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Melting temperature and re-crystallization rate are the two key differences between PA 66 and PA 6. PA 66 has a melting temperature of 262℃ compared to 220℃ for PA 6. As for re-crystallization, PA 66 “freezes” much faster than PA 6, making PA 66 ideal for fast cycle times in injection molding.

PA 66 and PA 6 behave similarly in terms of chemical resistance, mechanical properties, and moisture uptake.

• Chemical Resistance: Both offer very good chemical resistance to hydrocarbons, but poor chemical resistance to acids.
• Mechanical Properties: Both exhibit good mechanical properties when reinforced with mineral, glass, or carbon fiber. PA 66 will exhibit slightly higher properties compared to the same product based on PA 6. Impact modified PA 6 and PA 66 exhibit similar performance.
• Moisture Uptake: Both absorb moisture, but PA 6 absorbs slightly more than PA 66 at equilibrium conditions.

Most plastics suppliers, especially the large resin producers, push a standard list of materials and offer minimal support to molders who experience processing or performance issues with these standard grades. Often part, tooling, processing, and performance issues can be addressed with an optimized material solution, which can result in significant cost savings by improving manufacturing efficiencies or avoiding expensive tooling or equipment modifications.

PA 6 is the most common alternative to PA 66, particularly when the application has a low end-use temperature. Other common alternatives include polyesters such as PBT and PET, as well as polypropylene (PP) in certain applications.

All polyamides (nylons) absorb moisture, but the amount and rate of moisture absorption varies by type. Moisture affects polyamides in two ways:

1. By acting like a plasticizer, moisture reduces tensile strength and modulus of polyamides, but increases impact strength and elongation.
2. In terms of dimensional stability, increasing moisture uptake can adversely affect part dimensions.

A term coined in the 1970s, “super tough nylon” refers to Polyamide 66 (PA 66)-based compounds modified with rubbers and elastomers for increased impact resistance, toughness, and ductility. Additional benefits include lower specific gravity, reduced moisture absorption, and higher melt strength versus standard PA 66 resin.

Like most engineering thermoplastics, polyamides (nylons) are not inherently flame retardant. However, they can be optimized and formulated to meet many stringent flammability requirements.

Many polyamides (nylons) inherently possess very good hydrolysis resistance. In other cases, hydrolysis resistance can be much improved by specialty formulations; either by incorporating additives or by blending with polymers that are not sensitive to moisture.