Viscoelasticity analysis of spherical nano-CaCo₃-filled isotactic polypropylene during a uniaxial tensile test

The tensile behavior of spherical nano-CaCo₃ filled isotactic polypropylene over a wide range of strain rates were investigated to analyze the influence of nanofiller concentration and filler-matrix interaction on the motion of macromolecular chains and segments of iPP in the nonlinear region. The Eyring model can be well applied to describe the dependence of yield stress on strain rates. Both the activation energy and activation volume of the nanocomposites were higher than those of pure iPP, indicating the simultaneous restriction and activation effects of nanoparticles on the segmental mobility. Substantial reduction of yield stress was observed in the nanocomposites with increasing filler loading, especially at high strain rates. However, the yield stress of the nanocomposites containing 6 wt% stearic acid (SA)-treated CaCo₃was not further deteriorated relative to the nanocomposites containing 2 wt% SA-treated CaCO₃. It can be interpreted in light of a three-parameter constitutive model by the influence of compliance function being significantly weakened in the nanocomposites containing 6 wt% SA-treated CaCO₃, due to the stronger spatial restriction of better-dispersed nanoparticles on the segmental motion compared with the nanocomposites containing 2 wt% SA-treated CaCO₃.