liquids and the best result was found with PF6 anion.

Figure 7. Schematic representation of flame retardant cotton fabric treatment.

3.4.2. Antibacterial Synthesis for Cotton Fabric Antibacterial Cotton fabric synthesis versus cellulolytic bacteria and fungi is a very important and necessary element in the development of multifunctional textile. Most importantly, microbial resistance cotton fabric properties have attracted considerable attention due to their potential applications in various fields, such as health and medicine. For that several types of compounds are used as an antibacterial agents for cotton fabric synthesis to render it resistant to microbial attack and micro-organisms propagation. For instance, silver, quaternary ammonium salts, polyhexamethylene biguanide, triclosan, chitosan, dyes and regenerable N-halamine compounds and peroxyacids are used. Several works have been reported the detailed mechanisms of antibacterial treatment of cotton fabrics using different agents and techniques [54-56]. QingBo Xu et al. [57] synthesised an antibacterial cotton fabric by the reaction of cotton fabric hydroxyl group and carboxymethyl chitosan (CMC) via pad-dry-cure process. They observed that CMC molecules were covalently linked onto the cotton fabric surface, and the silver nanoparticles (Ag NPs) were adhered to the fiber surface by the coordination bonds with the amino groups of CMC (Figure 8), their results showed that the finished cotton fabrics have an excellent antibacterial function and outstanding

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laundering durability. They found that the modified cotton fabrics still show satisfactory bacterial reduction rates (BR) against both S. aureus and E. coli after 50 consecutive laundering tests, which are all higher than 94%.

Figure 8. The schematic diagram of the reactions to link CMC and to synthesize Ag NPs on the cotton fabrics.

Yunping Wu et al. [58] fabricated cotton fabrics with durable antibacterial activities finishing by Ag nanoparticles, In their study, they prepared size-tunable Ag NPs through a facile and mild liquid reduction method, and they demonstrated that Ag NPs have been fixed and well dispersed on the cotton fabric surface using Citric Acid (CA) as a crosslinking agent as it can provide ester bonding to combine cellulose and Ag NPs (Figure 9). They measured Ag contents in the hybrid fabrics by the techniques of inductively coupled plasma atomic emission spectroscopy and UV-vis, and they tested the antibacterial properties of hybrid fabrics by the shake flask and agar diffusion plate method, also they used SEM observation of bacteria in order to reveal the antibacterial mechanism of Ag NPs in cotton fabrics. Their results showed that the Ag NP coated cotton fabrics exhibit excellent antimicrobial activities against both the Gram-negative bacterium of Escherichia coli (E. coli) and the Gram-positive bacterium of Staphylococcus aureus (S. aureus). The percentages of reduction bacteria remain at 91.8% and 98.7% for S. aureus and E. coli, respectively, even after 50 cycles of consecutive laundering, which indicates that the antibiotic performance of the as-fabricated Ag-CA cotton fabrics is also durable.

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Figure 9. Schematic for fabrication of Ag-citric acid (CA) cotton fabrics and the supposed linkage mode between silver nanoparticles (Ag NPs) and fabrics through CA.

Hongru Tian et al. [59] synthesised an antibacterial cotton fabric using methylene- bis-acrylamide (MBA). They grafted MBA onto the cotton fabrics via covalent bondby the catalysis of aqueous sodium carbonate. They achieved a durable antibacterial cotton fabric containing stable noncyclic Nhalamine groups (cotton−MBA−Cl) by a facile chlorination in diluted NaOCl solution in order to convert the amide functional groups in cottonMBA to N-halamine ones (Figure 10). Their results showed that the cotton−MBA−Cl could effectively inactivate 5.78 × 107 CFU/mL of S. aureus and 7.58 × 108 CFU/mL of E. coli O157:H7 completely within 1 min of contact time, in addition, they demonstrated by washing durability test that 69.77% of MBA moieties remained on the surface of cotton−MBA−Cl fabrics after 50 washing cycles, and 0.30% of Cl+ could be reached by rechlorination which could still quickly kill bacteria. Their results showed also that the grafting and chlorination processes did not cause any significant damage to the structure of the cotton fabrics. Zongliang Li et al. [60] fabricated an antibacterial cotton fabric using polyhexamethylene guanidine hydrochloride and polypropylene glycol diglycidyl ether copolymer (PHMG-PPGDE) aqueous dispersion, they adhered the copolymer onto cotton fabrics through physical adsorption and chemical bonding using dipping-drying method (Figure 11). Their results showed that the cotton fabrics combined with PHMG-PPGDE have broadspectrum and excellent antimicrobial activities against Escherichia coli and Staphylococcus aureus were higher than 99.99%when the adsorption amount of the copolymer was above 35.5 mg/g. Furthermore, their study

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demonstrated the antimicrobial cotton fabrics remained the excellent antimicrobial properties even after washing durability test by cold water laundering, hot water extraction, and detergent solution laundering due to the chemical bonding between cotton fibers and PHMG-PPGDE copolymer.

Figure 10. Synthetic route for antimicrobial cotton−MBA−Cl.

Figure 11. The adsorption and chemical bonding of PHMG-PPGDE on the surface of cotton fabrics.

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3.4.3. Water Repellent Synthesis for Cotton Fabric Cotton fabric is a hydrophilic biopolymer, because of the abundant hydroxyl groups on its surface, which restricts its applicability as water repellent material [61-62]. Therefore, cotton needs surface modification to become hydrophobic (surface hydrophobization) and it is necessary to find ways to render cotton hydrophobic. To overcome this problem, many researchers have attempted to impart superhydrophobicity to the surface of the cotton fabric, because of its surface hydroxyl group can be easily modified by the correlation between its surface structure and a low energy material [63-64]. Generally, the surface roughness is generated by adding various micro or nano particles of TiO2, CuO, SiO2 and ZnO in different substances with low surface energy [65]. It is well documented that fluorocompoundsare one of the most important agents have been investigated to impart hydrophobic property to cotton fabric, due to their low surface energy [66]. For that several physical and chemical approaches have been used to makes it a proper candidate for superhydrophobic substrates, such as dipcoating methods [67-68], spry coating [69], polymerization techniques [62, 70-71], chemical vapor deposition [72-73], plasma treatment [7475],solution immersion [76-77] layer-by-layer assembly [78-79] and the solgel method [80-83]. Superhydrophobic fabrics have potential applications in a number of areas including personal protection, anticontamination, oil–water separation, anti-ice, anti-adhesion and functional sportswear [84]. In our previous studies [85], we modified the surface of cotton, PES and PA fabrics by the sol–gel process in order to achieve silica based hybrid coatings onto the fibers (Figure 12) for enhancing their water repellency, thermal stability and mechanical properties. We investigated the effects of synthesis parameters such as the concentration of the alkoxysilane used as main precursor, the chloropropyltriethoxysilane (CPTS), and the impregnation time of the fabrics in the solution (sol) prepared, aiming at the optimization of the targeted properties. Concerning cotton fabric, our results showed that the droplet shapes analysis confirmed that the water repellency of the fabric was dramatically improved after sol–gel treatment (Figure 13)

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and the mechanical properties of sol–gel treated cotton fabric remain unchanged in comparison with untreated.

Figure 12. Synthesis of water repellent cotton fabric by the sol gel process based on CPTS.

. Figure 13. Water droplet in the surface of (a) untreated CO sample and (b) treated one.

Qianhong Gao et al. [86] synthesised superhydrophobic cotton fabric by simultaneous radiation-induced graft polymerization of γ-methacryloxypropyltrimethoxysilane (MAPS) and subsequent end-capping modification with hexamethyldisilazane (HMDS), Their results showed that, the prepared

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Co-g-EN/PMAPS fabric (Figure 14) exhibited excellent superhydrophobicity with a static WCA 165°and it retains superhydrophobicity even after 30 laundering cycles or 400 cycles of abrasion, also afforded a high efficiency of oil-water separation (96%), In addition, their study showed that the Co-g-EN/PMAPS fabric afforded excellent oil-water separation property with high efficiency (96%), which makes it a good candidate for industrial application, for instance, oily wastewater treatment. Theoretical models and fabrication strategies of hydrophobic and superhydrophobic textiles have been discussed in a recent review [87].

Figure 14. The preparation of Co-g-EN/PMAPS.

3.4.3.1. Synthesis of Multifunctional Cotton Fabric In our previous studies [88], we have been investigated the flame retardancy and water repellency properties of cotton fabric treated with sols containing 1-methylimidazolium chloride propyltriethoxysilane (MCPTS) and 1-pyridinium chloride propyltriethoxysilane (PCPTS) salts synthesized. We have demonstrated that the immobilization of MCPTS and PCPTS onto cotton fabric can be achieved by the sol–gel process (Figure 15). Our results

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showed that the synthesized fabrics exhibit excellent water-repellent and flame-retardant properties. Indeed, untreated cottons keep burning for 45 s after removal of the flame, unlike those functionalized with [MCPTS]PF6 and [PCPTS]PF6, which did not burn. In addition, the thermal study showed that the fabrics coated with hybrid materials based on ionic liquids are more thermally stable compared to the untreated ones and the weight of residue of treated fabric samples regarding untreated fabric increased from 1 to 93% which is higher than the test results (48%) reported by Alongi et al. [89]. The fabric samples lost their flame retardancy properties after three washing process and entirely burnt. Our results indicated also that the water uptake values with dip test with regard to untreated fabric decreased from 340 to 50%.

Figure 15. Synthesis of multifunctional cotton fabric by the sol gel process based on ionic liquids.

