Fiber

Image of a bend in a polyester fiber with a high surface area, as seen at high magnification with a scanning electron microscope.

The term fiber (or fibre) is used for a class of materials that consist of continuous filaments or are in discrete elongated pieces, similar to lengths of thread. Fibers are of great importance in the biology of both plants and animals, for holding tissues together. Humans use natural and synthetic fibers for diverse purposes. For instance, some fibers are spun into filaments, thread, string or rope. Some are components of composite materials, others are matted into sheets for products such as paper or felt.

A three-dimensional model of a cellulose chain.

Natural fibers

Natural fibers include those derived from plant, animal, and mineral sources. Examples of natural fibers and their sources are given below.

Plant fibers

Plant fibers may be derived from fiber crops (such as cotton), trees, straw, bamboo, and sugarcane. Their main constituent is cellulose, which may also contain lignin. These fibers serve in the manufacture of paper and cloth and can be further categorized as follows.

• Seed fiber: The fiber is obtained from the seed, such as cotton and kapok.
• Leaf fiber: The fiber is derived from the leaf, such as sisal and agave.
• Bast fiber or skin fiber: The fiber is collected from the skin or base surrounding the plant stem. These fibers have higher tensile strength than other fibers. They are therefore useful for durable yarn and fabric for packaging and paper. Examples include jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, vine fiber, and banana fiber.
• Fruit fiber: The fiber is collected from the fruit of the plant, such as coconut fiber (coir).
• Stalk fiber: The fiber is derived from stalks of wheat, rice, barley, and other crops.

Animal fibers

Animal fibers are generally made of proteins. They can be subdivided as follows.

• Animal hair: Various fibers are obtained from hairy mammals. Examples include wool (from sheep), goat hair (alpaca, cashmere), horse hair, and so forth.
• Silk fiber: This type of fiber is collected from the dried saliva of insect larvae that prepare cocoons. The main example is silk from silkworms.
• Avian fiber: Some fibers are obtained from birds. Examples are feathers and feather fiber.
• Catgut: It is derived mainly from sheep intestines.
• Sinew: Fibers obtained from animal tendons.

Mineral fibers

Mineral fibers may be used in their naturally occurring form or slightly modified before use. These fibers can be categorized as follows.

• Asbestos: It is the only naturally occurring, long mineral fiber. Varieties are serpentine (chrysolite) and amphiboles (amosite, crocidolite, tremolite, actinolite, and anthophyllite). (Short, fiberlike minerals include wollastinite, attapulgite, and halloysite.)
• Ceramic fibers: Glass fibers (glass wool and quartz), aluminum oxide, silicon carbide, and boron carbide.
• Metal fibers: Some metals may be drawn out into fibers. An example is aluminum fibers.

Artificial fibers

Some artificial fibers are prepared by modifying natural raw materials, others are produced by chemical synthetic methods.

Modified natural materials

• Many types of fiber are manufactured from natural cellulose. They include rayon, modal, and the more recently developed Lyocell. Cellulose-based fibers are of two types: (a) regenerated or pure cellulose, such as from the cupro-ammonium process; and (b) modified or derivatized cellulose, such as cellulose acetates.
• Fiberglass, made from specific glass formulas, and optical fiber, made from purified natural quartz, are also prepared by modifying natural raw materials.
• Some metallic fibers are drawn from ductile metals such as copper, silver, or gold. Others are extruded or deposited from relatively brittle metals, such as nickel, aluminum, or iron.

Synthetic fibers

Synthetic fibers are artificially prepared by chemical processes. The starting materials are often obtained from petrochemical sources rather than from natural fibers. Examples of synthetic fibers include nylon (polyamide), polyester (polyethylene terephthalate, or PET), phenol-formaldehyde (PF), polyvinyl alcohol fiber (PVOH), polyvinyl chloride fiber (PVC), polyolefins (PP and PE), and acrylic polymers. Traditional acrylic fiber is used more often as a synthetic replacement for wool.

