Sunlight breaks down most plastics. The first signs are fading, yellowing or a chalky surface. Later the part turns brittle and cracks. How fast it happens depends on the resin, the color and the additive package.
Which resins hold up, and which don’t
| Resin | Outdoors without UV protection |
|---|---|
| ABS, polystyrene | Poor. Yellows and becomes brittle. |
| Polycarbonate | Yellows and hazes over time unless UV-stabilized. |
| Polypropylene, polyethylene | Chalk and embrittle unless stabilized. |
| Nylon, acetal | Fair to poor without stabilizers. |
| ASA | Good. The usual outdoor replacement for ABS. |
| Acrylic (PMMA) | Very good. |
| PVDF | Excellent. |
Fixes
- A UV-stabilized grade of the resin you already run. Stabilizers (UV absorbers and HALS) slow the damage a lot.
- ASA instead of ABS. It processes much like ABS but is built for outdoor use. ASA / SAN
- A UV concentrate added at the press, if you color in-house. Additive concentrates
- Darker colors and carbon black protect better than light colors and naturals.
- A weatherable cap layer (ASA, acrylic or PVDF) over a cheaper substrate, for extruded profiles and sheet.