CN111636239B - Preparation method of polyimide fibrid electromagnetic shielding paper - Google Patents

Preparation method of polyimide fibrid electromagnetic shielding paper Download PDF

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CN111636239B
CN111636239B CN202010498480.4A CN202010498480A CN111636239B CN 111636239 B CN111636239 B CN 111636239B CN 202010498480 A CN202010498480 A CN 202010498480A CN 111636239 B CN111636239 B CN 111636239B
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polyimide
fibrid
electromagnetic shielding
dianhydride
mxene
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CN111636239A (en
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赵昕
秦秀芝
张清华
董杰
方玉婷
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Jiangsu new vision advanced functional fiber Innovation Center Co.,Ltd.
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Donghua University
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H13/26—Polyamides; Polyimides
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M11/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising
    • D06M11/73—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with carbon or compounds thereof
    • D06M11/74—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with carbon or compounds thereof with carbon or graphite; with carbides; with graphitic acids or their salts
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
    • D06M2101/16—Synthetic fibres, other than mineral fibres
    • D06M2101/30—Synthetic polymers consisting of macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds

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  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

The invention relates to a preparation method of polyimide fibrid electromagnetic shielding paper, which comprises the following steps: injecting the polyimide solution into a coagulating bath containing an MXene aqueous solution to obtain an MXene-loaded polyimide fibrid; mixing the fibrid with polyimide chopped fiber, making paper, and hot-pressing. The fibrid obtained by the invention not only has good mechanical property and thermal stability, but also the electromagnetic shielding paper further has good conductivity and electromagnetic shielding property.

Description

Preparation method of polyimide fibrid electromagnetic shielding paper
Technical Field
The invention belongs to the field of functional paper, and particularly relates to a preparation method of polyimide fibrid electromagnetic shielding paper.
Background
The Polyimide (PI) fibrid is a fibrous or film-like fibrid formed by applying a certain shear force to a polyimide solution to precipitate the polyimide from a poor solvent. The method has simple process, and the prepared fibrid has stable performance, not only has good thermal stability, mechanical property and the like of the conventional fiber, but also has special advantages, such as large specific surface area, lower crystallinity, easy processing and forming and the like. In the process of making paper, polyimide chopped fibers are added to bear stress, polyimide fibrids play a role in connecting the chopped fibers and filling the chopped fibers, and the fibrids tightly wrap the chopped fibers together in the process of hot-press molding, so that the effect of stress transmission is achieved, and the mechanical property, the thermal property and the like of finished paper are further improved.
With the widespread use of electronic appliances and telecommunications, electromagnetic radiation has become a public nuisance in today's society. Electromagnetic waves not only interfere with the normal operation of various electronic and communication devices, but also threaten the health of human beings. In recent years, a large number of efforts have been made to design and manufacture a wide-band and thin electromagnetic shielding material. The paper-based electromagnetic shielding material is a structural function integrated composite material with light weight and good flexibility, has simple and environment-friendly preparation process, meets the development trend of material light weight, can be applied to radiation protection and interference resistance of commercial or electronic equipment, is used as a shielding cover, a shielding plate and the like of electronic equipment by being compounded with other materials such as wall surfaces in the field of buildings, and is a novel electromagnetic shielding material with development prospect.
Patent No. CN105506769A discloses a polyimide fibrid and a preparation method thereof, which comprises preparing polyamide acid fibrid, and then obtaining polyimide fibrid by thermal imidization. However, in the thermal imidization process, the fibrids obtained at an excessively high temperature tend to shrink, and the quality of the polyimide fibrids is deteriorated. Patent No. CN108794790A discloses an aramid fiber electromagnetic shielding paper and a preparation method thereof, wherein a material obtained by mixing carbon nanotube powder and aramid fiber powder is coated on the surface of a substrate film, and the aramid fiber electromagnetic shielding paper is obtained by hot press molding, wherein the phenomenon of untight bonding of an interface possibly exists between the substrate and the powder, so that the mechanical property is reduced. Patent No. CN109098038A discloses an electromagnetic shielding paper and a preparation method thereof, the electromagnetic shielding paper is composed of lignocellulose nanofiber and surface modified MXene, and due to modification of MXene, the regular lamellar structure of the MXene is damaged, and the conductivity of the MXene is slightly reduced.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of polyimide fibrid electromagnetic shielding paper, wherein the fibrid obtained by the method has good mechanical property and thermal stability, and the electromagnetic shielding paper further has good electrical conductivity and electromagnetic shielding property.
