Preparation method of dynamic fatigue resistant polyimide aerogel thermal insulation material

Abstract

The invention belongs to the technical field of thermal protection materials for aerospace crafts, and particularly relates to a preparation method of a dynamic fatigue resistant polyimide aerogel thermal insulation material. In the traditional polyimide aerogel preparation process, polyacrylonitrile short filaments are added, and the types and dosages of dianhydride, diamine and a catalyst as well as the length, radius and dosages of the polyacrylonitrile short filaments are regulated and controlled, so that the flexibility of the polyimide aerogel thermal insulation material is further enhanced, the mechanical property of the polyimide aerogel thermal insulation material is improved, and the dynamic fatigue resistant polyimide aerogel thermal insulation material is obtained; the polyacrylonitrile short filaments are creatively added and subjected to ultrasonic dispersion, polyacrylonitrile has excellent flexibility, and the structural stability of the material and the mutual supporting effect between molecular chains are promoted through hydrogen-bond interaction and combination with polyimide molecules; the polyimide aerogel thermal insulation material is endowed with excellent mechanical properties and dynamic fatigue resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal protection materials for aerospace vehicles, and in particular relates to a method for preparing a dynamic fatigue resistant polyimide aerogel thermal insulation material. Background Art

[0002] Advanced aerospace vehicles are constantly developing towards high speed, high maneuverability and long range, and facing a more complex space environment. Their thermal protection systems have placed higher requirements on high-performance thermal insulation materials. The performance of thermal insulation materials directly affects the safety and life of aerospace vehicles.

[0003] With its outstanding thermal insulation properties, high-temperature resistance, and chemical stability, polyimide aerogels have shown great application potential in high-end fields such as aerospace, electronics, and new energy equipment. Its unique nanoporous structure imparts extremely low thermal conductivity, making it an ideal material for efficient thermal insulation. However, in actual application scenarios, especially under conditions involving dynamic loads such as frequent vibration and deformation, polyimide aerogels are prone to structural fatigue damage, resulting in a decline in mechanical properties and failure of thermal insulation functions. This seriously restricts its large-scale promotion and application in dynamic and complex environments. Under the action of long-term dynamic stress, the internal pore structure of most traditional polyimide aerogels will gradually collapse, the nano-network skeleton will break, and it will be difficult to maintain stable thermal insulation performance. Therefore, the development of polyimide aerogel materials that can effectively resist dynamic fatigue and maintain structural integrity and thermal insulation reliability during continuous stress and deformation has become a research hotspot in the field of high-performance thermal insulation materials.

[0004] Recently, a Chinese invention patent application (CN202411274380.8, publication date: 2024.11.08) reported a high-temperature resistant polyimide aerogel, its preparation method, and application. The material has the characteristics of high temperature resistance (thermal decomposition temperature greater than 700°C), high strength (stress of 0.3-0.8 MPa under 3% stress compression conditions) and low thermal conductivity (thermal conductivity of 0.020-0.032 W / (m·K) at room temperature and pressure); the invention patent (ZL201810204173.3) reported a high specific surface area (greater than 200 m 2 / g), high strength (compressive Young's modulus greater than 10 MPa), low thermal conductivity, high thermal stability (thermal degradation temperature greater than 400°C), and high transparency (transmittance greater than 50%). A Chinese invention patent application (CN201910109671.4, published on June 21, 2019) reports a lightweight, high-strength, and flame-retardant polyimide aerogel. These research findings describe the heat resistance, high strength, and low thermal conductivity of polyimide aerogels, but their dynamic fatigue resistance has not been studied.

[0005] Kaiqing Yao et al. (Kaiqing Yao, Chonghu Song, Hong Fang, et al. Freezing-Extraction / Vacuum-Drying Method for Robust and Fatigue-Resistant Polyimide Fibrous Aerogels and Their Composites with Enhanced Fire Retardancy, Engineering 21 (2023) 152–161.) proposed a freeze-extraction / vacuum-drying method to prepare robust and fatigue-resistant polyimide fiber aerogels and their composites with enhanced fire retardancy. This material, which utilizes chopped electrospun polyimide fibers as a support structure, is lightweight, high-strength, and exhibits fatigue resistance up to 20,000 cycles. However, its preparation process is complex, and its high thermal conductivity, exceeding 0.0404 W / (m·K) at ultra-low density, makes it difficult to achieve efficient thermal insulation. Therefore, obtaining lightweight, low-thermal-conductivity polyimide aerogel insulation materials that exhibit fatigue resistance in dynamic environments remains a key technical challenge for those skilled in the art. Summary of the Invention

