Impact of common face mask regeneration processes on the structure, morphology and aerosol filtration efficiency of porous flat sheet polysulfone membranes fabricated via nonsolvent-induced phase separation (NIPS)

The potential of flat sheet polymeric membranes as a sustainable solution for reusable facemask filters was investigated by analyzing the effect of common face mask regeneration processes on polysulfone (PSf) membranes’ structure, morphology, and aerosol filtration efficiency. The impact of regeneration processes, such as isopropanol (IPA), detergent and bleach washes, and ultraviolet light exposure, was for the first time compared between surgical masks, N95 masks and flat sheet PSf membranes. The PSf membranes were fabricated via non-solvent induced phase separation (NIPS), and demonstrated a higher particulate filtration efficiency (99.06 ± 1.38%) for PM_0.3 i.e., particulate matter of 0.3 µm aerodynamic diameter compared to surgical mask (70.93 ± 2.82%) and N95 (N95-1: 97.09 ± 7.37%; N95-2: 91.46 ± 1.45%). Scanning electron microscopy (SEM) analysis revealed no significant changes in morphology of treated membrane pores. Fourier transform infrared spectroscopy (FTIR), contact angle goniometry, and Xray photoelectron spectroscopy (XPS) analyses revealed retained membrane surface composition, hydrophobicity, and showed no residual elements from sterilizing chemicals after rinsing for 30 min. Statistically insignificant differences in treated and untreated PSf membrane pore size, porosity, and mechanical strength obtained in this work suggest the absence of chain scission due to radical formation, which can arise from polymer chains exposure to UV and bleach (NaClO), and change in polymer chain conformation. Treatment with IPA and detergent, which resulted in 46.7 ± 5.5% and 64.3 ± 12.9 % reduction of 0.3 µm aerosol filtration efficiency, respectively, for commercially available face masks, showed an insignificant decrease in PSf membrane filtration performance, which was attributed to dissipation of electrostatic charges responsible for the high filtration efficiency of non-woven face masks.