A polymer composite film for isolating nanoscale solid materials and its preparation process

Abstract

This invention provides a polymer composite membrane for isolating nanoscale solid materials and its preparation process. The polymer composite membrane includes a mechanical support layer and a filter layer coated on the surface of the mechanical support layer. The filter layer and the mechanical support layer are bonded together by a phase inversion method. In this invention, a cross-linked structure is formed at the interface between the support layer and the filter layer through a photothermal curing reaction. This cross-linked structure has high mechanical strength and can prevent the filter layer from falling off. The filter layer of this invention has a dense layer structure, which can block solid particles larger than a few nanometers at the membrane surface, allowing only water molecules to pass through the membrane. The mechanical support layer has a microporous structure, which utilizes carboxylated nanofiber crystals to combine with doped amino carbon nitride through an amidation reaction, thereby improving the mechanical strength and thermal stability of the composite membrane and significantly improving the retention capacity and retention efficiency of the composite membrane.

Description

Technical Field

[0001] This invention relates to the field of membrane separation, specifically to a polymer composite membrane for isolating nanoscale solids and its preparation process. Background Technology

[0002] Membrane separation technology is a high-end emerging treatment technology that can not only separate and purify a variety of different components, but also does not produce environmental pollution or other negative effects in the process. With water resources becoming increasingly scarce, people's demand for freshwater is growing, but the Earth's freshwater resources are very limited. However, the amount of other water, such as seawater, domestic wastewater, and industrial wastewater, is very large. Therefore, extracting usable freshwater from these waters has become a research hotspot.

[0003] Current membranes used in the seawater desalination and water treatment industries typically consist of three layers: a polyimide layer, a polysulfone layer, and a polyester support layer. Commonly used membranes are over 120 μm thick, and suffer from low efficiency, high cost, complex manufacturing processes, and large membrane elements, resulting in excessively high maintenance costs in practical applications. Therefore, this invention provides a novel membrane using low-cost polyethylene material with superior physical properties, enabling the separation of nanoscale solids. This composite membrane can be applied to the separation of minute solids in liquids, achieving a separation precision down to the tens of nanometers level. Summary of the Invention

[0004] The purpose of this invention is to provide a polymer composite film for isolating nanoscale solid materials and its preparation process, so as to solve the problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A process for preparing a polymer composite film for isolating nanoscale solid materials includes the following steps:

[0007] S1. Preparation of the mechanical support layer

[0008] (1) Prepare polyethylene raw materials, antioxidants and prepolymer additives, and then mix and stir to obtain a mixture;

[0009] (2) Mechanical support layer is prepared by using the mixture through dry or wet methods;

[0010] In this invention, antioxidants and prepolymer additives are added to polyethylene raw materials as a mechanical support layer. The antioxidants must be specially formulated because it is necessary to prevent the molecular chain structure of polyethylene from being excessively damaged during processing, while ensuring that the prepolymer additives are not decomposed during processing. Since the prepolymer additives are easily decomposed or polymerized under high temperature and shear during processing, the amount of prepolymer that can be polymerized again in the finished product is reduced, which is not conducive to subsequent coating modification.

[0011] Furthermore, in step S1(1), the antioxidant is composed of antioxidant 1010, antioxidant 168 and antioxidant CA in a specific ratio.

[0012] The amounts of antioxidants 1010 and 168 are determined based on the total amount of polyethylene, while the amount of antioxidant CA is determined based on the content of acrylate in the prepolymer additive. Antioxidants 1010 and 168 provide excellent protection for polyethylene, while antioxidant CA provides good protection for acrylate. The total amount added must be controlled below 1000 ppm of the total raw material content; otherwise, it will affect the mixing and plasticizing process. Therefore, the mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1, and the mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000. The ratio of antioxidant content to polyethylene raw material in the mixture is 500 ppm, and the ratio of prepolymer additive content to polyethylene raw material content is 10%.

[0013] This invention prepares a multilayered microporous film from polyethylene containing additives by biaxial stretching, and controls the pore size by stretching ratio.