The invention provides a preparation method of polyimide fibrid electromagnetic shielding paper, which comprises the following steps:
(1) under the protective atmosphere, injecting the polyimide PI stock solution subjected to post-treatment into a coagulating bath containing MXene aqueous solution under the stirring condition to obtain polyimide PI fibrid suspension; washing, filtering and vacuum drying to obtain MXene-loaded PI fibrids;
(2) mixing the MXene-loaded PI fibrids and polyimide chopped fibers in a mass ratio of 9: 1-1: 9, putting the mixture into water, and adding a dispersant to obtain uniform slurry; and performing papermaking, vacuum drying and hot pressing to obtain the polyimide fibrid electromagnetic shielding paper.
The preparation method of the polyimide PI stock solution in the step (1) comprises the following steps: adding a diamine monomer into an aprotic polar organic solvent at 0-25 ℃ under the protection of nitrogen, adding a dianhydride monomer after complete dissolution, stirring, and then adding a catalyst for heating cyclization or adding a chemical cyclization agent for chemical cyclization to obtain a polyimide stock solution.
The diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, hexafluoro-diamine, bisphenol A diether diamine, 4 '-diaminodiphenylmethane and 4, 4' -methylene diphenylamine.
The dianhydride monomer is one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride and hydroquinone diether dianhydride.
The aprotic polar organic solvent is dimethylacetamide or N-methylpyrrolidone.
The catalyst is one or more of isoquinoline, acetic anhydride and triethylamine.
The chemical cyclizing agent is one or more of triethylamine, acetic anhydride and pyridine.
The reaction time after the dianhydride is added is 4-8 h, and the stirring speed is 200-300 r/min.
The dropping speed of the catalyst is 1 mL/min.
The reaction parameters of the heating cyclization are as follows: polymerizing for 1-3 h at 100 ℃, heating to 120 ℃, polymerizing for 3-5 h, and heating to 180 ℃ for polymerizing for 5-15 h.
The molar ratio of the chemical cyclizing agent to the diamine is 0: 1-1: 1; the reaction temperature of the chemical cyclization is 60-80 ℃.
Preferably, the aprotic polar organic solvent is N-methylpyrrolidone; the diamine is a mixture of 2, 4-diaminotoluene (TDA) and 4, 4' -diaminodiphenylmethane (MDA); the dianhydride is 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride (BTDA).
The post-treatment in the step (1) comprises filtering, defoaming and diluting.
The injection in the step (1) is specifically as follows: the stirring speed is 2000-10000 r/min, the injection speed is 0.5-1 mL/min, and the stirring time is 1-2 min after the solution is completely injected.
The concentration of the MXene aqueous solution in the step (1) is 2-10 mg/mL.
The MXene is prepared by the following method: concentrated hydrofluoric acid (40%) was slowly added dropwise to a solution containing titanium aluminum carbide (Ti)3AlC2) Stirring the suspension liquid in a tetrafluoroethylene beaker at 35 ℃ for 24 hours, respectively centrifugally cleaning the suspension liquid for a plurality of times by using deionized water and absolute ethyl alcohol, and drying the suspension liquid in vacuum to obtain multilayer Ti3C2TxAnd (3) powder. A plurality of layers of Ti3C2TxMixing the powder with deionized water, performing ultrasonic treatment and centrifugation to obtain single-layer or few-layer Ti3C2TxColloidal suspension, i.e., MXene.
