Artificial fibers
Artificial fibers
Artificial fibers are threads produced from man-made materials, unlike natural fibers like cotton, silk, and hemp.
| Table 1. Artificial Polymeric Fibers. (Thomson Gale.) | |
|---|---|
| Artificial polymeric fibers | |
| Acrylic | |
| Composition | At least 85% acrylonitrile units. Anidex is a cross-linked polyacrylate consisting of at least 50 wt% esters of a monohydric alcohol and acrylic acid. |
| Processing | Orion® is made by dissolving acrylonitrile in an organic solvent. The solvent is filtered and dry-spun. Fibers are drawn at high temperature to 3 to 8 times their original length and the molecules are oriented into long parallel chains. |
| Properties | Resistant to dilute acids and alkalies, solvents, insects, mildew, weather. Damaged by alkalies and acids, heat above 356° F (180° C), acetone, ketones. |
| Uses | Sweaters, women’s coats, men’s winter suiting, carpets, blankets, out- door fabrics, knits, fur-like fabrics, blankets. Orion® and Acrilan® have been used as wool substitutes. |
| Trade names | Orion® (E.I. duPont de Nemours & Co., Inc.), Acrilan® (Monsanto Co.), Cantrece® (E.I. duPont de Nemours & Co., Inc.). |
| Modacrylic | |
| Composition | 35 to 85% acrylonitrile units. |
| Processing | Union Carbide makes Dynel®, a staple copolymer modacrylic fiber made from resin of 40% acrylonitrile and 60% vinyl chloride. It is converted into staple in a continuous wet-spinning process. The resin powder dissolved in acetone, filtered and spun. Fiber is dried, cut and crimped. |
| Uses | Dynel® resembles wool. Used for work clothing, water-softener bags, dye nets, filter cloth, blankets, draperies, sweaters, pile fabric. |
| Trade names | Verel®-copolymer (Tennessee Eastman Co.), Dynel®-copolymer (E.I. duPont de Nemours & Co., Inc.) |
| Polyester | |
| Compostition | 85% ester of a dihydnc alcohol and terephthalic acid. |
| Processing | Melt spinning. |
| Properties | Resistant to weak acids and alkalies, solvents, oils, mildew, moths. Damaged by phenol, heat above 338° F (170° C). |
| Uses | Apparel, curtains, rope, twine, sailcloth, belting, fiberfill, tire cord, belts, blankets, blends with cotton. |
| Trade Names | Decron® (E. I. duPont de Nemours & Co., Inc.), Kodel® (Tennessee Eastman Co.), Fortrel® (Fiber Industries, Inc.) |
| Rayon | |
| Composition | The pioneer artificial fibers viscose, cuprammonium cellulose, and cellulose acetate were orginally referred to as rayon. This name now is reserved for viscose. Rayon is now a generic name for a semisythetic fiber composed of regenerated cellulose and manufatured fibers consisting of regenerated cellulose in which substituents have replaced not more than 15% of the hydroxyl group hydrogens. |
| Processing | Rayon was first made by denitration of cellulose nitrate fibers, but now most is made from wood pulp by the viscose process. This viscose process produces filaments of regenerated cellulose. First, a solution of cellulose undergoes chemical reaction, ageing, or solution ripening; followed by filtration and removal of air; spinning of fiber; combining of the filaments into yarn; and finishing (bleaching, washing, oiling, and drying). |
| Properties | Rayon can be selectively dyed in combination with cotton. Hydroxyl groups in the cellulose molecules cause the fiber to absorb water—this causes low wet strength. In the dry state, the hydroxyl groups are hydrogen bonded, and the molecules are held together. Thus the dry fibers maintain their strength even at high temperatures. |
| Uses | High tenacity viscose yarn is used in cords for tires, hose, and belting. Strength is achieved by orienting the fiber molecules when they are made. Textile rayon is used primarily in women’s apparel, draperies, upholstery, and in blends with wool in carpets and rugs. Surgical dressings. |
| Acetate (Cellulose Acetate) | |
| Composition | Cellulose acetate and its homologs are esters of cellulose and are not regenerated cellulose. Where not less than 92% of the hydroxyl groups are acetylated, the product is called a triacetate. |
| Processing | Cellulose is converted to cellulose acetate by treatment with a mix containing acetic anhydride. No process exists whereby the desired number of acetyl groups can be achieved directly. The process involves first producing the triacetate, then hydrolyzing a portion of the acetate groups. The desired material is usually about half way between triacetate and diacetate. Arnel® (cellulose triacetate) is produced by Celanese Corp. It is a machine-washable fiber, that shows low shrinkage when stretched, and has good crease and pleat resistance. |
| Uses | Blankets, carpets, modacrylic fibers, cigarette filters. |
| Trade Names | Arnel® (Celanese Corp.). |
| Vinyls and Vinylidenes | |
| Composition | Saran is a copolymer of vinyl chloride and vinylidene chloride (at least 80% by weight vinylidene chloride units). Vinyon is the trade name given to copolymers of 90% vinyl chloride and 10% vinyl acetate (at least 85% vinyl chloride units). |
| Processing | Saran is prepared by mixing the two monomers and heating. The copolymer is heated, extruded at 356° F (180° C), air-cooled, and stretched. The vinyon copolymer is dissolved in acetone to 22% solids and filtered. The fibers are extruded by dry spinning, left to stand, then wet-twisted and stretched. The fibers are resistant to acids and alkalies, sunlight, and aging. Vinyon is useful in heat-sealing fabrics, work clothing. Bayer chemists first spun polyvinyl chloride into this chemically resistant and rot-proof fiber in 1931. |