[0014] Furthermore, the dry process involves directly melting and extruding the mixture into shape, and then stretching it uniaxially or biaxially to obtain a microporous membrane; the wet process involves adding additives such as white oil or paraffin oil to the mixture, mixing it, melting and extruding it into shape, stretching it biaxially, and then using an extraction solvent to extract the additives such as white oil or paraffin oil from the membrane to obtain a microporous membrane.

[0015] The selected mechanical support layer membrane needs to have a certain pore size and mechanical strength; the pore size distribution of the mechanical support layer should be as narrow as possible. As can be seen from the experimental results in the examples, when the relationship between the pore size distribution and the filter layer thickness reaches a certain range, the compressive strength and water flux of the composite membrane reach the optimal state at the same time.

[0016] The average pore size of the micropores in the middle layer of this invention can be controlled by the stretching ratio of the biaxial stretching process. The membrane of this invention is selected with an average pore size of 30-50 nm. The smaller the pore size distribution, the better its uniformity and the better its support performance. The pore size distribution is represented by the pore size distribution coefficient m (the percentage of the total number of pores with a pore size less than or equal to the average pore size). In this invention, microporous membranes with a pore size distribution coefficient of 50%-80% are preferred. The thickness is selected as a membrane between 5 μm and 30 μm. Selecting a membrane in this thickness range can not only reduce the volume of the unit component but also effectively improve the mechanical properties.

[0017] S2. Preparation of the filter layer

[0018] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate and stir until homogeneous;

[0019] (2) Preparation of secondary precursor solution: a hexane solution of benzotricarboxylic acid chloride was prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride was 0.12-0.48 mol / L.

[0020] (3) Add photoinitiator to the secondary precursor solution and mix well to obtain a mixture;

[0021] (4) The primary precursor solution in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying. Then the mixture in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 50-60℃ for 30-60 min, then washed with deionized water, and then dried at 50-60℃ for 20-30 min to obtain the composite membrane.

[0022] (5) Place the composite film in a light treatment oven and then cure and crosslink it with ultraviolet light at 70°C to obtain a polymer composite film.

[0023] Furthermore, in step S2(3), the photoinitiator is one or more of 173 (2-hydroxy-2-methyl-1-phenylpropanone), 184 (1-hydroxycyclohexylphenyl ketone), and 907 (2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone), and the mass fraction of the photoinitiator is 0.8%.

[0024] Furthermore, during the spraying in step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 0.8-1.2, and cannot be 1, so as to ensure that the total amount of matter on the reaction side is higher than the molar concentration on the product side. This can make the reaction proceed as positively as possible and improve the quality of the product.

[0025] Furthermore, in step S2(4), when spraying the precursor solution once, the spraying rate is 0.5 g / (m·s).

[0026] Furthermore, in step S2(4), drying is performed using a hot air oven.

[0027] Furthermore, in step S2(5), the ultraviolet light wavelength is 365 nm and the ultraviolet light intensity is 140 mW / m. 2 .

[0028] m-Phenylenediamine is mixed with a certain amount of deionized water to prepare a homogeneous solution with a certain molar concentration. 10% acrylate is added to the solution as an interfacial prepolymer additive and mixed evenly. The purity of m-Phenylenediamine is analytical grade to avoid introducing impurities into the membrane. The molar concentration of the prepared solution should be selected within 0.1-0.4 mol / L. If the concentration is too low, it will affect the incomplete coverage of the filter layer on the support layer. If the concentration is too high, it will cause the reaction process with benzotrimethylammonium chloride to proceed in reverse, resulting in incomplete reaction and surface defects.

[0029] Curing and crosslinking: The prepared composite film is placed in a light treatment oven at 70°C and irradiated with ultraviolet light to initiate the polymerization of acrylic acid in polyethylene material and acrylate in filter layer, so that curing and crosslinking reaction occurs at the interface of the two layers to form a stable bilayer composite structure and improve the coating's anti-peeling performance.

[0030] Furthermore, modified carbon nitride is added to step S1(1); the ratio of modified carbon nitride to polyethylene raw material in the mixture is 4-8%.

