ABSTRACT
Silica has gained commercial importance as filler in the 1970s in heavy-service tires for earth moving and mining equipment. It has become a common practice to improve the cutting and chipping resistance of heavy truck tires by adding 10–25 phr of silica to the conventional carbon black-loaded tread compounds, with adjustment of the carbon black level to maintain appropriate compound hardness. The surface of silica is covered by a layer of acidic silanol and siloxane groups. This highly polar and hydrophilic character of the filler surface results in a low compatibility with the rather apolar polymer. Besides, highly attractive forces between silica particles result in strong agglomeration forces. The coupling agents need a moiety enabling them to react with the polymer during vulcanization in order to be reinforcing. This is shown in experiments with coupling agents, which can react with the filler but not with the polymer: the reinforcing effect is reduced, as the formation of bond rubber is impossible.