[0006] In response to the problem that it is difficult to strike a balance between the thermal insulation effect and dynamic fatigue resistance of polyimide aerogel insulation materials in the existing technology, the present invention proposes a method for preparing a dynamic fatigue-resistant polyimide aerogel insulation material. By adding polyacrylonitrile short filaments during the traditional polyimide aerogel preparation process, and regulating the type and amount of dianhydride, diamine, and catalyst, as well as the length, radius, and amount of the polyacrylonitrile short filaments, its flexibility is further enhanced and its mechanical properties are improved, thereby obtaining a dynamic fatigue-resistant polyimide aerogel insulation material.

[0007] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a dynamic fatigue-resistant polyimide aerogel thermal insulation material comprises the following steps: S1. At room temperature (25°C), add diamine and dianhydride into an organic solvent in a mass ratio of 1:1 to 1:2.5, respectively, and stir for 20 to 25 minutes to obtain a polyamic acid solution; S2. Adding the polyacrylonitrile short filaments to the polyamic acid solution and performing ultrasonic dispersion to obtain a polyamic acid solution containing the polyacrylonitrile short filaments, wherein the mass ratio of the polyacrylonitrile short filaments to the polyamic acid solution is 0.05-0.15; S3. Adding a catalyst and a dehydrating agent to the polyamic acid solution containing polyacrylonitrile staple fibers and continuously stirring to form a polyimide sol containing polyacrylonitrile staple fibers, wherein the catalyst is picoline, the dehydrating agent is acetic anhydride, and the mass ratio of the catalyst, the dehydrating agent, and the diamine is (1.0-1.5):(3.0-5.0):12; S4, placing the polyimide sol containing polyacrylonitrile short fibers in a water-soluble pot at 50°C to 80°C for gelation for 5 to 60 hours to obtain an initial state of dynamic fatigue-resistant polyimide aerogel; S5, aging the initial state of the dynamic fatigue resistant polyimide aerogel for 18 to 72 hours to obtain an aged state of the dynamic fatigue resistant polyimide aerogel; S6. Solvent-replace the aged dynamic fatigue resistant polyimide gel with an organic solvent at room temperature (25° C.) to obtain a final dynamic fatigue resistant polyimide gel; the solvent replacement is performed 3 to 5 times, and each replacement time is 8 to 10 hours; S7. Drying the dynamic fatigue resistant polyimide final gel with CO2 supercritical fluid to obtain a dynamic fatigue resistant polyimide aerogel thermal insulation material.

[0008] Preferably, the diamine described in S1 is one or a mixture of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diamino-2,2'-dimethylbiphenyl; the dianhydride is one or a mixture of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and pyromellitic dianhydride; and the organic solvent is one or a mixture of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0009] Preferably, the length of the polyacrylonitrile short filament in S2 is 3 mm, 6 mm, 9 mm or 12 mm, and the diameter is 10-13 um.

[0010] Preferably, the catalyst in S3 may also be triethylamine or pyridine, and the dehydrating agent may also be acetyl chloride or propionic anhydride.

[0011] Preferably, the organic solvent in S6 is one or a mixture of methanol, ethanol, isopropanol or acetone.

[0012] Preferably, the pressure of the CO2 supercritical fluid during drying in S7 is 8-15 MPa, the temperature is 40-60°C, the drying time is 8-18 h, and the pressure is released at a rate of 80-190 kPa / min after drying is completed.

[0013] The beneficial effects of the present invention are as follows: 1. In the second step (S2) of the present invention's method for preparing a dynamic fatigue-resistant polyimide aerogel insulation material, short polyacrylonitrile filaments are innovatively added and ultrasonically dispersed. Polyacrylonitrile, which possesses excellent flexibility, combines with polyimide molecules through hydrogen bonding, promoting the material's structural stability and providing mutual support between molecular chains. This imparts the polyimide aerogel insulation material with excellent mechanical properties and dynamic fatigue resistance. Furthermore, a supercritical fluid drying method (S7) is employed to impart a nanoporous network structure to the material, thereby endowing the dynamic fatigue-resistant polyimide aerogel insulation material with lightweight and highly effective thermal insulation properties.

