Air Filtration Materials Research Articles

Efficient, Breathable, and Compostable Multilayer Air Filter Material Prepared from Plant-Derived Biopolymers.

State-of-art face masks and respirators are fabricated as single-use devices using microfibrous polypropylene fabrics, which are challenging to be collected and recycled at a community scale. Compostable face masks and respirators can offer a viable alternative to reducing their environmental impact. In this work, we have developed a compostable air filter produced by electrospinning a plant-derived protein, zein, on a craft paper-based substrate. The electrospun material is tailored to be humidity tolerant and mechanically durable by crosslinking zein with citric acid. The electrospun material demonstrated a high particle filtration efficiency (PFE) of 91.15% and a high pressure drop (PD) of 191.2 Pa using an aerosol particle diameter of 75 ± 2 nm at a face velocity of 10 cm/s. We deployed a pleated structure to reduce the PD or improve the breathability of the electrospun material without compromising the PFE over short- and long-duration tests. Over a 1 h salt loading test, the PD of a single-layer pleated filter increased from 28.9 to 39.1 Pa, while that of the flat sample increased from 169.3 to 327 Pa. The stacking of pleated layers enhanced the PFE while retaining a low PD; a two-layer stack with a pleat width of 5 mm offers a PFE of 95.4 ± 0.34% and a low PD of 75.2 ± 6.1 Pa.

Preparation of CS@BAC composite aerogel with excellent flame-retardant performance, good filtration for PM2.5 and strong adsorption for formaldehyde

At present, it is still a challenge to prepare an air filtration material with high filter, low pressure drop and good environmental protection. In this study, a porous material with good filtration capacity for PM2.5 and excellent adsorption for harmful gases was developed. Chitosan (CS) was used as the frame matrix, and bamboo activated carbon (BAC) as the functional particles and methyl trimethoxylsilane (MTMS) as the hydrophobic modifier were introduced to the CS system, followed by freeze-dry to achieve the aerogel sheet with high porosity, flame retardant and hydrophobicity. The resulted CS@BAC composite aerogel showed excellent removal ability for both PM2.5 and formaldehyde in the filtration rate of 94.2% for PM2.5 and the formaldehyde adsorption amount of 61.6 mg/g, which was benefited from the dual removal system, the 3D network structure of the CS based aerogel formed during freeze-dry and the high surface area of BAC itself. In addition, the aerogel displayed outstanding flame-retardant property and its total heat release rate (THR) and maximum heat release rate (PHRR) were only 5.30 kJ/g and 28.2 W/g, respectively, the loss on ignition (LOI) value reaching 33.8%. At the same time, after the modification of MTMS, the aerogel realized the transformation from hydrophilic to hydrophobic, which could be used repeatedly.

Investigation of Fiber-Based Bag Filter Coated with Metal Oxides for Dust Adsorption

The production of cement increases every year, which leads to the emission of dust/gas/ particulate matter. The emission of unfiltered dust would create a significant environmental impact. Hence, it is the responsibility of industries to control the emission of dust. Air filters and electrostatic precipitators (ESP) play a significant role in controlling pollutants. Synthetic filter media which are dangerous to our environment are widely used in most industries. The disposal of synthetic filters is an arduous task as the biodegradability of synthetic materials is poor. Hence, it is essential to develop an eco-friendly air filter material. In this paper, a new type of bag filter was designed by using natural sisal fiber as filtering media. The biodegradability of sisal fiber is better than the synthetic polyester media and also sisal fiber is less expensive. The natural fibers were coated with zinc oxide and iron oxide nanoparticles to improve the dust adsorption rate. Various tests were conducted as per standards to validate the performance of the filler media. The results were impressive. Hence, the proposed sisal fiber-based filter media can be used in cement industries for dust adsorption to minimize the environmental impact.

