Corona viruses are tiny – much smaller than bacteria. Corona viruses, for example, are at 0.12 micrometres. In order to filter them out, a sophisticated substance is required which is produced in a melting process: meltblown. The decisive filter layer of our Atemious per breathing mask consists of this substance, which is created by melt bubbles (so the direct translation).
Meltblown consists of polypropylene, a well-known plastic, virtually an all-rounder. Polypropylene is used in machine and vehicle construction, the textile industry, electrical engineering and many other applications. In the production of meltblown, the plastic is first melted until it is viscous. Then it flows through hundreds of tiny nozzles and forms a wafer-thin thread underneath. But it is far from being as thin as it should be later.
To obtain the desired dimension in the micrometer range, the molten thread is blown. The air is about 250 degrees hot. The air collects the plastic threads and whirls them around. This makes the threads – also called filaments – extremely thin. One art of making meltblown fleece is to ensure that the filaments do not break off. This requires the optimum temperature of the molten plastic, the correct temperature of the air and the correct speed of the air flow. A celebration, so to speak, for the process engineers.
These deliberate chaotic movements form a so-called tangled web. Because the plastic threads are not yet completely cold, they stick together. This network has a physical pore size of about ten micrometres. The filaments that make up the net are only half a micrometer thin. Although it is already very fine, the nonwoven mesh would still be far from being sufficient to screen viruses safely out of the air simply because of their size. This is why physics also comes into play, such as the efforts of small particles to attach themselves to surfaces.
Polypropylene is also used as the basic material for meltblown because it is lipophilic, i.e. it attracts fat. Viruses therefore remain attached to the fibres. The fleece used in the Atemious pro is also electrostatically charged, so the filter performance is further enhanced by its attraction to the extremely small viruses found in aerosols.