Polyimide-based carbon aerogel and application of polyimide-based composite carbon aerogel in preparation of ultra-high-temperature thermal insulation material

Abstract

The invention provides use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in preparation of an ultrahigh-temperature thermal insulation material, and belongs to the field of high polymer materials. The carbon aerogel disclosed by the invention can bear ultrahigh temperature and has a good heat insulation effect at ultrahigh temperature. Therefore, the carbon aerogel serving as a thermal protection material has a wide application prospect in extreme thermal environments in important fields such as aerospace and weaponry.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to the use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in the preparation of ultra-high temperature thermal insulation materials. Background Art

[0002] Ultra-high temperature thermal insulation materials are an important guarantee for the safe service of aerospace vehicles in extreme environments. With the rapid development of modern space technology and the new military revolution, the flight missions of new high-speed aircraft are becoming more and more arduous, and the characteristics of high speed and high maneuverability are becoming increasingly prominent. The special and harsh service environment puts forward higher requirements for thermal insulation materials and their structures. In terms of material selection, in addition to having ultra-high temperature thermal insulation capabilities, it is also necessary to minimize the weight of the thermal insulation material itself, thereby realizing the lightweight of the thermal insulation system.

[0003] Although existing thermal insulation materials such as ceramic fiber rigid thermal insulation tiles and fiber felts have the advantages of light weight, low room temperature thermal conductivity, and high temperature resistance, they have the problem of too rapid increase in thermal conductivity at high temperatures; while oxide aerogel thermal insulation materials such as silica (SiO2) and alumina (Al2O3) have excellent thermal insulation performance, but their service temperature generally does not exceed 1200 °C. Therefore, most current thermal insulation materials are difficult to meet the development needs of new hypersonic aircraft, and the development of a thermal insulation material with ultra-high temperature resistance is of great significance for the aerospace field.

[0004] Carbon aerogel has a high specific extinction coefficient, strong infrared radiation shielding ability, and exhibits good high-temperature thermal insulation performance. Traditional polymer-based carbon aerogels are prepared by pyrolyzing organic aerogels in an inert atmosphere. Polyimide (PI) has a high char yield (char yield at 800 °C > 60%) in a high-temperature inert atmosphere; at the same time, the material can still maintain considerable mechanical strength after carbonization; the carbonization process is also relatively simple, and it is considered an ideal polymer precursor for preparing carbon materials. PI aerogel not only inherits the excellent properties of polyimide but also has the characteristics of aerogel materials such as low density, high specific surface area, and high porosity, so it is an ideal carbon aerogel precursor. The preparation and performance research of PI-derived carbon aerogels have attracted people's attention. However, whether PI carbon aerogel can be used as an ultra-high temperature thermal insulation material still needs further research. Summary of the Invention

[0005] The purpose of the present invention is to provide the use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in the preparation of ultra-high temperature thermal insulation materials.

[0006] The present invention provides the use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in the preparation of ultra-high temperature thermal insulation materials:

[0007] The polyimide-based composite carbon aerogel is composed of a polyimide-based carbon aerogel and a carbon nanometer filler;

[0008] The polyimide-based carbon aerogel is obtained by carbonizing a polyimide aerogel; the polyimide aerogel is obtained by freeze-drying a gel obtained by crosslinking and curing a polyamic acid solution and imidizing it.

[0009] Furthermore, the mass of the carbon nanometer filler is 2% to 20% of the mass of the polyamic acid; preferably 6 to 10%; more preferably 10%;

[0010] Preferably, the carbon nanometer filler is multi-walled carbon nanotubes, amino-functionalized multi-walled carbon nanotubes or carbon nanofibers; more preferably multi-walled carbon nanotubes.

[0011] Furthermore, the solid content of the polyamic acid solution is 3 to 5 wt%, and the degree of polymerization of the polyamic acid is 20 to 40; preferably, the solid content of the polyamic acid solution is 3 wt%, and the degree of polymerization of the polyamic acid is 40.

[0012] Furthermore, the crosslinking and curing is a reaction with a crosslinking agent, and the crosslinking agent is a polyamine; preferably a triamine, more preferably 1,3,5-tris(4-aminophenoxy)benzene.

