MadSci Network: Other
Query:

Re: Cotton in clothes

Area: Other
Posted By: Gary Bachman, Grad Student Horticulture-Plant Physiology, Ohio State University.
Date: Mon Mar 25 06:15:40 1996


Cotton is the most important vegetable fiber used for producing textiles. Its history as a cultivated plant began in the ancient civilizations of Egypt, India, and China. In the New World, cotton was known in Mexico as early as 5000 BC and in Peru by about 2500 BC. Today it is grown in more than 70 countries throughout the world, and in the mid-1980s, total annual production exceeded 80 million 218-kg (480-lb) bales. China is the world's largest producer, growing well over one-quarter of the total. The United States and the USSR each produce about one-eighth of the total. India and Pakistan are also major producers. Brazil, with 3 million bales, and Turkey and Egypt, each with about 2 million bales, complete the list of significant cotton growers.

THE COTTON PLANT

The cotton plant, Gossypium, belongs to the mallow family, some of whose other members are hibiscus, hollyhock, and okra. Although more than 30 species of cotton are in this genus, only three have commercial significance: G. barbadense, G. herbaceum, and G. hirsutum. The last of these is the most prominent and is commonly known as upland cotton. Approximately 99% of all U.S. cotton and 88% of all varieties grown worldwide are of this species. Its staple length (the average length of fiber) is between that of the other two species. Gossypium barbadense includes all long staple cottons such as Sea Island, Egyptian, Peruvian, and the pimas. Their fine fibers can be woven into sheer, strong, lighter weight fabrics. Gossypium herbaceum has the shortest staple length and is a rather coarse fiber. It is primarily grown in Asian countries.

In its wild state cotton is a perennial, but in cultivation it must be planted annually. The cotton plant grows upright to a height of 1 to 2 m (3 to 6 ft) and has a long taproot. Flowers are normally cream-colored on opening but change as they fade to pink and finally purple. Because the flowers have both pollen-bearing stamens and an ovary with several ovules, the probability for self-pollination is high and usually takes place the morning the flower opens. Immediately after fertilization the boll, which contains seeds and fibers, begins to form. Individual fibers grow from cells on the surface of the seed. About 3 weeks after fertilization, fibers reach their full length, and they become thin-walled hollow tubes filled with plant juices. Now the plant begins to deposit layers of CELLULOSE (a complex carbohydrate constituting 95% of the weight of the mature fiber), at the rate of a layer a day for 3 more weeks, until maturity. When the boll finally bursts open, it contains up to 50 seeds with the fibers, called lint, attached. Short fuzz fibers, linters, are also attached to the seed. Linters have thicker walls and a larger diameter. If a lint fiber is of average length, 25.4 mm (1 in), the linters will be 2.5 to 5 mm (0.1 to 0.2 in) long.

COTTON CULTIVATION IN THE UNITED STATES

Cotton grows in a temperate to hot climate and is therefore confined to the region from 47 deg north latitude to 30 deg south latitude. In the United States the area is a line from central California to southern South Carolina and south to the southern tip of Texas. Major growing areas are Texas, California, the Mississippi River valley, and southern Arizona. In 1492, Columbus reported cotton growing in the Bahamas. It is believed that colonists planted cotton in Florida in 1556 and in Virginia in the early 1600s. Before the COTTON GIN was invented (1793) by Eli Whitney, seed was picked by hand and cotton processed primarily in the home. It is estimated that cotton production in 1792 was about 6,000 bales. Within 7 years production rose to 100,000 bales, and to a record 19 million bales in the United States in 1937. Because of Whitney's gin, cotton became the top agricultural cash crop in the United States.

Cotton Planting

In the United States cotton is planted from March through May and harvested from late summer to early fall. It requires fertile, well-drained soil, sufficient moisture, and warm to hot temperature (17 deg-27 deg C/62 deg-80 deg F) during the growing season. Approximately 70% of U.S. cotton is rain grown. Irrigation is required in the western states and in the Rio Grande valley of Texas. Today cotton is mechanically planted in rows, with seeds set at regular intervals or in small groups called hills. Seedlings must be thinned to leave only two or three plants in a hill, with hills about 30 cm (1 ft) apart. Cotton is thinned, or chopped, with hoes or with mechanical choppers. Weeds are removed at the same time, usually with herbicides. When the stem of the cotton plant somewhat hardened, the rows can be flamed--fired by quick jets of flame that kill weeds without hurting the cotton. Fertilizers are vital for cotton growth and, with mechanical planters, can be injected into the soil when the seed is planted.

