Ultralight, Mechanically Robust, and Flame-Retardant Polyimide/Silica Nanofibrous Sponges for Thermal Insulation

The development of lightweight, flame-retardant thermal insulation materials capable of withstanding both extreme cold and potential fire hazards continues to be a significant challenge in the field of personal protective equipment. This study presents a facile method based on humidity-induced electrospinning to fabricate polyimide/silica (PI/SiO₂) nanofibrous sponges (NFS) for high-performance thermal insulation. Regulating the rapid phase inversion within the whipping jet leads to the formation of a fluffy assembly of curly, porous nanofibers, and the PI nanofibrous sponge is further obtained following the imidization process. Furthermore, the introduction of nano-SiO₂ particles creates a synergistic effect with the PI matrix at high temperature, promoting a dense, stable composite carbon layer that significantly improves flame retardancy. The final PI/SiO₂-NFS exhibits ultralight property (2.77 mg cm^-3), robust mechanical properties (withstand loads 10,000 times its own weight and remarkable elasticity and fatigue resistance), a low thermal conductivity (25.1 mW m^-1 K^-1), as well as outstanding flame retardancy. This work presents a novel pathway for developing next-generation high-performance thermal protection materials for personal safety in harsh environments.