| Five monoepoxy compounds were studied to investigate antiplasticization in the epoxy resins. This study was divided in two parts. In the first, the volumetric behavior associated with antiplasticization was investigated and in the second, various applications were explored for antiplasticizing additives, both with and without rubber toughening agents.;Using a simple free volume model, it is demonstrated that reduction in the free volume is the cause of antiplasticization in the studied epoxy networks. The reduction in the free volume upon incorporation of an antiplasticizing additive was considered to be due to two factors. The first one corresponds to the reduction in the glass transition temperature, and the second corresponds to the molecular interaction of an additive with the epoxy network. A scheme was developed to find the fractional contribution of an additive function in reducing the free volume of the system. In situations where the chemical structures are similar, apart from the reacting group, an additive which can react with the system contributes more effectively to reducing the free volume than a non-reactive additive. Using the same free volume model, it was further demonstrated that the yielding of the modified epoxy matrix relates to the change in the free volume associated with both deformation and thermal expansion.;A synergism was observed in the case of additive VCDHAA and elastomer additives in epoxy resins. The fracture toughness was increased without any loss in modulus and strength of the epoxy resin. We attribute this behavior to antiplasticization of the continuous phase along with a modified morphology (bimodal distribution of phase sizes) of the dispersed phase. Studies of adhesive joints showed that the strength of joints reflect the improvements in the ultimate strength and modulus of the resin. It was also demonstrated that the properties of the adhesive joints can be improved by creating a modulus gradient at the interphase between adhesive and adherend. |
