Natural fibers may be of animal, vegetable, or mineral origin. Although the annual production of vegetable fibers outweighs that of animal or mineral fibers, all have long been useful to humans.

Animal fibers

Animal hair fibers consist of a protein known as keratin. It has a composition similar to human hair. Keratin proteins are actually crystalline copolymers of nylon, where the repeating units are amino acids. The fibrous proteins form crystals. They also crosslink through disulfide bonds present in the cystine amino acid.

Silks are partially crystalline protein fibers. Animal tendons consist of collagen, another fibrous protein with a complex hierarchical structure.

Wool

Wool forms the protective covering of sheep, screening them from heat and cold, and allowing them

Table 1. Specialty Animal Fibers. (Thomson Gale. )
Specialty Animal Fibers
Animal fiber	Uses	Animal’s natural or domesticated habitat
Alpaca	Luxurious fabrics	Arequipa, Peru
Angora goat (Mohair)	Carpets, upholstery, curtains, automobile cloth, clothing	Turkey, South Africa, southwestern United States
Angora	Rabbit knitted sweaters, mittens, baby clothes	Turkey, Asia Minor
Beaver	Textile use, hats	Europe, United States
Camel hair	Overcoats, topcoats, sportswear, and sports hosiery	Chinese and Mongolian deserts
Cashmere goat	Soft fibers for textiles	Tibet, China, Persia, Turkestan, Outer Mongolia
Chinchilla	Fur	South American Andes
Fox	Furs, scarves, muffs, jackets, coats, trimmings	all parts of the world
Guanaco	Luxury fleece	Southern Argentina
Hare or jackrabbit	Felt	United States; all parts of the world except Madagascar
Llama	Textiles requiring impressive luster, warmth, and light weights	South America
Muskrat	Fur	North America
Nutria	Soft blends	South America
Opossum	Trimming for cloth coats	Australia, southern United States, South America
Rabbit or coney	Textile blends	Australia, domesticated all over the world
Raccoon	Sportswear	United States
Vicuna	Very soft cloth	Peru
Weasel family, including mink	Furs for coats, trimmings, capes, etc.	Europe, Asia, United States

Table 2. Seed-hair Fibers. (Thomson Gale. )
Seed-hair fibers
Fiber	Uses	Place of origin
Kapok	Stuffing for mattresses,	Africa, Southeast Asia
	pillow, and furniture;
	life preservers
Cotton	Textiles, cordage	United States, Asia,
		Africa

to maintain even body temperatures. The following are important characteristics of wool fibers: (1) They are 1-14 in (2.54-35.56 cm) or more in length, with diameters of 1/600th-1/3,000th in (0.04-0.008 mm). (2) Their average chemical compositions are: carbon, 50%; hydrogen, 7%; oxygen, 22-25%; nitrogen, 16-17%; and sulphur, 3-4%. (3) They are extremely flexible and can be bent 20,000 times without breaking. (4) They are naturally resilient. (5) They are capable of trapping air and providing insulation. (6) They absorb up to 30% of their weight in moisture. (7) They are thermally stable, and begin to decompose only at 212^°F (100^°C).

Production of wool fabric

The conversion of wool fiber into fabric begins with the shearing of the sheep. In most of the United States, sheep shearing takes place in the spring. Professional shearers travel from place to place, where they are paid by the number of fleeces they shear. A good sheep shearer can shear 200 sheep per day.

Wool fleeces are sorted by hand according to their quality. The shoulder wool usually produces the best fiber, followed in order of quality by the side, neck, and back wool. After sorting, the wool is scoured to clean it and to prepare it for dyeing. After the wool has been dyed, it is carded to open the fibers. The fibers are then drawn into yarn, and any kinks present are removed by steam pressure. The yarn is next woven, examined, and burled to remove all knots and loose threads. In the finishing process, the cloth is shrunk, washed and rinsed to remove all impurities and dirt picked up in the earlier operations. Then the cloth is dried and straightened to remove all wrinkles. Finally, the cloth is sheared to give it uniformity, and then moistened and passed through heated rollers for pressing.

