Can you charge a used N95 mask to restore its filtration ability so it's as good as new again? In a report by IEEE Spectrum, Technion-ITT biophysics professor Dov Levine said: "Well, it turns out you can."
Levine and fellow researcher Shankar Ghosh at Tata Institute of Fundamental Research in India showed that a used N95 mask that has been decontaminated can be "rejuvenated" with a jolt of electricity that restores its electrostatic charge.
"N95 respirators employ an electrostatic mechanism to attract and intercept foreign particles (charged or uncharged)," the researchers wrote in a report published in the Physics Of Fluid journal.
A mask's filtration efficiency reduces over time – usually within just a day – as its electrostatic charge leaks into the air, making it less efficient at trapping particles.
"It is these electrostatic interactions that raise the filtration of N95 masks to the 95% (efficiency) level," they said.
Researchers used an electric field with the strength of 800 volts per millimetre to charge the mask, explaining that the field had to be strong enough to make the mask conductive to electric charges.
The researchers claimed they were able to restore efficiency back to 95% after about an hour of charging.
While their work shows that it's possible to recharge a mask to restore filtration efficiency, they acknowledged that more needs to be done before it's developed for practical applications.
Also, the inventor of the N95 mask, Peter Tsai, felt that the method used by the researchers to test the mask was insufficient.
"Without using a reliable commercial filtration tester, the tested data from a rough apparatus are likely questionable, ” he said in the IEEE Spectrum report.
The researchers wanted to help address the demand for N95 masks as they have become a vital personal protection equipment in the fight against the Covid-19 pandemic.
Though the mask is meant only to be used one time, serious shortage has led to a worldwide effort to develop decontamination and re-use procedures, the researchers said.
"In particular, this method may allow for N95 masks to be used for a considerably longer period of time than is the current norm, which can have a significant effect in hospitals where mask supply is insufficient. Additionally, we envisage that our method may find applications in a variety of air filtration contexts," they said in the report.
The researchers also developed a battery-powered mask with removable filters that can be charged to maintain a high level of filtration. The 3D-printed prototype has layers of N95 mask material and two porous metal screens attached to a small battery.
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