Evaluation of filtration characteristics of different Face mask substrates

Face masks have been used as physical barriers to stop respiratory infections for many years. Due to insufficient and low supply of certified masks, alternative face covers such as face shields, neck gaiters and fabric reusable masks gained attention during the COVID-19 pandemic. However, for these alternate face masks to fulfill their intended function, they must be effective. Additionally, the level of breathability provided by the makeshift masks must be at a certain level. The work reported in this paper was carried out to determine the relationship between filtration efficiency (FE), breathability, and important characteristics of mask substrates. The fiber diameter and the core filter layer were also determined using a scanning electron microscope. Five types of face masks (two types of N95, two types of surgical masks and a 100% knitted cotton fabric) were tested for their FE and breathability using Moisture Vapor Transmission Rate (MVTR). The cotton knitted mask had the lowest FE (5.10% - 26.47%), while the NIOSH-certified N95 mask had the highest FE values (92.10% - 99.65%). However, the cotton mask outperformed the N95 in terms of the pressure drop meaning higher comfort. In general, the N95 face mask provided the best protection against aerosolized particles. According to the regression analysis, the fiber diameter of the masks filter substrate serves as an important predictor of FE of mask substrates. In this study it was confirmed that fiber diameter is directly related to the porosity of the fabric substrate and is inversely related to the filtration ability. Results show that compact structure with finer fibers will enable higher filtration efficiency. The study lends itself to developing layered facemasks to obtain optimum filter with filtration, better fit, and acceptable comfort for the wearer.

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