CN110172175B - Preparation method of porous polyimide conductive composite material - Google Patents
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Abstract
The invention provides a preparation method of a porous polyimide conductive composite material, which adopts an in-situ polymerization method to prepare composite polyamic acid dispersion liquid I and II; pouring the composite polyamic acid dispersion liquid I into a mould, and preparing a composite polyamic acid porous layer by a thermally induced phase separation method; pouring the composite polyamic acid dispersion liquid II on the surface of the composite polyamic acid porous layer to form a sealing layer, so as to obtain a polyamic acid composite material with a double-layer structure; carrying out programmed heating on the polyamic acid composite material with the double-layer structure to realize imidization of polyamic acid and finally obtaining the porous polyimide conductive composite material; the invention develops a novel porous light functionalized electromagnetic shielding composite material with a double-layer structure by taking polyimide as a matrix and taking a carbon material as a conductive filler, can overcome the defects of high specific density, poor corrosion resistance, difficulty in processing and forming and the like of the traditional electromagnetic shielding material, and has the characteristic of good heat resistance.
Description
Technical Field
The invention relates to a preparation method of a conductive composite material, in particular to a preparation method of a porous polyimide conductive composite material, and belongs to the field of preparation of composite materials.
Background
With the development of society, new materials are increasingly developed in various technical fields such as aerospace, automobile industry, medical instruments and construction engineering. The lightweight, functional and environmental protection of the material structural component puts higher requirements on the material, and the polymer matrix composite material has outstanding advantages in the aspects of lightweight and functional as a novel material. Thus, polymer-based composites have gained widespread interest and use in numerous areas of life. Due to the rapid development of electronic information technology, the capture and positioning of targets are increasingly precise due to the great application of detection technologies such as radar, infrared and laser, and therefore, the electromagnetic shielding technology becomes a focus. In addition, electromagnetic radiation also has adverse effects on the human body, and for example, the incidence of diseases such as cancer and leukemia is increased in some cases in relation to the increase in the amount of electromagnetic radiation. Therefore, the exploration of light and efficient electromagnetic shielding composite materials to achieve the purpose of microwave absorption and prevent electromagnetic shielding pollution is a problem which needs to be solved urgently in the present society.
Disclosure of Invention
The invention aims to provide a preparation method of a porous polyimide conductive composite material with the multifunctional integration of electromagnetic shielding, heat insulation, flame retardance, sound absorption, noise reduction and the like.
The purpose of the invention is realized as follows:
a preparation method of a porous polyimide conductive composite material comprises the following steps:
the method comprises the following steps: preparing composite polyamic acid dispersion liquid I and II by adopting an in-situ polymerization method;
step two: pouring the composite polyamic acid dispersion liquid I into a mould, and preparing a composite polyamic acid porous layer by a thermally induced phase separation method; pouring the composite polyamic acid dispersion liquid II on the surface of the composite polyamic acid porous layer to form a closed layer, and carrying out vacuum drying at 60-90 ℃ for 4-12 h to obtain a polyamic acid composite material with a double-layer structure;
step three: carrying out programmed heating on the polyamic acid composite material with the double-layer structure to realize imidization of polyamic acid, and finally obtaining the porous polyimide conductive composite material with the upper layer being a closed layer and the lower layer being a porous layer with a coral-shaped hollow structure
The invention also includes such features:
1. the volume ratio of the composite polyamic acid dispersion liquid I to the composite polyamic acid dispersion liquid II is 1-15: 1;
2. the preparation method of the composite polyamic acid dispersion liquid I comprises the following steps: respectively and uniformly dispersing a pore-foaming agent and a conductive filler in a solvent at normal temperature and normal pressure, and sequentially adding diamine and dianhydride monomers under the protection of inert gas, wherein the volume ratio of the pore-foaming agent to the solvent is 1: 1-10; the reaction temperature is 20-30 ℃, the reaction time is 3-24 h, and polyamic acid dispersion liquid I with the solid content of 10-20% is obtained;
3. the preparation method of the composite polyamic acid dispersion liquid II comprises the following steps: uniformly dispersing conductive filler in a solvent at normal temperature and normal pressure, sequentially adding diamine and dianhydride monomers under the protection of inert gas, wherein the reaction temperature is 20-30 ℃, and the reaction time is 3-24 hours, so as to obtain a composite polyamide acid dispersion liquid II with the solid content of 10-20%;
4. the molar ratio of the diamine monomer to the dianhydride monomer is 1: 1.01-1.1; the mass ratio of the conductive filler to the monomer is 1-20: 100; the monomer is the sum of the mass of diamine monomer and dianhydride monomer;
5. the programmed heating process is constant temperature of 100 ℃ for 1-2 h; keeping the temperature at 120 ℃ for 1-2 h; keeping the temperature at 180 ℃ for 1-2 h; keeping the temperature at 300 ℃ for 0.5-1 h;
6. the conductive filler is one or more of modified graphene oxide, graphene, carbon black and multi-walled carbon nanotubes; the pore-foaming agent is dibutyl phthalate and/or polyethylene glycol;
7. the diamine monomer is one or more of 4,4 '-diaminodiphenyl ether, 4' -diaminodiphenylmethane, p-phenylenediamine and m-phenylenediamine; the dianhydride monomer is one or more of 3,3',4,4' -benzophenone tetracarboxylic dianhydride, bisphenol A dianhydride and 4,4' -diphenyl ether dianhydride;
8. the solvent is N, N-dimethylacetamide, N-dimethylformamide or N-methylpyrrolidone, and the inert gas is nitrogen or argon.
