Composite nanofiber membrane and preparation method thereof

Abstract

The present invention relates to a composite nanofiber membrane and a method for preparing the same. The method comprises the following steps: (1) preparing a nanofiber membrane; (2) preparing a slurry using a polymer, an easily decomposable material, a hydrophobic material, and a solvent; (3) performing an infiltration treatment on the nanofiber membrane using the slurry, and then drying to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane; (4) performing a heat treatment on the nanofiber membrane containing the initial coating to remove the easily decomposable material and convert the initial coating into a porous coating. The composite nanofiber membrane comprises nanofibers as a skeleton and a porous coating formed on the nanofibers, wherein the porous coating comprises the polymer and the hydrophobic material. The composite nanofiber membrane can have both high air permeability and high hydrostatic pressure resistance while maintaining high filtration efficiency.

Description

Technical Field

[0001] The present invention relates to the field of protective clothing, and in particular to a composite nanofiber membrane with high filtration efficiency, high air permeability and high hydrostatic pressure resistance and a preparation method thereof. Background Art

[0002] Nanofibers have the characteristics of small diameter and large specific surface area, so nanofiber products can be used for air filtration or liquid filtration, and are widely used in human protective clothing, battery separators, drug sustained release, environmental protection, sound absorbing materials and other fields.

[0003] Nanofiber membranes are the main products of nanofibers and play a very important role in all of the above fields. When using nanofiber membranes for air filtration, particle interception efficiency is an important indicator to measure its filtration performance. Nanofiber membranes have ultra-fine fiber diameters and porous three-dimensional structures, resulting in excellent particle interception efficiency (i.e., high filtration efficiency) and long-term effectiveness. However, due to the high porosity of nanofiber membranes, their hydrostatic pressure resistance is generally low.

[0004] To improve the hydrostatic pressure resistance of nanofiber membranes, they are usually treated with waterproofing. However, while waterproofing improves the hydrostatic pressure resistance of nanofiber membranes, it also significantly reduces their air permeability.

[0005] In order to improve the air permeability of nanofiber membranes, nanofiber membranes with porous surfaces are currently commonly used. The nanofiber membranes with porous surfaces are generally prepared by using the following two methods.

[0006] The first method is to control the spinning humidity and achieve a porous fiber surface through the principle of phase separation. However, excessively high humidity conditions will prevent many polymers from being electrospun properly, making humidity control difficult during large-scale production and easily causing high-voltage discharges.

[0007] Another approach involves preparing core-shell nanofibers through coaxial electrospinning and then creating pores on the fiber surface through heat treatment. However, this method is complex to operate, difficult to control, and not easily scalable.

[0008] Therefore, it is necessary to develop a new method with simple process and easy large-scale production, which can prepare new nanofiber membrane materials with high air permeability and high hydrostatic pressure resistance while maintaining high filtration efficiency. Summary of the Invention

[0009] Technical issues

[0010] The first object of the present invention is to provide a method for preparing a composite nanofiber membrane, which is simple in process and easy to carry out large-scale production.

[0011] A second object of the present invention is to provide a novel composite nanofiber membrane that can have both high air permeability and high hydrostatic pressure resistance while maintaining high filtration efficiency.

[0012] Technical Solution

[0013] According to a first aspect of the present invention, there is provided a method for preparing a composite nanofiber membrane, the method comprising the following steps:

[0014] (1) Preparing nanofiber membrane;

[0015] (2) preparing a slurry using a polymer, a decomposable material, a hydrophobic material, and a solvent;

[0016] (3) performing an infiltration treatment on the nanofiber membrane using the slurry, and then drying to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane;

[0017] (4) heat-treating the nanofiber membrane containing the initial coating layer to remove the easily decomposable material and convert the initial coating layer into a porous coating layer.

[0018] In one embodiment, in step (1),

[0019] The preparation of the nanofiber membrane comprises: preparing the nanofiber membrane by electrostatic spinning, wherein the electrostatic spinning is solution electrostatic spinning or melt electrostatic spinning,

[0020] The raw material for preparing the nanofiber membrane is a water-insoluble polymer, which is one or more selected from the following: polyacrylonitrile, nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone and polyvinylidene fluoride.

[0021] In one embodiment, in step (2),

[0022] The solvent is an organic solvent, and is one or more selected from hexafluoroisopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, formic acid, methanol, ethanol, acetone and dichloromethane;

[0023] The polymer is in solid form and is one or more selected from polycaprolactone, nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone and polyvinylidene fluoride;

[0024] The easily decomposable material is in the form of an aqueous solution.

[0025] In one embodiment, in step (2),

[0026] The solvent is water;

[0027] The polymer is in the form of an emulsion, and the emulsion is one or more selected from aqueous polyurethane emulsion, aqueous EVA emulsion and aqueous polyacrylate emulsion;

[0028] The easily decomposable material is in the form of an aqueous solution or a solid.

[0029] In one embodiment, in step (2),

[0030] The easily decomposable material is one or more selected from bicarbonate, carbonate, nitrate, ammonium salt, amine salt and oxalate;

[0031] The hydrophobic material is one or more selected from organic silicon, organic fluorine and super hydrophobic silica.

[0032] In one embodiment, in step (2), relative to the total weight of the slurry,

[0033] The content of the polymer is 1-20% by weight,

[0034] The content of the easily decomposable material is 1-15% by weight.

