A multi-stage gradient vertical multi-layer fibrous air filtration membrane for filtering PM0.3 microparticles

Abstract

The application discloses a kind of multistage gradient vertical multilayer fiber air filtration membranes for filtering PM0.3 microparticle, comprising (1) primary skeleton layer: it is made by electrospinning using polyacrylonitrile, and it is formed by the interlacing of micron fiber and submicron fiber to form a multi-scale coarse pore structure;(2) high-efficiency interception layer: vertically deposited on the surface of the primary skeleton layer, made by electrospinning using metal salt modified PA56, with a bimodal pore size interception network formed by the interlacing of submicron fiber and nanometer branch fiber.The application separates airflow management and particle capture function independently through spatial layering structure engineering, while achieving PM0.3 ultra-high capture efficiency, it maintains extremely low air resistance and excellent cycle service life.

Description

Technical Field

[0001] This invention relates to the field of filter material production technology, and in particular to a multi-level gradient vertical multilayer fiber air filter membrane for filtering PM0.3 particles. Background Technology

[0002] With the increasing severity of air pollution, particulate matter (PM) suspended in the air poses a profound threat to sustainable ecological development and public health. Among numerous air pollutants, submicron aerosols (such as PM0.3, with an aerodynamic diameter of approximately 0.3 μm) fall precisely within the range of most easily penetrating particle sizes. These fine particles readily bypass the natural defenses of the human respiratory system, penetrating deep into the lungs and ultimately entering the bloodstream, inducing serious health risks. Therefore, developing high-performance air filtration materials capable of efficiently capturing these highly penetrating particles is of paramount importance.

[0003] Currently, commercially available protective equipment (such as N95 respirators) typically relies on electret meltblown nonwoven fabric to intercept PM0.3. However, the diameter of traditional meltblown fibers is generally in the micrometer range, and the pore size inside the material is relatively large. This makes it difficult for a single layer of meltblown material to achieve an initial PM0.3 capture efficiency of over 99%. In existing engineering practices, to further improve the particulate matter capture rate, strategies such as increasing the filter membrane thickness or stacking multiple layers of filter material are commonly adopted. However, this simple structural stacking inevitably leads to a sharp increase in airflow resistance (i.e., pressure drop), which manifests as increased breathing resistance and a significant decrease in wearing comfort in practical applications. It also significantly increases material consumption and production costs.

[0004] In recent years, electrospinning technology has attracted widespread attention due to its ability to prepare micro / nano-scale fiber membranes. The micro / nano-fiber networks formed by electrospinning possess ultra-high specific surface area and tunable pore size, making them an ideal choice for constructing high-performance air filtration materials. In the field of electrospinning, polyacrylonitrile (PAN) is often used as a reliable framework for particle interception due to its excellent filamentation properties, robust mechanical properties, and electrostatic attraction resulting from its strong dipole moment. However, these traditional petroleum-based polymers have a significant environmental footprint during production and waste disposal, which is inconsistent with the trend of green environmental protection. Although the introduction of environmentally friendly materials such as bio-based polyamide 56 (PA56) can impart excellent biodegradability to filter materials while maintaining good spinnability, how to organically combine the advantages of different polymers through reasonable structural design and completely overcome the bottleneck of the mutual exclusion between "high efficiency" and "low resistance" in air filtration remains a pressing technical challenge in the field of electrospinned filter materials. While some studies have attempted to alleviate this contradiction through multi-layer gradient design, at the ultrafine nanofiber scale, the dense network still easily generates significant airflow obstruction.

[0005] Therefore, how to further optimize pore size distribution at the nanoscale through structural engineering and induce fibers to form complex spatial topologies to promote gas slip effect, thereby significantly reducing air resistance and improving cycle life while ensuring ultra-high PM0.3 interception rate, is the core challenge currently faced in the research and development of high-performance green air filter materials. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-level gradient vertical multilayer fiber air filter membrane for filtering PM0.3 particles. Through spatial layering structure engineering, airflow management and particle capture functions are independently separated, achieving ultra-high PM0.3 capture efficiency while maintaining extremely low air resistance and excellent cycle life.

[0007] The technical solution adopted by this invention to solve its technical problem is: A multi-level gradient vertical multilayer fiber air filter membrane for filtering PM0.3 particles is prepared by the following method: (1) Preparation of primary skeleton layer spinning solution: Dissolve polyacrylonitrile in an organic solvent and mix evenly to obtain the first precursor solution; (2) Preparation of high-efficiency intercepting layer spinning solution: Dissolve PA56 and metal salt in organic solvent and mix evenly to obtain second precursor solution; (3) Constructing the primary framework layer: The first precursor solution is electrospun and deposited on the receiving device to form the primary framework layer; (4) Constructing a high-efficiency interception layer: Continue to electrospin the second precursor solution sequentially on the primary skeleton layer, and generate a secondary jet by utilizing the fluid jet instability induced by the metal salt. A high-efficiency interception layer rich in nano-branching is vertically deposited on the surface of the primary skeleton layer to obtain a multi-level gradient vertical multilayer fiber air filter membrane.