Compared with the prior art, the invention has the beneficial effects that:
the invention develops a novel porous light functionalized electromagnetic shielding composite material with a double-layer structure by taking polyimide as a matrix and taking a carbon material as a conductive filler, can overcome the defects of high specific density, poor corrosion resistance, difficulty in processing and forming and the like of the traditional electromagnetic shielding material, and has the characteristic of good heat resistance.
Drawings
FIG. 1a is a SEM picture of the surface of a porous polyimide conductive composite sealing layer prepared in example 3 of the invention;
FIG. 1b is an SEM picture of a cross section of a two-layer structure of a porous polyimide conductive composite prepared in example 3 of the present invention;
FIG. 1c is an SEM picture plane of the surface of a porous layer of the porous polyimide conductive composite prepared in example 3 of the present invention;
FIG. 2 is an SEM sectional view of a coral-shaped pore structure of a porous layer of the porous polyimide conductive composite prepared in example 1 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
A preparation method of a polyimide conductive composite material, (1) preparing a composite polyamic acid dispersion liquid I (CPAA-I) containing a pore-foaming agent and a conductive filler by adopting an in-situ polymerization method, and pouring the CPAA-I into a mold. The composite polyamic acid porous layer is prepared by a thermally induced phase separation method. (2) Preparing a composite polyamic acid dispersion liquid II (CPAA-II) containing a conductive filler by adopting an in-situ polymerization method, and pouring the CPAA-II on the surface of the composite polyamic acid porous layer obtained in the step 1 according to the volume ratio of the CPAA-I to the CPAA-II of 1-15: 1. And (3) drying for 4-12 h at 60-90 ℃ in vacuum, and forming a sealing layer on the surface of the composite polyamide acid porous layer to obtain the polyamide acid composite material with a double-layer structure. (3) And (3) carrying out programmed heating on the polyamic acid composite material with the double-layer structure to realize imidization of polyamic acid and prepare the porous polyimide conductive composite material with the double-layer structure. The preparation method of the CPAA-I comprises the following steps: respectively and uniformly dispersing a pore-foaming agent and a conductive filler in a solvent at normal temperature and normal pressure, and sequentially adding a diamine monomer and a dianhydride monomer under the protection of inert gas, wherein the reaction temperature is 20-30 ℃, and the reaction time is 3-24 hours. The volume ratio of the pore-foaming agent to the solvent is 1: 1-10; the molar ratio of the diamine monomer to the dianhydride monomer is 1: 1.01-1.1; the solid content of the polyamic acid solution is 10-20 percent; the mass ratio of the conductive filler to the monomer (the sum of the mass of the diamine monomer and the mass of the dianhydride monomer) is 1-20: 100. The preparation method of the CPAA-II comprises the following steps: uniformly dispersing the conductive filler in a solvent at normal temperature and normal pressure, and sequentially adding diamine and dianhydride monomers under the protection of inert gas, wherein the reaction temperature is 20-30 ℃, and the reaction time is 3-24 hours. The molar ratio of the diamine monomer to the dianhydride monomer is 1: 1.01-1.1; the solid content of the polyamic acid solution is 10-20 percent; the mass ratio of the conductive filler to the monomer (the sum of the mass of the diamine monomer and the mass of the dianhydride monomer) is 1-20: 100; the thermally induced phase separation method is to carry out vacuum heating treatment, wherein the treatment temperature is 60-90 ℃, and the treatment time is 6-12 hours. The programmed heating process is constant temperature of 100 ℃ for 1-2 h; keeping the temperature at 120 ℃ for 1-2 h; keeping the temperature at 180 ℃ for 1-2 h; keeping the temperature at 300 ℃ for 0.5-1 h. The pore-foaming agent is one or two of dibutyl phthalate (DBP) and polyethylene glycol (PEG). The solvent is one of N, N-dimethylacetamide (DMAc), N, N-Dimethylformamide (DMF) and N-methylpyrrolidone (NMP); the conductive filler is one or more of modified graphene oxide, graphene, carbon black and multi-walled carbon nanotubes; the inert gas is one