Electrical Study of Filler Effects on Ethylene Propylene Rubber.

Electrical behaviour in Ethylene Propylene Rubber (EPR) with fillers (clay, alumina, silica) has been studied with particular attention devoted to the charge transport and storage. The primary concern of this research is the modification of EPR properties with fillers and the study of their electrical behaviour in composites. The measurements were carried out with the methods of electrical conductivity, thermally stimulated current, and dielectric relaxation. The main constituent of the samples in this research is a copolymer of Ethylene Propylene Rubber which is Nordel 1040 of DuPont. Samples containing 5 wt. percentages of Dicumyl Peroxide and filler (clay, alumina, or silica) were prepared. The measurements of conduction current were carried out in the temperature up to 100^circ C at electrical field of 10 kV/cm to 100 kV/cm. Two -side gold-metalized samples yield steady-state current after long field application. The current-field characteristics are almost to follow the Poole-Frenkel effect, while the current-temperature characteristics follow an Arrhenius equation. The fillers of clay, alumina, and silica on EPR are found to provide traps which change the conduction current and the activation energy. The conduction current of filled EPR is usually lower than that of unfilled EPR in those ranges of field and temperature, while activation energy of filler EPR is higher than that of unfilled EPR. Thermally stimulated currents (TSC) has been measured with poling temperature range of 30 to 130^ circC and poling electric field of 50 kV/cm to 150 kV/cm in the temperature up to 170^ circC. The type of peak was obtained by 2 kinds of technique. A dipole peak shows that the peak current increases almost linearly in those range of field and the peak temperature is almost constant. A space-charge peak shows that the peak temperature becomes increasing with increasing poling temperature. The measurements of dielectric constant and loss tangent over a frequency range of 500 Hz to 50 kHz at room temperature indicate both dielectric constant and loss tangent increase as more silica or alumina is added. Loss tangent decreases with increasing frequency, while dielectric constant is constant over the frequency range. The Maxwell -Wagner type interfacial polarization leads to a rise in the value of the dielectric properties, as the filler (silica, alumina) concentration increases.