Preparation method of anisotropic polyimide aerogel composite material

Abstract

The invention provides a preparation method of an anisotropic polyimide aerogel composite material, and belongs to the technical field of aerogel material preparation. According to the anisotropic polyimide aerogel composite material prepared through the preparation method, the density ranges from 0.020 g / cm < 3 > to 0.048 g / cm < 3 >, the drying shrinkage rate ranges from 1.75% to 6.75%, the radial thermal diffusion coefficient ranges from 0.601 mm < 2 > / s to 1.309 mm < 2 > / s, and the axial thermal diffusion coefficient ranges from 2.074 mm < 2 > / s to 13.182 mm < 2 > / s. The physical properties are obviously superior to those of Py series aerogel heat insulation materials in the current market.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel material preparation, and particularly relates to a preparation method of an anisotropic polyimide aerogel composite material. Background Art

[0002] An aerogel is a porous lightweight material composed of aggregates of macromolecular polymers, with low density and a large specific surface area. Due to its characteristics such as low density, high porosity, high specific surface area, and low thermal conductivity, it is recognized as the "legendary material of the 21st century". As early as 1931, American scholar Kistler first prepared silica (SiO2) aerogel in the laboratory. The emergence of silica-based aerogels once became one of the lightest thermal protection materials and was attracted by the aerospace application field. However, due to its poor mechanical properties, low flexibility, and high brittleness, its development in the heat insulation field has been greatly restricted.

[0003] The emergence of organic polymer-based aerogels has natural advantages in flexibility and mechanical properties, making them widely used in the aerospace field. In recent years, polyimide aerogels (PIAs) have gradually come into people's view as a new type of organic lightweight aerogel material.

[0004] Polyimide is a high molecular polymer containing imide groups (—CO—N—CO—) in its main chain. Because the aromatic heterocyclic structure of the polyamide ring itself can increase the bond energy of the main chain and the intermolecular interaction force, it has good thermodynamic properties itself. Therefore, PIAs combine the excellent properties of PI and aerogel, having both good thermodynamic properties and high porosity and mesoporous structure, making it an excellent thermal protection and insulation material.

[0005] However, most of the polyimide aerogel materials on the market currently have problems such as high density, high drying shrinkage rate, and poor heat insulation performance. Therefore, it is very necessary to provide an aerogel composite material with better physical properties. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of an anisotropic polyimide aerogel composite material, wherein the density of the aerogel composite material is 0.020 - 0.048 g / cm 3 , the drying shrinkage rate is 1.75 - 6.75%, the radial thermal diffusion coefficient is 0.601 - 1.309 mm 2 / s, and the axial thermal diffusion coefficient is 2.074 - 13.182 mm 2 / s.

[0007] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing an anisotropic polyimide aerogel composite material, comprising the following steps:

[0009] (1) Add the calcined glass fiber into ethanol, then add 3-aminopropyltriethoxysilane, and perform ultrasonic treatment to obtain chopped glass fiber;

[0010] (2) Mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide, and perform nitrogen sealing treatment in an ice-water bath to obtain a polyamic acid solution;

[0011] (3) Place the polyamic acid solution obtained in step (2) in water, and after obtaining a white solid, perform washing and grinding treatments in sequence to obtain polyamic acid powder;

[0012] (4) Add the polyamic acid powder obtained in step (3) into a diethylamine solution, then add the chopped glass fiber obtained in step (1), stir and place it in a mold, and perform liquid nitrogen freezing treatment and vacuum freeze-drying treatment in sequence to obtain a polyimide aerogel;

[0013] (5) Perform gradient heat treatment on the polyimide aerogel obtained in step (4) to obtain an anisotropic polyimide aerogel composite material.

[0014] Preferably, the calcination temperature in step (1) is 400-460 °C, and the calcination time is 1-1.5 h; the mass-volume ratio of the glass fiber to ethanol is 1-2 g:10 ml; the volume ratio of 3-aminopropyltriethoxysilane to ethanol is 7-10:100; the ultrasonic power is 240-250 w, and the ultrasonic time is 10-15 h.

[0015] Preferably, the molar ratio of 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in step (2) is 1:1:35-41.5; the time for nitrogen sealing treatment in the ice-water bath is 10-15 h, and the nitrogen content during the nitrogen sealing treatment in the ice-water bath is 99.0-99.9%.

