Nanofibrous media have a low basis weight, high permeability and small pore size that make them appropriate for a wide range of filtration applications, particularly for smaller particles. In contrast to electrostatic filter media, nanofibers' filtration efficiencies depend on the mechanical filtration mechanism and do not degrade with time. In this study, the National Institute for Occupational Safety and Health (NIOSH) requirements for the N95 particulate filtering half mask were achieved using electrospun cellulose acetate (CA) and polyvinylidene fluoride (PVDF) nanofiber coated polypropylene spunbond layers. Specifically, 16 and 15% (w/v), and 14, 12 and 10% (w/w) polymer concentrations were selected for CA nanofibers and PVDF nanofibers, respectively, to adjust the nanofiber diameters. The diameters of CA and PVDF nanofibers were decreased with decreasing polymer concentration for both CA (319.02 to 264.02 nm) and PVDF (236.50 to 142.59 nm) nanofibers. The thickness of the electrospun 16CA, 15CA and 14PVDF, 12PVDF, 10PVDF mats was adjusted by varying the collection period (15 min, 30 min, 60 min). The effects of electrospun CA and PVDF nanofiber diameter on the pore size and the thickness of the mats were compared in terms of filtration performance. 16CA with a nanofiber diameter of 319.02 nm had the largest first bubble point of 26.5 µm and mean flow pore size of 5.71 µm at 15 min with a thickness of 0.019 mm. The smallest first bubble point and mean flow pore values and the smallest pore size were achieved with the finest nanofibers of 10PVDF. Filtration performances were given as initial penetration and air flow resistance (ΔP). 16CA-60 min and 15CA-30 min mats both met the NIOSH requirements with their bulky structure. For PVDF, thinner nanofibers with smaller pores were produced compared to the CA nanofibers, and the NIOSH requirements were only achieved using double-layered, face-to-face 10PVDF-15 min nanofiber mats with the penetration of 1.85% and ΔP of 33.87 mmH₂O.

Composite structures with various stacking sequences were formed by combining electrospun polyurethane (PU) nanofibers with needle-punched recycled nonwovens from polyester textile wastes and bottles as a new sound absorption material in order to contribute to the solution of noise control and waste generation. PU solutions of 12, 13, 14 and 15 wt % concentrations were prepared for nanofiber optimization studies. Scanning electron microscope (SEM) images showed that the bead free nanofibers were obtained with diameters 296.5 and 509.9 nm from 13 and 15 wt % PU concentrations, respectively. In order to evaluate the potential of nanofibers and nanofiber-recycled nonwoven composites as noise reduction materials; sound absorption coefficients (SACs) were measured and noise reduction coefficients (NRCs) were calculated. The most ideal sample was regarded as the 3.24 mm thick sandwich structure (recycled nonwoven-nanofiber-recycled nonwoven), coded with A250-1320-A250 with a 0.504 NRC value. When the two nanofiber diameters were compared, finer nanofibers (296.5 nm) and finer nanofiber enhanced nonwovens had better NRCs than the thickers (509.9 nm) of the same. The developed composite materials can be regarded as promising sound absorbers.

The electrospinning process is highlighted with the ability of fabricating fibers with diameters on the nanometer scale, small inter-fibrous pore size and high porosity, vast possibilities for functionalization with high surface area to volume or mass ratio, ease of use and instrument setup, and adaptability. It attracted a great deal of attention due to its unique properties. More than 100 different polymers have been successfully electrospun into ultrafine fibers using this technique including synthetic polymers such as polyurethane (PU). Electrospun PU nanofiber mats exhibiting good mechanical properties may have a wide variety of potential applications in high-performance air filters, protective textiles, wound dressing materials, sensors, drug delivery, etc. This chapter deals with the electrospinning of polyurethane nanofibers and their potential applications.