A large surface area, scalable porosity, and versatility have made nanofibres one of the most widely investigated morphologies among the nanomaterials. The characteristic properties of nanofibres have made them useful in a broad range of applications, such as filters, membranes, tissue engineering, wound dressings, protective clothing, reinforcement in composite materials, and sensors. So far, various top-down and bottom-up approaches were proposed to produce nanofibres. In this paper, a comprehensive review is presented on non-electro fiber spinning techniques, along with their mechanisms. The parameters of these techniques are also discussed in detail, while process-specific gains were emphasized according to the end uses. This review paper also provides a literature insight into the biomedical, filtration, optical, and energy applications of nanofibres produced via the most typical and widely used methods.

In this study, silica based nanofibers were produced via centrifugal spinning (C-spin) and subsequent calcination. The produced heat resistant media was challenged with NaCl nanoparticles to investigate their filtration performance. To obtain inorganic SiO₂ nanofibers, C-spun organic PVP – TEOS nanofibers were calcinated at 300-600 °C. Effects of solution concentration and calcination temperature on crystallinity, morphology and air filtration performance of nanofibers were investigated. Scanning electron microscopy (SEM) analysis was performed to analyze fiber diameter and morphology of nanofibrous webs. Differential thermal analysis (DTA) was realized for the thermal behavior of samples. Moreover, X-ray Diffraction (XRD) and Fourier Transform Infrared Spectra (FTIR) analysis were realized for further characterization. In addition to the chemical and morphological analysis, the ductility of the samples was investigated via tensile tests. Finally, calcinated webs were challenged with 0.4μm salt particles to analyze their filtration performance. The calcinated 5wt% TEOS/PVP silica nanofiber webs were more brittle due to three times lower precursor content. Therefore, flexibility (percent elongation) of 15wt%TEOS/PVP sample was nearly five times higher than 5wt%TEOS/PVP sample. The calcinated 15wt%TEOS/PVP sample showed the highest filtration performance among all the silica nanofibers. The average fiber diameter of the optimized web was found to be the lowest, which is around 521 ± 308 nm, which resulted in enhanced filtration efficiency around 75.89%. Copyright © 2019 American Association for Aerosol Research

Particles with diameters smaller than 2.5 μm (PM_2.5) can penetrate the respiratory system and have negative impacts on human health. Filter media with a porous surface and nanofiber/nanonet structure demonstrate superior filtration performance compared to traditional nano- and microfiber-based filters. In this study, nanostructured filters were produced using the electroblowing method from solutions containing different ratios of poly(vinylidene fluoride) (PVDF) and polyethylene glycol (PEG) polymers for the first time. By increasing the water-soluble PEG ratio in PVDF/PEG blend nanofibers and employing a water bath treatment to the produced mat afterward, a more porous fibrous structure was obtained with a lower average fiber diameter. Notably, the removal of PEG from the PVDF/PEG (3-7) sample, which had the highest PEG content, exhibited clustered nanofiber-/nanonet-like structures with average diameters of 170 and 50 nm at the points where the fibers intersect. Although this process resulted in a slight decrease in the filtration efficiency (-1.3%), the significant reduction observed in pressure drop led to a 3.2% increase in the quality factor (QF). Additionally, by exploiting the polarizability of PVDF under an electric field, the filtration efficiency of the nanostructured PVDF filters enhanced with a ratio of 3.6% after corona discharge treatment leading to a 60% improvement in the QF. As a result, the PVDF/PEG (3-7) sample presented an impressive filtration efficiency of 99.57%, a pressure drop (ΔP) of 158 Pa, and a QF of 0.0345 Pa^-1.

High-pressure drop and lower dust holding capacity reduce the performance of nanofibrous air filters. For that reason, this study was carried out to form filters with high-quality factor and high dust holding capacity, thanks to the glass particle additives. In this study, as an approach to such modifications, fluffy nanofiber webs were produced via solution blowing. Polyamide 6 (PA6) was chosen as the base for the nanofibrous mats, where glass microparticles were embedded as an additive to reduce web solidity. The effects of glass microparticle embedding on the filtration performance and pressure drop of the mats were investigated. SEM analysis was performed to analyze nanofiber diameter and morphology. Also, the barrier properties of samples were examined by air filtration and air permeability tests. Findings showed that the addition of glass particles did not alter fiber morphology significantly. However, lowering the pressure drop resulted in higher air permeability and better filtration performance in terms of the quality factor. Glass particles embedded composite samples exhibited a higher quality factor compared to the neat PA6 sample, and the PA6 + 5%GP sample has the highest quality factor value around 0.43. The filtration efficiency of this sample was 99.97% at an expense of 187.3 Pa pressure drop. The obtained enhancement was conducted to the lower solidity of composite webs which was 36% lower for the PA6 + 5%GP sample.