Electrical, Dielectric, and Electromagnetic Shielding Properties of Polypropylene-Graphite Composites

The conducting polymer composite material is desired to have a high dielectric constant and high dissipation factor in low and high frequency ranges, so that it can be used in charge storing devices, decoupling capacitors, and electromagnetic interference (EMI) shielding applications. Currently, on-going research is trying to enhance the dielectric constant of ceramic powder-polymer, metal powder-polymer, and nanotube-polymer composites in the low frequency region. In this article, we present the dielectric properties of polypropylene (PP)-graphite (Gr) composites in low and radio frequency ranges. Furthermore, the EMI shielding properties of these composites are examined in the radio frequency range. The PP-Gr composites were prepared by mixing and the hot compression mold technique. The electrical conductivity and dielectric constant of PP-Gr composites with graphite volume fraction follow the power law model of percolation theory. The percolation threshold of the composites is estimated to be 0.0257 (similar to 5wt % of Gr). The current of PP-Gr composites as a function of voltage shows a nearly ohmic behavior above the percolation threshold. Shore-D hardness of the composites is decreased with the addition of conducting filler. The PP-Gr composites exhibit a high dielectric constant and high dissipation factor with the addition of graphite in low frequency and radio frequency regions, so they can be used in the proposed applications. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1306-1314, 2010