Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
Korea Institute of Chemical Technology (KRICT) Biobased Chemistry Research Center, Ulsan, 44429, Republic of Korea
Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon, 34113 Republic of Korea
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Due to the coronavirus pandemic and issues related to particulate matter (PM) in the air, the demand for masks has grown exponentially. However, traditional mask filters based on static electricity and nano sieve are all disposable, non-degradable or recyclable, which will cause serious waste problems. In addition, the former will lose its function under humid conditions, while the latter will operate with a significant air pressure drop and relatively fast pore clogging will occur. Here, a biodegradable, moisture-proof, highly breathable, high-performance fiber mask filter has been developed. In short, two biodegradable ultrafine fibers and nanofiber mats are integrated into the Janus membrane filter, and then coated with cationically charged chitosan nanowhiskers. This filter is as efficient as the commercial N95 filter and can remove 98.3% of 2.5 µm PM. Nanofibers physically screen fine particles, and ultrafine fibers provide a low pressure difference of 59 Pa, which is suitable for human breathing. Contrary to the sharp decline in performance of commercial N95 filters when exposed to moisture, the performance loss of this filter is negligible, so it can be used multiple times because the permanent dipole of chitosan adsorbs ultrafine PM (for example, nitrogen). And sulfur oxides). It is important that this filter completely decomposes in the composted soil within 4 weeks.
The current unprecedented coronavirus pandemic (COVID-19) is driving a huge demand for masks. [1] The World Health Organization (WHO) estimates that 89 million medical masks are needed every month this year. [1] Not only do healthcare professionals need high-efficiency N95 masks, but general-purpose masks for all individuals have also become indispensable daily equipment for the prevention of this respiratory infectious disease. [1] In addition, relevant ministries strongly recommend the use of disposable masks every day, [1] this has led to environmental problems related to large amounts of mask waste.
Since particulate matter (PM) is currently the most problematic air pollution problem, masks have become the most effective countermeasure available to individuals. PM is divided into PM2.5 and PM10 according to the particle size (2.5 and 10μm respectively), which seriously affects the natural environment [2] and the quality of human life in various ways. [2] Every year, PM causes 4.2 million deaths and 103.1 million disability adjusted life years. [2] PM2.5 poses a particularly serious threat to health and is officially designated as a group I carcinogen. [2] Therefore, it is timely and important to research and develop an efficient mask filter in terms of air permeability and PM removal. [3]
Generally speaking, traditional fiber filters capture PM in two different ways: through physical sieving based on nanofibers and electrostatic adsorption based on microfibers (Figure 1a). The use of nanofiber-based filters, especially electrospun nanofiber mats, has proven to be an effective strategy to remove PM, which is the result of extensive material availability and controllable product structure. [3] The nanofiber mat can remove particles of the target size, which is caused by the size difference between the particles and the pores. [3] However, nano-scale fibers need to be densely stacked to form extremely small pores, which are harmful to comfortable human breathing due to the associated high pressure difference. In addition, the small holes will inevitably be blocked relatively quickly.
On the other hand, the meltblown ultra-fine fiber mat is electrostatically charged by a high-energy electric field, and very small particles are captured by electrostatic adsorption. [4] As a representative example, the N95 respirator is a particle-filtering face-mask respirator that meets the requirements of the National Institute of Occupational Safety and Health because it can filter at least 95% of airborne particles. This type of filter absorbs ultrafine PM, which is usually composed of anionic substances such as SO42− and NO3−, through strong electrostatic attraction. However, the static charge on the surface of the fiber mat is easily dissipated in a humid environment, such as found in humid human breathing, [4] resulting in a decrease in adsorption capacity.
In order to further improve filtration performance or solve the trade-off between removal efficiency and pressure drop, filters based on nanofibers and microfibers are combined with high-k materials, such as carbon materials, metal organic frameworks, and PTFE nanoparticles. [4] However, the uncertain biological toxicity and charge dissipation of these additives are still unavoidable problems. [4] In particular, these two types of traditional filters are usually non-degradable, so they will eventually be buried in landfills or incinerated after use. Therefore, the development of improved mask filters to solve these waste problems and at the same time capture PM in a satisfactory and powerful manner is an important current need.
In order to solve the above problems, we have manufactured a Janus membrane filter integrated with poly(butylene succinate)-based (PBS-based)[5] microfiber and nanofiber mats. The Janus membrane filter is coated with chitosan nano whiskers (CsWs) [5] (Figure 1b). As we all know, PBS is a representative biodegradable polymer, which can produce ultrafine fiber and nanofiber nonwovens through electrospinning. Nano-scale fibers physically trap PM, while micro-scale nano-fibers reduce pressure drop and act as a CsW framework. Chitosan is a bio-based material that has been proven to have good biological properties, including biocompatibility, biodegradability and relatively low toxicity, [5] which can reduce the anxiety associated with accidental inhalation of users. [5] In addition, chitosan has cationic sites and polar amide groups. [5] Even under humid conditions, it can attract polar ultrafine particles (such as SO42- and NO3-).
