Warm-keeping polyimide aerogel and preparation method thereof

Abstract

The invention discloses warm-keeping polyimide aerogel and a preparation method thereof, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: 1, synthesizing a polyamide acid solution; 2, adding amino-containing organic silicon into the polyamide acid solution, mixing, and defoaming to form a spinning solution; step 3, preparing a nanofiber membrane by electrostatic spinning of the spinning solution; 4, crushing the nanofiber membrane, dispersing the crushed nanofiber membrane in a solvent, standing for 24-48 hours, and freeze-drying to obtain aerogel; and step 5, carrying out stepped heating thermal imidization treatment to obtain the polyimide aerogel. Amino-containing organic silicon is used as a cross-linking agent of polyamide acid, chemical connection is added for a three-dimensional network structure of the gel, and the structural stability of the aerogel is improved. In the thermal imidization process, organic silicon generates a silicon oxide and Si-O-Si network through staged pyrolysis, the silicon oxide exists in fiber gaps and forms an organic-inorganic hybrid interface with PI fibers, and the structural stability is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a thermal insulation polyimide aerogel and a preparation method thereof. Background Art

[0002] Aerogels are currently the world's lowest-density, lowest-thermal-conductivity solid materials. Organic aerogels made from high-performance polyimide (PI) have attracted significant attention due to their ultra-lightweight, low thermal conductivity, and corrosion resistance. PI aerogels can be prepared using the traditional sol-gel method and the nanofiber method. The sol-gel method involves adding a dispersant and a crosslinker to the precursor polyamic acid (PAA) to form a sol. The aerogel is then removed by supercritical drying or freeze-drying to remove the solvent. While the resulting PI aerogels offer high tunability in structure and performance, they also suffer from disadvantages such as high thermal shrinkage, brittleness, and low elasticity, limiting their application in applications requiring high elasticity. The nanofiber method involves electrospinning the PAA precursor into nanofibers, which are then dissolved and dried to form the PI aerogels. Compared to the sol-gel method, the nanofiber method significantly reduces the number of particle connection points within the aerogel skeleton, avoiding stress concentration. The resulting PI nanofiber aerogels form a physically entangled three-dimensional network using nanofibers as building blocks.

[0003] The polyimide nanofiber aerogel prepared by electrospinning has the characteristics of being ultra-light, washable, and heat-insulating. As a thermal insulation material, its thermal insulation performance is closely related to the porosity. The fibers in the conventionally prepared polyimide nanofiber aerogel are only physically overlapped, and the network structure stability is poor. The shrinkage rate is large during thermal imidization treatment, and the porosity will be reduced. In actual application, the compression resilience is poor, and irreversible structural collapse is prone to occur, which leads to a decrease in thermal insulation performance. Summary of the Invention

[0004] The present invention provides a thermal insulation polyimide aerogel and a preparation method thereof, which can solve the problem of poor structural stability of polyimide fiber aerogel in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a thermal insulation polyimide aerogel comprises the following steps:

[0007] Step 1, synthesizing a polyamic acid solution;

[0008] Step 2: adding amino-containing organosilicon to the polyamic acid solution, mixing and degassing to form a spinning solution;

[0009] Step 3: preparing nanofiber membrane by electrospinning the spinning solution;

[0010] Step 4: The nanofiber membrane is crushed and dispersed in a solvent, and then freeze-dried after standing for 24-48 hours to obtain an aerogel;

[0011] Step 5: Stepwise heating and thermal imidization treatment to obtain polyimide aerogel.

[0012] Polyamic acid (PAA) is a precursor of polyimide (PI) and is soluble in polar solvents (such as DMF and NMP). Its solution has high stability and is suitable for electrospinning. Amino-containing silicone is added to the polyamic acid solution. On the one hand, the silicone can improve the hydrophobicity and flexibility of the prepared aerogel. On the other hand, during the mixed spinning process, the amino groups of the amino-containing silicone and the carboxylic acid groups on the polyamic acid can be chemically bonded. After the nanofiber membrane is dispersed in the solvent, a molecular-level chemical cross-linking network is formed between the silicone and the polyamic acid. The silanols generated by the hydrolysis of the silicone gradually condense in the solvent to form flexible Si-O-Si segments, which form an interpenetrating network with the polyamic acid fibers through physical entanglement. The hydrogen bonds and physical entanglement cross-linking in the gel enhance the rigidity of the gel skeleton and make the network structure more stable.

