Nonwovens: Process, Structure, Properties and Applications 9385059122, 9789385059124

Table of contents :
Content: Introduction to nonwovensDefinition of nonwovenClassification of nonwovensHistory of nonwovensMarket growth of nonwoven industryFeatures of nonwoven fabricsRaw materials for nonwovensProduct properties and applications of nonwovens Web formationIntroductionStaple fiber web formation systemPolymer lay processComparison of different web forming techniques Nonwoven bonding techniquesIntroductionMechanical bondingChemical bondingThermal bondingComparison of different web bonding techniques Finishing of nonwovensIntroductionMechanical finishingChemical finishing Testing of nonwovensIntroductionCharacterization of bonding structuresTesting of nonwovens Applications of nonwovensIntroductionApplication of nonwovens in apparelApplication of nonwovens in agricultureApplication of nonwovens in geotextilesApplication of nonwovens in medical textilesApplication of nonwoven in automotive textilesApplication of nonwovens in filtrationApplication of nonwovens in home textilesApplication of nonwovens in roofing and constructionApplication of nonwovens in packaging Composite nonwovensDefinitionImportance of composite nonwovensTypes of composite nonwovensComposite nonwoven manufacturing processesApplication of composite nonwoven structures Natural fiber nonwovensIntroductionCotton fiber nonwovensFlax fiber nonwovensJute fiber nonwovensHemp fiber nonwovensKenaf fiber nonwovensMilkweed fiber nonwovensPineapple fiber nonwovensAbaca fiber nonwovensSisal fiber nonwovensWool fiber nonwovensKapok fiber nonwovens

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Nonwovens: Process, structure, properties and applications

Nonwovens: Process, structure, properties and applications

T. Karthik R. Rathinamoorthy C. Praba Karan

WOODHEAD PUBLISHING INDIA PVT LTD New Delhi

Published by Woodhead Publishing India Pvt. Ltd. Woodhead Publishing India Pvt. Ltd., 303, Vardaan House, 7/28, Ansari Road, Daryaganj, New Delhi - 110002, India www.woodheadpublishingindia.com

First published 2016, Woodhead Publishing India Pvt. Ltd. © Woodhead Publishing India Pvt. Ltd., 2016 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing India Pvt. Ltd. The consent of Woodhead Publishing India Pvt. Ltd. does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing India Pvt. Ltd. for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. Woodhead Publishing India Pvt. Ltd. ISBN: 978-93-85059-12-4 Woodhead Publishing India Pvt. Ltd. e-ISBN: 978-93-85059-64-3

Contents

Preface

ix

Foreword

xiii

List of figures

xv

List of tables

xxi

1. Introduction to nonwovens

1

1.1

Definition of nonwoven

2

1.2

Classification of nonwovens

3

1.3

History of nonwovens

4

1.4

Market growth of nonwoven industry

6

1.5

Features of nonwoven fabrics

10

1.6

Raw materials for nonwovens

11

1.7

Product properties and applications of nonwovens

27

2. Web formation

34

2.1 Introduction

34

2.2

Staple fiber web formation system

35

2.3

Polymer lay process

75

2.4

Comparison of different web forming techniques

88

3. Nonwoven bonding techniques

95

3.1 Introduction

95

3.2

Mechanical bonding

97

3.3

Chemical bonding

132

3.4

Thermal bonding

138

3.5

Comparison of different web bonding techniques

150

vi

Nonwoven: Process, structure, properties and applications

4. Finishing of nonwovens

156

4.1 Introduction

156

4.2

Mechanical finishing

157

4.3

Chemical finishing

167

5. Testing of nonwovens

181

5.1 Introduction

181

5.2

Characterization of bonding structures

182

5.3

Testing of nonwovens

185

6. Applications of nonwovens

211

6.1 Introduction

211

6.2

Application of nonwovens in apparel

215

6.3

Application of nonwovens in agriculture

218

6.4

Application of nonwovens in geotextiles

222

6.5

Application of nonwovens in medical textiles

225

6.6

Application of nonwoven in automotive textiles

232

6.7

Application of nonwovens in filtration

235

6.8

Application of nonwovens in home textiles

242

6.9

Application of nonwovens in roofing and construction

244

6.10 Application of nonwovens in packaging 7. Composite nonwovens

244 249

7.1

Definition

249

7.2

Importance of composite nonwovens

250

7.3

Types of composite nonwovens

250

7.4

Composite nonwoven manufacturing processes

251

7.5

Application of composite nonwoven structures

271

8. Natural fiber nonwovens

285

8.1 Introduction

285

8.2

287

Cotton fiber nonwovens

Contents vii

8.3

Flax fiber nonwovens

289

8.4

Jute fiber nonwovens

292

8.5

Hemp fiber nonwovens

295

8.6

Kenaf fiber nonwovens

298

8.7

Milkweed fiber nonwovens

299

8.8

Pineapple fiber nonwovens

303

8.9

Abaca fiber nonwovens

304

8.10 Sisal fiber nonwovens

305

8.11 Wool fiber nonwovens

307

8.12 Kapok fiber nonwovens

307

Index

315

Preface

Industries play a vital role in economy of nations as these industries manufacture different kind of products and relive the nation from importing them from other countries. Textile industries are also manufacturing different kind of fabric for clothing, furnishing, and industrial utility applications. In the conventional fabric, the fibre is first made into yarns; on the other hand, nonwovens are manufactured sheets or webs directionally or randomly orientated fibres, bonded through resistance, solidity or sticking together into a fabric. The demands for fabrics have increased sharply over the years and conventional textiles are not in a position to meet the production cost and higher cost of upgradation along with demanding consumers in new fields of consumption. With better customization of characteristics into the fabric and appropriateness to certain end uses being advantages, nonwovens have emerged rapidly as the fabrics of the future. The ability to produce nonwovens with excellent characteristics in lesser response time and at affordable cost is the most vital factor contributing to its rapid development and commercial acceptance worldwide. On the other hand, nonwoven fabrics hold some natural characteristics, which led them to be counted for non-usable in certain applications. At present, many research and development has been conducted on enhancing the characteristics of nonwoven fabrics. Nonwovens are also entering into some astonishing fields, with making its mark in fashion apparel also. Demand for nonwovens in developed countries is expected to accelerate from the pace set from 2007 to 2012, when recessionary conditions for most of the period brought outright declines in manufacturing and construction activity. Between 2013 and 2018, the global nonwovens market will experience projected annual growth rates of 7.6% (tonnage), 7.5% ($) and 8.2% (m2) according to a new market report by Smithers Apex. Nonwovens are divided into two major categories: disposable and durable nonwovens. According to the report, disposable nonwovens surpassed durables in value growth between 2008 and 2013, increasing from $9.1 billion to $12.5 billion, resulting in an annual growth rate of 6.7%. Within the same timeframe, durable nonwovens grew from $15.3 billion to $20.6 billion tonnes, at an annual growth rate

x

Nonwoven: Process, structure, properties and applications

of 6.1%. According to The Future of Global Nonwovens to 2018, spunlaid is projected to grow at the highest rate of all processes, with consumption projected to reach 5.8 million tonnes by 2018. This book ‘Nonwovens: Process, Structure, Properties and Applications’ plays a vital role in outlining the basic concepts of selection of raw material, manufacturing principles of nonwoven, finishing and characterization of nonwovens. Further, the book provides brief about the composite nonwoven structures and its applications and the application of natural fibre nonwovens in various sectors. Chapter 1 outlines the various definitions of nonwoven, their classification and market potential of nonwoven based on manufacturing technologies and application areas. Further, the raw material requirements for the manufacturing of nonwoven such as fibres, additives and binders are also discussed in detail. Chapter 2 outlines the various web formation techniques for the manufacturing of nonwovens such as drylaid, wetlaid, spunbond and meltblown. The web formation principle, influence of material and process variables on web formation and product characteristics are discussed in detail for all web formation techniques. Chapter 3 discusses the different web bonding techniques such as mechanical, chemical and thermal bonding methods. In case of mechanical bonding needle punching, stitch bonding and hydroentanglement; in chemical bonding saturation, spray, print, foam and powder bonding; in case of thermal bonding hot and belt calendaring, through-air thermal bonding, ultrasonic and radiant heat bonding methods are dealt in detail with respect to principle, influence of machine and process parameters on bonding, product characteristics. Further, comprehensive comparison of three web bonding methods is also given in detail. Chapter 4 provides brief information about the various kinds of finishes for nonwoven structures categorized as mechanical, chemical and specialty finishes with respect to the principle of finishing process, their application areas and limitations. Chapter 5 provides the comprehensive information about the various testing methods and standards for testing of raw materials and nonwoven products. Apart from the basic testing methods, porosity of nonwoven structure, fibre orientation angle and distribution and contact angle measurement are also discussed. Further, product-specific testing of nonwovens such as testing parameters and standards for medical and hygiene textiles, house hold products, protective clothing, geotextiles and filter media are also provided.

Preface xi

Chapter 6 discusses about the application areas of nonwoven products in various sectors such as apparel, agrotech, geotech, medical and hygiene, automotive textiles, filtration products, home textiles, roofing and construction and packaging. Chapter 7 provides brief information about the advanced method of production of nonwoven called as composite nonwoven structures for specific end-use applications. Various methods of production of composite nonwoven such as blending of two or more fibres, layered composite nonwovens, laminated composite nonwovens, hybrid nonwovens, particulate nonwovens and nanofibre nonwovens and their application in medical & hygiene, filtration, sound and thermal insulation products are discussed in detail. The last chapter (Chapter 8) reviews the application potential of natural fibre based nonwovens in various sectors. The natural fibres such as cotton, flax, jute, hemp, kenaf, milkweed, pineapple, abaca, sisal, wool and kapok are discussed with respect to their application as nonwoven structures. This book is primarily a text book intended for Textile Technology and Fashion Technology students in universities and colleges, researchers, industrialists and academicians, as well as professionals in the apparel and textile industry.

Foreword

This book ‘Nonwovens: Process, Structure, Properties and Applications’ has been authored by T. Karthik, C. Praba Karan and R. Rathinamoorthi. The authors have several years of experience in the field teaching of textile technology and apparel science to graduate and post-graduate students. They have put huge efforts and used their practical experience in writing this book. I could find everything about nonwovens in this book. This book begins with a well-structured introduction of nonwovens, commencing with classifications and then proceeds to nonwoven market, raw materials and applications. The chapters on web formation and bonding technologies are dwelt in details and finally comparisons of different techniques are discussed. The readers especially students would find this book very useful as a text book for graduating students and serve as a reference book for students of higher learning. Mechanical and chemical finishing of nonwovens is discussed in detail in this book with many references. One can find a wealth of information in these chapters. Testing methods of nonwovens with reference to standards are presented exhaustively. This would be definitely helpful especially to personnel from industry. The applications of nonwovens in various fields such as apparel, agriculture, geotextiles, medical textiles, automotive, filtration, home textiles, civil engineering and packaging industry are well documented. This will be ready reckoner for people engaged in development of technical textiles. Composite nonwovens are growing at a faster rate due to their appealing functionality. Various composite nonwovens, manufacturing process and their applications are discussed in detail in this book. Sustainable nonwovens are the future to combat pollution arising out of disposing the nonwovens after their use. Natural fibres have unique place which must be exploited by the industry in developing sustainable nonwoven products in order to reduce carbon footprint. The authors have explored many natural fibres for their use in development of bio-degradable nonwovens. The chapter on natural fibre nonwovens would be very useful to the readers.

xiv

Nonwoven: Process, structure, properties and applications

The authors have put commendable effort in bring this book. This book will be certainly useful to students, academicians, researchers and personnel from industry. Prof. R. S. Rengasamy Department of Textile Technology Indian Institute of Technology, Delhi New Delhi-16

List of figures

Figure No. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 2.1 2.2 2.3 2.4 2.5

2.6 2.7 2.8 2.9

2.10 2.11 2.12 2.13

2.14

Description Structure of woven, knitted and nonwoven fabrics Classification of Nonwovens based on production techniques Classification of Nonwovens based on structure Worldwide production of nonwovens by quantity Worldwide productions of nonwovens by region Nonwoven productions by web-forming processes Nonwoven production by web-bonding processes Worldwide Nonwoven Consumption in Leading Application areas World consumption of raw materials Types of bi-component fibers Classification of nonwoven based on web formation techniques Dry-laid manufacturing process Typical Blowroom line for processing of nonwoven Schematic representation of a Bale breaker Arrangement of beaters in Cleanomat Multimixer blending machine Tuft blender Continuous dosing system Storage trunk Contifeed feeding system Universal Roller Card Action of Worker and stripper in card Nonwoven Single Card Tandem card

xvi

Nonwoven: Process, structure, properties and applications

Figure No. 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 2.25 2.26 2.27 2.28 2.29 2.30 2.31 2.32 2.33 2.34 2.35 2.36 2.37 2.38 2.39 3.1

Description Double doffer nonwoven card Vibrating chute arrangment Scan Feed Tuft Feeder Micro-Weighing system Scanning of feed weight Parallel laying process Camel back cross-laying process Horizontal laying process Diagramatic representation of Cross lapping angle Struto perpendicular laying process Principle of air-lay machine Danweb air-laying process Rando Opener Random Card Random Card K12 Random card K21 Wet-laid manufacturing process Wet-laid nonwoven process Pilot wet lay machine Spunbonding process Spunbonding process with a belt collector Meltblown web formation process Die design for meltblowing process Web formation process Schematic diagram of Meltblowing Process

3.2

Classification of bonding techniques used in nonwoven bonding process The basic principle of Needle punching process

3.3

Needle punching line



List of figures

xvii

Figure No.

Description

3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12

Process flow in Needle punching Needle Punching Technology Needle punching needle barb structure Structure of a felting needle Structure of structuring needle Conical needle Stitch bonding process The basic types of stitch structures Stitch-bonding point and loop-formation cycle of Maliwatt stitch-bonding machine Steps in Stitch formation Maliwatt stitch formation process and stitched nonwoven sample Malivlies stitch formation process and the stitched fabric Malimo stitch formation process Malipol stitch formation Voltex stitch formation process Principle of hydro entanglement process Working of hydro entanglement process Hydroentangling Equipment and spunlace fabric Chemical bonding of Nonwoven Saturation bonding process Foam bonding process Spray bonding method for nonwovens Print bonding technique for nonwoven

3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25

3.26 3.27 3.28 3.29 3.30 3.31 3.32

3.33

Powder adhesive sprinkling method Types of calendar roller Point bonding rollers Embossing calendaring Belt calendaring process Through-air bonding with horizontal belt Through-air bonding with rotary drum

xviii

Nonwoven: Process, structure, properties and applications

Figure No. 3.34

Description

3.35 4.1

Infra-red bonding machine Classification of Nonwoven finishing methods Process of Nonwoven Compacting

4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 5.1 5.2 5.3 5.4 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8

Ultrasonic bonding process

Mechanism of Creping of nonwoven Shearing process working mechanism Raising rollers Raising (napping) machine Raising the face of the fabric Line diagram of rotary-cylinder singeing machine Principle of gas singeing Line diagram of gas singeing machine Rotogravure coating Rotary screen coating Spray coating Wet or Cold laminating Dry or Hot Laminating Measurement of fiber orientation and orientation angle Schematic diagram of GATS tester Contact angle on different materials Schematic diagram of contact angle Nonwoven consumption of different product groups Application of nonwovens in technical textiles Market share of nonwovens in different application areas Fashion apparel produced from nonwoven fabrics Nonwoven frost covering fabric Nonwoven mulching fabric Nonwoven blanket fabric Various functions of geotextile fabrics

List of figures

Figure No. 6.9 6.10 6.11 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9

7.10 7.11 7.12 7.13

7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23

xix

Description Nonwoven in medical textiles Application of nonwoven in a car Global nonwoven filter market Sandwich web-laying using multi card Single stage multi-layered nonwoven using divider in card line Multi-forming air-laid process Three-layer headbox in wet-laid Modified headbox system for improving the integrity of layered nonwoven Spunbond-spunbond-spunbond production process and fabric SMS production process of Zimmer AG SMS production process from same spinning line SEM image of SMS nonwoven structure CoForm® layered composite nonwoven process Hydroknit® integrated spunbond-spunlace process Evolon® spunlace process SEM image of micro-fibers of splitted fibers Laminated composite nonwoven structure from LDPE Flame-lamination process Hybrid nonwoven structure with scrim VAPORWEB process Principle of Electro Bubble Spinning Production process of PVA nanofiber overlaid nonwoven SEM micrograph of nanofiber overlaid nonwoven Basic processes involved in production of nanofiber coated textiles SEM micrographs of nylon 6,6 electrospun fibers thermally bonded onto viscose nonwoven Particulates incorporated within the base substrate

xx

Nonwoven: Process, structure, properties and applications

Figure No. 7.24 7.25 7.26 7.27 7.28 7.29 7.30 7.31 8.1 8.2

Description SEM images of bonded particles between two nonwoven structures SEM photograph showing functional particles bonded to bicomponent fibers Decontamination three-layered wipe SEM micrograph of three-layered composite nonwoven Process sequence of production of pile-composite structure Construction of composite nonwoven structure 3D Napco structure 3D Napco structure with PCM granules Natural fiber classification Oil sorption capacities of various natural fibers

List of table

Table No 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3.1 3.2 3.3 5.1 5.2 5.3 5.4

Description Definitions of nonwovens Worldwide Nonwovens Production by region Worldwide Nonwovens Production in quantity Properties of nonwoven fabrics Fibers used in Nonwoven industry Special types of binders and their application Properties and application of nonwoven based on web formation methods Properties and application of nonwoven based on web bonding methods Wire point density for various parts of card (PPSI) Card Width and Production rates Relative merits of cross laying and parallel laying process Merits and Limitations of Card Cross-lapping and Air laying process Relative merits of filament bonded and staple fiber bonded Nonwovens Comparison of Spunbond and meltblown fabrics Comparison of Web Formation techniques Different types of stitch bonding process Application of thermobonded nonwovens Comparison of different Web Bonding techniques Standards for measurement of fiber properties Various category of testing of various characteristics of nonwoven products ASTM Standards for testing of nonwoven Standard conditions for measurement of nonwoven thickness

xxii

Nonwoven: Process, structure, properties and applications

Table No 5.5 6.1 6.2 6.3 6.4 6.5 6.6 7.1 8.1 8.2 8.3 8.4

Description Common testing parameters and standards for nonwoven application in different areas Application fields of nonwoven fabrics Application of different types of nonwoven fabrics Application of nonwovens and fibers in different fields of medical textiles Application of nonwoven technology in automotive textiles Comparison of Nonwoven technologies used in filtration Application of different nonwoven products in home textiles Composite nonwoven filters Comparative properties of flax and other high modulus synthetic fiber Potential end uses of Jute based Nonwovens Chemical composition of abaca fiber and natural fibers Comparison of physical properties of natural fibers with sisal fiber

1 Introduction to nonwovens

Abstract: This chapter provides the overall view of nonwoven industry. It discusses the various definitions of nonwoven, classification of nonwoven based on production technique and structure. The market growth potential of nonwoven as well as features of nonwoven fabrics has also been discussed. The raw materials for the production of nonwoven such as fibres, binders and additives were discussed in detail. The brief description of various nonwoven products and their properties and application were also provided. Key words: nonwoven, binders, additives, bi-component fibres, nano fibres

Fabrics can be made from fibers as well as from yarns. In conventional fabric production such as weaving and knitting, the fibers are converted into yarns and consequently into fabric. The construction of woven, knitted and nonwoven structures are shown in Figure 1.1. In nonwoven process, the fibers are directly converted into fabrics. It eliminates the yarn production process and makes the fabric directly from fibers. Nonwovens are unique engineered fabrics offering cost effective solutions for an increasingly wide variety of applications. Nonwovens are products with many different qualities.

Figure 1.1  Structure of woven, knitted and nonwoven fabrics [Source: intech.com]

The major advantages in nonwoven fabrics are the higher production rate compared to conventional fabric formation since all yarn preparation steps are eliminated. For example, to manufacture 600,000 meters of woven fabric need two months of yarn preparation, three months of weaving on 60 looms and one month for processing and finishing. Nonwoven structure can be produced with the same quantity within 2 months from order. Apart from higher production rate, automation is possible is this system and need less manpower and energy compared to conventional systems.

2

1.1

Nonwoven: Process, structure, properties and applications

Definition of nonwoven

A great deal of work has been done to define nonwovens and to distinguish them from paper. Table 1.1 lists the various definitions of nonwovens. Table 1.1  Definitions of nonwovens [Source: Hutten 2007] S. no.

Source

Definition

1

Manual of Nonwovens (Krema 1971)

Nonwoven fabrics are textile fabrics made of a fibrous layer, which may be a carded web, a fiber web, or any system of randomly laid or oriented fibers or threads, possibly combined with textile or non-textile materials such as conventional woven fabrics, plastic films, foam layers, metal foils, etc., and forming them with a mechanically bound or chemically bonded textile product.

2

Annual Book of Standards, 1989. ASTM International ASTM D 1117-01

Nonwoven fabrics is a structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and the combination thereof. The term does not include paper or fabrics that are woven, tufted or those made by wool or other felting.

3

Man-Made Fiber and Textile Dictionary

Nonwoven fabric is an assembly of textile fibers held together by mechanical interlocking in a random web or mat by fusing of the fibers (in case of thermoplastic fibers), or by bonding with cementing medium such as starch, glue, casein, rubber, latex, or one of the cellulose derivatives or synthetic resins.

4

Nonwovens: Theory, Process, Performance and Testing ISO-9092:1988 (Houfek 1993)

Nonwoven is a manufactured sheet, web or batt of directionally or randomly orientated fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitchbonded incorporating binding yarns or filaments, or felted by wet-milling, whether or not additionally needled. The fibers may be of natural or man-made origin.

5

The Dictionary of Paper

Nonwoven fabric is a cloth-like material made of fibers longer than those normally used in papermaking which, instead of being woven on a loom, is formed by felting on a line mesh screen from an air or water suspension with or without binders.

6

Nonwoven fabrics Handbook (INDA) – (Association of Nonwoven Fabrics Industry, USA) (Wakeman 1985)

A sheet, web or batt of natural and/or man-made fibers or filaments, excluding paper, that have not been converted into yarn, and that are bonded to each other by any of several means. Note: 1. To distinguish wet-laid nonwovens from wet-laid paper materials the following differentiation is made. (a) More than 50% by mass of its fibrous content is made up of fibers with a length to diameter ratio greater than 300. Contd...



Introduction to nonwovens

3

Contd...

S. no.

Source

Definition Other types of fabrics can be classified as nonwoven if, (b) More than 30% by mass of its fibrous content is made up of fibers with a length to diameter ratio greater than 600 and/or the density of the fabric is less than 0.4 g/cm3.

7

EDANA (European Disposables and Nonwovens Association)

A manufactured sheet, web or batt of directionally or randomly oriented fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products, which are woven, knitted, tufted or stitch-bonded, or felted by wet-milling, whether or not additionally needled. The fibers may be of material or manmade origin. They may be staple or continuous filaments or be formed in situ. Note: 1. To distinguish wet-laid nonwovens from wet-laid papers, a material shall be regarded as a nonwoven if, (a) More than 50% by mass of its fibrous content is madeup of fibers with a length to diameter ratio greater than 300; or (b) More than 30% by mass of its fibrous content is made up of fibers with a length to diameter ratio greater than 300 and its density is less than 0.40 g/cm3.

8

A New System for Classifying Nonwovens, TAPPI Press (Hansen 1993)

Structure-based definition of nonwoven: • Fiber web structures: Includes all textile sheet structures made from fibrous webs, bonded by frictional/mechanical restraints and/or covalent bonds obtained through the use of resins, thermal fusion, or formation of chemical complexes. Here, fibers or filaments are bonded so that the average bond-to-bond distances are greater than 50– 100 times the fiber diameter giving textile-like qualities of low bending and low in-plane stiffness. • Net-like structures: Structures formed by extruding one or more fiber-forming polymers in the form of a network or film. The film may then be uniaxially or biaxially oriented to fibrillate into a net-like structure. • Multiplex structures: This class of fabrics combine and utilize characteristics of several primary and/or secondary structures, at least one of which is a recognized nonwoven textile structure, into a single unitized structure.

1.2

Classification of nonwovens

Nonwoven can be broadly classified based on two aspects as shown in Figures 1.2 and 1.3 as 1. Based on production techniques 2. Based on structures

4

Nonwoven: Process, structure, properties and applications Classification based on production techniques

Based on web formation

Dry-laid nonwovens 1. Card laid   • Parallel laid   • Cross-laid 2. Random air-laid

Based on web bonding

Based on web finishing

1. Coated 2. Laminated 3. Crimped 4. Printed 5. Special finish

Wet-laid nonwovens

Spun laid nonwovens 1. Spunbond 2. Metblown

Mechanical Bonding 1. Needle punch 2. Spun laced 3. Stitch bonded

Thermal bonding 1. Calendering 2. Through air bonding 3. Sonic bonding

Chemical bonding 1. Impregnating 2. Foam coating 3. Spraying 4. Print bonding

Figure 1.2  Classification of nonwovens based on production techniques

Classification based on structure

Classification with respect to bonding

Classification with respect to position of fibers

Fiber situated in the fabric plane

Fiber situated perpendicular to the fabric plane

Bonded by single fibers

Bonded by fiber bundles

Mechanically bonded textiles

Bonded by threads

Segment structure

Chemically and thermally bonded textiles

Agglomerate structure

Point structure

Figure 1.3  Classification of nonwovens based on structure

1.3

History of nonwovens

The nonwoven industry has a different organisation in contrast to the conventional textile industry. In spite of these two industries sharing a certain legacy, the nonwoven industry has distinctive features of having its



Introduction to nonwovens

5

advancements bolstered by the present wide production of synthetic fibers, by the high production speed of its machinery and in many cases by the reduced cost of its products, favoured by the use of technologies and innovative processes with high value addition. Along these lines, the nonwoven industry has developed a unique identity, different from that of the traditional textile industry which is based on apparels and household fabrics. When England was the principal textile producing country in the 19th century, recognizing that huge amount of fiber were wasted as a trim, Mr. Garnett, a textile engineer, developed a specialized carding machine (known as Garnett machine) to tear up the waste material into fibrous form which can be utilized as a filling material for pillows and beds. Afterwards, machinery manufacturers in Northern England region started binding the fibers using needles (mechanical) or by using binders (chemical) into webs which are the precursors of today’s nonwovens. This method remained similar in the middle of the 20th century and these batts are specifically produced for insulation of railroad box cars in the United States of America (Albrecht 2003). At present, the nonwoven fabric was utilized between the Space Shuttle Discovery’s heat resistant tiles and the spaceship’s skin and nonwovens were component of the space suits worn to the moon. The development in nonwoven sector over the years is given below: • 1936 Dr. Carl Nottebohm initiates development of nonwovens in Weinheim • 1948 Start of dry-laid staple fiber nonwovens production, introduction of Vliesline garment interlinings and Vildea window cloth. • 1950 Joint Venture to produce dry-laid nonwovens in USA (Pellon) • 1960 Joint Venture to produce dry-laid nonwovens in Japan (Japan Vilene Company) • 1965 Introduction of spunbonded polyamide nonwovens technology developed by Dr. Ludwig Hartmann. • 1973 Production of wet-laid nonwovens is started. Production of polyester spunbond begins at new Kaiserslautern plant. • 1982 Production of lightweight polypropylene nonwovens. • 1984 Start-up of the first non-European facility to produce polyester spunbonded nonwovens in North Carolina (USA). • 1985 Acquisition of a leading producer of staple fiber nonwovens in Brazil • 1988 Opening of a new research and development centre for staple fiber nonwovens incorporation using hydro entanglement technology in Weinheim.

6





1.4

Nonwoven: Process, structure, properties and applications

• 1994 Joint Venture with Japanese partner Japan Vilene Company to produce interlinings in Suzhou/China. • 1997 Merging of the staple-fiber and spunbonded Nonwovens Business Groups. Formation of 6 divisions with global responsibilities. • 1998 The Italian company Marelli & Berta, a manufacturer of woven interlinings joins the Freudenberg Group. • 1999 Evolon, a new technological breakthrough is achieved. The first continuous microfiber spunlaced fabric is developed with a large number of applications. • 2002 New Plant Concept: A 50 million investment to modernize and restructure the facilities in Europe and North America. • 2006 Freudenberg Nonwovens acquires Scimat Ltd, Swindon/UK – the leading finisher of battery separators. • 2007 Restructuring of the North American industrial business to simplify product ranges and improve supply chain efficiency. Commissioning of a new spunbond line at Fiberweb’s site at Norrköping, Sweden. • 2008 Creation of two global hygiene business units – Consumer Fabrics and Airlaid Fabrics, and three regional industrial businesses – Americas Industrial, Europe Industrial and Terram. Acquisition of a Chinese polyester nonwoven fabric producer – Hengguan • 2009 Commissioning of a new spunbond line at Fiberweb’s site at Trezzano Rosa, Italy. Formation of a 50/50 JV between Petropar (Brazil) and Fiber web, comprising Fitesa Brazil and Fiber web spunbond sites at Washougal, USA and Queretaro, Mexico to form Fitesa Fiber web, the second-largest spunbond producer in the America.

Market growth of nonwoven industry

The nonwoven industry is one of the rapidly developing industries in the world. It is acquiring a sophisticated and diverse market over the years. For the past 30 years, it has been exhibiting an average growth of about 8% and is expected to sustain this rate of growth for the next ten years. The technology in nonwoven industry has seen a marked improvement in nearly all available major manufacturing processes, including those of spunbond, meltblown, needle punched, spunlaced, wet laid and dry laid fabrication (Ramkumar 2012; INDA 2004, 2006, 2007). The ability to produce nonwovens with extraordinary properties in less time and at affordable prices is the most critical



Introduction to nonwovens

7

factor contributing to its rapid development and commercial acceptance worldwide. The nonwoven industry developed in the three fundamental industrialized regions of the world, the USA, Western Europe and Japan. All of them have made a significant contribution to the technological development of the nonwovens industry and also fuelling its growth by finding new applications for nonwovens (Russell 2007). The worldwide-nonwoven production in terms of quantity and in different regions of the world is given in Tables 1.2 and 1.3 and Figures 1.4 and 1.5, respectively. From the tables and figures, it can be clearly seen that the nonwoven production has a very good growth rate in the upcoming years and Asian countries have immense potential to increase their contribution in the nonwoven market. Table 1.2  Worldwide nonwovens production by region [Source: INDA Estimates & Rory Holmes, INDA-CAB Conference 2012. www.inda.org] 1997

2002

2011

2016

Growth Rate 1997–2010 (%/Year)

Growth Rate 2011–2016 (%/Year)

Dollars (billions)

$11

$15

$26

$37

6.2%

7.8%

Sq Meters (billions)

61

93

205

305

8.7%

9.0%

Tonnes (millions)

2.7

4.0

7.6

11.1

7.7%

7.8%

Table 1.3  Worldwide nonwovens production in quantity (millions of tonnes) [Source: INDA Estimates & Rory Holmes, INDA-CAB Conference 2012. www.inda.org] 2006

2011

2016

Growth Rate 2006–2011 (%/Year)

Growth Rate 2011-2016 (%/Year)

NAFTA

1.61

1.87

2.2

3.00%

3.30%

Europe

1.56

1.95

2.6

4.60%

5.90%

China

0.97

1.65

2.82

10.50%

12.00%

Other Asia Pacific

0.51

0.59

0.78

3.00%

5.70%

Japan

0.33

0.33

0.35

0.00%

1.20%

Middle East

0.26

0.32

0.45

3.60%

7.70%

Rest of World

0.44

0.9

1.88

16.60%

14.60%

TOTAL

5.68

7.61

11.08

6.00%

7.80%

8

Nonwoven: Process, structure, properties and applications

12

300000

10

250000

8

200000

6

150200

4

100000

2

50000

0

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Tonnes (millions) m2 (millions)

0

Figure 1.4  Worldwide production of nonwovens by quantity [Source: INDA, 2012]

In '000 tonnes

NAFTA

Greater Europe

Asia

ROW

8000 7000 6000 5000 4000 3000 2000 1000 0 2001 2006 2011

Figure 1.5  Worldwide productions of nonwovens by region [Source: INDA, 2012]

By considering the nonwoven market with respect to web forming and web-bonding technologies as shown in Figures 1.6 and 1.7, respectively, it is clearly shown that the dry laid, polymer laid web forming technologies and needle punched web-bonding technology dominates the nonwoven market. The spunlace technology growth is also found to be rapid particularly in specific application areas (INDA 2004, 2006, 2007).



Introduction to nonwovens

9

4000 3500

In '000 tonnes

3000 2500

Dry-laid

2000

Wet-laid

1500

Polymer-to-web

1000 500 0

2001 2006 2011

Figure 1.6  Nonwoven productions by web-forming processes [Source: INDA, 2012] 1800 1600

In '000 tonnes

1400 1200 Needle punched

1000

Spunlace

800

Thermal/Resin

600 400 200 0 2001 2006 2011

Figure 1.7  Nonwoven production by web-bonding processes [Source: INDA, 2012]

The drylaid process has continually progressed and has established itself as the primary web forming technique. It is however very varied, especially in terms of web bonding. In recent years, there has been a remarkable increase of hydro-entangling, particularly related to the development of wiping applications (Schoffmann and Schwend 1991; INDA 2007). Airlaid fabrics using short fibers, which are the latest newcomer, are also making quick progress. Although the wetlaid sectors have doubled their inputs in that same time span, this appears to be insignificant when compared to the other

10

Nonwoven: Process, structure, properties and applications

processes. The market consumption of nonwovens in different application areas are shown in Figure 1.8.

Others 13% Construction 13% Other industrials 4% Automotive 6% Filtration 7%

Hygiene 26%

Medical 5%

HF&B 9%

Wipes 12% Apparel 5%

Figure 1.8  Worldwide Nonwoven Consumption in Leading Application areas [Source: INDA, 2012]

From Figure 1.8, it is clear that the hygiene sector plays a vital role in consumption of nonwovens. Nonwovens are widely employed in the development of incontinence products and also in the baby care sector like cover stocking, leg cuffs, tapes, acquisition/distribution layer, textile back sheets, etc. Unfortunately, the oligopolistic market condition in the hygiene sector has caused the nonwovens manufacturers to reap lower profits in this sector (EDANA 2014). Another sector, which took off recently, is the wipes sector, be it for personal, industrial or household applications. The geotextiles and roofing applications have trebled in 15 years time.

1.5

Features of nonwoven fabrics

Nonwovens neither depend on an organized geometrical structure or the interlacing of yarn for internal cohesion. They are essentially the effect of the relationship between a single fiber and another. Hence nonwoven fabrics have characteristics of their own, with new or improved properties (absorption, filtration). These properties open them up to a wider range of applications. Nonwovens are versatile owing to their ability to provide innovative, economical and sometimes unexpected solutions to innumerable business challenges. Innovative products and solutions can be created using nonwovens which helps to solve intricate problems and meet specific needs



Introduction to nonwovens

11

by incorporating appropriate properties. These properties are frequently used in combinations to create fabrics suited for specific end use, while achieving a decent balance between product use-life and cost (Batra and Pourdeyhimi 2012). By selecting suitable raw materials and methods or by adopting finishing treatments to nonwovens, such as printing, embossing, moulding, laminating etc, the desired properties can be developed in the nonwovens. The basic properties expected from nonwovens are given in Table 1.4. Table 1.4  Properties of nonwoven fabrics •  Abrasion resistant •  Absorbent •  Antistatic •  Biodegradable •  Breathable •  Colour fast •  Conductive •  Crease resistant •  Dense •  Drapeable •  Dry cleanable •  Durable •  Dust free •  Dyeable •  Stiff •  Strong

1.6

•  Lint free •  Liquid repellent •  Long-lasting •  Mouldable •  Non-conductive •  Non-fading •  Permeable •  Porous •  Printable •  Protective •  Tear resistant •  Washable •  Weatherproof •  Weldable •  Stretchable •  Sterilisable

•  Elastic •  Filtration •  Flame resistant •  Foldable •  Glueable •  Heat sealable •  Impermeable •  Ironable •  Kind to skin •  Light •  Resilient •  Rot and mildew resistant •  Sewable •  Smooth •  Soft •  Stable

Raw materials for nonwovens

The three main categories of raw materials used to produce a nonwoven fabric are: • Fibers • Binders • Additives

1.6.1 Fibers Nonwoven structures are fundamentally composed of fibers. Consequently, the utility properties and performance of a nonwoven is dependent on the fibers used to a significant extent. A fiber may be defined as any natural or manmade substance, characterized by a high ratio of length to width,

12

Nonwoven: Process, structure, properties and applications

flexibility, a certain minimum strength, elasticity and sufficient temperature stability which is suitable for being processed into a fabric. The choice of fibers in the manufacture of nonwovens is markedly dependent on intended application of the fabric such as strength characteristics, abrasion resistance, resistance to water, chemicals, weather and light. A wide range of fibers, both natural and manmade, has been employed in the production of nonwovens. Almost all the fibers known to mankind have been used in the production of nonwovens at one time or another. However, the commercially significant nonwoven fabrics have been restricted to relatively few types of fibers, owing to their availability and properties (Batra 1989). These include both the conventional fibers, as well as the high performance fibers. The properties of the final nonwoven product depend on the choice of fibers. The factors influencing the choice of fibers are customer requirement, cost, process ability, changes of properties because of web formation and consolidation. The fibers can be in the form of staple fiber, filament or even yarn. Table 1.5 lists the significant fibers used in the nonwovens industry all over the world. The world consumption pattern of different natural as well as synthetic fibers is shown in Figure 1.9. Table 1.5  Fibers used in nonwoven industry Traditional fibers

High performance fibers

•  PET

•  Aramid (Nomex/Kevlar)

•  Polyolefin (PP/PE)

•  Conductive Nylon

•  Nylon

•  Bi-component

•  Cotton

•  Melamine (heat & flame resistant)

•  Rayon

•  Superabsorbent

•  Wool

•  Hollow fibers

•  Lyocell

•  Spandex fibers (polyether)

•  Modacrylic

•  Fusible co-PET fiber •  PA-6 support/matrix fiber •  Glass micro-fiber •  Chlorofiber •  Antibacterial fiber •  Stainless steel •  Rubber thread •  PTFE •  Nanofibers



Introduction to nonwovens

13

Figure 1.9  World consumption of raw materials [Source: ANFA, EDANA, INDA]

Wood pulp is the only natural fiber to be used in large quantities in the nonwoven industry. Wood pulp is characterized by high water absorbency, bulk and low cost which makes it preferable despite of being far shorter in length than the traditional fibers. Cotton fibers facilitate easy fabrication into nonwovens owing to their excellent inherent properties. The disposables and sanitary products sector extensively makes use of viscose rayon fibers. Rayon fibers can be effectively processed into webs and easily bonded into nonwovens fabrics (Hansen 1993). The fibers like cotton, rayon and acetate, being composed of cellulose, are moisture absorbent in nature. This moisture absorbing tendency makes them act as carriers for microbes, thereby providing them strength along with biodegradability. Viscose rayon was a prominently used in the nonwovens manufacturing until 1985. Over the years, the US and Western Europe have gradually cut down the production of viscose rayon due to higher costs of the fiber. The reduction in the costs of PP and PET in comparison with viscose rayon, (especially there was big drop in 1989) and the inherent superior tensile properties of these fibers forced the slow decline of shipment of viscose rayon fibers. Due to the cleanliness and absorptive properties of viscose rayon fibers, nonwovens manufactured from these are mainly utilized in medical/surgical/sanitary sectors and in wet wipes (Lee and Cassill 2006). Likewise, the tampon and incontinence products make use of cotton fibers. The utilization of cotton fibers has stabilized at 40–45 million pounds. Polypropylene (PP) is the most widely used man-made fiber. PP fibers are well-known for their hydrophobicity, voluminous and thermoplastic nature. PP is cheap and possesses good rheological characteristics to form fine fibers. Polyethylene terephthalate (PET) is used in nonwovens requiring tensile strength and mechanical properties to a greater extent. Nylon fibers are utilized in nonwovens owing to their excellent resiliency properties (Albrecht 2003). Being more expensive than most of the other fibers, nylon is less used.

14

Nonwoven: Process, structure, properties and applications

The other “special fibers” listed in Table 1.1 have only a limited market share, probably no more than 15 percent of the whole nonwovens market. Bi-component fibers, fibers containing dissimilar polymers in the core and sheath find extensive applications in thermally bonded nonwovens. The segmented pie and islands in sea structures are recent developments in bicomponent fiber structures. The nature of the product being manufactured and the fabrication process being used determines the properties required by the constituent fibers. Considering that each manufacturing process produces a range of fabrics with distinct properties, all the fibers cannot be used in equal volumes in all nonwoven processes. In spite of the availability of a large number of fibers, few fibers namely, the polyolefins, polyester, and rayon dominate the commercially important nonwoven fabrics. These three fibers constitute a major share of the nonwovens market. The olefin-based fibers are gaining constantly importance, replacing the natural fibers, viscose rayon and polyester in many applications. This shift in fiber consumption can be regarded as the effect of increased use of olefinbased nonwovens in absorbent products around the world. The reasons for high consumption of PP in nonwoven sector are due to the following properties: • Low density enabling lightweight fabrics to be made • Low glass transition and melting temperature, economical for thermal bonding • Inherent hydrophobicity • Good bulk and cover • Chemical stability • Resistance to mildew, perspiration • Stain and soil release • Good mechanical strength and abrasion resistance The two unconventional fibers emerging in nonwoven applications namely, bicomponent fibers and nanofibers are discussed in detail below. 1.6.1.1

Bi-component fibers

Bicomponent fibers can be defined as fibers composed of two components which are distributed over the entire length of the fiber. Each component may possess different physical or chemical properties. The components may either be similar polymers or entirely different polymer types (Russell 2007). By “co-extruding” two polymers into one single fiber, the different properties of both polymers are combined. Hence the newly created fiber has improved



Introduction to nonwovens

15

properties and can be designed to suit many new applications. The properties of the individual components, the choice of combination of the different polymers, additives and the shape of the bicomponent fiber are the major factors influencing the resultant properties and possible applications of the bicomponent fibers. Common bicomponent configurations Most commercially available bicomponent fibers are configured in a sheath/ core, side-by-side, or eccentric sheath/core arrangement as shown in Figure 1.10.

(a) Concentric sheath/core (b) Eccentric sheath/core (c) Side-by-side (d) Pie Wedge (e) Island/Sea

Figure 1.10  Types of bi-component fibers [Source: www.centexbel.be]

(a) Concentric sheath/core This concentric sheath/core configuration is mainly used in melt fibers; fibers with a sheath made of polymers with a low melting point around a core with a high melting point. When melt fibers are heated, the sheath will melt; the consequent cooling will bind the nonwoven or composite structure without affecting the core polymer. This configuration can also be used to produce fibers with an expensive core with weaker/cheaper polymer layer forming the sheath and vice versa. (b) Eccentric sheath/core In the eccentric sheath/core configuration, the core polymer is eccentric or moved out of the radial centre. Both the polymers have different shrinking ratios, causing the fiber to curl when it is heated in a relaxed state. This process adds to add crimp and volume to the fiber. (c) Side-by-side In the side-by-side configuration, both the polymers occupy an equal part of the fiber surface. Depending on the difference in shrinkage nature of the chosen polymers, the fiber may develop more crimp than the eccentric sheath/ core configuration.

16

Nonwoven: Process, structure, properties and applications

(d) Pie wedge This construction contains sixteen adjoining “pie wedges”. Every pie wedge of a particular polymer A is separated from wedges of the same polymer on both sides by wedges of another polymer B. The pie wedge arrangement is made to split into microfibers of 0.1 to 0.2 denier be the action of mechanical forces. (e) Islands/Sea In this configuration, polymer A represents the islands, and polymer B represents the sea. This fiber structure facilitates numerous fine filaments of one polymer to be dispersed in the matrix of another soluble polymer. By dissolving the latter, the fabric structure is made up on the basis of very fine microfibers. Hence, microfibers can also be produced in this method apart from the direct extrusion methods. These five basic configurations can be adapted in function of the desired fiber or yarn properties. It is for example possible to limit the number of islands to produce conductive yarns. On the other hand, it is possible to provide a hole in the pie-wedge configuration (hollow pie wedge) to split the filaments even more easily. The yarn diameter can be adapted to produce trilobal (instead of round) filaments with a sheath/core or side/side structure for carpet applications. Polymers for bi-component fibers A wide range of polymers apart from the regular polymers like polyethylene terephthalate (PET), nylon, and polypropylene (PP) can be used in a bicomponent fiber. Polymers such as polycyclohexanedimethanol terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, PET glycol and a huge range of copolyesters are being utilized. Aliphatic polyesters such as polylactic acid and polyhydroxyalkanoates, which are environment friendly and derivable from renewable sources are gaining importance. The range of available polyamides and polyolefins has been augmented by the co-polymerisation technology. The expanded range include nylon 6; nylon 6,6; nylon 11 and nylon 12; copolyamides; high-density polyethylene (HDPE); linear low-density LDPE; syndiotactic PP; and polymethylpentene. But the most captivating aspect is the application of engineering polymers in nonwovens manufacturing. These polymers have extra-ordinary properties but their usage in commodity applications has been restricted by their costs. The list of engineering polymers includes polyphenylene sulfide, polyvinyl alcohol, polyetherimide, and thermoplastic polyurethanes and many more polymers are also available.



Introduction to nonwovens

17

Applications of bicomponent fibers Bicomponent fibers can provide:

• Thermal bonding



• Self bulking/self crimping



• Very fine fibers (microfibers/nanofibers)



• Unique cross sections



• The functionality of special polymers or additives at reduced cost

Applications requiring engineering polymers make use of the basic sheath/core configuration. Engineered polymers having excellent surface properties can be used as the sheath in bicomponent fibers. Subsequently, the fiber’s core can be made with a suitable lower-cost polymer. This helps to deliver the benefits of the more expensive polymer at a lower cost.  Side-by-side bicomponent fibers typically are based on the difference in shrinkage characteristics between the two polymers to produce self crimping fibers. The application of heat introduces shrinkage in the fibers. On the application of heat, the two polymers shrink at different rates, causing the fiber to curl into a helix. Hence the nonwoven can be manufactured flat and can be made to expand during application.  Microfibers are produced using the pie wedge configuration. Direct spinning of microfibers is a costly process producing low throughputs. Also direct spinning of microfibers cannot produce fibers as fine as 0.3 to 0.5 denier per filament (dpf) – and expensive, as throughputs are low. Whereas spinning a 2–3 dpf pie-wedge fiber overcomes the throughput limitations (Gamayunov et al. 1994). Once a nonwoven web is formed from these fibers, it can be split into microfibers usually about 16 segments per fiber by subjecting to mechanical agitation like hydroentangling process. This drastically reduces the cost of production compared to direct spinning.  Further advancements are hollow and partial-wrap versions of this cross section that improve of the fiber›s relative splittability. The sea/islands configuration also generates microfibers. In this case, the microfibers are obtained by dissolution of the sea polymer in a suitable solvent – typically, a light, hot caustic bath or warm water. The nonwoven fabric made of sea/islands fibers is passed through the solvent bath to produce the microfiber fabric. One major drawback associated with this method is that some of the microfibers may also be washed down the drain. More finer microfibers can be produced using this configuration compared to the piewedge configuration.

18

Nonwoven: Process, structure, properties and applications

Advantages of bicomponent thermal binder fibers • Uniform distribution of adhesive can be achieved •

Fiber remains as a part of the structure and adds integrity

•

Customized sheath materials can be selected to bond various materials

•

Wide range of bonding temperatures

•

Cleaner and environmentally friendly fabrication (no effluent)

•

Recyclable

•

Lamination/molding/densification of composites also possible

1.6.1.2

Nano fibers

The National Science Foundation (NSF) defines nanofibers as fibers having at least one dimension of 100 nanometer (nm) or less. But in general, the nonwoven industry treats fibers having a diameter of less than one micron as nanofibers. Nanofibers are a relatively new class of materials utilized in many important applications like medical, filtration, barrier, wipes, personal care, composite, garments, insulation, and energy storage (Huang et al. 2003). Nanofibers find applications in many sectors ranging from medical to consumer products and industrial to high-tech applications for aerospace, capacitors, transistors, drug delivery systems, battery separators, energy storage, fuel cells, and information technology owing to their unique properties. By and large, the electro spinning process is adopted to produce polymeric nanofibers. The fibers produced by this process have diameters ranging from 10 nm to several hundred nanometers. The factors influencing the spun fiber properties include field uniformity, polymer viscosity, electric field strength and DCD (distance between nozzle and collector). Alternatively, nanofibers can be produced by spinning bi-component fibers with Islands-In-The-Sea configuration. Usually, these bi-component fibers are spun in deniers of 1–3 with about 240 to as much as 1120 filaments of one polymer surrounded by a dissolvable polymer (Subbiah et al. 2005). On dissolving the surrounding polymer, the matrix of nanofibers is left behind, which can be further subjected to stretching or mechanical agitation. Fibers such as nylon, polystyrene, polyacrylonitrile, polycarbonate, PEO, PET and water-soluble polymers are commonly used. The island: sea ratio in the bicomponent fiber is generally around 80:20. The resulting nanofibers will have a diameter of approximately 300 nm (Bognitzki et al. 2001; Baumgarten 1971). In comparison with electrospinning, nanofibers produced from bicomponent fibers are coarser and will have a very narrow diameter range.



Introduction to nonwovens

19

Properties of nanofibers Nanofibers are characterized by special properties chiefly due to extremely high surface to weight ratio compared to conventional nonwovens. Nanofiber nonwovens are suitable for specific filtration applications due to its low density, large surface area to mass, high pore volume, and tight pore size. Application of nanofibers Nanofiber webs have higher surface area compared to meltblown webs and hence have substituted meltblown webs in critical filtration areas. Their highly porous structure with high surface area makes them ideal for many filtration applications. These nonwovens are most suitable for filtering submicron particles from air or water. Some of the applications of nanofiber-based nonwovens are aerosol filters, facemasks, and protective clothing (Li and Xia 2004). Recently, military fabrics make use of laminated layers of nanofibers along with carbon fibers to enhance chemical and biological protection. Nanofibers are also utilized in medical applications like drug and genes delivery, artificial blood vessels, artificial organs, and medical facemasks. In this field, carbon fiber hollow nano tubes which are finer than the blood vessels are widely use. These carbon fiber hollow nano tubes have potential to carry drugs into the blood cells thus enabling medicines to be directly transferred to internal tissues (Baumgarten 1971). Companies like Johnson & Johnson and Genzyme Corporation have developed anti-adhesion materials.  Researchers have developed nanofibers from compounds naturally present in blood for applications in bandages and sutures which are capable of gradually dissolving in blood. It has the advantages of reduced infection rates, minimized blood loss and is capable of disintegrating without causing harm to the body Layered composite structures are used to meet specific filtration applications. These filters are composed with multiple meltblown layers structured using fine to coarse filaments to constitute the bulk. These MB layers are combined nanofiber webs. The MB layers incorporate fluid resistance properties and the nanofiber layers provide smoothness for health, wear and comfort (Doshi and Reneker 1995).

1.6.2 Binders In fiber bonding, adhesives are usually polymeric in nature and for optimum performance the adhesive-fiber combination should have most of these characteristics: • Polarity – The adhesive and fiber should be of similar polarity. Thus, polar water soluble animal glue will stick to cellulose as both are

20

Nonwoven: Process, structure, properties and applications

highly polar. But rubber adhesive will not adhere to cellulose. • Surface tension – The adhesive must be capable of wetting the fiber, thus reducing the surface energy between the adhesive and fiber. This essentially means lowering the contact angle between the two surfaces. • Surface properties of fibers – The fiber characteristics, especially physical surface properties, are also determinant of magnitude of adhesive bonding strength. The three most important variables are (i) primary fiber roughness, (ii) fiber cross-section, and (iii) multi-fiber substrate geometry and porosity. (a) Primary fiber roughness – With the increase in the roughness of the fiber the adhesive bond strength increases. However, the wetting of the fiber by the adhesive is of great importance as good wetting increases the adhesion. (b) Fiber cross-section – Generally fibers are of circular crosssection. However, crenulated cross-section increases the surface area and as a consequence adhesion increases. However, this is to be weighed against increased stiffness of the nonwoven product. (c) Multi-fiber substrate geometry and porosity – It is known that substrate geometry and total porosity affect adhesion characteristics substantially. • Glass transition temperature (Tg) – One of the most important factor for adhesive binder in nonwoven is Tg. Hardness and flexibility of the polymer at normal temperature is dependent on the Tg of the binder. Tg of the binder is adjusted as per the requirement of the finished fabrics by copolymerisation of different monomers. For a long time, the structural integrity is imparted to most of the nonwovens by means of chemical binder. Moreover, the binders were selected accordingly to contribute properties required to enhance the performance of the nonwoven. In the initial stages, nonwovens were bonded using different types of natural resins and glues. Later on, synthetic binding agents were engineered to satisfy the requirements in terms of structural and performance aspects of nonwoven fabrics. Latex binders provide economical methods of web bonding and achieving specific properties. In most cases latex binders prove to be cheaper than the use of special binder fiber. As a general practice, synthetic binders are used in combination with mechanical and thermal bonding techniques, to achieve the finished fabric which otherwise cannot be produced by using either one of



Introduction to nonwovens

21

the techniques alone (Young 1996). Also, most binder systems are compatible with pigments and dyes and help in colouration of nonwoven fabrics. Binders may be classified, by their physical state at the time of application, into the two broad classifications of dry or wet binders. The dry systems are made up of thermoplastic fibers or powders. Wet systems include solutions, of both aqueous and solvent types, as well as polymer dispersions and emulsions. 1.6.2.1

Dry binders

Attempts have been made to use thermoplastic polymers in powder form for binding nonwoven fabrics. Some thermoplastic polymer powders have been developed commercially. Even though these thermoplastic powders are satisfactory for binding, their usage has been limited due to problems of uniform powder distribution in the web and holding them in required places for efficient binding. Meanwhile, the use of thermoplastic fibers is practicable and is in commercial usage. This method provides a more uniform distribution of the binder throughout the web, the fiber itself a binder which can be incorporated into a fiber blend (Young 1996; Morris and Mlynar 1995). The actual bonding may be achieved by passing the web containing the bonding fiber between heated smooth or patterned rolls, depending on the type of end product desired and the amount of bonding fiber present. Infrared or hot air heating may also be used for bonding. Theoretically, any fiber which softens and flows at a temperature lower than that of the remainder of the web can be used as a thermoplastic fiber. In actual practice, polyviny1 chloride, polyethylene, or vinylidene polymers and copolymers, polyamides or polyesters or acetate fibers with very low melting points are used. Thermoplastic fibers offer a number of advantages as binders for nonwoven fabrics. The exact amount of binder used can be determined exactly as it is part of the web blend. The distribution of the binding fiber can be controlled very well depending upon the type of web forming equipment used. Special impregnating system is not required as the binder was part of original web (Walton 1996). Thermoplastic fibers may also serve in heat sealing the product to other materials. However, thermoplastic fibers have not gained much prominence as nonwoven binders probably because of the nature of the fibers themselves. To have a low melt temperature the polymers should have low molecular weight and therefore inherently low strength. Such fibers generally are not compatible where for high strength applications. The use of latex binders restricts the operational flexibility and the type of products being manufactured.

