Cotton

Science and Technology

S. Gordon, Y L Hsieh

• Publisher: Woodhead Publishing
• Year: 2006
• ISBN:
  9781845692483
• Topic: Technology & Engineering
• Subtopic: Agronomy
• Index: Technology & Engineering

Despite the increased variety of manufactured fibres available to the textile industry, demand for cotton remains high because of its suitability on the basis of price, quality and comfort across a wide range of textile products. Cotton producing nations are also embracing sustainable production practices to meet growing consumer demand for sustainable resource production. This important book provides a comprehensive analysis of the key scientific and technological advances that ensure the quality of cotton is maintained from the field to fabric.The first part of the book discusses the fundamental chemical and physical structure of cotton and its various properties. Advice is offered on measuring and ensuring the quality of cotton fibre. Building on these basics, Part two analyses various means for producing cotton such as genetic modification and organic production. Chapters focus on spinning, knitting and weaving technologies as well as techniques in dyeing. The final section of the book concludes with chapters concerned with practical aspects within the industry such as health and safety issues and recycling methods for used cotton.Written by an array of international experts within the field, Cotton: science and technology is an essential reference for all those concerned with the manufacture and quality control of cotton.

• Summarises key scientific and technological issues in ensuring cotton quality
• Discusses the fundamental chemical and physical structure of cotton
• Individual chapters focus on spinning, knitting and weaving technologies

Part I

The structure and properties of cotton

1

Chemical structure and properties of cotton

Y.L. Hsieh University of California, USA

1.1 Introduction

Cotton fibers are the purest form of cellulose, nature’s most abundant polymer. Nearly 90% of the cotton fibers are cellulose. All plants consist of cellulose, but to varying extents. Bast fibers, such as flax, jute, ramie and kenaf, from the stalks of the plants are about three-quarters cellulose. Wood, both coniferous and deciduous, contains 40–50% cellulose, whereas other plant species or parts contain much less cellulose. The cellulose in cotton fibers is also of the highest molecular weight among all plant fibers and highest structural order, i.e., highly crystalline, oriented and fibrillar. Cotton, with this high quantity and structural order of the most abundant natural polymer, is, not surprisingly, viewed as a premier fiber and biomass.

This chapter focuses on the chemical structure of cotton fibers and its structural relationship to cellulose synthesis, fiber development and dehydration as well as other chemical and structural aspects (physical properties, dyeing and finishing) not dealt with in the following chapters. Cotton fiber cells are developed in four overlapping but distinct stages of initiation, elongation, secondary cell wall thickening and maturation and desiccation (Naithani et al., 1982). Structural development and properties of cotton fibers during the primary wall formation (elongation) and secondary wall thickening (cellulose synthesis) as well as during desiccation (transition from mobile to highly hydrogen-bonded structure) are detailed.

1.2 Chemistry

1.2.1 Chemical composition

Cotton fibers are composed of mostly α-cellulose (88.0–96.5%) (Goldwaith and Guthrie, 1954). The noncellulosics are located either on the outer layers (cuticle and primary cell wall) or inside the lumens of the fibers whereas the secondary cell wall is purely cellulose. The specific chemical compositions of cotton fibers vary by their varieties, growing environments (soil, water, temperature, pest, etc.) and maturity. The noncellulosics include proteins (1.0–1.9%), waxes (0.4–1.2%), pectins (0.4–1.2%), inorganics (0.7–1.6%), and other (0.5–8.0%) substances. In less developed or immature fibers, the non-cellulosic contents are much higher.

The primary cell walls of cotton fibers contain less than 30% cellulose, noncellulosic polymers, neutral sugars, uronic acid, and various proteins (Huwyler et al., 1979; Meinert and Delmer, 1977). The cellulose in the primary cell walls has lower molecular weight, with the degree of polymerization (DP) between 2,000 and 6,000 and their distributions are broader (Goring and Timell, 1962; Hessler et al., 1948). The secondary wall of the cotton fiber is nearly 100% cellulose. The DP of the cellulose in the secondary wall is about 14,000, and the molecular weight distribution is more uniform (Figini, 1982). The high molecular weight cellulose characteristic of mature cotton has been detected in fibers as young as eight days old. In the later stage of elongation or 10–18 days following initiation, the higher molecular weight cellulose decreases while the lower-molecular weight cell wall components increase, possibly from hydrolysis (Timpa and Triplett, 1993). Between the ages of 30 and 45 days, the DPs estimated from intrinsic viscosities of fibers have been shown to remain constant (Nelson and Mares, 1965).

Of the non-cellulosic components in the cotton fibers, the waxes and pectins are most responsible for the hydrophobicity or low water wettability of raw cotton fibers. The term ‘cotton waxes’ has been used to encompass all lipid compounds found on cotton fiber surfaces including waxes, fats, and resins (Freytag and Donze, 1983). True waxes are esters, including gossypyl carnaubate, gossypyl gossypate, and montanyl montanate. Alcohols and higher fatty acids, hydrocarbons, aldehydes, glycerides, sterols, acyl components, resins, cutin, and suberin are also found in the wax portion of the cuticle in varying quantities. Pectins are composed primarily of poly(β-1,4-polygalacturonic acid) and rhamose to make up the rhamnogalacturonan backbone (Heredia et al., 1993). The side chains are composed of arabinose, galactose, 2-O-methylfucose, 2-O-methylxylose and apiose. Eighty-five percent of the polygalacturonic acid groups are methylated leading to a highly hydrophobic substance. Proteins are located primarily in the lumen, but small amounts of hydroxyproline rich proteins are present on the fiber surface (Darvill et al., 1980). The far lower extents of the non-cellulosics than cellulose make their detection in mature cotton fibers challenging. Extraction and reaction techniques are often employed to separate the non-cellulosic cell wall components for characterization. These procedures, however, tend to disrupt their organization and possibly alter their chemical compositions.

The amounts of the noncellulosic components change during fiber elongation and the transition from primary to secondary wall, but discrepancies remain in the exact quantities of these changes. Some of the protein constituents (enzymatic, structural or regulatory) are unique to cotton fiber cells and have been found to be developmentally regulated (Meinert and Delmer, 1977). The non-cellulosic constituents in developing cotton fibers through the onset of secondary cell wall synthesis can be clearly identified by analytical techniques, including FTIR/ATR, DSC, TGA, and pyrolysis-GC/MS methods (Hartzell-Lawson and Hsieh, 2000). The waxy compounds in developing fibers up to 17 days old are detected by their melting endotherms in the DSC. Pectins can be detected by FTIR in the 14-day-old as well as the mature fibers. FTIR/ATR measurements indicated the presence of proteins in developing fibers up to 16 dpa. The presence of proteins can be measured by FTIR/STR methods in up to 16-day-old fibers and by pyrolysis-GC/MS in up to 14-day-old fibers. On...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Introduction
• Part I: The structure and properties of cotton
• Part II: Production processes for cotton
• Part III: Quality and other issues
• Index