If you work with nylon 6 (PA6), one of the first questions in processing or material selection is: What is the melting point of nylon 6?
The answer is clear: PA6 has a true melting point of approximately 220–225°C for unfilled grades. As a semi-crystalline polymer, PA6 melts sharply, unlike amorphous plastics such as ABS or PC. However, PA6 is also hygroscopic, and moisture significantly affects both processing and end-use properties.
This guide covers PA6 melting behavior, the role of moisture, drying, injection molding parameters, safety considerations, and typical data for common PA6 grades.
1. Direct Answer: What Is the Melting Point of PA6?
The melting point (Tm) of nylon 6 is typically 220–225°C for unfilled, general-purpose grades — the temperature at which crystalline regions break down and the polymer transitions from solid to liquid.
For injection molding, PA6 is processed at 240–270°C to achieve adequate flow. Exact Tm varies with grade, molecular weight, and additives.
Key takeaway: True Tm of PA6 ≈ 220–225°C. Melt processing temperature must be higher (240–270°C) for moldable viscosity.
2. PA6 Thermal Properties Data Table
| Property | Unfilled PA6 | PA6 + 30% Glass Fiber | Test Method |
|---|---|---|---|
| Melting Point (Tm) | 220–225°C | 220–225°C | DSC (ISO 11357) |
| Glass Transition (Tg) | 50–60°C (dry) | 50–60°C (dry) | DSC |
| Vicat Softening (B/50) | 180–200°C | 210–220°C | ISO 306 |
| HDT @ 1.8 MPa | 60–100°C | 200–210°C | ISO 75 / ASTM D648 |
| HDT @ 0.45 MPa | 160–190°C | 215–225°C | ISO 75 / ASTM D648 |
| Continuous Use Temp (RTI) | 80–120°C | 120–150°C | UL 746B |
| Thermal Degradation Onset | > 300°C | > 300°C | TGA |
| Injection Melt Temp | 240–270°C | 260–280°C | — |
| Mold Temp | 60–90°C | 80–100°C | — |
| Drying Condition | 80°C / 4–8 h | 80°C / 4–8 h | Dehumidifying dryer |
Note: HDT for unfilled PA6 depends strongly on moisture. Dry-as-molded PA6 has higher HDT than conditioned PA6.
3. Why PA6 Has a True Melting Point
PA6 (polycaprolactam) is produced by ring-opening polymerization of caprolactam. Its linear chains pack into crystalline regions, giving PA6 a semi-crystalline structure. On heating, these crystallites melt at Tm ≈ 220–225°C.
Factors that influence Tm:
- Molecular weight: Higher MW → slightly higher Tm.
- Copolymerization: PA6/66 copolymers have lower Tm because comonomers disrupt crystallinity.
- Additives: Glass fiber does not change Tm of the matrix but raises HDT and reduces creep.
- Moisture: Acts as a plasticizer — lowers Tg and HDT, but does not significantly change Tm. However, processing wet PA6 causes hydrolytic degradation.
Melting vs. Softening vs. HDT vs. CUT — don’t confuse them:
- Tm (220–225°C) — where crystallites melt (DSC).
- Vicat softening (~180–200°C) — where a needle penetrates under load (ISO 306).
- HDT (60–100°C @ 1.8 MPa) — where a bar deflects under bending load.
- CUT / RTI (80–120°C) — long-term thermal endurance (UL 746B).
For most PA6 end-use decisions, CUT and HDT — not Tm — set the ceiling.
Thermal degradation vs. hydrolysis (two distinct pathways):
- Thermal degradation starts above ~300°C: chain scission, yellowing, and release of toxic gases (ammonia NH₃, carbon monoxide CO, and trace hydrogen cyanide HCN).
- Hydrolysis occurs when moist PA6 is melted: water chemically cleaves the amide bond, reducing molecular weight and mechanical properties permanently — even if the part looks fine visually.
Both must be avoided in processing.
4. Grade Comparison: Typical PA6 Injection Molding Grades
| Grade Type | Tm (°C) | MFI (g/10 min, 235°C/2.16 kg) | Tensile Strength (MPa, dry) | Typical Applications |
|---|---|---|---|---|
| General-purpose unfilled | 220–225 | 10–20 | 75–85 | Connectors, fasteners, automotive clips |
| High-flow unfilled | 220–225 | 30–60 | 70–80 | Thin-wall parts, high-speed molding |
| High-impact modified | 215–222 | 5–15 | 55–65 | Impact parts, automotive interiors |
| 30% Glass-filled | 220–225 | 5–15 | 160–180 | Structural parts, housings, brackets |
Values are typical industry ranges. Verify against supplier TDS for critical use.
