Introduction

Wool, common name applied to the soft, curly fibers obtained chiefly from the fleece of domesticated sheep, and used extensively in textile manufacturing. Wool may be differentiated from hair mainly by the nature of the scales that cover the outer surface of each fiber. Wool scales are numerous, minute, and pointed and are attached only at their bases; thus the fibers interlock under pressure . The number of scales varies with the fineness and curliness of the fiber. Because of its crimp, or curl, wool has considerable resilience. This quality, together with its high tensile strength and elasticity, gives fine woolen fabrics the ability to retain shape better than cloth made from other natural fibers. Other characteristics of wool, which make it especially desirable for clothing, are its lightness, its ability to absorb moisture, and its insulating properties.

Sources of Wool

Wild species of sheep have a short, woolly undercoat covered by long, coarse, straight hair. The hair has entirely disappeared in domestic breeds; selective breeding has improved both the quality and abundance of wool. Wool production of sheep is also influenced by nutrition, climate, and care. Neglected domesticated animals have a tendency to produce hair instead of wool.

The fleece of sheep raised for wool is generally shorn once yearly, in the spring or early summer. In regions where the climate is warm throughout the year, shearing may occur twice annually. The fleece is cut close to the skin, usually with mechanical shears, and removed in one piece. The average weight of the fleece shorn from better wool-producing breeds is about 4.5 kg (about 10 lb). Small amounts of wool come from the skins of lambs slaughtered for meat.

Wool from different parts of the same fleece varies greatly in length of fiber, fineness, and structure. Wool from the shoulders and sides of the sheep is usually superior to that from other parts of the body. Quality varies also with the different breeds of sheep. Pure merino sheep bear the finest wool, and this type has been crossed with hardy sheep producing longer, coarser wool. About 40 percent of the world's total wool production consists of merino wool, and about 43 percent is obtained from crossbred varieties. The remainder is composed largely of carpet wools, which are derived mostly from special types of sheep and are employed in the manufacture of blankets, carpets, and tapestries. In addition, a small quantity of fine wool used for apparel is obtained from animals other than sheep. These wool-bearing animals include the camel, the alpaca, the Angora and Kashmir goats, the llama, and the vicuña.

Types and Labeling of Wool

The value of wool on the market depends primarily on fineness and length of fiber. Strength, elasticity, amount of crimp, and uniformity are also considered. Two different systems are followed in wool processing, the woolen system and the worsted system. In the woolen system, the fibers are carded and then spun. In the worsted system, the fibers proceed to a combing process, which separates the long from the short fibers. The long fibers are then formed into smooth compact strands ready for spinning into yarn. Worsteds are not napped but are finished with a smooth surface. Uniform lengths of relatively fine fibers are very important in the worsted system, because short fibers are difficult to spin. In the woolen system, on the other hand, fibers of mixed lengths may be used. Fine wools are classified according to the length of fiber. Longer fibers used in the manufacture of worsteds are called combing wool; shorter fibers employed for yarns used in soft, woven fabrics are known as carding wool.

In 1939, to protect the consumer, the U.S. Congress passed the Wool Products Labeling Act. This law requires that all fabric containing wool carry identification indicating the percentage of wool in the cloth. The act also specifies the proper legal description for the fiber according to category, such as new, reprocessed, or reused wool. New wool, or virgin wool, is wool that never before has been used in manufacture. Reprocessed wool refers to fiber reclaimed from woven scraps and clips accumulated from the cutting table, from samples, and from mill ends. These remnants, never previously used, are reconverted into a fibrous state and then reprocessed into the manufactured product. Reused wool is wool fiber recovered from products used by consumers, respun, and rewoven. This category is less important now than formerly, because of competition from synthetics.

Wool Production

Australia is the world's largest producer of raw wool, growing about 30 percent of the total world supply. Other leading producers are China, New Zealand, Iran, the United Kingdom, Argentina, South Africa, and Uruguay. In 2002 annual U.S. wool production was 21,000 metric tons when weighed before cleaning; most of the wool came from sheep raised in Texas, Wyoming, California, Colorado, Montana, and South Dakota. All the carpet wool and more than one-half of the apparel wool consumed in U.S. mills is imported from other countries.

