Cotton is one of the major fiber crops of global importance. Despite the increasing production of synthetic fiber or man made fiber, cotton retains its reputation as “Queen of the fiber plants”. Cotton lint and other byproducts are used in a variety of ways. For multiple uses of lint and by products, cotton is also referred as “white gold”. Cotton is the most widely used vegetable fiber for textile purpose. In other words, cotton fiber is leading in terms of quantity consumed by textile mills. Cotton fiber has several desirable qualities which are as follows; (a) It is easily washable. This is very important quality. It becomes stronger on getting wet. The wet fiber is 25 % stronger than dry fiber. (b) Cotton fiber is resistant to heat. No other fiber surpasses it in its ability to with stand high heat during home laundering and drying. (c) Cotton fiber has excellent resistance to rubbing which is also an important quality. Resistance to rubbing enhances the life of cotton fabric or cloth. (d) High fiber strength is of primary importance in many textile uses. Cotton fiber has good strength. High strength is required for open and spinning and high speed spinning. (e) Cotton is an absorbent fiber, which is highly desirable for apparel as well as for other textile uses. (g) Cotton fabrics are suitable for both warm weather as well as cold weather wear.
Cotton crop is mainly cultivated for its lint. In other words, the main product of cotton crop is lint or fiber. Now cotton has become a fiber cum oil yielding crop. Its seed also contain 20-25 % protein. In future, cotton may become a fiber, oil and protein yielding crop. There are four products of cotton plant, viz. Lint seed, stalk and leaves. Out of these, lint is the main product and rests are by products.
Lint is utilized in a very great variety of ways. It is used for preparing thread, yarns, and medical cotton; mixing with synthetic fiber; and various other purposes. The yarn in turn is used for manufacturing textiles of various types. Fabrics ranging from sheer soft crisp materials to heavy, coarse and strong nature are manufactured.
The oil content varies from 19 % to 22 % in the seed and from 31 % to 34 % in the kernel depending upon the species. Cotton seed oil is rich in essential fatty acid, such as myristic acid, palmitic, palmitoelic, steric, oleic and linoleic. Linoleic acid which is the most important one is present to the extent of 51 %. The deficiency of above acids, leads to narrowing of arteries causing reduced blood supply to the heart. Presently, refined cotton seed oil is widely used for edible purposes. It is also used for making hydrogenated oils. The coefficient of digestibility of the oil is 97 % and its nutritive value is around 9 K. calories per gram. The keeping quality of the oil is comparable with that of groundnut and safflower oil. The crude oil is used for making soap, lubrication and lightening in villages in the remote areas.
The portion of kernel which remains after extraction of oil is called cake or cotton seed meal. It is mainly a protein fraction of the seed which contains about 50 % protein. The quality of any protein is determined by its amino acids composition. Cotton seed protein contains 70 % of the essential amino acids. However, cotton seed protein is deficient in methionine, tryptophan, and lysine. Binding of gossypol with lysine causes its deficiency in cotton seed meal. The lysine deficiency can be over come by growing glandless cotton cultivars. Cotton seed meal is mainly used as livestock feed. It is also used as organic manure in many countries including Pakistan. Development of glandless varieties will help in expanding the use of cotton seed meal for human consumption as protein rich diet. Now efforts are being made to prepare peptone from cotton seed protein. Peptone is a value added product.
Cotton oil contains gossypol phenolic substance which is harmful to mono-gastric animals like human beings. It should be not more than 0.04 % in the food products. Gossypol produces undesirable color in the oil. Removal of gossypol from the oil requires additional processing, materials and energy which add to the cost of the oil production. In addition to this, gossypol combines with the proteins of the cotton seed. It reduces nutritional quality by reacting with the first limiting amino acid lysine. By cross linking with proteins, it modifies their functional characteristics. Gossypol can be eliminated from the oil by liquid cyclone process which is very expensive.
Aflatoxins are the most toxic chemicals substances which are produced by two fungi. The pink boll worm infested bolls are usually infested with Aspergillus flaviens which are main source of aflatoxins. Aflatoxins can cause a variety of disorders in animals, birds and fish ranging from poor growth to liver cancer. The best way to overcome this problem is to develop aflatoxin resistant varieties.
Reffinose is one of the complex carbohydrates in vegetable protein products. In cotton, it limits the acceptability of seed flour and concentrates as edible food products. It is believed to contribute to production of flatulence in animal and man. Hence, low level of reffinose in seed is a desirable character.
Short fibers which are left on the seed after removal of long fibers through ginning are known as linters or fuzz. The percentage of linters varies from 1 to 10 % in cultivated species. The mean value of linters in Asiatic species varies from 4.3 to 5.9 %. Linters are mainly composed of cellulose, they constitute valuable raw material for various cellulose based chemical industries. Linters are used in a variety of ways. The are used in making high grade writing paper, rayon, photographic paper, x- ray films, explosives, shatter proof glasses, plastics and several other items. Linters can be separated from the seed by delinting machines.
The outer most covering of the seed which bears lint and linters is known as hull. In other words, hull is the seed coat. Hull constitutes about 37 % weight of the cotton seed. Hulls contain about 35 % to 47 % of alpha cellulose, 19 % to 27 % pentosans, 15 to 20 % lignin and 5 % ash, protein, fat etc. Cotton seed hulls can be profitably utilized for the production of a chemical furfural and particle boards. About 12 % furfural can be obtained from hulls. Edible mushroom can be grown on cotton seed hulls.
The woody parts of cotton plant which are left in the field after final picking are known as cotton stalks. Cotton stalks are usually burnt as fuel after of the crop in Pakistan. Stalk contains about 79 % holocellulose, 27 % legnin, and 7 % ash. In comparison of other agricultural crop residues, cotton stalk is closer to hardwood in respect of its fibrous structure. Cotton stalks are used for manufacture of particle boards, pulp and paper, hard boards, corrugated boards and boxes, micro crystalline cellulose, cellulose derivates and as a substrate for cultivation of edible mushrooms.
Particle boards are used for interior decoration, false ceiling, partitioning, and paneling. Hard boards can be used in furniture, table tops, and building materials etc. These boards can be made water proof through chemical treatment. High grade pulp can be prepared from cotton stalks employing special techniques in pulping, bleaching and purification processes. High grade pulp contains cellulose in a highly pure form which can be used for preparation of rayon, viscose acetate, cellulose nitrate, celluloid, explosives and propellants, smokeless powder, carboxy-methyl etc.
Cotton leaves contain citric acid (4.2- 7.2 %) and malic acid (13.6- 16.5%). Hence cotton leaves can be used for production of these two organic acids. Cotton leaves are also used in green stage (after harvest) as cattle feed.
