Polyamide, commonly known as Nylon and abbreviated as PA in English, encompasses a family of high polymers characterized by amide groups in their molecular chains.

Among the engineering plastics, PA stands out for its extensive production, diverse types, and broad application range. It's often alloyed or blended to satisfy unique requirements and serves as an alternative to conventional materials such as metals and wood.

Nylon's predominant forms are Nylon 6 (PA6) and Nylon 66 (PA66), which are preeminent in the industry.

What, then, distinguishes PA6 from PA66 at their core?

Fundamental Physical Distinctions

Nylon 6 (PA6) is synthesized from polycaprolactam, whereas Nylon 66 (PA66) from polyhexamethylene adipamide, making PA66 approximately 12% stiffer than PA6.

PA6 shares many chemical and physical characteristics with PA66 but has a lower melting point and a wider processing temperature range. It surpasses PA66 in impact and solvent resistance, albeit with greater moisture absorption.

PA66, as a semi-crystalline material, boasts a higher melting point and sustains considerable strength and rigidity even under elevated temperatures.

Divergence in Product Performance

PA6 shines with its exceptional thermal stability, resistance to high temperatures, and excellent dimensional and surface quality. It also resists warping effectively.

Melting point: 210 - 220 ℃

Decomposition temperature: >300℃

Flash point: >400 ℃

Auto-ignition temperature: >450 ℃

State: Solid granules

Odor: Non-toxic

Recyclability: Yes

Disposal: Soil (non-hazardous industrial waste)

Extinguishing media: Compatible with various agents (water, foam, powder, CO2, sand)

Transportation: Non-hazardous, suitable for all transport methods

EU classification: Non-hazardous

PA66 is renowned for its excellent wear resistance and high-impact durability, along with stable dimensions.

Melting point: 250-270℃

Decomposition temperature: >350 ℃

Flash point: >400 ℃

Auto-ignition temperature: >450℃

State: Solid granules

Odor: Non-toxic

Recyclability: Yes

Disposal: Soil (non-hazardous industrial waste)

Extinguishing media: Compatible with various agents (water, foam, powder, CO2, sand)

Transportation: Non-hazardous, suitable for all transport methods

EU classification: Non-hazardous

Application Variances

PA6 typically finds its use in automotive components, machinery parts, electronics, and engineering fittings.

PA66, with its superior impact resistance and strength, is more extensively utilized in the automotive sector, instrument casings, and products like marine propellers, gears, and high-pressure seals, among others.

Injection Molding Process Variations

For PA6 - Injection Molding Process Conditions

PA6's many quality traits are influenced by its hygroscopic nature, which must be factored into product design.

Modifiers, like glass fibers or synthetic rubbers such as EPDM and SBR, are often added to enhance PA6's mechanical properties.

Unfilled PA6 typically has a shrinkage rate ranging from 1% to 1.5%. Glass fiber reinforcement can reduce this to about 0.3%, although it may vary with the direction of flow. Shrinkage is mainly influenced by the material's crystallinity and moisture absorption.

Drying is crucial for PA6 due to its propensity to absorb moisture. If supplied in waterproof packaging, keep the container sealed. For material with over 0.2% humidity, drying in hot air above 80℃ for 16 hours is advisable. Exposed materials should undergo vacuum drying at 105℃ for at least 8 hours.

The melting temperature ranges from 230, 280℃, or 250,280℃ for reinforced Nylon.

Mold temperature significantly impacts crystallinity and thus the mechanical properties of the parts. For structural components, a mold temperature of 80, 90℃ is recommended. For parts with greater wall thicknesses, a lower mold temperature of 20, 40℃ may be used, while glass-reinforced materials should have a mold temperature above 80℃.

Injection pressures typically span 750~1250bar, depending on material and design specifics.

For PA66 - Injection Molding Process Conditions

Post-molding, PA66 retains hygroscopic properties, which vary with material composition, wall thickness, and environmental conditions. This must be considered in product design for geometric stability.

PA66's lower viscosity grants it excellent flow properties, suitable for manufacturing very thin components, though it's more temperature-sensitive than PA6.

Shrinkage rates for PA66 lie between 1% and 2%, which can be reduced to 0.2%~1% with glass fiber modification. Shrinkage disparity is more pronounced between the flow and cross-flow directions.

PA66 resists many solvents but is less resistant to acids and some chlorides.

If sealed, PA66 doesn't require pre-processing drying. However, if the container has been opened, drying in 85℃ hot air is recommended. For humidity above 0.2%, additional vacuum drying at 105℃ for 12 hours is necessary.

The melting temperature should be 260~290℃, avoiding exceeding 300℃.

A mold temperature of 80℃ is advised to influence crystallinity and the physical properties of the product. For thin-walled parts, maintaining geometric stability may require annealing if mold temperatures are below 40℃.

Injection pressures are similar to PA6, and high injection speeds are recommended, slightly reduced for reinforced materials.

In Summary

The choice between PA6 and PA66 depends on the specific requirements of the application, considering their distinct properties. Both materials are versatile and offer unique benefits for a range of industrial applications. Key considerations such as moisture absorption, melting temperature, and shrinkage play a pivotal role in determining the suitability of each polyamide type.