Fiber and Fiber Products

Fibers are strands of cells that are characterized by an elongate shape and a thickened secondary cell wall composed of cellulose and hemicellulose. Dead at maturity, fiber cells possess tapered, overlapping ends that form long, multicellular fibers. These fibers impart elastic strength to stems, leaves, roots, fruits, and seeds of flowering plants. Most fiber cells arise from vascular tissues and are commonly found in association with phloem tissue, although fibers may also be found in xylem or independent of vascular tissue. Fiber cells typically incorporate lignin in their secondary wall, a substance that creates additional stiffness in fiber cells.

In commerce, plant fibers are broadly defined to include materials that can be spun or twined to make fabrics and cordage, used directly as filling materials, or included in paper production. Plant fibers of commerce are

classified by the part of the plant from which they are obtained: (1) stem or bast fibers of dicotyledonous plants arise from phloem tissues and run the length of the plant between the bark and the phloem; (2) leaf or hard fibers of monocotyledonous plants arise from vascular tissue and run lengthwise along a leaf; and (3) seed or fruit fibers arise from seed hairs, seed pods, or fibrous fruit husks. Other minor sources of plant fibers include entire grass stems and strips of leaves or leaf sheaths from palms.

Bast Fibers.

Bast fibers arise from phloem cells in the stems of a variety of dicotyledonous plant species. Fiber cells range from 1 millimeter in jute to more than 250 millimeters in ramie, and individual fibers may be comprised of thousands of cells extending up to 1 meter (3.3 feet) in length. Bast fibers from a number of plant species are employed in the weaving of fine textiles, the manufacture of cordage (rope and twine), and paper production. Bast fibers from flax (Linum ) are used to make linen, the fabric used in wrapping Egyptian mummies more than four thousand years ago. Fibers from jute (Corchorus ) have been used since biblical times, and it remains the world's most important source of bast fibers, yielding twice as much fiber as all other sources combined. Coarse cloths, rope, and twine are produced from hemp (Cannabis ), ramie (Boehmeria ), and sunnhemp (Crotalaria ), while bast fibers from a number of plants such as hemp, sunnhemp, and Urena are important in paper production.

Bast fibers are localized inside the stem and are cemented to adjacent cells with pectins (a form of carbohydrate). Because of this intimate association, bast fibers are isolated from surrounding tissues using a combination of processes that incorporate bacterial decomposition (called retting), mechanical separation of fiber from wood and bark (scutching), and fine combing to separate individual fiber strands (hackling). In retting, stems are bundled after harvest and allowed to partially decompose in fields, ponds, streams, or tanks. This process of slow decomposition degrades pectins and allows fiber strands to dissociate from adjacent tissues. After retting, the stems are rinsed and dried, and the woody portion of the plant is removed from the fibers by scutching, a process that involves crushing stems in a series of fluted metal rollers. After scutching, bast fibers are hackled by drawing them through sets of progressively finer combs. This separates the long, fine fibers used for spinning and weaving from short fibers that are used in other applications.

Hard Fibers.

Hard fibers are obtained from leaves of certain monocotyledonous plants. Individual hard fiber cells range from 1 millimeter in sisal to more than 12 millimeters in abacá. Although individual hard fiber cells are usually shorter than bast fiber cells, fiber strands from abacá can exceed 4.5 meters (15 feet) in length. Hard fibers possess thick, lignified secondary cell walls that impart additional stiffness and rigidity to the fibers. Hard fibers find their primary application in cordage, although they are also used in the manufacture of sacks, carpets, and specialty papers. The most important species for hard fibers include sisal (Agave sisalana ), henequen (A. fourcroydes ), and abacá or Manila hemp (Musa textilis ). Sisal and henequen originated in Mexico and have been used extensively since the Mayan era. Present-day uses for sisal and henequen fibers include sacking, cordage, and mats. Abacá fiber comes from the leaves of Musa textilis, a member of the banana family. Abacá originates in the Philippines, and its fibers were used to make cloth prior to the arrival of explorer Ferdinand Magellan in 1521. Fibers from abacá are resistant to decay from salt water, making them the preferred source for marine cordage. In addition, abacá fiber is used to make mats, coarse fabrics, and paper stock for currency.

The extraction of hard fiber from leaves is a simple process, as entire leaves from sisal, henequen, or abacá are fed into a machine called a decorticator, which crushes the stalks and washes away the nonfiber pulp. The resulting ribbons of fiber are then washed and dried and can either be dyed or used directly.

Seed and Fruit Fibers.

Only three seed and fruit fibers have commercial importance: cotton, kapok, and coir. Cotton is the most widely used of all fiber plants. Cotton fibers are unicellular hairs (trichomes) that emerge from the seed coat after fertilization. Cotton fibers exhibit two forms: the long "lint" fibers that are twisted into thread and woven into fabrics, and short "fuzz" fibers that are used for batting, felts, and paper production. Single-celled lint fibers grow rapidly and expand approximately 2,500-fold (from 0.020 to 50 millimeters) during maturation. Cultivated for over four thousand years, cotton fiber has historically been obtained from two diploid species (G. arboreum, G. herbaceum ) native to Africa and Asia, and two tetraploid species (G. barbadense, G. hirsutum ) native to the Americas. Presently, the tetraploid species account for nearly all of the worldwide production of cotton fiber.

Unlike the seed hair of cotton, kapok fibers are produced by the inner surface of fruit pods (capsules) from the silk cotton tree Ceiba pentandra. Kapok fibers reach 20 millimeters in length at maturity, and are waxier and one-sixth the weight of cotton fibers. These properties make kapok difficult to spin; however, its water resistance, light weight, and resilience make kapok an excellent waterproof material for upholstery and life-preservers. Coir fiber is made from the husk (mesocarp) of fruits from the coconut palm Cocosnucifera. To produce coir, the husks are retted for up to a year, then beaten to separate individual fibers. The cleaned fibers can be spun into coarse yarns for use in ropes and matting, or for bristles in brushes and brooms.

see also Cannabis; Cotton; Economic Importance of Plants; Paper.

Richard Cronn

Bibliography

Esau, K. Anatomy of Seed Plants, 2nd ed. New York: John Wiley & Sons, 1977.

FAO Production Yearbook for 1998, vol. 52. Rome: Food and Agriculture Organization of the United Nations, 1999.

Simpson, B. B., and M. Conner-Ogorzaly. Economic Botany: Plants in Our World, 2nd ed. New York: McGraw-Hill, 1995.