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.

Nanosponges: As a Dynamic Drug Delivery Approach for Targeted Delivery

Recent advancements in nanotechnology have resulted in improved medicine delivery to the target site. Nanosponges are three-dimensional drug delivery systems that are nanoscale in size and created by cross-linking polymers. The introduction of Nanosponges has been a significant step toward overcoming issues such as drug toxicity, low bioavailability, and predictable medication release. Using a new way of nanotechnology, nanosponges, which are porous with small sponges (below one microm) flowing throughout the body, have demonstrated excellent results in delivering drugs. As a result, they reach the target place, attach to the skin's surface, and slowly release the medicine. Nanosponges can be used to encapsulate a wide range of medicines, including both hydrophilic and lipophilic pharmaceuticals. The medication delivery method using nanosponges is one of the most promising fields in pharmacy. It can be used as a biocatalyst carrier for vaccines, antibodies, enzymes, and proteins to be released. The existing study enlightens on the preparation method, evaluation, and prospective application in a medication delivery system and also focuses on patents filed in the field of nanosponges.Copyright © 2023 The Authors.

Electrospun Polymer Nanofibers for Technology Applications: A Short Review

Nanofibers are a type of nanomaterial with a diameter ranging from ten to a few hundred nanometers with a high surface-to-volume ratio and porosity. They can build a network of high-porosity material with excellent connectivity within the pores, making them a preferred option for numerous applications. This review explores nanofibers from the synthesis techniques to fabricate nanofibers, with an emphasis on the technological applications of nanofibers like water and air filtration, photovoltaics, batteries and fuel cells, gas sensing, photocatalysis, and biomedical applications like wound dressing and drug delivery. The nanofiber production market has an expected compound annual growth rate (CAGR) of 6% and should reach around 26 million US $ in 2026. The limitations and potential opportunities for large-scale applications of nano-fibrous membranes are also discussed. We expect this review could provide enriched information to better understand Electrospun Polymer Nanofiber Technology and recent advances in this field. © 2023 Bentham Science Publishers.

Biodegradable Bio-based Material for Wearable Air Filtering Skin

COVID-19, imagine having a temporary lip sticker that offers the protection of an n95 mask without the uncomfortable bulk. Using green electrospun nanofibers the lip sticker filters the virus and can communicate geospatial data to your phone using embedded NFC technology. Available in different designs and skins, some fiber formations can display temperature changes on your face. This paper investigates several prototypes of the described product. © 2022 Owner/Author.

Electrospun film composed of pearl-string-like microfibers exhibiting excellent radiative cooling performance, moisture permeability and self-cleaning function

The double threat of extremely hot summer and the pandemic of Covid-19 makes it important to develop protective clothing with remarkable advantage of personal thermal management. Meanwhile, radiative coolers with strong solar reflection and atmospheric window (8–13 μm) emission can cool objects without the requirement of extra energy input. Passive daytime radiative cooling has attracted extensive attention in the field of personal thermal management. However, radiative cooling textile for protective clothing remains to be explored. In this work, electrospinning technique was applied to prepare radiative cooling flexible film for protective clothing. The prepared film is composed of microfibers with pearl-string-like structures that result in high average solar reflectance (98.1%) and high average atmospheric window emittance (94.9%). The film delivers an average temperature drop of 6.1 °C and an average radiative cooling power of 79 W m−2. The radiative cooling film has good moisture permeability and self-cleaning function. This study has opened up a promising way for the design and fabrication of protective clothing that has excellent passive daytime radiative cooling performance.

Electrospray-on-Electrospun Breathable, Biodegradable, and Robust Nanofibrous Membranes with Photocatalytic Bactericidal Activity

