Effect of Hexadiene and Vinyl Acetate Content on the EPDM and EVA Blends

Abstract

Melt mixed blends of EPDM rubber and thermoplastic/elastomeric EVA copolymer in the presence of dicumyl peroxide have been studied over the entire composi tion range with special reference to the effect of hexadiene (HD) content of EPDM and vinyl acetate (VA) content of EVA copolymer. Viscosity of the blends decreases as the EPDM/EVA ratio decreases with more pronounced effect associated with VA content of EVA for high HD containing EPDM. For low HD content, VA has no effect up to 20% of EVA in the blend. Lower VA and higher HD are associated with lowering of scorch safety of the compound. For higher HD containing EPDM, state of cure drastically decreases as EVA percentage in the blend increases. With lower HD containing EPDM, there is an in flexion around 50:50 blend ratio irrespective of the VA content of EVA. Initially, rate con stant decreases rapidly for higher HD containing EPDM up to 55 % of EVA in the blend, whereas high VA containing EVA gives rise to flat minimum extending up to 55 % of EVA. A sharp increase in activation energy was observed beyond 60% of EVA especially for high VA containing EVA. Weight loss is more in the case of low HD containing EPDM and high VA containing EVA blends as observed from DTA/TGA study. Failure mode of the blend depends on the HD and VA content as observed from an SEM study, which once again depends on the crystallinity of the blends.