| Properties | These fibers are resistant to mildew, bacterial, and insect attack. Polyvinyl chloride is resistant to acids and alkalies, insects, mildew, alcohol, oils. Polyvinylidene chloride is resistant to acids, most alkalies, alcohol, bleaches, insects, mildew, and weather. Polyvinyl chloride is damaged by ethers, esters, aromatic hydrocarbons, ketones, hot acids, and heat above 158° F (70° C). Polyvinylidene chloride is damaged by heat above 194° F (90° C) and by many solvents. |
| Uses | Saran can be used for insect screens. Widest use is for automobile seat covers and home upholstery. Typical polyvinyl chloride uses include nonwoven materials, felts, fibers, and blends with other fibers. Typical polyvinylidene chloride uses include outdoor fabrics, insect screens, curtains, upholstery, carpets, work clothes. |
| Trade Names | Proprietary polyvinylidene chloride names include Dynel® –copolymer (Uniroyal, Inc.). Saran is a generic name for polyvinylidene chloride. |
| Nylon | |
| Composition | Nylon is a generic name for a family of polyamide polymers characterized by the presence of an amide group. Common types are nylon 66, nylon 6, nylon 4, nylon 9, nylon 11, and nylon 12. |
| Processing | Nylon 66 was developed by Carothers by reacting adipic acid and hexamethylenediamine in 1935. Nylon 6 is based on caprolactam. It was developed by I. G. Farbenindustrie in 1940. |
| Properties | Resistant to alkalies, molds, solvents, moths. Damaged by strong acids, phenol, bleaches, and heat above 338° F (170° C). |
| Uses | Typical uses include tire cord, carpets, upholstery, apparel, belting, hose, tents, toothbrush bristles, hairbrushes, fish nets and lines, tennis rackets, parachutes, and surgical sutures. |
| Trade | Names Chemstrand nylon® (Monsanto Co.). |
| Spandex | |
| Composition | At least 85% by weight segmented polyurethane. |
| Processing | Segmented polyurethanes are produced by reacting diisocyanates with long–chain glycols. The product is chain-extended or coupled, then converted to fibers by dry spinning. |
| Properties | Resistant to solvents, oils, alkalies, insects, oxidation. Damaged by heat above 284° F (140° C), strong acids. |
| Uses | Fibers are used in foundation garments, hose, swimwear, surgical hose, and other elastic products. |
| Trade Names | Proprietary names include Lycra® (E. I. duPont de Nemours & Co., Inc.), Spandelle® (Firestone Synthetic Fibers Co.). |
| Olefin | |
| Composition | At least 85 wt% ethylene, propylene, or other olefin units other than amorphous rubber polyolefins. |
| Processing | Polymer is spun from a melt at about 212° F (100° C) above the melting point because the polymer is very viscous near its melting point. |
| Properties | Difficult to dye. Low melting points. Polypropylene has a very low specific gravity, making it very light and suitable for blankets. It has 3 to 4 times the resistance of nylon to snags and runs, and is softer, smoother, and lighter. Polypropylene is resistant to alkalies, acids, solvents, insects, mildew. Polyethylene is resistant to alkalies, acids (except nitric), insects, mildew. Polypropylene is damaged by heat above 230° F (110° C). Polyethylene is damaged by oil and grease, heat above 212° F (100° C), oxidizers. |
| Uses | Olefins make excellent ropes, laundry nets, carpets, blankets, and carpet backing. Polypropylene is typically used for rope, twine, outdoor fabrics, carpets, upholstery. High density polyethylene is typically used for rope, twine, and fishnets. Low density polyethylene is typically used for outdoor fabrics, filter fabrics, decorative coverings. |
| Trade Names | Proprietary names for polypropylene include Herculon® (Hercules Powder Co.), Polycrest® (Uniroyal, Inc.); proprietary polyethylene names include DLP® (W. R. Grace & Co.). |
| Fluorocarbon | |
| Composition | Long chain carbon molecules with bonds saturated by fluorine. Teflon is polytetrafluorethylene. |
| Processing | Fluorocarbon sheets are made by combining polytetrafluoroethylene with another microgranular material to form thin, flexible sheets. The filler is then dissolved out, leaving a pure, porous polytetrafluorethylene sheet. The pores must be small enough to be vapor permeable but large enough to extend through the fabric. The sheet has to be very thin, and is therefore fragile. GoreTex® has to protected by being sandwiched between robust fabrics such as polyester or nylon weave. |
| Properties | As a fiber, Teflon is highly resistant to oxidation and the action of chemicals, including strong acids, alkalies, and oxidizing agents. It is nonflammable. It retains these properties at high temperatures 446°–554° F (230°–290° C). It is strong and tough. It exhibits low friction, which coupled with its chemical inertness, makes it suitable in pump packings and shift bearings. Polytetraflurothylene is resistant to almost all chemicals, solvents, insects, mildew. Polytetrafluoroethylene is damaged by heat above 482° F (250° C), and by fluorine at high temperatures. |
| Uses | Typical uses include corrosion–resistant packings, etc., tapes, filters, bearings, weatherproof outdoorwear. |
| Trade Name | Teflon® (E.I. duPont de Nemours & Co., Inc.) and GoreTex® (W.L. Gore & Associates) are proprietary names. |
| Vinal | |
| Composition | Vinal is the U.S. term for vinyl alcohol fibers. At least 50 wt% of the long synthetic polymer chain is composed of vinyl alcohol units. The total of the vinyl alcohol units and any one or more of the various acetal units is at least 85 wt% of the fiber. |
| Processing | Vinyl acetate is first polymerized, then saponified to polyvinyl alcohol. The fiber is spun, then treated with formalin and heat to make it insoluble in water. Production has remained largely confined to |
| Properties | The fiber has reasonable tensile strength, a moderately low melting point (432°F [222°C]), limited elastic recovery, good chemical resistance, low affinity for water, good resistance to mildew and fungi. Combustible. Used for fishing nets, stockings, gloves, hats, rainwear, swimsuits. Polyvinyl alcohol is resistant to acids, alkalies, insects, mildew, oils; it is damaged by heat above 320° F (160° C), phenol, cresol, and formic acid. |
