Production of Cotton Fiber From Field to Mill

Cotton Fiber

Cotton:

Cotton, the purest form of cellulose found in the nature is the seed hair of the plants of the genus Gossypium. It is classified as natural, cellulosic, mono-cellular, staple fiber. Cotton has been cultivated for more than 5000 years. Archeologists found that it was grown and used for textile purposes in the Indus Valley well before 2100 BC, and in Mexico by 3500 BC Cotton has been of service to mankind for so long that its versatility is almost unlimited and new uses are constantly being discovered.

 
Cultivation: Cotton requires about two hundred days of continuous warm weather with adequate moisture and sunlight; frost is harmful to the plant. Usually in March or April selected cottonseeds are planted. The flowers in cotton plants appear in June or July and the cotton is usually ripe for gathering between August and October. The seasons may differ in the different places of the world. As the flower withers it is succeeded by a closed pod. This contains seeds, which are wrapped up in young actively growing hairs. Each cottonseed may produce as many as 20,000 fibres. When the seeds are nearly ripe the pod burst open and the cotton hairs project, forming a white fluffy mass called a boll. During this period, the plant is subject to attack by many insects (e.g. Boll weevil, Boll worm, Caterpillar). Insecticides are sprayed to protect the plants at this stage. The fibers are now exposed to the sun when they complete their ripening, and the cell gradually dries up, leaving the cotton in fit state for harvesting.

Harvesting: The ripe bolls having matured fibers are picked by machines in developed countries and by hand in developing countries. Mechanical picking, a faster and cost-effective method of harvesting, has some disadvantages as machine picks the immature bolls, as well as leaves, stem fragments with the matured bolls. On the other hand higher grade of cotton is obtained by a selective and good hand picking. An expert picker can easily trace out the matured bolls and does not pick leaves or stem fragments with it. This method is slower and the most expensive in developed countries but better for developing countries.

Ginning: After the crop has been gathered the fibers are separated from the seeds by a process known as ginning. Gins (i.e. ginning machines) may be classified into two types the saw gin and the roller gin. A saw gin consists of a series of circular saws having specially shaped teeth and used mainly for short and medium staple cottons.

Modern gins have 80-120 saws mounted on a long, horizontal shaft at suitable intervals. Seed cotton is fed through a hopper and the saws operate against it as the fibres known as lints become separated from the seed. In a roller gin, a knife jerks the seed from the fibre while the latter is pulled away between a roller and a fixed knife. McCarthy gin is a special type of roller gin. Roller ginning which is often preferred for longer fibres is slower and more costly process.

Cotton linters are the short, fuzzy hair-like fibres that remain on the seeds after ginning has been done. The cotton linters are removed by a second ginning process. They are used in the manufacture of viscose (or rayons) and acetates, plastics, shatter proof glass, photographic film and for other purposes.

Baling: After ginning, the lints are compressed into rectangular bales, which are covered with jute or polypropylene bagging and bound with iron bands. The bales generally weigh about 480 or 500 pounds each. These bales are then sent to the yarn manufacturing mills

Grading: The assessment of cotton is carried out traditionally by the cotton classer, who depends upon personal skill and long experience in judging cotton quality by inspection and feel. The assessment is based on (1) the staple length, (2) the colour and (3) the amount of impurity in the cotton. The classer works usually by a hand-examination of the cotton. Staple length is judged by taking a sample and pulling it to display a filmy web of fibre.