Transparent Polyurethane Nanofiber Air Filter for High-Efficiency PM2.5 Capture

Scalable, solvent-free transparent film-based air filter with high particulate matter 2.5 filtration efficiency

Over the course of the COVID-19 pandemic, people have realized the importance of wearing a mask. However, conventional nanofiber-based face masks impede communication between people because of their opacity. Moreover, it remains challenging to achieve both high filtration performance and transparency through fibrous mask filters without using harmful solvents. Herein, scalable transparent film-based filters with high transparency and collection efficiency are fabricated in a facile manner by means of corona discharging and punch stamping. Both methods improve the surface potential of the film while the punch stamping procedure generates micropores in the film, which enhances the electrostatic force between the film and particulate matter (PM), thereby improving the collection efficiency of the film. Moreover, the suggested fabrication method involves no nanofibers and harmful solvents, which mitigates the generation of microplastics and potential risks for the human body. The film-based filter provides a high PM2.5 collection efficiency of 99.9 % while maintaining a transparency of 52 % at the wavelength of 550 nm. This enables people to distinguish the facial expressions of a person wearing a mask composed of the proposed film-based filter. Moreover, the results of durability experiments indicate that the developed film-based filter is anti-fouling, liquid-resistant, microplastic-free and foldability.

Functionalized nanofibers in gas sorption process: a critical review on the challenges and prospective research

Air pollution has become the most important environmental and human health threat as it is accounting for about 7 million deaths across the globe every year. Particulate matter (PM) derived from the combustion of fossil fuels, biomass, and other agricultural residues pollutes the atmospheric air which affects the quality of the environment and poses a great threat to human health. Ecological imbalance, climatic variation, and cardiovascular and respiratory problems among humans are significant extortions due to PM pollution. Scientific approaches were initiated to limit the levels of PM in the atmospheric air and the use of nanofiber mats has received wide attention as these possess versatile properties including nanoscale-sized pore structure, homogeneity in their size distribution with high specific surface area, and low basis weight. To exploit their filtration potential towards wide classes of pollutants and also to enhance the capturing efficacy, functionalized nanofibers are currently in practice with tailor-made modifications on the surface. The present review provides a comprehensive report on the different fabrication processes of functionalized nanofibers along with the controlling factors affecting the efficacy of the gas separation process. Also, it provides technical insights on the mass transfer aspects of PM filtration by elucidation their mechanism which can provide vital information on the rate-controlling diffusive flux(es). Conclusively, the practical challenges encountered in the large-scale air filtration systems such as filter cleaning, flow-rate regulation, pressure drop, and extent of reusability are discussed, and the review has identified potential gaps in the current research and can be considered for the prospective research in the area of PM separation process.

Nanostructured Bioaerogels as a Potential Solution for Particulate Matter Pollution

Particulate matter (PM) pollution is a significant environmental and public health issue globally. Exposure to high levels of PM, especially fine particles, can have severe health consequences. These particles can come from a variety of sources, including natural events like dust storms and wildfires, as well as human activities such as industrial processes and transportation. Although an extensive development in air filtration techniques has been made in the past few years, fine particulate matter still poses a serios and dangerous threat to human health and to our environment. Conventional air filters are fabricated from non-biodegradable and non-ecofriendly materials which can cause further environmental pollution as a result of their excessive use. Nanostructured biopolymer aerogels have shown great promise in the field of particulate matter removal. Their unique properties, renewable nature, and potential for customization make them attractive materials for air pollution control. In the present review, we discuss the meaning, properties, and advantages of nanostructured aerogels and their potential in particulate matter removal. Particulate matter pollution, types and sources of particulate matter, health effect, environmental effect, and the challenges facing scientists in particulate matter removal are also discussed in the present review. Finally, we present the most recent advances in using nanostructured bioaerogels in the removal of different types of particulate matter and discuss the challenges that we face in these applications.

Nanofibers in Respiratory Masks: An Alternative to Prevent Pathogen Transmission

Recent global outbreak of COVID-19 has raised serious awareness about our abilities to protect ourselves from hazardous pathogens and volatile organic compounds. Evidence suggests that personal protection equipment such as respiratory masks can radically decrease rates of transmission and infections due to contagious pathogens. To increase filtration efficiency without compromising breathability, application of nanofibers in production of respiratory masks have been proposed. The emergence of nanofibers in the industry has since introduced a next generation of respiratory masks that promises improved filtration efficiency and breathability via nanometric pores and thin fiber thickness. In addition, the surface of nanofibers can be functionalized and enhanced to capture specific particles. In addition to conventional techniques such as melt-blown, respiratory masks by nanofibers have provided an opportunity to prevent pathogen transmission. As the surge in global demand for respiratory masks increases, herein, we reviewed recent advancement of nanofibers as an alternative technique to be used in respiratory mask production.