Zhonghua Mai et al. [90] fabricated cotton fabrics with Ultraviolet (UV) shielding, superhydrophobic and antimicrobial properties using functional coatings combined with advantages of polyvinylsilses quioxane and ZnO nanoparticles (ZnO/PVSQ) by solution immersion (Figure 16). They investigated the influence of composite coatings on surface morphology, water-repellence, UV shielding property, mechanical property, thermal degradation behaviour and antibacterial property of the cotton fabrics respectively. Their results showed that the cotton fabrics functionalized by composite coatings exhibited excellent UV shielding, durable superhydrophobic and antimicrobial properties as compared to the reference

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materials. Moreover, their treatment does not affect the mechanical properties of cotton fabrics, in contrast, they was significantly improved by surface treatment of the composite coatings without compromising their thermal stability as compared to the pristine cotton fabric. Mehrez E. El-Naggar et al. [91] synthesized zinc oxide nanoparticles (ZnO-NPs) by using sodium alginate as anti-agglomeration agent in the presence of sodium hydroxide as alkali and they modified them with SiO2 nanoparticles by the sol-gel process aiming to obtain SiO2@ZnO-NPsand in order to improve their multifunctional properties, SiO2@ZnO-NPs was conducted successfully thanks to (aminopropyl) triethoxysilan (APTES) and vinyltriethoxysilan (VTES) (Figure 17), they applied the synthesized nanocomposites on cotton fabric by pad dry cure method to render cotton fabrics multifunctional properties such as antibacterial and UV protection. Their results showed that the cotton fabrics treated ZnO-NPs, SiO2@ZnONPs, SiO2@ZnO-NPs/APTES and SiO2@ZnO-NPs/VTES nanocomposites yielded excellent antibacterial and UV protection properties with high durability even after 20 washing cycles.

Figure 16. Illustration of Synthesis of multifunctional cotton fabric functionalized by composite coatings combined with the PVSQ polymer and nano-ZnO particles.

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Figure 17. ZnO-NPs surface functionalization using silan compounds.

Bouazizi Nabil et al. [92] synthesized a polyfunctional cotton fabric using copper oxide, 3-chloropropyltriethoxisilane (CPTES) and diethanolamine (Figure 18), their results showed that the fabricated fabric exhibited excellent catalytic activity in 4-nitrophenol (4-NP) reduction, Methylene Blue degradation and antibacterial activity, due mainly to terminal diethanolamine group that protonates in acidic media, favouring adsorption via electrostatic interactions. They found that 4-NP catalytic reduction to obey 1st-order kinetics, according 98% conversion even after 7 successive reuses. Their results showed also that the synthesis fabric exhibited appreciable antibacterial capacity against Staphylococcus epidermidis (S.epidermidis) and Escherichia coli (E. coli). According to the authors, this property is assumed to arise from CuO dispersion which acts as Cu+ cation reservoir and protonated diethanolamine group that behaves as cell membrane inhibitor.

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Figure 18. Schematic illustration of polyfunctional cotton fabric synthesis with catalytic activity and antibacterial capacity.

CONCLUSION As pointed out in this chapter, Cotton fabric is the most important natural fibre for textile manufacturing. It is used for a variety of purposes, but especially to make textiles used in the manufacture of a large scale of not only man’s clothing but also in technical textile including composite and value-added materials. Cotton fibers should benefit from the recent advances in techniques and procedures such is plasma, sol-gel, polymer coating, microencapsulation and nanotechnologies. Within these techniques, a multifunctional cotton fibres are born and a new field of research are in progress. The functionalization of based cotton- textile allows the Improvement of existing properties and the creation of new material properties, among others: flame retardancy, antibacterial properties, UV- Protection and water repellence properties. Among these functional properties, durability against physical and chemistry damages is an important consideration for the

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sustainable development and application, and more efforts are clearly needed.

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solution of organosilanes. Chemical Communications 2013, 49 (98), 11509-11511. Sasaki, K.; Tenjimbayashi, M.; Manabe, K.; Shiratori, S., Asymmetric superhydrophobic/superhydrophilic cotton fabrics designed by spraying polymer and nanoparticles. ACS applied materials & interfaces 2015, 8 (1), 651-659. Jiang, B.; Chen, Z.; Sun, Y.; Yang, H.; Zhang, H.; Dou, H.; Zhang, L., Fabrication of superhydrophobic cotton fabrics using crosslinking polymerization method. Appl. Surf. Sci. 2018, 441, 554-563. Hu, J.; Gao, Q.; Xu, L.; Wang, M.; Zhang, M.; Zhang, K.; Liu, W.; Wu, G., Functionalization of cotton fabrics with highly durable polysiloxane–TiO2 hybrid layers: potential applications for photoinduced water–oil separation, UV shielding, and self-cleaning. Journal of Materials Chemistry A 2018, 6 (14), 6085-6095. Zimmermann, J.; Reifler, F. A.; Fortunato, G.; Gerhardt, L. C.; Seeger, S., A simple, one‐ step approach to durable and robust superhydrophobic textiles. Advanced Functional Materials 2008, 18 (22), 3662-3669. Bao, X.-M.; Cui, J.-F.; Sun, H.-X.; Liang, W.-D.; Zhu, Z.-Q.; An, J.; Yang, B.-P.; La, P.-Q.; Li, A., Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles. Appl. Surf. Sci. 2014, 303, 473-480. Yang, S. H.; Liu, C.-H.; Hsu, W.-T.; Chen, H., Preparation of superhydrophobic films using pulsed hexafluorobenzene plasma. Surface and Coatings Technology 2009, 203 (10-11), 1379-1383. Zhang, J.; France, P.; Radomyselskiy, A.; Datta, S.; Zhao, J.; van Ooij, W., Hydrophobic cotton fabric coated by a thin nanoparticulate plasma film. Journal of Applied Polymer Science 2003, 88 (6), 14731481. Li, S.; Zhang, S.; Wang, X., Fabrication of superhydrophobic cellulose-based materials through a solution-immersion process. Langmuir 2008, 24 (10), 5585-5590. Panda, A.; Varshney, P.; Mohapatra, S. S.; Kumar, A., Development of liquid repellent coating on cotton fabric by simple binary

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Aziz Bentis, Aicha Boukhriss, Mehdi El Bouchti et al. silanization with excellent self-cleaning and oil-water separation properties. Carbohydr. Polym. 2018, 181, 1052-1060. Zhang, Z.; Ge, B.; Men, X.; Li, Y., Mechanically durable, superhydrophobic coatings prepared by dual-layer method for anticorrosion and self-cleaning. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2016, 490, 182-188. Chen, F.-F.; Zhu, Y.-J.; Xiong, Z.-C.; Sun, T.-W.; Shen, Y.-Q., Highly flexible superhydrophobic and fire-resistant layered inorganic paper. ACS applied materials & interfaces 2016, 8 (50), 34715-34724. Su, X.; Li, H.; Lai, X.; Zhang, L.; Wang, J.; Liao, X.; Zeng, X., VaporLiquid Sol-Gel Approach to Fabricating Highly Durable and Robust Superhydrophobic Polydimethylsiloxane@Silica Surface on Polyester Textile for Oil-Water Separation. ACS applied materials & interfaces 2017, 9 (33), 28089-28099. Zhang, D.; Williams, B. L.; Shrestha, S. B.; Nasir, Z.; Becher, E. M.; Lofink, B. J.; Santos, V. H.; Patel, H.; Peng, X.; Sun, L., Flame retardant and hydrophobic coatings on cotton fabrics via sol-gel and self-assembly techniques. Journal of colloid and interface science 2017, 505, 892-899. Periolatto, M.; Ferrero, F.; Montarsolo, A.; Mossotti, R., Hydrorepellent finishing of cotton fabrics by chemically modified TEOS based nanosol. Cellulose 2013, 20 (1), 355-364. Liu, F.; Ma, M.; Zang, D.; Gao, Z.; Wang, C., Fabrication of superhydrophobic/superoleophilic cotton for application in the field of water/oil separation. Carbohydr. Polym. 2014, 103, 480-7. Wang, H.; Zhou, H.; Liu, S.; Shao, H.; Fu, S.; Rutledge, G. C.; Lin, T., Durable, self-healing, superhydrophobic fabrics from fluorinefree, waterborne, polydopamine/alkyl silane coatings. RSC Advances 2017, 7 (54), 33986-33993. Boukhriss, A.; Boyer, D.; Hannache, H.; Roblin, J.-P.; Mahiou, R.; Cherkaoui, O.; Therias, S.; Gmouh, S., Sol–gel based water repellent coatings for textiles. Cellulose 2015, 22 (2), 1415-1425. Gao, Q.; Hu, J.; Li, R.; Pang, L.; Xing, Z.; Xu, L.; Wang, M.; Guo, X.; Wu, G., Preparation and characterization of superhydrophobic

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organic-inorganic hybrid cotton fabrics via γ-radiation-induced graft polymerization. Carbohydrate polymers 2016, 149, 308-316. Li, S.; Huang, J.; Chen, Z.; Chen, G.; Lai, Y., A review on special wettability textiles: theoretical models, fabrication technologies and multifunctional applications. Journal of Materials Chemistry A 2017, 5 (1), 31-55. Boukhriss, A.; Gmouh, S.; Hannach, H.; Roblin, J.-P.; Cherkaoui, O.; Boyer, D., Treatment of cotton fabrics by ionic liquid with PF6 − anion for enhancing their flame retardancy and water repellency. Cellulose 2016, 23 (5), 3355-3364. Alongi, J.; Ciobanu, M.; Malucelli, G., Sol–gel treatments on cotton fabrics for improving thermal and flame stability: effect of the structure of the alkoxysilane precursor. Carbohydrate polymers 2012, 87 (1), 627-635. Mai, Z.; Xiong, Z.; Shu, X.; Liu, X.; Zhang, H.; Yin, X.; Zhou, Y.; Liu, M.; Zhang, M.; Xu, W., Multifunctionalization of cotton fabrics with polyvinylsilsesquioxane/ZnO composite coatings. Carbohydrate polymers 2018, 199, 516-525. El-Naggar, M. E.; Hassabo, A. G.; Mohamed, A. L.; Shaheen, T. I., Surface modification of SiO2 coated ZnO nanoparticles for multifunctional cotton fabrics. Journal of colloid and interface science 2017, 498, 413-422. Nabil, B.; Ahmida, E.-A.; Christine, C.; Julien, V.; Abdelkrim, A., Polyfunctional cotton fabrics with catalytic activity and antibacterial capacity. Chemical Engineering Journal 2018.

