Polystyrene (PS)
Glass-clear, dimensionally perfect and brittle enough to snap in your fingers. Adding a dispersed rubber phase fixes the brittleness and costs the clarity — which is why polystyrene is sold as two different materials.
Molecular Structure
What is Polystyrene (PS)?
Polystyrene carries a benzene ring on every second backbone carbon. Those rings are bulky and arranged irregularly, so the chains cannot crystallise — commercial polystyrene is wholly amorphous. That is why it is glass-clear, why it has virtually no shrinkage or moisture uptake, and why it holds dimensions better than almost any other commodity plastic.
It is also why it is brittle. An amorphous glassy polymer below its glass transition has no mechanism for absorbing impact energy, so general purpose polystyrene fractures rather than yields. The industry's answer is high impact polystyrene: polybutadiene rubber is dissolved in the styrene before polymerisation and ends up as discrete rubber particles grafted into the matrix, which stop crack propagation. The material becomes tough and opaque at the same time.
Production is by continuous bulk free radical polymerisation of styrene, which gives good control of molecular weight and leaves little residual monomer. The two families cover very different markets — clear packaging and lab ware for GPPS, thermoformed dairy pots and appliance liners for HIPS.
Polystyrene resists water, acids and alkalis but is attacked by almost every hydrocarbon, oil, ester and ketone it meets. Citrus oils, cooking oils, solvents and many adhesives will craze or dissolve it. Chemical compatibility deserves checking before the packaging design is finished, not after.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
A backbone carrying a phenyl ring on every second carbon. The rings are bulky and irregularly arranged, which prevents crystallisation entirely — the source of polystyrene's optical clarity, its dimensional stability and its brittleness alike.
Chain architecture — phenyl ring on every second backbone carbon
Structural Identity
- PolymerPolystyrene
- Repeat unit(C₈H₈)ₙ — styrene
- Repeat unit mass104.15 g/mol
- MorphologyAmorphous — atactic, cannot crystallise
- FamiliesGPPS (crystal) and HIPS (rubber modified)
- HIPS modifierPolybutadiene, grafted, 5 – 10%
- Made byContinuous bulk free radical polymerisation
- Chemical resistancePoor to hydrocarbons, oils, esters
- Key limitationBrittle below Tg unless rubber modified
- CAS Number9003-53-6
- Specified byFamily, MFR, Vicat, impact
Product Specifications
Chelora supplies Polystyrene (PS) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Polystyrene |
|---|---|
| CAS Number | 9003-53-6 |
| Repeat unit | (C₈H₈)ₙ |
| Families | General purpose (GPPS) and high impact (HIPS) |
| Density | 1.04 – 1.05 g/cm³ (ISO 1183) |
| Melt flow rate | 1.5 – 25 g/10 min at 200 °C / 5 kg (ISO 1133) |
| Vicat softening point | 88 – 102 °C at 50 N |
| Tensile strength at break | 35 – 50 MPa GPPS; 20 – 30 MPa HIPS |
| Elongation at break | 2 – 4% GPPS; 30 – 60% HIPS |
| Notched Izod at 23 °C | 1.5 – 2.5 kJ/m² GPPS; 7 – 14 kJ/m² HIPS |
| Flexural modulus | 2900 – 3400 MPa GPPS; 1600 – 2300 MPa HIPS |
| Light transmission (GPPS) | ≥ 88% |
| Haze (GPPS, max) | ≤ 3% |
| Rubber content (HIPS) | 5 – 10 wt% polybutadiene |
| Residual styrene monomer (max) | ≤ 500 ppm; lower for food grade |
| Total volatiles (max) | ≤ 0.10 wt% |
| Additive package | Mineral oil, lubricant, antioxidant; mould release to order |
| Food contact | FDA 21 CFR and EU 10/2011 declarations available |
| Packaging | 25 kg bags, 500 – 1250 kg jumbo bags, bulk |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Polystyrene (PS).
Thermoformed Packaging
HIPS sheet thermoformed into yoghurt and dairy pots, portion packs and trays — excellent formability, clean cut edges and dependable stacking.
