Fibers are the raw material from which textiles are made for use in clothing, the household, floor coverings, and industry. For convenience, fibers are generally classified as being either natural or synthetic (formed by chemical processes, usually involving extrusion of the fiber).
Since 1971, world production of natural fibers has expanded only slightly, while production of synthetic fibers has increased at a slightly faster rate. While synthetic fibers have relied on petrochemical expansion, the expansion of natural fiber production relies on developments in agriculture and competition for land utilization. In 2000, the world production of cotton was estimated at 21 million tons (19 million tonnes). The estimate for jute, kenaf, and other similar fibers was a total of 2.8 million tons (2.5 million tonnes).
The use of natural fibers goes back to the Stone Age, when flax and hemp were exploited. Eventually wool, silk, and cotton fibers were utilized and were known to have been in use for several thousand years B.C.E. In medieval times, wool processing was a major occupation, but industrial processing, mainly of wool and cotton, dates from about 1750 C.E Currently, textile fibers are made using animal, vegetable, and mineral sources.
Animal fibers
The hair of many mammals is potentially useful for producing textiles, but the principal fiber used is sheep’s wool. Many different breeds of sheep are used to provide fibers differing in fineness. The products vary greatly—from lambswool (baby wool), Merino (fine and soft), crossbred (medium wool for mixing and for use in domestic fabrics) to upland and mountain wool (coarse and wiry for carpets).
Wool clipped or sheared from sheep or sliped wool, pulled from the skins of dead sheep, is not of constant quality from the same animal, and distinction is made between fine, coarse, outercoat, and kemp hairs, which are thick white fibers. The sorting of wool, usually at the country of origin, is programmed to separate the various grades of fiber to suit the intended use. Fibers are sorted according to their fineness, color, and length.
Each wool fiber consists of the protein keratin and is built up of spindle-shaped cells. The main cell material, or cortex, is covered by a layer of thin overlapping scales (cuticle) that is visible under a microscope and gives wool its characteristic ability to felt or mat. Pigment streaks in colored wools are distributed in the cortex. Wool often has a crimp wave, which gives it springiness and warmth in finished products such as sweaters.
The principal producing areas are Australia, New Zealand, Russia, South Africa, China, and Argentina, although most countries with appreciable pasture produce wool. Clothing accounts for about 76 percent of the wool produced.
Other animal fibers in use include camel, llama, rabbit, horse, cow, and goat hairs—chiefly mohair from the Angora goat, cashmere from the cashmere goat, and common goat.
Silk is the extrudate, or spun thread, of the silkworm Bombyx mori. Silk is used by the worm to create a cocoon in which it will metamorphose into a silk moth. Cultivated silk is produced under factory conditions where the worms, fed on mulberry leaves, eventually grow to several inches in length. Each worm contains twin sacs of fibroin, or liquid silk protein. When it is ready to spin its cocoon, the worm attaches itself to a twig and extrudes the whole of its fibroin by muscular action through a small hole, or spinneret, forming a cocoon of endless thread several yards long. Since the emerging moth would break open the cocoon and spoil the thread continuity, the cocoons are stifled with heat, steam, or other gas. Next the cocoons are floated on water and reeled, several filaments being combined to form a fine and lustrous yarn. Japan and China are the main silk producing countries.
Wild silk, especially tussah and anaphé, is obtained from cocoons found in the open in Far Eastern countries. These cocoons are usually communal, and also broken, and cannot be reeled. The fiber is recovered by mechanical action and forms cut, or staple, fiber, which is made into yarn by twisting. A typical fabric made from this source is shantung.