[0016] Preferably, the volume ratio of the polyamic acid solution to water in step (3) is 1-2:10; the water is ultrapure water; the temperature of the water used for washing is 85-95 °C, and the number of washing and grinding times is based on completely washing the solvent in the white solid.

[0017] Preferably, after the washing and grinding treatments are completed, wash with ethanol 3-4 times and perform vacuum drying treatment.

[0018] More preferably, the temperature of the vacuum drying is 60-80 °C, and the time of the vacuum drying is 10-12 h.

[0019] Preferably, the mass-to-volume ratio of the polyamic acid powder to the diethylamine solution in step (4) is 25-35 g: 1-30 ml; the mass ratio of the chopped glass fiber to the polyamic acid powder is 0.1-1: 25-35.

[0020] Preferably, the rotation speed of the stirring in step (4) is 500-1000 r / min, and the stirring time is 5-8 h; the time of the liquid nitrogen freezing treatment is 10-15 min; the time of the vacuum freeze-drying treatment is 48-72 h.

[0021] Preferably, the method of the gradient heat treatment in step (5) is to place the polyimide aerogel in an oven, and the temperature is set to 55-65 °C, 85-95 °C, 115-125 °C, 145-155 °C, 175-185 °C, 205-215 °C, 235-245 °C, 265-275 °C, 295-305 °C in sequence, and each temperature is treated for 1-1.5 h.

[0022] More preferably, the temperature is set to 58-62 °C, 88-92 °C, 118-122 °C, 148-152 °C, 178-182 °C, 208-212 °C, 238-242 °C, 268-272 °C, 298-302 °C.

[0023] The beneficial effects of the present invention compared with the prior art are as follows:

[0024] 1. The density of the anisotropic polyimide aerogel composite material provided by the present invention is as low as 0.02 g / cm 3 , which is significantly lower than that of the conventional Py series aerogel thermal insulation materials commonly used in the market; and its radial thermal diffusivity is as low as 0.601 W·m -1 ·K -1 , having significant anisotropic thermal conductivity; the drying shrinkage rate is as low as 1.75%, which is significantly lower than that of the conventional Py series aerogel thermal insulation materials commonly used in the market. In addition, the composite material provided by the present invention has the advantage of anisotropy, and the thermal conductivity in two directions is different, while the Py series aerogel thermal insulation materials are relatively consistent in each direction. Anisotropy can make it insulate heat in one direction and transfer heat in the other direction; for example, it can play a heat insulation role radially at high temperature, and after the temperature rises, it can transfer heat axially, reducing the invasion of high temperature and improving the tolerance of the material.

[0025] 2. PAA is polyamic acid, which finally becomes polyimide after imidization in two ways. One is to add a catalyst and a coagulant to the PAA solution for reaction to directly produce a solid polyimide wet gel, and then through a series of acetone or ethanol solvent replacements to replace the solvent of the wet gel, and then through supercritical drying for drying, the steps are very complicated; while the other method is to prepare polyimide by thermal imidization, without a catalyst, and react after high-temperature heating. Before this, the polyamic acid needs to be completely separated from the solvent, so it becomes fine powder. Then, an aqueous solution is used for forming pores. The aqueous solution quickly becomes an ice solid, and then through the drying method of vacuum sublimation, not only the solid shape is retained, but also countless voids can be quickly constructed to become a complete and pure polyamic acid aerogel, and then it becomes a polyimide solid aerogel through thermal imidization. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 SEM structural diagrams of anisotropic polyimide aerogel composites with a polyimide solid concentration of 2%, where the left figure is the radial direction and the right figure is the axial direction;

[0028] Figure 2 SEM structural diagrams of anisotropic polyimide aerogel composites with a polyimide solid concentration of 3%, where the left figure is the radial direction and the right figure is the axial direction;

[0029] Figure 3 SEM structural diagrams of anisotropic polyimide aerogel composites with a polyimide solid concentration of 4%, where the left figure is the radial direction and the right figure is the axial direction;

