Unique Tackification Behavior of Needle-like Sepiolite Nanoclay in Brominated Isobutylene-co-p-methylstyrene (BIMS) Rubber

Adhesion between two unvulcanized rubber surfaces of the same material is termed autohesive tack. Interdiffusion of polymer chains that takes place across the interface and their bulk properties controls the strength of the interface. In this work, for the first time, we have studied the influence of sepiolite nanoclay on the autohesive tack strength of brominated isobutylene-co-p-methylstyrene (BIMS) rubber. The tack strength of BIMS rubber dramatically increases with nanoclay concentration. For example, the tack strength of 8 phr of nanoclay loaded sample is nearly 300% higher than the tack strength of neat BIMS rubber. Various tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation times, self-diffusion coefficient, average penetration depth of rubber chains, and monomer friction coefficient have been analyzed. The addition of nanoclay reduces the extent of molecular diffusion across the interface by reducing the chain mobility; however, the diffusion level is still sufficient to form entanglements on either side of the interface. The entanglements arising from the diffused chains of the nanocomposite samples show greater resistance to separation due to an increase in cohesive strength, onset of transition zone relaxation time, and monomer friction coefficient value of the BIMS rubber matrix by the nanoclay reinforcement. On the other hand, the diffused chains of the unfilled sample exhibit facile chain separation due to the less cohesive strength of the BIMS rubber matrix.