Viscoelastic Behavior of an Epoxy Compound with High Fillers During Cure.

Abstract

Chemorheology of an epoxy resin with 90wt% silica fillers was investigated using a parallel-plates viscometer. Viscosity-time curves at four frequencies were measured at intervals of 10°C in the range of 50°C to 130°C. Within the range of 130°C to 180°C, viscosity-time curves of samples, in which the concentrations of a curing catalyst had been decreased in order to lower the rate of reaction, were measured. Parameters of an Arrhenius type equation, considering the frequency dependence, were obtained from these data for the prediction of the resin viscosity variation during cure. In particular, the parameters at high temperature were estimated by extrapolation of the normal concentration of a curing catalyst. The calculated viscosity profile coincided with the experimental data. The gel point at 100°C was obtained using two methods: (i) crossover of the tanδ-time curves at several frequencies (ii) same power law dependence of G'(ω) and G(ω) on frequency. Both values coincided. Values of the power exponent from the two methods were 0.62 and 0.70, respectively. These values were in agreement with the value predicted by the dynamic scaling theory. The appearance of an insoluble fraction at the gel point was confirmed by GPC. The degree of cure at the gel point was 0.50 by DSC.