[0014] 2. The dynamic fatigue resistant polyimide aerogel thermal insulation material prepared by the method of the present invention has the characteristics of three-dimensional interconnected nanoporous network structure, low density and low thermal conductivity, excellent compression performance and dynamic fatigue resistance, etc. Its density is 0.082-0.231 g / cm 3 The thermal conductivity is 0.0205-0.0311 W / (m·K), and the compressive strength at 3% deformation is 0.682 MPa-0.893 MPa. When compressed 10,000 times at 1% deformation and a frequency of 4 Hz, the pressure reaches 0.392 MPa-0.596 MPa. These excellent comprehensive properties well match the current aerospace demand for lightweight, high-strength, and dynamic fatigue-resistant thermal insulation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an overall flow chart of the method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material of the present invention; Figure 2 This is a macroscopic morphology of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared by the present invention; Figure 3 This is a microstructure diagram of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared by the present invention; Figure 4 Because the diamine and dianhydride are not in the appropriate ratio range, it is difficult to obtain the polyimide sol of its gel. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 In the first step, at room temperature, p-phenylenediamine and pyromellitic anhydride in a ratio of 1:1.5 were added to dimethylacetamide solvent, stirred for 25 minutes, and 50 g of polyamic acid solution was obtained.

[0018] In the second step, 2.5 g of polyacrylonitrile short fibers with a length of 3 mm and a diameter of 10 μm were added to the polyamic acid solution obtained in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short fibers; The third step is to add a catalyst picoline and a dehydrating agent acetic anhydride to the polyamic acid solution containing the polyacrylonitrile short fibers, wherein the mass ratio of the catalyst picoline, the dehydrating agent acetic anhydride and the p-phenylenediamine is 1.0:3.0:12, and continuously stir to form a polyimide sol containing the polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 50°C for gelation for 5 h to obtain the initial state of dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 18 hours to obtain an aged state of the dynamic fatigue resistant polyimide aerogel. Step 6: Solvent replacement is performed on the aged dynamic fatigue resistant polyimide gel using an organic solvent, methanol, at room temperature to obtain a final state dynamic fatigue resistant polyimide gel; the number of solvent replacements is 3, and each replacement time is 8 hours; In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 8 MPa and a temperature of 40°C for 8 hours. After drying, the pressure is released at a rate of 80 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0019] The macroscopic structure of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is as follows: Figure 2 As shown, its density is 0.082 g / cm 3 ,from Figure 3 The microstructure shows that the polyimide aerogel is tightly attached to the polyacrylonitrile filaments, forming a strong bond. The polyimide aerogel exhibits a three-dimensional network structure, which gives it excellent mechanical strength and low thermal conductivity. The thermal conductivity at room temperature and pressure is 0.0205 W / (m·K), and the compressive stress at 3% compressive strain is 0.682 MPa. When compressed 10,000 times at a frequency of 4 Hz and a compression strain of 1%, the pressure reached 0.392 MPa.

[0020] Example 2 In the first step, at room temperature, p-phenylenediamine and pyromellitic anhydride in a ratio of 1:1.5 were added to dimethylacetamide solvent, stirred for 25 minutes, and 50 g of polyamic acid solution was obtained.

[0021] In the second step, 2.5 g of polyacrylonitrile short fibers with a length of 6 mm and a diameter of 10 μm were added to the polyamic acid solution obtained in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short fibers; The third step is to add a catalyst picoline and a dehydrating agent acetic anhydride to the polyamic acid solution containing the polyacrylonitrile short fibers, wherein the mass ratio of the catalyst picoline, the dehydrating agent acetic anhydride and the p-phenylenediamine is 1.0:3.0:12, and continuously stir to form a polyimide sol containing the polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 50°C for gelation for 10 h to obtain the initial state of dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 22 h to obtain the dynamic fatigue resistant polyimide aged state gel. Step 6: Solvent replacement is performed on the aged dynamic fatigue resistant polyimide gel using an organic solvent, methanol, at room temperature to obtain a final state dynamic fatigue resistant polyimide gel; the number of solvent replacements is 3, and each replacement time is 8 hours; In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 8 MPa and a temperature of 40°C for 8 hours. After drying, the pressure is released at a rate of 80 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0022] The density of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is 0.097 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0245 W / (m·K), and the compressive stress at 3% compressive strain is 0.737 MPa. When compressed 10,000 times at a compression strain of 1% and a frequency of 4 Hz, the pressure reaches 0.455 MPa.

