Percolation behaviour of ultrahigh molecular weight polyethylene/multi-walled carbon nanotubes composites

The electrical conductivity of polyrner/multi-walled carbon nanotubes (MWCNTs) composites in a powder and in a hot-pressed compacted state, prepared by mechanical mixing, was studied. The senticrystalline ultrahigh molecular weight polyethylene (UHMWPE) was used as a polymer matrix. The data clearly evidence the presence of a percolation threshold (pc at a very small volume fraction of the MWCNTs phi in a polymer matrix, phi(c) approximate to 0.0004-0.0007. The ultralow percolation threshold in UHMWPE/MWCNTs thermoplastic composites was explained by high aspect ratio of the nanotubes and their segregated distribution inside the polymer matrix. The method of composite preparation effects the values of percolation threshold concentration (pc and critical exponent t. A noticeable positive temperature coefficient of resistivity (PTC effect) was observed in the region of temperatures higher than melting point. It was explained by influence of thermal expansion of the polymer matrix and independence from the melting process that is a result of specific structure of conductive phase. (c) 2006 Published by Elsevier Ltd.