Nanofibres in filtration

It is expected that the smaller size of these nanofibres will lead to a higher pressure drop and the interception and inertial impaction efficiencies will increase faster, which can more than compensate for the pressure drop inaease. Nanowebs have been used in many air filtration applications. Airborne contamination in the personnel cabins of mining equipment is of concern to mining workers, and it has been reported that nanofibre filter media can considerably reduce cabin dust concentration as compared to the standard (cellulose) filter media.  

Qin et have studied the filtration characteristics of nanofibre layers with different area densities that were electrospun onto spunlaid or meltblown substrates. The fibre diameter, pore diameter, filtration efficiency, and filtration resistance of nanofibre webs and sublayers were determined. It was found that the pore diameter of nanofibre web is much smaller than sublayers and the coefficient of variation of the pore diameter of nanofibre webs is also smaller than that of the sublayers. Consequently, the filtration efficiency and filtration resistance of sublayers are lower than the nanofibre webs. These researchers also found that there is an optimum region for the maximum filtration efficiency at minimum pressure drop and that this optimum is at a lower add-on weight for meltblown webs than for spunlaid webs. 

More recently, a composite aerosol filter media has been prepared by depositing polyvinyl alcohol (PVA) nanofibres with mean diameters of about lOOnm on nonwoven fabric substrates by using needleless electrospinning technique. The filtration performance of the composite filter was evaluated by measuring the filtration of sodium chloride nanoparticles (75 20nm). The results showed that the filtration efficiency of the composite filter media for nanoparticles was increased with the increase in thickness of the nanofibre mats, which was controlled by the deposition time of the electrospinning process. 

There are some commercially available electrospinning processes, such as the Nanospider electrospun nanofibres, which can provide thin coatings on traditional filtration substrates and enhance the filtration performance of these materials many fold. This technology can yield nanofibres with a narrow diameter distribution and distinct diameter size that can be used to optimise the filtration behaviour of the filter substrates for many applications, where particle retention efficiency is a critical requirement. These suhmicron fibres can significantly improve the air filtration efficiency of a variety of media and filters. The submicron fibres provide improved filter efficiency in the interception and inertial impaction regimes.  

Nanoparticle penetration has been measured with a wide range of filter media by using silver nanoparticles from 3 nm to 20 nm at three different face velocities in order to define nanoparticle filtration characteristics of commercial fibrous filter media. After size classification by using a nano-DMA, the particle counts were measured by an ultrafine condensation particle counter (UCPC) both upstream and downstream of the test filter in order to determine the nanoparticle penetration for each specific 

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