Chemical Composition of Cotton Fiber

Last Updated on 16/01/2021

Chemical Composition of Cotton Fiber

Ahsanul Islam Shawn
Textile Engineer
Rahim Textile Mills Ltd.
University of South Asia, Bangladesh
Email: eng.ahsanulislam@gmail.com

 

Cotton Fiber
Cotton is a natural cellulosic fiber. Cotton fibers are seed hairs from plants. Cotton is a soft fiber that grows around the seeds of the cotton plant and is the purest form of cellulose available in nature. 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. It has 8% moisture regain. (Raw conditioned 8.5%, saturation 20–25%, mercerized cotton 8.5–10.3%.) The fiber contains 90% cellulose and it is arranged in a way that gives cotton unique properties of strength, durability and absorbency. It is fresh, crisp, comfortable, absorbent and flexible, and it has no pilling problems and has good resistance to alkalis.

cotton fiber
Fig: Cotton

But cotton has poor wrinkle resistance, shrinkage, poor acid resistance, less abrasion resistance, susceptible to damage by moths and mildew, needs lots of maintenance and stains are difficult to remove. Its fiber length ranges from 1/2 to 2 in. It has 10% increase in strength when wet. It has a density of 1.54–1.56 g/cm3. It has a twisted tube shape. 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 chemical composition of cotton fiber.

Chemical Composition of Cotton Fiber

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    

Major chemical composition of cotton fiber are briefly described below:

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
Fig: 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:

  • Glycerides which are readily saponifiable oils and fats
  • Waxes which are saponifiable with difficulties
  • Unsaponifiable oils
  • Free fatty acids and
  • Traces of soaps

You may also like:

  1. Technical Properties of Cotton Fiber
  2. Blending of Cotton-Polyester Fibre to Produce PC / CVC Yarn

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