Plastics are long chains — Chemistry, 7–10 years
Many plastics are polymers: very long molecules made by joining many small repeating parts. Their chain structure can make them light, flexible or tough, but it also means many plastics break down slowly in nature.
A molecule like a chain
A polymer is a very long molecule built from many smaller parts joined in a row. Imagine a necklace made from lots of similar beads, although a real polymer is far too small to see. Changing the small parts or the links can change the material's behaviour.
Why make long chains?
Natural materials do not always have the combination of strength, lightness and flexibility people need. Making long chains lets chemists design materials for particular jobs. The problem is that a useful object can become waste that stays around for a very long time after it is thrown away.
From a small part to a chain
Suppose one repeating part has a mass of 28 units. A short polymer chain made from 100 of these parts has a mass of about 2,800 units, ignoring the tiny change from joining them. The same joining idea, repeated many times, creates a material with properties different from one small part.
Not all polymers are plastic
It is reasonable to connect polymers with shopping bags because many everyday plastics are polymers. But polymer means a long chain of repeating parts, not one particular material. Wool, cotton and natural rubber contain natural polymers too, so polymers can come from living things or factories.
In clothes and packaging
Polyester clothing, nylon rope and many food packages use polymers. Their long chains can be chosen to make fibres strong, bottles light or films flexible. When choosing or throwing away such items, remember that the useful properties do not automatically make the material easy to recycle.
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