A single-layer nanofiber web / electrospun fiber composite membrane and a preparation method thereof

Abstract

The present application relates to a kind of single-layer nanofiber net / electrostatic fiber composite film and its preparation method, in the preparation process, first, electrostatic fiber substrate is impregnated in high surface energy inorganic salt solution to reach saturation state;Low surface energy polymer solution is then dropped on the surface of the saturated substrate of impregnation in multiple points, and continuous ultrathin polymer liquid film is formed by spontaneous super-spreading of droplet, and non-solvent induced phase separation occurs, forming solvent-rich phase and polymer-rich phase;Then, the above-mentioned material is pre-frozen, and the polymer-rich phase is grown by solvent-rich phase ice crystal nucleation and is expelled to form a two-dimensional mesh structure;Finally, the above-mentioned material is vacuum freeze-dried, and solvent and non-solvent are removed, to obtain a single-layer nanofiber net continuously covered on the electrostatic fiber substrate.Compared with the prior art, the material obtained by the present application significantly reduces the pore size of electrostatic nanofiber material, and maintains the original high porosity and permeability, so that the composite film material has low filtration resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber membrane materials, in particular to a preparation method of a single-layer nanofiber web / electrospun fiber composite membrane and the preparation method thereof. BACKGROUND

[0002] Electrospun fiber membrane materials have the characteristics of fine fiber diameter, small pore size, and high porosity, and have broad application prospects in the fields of air filtration, oil-water separation, waterproof and moisture permeable, etc. However, the diameter of the electrospun fiber is usually above 100 nm, which leads to the inability to further reduce the pore size, and it is difficult to filter and separate sub-micron particle pollutants with a diameter below 1 μm. The porous structure of the electrospun fiber membrane material is formed by stacking nanofiber layers, which leads to a large thickness and high resistance pressure drop, limiting the further improvement of the filtration performance.

[0003] Patent CN202010951106.5 discloses “An electrospun fiber-based ultra-thin continuous nanospider web fiber material and a preparation method thereof”, which coats a polymer solution on the surface of an electrospun fiber substrate, and obtains a nanospider web composite material by the method of phase separation in a non-solvent bath. The film forming step in this method is easy to cause the polymer solution to penetrate into the electrospun fiber substrate under capillary action, and it is difficult to accurately control the continuity and uniformity of the liquid film; and the other core step of phase separation in a non-solvent bath is difficult to control the diffusion speed of the solvent and the non-solvent, so as to realize effective regulation of the pore structure formed by phase separation.

[0004] Patent CN201810555559.9 discloses “A method for preparing an interface thin layer porous membrane by freeze-drying technology”, which coats a liquid film on a glass substrate by spin coating, and obtains a thin layer porous membrane after freeze-drying. This method forms a liquid film on a glass substrate by spin coating, and there is a problem that the solution is difficult to form a uniform film on the glass substrate due to surface tension, resulting in a non-uniform thickness of the obtained porous membrane and discontinuous pore structure.

[0005] Patent CN201710649234.2 discloses “A bacterial cellulose nanofiber composite filter membrane and a preparation method thereof”, which spreads a bacterial cellulose suspension on the surface of a porous fiber substrate, removes the solvent, and then cross-links to obtain a two-dimensional network structure of bacterial cellulose nanofiber composite filter membrane. This method is based on the interlocking of bacterial cellulose short fibers to construct a two-dimensional network structure, and in the preparation process of the cellulose suspension, the cellulose short fibers are difficult to disperse uniformly, and there is a problem that the cellulose short fibers are easy to cluster and the network aperture uniformity is poor. SUMMARY

[0006] The present application aims to overcome the defects of the prior art, and provides a single-layer nanofiber mesh / electrospun fiber composite film and a preparation method thereof, so as to obtain a continuous single-layer two-dimensional mesh material with controllable pore size, thereby significantly reducing the pore size of the electrospun nanofiber material, maintaining the original high porosity and permeability, and making the composite film material have low filtration resistance.

