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One of the useful properties of polymers is that they are unreactive. This means they are suitable for storing food and other substances safely. Unfortunately, this property makes it difficult to dispose of polymers.

Most polymers, including poly(ethene) and poly(propene), are not biodegradable. This means that microorganisms cannot break them down so they:

• cause a litter problem if disposed of carelessly
• last for many years in landfill sites

Suitable locations for landfill sites are difficult to find. Space in landfill sites is wasted if it is filled with non-biodegradable polymers.

Incineration

Waste polymers can be incinerated. This involves combustion at very high temperatures. Incineration releases a lot of energy which can be used to heat homes or to generate electricity.

There are problems with incineration. Waste gases are produced, including:

• carbon dioxide, a greenhouse gas which contributes to global warming
• toxic gases, which need removing before they leave the chimney

The use of landfill and incineration wastes valuable resources. Crude oil is the raw material for making most polymers, and it is a finite resource.

Recycling reduces the problems of disposal, and also reduces the volume of crude oil used.

Recycling of PET plastics

PET (polyethylene terephthalate) is a polyester (a plastic). There are two methods to recycle PET:

Open-loop recycling

The flaked PET is not totally pure, so the quality of the recycled material is less than the original polymer. Once the recycled material has been used it cannot be recycled again. It is likely to end up in landfill sites.

Closed-loop recycling

The quality of the recycled material is as high as the original material, so it may be recycled again. This reduces the use of raw material (crude oil) and landfill even more than open-loop recycling.