[0008] This invention prepares multi-level gradient vertical multilayer fibers by continuously and integrally forming them on the same receiving device through a sequential electrospinning process.

[0009] The high-efficiency interception layer is formed by introducing metal salt ions into the PA56 precursor solution to improve the solution conductivity and surface charge density. In the electrospinning process, the fluid jet instability is used to trigger secondary jetting, thereby inducing the formation of a nano-branch topology with two-dimensional nano-network or multi-level bifurcation.

[0010] This invention first constructs a robust main framework composed of micron and submicron fibers (0.65–1.31 μm in diameter) to provide ample airflow channels. Subsequently, utilizing fluid jet instability, a bimodal high-efficiency interception layer composed of submicron fibers (approximately 130 nm) and nanofibers (approximately 28 nm) is deposited on the main framework. This multi-scale vertical layered design achieves functional separation of airflow management and particle trapping, broadening the pore size distribution while ensuring high fluid permeability. Tests show that this multilayer fiber membrane achieves a PM0.3 filtration efficiency exceeding 99%, with a pressure drop of only 88.3 Pa and a quality factor of 0.055 Pa. -1 This invention successfully breaks the constraint between high efficiency and low resistance in traditional air filter materials, and has broad application prospects in the field of air purification.

[0011] The air filter fiber membrane prepared by this invention has excellent filtration efficiency and low initial pressure drop, as well as good cyclic filtration stability. The overall filter membrane has an initial filtration efficiency of ≥99% for PM0.3 particles, and an initial pressure drop of ≤88.3 Pa when fluid passes through. After 20 consecutive filtration cycles, the filtration efficiency for PM0.3 remains above 99.78%, and the pressure drop is ≤118.3 Pa.

[0012] The first precursor solution consists of: 1.6-3 g of polyacrylonitrile and 7-8.4 g of N,N-dimethylformamide.

[0013] The second precursor solution consists of: PA56 1.5-3.5 g, formic acid 6.5-8.5 g, and metal salt 0.1-0.3 g.

[0014] The metal salt is a soluble metal salt selected from KCl, CaCl2, MgCl2 and NaCl.

[0015] The parameters for electrospinning in step (3) are: spinning voltage 15-25kV, spinning rate 0.5-2.5mL / h, spinning distance 10-25cm, spinning temperature 25-35℃, and spinning humidity 30-50%.

[0016] The parameters for electrospinning in step (4) are: spinning voltage 15-25kV, spinning rate 0.5-2.5mL / h, spinning distance 10-25cm, spinning temperature 25-35℃, and spinning humidity 30-50%.

[0017] The primary framework layer has a multi-scale coarse-porous structure formed by the interweaving of micron and submicron fibers.

[0018] The high-efficiency interception layer has a bimodal aperture interception network composed of interwoven submicron fibers and nanofibers. In the high-efficiency interception layer, the submicron fibers have a diameter of approximately 125-135 nm, and the nanofibers have a diameter of approximately 25-350 nm.

[0019] The fiber diameter in the primary skeleton layer ranges from 0.65 μm to 1.31 μm; the fiber diameter in the high-efficiency interception layer is 25-30 nm.

[0020] The multi-level gradient vertical multilayer fiber air filter membrane has an initial filtration efficiency of ≥99% for PM0.3 particles, and an initial pressure drop of ≤88.3 Pa when fluid passes through it.

[0021] The beneficial effects of this invention are: 1. This invention constructs a vertical multilayer structure through sequential electrospinning, spatially isolating the functions of "airflow management" and "particle trapping". The bottom layer of coarse PAN framework provides a wide gas passage, broadening the overall pore size distribution; the top layer of PA56 ultrafine nano-branched network is responsible for precise interception. The two work together to achieve a balance between high permeability and ultra-high interception rate.

[0022] 2. Significantly reduced pressure drop by leveraging the slip effect: An ultrafine two-dimensional nanobranched network with a diameter of only about 28 nm was successfully induced by introducing metal salts. This microstructure significantly increases the specific surface area of ​​the filter membrane and effectively triggers the slip effect of gas molecules on the fiber surface, promoting particle collision deposition while minimizing airflow resistance.

