CN113929955B - Hard polyimide foam and preparation method thereof - Google Patents

Hard polyimide foam and preparation method thereof Download PDF

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CN113929955B
CN113929955B CN202111274726.0A CN202111274726A CN113929955B CN 113929955 B CN113929955 B CN 113929955B CN 202111274726 A CN202111274726 A CN 202111274726A CN 113929955 B CN113929955 B CN 113929955B
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pressure
polyimide foam
polyimide
gel
temperature
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CN113929955A (en
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马晶晶
酒永斌
赵一搏
滕冲
杨汝平
王方颉
王在铎
朱明明
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Aerospace Research Institute of Materials and Processing Technology
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • C08J9/122—Hydrogen, oxygen, CO2, nitrogen or noble gases
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1003—Preparatory processes
    • C08G73/1035—Preparatory processes from tetracarboxylic acids or derivatives and diisocyanates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/06—CO2, N2 or noble gases
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/08—Supercritical fluid
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2205/00—Foams characterised by their properties
    • C08J2205/04—Foams characterised by their properties characterised by the foam pores
    • C08J2205/042—Nanopores, i.e. the average diameter being smaller than 0,1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2205/00—Foams characterised by their properties
    • C08J2205/10—Rigid foams
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
    • C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
    • C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

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  • Materials Engineering (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Abstract

The invention discloses a hard polyimide foamFoam and a preparation method thereof, belonging to the technical field of preparation of high polymer polyimide foam materials. In the preparation method, firstly, the polyimide foam precursor solution is prepared, then the polyimide foam precursor solution and the polyisocyanate compound are quickly injected into a high-pressure container, and high-pressure CO is introduced 2 Wet gelling under high pressure, and supercritical CO utilization 2 And extracting the polar solvent to obtain porous polyimide gel, and imidizing the porous polyimide gel to obtain the polyimide foam. The preparation method of the pressurized gel/foam effectively reduces the material cost and improves the production efficiency, and the prepared polyimide foam material has the advantages of high temperature resistance, high compression strength, low thermal conductivity, small pore diameter, uniform pores, easy control of density, excellent performance and better application prospect.

Description

Hard polyimide foam and preparation method thereof
Technical Field
The invention belongs to the technical field of preparation of high polymer materials, and particularly relates to hard polyimide foam and a preparation method thereof.
Background
The polyimide foam material is a high-performance foam material, has excellent performances such as outstanding heat resistance, self-flame resistance, low smoke generation, harmless gas release and the like, can be divided into soft and hard polyimide foam materials according to the difference of mechanical properties, wherein the soft open-cell polyimide foam material such as solimide series foam is widely applied in the heat insulation and sound absorption fields of various foreign ships, and the foam material is a soft foam material with lower compression strength; the rigid polyimide foam is a foam material with higher compressive strength, wherein the side chain type polyimide PMI foam material is most widely applied and has been applied and popularized in the industries of aerospace, medical treatment, sports and the like at present, however, with the upgrading and updating of equipment, the temperature resistance requirement of certain application fields on the material is higher and higher, the material is required to resist more than 200 ℃ and even more than 250 ℃, and PMI and several traditional types of rigid foam materials also face the situation that the use requirement of higher temperature is difficult to achieve.
The main chain type polyimide foam material is a material with good temperature resistance, can resist the temperature of 200 ℃ and above, can be mainly divided into two types according to the types of raw materials and different preparation methods, and is a preparation method of aromatic dianhydride and isocyanate and a preparation method based on aromatic dianhydride and aromatic diamine.
Aromatic dianhydride, low molecular alcohol, a catalyst, a surfactant and the like are mixed in a polar solvent according to a certain proportion to perform esterification reaction to form solution A of a foam precursor, then the solution A is mixed with isocyanate of solution B for foaming, the foaming form is similar to polyurethane foaming, and further the polyimide foam is obtained through microwave treatment and heat treatment, wherein the rigid polyimide foam prepared from the two main raw materials is adopted in Chinese patent CN102127225A and patent CN 107459669A.
The preparation of the rigid foam material by using the aromatic dianhydride and the aromatic diamine as main raw materials requires that the American NASA (national Nano chemical industries for industries) firstly prepares microspheres by using the method and then prepares the rigid polyimide foam material by carrying out hot pressing on the microspheres.