[0031] Furthermore, the preparation steps for modified carbon nitride are as follows:

[0032] (1) The nanofiber crystals were ultrasonically stirred with ammonium persulfate solution at 70-80℃ for 1-2 hours, then distilled water was added and stirred. After centrifugation, the mixture was washed with water until neutral, dried, and then ball-milled to obtain modified nanofiber crystals for later use.

[0033] (2) Urea and melamine are ultrasonically dispersed in deionized water, hydrochloric acid is added under stirring, and then reacted in a polytetrafluoroethylene-lined reactor at 170-185℃ for 9-11h. After cooling, the mixture is vacuum dried at 50-60℃ and then reacted at 540-555℃ for 2.8-3.2h to obtain doped amino carbon nitride.

[0034] (3) Doped amino carbon nitride and modified nanofiber crystals are ultrasonically dispersed in deionized water and reacted at 50-60℃ for 30-60 min. After filtration and drying, modified carbon nitride is obtained.

[0035] Furthermore, the concentration of the ammonium persulfate solution is 1.8-2.2 mol / L; the mass ratio of doped amino carbon nitride to modified nanofiber crystals is (1-2):1;

[0036] Because the polyhydroxyl groups of the fiber crystals are hydrophilic, the nanofiber crystals are prone to agglomeration during the composite process with the hydrophobic polymer matrix. Adding ammonium persulfate solution to carboxylate the fiber crystals improves their hydrophilicity. The carboxylated nanofiber crystals can be combined with doped amino carbon nitride through an amidation reaction.

[0037] Doped amino-carbon nitride has a sheet-like structure. The sheet size varies in the sheet-like structure, and the surface presents more active sites. When combined with carboxylated nanofiber crystals, it changes the molecular weight and surface structure, changes the interfacial interaction, and improves the thermal stability and mechanical strength of the composite membrane. The fiber entanglement of macromolecular chains increases the stress transmission path and plays a role in dispersing stress, thereby improving the retention capacity and retention efficiency of the composite membrane.

[0038] Furthermore, a polymer composite membrane for isolating nanoscale solids is a bilayer microporous membrane, comprising a mechanical support layer and a filter layer coated on the surface of the mechanical support layer, wherein the filter layer and the mechanical support layer are combined by a phase inversion method.

[0039] Polymer composite films prepared by the above methods:

[0040] (a) The total thickness is between 5 μm and 40 μm, and the thickness of the filter layer is between 0.5 μm and 6 μm. The specific thickness is determined by the molar concentration of the precursor solution and conforms to the following formula:

[0041] The filter layer thickness D = {(C1+C2)·d} / 4.11

[0042] Where C1 and C2 are the molar concentrations of the primary and secondary precursor solutions, respectively;

[0043] 4.11 is the bulk density coefficient; d is the thickness of the coated support layer;

[0044] (b) The composite membrane has an average solid material retention capacity (average particle size) of 10 nm or more, and can withstand a maximum pressure of 1200 psi at a temperature of 50 °C or below.

[0045] (c) The membrane has an organic matter rejection efficiency of more than 90% for organic matter with a molecular weight less than 200, more than 95% for organic matter with a molecular weight between 200 and 500, and more than 99% for organic matter with a molecular weight greater than 500.

[0046] The beneficial effects of this invention are:

[0047] This invention provides a polymer composite membrane for isolating nanoscale solid materials, comprising a mechanical support layer and a filter layer coated on the surface of the mechanical support layer, wherein the filter layer and the mechanical support layer are bonded together by a phase inversion method.

[0048] Conventional filter structures typically only have an adhesive effect and are prone to peeling off, which is completely different from conventional filter structures. In this invention, a cross-linked structure is formed at the interface between the support layer and the filter layer through a photothermal curing reaction. This cross-linked structure has high mechanical strength and can prevent the filter layer from peeling off. At the same time, the special formula and processing process ensure that the structure does not affect the filtration performance.

[0049] The thickness of the filter layer in this invention ranges from 0.1 to 10 μm, and the thickness of the support layer ranges from 5 to 30 μm. The filter layer has a dense layer structure, which can block solid particles larger than a few nanometers on the membrane surface, preventing them from passing through the membrane to the other side, and only allowing water molecules to pass through the membrane. The mechanical support layer has a microporous structure and is a microporous laminate composed of hundreds to thousands of microporous layers with an average pore size between 30 and 100 nm. At the same time, it has high tensile strength, high tensile strength, and high filter layer peel strength, which can protect the filter layer composited on its surface from damage and ensure the permeability of water molecules.