The increasing emergence of infectious diseases like COVID-19 has created an urgent need for filtration/purification materials coupled with multifunctional features such as mechanical integrity, excellent airflow/filtration, and antibacterial/antimicrobial properties. Polymer membranes and metal-organic frameworks (MOFs) have demonstrated high effectiveness in air filtration and purification. MOF nanoparticles have been introduced into electrospun polymer nanofibrous membranes through embedding or postsolution growth. However, the derived hybrids are still facing the issue of (1) limited MOF exposure, which leads to low efficacy;and (2) uncontrollable growth, which leads to pore blocking and low breathability. In this work, we customized an electrospray-on-electrospinning in situ process to dynamically integrate MOF nanoparticles into a robust and elastic continuous nanofibrous membrane for advanced properties including high mechanical strength and flexibility, excellent breathability, particle filtration, and good antimicrobial performance. Biodegradable polylactic acid was reinforced by the poly(hydroxybutyrate)-di-poly(DLA-CL)x copolymer (PHBR) and used as an electrospinning matrix, while MOF nanoparticles were simultaneously electrically sprayed onto the nanofibers with easily controllable MOF loading. The MOF nanoparticles were homogeneously deposited onto nanofibers without clogging the pores in the membrane. The collision of PLA and MOF under the wet status during electrospinning and the hydrogen bonding through C=O and N-H bonds strengthen the affinity between PLA nanofibers and MOF nanoparticles. Because of these factors, the MOF-incorporated PLA/PHBR nanofibrous membrane achieved over 95% particle filtration efficiency with enhanced mechanical properties while maintaining high breathability. Meanwhile, it exhibits excellent photocatalytic antibacterial performance, which is necessary to kill microbes. The electrospray-on-electrospinning in situ process provides an efficient and straightforward way to hybridize one-dimensional (1D) or two-dimensional (2D) nanomaterials into a continuous nanofibrous membrane with strong interaction and controllable loading. Upon integrating proper functionalities from the materials, the obtained hybrids are able to achieve multifunctionalities for various applications.

Functional Textile Materials for Blocking COVID-19 Transmission.

The outbreak of COVID-19 provided a warning sign for society worldwide: that is, we urgently need to explore effective strategies for combating unpredictable viral pandemics. Protective textiles such as surgery masks have played an important role in the mitigation of the COVID-19 pandemic, while revealing serious challenges in terms of supply, cross-infection risk, and environmental pollution. In this context, textiles with an antivirus functionality have attracted increasing attention, and many innovative proposals with exciting commercial possibilities have been reported over the past three years. In this review, we illustrate the progress of textile filtration for pandemics and summarize the recent development of antiviral textiles for personal protective purposes by cataloging them into three classes: metal-based, carbon-based, and polymer-based materials. We focused on the preparation routes of emerging antiviral textiles, providing a forward-looking perspective on their opportunities and challenges, to evaluate their efficacy, scale up their manufacturing processes, and expand their high-volume applications. Based on this review, we conclude that ideal antiviral textiles are characterized by a high filtration efficiency, reliable antiviral effect, long storage life, and recyclability. The expected manufacturing processes should be economically feasible, scalable, and quickly responsive.

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.

Efficient, Breathable and Biodegradable Filter Media for Face Masks

The global outbreak of COVID-19 results in the surge of disposable sanitary supplies, especially personal protective face masks. However, the charge dissipation of the electret meltblown nonwovens, which predominate in the commercial face mask filters, confines the durability and safety of commercial face masks. Furthermore, most of the face masks are made from nondegradable materials (such as PP) or part of their degradation products are toxic and contaminative to the environment. Herein, a type of face mask with biodegradable and highly effective PLA bi-layer complex fibrous membrane as filter core is reported. The prepared PLA complex membrane possesses a high-filtration efficiency of 99.1% for PM0.3 while providing a favorable pressure drop of 93.2 Pa. With the PLA complex membrane as the filter core, our face mask exhibits comparable or even higher wearability to commercial face masks, which further manifests our designed PLA complex membrane a promising filter media for face masks. © 2023, The Author(s), under exclusive licence to the Korean Fiber Society.

Nanofibrous Polymeric Membranes for Air Filtration Application: A Review of Progress after the COVID-19 Pandemic

Air pollution is one of the major global problems causing around 7 million dead per year. In fact, a connection between infectious disease transmission, including COVID-19, and air pollution has been proved: COVID-19 consequences on human health are found to be more severe in areas characterized by high levels of particulate matter (PM). Therefore, after the COVID-19 pandemic, the production of air filtration devices with high filtration efficiency has gained more and more attention. Herein, a review of the post-COVID-19 pandemic progress in nanofibrous polymeric membranes for air filtration is provided. First, a brief discussion on the different types of filtration mechanism and the key parameters of air filtration is proposed. The materials recently used for the production of nanofibrous filter membranes are presented, distinguishing between non-biodegradable polymeric materials and biodegradable ones. Subsequently, production technique proposed for the fabrication of nanofibrous membranes, i.e., electrospinning and solution blow spinning, are presented aiming to analyze and compare filtration efficiency, pressure drop, reusability and durability of the different polymeric system processed with different techniques. Finally, present challenges and future perspectives of nanofibrous polymeric membranes for air filtration are discussed with a particular emphasis on strategies to produce greener and more performant devices. © 2023 The Authors. Macromolecular Materials and Engineering published by Wiley-VCH GmbH.

