Polyimide aerogel fiber as well as preparation method and application thereof

Abstract

The invention relates to the technical field of aerogel fiber preparation, and discloses a polyimide aerogel fiber as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing a polyamide acid precursor spinning solution; carrying out wet spinning on the polyamide acid precursor spinning solution, rolling in a coagulating bath, and standing to obtain polyimide wet gel fibers; and carrying out solvent replacement on the polyimide wet gel fiber, and rapidly drying at normal pressure to obtain the polyimide aerogel fiber. The preparation method disclosed by the invention is simple in process, the use of a tedious drying process and expensive drying equipment is avoided, continuous forming preparation is successfully realized, and the large-scale preparation prospect is good. The aerogel fiber prepared by the invention has excellent tensile strength, and the tensile strength can reach 20.5 MPa; the density is low (0.34-0.53 g.cm <-3 >), the porosity is high (63-76%), the heat insulation performance is excellent, and the heat conductivity can be as low as 36.9 W.m <-1 >. K <-1 >; and the heat preservation effect is good in various complex occasions.

Description

Technical Field

[0001] The present application relates to the technical field of aerogel fiber preparation, and particularly relates to a polyimide aerogel fiber, a preparation method thereof, and an application thereof. Background Art

[0002] Intelligent temperature-regulating textiles have attracted much attention because they can adapt to changing environmental temperatures and bring excellent thermal comfort to users. In demanding working environments such as aerospace and fire rescue, lightweight and ultra-thin intelligent temperature-regulating fabrics play a crucial role in improving work efficiency and protecting the safety of staff. Aerogel fibers / fabrics combine the three-dimensional porous structure of aerogels and the softness of fibers. The highly porous nature endows them with a low thermal conductivity, which helps reduce heat loss; and their unique microstructure also provides advantages for integrating intelligent materials such as phase change materials. The above advantages make aerogel fibers / fabrics show great application potential in the development of intelligent temperature-regulating textiles and have great development prospects in the field of human thermal management.

[0003] At present, researchers have developed some aerogel fibers with different functional characteristics, such as silica aerogel fibers, polyimide aerogel fibers, polyurethane aerogel fibers, and aramid nanofiber aerogel fibers. Among them, polyimide aerogel fibers have excellent application prospects in weaving and clothing applications due to their high temperature resistance and good mechanical properties. At present, the drying methods of polyimide aerogel fibers mostly adopt freeze-drying or supercritical drying. For example, the literature (Chemical Engineering Journal, 2020, 390: 124623) discloses that gel fibers are obtained by freeze-spinning, and then porous polyimide aerogel fibers are obtained by freeze-drying and thermal imidization; Patent CN113355772B discloses that a polyamic acid hydrogel spinning solution is extruded and spun into a mixed coagulation bath of water / alcohol / acid for solvent replacement to obtain a polyamic acid hydrogel fiber with a skin-core structure, and then freeze-drying and thermal imidization are carried out in sequence to obtain a polyimide aerogel fiber with a skin-core structure. Another researcher drives the aerogel precursor polyamic acid sol into the capillary through surface tension, and then through a static sol-gel process, polyimide gel fibers are easily formed in a narrow space, and finally mesoporous aerogel fibers are obtained through a supercritical drying process (ACS Nano 2021, 15, 4759-4768). The above two drying methods can obtain aerogel fibers with good pore structures. However, the above methods have complex preparation processes, and their long drying processes and expensive equipment limit their large-scale production and development applications.

[0004] At present, relevant research literature (Nature Communication, 2023, 14: 2041 - 1723) reported the preparation of polyimide aerogel fibers by atmospheric pressure drying, using wet spinning and atmospheric pressure drying through an ultraviolet-enhanced dynamic gel strategy, avoiding the long drying process of freeze drying and the expensive equipment requirements. This strategy enables the rapid sol-gel transition of photosensitive polyimide, generating a strongly cross-linked gel skeleton, effectively maintaining the fiber shape and porous nanostructure. However, the density of the aerogel fibers prepared by this method is as high as 0.5 - 0.9 g / cm 3 , and sufficient ultraviolet light-assisted cross-linking is required during forming, and the steps are rather cumbersome.

[0005] Based on this, how to prepare polyimide aerogel fibers with low density and high strength through a simple and efficient rapid atmospheric pressure drying method is the current research difficulty. Summary of the Invention

[0006] This application provides a polyimide aerogel fiber, its preparation method and application, aiming to solve the technical problems of the complex preparation process and low tensile strength of the existing polyimide aerogel fibers.

