Preparation and Properties of an Efficient Purification Material for Personal Protection

At present, the filtration of virus and other small particles in the air by meltblown cloth produced by electret treatment mainly depends on its electrostatic adsorption mechanism. However, because the surface charge of melt blown fabric can not be maintained for a long time, it can not maintain high efficiency filtration for a long time. Therefore, there is no guarantee for the medical staffs to not be infected by COVID-19. Therefore, it is necessary to improve the mechanical filtration efficiency of melt blown fabric in the situation of an electric charge loss. In this paper, nylon 6 (PA6) nanofibers were electrospun on melt blown cloth by electrospinning technology, and a sandwich material with melt blown cloth as surface layer and PA6 nanofibers as middle layer was made by hot- pressing technology;the surface morphology, thermal and mechanical properties of the sandwich material were characterized, and its filtration performance was tested. The experimental results show that the surface integrity of the sandwich material is high, and the diameter of nanofibers can reach about 67 nm;without the electret treatment, the filtration efficiency of the sandwich material for particles in an size of 0.2 μm is more than 95%,while the filtration efficiency of non-woven fabric is zero;the filtration resistance of the material is about 284 Pa, which is suitable for personal protection. © 2023 Chengdu University of Science and Technology. All rights reserved.

Preparation of green-solvent-based polyamide nanofiber membrane and its air filtration performance

Objective The epidemic of COVID-19 and its variants is endangering human health. Wearing protective masks can effectively reduce the infection risk by resisting the inhalation of the polluted air containing the coronavirus. Electrospun polyamide nanofibers can be used as the core layer of protective masks and have lately received growing attention because of their high filtration performance and robust mechanical properties. However, existing electrospun polyamide nanofiber filters are usually prepared from toxic solvents which could cause severe environmental pollution and endanger workers' health, hence, their practical application should be restricted. Therefore, it is imperative to seek and develop green-solvent-based polyamide nanofiber filters. Method Innovative polyamide nanofiber filters were developed by direct electrospinning technique based on green solvents (Fig. 1). Ethanol as the solvent and water as the nonsolvent were adopted to prepare the green-solvent-based polyamide (GSPA) nanofibers by designing spinning solutions with different ethanol/water mass ratios (i.e., 10: 0, 9: 1, 8: 2, 7: 3, and 6: 4) . During electrospinning process, the working voltage, tip-to-collector distance, and solution extrusion speed were set as 30 kV, 15 cm and 1 mL/h, respectively. The nanofibers prepared with the different ethanol/water ratios were denoted as GSPA - 0, GSPA - 1, GSPA - 2, GSPA-3, and GSPA-4, respectively. Results It was found that water content had a great influence on the morphological structures of polyamide nanofibers (Fig. 2) - After introducing a small amount of water, the obtained GSPA - 1 nanofibers featuring thinner diameter of 332 nm were compared to the GSPA-0 nanofibers (499 nm). The enhanced conductivity (10. 5 μS/cm) of waterborne spinning solutions (Fig. 3) stimulated more charges on spinning jets and led to larger electrostatic force, thus greatly elongating the jets and thinning the fiber diameter. However, with the further increment of water concentrations from 20% to 40%, the obtained fibers exhibited an increased average diameter ranging from 443 to 1 553 nm, which was mainly attributed to the larger viscosity of spinning solutions. Although water cannot dissolve polyamide, homogenous waterborne polyamide/ethanol solutions can still be obtained with different ethanol/water mass ratios within a broad area in the stable region (Fig. 3) - The average pore size of GSPA -1 membranes decreased by 55% compared with that of GSPA-0 membranes, contributing to high filtration efficiency. Moreover, with different concentrations (10%, 20%, 30%) of water, the fluffy structure of GSPA nanofibers were achieved with a high porosity (> 80%), which would offer more passageways to transmit air rapidly. As the water concentration increased, the breaking strength of membranes increased at first and then decreased (Fig. 5), and the GSPA- 1 membranes exhibited the highest breaking strength of 5. 6 MPa, which was believed to be related to the enhanced entanglements and contacts among the adjacent fibers because of the small fiber diameter. The GSPA -1 membranes displayed the highest filtration efficiency (99. 02%) for the most penetration particles (PM0.3) by virtue of the small fiber diameter but suffered from poor permeability with a pressure drop of 158 Pa. Moreover, the GSPA- 1 membranes possessed the highest quality factor of 0. 029 3 Pa, suggesting the optimal filtration performance among different GSPA membranes. A high PM0.3 removal efficiency (>95%) was achieved for GSPA-1 filters under various airflow velocities ranging from 10 to 90 L/min (Fig. 7). Compared with conventional melt-blown fibers, the GSPA nanofibers featured a smaller diameter and higher Knudsen number (Fig. 8), and PM0.3 were captured mainly on the surfaces of green polyamide nanofibers (Fig. 9), demonstrating the higher adsorption ability benefiting from the larger specific surface area. Conclusion A cleaner production of polyamide nanofibers for air filtration was proposed by direct electrospinning based on green and sustaina le binary solvents of water and ethanol. For the first time, the structure including fiber diameter, porosity, and pore size of electrospun polyamide nanofibers were precisely tailored by manipulating water concentration in spinning solutions. The prepared environmentally friendly polyamide nanofiber filters feature the interconnected porous structure with the nanoscale ID building blocks (332 nm), mean pore size (0.7 μm), and porosity (84%), thus achieving efficient PM0.3 capture performance with the filtration efficiency of 99. 02% and pressure drop of 158 Pa, which could be comparable to previous toxic-solvent-processed nanofibers. Moreover, the GSPA nanofibers exhibit robust mechanical properties with an impressive breaking strength (5 . 6 MPa) and elongation (163. 9%), contributing to withstanding the external forces and deformation in the practical assembly and usage of resultant filters. It is envisaged that the green-solvent-based polyamide nanofibers could be used as promising candidates for next-generation air filters, and the proposed waterborne spinning strategy can provide valuable insights for cleaner production of advanced polyamide textiles. © 2023 China Textile Engineering Society. All rights reserved.