[0035] The content of the hydrophobic material is 1-10% by weight.

[0036] In one embodiment, in step (2), the absolute viscosity of the slurry is 100-5,000 mPa·s.

[0037] In one embodiment, in step (3),

[0038] The penetration treatment is performed by roller coating or dip coating, and

[0039] The drying is performed by hot air drying, and the hot air temperature is 50-80°C.

[0040] In one embodiment, in step (4),

[0041] The temperature of the heat treatment is higher than the decomposition temperature of the easily decomposable material and lower than the glass transition temperature of the nanofiber membrane.

[0042] The heat treatment time is 2-30 minutes.

[0043] According to a second aspect of the present invention, there is provided a composite nanofiber membrane, which is prepared by the above method, wherein:

[0044] The composite nanofiber membrane comprises nanofibers as a skeleton and a porous coating formed on the nanofibers.

[0045] The porous coating layer comprises the polymer and the hydrophobic material.

[0046] Beneficial effects

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] (1) The preparation method of the present invention has a simple process, has no particular restrictions on ambient temperature and humidity, and has no particular restrictions on spinning methods, and can be easily carried out for large-scale production.

[0049] (2) The composite nanofiber membrane of the present invention comprises coated nanofibers, wherein the coated nanofibers are in the form of filaments and have a core-shell structure. Specifically, in the composite nanofiber membrane, a specific porous coating is formed on the outer surface of the nanofibers serving as a skeleton, and the nanofibers and the porous coating form a core-shell structure. The porous coating comprises a polymer and a hydrophobic material.

[0050] The pores in the porous coating are formed by removing the easily decomposable materials in the slurry through heat treatment, which can improve the air permeability of the composite nanofiber membrane.

[0051] By filling the pores in the nanofiber membrane with a porous coating and utilizing the hydrophobic effect of the hydrophobic material, the hydrostatic pressure resistance of the nanofiber membrane can be synergistically improved.

[0052] Therefore, the composite nanofiber membrane of the present invention can improve the hydrostatic pressure resistance and air permeability while maintaining the same or similar high filtration efficiency as that of conventional nanofiber membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a scanning electron microscope (SEM) photograph of the product (composite nanofiber membrane) prepared in Example 1-1.

[0054] Figure 2 is a scanning electron microscope (SEM) photograph of the product (blank nanofiber membrane) prepared in Comparative Example 1-1. DETAILED DESCRIPTION

[0055] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The terms or words used in this specification and claims should not be restrictively interpreted as common or dictionary definitions, but should be interpreted as meanings and concepts corresponding to the technical ideas of the present invention on the basis that the inventor can appropriately define the concepts of the terms to describe the principles of the invention in the best possible way.

[0056] When the conditions and methods for measuring a property or parameter described in this specification are not specifically described, the property or parameter can be measured using measurement conditions and methods generally used by those skilled in the art.

[0057] In the present invention, polyester refers to a polymer obtained by polycondensation of polyols and polyacids. For example, the polyester may include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc., but does not include polyurethane, polycaprolactone or polycarbonate.

[0058] Unless otherwise specified, "%" used herein refers to weight %.

[0059] Method for preparing composite nanofiber membrane

[0060] According to a first aspect of the present invention, there is provided a method for preparing a composite nanofiber membrane, the method comprising the following steps:

[0061] (1) Preparing nanofiber membrane;

[0062] (2) preparing a slurry using a polymer, a decomposable material, a hydrophobic material, and a solvent;

[0063] (3) performing an infiltration treatment on the nanofiber membrane using the slurry, and then drying to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane;

[0064] (4) heat-treating the nanofiber membrane containing the initial coating to remove the easily decomposable material and convert the initial coating into a porous coating.

[0065] In the following, each step will be described in detail.

[0066] Step (1) Preparation of nanofiber membrane

[0067] The nanofiber membrane can be prepared by commercially purchasing or preparing the nanofiber membrane. There is no particular limitation on the method for preparing the nanofiber membrane, and a known preparation method can be used. For example, the nanofiber membrane can be prepared by electrospinning, wherein the electrospinning can be solution electrospinning or melt electrospinning.

[0068] Electrospinning is a simple and effective technique for producing micron- to nanometer-scale fibers. It involves causing an electrostatically charged polymer solution or melt to flow and deform in an electrostatic field, solidifying upon solvent evaporation or fiber cooling to form a fibrous material. Electrospinning can be used to easily and effectively produce continuous nanofibers and nanofiber membranes. These nanofibers are typically solid, i.e., not hollow.

[0069] The raw material for preparing the nanofiber membrane may be a water-insoluble polymer, which may be one or more selected from the group consisting of polyacrylonitrile, nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone, and polyvinylidene fluoride.

[0070] The porosity of nanofiber membranes is usually greater than 30%, and the fiber diameter is usually 0.1-3 microns.

[0071] There is no particular limitation on the thickness of the nanofiber membrane, and for example, it may be 20 to 80 microns, specifically 20 to 30 microns, or 40 to 50 microns.

[0072] Step (2) preparing slurry

[0073] The slurry is prepared using a polymer, an easily decomposable material, a hydrophobic material and a solvent. Specifically, the slurry can be formed by uniformly mixing the polymer, the easily decomposable material and the hydrophobic material in a solvent.

