Comprehensive promotion of mechanical properties of epoxy by electrical insulating filler of Si₃N₄ whiskers at low content

Abstract The improvement of the mechanical properties of brittle epoxies by various fillers, especially by carbon‐related materials, has attracted significant attention and achieved impressive results. However, the dielectric properties of an epoxy may be compromised along with the improvement, and there is an urgent need to develop electrical insulating fillers to address this issue. In this study, Si₃N₄ whiskers (Si₃N_4w) are first introduced as the filler used to prepare a composite of Si₃N_4w/epoxy. The results indicate that Si₃N_4w has an outstanding capability to comprehensively improve the mechanical properties of an epoxy. The maximal reinforcing and toughening effect could be obtained at a low filler content of 3.0%. The bending strength, Young's modulus, K_IC and work of fracture of the composite can be augmented by 34.05%, 23.00%, 57.53%, and 513.50%, respectively, in comparison with those of the neat epoxy. The abundant energy dissipation mechanisms responsible for these effects are observed and interpreted. Finally, a brief phenomenological fracture process of Si₃N_4w/epoxy is proposed.