PA6 / PEO micro / nanofiber air filter membrane with curved shape and its preparation method

Abstract

This invention discloses a method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape, comprising: (1) weighing a certain mass of PA6 particles and PEO powder, dissolving them in a formic acid solution with a mass fraction of 88% to obtain a mixed solution; (2) stirring the mixed solution to obtain a PA6 / PEO spinning solution; (3) forming a fiber membrane under room temperature drying conditions using a gas jet spinning machine; (4) drying overnight at 60°C to remove residual solvent; (5) placing it in an oven for heat treatment; (6) at room temperature, placing the heat-treated fiber membrane in a container and adding deionized water to immerse the fiber membrane; (7) heating the container in a water bath and repeating the water bath treatment twice; (8) immediately removing the sample after the treatment and performing vacuum drying. This invention can simultaneously and efficiently filter oily and saline ultrafine particles. By optimizing the structural characteristics of the fiber membrane, it solves the technical problem in the prior art of effectively filtering both fine oily and saline particles.

Description

Technical Field

[0001] This invention belongs to the field of functional fiber filter materials technology, and particularly relates to a PA6 / PEO micro / nanofiber air filter membrane with a curved shape and its preparation method. Background Technology

[0002] Today, with rapid industrialization and urbanization, environmental problems caused by climate change and pollution from human activities have become a global focus, and air quality has become one of the most pressing issues. Fine particulate matter (PM2.5), viruses, bacteria, and other harmful substances in the air pose a serious threat to human health and the ecological environment. According to data released by the World Health Organization (WHO), more than 7 million people die prematurely each year globally due to air pollution, and in recent years, the annual average concentration in most Chinese cities has exceeded national limits. Therefore, air quality has become a global concern, making the development of highly efficient and low-resistance air filtration materials particularly important.

[0003] Existing filtration technologies mainly include nanofiber filtration and electrostatic filtration. Nanofiber membranes, with their fine fiber structure, not only offer higher particle interception efficiency than traditional mechanical filtration, but also achieve lower filtration resistance and energy consumption due to the high porosity between the fibers. Compared to electrostatic filtration, nanofiber materials have stronger chemical and physical stability and reduced sensitivity to humidity and temperature changes, thus extending their service life and reducing maintenance costs. Currently, the following are patented nanofiber membrane technologies related to air filtration and purification:

[0004] CN114452719A discloses a method for preparing an air filter electrospun nanofiber membrane, belonging to the field of fiber membrane preparation technology. The method involves in-situ loading of silica nanoparticles onto the surface of modified polyacrylonitrile nanofibers using a sol-gel method, followed by surface modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane to impart hydrophobic and oleophobic properties. Compared to previously reported self-cleaning filter membranes, this patented method requires less equipment and achieves excellent filtration performance, self-cleaning properties, flexibility, and corrosion resistance at a low cost. It is suitable for air filtration and purification in complex environments, offering advantages such as effective filtration, easy self-cleaning, corrosion resistance, low cost, and ease of use.

[0005] CN 119261345A discloses a high-efficiency, low-resistance electrospun multilayer filter material for mask filter elements and its preparation method. The method includes the following steps: First, ODA and PMDA raw materials are dissolved in a solvent to prepare a first PAA solution; then, the solution is electrospinned to form a first beaded PAA nanofiber membrane. Next, ZIF-8 raw material is dissolved in a solvent and mixed with ODA and PMDA to form a second PAA / ZIF-8 solution. The second PAA / ZIF-8 nanofiber layers are then stacked on top of the first layer using electrospinning technology, and after thermal imidization treatment, a multilayer filter material with a ZIF-8 modified PI / beaded PI / ZIF-8 modified PI structure is successfully prepared. The preparation process of this invention is simple and efficient, and the resulting beaded multilayer filter material not only has excellent filtration efficiency and low resistance, but also shows great application potential in the field of air purification.

[0006] CN105536352A discloses a high-efficiency, low-resistance interlaced nanofiber composite material and its preparation method. This high-efficiency, low-resistance nanofiber composite material exhibits an interlaced structure of fibers with nanoporous surfaces. The composite material achieves an air filtration efficiency of over 99.99% for sodium chloride aerosol particles with a median diameter of 260 nm, and a filtration resistance of less than 140 Pa. The preparation method involves using a fully automated transverse roller receiving device during electrospinning to interlacedly combine nanofibers of approximately 100–300 nm with nanoporous fibers of 1.2–1.8 μm in size, thus preparing a high-efficiency, low-resistance composite nanofiber filter material in one step. This preparation method is simple, has high yield, and low cost. The prepared interlaced composite filter material exhibits high filtration efficiency and low filtration resistance for fine particulate matter, showing broad application prospects in personal protective equipment and air purification.

[0007] As can be seen from the above patented technologies, current filtration technologies for atmospheric particulate matter mainly focus on nanofiber membranes prepared by electrospinning. These technologies improve the filtration and interception effect and efficiency by changing the arrangement and orientation of nanofibers in the fiber membrane and by adding other components to form a beaded structure on the fibers, thereby reducing the pore size and increasing the roughness. This achieves the goal of high efficiency, low resistance and excellent filtration efficiency, but some shortcomings still exist.