22 1.6.2.2

Nonwoven: Process, structure, properties and applications Wet binders

Only very few nonwoven fabrics are manufactured using solvent solutions as binders. Although both the process efficiency and the end product are excellent, the major problem arises from the use of solvents. The use of solvents is costly unless recovery systems, which are very expensive, are available. Furthermore, solvents are hazardous in nature, both by fire and toxicity (Morris and Mlynar 1995). Water solutions of natural gums, proteins, starches, and some synthetic water soluble polymers are limited in use as binders. None of these are used as the primary binder for quality items except where stiffness can be tolerated as in cheaper decorative fabrics. In some cases these materials are used as pre-bonding agents before other treatments. The water-based emulsion systems, which include the polymer lattices dispersed and stabilised in water medium, are the most versatile and popular of the nonwoven binders. Their ease of handling and non-hazardous nature makes them attractive in comparison with other wet binders. Special types of binders along with their application areas are shown in Table 1.6. Table 1.6  Special types of binders and their application [Source: Mukherjee et al. 1992] S. no

Type of binders

Applications

Acrylic Binders 1.

Acrylic acid grafted oxidised starched copolymers cross-linked with N,N’, methylene bisacrylarnide

Super absorbent wet by nonwovens

2.

Alkyl methacrylate, methacrylic acid; C-polyol methacrylate copolymer

Self-sealing materials for water roofing cable lines, geotextiles, medicines

3.

Copolymers of unsaturated water soluble carboxylic acid or derivatives and methacrylic acid hydroxy alkyl ester monomers combined with a SBR latex

Useful for bonding cellulose fibers and pulp in paper, wipes or towels, diapers

4.

Copolymer of 2-ethylhexyl acrylate, styrene, acrylic acid & vinyl acetate emulsion starch based binder

Web-based wallpaper with extending gluing time.

5.

Acrylic polymer emulsion, paraffin emulsion and water 6

Moisture permeable – waterproof nonwoven fabrics

6.

Acrylic acid, Bu-arylate, styrene copolymer (Mol Wt 636000 and Tg 45°C)

Coated nonwoven emulsion binder with reduced flammability

7.

Aqueous 65% potassium acrylate cross-linked with 0.085% N,N’, methyl bisacrylamide

Highly hygroscopic webs for disposable diapers

8.

Copolymer of CI–4 alkyl acrylates, CI-4 alkyl methacrylates and unsaturated C3-Scarboxylic acid

Binders for nonwovens with good impregnating properties

9.

Emulsion polymer of methyl methacrylate, ethylhexyl acrylate, methacrylic acid and acrylamide

Emulsion adhesive for heal sealing of tea bags

Contd...



23

Introduction to nonwovens

Contd... S. no

Type of binders

Applications

10

Butyl-acrylate, styrene copolymer

Self cross-linking resin for porous separator material in batteries

11.

Butyl acrylate copolymer

Adhesive tape for water proof fabrics

12.

Copolymer of Bu-acrylate, acrylonitrile and N-methylol acrylamide

Nonwoven material with improved ironability

13.

Emulsion polymer of acrylic unsaturated monomers (homo or copolymer; Tg = 2500K) and aqueous dispersion of polymers prepared by emulsion polymerization of ethylenic monomers

Aqueous dispersion type pressure sensitive adhesives for nonwoven

14.

Acrylic acid ester copolymer; blended with 20% SBR emulsion

Interlining materials with good resilience, improved tensile strength

15.

Butyl acrylate-vinyl acetate copolymer dispersion

Air permeable nonwovens with shape memory

16.

Butyl acrylate, acrylonitrile, N-methylol acrylamide copolymer

Nonwoven fabric for lining with good laundering and dry cleaning resistance

17.

Latex containing acrylic acid-2-ethyl hexylacrylate-vinyl chloride-vinylidine chloride copolymer

Polyolefin nonwovens with high wet strength retention

18.

Carbonized sulfonated styrene-di-vinyl benzene copolymer later o a suitable acrylate

Spun-bonded nonwoven protective fabric having flame resistant and flexibility

19.

Acrylic polymer emulsion blend with ethylene vinyl acetate copolymer

Stretchable wrinkle fibrous sheet

20.

Acrylic acid-acrylonitrile copolymer

Hygroscopic products for sanitary goods and sealing materials

21.

Acrylic resin modified with chlorohexidine

Antibacterial electric fiber webs for filters and wipers are prepared using the binder

22.

Emulsion polymer of acrylic acid ester, M.F. resin, organic amine

Laminated pattern paper for textile printing

23.

Acrylic polymer emulsion (Tg – 80–0°C)

Two ply nonwoven fabric laminate

24.

Cross-linkable polyacrylates impregnated with binder containing 10% silicone dispersion

Non-blocking, non cross-linking adhesively bonded fleeces

25.

Vinyl chloride emulsion blended with small amount of aminoplast

High loft polyester nonwovens.

26.

Ethylene-vinyl chloride copolymer

Laminates of nonwoven fabric with wood composite base for rear package automobile interiors

27.

Polyvinyl chloride emulsion

Antistatic finish for textile and carpet backings

28.

Vinyl chloride-vinylidine chloride- copolymer or Ethylene vinyl acetate copolymer

Chemical resistant fabrics for protective garments

Good flame resistance better wash and dry-cleaning resistance, resilience and compression recovery

Contd...

24

Nonwoven: Process, structure, properties and applications

Contd... S. no

Type of binders

Applications

29.

Vinyl chloride homo or copolymer with plasticiser and chemical stabiliser

Fire resistant particulate binders for automobile felts

30.

PVC emulsion binders

Glass fiber nonwovens with good tensile strength, breaking strength

31.

Ethylene vinyl ester-vinyl chloride copolymer binder emulsion

Composition for fabric and paper

32.

Ethylene vinyl acetate copolymer emulsion

Synthetic nonwovens for retention of volatile liquid

33.

Ethyl vinyl acetate copolymer

Adhesives for bonding textiles (polyester cotton fabrics)

34.

Polyvinyl acetate aqueous emulsion

Thermal insulating nonwoven bulky product

35.

Ethylene vinyl acetate copolymer blended with 40% SBR latex

Coated nonwoven fabric with increased oil adsorption

36.

Polyvinyl acetate, blended with lubricating oil, epichlorohydrin-polyamide copolymers

Reinforcing glass fiber material

37.

Copolymers of ethylene, vinyl acetate and N-methylol compound

Nonwoven textiles

38.

Aqueous latexes or emulsion of vinyl acetate and natural rubber

Ageing resistant, cold sealable coatings for packaging materials

39.

Polyvinyl acetate hot melt adhesive

Interlining

40.

Ethylene vinyl acetate copolymer emulsion

Highly absorptive binders for polyester nonwovens

41.

Polymer of ethylenic unsaturated carboxylic acid with ethylene or vinyl acetate and compound containing atidirine

Water-resistant binders for polyester nonwovens

42.

Vinyl butyl resin solution

Nonwoven reinforcement for composite (carbon fiber and glass fiber)

SBR BINDERS 43.

SBR latex binder, mica, titanium pigment, kaolin clay, sodium pyrophate, casein, ammonia, antifoaming agent

Nonwoven coated paper or cloth with pearly gloss, good printed gloss and printability

44.

Binder comprises a copolymer of butadiene styrene, ethynically unsaturated carboxylic acid

Nonwoven webs for sanitary use

45.

SBR latexes of acrylate polymers

High strength, high modulus interlining fabrics

46.

Emulsion of styrene butadiene, MAA, N(butoxymethyl acrylamide)

Binders for nonwoven fabrics for imparting stiffness, water and solvent resistance

47.

Carboxylated SBR (carboxy content 0.5–2%)

Alkali resistance nylon nonwoven fabrics for elastic rolls

48.

SBR latex, U.F. resin, ethylene glycol, Na CMcellulose

General adhesives for nonwovens

49.

Carboxylated SBR latex

Carpet backing adhesive Contd...



Introduction to nonwovens

25

Contd... S. no

Type of binders

Applications

50.

Copolymer latex of butadiene, styrene and acrylamide

Hydrophobic nonwoven fabrics suitable for use as diaper coverstock, prepared by bonding polyester fibers with the binder

51.

SBR latex

Nonwoven fabrics for floor covering with good pilling and wear resistance (carpet water proofing siloxane)

NBR Binders 52.

Butadiene aerylonitrile latexes

Impregnating heat sensitive binder for nonwoven fabrics

53.

Carboxyl containing butadiene acrylonitrile latex and a dispersion of chloroprene-Me methacrylate copolymer

Polyester fabric nonwoven polishing material

54.

Different binder layers of vulcanised nitrile rubber and plasticised PVC

Laminated floor covering (Floor covering consist of a base of nonwoven needle punched fabric, a layer of vulcanised nitrile rubber, and a layer of plasticized PVC)

55.

Nitrile rubber phenolic blend

Abrasive nonwoven polyester fabrics with high tensile strength

56.

Carboxylated nitrile rubber latex crosslinked with hexamethylol melamine

Nonwoven fabric lining and filtering material with high strength

Natural rubber 57.

Natural rubber

Adhesive tape coated on both sides with adhesive

58.

Phenol formaldehyde resin

Laminates of carbon fleece and graphite foil with improved flexural, compressive strength, thermal conductivity and permeability Nonwovens glass wool or rock wool for thermal insulation

59.

Water soluble phenolics, urea resins and optionally ureas

Thermosetting adhesive sheets

60.

Powdered adhesive containing hydro-quinone diglycidyl ether polymer, phenolic novolak, 2-methyl imidazole

Impregnating compositions for nonwoven glass fabric with high flexibility, elasticity and improved deformation properties

61.

Bisphenol-A epoxy resin

Waterproof sheets are prepared by forming a nonwoven fabric from blends containing melt-resistant synthetic fibers with low softening temperature and vinyl fibers on a paper making machine and then impregnating the web with melted asphalt

62.

Asphalt binder

Water resistant felt of nonwoven cloth Contd...

Other types

26

Nonwoven: Process, structure, properties and applications

Contd... S. no

Type of binders

Applications

63.

Coal tar and coal pitch 100, PVC 8–14, calcium stearate and tribasic lead sulfate 0.S-2, plasticizer 4–12, talc 50–70

Filter media are prepared by dispersing inorganic micro-fibers having negative zeta potential in the binder

64.

Thermosetting polyamine-epichloro-hydrin resin. A precipitating agent is added to precipitate the binder and coat the fibers

Glass fiber, polyester fiber (SO: 50) laminates with improved bendability

65.

Bisphenol-A epoxy resins containing 30% epoxidised polybutadiene and 20% Br

Aramid fiber nonwoven laminates for printed circuit board

66.

Epoxy resin modified with phenol or cresol novolak

Adhesives for interlinings with improved softness, shear strength, flexibility, peel strength

67.

Epoxy modified silicone emulsion, polyether modified silicone oil

Insulating nonwoven fabric

68.

Epoxy resin

Filtering material (laminated with bulky nonwoven fabric from polyester fibers and nylon fibers)

69.

Emulsion copolymer of epichloro- hydrin, bisphenol-A modified with amino polyamide and glass beads

Useful for bonding acrylic nonwoven fabrics to polystyrene (Laminates having good bonding strength)

70.

Polyesters or epoxy resins modified with cis-3methyl 4-cyclohexane, cis 1,2-di-carboxylic add or its anhydride are grafted with styrene

Luminescent nonwoven textile

71.

Acrylic or vinyl binder

Products (e.g. carpets, wall coverings) for improving orientation and safety in dark rooms, are prepared by adding a luminescent material having a long after glow, such as Cu-activated Zns, to binder or dyeing the fibers with a luminescent dye because of poor wet adhesion

72.

UV curable binder, i.e. binders, are emulsion polymers (do not contain solvent, monomer, HCHO or other toxic materials)

These binders are used in pp nonwoven fabric. UV light or UV irradiation induced reaction between binder and pp by cross-linking

73.

Polyurethane

Leather substitutes or leather-like materials

1.6.2.3

Evaluation of properties and testing of binders

Evaluation of binder adhesives is essential, (i) to assist in selecting an adhesive for a particular use, (ii) to monitor the quality of an incoming product, and (iii) to confirm the effectiveness of the bonding process. The most commonly used tests for properties of adhesive materials measure viscosity, shelf life, pot life, tack, cure rate, per cent solids and applied weight per unit area. Besides, to evaluate the performance characteristics of the binders, the following tests may also be carried out:



27

Introduction to nonwovens



• Adhesion (peel, shear, tensile cleavage) • Impact resistance • Resistance to environmental effects (heat, condensing humidity, salt spray, temperature cycles) • Flexibility • Strength retention



1.6.3 Additives Many materials apart from the constituent fibers are used in the manufacture, bonding and finishing of nonwoven webs. Some additive materials form an integral part of the nonwoven and added to the fiber or filament structure during web laying. Examples of such additives are thermally active powders and absorbents. But many of the additives are applied in one form or another to the preformed web usually after bonding and are treated as an auxiliary process.

1.7

Product properties and applications of nonwovens

The properties and application of nonwoven products based on different web formation technique and web-binding methods are given in Tables 1.7 and 1.8, respectively. Table 1.7  Properties and application of nonwoven based on web formation methods Web forming

Web bonding

Properties

Applications

Carded parallel laid

Latex Saturation, Print

• High MD strength • Low CD strength • Wet strength retention • Reasonable softness (binder selection) • Low cost

• Headrest covers • Interlinings • Cable insulation • Fabric softeners • Filtration • ‘Pop-up’ wipes

Carded crosslaid

Latex Saturation, Print

Better MD / CD tensile ration than parallel laid

• Wipes • CD liners • Dusters • Table covers / Table napkins

Carded Mechanically randomized

Latex Saturation, Print Hydroentangled

• Flexural strength • MD / CD approaching isotropic • Good wet strength • Low lint • Binder free • Absorbent substrate

• Dry and wet wipes • Filtration • Medical fabrics

Drylaid nonwoven

Contd...

28

Nonwoven: Process, structure, properties and applications

Contd... Web forming

Web bonding

Properties

Applications

Carded and airformed highloft

Latex Spray, Foam; Thermal Through-air

• Low density stabilized web

• Thermal insulation

• Layered structures

• Filtration

• Automotive liners

Wet-laid nonwoven Wet laid - Rotary former - Inclined wire

• Cellulose (hydrogen bonding) • Wet end addition of latex • Thermal bonding through the addition of fusible fibers • Inorganic binder systems

• High web uniformity • Isotropic webs possible • Moderate to high MD / CD strength • Wide web weight range 8 g/m² to 1000 g/m² and higher • 100% inorganic webs

• Surfacing veils and tissues • Filtration liquid and air • Very high temperature insulation • Low temperature cryogenics • Wall coverings • Coating substrates • Window curtains • Shoe components • Flocking substrates • Battery separators • Electrolytic layers • Roofing – glass / polyester • Teabags • Surgical wrap

Short Fiber Airlaid

• Hydrogen bonded (point pressure)

• Lower strength but no added binders

• Food contact absorbent products

• Hydroentangled / thermal

• Web produced with bicomponent fibers initially hydroentangled and then thermally set

• Feminine Hygiene products • Acquisition layers • Wipes

• Top end of market product – reduced (zero) linting • Improved strength Spunbond nonwoven Spunbond Polypropylene – lightweight

Thermal

• Improved strength breathability

• Medical gowns

• Resistance to fluid penetration

• Sterilizable packs

Lint free • Sterilizable (some systems) • Can be made impervious to bacteria

• Shoe covers • Baby diaper coverstock • Feminine hygiene • Adult incontinence • Composites – protective clothing

Contd...



29

Introduction to nonwovens

Contd... Web forming

Web bonding

Properties

Applications

Spunbond Polypropylene – heavy weight

• Thermal

• Chemical / Physical stability • High strength / cost ratio

• Building wrap • Geotextile – drainage • Stabilization • Erosion control • Automotive trim • Carpet backing

Spunbond Polyester – heavy weight

• Thermal / Thermal set

• High temperature stability • Porosity / strength

• Roofing substrates • Geotextiles (some soil types)

• Thermal

• High strength / low web weight very soft with low temperature bonding

• Coverstock

Meltblown Polypropylene

• Thermal

• Microfiber structures 10–20 microns 1–5 micron L  ess than 1 micron • Microfiber structure • High opacity

• Oil absorption • Barrier (composite) layers • Filtration HEPA and ULPA artificial leather • Thermal insulation (clothing) • Acquisition layers sanitary napkin and panty shields

Meltblown Elastomeric

Stretch bonded

Elastic structures

• Side panels in Training pants • Feminine hygiene products

Meltblown Poly vinyl alcohol

Thermal

Water dispersible

Flushable products

• Needlepunch

• Needlepunch Spunbond Bicomponent

Meltblown nonwoven • Electric charging

Table 1.8  Properties and application of nonwoven based on web bonding methods Bonding technology

Binder type

Application method

Positive aspects

Negative aspects

Applications

Mechanical Bonding Mechanical – needlepunch

• Uses web matrix fiber • Sometimes combined with latex and/or thermal

• Use of purpose built needle looms such as DILO, FEHRER, ASSELIN etc.

• Strong bonded fabrics without additional binders particularly suitable for heavy weight and high denier fabrics

• Not very suitable for low web weights

• Geotextiles • Roofing • Automotive • Carpet backings

Mechanical – stitchbonding

• Uses web matrix fiber • Most stitchbonded fabrics are made with added threads

• Use of purpose built machines such as MALIMO, ARACHNE, MALIWATT etc.

• High productivity compared to knitted fabrics

• Low output rate compared to other nonwoven processes

• Furniture/ furnishings • Automotive • Shoes • insulation

Contd...

30

Nonwoven: Process, structure, properties and applications

Contd... Bonding technology

Binder type

Application method

Positive aspects

Negative aspects

Applications

Mechanical – hydroentanglement

•U  ses web matrix fiber

• Use of purpose build machines with high energy water jets such as REITER PERFOJET, FLEISSNER etc

• Binder free materials

• High cost (slowly reducing) of process and equipment

• Medical fabrics

• Acrylics

• Impregnation

•S  tyrene/ butadiene

• Spray

• Loss of porosity and absorbency

• Roofing polyester and glass

•E  thyl vinyl acetate

• Print bond

• Web saturated with binder – maximum strength • Useful for high loft webs

• Stiffness

• Flooring

• High drying energy requirement

• Batts

• Good housekeeping essential to avoid contamination

• Short fiber airlaid

•C  an be combined with thermal and/or latex bonding

• Very good strength/ stiffness relationship • Lint free webs • High absorbency

• Significant ‘learning’ curve

• Wipes • Coating substrates • Furnishing fabrics • Protective clothing

Chemical Bonding Chemical latex

•N  itriles •E  lastomers

• Foam • Precipitation (wetlaid only)

• Economical Surface only effect

•P  VC

• Much lower energy required • Penetrates web without blocking • Bonded area controlled by print pattern • Absorbency maintained • Incorporation of colours and other chemical treatments

• Highloft nonwovens

• Battery separators • Medical

• Modern strength

• Wall coverings

• Loose fibers in non-bonded areas

• Flooring substrates

• Can be difficult to control

• Ceiling tiles

• Wipes • Medical • Gaskets • Book covers

• Loose surface fibers

• Ceramics

• High temperature insulation

• Deposits binder in web formation stage

• Battery separators

• Good strength per unit of binder Chemical inorganic

•H  ydrated aluminium hydroxide

• Wet deposition

• High temperature binders

• Stiffness

• High intensity heated calender

• No added binder

• Bonding only at densified points

•H  ydrated silicic acid Chemical hydrogen

•U  ses the ability of cellulose to form hydrogen bonds when water is present

• Low (but adequate) strength

• Feminine hygiene • Food contact absorbents

Contd...



Introduction to nonwovens

31

Contd... Bonding technology

Binder type

Application method

Positive aspects

Negative aspects

Applications

Chemical solvent

•U  ses solvation of surface layer of matrix fiber

• Gas/liquid treatment usually at raised temperature

• No added binder

• Partly solvated surface

• Building wrap nylon spunlaids

• Matrix • Used with polyester calender, through-air or ultrasonic application of heat

• Chemical nature of ‘binder’ same as main component fiber • Physical properties maximised for a given bond area

• Bonded area can be destroyed under tensile stress (point bonding)

• Point bonded spunlaid and meltblown webs • Point bonded carded web of polypropylene • Coverstock • Leg cuff materials • Wipes • Protective clothing • Cloth-like backsheets

• Sprinkle bar addition onto pre-formed fiber web • Fused by application of heat in flat oven

• Open bonded structure (highloft) • Re-loftable fabrics

• Some powder binders difficult to retain in web

• Clothing insulation • Filtration • packaging

• Fiber added at web forming stage

• Range of bicomponent fibers now available • Good bond strength • Bond cellulose fibers effectively • Absorbency largely retained

• Surface fiber linting • Relatively low strength fabrics produced

• Pre-formed absorbent products by short fiber airlaid technology • Thermoformable webs

• Melted by heat • Fibers added at web forming stage

• Useful for bonding inorganic fiber webs

• Brittle bonds • Requires additional ‘green strength’ binder

• Ceramics • Silica • Alumina • High temperature insulation

Thermal Bonding Thermal – fusible fibers

•P  olyethylene •P  olypropylene •C  opolyesters

Thermal – fusible powder

•P  olyethylene •C  opolymers •C  opolyesters

Thermal – bicomponents

•P  P/PE •P  ET/CoPET •P  P/PA •P  VALC/PE etc

Thermal – high temperature fusible fibers

•G  lass

References 1. ASTM (1989). Annual Book of Standards. ASTM Standards. 2. Batra SK, Hersh SP, Barker RL, Buchanan DR, Gupta BS, George TW, Mohamed MH (1989). A New System for Classifying Nonwovens. Eds Turbak AE, Vigo TL, Nonwovens – An Advanced Tutorial. TAPPI Press.

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Nonwoven: Process, structure, properties and applications

3. Batra SK, Pourdeyhimi BP (2012). Introduction to Nonwoven Technology. DEStech Publications, Lancaster. 4. Baumgarten PK (1971). Electrostatic spinning of acrylic microfibers. J of Colloid and Interface Sci 36:71–79. 5. Bognitzki M., Czado W., Frese T., Schaper A., Hellwig M., Steinhart M. (2001). Nanostructured fibers via electrospinning. Adv Mater 13:70–72. 6. Challenges & Opportunities for Nonwovens Global & Regional Market Trends, ITMF Annual Conference ITMF Annual Conference, 6th November, 2012. www.edana.org. Accessed on November 2, 2014. 7. Dan Li, Younan Xia (2004). Electrospinning of nanofibers: Reinventing the wheel? Adv Mater 16(14): 1151–1170. 8. Doshi J, Reneker DH (1995). Electrospinning process and applications of electrospun fibers. J Electrostatics 35(2–3): 151–160. 9. EDANA (1989). Definition of Nonwovens ISO 9092: 1988. http://www.edana.org/ story.cfm?section=edana_nonwovens&story=definition.xml. Accessed on February 12, 2015. 10. Emerging Market Opportunities for Nonwovens Companies. http://www.inda.org. Accessed on November 12, 2014. 11. Gamayunov NI, Kalabin AL, Svistunov VA (1994). Simulation of diffusion in bicomponent fibers of the core-cladding type. Theore Found Chem Eng 28(3): 257– 259. 12. Hansen SM, (1993). Nonwoven Engineering Principals. Ed Turbak AF, In Nonwovens: Theory, Process, Performance and Testing. TAPPI Press. 13. Hoon Joo Lee, Nancy Cassill (2006). Analysis of World Nonwovens Market. J Text Appar Techno Manage 5(3): 1–19. 14. Houfek WE (1993). Nonwoven Terminology. Ed Turbak AF, Nonwovens: Theory, Process, Performance and Testing. TAPPI Press. 15. INDA (2004). Worldwide Outlook for the Nonwovens Industry: 2004–2009. Cary, NC, USA. 16. INDA (2006). The Absorbent Hygiene Industry in North America 2006–2011, Cary, NC, USA. 17. INDA (2007). Worldwide Outlook for the Nonwovens Industry: 2007–2012, Cary, NC, USA. 18. Irwin Hutten (2007). Handbook of Nonwoven Filter Media. Elsevier Science & Technology Books, UK. 19. Krema R (1971). Manual of Nonwovens, Textile Trade Press. 20. Man-Made Fiber and Textile Dictionary (1988). Hoechst Celanese Corp. 21. Morris HC, Mlynar M (1995). Chemical binders and adhesives for nonwoven fabrics. INDA-TEC St. Petersburg USA. 22. Mukherjee AK, Mohanty RK, Sriram N, Barar P (1992). Adhesive binders for



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nonwoven fabrics, International conference on Nonwovens, Textile Institute, North India Section, Porritts and Spencer, India. 23. Nonwoven fabrics market overview of India. https://nonowovenindustryupdate. wordpress.com. Accessed on November 14, 2014. 24. Nonwovens Mission 2020. http://www.edana.org. Accessed on November 12, 2014. 25. Nonwovens to 2016-Demand and sales forecasts, market share, market size, market leaders. www.freedoniagroup.com. Accessed on November 14, 2014. 26. Nonwovens: Tutorial, http://www.thenonwoveninstitute.com. Accessed on March 5, 2015. 27. Russell SJ (2007). Handbook of nonwovens. CRC Press, Cambridge. 28. Schoffmann E, Schwend F (1991). Meeting trend developments in wet forming. TAPPI Nonwovens Conference, Marco Island, USA. 29. Seshadri Ramkumar (2012). Nonwovens: Product Applications Trends – World and India. Techtextil India Symposium. 30. Thandavamoorthy Subbiah, Bhat GS, Tock RW, Parameswaran S, Ramkumar SS (2005). Electrospinning of nanofibers. J Applied Polym Sci 96: 557–569. 31. The Dictionary of Paper (1980). American Paper Institute. Inc. 32. Wakeman RJ (1985). Filtration Dictionary and Glossary. The Filtration Society, UK. 33. Walton JH (1996). Low formaldehyde, high performance nonwoven binders for airlaid pulp applications. INDA-TEC 96 Crystal City, USA. 34. Wilhelm Albrecht, Hilmar Fuchs, Walter Kittelmann (2003). Nonwoven fabrics: Raw Materials, Manufacture, Applications, Characteristics, Testing Processes. WILEYVCH Verlag GmbH & Co. KGaA, Weinheim. 35. Young GC (1996). Waterborne epoxy resin systems for the use as binders in nonwovens and textiles. TAPPI Proc Charlotte, USA. 36. Zheng-Ming Huang, Zhang YZ, Kotaki M, Ramakrishna S (2003). A review on polymer nanofibers by electrospinning. Comp Sci Tech 63: 2223–2253.

2 Web formation

Abstract: This chapter discusses about the various methods of web formation such as dry laid, wet laid and spun laid for nonwoven production. The details of raw material requirements, working mechanism and characteristics of dry laid and wet laid process have also been provided. The fibre preparation methods, card and various kinds of web stacking process such as parallel lay, cross lay, perpendicular lay and random lay have been discussed in detail. The raw material requirements and product characteristics of polymer-laid processes such as spunbond and melt-blown are discussed in detail. Key words: batt, dry lay, wet lay, air lay, spunbond, melt blown

2.1 Introduction Nonwoven manufacturing is basically a continuous process in which the web laying and web bonding are performed by two consecutive machines. A web is nothing but a thin layer of fiber distribution. In the web laying process, several webs are laid on top of each other to form a batt, which is taken directly to bonding. Nonwoven can be classified based on web formation techniques as shown in Figure 2.1. Web formation from

Staple fiber system

1. Dry Laid   • Carding   • Aerodynamic (Air lay)   • Centrifugal dynamic (Random carding) 2. Wet laid

Polymer system

1. Spunbond 2. Meltblown

Figure 2.1  Classification of nonwoven based on web formation techniques



Web formation

35

Wet and dry laid technologies are the main methods of batt formation. Alternative methods of batt formation like the spunbonding and meltblown technologies were developed later. The contributions of each web laying technology to the entire nonwovens market are: Wet laid nonwovens – 16.0%; dry laid nonwovens – 44%; air-laid – 3%; spunbonding and meltblown about – 37% (Russel 1997, Balasubramanian 2009). Versatility, process flexibility and ability to produce wide range of products make the dry lay systems more popular. The wet lay technology has been adapted from the paper-making industry, which processes very short fibers into highly even web structures with good flow through properties. The polymer-based web forming system is based on the polymer extrusion technology. This system is similar to the synthetic filament and yarn manufacturing process. It has two major subdivisions: the spunbonding process and the meltblown process. In the spunbond process, the polymer chips are converted into a molten form and forced through the small holes in the spinneret (Balasubramanian 2004). The web structure is formed by collecting and condensing the extruded individual filaments from the spinneret on a forming apron. The second system is the meltblown process. The molten polymer being extruded at the spinneret is subjected to hot, rapidly moving air at the extrusion point. This causes the extruded filament to be blown into very fine fibers of variable length which are received on the collecting surface.

2.2

Staple fiber web formation system

2.2.1

Dry-laid process

The staple-fiber-based web laying process involves three major steps. They are fiber preparation (by opening and mixing processes), web formation (by carding or by air-lay processes) and finally web stacking (by parallellay, cross-lay, and perpendicular-lay processes). Hence, the staple fibers are processed into a uniform web or batt structure with the required weight per unit area (Balasubramanian 2009). All staple fibers which are capable of being carded or dispersed in air or water can be used in this process. The sequence of operations in the dry-laid process is highlighted in Figure 2.2. The nonwoven processing sequence is similar to the short staple yarn manufacturing process to some extent. Yarn manufacturing requires greater levels of fiber opening and has more processing stages after the carding stage to achieve uniformity in the final product. However, nonwoven manufacturing does not involve extensive fiber opening and the scope for improving the product levelness is limited. The nonwoven line must be designed with intense

36

Nonwoven: Process, structure, properties and applications

opening and blending stages before carding and the card should be capable of achieving higher level of opening. Raw material (Natural fibers, man-made fibers, inorganic fibers)

Preparation (Opening to loose material, blending)

Web forming 1. Carding process (Parallel laid, cross laid) 2. Aerodynamic process (Random laid web)

Web bonding (Mechanical bonding/thermal bonding/ chemical bonding)

Processing (Finishing, dyeing, printing, coating)

Product (Fiber nonwoven)

Figure 2.2  Dry-laid manufacturing process

The nonwoven lines can utilize either the short-staple revolving flat cards or long-staple roller cards on a theoretical basis. The short-staple revolving cards have certain advantages like higher production rates and higher opening power (especially in terms of per unit of floor space occupied). The major drawback pertaining to short-staple cards is their very narrow operating widths. This drawback is overcome by the long-staple cards which are many times wider, making them much more suitable for nonwoven manufacture. Since many end applications require wider width nonwovens, the long staple cards are highly preferred in most cases (Russel 1997). A typical nonwoven



Web formation

37

line comprises of automatic fiber opening and blending machines followed by automatic feeding to one or more wide long staple cards. Autolevellers are installed in the cards to control the mass per unit area of the output web. 2.2.1.1

Fiber preparation The initial stage in the batt preparation process is fiber opening. Depending upon the nature of the fiber i.e., cotton or synthetic fiber, the opening line installation is varied. In case of synthetic fibers, the blending line generally comprises a hopper bale opener or a pair of bale openers feeding to a cross lattice. The delivery end of hopper bale opener is provided with autolevellers to achieve uniform material throughput to the next machine (www.dilo.de). Typical fiber opening line for processing of nonwoven is shown in Figure 2.3.

Figure 2.3  Typical blowroom line for processing of nonwoven [Source: http://www.laroche.fr/]

Fiber opening machine The fibers, which are the raw materials for the nonwovens line, are supplied in the form of dense press-packed bales. These bales must be opened prior to carding. In high production installations, it is necessary to ensure sufficient reduction in tuft size to provide consistent fiber feeding to the card. The volume of opened fiber is influenced by the fiber type, fiber fineness, crimp and stiffness. Hence the same machine settings cannot be used to process fibers having different specifications. The need for opening • The fibers must be reduced to the smallest aggregate form in order to clean, mix and blend them. This process of re-opening the baled

38



Nonwoven: Process, structure, properties and applications

material into small tufts becomes essential as only well-opened material can be effectively cleaned. • The fibers must be thoroughly opened to enable blending. • The fibers must be prepared for the carding operation by opening to the extent where there will be minimal fiber damage.

The need for cleaning For effective nonwoven fabrication, the trash and other impurities contained in the cotton received must be removed as completely as possible. Synthetic fibers do not require intensive cleaning as in the case of cotton fibers. The factors influencing cleaning are: • Trash and other impurities are separated from cotton by the action of centrifugal force. • The material is moved at high speed in a circular motion. • The trash particles which are heavier than the fibers tend to sling out from the fiber surface. • Grid bars facilitate the trash to escape and separate from the fibers that pass over the grid bars. • The grid bars settings namely grid bar angle and spacing influences the quantity of trash removed. • Increasing the grid bar opening also increases the amount of good fibers that are lost along with the trash. • In general, the good fibers lost in the waste should be maintained at a minimal level. However, in instances where maximum cleaning is required, higher good fiber loss is inevitable. • New tuft surfaces must be generated continuously to facilitate cleaning. • It is relatively easier to remove larger and heavier trash particles from the fibers. • Beating devices tend to break large trash particles causing fragmentation of the trash particles. These smaller particles make the cleaning process more difficult. For this reason, large trash particles should be removed at the beginning of the cleaning process. • The transport air carries the extremely small trash particles along with the fibers and it is difficult to separate them. These dust sized particles are removed by condensers and fiber separators. The conventional machines developed for the processing of cotton and wool fibers have been customised for the purpose of fiber opening in nonwoven production lines. For most of the applications, the multi-roller



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39

openers, the tearing machines or the small openers serve the purpose. Fibers of staple length up to 100 mm can be sufficiently opened by the small openers. For opening of polyester fibers, the single roll openers are more suitable. Whereas cotton or viscose rayon fibers have more entangled tufts and require multi-roller openers (Rupp 2012). (1) Bale openers The nonwoven industry incorporates a fiber preparation process which is very similar to the process carried out in a conventional blowroom line. Figure 2.4 illustrates a bale opening machine. Several bales can be arranged on either side of the wide bale opening machine according to the requirement. The arranged bales may be composed of the same fiber or a combination of several fibers to obtain the required blend. The bale opener opens the fibers from these bales and mixes them to a certain extent (Rakshit et al. 1989).

Figure 2.4  Schematic representation of a Bale breaker (Courtesy: Trützschler GmbH, Germany)

(2) Opening and cleaning machines The fibers spanning up to about 100 mm in length can be opened efficiently using fine openers. These fine openers are placed horizontally or vertically in the nonwovens line and can also be accommodated in feeding units, chutes and blending hoppers. Synthetic fibers like polyester are opened using single roller openers whereas bleached cotton or viscose rayon fibers are heavily entangled and make use of multi-roll openers for opening. The Cleanomat Cl-C3 Cleaner (Figure 2.5) can be universally employed as a fine cleaner in the cotton processing lines. This stand-alone cleaner has been designed for processing cotton with medium soiling. The fibers from the

40

Nonwoven: Process, structure, properties and applications

bale opener are transported over the feed lattice (1) and then to the pressure rolls (2). The two feed rolls (3) uniformly transport the fibers to the needle roll or fully spiked roll (4). The fully spike roll then transfers the fibers to the coarse or medium saw-tooth roll (5), which is followed by the fine saw-tooth roll (6). The exhaust unit (7) transports the cleaned fibers to the next machine.

Figure 2.5 Arrangement of beaters in Cleanomat (Courtesy of Trützschler GmbH, Germany)

(3) Blending machines The differences in varieties, countries, regions, climatic conditions, farming methods, harvesting and storage techniques have a considerable influence on the properties of the natural fibers. This variation of properties can also be observed within the fibers of one cotton-boll. The fibers vary in all their



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basic properties like length, fineness, strength, colour and maturity. Impurities of various kinds are also present in the baled cotton. Every production line aims to produce nonwovens with high levels of uniformity and maximum efficiency (Balasubramanian 1991). To achieve this, homogeneous and consistent blending must be ensured. The price of cotton fibers also influences the composition of the raw materials. Every quality of nonwovens has a corresponding market value. Whenever some lower quality fibers are used for reducing the manufacturing costs and enable, these fibers require careful handling and blending to avoid processing problems. The quality of blending is a crucial parameter influencing the web characteristics. The blended fibers should have consistent proportion in all instances to minimise product variations as the properties of a nonwoven fabric are fundamentally the function of the blend composition. Inefficient blending leads to various in process as well as quality oriented problems. An example of a type of blending machine, the multimixer from Trutzschler is shown in Figure 2.6. The multimixer is designed with a series of individual silos into which fiber is alternately fed.

Figure 2.6  Multimixer blending machine (Courtesy: Trützschler GmbH, Germany)

The fibers enter through the connection for material feed (1) and fill the trunks (2) by means of an external fan. The next machine in the line is mechanically coupled with the conveyor belt of the feed lattice (10). Depending on the material requirement by the subsequent machine, the fibers are drawn out of the trunks by the delivery rolls (6) and the continuously running opening rolls (7). These drawn out fibers are thrown onto the conveyor belt (8). The feed lattice (10) and the pressure apron (9) receive the fibers

42

Nonwoven: Process, structure, properties and applications

from the conveyor belt. The feed lattice transfers the fibers to the subsequent machine. For trouble-free running, any accumulations of impurities are continuously extracted via the waste tray (11) and are fed into the pipeline for dust exhaust (12). During running, a least one trunk remains unobstructed and receives fibers from the previous machine. The trunks are filled in sequence until the set pressure is reached. In the instance of all top light barriers (4) being obstructed when the flaps (3) are switched to the next trunk, the material feed will turned off. To sustain the corresponding pressure on the fibers in the trunks, the material transport fan is always kept in operation. When the mixer is full, the flaps of the trunks (3) continue switching in a one minute cycle to avoid turbulence disturbing the material in one of the trunks. As soon as one of the upper light barriers (4) becomes free again, new fibers will be fed into that trunk. (4) Tuft blender (Dosing system) The tuft blending installations as in Figure 2.7 provide flexibility in the manufacturing process – 2 to 6 different types of fibers can be blended to cover a wide application range including even the addition of smallest portions (e.g. 1% black fibers / 99% white fibers). The blends can be reproduced with consistent high-end quality. The continuous dosing system for accurate blending of fibers is shown in Figure 2.8. The most widely-used dosing systems are: 1. Weighing pan system 2. Roller weighing system 3. Scanfeed system

Figure 2.7  Tuft blender (Courtesy: Trützschler GmbH, Germany)



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Figure 2.8  Continuous dosing system (Courtesy: Trützschler GmbH, Germany)

Depending upon the production volumes, different types of dosing systems are available. Blending systems with weighing baskets ensuring extremely accurate weighing values (±1%) are utilized in the case of medium-low productions (up to 350 kg/h). Weighing hoppers with special designs to lower the ratio between the mass of the weighed fiber and the mass of the empty hopper facilitates high levels of accuracy. Aerodynamic mixing systems are preferred medium-high productions (up to 700 kg/h). These systems provide precision levels of ±2.5%. The aerodynamic mixing systems finely open the fibers of each component in the blend initially and then mix them in an air for a homogenous distribution of the fiber blend. Continuous blending systems with a precision of ±3% are preferred for high productions (up to 1000 kg/h). In this system, the required quantities of fibers are accurately carried by electronic weighing belts and are laid on a transverse conveyor mat to form a homogeneous lay-up with the required fiber types. A final opener will open and thoroughly mix this homogeneous fiber lay-up (Rupp 2012). (5) Auxilliary systems • Metal detectors: The fiber bales supplied to the industry may contain metal particles in the form of wire, screws, card clothing, small machine parts, spikes from conveyors, and any number of unusual objects sometimes occurs. This makes it essential to install metal detectors in the processing line to eliminate the risk of machinery damage and fire accidents. The ‘magnetic hump’ is the most basic version of metal detectors. In this case, powerful magnets are placed at several points to catch the metal particles. These magnetic hump units are fitted in-line within the fiber transportation ducts. Microprocessor controlled diverting devices can also installed along with the ductwork to detect metal particles. When metal particles are detected, these devices open the duct to divert the contaminated fiber to a holding bin where the metal is manually separated and the fiber can be recovered.

44

Nonwoven: Process, structure, properties and applications

• Fiber lubrication and spray systems: In most cases, the manmade fiber manufacturers provide fibers applied with spin finish oil, and fiber lubrication during processing is not required. However, to improve blending some liquids can be added. As a general practise, lubricants are added while processing natural fibers and anti-static agent are included for synthetic fibers. In some cases, the water alone is added to facilitate efficient processing. Spray systems accurately dose and apply the required additives directly onto the fiber. Water can also be added using an atomiser which sprays a fine mist prior to carding. • Buffer zones: Buffer zones providing interim storage are essential to ensure continuous material flow through the machine. These are usually in the form of silos with delivery rolls at the base (Figure 2.9). Such storage devices can be used within the blending machines and also between blending and carding machines for supplying the materials continuously.

Figure 2.9  Storage trunk (Courtesy: Trützschler GmbH, Germany)

(6) Chute feeder The chute feeder serves as material buffer between blending line and card feeding (Figure 2.10). It features feed rolls and a pinned opening roller that ensures uniform card feeding with small tufts. The speed of the feed rolls is continuously adjusted (Contifeed) via a pressure monitoring system that monitors the filling level in the downstream card feeder. This guarantees a consistently high web quality in the finished product.



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Figure 2.10  Contifeed feeding system (Courtesy: Trützschler GmbH, Germany)

2.2.2.2 Card

The fibers after opening and cleaning are supplied to the carding machine. The carding process aims at separation of small tufts into individual fibers and parallelization of fibers and to produce uniform webs. The major functions of the carding process are: • Individualization of fiber tufts to almost single fiber • Mixing of fibers to average out variations in fiber characteristics • Forming a homogenous web of uniform weight per unit area Roller and clearer type cards are widely used in the nonwoven industry. The parallel laying process alone utilizes revolving flat cards. In contrast to the revolving flat card, the roller card consists of a larger main cylinder, ranging from 2.5 to over 5 meters in width. Spirals of sharp pointed and fine gauge wire are used to cover the cylinder. A chute feeds the fibers from the blending machine to the card. The primary function of the chute is to convert the loose fiber into a compact mat of consistent density and to continuously feed this mat to the card. The wire points on the main cylinder collect the fibers from the feed rollers. Usually the main cylinder follows a breast roller. The tandem type card with breaker and finisher cylinders can also be found in the nonwoven industry. Figure 2.11 illustrates a roller top card. This card is quite identical to the revolving flat card in its basic features with major differences in the design of the main carding fields region. Above the main cylinder are pairs of smaller wire covered rolls. The largest of the pair is called the worker roll. The worker roll collects fiber from the main cylinder. This process straightens the fiber and aligns it somewhat in the machine direction. This action also creates some blending of the fibers

46

Nonwoven: Process, structure, properties and applications

1 – Drawing in roller; 2 – Feed roller; 3 – Compacting roller; 4 – Licker-in; 5 – Worker at lickerin; 6 – Clearer at licker-in; 7 – Transfer roller; 8 – Main cylinder; 9 – Worker at main cylinder; 10 – Clearer at main cylinder; 11 – Doffer; 12 – Stuffing roller; 13 – Take-off roller

Figure 2.11  Universal Roller Card (Courtesy: Spinnbau GmbH, Bremen)

which is a distinct advantage of the roller type card. The smaller roll behind the worker roll is called the stripper roll. It is designed to take the fiber from the worker roll and transfer it back onto the main cylinder where it is passed forward to the next set of rolls. The action of worker and stripper against the main cylinder is shown in Figure 2.12. In front of the main cylinder, one or two additional wire covered rolls, called doffer rolls, are positioned to remove a certain percentage of fiber



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from the main cylinder. The diameters of the doffer rolls are smaller than the diameter of the main cylinder. As the fibers are deposited onto the doffer roll from the main cylinder, a condensing action occurs. This condensing action creates some fiber to fiber cohesion which is needed to hold the web structure together as the web is transferred from the doffer roll. The use of more than one doffer roll allows for faster removal of fiber from the main cylinder and, therefore, more pounds per hour delivered.

Figure 2.12  Action of Worker and stripper in card (Courtesy: Spinnbau GmbH, Bremen)

The wire points on the worker roller oppose the wire points on the cylinder to establish a point-to-point relationship. As the cylinder rotates, it conveys the fibers towards the worker. When the fiber passes below the worker teeth, some of the fibers are trapped on the worker teeth owing to the lower surface speed of the worker. The fiber tufts which are partly trapped on the worker and also trapped on the cylinder undergo a separation or carding action. The fibers trapped by the worker are carried around as the roller rotates. The stripper removes the fibers from the worker and re-presents them back onto the cylinder. On the whole, the ‘working’ action occurs initially between the worker and the cylinder followed by the stripping action takes place between the stripper and the worker (Russel 1997). This series of actions represent the fundamental operational function of a carding machine. Hence, the fibers are progressively ‘worked’ and ‘stripped’ within a carding machine for individualisation and parallelisation of fibers to produce a homogeneous web. The striking difference between the nonwoven card and roller and clearer card is the presence of a randomising roller between cylinder and doffer. The preferential longitudinal orientation of fibers in the web is altered to a more random orientation by the action of the randomising cylinder. Randomising roller rotates is shown in Figure 2.13. The randomising cylinder is made to rotate in a direction opposite to that of the main cylinder. The wires on this roller are wound in inclined angle

48

Nonwoven: Process, structure, properties and applications

to facilitate the randomising effect. The aerodynamic forces are largely responsible for transferring the fibers from main cylinder to randomising roller. Part of the fibers on randomising roller is also fed back to main cylinder. These actions tend to change the fiber orientation to a more random direction. The speed ratio between randomising roller and main cylinder is the prime factor controlling the extent of randomisation. The condensing rollers located between doffer and take off roller also produce some randomising effects. The randomising roller and condensing rollers improve the cross direction to machine direction strength (denoted as CD/MD) from 5:1 to 1.5:1. When a prominent longitudinal orientation of fibers is desired in the end product, the condensing rollers can be detached and doffing is done directly (Rakshit et al. 1989).

1 – Delivery roller; 2 – Doffer; 3 – Random roller; 4 – Cylinder; 5 – Transfer roller; 6 – Breast cylinder; 7 – Licker-in; 8 – Feed roller; 9 – Worker and stripper; 10 – Condenser rollers

Figure 2.13  Nonwoven single card (Balasubramanian 2009)

For achieving better opening and fiber individualisation of fibers, the tandem type nonwoven cards are preferred. A typical nonwoven tandem card is illustrated in Figure 2.14. Tandem card provide better individualisation of fibers and neps removal efficiency. Machinery manufacturers have designed double doffer cards to increase the web thickness and card productivity (Figure 2.15). In the Bremen double doffer card, there is an option to turn the top and bottom webs by 90°, using a web deflector to lay both the webs side by side so as to get double the width.



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1 – Doffer; 2 – Random roller; 3 – Finisher cylinder; 4 – Transfer roller; 5 – Breaker cylinder; 6 – Breast cylinder; 7 – Feed roller; 8 – Worker and stripper; 9 – Worker and stripper

Figure 2.14  Tandem card (Source: Spinnbau, Germany)

1 – Conveyor lattice; 2 – Doffer; 3 – Random roller; 4 – Cylinder; 5 – Transfer roller; 6 – Breast cylinder; 7 – Licker-in; 8 – Feed roller; 9 – Worker and stripper; 10 – Random roller; 11 – Doffer; 12 – Condensing rollers; 13 – Take-off rollers

Figure 2.15  Double doffer nonwoven card (Source: Spinnbau, Germany)

Batt uniformity The critical parameter influencing the appearance, strength and all other properties of nonwovens is the weight uniformity of batt produced. A typical nonwoven is expected to have weight uniformity of ±2.5%. The batt uniformity is directly controlled by the uniformity of the web from the card

50

Nonwoven: Process, structure, properties and applications

and the number doublings in crosslapping. The following in feeding systems contribute to web uniformity in the card: 1. Continuous volumetric feeding 2. Non continuous feed from weighing hopper and micro weighing systems 3. Autolevelling Continuous volumetric feed The material inside the hopper feeder chute is always maintained at the set weight by employing photo cells or pressure transducers in the feed trunk of the chute feed system. The filling of fibers across the entire width of the trunk gives rise to some variation, which is balanced automatically by adjusting the material flow (Malkan 1989). The Hergeth and Spinnbau cards are provided with vibratory arrangements to eliminate void spaces in the trunk and maintain uniform filling height across the width (Figure 2.16).

Figure 2.16  Vibrating chute arrangment (Courtesy: Spinnbau GmbH, Bremen)

In the case of Thiebeau card and Hergeth, ultrasonic control sytem is used. Ultrasonic signals monitor the density of the feed across the width and send corresponding signals to control the frequency of joggle units to maintain a uniform feed density in cross as well as longitudinal directions. In addition to these technologies, Hergeth employs a gravimetric fiber metering system in the blending line to ensure a constant flow of material. Trutzschler has developed a different system known as web profile integrated tuft feeder system to ensure web uniformity (Parikh et al. 1999).



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1 – Spring loaded sectional flap; 2 – Feed roller; 3 – Opeing roller; 4 – Feed trunk; 5 – Web thickness adjustment; 6 – Delivery roller; 7 – Spring loaded sectional measuring tray; 8 – Conveyor belt; 9 – Card feed roller; 10 – Licker-in

Figure 2.17  Scan Feed Tuft Feeder (Source: www.nptel.ac.in)

The tufts from opening roller section are drawn by a fan into an upper trunk. The filling height is maintained constant by pneumatic pressure controlled by combs covering air inlet. Feed roller at the lower end of trunk feeds the material through a spring weighted feed plate to an opening roller. Opened tufts are fed to lower trunk. The fibers are blown by air into lower trunk and as air takes line of least resistance, uniformity across the width is maintained. The fiber mass in lower trunk is pneumatically compressed and the sheet is fed to a feed roller through a spring weighted segment. Material thickness is automatically adjusted by the spring pressure on the segments of feed plate. An optimal supplement is the web profile unit which improves uniformity both in longitudinal and cross directions. Selective web profile across the width can also be obtained with web profile unit (Rakshit et al. 1989). Micro-weighing system The micro weigh system, developed by Heigh chandwick and Temafa, is designed to reduce variations in feed sheet to card (Figure 2.18). The microprocessor controls the entire system comprising of a sensitive weigh pan provided with pneumatically activated shutters solenoids, which inturn is

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Nonwoven: Process, structure, properties and applications

mounted on transducers. The small tufts are capable of being dropped into the pan with an accuracy level of ±2 g. The actual weight of the pan is constantly compared with the required mass and when the required weight is attained, the microprocessor opens the weigh pan to drop the material into the chute feed. Hence this configuration reduces the batch to batch variation to as low as ±1%.

Soilnoid

Micro weighing pans

Figure 2.18  Micro-weighing system

Autoleveller The following type of autolevelling (Figure 2.19) is commonly used in the industry. • The feed sheet to the card is passed over the balance and the thickness is monitored by a sensitive load beam transducer. The force acting on the beam generates a corresponding signal to control the speed of feed rollers.



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Figure. 2.19  Scanning of feed weight

In the NSC Nonwovens line, the batt fed to the card is continually monitored by 4 weighing gauges and front roller speed is altered in accordance to the measured weight. An alternative system measures the batt density with reference to a constant thickness and changes feed roller speed. Spinbau controls the feed roller speed based on the weight of the batt which is measured by an electronic belt weigher (Balasubramanian 2009). Web monitor The web from the card is passed through the WIRA Web monitor, which consists of a pair of rolers. The small top roller acts as the measuring roller i.e., the thickness variation in the web is assessed by the vertical movement of top roller coupled with a transducer. The deviation from the set value is used to adjust the speed of feed roller. Apart from these feeding systems, the basic method of improving the batt uniformity is to produce finer finer card webs accompanied with proportional increase in the number of doublings in crosslapper. Card clothing The nonwoven roller and clearer cards are generally installed with Garnett type interlocking wire. In the case of wire damage, it is sufficient to rework the damaged strips alone which lowers the maintainance costs. Hence these interlocking wires are preferred in the industry. Finer fibers require the use of finer type of wire clothing for cylinder and worker rolls. Wire point density details are mentioned in Table 2.1. While processing coarser fibers, the wire

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Nonwoven: Process, structure, properties and applications

height for cylinder, worker and doffer should be higher than that for finer fibers. For easy transfer of fibers, doffer wire has greater front angle and height than that of the cylinder and random roller wires (Crook 1993). Table 2.1  Wire point density for various parts of card (PPSI) (Balasubramanian 2009) Card part

8–30 den

1.5–6 den

Feed Roller

25–30

35–45

Breast Roller

90–120

150–250

Worker

175–250

300–350

Stripper

80–120

200–250

Cylinder

300–350

400–450

Doffer

200–250

300–350

Random roller

400–450

500–550

Condensing roller

100–120

130–180

85–95

100–110

Take off roller

Dust removal The carding room can be made dust free by setting up securely sealed air cleaning dust removal systems. The mordern cards do no not require frequent cleaning as in the traditional cards. Production rates The production rates of different cards utilized in the nonwoven industry has been analyzed in Table 2.2. Table 2.2  Card Width and Production rates (Balasubramanian 2009) Manufacturer

Make

Width (mm)

Production rate

Spinbau

Universal Super servo double doffer card

1000–3500

150 m/min

Delta Card

1000–3500

200 m/min

High capacity Random Card, Hyperspeed card

4000–6000

400 m/min

Alpha Card

2500

80 m/min

Injection card with 2 doffers

Up to 3500

250 m/min

Injection card with 3 doffers

Up to 3500

250 m/min

Card mm 2+2

Up to 3500

300 m/min

Oerlikon Neumag

Contd...