The solvent of the coagulating bath in the step (1) is one or more of ethanol, methanol and an aprotic polar organic solvent; the volume ratio of the coagulating bath to the polyimide PI stock solution is 10-50: 1.
The mass volume ratio of the fibrid or chopped fiber and water in the step (2) is 1g: 100-1000 mL.
The dispersing agent in the step (2) is one or more of polyoxyethylene, anionic polyacrylamide and methyl cellulose; the addition amount is 0.01-5% of the polyimide chopped fiber.
The hot pressing process parameters in the step (2) are as follows: the pressure is 5-25 MPa, and the time is 5-240 min; the technological parameters of vacuum drying are as follows: the temperature is 40-80 ℃ and the time is 1-10 h.
The electromagnetic shielding paper of the polyimide fibrid is made from polyimide chopped fibers and polyimide fibrid as raw materials by papermaking, MXene aqueous solution and solvent are mixed to be used as a precipitant, the MXene two-dimensional sheet layer is in a brick structure in the forming process, the fibrid is used as mud of a reinforcing material to obtain the MXene-loaded fibrid, and then the electromagnetic shielding paper with good conductivity and electromagnetic shielding performance is obtained by a simple papermaking process.
Advantageous effects
(1) The soluble polyimide stock solution is synthesized by a one-step method, MXene aqueous solution is used as a precipitating agent, and the MXene can be directly loaded in the precipitating process of the polyimide stock solution, so that the process is simple, the cost is lower, and the production efficiency is high;
(2) the polyimide fibrid obtained by the invention has higher specific surface area, good mechanical property, heat resistance and conductivity, and can be directly used for preparing high-performance composite paper;
(3) the MXene-loaded fibrids and the polyimide chopped fibers are mixed to be made into paper, and the obtained composite paper has good mechanical property, high heat resistance, good conductivity and electromagnetic shielding property.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
First, experimental medicine
Figure BDA0002523845120000031
Figure BDA0002523845120000041
Second, testing method
1. Tensile index
According to GB/T12914-2008 constant-rate loading method, a tensile strength tester is used to stretch a specimen of a prescribed size to break under constant-rate loading, measure the tensile strength thereof, and calculate the tensile index from the obtained result and the quantitative amount of the specimen.
2. Conductivity test
And testing the conductivity of the composite paper by using an RTS-8 four-probe tester.
3. Electromagnetic shielding performance test
And the vector network analyzer N5247A is used for measuring the shielding effect of the sample on the electromagnetic waves.
4. Thermal stability test
And (3) testing the temperature index of the sample at the thermal weight loss of 5% by using a thermogravimetric analyzer to represent the thermal stability of the composite paper.
Example 1
(1) 171mL of N-methylpyrrolidone was added to a 250mL three-necked flask under nitrogen, and 3.0364g of 2, 4-diaminotoluene and 4.9354g of diphenylmethanediamine were added at room temperature with stirring. After stirring to dissolve, 16.0282g of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride was added and stirring was continued for 5 hours. Then 2.5556g of isoquinoline was added, the temperature was raised to 100 ℃ for reaction for 1 hour, the temperature was raised to 120 ℃ for reaction for 3 hours, and the temperature was raised to 180 ℃ for reaction for 12 hours. To obtain polyimide stock solution with solid content of 15 percent.
(2) And (2) carrying out post-treatment on the polyimide stock solution in the step (1), including filtration, defoaming and dilution to 5 wt%. Then, 10mL of the stock solution was injected into a coagulating bath containing 20mL of a 10mg/mL MXene aqueous solution and 180mL of ethanol at a rate of 1mL/min by using a 20mL syringe having a diameter of 2.1cm and a stirring speed of 5000r/min to obtain an MXene-loaded polyimide fibrid suspension, which was washed, filtered and dried to obtain polyimide fibrids.
