Quantitative analysis of the phase-separated structure and mechanical properties of acrylic copolymer/epoxy thermosetting resin composites

The effects of thermal curing reactivity on the phase-separated structures of acrylic copolymer/epoxy thermosetting resin composites containing various accelerator amounts were investigated to elucidate their phase separation behavior. These composites exhibited a sea-island structure, in which the island size decreased as the amount of accelerator increased. The island diameter distribution was represented as a lognormal plot. Island formation is explained by the law of proportionate effect. As observed during the last stage of phase separation via spinodal decomposition, small domains formed prior to coalescing. The effects of material composition on the phase structures and mechanical properties of acrylic copolymer/epoxy thermosetting resin composites were also examined. The morphologies varied depending on the components, and in particular, the total island area fractions and fracture surface shapes after the tensile tests differed. A small fraction of island area resulted in a lower fracture surface roughness and higher mechanical strength, indicating that in stronger composites, many epoxy components remained in the acrylic copolymer-rich sea phases. In addition, the destruction of resin composites was propagated through phase boundaries because the network formation states of the sea and island phases do not significantly differ.