Melt Viscoelastic Properties of Peroxide Cured Polypropylene-Ethylene Octene Copolymer Thermoplastic Vulcanizates

The dynamic viscoelastic properties of uncrosslinked and dynamically crosslinked blends of polypropylene (PP) and ethylene octene copolymer (EOC) were investigated in the melt state to study the mechanism of reinforcement, influence of particle size, and kinetics of modulus recovery. Dynamic vulcanization was performed by coagent assisted peroxide crosslinking system. Addition of peroxide in PP/EOC blend involves two major competing reactions: crosslinking in EOC and degradation of PP by beta chain-scission. In this article, morphological and melt rheological properties of the TPVs were studied with special reference to the effect of mixing protocol. Three different mixing techniques were investigated. They are: (i) conventional or preblending method-melt mixing of PP and EOC followed by dynamic vulcanization (ii) phase mixing method-curative master batch of EOC added on the molten PP (iii) split addition of PP-preblending method followed by addition of half part of PP (dilution procedure). The type of mixing protocol has a significant influence on the rheological behavior. Rheological properties have been evaluated at the processing temperature (180 degrees C) in a Rubber Process Analyzer (RPA 2000). A variety of rheological observations such as Payne effect, modulus recovery and shear rate sensitivity were studied by carrying out frequency and strain amplitude sweeps. POLYM. ENG. SCI., 50:455-467, 2010. (C) 2009 Society of Plastics Engineers