With the global spread of coronavirus infections, personal protective equipment, especially N95 masks, are difficult to obtain, so there is an urgent need for a safe method of prolonging their usability through disinfection and reuse with minimal loss of the performance and integrity. Particulate filtration and air permeability are key factors in determining performance while cleaning and disinfecting N95 certified masks. This is crucial in preventing infections. 

Researchers from Shinshu University in Japan have looked into the effectiveness of sterilizing N95 masks. They looked at commercially available melt-blown nonwoven fabric N95 masks and nonwoven nanofiber masks with N95 filters. They examined the filtration efficiency, comfort of the wearer, and filter shape change after washing and disinfecting. The methods of disinfection test were directly spraying 75% ethanol on the mask filter and air drying and soaking the mask filter in 75% ethanol solution for 5 minutes to 24 hours and leaving it to air dry naturally.

Filtration efficiency of both of the filters (melt-blown filter and the nanofiber filter) was 95% or more before. The tests clarified that the inside of each type of filter can be effectively sterilized by spraying ethanol three times or more or immersing it in an ethanol solution for more than 5 minutes. However, when the mask was reused after the ethanol disinfection, the filtration efficiency of the melt-blown filter decreased to 64%. On the other hand, the nanofiber filter did not deteriorate in filter performance even after 10 or more uses.

In addition, the nanofiber filter has higher heat emission and carbon dioxide emission performance than the melt-blown filter, and exhibits excellent breathability. Similarly, it was confirmed that the nanofiber filter had lower cytotoxicity than the melt-blown filter when a safety experiment using human skin and vascular cells was performed.

In sum, both mask filters have similar filtering performance at the time of first use, but after disinfecting and reusing, the nanofiber filter does not exhibit performance deterioration. In other words, nanofiber filters can be easily sterilized with ethanol at home and reused multiple times.

“This research is an experimental verification of the biological safety of nanofiber masks and the maintenance of filtration efficiency after washing, which has recently become a problem,” says Cha Hyung Joon, PhD. The researchers hope that nanofiber masks will serve as a means of prevention in the second and third wave of coronavirus infections.

Find the study in ACS Applied Nano Materials

Featured image: Comparison of mask filter performance after ethanol disinfection: The nanofiber filter has air permeability even after being washed. The melt-blown filter has its mesh structure changed by ethanol sterilization and its performance is deteriorated. Copyright © 2020 American Chemical Society.