Preparation method of anti-dynamic fatigue polyimide aerogel thermal insulation material

Abstract

The application belongs to the technical field of aerospace vehicle thermal protection materials, 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, the types and dosages of dianhydride, diamine and catalyst, and the length, radius and dosage of the polyacrylonitrile short filaments are regulated, the flexibility is further enhanced, the mechanical properties are improved, and the dynamic fatigue-resistant polyimide aerogel thermal insulation material is obtained; the polyacrylonitrile short filaments are innovatively added and ultrasonically dispersed, the polyacrylonitrile has excellent flexibility, and is combined with the polyimide molecules through hydrogen bond action to promote the structural stability of the material and the mutual support effect between the molecular chains, so that the polyimide aerogel thermal insulation material is endowed with excellent mechanical properties and dynamic fatigue resistance.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection materials technology for aerospace vehicles, specifically relating to a method for preparing a dynamic fatigue resistant polyimide aerogel thermal insulation material. Background Technology

[0002] As advanced aerospace vehicles continue to develop towards higher speeds, higher maneuverability, and longer ranges, they face increasingly complex space environments. This places higher demands on high-performance thermal insulation materials for their thermal protection systems, and the performance of these materials directly affects the safety and lifespan of aerospace vehicles.

[0003] Polyimide aerogels, with their excellent thermal insulation properties, high-temperature resistance, and chemical stability, have shown great application potential in high-end fields such as aerospace, electronics, and new energy equipment. Their unique nanoporous structure endows them with extremely low thermal conductivity, making them ideal materials for efficient thermal insulation. However, in practical applications, especially under dynamic loads involving frequent vibration and deformation, polyimide aerogels are prone to structural fatigue damage, leading to a decline in mechanical properties and failure of thermal insulation function. This severely restricts their large-scale application in dynamic and complex environments. Under long-term dynamic stress, the internal pore structure of most traditional polyimide aerogels gradually collapses, and the nanonetwork skeleton breaks, making it difficult to maintain stable thermal insulation performance. Therefore, developing 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, Chinese invention patent application (CN202411274380.8, publication date: 2024.11.08) reported a high-temperature resistant polyimide aerogel, its preparation method, and its applications. This material possesses characteristics such as high temperature resistance (thermal decomposition temperature greater than 700℃), high strength (stress of 0.3–0.8 MPa under 3% stress compression), and low thermal conductivity (thermal conductivity at room temperature and pressure is 0.020–0.032 W / (m·K). Invention patent (ZL201810204173.3) reported a material with a high specific surface area (greater than 200 m²). 2 Polyimide aerogel materials possess properties such as high strength (compressive Young's modulus greater than 10 MPa), low thermal conductivity, high thermal stability (thermal degradation temperature greater than 400℃), and high transparency (transmittance greater than 50%). Chinese invention patent application (CN201910109671.4, publication date: 2019.06.21) reports a lightweight, high-strength, and flame-retardant polyimide aerogel. These research findings describe the temperature resistance, high strength, and low thermal conductivity of polyimide aerogels, but no related research has been conducted on their dynamic fatigue resistance.

[0005] Kaiqing Yao et al. (Kaiqing Yao, Chonghu Song, Hong Fang, et al. Freezing-Extraction / Vacuum-Drying Method for Robust and Fatigue-Resistant Polyimide Fiber 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 enhanced flame-retardant composites. This material utilizes chopped electrospun polyimide fibers as a supporting skeleton, exhibiting lightweight and high strength, and its fatigue resistance can be cycled up to 20,000 times. However, its preparation process is complex, and its thermal conductivity is high, exceeding 0.0404 W / (m·K) at ultra-low densities, making it difficult to achieve efficient thermal insulation. Therefore, how to obtain lightweight, low thermal conductivity polyimide aerogel insulation materials with fatigue resistance under dynamic environments is a key technical challenge of concern to those skilled in the art. Summary of the Invention

[0006] To address the challenge of simultaneously achieving both thermal insulation performance and dynamic fatigue resistance in existing polyimide aerogel insulation materials, this invention proposes a method for preparing a dynamic fatigue-resistant polyimide aerogel insulation material. This method involves adding polyacrylonitrile short filaments during the traditional polyimide aerogel preparation process, and adjusting the type and amount of dianhydride, diamine, and catalyst, as well as the length, radius, and amount of the polyacrylonitrile short filaments. This further enhances the material's flexibility and improves its mechanical properties, resulting in a dynamic fatigue-resistant polyimide aerogel insulation material.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a dynamic fatigue resistant polyimide aerogel thermal insulation material comprises the following steps:

[0009] S1. At room temperature (25℃), diamine and dianhydride are added to an organic solvent at a mass ratio of 1:1 to 1:2.5 and stirred for 20 to 25 minutes to obtain a polyamic acid solution.