Table 3. Leaf Fibers. (Thomson Gale. )
Leaf fibers
Fiber	Uses	Place of origin
Abaca	Coarse sacks, coffee and sugar bags, floor coverings,	Philippines, Central America, Indonesia
	webbing, industrial ropes, hoisting and drilling cables,
	nets, agricultural twines, hawsersand ships’ cables,
	paper, tea bags
Sisal	Coarse sacks, coffee and sugar bags, floor coverings,	Western Hemisphere, Africa, Asia, Oceania
	webbing, industrial ropes, hoisting and drilling cables,
	nets, agricultural twines, stuffing and upholstery
	materials, paper
Henequen	Coarse sacks, coffee and sugar bags, floor coverings,	Mexico
	webbing, industrial ropes, hoisting and drilling cables,
	nets, agricultural twines, paper
Cantala	Cordage	Philippines, Indonesia
Istle	Scrubbing and scraping brushes, brooms	Mexico
Mauritius	Coarse sacks, coffee and sugar bags, floor coverings,	Brazil, island of Mauritius
	webbing, cordage, paper
Phornium	Cordage, paper	New Zealand
Sansevieria	Cigarette paper	Africa, Arabia, India, Sri Lanka
Caroa	Paper	Brazil
Piassava	Scrubbing and scraping brushes, brooms	Brazil
Broomroot	Scrubbing and scraping brushes, brooms	Mexico

Table 4. Bast (Soft) Fibers. (Thomson Gale. )
Bast (soft) fibers
Fiber	Uses	Place of origin
Flax	Clothing, sacks and bags, canvas and sailcloth, fabrics,	France, Belgium, Ireland, and Eastern Europe
	string and yarns, cigarette paper
Hemp	Clothing, sacks and bags, canvas and sailcloth, fabrics, nets	People’s Republic of China, Philippines, Brazil, Taiwan,
		Japan
Jute	Clothing, sacks and bags, canvas and sailcloth, fabrics	India, Banbladesh, other Asian countries, Brazil
Kenaf and roselle	Clothing, sacks and bags, canvas and sailcloth, fabrics,	People’s Republic of China, former Soviet Union, Egypt,
	nets (kenaf)	India, and Thailand (roselle)
Urena	Packaging	Brazil, Zaire
China jute	Packaging	People’s Republic of China, former Soviet Union, Japan,
		Korea, Argentina
Sunn hemp	Soft cordage	India

Worsteds are produced in a similar process, but the wool fibers are twisted during processing to produce a smoother, harder surface. As a result, worsteds have harder surface finishes, greater durability, and sharper colorings than woolens.

Silk

Silk is a continuous protein filament spun by the silkworm to form its cocoon. The principle species used in commercial production is the mulberry silkworm, which is the larva of the silk moth, Bombyx mori. It belongs to the order Lepidoptera.

Silk and sericulture (the culturing of silk) probably began in China more than 4,000 years ago. The Chinese used silk for clothing, wall hangings, paintings, religious ornamentation, interior decoration, and to maintain religious records. Knowledge of the silkworm passed from China to Japan through Korea. The production

Miscellaneous vegetable fibers

Table 5. Miscellaneous Vegetable Fibers. (Thomson Gale. )
Miscellaneous vegetable fibers
Fiber	Uses	Place of origin
Broom root	Brooms, brushes	Mexico
Crin vegtal	Stuffing	North Africa
Piassava	Cordage, brushes	Brazil
Coir	Scrubbing and scraping brushes, brooms, door mats	Sir Lanka, India

Table 6. Fibers of Mineral Origin. (Thomson Gale. )
Fibers of mineral origin
Fiber	Uses	Place of origin
Asbestos	Safety clothing, thermal insulation jacketing fabrics, barbecue	Canada, former Soviet Union
	mitts, commercial laundry and dry cleaning press covers,
	conveyor belts, dust filters, heating and ventilating ducts,
	electrical insulating tapes, yarns for electric wire insulation,
	fireproof draperies, fire-smothering blankets, brake linings
Glass	Composites, insulation, draperies, tire cord, filters	United States
Aluminum silicate	Packings and insulation for high temperatures	United States

of silk transformed the tiny, technologically backward Japanese islands into a world power.

Silk was also passed to Persia and Central Asia where it was encountered by the Greeks. Aristotle was the first Western writer to describe the silkworm. In AD 550, the Emperor Justinian acquired silkworm eggs and mulberry seeds, beginning the varieties of silkworms that supplied the Western world with silk for 1,400 years.

After World War II, the women’s silk hosiery market, silk’s single largest market, mostly was overtaken by nylon.

Properties

Silk fibers are smooth, translucent, rod-like filaments with occasional swellings along their length. The raw silk fiber actually consists of two filaments called fibroin bound by a soluble silk gum called sericin. Fibroin and sericin are made up of carbon, hydrogen, nitrogen, and oxygen.

Silk has several important qualities: (1) It is lower in density than wool, cotton, or rayon. (2) It is a poor conductor of heat and electricity. (3) It is capable of soaking up to 30% of its weight in moisture. (4) It is extremely strong, with a breaking strength as high as 65,000 psi. (5) It will stretch to as much as 20% of its length without breaking. (6) It is thermally stable; it is able to withstand temperatures as high as 284^°F (140^°C). (7) It becomes smooth, lustrous, and luxurious when processed. (8) It is remarkably resilient, and shows excellent wrinkle recovery.