[0074] The polymer is a material used to form the skeleton of the final porous coating. According to the form in which it is used, polymers can be divided into the following two categories:

[0075] The first type of polymer is in solid form and can be one or more selected from polycaprolactone, nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone and polyvinylidene fluoride;

[0076] The second type of polymer is in the form of an emulsion, and the emulsion can be one or more selected from aqueous polymer emulsions, such as aqueous polyurethane emulsions, aqueous EVA emulsions, and aqueous polyacrylate emulsions.

[0077] The aqueous polymer emulsion can be obtained commercially. For example, a concentrated solution of the emulsion can be purchased and then diluted with water for subsequent use.

[0078] The solvent is used to dissolve or mix the polymer, easily decomposable material and hydrophobic material. According to the material type of the solvent itself, the solvent can be divided into the following two categories:

[0079] The first type of solvent is an organic solvent, which can be one or more selected from hexafluoroisopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, formic acid, methanol, ethanol, acetone and dichloromethane;

[0080] The second type of solvent is water.

[0081] The readily decomposable material refers to a material having a decomposition temperature lower than that of the nanofiber membrane, and may be one or more selected from bicarbonates, carbonates, nitrates, ammonium salts, amine salts, and oxalates. The readily decomposable material can be decomposed by subsequent heat treatment to form pores in the initial coating, thereby obtaining a porous coating and improving the air permeability of the nanofiber membrane.

[0082] The type of easily decomposable material can be selected according to the type of nanofiber membrane material.

[0083] For example, when the nanofiber membrane material is polyurethane, which has a decomposition temperature of 200°C, ammonium carbonate can be used as the easily decomposable material, which has a decomposition temperature of 58°C.

[0084] In addition, when the nanofiber membrane material is polyester (PET), its decomposition temperature is 305°C, and ammonium oxalate is used as the easily decomposable material, and its decomposition temperature is 95°C.

[0085] The easily decomposable material can be dissolved in water to prepare an aqueous solution, preferably a saturated aqueous solution, to prepare the slurry.

[0086] The types of polymer and easily decomposable material can be appropriately selected and used in combination according to the type of solvent.

[0087] For example, when the solvent is an organic solvent, the polymer may be in a solid form, and the easily decomposable material may be in an aqueous solution form;

[0088] When the solvent is water, the polymer may be in the form of an emulsion, and the easily decomposable material may be in the form of an aqueous solution or a solid.

[0089] A hydrophobic material is a material that is extremely water-repellent, typically having a micro-nanoscale surface roughness and / or low surface energy. The hydrophobic material is used to further enhance the hydrophobic properties of the nanofiber membrane and improve its resistance to hydrostatic pressure. The hydrophobic material can be one or more selected from organosilicon, organofluorine, and super-hydrophobic silica. The organofluorine can be a polytetrafluoroethylene (PTFE)-based hydrophobic material.

[0090] There are no particular restrictions on mixing, as long as the resulting slurry is uniformly mixed. Common mixing methods, such as stirring, can be used. In addition, the polymer, easily decomposable material, hydrophobic material, and solvent can be mixed at room temperature (e.g., 20-25° C.) and normal pressure according to a certain weight ratio to prepare a slurry.

[0091] The polymer content can be 1-20% by weight, preferably 1-10% by weight, and more preferably 3-8% by weight, relative to the total weight of the slurry. If the polymer content is less than 0.1% by weight, the resulting initial coating is too thin and difficult to form a porous structure. If the polymer content is greater than 20% by weight, the resulting initial coating is too thick, reducing air permeability.

[0092] The content of the readily decomposable material may be 1-15% by weight, preferably 2-12% by weight, and more preferably 5-10% by weight, relative to the total weight of the slurry. If the content of the readily decomposable material is less than 1% by weight, the porosity of the resulting initial coating is too low, failing to effectively increase air permeability. If the content of the readily decomposable material is greater than 50% by weight, the resulting initial coating has too many pores and too large a pore diameter, resulting in reduced hydrostatic pressure resistance.

[0093] The hydrophobic material content can be 1-10% by weight, preferably 2-8% by weight, and more preferably 3-5% by weight, relative to the total weight of the slurry. If the hydrophobic material content is less than 1% by weight, the hydrostatic pressure resistance may not be effectively improved. If the hydrophobic material content exceeds 10% by weight, the porous structure of the resulting initial coating may become severely clogged, reducing air permeability.

[0094] The absolute viscosity of the slurry can be 100-5000 mPa·s, preferably 200-4000 mPa·s, and more preferably 500-2000 mPa·s. If the absolute viscosity of the slurry is less than 100 mPa·s, the resulting initial coating is too thin, making it difficult to form a porous structure, which affects air permeability. If the absolute viscosity of the slurry is greater than 5000 mPa·s, the resulting initial coating is too thick, reducing air permeability and causing slurry to remain on the surface of the nanofiber membrane. The absolute viscosity of the slurry can be measured according to GB_T 2794-2022 (Determination of viscosity of adhesives).

[0095] There is no particular limitation on the order of the above steps (1) and (2), and one of the steps may be performed first and then the other.

[0096] The types and ratios of the various components in the slurry can be varied according to actual needs. By adjusting the types and contents of the polymer, easily degradable substance, and hydrophobic material in the slurry, a composite nanofiber membrane with high filtration efficiency, high air permeability, and high hydrostatic pressure resistance can be prepared.