Wool Manufacturing

The first step in the processing of wool preparatory to cloth making is the sorting of the fibers. As each fleece is pulled apart, the fibers are sorted into separate piles of similar nature and characteristics, mainly on the basis of fineness, length, and freedom from defects. After sorting, the fibers are cleaned, because wool contains an oily substance, called yolk, consisting of lanolin and suint, which is dried perspiration. The wool is scoured by a soap-alkali preparation or other detergent or solvent to remove the grease and other foreign substances.

The scoured wool fibers are disentangled and drawn straight into a continuous form in a process called carding, which employs a carding machine. In this process, the fibers are passed between pairs of rotating cylinders covered with a material called card clothing, which contains fine, pliable wire teeth. The wool emerges from the rollers in the form of a thin film known as the web. The processing of the web varies according to whether woolen or worsted yarn is to be produced.

Woolen fabrics, such as tweeds, are woven from bulky yarns containing short wool fibers arranged at random, so that the fabric is relatively thick and has a fuzzy surface. Worsted fabrics, such as gabardines, are woven from yarns composed of longer, thinner wool fibers, tightly twisted for a smooth surface.
For the production of woolen yarn, the web is split into soft, thin strands called roving, and then it is ready to be spun. For worsted yarn, the web is processed by machines that straighten the fibers, make them parallel, and remove all the short pieces. The resultant thick strand is then condensed by passing it through several machines until a very thin strand of worsted roving is obtained. From this type of roving can be spun the smooth yarn that produces firm, smooth-textured worsted fabrics.

Introduction

Cotton, natural vegetable fiber of great economic importance as a raw material for cloth. Its widespread use is largely due to the ease with which its fibers are spun into yarns. Cotton's strength, absorbency, and capacity to be washed and dyed also make it adaptable to a considerable variety of textile products.

Cotton Plants

Cotton is produced by small trees and shrubs of a genus belonging to the mallow family, which also includes hibiscus, okra, and the familiar swamp mallow. The immature flower bud, called a square, blossoms and develops into an oval boll that splits open at maturity, revealing a mass of long white seed hairs, called lint, that cover a large number of brown or black seeds. When fully mature and dry, each of these hairs is a thin flattened tubular cell with a pronounced spiral twist and is attached to a seed. The length of the individual fibers ranges from 1.3 to 6 cm (0.5 to 2.5 in). Shorter fibers that grow from the seeds are called linters.

A few species are grown commercially; these range from a small tree of Asia, to the common American Upland cotton, a low, multibranched shrub that is grown as an annual. Another species includes the long-fiber Egyptian and Sea Island cottons botanically derived from the Egyptian species brought to the United States about 1900. Sea Island cotton thrives in the unique climate of the Sea Islands, located off the southeastern coast of the United States, and on the islands of the West Indies such as Barbados. As with Egyptian cotton, the fiber is white and lustrous but its fiber length is longer than that of any other type of cotton, which permits the spinning of extremely fine yarns. Pima, originally called American-Egyptian cotton, is a hybrid type. It is the only variety of long-fiber cotton now grown in commercially significant quantities in the United States, where it is cultivated under irrigation in the Southwest.

It is almost impossible to determine the original habitats of the various species of cotton. Scientists have determined fiber and boll fragments from the Tehuacán Valley of Mexico to be about 7000 years old. The plant has certainly been grown and used in India for at least 5000 years and probably for much longer. Cotton was used also by the ancient Chinese, Egyptians, and North and South Americans. It was one of the earliest crops grown by European settlers, having been planted at the Jamestown colony in 1607.

Cultivation

Successful cultivation of cotton requires a long growing season, plenty of sunshine and water during the period of growth, and dry weather for harvest. In general, these conditions are met within tropical and warm subtropical latitudes in the northern and southern hemispheres. The U.S. Cotton Belt stretches from northern Florida to North Carolina and westward to California.

