Introduction
PA66 (Polyamide 66, commonly known as Nylon 66) is one of the most widely used thermoplastic engineering plastics. It is produced by the condensation polymerization of adipic acid and hexamethylenediamine — both containing 6 carbon atoms, hence the designation "66".
The strong hydrogen bonding between amide groups in the molecular chain gives PA66 its characteristic combination of high strength, high rigidity, excellent wear resistance, and good oil resistance. With a melting point of approximately 260°C (significantly higher than PA6 at 220°C), PA66 maintains stable performance across a wide temperature range.
PA66 is easily processed by injection molding and extrusion, and its properties can be further enhanced through glass fiber reinforcement, flame retardant modification, and other compounding techniques. It appears as a semi-transparent, white, or black crystalline polymer in its base form.
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Chemical Composition
| Grade | Polycaprolactam / Polyamide Base (%) | Adipic Acid Residue (%) | Other Impurities (%) |
|---|---|---|---|
| PA66 | 95–97 | 2–4 | < 1 |
Synthesis route: Adipic acid (HOOC–(CH₂)₄–COOH) + Hexamethylenediamine (H₂N–(CH₂)₆–NH₂) → PA66 + H₂O (condensation polymerization)
Mechanical Properties
| Property | Value / Range |
|---|---|
| Tensile Strength | 50–95 MPa |
| Yield Elongation | 3.4–30% |
| Elongation at Break | 150–300% |
| Elastic Modulus | 0.8–3.0 GPa |
| Young’s Modulus | 1.0–3.5 GPa |
| Toughness | 50–150 J/m |
| Low-temperature Toughness (Izod) | 27–35 J/m |
| Shore D Hardness | 80–95 |
| Rockwell Hardness (R scale) | ~110–120 |
Physical Properties
| Property | Value |
|---|---|
| Density | 1.14–1.15 g/cm³ |
| Melting Point | ~260 °C (vs. ~220 °C for PA6) |
| Thermal Expansion Coefficient | 80–140 × 10⁻⁶ /°C |
| Moisture Absorption (23°C, 50% RH) | ~2.5% (equilibrium) |
| Moisture Absorption (fully saturated) | 8–10% |
| Dimensional change due to moisture | ~0.3–1.5% |
| Appearance | Semi-transparent to milky white (unfilled); opaque when modified |
Important note on moisture: PA66 is hygroscopic. Moisture absorption causes dimensional changes (0.3–1.5%) and reduces mechanical properties. Raw material must be dried to ≤ 0.1% moisture content before processing to prevent bubbles, cracking, and surface defects in finished parts.
PA66 vs PA6: Key Differences
| Property | PA66 | PA6 |
|---|---|---|
| Melting Point | ~260 °C | ~220 °C |
| Tensile Strength | Higher | Moderate |
| Rigidity / Stiffness | Higher | Lower |
| Wear Resistance | Excellent | Good |
| Moisture Absorption | Slightly higher | Slightly lower |
| Processing temperature | Higher (250–290°C) | Lower (230–260°C) |
| Cost | Slightly higher | Lower |
| Best for | High-temp, high-load structural parts | General purpose, lower-cost applications |
Applications of PA66
PA66 is used across virtually every industry requiring a lightweight, strong, and wear-resistant engineering material:
- Automotive — engine peripheral components (oil pans, intake manifolds), transmission parts (gears, bearing cages), interior structural frames; enables lightweighting and weather resistance
- Electronics & Electrical — connectors, insulating brackets, switch housings, coil bobbins; leverages electrical insulation and impact resistance
- Mechanical Manufacturing — precision gears, pulleys, pump bodies, sliders, and wear-resistant components replacing metal parts to reduce cost and weight
- Textile Industry — high-strength industrial yarn for tire cord, conveyor belts, and ropes
- Consumer Products — zippers, toothbrush handles, kitchen utensil handles, and sporting goods
- Fasteners & Hardware — nylon nuts, washers, cable ties, and insulating fastener components
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Processing Characteristics
Drying (Critical)
PA66 must be dried to ≤ 0.1% moisture content before processing. Insufficient drying causes bubbles, surface cracking, and reduced mechanical properties in finished parts. Recommended drying: 80–90°C for 4–8 hours in a dehumidifying dryer.
Injection Molding Parameters
| Parameter | Recommended Range |
|---|---|
| Melt temperature | 250–290 °C |
| Mold temperature | 60–120 °C |
| Injection pressure | Medium to high |
Temperature control is critical: excessive temperature causes thermal degradation; insufficient temperature leads to uneven crystallization, warpage, and sink marks. Mold design must include appropriate gate placement and venting to minimize defects.
Reinforcement & Modification
- Glass fiber reinforcement (GF): Significantly increases tensile strength, rigidity, and heat deflection temperature. Common grades: PA66-GF15, PA66-GF30, PA66-GF50.
- Flame retardant modification: Adds halogen-free or halogenated flame retardants for electrical and electronic applications.
- Lubrication modification: PTFE or MoS₂ additions improve wear resistance and reduce friction coefficient for bearing and gear applications.
Standards reference: ISO 1874 (PA66) | ASTM D4066 | GB/T 1040 (tensile properties) | GB/T 1843 (impact strength)
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