[0013] The nanofibers formed by electrospinning provide the backbone for the gel network structure, retaining three-dimensional through-pores after freeze-drying. Chemical bonding between silicone and PI strengthens the fiber node connections, enhancing the stability of the aerogel network structure based on the physical entanglement structure and suppressing structural collapse caused by stress concentration. The flexible Si-O chains of silicone act as "molecular springs" to absorb external forces and improve the aerogel's compressive resilience.

[0014] Furthermore, the mass concentration of the polyamic acid solution is 15-25 wt %. The concentration of the polyamic acid solution should not be too high. When the concentration is too high, the fluidity of the solution is poor, which is not conducive to spinning.

[0015] Furthermore, the amino-containing organosilicon is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

[0016] Furthermore, the concentration of the amino-containing organosilicon in the spinning solution is 1-10 wt %. The amount of organosilicon added to the spinning solution needs to be strictly controlled to avoid the influence of excessive addition on spinning and fiber formation.

[0017] Furthermore, the fiber diameter of the nanofiber membrane is 100-500 nm.

[0018] Furthermore, the process parameters of the electrospinning are set as follows:

[0019] The voltage is 15-25 kV, the spinning solution flow rate is 0.5-1.5 mL / h, the receiving distance is 15-25 cm, and the ambient humidity is <30% RH.

[0020] Furthermore, the solvent is a mixed solvent of ethanol and water, and the volume ratio of ethanol to water is (1-3): 1. The mixed solvent can promote the swelling of the fiber.

[0021] Furthermore, in step 4, the nanofiber membrane is dispersed in the solvent at a mass concentration of 1-3 wt%.

[0022] Furthermore, the process parameters of the step-by-step temperature thermal imidization treatment are set as follows:

[0023] Raise the temperature step by step under nitrogen atmosphere, first raise the temperature to 130-180℃, keep warm for 1-3h, then raise the temperature to 220-270℃, keep warm for 1-3h, and finally raise the temperature to 300-350℃, keep warm for 1-2h.

[0024] During the thermal imidization process, polyamic acid is converted into polyimide, and the Si-O-Si network of the silicone shrinks during the thermal imidization process to produce submicron pores, thereby increasing the porosity of the aerogel. The decomposition product silicon oxide improves the temperature resistance of the aerogel.

[0025] The present invention also provides a thermal insulation polyimide aerogel, which is prepared by adopting the above preparation method.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention uses amino-containing organosilicon as a crosslinking agent for polyamic acid to add chemical connections to the three-dimensional network structure of the gel, thereby improving the structural stability of the aerogel. Through the in-situ amidation reaction between the amino groups of the organosilicon and the carboxylic acid groups of the polyamic acid, a molecularly dispersed chemical crosslinking network is formed in the electrospinning solution, breaking through the phase separation limitations caused by traditional blending modification. The pre-crosslinking reaction of the amino-containing silane and the polyamic acid can simultaneously improve the fiber strength and gel stability.

[0028] (2) During the thermal imidization process, silicone generates silicon oxide and Si-O-Si network through staged pyrolysis. Silicon oxide exists in the gaps between fibers and forms an organic-inorganic hybrid interface with PI fibers, which relieves stress concentration and improves structural stability and temperature resistance.

[0029] (3) The aerogel material provided by the present invention has high porosity and nanoscale pores, which reduces solid heat conduction and increases air insulation. It has a low thermal conductivity coefficient. The porous structure restricts air flow, reduces convective heat transfer, and has excellent thermal insulation performance. The Si-O-Si chain segments of the silicone migrate to the surface, reducing the surface, improving the hydrophobicity of the aerogel, avoiding the increase in thermal conductivity caused by water vapor condensation, and improving the thermal insulation performance in humid environments. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] Example 1

[0032] Preparation of polyimide aerogel:

[0033] Step 1: Synthesize polyamic acid solution:

[0034] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0035] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 1 wt%.

[0036] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0037] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0038] Step 5: Thermal imidization treatment: Place the aerogel in a tubular furnace and heat it stepwise under a nitrogen atmosphere, first heating it to 150°C, keeping it warm for 2 hours, then heating it to 250°C, keeping it warm for 2 hours, and finally heating it to 320°C, keeping it warm for 2 hours to obtain polyimide aerogel.

[0039] Example 2

[0040] The only difference from Example 1 is that the concentration of γ-aminopropyltriethoxysilane in the spinning solution is increased from 1 wt % to 5 wt %.

[0041] Preparation of polyimide aerogel:

[0042] Step 1: Synthesize polyamic acid solution:

[0043] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0044] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 5 wt %.