[0050] This invention utilizes carboxylated nanofiber crystals to combine with doped amino carbon nitride through an amidation reaction, thereby improving the mechanical strength and thermal stability of the composite membrane. The fiber entanglement macromolecular chains play a role in dispersing stress, significantly improving the retention capacity and retention efficiency of the composite membrane.

[0051] The composite membrane prepared by the method of the present invention has an average retention capacity (average particle size) of more than 10 nm for solid materials, and can withstand a maximum pressure of 1200 psi when the temperature is below 50°C. The retention efficiency for organic matter is as follows: the retention rate of organic matter with a molecular weight less than 200 is more than 90%, the retention rate of organic matter with a molecular weight between 200 and 500 is more than 95%, and the retention rate of organic matter with a molecular weight greater than 500 is more than 99%. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] It should be noted that if the embodiments of the present invention involve directional indicators such as up, down, left, right, front, back, etc., these directional indicators are only used to explain the relative positional relationship and movement of components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0054] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0055] Example 1

[0056] S1. Preparation of the mechanical support layer

[0057] Prepare polyethylene raw materials, antioxidant 1010, antioxidant 168, antioxidant CA, and acrylate nanoparticles, and then mix and stir to obtain a mixture;

[0058] Take 100 kg of polyethylene raw material. The ratio of antioxidant to polyethylene raw material in the mixture is 500 ppm. The ratio of prepolymer additive to polyethylene raw material in the mixture is 10%. The mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1. The mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000.

[0059] (1) A mechanical support layer is prepared by dry method using a mixture;

[0060] The dry process involves directly melting and extruding the mixture into a mold, followed by biaxial stretching to obtain a microporous membrane.

[0061] S2. Preparation of the filter layer

[0062] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate ester and stir until homogeneous;

[0063] (2) Preparation of secondary precursor solution: A hexane solution of benzotricarboxylic acid chloride is prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride is 0.12 mol / L.

[0064] (3) Add photoinitiator 173 to the secondary precursor solution and mix well to obtain a mixture;

[0065] (4) The primary precursor solution described in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying. Then the mixture described in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 50°C for 60 min, then washed with deionized water, and then dried in a hot air oven at 50°C for 30 min to obtain the composite membrane.

[0066] In step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 1.2; when spraying the primary precursor solution, the spraying rate is 0.5 g / (m·s).

[0067] (5) The composite film was placed in a light treatment oven and then cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film; the ultraviolet light wavelength was 365nm and the ultraviolet light intensity was 140mW / m 2 .

[0068] Example 2

[0069] S1. Preparation of the mechanical support layer

[0070] (1) Prepare polyethylene raw materials, antioxidant 1010, antioxidant 168, antioxidant CA, and acrylate nanoparticles, and then mix and stir to obtain a mixture;

[0071] Take 100 kg of polyethylene raw material. The ratio of antioxidant to polyethylene raw material in the mixture is 500 ppm. The ratio of prepolymer additive to polyethylene raw material in the mixture is 10%. The mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1. The mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000.

[0072] (2) A mechanical support layer is prepared by dry method using a mixture;

[0073] The dry process involves directly melting and extruding the mixture into a mold, followed by biaxial stretching to obtain a microporous membrane.

[0074] S2. Preparation of the filter layer

[0075] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate ester and stir until homogeneous;

[0076] (2) Preparation of secondary precursor solution: A hexane solution of benzotricarboxylic acid chloride is prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride is 0.2 mol / L.

[0077] (3) Add photoinitiator 173 to the secondary precursor solution and mix well to obtain a mixture;

[0078] (4) The primary precursor solution described in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying. Then the mixture described in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 55°C for 40 min, then washed with deionized water, and then dried in a hot air oven at 55°C for 25 min to obtain the composite membrane.

[0079] In step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 0.8; when spraying the primary precursor solution, the spraying rate is 0.5 g / (m·s).

