Protection of Very Small Particles Such as Viruses and Bacteria by Washable and Wearable Z-Nanofiber Sheet Mask

The diameter of the COVID-19 virus is considered to be about 50nm to 150nm, and the aerosol diameter containing it by cough about 300nm. 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 (1) 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 socalled hydrophobic bond, which induces the washable property of the mask. Table1 shows the PFE and the PD of seven Nanofiber sheet samples of PP. PFE was measured by using the NaCl particles whose diameters are from 25nm to 131nm, where measurement conditions are 100cm2 of measurement area, 31.8L/min of ventilation volume, and 5.3cm/sec of flow velocity, respectively. PFE and PD of each sample are more than 99% and less than 70Pa, respectively, which means that we can prepare the non-suffocating mask with high virus capture efficiency [1].