[0007] To achieve the above purpose, this application adopts the following technical solutions to be realized.

[0008] In the first aspect of this application, a preparation method of polyimide aerogel fibers is provided, including:

[0009] S1, preparing a polyamic acid precursor spinning solution;

[0010] S2, wet spinning the polyamic acid precursor spinning solution, winding and standing in a coagulation bath to obtain polyimide wet gel fibers;

[0011] S3, performing solvent replacement on the polyimide wet gel fibers and rapidly drying them under atmospheric pressure to obtain polyimide aerogel fibers.

[0012] Preferably, the preparation of the polyamic acid precursor spinning solution specifically includes:

[0013] Dissolving 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole in a composite solvent, and performing a condensation reaction under an inert atmosphere to obtain a polyamic acid precursor spinning solution;

[0014] The composite solvent is a mixture of dimethyl sulfoxide and N,N-dimethylacetamide.

[0015] Preferably, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to 2-(4-aminophenyl)-5-aminobenzimidazole is 1:1;

[0016] The volume ratio of the dimethyl sulfoxide to the N,N-dimethylacetamide is (7:3) to (3:7).

[0017] In the polyamic acid precursor spinning solution, the total concentration of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole is 10 to 14 wt%.

[0018] Preferably, the inert atmosphere is a nitrogen atmosphere; the temperature of the condensation reaction is 0 °C, and the reaction time is 3 to 5 h.

[0019] Preferably, the coagulation bath is a mixed bath of acetone, acetic anhydride and pyridine;

[0020] Among them, the volume ratio of acetic anhydride, pyridine and acetone is 1:1:(20 to 60).

[0021] Preferably, the extrusion speed of the wet spinning is 5 to 20 mL / h.

[0022] Preferably, the temperature of the drying is 60 to 100 °C.

[0023] Preferably, the solvent used for the solvent replacement is acetone.

[0024] In the second aspect of the present application, a polyimide aerogel fiber prepared by the above preparation method is provided.

[0025] In the third aspect of the present application, the application of the above polyimide aerogel fiber in a thermal insulation fabric is provided.

[0026] Compared with the prior art, the beneficial effects of the present application are as follows:

[0027] In the present application, the polyamic acid precursor spinning solution is allowed to stand in a special coagulation bath for imidization, and then dried under normal pressure at 60 to 100 °C to obtain the polyimide aerogel fiber. The preparation process is simple, and the use of a long drying process and expensive drying equipment is avoided. The continuous forming preparation is successfully realized, and the prospect of large-scale preparation is good.

[0028] The aerogel fiber prepared in the present application has a skin-core structure and has excellent tensile strength, which can reach 20.5 MPa. Its highly porous structure inside makes the aerogel thermal insulation yarn have a low density (0.34 - 0.53 g·cm -3 ), a high porosity (63 - 76%) and excellent heat insulation performance, and its thermal conductivity can be as low as 36.9 W·m -1 ·K -1In addition, the polyimide aerogel fibers of the present application have good weavability and heat resistance. The woven thermal insulation fabric can be used for human body thermal insulation, and still has good thermal insulation effect in various complex occasions, with broad application scenarios. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is the process flow chart for preparing polyimide aerogel fibers of the present application;

[0031] Figure 2 It is the thermogravimetric curve of polyimide aerogel fibers in nitrogen;

[0032] Figure 3 It is the thermogravimetric curve of polyimide aerogel fibers in air;

[0033] Figure 4 It is the SEM image of the cross-section of polyimide aerogel fibers;

[0034] Figure 5 It is the physical image of the fabric woven from polyimide aerogel fibers. Detailed Embodiments

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0036] In the following description of this embodiment, the terms "include", "comprise", "have" and "contain" are all open-ended terms, that is, they are meant to include but not limited to.

[0037] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and both A and B exist simultaneously. Where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are an "or" relationship.

[0038] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or a similar expression means any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0039] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0040] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0041] Those skilled in the art should understand that the numerical ranges in the embodiments of this application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. The intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in this application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0042] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0043] In a first aspect, this application provides a method for preparing polyimide aerogel fibers, including:

[0044] S1, preparing a polyamic acid precursor spinning solution;

[0045] In this application, preparing the polyamic acid precursor spinning solution specifically includes:

[0046] Dissolve 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole in a composite solvent, and carry out a condensation reaction under an inert atmosphere to obtain a polyamic acid precursor spinning solution.

