The difference between nylon PA6 and PA66

Pa6 and Pa66 are both polyamide polymers (commonly known as nylon), both of which are translucent or milky white in appearance. They are widely used due to their excellent toughness, chemical resistance, fatigue resistance, and light weight. Although there is only one word difference between PA6 and PA66, what is the difference in their performance, and how should they be selected in industrial applications?

PA6 is formed by the polycondensation of caprolactam, while PA66 is formed by the polycondensation of adipic acid and hexamethylenediamine. From the molecular structure point of view, the two are very similar, so their physical and chemical properties are basically similar. The difference is that the hydrogen bonds between adjacent molecules of PA66 are more firmly bonded, so its melting point is as high as 260°C, which is 20-40°C higher than that of PA6. It has superior heat resistance, but its resilience and fatigue resistance are not as good as PA6. Feel its surface hardness by hand, PA66 is harder than PA6.

PA6 and PA66 structural difference

PA6 is obtained by ring-opening polymerization of caprolactam, while PA66 is obtained by condensation polymer of hexamethylenediamine and adipic acid. The two have the same molecular formula, but the structure is quite different. The number of hydrogen bonds of PA66 is higher than that of PA6, and the molecular force is also stronger than that of PA6, so PA66 has better thermal properties and requires higher processing temperature.

The hardness of PA66 is 12% stronger than that of PA6. From the perspective of a single fiber, PA6 has better toughness, and PA66 has better rigidity. This is precisely because of the molecular structure. caused by different hydrogen bonds.

PA6 and PA66 performance difference

The melting point of PA6 is 220°C, and the melting temperature is 230~280°C (250~280°C for enhanced varieties), and the flame is light yellow when burning. It is easy to process, has high tensile strength, impact resistance, ideal wear resistance, chemical resistance, self-lubricating property and low friction coefficient, and its oil resistance is better than PA66. It has good surface gloss, excellent low temperature performance, self-extinguishing, wide temperature range, can be used for a long time under harsh conditions, and can still maintain sufficient stress in a wide temperature range for long-term use. However, compared with PA66, PA6 has a higher water absorption rate, so its dimensional stability is poor. The application of PA6 will also have better comprehensive performance by adding glass fiber, mineral modification and adding flame retardants.

The melting point of PA66 is 260~265°C, and the melting temperature is 260~290°C (275~280°C for glass additive products. The melting temperature should not be higher than 300°C), and the flame is blue when burning. It has high strength and rigidity, good impact resistance, oil resistance, wear resistance, chemical resistance and self-lubricating property, and its hardness, rigidity, heat resistance and creep resistance are better.

PA6 and PA66 process difference

· Drying

PA6 has a high water absorption rate, so special attention should be paid to its drying before processing. The material storage container needs to be airtight. If the humidity is > 0.2%, it is recommended to dry in hot dry air above 80°C for 3-4 hours. If the material has been exposed to the air for more than 8 hours, it is recommended to dry it at a temperature of 105°C. Carry out vacuum drying for more than 1~2 hours.

PA66 does not need to be dried if the material is sealed and stored. If the storage container is opened, it is recommended to dry it in hot dry air at 85°C. If the humidity is greater than 0.2%, it needs to be vacuum dried at 105°C for 1~2 hours. .

· Mold temperature

PA6: 80~90℃. Mold temperature significantly affects crystallinity, which in turn affects mechanical properties of plastic parts.

For thin-walled plastic parts with a long process, it is recommended to use a higher mold temperature. Increasing the mold temperature can increase the strength and rigidity of the plastic part, but it will also reduce its toughness accordingly. If the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold at 20~40°C, and for glass-reinforced materials, the mold temperature should be greater than 80°C.

PA66: 80°C is recommended. Mold temperature will affect the degree of crystallinity which will affect the physical properties of the product.

For thin-walled plastic parts, if the mold temperature is lower than 40°C, the crystallinity of the plastic part will change with time. In order to maintain the geometric stability of the plastic part, annealing treatment is also required.

PA6 and PA66 Application difference

PA6 is used in industrial fields such as electronics and automobiles. Its civilian silk industry consumes a relatively high proportion of nylon filament for clothing, about 58%. The use of PA6 in the tire frame nylon cord market accounts for about 13%. Engineering plastics use PA6 accounted for 12%, including injection plastics and modified plastics. PA6 accounts for about 6% of fishing net wire. Plastic film-grade PA6 for the production of BOPA film accounts for 4%, staple fiber PA6 for the production of carpets, sweaters, non-woven fabrics and other supplies accounts for 4%, and other PA6 for the production of PA rods, PA tapes, etc. accounts for 3%.

PA66 is widely used in clothing, decoration, engineering plastics and other fields. The highest proportion of its 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 because of their excess rigidity and insufficient toughness.