The ternary nano-composites based on ethylene-vinyl acetate copolymer (EVA, 18 percent vinyl-acetate group) without and with 1 wt. percent of EVAgMA (EVA - grafted - maleic anhydride) and 2 - 5 wt. percent of nano-silica were prepared by melt mixing in a Haake intermixer at 160oC, roto speed of 50 rpm for 5 minutes. The volume resistivity, dielectric breakdown and dielectric loss of the nano-composites were measured in according to ASTM D257, D149 and D150, respectively. The nano-composites were tested in a hot air circulating oven at 70oC for 168 hours to investigate thermal oxidation aging stability. The obtained results showed that nano-silica decreased volume resistivity and dielectric loss of the nano-composites but it increased dielectric breakdown of EVA. The dielectric constant of the EVA/EVAgMA/silica nano-composites is lower than that of the EVA/silica nano-composites. The EVA/silica nano-composites without and with EVAgMA are good electrical insulation materials (volume resistivity in the range of 10 exponent 13 - 10 exponent 14 Om.cm, dielectric loss of about 10-3 and dielectric breakdown in the range of 22.1 - 26.7 kV/mm). The percentage of retention in mechanical properties of the EVA/EVAgMA/silica nano-composites is higher than that of EVA. FTIR analyses of the nano-composites before and after thermal oxidation aging indicated that nano-silica and EVAgMA limited to degrade EVA macromolecules.
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