[0013] Furthermore, the polyamic acid is an acid anhydride-terminated polyamic acid, and the acid anhydride group of the polyamic acid and the amino group of the crosslinking agent are in an equimolar ratio.

[0014] Furthermore, the acid anhydride-terminated polyamic acid is polymerized from a diamine and a dianhydride, and the molar ratio of the diamine to the dianhydride is n:(n + 1), where n is the degree of polymerization of the polyamic acid;

[0015] Preferably, the diamine is 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and the dianhydride is biphenyltetracarboxylic dianhydride.

[0016] Furthermore, the imidization is a reaction under the action of a dehydrating agent and a catalyst; preferably, the dehydrating agent is acetic anhydride, and the catalyst is pyridine;

[0017] Preferably, the molar ratio of the dehydrating agent to the dianhydride is (6 to 10):1, preferably 8:1; the dehydrating agent and the catalyst are in an equimolar ratio.

[0018] Furthermore, the solvent of the polyamic acid solution is an organic solvent, preferably DMAc.

[0019] Furthermore, the preparation method of the polyimide-based composite carbon aerogel includes the following steps: carbonizing the polyimide composite aerogel at 800 to 900 °C for 1 to 3 hours in an inert atmosphere;

[0020] Preferably, the polyimide composite aerogel is prepared according to the following steps:

[0021] (1) Add the polyamic acid solution and carbon nano-fillers and mix evenly, then add a cross-linking agent, and carry out a cross-linking and curing reaction at room temperature for 30 to 50 minutes;

[0022] (2) Add a dehydrating agent and a catalyst, and carry out an imidization reaction at room temperature for 3 to 10 minutes, and let it stand to obtain a gel;

[0023] (3) Age the gel at room temperature for 20 to 30 hours, sequentially carry out solvent replacement with tert-butanol solutions with a volume fraction of 25% and 75% and tert-butanol, and then carry out freeze-drying to obtain it; the solvent of the tert-butanol solution is the solvent of the polyamic acid solution.

[0024] Furthermore, the preparation method of the polyimide-based carbon aerogel includes the following steps: carbonize the polyimide aerogel in an inert atmosphere at 800 to 900 °C for 1 to 3 hours;

[0025] Preferably, the polyimide aerogel is prepared according to the following steps:

[0026] (A) Add a cross-linking agent to the polyamic acid solution, and carry out a cross-linking and curing reaction at room temperature for 30 to 50 minutes;

[0027] (B) Add a dehydrating agent and a catalyst, and carry out an imidization reaction at room temperature for 3 to 10 minutes, and let it stand to obtain a gel;

[0028] (C) Age the gel at room temperature for 20 to 30 hours, sequentially carry out solvent replacement with tert-butanol solutions with a volume fraction of 25% and 75% and tert-butanol, and then carry out freeze-drying to obtain it; the solvent of the tert-butanol solution is the solvent of the polyamic acid solution.

[0029] The present invention has achieved the following beneficial effects:

[0030] The present invention provides the use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in the preparation of ultra-high temperature thermal insulation materials. The carbon aerogel of the present invention can withstand ultra-high temperatures and has good thermal insulation effects at ultra-high temperatures. Therefore, the carbon aerogel of the present invention has broad application prospects in extreme thermal environments in important fields such as aerospace and weaponry as a thermal protection material.

[0031] The "degree of polymerization of polyamic acid" in the present invention is the theoretical degree of polymerization of polyamic acid. That is, it is calculated according to the feeding molar ratio of diamine and dianhydride for synthesizing polyamic acid: (N + 1) / N = n 二元酐 / n 二元胺 , where N refers to the degree of polymerization and n represents the amount of substance.

[0032] The "solid content of polyamic acid solution" in the present invention refers to the mass fraction of polyamic acid in the polyamic acid solution.

[0033] The "room temperature" in the present invention refers to the temperature range of 20 - 30 °C.

[0034] The "DMAc" in the present invention refers to N,N - dimethylacetamide.

[0035] The "inert atmosphere" in the present invention refers to the environmental protection conditions of inert gases such as nitrogen and argon.

[0036] The "ultra - high temperature" in the present invention refers to a temperature greater than 1500 °C.