[0008] Atmospheric particulate matter mainly consists of inorganic, organic, and water-soluble components. Inorganic components primarily include oxides of elements such as silicon, aluminum, calcium, phosphorus, and potassium, as well as trace amounts of metallic elements such as mercury, lead, and cadmium. Organic components include aliphatic hydrocarbons, aromatic hydrocarbons, and polycyclic aromatic hydrocarbons (PAHs), some of which are carcinogenic.12 In addition, water-soluble components mainly include sulfates, nitrates, and chlorides. It is evident that the variety, complex chemical composition, and different particle sizes of atmospheric particulate matter pose significant challenges to adsorption and filtration materials. In particular, oily particulate matter from oil fumes, oil mist, asphalt fumes, coke oven fumes, and diesel engine exhaust, as well as saline particulate matter such as sulfates, nitrates, and ammonium salts, pose a particularly serious threat to human health due to their small size, high concentration, and complex chemical composition. Furthermore, the chemical effects of oily particles are mainly manifested in hydrophobic interactions and intermolecular affinity, lacking a specific shape and structure. Oily particles also typically exhibit strong adhesion, easily forming an oil film after being intercepted and retained within the fibrous membrane. Prolonged accumulation of this oil film can clog the nanofiber membrane, affecting its filtration efficiency. While beaded structures further reduce pore size and porosity, they can actually exacerbate the clogging problem for oily particles. Salty particles generally possess high surface tension and polarity, along with a more pronounced crystalline structure. Once inside the fibrous membrane and in contact with the fibers, they cannot be confined within the pores. Even in nanofiber membranes with high porosity, low pore size, and relatively high roughness, it is difficult to achieve effective interception and blocking of these salty particles.

[0009] It is evident that current membrane materials on the market cannot simultaneously and efficiently filter both oily and saline particles. Therefore, how to optimize the structural characteristics of membranes while maintaining filtration efficiency, enabling fiber membrane materials to effectively filter both fine oily and saline particles, while also achieving high filtration efficiency, good air permeability, and extended service life, has become a pressing challenge for engineers in the field of functional fiber filter materials. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a PA6 / PEO micro / nanofiber air filter membrane with a curved shape, which enables the fiber membrane material to effectively filter both fine oily and saline particles, while also achieving high filtration efficiency and good air permeability, and a method for preparing the same.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape, characterized by comprising the following steps:

[0012] I. Preparation of spinning solution:

[0013] (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution;

[0014] (2) Stir the mixed solution magnetically at room temperature for 6-8 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution.

[0015] II. Preparation of Fiber Membranes:

[0016] (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine;

[0017] (4) Adjust the output air pressure of the air compressor, connect the spinning needle to the air flow nozzle, and under certain pushing speed and receiving distance conditions, the PA6 / PEO spinning solution is squeezed out by the needle and mixed with the high pressure air flow. After being stretched and refined, it is sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions.

[0018] (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent;

[0019] III. Heat treatment and deionized water etching:

[0020] (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 100-120℃ and the heating time to 0.3-0.6h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature.

[0021] (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:40-1:60, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside.

[0022] (8) Place the container in a water bath at 60-80℃ and heat it in the water bath for 0.8-1.2 hours. Repeat the water bath treatment twice.

[0023] (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

[0024] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (1), the molecular weight of PEO powder is 100,000-1,000,000.

[0025] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, the concentration of PA6 in the PA6 / PEO spinning solution obtained in step (2) is 5-7%, and the concentration of PEO is 0.5-1.5%.

[0026] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (4), the air compressor output pressure is 0.04-0.08MPa, the propulsion speed is 1.5-2.5ml / h, the receiving distance is 28-32cm, and the inner diameter of the spinning needle is 0.33mm.

[0027] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (6), the heat treatment heating temperature is 110°C and the heating time is set to 0.5h.

[0028] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (7), the mass ratio of fiber membrane to deionized water is 1:50.

[0029] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (8), the water bath temperature is set to 70°C and the water bath time is 1 hour.

[0030] In the above-mentioned method for preparing PA6 / PEO micro / nanofiber air filter membrane with a curved shape, in step (4), the air compressor output pressure is 0.06MPa, the propulsion speed is 2ml / h, and the receiving distance is 30cm.

[0031] A PA6 / PEO micro / nanofiber air filter membrane with a curved shape is prepared by the above-described method.

[0032] The aforementioned PA6 / PEO micro / nanofiber air filter membrane with a curved shape has an average fiber diameter of 212-4110 nm and a porosity of 69.02%-93.09%.

[0033] The advantages of the PA6 / PEO micro / nanofiber air filter membrane with a curved morphology and its preparation method are as follows: Due to the hydrophilicity of PEO and the low concentration of formic acid at the gas-liquid interface, more PEO is attracted to aggregate. This also means that although the solution is homogeneous overall after complete dissolution into the spinning solution, the solute is not completely uniformly distributed in some areas. Therefore, during the heat treatment stage, the non-uniform distribution of PEO on the surface of the micro / nanofibers results in a highly curved surface morphology after heating. Simultaneously, during the water bath treatment stage, the heated and dissolved PEO is more likely to aggregate, and its water-soluble nature allows for the effective removal of most of the surface PEO after multiple water bath treatments, resulting in a rough surface morphology. This method optimizes the structural characteristics of the fiber membrane (fiber curvature and fiber surface roughness), significantly improving the capture capacity for both oily and salty ultrafine particles. It solves the technical problem of existing micro / nanofiber membranes' inability to effectively filter both fine oily and salty particles. Attached Figure Description

[0034] Figure 1 This is a product image of the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to the present invention.

