Influence of carbon fiber surface treatments on the structure and properties of conductive carbon fiber/polyethylene films

Abstract

Effects of carbon fiber (CF) surface modification on the crystalline structure and both electrical and mechanical properties of conductive CF/high-density polyethylene (HDPE) films were studied. Three different types of surface-treated CF, epoxy-sized, unsized, and sized but thermally treated, were considered. It was found that the uniformity of the transcrystalline zone around CF and the overall crystallinity of the polyethylene matrix decreased when epoxy-sized CF was used. Epoxy-sized CF caused a significant reduction not only in electrical resistivity and temperature coefficient of resistivity (TCR) but also tensile strength and coefficient of linear thermal expansion (CLTE) of composite films compared with that of unsized or sized CF that was thermally treated. We observed the systematic changes of TCR and CLTE values in accordance with CF surface modification and CF content in composite films. It was concluded that thermal expansion of the polymer matrix is the main reason for the positive TCR of CF/HDPE films. As the most probable reasons for decreased resistivity and strength of the CF/HDPE films with epoxy-sized CF, the diffusion of epoxy sizing agent into the polyethylene matrix and the formation of loosened semiconductive interphase structure in the film are considered.