Surface fibrillation of para-aramid nonwoven as a multi-functional air filter with ultralow pressure drop

Abstract

Nonwovens are widely applied in the air filtration field for their multi-layered fibrous structures and interconnected pores. Despite their intensive use, conventional microfiber nonwovens usually suffer from low filtration efficiencies due to their large pore size, while most nanofiber nonwovens are still confined within the laboratory due to the difficulties of reconciling the comprehensive requirements (such as low pressure drop, high fluffiness, strength and long-term reliability) raised from practical applications. Herein, we report a simple and scalable method that can generate more nanofibrils in a para-aramid microfiber nonwoven without interfering with the three-dimensional nonwoven structure. The success of this method relies on treating the whole nonwoven, rather than individual fibers, with phosphoric acid to trigger a surface fibrillation process of para-aramid microfibers. The structural reinforcement from microfibers, in combination with the enlarged surface area and the reduced pore size brought by nanofibrils, improves the filtration efficiency of the fibrillated nonwoven by 84.7% and maintains the pressure drop at an ultralow value of 3.5 Pa. Further synthesis and loading of a novel catalyst (CuO–CeO₂) onto the nonwoven demonstrates a higher catalyst-loading capacity after fibrillation. The resulting nonwoven filter shows high elimination rates against a variety of solid and gaseous pollutants (including particulate matter, carbon monoxide and toluene), and is applicable at both room and elevated temperatures. We believe that the generation of nanofibrils in microfiber nonwovens and the subsequent loading of catalysts will find extensive utility in the purification of industrial emissions, automobile exhausts and indoor air.