Processing-structure relationships for multiphase epoxy matrix systems

A styrene-modified diglycidyl ether of bisphenol-A (DGEBA) epoxy system cured with trimellitic anhydride (TMA) has been investigated to explore processing and structure relationships. During cure, the reactive styrene precipitated with polymerization into phase domains separate from the epoxy phase. Dynamic mechanical analysis and microscopy studies were performed to gain insight to matrix structure. The DMA studies showed that the styrenemodified epoxy system after cure exhibited two partially overlapped but distinct relaxation peaks, which are associated with the T _gs of the polystyrene and epoxy phases. The glass transition of the polystyrene phase was shown to be broadened and the T _g to depend strongly on processing temperature profiles. While the T _g of the epoxy phase increases with curing agent concentrations, the T _g of the polystyrene phase does not. Microscopic studies showed that the styrene-modified system exhibited a rougher fracture surface but did not reveal well defined phase domains in which the precipitated polystyrene component was aggregated. Overall, the study has demonstrated correlations of the kinetic factors in controlling the morphology in reactive modifier-epoxy systems.