PS Material Guide for Thin-Wall Food Packaging Production

General-purpose polystyrene (GPPS) is an amorphous thermoplastic with exceptional optical clarity (light transmission >88%, haze <3%), high stiffness (flexural modulus 2,800-3,400 MPa, approximately 2x PP homopolymer), and excellent dimensional stability due to low shrinkage of 0.4-0.6%. GPPS density is 1.04-1.06 g/cm3, approximately 15% heavier than PP. Glass transition temperature (Tg) is 90-100C, defining the maximum use temperature. High-impact polystyrene (HIPS) contains 5-12% polybutadiene rubber phase that improves impact strength to 5-12 kJ/m2 (Izod, ISO 180) versus <2 kJ/m2 for GPPS, at the cost of transparency (HIPS is opaque). Both grades are FDA 21 CFR 177.1640 compliant and EU 10/2011 approved for food contact. PS carries resin identification code 6 with limited recycling infrastructure compared to PP (code 5) and PET (code 1). For thin-wall injection molding, PS offers the advantage of being amorphous, meaning no crystallization phase during cooling, enabling shorter cooling times versus semi-crystalline PP at equivalent wall thickness.

PS processing differs significantly from PP due to its amorphous nature and higher glass transition temperature. Barrel temperature profile: zone 1 (feed) 180-190C, zone 2 200-220C, zone 3 220-240C, zone 4 (nozzle) 230-250C. PS is sensitive to thermal degradation above 260C, producing styrene monomer gas and yellowing. Keep melt residence time under 5 minutes. Mold temperature: 20-50C for GPPS (lower for cycle speed, higher for surface gloss), 30-60C for HIPS. Injection speed: 250-380mm/s for thin-wall PS on the SPV5, generally 10-15% lower than PP speeds because PS has higher melt viscosity at equivalent MFI designation due to different test conditions (200C/5kg versus 230C/2.16kg for PP). Injection pressure: 120-180 MPa, lower than PP due to PS's better flow characteristics in thin sections once above Tg. Hold pressure: 30-50% of injection pressure for 0.3-0.6 seconds. Back pressure: 5-10 MPa (lower than PP). Key processing advantage: PS has zero crystallization, so cooling is governed purely by heat conduction to reach ejection temperature of 60-70C. This typically allows 0.3-0.5 second shorter cooling times than PP at equivalent wall thickness.

GPPS transparent containers are widely used for deli packaging, bakery display cases, salad containers, and fruit/berry punnets where product visibility drives consumer purchase decisions. On HWAMDA SPV5 machines, typical GPPS container production: 400ml deli container at 12-18g, 0.45-0.5mm wall, 4-6 cavity mold on SPV5-450/480, cycle time 5-7 seconds, producing 2,060-4,320 containers per hour. Clarity advantage: GPPS at <3% haze versus clarified PPR at 5-10% provides visually superior product presentation. HIPS disposable tableware production: forks/spoons at 3-5g, 0.4mm wall, 24-48 cavity on SPV5-270/320, cycle time 3-4 seconds, producing 21,600-57,600 pieces per hour. HIPS plates at 6-10g, 8-16 cavity on SPV5-320, cycle time 4-5 seconds. For cups (drinking cups, cold-beverage cups), GPPS provides clarity while HIPS provides impact resistance for vending applications. Thermoformed PS dominates large-volume cup production, but injection-molded PS cups at 4-8 cavity on SPV5-270/320 serve markets requiring custom shapes, thick rims, or interlocking stackability features not achievable in thermoforming.

PS faces increasing regulatory pressure in several markets that must be factored into investment decisions. The EU Single-Use Plastics Directive (2019/904) restricts expanded polystyrene (EPS) food containers but does not specifically restrict injection-molded PS tableware, though individual EU member states may implement broader restrictions. France has banned certain PS food containers. Several US states and cities have banned EPS food packaging with some extending restrictions to solid PS. China's plastic pollution plan targets single-use PS tableware reduction. However, injection-molded PS remains fully legal and widely used for food packaging in most global markets as of 2026. Food-contact compliance: GPPS and HIPS meet FDA 21 CFR 177.1640 and EU 10/2011 requirements. Overall migration limit: 10 mg/dm2. Specific migration of styrene monomer: maximum 0.05% residual in polymer. HWAMDA SPV5 machines process PS with standard barrel and screw configurations (no special screw geometry needed). For producers planning long-term investment, consider dual-material capability: the SPV5 processes both PS and PP without hardware changes, enabling product line transitions if regulatory environments shift toward PP dominance.