A group of polyamide resins which are long-chain polymeric amides in which the amide groups form an integral part of the main polymer chain, and which have the characteristic that when formed into a filament the structural elements are oriented in the direction of the axis. Nylon was originally developed as a textile fiber, and high tensile strengths, above 50,000 lb/in2 (344Mpa), are obtainable in the fibers and films. But this high strength is not obtained in the molded or extruded resins because of the lack of oriented stretching. When nylon powder that has been precipitated from solution is pressed and sintered, the parts have high crystallinity and very high compressive strength, but they are not as though as molded nylon.
Nylons are produced from the polymerization of a dibasic acid and a diamine. The most common one of the group is that obtained by the reaction of adipic acid with hexamethylenediamine. The nylon molding and extruding resin of Du Pont, Elvamide 8042, formerly Zytel 42, has a tensile strength of 12,500 lb/in2 (106Mpa) with elongation above 100%,a flexural strength of 13,800 lb/in2 (95Mpa), hardness of Rockwell R118, a flow temperature of 480°F (249°C) and dielectric strength of 350 volts per mil (14 X 106 volts per meter).
All of the nylons are highly resistant to common solvents and to alkalies, but are attacked by strong mineral acids. Molded parts have light weight, with a specific gravity about 1.14, good shock-absorbing ability, good abrasion resistance, very low coefficient of friction, and high melting point, up to about 482°F (250°C). A disadvantage is their high water absorption and the resulting dimensional changes in moldings in service. They are much used for such parts as gears, bearings, cams, and linkages. The electrical characteristics are about the same as those of the cellulosic plastics. As a wire insulation, nylon is valued for its toughness and solvents resistance. Nylon fibers are strong, tough, and elastic, and have high gloss. The finer fibers are easily spun into yarns for weaving or knitting either alone or in blends with other fibers, and they can be crimped and heat-set. The Nylon fiber of the Firestone Tire & Rubber Co., used for making carpets, is nylon staple fiber, lofted, or wrinkled, to give the carpet a bulky texture resembling wool. Caprolan tire cord, made from nylon 6 of high molecular weight, has the yarn drawn to four or five time its original length to orient the polymer and give one-half twist per inch. Nylon film is made in thickness down to 0.002 in (0.005 cm) for heat-sealed wrapping, especially for food products where tight impermeable enclosures are needed. Nylon sheet, for gaskets and laminated facings, comes transparent or in colors in thickness from 0.005 to 0.060 in (0.013 to 0.152 cm). Nylon monofilament is used for brushes, surgical sutures, tennis strings, and fishing lines. Filament and fiber, when stretched, have a low specific gravity down to 1.068, and the tensile strength may be well above 50,000 lb/in2 (344MPa). Nylon fibers made by condensation with oxalic acid esters have high resistance to fatigue when wet.
Nylon 6 is made from caprolactam, which has the empirical formula (CH2)5NH ·C: O, with a single 6-carbon ring. Molded parts have a tensile strength of 11,700 lb/in2 (79MPa), elongation 70%, dielectric strength 440 volts per mil (17.3 X 106 volts per meter) and melting point 420°F (216°C). Nylon foam, or cellular nylon, for lightweight buoys and flotation products, is made from nylon 6. The foam is produced by Du Pont in slabs, rods, and sheets. Densities range from 1 to 8 lb/ft3 (16 to 128 kg/m3). The low densities are flexible, but the high-density material is rigid with a load-carrying capacity about the same as that of balsa wood. Nylon 6/10 is tough, relatively heat-resistance, and has a very low brittleness temperature. It absorbs about one-third as much moisture as type 6 and half as much as type 6/6. Nylon 9 is made from soybean oil by reacting with ozone. It has better water resistance than other nylons and is used for coatings. Nylon 11, originally marketed in France as Rilsan, is a polycondensation products of aminoundeconic acid which is made by a complex process from the recinoleic acid of castor oil. This type of nylon has superior dimensional stability and is valued for injection moldings. Nylon 12 is a similar plastic. It is a lauro lactam synthesized from butadiene. It has a low water absorption and good strength and stability, and it is used for packaging film, coatings for metals, and moldings. Nylon 4 is a polypyrrolidine used for textile fibers. The molecular chain has more amide groups than do the chains of the other nylons, and its ability to absorb moisture is about the same as that of cotton. Fabrics made from it do not have the hot feel usual with other synthetic fibers and they have better pressability and are free of static. Alrac Nylon, of the Radiation Research Corp., is nylon 4. Moldings of nylon 6/6 have a specific gravity of 1.14 and have a tensile strength of 11,500 lb/in2 (78MPa). It is used for gears and mechanical parts, and mechanical parts, and its physical properties may be further increased by adding glass fibers or spheres as fillers. Nylon copolymers of types 6 and 6/6 are flexible materials with extra-high impact resistance, even at —40°F (—40°C), and good heat resistanc .
Nylon products are marketed under many trade names. Nylatron G, of the Polymer Corp., is graphite-impregnated nylon in rods and strip for making gears, bearings, and packings. Nylasint, of this company, for bearings, is sintered nylon impregnated with oil. Flafon, of Hewitt-Robbins, Inc., is a rayon-nylon fabric with nylon traverse threads. It is flexible and has about twice the strength of cotton fabric. It is used for conveyor belts. Fiberthin, of the U.S. Rubber Co., is a thin waterproof fabric used to replaced heavier tarpaulins for protective coverings. It is woven of nylon and coated with plastic. It weighs 5 oz/yd2 (0.17 kg/m2) and has a tensile strength of 175 lb/in (31kg/cm) of width. Facilon, of the Sun Chemical Corp., a caprolan nylon fabric impregnated with vinyl resin, is used for facing wall panels and flexible floor coverings. It comes in colors and embossing.
Application of Nylon 6, Nylon 66, and Nylon 11·12
· Gears, cams, bearings
· Packaging materials
PA6 Nylon 6
PA6-GF Nylon 6 glass fiber 30%
PA66 Nylon 66
PA66-GF Nylon 66 glass fiber 30%
PA 11 • 12 Nylon 11 • 12
PA 46-GF Nylon • 46