[0007] The object of the present application can be achieved by the following technical solutions:

[0008] The present application provides a preparation method of a single-layer nanofiber mesh / electrospun fiber composite film, comprising the following steps:

[0009] S1: adding a polymer and a surfactant into a solvent and stirring uniformly to obtain a low-surface-energy polymer solution, and simultaneously, adding an inorganic salt into a non-solvent and stirring uniformly to obtain a high-surface-energy inorganic salt solution;

[0010] S2: immersing an electrospun fiber substrate in the high-surface-energy inorganic salt solution until saturation to obtain a high-surface-energy electrospun fiber substrate;

[0011] S3: dripping the low-surface-energy polymer solution at multiple points on the surface of the high-surface-energy electrospun fiber substrate, so that the low-surface-energy polymer solution spontaneously super-spreads on the high-surface-energy electrospun fiber substrate without penetration, forming a continuous ultra-thin polymer liquid film, and the polymer liquid film and the high-surface-energy electrospun fiber substrate surface contact a non-solvent to form a solvent-rich phase and a polymer-rich phase;

[0012] S4: pre-freezing the material obtained in S3 to make ice crystals in the solvent-rich phase nucleate and grow, and the polymer-rich phase is pushed away by the ice crystals to form a two-dimensional mesh structure;

[0013] S5: vacuum freeze-drying the pre-frozen substrate to remove the solvent and the non-solvent, and finally obtaining a composite material with a continuous single-layer nanofiber mesh on the surface of the electrospun fiber substrate.

[0014] Further, in S4, the ice crystal nucleation and growth process is regulated by changing the freezing rate, so as to accurately regulate the two-dimensional mesh structure.

[0015] Further, in S1, the polymer is selected from one or more of polyvinylidene fluoride, polyacrylonitrile, polyamide, polyurethane, polyvinyl alcohol, polyamide-imide, polyether-imide, and polystyrene, and the mass fraction of the polymer is 0.1-10wt%.

[0016] Further, in S1, the surface tension of the low-surface-energy polymer solution is ≤35mN / m.

[0017] The surface tension of the high-surface-energy non-solvent is ≥ 50 mN / m.

[0018] Further, in S1, the solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidone, ethanol, isobutanol, n-propanol, ethyl acetate, and acetone.

[0019] The surface tension of the high-surface-energy non-solvent is ≥ 50 mN / m.

[0020] The inorganic salt is selected from one or more of sodium chloride, lithium chloride, zinc chloride, calcium chloride, copper chloride, sodium acetate, sodium benzoate, sodium sulfate, aluminum sulfate, and zinc sulfate, and the mass fraction of the inorganic salt is 0.001-0.5 wt%.

[0021] The non-solvent is selected from one or more of water, methanol, ethanol, propanol, isobutanol, ethylene glycol, acetone, methyl phenol, and cyclohexane.

[0022] Further, in S2, the electrospun fiber substrate is selected from one of a polyamide electrospun nanofiber membrane, a polytetrafluoroethylene electrospun nanofiber membrane, a polypropylene electrospun nanofiber membrane, a polyimide electrospun nanofiber membrane, a polyethylene terephthalate electrospun nanofiber membrane, and a silicon dioxide electrospun nanofiber, the substrate has a diameter of 0.2-2 μm, a pore size of 1-10 μm, and a thickness of 5-100 μm.

[0023] In S2, the immersion time is 10-60 min.

[0024] Further, in S3, the multi-point dripping is micro-injection using a plurality of syringes, wherein the syringes are arranged in A rows and B syringes per row, A ≥ 2 and B ≥ 3, the distance between the syringes is 1-10 cm, the inner diameter of the needle tube of the syringe is 0.1-5 mm, the outer diameter of the needle tube of the syringe is 0.3-5.3 mm, and the liquid discharge speed of the syringe is 0.1-100 μl / s.

[0025] Further, in S4, the pre-freezing temperature is ≤-50℃, the cooling rate is 5-15℃ / min, and the pre-freezing time is 3-10h. The cooling rate can affect the ice crystal nucleation and growth process, thereby realizing the regulation of the two-dimensional mesh structure; the faster the cooling rate, the more the fine crystals with small size are generated in the solvent-rich phase, so that the two-dimensional mesh diameter is reduced and the porosity is increased; on the contrary, the slower the cooling rate, the more the ice crystals with large size are generated, so that the two-dimensional mesh diameter is increased and the porosity is reduced.

