EFFECT OF AGING ON THE DIELECTRIC BEHAVIOR OF SILICONE-EPDM BLENDS

Dielectric measurements in the frequency (1 - 10(5) Hz) and temperatur e (25 - 200 degrees C) domains have been carried out for silicone, EPD M, and their 50/50 (by weight) blend before and after ageing in water, steam and air. Low values of permittivity and loss tangent for EPDM r eflect its non-polar and loss-free nature. Thermal depolarisation is a lso observed with EPDM and the air-aged specimen shows little rising t rend due to dipole orientation. Silicone is found to be polarised in t wo steps. Changes in dielectric properties and DC resistivity on hydro thermal weathering and air ageing confirms that charge carriers contri bute in the low-temperature step and polar silanol groups contribute i n the high-temperature region. The properties of the 50:50 blend are v ery much sensitive to the medium of ageing. Hydrothermal ageing improv es the quality of the dielectric of silicone due to removal of charge carriers and the suppression of silicone hydrolysis by EPDM. Ageing of the blend in air increases the polarisation to a very high level owin g to the charge carriers, the additional interface and the dipoles for med during ageing. Activation energies suggest that the low temperatur e polarisation step is associated with charge carrier mobility and ori entation of pendent groups.