Recycling

Even where plastics have a relatively short functional lifespan, it can take a very long time for them to decompose in the natural environment. On waste tips, plastic is a problem in terms of volume as well as pollution from the additives that seep into the soil and ground water. Residues of fluorocarbon foaming agents will be emitted continually.

These problems can be greatly reduced by controlled collection and recycling of plastic materials; however, in many countries today only a small fraction of plastics are effectively recovered.

Recycling by re-use of whole components is seldom really practicable due to limited durability and necessary quality assurances being difficult to perform. Material recycling through melting is an option for thermoplastics and even a few of the thermosetting plastics. Amongst these are PVC, polyethylene and polypropylene. Material recycling for purified polyurethane products is also possible, in theory, but is not occurring much at present. Synthetic rubbers can be crumbled for use as a filler.

The maximum potential for future plastics recycling is estimated at 20-30% in the form of down-cycling only. Almost all plastics are impure, due to additives, which makes reclamation of the original materials technically difficult. The quality of the plastic also becomes lower for every cycle performed. After three cycles of recycling polystyrene suffers a 9% reduction in the size of its polymer chains and a 34% reduction in impact strength (Stevens, 2002).

Uses for recycled plastic vary from park benches, sound barriers and flowerpots to huge timber-like prefabricated building units for construction. The latter are now in production in Great Britain, Sweden and the USA, based on melted polystyrene waste with 4% talcum powder and

11% other additives. Polystyrene can also be ground and added to concrete to increase its insulation value.

Energy down-cycling recovers the energy content (calorific value) of the original raw materials. In the case of plastics this is considerable, since they were derived from fossil fuels. However, the problematic polymers and additives often require very advanced combustion technology and flue gas cleaning in order to avoid serious toxic emissions. If one burns plastic wastes, release of carbon dioxide equivalent to burning the same quantity of fossil fuel is also unavoidable. From a climate change perspective, one could thus argue that depositing and storing these materials would be a better option.

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