[0023] Example 3 In the first step, 4,4'-diamino-2,2'-dimethylbiphenyl and 4'-biphenyltetracarboxylic dianhydride were added to dimethyl sulfoxide amine solvent at a ratio of 1:1.5 at room temperature and stirred for 25 minutes to obtain 50 g of polyamic acid solution.

[0024] In the second step, 2.5 g of polyacrylonitrile short fibers with a length of 3 mm and a diameter of 12 μm were added to the polyamic acid solution obtained in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short fibers; The third step is to add a catalyst picoline and a dehydrating agent acetic anhydride to the polyamic acid solution containing the polyacrylonitrile short fibers, wherein the mass ratio of the catalyst picoline, the dehydrating agent acetic anhydride and 4,4'-diamino-2,2'-dimethylbiphenyl is 1.0:4.0:12, and the mixture is continuously stirred to form a polyimide sol containing the polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 60°C for gelation for 10 h to obtain the initial state of dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 18 hours to obtain an aged state of the dynamic fatigue resistant polyimide aerogel. Step 6: Solvent replacement is performed on the aged dynamic fatigue resistant polyimide gel using an organic solvent, methanol, at room temperature to obtain a final state dynamic fatigue resistant polyimide gel; the number of solvent replacements is 3, and each replacement time is 8 hours; In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 10 MPa and a temperature of 40°C for 8 hours. After drying, the pressure is released at a rate of 90 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0025] The density of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is 0.089 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0233 W / (m·K), and the compressive stress at 3% compressive strain is 0.710 MPa. When compressed 10,000 times at a compression strain of 1% and a frequency of 4 Hz, the pressure reaches 0.412 MPa.

[0026] Example 4 In the first step, at room temperature, 1:1.5 of 4,4'-diamino-2,2'-dimethylbiphenyl and pyromellitic anhydride were added to dimethylacetamide solvent and stirred for 25 minutes to obtain 50 g of polyamic acid solution.

[0027] In the second step, 6.5 g of polyacrylonitrile short filaments with a length of 9 mm and a diameter of 11 μm were added to the polyamic acid solution obtained in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments; The third step is to add a catalyst picoline and a dehydrating agent acetic anhydride to the polyamic acid solution containing the polyacrylonitrile short fibers, wherein the mass ratio of the catalyst picoline, the dehydrating agent acetic anhydride and the p-phenylenediamine is 1.2:3.5:12, and continuously stir to form a polyimide sol containing the polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 50°C for gelation for 15 h to obtain the initial state of the dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 50 h to obtain the dynamic fatigue resistant polyimide aged state gel. Step 6: Solvent replacement is performed on the aged dynamic fatigue resistant polyimide gel using an organic solvent, methanol, at room temperature to obtain a final state dynamic fatigue resistant polyimide gel; the number of solvent replacements is 3, and each replacement time is 8 hours; In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 10 MPa and a temperature of 50°C for 12 h. After drying, the pressure is released at a rate of 130 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0028] The density of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is 0.187 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0295 W / (m·K), and the compressive stress at 3% compressive strain is 0.804 MPa. When compressed 10,000 times at a compression strain of 1% and a frequency of 4 Hz, the pressure reaches 0.493 MPa.

[0029] Example 5 In the first step, p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride were added to N,N-dimethylformamide amine solvent at a ratio of 1:2.0 at room temperature and stirred for 25 minutes to obtain 50 g of polyamic acid solution.