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55

Contd...

Manufacturer

Make

Width (mm)

Production rate

Erko Truetzschler

EK 150 single doffer

1000–4200

120–240 kg/hr for 1m width

Ek 150 double doffer

1000–4400

80–400 kg/hr for 1 m width

EWK413 Random Card

1000–4500

300 kg/hr/m

CA 21

2500

100 m/min

Excelle Card

2500–3500

250 m/min

CV641

1800–2400

350 kg/hr/1m

CV661

1800–2400

600 kg/hr/1m

CV691

2200–2500

1000 kg/hr/1m

CV791

2500–3500

1250 kg/hr/1m

NSC Befama

The accurate production rate of the card can be determined only by taking several factors into consideration. These factors include nature of fiber, denier, wire type, condition of wire, humidity and temperature in card room. Usually, polypropylene is processed with reduced production rates when compared with polyester fibers. The heat generation will be more at higher the production speed (Horrocks & Anand 2000; Balasubramanian 2009). Hence at higher production speeds, this heat is sufficient to form globules in the case of polypropylene due to its low melting temperature. These tend to get attached to the wire resulting in fiber loading. Finer fibers also have to be processed slowly to avoid fiber loading problems. Generation of static charges causes fiber loading which lowers the doffer speed. Suitable wire profiles are to be selected according to the fiber denier. Blunt wire points, as a result of over usage decreases the production rate. The performance and productivity of the card depends on the humidity and temperature. Hence humidification system is essential to effectively control the humidity and temperature (Smith 1998). Inappropriate humidity levels causes fiber lapping around the wires either due to stickiness or static charge generation. The recomended conditions are: relative humidity of 55–60% and temperature of 90–95°F. Carding quality The quality of final product depends largely on the carding quality. The quality of carding is evaluated by the degree of fiber opening and nep removal efficiency. The following factors are considered to improve carding quality: • By selecting appropriate production rates for processing the fiber. Increasing the card production rates beyond the optimum rates lowers

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Nonwoven: Process, structure, properties and applications

carding quality. The fiber characteristics, processing condition and atmospheric conditions determines the optimum production rates. • Proper settings at various points in the card can improve the carding quality. The following settings are crucial in improving the quality. 1. Setting between feed plate and lickerin roller. 2. Setting between workers and main cylinder and between worker and stripper. 3. Setting between main cylinder and doffer/randomising roller. • The condition of the wire points also influences the carding quality. The wire tips lose their sharpness and become blunt after certain period of usage. Hence it is necessary to replace the wires as per the maintainance schedules maintain quality. • The feed weight variations, functioning of auto leveller and lapping incidences Another important point to be controlled in carding is web weight uniformity. Web weight uniformity is affected.

Process control and maintenance • The raw material should be free of molten fibers, undrawn fibers and other external substances. • Scheduled checking of the lags and wire points in the Hopper Feeder and opener and replacement of damaged and bent points. • Random checking of spinfinish content in fibers to ensure uniform application of spinfinish oil in the entire material lot. • The cards must be thoroughly cleaned every week. The wire points of breast roller, cylinder, stripper, worker, doffer and transfer rollers should be cleaned using wire brush and petrol to remove embedded materials. Interspaces of cylinder/doffer and framings should also cleaned properly. • Inspection of the card wires for damaged strips and replacement of the damaged wire points once in 3 months. • Inspection of card settings should be done atleast once in 3 months. • The fiber quality, virgin or recycled fiber, card production rate and maintenance practices determine the life of the wire. The general practise is to replace the wires after a duration of 18–24 months. Once in every week, webs are taken from different locations using a template measuring of 25 × 25 cm and weighed to calculate the web linear density and its variation. For the process to be under control, the calculated CV% should be less than 5%.

2.2.2.3

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Web stacking processes

The important tasks of the web laying process are: • Increasing the web mass – The web mass can be increased by a direct multiple of the card web mass to the required product weight • Increasing the web width – Web laying machines can produce webs in widths (laying widths) of up to 7 m. • Determining the web strength in the length and cross directions – The orientation of the fiber layer determines the lengthwise/transverse strength ratio in the end product. • Improving the end product quality – Distortions during web consolidation (mechanical, thermal, chemical) – Overall web width are not equal, but are concentrated more strongly at the edge – Areal density in the edge regions of the end product is higher than in the rest of it. The web coming out of the card can be formed into a batt by the following methods: • Parallel laying • Cross laying • Perpendicular laying Parallel lay procecss Parallel lay process makes use of several revolving flat cards (coton cards). A conveyor lattice runs below all the cards for the entire length. The webs from the cards are laid on the continuous conveyor lattice. By this way, webs from successive cards are laid over each, one at a time other until the desired batt weight is achieved (Figure 2.20). The conveyor carries the laid down batt to the bonding process. The parallel laid batt is typically a layered structure with fibers being oriented in the longitudinal direction predominantly. Due to this the resulting nonwoven will have 8–10 times higher strength in the longitudinal direction than in the cross direction. The major limitation of this sytem is that the width of the batt is equal to the width of the carding machine (Paschen & Wulfhorst 2001). The direction in which the web is produced is called the machine-direction and the other direction is called the cross-direction. Since the fibers are oriented in the machine- direction, a bonded web will have more strength lengthwise due to the bonds reinforced by the fibers. The strength in the cross direction

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Nonwoven: Process, structure, properties and applications

is very low since there are very few fibers in this direction. The strength in the machine direction is substantially greater than in the cross direction, the strength ratio may be about 10:1. Such nonwovens find applications in different end-uses such as tapes, interlinings, cable winding, filtration, etc.

Figure 2.20  Parallel laying process

In some cards, for disorienting the fibers, a randomising doffer is used, which runs in the opposite direction to a normal doffer, so creating more air turbulence. Some fiber-disorientation is also obtained by the presence of two small wire-covered scrambler rollers installed on the doffer delivery. The first scrambler roller runs slower than the fibers and the second roller runs still slower. The result is that the tail end of fibers are running faster than the leading ends so that fibers are buckled, thus increasing the number of fiber segments lying in the cross direction (Horrocks & Anand 2000). Naturally, the weight per unit area of the card web is increased by the scrambler rollers. The web is in an unstable stage, so care should be taken not to stretch it back during bonding. For parallel-laid webs, cards have normally two doffers, thus producing two webs, which are layered. The web doubling improves the final web uniformity and helps in increasing the line production. In certain cases, two or three cards are installed in tandem and the webs are layered after each card. Nonwovens from parallel-laid webs may be produced in the weight range 15–100 gsm. The web speeds on modern cards have increased considerably and may reach values of 300 m/min. These speeds are used in the production of thermo bonded cover stock material for baby diapers with very high production efficiency. Cross lay process This is the most common batt formation process. The cross lapper, located at the exit of the card, takes in the web from the card. The cross lapper consists of a fast moving laying lattice which takes the web forward and deflects the direction of the web by 90°. The deflected web is laid in a zig- zag manner over a slow moving draw off lattice to form a batt (Adanur 1995). The desired batt weight can be obtained by adjusting the laying width and the ratio of



Web formation

59

laying speed to draw off speed. The cross-lay process performs the following functions: • To produce batts with higher weight per unit area than that of the card web • To produce batts with higher width than that of the card web • To obtain preferentially orientation of fibers in the transverse direction • To obtain batt with a layered structure The cross-laying process can be done in two methods namely, camel back laying and horizontal laying. Figure 2.21 illustratres the camel back laying process. In camel back laying, the web coming out of the card is carried upwards to a pivot point by means of a conveyor. The lower conveyor system is designed to reciprocate from the pivot point in order to lay the web onto a cross conveyor below this arrangement. The machine height and the machine throughput are the important factors influencing the width of the batt.

Figure 2.21  Camel back cross-laying process (Soure: www.nptel.ac.in)

The horizontal laying process is shown in Figure 2.22. This process comprises of several conveyor belts operating in combination with traversing carriages and drive rollers. The feed conveyor takes-in the web emerging from the carding machine and transports it to the top sheet or belt assembly. The web is reciprocated by this carriage assembly. As a result, web is layered in a zig-zag pattern onto the delivery conveyor which runs perpendicular to the feed direction (Horrocks & Anand 2000; www.nptel.ac.in). The laying width does not change with the machine height in this process. The resulting batt tends to be heavier at the edges.The lay-down width can be set slightly narrower than required to minimize this problem. It can also be partially compensated by increasing the layering speed in the edges as to the

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Nonwoven: Process, structure, properties and applications

layering speed in the middle region of the batt. The basic factors influencing the laying speed are: • web characteristic (fiber orientation) • fiber type (synthetic fibers, viscose fibers, natural fibers) • fiber dimensions (fineness and length) • fiber elasticity (crimp) • web mass • spin finish and ambient conditions (temperature and relative humidity)

1 – Fibrous web; 2 – Feed conveyor; 3 – Lower conveyor belt; 4 – Delivery conveyor; 5 – Web; 6 – Upper conveyor belt

Figure 2.22  Horizontal laying process

The important aspect in cross lapping is the lapping angle and number of layers (Figure 2.23), which are given by the formula:

α = tan–1



N =

vmb vcl

vcl vmb

Where Α – Lapping angle with respect to cross-machine direction vcl – Linear speed of the cross-lapper (m/min) vmb – Linear speed of the moving belt in the machine direction (m/min) N – Number of layers



Web formation CD

61

B α vcl

A

vmb

C MD

Figure 2.23  Diagramatic representation of cross lapping angle

Any cross-lapper may be manufactured to lay any width even up to 16 m, used in paper felts. The number of laps is always even and the minimum number of laps may be 2. The modern cross-lappers may run at speeds up to 150 m/min. The high lapper speeds allow obtaining maximum card production. Further, for a given batt weight, it is better to have as many layers as possible for better batt regularity. In such cases, relatively lightweight webs are produced by the card. After cross lapping, especially with parallel webs coming out from the card, the fibers lie mainly in the cross direction and the machine direction tends to be weak. It is a standard practice now to draw the cross-laid batt in the machine direction using a web-drafting machine (Tanchis 2008). The drafting increases the machine-direction fiber orientation. The drafter also permits to produce low weight cross-laid webs. The drafting also helps to use better the card production even if the cross-lapper has a slow speed. In this case, heavyweight batts are produced by the lapper, which are then drafted to obtain the required weight increasing the productivity. One of the problems of the crosslapped batts has been the lack of weight uniformity across the entire width. Generally, the batt weight is lower in the centre and higher at the edges because of inversion of crosslapper carriage and due to the card web tension created by the carriage movement. In such cases, it is a normal practice to slit almost 15 cm wide edges to eliminate heavy borders. In most cases, these edges are recycled but they certainly create many problems in reopening and transporting the fibers. The use of recycled fiber has always a detriment effect on the felt quality and some fiber loss as felt waste always takes place (Crook 1993). Further, in processes like synthetic leather, the needle punched felts have to be impregnated and buffed. A fabric with uneven thickness generates more dust waste. On the modern lappers, it is possible to regulate the speed in a way that more web is laid in the middle as compared to edges. During drafting and needling, the batt is stretched and

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Nonwoven: Process, structure, properties and applications

attains an uniformity in the cross section. It is possible to produce needled felts with a regular weight profile in cross and machine direction. CV values of around 1% are achievable. A critical comparison of the parallel and cross laying process is given in Table 2.3. Table 2.3  Relative merits of cross laying and parallel laying process Cross laying

Parallel laying

Width is restricted by card width. As Very wide widths of nonwovens up to 30 a result widths beyond 2–4 m are not m can be formed. possible. Greater uniformity in strength between Cross direction strength is very low in longitudinal and cross direction. CD/MD relation to longitudinal direction. MD/CD ratio up to 1 : 1.3 can be obtained by use ratio is 8–10 times. of randomising and condensing rollers in card and web drafting. Investment is high as machinery costs are Investment is low and second hand high. cards disposed by spinning mils are easily available.

Pependicular laying process The perpendicular-lay process is a unique process to lay batts with prominent z-directional orientation of fibers. The reciprocating lapper (Struto© technology) or rotary lapper (Wavemaker technology) can be used to produce perpendicular batts (Desai & Balasubramanian 1991). The struto technology is shown in Figure 2.24. In this system, the web from the card is consolidated into a vertically folded batt by the action of a reciprocating lapping device. The so formed batt is then take to through-air bonding machine.

1 – Carded web; 2 – Struto product; 3 – Forming comb; 4 – Pressure bar; 5 – Grid; 6 – Cover plate; 7 – Conveyor belt

Figure 2.24  Struto perpendicular laying process

2.2.2.4

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63

Air laying

The airlaying process, which is also a part of dry laying, makes use of air as the transportation medium in the web forming sequence. Perforated rotary rollers or distribution systems are used to form the web and deposit it on the delivery conveyor belt. Airlaid webs are isotropic in nature (at least in two directions). Depending on the fiber specifications and machine parameters, MD:CD ratios close to 1 can be achieved. Hence air laid webs are referred to as ‘random-laid’. Additionally, airlay processes are highly versatile as they can process different types of fiber with varied specifications. This versatility is a result of the various design concepts, fiber transportation and deposition principles used in airlaying (Kleppe 1990). The air flow disperses the incoming fibers into single fibers and this air/ fiber mixture is conveyed towards a permeable net or forming screen, where air is separated and the fibers are laid to form a web. The uniformity of the final web largely depends on the separation of the fibers in the airflow. The fibers can be transported from the opening unit to the web formation section using the following methods: • Free drop • Compressed air • Suction • Closed air circuit • A combination of compressed air and suction systems

1 – Pre-opened fibers; 2 – Feed rollers; 3 – Main cylinder; 4 – Air blower; 5 – Suction; 6 – Conveyor belt; 7 – Air-laid web

Figure 2.25  Principle of air-lay machine (Russel 1997)

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Nonwoven: Process, structure, properties and applications

Figure 2.25 illustrates the principle of an air-lay machine (the actual machine designs may vary considerably from this outline). The three major units of the airlay machine are: feeding, opening and mixing, and web formation. The fibers are fed to an opening roller at a constant rate by means of the feed rollers. Simultaneous gripping of fibers by the feed rollers and beating by the opening roller opens the fibers. The sharp wire points in the opening roller carry the fibers following which the fibers are removed by a high-velocity stream of air directed over the wire teeth surface. Hence, the fibers are carried by air onto a perforated conveyor where the fibers are laid down to form a web. The fibers or tufts of fibers are thrown down on the conveyor individually and there is therefore no inter-fiber entanglement as in the case of carded batts. This makes air-laid webs very weak and in lightweights there could be processing difficulties. Another important characteristic of air-laid webs is that fibers lie at a certain angle to the plane of the fabric. This property makes the air-laid webs more resilient to compression and has more resistance to delamination as compared to cross-lapped batts. The air-laid webs are quite isotropic in structure, have a three dimensional formation and show a typical cloudiness in their structure.

Figure 2.26  Danweb air-laying process



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65

The fiber webs are formed by drums in some air-lay systems. An example for this system is the as Dan web system (Denmark). This system has been illustrated in Figure 2.26. It consists of two perforated drums connected to fixed pipes and rotating in opposte directions located transversely above forming wire. A rotating brush roll is arranged transversely to the conveyor belt inside the drums. It directs the fibers from the airstream and onto the perforated drums (Adanur 1995). A vacuum located below the forming head forms the web on the wire. This system can process fibers upto 15 mm in length and reduces fiber accumulation inside the system. A highly uniform distribution of fibers across the web can be achieved. Machines used for air laying: The two commonly used air-laying systems are • Rando Opener • Random Cards Rando Opener Rando Opener system was introduced by the Rando Machine Corporation. A blowroom line opens the fibers. A hopper feeder and feed plate transports the opened fibers to a saw tooth opening roller. The teeth of opening roller carry the fibers almost individually. An air stream deposits the fibers on a perforated lattice moving slowly for forming the batt (Figure 2.27). At the exit of the opening roller, air is blown through a narrow duct by a powerful fan arrangement. A suction system is provided underneath the perforated lattice. This causes the fibers to randomly deposit on the lattice (Jakob 1989).

1 – Perforated lattice with suction; 2 – Opening roller; 3 – Feed roller; 4 – Blower fan

Figure 2.27  Rando Opener (Balasubramanian 2009)

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Nonwoven: Process, structure, properties and applications

The batt produced by the rando opener is isotropic in nature. This random orientation of fibers significantly improves the insulation properties and bulkiness of the batt. These batts are widely used for wadding, high lofts used in winter clothing. Additionally, sound insulation material, absorbent pads, wipes and hygiene products are manufactured using this system. In the Schirp system, a similar principle is employed. A perforated drum connected to a special air system forms the batt by laying down the webs. The drum is provided with a pin or saw tooth wire profile (Desai & Balasubramanian 1990). Batts ranging from 100 to 200 gsm can be produced using this system with production rates up to 14 m/min. Random Card The random card was introduced by Fehrer. This card is based on aerodynamic principles. In this card, small carding cylinders along with worker and stripper rollers are arranged sequentially. The first card delivers some portion of the fibers into a duct while the remaining fibers are transferred to the next card. Individual ducts provided in each card carry the delivered fibers and deposit on a common perforated surface and the fiber layers are taken forward by a conveyor belt (Figure 2.28).

Figure 2.28  Random Card (Balasubramanian 2009)

One over another deposition of fiber layers from the individual ducts on the conveyor, results in excellent doubling and randomisation of fibers. This significantly improves the batt uniformity. The working width of these cards ranges from 1 m to 2.5 m. The technologically advanced batt forming line from Fehrer utilizes a prior machine called pre web former V21/R decreases the tuft size using opening roller arrangement to form batts with 300–500 gsm (Singh 2007). The output of the pre-web forming machine is fed to the Random card K12 (Figure 2.29) comprising of a cylinder fitted with a pair of workers and strippers. A transversal blower carries fibers delivered by the card to a perforated conveyor lattice. Suction systems are provided in the high loft device at the delivery section to increase the batt height and volume (Chapman 2010). ‘High Loft’ material suitable for insulating applications can be produced in this system. This “high loft” device is optional.



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67

(a) 1 – Deliver conveyor; 2 – K12 card; 3 – Pre-web former; 4 – Weighing belt; 5 – Worker and stripper; 6 – Transversal blower; 7 – High loft device

(b)

Figure 2.29  Random Card K12 (www.nptel.ac.in)

K21 high-performance random airlaying machine was developed to produce lighter-weight webs ranging 10–100 g/m2. The K21 card is shown in Figure 2.30. In comparison with the K12 card, this card is designed with four carding cylinders, each cylinder is fitted a pair of worker-stripper rollers. Each cylinder lays down a certain quantity of the incoming fibers onto a common conveyor belt. The combination of the centrifugal force arising from the rapid rotation of the cylinders (30–40 m/s) and the suction systems under the conveyor belt causes the airlaying of the webs. The four cylinders

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Nonwoven: Process, structure, properties and applications

deposit the fibers in four different positions of the conveyor belt and hence thorough doubling is required in the collection zone to minimize the localised variations. Unlike the K12, the K21 card has a closed web forming system (Lin & Tsai 2001). Synthetic and viscose rayon fibes of fineness ranging from 1.7 to 3.3 dtex can be processed with a throughput rates of 300 kg/h.

Figure 2.30  Random card K21 (Russel 1997)

Comparison of card cross lapping and air-laying process The advantages and disadvantages of the carding – cross-lapping process and the air laying process are mentioned in Table 2.4. Table 2.4  Merits and Limitations of Card Cross-lapping and Air laying process Carding cross-lapping

Air laying

Very wide widths of fabrics up to 15–20 metres are possible.

Width is limited up to 2–3 metres.

A wide range of fabric weights from 75 to 2500 gsm are possible by varying take-off speed of laying lattice in relation to speed of delivery lattice.

GSM lower than 150 are not normally possible.

Highly uniform fabrics can be made in respect of weight per unit length. Variations in weight per unit length in longitudinal and lateral directions are within ±2.5%.

It is difficult to achieve good uniformity in weight/unit length particularly in low weight nonwovens.

Contd...



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69

Contd...

Carding cross-lapping

Air laying

Ability to process a wide range of staple lengths.

Mainly suitable for short fibers. With long fibers it is difficult to get satisfactory uniformity.

There is no randomisation between lateral and vertical planes. Anisotropy in strength is also present in the lateral plane. Strength is generally higher in cross direction than longitudinal direction though this is minimised to some extent by the use of randomising rollers in carding and web drafting prior to bonding.

Fiber orientation is random in all the 3 dimensions though longitudinal direction strength is slightly higher than cross direction strength. The isotropic distribution gives a high degree of insulation properties. But strength is reduced as fibers in the vertical direction do not contribute to strength. Further anisotropic material cannot be made.

Advantages and limitations The main advantages of the air laying process are: • Isotropic properties of the web. • Three-dimensional structures can be obtained if the basis weight is above 50 g/m2. • Producing voluminous, high-loft structures than compared to any other web formation technology. • Compatibility with a wide variety of generic fiber types including natural fibers, synthetic polymer fibers and high-performance fibers. The limitations of the air alying process are: • Fabric uniformity is highly dependent on fiber opening and individualisation prior to web forming. • Irregular air flow adjacent to the walls of the ducts leads to variability across the web structure. • Fiber entanglement during transportation by the air stream can lead to web faults. In general, the pneumatic processes are not easy to handle and may present the following difficulties: • Compared to a card, these processes have little fiber opening capacity, so the fibre must be well pre-opened before working. • It is difficult to produce very light weight webs at high speeds. • The process is subject to static build-up problems and needs controlled room conditions. • Addition of antistatic oils is troublesome in processing.

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• The process is not very suitable for very fine, long or highly crimped fibers. • The air flotation tends to separate fibers of different deniers or densities. • In general, such plants are not very flexible to raw material changes. • Pneumatic laying machines generate more noise. • It is not possible to produce such nonwovens in large widths, at least not as wide as crosslapped battings. For the above-mentioned reasons, these machines are less popular as compared to roller cards and are used mainly for processing high denier and waste fibers or in those cases where random webs are required (Lin & Tsai 2001). Applications of air-laid nonwoven products Based on the choice of fibers and the bonding methods, air-laid nonwovens are utilized in numerous applications. Some of the application are high-loft products for the clothing and furniture industry, wadding, medical and hygiene fabrics, geotextiles and roofing felts, filters, insulation and barrier materials, wall and floor coverings, moulded products, wipes, preformed automotive components, absorbent cores, acquisition and distribution layers, etc.

2.2.2

Wet lay process

The wet laid technology is essentially based upon the paper making process. The wet lay process is suitable for fibers which can be dispersed in fluids. Like in the paper making process, very short fibers dispersed in water are laid on a traversing perforated lattice. The wet laid nonwoven is different from paper by any one of the following criterions as defined by INDA. • More than 50% of the material is made of fibers (excluding chemically digested vegetable fibers) with a length to diameter ratio greater than 300. • If the above condition does not apply and if the following condition is fulfilled. More than 30% of material is made of fibers (excluding chemically digested vegetable fibers) with a length to diameter ratio more than 300 and density is less than 0.4 g/cm3. The typical applications of the wet laid technology includes disposable fabrics like tea bags, baby diaper cover, sanitary napkins, surgical clothing, table cloths, bed linen and liners, household cloth, filters, shoe uppers, protective clothing and sterile packs in medical fields. The characteristic features of the wet laying technology:



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• Excellent product homogeneity • Versatility in the product scale • Higher production rates Figure 2.31 illustrates the various processes involved in the manufacturing of wet laid webs. The basic process stages include: • Dispersion of fibers in water, • Continuous web forming on a wire cloth through filtration, • Consolidation, drying and batching up the web. Raw material (Short fibers, cellulose)

Preparation (Blending, manufacturing of fiber-water suspension)

Web forming (Spreading of suspension into a screen belt)

Web bonding (mechanical bonding/thermal bonding/chemical bonding)

Processing (Finishing, dyeing, printing, coating)

Product (Fiber nonwoven)

Figure 2.31  Wet-laid manufacturing process

2.2.2.1

Raw materials

The main factor to be considered for the wet lay process is the dispersability of fibers in a fluid. Easy individualization of the raw fibers in the preparation

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Nonwoven: Process, structure, properties and applications

stage is essential. Then, the dispersed single fibers should be capable of remaining uniformly distributed in the suspension until web lay down. Lower costs and ease of application makes wood pulp as one of the preferred components. Other components include cotton, viscose, manila, hemp or bast fibers. Synthetic fibers and glass fibers are very rarely used for specialised applications. Fibers of shorter lengths (2–10 mm) can only be processed in order to maintain uniform fiber dispersion. Dilution, nothing but the weight proportion of fibers in suspension should be kept at 0.005–0.05%. The problem of flocculation arises with increase in dilution. The dispersing behaviour of the fiber largely depends on the following factors: • Fineness ratio, based on the fiber length and the fiber fineness • Fiber stiffness in a liquid medium (wet modulus) • Type of crimp • Wettability • Fiber staple quality (fiber length) An increase in the fiber fineness ratio accompanied by a decrease in fiber stiffness decreases the fiber dispersability. Additionally, the type of fiber also influences fiber processing. Generally, it is easier to form homogeneous suspensions using non-crimped fibers rather than long, fine, fibrillated or crimped fibers. These fibers tend to form clumps. Other factors influencing wet laying are the fiber surface profile, fibrillation, the viscosity of the liquid and the type of mechanism employed in the production the suspension. In the case of synthetic fibers, the wettability can be improved by either adding wetting agents to the suspension or by applying suitable spin finishes. 2.2.2.2

Manufacturing of wet-laid process

The first step is to prepare a homogeneous suspension with wood pulp and water in the ratio of 0.003–0.007 (w/w). This suspension is pumped to the headbox provided with an opening called slice. From the slice in the headbox, the fiber-water suspension is deposited onto the moving perforated wires through a regulator (Figure 2.32). The vacuum arrangement underneath the screen drains the water leaving behind the fibers on wires to form the web. Any residual water can be removed from the resulting web by applying suction pressure. The dried web is then bonded by applying latex binders like polyacrylate or styrene butadiene rubber (Meierhoefer 1989). The spray printing or dot printing process can be adopted for web bonding. The pilot wet-laying machine is shown in Figure 2.33.



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Figure 2.32  Wet-laid nonwoven process (Source: Glens Falls Interweb. Inc. New York)

Figure 2.33  Pilot wet lay machine (Source: www.andritz.com)

2.2.2.3

Factors influencing the web formation The important process factors are known to be the ratio of fiber-to-water weight or volume, dispersion time, and impeller speed. The higher is the relative

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Nonwoven: Process, structure, properties and applications

volume occupied by the fibers as compared to that occupied by the water results in more crowding of fibers at the time of dispersion that ultimately results in poor quality of webs (Safavi et al. 2009). This can be explained by the following expression of fiber crowding factor as shown below

nf =

2 3

cv

l d

Where cv – Volume fraction (ratio of the volume occupied by fibers to the volume of water) l – Fiber length and d – Fiber diameter The velocity of water in relation to the velocity of wire determines the structure of the web. When both the velocities are equal then the fiber laydown is found to be practically random. When the velocity of wire is higher than the velocity of water then fibers are found to be preferentially orientated in the machine direction, but when the velocity of wire is lower than the velocity of water then fibers are found to be preferentially orientated in the cross direction. It is known that the fiber–water dispersion quality primarily dictates the quality of the wet-laid nonwovens. The important fiber characteristics that determine this dispersion are fiber length, fiber aspect ratio, and fiber bending rigidity. The higher fiber length, fiber aspect ratio, and fiber bending rigidity result in more fabric defects and vice-versa. The wet-laid process involves suspension of fibers in water and nonwoven is made by draining the water solution through a forming mesh. At this step, the preponderance of fibers is in the form of clumps and which has to be split into individual fibers in a mixing tank by means of shear applied on them by the flow field. To produce uniform nonwoven structure, fibers must be well dispersed prior to be laid-down; or else they remain as clumps and appear as defects (log defects) in the final product. Logs are characterized by bundles of fibers with aligned cut ends that are not dispersed, which happen mainly due to fiber supply problem or can be the result of low under agitation of the initial dispersion. Rope formation is another main concern particularly when fibers with varying degree of stiffness are mixed. Ropes are characterized by assemblages of fibers, with unaligned ends, that are clearly more agglomerated than in the general dispersion. They are formed when fibers are encountered a vortex that facilitates in entangling the fibers to form ropes. In this case, the more flexible fibers will twist and wrap around the stiffer fibers.



Web formation

2.3

75

Polymer lay process

Polymer-laid or spunlaid nonwoven fabrics are based on the polymer extrusion principle. But instead of forming tows or yarns as in the traditional process, the filaments are directly collected and condensed into a web. The elimination of the intermediate processes increases the production rates and lowers the manufacturing costs (Adanur 1995; Russel 1997). Spunbonding (spunbond) and meltblowing (meltblown) are the two major types of polymer lay process.

2.3.1

Spun-bonding process

The spunbonding process is quite identical to synthetic filament spinning. This process involves the extrusion, drawing and laying of the filaments on a moving conveyor belt to form the nonwoven. 2.3.1.1

Raw materials

Synthetic fibers such as polypropylene, polyester, nylon, polyethylene and polyurethane are used as raw materials.

• The most widely used fiber is polypropylene (constitutes about 80%). The most important characteristic of polypropylene is its low density. Additionally, the availability of polypropylene in many forms like virgin fiber, dope dyed form, recycled makes it more popular (Moore 1996). The limitations of the fiber are low UV stability, low creep resistance and lower melting point.



• Polyester follows polypropylene as the next widely used fiber. Polyester is used in applications requiring higher strength and UV resistance. However, polyester has low resistance to alkali.



• Nylon 6 and 66 are also used in spunbonding. The higher moisture regain values of nylon make it suitable in certain applications. The major limitation is the higher energy costs involved in processing.



• Polyethylene is also used due to its low cost. The use of polyethylene is limited by its lower strength and low melting point.



• Polyurethane finds application in apparels and other products where higher stretch and recovery is required.



• Core/sheath and side by side bicomponent fibers can also be used in this process. These fibers can be bonded thermally without addition of any low melt fiber by using a combination of low melt polymer on the surface and high melt fiber in the core of the fiber. Manufacturing

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Nonwoven: Process, structure, properties and applications

of eco-friendly fabrics is feasible using bicomponent fiber made of polylactic acid (PLA) fiber in the core and polypropylene on the surface. Raw material parameters: • Melt index MFI : 20–40 g per 10 min (with spunlaid nonwovens) 100–1,600 g per 10 min (with meltblown nonwovens) • Polydispersity (MW/MN) : 3.5–7 unit to measure mole weight distribution MW – mol weight average weight MN – mol weight arithmetical average • Atactic share : < 2.5% • Intrinsic viscosity : < 0.64 • Water content : < 0.004% • Low share in COOH-groups • High crystallinity 2.3.1.2

Batt manufacturing process

The spunbonding sequence is shown in Figure 2.34. Polymer melting

Winding on roll

Cooling & filtering

Bonding

Spinning

Drawing

Laying on the formation net

Figure 2.34  Spunbonding process

The melt, dry or wet extrusion spinning techniques can be adapted in a spunbonding process. However, melt spinning is the prominently used technique (Figure 2.35). The hopper feeds the polymer chips to an extruder where they are melted. The molten polymer is filtered and is extruded through the spinneret to form the filaments. Depending upon the fabric width, two or three spinnerets are laid side by side to increase the number of filaments. The extruded filaments are quenched by a stream of cold air and are subjected to either mechanically or pneumatically attenuation for orienting the molecules thereby increasing the strength (Malkan & Wadsworth 1992).



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(a) 1 – Winder; 2 – Calendar; 3 – Guide roller; 4 – Edge guide; 5 – Forming belt; 6 – Extruder; 7 – Extruder drive; 8 – Compaction roller; 9 – Attenuation; 10 – Quench air; 11 – Spin pack; 12 – Pump; 13 – Filter; 14 – Polymer hopper

(b)

Figure 2.35  Spunbonding process with a belt collector (Source: www.reicofil.com)



• Polymer melting: The polymer pellets or granules or chips are transferred into the extruder hopper. The hopper feeds chips to the

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Nonwoven: Process, structure, properties and applications

screw rotating inside the heated barrel by means of gravity. The polymer melts gradually in the barrel owing to the heat and friction of the viscous flow and the mechanical forces between the screw and barrel. The screw has three sections: feed, transition, and metering zones (Malkan & Wadsworth 1993). The screw is designed with a decreasing depth channel so as to compress the polymer chips and facilitate homogeneous melting. The function of the feed zone is to preheat the polymer chips and convey them to the transition zone. The chips undergo complete melting in the transition zone. The molten polymer is conveyed to the metering zone.

• Metering of the melt: A uniform flow of the molten polymer mix with the required process parameters of viscosity, pressure, and temperature is essential for proper filament extrusion. For this purpose, a positive displacement volume metering device is used to deliver the polymer to the die assembly.



• Die block assembly: The die assembly is the critical element in the spunbond process. The die assembly can be divided into the polymer feed distribution section and the spinneret section. The feed distribution supplies the polymer delivered by the metering device to all the spinnerets evenly and eliminates the dependency on the shear sensitivity of the polymer. Both the T-type (tapered and untapered) and the coat-hanger type feed distribution systems can be used. From the feed distribution channel the polymer melt goes is directed into the spinneret (Lim 2010). A spinneret is typically a single block of metal with several holes orifices or holes drilled into it corresponding to the number of filaments required. In commercial spunbonding processes, many spinnerets are placed side by side to produce a wide web (of up to about 5 m). These grouped spinnerets are often referred to as block or bank.



• Filament spinning, drawing, and deposition: This involves filament spinning, drawing, and deposition of the filaments. The drawn filaments are entangled and deposited onto an air-permeable conveyor belt or collector. Fanning or entangler units based on aerodynamic principles are adapted for proper filament deposition. Additionally, the fanning unit crosses or translates adjacent filaments to increase cross-directional integrity of the web.



There are two variants in the batt formation process:



• Partial orientation



• Full orientation



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79

For most of regular use products like cover stock for diapers and hygiene materials, partial orientation is sufficient to provide the required strength. Partial orientation also permits higher production rates. An air generation unit is required to achieve partial orientation. The products like geotextiles, carpet backing, roofing and industrial products require full orientation of the polymer (Fourné 1992; Smorada 1992). For full orientation, the filaments are drawn over heated godet rollers, with draw ratio of 1: 3 or 4 followed by pneumatic acceleration. Following this, the uniformity and cover is improved by passing the filaments through a pneumatic air gun where high velocity air is forced through a constricted area of low pressure. Electrostatic charges are applied to avoid filament entanglement during the drawing process. These filaments are deposited on a moving conveyor belt in a random and uniform manner. This batt is then bonded. In both the partial and full orientation, the lay down can also be done in the cross direction depending on the end use. The randomisation can be additionally enhanced by using suction systems underneath the conveyor (Gilmor 1992). The complex spunbonding process involves many operating variables such as polymer throughput, polymer and die temperatures, quench environment, bonding conditions and material variables as polymer type, molecular weight, molecular weight distribution and many others. All these variables affect the fiber diameter, fiber structure, web-lay down and physical and tensile properties of the web (Brenk 2004; Lim 2010). The major performance characteristics of spunbond fabrics such as strength, chemical and thermal resistance are controlled by the characteristics of the polymer systems used. The structure and properties of the final fabric are determined by the polymer and the processing conditions (Rupp 2012). • The Production rate of spunbonding machine per metre working width in kg/hr m × n × n × 60 PSP = 1000 m = throughput per nozzle (g/min) n = number of nozzles per metre of spinning width (m–1) • The mass per unit area of the web created on the perforated belt

mv =

PSP VT

mv = Mass per unit area of the nonwoven (g/m2) PSP = kg/h·m VT = Speed of belt (m/min)

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Nonwoven: Process, structure, properties and applications

2.3.1.3

Comparison of filament bonding and staple fiber bonding system

The relative merits of filament bonding and staple fiber bonding are highlighted in Table 2.5. Table 2.5  Relative merits of filament bonded and staple fiber bonded nonwovens Filament bonding

Staple fiber bonding

Higher strength

Lower strength

Lower elongation

Higher elongation

Higher uniformity in thickness and GSM

Lower uniformity in thickness and GSM

Lacking in textile character and feel

Has good textile character and feel

Higher tear strength

Lower tear strength

Products are normally of low to medium Wide range of products from low to GSM (20–250) medium to high GSM are available (20– 1500) Less flexibility in regard to raw material. All types of raw material can be processed Generally line is suitable for either in the same line. polypropylene or polyester or Nylon or bicomponent fiber. Some latest models however claim flexibility in regard to fiber High plant capacity in terms of production Low to medium capacity in terms of production High capital investment

Low to medium capital investment

Two stages of manufacture

Single stage of manufacture

2.3.1.4



• • • • • • • •

2.3.2

Major applications

Cover stock for diapers and hygiene products Surgical materials Carpet backing Bedding and furniture Geotextiles Roof Materials and other construction material Filters Industrial products

Meltblowing process

Meltblowing is a process for producing fibrous webs or articles directly from polymers or resins using high-velocity air or another appropriate force to attenuate the filaments. This is the latest technique developed in nonwoven



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81

manufacturing. The major advantage of this process is its ability to produce microfiber webs. Meltblown microfibers have diameters ranging from 0.1 mm to 15 mm but diameters of 2–4 mm are widely used. The degree of softness, cover or opacity, and porosity are controlled by the filament size (Elsharkawy 2008). The typical meltblowing process involves extrusion of thermoplastic fibers through a linear dies. Convergent streams of hot air (exiting from the top and bottom sides of the die nosepiece) rapidly attenuate the extruded polymer filaments to form extremely fine fibers. The attenuated fibers collected on a conveyor belt to form a fibered self-bonded nonwoven meltblown web. 2.3.2.1

Raw materials Unlike the spunbond process which requires high orientation, the meltblown process has no or little orientation after extrusion. Hence many polymers apart from PP and PET can be processed: • Polyethylene of high density (HDPE) • Polyethylene of low density (LDPE, LLDPE) • Polyamides (PA 6, PA 6.6, PA 10) • Polystyrene (PS) • Polytrifluorochloroethene (PCTFE) • Polycarbonate (PC) • Polyurethane (PUR) The meltblown nonwovens are usually characterized by very fine fibers of low strength compared to spunbonded nonwovens. 2.3.2.2

Meltblown process

Meltblowing is single stage process in which high-velocity air blows a molten thermoplastic resin from an extruder die tip onto a conveyor or take-up screen to form a fine fibrous and self-bonding web as shown in Figure 2.36. The components of the meltblowing process are: 1. Extruder – From the hopper feeder, the polymer chips are feds to the Archimedean screw, which rotates inside the cylinder. The rotation of the screw pushes the chips forward along the hot walls of the cylinder and the melts the polymer by heat and frictional forces. The screw is divided into feed, transition, and metering zones. • The feed zone preheats the polymer pellets • Transition zone compresses and homogenizes the melting polymer

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Nonwoven: Process, structure, properties and applications

• Metering zone serves to generate maximum pressure for extrusion.

(a) 1 – Winder unit; 2 – Collector; 3 – Blower; 4 – Air compressor; 5 – Resin tank; 6 – Barow tank; 7 – Resin bag; 8 – Vacuum pump; 9 – Extruder; 10 – Polymer filter; 11 – Gear pump; 12 – Static mixer; 13 – Meltblown die; 14 – Embossing unit

(b)

Figure 2.36  Meltblown web formation process (Source: www.kasen.co.jp)

2. Metering pump – It controls the delivery of the melt to the die assembly ensuring consistent flow of polymer with the required viscosity, pressure, and temperature. The metering pump is generally designed with two intermeshing and counter-rotating toothed gears.







Web formation

83

3. Die assembly • Feed distribution: It distributes the flow evenly to all the spinnerets flow and ensures constant residence time across the width of the die in all instances. The two types of feed distributions are T-type (tapered and un tapered) and coat hanger type (widely used due to better balancing of flow and residence time) • Die Nosepiece: The web uniformity depends upon the design of the nosepiece. The spinneret used in spunbonding process is replaced with the die nosepiece. This nosepiece is typically a hollow and tapered piece of metal having linear arrangement of several hundred orifices along its width. The polymer melt is extruded through these holes and the emerging filaments are quenched using hot air. The usual dimensions of the nosepiece include a diameter of 0.4 mm and the number of orifices per mm ranges from 1 to 4. Figure 2.37 shows the design of the die.

Figure 2.37  Die design for meltblowing process (Source: www.nippon-nz.com)





• Air manifolds: The die nosepiece is designed with slots through which the air manifolds supply the high velocity hot air. The air from a compressor is passed through a heat exchange unit to heat the air to desired temperatures. The general process parameters are air temperatures of 230°C to 360°C and air velocities of 0.5–0.8% of the speed of sound. 4. Web formation – Immediately after the extrusion of polymer from the die holes, hot air streams of high velocity exiting from the die nosepiece attenuate the polymer filaments to form micro fibers (Tanchis 2008). The hot air stream directs the microfibers to a

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Nonwoven: Process, structure, properties and applications

collecting screen. On the way to the collecting screen, the secondary air cools and solidifies the fibers (Figure 2.38). The solidified fibers deposit randomly and entangle themselves on the screen. Hence the air turbulence forms a self-bonded nonwoven web (Figure 2.39).

Figure 2.38  Web formation process

Figure 2.39  Schematic diagram of Meltblowing Process (Source: www.nonwoventools.com)

Different types of meltblowns can be produced by varying the collector speed and the distance of the die nosepiece from the collector screen. The hot air laying the fibers can be withdrawn by applying vacuum inside of the collector screen. 5. Winding – The melt-blown web is usually wound onto a cardboard core and processed according to the end-use requirement. 6. Bonding – The meltblown web may be subjected to additional bonding process such as thermal bonding to improve the fiber adhesion and web characteristics. Either overall (area bonding) or spot (pattern bonding) techniques can be adapted. This essentially improves the web strength and abrasion resistance.





Web formation

85

7. Finishing – Although finishing treatments are not mandatory, finishing treatments such as calendaring, embossing, and flame retardant treatments can be performed at the end of the production line.

2.3.2.3

Process variables in meltblowing process The process variables can be classified into two categories: operational/online variables and off-line variables. The type of polymer and its throughput, polymer/die design and air temperature, die-to-collector distance, and quench environments are the on-line variables (Lokesh 2013; McCrum 1988). The offline variables are hole size, die setback, air gap, air angle, web collection type, and polymer/air distribution (Sun et al. 1996). The variables in meltblown production are listed below. • Polymer type • Polymer characteristics: molecular weight, melt viscosity, melt strength • Extruder conditions: temperature, shear, polymer degradation • Filtration • Die tip geometry: hole diameter, air gap, die tip position • Hot air conditions: volume, temperature, velocity • Polymer conditions: temperature, flow rate, shear rate • Die conditions: temperature profile, gas flow rate profile, polymer flow rate profile • Ambient air conditions: temperature, lack of turbulence • Distance from the die to the forming drum or belt • Laydown conditions Basically any fiber forming polymer that has an acceptable melt viscosity at a suitable processing temperature and can solidify before landing on the collector screen can be processed by spunbonding. A wide range of polymers has been spunbond (Shambaugh 1992). In general, high molecular weight and broad molecular weight distribution polymers such as PP, PET, Polyamide, etc., can be processed by spunbonding to produce uniform webs (Tsai 1998; Butler 1999). Isotactic polypropylene is the most widely used polymer for spunbond nonwovens production as it provides the highest yield of fiber per mass and covering power at the lowest cost because of its low density (Lee & Wadsworth 1992; Milligan & Haynes 1998). 2.3.2.4

Web characteristics and properties

Uniformity: The distribution of fiber in the air stream and the vacuum settings below the collecting screen determine the web uniformity. Non-uniform distribution of fiber in the air stream can be caused due to poor die design and

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Nonwoven: Process, structure, properties and applications

improper airflow in the air stream. The vacuum under the collector should be capable of withdrawing the entire air stream through the perforations and randomly lock the fibers in place (Choi et al. 1988; Wehamann 1992). Usually, as the distance between the die and the collecting screen decreases, the web uniformity increases. Product characteristics The main characteristics and properties of melt-blown webs are as follows: 1. Random fiber orientation in the web. 2. Lower to moderate web strength, the strength is a result of the mechanical entanglement and frictional forces. 3. Generally meltblown products have high opacity due to a high cover factor. 4. Unique method to produce low GSM material. 5. Fiber diameter ranges from 0.5 to 30 m, but typically 2–7 m. 6. Basis weight ranges from 8 to 350 g/m2, but typically 20–200 g/m2. 7. Microfibers provide a high surface area for good insulation and filtration characteristics. 8. Fibers have a smooth and soft surface texture and are circular in cross-section. 9. Most melt-blown webs have a layered structure, the number of layers increases with basis weight. 2.3.2.5



Applications of meltblown nonwoven • Medical fabrics: Disposable gown, drape market, sterilization, wrap segment, Sanitary products etc. • Adsorbents: Sorbents to pick up oil from the surface of water, such as encountered in an accidental oil etc. • Filtration media: Filter media, cartridge filters, clean room filters and others • Apparel: Thermal insulation, disposable industrial apparel and substrate for synthetic leather. • Electronic specialties: Liner fabric in computer floppy disks, battery separators and as insulation capacitors. • Miscellaneous applications: Manufacture of tents, elastomeric nonwoven fabrics etc.

2.3.2.6

Comparison of melt-blown and spunbond process

The spunbond and melt-blown processes are quite identical from machinery and operator point of view. But the two major differences are:



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87



• The temperature and volume of the air used to attenuate the filaments and • The point of application of filament drawing or attenuation force. Higher temperatures and higher volumes of air are used for attenuation in meltblown process. The air temperature is close to the melting temperature of the polymer. Conversely, the spunbond process generally uses a smaller volume of air close at ambient temperature to for drawing the filaments (McCulloch et al. 2003). A melt-blown process uses large amounts of high-temperature air to attenuate the filaments. The air temperature is typically as higher than the temperature of the polymer. In contrast, the spunbond process generally uses a smaller volume of air close to ambient temperature to apply the attenuation force (Dhoke 2015). In the melt-blown process, the attenuation force is applied at the tip of the nosepiece for forming microfibers. This inhibits the polymer orientation to build good physical properties. In the spunbond process, the polymer is subjected to the drawing force after cooling. As a result the polymer is well oriented but is not suitable to form microfibers. A critical comparison of spunbond and meltblown process fabrics is given in Table 2.6. Table 2.6   Comparison of spunbond and meltblown fabrics Meltblown

Spunbond

Developed

1950s

Opacity

Opaque

Color

Typically white, can be colored

Finishing

Calendar, laminating, point bonding

Pleatable (Y/N)

Yes, when heavy enough

Basis weight avg.

20–200 gsm

10–200 gsm

Basis weight range

8–350 gsm

5–800 gsm

Fiber diameter avg.

2–6 μm

15–35 μm

Fiber diameter range

0.5–15 μm

1–50 μm

Fiber length

Discontinuous

Continuous

Random

Random somewhat aligned

Fiber orientation Fiber attenuation polymers

typical Strong air, at die exit

Less air, away from die

PP, PE, PBT, etc.

PP, PET, PBT

Economics

Less capital

Faster, cheaper production

Binders

Self-bonding, binders Chemical binders, needling optional

Comparison of different web forming techniques (Table 2.7)

88

2.4

The comprehensive comparison of different web formation methods are given in Table 2.7.

Process origin

Name

Technology

Structure & fiber orientation

Raw material

Dry-laid (Staple Fiber)

Carded

Opening, cleaning, removing short fibers; Separation and rearrangement of fibers by main cylinders, strippers, workers, and doffers; Converting the individual fibers into a uniform fibrous web

Random with some MD directionality:

Most fiber types can be carded; PP and PET staple fibers most used; Bicomponents as binder fibers are common for thermally bonded nonwovens; Recycled fibers are also used if length is long enough; Very short fibers (pulp or fluff) cannot be processed by carding

Carded + crosslapping

Somewhat random and sometimes bimodal

Mixture

Production rate (m2/min)1

Fabric weight

125 ~ 600; Cards produces high quality webs at relatively high speeds

Very low speed and output, it still existing because: It can be in continuous process with needle punching, thermal, stitch bonding, spunlacing and chemical bonding.

Web weight: at least 80 g/ m2 to 1,000 g/ m2 or more; Web width: 2.5 m to 16 m, usually, web of 2.5m to 6.0m

Considerations

Products & applications

Benefits/disadvantages

New cards allow the fiber arrays to be randomized; High-quality products require a constant climate during all production stages; Webs must be prebonded or bonded just after web forming to transport them

disposables for hygiene, medicals, wipes, or durable products for apparel and shoe interlinings, support for plastics, packages, tea bags, etc.; High-loft products for mattress, insulation, high filter media, etc. using by new carding equipment

Since carding begins with staple fibers, one of the benefits is the ability to blend different fiber types together to produce a nonwoven.; In addition, depending upon how many cards are used, multiple layers can be made to achieve different performance characteristics.

Diverse applications is filters, apparel, insulation, carpets, etc.

Randomize the ODF; Create uniform heavy weight webs for needle punching or thru-air bonding

Contd...

Nonwoven: Process, structure, properties and applications

Table 2.7  omparison of web formation techniques (Source: www.acaemia.edu)

Wet-laid

Process origin

Contd...

Made by suspending short fibers in water and processing them into a fabric using a modified papermaking process; Produce structures with textile fabric characteristics (flexibility, strength) at speed associated with making paper

Opening, cleaning, removing short fibers; Fibers are suspended in air within a forming system then deposited them as a batt/web in a random orientation on a moving forming screen or rotating perforated cylinder

Air-laid

Wet-laid

Technology

Name

Random with some MD directionality:

Isotropic; Random with some MD directionality:

Structure & fiber orientation

Long fibers; Any natural or synthetic fibers, etc. (Wood pulp, glass, polyester, polyolefins, Nylon, Metal)

short 3 – 4 mm (pulp) to long (flax fibers) fibers; very low to very heavy dtex fibers; Woollen fibers only for some special products; Natural fibers; Man-made fibers especially PET, PP and PAN; Recycled fibers; Superabsorbent powders; Particles;

Raw material

Synthetic Fibers Offer uniformity and consistency of supply, More difficulty in getting good dispersion for crimped fibers, 20 to 50% more expensive, Less compatible with water

Percentage of longest fiber must be kept to a minimum value because those can gather into big “lumps” that can block some parts of the equipments in motion such as rollers, belts, etc; For some fibers, except those of pulp and fluff, the percentage of fibers less than 5 – 10 mm must be kept to a minimum because they can be removed in air suction as waste

Mixture

750 ~ 3000

75 ~ 250

Production rate (m2/min)1

Web structure is closer, stiffer and weaker than dry-laid webs, Fibers in the web can be random or longitudinally oriented, Broad range of weights, High productivity

Lightweight and heavy high loft nonwovens are possible ~ from 100 g/ m2 to 8,000 g/ m2 made from standard or coarser fibers

Fabric weight

Limited by cost and availability; Important properties: Aspect ratio (Length); Tensile properties (Shrinkage); Flex resistance (Density); Special Fabric Features: Web structure is closer, stiffer and weaker than drylaid webs;

Maximum and minimum fibrous web average weight, characteristics of the raw material processed, special properties of the nonwovens such as high loft, absorbency, fiber web uniformity, delivery speed range, output in kg per hour, power consumption, machine dimensions and production related to the floor space unit the number of operatives involved, working width, noise level, the environmental task, equipment price, etc.

Considerations

Special papers (synthetic fiber paper, dust filters, filters for liquids, etc.); Industrial (waterproof sheeting roof, shingling, separators, filters, etc.); Clothing (surgical, bed-linen, table cloths, etc.)

Products & applications

Web formation Contd...

Very capital intensive, Flexible in weight, and composition but inflexible in scheduling, Energy intensive, High fiber quality requirements, Draining large volumes of water from the web as it is forming, Control of fiber orientation during web formation

Composite are easily achieved, The basis weight range flexibility is high, as is the ability to produce various densities being very low and very high, Stiffness and softness easily controllable over a wide range, Diversity of raw materials, High capital costs. Can use the intermediate process stacking

Benefits/disadvantages



89

Name

Spunbond

Process origin

Polymerlaid

Contd...

Small volume of air at ambient temp. to quench & attenuate, Ambient air temperature, Drawing force applied after polymer cooled, Allows polymer orientation; Technologies: Creel Fed Laydown, Typar, Original Reemay, Lurgi Process, Tyvek, Curtain Spinning: Open vs. closed system, Coathanger vs. multipump spin beams

Technology

Web Formation: Air transport of fiber to moving porous screen, Many proprietary devices are used (Spreader plates, Coanda devices); Electrostatic charging, Uniform air velocity through collection screen or belt is critical to laying down uniform web; Multiple layers get tricky (must lay down without disturbing incoming layer), Compaction of Web provides some integrity, Compaction roll set and Heating

Structure & fiber orientation Polymers (Polypropylene, Polyethelene, Polyester, Polyamide); New polymers (Bio-Polymers, Elastomers, CoPolymers, etc.)

Raw material

Multicomponent: Non-splitting ( Sheath/Core, Side-by-Side, mixed filaments, etc), Splittables (Pie, Islands-ina-Sea, Tipped Trilobal, etc), Self Bulking ( Side-by-Side)

Mixture

30 ~ 300

Production rate (m2/min)1

Fabric weight

Open Versus Closed System: Open (High Filament Speed, Finer Fibers, Flexible, Most Polymers, Shorter Height), Closed (Better Bonding, Good Uniformity, Well Defined Process, Mostly PP, Not affected by room air)

Considerations

Disposables: Hygiene, Medical fabrics, Wipes, Filtration, Crop covers, Disposable clothing, Fabric softener sheets, Synthetic paper, Battery separators; Durables: Furniture, Bedding, Clothing interlinings, Shoes/ Leather goods, Geotextiles, House wrap, Roofing, Carpet backing, Car covers, Coating Substrates, Wall coverings.