[0010] S2. Add the polyacrylonitrile short filaments to the polyamic acid solution and disperse them by ultrasonication to obtain a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of polyacrylonitrile short filaments to polyamic acid solution is 0.05~0.15.

[0011] S3. Add a catalyst and a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments and stir continuously to form a polyimide sol containing polyacrylonitrile short filaments. The catalyst is methylpyridine, the dehydrating agent is acetic anhydride, and the mass ratio of the catalyst, dehydrating agent and diamine is (1.0~1.5):(3.0~5.0):12.

[0012] S4. The polyimide sol containing polyacrylonitrile short filaments is placed in a water-soluble pot at 50℃~80℃ for gelation for 5~60 h to obtain the initial state gel of the anti-dynamic fatigue polyimide aerogel.

[0013] S5. The initial state of the anti-dynamic fatigue polyimide aerogel is aged for 18-72 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0014] S6. The anti-dynamic fatigue polyimide aging gel is solvent-displaced with an organic solvent at room temperature (25℃) to obtain the anti-dynamic fatigue polyimide final gel; the number of solvent displacements is 3 to 5 times, and the displacement time is 8 to 10 hours each time;

[0015] S7. The dynamic fatigue resistant polyimide final state gel is dried with supercritical CO2 fluid to obtain dynamic fatigue resistant polyimide aerogel thermal insulation material.

[0016] Preferably, the diamine in S1 is one or a mixture of several of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diamino-2,2'-dimethylbiphenyl; the dianhydride is one or a mixture of several of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and pyromellitic dianhydride; and the organic solvent is one or a mixture of several of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0017] 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 μm.

[0018] Preferably, the catalyst in S3 can also be triethylamine or pyridine, and the dehydrating agent can also be acetyl chloride or propionic anhydride.

[0019] Preferably, the organic solvent in S6 is one or a mixture of methanol, ethanol, isopropanol or acetone.

[0020] Preferably, the pressure of the CO2 supercritical fluid during drying in S7 is 8~15 MPa, the temperature is 40~60℃, the drying time is 8~18 h, and the pressure is released at a rate of 80~190 kPa / min after drying.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. In the second step (S2) of the preparation method of the dynamic fatigue resistant polyimide aerogel insulation material of this invention, polyacrylonitrile short filaments are innovatively added and ultrasonically dispersed. Polyacrylonitrile itself has excellent flexibility and, through hydrogen bonding, combines with polyimide molecules to promote the structural stability of the material and the mutual support between molecular chains, thus endowing the polyimide aerogel insulation material with excellent mechanical properties and dynamic fatigue resistance. At the same time, the supercritical fluid drying method (S7) is used to give the material a nanoporous network structure, thereby endowing the dynamic fatigue resistant polyimide aerogel insulation material with lightweight and high-efficiency thermal insulation properties.

[0023] 2. The dynamic fatigue-resistant polyimide aerogel thermal insulation material prepared by the method of this invention has a three-dimensional interconnected nanoporous network structure, low density and low thermal conductivity, excellent compressibility and dynamic fatigue resistance, and its density is 0.082-0.231 g / cm³. 3 The thermal conductivity is 0.0205-0.0311 W / (m·K), and the compressive strength with 3% deformation is 0.682 MPa~0.893 MPa; under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4 Hz, the pressure reaches 0.392 MPa~0.596 MPa. Its excellent comprehensive performance effectively matches the current aerospace field's demand for lightweight, high-strength, and dynamic fatigue-resistant thermal insulation materials. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the overall process for preparing the dynamic fatigue resistant polyimide aerogel thermal insulation material of the present invention.

[0025] Figure 2 This is a macroscopic morphology image of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared according to the present invention.

[0026] Figure 3 This is a microstructure diagram of the dynamic fatigue resistant polyimide aerogel thermal insulation material prepared according to the present invention.

[0027] Figure 4 Polyimide sols are difficult to obtain because the diamine and dianhydride are not in the appropriate ratio range. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] The first step is to add p-phenylenediamine and pyromellitic anhydride in a 1:1.5 ratio to dimethylacetamide solvent at room temperature and stir for 25 min to obtain 50 g of polyamic acid solution.

