The effect of aggregation of cured rubber particles on rheology of thermoplastic vulcanizates

Abstract In this work, we study the effect of microstructure of rubber particle aggregates on linear and nonlinear viscoelastic properties of olefinic thermoplastic vulcanizates (TPVs) based on ethylene‐propylene‐diene rubber (EPDM) and polypropylene (PP). TPVs samples with identical rubber content and different extent of rubber particle aggregation are prepared through dynamic vulcanization of PP/EPDM blends (conventional method) with different compositions as well as dilution of PP/EPDM 40/60 TPVs. Morphological observations show larger aggregates of cured rubber particles in the diluted samples (D) compared to the ones prepared by conventional method (B). The difference between the microstructures of the two series of samples decreases with increasing rubber content. Linear viscoelastic measurements demonstrate higher elastic modulus and dynamic viscosity at low frequency for D samples compared to B ones, representing the effect of aggregation of the dispersed rubber phase. The higher extent of aggregation in D samples also leads to a lower percolation threshold and smaller linear viscoelastic region. From fitting of a structure‐dependent model on the stress growth results, longer characteristic relaxation times are obtained for D samples due to the presence of rubber aggregates. Additionally, A higher degree of orientation and less contribution of rubber aggregate destruction are found under shear flow in D samples.