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hydroxyl groups, one primary on C-6 and two secondary on C-2 and C-3. The abundant
hydroxyl groups and the chain conformation allow extensive inter-molecular and intra-
molecular hydrogen bonding to further enhance the rigidity of the cellulose structure
The structure of cotton fibres can be viewed along the fiber axis and across the fiber section.
Current understanding of cotton fiber structure has been mainly from investigation of the
matured fibers in their dried state. Although the biochemical nature of cotton cell structure,
particularly during early cell growth, has been extensively studied, the development
macrostructure of the main constituent of the fiber, cellulose, is not as well understood.
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Fig: microscopic view of cotton
Cotton fibers are composed of mostly a-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