(3) And (3) mixing the fibrid in the step (2) with the polyimide chopped fiber according to the mass ratio of 7:3, putting the mixture into water, wherein the mass volume ratio of the fibrid or the chopped fiber to the water is 1g:200mL, adding polyoxyethylene (1% of the mass of the chopped fiber) to obtain uniform slurry, papermaking, vacuum drying at 60 ℃ for 5h, and hot pressing at 10MPa for 100min to obtain the polyimide fibrid electromagnetic shielding paper.
The average length of the fibrids obtained in this example was 1.5mm(ii) a The specific surface area is 53m2(ii)/g; the tensile index of the polyimide fibrid electromagnetic shielding paper is 45 N.m/g; the temperature at which the thermal weight loss is 5% is 495 ℃; the conductivity is 460S/cm; the electromagnetic shielding effectiveness is 29dB over the entire X-band.
Example 2
(1) 171mL of N-methylpyrrolidone was added to a 250mL three-necked flask under nitrogen, and 3.0364g of 2, 4-diaminotoluene and 4.9354g of diphenylmethanediamine were added at room temperature with stirring. After stirring to dissolve, 16.0282g of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride was added and stirring was continued for 5 hours. Then 2.5556g of isoquinoline was added, the temperature was raised to 100 ℃ for reaction for 1 hour, the temperature was raised to 120 ℃ for reaction for 3 hours, and the temperature was raised to 180 ℃ for reaction for 12 hours. To obtain polyimide stock solution with solid content of 15 percent.
(2) And (2) carrying out post-treatment on the polyimide stock solution in the step (1), including filtration, defoaming and dilution to 5 wt%. Then, 10mL of the stock solution was injected into a coagulating bath of 20mL of 10mg/mL MXene aqueous solution and 180mL of ethanol at a rate of 1mL/min by using a 20mL syringe having a diameter of 2.1cm and a stirring speed of 5000r/min to obtain an MXene-loaded polyimide fibrid suspension, which was washed, filtered and dried to obtain polyimide fibrids.
(3) And (3) mixing the fibrid in the step (2) with the polyimide chopped fiber according to the mass ratio of 5:5, putting the mixture into water, wherein the mass volume ratio of the fibrid or the chopped fiber to the water is 1g:200mL, adding polyoxyethylene (1% of the mass of the chopped fiber) to obtain uniform slurry, papermaking, vacuum drying at 60 ℃ for 5h, and hot pressing at 10MPa for 100min to obtain the polyimide fibrid electromagnetic shielding paper.
The average length of the fibrids obtained in this example is 1.5 mm; the specific surface area is 55m2(ii)/g; the tensile index of the polyimide fibrid electromagnetic shielding paper is 42 N.m/g; the temperature when the thermal weight loss is 5 percent is 507 ℃; the conductivity is 430S/cm; the electromagnetic shielding effectiveness is 26dB over the entire X-band.
Example 3
(1) 171mL of N-methylpyrrolidone was added to a 250mL three-necked flask under nitrogen, and 3.0364g of 2, 4-diaminotoluene and 4.9354g of diphenylmethanediamine were added at room temperature with stirring. After stirring to dissolve, 16.0282g of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride was added and stirring was continued for 5 hours. Then 2.5556g of isoquinoline was added, the temperature was raised to 100 ℃ for reaction for 1 hour, the temperature was raised to 120 ℃ for reaction for 3 hours, and the temperature was raised to 180 ℃ for reaction for 12 hours. To obtain polyimide stock solution with solid content of 15 percent.
(2) And (2) carrying out post-treatment on the polyimide stock solution in the step (1), including filtration, defoaming and dilution to 5 wt%. Then, 10mL of the stock solution was injected into a coagulating bath containing 20mL of 10mg/mL MXene aqueous solution, 20mL of N-methylpyrrolidone and 180mL of ethanol at a rate of 1mL/min by using a 20mL syringe having a diameter of 2.1cm and a stirring speed of 5000r/min to obtain an MXene-loaded polyimide fibrid suspension, which was washed, filtered and dried to obtain an MXene-loaded polyimide fibrid.