A nanofiber Murray membrane with antibacterial properties for high efficiency oily particulate filtration

Particulate air pollution represented by PM2.5 is one of the biggest environmental challenges in the 21st century. Especially in 2020, the global outbreak of COVID-19 has brought new challenges to melt-blown filter materials, such as the attenuation of filtration efficiency with breathing, even no filtration effect for viruses as their smaller diameter, the sharp decline of filter efficiency after oily filtration cycle, and its limit in some explosive occasions. Here, using the diameter difference of polystyrene (PS), polyvinylidene fluoride (PVDF) and nylon 6(PA6) fibers, we report a multistage structure nanofiber membrane (PS/PVDF/PA6&Ag MSNMs) with high efficiency, low resistance and antibacterial effect by constructing gradient pore structure and introducing silver nanoparticles (Ag NPs), overcoming the above defects. The average filtration efficiency of PS/PVDF/PA6&Ag MSNMs for diisooctyl sebacate (DEHS) monodisperse particles from 0.2 μm to 4.9 μm was 99.88%, and the pressure drop was only 128 Pa. After repeated circulation for 100 times, the filtration efficiency and pressure drop remained stable. Above all, the antibacterial nanofiber membrane with high efficiency and low resistance has been preliminarily constructed, the future research will further focus on the performance after circulation. © 2023 Elsevier Ltd

Development of Carbon-Nanodot-Loaded PLA Nanofibers and Study of Their Barrier Performance for Medical Applications.

The COVID-19 pandemic has increased the usage of personal protective equipment (PPE) all round the world and, in turn, it has also increased the waste caused by disposable PPE. This has exerted a severe environmental impact, so in our work, we propose the utilization of a sustainable electrospun nanofiber based on poly lactic acid (PLA), as it is biobased and conditionally degradable. We optimized the weight percentage of the PLA-precursor solution and found that 19% PLA produces fine nanofibers with good morphology. We also introduced carbon nanodots (CNDs) in the nanofibers and evaluated their antibacterial efficiency. We used 1, 2, 3, and 4% CNDs with 19% PLA and found increased antibacterial activity with increased concentrations of CNDs. Additionally, we also applied a spunbond-nanofiber layered assembly for the medical face masks and found that with the addition of only 0.45 mg/cm2 on the nonwoven sheet, excellent particle filtration efficiency of 96.5% and a differential pressure of 39 Pa/cm2 were achieved, meeting the basic requirements for Type I medical face masks (ASTM-F2100).

In situ electrospun aloe-nanofiber membrane for chronic wound healing.

Alleviating excessive inflammation while accelerating chronic wound healing to prevent wound infection has remained challenging, especially during the coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 when patients experienced difficulties with receive appropriate healthcare. We addressed this issue by developing handheld electrospun aloe-nanofiber membranes (ANFMs) with convenient, environmentally friendly properties and a therapeutic capacity for wound closure. Our results showed that ANFMs fabricated with high molecular weight polyvinyl alcohol (PVA) to form fibers during electrospinning had uniform fibrous architecture and a porous structure. Given the value of aloe gel in accelerating wound healing, liquid extracts from ANFMs significantly downregulated the expression of the pro-inflammatory genes, interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS), and markedly suppress the generation of reactive oxygen species (ROS) induced by lipopolysaccharide in RAW264.7 macrophages. These results indicated the excellent antioxidant and anti-inflammatory effects of ANFMs. After implantation into a mouse diabetic wound model for 12 days in situ, ANFMs notably expedited chronic wound healing via promoting angiogenesis and enhancing cell viability. Our ANFMs generated by handheld electrospinning in situ healed chronic wounds offer a convenient and promising alternative for patients to heal their own wounds under variable conditions.

A Novel Vision of Reinforcing Nanofibrous Masks with Metal Nanoparticles: Antiviral Mechanisms Investigation.