[0097] Step (3) forming an initial coating

[0098] The nanofiber membrane is subjected to an infiltration treatment using the slurry, and then dried to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane.

[0099] Specifically, the slurry can be allowed to penetrate into the entire nanofiber membrane, thereby wrapping or surrounding the nanofibers therein, and forming an initial coating on the outer surface of the nanofibers after drying.

[0100] The penetration treatment can be performed using conventional coating methods, which are widely used in coating and laminating of substrates such as paper and film, and can include roller coating, blade coating, and dip coating.

[0101] In one embodiment, the infiltration treatment can be performed by dip coating, followed by removal. If excess slurry remains on the surface of the nanofiber membrane, it can be removed with a scraper. Next, drying is performed to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane.

[0102] In one embodiment, the infiltration treatment can be performed using roller coating, wherein both surfaces of the nanofiber membrane are coated with the slurry, the slurry being allowed to fully penetrate the interior of the nanofiber membrane, and then dried to form an initial coating on the outer surface of the nanofibers. In addition, the amount of slurry applied can be controlled by the type of coating roller (e.g., a micro-concave roller with a specific pore size) so that there is substantially no excess slurry on the surface of the nanofiber membrane, and preferably no slurry residue on the surface. The coating speed can be 0.5-50 m / min.

[0103] The nanofiber membrane containing the slurry can be dried by hot air drying to remove the solvent. The hot air temperature can be 50-80°C. If the hot air temperature is too low, production efficiency will be reduced; if the hot air temperature is too high, the nanofiber membrane may shrink.

[0104] The appropriate hot air temperature can be selected according to the material types of the nanofiber membrane and the easily decomposable material.

[0105] For example, when the nanofiber membrane is polyurethane and the easily decomposable material is ammonium carbonate, the drying temperature may be 50°C.

[0106] In addition, when the nanofiber membrane is polyester (PET) and the easily decomposable material is ammonium oxalate, the drying temperature can be 80°C.

[0107] The drying time can be 3-30 minutes. If the drying time is too short, the solvent may not have enough time to evaporate. If the drying time is too long, production efficiency will be reduced.

[0108] Step (4) heat treatment

[0109] The nanofiber membrane including the initial coating is subjected to a heat treatment to remove easily decomposable materials and convert the initial coating into a porous coating.

[0110] The porous coating can improve the hydrostatic pressure resistance of the nanofiber membrane by filling the pores in the nanofiber membrane.

[0111] There is no particular limitation on the heat treatment, and conventional heat treatment apparatuses and process conditions can be used. The heat treatment apparatus can be, for example, an industrial oven or a tunnel furnace, and the heat treatment can be performed in the heat treatment apparatus in an intermittent or continuous manner.

[0112] The easily decomposable material can be decomposed and removed by heat treatment, thereby forming a large number of pores in the initial coating, i.e., a porous coating. The pores in the porous coating are micro-nanoscale, for example, 10-1000 nanometers, specifically 100-500 nanometers, or 200-300 nanometers.

[0113] The heat treatment temperature should be higher than the decomposition temperature of the easily decomposable material and lower than the glass transition temperature or decomposition temperature of the nanofiber membrane. For example, when the nanofiber membrane is polyurethane and the easily decomposable material is ammonium carbonate, the heat treatment temperature can be 100°C. When the nanofiber membrane is polyester (PET) and the easily decomposable material is ammonium oxalate, the heat treatment temperature can be 150°C.

[0114] The heat treatment time can be 2-30 minutes, for example, 5-20 minutes, or 10-15 minutes. If the heat treatment time is less than 2 minutes, the easily decomposable material may not be completely decomposed, and sufficient pores may not be formed. If the heat treatment time is greater than 30 minutes, the porous structure formed is already stable, and extending the heat treatment time will only increase energy consumption and reduce production efficiency.

[0115] The composite nanofiber membrane comprising the porous coating layer obtained by heat treatment may have an increase in thickness of about 5-20%, typically 5-10%, relative to the thickness of the initial nanofiber membrane.

[0116] Composite nanofiber membrane

[0117] According to a second aspect of the present invention, a composite nanofiber membrane is provided, comprising nanofibers as a skeleton and a porous coating formed on the nanofibers. Specifically, the composite nanofiber membrane comprises coated nanofibers having a core-shell structure in the form of filaments, wherein a specific porous coating is formed on the outer surface of the nanofibers as the skeleton, thereby forming a core-shell structure.

[0118] The porous coating comprises a uniform mixture of the above polymer and a hydrophobic material, wherein the polymer serves as a skeleton. The pores in the porous coating are micro-nanoscale, for example, 10-1,000 nanometers, specifically 100-500 nanometers, or 200-300 nanometers.

[0119] In particular, no separate flake coating layer is formed on the surface of the composite nanofiber membrane.

[0120] The composite nanofiber membrane can be prepared by the above method.

[0121] The filtration efficiency of the composite nanofiber membrane can be greater than 85% (i.e., particle interception efficiency), preferably greater than 90%. The filtration efficiency can be measured according to GB / T 38413-2019 (Test method for filtration performance of fine particles of textiles) (test flow rate 85 L / min).

