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oilseed

cottonseed, seed of the cotton plant, important commercially for its oil and other products. Cottonseed oil is used in salad and cooking oils and, after hydrogenation, in shortenings and margarine. The cake, or meal, remaining after the oil is extracted is used in poultry and livestock feeds. Linters, the short cellulose fibres left on the seed after the staple cotton is removed by ginning, are used to make coarse yarns and many cellulose products. The hulls, or outer seed coverings, are used in ruminant animal feed as roughage.

The ancient Chinese and Hindus had crude methods for recovering cottonseed oil and used it as medicine and in lamps, but large-scale commercial use of cottonseed is a relatively modern development. In the mid-19th century cottonseed was used mainly for planting cotton, and the leftover seed was considered a pollution and health problem. In 1833, however, the first successful cottonseed-oil mill was established in Natchez, Miss., and the industry expanded after the American Civil War. Cottonseed is now used either for oil production, for planting, or as animal feed. The United States has continued as the largest consumer, but cottonseed is also produced in quantity by India, China, Mexico, Egypt, Pakistan, and Brazil.

Following cleaning to remove extraneous matter, the linters are removed by machines similar to gins but with circular saws and finer teeth. Linters removed in the first cut are used to make high-quality mattresses and in the manufacture of coarse cotton yarns. Subsequently cut linters are purified and used in the production of explosives, cellulose acetate, rayon, ethyl cellulose, lacquers, and many plastic and other products requiring high-quality cellulose as the raw material.

The delintered seed is hulled, and the hulls ground for incorporation as roughage in beef and dairy cattle feed. The seed kernels are flaked between steel rollers and cooked at about 113° C (235° F) to facilitate recovery of the oil, by pressing or by solvent extraction or both.

The pressed cake is sometimes broken and sold as cottonseed cake, but most is ground and sold as meal. The principal use of both is as high-protein and supplements in feed for cattle; swine and poultry can also eat it after processing to reduce the influence of gossypol, a toxic cotton plant pigment. Cottonseed meal is also used in making starch-free flour for human consumption.

The crude, dark-coloured cottonseed oil contains constituents that must be removed to produce edible oil. After filtration, the oil is refined by means of treatment with an alkaline solution that reacts with free fatty acids to form soap, which settles. The oil is separated from the soap stock by drawing off or centrifuging and then is washed with water to remove remaining soap particles.

For salad and cooking purposes, the oil is further purified by bleaching agents such as fuller’s earth and acid-activated bleaching clays. Then it is winterized—that is, made to stay liquid at ordinary refrigeration temperatures—by removing the saturated glycerides; this is done commercially by chilling and then separating the clear oil from the solidified portion. Odoriferous components are removed by heating the oil in a vacuum.

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For shortening and margarine, the oil is partially hardened by hydrogenation (combining hydrogen with the oil to chemically convert part of the unsaturated fatty acids to saturated acids).

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cotton, seed-hair fibre of several species of plants of the genus Gossypium, belonging to the hibiscus, or mallow, family (Malvaceae).

Cotton, one of the world’s leading agricultural crops, is plentiful and economically produced, making cotton products relatively inexpensive. The fibres can be made into a wide variety of fabrics ranging from lightweight voiles and laces to heavy sailcloths and thick-piled velveteens, suitable for a great variety of wearing apparel, home furnishings, and industrial uses. Cotton fabrics can be extremely durable and resistant to abrasion. Cotton accepts many dyes, is usually washable, and can be ironed at relatively high temperatures. It is comfortable to wear because it absorbs and releases moisture quickly. When warmth is desired, it can be napped, a process giving the fabric a downy surface. Various finishing processes have been developed to make cotton resistant to stains, water, and mildew; to increase resistance to wrinkling, thus reducing or eliminating the need for ironing; and to reduce shrinkage in laundering to not more than 1 percent. Nonwoven cotton, made by fusing or bonding the fibres together, is useful for making disposable products to be used as towels, polishing cloths, tea bags, tablecloths, bandages, and disposable uniforms and sheets for hospital and other medical uses.

