"Our work is the first to use new coronavirus aerosols to evaluate the filtration efficiency of masks and air filters." Corresponding author Yun Shen, an assistant professor of chemical and environmental engineering at UC Riverside, said, "Previous studies have used salt solutions, polystyrene beads and alternatives to phage, a virus that infects bacteria."
The study, led by engineers at the University of California, Riverside and George Washington University, compared the effectiveness of surgical masks and cotton masks, neck covers and electrostatically spun nanofiber membranes in removing neocoronavirus aerosols to prevent airborne transmission. Cotton masks and neck covers removed only about 45%-73% of the aerosol. Medical masks were much more effective, removing 98% of the new coronavirus aerosols. However, nanofiber filters removed almost all aerosols of coronaviruses.
Both the World Health Organization and the U.S. Centers for Disease Control recognize aerosols as the primary mechanism of COVID-19 virus transmission. Aerosols are tiny particles of water or other substances that can remain suspended in the air for long periods of time and are small enough to penetrate the respiratory system.
People release aerosols when they breathe, cough, talk, shout or sing. If they are infected with COVID-19, these aerosols can also contain the virus. Inhaling sufficient amounts of new coronavirus aerosols can make people sick. Reducing personal exposure and reducing the total amount of aerosols in the environment by requiring people to wear masks and improving indoor ventilation and air filtration systems are priorities for curbing the spread of new coronavirus aerosols.
It is relatively rare that studies of new viruses that are infectious are dangerous and are conducted in laboratories with the highest biosafety ratings. To date, all studies on mask or filtration efficiency during pandemics have used other materials thought to mimic the aerosol size and behavior of new coronaviruses. This new study improves on that by testing nebulized saline solutions and aerosols containing coronaviruses of the same family as the virus that causes COVID-19 but that infect only mice.
Yun Shen and George Washington University colleague Danmeng Shuai made a nanofiber filter that delivers a high voltage through a drop of polyvinylidene fluoride liquid to a spinning thread that is about 300 nanometers in diameter - about 167 times thinner than a human hair. This process produced holes only a few microns in diameter on the surface of the nanofibers, helping them capture 99.9 percent of coronavirus aerosols.
This production technique, known as electrostatic spinning, is cost-effective and can be used to mass-produce nanofiber filters for personal protective equipment and air filtration systems. Electrostatic spinning also leaves an electrostatic charge on the nanofibers, which enhances their ability to trap aerosols, and their high porosity makes it easier to breathe while wearing electrostatic spun nanofiber filters.
"Electrostatic spinning technology can facilitate the design and manufacture of masks and air filters." Prof. Yun Shen said, "The development of new masks and air filters using electrostatic spinning technology is promising because of its good filtration performance, economic feasibility and scalability to meet the needs of field masks and air filters."