Upcycling of Waste Fabrics into High-Efficiency Air Filters Using Flexible Polyimide Aerogel Coatings

This work investigates scalable dip coating and roll coating of common woven and nonwoven fabrics with polyimide (PI) sol to obtain high permeability, high-efficiency filter media. After sol–gel transition, the gel-coated fabrics are dried under supercritical conditions to produce aerogel-coated flexible fabrics with significant mesopores that are in turn used in removal of airborne nanoparticles of diameter 25–150 nm. The air permeability, air filtration efficiency, and thermal and mechanical properties are determined. The highest filtration efficiency of 99.82% is obtained for aerogel-coated muslin fabric, followed by cotton (97.99%), polyester (95.54%), and nylon (82.2%) fabrics, compared to the 62% efficiency of a representative surgical mask. The aerogel-coated fabrics show acceptable air permeability of the order of 10–10 m2. The high filtration efficiency in aerogel-coated fabrics originates from the static charge rendered in the PI coating and the size exclusion of particles by mesopores. This work serves as a motivation for conversion of after-use facemasks, surgical masks, and waste fabrics from clothing materials into high-efficiency filter media.