A numerical model of the viscosity of an epoxy prepreg resin system

The development of the viscosity of a thermoset material during processing is complicated because of the dependence of the initial material state and the kinetic rate of conversion from a liquid to a solid material. Uncured t hermoset materials typically have a low enough viscosity such that the cons umption of energy to generate flow is relatively low. However, as the curin g process advances, the flow mechanisms become hindered by the development of a network gel during crosslinking. Once the resin has reached the approp riate degree of cure for gelation, the resin system is incapable of large f luid-like deformations. In this research, the rheological properties of an epoxy resin system used in laminate processing were measured and numericall y fit with a modification to the dual Arrhenius model to predict the progre ssion of the viscosity during cure. The numerical results were compared wit h the experimental measurements, and it was found that the model predicts t he experimental observations quite well. It was found that the initial degr ee of cure of the prepreg is not as significant a factor as the temperature rate dependence on the processing time between the point of now onset and gelation. However, the minimum viscosity during processing is strongly infl uenced by the initial degree of cure of the prepreg system.