In: Cotton Fabrics Editor: Fabien Salaün

ISBN: 978-1-53615-006-3 © 2019 Nova Science Publishers, Inc.

Chapter 2

A NEW METHOD FOR MEASURING WATER VAPOUR TRANSFERS THROUGH FABRICS Adeline Marolleau1,2,3,*, Fabien Salaün1, Daniel Dupont2, Hayriye Gidik2 and Sylvie Ducept3 1

ENSAIT, GEMTEX, Laboratoire de Génie et Matériaux Textiles, Lille, France 2 HEI-Yncréa, Lille, France 3 DAMART, Roubaix, France

ABSTRACT Physical, physiological and psychological parameters of comfort are described. Physical factors concerns thermal and hydric exchange between the body, the clothing and the external environment like conduction, convection, radiation, evaporative and respiration losses. Thermoregulation processes like thermogenesis and thermolysis lead to maintain

* Corresponding Author Email: [email protected].

38

Adeline Marolleau, Fabien Salaün, Daniel Dupont et al. the body’s core at 37°C (physiological comfort). For the psychological aspect, the reception and evaluation of sensory stimuli are treated by the brain and the subjective formulation of comfort is created. The impact of thermal and hydric transfers (dynamic and static) on fibers depends mainly of the chemical nature of them. More specifically, the hydric behaviour of cotton is studied. Water vapour and liquid transfers are then measured for different fabrics with natural and synthetic fibers thanks to the Dynamic Vapour Sorption (DVS) and frame tests. The DVS measures the sorption and desorption capacity of the fabric subjected to different humidity levels. In order to extract information on the sorption/desorption mechanisms involved, results are modelled according to the parallel exponential kinetic (PEK), the Hailwood-Horrobin (HH), the Brunauer-Emmet-Teller (BET) and the Guggenhein-Anderson-Boer (GAB) models. For the frame test, an additionnal component is added to the sweating guarded hot plate in order to model the air gap in the microclimate and perform dynamic tests. A new protocol is developped for studying the dynamic barrier effect of textiles on the passage of water vapor flows.

Keywords: thermal comfort, mass and heat transfers, cotton fabrics

1. COMFORT GENERALITY Comfort is defined as a state of physiological, psychological and physical harmony between our body and the environment [1]. It may also mean no discomfort or inconvenience [2]. Factors influencing the sensations of clothing comfort are divided into three main groups.   

Physical factors result from the interactions between the body, the clothing and the external environment. Physiological factors relates to the body's thermoregulatory response in interaction with the external environment. Psychological perceptions result from the complex relationships between the different sensory stimuli received by the brain. This aspect of comfort also corresponds to the feeling of being dressed in a way adapted to one's economic, social and functional status.

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39

Thus, the comfort of clothing felt by people depends on all these factors and their interactions. Figure 1 summarizes the interactions between these factors.

Figure 1. Factors influencing comfort.

1.1. Physical Comfort: Human-Clothing-Environment Humans are homeothermic and must maintain their internal temperature at 37°C whatever the surrounding conditions or physical activity. The heat balance between the flows produced by man and those exchanged with the environment must be zero to respect this condition. The model used to represent these exchanges is the two-node model represented according to the Figure 2. Heat exchanges between the human body and the external environment are mainly achieved by conduction, convection, radiation, respiration and evaporation. The human body creates energy through metabolism and stores excess heat for later use [4].

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Figure 2. The two-node model (adapted from [3]).

1.1.1. Conduction Heat exchange is made possible by direct contact between two solids without material transfer. This mode of heat exchange tends to a homogeneous distribution within the medium and occurs spontaneously from a hot solid to a cold solid. The human body can gain or lose heat by conduction, i.e., the contact of the feet with the ground, the lying or sitting position of its body on a surface of different temperature. Conduction heat losses are minimal and can reach about 3 to 5% of the total heat dissipated. The amount of heat exchanged depends on several parameters:   

the difference in temperature gradient between the two surfaces, the contact surface (standing 3% and sitting or lying 8 to 40%) [5], the thermal conductivity of both surfaces (ease of heat transfer through the solid).

The equation 1 characterizing heat flow by conduction is based on Fourier's law.

A New Method for Measuring Water Vapour Transfers … Qcond = -l ´ gradT = l ´ grad(Tsk -Tsolide )

41 (1)

with Qcond heat flow by conduction (W.m-2), λ the thermal conductivity (W.m-1.K-1), Tsk and Tsolid are skin and body temperatures, respectively (K).

1.1.2. Convection Heat transfer by convection is caused by the movement of a fluid (liquid or gas) between different environments with different temperatures. The amount of heat by convection depends on several parameters [6], i.e., (i) the temperature gradient between the two environments, and (ii) the movement of the fluid with which the body is in contact. In the case of exchanges between the ambient air and the skin, the heat flow by convection is given by equation 2 [3]. Qconv  hc  (Ta  Tsk )  Fcl  Ac

(2)

with Qconv is the convection heat flow (W.m-2), hc is the convection heat transfer coefficient (W.m-2.K-1), Ta and Tsk (K) are the temperature of ambient air and average skin, respectively; Fcl is the clothing area factor, Ac is the effective convection of the body surface (equivalent to Ad defined by the DuBois area according to equation 3).

Ad  0.2025  m0.425  l 0.725

(3)

with Ad the body area of DuBois, m the body mass, l the height of the body.

1.1.3. Radiation In general, all bodies emit and absorb energy in the form of electromagnetic radiation. Radiation corresponds to a transfer of thermal energy and the ability of a body to exchange this, is called emissivity. The emissivity and the absorption capacity of a body depend on the wavelength of the radiation and the characteristics of it. The surface of the body participating in the exchanges depends on the posture of the person. Thus,

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parameters modifying the radiation heat exchanges are the fraction of radiative surface, the difference between the average surface temperatures of the two bodies, emissivity, reflexivity and absorbance of the body [6]. Taking into account the exchanges between the body and the environment, heat flux by radiation is expressed according to equation 4 [3]. Qrad = hr ´ (Tr -Tsk ) ´ Fcl ´ Ar

(4)

with Qrad the radiation heat flux (W.m-2), hr the radiation heat transfer coefficient (W.m-2.K-1), Tr and Tsk (K) are the mean radiant and skin temperatures, respectively, Ar is the effective radiation area of the body according to equation 5, Fcl the clothing area factor. A Ar  ( r )  Ad Ad

(5)

with Ar the effective radiation surface of the skin, Ad the body surface of DuBois. The fraction

Ar is equivalent to 0.67 for a squatting person; 0.70 Ad

for a sitting person and 0.77 for a standing person.

1.1.4. Respiration Losses Dry convective losses take place between the human body and the external environment. They are caused by inhaling cold air, then warmed in the lungs to body temperature and transferred to the outside environment by exhaled air (Equation 6). Cres  mres  c pa  (Tex  Ta )

(6)

with Cres convective breathing losses (W.m-2), mres the breathing rate (kg.s1 .m-2) defined according to equation 7, Cpa the thermal capacity of the air (J.kg-1.K-1), Tex the temperature of the exhaled air (K).

A New Method for Measuring Water Vapour Transfers …

mres  K res 

M A

43

(7)

with M the metabolic rate (W.m-2), Kres a proportionality constant equal to 2.58 kg.m2.MJ-1, A the body surface estimated at 1.8 m2. During the breathing process, the inhaled outdoor air is humidified to saturation by the lungs. During exhalation, this humid air is transferred to the outside environment. These exchanges correspond to evaporative losses per respiration defined according to equation 8. Eres  mres  h fg  (Wex  Wa )

(8)

with Eres evaporative losses by respiration (W.m-2), hfg the heat of vaporization of the water which is of 2423 KJ.Kg-1, Wa the humidity ratio of the environment, Wex the humidity ratio of the exhaled air.

1.1.5. Evaporative Skin Heat Loss Evaporation of sweat on the surface of the skin allows the human being to evacuate heat most efficiently (1 g of sweat at 35°C absorbs 2.4 KJ and at a loss of 0.580 kcal). The evaporation intensity depends on the relative humidity and air speed, the fraction of wet skin surface and the temperature, and the pressure gradient of water vapour between the skin and the environment [6]. Evaporative skin heat losses are defined according to equation 9 [3-4]. E sk 

w  ( Psk , s  Pa ) 1 Re, cl  Fcl  he

(9)

with Esk skin heat loss through evaporation (W.m-2), w the skin moisture, Psk,s the water vapour pressure in saturated air at the temperature of the skin (kPa), Pa the water vapour pressure in ambient air (kPa), Re,cl the evaporative resistance of the garment (m2.kPa.W-1), Fcl the clothing area factor, he the evaporative heat transfer coefficient (W.m-2.K-1).

