Alternating current electrical conductivity of high-density polyethylene-carbon nanofiber composites.

High-density polyethylene (HDPE)-carbon nanofiber (CNF) composites with good dispersion of fillers in the polymer matrix were melt-compounded in a Haake mixer. The dependences of the alternating current conductivity of such nanocomposites on the filler content, temperature, and DC bias were investigated. The results showed that the electrical conducting behavior of HDPE-CNF nanocomposites can be well characterized by the direct current conductivity (sigmaDC, characteristic frequency (fc) and critical exponent (s). It was found that sigmaDC of percolating HDPE-CNF nanocomposites increases with increasing filler concentration and follows the scaling law of percolation theory. Increasing temperature caused a reduction of sigmaDC, leading to the occurrence of positive-temperature-coefficient effect near the melting temperature of HDPE matrix. Application of DC bias led to an increase of sigmaDC due to the creation of additional conducting paths within the polymer composites. The characteristic frequency generally followed the same tendency as sigmaDC. The s values of percolating composites were slightly higher than those predicted by the percolation theory, indicating the presence of tunneling or hopping conduction in these composites.