Rheological and mechanical behavior of blends of styrene-butadiene rubber with polypropylene

The microstructural, rheological, and mechanical properties of polymer blends composed of continuous polypropylene (PP) and styrene‐butadiene rubber (SBR) phases are reported. Two series of materials are studied: a commercial SBR and PP fraction varied over 20–45 wt% and four custom synthesized SBR materials, including branched and linear configurations, at fixed PP fraction of 35 wt%. The μm‐scale microstructural features are characterized by force microscopy, melt viscosity measured via capillary rheometry, and solid deformation properties determined by uniaxial tensile and Vickers indentation hardness tests. Melt viscosity decreased, and solid modulus, yield stress, hardness, ultimate tensile strength, and failure strain all increased with PP content. Melt viscosity, modulus, and hardness all increased with increasing microstructural scale, independent of SBR type. The results suggest that such composites are good candidates for soft touch materials, combining the melt processing characteristics of PP with the solid elastomeric characteristics of SBR, and that there is great flexibility in tuning the composition to optimize both processing and mechanical properties. POLYM. ENG. SCI., 45:1487–1497, 2005. © 2005 Society of Plastics Engineers