Evaluation of foam materials as air filters against fungal contamination

Abstract

Current air filters used in food storage facilities are expensive and disposable. The ability to use polyurethane foam as air filters against fungal spores would be beneficial as they are both cheap and re-usable. The aim of this study was to evaluate the air filtration capabilities, in terms of fungal spores, of a selection of polyurethane foam(s) of differing combinations of pores per inch (PPI) (50 to 90 PPI) and thickness (15 to 20 mm). Additionally, the filtration capabilities of auxetic foams manufactured by subjecting 50 PPI polyurethane foam to a tri-axial compression of 28% were also assessed. Environmental air was used as a source of fungal spores and membrane filtration was used to assess the filtration capabilities of the foams. Spores capable of passing through the foams were captured on cellulose nitrate membrane filters and quantified in CFU counts. Apart from the 50 PPI foam of 15 mm thickness, all the foam samples were effective at significantly reducing the number of spores. For conventional foam, the PPI was found to be 2 times more influential on the efficiency of the foam material than the foam thickness. This may be explained through the higher number of pores present and the decrease in thickness of the ribs composing the microstructure of the foam as shown through scanning electron microscope (SEM) micrographs. The auxetic foam was found to have a good efficiency potentially due to its highly convoluted structure contributing to a more turbulent passage of air. Overall, the auxetic foam is clearly an ideal material for use as an air filter and could be considered for future multi-pass applications due to the fact that this type of foam may be easily cleaned.