[0023] 2. This invention achieves a filtration efficiency exceeding 99% for the most easily penetrating PM0.3 particles, while maintaining an airflow pressure drop of only 88.3 Pa, surpassing traditional meltblown and conventional single-component electrospun membranes. Furthermore, it exhibits excellent durability and cycle life: the layered structure endows the material with outstanding cycle resistance. After 20 consecutive filtration cycles, the PM0.3 capture efficiency remains consistently above 99.78%, with the pressure drop only slightly increasing to 118.3 Pa, demonstrating its value for industrial applications and commercial protection. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the primary skeleton PAN layer prepared according to the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the highly efficient intercepting PA56 layer prepared by adding metal salts according to the present invention.

[0026] Figure 3 This is a scanning electron microscope image of PA56 layers without the addition of metal salts prepared according to the present invention.

[0027] Figure 4 This is the infrared spectrum of the primary framework PAN layer prepared by this invention.

[0028] Figure 5 This is the infrared spectrum of the highly efficient intercepting PA56 layer prepared by adding metal salts according to the present invention.

[0029] Figure 6 This is a graph showing the PM0.3 filtration efficiency and initial pressure drop of the high-efficiency intercepting PA56 layer prepared in this invention with and without the addition of metal salts.

[0030] Figure 7 This is a graph showing the PM0.3 filtration efficiency and initial pressure drop of the multi-level gradient vertical multilayer fiber air filter membrane prepared by this invention at different spinning times.

[0031] Figure 8 The graph shows the PM0.3 filtration efficiency and initial pressure drop of the multi-level gradient vertical multilayer fiber air filter membrane prepared by this invention in a 20-cycle test. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0033] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available or commonly used in the field. The methods described in the following embodiments are conventional methods in the field, unless otherwise specified.

[0034] N,N-dimethylformamide and formic acid (98% analytical grade) were supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. Polyacrylonitrile, PA56, and metal salts were purchased from Shanghai Maclean Biochemical Co., Ltd.

[0035] Example 1: A spinning solution was prepared by weighing 1.6 g of polyacrylonitrile and adding it to 8.4 g of N,N-dimethylformamide, and stirring thoroughly to obtain a homogeneous PAN layer spinning solution. 1.5 g of PA56 and 0.1 g of KCl were weighed and added to 8.5 g of formic acid, and stirred thoroughly to obtain a homogeneous PA6 layer spinning solution. A multi-level gradient vertical multilayer fiber air filter membrane was prepared by sequential electrospinning. First, the PAN layer spinning solution was transferred to a 10 mL syringe for electrospinning. After spinning for 20 min, the spinning solution was replaced with PA6 layer, and spinning continued for another 15 min, ultimately obtaining a multi-level gradient vertical multilayer fiber air filter membrane. The spinning process was as follows: spinning voltage 15 kV, spinning rate 0.5 mL / h, spinning distance 10 cm, temperature 25℃, and humidity 30%.

[0036] Example 2: A spinning solution was prepared by weighing 3g of polyacrylonitrile and adding it to 7g of N,N-dimethylformamide, and stirring thoroughly to obtain a homogeneous PAN layer spinning solution. 2g of PA56 and 0.15g of CaCl2 were weighed and added to 8g of formic acid, and stirred thoroughly to obtain a homogeneous PA6 layer spinning solution. A multi-level gradient vertical multilayer fiber air filter membrane was prepared by sequential electrospinning. First, the PAN layer spinning solution was transferred to a 10 mL syringe for electrospinning. After spinning for 15 min, the spinning solution was replaced with PA6 layer, and spinning continued for 20 min, finally obtaining a multi-level gradient vertical multilayer fiber air filter membrane. The spinning process was as follows: spinning voltage 20kV, spinning rate 1mL / h, spinning distance 15cm, temperature 30℃, and humidity 40%.

[0037] Example 3: A spinning solution was prepared by weighing 2g of polyacrylonitrile and adding it to 8g of N,N-dimethylformamide, and stirring thoroughly to obtain a homogeneous PAN layer spinning solution. 3.5g of PA56 and 0.3g of NaCl were weighed and added to 6.5g of formic acid, and stirred thoroughly to obtain a homogeneous PA6 layer spinning solution. A multi-level gradient vertical multilayer fiber air filter membrane was prepared by sequential electrospinning. First, the PAN layer spinning solution was transferred to a 10 mL syringe for electrospinning. After spinning for 25 min, the spinning solution was replaced with PA6 layer, and spinning continued for another 10 min, finally obtaining a multi-level gradient vertical multilayer fiber air filter membrane. The spinning process was as follows: spinning voltage 25kV, spinning rate 2mL / h, spinning distance 25cm, temperature 35℃, and humidity 50%.

[0038] Figure 1 This is a scanning electron microscope image of the primary framework PAN layer prepared in Example 1 of the present invention. It can be seen that the PAN nanofibers are of uniform thickness and can be used to construct a good primary framework layer for air filtration.