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1.1.6. Metabolism The body needs energy to grow, for organ and muscle function, blood circulation and breathing. Man must then use the energy present in the food by converting it into electrochemical energy to ensure the proper functioning of his vital functions. In our body, only 20% of the potential energy in food is usable for activities. The rest, 80%, takes the form of heat which is rejected by the body. The rate of heat production in the body is called metabolism, and it corresponds to the heat released by the body through a unit of skin expressed in met (1met = 18.4 Btuh.ft-2 (of the body surface) = 58.2 W.m-2 = 50 kcal.m-2.hr-1) [7]. The body surface for an adult is estimated at 1.8 m2.

1.1.7. Stored Heat When the body produces too much energy, it is stored in the tissues for later use. The human body is modelled into two thermal and concentric compartments: the body and the skin. For each compartment, the amount of heat stored by the skin Ssk and body Scr is expressed according to equations 10 and 11 [3]. S sk 

S cr 

 sk  mc p, b Ad



dTsk dt

(1   sk )  mc p, b Ad



dTcr dt

(10)

(11)

with Ssk the amount of heat stored by the skin (W.m-2), Scr the amount of heat stored by the body (W.m-2), αsk the fraction of the total body mass concentrated in the compartment.

1.1.8. Heat Balance of the Two-Node Model In the two-node model, the human body is divided into two concentric thermal compartments, i.e., the core and the skin (Figure 2). The amount of

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45

heat produced by metabolism (M) in the center (core) is necessary to carry out everyday activities. The muscles use a portion of this energy (W). Heat production in the human body (M-W) can also be stored (S) for later use. In the skin, heat is lost through evaporation (Esk). Besides, heat exchanges between the external environment and the skin surface (covered or not by clothing) are ensured by convection (Qconv), radiation (Qrad) and conduction (Qcond). Heat is also exchanged according to the respiratory tract (Cres, Eres). Thus, the heat balance of the human body is defined according to equation 12 [3]. M  W  qsk  qres  S  (Qcond  Qconv  Qrad  Esk )  (Cres  Eres )  (S sk  Scr )

(12) with M heat produced by metabolism (W.m-2), W the work done by the body (W.m-2), Qcond the conduction heat flux exchanged with the external environment (W.m-2), Qconv the heat flux exchanged by convection (W.m-2), Qrad the heat flux exchanged by radiation (W.m-2), Esk skin heat loss through evaporation (W.m-2), Cres convective breathing losses (W.m-2), Eres evaporative losses by respiration (W.m-2), Ssk the amount of heat stored by the skin and Scr by the body (W.m-2).

1.2. Physiological Comfort: Thermoregulation The human is homeotherm and assimilated to a core (representing 2/3 of tissues) surrounded by a skin envelope (1/3 of tissues). In order to stabilize the temperature of its core following changes in the environment, man has a long-term regulation system (biological rhythms) and a short-term regulation system (feedback control) (Figure 3).

Figure 3. Thermoregulation (adapted from [8]).

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47

1.2.1. Thermoreceptors and Nociceptors The external temperature variation is felt initially by the skin (the envelope) then by the rest of the body (central core). The skin allows interaction with the external environment thanks to different elements constituting it such as the free nerve endings otherwise called thermoreceptors making it possible to detect the differences between hot and cold temperatures. Others endings named nociceptors can detect pain at extreme temperatures. These receptors convert the energy associated with the stimulus into bioelectrical signals (transduction phenomenon). These signals code the information concerning intensity, duration, position, and direction. This information is then transmitted through specific nerve fibers to the nervous system via the sensory spinal ganglion in the spinal cord. The brain interprets these signals and reacts accordingly to the perceived environment. These receptors located in the dermis at a depth between 0.15 and 0.17 mm for cold-sensitive receptors and between 0.3 and 0.6 mm for the heatsensitive receptors. The number of receivers for cold is much higher than for hot, so the human body is more sensitive to danger from cold than from hot [9]. Each receiver is stimulated in a specific temperature range. For example, at high temperatures, the receptors of warm pain react while the cold ones are inhibited. For the cold receivers, the temperature range is between 20 and 30°C, while for the warm ones it is between 37 and 47°C. If the temperature is constant and stable, then the pulse is static. Thermoreceptors can adapt to sudden temperature changes. Indeed, in the beginning, they are strongly stimulated, and fast pulses at high frequencies are sent. They decrease rapidly during the first minute until they gradually stabilize. The sudden increase in temperature from T1 to T2 triggers the discharge of the receiver sensitive to hot what stops the discharge of the one who is sensitive to the cold. After a few seconds at temperature T2, the pulse frequency of the warm, sensitive receiver slows down while that of the receiver sensitive to cold increases gradually again. During a sudden decrease in temperature (T2 to T1), the receptor responses are opposite to the previous ones. The hot receiver stops abruptly while the

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frequency of the cold receiver pulse increases sharply. After that, their respective discharges return to normal [9]. At a molecular scale, free nerves terminations are made up of sensors called TRP (Transient Receptor Potential), they are heat-sensitive ion channels. There are 9, but only 6 detect temperature variations. The ion channels TRPV1 (≥ 43°C), TRPV2 (≥ 52°C), TRPV3 (≥ 32 to 39°C) and TRPV4 (between 27 and 42°C) are sensitive to heat. The TRPM8 channels (between 8 and 25°C) and TRPA1 (≤ 17°C) are stimulated at cold temperatures.

1.2.2. Hypothalamus The hypothalamus is the center of thermoregulation of the brain; it has an integrating role. By receiving information about skin temperatures from peripheral thermoreceptors and blood temperatures through the central thermoreceptors, it regulates the body's internal temperature to maintain it at 37°C. The anterior and posterior hypothalamus play distinct roles in thermoregulation [10]. When the measured temperature exceeds the setpoint zone, the heat control mechanisms are put in place in the Anterior hypothalamic area. The posterior hypothalamic area triggers the mechanisms of cold control when the temperature measured by thermoreceptors is too low. These two areas have a reciprocal inhibition action in order to stop mechanisms put in place by one or the other if the external conditions change. Thus, according to figure 3, the temperature difference between the external environment and our body is transmitted to the hypothalamus through thermoreceptors and nociceptors. Subsequently, the information is analyzed by comparing the measured temperature with an average internal temperature at which our body must maintain itself to survive, i.e., 37°C. If the temperature is lower than the reference temperature, our body will put in place physiological mechanisms that will help us to fight against the cold: this is thermogenesis. Otherwise, if the temperature felt is more important than the set temperature then the heat control mechanisms are activated, it is thermolysis.

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49

1.2.3. Thermogenesis Different mechanisms are put in place to fight against the cold by minimizing the dissipation of body heat, i.e., shivering, vasoconstriction, piloerection, and cellular metabolism. During a significant drop in temperature, the body does not arrive not to raise its temperature by vasoconstriction; then it produces heat by involuntarily contracting skeletal muscles, it is the shivers. This mechanism increases body temperature as muscle activity releases large amounts of heat. This phenomenon is caused by the extrapyramidal system representing the whole central nervous system which controls the postures of the body and movements through the autonomic nervous system. During the vasoconstriction, the diameter of the blood vessels decreases and the blood flow is then reduced to a low value between 30 mL.min-1 and 450 mL.min-1. The autonomic nervous system and in particular, the sympathetic system (SNS) control this action. This later acts by activating the postganglionic adrenergic fibers through the secretion of norepinephrine. Parts of the body such as fingers, hands, feet, and ears have an additional vascular control system, arterio-venous anastomoses (AVA). They are present in these areas in large numbers. Opening their valves shortens the normal blood flow and prevents heat transfer to the outside. The piloerection corresponds to the straightening of the hair on the surface of the skin, is controlled by the same pathways as vasoconstriction. This hair helps to preserve heat by creating an insulating layer. However, this phenomenon has little impact on thermogenesis because Man is less and less hairy [10]. To fight the cold, the body needs to produce energy to ensure the normal functioning of our body. Different organs stimulate this metabolism, such as thyroid, adrenal medulla, and cortex.

1.2.4. Thermolysis The two mains mechanisms put in place to reduce the body temperature when this later exceeds its reference, are the dilation of cutaneous blood vessels (vasodilation) and the sweating. The first one increases the diameter of the vessels and consequently that of the blood flow by multiplying it by 10. Excess heat is transmitted to the skin by conductance. For the second one, sweat glands, apocrine and eccrine, secrete an average of 0.6 to 1.5

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L.day-1 with a maximum of 10 L.day-1 under extreme conditions. Eccrine glands, in the majority compared to the apocrine ones, are positioned on the skin as a whole and mainly on the palms of the hands and soles of the feet. The sympathetic autonomic nervous system controls the secretion of this sweat whose evaporation cool the body. These glands are stimulated by stress, and the release of chemicals such as acetylcholine (neurotransmitters) and their secretion is inhibited by atropine. When body temperature rises, the sweat glands of the skin are stimulated and open their pores to evacuate fluid from the body [10].

1.3. Psychological Comfort Psychological comfort is defined according to a succession of processes, i.e., (i) the reception of individual sensory stimuli by the brain, (ii) the evaluation of its sensations and the identification of their importance, (iii) the subjective formulation of the general perception of comfort. Finally, a judgment is made on the state of comfort and preferences taking into account past experiences (psychology and sensorial comfort).

