Toughening of epoxy hybrid nanocomposites modified with silica nanoparticles and epoxidized natural rubber

Abstract

Silica nanoparticles (SN) and epoxidized natural rubber (ENR) were used as binary component fillers in toughening diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine. For a single component filler system, the addition of ENR resulted in significantly improved fracture toughness (KIC) but reduction of glass transition temperature (Tg) and modulus of epoxy resins. On the other hand, the addition of SN resulted in a modest increase in toughness and Tg but significant improvement in modulus. Combining and balancing both fillers in hybrid ENR/SN/epoxy systems exhibited improvements in the Young’s modulus and Tg, and most importantly the KIC, which can be explained by synergistic impact from the inherent characteristics associated with each filler. The highest KIC was achieved with addition of small amounts of SN (5 wt.%) to the epoxy containing 5–7.5 wt.% ENR, where the KIC was distinctly higher than with the epoxy containing ENR alone at the same total filler content. Evidence through scanning electron microscopy (SEM) and transmission optical microscopy (TOM) revealed that cavitation of rubber particles with matrix shear yielding and particle debonding with subsequent void growth of silica nanoparticles were the main toughening mechanisms for the toughness improvements for epoxy. The fracture toughness enhancement for hybrid nanocomposites involved an increase in damage zone size in epoxy matrix due to the presence of ENR and SN, which led to dissipating more energy near the crack-tip region.