Crop Protection

Disease-resistant strains of cotton and good cultivation practices can be effective in controlling the many pests and diseases to which cotton is subject. The two pests most difficult to eradicate are the WEEVIL and the pink bollworm; both cause huge crop losses when they are not controlled. Many different insecticides have been used against the weevil, but because of unwanted side effects, or because the weevil develops resistance, new insecticides must constantly be found. The pink bollworm is a fairly recent problem. It is present in huge numbers in cotton fields because the heavy pesticide campaigns against weevils also killed the insects that were the bollworm's natural enemies. It has proven even more difficult to control than the weevil. As larvae, the worms overwinter in the soil. As adult moths, they lay their eggs in early spring blossoms. The larvae destroy the new bolls when they hatch.

Two innovative methods have recently proven notably successful in eliminating the threat from these pests. Both methods involve the use of PHEROMONES, the sex-attractant chemicals released by adult female insects to signal their readiness to mate. Sex pheromones for both the weevil and the bollworm have been synthesized. In one eradication method, the synthetic pheromones bait a trap, attracting male insects. A farmer can judge by the number of insects within the trap how heavily the cottonfield is infested. Heavy infestations require pesticide spray in the fall, killing the young larvae when they are most vulnerable, and again in the spring. The traps remain in the field to monitor the number of weevils, and more spraying is done if it is needed. In the second method, synthetic pheromone is incorporated into plastic "twists", which are tied to some of the cotton plants. The twists exude pheromone into the air, but because it is so widely dispersed, the male adult moth is frustrated in his futile search for the female. Mating does not take place, and within a few seasons, the infestation is controlled.

The first method has been a success in trials in North and South Carolina, where--despite the fact that pesticide use has been dramatically reduced--the boll weevil is now effectively wiped out. The second method has been used to good effect against the pink bollworm in Pakistani fields.

Harvesting

About 16 to 25 weeks after planting, depending on variety and growing conditions, the bolls mature and burst open, and the fluffed-out cotton fibers dry and are ready for harvest. Today, 99% of U.S. cotton is mechanically harvested. Before the harvest, chemical defoliants strip the plants of their leaves, leaving the ripe cotton bolls accessible to the machine. Two types of machines are used. The cotton stripper removes the entire boll; the spindle harvester, or picker, uses revolving, barbed spindles that gather and wind up only the lint and seeds from the open bolls.

Ginning

At the turn of the century most cotton gins were located on plantations. Today cotton is trucked from the field to modern installations that can handle more than 20 bales an hour for each gin stand. Cotton is sucked through pipes into a drier, where excess moisture is removed, and then into a cleaner that separates the lint from the debris picked up in the harvesting process. Finally it goes to the gin stand, where revolving teeth pull the lint through narrow steel gratings, leaving the seeds behind. The deseeded fiber is cleaned again and then fed to a gin press. Cotton is normally pressed in a 218-kg (480-lb) bale, but for more efficient transportation, gin bales are often compressed to half that volume. Baled cotton is either exported or sent to a SPINNING plant for processing into yarn.

Cottonseed

Cottonseed removed during the ginning process is shipped to an oil mill. Here the linters remaining on the seeds are removed in a process similar to the original ginning operation. The principal uses of linters are in padding for upholstery, mattresses, photographic film, paper products, and surgical supplies.

Cottonseed accounts for two-thirds of the weight of usable material in the cotton boll. Major products from the seed are meal, hulls, and oil, which is of high quality and is used as a salad oil, in the preparation of shortening and margarine, and in the manufacture of cosmetics, soaps, detergents, and paints. Chemical treatment converts cottonseed oil into specialized fats and food coatings. Cottonseed meal, the residue from oil extraction, is a premier animal feed and, to some extent, an organic fertilizer. Recent research has resulted in food-grade meal products with up to 95% protein content. Hulls are also used, primarily in animal feeds.

THE COTTON MARKET

In the past, uncontrolled cotton production has usually outstripped demand, driving the value of the crop sharply downward. Since 1933 the federal government has taken steps to stabilize production and assure the farmer a fair profit on crops. Farmers have been paid directly for land diversion and conservation programs on diverted land; they have been subsidized for cotton grown for export, and they have received price supports. Under the price-support plan, the government sets a minimum price and, through the Commodity Credit Corporation (CCC), buys the cotton if the market price falls below this minimum. At one time the CCC owned more than 10 million bales.

Within the past quarter century, the increased use of SYNTHETIC FIBERS has greatly reduced the demand for cotton fabrics. Cotton's share of the total U.S. fibers market dropped from almost half in 1966 to about 30% two decades later. This natural fiber offers unique qualities of comfort and wear, however, and consumer demand for all-cotton fabrics, or blends of cotton and synthetics, is on the rise once again. All-cotton fabrics with a durable-press finish are now available, and experts expect that, in time, cotton will rival the synthetics as a convenience fabric.

(From Groliers Encyclopedia, 1994)

Current Queue | Current Queue for Other | Other archives

Return to MadSci Network




MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci
© Copyright 1996, Washington University. All rights reserved.
webadmin@www.madsci.org