[0037] Obviously, based on the above - mentioned content of the present invention, according to the common general technical knowledge and conventional means in the art, without departing from the above - mentioned basic technical idea of the present invention, various other forms of modifications, substitutions or changes can be made.

[0038] The following is a further detailed description of the above - mentioned content of the present invention through specific embodiments in the form of examples. However, this should not be understood as limiting the scope of the above - mentioned subject matter of the present invention to the following examples. All technologies implemented based on the above - mentioned content of the present invention fall within the scope of the present invention. Specific Embodiments

[0039] The raw materials and equipment used in the present invention are all known products, obtained by purchasing commercially available products.

[0040] Example 1. Preparation of the polyimide aerogel of the present invention

[0041] 1. Preparation of polyamic acid (PAA): First, add 4,4’ - diamino - 2,2’ - dimethyl - 1,1’ - biphenyl (DMBZ) (12.7374 g) to 277.5 g of N,N - dimethylacetamide (DMAc), and stir for 20 min under the condition of nitrogen as the protective gas to fully dissolve the diamine. Subsequently, add biphenyltetracarboxylic dianhydride (BPDA) (18.0945 g) and react at room temperature for 3 h to obtain a PAA solution with a degree of polymerization (N) = 40 and a solid content of 10 wt%.

[0042] 2. Preparation of polyimide (PI) aerogel: First, prepare a PAA solution with a solid content of 4 wt%. Take 80 g of the PAA solution prepared in the previous step in a beaker, add 112 g of DMAc thereto, and stir well to obtain it. Then, add 8 g of DMAc solution containing the cross-linking agent 1,3,5-tris(4-aminophenoxy)benzene (TAB) (0.1238 g), continue stirring and reacting at room temperature for 20 min, add acetic anhydride (13.03 g) and pyridine (10.1 g), after stirring and reacting for 5 min, pour the solution into a mold, let it stand, and after the solution forms a gel, age it at room temperature for 24 h. Prepare mixed solutions with volume ratios of DMAc / tert-butanol of 75 / 25 and 25 / 75 respectively, and perform solvent replacement on the obtained wet gel every 12 h in this order, and then repeat the replacement of the wet gel with pure tert-butanol six times. After the replacement is completed, place the wet gel in a freeze dryer and freeze-dry it for 48 h to obtain polyimide aerogel (PI-4%).

[0043] Referring to the above method, with the feeding amounts shown in Table 1 and the other conditions remaining unchanged, polyimide aerogels (PI-3%) with a PAA polymerization degree of 40 and a PAA solid content of 3 wt% and polyimide aerogels (PI-5%) with a PAA solid content of 5 wt% are prepared.

[0044] Note: The PAA solid content is the mass percentage of the total mass of BPDA and DMBZ in the total mass of BPDA, DMBZ, and DMAc.

[0045] Table 1. Feeding amounts in the examples

[0046]

[0047] Example 2. Preparation of the polyimide composite aerogel of the present invention

[0048] Using the polyamic acid solution with a PAA solid content of 10 wt% prepared in Example 1, polyimide / carbon nanotube composite aerogels with multi-walled carbon nanotube (MWCNT) addition amounts of 2 phr, 6 phr, and 10 phr are prepared, denoted as PI / MWCNT-2, PI / MWCNT-6, and PI / MWCNT-10.

[0049] 1. Preparation of the multi-walled carbon nanotube dispersion: Dissolve 0.6 g of the dispersant TNNDIS in 99 g of the DMAc solvent, then add 1 g of MWCNT, stir to make it fully infiltrated in the solvent, and disperse the above dispersion with a cell crusher for 60 min to obtain a DMAc dispersion of MWCNT with a mass fraction of 1 wt%.