Here, we report a biodegradable, high-efficiency, moisture-proof and low-pressure drop mask filter based on readily available biodegradable materials. Due to the combination of physical sieving and electrostatic adsorption, the CsW-coated microfiber/nanofiber integrated filter has a high PM2.5 removal efficiency (up to 98%), and at the same time, the maximum pressure drop on the thickest filter is only It is 59 Pa, suitable for human breathing. Compared to the significant performance degradation exhibited by the N95 commercial filter, this filter exhibits a negligible loss of PM removal efficiency (<1%) even when fully wet, due to the permanent CsW charge. In addition, our filters are completely biodegradable in composted soil within 4 weeks. Compared with other studies with similar concepts, in which the filter part is composed of biodegradable materials, or shows limited performance in potential biopolymer nonwoven applications, [6] this filter directly shows Biodegradability of advanced features (movie S1, supporting information).
As a component of the Janus membrane filter, nanofiber and superfine fiber PBS mats were first prepared. Therefore, 11% and 12% PBS solutions were electrospun to produce nanometer and micrometer fibers, respectively, due to their difference in viscosity. [7] The detailed information of the solution characteristics and optimal electrospinning conditions are listed in Tables S1 and S2, in the supporting information. Since the as-spun fiber still contains residual solvent, an additional water coagulation bath is added to a typical electrospinning device, as shown in Figure 2a. In addition, the water bath can also use the frame to collect the coagulated pure PBS fiber mat, which is different from the solid matrix in the traditional setting (Figure 2b). [7] The average fiber diameters of the microfiber and nanofiber mats are 2.25 and 0.51 µm, respectively, and the average pore diameters are 13.1 and 3.5 µm, respectively (Figure 2c, d). As the 9:1 chloroform/ethanol solvent evaporates quickly after being released from the nozzle, the viscosity difference between 11 and 12 wt% solutions increases rapidly (Figure S1, supporting information). [7] Therefore, a concentration difference of only 1 wt% can cause a significant change in fiber diameter.
Before checking the filter performance (Figure S2, supporting information), in order to compare various filters reasonably, electrospun nonwovens of standard thickness were manufactured, because the thickness is an important factor that affects the pressure difference and filtration efficiency of the filter performance. Since nonwovens are soft and porous, it is difficult to directly determine the thickness of electrospun nonwovens. The thickness of the fabric is generally proportional to the surface density (weight per unit area, basis weight). Therefore, in this study, we use basis weight (gm-2) as an effective measure of thickness. [8] The thickness is controlled by changing the electrospinning time, as shown in Figure 2e. As the spinning time increases from 1 minute to 10 minutes, the thickness of the microfiber mat increases to 0.2, 2.0, 5.2, and 9.1 gm-2, respectively. In the same way, the thickness of the nanofiber mat was increased to 0.2, 1.0, 2.5, and 4.8 gm-2, respectively. Microfiber and nanofiber mats are designated by their thickness values (gm-2) as: M0.2, M2.0, M5.2 and M9.1, and N0.2, N1.0, N2.5 and N4.8.
The air pressure difference (ΔP) of the entire sample is an important indicator of filter performance. [9] Breathing through a filter with a high pressure drop is uncomfortable for the user. Naturally, it is observed that the pressure drop increases as the thickness of the filter increases, as shown in Figure S3, supporting information. The nanofiber mat (N4.8) shows a higher pressure drop than the microfiber (M5.2) mat at a comparable thickness because the nanofiber mat has smaller pores. As the air passes through the filter at a speed between 0.5 and 13.2 ms-1, the pressure drop of the two different types of filters gradually increases from 101 Pa to 102 Pa. The thickness should be optimized to balance the pressure drop and PM removal efficiency; an air velocity of 1.0 ms-1 is reasonable because the time it takes for humans to breathe through the mouth is about 1.3 ms-1. [10] In this regard, the pressure drop of M5.2 and N4.8 is acceptable at an air velocity of 1.0 ms-1 (less than 50 Pa) (Figure S4, supporting information). Please note that the pressure drop of N95 and similar Korean filter standard (KF94) masks is 50 to 70 Pa, respectively. Further CsW processing and micro/nano filter integration can increase air resistance; therefore, in order to provide pressure drop margin, we analyzed N2.5 and M2.0 before analyzing M5.2 and N4.8.