Production of silk fabric

Sericulture requires scrupulous care and painstaking attention to detail. Breeder moths are first selected with great care. Eggs from the moths are repeatedly tested to ensure the quality of the larvae. The selected eggs are placed in cold storage until the early spring when they are incubated. After about a week, the eggs hatch into tiny silkworms. The worms are kept in clean conditions on trays of mulberry leaves. Young silkworms have voracious appetites, eating every couple of hours day and night for five weeks. To produce a pound of silk, one silkworm would have to eat 200 lb (90.8 kg) of mulberry leaves. In these first five weeks of life, the worms grow to 70 times their original size.

Once the silkworm’s appetite has been sated, the worm is placed on a pile of straw or heather, where it

begins spinning its cocoon. The silkworm first attaches itself to a twig. Then it begins spinning filaments of silk in an endless series of figure eights. This builds up walls within walls which are held together by gummy sericin that dries and hardens following exposure to air.

Without human intervention, the worm inside the cocoon would develop into a chrysalis and later into a moth. The moth would then burst the cocoon and break the one long strand of silk into many short ones. But sericulture destroys the worm inside the cocoon by stifling it with heat.

The next step in sericulture is to unwind the cocoon. This process is called reeling. To produce uniform strands of raw silk for commercial use, filaments of 5-10 cocoons are combined into a single thread. To do this, the cocoons are first soaked in hot water. After the ends of the filaments have been located, the filaments are passed through porcelain guides where they are twisted into fibers of uniform length and regularity. Reeling may be done automatically or by hand.

Raw silk is wound into skeins. Thirty skeins constitute one book, which weighs around 4.3 lb (1.95 kg). Thirty books make a bale, which weighs 132.3 lb (60.06 kg). The bale is the basic unit of commercial transactions. About 900 lb (408.6 kg) of cocoons are required to produce one bale of raw silk.

Raw silk taken directly from the filature is too fine to be woven. It must first be made into a thicker and more substantial yarn in a process known as throwing. Throwing consists of: sorting the skeins according to quality; soaking selected skeins to remove the sericin; drying any skeins that have been soaked; rewinding the skeins onto bobbins; twisting the threads from two or more bobbins to form single strands; again twisting to produce a fine thread; and finally conditioning the highly twisted thread.

Specialty fibers from animals

In addition to wool and silk, a number of specialty fibers are also obtained from animals. In most cases, animal fibers are similar to each other. They grow in two principal coats: the shiny and stiff outer coat or hair; and the undergrowth or fur. Hair forms a protective shield around the animal’s body against the elements; fur is closer to the skin and consists of shorter fibers than the hair that acts as insulation against heat or cold.

Fabrics containing specialty fibers are expensive because of the difficulties in obtaining the fibers, and the amount of processing required to prepare the fibers for use. Unlimited combinations of specialty fibers with wool are possible. Specialty fibers may be used to add softness or luster to fabrics. They also enhance the insulating properties of blended fabrics.

Vegetable fibers

Vegetable fibers were used by ancient man for fishing and trapping. Evidence exists that man made ropes and cords as early as 20,000 BC. The Egyptians probably produced ropes and cords from reeds, grasses, and flax around 4000 BC. They later produced matting from vegetable fibers, rushes, reeds, and papyrus grasses bound with flax string.

Vegetable fibers consist of cellulose, i.e., polysaccharides made up of anhydroglucose units joined by an oxygen linkage to form long molecular chains that are essentially linear, bound to lignin, and associated with various amounts of other materials.

Vegetable fibers are classified according to the part of the plant that they come from. The four groupings are: seed-hair fibers, leaf fibers, bast fibers, and miscellaneous fibers.

Seed-hair fibers

The first category of vegetable fiber is of seed-hair fibers, which includes: cotton, kapok, flosses obtained from seeds, seedpods, and the inner walls of fruit.

Cotton

Perhaps no other natural product has influenced the destiny of humankind as has cotton. It has clothed nations, enslaved men and women, monopolized labor, and given direction to entire industries.

The first historical mention of cotton was in the writings of Herodotus. Writing in 484 BC, he described trees with fleece growing in them in India. Archeological discoveries have placed the use of cotton in India to 3000 BC. or earlier. Cotton spread by trade to the Middle East, particularly Egypt, and later, in the seventh and eighth centuries, it was brought to Spain by the Moors.

New World explorers found cotton fabrics being manufactured in Peru, Mexico, and what is now the southwestern United States. Carbon 14 tests have dated the use of cotton in Peru as far back as 2500 BC.

