Electrical conductivity and mechanical properties of vapor-grown carbon nanofibers/trifunctional epoxy composites prepared by direct mixing

Vapor-grown carbon nanofibers (VGCNFs)/trifunctional epoxy resin composites were prepared by directly mixing the VGCNFs and the epoxy resin using ultrasounds to improve dispersion. Different weight fractions of VGCNFs were studied, from 0.05 to 2 wt.%. The dispersion degree of the VGCNFs was analyzed in the uncured stage by optical microscopy and after the curing reaction by Scanning Electron Microscopy (SEM). The electrical conductivity of the epoxy composites, measured by means of surface electrical conductivity, increased with the addition of VGCNFs content, reaching a conductivity value of around 10−6 S/cm at 2 wt.% loading, which is an increase of eight orders of magnitude over the pure epoxy matrix. A very low critical weight fraction corresponding to the formation of a tunneling conductive network was found. To identify the effect of adding VGCNFs on the mechanical properties of epoxy resin, flexural tests were performed on neat epoxy and the composites. The highest improvement in flexural modulus was obtained with 0.1 wt.% loading of VGCNFs.