Effect of microstructural damage on the mechanical properties of silica nanoparticle-reinforced silicone rubber composites

Many experiments have apparently shown that hard nanoparticle-reinforced elastomer matrix composites have not only an improved loading bearing capacity but also a good flexibility. The microscopic damage mechanism and its effect on the mechanical properties of such composites are systematically investigated in this paper by both tensile and tear experiments on nano-silica-particle reinforced silicone rubber composites, in which not only the case of surface unmodified nano-silica particles but also that of surface modified nano-silica particles is considered. It is found that both the ultimate strength and toughness of both composites increase monotonically with an increasing weight fraction of nanoparticles. The improved strength and toughness of silicone rubber composites reinforced by surface unmodified nanoparticles are attributed to the blocking effect of micro-sized agglomerations on crack propagation and the weak interface debonding between agglomerations and matrix, respectively. As for the composites with surface modified nanoparticles, not only the filler-blocking effect but also the strong interface between fillers and matrix is responsible for the remarkable strengthening, while the improved toughness is attributed to the crack-pinning and interface debonding around fillers. Another interesting finding is that, with the increase of nanoparticle fractions, formation of the main crack in both composites is firstly inhibited by the filler-blocking effect, and then re-activated by micro-crack coalescences. As a result, the final fracture elongation changes from increase to decrease when the nanoparticle fraction is beyond a critical value. The results in the present paper disclose different microscopic mechanisms that influence the strength and toughness of silicone rubber-based composites reinforced by surface unmodified and modified nanoparticles, which is helpful not only for the understanding of mechanical performance of nanoparticle-reinforced flexible elastomer composites, but also for the design of novel flexible composites with matching strength and toughness.