The deposition of nanofibers onto a traditional filtration medium and their effects on filtration efficiency

Abstract

Traditional filtration media composed of fibers with sizes on the micrometer scale have difficulty filtering particles a little smaller than 300 nm. Even though nanofibrous materials are able to capture these particles and can have excellent filtration efficiency, their widespread use continues to be inhibited by several obstacles, particularly an excessive pressure drop and the inability to form self-supporting filtration membranes. We have prepared two types of composite materials, namely an ultra-thin nanofibrous layer made of polyurethane or nylon with various fiber diameters and pore areas. Scanning electron microscopy was used for their characterization. The nanofibrous layer was deposited directly onto a traditional melt-blown polypropylene filtration fabric with a very low area weight of 30 g/m², which facilitates handling and bypasses the need for the layer to be self-supporting. Moreover, a fine polyethylene mesh was added as a separate layer to prevent humidity from passing through the filtration material as well as to cover fabrics. The filtration efficiency and the pressure drop of the prepared materials were determined. The results showed that the incorporation of a nylon nanofibrous layer with smaller fiber diameters and pore areas leads to a significant increase in the filtration efficiency (92%) against the most penetrating particles, the critical size of which decreased to 50 nm, while the pressure drop was comparable to the pressure drop of a commercially available FFP2 respirator. The prepared filtration material could be used to manufacture respirators.