[0035] Figure 2 SEM image of the air filter membrane prepared by adding medium molecular weight PEO in Example 2;

[0036] Figure 3 This is a diagram showing the diameter distribution of fibers in the air filter membrane prepared by adding medium molecular weight PEO in Example 2.

[0037] Figure 4 Comparison of fiber morphology and diameter distribution before and after heat treatment and deionized water etching treatment of the air filter membrane with added low molecular weight PEO under the preparation conditions of Example 2;

[0038] Figure 5 Comparison of fiber morphology and diameter distribution before and after heat treatment and deionized water etching treatment of the air filter membrane with medium molecular weight PEO added under the preparation conditions of Example 2;

[0039] Figure 6 Comparison of fiber morphology and diameter distribution before and after heat treatment and deionized water etching treatment of the air filter membrane with added high molecular weight PEO under the preparation conditions of Example 2;

[0040] Figure 7 Multiple light scattering diagrams of solute dissolution processes in PEO spinning solutions of different molecular weights;

[0041] Figure 8 Multiple light scattering diagrams of PEO spinning solutions of different molecular weights after complete solute dissolution;

[0042] Figure 9 This is a schematic diagram showing the changes in fiber morphology of the air filter membrane of the present invention after heat treatment and deionized water etching.

[0043] Figure 10 A comparison of fiber morphology changes and schematic diagrams before and after heat treatment and deionized water etching in air filter membranes.

[0044] Figure 11 Pore ​​size distribution of fiber membranes after spinning of 1% PEO and 6% PA6 with different molecular weights;

[0045] Figure 12 The infrared spectra of the fiber membrane before and after treatment under the conditions of Example 2 are shown.

[0046] Figure 13 The porosity test diagrams for air filter membranes with different molecular weight PEO added under the preparation conditions of Example 2 are shown.

[0047] Figure 14 This is a high-magnification SEM image of the fibers in the air filter membrane prepared in Example 2 of the present invention;

[0048] Figure 15 This is a schematic diagram illustrating the proportion of fine pores on the surface of a fiber membrane using the ImageJ tool.

[0049] Figure 16 This is a schematic diagram illustrating the process by which the air filter membrane of the present invention intercepts fine oily and salty particles.

[0050] Figure 17 The graph shows the filtration efficiency of the air filter membranes before and after treatment for oily and salty particulate matter. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] A method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape includes the following steps:

[0053] I. Preparation of spinning solution:

[0054] (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution;

[0055] (2) Stir the mixed solution magnetically at room temperature for 6-8 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution.

[0056] II. Preparation of Fiber Membranes:

[0057] (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine;

[0058] (4) Adjust the output air pressure of the air compressor, connect the spinning needle to the air flow nozzle, and under certain pushing speed and receiving distance conditions, the PA6 / PEO spinning solution is squeezed out by the needle and mixed with the high pressure air flow. After being stretched and refined, it is sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions.

[0059] (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent;

[0060] III. Heat treatment and deionized water etching:

[0061] (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 100-120℃ and the heating time to 0.3-0.6h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature.

[0062] (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:40-1:60, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside.

[0063] (8) Place the container in a water bath at 60-80℃ and heat it in the water bath for 0.8-1.2 hours. Repeat the water bath treatment twice.

[0064] (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

[0065] The materials and equipment used in the product of this invention are as follows: polycaprolactam (PA6, general grade, granules, dielectric constant 0.65, Shanghai Maclean Biochemical Technology Co., Ltd., CAS: 25038-54-4), selected based on its good fiber-forming properties and mechanical properties; polyethylene oxide (PEO, Mv~600000, Mv~100000, Mv~1000000, powder, Shanghai Maclean Biochemical Technology Co., Ltd., CAS: 68441-17-8), because its different molecular weights have a significant impact on the morphology and porosity of the fiber membrane; and formic acid (analytical grade AR88%, Shanghai Aladdin Biochemical Technology Co., Ltd., CAS: 64-18-6), used to dissolve PA6 and PEO, because it has good solubility for both materials. The air compressor uses a silent oil-free air compressor (Zhejiang Shengyuan Air Compressor Manufacturing Co., Ltd.) to provide air pressure, and the spinning machine uses a JNS-SBS-01 microfluidic nano gas jet spinning machine (Janus New Materials Co., Ltd.) to control the spray flow of the spinning solution.

[0066] like Figure 1 As shown, where, Figure 1 (a) is a physical image of the prepared PA6 / PEO micro / nanofiber air filter membrane with a curved shape. Figure 1 (b) is a physical image of a multilayer filter membrane. The membrane thickness can be manufactured or stacked according to actual filtration application products, application environment, or filtration requirements.