[0047] In this application, the composite solvent is a mixture of dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc). Among them, the volume ratio of dimethyl sulfoxide to N,N-dimethylacetamide is preferably (7:3) to (3:7), such as 7:3, 5:5, 3:7, or any ratio within this ratio range.

[0048] In this application, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to 2-(4-aminophenyl)-5-aminobenzimidazole is preferably 1:1; the total concentration of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole in the polyamic acid precursor spinning solution is preferably 10 to 14 wt%, such as 10%, 12%, 14%, or any concentration within this concentration range.

[0049] In this application, the inert atmosphere is a nitrogen atmosphere; the temperature of the condensation reaction is 0 °C, and the reaction time is 3 to 5 h.

[0050] S2. Wet-spin the polyamic acid precursor spinning solution, wind it up and let it stand in a coagulation bath to obtain polyimide wet gel fibers;

[0051] In this application, the extrusion speed of the wet spinning is 5 to 20 mL / h; the standing time in the coagulation bath is 1 to 24 h.

[0052] In this application, the coagulation bath is a mixed bath of acetone, acetic anhydride and pyridine; the volume ratio of acetic anhydride, pyridine and acetone is 1:1:(20 to 60), such as 1:1:20, 1:1:40, 1:1:60, or any ratio within this ratio range.

[0053] S3. Carry out solvent replacement on the polyimide wet gel fibers and quickly dry them under normal pressure to obtain polyimide aerogel fibers.

[0054] In this application, soak the polyimide wet gel fibers in acetone for solvent replacement, and preferably carry out solvent replacement 2 times. The fibers after solvent replacement are dried at 60 to 100 °C under normal pressure to obtain polyimide aerogel fibers.

[0055] The preparation method of this application has the following reaction principle:

[0056]

[0057] As Figure 1As shown, it is the process flow chart of this application. In this application, the polyamic acid precursor spinning solution is allowed to stand in a special coagulation bath for imidization, and then dried under normal pressure at 60-100 °C to obtain polyimide aerogel fibers. The preparation method of this application has a simple process, avoids the use of a long drying process and expensive drying equipment, and successfully realizes continuous forming preparation, with good prospects for large-scale preparation.

[0058] The polyimide aerogel fibers prepared in this application have a skin-core structure and excellent tensile strength, which can reach 20.5 MPa. Its highly porous internal structure makes the aerogel thermal insulation yarn have a low density (0.34-0.53 g·cm -3 ), a high porosity (63-76%), and excellent heat insulation performance, and its thermal conductivity can be as low as 36.9 W·m -1 ·K -1 .

[0059] In addition, the polyimide aerogel fibers of this application have good weavability and heat resistance, can be used to prepare thermal insulation fabric materials, and then used for thermal insulation fabrics. The thermal insulation fabric woven from the polyimide aerogel fibers of this application can be used for human body thermal insulation and still has good thermal insulation effect in various complex occasions, with a wide range of application scenarios.

[0060] The following further illustrates this application through examples.

[0061] Example 1

[0062] This example provides a method for preparing polyimide aerogel fibers, including:

[0063] S1, Add 0.979 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1.284 g of 2-(4-aminophenyl)-5-aminobenzimidazole to 20 ml of a composite solvent of dimethyl sulfoxide and N,N-dimethylacetamide (the volume ratio of dimethyl sulfoxide to N,N-dimethylacetamide is 1:1), and carry out a polycondensation reaction under a nitrogen atmosphere at 0 °C for 4 h. After the reaction, a polyamic acid precursor spinning solution with a mass concentration of 10 wt% is obtained.

[0064] S2, Spin the polyamic acid precursor spinning solution into the coagulation bath through a spinneret at an extrusion speed of 10 mL / h, wind it up and let it stand in the coagulation bath for 10 h to obtain polyimide wet gel fibers; among them, the coagulation bath is a mixed bath of acetone, acetic anhydride and pyridine in a volume ratio of 1:1:20.

[0065] S3, Immerse the polyimide wet gel fibers in acetone for solvent replacement; after 2 times of solvent replacement, quickly dry them at 80 °C under normal pressure to obtain polyimide aerogel fibers.

