Question

explain chemical composition of cotton fibre

Answer 1

After scouring and bleaching, cotton is 99% cellulose. Cellulose is a macromolecule –– a polymer made up of a long chain of glucose molecules linked by C-1 to C-4 oxygen bridges with elimination of water (glycoside bonds). The anhydroglucose units are linked together as beta-cellobiose; therefore, anhydro-beta-cellobiose is the repeating unit of the polymer chain (see Figure 5 ). The number of repeat units linked together to form the cellulose polymer is referred to as the “degree of polymerization.”
Figure 6 Chemical Structure of Cellulose

Wood pulp, rayon and cellophane (all three derived from wood cellulose) are also constructed of cellulose polymers. Cotton cellulose differs from wood cellulose primarily by having a higher degree of polymerization and crystallinity. Crystallinity indicates that the fiber molecules are closely packed and parallel to one another (as illustrated in Figure 6 ). Table 5 (see page 24) shows the average degree of polymerization and the average crystallinity of the cellulose fibers cotton, viscose rayon and wood pulp. Higher degree of polymerization and crystallinity are associated with higher fiber strengths.
The cellulose chains within cotton fibers tend to be held in place by hydrogen bonding. These hydrogen bonds occur between the hydroxyl groups of adjacent molecules and are most prevalent between the parallel, closely packed molecules in the crystalline areas of the fiber.

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