Nanofibers for High Efficiency Filtration

Nanofiber is a broad phrase generally referring to a fibre with a diameter less than 1 micron. While glass fibres have existed in the sub-micron range for some time and polymeric meltblown fibres are just beginning to break the micron barrier, sub-half-micron diameters have been used for air filtration in commercial, industrial and defence applications for more than twenty years. They have been shown to deliver improved filter life, increased contaminate holding capacity and enhanced filtration efficiency. Small fibres in the sub-micron range, in comparison with larger ones, are well known to provide higher filter efficiency at the same pressure drop in the interception and inertial impaction stages of the filtration process. In particular, nanofibers provide marked increases in filtration efficiency at relatively small (and in some cases immeasurable) decreases in permeability. Nanofiber filter media have enabled new levels of filtration performance in several diverse applications with a broad range of environments and contaminants. While nano fibre size lead to a higher pressure drop, interception and inertial impaction efficiencies will increase faster, and therefore more than compensating for the rise in pressure drop. Thus, in the particle size of interest, i.e. from sub-micron upwards, better filter efficiency can be achieved at the same pressure drop, or conversely, the same filter efficiency at a lower pressure drop can be achieved with nanofibres. This paper will discuss a process for making nanofibers, as well as the benefits, limitations, construction, and applications of filters using nanofiber media.