Air-Drying for Rapid Manufacture of Flexible Aramid Nanofiber Aerogel Fibers with Robust Mechanical Properties and Thermal Insulation in Harsh Environments.

Aerogel fibers uniting characteristics of both aerogels (lightweight and porosity) and fibers (flexibility and wearability) exhibit a great potential for the production of the next generation of thermal protection textiles; still, the complex drying procedures and mechanical brittleness remain the main obstacles toward further exploitation. Herein, flexible and robust aramid nanofiber aerogel fibers (ANAFs) are scalably prepared by continuous wet-spinning coupled with fast air-drying. This synthesis involves calcium ions (Ca⁺) cross-linking and solvent displacement by low surface tension solvents, to enhance skeleton strength and reduce the capillary force during evaporation, respectively, thus minimizing shrinkage to 29.0% and maximizing specific surface area to 225.0 m g for ANAF. Surprisingly, the air-dried ANAF showed excellent tensile strength (13.5 MPa) and toughness (7.0 MJ m), allowing their easy weaving into the textile without damage. Importantly, the ANAF textile with a skin-core porous structure exhibited low thermal conductivity (≈38.5 mW m K) and excellent thermal insulation ability in the wide temperature range (-196 to 400 °C). Besides, the aramid molecular structure, as well as Ca⁺ cross-linking, endowed the ANAF with high thermal stability and flame retardancy. Consequently, the robust ANAF with a fast-air-drying method is promising for thermal protection in extreme environments, such as in spacesuits.