Polyamide (PA) is one of the five major engineering plastics due to its wide variety, large output and wide application. However, due to the wide variety of polyamides, some products have similarities in application fields, and some have considerable differences, which require careful distinction.
Polyamide, commonly known as nylon, is a general term for thermoplastic resins containing repeating amide groups—[NHCO]—on the molecular backbone.
The main varieties of nylon are PA6 and PA66, occupying an absolute dominant position; followed by PA11, PA12, PA610, PA612, and PA1010, PA46, PA7, PA9, PA13. New varieties include nylon 6I, nylon 9T, special nylon MXD6 (barrier resin), etc.; modified varieties include: reinforced nylon, monomer cast nylon (MC nylon), reaction injection molding (RIM) nylon, aromatic nylon, transparent nylon , High impact (super tough) nylon, electroplated nylon, conductive nylon, flame-retardant nylon, nylon and other polymer blends and alloys, etc.
Nylon is a tough angular translucent or milky white crystalline resin. The molecular weight of nylon as an engineering plastic is generally 15,000 to 30,000. Nylon has high mechanical strength, high softening point, heat resistance, low friction coefficient, abrasion resistance, self-lubrication, shock absorption and noise reduction, oil resistance, weak acid resistance, alkali resistance and general solvent; good electrical insulation, It is self-extinguishing, non-toxic, odorless, and good weather resistance. Nylon has a very good affinity with glass fiber, so it is easy to strengthen. However, nylon has poor dyeability and is not easy to color. Nylon has high water absorption, which affects dimensional stability and electrical properties. Fiber reinforcement can reduce the water absorption rate of resin so that it can work under high temperature and high humidity. Among them, nylon 66 has the highest hardness and rigidity, but the toughest. The flammability of nylon is UL94V2, and the oxygen index is 24-28. The decomposition temperature of nylon is >299℃, spontaneous combustion will occur at 449℃-499℃. Nylon has good melt fluidity, so the wall thickness of the product can be as small as 1mm. Table 1 shows the technical performance indicators of the main varieties of polyamide.
Performance characteristics and uses
Physical properties: milky white or light yellow transparent to opaque keratinous crystalline polymer; freely colorable, toughness, abrasion resistance, good self-lubricity, low rigidity, low temperature resistance, bacteria resistance, slow burning, slow extinguishing from fire, dripping Falling, blistering phenomenon. The maximum operating temperature can reach 180℃, and it will drop to 160℃ after adding impact modifier; it can be increased to 199℃ with 15%-50% glass fiber reinforced, and inorganic filled PA can increase its heat distortion temperature.
Processing The molding processability is excellent: injection molding, blow molding, casting, spraying, powder molding, machining, welding, and bonding can be used.
PA6 is the PA with the highest water absorption rate, which has poor dimensional stability and affects electrical performance (breakdown voltage).
Application Bearings, gears, cams, rollers, pulleys, rollers, screws, nuts, gaskets, high-pressure oil pipes, oil storage containers, etc.
A translucent or opaque milky white crystalline polymer that emits purple-white or blue-white light when exposed to ultraviolet light. It has high mechanical strength and good stress crack resistance. It is the PA with the best abrasion resistance and has excellent self-lubricating properties. Second to polytetrafluoroethylene and polyoxymethylene, it also has better heat resistance. It is a self-extinguishing material with good chemical stability, especially oil resistance, but it is easily soluble in polar solvents such as phenol and formic acid. It can be added with carbon black. Improve weather resistance; high water absorption, so poor dimensional stability.
Processing The molding processability is good, and it can be used for injection molding, extrusion, blow molding, spraying, casting molding, machining, welding, and bonding.
The application is basically the same as nylon 6, and it can also be used as a handle, shell, support frame, etc.
Translucent, milky white crystalline thermoplastic polymer with properties between PA6 and PA66, but with low relative density, good mechanical strength and toughness; low water absorption, so good dimensional stability; strong alkali resistance, better than PA6 And PA66 is more resistant to weak acids and organic solvents, but it is also soluble in phenols and formic acid; it is a self-extinguishing material. As an important engineering plastic, nylon 610 (PA610) can be used to make various structural parts, but under high temperature (≥150℃), brine, oil and strong external force impact, the structural parts will deform or even break, so it must modified. Modification methods include grafting, copolymerization, blending, in-situ polymerization, filling and cross-linking, etc., but a single modification cannot achieve satisfactory results. Using glass fiber (GF) reinforcement and irradiation to modify PA610 can improve the mechanical strength, temperature resistance, oil and water resistance of PA610.