At a target air velocity of 1.0 ms-1, the removal efficiency of PM1.0, PM2.5, and PM10 of PBS microfiber and nanofiber mats was studied without static charge (Figure S5, supporting information). It is observed that the PM removal efficiency generally increases with the increase in thickness and PM size. The removal efficiency of N2.5 is better than M2.0 due to its smaller pores. The removal efficiencies of M2.0 for PM1.0, PM2.5 and PM10 were 55.5%, 64.6% and 78.8%, respectively, while the similar values of N2.5 were 71.9%, 80.1% and 89.6% (Figure 2f). We noticed that the biggest difference in efficiency between M2.0 and N2.5 is PM1.0, which indicates that the physical sieving of the microfiber mesh is effective for micron-level PM, but is not effective for nano-level PM (Figure S6, supporting information). , M2.0 and N2.5 both show a low PM capture ability of less than 90%. In addition, N2.5 may be more susceptible to dust than M2.0, because dust particles can easily block the smaller pores of N2.5. In the absence of static charge, physical sieving is limited in its ability to achieve the required pressure drop and removal efficiency at the same time because of the trade-off relationship between them.
Electrostatic adsorption is the most widely used method to capture PM in an efficient manner. [11] Generally, static charge is forcibly applied to the non-woven filter through a high-energy electric field; however, this static charge is easily dissipated under humid conditions, resulting in the loss of PM capture ability. [4] As a bio-based material for electrostatic filtration, we introduced 200 nm long and 40 nm wide CsW; due to their ammonium groups and polar amide groups, these nanowhiskers contain permanent cationic charges. The available positive charge on the surface of CsW is represented by its zeta potential (ZP); CsW is dispersed in water with a pH of 4.8, and their ZP is found to be +49.8 mV (Figure S7, supporting information).
CsW-coated PBS microfibers (ChMs) and nanofibers (ChNs) were prepared by simple dip coating in 0.2 wt% CsW water dispersion, which is the appropriate concentration to attach the maximum amount of CsWs to the surface of PBS fibers, as shown in the figure Shown in Figure 3a and Figure S8, supporting information. The nitrogen energy dispersive X-ray spectroscopy (EDS) image shows that the surface of the PBS fiber is uniformly coated with CsW particles, which is also evident in the scanning electron microscope (SEM) image (Figure 3b; Figure S9, supporting information). In addition, this This coating method enables charged nanomaterials to finely wrap the fiber surface, thereby maximizing the electrostatic PM removal capability (Figure S10, supporting information).
The PM removal efficiency of ChM and ChN was studied (Figure 3c). M2.0 and N2.5 were coated with CsW to produce ChM2.0 and ChN2.5, respectively. The removal efficiencies of ChM2.0 for PM1.0, PM2.5 and PM10 were 70.1%, 78.8% and 86.3%, respectively, while the similar values of ChN2.5 were 77.0%, 87.7% and 94.6% respectively. The CsW coating greatly improves the removal efficiency of M2.0 and N2.5, and the effect observed for slightly smaller PM is more significant. In particular, chitosan nanowhiskers increased the removal efficiency of M2.0′s PM0.5 and PM1.0 by 15% and 13%, respectively (Figure S11, supporting information). Although M2.0 is difficult to exclude the smaller PM1.0 due to its relatively wide fibril spacing (Figure 2c), ChM2.0 adsorbs PM1.0 because the cations and amides in CsWs pass through ion-ion, coupling Pole-ion interaction, and dipole-dipole interaction with dust. Due to its CsW coating, the PM removal efficiency of ChM2.0 and ChN2.5 is as high as that of thicker M5.2 and N4.8 (Table S3, supporting information).
Interestingly, although the PM removal efficiency is greatly improved, the CsW coating hardly affects the pressure drop. The pressure drop of ChM2.0 and ChN2.5 increased slightly to 15 and 23 Pa, almost half the increase observed for M5.2 and N4.8 (Figure 3d; Table S3, supporting information). Therefore, coating with bio-based materials is a suitable method to meet the performance requirements of two basic filters; that is, PM removal efficiency and air pressure difference, which are mutually exclusive. However, the PM1.0 and PM2.5 removal efficiency of ChM2.0 and ChN2.5 are both lower than 90%; obviously, this performance needs to be improved.
An integrated filtration system composed of multiple membranes with gradually changing fiber diameters and pore sizes can solve the above problems [12]. The integrated air filter has the advantages of two different nanofibers and superfine fiber nets. In this regard, ChM and ChN are simply stacked to produce integrated filters (Int-MNs). For example, Int-MN4.5 is prepared using ChM2.0 and ChN2.5, and its performance is compared with ChN4.8 and ChM5.2 which have similar areal densities (ie thickness). In the PM removal efficiency experiment, the ultrafine fiber side of Int-MN4.5 was exposed in the dusty room because the ultrafine fiber side was more resistant to clogging than the nanofiber side. As shown in Figure 4a, Int-MN4.5 shows better PM removal efficiency and pressure difference than two single-component filters, with a pressure drop of 37 Pa, which is similar to ChM5.2 and much lower than ChM5.2 ChN4. 8. In addition, the PM1.0 removal efficiency of Int-MN4.5 is 91% (Figure 4b). On the other hand, ChM5.2 did not show such a high PM1.0 removal efficiency because its pores are larger than those of Int-MN4.5.
Post time: Nov-03-2021
