Ultra-thin and highly porous PVDF-filters prepared via phase inversion for potential medical (COVID-19) and industrial use

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The COVID-19 pandemic has resulted in an increased demand for air-filtration based personal protective equipment. Existing filter masks are mostly based on melt-blow fabrics, which had production upscaling issues because of long lead-times for additional production equipment and the limited number of polymer materials that can be used. Phase inversion is a readily scalable technique for the production of porous films and is compatible with a large number of polymers. As such, the potential for phase inversion to produce comparable air-filtration masks, and filters in general, was herein investigated. Polymer solutions based on various PVDF-types, solvents and additives were prepared and cast onto a widely available industrial type of supporting fabric. From the various solvents and additives tested, only DMF and Tamisolve® NxG-based solutions with LiCl as an additive resulted in filters with suitable pore size and acceptable pore size distribution. The effects of polymer and additive concentration were investigated through SEM-based observation of the pore size and pore size distribution analysis via porometry. As expected, phase inversion proved to be a versatile tool to tune and control the pore size. Porometry-based comparison of the produced filters with a commercial surgical and FFP2-mask showed that comparable pore sizes could be easily obtained. The best membranes were tested for aerosol retention, proving them to be highly promising alternative materials for current masks and air filters in more general.