[0031] In the second step, 2.5g of polyacrylonitrile short filaments with a length of 3mm and a diameter of 10μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0032] The third step involves adding methylpyridine as a catalyst and acetic anhydride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of methylpyridine, acetic anhydride, and p-phenylenediamine is 1.0:3.0:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0033] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in a water-soluble pot at 50°C for gelation for 5 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0034] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 18 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0035] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent methanol at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 3 times, with each displacement lasting 8 hours;

[0036] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 8 MPa and a temperature of 40℃ for 8 h. After drying, the pressure is released at a rate of 80 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0037] The macroscopic structure of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is as follows: Figure 2 As shown, its density is 0.082 g / cm³. 3 ,from Figure 3 The microstructure reveals that the polyimide aerogel is tightly adhered to the polyacrylonitrile short filaments, exhibiting excellent bonding. The polyimide aerogel displays a three-dimensional network structure, which endows it with good mechanical strength and low thermal conductivity. Its thermal conductivity at room temperature and pressure is 0.0205 W / (m·K), and the compressive stress under 3% compressive strain is 0.682 MPa. Under 1% compressive deformation and 10,000 compression cycles at a compression frequency of 4 Hz, the pressure reaches 0.392 MPa.

[0038] Example 2

[0039] The first step is to add p-phenylenediamine and pyromellitic anhydride in a 1:1.5 ratio to dimethylacetamide solvent at room temperature and stir for 25 min to obtain 50 g of polyamic acid solution.

[0040] In the second step, 2.5g of polyacrylonitrile short filaments with a length of 6mm and a diameter of 10μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0041] The third step involves adding methylpyridine as a catalyst and acetic anhydride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of methylpyridine, acetic anhydride, and p-phenylenediamine is 1.0:3.0:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0042] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in a water-soluble pot at 50°C for gelation for 10 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0043] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 22 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0044] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent methanol at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 3 times, with each displacement lasting 8 hours;

[0045] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 8 MPa and a temperature of 40℃ for 8 h. After drying, the pressure is released at a rate of 80 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel insulation material.

[0046] The density of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is 0.097 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0245 W / (m·K), and the compressive stress under 3% compressive strain is 0.737 MPa. Under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4 Hz, the pressure reaches 0.455 MPa.

[0047] Example 3

[0048] First, at room temperature, 4,4'-diamino-2,2'-dimethylbiphenyl and 4'-biphenyltetracarboxylic dianhydride in a 1:1.5 ratio were added to dimethyl sulfoxide solvent and stirred for 25 min to obtain 50 g of polyamic acid solution.

[0049] In the second step, 2.5g of polyacrylonitrile short filaments with a length of 3mm and a diameter of 12μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0050] The third step involves adding methylpyridine as a catalyst and acetic anhydride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of methylpyridine, acetic anhydride, and 4,4'-diamino-2,2'-dimethylbiphenyl is 1.0:4.0:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0051] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in a water-soluble pot at 60°C for gelation for 10 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0052] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 18 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0053] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent methanol at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 3 times, with each displacement lasting 8 hours;

[0054] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 10 MPa and a temperature of 40℃ 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.

[0055] The density of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is 0.089 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0233 W / (m·K), and the compressive stress under 3% compressive strain is 0.710 MPa. Under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4Hz, the pressure reaches 0.412 MPa.

[0056] Example 4

[0057] First, at room temperature, 4,4'-diamino-2,2'-dimethylbiphenyl and pyromellitic anhydride in a 1:1.5 ratio were added to dimethylacetamide solvent and stirred for 25 min to obtain 50 g of polyamic acid solution.

[0058] In the second step, 6.5g of polyacrylonitrile short filaments with a length of 9mm and a diameter of 11μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0059] The third step involves adding methylpyridine as a catalyst and acetic anhydride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of methylpyridine, acetic anhydride, and p-phenylenediamine is 1.2:3.5:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0060] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in a water bath at 50°C for gelation for 15 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0061] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 50 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0062] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent methanol at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 3 times, with each displacement lasting 8 hours;

[0063] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 10 MPa and a temperature of 50℃ 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.

[0064] The density of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is 0.187 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0295 W / (m·K), and the compressive stress under 3% compressive strain is 0.804 MPa. Under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4Hz, the pressure reaches 0.493 MPa.