1.3.1. Integration and Evaluation of Sensory Stimuli The spinothalamic pathway brings information from stimuli to the sensory areas of the cerebral cortex. The sensation awareness regions are located in the parietal, temporal and occipital lobes of the brain. It is in the somatosensitive areas, located in the parietal lobe that the psychological phenomenon linked to sensation is formed. The temporal lobe processes auditory information and the occipital lobe processes visual information. Information from the primary somesthesic cortex (temperature, pressure, ...) is integrated by the associative somesthesic cortex located behind it in the parietal lobe. This step removes a global meaning from this information. Subsequently, neural fibers from the parietal and temporal lobes direct information to the frontal lobes involved in the formation of memory. Conscious perception is possible when the sensations, projected on the field of consciousness, have been confronted with the memory, the previous

A New Method for Measuring Water Vapour Transfers …

51

experience, the physiological and psychological state of the individual. It then corresponds to the process by which the person acquires a conscious knowledge of the outside world from his sensory activity. The thermal feeling is possible from a certain threshold defined as the lowest temperature necessary to generate the expression of a perception of heat or cold.

1.3.2. Formulation of the Feeling When the perception of temperature change is clear, judgment scales are used to assess it. Verbal responses are formulated through Broca's area located in front of the motor cortex corresponding to the center of the language transforming thoughts into words [4]. Three scales have been set up by the ISO 10551 standard to judge of the thermal constraint. They should be used in the following order to describe the thermal feeling, i.e., perceptual, evaluative and preferential. Following the previous judgments, people express the personal acceptability or rejection of the thermal constraint as well as their tolerance.

1.4. Influence of Physical and Physiological Factors Different main factors influence psychological comfort. 



The acclimatization of the subject in a given environment affects his perception of the thermal feeling. Indeed, when an individual is subjected to a thermal simulation belonging to the zone called “physiological zero” or “neutral” zone between 30 and 36°C, the thermal sensation disappears after a specific simulation time. Beyond this zone, the sensation of hot (above 36°C) or cold (below 30°C) will persist. This phenomenon of adaptation to our environment is possible thanks to the ability of thermoreceptors to react dynamically during a thermal stimulus. The increase in age tends to increase the thermal threshold, i.e., to decrease the body's ability to detect small temperature variations.

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

Thus, tolerance to discomfort becomes more important for older people. Ethnicity influences the thermal thresholds of individuals. People living in the tropics, for example, are less sensitive when detecting warm thresholds than those living in temperate zones.

2. COMFORT AND TEXTILE 2.1. Moisture Transfer Moisture transfers in porous media are caused by diffusion, capillarity, evaporation-condensation, and liquid water flow phenomena.

2.1.1. Diffusion Diffusion processes are of several types: molecular diffusion, Knuden diffusion and surface diffusion. The first two are governed by the size of the pores and the average free path. All these processes are not dissociated and occur simultaneously within the material. 

The mean free path The mean free path lpm is the distance travelled by water vapour between two molecular shocks. It depends on the number of molecules present in the media and therefore on the total gas pressure. It is defined according to equation 13 [11]. lpm 

1 2   2  n  N AV   molecule

(13)

with lpm the free mean path (m), n the molar concentration (mol. m-3), n.NAV the molecular concentration (m-3), δmolécule the diameter of molecules (m).

A New Method for Measuring Water Vapour Transfers … 

53

Molecular diffusion Molecular diffusion takes place in pores with a radius greater than the mean free path where shocks between molecules are more frequent than those between molecules and the pore wall (Figure 4). This phenomenon occurs under the effect of a partial water vapour pressure gradient.

Figure 4. Molecular diffusion.

This phenomenon is described by Fick's law according to equation 14.

m    m  Dv  A 

X L

(14)

with ϕm the mass flow (g.s-1), ρm the density (g.m-3), Dv the molecular diffusion coefficient (m2.s-1), A the surface of porous media (m2), X the water vapour concentration (geau.gmasse-1), L the length (m). The diffusion coefficient Dv depends on the total pressure and temperature. It is defined in the literature according to equation 15. 8  Rcn  T 1 Dv   lpm  3   Mm

(15)

with Dv the molecular diffusion coefficient (m2.s-1), lpm the mean free path (m), Rcn the constant of perfect gases (J.mol-1.K-1), T the temperature (K), Mm the molar mass (g.mol-1).

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Adeline Marolleau, Fabien Salaün, Daniel Dupont et al. 

The Knudsen diffusion In pores with a radius smaller than the average free path, water vapour transfer takes place according to the diffusion of Knudsen (Figure 5). In this case, shocks of molecules against the pore walls are more frequent than between molecules themselves.

Figure 5. Knudsen diffusion.

This phenomenon, like molecular diffusion, is also governed by Fick's law according to equation 16. 8  Rcn  T 2 DK   r  3   Mm

(16)

with DK the Knudsen diffusion coefficient (m2.s-1), r the pore radius (m), Rcn the constant of perfect gases (J.mol-1.K-1), T the temperature (K), Mm the molar mass (g.mol-1). The Knudsen number (equation 17), expressed as a function of the mean free path and pore diameter, is equal to or greater than 1 when the water vapour transfer is carried out according to the diffusion of Knudsen. Kn 

lpm

 pore

(17)

with Kn the number of Knudsen (without units), lpm the mean free path (m), δpore the diameter of a pore (m).

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Surface diffusion Initially, the molecules are adsorbed directly on the surface of the pores and they form a monolayer film, then the following ones accumulate one on the other when the adsorption sites are all occupied. The molecules weakly bound with the material, i.e., those located on the upper layers, can move from one adsorption site to another to diffuse towards regions with lower water vapour concentration. This phenomenon, called surface diffusion, is represented in Figure 6.

Figure 6. Surface diffusion.

2.1.2. Capillarity A capillary pressure gradient governs the transport of moisture into the pores. The water molecules adsorb on the pore surface until they form a monolayer (Figure 7). The following molecules accumulate on top of them until molecules adsorbed on the two walls meet all together and form a narrow bridge. The Laplace and Kelvin laws describe this molecular interface. The liquid phase present within the material, filling some pores in the porous media and forming more or less large clusters, is defined as capillary water.  Laplace law For a high relative humidity, within a pore, the plurimolecular layers of water molecules accumulate and even join if the pore diameter is small enough. Thus, within the material, two phases are in equilibrium, i.e., liquid and gaseous. This mechanical balance is made possible under the effect of

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interfacial tension forces acting on its perimeter and by pressure forces acting to on both sides of its surface.

Figure 7. Moisture transport by capillarity.

A capillary interface is formed between the liquid phase and the gas phase. This interface can be hemispherical by leaning tangentially on a cylindrical pore or cylindrical by leaning tangentially on the walls. The pressure in the non-wetting fluid (gas phase) of index n is higher than that of the wetting fluid (liquid phase) of index m. Laplace's law reflects this phenomenon according to equation 18. Pc  Pn  Pm 

 Rc

(18)

with Pc the capillary pressure (Pa), σ the interfacial tension (N.m-1), Rc the radius of curvature (m), Ψ the capillary potential (Pa). The bending radius for a spherical interface is

Rc 

d 4

. In this case,

Laplace's law is written according to equation 19. Pc 

 Rc



4  d

with d the diameter of a pore (m).

(19)

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 Kelvin law The curvature of the capillary interfaces and the lowering of the pressure in the liquid phase tend to modify the equilibrium conditions with water vapor. The relationship between capillary pressure and water vapor saturation rate is obtained by expressing the equality of thermodynamic potentials. The thermodynamic potential of a body in the liquid state, of invariable density ρl, is given according to equation 20. l 

Pl  Pvs

l

(20)

with ϕl the thermodynamic potential of the liquid (J.kg-1), Pl the pressure of the liquid phase (Pa), Pvs the saturated vapour pressure (Pa), ρl the density of the liquid phase (kg.m-3). The thermodynamic potential of water vapour, a perfect gas component, is expressed according to equation 21. v 

P RT  ln( v ) M Pg

(21)

with ϕv the thermodynamic potential of the water vapour phase (J.kg-1), Pv the water vapour phase pressure (Pa), Pg the gas pressure (Pa), R the perfect gas constant (J.mol-1.K-1), T the temperature (K), M the molar mass (kg.mol-1). By expressing the equality of potentials, Kelvin's law is described according to equation 22. l  v  Pg  Pl  

l  RT M

P  ln( v ) Pvs

(22)

Laplace's and Kelvin's law can be related (equation 23) and this allows to determine for a given relative humidity, which pores (spherical shape in this case) are filled with liquid water.

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Adeline Marolleau, Fabien Salaün, Daniel Dupont et al.   RT P  4  Pc  Pg  Pl   l  ln( v )   M Pvs Rc d

(23)

Thus, for a given relative humidity, all the pores of radius Rc checking equation 24 are saturated with capillary water. 

 M l  RT  ln(

Rc
2O>>>3O,4O,5O. At 4.6% of moisture, aggregates of water molecules are formed. In addition to previous bonds 6O and 2O, the hydroxyl group 3O is involved in interaction with water molecules. The ranking of interactions is preferably done according to 6O>2O=3O>>>4O,5O. At 18% of moisture, large aggregates of water molecules are created with the increase of humidity. They occupy the existing space between celluloses chains. In this environment, acetal oxygens interact with water molecules, and the ranking preference is 6 O=2O=3O>4O=5O.

3.2.3. Hysteresis The hysteresis is caused by a difference in water quantity taken by the material between the sorption and desorption. This phenomenon is more significant for materials containing fewer crystallines phases. At low

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humidity, the hysteresis phenomenon is associated with swelling of the fiber or other interaction between the polymer and water molecules. Water molecules reacting with these sites replace the polymer-polymer interactions. At high humidity, in pores can be caused by pores with “ink bottle” shape or to a difference in menisci between sorption and desorption in cylindrical pores. The pore in Figure 11 is initially filled with water. During the desorption process, capillary pressures gradually increase from Pc(r5) to Pc(r4) (diagram b). In the beginning, the narrow opening of the pore of radius r0 does not allow moisture to be transported into the ambient environment for pressures Pc(r5), Pc(r3) and Pc(r1) which would potentially be able to evacuate the water contained in their compartment. Once the pressure exceeds Pc(r0), the pressure balance at the meniscus r0 is no longer possible, and in this case, the moisture present at r0 and r1 is suddenly evacuated. The same process takes place when the capillary pressure exceeds Pc(r 2) and Pc(r4). During the adsorption process, the areas of radius r4, r2, r0, r3 and r5 fill. Desorption is more influenced by the opening of the pore throats while the adsorption process depends mainly on the shape of the pore.

