Change of viscoelastic properties of epoxy resin in the curing process

Abstract

This paper is concerned with the relation between the time and temperature dependences of the flexural properties and the curing conditions for the bisphenol A-type epoxy resin with acid anhydride hardener. Relaxation moduli of epoxy resin, prepared at several curing temperatures and times, were measured in the temperature range from Tg −70°C to Tg. The master curves of relaxation modulus for the epoxy resin could be constructed, using their thermorheological simple properties. The time–temperature shift factors of the epoxy resin could be approximately expressed by the Arrhenius equation with the activation energy 59.4 kcal/mole. independent of its curing conditions. The curing time and temperature were equivalent, that is, the short curing time at high temperature corresponded to the long curing time at low temperature. The curing time–temperature shift factor could be approximately expressed by the Arrhenius equation with the activation energy 21.3 kcal/mole, which was higher than the activation energy 14.2 kcal/mole obtained in the measurements of gel times. The increase in the values shows that the temperature dependences of reaction rates increase with progressing gelation.