[0045] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0046] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0047] Step 5: Thermal imidization treatment: Place the aerogel in a tubular furnace and heat it stepwise under a nitrogen atmosphere, first heating it to 150°C, keeping it warm for 2 hours, then heating it to 250°C, keeping it warm for 2 hours, and finally heating it to 320°C, keeping it warm for 2 hours to obtain polyimide aerogel.

[0048] Example 3

[0049] The only difference from Example 1 is that the concentration of γ-aminopropyltriethoxysilane in the spinning solution is increased from 1 wt % to 8 wt %.

[0050] Preparation of polyimide aerogel:

[0051] Step 1: Synthesize polyamic acid solution:

[0052] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0053] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 8 wt %.

[0054] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0055] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0056] Step 5, thermal imidization treatment: the aerogel was placed in a tubular furnace and heated stepwise under a nitrogen atmosphere, first to 150°C, kept warm for 2 hours, then to 250°C, kept warm for 2 hours, and finally to 320°C, kept warm for 2 hours, and then cooled to obtain polyimide aerogel.

[0057] Example 4

[0058] The only difference from Example 1 is that the concentration of γ-aminopropyltriethoxysilane in the spinning solution is increased from 1 wt % to 10 wt %.

[0059] Preparation of polyimide aerogel:

[0060] Step 1: Synthesize polyamic acid solution:

[0061] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0062] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 10 wt %.

[0063] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0064] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0065] Step 5, thermal imidization treatment: the aerogel was placed in a tubular furnace and heated stepwise under a nitrogen atmosphere, first to 150°C, kept warm for 2 hours, then to 250°C, kept warm for 2 hours, and finally to 320°C, kept warm for 2 hours, and then cooled to obtain polyimide aerogel.

[0066] Example 5

[0067] The only difference from Example 3 is that the volume ratio of ethanol to water in the solvent is 2:1.

[0068] Preparation of polyimide aerogel:

[0069] Step 1: Synthesize polyamic acid solution:

[0070] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0071] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 8 wt %.

[0072] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0073] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 2:1 to prepare a mixed solvent, the nanofiber membrane was chopped into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0074] Step 5, thermal imidization treatment: the aerogel was placed in a tubular furnace and heated stepwise under a nitrogen atmosphere, first to 150°C, kept warm for 2 hours, then to 250°C, kept warm for 2 hours, and finally to 320°C, kept warm for 2 hours, and then cooled to obtain polyimide aerogel.

[0075] Example 6

[0076] The only difference from Example 1 is that the volume ratio of ethanol to water in the solvent is 3:1.

[0077] Preparation of polyimide aerogel:

[0078] Step 1: Synthesize polyamic acid solution:

[0079] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0080] Step 2, preparing spinning solution: adding γ-aminopropyltriethoxysilane to the polyamic acid solution, stirring and mixing, and vacuum degassing to form a spinning solution, wherein the concentration of γ-aminopropyltriethoxysilane in the spinning solution is 8 wt %.

[0081] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0082] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 3:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 minutes, and allowed to stand for 24 hours before being quickly frozen with liquid nitrogen and then freeze-dried to obtain an aerogel.

[0083] Step 5, thermal imidization treatment: the aerogel was placed in a tubular furnace and heated stepwise under a nitrogen atmosphere, first to 150°C, kept warm for 2 hours, then to 250°C, kept warm for 2 hours, and finally to 320°C, kept warm for 2 hours, and then cooled to obtain polyimide aerogel.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that in this comparative example, no amino-containing silicone is added when preparing the polyimide aerogel, that is, no γ-aminopropyltriethoxysilane is added.

[0086] Preparation of polyimide aerogel:

[0087] Step 1: Synthesize polyamic acid solution:

[0088] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0089] Step 2: preparing spinning solution: vacuum degassing the polyamic acid solution to form spinning solution.

[0090] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0091] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0092] Step 5: Thermal imidization treatment: Place the aerogel in a tubular furnace and heat it stepwise under a nitrogen atmosphere, first heating it to 150°C, keeping it warm for 2 hours, then heating it to 250°C, keeping it warm for 2 hours, and finally heating it to 320°C, keeping it warm for 2 hours to obtain polyimide aerogel.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that in this comparative example, γ-aminopropyltriethoxysilane is not added when preparing the spinning solution. Instead, the polyimide aerogel is prepared and then modified with γ-aminopropyltriethoxysilane.

[0095] Preparation of polyimide aerogel:

[0096] Step 1: Synthesize polyamic acid solution:

[0097] Pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were weighed in a molar ratio of 1.01:1, added to N-methylpyrrolidone (NMP), mixed, and stirred at 20°C for 8 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0098] Step 2: preparing spinning solution: vacuum degassing the polyamic acid solution to form spinning solution.