Cotton fibre processing

Cotton fibres may be classified roughly into three large groups, based on staple length (average length of the fibres making up a sample or bale of cotton) and appearance. The first group includes the fine, lustrous fibres with staple length ranging from about 2.5 to 6.5 cm (about 1 to 2.5 inches) and includes types of the highest quality—such as Sea Island, Egyptian, and pima cottons. Least plentiful and most difficult to grow, long-staple cottons are costly and are used mainly for fine fabrics, yarns, and hosiery. The second group contains the standard medium-staple cotton, such as American Upland, with staple length from about 1.3 to 3.3 cm (0.5 to 1.3 inches). The third group includes the short-staple, coarse cottons, ranging from about 1 to 2.5 cm (0.5 to 1 inch) in length, used to make carpets and blankets, coarse and inexpensive fabrics, and blends with other fibres.

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origins of agriculture: Mechanized equipment for cotton

Most of the seeds (cottonseed) are separated from the fibres by a mechanical process called ginning. Ginned cotton is shipped in bales to a textile mill for yarn manufacturing. A traditional and still common processing method is ring spinning, by which the mass of cotton may be subjected to opening and cleaning, picking, carding, combing, drawing, roving, and spinning. The cotton bale is opened, and its fibres are raked mechanically to remove foreign matter (e.g., soil and seeds). A picker (picking machine) then wraps the fibres into a lap. A card (carding) machine brushes the loose fibres into rows that are joined as a soft sheet, or web, and forms them into loose untwisted rope known as card sliver. For higher-quality yarn, card sliver is put through a combing machine, which straightens the staple further and removes unwanted short lengths, or noils. In the drawing (drafting) stage, a series of variable-speed rollers attenuates and reduces the sliver to firm uniform strands of usable size. Thinner strands are produced by the roving (slubbing) process, in which the sliver is converted to roving by being pulled and slightly twisted. Finally, the roving is transferred to a spinning frame, where it is drawn further, twisted on a ring spinner, and wound on a bobbin as yarn.

Faster production methods include rotor spinning (a type of open-end spinning), in which fibres are detached from the card sliver and twisted, within a rotor, as they are joined to the end of the yarn. For the production of cotton blends, air-jet spinning may be used; in this high-speed method, air currents wrap loose fibres around a straight sliver core. Blends (composites) are made during yarn processing by joining drawn cotton with other staple fibres, such as polyester or casein.

The procedure for weaving cotton yarn into fabric is similar to that for other fibres. Cotton looms interlace the tense lengthwise yarns, called warp, with crosswise yarns called weft, or filling. Warp yarns often are treated chemically to prevent breaking during weaving.

Cultivation of the cotton plant

The various species of cotton grown as agricultural crops are native to most subtropical parts of the world and were domesticated independently multiple times. Cotton can be found as perennial treelike plants in tropical climates but is normally cultivated as a shrubby annual in temperate climates. Whereas it grows up to 6 metres (20 feet) high in the tropics, it characteristically ranges from 1 to 2 metres (3 to 6.5 feet) in height under cultivation. Within 80–100 days after planting, the plant develops white blossoms, which change to a reddish colour. The fertilized blossoms fall off after a few days and are replaced by small green triangular pods, called bolls, that mature after a period of 55–80 days. During this period the seeds and their attached hairs develop within the boll, which increases considerably in size. The seed hair, or cotton fibre, reaching a maximum length of about 6 cm (2.5 inches) in long-fibre varieties, is known as lint. Linters, fibres considerably shorter than the seed hair and more closely connected to the seed, come from a second growth beginning about 10 days after the first seed hairs begin to develop. When ripe, the boll bursts into a white, fluffy ball containing three to five cells, each having 7 to 10 seeds embedded in a mass of seed fibres. Two-thirds of the weight of the seed cotton (i.e., the seed with the adhering seed hair) consists of the seeds. The fibres are composed of about 87 to 90 percent cellulose (a carbohydrate plant substance), 5 to 8 percent water, and 4 to 6 percent natural impurities.