In the United States, production of the crop for a given year starts soon after harvesting the preceding fall, when many cotton farmers chop or shred the stalks with machines. The residue is plowed under and the land usually left rough until spring tillage. Planting time varies from the beginning of February in southern Texas to the beginning of June in the northern sections of the Cotton Belt.

A number of methods, chemical and mechanical, have been used to control weeds and grass, including intensive spraying of herbicide before and after planting. The cultivator, rotary hoe, and flame cultivator are also used to destroy weeds.

Approximately 95 percent of the cotton in the United States is now harvested mechanically with spindle-type pickers or strippers. Pickers are used extensively in irrigated lands. The picker has vertical drums equipped with wire spindles that engage and pull the cotton from open bolls. Strippers are used primarily in western Texas and western Oklahoma. They are “once-over” machines that pull the bolls from the plant.

Cotton Insects and Diseases

In addition to the flowers, the underside of each leaf of the cotton plant contains a small cuplike structure holding nectar. These deposits and the succulent stem make the plant attractive to a variety of insect pests. Chief among these is the boll weevil. The use of early maturing strains of cotton plus the application of several chemicals and control methods have greatly reduced losses from boll-weevil infestation. The bollworm, the pink larva of a small moth, is believed to have been a native of India but is now parasitic on cotton all over the world. The larvae burrow into the bolls and eat the seeds. In the United States the pink bollworm is largely confined to Texas and the western sections of the Cotton Belt. Quarantine, fumigation of seed, and destruction of trash removed from the cotton in ginning are control measures. The bollworm-tobacco budworm also is one of the most damaging cotton pests in terms of losses and control costs. Armyworm, thrips, lygus, and red spider are among other significant pests.
Among the serious diseases to which the cotton plant is subject is the wilt caused by a fungus which enters the roots from the soil and manufactures a poison. No treatment is known, but wilt-resistant strains of cotton have been developed. Another fungus disease is boll rot or anthracnose, caused by sac fungus. The best control is using seed from fungus-free fields.

Processing

When cotton arrives at the cotton gin, it is sucked into the building through pipes placed in the trailers or trucks. In many plants it first enters driers that reduce the moisture content for easier processing. The cotton travels next to equipment that removes burrs, sticks, dirt, leaf trash, and other foreign matter. It then moves to the gin stand, where lint is separated from the seeds. After separation from the seeds, the lint is packed tightly into bales. For the processing of cotton fiber to make yarn, cloth, and cordage, see Spinning; Textiles.

Marketing

In determining the value of cotton, workers class samples from each bale according to staple, grade, and character. Staple refers to fiber length. Short staple accounts for about 25 percent of the domestic crop and is used in many coarser textiles. Medium staple accounts for about 70 percent of U.S. cotton, and long staple and extra-long staple for about 5 percent.

Grade refers to color, brightness, and amount of foreign matter. Standards for grading U.S. cotton are established by the U.S. Department of Agriculture and revised from time to time. The highest of the grades are Good Middling and Strict Middling. Six color groupings indicate the degree of whiteness from white to gray. Character refers to the diameter, strength, body, maturity (that is, ratio of mature to immature fibers), uniformity, and smoothness of the fibers.

Cottonseed

Once a waste-disposal problem for gins, cottonseed is now a valuable by-product. The seed goes to oil mills, where it is delinted of its linters in an operation similar to ginning. The bare seed is then cracked and the kernel removed. The meal that remains after the oil has been extracted is high in protein. Linters are used for padding in furniture and automobiles, for absorbent cotton swabs, and for manufacture of many cellulose products such as rayon, plastics, lacquers, and smokeless powder for munitions. The hulls, or husks, are used as feed for cattle. Kernels, or meats, provide cottonseed oil. The cake and meal are used for feed and flour. Foots, the sediment left by cottonseed oil refining, provides fatty acids for industrial products.