[0039] Figure 2 This is a scanning electron microscope image of the high-efficiency intercepting PA56 layer prepared by adding metal salt in Example 1 of the present invention. It can be seen that after adding metal salt, the fiber surface has a network of nanofibers rich in nano-branchings, which can effectively intercept particles.

[0040] Figure 3 The image shows a scanning electron microscope image of a PA56 layer without the addition of metal salt prepared according to the present invention. It can be seen that no nano-branched nanofibers appear on the surface of the fiber, indicating that the addition of metal salt is beneficial to the formation of the branched network fiber.

[0041] Figure 4 This is the infrared spectrum of the primary skeleton PAN layer prepared in Example 1 of the present invention. It can be seen that the fiber layer was successfully prepared and is mainly composed of PAN.

[0042] Figure 5 The image shows the infrared spectrum of the high-efficiency intercepting PA56 layer prepared by adding metal salt in Example 1 of this invention. It can be seen that the infrared spectrum after adding metal salt is consistent with the infrared spectrum of pure PA56 (without metal salt), indicating that the addition of metal salt has no effect on the structure of PA56.

[0043] Figure 6 This is a graph showing the PM0.3 filtration efficiency and initial pressure drop of the PA56 layer prepared in Example 1 of this invention with and without the addition of metal salts. The graph illustrates that the addition of metal salts is beneficial to improving the PM0.3 filtration effect.

[0044] Figure 7 This is a graph showing the PM0.3 filtration efficiency and initial pressure drop of a multi-level gradient vertical multilayer fiber air filter membrane prepared in Example 1 of the present invention at different spinning times. The filter membrane has a PM0.3 particle filtration efficiency of over 99% while the airflow pressure drop is only 88.3 Pa, indicating that it has excellent filtration performance.

[0045] Figure 8 The graph showing the PM0.3 filtration efficiency and initial pressure drop of a multi-level gradient vertical multilayer fiber air filter membrane prepared in Example 1 after 20 cycles demonstrates its excellent durability and cycle life. The layered structure endows the material with outstanding cycle resistance. After 20 consecutive filtration cycles, the PM0.3 capture efficiency remained consistently above 99.78%, and the pressure drop only increased slightly to 118.3 Pa.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A multi-level gradient vertical multilayer fiber air filter membrane for filtering PM0.3 particles, characterized in that, It is prepared by the following method: (1) Preparation of primary skeleton layer spinning solution: Dissolve polyacrylonitrile in an organic solvent and mix evenly to obtain the first precursor solution; (2) Preparation of high-efficiency intercepting layer spinning solution: Dissolve PA56 and metal salt in organic solvent and mix evenly to obtain second precursor solution; (3) Constructing the primary framework layer: The first precursor solution is electrospun and deposited on the receiving device to form the primary framework layer; (4) Constructing a high-efficiency interception layer: Continue to electrospin the second precursor solution sequentially on the primary skeleton layer, and generate a secondary jet by utilizing the fluid jet instability induced by the metal salt. A high-efficiency interception layer rich in nano-branching is vertically deposited on the surface of the primary skeleton layer to obtain a multi-level gradient vertical multilayer fiber air filter membrane.

2. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, characterized in that, The first precursor solution consists of: 1.6-3 g of polyacrylonitrile and 7-8.4 g of N,N-dimethylformamide.

3. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, characterized in that, The second precursor solution consists of: PA56 1.5-3.5g, formic acid 6.5-8.5g, and metal salt 0.1-0.3g.

4. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The metal salt is a soluble metal salt selected from KCl, CaCl2, MgCl2 and NaCl.

5. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The parameters for electrospinning in step (3) are: spinning voltage 15-25kV, spinning rate 0.5-2.5mL / h, spinning distance 10-25cm, spinning temperature 25-35℃, and spinning humidity 30-50%.

6. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The parameters for electrospinning in step (4) are: spinning voltage 15-25kV, spinning rate 0.5-2.5mL / h, spinning distance 10-25cm, spinning temperature 25-35℃, and spinning humidity 30-50%.

7. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The primary framework layer has a multi-scale coarse porous structure formed by interwoven micron and submicron fibers.

8. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The high-efficiency interception layer has a bimodal aperture interception network formed by interwoven submicron and nano-branched fibers.

9. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The fiber diameter in the primary skeleton layer ranges from 0.65 μm to 1.31 μm; the fiber diameter in the high-efficiency interception layer is 25-30 nm.

10. The multi-level gradient vertical multilayer fiber air filter membrane according to claim 1, 2, or 3, characterized in that, The multi-level gradient vertical multilayer fiber air filter membrane has an initial filtration efficiency of ≥99% for PM0.3 particles, and an initial pressure drop of ≤88.3 Pa when fluid passes through it.

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