The Response to Water of Silica-filled ENR-25 Tread Compounds

The presence of silica filler in rubber vulcanisates has been shown to induce higher levels of water absorption than in either black-filled vulcanisates, or in silica-filled vulcanisates where the silica is shielded by a silane coupling agent.  A particular affinity of silica-filled ENR-25 vulcanisates for water is demonstrated by the reduced contact angle measured, compared with that for other filled vulcanisates. 
Water absorption in silica-filled ENR-25 vulcanisates is found to have a profound effect on equilibrium solvent swelling behaviour in toluene, reducing Vr by some 20%, indicating a reduction in the degree of interaction between ENR-25 and silica filler.  Water absorption also modifies a range of physical characteristics that relate to tyre tread performance including tensile properties and damping characteristics.  The changes observed in the physical characteristics of silica-filled ENR-25 vulcanisate upon exposure to water give an insight into the superior wet traction performance of this tread compound. This is believed to be the first example of a tyre tread compound that is able to respond to its environment in this way.