Electrical and mechanical properties of carbon nanotube/ultrahigh-molecular-weight polyethylene composites prepared by a filler prelocalization method

The method of preparation and the properties of conductive composites of ultrahigh-molecular-weight polyethylene with different carbon nanotubes (CNTs) as conductive fillers are presented. The composites were prepared through the covering of the surface of polyethylene granules with CNTs and sintering under optimized conditions. The electrical and mechanical properties of the composites were investigated as functions of the CNT concentration and CNT dispersion process for several kinds of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). The CNTs were not uniformly dispersed in the composites but were prelocalized on the granule boundaries, very efficiently forming conductive networks. It was, however, critically important to ensure the good dispersion of the nanotubes in the microscale, and this was performed by sonication in sol vents before dry mixing. Ultralow percolation thresholds were obtained: 0.095 wt % for SWCNTs and 0.05 wt % for MWCNTs (ca. 0.045 vol % for SWCNTs and 0.021 vol % for MWCNTs). The critical exponents were higher than those for uniformly dispersed conductive particles: 2.2 and 2.6 for SWCNTs and for MWCNTs, respectively. The mechanical properties of the composites were also strongly modified by the presence of CNTs. The modulus and ultimate strength increased by about 100% with 2% CNTs. The elongation at break decreased but was still about 500-1000%. Near the electrical percolation threshold, the mechanical properties were not significantly modified. (C) 2007 Wiley Periodicals, Inc.