Biodegradable hydro-charging polylactic acid melt-blown nonwovens with efficient PM0.3 removal

Polylactic acid (PLA) melt-blown nonwovens are attractive candidates for existing non-degradable air filtration materials due to their unique balance between durability in use and biodegradability at their end-of-life. However, owing to the charge instability caused by conventional corona electret treatment, the filtration performance of PLA melt-blown nonwovens is insufficient to be utilized in practical applications. Herein, we presented an effective hydro-charging treatment strategy to prepare biodegradable PLA melt-blown nonwovens with efficient PM0.3 removal. In this process, a large amount of unstable charge was generated by friction between pressurized deionized water and PLA melt-blown microfibers under the influence of negative pressure suction. Then, the unstable charge on microfibers was transformed into stable charge by hot air drying. Through the adjustment of water pressure, conveyer belt speed and drying temperature, we optimized the hydro-charging treatment process. The resulting hydro-charging PLA melt-blown nonwovens (HC-PLA) shown improved PM0.3 removal efficiency (94.63%), a lower pressure drop (11.74 Pa) and a reasonable quality factor (0.249 Pa−1). After experiencing a hydro-charging treatment, PLA melt-blown nonwovens appear to carry more stable and plentiful charges, according to thesurface potential and thermally stimulated discharge (TSD). In addition, plausible charge generation and stable storage mechanisms were proposed based on the optimal performance, which provide promising benefits for the development of long-term and highly efficient filtration materials.

Promoting Electrospun Lignin/PEO Nanofiber for High-Performance CO Filtration

ABSTRACT In recent years, the development of air filter materials that are cheap, abundantly available in nature, environmentally friendly, and easy to process has attracted the attention of researchers. The current study produced lignin/PEO nanofiber using electrospinning method with the concentration of lignin from 5, 10 to 15 w/v%. The viscosity of PEO solution was 1790 mPas and decreased with the presence of lignin (5, 10 to 15 w/v%) into 345 mPas, 448 mPas, and 621 mPas, while the conductivity of lignin/PEO solution increased with the increasing lignin content. The thermal properties of lignin/PEO nanofiber were studied using DSC and TGA. SEM images showed that the diameter of the nanofiber of lignin/PEO decreased with increasing the concentration of lignin. FTIR analysis showed that there was a wide hydroxyl-stretching adsorption band of PEO shifted to a lower wavenumber region upon blending with lignin, indicating that a vast number of hydrogen bonds were formed between the lignin and PEO. The lignin nanofibers produced have porous fibers and are capable to filter CO gas. The maximum nanofiber was able to filter 88.89% efficiency of CO gas.

Fabrication and Application of Halloysite Nanotube-Embedded Photocatalytic Nanofibers with Antibacterial Properties.

With decreasing indoor air quality, increased time spent at indoors, and especially with the COVID-19 pandemic, the development of new materials for bacteria and viruses has become even more important. Less material consumption due to the electrospinning process, the easy availability/affordability of the halloysite nanotube (HNT), and the antibacterial effect of both TiO2 and ZnO nanoparticles make the study even more interesting. HNTs have attracted research attention in recent years due to their low cost, high mechanical strength, natural and environmentally friendly structure, and non-toxicity to human health and ecosystem. In this study, HNT-embedded composite nanofiber filters were fabricated as filter materials using the electrospinning method. Photocatalysts (TiO2 and ZnO) were incorporated into the composite nanofibers by the electrospraying method. The results showed that the combination of both HNT/TiO2 and HNT/ZnO additives was successfully integrated into the filter structure. The effect of embedding the HNT and spraying photocatalysts enables the fabrication of composite filters with lower pressure drop, high filtration efficiency, improved mechanical properties, and high antibacterial properties against Escherichia coli, making the nanofibers suitable and promising for face masks and air filter materials.

Improvement of Aerosol Filtering Performance of PLLA/PAN Composite Fiber with Gradient Structure.

Since commercial non-woven air filtering materials have unstable filtering efficiency and poor moisture permeability for the abundant condensed aerosol particles in the highly humid atmospheric environment, the PLLA/PAN composite fiber material with a hydrophobic and hydrophilic gradient structure is designed and prepared by using electrode sputtering electro spinning technology. By characterizing and testing the filtrating effect of SEM, XRD, FTIR, wettability, mechanical property, N2 adsorption isotherm, and BET surface area, NaCl aerosol of PLLA fiber, PAN fiber, and PLLA/PAN composite fiber membranes, the study found that the electrode sputtering electrospinning is fine, the fiber mesh is dense, and fiber distribution is uniform when the diameter of the PAN fiber is 140-300 nm, and the PLLA fiber is 700-850 nm. In this case, PLLA/PAN composite fiber materials gather the hydrophobicity of PLLA fiber and the hydrophilicity of PAN fiber; its electrostatic effect is stable, its physical capturing performance is excellent, it can realize the step filtration of gas-solid liquid multiphase flow to avoid the rapid increase of air resistance in a high-humidity environment, and the filtrating efficiency η of NaCl aerosol particles with 0.3 μm reaches 99.98%, and the quality factor QF 0.0968 Pa-1. The manufacturing of PLLA/PAN composite fiber material provides a new method for designing and developing high-performance air filtration materials and a new technical means for the large-scale production of high-performance, high-stability, and low-cost polylactic acid nanofiber composites.

