A flash-steamed HDPE nonwoven fabric reinforced para-aromatic polyamide composite film and its preparation method

Abstract

The present invention relates to the field of membrane technology and provides a flash-evaporated HDPE nonwoven fabric reinforced para-aromatic polyamide composite membrane and a preparation method thereof, which solves the defects of the prior art separation membrane preparation process, such as complex process, high cost, and mediocre mechanical properties. The invention comprises the following steps: (1) flash-evaporating the HDPE nonwoven fabric reinforcement; (2) pre-treating the surface of the flash-evaporated HDPE nonwoven fabric; (3) preparing a para-aromatic polyamide casting solution; and (4) preparing the para-aromatic polyamide composite membrane.

Description

Technical Field

[0001] The invention relates to the technical field of membranes, and in particular to a flash-evaporated HDPE nonwoven fabric-reinforced para-aromatic polyamide composite membrane and a preparation method thereof. Background Art

[0002] With the development of modern industry, particularly in the petrochemical, paint and dyeing, food and pharmaceutical industries, there is a growing demand for efficient, environmentally friendly, and durable separation technologies. Common separation membrane materials, such as polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride, have poor physical and chemical stability and are prone to swelling or even dissolution under harsh conditions such as high temperatures and organic solvents, severely limiting the membrane's service life. Inorganic ceramic membranes offer advantages such as high flux, excellent solvent resistance, and long service life, but they also suffer from complex preparation processes, high production costs, and brittleness.

[0003] Para-aromatic polyamide (PPTA) molecular chains contain numerous benzene rings and amide bond structures, resulting in a planar, rigid, straight chain conformation. These molecules exhibit high crystallinity and strong hydrogen bonding capabilities, and the presence of numerous polar amide groups in the molecular chain endows PPTA with excellent hydrophilic, mechanical, heat, and solvent resistance. This makes it an ideal material for high-performance separation membranes and is widely used in wastewater separation and purification in the chemical, pharmaceutical, biological, and food industries. However, due to its insoluble and infusible properties, it is generally soluble only in a few inorganic acid solutions, such as concentrated sulfuric acid, hindering its application in functional membranes and fibers.

[0004] In the prior art, Chinese invention patent publication number CN104801205A discloses a method for preparing a homogeneous reinforced para-aromatic polyamide hollow fiber membrane. The obtained hollow fiber membrane has a relatively thick outer diameter (>2mm), a high membrane assembly cost, a low packing density, poor permeation efficiency, and a problem of easy falling off of the separation layer, which limits its widespread application. Chinese invention patent publication numbers CN115532078A and CN113117534A disclose a heterogeneous reinforced para-aromatic polyamide hollow fiber membrane, which can effectively improve the tensile strength of the hollow fiber membrane. However, the former method requires a complex and harsh process to prepare solid sulfuric acid particles, and the latter requires precise control of the uniform distribution of filament fibers and embedding them into the membrane wall, which places high difficulty requirements on the film forming process and reduces production efficiency. In addition, the surface separation layer of both has a high solid content concentration and poor permeation efficiency, which limits their widespread use in practical applications. Summary of the Invention

[0005] Therefore, in order to solve the above problems, the present invention provides a flash-evaporated HDPE nonwoven fabric reinforced para-aromatic polyamide composite membrane and a preparation method thereof, which solves the defects of the prior art separation membrane preparation process being complex, high cost and mediocre mechanical properties.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a flash-evaporated HDPE nonwoven reinforced para-aromatic polyamide composite film, comprising the following steps:

[0007] (1) Flash-steamed HDPE nonwoven reinforcement: A nonwoven fabric made of fibers produced by flash-steaming high-density polyethylene (HDPE) and then bonded by heat and pressure, and used as a reinforcement for the composite film; the nonwoven fabric has a gram weight of 50 to 160 g / m 2 , thickness is 25-200μm, average pore size is 1-5μm, porosity is 50-90%, and breaking strength is >50MPa;

