Promotion of the mechanical properties and thermal conductivity of epoxy by low Si3N4 whisker content and its mechanisms

Si3N4 whisker (Si3N4w) is selected as epoxy filler. The influence of filler content on the bulk density, porosity, bending strength, Young's modulus, critical stress intensity factor, work of failure, morphologies of fracture surface, and thermal conductivity of Si3N4w/epoxy is investigated. The bending strength is 82.63 MPa at a Si3N4w content of 5 vol% and increases to 25.29% more than that of neat epoxy. Compared with that of neat epoxy, the work of failure and thermal conductivity increase by 455% and 34.78% to 18 248.92 J center dot m(-2) and 0.31 W center dot m(-1)center dot K-1, respectively, at a Si3N4w content of 7 vol%. However, Si3N4w/epoxy becomes sensitive to precrack due to a weak C-N bond and residual tensile stress at the interface, thereby resulting in the decline of critical stress intensity factor. The coexistence of various energy dissipation mechanisms, namely, steps, craters or depressions, stress whitening, plastic flow, pull out of Si3N4w, and rough fracture surface, is observed in Si3N4w/epoxy. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48721.