[0066] Example 2

[0067] The difference between Example 2 and Example 1 is that in S1, the dosage of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 1.202 g, and the dosage of 2-(4-aminophenyl)-5-aminobenzimidazole is 1.576 g, and the concentration of the polyamic acid precursor spinning solution obtained is 12 wt%; the rest are the same as in Example 1.

[0068] Example 3

[0069] The difference between Example 3 and Example 1 is that in S1, the dosage of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 1.434 g, and the dosage of 2-(4-aminophenyl)-5-aminobenzimidazole is 1.882 g, and the concentration of the polyamic acid precursor spinning solution obtained is 14 wt%; the rest are the same as in Example 1.

[0070] Example 4

[0071] The difference between Example 4 and Example 3 is that in S2, the volume ratio of acetone, acetic anhydride and pyridine in the coagulation bath is 1:1:40, and the rest are the same as in Example 3.

[0072] Example 5

[0073] The difference between Example 5 and Example 3 is that in S2, the volume ratio of acetone, acetic anhydride and pyridine in the coagulation bath is 1:1:60, and the rest are the same as in Example 3.

[0074] Example 6

[0075] The difference between Example 6 and Example 3 is that in S3, the drying temperature is 60 °C, and the rest are the same as in Example 3.

[0076] Example 7

[0077] The difference between Example 7 and Example 3 is that in S3, the drying temperature is 100 °C, and the rest are the same as in Example 3.

[0078] Example 8

[0079] The difference between Example 8 and Example 3 is that in S2, the extrusion speed is 5 ml / h, and the rest are the same as in Example 3.

[0080] Example 9

[0081] The difference between Example 9 and Example 3 is that in S2, the extrusion speed is 15 ml / h, and the rest are the same as in Example 3.

[0082] Example 10

[0083] Example 10 is different from Example 3 in that in S2, the standing time is 5 h, and the rest is the same as in Example 3.

[0084] Example 11

[0085] Example 11 is different from Example 3 in that in S2, the standing time is 15 h, and the rest is the same as in Example 3.

[0086] Comparative Example 1

[0087] S1. Add 1.434 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1.882 g of 2-(4-aminophenyl)-5-aminobenzimidazole into 20 ml of a composite solvent of dimethyl sulfoxide and N,N-dimethylacetamide (the volume ratio of dimethyl sulfoxide to N,N-dimethylacetamide is 1:1), and carry out a polycondensation reaction under the conditions of a nitrogen atmosphere and 0 °C for 4 h. After the reaction, a polyamic acid precursor spinning solution with a concentration of 12% is obtained.

[0088] S2. Spin the polyamic acid precursor spinning solution into a coagulation bath at an extrusion speed of 15 mL / h through a spinneret, wind it up and let it stand in the coagulation bath for 10 h to obtain polyimide wet gel fibers; wherein, the coagulation bath is acetone.

[0089] S3. Immerse the polyimide wet gel fibers in acetone for solvent replacement; after 2 times of solvent replacement, quickly dry them at 80 °C under normal pressure to obtain polyimide aerogel fibers.

[0090] Comparative Example 2

[0091] S1. Add 1.434 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1.882 g of 2-(4-aminophenyl)-5-aminobenzimidazole into 20 ml of a composite solvent of dimethyl sulfoxide and N,N-dimethylacetamide (the volume ratio of dimethyl sulfoxide to N,N-dimethylacetamide is 1:1), and carry out a polycondensation reaction under the conditions of a nitrogen atmosphere and 0 °C for 4 h. After the reaction, a polyamic acid precursor spinning solution with a concentration of 12% is obtained.

[0092] S2. Spin the polyamic acid precursor spinning solution into a coagulation bath at an extrusion speed of 10 mL / h through a spinneret, wind it up and let it stand in the coagulation bath for 10 h to obtain polyimide wet gel fibers; wherein, the coagulation bath is a mixed bath of acetone, acetic anhydride and pyridine with a volume ratio of 1:1:20.

[0093] S3. Immerse the polyimide wet gel fibers in tert-butanol for solvent replacement; after solvent replacement, freeze-dry them for 48 h to obtain polyimide aerogel fibers.

[0094] Tensile strengths of the polyimide aerogel fibers prepared in Test Examples 1-11 and Comparative Examples 1-2 were tested. The specific testing method was as follows: The static tensile and compression properties of the above polyimide aerogel fiber yarns were tested using an electronic universal material testing machine (Instron 5969). The testing speed was 10 mm / min -1 , the gauge length for the tensile test was 20 mm, and the test results are shown in Table 1.