[0008] (2) Surface pretreatment of flash-evaporated HDPE nonwoven fabric: using a weakly polar organic liquid to immerse or treat the flash-evaporated HDPE nonwoven fabric prepared in step (1), wherein the weakly polar organic liquid is methanol, ethanol, or isopropanol, the immersion time is 1 to 3 hours, and the oxygen plasma treatment time is 5 to 60 seconds;

[0009] (3) preparing a para-aromatic polyamide casting solution: the para-aromatic polyamide casting solution is prepared by first dissolving the para-aromatic polyamide resin in an inorganic acid solvent at 50 to 90° C. at a speed of >600 rpm for 2 to 5 hours, then sequentially adding a porogen, and then controlling the temperature and continuing to stir at a high speed for 0.5 to 2.5 hours, followed by vacuum degassing for 1 to 2 hours to obtain a highly uniform para-aromatic polyamide casting solution;

[0010] (4) Preparing a para-aromatic polyamide composite membrane: the para-aromatic polyamide casting solution prepared in step (3) is evenly coated on the surface of the flash-evaporated HDPE non-woven fabric fixed on a heatable glass plate by a manual or automatic scraper, and after being in an air bath for 0 to 120 seconds, it is immersed in a coagulation bath at 0 to 65° C. to solidify and form, thereby obtaining the para-aromatic polyamide composite membrane; the temperature of the heated glass plate is maintained at 50 to 90° C., and the scraping speed is 30 to 100 mm / s; the medium of the coagulation bath is water, or an aqueous solution of the inorganic acid solvent, and the mass fraction of the solvent is 0 to 30%.

[0011] Furthermore, the mass fraction composition of each substance in the para-aromatic polyamide casting solution is: 0.5-5wt% para-aromatic polyamide resin, 6-10wt% porogen, 85-93.5wt% inorganic acid solvent, and the sum of each component is 100wt%.

[0012] Furthermore: the mesh size of the para-aromatic polyamide resin is 50 to 1000 mesh; the porogen is at least one of PEG with an average molecular weight of 200 to 20,000 Da and PVP with an average molecular weight of 8,000 to 58,000 Da, and the two are mixed in a mass ratio of PEG / PVP = 10 / 0 to 1 / 1; adding the porogens in sequence means first adding PEG and stirring at high speed for 0.5 to 1 hour, and then adding PVP and stirring at high speed for 0.5 to 1.5 hours.

[0013] Furthermore: the temperature control refers to a temperature of 60 to 80°C.

[0014] Furthermore: the high-speed stirring rate is greater than 1200 rpm.

[0015] Furthermore: the inorganic acid solvent refers to concentrated sulfuric acid with a mass concentration of 93 to 100 wt%.

[0016] A flash-steamed HDPE nonwoven fabric reinforced para-aromatic polyamide composite film is prepared by adopting the above-mentioned preparation method of the flash-steamed HDPE nonwoven fabric reinforced para-aromatic polyamide composite film.

[0017] Furthermore, the composite membrane has an average pore size of 3 to 50 nm, a thickness of 50 to 300 μm, a water contact angle of 40 to 60°, and a pure water flux of 200 to 1000 L / m 2 / h / bar, organic solvent flux is 40~400L / m 2 / h / bar, a cut-off molecular weight of 3000 to 60000 Da, a dye retention molecular weight as low as 697.7 g / mol, and a breaking strength of 50 to 200 MPa; after 3.5 bovine serum albumin-water cycles, the composite membrane has a pure water flux recovery rate of up to 84% after simple water washing; after soaking the composite membrane in an organic solvent for one month, the Congo red retention rate remains stable at above 98%.