In addition to the above methods, rigid polyimide rigid foams can also be prepared using gases released during cross-linking of the polymer, CN102964834A discloses a rigid polyimide foam using nadic anhydride as a capping agent and alpha-isomeric biphenylic anhydride as a main dianhydride. The prepared foam has higher closed cell rate.
Among the above methods, the method using aromatic dianhydride and isocyanate as raw materials has a simple preparation process and low cost, and the product has a heat resistance of 200 ℃ or higher, and is a product with excellent comprehensive properties, but the sample has large cells, so that the formed foam has a high thermal conductivity, and the thermal conductivity at room temperature is greater than 0.037W/(m.K), and therefore, a novel rigid polyimide foam and a preparation method thereof are urgently needed to overcome the above problems.
Disclosure of Invention
The invention aims to overcome the defects and provides hard polyimide foam and a preparation method thereof, belonging to the technical field of preparation of high-molecular polyimide foam materials. In the preparation method, firstly, the polyimide foam precursor solution is prepared, then the polyimide foam precursor solution and the polyisocyanate compound are quickly injected into a high-pressure container, and high-pressure CO is introduced 2 Wet gelling under high pressure, and supercritical CO utilization 2 And extracting the polar solvent to obtain porous polyimide gel, and imidizing the porous polyimide gel to obtain the polyimide foam. The preparation method of the pressurized gel/foam effectively reduces the material cost and improves the production efficiency, and the prepared polyimide foam material has the advantages of high temperature resistance, high compression strength, low thermal conductivity, small pore diameter, uniform pores, easy control of density, excellent performance and better application prospect.
In order to achieve the purpose of the invention, the invention provides the following technical scheme:
a preparation method of rigid polyimide foam comprises the following steps:
(1) Sequentially adding aromatic dianhydride and fatty alcohol into a polar solvent to obtain a mixed solution;
(2) Heating the mixed solution obtained in the step (1) for 0.5-3h, adding water into the mixed solution, and reacting for a certain time to obtain a transparent polyimide foam precursor solution;
(3) Adding the obtained polyimide foam precursor solution into a storage tank A in a foaming machine, and adding a polyisocyanate compound into a storage tank B in the foaming machine;
(4) Injecting the materials in the material storage tank A and the material storage tank B into a high-pressure container, and introducing CO into the high-pressure container 2 Carrying out wet gel reaction to obtain wet gel; the pressure in the high-pressure container is 4-11 Mpa, and the CO is 2 In a supercritical state or a liquid state;
(5) When CO is present in step (4) 2 The high pressure container is heated to increase the temperature and pressure of the liquid CO 2 Conversion to supercritical state CO 2 When CO is present in step (4) 2 Maintaining the temperature and pressure of the high-pressure vessel unchanged or increasing the temperature and pressure of the high-pressure vessel to maintain CO in a supercritical state 2 A supercritical state of (a);
using supercritical CO in a high-pressure vessel 2 Extracting the polar solvent in the wet gel to obtain porous polyimide gel;
(6) And (3) putting the porous polyimide gel into a vacuum oven, and heating to imidize the porous polyimide gel to obtain the polyimide foam.
Further, in the step (1), the aromatic dianhydride is one or more of pyromellitic dianhydride, 2,3', 4' -diphenyl ether tetracarboxylic dianhydride, 3',4' -benzophenone tetracarboxylic dianhydride, bisphenol a diphenyl ether dianhydride or 2,3', 4' -biphenyl tetracarboxylic dianhydride;
the said memory solvent is one or more of dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone;
the aliphatic alcohol comprises one or more of methanol, ethanol, propanol or isopropanol.
Further, in the step (1), the ratio of the amount of the aliphatic alcohol to the amount of the aromatic dianhydride is 0.5 to 1.
Further, in the step (2), the mass of the added water accounts for 5-15% of the total mass of the mixed solution and the water;
in the step (2), the mass concentration of the obtained polyimide foam precursor solution is 10-65%;
in the step (2), the heating temperature range is 70-100 ℃; the reaction time is 0.5-3 h.
Further, in the step (3), the polyisocyanate compound includes one or more of polymethylene polyphenyl polyisocyanate, diphenylmethane diisocyanate or toluene diisocyanate.
Further, in the step (4), the materials in the material storage tank A and the material storage tank B are injected into the high-pressure container according to a mass ratio of 1.
Further, in the step (4), the reaction temperature of the wet gel reaction is 4-45 ℃, and the reaction time is 1-3 h.