[0026] Further, in S5, the vacuum freeze-drying time is 30-60h, and the vacuum degree is -0.05 to -0.1MPa.

[0027] The second aspect of the present application provides a single-layer nanofiber mesh / electrospun fiber composite film prepared by the above method, wherein the fiber diameter of the single-layer nanofiber mesh is 10-100nm, the two-dimensional mesh diameter of the single-layer nanofiber mesh / electrospun fiber composite film is 0.2-1μm, the thickness is 5-90μm, and the porosity is ≥80%.

[0028] The technical principle of the present application is as follows:

[0029] The single-layer nanofiber mesh / electrospun fiber composite film of the present application is obtained by constructing a continuous ultrathin polymer liquid film on an electrospun fiber substrate, and then performing phase separation, pre-freezing and vacuum freeze-drying. A low-surface-energy polymer solution is obtained by adding a surfactant to a polymer solution, and a high-surface-energy inorganic salt solution is obtained by adding an inorganic salt to a non-solvent. The electrospun fiber substrate is saturated by immersion in the inorganic salt solution, so as to increase the surface energy of the substrate, so that the surface tension of the solution is less than the surface tension of the substrate, thereby promoting the spontaneous ultraplay of the polymer solution on the substrate. First, a small amount of polymer solution is dropped on the surface of the saturated substrate, and the inorganic salt solution fills the small pores on the surface of the substrate, preventing the polymer solution from penetrating between the pores of the substrate due to capillary effect. Under the action of surface energy, the polymer droplets ultraplay on the surface of the substrate to form a continuous ultrathin polymer liquid film. At the same time, the polymer solution and the non-solvent on the surface of the substrate are in contact to form a solvent-rich phase and a polymer-rich phase in the polymer liquid film. Subsequently, the electrospun substrate covered with the continuous ultrathin liquid film is pre-frozen, and the ice crystals in the solvent-rich phase nucleate and grow, so that the polymer-rich phase is pushed away by the ice crystals to form a two-dimensional mesh structure. By changing the freezing rate, the nucleation and growth process of the ice crystals is regulated, thereby effectively regulating the two-dimensional mesh structure. Vacuum freeze-drying is performed, and under vacuum conditions, the solvent and non-solvent in the liquid film are removed, and the polymer-rich phase forms a two-dimensional mesh structure, thereby constructing a single-layer nanofiber mesh on the electrospun fiber film.

[0030] Compared with the prior art, the present application has the following technical advantages:

[0031] (1) The single-layer nanofiber net of the present application can significantly reduce the pore size of the electrospun nanofiber material and maintain the original high porosity and permeability, so that the composite film material has low filtration resistance.

[0032] (2) The single-layer nanofiber net of the present application can regulate its two-dimensional mesh structure by changing the polymer solution properties and freezing parameters, and has strong pore size adjustability, strong method universality, wide application range, and can meet the filtration requirements in various application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The electron microscope image of the single-layer nanofiber net / electrospun fiber composite film prepared in Example 1; in the figure, a is an electrospun fiber, and b is a single-layer nanofiber net. DETAILED DESCRIPTION

[0034] The single-layer nanofiber net / electrospun fiber composite film and the preparation method thereof in the present application, the method specifically comprises the following steps: first, the electrospun fiber substrate is immersed in a high surface energy inorganic salt solution to reach a saturated state; then, a low surface energy polymer solution is dropped on the surface of the saturated substrate at multiple points, the droplets spontaneously super-spread to form a continuous ultra-thin polymer liquid film, and non-solvent induced phase separation occurs to form a solvent-rich phase and a polymer-rich phase; then, the above-mentioned material is pre-frozen, so that the polymer-rich phase is nucleated and grown by the solvent-rich phase ice crystals to form a two-dimensional mesh structure; finally, the above-mentioned material is vacuum freeze-dried to remove the solvent and non-solvent, and a single-layer nanofiber net continuously covering the electrospun fiber substrate is obtained.

[0035] The nanofiber net obtained by the present application is a single-layer continuous two-dimensional mesh structure with a diameter of 10-100 nm, the single-layer nanofiber net / electrospun fiber composite material obtained has a pore size of 0.2-1 μm, a thickness of 5-90 μm, and a porosity of ≥80%, and has a good application prospect in the field of filtration and separation.