[0018] By adopting the above technical solution, the beneficial effects of the present invention are:

[0019] 1. The preparation method of the present invention adjusts the existing casting solution formula and adopts the method of flash-evaporated HDPE non-woven fabric reinforcement. The para-aromatic polyamide casting solution is evenly coated on the surface of the flash-evaporated HDPE non-woven fabric fixed on a heatable glass plate by a manual or automatic scraper. The membrane is formed by a phase inversion method in a coagulation bath under a certain air bath to obtain a flash-evaporated HDPE non-woven fabric reinforced para-aromatic polyamide composite membrane with excellent performance and low price (low cost, high permeation flux, high separation accuracy and high interface bonding strength).

[0020] 2. Compared with existing enhanced membranes, the present invention not only maintains the original good properties of the membrane material, but also significantly improves the mechanical strength of the para-aromatic polyamide composite membrane (breaking strength > 50MPa); the product has better interfacial bonding strength and high peel strength, can be backwashed under high pressure, and can operate stably for a long time under conditions such as high temperature (> 60°C) and polar aprotic organic solvents (such as DMF, DMSO, NMP).

[0021] 3. By selecting porogens and optimizing their ratios, addition sequence, and preparation conditions, precise control and meticulous manipulation are employed to avoid agglomeration during the dissolution of para-aromatic polyamide resin, PEG, and PVP, reduce resin degradation and porogen carbonization, and thereby improve the mixing uniformity of the casting solution. This effectively shortens the dissolution time and increases the dissolution rate, enabling the controllable preparation of highly homogeneous, low-concentration para-aromatic polyamide casting solutions. This allows for precise control of membrane structure and performance, while maintaining high-precision separation. While achieving narrower pore size (small pore size with narrow distribution, 3-6 nm), low dye molecular weight cut-off (≥697.7 g / mol), high temperature resistance (>60°C), ultra-high throughput, solvent resistance, acid and alkali resistance, simple preparation, high packing density, and low cost, these advantages meet the industrial production needs of demanding specialty separation applications (such as high temperature, organic solvents, and acid and alkali solutions), providing a highly efficient, environmentally friendly, and durable separation technology solution for modern industry.

[0022] 4. The para-aromatic polyamide composite membrane of the present invention has the characteristics of super hydrophilicity (contact angle <60°) and excellent anti-fouling performance, and can achieve high flux recovery through simple backwashing.

[0023] 5. Compared with the reinforcement obtained by the limitation of existing supporting materials, which has large pore size, low porosity, thick thickness and poor flexibility, different reinforcement tissue structures are designed through flash evaporation technology to produce flash-evaporated HDPE non-woven fabrics with excellent mechanical properties, smaller pore size, high porosity, thinner thickness and strong flexibility. It can effectively increase the interfacial bonding force and reduce the penetration of casting liquid into the interior of the flash-evaporated HDPE non-woven fabric, thereby increasing the penetration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM surface morphology image of the flash-steamed HDPE nonwoven fabric of the present invention;

[0025] Figure 2 The SEM surface morphology and cross-sectional morphology of the composite membrane of the present invention;

[0026] Figure 3 is the pure water flux of the composite membrane of the present invention;

[0027] Figure 4The pore size distribution of the composite membrane prepared in Example 1 of the present invention;

[0028] Figure 5 The organic reagent permeation flux of the composite membrane prepared in Example 1 of the present invention;

[0029] Figure 6 The separation performance of the composite membrane of the present invention for bovine serum albumin, (a) the permeation flux of the composite membrane changes with time, (b) the retention rate of the composite membrane changes with time;

[0030] Figure 7 The anti-fouling performance of the composite membrane prepared in Example 1 of the present invention, wherein (a) is the normalized flux of the composite membrane; (b) is the flux recovery and the anti-fouling ratio of the composite membrane (after 3 cycles). DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the claims of the present invention.