| Uses | Used in bristles, filter cloths, sewing thread, fishnets, and apparel. Polyvinyl alcohol is typically used for a wide range of industrial and apparel uses, rope, work clothes, fish nets. |
| Azlon | |
| Composition | Any regenerated naturally occurring protein. Azlon is the generic name for manufactured fiber in which the fiber–forming substance is composed of any regenerated naturally occurring protein. Proteins from corn, soybeans, peanuts, fish, and milk have been used. Azlon consists of polymeric amino acids. |
| Processing | Vegetable matter is first crushed and the oil is extracted. Then the remaining protein matter is dissolved in a caustic solution and aged. The resulting viscous solution is extruded through a spinneret into an acid bath to coagulate the filaments. The fiber is curedand stretched to give it strength. Then the fiber is washed, dried, and used in a filament or staple form. Casein fibers are extracted from skim milk, then dissolved inwater, and extruded under heat and pressure. The filaments are hardened and aged in an acid bath. Then they are washed, dried, and used in either filament or staple form. Seaweed fibers are made by extracting sodium alginate form brown seaweed using an alkali. The resulting solution is purified, filtered, and wet spun into a coagulating bath to form the fibers. |
| Properties | Azlon fibers have a soft hand, and blend well with other fibers. Combustible. |
| Uses | Used in blends to add a wool–like hand to other fibers, and to add loft, softness, and resiliency. Protein fibers resist moths and mildew, do not shrink, and impart a cashmere–like hand to blended fabrics. |
Polymeric fibers
Most synthetic fibers are polymer-based and are produced by a process known as spinning, in which a polymeric liquid is extruded through fine holes known as spinnerets. After spinning, the resulting fibers are oriented by stretching or drawing out, which increases the polymeric chain orientation and degree of crystallinity, and improves the fibers’ modulus and tensile strength. Fiber manufacture is classified by the type of spinning that the liquid polymer undergoes: melt, dry, or wet spinning.
Melt spinning is the simplest of these methods, The polymer is melted and forced through the spinnerets that contain from 50 to 500 holes. The fiber diameter immediately following extrusion exceeds the hole diameter. During cooling, the fiber is drawn to induce orientation. Further orientation may be achieved later by stretching the fiber to a higher draw ratio. Because melt spinning requires that the polymer be stable above its melting temperature, it is used with materials such as nylon, polyethylene, polyvinyl chloride, cellulose triacetate, and polyethylene terephthalate, as well as in the multifilament extrusion of polypropylene.
In dry spinning, the polymer is first dissolved in a solvent, and the solution is extruded through the spinnerets. The solvent is then evaporated with hot air and collected for reuse. The fiber then passes over rollers and is stretched to orient the molecules and increase fiber strength. Cellulose acetate, cellulose triacetate, acrylic, modacrylic, aromatic nylon, and polyvinyl chloride are made by dry spinning.
In wet spinning, the polymer solution is spun into a coagulating solution to precipitate the polymer. This process has been used with acrylic, modacrylic, aromatic nylon, and polyvinyl chloride fibers. Viscose rayon is produced from regenerated cellulose by a wet spinning technique.
| Table 2. Artificial Nonpolymeric Fibers. (Thomson Gale.) | |
|---|---|
| Artificial, nonpolymeric fibers | |
| Glass | |
| Composition | Comprised primarily of silica. |
| Processing | Continous filament process— molten glass drawn into fibers, which are wound mechanically. Winding stretches the fibers. Subsequently formed into glass fiber yarns and cords. Staple fiber process—uses jets of compressed air to attenuate or draw out molten glass into fine fibers. Used for yarns of various sizes. Wool process—molten glass attenuated into long, resilient fibers. Forms glass wool, used for thermal insulation or fabricated into other items. |
| Properties | Nonflammable. Can be subjected to temperatures as high as 1200° F (650° C) before they deteriorate. Non–absorbent. Impervious. They resist most chemicals, and do not break when washed in water. Mothproof, mildew–proof, do not degrade in sunlight or with age. Strong. Among the strongest man–made fibers. Derived from limestone, silica sand, boric acid, clay, coal, and fluospar. Different amounts of these ingredients result in different properties. |
| Uses | Decorative fabrics, fireproof clothing, soundproofing, plastics reinforcement, tires, upholstery, electrical and thermal insulation, air filters, insect screens, roofing, ceiling panels. |
| Metal | |
| Composition | Whiskers are single–crystal fibers up to 2 in (5 cm) long. They are made from tungsten, cobalt, tantalum, and other metals, and are used largely in composite structures for specialized functions. Metallic yarns consist of metallized polyester film. |
| Processing | Filaments are alloys drawn through diamond dies to diameters as small as 0.002 cm. In ancient times, gold and silver threads were widely used in royal and ecclesiastical garments. Today, metallic yarns usually consist of a core of single–ply polyester film that is metallized on one side by vacuum–depositing aluminum. The film is then lacquered on both sides with clear or tinted colors. |
| Properties | Metallic whiskers may have extremely high tensile strength. Modern metallic yarns are soft, lightweight, and do not tarnish. |
