Radiation Cross-Linked Polyurethane/Aluminum Hydroxide Composites with High Strength, Self-Healing, Thermal Insulation, and Flame Retardancy.

Despite the demand for polymer-based porous materials offering both high thermal insulation and flame retardancy, hurdles remain in fabricating low thermal conductivity foams and achieving satisfactory fire-retardant efficiency. We successfully loaded the environmentally friendly flame-retardant agent aluminum hydroxide (ATH) in polyurethane (PU) foam and simultaneously constructed radiation cross-linked structure to obtain polyurethane/aluminum hydroxide (PU/ATH-X) foams, achieving efficient insulation and flame-retardant properties. With a low expansion ratio of 9.4, the thermal conductivity decreased to 41.2 mW/(m·K), and the flame-retardant grade reached V-2 (UL 94). It was noteworthy that the ATH not only played an efficient flame-retardant role but also enhanced the heterogeneous nucleation to improve the microstructure, manifested as smaller cell diameters, and increased cell density. This excellent insulation property was attributed to the increased air conduction frequency, enhanced Knudsen effect, and interface phonon scattering effect. The outstanding flame-retardant performance was due to the synergistic effect of ATH and the cross-linked structure, where ATH decomposed to dissipate heat and block air, and the cross-linked structure promoted the densification of the residual combustion carbon layer to enhance the barrier to air and heat. In addition, the cross-linked structure significantly enhanced the mechanical property. Moreover, the foams also exhibited excellent self-healing and hydrophobic properties. This study opens up a simple path for developing multifunctional foams with high insulation, flame-retardant, and self-healing properties, providing important support for further expanding its practical applications.