Research on Water Resistance of Low-Smoke Halogen-Free Flame Retardant Polyolefin Insulation

Due to the strong hygroscopicity of low-smoke halogen-free flame retardant polyolefin insulation, which seriously affects the long-term operational stability and safety of low-smoke halogen-free cable, influence of different types of resins, various flame retardants and irradiation cross-linking on water resistance of insulation materials was investigated using the gravimetric method. Results indicated that water absorption rate of the insulation material decreased as the mass fraction of ethylene-vinyl acetate copolymer (EVA) decreased, and it also decreased with the increase in mass fraction of metallocene linear low-density polyethylene (mLLDPE) and ethylene-octene copolymer (EOC). Among flame retardants, magnesium hydroxide (MDH) raw powder exhibited a significantly higher water absorption rate than aluminum hydroxide (ATH) raw powder, whereas calcium carbonate (CaCO₃) raw powder demonstrated the lowest. Additionally, modified inorganic flame retardants showed a lower water absorption rate. Furthermore, as the irradiation dose gradually increased, the degree of cross-linking rose, leading to a progressive reduction in water absorption rate of the insulation material. The above research results could provide reference for the selection of cable materials, especially low-smoke halogen-free flame retardant insulating materials with humidity requirements.