Preparation method of reusable 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 reusable polyimide aerogel thermal insulation material. According to the method, the ceramic fiber powder is added into the polyimide aerogel, and the types and dosages of dianhydride, diamine and a catalyst and the dosage of the ceramic fiber powder are regulated and controlled, so that the mechanical property and the high-temperature resistance of the polyimide aerogel thermal insulation material are further improved, and the reusable characteristic of the polyimide aerogel thermal insulation material is enhanced; the reusable polyimide aerogel thermal insulation material is obtained; nanoscale ceramic fiber powder is creatively added and subjected to ultrasonic dispersion, ceramic fibers have high strength and modulus and are ground into powder to fill pores of aerogel, the mechanical property of the aerogel is improved, the bearing capacity and the deformation resistance of the aerogel are enhanced, and then the aerogel is endowed with high mechanical property.

Description

Technical Field

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

[0002] With the rapid development of aerospace technology, reusable high-speed aircraft have demonstrated unparalleled advantages in intelligence reconnaissance, rapid response defense, and other areas. During high-speed flight, reusable aircraft experience extremely high surface temperatures. Furthermore, they are inevitably soaked by rain when passing through cumulonimbus clouds and low-temperature airspace. Therefore, there is an urgent need for reusable insulation materials with excellent thermal insulation and rain resistance to ensure the normal operation of the aircraft. Aerogel is a high-performance thermal insulation material widely used in aerospace due to its low density and high porosity. Its nanoscale porous structure provides excellent thermal insulation, with a thermal conductivity as low as 0.013 W / (m·K) at room temperature. It is also lighter than traditional ceramic insulation materials, effectively reducing the weight of spacecraft. Aerogel must withstand frequent high- and low-temperature cycles while ensuring no significant degradation in performance after repeated use to ensure its reusability.

[0003] Polyimide aerogel thermal insulation, a new type of nanoporous material, boasts low density, high strength, and excellent thermal stability. It shows great potential for application in aerospace thermal protection materials. A Chinese patent application (CN202411274380.8, published on November 8, 2024) discloses a high-temperature-resistant polyimide aerogel composite material. It can be used in environments up to 420°C, with a thermal decomposition temperature of 700°C. It exhibits excellent high-temperature resistance and strong thermal stability, with a thermal conductivity of 0.020 to 0.032 W / (m·K) at room temperature and pressure. Its low density (0.09 to 0.20 g / cm³) and high strength (0.3 to 0.8 MPa at 3% compression) make it a good match for the current demand for lightweight, high-strength, high-performance organic thermal protection materials in the aerospace industry. However, no mention is made of the material's reusability. Chinese patent application (CN118930956A) reports a polyimide composite aerogel material for thermal insulation, which has a low density (as low as 0.184 g / cm 3 The patent does not discuss the reusability of the material. Therefore, it is urgent to conduct research on the reusability of polyimide aerogels and to develop polyimide aerogel insulation materials that combine lightweight, low thermal conductivity, low density, high strength, and reusability. Summary of the Invention

[0004] To meet the current demand for reusable thermal insulation materials in the aviation industry, the present invention provides a method for preparing a reusable polyimide aerogel thermal insulation material. By adding ceramic fiber powder to the polyimide aerogel, and adjusting the types and amounts of dianhydride, diamine, and catalyst, as well as the amount of ceramic fiber powder, the mechanical properties and high-temperature resistance of the polyimide aerogel thermal insulation material are further improved, enhancing its reusability.

