Acoustic analysis of bound rubber formed in silica/SBR compounds

The compressibility of the bound rubber around the silica particle was evaluated by an acoustic technique. The density and the longitudinal wave velocity of a silica/SBR compound were measured as a function of the silica content. The density increased linearly with the filler content. The longitudinal wave velocity was almost constant within the experimental error. The mass ratio of the bound rubber to the silica in the silica/SBR compounds was 1.08+/-0.03 kg kg(-1) which was measured by a thermal gravimetric analysis (TGA). The partial specific adiabatic compressibility of the silica was estimated as (0.1+/-0.5) x 10(-10) Pa(-1) on the basis of a three states model. The adiabatic compressibility of the bound rubbers in the silica/SBR compounds was (4.6+/-0.5) x 10(-10) Pa(-1). The compressibility was almost the same as that of the SBR, and the value was twice larger than the compressibility of the bound rubber formed in a CB/SBR composite.