of nitrogen or argon. The diamine monomer is one or more of 4,4' -diaminodiphenyl ether (ODA), 4,4' -diaminodiphenylmethane (MDA), p-phenylenediamine and m-phenylenediamine, and the dianhydride monomer is one or more of 3,3',4,4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), bisphenol A dianhydride (BPADA) and 4,4' -diphenyl ether dianhydride (ODPA); the porous polyimide conductive composite material with the double-layer structure has higher electromagnetic shielding absorption efficiency; a porous polyimide conductive composite material has a double-layer structure, wherein the lower layer is a porous layer with a coral-shaped hole structure, and the upper layer is a sealing layer.
The polyimide of the present invention is used as a matrix material for a plurality of composite materials due to its excellent properties: first, the polyimide material has excellent high temperature resistance due to its structural characteristics, and is considered as one of the most excellent polymer materials in heat resistance, and has good low temperature resistance. Secondly, the five-membered imide ring in the polyimide comprises the benzene ring in the aromatic polyimide, so that the interaction force between polyimide molecular chains is large, and the polyimide has excellent mechanical properties. And thirdly, the polyimide is taken as a high polymer material with a low expansion coefficient, so that the dimensional stability of the polyimide in the use process is greatly improved. Fourth, polyimides have good chemical resistance and can be used in some more specific environments. Therefore, the polyimide is selected as the matrix of the composite material, so that the functional design of the composite material is more diversified, and the composite material is endowed with excellent properties. The carbon-based filler is an important conductive filler due to the advantages of small density, corrosion resistance, stable conductivity and the like. These carbon materials not only have low density, light weight characteristics, but also have high aspect ratios and can form effective conductive networks in polymer matrix composites, thereby imparting their desirable electrical and shielding properties.
The composite polyamic acid dispersion liquid CPAA-I and CPAA-II are prepared by an in-situ polymerization method, the CPAA-I is poured into a mould, and a polyamic acid porous layer is prepared by a thermally induced phase separation method. Pouring CPAA-II on the surface of the porous layer, heating to remove the solvent, forming a sealing layer on the surface of the porous layer, endowing the polyamic acid conductive composite material with the characteristic of a double-layer structure, and realizing imidization of the polyamic acid through a programmed heating process to prepare the porous polyimide conductive composite material with the double-layer structure. The porous composite material with the double-layer structure is prepared by taking the polyimide as the matrix and the carbon material as the conductive filler, has good electromagnetic shielding performance, has the characteristics of light weight, good heat resistance and good durability, has good application prospect in the field of electromagnetic shielding, particularly has obvious advantages in the field of multifunctional integration requirements of electromagnetic shielding, heat insulation, flame retardance, sound absorption, noise reduction and the like, and also has application potential in the field of electrochemistry.
Example 1:
1. the preparation method of the composite polyamic acid porous layer with the conductive filler content of 8 percent comprises the following steps: 6ml of DBP and 25ml of DMAc are weighed and put into a two-neck flask for uniform dispersion at normal temperature and normal pressure according to the volume ratio of the pore-forming agent DBP to the solvent DMAc of 1: 4.2. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.36g of conductive filler (modified graphene oxide ═ 0.18g of multiwall carbon nanotube) was weighed out in a mass ratio of conductive filler to monomer (sum of diamine monomer and dianhydride monomer) of 8.7: 100. Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamic acid dispersion liquid I-8% (CPAA-I-8%) with a solid content of 15%. Pouring CPAA-I-8% into a mold, and keeping the temperature constant at 80 ℃ for 12h to obtain the composite polyamic acid porous layer with the conductive filler content of 8%.
