Interplay between bulk viscoelasticity and surface energy in autohesive tack of rubber-tackifier blends

Abstract

The effects of change in surface energy and bulk viscoelastic properties on the autohesive tack strength of brominated isobutylene-co-p-methylstyrene (BIMS) rubber have been investigated by the addition of hydrocarbon resin (HCR) tackifier and maleated hydrocarbon resin (MA-g-HCR) tackifier. The addition of compatible HCR tackifier results in a reasonable increment in the tack strength of BIMS rubber by modifying only the bulk viscoelastic properties (compliance, entanglement molecular weight, relaxation time, self-diffusion, and monomer friction coefficient values) of BIMS rubber to perform better during the course of bonding and debonding steps of the peel test. Incorporation of MA-g-HCR tackifier (containing 5―20 wt % of grafted maleic anhydride) steadily increases the tack strength of BIMS rubber further by precisely modifying both the surface energy and bulk viscoelastic properties to perform much better in the bonding and debonding steps. However, beyond 20 wt % of grafted maleic anhydride in the HCR tackifier, the tack strength starts decreasing due to the incompatibility between the blend components, and hence, the bulk viscoelastic properties required for bond formation are severely retarded by the interrelated reinforcing effect and the phase separation effect of the brittle MA-g-HCR tackifier in the BIMS rubber. Hence, the polar groups in a tackifier will contribute to significant enhancement of autohesive tack strength only if the bulk viscoelastic property of the rubber-tackifier blend is favorable for bond formation and bond separation.