[0005] The purpose of the present invention is achieved through the following technical solutions: S1: In an ice bath, start a stirring device, add diamine and dianhydride into an organic solvent at a molar ratio of 1:0.8 to 1:2, and continue stirring for 20 to 50 minutes to obtain a polyamic acid solution; S2: placing the ceramic fiber into a grinding device and grinding it into powder to obtain ceramic fiber powder; S3: adding the ceramic fiber powder obtained in S2 to the polyamic acid solution obtained in S1 and performing ultrasonic dispersion to obtain a polyamic acid solution containing ceramic fiber powder; S4: adding a catalyst and a dehydrating agent to the polyamic acid solution containing ceramic fiber powder obtained in S3 and continuously stirring to form a polyimide sol containing ceramic fiber powder; S5: placing the polyimide sol containing ceramic fiber powder obtained in S4 in a water-soluble pot at 50°C to 80°C for gelation for 10 to 70 hours to obtain a reusable polyimide aerogel initial gel; S6: placing the reusable polyimide aerogel obtained in S5 into an oven for aging for 18 to 72 hours to obtain a reusable polyimide aged gel; S7: exchanging the aged reusable polyimide gel obtained in S6 with an organic solvent at room temperature (usually 25° C.) to obtain a final reusable polyimide gel; the organic solvent is exchanged 3 to 8 times, and each exchange takes 3 to 10 hours; S8: drying the reusable polyimide final gel obtained in S7 with CO2 supercritical fluid to obtain a reusable polyimide aerogel material; Preferably, in S1, the diamine is p-phenylenediamine or 4,4'-diaminodiphenyl ether, or a mixture of both; the dianhydride is pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride, or a mixture of both; and the organic solvent is dimethylacetamide or N,N-dimethylformamide, or a mixture of both.

[0006] Preferably, the particle size of the ceramic fiber powder ground in S2 is in the range of 100-200 nm.

[0007] Preferably, the catalyst in S3 is one of picoline, triethylamine or pyridine; the dehydrating agent is one of acetic anhydride, acetyl chloride or propionic anhydride; the ultrasonic dispersion power is 100-500 W, the frequency is 20-80 kHz, the temperature is preferably 20-50 ° C, and the time is preferably 10-60 min; Preferably, the mass ratio of ceramic fiber powder to polyamic acid solution in S3 is 0.05-0.15; Preferably, the molar ratio of the catalyst, the dehydrating agent and the polyamic acid solution containing ceramic fiber powder in step S4 is 1.0-1.5:3.0-5.0:12 Preferably, the organic solvent in S7 is one of methanol, ethanol, isopropanol or acetone.

[0008] Preferably, the pressure of the CO2 supercritical fluid 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.

[0009] The present invention has the following beneficial effects: 1. In the third step (S3) of the present invention's method for preparing reusable polyimide aerogel thermal insulation materials, nano-scale ceramic fiber powder is innovatively added and ultrasonically dispersed. Ceramic fibers inherently possess high strength and modulus. The ground powder fills the aerogel's pores, improving its mechanical properties, enhancing its load-bearing capacity and deformation resistance, and thus imparting high mechanical properties. Simultaneously, a supercritical drying method (S8) imparts a nanoporous network structure to the material, thereby endowing the reusable polyimide aerogel thermal insulation material with high strength and thermal insulation properties.

[0010] 2. The experimentally prepared reusable polyimide aerogel insulation material has a room temperature density range of 0.09–0.20 g / cm³, a thermal conductivity of 0.025–0.059 W / (m·K) at room temperature and pressure, and a stress of 0.57–0.96 MPa at a 3% compressive strain. After 10 high-temperature water immersion cycles (up to 350°C for 1 hour), the density decreased by 1–1.5%, the room temperature thermal conductivity increased by 3–5%, and the compressive strength decreased by 5–10%. Its excellent mechanical properties and high-temperature resistance provide reliable thermal protection for equipment and components in high-temperature environments, effectively meeting the current demand for high-strength, reusable insulation materials in the aerospace industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1This is an overall flow chart of the preparation method of the reusable polyimide aerogel thermal insulation material of the present invention; Figure 2 The macroscopic morphology of the reusable polyimide aerogel thermal insulation material of the present invention is shown; Figure 3 The microstructure of the reusable polyimide aerogel thermal insulation material of the present invention; Figure 4 Because the diamine and dianhydride of the present invention are not within the appropriate ratio range, it is difficult to form a polyimide sol with a gel structure. DETAILED DESCRIPTION

[0012] The present invention is described in detail below through a series of specific embodiments.