[0122] The hydrostatic pressure resistance of the composite nanofiber membrane can be 1-40 kPa, specifically 10-20 kPa, or 25-35 kPa, or 30-35 kPa. The hydrostatic pressure resistance can be measured according to GB / T 4744-2013 (Testing and evaluating the waterproof performance of textiles - Hydrostatic pressure method).

[0123] The air permeability of the composite nanofiber membrane (corresponding to the gas flow rate) can be 5-120 mm / s, specifically 30-100 mm / s, or 50-80 mm / s, or 60-70 mm / s. The air permeability can be measured according to GB / T5453-1997 (Determination of Air Permeability of Textile Fabrics).

[0124] As previously mentioned, there is a trade-off between these parameters. For example, excessively increasing hydrostatic pressure resistance may result in decreased air permeability, and vice versa. Therefore, the present invention maintains these parameters simultaneously within an optimal range by forming a specific porous coating on the nanofibers in the nanofiber membrane. This results in a composite nanofiber membrane that combines high air permeability with high hydrostatic pressure resistance while maintaining high filtration efficiency.

[0125] Example

[0126] Hereinafter, the present invention will be described in detail with reference to Examples to specifically describe the present invention. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

[0127] Unless otherwise specified, the experimental methods in the following examples are generally based on conventional conditions in the art or conditions recommended by the manufacturer; the raw materials and equipment used are all commercially available from conventional markets, unless otherwise specified.

[0128] The relevant indicators of the films prepared in the following examples and comparative examples were tested using the following testing standards:

[0129] Filtration efficiency: GB / T 38413-2019 (Test method for filtration performance of fine particles in textiles) (test flow rate 85L / min)

[0130] Air permeability: GB / T5453-1997 (Determination of air permeability of textile fabrics)

[0131] Hydrostatic pressure resistance: GB / T 4744-2013 (Testing and evaluation of waterproof performance of textiles - Hydrostatic pressure method)

[0132] Examples 1-1 to 1-4 (Using a polyurethane nanofiber membrane, and preparing a slurry using a solid polymer, an easily decomposable material in the form of an aqueous solution, and an organic solvent)

[0133] The raw materials used are as follows:

[0134] 1. Polymer raw materials used to prepare nanofiber membranes: Polyurethane, TPU 85A, BASF, Germany

[0135] 2. Polymer material used for preparing slurry: Nylon, PA 1013B, Ube Corporation, Japan

[0136] 3. Easily decomposable materials: ammonium carbonate, Sinopharm Group

[0137] 4. Hydrophobic material: Fluorinated C6 oil, HG-6307, Zhejiang Huikai Dingrui New Materials Co., Ltd.

[0138] 5.Slurry solvent: industrial formic acid

[0139] The composite nanofiber membranes of Examples 1-1 to 1-4 were prepared by the following steps, wherein only the raw material ratio was changed in step (2) to obtain the respective composite nanofiber membranes.

[0140] Step (1): Preparation of nanofiber membrane

[0141] Polyurethane TPU 85A was dissolved in dimethylacetamide to obtain a spinning solution with a concentration of 17 wt%. Through electrospinning, the surface density was 5.3 g / ㎡ and the density was 0.38 g / cm 3 The polyurethane nanofiber membrane has a thickness of 14 μm.

[0142] Step (2): Prepare slurry

[0143] Nylon PA 1013B was dissolved in formic acid (as a solvent) to obtain a first solution.

[0144] Ammonium carbonate (as an easily decomposable material) is dissolved in water to prepare a saturated solution, which is then added to the first solution and mixed to obtain a second solution.

[0145] Fluorine-containing C6 oil HG-6307 (as a hydrophobic material) was added to the second solution and stirred to obtain a slurry at a stirring speed of 150 r / min, a stirring time of 60 min, and a stirring temperature of room temperature (25° C.).

[0146] Wherein, the weight ratio of nylon / slurry is A;

[0147] The weight ratio of ammonium carbonate / slurry is B;

[0148] The weight ratio of fluorinated C6 oil to slurry is C.

[0149] For Examples 1-1 to 1-4, the above-mentioned A, B, and C are respectively shown in Table 1 below.

[0150] Table 1

[0151] A B C Example 1-1 5 / 100 6 / 100 4 / 100 Example 1-2 5 / 100 12 / 100 4 / 100 Examples 1-3 5 / 100 6 / 100 8 / 100 Examples 1-4 10 / 100 6 / 100 4 / 100

[0152] Step (3): Forming the initial coating

[0153] The slurry was evenly applied to one surface of the polyurethane nanofiber membrane prepared in step 1 by roller coating using a coating machine (Xinjiatuo, KTBG1200C micro-gravure coater), allowing the slurry to penetrate the nanofiber membrane. The membrane was then dried with hot air to remove formic acid, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane, thereby obtaining a nanofiber membrane containing the initial coating.

[0154] The coating speed is 1 m / min, the hot air temperature is 50°C, and the drying time is 30 min.

[0155] Step (4): Heat treatment

[0156] The nanofiber membrane including the initial coating was heat-treated in a tunnel furnace (RTL Tunnel Furnace, Hefei Rixin) to remove ammonium carbonate, thereby obtaining a composite nanofiber membrane including a porous coating.

[0157] The heat treatment temperature is 100°C and the time is 10 minutes.