[0067] Compared to traditional electrospinning processes for preparing micro / nanofiber membranes, this invention employs an air-jet spinning process, utilizing a high-speed airflow to stretch and solidify polymer liquid fibers, forming a continuous fiber membrane. Because electrospinning involves high-speed stretching, solvent evaporation, and solidification of the spinning solution under an electric field, ultimately depositing on a receiving plate to form polymer fibers, the electric field is unstable from the needle to the receiving roller. This leads to uneven distribution of functional additives in the spinning solution during fiber formation. This invention, using an air-jet spinning process, ensures the uniformity of the polymer PEO within the fibers, improving fiber quality and providing assurance for subsequent heat treatment and water bath treatment. Existing micro / nanofiber membrane materials prepared by electrospinning technology often struggle to form highly flexible and porous structures conducive to filtration due to the characteristics of the spinning solution itself, as well as the traction force and receiving roller configuration, thus making it difficult to guarantee efficient filtration of two types of particulate matter. Furthermore, electrospinning technology has low output and slow production speed, and requires high-quality raw materials as spinning solution and a high-voltage electric field, resulting in relatively high costs. In contrast, air-jet spinning does not require a high-voltage electric field, and only needs to accurately control the airflow and temperature to achieve stable production. The equipment cost is relatively low, and it can achieve the industrialization goal of high output, continuous production, and open production.

[0068] Regarding the use of additives in spinning solutions, PEG200 increases the viscosity of the solution, which helps buffer the contact between PEO particles and water, preventing excessively rapid local dissolution and clumping, thereby promoting more uniform dissolution. Both PEG200 and PEO are polyether materials; PEG200 can act as a co-solvent to increase the solubility of PEO, promoting its dissolution process in water. Simultaneously, PEG200 can reduce the surface tension of water, promoting the wetting of PEO particles and thus accelerating dissolution. Through its interaction with the PEO molecular chains, PEG200 can accelerate the chain-breaking process of PEO, thereby increasing the dissolution rate.

[0069] Regarding the process parameter range and liquor ratio range, 0.06MPa was chosen because excessively high pressure can lead to instability in the spinning solution jet, making it difficult to collect micro / nanofibers. Insufficient pressure can result in incomplete solvent evaporation in the spinning solution and weak stretching effect of the airflow. The propulsion pump speed was chosen at 2ml / h because excessively high speeds would cause incomplete solvent evaporation in the spinning solution; using the highest possible speed ensures rapid production of large quantities of fiber membranes. The receiving distance was chosen at 30cm because too close a distance would result in incomplete evaporation of the spinning solution, while too far a distance would lead to discontinuous spinning solution jets. A larger distance ensures that the macromolecular chains in the spinning solution are fully stretched and oriented, resulting in finer and more uniform fibers. The water treatment temperature was chosen at 70℃ because excessively high temperatures can cause the fiber membrane to shrink and damage its original mechanical properties. The glass transition temperature of PEO in the fiber is 65℃, at which temperature the macromolecular chain segments begin to move freely. The reason for choosing a 1:50 ratio of fiber membrane to water is that heating is difficult when there is too much water, while a membrane-to-water ratio that is too low will result in insufficient dissolution and removal of PEO. The reason for choosing a heat treatment temperature of 110℃ is that if the temperature is too low, the fiber bending will be insufficient, and if the temperature is too high, the fiber membrane will age too quickly due to heat.

[0070] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0071] Example 1:

[0072] A method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape includes the following steps:

[0073] I. Preparation of spinning solution:

[0074] (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution; wherein, the molecular weight of PEO powder is 100,000.

[0075] (2) Stir the mixed solution magnetically at room temperature for 6 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution; in the PA6 / PEO spinning solution, the concentration of PA6 is 5% and the concentration of PEO is 0.5%;

[0076] II. Preparation of Fiber Membranes:

[0077] (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine;

[0078] (4) Adjust the air compressor output pressure to 0.04MPa, connect the spinning needle to the airflow nozzle, set the feed speed to 1.5ml / h, the receiving distance to 28cm, and the inner diameter of the spinning needle to 0.33mm. After the PA6 / PEO spinning solution is extruded through the needle, it is mixed with the high-pressure airflow, stretched and refined, and then sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions.

[0079] (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent;

[0080] III. Heat treatment and deionized water etching:

[0081] (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 100°C and the heating time to 0.3h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature.

[0082] (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:40, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside.

[0083] (8) Place the container in an 80°C water bath and heat it in the water bath for 0.8 hours. Repeat the water bath treatment twice.

[0084] (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

[0085] In the PA6 / PEO micro / nanofiber air filter membrane with a curved shape prepared in this embodiment, the average diameter of the fibers is 212 nm and the porosity is 69.02%.

[0086] Example 2:

[0087] A method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape includes the following steps:

[0088] I. Preparation of spinning solution:

[0089] (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution; wherein, the molecular weight of PEO powder is 600,000.

[0090] (2) Stir the mixed solution magnetically at room temperature for 7 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution; in the PA6 / PEO spinning solution, the concentration of PA6 is 6% and the concentration of PEO is 1%.

[0091] II. Preparation of Fiber Membranes:

[0092] (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine;

[0093] (4) Adjust the output air pressure of the air compressor to 0.06MPa, connect the spinning needle to the airflow nozzle, set the feed speed to 2ml / h, the receiving distance to 30cm, and the inner diameter of the spinning needle to 0.33mm. After the PA6 / PEO spinning solution is extruded through the needle, it is mixed with the high-pressure airflow, stretched and refined, and then sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions.

[0094] (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent;

[0095] III. Heat treatment and deionized water etching:

[0096] (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 110°C and the heating time to 0.5h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature.

[0097] (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:50, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside.

[0098] (8) Place the container in a 70°C water bath and heat it in the water bath for 1 hour. Repeat the water bath treatment twice.

