Continuous production and properties of mutil-level nanofiber air filters by blow spinning

High-Temperature-Resistant Dual-Scale Ceramic Nanofiber Films toward Improved Air Filtration

Currently, air pollution primarily arises from industrial emissions, coal combustion, and automobile exhaust, posing significant challenges for mitigation. This highlights the urgent need for advanced and efficient filtration materials with low pressure drop and high-temperature resistance. Traditionally, improving filtration property has involved increasing the thickness of the filtration materials, which consequently leads to higher costs. Here, dual-scale mullite nanofiber (MNF) films containing interwoven thick nanofibers (606 nm) and thin nanofibers (186 nm) are prepared using solution blow spinning. The dual-scale structure design enables the films to maintain a low pressure drop while achieving high filtration efficiency. At an airflow velocity of 5.3 cm s-1, the films with an areal density of 3.8 mg cm-2, achieve a filtration efficiency of 98.23% and a pressure drop of 141 Pa for PM0.3. In addition, the MNF films exhibit excellent flexibility and high-temperature resistance, making them have great potential for use in high-temperature flue gas filtration.

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.

Fabrication of Laminated Micro/Nano Filter and Its Application for Inhalable PM Removal

Particulate matter (PM) with a diameter of 0.3 µm is inhalable and brings great threats to human health. Traditional meltblown nonwovens used for air filtration need to be treated by high voltage corona charging, which has the problem of electrostatic dissipation and thus reduces the filtration efficiency. In this work, a kind of composite air-filter with high efficiency and low resistance was fabricated by alternating lamination of ultrathin electronspun nano-layer and melt-blown layer without corona charging treatment. The effects of fiber diameter, pore size, porosity, layer number, and weight on filtration performance were investigated. Meanwhile, the surface hydrophobicity, loading capacity, and storage stability of the composite filter were studied. The results indicate that the filters (18.5 gsm) laminated by 10 layers fiber-webs present excellent filtration efficiency (97.94%), low pressure drop (53.2 Pa), high quality factor (QF 0.073 Pa−1), and high dust holding capacity (9.72 g/m2) for NaCl aerosol particles. Increasing the layers and reducing individual layer weight can significantly improve filtration efficiency and reduce pressure drop of the filter. The filtration efficiency decayed slightly from 97.94% to 96.48% after 80 days storage. The alternate arrangement of ultra-thin nano and melt-blown layers constructed a layer-by-layer interception and collaborative filtering effect in the composite filter, realizing the high filtration efficiency and low resistance without high voltage corona charging. These results provided new insights for the application of nonwoven fabrics in air filtration.

Development and Performance Evaluation of Polytetrafluoroethylene-Membrane-Based Automotive Cabin Air Filter

A high-efficiency, long-life cabin filter unit is required for the effective purification of the air inside a vehicle. However, conventional cabin air filters that utilize electrostatic effects are less efficient and less effective owing to environmental factors. Polytetrafluoroethylene (PTFE) membranes exhibit a high porosity and surface-to-surface dust-removal performance, and maintain a stable pressure drop, indicating their good potential as filter materials. Therefore, in this study, the use of PTFE membranes for the fabrication of automobile filters and the filtration performance of the filters were examined. To this end, first, the properties of PTFE membranes mainly used in HEPA air conditioning filters and those of membranes used as vehicle cabin filters were compared. Next, the thickness, weight, stiffness, pore size, and filtration performance characteristics of filter media fabricated by blending melt-blown (MB) nonwoven, PTFE membranes, and supporting nonwoven into a total filtration layer were compared and analyzed. Lastly, the environmental change durability performance of the automobile cabin filter based on PTFE membrane and the results of the test after the installation of the filter in a vehicle were demonstrated.

Mass Production of Hierarchically Designed Engine-Intake Air Filters by Multinozzle Electroblow Spinning

Particulate matter damages engines of vehicles when blown into the ventilation system. Conventional engine-intake filter is cellulose microfiber board with an average diameter larger than ten microns, which has low removal efficiency of ultrafine particular matter. In this work, we apply ultrafine polyurethane nanofibers (∼122.8 nm) onto pleated cellulose board using scalable multinozzle electroblow spinning technology, which improves filtration efficiency of particulate matter with a diameter of less than 0.3 μm PM_0.3 greatly. The thermoplastic polyurethane 85A nanofiber membranes are transparent, and display superior filtration performance which meets up with the 95% filtration efficiency standard in GB 19083-2010 technical requirements for protective face mask for medical use. The lightweight pleated thermoplastic polyurethane/cellulose composites intercept ∼90% ultrafine PM_0.3 under airflow velocity of 32 L min^-1 and possess great resistance to shock. These hierarchically designed filters follow a mechanical mechanism and can be used in on-road and off-road cars in the long run.

Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic

The coronavirus disease 2019 (COVID-19) pandemic has caused a surge in demand for face masks, with the massive consumption of masks leading to an increase in resource-related and environmental concerns. In this work, we fabricated meltblown polypropylene (mb-PP)-based high-performance planar face masks and investigated the effects of six commonly used disinfection methods and various mask-wearing periods on the reusability of these masks. The results show that, after three cycles of treatment using hot water at 70 °C for 30 min, which is one of the most scalable, user-friendly methods for viral disinfection, the particle filtration efficiency (PFE) of the mask remained almost unchanged. After mask wearing for 24 h and subsequent disinfection using the same treatment procedures, the PFE decreased to 91.3%; the average number of bacterial and fungal colonies was assessed to be 9.2 and 51.6 colony-forming units per gram (CFU∙g- 1), respectively; and coliform and pyogenic bacteria were not detected. Both the PFE and the microbial indicators are well above the standard for reusable masks after disinfection. Schlieren photography was then used to assess the capabilities of used and disinfected masks during use; it showed that the masks exhibit a high performance in suppressing the spread of breathed air.

Improvement of Polytetrafluoroethylene Membrane High-Efficiency Particulate Air Filter Performance with Melt-Blown Media

Polytetrafluoroethylene (PTFE) membrane filters are widely used in low-load application areas, such as industrial cleanrooms, due to their low initial pressure drop. In this study, melt-blown (MB) nonwoven was introduced as a pre-filtration layer at the front end of a high-efficiency particulate air (HEPA) filter to improve the filter performance of the PTFE membrane. Pre-filtration reduces the average particle size, which reaches the PTFE membrane and reduces the dust load on the HEPA filters. A comparative analysis of the HEPA filters by composite MB and PTFE was conducted. Regarding the MB composite on the PTFE, low-weight and high-weight MB composites were effective in increasing dust filtration efficiency, and the dust loading capacity of the PTFE composite with high-weight MB increased by approximately three times that of the PTFE membrane. In addition, the filter was installed on an external air conditioner in an actual use environment and showed a high efficiency of 99.984% without a change in differential pressure after 120 days.

High-Speed Blow Spinning of Neat Graphene Fibrous Materials

Achieving high spinning speed is critical to the production efficiency and viable application of fiber species. Graphene fiber (GF) has recently emerged as a carbonaceous fiber with excellent functionality. However, the extremely low wet spinning speed of GF has limited its applications. We realized high-speed blow spinning of neat GF and fabric by modulating the rheological properties of the graphene oxide (GO) dispersion. We achieved a speed of 556 m min^-1, 2 orders of magnitude faster than that for wet spinning. We chose ultrahigh molecular weight polymers as transient additives to circumvent the intrinsic barrier effect of GO and achieve high spinning dope stretchability at low polymer percentages-down to 25 wt %. Minimizing the polymer additive content ensures the high electrical/thermal conductivity of the blow-spun fiber and fabric. This work provides insight into the unique flow properties of 2D sheets and will promote the efficient production of graphene-based fibrous materials.

The Effects of Electric Field Dynamics on the Quality of Large-Area Nanofibrous Layers

This paper presents technological modifications of an electrostatic spinning device, which significantly increase the thickness homogeneity (i.e., quality) of produced layers by creating auxiliary dynamic electric fields in the vicinity of the spinning and collector electrodes. A moving body was installed above the needleless spinning electrode, which destabilized the standing wave occurring on the free surface of the spinning solution. Furthermore, an endless belt design was used for the collector electrode instead of a roll-to-roll design, which made it possible to substantially increase the surface speed of the substrate and, therefore, the dynamics of the electric field at the place of collection of the fibers being spun. As a result, the coefficient of variation of the area weight of 912 samples cut out from the deposited nanofibrous layer, which was (1000 × 500) mm2 in size and had an average area weight of (17.2 ± 0.8) g/m2, was less than 4.5%. These results were obtained only when the dynamics of both the spinning and collector electrodes were increased at the same time. These modifications resulted in a significant increase in the quality of deposited nanofibrous layers up to the standard required for their use in pharmaceutical applications.