About Harboro Rubber Engineering in Rubber      Contents      Introduction      Uses of Rubber      Processing Rubber          Compounding          Mixing          Pre-Forming          Moulding          Finishing      Designing With Rubber      Selecting / Specifying Rubber      Quality In Rubber      Rubber Directory      Health & Safety      Measuring Properties      Glossary of Terms      Request A Copy Contact Information

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.