Binary Polyamide-Imide Fibrous Superelastic Aerogels for Fire-Retardant and High-Temperature Air Filtration.

Fibrous air filtration materials are highly desirable for particle removal from high-temperature emission sources. However, the existing commercial filter materials suffer from either low filtration efficiency or high pressure drop, due to the difficulty in achieving small fiber diameter and high porosity simultaneously. Herein, we report a facile strategy to fabricate mechanical robust fibrous aerogels by using dual-scale sized PAI/BMI filaments and fibers, which are derived from wet spinning and electrospinning technologies, respectively. The creativity of this design is that PAI/BMI filaments can serve as the enhancing skeleton and PAI/BMI fibers can assemble into high-porosity interconnected networks, enabling the improvement of both mechanical property and air filtration performance. The resultant dual-scale sized PAI/PBMI fibrous aerogels show a compressive stress of 8.36 MPa, a high filtration efficiency of 90.78% (particle diameter of 2.5 μm); for particle diameter over 5 μm, they have 99.99% ultra-high filtration efficiency, a low pressure drop of 20 Pa, and high QF of 0.12 Pa-1, as well as thermostable and fire-retardant properties (thermal decomposition temperature up to 342.7 °C). The successive fabrication of this material is of great significance for the govern of industrial dust.

Chitosan/PVA Nanofibrous Membranes as Air Filter Material

Nanofiber membranes made of polymer materials are being extensively investigated and developed as air filter materials. This research aims to make and characterize the nanofiber membranes as filter materials capable of filtering gaseous pollutants from cigarette smoke. The electrospinning method manufactured the chitosan (CS)/PVA blend nanofiber membranes with CS/PVA ratios of (0/100, 20/80, 30/70, and 40/60 w/w) using low molecular weight (LMw) PVA and the ratios of (0/100, 10/90, 20/80, and 30/70 w/w) with high Mw (HMw) PVA. The CS concentration increased the CS-PVA solution‘s electrical conductivity and decreased the membrane‘s average fiber diameter and tensile properties. The filtration test on neat PVA and CS/LMw PVA (20/80) membranes set on the metallic substrate with a 0.08 mm hole size was conducted by varying membrane thickness (20, 35, and 45 µm). The filtration efficiency increased with the membrane thickness because membrane pores tend to be smaller, indicating that reducing the fiber diameter by adding CS increases pore size. The filtration test on CS/HMw PVA (20/80) membranes with 45 µm thickness on different substrate¢s hole sizes of (0.08, 1.19, and 1.41 mm) showed that the larger the hole size, the lower the filtration efficiency. By similar CS/PVA ratio, membrane thickness, and substrate size hole, the CS/HMw PVA's filtration efficiency (87.15%) is higher than CS/LMw PVA (85.79%). However, the CS/LMw PVA membrane showed higher tensile strength, low stiffness, and more economical air filtration material than CS/HMw PVA.

Superelastic and multifunctional fibroin aerogels from multiscale silk micro-nanofibrils exfoliated via deep eutectic solvent

Superelastic silk fibroin (SF)-based aerogels can be used as multifunctional substrates, exhibiting a promising prospect in air filtration, thermal insulation, and biomedical materials. However, fabrication of the superelastic pure SF aerogels without adding synthetic polymers remains challenging. Here, the SF micro-nano fibrils (SMNFs) that preserved mesostructures are extracted from SF fibers as building blocks of aerogels by a controllable deep eutectic solvent liquid exfoliation technique. SMNFs can assemble into multiscale fibril networks during the freeze-inducing process, resulting in all-natural SMNF aerogels (SMNFAs) with hierarchical cellular architectures after lyophilization. Benefiting from these structural features, the SMNFAs demonstrate desirable properties including ultra-low density (as low as 4.71 mg/cm3) and superelasticity (over 85 % stress retention after 100 compression cycles at 60 % strain). Furthermore, the potential applications of superelastic SMNFAs in air purification and thermal insulation are investigated to exhibit their functionality, mechanical elasticity, and structural stability. This work provides a reliable approach for the fabrication of highly elastic SF aerogels and endows application prospects in air purification and thermal insulation opportunities.