[0099] (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

[0100] In the PA6 / PEO micro / nanofiber air filter membrane with a curved shape prepared in this embodiment, the average diameter of the fibers is 673 nm and the porosity is 72.13%.

[0101] Example 3:

[0102] A method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape includes the following steps:

[0103] I. Preparation of spinning solution:

[0104] (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution; wherein, the molecular weight of PEO powder is 1,000,000.

[0105] (2) Stir the mixed solution magnetically at room temperature for 8 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution; in the PA6 / PEO spinning solution, the concentration of PA6 is 7% and the concentration of PEO is 1.5%;

[0106] II. Preparation of Fiber Membranes:

[0107] (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine;

[0108] (4) Adjust the air compressor output pressure to 0.08MPa, connect the spinning needle to the airflow nozzle, set the feed speed to 2.5ml / h, the receiving distance to 32cm, and the inner diameter of the spinning needle to 0.33mm. After the PA6 / PEO spinning solution is extruded through the needle, it is mixed with the high-pressure airflow, stretched and refined, and then sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions.

[0109] (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent;

[0110] III. Heat treatment and deionized water etching:

[0111] (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 120°C and the heating time to 0.6h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature.

[0112] (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:60, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside.

[0113] (8) Place the container in a 60°C water bath and heat it in the water bath for 1.2 hours. Repeat the water bath treatment twice.

[0114] (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

[0115] In the PA6 / PEO micro / nanofiber air filter membrane with a curved shape prepared in this embodiment, the fiber diameter is 4110 nm and the porosity is 93.09%.

[0116] The performance test results of the PA6 / PEO micro / nanofiber air filter membrane with a curved shape of the present invention are as follows:

[0117] 1. Regarding fiber morphology (diameter, curvature):

[0118] like Figure 2 , 3 As shown, PA6 can be well dissolved in formic acid at a certain concentration. However, excessively high concentrations can lead to thicker fiber diameters and excessively high viscosity in the spinning solution, which can clog the spinning needles and prevent spinning. Low molecular weight PEO can dissolve well in formic acid, but excessively high concentrations slow down the dissolution process. The addition of PEO also increases the viscosity of the solution, hindering smooth spinning. Medium molecular weight PEO can dissolve well in formic acid. The reason for not using high concentrations is similar to the previous methods; low concentrations of medium molecular weight PEO have limited coating effect on the fibers, and the effect after dissolution is not obvious. High molecular weight PEO can dissolve well in formic acid. To ensure a single variable is considered for comparison, and because high concentrations of PEO can thicken the fiber diameter, thus improving mechanical properties, the fiber state obtained from the air filter membrane with a medium amount of PEO in Example 2 is considered optimal.

[0119] like Figure 4 As shown, where, Figure 4 (a) and (b) are the fiber morphology and diameter distribution of the air filter membrane with added low molecular weight PEO before heat treatment and deionized water etching under the preparation conditions of Example 2. Figure 4(c) and (d) are the fiber morphology and diameter distribution of the air filter membrane with added low molecular weight PEO after heat treatment and deionized water etching under the preparation conditions of Example 2.

[0120] like Figure 5 As shown, where, Figure 5 (a) and (b) are the fiber morphology and diameter distribution of the air filter membrane with medium molecular weight PEO added under the preparation conditions of Example 2 before heat treatment and deionized water etching. Figure 5 (c) and (d) are the fiber morphology and diameter distribution of the air filter membrane with medium molecular weight PEO added under the preparation conditions of Example 2 after heat treatment and deionized water etching.

[0121] like Figure 6 As shown, where, Figure 6 (a) and (b) are the fiber morphology and diameter distribution of the air filter membrane with added high molecular weight PEO before heat treatment and deionized water etching under the preparation conditions of Example 2. Figure 6 (c) and (d) are the fiber morphology and diameter distribution of the air filter membrane with added high molecular weight PEO after heat treatment and deionized water etching under the preparation conditions of Example 2.

[0122] from Figure 4-6 The comparison shows that, from the fiber morphology diagram and diameter distribution diagram, it is clear that, at the same PEO concentration, firstly, compared with the three untreated PEO air filter membranes with different molecular weights of PEO, as the molecular weight of PEO increases, the diameter of the nanofibers in the fiber membrane gradually increases, and the fiber diameter distribution range becomes narrower; secondly, regardless of the molecular weight of PEO added, the fiber diameter of the air filter membrane after heat treatment and deionized water etching is significantly smaller than that of the untreated membrane.

[0123] contrast Figure 4 (c), (d) Figure 6(c) and (d) show that with the increase of PEO molecular weight, the average fiber diameter of the fiber membrane with added PEO L (low molecular weight) is approximately 356 nm, the average fiber diameter of the fiber membrane with added PEO M (medium molecular weight) is approximately 1020 nm, and the average fiber diameter of the fiber membrane with added PEO H (high molecular weight) is 4870 nm. Observing the pore size distribution of the membrane fibers, a positive correlation can be seen between pore size and fiber diameter. The morphology and fiber diameter distribution diagrams of the micro-nano fibers after hydrothermal treatment show that the average diameters of the PEO L, PEO M, and PEO H solutions decreased to 355 nm, 639 nm, and 1163 nm, respectively, with the overall fiber morphology becoming more curved. Thirdly, the fibers of the air filter membranes prepared with the three molecular weights all exhibited very obvious curved morphology after treatment. This is because, during the water bath treatment stage, the water-soluble nature of PEO allows for the effective removal of most of the PEO from the fiber surface during heat treatment and deionized water etching. This results in a reduction in fiber diameter, thereby increasing the specific surface area of ​​the nanofibers in the air filter membrane, and simultaneously increasing the pore size and porosity. Therefore, the air filter membrane treated with heat treatment and deionized water etching exhibits better overall filtration performance. Since excessively small diameters result in low porosity and poor air permeability, while a large diameter distribution concentrated in the larger diameter area is unfavorable for the adsorption and blocking of fine particles, considering all factors, the air filter membrane prepared by adding medium molecular weight PEO in this invention exhibits the best performance.

