Synergistic fracture toughness enhancement of epoxy-amine matrices via combination of network topology modification and silica nanoparticle reinforcement

A strategy for enhancing fracture toughness of nanosilica particle (NSP) reinforced high T-g epoxy thermosets via topological rearrangement of cross-linked networks is presented. Hybrid systems consisting of NSP with an average particle size of 20 nm and monoamine functionalized partially reacted substructures (mPRS) were prepared using high T-g tetraglycidyl ether of diaminodiphenylmethane (TGDDM) and a low Tg diglycidyl ether of bisphenol A (DGBEA) epoxies cured with Jeffamine D230. A synergistic effect on fracture toughness improvement was observed for all hybrid systems. For the high T-g TGDDM system, the fracture energy of the base epoxy polymer showed a moderate increase from 119 J/m(2) to 203 J/m(2) with the addition of 10 wt% NSP. Modifying the network topology of this system using 15 wt % mPRS tripled the fracture energy to 652 J/m(2). It was found that the addition of mPRS results in hybrid modified systems capable of exceptional tensile failure strains, thus significant plastic shear deformation is induced near the crack-tip region enhancing NSP debonding and subsequent void growth and energy dissipation. Fracture morphologies of the hybrid systems using scanning electron microscope (SEM) showed increasing number of voids and enhanced void growth with increasing weight ratio of mPRS. Impact tests showed the role of these toughening mechanisms on high strain rate deformation and energy dissipation.