Measuring and modeling the cure-dependent rubbery moduli of epoxy molding compound

The rubbery (equilibrium) modulus of thermosetting polymers dominates the mechanical behavior at elevated temperature or at long times. It also plays a major role in the residual stress induced during the curing process. In this paper, ai extensive study on the cure-dependent rubbery moduli of silica spheres filled epoxy resin is carried out both experimentally and theoretically. DSC measurements were used for characterization of the cure kinetics and T_g-conversion relationship. Low frequency DMA was used to measure the rubbery modulus build-up during cure. A model based on scaling analysis was applied to describe the evolution of the rubbery shear modulus. A similar model was proposed for the cure-dependent rubbery bulk modulus. Models from the theory of particulate-filled composites were used to predict the rubbery moduli of the molding compound with different filler concentration. The effect of the filler percentage on the rubbery moduli was discussed.