[0158] Examples 2-1 to 2-4 (Using a polyester nanofiber membrane, and preparing a slurry using a polymer in the form of an emulsion, an easily decomposable material in the form of an aqueous solution, and water)

[0159] The raw materials used are as follows:

[0160] 1. Polymer raw material for preparing nanofiber membrane: Polyester PET YS-W01, Shanghai Xinmengxin Plastics Co., Ltd.

[0161] 2. Polymer material used to prepare slurry: Polyurethane PU aqueous emulsion PU-F0410, Shenzhen Jitian Chemical Co., Ltd.

[0162] 3. Easily decomposable materials: ammonium oxalate, Sinopharm Group

[0163] 4. Hydrophobic material: hydrophobic silica HB-630, Hubei Huifu Nanomaterials Co., Ltd.

[0164] 5.Slurry solvent: pure water

[0165] The composite nanofiber membranes of Examples 2-1 to 2-4 were prepared by the following steps, wherein only the raw material ratio was changed in step (2) to obtain the respective composite nanofiber membranes.

[0166] Step (1): Preparation of nanofiber membrane

[0167] Polyester YS-W01 was dissolved in dimethylacetamide to obtain a 20% spinning solution. Electrospinning was performed to produce a polyester nanofiber membrane with an area density of 3.5 g / m2 and a density of 0.15 g / cm3. The nanofiber membrane had a thickness of 23 μm.

[0168] Step (2): Prepare slurry

[0169] The PU-F0410 emulsion was diluted into water (as a solvent) to obtain a first solution.

[0170] Ammonium oxalate (as an easily decomposable material) is dissolved in water to prepare a saturated solution; and then the saturated solution is added to the first solution and mixed to obtain a second solution.

[0171] Hydrophobic fumed silica HB-630 (as a hydrophobic material) was added to the second solution and stirred to obtain a slurry at a stirring speed of 500 r / min, a stirring time of 60 min, and a stirring temperature of room temperature (25° C.).

[0172] Among them, the weight ratio of polyester PET / slurry is A;

[0173] The weight ratio of ammonium oxalate to slurry is B;

[0174] The weight ratio of hydrophobic fumed silica HB-630 to slurry is C.

[0175] For Examples 2-1 to 2-4, the above A, B, and C are shown in Table 2 below.

[0176] Table 2

[0177] A B C Example 2-1 6 / 100 10 / 100 5 / 100 Example 2-2 6 / 100 15 / 100 5 / 100 Example 2-3 6 / 100 10 / 100 10 / 100 Examples 2-4 12 / 100 10 / 100 5 / 100

[0178] Step (3): Forming the initial coating

[0179] The slurry was evenly coated on the surface of the polyester nanofiber membrane prepared in step 1 by roller coating using a coating machine (Xinjiatuo, KTBG1200C micro-gravure coater), allowing the slurry to penetrate the nanofiber membrane. The membrane was then dried with hot air to remove water, forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane.

[0180] The coating speed is 1 m / min, the drying temperature is 80°C, and the time is 30 min.

[0181] Step (4): Heat treatment

[0182] The nanofiber membrane containing the initial coating was heat-treated in a tunnel furnace (RTL Tunnel Furnace, Hefei Rixin) to remove the ammonium oxalate, thereby obtaining a composite nanofiber membrane containing a porous coating.

[0183] The heat treatment temperature is 150°C and the time is 8 minutes.

[0184] Comparative Examples 1-1 to 1-5 (Using Polyurethane Nanofiber Membrane)

[0185] Comparative Examples 1-1 to 1-5 were prepared by the same method as Example 1-1, except that:

[0186] Comparative Example 1-1: Steps (2), (3) and (4) in Example 1-1 were omitted to obtain a blank nanofiber membrane.

[0187] Comparative Example 1-2: In step (2), the slurry does not contain polymer materials and easily decomposable materials, and the resulting nanofiber membrane is treated only with a hydrophobic material;

[0188] Comparative Example 1-3: In step (2), the slurry does not contain easily decomposable materials and hydrophobic materials, and the resulting composite nanofiber membrane only contains the polymer material as a coating;

[0189] Comparative Example 1-4: In step (2), the slurry does not contain a hydrophobic material, and the composite nanofiber membrane finally obtained contains only a polymer material as a coating.

[0190] Comparative Example 1-5: In step (2), the slurry does not contain easily decomposable materials.

[0191] For Comparative Examples 1-2 to 1-5, A, B, and C in step (2) are respectively shown in Table 3 below.

[0192] Table 3

[0193] A B C Comparative Example 1-2 0 0 4 / 100 Comparative Examples 1-3 5 / 100 0 0 Comparative Examples 1-4 5 / 100 6 / 100 0 Comparative Examples 1-5 5 / 100 0 4 / 100

[0194] Comparative Examples 2-1 to 2-5 (using polyester nanofiber membrane)

[0195] Comparative Examples 2-1 to 2-5 were prepared by the same procedure as Example 2-1, except that:

[0196] Comparative Example 2-1: Steps (2), (3) and (4) in Example 2-1 were omitted to obtain a blank nanofiber membrane.

