Nylon 66 (PA66) is one of the most widely used engineering thermoplastics, valued for its mechanical strength, wear resistance, and heat resistance. If you process or spec PA66, the first question is: What is the melting point of nylon 66?
PA66 has a true melting point of approximately 255–265°C for unfilled grades. As a semi-crystalline polymer, PA66 melts sharply — unlike amorphous plastics such as ABS or PC. It is also hygroscopic, and moisture strongly affects processing and properties.
This guide covers PA66 melting behavior, moisture effects, drying, processing parameters, safety, and data for common PA66 grades.
1. Direct Answer: What Is the Melting Point of PA66?
Tm of PA66 is typically 255–265°C for unfilled, general-purpose grades. For injection molding, PA66 is processed at 270–300°C for adequate flow. Exact Tm varies with grade, MW, and additives.
Key takeaway: True Tm of PA66 ≈ 255–265°C. Melt processing must be higher (270–300°C) for moldable viscosity.
2. PA66 Thermal Properties Data Table
| Property | Unfilled PA66 | PA66 + 30% Glass Fiber | Test Method |
|---|---|---|---|
| Melting Point (Tm) | 255–265°C | 255–265°C | DSC (ISO 11357) |
| Glass Transition (Tg) | 50–70°C (dry) | 50–70°C (dry) | DSC |
| Vicat Softening (B/50) | 200–220°C | 240–255°C | ISO 306 |
| HDT @ 1.8 MPa | 70–100°C | 240–255°C | ISO 75 / ASTM D648 |
| HDT @ 0.45 MPa | 180–220°C | 250–260°C | ISO 75 / ASTM D648 |
| Continuous Use Temp (RTI) | 100–120°C | 130–150°C | UL 746B |
| Thermal Degradation Onset | > 300°C | > 300°C | TGA |
| Injection Melt Temp | 270–300°C | 280–310°C | — |
| Mold Temp | 60–100°C | 80–120°C | — |
| Drying Condition | 80°C / 4–8 h | 80°C / 4–8 h | Dehumidifying dryer |
Note: HDT for unfilled PA66 depends strongly on moisture. Dry-as-molded > conditioned.
3. Why PA66 Has a True Melting Point
PA66 (polyhexamethylene adipamide) is synthesized from hexamethylenediamine and adipic acid. Its symmetrical, linear chains pack tightly into crystallites that melt at Tm ≈ 255–265°C.
Why PA66 melts higher than PA6: more symmetrical repeat unit, stronger inter-chain hydrogen bonding — which also delivers better heat resistance, stiffness, and creep resistance.
Factors influencing Tm:
- Molecular weight: Higher MW → slightly higher Tm.
- Copolymerization: PA66/6 or PA66/6T copolymers depress Tm.
- Additives: Glass fiber does not change Tm but sharply raises HDT and reduces creep.
- Moisture: Plasticizer effect — lowers Tg/HDT; does not shift Tm; but wet melting causes hydrolysis.
Tm vs. Softening vs. HDT vs. CUT — clarified:
- Tm (255–265°C) — DSC crystallite melting.
- Vicat softening (~200–220°C) — needle penetration under load (ISO 306).
- HDT (70–100°C @ 1.8 MPa unfilled) — bending deflection.
- CUT / RTI (100–120°C unfilled) — long-term thermal endurance.
For end-use spec, CUT and HDT set the ceiling — not Tm.
Thermal degradation vs. hydrolysis:
- Thermal degradation > 300°C: chain scission, yellowing, and release of NH₃, CO, and trace HCN.
- Hydrolysis when wet PA66 is melted: irreversible chain cleavage at the amide bond, MW drops, mechanical properties fall — often invisible to the naked eye.
Both must be avoided in processing.
4. Grade Comparison: Typical PA66 Injection Molding Grades
| Grade Type | Tm (°C) | MFI (g/10 min, 275°C/5 kg) | Tensile Strength (MPa, dry) | Typical Applications |
|---|---|---|---|---|
| General-purpose unfilled | 255–265 | 10–20 | 80–90 | Connectors, fasteners, automotive clips |
| High-flow unfilled | 255–265 | 30–60 | 75–85 | Thin-wall parts, high-speed molding |
| High-impact modified | 250–260 | 5–15 | 55–65 | Impact-resistant automotive parts |
| 30% Glass-filled | 255–265 | 5–15 | 170–190 | Structural components, under-the-hood housings |
Values are typical industry ranges. Verify against supplier TDS for critical use.
How to use this table:
- General-purpose → medium-flow unfilled PA66.
- Thin-wall parts → high-flow grades.
- Structural / high-stiffness → glass-filled PA66; Tm unchanged, HDT jumps to 240–255°C.
5. Processing Guide for PA66
5.1 Drying
PA66 absorbs up to 8–9% water at saturation. Wet processing → silver streaks, bubbles/voids, impact loss, dimensional drift.