Application Machinery manufacturing (automobile gears, gaskets, bearings, pulleys, etc.), precision parts, oil pipelines, oil storage containers, transmission belts, instrument housings, textile machinery parts, etc.
Physical properties In addition to the general characteristics of PA, it also has the advantages of relatively small width, low water absorption, good dimensional stability, and high tensile strength and impact strength.
Application Precision mechanical parts, wire and cable insulation, butt stock, ammunition box tool holder, coil, etc.
Physical properties: white, translucent crystalline polymer, low relative density, low melting point, low water absorption, good dimensional stability, good flexibility, tortuous resistance, good low-temperature impact resistance, wide molding temperature range, good fiber formation, poor dyeability, It can be modified by adding graphite, molybdenum disulfide, and glass fiber.
Processing Using general thermoplastic molding technology, it can be sintered, cast into film, metal surface electrostatic powder coating, flame spraying, and foaming.
Application Hard pipes and hoses for conveying gasoline, cable sheaths, food packaging films, foamed building materials, electrostatic spraying, etc.
Physical properties: Nylon 12 and nylon 11 have similar properties, low relative density, only 1.02, which is the smallest in the nylon series; low water absorption, good dimensional stability; excellent low temperature resistance, up to -70°C; low melting point, easy molding and processing, The molding temperature range is wide; the flexibility, chemical stability, oil resistance and abrasion resistance are all good, and it is a self-extinguishing material. The long-term use temperature is 80°C (up to 90°C after heat treatment), it can work at 100°C for a long time in oil, and it can work at 110°C in inert gas.
Processing can be processed into monofilaments, films, plates, rods, profiles by injection molding, extrusion, etc. The powder can be processed by fluidized bed dipping, electrostatic coating, rotational molding and other methods, especially suitable for coating and spraying on metal surfaces .
Applications Bearings, gears, precision parts, oil pipes, hoses, wire and cable sheaths, etc.
Physical properties White or light yellow translucent particles. It is light and hard, has the characteristics of low water absorption, good dimensional stability, non-toxicity, and excellent electrical insulation performance. It still maintains a certain degree of toughness at -40°C. After reinforcement, it has the advantages of high strength and wear resistance, and improves the thermal stability and dimensional stability of the original resin. It is an excellent engineering plastic.
Application Widely used in aerospace, shipbuilding, automobile, textile, instrumentation, electrical, medical equipment and other fields. After enhancement, it can be used as the impeller of the pump, the cam of the automatic typewriter, various high-load mechanical parts, tool handles, electrical switches, equipment and building structure parts, the oil filler cap bearings of automobiles and ships, gears, etc.
In order to obtain excellent comprehensive properties, nylon is often modified before use. The most typical modification method is strengthening and toughening.
Use reinforcing materials to improve nylon performance. Reinforcing materials include glass fiber, asbestos fiber, carbon fiber, titanium metal, etc., of which glass fiber is the main component to improve the heat resistance, dimensional stability, rigidity, mechanical properties (tensile strength and bending strength) of nylon, especially for machinery Improved performance makes it an engineering plastic with excellent performance.
Toughened nylon, also known as high-impact nylon, is made by blending with grafted tough polymers with nylon 66 and nylon 6 as the matrix. Although the strength, rigidity and heat resistance are lower than the parent nylon, the impact strength can be increased by more than 10 times, and it has excellent wear resistance and dimensional stability.
Attachment: Commonly used polyamide product name
PA polyamide (nylon)
PA-1010 Poly sebacic acid decane diamine (nylon 1010)
PA-11 Polyundecamide (nylon 11)
PA-12 polydodecanamide (nylon 12)
PA-6 polycaprolactam (nylon 6)
PA-610 Polyethylene diamide sebacamide (nylon 610)
PA-612 Polydodecanedioic ethylene diamide (nylon 612)
PA-66 Polyhexamethylene adipate (nylon 66)
PA-8 polyoctylamide (nylon 8)
PA-9 poly 9-aminononanoic acid (nylon 9