Filtration Performance and Fiber Shedding Behavior in Common Respirator and Face Mask Materials

Wearing respirators and face masks is effective for protecting the public from COVID-19 infection. Thus, there is a need to evaluate the performance of the commonly used respirators and face masks. Two experimental systems were developed to investigate seven different mask materials, which have a fiber size range from 0.1 µm (100 nm) to 20 µm (20,000 nm). One of the systems is a computer-controlled setup for measuring the filtration performance, including size-dependent filtration efficiency and pressure drop, while the other system is for testing the fiber shedding behavior of the materials. The technique of scanning electron microscope (SEM) was applied to observe the dimensions and structures of those materials, which are made of nonwoven-fabrics electret-treated media, cotton woven fabrics, or nanofiber media. The study indicated that the 3M N95 respirator has the best overall filtration performance with over 95% efficiency and low pressure drop of 74.1 Pa. The two commercial cotton face masks have the worst filtration performance in general, with a filtration efficiency of around 25%. No broken fibers from by the seven tested respirator and face mask materials were discovered;however, dendrite structures likely shed by the SHEMA97 face mask with a size comparable to its nanoscale fibers were identified. The reason for this phenomena is presented. © 2023, AAGR Aerosol and Air Quality Research. All rights reserved.

Preparation and property of electrospining nanocopper oxide antibacterial composite nonwovens