[0124] like Figure 7 As shown, the concentrations of PA6 and PEO in the spinning solution were 6% and 1%, respectively. From top to bottom, the images show the multiple light scattering diagrams of the dissolution process over 24 hours with the addition of low molecular weight PEO, medium molecular weight PEO, and high molecular weight PEO. This diagram illustrates the motion state of PEO macromolecular chains of different molecular weights in the solution. It demonstrates that the addition of high molecular weight PEO makes the movement of macromolecules in the solution more difficult, thus making the solute less soluble. This less soluble solute leads to an increase in fiber diameter and a wider pore size distribution during spinning.

[0125] like Figure 8 The figures show, from top to bottom, the multiple light scattering (PSS) images of the dissolution process after 24 hours with low molecular weight PEO, medium molecular weight PEO, and high molecular weight PEO added. These images also show the PSS images of the solutions after 24 hours of standing with low molecular weight PEO, medium molecular weight PEO, and high molecular weight PEO added. This indicates that the spinning solution is uniform and stable after complete solute dissolution, thus allowing for smooth spinning. Furthermore, even with prolonged spinning, PEO and PA6 do not separate and can be spun out simultaneously.

[0126] pass Figure 7-8 This can be explained as follows:

[0127] 1. The above experimental phenomena demonstrate that formic acid, as a solvent, can effectively dissolve PA6 and PEO, forming a relatively homogeneous and stable polymer solution. This stable solution ensures the stable preparation of the fiber membrane from the sample.

[0128] 2. The data also illustrates that the molecular weight of macromolecules directly affects the behavior of PEO and PA6 in solution. Formic acid, as a volatile acid, has a lower concentration at the gas-liquid interface, thus attracting more PEO to aggregate.

[0129] 3. This also shows that after the solution is completely dissolved into spinning solution, the entire solution is very stable and homogeneous as a whole. However, the solute is not completely uniformly distributed in some places. This provides a theoretical basis for treating PEO on PA6 / PEO fiber membrane at the molecular level. The behavior of macromolecules in solution is the essential reason for deionized water etching and heat treatment.

[0130] like Figure 9-10 As shown, the air filter membrane exhibits a significantly high degree of bending in its internal nanofibers after treatment. This is because the nylon 6 and PEO mixed solution initially forms composite fibers through SBS (solution blown spinning), and stress accumulates within the fibers after they reach the receiving mesh. During subsequent heat treatment, stress further accumulates within the fibers due to the difference in thermal properties between the two polymers and the phase separation structure demonstrated earlier. Next, water washing removes the PEO from the fiber surface. This process not only alters the fiber surface morphology, such as increasing porosity and surface roughness, but also exacerbates the inhomogeneity of the internal structure. The removal of PEO releases the stress accumulated during spinning and heat setting. Simultaneously, the combined effect of the inhomogeneity of the internal structure and the changes in surface morphology makes the fibers prone to uneven deformation under stress, ultimately resulting in a significant bending morphology. The average curvature of the fibers differs by more than an order of magnitude before and after treatment. The filter device assembled from these highly bent PA6 nanofibers exhibits excellent filtration performance.

[0131] In summary, the curved nanofibers form an integral three-dimensional network structure within the air filter membrane. This three-dimensional network structure, formed by the curved nanofibers, is equivalent to constructing a multi-level barrier, permeable, and tortuous filtration system within the air filter membrane. This structure provides better barrier capability against tiny particles and also enhances the mechanical strength, stability, and permeability of the air filter membrane. Therefore, it structurally ensures improved adsorption performance, mechanical strength, and permeability.

[0132] 2. Regarding pore size and porosity:

[0133] like Figure 11 As shown, pore size refers to the size of the pores in the nanofiber membrane, which directly affects the membrane's filtration efficiency and air resistance. The pore size distribution of the fiber membrane obtained after hydrothermal treatment is relatively narrow because the PEO that aids in spinning on the surface is removed, leaving relatively pure PA6 fibers. Therefore, the pore size distribution of the resulting fibers is within a narrow range, especially the fiber membrane with added medium molecular weight (6*10^5) PEO, which exhibits an extremely narrow pore size distribution. This is beneficial for the precise filtration of fine particles. The filtration effect is particularly good for small-sized oily and salty particles as described in this invention.