Further, in the step (5), when CO is generated in the step (4) 2 The temperature of the high-pressure container is increased to 31.1-100 ℃ and the pressure is increased to 7.52-40 MPa to ensure that the liquid CO is in a liquid state 2 Conversion to supercritical state CO 2 When CO is present in step (4) 2 Keeping the temperature and pressure of the high-pressure container unchanged or increasing the temperature of the high-pressure container to 31.1-100 ℃ and the pressure to 7.52-40 Mpa in a supercritical state, and maintaining CO 2 The supercritical state of (1).
Further, in the step (6), the polyimide gel is placed in a vacuum oven and heated for 1 to 4 hours under the conditions of the vacuum degree of-0.03 to-0.1 Mpa and the temperature of 200 to 300 ℃ to imidize the polyimide gel, so that the polyimide foam is obtained.
The hard polyimide foam is prepared by the preparation method of the hard polyimide foam, and the density of the hard polyimide foam is 100-500kg/m 3 The compression strength is 2-15 MPa, and the room temperature thermal conductivity is 0.03-0.039W/m.K.
Compared with the prior art, the invention has the following beneficial effects:
(1) In the preparation method of the hard polyimide foam material, a pressurized gelling/foaming method is adopted, so that the pore diameter of the prepared foam material is reduced from micron (200-800 um) to nanometer (50-300 nm), and the thermal conductivity of the foam material is effectively reduced;
(2) Compared with the traditional method for preparing porous polyimide, the method for preparing the rigid polyimide foam material has the advantages that the raw material sources are wide, foaming, gelling and supercritical extraction are carried out in the same device, solvent replacement is not needed, the preparation period is greatly shortened, and the preparation efficiency is improved;
(3) The preparation method of the rigid polyimide foam material has high preparation efficiency and low raw material cost, so that the preparation cost of the polyimide foam material is greatly reduced, and the prepared polyimide foam material can be applied to occasions with the use temperature of more than 200 ℃ and certain requirements on heat conductivity and strength, replaces other rigid polymer foams which are not heat-resistant, and has high popularization and application values;
(4) Compared with the existing polyimide foam, the polyimide foam prepared by the invention has the advantages of low heat conductivity coefficient and uniform foam holes, and the foam material is easy to control in density, excellent in performance and better in application prospect.
Drawings
FIG. 1 is a photograph showing the morphology of a polyimide foam obtained in example 1 of the present invention.
FIG. 2 is a photograph showing the morphology of the polyimide foam obtained in comparative example 1 of the present invention.
Detailed Description
The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.
The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
The invention relates to a preparation method of rigid polyimide foam, which comprises the following steps:
in a first aspect, a method for preparing a rigid polyimide foam comprises the steps of:
adding aromatic dianhydride into a polar solvent, then adding fatty alcohol, heating for reaction for 0.5-3h, and then adding water to obtain a transparent polyimide foam precursor solution, wherein the solution is marked as material A;
adding the material A into a material storage tank A in a foaming machine, simultaneously adding a polyisocyanate compound into a material storage tank B, and marking the polyisocyanate compound as a material B; quickly injecting the material A and the material B into a high-pressure container according to the proportion, and then introducing CO 2 Wetting the injected mixed solution into gel under high pressure; this step CO 2 In a supercritical or liquid state；
Step (3), heating and pressurizing (when CO is in the last step) 2 In the supercritical state, heating and pressurizing may not be performed), CO in the high-pressure vessel is allowed to be present 2 Supercritical state, supercritical state CO 2 The polyimide gel is used for extracting a polar solvent, porous polyimide gel is obtained through repeated extraction and separation, and then the porous polyimide gel is placed in a vacuum oven to be heated for imidization, so that polyimide foam is obtained.
In a preferred embodiment, the aromatic dianhydride in step (1) comprises one or a combination of pyromellitic dianhydride, 2,3', 4' -diphenyl ether tetracarboxylic dianhydride, 3',4' -benzophenone tetracarboxylic dianhydride, bisphenol a type diphenyl ether dianhydride or 2,3', 4' -biphenyl tetracarboxylic dianhydride;
in a preferred embodiment, the polar solvent in step (1) is one or more of dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; the aliphatic alcohol is one or more of methanol, ethanol, propanol or isopropanol.
In a preferred embodiment, the mass solution concentration of the material A in the step (1) is 10-65%, the mass ratio of the aliphatic alcohol to the aromatic dianhydride is 0.5-1, and the addition amount of the water is 5-15% of the total weight (namely the mass sum of the aromatic dianhydride, the aliphatic alcohol, the polar solvent and the water).
