High-Performance Polyimide/Silica Composite Aerogelsvia KH550-Mediated Chemical Bridging for Improved Thermal Insulationand Flame Retardancy

Abstract Aerospace thermal protection requires lightweight, thermally insulating and flame-retardant materials. However, pure polyimide aerogels suffer from high-temperature shrinkage and insufficient strength. Direct incorporation of unmodified silica leads to serious nanoparticle agglomeration and poor interfacial compatibility, which greatly deteriorate structural stability, thermal insulation and mechanical properties. Herein, PI/SiO2 composite aerogels were prepared via a KH550-mediated chemical bridging strategy that effectively resolves the critical issues of silica nanoparticle agglomeration and inadequate interfacial compatibility between SiO2 and the PI matrix via covalent bonding. PK-15 (15 wt·% KH550-SiO2) exhibited optimal performance with 95.58% porosity, 600 °C service temperature, enhanced mechanical strength, superior thermal insulation (thermal conductivity:49.85 mW·m·K–1) and instantaneous self-extinguishing flame retardancy (Peak Heat Release Rate:50.4 W/g). The hierarchical porous structure and in situ formed SiO2-carbon protective layer synergistically realized structural thermal insulation and condensed-phase flame retardancy. This composite aerogel holds great promise for aerospace thermal protection and provides a covalent hybridization approach for organic–inorganic composite aerogel design.