Friction in rubbers and effect of particulate fillers on it

Rubber products have many applications in the industry and their performances must be evaluated and optimized for different applications. One of these applications is tribological aspect of rubber compounds, especially friction and grip of tread vulcanizates on the road surfaces. Studies have shown that rubber friction is directly correlated to the dynamic loss tangent (tan δ). Reinforcing fillers and their various characteristics have strong influences on the viscoelastic properties of rubber including tan δ. The important point of all these characteristics is the ability of filler aggregates to trap and immobilize the rubber chains in their structure which has direct influence on reinforcement and improvement of the vulcanizate performance. Studies have shown that every changes in the filler characteristics which reduces the distance between the filler particles in the vulcanizates, will increase the amount of immobilized rubber and improves the vulcanizate performance. Some of these changes are increasing the volume fraction of filler, reducing the particle size, changing the particle shapes and surface modification of polar fillers such as silica. This article will review the mechanisms causing rubber friction on various surfaces, its relation to viscoelastic behaviour of vulcanizats, and the role of common particulate fillers such as carbon black and silica.