An Efficient Ethanol-Vacuum Method for the Decontamination and Restoration of Polypropylene Microfiber Medical Masks & Respirators

Albert I. Nazeeri; Isaac A. Hilburn; Daw-An Wu; Kabir A. Mohammed; D. Yovan Badal; Moses H.W. Chan; Joseph L. Kirschvink

We report here the discovery that decontaminating polypropylene microfiber filters in a 70% v/v solution of ethanol and deionized (DI) water, using standard medical procedures including air drying, does not permanently damage the microfibers as has been suggested 3, 4, 7 . Instead, this washing procedure appears to leave a film of water molecules adsorbed hygroscopically on the surface that reduces the particulate absorption efficiency; approximately 2-4 g of water remains firmly on a typical respirator even after extensive air drying due to the large surface area of the fibers. We found that this layer of adsorbed water can be removed by further drying in a partial vacuum to below 6 mBar (0.6 kPa), after which we observe the filtration efficiency returning to within 2% of the original values. As shown in Table 2 , we have repeated this on three different types of N95 respirators for five cycles and see no long-term degradation at this time.