[0050] 2. Preparation of polyimide composite aerogel: First, prepare a PAA / MWCNTs dispersion with a PAA solid content of 4 wt% and an MWCNTs addition amount of 10 phr relative to PAA. Take 80 g of the PAA solution (10 wt%) prepared in Example 1 in a beaker, add 80 g of MWCNT dispersion and 32 g of DMAc, mechanically stir for 1 h to make it evenly dispersed, then dropwise add 8 g of DMAc dissolved with the cross-linking agent TAB (0.1238 g), continue to stir and react at room temperature for 20 min, add acetic anhydride (13.03 g) and pyridine (10.1 g), after stirring and reacting for 5 min, pour the solution into a mold, let it stand, and after the solution forms a gel, age it at room temperature for 24 h. Prepare mixed solutions with volume ratios of DMAc / tert-butanol of 75 / 25 and 25 / 75 respectively, and perform solvent replacement on the obtained wet gel every 12 h in this order, and then repeat the replacement of the wet gel with pure tert-butanol six times. After the replacement is completed, place the wet gel in a freeze dryer and freeze-dry it for 48 h to obtain a polyimide / carbon nanotube composite aerogel (PI / MWCNT-10) with a PAA solid content of 4 wt% and an MWCNT addition amount of 10 phr.

[0051] Referring to the above preparation method, the feeding amounts are shown in Table 1, and the other conditions remain unchanged, to prepare polyimide / carbon nanotube composite aerogels PI / MWCNT-2 and PI / MWCNT-6.

[0052] Example 3. Preparation of polyimide-based carbon aerogel of the present invention

[0053] Use the polyimide aerogel (PI-4%) prepared in Example 1 for preparation. The specific method is as follows: After polishing the polyimide aerogel into a regular shape, place it in a tubular furnace. Under a flowing inert atmosphere, heat it at a heating rate of 2 °C / min to 800 °C, keep it warm for 1 h, naturally cool to room temperature, and then open the furnace to take out the sample to obtain a polyimide-based carbon aerogel (CPI-4%) with a PAA polymerization degree of 40 and a solid content of 4 wt%.

[0054] Referring to the above method, replace PI-4% with PI-3% and PI-5% to prepare a polyimide-based carbon aerogel (CPI-4%) with a PAA solid content of 3 wt% and a polyimide-based carbon aerogel (CPI-5%) with a PAA solid content of 5 wt%.

[0055] Example 4. Preparation of polyimide-based composite carbon aerogel of the present invention

[0056] Using the polyimide / carbon nanotube composite aerogel with a PAA solid content of 4 wt% prepared in Example 2, polyimide-based composite carbon aerogels with MWCNT addition amounts of 2 phr, 6 phr, and 10 phr were prepared, denoted as CPI / MWCNT-2, CPI / MWCNT-6, and CPI / MWCNT-10.

[0057] The polyimide / carbon nanotube composite aerogel (PI / MWCNT-10) prepared in Example 2 was used for preparation. The specific method is as follows: After grinding the composite aerogel into a regular shape, it was placed in a tubular furnace. Under a flowing inert atmosphere, it was heated to 800 °C at a heating rate of 2 °C / min, held for 1 h, and then naturally cooled to room temperature. After opening the furnace, the sample was taken out to obtain the composite carbon aerogel (CPI / MWCNT-10) with an MWCNT addition amount of 10 phr.

[0058] Referring to the above method, by replacing PI / MWCNT-10 with PI / MWCNT-2 and PI / MWCNT-6, composite carbon aerogels CPI / MWCNT-2 and CPI / MWCNT-6 with MWCNT addition amounts of 2 phr and 6 phr were prepared.

[0059] The beneficial effects of the present invention are demonstrated by the following specific test examples.

[0060] Test Example 1: Measurement of Thermal Diffusion Coefficient and Thermal Conductivity

[0061] The samples prepared in Example 1 were taken for testing.

[0062] In the test temperature range of 1000 - 2000 °C, the thermal diffusion coefficient (α) under an argon atmosphere of 0.1 MPa was measured using a NETZSCH LFA427 laser thermal conductivity meter. The sample size was Φ12.7 mm × 2 mm. According to the measured thermal diffusion coefficient (α), the sample density (ρ), and a relevant literature (Wiener M, Reichenauer G, Braxmeier S, et al. Carbon aerogel-based high-temperature thermal insulation [J]. International Journal of Thermophysics, 2009, 30(4): 1372 - 1385., the specific heat capacity (c p ) of the carbon material given in this literature was used, and the thermal conductivity (λ) of the corresponding sample was calculated using Equation 1

[0063] λ = αρc p (T) (1)

[0064] Wherein, T is the test temperature. Since the specific heat mainly depends on the composition of the material, and the main components of both carbon aerogel and composite carbon aerogel are carbon, the same specific heat is used for carbon aerogel and composite carbon aerogel when calculating the thermal conductivity.