Properties of synthetic fibers

• Fiber structures: Most synthetic fibers have a rounded cross-section, but some fibers have special designs such as hollow, oval, star-shaped, or trilobal. Newer fiber designs include extruding fiber that splits into multiple finer fibers. Coextruded fibers have two distinct polymers forming the fiber. Some fibers (such as aramids) have strong bonding between polymer chains, others have extremely long chains (including Dyneema or Spectra).

• Fiber surfaces: These can be dull or bright. Dull surfaces reflect more light, while bright surfaces tend to transmit light and make the fibers more transparent.

• Crimping: Synthetic textile fibers are often crimped to provide bulk in a woven, nonwoven, or knitted stucture.

• Response to heat: Carbon fibers and PF fibers are resin-based fibers that are not thermoplastic, although most others can be melted. Aromatic nylons such as Kevlar and Nomex thermally degrade at high temperatures and do not melt.

• Coated fibers: Some fibers may be nickel-coated to provide static elimination; silver-coated to provide anti-bacterial properties, or aluminum-coated to provide radar chaff. Radar chaff is a spool of continuous glass tow that has been aluminum coated. An aircraft-mounted high speed cutter chops it up as it spews from a moving aircraft to foil radar signals.

• Microfibers: In textiles, the term "microfiber" refers to sub-denier fiber (such as polyester drawn to 0.5 dn). Denier and Detex are two measurements of fiber yield based on weight and length. In the case of technical fibers, the term "microfibers" refers to ultrafine fibers (glass or meltblown thermoplastics) often used in filtration.

Uses of fibers

• Papermaking: Wood fibers are treated by combining them with other additives. They are then processed into a network of wood fibres, which constitutes the sheet of paper. The end paper product (paper, paperboard, tissue, etc.) dictates the species, or species blend, that is best suited to provide the desirable sheet characteristics, and also dictates the required fiber processing (chemical treatment, heat treatment, mechanical 'brushing' or refining etc.).

• Manufacture of cloth, carpeting, and so forth.

• Production of rope, string, and so forth.

• Data communications by optical fibers: An optical fiber is a glass or plastic fiber designed to guide light along its length by total internal reflection. These fibers are widely used in fiber-optic communication, which permits digital data transmission over longer distances and at higher data rates than electronic communication. They are also used to form sensors and for various other applications.

Dietary fiber

Dietary fibers are the indigestible portion of plant foods that move food through the digestive system, absorbing water. Chemically, dietary fiber consists of non-starch polysaccharides and several other plant components such as cellulose, lignin, waxes, chitins, pectins, beta-glucans, inulin, and oligosaccharides.

Dietary fibers are usually subdivided as “insoluble” and “soluble,” based on their solubility in water. Both types are present in all plant foods, with varying degrees of each according to a plant’s characteristics. Insoluble fibers have passive, water-attracting properties that help increase bulk, soften stools, and shorten transit time through the intestinal tract. Soluble fibers undergo active, metabolic processing to yield end-products with broad, significant health effects.

A study published in the Archives of Internal Medicine suggests that eating high fiber foods, such as legumes, helps prevent heart disease (Bazzano et al. 2003). Almost 10,000 American adults participated in this study and were followed for 19 years. People eating the most fiber, 21 grams per day, had 12 percent less coronary heart disease (CHD) and 11 percent less cardiovascular disease (CVD) compared to those eating the least, five grams daily. Those eating the most water-soluble dietary fiber fared even better with a 15 percent reduction in risk of CHD and a ten percent risk reduction in CVD.

See also

• Cellulose
• Cotton
• Dietary fiber
• Optical fiber
• Plastic
• Textile
• Wool

References

ISBN links support NWE through referral fees

• Hecht, Jeff. City of Light: The Story of Fiber Optics. New York: Oxford University Press, 1999. ISBN 0195108183
• Hecht, Jeff. Understanding Fiber Optics, 5th ed. Prentice Hall, 2005. ISBN 0131174290
• Lorenzani, Shirley S. Dietary Fiber. McGraw-Hill Education, 1998. ISBN 087983479X
• Morgan, Peter. Carbon Fibers and Their Composites. Boca Raton, Florida: CRC Press, 2005. ISBN 0824709837
• Wallenberger, Frederick T., and Norman E. Weston. Natural Fibers, Polymers and Composites. Springer, 2004. ISBN 1402076436

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