[0013] Example 1 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:0.8. Continue stirring for 20 minutes to prepare a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.05:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 100 W, the frequency was 20 kHz, the temperature was 20°C, and the time was 10 min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid are added to the solution at a molar ratio of 1.0:3.0 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 50° C. for gelation for 10 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 30° C. oven for aging for 18 h to obtain a reusable polyimide aged gel; Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature, the number of solvent replacements is 3, and the time for each replacement is 10 hours to obtain a reusable polyimide final gel; In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 8 MPa, the temperature is 40°C, and the drying time is 8 hours. After the drying is completed, the pressure is released at a rate of 80 kPa / min to obtain a reusable polyimide aerogel material. Figure 2 This is the macroscopic morphology of the aerogel material. The sample has the characteristics of good formability, light weight and low thermal conductivity. Figure 3 The microstructure of a reusable polyimide aerogel thermal insulation material demonstrates a nanoporous network structure, with ceramic fiber powder and polyimide aerogel well bonded together, resulting in low thermal conductivity and superior mechanical properties. The material has a density of 0.09 g / cm³ and a thermal conductivity of 0.025 W / (m·K) at room temperature and pressure. The material exhibits a stress of 0.57 MPa at 3% compressive strain. After 10 cycles of high-temperature water immersion (up to 350°C for 1 hour), the material exhibits a 1.5% decrease in density, a 5% increase in room-temperature thermal conductivity, and a 10% decrease in compressive strength.

[0014] Example 2 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1. Stir continuously for 24 minutes to obtain a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.06:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 150 W, the frequency was 25 kHz, the temperature was 25°C, and the time was 20 min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid are added to the solution at a molar ratio of 1.1:3.2 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 55° C. for gelation for 20 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 35°C oven for aging for 28 hours to obtain a reusable polyimide aged gel; Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature. The number of solvent replacements is 4, and each replacement time is 9 hours to obtain a reusable polyimide final gel. In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 9 MPa, the temperature is 42°C, and the drying time is 9 hours. After the drying is completed, the pressure is released at a rate of 90 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.10 g / cm³ and a thermal conductivity of 0.030 W / (m·K) at room temperature and pressure. The stress reached 0.60 MPa at a 3% compressive strain. After 10 cycles of high-temperature water immersion (350°C for 1 hour), the density decreased by 1.45%, the room-temperature thermal conductivity increased by 4.8%, and the compressive strength decreased by 9.6%.

[0015] Example 3 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1.2. Stir for 28 minutes to obtain a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.08:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 200 W, the frequency was 30 kHz, the temperature was 30° C., and the time was 25 min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid are added to the solution at a molar ratio of 1.2:3.4 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 56° C. for gelation for 30 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 40° C. oven for aging for 38 h to obtain a reusable polyimide aged gel. Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature, the number of solvent replacements is 5, and the time for each replacement is 8 hours to obtain a reusable polyimide final gel; In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The CO2 supercritical fluid drying pressure is 10 MPa, the temperature is 48°C, and the drying time is 10 h. After the drying is completed, the pressure is released at a rate of 100 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.12 g / cm³ and a thermal conductivity of 0.032 W / (m·K) at room temperature and pressure. The stress reached 0.62 MPa at a 3% compressive strain. After 10 cycles of high-temperature water immersion (350°C for 1 hour), the density decreased by 1.4%, the room-temperature thermal conductivity increased by 4.5%, and the compressive strength decreased by 8.4%.

