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Compounding
Raw rubbers have few uses in their natural state. To achieve the desired range of properties, the raw rubber must be combined with a range of additives. The selection of appropriate additives, and their skilful and consistent mixing, is known as compounding.
The additives in a rubber compound may vary from 2-3% (in the case of a rubber band) to over 60% by
weight and will include some or all of the following:
Curatives
Active chemicals which bring about the cross-linking of the long chain rubber polymer. Sulphur was the first to be discovered and is still commonly used.
Accelerators
Chemicals which vary the speed and timing of the curing reaction.
Reinforcing Fillers
Materials which increase the strength of the material. Carbon black and silicas are the most commonly used.
Fillers
Relatively inert chemicals, such as clays, which increase the bulk of the compound.
Pigments
Added to produce specified colours. They can only be used with compounds which do not contain carbon black.
Plasticisers
Added to aid processability or to produce specified properties.
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