[0030] Figure 4 SEM structural diagrams of anisotropic polyimide aerogel composites with a polyimide solid concentration of 5%, where the left figure is the radial direction and the right figure is the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0031] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0032] It should be understood that the terms described in this invention are only for describing specific embodiments and are not used to limit the invention. Additionally, for the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0034] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0035] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0036] This invention provides a method for preparing an anisotropic polyimide aerogel composite material, comprising the following steps:

[0037] (1) Add the calcined glass fiber into ethanol, then add 3-aminopropyltriethoxysilane, and ultrasonicate to obtain chopped glass fiber;

[0038] (2) Mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide, and perform nitrogen sealing treatment in an ice-water bath to obtain a polyamic acid solution;

[0039] (3) Place the polyamic acid solution obtained in step (2) in water, and after obtaining a white solid, perform washing and grinding treatments in sequence to obtain polyamic acid powder;

[0040] (4) Add the polyamic acid powder obtained in step (3) into a diethylamine solution, then add the chopped glass fiber obtained in step (1), stir and place it in a mold, and perform liquid nitrogen freezing treatment and vacuum freeze-drying treatment in sequence to obtain a polyimide aerogel;

[0041] (5) Gradient heat treatment is performed on the polyimide aerogel obtained in step (4) to obtain an anisotropic polyimide aerogel composite material.

[0042] In the present invention, the temperature of the calcination in step (1) is preferably 400 - 460 °C, more preferably 410 - 450 °C, still more preferably 420 - 440 °C, and even more preferably 430 °C; the time of the calcination is preferably 1 - 1.5 h, more preferably 1.2 - 1.4 h, still more preferably 1.3 h; after the calcination, the surface moisture of the glass fiber is preferably washed with ultrapure water and dried; the mass-volume ratio of the glass fiber to ethanol is preferably 1 - 2 g:10 ml, more preferably 1.2 - 1.8 g:10 ml, still more preferably 1.4 - 1.6 g:10 ml; the ethanol is preferably an ethanol aqueous solution with a volume ratio of 90:10 - 95:5; the volume ratio of 3-aminopropyltriethoxysilane to ethanol is preferably 7 - 10:100, more preferably 8 - 9:100, still more preferably 8.5:100; the temperature of the ultrasonic treatment is preferably room temperature, more preferably 25 - 30 °C, still more preferably 26 - 28 °C; the power of the ultrasonic treatment is preferably 240 - 250 w, more preferably 242 - 248 w, still more preferably 244 - 246 w; the time of the ultrasonic treatment is preferably 10 - 15 h, more preferably 12 - 14 h, still more preferably 13 h; after the ultrasonic treatment, the chopped glass fiber is preferably washed with ethanol and ultrapure water and dried; the ethanol is preferably an ethanol solution with a volume percentage of 98 - 99%; the number of times of washing with ethanol and ultrapure water is preferably 3 times each; the aspect ratio of the obtained chopped glass fiber is preferably 500 - 900, more preferably 600 - 800, still more preferably 700.

[0043] In the present invention, the molar ratio of 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in step (2) is preferably 1:1:35 to 41.5, more preferably 1:1:36 to 40, still more preferably 1:1:37 to 39, and even more preferably 1:1:38; the time for the ice-water bath nitrogen sealing treatment is preferably 10 to 15 h, more preferably 12 to 14 h, still more preferably 13 h; the nitrogen content during the ice-water bath nitrogen sealing treatment is preferably 99.0 to 99.9%, more preferably 99.2 to 99.6%, still more preferably 99.5%; the ice-water bath nitrogen sealing is preferably accompanied by stirring, and the stirring speed is preferably 800 to 1000 r / min, more preferably 850 to 950 r / min, still more preferably 900 r / min; step (2) is preferably carried out under the protection of nitrogen; the nitrogen concentration is preferably 99.0 to 99.9%, more preferably 99.2 to 99.6%, still more preferably 99.5%.

[0044] In the present invention, the volume ratio of the polyamic acid solution to water in step (3) is preferably 1 to 2:10, more preferably 1.2 to 1.8:10, still more preferably 1.4 to 1.6:10; the water is preferably ultrapure water; the temperature of the water used for washing is preferably 85 to 95 °C, more preferably 88 to 92 °C, still more preferably 90 °C; the number of washing and grinding times is preferably based on completely washing the solvent in the white solid; after the washing and grinding treatment, it is preferably washed with ethanol 3 to 4 times and subjected to vacuum drying treatment; the ethanol used for washing is preferably boiling ethanol, and the temperature of the boiling ethanol is 78.3 °C; the temperature of the vacuum drying is preferably 60 to 80 °C, more preferably 65 to 75 °C, still more preferably 70 °C; the time for the vacuum drying is preferably 10 to 12 h, more preferably 10.5 to 11.5 h, still more preferably 11 h.

