Polystyrene Recycling Guide: HIPS vs GPPS, Sources and Uses

Polystyrene is used in everything from refrigerator liners to disposable cups and clear display boxes. Recycled polystyrene granules are bought by moulders and extruders making household items, stationery, hangers, trays and many other products. To trade it well, suppliers and buyers need to understand the two main types, high impact polystyrene and general purpose polystyrene, and keep them apart.

This guide explains the difference, the common scrap sources, how to deal with brittleness, and where recycled material is used.

HIPS vs GPPS

Point	GPPS	HIPS
Appearance	Clear and glossy in natural form	Opaque, usually white
Toughness	Rigid and brittle	Tougher, thanks to rubber modification
Typical products	Clear boxes, cups, cutlery, display parts	Appliance liners, trays, toys, housings
How it breaks	Snaps cleanly, often with a glassy edge	Bends and whitens before breaking

GPPS is plain polystyrene. HIPS is polystyrene with added rubber particles, which absorb impact and make it less likely to crack. Both have a density around 1.04-1.05 g/cm3, so they sink in plain water and cannot be told apart by a float test. A simple bend test is usually the quickest check: GPPS snaps, HIPS bends and turns white at the stress point. See the knowledge page on HIPS for more on rubber modification.

Common scrap sources

• Appliance liners and parts: refrigerator inner liners, trays and covers are often HIPS. They may carry foam insulation, adhesive or metal fittings that must be removed.
• Disposables: cups, plates and cutlery may be GPPS or HIPS. Post-consumer disposables are often dirty and need washing.
• Packaging: clear boxes and blister parts are often GPPS, while some trays are HIPS. Expanded polystyrene foam is a different stream and is usually densified separately.
• Post-industrial scrap: runners, sheet trim and rejected parts from moulders and thermoformers. These are the cleanest and most consistent sources.

Keeping streams clean

Mixing HIPS and GPPS gives a material with properties somewhere in between, which may suit some buyers but not those who need a specific grade. Keep them separate where you can and say clearly when a lot is mixed. ABS is another common contaminant because it looks similar to HIPS in appliance scrap; the two do not mix well and should be sorted. See ABS and engineering plastics recycling for ABS handling.

Dealing with brittleness

Recycled polystyrene, especially GPPS, can become more brittle after each heat cycle. To limit this:

• avoid overheating during grinding and pelletising;
• keep runs short when the material is in the melt;
• blend GPPS with HIPS if the buyer accepts a mixed grade and needs more toughness;
• test impact strength and MFI on regular lots so changes are noticed.

Buyers should run trials with the actual lot they intend to use, since brittleness shows up in the finished part, not always in the granules.

Where recycled polystyrene is used

Recycled HIPS is used for hangers, stationery, toys that do not touch food, trays, household items and internal appliance parts. Recycled GPPS goes into clear or tinted products where small specks are acceptable, and into blends. Darker and mixed lots are often coloured black. See recycled HIPS granules and recycled GPPS granules for product details.

Processing recycled polystyrene

Polystyrene does not absorb much moisture, so drying is often less critical than for PC or nylon, though damp regrind from washing lines should still be dried. It melts and flows easily, which suits injection moulding and sheet extrusion. Grind sizes should be kept even, because fines from brittle GPPS can cause uneven feeding. When pelletising appliance scrap, use melt filtration to remove foam particles and paper that survived manual cleaning.

What to state in a listing or requirement

Both sides should be specific: HIPS, GPPS or mixed; source such as appliance liners or post-industrial sheet; form such as regrind or granules; colour; and any test values. Buyers should say what product they are making, as this decides how much toughness and clarity they need.

On PlasticSetu

Suppliers can list your materials with the polystyrene type and source, and the sourcing desk will contact you when a buyer requirement matches. Buyers can get quotes and request samples for trials.