Polymers - 8
Rubber
Natural rubber was first introduced to Europe in the mid. 18th century - and is an example of an elastomer - an elastic polymer. A problem was that matural rubber is a very weak, soft thermoplastic when heated - but very brittle when cold. A process, vulcanisation, was invented by Goodyear, where rubber heated with sulphur produces a harder, less tacky elastic material. Here the long polymer chains are bonded together by sulphur atoms. The sulphur links gives the polymer a measure of rigidity - so that it does not undergo permanent change when stretched - and springs back to its original shape and size when the stress is removed.