Europeans first planted cotton in the New World in Virginia, using seeds from the West Indies. The need to harvest cotton when the weather is perfectly dry meant at first that the European colonists had to spend long days working in the hot sun. They eventually circumvented their dislike for this labor by importing slaves to do the work for them.

In 1793 a young inventor named Eli Whitney developed the cotton gin, which allowed cotton seeds to be rapidly separated from the fiber mechanically. This single invention raised cotton exports from 400 bales a year in 1791 to 30,000 bales in 1800 and 180,000 bales in 1810. As a corollary, between 1790 and 1800, the slave population of the United States increased by 33%. By 1810 there were more than a million slaves in the Southern states; by 1860 the number had risen to more than 4 million.

Since the end of World War II, demand for cotton has been largely supplanted by one for synthetic fibers, particularly polyester and nylon. Incursions into the cotton market are due in part to the dwindling availability of land to raise cotton.

Cultivation and processing of cotton

Cotton cultivation requires a warm, humid climate and sandy soil. It takes from 80 to 110 days for planting and flowering; another 55 to 80 days are required for the flower to produce the cotton ball.

Today mechanical harvesters are used most often to gather cotton from the plants. A mechanical harvester can pick up to 650 lb (295.1 kg) per hour compared to the 15 lb (6.81 kg) that a hand picker can gather at the same time. Even so, hand pickers are still sometimes preferred because mechanical harvesters tend to gather a great deal of waste matter along with the fiber.

After cotton has been harvested, the seeds must be removed. Essentially the same method devised by Whitney in 1793 is used. The seed cotton is fed into a gin consisting of a series of circular saws that separate the fiber from the seeds. The fiber is then compressed into bales weighing about 478 lb (217 kg). A second ginning separates out the short fibers leaving the more desirable longer fibers.

Turning the raw cotton into yarn requires many steps. First, any heavy impurities such as dirt or seeds are removed from the opened bales of cotton at the mill. Then the fibers are drawn into wide thin webs which are gathered into ropes or strands. The finer quality fibers are combed until all short lengths have been removed. Both combed and uncombed fibers are drawn and twisted to produce the finished yarn. Weaving the cotton fabric consists of interlacing lengthwise yarns with crosswise yarns to produce cotton cloth.

Leaf fibers

Leaf fibers come from the leaves of monocotyledonous plants. They are primarily used for cordage.

Bast fibers

Bast fibers come from the bast tissue or bark of plant stem. They are primarily used for textiles, thread, yarn, and twine.

Miscellaneous fibers

Miscellaneous fibers come from the sheathing leaf-stalks of palms, stem segments, stems, and fibrous husks. They are used primarily for brush and broom bristles, matting, and stuffing.

Mineral fibers

Table 6 lists the three principal natural fibers. But of the three fibers only asbestos is a true natural fiber. Glass and aluminum silicate fibers require human intervention in their processing, and might be better considered man-made fibers.

Asbestos

Asbestos is a fibrous mineral mined from rock deposits. There are approximately 30 types of minerals in the asbestos group. Of the six that have commercial importance, only oneotile, a hydrated silicate of magnesium that contains small amounts of iron and aluminum, oxides, is used in fiber processing.

Asbestos probably formed prehistorically when hot waters containing carbon dioxide and dissolved

Key Terms

Fiber —A complex morphological unit with an extremely high ratio of length to diameter (typically several hundred to one) and a relatively high tenacity.

salts under high pressure acted upon rock deposits of iron, magnesia, and silica.

The ancient Greeks knew of asbestos as early as the first century AD; the name comes from the Greek word for inconsumable. But asbestos did not find commercial use until it was used for packing and insulation when the steam engine was invented. Currently the world’s leading suppliers of asbestos are Canada and the former Soviet Union.

Useful for heat protection, the most notable characteristic of asbestos is that it will not burn. It can be spun and woven into textiles. However, asbestos is a known carcinogen. It is highly toxic when inhaled as dust particles. The American Conference of Governmental Industrial Hygienists has established a maximum exposure level to chrysotile fibers. A worker may be exposed, without adverse effects, to 2 fibers/cc more than 5 microns long.

The first step in processing asbestos fibers is to separate the longer fibers—from 3/4-3/8 in (1.91-0.94 cm)—from rock by pounding. The shorter fibers—up to 3/8 in (0.94 cm) long—are separated from the rock by crushing and screening. The fibers are next graded according to length. Different grades of fibers are blended, combed, cleaned, and aligned in webs. The web is separated into ribbons or rope-like strands. (Slivers are formed into rolls or laps for electrical insulation). The strands are spun and twisted into yarns of various sizes, depending upon end use. Finally the yarns are woven into fabrics or plaited into braids using mechanical braiders.

See also Artificial fibers; Cellulose.