[0045] In the present invention, the mass-volume ratio of the polyamic acid powder to the diethylamine solution in step (4) is preferably 25-35 g: 1-30 ml, more preferably 28-34 g: 5-20 ml, and even more preferably 30-32 g: 10-15 ml; the mass ratio of the chopped glass fiber to the polyamic acid powder is preferably 0.1-1: 25-35, more preferably 0.4-0.8: 28-34, and even more preferably 0.5-0.6: 30-32; the rotation speed of the stirring is preferably 500-1000 r / min, more preferably 600-900 r / min, even more preferably 700-800 r / min, and still more preferably 750 r / min; the stirring time is preferably 5-8 h, more preferably 5.5-7.5 h, even more preferably 6-7 h; after stirring, a polyamic acid solution with a uniformly dispersed solid content of 2-11% is preferably obtained, more preferably 5-10%, and even more preferably 6-8%; the mold is preferably a polytetrafluoroethylene cup-shaped mold with a copper plate bottom; the time of the liquid nitrogen freezing treatment is preferably 10-15 min, more preferably 12-14 min, and even more preferably 13 min; the time of the vacuum freeze-drying treatment is preferably 48-72 h, more preferably 50-70 h, even more preferably 55-65 h, and still more preferably 60 h.

[0046] In the present invention, the reason for adding the chopped glass fiber is that during the process of the polyamic acid powder drying into a xerogel, there will be a large shrinkage, and adding the chopped glass fiber can fix the polymer organic molecules through hydrogen bonds and reduce the shrinkage.

[0047] In the present invention, the method of the gradient heat treatment in step (5) is preferably to place the polyimide aerogel in an oven, and the temperature is set to 55-65 °C, 85-95 °C, 115-125 °C, 145-155 °C, 175-185 °C, 205-215 °C, 235-245 °C, 265-275 °C, 295-305 °C in sequence, and each temperature is treated for 1-1.5 h. The temperature setting is further preferably 58-62 °C, 88-92 °C, 118-122 °C, 148-152 °C, 178-182 °C, 208-212 °C, 238-242 °C, 268-272 °C, 298-302 °C, and each temperature is treated for 1.2-1.4 h. Even more preferably, it is 60 °C, 90 °C, 120 °C, 150 °C, 180 °C, 210 °C, 240 °C, 270 °C, 300 °C, and each temperature is treated for 1.3 h; the gradient heat treatment is preferably carried out for heating up in a high-temperature oven.

[0048] Example 1

[0049] A method for preparing an anisotropic polyimide aerogel composite material comprises the following steps:

[0050] (1) Place glass fibers in an environment of 450 °C and calcine for 1.5 h. After calcination, wash the surface moisture of the glass fibers with ultrapure water and dry them to obtain 10 g of calcined glass fibers. Add the calcined glass fibers to 100 ml of an ethanol aqueous solution with a volume ratio of 90:10, then add 8 ml of 3-aminopropyltriethoxysilane, and ultrasonicate at 25 °C and 245 w for 12 h. After ultrasonication, wash 3 times with ethanol with a volume percentage of 99% and ultrapure water and then dry to obtain short-cut glass fibers with an aspect ratio of 700;

[0051] (2) Under the protection of nitrogen (with a content of 99.9%), mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in a molar ratio of 1:1:41.5. Perform ice-water bath nitrogen sealing treatment in an environment with a nitrogen content of 99.9%, and stir at 1000 r / min for 15 h to obtain a polyamic acid solution;

[0052] (3) Place 200 ml of the polyamic acid solution obtained in step (2) into 2000 ml of ultrapure water. After obtaining a white solid, wash it with water at 90 °C and grind it with a mortar. After all the solvent in the white solid is washed out, wash it 3 times with boiling ethanol at 78.3 °C and perform vacuum drying treatment at 70 °C for 10 h to obtain polyamic acid powder;