| Uses | Whiskers are used in biconstituent structures composed of a metal and a polymeric material. Examples include aluminum filaments covered with cellulose acetate butyrate. Steels for tire cord and antistatic devices have also been developed. Metallic yarns are used for draperies, fabrics, suits, dresses, coats, ribbons, tapes, and shoelaces. |
| Trade Names | Producers of metallic yarns include Metlon Corp.; Metal Film Co.; and Multi–tex Products Co. Dobeckman Co. produced the first widely used metallic yarn under the tradename Lurex®. |
| Ceramic | |
| Composition | Alumina and silica. |
| Processing | Insertion of aluminum ions into silica. |
| Properties | Retains properties to 2300°F (1260°C), and under some conditions to 3000° F (1648° C), lightweight, inert to most acids and unaffected by hydrogen atmosphere, resilient. |
| Uses | Used for high temperature insulation of kilns and furnaces, packing expansion joints, heating elements, burner blocks, rolls for roller hearth furnaces and piping, fine filtration, insulating electrical wire and motors, insulating jet motors, sound deadening. |
| Trade Names | Fiberfrax® (Carborundum). |
| Carbon | |
| Composition | Carbonized rayon, polyacrylonitrile, pitch or coal tar. |
| Processing | High modulus carbon fibers are made from rayon, polyacrylonitrile, or pitch. Rayon fibers are charred at 413°– 662° F (200°– 350°C), then carbonized at 1832°– 3632°F (1000°– 2000° C). The resulting carbon fibers are then heat treated at 5432° F (3000° C) and stretched during the heat treatment. Carbon fibers are also obtained by heat treating polyacrylonitrile, coal tar, or petroleum pitch. |
| Properties | Capable of withstanding high temperatures. |
| Uses | Carbon fibers come in three forms. Low modulus fibers used for electrically conducting surfaces. Medium modulus fibers used for fabrics. High modulus fibers used for stiff yarn. Used in the manufacture of heat shields for aerospace vehicles and for aircraft brakes. Carbon fibers are also used to reinforce plastics. These plastics may be used for sporting goods and engineering plastics. |
Table 1 (Artificial Polymeric Fibers) provides detailed information about each of the important classes of spun fibers.
Other synthetic fibers
Besides the polymer-based synthetic fibers described above, there are other types of synthetic fibers that have special commercial applications. These include the fibers made of glass, metal, ceramics, and carbon described in Table 2 (Artificial, Nonpolymeric Fibers).
Resources
BOOKS
Basta, Nicholas. Shreve’s Chemical Process Industries. New York: McGraw-Hill Book Company. 1999.
Jerde, Judith. The New Encyclopedia of Textiles. New York: Facts on File, 1992.
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.
- Polymer
- —A substance, usually organic, composed of very large molecular chains that consist of recurring structural units. From the Greek “poly” meaning many, and “meros” meaning parts.
- Synthetic
- —Referring to a substance that either reproduces a natural product or that is a unique material not found in nature and is produced by means of chemical reactions.
Lynch, Charles T. Practical Handbook of Materials Science. Boca Raton, FL: CRC Press, Inc. 1989.
Sperling, L. H. Introduction to Physical Polymer Science. New York: John Wiley & Sons, Inc. 1992.
Artificial Fibers
Artificial fibers
Polymeric fibers
Most synthetic fibers are polymer-based, and are produced by a process known as spinning. This process involves extrusion of a polymeric liquid through fine holes known as spinnerets. After the liquid has been spun, the resulting fibers are oriented by stretching or drawing. This increases the polymeric chain orientation and degree of crystallinity, and has the effect of increasing the modulus and tensile strength of the fibers. Fiber manufacture is classified according to the type of spinning that the polymer liquid undergoes: this may be melt spinning, dry spinning, or wet spinning.
Melt spinning is the simplest of these three methods, but it still requires that the polymer constituent be stable above its melting temperature . In melt spinning, the polymer is melted and forced through the spinnerets, which may contain from 50-500 holes. The diameter of the fiber immediately following extrusion exceeds the hole diameter. During the cooling process, the fiber is drawn to induce orientation. Further orientation may later be achieved by stretching the fiber to a higher draw ratio . Melt spinning is used with polymers such as nylon, polyethylene, polyvinyl chloride, cellulose triacetate, and polyethylene terephthalate, and in the multifilament extrusion of polypropylene.
In dry spinning, the polymer is first dissolved in a solvent. The polymer solution is extruded through the spinnerets. The solvent is evaporated with hot air and collected for reuse. The fiber then passes over rollers, and is stretched to orient the molecules and increase the fiber strength. Cellulose acetate, cellulose triacetate, acrylic, modacrylic, aromatic nylon, and polyvinyl chloride are made by dry spinning.
In wet spinning, the polymer solution is spun into a coagulating solution to precipitate the polymer. This process has been used with acrylic, modacrylic, aromatic nylon, and polyvinyl chloride fibers. Viscose rayon is produced from regenerated cellulose by a wet spinning technique.
Table 1 (Artificial Polymeric Fibers) provides detailed information about each of the important classes of spun fibers.
Other synthetic fibers
Besides the polymer-based synthetic fibers described above, there are other types of synthetic fibers that have special commercial applications. These include the fibers made of glass , metal , ceramics , and carbon described in Table 2 (Artificial, Nonpolymeric Fibers).