[0080] (5) The composite film was placed in a light treatment oven and then cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film; the ultraviolet light wavelength was 365nm and the ultraviolet light intensity was 140mW / m 2 .

[0081] Example 3

[0082] S1. Preparation of the mechanical support layer

[0083] (1) Prepare polyethylene raw materials, antioxidant 1010, antioxidant 168, antioxidant CA, and acrylate nanoparticles, and then mix and stir to obtain a mixture;

[0084] Take 100 kg of polyethylene raw material. The ratio of antioxidant to polyethylene raw material in the mixture is 500 ppm. The ratio of prepolymer additive to polyethylene raw material in the mixture is 10%. The mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1. The mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000.

[0085] (2) A mechanical support layer is prepared by dry method using a mixture;

[0086] The dry process involves directly melting and extruding the mixture into a mold, followed by biaxial stretching to obtain a microporous membrane.

[0087] S2. Preparation of the filter layer

[0088] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate ester and stir until homogeneous;

[0089] (2) Preparation of secondary precursor solution: A hexane solution of benzotricarboxylic acid chloride is prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride is 0.48 mol / L.

[0090] (3) Add photoinitiator 173 to the secondary precursor solution and mix well to obtain a mixture;

[0091] (4) The primary precursor solution described in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying, and then the mixture described in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 60°C for 30 min, and then dried in a hot air oven at 60°C for 20 min to obtain a composite film.

[0092] In step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 1.2; when spraying the primary precursor solution, the spraying rate is 0.5 g / (m·s).

[0093] (5) The composite film was placed in a light treatment oven and then cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film; the ultraviolet light wavelength was 365nm and the ultraviolet light intensity was 140mW / m 2 .

[0094] Example 4

[0095] S1. Preparation of the mechanical support layer

[0096] (1) Prepare polyethylene raw materials, antioxidant 1010, antioxidant 168, antioxidant CA, and acrylate nanoparticles, and then mix and stir to obtain a mixture;

[0097] Take 100 kg of polyethylene raw material. The ratio of antioxidant to polyethylene raw material in the mixture is 500 ppm. The ratio of prepolymer additive to polyethylene raw material in the mixture is 10%. The mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1. The mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000.

[0098] (2) A mechanical support layer is prepared by dry method using a mixture;

[0099] The dry process involves directly melting and extruding the mixture into a mold, followed by biaxial stretching to obtain a microporous membrane.

[0100] S2. Preparation of the filter layer

[0101] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate ester and stir until homogeneous;

[0102] (2) Preparation of secondary precursor solution: A hexane solution of benzotricarboxylic acid chloride is prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride is 0.27 mol / L.

[0103] (3) Add photoinitiator 173 to the secondary precursor solution and mix well to obtain a mixture;

[0104] (4) The primary precursor solution described in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying. Then the mixture described in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 55°C for 40 min, then washed with deionized water, and then dried in a hot air oven at 55°C for 25 min to obtain the composite membrane.

[0105] In step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 0.9; when spraying the primary precursor solution, the spraying rate is 0.5 g / (m·s).

[0106] (4) The composite film is placed in a light treatment oven and then cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film; the ultraviolet light wavelength is 365nm and the ultraviolet light intensity is 140mW / m 2 .

[0107] Example 5

[0108] S1. Preparation of the mechanical support layer

[0109] (1) Prepare polyethylene raw materials, antioxidant 1010, antioxidant 168, antioxidant CA, acrylate nanoparticles, and modified carbon nitride, and then mix and stir to obtain a mixture;

[0110] Take 100 kg of polyethylene raw material. The ratio of antioxidant to polyethylene raw material in the mixture is 500 ppm; the ratio of prepolymer additive to polyethylene raw material in the mixture is 10%; the mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:1; the mass ratio of antioxidant CA to acrylate nanoparticles is 1:1000; and the content ratio of modified carbon nitride to polyethylene is 6%.