Prevention of spreading viral respiratory disease, especially in case of a pandemic such as coronavirus disease of 2019 (COVID-19), has been proved impossible without considering obligatory face mask-wearing protocols for both healthy and contaminated populations. The widespread application of face masks for long hours and almost everywhere increases the risks of bacterial growth in the warm and humid environment inside the mask. On the other hand, in the absence of antiviral agents on the surface of the mask, the virus may have a chance to stay alive and be carried to different places or even put the wearers at risk of contamination when touching or disposing the masks. In this article, the antiviral activity and mechanism of action of some of the potent metal and metal oxide nanoparticles in the role of promising virucidal agents have been reviewed, and incorporation of them in an electrospun nanofibrous structure has been considered an applicable method for the fabrication of innovative respiratory protecting materials with upgraded safety levels.

A Review on Current Nanofiber Technologies: Electrospinning, Centrifugal Spinning, and Electro‐Centrifugal Spinning

Nanofiber‐based products are widely used in the fields of public health, air/water filtration, energy storage, etc. The demand for nonwoven products is rapidly increasing especially after COVID‐19 pandemic. Electrospinning is the most popular technology to produce nanofiber‐based products from various kinds of materials in bench and commercial scales. While centrifugal spinning and electro‐centrifugal spinning are considered to be the other two well‐known technologies to fabricate nanofibers. However, their developments are restricted mainly due to the unnormalized spinning devices and spinning principles. High solution concentration and high production efficiency are the two main strengths of centrifugal spinning, but beaded fibers can be formed easily due to air perturbation or device vibration. Electro‐centrifugal spinning is formed by introducing a high voltage electrostatic field into the centrifugal spinning system, which suppresses the formation of beaded fibers and results in producing elegant nanofibers. It is believed that electrospinning can be replaced by electro‐centrifugal spinning in some specific application areas. This article gives an overview on the existing devices and the crucial processing parameters of these nanofiber technologies, also constructive suggestions are proposed to facilitate the development of centrifugal and electro‐centrifugal spinning.

Electrospun transparent nanofibers as a next generation face filtration media: A review.

The development of fascinating materials with functional properties has revolutionized the humankind with materials comfort, stopped the spreading of diseases, relieving the environmental pollution pressure, economized government research funds, and prolonged their serving life. The outbreak of Coronavirus Disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has triggered great global public health concern. Face masks are crucial tools to impede the spreading of SARS-CoV-2 from human to human. However, current face masks exhibit in a variety of colors (opaque), like blue, black, red, etc., leading to a communication barrier between the doctor and the deaf-mute patient when wearing a mask. High optical transparency filters can be utilized for both personal protection and lip-reading. Thus, shaping face air filter into a transparent appearance is an urgent need. Electrospinning technology, as a mature technology, is commonly used to form nanofiber materials utilizing high electrical voltage. With the alteration of the diameters of nanofibers, and proper material selection, it would be possible to make the transparent face mask. In this article, the research progress in the transparent face air filter is reviewed with emphasis on three parts: mechanism of the electrospinning process and light transmission, preparation of transparent face air filter, and their innovative potential. Through the assessment of classic cases, the benefits and drawbacks of various preparation strategies and products are evaluated, to provide general knowledge for the needs of different application scenarios. In the end, the development directions of transparent face masks in protective gear, particularly their novel functional applications and potential contributions in the prevention and control of the epidemic are also proposed.

The anti SARS-CoV-2 activity of nanofibrous filter materials activated with metal clusters.

Nanofibrous filter materials were prepared by electrospinning a solution of 28 wt% poly(vinylidene fluoride) in N,N-dimethylacetamide with and without the addition of 2 wt% AgNO3, Cu(NO3)2·2.5H2O or ZnCl2. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectroscopy, thermogravimetric analysis, contact angle measurement, nitrogen sorption, and mercury intrusion porosimetry methods were used for the characterization of physical structure as well as the chemical composition of the electrospun materials. Particle filtration efficiency and antiviral activity against the SARS-CoV-2 alpha variant were tested in order to estimate the suitability of the prepared electrospun filter materials for application as indoor air filtration systems with virucidal properties. All filter materials prepared with salts demonstrated very high particle filtration efficiency (≥98.0%). The best antiviral activity was demonstrated by a material containing Cu(NO3)2·2.5H2O in the spinning solution, which displayed the decrease in the number of infectious virions by three orders of magnitude after a contact time of 12 h. Materials with the addition of AgNO3 and ZnCl2 decreased the number of infectious virions after the same contact time by only ∼8 and ∼11 times, respectively.