Figure 11. Sorption and desorption of water vapor molecules in pores with "ink bottle” shape.

3.2.4. Diffusion Phenomenon The diffusion process takes place mainly in the amorphous regions of cotton. The quantity of water molecules which diffuses depending on the amount of amorphous zones contained in the sample [31]. When a difference

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in water vapor concentration gradient exists between two sides of a polymer, then the material dissolves the water molecules in the material and diffuses through it to subsequently desorb to the external environment with low water vapor concentration. When the cellulose fiber swells in contact with water, then less interaction is possible between the cellulose chains increasing in pore size or free volume within the polymer. Thus, the diffusion of water vapor within the pores increases. At low humidity RH50%, the formation of water molecules clusters which is consistent with the Park model leads to the decrease of coefficients D1 and D2 (diffusion of water within the material). In this model, the first molecules located on the surface of the fiber are not mobile, and the others diffuse within the material to form aggregates at higher humidity which decrease the mobility of the dissolved water molecules [32]. The surface pores filled with water provide additional resistance to mass transfer [28]. At high humidity, the formation of water vapor molecules clusters which reduces the mobility of others molecules leads to the reduction of the diffusion phenomenon [28]. During sorption when the humidity rise, water molecules have more and more difficulty penetrating the material due to a strong cohesion between the cellulosic chains. Water diffusion is then mainly governed by a surface effect rather than by swelling at the core of the material because of the barrier effect due to the presence of water molecules on the polymer surface.

3.2.5. Influence of the Crystallinity Degree As the degree of crystallinity increases, freezing bound and unbound water decreases because the number of sorption sites decreases within the fibrous structure [33]. For a fiber with a high crystallinity rate, the path is

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more tortuous for the transport of water molecules which also reduces the water vapor transmission rate WVTR [28]. Thus, water molecules are mainly taken into amorphous and crystalline regions [34], they can only be taken at their surface in small quantities [30].

3.2.6. Influence of Porosity At high humidity, for materials with high porosity, the quantity of water taken by them is superior to others materials with lower porosity. It can be caused by capillary condensation within the porous network; water molecules fill large pores, that allows the fibrous structure to entrap them [33].

3.2.7. Influence of the Surface Area The crystallinity of the material has a significant influence on the ability to sorb the water. Thus, samples with few crystalline phases have a higher specific surface area available for moisture sorption [33]. Besides, when water molecules cause the swelling of the fiber, the area increases because more volume is available for the sorption or desorption of water molecules [28]. Thus, the water behavior of cotton is an important parameter to consider because of its strong affinity with water molecules. Many phenomena take place such as the swelling of the cotton fiber which can considerably modify exchanges with the external environment and consequently sensations for the wearer. Its impact on comfort is not negligible.

3.3. Impact of Cotton on Comfort According to Stankovic et al., the thermal comfort of textile is influenced by different factors, i.e., fibers morphological characteristics (microscopic level), yarn structure (mesoscopic level), fabric structural and physical characteristics (macroscopic level) [15]. Others fabrics properties can also influence the comfort like the thermal resistance, air permeability, water-vapor permeability and liquid water vapor permeability [2].

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Furthermore, Yoon and Buckley describes an ideal clothing like a piece of fabric which possesses a high value of thermal resistance for protection during cold weather, a low water vapor resistance to transmit heat to the outside environment under soft thermal stress condition, and rapid liquid transport characteristics for eliminating unpleasant sensation [18]. In the case of textile made with cotton, different fabric physical parameters influence the thermal proprieties of textile. The fabric design, the yarn count, the twist coefficient and the fabric tightness influence the thermal conductivity, thermal resistance, thermal absorptivity (or effusivity), water vapor permeability and moisture management.

3.3.1. Thermal Conductivity Thermal conductivity is more important for a textile with interlock structure followed by 1*1 rib and single jersey design. The amount of fibers present within the interlock structure is greater than a single jersey and as is know the thermal conductivity of fibers is higher than that of air. Thus, a structure with a high weight in the unit area possesses a better thermal conductivity value [35]. The twist coefficient does not have any impact on thermal conductivity according to statistical analysis for a value of αe=4.13 [36]. For others coefficients (αe=3.50 or 3.69), the loose fabric shows a decrease of fabric thickness with the thermal conductivity.

3.3.2. Thermal Resistance Thermal resistance is defined as the ratio between the thickness and the thermal conductivity. It increases with the thickness of the textile because more air is trapped in the fibrous structure, and then the heat transfer decreases. Thus, it rises in increasing order for this different fabric design, single jersey, 1*1 rib, and interlock [35]. According to multiple linear regression, the parameters thickness, mass per unit area, cover factor and porosity influence mainly the thermal resistance [37]. When the yarn twist increase, the thermal resistance decrease [36]. The yarn becomes thinner with a high twist coefficient. The structure becomes loose, and the air is entrapped in the structure and diminish the heat transfer.

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3.3.3. Thermal Absorptivity (or Effusivity) The measurement of this parameter determines the warm-cool feeling which is the sensation of first touched. For an important thermal absorptivity value then the textile gives a cooler feeling at first contact. This parameter is most important for interlock followed by 1*1 rib and single jersey fabric design. The heat flow increases with the thermal conductivity of the material, so more heat is easily transferred to the material and therefore the sensation at the first touch is cooler [16, 35]. It is the same first sensation when the contact surface between the textile and the skin is more important for textiles with a smooth surface. The thermal effusivity for the cellulose is between 106.12 to 119.0 J.s1/2 .m-2.K-1 which give a cool thermal sensation [5, 13]. Thermal absorptivity decreases with the fineness of the yarn, the resulting fabric is looser which gives a warmer feeling. For twist values between αe=3.5 or 3.69, thermal absorptivity is not impacted [36]. Then, for others values, this parameter increases with the twist coefficient. The less hairiness of the yarn is associated with higher twist coefficient and decreasing the hairiness will increase the surface area between the skin and fabric which give a cooler effect. When the tightness of the fabric decrease, the thermal absorptivity follow the same tendency and the fabric provides a warmer feeling except for the twist coefficient of αe=3.50.

3.3.4. Water Vapor Permeability If the moisture resistance is too significant, then the evacuation of the excess heat produced towards the outside is not possible, and this generates a feeling of discomfort. The design of the textile fabric affects the water vapor permeability values. Thus, the single jersey one is higher than for a 1*1 rib followed by interlock one. Moisture transfer is more effective in a thin textile than in a thick textile. Thus, the interlock of 1*1 rib structure is more suitable for winter uses (higher thermal insulation) while for sports applications required high moisture management properties, the jersey structure is better adapted [35]. Water vapor permeability increases with the yarn count for thigh and medium fabrics. When the yarn is thinner, the porosity increases and this parameter follow the same tendency. A loose

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fabric presents a high twist value, less hairy surface, and a porous surface, which leads to an improvement of its water vapor permeability properties. Variation is not statistically significant for twist coefficient of αe=3.5 or 3.69. For others, the twist coefficient increase with this parameter. Yarns with high twist coefficients have less hairy surface and the fabric associated is more porous [36].

3.3.5. Moisture Management Propreties (MMT) Different parameters are measured with MMT on textile water management like the wetting time, absorption rate, spreading speed, and maximum wetted radius. For single jersey, the wetting capacity increases proportionally with the mass for compact textiles while for rib fabric there is no difference observed [38]. Thus, a thinner yarn is associated with a lower wetting time [39]. When the twist factor increases, then the diameter and the hairiness of the yarn decreases, which makes the yarn more compact and increases the wetting time. The absorption rate is defined as the moisture absorption ability during a pump time of 20 seconds. This parameter increases for thinner fabric and decreases inversely with the twist factor. Yarn with high twist value is more compact, and less contact between fibers happen [39]. The spreading speed of jersey increases with the rise of yarn count but decreases inversely with the fabric mass variation. Thus, cotton textiles with a Ne 30/1 decrease their moisture management properties when the fabric mass decreases [38]. When the yarn twist is high, the spreading speed is low because the yarn become more compact and the space between inter yarn is higher which decrease the contact between fiber. The maximum wetted radius increases with fabrics made from thinner yarns with a low twist value. The thermal properties of a cotton fabric such as thermal conductivity, thermal effusivity, thermal resistance, depend mainly on the fabric design, yarn count, twist coefficient and fabric tightness. The thermal conductivity and the thermal effusivity is higher for a textile with interlock structure followed by 1*1 rib and single jersey design. A more cooling feeling is obtained for interlock textiles. It is the opposite tendency for the thermal resistance and water vapor permeability. A thin thickness enhances the

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moisture wicking. The thickness of the fabric decreases, and if the thickness reduces more than the thermal conductivity, then the thermal resistance also decreases [36]. Thus, they lead to the fabric a low thermal conductivity and a water vapor permeability values. The thermal absorptivity diminishes, and the fabric has a warmer feeling at first contact. According to MMT result, the use of thinner yarns to manufacture the fabric allows to increase the absorption rate, the spreading speed, and the maximum wetted radius, and to decrease its wetting time [39]. With the increase of twist coefficient, thermal absorptivity and water vapor permeability of fabrics follow the same tendency. The fabric has a more refreshing feeling with a high thermal absorptivity. In this case, the thermal resistance decreases. The yarn twist coefficient does not affect fabric conductivity. For MMT result, a higher twist coefficient will create a thick fabric and the decrease of absorption rate, spreading speed and wetted radius. In this case, the wetting time decreases [39]. This parameter does not have a significant impact on thermal resistance, thermal conductivity, thermal absorptivity according to linear regression [36].