[0036] The present application will be described in detail below in combination with the drawings and specific examples. In the technical solution, if the preparation means, materials, structure or composition ratio and other features are not explicitly stated, they are regarded as common technical features disclosed in the prior art.

[0037] Example 1

[0038] The single-layer nanofiber net / electrospun fiber composite film and the preparation method thereof in the present embodiment, the specific steps are as follows:

[0039] First step: 10g of polyacrylonitrile is dissolved in 1000g of N,N-dimethylacetamide, 1g of sodium dodecyl benzene sulfonate is added, and mixed and stirred to obtain a polymer solution; 1g of sodium chloride is dissolved in 1000g of ethanol, and mixed and stirred to obtain an inorganic salt solution;

[0040] Second step: select the substrate as polyamide electrospinning nanofiber membrane, fiber diameter is 0.2 μm, pore size is 1 μm, thickness is 5 μm, immerse in inorganic salt solution for 60 min;

[0041] Third step: add polymer solution into syringe, set injection point position to have 2 rows, each row has 3, interval is 5 cm, liquid outlet speed is 20 μl / s, carry out dripping, form continuous ultrathin polymer liquid film on above-mentioned substrate surface and phase separation occurs;

[0042] Fourth step: pre-freeze above-mentioned material for 5 h, freezing temperature is -60 ℃, temperature decreasing rate is 10 ℃ / min;

[0043] Fifth step: vacuum freeze dry above-mentioned material for 60 h, vacuum degree is -0.1 MPa, finally obtain single layer nanofiber web diameter is 60 nm, composite membrane pore size is 0.3 μm, thickness is 6 μm, porosity is 90%. Figure 1 Electron microscope diagram of single layer nanofiber web / electrospinning fiber composite membrane prepared in example 1; in the diagram, a is electrospinning fiber, b is single layer nanofiber web.

[0044] Example 2

[0045] Single layer nanofiber web / electrospinning fiber composite membrane and preparation method thereof in the example, the specific steps are as follows:

[0046] First step: dissolve 5 g of polyvinylidene fluoride in 1000 g of N,N-dimethylformamide, add 0.5 g of monolauryl phosphate, mix and stir to obtain a polymer solution; dissolve 2 g of lithium chloride in 1000 g of water, mix and stir to obtain an inorganic salt solution;

[0047] Second step: select the substrate as polyamide electrospinning nanofiber membrane, fiber diameter is 0.6 μm, pore size is 5 μm, thickness is 50 μm, immerse in inorganic salt solution for 40 min;

[0048] Third step: add polymer solution into syringe, set injection point position to have 2 rows, each row has 5, interval is 5 cm, liquid outlet speed is 10 μl / s, carry out dripping, form continuous ultrathin polymer liquid film on above-mentioned substrate surface and phase separation occurs;

[0049] Fourth step: pre-freeze above-mentioned material for 3 h, freezing temperature is -80 ℃, temperature decreasing rate is 15 ℃ / min;

[0050] Fifth step: vacuum freeze dry above-mentioned material for 40 h, vacuum degree is -0.08 MPa, finally obtain single layer nanofiber web diameter is 40 nm, composite membrane pore size is 1 μm, thickness is 50 μm, porosity is 85%.

[0051] Example 3

[0052] The single-layer nanofiber web / electrospun fiber composite membrane and the preparation method thereof in the embodiment are as follows:

[0053] First step: 10g of polystyrene is dissolved in 800g of N,N-dimethylacetamide, 0.4g of monolauryl phosphate is added, and mixed and stirred to obtain a polymer solution; 18g of sodium sulfate is dissolved in 800g of water, and mixed and stirred to obtain an inorganic salt solution;

[0054] Second step: the substrate is selected as a polypropylene electrospun nanofiber membrane, the fiber diameter is 2μm, the pore size is 8μm, and the thickness is 100μm, and the substrate is immersed in the inorganic salt solution for 10min;

[0055] Third step: the polymer solution is added to a syringe, and a total of 2 rows of injection points are set, each row has 5 points, the interval is 5cm, the liquid outlet speed is 10μl / s, and dripping is performed to form a continuous ultrathin polymer liquid film on the surface of the substrate and cause phase separation;

[0056] Fourth step: the above material is pre-frozen for 6h, the freezing temperature is-65℃, and the cooling rate is 8℃ / min;

[0057] Fifth step: the above material is vacuum freeze-dried for 45h, the vacuum degree is-0.06MPa, and finally a single-layer nanofiber web with a diameter of 100nm, a composite membrane with a pore size of 0.8μm, and a thickness of 100μm, and a porosity of 80% is obtained.