[0134] like Figure 12 As shown in the infrared spectrum before processing, the absorption peaks at 3295 cm⁻¹ are the stretching vibrations of NH in nylon and OH in PEO, and at 2936 and 2862 cm⁻¹, respectively. -1 The absorption peak for the stretching vibration of CH is at 1637 cm⁻¹. -1 The absorption peak at 1540 cm⁻¹ is the C=O stretching vibration in nylon, and the absorption peak at 1463 cm⁻¹ is the NH bending vibration in nylon. -1 The absorption peak at 1263 cm⁻¹ is the bending vibration absorption peak of -CH₂-. -1 The peak at 1106 cm⁻¹ is the absorption peak of the stretching vibration of CN in nylon. -1 The absorption peak at 690 cm⁻¹ is the stretching vibration absorption peak of COC in PEO. -1 The peak at 1106 cm⁻¹ represents the out-of-plane bending vibration absorption peak of CH. Comparing the processed infrared spectrum, we found an increase in the intensity of the infrared absorption peak. This is attributed to the appearance of the group absorption peaks of nylon after PEO dissolution, resulting in a significant increase in the intensity of the infrared group peaks. Simultaneously, the absorption peak at 1106 cm⁻¹ essentially disappeared. This is because the COC was destroyed after PEO dissolution, further confirming the dissolution of PEO on the nylon surface. (3295 cm⁻¹) -1 The peaks at 2936 and 2862 cm⁻¹ represent the stretching vibration absorption peaks of NH₄⁺ in nylon, and may also contain residual OH⁻ absorption peaks from PEO. -1 The peak at 1637 cm⁻¹ is the absorption peak of the stretching vibration of CH in nylon. -1 The peak at 1540 cm⁻¹ is the absorption peak of the stretching vibration of C=O in nylon. -1 The peak at 1463 cm⁻¹ is the absorption peak of the bending vibration of NH in nylon. -1 The absorption peak at 1263 cm⁻¹ is the bending vibration absorption peak of -CH₂- at 60°C. -1 The absorption peak of CN in nylon is located at 690 cm⁻¹. -1The peak at this location is the out-of-plane bending vibration absorption peak of CH. This demonstrates that, in the water bath treatment stage of this invention, the PEO dissolved by heating is more likely to aggregate together. Furthermore, its water-soluble nature allows most of the PEO on the surface to be effectively removed after multiple water bath treatments, further reducing the fiber diameter while increasing the pore size and porosity.

[0135] like Figure 13 As shown, compared with the porosity statistics of different molecular weights, the porosity of PEO L (low molecular weight PEO) is 69.02%, that of PEO M (medium molecular weight PEO) is 72.13%, and that of PEO H (high molecular weight PEO) is 93.09%. This indicates that porosity is significantly affected by different types of PEO, especially PEO H (high molecular weight PEO), which exhibits the highest porosity. This is because although the fiber diameter obtained from high molecular weight PEO is inherently larger, the bending morphology of the fiber leads to the formation of a three-dimensional network structure inside the air filter membrane, further increasing the porosity of the fiber membrane. This also proves the result of the fiber forming a bending morphology after heat treatment and water bath treatment in this invention.

[0136] 3. Regarding fiber surface roughness:

[0137] like Figure 14As shown, the significant roughness effect on the fiber surface is evident. Due to hydrothermal treatment, the fiber diameter of the fiber membrane with added polymer PEO decreases. Furthermore, the addition of PEO not only reduces the average fiber diameter but also creates pores on the fiber surface, making it rougher. This is because the PEO molecular chains are flexible. During fiber formation, as the solvent evaporates, the PEO macromolecules gradually move towards the gas-liquid interface. Simultaneously, the rapid evaporation of formic acid leads to a rapid increase in fiber viscosity, ultimately causing PEO to accumulate on the outer layer of the fiber. Moreover, the long molecular chains of higher molecular weight PEO are not easily able to move completely in the spinning solution during fiber formation and are difficult to disperse uniformly on the fiber surface during solvent evaporation. Therefore, when dissolved in water, more depressions and pores are formed. Simultaneously, during heat treatment, the fiber orientation also shrinks and bends due to uneven component distribution. The resulting bends, finer fibers, and rougher surfaces are all beneficial for filtering fine oil and salt particles. Therefore, after removing PEO from the surface of the fiber membrane, the hydrophobicity of the fiber membrane is significantly improved. Simultaneously, the numerous depressions and pores formed on the surface are more conducive to the adsorption and spreading of oily particles, alleviating the problem of oily particles accumulating in the pores between fibers and slowing down the time it takes for oily particles to clog the fiber membrane. This not only improves the filtration efficiency but also extends its service life. At the same time, the crystalline structure of saline particles can be adsorbed and confined within the depressions and pores on the fiber surface, making interception easier. Combined with the network-like multi-level interception structure formed by the highly tortuous fiber membrane, saline particles can be better blocked and intercepted.

[0138] like Figure 15 As shown, the proportion of pores formed on the surface of the fiber membrane was characterized using the ImageJ tool: In terms of area: firstly, image processing tools, such as... Figure 15 As shown in (a), the fiber membrane Figure 15 (b) Removing the background to obtain Figure 15 (c) Using the ImageJ tool, calculate the total area S1 of the fiber membrane and the total area S2 of the blank area, as follows: Figure 15 (d) The total area of ​​fine pores on the fiber surface, S3, is as follows: Figure 15 (e), according to Figure 5Using the same summation method, the proportion of surface pores to the fiber surface, N = S3 / (S1-S2)×100% = 10210 / (2209682-1282576)×100% = 1.1%. In terms of quantity: the total number of pores is 143 / 8 fibers ≈ 18 pores / fiber, meaning that even under 10,000x magnification, each fiber still has approximately 18 pores. This proves that the process of this invention truly creates a large number of depressions and pores on the fiber surface, increasing the surface roughness. Compared to the traditional beaded structure that simply increases roughness, this invention, while increasing roughness, also reduces the fiber diameter, increases the pore size and porosity. Under the same filtration performance conditions, it greatly improves the air permeability of the air filter membrane, increases filtration efficiency, and has a significant interception and filtration effect, especially for small-sized oily and salty particles.

