## 8 Relevant Applications of Melt Electrospinning
### Filtration and Separation  
Micro/nanofiber membranes are potential systems for water (fresh or waste) and air filtration, petrochemical, electronic, fuel cells, and clean energy systems in industrial scales. However, novel, efficient and long-time usage systems are still being developed in filtration and separation applications. Nanofibrous materials have some advantages that are not present in commonly used materials, such as high surface energy, porous structure with controllable small pore size, and relatively high strength [175]. Nanofiltration is used as a pre-treatment of waste water before the typical reverse osmosis process. Filtration can operate with a high flux and significantly reduces power consumption and system maintenance costs [176]. Regarding to this large-scale consumption (for both industrial and domestical uses), filters obtained by solution electrospinning should cause a large increase in the production of toxic solvents and the corresponding wastes, which can be avoided by means of fusion electrospinning techniques. Among fibrous systems, polypropylene, poly (ethylene terephthalate), polyethylene and nylon are of high interest in industrial filtration [39; 49; 177]. As it was explained in previous sections, viscosity modifiers and improvement of polarization are fundamental to properly process these polymers, especially PP, into fine and continuous fibers. It was found that gas-assisted melt electrospinning allowed to get PP fibrous membranes with a diameter of 600 nm and a porosity of 99.4%, which rendered much higher performance compared to traditional webs produced for water treatment applications [178].  
Figure 12: Comparison of PP/PVB and PP (after PVB removal) fiber diameters (**a**) and SEM images of PP fibers after PVB removal (**b**). (**c**,**d**) core–shell structure of PP/EVOH based fibers after EVOH removal. Copyright 2019 John Wiley & Sons [61]. Copyright 2018 John Wiley & Sons [174].  
Membranes constituted by polyamide (PA) fibers have great interest for filtration of suspended particles from gases, in particular, air. The filters with thicker fiber diameters (i.e., pure PA) showed less efficiency, 21%, while modification of PA with the SS additive increased efficiency to 98% due to its better packing density and surface chemistry [76]. Different commercial polyamide 12 (PA12) and block polyether amide filaments were incorporated in a melt-electrospinning process and the highest filtration performance was showed by PA12 with MFI of 132 g/10 min supplied by Evonik Industries AG [179]. The maximum filtering efficiency was found to be 80% fibers with an average diameter of 15 \(\upmu\)m. In addition to PA and PP, melt electrospun polyphenylene sulphide (PPS) superfine fibers proved to be a promising and highly efficient material for high temperature dedusting [180]. Prior to melt electrospinning, PP was added to PPS as an additive to provide suitable finer fibers for filtration. By decreasing the fiber diameter to 4.12 \(\upmu\)m, the filter efficiency increased to 98.05% which was much higher than the commercial filter bag for the high temperature filtration of flue gas emission.  
To sum up, modification of materials and melt electrospinninging processes seem to be the efficient ways to provide membranes with filtration coefficients comparable with those of materials prepared via solution electrospinning. In addition to the research studies, several companies in USA and Germany provide nanofiber filters that mostly focus on solution electrospinning. In this area, there is the possibility to replace this process by melt electrospinninging by modification of materials using additives and changing the processes as previously discussed.