Resources
books
Basta, Nicholas. Shreve's Chemical Process Industries. New York: McGraw-Hill Book Company. 1999.
| A crylic | |
| Compostion | At least 85% acrylonitrile units. Anidex is a cross-linked polyacrylat consisting of at least 50 wt% esters of a monohydric alcohol and acrylic acid. |
| Processing | Orlon® is made by dissolving acrylonitrile in an organic solvent. The solvent is filtered and dry-spun. Fibers are drawn at high temperature to 3 to 8 times their original length and the molecules are oriented into long parallel chains. |
| Properties | Resistant to dilute acids and alkalies, solvents, insects, mildew, weather. Damaged by alkalies and acids, heat above 356˚ F (180˚ C), acetone, ketones. |
| Uses | Sweaters, women's coats, men's winter suiting, carpets, blankets, outdoor fabrics, knits, fur-like fabrics, blankets. Orlon® and Acrilan® have been used as wool substitutes. |
| Trade Names | Orlon® (E.I. duPont de Nemours & Co., Inc.), Acrilan® (Monsanto Co.), Cantrece® (E.I. duPont de Nemours & Co., Inc.). |
| M odacrylic | |
| Composition | 35 to 85% acrylonitrile units. |
| Processing | Union Carbide makes Dynel®, a staple copolymer modacrylic fiber made from resin of 40% acrylonitrile and 60% vinyl chloride. It is converted into staple in a continuous wet-spinning process. The resin powder dissolved in acetone, filtered and spun. Fiber is dried, cut and crimped. |
| Uses | Dynel® resembles wool. Used for work clothing, water-softener bags, dye nets, filter cloth, blankets, draperies, sweaters, pile fabric. |
| Trade Names | Verel®-copolymer (Tennessee Eastman Co.), Dynel®-copolymer (E.I. duPont de Nemours & Co., Inc.) |
| P olyester | |
| Composition | 85% ester of a dihydric alcohol and terephthalic acid. |
| Processing | Melt spinning. |
| Properties | Resistant to weak acids and alkalies, solvents, oils, mildew, moths. Damaged by phenol, heat above 338˚ F (170˚ C). |
| Uses | Apparel, curtains, rope, twine, sailcloth, belting, fiberfill, tire cord, belts, blankets, blends with cotton. |
| Trade Names | Dacron® (E.I. duPont de Nemours & Co., Inc.), Kodel® (Tennessee Eastman Co.), Fortrel® (Fiber Industries, Inc. |
| R ayon | |
| Composition | The pioneer artificial fibers viscose, cuprammonium cellulose, and cellulose acetate were originally referred to as rayon. This name now is reserved for viscose. Rayon is now a generic name for a semisynthetic fiber composed of regenerated cellulose and manufactured fibers consisting of regenerated cellulose in which substituents have replaced not more than 15% of the hydroxyl group hydrogens. |
| Processing | Rayon was first made by denitration of cellulose nitrate fibers, but now most is made from wood pulp by the viscose process. The viscose process produces filaments of regenerated cellulose. First, a solution of cellulose undergoes chemical reaction, ageing, or solution ripening; followed by filtration and removal of air; spinning of fiber; combining of the filaments into yarn; and finishing (bleaching, washing, oiling, and drying). |
| Properties | Rayon can be selectively dyed in combination with cotton. Hydroxyl groups in the cellulose molecules cause the fiber to absorb water—this causes low wet strength. In the dry state, the hydroxyl groups are hydrogen bonded, and the molecules are held together. Thus the dry fibers maintain their strength even at high temperatures. |
| Uses | High tenacity viscose yarn is used in cords for tires, hose, and belting. Strength is achieved by orienting the fiber molecules when they are made. Textile rayon is used primarily in women's apparel, draperies, upholstery, and in blends with wool in carpets and rugs. Surgical dressings. |
| A cetate( cellulose acetate) | |
| Composition | Cellulose acetate and its homologs are esters of cellulose and are not regenerated cellulose. Where not less than 92% of the hydroxyl groups are acetylated, the product is called a triacetate. |
| Processing | Cellulose is converted to cellulose acetate by treatment with a mix containing acetic anhydride. No process exists whereby the desired number of acetyl groups can be achieved directly. The process involves first producing the triacetate, then hydrolyzing a portion of the acetate groups. The desired material is usually about half way between triacetate and diacetate. |
| Arnel® (cellulose triacetate) is produced by Celanese Corp. It is a machine-washable fiber, that shows low shrinkage when stretched, and has good crease and pleat resistance. | |
| Uses | Blankets, carpets, modacrylic fibers, cigarette filters. |
| Trade Names | Arnel® (Celanese Corp.). |
| V inyls and vinylidenes | |
| Composition | Saran is a copolymer of vinyl chloride and vinylidene chloride (atleast 80% by weight vinylidene chloride units). Vinyon is the trade name given to copolymers of 90% vinyl chloride and 10% vinyl acetate (at least 85% vinyl chloride units). |
| Processing | Saran is prepared by mixing the two monomers and heating. The copolymer is heated, extruded at 356˚ F (180˚ C), air-cooled, and stretched. The vinyon copolymer is dissolved in acetone to 22% solids and filtered. The fibers are extruded by dry spinning, left to stand, then wet-twisted and stretched. The fibers are resistant to acids and alkalies, sunlight, and aging. Vinyon is useful in heat-sealing fabrics, work clothing. Bayer chemists first spun polyvinyl chloride into this chemically resistant and rot-proof fiber in 1931. |
| Properties | These fibers are resistant to mildew, bacterial, and insect attack. Polyvinyl chloride is resistant to acids and alkalies, insects, mildew, alcohol, oils. Polyvinylidene chloride is resistant to acids, most alkalies, alcohol, bleaches, insects, mildew, and weather. Polyvinyl chloride is damaged by ethers, esters, aromatic hydrocarbons, ketones, hot acids, and heat above 158˚ F (70˚ C). Polyvinylidene chloride is damaged by heat above 194˚ F (90˚ C) and by many solvents. |
