Bilayer Electrospun Nanofibre Structures to Improve Quality Factor in Air Filtration

Abstract

Electrospun nanofibres have been used in air filtration applications ranging from indoor filters to personal protective respirators. Nanofibres based filter exhibit excellent filtration efficiency but high pressure drop. The function of filtration efficiency and pressure drop is expressed by a term called quality factor. This study identified a method to improve the quality factor of layered nanofibre structures by reducing the pressure drop. Single and bilayer structures from polyacrylonitrile nanofibres of equal mass coverage were produced by optimising electrospinning time. Further, the stacking order of nanofibres in the bilayer structure was altered and compared. This alteration changed the surface morphology of the nanofibre structures influencing fibre diameter, pore size, and pore size distribution. The fibre diameter and pore size were determined using field emission scanning electron microscope (FE-SEM) and capillary flow porometer, respectively. The thickness of the nanofibre structure was measured using laser microscopy. The thickness and packing density of single layer and bilayer nanofibre structures differed despite equal mass coverage. Furthermore, change in the layering order of bilayer nanofibre structures also had an effect on packing density which consequently affected the filtration efficiency and pressure drop. A bilayer structure with 400 nm average fibre diameter at the top covering 200 nm beneath considerably reduced the pressure drop as compared to its single structure counterparts. This bilayer nanofibre stacking arrangement was also improved quality factor significantly as compared to that of single layer structures.