The effect of the ratios of sulfur to peroxide in mixed vulcanization systems on the properties of dynamic vulcanized natural rubber and polypropylene blends

This study investigated the influence of various ratios of sulfur to peroxide during vulcanization on the rheologicalproperties, morphology and crystallinity of natural rubber/polypropylene thermoplastic vulcanizates (TPVs) blended at afixed ratio of 60/40. The results show that the addition of peroxide into the mixed vulcanization system has an important effecton the properties of the TPVs as a result of two competing reactions which occur simultaneously in the natural rubber (NR)and the polypropylene (PP) phases. These are cross-link reactions of NR molecules with different cross-link patterns, crosslink density being caused by the proportions of sulfur and peroxide curing agents and the degradation of the PP through -chain scission. This causes significant variations in the phase morphology of the TPVs and the crystallization of the PP.Further, different trends of changes in properties were observed according to the peroxide content in the mixed vulcanizationsystem. This study found that a ratio of 70/30 parts of sulfur to peroxide provided a better overall balance of properties of theNR/PP TPVs than those of TPVs produced using sulfur or peroxide alone or other ratios of mixed sulfur/peroxide vulcanization systems.