Optical Properties of Electrospun Nanofiber Mats

Electrospun nanofiber mats are usually applied in fields where their high specific surface area and small pore sizes are important, such as biotechnology or filtration. Optically, they are mostly white due to scattering from the irregularly distributed, thin nanofibers. Nevertheless, their optical properties can be modified and become highly important for different applications, e.g., in sensing devices or solar cells, and sometimes for investigating their electronic or mechanical properties. This review gives an overview of typical optical properties of electrospun nanofiber mats, such as absorption and transmission, fluorescence and phosphorescence, scattering, polarized emission, dyeing and bathochromic shift as well as the correlation with dielectric constants and the extinction coefficient, showing which effects may occur and can be measured by which instruments or used for different applications.

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.

Biofunctionalization and Applications of Polymeric Nanofibers in Tissue Engineering and Regenerative Medicine

The limited ability of most human tissues to regenerate has necessitated the interventions namely autograft and allograft, both of which carry the limitations of its own. An alternative to such interventions could be the capability to regenerate the tissue in vivo.Regeneration of tissue using the innate capacity of the cells to regenerate is studied under the discipline of tissue engineering and regenerative medicine (TERM). Besides the cells and growth-controlling bioactives, scaffolds play the central role in TERM which is analogous to the role performed by extracellular matrix (ECM) in the vivo. Mimicking the structure of ECM at the nanoscale is one of the critical attributes demonstrated by nanofibers. This unique feature and its customizable structure to befit different types of tissues make nanofibers a competent candidate for tissue engineering. This review discusses broad range of natural and synthetic biodegradable polymers employed to construct nanofibers as well as biofunctionalization of polymers to improve cellular interaction and tissue integration. Amongst the diverse ways to fabricate nanofibers, electrospinning has been discussed in detail along with advances in this technique. Review also presents a discourse on application of nanofibers for a range of tissues, namely neural, vascular, cartilage, bone, dermal and cardiac.

Nude and Modified Electrospun Nanofibers, Application to Air Purification

Air transports several pollutants, including particulate matter (PM), which can produce cardiovascular and respiratory diseases. Thus, it is a challenge to control pollutant emissions before releasing them to the environment. Until now, filtration has been the most efficient processes for removing PM. Therefore, the electrospinning procedure has been applied to obtain membranes with a high filtration efficiency and low pressure drop. This review addressed the synthesis of polymers that are used for fabricating high-performance membranes by electrospinning to remove air pollutants. Then, the most influential parameters to produce electrospun membranes are indicated. The main results show that electrospun membranes are an excellent alternative to having air filters due to the versatility of the process, the capacity for controlling the fiber diameter, porosity, high filtration efficiency and low-pressure drop.

Electrospun-Based Membranes as a Key Tool to Prevent Respiratory Infections

The use of electrospun meshes has been proposed as highly efficient protective equipment to prevent respiratory infections. Those infections can result from the activity of micro-organisms and other small dust particles, such as those resulting from air pollution, that impair the respiratory tract, induce cellular damage and compromise breathing capacity. Therefore, electrospun meshes can contribute to promoting air-breathing quality and controlling the spread of such epidemic-disrupting agents due to their intrinsic characteristics, namely, low pore size, and high porosity and surface area. In this review, the mechanisms behind the pathogenesis of several stressors of the respiratory system are covered as well as the strategies adopted to inhibit their action. The main goal is to discuss the performance of antimicrobial electrospun nanofibers by comparing the results already reported in the literature. Further, the main aspects of the certification of filtering systems are highlighted, and the expected technology developments in the industry are also discussed.

