The use of fillers in rubber is almost as old as the use of rubber itself. It has been observed since long that incorporation of particulate fillers such as carbon black increases the strength of vulcanized rubbers significantly, even more than tenfold by reinforcing it. Thus it is hardly surprising that relatively few applications of elastomers use the polymer in the unfilled state.
Reinforcement has been defined as the incorporation of small particles of materials, known as fillers, into rubber which improves the modulus and failure properties (tensile strength, tear resistance and abrasion resistance) of the final vulcanizate. In general, when a reinforcing agent is added to a base pure gum recipe, that agent imparts greater stiffness and higher ultimate tensile strength than would be obtained by using an equal volume of a common filler, e.g. coarse particle size whiting. The usual quantities of these materials are, 10-50 parts per 100 parts by volume of rubber.