Correlation between phase separation and rheological behavior in bitumen/SBS/PE blends

The polymer blend as a modifier for bitumen provides a new route to enhance its rheological properties directly related to service performance. The blending of crystalline polyethylene (PE) and thermoplastic elastomer styrene–butadiene–styrene (SBS) is a good choice for bitumen modification due to the possible combination of excellent rigidity and elasticity originating from PE and SBS, respectively. However, the immiscibility between SBS/PE and either of them with bitumen would make the phase structure evolution complicated. In this paper, the phase structure evolution of bitumen/SBS/PE during annealing is studied by in situ observation under optical microscopy. Two different composition ratios of SBS/PE are chosen to distinguish the role of crystalline polymer and elastomer in the phase structure and rheological behavior. It is found that the phase morphology evolution is mainly dependent on the compositional ratio of polymer blend, which accordingly influences the evolution of SBS-rich droplets. The immersion of SBS-rich droplets into bitumen would effectively enhance the rheological properties in terms of complex modulus and viscosity.