PA6 and PA66 share similar chemical and physical profiles, but critical differences exist, especially regarding moisture absorption, which profoundly affects processing and final part performance.
PA6 (Polyamide 6) exhibits properties akin to PA66 but with a lower melting point and a broader processing temperature window. It generally offers better impact resistance and solubility but is also more hygroscopic, possessing a higher moisture absorption capacity. Since moisture absorption influences dimensions, strength, and appearance, it is a paramount consideration in product design. PA6 is often modified with additives; glass fiber is the most common for enhancing mechanical properties, while synthetic rubbers like EPDM improve impact strength. Unfilled PA6 has a molding shrinkage of 1% to 1.5%, reduced to about 0.3% with glass fiber (though slightly higher perpendicular to flow). Its processing is highly sensitive to moisture: proper drying is essential, requiring hot air drying at >80°C for >16 hours if moisture exceeds 0.2%, or vacuum drying at 105°C if exposed to air. The melting temperature ranges from 230-280°C (250-280°C for reinforced grades), with a recommended mold temperature of 80-90°C to optimize crystallinity and mechanical properties. Injection pressure typically falls between 750-1250 bar, with high injection speeds. Gate design is critical due to rapid solidification; gate diameter should be at least 0.5t (part thickness).
PA66 (Polyamide 66) has a higher melting point among polyamides, retaining strength and stiffness at elevated temperatures. It also remains hygroscopic post-molding, with the absorption level dependent on material composition, wall thickness, and environment. Its viscosity is lower than PA6's, offering better flow for thin-walled parts but greater sensitivity to temperature. Shrinkage for unfilled PA66 is 1.5%-2.0%, reducing to 0.2%-1.0% with glass fiber, with significant anisotropy between flow and cross-flow directions. Chemically, it resists many solvents but is weaker against acids and chlorinating agents. For processing, drying at 85°C is recommended if the package has been opened, or vacuum drying at 105°C if moisture >0.2%. The melting temperature is 260-290°C (275-280°C for glass-filled), and should not exceed 300°C. A mold temperature of 80°C is standard to control crystallinity; for thin walls below 40°C, annealing may be needed for stability. Injection parameters are similar to PA6, with the same emphasis on gate design to manage the short solidification time.
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