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

Abstract

In\nthis study, we report a series of lightweight, anisotropic polyimide/cellulose\nnanofibril (PI/CNF) composite aerogels with outstanding thermal insulation\nand flame retardancy via unidirectional drying and freeze drying methods.\nAlong the axial direction, PI/CNF composite aerogels exhibit an arranged\ntube-like structure in parallel to ice crystal growth, thus providing\nsuperior mechanical properties. Conversely, the composite aerogels\nshow a honeycomb-like pore structure along the radial direction, exhibiting\nexcellent elastic properties. More importantly, the addition of CNF\nendows the composite aerogels with low thermal conductivity along\nthe radial direction. The surface temperature of the composite aerogels\nwith a thickness of 15 mm is 70% lower than that of hot stage annealing\nat 180 °C for 60 min. Furthermore, the composite aerogels show\nflame retardant and self-extinguishing performance in the combustion\nexperiment. Therefore, the anisotropic PI/CNF composite aerogels with\nthermal insulation and flame retardancy are promising for expanding\npotential applications in aerospace fields.