Epoxy resin modified with epoxidized soybean rubber

Epoxy resin is widely used for coatings, adhesives, casting, electrical insulation materials, and other applications. However, unsolved problems still remain in these applications. The main problem is low toughness: cured epoxy resin is rather brittle with poor resistance to the propagation of cracks, derived from the internal stress generated from shrinkage in the cooling process from cure temperature to room temperature. To solve this problem epoxidized soybean oil (ESO) has been used to toughen epoxy resin cured with an ambient temperature hardener, Tris-2,4,6-(N,N-dimethyl amino methyl) phenol to reduce the internal stress, by introducing a two-phase structure. The ESO was prepolymerized with the amine hardener to obtain the liquid epoxidized soybean rubber (ESR). The ESR-modified epoxy networks were evaluated for their impact and adhesive properties. The epoxy-ESR compositions were systematically varied to study the effect of modifier concentration on adhesion and impact strength. Optimum properties were obtained at a concentration of 20% ESR polymerized for 60 hr. The scanning electron microscopy analysis indicates phase separation between the epoxy-rich phase and ESO-rich phase.