Double-Grafted PET Fiber Material to Remove Airborne Bacteria with High Efficiency.

Air pollution caused by bacteria and viruses has posed a serious threat to public health. Commercial air purifiers based on dense fibrous filters can remove particulate matter, including airborne pathogens, but do not kill them efficiently. Here, we developed a double-grafted antibacterial fiber material for the high-efficiency capture and inactivation of airborne microorganisms. Tetracarboxyl phthalocyanine zinc, a photosensitizer, was first grafted onto the polyester (PET) fiber, followed by coating with chitosan on the surface of PET fiber to make a double-grafted fiber material. Under the irradiation of light with a specific wavelength (680 nm), double-grafted fiber materials killed up to 99.99% of Gram-positive bacteria and Gram-negative bacteria and had a significant antibacterial effect on drug-resistant bacteria. The double-grafted PET fiber showed broad-spectrum antibacterial activities and was capable to inactivate drug-resistant bacteria. Notably, in filtration experiments for airborne bacteria, this double-grafted PET fiber demonstrated a high bacteria capture efficiency (95.68%) better than the untreated PET fiber (64.87%). Besides, the double-grafted PET fiber was capable of efficiently killing airborne bacteria. This work provides a new idea for the development of air filtration materials that can efficiently kill airborne pathogen and has good biosafety.

Hierarchical fiber with granular-convex structure for highly efficient PM2.5 capture

Air pollution has seriously affected human health and the atmospheric environment. Preparation of fiber membrane with hierarchical structure provides an advanced method for high-performance air filtration. However, indistinctive secondary structure and complicated preparation present constantly in the formation of fiber with hierarchical structure, inevitably limited in the application of air filtration. In this work, a typical granular-convex structure was created in the surface of thermal-crosslinked sodium phytate/polyvinyl alcohol (T-PANa/PVA) fiber via green preparation. Unique secondary structure endowed fiber with efficient physical interception and polar adsorption, which exhibited excellent the removal of air pollutants (removal of PM2.5 high than 99.9% while low air resistance of 36.5 Pa). In addition, due to the exist of crosslinked network, T-PANa/PVA fiber membrane expresses water-resistant and mechanical properties. This work provides a positive strategy to fabricate hierarchical fiber membranes via green preparation for high-performance air filtration, which is expected to substitute traditional air filtration materials and adapt to the sustainable development of future.

Fabrication of fully degradable branched poly (lactic acid) nanofiber membranes for high‐efficiency filter paper materials

AbstractAir pollution caused by particulate matter (PM) poses an imminent threat to the global environment and public health. However, balancing the removal efficiency and pressure drop of most filter materials is difficult. Moreover, filter materials are non‐degradable and non‐recyclable, causing serious harm to the environment. Herein, a strategy to create fully degradable branched poly (lactic acid) (PLA) nanofibers based on electrospinning by adjusting the spinning solution properties was reported and branched PLA nanofibers were applied as nanofiber filter paper for air filtration materials. When the PLA and tetrabutylammonium chloride concentrations were 8 and 5 wt%, respectively, PLA nanofibers with branched structures were obtained. The obtained nanofibers possessed a small pore size (0.70 μm), high porosity (92.3%), appropriate mechanical properties, resulting in high PM0.3 removal efficiency (99.95%), low air resistance (79.67 Pa), and promising long‐term PM2.5 purification. Notably, branched T‐PLA‐5 nanofibers exhibited excellent filtration performance when applied to cellulose wood pulp paper. The filtration efficiency of the nanofiber filter paper remained stable above 85% for PM0.3 (32 L min−1) after 5000 backflushings. Thus, the preparation of such nanomaterials may provide new insights into the design and development of high‐performance degradable filtration materials for various applications.