[0065] The sample density (ρ) is the volume density obtained by dividing the sample mass by the sample volume, and not less than 5 samples are used in each group during the test.

[0066] Table 2. Thermal diffusivity of CPI and CPI / MWCNT aerogels

[0067]

[0068] The thermal diffusivity refers to the ability of the material to make the internal temperature tend to be uniform, and it is an important index to measure the heat insulation performance of heat insulation materials under transient heating conditions. In the present invention, the laser flash method was used to measure the thermal diffusivity of polyimide-based carbon aerogel at 1000 - 2000 °C, and the results are shown in Table 2. As can be seen from Table 2, the thermal diffusivities of CPI-3%, CPI-4%, and CPI / MWCNT-6 all increase with the increase of temperature, and at the same time, the thermal diffusivity is positively correlated with the solid content. At a high temperature of 2000 °C, the thermal diffusivity of CPI-3% with the lowest density (density 0.19 g / cm 3 ) can be as low as 0.455 mm 2 / s. At the same temperature, the thermal diffusivity of the composite carbon aerogel (CPI / MWCNT-6) is higher than that of the pure carbon aerogel (CPI-4%).

[0069] According to the measured density and the specific heat value in the literature, the formula (1) was used for calculation to obtain the variation law of the thermal conductivity of the sample with temperature, as shown in Table 3. As can be seen from Table 3, the thermal conductivity of the carbon aerogel increases with the increase of temperature. At 1000 °C, the thermal conductivities of CPI-3% and CPI-4% are 0.12 and 0.29 W / (m·K) respectively. When the temperature rises to 2000 °C, the corresponding thermal conductivities rise to 0.18 and 0.43 W / (m·K) respectively. The thermal conductivity of the composite carbon aerogel is always lower than that of the pure carbon aerogel with the same solid content (CPI-4%, density 0.31 g / cm 3 ), which is mainly because the density of the CPI / MWCNT-6 composite carbon aerogel (0.20 g / cm 3 ) is lower, resulting in a lower solid thermal conductivity.

[0070] Table 3. Thermal conductivity of CPI and CPI / MWCNT aerogels

[0071]

[0072]

[0073] Table 4. Comparison of high-temperature thermal conductivities of carbon aerogels reported in the literature

[0074]

[0075] References:

[0076] 1. Wu K, Zhou Q, Cao J, et al. Ultrahigh-strength carbon aerogels for high-temperature thermal insulation[J]. Journal of Colloid and Interface Science, 2022, 609: 667-675.

[0077] 2. Li L, Liu F, Feng J, et al. Effects of carbonization temperature on mechanical and thermal insulation properties of carbon aerogel composites using phenolic fibers as reinforcement[J]. Journal of Nanomaterials, 2023, doi.org / 10.1155 / 2023 / 1113343.

[0078] 3. Feng Junzong. Preparation and properties of carbon aerogels and their thermal insulation composites[D]; National University of Defense Technology, 2012.

[0079] 4. Zheng Zixuan. Structure regulation and thermal insulation performance research of polyimide-based carbon aerogel composites[D]. Academy of Military Sciences, 2022.

[0080] To better understand the thermal insulation performance level of the samples, the present invention consulted the high-temperature thermal conductivity data of carbon aerogels prepared by others recently and made a comparison. The specific data are listed in Table 4. It can be seen from Table 4 that the PI-based carbon aerogel prepared by the present invention has a lower high-temperature thermal conductivity and has more excellent ultra-high-temperature thermal insulation performance.

[0081] In summary, the present invention provides the use of polyimide-based carbon aerogels and polyimide-based composite carbon aerogels in the preparation of ultra-high-temperature thermal insulation materials. The carbon aerogel of the present invention can withstand ultra-high temperatures and has good thermal insulation effects at ultra-high temperatures. Therefore, the carbon aerogel of the present invention has broad application prospects in extreme thermal environments in important fields such as aerospace and weaponry as a thermal protection material.