2. The preparation method of the composite polyamic acid double-layer structure with the conductive filler content of 8 percent comprises the following steps: 25ml of DMAc was taken in a two-necked flask at normal temperature and pressure. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.36g of conductive filler (modified graphene oxide ═ 0.18g of multiwall carbon nanotube) was weighed out in a mass ratio of conductive filler to monomer (sum of diamine monomer and dianhydride monomer) of 8.7: 100. Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamide acid dispersion liquid II-8% (CPAA-II-8%) with a solid content of 15%. Pouring CPAA-II-8% on the surface of the porous layer prepared in the step 1 according to the volume ratio of CPAA-I-8% to CPAA-II-8% of 3: 1, and keeping the temperature constant for 6h at the temperature of 80 ℃ to obtain the polyamic acid composite material with the double-layer structure, wherein the content of the conductive filler is 8%.
3. Keeping the constant temperature of the polyamic acid composite material with the double-layer structure prepared in the step 2 at 100 ℃ for 2 h; keeping the temperature of 120 ℃ for 2 h; keeping the temperature at 180 ℃ for 1 h; the thermal imidization is finished in the programmed heating process of keeping the temperature at 300 ℃ for 0.5 h. And demolding to obtain the porous polyimide conductive composite material with the double-layer structure and the conductive filler content of 8%.
The porous polyimide conductive composite material has a porous layer thickness of 1.5mm, and is sealedThe closed layer is 0.5mm, the whole thickness is 2mm, and the density is 0.8217g/cm3The glass transition temperature was 214.13 ℃ and the carbon residue rate at 800 ℃ was 50%. An X-band waveguide method is adopted to carry out electromagnetic shielding performance test on the porous polyimide conductive composite material with the double-layer structure, and the result shows that the reflection loss efficiency of the porous polyimide conductive composite material is 0-26 dB within 8-12 GHz.
Example 2:
1. the preparation method of the composite polyamic acid porous layer with 10 percent of conductive filler comprises the following steps: 6ml of DBP and 25ml of DMAc are weighed and put into a two-neck flask for uniform dispersion at normal temperature and normal pressure according to the volume ratio of the pore-forming agent DBP to the solvent DMAc of 1: 4.2. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.459g of conductive filler (modified graphene oxide: multiwall carbon nanotube: 0.2295g) is weighed according to the mass ratio of the conductive filler to the monomer (the sum of the mass of the diamine monomer and the mass of the dianhydride monomer) of 11: 100. Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamic acid dispersion liquid I-10% (CPAA-I-10%) with a solid content of 15%. Pouring CPAA-I-10% into a mold, and keeping the temperature constant at 80 ℃ for 12h to obtain the composite polyamic acid porous layer with the conductive filler content of 10%.
2. The preparation method of the composite polyamic acid double-layer structure with 10 percent of conductive filler comprises the following steps: 25ml of DMAc was taken in a two-necked flask at normal temperature and pressure. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.459g of conductive filler (modified graphene oxide: multiwall carbon nanotube: 0.2295g) is weighed according to the mass ratio of the conductive filler to the monomer (the sum of the mass of the diamine monomer and the mass of the dianhydride monomer) of 11: 100. Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamide acid dispersion liquid II-10% (CPAA-II-10%) with a solid content of 15%. Pouring CPAA-II-10% on the surface of the porous layer prepared in the step 1 according to the volume ratio of CPAA-I-10% to CPAA-II-10% of 3: 1, and keeping the temperature constant for 6h at the temperature of 80 ℃ to obtain the polyamic acid composite material with the double-layer structure, wherein the content of the conductive filler is 10%.
3. Keeping the constant temperature of the polyamic acid composite material with the double-layer structure prepared in the step 2 at 100 ℃ for 2 h; keeping the temperature of 120 ℃ for 2 h; keeping the temperature at 180 ℃ for 1 h; the thermal imidization is finished in the programmed heating process of keeping the temperature at 300 ℃ for 0.5 h. And demolding to obtain the porous polyimide conductive composite material with the double-layer structure and the conductive filler content of 10%.
The porous polyimide conductive composite material has the porous layer thickness of 1.5mm, the sealing layer thickness of 0.5mm and the whole thickness of 2mm, and the density of the porous polyimide conductive composite material is 0.7837g/cm3The glass transition temperature was 220.91 ℃, and the carbon residue rate at 800 ℃ reached 55%. The electromagnetic shielding effectiveness test is carried out on the porous polyimide conductive composite material with the double-layer structure by adopting an X-waveband waveguide method, and the result shows that the reflection loss effectiveness of the porous polyimide conductive composite material is 0-36 dB within 8-12 GHz.