[0053] (4) Take 30 g of the polyamic acid powder obtained in step (3) and add it to 30 ml of a diethylamine solution, then add 1 g of the short-cut glass fibers obtained in step (1), and stir at 1000 r / min for 5 h to obtain a polyamic acid solution with a uniformly dispersed solid content of 5%. Then place the obtained polyamic acid solution in a mold with a polytetrafluoroethylene cup-shaped bottom made of copper plate, perform liquid nitrogen freezing treatment for 10 min and vacuum freeze-drying treatment for 48 h to obtain a polyimide aerogel;

[0054] (5) Place the polyimide aerogel obtained in step (4) in a high-temperature oven and perform gradient heating heat treatment at 60 °C, 90 °C, 120 °C, 150 °C, 180 °C, 210 °C, 240 °C, 270 °C, and 300 °C respectively, with each temperature treatment for 1 h, to obtain an anisotropic polyimide aerogel composite material with a polyimide solid concentration of 5%.

[0055] Example 2

[0056] A method for preparing an anisotropic polyimide aerogel composite material comprises the following steps:

[0057] (1) Place the glass fiber in an environment of 400 °C and calcine it for 1.5 h. After calcination, wash the surface of the glass fiber with ultrapure water and dry it to obtain 20 g of calcined glass fiber. Add the calcined glass fiber to 100 ml of an ethanol aqueous solution with a volume ratio of 95:5, then add 10 ml of 3-aminopropyltriethoxysilane, and ultrasonicate at 30 °C and 250 w for 10 h. After ultrasonication, wash it 3 times with ethanol with a volume percentage of 98% and ultrapure water and then dry it to obtain short-cut glass fiber with an aspect ratio of 500;

[0058] (2) Under the protection of nitrogen (with a content of 99.0%), mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in a molar ratio of 1:1:35. Perform ice bath nitrogen sealing treatment in an environment with a nitrogen content of 99.0%, and stir at 800 r / min for 10 h to obtain 200 ml of polyamic acid solution;

[0059] (3) Take 100 ml of the polyamic acid solution obtained in step (2) and place it in 1000 ml of ultrapure water. After obtaining a white solid, wash it with water at a temperature of 85 °C and grind it with a mortar. After all the solvent in the white solid is washed away, wash it 4 times with boiling ethanol at 78.3 °C and perform vacuum drying treatment at 60 °C for 12 h to obtain polyamic acid powder;

[0060] (4) Take 25 g of the polyamic acid powder obtained in step (3) and add it to 20 ml of diethylamine solution, then add 0.1 g of the short-cut glass fiber obtained in step (1), and stir at 500 r / min for 8 h to obtain a polyamic acid solution with a uniformly dispersed solid content of 11%; then place the obtained polyamic acid solution in a mold with a copper plate bottom and a polytetrafluoroethylene cup shape, perform liquid nitrogen freezing treatment for 15 min and vacuum freeze-drying treatment for 72 h to obtain polyimide aerogel;

[0061] (5) Place the polyimide aerogel obtained in step (4) in a high-temperature oven and perform gradient heating heat treatment at 55 °C, 85 °C, 115 °C, 145 °C, 175 °C, 205 °C, 235 °C, 265 °C, and 295 °C respectively, with each temperature treatment for 1.5 h to obtain an anisotropic polyimide aerogel composite material with a polyimide solid concentration of 11%.

[0062] Example 3

[0063] A preparation method of an anisotropic polyimide aerogel composite material, the steps are as follows:

[0064] (1) Place the glass fiber in an environment of 460 °C and calcine it for 1.2 h. After calcination, wash the surface of the glass fiber with ultrapure water and dry it to obtain 15 g of calcined glass fiber. Add the calcined glass fiber to 100 ml of an ethanol aqueous solution with a volume ratio of 92:8, then add 7 ml of 3-aminopropyltriethoxysilane, and ultrasonicate at 25 °C and 240 w for 15 h. After ultrasonication, wash with ethanol with a volume percentage of 99% and ultrapure water 3 times each and then dry to obtain short-cut glass fiber with an aspect ratio of 900;