Products & applications

Contd...

Various fiber shapes and sizes (Single layer, Multiple layers), Composite with other technologies (example spunbond / meltblown / spunbond) , Second step composites (example -film/spunbond laminate)

Benefits/disadvantages

90 Nonwoven: Process, structure, properties and applications



Technology

Extrude low viscosity polymer melt through fine capillaries; High velocity hot air is blown to the molten polymer and attenuates the polymer melt; The molten polymer is cooled by the turbulent ambient air to form fine fiber; The fiber is deposited on a collecting device to form useful articles (web, tube, etc.)

Name

Meltblown

9,075 + 5,930 = 15005

Process origin

Contd...

Meltblown process is a one-step process that converts resin to fine diameter fiber nonwoven web or structure, Key attributes of meltblown process: Produce fine fiber (2-8 microns) for applications where small fiber, large fiber surface area and pore size are required

Structure & fiber orientation

Mixture

Combination of PP meltblown fibers with other materials greatly enhance the utility of meltblown product

Raw material

Produce fine fiber (2-8 microns) for applications where small fiber, large fiber surface area and pore size are required. PP, PES (high temperature is required), and PA. Majority of the meltblown product uses PP because of ease of processing, chemically inert, safety, and attractiveness cost/benefit ratio;

Production rate (m2/min)1 Typical PPMB fabric

Fabric weight

“Shot” formation, Fibers colliding together while still in melt state, Fiber break occurs and the newly formed fiber has an undrawn fiber end (droplet), usually caused by partially obstructed capillary, lower than normal output rate (gram/hole/min) for the process air, can be traced to the same CD location; Dirty die tip, fibers bending to one side

Considerations

Filtration, Sorbents and Wipes, Coform, Adhesive, Apparel, Acoustic insulation, Battery separator,

Products & applications

Benefits/disadvantages

Web formation

91

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References 1. Abhijit R. Dhoke (2015). Meltblown Polymers. www.textilelearner.blogspot.com. Accessed on March 12, 2015. 2. Adanur S (1995). Wellington Sears Handbook of Industrial Textiles. Technomic Publishing, Co. Inc, Lancaster. 3. Balasubramanian N (2004). Relative Merits of Polypropylene and Polyester, Indian Text J 32:32–38. 4. Balasubramanian N (2009). Batt formation in nonwovens: Methods, merits & measures. The Indian Text J 32(4): 22–29. 5. Balasubramanian N, Rakshit AK, Patel VK (1991). Opening Size and Water Permeability of Nonwoven Geotextile. Indian Text J 6:26–32. 6. Brenk J (2004). Higher added values for PET staple fibers and spunbonds. Chem Fiber Intern 54(1): 37–40. 7. Butler I (1999). Spunbonded and Meltblown Technology Handbook (Eds) Vaughn E, Wadsworth LC, INDA. 8. Chapman RA (2010). Applications of nonwovens in technical textiles. Woodhead Publishing Limited, CRC Press, New York. 9. Choi KJ, Spruiell JE, Fellers JF, Wadsworth LC (1988). Strength properties of meltblown nonwoven webs, Polym Engn Sci 28(2): 81–89. 10. Crook L (1993). Dry Laid Systems (Chapter 7), Nonwovens: Theory, Process, Performance and Testing. Eds Turbak AE. TAPPI Press, pp. 155–170. 11. Desai AN, Balasubramanian N (1990). Influence of Processing Conditions on Functional Properties of High Loft Structures. Indian J Fiber Text Res 15: 169–177. 12. Desai AN, Balasubramanian N (1991). Development of a Geocomposite Canal Liner – BTRA’s Experience, J Text Asso 4: 187–192. 13. Edmir Silva, Comparison of web formation and bonding methods. http://www. academia.edu/440297/Comparison_of_web_formation_and_bonding_methods. Accessed on May 12, 2015. 14. Engineering excellence in needle looms. www.dilo.de. Accessed on March 2, 2015. 15. Fourné F (1992). New processes for spunbond fabric production. In Spunbond technology today 2: Onstream in the 90’s (pp. 169–174). San Francisco, California: Miller Freeman, Inc. 16. Fu-Jiun Lin, I-Shou Tsai (2001). Configuration of PET fiber arrangement in roller drafting air-laid webs. Text Res J 71(1): 75–80. 17. Gilmor TF (1992). Spunbond Web Formation Processes: A critical Review. In Spunbond technology today 2: Onstream in the 90’s (pp. 139–145). San Francisco, California: Miller Freeman, Inc. 18. Giovanni Tanchis (2008). The nonwovens, ACIMIT. 19. Horrocks AR, Anand SC (2000). Handbook of Technical Textiles. Woodhead Publishing Limited, The Textile Institute, Cambridge.



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20. Hosum Lim (2010). A review of spunbond process. J Text Apparel Technol Manage 6(3): 1–13. 21. Jakob H. (1989). Experience with random web technology. Melliand Textilberichte, 70(3): 76–78. 22. Jürg Rupp, Dry-laid Nonwovens. www.textileworld.com/nonwovens. Accessed on February 18, 2015. 23. Jürg Rupp, Needlepunched Nonwovens. Accessed on February 18, 2015.

www.textileworld.com/nonwovens.

24. Jürg Rupp, Spunlaced Or Hydroentangled Nonwovens. www.textileworld.com/ nonwovens. Accessed on February 8, 2015. 25. Kleppe J (1990). Air-laid: Care and feeding of a growing market. Nonwoven World 22: 27–29. 26. Lee Y, Wadsworth LC (1992). Effects of meltblowing process conditions on morphological and mechanical properties of polypropylene webs. Polym 33(6): 1200–1209. 27. Lokesh, KV (2013). Meltblown Nonwoven. www.textilelearner.blogspot.com. Accessed on March 12, 2015. 28. Malkan SR (1989). Nonwovens – An Advanced Tutorial. TAPPI Press, Atlanta, GA, USA. 29. Malkan SR, Wadsworth LC (1992). A review on spunbond technology: Part I. INB, Nonwovens, 3: 4–14. 30. Malkan SR, Wadsworth LC (1993). Polymer Laid Systems (Chapter 7), Nonwovens: Theory, Process, Performance and Testing. Eds Turbak AE. TAPPI Press, pp. 171–192. 31. McCrum NG (1988). Principles of Polymer Engineering. Oxford University Press, New York. 32. McCulloch J, Pourdeyhimi B, Zamfir M (2003). Recent developments in spunbonding and meltblowing. Nonwoven Ind 34: 48–52. 33. Meierhoefer AW (1989). Wetlaid nonwovens – a survey of the fundamentals of making speciality fabrics on papermaking machinery, Nonwoven Fabrics Forum, Clemson University, Clemson USA. 34. Milligan MW, Haynes BD (1998). Air Drag on Monofilament Fibers – Meltblowing Application. American Soc Mech Eng 54: 47–50. 35. Mohamed Elsharkawy (2008). Hydroentanglement Bonding Process for Production of Nonwoven Fabric (Part-2). http://textilelearner.blogspot.in/2014/12/ hydroentanglement-bonding-process-part-2.html. Accessed on February 18, 2015. 36. Moore EP (1996). Polypropylene Handbook. Carl Hanser Verlag, München, Germany. 37. Nonwovens: Tutorial. http://www.thenonwoveninstitute.com. Accessed on March 5, 2015. 38. Parikh DV, Calamari TA, Sawhney, APS, Sachinwala, ND, Goynes, WR, Hemstreet JM, Van Hoven T (1999). Woven and Nonwoven Medical/Surgical Materials. Int Nonwoven 23: 12–15.

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39. Paschen A, Wulfhorst B (2001). Aerodynamic web formation for the creation of new nonwoven structures. Technical Text 44: 13–16. 40. Rakshit, AK, Desai AN, Balasubramanian N (1987). Nonwovens – Technology of Manufacture and Properties. Proceedings of Symposium on Nonwovens, BTRA. 41. Ramandeep Singh (2008). Air-Laid Web Formation. www.textilelearner.blogspot. com. Accessed on March 12, 2015. 42. Russell SJ (2007). Handbook of nonwovens. CRC Press, Cambridge. 43. Safavi A, Fathi S, Babaei MR, Mansoori1 Z, Latif M (2009). Experimental and Numerical Analysis of Fiber Characteristics Effects on Fiber Dispersion for Wet-laid Nonwoven. Fiber Polym 10(2): 231–236. 44. Shambaugh RL (1992). A Macroscopic View of the Melt-Blowing Process for Producing Microfibers. Ind. Eng. Chem. Res. 27(12): 2363–2372. 45. Smith JE (1998). Cellulose acetate fiberts: A fibrillated high surface area pulp for speciality industrial applications, TAPPI Nonwovens Conference Proceedings. 237– 243. 46. Smorada R (1992). Spunbonding: Characteristics, Applications, Technologies. In Spunbond technology today 2: Onstream in the 90’s (pp. 17–33). San Francisco, California: Miller Freeman, Inc. 47. Sun Q, Zhang D, Chen B, Wadsworth LC (1996). Application of Neural Networks to Meltblown Process Control. J Applied Polym Sci 62: 1605–1611. 48. Tsai PP (1998). Theory and Techniques of Electrostatic Charging of Melt-Blown Nonwoven Webs. TAPPI Journal 81(1): 274–278. 49. Wehamann M (1992). Production of Nonwovens According to the Spunbond and Meltblown System. In Spunbond technology today 2: Onstream in the 90’s (pp. 149– 152). San Francisco, California: Miller Freeman, Inc. 50. Wilhelm A, Hilmer F, Walter K (2002). Nonwoven Fabrics; Raw Materials, Manufacture, Applications, Characteristics, Testing Processes. Weinheim: WileyVCH.

3 Nonwoven bonding techniques

Abstract: This chapter deals with different types of bonding techniques used in the nonwoven manufacturing. The first part of the chapter details the mechanical bonding methods like needle punching, stitch bonding and hydro entanglement. The second part discusses different chemical bonding method. In this process, the methods like saturation, spray and etc were detailed. As a final, the thermal bonding methods used in nonwoven manufacturing, like hot calendaring, belt calendaring, ultrasonic bonding and etc., are detailed with clear illustration. Key words: bonding, needle punching, hydro-entanglement, chemical bonding, thermal bonding

3.1 Introduction Nonwovens are characterized as fabrics formed by the assembly of fiber structures and the adjustment, or bonding, of these filaments utilizing mechanical, compound or warm routines. Nonwoven webs, whether made from staple fiber by the dry process or from filaments, lack structural integrity. The only exception is paper made from wood pulp, where hydrogen bonding holds the fibers together. Consequently, the fibers have to be held together either by entangling them or by incorporating a bonding agent such as a resin, solvent, or a polymer melt. Besides the characteristics of the fiber (length, fineness, crimp, fiber surface, cross-sectional shape, etc.), the method of web making, the bonding type has a great influence on the mechanical (strength, elongation, recovery from deformation, stiffness, tear, etc.) and the physical properties (handle, drape, abrasion, softness, bulk, surface characteristics, etc.) of the product. There have been a number of developments in the technology of bonding. All these technologies, singly and in combination, have given versatile tools in the hands of industry to tailor-make a product to meet the end-use requirements. The filaments in the fiber structure can be adjusted essentially in the length bearing, basically in the width course or similarly in both directions. The estimation of the procedure is that by utilizing the highlight of fiber arrangement and shifting the type of bonding process, the product attributes can be changed, consequently yielding a really engineered product. The production of a nonwoven fabric includes a progression of individual steps. The principal step is to focus the desirable product end use properties and

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choose the right fiber to match those necessities. The selected fiber must be appropriately arranged for the kind of procedure to be utilized. The fiber is then framed into a web structure with the right fiber arrangement, weight and measurements. The following step is to choose the bonding system expected to get the sorts of structure stabilization required for the end product. A flat stiff structure requires a different bonding method than a lofty or soft flexible product. Finishing of the product may be as simple as cutting the wide delivered fabric into to narrower widths. It might likewise include applying chemical or mechanical finishes, or it might be printing or colouring certain sorts of these nonwoven fabrics. Nonwoven bonding techniques

Mechanical bonding

Chemical bonding

Thermal bonding

Needle punching

Saturation

Hot calendering

Stitch bonding

Spray

Belt calendering

Print

Through-air thermal bonding

Hydro entanglement (spunlace)

Foam Powdered

Ultrasonic bonding Radiant heat bonding

Figure 3.1  Classification of bonding techniques used in nonwoven bonding process

The structures shaped in the web framing procedures are frequently feeble and temperamental. To get the strength and stability, the structures must undergo some form of bonding. Major methods of bonding can be divided into three categories-mechanical, chemical, and thermal. The discussion of mechanical bonding includes needle punching, stitch bonding and hydro entangling or spunlacing technologies (www.aatcc.org). Chemical bonding includes saturation, printing and spray bonding techniques. The thermal methods are air bonding and calendar bonding. The ultrasonic method uses



Nonwoven bonding techniques

97

high frequency sound waves to create molecular motion in the fibers. This motion creates heat in the structure which reacts with the thermoplastic polymer to create bonds between fibers. The powder bond process uses thermoplastic polymer powders sprinkled into the fiber webs and heated to form the bonds. Figure 3.1 explains the classification of different bonding techniques used in the bonding of nonwoven web.

3.2

Mechanical bonding

3.2.1

Needle punching

Needle punching can be characterized as a physical system for mechanically interlocking strands networks by utilizing spiked needles to reposition a percentage of the fibers from a flat to a vertical introduction. A large number of needles interlock fibers in a web. Needle punching is the most utilised method for delivering nonwoven products. The needle punching framework is used to bond dry laid and spun laid networks. The needle-punched fabrics are delivered when pointed needles are pushed through a stringy cross-laid web driving a few filaments through the web, where they remain when the needles are withdrawn. The principle of needle puching process is shown in Figure 3.2. A needle-punched nonwoven is a fabric made from webs or batts of fibers in which some of the fibers have been driven upward or downward or both by barbed needles. This needling action interlocks fibers and holds the structure together by friction forces.

Figure 3.2  The basic principle of needle punching process

3.2.1.1

Working mechanism of needle punching technology

In needle punching the bonding of the fiber web is the result of intertwining of the fibers and of the inter fiber friction caused by the compression of the web. The entire setup of needle punching line and the phases of needle punching process are shown in Figures 3.3 and 3.4, respectively.

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Nonwoven: Process, structure, properties and applications

Figure 3.3  Needle punching line

Figure 3.4  Process flow in needle punching

Needle-punched nonwovens are created by mechanically orienting and interlocking the fibers of a spun bonded or carded web. This mechanical interlocking is achieved with thousands of barbed felting needles repeatedly passing into and out of the web. The cross-lapped batts are needle punched to make a felt. A versatile material for industrial and apparel uses, felt is



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characterised by intimate, three-dimensional fiber-entanglement. The resultant high frictional forces confirms fabric integrity and particularly high resistance to de-lamination. The three-dimensional nature of fiber entanglement distinguishes a needled felt from felt-like nonwoven structures where the entanglement is mostly two-dimensional (woollen felts). It is possible to cut articles of any shape. The cut edges are not subject to raveling, since they are not woven. Figure 3.5 outlines the fundamental parts of needle punching machine (Jangala & Huang 2011).



1 – Fiber layer

2 – Input device

3 – Stripper plate



4 – Bed plate

5 – Needle board

6 – Needles



7 – Main drive

Figure 3.5  Needle punching technology (Source: www.dvc500.com)

After the preparation of fibers by opening and blending, the web formation has been done on a nonwoven card and then webs are laid by a cross-lapper to produce a batt to the required width and basis weight. Drafting operation to reduce the basis weight of fabric could takes place before, during or after pre-needling operation. Generally, the needle loom comprises three main components, namely, needle board, bed plate and stripper plate as shown in Figure 3.5. The web passes through two heavy and substantial frames, a bed plate at the bottom and a stripper plate at the top. Corresponding holes are located in each plate and between each hole, the barb needles which are fixed on needle board passes thought the web in and out. The bed plate provides the

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platform for the fibrous web to passes through the loom while, the stripper plate strips the fibers from the needle so the material can advance through the needle loom. The needle board carrying the needles is driven with some simple harmonic motion so that the needles will move up and down through the web. The fibrous webs are normally guided between two conveyor belts or aprons to prevent fiber slippage in the sheath and core part of the web. The distance between the stripper plate and base plate can be adjusted to control the web compression during needling. Most of the needle loom comprises two needle boards i.e. pre-needling and final needling for effective needling operation and to reduce the thickness of the batt. After final needling, the fabric is transported away from the needling zone by take-up rollers, the movement of which may be intermittent or continuous. On the off chance that adequate strands are suitably dislodged the web is changed over into a fabric by the consolidating impact of these fibers plugs or tufts. This activity happens in needle punching machines where a board normally containing a few thousand spiked needles, in responded at pace of around 2000 strokes every moment, contingent upon the machine width. This activity normally occurs in vertical course and a few machines may have two arrangements of needles, one working downwards and different upwards, so that both sides of web are needled. Fabric properties are dependent on number of factors, the two main ones being punch density and needle penetration. The operation consists of pre-needler, drafter and a finish needle loom. During needle punching, the webs are subject to stretching particularly in the pre-needling machine. In the case of lightweight webs, the draft creates thick and thin areas due to weight variations and the borders become heavier because of width shrinkage. For producing lightweight felts, it is advisable to work on larger widths and then slit the material after needling. The needle punch webs offer a wide range of product characteristics such as (Milin Patel & Bhrambhatt 2011), 1. Unique physical property, i.e. elongation in all (x, y, & z) directions for moldable applications. 2. Ability to attach layers of different types of fiber webs to produce nonwoven composite as well as reinforcement in composites. 3. High opacity per unit area. 4. High strength makes them overwhelming choice for geotextiles fabrics. 3.2.1.2

Types of looms

There are three basic types of needle looms in the needle punching industry.



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They are (Anwer 2014),

1. The felting loom



2. The structuring loom



3. The random velour loom



• The felting looms are the sort simply depicted earlier. These needle looms have one to four needle boards and needles from the top, base or top and base. The essential capacity of this sort of machine is to do interlocking of strands bringing about a level, one measurement fabric. The type of products made with this process and needle loom are different and multifaceted. They exist in mixture of industrial products, geotextiles, automotives, interlinings, home furniture, and so forth.



• Structuring looms use what are called fork needles. As opposed to conveying strands into bedplate opening, the fork needles convey fiber tufts into lamella bars that stretch out from the section to the way out of the needle loom. These fork needles convey huge tufts of strands into parallel lamella bars. These bars convey the tuft of fiber from the passage to the way out side of the loom. Contingent upon the introduction of the fork needle, a rib or velour surface is presented. The most popular products made with structuring looms include home and commercial carpets and floor mats, automotive rib and velour products, wall covering and marine products.



• Random velour looms are the type of needle looms, having only been available since the mid 1980s. The random velour looms are used to produce velour surfaces. Unlike the structuring looms, the velour products produced by this loom are completely isotropic. It is almost impossible to distinguish the cross direction from the machine direction. Unique to this type of needle loom is the bristle-brush, bedplate system. Special crown type needles or fork needles are used in this loom design. The needles push fibers into a moving brush bed plate. The fibers are conveyed in this brush from the passage to the way out of the loom with zero draft. This takes into consideration the totally nonlinear look, ideal for shaped items. Random velour sort items have been exceptionally prevalent in the European and Japanese auto industry. While all U.S. car makers have the arbitrary velour machine, this sort of item has yet to end up well known in this nation. The most prevalent items made with this sort of needle loom are all more popular around the automotive industry.

102 3.2.1.3

Nonwoven: Process, structure, properties and applications Parameters influencing the properties of needle-punched fabric

Factors which influence the properties of needle-punched fabrics are given below: Raw material variables • Fibre type • Fibre length, fineness, cross-section, crimp, contour • Mechanical properties of fibres Web characteristics • Orientation of fibre in the web (parallel-laid, cross-laid or randomlaid) • Web weight and uniformity • Presence of scrim Machine variables • Needle punching density • Needle penetration • Entry and exit speed Machine design parameters • Needle density on board • Pattern arrangement of needles in the needle board • Type of needle/needle shape, size, number of barbs • Single or both sided needling • Pre-needling/finish needling • Straight/inclined punching/elliptical needling • Special arrangement for pattern fabric Finishing • Heat setting • Calendaring • Chemical bonding • Coating • Lamination Needle punch density: The punch density defines the number of needle penetrations per unit area (punches/cm2) and directly affects fabric properties and dimensions. It depends on following parameters



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• The density of needles in the needle board (Nd) • The rate of material feed • The frequency of punching • The effective width of the needle board (NbT) • Number of runs The puncture density per run Edpass = [n*F] / [V*W] Where, n = number of needles within a needle board F = Frequency of punching V = Rate of material feed W = Effective width of the needle board The puncture density in the needled fabric EdNV depends on the number of runs Npass; EdNV = Edpass * Npass The needle punching density influences the compactness of fibers in the web due to the higher number of penetration of needles. The punching density normally expressed as number of punches per square centimeter is the product of machine strokes per centimeter of web advance and the number of needles per centimeter of working width of machine (Midha & Mukhopadhyay 2005). The punch density could be determined as, nn Pd = A Where, A is the advance per stroke (cm) which is given by A = P/Sf P = Fabric production speed (cm/min), Sf = Punch (stroke) frequency (punches/min). nn is the number of needles per cm width of the needle board and Pd is the punch density (punches/cm2). Effect of needle punching density The influence of needle punching density on fabric characteristics are given below: • With increase in needling density, the tenacity of fabric increases initially due to better entanglement of fibers and then decreases sharply at higher needling density due to the occurrence of fiber breakage. • Higher needling density restricts fiber mobility during bending and this in turn results in higher bending length. An excessive needle depth and/or needling density results in severe fiber breakage, which leads to poor stiffness.

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• Basis weight of a needle punched nonwoven decreases with increase in needling density due to the increase in drafting and spreading of fibers during needle punching. • Owing to the higher fiber locking with increase in needle density, the thickness of fabric for the same basis weight decreases. So when the needle is withdrawn from the web structure, it resists the fibers to bounce back to their original position. Further increase in needling density may increase the thickness of fabric. The protruding fibers on the surface of fabric due to fiber breakage at excessive number of needling density exhibited greater thickness. • With initial increase in needling density, the fabric density increases due to better interlocking of fibers and then decreases with further increase in needling density due to the increase in number of pegs and spreading of fabric. • Thermal insulation properties of the fabrics increase initially and then decreases with increase in number of needle penetrations. At higher needle penetrations, due to increase in density of fabric, holding capacity of fabric to the air will be less leading to decrease in thermal insulation properties. • As like thermal insulation, the air permeability of fabric decreases with initial increase in needling density due to better entanglement of fibers and compact structure but air permeability increases at higher needling density due holes in fabric due to fiber damage at higher needling density. • As the number of penetrations increases, the abrasion resistance increases linearly and the softness decreases. The fabrics with soft handling properties have poor abrasion properties and vice versa. • Initially the modulus, tenacity and breaking extension increase with the increase in amount of needling, but at high needling the modulus and tenacity begin to decrease. The initial increase is due to the increase in entanglements, while the fall must be due to web tearing and breaking of fibers. • Along the machine direction, the bending length and bending modulus reduces, as amount of needling density is increased (Kamath 2004).

Depth of needle penetration The distance or gap between the top surface of the bed plate and the tip portion of the needle is known as needle penetration depth, when the needles are positioned at the bottom dead center. The important property influenced by the depth of needle penetration during the needling process is the fabric



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stretch. During needling operation, the fabric tends to stretch and the amount of this stretch increases with increase in penetration depth. Further, needle penetration decides the number of fibers carried by the needle barbs during the travel as well as the extent of fiber movement. The structural changes occur during the needle punching process are given below. • Fiber breakage could happen at higher depth of needle penetration as the fabric is stretched. • With increase in depth of penetration, the reorientation of fibers and the more pressure exerted on fibers leads to decrease in fabric thickness. • At lower depth of needle penetration, the punched loops do not protrude from the bottom surface of fabric. • With increase in needle penetration, number of barbs penetrating the web also increases which leads to better consolidation of fibers resulted in higher density of fabric. The increase in fabric density could exhibit the following characteristic on a fabric. – The thermal resistance of fabric decreases due to increase in fabric density. – Air permeability decreases with the increase in needle penetration due to increase in density. • Owing to the reorientation of fibers into the vertical structure at higher needle penetration, the initial modulus of fabric could increase. • The bending length of fabric increases initially with increase in needle penetration up to a certain level and then decreases. • The compressibility of fabric decreases and recovery increases with increase in depth of needle penetration owing to the higher entanglement of fibers and web consolidation. Effect of needling directions • As the needles penetrate through a longer path and there is a possibility of better entanglement of the fibers, oblique needling gives better strengthening of the fibers in the web structure. • Fabrics produced from double-sided oblique needling technique gives higher tenacity. • The fabric produced from the oblique needling method gives lower extensibility, higher density and lower air permeability compared to fabrics produced by single-sided perpendicular punching. • Longitudinal extensibility and air permeability decrease and the fabric density increases with an increased needle inclination.

106 3.2.1.4

Nonwoven: Process, structure, properties and applications Selection of fibers for needle punching process

Virtually all types of fibrous material can be used to make nonwoven bonded fabrics, the choice being dependent on: • The required profile of the fabric • The cost/ use ratio (cost effectiveness) • The demands of further processing Since nonwoven-bonded fabrics are almost always developed to meet specific requirements, the correct choice of fiber is of supreme importance. It is not only a question of finding the best kind of fibers, but of taking special fiber properties (fineness, length, crimp%, cross sectional shape, finish) into consideration. It is essential for the development and production of nonwoven bonded fabrics for a comprehensive study to be made of the properties of different fibers. This can be done by comparing the requirements to be met by the particular fabric with results obtained from the various individual fibers. Mainly the following fiber properties are taken into the consideration (Kamath 2004; Hearle & Purdy 1972; Igwe 1988; Hearle & Sultan 1968). Crimp – Highly crimped fibers tend to form more uniform web which will retain its original structure during the subsequent process. The amount and type of crimp may be determined by the requirements of the finished product. Denier – The use of the finer fibers results in great density, strength and softness and at the same time a more opaque sheet (fine fiber has more “covering” power). Heavy deniers are easier to open for production of a uniform web at higher speeds than fine deniers. Length – The staple length of the fibers to be used depends on the type of web forming equipment. But low production rates and poor quality fabrics usually result from the use of fibers that are too long. Finish – The finish on the fiber surface is usually designated as “bright”, “dull”, or “semi-dull” and the selection is arbitrary depending on the lecture or appearance desired in the end product. 3.2.1.5

Needle punching needle Needles are the core of the needle punch process. There are a great many, which make diverse impacts in the needled fabric. The needle itself contains different parts, all of which can be changed, yielding particular properties in the fabric. The needle sharpened steel shape can be changed. The number, shape and profundity of the points cut into the sides of the needle-sharpened steel can be modified. Furthermore, the point can be changed too. The course of action of the needles in the board likewise has an impact on the fabric appearance and properties (http://www.fosterneedleusa.com/tch_pprs/ designs.html).



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Parts of a needle The different parts of barb needle and its structure are shown in Figure 3.6.

Figure 3.6  Needle punching needle barb structure (Source: Senthil Kumar et al. 2010; Russel 2006)



1. Point – Sharp or ballpoint depends on the felted textile (ballpoint is more fine for fibers). 2. Working blade – Length: 20–30 mm, diameter 0.33–2.5 mm; 3. Barbs – The barbs are the most important part of the needle. It is the barb that carries and interlocks the fibers. The shape and sized of the barbs can dramatically affect the needled product. The theoretical number of fibers that may be collected in the barbs of a needle can be calculated as follows: (Kamath 2004)



nf =

2bd df

× nb

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Nonwoven: Process, structure, properties and applications

Where bd is the barb depth, df is the fiber diameter, nb is the number of acting barbs on the needle and nf is the number of fibers collected by the barbs. 4. Intermediate blade – The intermediate blade is put on fine gauge needles to make them more flexible and somewhat easier to put inside the needle board. This is typically put on 32 gauge needles and finer. It is used to obtain smaller holes in felted textile, to obtain lower weight of the needle board and to obtain better mechanical properties of the needle. 5. Shank – The shank is the thickest part of the needle. The shank is that part of the needle that fits directly in the needle board itself. 6. Crank – The crank is the 90° bend on the top of the needle. It seats the needle when inserted into the needle board. For needle with the tear drop shape of working blade is important the orientation of crank on the needle board. Figure 3.6 demonstrates the real barbs cut or framed into the needle blade. The outline underneath demonstrates a side perspective of the needle point in more detail. Each of the named parts can be modified and are imperative to the activity given to the fabric by the needle. The point kick-up is the separation measured from the needle surface to the highest point of the spike point after it is cut into the needle edge. This can be changed from no kick-up to high kick-up. The higher kick-up expands the fiber conveying capacity of the needle thorn however can likewise bring about some fiber harm. The kick‐up, while expanding fiber conveying capacity, does not expand interlocking of the filaments. It improves the web however causes fiber harm. For fabrics requiring high elasticity, kick‐up ought to be very less. The thorn edge is the quantity of degrees the fiber connecting with surface is dislodged from a vertical position. The edge can be fluctuated from zero to 20 degrees. Lower point permits fiber to slip from the thorn as the needle infiltrates the web. This yields loftier, less snared structures. For fabrics obliging high rigidity, higher spike edges ought to be utilized. The throat depth is additionally a vital figure for fiber conveying limit. The depth is the separation the thorn is cut into the needle. A more profound throat depth brings about more fiber conveying limit. An open throat allows the fibers to enter the barb easier and can increase the effectiveness of the needling. Types of needles Felting needles The felting needles are mechanically compact fibrous material. These needle looms may have one to four needle boards and needles from the top, bottom or



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top and bottom. The primary function of this type of loom is to do interlocking of fibers resulting in a flat, one dimension fabric. The structure of felting needle is shown in Figure 3.7.



1 – Point

2 – Working blade

3 – Barb



4 – Taper

5 – Intermediate blade

6 – Cranked shank



7 – Crank

Figure 3.7  Structure of a felting needle

The types of products made with this process and needle loom are diverse and multifaceted. They exist in variety of industrial products, geotextiles, automotives, interlinings, home furnishings, etc. Structuring needles



1 – Fork

2 – Working blade



3 – Intermediate blade

4 – Crank

Figure 3.8  Structure of structuring needle

Depending on the orientation of the fork needle, a rib or velour surface is introduced. The most popular products made with structuring looms include home and commercial carpets and floor mats, automotive rib and velour products, wall covering and marine products. Special shape of working parts Vario barb needle – Barbs are smaller towards the point. The needle is deflected to a lesser extent – reduced risk of breaking. Suitable for natural

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Nonwoven: Process, structure, properties and applications

fibers and waste. Conical needle – Working part smoothly passes into the reduced part as shown in Figure 3.9. Thus the fibrous material is penetrated with less resistance. Suitable for waste materials and for heavy products with area density higher than 1000 g/m2.

Figure 3.9  Conical needle

Working blade cross-sections • Triangular – standard for the most of applications • Tri star or cross star – more efficient fiber holding – more efficient needling proces with the same needle density (suitable for manmade fibers); Cross star is suitable for high density materials (geotextiles) • Tear drop shape – for woven fabrics (to obtain special properties – adhesion for subsequent fixing, roughened appearance) (www.grozbeckert.com) Direction of needling At the point when the needle sheets are orchestrated “inverse to one another”, two needling modes “synchronized” and “rotating” are conceivable. The needling “synchronized” mode implies that both loads up enter the felt in the meantime. In this manner just a large portion of the needles can be embedded in exchanging lines in every board to counteract encounter of the needles. To achieve certain and higher pressure, the necessary total penetration density is shared between a few needle looms. The needle looms are orchestrated one behind the other in supposed needling lines. Selection and maintenance of needles The felt density must be kept constant in time. As the needles wear out, there is less fiber transport and the felt density a decrease, if the needles are worn more on one side of the machine, the felt rolls will have a conical shape. Such rolls create problems during impregnation and post treatments. It is evident that the batt weight and tension must be equal on both sides of the machine. After a certain quantity of felt production, the new ones must replace the worn needles. If the whole board is changed in one time, the felt will be dense and highly marked. It is a general practice to change the needles of a part or half of



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the board, keeping the new needles at the entry side. If a partial re-needling of a board is made necessary because of an accident, it is advisable to replace the broken needles with used ones to avoid needle marks. New generation needle looms can be equipped with complete suction devices system, in order to avoid dust accumulation and reduce to the minimum the times of maintenance and needle board changing during working time. For a given fiber blend, the type of felting needle has great influence on the felt quality, needle wear and needle breakage. Presently, the felting needle styles are in the range of 32–42 gauges, which are suitable for processing fibers in the range 1–18 denier. Coarse needles like 20 and 25 gauges are predominantly used to needle waste fibers. The use of finer needles indicates that the industry is processing finer denier and virgin fibers for producing higher quality felts. Needle breakage in heavyweight felts is a problem. Certain types of fiber finishes are used to reduce fiber–metal friction, to reduce static electricity and increase wetting properties in case there is a post-chemical treatment. The needle marks are often visible on the felt surface. Three types of patterns may be seen: machine direction lines, horizontal lines and inclined lines. The formation of horizontal lines is due to a high output speed as compared to needle punching strokes. This pattern is seen especially in low weight materials. This type of felt has poor bending characteristics. The presence of longitudinal lines means intensive needling and that the material speed is too slow compared to strokes. If the needle gauge, penetration, number and type of needle punching machines are not suitable, such lines are highly marked. Hence, during needle punching, the machine stroke should be adjusted to have uniform surfaces. Machines with high density needle boards are helpful in producing smooth surface felts. 3.2.1.6

Characteristics of needle-punched nonwovens

Needle felts have a high breaking tenacity and also high tear strength but the modulus is low and the recovery from extension is also poor. In order to improve the recovery, it is conventional include yarns, nets or fabric scrims in the structure. A typical example is the production filtration felts where some type of scrim fabric is introduced during needle punching. In case injected shoes, the insole material is a nonwoven reinforced with a polypropylene raffia fabric with GSM of about 105. Their unique physical properties like elongation in all (x, y & z) directions for mouldable applications is good. High strength makes them an overwhelming choice of geo-textiles. The principal advantage is that the nonwoven is practically homogeneous in comparison with a woven fabric so

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that the whole area of a nonwoven filter can be used for filtration, whereas in a woven fabric the yarns effectively stop the flow, leaving only the spaces between the yarns for filtration. Generally important characteristics of needle felts are the degree of felt compression, the strength-elongation ratio and the permeability characteristics (Wilhelm Albrecht et al. 2003). For highly entangled fiber felts for synthetic leather, the punching density may vary between 500 and 1200 punches/cm2. Due to high needle punching intensity, the production of synthetic leather needs 4–6 machines installed in tandem. For filter felts, it may be up to 650 punches/cm2.

• Longer fiber lengths result in higher strength, higher felt density and less air permeability.



• Finer fibers lead to smaller felt thickness and to lower air permeability. The needling of finer fibers requires inevitably also the use of finer needles to achieve sufficient strength characteristics



• Higher crimp results in a higher tear resistance and elongation and a better dimensional stability of the needle felts.



• The characteristics and the structure of needle felts also depend on the web structure and the area mass. Machine-oriented web results in a high strength in the longitudinal direction and predominantly crossoriented webs result in a high strength in cross direction.



• The web area mass has a great influence on air permeability.



• The area ratio of the fiber plugs in the needle felt is in the range of 2–12%. The fiber length of the plug is 6–20% and the fibers are more densely packed in the fiber plug than in the needle felt.

3.2.1.7

Applications of needle-punched fabric

Needle-punched structures have a wide range of applications in both domestic and industrial markets. The applications of needle-punched fabrics are extensive and listed as follows (Rupp 2008): • Geotextiles • Automotive • Filter media • Floor coverings • Blankets • Insulation padding • Tennis court surfaces • Wall coverings



3.2.2

Nonwoven bonding techniques

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Stitch bonding

A stitch-bond nonwoven fabric is made on a weaving machine that bonds the web, or holds the web set up, with longitudinal yarns. While other basic fiber-bonding techniques utilized as a part of the creation of nonwoven fabrics, needle-punch, thermal bond or chemical bond have the downside of solidifying the surface of nonwoven fabrics, the stitch-bonding system gives nonwoven fabric a composition as delicate as that of the original web. (http:// www.nonwovensindia.com) Stitch bonding is a half and half innovation utilizing components of nonwoven, sewing and weaving procedures to create an extensive variety of fabrics that are utilized as a part of home decorations and modern fabrics, including composite basic applications. The introductory chip away at stitch bonding occurred in Czechoslovakia and East Germany amid the 1960s utilizing short-staple fibers to deliver fabrics for modern and utilitarian nonstyled family employments. These fabrics were made utilizing creel-bolstered, spun stitching yarns. As the utilization of stitch bonding spread to the United Kingdom and different nations, nylon and polyester fiber yarns turned into the favored materials for the stitching part Malimo Stitch bonding Systems, the Mali system of stitch bonding was initiated during the late 1940s by Heinrich Mauersberger of East Germany. His US Patent #2,890,579 was issued on June 16, 1959. Mauersbergers first fabrics were based on joining warp and filling yarns with a stitching yarn to produce a woven-like fabric. The first product produced by the Malimo stitch bonding process was a toweling, made in 1952 (Mansfield 2002). Stitch bond is a nonwoven development where the fabric is framed by stitching or knitting the fibers to frame a fabric with the presence of a knit fabric. In the most well-known cases it includes warp knitting of yarns through a fibrous mat. It can likewise be knitting of fibers without yarns or knitting of yarns around laid twist and filling yarns which don‘t interweave with one another. 3.2.2.1

Manufacturing method

As per the maliwatt method in the German Democratic Republic [GDR] and the Arachne procedure in Czechoslovakia, stitched nonwoven materials are made by joining fibers into the fabric, which is traveling through a knittingstitching machine, stitching with strings set and joined like foundation stitches on a knitting machine. (http://www.nonwovensindia.com). Such nonwoven materials are utilized as warm protection or pressing material or as the establishment in the production of coverlets, covers and coats. The stitch bonding process is shown in Figure 3.10.

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1 – Needle motion

2 – Knock over and support combs



3 – Guide bar

4 – Device for transport of the web



5 – Fabric draw-off from the needle motion and fabrics take-up



6 – Device for feeding and guiding the warp threads

Figure 3.10  Stitch bonding process (Source: Batra & Pourdeyhimi 2012; Gupta 2013)



Figure 3.11  The basic types of stitch structures (Source: Albrecht et al. 2003)



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Stitch-bonding Maliwatt means bonding fiber webs or spun bonded webs incline toward capably transverse fiber webs, utilizing strings to accomplish the bonding. The fibers are bonded into the loops however don’t add to loop formation. The essential sorts of structure are pillar-stitch and tricot-stitch as shown in Figure 3.11. 3.2.2.2

Stitchbond stages

The loop formation process based on threads is shown in Figure 3.12. The web- bonding process with its main elements compound needle, closing wire, com- pound needle hook and guide can be seen in process steps. The various steps in stitch formation process are shown in Figure 3.13.



1 – Compound needle

2 – Closing wire



3 – Knocking-over sinker

4 – Support rail



5 – Guide

6 – Counter reacting pin



7 – Warp yarn

8 – Fiber web

Figure 3.12  Stitch-bonding point and loop-formation cycle of Maliwatt stitch-bonding machine (Source: Albrecht et al. 2003)

The level of bonding accomplished with web stitch-bonded materials relies on upon the quantity of loops of strings every unit zone. This number is comprised of the density of loop wales (number of wales every length unit) and course density (number of courses every length unit). Wales in the nonwoven keep running in machine-heading, courses run across. The density of wales is controlled by machine gage, e.g. the quantity of knitting components in every 25 cm of working width. With respect to stitch-bonding, it is at present conceivable to place a most extreme of 22 loop wales with in 25 cm of working width. Course density is controlled by stitch length (Cotterill 1975).

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Nonwoven: Process, structure, properties and applications

1. Penetration, 2. Lapping, 3. Closing, 4. Knocking-over, 5. Take-down

Figure 3.13  Steps in Stitch formation (Source: Batra & Purdeyhimi 2012)

Equipment available allows stitch lengths of 0.5–5 mm. Machine gauge and stitch length are process values depending on the product to be made. The basic tools applied in the stitch bonding process are compound needle, closing wire and knocking-over sinker. Compound needles, for instance, may be coarse, medium, fine or very fine. For better stability, it is common practice to combine two different needle gauges, such as fine/very fine. The length of the compound needle corresponds with lower gauge whereas its width corresponds with higher gauge. Except for the basic knitting tools, further types of tools are available, which are used in the different variants of the stitch-bonding process. A large variety of patterned stitch-bonded materials are achievable (Albrecht et al. 2003) by means of • change to bonding • change to the initial position of the cam discs (turning the cam discs round their axis) • change to the direction of rotation of the cam discs (turning around the cam discs) • change to the initial position of the guide bars • change to the thread insertion and • use of coloured warps of coloured yarn



Nonwoven bonding techniques

3.2.2.3

117

Types of stitch bonding system

The different types of stitch bonding systems were given in Table 3.1. Table 3.1  Different types of stitch bonding process (Source: Mansfield 2002) S. no.

System type

Description

1.

Malimo

Uses crossed layers of the warp and filling threads, which are knitted together by a sewing yarn to form the structure

2.

Maliwatt

Uses a nonwoven batting that is knitted together by a stitching yarn. The unit has only one guide bar

3.

Arachne

Similar in principle to the Maliwatt, except that it has two gude bars for better pattern capability

4.

Malipol

Similar in principle to Malimo. It forms a single-face pile or loop by stitching a yarn through a substrate. The substrate can be nonwoven, woven or knitted. The loop is formed by the use of sinker bar.

5.

Voltex

Essentially, a Malipol unit used with woolen yarn. Stitching yarns are not needed to form the pile. The fiber from the batt is stitched through the base fabric to form a pile.

6.

Malivlies

Similar to Maliwatt. However, stitching yarn is not used. Stitching needles catch fibers from the web and knit them into the web structure.

7.

Arabeva

Similar to Arachne, but it does not use a stitching yarn. Fibers are taken from the web and stitched into web.

8.

Araloop

An Arachne-type unit used to stitch loops into a nonwoven, woven or knitted substrate. It is analogous to the Malipol unit.

9.

Araknit

Produces a warp knit tabbed fabric. The fabrics are similar to a two-bar raschel fabric.

10.

Malifol

Basically a Malimo unit, but the warp direction yarns are split from a roll of polyester or polypropylene case oriented film. Recycled polymers can be used in the making of film. The fill-in is formed on a separate but attached, film former.

Maliwatt The stitch formation process in Maliwatt machine and the resultant fabric is shown in Figure 3.14. The horizontal compound needle and closing wire framework, which works in conjunction with the knock-over sinker and the supporting rail, enters through the substrate which is typically a cross-laid web. The sheet of stitching yarn, which is embedded through the aides away from any confining influence open hooks of the compound needles, frames stitches that enter the web. The Maliwatt system consists of following components:

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• • • • •

Stitch bonding unit with a control system for the working elements Web feeding system Yarn feeding and monitoring systems Winding and storage system for the stitch-bonded fabrics Cutting unit with a control system for the machine

Figure 3.14  Maliwatt stitch formation process and stitched nonwoven sample

The flat needle structure and the bonding arrangement of the yarn, which works together with the instrument to evacuate officially shaped stitches so as to make space for those to be framed, and the support guide, enter through the substrate which is a web put across to the machine. The stitching yarn is strung through the guides into the open needle hooks and forms the stitches, which penetrate the web. Pillar and tricot stitches can be created by a cam shogging. By modifying the needle framework and the bonding arrangement of the yarn, it is conceivable to fuse in the meantime the fibers inside the stitches and keep the withdrawal of the stitches from the limit of last shaped stitch. With tricot weave, a yarn system parallel to warp can be arranged inside the web and later on fused into the stitch bonded fabric. (Wilhelm Albrecht et al. 2003; Russell 2006) Maliwatt – applications • Soft furnishings, upholstery fabrics for mattresses and camping chairs, blankets, • Transportation cloth, • Cleaning cloths, fabrics for hygiene and sanitary purposes, • Secondary carpet backing, • Lining fabrics, interlining for shoes and apparel,





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• Adhesive tapes (e.g., those used for harnessing electric cables in automobiles), • Velcro-type fasteners, • Laminating fabrics, coating substrate, • Insulating materials, • Geotextiles, filter fabrics, • Composites and flame-retardant fabrics

Malivlies The stitch formation process in malivlies machine and the resultant fabric is shown in Figure 3.15. The laying-in sinker averts web movements amid the infiltration process. When the needle framework moves back to the knocking over position, the fibers which are in the front of the web hold tight the hooks of the needles, are conveyed to within the hook of the end wire and drawn through the thickness of the web. When these fibers are drawn through the stitches shaped by the fibers on the former course, while they are as yet hanging at the needle hooks, new stitches are framed through the current stitches, which are skipped by the shut snares of the needles.



1 – Stitching needle 3 – Knocking-over sinker 5 – Stitch bonded fabric

2 – Closing wire 4 – Support rail 6 – Laying-in sinker

Figure 3.15  Malivlies stitch formation process and the stitched fabric (Source: Albrecht et al. 2003)

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The laying-in sinker averts web movements amid the infiltration process. When the needle framework moves back to the knocking over position, the fibers which are in the front of the web hold tight the hooks of the needles, are conveyed to within the hook of the end wire and drawn through the thickness of the web. When these fibers are drawn through the stitches shaped by the fibers on the former course, while they are as yet hanging at the needle hooks, new stitches are framed through the current stitches, which are skipped by the shut snares of the needles. The Malivlies fabrics made completely out of fibers are mechanically reclaimable. The principle sorts of fiber being used are polyester, polypropylene, viscose and recovered fibers and the created fabrics have an area mass going from 120 to 1200 g/m2. The primary applications are auto inside spreads, felts for material blankets, sponges, cleaning fabrics, geotextiles and channel materials, covering substrates and covers, items for therapeutic, hygienic and clean utilize, rug sponsorships. Malimo



1 – Compound needle 3a – Guide, 1st guide bar 4 – Knocking-over sinker 6 – Backing rail 8 – New overlaps 10 – Warp threads 12 – Malimo fabric

2 – Closing wire 3b – Guide, 2nd guide bar 5 - Reacting pin 7 - Old loop 9 – Weft threads 11 – Fiber web

Figure 3.16  Malimo stitch formation process (Source: Russell 2006)



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Figure 3.16 shows the relative positions of a Malimo stitch-bonding unit. The needle system (1) infiltrates the yarn layers (in weft and in warp), the webs, the support fabrics, the films, the paper and whatever other layer of material, which can be presented. The guide (3a–3b) spots the fabrics to be stitched in the open hooks of the needle framework. The already shaped stitches let the stitched material slide, while closing the stitches. The needles start to come back to their knocking over position (4), the hooks of the needle system with the new overlaid stitched yarns are presently shut by the end yarn so that the old stitches can slide over the highest point of the needles. The old stitches are secured over the highest point of the needles and new loops are attracted through the stitches to finish the new course. Also, the guides shock to place the stitching yarns in the right position for the resulting machine cycle, which relates to another course. Areas of appilcation • Industrial textiles: Composites for high-tech areas (fiberglass, carbon, Kevlar, HD-PE), sandwiche nonwovens, geotextiles, insulating materials, laminating substrates, packing textiles • Furnishing fabrics, home and household textiles: Furnishing fabrics, upholstery fabrics, textile wall coverings, cleaning and polishing cloths. Based on the Malimo platform, different versions and auxiliary devices have been developed. These developments enable: • Non-continuous and continuous parallel weft insertion • Multiaxial constructions • Cross weft insertion • Glass fabric manufacture Malipol Malipol stitch bonding systems have the following main elements: • pile yarn • ground fabric • stitch bonding head • fabric take-down and batching The stitch formation process in Malipol machine is shown in Figure 3.17. The compound needles penetrate the ground fabric and the stitching or pile yarn is overlapped in the needle hook. The pile yarn is also laid on top of the pile sinker at the same time so that a tricot movement is used to create the pile and knit the yarn into the ground structure. The needles enter the fabric

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ground, and the stitching yarn is embedded into the needle hook. The loop yarn is put over the knock over sinker in the meantime, so that a tricot racking, for example 1-0/1-2, is utilized to make the pile and to stitch the yarn inside of the essential structure. The machine is accessible in the gages 10,12 and 14 (number of needles/25 mm), with pile sinker tallness somewhere around 1 and 11 mm and stitch lengths somewhere around 1 and 3 mm, realistic through gear controls. The machine rate ranges from 900 to 1300 stitches every moment.



1 – Compound needle bar

2 – Closing wire bar

3 – Guide bar for pile yarn



4 – Knock-over sinker bar

5 – Pile sinker bar

6 – Pile yarn



7 – Ground fabric

Figure 3.17  Malipol stitch formation (Source: Albrecht et al. 2003; Russell 2006)

The decision of the feeding system is depends upon the quality and qualities of the item. Any substrate, which can be gone through by needles, can be utilized as ground fabric, on condition that it stays undamaged. Concerning weaves, sateens and twills are the most suitable, albeit likewise level, not exceptionally conservative but rather wavy fabrics are good with this sort of procedure. The options are the stitch bonded fabrics, latex, sews and movies. Cotton or viscose fabrics ranging from 100 to 200 g/m2 are the most common materials for blankets and waddings, whereas fabrics made of polyester and polyamide continuous filament weighing between 50 and 200 g/m2 are to be preferred for the production of plush and imitations fur.



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Application • blankets • cleaning textiles (wiping mop) • pile fabric for velcro fastening stripes • lining plush and soft-toy plush • bathroom sets • one-sided terry fabric Voltex Voltex fabrics are high-pile fabrics or plush fabrics based on two pre-formed main elements: a ground fabric and a web. No preparation for stitching yarns, as cone-winding or warping is required. The main elements of a voltex machine are indicated in Figure 3.18. High pile or high plush fabrics based on two principal reformed elements, a ground fabric and a web, which are continuously introduced. No stitching yarn or yarn preparation, such as winding or warping are required. The voltex stitch bonded fabrics are mainly used in lining fabrics, imitation furs, soft-toy plush, shoe uppers and shoe lining, floor coverings and upholstery fabrics.



1 – Compound needle bar 4 – Knock-over sinker bar

2 – Closing wire bar 5 – Pile sinker bar

3 – Fiber web 6 – Ground fabric

Figure 3.18  Voltex stitch formation process (Source: Russell 2006)

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3.2.3

Nonwoven: Process, structure, properties and applications

Hydro entanglement/spun lacing system

The ‘spunlace’ technology developed by du Pont, where a nonwoven web is impinged by very fine jets of water at high pressure, up to 250 bars, thereby whirling the fibers that results in their entanglement. Because the only bonding that is achieved between the fibers is due to the entanglement of the fibers, the fabric thus produced is highly flexible and has a supple hand. Precursor webs, made by either carding, wet laying, spun-bonding, whether from one type or blends of fibers including wood pulp, may be used (Suzuki 1984). The principle of hydroentanglement process is shown in Figure 3.19. Hydroentanglement (spunlace) the fibers are mechanically entrapped together by high-speed velocity of water that are coordinated onto the web (White 1990; Relich 1988). The water weight can be 20–600 bar. The jet tangles, twists and improves the fibers to make bonding and at times to present designing impacts. Examples and gaps in the fabric are delivered by adjusting the outline of the transport sleeve surface.

Figure 3.19  Principle of hydro entanglement process (Source: www.tikp.co.uk)

Various important steps in the hydro entangling process are shown in Figure 3.20 and the hydroentangling equipment and the resultant fabric is shown in Figure 3.21. While some of them are typical in a nonwoven process, some of them are unique to the process of spunlacing.



