The objective of this study is to evaluate the effect of poly(ether sulfone) (PES) concentration on microstructure of the electrospun hanofifers and the effect of nanofiber layer density on filtration efficiency and pressure drop of filters with nanofibers coated on a substrate.In order to reduce the pressure drop

the influence of composite methods on the filter performance by adding a certain amount of microspheres into the fibers was studied.The substrate is a non-woven polypropylene (PP) medium with negligible filtration efficiency and pressure drop as compared to the nanofiber layer.Experimental results show that when PES concentration(W/V) is 280 g/L well-distributed nanofibers with mean diameter of 510 nm are formed

and when PES concentration is 200 g/L a structure of microspheres with mean diameter of 2.74 m is obtained.The pressure drop increases from 706.58 Pa to 1444.52 Pa when packing density increases from 7.5 g/m2 to 10.5 g/m2

while the filtration efficiency can generally reach to 99.99%.This suggests nanofiber packing density has less prominent effect on filtration efficiency than pressure drop.By adding microspheres between two layers of fibers

the pressure drop across the filter decreases but the filtration efficiency also decreases.For the microspheres/fiber composite membranes

an appropriate amount of microspheres in the fibers will reduce the pressure drop but the filtration efficiency is reduced little.However too much microspheres will increase the filter pressure drop.Hence

the method of adding microspheres into nanofiber is proposed to fabricate nanofiber filter with greatly reduced pressure drop.This is advantageous for high efficiency applications with nanofibers of low pressure drop.