[0065] (2) Under the protection of nitrogen (content 99.5%), mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in a molar ratio of 1:1:40. Perform ice bath nitrogen sealing treatment in an environment with a nitrogen content of 99.5%, and stir at 900 r / min for 12 h to obtain a polyamic acid solution;

[0066] (3) Take 150 ml of the polyamic acid solution obtained in step (2) and place it in 1500 ml of ultrapure water. After obtaining a white solid, wash it with water at 95 °C and grind it with a mortar. After all the solvent in the white solid is washed away, wash it 3 times with boiling ethanol at 78.3 °C and perform vacuum drying treatment at 80 °C for 11 h to obtain polyamic acid powder;

[0067] (4) Take 35 g of the polyamic acid powder obtained in step (3) and add it to 25 ml of diethylamine solution, then add 0.5 g of the short-cut glass fiber obtained in step (1), and stir at 800 r / min for 7 h to obtain a polyamic acid solution with a uniformly dispersed solid content of 2%; then place the obtained polyamic acid solution in a mold with a copper plate bottom and a polytetrafluoroethylene cup shape, perform liquid nitrogen freezing treatment for 12 min and vacuum freeze-drying treatment for 60 h to obtain a polyimide aerogel;

[0068] (5) Place the polyimide aerogel obtained in step (4) in a high-temperature oven and perform gradient heating heat treatment at 65 °C, 95 °C, 125 °C, 155 °C, 185 °C, 215 °C, 245 °C, 275 °C, and 305 °C respectively, with each temperature treatment for 1.2 h to obtain an anisotropic polyimide aerogel composite material with a polyimide solid concentration of 2%.

[0069] Experimental Example 1 Screening of the aspect ratio of short-cut glass fiber

[0070] Determine the influence of short-cut glass fibers with different aspect ratios on the properties of the prepared anisotropic polyimide aerogel composite material.

[0071] The fiber structure of the anisotropic polyimide aerogel composite material was observed under a scanning electron microscope at a magnification of 100 times. The length of the sample and the length of the mold (the mold is a cup-shaped mold with a polytetrafluoroethylene cup body and a copper plate bottom, with a diameter of 25 mm and a height of 20 mm) were measured with a vernier caliper, and the drying shrinkage rate was calculated by formula Ⅰ. The results are shown in Table 1.

[0072] S = (1 - M / D) * 100% formula Ⅰ;

[0073] Where S is the sample shrinkage rate, M is the sample length, and D is the mold length.

[0074] Table 1 Experimental results of the selection of the aspect ratio of the reinforcing fiber of the polyimide aerogel composite material

[0075]

[0076] As can be seen from Table 1, the larger the aspect ratio of the chopped glass fiber, the more macromolecules can be intertwined to further reduce the drying shrinkage rate of the aerogel composite material and improve the strength of the aerogel composite material. However, if the aspect ratio is too large, it is easy to cause the glass fiber in the diethylamine aqueous solution of polyamic acid to sink and the dispersion to be uneven.

[0077] Test Example 2 Performance determination

[0078] Anisotropic polyimide aerogel composite materials with polyimide solid concentrations of 2%, 3%, 4%, and 5% were prepared according to the method in Example 1, and the physical property indexes of the anisotropic polyimide aerogel composite materials with different polyimide solid concentrations were measured. At the same time, a comparison material (Py series aerogel thermal insulation materials on the market) was set.

[0079] When measuring, an electronic densitometer (MH-300A, purchased from Shanghai Qigong Instrument and Equipment Co., Ltd., China) was used to measure the sample density. The drying shrinkage rate of the aerogel composite material was calculated by formula Ⅰ; a laser thermal conductivity meter (LFA467, purchased from NETZSCH, Germany) was used to measure the thermal diffusivity of the anisotropic polyimide aerogel composite material (PI aerogel composite material) at room temperature.

[0080] The results are shown in Table 2 and Figures 1 to 4 as follows.

[0081] Table 2 Measurement results of physical property indexes

[0082]

[0083] The results show that the density of the anisotropic polyimide aerogel composite material provided by the present invention is as low as 0.02 g / cm 3, while the density of the Py series aerogel thermal insulation materials on the market is 0.22 g / cm 3 ; the radial thermal diffusivity is as low as 0.601 W·m -1 ·K -1 , showing significant anisotropic thermal conductivity; the drying shrinkage rate is as low as 1.75%, while the drying shrinkage rate of the Py series aerogel thermal insulation materials on the market is greater than 20%.