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Although cotton can be grown between latitudes 30° N and 30° S, yield and fibre quality are considerably influenced by climatic conditions, and best qualities are obtained with high moisture levels resulting from rainfall or irrigation during the growing season and a dry, warm season during the picking period.

To avoid damage to the cotton by wind or rain, it is picked as soon as the bolls open, but since the bolls do not all reach maturity simultaneously, an optimum time is chosen for harvesting by mechanical means. Handpicking, carried out over a period of several days, allows selection of the mature and opened bolls, so that a higher yield is possible. Handpicking also produces considerably cleaner cotton; mechanical harvesters pick the bolls by suction, accumulating loose material, dust, and dirt, and cannot distinguish between good and discoloured cotton. A chemical defoliant is usually applied before mechanical picking to cause the plants to shed their leaves, thus encouraging more uniform ripening of the bolls.

Pests and diseases

Cotton is attacked by several hundred species of insects, including such harmful species as the boll weevil, pink bollworm, cotton leafworm, cotton fleahopper, cotton aphid, rapid plant bug, conchuela, southern green stinkbug, spider mites (red spiders), grasshoppers, thrips, and tarnished plant bugs. Limited control of damage by insect pests can be achieved by proper timing of planting and other cultural practices or by selective breeding of varieties having some resistance to insect damage. Chemical insecticides, which were first introduced in the early 1900s, require careful and selective use because of ecological considerations but appear to be the most effective and efficient means of control. Conventional cotton production requires more insecticides than any other major crop, and the production of organic cotton, which relies on nonsynthetic insecticides, has been increasing in many places worldwide. Additionally, genetically modifiedBt cotton” was developed to produce bacterial proteins that are toxic to herbivorous insects, ostensibly reducing the amount of pesticides needed. Glyphosate-resistant cotton, which can tolerate the herbicide glyphosate, was also developed through genetic engineering.

The boll weevil (Anthonomus grandis), the most serious cotton pest in the United States in the early 1900s, was finally controlled by appropriate cultivation methods and by the application of such insecticides as chlorinated hydrocarbons and organophosphates. A species of boll weevil resistant to chlorinated hydrocarbons was recorded in the late 1950s; this species is combatted effectively with a mixture of toxaphene and DDT (dichlorodiphenyltrichloroethane), which has been outlawed in the United States and some other countries, however. The pink bollworm (Pectinophora gossypiella), originally reported in India in 1842, has spread throughout the cotton-producing countries, causing average annual crop losses of up to 25 percent in, for example, India, Egypt, China, and Brazil. Controls and quarantines of affected areas have helped limit the spread of the insect, and eradication has been possible in a few relatively small areas with sufficiently strict controls. The bollworm (Heliothis zea, also known as the corn earworm) feeds on cotton and many other wild and cultivated plants. Properly timed insecticide application provides fairly effective control.

Cotton plants are subject to diseases caused by various pathogenic fungi, bacteria, and viruses and to damage by nematodes (parasitic worms) and physiological disturbances also classified as diseases. Losses have been estimated as high as 50 percent in some African countries and in Brazil. Because young seedlings are especially sensitive to attack by a complex of disease organisms, treatment of seeds before planting is common. Some varieties have been bred that are resistant to a bacterial disease called angular leaf spot. Soil fumigation moderately succeeded in combatting such fungus diseases as fusarium wilt, verticillium wilt, and Texas root rot, which are restricted to certain conditions of soil, rainfall, and general climate. The breeding of resistant varieties, however, has been more effective.

Hans-Dietrich H. Weigmann
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