Relationship among microstructure, linear viscoelastic behavior and mechanical properties of SBS triblock copolymer-compatibilized PP/SAN blend

Abstract

Morphological, rheological and mechanical properties of the polypropylene (PP) and poly(styrene-co-acrylonitrile) (SAN) blend containing poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer (ranging from 0 to 20 wt%) were studied by scanning electron microscopy (SEM), small amplitude oscillatory shear analysis, and both tensile and impact tests, respectively. SEM observations showed that SBS reduced the diameter of the SAN dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Close examination of SEM micrographs further revealed that the dispersed phase domains were complex aggregates of SAN particles enveloped and joined together with the SBS compatibilizer in the PP matrix. The variation of the dynamic rheological parameters, including dynamic moduli (G′ and G″), complex viscosity ( $$ \eta^{ * } $$ ), loss factor (tan δ), together with Cole–Cole diagrams, with blend composition particularly at low frequency regions were determined to evaluate the interfacial activity of SBS copolymer. A specific viscoelastic phenomenon, i.e., “the second plateau”, appeared at low frequencies for PP/SAN blend containing 20 wt% of SBS and exhibited a certain dependence on the SBS amount and dispersion state in the matrix. This phenomenon was attributed to the formation of aggregate structure between SAN particles and SBS triblock copolymer. Finally, the results of uniaxial tensile and Charpy impact tests conducted on both unnotched and notched specimens indicated that in PP/SAN blend, SBS functions as both compatibilizer and toughening agent.