Example 3:
1. the preparation method of the composite polyamic acid porous layer with the conductive filler content of 12 percent comprises the following steps: 6ml of DBP and 25ml of DMAc are weighed and put into a two-neck flask for uniform dispersion at normal temperature and normal pressure according to the volume ratio of the pore-forming agent DBP to the solvent DMAc of 1: 4.2. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.563g of conductive filler (modified graphene oxide: multiwall carbon nanotube: 0.2815g) was weighed out in a mass ratio of 13.6:100 between the conductive filler and the monomer (sum of the masses of diamine monomer and dianhydride monomer). Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamic acid dispersion liquid I-12% (CPAA-I-12%) with a solid content of 15%. Pouring CPAA-I-12% into a mold, and keeping the temperature constant at 80 ℃ for 12h to obtain the composite polyamic acid porous layer with the conductive filler content of 12%.
2. The preparation method of the composite polyamic acid double-layer structure with the conductive filler content of 12 percent comprises the following steps: 25ml of DMAc was taken in a two-necked flask at normal temperature and pressure. 1.139g of ODA and 2.99g of BPADA were weighed out in a molar ratio of 1:1.01 between the diamine monomer ODA and the dianhydride monomer BPADA. 0.563g of conductive filler (modified graphene oxide: multiwall carbon nanotube: 0.2815g) was weighed out in a mass ratio of 13.6:100 between the conductive filler and the monomer (sum of the masses of diamine monomer and dianhydride monomer). Uniformly dispersing a conductive filler in a dispersion liquid of DBP and DMAc, sequentially adding ODA and BPADA monomers under the protection of nitrogen, and reacting for 4h at 25 ℃ to obtain a composite polyamic acid dispersion liquid II-12% (CPAA-II-12%) with a solid content of 15%. Pouring CPAA-II-12% on the surface of the porous layer prepared in the step 1 according to the volume ratio of CPAA-I-12% to CPAA-II-12% of 3: 1, and keeping the temperature constant for 6h at the temperature of 80 ℃ to obtain the polyamic acid composite material with the double-layer structure, wherein the content of the conductive filler is 12%.
3. Keeping the constant temperature of the polyamic acid composite material with the double-layer structure prepared in the step 2 at 100 ℃ for 2 h; keeping the temperature of 120 ℃ for 2 h; keeping the temperature at 180 ℃ for 1 h; the thermal imidization is finished in the programmed heating process of keeping the temperature at 300 ℃ for 0.5 h. And demolding to obtain the porous polyimide conductive composite material with the double-layer structure and the conductive filler content of 12%.
The porous polyimide conductive composite material has a porous layer of 1.5mm, a sealing layer of 0.5mm and an integral thickness of 2mm, and has a density of 0.5576g/cm3The glass transition temperature is 223.15 ℃, and the carbon residue rate at 800 ℃ is as high as 59%. An X-band waveguide method is adopted to carry out electromagnetic shielding effectiveness test on the porous polyimide conductive composite material with the double-layer structure, and the result shows that the reflection loss effectiveness of the porous polyimide conductive composite material is 0-44 dB within 8-12 GHz.
In summary, the following steps: the invention provides a preparation method of a porous polyimide conductive composite material and an electromagnetic shielding function of the porous polyimide conductive composite material. The porous polyimide conductive composite material has a double-layer structure, wherein the bottom is a porous layer, and the top is a closed layer. Preparing a composite polyamic acid dispersion solution I containing a conductive filler and a pore-foaming agent by an in-situ polymerization method, and preparing a polyamic acid porous layer by a thermally induced phase separation method; forming a sealing layer on the upper part of the porous layer by pouring a composite polyamic acid dispersion liquid II containing a conductive filler on the porous layer and performing heat treatment to volatilize a solvent; and imidizing the polyamic acid by programmed heating to prepare the porous polyimide conductive composite material. The top sealing layer isolates the invasion of external water vapor and pollution particles in the using process, and the service life of the porous composite material is prolonged. The bottom porous layer has a coralline pore structure, and the porous structure endows the composite material with the characteristic of light weight. The porous polyimide composite material has the advantages of simple preparation steps, convenience in operation and designability. Provides a new idea for preparing the light conductive porous polymer matrix composite material with the multifunctional integration of electromagnetic shielding, heat insulation, flame retardation, sound absorption, noise reduction and the like.
