Ethanol-Drying Regeneration of N95 Respirators

Abstract

<jats:p>A critical shortage of respirators, masks and other personal protective equipment (PPE) exists due to the COVID-19 pandemic. Of particular need are N95 respirators, which use meltblown microfibers of charged polypropylene. An intensive search is underway to find reliable methods to lengthen the useful life of these normally disposable units. Recent experiments on respirators cleaned with ethanol solutions found drastic post-treatment drops infiltration efficiency (&gt;40%). This has been attributed to a mechanism whereby ethanol disrupts the charges in the microfibers, reducing their ability to trap particles. The CDC/NIOSH has issued guidance directing clinicians and researchers to pursue other methods of decontamination. In our experiments, we replicated the drop in efficiency after 70% ethanol treatment, but we found that the efficiency rose again after more effective drying, which we achieved with a vacuum chamber. After drying at pressures of &lt; ~6 mbar (0.6 kPa), the measured filtering efficiency rose to within 2% of the pre-washing value, and we found that this was sustained for 5 cleaning-drying cycles in three models of N95 masks. We stress that our tests are not meant to certify that the respirators are safe for use, which would require further, standardized, testing under NIOSH protocols. The tests presented here are used to understand basic mechanisms by which treatments can decrease or increase filtration efficiency. The main mechanism underlying the loss and recovery of filter efficiency seems to be the deposition and removal of water molecules adsorbed on the fiber surfaces, a hypothesis which is supported by several observations: (A) the filtering efficiency increases non-linearly with the weight loss during drying. (B) filtration efficiency shows an abrupt recovery as the vacuum pressure drops from 13 to 6 mbar, the range physically attributable to the removal of adsorbed water. (C) Optical microscopy of the microfiber layer reveals surface wetting of the fibers, which is most resistant to drying in dense regions of the fiber network. These observations indicate that losses in filter efficiency may be caused by the wicking of water into the dense fiber networks, reducing the available surface area for filtration. Such a degradation mechanism has two implications: (A) Ethanol and other aqueous decontamination methods may be more viable than previously assumed. Investigations of such methods should specify drying methods in their protocols. We employ vacuum chambers in this study, but other methods of removing adsorbed water could be equivalent. (B) This mechanism presents the possibility that mask filtration performance may be subject to degradation by other sources of moisture, and that the mask would continue to be compromised even if it appears dry. Further research is needed to determine the conditions under which such risks apply, and whether drying should be a routine practice for respirators undergoing extended use. This study introduces a number of methods which could be developed and validated for use in resource-limited settings. As the pandemic continues to spread in rural areas and developing nations, these would allow for local efforts to decontaminate, restore, and test medical masks.</jats:p>

Copper@ZIF‐8 Core‐Shell Nanowires for Reusable Antimicrobial Face Masks

“…This drop in filtration efficiency can be restored using methods such as triboelectric charging, [ 47 ] and vacuum filtration. [ 48 ] We report a similar observation, when samples treated in 75% ethanolic nanocomposite solutions of varying concentrations were dried overnight in a vacuum oven, the filtration efficiency was restored closer to the initial value for bare untreated filter media. We also observed that on increasing the concentration of Cu@ZIF‐8 NWs beyond 0.25 mg mL −1 , the filtration efficiency surpassed the efficiency of bare filter media.…”

“…This drop in filtration efficiency can be restored using methods such as triboelectric charging, [47] and vacuum filtration. [48] We report a similar observation, when samples treated in 75% ethanolic nanocomposite solutions of varying concentrations were…”

“…Surface charge is an important factor in filtration efficiency. [ 48 ] The average zeta potential of Cu@ZIF‐8 NWs measured in DI water at neutral pH was 6.54 mV, but the surface charge under dry conditions is likely different. The pressure drop increased slightly upon functionalization with Cu@ZIF‐8 NWs.…”

Can N95 Respirators Be Reused after Disinfection? How Many Times?

“…In the case of disinfection with ethanol-based solutions, recent preliminary work also shows that vacuum drying may be able to restore the efficiency of FFRs. 33 It is also possible that the chlorine-based solution may degrade the efficiency less than the alcohol-based solution due to the higher water content. As polypropylene is hydrophobic, the chlorine-based solution may have a more difficult time penetrating the fabric and the static charge of fibers deeper within the meltblown may be less affected.…”

Toward nanotechnology-enabled face masks against SARS-CoV-2 and pandemic respiratory diseases

“…This efficiency is shown to get lower for smaller particles sizes. Moreover, most of the existing face masks are hydrophilic and inefficient when wet where their performance in repelling water droplets and allowing appropriate respiration degrades [21]. Another important characteristic of face masks is the breathability.…”