[0016] Example 4 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1.4. Stirring is continued for 32 minutes to prepare a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.09:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 250W, the frequency was 36kHz, the temperature was 35°C, and the time was 30min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid were added to the solution at a molar ratio of 1.25:3.50 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 60° C. for gelation for 40 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 45° C. oven for aging for 48 h to obtain a reusable polyimide aged gel. Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature. The number of solvent replacements is 6, and each replacement time is 7 hours to obtain a reusable polyimide final gel. In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 11 MPa, the temperature is 50°C, and the drying time is 11 h. After the drying is completed, the pressure is released at a rate of 120 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.13 g / cm³ and a thermal conductivity of 0.036 W / (m·K) at room temperature and pressure. The stress reached 0.68 MPa at a 3% compressive strain. After 10 cycles of high-temperature water immersion (350°C for 1 hour), the density decreased by 1.35%, the room-temperature thermal conductivity increased by 4.2%, and the compressive strength decreased by 7.2%.

[0017] Example 5 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1.5. Stirring is continued for 36 minutes to obtain a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.10:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 300W, the frequency was 40kHz, the temperature was 40°C, and the time was 40min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid were added to the solution at a molar ratio of 1.35:3.60 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 64° C. for gelation for 50 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 50° C. oven for aging for 58 h to obtain a reusable polyimide aged gel. Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature, the number of solvent replacements is 7, and the time for each replacement is 6 hours to obtain a reusable polyimide final gel; In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 12 MPa, the temperature is 52°C, and the drying time is 12 h. After the drying is completed, the pressure is released at a rate of 140 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.14 g / cm³ and a thermal conductivity of 0.040 W / (m·K) at room temperature and pressure. The stress reached 0.72 MPa at a 3% compressive strain. After 10 cycles of high-temperature water immersion (350°C for 1 hour), the density decreased by 1.25%, the room-temperature thermal conductivity increased by 4.0%, and the compressive strength decreased by 6.4%.

[0018] Example 6 In the first step, in an ice bath, start the stirring equipment and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1.6. Continue stirring for 45 minutes to prepare a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.12:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 360W, the frequency was 50kHz, the temperature was 42°C, and the time was 50min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid were added to the solution at a molar ratio of 1.36:3.80 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 68° C. for gelation for 60 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 55° C. oven for aging for 68 h to obtain a reusable polyimide aged gel. Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature. The number of solvent replacements is 8, and each replacement time is 5 hours to obtain a reusable polyimide final gel. In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 13 MPa, the temperature is 54°C, and the drying time is 14 h. After the drying is completed, the pressure is released at a rate of 150 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.15 g / cm³ and a thermal conductivity of 0.045 W / (m·K) at room temperature and pressure. The stress reached 0.78 MPa at a 3% compressive strain. After 10 high-temperature water soaking cycles (350°C for 1 hour), the density decreased by 1.15%, the room-temperature thermal conductivity increased by 3.6%, and the compressive strength decreased by 6.2%.

[0019] Example 7 In the first step, in an ice bath, start a stirring device and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:1.8. Stir for 48 minutes to obtain a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.14:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 420W, the frequency was 60kHz, the temperature was 45°C, and the time was 55min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid were added to the solution at a molar ratio of 1.40:4.0 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 70° C. for gelation for 65 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 60° C. oven for aging for 70 h to obtain a reusable polyimide aged gel; Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature. The number of solvent replacements is 9 times, and each replacement time is 4 hours to obtain a reusable polyimide final gel. In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The CO2 supercritical fluid drying pressure is 14 MPa, the temperature is 56°C, and the drying time is 15 h. After the drying is completed, the pressure is released at a rate of 160 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.16 g / cm³ and a thermal conductivity of 0.052 W / (m·K) at room temperature and pressure. The stress reached 0.84 MPa at a 3% compressive strain. After 10 high-temperature water soaking cycles (350°C for 1 hour), the density decreased by 1.05%, the room-temperature thermal conductivity increased by 3.2%, and the compressive strength decreased by 5.6%.