[0065] Example 5

[0066] The first step is to add p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a 1:2.0 ratio to N,N-dimethylformamide amine solvent under room temperature conditions, and stir for 25 min to obtain 50 g of polyamic acid solution.

[0067] In the second step, 3.0g of polyacrylonitrile short filaments with a length of 6mm and a diameter of 10μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0068] The third step involves adding pyridine as a catalyst and acetyl chloride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of pyridine, acetyl chloride, and p-phenylenediamine is 1.0:3.0:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0069] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in a water bath at 70°C for gelation for 40 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0070] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 56 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0071] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent methanol at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 4 times, with each displacement lasting 8 hours;

[0072] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 13 MPa and a temperature of 50℃ 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.

[0073] The density of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is 0.201 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0305 W / (m·K), and the compressive stress under 3% compressive strain is 0.853 MPa. Under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4Hz, the pressure reaches 0.545 MPa.

[0074] Example 6

[0075] First, at room temperature, 4,4'-diaminodiphenyl ether and 4,4'-oxophthalic anhydride in a 1:2.5 ratio were added to N-methylpyrrolidone solvent and stirred for 25 min to obtain 50 g of polyamic acid solution.

[0076] In the second step, 7.5 g of polyacrylonitrile short filaments with a length of 12 mm and a diameter of 13 μm were added to the polyamic acid solution from the first step and ultrasonically dispersed to obtain a polyamic acid solution containing polyacrylonitrile short filaments.

[0077] The third step involves adding triethylamine as a catalyst and propionic anhydride as a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of triethylamine, propionic anhydride, and 4,4'-diaminodiphenyl ether is 1.5:5.0:12. The mixture is stirred continuously to form a polyimide sol containing polyacrylonitrile short filaments.

[0078] The fourth step involves placing the polyimide sol containing polyacrylonitrile short filaments in an 80°C water bath for gelation for 60 hours to obtain the initial state of the anti-dynamic fatigue polyimide aerogel.

[0079] The fifth step is to age the initial state of the anti-dynamic fatigue polyimide aerogel for 72 hours to obtain the anti-dynamic fatigue polyimide aged state gel.

[0080] Step 6: The aged anti-dynamic fatigue polyimide gel was solvent-displaced using the organic solvent acetone at room temperature to obtain the final state anti-dynamic fatigue polyimide gel; the solvent displacement was performed 5 times, and each displacement lasted for 10 hours.

[0081] Step 7: The dynamic fatigue resistant polyimide final gel is dried with supercritical CO2 fluid at a pressure of 15 MPa and a temperature of 60℃ for 18 h. After drying, the pressure is released at a rate of 190 kPa / min to obtain the dynamic fatigue resistant polyimide aerogel thermal insulation material.

[0082] The density of the dynamic fatigue resistant polyimide aerogel insulation material prepared in this embodiment is 0.231 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0311 W / (m·K), and the compressive stress under 3% compressive strain is 0.893 MPa. Under 1% compressive deformation, after 10,000 compression cycles at a compression frequency of 4 Hz, the pressure reaches 0.596 MPa.

[0083] In this invention, as long as the gel temperature, aging time, temperature, solvent type, number of replacements, and replacement time are within the specified range, their effects on the density, thermal conductivity, compressive strength, and dynamic fatigue resistance of the anti-dynamic fatigue polyimide aerogel are negligible. The density, thermal conductivity, and mechanical strength properties of the anti-dynamic fatigue polyimide aerogel are mainly affected by the molar ratio of diamine to dianhydride, the length of polyacrylonitrile filaments, and the amount added. Specifically, the higher the molar ratio of diamine to dianhydride, the higher the density, thermal conductivity, and mechanical strength of the polyimide aerogel; the longer the polyacrylonitrile filaments, the higher the density, thermal conductivity, mechanical strength, and dynamic fatigue resistance of the polyimide aerogel; and the greater the amount of polyacrylonitrile filaments added, the higher the density, thermal conductivity, mechanical strength, and dynamic fatigue resistance of the polyimide aerogel.

[0084] Comparative Example 1:

[0085] The difference between Comparative Example 1 and Example 1 is that the addition of polyacrylonitrile short filaments in step 2) is omitted; otherwise, they are the same as in Example 1.

[0086] The density of the obtained polyimide aerogel insulation material is 0.096 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0208 W / (m·K), and the compressive stress under 3% compressive strain is 0.520 MPa. After 1000 compression cycles at 1% compressive deformation and a compression frequency of 4 Hz, microcracks appear on the surface.

