What is the Difference Between PA6 and PA66?
Polyamide resin, known in English as polyamide and abbreviated as PA, is commonly referred to as Nylon. It is a general term for high polymers whose main chain of the molecule contains amide groups.
PA is the most produced, varied, and widely used among the five major engineering plastics. It is often blended with other polymers, compounds, and alloys to meet different special requirements and is widely used as a substitute for traditional materials like metal and wood.
The main varieties of Nylon are Nylon 6 (PA6) and Nylon 66 (PA66), which hold a dominant position in the market.
So, what are the essential differences between PA6 and PA66?
Basic Physical Properties
Nylon 6 (PA6) is made of polycaprolactam, while Nylon 66 (PA66) is made of polyhexamethylene adipamide. PA66 is about 12% harder than PA6.
PA6 has chemical and physical properties similar to PA66; however, it has a lower melting point and a broader processing temperature range. It has better impact resistance and solvent resistance than PA66 but also a higher moisture absorption.
PA66 is a semi-crystalline-crystalline material with a higher melting point and can maintain significant strength and stiffness at higher temperatures.
Product Performance Differences
PA6: Exhibits excellent thermal stability, high heat resistance, good dimensional stability, high surface quality, and good resistance to warping.
l Melting point: 210–220 ℃
l Decomposition temperature: >300℃
l Flash point: >400 ℃
l Auto-ignition temperature: >450 ℃
l Physical state: Solid particles
l Odor: Non-toxic
l Recyclability: Yes
l Final treatment: Soil (harmless industrial waste)
l Fire extinguishing agents: Various fire extinguishing agents can be used (water, foam, powder, CO2, sand)
l Transport: Non-hazardous goods, suitable for various modes of transport
l EU standards: Non-hazardous goods
PA66: Has excellent wear resistance, good high-impact resistance, and good dimensional stability.
l Melting point: 250–270℃
l Decomposition temperature: >350 ℃
l Flash point: >400 ℃
l Auto-ignition temperature: >450℃
l Physical state: Solid particles
l Odor: Non-toxic
l Recyclability: Yes
l Final treatment: Soil (harmless industrial waste)
l Fire extinguishing agents: Various fire extinguishing agents can be used (water, foam, powder, CO2, sand)
l Transport: Non-hazardous goods, suitable for various modes of transport
l EU standards: Non-hazardous goods
Differences in Applications
PA6 is generally used for automotive parts, mechanical components, electronic and electrical products, engineering accessories, and more.
PA66 is more widely used in the automotive industry, instrument casings, and other products that require impact resistance and high strength, such as marine propellers, gears, rollers, pulleys, roller shafts, pump impellers, fan blades, high-pressure seals, valve seats, gaskets, bushings, various handles, support frames, wire package inner layers, etc.
Differences in Injection Molding Process
PA6 — Injection Molding Process Conditions
Due to the impact of moisture absorption on many quality characteristics of plastic parts, this factor must be fully considered when designing products with PA6.
To improve the mechanical properties of PA6, various modifiers are often added. Glass fiber is the most common additive, and sometimes synthetic rubber such as EPDM and SBR is added to improve impact resistance.
For products without additives, the shrinkage rate of PA6 is between 1% and 1.5%. The addition of glass fiber-reinforced Nylon can reduce the shrinkage rate to 0.3% (although it will be slightly higher in the direction perpendicular to the flow). The shrinkage rate of the molded assembly is mainly affected by the crystallinity of the material and its moisture absorption.
Drying Treatment
Since PA6 easily absorbs moisture, special attention should be paid to drying before processing.
If the material is supplied in waterproof packaging, the container should remain sealed.
If the humidity is greater than 0.2%, it is recommended to dry in hot air above 80℃ for 16 hours.
If the material has been exposed to air for more than 8 hours, vacuum drying at 105℃ for more than 8 hours is recommended.
Melting Temperature
230280℃, for reinforced Nylon it is 250280℃.
Mold Temperature
80~90℃.
Mold temperature significantly affects crystallinity, which in turn affects the mechanical properties of plastic parts. Crystallinity is important for structural parts, so a mold temperature of 80~90℃ is recommended.
For thin-walled, long-flow plastic parts, a higher mold temperature is also recommended.
Increasing the mold temperature can improve the strength and stiffness of the plastic parts but will reduce toughness.
For wall thicknesses greater than 3mm, a low mold temperature of 20~40℃ is recommended. For glass-reinforced materials, the mold temperature should be above 80℃.
Injection Pressure
Generally between 750~1250bar (depending on the material and product design).
Injection Speed
High speed (slightly reduced for reinforced Nylon).
Runners and Gates
Due to the short solidification time of PA6, the position of the gate is very important.
The gate diameter should not be less than 0.5*t (where t is the thickness of the plastic part).
If using a hot runner, the gate size should be smaller than when using a conventional runner, as the hot runner can help prevent the material from solidifying too early.
If using a submersible gate, the minimum diameter of the gate should be 0.75mm.
PA66 — Injection Molding Process Conditions
PA66 still has hygroscopicity after molding, which mainly depends on the composition of the material, wall thickness, and environmental conditions. When designing products, the impact of hygroscopicity on geometric stability must be considered.
PA66 has lower viscosity, so it has good fluidity (but not as good as PA6). This property can be used to process very thin components. Viscosity is very sensitive to temperature changes.
The shrinkage rate of PA66 is between 1% and 2%, and the addition of glass fiber modification can reduce the shrinkage rate to 0.2%~1%. The difference in shrinkage rate in the direction of flow and perpendicular to the direction of flow is significant.
PA66 has resistance to many solvents but is less resistant to acids and some chlorides.
Drying Treatment
If the material is sealed before processing, then drying is not necessary.
If the storage container has been opened, then it is recommended to dry in hot air at 85℃.
If the humidity is greater than 0.2%, additional vacuum drying at 105℃ for 12 hours is needed.
Melting Temperature
260~290℃.
For glass-modified products, it is 275~280℃.
The melting temperature should avoid exceeding 300℃.
Mold Temperature
A mold temperature of 80℃ is 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℃ is used, the crystallinity of the plastic parts will change over time. To maintain the geometric stability of the plastic parts, annealing treatment is necessary.
Injection Pressure
Typically between 750~1250bar, depending on the material and product design.
Injection Speed
High speed (should be slightly lower for reinforced materials).
Runners and Gates
Due to the short solidification time of PA66, the position of the gate is very important.
The gate diameter should not be less than 0.5*t (where t is the thickness of the plastic part).
If using a hot runner, the gate size should be smaller than when using a conventional runner, as the hot runner can help prevent the material from solidifying too early.
If using a submersible gate, the minimum diameter of the gate should be 0.75mm.
Conclusion
Understanding the differences between PA6 and PA66 is crucial for manufacturers and designers who rely on these materials for their products. Both types of polyamide offer unique properties that make them suitable for various applications, from automotive components to electronic casings. By considering factors such as moisture absorption, melting temperature, and shrinkage, professionals can choose the appropriate material to ensure product quality and performance.
For more detailed information on polyamide injection molding, including the use of PA6 and PA66, visit Polyamide Injection Molding.
