This paper reports the results of studies on the thermal and electrical properties of gamma radiation cured composites based on ethylene propylene dieyne rubber (EPDM) reinforced with different concentrations of micro- and nano-silica. The effect of gamma irradiation in the presence of ethylene glycol dimethacrylate (EGDM) as radiation sensitizer on melt flow properties of EPDM was also studied. Thermogravimetric studies of the composites show that the degradation of vulcanizates is controlled mainly by the silica type and its concentration. Increasing the amount of micro- or nano-silica in the vulcanizate decreases the maximum rate of decomposition of the major degradation step compared with that of the unfilled-cured one. The micro- and nano-composites exhibited remarkable heat resistance properties compared with that of the pure EPDM as the filler dispersion of silica inhibited the thermal degradation of the polymeric matrix, which led to the micro and nano-composites showing great improvement in thermal stability. A considerable change in decomposition rate is observed by increasing filler loading from 10 to 39 phr. The dielectric properties of such composites are affected by the silica type and concentration. The dielectric constant and ac-conductivity for all composites were found to increase with increasing silica loading, which is mainly due to the interfacial polarization. The ac-conductivity values of silica/EPDM composites exhibit a strong frequency dependence with both fillers used. The conductance and dielectric constant values have been fitted using a conduction model for all samples.
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M. Madani (2008) studied this question.