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1 – Winding 2 – Dewatering system 3 – Belt with suction 4 – Water purification 5 – Fibrous web 6 – Water jets 7 – Drying system

Figure 3.20  Working of hydro entanglement process

Figure 3.21  Hydroentangling equipment and spunlace fabric

The shaped web (for the most part air-laid or wet-laid, however in some cases spun bond or melt-blown, and so on.) is initially compacted and pre wetted to kill air pockets and after that water-needled. The water pressure

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for the most part increments from the first to the last injectors. Pressures as high as 2200 psi are utilized to direct the water planes onto the web. This pressure is adequate for most nonwoven fibers, albeit higher weights are utilized as a part of specific applications. It has been contended that 10 lines of injectors (five from every side of the fabric) ought to accomplish complete fabric bonding. Injector opening diameters range from 100 to 120 micro meter and the gaps are orchestrated in lines with 3–5 mm dividing, with one line containing 30–80 openings per 25 mm (Allen 1997). The impinging of the water streams on the web causes the snare of fibers. The jets debilitate a large portion of the active vitality fundamentally in revamping fibers inside of the web and, also, in bouncing back against the substrates, dispersing vitality to the fibers. A vacuum inside of the move expels utilized water from the product, counteracting flooding of the item and decrease in the viability of the jets to move the fibers and bring about ensnarement. The main entanglement move follows up on the first side various times with a specific end goal to bestow to the web the fancied measure of bonding and quality. The web then ignores a second entanglement come in a converse bearing to treat and, in this way, solidify the opposite side of the fabric. Hydroentanglement did at standard conditions oblige 800 pounds of water every pound of item. Hence it is important to add to another filtration framework ready to successfully supply clean water with this high throughput; generally, water jets openings get to be clogged up. This framework comprises of three stages: chemical mixing and flocculation, dissolved air flotation and sand filtration. Spunlaced fabrics have led to a lot of speculation regarding their manufacture because most of the manufacturing process details are considered as proprietary (Elsharkawy, 2014). 3.2.3.1

Elements in hydroentanglement process

Spunlaced fabrics are alternately called water-jet-entangled, hydroentangled or hydraulically-needled nonwovens. The spunlace or hydroentanglement process involves the following elements: • Fiber • Web forming • Water jets • Needling substrate • Water system • Drying • Finishing



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Fiber The choice of fiber will have a great effect on the productivity, amount of entanglement, and final product characteristics. The fiber used in spunlaced nonwoven should think about following fiber characteristics (Jürg Rupp, 2008 b). • Modulus – In general, fibers with low bending modulus entangle more easily than fibers with high bending modulus. Thus, cotton and rayon entangle with much less energy input than polyester. The temperature of the high pressure water is generally kept as high as possible because warm water reduces bending modulus and increases entanglement. Bending modulus also decreases as the filament size (denier) is decreased. • Fineness – For a given polymer type, larger diameter fibers are more difficult to entangle than smaller diameter fibers because of their greater bending rigidity. • Cross section – Since the fiber cross-section affects bending modulus, fibers of the same polymer type with a ribbon cross-section entangle more easily than trilobal fibers. For a given polymer type and fiber denier, a triangular shaped fiber will have 1.4 times the bending stiffness of a round fiber. An extremely flat, oval or elliptical shaped fiber could have only 0.1 times the bending stiffness of a round fiber. • Length – The number of tie points or entangled areas is directly proportional to the number of fiber ends present in the web; therefore, short fibers will produce more tie points than long fibers. However, fabric strength is also directly proportional to fiber length; and a balance between fiber ends for more tie points and fiber length for increased fabric strength is necessary. Wood pulp fibers are short and create many tie points but are not long enough to provide fabric strength. • Crimp – Crimp is required in staple fiber processing systems and contributes to fabric bulk. Too much crimp can result in lower fabric strength and entanglement. • Fiber wetability – Hydrophilic fibers entangle more easily than hydrophobic fibers because of the higher drag forces. Hydroentanglement could be carried out using dry-laid (carded or airlaid) or wet-laid webs as a precursor. Most commonly, precursors are mixtures of cellulose and man-made fibers (PET, nylon, acrylics, Kevlar (P84, (imide) etc). In addition, Asahi Chemical Industry has used very fine fibers produced from splittable composite fibers to produce hydroentangled substrates for

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synthetic suede leather products. As a rule, cellulosic fibers are favored for their high quality, flexibility, plastic deformation resistance and water insolubility. Cellulosic fibers are hydrophilic, chemically stable and generally dry. Another favorable position is that cellulose has an inborn holding capacity created by a high substance of hydroxyl gatherings, which draw in water atoms. As the water dissipates from the fabric, the hydroxyl gathers on fiber surface connection together by hydrogen bonds. For the most part, low micronaire cotton is not prescribed for hydroentangled nonwovens due to higher number of neps and little packages of entrapped fibers, bringing about unattractive seeming fabric. Despite this, fabrics made with lower micronaire fiber show higher quality, likely created by a higher number of fine fibers and more prominent surface region. In addition, greige cotton has been used in spunlacing technology. It has been shown that the absorbency rate increases with increasing hydroentangling energy. This is the result of oil and wax removal from the fiber surface. These nonwovens can be subsequently bleached, which should raise the strength of the fabric (Chellamani et al. 2013). Web forming Both dry and wet laid systems are employed to prepare precursor webs for spunlace processes. When cards are used to prepare the web, the final product has much higher machine direction strength than cross direction strength. These non-isotropic products are acceptable for some of the spunlace market; however, when balanced Machine Direction (MD) / Cross Direction (CD) properties are required, they are not acceptable. The two major producers, Chicopee and du Pont, have developed proprietary high speed air-lay systems that produce isotropic webs. These products have MD/CD ratios of as low as 1.2–1.5 as produced on the spunlace machine. More recently, wetlaid processes have been used to prepare the webs. These systems have the capability of producing very uniform webs with balanced MD/CD properties. Water jets The objective of the high pressure water system is to create fine, high velocity columnar streams of water. Small holes are placed in a jet strip in one or two rows with a density of 10–20 per cm. The holes range in diameter from 0.08 mm to 0.25 mm but usually are either 0.12–0.18 mm. The holes are highly finished to smooth surfaces and produce columnar jet streams. Small imperfections in a hole will cause the jet stream to break up and be less efficient. The jets arc placed as close to the web as possible to assure that the jet streams do not break up and dissipate their energy. The usual jet to substrate or screen distance is 2 inches (50 mm) or less. Special care must be



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taken in designing the manifold or water distributing system to assure that each hole is supplied with adequate water with minimum turbulence. Each jet strip is placed perpendicular to the direction of web travel with as many as ten strips in series making up an entanglement station. Water pressure is increased step-wise from the first to the last jets. Occasionally, the last jet will have lower pressure to provide for improved surface integrity. Two types of substrate configurations are used in spunlac production: a travelling screen or belt and a rotating drum fitted with a perforated cover. Under some conditions, the drum entangling units give higher entangling efficiency, better machine efficiency, and longer life than belt units. Vacuum is applied underneath the needling substrate to remove water. If sufficient water is not removed, the excess absorbs some of the energy provided by the water jets and reduces entangling efficiency. Entangling can be achieved with a single needling station, or multiple stations can be employed. Also, a fabric may be needled on only one side, or both sides may be needled. Hydro entanglement is an energy transfer process where the system provides high energy to water jets and then transfers the energy to the precursor. In other words, the energy is delivered to the web by the water needles produced by the injector. Therefore, we can calculate the energy from the combination of the water velocity, and the water flow rate (Hsu-Yeh Huang & Xiao GAO 2004). Flow rate = P½ × D2 × N × 2572 × 10−8 m3/hour/injector/meter Energy = P3/2 × D2 × N × 7 × 10−10 kWh/injector/meter Where P = Water pressure (bar) D = Hole diameter (μm) N = Number of holes (per injector per meter) In general, the diameter of water needle ranges from 100 to 170 μm. The highest number of needles is 1666 needles per meter of injector, corresponding to the smaller diameter. The water pressure ranges from 30 bars to 250 bars and it is increased stepwise from injector to injector. The factors controlling the entanglement in spunlacing process are water pressure, water jet and diameter of holes, line speed, vacuum and forming surface. Needling substrate Needling substrates play an important role in hydro entanglement process. In addition to holding the web in place, substrates are designed to increase needling efficiency and to create either non-patterned or patterned products. Joining the belt, screen, or drum sleeve together in the right length is a

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particularly complicated process. Substrates can be constructed to produce virtually any design desired. However, with the moving belt or screen systems, patterns are limited by the physical constraints of that system. A drum sleeve is much more versatile because very coarse screens and metal plates can be used as substrates. Water system The high pressure water system requires a large amount of water that has a nearly neutral pH, contains almost no particulate matter, is low in metallic ions such as Ca, is at a prescribed temperature, and contains no bacteria or other organic materials. Because of the large amounts used, water must be filtered and reused. This requires a complicated and efficient water filtration system. Depending on the raw materials, a combination of the following filtration processes is employed: air/water separators, bag filters, settling ponds or clarifiers, precoat-filters, cartridge filters, and deionization units. In addition, at some point, bacteria and other organic organisms must be eliminated. Centrifugal pumps have been installed on virtually all of the large commercial installations. Reciprocating pumps are often used in small laboratory or prototype units. For a typical high pressure system, pressure at the pump is usually maintained at approximately 150 bar. At the needling station, this pressure is reduced for individual jets where pressures range from 15 to 150 bar. Drying Thorough air and drum drying are used in spunlace operations. For 100% fiber products, the fabric is not affected by the drying method. For wood pulp/ polyester products, thorough air drying will produce a softer, loftier product than drum drying. Finishing Although most nonwovens are considered finished when they are rolled up at the end of the production line, many receive some other chemical or physical treatment to provide special characteristics. Some of these treatments can be applied during production, while other must be applied in separate finishing operations. Examples of finishing treatments are as follows: • Flame retardant • Rewet agents • Hydrophobic agents • Coloration • Printing





Nonwoven bonding techniques

• Antistat agents • Bonding • Stretching

3.2.3.2







• • • • • • •

3.2.3.4





Properties of spunlaced fabrics

• Good dimensional stability, which is likewise responsible for drape, non-abrasiveness, and great quality/weight properties of the fabric, pilling and abrasion behavior (Connolly & Parent 1993). • Wash strength is extensively lower than that of woven or knitted fabrics. • The softness of the fabric is clarified by the way that the caught structures are more compressible than fortified ones, and also having versatility and fractional arrangement of fibers in the thickness direction. • Spunlaced fabrics demonstrate high drape, non-abrasiveness and agreeable handle (in light of the fact that more fiber entanglement prompts expanded quality without an increment in shear modulus). Shear modulus stays low and is essentially free of the level of entanglement. (Chellamani et al. 2013)

3.2.3.3



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Advantages of spunlace fabric

Replaces chemical binders Softer/drapeable fabric Absorbency, strength, flexibility Allows for designs/patterns Lint free No binder/easier to recycle Light weights: Faster & lower cost vs. Needle punch Applications (Vaughn 1978)

• Spunlace fabrics can be further finished, usually dyed and/or printed, treated with binders to allow for wash durability, or fire retardants can be applied to resist burning. • The fabric can be treated by antimicrobial agents to enhance resistance against microorganisms. • Surgical packs and gowns. • Protective clothing as chemical barriers to wipes.

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Nonwoven: Process, structure, properties and applications

• Towels and sponges for industrial, medical, food service and consumer applications. • The main reason for wide use of these fabrics in medical applications is based on relatively high absorption abilities. Another important criterion is absence of a binder in the fabric allowing sterilization of the fabric at high temperatures. • Bacteria-proof cloth.

Chemical bonding

Chemical or resin bonding is a generic term for interlocking fibers by the application of a chemical binder. The chemical binder most frequently used to consolidate fiber webs today is water-borne latex. Most latex binders are made from vinyl materials, such as polyvinylacetate, polyvinylchloride, styrene/ butadiene resin, butadiene, and polyacrylic, or their combinations. Latexes are extensively used as nonwoven binders, because they are economical, versatile, easily applied, and effective adhesives. The versatility of a chemical binder system can be indicated by enumerating a few factors that are considered when such a system is formulated. Chemical binders are applied to webs in amounts ranging from about 5% to as much as 60% by weight. In some instances, when clays or other weighty additives are included, add-on levels can approach or even exceed the weight of the web. Waterborne binders are applied by spray, saturation, print, and foam methods. A general objective of each method is to apply the binder material in a manner sufficient to hold the fibers and provide fabric properties required of the intended fabric usage (Sakthivel & Ramachandran 2012). The chemical bonding process is shown in Figure 3.22.

Figure 3.22  Chemical bonding of nonwoven (Source: www.edana.org)



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3.3.1

133

Chemical binders

In the early phases of nonwovens improvement, diverse sorts of natural resins and glues were utilized to bond nonwovens. While they passed on some integrity and strength these webs, they likewise had numerous clear inadequacies. Hence, engineered binders were produced to meet the auxiliary and execution necessities of nonwoven fabrics. Polyvinyl acetic acid derivation was the first effective manufactured binder utilized as a part of generous volume. This material had unmistakably prevalent adhesive properties, quality, and execution contrasted with the early regular adhesives. This binder is adaptable and it can be connected to fiber networks by numerous ways including print bonding. The industry was faced with the inevitable compromise in fabric properties of nonwovens bonded with synthetic materials. In order to build strength in the fabric, increasing amounts of resin must be applied, which results in more stiffness. If softness is necessary, it can be achieved, but primarily by sacrificing strength. A significant change in this exchange of and softness was accomplished with the presentation of acrylic-based latex binders in the 1950s and 1960s. By fitting determination of co-monomers, it is conceivable to manufacture enhanced softness properties with satisfactory quality. Consequently, these binders turned out to be broadly utilized by a large portion of the nonwovens business, regardless higher expense. As polymer innovation for producers of engineered binder frameworks enhanced, a more noteworthy mixed bag of chemical building blocks got to be accessible with much more flexibility regarding binder quality, strength, and different properties. The presentation of cross-linkable and self-crosslinking binder polymers turned out a totally new scope of fabric properties. This was especially vital in solid nonwovens where such toughness includes as launderability and cleanability were important. (Meazey 1971) 3.3.1.1

Properties desired in a binder

The following list are some general considerations required for an ideal binder. The required properties can be varied depending on the end-uses (Kannadaguli & Kotra 2004).

• Strength: The strength of a nonwoven fabric is more closely related to the strength of the applied binder.



• Adhesion to fibers: Even though the mechanism of adhesion is not completely understood, the adhesion strength of the binder-to-fiber bond and binder-to-binder strength has to be considered.

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• Flexibility/handle: The some movements of fibers should be allowed, especially when a soft hand is desired. • Elastic recovery: To avoid the permanent deformation of fabric, good elastic recovery is required under strain. • Resistance to washing/ drying cleaning: Some nonwoven products need durability in cleaning processes according to their end-uses. • Resistance to aging: The binder should be stable and not be degraded in the fabric during storage and use. • Good color and color retention: Diverse ranges of colors are required, and the colorfastness and yellowing problems should be considered. • Economical: Minimizing the cost is an ongoing requirement. • Other special requirements: Such as flame resistance, resistance to chemicals, air, oxygen, light, heat, etc.

3.3.2

Methods of binder application

The most common methods of applying a binder to a dry-laid web are saturation, foam, spray, and print bonding methods. For wet-laid nonwovens, most of the same methods can be used but bonding must be applied after partial drying. For printing, the web must be dry. Saturation bonding process Saturation chemical bonding includes complete drenching of the nonwoven web in a shower containing binder. The abundance binder can be uprooted by a couple of nip rolls. Figure 3.23 demonstrates the essential routines for immersion utilizing horizontal padding (a) and vertical padding (b).

Figure. 3.23  Saturation bonding process (Source: http://www.nptel.ac.in)



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The nonwoven web is guided through the immersion shower by rollers and afterward presses between a couple of nip rolls to press out overabundance fluid. The measure of binder taken up by the nonwoven relies on upon the premise weight of the nonwoven, time allotment spent in the shower, wettability of the fibers and nip weight. This technique can give higher binder to fiber levels consistently all through the nonwoven. Anyhow, as it incorporates short wetting time, the strategy is more suitable for lightweight and very penetrable nonwovens. 3.3.2.2

Foam bonding process

Foam bonding is intends to apply binder at low water and high bindersolids focus levels. The fundamental idea utilized includes utilizing air and also water as the binder diluents and transporter medium. Foam-reinforced nonwovens require less vitality in drying, following less water is utilized (Parsons 1999). The foam is created by bringing air into the planned latex while mechanically disturbing the binder arrangement. Air/latex dilutions or blow proportions in the order of 5:25 are practiced for various products. With the expansion of a stabilizing agent to the binder arrangement, the foam can oppose collapsing during application and curing, and the reinforced fabric will show upgraded space, hand, and strength. Non-stabilized out foams are alluded to as froths; foam reinforced fabrics are comparable in properties to some immersion bonded nonwovens (Horrocks & Anand 2000). Sample of this bonding is delineated in Figure 3.24. The favorable circumstances incorporate less energy needed to dry the web, less binder movement and controllable softness by decisions and measure of binders. The weaknesses are challenges in controlling procedure and satisfactory foaming.



1 – Vacuum slot 4 – Pressurized application head

2 – Screen 5 – Foam feed

3 – Web feeding

Figure 3.24  Foam bonding process (Source: Patel & Bhrambhatt 2011)

136 3.3.2.3

Nonwoven: Process, structure, properties and applications Spray bonding

In spray bonding, binders are sprayed onto moving webs. Spray bonding is utilized for fabric applications that which require the upkeep of high loft, for example, fiberfill and air-laid pulp wipes (Kannadaguli & Kotra 2004). The binder is atomized via pneumatic force, pressure driven weight, or divergent compel and is connected to the upper surfaces of the web in fine bead frame through an arrangement of spouts. Lower-web-surface binder expansion is refined by switching web heading on a second transport and passing the web under a second spray station. After every spraying, the web is gone through a heating zone to evacuate water, and the binder is cured (set/cross-connected) in a third heating zone. For uniform binder appropriation, spray nozzles are deliberately designed. Typical spray bonding is illustrated in Figure 3.25.

Figure 3.25  Spray bonding method for nonwovens (Source: www.aatcc.org)

3.3.2.4

Print bonding

Print bonding applies binder only in predetermined areas. It is used for fabric applications that require a part of the area of the fabric to be binder-free, such as wipes and cover stocks (Pangrazi 1997). Many lightweight nonwovens are print bonded. Printing patterns are designed to enhance strength, fluid transport, softness, hand, absorbency, and drape. Print bonding is most often carded out with gravure rolls. Binder addition levels are dependent on engraved area and depth as well as binder-solids level. Increased pattern versatility can be achieved with the use of rotary screen rolls. Drying and curing are carried out on heated



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drums or steam-heated cans. In print bonding, high viscose binders are applied to limited, patterned areas (Russell 2006). A prewet/prebond step is required for enough strength of webs, and typical steps in this bonding are in Figure 3.26.

Figure 3.26  Print bonding technique for nonwoven (Source: www.aatcc.org)

3.3.2.5

Powder bonding

In powder bonding, the adhesive powder of thermoplastic polymers is applied onto webs by heat and pressure. Polyesters and polyolefins with low Tg’s and low molecular weight can be used as powder binders. A typical bonding line is illustrated in Figure 3.27. The advantages are the bulky structure of dense nonwovens and the applicability of polyester or polypropylene webs. The disadvantage lies in difficulties of suitable particle sizes and ranges, and their distribution (Kalinova 2015).



1 – Infrared energy 4 – Powder metering

2 – Infrared oven 5 – Unbonded batt

3 – Rotating brush 6 – Adhesive powder

Figure 3.27  Powder adhesive sprinkling method (Source: Kannadaguli & Kotra 2004).

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Nonwoven: Process, structure, properties and applications

Product characteristics The fabric property is represented by the flexible nature of the fiber and the resin. Thus the fabric modulus is of the request of the fiber modulus that is greatly high. A high modulus in a spatially uniform material implies that it will be solid, which clarifies why saturation bonded fabrics are hardened with respect to ordinary materials. In the meantime elasticity is low, in light of the fact that the bonds have a tendency to break before most strands break. Print-bonded fabrics are much milder in feel furthermore considerably more flexible to solid impact of the free fibers in the unbounded regions. They are significantly weaker than saturation-bonded fabrics attributable to the fiber slipping in unbounded ranges, but knowing the fiber length and the fiber orientation it is possible to plan a print design which will minimize the quality misfortune. Every spray application adjusts the thickness of the matt somewhat, however it is still left generous lofty, the drying and curing stage additionally causes some little dimensional changes. Finally the product is a thick, open and grand fabric utilized generally as the filling as a part of knitted fabrics, for duvets, for some upholstery furthermore for a few sorts of filter media. (Dhanabalan 2013) Applications Nonwoven products in which binders are utilized: • Wipes and towels • Medical nonwovens • Roofing products • Apparel interlinings • Filter media • Coating substrates • Automotive trim • Carrier fabrics • Bedding products (high loft) • Furniture applications (high loft) • Apparel • Pillows (high loft)

3.4

Thermal bonding

The advancement of the previous couple of years has demonstrated that the offer of thermally bonded webs is becoming consistently. The first thermally reinforced nonwovens were delivered in 1940s. Starting items utilized rayon



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as the bearer fiber and plasticized cellulose acetic acid derivation (polycaproic acid – PCA) or polyvinyl chloride (PVC) as the binder fiber (Hoyle 1990). The suitability of the thermal bonding procedure is established in the value point of interest got by lower energy costs. In any case, the thermal bonding process additionally addresses the requesting quality necessities of the commercial center. The advancement of new raw materials, better web arrangement innovations and higher production speeds have made thermal bonding a reasonable process for the production of both durable and dispensable nonwovens.

3.4.1 Binders Many materials that can be used as a binder for thermally bonded nonwovens. • Binding fibers • Binding powder • Binding web 3.4.1.1

Binding fibers

Single-part and bi-segment fibers, as binder fibers, are most generally utilized as a part of thermal bonding of nonwovens. Single-segment fibers are the slightest complex and most sparing in light of the fact that the filaments are regularly as of now in presence and low in expense. The short bond that is formed is subject to a few elements including fiber chemistry, morphology, linear density, staple length, crimp, and processing conditions. The significant weakness experienced when utilizing 100 percent single-part filaments is the limited temperature, that is essential when thermal bonding. In the event that the temperature is too low, there is insufficient bond quality. In the event that the temperature is too high, the web will liquefy too much and lose its way of life as a web. At the point when bi-part strands are utilized to deliver thermal bonded nonwoven, the adequate temperature range for bonding may be as great as 25°C. At the point when thermal bonding, the high dissolving bit of the fiber maintains the uprightness of the web, while the low liquefying point bit dissolves and will bond with different strands at the fiber crossover points. The product produced tends to have bulk and exceptional softness. 3.4.1.2

Binding powder

Powdered polymers are here and there utilized as a part of thermal bonding of nonwovens. The most predominant utilization is powdered polyethylene. The powder can be connected between layers of filaments when cross-laying, air

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laying, or as an after treatment. A short introduction in an oven is adequate to liquefy and circuit the powder. It is regularly utilized when a light weight and open structure is needed with a delicate hand or when a strengthened, formed item is essential. 3.4.1.3

Binding web

A very open-structured, low-melting-point thermoplastic fabric is set between the webs and, during thermal bonding between the calender rolls, the fabric melts totally bonding the webs together. The nonwoven created by this strategy is delicate and bulky. Thermoplastic coatings and hot melt print bonding have been utilized to a restricted degree in controlled porosity channels, impermeable films and different things. In any case, the utilization of this strategy for bonding is not anticipated that would accomplish an abnormal state of significance.

3.4.2

• • • • •

3.4.2.1

Methods of thermal bonding Hot calendering Belt calendering Through-air thermal bonding Ultrasonic bonding Radiant-heat bonding, etc. Hot calendering

A heat calendar should fulfill two basic processing conditions: • Precise temperature control of the two heated rollers. The value of thermal delta must not be higher than ±1°C. This precision must be kept with or without material. • Constant nip pressure over the calendar width Pressure Within the roller gap, required heat to reach the fiber melting point is transferred to the web. For this heat transfer, a special gap pressure is applied. The nip pressure needs to be adjusted according to the web weight, type of engraving and the end product. General line pressure ranges from 20 to 120 N/mm2; in certain models, it may be up to 250 N/mm2 (high pressure type). The pressure causes a substantial increase in the number of fibers in contact, thereby affecting the strength and other properties of the bonded web. Pressure also forces flow of the molten polymer and modifies the temperature and time requirements for bonding. The pressure required will depend upon the following factors:







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• Type of web: In the same weight range, a staple fiber web will require less pressure than filament because of its softness. • Web weight: Heavier webs need higher pressures. A 75–150 gsm spunbonded webs may require pressures in the range 80–110 N/mm2 while lower weights (15–70 gsm) need pressures in the range 50–80 N/mm2. • Contact time: This is influenced by the machine speed. In case the speed is increased, the contact time decreases. It means that the nip pressure must be increased.

Temperature When the web reaches the entrance cone created by the roll diameters, the air at room temperature is dragged in which tends to cool the roll surfaces. But the material is heated rapidly due to the following reasons: • The movement of the rolls creates the formation of hot air rings around their circumferences. This hot air is pulled in by the rolls and the material gets preheated by convection. • In the cone area, the fabric is also heated by radiation heat waves emitted by the hot rolls. • In the nip, the material is in direct contact with roll surfaces and is heated by conduction. • The heating and bonding of the inner layers is also due to the flowing of the molten polymer from outside to inside caused by pressure. The working temperature will depend upon the type of polymer, for example: • Polypropylene – 140–170°C • Polyethylene – 85–115°C • Homopolymer polyester – 230–260°C • Bicomponent polyester – 120–200°C • Nylon 6.6 – 220–260°C • Nylon 6 – 170–225°C The temperature has a direct influence on the fabric handle. Keeping other parameters constant, with the increase of temperature, the fabric strength increases up to a certain maximum value, after which strength declines. Types of calendaring There are three main types of hot calendaring (Russell 2006). • Area bonding • Point bonding • Embossing

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There are two kinds of calender rollers namely embossed and flat calender rollers as shown in Figure 3.28 where point, stick and grid bonding are embossed one and area bonding is flat roller. It is generally known that the point bonding results in softer fabric and the area bonding results in stiffer fabric.

Figure 3.28  Types of calendar roller

Area bonding This procedure includes the utilization of a calender with a hot metal roll contradicted by a fleece felt, cotton or special composition roll. Two, three or four roll calenders can be utilized; contingent upon the heaviness of the web to be bonded and the level of bonding heated roll on the top and base, with the two compositions come in the center. The formless or co-polymeric binder fibers utilized as a part of this procedure give holding at all cross-over points between the carrier and binder fibers. The resultant item – normally utilized as a part of electrical protection and covering substrates – is smooth, slim and hardened. The material is constantly two sided; however, this impact is most evident in material prepared through two and three move calenders. The utilization of heat from the outside creates a material whose inward range is less reinforced than its external surface. This turns out to be more declared as the item weight increments past 35 g/m2 and can get to be unfavorable unless restorative measures are taken. These incorporate increasing heat, slowing speed, or increasing the binder/carrier fiber ratio. The two-roll calender is utilized for low-to-medium weight items with light-tomedium bonding. The three-roll calender is utilized for special bonding and finish effects on a single surface. The four roll calender creates the amplest weight range of materials on the grounds that it gives more adaptability in the use of heat (Gao & Huang 2004).



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Point bonding Point-bond hot calendering is the main method of thermally bonding in disposables as diaper, sanitary products, and medical products. This method involves the use of a two-roll nip consisting of a heated male patterned metal roll and a smooth or patterned metal roll. The profile of point bonded calendar rollers are shown in Figure 3.29.

Figure 3.29  Point bonding rollers (Source: Steve Gunter 2002)

For light and medium weight fabrics, 10–200 GSM, a 2-roll heat calendar is used. Heavier weight nonwovens, therefore having high thickness, are difficult to be bonded with a heat calendar because of de-lamination problem. One roll is engraved while the other one has a smooth surface. The type of engraving influences the properties and quality of the final product. Engraving pattern is usually of geometrical type having square, rectangular, rhomboidal, circle or oval section. The number of points determines the fabric softness and the melting area influences the mechanical properties. The bond area is generally designed in 5–25% range. For example, for a lightweight fabric (15–35 GSM), a 20% contact area may be necessary whereas for heavier webs (70–100 GSM), a 10% contact surface is sufficient. In a 2-roll heat calendar, the two operating rolls are designed with an outside diameter which is “almost” equal, and which grants a similar rotation speed. Roll diameters are not identical in order to allow that the contact of the engraving point against the smooth roll, at each rotation is joggled, granting a homogeneous wear of the smooth roll, which does not become spotted. In a typical production line, the web is fed by an apron leading to a calender nip and the fiber temperature is raised to the point at which tackiness and melting cause fiber segments caught between the tips of engraved points and the smooth roll to adhere together. The heating time is typically of the

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order of milliseconds. The fabric properties are dependent on the process temperature and pressure and other parameters like the contact time, quench rate and calender pattern. Experimental results show that for a given nip line pressure and calendering speed, the breaking strength reaches a maximum at a critical bonding temperature; on keeping the nip line pressure constant, the critical temperature was found to be a function of the calendering speed (Dharmadhikary et al. 1995). Embossing The embossing method is a figured or sculptured area-bond hot calendering as shown in Figure 3.30. In this case, though, the area bonding is three dimensional. A “bulky but thin” product can be made in any pleasing or functional construction, depending on the faces of the embossing rolls. The calender roll combination has a male patterned heatable metal roll and a matching female patterned felt roll.

Figure 3.30  Types of embossing calendaring

3.4.2.2

Belt calendering

Belt calendering is a changed type of hot roll calendering. The two principle contrasts are the time in the nip and the level of pressure applied. In belt



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calendering, time in the nip is 1–10 seconds. The pressure applied is around 1/10th of the weight connected in the hot calendering procedure (Russell 2006). The belt bonder comprises of a warmed roll and an elastic cover as shown in Figure 3.31.

Figure 3.31  Belt calendaring process (Source: www.klieverik.com)

The nonwoven fabric is heat bonded by running it between the roll and the cover Pressure is applied by varying: (a) The tension on the blanket against the heated roll (b) The pressure on the exit guide roll inside the rubber blanket Belt calendered products are much less dense and papery compared to hot roll calendering. The belt bonder facilitates the use of binders with sharp melting and flow properties. Such binders can present difficulties in a hot roll calendering process. 3.4.2.3

Through-air bonding

Through-air thermal bonding includes the utilization of hot air to the surface of the nonwoven fabric. The hot wind currents through openings in a plenum situated simply over the nonwoven. Nonetheless, the air is not pushed through the nonwoven, as in like manner hot air ovens. Negative weight or suction, pulls the air through the open transport smock that backings the nonwoven as it passes exhaustive the broiler. The through-air bonding with horizontal belt type and rotary drum type are shown in Figure 3.32 and 3.33 respectively. Pulling the air through the nonwoven fabric permits significantly more fast and even transmission of warmth and minimizes fabric contortion (Randall 1984).

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Figure 3.32  Through-air bonding with horizontal belt

Figure 3.33  Through-air bonding with rotary drum

Binders utilized as a part of through-air thermal holding incorporate crystalline binder fibers, bi-segment binder fibers, and powders. At the point when utilizing binder fibers filaments or powders, the binder melts completely and structures liquid beads all through the nonwoven’s cross-area. Bonding happens at these focuses after cooling (Randal 1985). On account of sheath/ core binder fibers, the sheath is the binder and the core is the carrier fiber. Items made utilizing through-air ovens have a tendency to be bulky, open, soft, strong, extensible, breathable and absorbent. Through-air holding took after by prompt cool calendering results in thicknesses between a hot roll calendered item and one that has been however air bonded without pressure. Indeed, even after cold calendering, this item is milder, more adaptable and



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more extensible than area bond hot-calendered material. Kim et al. (1997) investigated experimentally the formation of bond and the bonding time for different fiber diameters between two fibers laying orthogonal to each other. Kim et al. (1999) in a follow up article investigated the bond formation and development between two fibers by using a simple computational model and predicted the characteristics shape. 3.4.2.4

Ultrasonic bonding

This process involves the application of rapidly alternating compressive forces to localized areas of fibers in the web. The stress created by these compressive forces is converted to thermal energy, which softens the fibers as they are pressed against each other (Figure 3.34). Upon removal from the source of ultrasonic vibration, the softened fibers cool, solidifying the bond points. This method is frequently used for spot or patterned bonding of mechanically bonded materials.

Figure 3.34  Ultrasonic bonding process

No binder is necessary when synthetic fibers (thermoplastic) are used since these are self-bonding. To bond natural fibers, some amount of synthetic fiber (thermoplastic) must be blended with the natural fiber. Fabrics produced by this technique are soft, breathable, absorbent, and strong. This bonding method is used to make patterned composites and laminates, such as quilts and outdoor jackets (Watzi 1994; Russell 2006).

148 3.4.2.5

Nonwoven: Process, structure, properties and applications Radiant heat bonding

Radiant heat bonding happens by uncovering the web or mat to a source of radiant energy in the infrared extent. The electromagnetic energy transmitted from the source is consumed by the web, expanding its temperature. The use of radiant heat is controlled so it softens the binder without influencing the carrier fiber. Bonding occurs when the binder re-solidifies upon removal of the source of radiant heat. Figure 3.35 shows the infrared bonding machine. Lower energy and shipping expenses make this a favored strategy for handling powder-bonded nonwovens. Adaptability and lower delivery expenses are additionally considers. Post-calendered rolls can be sent in slight, compacted shape and re-bulked by reapplication of heat, without weight or restrictions, to the wanted state at the season of utilization. Powder bonded items made in this way are delicate, open, and permeable with low-tomedium quality. They likewise can be reactivated by warmth for utilization in the assembling of laminated composites.

Figure 3.35  Infra-red bonding machine (Source: Kalinova 2012)

Product characteristics Products can be relatively soft and textile-like depending on blend composition and bond area. The material production does not involve any chemical use making it environment friendly and 100% recycling of fiber components can be achieved. High bulk products can be bonded uniformly throughout the web cross section. 3.4.2.6

Application of thermobonded nonwovens

Application of different methods of thermo bonding along with their web forming methods and range of GSM for particular application are given in Table 3.2.



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Table 3.2  Application of thermo bonded nonwovens (Source: Goswami & Rajasekar 1992) Type of web Weight range forming

Application

Bonding method

Carded or aerodynamic

Lightweight webs (disposables) 18–25 g/m2

Cover stock, medical and sanitary webs

Calender, combination air flow principle/ calender, air flow principle (bicomponent fibers and blends)

Spunbonded

Lightweight webs (disposables) 18–25 g/m2

Cover stock, medical and sanitary webs

Calender

Carded or aerodynamic

25–150 g/m2

Inter linings

Calender, straight-through air-flow treatment

Carded or aerodynamic

100–1000 g/m2

Filtration webs, high-loft webs or needled webs

Straight-through airflow treatment

Carded or aerodynamic and spunbonded

80–400 g/m1

Geotextiles

Straight-through airflow treatment, special stretching frame with air jetting

Spun-bonded

150–200 g/m2

Carpet backing

Straight-through airflow treatment

Carded or aerodynamic

80–2000 g/m2

Industrial textiles, coating substrates, protective material, insulating material, decorative webs, nonwoven covers, webs for upholstery industry, non woven wall coverings

Straight-through airflow treatment

Carded or aerodynamic

80–2000 g/m2

Padding material fiber fill webs

Straight-through airflow treatment

Carded or aerodynamic

100–250 g/m2

Wiping cloths

Straight-through airflow treatment

Carded or aerodynamic

80–3000 g/m2

Waste-fiber webs for various applications

Straight-through airflow treatment

Carded or aerodynamic

300–800 g/m2

Needle-punched carpets

Straight-through airflow treatment

Carded or aerodynamic

150–350 g/m2

Roofing felts

Heat-setting with straightthrough airflow treatment

Light-weight webs, decorative webs, tea bag paper

Straight-through airflow treatment

Wiping cloths, technical products, medical and sanitary webs

Straight-through airflow treatment

Web forming machine Dry-laid paper

20–200 g/m2

Comparison of different web bonding techniques (Table 3.3)

150

3.5

Process

Name

Technique

Process

Web support system

Fabric weights

Applications & products

Considerations & benefits

Thermal

Calender

Fibers are formed into a web; fibers

Heating via: Conduction,

are bonded by application of heat;

Convection and Radiation;

12–20 g/m2 (0.35–0.58 oz/ sq yd)

fibers cool to ambient; bonded web is

Work (Mechanical (frictional),

Heat applied everywhere = area bonded; Heat applied in specific locations = point bonded; Calendar bonding – between lands (Thin, squeezed)

Coverstock for sanitary products, Interlings, Geotextiles, Carpet backing, Insulations, Upholstery, Wiping cloths, Tea bag, Food coverings

Heat applied wherever fibers cross = High loft (not squeezed)

9–150 g/m2 (0.27–4.4 oz/ sq yd)

Radiation – wherever fibers cross under ultrasonic horn

Used primarily to pre-heat

Wherein a thermoplastic element, in the form of a film (continuous or fibrillated), fiber or powder (but not aqueous dispersion of film forming, emulsion polymerized polymers), is integrated into the web, Wherein thermal energy (extrinsic or intrinsic) initiates bonding between fibers in the web, Wherein, in general, no fluids need be evaporated (except when using wet-laid webs).

Can attach layers producing composites, Achieve extremely high densities, High strength overwhelming choice geotextiles, that plus superior filtration choice for filtration media, X/Y/Z direction elongation unbeatable in moldable applications.

Smooth or ribbed and velours surfaces by structure, flat or circular by surface form, 80 g/m2 to 3,000 g/ m2, small pads to up to 16 m geotextiles, small diameter (25 mm) to papermakers felts.

Automotive, Filtration, Furniture & Bedding, Geotextiles, Roofing, Aerospace, Agriculture, Advanced composites, Industrial, Insulators, Marine, Medical, Paper, Protective clothing, Sports felts, Synthetic leather/ shoes, Wall coverings.

Factors influencing needling: Fiber web (weight, thickness, closeness, orientation and opening of fibers), Machine (construction, variable settings, punch depth, density, no. of runs, barbs, frequency, plate design), Binding Needle (type, shape and # of barbs, thickness, Neck/kick-up, wear), Environment.

wound up Through-Air

Electrical, Chemical); Calendar bonding; Through air bonding; Infrared bonding

Ultrasound

Mechanical

Needle punch; Felting; Needling; Needle punching

The fibers are forced to entangle in the z direction and inter-lock with other neighboring fibers. There are 7 board arrangements, and the web can be single or double sided punched. Needle barb spacing can influence needle efficiency and fabric surface

Technology in which the fabric is formed by means of fiber entanglement achieved by the repeated penetration of barbed needles through a preformed dry fiber web (carded and crosslapped or airlaid).

Contd....

Nonwoven: Process, structure, properties and applications

Table 3.3  Comparison of different Web Bonding techniques (Silva, www.acaemia.edu)

Chemical

Process

Contd....

Binder application to nonwoven; Removal of moisture or solvent; Formation of strong bond between binder and nonwoven web

The fibers twist around their neighbors and / or interlock with them

Fluid entanglement; Spunlacing; Jet entangling; Water entangling; Hydroentangling; Hydraulic needling

Common methods of application include saturation, foam, spray, print and powder bonding

Technique

Name

Binders contain polymer produced by the reaction of monomer in the presence of initiators or catalyst. During moisture removal film formation takes place. Chemical binder most used today is water-borne latex, Applied in amounts ranging from 5% to 60% by weight.

Three main factors: Water pressure, Energy transfer and Web support system; Energy transfer: determines hydroentanglement efficiency Insufficient energy transfer (low pressure) rearranges but not entangles fibers, Excess energy (high pressure) produces weak areas & nonuniformity

Process

Strength – nonwoven strength is closely related to binder strength; Adhesion to Fibers – adhesion strength of the binder to fiber bond is important; Flexibility/ handle – some fiber movement is required; Elastic Recovery – good recovery under stain is needed to avoid permanent fabric deformation.

Forming wire surface characteristics determine properties & aesthetics of fabric, Surface topography of forming wire is extremely important and has direct influence on final product appearance

Web support system 20 g/m2 to 600 g/m2

Fabric weights

Wipes and towels, Automotive trim, Medical nonwovens, Carrier fabrics, Roofing products, Bedding products (high loft), Apparel interlinings, Furniture fabrics (High loft), Filter media, Apparel, Coating substrates, Pillows (high loft

Mostly used for fine fiber webs intended for the medical, personal care, baby care and consumer and hygiene markets. Most wipes (dry & wet wipe) are made by hydroentangling or by Spun Melt

Applications & products

Nonwoven bonding techniques Contd....

In the early history of nonwovens almost all nonwoven fabrics required a chemical binder. In very early stages of nonwoven development natural resins and glues were used as bonding agents. However, because of the fabric properties chemically bonded fabrics were not fully accepted.

It is the fastest growing bonding technology Worldwide, The spunlacing process yields the most textile like product of any of the current processes; Spunlaced nonwovens, depending upon the fibers processed, are strong, soft and pliable and can be dense or open and are typically highly absorbent

Considerations & benefits



151

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52. Vignesh Dhanabalan, (2013). Nonwoven technologies: A critical analysis, http:// www.slideshare.net/vigneshdhanabalan/nonwoven-technologies-a-critical-analysysby-vignesh-dhanabalan, Accessed on June 10th 2015. 53. Vinay Kumar Midha & A Mukhopadyay (2005). Bulk and physical properties of needle-punched nonwoven fabrics, Indian Journal of Fiber & Textile Research, 30, 218–229. 54. Web bonding processes, http://www.nptel.ac.in/courses/116102014/8, Accessed on June 10th 2015. 55. White, CF (1990). Hydroentanglement Technology Applied to Wet Formed and Other Precursor Webs, TAPPI Nonwovens Conference, 177–187. 56. Wilhelm Albrecht, Hilmar Fuchs, Walter Kittelmann (2003). Nonwoven Fabrics: Raw Materials, Manufacture, Applications, Characteristics and testing process. WeilyVCH Verlag GmbH & Co. 57. Xiao Gao & Hsu-Yeh Huang (2004). Thermal bonding of nonwoven fabrics, http:// www.engr.utk.edu/mse/Textiles/Thermal%20Bonding.htm, Accessed on June 10th 2015.

4 Finishing of nonwovens

Abstract: This chapter discusses about the basic finishing of nonwoven fabrics such as mechanical and chemical finishes and special finishes such as plasma and micro-encapsulation. In mechanical finishing, the principle of perforation, splitting and winding, shrinking, compacting, embossing, creping, calendaring, shearing and raising has been discussed. In chemical finishing of nonwoven, dyeing, printing aspects and value-added finishes such as antistatic, flame resistant, water repellant and softeners were also discussed in detail. Key words: Mechanical finishing, chemical finishing, calendaring, compacting, creping, flame resistant, plasma, micro-encapsualtion

4.1 Introduction The finishing of nonwovens is gaining importance among the manufacturers, as it contributes to the specialized and aesthetical functionalities of the materials to render them more suitable to the market requirements. Various types of nonwovens are subjected to finishing treatments amid their processing cycle. The wide range of finishing techniques, both chemical and mechanical, has broadened the range of applications of nonwovens. The nonwoven finishing techniques can be classified as shown in Figure 4.1. Non woven finishing methods Mechanical finishes

Chemical finishes

Special finishes

Splitting and winding

Washing

Plasma finish

Perforation

Dyeing

Microencapsulation

Printing

Other methods

Shrinking Drying

Antistatic finishes

Compacting

Antimicrobial antifungal finishes

Embossing

Flame resistant finishes

Emerising/sued finishing

Lubricants

Creping

Water repellent finishes

Calendering

Softeners

Shearing

Stiffeners

Raising

UV Stabilizing finishes

Singeing

Figure 4.1  Classification of nonwoven finishing methods



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4.2

Mechanical finishing

4.2.1

Splitting and winding

157

Producing thicker nonwoven structures and parting (leveling) them to the desired thickness is one of the convenient methods of manufacturing high density nonwoven fabrics with generally low thickness. To achieve this, a splitting machine is utilized. The construction of the splitting machine includes a settled part comprising the upper scaffold and the feeding bench, on which the feeding table is mounted. The flywheels, sharpened blade with its controlling device and the sharpening attachment are all mounted on the settled part. To ensure a fast and accurate splitting of the material, the blade must be continuously sharpened by drum shaped grinding wheels. The nonwoven is placed over the feeding table and passed with predetermined pressure through the support, under a rotating precision sharp edge blade. The arrangement of the unique rolls isolates the so-formed two layers. The calibrator roll, which is the upper conveyor move, determines the thickness of the material. The accuracy in splitting increases with the closeness of the calibrator roll to the sharpened steel blade. The feed material must perfectly cling on to the upper calibrator roll to maintain the required thickness. The lower pressure roll is designed to continuously deform to adjust to the varying thickness of the feed material as it pushes the material against the blade. The pressure roll consists of several small rolls arranged in a sequential manner. All nonwoven materials, evenly the intensely stitchbonded nonwovens, leather like imitation fabrics and chemically bonded fabrics with high areal mass can be subjected to splitting by making suitable mechanical alterations (Russel 2006).

4.2.2

Perforation and slitting

Nonwovens can be perforated by using heated needles or modified calendar rolls. The process of perforating is done to facilitate vertical exchange of the fluids inside the cover stocks (cardstock) of items used in personal cleanliness or to increase the drapability and delicateness of coating fabrics. The vertical profile of the puncturing can be altered according to the requirement. Funnelshaped profiles can be obtained by using suitable puncturing needle so as to control the waste limit of the cover stocks. In the case of chemically bonded nonwovens, puncturing with red-hot needles can facilitate the crosslinking of the resinous bonding agents. The slitting process creates longer holes (openings) in the nonwovens. The length of the opening and the distance between openings need not necessarily lower the fabric quality. (Russel 2006; Purdy 1983)

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Shrinking

The fibres have a tendency of reverting back to their original state in order to release the stress built up during processing. This results in shrinkage of the fabric. To avoid the subsequent shrinkage, the nonwoven can be subjected to intentional shrinkage by immersing in cold water, steaming or providing resin/chemical treatment (Kamath et al. 2004).

4.2.4

Drying and heat setting

The nonwoven fabrics are subjected to strain during manufacturing, which may cause the fabrics to distort dimensionally. The strain experienced by the fabric causes it to extend along the length and shrink in width. This phenomenon is more significant for hot and wet webs. The dimensional instability of the webs results in shrinkage at later stage. To overcome this issue, the drying process for nonwovens was introduced. Sometimes, the drying process is used for coagulation of thermo sensitive binders and sintering of binder powders in the fabrics. The drying procedure varies depending upon the type of material and the end use of the nonwoven fabric. Drying can be achieved by using any one of the methods like stenter frames, fusion ovens, drum drying, hot pipe dryers, infrared heaters, and so on. In stenter frames, the fabric is clamped at the edges with the movable frame to maintain a constant open width. The frame carries the clamped fabric through the drying chamber. The conformity of the rail or chain conveying the fabric controls the width of the fabrics. Overfeed to the stenter pins provides stabilization of the fabric by permitting shrinkage along the length of the fabric. Sensors in the stenter electronically control the air stream, moisture and temperature at the set levels (www.nptel.ac.in). The most remarkable drying method is the through air drum drying and heat setting. This method also provides flexibility in terms of machine setups like single drum, twin drum or various drum setups. The drums are arranged in vertical or horizontal progression as per the requirement. A high limit outspread fan controls the hot air in and out the drum with the assistance of some heating element (which heat the air). Overfeed of fabric to the drum allows shrinkage to occur. The resulting fabric develops the required delicateness and bulk characteristics. This technique offers maximum heat and mass exchange through the thickness of the fabric, thereby increasing the productivity and minimizing the energy utilization.

4.2.5

Compacting

Compacting of fabrics is a simple mechanical process in which the fabric is subjected to compressive forces along the length. In general, the nonwoven



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fabric is fed into a converging passage, securely gripped and lead into the treatment cavity, where the compaction takes place. Figure 4.2 shows the nonwoven compacting process. For compacting a nonwoven fabrics, the machinery setup includes a pair of juxtaposed rollers (2,3) and a superposed roller (4) which are arranged in such a way to produce fibre compacting. The central superposed roller (4) extends in preset space (9) between the juxtaposed rollers (2,3) to achieve fibre compacting. Each of the rolls has perforations (5) extending through the surface of a shell (6). The first conveyor (16,19) feeds the nonwoven to the roller arrangement while the second conveyor belt (17,20) draws the fibres away from the roller arrangement after compacting. The conveyor belts (19,20) may also be perforated and surround the juxtaposed rollers (2,3), respectively. The compacting process is assisted by means of suction applied to the interior of the rollers, which draws the fibres through the perforations (5) in the rollers (Lasenga 1989).

Figure 4.2  Process of nonwoven compacting (Source: Lasenga 1989)

4.2.6

Embossing

The process of embossing produces a raised texture on the surface of the nonwoven fabrics. Embossing is done by means of heated engraved rollers. This process is suitable for all nonwovens except for woolen felts. Permanent embossing can be achieved by combining the process with certain chemical resins.

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4.2.7

Creping

The nonwoven web is attached to the surface of a roll or drum by means of an adhesive and then the adhered nonwoven is mechanically detached from the surface of the roll or drum. The absorbency (in case of hydrophilic fibres), softness, and bulk of the nonwoven is improved as the fibre positions are disturbed and are altered within the web during detachment process. Creping can also be observed in the papermaking art. Water-based adhesives, like latex adhesives, are widely used to attach the nonwoven fibrous web to the creping roll or creping drum in the creping process. To ensure proper adherence between the nonwoven web and the creping roll or creping drum, the water must be removed from the adhesive by drying. To achieve this, huge heated rolls or drums, like the Yankee Roll (Figure 4.3), are used to dry the water-based adhesive. These drums are expensive and consume a large amount of energy to efficiently dry the waterbased adhesive (Sayovitz 2004).

Figure 4.3  Mechanism of creping of nonwoven (Source: Sayovitz 2004)

4.2.8

Calendaring

Calendaring is a non-durable mechanical finishing technique which can be applied to nonwovens made of cellulose, protein and synthetic fibres. This machine includes one or several pairs of rollers pressing against each other. These rollers are provided with movable weight and identical nip speeds. The fabric is subjected to a smoothing and a squeezing activity when passed through these rollers. The surface of the rollers can either be hard or milder depending on the material being processed. Stiff rollers are typically made of steel or hardened cast iron with chrome-plated or nickel-plated or stainless steel surfaces. The roller can be subjected to treatments that provide:



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• a matt appearance which is similar to abrasive blasting; • a cross-stripe engraving to improve the fabric grip and resistance to sliding; • a very thin diagonal stripe patterning with a smooth appearance; • a patterned engraving with embossed effects. When the nonwoven is passed through the calendar rollers, it is subjected to an extremely uniform pressure along the entire width of the rollers. Hence, the calendaring process can be regarded as a more serious type of compaction procedure. Calendaring decreases the nonwoven thickness and provides a smooth surface. Either hot or cold calendaring can be done. The calendar rollers can have two configurations, namely L type and I type (Goivanni Tanchis 2008). In the I type, the rollers are set in line such that one roller is vertically over the other. Whereas in the L type, the course of action the base roller is set somewhat forward. The rollers are outlined to facilitate uniform appropriation of nip line pressure over the entire width of fabric being fed. Some rollers have a lump surface, i.e. breadth in the center is more prominent than the distance across at the edges. Additionally, the rollers are secured with resilient material for fitting weight conveyance. In case of hot calendaring, the calendar rollers are heated by means of heated oil. Another variant of calendaring is the belt calendaring, which provides the fabric a less solid feel compared to the roller calendaring. This involves squeezing of the nonwoven fabric against a heated drum with the help of a tensioned belt or cover running over the surface of the roller. The pressure applied by this means is lower compared to the ordinary calendaring process. But the contact time of the nonwoven fabric with heated element (drum) is more prominent than in roller calendaring (Tanchis 2008).

4.2.9

Emerising/sued finishing

The sueding process is quite similar to the raising process. It is distinct from the raising process as the nonwoven fabric surface is rubbed by emerising filet and not by raising wires. This procedure generates thick pile with intricate quality and curbed appearance. Also, a sueder may be referred to as a sander since it consists of one or more rolls secured with sand paper which acts as the rough rubbing medium. When the nonwovens are passed over these rollers, they produce a low pile which provides the fabric surface to feel like suede leather. The sueding machines can be categorized into two fundamental classes: the single cylinder and multi-cylinder machines (Wilhelm Albrecht et al. 2003). A typical multi-cylinder machine has five pivoting cylinders, with individual drive controls for each cylinder, i.e. the direction of rotation of each

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cylinder can be varied independently. The single cylinder sueder consists of one grating secured metallic roller and one elastic secured pressure roller. There is a chance for the abrasive covered cylinder to expand due to the heat generated from continuous grating. To overcome this expansion, water is circulated inside the cylinder to maintain lower temperatures. The function of the pressure roller is to press the fabric against the abrasive cylinder, and it can be adjusted with micrometer accuracy. Hence, at the nip of the pressure roller and the abrasive cylinder, the fibres on the surface of the nonwoven undergo abrasion.

4.2.10

Shearing

Shearing is a method of trimming or cutting adopted to expel the surface fibres from the nonwoven fabric. Shearing is a distinct alternative to the singeing process. The shearing process facilitates only a fractional surface fibre removal. The fabric surface morphology is the main factor determining the cutting stature. A shearing machine is demonstrated in Figure 4.4. The shearing head consists of a winding spiral blade and a ledger plate. The spiral blade is capable of revolving on its own axis and remains in contact with the ledger plate. This arrangement replicates the trimming activity similar to that of a scissors. When the nonwoven is passed through the shearing head, the protruding surface fibres will come in contact with the ledger plate and subsequently get cut by the sharpened steel (www.nptel.ac.in).

Figure 4.4  Shearing process working mechanism (Source: http://www.nptel.ac.in/)

A cloth rest is provided such that the fabric forms an acute angle when it is presented to the ledger plate. This sharp turn causes the pile to stand erect



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and can be more easily cut. The distance between the cloth rest and the ledger blade can be adjusted according to the height of the pile.

4.2.11

Raising

Raising is a finishing process which, in contrast to the other finishing process, raises the surface fibres in the nonwoven fabric. This is achieved by passing the nonwoven through fast rotating rollers secured with metal points or teasel. Raising is also known as the napping process. Excursion, wool, and fleece broadcloth get their wool like appearance by this process. Additionally, napping can be utilized for certain knit goods, covers, and different fabrics with a raised surface. This operation is particularly well suited for wool and cotton fabrics as a fluffy surface can be generated in these fabrics by rubbing the material and pulling the fibre end to the surface. By providing a fluffy or shaggy surface to the fabrics, the fabric appearance, fabric mass and fabric handle (mild and more full hand value) can be varied. The warmth protection of the material is enhanced due to the entrapment of air by the fuzzy surface of the fabric and makes it suitable for wear in cold climatic conditions. The metal needles or points secured to the raising roller surface rub the nonwoven surface and pull out the fibres as illustrated in Figure 4.5. Typically, the needles are 45° hooks projecting from the raising rollers. The needles are fitted onto an elastic belt which is spiral wound on the raising rollers. Moreover, the thickness and length of the needles can be changed according to the nonwoven being processed (Mazharul Islam Kiron 2012). In general, a couple of rollers are used. A roller with its hooks directed in the direction of fabric feed (pile roller), is alternated with another roller with its hooks mounted in the direction opposite to the fabric feed (counterpile roller).

Figure 4.5  Raising rollers (Source: Kiron 2012)

Rotating brushes are also included in the machine in order to suctionclean the needle points in the rollers (Figure 4.6). The present trend employs raising roller to pile rollers in the ratio of 1:3 or higher ratios. The raising and

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pile rollers have independent drives and can rotate with different speeds and direction to produce a variety of fascinating effects.

