There are many materials that utilize air pockets as part of their structure; by doing so they reduce the quantity of material and so reduce the weight of that part. Clearly these qualities are valuable in reducing carbon footprints. However, the main issue with expanded polystyrene (EPS), approximately 98 per cent air, and expanded polypropylene (EPP) is that they are used as bulky packaging for transient types of products, which is extremely difficult to get rid of.
One way of looking at this issue is to look at the timespan of the usage against the time it takes to make the oil/plastic and the time it will take the plastic to degrade. For example, it takes millions of years to produce the ingredients from which petroleum-based plastics are derived, and sandwiched between that and the hundreds of years that they take to fully degrade is a microscopically small amount of time in which the products are actually used. A lot of valuable and limited materials are used to produce something that has a very short lifespan and then is just thrown away.
However, these foams can have a much richer range of potential applications than we might assume. The advantage they can bring to more long-term use products is that they are very lightweight and, because they are foams, use very little raw material compared to solid mouldings of plastics. As the basis for ABS, SAN, ASA and HIPS, polystyrene belongs to the styrene family of polymers, which is a naturally occurring substance found in the environment.
Image: Tom Dixon’s EPS chairs
•Inexpensive
•Lightweight
•Good insulation properties
•Good thermal insulation
•Cushioning
•Recyclable
Sources
Widely available from multiple suppliers.
Cost
Low cost: £1.30 ($2) per kg.
Sustainability issues
Although 98% air, it is often viewed as not being environmentally friendly. However, polystyrene foam has never used CFCs or HCFCs during production. The perception of bulky packaging not being recycled but left to accumulate enforces the perception of the material being unenvironmental. As a result, big steps have taken place in the last few years to provide recycling facilities. Once collected, the waste is compacted and remoulded in its compacted form or ground down to be used in new products.
Production
Polystyrene foam production is based on tiny polystyrene beads that are expanded to 40 times their original size using steam and pentane. Steam is then used in the final phase to inject the material into the mould. Polystyrene is much less of a performance material than EPP, not having its range of densities, flexibility and strength. In other forms, foamed polystyrene is extruded and thermoformed into trays. Like EPP, components are formed in aluminium male and female mould tools with steam introduced from behind each half of the tool.
Typical applications
Historically found in disposable drinking cups and food trays (although now often replaced by laminated paper) and in packing. Expanded polystyrene has also been used on a much larger scale in housing. In the Netherlands it has been used as a buoyant platform and a house in the UK has been made entirely of expanded polystyrene. In horticultural applications it is used to control temperature around root growth.
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–Inexpensive –Lightweight –Shock absorbent –Offers good insulation –Recyclable |
–Perceived as being environmentally unfriendly –Not especially strong or flexible |