The spread and variation of COVID-19 in the world have seriously threatened human health. Therefore the current focus of research is to develop medical and antiepidemic textiles with high filtering efficiency and bacteriostasis and low filtering resistance. Polypropylene PP melt-blown nonwovens are commonly used as raw materials for medical antiepidemic textiles. PP melt-blown nonwovens as the core filter layer of medical textiles were difficult to buy during the outbreak of the epidemic. However the traditional PP melt-blown nonwovens have low antibacterial performance and medical staff are vulnerable to virus infection and microbial damage in the process of use for their single function and certain limitations in protective ability. Therefore in the post-pandemic era PP melt-blown nonwovens should not only be able to meet the rigid demand of the market but also evolve to be high-end and functional in the face of mutating COVID-19 and the possibility of a return at any time. The research combines the PP melt-blown nonwoven with the electrospinning nanofiber membrane to prepare compound nonwoven fabrics with high antibacterial activity. In order to improve the antibacterial property of PP melt-blown nonwovens composite nanofiber membranes were synthesized on PP melt-blown nonwovens by electrospinning technology. Firstly the PP melt-blown nonwoven was used as receiving substrate of electrospinning equipment and nano copper oxide CuO-NPS was used as anti-bacterial material to prepare the PP / PAN / CuO-NPS composite nonwovens with high antibacte-rial performance. On the basis of that effects of the CuO-NPS mass fraction and electrospinning time on the surface morphology fiber diameter distribution chemical constitution filtration performance hydrophobicity and antibacterial property of composite nonwovens were studied. The results show that the bacteriostasis rates of composite nonwovens to gram-negative E. coli and gram-positive S. aureus are both greater than 99. 99% in the range of CuO-NPS mass fraction of 0. 3% - 0. 9% and the spinning time is 1 h. When the spinning time is 1 h as the mass fraction of CuO-NPS increases the fiber diameter of the composite nonwoven increases and its distribution uniformity of diameter and hydrophobic property both decrease. Under the condition of constant mass fraction of CuO-NPS the filtration efficiency of composite nonwovens improves with the extension of the spinning time but the permeability decreases. With the same spinning time the filtration efficiency of composite nonwovens increases with the increase in CuO-NPS mass fraction. In addition in-corporating CuO-NPs into PAN nanofiber membrane does not change the chemical structure of the membrane. We select polyacrylonitrile PAN with good spinning performance as the raw material and CuO-NPs as the antibacterial material to prepare CuO-NPs powder with antibacterial properties to prepare electrostatic spinning solution. The composites of PP melt-blown nonwovens and electrospun PAN / CuO-NPs nanofibrous membrane have been obtained which not only improves the filtration performance of PP melt-blown nonwovens but also endows them with efficient antibacterial property. This paper provides a reference for further studies on the production and application of PP melt-blown nonwovens. (English) [ABSTRACT FROM AUTHOR] 针对聚丙烯( PP)熔喷非织造布抗菌性能不足的问题,本文以 PP 熔喷非织造布为静电纺丝装置的接受基布、 CuO-NPs 为抗菌材料,制备具有高效抗菌性能的聚丙烯 / 聚丙烯腈 / 纳米氧化铜( PP / PAN / CuO-NPs) 复合非织造布。 研究了 CuO-NPs 质量分数 与 静 电 纺 丝 时 间 对 复 合 非 织 造 布 抗 菌 等 性 能 的 影 响。 结 果 表 明:当 纺 丝 时 间 为 1 h、 CuO-NPs 质量分数在 0. 3% ~ 0. 9% 时,复合非织造布对 E. coli 和 S. aureus 的抑菌率均 > 99. 99% 。 纺丝时间为 1 h, 随着 CuO-NPs 质量分数增大,复合非织造布纤维直径增大、直径分布均匀性降低、疏水性能下降。 CuO-NPs 质量分 数不变,随着纺丝时间增加,复合非织造布的过滤效率提升,透气性却下降。 纺丝时间相同,复合非织造布的过滤效 率随着 CuO-NPs 质量分数增大而增大;CuO-NPs 质量分数增大时,复合非织造布的透气性在较短纺丝时间( 0. 5 ~ 1 h)内先下降后提升,在较长纺丝时间(1. 5 ~ 2. 5 h)内显著下降。 此外,CuO-NPs 的加入不会改变 PAN 纳米纤维膜 的化学结构。 静电纺纳米纤维膜与 PP 基布的复合可以制备高效过滤和抑菌的医用防疫纺织品。 (Chinese) [ABSTRACT FROM AUTHOR] Copyright of Journal of Silk is the property of Zhejiang Sci-Tech University Magazines and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Environmental storage conditions influencing the filtration behavior of electret filters with repeated use

