Rheology and Flow Instabilities of Thermoplastic Vulcanizates (TPVs)

A. Doufas, K. Iyer, N. Ghahramani, S.G. Hatzikiriakos
ExxonMobil Chemical Company,
United States

Keywords: thermoplastic vulcanizates, polymers, polymer blends

Summary:

Thermoplastic vulcanizates (TPVs) are a special class of polymer blends of polypropylene (PP) and EPDM rubber in which a high content of rubber (EPDM) is simultaneously crosslinked and dispersed in a thermoplastic matrix (PP). Due to the presence of rubber, their rheology is complicated presenting characteristics similar to those of soft solids. Moreover, they exhibit flow instabilities in extrusion such as melt fracture depending on the molecular characteristics and architecture of their constituents and composition. In this study, the rheology of several TPVs is studied in terms of the rheology of their primary constituent components (PP and EPDM). The effects of long chain branching of their constituents, the level of curing, and amount of filler on their rheology is studied. Their processing as can be assessed by capillary rheometry is also studied as a function of temperature and shear rate in terms of critical shear rates and stresses for the onset of melt fracture phenomena. Correlations between these critical values and the molecular characteristics of TPVs are also developed and discussed.