Claims

1. Use of polyimide-based carbon aerogel and polyimide-based composite carbon aerogel in the preparation of ultra-high temperature thermal insulation materials: The polyimide-based composite carbon aerogel is composed of a polyimide-based carbon aerogel and a carbon nanotube filler; The polyimide-based carbon aerogel is obtained by carbonizing a polyimide aerogel; the polyimide aerogel is obtained by freeze-drying a gel obtained by crosslinking and curing a polyamic acid solution and imidizing it.

2. The use according to claim 1, characterized in that: The mass of the carbon nanotube filler is 2% - 20% of the mass of the polyamic acid; preferably 6 - 10%; more preferably 10%; Preferably, the carbon nanotube filler is multi-walled carbon nanotubes, amino-functionalized multi-walled carbon nanotubes or carbon nanofibers; more preferably multi-walled carbon nanotubes.

3. The use according to claim 1, wherein: The solid content of the polyamic acid solution is 3 - 5 wt%, and the degree of polymerization of the polyamic acid is 20 - 40; preferably, the solid content of the polyamic acid solution is 3 wt%, and the degree of polymerization of the polyamic acid is 40.

4. The use according to any one of claims 1 to 3, characterized in that: The crosslinking and curing is a reaction with a crosslinking agent, and the crosslinking agent is a polyamine; preferably a triamine, more preferably 1,3,5-tris(4-aminophenoxy)benzene.

5. The use according to claim 4, wherein: The polyamic acid is an acid anhydride-terminated polyamic acid, and the acid anhydride group of the polyamic acid and the amino group of the crosslinking agent are in an equimolar ratio.

6. The use according to claim 5, wherein: The acid anhydride-terminated polyamic acid is polymerized from a diamine and a dianhydride, and the molar ratio of the diamine to the dianhydride is n:(n + 1), where n is the degree of polymerization of the polyamic acid; Preferably, the diamine is 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and the dianhydride is biphenyltetracarboxylic dianhydride.

7. The use according to claim 6, wherein: The imidization is a reaction under the action of a dehydrating agent and a catalyst; preferably, the dehydrating agent is acetic anhydride, and the catalyst is pyridine; Preferably, the molar ratio of the dehydrating agent to the dianhydride is (6 - 10):1, preferably 8:1; the dehydrating agent and the catalyst are in an equimolar ratio.

8. The use according to claim 1, wherein: The solvent of the polyamic acid solution is an organic solvent, preferably DMAc.

9. The use according to claim 1, characterized in that: The preparation method of the polyimide-based composite carbon aerogel includes the following steps: the polyimide composite aerogel is carbonized at 800 - 900 °C for 1 - 3 hours in an inert atmosphere; Preferably, the polyimide composite aerogel is prepared according to the following steps: (1) The polyamic acid solution is added with a carbon nanotube filler and mixed evenly, and then a crosslinking agent is added, and a crosslinking and curing reaction is carried out at room temperature for 30 - 50 min; (2) A dehydrating agent and a catalyst are added, and an imidization reaction is carried out at room temperature for 3 - 10 min, and then left standing to obtain a gel; (3) The gel is aged at room temperature for 20 - 30 h, and the solvent is replaced successively with tert-butanol solutions with a volume fraction of 25% and 75% and tert-butanol, and then freeze-dried to obtain it; the solvent of the tert-butanol solution is the solvent of the polyamic acid solution.

10. The use according to claim 1, characterized in that: The preparation method of the polyimide-based carbon aerogel includes the following steps: the polyimide aerogel is carbonized at 800 - 900 °C for 1 - 3 hours in an inert atmosphere; Preferably, the polyimide aerogel is prepared according to the following steps: (A) The polyamic acid solution is added with a crosslinking agent, and a crosslinking and curing reaction is carried out at room temperature for 30 - 50 min; (B) Add a dehydrating agent and a catalyst, and carry out an imidization reaction at room temperature for 3 to 10 minutes, then let it stand to obtain a gel; (C) Age the gel at room temperature for 20 to 30 hours, successively perform solvent replacement with tert-butanol solutions with volume fractions of 25% and 75% and tert-butanol, and then carry out freeze-drying to obtain the product; the solvent of the tert-butanol solution is the same as the solvent of the polyamic acid solution.

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