Cellulose acetate and polyvinylidene fluoride nanofiber mats for N95 respirators

Nanofibrous media have a low basis weight, high permeability and small pore size that make them appropriate for a wide range of filtration applications, particularly for smaller particles. In contrast to electrostatic filter media, nanofibers' filtration efficiencies depend on the mechanical filtration mechanism and do not degrade with time. In this study, the National Institute for Occupational Safety and Health (NIOSH) requirements for the N95 particulate filtering half mask were achieved using electrospun cellulose acetate (CA) and polyvinylidene fluoride (PVDF) nanofiber coated polypropylene spunbond layers. Specifically, 16 and 15% (w/v), and 14, 12 and 10% (w/w) polymer concentrations were selected for CA nanofibers and PVDF nanofibers, respectively, to adjust the nanofiber diameters. The diameters of CA and PVDF nanofibers were decreased with decreasing polymer concentration for both CA (319.02 to 264.02 nm) and PVDF (236.50 to 142.59 nm) nanofibers. The thickness of the electrospun 16CA, 15CA and 14PVDF, 12PVDF, 10PVDF mats was adjusted by varying the collection period (15 min, 30 min, 60 min). The effects of electrospun CA and PVDF nanofiber diameter on the pore size and the thickness of the mats were compared in terms of filtration performance. 16CA with a nanofiber diameter of 319.02 nm had the largest first bubble point of 26.5 µm and mean flow pore size of 5.71 µm at 15 min with a thickness of 0.019 mm. The smallest first bubble point and mean flow pore values and the smallest pore size were achieved with the finest nanofibers of 10PVDF. Filtration performances were given as initial penetration and air flow resistance (ΔP). 16CA-60 min and 15CA-30 min mats both met the NIOSH requirements with their bulky structure. For PVDF, thinner nanofibers with smaller pores were produced compared to the CA nanofibers, and the NIOSH requirements were only achieved using double-layered, face-to-face 10PVDF-15 min nanofiber mats with the penetration of 1.85% and ΔP of 33.87 mmH ₂ O.