[0030] In the second step, 3.0 g of polyacrylonitrile short filaments with a length of 6 mm and a diameter of 10 μm were added to the polyamic acid solution obtained in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments; The third step is to add pyridine as a catalyst and acetyl chloride as a dehydrating agent to the polyamic acid solution containing polyacrylonitrile short fibers, wherein the mass ratio of pyridine as catalyst, acetyl chloride as dehydrating agent and p-phenylenediamine is 1.0:3.0:12, and the mixture is continuously stirred to form a polyimide sol containing polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 70°C for gelation for 40 h to obtain the initial state of dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 56 h to obtain the dynamic fatigue resistant polyimide aged state gel. Step 6: Solvent replacement of the aged dynamic fatigue resistant polyimide gel with methanol, an organic solvent, at room temperature to obtain a final state dynamic fatigue resistant polyimide gel; the number of solvent replacements is 4, and each replacement time is 8 hours; In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 13 MPa and a temperature of 50°C for 14 h. After drying, the pressure is released at a rate of 150 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0031] The density of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is 0.201 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0305 W / (m·K), and the compressive stress at 3% compressive strain is 0.853 MPa. When compressed 10,000 times at a compression strain of 1% and a frequency of 4 Hz, the pressure reaches 0.545 MPa.

[0032] Example 6 In the first step, at room temperature, 1:2.5 of 4,4'-diaminodiphenyl ether and 4,4'-oxydiphthalic anhydride were added to N-methylpyrrolidone solvent and stirred for 25 minutes to obtain 50 g of polyamic acid solution.

[0033] In the second step, 7.5 g of polyacrylonitrile short fibers with a length of 12 mm and a diameter of 13 μm were added to the polyamic acid solution prepared in the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short fibers. The third step is to add a catalyst triethylamine and a dehydrating agent propionic anhydride to the polyamic acid solution containing the polyacrylonitrile short fibers, wherein the mass ratio of the catalyst triethylamine, the dehydrating agent propionic anhydride and the 4,4'-diaminodiphenyl ether is 1.5:5.0:12, and continuously stir to form a polyimide sol containing the polyacrylonitrile short fibers; In the fourth step, the polyimide sol containing polyacrylonitrile short fibers was placed in a water-soluble pot at 80°C for gelation for 60 h to obtain the initial state of dynamic fatigue-resistant polyimide aerogel. The fifth step is to age the initial state of the dynamic fatigue resistant polyimide aerogel for 72 h to obtain the dynamic fatigue resistant polyimide aged state gel. Step 6: Solvent replacement of the aged dynamic fatigue resistant polyimide gel with acetone, an organic solvent, at room temperature to obtain a final dynamic fatigue resistant polyimide gel; the solvent replacement was repeated 5 times, with each replacement lasting 10 h. In the seventh step, the dynamic fatigue resistant polyimide final gel is placed in a CO2 supercritical fluid drying condition at a pressure of 15 MPa and a temperature of 60°C for 18 hours. After drying, the pressure is released at a rate of 190 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0034] The density of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared in this embodiment is 0.231 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0311 W / (m·K), and the compressive stress at 3% compressive strain is 0.893 MPa. When compressed 10,000 times at a compression strain of 1% and a frequency of 4 Hz, the pressure reaches 0.596 MPa.

[0035] In the present invention, as long as the gelation temperature, aging time, temperature, solvent type, number of replacements, and replacement time during solvent replacement are within the stated ranges, the effects on the density, thermal conductivity, compressive strength, and dynamic fatigue resistance of the dynamic fatigue-resistant polyimide aerogel are essentially negligible. The density, thermal conductivity, and mechanical strength of the dynamic fatigue-resistant polyimide aerogel are primarily affected by the molar ratio of diamine to dianhydride, the length of the polyacrylonitrile filaments, and the amount of polyacrylonitrile added. A greater molar ratio of diamine to dianhydride increases the density, thermal conductivity, and mechanical strength of the polyimide aerogel; a longer polyacrylonitrile filament increases the density, thermal conductivity, mechanical strength, and dynamic fatigue resistance of the polyimide aerogel; and a greater amount of polyacrylonitrile filaments added increases the density, thermal conductivity, mechanical strength, and dynamic fatigue resistance of the polyimide aerogel.

[0036] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the addition of polyacrylonitrile short filaments in step 2) is omitted, and the other steps are the same as those in Example 1; The density of the obtained polyimide aerogel thermal insulation material is 0.096 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0208 W / (m·K), and the compressive stress at 3% compressive strain is 0.520 MPa. Microcracks are generated on the surface after 1000 compression cycles at a compression frequency of 4 Hz and a compression strain of 1%.

