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Lesson OneCotton GrowingCotton is the world's most widely used fiber. Its popularity stems from both its relative ease of production and its applicability to a wide variety of textile products. The price of cotton yarn, however, is strongly dependent upon the cost of labor, so that in the industrialized nations, where labor is expensive, cotton yarns may be relatively high priced. Until relatively recent times, however, cotton was not as widely used as wool and linen. This was because it was easier to spin wool or flax into yam because of their greater length. In addition, cotton fibers have to be separated from the seeds to which they cling. This procedure was very tedious and time-consuming when done by hand. Early machinery could be used on only the longest staple cotton. So labor costs tended to be very high.The invention of the saw-type cotton gin made possible the exploitation of the short staple fiber, which thrived in the Carolinas and Virginia of the United States. The dramatic increase in productivity, coupled with the low cost of labor in the southern United States, gave cotton a continually expanding portion of the world textile market. Increasing mechanization of fiber and yarn production helped keep the cost of cotton goods low. The, development of the textile machinery enlarged the production base.Cotton cultivation requires warm climates with a high level of moisture or irrigation. The growing season is from six to seven months long. During this period the seeds sprout and grow, producing a white blossom in about 100 days. The blossom produces a seed pod, which matures during the next two months. When the pod bursts, the cotton fibers are ready for picking.Before yam manufacture, cotton is graded, sorted, and blended to insure uniform yam quality. Cotton is graded on the basis of color, staple length, fineness, and freedom from foreign matter. In the United States, cottons are divided into grades according to length of staple, uniformity, strength, color, cleanness and flexibility. These are compared with a standard supplied by the United States Department of Agriculture. The standard provides 6 grades above and 6 grades below the Middling grade. The most common grades are:(1) Strict good middling.(2) Good middling.(3) Strict middling.(4) Middling.(5) Strict low middling(6) Low middling.(7) Strict good ordinary.The cotton fiber may be from 0.3 to 5.5 cm long. Under themicroscope it appears as a ribbon like structure that is twisted at irregular intervals along its length. The twists, called convolutions, increase the fiber-to-fiber friction necessary to secure a strong spun yarn. The fiber ranges in color from a yellowish to pure white, and may be very lustrous. However, most cotton dull.A cross-sectional view reveals that the fiber is kidney-shaped with central hollow core known as the lumen. The lumen provides a channel for nutrients while the plant is growing. The fiber consists of an outer shell, or cuticle, which surrounds the primary wall. The primary wall, in turn, covers the secondary wall surrounding the lumen. The cuticle is a thin, hard shell which protects the fiber from bruising and damage during growth. In use as a textile fiber, the cuticle provides abrasion resistance to cotton.Lesson TwoCotton Properties and UsesA relatively high level of moisture absorption and good wicking properties help make cotton one of the more comfortable fibers. Because of the hydroxyl groups in the cellulose, cotton has a high attraction for water. As water enters the fiber, cotton swells and its cross section becomes more rounded. The high affinity for moisture and the ability toswell when wet allow cotton to absorb about one-fourth of its weight in water. This means that in hot weather perspiration from the body will be absorbed in cotton fabrics, transported along the yarns to the outer surface of the cloth and evaporated into the air. Thus, the body will be aided in maintaining its temperature.Unfortunately, the hydrophilic nature of cotton makes it susceptible to water-borne stains. Water-soluble colorants such as those in coffee or grape juice will penetrate the fiber along with the water; when the water evaporates, the colorant is trapped in the fiber. Perhaps the major disadvantage to cotton goods is their tendency to wrinkle and the difficulty of removing wrinkles. The rigidity of cotton fiber reduces the ability of yarns to resist wrinkling. When the fibers are bent to a new configuration, the hydrogen bonds which hold the cellulose chains together are ruptured and the molecules slide in order to minimize the stress within the fiber. The hydrogen bonds reform in the new positions, so that when the crushing force is removed the fibers stay in the new positions. It is the rupture and reformation of the hydrogen bonds that helps to maintain wrinkles, so that cotton goods must be ironed.Cotton is a moderately strong fiber with good abrasion resistance and good dimensional stability. It is resistant to the acids, alkalies, and organic solvents normally available to consumers. But since it is a natural material, it is subject to attack by insects, molds and fungus. Mostprominent is the tendency for cotton to mildew if allowed to remain damp.Cotton resists sunlight and heat well, although direct exposure to constant strong sunlight will cause yellowing and eventual degradation of the fiber. Y ellowing may also occur when cotton goods are dried in gas dryers. The color change is the result of a chemical reaction between cellulose and oxygen or nitrogen oxides in the hot air in the dryer. Cottons will retain their whiteness longer when line-dried or dried in the electric dryer.Of major interest is the fact that cotton yarn is stronger when wet than when dry. This property is a consequence of the macro-and micro-structural features of the fiber. As water is absorbed, the fiber swells and its cross section becomes more rounded. Usually the absorption of such a large amount of foreign material would cause a high degree of internal stress and lead to weakening of the fiber. In cotton, however, the absorption of water causes a decrease in the internal stresses. Thus, with less internal stresses to overcome, the swollen fiber becomes stronger. At the same time, the swollen fibers within the yarns press upon each other more strongly. The internal friction strengthens the yarns. In addition, the absorbed water acts as an internal lubricant which imparts a higher level of flexibility to the fibers. This accounts for the fact that cotton garments are more easily ironed when damp. Cotton fabrics aresusceptible to shrinkage upon laundering.Perhaps more than any other fiber, cotton satisfies the requirements of apparel, home furnishings, recreational, and industrial uses. It provides fabrics that are strong, lightweight, pliable, easily dried, and readily laundered. In apparel, cotton provides garments that are comfortable, readily dried in bright, long-lasting colors, and easy to care for. The major drawbacks are a propensity for cotton yams to shrink and for cotton cloth to wrinkle. Shrinkage may be controlled by the application of shrink-resistant finishes. Durable-press properties may be imparted by chemical treatment or by blending cotton with more wrinkle-resistant fibers, such as polyester.In home furnishings, cotton serves in durable, general-service fabrics. Although they may lack the formal appearance of materials made from other fibers, cotton goods provide a comfortable, homey environment. Cotton fabrics have been the mainstay of bed linens and towels for decades, because they are comfortable, durable, and moisture-absorbent. Polyester/cotton blends provide the modern consumer with no-iron sheets and pillowcases that retain a crisp, fresh feel.For recreational use, cotton has traditionally been used for tenting and camping gear, boat sails, tennis shoes and sportswear. Cotton is particularly well-suited for tent. A tent fabric must be able to "breath", so that the occupants are not smothered in their own carbon dioxide.Furthermore, exchange of air with the outside atmosphere reduces the humidity within the tent and keeps it from becoming stuffy. Fabrics woven from cotton can be open enough to provide good air permeability for comfort. Tents should also shed water, when wet by rain, cotton yarns swell, reducing the interstices between the yarns and resisting the penetration of water. Today, however, heavy canvas gear is being supplanted by light-weight nylon in tenting equipment.Cotton cord, twine and ropes are used in industry to bind, hold, and lash all kinds of things, from bales to boats. Cotton yarns are used to reinforce belts on drive motors and in work clothing.。