Dielectric and thermal properties of self-healing carboxylated nitrile rubber ionically cross-linked with zinc oxide

Dielectric and thermal properties of carboxylated nitrile rubber (XNBR), ionically cross-linked with zinc oxide (ZnO), were characterized to verify its suitability for a high-voltage insulation application. Moreover, the material self-healing (SH) capabilities were assessed after dielectric strength measurement by following IEC 60243. The initial thermal characterization via simultaneous thermal analysis (STA) showed that the material is thermo-oxidatively stable to around 330 °C when the weight loss reaches about 3 %. The dielectric properties of the material as a function of temperature and frequency were analyzed using broadband dielectric spectroscopy (BDS). BDS revealed that dielectric constant and loss factor values reach the generally acceptable level for an insulation material at the industrial frequency (50 Hz) and temperatures below -20 °C. At higher frequencies (specifically at 1 MHz) and temperatures of 60 °C, a significant increase of the values are evidenced, which is affected by polarization processes. Furthermore, it was found that the tested material achieves mean values of volume and surface resistivity of 5.12E+08 Ω•cm and 2.01E+10 Ω, respectively, and a relatively low value of dielectric strength (12 kV/mm). A detailed analysis of the dynamic electrical breakdown process showed that the tested material could partly heal its chain structure, especially in the early stages of breakdown's channel formation.