[0020] Example 8 In the first step, in an ice bath, start a stirring device and add p-phenylenediamine and pyromellitic anhydride to dimethylacetamide solvent at a molar ratio of 1:2.0. Continue stirring for 50 minutes to prepare a polyamic acid solution. The second step is to put the ceramic fiber into a grinding device and grind it into powder to obtain ceramic fiber powder; In the third step, the ceramic fiber powder obtained in the second step was added to the polyamic acid solution obtained in the first step at a mass ratio of 0.15:1 for ultrasonic dispersion, wherein the ultrasonic dispersion power was 500W, the frequency was 80kHz, the temperature was 50°C, and the time was 60min to obtain a polyamic acid solution containing ceramic fiber powder; In the fourth step, picoline and hepatic acid are added to the solution at a molar ratio of 1.50:5.0 and stirred evenly to obtain a polyimide sol containing ceramic fiber powder; In the fifth step, the polyimide sol containing ceramic fiber powder obtained in the fourth step is placed in a water-soluble pot at 80° C. for gelation for 70 hours to obtain a reusable polyimide aerogel initial gel; Step 6: The reusable polyimide aerogel obtained in the step 5 is placed in a 65° C. oven for aging for 72 h to obtain a reusable polyimide aged gel. Step 7: The reusable polyimide aged gel obtained in Step 6 is subjected to organic solvent replacement at room temperature. The number of solvent replacements is 10, and each replacement time is 3 hours to obtain a reusable polyimide final gel. In the eighth step, the reusable polyimide final gel obtained in the seventh step is dried using a CO2 supercritical fluid. The pressure of the CO2 supercritical fluid drying is 15 MPa, the temperature is 60°C, and the drying time is 18 hours. After the drying is completed, the pressure is released at a rate of 190 kPa / min to obtain a reusable polyimide aerogel material. Testing revealed that the aerogel material has a density of 0.20 g / cm³ and a thermal conductivity of 0.059 W / (m·K) at room temperature and pressure. The stress reached 0.96 MPa at a 3% compressive strain. After 10 cycles of high-temperature water immersion (350°C for 1 hour), the density decreased by 1.0%, the room-temperature thermal conductivity increased by 3.0%, and the compressive strength decreased by 5.0%.

[0021] In the present invention, as long as the gel temperature, aging time and temperature, solvent type during solvent replacement, number of replacements, and replacement time are within the stated ranges, the effects on the density, thermal conductivity, compressive strength, and reusability of the reusable polyimide aerogel can be essentially ignored. The density, thermal conductivity, and mechanical strength of the reusable polyimide aerogel are primarily affected by the molar ratio of diamine to dianhydride and the amount of ceramic fiber added. The greater the molar ratio of diamine to dianhydride, the greater the density, thermal conductivity, and mechanical strength of the polyimide aerogel; and the greater the amount of ceramic fiber added, the greater the density, thermal conductivity, mechanical strength, and reusability of the polyimide aerogel.

[0022] Comparative Example 1 Comparative Example 1 is substantially the same as Example 1, except that no nano-ceramic fiber powder is added in step S3.

[0023] Performance test results: density is 0.08 g / cm³, thermal conductivity is 0.019 W / (m·K) at room temperature and pressure, and the internal structure of the aerosol material is destroyed after six high-temperature water soaking cycles (temperature up to 350°C, 1 hour).

[0024] The results show that the addition of ceramic fiber powder can improve the reusability of polyimide thermal insulation materials.

[0025] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the molar ratio of p-phenylenediamine to pyromellitic anhydride is 1:3 (greater than 1:2), and the other steps are the same as Example 1. However, it is difficult to obtain a stable polyimide gel.

[0026] The results show that it is difficult to obtain polyimide aerogel when the mass ratio of dianhydride to diamine exceeds the range of 1:0.8~1:2; Figure 4 The polyimide sol cannot form a gel (when the ratio of dianhydride to diamine exceeds the specified range, the polyimide gel cannot be formed, and thus the polyimide aerogel cannot be obtained).

