The toughening mechanism in hybrid epoxy-silica-rubber nanocomposites (HESRNs)

Two different size nanosilica (NS) particles, nominally 20 nm and 80 nm in diameter, and carboxyl terminated butadiene acrylonitrile (CTBN) were blended into a lightly crosslinked, DGEBA/piperidine epoxy system to investigate the toughening mechanisms in hybrid epoxy-silica-rubber nanocomposites (HESRNs). Adding small amount of NS particles into CTBN toughened epoxies further improved the fracture toughness to a level that could not be achieved by increasing CTBN content alone. Interestingly, this toughening effect is diminished when NS particles clustered at high CTBN contents. In addition, the effect of NS particle size on toughening behavior was not considerable, except the case when NS clustering is observed. According to the SEM and TOM investigations, the plastic zone, which consists of shear banding and matrix dilation, is further enlarged in front of the crack tip in HESRNs. Irwin’s model is used to evaluate the process zone concept and the result indicates that zone shielding is credited for the toughening mechanism in these HESRNs.