EXTRACTION STUDIES ON THE NATURE OF THE BONDING IN FILLER-REINFORCED ELASTOMERS

Particles of iron oxide were blended into samples of cis-1,4-polybutadiene and polyisobutylene, and portions of both the unfilled polymers and the resulting polymer-filler mixtures were cured with benzoyl peroxide. The fined networks were cloudy, but strips extracted using a toluene-hydrochloric acid mixture became as clear as the unfilled networks, suggesting effective removal of the filler particles. Measurements of equilibrium swelling and stress-strain isotherms in elongation were carried out on the unfilled elastomers, and on the filled ones both before and after extraction, in order to study the nature of the bonding between the filler particles and the polymer chains. There were no significant differences between the degrees of equilibrium swelling and the stress-strain isotherms of the unfilled networks and the corresponding properties of the previously-filled networks after the filler particles had been removed. This suggests that the bonding between the filler particles and the elastomer chains in these systems is primarily physical rather than chemical.