Investigation of electrical properties of ZnO@Ag/EPDM composites

In this study, Ag conductive nanoparticles were successfully grown on ZnO semi-conductive nanosheets (abbreviated as ZnO@Ag) by combined sol–gel and liquid-phase chemical reduction methods. Both ZnO and ZnO@Ag are chosen as inorganic fillers, respectively, and EPDM is used as the matrix. The microstructures and electrical performances of the EPDM-based composites with different content of fillers have been systematically investigated. The results show that no nonlinear conductivity can be observed in pristine ethylene-propylene rubber (EPDM); however, obvious nonlinear conductivity appears in ZnO/EPDM composites with 10 wt. % ZnO. Especially, after introducing 10 wt. % ZnO@Ag into EPDM, the nonlinear conductive characteristics become much more remarkable compared with 10 wt. % ZnO/EPDM. As the content of ZnO@Ag and measured temperature increase, the threshold field strength that corresponds to nonlinear conductivity decreases gradually. Besides, the increase in conductivity accompanies a decrease in breakdown field strength. Compared to pristine EPDM (breakdown strength of 133.6 kV/mm), the breakdown field strength of 30 wt. % ZnO@Ag/EPDM reduces to 75.86 kV/mm at 30 °C and 51.36 kV/mm at 70 °C. In addition, both the dielectric constant and dielectric loss gradually increase with the increase in ZnO@Ag filling content due to the semi-conductive/conductive characteristics of fillers. As a consequence, this study provides an effective way to induce nonlinear conductivity for EPDM, and ZnO@Ag/EPDM composites may be used to homogenize the electric field and improve the performances of cable accessories.