Any of a number of textile fibers produced from chemical substances of natural origin or synthetic origin; the latter are also known as synthetic fibers. Among the natural sources of manufactured fibers are plant cellulose and protein, rubber, metals, and nonmetallic inorganics. The synthetic fibers are produced from organic intermediates derived from petroleum, coal, and natural gas. See also Natural fiber.
With the exceptions of glass and metal fibers, the manufactured fibers are made from very long chainlike molecules called linear polymers. These polymers may be naturally occurring (cellulose from cotton or wood pulp) or may be synthetic (polyester). Irrespective of their chemical nature, fiber-forming polymers must possess the following characteristics: (1) great length—at least 200 monomer units must be joined in a chain; (2) a high degree of intramolecular and intermolecular attraction, whether through primary chemical bonds or other attractive forces; (3) the ability to be oriented along the axis of the fiber; and (4) the ability to form well-ordered crystals or pseudocrystals. All of these parameters are sensitive to the chemical nature of the polymer and the processes of manufacture of the fiber. In turn, they establish the properties of the fiber, such as strength, flexibility, resilience, and abrasion resistance, which contribute to their usefulness in various end uses for apparel, home furnishings, and commercial and industrial applications. See also Polymer.
Only a fraction of those substances capable of forming fibers prove to have all of the characteristics necessary for commercial success. The fiber types of major importance in the United States are classified by composition as follows: cellulosic (composed of regenerated cellulose, cellulose diacetate, and cellulose triacetate); synthetic (composed of polyamide, polyester, polyacrylic, polyvinyl, and polyolefin resins); and inorganic (composed of glass and metal).
All of the manufactured fibers are produced according to the same principles: (1) the fiber-forming material must first be made fluid; (2) the fluid is forced under pressure (extruded) through tiny holes into a medium which causes it to solidify; and (3) the solid fibers are further processed to obtain their optimum properties.
Typically one of three procedures is used to produce fibers. In wet spinning, (for example, the production of rayon by the viscose process), the polymer is dissolved in an applicable reagent to form the fluid (dope). The fluid is then pumped through metal plates (spinnerets) containing many small holes into a liquid bath of appropriate composition. A chemical reaction between the spinning dope and the bath causes the fiber to solidify. In dry spinning, the polymer is again dissolved in an appropriate solvent and extruded through a spinneret. However, the liquid bath is replaced by a stream of warm gas (usually air) which evaporates the solvent and allows the polymer to solidify as a filament. Cellulose diacetate and triacetate are produced in this manner. In melt spinning, Nylon, polyester, and the other thermoplastic fibers are produced by melt spinning. No solvents or reagents are required since the polymer can be melted without appreciable decomposition. Thus, the fluid consists of hot molten polymer which, upon extrusion into a stream of cold air, solidifies into a filament. Depending upon the end use, filaments may be produced in various sizes ranging from finer than a human hair to thick bristles for toothbrushes. They may also be produced with different cross-sectional shapes, such as round, lobed, square, or dogbone.
After extrusion, filaments are usually stretched (drawn). Drawing causes an increase in order (crystallinity) by extending the molecules of the fiber so that they pack more closely together, and orients the molecules along the longitudinal axis of the fiber. Higher orientation and increased crystallinity raise the strength of the fiber, decrease its stretch, and improve its elasticity.
Often, the manufactured fibers are textured to improve their comfort properties. Fabrics made from smooth, straight filament yarns are not as comfortable as those made from yarns spun from the shorter natural fibers. Texturing introduces irregularities (crimp) along the length of the filament and leads to bulkier filament yarns which are closer to spun yarns in their performance.
Advances in polymer and fiber technology have led to the development of fibers with exceptionally high temperature resistance and extremely high strength. These properties are desirable in applications such as upholstery and floor coverings in aircraft and other mass-transit vehicles, protective clothing for fire fighters and other emergency personnel, body armor for soldiers and police officers, tire cords, and industrial belting.
Metallic fibers of silver and gold have been used for millennia to decorate fabrics. Today metallic fibers serve useful as well as decorative purposes. These fibers are formed by drawing metal wires through successively finer dies to achieve the desired diameter. Although gold and silver are the easiest to draw, modern methods have allowed the manufacture of steel, tantalum, and zirconium fibers. Because they are electrical conductors, metal fibers have been blended into fabrics to reduce the tendency to develop static electrical charges.
Glass fibers are prepared by the melt spinning of previously formed glass marbles, and the molten filaments are drawn down to very fine dimensions. It is the fineness of the fibers that gives them their flexibility and allows them to be used in textiles. Unfortunately, the fibers are so stiff that when broken they can penetrate human skin. Thus, they are not well suited to use in apparel or upholstery. Glass is widely used in curtains and drapery because of its total resistance to the degrading effects of sunlight, its low cost, and its flame resistance. It provides a nonrotting, nonsettling insulating material for homes and industrial uses. See also Glass.
Fiber properties include the physical, mechanical, chemical, biological, and geometrical characteristics of fibers. Some of the more important ones are tensile strength, elongation at break, modulus of elasticity or stiffness, fatigue under repeated stress, resilience or ability to recover from deformation, moisture absorption and wettability, electrostatic properties, friction, color, luster, density, and resistance to light, heat, weathering, abrasion, laundering, mildew, insects, chemicals, and solvents; and finally a number of geometric features, such as diameter, cross-sectional shape, and crimp. Such properties play an important part in determining whether or not the fiber can be made into a fabric that will be wrinkle-resistant, pleasing to the touch, comfortable, easy to clean, durable, and attractive in color, luster, drape, and general appearance. With a knowledge of the physical properties of the available fibers, the textile engineer can choose the best fiber or best blend of several fibers to fit the intended use. The final result, however, is also dependent upon the proper choice and control of additional factors such as the yarn and fabric structure, the weave pattern, and the finishing of the cloth.
