Plastics and Polymers

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Plastics and Polymers

Polymers were first made in the early twentieth century and were known as ‘plastics’. Polymers are constructed from much smaller molecules (monomers) that are joined together to form long chains (polymers). The economy and many industrial companies rely on polymers as a vital resource. An advantage of using polymers over natural materials is that polymers can be manufactured very specifically with varying degrees of stiffness, density, heat resistance and electrical conductivity. The study of natural polymers has also led to great advances in medicine and nutrition. Polymers have a great many uses: sheets and films, adhesives, paints and inks and also synthetic fibres and yarns.

A very common polymer used widely in modern life is polyethylene (the simplest polymer). When it’s made into bags for supermarkets and other uses, it’s typically flexible and transparent. Its monomer (a single unit that is repeated) is Ethene (C2H4). It can be polymerised into polyethylene that generally contains around 105 Ethene monomers within its structure. The diagram shows the polymerisation of ethane into polyethene/polyethylene.

PVC (polyvinylchloride) is another widely used plastic containing Carbon, Hydrogen and Chlorine. Molecules of vinyl chloride combine to make long chain molecules of PVC. This synthetic polymer is quite cheap and easy to mould and is used to make a wide range of products including underground water pipes to thinner films used in packaging. Plasticisers can be used to make PVC softer and more flexible. They are small molecules that can dissolve into liquids that come into contact with them. The most common PVC plasticisers are phthalates. Some plasticisers, including phthalates have been banned in some areas of the EU after suspected feminisation of young children.

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The physical property of a particular polymer depends upon four variables:

  1. Chain Length – generally, the longer the chains the stronger the polymer as long chains tend to get tangled up in each other and stick together far more than shorter chain polymers. This means that the longer the chain, the stronger and the higher the melting point.
  2. Side groups – if the side groups in a polymer are polar, it gives stronger attraction between polymer chains.
  3. Branching – straight, unbranched chains can pack together more closely than highly branched chains, giving polymers a higher density, which in ...

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