Ultralight and Anisotropic Heterocyclic Para-aramid Nanofiber/Reduced Graphene Oxide Composite Aerogel for Efficient Thermal Insulation and Flame Retardancy

The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is growing.Based on the above background, a novel heterocyclic para-aramid nanofiber/reduced graphene oxide（HPAN/rGO） composite aerogel was prepared by combining electrospinning and unidirectional freeze-drying. The anisotropic HPAN/rGO composite aerogel exhibited a honeycomb morphology in the direction perpendicular to the growth of ice crystals, and a through-well structure of directed microchannels in the direction parallel to the temperature gradient. By varying the mass ratio of HPAN/rGO, a composite aerogel with an ultra-low density of 5.34-7.81 mg·cm-3 and an ultra-high porosity of 98%-99% was obtained. Benefiting from the anisotropic structure, the radial and axial thermal conductivities of HPAN/rGO-3 composite aerogel were 29.37 and 44.35 mW·m-1·K-1, respectively. A combination of software simulation and experiments was used to analyze the effect of anisotropic structures on the thermal insulation properties of aerogels. Moreover, due to the intrinsic self-extinguishing properties of heterocyclic para-aramid and the protection of the graphene carbon layer, the composite aerogel also exhibits excellent flame retardancy properties, and its total heat release rate（THR） was only 5.8 kJ·g-1, which is far superior to many reported aerogels. Therefore, ultralight anisotropic HPAN/rGO composite aerogels with excellent high-temperature thermal insulation and flame retardancy properties have broad application prospects in complex environments such as aerospace.