Effect of tackifiers on the autohesion of uncrosslinked styrene-butadiene rubber

The effect of a terpene resin tackifier, a phenolic resin tackifier, and a processing oil on the rheology and autohesion of a styrene-butadiene elastomer (SBR) was examined. Relative autohesion, G;Solution cast SBR/tackifier blends differed from mechanically mixed blends in two important ways. First, autohesion was strongly influenced by the composition and morphology of a resin-rich surface layer. Second, phase separation limited the amount of tackifier dissolved in the SBR and allowed the bulk region to remain rubbery at higher resin concentrations. For a partially soluble terpene resin, the enhanced resin concentration at the surface caused a large increase in autohesion at low resin concentrations. At higher resin concentrations, autohesion decreased sharply and became strongly dependent on contact pressure. Autohesion of solution cast blends depended strongly on sample preparation conditions and was difficult to control.;Adhesion between SBR and a polyisobutylene elastomer (PIB) was also examined. Although SBR and PIB are incompatible, a strong interfacial bond was formed. During bond separation deformation was confined primarily to the softer SBR layer. Addition of a phenolic resin to the SBR increased the cohesive strength of the SBR and adhesion to PIB in about the same proportion.