[0032] refer to Figures 1 to 6 A flash-steamed HDPE nonwoven reinforced para-aromatic polyamide composite film and a preparation method thereof, comprising the following steps:

[0033] (1) Flash-evaporated HDPE nonwoven reinforcement: HDPE was dissolved in dichloromethane at 200°C and heated with carbon dioxide at 690,000 cN / cm 2 The spinning solution is saturated under high pressure and then pressed into the air chamber through the spinneret, forming a bundle of filaments that are ejected at high speed. The dichloromethane solvent evaporates instantly, and the speed gradient is used to stretch the filaments at high magnification, forming an ultra-fine mesh fiber strip. Electrostatic methods are used to open the filaments and maintain them in a single-filament state, and an electrostatic device is used to condense the fibers into a web. This web is then hot-rolled to produce a flash-steamed HDPE nonwoven fabric.

[0034] The HDPE concentration is controlled at 12% to 13%; the filament fineness is 1,000 to 2,000 d; the high-speed ejection is 10,000 to 11,000 m / min; the single filament fineness of the ultrafine mesh fiber strip is 0.10 to 0.15 dtex; the coagulation speed is 90 to 110 m / min; the flash-steamed HDPE nonwoven fabric has a gram weight of 50 to 160 g / m2, a thickness of 25 to 200 μm, a pore size of 1 to 5 μm, a porosity of 50 to 90%, and a breaking strength of >50 MPa.

[0035] (2) pre-treating the surface of the flash-evaporated HDPE nonwoven fabric; using a weakly polar organic liquid to immerse the flash-evaporated HDPE nonwoven fabric prepared in step (1) or perform oxygen plasma treatment, wherein the weakly polar organic liquid is methanol, ethanol, or isopropanol, the immersion time is 1 to 3 hours, and the oxygen plasma treatment time is 5 to 60 seconds;

[0036] (3) preparing a para-aromatic polyamide casting solution; the para-aromatic polyamide casting solution is prepared by first dissolving a para-aromatic polyamide resin in an inorganic acid solvent at 50-90° C. at a stirring speed of greater than 600 rpm for 2-5 hours, then sequentially adding a porogen, and then controlling the temperature and continuing high-speed stirring for 0.5-2.5 hours, followed by vacuum degassing for 1-2 hours to obtain a highly uniform para-aromatic polyamide casting solution, the mass fraction of which is as follows:

[0037] Para-aromatic polyamide resin 0.5-5wt%;

[0038] Porogen 6-10wt%;

[0039] Inorganic acid solvent 85-93.5wt%, the sum of all components is 100wt%,

[0040] The para-aromatic polyamide resin has a mesh size of 50 to 1000 mesh; the porogen is at least one of PEG with an average molecular weight of 200 to 20,000 Da and PVP with an average molecular weight of 8,000 to 58,000 Da, and the two are mixed in a mass ratio of PEG / PVP = 10 / 0 to 1 / 1; the sequential addition of the porogens means first adding PEG and stirring at high speed for 0.5 to 1 hour, and then adding PVP and stirring at high speed for 0.5 to 1.5 hours; the temperature control means the temperature is 60 to 80° C.; the high-speed stirring rate is greater than 1200 rpm; the inorganic acid solvent is concentrated sulfuric acid with a mass concentration of 93 to 100 wt%;

[0041] (4) preparing a para-aromatic polyamide composite film; applying the prepared para-aromatic polyamide casting solution evenly to the surface of the flash-evaporated HDPE non-woven fabric fixed on a heatable glass plate by a manual or automatic scraper, and after being in an air bath for 0 to 120 seconds, immersing the film in a coagulation bath at 0 to 65° C. to solidify and form the para-aromatic polyamide composite film; the temperature of the heated glass plate is maintained at 50 to 90° C., and the scraping speed is 30 to 100 mm / s; the medium of the coagulation bath is water or an aqueous solution of the inorganic acid solvent, and the mass fraction of the solvent is 0 to 30%.

