June 17, 2020
With the global spread of coronavirus infection, personal protective equipment, especially masks, has received widespread attention. Masks are the main protective equipment that protects the respiratory tract from viruses and bacteria that spread through the air in the form of droplets.
Because it is currently difficult to obtain, there is an urgent need for a safe method that prolongs its usability through sterilization and repeated use without losing performance and integrity. Particulate filtration and breathability are key factors in determining performance when cleaning and disinfecting N95 certified masks. This is essential to prevent infection. Since the outbreak of the coronavirus, Shinshu University has been conducting research on the production method and application of "Nano-fiber nonwoven fabrics".
In the current social context, a research team led by Professor Ick Soo Kim from the School of Fiber Engineering (IFES) of Shinshu University received a Ph.D. The students Sana Ullah and Azeem Ullah of POSTECH (invited professor of IFES) and Professor Cha Hyung Joon received their Ph.D. Students of Lee Jaeyun and Yeonsu Jeong studied the effect of disinfecting N95 masks. They studied commercially available meltblown nonwoven N95 masks and nonwoven nanofiber masks with N95 filters. They checked the filtration efficiency after cleaning and disinfection, the comfort of the wearer and the change in the shape of the filter. The method of disinfection test includes spraying 75% ethanol directly on the mask filter and air drying, then soaking the mask filter in 75% ethanol solution for 5 minutes to 24 hours, and then air drying.
Before use, the filtration efficiency of the two filters (melt blown filter and nanofiber filter) are 95% or higher, which shows that the wearer's respiratory organs can be effectively protected. Tests also show that by spraying ethanol for more than 3 times or immersing it in ethanol solution for more than 5 minutes, the inside of the filter can be effectively sterilized. However, when the mask is used again after ethanol disinfection, the filtration efficiency of the melt blown filter is reduced to 64%. On the other hand, even if it is used more than 10 times, the filter performance of the nanofiber filter will not decrease.
The melt blown filter works on the principle of electrostatic charge to remove particulates, because the spray or immersion of ethanol results in the loss of static charge on the surface of the melt blown filter, so the efficiency of the melt blown filter is significantly improved and reduced. On the other hand, the filtration mechanism of the nanofiber filter has nothing to do with static charge, and completely depends on the pore size, pore distribution and morphology of the nanofiber. As a result of the disinfection, the morphology of the nanofiber is not affected, so it also maintains the best filtering effect as before.
In addition, compared with melt blown filters, nanofiber filters have higher heat dissipation and carbon dioxide emission performance, and show excellent air permeability. Similarly, it was confirmed that the nanofiber filter has lower cytotoxicity than the melt-blown filter when performing safety experiments using human skin and blood vessel cells.
As mentioned above, the two mask filters have similar filtering performance when they are used for the first time, but after disinfection and reuse, the nanofiber filter will not show performance degradation. In other words, the nanofiber filter can be easily disinfected with ethanol at home and can be reused many times.
Professor Cha Hyung Joon, who co-hosted the research, said: “This research is an experimental verification of the biosafety of nanofiber masks and the maintenance of filtration efficiency after washing. This has recently become a problem.” Professor Jin Xiuxiu hopes
Masks will be used as a preventive measure for the second and third coronavirus infections.
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