Effect of Methacrylate Co-Agents on Peroxide Cured PP/EPDM Thermoplastic Vulcanizates

Abstract

Abstract Thermoplastic vulcanizates (TPVs) have gained large technical and economic importance. TPVs are characterized by a chemically crosslinked rubber phase, embedded in a thermoplastic matrix, produced by dynamic vulcanization during mixing with the thermoplastic in its molten state. Methacrylate species are investigated as co-agents for peroxide vulcanization of polypropylene/ethylene-propylene-diene-rubber (PP/EPDM) TPVs, whereby the weight fraction of the EPDM is varied from 30, 50 to 70%. Ethylene glycol dimethacrylate (EDMA), trimethylol propane trimethacrylate (TMPTMA, often referred to as TRIM) and zinc dimethacrylate (ZDMA) are tested. A fixed amount of dicumyl peroxide as crosslinker and varying contents of co-agents are employed, the latter to boost EPDM-crosslinking and prevent degradation of the PP by β-scission. Differences observed in mechanical properties point to diverse structures of the crosslink networks of the TPVs. Of the three co-agents, TMPTMA gives the best overall balance of properties by EPDM crosslinking and preventing PP-degradation. This is explained by the positioning of the solubility parameter of this co-agent between those of EPDM and PP, whilst EDMA presents a value far away from either one. ZDMA, although giving very good room temperature properties like tensile strength, shows signs of thermo-reversion of the crosslinks in the compression set measured at 70 °C.