Influences of chemical crosslinking, physical associating, and filler filling on nonlinear rheological responses of polyisoprene

Chemical crosslinking, physical associating, and filler filling play vital roles in nonlinear responses of rubbers under large amplitude oscillatory shear (LAOS). Herein, a systematical investigation was performed for polyisoprene rubber vulcanizates and compounds on the framework of LAOS analytical methods to quantify intra- and intercycle nonlinearities. It is shown that the Payne effect is featured by intercycle strain softening and intracycle hardening. Furthermore, chemical crosslinking and intermolecular association cause marked shear thickening at the medium range of rate amplitude, which is related to the nonideally crosslinked structures from numerical studies. Fillers can promote nonlinear viscoelastic behaviors. In compounds, modulus recovery during cyclic oscillatory shear deformation is not directly related to the reorganization of the filler phase, which is testified by simultaneous measurements of rheological responses and electrical resistivity during increasing-decreasing amplitude sweep cycles.