Worldwide attention has been paid to effective protection strategies against the COVID-19 pandemic. Filtering masks are generally kept for a certain period of shelf-life before being used, and frequently, they are used repeatedly with recurrent storages. This study investigates the effect of storage temperature and humidity on the structural characteristics and charges of an electret filter, associating with the filtration performance in terms of efficiency and pressure drop based on a practical use-storage scenario. For the repeated use conditions with recurrent storage, humid storage conditions significantly deteriorated the filtration efficiency as hygroscopic particles quickly wetted the surface and masked the surface charges. The high temperature rapidly deteriorated the filter charges and caused a lowered electrostatic filtration efficiency. In a heated condition, the web became fluffier, yet it did not directly affect the pressure drop or mechanical filtration efficiency. The approach of this study is progressive in that rigorous analysis was performed on examining the particle morphology and internal structure of filter media with varied storage conditions to link with the filtration performance and the effective lifetime. This study intends to provide a scientific reference guiding a desirable storage condition and replacement cycle of filtering masks considering the actual use habits and storage environment. © The Author(s) 2022.

Numerical simulation of aerosol permeation through microstructure of face masks coordinating with x-ray computed tomography images

Face masks act as air filters that collect droplets and aerosols, and they are widely used to prevent infectious diseases, such as COVID-19. Herein, we present a numerical simulation model to understand the collection behavior of aerosols containing submicron-sized droplets inside a realistic microstructure of commercially available face masks. Three-dimensional image analysis by x-ray computed tomography is used to obtain the microstructures of two types of commercial face masks, and the aerosol permeation behavior in the obtained microstructures is investigated with a numerical method coupled with computational fluid dynamics and a discrete phase model. To describe the complex geometry of the actual fibers, a wall boundary model is used, in which the immersed boundary method is used for the fluid phase, and the signed distance function is used to determine the contact between the droplet and fiber surface. Six different face-mask domains are prepared, and the pressure drop and droplet collection efficiency are calculated for two different droplet diameters. The face-mask microstructure with the relatively larger pore, penetrating the main flow direction, shows a high quality factor. A few droplets approach the pore accompanied by fluid flow and fibers collect them near the pore. To verify the effect of the pore on the collection behavior, six different model face-mask domains of variable pore sizes were created. Additionally, droplet collection near the pore is observed in the model face-mask domains. Specific pore-sized model masks performed better than those without, suggesting that the large pore may enhance performance.

A Rapid and High-Throughput Assay for Light Scattering of SARS-CoV-2 Virion-Sized Particulates via Microfluidic Spray Device Reveals the Protection Performance of Face Masks against Virus Infection.

To prevent interhuman transmission of viruses, new mask types─claiming improved filtration─require careful performance characterization. Here, a microfluidic spray device that can effectively simulate droplets emitted during coughing or sneezing was developed to spray droplets containing gold nanoparticles (AuNPs) that mimic SARS-CoV-2 to overcome the shortcomings associated with using biosamples. The light scattered by the AuNPs passing through the mask is successfully analyzed by using an automated scattering light mapping system within a duration of 2 min, thereby enabling high-throughput analysis of the filtering efficiency of various types of commercial masks. The differences in efficiency in terms of same mask type from different manufacturers, double masking, and prolonged usage, which are challenging to analyze with conventional testing systems, can also be assessed. AuNP-mediated mask performance evaluation enables the rapid determination of mask efficiency according to particle size and can contribute to the rapid response to counter new emerging infectious biohazards.

Filtration performance and breathing resistance of elastomeric half mask respirator P100 filter cartridges after repeated and extended use in healthcare settings.

