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

Dielectric measurements in the frequency (1 - 10(5) Hz) and temperature (25 - 200 degrees C) domains have been carried out for silicone, EPDM, 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 reflect its non-polar and loss-free nature. Thermal depolarisation is also observed with EPDM and the air-aged specimen shows little rising trend due to dipole orientation. Silicone is found to be polarised in two steps. Changes in dielectric properties and DC resistivity on hydrothermal weathering and air ageing confirms that charge carriers contribute in the low-temperature step and polar silanol groups contribute in the high-temperature region. The properties of the 50:50 blend are very much sensitive to the medium of ageing. Hydrothermal ageing improves 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 owing to the charge carriers, the additional interface and the dipoles formed during ageing. Activation energies suggest that the low temperature polarisation step is associated with charge carrier mobility and orientation of pendent groups.