[0197] Comparative Example 2-2: In step (2), the slurry does not contain polymers and easily decomposable materials, and the resulting nanofiber membrane is treated only with a hydrophobic material;

[0198] Comparative Example 2-3: In step (2), the slurry does not contain easily decomposable materials and hydrophobic materials, and the resulting composite nanofiber membrane only contains the polymer material as a coating;

[0199] Comparative Example 2-4: In step (2), the slurry does not contain a hydrophobic material, and the resulting composite nanofiber membrane only contains a polymer material as a coating;

[0200] Comparative Example 2-5: In step (2), the slurry does not contain easily decomposable materials.

[0201] For Comparative Examples 2-2 to 2-5, A, B, and C in step (2) are respectively shown in Table 4 below.

[0202] Table 4

[0203] A B C Comparative Example 2-2 0 0 5 / 100 Comparative Examples 2-3 6 / 100 0 0 Comparative Examples 2-4 6 / 100 10 / 100 0 Comparative Examples 2-5 6 / 100 0 5 / 100

[0204] Experimental Example 1 Measurement of membrane filtration efficiency, air permeability and hydrostatic pressure resistance

[0205] The filtration efficiency, air permeability, and hydrostatic pressure resistance of the products of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-5 were measured. The results are shown in Table 5 below.

[0206] Table 5

[0207]

[0208] According to Table 5, by comparing the various embodiments and comparative examples with each other, the following conclusions can be drawn.

[0209] By comparing Example 1-1 to Example 1-4, it can be found that by adjusting the ratio of polymer, easily decomposable material and hydrophobic material in the slurry, Example 1-1 exhibits excellent resistance to hydrostatic pressure and air permeability, while the filtration efficiency also maintains a high index.

[0210] In addition, compared with Comparative Examples 1-1 to 1-5, the products of Examples 1-1 to 1-4 prepared by the method of the present invention have obvious comprehensive advantages.

[0211] Specifically, by comparing Example 1-1 with Example 1-2, it can be found that increasing the content of easily decomposable materials in the slurry can increase the air permeability of the composite nanofiber membrane, but will reduce its resistance to hydrostatic pressure;

[0212] By comparing Example 1-1 with Example 1-3, it can be found that increasing the content of the hydrophobic material in the slurry can increase the hydrostatic pressure resistance of the composite nanofiber membrane, but will reduce its air permeability;

[0213] By comparing Example 1-1 with Example 1-4, it can be found that increasing the polymer content in the slurry can improve the filtration efficiency of the composite nanofiber membrane, but will reduce its air permeability.

[0214] In addition, by comparing Example 1-1 with Comparative Example 1-1 (blank nanofiber membrane), it can be found that the composite nanofiber membrane of Example 1-1 simultaneously improves comprehensive performance such as filtration efficiency, air permeability and hydrostatic pressure resistance.

[0215] By comparing Example 1-1 with Comparative Example 1-2, it can be found that adding polymers and easily decomposable materials to the slurry can significantly improve the air permeability of the composite nanofiber membrane, and the synergistic combination of the porous structure and the hydrophobic material significantly improves the hydrostatic pressure resistance of the composite nanofiber membrane.

[0216] By comparing Example 1-1 with Comparative Examples 1-3, it can be found that adding easily decomposable materials to the slurry can significantly improve the air permeability of the composite nanofiber membrane; and adding hydrophobic materials to the slurry can significantly improve the hydrostatic pressure resistance of the composite nanofiber membrane.

[0217] By comparing Example 1-1 with Comparative Examples 1-4, it can be found that adding hydrophobic material to the slurry can significantly improve the hydrostatic pressure resistance of the composite nanofiber membrane.

[0218] By comparing Example 1-1 with Comparative Examples 1-5, it can be found that adding easily decomposable materials to the slurry can significantly improve the air permeability of the composite nanofiber membrane.

[0219] Experimental Example 2 Measurement of membrane filtration efficiency, air permeability and hydrostatic pressure resistance

[0220] The filtration efficiency, air permeability, and hydrostatic pressure resistance of the products of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-5 were measured. The results are shown in Table 6 below.

[0221] Table 6

[0222]

[0223] According to Table 6, by comparing the various embodiments and comparative examples with each other, the following conclusions can be drawn.

[0224] By comparing Example 2-1 to Example 2-4, it can be found that by adjusting the ratio of polymer, easily decomposable material and hydrophobic material in the slurry, Example 2-1 exhibits excellent resistance to hydrostatic pressure and air permeability, while the filtration efficiency also maintains a high index.

[0225] In addition, compared with Comparative Examples 2-1 to 2-5, the products of Examples 2-1 to 2-4 prepared by the method of the present invention have obvious comprehensive advantages.

[0226] Specifically, by comparing Example 2-1 with Example 2-2, it can be found that increasing the content of easily decomposable materials in the slurry can significantly increase the air permeability of the composite nanofiber membrane, but will reduce its resistance to hydrostatic pressure.

[0227] By comparing Example 2-1 with Example 2-3, it can be found that increasing the content of hydrophobic material in the slurry can significantly improve the hydrostatic pressure resistance of the composite nanofiber membrane, but will reduce its air permeability.

[0228] By comparing Example 2-1 with Example 2-4, it can be found that increasing the polymer content in the slurry can significantly improve the filtration efficiency of the composite nanofiber membrane, but will reduce its air permeability.

[0229] In addition, by comparing Example 2-1 with Comparative Example 2-1, it can be found that Example 2-1 simultaneously improves comprehensive performance such as filtration efficiency, air permeability and hydrostatic pressure resistance.

