Nylons (polyamides), the first of the thermoplastic engineering resins, were developed originally as high-strength textile These semicrystalline plastics are le in compositions for molding and extrudding, for solution and fluidized-bed gs, and for casting.
Nylons (dry as molded) ASTM or Type UL test Property 4/6 6/6 6 6/12 11 Cast 6 D79 PHYSICAL
Specific gravity 1.13 1.14 1.14 1.07 1.04 1.15 Specific volume (cu. inAb) 23.5 24.3 24.3 25.9 26.6 24.1 D570 Water absorption, 24 hr
1/8 in. thick (%) 2.3 1.5 1.6 0.4 0.4 1.6 D638 MECHANICAL
Tensile strength (psi) 14000 12000 11500 8800 8600 11000 D638 Elongation (%) 30 60 100 150 300 15-50 D790 Flexural modulus (Kpsi) 460 440 420 150 150 400 D2117 THERMAL
Melt point (crystalline)(°F) 663 509 428 419 374 419 D696 Coef. of thermal expansion
(IE-05 in/in/F) 4.2 4.4 4.5 5.0 5.1 5.0 D648 Deflection temperature (°F)
At 264 psi 240 190 152 150 180 140 UL94 Flammability rating V-2 V-2 V-2 - 2 - - HB D150 Dielectric constant, 73 °F
At 1 kHz 4.0 3.9 3.8 4.0 3.7 4.0 D257 Volume resistivity (ohm-cm) 1E + 15 1E + 16 1E + 15 1E + 12 IE + 13
Ion 6/6 is the most widely used of the n plastics because of its overall balance properties. The second most widely used nylon family is nylon 6. Type 6/6 nylon resins have higher heat resistance, abrasion resistance, strength, stiffness and hard than type 6 nylons. The type 6 nylon ns are tougher and more flexible than 6/6 nylons, and they have a wider proing window.
Nylon 6/12 absorbs less moisture and, refore, maintains both mechanical and ectrical properties better in high-humidity vironments. But the reduced moisture nsitivity is accompanied by lower ength, lower stiffness, lower use temperres, and higher cost.
Nylons 11 and 12 have lower moisture sorption combined with superior resisce to fuels, hydraulic oils, and most automotive fluids. The melting points of nylon 11 and 12 (355 to 365°F) are the lowest of the commercial polyamides. These two polyaraides are often combined with plasticizers to generate a flexible, tough material suitable for tubing extrusion. Recently nylon 12/12 has been introduced with a slightly higher use temperature while main taining good fuel resistance. Nylon 6/6T resins, available from BASF Corporation Plastic Materials, have low moisture absorption and they are much stronger, stiffer, tougher, fatigue resistant, and more heat resistant than type 6/6 nylons. The Ultramid type 6/6T resins also have better resistance to hot oils and fats than type 6/6 nylons. Reinforced grades of type 6/6T nylon resins also are available.
Nylon 4/6 is the latest version of the short repeat-unit polyamides. Its melting point of 565°F is 54 °F above that for nylon 6/6 and is the highest in the polyamide family. The inherent molecular symmetry of nylon 4/6 results in self -nucleation, rapid crystal growth and, thus, a higher level of crystallinity. This higher level of crystallinity leads to faster set up and, hence, faster inj ecti on -molding, cycles, up to 30% faster than for 6/6. Nylon 4/6 absorbs more water than nylon; however, its dimensional stability is similar to nylon 6/6 due to its high crystallinity.
Higher crystallinity has a major effect on nearly all properties leading to higher strength, higher stiffness, high heat-deflection temperature (HDT), high fatigue resistance, high wear resistance, and high creep resistance. Semicrystalline polymers maintain useful properties above the glass transition in contrast to amorphous polymers which transform into a viscous mass. Nylon 4/6, with its unusually high crystallinity, maintains a higher level of performance at elevated temperatures. The HDT for reinforced nylon 4/6 is 545°C.
Nylon resin is available in a wide range of reinforcement levels, filler types, toughening agents, stabilizers and flame-retardant additives. Newer flame retardants can provide good flammability ratings (UL 94V-0) while maintaining acceptable electrical properties.
Toughening technology has reduced notch sensitivity providing notched Izod values over 15 ft-lb/in. Some of these impact modifiers also provide Gardner dropweight impact strengths in excess of 480 inAb (1/8,in.-thick disks).
Nylon is available in several physical forms. Nylon 6 and certain block copolymers can be cast as monomer into large shapes that polymerize into solids at room temperature. Parts several inches thick and weighing several hundred pounds can be cast. Axially symmetric shapes can be extruded. Nylon rod, and plate and tubular bar are available as stock shapes. Tubing and profile extrusions are available as custom shapes.
Properties: Property comparisons among commercial grades of nylon vary widely because so many formulations are available. In general, however, nylons have excellent fatigue resistance, low coefficient of friction, good toughness (depending on degree of crystallinity), and they resist a wide spectrum of fuels, oils, and chemicals. They are inert to biological attack, and have adequate electrical properties for most voltages and frequencies.
The crystalline structure of nylons, which can be controlled to some degree in processing, affects stiffness, strength, and heat resistance. Low crystallinity imparts greater toughness, elongation, and impact resistance, but at the sacrifice of tensile strength and stiifness.
Nylons 6/6, 6/6T, and 4/6 have the lowest permeability of the nylons by gasoline, mineral oil, and fluorocarbon refrigerants. Nylon 6/12 and 6/6T are used where lower moisture absorption (and better dimensional stability) are needed.
All nylons absorb moisture from the environment, however, type 6/6T nylon has much lower moisture absorption than any other type of nylon resin. Moisture absorption leads to dimensional and property changes dependent upon the equilibrium level absorbed. At elevated temperatures, the moisture equilibrium level decreased above 190°, nylon begins to dry out by a combination of internal diffusion and surface volatile emission. Extended exposure to temperatures above 250° F will reduce moisture content to about 0.1% (similar to dry-as-molded content).
Nylons are sensitive to ultraviolet (UV) radiation. Weatherability will be reduced unless UV stabilizers are incorporated into the formulation. Carbon black is the most commonly used UV stabilizer. Carbon black lowers the ductility and toughness as a trade-off for UV stability.
Nylons have good resistance to creep and cold flow compared to many less rigid thermoplastics. Creep resistance is better at higher levels of crystallinity as demonstrated in nylon 4/6. Creep can be calculated from long-term apparent modulus under load data.