[0095] Table 1 Strengths of each yarn

[0096] Sample Tensile Strength (MPa) Elongation at Break (%) Example 1 9.6 16.2 Example 2 13.4 22.3 Example 3 22.1 26.1 Example 4 18.6 24.3 Example 5 10.7 15.3 Example 6 21.4 26.3 Example 7 22.9 23.9 Example 8 20.1 30.2 Example 9 26.3 19.2 Example 10 12.3 10.4 Example 11 23.2 24.3 Comparative Example 1 6.7 5.2 Comparative Example 2 17.6 20.2

[0097] As can be seen from Table 1, the polyimide aerogel fibers prepared in this application all have relatively high breaking strength and elongation at break. The polyimide aerogel fiber prepared in Example 9 has a breaking strength of 26.1 MPa. While for the polyimide aerogel fiber prepared in Comparative Example 1, both its breaking strength and elongation at break are lower than those of the polyimide aerogel fibers of this application.

[0098] As can be seen from the test results of Examples 1-3, with the increase in the concentration of the polyamic acid spinning solution, the breaking strength and elongation at break of the fibers continuously increase.

[0099] As can be seen from Example 3, Example 4 and Example 5, with the increase in the contents of acetic anhydride and pyridine in the coagulation bath, the strength of the obtained polyimide aerogel fibers increases. This is because the higher the concentration of acetic anhydride and pyridine, the more sufficient the rate of chemical cyclization, and the higher the strength of the obtained polyimide aerogel fibers.

[0100] As can be seen from Example 3, Example 6 and Example 7, the drying temperature has little effect on the aerogel fibers, indicating that the polyimide wet gel fibers obtained by us have sufficient structural stability. Therefore, the drying speed (solvent evaporation speed) controlled by the drying temperature has almost no effect on the structure of the polyimide wet gel fibers, and this application does not require expensive drying equipment and complex drying steps.

[0101] As can be seen from Example 3, Example 8 and Example 9, with the increase in the spinning extrusion speed, the breaking strength of the aerogel fibers increases while the elongation at break decreases. This is because with the increase in the extrusion speed, the molecular chains are oriented along the extrusion direction at the needle tip, thereby improving the strength of the fibers in the orientation direction (fiber axial direction).

[0102] As can be seen from Table 1, the polyimide aerogel fibers obtained by atmospheric drying in this application have comparable mechanical properties, and even better, compared with the polyimide aerogel fibers obtained by freeze forming. However, the preparation process of the polyimide aerogel fibers obtained by atmospheric drying in this application is simple, and it avoids the use of a long drying process and expensive drying equipment, successfully realizing continuous forming preparation with a faster forming speed. Among them, when Example 3 is compared with Comparative Example 2, only the drying method is different, and the other conditions are the same. The polyimide aerogel fibers obtained by atmospheric drying in Example 3 not only have a faster forming speed, but also have better mechanical properties than the aerogel fibers obtained by freeze drying in Comparative Example 2. This is because during the solvent drying process, the densification of the cortical structure is caused, resulting in a higher breaking strength in Example 3.

[0103] As can be seen from Example 3, Example 10, Example 11 and Comparative Example 1, the longer the standing time in the coagulation bath, the higher the degree of chemical imidization; however, when the imidization time is 15 hours compared to 10 hours, the improvement in mechanical properties is not significant. Therefore, a relatively high degree of chemical imidization has been obtained at 10 h.

[0104] The thermal conductivity of the aerogel fibers of Examples 1-3, Examples 8-9 and Comparative Example 1 was tested. The specific test method was as follows: The thermal conductivity was measured using a hot wire thermal conductivity meter (XIATECH TC3000E), and the test mode was the aerogel measurement mode. The ambient temperature and humidity were controlled at 25 °C and 50% respectively. Two identical samples were placed above and below the sensor, and 5 parallel tests were carried out. The test results are shown in Table 2.