In a preferred embodiment, the isocyanate in step (2) comprises one or more of polymethylene polyphenyl polyisocyanate (PAPI), diphenylmethane diisocyanate (MDI), toluene Diisocyanate (TDI), and the like; the mass ratio of the material A to the material B is 1.
In a preferred embodiment, step (2) foams the gel under high pressure, and materials A and B foam the gel under pressure sufficient to allow CO to be present 2 The gel becomes liquid state or supercritical state, the pressure range in a high-pressure container is 4-11 MPa, the temperature is 4-45 ℃, and the gel time is 1-3 h.
In a preferred embodiment, supercritical CO is used in step (3) 2 The temperature in the high-pressure vessel is at the time of extraction31.1-100 ℃, and the pressure is 7.52-40 MPa; the processing temperature in the vacuum oven is 200-300 ℃, the vacuum degree is-0.03 to-0.1 MPa, and the processing time is 1-4 h.
The rigid polyimide foam is prepared by the preparation method, and the density of the polyimide foam is 100-500kg/m 3 The compression strength is 2-15 MPa, and the room temperature thermal conductivity is 0.03-0.039W/m K.
Example 1
The preparation method of the polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: taking 31.2kg of N, N-dimethylformamide, adding 32.20kg of 3,3',4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), adding 4.50kg of ethanol, heating to 90 ℃, stirring at constant temperature for 2.5h, then adding 4.80kg of water, stirring for reacting for 1h, cooling to room temperature, and filling into a foaming machine storage tank A;
(2) A certain amount of PAPI (liquid B) is filled into a material storage tank B of a foaming machine;
(3) And (2) mixing the solution A and the solution B by using a high-pressure foaming machine according to the mass ratio of 1, wherein the mixing temperature is 20 ℃, injecting the mixture into a high-pressure tank, and quickly introducing CO into the high-pressure tank 2 The gas is raised to a pressure of 7MPa and kept for a gelling time of 2h, at which point CO 2 Is in liquid state;
(4) Increasing the pressure to 8MPa and the temperature to 32 ℃ to ensure that liquid CO is generated 2 Conversion to supercritical CO 2 Using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out the sample, placing in a vacuum oven for treatment at the treatment temperature of 250 ℃/2h, wherein the obtained foam cell structure is shown in figure 1, and as can be seen from figure 1, the pore diameter of the foam prepared by the method is nano-scale, and the foam density is 350kg/m 3 The compression strength is 10MPa, and the thermal conductivity is 0.035W/(m.K).
Example 2
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: the same as example 1;
(2) Filling PAPI (liquid B) into a material storage tank B of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1, injecting the mixture into a high-pressure tank at the mixing temperature of 5 ℃, and quickly introducing CO into the high-pressure tank 2 The gas is raised to a pressure of 5MPa and kept for a gelling time of 2h, at which point CO 2 Is in liquid state;
(4) Increasing the pressure to 8MPa and the temperature to 32 ℃ to ensure that liquid CO is obtained 2 Conversion to supercritical CO 2 Using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out sample, treating in vacuum oven at 250 deg.C/2 h to obtain foam with density of 410kg/m 3 The compression strength is 12MPa, and the thermal conductivity is 0.037W/(m.K).
Example 3
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: taking 31.2kg of N, N-dimethylformamide, adding 16.1kg of 3,3',4' -Benzophenone Tetracarboxylic Dianhydride (BTDA) into the N, N-dimethylformamide, heating to 90 ℃, adding 3.2kg of ethanol, stirring at constant temperature for 2.5h, then adding 3.6kg of water, stirring for reacting for 1h, cooling to room temperature, and filling into a foaming machine storage tank A;
(2) Filling a certain amount of PAPI (liquid B) into a material storage tank B of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1.2, then injecting the mixture into a high-pressure tank at the mixing temperature of 20 ℃, and rapidly introducing CO 2 The gas is raised to a pressure of 7MPa and kept for a gelling time of 2h, at which point CO 2 Is in liquid state;
(4) Increasing the pressure to 8MPa and the temperature to 32 ℃ to ensure that liquid CO is obtained 2 Conversion to supercritical CO 2 By using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out the sample, and placing the sample in a vacuum oven for treatment at the treatment temperature of 250 ℃/2h to obtainThe density of the foam of (1) is 230kg/m 3 The compressive strength is 3MPa, and the thermal conductivity is 0.031W/(m.K).