[0058] Example 4

[0059] The single-layer nanofiber web / electrospun fiber composite membrane and the preparation method thereof in the embodiment are as follows:

[0060] First step: 10g of polyamide-imide is dissolved in 1200g of N,N-dimethylacetamide, 2g of sodium dodecylbenzenesulfonate is added, and mixed and stirred to obtain a polymer solution; 10g of copper chloride is dissolved in 600g of methanol, and mixed and stirred to obtain an inorganic salt solution;

[0061] Second step: the substrate is selected as a silicon dioxide electrospun nanofiber membrane, the fiber diameter is 0.4μm, the pore size is 2μm, and the thickness is 20μm, and the substrate is immersed in the inorganic salt solution for 20min;

[0062] Third step: the polymer solution is added to a syringe, and a total of 3 rows of injection points are set, each row has 6 points, the interval is 1cm, the liquid outlet speed is 0.1μl / s, and dripping is performed to form a continuous ultrathin polymer liquid film on the surface of the substrate and cause phase separation;

[0063] Fourth step: the above material is pre-frozen for 10h, the freezing temperature is-55℃, and the cooling rate is 5℃ / min;

[0064] Fifth step: vacuum freeze-drying the above material for 40 h at a vacuum degree of -0.1 MPa, to obtain a single-layer nanofiber web with a diameter of 10 nm, a composite membrane with a pore size of 0.2 μm, a thickness of 20 μm, and a porosity of 95%.

[0065] Example 5

[0066] The single-layer nanofiber web / electrospun fiber composite membrane and the preparation method thereof in this example are as follows:

[0067] First step: dissolve 10 g of polyurethane in 500 g of N-methyl pyrrolidone, add 0.5 g of sodium dodecyl benzene sulfonate, mix and stir to obtain a polymer solution; dissolve 10 g of aluminum sulfate in 600 g of water, mix and stir to obtain an inorganic salt solution;

[0068] Second step: select a substrate of a polyimide electrospun nanofiber membrane with a fiber diameter of 0.6 μm, a pore size of 3 μm, and a thickness of 30 μm, and immerse it in the inorganic salt solution for 30 min;

[0069] Third step: add the polymer solution into a syringe, set 3 rows of injection points with 4 points in each row, with a spacing of 6 cm, and a liquid discharge speed of 10 μl / s, to perform dripping, to form a continuous ultra-thin polymer liquid film on the surface of the substrate and cause phase separation;

[0070] Fourth step: pre-freeze the above material for 6 h at a freezing temperature of -75 °C and a cooling rate of 10 °C / min

[0071] Fifth step: vacuum freeze-dry the above material for 50 h at a vacuum degree of -0.05 MPa, to obtain a single-layer nanofiber web with a diameter of 80 nm, a composite membrane with a pore size of 0.4 μm, a thickness of 30 μm, and a porosity of 91%.

