Environmental stress cracking happens when a part under stress (from molding, assembly or load) touches a chemical that doesn’t dissolve it but does attack it at the stressed spots. Cracks appear days or months later, often near screws, snap fits or press fits. It’s one of the most common causes of plastic part failure in the field.
Who is vulnerable to what
| Resin | Commonly attacked by |
|---|---|
| Polycarbonate, PC/ABS | Many solvents, some cleaners, oils and plasticizers |
| ABS, polystyrene | Oils, fats, some cleaners and solvents |
| Acrylic | Alcohols and solvents |
| Polyethylene | Detergents and surfactants (measured as ESCR) |
General patterns only. Test with the actual chemical, concentration and temperature.
Fixes
- Reduce the stress: radius sharp corners, avoid over-tight screws and press fits, anneal if appropriate.
- Pick a higher-resistance grade of the same resin: for polyethylene, lower-MI and bimodal grades have much better ESCR. HMW-HDPE
- Move to a semi-crystalline resin: polypropylene, nylon, PBT and acetal resist most oils and solvents far better than amorphous resins.
- For harsh chemicals: PVDF or other fluoropolymers. PVDF