Production

Cotton ranks just behind corn, soybeans, wheat, and hay among the leading cash crops of United States agriculture and is among the nation's principal agricultural exports. The leading cotton-producing states are Texas, California, Georgia, Mississippi, Arkansas, Louisiana, North Carolina, and Arizona.
Surplus stocks of cotton on hand in the United States fluctuated widely during the 1970s. The world economic recession of 1973-74 ushered in a period during which both production and consumption of cotton dropped. Production, however, fell faster than consumption, and by the mid-1970s the U.S. surplus had been reduced to the lowest level in 50 years in order to compensate. Toward the end of the decade, rising prices caused by the shortages had stimulated increased production, but at the same time these higher prices made domestic cotton more vulnerable to competition from artificial fibers and imported cotton goods. World demand for cotton continued to be erratic, and some groups lobbied for increased price-supports, but an upward trend began in the 1980s.
Cotton is still a principal raw material for the world's textile industry, but its dominant position has been seriously eroded by synthetic fibers. In the United States, cotton accounts today for about 35 percent of the materials processed in textile mills, as against 80 percent before World War II. Net per capita consumption of cotton fibers in the United States, after declining by more than one-third between 1950 and 1970, increased during the 1980s and by the early 1990s was about 12 kg (about 27 lb) per year.
World production of cotton in the early 1990s stood at 18.9 million metric tons annually. In the 1930s, the United States produced more than half the world's cotton; by the early 1990s it was turning out about a sixth. The other leading producers included China, India, Pakistan, Brazil, and Turkey.

Introduction

Silk, fiber produced as a cocoon covering by the silkworm, and valuable for its use in fine fabrics and textiles. The silkworm, in fact, is not a worm but a caterpillar. Although cocoon coverings of fiber are made by a large number of insects, only those of the mulberry silk moth, Bombyx mori, and a few other moths closely akin to it, are used by the silk industry. The silk of other insects, notably the spider, is used for certain manufacturing purposes, particularly for the cross hairs of telescopes and other optical instruments. For a description of the life and habits of the silk moth, see Silkworm.

History

Silk is one of the oldest known textile fibers and, according to Chinese tradition, was used as long ago as the 27th century bc. The silkworm moth was originally a native of China, and for about 30 centuries the gathering and weaving of silk was a secret process, known only to the Chinese. Tradition credits Hsi-ling-shi, the 14-year-old bride of the Emperor Huang Ti, with the discovery of the potential of the cocoon and the invention of the first silk reel. China successfully guarded the secret until ad300, when Japan, and later India, penetrated the secrecy.

References in the Old Testament indicate that silk was known in biblical times in western Asia, from which it was presumably transplanted to the Greek Islands of the Aegean Sea. The Chinese are believed to have built up a lucrative trade with the West from the days of the Han dynasty in the 2nd century bc. The ancient Persian courts used Chinese silks, unraveled and rewoven into Persian designs. When Darius III, king of Persia, surrendered to Alexander the Great, he was clothed in such silken splendor that Alexander was completely overshadowed and demanded as spoils the equivalent of $7 million in silk. Caravans carried silk on camelback from the heart of Asia to Damascus, Syria, the marketplace at which East and West met. Here silk was traded for Western luxuries, some of which survive in China today. Silk became a valuable commodity in both Greece and Rome. The Roman statesman and general Gaius Julius Caesar restricted silk to his exclusive use and to use for the purple Roman stripes on the togas of officials he favored. Despite this, however, the use of silk in Rome spread in the era of pomp and display.

Until ad550 all silk woven in Europe was derived from Asiatic sources. About that time, however, the Roman emperor Justinian I sent two Nestorian monks to China, where, at the risk of their lives, they stole mulberry seeds and silkworm eggs, secreted them in their walking staffs, and brought them to Byzantium. Thus, the Chinese and Persian silk monopolies ended. With the spread of Islam, the silkworm came to Sicily and Spain. By the 12th and 13th centuries Italy had become the silk center of the West, but by the 17th century France was challenging Italy's leadership, and the silk looms established in the Lyons area at that time are still famous today for the unique beauty of their weaving.