| Uses | Saran can be used for insect screens. Widest use is for automobile seat covers and home upholstery. Typical polyvinyl chloride uses include nonwoven materials, felts, filters, and blends with other fibers. Typical polyvinylidene chloride uses include outdoor fabrics, insect screens, curtains, upholstery, carpets, work clothes. |
| Trade Names | Proprietary polyvinylidene chloride names include Dynel®-copolymer (Uniroyal, Inc.). Saran is a generic name for polyvinylidene chloride. |
| N ylon | |
| Composition | Nylon is a generic name for a family of polyamide polymers characterized by the presence of an amide group. Common types are nylon 66, nylon 6, nylon 4, nylon 9, nylon 11, and nylon 12. |
| Processing | Nylon 66 was developed by Carothers by reacting adipic acid and hexamethylenediamine in 1935. Nylon 6 is based on caprolactam. It was developed by I.G. Farbenindustrie in 1940. |
| Properties | Resistant to alkalies, molds, solvents, moths. Damaged by strong acids, phenol, bleaches, and heat above 338˚ F (170˚ C). |
| Uses | Typical uses include tire cord, carpets, upholstery, apparel, belting, hose, tents, toothbrush bristles, hairbrushes, fish nets and lines, tennis rackets, parachutes, and surgical sutures. |
| Trade Names | Chemstrand nylon® (Monsanto Co.). |
| S pandex | |
| Composition | At least 85% by weight segmented polyurethane. |
| Processing | Segmented polyurethanes are produced by reacting diisocyanates with long-chain glycols. The product is chain-extended or coupled, then converted to fibers by dry spinning. |
| Properties | Resistant to solvents, oils, alkalies, insects, oxidation. Damaged by heat above 284˚ F(140˚ C), strong acids. |
| Uses | Fibers are used in foundation garments, hose, swimwear, surgical hose, and other elastic products. |
| Trade Names | Proprietary names include Lycra® (E.I. duPont de Nemours & Co., Inc.), Spandelle® (Firestone Synthetic Fibers Co.). |
| O lefin | |
| Composition | At least 85 wt% ethylene, propylene, or other olefin units other than amorphous rubber polyolefins. |
| Processing | Polymer is spun from a melt at about 212˚ F (100˚ C) above the melting point because the polymer is very viscous near its melting point. |
| Properties | Difficult to dye. Low melting points. Polypropylene has a very low specific gravity, making it very light and suitable for blankets. It has 3 to 4 times the resistance of nylon to snags and runs, and is softer, smoother, and lighter. Polypropylene is resistant to alkalies, acids, solvents, insects, mildew. Polyethylene is resistant to alkalies, acids (except nitric), insects, mildew. Polypropylene is damaged by heat above 230˚ F (110˚ C). Polyethylene is damaged by oil and grease, heat above 212˚ F (100˚ C), oxidizers. |
| Uses | Olefins make excellent ropes, laundry nets, carpets, blankets, and carpet backing. Polypropylene is typically used for rope, twine, outdoor fabrics, carpets, upholstery. High density polyethylene is typically used for rope, twine, and fishnets. Low density polyethylene is typically used for outdoor fabrics, filter fabrics, decorative coverings. |
| Trade Names | Proprietary names for polypropylene include Herculon® (Hercules Powder Co.), Polycrest® (Uniroyal, Inc.); proprietary polyethylene names include DLP® (W. R. Grace & Co.). |
| F luorocarbon | |
| Composition | Long chain carbon molecules with bonds saturated by fluorine. Teflon is polytetrafluoroethylene. |
| Processing | Fluorocarbon sheets are made by combining polytetrafluoroethylene with another microgranular material to form thin, flexible sheets. The filler is then dissolved out, leaving a pure, porous polytetrafluroethylene sheet. The pores must be small enough to be vapor permeable but large enough to extend through the fabric. The sheet has to be very thin, and is therefore fragile. GoreTex® has to protected by being sandwiched between robust fabrics such as polyester or nylon weave. |
| Properties | As a fiber, Teflon is highly resistant to oxidation and the action of chemicals, including strong acids, alkalies, and oxidizing agents. It is nonflammable. It retains these properties at high temperatures 446˚-554˚ F (230˚-290˚ C). It is strong and tough. It exhibits low friction, which coupled with its chemical inertness, makes it suitable in pump packings and shift bearings. Polytetrafluoroethylene is resistant to almost all chemicals, solvents, insects, mildew. Polytetrafluoroethylene is damaged by heat above 482˚ F (250˚ C), and by fluorine at high temperatures. |
| Uses | Typical uses include corrosion-resistant packings, etc., tapes, filters, bearings, weatherproof outdoorwear. |
| Trade Name | Teflon® (E.I. duPont de Nemours & Co., Inc.) and GoreTex® (W. L. Gore & Associates) are proprietary names. |
| V inal | |
| Composition | Vinal is the U.S. term for vinyl alcohol fibers. At least 50 wt% of the long synthetic polymer chain is composed of vinyl alcohol units. The total of the vinyl alcohol units and any one or more of the various acetal units is at least 85 wt% of the fiber. |
| Processing | Vinyl acetate is first polymerized, then saponified to polyvinyl alcohol. The fiber is spun, then treated with formalin and heat to make it insoluble in water. Production has remained largely confined to Japan. |
| Properties | The fiber has reasonable tensile strength, a moderately low melting point (432˚ F [222˚ C]), limited elastic recovery, good chemical resistance, and resistance to degradation by organisms. Has good chemical resistance, low affinity for water, good resistance to mildew and fungi. Combustible. Used for fishing nets, stockings, gloves, hats, rainwear, swimsuits. Polyvinyl alcohol is resistant to acids, alkalies, insects, mildew, oils; it is damaged by heat above 320˚ F (160˚ C), phenol, cresol, and formic acid. |
| Uses | Used in bristles, filter cloths, sewing thread, fishnets, and apparel. Polyvinyl alcohol is typically used for a wide range of industrial and apparel uses, rope, work clothes, fish nets. |
| A zlon | |
| Composition | Any regenerated naturally occurring protein. Azlon is the generic name for manufactured fiber in which the fiber-forming substance is composed of any regenerated naturally occurring protein. Proteins from corn, soybeans, peanuts, fish, and milk have been used. Azlon consists of polymeric amino acids. |