Example 4
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: the same as example 3;
(2) Filling a certain amount of PAPI (liquid B) into a liquid B storage tank of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1.2 to 1, injecting the mixture into a high-pressure tank at the mixing temperature of 35 ℃, and quickly introducing CO 2 The gas is raised to 8MPa and kept for a gelling time of 2h, at which time CO 2 Is in a supercritical state;
(4) Then separating the supercritical CO 2 Circulating with solvent for 3 times to perform extraction, then relieving pressure, taking out sample, placing in vacuum oven for treatment at 250 deg.C/2 h to obtain foam with density of 180kg/m 3 The compression strength is 2.4MPa, and the thermal conductivity is 0.030W/(m.K).
Example 5
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: the same as in example 1.
(2) Filling a certain amount of PAPI (liquid B) into a material storage tank B of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1, injecting the mixture into a high-pressure tank at the mixing temperature of 32 ℃, and quickly introducing CO into the high-pressure tank 2 The gas is raised to a pressure of 8MPa and kept for a gelling time of 2h, at which time CO 2 Is in a supercritical state;
(4) By using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out sample, placing in vacuum oven for treatment at 250 deg.C/2 h to obtain foam with density of 330kg/m 3 The compression strength is 9.6MPa, and the thermal conductivity is 0.033W/(m.K).
Example 6
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: taking 31.2kg of N, N-dimethylformamide, adding 48.3kg of 3,3',4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), heating to 90 ℃, adding 7kg of ethanol, stirring at constant temperature for 2.5h, then adding 5.2kg of water, stirring for reacting for 1h, cooling to room temperature, and filling into a foaming machine storage tank A;
(2) A certain amount of PAPI (liquid B) is filled into a liquid B storage tank of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1 2 The gas is raised to a pressure of 8MPa and kept for a gelling time of 2h, at which time CO 2 Is in a supercritical state;
(4) By using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out the sample, placing in a vacuum oven for treatment at 250 ℃/2h, and obtaining the foam with the density of 490kg/m 3 The compression strength is 15MPa, and the thermal conductivity is 0.039W/(m.K).
Example 7
A preparation method of polyimide foam mainly comprises the following steps:
(1) And (3) synthesis of solution A: the same as in example 6;
(2) A certain amount of PAPI (liquid B) is filled into a material storage tank B of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to the mass ratio of 1.1 to 1, injecting the mixture into a high-pressure tank at the mixing temperature of 40 ℃, quickly increasing the pressure to 10MPa, and keeping the gelling time for 2h, wherein at the moment, the CO is obtained by mixing the solution A and the solution B 2 Is in a supercritical state;
(4) By using supercritical CO 2 Extracting the solvent in the gel for 2h, and separating supercritical CO 2 Circulating with solvent for 3 times, then decompressing, taking out the sample, placing in a vacuum oven for treatment at 230 ℃/2h, and obtaining the foam with the density of 310kg/m 3 The compression strength is 9.5MPa, and the thermal conductivity is 0.035W/(m.K).
Comparative example 1
(1) And (3) synthesis of solution A: taking 31.2kg of N, N-dimethylformamide, adding 32.20kg of 3,3',4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), adding 4.50kg of ethanol, heating to 90 ℃, stirring at constant temperature for 2.5h, then adding 4.80kg of water, stirring for reacting for 1h, cooling to room temperature, and filling into a foaming machine storage tank A;
(2) A certain amount of PAPI (liquid B) is filled into a material storage tank B of a foaming machine;
(3) Mixing the solution A and the solution B by a high-pressure foaming machine according to a mass ratio of 1;
(4) Taking out the foam intermediate, placing in a vacuum oven for treatment at 250 deg.C/2 h, wherein the obtained foam microstructure is shown in figure 2, and as can be seen from figure 2, the foam pore diameter is micrometer, and the foam density is 180kg/m 3 The compression strength is 2.4MPa, and the thermal conductivity is 0.042W/(m.K).
Compared with the embodiment 1, the density and the compressive strength of the prepared foam are greatly reduced, and the heat conductivity coefficient is increased, which shows that the method for pressurizing gel/foaming can effectively improve various properties of the foam, and has better application prospect.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are not particularly limited to the specific examples described herein.