[0084] As can be seen from the above embodiments, the present invention provides a method for preparing an anisotropic polyimide aerogel composite material, and the density of the aerogel composite material is in the range of 0.020 - 0.048 g / cm 3 , the drying shrinkage rate is in the range of 1.75 - 6.75%, the radial thermal diffusivity is in the range of 0.601 - 1.309 mm 2 / s, and the axial thermal diffusivity is in the range of 2.074 - 13.182 mm 2 / s.

[0085] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of an anisotropic polyimide aerogel composite material, characterized in that, It includes the following steps: (1) Add the calcined glass fiber into ethanol, then add 3-aminopropyltriethoxysilane, and perform ultrasonic treatment to obtain chopped glass fiber; (2) Mix 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide, and perform nitrogen sealing treatment in an ice-water bath to obtain a polyamic acid solution; (3) Place the polyamic acid solution obtained in step (2) in water. After obtaining a white solid, perform washing and grinding treatments in sequence to obtain polyamic acid powder; (4) Add the polyamic acid powder obtained in step (3) into a diethylamine solution, then add the chopped glass fiber obtained in step (1), stir and place it in a mold, and perform liquid nitrogen freezing treatment and vacuum freeze-drying treatment in sequence to obtain a polyimide aerogel; (5) Perform gradient heat treatment on the polyimide aerogel obtained in step (4) to obtain an anisotropic polyimide aerogel composite material.

2. The preparation method according to claim 1, wherein, The temperature of the calcination in step (1) is 400 - 460 °C, and the time of the calcination is 1 - 1.5 h; the mass-volume ratio of the glass fiber to ethanol is 1 - 2 g:10 ml; the volume ratio of 3-aminopropyltriethoxysilane to ethanol is 7 - 10:100; the power of the ultrasonic treatment is 240 - 250 W, and the time of the ultrasonic treatment is 10 - 15 h.

3. The preparation method according to claim 1, wherein, The molar ratio of 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and N,N-dimethylacetamide in step (2) is 1:1:35 - 41.5; the time of the nitrogen sealing treatment in the ice-water bath is 10 - 15 h, and the content of nitrogen during the nitrogen sealing treatment in the ice-water bath is 99.0 - 99.9%.

4. The preparation method according to claim 1, wherein The volume ratio of the polyamic acid solution to water in step (3) is 1 - 2:10; the water is ultrapure water; the temperature of the water used for washing is 85 - 95 °C, and the number of times of washing and grinding is based on completely washing the solvent in the white solid.

5. The preparation method according to claim 1 or 4, characterized in that, After the washing and grinding treatments are completed, wash with ethanol 3 - 4 times and perform vacuum drying treatment.

6. The preparation method according to claim 5, characterized in that, The temperature of the vacuum drying is 60 - 80 °C, and the time of the vacuum drying is 10 - 12 h.

7. The preparation method according to claim 1, characterized in that, The mass-volume ratio of the polyamic acid powder to the diethylamine solution in step (4) is 25 - 35 g:1 - 30 ml; the mass ratio of the chopped glass fiber to the polyamic acid powder is 0.1 - 1:25 - 35.

8. The preparation method according to claim 1, wherein The rotation speed of the stirring in step (4) is 500 - 1000 r / min, and the time of the stirring is 5 - 8 h; the time of the liquid nitrogen freezing treatment is 10 - 15 min; the time of the vacuum freeze-drying treatment is 48 - 72 h.

9. The preparation method according to claim 1, characterized in that The method of the gradient heat treatment in step (5) is to place the polyimide aerogel in an oven, and sequentially set the temperatures to 55 - 65 °C, 85 - 95 °C, 115 - 125 °C, 145 - 155 °C, 175 - 185 °C, 205 - 215 °C, 235 - 245 °C, 265 - 275 °C, 295 - 305 °C, and treat at each temperature for 1 - 1.5 h.

10. The preparation method according to claim 9, wherein, The temperature is set to 58~62°C, 88~92°C, 118~122°C, 148~152°C, 178~182°C, 208~212°C, 238~242°C, 268~272°C, 298~302°C.

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