Table of Contents
Although PA6 and PA66 look similar in name and have very similar chemical and physical properties, their respective differences also determine their application fields.
Structural differences
PA6 is produced by ring-opening polymerization of caprolactam, and PA66 is obtained from a condensation polymer of hexanediamine and adipic acid. Both have the same molecular formula, but the structure is much 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 the thermal properties of PA66 are better and require higher processing temperatures.
PA66 is 12% harder than PA6, as far as a single fiber is concerned, so compared with the two, PA6 has better toughness, PA66 has better rigidity, and this is precisely because of the difference in hydrogen bonds in the molecular structure.
Performance difference
The melting point of PA6 is 220 °C, 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-lubrication and low coefficient of friction, and better oil resistance than PA66. Its surface gloss is good, low temperature performance is excellent, self-extinguishing, wide use temperature range, can be used for a long time under harsh conditions, and can still maintain sufficient stress and long-term use in a wide temperature range. However, compared with PA66, PA6 has a higher water absorption, so its dimensional stability is poor. The application of PA6 will also be modified by adding glass fiber, mineral modification and flame retardants, which can make it have better comprehensive performance.
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 be avoided above 300 ° C), and the flame is blue when burning. It has high strength and rigidity, impact resistance, oil resistance, wear resistance, chemical resistance, self-lubrication is also very good, and its hardness, rigidity, heat resistance and creep are better.
Process differences
（1）Drying process
PA6 has a high water absorption, so its drying before processing requires special attention. The material storage container needs to be sealed, if the humidity > 0.2%, it is recommended to dry in hot dry air above 80 °C for 3~4 hours, and if the material has been exposed to the air for more than 8 hours, it is recommended to vacuum drying at a temperature of 105 °C for more than 1~2 hours.
PA66 does not need to be dried under the premise of sealed storage of materials, if the storage container is opened, it is recommended to dry in hot dry air at 85 °C, if the humidity is greater than 0.2%, it is also necessary to carry out vacuum drying at 105 °C, 1~2 hours.
（2）Mold temperature
PA6：80~90℃。 The mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of the plastic part.
For thin-walled, long-process plastic parts, higher mold temperatures are recommended. Increasing the mold temperature can increase the strength and stiffness of the plastic part, but it will also reduce its toughness. If the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold of 20~40 °C, and the mold temperature should be greater than 80 °C for glass reinforced materials.
PA66: 80°C recommended. The mold temperature will affect the crystallinity, and the crystallinity will affect the physical properties of the product.
For thin-walled plastic parts, if a mold temperature below 40°C is used, the crystallinity of the plastic part will change over time, and annealing treatment is also required to maintain the geometric stability of the plastic part.
Application differences
PA6 is used in electronics, automotive and other industrial fields. Its civilian silk industry has a high proportion of consumption, and nylon filament yarn for clothing is about 58%. The tire frame nylon cord market uses PA6 for about 13%. PA6 accounts for 12% of engineering plastics, including injection plastics and modified plastics. PA6 for fishing net wire accounts for about 6%. The plastic film grade PA6 for the production of BOPA film accounts for 4%, the short fiber PA6 for the production of carpets, wool sweaters, non-woven fabrics and other products accounts for 4%, and other PA6 for the production of PA rods, PA tapes and other uses accounts for 3%.
PA66 is a kind of engineering plastic, widely used, stable, good mechanical properties, superior electrical insulation properties, small specific gravity, easy processing and molding, self-extinguishing and good wear resistance. Therefore, it is widely used in automotive, electronic appliances, chemical, mechanical instrumentation, construction and other industries. However, its high-water absorption, poor acid resistance, low dry and low temperature impact strength, and easy deformation after water absorption, which affects the dimensional stability of the product. People have modified PA66 in various ways, and adding PA66 fiber is one of them.
With the addition of PA66, its impact force, thermal deformation, mechanical properties, molding processability and chemical resistance are enhanced. Glass fiber is an inorganic non-metallic material with excellent properties, it has the advantages of low cost, non-combustibility, heat resistance, chemical resistance, high tensile strength and impact strength, small elongation at break, good thermal insulation and good insulation, and is often used as a reinforcing material for organic polymers or inorganic non-metallic and composite materials.