[0105] Table 2 Thermal Conductivity of Each Sample

[0106] Sample <![CDATA[Thermal conductivity (mWm -1 K -1 )]]> Example 1 47.5 Example 2 36.9 Example 3 41.1 Example 8 40.3 Comparative Example 9 39.1 Comparative Example 1 54.8

[0107] As can be seen from Table 2, the aerogel fibers prepared in this application have lower thermal conductivities compared with the comparative examples. Among them, for the aerogel fibers of Examples 1-3, as the concentration of the spinning solution increases, the thermal conductivity of the yarn first decreases and then increases. The aerogel fiber with a solid content of 12% has the lowest thermal conductivity of 36.9 mW m -1 K -1 , showing good heat insulation effect. The reason is that the aerogel fibers with a solid content of 10% have too low a concentration, and the fiber shrinkage during spinning is relatively obvious compared with the other two components. Therefore, this phenomenon causes an increase in fiber density and a decrease in porosity, resulting in a higher thermal conductivity. For the aerogel fibers with a concentration of 14%, as the concentration increases, the fiber density increases and the porosity increases, leading to an increase in thermal conductivity.

[0108] As can be seen from Example 3, Example 8 and Example 9, as the extrusion speed increases, the thermal conductivity of the aerogel fiber decreases. This is because the molecular weight is oriented along the fiber axis, and during the heat transfer process of the fabric, the heat transfer along the radial direction is more hindered, thus increasing the thermal resistance and resulting in a decrease in the thermal conductivity of the fiber fabric.

[0109] The aerogel fiber prepared in Example 3 of the present application has high heat insulation performance and good tensile strength, and its microscopic morphology and thermal decomposition performance are tested.

[0110] The test results of the thermal decomposition temperature of the aerogel fiber prepared in Example 3 are as Figure 2 and Figure 3 shown. It can be seen from Figure 2 and Figure 3 that the aerogel fiber of Example 3 has an extremely high thermal decomposition temperature. In an air atmosphere, the highest thermal decomposition temperature is 672 °C; in a nitrogen atmosphere, the highest thermal decomposition temperature is 656 °C. This indicates that the polyimide aerogel fiber prepared in the present application has extremely high heat resistance and can be applied to extreme high-temperature environments.

[0111] The cross-sectional SEM test results of the aerogel fiber prepared in Example 3 are as Figure 4 shown. Figure 4 It shows that the polyimide aerogel fiber has a typical core-shell structure and a highly porous network. Since in wet spinning, the part that first contacts the coagulation bath has an obvious double-diffusion effect, the densification degree of the shell layer is relatively high, while the densification degree of the core layer is relatively low.

[0112] The polyimide aerogel fiber prepared in Example 3 has good spinnability, and the fabric picture woven from it is as Figure 5 shown.

[0113] Although the present application has been described in detail with general descriptions and specific implementation examples in this specification, based on the present application, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present application fall within the scope of protection required by the present application.

Claims

1. A method for preparing a polyimide aerogel fiber, characterized in that: include: S1, preparing a polyamic acid precursor spinning solution; S2, wet spinning the polyamic acid precursor spinning solution, winding it up in a coagulation bath and letting it stand to obtain a polyimide wet gel fiber; S3, replacing the solvent of the polyimide wet gel fiber, and rapidly drying it under normal pressure to obtain the polyimide aerogel fiber.

2. The preparation method according to claim 1, characterized in that: The preparation of the polyamic acid precursor spinning solution specifically comprises: Dissolving 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole in a composite solvent, and carrying out a condensation reaction under an inert atmosphere to obtain a polyamic acid precursor spinning solution; The composite solvent is a mixture of dimethyl sulfoxide and N,N-dimethylacetamide.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the 3,3',4,4'-biphenyltetracarboxylic dianhydride to 2-(4-aminophenyl)-5-aminobenzimidazole is 1:1; The volume ratio of dimethyl sulfoxide to N,N-dimethylacetamide is (7:3) to (3:7); In the polyamic acid precursor spinning solution, the total concentration of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2-(4-aminophenyl)-5-aminobenzimidazole is 10-14 wt %.

4. The preparation method according to claim 2, characterized in that: The inert atmosphere is a nitrogen atmosphere; the temperature of the condensation reaction is 0° C., and the reaction time is 3 to 5 hours.

5. The preparation method according to claim 1, characterized in that: The coagulation bath is a mixed bath of acetone, acetic anhydride and pyridine; Wherein, the volume ratio of acetic anhydride, pyridine and acetone is 1:1:(20-60).

6. The preparation method according to claim 1, characterized in that: The extrusion speed of the wet spinning is 5 to 20 mL / h.

7. The preparation method according to claim 1, characterized in that: The drying temperature is 60-100°C.

8. The preparation method according to claim 1, characterized in that: The solvent used in the solvent replacement is acetone.

9. The polyimide aerogel fiber prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the polyimide aerogel fiber according to claim 9 in thermal insulation fabrics.

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