PA6 and PA66 are mostly used for clothing in civilian yarns, cord fabrics in industrial yarns, fishing nets, conveyor belts, and high wear-resistant insulators in plastic injection due to their thermoplasticity, light weight, good toughness, chemical resistance and durability. parts, as well as daily necessities and packaging films, etc. But at the same time, there are subtle differences between the two products, and there are also different application fields due to differences in characteristics. Below we analyze the difference between the two from various aspects.
Both PA6 and PA66 are translucent or opaque milky white crystalline polymers. However, there are big differences in the production raw materials: the raw material of PA6 is caprolactam, which is obtained by the ring-opening polymerization of caprolactam; the preparation of raw materials is mainly petroleum benzene, and some manufacturers use hydrogenated benzene due to insufficient supply of petroleum benzene, but the quantity is extremely high. few. PA66 is obtained by polycondensation of hexamethylene diamine and adipic acid.
Compared with PA66, PA6 has a lower melting point and a wide process temperature range. It has better impact and dissolution resistance than PA66, but is also more hygroscopic. Because many quality characteristics of plastic parts are affected by hygroscopicity, more attention should be paid during use. The molecular arrangement of PA66 is symmetrical, and all flag groups and amino groups can form hydrogen bonds. In addition, during the spinning process, its kinetic crystallization ability is about 20 times higher than that of PA6, so the cracking strength of PA66 industrial knot has reached 9.7 g/d, while the strength of PA6 industrial yarn is only about 9.0g/d under the same conditions.
PA6 engineering plastic has high tensile strength, good impact resistance, excellent wear resistance, chemical resistance and low friction coefficient. It can be modified by glass fiber, mineral filling and adding flame retardant. To make its comprehensive performance more excellent, it is mainly used in the automotive industry and electronic and electrical fields. Glass is the most common additive, and sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance.
For products without additives, PA6 shrinks between 1% and 1.5%. Adding glass fiber additives can reduce the shrinkage to 0.3% (but slightly higher in the direction perpendicular to the process). The shrinkage of molding assembly is mainly affected by the crystallinity and hygroscopicity of the material.
The comprehensive performance of PA66 is good, it has the advantages of high strength, good rigidity, impact resistance, oil and chemical resistance, wear resistance and self-lubrication, especially the hardness, rigidity, heat resistance and creep performance are better, and the raw materials are easily available, The cost is low, so it is widely used in various fields such as industry, clothing, decoration, engineering plastics and so on. Because of its higher strength than PA6, PA66 is more used in the production of industrial yarns such as cords.
The highest proportion of PA6 consumption is in the civilian silk industry, and nylon filament for clothing is about 58%. The use of PA6 in the tire frame nylon cord fabric market accounts for about 13%. Engineering plastics use PA6 accounting for 12%, including injection plastics and modified plastics. About 6% of PA6 is used for fishing nets. The plastic film grade PA6 for the production of BOPA film accounts for 4%, the staple fiber PA6 for the production of carpets, sweaters, non-woven fabrics and other products accounts for 4%, and other PA6 for the production of PA sticks, PA tapes, etc. accounts for 3%.
Among the physical properties of PA6 itself, its shrinkage rate and molding shrinkage rate are poor, which cannot be improved by improving the production process. Instead, it is solved by adding auxiliary materials, auxiliaries, or relying on textile methods, and composite use in the process of producing products. For example, BOPA film, in order to reduce the influence of its shrinkage rate, should be used in combination, and other films are used to reduce the overall shrinkage rate.
The highest proportion of PA66 consumption is engineering plastics, accounting for 65% of the total consumption, while industrial yarn accounts for 20%, and others account for 15% of the total consumption. The downstream products of PA66 are mostly concentrated in engineering plastics, which are not suitable for spinning due to their excess rigidity and insufficient toughness.
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