STRUCTURE AND ELECTRICAL-CONDUCTIVITY OF COMPOSITES OF POLYETHYLENE AND CONDUCTIVE POWDER

Composites were prepared of low density polyethylene (LDPE) and an inorganic powder such as graphite or SnO2 in various volume fractions up to 0.6 of phi. The influence of the morphology and polarity of particles on their dispersion in LDPE and the electrical conductivity of composites was investigated. The composite contained graphite particles which have plate-like shapes ordered along the direction of mixing-roll. Crystallinity (X(cryst)) and crystallite size of (110) plane of polyethylene crystal (C110) were remarkably affected by the nature of the compounded powder. For the diffraction measurement, X-ray beam was radiated on a rolled plane or on a cross section of the sample. C110 (rolled plane) increased with phi, whereas C110 (cross section) decreased with increase of phi. This result was interpreted as due to the orientation of PE crystallite. Their electrical conductivity remarkably increased with phi. Critical volume fraction, phi(c), was calculated through the percolation equation for these composites. phi(c) was 0.199 for graphite and 0.249 for SnO2. The composites containing spherical and hydrophilic SnO2 were comprised of continuous LDPE phase and small aggregates of particles up to 0.25 of phi. Above 0.25 of phi, the particles contact each other and then a continuous electrical conductivity path was formed in the composite. C110 of the SnO2 in phi > 0.25 remarkably increased with phi. This remarkable increase in phi > 0.25 was attributed to the orientation of PE crystallite. It was clear that the shape and polarity of particles affected their dispersion in LDPE and the electrical conductivity of composites.