Effect of particle size of graphites on electrical conductivity of graphite/polymer composite

The effect of particle size of graphite particles on the dispersion state of graphite particles and electrical conductivity of graphite/low-density polyethylene (LDPE) composites is investigated. Graphite particles which have plate-like and spherical shapes and mean particle sizes of 2.1 to 82.6 mu m are used. Scanning electron microscopy observation showed that graphite particles are not aggregated and ordered along the direction of mixing-roil in the polymer matrix. X-ray diffraction measurements show that crystallite size of the (110) plane of polyethylene crystal and the crystallinity are significantly affected by the particle size of graphite particles. These results were interpreted as due to the orientation of PE crystallites. The electrical conductivity of composites changes discontinuously at the critical volume fraction of particles, phi(C). The phi(C) values given by the percolation equation increase with decreasing of the particle size of graphites. The plate-like graphite particles with a mean particle size of 2.1 mu m could induce conductivity at phi(C) of 0.135. The values of phi(C) increased linearly with increasing of the mean particle sizes of the plate-like graphites. The value of phi(C) of spherical graphite particle is the largest value, 0.292, in all specimens.