How to use this table:
- General-purpose applications → medium-flow unfilled PA6 is most versatile.
- Thin-wall parts → high-flow grades fill easier, with slightly lower mechanicals.
- Structural / creep-resistant parts → glass-filled PA6; Tm stays similar but HDT rises dramatically.
5. Processing Guide for PA6
5.1 Drying
PA6 is highly hygroscopic — up to 9–10% water at saturation. Processing wet PA6 causes hydrolytic degradation: silver streaks, bubbles/voids, reduced impact strength, dimensional drift.
- Temperature: 80°C
- Time: 4–8 hours (depending on initial moisture)
- Dehumidifying dryer, dew point ≤ −20°C
- Target moisture < 0.10% before molding
- Avoid over-drying above 90°C (discoloration risk)
5.2 Injection Molding
- Barrel profile: 240°C (rear) → 250–260°C (middle) → 250–270°C (nozzle). Do not exceed 290°C.
- Mold temperature: 60–90°C unfilled; 80–100°C glass-filled.
- Injection pressure: medium to high; PA6 melt viscosity is low.
- Back pressure: 5–10 bar.
- Screw speed: 60–120 rpm.
5.3 Extrusion
Film, monofilament, or profile — melt 240–270°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 at 80°C for 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 60–90°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 (yellowing) | Melt temp too high | Lower barrel temp; purge regularly |
5.5 Safety & Storage
- Never exceed 300°C. Thermal degradation releases NH₃, CO, and trace HCN — all toxic.
- Use local exhaust ventilation (LEV) at the machine hopper and nozzle area.
- Operators: heat-resistant gloves, safety goggles; respiratory protection where fume exposure exists.
- Store pellets in sealed, moisture-barrier containers, away from direct sunlight; reseal opened bags immediately.
6. Frequently Asked Questions
What is the exact melting point of PA6?
Unfilled PA6 melts at 220–225°C (DSC). Exact value varies slightly by grade and test method.
Does moisture affect the melting point of PA6?
Not significantly. But moisture lowers Tg and HDT, and causes hydrolytic degradation during melting — which is why drying is critical.
How long should I dry PA6 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 more symmetrical structure and stronger hydrogen bonding.
Can PA6 be used above 100°C?
Unfilled PA6 tolerates intermittent 120–150°C, but continuous > 100°C causes softening. Glass-filled PA6 can be used continuously up to ~150°C.
Is PA6 the same as nylon 6?
Yes. PA6 is the ISO designation for nylon 6, also called polycaprolactam.
7. PA6 vs. Other Plastics: Melting Point & Heat Resistance
| Material | Type | Tm (°C) | Tg (°C) | HDT @ 1.8 MPa (°C) | Continuous Use (°C) |
|---|---|---|---|---|---|
| PA6 | Semi-crystalline | 220–225 | 50–60 | 60–100 (unfilled) | 80–120 |
| PA66 | Semi-crystalline | 255–265 | 50–70 | 70–100 (unfilled) | 100–120 |
| 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 |
PA6 offers a strong balance of mechanical properties, wear resistance, and processability. When higher heat resistance is required, PA66 is the natural upgrade; for extreme heat, PEEK is the choice.
8. Why Melting Point Matters for Procurement
- Processing window: Tm defines the minimum melt temperature; too close to Tm → incomplete melting; too far above → thermal degradation.
- Application fit: Never spec by Tm alone. Use HDT and CUT for load-bearing service temperature ceilings.
- Total cost: Correct barrel/mold temps directly affect cycle time, scrap rate, and energy cost — a 10°C error in either direction can shift piece cost by 3–8%.
- Safety compliance: Melt above 300°C releases toxic fumes; EHS documentation should reflect this.
9. Data Sources & Disclaimer
Data compiled from publicly available TDS for general-purpose PA6 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.
10. Related Resources
- Plastic Raw Material Melting Point: Complete Guide
- Nylon Melting Point: PA6 vs PA66 vs Specialty Grades
- PA66 Melting Point: Nylon 66 Melting Temperature & Processing Guide
- PP Melting Point: Crystalline Melting Range & Processing Temperatures
- PA6 Density: Nylon 6 Density Values & Moisture Effect
- PA6 Water Absorption: High Moisture Uptake & Drying Requirements
