FILTRATION PERFORMANCE AGAINST NANOPARTICLES BY ELECTROSPUN NYLON-6 MEDIA CONTAINING ULTRATHIN NANOFIBERS

Abstract

Electrospinning is a straightforward process that uses an electric field to produce polymer ultrathin nanofibers with a diameter of 100 nm (NFs) and ultrathin nanofibers with a diameter of 20 nm (UNFs). The electrospinning process is composed by a creation followed by an elongation of an electrified driven jet of polymer solution. This method produces fibers with different sizes and shapes among which beads, spider webs, branches, flat ribbons, and longitudinally split fibers. The first aim of this study was to understand the electrospinning process at a scientific level in order to correlate the effects of the operational parameters on the nanofibers structure. Solutions properties such as concentration and age, operational and ambient parameters such as distance tip-to-collector and humidity are the key factors that influence the nanofibers structure. The sequence that ribbon-like fibers are stretched by the electric force, followed by rapid phase separation of the splitting film is proposed as a formation mechanism of the UNFs. The second aim of the study was to verify if and how the fibers influence the efficiency of a commercial filter when split on its surface. The filtration tests were performed in different set-up conditions, analysing the efficiencies of two different types of filters with and without nanofibers on the surface. Different polymer solutions resulted in different nanofibers morphologies. Based on the morphological study a model of hexagonal nets is developed in order to estimate the filtration efficiency by the UNF structure. The estimated efficiency due to the UNFs is then combined with the contribution from the un-split nanofibers (NFs) to compute the total filtration efficiency and pressure drop for each of the electrospun media by applying a layered multiple zone model. Its has been found that ultrathin nanofibers strongly improve the efficiency of a commercial filter if split on its surface. An increase of the efficiency and pressure drop has been recorded with nanofibers created with high viscosity of the solution, long collecting time, short distance tip-to-collector and tested with low face velocity. This research shows that a filtration process with high filtration efficiency requirements but only limited space available and/or light weight limitations, could be performed by using UNFs.