Degradable, antibacterial and ultrathin filtrating electrospinning membranes of Ag-MOFs/poly(l-lactide) for air pollution control and medical protection

The widely used melt-blown polypropylene (PP) non-woven fabrics had no antibacterial functions and its large-scale use also increased the burden on the environment owing to its non-degradable property. Herein, silver (I) metal organic frameworks (Ag-2MI) were prepared with AgNO3 and 2-methylimidazole and embedded into degradable poly(l-lactide) (PLLA) to make an ultrathin filtration and antibacterial membrane by electrospinning technology with low loading of Ag-2MI. The morphology, mechanical properties, adsorption performance and antibacterial activities of the prepared films were tested and the results indicated that the addition of Ag-2MI could reduce the diameter of PLLA fibers from 910 nm to 520 nm (1.8 wt% of Ag-2MI), while the tensile strength, elongation at break of the membrane and the contact angle of the films were enhanced. Although the thickness of the prepared membranes was only about one-third of that of commercially available melt-blown cloth, they exhibited better filtering performances than the melt-blown cloth. The fiber membrane with low loading of 1.8 wt% Ag-2MI showed 99.99% inhibition rate against Escherichia coli and Staphylococcus aureus.

ZIF-8/PI Nanofibrous Membranes With High-Temperature Resistance for Highly Efficient PM0.3 Air Filtration and Oil-Water Separation

Air and water pollution poses a serious threat to public health and the ecological environment worldwide. Particulate matter (PM) is the major air pollutant, and its primary sources are processes that require high temperatures, such as fossil fuel combustion and vehicle exhaust. PM_0.3 can penetrate and seriously harm the bronchi of the lungs, but it is difficult to remove PM_0.3 due to its small size. Therefore, PM_0.3 air filters that are highly efficient and resistant to high temperatures must be developed. Polyimide (PI) is an excellent polymer with a high temperature resistance and a good mechanical property. Air filters made from PI nanofibers have a high PM removal efficiency and a low air flow resistance. Herein, zeolitic imidazolate framework-8 (ZIF-8) was used to modify PI nanofibers to fabricate air filters with a high specific surface area and filtration efficiency. Compared with traditional PI membranes, the ZIF-8/PI multifunction nanofiber membranes achieved super-high filtration efficiency for ultrafine particles (PM_0.3, 100%), and the pressure drop was only 63 Pa. The filtration mechanism of performance improvement caused by the introduction of ZIF-8/PI nanofiber membrane is explored. Moreover, the ZIF-8/PI nanofiber membranes exhibited excellent thermal stability (300 C) and efficient water–oil separation ability (99.85%).

Elastic Nanofibrous Membranes for Medical and Personal Protection Applications: Manufacturing, Anti-COVID-19, and Anti-Colistin Resistant Bacteria Evaluation

Herein, in the present work two series of thermoplastic polyurethane (TPU) nanofibers were manufactured using the electrospinning techniques with ZnO and CuO nanoparticles for a potential use as an elastic functional layer in antimicrobial applications. Percentages of 0%, 2 wt%, and 4 wt% of the nanoparticles were used. The morphological characterization of the electrospun TPU and TPU/NPs composites nanofibers were observed by using scanning electron microscopy to show the average fiber diameter and it was in the range of 90-150 nm with a significant impact of the nanoparticle type. Mechanical characterization showed that TPU nanofiber membranes exhibit excellent mechanical properties with ultra-high elastic properties. Elongation at break reached up to 92.5%. The assessment of the developed nanofiber membranes for medical and personal protection applications was done against various colistin resistant bacterial strains and the results showed an increment activity by increasing the metal oxide concentration up to 83% reduction rate by using TPU/ZnO 4% nanofibers against K. pneumoniae strain 10. The bacterial growth was completely eradicated after 8 and 16 h incubation with TPU/ZnO and TPU/CuO nanofibers, respectively. The nanofibers SEM study reveals the adsorption of the bacterial cells on the metal oxides nanofibers surface which led to cell lysis and releasing of their content. Finally, in vitro study against Spike S-protein from SARS-CoV-2 was also evaluated to investigate the potent effectiveness of the proposed nanofibers in the virus deactivation. The results showed that the metal oxide concentration is an effective factor in the antiviral activity due to the observed pattern of increasing the antibacterial and antiviral activity by increasing the metal oxide concentration; however, TPU/ZnO nanofibers showed a potent antiviral activity in relation to TPU/CuO.

Progress of superconducting nanofibers via electrospinning

Superconducting nanofibers have attracted much attention in basic researches and practical applications due to their unique physical properties such as broad phase transition temperature, excellent heat conductivity, and high critical current density, etc. Electrospinning, as a common method to prepare nanofibers, also has many applications for the preparation of superconducting nanofibers. However, a few of the new methods to fabricate superconducting nanofibers via electrospinning still need further investigations. This review firstly introduces several potential electrospinning methods to obtain superconducting nanofibers, then proceeds to summarize the recent progress in the field of electrospun superconducting materials. The preparation process, difficulties and problems, physical properties of the superconducting nanofibers or nanonetworks (such as superconducting transition temperature, critical current density, critical magnetic field strength, fiber morphology, and structure, etc), theoretical analysis of the properties, and the techniques to improve the performance are also reviewed. In addition, some suggestions and prospects for the development and applications of electrospun superconducting materials in the future are discussed.

