Effect of isocyanate molar ratio on the properties of polyurea-based self-healing local insulating materials with dynamic imine bonds

The insulation strength of the air gap in transmission line towers can be effectively improved by spraying or brushing a local insulation layer in transmission line towers and cross-arms. However, this layer is susceptible to aging, peeling, and costly secondary repairs. To address these issues, the authors synthesized self-healing polyurea-based resin materials with varying isocyanate molar ratios by introducing a dynamic imine bond. The influence of these ratios on the material’s comprehensive performance was investigated through experimental analysis of their thermal, mechanical, and electrical service characteristics, as well as self-healing properties. Results revealed that considerably large or small isophorone diisocyanate: hexamethylene diisocyanate (IPDI:HDI) molar ratios adversely influence the comprehensive performance of the resin materials. When IPDI:HDI was optimized at 6:4, the resin material exhibited excellent physicochemical and electrical performance, with a static water contact angle of 102.37°, a low surface free energy of 18.61 mN m −1 , and tensile strength of 13.87 MPa. The material exhibited no mass loss between 0℃ and 250℃ and achieved a dielectric strength of 43.89 kV mm −1 . In addition, it maintained a dielectric constant of 3.72 and dissipation factor of 0.26 % at 25℃ and 50 Hz, while showcasing excellent self-healing capabilities, enabling scratch recovery within 45–90 min at 50℃. These findings highlight the potential of self-healing polyurea-based resins containing dynamic imine bonds as a new and promising solution for enhancing the durability and reliability of local insulating materials for use in transmission line towers.