MULTIPHASE TOUGHENED EPOXY WITH POLY(ETHER SULFONE) AND CARBOXYL-TERMINATED BUTADIENE-ACRYLONITRILE RUBBER

The structure and properties of ternary blends of epoxy with poly(ethe r sulphone) (PES) and carboxyl-terminated butadiene-acrylonitrile rubb er (CTBN) have been investigated. In these blends, the phase separatio n occurs in two stages: a macrophase separation during mixing and a mi crophase separation during curing. At low PES compositions, the RES-ri ch spherical domains are dispersed. With increasing PES composition, a co-continuous structure develops and, eventually, the phases are inve rted. Regardless of structure change, the modulus and yield stress cha nges with composition just follow the simple rule of mixtures. However , the fracture toughness of these blends exhibits a synergistic effect . Among the various compositions, 5:5 weight ratio of CTBN to PES exhi bited the maximum toughness, which was 140% larger than that calculate d from the rule of mixtures. The synergism is believed to be due to th e bridging by the RES-rich phase followed by a lowering of the yield s tress. The lowering of the yield stress can enlarge the process zone s ize and the amount of plastic dilatation of the matrix.