Claims (9)

1. A preparation method of rigid polyimide foam is characterized by comprising the following steps:
(1) Sequentially adding aromatic dianhydride and aliphatic alcohol into a polar solvent to obtain a mixed solution;
(2) Heating the mixed solution obtained in the step (1) for 0.5-3h, and then adding water into the mixed solution to obtain a transparent polyimide foam precursor solution;
(3) Adding the obtained polyimide foam precursor solution into a storage tank A in a foaming machine, and adding a polyisocyanate compound into a storage tank B in the foaming machine;
(4) Injecting the materials in the material storage tank A and the material storage tank B into a high-pressure container, and introducing CO into the high-pressure container 2 Carrying out wet gel reaction to obtain wet gel; the pressure in the high-pressure container is 4-11 Mpa, and the CO is 2 In a supercritical state or a liquid state;
(5) When CO is present in step (4) 2 The high pressure container is heated to increase the temperature and pressure of the liquid CO 2 Conversion to supercritical state CO 2 When CO is present in step (4) 2 Maintaining the temperature and pressure of the high-pressure vessel constant or increasing the temperature and pressure of the high-pressure vessel to maintain CO in a supercritical state 2 The supercritical state of (a);
using supercritical state CO in a high-pressure vessel 2 Extracting the polar solvent in the wet gel to obtain porous polyimide gel;
(6) Putting the porous polyimide gel in a vacuum oven, and heating to imidize the porous polyimide gel to obtain polyimide foam;
in the step (4), the reaction temperature of the wet gel reaction is 4-45 ℃, and the reaction time is 1-3 h;
the density of the polyimide foam is 100-500kg/m 3 The compression strength is 2-15 MPa, and the room temperature thermal conductivity is 0.03-0.039W/m.K; the aperture of the polyimide foam is 50-300 nm.
2. The method of claim 1, wherein in the step (1), the aromatic dianhydride is one or more selected from pyromellitic dianhydride, 2,3', 4' -diphenyl ether tetracarboxylic dianhydride, 3',4' -benzophenone tetracarboxylic dianhydride, bisphenol A diphenyl ether dianhydride or 2,3', 4' -biphenyl tetracarboxylic dianhydride;
the polar solvent is one or the combination of more than one of dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone;
the aliphatic alcohol comprises one or more of methanol, ethanol, propanol or isopropanol.
3. The method for preparing a rigid polyimide foam according to claim 1, wherein in the step (1), the ratio of the amount of the aliphatic alcohol to the amount of the aromatic dianhydride is 0.5.
4. The method for preparing a rigid polyimide foam according to claim 1, wherein in the step (2), the mass of the added water accounts for 5-15% of the total mass of the mixed solution and the water;
in the step (2), the mass concentration of the obtained polyimide foam precursor solution is 10-65%;
in the step (2), the heating temperature range is 70-100 ℃; the reaction time is 0.5-3 h.
5. The method of claim 1, wherein in the step (3), the polyisocyanate compound comprises one or more of polymethylene polyphenyl polyisocyanate, diphenylmethane diisocyanate and toluene diisocyanate.
6. The method for preparing a rigid polyimide foam according to claim 1, wherein in the step (4), the materials in the material storage tank A and the material storage tank B are injected into the high-pressure container according to a mass ratio of 1.
7. The method for preparing a rigid polyimide foam according to claim 1, wherein in the step (5), when the step(4) Middle CO 2 The temperature of the high-pressure container is increased to 31.1-100 ℃ and the pressure is increased to 7.52-40 MPa to ensure that the liquid CO is in a liquid state 2 Conversion to supercritical state CO 2 When CO is present in step (4) 2 Keeping the temperature and pressure of the high-pressure container unchanged or increasing the temperature of the high-pressure container to 31.1-100 ℃ and the pressure to 7.52-40 Mpa in a supercritical state, and maintaining CO 2 The supercritical state of (1).
8. The method of claim 1, wherein in the step (6), the polyimide gel is heated in a vacuum oven at a vacuum degree of-0.03 to-0.1 Mpa and a temperature of 200 to 300 ℃ for 1 to 4 hours to imidize the polyimide gel, thereby obtaining the polyimide foam.
9. A rigid polyimide foam obtained by the process for producing a rigid polyimide foam according to any one of claims 1 to 8, wherein the rigid polyimide foam has a density of 100 to 500kg/m 3 The compression strength is 2-15 MPa, and the room temperature thermal conductivity is 0.03-0.039W/m.K.
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