The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within 3-1/2 months since outbreak in December 2019, over 1.3 million people have been infected across 206 countries with over 70,000 deaths. COVID-19 has a size of 60-140nm with mean size of the nano-aerosols, 100nm. The virus can be airborne by attaching to human secretion (fine particles, nasal/saliva droplets) of infected person or suspended fine particulates in air. While NIOSH has standardized N95 and N98 at 300nm, to-date there is no filter standards, nor special filter technologies, tailored for capturing airborne viruses and 100nm nano-aerosols. The latter also are present in high number concentration in atmospheric pollutants. This study addresses developing novel charged PVDF nanofiber filter technology to effectively capture the deadly airborne coronavirus with our target set at 100nm (nano-aerosol), and not 300nm. The virus and its attached particle were simulated by sodium chloride aerosols, 50-500nm, generated from sub-micron aerosol generator. PVDF nanofibers were produced with fiber diameters 84, 191, 349 and 525nm with excellent morphology. The fibers were subsequently charged by corona discharge. The amounts of charged fibers in a filter were increased to achieve high efficiency of 90% for the virus filter but the electrical interference between neighbouring fibers resulted in progressively marginal increase in efficiency and concurrently much higher pressure drop across the filter. The quality factor which measured the efficiency-to-pressure-drop kept decreasing. By redistributing the fibers in the filter into several modules, each separated by a permeable scrim material, the electrical interference was reduced, if not fully mitigated. Also, the additional scrim materials introduced macropores into the filter that further reduced the airflow resistance. With this approach, the quality factor can maintain relatively constant with increasing fiber amounts to achieve high filter efficiency. The optimal amounts of fiber in each module depended on the diameter of fibers in the module. Small fiber diameter that has already high performance required small amount of fibers per module. In contrast, large diameter fiber required more amounts of fiber per module to compensate for the poorer performance without incurring higher pressure drop. This approach was applied to develop four new nanofiber filters tailored for capturing 100nm airborne COVID-19 to achieve over 90% efficiency with pressure drop below 30Pa (3.1mm water). One filter developed meeting the 90% efficiency has ultralow pressure drop of only 18Pa (1.9mm water) while another filter meeting the 30Pa limit has high efficiency reaching 94%. These optimized filters based on rigorous engineering approach provide the badly needed technology for protecting the general public from the deadly airborne COVID-19 and other viruses, and nano-aerosols from air pollution which lead to chronic diseases.
Electrostatic Charged Nanofiber Filter for Filtering Airborne Novel Coronavirus (COVID-19) and Nano-aerosols