Cotton

History: Cotton was grown and used for textile purpose in the Indus Valley well before 2100 B.C., in Mexico by 3500 B.C., in Peru by 2500 B.C. and in the southwestern United States by 500 B.C. The oldest founds were dating from 5800 B.C. in Mexico. Cotton was used extensively in the Medo-Persian Empire and may have been used in Egypt as well. The use of cotton in England is mentioned in writings of the 13th century. In the USA, cotton was cultivated by the colonists in the early 17th century.

Cotton fabrics have been well known and extensively used throughout the world for hundreds of years as well as the spinning of the cotton fibre into yarn and the wearing of cotton fabrics.

Structure of Cotton
The cotton fibre composes itself of the following layers:

Cuticula - this is the layer outside the fibre and exists to the largest part from wax
Fibre wall - consists of closely together lying fibrils
Lumen - this is the layer inside the fibre and consists of a cavity.












Kinds and Types of Cotton
Different kinds and types of cotton are grown in various parts of the world. Variation among cotton fibres also occurs because of growth conditions. The quality of the cotton fibre is based on its colour, length, fineness and strength. Normally the longer fibres are finer and stronger.

The kind of cotton is often identified by the name of the country or geographical area where it is produced. The better known kinds and types are Upland, American Pima, Egyptian and Asiatic cotton.


Upland Cotton:
It is fairly white, strong and ranges in staple length from 22 mm to 32 mm. This type is categorized as short-, medium-, and long - staple. The short - staple cottons are less than 25 mm, medium staple cottons from 26 mm to 28 mm and the long - staple cottons are 29 mm or longer.

American Pima:
The staple length of American Pima is from 35 mm to 38 mm and the fibre is fine, strong, silky and creamy-brown-white in colour. This kind of cotton is used primarily for sewing thread although a small amount is used in high-quality broadcloth.


Egyptian Cotton:
Menoufi and Giza 68 are the varieties used to produce most of exported crop. The fibres are light brown, fine and 32 mm to 38 mm in length. They are used in the same applications as American Pima.

Asiatic Cotton:
Asiatic cottons are produced in India, China and the Near East. For the most part these are coarse fibres less than 25 mm in length. The major usage is in surgical supplies.


From Field to Factory
Cultivating Cotton:
Cotton can be cultivated only in warm places, which is the reason for its cultivation in the area around the Equator. Cotton requires about 200 days a year of continuous warm weather. Frost is harmful to the plant. Usually in March or April, carefully selected cottonseeds are planted in rows. About 35 days pass before the seeds develop. The plants are generally sorted out when they are from 15 cm to 20 cm tall. Chemicals specifically developed to kill weed and grass seeds are often sprayed on the ground at the time the cotton is planted.

Buds appear a few weeks after the plant emerges. They begin to bloom as creamy white blossoms about three weeks later in June or July. These blossoms change to pink and then to reddish purple. Within three days their petals fall off.

The cotton bolls grow to full size by August or September, a month and a half to two months after the blossom first appeared. When fully grown, the cotton plant may be from one to two meters in height.


Harvesting:
By the time the bolls have all opened, some leaves will have fallen off. To remove all of the leaves, the plants are defoliated by spraying them with a chemical, causing the remaining leaves to wither and fall. The full, ripe bolls are then picked by machine, one or two rows at the same time.

Ginning and Baling:
When the raw cotton is harvested, it contains seeds, dirt and other material that must be removed before the fibre can be baled. Cottonseeds alone constitute about two-thirds of the weight of the cotton when first picked. The seeds are removed by the cotton gin.

Essentially, the cotton gin has rows of revolving saw-toothed bands that pull the fibre away from the seeds as well as remove dirt and other material. The cotton fibre is compressed into bales, which are covered with polypropylene bags.


Byproducts of Cotton
The cotton passes through several cleaning processes before it is baled as well as after it is unbaled at the cotton factory. As a result, the grower obtains valuable byproducts that amount to on-sixth of the entire income derived from the cotton plant.

Cotton Linters:
Linters are the short fibres that remain on the seeds after they have been separated from the fibre in the cotton gin. They are used in the manufacture of rayons and acetates, plastics, photographic films and for other purposes.


Hulls:
The hulls, which are the outside portion of the cottonseeds, are obtained after the linters have been removed. The hulls are rich in nitrogen and are used in the manufacture of paper, plastics and as a base for explosives.

Processing, Blending and Mixing
Cotton fibre may be spun alone or blended with other fibres in making yarns. Cotton yarns are also combined or mixed with other yarns in making fabrics. These techniques contribute to fabrics such properties as softness, strength and affinity for colour.