Natural Fibers

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 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 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).

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 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 A.D. 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.

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 B.C., he described trees with fleece growing in them in India. Archeological discoveries have placed the use of cotton in India to 3000 B.C. 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 B.C.

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.

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 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.

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.