| Processing | Vegetable matter is first crushed and the oil is extracted. Then the remaining protein matter is dissolved in a caustic solution and aged. The resulting viscous solution is extruded through a spinneret into an acid bath to coagulate the filaments. The fiber is cured and stretched to give it strength. Then the fiber is washed, dried, and used in a filament or staple form. Casein fibers are extracted from skim milk, then dissolved in water, and extruded under heat and pressure. The filaments are hardened and aged in an acid bath. Then they are washed, dried, and used in either filament or staple form. Seaweed fibers are made by extracting sodium alginate from brown seaweed using an alkali. The resulting solution is purified, filtered, and wet spun into a coagulating bath to form the fibers. |
| Properties | Azlon fibers have a soft hand, and blend well with other fibers. Combustible. |
| Uses | Used in blends to add a wool-like hand to other fibers, and to add loft, softness, and resiliency. Protein fibers resist moths and mildew, do not shrink, and impart a cashmere-like hand to blended fabrics. |
| G lass | |
| Composition | Comprised primarily of silica. |
| Processing | Continuous filament process—molten glass drawn into fibers, which are wound mechanically. Winding stretches the fibers. Subsequently formed into glass fiber yarns and cords. Staple fiber process—uses jets of compressed air to attenuate or draw out molten glass into fine fibers. Used for yarns of various sizes. Wool process—molten glass attenuated into long, resilient fibers. Forms glass wool, used for thermal insulation or fabricated into other items. |
| Properties | Nonflammable. Can be subjected to temperatures as high as 1200˚ F (650˚ C) before they deteriorate. Non-absorbent Impervious. They resist most chemicals, and do not break when washed in water. Mothproof, mildew-proof, do not degrade in sunlight or with age. Strong. Among the strongest man-made fibers. Derived from limestone, silica sand, boric acid, clay, coal, and fluospar. Different amounts of these ingredients result in different properties. |
| Uses | Decorative fabrics, fireproof clothing, soundproofing, plastics reinforcement, tires, upholstery, electrical and thermal insulation, air filters, insect screens, roofing, ceiling panels. |
| M etal | |
| Composition | Whiskers are single-crystal fibers up to 2 in (5 cm) long. They are made from tungsten, cobalt, tantalum, and other metals, and are used largely in composite structures for specialized functions. Metallic yarns consist of metallized polyester film. |
| Processing | Filaments are alloys drawn through diamond dies to diameters as small as 0.002 cm. In ancient times, gold and silver threads were widely used in royal and ecclesiastical garments. Today, metallic yarns usually consist of a core of single-ply polyester film that is metallized on one side by vacuum-depositing aluminum. The film is then lacquered on both sides with clear or tinted colors. |
| Properties | Metallic whiskers may have extremely high tensile strength. Modern metallic yarns are soft, lightweight, and do not tarnish. |
| Uses | Whiskers are used in biconstituent structures composed of a metal and a polymeric material. Examples include aluminum filaments covered with cellulose acetate butyrate. Steels for tire cord and antistatic devices have also been developed. Metallic yarns are used for draperies, fabrics, suits, dresses, coats, ribbons, tapes, and shoelaces. |
| Trade Names | Producers of metallic yarns include Metlon Corp.; Metal Film Co.; and Multi-tex Products Co. Dobeckman Co. produced the first widely used metallic yarn under the tradename Lurex®. |
| C eramic | |
| Composition | Alumina and silica. |
| Processing | Insertion of aluminum ions into silica. |
| Properties | Retains properties to 2300˚ F (1260˚ C), and under some conditions to 3000˚ F (1648˚ C), lightweight, inert to most acids and unaffected by hydrogen atmosphere, resilient. |
| Uses | Used for high temperature insulation of kilns and furnaces, packing expansion joints, heating elements, burner blocks, rolls for roller hearth furnaces and piping, fine filtration, insulating electrical wire and motors, insulating jet motors, sound deadening. |
| Trade Names | Fiberfrax® (Carborundum). |
| C arbon | |
| Composition | Carbonized rayon, polyacrylonitrile, pitch or coal tar. |
| Processing | High modulus carbon fibers are made from rayon, polyacrylonitrile, or pitch. Rayon fibers are charred at 413˚-662˚ F (200˚-350˚ C), then carbonized at 1832˚-3632˚ F (1000˚ to 2000˚ C). The resulting carbon fibers are then heat treated at 5432˚ F (3000˚ C) and stretched during the heat treatment. Carbon fibers are also obtained by heat treating polyacrylonitrile, coal tar or petroleum pitch. |
| Properties | Capable of withstanding high temperatures. |
| Uses | Carbon fibers come in three forms. Low modulus fibers used for electrically conducting surfaces. Medium modulus fibers used for fabrics. High modulus fibers used for stiff yarn. Used in the manufacture of heat shields for aerospace vehicles and for aircraft brakes. Carbon fibers are also used to reinforce plastics. These plastics may be used for sporting goods and engineering plastics. |
Jerde, Judith. The New Encyclopedia of Textiles. New York: Facts on File, 1992.
Lynch, Charles T. Practical Handbook of Materials Science. Boca Raton, FL: CRC Press, Inc. 1989.
Sperling, L. H. Introduction to Physical Polymer Science. New York: John Wiley & Sons, Inc. 1992.
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.
- Nonpolymeric fibers
—Fibers made of materials other than polymeric liquid, including glass, metal, ceramics, and carbon. These fibers have special commercial applications.
- Polymer
—A substance, usually organic, composed of very large molecular chains that consist of recurring structural units. From the Greek "poly" meaning many, and "meros" meaning parts.
