Small deformation viscoelastic response of gum and highly filled elastomers

Small deformation viscoelastic response has been investigated in a series of five elastomeric binders, both with and without nonreinforcing filler. The filled systems were found to be both nonlinear viscoelastic and thermorheologically complex. These behaviors suggest the existence of a secondary relaxation process. The origin of this secondary process was modeled as an interphase of polymer weakly adsorbed on the filler surface. Decomposition of timetemperature shift factors for filled vs unfilled properties showed that the mechanical response of this interphase followed Arrhenius behavior. Measured activation energies ranged from 24 to 76kJ/mole, depending on the cohesiveenergy density of the elastomeric binder. Finally, these activation energies were related to the strain amplitude dependent nonlinear factors for the polymeric systems which contained no polar groups in their backbone, suggesting that in these systems both the nonlinear and thermorheologically complex nature of the filled materials' viscoelastic response originate from relaxations within this interphase.