A bimodal rubber-particle distributed epoxy resin was made by simultaneous addition of two kinds of liquid rubbers, CTBN1300X9 and CTBN1300X13. These rubbers were added at a constant total rubber content but with varying weight ratios. The microstructure and fracture behaviour of these rubber-modified epoxy resins have been studied. A strong increase in the fracture resistance was found for the bimodal rubber-particle distributed epoxy resin. The role of the small particle is thought to toughen the shear bands between large particles. The role of large particle is thought to induce a large-scale shear deformation in the crack front. The synergistic effect of these particles gives rise to a strong increase in the toughness of these bimodal rubber-particle distributed epoxy systems.
