Influence of various peroxides in PP/EPDM thermoplastic vulcanizates at varied blend ratios

Thermoplastic vulcanizates (TPVs) or dynamic vulcanizates containing finely dispersed micron-size cross-linked rubber particles in a thermoplastic matrix exhibit performance properties of the conventional vulcanized rubbers, however, they can be processed as thermoplastics. The basic objective of the present study is to investigate the effects of different types of peroxides as cross-linking agents at varied PP/EPDM blend ratios in dynamically vulcanized products. The TPVs were prepared by batch melt mixing of polypropylene (PP) with ethylene propylene diene monomer (EPDM), using various peroxides and triallyl-cyanurate (TAC) as co-agent. The physical properties of the TPVs change significantly with the PP/EPDM blend ratios, chemical nature of the peroxides, the extent of cross-linking in the EPDM phase, and the extent of degradation in the PP phase. The reason of increased tensile strength, modulus, and hardness with the increasing amount of PP is due to the increased thermoplastic hard component in the blend. Irrespective of the PP/EPDM blend ratios, in most cases dicumyl-peroxide (DCP), out of four different types of peroxides investigated, gives the best overall balance of physical properties. Special emphasis is laid on the interpretation of the different behavior of the various peroxides.