[0042] Since the flash-evaporated HDPE nonwoven reinforcement will undergo a certain degree of etching in the solvent, the immersion time in the casting solution must be effectively controlled. On the one hand, if the immersion time is too long, the flash-evaporated HDPE nonwoven reinforcement will be severely etched, and the mechanical properties of the composite film will be reduced; on the other hand, if the immersion time is too short, the casting solution will have a poor infiltration effect on the reinforcement, and the interface bonding strength will be low, affecting the overall performance of the composite film. Therefore, the air gap and the scraping speed jointly determine the immersion or residence time of the reinforcement in the casting solution, that is, the degree of its etching. The present invention recommends an air bath of 0 to 120 seconds and a scraping speed of 30 to 100 mm / s. The comprehensive performance of the composite film obtained under these process conditions is better.

[0043] The method for preparing a flash-spun HDPE nonwoven reinforced composite membrane according to the present invention can produce a flash-spun HDPE nonwoven reinforced para-aromatic polyamide composite membrane. This composite membrane combines the characteristics of flash spinning and liquid crystal spinning, significantly improving the interfacial bonding strength of the para-aromatic polyamide composite membrane while also enhancing the membrane's mechanical properties.

[0044] Any matters not described in the present invention are applicable to the prior art.

[0045] Specific embodiments of the present invention are given below.

[0046] Example 1

[0047] A flash-steamed HDPE nonwoven reinforced para-aromatic polyamide composite film and a preparation method thereof, comprising the following steps:

[0048] (1) Preparation of reinforcement: HDPE with a concentration of 12% was dissolved in dichloromethane at 200°C and heated with carbon dioxide at 690,000 cN / cm 2 The spinning solution is saturated under high pressure and is pressed into the air chamber through the spinneret to form a bundle of filaments with a fineness of 1200d. It is then ejected at a high speed of 11,000 m / min. The dichloromethane solvent evaporates instantly, and the filaments are stretched at a high rate by varying the speed gradient, forming an ultra-fine mesh fiber strip with a single filament fineness of 0.14d. At the same time, an electrostatic method is used to open the filaments to maintain a single filament state, and an electrostatic device is used to condense the fibers into a web at a speed of 100 m / min. After hot rolling, a flash-steamed HDPE nonwoven fabric with a gram weight of 50g / m2, a thickness of 90μm, a pore size of 3μm, a porosity of 60%, and a breaking strength of 60MPa is produced.

[0049] (2) impregnating the flash-evaporated HDPE nonwoven fabric prepared in step (1) with ethanol for 1 h;

[0050] (3) 1.5 wt% para-aromatic polyamide resin (100 mesh) was first dissolved in 98 wt% concentrated sulfuric acid at 70°C at 800 rpm for 4 h, and then 10 wt% PEG (molecular weight 2000) was added and stirred at 1200 rpm for 0.5 h. PVP (K30, molecular weight 40000) was then added in sequence. The two were mixed at a mass ratio of PEG / PVP = 9:1. After further stirring at 65°C for 0.5 h, vacuum degassing was performed for 2 h to obtain a highly uniform para-aromatic polyamide casting solution.

[0051] (4) preparing a para-aromatic polyamide composite membrane; the prepared para-aromatic polyamide casting liquid is evenly coated on the surface of a flash-steamed HDPE non-woven fabric fixed on a 65°C glass plate by a manual or automatic scraper at a scraping speed of 75 mm / s, and after being in an air bath for 15 seconds, it is immersed in a coagulation bath (water) at 30°C for solidification and forming, thereby obtaining the para-aromatic polyamide composite membrane.

[0052] The composite membrane obtained in this example has a room temperature pure water flux of 585.1 LMH / bar at 1 bar and a DMF solvent flux of 219.8 LMH / bar. After being immersed in DMF solvent for 30 days, the bovine serum albumin content is still greater than 99.0%.

[0053] Comparative Example 1

[0054] A para-aromatic polyamide composite film with PET non-woven fabric as a reinforcement was prepared as a comparative example of the present invention: the casting solution formula of Example 1 was followed, and the preparation process was exactly the same as that of Example 1.