(3) And (3) mixing the fibrid in the step (2) with the polyimide chopped fiber according to the mass ratio of 7:3, putting the mixture into water, wherein the mass volume ratio of the fibrid or the chopped fiber to the water is 1g:200mL, adding polyoxyethylene (1% of the mass of the chopped fiber) to obtain uniform slurry, papermaking, vacuum drying at 60 ℃ for 5h, and hot pressing at 10MPa for 100min to obtain the polyimide fibrid electromagnetic shielding paper.
The average length of the fibrids obtained in this example is 0.9 mm; the specific surface area is 58m2(ii)/g; the tensile index of the polyimide fibrid electromagnetic shielding paper is 50 N.m/g; the temperature at which the thermal weight loss is 5% is 495 ℃; the conductivity is 500S/cm; the electromagnetic shielding effectiveness is 30dB over the entire X-band.
Example 4
(1) 171mL of N-methylpyrrolidone was added to a 250mL three-necked flask under nitrogen, and 3.0364g of 2, 4-diaminotoluene and 4.9354g of diphenylmethanediamine were added at room temperature with stirring. After stirring to dissolve, 16.0282g of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride was added and stirring was continued for 5 hours. Then 2.5556g of isoquinoline was added, the temperature was raised to 100 ℃ for reaction for 1 hour, the temperature was raised to 120 ℃ for reaction for 3 hours, and the temperature was raised to 180 ℃ for reaction for 12 hours. To obtain polyimide stock solution with solid content of 15 percent.
(2) And (2) carrying out post-treatment on the polyimide stock solution in the step (1), including filtration, defoaming and dilution to 5 wt%. Then, 10mL of the stock solution was injected into a coagulating bath containing 20mL of 10mg/mL MXene aqueous solution, 20mL of N-methylpyrrolidone and 180mL of ethanol at a rate of 1mL/min by using a 20mL syringe having a diameter of 2.1cm and a stirring speed of 5000r/min to obtain an MXene-loaded polyimide fibrid suspension, which was washed, filtered and dried to obtain an MXene-loaded polyimide fibrid.
(3) And (3) mixing the fibrid in the step (2) with the polyimide chopped fiber according to the mass ratio of 5:5, putting the mixture into water, wherein the mass volume ratio of the fibrid or the chopped fiber to the water is 1g:200mL, adding polyoxyethylene (1% of the mass of the chopped fiber) to obtain uniform slurry, papermaking, vacuum drying at 60 ℃ for 5h, and hot pressing at 10MPa for 100min to obtain the polyimide fibrid electromagnetic shielding paper.
The average length of the fibrids obtained in this example is 0.9 mm; the specific surface area is 58m2(ii)/g; the tensile index of the polyimide fibrid electromagnetic shielding paper is 45 N.m/g; the temperature when the thermal weight loss is 5 percent is 505 ℃; the conductivity is 455S/cm; the electromagnetic shielding effectiveness was 27dB over the entire X-band.
Example 5
(1) 171mL of N-methylpyrrolidone was added to a 250mL three-necked flask under nitrogen, and 3.0364g of 2, 4-diaminotoluene and 4.9354g of diphenylmethanediamine were added at room temperature with stirring. After stirring to dissolve, 16.0282g of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride was added and stirring was continued for 5 hours. 3.5732g of acetic anhydride and 3.5417g of triethylamine were then added and the reaction was carried out at 70 ℃ for 12 h. To obtain polyimide stock solution with solid content of 15 percent.
(2) And (2) carrying out post-treatment on the polyimide stock solution in the step (1), including filtration, defoaming and dilution to 5 wt%. Then, 10mL of the stock solution was injected into a coagulating bath of 20mL of 10mg/mL MXene aqueous solution and 180mL of ethanol at a rate of 1mL/min by using a 20mL syringe having a diameter of 2.1cm and a stirring speed of 5000r/min to obtain an MXene-loaded polyimide fibrid suspension, which was washed, filtered and dried to obtain polyimide fibrids.