[0139] 4. Regarding filtration effect:

[0140] like Figure 16-17 As shown, a comparison of the filtration effects of the fiber membrane before and after treatment on small-diameter oily and saline particles reveals that, compared to before treatment... Figure 17 (a) In comparison, after removing PEO, such as Figure 17 As shown in (b), the filtration efficiency of the fibrous membrane for oily and salty particles is significantly improved. The filtration efficiency for the same particle size remains essentially above 98% because the specific filtration efficiency depends primarily on the fiber arrangement, membrane thickness, and fluid properties. The combined effect of curved fibers and a rough surface leads to increased filtration efficiency due to reduced fiber diameter and increased surface roughness. Generally, fibrous membranes with curved fibers exhibit lower gas resistance due to higher porosity between the curved fibers and smoother gas flow. Simultaneously, increased surface roughness may lead to increased turbulence in the airflow, which increases air resistance. Therefore, the variation in filtration efficiency for particles with different properties is a combination of curved fibers and a rough surface. Ultimately, while air resistance increases slightly, filtration efficiency is significantly improved. This makes the nanofiber membrane perform excellently in filtering oily and salty ultrafine particles and effectively capture particles of different diameters, particularly small particles and complex contaminants. Considering all factors, Example 2 of the present invention is the preferred embodiment.

[0141] In summary, the PA6 / PEO micro / nanofiber air filter membrane of this invention, with its curved shape, can simultaneously and efficiently filter both oily and salty ultrafine particles. By optimizing the structural characteristics of the fiber membrane, it solves the technical problem in the prior art of effectively filtering both fine oily and salty particles.

[0142] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A method for preparing a PA6 / PEO micro / nanofiber air filter membrane with a curved shape, characterized in that, Includes the following steps: I. Preparation of spinning solution: (1) Weigh a certain amount of PA6 particles and PEO powder, dissolve them in a formic acid solution with a mass fraction of 88%, and obtain a mixed solution; (2) Stir the mixed solution magnetically at room temperature for 6-8 hours until it is completely dissolved to obtain a uniform PA6 / PEO spinning solution. II. Preparation of Fiber Membranes: (3) The PA6 / PEO spinning solution prepared in step (2) is drawn out with a 10ml syringe and installed on the gas jet spinning machine; (4) Adjust the output air pressure of the air compressor, connect the spinning needle to the air flow nozzle, and under certain pushing speed and receiving distance conditions, the PA6 / PEO spinning solution is squeezed out by the needle and mixed with the high pressure air flow. After being stretched and refined, it is sprayed onto the rolling receiving roller to form a fiber film under room temperature drying conditions. (5) The obtained fiber membrane is dried at 60°C overnight to remove residual solvent; III. Heat treatment and deionized water etching: (6) Place the fiber membrane obtained in step (5) into an oven for heat treatment. Set the heating temperature to 100-120℃ and the heating time to 0.3-0.6h. After heating, immediately remove the fiber membrane and allow it to cool naturally to room temperature. (7) At room temperature, place the heat-treated fiber membrane in a container, add deionized water to immerse the fiber membrane, the mass ratio of fiber membrane to deionized water is 1:40-1:60, then add PEG200 to the water until the concentration of PEG200 reaches 1%, and set aside. (8) Place the container in a water bath at 60-80℃ and heat it in the water bath for 0.8-1.2 hours. Repeat the water bath treatment twice. (9) After the process is completed, the sample is taken out immediately and vacuum dried at a temperature of 60°C for 2 hours to ensure that the sample is completely dry and does not deform, thus obtaining a PA6 / PEO micro / nanofiber air filter membrane with a curved shape.

2. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In step (1), the molecular weight of the PEO powder is 100,000-1,000,000.

3. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In the PA6 / PEO spinning solution obtained in step (2), the concentration of PA6 is 5-7% and the concentration of PEO is 0.5-1.5%.

4. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In step (4), the air compressor output pressure is 0.04-0.08MPa, the propulsion speed is 1.5-2.5ml / h, the receiving distance is 28-32cm, and the inner diameter of the spinning needle is 0.33mm.

5. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In step (6), the heat treatment heating temperature is 110℃ and the heating time is set to 0.5h.

6. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In step (7), the mass ratio of the fiber membrane to deionized water is 1:

50.

7. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 1, characterized in that: In step (8), the water bath temperature is set to 70°C and the water bath time is 1 hour.

8. The method for preparing the PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 4, characterized in that: In step (4), the air compressor outputs an air pressure of 0.06 MPa, a propulsion speed of 2 ml / h, and a receiving distance of 30 cm.

9. A PA6 / PEO micro / nanofiber air filter membrane with a curved shape, characterized in that: It is prepared by the preparation method according to any one of claims 1-8.

10. The PA6 / PEO micro / nanofiber air filter membrane with a curved shape according to claim 9, characterized in that: The fibers have an average diameter of 212-4110 nm and a porosity of 69.02%-93.09%.

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