The effect of mixing sequence on the block copolymer compatibilization of polybutadiene-natural rubber blend

The remarkable effect of the mixing sequence on the block copolymer compatibilization was investigated in this study, where a liquid butadiene-isoprene copolymer rubber (LIR-390) was used to compatibilize the polybutadiene/natural rubber (BR/NR, 30/70) blend. We have found that properly chosen mixing sequence would greatly improve the effectiveness of LIR-390 compatibilization in NR/BR blend. When LIR was first mixed with NR, and then blended with BR, the NR/BR/LIR blend showed the best compatibilization, as the AFM phase morphology revealed the significantly reduced domain size of dispersed BR phases. It is unusual that both the processing characteristics of this unvulcanized blend and the mechanical properties of its vulcanizate are improved: the unvulcanized blend had the lowest G and *, while the vulcanizate had the highest G and * among four controls. We attribute this phenomenon to the "sliding effect" of the uncured sample and the "networking effect" of LIR with NR and BR at the interface after vulcanization. The fatigue crack propagation measurement revealed the lowest crack growth rate for M3.