While nonwoven fabrics have existed for several decades, their usage in personal protective equipment (PPE) has been met with a rapid surge of demands, in part due to the recent COVID-19 pandemic. This review aims to critically examine the current state of nonwoven PPE fabrics by exploring (i) the material constituents and processing steps to produce fibers and bond them, and (ii) how each fabric layer is integrated into a textile, and how the assembled textiles are used as PPE. Firstly, filament fibers are manufactured via dry, wet, and polymer-laid fiber spinning methods. Then the fibers are bonded via chemical, thermal, and mechanical means. Emergent nonwoven processes such as electrospinning and centrifugal spinning to produce unique ultrafine nanofibers are discussed. Nonwoven PPE applications are categorized as filters, medical usage, and protective garments. The role of each nonwoven layer, its role, and textile integration are discussed. Finally, the challenges stemming from the single-use nature of nonwoven PPEs are discussed, especially in the context of growing concerns over sustainability. Then, emerging solutions to address sustainability issues with material and processing innovations are explored.
This work aims to provide effective strategies and practical tools to control the diameter of fibers, a long-lasting challenge in the application of free surface melt electrospinning, mainly by highlighting the importance of the solidification point. A systematic approach to mapping the solidification point and temperature profile in an electrohydrodynamic jet in the melt electrospinning process was developed experimentally through the backlit imaging technique and numerically through computational fluid dynamics. The effect of the different spin-line temperature profiles on the robustness of the process as well as the fiber morphology was investigated. Scanning electron microscopy analysis demonstrated that at high spin-line temperature profiles, the fiber diameter dropped by four times compared to the room temperature spin-line environment. Both in situ backlit images from the jets in the spin line and the numerical phase fraction analysis revealed an immediate solidification of the jet, which is elongated twice in the case of the high spin-line temperature profiles. The elongated freezing length for the high spin-line temperature profiles as a result of the delayed solidification was identified as one of the main factors contributing to the jet thinning and subsequent fiber diameter reduction. Based on the simulation, the temperature profile of the jet demonstrated an approximately 20 °C drop along the jet length in the nonsolidified portion (freezing length), proposing the viscosity drop as a second factor in the fiber diameter reduction mechanism. Ultimately, the molten film thickness on the plate was identified as a semiphysical confinement parameter, controlling the size of the formed cones and subsequently the fiber diameter, despite the free surface nature of the unconfined melt electrospinning.
The covid‐19 pandemic has revealed the need for alternative production approaches with low startup costs like electrospinning for filter needs, the most imperative element of the personal protective equipment (PPE). Current attempts in advancing melt electrospinning deal with developing strategies for fiber diameter attenuation toward sub‐micron scale. Here, the attunement in the spinning‐zone temperature known as ''spin‐line temperature profile'' was utilized as a baseline for fiber diameter reduction. The mechanical performance of the melt‐electrospun linear low‐density polyethylene (LLDPE) fibers is reported to characterize their structural transformation with respect to various spin‐line temperature profiles. With an increase in the spin‐line temperature to above 100°C in the area of cone formation, an increased tensile and yield strength along with fiber diameter reduction by four‐folds was demonstrated. A significant increase in toughness, by almost three times, without compromising the stiffness and Young's modulus was observed. The dynamic mechanical analysis revealed that spinning in high temperatures produces changes in the alpha (α) relaxation, contributing to the significant increase in strain at break. These results are significant because polyolefin fibers are an imperative element of medical textiles and PPE. Therefore, developing a correlation for process‐structure‐properties for emerging production techniques like melt electrospinning becomes critical.
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