Electrospinning of Nanofibrous Membrane and Its Applications in Air Filtration: A Review

Air pollution caused by particulate matter and toxic gases is violating individual’s health and safety. Nanofibrous membrane, being a reliable filter medium for particulate matter, has been extensively studied and applied in the field of air purification. Among the different fabrication approaches of nanofibrous membrane, electrospinning is considered as the most favorable and effective due to its advantages of controllable process, high production efficiency, and low cost. The electrospun membranes, made of different materials and unique structures, exhibit good PM2.5 filtration performance and multi-functions, and are used as masks and filters against PM2.5. This review presents a brief overview of electrospinning techniques, different structures of electrospun nanofibrous membranes, unique characteristics and functions of the fabricated membranes, and summarization of the outdoor and indoor applications in PM filtration.

Electrospun Nanofiber Mats for Filtering Applications-Technology, Structure and Materials

Air pollution is one of the biggest health and environmental problems in the world and a huge threat to human health on a global scale. Due to the great impact of respiratory viral infections, chronic obstructive pulmonary disease, lung cancer, asthma, bronchitis, emphysema, lung disease, and heart disease, respiratory allergies are increasing significantly every year. Because of the special properties of electrospun nanofiber mats, e.g., large surface-to-volume ratio and low basis weight, uniform size, and nanoporous structure, nanofiber mats are the preferred choice for use in large-scale air filtration applications. In this review, we summarize the significant studies on electrospun nanofiber mats for filtration applications, present the electrospinning technology, show the structure and mechanism of air filtration. In addition, an overview of current air filtration materials derived from bio- and synthetic polymers and blends is provided. Apart from this, the use of biopolymers in filtration applications is still relatively new and this field is still under-researched. The application areas of air filtration materials are discussed here and future prospects are summarized in conclusion. In order to develop new effective filtration materials, it is necessary to understand the interaction between technology, materials, and filtration mechanisms, and this study was intended to contribute to this effort.

Preparation and Applications of Electrospun Optically Transparent Fibrous Membrane

The optically transparent electrospun fibrous membrane has been widely used in many fields due to its simple operation, flexible design, controllable structure, high specific surface area, high porosity, and unique excellent optical properties. This paper comprehensively summarizes the preparation methods and applications of an electrospun optically transparent fibrous membrane in view of the selection of raw materials and structure modulation during preparation. We start by the factors that affect transmittance among different materials and explain the light transmission mechanism of the fibrous membrane. This paper also provides an overview of the methods to fabricate a transparent nanofibrous membrane based on the electrospinning technology including direct electrospinning, solution treatment after electrospinning, heat treatment after electrospinning, and surface modification after electrospinning. It further summarizes the differences in the processes and mechanisms between different transparent fibrous membranes prepared by different methods. Additionally, we study the utilization of transparent as-spun membranes as flexible functional materials, namely alcohol dipstick, air purification, self-cleaning materials, biomedicine, sensors, energy and optoelectronics, oil-water separation, food packaging, anti-icing coating, and anti-corrosion materials. It demonstrates the high transparency of the nanofibers' effects on the applications as well as upgrades the product performance.

Electrospun ultrafine fibers for advanced face masks

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 essential tools to reduce the spread of SARS-CoV-2 from human to human. However, there are still challenges to prolong the serving life and maintain the filtering performance of the current commercial mask. Filters composed of ultrafine fibers with diameter down to tens of nanometers have the potential to physically block viruses. With adjustable composition and nanostructures, the electrospun ultrafine fiber filter is possible to achieve other necessary functions beyond virus blocking, such as antiviral, transparent, and degradable, making it an important part of fighting the epidemic. In this review, beginning with the basic information of the viruses, we summarize the knowledge of masks and respirators, including the filtering mechanism, structure, classification, and standards. We further present the fabrication method, filtering performance, and reusable potential of electrospun ultrafine fiber-based masks. In the end, we discuss the development directions of ultrafine fibers in protective devices, especially their new functional applications and possible contributions in the prevention and control of the epidemic.