[0111] The preparation steps for modified carbon nitride are as follows:

[0112] (1) The nanofiber crystals were ultrasonically stirred with ammonium persulfate solution at 75°C for 1.5 h, then distilled water was added and stirred. After centrifugation, the mixture was washed with water until neutral, dried, and then ball-milled to obtain modified nanofiber crystals for later use.

[0113] (2) Urea and melamine were ultrasonically dispersed in deionized water, hydrochloric acid was added under stirring, and then reacted in a polytetrafluoroethylene-lined reactor at 180°C for 10 h. After cooling, the mixture was vacuum dried at 55°C and then reacted at 550°C for 3 h to obtain doped amino carbon nitride.

[0114] (3) Doped amino nitride and modified nanofiber crystals in a mass ratio of 1:1 were ultrasonically dispersed in deionized water, reacted at 55°C for 45 min, filtered and dried to obtain modified nitride.

[0115] (2) A mechanical support layer is prepared by dry method using a mixture;

[0116] The dry process involves directly melting and extruding the mixture into a mold, followed by uniaxial or biaxial stretching to obtain a microporous membrane.

[0117] S2. Preparation of the filter layer

[0118] (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add 10% propionate ester and stir until homogeneous;

[0119] (2) Preparation of secondary precursor solution: A hexane solution of benzotricarboxylic acid chloride is prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; the molar concentration of the hexane solution of benzotricarboxylic acid chloride is 0.27 mol / L.

[0120] (3) Add photoinitiator 173 to the secondary precursor solution and mix well to obtain a mixture;

[0121] (3) The primary precursor solution described in step S2(1) is coated onto the surface of the mechanical support layer prepared in step S1 by spraying, and then the mixture described in step S2(3) is sprayed onto the surface of the primary precursor solution. The mixture is allowed to stand at 55°C for 40 min, and then dried in a hot air oven at 55°C for 25 min to obtain a composite film.

[0122] In step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 0.9; when spraying the primary precursor solution, the spraying rate is 0.5 g / (m·s).

[0123] (4) The composite film is placed in a light treatment oven and then cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film; the ultraviolet light wavelength is 365nm and the ultraviolet light intensity is 140mW / m 2 .

[0124] Performance testing:

[0125] The composite membranes prepared in Examples 1-5 were subjected to performance tests. The 50°C working pressure refers to the maximum pressure that the composite membrane can withstand under normal working conditions at 50°C. Generally, the water column method is used, which measures the height of the water column that the membrane can withstand per unit area and then converts it into pressure. The retention capacity and retention rate of the composite membrane were tested. The retention capacity is obtained by detecting the maximum particle size of the filtered material. Generally, the filtration method is used. The filtered sample is observed and measured under a scanning electron microscope. The test results are shown in Table 1.

[0126]

[0127]

[0128]

[0129] Table 1

[0130] The above tests show that the polymer composite films obtained in Examples 1-5 are:

[0131] (a) The total thickness is between 5 μm and 40 μm, and the thickness of the filter layer is between 0.5 μm and 6 μm. The specific thickness is determined by the molar concentration of the precursor solution and conforms to the following formula:

[0132] The filter layer thickness D = {(C1+C2)·d} / 4.11

[0133] Where C1 and C2 are the molar concentrations of the primary and secondary precursor solutions, respectively;

[0134] 4.11 is the bulk density coefficient; d is the thickness of the coated support layer;

[0135] (b) The composite membrane has an average solid material retention capacity (average particle size) of 10 nm or more, and can withstand a maximum pressure of 1200 psi at a temperature of 50 °C or below.

[0136] (c) The membrane has an organic matter rejection efficiency of more than 90% for organic matter with a molecular weight less than 200, more than 95% for organic matter with a molecular weight between 200 and 500, and more than 99% for organic matter with a molecular weight greater than 500.

[0137] A comparison of Example 5 and Example 4 shows that, with the same concentration of the precursor solution used for the first and second coatings and the same thickness of the support layer, the addition of modified carbon nitride to the mechanical support layer in Example 5 resulted in a composite membrane that outperformed Example 4 in terms of working pressure at 50°C, solid matter retention capacity, filter layer peel strength, and organic matter retention capacity. This indicates a significant improvement in the mechanical properties and solid matter retention capacity of the composite membrane.