(3) And (3) mixing the fibrid in the step (2) with the polyimide chopped fiber according to the mass ratio of 3:7, putting the mixture into water, wherein the mass volume ratio of the fibrid or the chopped fiber to the water is 1g:200mL, adding polyoxyethylene (1% of the mass of the chopped fiber) to obtain uniform slurry, papermaking, vacuum drying at 60 ℃ for 5h, and hot pressing at 10MPa for 100min to obtain the polyimide fibrid electromagnetic shielding paper.
The average length of the fibrids obtained in this example is 1.2 mm; the specific surface area is 57m2(ii)/g; the tensile index of the polyimide fibrid electromagnetic shielding paper is 39 N.m/g; the temperature when the thermal weight loss is 5 percent is 486 ℃; the conductivity is 420S/cm; the electromagnetic shielding effectiveness was 27dB over the entire X-band.

Claims (8)

1. A preparation method of polyimide fibrid electromagnetic shielding paper comprises the following steps:
(1) under the protective atmosphere, injecting the polyimide PI stock solution subjected to post-treatment into a coagulating bath containing MXene aqueous solution under the stirring condition to obtain polyimide PI fibrid suspension; washing, filtering and vacuum drying to obtain MXene-loaded PI fibrids; wherein, the injection is specifically as follows: stirring at 2000-10000 r/min, injecting at 0.5-1 mL/min, and stirring for 1-2 min after the solution is completely injected; the concentration of the MXene aqueous solution is 2-10 mg/mL;
(2) mixing the MXene-loaded PI fibrids and polyimide chopped fibers in a mass ratio of 9: 1-1: 9, putting the mixture into water, and adding a dispersant to obtain uniform slurry; and performing papermaking, vacuum drying and hot pressing to obtain the polyimide fibrid electromagnetic shielding paper.
2. The method of claim 1, wherein: the preparation method of the polyimide PI stock solution in the step (1) comprises the following steps: adding a diamine monomer into an aprotic polar organic solvent at 0-25 ℃ under the protection of nitrogen, adding a dianhydride monomer after complete dissolution, stirring, and then adding a catalyst for heating cyclization or adding a chemical cyclization agent for chemical cyclization to obtain a polyimide stock solution.
3. The method of claim 2, wherein: the diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, hexafluoro-diamine, bisphenol A diether diamine, 4 '-diaminodiphenylmethane and 4, 4' -methylene diphenylamine; the dianhydride monomer is one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride and hydroquinone diether dianhydride; the aprotic polar organic solvent is dimethylacetamide or N-methylpyrrolidone; the catalyst is one or more of isoquinoline, acetic anhydride and triethylamine; the chemical cyclizing agent is one or more of triethylamine, acetic anhydride and pyridine.
4. The method of claim 1, wherein: the post-treatment in the step (1) comprises filtering, defoaming and diluting.
5. The method of claim 1, wherein: the solvent of the coagulating bath in the step (1) is one or more of ethanol, methanol and an aprotic polar organic solvent; the volume ratio of the coagulating bath to the polyimide PI stock solution is 10-50: 1.
6. The method of claim 1, wherein: the mass volume ratio of the fibrid or chopped fiber and water in the step (2) is 1g: 100-1000 mL.
7. The method of claim 1, wherein: the dispersing agent in the step (2) is one or more of polyoxyethylene, anionic polyacrylamide and methyl cellulose; the addition amount is 0.01-5% of the polyimide chopped fiber.
8. The method of claim 1, wherein: the hot pressing process parameters in the step (2) are as follows: the pressure is 5-25 MPa, and the time is 5-240 min; the technological parameters of vacuum drying are as follows: the temperature is 40-80 ℃ and the time is 1-10 h.
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