[0230] By comparing Example 2-1 with Comparative Example 2-2, it can be found that the polymer and easily decomposable material in the slurry can significantly improve the air permeability of the composite nanofiber membrane, and the synergistic combination of the porous structure and the hydrophobic material significantly improves the hydrostatic pressure resistance of the composite nanofiber membrane.

[0231] By comparing Example 2-1 with Comparative Example 2-3, it can be found that the easily decomposable material in the slurry significantly improves the air permeability of the composite nanofiber membrane, and the hydrophobic material in the slurry significantly improves the hydrostatic pressure resistance of the composite nanofiber membrane.

[0232] By comparing Example 2-1 with Comparative Example 2-4, it can be found that the hydrophobic material in the slurry significantly improves the hydrostatic pressure resistance of the composite nanofiber membrane.

[0233] By comparing Example 2-1 with Comparative Example 2-5, it can be found that the easily decomposable material in the slurry significantly improves the air permeability of the composite nanofiber membrane.

[0234] Experimental Example 3: Morphology Observation Using a Scanning Electron Microscope

[0235] The product prepared in Example 1-1 (polyurethane composite nanofiber membrane) and the product prepared in Comparative Example 1-1 (blank polyurethane nanofiber membrane) were observed by scanning electron microscopy (SEM), and the results are shown in Figure 1 and Figure 2 middle.

[0236] from Figure 1 As can be seen in the figure, the average diameter of the nanofibers in the polyurethane-based composite nanofiber membrane of the present invention is approximately 700 nm, and the outer surface of the nanofibers is clearly surrounded by a porous structure (i.e., a porous coating). The pores in this porous structure are formed by heat-treating the slurry to remove easily decomposable materials, and these pores enhance the air permeability of the composite nanofiber membrane.

[0237] In addition, by using a porous structure to fill the pores in the nanofiber membrane and utilizing the hydrophobic effect of the hydrophobic material, the hydrostatic pressure resistance of the nanofiber membrane can be synergistically improved.

[0238] from Figure 2 It can be seen from the figure that the average diameter of the nanofibers in the blank polyurethane nanofiber membrane is about 500 nm, and the fiber surface is smooth.

[0239] In addition, according to Table 5 above, compared with the blank nanofiber membrane of Comparative Example 1-1, the composite nanofiber membrane of Example 1-1 is improved in filtration efficiency, air permeability and hydrostatic pressure resistance.

[0240] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a composite nanofiber membrane, the method comprising the following steps: (1) Preparation of nanofiber membranes by electrospinning; (2) using polymers, easily decomposable materials, hydrophobic materials and solvents to prepare slurry, Wherein, the easily decomposable material is one or more selected from bicarbonate, carbonate, nitrate, ammonium salt, amine salt and oxalate, The hydrophobic material is one or more selected from organosilicon, organofluorine and super hydrophobic silica; (3) performing an infiltration treatment on the nanofiber membrane using the slurry so that the slurry penetrates into the entire nanofiber membrane and no slurry remains on the surface of the nanofiber membrane, and then drying to remove the solvent, thereby forming an initial coating on the outer surface of the nanofibers in the nanofiber membrane; (4) heat-treating the nanofiber membrane containing the initial coating layer to remove the easily decomposable material and convert the initial coating layer into a porous coating layer.

2. The method according to claim 1, wherein In step (1), The electrospinning is solution electrospinning or melt electrospinning. The raw material for preparing the nanofiber membrane is a water-insoluble polymer, which is one or more selected from the following: polyacrylonitrile, nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone and polyvinylidene fluoride.

3. The method according to claim 1, wherein In step (2), The solvent is an organic solvent, and is one or more selected from hexafluoroisopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, formic acid, methanol, ethanol, acetone and dichloromethane; The polymer is in solid form and is one or more selected from nylon, polyurethane, polyester, polyimide, polyethersulfone, polyetheretherketone and polyvinylidene fluoride; The easily decomposable material is in the form of an aqueous solution.

4. The method according to claim 1, wherein In step (2), The solvent is water; The polymer is in the form of an emulsion, and the emulsion is one or more selected from aqueous polyurethane emulsion, aqueous EVA emulsion and aqueous polyacrylate emulsion; The easily decomposable material is in the form of an aqueous solution or a solid.

5. The method according to claim 1, wherein In step (2), relative to the total weight of the slurry, The content of the polymer is 1-20% by weight, The content of the easily decomposable material is 1-15% by weight. The content of the hydrophobic material is 1-10% by weight.

6. The method according to claim 1, wherein In step (2), the absolute viscosity of the slurry is 100-5,000 mPa·s.

7. The method according to claim 1, wherein In step (3), The penetration treatment is performed by roller coating or dip coating, and The drying is performed by hot air drying, and the hot air temperature is 50-80°C.

8. The method according to claim 1, wherein In step (4), The temperature of the heat treatment is higher than the decomposition temperature of the easily decomposable material and lower than the glass transition temperature of the nanofiber membrane. The heat treatment time is 2-30 minutes.

9. A composite nanofiber membrane, which is prepared by the method according to claim 1, wherein The composite nanofiber membrane comprises nanofibers as a skeleton and a porous coating formed on the nanofibers. The porous coating layer comprises the polymer and the hydrophobic material.

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