There are many different types of plastic; they can all be divided into two main groups. These are called ‘thermoplastics’ and ‘thermosetting plastics’. Thermoplastics include polypropylene, polystyrene, polyester, acrylics and nylons. These types of plastic melt when heated and become solid again as they cool. Thermosetting plastics do not behave in this way. Bakelite and melamine are both thermosetting plastics.
• When plastics are made they are either in the form of thick liquid or solid granules. This material is called ‘raw plastic’.
• The granules are tipped into a container and heated until they melt. They may contain a colouring dye.
• The liquid plastic is then poured into a mould. The shape inside the mould is exactly the same shape as the finished article.
• Until this point the thermoplastics and the thermosetting plastics are treated in the same way.
Thermoplastics are often used for clothing and packaging material, both of which can be recycled. Thermosetting plastics are resistant to high temperatures. For this reason they are often used to make saucepan handles and ashtrays.
The strong polymer links of the thermosetting plastic mean that it holds its shape even when heated. Plastics of this kind cannot be melted down and used again easily.
THERMOSETTING PLASTICS
- When the thermosetting plastic is heated, links form between the polymers in the plastic. They become joined together into a permanent structure.
THERMOPLASTICS
- The thermoplastic, however, has different types of links and can be melted down and used again.
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