- Polymeric fibers
—Fibers created by "spinning" and divided into the following classes: acrylic, modacrylic, rayon, acetate, vinyls and vinylidenes, nylon, spandex, olefin, fluorocarbon, vinal, and azlon.
- Spinning
—The process by which most polymer-based synthetic fibers are created. It involves extrusion of polymeric liquid through spinnerets. Fiber manufacture is classified by the type of spinning involved: melt spinning, dry spinning, or wet spinning.
- Synthetic
—Referring to a substance that either reproduces a natural product or that is a unique material not found in nature, and which is produced by means of chemical reactions.
Artificial Fibers
Artificial fibers
An artificial fiber is a threadlike material invented by human researchers. Such fibers do not exist naturally. Some examples of artificial fibers include nylon, rayon, Dacron™, and Orlon™. These terms illustrate that some names of artificial fibers are, or have become, common chemical names (nylon and rayon), while others (Dacron™ and Orlon™) are proprietary names. Proprietary names are names that are owned by some company and are properly written to indicate that the name is a registered trademark (™).
Most artificial fibers are polymers. A polymer is a chemical substance that is produced when one or two small molecules are reacted with each other over and over again. The beginning molecule used in making a polymer is called a monomer. When two different monomers are used, the product that results is called a copolymer.
An example of a copolymer is nylon, first invented by American chemist Wallace Carothers (1896–1937) in 1928. The two monomers of which nylon is made are complicated substances called adipic acid and hexamethylenediamine. For simplicity, call the first monomer A and the second monomer B. A molecule of nylon, then, has a structure something like this:
-A-B-A-B-A-B-A-B-A-B-A-B
The dashes at the beginning and end of the molecule indicate that the -A-B- sequences goes on and on until it contains hundreds or thousands of monomer units.
The usual process by which artificial fibers are produced is called spinning. When a polymer is first produced, it is generally a thick, viscous (sticky) liquid. That liquid is forced through a disk containing fine holes known as a spinneret. The spinneret may be suspended in the air or it may be submerged under water. As the polymeric liquid passes through the spinneret holes, it become solid, forming long, thin threads.
The properties of an artificial fiber can be changed in a number of ways, including the way in which the polymer is first produced, additives that may be attached to the polymer, and the way the polymer is processed through the spinneret.
Other synthetic fibers
Artificial fibers can be made by processes other than polymerization. Glass fibers, for example, can be produced by melting certain kinds of glass and then forcing the melted material through a spinneret to form long, thin threads. Many of these artificial fibers not made from polymers are the result of recent chemical research and show exciting promise for new applications in industry.
[See also Polymer ]
Artificial Fibers
Artificial Fibers
Investigation of a crime or accident scene involves the collection of evidence . This collection must be scrupulous; every piece of evidence is important in deciphering the course of events, identifying the victim, and in implicating a suspect.
One piece of evidence that can be important is fibers ; the material that makes up clothing and other material. Even wigs may be comprised of fibers.
Fibers can be made of a natural material (i.e., wool) or a synthetic compound or blend. The differentiation of these fibers types can be important. For example, if a suspect was wearing rayon trousers, then it would be of interest to determine if the fibers found at the scene were rayon.
Most synthetic fibers are polymer-based, and are produced by a process known as spinning. This process involves extrusion of a polymeric liquid through fine holes known as spinnerets. After the liquid has been spun, the resulting fibers are oriented by stretching or drawing out of the fibers. This increases the polymeric chain orientation and degree of crystallinity, and has the effect of increasing the modulus and tensile strength of the fibers.
Fiber manufacture is classified according to the type of spinning that the polymer liquid undergoes: melt spinning, dry spinning, or wet spinning.
Melt spinning is the simplest of these three methods, but it requires that the polymer constituent be stable above its melting temperature. In melt spinning, the polymer is melted and forced through the spinnerets, which may contain from 50 to 500 holes. The diameter of the fiber immediately following extrusion exceeds the hole diameter. During the cooling process, the fiber is drawn to induce orientation. Further orientation may later be achieved by stretching the fiber to what is known as a higher draw ratio.
Melt spinning is used with polymers such as nylon, polyethylene, polyvinyl chloride, cellulose triacetate, and polyethylene terephthalate, and in the multifilament extrusion of polypropylene.
In dry spinning, the polymer is first dissolved in a solvent. The polymer solution is extruded through the spinnerets. The solvent is evaporated with hot air and collected for reuse. The fiber then passes over rollers, and is stretched to orient the molecules and increase the fiber strength. Cellulose acetate, cellulose triacetate, acrylic, modacrylic, aromatic nylon, and polyvinyl chloride are made by dry spinning.
In wet spinning, the polymer solution is spun into a coagulating solution to precipitate the polymer. This process has been used with acrylic, modacrylic, aromatic nylon, and polyvinyl chloride fibers. Viscose rayon is produced from regenerated cellulose by a wet spinning technique.
In a forensic examination, fibers are most easily collected using adhesive tape. The collected fibers are separated based on color and other appearance characteristics (i.e., wooly versus string-like).
Forensic analysis of fibers is conducted in several ways. Synthetic fiber polymers can be suited to examination using infrared spectroscopy . Specified guidelines exist for this type of examination, which makes the technique standard and so more easily legally admissible.
The constituents of the dye that has been used to color fibers can be separated using chromatography , which can separate compounds based on differences of size or charge.
Artificial fibers can also act as lenses, by virtue of the drawing out process of manufacture. Based on the optical properties of a fiber, shining a light on it will either focus the light towards the center or the edge of the fiber. This can aid in identifying the nature of a fiber sample.
see also Crime scene investigation; Evidence; Fourier transform infrared spectrophotometer (FTIR).