[0037] The results show that the introduction of polyacrylonitrile can improve the mechanical properties of polyimide aerogel and effectively enhance its dynamic fatigue resistance.

[0038] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the ratio of the amount of diamine and dianhydride added in step 1) is 1:0.5, and the rest is the same as Example 1; however, a stable gel is obtained, and it is difficult to obtain a stable dynamic fatigue-resistant polyimide aerogel. Figure 4 For polyimide sol, the ratio of diamine and dianhydride is not within the appropriate range and it is difficult to form a gel.

[0039] The results showed that it was difficult to obtain a stable gel when the molar ratio of diamine to dianhydride was outside the range of 1:1 to 1:2.

[0040] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that the amount of polyacrylonitrile short filaments added in step 3) is 9.0 g, and the rest is the same as Example 4; The density of the obtained polyimide aerogel is 0.486 g / cm 3 The thermal conductivity at room temperature and pressure is 0.0505 W / (m·K), and the compressive stress under 3% compressive strain conditions is 1.23 MPa.

[0041] The results show that the amount of polyacrylonitrile short filaments is too high (greater than 7.5 g), and the mechanical strength of the polyimide aerogel insulation material obtained is high, but the density and thermal conductivity increase, making it unsuitable for the field of high-efficiency thermal insulation.

[0042] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. Various process solutions that have no substantial difference from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a dynamic fatigue resistant polyimide aerogel thermal insulation material, characterized in that: The method is divided into the following steps: S1. At room temperature, diamine and dianhydride are added to an organic solvent in a mass ratio of 1:1 to 1:2.5, respectively, and stirred for 20 to 25 minutes to obtain a polyamic acid solution; S2. Adding the polyacrylonitrile short filaments to the polyamic acid solution and performing ultrasonic dispersion to obtain a polyamic acid solution containing the polyacrylonitrile short filaments, wherein the mass ratio of the polyacrylonitrile short filaments to the polyamic acid solution is 0.05-0.15; S3. Adding a catalyst and a dehydrating agent to the polyamic acid solution containing polyacrylonitrile staple fibers and continuously stirring to form a polyimide sol containing polyacrylonitrile staple fibers, wherein the catalyst is picoline, the dehydrating agent is acetic anhydride, and the mass ratio of the catalyst, the dehydrating agent, and the diamine is (1.0-1.5):(3.0-5.0):12; S4, placing the polyimide sol containing polyacrylonitrile short fibers in a water-soluble pot at 50°C to 80°C for gelation for 5 to 60 hours to obtain an initial state of dynamic fatigue-resistant polyimide aerogel; S5, aging the initial state of the dynamic fatigue resistant polyimide aerogel for 18 to 72 hours to obtain an aged state of the dynamic fatigue resistant polyimide aerogel; S6. Solvent-replace the aged dynamic fatigue resistant polyimide gel with an organic solvent at room temperature to obtain a final dynamic fatigue resistant polyimide gel; the number of solvent replacements is 3 to 5 times, and the time for each replacement is 8 to 10 hours; S7. Drying the dynamic fatigue resistant polyimide final gel with CO2 supercritical fluid to obtain a dynamic fatigue resistant polyimide aerogel thermal insulation material.

2. The method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material according to claim 1, characterized in that: The diamine described in S1 is one or a mixture of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diamino-2,2'-dimethylbiphenyl; the dianhydride is one or a mixture of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and pyromellitic dianhydride; and the organic solvent is one or a mixture of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

3. The method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material according to claim 1, characterized in that: The length of the polyacrylonitrile short filament in S2 is 3 mm, 6 mm, 9 mm or 12 mm, and the diameter is 10-13 um.

4. The method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material according to claim 1, characterized in that: The catalyst in S3 may also be triethylamine or pyridine, and the dehydrating agent may also be acetyl chloride or propionic anhydride.

5. The method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material according to claim 1, characterized in that: The organic solvent in S6 is one or a mixture of methanol, ethanol, isopropanol or acetone.

6. The method for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material according to claim 1, characterized in that: The pressure of the CO2 supercritical fluid in S7 during drying is 8-15 MPa, the temperature is 40-60°C, the drying time is 8-18 h, and the pressure is released at a rate of 80-190 kPa / min after drying is completed.

Images