Investigation of electrical and mechanical properties of silver-hexagonal boron nitride/EPDM composites

Ethylene propylene diene monomer (EPDM) is widely used as the reinforced insulation material for high voltage direct current (HVDC) cable accessories due to its excellent insulation properties, but its field-dependent conductivity is weak. In this paper, the silver particles (Ag) was prepared and filled into EPDM. The nonlinear conductivity characteristics and breakdown characteristics of the Ag/EPDM composites have been investigated. As the filled Ag content increases, the nonlinear conductivity becomes more obvious, with the maximum nonlinear coefficient reaching 2.45, however, the breakdown field strength is degraded seriously, when the Ag content of the composites reaches 0.5 wt%, the characteristic breakdown strength of the Ag/EPDM composites is reduced to 70.5 kV/mm (neat EPDM is 137.1/kV/mm). In order to relieve the severe degradation of breakdown field strength of Ag/EPDM composites, hexagonal boron nitride (BN), with perfect insulation and thermal properties, is introduced into Ag/EPDM composites. The results show that when 10 wt% of BN and 0.5 wt% of Ag are co-doped into EPDM, the characteristic breakdown field strength is 109.7 kV/mm, which increases by 55.6% compared to that of 0.5 wt% Ag/EPDM (70.5 kV/mm). In addition, the mechanical properties of BN/EPDM composites and Ag/BN/EPDM are improved significantly compared with neat EPDM.