In 2020, the Centers for Disease Control and Prevention recommended the use of the National Institute for Occupational Safety and Health-certified Elastomeric Half Mask Respirators equipped with N95 or P100 respirator filter cartridges for protection against the SARS-CoV-2 viral agent, as a viable alternative to N95 filtering facepiece respirators. Additionally, the Centers for Disease Control and Prevention recommendations stated that based on current practice, it was acceptable to repeatedly use these filter cartridges for up to 12 months as a contingency capacity strategy during anticipated respirator shortages. To validate this recommendation, an investigation was undertaken in which Elastomeric Half Mask Respirators equipped with P100 respirator filter cartridges were deployed and used by healthcare professionals in clinical settings (i.e., inpatient nursing units, operating rooms) for extended periods. These filter cartridges were subsequently tested to accurately quantify their filtration efficiency and breathing resistance to determine if they continued to meet National Institute for Occupational Safety and Health's performance requirements. Findings from this investigation confirmed that an Elastomeric Half Mask Respirator when equipped with a P100 filter cartridge continues to provide a high level of aerosol filtration performance (≥99.97%) and exhibits little change in breathing resistance even after 12 months of repeated use (i.e., wear, cleaning, and disinfection between patient use and at the end of work shift) in healthcare settings.

Factors influencing the filtration performance of homemade face masks.

The outbreak of the COVID-19 pandemic is causing a shortage of personal protective equipment (PPE) across the world. As a public health response to control the pandemic, wearing homemade face coverings has been proven as a resort to protect both the wearer and others from droplets and aerosols transmission. Although aerosols and droplets can be removed through these non-medical materials with a series of filtration mechanisms, their filtration performances have not been evaluated in detail. Moreover, many factors, such as the fabric properties and the method of usage, also affect filtration performance. In this study, the size-dependent filtration performances of non-medical materials as candidates for face coverings were evaluated comprehensively. The flow resistance across these filter materials, an indicator of breathability, was also examined. The effect of materials properties, washing and drying cycles, and triboelectric effect on particle filtration was also studied. Results showed that the filtration efficiency varied considerably from 5-50% among fabrics materials due to the material properties, such as density and microscopic structure of the materials. Microfiber cloth demonstrated the highest efficiency among the tested materials. In general, fabric materials with higher grams per square meter (GSM) show higher particle filtration efficiency. The results on washing and drying fabric materials indicated decent reusability for fabric materials. The triboelectric charge could increase the filtration performance of the tested fabric materials, but this effect diminishes soon due to the dissipation of charges, meaning that triboelectric charging may not be effective in manufacturing homemade face coverings.

Evaluation of Regeneration Processes for Filtering Facepiece Respirators in Terms of the Bacteria Inactivation Efficiency and Influences on Filtration Performance.

The regeneration of filtering facepiece respirators (FFRs) is of critical importance because of the severe shortage of FFRs during large-scale outbreaks of respiratory epidemics, such as COVID-19. Comprehensive experiments regarding FFR regeneration were performed in this study with model bacteria to illustrate the decontamination performance of the regeneration processes. The results showed that it is dangerous to use a contaminated FFR without any microbe inactivation treatment because the bacteria can live for more than 8 h. The filtration efficiency and surface electrostatic potential of 75% ethanol-treated FFRs were significantly reduced, and a most penetrating particle size of 200 nm was observed. Steam and microwave irradiation (MWI) showed promising decontamination performances, achieving 100% inactivation in 90 and 30 min, respectively. The filtration efficiencies of steam-treated FFRs for 50 and 100 nm particles decreased from 98.86% and 99.51% to 97.58% and 98.79%, respectively. Ultraviolet irradiation (UVI) effectively inactivated the surface bacteria with a short treatment of 5 min and did not affect the filtration performance. However, the UV dose reaching different layers of the FFP2 mask sample gradually decreased from the outermost layer to the innermost layer, while the model bacteria on the second and third layers could not be killed completely. UVI+MWI and steam were recommended to effectively decontaminate the used respirators and still maintain the respirators' filtration efficiency. The present work provides a comprehensive evaluation for FFR regeneration in terms of the filtration efficiencies for 50-500 nm particles, the electrostatic properties, mechanical properties, and decontamination effects.