Lost and found
Ellen and Kathy get messy with rubber in the lost at sea video extra.
Lost at sea diaries
Related programme
In the Rough Science programme Lost at Sea, the Rough Scientists Ellen and Kathy are given the task of making a life-jacket. They decide to use kapok to fill the jacket but need to make it waterproof so the contents don’t get wet. Zanzibar has a rich variety of plants and on one of her trips inland Ellen spotted some rubber trees – so they know they can get some fresh latex, but the problem is how to make this cover the life-jacket to give a strong but flexible barrier. The answer is Vulcanisation, precipitating out the rubber particles, mixing them with sulphur and heating the treated material over a fire.
To find out more about the process of vulcanisation read the following extract from the second level OU course Our Chemical Environment (ST240).
We can form covalent bonds between the polymer molecules, and if we do this the material will become much more rigid because the chains are no longer free to move apart. The more cross-links between chains, the more rigid the rubber until eventually the polymer is so cross-linked that it is no longer rubbery because there is no flexibility of the chains between the cross-links. Goodyear’s vulcanization process produces a controlled amount of cross-linking. The sulfur reacts with the double bonds and forms sulfur bridges as cross-links between the chains, resulting in a huge three-dimensional network as you can see here.
(a) Unvulcanized natural rubber molecules have few if any cross-links.
(b) Vulcanized rubber has a network structure with cross-links.
(c) Vulcanized rubber on stretching.
The covalent cross-links survive the stretching and help the molecules to spring back once the tension has been relaxed. This type of network molecular structure lies behind the explanation of why rubber is rubbery.
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Content last updated: 01/02/2005