Simulation of particle interception of seamless knitted composite filter material based on the discrete phase model

In this research, a three-dimensional geometric model of knitted cylindrical air filter material is constructed. Due to the isotropy of the three-dimensional structure, a certain cyclic structure is selected for the flow calculation domain in this research. According to the principle of air filter particle testing, the pressure drop of the filter material and the particle collection efficiency are simulated and calculated. Applying ANSYS finite element analysis software, based on Fluent's fluid Lagrangian discrete model, the geometric model is meshed and the particle materials and boundary conditions are set. Air is the continuous phase, and its velocity is set at 0.27 m/s. The jet particles are used as discrete phases to track the particle trajectory in real time. Based on the above conditions, the simulation of the capture efficiency of weft-knitted tubular air filter material for different particle sizes can not only predict and evaluate the filtering efficiency of the knitted tubular air filter material, but also provide a theoretical reference for fluid simulation of the knitted filter material.

Dual-bionic, fluffy, and flame resistant polyamide-imide ultrafine fibers for high-temperature air filtration

Particulate matter (PM) pollution has been acknowledged as a serious health hazard globally, calling for thermo-stable air filtration materials to remove particles from high-temperature emission sources. However, the commercial filter media suffer from large fiber diameter and compact assembling architecture, resulting in the difficulty in achieving a balance between filtration efficiency and pressure drop. Herein, a dual-bionic strategy is proposed to prepare high-performance polyamide-imide (PAI) fibrous assemblies for the application in high-temperature air filtration. Inspired by the fact that Masson Pine shows attractive capability of particle retention, PAI fibers with biomimetic groove structure are constructed via asynchronous phase separation principle, meanwhile showing fluffy assembling architecture via humidity-induced electrospinning technology. Furthermore, the stiff cellulose networks within loofah sponges, which contributes to robust mechanical property, inspired us to construct semi-interpenetrating polymer network (semi-IPN) structure within PAI fibers. Benefitting from the hierarchical structure and intrinsic flame resistant property, the resulting PAI ultrafine fibers present distinct characteristics of high specific surface area (25.97 m2/g) and high porosity (90.44 %), contributing to a high PM2.5 filtration efficiency (98 % at severe pollution), a low pressure drop (only 46.35 Pa), and satisfying long serving time at 220℃. The successful fabrication of PAI filter media brings new insights for designing next-generation thermo-stable air filters.

Single-Side Superhydrophobicity in Si3N4-Doped and SiO2-Treated Polypropylene Nonwoven Webs with Antibacterial Activity

Meltblown (MB) nonwovens as air filter materials have played an important role in protecting people from microbe infection in the COVID-19 pandemic. As the pandemic enters the third year in this current global event, it becomes more and more beneficial to develop more functional MB nonwovens with special surface selectivity as well as antibacterial activities. In this article, an antibacterial polypropylene MB nonwoven doped with nano silicon nitride (Si3N4), one of ceramic materials, was developed. With the introduction of Si3N4, both the average diameter of the fibers and the pore diameter and porosity of the nonwovens can be tailored. Moreover, the nonwovens having a single-side moisture transportation, which would be more comfortable in use for respirators or masks, was designed by imparting a hydrophobicity gradient through the single-side superhydrophobic finishing of reactive organic/inorganic silicon coprecipitation in situ. After a nano/micro structural SiO2 precipitation on one side of the fabric surfaces, the contact angles were up to 161.7° from 141.0° originally. The nonwovens were evaluated on antibacterial activity, the result of which indicated that they had a high antibacterial activity when the dosage of Si3N4 was 0.6 wt%. The bacteriostatic rate against E. coli and S. aureus was up to over 96%. Due to the nontoxicity and excellent antibacterial activity of Si3N4, this MB nonwovens are promising as a high-efficiency air filter material, particularly during the pandemic.

