Influence of 1,2-polybutadiene as coagent in peroxide cured polypropylene/ethylene octene copolymer thermoplastic vulcanizates

The present study investigates the influence of 1,2-polybutadiene (1,2-PB) as a coagent for peroxide cured polypropylene (PP) and ethylene octene copolymer (EOC) thermoplastic vulcanizates (TPVs). Addition of peroxide in PP/EOC blend leads to cause crosslinking in EOC phase and β-chain scission in PP phase. As a result, the final properties are determined primarily by the ratio of those two competing reactions. Coagent assisted peroxide system is always an attractive and effective choice in order to avoid the β-chain scission in PP, to increase the crosslink density in EOC phase and to induce the interfacial reactions. In this paper, mechanical, morphological, thermal and rheological characteristics were studied with special reference to the effect of concentration of 1,2-PB. The best overall balance of mechanical properties was observed at 3 phr concentration of 1,2-PB. However, modulus and crosslink density values increase gradually as a function of concentration of coagent. The changes in the melting and crystallizing behavior of the blends were investigated using differential scanning calorimetry (DSC). Scanning electron micrography (SEM) analyses were performed to understand the particle size of the dispersed phase. Fractography was pursued to understand the mode of failure. Rheological properties were studied at different shear modes: oscillatory shear and rate controlled capillary rheometer. A variety of rheological observations such as Payne effect, modulus recovery and comparison of oscillatory and shear mode rheological results were discussed in details.