1: Roller; 2: Rollers equipped with hooks; 3: Fabric; 4: Nib cleaning brushes; 5: Fabric tension adjustment

Figure 4.6  Raising (napping) machine (Source: Kiron 2012)

Figure 4.7  Raising the face of the fabric (Source: Kiron 2012)

The effectiveness of the raising process largely depends upon the fabric strain (5) or the fabric velocity and the direction of roller rotation (2). By varying these parameters, the extent of raising can be altered. Aggressive raising activity subjects the fabric to extreme mechanical stress and can potentially damage the fabrics. To avoid such fabrics damages, it is better to



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pass the wet fabric through the raising machine several times with mild raising effects (dry when handling cotton fabrics). Wetting the material reduced the friction between the fibres in case of synthetic fibres and enables easy pulling out of fibres. Treating the fabric with softening-greasing agents also helps tit prevent fabrics damage during raising (Figure 4.7).

4.2.12

Singeing

Singeing is the process of burning externally. The free fibres which are loosely held on the surface are burnt-off in this process. Singeing is crucial finishing treatment as it involves of burning of the fibres. Hazy print patterns, mottled fabric surfaces, and pilling are some of the consequences of improper process parameters in singeing. The main objectives of singeing are (Hussain 2012) Singeing of a fabric produces a smooth and clean fabric surface. • Singed fabrics show a lower soiling tendency compared to un-singed fabrics. • Singeing reduces the risk of pilling, especially with synthetics and their blends. • Printing of fine intricate patterns is possible in singed fabrics. • The removal of randomly protruding fibres from the nonwoven prevents the diffused reflection of light. In this process, the fabric surface is initially brushed gently to raise the undesirable and loose fibre ends. After this, the fabric can be singed by means of heated copper plates or open gas flames. As the fabrics passes over the heated plates or the flame, the fibre ends burn off. The fabric is moved quickly such that the time of exposure is just sufficient to burn the protruding fibre ends and not the entire fabric. A water bath or desizing bath is located at the end of the singeing machine. This is essential to put off any singeing afterglow or sparks that may degrade the fabric. There are three main categories of singeing machines are listed below (Hussain 2012): 1. Plate singeing machine 2. Rotary-cylinder singeing machine 3. Gas singeing machine 4.2.12.1

Plate singeing machine

In the plate singeing machine, the nonwoven is passed over a couple of hot curved copper plates which have a thickness ranging from 1 to 2 inches. The plates are heated by burners fuelled by a mixture of gas and air. The plates

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are usually heated to splendid redness and then the nonwoven is passed over the plates. The contact time of the nonwoven with the plates is decided by the speed of the fabric movement. Generally, the nonwovens are delivered at a speed of 150–250 yards every second to the machine. The machine can be designed to ensure that both the sides of the nonwoven come in contact with the plates in a single passage of the nonwoven through the machine. To avoid localized cooling of the plates due to constant material passage, an automatic traversing mechanism is fitted to the machine. This mechanism constantly changes the part of the plates which come in contact with the nonwoven, thereby preventing localized cooling and wearing of the plates. 4.2.12.2

Rotary-cylinder singeing machine This type of singeing machine utilizes heated rotary cylinders made of copper or cast iron for singeing. The revolving cylinder is provided with an internal firing system to rise the temperature. This cylinder rotates gradually so that a new surface of the roller is exposed to the material at every instant. This overcomes the problem of localized cooling of the cylinders. The cylinder rotates in the direction opposite to that of the material movement in order to raise the protruding fibres or nap (Figure 4.8). The machine can also be designed with two cylinders for singeing both side of the nonwoven.

Figure 4.8  Line diagram of rotary-cylinder singeing machine (Source: Hussain 2012)

4.2.12.3

Gas singeing machine

Figure 4.9 illustrates the principle of a gas singeing machine. In this machine (Figure 4.10), singeing is performed by passing the nonwoven fabric over a burning gas flame. The speed of the fabric movement through the machine should be adjusted such that the flame only burns the protruding fibres and not the fabric. This is the most widely used singeing machine.



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Figure 4.9  Principle of gas singeing (Hussain 2012)

Figure 4.10  Line diagram of gas singeing machine (Source: http://www.swastiktextile.com/)

4.3

Chemical finishing

4.3.1

Washing

Washing is a simple process that aims at removing undesirable substances or dirt present in the fabric. In wet washing, the washing efficiency is improved by adding a suitable cleanser to the washing medium which is usually water. Anionic washing agents are also capable of softening the nonwoven fabric

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apart from strengthening the washing effect. Nonionic washing agents are more productive at particular temperatures. The material must be subjected to a certain amount of pressure in both the wet and dry washing procedures. The applied pressure should not distort or expand the nonwoven.

4.3.2

Dyeing

Nonwovens can be dyed at different stages of nonwoven manufacturing as per the end product requirement. They are explained in detail below (Aspland & Jarvis 2007). Dyeing of polymer – In the case of polymers like polyester, the colouring agents can be added as a concentrate to the polymer melt just before the filament extrusion. This method can be treated as a bulk colouration or melts dyeing process. The concentrates added to the polymer melt are basically pellets or beads with a high concentration of dyes or pigments. Polymer dyeing offers several advantages compared to the other methods. This process is much faster and does not require the newly formed fibre webs to undergo a vigorous dyeing process which may distort the webs. Moreover, polymer dyed fibres show superior colour fastness properties. Staple and mass dyeing – Wet processing like dyeing and printing is a time-consuming process with high energy and cost requirements. Wet processing of nonwovens is frequently linked with the other wet processes involved in the web bonding procedure. Alternatively, the fibres can be dyed in the staple form. Dyeing and bonding – The dyeing and bonding procedure is suitable for chemically bonded webs. The colouring agents are added to the tank or reservoir containing chemicals for web bonding. Finely dispersed pigments are used as the colouring agent as the bonding agents perform bonding action by coating the filaments of the web. The bonding agents show strong adhesion to the fibres, thereby enhancing the rubbing fastness and colour fastness properties of the pigments. Dyes with excellent fibre affinity can be used instead of pigments in the bonding processes where the banding agent is not uniformly dispersed over the web. This improves the dyeing uniformity despite the uneven distribution of the bonding agent. Subsequent dyeing – Dyeing and bonding process is not suitable when various fibres are blended in the web. In such situations, the dyeing process is performed later. The nonwoven fabric is considered as a woven or knitted fabric and is dyed using the conventional techniques. Cold pad batch dyeing – Cold pad batch dyeing was originally licensed by Farbwerke Hoechst for the dyeing of polyamide-bonded webs. This method



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is used for dyeing spun bond or cross laid (card) nonwovens developed for curtain and table linen applications. These nonwovens are bonded with the help of acrylic acid esters and are coloured using coloured acid or metal complex dyes. Acids can be added along with the dyes in order to form hydrogen bonds between the acids and the cold wetting agents. This bonding with the cold wetting agents facilitates migration of the dye molecules during the batching period and helps in achieving better dyeing uniformity. Then, the fabric is padded, batched and secured with polyethylene film. After 24 hours time, the fabric is subjected to soaping and warm washing. Continuous dyeing – Nonwoven fabrics with higher weight per unit area can be dyed in a continuous dyeing range. The conventional pad-steam process is preferred for continuous dyeing. Steaming is essential to properly fix the dye molecules to the fibres. After padding and steaming, the nonwovens are rinsed and washed (Kamath et al. 2004).

4.3.3

Printing

The printing systems and the colour range for printing nonwovens has extensively developed due to the ever increasing utilization of nonwovens in the home textiles sector. Similar to woven or knitted fabric printing, screen printing and rotary screen-printing are widely used to print nonwovens. The nonwoven fabric is placed on the printing backcloth and printed with suitable dyestuffs depending on the nature of the fibre. It is then dried by steaming and washed. Pigment printing is critical as pigment binders used also help in bonding the fabric to a greater extent. The influence of pigment binders is more significant in spunbonded fabrics. • Printing of light nonwoven bonded fabrics: Almost the entire range of light, nonwoven bonded fabrics can be printed using pigments. Higher dye concentrations are required for printing light nonwoven bonded fabrics. • Printing of heavy nonwoven bonded fabrics: The composition and viscosity of the printing paste used for printing of needled punched fabrics is drastically different to the printing paste used for light nonwoven fabrics. Additionally, heavy nonwovens must be printer at slower speeds. • Transfer printing: In transfer printing, dyes which are capable of subliming are initially printed on a release paper and then transferred from on to the nonwoven bonded fabric by means of heat and pressure. Disperse dyes are widely used to print polyester fibres based nonwovens in this method.

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4.3.4

Types of chemical finishes for nonwoven fabrics

4.3.4.1

Antistatic finishes

Nonwovens, especially those composed of man-made fibres as polyester and polyamide fibres, are prone to build up of static charges. These static charges tend to attract dirt and other particles dispersed in the atmosphere. For this reason, the use of antistatic chemicals for nonwovens composed of manmade fibres becomes mandatory. The antistatic agents can be classified into two types depending upon their working nature. One group of antistatic agents dissipates the static charges by increasing the surface conductivity of the fabric by attaching hydrophilic compounds to the surface of the fibres. Other antistatic agents generate charges opposite to the charge building up in the fabric and thereby neutralize the fabric. Antistatic agents are commonly used in home textiles, especially floor covering materials, wall hangings, wallpapers and upholstery fabric (Kamath et al. 2004; Russel 2006; Tanchis 2008). 4.3.4.2

Antimicrobial, anti-fungal finishes

Antibacterial or antifungal finishes are of prime importance in the hygiene and medical sectors. These finishes also find application in sportswear, bedding components, insulating materials, mattress coverings, home textiles, carpets and products for body care. Their function is to prevent the degradation of the fabrics due to microbial or fungal activity. These finishes should retard the microbes but at the same time, they do not have any harmful effect on the human body. These finishes also help to control the odour emission caused by biological degradation (Milin Patel & Dhruvkumar Bhrambhatt 2011). The antimicrobial agents can be classified into non-leachable or leachable categories. As the name suggests, the leachable antimicrobial agents are not chemically bonded with the nonwoven and can be easily removed or can be transferred to the surrounding by contact with moisture or water. These agents are primarily composed of compounds which contain metals like silver, or biopolymers like chitosan. Collagen, tea-tree oil, aloe vera, camomilea are widely used formulating antimicrobial agents for wounds and skin regeneration. Cetyl Trimethyl Ammonium Bromide (CTAB) in combination with fluorochemical-based water-repellent agent performs well as an antimicrobial agent for polyester, polypropylene and viscose nonwoven fabrics. CTAB has showed excellent a good antimicrobial, water and blood repellency properties in various trials. 4.3.4.3 Lubricants

Lubricants perform the task of reducing the fibre to fibre friction or in some cases, the fibre to metal friction in nonwovens. The application of lubricant



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also makes the nonwoven feel softer. Lubrication is also essential in the the stitching operation, as the rapid movement of the needles generate a lot of heat while penetrating into the nonwoven fabric. If lubrication is not provided, the overheated needles can damage the nonwoven fabric. 4.3.4.4

Flame-resistant finishes

Flame-resistant finishes are imparted to nonwovens to mitigate the consequences of combustion namely flame propagation, post combustion, carbonizing and smoke mission. Nitrogen phosphorous compounds are the main constituents of flame resistant agents. Variants of azo-phosphoric compounds in combination with hygroscopic auxiliaries also reduce the risk of flammability in cellulosic fabrics. These finishes can be imparted as fibres or as dispersion to the nonwoven. In case of fibre form, the flame retardant fibres can be blended along with the constituent fibres during the process of manufacturing. The flame retardant agents can be mixed as dispersion in the coating polymer in coated nonwovens. Flame retardant finishing also produces some undesirable effects like yellowing of the fabric, decrease in tensile strength, and colour changes. (Kamath et al. 2004; Russel 2006; Tanchis 2008) Majority of nonwoven are fabricated using synthetic fibres in order to meet the specific end requirements. The commonly utilized fibres like polyolefin, polyester or nylon are quite flammable. Polypropylene has an entirely aliphatic structure; and hence once it ignites, the fire propagates rapidly. Polypropylene generates only a low amount of smoke during combustion and does not leave any char residue. Such nonwovens made from synthetic fibres are prone to catch fire which is undesirable. The following methods have been adopted to enhance the flame retardant characteristics of nonwovens: 1. The nonwoven can be protected from extreme heats by coatings and/ or other finishing techniques; the layer coated on the fabrics prevents volatilization of flammable material. 2. Nonwovens can be provided with back-coating containing thermally unstable chemicals like inorganic carbonates or hydrates, to retain the surface properties of the fabric. 3. The nonwoven can be maintained at a temperature lower than the ignition temperature on exposure to heat; this is achieved by including materials that can dissipate large amounts of heat (PCM or good conductors) in the nonwoven structure. 4. Nonwovens can be subjected to char promoting chemical treatments. The durability of the treatment depends on the interaction of the chemical with the constituent fibres.

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5. Incorporating chemicals which liberate free radical trapping agents such as organobromine or organochlorine compounds on exposure to heat, in the nonwoven fabric. 6. Suitable modifications can be performed in the fibre manufacturing stage itself; the synthetic fibres can be copolymerized with flame resistant additives like microfillers or nanoparticles. The two basic ways of achieving flame-resistant properties in nonwovens are added substance (the FR agent is added to the polymer dope and then the polymer is extruded) and topical (coating the nonwoven with the FR polymer). The first method incorporates flame retardancy within the fibre structure and hence these fabrics exhibit superior flame-retardant characteristics. But this method is suitable only for thermoplastic fibres. However, thermoplastics, thermosets and common fibres can be made flame retardant by the topical method. In this technique, the flame-retardant agent forms a durable layer over the nonwoven by means of suitable binding agents. Apart from these two techniques, flame retardants like smaller scale or nano-dispersed particles can be fused in the nonwoven directly or can be dispersed in some polymer coating over the nonwovens (Kamath et al. 2004; Russel 2006; Wilhelm Albrecht et al. 2003). The flame-retardant additives which satisfy the following requirements can only be used in nonwovens: • The additive must not adversely affect the natural colourants or the added colouring agents in the fibre to a large extent. • The additives should not emit smoke during fibre synthesis. • It must not significantly alter the short- and long-term fibre properties. • Ultraviolet (UV) durability should not be deteriorated by the additives. • It must comply with latest quality and environment standards at the international level. 4.3.4.5

Water-repellent finishes Water repellant finishes render the nonwovens impermeable to water. The impregnation of the nonwovens with silicone or fluorocarbon compounds restricts the wetting of the nonwovens by water. Spraying or padding techniques are utilized to impregnate the nonwoven with the aqueous dispersion of silicone and fluorocarbon-based compounds. Fluorocarbonic dispersions impart water repellency as well as oil repellency to the nonwovens owing to their extremely low surface tensions. Perfluorated alkyl triethyloxysilanes impart soil, water and oil-repellent characteristics to the nonwoven fabrics. 4.3.4.6 Softeners

The application of softeners provides a soft and delicate feel to the nonwovens. Nonwovens which are in close contact with the skin like sanitary



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napkins, wipes, etc., require softening treatment. In general, the softeners are hydrophilic in nature which in turn increases the wettability of the fabric. 4.3.4.7 Stiffeners

The stiffness or firmness of nonwovens can be improved by using stiffening agents. The weight, compactness and volume of the nonwoven fabric are increased by the addition of stiffeners and fillers. Consequently, the physical properties like the tensile strength and abrasion resistance are enhanced. When stiffeners are applied in the form of polymer dispersion by spraying or padding, they cause bonding of adjacent fibres in the nonwoven fabric and enhance the dimensional stability. 4.3.4.8

UV stabilizing agents

UV rays are capable of degrading the constituent polymers and adhesives in the nonwovens. The polymers undergo fading and loss of mechanical properties due to photo-degradation. To overcome this, UV stabilizers are used to protect the adhesives and polymers against photo-degradation. UV stabilizers are basically UV absorbers which protect the polymers by absorbing the harmful UV radiations. Some UV stabilizers contain controlled amines which provide UV protection by a different mechanism. Instead of absorbing the UV radiations, the controlled amines undergo complex reactions when exposed to UV light, thereby protecting the polymer against degradation.

4.3.5

Application methods of chemical finishes

4.3.5.1 Padding

Padding is a simple finishing technique in which the nonwoven is impregnated with liquor or foam containing the required finishing agent. The impregnated fabric is passed through a pair of squeeze rollers. The pressure setting in the squeeze rollers is altered in accordance with the desired pick-up or add-on level. The pick-up level is decided by the type of fibre and the end usage of the nonwoven. The excess water present in the nonwoven after padding is eliminated by the drying process. The drying process must be carried out in a controlled manner to ensure minimum energy utilization and minimum chemical migration. Padding can be done by two methods: wet on wet padding or wet on dry padding. In wet on wet padding method the nonwoven to be padded must be wetted. The prewet nonwoven is passed through the treatment liquor. The exchange of the treatment liquor with the water present in the nonwoven determines the pick-up level.

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In the other method, wet on dry padding, the dry nonwoven is impregnated with treatment liquor. During padding, the air in the nonwoven must be eliminated and should be replaced with the treatment liquor. To achieve higher pick-up levels, it is essential to de-aerate the nonwoven before impregnation. Similar to calendaring, the squeeze rollers should exert uniform pressure along the entire nip line. The treatment liquor is prepared depending upon the required pick-up level. 4.3.5.2 Coating

In the coating process, the finishing agents are applied to the nonwoven in fluid forms like solution or foam or dispersion. The coating process is followed by the drying and curing process. There are different drying methods depending upon the nature of the nonwoven and the water content to be removed. Coating can be done as a single layer or as multiple layers. Consistent coating thickness can be achieved with single layer coating. Multilayer coatings fill the holes and gaps in the fabric surface providing a smooth and uniform surface to the nonwoven. The major factor to be considered while coating nonwovens is the rate of fabric let-off. If the rate of let-off is not set properly, it will result in uncontrolled stretching of the fabrics. The rotating roller (slop padding or kiss roll) is the most common method of coating nonwovens. The slop padding roller is dipped halfway in the coating solution and the nonwoven is passed over the roller making contact with the other half of the roller. The pick-up level is determined by the process parameters like slop padding roller speed, depth of roller penetration in the coating solution and direction of roller rotation. The nonwoven can be passed over the roller either in the direction of roller rotation or in a direction opposite to the roller rotation. Penetration of coating solution is better when the nonwoven is passed in the direction of the roller rotation, more noteworthy. When the nonwoven is passed opposite to the direction of the padding roller, the machine design is varied. The machine arrangement consists of a pair of rollers, namely the application roller and the support roller. The nonwoven is passed through the nip of the two rollers and the nip pressure determines level of pick-up in the fabric. Attachments like scrubber, doctor blades, or metering rods can be provided to remove the excess coating solution from the nonwoven. The coating solution can be uniformly distributed through the entire width of the fabric by means of special blades. The coating thickness can be varied by altering the blade profile and the distance between the blade and the nonwoven. Besides roller coating, various other technologies like rotogravure coating, rotary screen coating, extrusion coating and non contact coating are



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also available for coating nonwovens. Rotogravure rollers (Figure 4.11) are used to impart patterned coating to the nonwovens. The rollers maintained at higher temperatures to assist the bonding of thermoplastic components. Rotary screen coating (Figure 4.12) is quite similar to the rotary screen printing process. It is used to coat fusible nonwoven interlinings at higher production rates. In this technique, the coating material can be in the form of a fluid or powder. In case of powder coating, size and shape of the particles in the powder should be compatible with the pores in the coating screen. Patterned coating can also be achieved by using fine meshed screens. The extrusion coating process involves lamination of the nonwoven by the extrusion of thermoplastic polymers. This technique is used when the nonwoven must be rendered impermeable. In non contact coating, the coating material is sprayed on the nonwoven with the help of spray nozzles (Figure 4.13). This method is of prime importance for coating nonwovens with poor dimensional stability and a highly irregular surface. It also helps in achieving low add-on percentages. (Lünenschloss & Albrecht 1985)

Figure 4.11  Rotogravure coating

Figure 4.12  Rotary screen coating

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Figure 4.13  Spray coating (Non-contact coating)

4.3.5.3 Laminating

Lamination is the process of securely attaching two or more pre-assembled fabrics to produce a combined structure. If the components of the lamination do not possess self-adhesion properties which are triggered by specific conditions, a bonding agent must also be included in the lamination process. (Bellini et al. 2001). Wet laminating: A simple configuration for the wet lamination process is illustrated in Figure 4.14. The adhesives used in the wet lamination process are dissolved or dispersed in a suitable solvent. In wet lamination, the adhesive is applied in the fluid form along the length of one of the component fabrics which is to be joined. The second component fabric is then placed over it with sufficient pressure to induce bonding between the layers. The amount of pressure determines the extent of consolidation of the attached fabrics layers.

Figure 4.14  Wet or cold laminating



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Dry laminating: Dry laminating is suitable for thermoplastics including powders, plastisols, or melt adhesives. Numerous machines are available for applying the thermoplastic adhesives to the substrates that are to be joined together. Figure 4.15 shows a simple roller arrangement for the dry laminating process. Dry laminated nonwovens have a soft feel compare to their wet laminated counterparts.

Figure 4.15  Dry or hot laminating

4.3.5.4 Flocking

Flocking is the process of creating three-dimensional piles on the surface of the backing fabrics in a nonwoven. Synthetic fibres are more convenient for flocking as they are manufactured in uniform pre-determined lengths. Natural fibres should be ground into short fibres to make them suitable for flocking. The base fabric is treated with an adhesive resin to secure the flock fibres to its surface. The adhesive can be applied over the entire fabric in case of aggregate flocking. Alternatively, the adhesive can be applied in specific areas of the base fabric by means of printing to create flocked designs. The mechanical flocking techniques include the shaking process and the sprinkling process. These techniques create random piles on the fabric surface as they cannot control the alignment of the fibres. The electrostatic flocking process is preferred to create velvet finishes. In this process, the created electrostatic field aligns the fibres vertically as they make contact with the backing fabric. Flocked products find numerous applications like automotive interior panels, shoes, apparels, filters, drapes and as patterned decoration effects (Tanchis 2008).

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4.3.6

Emerging technologies in nonwoven finishing

4.3.6.1

Plasma finishing

Plasma is referred to as the fourth state of matter apart from the solid, liquid and gaseous states. Plasma is a gaseous state comprising of a dynamic combination of ions, electrons, free radicals, metastable excited particles, molecular and polymeric fragments, and large amounts of visible, UV, and IR radiation. Plasma is capable of modifying the surface characteristics of materials by the transfer of energy from the excited plasma particles to the material. The plasma interacts with the material through various mechanisms like etching, surface activation, decrystallization, cross-linking, chain scission, oxidation, and chemical reactions and results in surface modification. The main advantage of plasma treatment is that it is eco-friendly and energy efficient process. Plasma treatments are widely employed in finishing of nonwovens. The most prominent application of plasma treatment is to impart surface hydrophilicity to the polypropylene nonwovens in the hygiene sector. Additionally, plasma treatment improves the interaction of the nonwoven with dyestuffs, pigments and chemical finishes. Plasma treatment is a superior alternative to fluorochemical treatments to impart hydrophobic characteristics to fibres in nonwovens for specific applications. Plasma treatment, being a dry process, does not generate pollution problems. (Wilhelm Albrecht et al. 2003; Kamath et al. 2004; Russel 2006) 4.3.6.2 Microencapsulation

Microencapsulation is a technique in which the droplets of active finishing agent are surrounded by a thin coating to provide small capsules with numerous functional properties. These microcapsules can be utilized to impart various properties like antimicrobial property, flame retardancy, etc., to any kind of fibre. The resulting property can either be durable or temporary depending on the method adopted. In comparison to conventional finishing techniques, microencapsulation imparts specific properties to the nonwovens with improved stability along with controlled release of the active compounds. In this process, the microcapsules containing the active compounds are incorporated into the nonwoven during the finishing treatment. Microencapsulation is being increasingly used in nonwovens for cosmetic, pharmaceutical and industrial applications. The active compound is released in a controlled manner by several mechanisms. Usually, the capsule wall is designed to break and release the active compounds. In another mechanism, the capsule wall acts as a permeable medium allowing the diffusion of



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the active compound from the capsule to the nonwoven in a controlled manner. Perfumes, cosmetics, lotions, thermo-chromic inks, phase-change thermo-active materials (BCMs) and antimicrobial substances are generally microencapsulated into nonwovens along with a binder. Capsules composed of derivatives of β-cyclodextrines can be chemically bound to the fibres and do not require a binder. 4.3.6.3





Other techniques

• Laser etching – Lasers are also capable of physically modifying the surface of the fibres in nonwovens. It can also be utilized as an impingement method for patterning the nonwoven fabrics. • Biomimetic finishes – The biomimetic finishes are designed to replicate certain biological structures along with their characteristics. This technique was developed as an attempt to mimic water-repellency of lotus leaves. • Electrochemical finishes – This technique is adopted to make the surface conductive and also to realize electro-luminescent nonwovens. It can also be used to develop fabrics serving as electrodes or sensors. The material surface should pre-metalized prior to the electrochemical treatments (www.textileworld.com).

References 1. Russel SJ (2006). Handbook of Nonwovens. Woodhead Publishing Ltd. Cambridge. 2. Purdy AT (1983). Developments in Nonwoven Fabrics. Textile Progress, The Textile Institute, Manchester, UK. 3. Wilhelm Albrecht, Hilmar Fuchs, Walter Kittelmann (2003). Nonwoven Fabrics: Raw Materials, Manufacture, Applications, Characteristics and testing process. WileyVCH Verlag GmbH & Co. 4. Joachim Lünenschloss, Wilhelm Albrecht (1985). Nonwoven bonded fabrics (Ellis Horwood series in applied science and industrial technology). E. Horwood publisher, 1985. ISBN: 9780853126362. 5. Aspland JR, Jarvis CW (2007). The Coloration and Finishing of Nonwoven Fabrics. Clemson University, Clemson, SC. 6. Kamath MG, Atul Dahiya, Raghavendra R. Hegde (2004). Finishing of Nonwoven Bonded fabrics. 7. http://www.engr.utk.edu/mse/Textiles/Finishing%20of%20Nonwovens.htm Accessed on May 20, 2015. 8. Finishing process of Nonwoven. http://www.nptel.ac.in/courses/116102014/11. Accessed on May 20, 2015.

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9. Mazharul Islam Kiron (2012). Singeing process. http://textilelearner.blogspot. in/2012/03/what-is-singeing-process-of-singeing.html Accessed on May 20, 2015. 10. Milin Patel, Dhruvkumar Bhrambhatt (2011). Nonwoven technology for unconventional fabric. https://textlnfo.wordpress.com/2011/10/25/nonwoventechnology-for-unconventional-fabrics/ Accessed on May 20, 2015. 11. Pietro Bellini, Ferruccio Bonetti, Ester Franzetti, Giuseppe Rosace and Sergio Vago (2001). Finishing – reference book of textile technologies. The ACIMIT foundation, Milano. 12. Sayovitz (2004). Method for producing creped nonwoven webs. US Patent 6,835,264 B2. 13. Lasenga (1989). Apparatus for compacting a nonwoven fabric. US Patent 4809404. 14. Tanveer Hussain, (2012). Singeing fundamentals. http://www.fibre2fashion.com/ industry-article/13/1226/singeing-fundamentals11.asp, Accessed on May 20, 2015. 15. Anonyms, Gas singeing machines, http://www.swastiktextile.com/gas_singening_ machine_super_singe.html Accessed on May 20 2015. 16. Anonyms, Surface Finishing Gains New Precision. http://www.textileworld.com/ Issues/2000/May/Textile_News/Surface_Finishing_Gains_New_Precision Accessed on May 20, 2015. 17. Goivanni Tanchis (2008). The nonwoven – reference book of textile technologies. The ACIMIT foundation, Milano.

5 Testing of nonwovens

Abstract: This chapter discusses about the characterization of various kinds of nonwoven structures, testing standards and methods available for testing of nonwoven fabrics. Testing standards for fibres and various physical characteristics to be tested for nonwoven fabrics and the respective standards are given in detail. Testing of fibre orientation and porosity in nonwoven structure has also been discussed. The various parameters to be tested on nonwoven materials and the respective standards, based on its application fields such as medical & hygiene, protective textiles, geo-textiles and filter media have also been provided. Key words: ASTM, orientation, porosity, contact angle, filter textile, geo textile, nonwoven, medical textiles

5.1 Introduction With present indecisive economic circumstances, industries need to be far more competitive to make sure their products get into market first. This indicates that a business has an advantage over its competitors by being the initial occupant of a market sector and this phenomenon plays heavily in the testing field. Industries should need to develop a balance between being first to market and being the best in the market. Testing is not a process that can be done in a hurry but it is vital for businesses to make sure their products meet their customer’s expectations and yet the product needs to be ready in time to ensure a competitive edge. Testing is extremely important when developing a new product and many problems can be easily unseen in the rush to get a product to market. Unfortunately testing is quite often looked as an overhead as industries are very keen to reach the end product and cannot see the tangible return-oninvestment testing can bring. Testing is the way of control or the process to check or verify the nature, kind or character of fiber, yarn, fabric or any material, hence to control the degree of excellence.

5.1.1

Objectives of textile testing

• Selection of raw materials • Process control • Product control

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• Process development • Product development & research • Specification test

5.1.2

• To determine the properties and characteristics of fiber, yarn, fabric and end products • To compare the qualities of textile raw materials, intermediate products or finished products • To maintain the standard established by different organisation or countries • To meet market/consumer demand/standard • To improve quality and cost ratio • To control and improve processing technique

5.1.3

5.2

Importance of testing

Benefits of testing

• Minimizes the risk to all parties in supply chain from yarn and fabric producers to high-end retailers and ultimately the end user • Confirms the quality of textile merchandise at any point in the production chain and reduces costly mistakes • Limits any customer liability • Provide an independent expert opinion

Characterization of bonding structures

Nonwovens comprising binder structures could be characterized based on its type, dimensions, form, rigidity and density. The bonding type can be further classified as solid and rigid bonds and flexible and elastic bonds. For example, in case of needle punched and spunlace nonwoven systems, the fibers are interlocked by means of mechanical means by free fibrous interlacements, which are flexible and elastic. On the other hand, thermal and chemical bonded nonwovens are made by cohesion or adhesion of molten polymer which forms a tiny fibrous net resulted in very little freedom for movement leading to rigid bonds. The rigidity of solid bonding points could be evaluated by means of tension properties by measuring traction and elasticity, etc. whereas the bonding level can be determined directly by the microscopic analysis of fabric cross-section.



5.2.1

Testing of nonwovens

183

Needle punched nonwovens

Needle punched nonwovens have regular characteristics due to the interaction between the fibers and the barbs of the needle punching needles in their structural design. The fibers are realigned or reoriented from outside to inside of the web or vice-versa forming a interlocking pillar structures which are normally oriented approximately perpendicularly to the plane. Often, the needle marks are evident on fabric surface. By analysing at micro-structural level, the needle punched fabrics comprises of two distinct regions: the first, the portion of fibers in the nonwoven fabric which are not affected by the impact of punching needle which looks similar to the non-bonded web. In second region, the fiber segments are having the impact of penetration of punching needles, leading to re-orientation of fibers in perpendicular plane (Tanchis 2008). The re-orientation of fibers due to the impact of barb needles during the needle punching process increase the anisotropy nature in nonwoven structure which makes the needle punched nonwoven heterogeneous. The number of needle marks and the penetration depth of the fibers are correlated with the bonding quality of the fabric and with tension resistance (Huang & Bresee 1993). The needle penetration depth, the number and distance of the barbs crossing the web are very important variables, because they can modify the microstructure. Recent studies have proved that the maximum tenacity of a nonwoven can be obtained with only three barbs per needle, if penetration depth is adjusted perfectly.

5.2.2

Wetlaid nonwovens

The wetlaid nonwoven microstructure are quite different from needle punched nonwovens, since absence of formation of fiber pillars in the cross-section. Besides the high velocity water jets allow fibers to migrate in crosswise as well as length/machine direction. The strength of fiber bonding depends on the interaction between the fibers in the web. The structure of wetlaid nonwovens mainly depends on fiber properties and process parameters. At lower water-jet pressure, only a small area of the fibrous segments on web surface get tangled and bonded together. But at high pressures, more fibers are re-oriented towards the opposite part of the web and finally, some fibers protrude. Wetlaid nonwoven properties are mainly governed by the fiber properties such as rigidity and bending recovery which influences the capacity of the jet to produce interlocking or entanglements in the fibrous web (Russell 2007; Tanchis 2008).

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5.2.3

Stitch bonded nonwovens

Based on the various processing types, four main stitch bonded structures are:

• Malivlies – These kinds of nonwovens are comprised of staple fibers which are bonded by fibers stitched into the web and by additional yarns mostly filaments.



• K unit – These are 3-D nonwoven structures comprises of a carded web pleated through a swinging element, which has on one side a knitted structure produced through needles.



• Multiknit (Malimo) – These nonwovens are made from one or two K unit layers, inside which further layers can be introduced which are stitched by a multiknit machine on the pile side to produce a flat surface on both sides of nonwoven.



• Maliwatt – These are fibrous webs stitched by one or two yarns, which lend their form (stitch forming). Both fabric sides have the same type of yarn sewing.

The stitch bonded fabric structure is influenced by the fiber properties, web structure and density, sewing thread and its density, number of needles per inch (gauge) and warp knitting action. The pile height in stitch bonded nonwovens could range between 2 and 20 mm. Normally the warp knitted structures have an open construction and short pleats and have good extensibility in lengthwise as well as crosswise directions (Krcma 1972).

5.2.4

Thermal bonded nonwovens

The structure of thermal bonded nonwovens depends on the method of application of heat to the fibers, the structure of the web and on the type of bonds existing inside the fibers. In calendared nonwovens with thermal bonding points, the fibers are pressed together and the heat is delivered by conduction. This leads to fiber deformation and a flow of the polymer around the bonding points. In the closeness of the bonding points, the heating of the surrounding fibers can induce the formation of bonds between the interfaces of the points of contact of the non-compressed fibers. In case of nonwovens bonded with hot air, bi-component fibers are normally used and the convective heat introduced during the process creates soft and pliable bonds between the points of contact of the polymer (Huang & Bresee 1993). With this process, no associated deformation of the fiber in these points were noticed, hence the density of the nonwoven fabrics is lower if compared to fabrics with calender-operated.



5.2.5

Testing of nonwovens

185

Chemically bonded nonwovens

Chemical bonded nonwovens are made by applying mixture of resins to the web, which is then dried and treated. The uniform dispersion of binder resins across the fabric is influenced by the application method and flow properties of the resins. More number of fibers could be bound by the binder, which adjoins only the points of contact among the fibers, but also the interspaces in the fibers. On the other hand, the polymer could be concentrated in the points of contact of the fibers, making the binders located in these particular regions (Tanchis 2008).

5.3

Testing of nonwovens

The physical, chemical and mechanical properties of nonwoven that govern their suitability for use are based on the characteristics of the raw material, composition and the fabric structure. Hence, the testing of a raw material and nonwoven is vital process after/during the manufacturing process. Raw material properties and arrangement of raw materials during web formation and bonding technique decides the characters of a nonwoven material. The structure and properties of a nonwoven fabric are determined by fiber properties, the type of bonding elements, the bonding interfaces between the fibers and binder elements (if present) and the fabric structural architecture (Russel 2007). Characterization of nonwoven may be done at different stages as mentioned below. 1. Raw material testing 2. Testing of finished products 3. Specific testing procedures based on applications Importance of testing/characterization is that, if the choice of raw material was appropriate and system of process control has been kept at the stipulated standard levels, then the end products could be packed into cases with confidence, knowing that they would fulfill their intended purpose satisfactorily.

5.3.1

Testing of properties of a raw material

The following fiber parameters are tested before taking into actual manufacturing process. All these tests are not required all the times. The important tests are listed below (Behery 1993)

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1. Fiber dimensions • Fiber diameter and its variation • Cross-sectional shape • Crimp wave frequency and amplitude • Length • Density 2. Physical properties of fiber • Young’s modulus, elasticity • Tenacity • Bending and torsion • Rigidity • Compression • Friction coefficient • Fibrillation propensity • Surface chemistry and wetting angle 3. Structural parameters of a nonwoven • Fiber alignment: fiber orientation distribution • Porous structural parameters: fabric porosity, pore size, pore size distribution, pore shape

5.3.1.1

Various methods and standards adopted to measure the fiber properties

The standard methods and procedures for the measurement of various fiber properties are given in Table 5.1. Table 5.1  Standards for measurement of fiber properties S. no.

Fiber parameter

Standards available

Principle of measurement

Technology to be more important

1

Determination of linear density

DIN EN ISO 1973: 1995-12

Parallelized fiber bundles are cut to a specified length. 5 fibers are removed from each of 10 fiber bundles. The mass of the resulting fiber bundle, which consists of 50 fibers all, having the same length, is determined. The quotient of the mass and the cut length, multiplied by the number of fibers in the bundle, gives the fiber linear density value. The mean value of at least 10 bundles, each consisting of 50 fibers, is calculated arithmetically. The linear density is given in dtex.

Needle punching technology, hydroentanglement, etc.

Contd...



Testing of nonwovens

187

Contd... S. no.

Fiber parameter

Standards available

Principle of measurement

DIN EN ISO 1973: 1995-12

Alternate method:

Technology to be more important

Determination of linear density, Vibroscope method The linear density of individual fibers is determined by the oscillating principle at a constant test length and constant fiber loading. A brief acoustic vibration is applied, which causes the fiber to oscillate transversely. The fiber linear density is calculated from the resonance frequency of the fiber

2

3

ISO 2403:2014

Textiles – Cotton fibers – Determination of micronaire value

DIN 53 811: 1970-07

Determination of the diameter of fibers from longitudinal view by microscope projection

ASTM D6466 – 10

Alternate method:

ISO 1136:2015

2. Wool – Determination of mean diameter of fibers – Air permeability method

Determination of length of fibers by measuring of individual fibers

DIN 53 8081: 1982-02

A glass plate in a contrasting colour is smeared with a thin layer of paraffin oil or vaseline. The fibers that are to be measured are picked up with a pair of tweezers, laid carefully onto the glass plate, and straightened to remove the crimp (tweezers technique). The fibers should not be stretched at all.

Standard Test Method for Length and Length Distribution of Manufactured Staple Fibers (Single-Fiber Test)

ASTM D5103 07(2012)

Alternative method: Determination of length of fibers, Almeter method (Zellweger Uster, formerly Peyer)

Length and uniformity index

ISO 4913:1981

Fiber diameter

Hydroentanglement, etc. needle punching technology, etc.

1. Standard Test Method for diameter of wool and other animal fibers by Sirolan-Laserscan Fiber Diameter Analyser

Wet laid technology, dry laid technology

This test method covers the determination of average staple length and staple length distribution of both manufactured and natural fibers by manually measuring single fiber lengths. This test method is also used to measure the length of fibers removed from a staple yarn, but such a measurement may not represent the fiber’s staple length, as manufactured. Textiles – Cotton fibers – Determination of length (span length) and uniformity index Contd...

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Contd... S. no.

Fiber parameter

4

Testing of fiber crimp

5

Determination of breaking force and elongation at break

Standards available

Principle of measurement

Technology to be more important

The fiber is clamped in a take-off device with a fixed and a vertically movable clamp under a pretensioning force of 0.05 mN/tex. The clamping length will depend on the nominal length of the fibers. At least 100 fibers are tested. DIN EN ISO 5079: 1996-02

Direct measurement by TelescopeGoniometer

All technologies

Direct measurement by TelescopeGoniometer

Filters and absorbent materials

of individual fibers 6

Contact angle of a fiber

5.3.2

Testing of a nonwoven structure

The characterization of the nonwoven structure includes the determination and measurement of the numerous properties which are applicable for any particular application. The properties/ characters of nonwoven material could be classified as • Physical properties • Chemical properties • Aesthetic properties • Commercial properties The list of physical, chemical, aesthetic and commercial properties to be tested for nonwoven products is given in Table 5.2. Table 5.2  Various category of testing of various characteristics of nonwoven products Physical properties

Chemical properties

Aesthetic properties

Commercial properties

• Tensile Strength(Wet/ Dry), (Machine/Cross)

• UV Resistance

• Soft/Stiff

• Price

• Elongation

• Thermal Behavior

• Opaque/Transparent

• Cost Effectiveness

• Active/Inert

• Fragrance/Odor

• Quantity

• Polymer Properties

• Shiny/Dull

• Availability

• Flammability

• Fuzzy/Flat

• Contract Terms

• Chemical Resistance

• Smooth/Rough

• Width

• Chem. Sensitivity

• Pliable/Crunchy

• Packaging

• Hydrophobic/philic

• Color

• Put-Ups

• Burst Strength • Tear Strength • Toughness • Impact Resistance • Tear Propagation

Contd...



Testing of nonwovens

189

Contd... Physical properties

Chemical properties

Aesthetic properties

Commercial properties

• Seam Strength

• Oleophobic/philic

• Surface Decoration

• Shipping

• Flex Fatigue

• Static Generation

• Surface Texture

• Exclusivity

• Shear Behavior

• Electric Charge

• Slick/Scroopy

• Delivery Cycle

• Abrasion Resistance

• Adhesion/Cohesion

• Drape

• Tariffs

• Compression Resist

• Bioactivity

• Warm/Cold

• Liability

• Elasticity/Brittle

• Liquid Repellency

• Comfortable

• Patent Protection

• Surface Friction

• Dyeability

• Clammy

• Volume Breaks

• To self

• Biodegradability

• Stretchy

• Licensing

• To other surface

• Thermoplastic/Set

• Bouncy/Dead

• Royalties

• Moisture Vapor

• Dye Stability

• Fluffy/Hard

• Trademarks

• Air Permeability

• Melting Behavior

• Bright/Dull

• Merchandising

• Fluid Porosity

• Wetting Behavior

• Reversible

• Hot/Old News

• Water Repellency

• Absorbency

• Textile/Papery

• Converting

• Thickness

• Cleanability

• Feminine/Masculine

• Safety

• Density/Bulk

• Color

• Cute

• Efficacy

• Bending Resistance

• Toxicity

• Pretty

• Regulatory Rules

• Surface Topography

• Carcinogenicity

• Sophisticated

• Unique

• Thermal Conductivity

• Printable

• Trendy/Classic

• Disposable/Durable

• Liquid Transport

• Sterilizable

• Quiet/Noisy

• Environmental

• Fashionable

• Impact

• Pore Size • Absorbency • Fluid Uptake Rate • Fluid Retention • Sewability • Wrinkle Resistance • Weight/Mass • Piling Resistance • Cutting Behavior

5.3.3

Testing of nonwovens based on applications

Apart from the regular tests and test methods, some of the specialized testing procedures have to be adopted in order to determine the suitability of a product. The following properties are required to be checked for nonwoven waddings depending upon the end use: 1. Resistance to sweatings, compressional resilience 2. Resistant to repeated and long term loading 3. Ability to keep thickness during loading, light weight, fit and loftiness 4. Thermal regulation, safety, high tenacity & stretchability 5. Resistance to abrasion 6. Sweat absorption & fast drying (low fluid resistant)

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7. Moisture management

5.3.4

Standards for nonwoven testing

Various testing methods and techniques have been developed for the measurement of nonwoven fabric properties. These test methods can be grouped as follows (Chatterjee & Gupta 2002): • Standard test methods defined by standard authorities (e.g., ISO, EN/ BS,ASTM, and ANSI) • Test methods established by industrial associations (e.g., INDA, EDANA, AATCC, TAPPI, etc.) and individual companies • Non-standard test techniques designed for research purposes. 5.3.4.1

Sampling of a nonwoven materials Standard test methods for characterization of nonwovens are given by ASTM under the designation D-1117. While taking the sample at random manner from the number of rolls it is referred to as lot sample. A piece of fabric taken from the lot sample and extending them in the width-wise direction by approximately 1 meter along the machine direction is referred to as laboratory sample. These samples should be conditioned before testing as per ASTM D1776 at 65±2 % RH (relative humidity) and 21±1°C temperature before the tests are performed on them. 5.3.4.2

Measurement of basic nonwoven parameters Some of the nonwoven parameter and its testing procedures are listed below. But these lists are not exhaustive and the level of reliability is subjected to nature of material and standards compatibility. The basic list of ASTM standards for testing of nonwovens is given in Table 5.3. Table 5.3  ASTM Standards for testing of nonwoven (Kamath 2004) S. no.

Test

1

Standard

Description

IST

ASTM

Thickness (mm)

120

D5729-97

Determined by observing the linear distance that a movable plane is displaced from a parallel surface by the sample while under specified pressure.

2

Basis weight (g/m2)

130

D3776-96

Sample of known area is weighed

3

Stiffness (mm)

90.1

D5732-95

Sample is slid in a direction parallel to its length. The length of the overhang when tip is depressed under its own weight at an angle 41.5°

4

Tensile strength (lb or N/)

110

D5035-95

Sample is clamped and a force applied until break. Values of breaking force and elongation are obtained Contd...



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Contd... S. no.

Test

5

Standard

Description

IST

ASTM

Bursting strength (psi or kPa)

30.1

D3786-87

Sample is clamped over a diaphragm that is expanded by fluid pressure to the point of rupture. It is the pressure difference between the pressure to rupture and to inflate

6

Elmendorf strength (gf)

Tear

100

D5734-95

Sample is fastened in the clamp, tear is started. Pendulum is released and the sample is torn. The force to tear is calculated.

7

Hydrostatic Head (mbar or Wc)

80.6

8

Air permeability (cm3/s/cm2)

70.1

Sample is subjected to standardised water pressure, increased until leakage appears. Pressure at first sign of leakage is hydro head. D737-96

Calculated from the rate of air flow passing perpendicularly through the known area of fabric to obtain a prescribed pressure differential

Determination of mass per unit area It is the determination of the area and mass of a test piece and calculation of its mass per unit area in grams per square metre. In order to meet the specific needs of nonwovens, alternative requirements to those listed in ISO 3801 are specified in the part of ISO 9073. These are as follows: (a) A different sampling procedure; (b) An alternative specification for dimensions of test piece; (c) A greater accuracy for the balance. ASTM D 3776 covers the determination of fabric mass per unit area which is applicable to majority of fabric types. The method describes four approved options for use in the measurement of basis weight. Option A – Full Piece, Roll, Bolt or Cut (Section 7) Option B – Full Width Sample (Section 8) Option C – Small Swatch of Fabric (Section 9) Option D – Narrow Fabrics (Section 10) The values affirmed in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Fabric thickness Determination of thickness is the fundamental physical properties of highloft nonwoven structures. In specific industrial applications, the thickness of material warrants stiff control within specified limits. Determination of

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thickness of nonwoven structures is quite similar to conventional textile fabrics however due to the higher unevenness and compressibility of nonwovens, different sampling procedure should be adopted. Three different test methods, namely, ASTM D5729-97, ASTM D573601 and ASTM D6571-01 are available for the determination of thickness, compression and recovery of conventional nonwovens and high-loft nonwovens. The thickness of material plays a vital role in bulk and warmth properties of high-loft nonwoven fabrics and determination of thickness is also useful in measuring performance characteristics, such as before and after abrasion or shrinkage. The thickness of a nonwoven fabric can be defined as the distance between the face and back of the material and is determined as the distance between a reference plate on which the nonwoven is kept and a parallel presser-foot that applies a pressure to the fabric (EN ISO 9703-2:1995). Nonwoven fabrics having higher specific volume, i.e. high-loft or bulky fabrics need a special procedure. In this context, bulky fabrics are defined as those that are compressible by 20% or more when the pressure applied changes from 0.1 kPa to 0.5 kPa (Russel 2007). The thickness of high-loft nonwoven fabrics could differ significantly based on the pressure applied to the material at the time of thickness measurement. In such circumstances, the apparent thickness varies inversely with the pressure applied. For this reason, it is essential that the pressure be specified when discussing or listing any thickness value. The standard conditions for determination of thickness for conventional and highloft nonwoven are given in Table 5.4. Table 5.4  Standard conditions for measurement of nonwoven thickness (Source: Russel 2007)

Thickness

Conventional nonwovens (ASTM D5729-97)

Dimensions of presser foot plate (mm)

Pressure (kPa)

Sample size

No. of samples

Duration of testing

Diameter 25.4 ± 0.02

4.14 ± 0.21

10

5s

300 × 300 mm

0.03

20% Greater than presser foot

5

9-10s

5

10s/30 min/5 min

High-loft nonwovens (ASTM D5736-95) Compression and recovery of high-loft nonwovens

ASTM D6571-01 Repeated compression and recovery (ITS 120.4, 120.5)

130 × 80 mm 230 × 230 × 6.4 mm

0.03 / 1.73 / 0.03 1.83

200 × 200 mm 200 × 200 × 100 mm

Applied and removed at a series of time intervals

10 min to 56 hours



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Uniformity of nonwoven fabric The uniformity or evenness of nonwoven structure is concerned with the variations in thickness and density but is generally expressed as weight variation per area unit. To measure the evenness of nonwoven structure either subjective or objective methods could be used. The subjective assessment of nonwoven for evenness can explore the uneven up to 10 mm2 surface from 30 cm distance (Behery 1993). The indirect objective evaluation have been developed based on the changes in other characteristics of nonwoven which vary with the changes in areal mass, including transmission and reflection of beta rays, gamma rays, laser rays, visible light and infrared light, as well as variations in the tensile strength. The uniformity of nonwoven structures can be explored using optical scanning methods through an electronic optical method which can differentiate 32 different shades in the grey scale. The depth of grey shades gives an idea about the uniformity of nonwoven structures. The optical method could be combined with image analysis to determine the variation coefficient of grey level depth resulting from the scanned images of the nonwoven (Chen & Huang1999). Normally, the evenness of the nonwoven structure is based on fiber properties, weight of fabric and processing conditions. From the various studies, it is revealed that with increase in average weight of nonwoven structures, the thickness and weight variation decreases. Wetlaid nonwoven structures are normally more uniform with respect to thickness, compared to drylaid nonwovens. Airlaid nonwovens in short fibers are on the whole more uniform than carded fabrics and spunbonded and meltblown nonwovens are often more uniform than fabrics produced with staple fibers (Chhabra 2003). Tensile strength of fabric by strip method Breaking force and elongation of textile fabrics (strip method) ASTM standard D 5035 covers raveled strip as well as cut strip method for the determination of the breaking force and elongation of textile fabrics. The raveled strip method is relevant to woven fabrics whereas the cut strip method is pertinent to nonwovens, felts and coated fabrics. The values stated in either acceptable metric units or in other units shall be regarded separately as standard. ASTM standard D5034 test method for the determination of breaking force and elongation of textile fabrics could also be used to for measuring the tensile properties of nonwoven structures. As per ISO 9073-3:1989 Textiles, test methods for nonwovens for the determination of tensile strength and elongation stated that application of a force longitudinally to a test piece of a specified length and width at a constant

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Nonwoven: Process, structure, properties and applications

rate of extension. Determination of breaking strength and elongation could be derived from the recorded force-elongation curve. In order to meet the explicit needs of nonwovens, alternative requirements to those listed in ISO 5081 are established in this part of ISO 9073. These are: (a) Different sampling procedure; (b) Constant rate of extension (100 mm/min). Bursting strength of textile fabrics Bursting strength of fabric is normally determined by means of measuring the resistance of the material evaluated to bursting using a pneumatic diaphragmbursting tester. This testing procedure is utilized for a various end-use applications and could be suitable for woven, knitted, as well as nonwoven materials. • ASTM Standard D6797 – Constant-Rate-of-Extension (CRE) Ball Burst Test – It depicts the determination of bursting strength of woven and knitted structures. The values stated in either SI units or US customary units are to be regarded as standard, but must be used independently of each other. • ASTM standard D3786 – Bursting Strength (Diaphragm Method) Tear strength of fabric by Trapezoid method ASTM standard D 5733 illustrates the determination of tearing strength of nonwoven structures using trapezoid method in tensile testing machine. The Constant Rate of Extension (CRE) tensile testing machine is the ideal principle for determining trapezoid tearing strength though constant-rate-oftraverse (CRT) tensile testing machines are used rarely. Hence, the principle used for testing should be agreed upon between the purchaser and the supplier before testing the material. This standard method is applicable for most of the nonwoven fabrics such as treated or untreated, heavily sized, coated, or resin-treated. But this method is not suitable for high-loft nonwoven structures. Trapezoid tear strength determined in this method is the maximum tearing force necessary to propagate a tear started previously in the testing specimen and is not directly related to the force required to initiate a tear. Abrasion resistance of textile fabrics ((ASTM D3884 - 09(2013)e1 Rotary Platform, Double-Head Method) The resistance of fabric to abrasion is mainly influenced by the testing conditions like nature of abradant, variable action of the abradant over the area of specimen abraded, the tension of the specimen, the pressure between the specimen and abradant and the dimensional changes in the specimens.



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The abrasion resistance of the textile materials is a vital characteristic which contributes directly to wear performance or durability of the material. While abrasion resistance and durability are frequently related, the relationship varies with different end uses, and different factors may be necessary in determination of predicted durability from specific abrasion data. Alternative test methods available for determination of abrasion resistance of fabric are D3885 Test Method for Abrasion Resistance of Textile Fabrics (Flexing and Abrasion Method), D3886 Test Method for Abrasion Resistance of Textile Fabrics (Inflated Diaphragm Method), D4158 Test Method for Abrasion Resistance of Textile Fabrics (Uniform Abrasion Method). Air permeability of fabric The air permeability is defined as volume flow rate per unit area of a fabric when there is a specified pressure differential across two faces of the fabric. Air permeability of the samples is measured via standard TS 391 EN ISO 9237 method. The measurements should be performed for 10 samples at a constant pressure drop of 100 Pa (20 cm2 test area). Water vapour transmission of fabric The water vapour transmission rate through a nonwoven refers to the mass of the water vapour (or moisture) at a steady state flow through a thickness of unit area per unit time. This is taken at a unit differential pressure across the fabric thickness under specific conditions of temperature and humidity. Evaporative dish method based on the British Standard, BS 7209 is normally used to determine the moisture water vapor permeability (MVTR). In this method, a sample covers a cup containing distilled water in the cup of 46 ml and a constant air gap was set between the water surface and the sample. The MVTR in g/m2/day is calculated as MVTR = 24M/At Where, M is the loss in mass of the assembly over the time period t in grams; t is the time between successive weighing of the assembly in hours and A is the area of the exposed test fabric (0.005413 m2). Thermal resistance of fabric (UNI EN 31092) The thermal resistance of a nonwoven structure in stationary condition (Rct) is evaluated at standard relative humidity and temperature, by keeping the nonwoven on an electrically heated (35°C) plate made of sintered steel. The thermal resistance (m2K°/W) is determined from the value of the electrical power which is used to maintain the temperature gradient between plate and room.