Electrospun Cyclodextrin/Poly(L-lactic acid) Nanofibers for Efficient Air Filter: Their PM and VOC Removal Efficiency and Triboelectric Outputs.

In this work, PLLA and CD/PLLA nanofibers were fabricated using electrospinning and utilized as a particulate matter (PM) and volatile organic compounds (VOCs) filter. The electrospun PLLA and CD/PLLA were characterized with various techniques, including SEM, BET, FTIR, XRD, XPS, WCA, DSC, tensile strength testing, PM and VOCs removal efficiency, and triboelectric performance. The results demonstrated that the best air filter was 2.5 wt%CD/PLLA, which performed the highest filtration efficiencies of 96.84 ± 1.51% and 99.38 ± 0.43% for capturing PM2.5 and PM10, respectively. Its PM2.5 removal efficiency was 16% higher than that of pure PLLA, which were contributed by their higher surface area and porosity. These 2.5 wt%CD/PLLA nanofibers also exhibited the highest and the fastest VOC entrapment. For triboelectric outputs, the 2.5 wt%CD/PLLA-based triboelectric nanogenerator provided the highest electrical outputs as 245 V and 84.70 µA. These give rise to a three-fold enhancement of electrical outputs. These results indicated that the 2.5 wt%CD/PLLA can improve surface charge density that could capture more PM via electrostatic interaction under surrounding vibration. Therefore, this study suggested that 2.5 wt%CD/PLLA is a good candidate for a multifunction nanofibrous air filter that offers efficient PM and VOC removal.

Preparation, characterization, and air filtration property of electrospun bimodal fibrous membrane based on low conductivity blended polymers solution

One–step preparation of electrospun bimodal fibrous membrane based on single nozzle is the key to the efficient fabrication of high–performance air filter. However, the preparation mechanism of electrospun bimodal fibers at low conductivity solution system is not clear, and there is a lack of evaluation methods for the quality of bimodal nanofibers, which limits the applicability of single nozzle electrospinning and the preparation efficiency of electrospun bimodal fibers. Here, three electrospinning processes at low conductivity solution systems of polyamide–6 (PA6), PA6 blended PVP (PA6/PVP), and PA6 blended polyethylene oxide (PA6/PEO) were studied according to the rheological properties and the fluid electrics (i.e., zeta potential), and the quality of the prepared bimodal fibrous membrane was creatively evaluated by R value. Inhomogeneous phase separations of the electrospinning jet along the direction parallel (x–axis) or perpendicular (y–axis) to the electric field were responsible for the formation of bimodal fibers. In addition, for the same solution system, the R value had a positive correlation with the air filtration performance. This work will greatly enhance the applicability of one–step single nozzle electrospinning for the preparation of bimodal nanofibers, improve the preparation efficiency, and promote the development of high–performance air filter. © 2022 Elsevier Ltd

Biobased polymer SF/PHBV composite nanofiber membranes as filtration and protection materials

With the emergence of the COVID-19, masks and protective clothing have been used in huge quantities. A large number of non-degradable materials have severely damaged the ecological environment. Now, people are increasingly pursuing the use of environmentally friendly materials to replace traditional chemical materials. Silk fibroin (SF) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) have received increasing attention because of their unique biodegradability and biocompatibility. In this paper, a series of biodegradable SF/PHBV nanofiber membranes with different PHBV content were fabricated by using electrospinning technology. The morphology of the electrospun SF/PHBV composite nanofiber was observed by scanning electron microscopy (SEM). The average diameters of the pure SF, SF/PHBV (4/1), SF/PHBV (3/1), and SF/PHBV (2/1) nanofibers were 55.16 ± 12.38 nm, 75.93 ± 21.83 nm, 69.35 ± 21.55 nm, and 61.40 ± 12.31 nm, respectively. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were used to explore the microstructure of the electrospun SF/PHBV composite nanofiber. The crystallization ability of the composite nanofiber was greatly improved with the addition of PHBV. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that the thermal stability of SF was better than PHBV obviously, so SF could improve the thermal stability of the composite materials within a certain range. The mechanical properties of the electrospun nanofiber membranes were evaluated by using a universal testing machine. In general, the elongation of the composite nanofiber membranes decreased, and the breaking strength increased with the addition of PHBV. The small pore size of the nanofiber membranes ensured that they had good application prospects in the field of filtration and protection. When the spinning time was 1 h, the filtration efficiency of SF/PHBV/PLA composite materials remained above 95%. © 2021 The Textile Institute.