Claims (10)
1. A preparation method of a porous polyimide conductive composite material is characterized by comprising the following steps:
the method comprises the following steps: preparing composite polyamic acid dispersion liquid I and composite polyamic acid dispersion liquid II both containing conductive filler by adopting an in-situ polymerization method;
step two: pouring the composite polyamic acid dispersion liquid I into a mould, and preparing a composite polyamic acid porous layer by a thermally induced phase separation method; pouring the composite polyamic acid dispersion liquid II on the surface of the composite polyamic acid porous layer to form a closed layer, and carrying out vacuum drying at 60-90 ℃ for 4-12 h to obtain a polyamic acid composite material with a double-layer structure;
step three: and (3) carrying out programmed heating on the polyamic acid composite material with the double-layer structure to realize imidization of the polyamic acid, and finally obtaining the porous polyimide conductive composite material with the upper layer being a closed layer and the lower layer being a porous layer with a coral-shaped hollow structure.
2. The preparation method of the porous polyimide conductive composite material as claimed in claim 1, wherein the volume ratio of the composite polyamic acid dispersion liquid I to the composite polyamic acid dispersion liquid II is 1-15: 1.
3. The preparation method of the porous polyimide conductive composite material as claimed in claim 1, wherein the preparation method of the composite polyamic acid dispersion liquid I comprises the following steps: respectively and uniformly dispersing a pore-foaming agent and a conductive filler in a solvent at normal temperature and normal pressure, and sequentially adding diamine and dianhydride monomers under the protection of inert gas, wherein the volume ratio of the pore-foaming agent to the solvent is 1: 1-10; the reaction temperature is 20-30 ℃, the reaction time is 3-24 h, and the polyamic acid dispersion liquid I with the solid content of 10-20% is obtained.
4. The preparation method of the porous polyimide conductive composite material as claimed in claim 1, wherein the preparation method of the composite polyamic acid dispersion liquid II comprises the following steps: uniformly dispersing conductive filler in a solvent at normal temperature and normal pressure, sequentially adding diamine and dianhydride monomers under the protection of inert gas, wherein the reaction temperature is 20-30 ℃, and the reaction time is 3-24 hours, so as to obtain a composite polyamide acid dispersion liquid II with the solid content of 10-20%.
5. The preparation method of the porous polyimide conductive composite material according to claim 3 or 4, wherein the molar ratio of the diamine monomer to the dianhydride monomer is 1: 1.01-1.1; the mass ratio of the conductive filler to the monomer is 1-20: 100; the monomer is the sum of the mass of diamine monomer and dianhydride monomer.
6. The preparation method of the porous polyimide conductive composite material as claimed in any one of claims 1 to 4, wherein the programmed heating process is constant temperature of 100 ℃ for 1-2 h; keeping the temperature at 120 ℃ for 1-2 h; keeping the temperature at 180 ℃ for 1-2 h; keeping the temperature at 300 ℃ for 0.5-1 h.
7. The preparation method of the porous polyimide conductive composite material as claimed in claim 5, wherein the programmed heating process is constant temperature of 100 ℃ for 1-2 h; keeping the temperature at 120 ℃ for 1-2 h; keeping the temperature at 180 ℃ for 1-2 h; keeping the temperature at 300 ℃ for 0.5-1 h.
8. The preparation method of the porous polyimide conductive composite material as claimed in claim 3 or 7, wherein the conductive filler is one or more of modified graphene oxide, graphene, carbon black and multi-walled carbon nanotubes; the pore-foaming agent is dibutyl phthalate and/or polyethylene glycol.
9. The method for preparing the porous polyimide conductive composite material according to claim 3, 4 or 7, wherein the diamine monomer is one or more of 4,4 '-diaminodiphenyl ether, 4' -diaminodiphenylmethane, p-phenylenediamine and m-phenylenediamine; the dianhydride monomer is one or more of 3,3',4,4' -benzophenone tetracarboxylic dianhydride, bisphenol A dianhydride and 4,4' -diphenyl ether dianhydride.
10. The method for preparing a porous polyimide conductive composite material according to claim 3, 4 or 7, wherein the solvent is N, N-dimethylacetamide, N-dimethylformamide or N-methylpyrrolidone, and the inert gas is nitrogen or argon.
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