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).

Chains of natural rubber are very long and have few if any cross-links, and so the material is a thermoplastic, becoming soft and sticky in the summer and hard and brittle in the winter. These disadvantages were overcome in 1839 by a discovery made accidentally by Charles Goodyear in Woburn, Massachusetts. The story goes that after many years of experimenting, he had spilt or accidentally placed a mixture of rubber, sulfur and lead oxide on a hot stove. The rubber was no longer sticky but had been converted to a tough, elastic substance stable to heat and cold. It also did not dissolve in the solvents that dissolved natural rubber. He had invented the process now known as vulcanization.

Vulcanization is a chemical reaction between sulfur and rubber resulting in cross-links being formed between the rubber polymer chains. Notice here:

that there are double bonds present in the polymer molecule. You should remember that double bonds provide a major route to the formation of polymers, so it should not be a surprise to find that these double bonds can serve to provide covalent links between the chains.

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