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Nonwoven: Process, structure, properties and applications

Steam resistance of fabric (UNI EN 31092) Steam resistance testing of nonwoven is carried on a porous plate which is electrically heated (35°C) and covered by a stream permeable membrane however impermeable to water. By placing the surface of the material on the membrane, the heat flow required to necessary to keep the plate temperature at 35°C gives the value of the water evaporation flow. The steam resistance (m2Pa/W) of the material is inferred from the water evaporation flow. Liquid absorption of fabric In a porous nonwoven the liquid passes through it by means of application of an external pressure gradient. The most important tests provides the results such as absorption time, the absorption capacity and the absorption speed of the nonwoven material compared with the water. Fire resistance of fabric The fire resistance which refers to the complex of physical and chemical changes to which the material is subjected under the action of fire. To evaluate the fire resistance of nonwoven material, the following parameters have to be evaluated. • Inflammability – The ability of a nonwoven to enter and to stay in a combustion condition, with release of flames, during and/or after the material has been submitted to the action of a heat. • Flame propagation speed – The rate at which the flame spreads in a nonwoven structure • Calorific value – The thermal power which a unit material mass is capable to build up during its complete combustion. • Heat development in the time unit – Quantity of emitted heat in the time unit by a material during combustion • Production of smoke and noxious substances – Emission of nonwoven materials by the material of a visible complex of solid and/or liquid particles, of gaseous particles and of noxious fumes at specific combustion conditions. 5.3.4.3

Fiber orientation angle and distribution of fiber orientation

The fibers in a nonwoven fabric are rarely completely randomly orientated, rather, individual fibers are aligned in various directions mostly in-plane. These fiber alignments are inherited from the web formation and bonding processes. The fiber segment orientations in a nonwoven fabric are in two and three dimensions and the orientation angle can be determined. In the two-dimensional fabric surface, fiber orientation is measured by the fiber



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orientation angle, which is defined as the relative directional position of individual fibers in the structure relative to the machine direction as shown in Figure 5.1.

Figure 5.1  Measurement of fiber orientation and orientation angle (Source: Russel 1997)

The frequency distribution (or statistical function) of the fiber orientation angles in a nonwoven fabric is known as fiber orientation distribution (FOD) or ODF (orientation distribution function). Frequency distributions are obtained by determining the fraction of the total number of fibers (fiber segments) falling within a series of predefined ranges of orientation angle. Discrete frequency distributions are used to estimate continuous probability density functions (Tsai & Bresse 1991; Pourdeyhimi & Nayernouri 1993). The quantitative evaluation of the anisotropic characteristics of a nonwoven structure is very significant to attain a precise measurement of the distribution of fiber orientation. Though numerous methods have been developed for measurement of fiber orientation, the manual and visual method provides accurate measurement (Kallmes 1969). Manual measures are carried out on the angles of the fibrous segments for a given direction, and on the lengths of the curves of the segments, which have been obtained within a given value. The optical method which utilizes a dull mask in an optical microscope to highlight the fibrous segments which are oriented in a known direction could also be used for determination of fiber orientation. But this method is of limited use due to longer time consumption in the visual examination. Chuleigh (1983) developed an optical processing method in which an opaque mask was used in a light microscope to highlight fiber segments that are orientated in a known direction. To determine the distribution of fiber orientation, the computerized analysis method to monitor fiber orientation in moving web structure, based on phenomenon of light diffraction and X-ray diffraction could be used.

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Nonwoven: Process, structure, properties and applications

Other methods of indirect analysis comprises of microwaves, ultrasounds, light diffraction methods and electric measurements. In recent years, image analysis technique has been used to discover the fibers and their orientation, and computerized simulation techniques have been used for the creation of virtual models of various types of nonwovens. Stenemur (1992) devised a computer system to monitor fiber orientation on running webs based on the light diffraction phenomenon. Huang and Bressee (1993) developed a random sampling algorithm and software to analyse fiber orientation in thin webs. In this method, fibers are randomly selected and traced to estimate the orientation angles; test results showed excellent agreement with results from visual measurements.

3.4.4

Determination of porosity of fiber assembly

The porous nature of the material influences the physical properties, adsorption, permeability, mechanical resistance, density and other factors. The pore structure of nonwoven material could be characterized in terms of total pore volume, pore dimensions, distribution of the pores and its size and of connectivity among the pores. Porosity is defined as the ratio between the sum of the volumes of the small cavities, slits and inter-granular spaces existing inside a material. Porosity provides information on the overall pore volume of a porous material and is defined as the ratio of the non-solid volume (voids) to the total volume of the nonwoven fabric. The specific volume fraction of fiber is defined as the ratio of solid fiber material to the total volume of the fabric. ρfabric × 100 f (%) = ρ fibre ε (%) = (1 – f) × 100 Where ε is the fabric porosity (%), ρfabric is the volume fraction of solid material (%), (kg/m3) is the fabric bulk density and ρfibre (kg/ m3) is the fiber density. A sample of known volume should be cut from the fiber assembly and then the mass of dry sample should be noted. The sample is then immersed in n-decane till saturation was achieved. After that, the mass of the wet sample should be noted down. The difference in the mass of the wet and dry sample gave the mass of n-decane absorbed. The quotient of this mass to the density of n-decane resulted in the volume of n-decane absorbed. The quotient of the volume of n-decane to the volume of the sample resulted in porosity of the sample (Rengasamy et al. 2011; Dierickx 1999). Moreover, apart from direct determination of porosity, for resin impregnated composite nonwovens, the porosity can also be determined with density measurement on basis of the



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199

floating of the material in a liquid or by porosimetry through expansion in a gas. Measurement of pore size and porosity Pore characteristics in a nonwoven fabric are probably the most important structural features that determine utility of nonwoven fabrics. Pore size and shape distributions can tremendously influence permeability and filtration properties of nonwoven fabrics. Pore orientation reflects fiber orientation and pore placement indicates the structure uniformity, and therefore, both have fundamental impacts on fabric mechanical properties such as strength and elongation (Pouredyhimi & Xu 1993). An increasing use of nonwoven fabrics in various areas has intensified the necessity to develop efficient and reliable methods for measurement of pore size, shape and other pore characteristics. Three pore diameters, namely • equivalent, • hydrodynamic and • thickness (i.e., opening diameter), were defined and measured The force required to drive a liquid out of a capillary is dependent upon the diameter of the capillary as well as the surface tension of the liquid and its contact angle with the material of the capillary. If a specimen of a porous material having capillaries is saturated with a liquid and rotated in a centrifuge, the force acting on the liquid is dependent upon the speed and the geometry of rotation. In this apparatus, a sample impregnated with a known liquid is rotated in a predetermined manner at the incremental constant speeds and the volume of liquid driven out of the sample is measured for each speed of rotation. From this information, a size-volume distribution ‘d’ porosity of the sample and, therefore, of the material from which the sample was derived can be made. Alternate methods to measure the pore dimensions and their distributions can be measured by • Measuring pore characteristics includes sieving dry (ASTM D4751, 1987) • Optical methods • Determining the gas absorption and expansion • Determination of electrical resistance • Porometry • Image analysis (the application of image systems in analysis of nonwoven structure has greatly increased. The size of the opening pore is determined by passing the spherical glass marbles of several dimensions ranging from 50 to 500 µ through the

200

Nonwoven: Process, structure, properties and applications

largest pore dimension on specific conditions. Pore dimensions are vital to conclude filtration and retention characteristics of nonwoven geotextiles and authorize their classification as filtering materials (Bhatia & Smith 1996). The constriction pore size is different from apparent opening pore size of the nonwoven and represents the dimension of the smallest part of a flow channel in a pore; it is indicative of fluid transport through a nonwoven, and its value is related to the retention level and to the filtration characteristics of the nonwoven (Votava 1982). The image analysis technique could be utilized to measure the apparent opening (AOS) of the nonwoven structure. Thin sections of the material impregnated with epoxy resins should be prepared and then the sample is cut and analysed with the help of an optical microscope or SEM to obtain photos for image analysis (Xu 1996; Aydilek et al. 2002). 5.3.4.5

Absorbency and wicking rate using GATS Gravimetric absorbency testing system (GATS) is used to determine the absorbency or wicking as a function of time of absorption (ASTM D5802, TAPPI T-561). The schematic diagram of this instrument is shown in Figure 5.2. This testing method provides the lateral wicking capability of a material, or the capacity of the material to take-up liquid impulsively in the perpendicular direction of its plane which is normally known as demand wettability (Behery 1993). It is determined by the amount of water drawn from a water filled reservoir through a tube connected to a porous, sintered glass test plate designed to imitate sweating skin. The test plate self adjusts to maintain a zero hydrostatic pressure differential relative to the water reservoir; water is drawn into the test fabric via capillary action (Song 2011; Yoo & Barker 2005).

Figure 5.2  Schematic diagram of GATS tester

The following measurements have to be noted for the calculation of various parameters.



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201

Wd – Dry weight of the conditioned sample specimen, grams Ww – Wet weight of the sample specimen at the end of the test, grams V – Amount of water passed from the reservoir during 1000 seconds, grams T – Time, minutes. Absorption parameters determined from the above measurements are • Absorbent capacity (C) in grams – It is the amount of water contained in the sample at the end of the test. • Absorbency rate (Q) in g/min – It denotes the rapid rate of fluid loss which is indicated by the high slope in the initial phase of the test. • Evaporation parameters calculated from the above measurements are • Percent evaporation (Ep) – It indicates the ratio of evaporated moisture to moisture absorbed. 5.3.4.6

Contact angle measurement

As an interface exists between a liquid and a solid, the angle between the surface of the liquid and the outline of the contact surface is known as the contact angle (θ). The contact angle often known as wetting angle is a measure of the wettability of a solid by a liquid. The determination of contact angle is vital wherever the intensity of the phase contact between liquid and solid materials are needed to be evaluated such as for coating, printing, hydrophobic or hydrophilic coating, bonding, dispersing, etc.

Figure 5.3  Contact angle on different materials (Source: http://www.kruss.de/)

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Nonwoven: Process, structure, properties and applications

In the case of complete wetting of material by a liquid, then the contact angle is 0°. And between 0° and 90°, the solid is described as wettable and above 90° it is described as not wettable material. For ultra-hydrophobic materials known as lotus effect, the contact angle comes close to the theoretical limit of 180°. The contact angles of different materials are shown in Figure 5.3. According to Young’s equation, a relationship between the contact angle (θ), the surface tension of the liquid (σl), the interfacial tension between liquid and solid (σsl) and the surface free energy (σs) of the solid is shown in Figure 5.4 and is given by the equation σs = σsl + σl.cos θ

Figure 5.4  Schematic diagram of contact angle (Source: http://www.kruss.de/)

Several testing methods are existing for the measurement of contact angles for liquids against solid materials. Standard optical and Wilhelmy methods are complicated or impossible to solve if a sample swells when exposed to the liquid used for testing (Shang et al. 2008). Washburn theory specified that if a porous solid material is brought into contact with a liquid in a manner that the solid is not sunken in the liquid, however is slightly touching the surface of the liquid, then the rise of liquid into the pores of the solid material due to capillary action will be governed by the following equation: m2 η t ρ2 σc For carrying out a Washburn experiment, a liquid of known density (ρ), viscosity (η), and surface tension (σ) should be taken for the experiment. By looking into the above equation, it is observed that the mass of liquid which rises into the porous solid material could be monitored as a function of time. Then two unknown parameters remaining are the contact angle of the liquid on the solid material (θ) and the solid material constant (c). On the other hand, if a Washburn experiment is carried out with a liquid which is having a contact angle of θ = 0° (cos θ = 1) on the solid material, then the solid

cos θ =



Testing of nonwovens

203

material constant (c) is the only unknown parameter which can be determined. N-hexane chemical is a better choice as the liquid for determining material constants, due to its low surface tension (18.4 mN/m) at room temperature. After the calculation of the solid material constant (c) of a particular solid material, a second sample of the solid can be evaluated for wettability by means of another kind of liquid. The solid material constant determined by the N-hexane method is normally used in the Washburn equation, in combination with m2/t data obtained during testing with the second liquid. This permits determination of the contact angle between the second liquid and the solid. C is related to tortuosity (r5) and square of number of pores (Rengasamy et al. 2011). Washburn adsorption tests could be easily and automatically carried out on a numerous porous materials using a Krüss Processor Tensiometer K100 in combination with Krüss LabDesk software in the Adsorption mode. This solid material constant (c) contains information related to the pore structure, pore size, and number of pores in the solid sample. This must remain constant during an experiment for the resulting contact angle measurements to be correct. For swelling solids the pore structure will change, creating a change in the c-factor (Rengasamy et al. 2011). 5.3.4.7

Blood penetration resistance

ASTM standard F-1670 is used to assess the resistance of nonwoven structure used in protective clothing to penetration by synthetic blood under conditions of continuous liquid contact. Protective clothing evaluations are based on visual recognition of synthetic blood penetration. This testing method is not always efficient in analyzing the protective clothing which is thicker, where the inner liners can readily absorb the synthetic blood. Hence, this method is used for selection of protective clothing materials for subsequent testing with a more sophisticated barrier test as described in Test Method F1671. This procedure will not be appropriate for all forms of blood-borne pathogen exposure and the appropriateness of this test method for the particular application have to be analysed. This test method deals with only the performance of materials or material constructions (example seam) used in protective clothing and not concentrates on design, overall construction and components, or interfaces of garments, or other factors which could influence the overall protection provided by the protective clothing (Hutten 2007). 5.3.4.8

Common testing parameters and standards for nonwoven materials used in various application fields

Common testing parameters and standards for nonwoven materials used in various application fields are given in Table 5.5.

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Nonwoven: Process, structure, properties and applications

Table 5.5  Common testing parameters and standards for nonwoven application in different areas S. no.

Description

Testing standard

1

Medical and hygiene textiles

Bacterial filtration efficiency % (ASTM F 2101)

  •  Air permeability

This test method measures the percent efficiency at which the face mask filters bacteria passing through the mask. The maximum filtration efficiency that can be determined by this method is 99.9%

  • Bacterial filtration efficiency %

Barrier efficiency towards bacteria and liquids SS 8760019 EDANA 190.0-8, ASTM F 1670-97, ASTM F 1671-97, DIN EN 20811

  •  Splash resistance

Bacterial loading of products - DIN EN 1174

1. Face mask

Splash Resistance (ASTM F1862) This test method is used to evaluate the resistance of medical face masks to penetration by the impact of a small volume (2 ml) of a high velocity stream of synthetic blood. Medical face mask pass/ fail determinations are based on visual detection of synthetic blood penetration

2. Surgical gown

Level 1 – AATCC42:2000 Impact penetration test cotton > wool > kenaf. With the exception of kenaf, all natural sorbent materials sorbed more than 30 g oil per g fiber in the simulated seawater bath. Milkweed showed the highest oil sorption among the sorbents examined. Kenaf fiber sorbed only 5.6 g oil per g fiber (Choi and Jerry 1993). Figure 8.2 represents the oil sorption capacities of various natural fibers demonstrated by Choi and Jerry (1993).



8.3

Natural fiber nonwovens

289

Flax fiber nonwovens

Linens were produced only with fibers from the flax plant Linum usitatisimum. L. – Flax. The term “linen” alludes to fabric produced using flax fibers; however, today it is regularly utilized as a non-specific term to depict bed, shower, table and kitchen materials on the grounds that generally cloth was so broadly utilized for towels, sheets, and so forth. Flax fibers shift long from around 2 to 36 inches and normal 12–16 micrometers in diameter. There are two mixtures: shorter tow strands utilized for coarser fabrics and more line fibers utilized for finer fabrics. Flax fibers can be identified by their typical “nodes” which add to the flexibility and texture of the fabric. The crosssection of the fiber is made up of irregular polygonal shapes which contribute to the coarse texture of the fabric (www.saneco.com). In early years, the use of flax fibers for industrial applications was somewhat limited by the production cost. With new technologies employed to process flax, its price can drop making flax affordable for selected nonwoven composites. The very interesting application of flax nonwoven composites is in aquaculture. This process involves growing vegetables and plants in a nutrient solution without soil (Chiparus 2004). Linen generally offers better rigidity and modulus and lower prolongation, all extending between that of glass and aramid fibers. Good tensile strength is flax’s other potential points of interest for composite utilization incorporate vibration absorption, ultraviolet (UV) blocking, moisture retention, low density, no static charge, low relative cost, a natural resistance to insects and bacteria, and hypoallergenic properties (Kers et al. 2009; Rodie 2010). The main advantages of flax fibers are: there is no conceivable health danger, they are biodegradable and dispensable, apply low load on the environment, no contamination of air and water, no outflow of destructive chemicals like formaldehydes, isocyanates, organohalogens, chlorofluorocarbons, and so forth. The every year re-growing product is an endless asset that does not add to an unnatural weather change. And on the contrary during its growth, it converts the greenhouse gas CO2 into oxygen (Sen et al. 2011). Table 8.1 provides the comparative properties of flax and other high modulus synthetic fiber. The potential fields of utilization for long flax fiber nonwoven strengthened composite materials are automobile, marine, and windmill industry. The tensile properties of needle-punched nonwoven fabrics are affected by the fabric auxiliary parameters like fabric density, the amount, and profundity of fiber trap coming about because of the fabric formation process and fiber properties. The air permeability of the flax fiber nonwoven is the most important property of these materials for the application in dry filtration. The needle-punched nonwovens made of flax fiber showed satisfactory

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Nonwoven: Process, structure, properties and applications

performance with air permeability at test pressure difference of 200 Pa. Whereas air laid nonwovens showed air permeability about 2,000 Lm–2 s–1 (Kozłowski et al. 2008). Water-vapor permeability index of needle-punch flax was reported by Kozłowski et al. (2008). The value is about 0.5. It is in the middle of the range between 0 and 1. Materials of higher values ensure better physiological comfort. Table 8.1  Comparative properties of flax and other high modulus synthetic fiber (Source: Kers et al. 2009; Subhankar Maity et al. 2014) Fiber

Density (kg/m3)

Tensile strength (G Pa)

Elongation at break (%)

Specific tensile strength (G Pa m3kg-1)

Diameter of elementary fiber (µm)

Flax

1500

1.5

3

1

20

Hemp

1500

0.7

3

0.5

30

E-Glass

2600

2.4

2.5

0.9

3-30

Aramid (high modulus)

1500

3.1

1

2.1

12

Carbon (high modulus)

1800

2.2

0.5

1.2

8

Needle-punched nonwoven fabrics exhibited pervasive filtration capability with extraordinary dust atom arrestance and dust-holding limit. Dry and wet filtration is mainly directed by the pore size and its arrangement. The configuration thought for filter fabrics for a specific application starts from the choice of the strands to the fitting pore size to sift through the craved size of the particulates. The little scale pores should be humbler than the base atom size to ensure the needed filtration effectiveness. Also, a calendaring system was found to further extend the filtration capability of the fabrics by controlling their thickness and vulnerability. The fibers ended up being more solidly stuffed, in this way making it more troublesome for particles to experience the gathering of the fabric subsequent to calendaring. Other researchers evaluated the nonwoven mats made with flax or cotton fiber and flax/cotton fiber mixes for their capacity to sequester copper particle. In this process the nonwoven mats were treated with citric acid to upgrade the measure of negative charge on the mats and enhance their capacity to sequester copper particle. The treated mats were checked for changes in copper particle adsorption and fabric quality and contrasted with non-treated mats and process control mats. The outcomes



Natural fiber nonwovens

291

demonstrate that mats produced using 100% flax and 75%/25% flax/cotton mixes were like one another and fundamentally preferred at copper particle retention over 100% cotton or 50%/50% flax/cotton mixed nonwoven mats (Marshall et al. 2007). The flax fiber materials (fabrics, nonwovens) were also used in medical purpose like cancer and wound healing etc. (Janarthanan 2012). The medicinal uses of flax promotes heart health, lowers cholesterol, protects against strokes, lowers blood pressure, used for constipation, helps guard against breast cancer, and other cancers (Sen et al. 2011). The flax filaments could act as an antimicrobial material, which could be of interest not just in manufacture of sterile and therapeutic articles, additionally of industrial materials. Assembling of items for medicine, health, and cosmetology is turning into a standout amongst the most developed segments in the structure of generation of nonwovens, so that alteration of flax strands to make naturally dynamic dressings is of undoubted scientific and practical interest. Researchers also found that the spunlacing method helped the flax/PP nonwoven to grow the end use for auto interiors with specific specialized benefits. The developed nonwoven material were of improved tensile and flexural strengths, lesser thick with controllable weight, higher noise absorption coefficient and enhanced nonwoven flexibility along with fogging execution (Chen et al. 2008). The flax nonwoven materials were discovered for their solid capacity to absorb sound wave. In a study by Fages et al. (2013), flax fibers were mixed manufactured with binder fibers and nonwoven structures were made by wetlaid and subsequent thermal bonding. In general the acoustic assimilation at low frequencies (underneath 300 Hz) is low for these nonwovens, with retention coefficients in the 0.05–0.2 range. As in the case of flax: PVA nonwovens, the absorption coefficient increments up to estimations of around 0.4–0.5 in the 300 Hz to 2 kHz frequencies reach, showing intriguing and truly homogenous acoustic protection properties. For the spun laced flax/PP nonwoven boards (after hot-squeezing), the sound absorption coefficient was dependably beneath 0.3 inside of the entire testing scope of sound recurrence. The sound protection test performed by the impedance tube instrument uncovered that the spun laced flax/PP nonwoven boards behaved as a typical isotropic slight board with the reverberation frequencies of 366 and 354 Hz and the fortuitous event frequencies of 3576 and 3762 Hz relating to two distinctive machine settings for the spunlacing procedure (Chen et al. 2010). There likewise are other potential composite applications for flax in sports equipment. As a support layer in tennis racquets, spunlaced flax is lightweight and assimilates vibrations, and the surface designing potential

292

Nonwoven: Process, structure, properties and applications

outcomes could be of interest. The fiber’s UV resistance and regular woodlike appearance make it appealing as a development material for boats and canoes. Different conceivable outcomes incorporate support in foot bridges, for which flax offers lightweight quality and a natural appearance; and in wind turbine blades, again on the grounds that it is lightweight (Rodie 2010). The application of flax nonwoven in geo textile areas also evaluated very meagerly. The properties of geotextiles including thickness, pore size, and porosity have been examined for flax nonwovens. It has been found that substantial natural diversity in flax fiber length and fineness can bring about loss of elasticity and cause extensive range in smallest detected pore diameter. Researches were conducted to determine the potential of flax-based nonwovens obtained by the wet-laid process as candidate materials for thermal and acoustic insulation applications. To provide cohesion on nonwovens, different thermoplastic binder fibers have been used. The researchers found that nonwovens with different compositions are obtained in a hydro former station with processing parameters that ensure good handling and nonwoven formation. They concluded that the wet-laid technique is useful in obtaining nonwovens from natural flax fibers with different binder thermoplastic fibers. Although some anisotropy is detected because of the intrinsic preferential deposition direction, mechanical performance is enough to ensure good handling. Additionally, interesting acoustic and thermal insulation properties can be obtained by stacking different sheets, thus allowing the use of these materials as technical substrates for sound absorption or thermal insulation applications (Fages et al. 2013).

8.4

Jute fiber nonwovens

Jute is one of the important natural fiber possessing second place in budgetary centrality after cotton. Jute fibers stand out amongst the most crucial fibers used in modern applications. More than everything, jute is a commodity on which a huge number of families in a percentage of the nations depend for their money income. 95% of world wide jute yield were produced from the countries like India, Bangladesh, China, Nepal and Thailand. The prime reasons of developing business sector of jute-nonwovens in technical textile applications are as detailed below (Anon 2006). The jute fiber possesses: • High strength, modulus and dimension stability • Stiffness or moderate draping • Higher frictional properties • Coarseness • Easy rot / biodegradability and eco-friendliness



Natural fiber nonwovens

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• Good moisture absorption and breathability • Good bleachability, dyeability and printability • Low cost Jute is annually renewable and abundantly grown in India and neighboring countries. Utilization of mill wastes of jute i.e. use of short fiber for making jute based nonwoven. Due to the aforementioned special properties and lower costs of manufacturing process of nonwovens opened up new markets in numerous fields like household, industrial and technical end-use applications. Jute nonwoven products are being used in various applications (Maity et al. 2013) as shown in Table 8.2. Table 8.2  Potential end uses of jute-based nonwovens (Source: Maity et al. 2013) No.

Category

Specific example

1

Interlining

Sew-in, fusible, stiffeners

2

Footwear and leather industry

Luggage and handbag, sewn up socks, shoe liners

3

Dry filtration

Filter media

4

Automotive application

Cushioning, noise reduction layers, floor carpets, trays, dash-boards, etc.

5

House hold goods

Floor coverings, wall coverings, fillings, cover of furniture’s, beddings, etc.

6

Agriculture and horticulture

Crop covers, mulch matting, wind breakers, frost protectors, capillary, etc.

7

Civil engineering and building industry

Geo textiles, liners, pipe laggings, thermal insulation layers etc.

8

Other industrial applications

Cable wrappings, oil sorbents, load bearing components, insulators, panel and packaging bag and sockings, protective wrappings, etc.

Needle-punched jute or jute mixed needle-punched nonwoven fabric can be effectively utilized as a floor covering and carpets. These jute and jute-mixed needle-punched nonwovens system serves both the stylish and the utilitarian properties needed in such materials. These nonwovens mainly preferred over due to their less expensiveness than commercially existing woolen materials. However, these jute nonwoven material are rated as second grade based on their natural surface texture and appearance. In such cases the researchers recommended that woven sacking or hessian fabric is utilized

294

Nonwoven: Process, structure, properties and applications

at the posterior for support and coarse denier polypropylene/ acrylic fiber is utilized on top for aesthetic appeal and smooth appearance, keeping thick layer of jute fiber in the middle for strength (Sengupta et al. 1985). The previous research studies had showed that the jute needlepunched nonwovens were utilized in various applications like, as a part of disintegration control in expressway dike and cut slops, stream bank security, ground detachment capacities, filtration in street, fortification applications in provisional unpaved streets, etc. (Pandey et al. 1989; Samajpati 1998). In these applications, jute mainly preferred over the existing synthetic materials due to their eco-friendly nature. Jute fiber has a splendid similarity with soil and jute needle-punched nonwoven degrades in the soil within a couple of months aiding in soil adjustment, cake development, and vegetation to soil to develop plants (Majumdar 1999; 2001; Sengupta et al. 2008). For the application of thermal insulation medium, the jute needlepunched nonwovens are frequently preferred due to their thick and permeable structure. The nonwoven contains uniformly scattered void or air, which is in charge of thermal insulation. The added advantage of the jute fiber in the use of thermal insulator other than structural aspect, the fiber itself a very poor thermal conductive in nature. Based on the above-mentioned aspects, the woollenised jute fibers were used in garments as a filler material against cold weather as a warm garment (Debnath & Madhusoothanan 2011). Jute needle-punched nonwoven may be a successful reinforcing agent for the jute-based composites. By using jute needle-punched nonwoven fabric, the products like tabletop, chair, washbasin, toolbox, signal casing, serving tray rain pipe, corrugated sheet, fan blade, speaker box, and country boat have been successfully developed. Also the jute-based needled fabric can be used in decoration, furnishing, bags, soft luggage, apron, hat, gloves, file cover, handicraft items (Sengupta et al. 2005). Jute needle-punched nonwoven fabrics can be utilized as sound absorbent medium effectively. The main benefits of using jute nonwoven material as sound absorbent medium is their permeable surface and flexibility. These properties act as reason for sound retentiveness inside the nonwoven. These jute nonwovens can be utilized as wrapper of sound source or it can be utilized as a part of the divider to lessen the resonations. Floor blankets utilizing natural fibers (kenaf, jute, waste cotton, and flax) in mixes with polypropylene and polyester were produced as checked needle-punched nonwoven for acoustic retention in auto insides (Sengupta et al. 2008; Roy & Ray 2005; 2009). The steady state growth of use of jute-nonwovens in the automotive sector is as following (Ellison & McNaught 2000).





Natural fiber nonwovens

295

Comparative weight reduction of 10–30% in comparable parts Good mechanical properties The possibility of forming composites in a single machine passage Relatively good impact performance, with high stability and minimal splintering • No health hazard during handling • No emissions of toxic fumes when subject to heat • Sustainable and renewable raw material resource • Superior environmental balance during material and energetic use • Recycling possibilities • Relative cost advantages In recent years, the jute-nonwovens and its composites are used in making of door liners, boot liners parcel shelves in the automotives. Floor carpets and interior decorations are also made of these products. Since, they are weightless and low cost. The jute nonwovens utilized as a water sealer in geotechnical applications. It was found that jute: jute caddies (unspinable jute fiber) in 1:1 extent suitable for water proofing treatments (Debnath 1983). Proper planning of jute needle-punched nonwoven can be utilized as filter media. Such needle-punched nonwovens are suitable for coarse and medium filtration application and suitable for material, tobacco dust, wood flour, paper shreds, etc. (Subramanium et al. 1988).

8.5

• • • •

Hemp fiber nonwovens

Over a thousand of years, hemp has been used as a potential source for papermaking, sails/canvas and building materials. The cellulosic content from the natural fiber hemp stalk is made off higher toughness and can be effectively utilized as a part of the generation of materials, dress, canvas, rope, cordage, archival level paper, paper, and other development materials. There are two different kind of fibers extracted from hemp: (i) bast or long fibers and (ii) hurds or inward short fiber. Customarily hemp has been developed for its profitable and adaptable astounding bast fibers. Bast fibers represent 20–30 percent of the stalk (contingent upon the seed variety, and planting density). There are two sorts of bast fibers in general (www.binhaitimes.com): (i) Primary bast fibers with almost 70 percent of the fibers and are long, high in cellulose and low in lignin. Primary bast fibers are the most significant piece of the stalk, and are by and large thought to be among the most grounded plant fibers known.

296

Nonwoven: Process, structure, properties and applications

(ii) Secondary bast fibers make up the remaining 30 percent of the bast fibers and are medium long and higher in lignin. They are less profitable and turn out to be more pervasive when the hemp plants are become less densely, making shorter fatter stalks since they don’t have to compete for light. Hemp fibers are a renewable natural asset consolidating the advantages of a feasible advancement. The hemp is used as a replacement for synthetic fibers, for much variety of specialized applications including nonwoven items. The properties of hemp fibers like hygroscopic nature, low thickness and releases very low amount of harmful substances amid burning and heating give a potential industrial sector for this natural fiber. These fibers can be used as a thermal insulation material in industries and household application. Other than this, the hemp manufacturing process fundamentally consumes very less amount of pesticides and other synthetic sources to grow, thus reduces the environmental impact. There are thousands of items produced using hemp, and some of them, without a doubt, are being utilized as building insulation material, erosion control material and as a oil sorbent material. In this manner, hemp fiber nonwovens are utilized as a part of the creation of insulating materials to minimize the harm to nature, as they add to the lessening of CO2 outflows (Kozłowski et al. 2008), have a low energy demand in production, high potential for recycling, and positive effect on indoor (Kymäläinen, 2004). Due to its excellent properties, hemp fiber is widely used in automotives in the recent years. These natural fiber nonwovens are low cost, environmental friendly, high strength and comparable with glass fiber applications. Hence, these nonwoven mats are used as a replacement for glass fiber nonwovens in cars. The increasing commercial availability of hemp fiber and the demand for low cost, high strength fibers has resulted in new applications for hemp, particularly in automotive and construction products (Wubbe 2001). Liga Freivalde et al. (2002) investigated the application of hemp fiber nonwoven material in household and industrial utilization. The study revealed that, the hydroentanglement process is a good technology to develop for hemp fiber nonwoven with predefined properties as per the planned utilization. The major advantages of this hemp fiber nonwoven mats are their greater water vapor penetrability and relatively large thickness. It permits these nonwovens to apply in regular breathing bundle development for household, industrial and construction uses. The studies were performed to evaluate the thermal insulation properties of hemp fiber nonwovens. The nonwoven produced by hydroentangled method was used in this study and the results were very supportive. A material will be characterised as an insulator if its thermal conductivity is under



Natural fiber nonwovens

297

0.065 W/mK. A typical mineral wool has thermal conductivity in the extent 0.035–0.040 W/mK, wood 0.21 W/mK, air 0.026 W/mK. The authors had mentioned that the developed hemp fiber hydroentangled nonwovens had a phenomenal protection execution because of thermal insulation properties, where thermal conductivity is from 0.031 to 0.040 W/mK (Carus et al. 2011). The hemp fibers tows were traditionally used as insulation material between timbers in earlier days. After 1990s, when hemp was rediscovered throughout the world as an important raw material for bio-based products, their application area becomes versatile (Kymäläinen 2004). The bast fibers are commonly identified as better insulator material due to their permeable structure, small diameter, and a low fiber bulk density. In case of hemp fiber the bulk density is 1.48 g/cm3 and for glass fibers, it is 2.6 g/cm3. This helps the hemp fiber a great deal of air entrapment between the fibers and acts as an insulation material. Hemp nonwoven insulation can be utilized as an option material for glass wool or mineral wool insulation materials, and inward moistness regulation in structures. Furthermore, common fibers are ignitable without buildups while glass fibers are most certainly not. In result, incineration with energy recovery is a positive end-of-life alternative as distinct option for reusing. Even after all these benefits, natural fibers have also disadvantages, for instance, the increased moisture absorption, flammability (Freivalde et al. 2011). Liga Freivalde et al. (2013) evaluated the thermal properties of nonwoven samples of technical hemp fibers made through the thermal bonding, needle punching and hydroentanglement. Their results showed that hemp has the same or better thermal properties than other commonly used thermal insulation materials, e.g. mineral wool. In the comparative study results of different manufacturing technologies, the results revealed that all the three hydro-entangled, thermal bonded and needlepunched samples differ very less in their thermal conductivity. In view of manufacturers point, the hemps fibers have high quality, flexibility, ease of processing and recycling. But in the case of user point of view, there are few drawbacks which still exist. These setbacks are arising due to the purchasers’ newness to hemp fiber. Key inclinations of hemp fiber are its high quality and low cost, and there are various organizations so far foreseeing the usage of this fiber as it step by step propels into getting the chance to be another option for manufacturers. Moreover, hemp fiber’s staple length and quality can be modified by necessities of the purchaser. In spite of the way that the business area is worth insightful, using better attributes of characteristic of natural fibers results in lower value rejects, decreases downtime on the types of equipments, minimizes loss of fiber amid preparation (Gbhat & Hrong 2005).

298

8.6

Nonwoven: Process, structure, properties and applications

Kenaf fiber nonwovens

Kenaf is a 4000-year-old ancient African harvest plant. This plant is an individual from the hibiscus family (Hibiscus cannabinus L) and is identified with cotton and jute (Cook 1960). In 1940s, after World War II, when the jute fiber imports were cut off, as an after effect of war, the Kenaf harvesting and exporting was the main business in United States (Moreau et al. 1995; Ramaswamy et al. 1995). Kenaf has a solitary, straight, unbranched stem comprising of two sections: an outer fibrous bark and an inner woody core (www.siu.edu). The proportion of the core to bast is 65:35% of the entire stem weight. Kenaf develops rapidly, ascending to statures of 12–16 feet (4–5 m) in a 4–5 month developing season and 25–35 mm in width (Bert Nimmo 2002). Kenaf grows on different sorts of soil however is best developed during the stormy season for good yields. Yields of kenaf are from about 8–12 metric ton amounts of dry stem per hectare. Fundamental is that kenaf is a renewable and supportable option with a short growth time of just 4 months. Kenaf fiber nonwovens can assume a critical part in fluid/particle separation operations, like oil adsorption, combination, deep-bed filtration, and as filter aids for decreasing the resistance of filter cakes. Fibers can be utilized to enhance filtering attributes of domestic wastewater (Tiller & Cong, 1995). Kenaf fiber as of now has been utilized as a part of applications like composite sheets, car boards, insulation mats and geotextiles. The world’s leading automobile manufacturer and electrical equipment manufacturers like Toyota Motor Corporation and Panasonic Electric Works have led the pack in the worldwide kenaf industry. Toyota has created nonwovens from kenaf fibers for auto inside applications, and Panasonic, a basic divider board to supplant timberbased plywood (www.jeccomposites.com). Research work done by scientist had determined additionally that kenaf fibers are phenomenal oil malleable materials and keep the oil from spilling after ingestion. Each one of these properties will be gainful in minimizing industrial waste. This property of kenaf fiber opens a potential application in the area of oil spill cleanup in industries either in a loose form or as a nonwoven (Goforth, 1994). Kenaf fibers have been blended with different kinds of natural and synthetic fibers and made as nonwoven materials like kenaf/PP or kenaf/cotton/PP mixes for the applications like fabric softener sheets, furniture underlays, spread stocks, and barrier textiles for therapeutic and agricultural protective dress (Ramaswami & Boyd, 1994). As mentioned earlier, the two components of kenaf stem used in various different applications. The kenaf is a feasible source for mash paper only if the bast and center divisions were separated carefully. The separated outer layers used as a main element to produce low-thickness composites (Sellers et al.,



Natural fiber nonwovens

299

1993). The inner part of the kenaf fiber, called as core is used as a panel in manufacturing roof tiles, enlivening board substrates, floor tile substrates, and certain auxiliary segments. Another direct application of kenaf fiber is waste cleanup mats. Kenaf fibers treated with sodium hydroxide have been carded and needle punched into 100% kenaf and kenaf/cotton mixed mats. These mats are additionally biodegradable and have potential in the avoidance of soil disintegration, the control of weeds, and cleanup of waste fluids (Tao & Moreau, 1994). The various needle-punched nonwoven items like, lightweight seeded grass mats, wild bloom mats, vegetable strips, erosion control mats, oil retention tangles, cushions and pads, substrates for formed car parts, and composites were developed from kenaf fibers or by using the cleaned of core fibers as 100% or along with refined wood, synthetic and other natural fibers as a blend (Fisher, 1994). The study by de Guzman et al. (1982) was undertaken to explore a new material for novel textile products from abaca, kenaf and pineapple fibers using nonwoven techniques, specifically, needle-punching and adhesivebonding processes. One more advantageous aspect for nonwoven mats is that they can be tailored by blending with another fiber to achieve the desired mat properties. Tao et al. (1998) prepared nonwoven mats containing 100% kenaf or kenaf/cotton blends. They have mentioned that adding cotton fibers into kenaf mat increases mat strength and oil retention capacity, indicating that the blended mats have 24 potential applications in the prevention of soil erosion, weed control, and cleanup of waste liquids. Ramaswamy et al. (2003) have attempted to develop nonwoven kenaf mats for high value and highvolume end products like furniture, kitchen cabinets, fixtures, wall-coverings, displays, and various other products. The researcher suggested that to make kenaf mats as successful alternative materials for practical applications, the processing has to be developed using conventional equipment in nonwoven industries. Baldwin et al. (1999) demonstrated that nonwoven 100% kenaf bast fiber mats could be used as a growth medium for the establishment of some warm-season and cool-season grass species.

8.7

Milkweed fiber nonwovens

Milkweed, a perennial plant can adjust to unfavorable soil conditions, is being considered right now alternative source of fiber as of late. Milkweed has a place with the sort Asclepias, with more than 80 distinct species of which 45 are indigenous to the United States of America (USA). It beforehand fit in with the family Asclepiadaceae; however, it is presently grouped into the subfamily Asclepiadoideae of the dogbane family Apocynaceae. Agriculturists and researchers joined as an inseparable unit in the late 1980s to create milkweed

300

Nonwoven: Process, structure, properties and applications

at this very moment fiber source (Adams et al. 1984; Heise & Vidaver 1989; Witt & Knudsen 1993). There are two different kinds of fibers which can be obtained from the common milkweed plant. The first one is the long, solid, however fragile bast fiber and the next is the seed hair fibers known as floss. It was found that, like elastic substance (in the latex), the nature of the bast fibers fluctuated significantly with edaphic and climatic environment (the sort of soil 16 the plant is developing in and the season, that is, dry or wet year). Normal milkweed fiber (Asclepias syriaca) is a characteristic and biodegradable different option for polypropylene fiber in oil sorbent application. The microscopic evaluation revealed that, the lumina, or inward structure of the seed fibers are hollow, which permits the oil to be assimilated and held inside the individual fiber and also in the assembly. Seed fibers are made out of 55% cellulose and 18% lignin. Since these mixes are biodegradable, milkweed is an environmentally friendly distinct option for polypropylene material in oil spill cleaning process (Das, Praba Karan, & Rengasamy, 2011). Woven milkweed fibers have diverse properties than individual fibers. Nonwovens assembly can frame chains or networks of fibers that cooperate while keeping up attributes of individual fibers without alter (Fotheringham, Mather, Wei, & Yang, 2003). Small size pores in the nonwoven mess consider the retention and transportation of fluids and the fibers hold the oil all the time. Since nonwovens of these milkweed fibers have higher porosity than other fiber nonwovens, these nonwoven materials ought to work the best at engrossing and holding oils. Pretty nearly 300,000 tons of oil was spilled every year from a variety of sources. From 1998 to 2007, more or less 2,800 tons of greasing up oil was spilled every year in ports, adding to oil contamination (Fingas & Mervin, 2011). When oil has entered water, the properties of oil change, making it harder to uproot. Thus it is imperative to prevent initial pollution of oil from coming into contact with water and potentially emulsifying. Recently cellulose-based materials like milkweed fibers have been examined for their potential use in tidying up spilled oil on the grounds that they are effortlessly biodegradable, yet other potential materials to replace the existing synthetic materials like polypropylene and etc. (Hubbe, 2013). Milkweed and kapok were natural fibers have been found to have comparative properties on oil limits and recently used in oil spill cleanups. In case of the oil sorption activities, even thought the polypropylene has a high absorption capacity it possesses only minimum oil retention ability. The research report mentions that during the first moment after oil retention, a lot of oil is lost. From one minute to five minutes, the rate at which the oil is discharged from the polypropylene is diminished rapidly. It is essential that



Natural fiber nonwovens

301

oil should be consumed, but it is also likewise critical that the oil is held for a long time and not to discharge over into environment (Fotheringham, Mather, Wei, & Yang, 2003). In the case of milkweed fibers, when milkweed fiber retains oil, the condition of the oil changes from a fluid to a semi solid. This makes the fiber to absorb more amount of oil than the expected quantity. The researchers reported that at room temperature, milkweed has been indicated to absorb approximately 40 g of oil for every 1 g of fibers (Chol & Cloud, 1992). The thicker wax coat in the fiber inner structure aids the milkweed fibers to absorb more oil than cotton and also provides improved oil retention. Further it also evidenced that at a lower temperature, milkweed ingests more oil than the elevated temperature. This phenomenon was explained by the researcher as, the viscosity of the oil increases, the retention process becomes simpler. However, the reduction in temperature affects the internal capillary action of oil through the fiber pores and reduces the oil retention (Chol & Cloud, 1992). The researcher also evaluated the performance of the milkweed fiber, after soaking it in water, the results demonstrated that the process reduced the absorption capacities of the milkweed fiber. This cause was explained by the authors as the hydrophobic nature is dominant in the stage, the capacity might have reduced. Their study also confirmed that the deliberate uprooting process in the milkweed fiber will allow the fiber to re-use and assimilate more oil every time. In investigations of milkweed oil receptiveness, the capacity to retain oil just somewhat diminished for rehashed uses, so the fibers could possibly be reused for future utilization (Chol & Cloud, 1992). Estabragh, one of the milkweed fibers, a natural silky indigenous, which is generally extracted from a plant wildly grown in central plateau of the southern regions of Iran (Bakhtiari et al. 2015). The lustrous acicular appearance and physical properties of Estabragh fiber are very similar to other species which totally belong to Aclepiadacae family. The Estabragh fibers possess very lowdensity value of about 0.9 g/cm3 because of their hollow structural nature. Nonwovens due to their technical and economical merits are used extensively in numerous applications. These pliable fibrous structures can be manufactured in various densities; thus in addition to their aesthetical aspects, nonwovens also provide excellent sound insulation properties (Attenborough, 1971; Voronina, 1983, 1994). Hence, Sanaz Hassanzadeh et al. (2014) evaluated the effect of needle-punching process parameters on the sound absorption properties of Estabragh/polypropylene needle-punched nonwoven. They have evaluated the predictor variables like fiber blend ratio, punch density, and areal density. Their outcomes articulated that samples with higher extent of Estabragh fibers can be viewed as more effective means for noise absorption than the other proportion. This increased sound absorption capacity

302

Nonwoven: Process, structure, properties and applications

of the nonwoven fabric was due to the hollow structure of Estabragh fibers. In general, the geometry of fibers and their arrangement within the structure were the responsible for the acoustic performance of nonwoven structures. Hence, the physical property of the constituent fibers of a nonwoven structure was the main reason for the higher sound absorption nature of the assembly (Tascan, 2005). During the application of this natural fiber as a sound insulation material, the researchers found two fundamental factors which influence the end use of the nonwoven mat. 1. Higher the fiber entanglement achieved during needling operation higher will be the sound retentiveness of the needled nonwoven fabrics. 2. The increase in the areal density of the needle punching significantly increases the energy loose in samples. They researchers suggested that, due to their extraordinary characteristics of the Estabragh fibers, these nonwovens can be used as a replacement of conventional insulation materials in automotives and buildings. These nonwoven materials were versatile; they can be used in different porosity and mass rangers. Simple increment in the fiber per unit area will alter the nonwoven mass and porosity. Hence, the fabric assimilates more solid. Also it was found that the effect of punch density is insignificant as far as sound absorption is concerned. As connection to their previous study, researcher Sanaz Hassanzadeh et al. (2014) further analyzed the four diverse controllable parameters incorporating Estabragh fiber in the making of nonwoven fabric. They have analysed the fiber ratio in blend, layer weight, punch density and the frequency of sound were selected and the effects of each parameter on noise absorbency. They have presumed that the proportion of entire distance across to fiber width of Estabragh fibers is much higher than that of the hollow-polyester fibers. For this situation, more the milkweed fiber in blend creates higher amount of surface area of nonwoven subsequently than the normal nonwoven. This creates more frictional losses of sound energy while it enters into the nonwoven. Thus the tests would be resulted to the higher normal-incidence sound Absorption Coefficient (NAC) values for the nonwoven with higher Estabragh fiber content. The results additionally demonstrated that the layer weight has critical impact on nonwovens acoustic execution. Expanding the layer weight prompts builds the quantity of fibers inside of the structure which thus brings about more sound energy losses. Hasani et al. (2014) examined the effects of different thermal bonding process variables such as Estabragh fiber ratio in blend, layer weight, needle-



Natural fiber nonwovens

303

punching density, thermal process temperature, and calendering speed on uniaxial breaking force and bending rigidity of nonwovens produced from Estabragh/polypropylene fiber blends were investigated using Taguchi method. The findings of the research showed that the blend ratio of fibers, layer weight, and the applied temperature during the thermal bonding process significantly increased the nonwoven layer resistance against axial tensile forces. However, the variables like punch density and calendering speed had no significant effects on the breaking force values of the samples. In case of the samples’ bending rigidity, it was found that all the variables except the calendering speed have significant effects. To the extent the bending rigidity nature of nonwoven is concerned, it was noted that the mix proportion was the most influencing component. The less number of holding point framed in the higher weighted layers realizes lessening in the resistance of the samples against bending powers (Noushin Bahari 2015).

8.8

Pineapple fiber nonwovens

Pineapple fiber is made from fibers extracted out of pineapple leaves, which are usually discarded and left to rot during the pineapple harvesting process. The fine, flexible fibers are extracted from the leaf through a process called decortication. The decorticated fibers were degummed and used for the manufacturing application. The degumming process surprisingly provides a great amount of soft to the touch and breathable nature to the fiber. The degummed fibers are used either directly or in blend with other fibers to convert as nonwoven textile. Piñatex is one of the Philippines-based textile company started making these pineapple fibers from pineapple leaves. They were initially developed nonwovens for Philippines, because of the greater fiber properties and potential the requirement for the fiber increased in European countries recently (www.carefullycurated.co.uk). The current manufactures of this pineapple fibers and nonwoven fabrics were producing these nonwoven as an alternative to the leather material to avoid or eliminate the number of environmental hazardous processes involved in the leather tanning process. According to the company, they take a waste product and convert it into a new and sustainable product, which brings benefits to the farming communities. They developed a process called decortication to extracts the fibers from the leaves, which happens on the pineapple plantation. The by-product of this process is a biomass that can then be made into organic fertilizer or bio-gas, which can bring additional income to these farming communities. Following the extraction, the fibers go through an industrial process, using needle-punch technology, to be converted into a nonwoven textile.

304

Nonwoven: Process, structure, properties and applications

“Piñatex offers a compelling new material, which has unique properties inherent in the fibers being used: strong tensile strength, finesses, takes color very well, is pliable and durable and all these properties are well maintained in the nonwoven substrate made from pineapple leaf fibers,” Dr. Carmen Hijosa, the founder of the company adds. When it comes to using Piñatex nonwoven as a leather alterative, the unique textile can be used to make fashion items and accessories, home interiors and automotive and aeronautics interiors, according to the company (Tara Olivo, 2015).

8.9

Abaca fiber nonwovens

Abaca is a leaf fiber which fits in with banana group of plants with the organic name of musa textiles. These leaves are upright, pointed, smaller, and more decreasing than the leaves of banana. Abaca (Manila Hemp) is one among the common fiber-reinforcing materials. Abaca is a hard fiber and is altogether unique in relation to genuine hemp, which is a delicate fiber and is the result of Cannabis sativa. The best grades of Abaca are fine, radiant, light beige in shading and extremely solid. Abaca is the most grounded of every single normal fiber. It is utilization as crude material for cordage, fiber specialties, and mash for the creation of claim to fame paper items like security papers, tea packs, meat housings, nonwoven materials, and cigarette papers. Table 8.3  Chemical composition of Abaca fiber and natural fibers Chemical composition

Abaca (leaf)

Hemp (bast)

Jute (bast)

Sisal (leaf)

Linen (bast)

Cotton (Seed)

Cellulose (%)

68.32

77.5

64

71.5

82

80–90

19

10

20

18.1

2

4–6

Lignin (%)

12–13

6.8

13.3

5.9

4

0–1.5

Moisture content (%)

10–11

1.8

1.5

4

7.7

6–8

4.8

3.9

1.0

1

3.4

1–1.8

Hemi cellulose (%)

Ash content (%)

It has been approved as main component in the manufacture of composites used in automotive industry due to Abaca fiber’s lightness as compared to fiberglass. Mercedes Benz has used a mixture of polypropylene thermoplastic and abaca yarn in auto mobile body parts. These fibers also used in medical gas masks and gowns, diapers, hospital linen, bed sheets as nonwoven form (Vijayalakshmi et al. 2014). The chemical compositions of abaca fiber with other natural fibers were provided in Table 8.3.



Natural fiber nonwovens

305

Guzman et al. (1982) analysed the possibilities of utilizing abaca, kenaf and pineapple fibers nonwovens as household material. They also compared the performance of the developed products with the commercial items. Their study mainly focused on the likelihood of using abaca, kenaf and pineapple fibers as crude materials for nonwoven fabrication. They performed the ideal degumming conditions for abaca and kenaf fibers as first process of their study, the physical, chemical and microscopic characterization of each fiber were performed later. Finally, the mechanical and nonwoven processing of abaca kenaf and pineapple fibers was performed. Based on their research, they developed nonwoven fabrics as tablecloths, bags, wall covers, sound proofing materials and interlinings. The fabrics were produced from abaca, kenaf and pineapple fibers with polyester blends using the needle-punching and adhesive-bonding processes. They had also performed a physical properties evaluation of the nonwoven fabrics. The strength and drape properties of the needle-punched fabrics shoed the potential application possibilities of nonwoven as home textile.

8.10

Sisal fiber nonwovens

Sisal fiber is derived from the leaves of the sisal plant. The sisal fibers were decorticated from the leave using a machine, where the machine mechanically crushes the sisal plant leaf between the rollers to scrap the fibers out of it. The extracted fibers were then allowed to dry naturally or mechanically after a strong wash. The dried fiber represents only 4% of the total weight of the leaf. The dried and processed fiber is brushed double time to make it more lustrous. (www.sisal.ws). The sisal fiber is mainly utilized for the cordage uses in ship’s rigging and ship-related industries. This is because of its high strength, durability, ability to stretch, affinity for certain dyestuffs, and resistance to deterioration in saltwater. In general, there are three different grades of Sisal fibers were used by industries. The first grade sisal fiber yarns were used in home textile and carpet industries after required finishing and processing treatments. The second grade or medium grade sisal fibers were commonly used in cordage industry, where the ropes, balers and binder twines are manufactured. The resistant towards the saltwater makes this sisal fibers more opt for the applications like marine and agricultural purpose (www.wigglesworthfibres.com). The lower grade fibers contained higher amount of cellulose and hemicelluloses in their structure, this provides an opportunity to use this fibers in paper industry. The sisal fibers are also used in low cost and specialty paper, dartboards, buffing cloth, filters, geotextiles, mattresses, carpets, handicrafts, wire rope cores and macramé production other than general cordage and twine based applications.