Clear Rigid Packaging
GPPS for cosmetic containers, clear food trays, disposable cutlery, drinking cups and Petri dishes, where glass-like clarity is the selling point.
Appliance Liners
HIPS sheet for refrigerator inner liners and door panels, a long-standing application built on formability and consistent thickness distribution.
Durable Mouldings
Housings, hangers, toys, stationery and audio-visual parts, using HIPS where impact matters and GPPS where gloss and rigidity do.
Optical & Sheet
Light diffuser sheet, display and point-of-sale panels, and picture framing, exploiting GPPS's transparency and dimensional stability.
Copolymer Base
The base chemistry for SAN and ABS when copolymerised with acrylonitrile and butadiene, and for styrene-butadiene latex and SMA copolymers.
Why source Polystyrene (PS) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market or off-spec prime passed as prime.
Grade Flexibility
GPPS and HIPS supplied across injection, sheet extrusion and thermoforming grades. We match on melt flow rate, Vicat and impact together, since a single MFR figure describes very little on this polymer.
Full Documentation
Technical data sheet, CoA against the grade specification including residual styrene, SDS, REACH compliance, and food-contact declarations with every shipment.
Logistics Support
Experienced in polymer resin logistics — 25 kg bags, jumbo bags, containerised and bulk silo delivery, with pellet-loss controls in line with Operation Clean Sweep, for Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store pellets dry, indoors and out of direct sunlight. Polystyrene absorbs very little moisture, but surface condensation still causes splay and silver streaking in mouldings and sheet.
- Keep HIPS out of prolonged sunlight in particular. The polybutadiene rubber phase oxidises and the material yellows and loses impact strength, and neither change is reversible.
- Contain pellets rigorously. Spilled pellets reach watercourses through drains and are a recognised marine litter source — catch trays, drain screens and Operation Clean Sweep procedures at every transfer point.
- Control melt temperature and residence time. Polystyrene above about 260 °C depolymerises measurably back to styrene monomer, which raises residual monomer, causes odour and can cause splay in the part.
- Keep the resin away from hydrocarbons, oils, esters and ketones in storage as well as in service. Contaminated pellets craze and produce weak, hazy product.
- Ground and bond pneumatic conveying, and control fines — pellet fines cause specks and gels as well as presenting a dust explosion risk.
- Extract at the die and hopper. Styrene monomer released during processing has a low odour threshold, and its presence indicates the melt is running too hot or too long.
- Treat molten polymer as a serious thermal burn hazard — it adheres to skin and retains heat, so purging and die work need forearm and face protection.
- Segregate GPPS from HIPS and keep regrind streams separate. The two are visually distinguishable as pellets but not once blended, and cross-contamination ruins optical grades outright.
Hazard Summary
Classification: polystyrene in pellet form is not classified as hazardous under CLP. The polymer is inert and is widely used in food contact. The hazards are physical, process-related and — in the case of residual monomer — regulatory.
Residual styrene monomer: styrene is classified by IARC as probably carcinogenic to humans (Group 2A, following its 2019 re-evaluation) and is under continuing regulatory review in several jurisdictions. The polymer itself is inert; the concern is monomer migration from packaging into food, particularly fatty food. Commercial resin is held below 500 ppm total residual, and food-contact grades considerably lower. Confirm the residual figure on the certificate for food applications rather than assuming it.
Depolymerisation on overheating: polystyrene reverts to styrene monomer at elevated temperature more readily than most polymers. Running above roughly 260 °C, or holding material in a hot barrel, raises residual monomer in the finished part and produces a detectable odour. Melt temperature control is a food-safety control on this polymer, not just a quality one.
Poor chemical resistance: polystyrene is attacked by hydrocarbons, oils, fats, esters and ketones — including citrus and cooking oils, many adhesives and most solvents. Crazing and stress cracking follow, sometimes weeks after contact. This limits its use in packaging far more than any mechanical property does.
Brittleness: GPPS fails by brittle fracture with almost no warning and sharp edges. Where impact is credible in service, HIPS or a different polymer is the answer rather than a thicker GPPS wall.
