PS — Polystyrene
Polystyrene
PS (general-purpose polystyrene, GPPS) is a transparent, rigid and very economical amorphous thermoplastic with excellent flowability. Ideal for transparent or aesthetic parts in injection molding (displays, housings, cups), but it remains brittle.
- Mold temperature: 20-50°C
- Melt temperature: 180-240°C
- Shrinkage: 0.3-0.6%
- Density: 1.04-1.06
- Manufacturer grades: Polystyrol 143E (INEOS Styrolution), Styron 685D (Trinseo)
Processing
PS is not hygroscopic: no pre-drying is required. Its very good flowability eases filling of thin parts: run the melt between 180 and 240 °C with a mold regulated between 20 and 50 °C. Its low amorphous shrinkage (0.3 to 0.6 %) ensures good dimensional stability.
Advantages
- No drying required (non-hygroscopic): fast startup
- High transparency (GPPS) and excellent surface finish
- Very good flowability: easy filling of thin walls
- Good dimensional stability (amorphous, low shrinkage)
Limitations
- Brittle: low impact resistance (prefer HIPS/high-impact PS)
- UV-sensitive: yellowing and embrittlement outdoors
- Limited chemical resistance to solvents and hydrocarbons
- Moderate thermal resistance and flammable without additive
Common injection molding defects
- Brittleness / cracking — Brittle or over-sheared material: limit speed, refine holding and avoid thermal degradation
- Weld lines — Very visible in transparency: raise melt temperature and injection speed
- Jetting — Filling too fast at the gate: reduce initial speed and reposition the gate
Typical applications
Packaging, disposable cutlery, CD cases, toys