[0087] The results show that the introduction of polyacrylonitrile can improve the mechanical properties of polyimide aerogel and effectively enhance its resistance to dynamic fatigue.

[0088] Comparative Example 2

[0089] 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, while the rest is the same as in Example 1; however, it is difficult to obtain a stable gel and a stable anti-dynamic fatigue polyimide aerogel. Figure 4 Since the diamine and dianhydride are not in the appropriate ratio, it is difficult to form a gel.

[0090] The results showed that when the molar ratio of added diamine to dianhydride exceeded the range of 1:1 to 1:2, it was difficult to obtain a stable gel.

[0091] Comparative Example 3

[0092] 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 in Example 4;

[0093] The density of the obtained polyimide aerogel was 0.486 g / cm³. 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.

[0094] The results show that when the amount of polyacrylonitrile short filaments is too high (above 7.5 g), the polyimide aerogel insulation material can have higher mechanical strength, but the density and thermal conductivity will increase, making it unsuitable for high-efficiency insulation applications.

[0095] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Various process solutions that are not substantially different from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. An application of a polyimide aerogel in improving the dynamic fatigue resistance of materials, characterized in that, The preparation method of the polyimide aerogel includes the following steps: S1. Under normal temperature conditions, diamine and dianhydride are added to an organic solvent in a mass ratio of 1:1 to 1:2.5, and stirred for 20 to 25 minutes to obtain a polyamic acid solution. S2. Add the polyacrylonitrile short filaments to the polyamic acid solution and disperse them by ultrasonication to obtain a polyamic acid solution containing polyacrylonitrile short filaments. The mass ratio of polyacrylonitrile short filaments to polyamic acid solution is 0.05~0.

15. S3. Add a catalyst and a dehydrating agent to a polyamic acid solution containing polyacrylonitrile short filaments and stir continuously to form a polyimide sol containing polyacrylonitrile short filaments. The catalyst is methylpyridine, the dehydrating agent is acetic anhydride, and the mass ratio of the catalyst, dehydrating agent and diamine is (1.0~1.5):(3.0~5.0):

12. S4. The polyimide sol containing polyacrylonitrile short filaments is placed in a water-soluble pot at 50℃~80℃ for gelation for 5~60 h to obtain the initial state gel of the anti-dynamic fatigue polyimide aerogel. S5. The initial state of the anti-dynamic fatigue polyimide aerogel is aged for 18-72 hours to obtain the anti-dynamic fatigue polyimide aged state gel. S6. The anti-dynamic fatigue polyimide aging gel is solvent-displaced with an organic solvent at room temperature to obtain the anti-dynamic fatigue polyimide final state gel; the number of solvent displacements is 3 to 5 times, and the displacement time is 8 to 10 hours each time; S7. The dynamic fatigue resistant polyimide final state gel is dried with supercritical CO2 fluid to obtain dynamic fatigue resistant polyimide aerogel thermal insulation material.

2. The application of the polyimide aerogel according to claim 1 in improving the dynamic fatigue resistance of materials, characterized in that: The diamine mentioned in S1 is one or a mixture of several of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diamino-2,2'-dimethylbiphenyl; the dianhydride is one or a mixture of several of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and pyromellitic dianhydride; and the organic solvent is one or a mixture of several of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

3. The application of the polyimide aerogel according to claim 1 in improving the dynamic fatigue resistance of materials, characterized in that: The polyacrylonitrile short filaments described in S2 have a length of 3 mm, 6 mm, 9 mm or 12 mm and a diameter of 10-13 μm.

4. The application of the polyimide aerogel according to claim 1 in improving the dynamic fatigue resistance of materials, characterized in that: The catalyst in S3 can also be triethylamine or pyridine, and the dehydrating agent can also be acetyl chloride or propionic anhydride.

5. The application of the polyimide aerogel according to claim 1 in improving the dynamic fatigue resistance of materials, characterized in that: The organic solvent in S6 is one or a mixture of methanol, ethanol, isopropanol or acetone.

6. The application of the polyimide aerogel according to claim 1 in improving the dynamic fatigue resistance of materials, characterized in that: The pressure during CO2 supercritical fluid drying in S7 is 8~15 MPa, the temperature is 40~60℃, the drying time is 8~18 h, and the pressure is released at a rate of 80~190 kPa / min after drying.

Images