Single-use restrictions: polystyrene foodservice items are banned or restricted in a growing number of jurisdictions, and the EU Single-Use Plastics Directive prohibits expanded polystyrene food containers and cups. Confirm the position for your destination market and product form before committing.
Fire: polystyrene ignites readily and burns with a very smoky, sooty flame producing carbon monoxide and styrene vapour. Bulk pellet and finished-goods storage warrant specific fire design.
PPE minimum: safety glasses and gloves for pellet handling; heat-resistant gloves, arm protection and face shield for die work and purging.
Consult the full SDS and the grade technical data sheet for processing temperature limits, and confirm food-contact status and destination-market restrictions before use.
Frequently Asked Questions
Technical and commercial questions about Polystyrene (PS) sourcing and specifications.
What is polystyrene used for?
HIPS sheet dominates thermoformed packaging — yoghurt and dairy pots, portion packs, trays — and refrigerator inner liners. GPPS covers clear rigid packaging, cosmetic containers, disposable cutlery and cups, Petri dishes and other lab ware, and optical applications such as light diffuser sheet. Both go into injection moulded durables including housings, toys and stationery. Polystyrene chemistry is also the base for SAN and ABS.
What is the difference between GPPS and HIPS?
GPPS, sometimes called crystal polystyrene despite being entirely amorphous, is styrene alone. It is glass-clear, very rigid and dimensionally stable, and it is brittle — it fractures at 2 to 4% elongation. HIPS is made by dissolving polybutadiene rubber in the styrene before polymerisation, so the finished polymer contains discrete rubber particles grafted into the matrix. Those particles blunt and arrest propagating cracks, raising notched impact strength several-fold and elongation to 30 to 60%. The cost is optical clarity — the rubber phase scatters light, so HIPS is opaque — plus some stiffness and heat resistance. The two are not substitutes; they serve different applications.
Why is polystyrene so brittle, and why does rubber fix it?
Because it is a glassy amorphous polymer well below its glass transition at room temperature. The chains are frozen, there is no crystalline structure to redistribute load and no molecular mobility to absorb energy, so a crack once started runs straight through. Dispersing rubber particles through the matrix changes the failure mechanism entirely: when stress concentrates at a particle, the surrounding matrix crazes in many small locations rather than forming one large crack, and that distributed crazing absorbs a great deal of energy. It is one of the clearest illustrations in polymer science that toughness is about crack arrest rather than raw strength.
What should I know about residual styrene and food contact?
Two things. First, the numbers: commercial polystyrene holds residual styrene monomer below around 500 ppm, and grades intended for food contact are made to considerably lower levels and tested against migration limits under FDA 21 CFR and EU Regulation 10/2011. Second, the context: IARC reclassified styrene as probably carcinogenic to humans in 2019, and it remains under regulatory review in several jurisdictions. The polymer is inert — the question is only what migrates out of it, and migration is highest into fatty and hot food. For food applications, ask for the residual styrene figure on the lot certificate and the migration testing behind the food-contact declaration, and note that processing too hot generates fresh monomer regardless of what the resin arrived with.
How are single-use plastic rules affecting polystyrene?
Significantly, and the direction is one way. The EU Single-Use Plastics Directive has prohibited expanded polystyrene food containers, beverage containers and cups since July 2021, and many jurisdictions in North America and Asia have adopted comparable restrictions on foodservice polystyrene. The rules generally target specific product forms — cups, clamshells, trays for immediate consumption — rather than the polymer as such, so thermoformed dairy packaging, durable mouldings and industrial applications are largely unaffected. Anyone taking a position in foodservice packaging specifically should check their destination market's current rules rather than a general statement.
What documentation does Chelora provide?
Every shipment includes the grade technical data sheet, a Certificate of Analysis against the grade specification covering melt flow rate, Vicat softening point, density, residual styrene monomer, total volatiles and the relevant mechanical or optical properties; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; food-contact declarations under FDA 21 CFR and EU Regulation 10/2011 with migration testing where applicable; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Polystyrene (PS) grade, volume, logistics, documentation, and lead times. We respond within one business day.
