Nanosilica Modification of Elastomer-Modified VARTM Epoxy Resins for Improved Resin and Composite Toughness

Abstract : Recent publications have reported a synergy between rubber and silica in modified epoxy resins that results in significantly improved fracture toughness without reductions in other material properties. In this work, we seek to achieve the same type of synergy in commercial vacuum-assisted resin transfer molding (VARTM) epoxy resins, SC15 and SC79, produced by Applied Polymeric, Inc. Nanopox F400 (Hanse Chemie) containing 40 weight-percent epoxy-functional silica in a diglycidyl bisphenol-F (DGEBF) epoxy was blended with the VARTM resins to add various silica loadings in the systems. It was found that the presence of DGEBF influenced resin properties more than silica. This monomer impacted crosslink density and other material properties. The crosslink density of SC15 was increased and resulted in reductions in resin fracture toughness, mode II composite fracture toughness, and increased damage area in impact performance. The crosslink density of SC79 was reduced upon the addition of DGEBF contained in the Nanopox. At 10 weight-percent silica, resin fracture toughness, mode II composite toughness, and impact properties were improved due to decreased matrix crosslink density and the presence of silica. Finally, morphological studies showed that silica influences the rubber phase separation in a model epoxy system and VARTM epoxies. Further research will investigate the effects of epoxy-functional silica addition to phase separation mechanisms in rubber-toughened epoxies.