306

Nonwoven: Process, structure, properties and applications

The comparison of physical properties of natural fibers with sisal fibers were listed in Table 8.4 (Vijayalakshmi et al. 2014). Latest studies had evidenced that the sisal fibers has been utilized as a strengthening agent to replace asbestos and fiberglass as well as an environment-friendly component in the automobile industries (web.archive.org). Table 8.4  Comparison of physical properties of natural fibers with sisal fiber Physical properties

Sisal (leaf)

Abaca (leaf)

Hemp (bast)

Jute (bast)

Linen (bast)

Cotton (seed)

Density (g/cm3)

1.33

1.5

1.48

1.46

1.4

1.54

Fiber length

1m

2–4 m

1–2 m

3–3.5 m

up to 90 cm

10–65 mm

Fiber diameter in microns

100–300

150–260

16–50

60–110

12–60

11–12

Tensile strength (N/m

600–700

980

550–900

400–800

800

400

Elongation in %

4.3

1.1

1.6

1.8

2.7–3.5

3–10

Moisture regain in %

11

5.81

12

13.75

10–12

8.5

17–22

41

30–60

20–25

50–70

6–10

2)

Young’s modulus (Gpa)

Neira & Marinho (2005) conducted a study to analyse the thermal insulation ability of the sisal nonwoven blanket. Their results were promising that sisal fibers were not very different from those of commercial thermal insulation materials. Their experiments verified that the sisal fiber nonwoven mats was not resistant to applications beyond 160°C. During the study the researchers noted that the nonwoven blanket changed its color from natural to dark brown, which was attributed to the carbonization of the fibers. They have suggested that these fibrous materials can be still used in many situations of industry, as well as in domestic application, where the temperature does not reach more than 150°C. They have concluded that, the use of sisal blanket, besides providing significant decrease in the costs of thermal insulation when compared with the commercial materials with sustainable nature. Other researchers analysed the behavior of coir, jute, sisal and polyethylene terephthalate (PET) blended needle-punched nonwoven fabrics against its load withstanding ability as an application in geo textile material. They had developed the nonwoven fabrics by needle-punching technique. The developed nonwoven mats with different fiber combinations were analysed for their load withstanding capacity of the soil. They identified that the soil inserted with fabric samples showed improved load withstanding capability when compared to the standard one (without nonwoven) (Meenambika & Sunitha 2012).



8.11

Natural fiber nonwovens

307

Wool fiber nonwovens

Majam Radetica et al. (2003) utilised recycled wool-based nonwoven material as a sorbent in an oil spill cleanup. This material sorbed higher measures of base oil than diesel or unrefined petroleum from the surface of a demineralized or artificial seawater shower. The researchers identified that the free fibers of the same root right now have fundamentally higher sorption limits than explored nonwoven material. The authors mentioned that the recycled wool-based nonwoven material showed good sorption properties and adequate reusability, indicating that a material based on natural fibers could be a viable alternative to commercially available synthetic materials that have poor biodegradability. The researchers also treated the recycled wool with low temperature plasma and chitosan, to analyse the effect of these treatment on the oil absorbtion properties. They have concluded that the low temperature plasma treatment results in extremely high hydrophilization of the wool fiber because of the modification of a covalently bound layer of fatty acids on the fiber surface and the formation of new polar functional groups (Lee & Pavlath 1975). The researchers mentioned that their findings were in line with the findings of Choi and Moreau, where, they had mentioned that physical properties of the fiber such as crimp, twist, surface roughness, and porosity have significant influence on the oil sorption properties. The findings suggested that adsorption should be the most prominent mechanism of oil sorption on wool nonwoven because of (i) the existence of waxes and grease giving a hydrophobic nature to the fiber, (ii) the scale like structure with large pores, and (ii) the fiber crimp providing the space for the deposition of oil and formation of capillary bridges of oil between the fibers. (Choi & Moreau 1993)

8.12

Kapok fiber nonwovens

Kapok or ceiba pentandra is a plant which is available abundantly in our country. This plant is one of the widely available resources in India, which makes it less treasured than any other plant-based fiber material. This fiber materials commonly used in the fillings in pillows, hence, the fiber was never expected to perform in other applications. However, the kapok fibers look the same as cotton fibers in physical appearance. The fluffiness and softness of the both cotton and kapok fibers could not be easily differentiated by an inexperienced eyes. The only difference which makes the kapok unique is the

308

Nonwoven: Process, structure, properties and applications

brighter white colour. The cotton fibers might look a bit yellowish in colour than kapok fiber. It is meaningful to mention that though both cotton and kapok fibers appearance looks the same, the physical properties of both in terms of length, diameter and moisture regain are different for each materials. The careful microscopical examination of kapok fiber revealed that the kapok fibers have a hollow tubular shape with a large lumen while cotton appears like a kidney shape (Musa et al. 2011). In average the Kapok trees normally reach 30–50 metres high Asian sub continent. Furthermore, the trunk can also expand to 2.74 metres (9 feet) or 3.05 metres (10 feet) in diameter. The tree is deciduous, which means it will shed all of its leaves during the dry time (Mwaikambo, 2006). The kapok fibers are traditionally used as a stuffing’s and fillings in bedding, upholstery, life preservers and other water-safety equipment because of its excellent buoyancy (Zhang et al., 2013), and for insulation against sound and heat because of its air-filled lumen (Veerakumar and Selvakumar, 2012; Xiang et al., 2013). The kapok fiber possesses an excellent heat retention capacity. Hence, these fibers can be blended with other fibers to achieve apparel fabrics with improved heat retention characteristics (Hong et al., 2012). The other researchers studied the properties of kapok fiber nonwoven developed by different manufacturing methods. Their experiment resulted the findings like, for better performance, the nonwoven processing technology should not be affect hollow of the kapok fiber. The nonwoven technology also has an impact on products related performance like, products Gsm, different thickness, permeability, heat retention, and compression elasticity were different for various manufacturing methods (Li Suying et al. 2102).

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Index

A Aatcc 96, 136, 137, 153, 190, 204, 207, 208, 312 abaca 285, 286, 299, 304, 305, 306, 309, 314 abradant 194 abrasion 11, 12, 14, 84, 95, 104, 131, 162, 173, 189, 192, 194, 195, 212, 225, 227, 232, 242, 260, 268, 272, 274, 279 abrasive 25, 161, 162, 214, 269, 271, 281, 282 absorbency 13, 30, 31, 89, 128, 131, 136, 160, 189, 200, 201, 205, 209, 228, 229, 275, 287, 302 absorbent 11, 13, 14, 22, 27, 28, 31, 32, 66, 70, 146, 147, 151, 188, 201, 204, 208, 213, 226, 228, 229, 246, 260, 265, 269, 274, 275, 281, 282, 283, 287, 294, 310 absorption 10, 29, 132, 189, 196, 199, 200, 201, 204, 205, 229, 238, 252, 272, 273, 274, 285, 287, 288, 289, 291, 292, 293, 297, 300, 301, 302, 314 abundantly 293, 307 acceptable 85, 128, 193, 206 accomplish 115, 126, 140 acetate 13, 21, 22, 23, 24, 30, 94

acicular 301 aclepiadacae 301 acoustic 91, 187, 233, 257, 282, 291, 292, 294, 302, 310, 312, 313 acrylamide 22, 23, 24, 25 acrylate-vinyl 23 acute 162 adaptable 133, 146, 220, 295 add-on 132, 173, 175 additives 1, 11, 15, 17, 27, 44, 132, 172, 277 adhesion 2, 3, 20, 26, 27, 84, 110, 133, 151, 168, 182, 189, 263, 268, 274, 281 adhesive 18, 19, 20, 22, 23, 24, 25, 26, 32, 91, 119, 133, 137, 152, 160, 176, 177, 228, 243, 246, 251, 257, 262, 263, 268, 269, 270, 274, 279 adsorbent 271, 273, 274 adsorption 24, 198, 203, 274, 281, 288, 290, 298, 307 adult 28, 230, 260, 276 aerodynamic 34, 36, 43, 48, 66, 78, 94, 149, 246 aerosol 19, 207 agglomerate 4 aggregate 37, 177, 224 agitation 17, 18, 74

316

Nonwoven: Process, structure, properties and applications

agrotech 213, 218, 221 air-laid 4, 35, 63, 64, 70, 89, 92, 93, 94, 125, 127, 136, 253, 254, 265 airbags 213, 235 aliphatic 16, 171 alluded 135, 219 aluminium 30, 271 ambient 60, 85, 87, 90, 91, 150, 227 aminoplast 23 angle 20, 38, 47, 54, 60, 61, 64, 85, 162, 181, 186, 188, 190, 196, 197, 199, 201, 202, 203, 209 anisotropic 69, 197 anti-fungal 170 anti-microbial 243 antibacterial 12, 23, 170, 204, 229, 248 antimicrobial 131, 156, 170, 178, 179, 227, 228, 242, 248, 262, 277, 291 antistatic 11, 23, 69, 156, 170 apparels 5, 75, 177 apron 35, 41, 143, 294 aquaculture 289 aramid 12, 26, 289, 290 archimedean 81 aridness 229 arrestance 207, 290 artificial 19, 29, 226, 228, 265, 283, 307 asbestos 286, 306 asclepiadaceae 299 asphalt 25, 213 astm 2, 31, 181, 187, 190, 191, 192, 193, 194, 199, 200, 203, 204, 205, 206, 207, 208 asymmetry 210

atactic 76 automobile 23, 24, 232, 234, 246, 287, 289, 298, 306 automotives 101, 109, 211, 214, 234, 235, 247, 295, 296, 302 azo-phosphoric 171

B backings 23, 29, 145, 214, 233, 242, 243 bacteria 28, 130, 204, 207, 227, 229, 289 bale 37, 39, 40 ballpoint 107 banana 304 bandages 19, 226 barbed 97, 98, 150 barrel 78 bathrobes 262 batts 5, 30, 59, 61, 62, 64, 66, 97, 98 beaters 40 bed-linen 89 bedding 80, 90, 138, 150, 151, 170, 213, 224, 242, 308 benz 304 beta 193, 207 bi-component 1, 12, 14, 15, 16, 18, 184, 211, 217 bi-lamination 263 biaxially 3, 265 bio-based 286, 297, 309 biocide 225 biodegradability 13, 189, 292, 307 biomechanical 216 biopolymers 170

Index 317

bladder 230, 276 blasting 161 blood 19, 170, 203, 204, 227, 291 blood-borne 203, 275 blowroom 37, 39, 65 boding 251 bolster 233 booth 237 breathability 28, 212, 218, 262, 275, 293 bristle-brush 101 broadcloth 163 bu-acrylate 23 buckled 58 buildtech 213 burn-off 263 bursting 191, 194 butadiene 24, 25, 30, 72, 132 butyl-acrylate 23

C c-factor 203 calcium 26, 265 calendering 4, 96, 140, 143, 144, 145, 146, 156, 280, 281, 303 cancer 291 canvas 295 capacitors 18, 86 capsules 178, 179 captivating 16 carbonization 306 carbonizing 171 carcinogenicity 189 carriage 59, 61

cartilage 226 cartridge 86, 130, 239, 276 casein 2, 24 casinos 239 cavity 159, 244 ceiba 307 cement 224 centrifugal 34, 38, 67, 130 ceramics 30, 31 cetyl 170 chandwick 51 charge 55, 170, 189, 205, 211, 236, 289, 290, 294 chemotextiles 285 chlorofiber 12 chlorofluorocarbons 289 cholesterol 291 cigarette 304 cleaner 18, 39, 241 cleanomat 39, 40 climate 88, 218, 220, 244 clogged 126 clothtech 213 clumps 72, 74 co-polyamide 268, 269 coat-hanger 78 coatings 24, 140, 171, 174, 218, 228 coefficient 186, 193, 291, 302, 312 coform 91, 252, 257, 259, 260, 272 cohesion 2, 3, 10, 47, 182, 189, 292 collagen 170 colliding 91 color 87, 134, 188, 189, 232, 262, 304, 306 colorfastness 134

318

Nonwoven: Process, structure, properties and applications

combifil 278 combs 51, 114 commodity 16, 292 compactness 103, 173 compartment 232, 233, 235 compressor 82, 83 concentric 15 concrete 213, 221 cone-winding 123 constructions 121, 203, 237, 239, 274 consume 160, 237 contifeed 44, 45 convection 141, 150 copolymer 22, 23, 24, 25, 26 copper 165, 166, 276, 290, 291, 314 cordage 295, 304, 305 core-cladding 32 corona 278, 282 cosmetic 178, 230, 262 cosmetology 291 covelle 263 coverstock 25, 28, 29, 31, 150, 213, 226, 257 creel 90 crepe 246 cresol 26 cross-laid 4, 61, 97, 102, 117 cross-lapper 60, 61, 99 crosslinking 157 crude 304, 305 culvert 224 curl 15, 17 curtains 28, 214, 243 cushions 299 cyclodextrines 179

D dams 214, 244 danweb 64 dash-boards 293 de-aerate 174 de-lamination 99, 143, 242 deciduous 308 decitex 261 decrystallization 178 deep-frozen 244 deformability 216 deionization 130 delamination 64, 255 delta 54, 140 demineralized 307 dental 231 dermal 232 desizing 165 deteriorated 172 dewatering 125, 254 di-carboxylic 26 diapers 22, 58, 79, 80, 230, 251, 260, 272, 285, 287, 304 diaphragm 191, 194, 195, 206 diffusion 32, 178, 236, 275 dilo 29, 37, 92 dirt-holding 241 dislodged 100, 108 disorienting 58 disperse 169 dispersion 23, 25, 71, 72, 73, 74, 89, 94, 150, 171, 172, 173, 174, 185, 281 disposables 3, 13, 88, 90, 143, 149 dissipate 128, 171

Index 319

distilled 195 divergent 136 doctor 174, 283, 312 doffers 54, 58, 88 dogs 231 downstream 44, 278 drafting 61, 62, 69, 92, 99, 104 drapability 157 drapable 274 draw-off 114 dry-cleaning 23 duvets 138, 214, 243 dyestuffs 169, 178, 305 dynamic 34, 178, 224, 291

E eccentric 15 eco-friendliness 292 edana 3, 10, 13, 32, 33, 132, 152, 190, 204, 209, 249, 251, 272, 287, 312 efficient 21, 44, 110, 128, 130, 178, 199, 203, 219, 229, 235, 244, 275 elasticity 12, 25, 60, 108, 138, 182, 186, 189, 262, 292, 308 elastomers 30, 90 electrical 142, 150, 195, 199, 210, 213, 281, 298 electro-luminescent 179 electrolytic 28 electromagnetic 148, 263 electrospinning 18, 32, 33, 240 electrospintech 282 embankments 224 embedding 250

emission 170, 196, 232, 244 emulsifying 300 emulsions 21 encapsulating 254 encroachment 222 end-use 84, 95, 194, 232, 280, 293 endocrine 232 engraving 140, 143, 161 entangle 84, 127, 150 entrapped 124, 128 enumerating 132 environmentally 18, 286, 300, 312 epoxidised 26 epoxy 25, 26, 33, 200 ester 22, 23, 180 ethoxyperflurobutane 274 european 3, 101, 208, 303 evaporation 196, 201 expansion 135, 136, 162, 199, 216 expels 126 explicit 194 extraction 303 extruded 35, 76, 81, 83, 172, 278 extrusion 16, 35, 75, 76, 78, 81, 82, 83, 168, 174, 175, 251 exudates 227, 229

F facemasks 19, 257, 272, 276 fanning 78 fastness 168, 232 fatigue 189 faults 69 feathers 312

320

Nonwoven: Process, structure, properties and applications

feeble 96 feeder 44, 50, 51, 56, 65, 81, 253 felt 25, 61, 98, 99, 110, 111, 112, 142, 144, 231, 239, 277, 278 felting 2, 98, 101, 108, 109, 111, 150, 152 female 144, 287 fertilizer 277, 303 fiber-bonding 113 fiber-entanglement 99 fiber-reinforcing 304 fiberglass 121, 304, 306 fibrillate 3 fibroin 229 filament 12, 17, 27, 35, 75, 78, 79, 80, 81, 87, 90, 122, 127, 168, 216, 227, 243, 250, 257, 277 filling 5, 44, 50, 51, 113, 117, 138, 214 filtering 19, 25, 26, 76, 200, 212, 235, 298 filtermedia 257 finding 7, 106, 234, 263 fineness 37, 41, 60, 68, 72, 95, 102, 106, 127, 219, 292, 311 fitesa 6 flame-lamination 264 flame-resistant 171, 172 flammability 22, 171, 188, 204, 207, 232, 238, 297 flanges 242 fleece 25, 142, 163 fleissner 30 flexural 25, 27, 271, 291 flocculation 72, 126 flocking 28, 177 floodgates 223

floor-coverings 213 flooring 30, 234, 242 flotation 70, 126 fluctuated 108, 300 fluffiness 307 fluorocarbon 172 flywheels 157 fogging 291, 309 foot 192, 207, 292 footwear 293 fork 101, 109 formaldehyde 25, 33, 207 fortification 294 fraction 74, 197, 198, 238 fragile 241, 300 fragrance 188 freezing 224 frequency 50, 96, 103, 150, 186, 187, 197, 206, 302 freudenberg 6, 217, 237, 246, 261 friction 2, 3, 78, 97, 111, 165, 170, 186, 189, 206, 235 frost 218, 219, 293 fuelled 165 fundamental 7, 47, 99, 135, 161, 191, 199, 298, 302 fungal 170 fungicidal 229 fusible 12, 28, 31, 175, 293 fusion 3, 152, 158, 281 fuzzy 163, 188

G garment 5, 216, 217, 257, 294 garnett 5, 53 gas-permeable 275

Index 321

gaskets 30, 235 gauge 45, 108, 111, 116, 184, 205 gauze 214, 226, 227, 229, 275 gears 82 genzyme 19 geo-synthetics 244 geocomposite 92 geomembrane 225 geometry 20, 85, 199, 302 geotext 209 geotextiles 10, 22, 29, 70, 79, 80, 90, 100, 101, 109, 110, 112, 119, 120, 121, 149, 150, 154, 200, 206, 208, 211, 214, 218, 222, 223, 224, 225, 246, 292, 298, 305 gloss 24 glycol 16, 24 godet 79 gradient 195, 196, 207, 236, 252, 278 granules 77, 225, 280 graphite 25 gravimetric 50, 200, 208 gravity 78, 222 gravure 136 greenhouse 213, 218, 289 greige 128 grinding 157 groz-beckert 110, 152, 233 gulf 287

H handicraft 294 handling 22, 41, 104, 148, 165, 213, 292, 295

hanging 119, 120 hardness 20, 262 harmful 170, 173, 296 harnessing 119 harvesting 40, 298, 303, 314 hazardous 22, 213, 227, 303, 309 headbox 72, 254, 255, 256, 282 headgear 229 headliners 213, 214, 233, 234 healing 229, 274, 291 heat-setting 149, 152 heating 21, 90, 136, 141, 143, 150, 158, 184, 212, 296 heavyweight 61, 111 held 2, 95, 165, 211, 272, 300, 301 hemicelluloses 305 herbicide 221 heterogeneous 183 hexylacrylate-vinyl 23 high-density 16, 228 high-performance 67, 69 high-tech 18, 121 high-velocity 64, 80, 81 homogeneous 41, 43, 47, 72, 78, 111, 143, 251, 259 hoodliners 233, 235 hopper 37, 43, 50, 56, 65, 76, 77, 81 horticulture 218, 293 hot-calendered 147 hot-squeezing 291 housekeeping 30 humidity 27, 55, 60, 190, 195, 220 husbandry 218 hvac 237, 239, 241 hydraulic 151, 153, 225, 237, 247

322

Nonwoven: Process, structure, properties and applications

hydro-entanglement 30, 95, 152, 217, 231, 242 hydro-entangling 9, 216, 217 hydrocarbon 254 hydrogen 28, 30, 95, 128, 169 hydrophilic 127, 128, 160, 170, 173, 201, 228, 256, 275, 281 hydrophobicity 13, 14, 228 hydrostatic 191, 200, 204 hygiene 6, 10, 28, 29, 30, 32, 66, 70, 79, 80, 88, 90, 118, 151, 152, 170, 178, 181, 204, 211, 212, 226, 230, 231, 246, 249, 257, 260, 265, 271, 272, 275, 276, 283, 285, 287 hypoallergenic 287, 289

I identical 45, 75, 86, 143, 160 ignition 171 imidazole 25 imitation 123, 157 immersion 134, 135 immobilization 269, 283 implantable 226 impregnated 23, 61, 173, 174, 198, 199, 200, 225, 235, 274 impregnation 30, 110, 172, 174, 213 impurities 38, 41, 42 in-plane 3, 196, 216 inadequacies 133 incineration 297 indigenous 299, 301 inertness 281 inexpensive 275

inferior 268 infiltration 119, 120 inflated 195, 206, 223 infrared 21, 137, 148, 150, 158, 193 inorganic 26, 28, 30, 31, 36, 171, 286 inseparable 299 insulation 5, 18, 25, 27, 28, 29, 30, 31, 66, 69, 70, 86, 88, 91, 104, 112, 213, 214, 218, 232, 233, 234, 235, 242, 243, 244, 246, 249, 257, 280, 281, 292, 293, 294, 296, 297, 298, 301, 302, 306, 308, 309, 310, 311 insulators 150, 293 intensity 30, 112, 201, 223 inter-granular 198 interlinings 5, 6, 26, 27, 58, 88, 101, 109, 138, 151, 175, 214, 285, 305 ions 130, 178, 236, 250, 269 irradiation 26 irregular 69, 175, 289 islands-in-a-sea 90 isotactic 85 isotropically 270

J joggle 50 joining 113, 129 jute 222, 235, 285, 286, 292, 293, 294, 295, 298, 304, 306, 308, 311, 312, 313 jute-based 293, 294 jute-nonwovens 292, 294, 295 juxtaposed 159

Index 323

K kapok 209, 281, 285, 286, 288, 300, 307, 308, 309, 310, 314 kenaf 285, 286, 288, 294, 298, 299, 305, 308, 309, 310, 311, 312, 313, 314 kidney 308 kitchen 231, 289, 299 knit 113, 117, 121, 152, 163 knitted 1, 2, 3, 29, 117, 131, 138, 168, 169, 184, 194, 226, 234, 243, 250, 262, 264, 308 knock-over 117, 122, 123

L labdesk 203 laced 4, 287, 291 laggings 293 lamella 101, 254, 256 laminated 4, 19, 23, 25, 26, 148, 177, 221, 222, 239, 243, 249, 251, 260, 262, 263, 268, 269, 275, 276, 277 lamination 18, 102, 175, 176, 251, 262, 263 landfill 225 lapper 58, 61, 62 lapping 55, 56, 60, 61, 62, 68, 116 lasers 179 latex 2, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 72, 122, 132, 133, 135, 151, 160, 262, 300 lattice 37, 40, 41, 42, 49, 57, 58, 65, 66, 68, 70, 312 launderability 133

leather 26, 29, 61, 86, 90, 112, 128, 150, 157, 161, 213, 214, 262, 264, 265, 283, 293, 303, 304 ledger 162, 163 lengthwise 57, 184 lessening 296, 303 levelness 35 liberate 172 licker-in 46, 48, 49, 51 lifting 213 light-weight 149, 312 lightly-needled 312 linen 70, 169, 204, 230, 237, 242, 289, 304, 306 liners 27, 28, 70, 203, 213, 214, 225, 230, 233, 235, 245, 276, 293, 295 linting 28, 31, 204, 228 liquefying 139 liquids 44, 89, 202, 204, 225, 274, 299, 310 loading 55, 187, 189, 204, 205, 224, 281 lofts 66 long-staple 36 looms 1, 29, 92, 101, 108, 109, 110, 111, 234 loose 30, 36, 45, 165, 240, 298, 302 low-density 16, 263, 301, 312 low-melting-point 140 lower-web-surface 136 lubricants 44, 156, 170 lubrication 44, 171 luggage 213, 293, 294 luminescent 26 lustrous 301, 305 luxurious 234

324

Nonwoven: Process, structure, properties and applications

M machine-heading 115 maintenance 56, 110, 111 majority 91, 171, 191, 235 malimo 29, 113, 117, 120, 121, 184 malipol 117, 121, 122 malivlies 117, 119, 120, 184 maliwatt 29, 113, 115, 117, 118, 184 malkan 50, 76, 78, 93 malleable 298 man-made 2, 13, 32, 36, 89, 127, 170, 246, 310 manifold 129, 311 manila 72, 304 mankind 12 manufacturing 6, 13, 14, 16, 34, 35, 36, 41, 42, 71, 72, 75, 76, 81, 95, 113, 126, 153, 154, 157, 158, 168, 171, 172, 185, 215, 217, 225, 228, 230, 232, 234, 240, 241, 249, 250, 251, 252, 260, 265, 272, 280, 293, 296, 297, 299, 303, 308, 313 manville 255, 278 marelli 6 maschinenfabrik 265 mask 197, 204, 227, 228, 229, 257, 276 mattress 88, 170, 242, 243, 262 mauersberger 113 maze 240 mechanical 2, 3, 4, 5, 13, 14, 16, 17, 18, 20, 29, 30, 36, 57, 71, 78, 86, 93, 95, 96, 97, 98, 102, 108, 143, 150, 156, 157, 158, 160, 164, 173, 177, 182, 185, 198, 199, 212, 216, 217, 224, 252,

257, 260, 266, 274, 275, 292, 295, 305, 309, 311, 312 mechanisms 178, 236 medtech 213 melt-blown 34, 81, 84, 86, 87, 94, 125, 241, 283 melt-resistant 25 meltblown-spunbonded 275 melted 25, 31, 76 membranes 229, 239, 240, 275 merchandise 182 merv 207, 239, 240 mesh 2, 74, 229, 240, 278 meta-aramid 252 metallic 130, 162, 278 metblown 4 metering 50, 78, 81, 82, 137, 174 methacrylate 22, 25 mexico 6, 287 micro-encapsualtion 156 micro-organisms 218 microcapsules 178 microclimate 220 micrograph 267, 273 micrometers 289 micron 18, 29, 207, 240, 277 micronaire 128, 187 microprocessor 43, 51, 52 microscopic 182, 300, 305 migration 169, 173 mildew 11, 14, 223, 235 milkweed 209, 285, 286, 288, 299, 300, 301, 302, 308, 309, 310, 312, 314 mite-proof 262 mobiltech 213

Index 325

modacrylic 12 moderate 28, 86, 274, 292 modification 178, 282, 307 modifying 118, 178, 179 modulus 24, 72, 104, 105, 111, 127, 131, 138, 186, 271, 286, 289, 290, 292, 306 moisture 13, 22, 75, 151, 158, 170, 189, 190, 195, 201, 207, 218, 219, 221, 222, 223, 229, 238, 289, 293, 297, 304, 306, 308 moldability 232, 281 monofilament 93 monomers 20, 22, 23 morphological 93 morphology 139, 162 moulded 70, 235, 275 mulching 211, 218, 219, 220 multi-bonding 249, 260 multi-component 242 multi-layered 252, 253, 254, 273 multicomponent 90 multifunctional 250 multiknit 184

N n-decane 198 n-methylol 23, 24 nano-crystalline 229 nanofiber 19, 240, 266, 267, 268, 277, 281, 284 nanofibers 12, 14, 17, 18, 19, 32, 33, 229, 240, 266, 268, 269, 271, 277, 282 nanoparticles 172 napkins 27, 70, 173, 205, 214, 230, 242, 276

narrow 18, 36, 65, 191 needle 4, 6, 8, 9, 25, 29, 40, 61, 88, 92, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 129, 131, 150, 153, 154, 157, 163, 182, 183, 186, 187, 221, 222, 231, 232, 233, 234, 239, 251, 263, 274, 276, 277, 278, 279, 287, 297, 299, 302 needle-punched 97, 98, 102, 111, 112, 149, 155, 214, 226, 228, 232, 243, 251, 273, 276, 289, 290, 293, 294, 295, 297, 299, 301, 305, 306 needlefelt 241 neumag 54 nickel-plated 160 noise 70, 89, 213, 235, 247, 291, 293, 301, 302, 312 non-abrasiveness 131 non-adherent 275 non-allergic 227 non-biodegradable 232 non-blocking 23 non-bonded 30, 183 non-carcinogenic 227 non-conductive 11 non-conformance 191 non-contact 176 non-continuous 121 non-crimped 72 non-durable 160 non-elastic 226 non-fading 11 non-fray 242

326

Nonwoven: Process, structure, properties and applications

non-hazardous 22 non-healing 232 non-implantable 226 non-leachable 170 non-splitting 90 non-stabilized 135 non-styled 113 non-toxic 227 nonionic 168 nonlinear 101 nonstick 228 nonwoven-layered 268 nonwovens 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 16, 19, 20, 22, 23, 24, 25, 27, 30, 31, 32, 33, 35, 36, 37, 39, 41, 49, 53, 58, 62, 68, 70, 74, 76, 80, 81, 85, 88, 89, 92, 93, 94, 95, 98, 111, 121, 126, 128, 130, 133, 134, 135, 136, 137, 138, 139, 143, 148, 149, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 166, 168, 169, 170, 171, 172, 173, 174, 175, 177, 178, 179, 181, 182, 183, 184, 185, 189, 190, 191, 192, 193, 194, 198, 208, 209, 210, 211, 212, 214, 215, 216, 217, 218, 219, 220, 221, 222, 224, 225, 226, 227, 228, 229, 230, 231, 232, 234, 235, 240, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 257, 260, 262, 263, 264, 266, 268, 269, 270, 272, 276, 278, 281, 283, 284, 285, 286, 287, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 300, 301, 302, 303, 304, 305, 307, 309, 310, 311, 312, 313 norrköping 6

nottebohm 5 novolak 25, 26 nozzle 18, 79, 217, 266 nozzles 79, 136, 175 nurseries 218, 220 nylon 12, 13, 16, 18, 24, 26, 31, 75, 80, 89, 113, 127, 141, 171, 211, 234, 261, 268, 269, 282

O objective 128, 132, 193, 235, 240 obliging 108 obtain 39, 59, 61, 108, 110, 191, 200, 309 occur 105, 158, 281 odor 188, 213, 232 oekotech 213 off-seasonal 221 offshore 213 oil-repellent 172 oil-spill 309 olefin 223, 272 oleophobic 189 oligopolistic 10 on-line 85 onstream 92, 94 opacity 29, 81, 86, 87, 100, 272 opaque 87, 106, 188, 197 optical 193, 197, 199, 200, 202, 208 optimizing 218 orchestrated 110, 126 organic 23, 130, 286, 303, 304, 310 organobromine 172 organochlorine 172 organohalogens 289

Index 327

orientation 26, 47, 48, 57, 59, 60, 61, 62, 66, 69, 78, 79, 81, 86, 87, 88, 89, 90, 91, 102, 108, 109, 138, 150, 181, 186, 196, 197, 198, 199, 209, 210, 224 orifices 78, 83 orthogonal 147 oscillating 187 osmosis 218, 237, 277, 278 oven 31, 137, 139, 263 overfeed 158 overlapped 121 oxidation 178 oxygen 134, 289

P pacific 7 packaging 24, 31, 188, 213, 244, 245, 247, 257, 262, 263, 293 packtech 213 padded 169, 173 pads 66, 150, 213, 214, 230, 231, 242, 245, 262, 276, 299 panasonic 298 pant 230 panty 29, 230, 276 papermaking 2, 93, 160, 295 papers 3, 89, 154, 262, 284, 304, 309 para-aramid 252 paraffin 22, 187 parallelisation 47 parcel 213, 214, 233, 295 partial-wrap 17 particle 137, 207, 236, 237, 241, 252, 265, 269, 270, 271, 278, 283, 290, 291, 298

particulate 24, 130, 208, 213, 239, 240, 249, 250, 269, 270, 271, 276 patented 222, 259, 260, 261 pathogens 275 pathology 310 pavements 221 pellets 77, 81, 168 pendulum 191 penetrate 105, 118, 121 penetration 28, 100, 102, 103, 104, 105, 110, 111, 116, 150, 174, 183, 203, 204, 218, 222, 225, 275, 276, 279 penetrometers 207 perfojet 30 perforation 156, 157, 224, 244 performance 2, 11, 12, 19, 20, 26, 32, 33, 55, 79, 88, 92, 93, 192, 195, 203, 208, 209, 216, 225, 229, 232, 234, 235, 237, 242, 250, 263, 266, 267, 275, 278, 282, 287, 290, 292, 295, 301, 302, 305, 308, 309, 314 permeability 25, 92, 104, 105, 112, 187, 189, 191, 195, 198, 199, 204, 205, 207, 221, 222, 223, 225, 231, 236, 238, 244, 289, 290, 308 permittivity 207 perpendicular 4, 34, 57, 59, 62, 105, 129, 183, 200, 207 perpetually 286 pertaining 36 pervasive 290, 296 pesticides 215, 218, 219, 221, 296 petroleum 307 pharmaceutical 178, 237, 239

328

Nonwoven: Process, structure, properties and applications

phase-change 179 phenolic 25, 274 phenomenon 158, 181, 197, 198, 210, 301 philippines-based 303 philosophy 312 photo-degradation 173 photosynthesis 218 physiological 290 pigment 24, 169 pile-composite 279 piling 189 pillar 118, 183 pillar-stitch 115 pillows 5, 138, 151, 242, 243, 307 pineapples 312, 313 pipeline 42 pitch 26 pivoting 161 piñatex 303, 304, 312 plant-based 307 plasma 156, 178, 307 plasticized 25, 139 plastics 88, 213, 226, 262 pleatable 87 pneumatic 51, 69, 70, 79, 136, 194 polarity 19 polishing 25, 121, 214, 272 polyacrylates 23 polyamide 5, 26, 85, 90, 122, 170, 217, 226, 243, 262 polyamides 16, 21, 81 polycarbonate 18, 81 polycyclohexanedimethanol 16

polyester 5, 6, 14, 23, 24, 25, 26, 28, 29, 30, 31, 39, 55, 75, 80, 89, 90, 92, 113, 117, 120, 122, 127, 130, 137, 141, 168, 169, 170, 171, 211, 217, 220, 221, 226, 228, 229, 234, 235, 239, 240, 243, 244, 261, 262, 263, 272, 273, 274, 275, 277, 278, 294, 305 polyetherimide 16 polyetherurethane 284 polyethylene 13, 16, 21, 31, 75, 81, 139, 141, 153, 169, 222, 226, 228, 229, 263, 306 polylactic 16, 76 polymer 8, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 33, 34, 35, 69, 75, 76, 77, 78, 79, 81, 82, 83, 85, 87, 90, 91, 93, 95, 97, 127, 133, 140, 141, 151, 168, 171, 172, 173, 182, 184, 185, 188, 228, 234, 240, 256, 263, 266, 267, 271, 274, 281, 288, 309 polymeric 18, 19, 178, 265, 278, 279 polymerization 23 polyolefin 12, 23, 171, 262, 265, 266, 275 polyphenylene 16 polytrimethylene 16 polyvinylacetate 132 polyvinylchloride 132 porosimetry 199 porosity 20, 29, 30, 81, 140, 181, 186, 189, 198, 199, 207, 221, 225, 229, 232, 238, 250, 262, 274, 281, 300, 302, 307, 314 porous 11, 19, 23, 90, 186, 196, 198, 199, 200, 202, 203, 228, 273, 292, 308

Index 329

post-calendered 148 post-chemical 111 pots 213, 218 pre-assembled 176 pre-bonded 88 pre-filter 241 pre-metalized 179 pre-needled 279 pre-needling 99, 100, 102, 243 precision 43, 140, 157, 180, 218 precursor 124, 127, 128, 129, 155 predominantly 57, 111, 112, 243 preformed 27, 70, 150, 260 preheated 141 presence 47, 58, 102, 111, 113, 139, 151, 252 preservative 269 press-packed 37 presser-foot 192 pressurized 135 pretty 189, 247, 300 print-bonded 138 printability 24, 293 printed 4, 24, 26, 131, 169, 262 productivity 29, 48, 55, 61, 89, 127, 158, 218 progress 9, 152, 179, 281, 285 projecting 163 prolongation 289 prominently 13, 76 propagation 171, 188, 196, 221, 308 protech 213 protection 19, 113, 142, 163, 173, 189, 203, 205, 213, 214, 218, 219, 225, 227, 229, 244, 257, 262, 272, 275, 291, 297

protectors 293 proteins 22 prototype 130 protruding 104, 162, 165, 166 ptfe 12, 239, 278 pulling 145, 163, 165, 213 pumping-up 224 punched 6, 8, 9, 25, 61, 98, 105, 150, 153, 154, 169, 182, 183, 221, 222, 232, 234, 274, 278, 287, 299 puncture 102, 103, 206, 212, 223, 225 purifiers 276, 277 pvalc 31 pyrophate 24

Q qualities 1, 3, 122, 182, 244 quality 22, 26, 41, 42, 44, 55, 56, 57, 61, 72, 74, 88, 89, 106, 111, 122, 126, 128, 131, 133, 138, 139, 143, 148, 157, 161, 172, 182, 183, 212, 213, 220, 246, 272, 286, 287, 290, 292, 297, 310, 312 quantitative 197, 204 quantities 13, 43 quartz 269 quench 77, 79, 85, 90, 144 quick-drying 218 quickened 220 quiet 189 quilted 214 quilts 147, 242, 243

330

Nonwoven: Process, structure, properties and applications

R racquets 291 radiant 96, 148, 304 radiation 141, 150, 178 rail 115, 117, 119, 120, 158, 223, 244 railroad 5 railway 214, 224 raised 31, 143, 159, 163, 258 raising 156, 161, 163, 164, 165, 221 random-laid 63, 102 randomisation 48, 66, 69, 79 randomize 88 rangers 302 rapid 7, 8, 67, 171, 201, 229 raschel 117 rayon 12, 13, 14, 39, 68, 127, 138, 229, 231, 272 re-bulked 148 re-growing 289 re-loftable 31 re-needling 111 re-opening 37 re-orientation 183 re-oriented 183 re-presents 47 re-solidifies 148 re-use 301 re-wet 204 reactivated 148 realigned 183 reapplication 148 rear 23, 213, 233 rearrangement 88 receptiveness 301

reciprocating 62, 130 reclaimable 120 recognizable 249 rectangular 143, 274 recurrence 291 recycled 56, 61, 75, 88, 89, 117, 307, 311 rediscovered 297 reemay 90 regain 75, 306, 308 regeneration 170 regional 6, 32 regular 16, 62, 79, 133, 189, 286, 292, 296 reicofil 77 reinforcement 24, 100, 206, 211, 213, 223, 233, 244, 262 rejects 297 relatively 12, 18, 31, 38, 61, 88, 132, 148, 241, 274, 275, 287, 295, 296 relaxed 15 relief 231 remarkable 9, 158 repeatedly 98 repellency 170, 172, 189, 207, 225 replace 56, 110, 111, 206, 216, 243, 300, 306 report 211, 246, 287, 300, 308, 312, 314 represents 16, 200, 286, 288, 305 reproducibly 281 resiliency 13 resilient 11, 64, 161 resin 9, 23, 24, 25, 26, 33, 81, 82, 91, 95, 132, 133, 138, 158, 177, 198, 233, 263, 265, 270, 271, 277

Index 331

resin-treated 194 respiration 277 respirator 237, 272, 276 restructuring 6 retailers 182 retardancy 172, 178, 242, 274 retentiveness 294, 302 return-on-investment 181 reusable 244 reused 130, 301 revealed 193, 296, 297, 300, 308 reverse 237, 277, 278 rheological 13 ribbon 127 rigidity 74, 108, 127, 182, 183, 186, 289, 303 rinsed 169 risk 43, 109, 165, 171, 182, 242, 272 roadside 213 robust 241, 244 robustness 266 role 10, 129, 192, 225, 234, 249, 272, 287, 314 rollers 45, 48, 49, 52, 56, 58, 59, 62, 63, 64, 66, 67, 69, 79, 89, 100, 135, 140, 142, 143, 159, 160, 161, 163, 164, 173, 174, 175, 258, 305 roofing 10, 22, 28, 29, 30, 70, 79, 90, 138, 149, 150, 151, 211, 213, 214, 244 rooftops 244 rooms 26, 227, 230, 239 root 211, 213, 218, 221, 222, 225, 307 rotary-cylinder 165, 166

rotating 65, 78, 89, 110, 129, 137, 157, 163, 174, 277 rotogravure 174, 175 roughened 110 royalties 189 rubber 2, 12, 20, 24, 25, 72, 145, 206 running 41, 42, 58, 115, 145, 161, 198 rupture 191, 206

S sacking 293 safety 26, 91, 189, 229, 235, 278, 287 sailcloth 263 samples 190, 192, 195, 206, 297, 301, 302, 303, 306 sand 126, 161, 224 sandwich 253, 270 sanforizing 217 sanitary 13, 23, 24, 29, 70, 86, 118, 143, 149, 150, 172, 205, 214, 230, 257, 276 sateens 122 satisfactory 21, 69, 133, 135, 289 saturated 30, 199, 224, 231 scaffold 157, 226 schematic 39, 84, 200, 202 science 18, 32, 152, 179, 208, 209, 309, 311, 312, 313, 314 scientific 282, 291, 311 scissors 162 screen 2, 63, 71, 72, 81, 84, 85, 86, 89, 90, 128, 129, 130, 135, 136, 169, 174, 175, 269, 281

332

Nonwoven: Process, structure, properties and applications

screen-printing 169 screw 78, 81 scrubber 174 sealable 11, 24 season 148, 298, 300 seating 232, 234, 279 seawater 288, 307 sectors 9, 13, 18, 170, 243, 271, 278, 286 sedimentation 213, 314 seeding 218, 219 segement 261 self-adhesion 176 self-bonded 81, 84, 259 self-crosslinking 133 self-sealing 22 self-supporting 239 semi-durable 242 sensors 158, 179 separators 6, 18, 28, 30, 38, 86, 89, 90, 130, 213, 235 sequence 35, 42, 63, 76, 217, 268, 279 series 41, 47, 129, 153, 154, 179, 192, 197, 311 servo 54 setbacks 297 setting 54, 56, 102, 158, 173 settlements 224 severe 103, 219 sewing 113, 117, 184, 213 shade 232 shading 213, 218, 304 shaggy 163 sharpened 106, 157, 162 sharpness 56

shelf 26, 213, 233 shields 29, 213, 230, 276 ship-related 305 shipment 13 shoddy 234 shoe 28, 70, 88, 123, 213, 214, 228, 257, 293 shogging 118 short-staple 36, 113 shower 134, 135, 243, 289, 307 shut 119, 120, 121 sidewalks 221 significance 140, 249 signs 262 silicone 23, 26, 172, 277 siloxane 25 silver-coated 228 simultaneously 279 single-fiber 187 single-segment 139 sintered 195, 200 sisalplant 313 size-volume 199 sleeve 124, 129, 130 slick 189, 314 slip-free 206 slippage 100, 152, 238 slit 61, 100 slowly 30, 55, 65, 222 small-scale 231 smoke 171, 172, 196 soaking 301 sockings 293 softener 90, 285, 298 softens 21, 147, 148

Index 333

soilless 220, 308 solidifying 113, 147 soluble 16, 19, 22, 25 solution 24, 74, 174, 240, 250, 265, 266, 289 solvent-soaked 274 sophisticated 6, 189, 203 sorb 288 sorbed 288, 307 sorbents 86, 91, 288, 293, 309, 310 sorption 209, 285, 288, 300, 307, 309, 310 sources 16, 249, 286, 296, 300 spacing 38, 150 spandex 12 sparks 165 speaking 228 specialised 72 specialties 86, 304 specifically 5, 229, 299 specimen 194, 199, 201, 207 speculation 126 spherical 199, 206 spill 287, 288, 298, 300, 307, 309 spinfinish 56 spinneret 35, 76, 78, 83 spinning 17, 18, 32, 62, 75, 76, 78, 79, 90, 258, 266 spirals 45 splash 204, 205 splintering 295 split 16, 17, 74, 117, 261 split-up 232 splittability 17 splittables 90

splitting 156, 157 sponsorships 120 sportswear 170, 213 sporttech 213 spounbond 4 sprayed 136, 175, 254 spreading 71, 104, 230 sprinkling 137, 177 spun-bond 34, 90 spun-bonding 75, 124 spun-lacing 152 spunbonding 35, 75, 76, 77, 78, 79, 80, 83, 85, 93, 94, 228, 242, 256 spunlace 8, 9, 124, 125, 126, 128, 130, 131, 152, 153, 182, 214, 217, 229, 231, 235, 252, 260, 261, 264, 275, 276, 277 spunlaid 31, 75, 76, 226, 229, 232, 261 squeeze 173, 174 squeezing 160, 161, 281 stability 12, 14, 29, 75, 96, 112, 116, 131, 173, 175, 178, 189, 228, 238, 242, 243, 257, 260, 266, 275, 292, 295 stabilizers 173, 224 stacking 34, 35, 57, 89, 292 stainless 12, 160, 277 staple 3, 5, 12, 34, 35, 36, 37, 39, 69, 72, 80, 88, 92, 95, 106, 127, 139, 141, 168, 184, 187, 193, 212, 222, 241, 265, 278, 297 starch 2, 22 stenter 158 sterilised 229 sterilize 225 stickiness 55

334

Nonwoven: Process, structure, properties and applications

stiffeners 156, 173, 293 stitch-bonded 2, 3, 115, 116, 118, 154, 157, 214 stitchbonding 29 stocking 10 strategic 248, 287 strength-elongation 112 stretchable 11, 23 stretched 61, 105, 187 strike 204, 218 stripped 47 strips 53, 56, 100, 129, 299 strung 118 studies 183, 193, 294, 296, 306, 313 stylish 293 styrene 22, 23, 24, 25, 26, 30, 72, 132 subgrade 224 subject 69, 99, 100, 139, 295 subliming 169 submicron 19 suction 63, 65, 66, 67, 72, 79, 89, 111, 125, 145, 159, 208 sued 156, 161 sueder 161, 162 sueding 161, 217 suitability 139, 185, 189 sulfate 26 sulfide 16 sulfonated 23 sunlight 219 superabsorbent 12, 89, 226 superhydrophobicity 314 superimposing 281 surfacing 28, 213 surgeons 275

surgical 13, 28, 70, 80, 89, 93, 131, 204, 208, 214, 215, 226, 227, 229, 272, 275, 276, 277, 283, 285 surround 159 sustainability 287 sutures 19 swabs 213 swatch 191 sweating 200 swelling 203 synthetic 2, 5, 12, 20, 22, 24, 25, 35, 37, 38, 39, 44, 60, 61, 68, 69, 72, 75, 86, 89, 90, 112, 128, 133, 147, 150, 160, 165, 171, 172, 177, 203, 204, 214, 221, 224, 227, 228, 229, 239, 247, 252, 260, 262, 264, 277, 289, 290, 294, 296, 298, 299, 300, 307 syriaca 300

T tablecloth 257 tabletop 294 tackiness 143 tactile 256 taguchi 303, 313 tailor-make 95 tailored 299 take-off 46, 49, 68, 188 take-up 81, 100, 114, 200 taken 34, 56, 58, 66, 106, 117, 129, 135, 142, 190, 195, 202, 204, 207 takes-in 59 tampons 230

Index 335

tangible 181 tangles 124, 299 tanning 303 tape 23, 25, 274 tappi 3, 31, 32, 33, 92, 93, 94, 152, 154, 155, 190, 200, 207, 209, 210, 247, 309, 311, 313 tariffs 189 tear 5, 11, 80, 95, 108, 110, 111, 112, 188, 191, 194, 204, 206, 207, 216, 223, 225, 227, 242, 260, 272 teeth 47, 64, 65 teflon 277 temporary 178, 281 tennis 112, 291 tensile 13, 23, 24, 25, 27, 31, 79, 89, 171, 173, 188, 190, 193, 194, 204, 206, 207, 210, 225, 262, 288, 289, 290, 291, 303, 304, 306, 310 tensiometer 203 terephthalate 13, 16, 153, 306 terminology 32 theoretical 36, 107, 202 therapeutic 120, 212, 228, 285, 291, 298, 310 thermal 2, 3, 4, 9, 14, 17, 18, 20, 24, 25, 28, 29, 30, 31, 36, 57, 71, 79, 84, 86, 88, 95, 96, 104, 105, 113, 138, 139, 140, 145, 146, 147, 150, 152, 153, 154, 155, 182, 184, 188, 189, 195, 196, 204, 213, 214, 218, 228, 233, 238, 242, 244, 251, 256, 260, 265, 275, 281, 282, 291, 292, 293, 294, 296, 297, 302, 303, 306, 308, 310, 311 thermo-active 179

thermo-bonding 251 thermo-chromic 179 thermo-mechanical 266 thermo-physiological 216 thermobonded 148 thermoplastic 2, 13, 16, 21, 81, 97, 137, 140, 150, 172, 175, 177, 189, 241, 268, 269, 281, 292, 304, 309 thermosetting 25, 26 thicker 157, 203, 301 thorn 108 thousand 100, 295 thread 12, 116, 184 throughput 17, 37, 59, 68, 79, 85, 126 ticking 213 tiles 5, 30, 299 timbers 297 tires 235 tissues 19, 28, 213, 231, 232 titanium 24 tobacco 295 tonnes 7, 8, 9 topography 151, 189, 223 torsion 186 tough 212, 216 toweling 113 toxic 26, 271, 283, 295 toyota 298 traffic 224 transducers 50, 52 transfer 46, 48, 49, 54, 56, 129, 140, 151, 169, 178, 216, 287 transmission 145, 193, 195, 205, 225, 227, 244, 275

336

Nonwoven: Process, structure, properties and applications

transmissivity 207 transportation 43, 63, 69, 118, 300 transporter 135 transverse 43, 57, 59, 115 trapezoid 194, 206, 207 trapped 47 trash 38 trauma 227 travel 105, 129, 259 traveler 287 travelling 129 trend 33, 163, 287 trezzano 6 tri-lamination 263 triangular 110, 127 tricot-stitch 115 trifluralin 222 trilobal 16, 90, 127 triplex 275 trouble-free 42 troublesome 69, 290 trützschler 39, 40, 41, 42, 43, 44, 45 tubular 308 tuft 37, 38, 42, 50, 51, 66, 101 tufts 38, 39, 44, 45, 47, 51, 52, 64, 100, 101 turbulence 42, 58, 84, 85, 129, 256 tweezers 187 twills 122 twine 305 tyvek 90

U ultra-fine 278 ultra-hydrophobic 202

ultra-violet 218 ultrasonic 31, 50, 95, 96, 140, 147, 150, 251 ultrasound 150 ultraviolet 172, 206, 218, 289 unbeatable 150 unbonded 137 unbranched 298 under-pads 230 underbody 233 underlay 213, 234, 242, 244 underneath 65, 72, 79, 108, 129, 291 understood 133, 287 underwear 230, 276 undesirable 165, 167, 171 undrawn 56, 91 unevenness 192 unexploited 240 unfaltering 211 uniaxial 303 uniform 18, 21, 35, 37, 44, 45, 50, 56, 65, 68, 72, 74, 78, 79, 85, 88, 90, 106, 111, 128, 136, 138, 161, 174, 177, 185, 193, 195, 222 unique 1, 5, 17, 18, 62, 86, 100, 101, 111, 124, 157, 189, 304, 307 unobstructed 42 uprightness 139 uptake 189, 229 urethane 262, 275

V vacuum 65, 72, 82, 84, 85, 86, 126, 129, 135, 241, 277 value-added 156

Index 337

value-addition 250 vapour 195, 265, 274, 275 variable 35, 150, 194, 252, 281, 287 variations 41, 45, 51, 56, 68, 100, 193, 218 varying 68, 74, 84, 145, 157, 164, 210 vaseline 187 vegetable 70, 245, 299 vehicle 232, 246, 287 velcro-type 119 velocity 74, 79, 83, 85, 90, 91, 124, 128, 129, 164, 183, 204 velour 101, 109, 234 velvet 177 ventilation 208, 276 versatile 10, 22, 63, 95, 98, 130, 132, 241, 275, 297, 302 versatility 35, 63, 71, 131, 132, 136, 232, 272 vertically 39, 62, 161, 177, 188 vibration 147, 187, 206, 289, 308 vibroscope 187 vinylidene 21 viscose 13, 14, 39, 60, 68, 72, 120, 122, 137, 170, 226, 231, 268, 269, 273 viscosity 18, 26, 72, 76, 78, 82, 85, 91, 169, 202, 262, 301 visible 111, 178, 193, 196, 232 void 50, 270, 294 volatile 24 volatilization 171 voltex 117, 123 volumetric 50, 207 voluminous 13, 69

voronina 301, 314 vortex 74 vulcanised 25 vulnerability 290

W wadding 66, 70, 226, 242, 243 wall-coverings 299 wallpapers 170, 213 warping 123 washability 218, 262 washing 134, 156, 167, 168, 169 wastes 293 water-absorption 263 water-borne 132, 151 water-jet 183, 261 water-jet-entangled 126 water-repellency 179 water-resistant 24 water-safety 308 water-soluble 18 waterborne 33, 132 waterproof 22, 25, 89, 229, 274 wavemaker 62 waxes 307 wear 19, 25, 110, 111, 143, 150, 163, 195, 216 wearability 310 weather 12, 221, 289, 294 weatherproof 11 weaving 1, 113, 285 web-binding 27 web-bonding 8, 9, 252, 253 web-drafting 61

338

Nonwoven: Process, structure, properties and applications

web-forming 9, 256, 257 web-lay 79 web-laying 253 web-stitching-stitch-bonding-warpknitt 152 webbing 240 weed 211, 213, 218, 221, 299 welding 205, 263 well-opened 38 wet-milling 2, 3 wetability 127 wetlaid 9, 30, 93, 183, 193, 239, 240, 254 wetting 20, 72, 111, 135, 165, 169, 172, 186, 189, 201, 202, 247, 269 whirling 124 wicking 200, 205, 251, 275 winding 58, 76, 84, 118, 123, 125, 156, 157, 162 windmill 289 wiping 9, 123, 149, 150, 214 wire-covered 58 wool 2, 12, 25, 38, 163, 187, 217, 285, 286, 288, 297, 307, 310 woolen 117, 159, 293 woollenised 294 worker-stripper 67 wound 47, 84, 150, 163, 214, 228, 229, 231, 232, 271, 274, 275, 282, 291 woven 1, 2, 3, 6, 93, 99, 110, 111, 112, 117, 131, 149, 156, 168,

169, 193, 194, 204, 209, 216, 221, 226, 227, 234, 238, 243, 250, 262, 264, 265, 293, 300 wrap 28, 29, 31, 74, 86, 90, 213, 245 wrappings 293

X x-ray 197 xanthomad 310

Y yankee 160 yards 166, 217 yarn 1, 2, 10, 12, 16, 35, 113, 115, 116, 117, 118, 121, 122, 123, 181, 182, 184, 187, 238, 304 year-old 298 yellowing 134, 171 yellowish 308 yield 85, 218, 219, 220, 292 yielding 95, 106

Z zeolite 276 zero 28, 101, 108, 200 zeta 26 zig-zag 59 zimmer 258 zone 68, 78, 81, 82, 100, 115, 136, 222, 256