Information and FAQs on Performance, Protection, and Sterilization of Masks Against COVID-19
https://utrf.tennessee.edu/informat...tion-sterilization-of-masks-against-covid-19/
[ Sterilization using radioactive such as gamma rays has the potential to decompose the PP materials,
using alcohol will erase the charges. However, charges are retained by exposing the masks in the
hot air at elevated temperatures such as 70C for 30 minutes, which kills the coronavirus according to a report. But be sure to suspend the masks in the hot air
without contacting or being too close to a metal surface because the metal temperature is much higher than that of the hot air leading to a severe charge decay or to the damage of the masks... ]
[ Polymer PP has a surface energy of 35 dynes/cm, a hydrophobic material, much lower than the surface tension of room temperature water, 71.2 dynes/cm. Alcohol has a lower surface tension, 20 dynes/cm, than PP. Alcohol will penetrate into the MB PP fabric and erase the charges. Therefore,
face masks cannot be sterilized using alcohol because the charges are erased by either liquid or vapor alcohol. The testing standards to test a filter efficiency after erasing the charges by alcohol include ASHRAE 52.2 Appendix G, EN 776, and EN 16890... ]
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Q2: Can the masks be treated using alcohol?
A: No, face masks cannot be sterilized using alcohol because the charges will be erased by either alcohol liquid or its vapor as described in a previous section.
My friend, Dr. Cai, a retired filtration testing scientist, had experimental data conducted in February 2020 as in the below table that support my above results in the past.
Treatment using alcohol or soap water Experimental
Initial Filtration Efficiency (3-fold medical mask) 93.2%
After Immersion in medical alcohol 67.0%
After treatment with saturated IPA vapor (ISO) 47.4%
After washing by hand with soap/water for 2 minutes 54.0%
The first web link in Q3 had the similar results of charge decay in sterilization using alcohol. ]
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Q4: Can the masks be reused after hanging dry?
A: Not sure. According to a study published in New England Journal of Medicine (NEJM), The COVD-19 can survive in the air for three hours, four hours on a copper surface, 24 hours on a cardboard, two-three days on a stainless or a plastic surface. It is reported from CDC that the possibility of infection from a package being shipped for a few days from China is very slim, which is a similar result as in the NEJM. PP is a hydrophobic plastic material with zero moisture content. The virus needs a host – a cell – to survive.
A respirator can get dry in less than two-three days in a dry air environment. Based on the above reports,
three-four respirators can be numbered, let them get dry, and reuse in the numbered sequence. ]