The chemical
composition of cotton, when picked, is about 94 percent cellulose; in finished fabrics is it 99 percent cellulose. Cotton contains carbon, hydrogen, and oxygen with
reactive hydroxyl groups. Glucose is the basic unit of the cellulose molecule. Cotton may have as many as 10,000 glucose monomers
per molecule. The molecular chains
are arranged in long spiral linear chains within the fiber. The strength of a
fiber is directly related to chain length.
Hydrogen bonding occurs between cellulose chains in
a cotton fiber. There are three
hydroxyl groups that protrude from the ring formed by one oxygen and five
carbon atoms. These groups are polar meaning the electrons surrounding the
atoms are not evenly distributed. The hydrogen atoms of the hydroxyl group are
attracted to many of the oxygen atoms of the cellulose. This attraction is
called hydrogen bonding. The bonding of hydrogen's within the ordered regions
of the fibrils causes the molecules to draw closer to each other which
increases the strength of the fiber. Hydrogen bonding also aids in moisture
absorption. Cotton ranks among the most absorbent fibers because of Hydrogen bonding
which contributes to cotton's comfort.
The chemical
reactivity of cellulose is related to the hydroxyl groups of the glucose unit.
Moisture, dyes, and many finishes cause these groups to readily react. Chemicals
like chlorine bleaches attack the oxygen atom between or within the two ring
units breaking the molecular chain of the cellulose.