Chemical Composition of Cotton Fiber

Cotton Fiber:

Cotton

Cotton is a natural cellulosic fiber. It is widely used natural fiber. It is a soft, fluffy staple fiber that grows in a boll, or protective capsule. The fiber is almost pure cellulose. In order to understand the scouring and bleaching process it is necessary to know the constituents of cotton. As

scouring and bleaching were done on cotton it will be an advantage to throw light on composition of cotton:

Composition of cotton:

Component	Amount (dry basis)%	Main location	Primary wall (%)
Cellulose	94	Secondary wall	48
Protein	1.3	Lumen	12
Pectin substance	0.9	Primary wall	12
Oil, fat & wax	0.6	Cuticle	7
Ash	1.2		3
Malic, citric and other organic acids	0.8	Lumen	14
Total sugar	0.3	Primary wall
Pigment	Trace
Others	0.9

 

Cellulose:

Cellulose content of the raw cotton fiber ranges from 88 to 96 %. Cellulose is a polymer of ß-D-glucose with a specific configuration shown in figure. The cellobiose, repeating unit of cellulose, consist of two beta glucose molecules linked together at the 1:4 carbon atoms. Each successive glucose unit is rotated 1800 around the molecular axis. This gives a linear polymer chain that is almost flat therefore suitable for fiber formation.

Chemical Structure of Cotton

About 5000 cellobiose units are present in cotton that is degree of polymerization of cotton is 5000.

Protein:
These areas are derived from the protoplasm of living cell. Fiber contains a small percentage of nitrogen but not all of the nitrogen is present as protein. It is believed that nitrogen-containing compounds may be associated with the natural coloring matter.

Pectic substance:
Natural cotton contains derivatives of pectic acid. They appear as mainly calcium and methyl pectates. But free pectic acid and methyl pectate are also present.

Oil, fat and wax:
Oils and fats are esters of glycerol (glycerides) with higher saturated and unsaturated fatty acids. Waxes are esters of complex monohydric alcohol with fatty acid.

Oils, fats and waxes are all insoluble in water, oils and waxes of cotton consists of:

1. Glycerides which are readily saponifiable oils and fats
2. Waxes which are saponifiable with difficulties
3. Unsaponifiable oils
4. Free fatty acids and
5. Traces of soaps