[0138] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the present invention's specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A process for preparing a polymer composite film for isolating nanoscale solid materials, comprising the following steps: S1. Preparation of the mechanical support layer (1) Prepare polyethylene raw materials, antioxidants and prepolymer additives, and then mix and stir to obtain a mixture; (2) Mechanical support layer is prepared by using the mixture through dry or wet methods; S2. Preparation of the filter layer (1) Preparation of the precursor solution: Mix m-phenylenediamine with deionized water until homogeneous, then add acrylate and stir until homogeneous; (2) Preparation of secondary precursor solution: a hexane solution of benzotricarboxylic acid chloride was prepared using benzotricarboxylic acid chloride as solute and hexane as solvent; (3) Add photoinitiator to the secondary precursor solution and mix evenly to obtain a mixed solution; (4) The primary precursor solution described in step S2(1) is coated on the surface of the mechanical support layer prepared in step S1, and then the mixture described in step S2(3) is sprayed on the surface of the primary precursor solution. The mixture is allowed to stand at 50-60℃ for 30-60 min, then washed with deionized water, and then dried at 50-60℃ for 20-30 min to obtain the composite membrane. (5) Then the composite film is placed in a light treatment oven and cured and crosslinked by ultraviolet light at 70°C to obtain a polymer composite film. Add modified carbon nitride to step S1(1); the content ratio of the modified carbon nitride to polyethylene raw material in the mixture is 4-8%; The preparation steps of the modified carbon nitride are as follows: (1) The nanofiber crystals were ultrasonically stirred with ammonium persulfate solution at 70-80℃ for 1-2 hours, then distilled water was added and stirred. After centrifugation, the mixture was washed with water until neutral, dried, and then ball-milled to obtain modified nanofiber crystals for later use. (2) Urea and melamine are ultrasonically dispersed in deionized water, hydrochloric acid is added under stirring, and then reacted in a polytetrafluoroethylene-lined reactor at 170-185℃ for 9-11h. After cooling, the mixture is vacuum dried at 50-60℃ and then reacted at 540-555℃ for 2.8-3.2h to obtain doped amino carbon nitride. (3) Doped amino carbon nitride and modified nanofiber crystals are ultrasonically dispersed in deionized water, reacted at 50-60℃ for 30-60 min, filtered and dried to obtain modified carbon nitride. The prepolymer additive mentioned in step S1(1) is acrylate nanoparticles, and the content ratio of the prepolymer additive to polyethylene raw material in the mixture is 10%.

2. The preparation process of a polymer composite film for isolating nanoscale solid materials according to claim 1, characterized in that: The antioxidant mentioned in step S1(1) is composed of antioxidant 1010, antioxidant 168 and antioxidant CA in a certain ratio. The mass ratio of antioxidant 1010 to antioxidant 168 is 1.7:

1. The content ratio of antioxidant to polyethylene raw material in the mixture is 500ppm.

3. The preparation process of a polymer composite film for isolating nanoscale solid materials according to claim 2, characterized in that: The mass ratio of the antioxidant CA to the acrylate nanoparticles is 1:1000.

4. The preparation process of a polymer composite film for isolating nanoscale solid materials according to claim 1, characterized in that: During the spraying in step S2(4), the molar concentration ratio of the secondary precursor solution to the primary precursor solution is 0.8-1.2, and cannot be 1.

5. The preparation process of a polymer composite film for isolating nanoscale solid materials according to claim 1, characterized in that: The photoinitiator in step S2(3) is one or more of 173 (2-hydroxy-2-methyl-1-phenylpropanone), 184 (1-hydroxycyclohexylphenyl ketone), and 907 (2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone); the ultraviolet light wavelength in step S2(5) is 365 nm, and the ultraviolet light intensity is 140 mW / m 2 .

6. The preparation process of a polymer composite film for isolating nanoscale solid materials according to claim 1, characterized in that: In the preparation of modified carbon nitride, the mass ratio of the doped amino carbon nitride to the modified nanofiber crystals is (1-2):

1.

7. A polymer composite membrane for isolating nanoscale solid materials, characterized in that: It is prepared by the process described in any one of claims 1-6.

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