Anisotropic Polyimide/Cellulose Nanofibril Composite Aerogels for Thermal Insulation and Flame Retardancy

Inthis study, we report a series of lightweight, anisotropic polyimide/cellulosenanofibril (PI/CNF) composite aerogels with outstanding thermal insulationand flame retardancy via unidirectional drying and freeze drying methods.Along the axial direction, PI/CNF composite aerogels exhibit an arrangedtube-like structure in parallel to ice crystal growth, thus providingsuperior mechanical properties. Conversely, the composite aerogelsshow a honeycomb-like pore structure along the radial direction, exhibitingexcellent elastic properties. More importantly, the addition of CNFendows the composite aerogels with low thermal conductivity alongthe radial direction. The surface temperature of the composite aerogelswith a thickness of 15 mm is 70% lower than that of hot stage annealingat 180 degrees C for 60 min. Furthermore, the composite aerogels showflame retardant and self-extinguishing performance in the combustionexperiment. Therefore, the anisotropic PI/CNF composite aerogels withthermal insulation and flame retardancy are promising for expandingpotential applications in aerospace fields.