PVA-<i>co</i>-PE Nanofibrous Filter Media with Tailored Three-Dimensional Structure for High Performance and Safe Aerosol Filtration via Suspension-Drying Procedure

Abstract

High efficient filtration of air pollutants exerts a great demand for nanofiber-based materials with superior structures. In this work, a mixed solution of tert-butyl alcohol (TBA) and water was employed to stably disperse PVA-co-PE nanofibers. Nanofibrous filter media based on PP nonwoven fabric substrate with various porosity were then prepared via three nanofiber-suspension drying techniques: spray-air-drying, spray-freeze-drying, and container loading-freeze-drying. The prepared nanofiber composite filter media with average nanofiber diameter about 155 nm present controllable three-dimensional structure: nanofiber layer porosity increases from 76.6% to 97.3%, various pore sizes increase from 0.493 to 2.268 μm, as well as an increased nanofiber layer thickness from about 10 to 55.3 μm for filter media with 2.667 g/m2 nanofiber coverage density (NFCD). On the basis of the structure, filter media possess a best comprehensive filtration performance with the quality factor 1.110 mmH2O–1 (99.955% and 6.73 mmH2O) at NFCD = 2.677 g/m2 and a best efficient performance with efficiency 99.999% (0.645 mmH2O–1 and 17.86 mmH2O) at NFCD = 6.583 g/m2, respectively. The theoretical analysis shows the excellent properties are mainly derived from the stable three-dimensional structure of nanofiber network which can provide superior torturous channels for capturing airborne nanoparticles and facilitating the penetration of air flow indicating a typical deep bed filtration. The result of electret treatment test shows that the filter medium exhibits remarkably stable filtration properties and is basically insusceptible to the electrostatic charges rather than the commercial PP nonwoven fabric substrate. Furthermore, the repetitive-use test showed that present nanofibrous composite filters possess higher dust holding capability (24.3 g/m2) and longer service life (8.5 h) than commercial filter with the similar initial filtration property. This implies the superiority of present nanofiber composite filter media in the application as a high stable, cost-effective, and safer air filter medium.