Nylon Chemical Resistance: Acids, Bases, Solvents, Automotive Fluids, and Food Contact
Chemical resistance is the single most misunderstood property of nylon in engineering procurement. Most engineers treat “nylon” as a single material when assessing chemical compatibility, then are surprised when PA6 and PA12 behave dramatically differently in the same environment.
This guide provides systematic chemical resistance data for PA6, PA66, and PA12 across all major chemical classes, with clear guidance on when nylon is appropriate and when alternative materials should be specified.
Understanding Nylon Chemical Resistance Mechanisms
Nylon resistance to chemicals operates through three distinct mechanisms. Understanding which mechanism applies to your environment determines whether the material will perform reliably.
Physical resistance: The polymer matrix physically blocks chemical penetration. This is the dominant mechanism for non-polar solvents like gasoline and oils — nylon has excellent resistance because hydrocarbon molecules cannot penetrate the crystalline domains.
Chemical resistance: The polymer chain does not react with the chemical. This is why nylon is attacked by strong acids and bases — they hydrolyze the amide bonds in the polyamide chain.
Plasticization and swelling: Water and polar solvents penetrate the amorphous regions, swelling the polymer without breaking chemical bonds. This increases flexibility but reduces stiffness and dimensional accuracy.
| Chemical Class | PA6 | PA66 | PA12 | Primary Mechanism | Application Notes |
|---|---|---|---|---|---|
| Motor oils (mineral) | ممتاز | ممتاز | ممتاز | Physical barrier | Under-hood auto applications |
| Motor oils (synthetic) | ممتاز | ممتاز | ممتاز | Physical barrier | ATS, DCT fluids |
| Gasoline (aromatic) | Good (60°C) | Good (100°C) | ممتاز | Physical barrier | Fuel rails: PA66-GF30 |
| Ethanol blends (E85) | Limited | Limited (80°C) | ممتاز | Physical + swelling | Fuel lines: PA12 preferred |
| Diesel, Biodiesel | جيد | جيد | ممتاز | Physical barrier | Fuel system components |
| ATF / Transmission fluid | Good (120°C) | Excellent (150°C) | جيد | Physical barrier | Transmission oil pans |
| Glycol coolant (50/50) | Good (100°C) | Good (130°C) | ممتاز | Swelling (limited) | Coolant reservoirs |
| Brake fluids (DOT 3/4/5) | Poor | Poor | جيد | Chemical attack | Use PA12 for brake components |
| Weak acids (<10%) | Limited (elev T) | Limited (elev T) | جيد | Chemical hydrolysis | PA12 or PP for acid contact |
| Strong acids (>10%) | Not recommended | Not recommended | Limited | Rapid hydrolysis | PVDF or PTFE for acid |
Water Absorption and Its Effect on Chemical Resistance
Moisture absorption fundamentally changes nylon’s chemical resistance profile. Dry nylon is more chemically resistant to polar solvents (the plasticized, wet state actually resists further polar penetration) but is more susceptible to oxidative degradation. This creates a critical design consideration: parts in wet service should be tested in the conditioned (wet) state, not dry-as-molded.
| Conditioning State | PA6 Tensile Strength | PA6 Modulus | Chemical Resistance to Water | Chemical Resistance to Acids |
|---|---|---|---|---|
| Dry as molded (0%) | 85 MPa | 3,200 MPa | N/A | Poor (brittle failure) |
| Conditioned 50% RH (2.5%) | 65 MPa | 2,000 MPa | Moderate | Moderate (ductile) |
| Saturated (9.0%) | 45-50 MPa | 1,200 MPa | Swells significantly | Moderate (ductile) |
| After drying (0.1%) | 80+ MPa | 3,000 MPa | ممتاز | Poor (brittle failure) |
Industrial and Laboratory Chemical Environments
For chemical processing and industrial equipment, verify compatibility under actual operating conditions with immersion testing. The following table provides baseline guidance for common industrial chemicals.
| Chemical | PA6 | PA66 | PA12 | Max Service Temp (°C) | Alternative Material |
|---|---|---|---|---|---|
| Sulfuric acid (10%) | Limited | Not recommended | Limited | 40°C | PVDF, HDPE |
| Hydrochloric acid (10%) | Not recommended | Not recommended | Limited | 40°C | PVDF, PTFE |
| Sodium hydroxide (50%) | Limited (>60°C) | Not recommended | جيد | 80°C | PP, HDPE |
| Acetone | Limited | Not recommended | جيد | 60°C | PTFE |
| Ethanol | جيد | جيد | ممتاز | 100°C | PA12 preferred |
| Phenol (5%) | Not recommended | Not recommended | Not recommended | N/A | PTFE only |
| Formic acid (10%) | Not recommended | Not recommended | Limited | 40°C | PTFE, PVDF |
| Calcium chloride | Limited | Limited | جيد | 80°C | PA12 for salt contact |
| Steam (continuous) | Not recommended | Not recommended | Limited | 120°C | PPS, PTFE |
Automotive Fluids: The Most Common Real-World Exposure
Automotive under-hood applications define the largest volume of nylon use globally. The following data reflects ASTM D543 immersion testing results at specified temperatures and exposure durations (typically 1,000 hours = approximately 6 weeks of continuous exposure).
| Fluid | PA6 | PA66 | PA12 | Weight Change | Tensile Retention | Application Confidence |
|---|---|---|---|---|---|---|
| Engine oil SAE 5W-30 (150°C) | ممتاز | ممتاز | ممتاز | <1% | >95% | Full production use |
| Transmission fluid ATF (130°C) | جيد | ممتاز | جيد | <2% | >90% | Full production use |
| Power steering fluid (120°C) | جيد | جيد | ممتاز | <2% | >90% | Full production use |
| Coolant 50/50 EG (130°C) | جيد | جيد | ممتاز | <3% | >85% | Full production use |
| Brake fluid DOT 4 (120°C) | Poor | Poor | جيد | >10% | <60% | PA12 only |
| Windshield washer (60°C) | ممتاز | ممتاز | ممتاز | <0.5% | >99% | Full production use |
| Battery acid (25°C) | Not recommended | Not recommended | Not recommended | N/A | N/A | PP or PE only |
| AdBlue / DEF (urea) | جيد | جيد | ممتاز | <1% | >95% | SCR system components |
Frequently Asked Questions
Q: Is nylon suitable for fuel contact applications?
A: Standard nylon (PA6, PA66) is compatible with gasoline and diesel fuel for automotive applications. However, prolonged exposure to ethanol-blended fuels (>10% ethanol) can cause swelling and property reduction. For biodiesel or ethanol-rich fuels, consider specialty grades like PA12 or impact-modified PA6.
Q: How does temperature affect chemical resistance?
A: Chemical attack rates approximately double with every 10°C temperature increase. A chemical that shows negligible effect at 23°C may cause significant degradation at 60°C. Always test under actual operating temperatures, or apply appropriate safety factors based on Arrhenius acceleration principles.
Q: Can I use nylon with brake fluid?
A: Nylon is NOT recommended for brake fluid contact. Glycol-based brake fluids (DOT 3, 4, 5.1) attack nylon, causing stress cracking and property degradation. Silicone-based fluids (DOT 5) are less aggressive but still not recommended. Use POM, PP, or EPDM for brake system components.
Q: What about UV exposure?
A: Unfilled nylon has poor UV resistance, degrading within months of outdoor exposure. For outdoor applications, specify UV-stabilized grades (carbon black or HALS additives), or plan for paint/coating. Glass-filled grades offer improved UV resistance due to reduced surface polymer content.