[0055] After testing, the flux of pure water at room temperature is 64.9LMH / bar at 1 bar, and the flux of DMF solvent is 21.4LMH / bar. After soaking in DMF solvent for 30 days, the bovine serum albumin is still >99.0%.

[0056] Example 2

[0057] The method is basically the same as Example 1, except that 10 wt % of porogens PEG (molecular weight 2000) and PVP (K30, molecular weight 40000) (PEG / PVP=4:1) are added.

[0058] The composite membrane obtained in this embodiment has a room temperature pure water flux of 760.4 at 1 bar. + 4.5LMH / bar, DMF solvent flux is 286.6LMH / bar, and after immersion in DMF solvent for 30 days, the bovine serum albumin is still >99.0%.

[0059] Example 3

[0060] The method is basically the same as Example 1, except that 10 wt% of porogens PEG (molecular weight 2000) and PVP (K30, molecular weight 40000) (PEG / PVP=7:3) are added.

[0061] The composite membrane obtained in this example has a room temperature pure water flux of 930.0 LMH / bar at 1 bar and a DMF solvent flux of 343.8 LMH / bar. After being immersed in DMF solvent for 30 days, the bovine serum albumin content is still greater than 99.0%.

[0062] Example 4

[0063] The method is basically the same as Example 1, except that 10 wt% of porogens PEG (molecular weight 2000) and PVP (K30, molecular weight 40000) are added (PEG / PVP=10:0).

[0064] The composite membrane obtained in this example has a room temperature pure water flux of 322.2 LMH / bar at 1 bar and a DMF solvent flux of 121.1 LMH / bar. After being immersed in DMF solvent for 30 days, the bovine serum albumin content is still greater than 99.0%.

[0065] Example 5

[0066] Characterizing the composite membrane's dye removal performance: As described in Example 1, the resulting composite membrane was tested for its separation performance: five dyes: Rose Bengal (RB, 1017.6 g / mol), Coomassie Brilliant Blue (BBR, 826.0 g / mol), Congo Red (CR, 697.7 g / mol), Acid Fuchsin (AF, 584.5 g / mol), and Methyl Orange (MO, 327.3 g / mol). The composite membrane demonstrated a high retention rate of over 99.4% for dyes with a molecular weight greater than 697.7 g / mol, and even retained 56.2% of MO at 327.3 g / mol.

[0067] Example 6

[0068] Characterizing the anti-fouling properties of the composite membrane: The resulting composite membrane was subjected to a bovine serum albumin cycling test as described in Example 1. The test showed that after a simple rinse with clean water, the composite membrane had a pure water flux recovery rate of 84%, and after 3.5 cycles, it still outperformed commercial PES and PVDF membranes.

