Influence of Oil Contents in Dynamically Cured Natural Rubber and Polypropylene Blends

Mechanical, dynamic, thermal, and morphological properties of dynamically cured 60/40 NR/PP TPVs with various loading levels of paraffinic oil were investigated. It was found that stiffness, hardness, tensile strength, storage shear modulus, complex viscosity, glass transition temperature (T-g) of the vulcanized rubber phase, degree of crystallinity and crystalline melting temperature (T-m) of the polypropylene (PP) phase decreased with increasing loading levels of oil. This is attributed to distribution of oil into the PP and vulcanized rubber domains causing oil-swollen amorphous phase and vulcanized rubber domains. An increasing trend of elastic response in terms of tension set and damping factor was observed in the TPVs with loading levels of oil in a range of 0-20 phr. It is supposed that a major proportion of oil was first preferably migrated into the PP phase and caused an abrupt decreasing trend of degree of crystallinity and T-m of the PP phase. The dispersed vulcanized rubber domains remained small as particles with a low degree of swelling. Increasing loading levels of oil higher than 20 phr caused a decreasing trend of elongation at break and elastomeric properties. Saturation of oil in the PP phase was expected and the excess oil was transferred to the rubber phase which thereafter caused larger swollen vulcanized rubber domains. The remaining amount of oil was able to separate as sub-micron pools distributed in the PP matrix. This caused lowering of T-g, T-m, crystallinity of PP phase as well as strength, elastomeric, and dynamic properties of the TPVs. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 540-548, 2010