Flexible polyurethane foam as personal protective mask material: a numerical and experimental study

This work outlines a method for characterizing flexible polyurethane foam (FPF) for use as a filter material, particularly for personal protective equipment. Two different FPF samples were tested experimentally to establish their geometric and flow resistance properties, which were then used to calibrate a geometric idealization of the foam created using a discrete element modeling software. The idealized model was then used to conduct pore-level numerical simulations to estimate the filtration efficiency of the foam for particles with average of diameters in the range 0.2–200 µm for various airflow velocities. A parametric study was then done to estimate the particle penetration rate of a facile mask made of FPF under different breathing conditions. The results indicate that during inhalation, pressure and velocity variations on the inner surface of the mask are not significant and that estimates of the filtration efficiency can be made by considering the time-dependent filter velocity combined with prior results for filter effectiveness as a function of velocity and particle size. The results also show that a non-medical FPF mask can drastically reduce the risk of particle penetration for particles larger than 0.2 µm. The process demonstrated in this work can be used to estimate the overall effectiveness of an FPF mask when exposed to clouds of different sized particles and to study the impacts of mask shape and fit on filtration effectiveness.