Abstract
The diameter of the COVID–19 virus is considered to be about 50 nm to 150 nm, and the aerosol diameter containing it by cough about 300 nm. Usually, masks are indispensable for preventing both virus spread and inhalation. There are various types of masks from woven to nonwoven fabrics on the market, and the protective effect to virus varies from a few percent to over 99%. In general, the performance of a mask can be represented by the particle filtration efficiency (PFE) and pressure drop (PD) similar to an air filter. PFE corresponds to a measure of virus protection and PD to ease of breathing. Therefore, better performing masks have higher PFE and lower PD. PFE and PD are in a strong relationship with each other, that is, whenever we try to increase PFE, PD will increase. Generally, electrets are given to increase PFE in keeping PD low such as HEPA and ULPA. The electret, however, loses the effectiveness by water vapor in air, etc. Z–nanofiber sheet mask, which is produced by Z–melt spinning method of polypropylene (PP), can solve those problems, because nanofiber can adsorb virus and bacteria by the van der Waals force without giving electrical properties, that is so–called hydrophobic bond, which induces the washable property of the mask.