[0069] Although the present invention has been particularly shown and described in conjunction with preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the present invention without departing from the spirit and scope of the invention as defined in the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. A method for preparing a flash-evaporated HDPE nonwoven reinforced para-aromatic polyamide composite film, characterized in that: Use the following steps: (1) Flash-steamed HDPE nonwoven reinforcement: A nonwoven fabric made of fibers produced by flash-steaming high-density polyethylene (HDPE) and then bonded by heat and pressure, and used as a reinforcement for the composite film; the nonwoven fabric has a gram weight of 50 to 160 g / m 2 , thickness is 25-200μm, average pore size is 1-5μm, porosity is 50-90%, and fracture strength is >50MPa; (2) Surface pretreatment of flash-evaporated HDPE nonwoven fabric: the flash-evaporated HDPE nonwoven fabric prepared in step (1) is subjected to an impregnation treatment or an oxygen plasma treatment using a weakly polar organic liquid, wherein the weakly polar organic liquid is methanol, ethanol, or isopropanol, and the impregnation time is 1 to 3 hours, and the oxygen plasma treatment time is 5 to 60 seconds; (3) Preparation of para-aromatic polyamide casting solution: para-aromatic polyamide casting solution is prepared by first dissolving para-aromatic polyamide resin in an inorganic acid solvent at 50-90°C at a speed of >600 rpm for 2-5 hours, then adding porogens in sequence, and then controlling the temperature and continuing high-speed stirring for 0.5-2.5 hours, and vacuum degassing for 1-2 hours to obtain a highly uniform para-aromatic polyamide casting solution; (4) Preparation of a para-aromatic polyamide composite membrane: The para-aromatic polyamide casting solution prepared in step (3) is evenly coated on the surface of the flash-evaporated HDPE non-woven fabric fixed on a heatable glass plate by a manual or automatic scraper, and after a 15-second air bath, it is immersed in a 30°C coagulation bath for solidification to obtain the para-aromatic polyamide composite membrane; the temperature of the heated glass plate is maintained at 50 to 90°C, and the scraping speed is 30 to 100 mm / s; the medium of the coagulation bath is water or an aqueous solution of the inorganic acid solvent, the mass fraction of the solvent is 0 to 30%, and the mass fraction of the solvent is not 0.

2. The method for preparing a flash-evaporated HDPE nonwoven reinforced para-aromatic polyamide composite film according to claim 1, characterized in that: The mass fraction composition of the substances in the para-aromatic polyamide casting solution is as follows: 0.5-5 wt % of para-aromatic polyamide resin, 6-10 wt % of porogen, and 85-93.5 wt % of inorganic acid solvent, and the sum of the components is 100 wt %.

3. The method for preparing a flash-evaporated HDPE nonwoven reinforced para-aromatic polyamide composite film according to claim 1, characterized in that: The mesh size of the para-aromatic polyamide resin is 50 to 1000 mesh; the porogen is at least one of PEG with an average molecular weight of 200 to 20,000 Da and PVP with an average molecular weight of 8,000 to 58,000 Da, and the two are mixed in a mass ratio of PEG / PVP=10 / 0 to 1 / 1; adding the porogens sequentially means first adding PEG and stirring at high speed for 0.5 to 1 hour, and then adding PVP and stirring at high speed for 0.5 to 1.5 hours.

4. The method for preparing a flash-evaporated HDPE nonwoven reinforced para-aromatic polyamide composite film according to claim 1, characterized in that: The temperature control refers to a temperature of 60 to 80°C.

5. The method for preparing a flash-steamed HDPE nonwoven reinforced para-aromatic polyamide composite film according to claim 1, characterized in that: The high-speed stirring rate is greater than 1200 revolutions per minute.

6. The method for preparing a flash-steamed HDPE nonwoven reinforced para-aromatic polyamide composite film according to claim 1, characterized in that: The inorganic acid solvent refers to concentrated sulfuric acid with a mass concentration of 93 to 100 wt%.

7. A flash-steamed HDPE nonwoven reinforced para-aromatic polyamide composite film, characterized by: The composite film is prepared by the method for preparing a flash-steamed HDPE nonwoven fabric reinforced para-aromatic polyamide composite film according to any one of claims 1 to 6.

8. The flash-steamed HDPE nonwoven fabric reinforced para-aromatic polyamide composite film according to claim 7, characterized in that: The composite membrane has an average pore size of 3 to 50 nm, a thickness of 50 to 300 μm, a water contact angle of 40 to 60°, and a pure water flux of 200 to 1000 L / m 2 / h / bar, organic solvent flux is 40~400L / m 2 / h / bar, a cut-off molecular weight of 3000 to 60000 Da, a dye retention molecular weight as low as 697.7 g / mol, and a breaking strength of 50 to 200 MPa; after 3.5 bovine serum albumin-water cycles and simple water washing, the composite membrane has a pure water flux recovery rate of up to 84%; after soaking the composite membrane in an organic solvent for one month, the Congo red retention rate remains stable at above 98%.

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