It has become our unloved everyday companion: Since the worldwide spread of the corona virus, mouth-nose protection has become part of our daily lives. Initially, bandanas, scarves and cloth masks were used in everyday life, but due to the rapid spread of the virus, medical masks such as surgical or FFP2 masks replaced them. Once mouth-nose protection is put on, it is constantly in the wearer’s inhaling and exhaling respiratory flows. In particular, the exhaled breath stream is nearly saturated with 98% humidity during exhalation.
As a result, the mask material is continually moistened, thus reducing the filter function. Furthermore, the humid environment promotes proliferation of harmful bacteria and fungi within the filter material and can lead to infectious respiratory diseases for the mask wearers.
In our latest application note, the quantification of the moisture absorption for the mouth-nose protection is investigated as a function of the material used and following the recommended wearing time for half masks in accordance with German statutory accident insurance. To this end, a sample was prepared from both a cloth and an FFP2 mask. Due to the change from cloth to FFP2 masks, the structure changes from single-layer cotton fabric to multi-layer fleece. By means of thermogravimetric measurements at varying relative humidity content levels, the possible moisture absorption of the different mask types is characterized.
In addition, coupling of an STA 449 F3 Jupiter® equipped with copper furnace to a humidity generator offers the possibility of obtaining detailed insight into the mass change of a wide variety of samples as a function of variable humidity content levels. While mouth-nose protection is worn, it is continually exposed to moist respiratory air. By investigating the mass change at different moisture content levels, conclusions can be drawn about the absorption capacity or residual moisture load of the individual mask materials. The results clearly indicate that the cloth mask absorbs significantly higher amounts of moisture than the FFP2 mask and shows a residual load after the moisture content is reduced. The low load of the FFP2 mask can possibly be explained by the different layers as well as the materials used in the FFP2 mask. It is possible that the individual layers possess different properties with regard to their reaction with moisture. This characterization, however, requires further investigation.
The cloth mask sample shows a stronger moisture penetration which is only released in its entirety at elevated storage temperatures. The temperature treatment at 80°C therefore ensures complete drying of the mask and prevents spread of bacteria and/or fungi within the cloth.
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