Correlation between the Porosity and Permeability of a Polymer Filter Fabricated via CO2-Assisted Polymer Compression

A porous filter was fabricated by plasticizing polymer fibers with CO2, followed by pressing and adhering; then, its gas permeability, a basic physical property of filters, was measured using N2. The as-obtained filter was well compressed and expected to approximate a sintered porous material. Therefore, the fabricated filter was analyzed by applying the Darcy law, and the correlation between its gas permeability and porosity was clarified. The gas permeability decreased owing to both pore size and porosity reduction upon increasing the degree of compression, which is a feature of the CO2-assisted polymer compression method. In particular, without any contradiction of pore size data previously reported, the gas permeability was clearly determined by the filter porosity and pore size. This study can serve as a guide for designing filters via CO2-assisted polymer compression.

An acid and alkali-resistant triboelectric nanogenerator

With the development of technology, environmental problems have become more and more acute and the use of electronic devices in harsh environments has gradually attracted attention. For example, the friction layer of triboelectric nanogenerators (TENGs) may be contaminated and corroded in harsh environments (such as acidic, alkaline or oily environments), resulting in damage or destruction of the TENGs. In this study, we use electrospinning followed by a sintering process to prepare a super-hydrophobic sintered polyvinyl alcohol-polytetrafluoroethylene (S-PVA-PTFE) composite membrane and general industrial oil-absorbing paper to construct a TENG. The maximum power density of the TENG is 261 mW m-2, it can light up 100 blue LEDs, and can power a variety of small electronic devices. Moreover, after 72 h of soaking the friction layer in a strong acid solution followed by a strong alkali solution, the performance of the TENG has no obvious change. The TENG can work stably in an oily working environment. The TENG provides a novel approach for self-powered sensors that work in harsh environments.

Self-Powered Electrospun Composite Nanofiber Membrane for Highly Efficient Air Filtration

Highly efficient air filtration with low pressure drop is the key to air purification. In this work, a self-powered electrospun nanofiber membrane with an electrostatic adsorption effect was prepared to improve the filtration efficiency of micro/nano particles. The composite membrane was comprised of polyvinyl chloride (PVC) nanofibers and polyamide-6 (PA6) nanofibers. The triboelectric effect between the two adjacent nanofiber membranes generated electrostatic charges under the action of air vibration, by which the electrostatic adsorption with the same pressure drop was enhanced. The electrostatic voltage on the self-powered nanofiber membrane was 257.1 mV when the flow velocity was 0.1 m/s. For sodium chloride (NaCl) aerosol particles with a diameter of 0.3 μm, the removal efficiency of the self-powered composite nanofiber membrane was 98.75% and the pressure drop was 67.5 Pa, which showed a higher quality factor than the membrane without electrostatic charges. This work provides an effective way to improve the filtration performance of air filter membranes.

Predicted Studies of Branched and Cross-Linked Polyurethanes Based on Polyhydroxybutyrate with Polycaprolactone Triol in Soft Segments

The number of cross-links in the non-linear polyurethane structure is the basic factor affecting its properties. Selected properties of aliphatic polyurethanes with soft segments made of different amounts of polycaprolactonetriol, polycaprolactonediol and synthetic, telechelic poly([R,S]-3-hydroxybutyrate) were determined. On the basis of changes in polyurethane properties, the correlation between these properties and the construction of soft segments was found. The structure of polyurethanes, their morphology, hydrophilicity, thermal and mechanical properties were examined. These properties were changed linearly up to 15% content of polycaprolactonetriol in soft segments. A further increase in the amount of triol causes that these properties are mainly determined by the high number of cross-links.

Face Masks in the New COVID-19 Normal: Materials, Testing, and Perspectives

The increasing prevalence of infectious diseases in recent decades has posed a serious threat to public health. Routes of transmission differ, but the respiratory droplet or airborne route has the greatest potential to disrupt social intercourse, while being amenable to prevention by the humble face mask. Different types of masks give different levels of protection to the user. The ongoing COVID-19 pandemic has even resulted in a global shortage of face masks and the raw materials that go into them, driving individuals to self-produce masks from household items. At the same time, research has been accelerated towards improving the quality and performance of face masks, e.g., by introducing properties such as antimicrobial activity and superhydrophobicity. This review will cover mask-wearing from the public health perspective, the technical details of commercial and home-made masks, and recent advances in mask engineering, disinfection, and materials and discuss the sustainability of mask-wearing and mask production into the future.