Antibacterial Activity of AgNO3 Incorporated Polyacrylonitrile/Polyvinylidene Fluoride (PAN/PVDF) Electrospun Nanofibrous Membranes and Their Air Permeability Properties

Polyacrylonitrile (PAN)/polyvinylidene fluoride (PVDF) nanofibers incorporated with AgNO3 in various concentrations were produced as membranes and investigated for their antibacterial properties and air permeability. To characterize the AgNO3 incorporated PAN/PVDF nanofibers Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier-Transform Infrared (FT-IR) Spectroscopy, the Brunauer–Emmett–Teller (BET) method and air permeability analyses were carried out. Based on the SEM results, the prepared nanofibers had a smooth and beadless surface. For 20 wt% PVDF concentration, AgNO3 addition up to 20 wt% did not disrupt the fiber structure. The antibacterial activity of the AgNO3 incorporated PAN/PVDF nanofibrous membranes were investigated against bacterial strains of E. coli and S. aureus. For each AgNO3 concentration from 5 wt% to 20 wt%, the PAN/PVDF nanofibrous membranes showed antibacterial activity in correspondence with the measured inhibition zones. However, the 10 wt% AgNO3 concentration was found to be the optimum concentration providing desirable nanofiber morphology and antibacterial properties. Air permeability findings of the nanofibrous membranes did not show a significant difference for the tested AgNO3 concentrations. In summary, the results indicated that AgNO3 incorporated PAN/PVDF nanofibrous membranes are appropriate for use as air filtration materials.

Polymersomes as virus-surrogate particles for evaluating the performance of air filter materials

The development of antivirus air filter materials has attracted considerable interests due to the pandemic of coronavirus disease 2019 (COVID-19). Filtration efficiency (FE) of these materials against virus is critical in the assessment of their use in disease prevention. Due to the high cost and biosafety laboratory required for conducting research using actual virus samples, surrogates for virus are commonly used in the filtration test. Here, we explore the employment of polymersomes (polymeric vesicles) as a new type of surrogate. The polymersomes are hollow shell nanoparticles with amphiphilic bilayer membranes, which can be fabricated in nanosized, and possess similar size and structural features to virus. The performance of commercial KN95 mask and surgical mask with micro-sized fibers, and electrospun polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) nanofibers were chosen to be evaluated. The filtration tests against fluorescent-labeled virus-surrogate particles (VSPs), i.e. polymersomes, allowed the determination of the FE of the multilayered filter materials in a layer-specific manner. The results suggested the importance of hydrophobicity in designing the nanofibrous filter materials. The employment of VSPs in filtration performance evaluation allows a cost-effective way to estimate the FE against virus, providing guidance on future development of air filter materials.

Cellulose nanofibril/PVA/bamboo activated charcoal aerogel sheet with excellent capture for PM2.5 and thermal stability

It is still a challenge to prepare air filtration materials with high filtration efficiency and good thermal stability from renewable materials. In this study, cellulose nanofibril (CNF), poly (vinyl alcohol) (PVA), and bamboo activated charcoal (BAC) were used to build an air filtration system with double filtration by mixing and freeze-drying. The resulting CNF/PVA/BAC aerogel sheet reached a filtration efficiency of 99.69% for PM2.5 due to its double filtration from the network structure of CNF and electrostatic adsorption of BAC. The composite material also showed high thermal stability with its filtration efficiency over 95% even after exposure to 200 °C. After modification, the hydrophobic CNF/PVA/BAC filtration sheet could be reused for over 5 times by water washing whereby the filtration efficiency remained above 95%. The environmentally friendliness excellent filtration efficiency and simplistic fabrication make the aerogel sheet a potential material choice to cope with the severe air pollution today.

Synthesis and characterization of air filter media made from cellulosic ramie fiber (Boehmeria nivea)

At present, air filter materials are predominately made of synthetic polymers that are derived from petroleum. The production of these synthetic polymers negatively impacts the environment as well as entailing complex equipment and high production costs. Thus, air filter media made from natural fiber would have a significant benefit. The research done in this study supports the use of an alternative air filter media that is easily and cheaply made from the ramie plant (Boehmeria nivea), which grows the world over. This paper explains the method used to produce fiber from the ramie plant that can be used as an air filter media, based on the T205 standards of the Technical Association of the Pulp and Paper Industry (TAPPI). The research shows that ramie fiber can be successfully used as an air filter media as it meets all of the performance standard test requirements of air filter media; it has a tensile strength of 0.36±0.03 kN/m and can withstand degrading up to the temperatures of 280 °C. Ramie fiber also has an air filter media performance of PM2.5, and a 46% efficiency rating at a pressure drop of 167 Pa.