Not until after the revocation of the Edict of Nantes did Huguenot weavers from France cross the English Channel and establish silk mills in Spitalfields, a district in the East End of London. The silkworm, however, did not flourish in the English climate, nor has it ever flourished in the United States. The first silk mill in the U.S. was erected in 1810. With the advent of the power loom and with the help of the high tariffs, introduced during the American Civil War, against imported woven goods, the American silk-weaving industry entered a period of growth. Only in China, Japan, and, to a lesser extent, Italy and France was the silk itself produced, however.

In addition to the true silk from the cultivated mulberry silkworm, a number of so-called wild silks are produced from other related species of insects in the uncultivated state. Tussah silk, for example, is produced from a species that feeds on oak leaves. Douppioni is a silk produced from two silkworms that spin a cocoon together and thus produce a double thread. Special types of weaves, such as shantung and other irregular types, are woven from these types of silk.

Production

The advent of synthetic fibers such as nylon and polyester, which are stronger than silk and lower in price, but do not possess the same hand, or quality, has caused a tremendous reduction in silk production and consumption. World production in 1940 was 59 million kg (130 million lb). By 1950 it had dropped to 19 million kg (42 million lb), but by the mid-1980s had climbed to about 68 million kg (150 million lb).

In the U.S., silk is still used for clothing, including lightweight suits, coats and slacks, jackets, shirts and neckties, robes, loungewear, underwear, hosiery, and gloves. Silk is also used in lace, napery, draperies, linings, narrow fabrics, and handbags.

Sericulture

Sericulture, or the raising of silkworms, involves the incubation of the tiny eggs of the silkworm moth until they hatch and become worms. After hatching, the worms are placed under a layer of gauze, on which is spread a layer of finely chopped mulberry leaves. For six weeks, the worms eat almost continuously. At the end of this period, they are ready to spin their cocoons, and branches of trees or shrubs are placed in their rearing houses. The worms climb these branches and make their cocoons in one continuous thread, taking about eight days for the process. The amount of usable silk in each cocoon is small, and about 5500 silkworms are required to produce 1 kg (2.2 lb) of raw silk.

After the complete cocoons have been gathered, the initial step in silk manufacture is to kill the insects inside them. Thus, the cocoons are first boiled or treated in ovens, killing the insects by heat. The silk fiber is obtained from the cocoons by a delicate process known as reeling, or filature. The cocoons are first heated in boiling water to dissolve the gummy substance that holds the cocoon filament in place. After this heating, the filaments from four to eight cocoons are joined and twisted and are then combined with a number of other similarly twisted filaments to make a thread that is wound on a reel. When each cocoon is unwound, it is replaced with another cocoon. The resulting thread, called raw silk, consists usually of 48 individual silk fibers. The thread is continuous and, unlike the threads spun from other natural fibers such as cotton and wool, is made up of extremely long fibers. Along with cocoons damaged by emerging worms used for breeding stock, the filaments from the coarse outer portion of the cocoon, which is removed by brushing before reeling, and the inner portion of the cocoon, which remains after reeling the raw silk, are mixed to produce a low grade of silk staple that is spun into yarn.

The next step in the processing of silk is the twisting of one or more threads of the raw silk into a strand sufficiently strong for weaving or knitting. This procedure is called throwing. Four different types of silk thread may thus be produced: organzine, crepe, tram, and thrown singles. Organzine is a thread made by giving the raw-silk thread a preliminary twist in one direction and then twisting two of these threads together in the opposite direction at the rate of about 4 turns/cm (10 turns/in). Crepe is similar to organzine but is twisted to a much greater extent, usually between 16 and 32 turns/cm (40 and 80 turns/in). Tram is made by twisting in only one direction two or more raw-silk threads, with 8 to 12 turns/cm (20 to 30 turns/in). Thrown singles are individual raw-silk threads that are twisted in only one direction, the number of turns depending on the quality of thread desired. In general, organzine thread is used for the warp threads of materials, and tram threads for the weft, or filling. Crepe thread is employed in the weaving of characteristic crinkly fabrics, and single thread is used for sheer fabrics.