Evaluation of viscoelastic master curves of filled elastomers and applications to fracturemechanics

Abstract

The viscoelastic response of filler-reinforced elastomers has been investigated bydielectric- and dynamic-mechanical spectroscopy. Horizontal and vertical shifting factors areevaluated, which are used for the construction of viscoelastic master curves. They arediscussed in the framework of filler network effects and the slowed-down dynamics of apolymer layer close to the filler surface. The observed shifting behaviour is shown to berelated to the superposition of two relaxation processes, i.e. that of the polymer matrix andthe filler network, leading to a failure of the time–temperature superposition principle.While the matrix transforms according to the Vogel–Fulcher equation, the filler networkexhibits an Arrhenius dependence, which results from the thermal activation of filler–fillerbonds, i.e. glassy-like polymer bridges between adjacent filler particles. Based on theviscoelastic master curves relaxation time spectra are evaluated. By referring to a recentlydeveloped theory of crack propagation in viscoelastic solids it is demonstrated that thebehaviour of the scaling exponent of the relaxation time spectra correlates fairly well withthat of the crack propagation rates measured under moderate severity conditions.