- Temperature: 80°C
- Time: 4–8 hours
- Dehumidifying dryer, dew point ≤ −20°C
- Target moisture < 0.10%
- Avoid > 90°C over-drying (discoloration)
5.2 Injection Molding
- Barrel profile: 270°C (rear) → 280–290°C (middle) → 280–300°C (nozzle). Do not exceed 320°C.
- Mold temperature: 60–100°C unfilled; 80–120°C glass-filled. Higher mold temp → better crystallinity, dimensional stability, surface finish (longer cycle time).
- Injection pressure: medium to high.
- Back pressure: 5–10 bar.
- Screw speed: 60–120 rpm.
5.3 Extrusion
Rod, tube, profile — melt 270–300°C, die close to melt temp, cooling water 20–40°C.
5.4 Common Defects and Solutions
| Defect | Likely Cause | Solution |
|---|---|---|
| Silver streaks / splay | Moisture in resin | Dry 80°C / 4–8 h; verify moisture < 0.10% |
| Brittleness | Over-drying or thermal degradation | Lower barrel temp; shorten residence time |
| Warpage | Uneven cooling or high crystallinity | Optimize cooling; mold temp 60–100°C |
| Sink marks | Thick sections or low packing | Increase packing pressure; redesign part |
| Flash | High injection pressure or mold wear | Reduce pressure; inspect clamping |
| Discoloration | Melt temp too high | Lower barrel temp; purge regularly |
5.5 Safety & Storage
- Never exceed 320°C at the nozzle. Above ~300°C, PA66 releases NH₃, CO, and trace HCN — toxic and corrosive.
- Local exhaust ventilation (LEV) at hopper and nozzle mandatory.
- Operators: heat-resistant gloves, safety goggles; respiratory protection where fume exposure exists.
- Store pellets in sealed, moisture-barrier containers away from sunlight; reseal opened bags immediately.
6. Frequently Asked Questions
What is the exact melting point of PA66?
Unfilled PA66 melts at 255–265°C (DSC). Exact value varies slightly by grade and test method.
Does moisture affect the melting point of PA66?
Not significantly. But moisture lowers Tg and HDT, and causes hydrolytic degradation during melting.
How long should I dry PA66 before molding?
80°C for 4–8 hours in a dehumidifying dryer. Target < 0.10% moisture.
What is the difference between PA6 and PA66 in melting point?
PA66 (255–265°C) is higher than PA6 (220–225°C) due to symmetrical structure and stronger hydrogen bonding.
Can PA66 be used above 150°C?
Unfilled PA66 tolerates intermittent 150–180°C, but continuous use above 120°C causes softening. Glass-filled PA66 can be used continuously up to ~150°C.
Is PA66 the same as nylon 66?
Yes. PA66 is the ISO designation for nylon 66, also called polyhexamethylene adipamide.
7. PA66 vs. Other Plastics: Melting Point & Heat Resistance
| Material | Type | Tm (°C) | Tg (°C) | HDT @ 1.8 MPa (°C) | Continuous Use (°C) |
|---|---|---|---|---|---|
| PA66 | Semi-crystalline | 255–265 | 50–70 | 70–100 (unfilled) | 100–120 |
| PA6 | Semi-crystalline | 220–225 | 50–60 | 60–100 (unfilled) | 80–120 |
| PP | Semi-crystalline | 160–170 | ~ −10 | 50–60 | 80–100 |
| POM | Semi-crystalline | 165–185 | −60 to −80 | 110–125 | 90–110 |
| PC | Amorphous | No true Tm | ~145 | 125–135 | 115–130 |
| ABS | Amorphous | No true Tm | ~105 | 85–100 | 60–80 |
| PEEK | Semi-crystalline | 340–345 | ~143 | 150–160 | 240–260 |
PA66 delivers superior heat resistance and stiffness compared to PA6 and most commodity engineering plastics — a preferred choice for automotive under-the-hood, electrical, and industrial applications.
8. Why Melting Point Matters for Procurement
- Processing window: Tm sets the minimum melt temperature; PA66’s narrow window (270–320°C) demands tight barrel control.
- Application fit: Spec by HDT and CUT, not Tm — a GF30 grade with HDT 250°C is what qualifies PA66 for engine-bay use.
- Total cost: Barrel-temp errors on PA66 (higher energy cost, tighter degradation margin) hit piece cost faster than on PA6.
- Safety compliance: Melt > 300°C releases toxic fumes; EHS documentation and LEV are mandatory.
9. Data Sources & Disclaimer
Data compiled from publicly available TDS for general-purpose PA66 grades, plus ISO/ASTM/UL test methods. Actual values vary by grade, manufacturer, lot, and test conditions. For critical use, verify against supplier’s official TDS.
Related Resources:
- Plastic Raw Material Melting Point: Complete Guide
- Nylon Melting Point: PA6 vs PA66 vs Specialty Grades
- PA6 Melting Point: Nylon 6 Melting Temperature & Processing Guide
- POM Melting Point: Acetal Melting Temperature & Processing Guide
- PA66 Density: Nylon 66 Density & Glass-Filled Grades
- PA66 Water Absorption: Saturation Data & Dimensional Stability
