Polystyrene (PS)

0.7-1.6 usd/kg
Circularity potential
Medium
Strength
Medium
Production energy
Very high
Stiffness
Low
Embodied CO2
Medium
Density
Medium

Polystyrene (PS) is a cheap plastic used for moulded packaging and disposables, as well as a rigid foam, expanded PS (EPS). Both have their own unique set of qualities but may still be useful for the same applications, but for different reasons. For example, food containers – one thin and transparent, and the other an insulating and protective foam. While the monomer styrene is extremely hazardous and a known carcinogen, it is considered non-hazardous once polymerised. However, there may be instances where the monomer is not fully polymerised and can potentially leach out, such as into lipophilic food.

As a moulded plastic it has excellent transparency and resistance to water. It is predominately used in packaging and medical containers, as well as brightly coloured tableware and disposables. PS is brittle and will breakdown relatively quickly when exposed to sunlight, becoming yellow. Where transparency and durability are required, there are many alternative options available depending on the requirements, such as polycarbonate (PC), polymethyl methacrylate (PMMA), acrylic and polyethylene terephthalate (PET), polyester. Plastic free options include soda lime glass and borosilicate glass.

Expanded polystyrene (EPS) is a lightweight and rigid foam that provides excellent impact absorption and insulating properties. These qualities are utilised for packaging, safety and as a construction material. It provides an important role as insulation, saving energy throughout its life. However, it is quite voluminous and this presents some challenges with transportation and recycling. Only a very small percentage is PS (typically 2-5%), which means it may be considered too expensive or impractical to collect and recycle.

Recycled
rPS
Recycled polystyrene

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Sustainability concerns
Low circularity potential
Microplastics


Polystyrene (PS) is recyclable and available as post consumer recycled (PCR) material. However, it is not so common. There are two main reasons. Firstly, PS is not so as recognisable or easy to separate as some of the other commodity plastics like polyethylene terephthalate (PET), polyester, or polypropylene (PP). Secondly, expanded polystyrene (EPS), which makes up a large proportion of the use of PS, is mostly air. This means it is not always economical to collect and transport for recycling – it works out cheaper to make EPS from virgin PS. Some recycling centres have compaction equipment and this makes it possible to compress the EPS and convert it into a more valuable recycling feedstock.


Design properties
Cost usd/kg
0.7-1
Embodied energy MJ/kg
43-52
Carbon footprint kgCO2e/kg
0.6-1.9
Density kg/m3
1045
Tensile modulus GPa
3-3.6
Tensile strength MPa
30-44
Flexural modulus GPa
3.2
Flexural strength MPa
76
Compressive strength MPa
90
Hardness Mohs
1.5
Rockwell hardness R-scale
85-90 D
Poissons ratio
0.4
Thermal expansion (µm/m)/ºC
98-120
Heat deflection temperature ºC
90
Thermal conductivity W/mK
0.1-0.14
Temperature min-max °C
-20 to 60
Thermal
insulator
Electrical
insulator