[0099] Step 3, electrospinning: put the spinning solution into the electrospinning equipment, set the electrospinning voltage to 20kV, the flow rate of the spinning solution to 1.5mL / h, the receiving distance to 20cm, control the ambient humidity to <30%RH, collect the nanofiber membrane with a thickness of 200μm, and the fiber diameter in the nanofiber membrane is 200nm.

[0100] Step 4: Preparation of polyamic acid aerogel: Ethanol and water were mixed in a volume ratio of 1:1 to prepare a mixed solvent, the nanofiber membrane was cut into pieces at a mass concentration of 1 wt% and added to the mixed solvent, ultrasonically dispersed for 30 min, allowed to stand for 24 h, and then quickly frozen with liquid nitrogen and freeze-dried to obtain an aerogel.

[0101] Step 5: Thermal imidization treatment: Place the aerogel in a tubular furnace and heat it stepwise under a nitrogen atmosphere, first heating it to 150°C, keeping it warm for 2 hours, then heating it to 250°C, keeping it warm for 2 hours, and finally heating it to 320°C, keeping it warm for 2 hours to obtain polyimide aerogel.

[0102] Step 6: Dissolve γ-aminopropyltriethoxysilane in water at a mass concentration of 10 wt% to form a hydrolyzate, place the polyimide aerogel in the hydrolyzate and let it stand for 3-6 hours, take it out and freeze-dry it to obtain the modified polyimide aerogel.

[0103] The performance tests of the aerogels prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were performed, and the results are shown in Table 1:

[0104] Table 1

[0105]

[0106] Table 1 shows that the aerogel performance is optimal when the γ-aminopropyltriethoxysilane content in the spinning solution is 8 wt%. Combining the results of the Examples and Comparative Examples, it can be seen that without the addition of silane, the performance indicators of the polyimide show a downward trend. Although the surface modification treatment in Comparative Example 2 using silane improves performance compared to Comparative Example 1, the performance advantage is not as good as that of the Examples.

[0107] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0108] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a thermal insulation polyimide aerogel, characterized in that: The following steps are involved: Step 1, synthesizing a polyamic acid solution; Step 2: adding amino-containing organosilicon to the polyamic acid solution, mixing and degassing to form a spinning solution; Step 3: preparing nanofiber membrane by electrospinning the spinning solution; Step 4: The nanofiber membrane is crushed and dispersed in a solvent, and then freeze-dried after standing for 24-48 hours to obtain an aerogel; Step 5: Stepwise heating and thermal imidization treatment to obtain polyimide aerogel.

2. The method for preparing a thermal insulation polyimide aerogel according to claim 1, wherein: The solid content of the polyamic acid solution is 15-25 wt %.

3. The method for preparing a thermal insulation polyimide aerogel according to claim 1, wherein: The amino-containing organosilicon is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

4. The method for preparing a thermal insulation polyimide aerogel according to claim 1, wherein: The concentration of the amino-containing organosilicon in the spinning solution is 1-10 wt %.

5. The method for preparing a thermal insulation polyimide aerogel according to claim 1, wherein: The fiber diameter of the nanofiber membrane is 100-500 nm.

6. The method for preparing a thermal insulation polyimide aerogel according to claim 1, characterized in that: The process parameters of the electrospinning are set as follows: The voltage is 15-25 kV, the spinning solution flow rate is 0.5-1.5 mL / h, the receiving distance is 15-25 cm, and the ambient humidity is <30% RH.

7. The method for preparing a thermal insulation polyimide aerogel according to claim 1, characterized in that: The solvent is a mixed solvent of ethanol and water, and the volume ratio of ethanol to water is (1-3):

1.

8. The method for preparing a thermal insulation polyimide aerogel according to claim 1, characterized in that: In the fourth step, the nanofiber membrane is dispersed in the solvent at a mass concentration of 1-3 wt%.

9. The method for preparing a thermal insulation polyimide aerogel according to claim 1, characterized in that: The process parameters of the step-by-step thermal imidization treatment are set as follows: Raise the temperature step by step under nitrogen atmosphere, first raise the temperature to 130-180℃, keep warm for 1-3h, then raise the temperature to 220-270℃, keep warm for 1-3h, and finally raise the temperature to 300-350℃, keep warm for 1-2h.

10. A thermal insulation polyimide aerogel, characterized in that: The thermal insulation polyimide aerogel is prepared by the preparation method according to any one of claims 1 to 9.

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