Nanofibers improve the filtration of face masks, but need to be replaced often


September 7 (UPI) – New research, published Tuesday in the journal Physics of Fluids, suggests that the use of nanofibers may improve the filtration efficiency of face masks, but they need to be replaced quite frequently.

As rates of COVID-19 cases and hospitalizations increase in the United States, health officials are once again encouraging people to wear face masks indoors, regardless of their vaccination status.

Since the start of the pandemic, health experts and materials scientists have been trying to figure out the best ways to filter out viral particles. While N95 masks remain the norm for healthcare workers, single-use masks are not always practical for the general public.

While several studies have shown that multiple layers of fabric – or combinations of fabric, silk, and muslin – provide significant filtration, mask makers have also deployed nanofibers to boost protection against aerosolized viral particles.

Although nanofibers have been shown to be effective in increasing filtration, their resilience has not been extensively tested – until now.

“When COVID-19 first hit, face masks were extremely rare everywhere, and people came up with all kinds of ways to ‘rejuvenate’ used face masks,” study co-author Boyang said. Yu in a press release.

“It was like a chef’s competition, with boiling, steaming, grilling and even smoking. Our intuition told us that couldn’t be right. We have to look at this and see what exactly happened with it. nanofibers, ”said Yu, an engineer at the Southern University of Science and Technology in China.

To better understand the filtration capabilities and durability of nanofiber masks, the researchers used high-speed microscopic video to film different layers of polymer under exposure to water aerosols.

“Filming nanofibers is like taking portraits of babies,” Yu said. “They don’t like to sit still for the camera. That’s because nanofibers are very soft and fragile, especially with the flow. aerosol spray going through them. But with enough care, patience and luck, we finally got some nice pictures for our analysis. “

Video footage and images showed that the fibers irreversibly merge during the “droplet capture step”, reducing their filtration capabilities. Scientists found that fiber coalescence could be reduced by adding hydrophobic and orthogonally woven fibers.

“We have confirmed three things,” said co-author Weiwei Deng, also an engineer at the Southern University of Science and Technology. “First, nanofibers perfectly capture droplets in aerosols. Second, nanofibers are bonded together after capturing the aerosol. And third, this bond is tight and irreversible, even after the captured droplets evaporate.”

“Wet fibers tend to bind to each other in the same way that wet hair tends to cluster,” Deng said. “This is because of the capillary force, which becomes dominant as the size scale shrinks, and it is extremely strong for nanofibers.”

Researchers suggest that nanofiber masks be replaced more frequently during the winter. When it is cold, exhaled breaths contain more water droplets.

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