[0072] The above description of the embodiments is for the purpose of enabling and using the invention by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a single-layer nanofiber web / electrospun fiber composite film, characterized by, The method comprises the following steps: S1: adding a polymer and a surfactant into a solvent and stirring to obtain a low-surface-energy polymer solution, and adding an inorganic salt into a non-solvent and stirring to obtain a high-surface-energy inorganic salt solution; S2: immersing an electrospun fiber substrate into the high-surface-energy inorganic salt solution until saturation to obtain a high-surface-energy electrospun fiber substrate; S3: dripping the low-surface-energy polymer solution at multiple points on the surface of the high-surface-energy electrospun fiber substrate, so that the low-surface-energy polymer solution spontaneously super-spreads on the high-surface-energy electrospun fiber substrate without penetration, forming a continuous ultra-thin polymer liquid film, and the polymer liquid film and the high-surface-energy electrospun fiber substrate surface contact a non-solvent to form a solvent-rich phase and a polymer-rich phase; S4: pre-freezing the material obtained in S3 to make ice crystals in the solvent-rich phase nucleate and grow, and the polymer-rich phase is pushed away by the ice crystals to form a two-dimensional mesh structure; S5: vacuum freeze-drying the pre-frozen substrate to remove the solvent and the non-solvent, and finally obtaining a composite material with a continuous monolayer nanofiber mesh on the surface of the electrospun fiber substrate; In S4, the ice crystal nucleation and growth process is regulated by changing the freezing rate, so as to accurately regulate the two-dimensional mesh structure; In S1, the polymer is selected from one or more of polyvinylidene fluoride, polyacrylonitrile, polyamide, polyurethane, polyvinyl alcohol, polyamide-imide, polyether-imide and polystyrene, and the mass fraction of the polymer is 0.1-10wt%; In S1, the surface tension of the low-surface-energy polymer solution is ≤35mN / m; The surface tension of the high-surface-energy non-solvent is ≥50mN / m; In S2, the electrospun fiber substrate is selected from one of polyamide electrospun nanofiber membrane, polytetrafluoroethylene electrospun nanofiber membrane, polypropylene electrospun nanofiber membrane, polyimide electrospun nanofiber membrane, polyethylene terephthalate electrospun nanofiber membrane and silicon dioxide electrospun nanofiber, the diameter of the substrate is 0.2-2μm, the pore size is 1-10μm, and the thickness is 5-100μm; In S2, the immersion time is 10-60min.

2. The method for preparing a single-layer nanofiber web / electrospun fiber composite membrane according to claim 1, characterized in that, In S1, the solvent is selected from N , N - dimethylformamide, N , N - dimethylacetamide, dimethylsulfoxide, N - one or several of methylpyrrolidone, ethanol, isobutanol, n-propanol, ethyl acetate, acetone. The surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, dodecyltrimethylammonium bromide, disodium lauryl sulfosuccinate, monolauryl phosphate, potassium lauryl ether phosphate, ammonium fatty alcohol polyoxyethylene ether sulfate, lauryl amidopropyl betaine, coconut acid monoethanolamide and coconut acid diethanolamide, and the mass fraction of the surfactant is 0.01-5wt%; The inorganic salt is selected from one or more of sodium chloride, lithium chloride, zinc chloride, calcium chloride, copper chloride, sodium acetate, sodium benzoate, sodium sulfate, aluminum sulfate and zinc sulfate, and the mass fraction of the inorganic salt is 0.001-0.5wt%; The non-solvent is selected from one or more of water, methanol, ethanol, propanol, isobutyl alcohol, ethylene glycol, acetone, methyl phenol and cyclohexane.

3. The method for preparing a single-layer nanofiber web / electrospun fiber composite membrane according to claim 1, characterized in that, In S3, the multi-point site infusion is micro-injection using multiple syringes, wherein the syringes are arranged in A rows and B syringes per row, A≥2, B≥3, the distance between the syringes is 1-10 cm, the inner diameter of the syringe needle is 0.1-5 mm, the outer diameter of the syringe needle is 0.3-5.3 mm, and the liquid outlet speed of the syringe is 0.1-100 μl / s.

4. The method for preparing a single-layer nanofiber web / electrospun fiber composite membrane according to claim 1, characterized in that, In S4, the pre-freezing temperature is ≤-50℃, the cooling rate is 5-15℃ / min, and the pre-freezing time is 3-10 h.

5. The method for preparing a single-layer nanofiber web / electrospun fiber composite membrane according to claim 1, characterized in that, In S5, the vacuum freeze-drying time is 30-60 h, and the vacuum degree is -0.05--0.1 MPa.

6. A single-layer nanofiber / electrospun fiber composite membrane prepared by the method of any one of claims 1 to 5, characterized by, The fiber diameter in the single-layer nanofiber web is 10-100 nm, the pore size of the single-layer nanofiber web / electrostatically spun fiber composite membrane is 0.2-1 μm, the thickness is 5-90 μm, and the porosity is ≥80%.

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