4. MEASURES OF WATER VAPOUR AND LIQUID TRANSFER ON TEXTILES Hydric transfers (vapour and liquid) are measured for four differents textiles which differ in their composition (Table 2), i.e., (i) sample (A) is a blend of 50% polyester (PES) and 50% of polyacrylic fibers; (ii) sample (B) contains 85% of polyacrylic and 15% of moisture sensible synthetic fibers (polyacrylate); (iii) sample (C) is a blend of 66% polyester (PES), 28% viscose and 6% of elastane fibers; (iv) the sample (D) contains 95% of natural fibers (cotton) and 5% of elastane.

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Table 2. Physical characteristics of fabrics Sample Fabric code design

Fabric weight (kg.m-2)

Thickness (mm)

Density (kg.m-3)

Porosity (%)

A

0.215±0.002

1.31±0.03

165±4

0.156±0.004

1.22±0.06

0.141±0.003 0.166±0.001

0.82±0.02 1.05±0.02

B C D

1×1 interlock 1×1 interlock Jersey Jersey

Moisture regain (%)

87.7±2.9

Air permeability at 100 Pa (l.m-2.s-1) 1059±73

128±6

89.4±8.5

1311±60

5.18

171±1 158±3

88.6±4.5 89.5±2.3

1213±70 247±8

4.72 8.15

1.75

4.1. Water Vapour Transfer

4.1.1. Dynamic Vapour Sorption Test 4.1.1.1. Description The dynamic vapor sorption apparatus (DVS intrinsic) measures the sorption and desorption of water vapour by fabrics. Approximately 12 mg of fabric material is placed onto a sample holder and during the test, changing in mass is recorded by an electrical balance (SMS UltrabalanceTM) with an accuracy of ±0.1 µg. This instrument is located in a thermostatically controlled chamber with mass flow controllers (200 ml.min-1) which mix dry and water vapor saturated nitrogen gas in desired proportions to provide precise humidity at ±1%RH. The temperature is maintained constant at 35°C±0.1°C for simulate the temperature at the skin surface. Samples are initially dried for 600 minutes under a continuous flow of dry air to determine the dry weight. The humidity is modified by step of 10% RH between 0 and 90% RH, with a step of 5% RH between 90 and 95% RH and then with a step of 3% RH between 95 and 98% RH. During desorption, the same protocol is used. The sample is maintained at a constant RH step until the rate change in weight was less than 0.005% per minute. When the change rate falls below this threshold, the humidity level change to the next

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programmed one. Data are acquired every 20 seconds and two tests are carried out by samples in order to ensure the reproducibility of the results.

4.1.1.2. Modelisation OriginPro 9.0 software is used for modelling sorption and desorption curves from DVS results with different models described in literature: PEK (Parallel Exponentiel Kinetics), HH (Hailwood-Horrobin), BET (BrunauerEmmet-Teller) and GAB (Guggenhein-Anderson-Boer) models. 

PEK model Percentage of mass gain or loss, determined with DVS, is plotted against time at each step of RH with time zero corresponding to the change of humidity. Sorption and desorption curves are fitted with the Exponential Association function (ExpAssoc) in OriginPro 9.0 software, also named the PEK model. The parallel exponential kinetics model (PEK) is applicable to DVS results from 0 to 98%RH for a relaxation-limited diffusion situation where the rate of diffusion is faster than the rate of relaxation (equation 26) [40-41]. t  t    t1    MCt ,% RH  MC1,% RH  1  e   MC2,% RH  1  e t 2  i i i    

(26)

with MC (%) is the moisture content at time t (min), MC1 (%) and MC2 (%) are respectively moisture content at time t1 (min) and t2 (min). The fast and slow kinetic processes are described in the Equation 26 by the exponential terms, i.e., the first is expressed with (MC1, t1) and the second with (MC2, t2). The EMC is defined as the sum of MC1 and MC2 at each step of RH. These two processes differ by the sorption or desorption sites they used in the textile structure. Water molecules can create a direct or an indirect bond with hydroxyl groups present at the surface of fiber. Direct sorption/desorption of

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water molecules are possible onto external surface, amorphous regions, and inner surface of voids and crystallites [42]. Indirect moisture sorption/desorption concern additional water molecules that are bound to previous molecules already sorbed. Thus, fast process is associated with easily accessible sites like external surface of fiber and amorphous regions. The slow process concerns sites onto the inner surface and crystallites which are accessible with difficulty [43-46]. HH model The sorption part of the DVS is analyzed by fitting data with the Hailwood-Horrobin model (H-H) that is mainly used in the literature [29, 43, 47-50]. This model analyses two water vapour molecules sorption processes onto the fabric structure (equation 27), i.e., monolayer (Mh) and polylayer (Ms). The monolayer sorption concerns the sorption on the surface of the fabric and in pores with only one layer of water vapor molecules. The polylayer sorption is possible above first layer of water molecules already placed at the surface of the fabric and in pores. It concerns several layers of water vapor molecules piled.

M  Mh  Ms 

1800  K1 'K 2 'H  1800  K 2 'H     W 100  K1 'K 2 'H  W 100  K 2 'H  (27)



with M is the percentage of moisture content at a given RH (%), W is the molecular weight of cell wall polymer per sorption site, K1’ is the equilibrium constant of monolayer water formed from dissolved water and cell walls, K2’ is the equilibrium constant between water vapor and dissolved water. BET model The BET [51] model is used for the interpretation of multilayer sorption isotherm with sigmoid or S-shaped form for 0 < aw < 0.35. It provides an estimation of the amount of water sorbed or desorbed

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Adeline Marolleau, Fabien Salaün, Daniel Dupont et al. on the surface of materials as a monolayer. The theory of this model is based on 3 assumptions, i.e., (i) the rate of condensation on the first layer is equal to the rate of evaporation from the second layer, (ii) the binding energy of all of the adsorbate on the first layer is equal, (iii) the binding energy of the others layers is equal to those of the pure adsorbate. This model is expressed by equation 28.

M



M 0  Ce  aw (1  aw )  (1  (Ce  1)  aw )

(28)

with M is the moisture content (kg/kg dry solid), M0 is the monolayer moisture content (kg/kg dry solid), aw is the water activity defined as the ratio of vapor pressure of water in a material to the vapor pressure of pure water at the same temperature, and Ce is the energy constant related to the difference of free enthalpy (standard chemical potential) of the sorbate molecules in the pure liquid state and in the monolayer (first sorbed state) [52]. GAB model The GAB model [53] is a multimolecular model described by equation 29 for 0 < aw < 0.95. It is an extension of the BET model theory with an additional assumption which stipulates that the state of the sorbate molecule in the second and higher layers is equal but different from the liquid state. An additional parameter K is introduced in this model and it lets assumed that multilayer molecules have interactions with the sorbent that range in energy levels between those of the monolayer molecules and the bulk liquid. When K=1, the GAB equation turns back into the BET equation.

M

M 0  Ce  K  a w (1  K  aw )  (1  (Ce  1)  K  aw )

(29)

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with M is the moisture content (kg/kg dry solid), M0 is the monolayer moisture content, Ce and K are constants related to energies of interaction between the first and further molecules at the individual sorption sites. Ce and K are defined respectively with equations 30 and 31.

H H n ( m ) RT Ce  c0  e

(30)

H H n ( l ) K  k0  e RT

(31)

with c0 and k0 are entropic factors; Hm, Hn and Hl are respectively molar sorption enthalpies of the monolayer, multilayers and bulk liquid (kJ.mol-1).

4.1.1.3. DVS Results  PEK model Sorption and desorption isotherms for EMC, fast MC1, and slow MC2 processes are determined from the DVS results (Figure 12). The EMC represents the total moisture took by the fabric during the test. It is calculated by adding parameters MC1 and MC2 related to the total moisture contents associated with fast and slow processes, respectively. At each step of RH, as far as the relative humidity in the chamber increases, the moisture content for each sample increase too, underlining the ability of the textiles samples to absorb it. This sorption process increases linearly from 10 to 80% of RH, and promptly after that at high humidity rate, whatever the kind of textiles studied. The amount of moisture (EMC) contained in sample D is the more significant, followed by samples C, B, and A. Sample D is composed of natural fibers highly hygroscopic. Hydroxyl groups of cotton fibers present a high affinity with water molecules.

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Figure 12. PEK model results - EMC, fast MC1 and slow MC2 processes measured for the various samples with DVS apparatus.