[0027] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that the mass ratio of ceramic fiber powder to polyimide fiber added in the second step is 0.2:1, and the rest is the same as Example 3; the density of the obtained reusable polyimide aerogel insulation material is 0.232 gcm -3 , thermal conductivity is 0.0644 W m -1 K -1 After 10 cycles of high-temperature water soaking (temperature up to 350°C, 1h), the density decreased by 0.9%, the room temperature thermal conductivity increased by 2.8%, and the compressive strength decreased by 4.8%; The results show that a too high mass ratio of ceramic fiber to polyimide nanofiber (higher than 0.15:1) will lead to a decrease in the changes in density, thermal conductivity, and compressive strength after high-temperature water soaking cycles. A polyimide aerogel insulation material with high reusability can be obtained, but the density and thermal conductivity increase, making it unsuitable for the field of high-efficiency thermal insulation.

[0028] 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 reusable polyimide aerogel thermal insulation material, characterized in that: The method is divided into the following steps: S1: In an ice bath, start a stirring device, add diamine and dianhydride into an organic solvent at a molar ratio of 1:0.8 to 1:2, and continue stirring for 20 to 50 minutes to obtain a polyamic acid solution; S2: placing the ceramic fiber into a grinding device and grinding it into powder to obtain ceramic fiber powder; S3: adding the ceramic fiber powder obtained in S2 to the polyamic acid solution obtained in S1 and performing ultrasonic dispersion to obtain a polyamic acid solution containing ceramic fiber powder; S4: adding a catalyst and a dehydrating agent to the polyamic acid solution containing ceramic fiber powder obtained in S3 and continuously stirring to form a polyimide sol containing ceramic fiber powder; S5: placing the polyimide sol containing ceramic fiber powder obtained in S4 in a water-soluble pot at 50°C to 80°C for gelation for 10 to 70 hours to obtain a reusable polyimide aerogel initial gel; S6: placing the reusable polyimide aerogel obtained in S5 into an oven for aging for 18 to 72 hours to obtain a reusable polyimide aged gel; S7: exchanging the aged reusable polyimide gel obtained in S6 with an organic solvent at room temperature to obtain a final reusable polyimide gel; the number of organic solvent replacements is 3 to 8 times, and the time for each replacement is 3 to 10 hours; S8: The reusable polyimide final gel obtained in S7 is dried using CO2 supercritical fluid to obtain a reusable polyimide aerogel material.

2. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, characterized in that: In S1, the diamine is p-phenylenediamine or 4,4'-diaminodiphenyl ether, or a mixture of both; the dianhydride is pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride, or a mixture of both; and the organic solvent is dimethylacetamide or N,N-dimethylformamide, or a mixture of both.

3. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, characterized in that: The particle size of the ceramic fiber powder ground in S2 is in the range of 100~200 nm.

4. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, wherein: The catalyst in S3 is one of picoline, triethylamine or pyridine; the dehydrating agent is one of acetic anhydride, acetyl chloride or propionic anhydride, the power of ultrasonic dispersion is 100~500W, the frequency is 20~80kHz, the temperature is preferably 20~50℃, and the time is preferably 10~60min.

5. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, characterized in that: The mass ratio of ceramic fiber powder to polyamic acid solution in S3 is 0.05~0.

15.

6. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, wherein: The molar ratio of the catalyst, the dehydrating agent and the polyamic acid solution containing ceramic fiber powder in S4 is 1.0~1.5:3.0~5.0:

12.

7. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, characterized in that: The organic solvent in S7 is one of methanol, ethanol, isopropanol or acetone.

8. The method for preparing the reusable polyimide aerogel thermal insulation material according to claim 1, wherein: The pressure of the CO2 supercritical fluid 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.

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