ARENA case study in Aerosol Filtration Efficiency of Reusable Face Masks
The ARENA project has received funding from the England European Regional Development Fund as part of the European Structural and Investment Funds Growth Programme 2014-2020. The Ministry of Housing, Communities and Local Government (and in London the intermediate body Greater London Authority) is the Managing Authority for European Regional Development Fund.
Arena helped ADKN to evaluate the filtration efficiency of their reusable bamboo face mask against aerosols and particulate matters (PM 2.5 and PM10).
The emergence of a pandemic has resulted in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19.[i] The rapid shortage of medical N95 respirators or other certified masks creates an urgent demand for suitable alternatives.
ADKN is an animal-free, eco-friendly, sustainable and ethical fashion brand and garment manufacturer, based in England. ADKN has developed a 4 layered reusable face mask made from 100% organic materials including hydrophobic bamboo and Tencel. However, in the absence of available regulation testing facilities or the specific and costly equipment required, there is a need to replicate regulatory guidelines with methods that can provide reliability and assurance.
Figure 1. Schematic of the experimental setup.
How ARENA was able to help
We have developed a low-cost and accurate method inspired by the work of Schilling et.al. [ii] to quickly evaluate masks using an accessible approach that could be replicated in communities lacking the infrastructure necessary for regulation tests.
The method is designed to test face masks filtering efficiency. In doing so, we developed an experimental setup including two chambers as shown schematically in Figure 1 (above).
Aerosol and particulate mattered are generated by burning incense in chamber 1 (Ch1) and passed through the mask mounted on a dummy head as shown in Figure 2. The filtered air is then transferred to the second chamber (Ch2) through a suction force provided by an air pump.
The concentration of aerosols and particulate matters are measured in both chambers over 60 min of the testing period. The filtering efficiencies are then calculated by comparing concentrations measured in Ch2 before and after using the mask. The images of the experimental apparatus are shown in Figure 3.
Figure 2. The masks are made from a mix of bamboo and recycled polyethylene terephthalate (RPET) cloth fabric (hydrophilic inner and hydrophobic outer layer) and double filtration media (bamboo and Tencel), to provide a better environmentally friendly alternative to traditional cotton face masks.
Figure 3. Images of the experimental apparatus.
The study showed that ADKN face masks when used without a PM2.5 insert can provide filtering efficiencies for capturing particulate matters larger than ∼1μm to 10μm in the range of 2-3%, as shown in Figure 4. This is a relatively low level and can be attributed mainly to the physical barriers provided by the mask bamboo and RPET materials. However, when they are used with PM2.5 inserts, the filtering efficiency increases to levels around 30% for PM2.5 and PM10 which is above those measured for common surgical masks at around 20%.
The next stage of this study involves investigating the impact of washing on ADKN mask filtering efficiencies and capturing mechanisms using optical and electron microscopy.
[i]Konda, A., et al., 2020. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS nano, 14(5), pp.6339-6347.
[ii] Schilling, K., et al., 2020. An Accessible Method for Screening Aerosol Filtration Identifies Poor-Performing Commercial Masks and Respirators.
Figure 4. Results of air quality monitoring in terms of PM2.5 and PM10 concentrations in the air passed through the mask measured in Ch2. Blank data represents the trial test without using a mask. ADKN mask filtering efficiency with and without the use of PM2.5 filters can be seen as a reduction in concentrations of PM2.5 and PM10 over the 60 min of testing duration compared to the Blank setup. The filtering efficiency data of a common surgical mask tested with the same condition are presented for comparison.
Co-funded by London ERDF, ARENA is three year business support programme led by the Sustainable Research Institute, at the University of East London, in partnership with Barking Riverside Ltd.
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