In the situation where the fast process (MC1) predominates over the slow one (MC2), sample A has few sites with strong affinity to water molecules, so few bonds are possible in the core of the bulk material. Sample D has very hydrophilic sorption sites because of the cotton fibers it contains. The sorption of water molecules is first of all carried out on the surface of the material and then at the heart of it. Many sites are available on the surface and in amorphous zones, so sorption according to the rapid process remains predominant. For samples B, the water vapor is taken firstly in easily accessible sites of sorption like other textiles, and then water vapor molecules are sorbed onto the inner surface and crystallites of fabric (direct or indirect bond) which are harder to access previously at low humidity. Indeed, at higher humidity, new sorption sites become accessible once the fabric structure evolves. Before 30%RH, sample C takes the same quantity of water according to the fast and slow processes. At the same time, water molecules are taken on the sorption sites easily accessible like on the fabric surface and into amorphous regions; and also on the sites difficult to access as within

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pores. After that, it is the rapid process that becomes predominant for higher humidity. During desorption, for all samples, the quantity of water desorbs by the fast process is higher than for the slow one. Water molecules leave easily accessible sites (fast process) than those that are more difficult to access (slow process) because the fibrous structure evolves when the water molecules penetrate inside (polymer chain spacing). At high humidity rate, comparing sorption/desorption curves for all samples except D, slow process water sorption is always higher than desorption; for the fast process, it is the contrary. During sorption, in the first stage, the slow process sites, which are difficult to access, absorb the molecules of water vapor then the textile structure changes with the increase of ambient humidity. This structural change implies a modification of accessibility for slow process sorption sites by making them more easily accessible. This amount of water desorbing during the fast process and missing in the slow process is called “extra water” [54]. For sample D, water molecules with a strong affinity for cotton have entered the fibrous structure and sites that were previously easily accessible in sorption become difficult to access due to swelling of the fiber in desorption. This “extra water” phenomenon is also the reason that the shape of MC1 and MC2 for sorption/desorption curves are not closed whereas for the EMC, the moisture content at 98%RH is similar for sorption and desorption processes [52, 55]. 

HH, BET and GAB models Results obtained from the HH, BET and GAB models are summarised in Table 3. For the HH model, the parameter W is representative of the molecular weight of polymer structure per sorption site. When this

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Adeline Marolleau, Fabien Salaün, Daniel Dupont et al. Table 3. Results obtained from HH, BET and GAB models

Sample Code A B C D

W (HH model) 3322 1311 971 588

M0 (BET model) 0.39 1.21 1.77 2.65

M0 (GAB model) 0.53 1.34 1.72 2.83

parameter increases, it is meant that the fabric structure shows a reduction in the number of free hydroxyl groups available for the sorption of water vapor molecules [56]. The fabric containing the higher amount of hydrophobic fibers (Sample A) has a high W expressing a low affinity of the polymer with water vapor molecules as few sites are available for creating hydrogen bounds. The sample D, composed of highly hygroscopic cellulosic fibers, has a low W. Others samples composed of polyacrylate and viscose fibers have an intermediate number of sorption sites available for water vapor molecules. BET and GAB models provide an estimation of the number of water molecules sorbed in a monolayer at the surface of materials (M0). Samples composed of moisture-sensitive fibers have a high value (sample D) while those composed of hydrophobic fibers have a low coefficient like the fabric A. The coefficients extracted from the two models have similar values for each sample. Therefore, samples differ mainly in their sorption mechanism. Each model provides different information that can be compiled together as shown in Figure 13 to 17 below. For the HH model, the moisture transition between the monolayer and multilayer sorption are close for the four samples (between 52 and 55%RH), no significant difference is observed.

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Figure 13. Sorption mechanisms of sample A.

Figure 14. Sorption mechanisms of sample B.

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Figure 15. Sorption mechanisms of sample C.

Figure 16. Sorption mechanisms of sample D.

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4.1.2. Frame Test 4.1.2.1. Sweating Guarded Hot Plate (Skin Model) The sweating guarded hotplate is commonly used to measure thermal and water vapor resistances of fabric in steady-state conditions according to ISO 11092:2014. The thermal resistance is representative of the fabric heat insulation. For its measurement, the sample is placed above the measuring unit of the sweating guarded hot plate. The hotplate (measuring unit) is a porous sintered stainless steel plate where an air ducted of 1±0.05 m.s-1 flows across and parallel to the upper surface of the fabric. It is electrically heated at 35°C to simulate the skin temperature and maintain at this temperature during the whole test. For the determination of thermal resistance, the ambient conditions are settled to 20±0.1°C and 65±3%RH. The water vapor resistance is the capacity of the fabric to let pass water vapor through a material. A water vapor permeable and liquid-water impermeable membrane covers the measuring unit. Channels beneath the hotplate are used to supply water. Then, the water evaporates through pores of the plate to simulate sweat at the surface of the skin. Standard conditions for the measurement of this parameter are 35±0.1°C and 40±3%RH. In this part of this work, an additional module is added to the Skin model in order to represent an air gap between the skin and the textile. The frame is positioned between the guarded hot plate and the textile which is placed above it. It allows to measure water vapor flows through the textile with sensors. Its conception, instrumentation and tests implemented are described below. 4.1.2.2. Frame Design The frame with a size of 322×322 mm2 is positioned on the guarded hot plate designed according to Figure 17. It is made of aluminum to allow the homogenization of heat flows within its structure. It is composed of 3 parts. The first part consists of a solid plate attached to the frame body by screws. As the test is performed isothermally, this plate prevents hydric leaks from below. At the top of the central plate unwound in its center, a polyethylene mesh with openings of 2×2 cm2 is placed in order to maintain the textile flat

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by avoiding the belly effect. The height of the central plate (10 mm) until the mesh represents the thickness of the air gap between the textile and the guarded hot plate creating a microclimate for the exchange of hydric flows. Humidity sensors are positioned inside the central plate. Composite supports, made of vegetable fibers and waterproof polymer, are put on the surface of the solid plate and hold sensors in position (Figure 18). A passage for connecting the sensors has been created at the right end of the central plate. Once the textile is laid on the mesh, a cover is positioned over it to limit the passage of hydric flows on the sides. In order to ensure total water tightness of the system, rubber insulation joints are glued to the upper surface of the central plate and under the cover. Screws hold the cover in position and tightening them ensures contact between seals. Moreover, in order to avoid the passage of moisture through the screws, their heads are covered by tape. An air flow of 1m.s-1 passes horizontally over the surface of the entire system.

Figure 17. Schematic view of the fram design.

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Figure 18. Sensors positioning withing the frame.

4.1.2.3. Frame Instrumentation The frame is instrumented with four resistive humidity sensors EFS-10 from Conrad®. It consists of a substrate (ceramic) coated with a metal electrode and a hygroscopic polymer. When the sensor absorbs moisture, the ionic groups dissociate and increase its electrical conductivity. The impedance of the sensor varies between 1.5 KΩ and 3 MΩ. This variation is measured by placing the sensor in an electrical circuit powered by a low frequency generator set at 1 kHz. Other resistors have a fixed impedance of 100 KΩ and the signal recovered by a Keithley acquisition device is alternating current (AC). The measuring range of these sensors is between 20 and 90%RH with a response time of 12 seconds. They have also a good long-term stability and an average accuracy of 5%RH. Before testing, sensors are calibrated. This step is performed using as reference a capacitive humidity probe Testo 435 from Conrad ®. Its measuring accuracy is 3%RH. Within a climatic chamber, the sensor positioned as close as possible to the probe is subjected to different humidity levels from 40 to 90%RH with a step of 10%. From data recovered by the exceLINX (humidity sensors) and Testo Comfort X35 software, a calibration equation specific to each sensor is determined. This polynomial equation of degree four links the measured voltage within the electrical circuit with the surrounding humidity measured within the controlled climatic chamber.

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4.1.2.4. Test Protocol The test is carried out in isothermal conditions to measure only the water vapor flows passing through the textile. The temperature is set at 35°C and represents the temperature at the skin's surface. A textile sample is subjected to a humidity ramp from 40 to 90%RH with a speed of 10%HR.min-1 in order to simulate sudden sweating in a climatic chamber. Before and after this ramp, the relative humidity is kept constant for one hour at 40 and 90%RH, respectively.

Figure 19. Diagram of the protocol used for tests.

This protocol is used to test the dynamic barrier effect of textiles on the passage of water vapor flows according to Figure 19. If a textile lets the

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hydric flow through, the humidity ramp obtained in the microclimate will follow that set in the climatic chamber, so the textile has little influence on the flow of water vapor. Otherwise, the humidity within the microclimate will be lower than that of the climatic chamber and in this case, water vapor molecules take longer to pass through the textile. Sensors are placed in the frame according to Figure 27. Three tests per sample were carried out.

4.1.2.5. Frame Results The results obtained with this protocol are summarized in Table 4. Table 4. Results obtained from frame text Sample code A B C D

Moisture rate transfer (%RH.min-1) 10.4 ± 0.2 9.4 ± 0.4 8.6 ± 0.4 8.2 ± 0.5

The moisture rate transfer represents a transfer speed of water vapor molecules through the fabric. When this value is high the water vapor easily passes through the textile and if not, the transfer time is more significant. This parameter is the lowest for samples containing highly hygroscopic fibers such as sample D. In this case, moisture transfer to the external environment is slowed down because fibers first sorb moisture within the textile before it is transferred to the external environment. In contrary, values are relatively high for samples made up of fibers with a low water vapor affinity like A. Since the sample sorbs few water vapor molecules; the moisture is quickly transferred to the outside environment without being retained within fibers. The correlation between different fabric traits was determined using Pearson correlation coefficients (R software). Traits used were: fabric weight (kg.m-2), thickness (mm), density (kg.m-3), porosity (%), air permeability (l.m-2.s-1), moisture regain (%). Pearson correlation coefficients measure the strength of a linear association between two continuous variables. Values can range from -1 to 1. A value of 1 shows that the

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correlation between two variables is perfect and positive; -1 corresponds to a perfect negative correlation; 0, there is no correlation. Table 5. Pearson's correlation coefficients between moisture rate transfer and textile properties Textile properties Fabric weight Thickness Density Porosity Air permeability Moisture regain

Moisture rate transfer 0.778 0.754 -0.049 -0.788 0.536 -0.921

(p