A method for preparing core-shell structure Al2O3-Aramid hybrid aerogel fiber by freezing coagulation bath spinning

Abstract

The present invention belongs to the technical field of preparation of aerogel fiber materials, and discloses a freezing coagulation bath spinning preparation method of a core-shell structure Al2O3-Aramid hybrid aerogel fiber, comprising the steps of: preparing an aramid nanofiber dispersion, preparing an aluminum chloride aluminum sol coagulation bath, adopting a multiphase freezing coagulation bath spinning technology, freezing the coagulation bath at 20 to 80°C, and uniformly extruding the aramid nanofiber dispersion into a supercooled coagulation bath. Based on a two-phase gel and freezing reaction, while ensuring high-speed gelation of the spinning solution, an Al2O3-Aramid hybrid aerogel fiber with a core-shell structure is formed. The present invention can relatively simply prepare an Al2O3-Aramid hybrid aerogel fiber with a core-shell structure having braidability, high temperature resistance, and low thermal conductivity, thereby providing technical support for expanding its application.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of aerogel fiber materials, and in particular relates to a method for preparing Al2O3-Aramid hybrid aerogel fiber with a core-shell structure by freezing coagulation bath spinning. Background Art

[0002] Aerogel fibers are continuous fibers composed of overlapping aerogel particles, combining the characteristics of both aerogel and fiber materials. This unique structure gives aerogel fibers ultra-low density, ultra-high porosity, and a large specific surface area. Aerogel fibers offer excellent thermal insulation properties, far exceeding those of conventional fiber materials, and are considered the next generation of high-performance thermal insulation fibers. Over the past decade, researchers have developed a wide range of aerogel fibers, including graphene, silica, cellulose, aramid, and other types. These aerogel fibers show promising applications in thermal insulation, flame retardancy, electromagnetic shielding, and other fields.

[0003] However, the research and development of aerogel fibers also faces some challenges, such as the difficulty in achieving both low thermal conductivity and high strength, insufficient high-temperature resistance, and poor weavability. For example, aramid aerogel fibers have insufficient temperature resistance, and alumina aerogel fibers have poor mechanical properties. To address these issues, researchers are constantly exploring new preparation methods and processes to improve the mechanical properties and high-temperature resistance of aerogel fibers. In particular, for the preparation of core-shell aerogel fibers, traditional methods such as coaxial spinning, impregnation, and coating have problems such as poor bonding between the core and the shell, high thermal conductivity due to slow gelation rate, poor mechanical properties, and poor stability, which seriously limit their large-scale production and application.

[0004] In view of this, it is particularly urgent and important to accelerate the research and development of aerogel fiber technology with high temperature resistance, low thermal conductivity and excellent mechanical properties. In the future, aerogel fibers are expected to be widely used in more fields. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for preparing core-shell structured Al2O3-Aramid hybrid aerogel fibers by freezing coagulation bath spinning. Nano-aramid fibers are used as the "core fibers" and the Al2O3 aerogel layer is used as the outer shell layer. The instant freezing effect of the freezing coagulation bath and the chemical reaction of the wet reaction spinning are utilized to tightly combine the inner core and the outer shell together to obtain a new core-shell structured alumina-aramid hybrid aerogel fiber with high temperature resistance, low thermal conductivity and excellent mechanical properties.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a core-shell structured Al2O3-Aramid hybrid aerogel fiber by freezing coagulation bath spinning comprises the following steps:

[0008] (1) Add 2-8 mm aramid short-cut fibers to N-methylpyrrolidone and soak for 10-14 hours, ultrasonically treat for 20-40 minutes to remove impurities and sizing agents on the fiber surface, and then wash with anhydrous ethanol and pure water in sequence and place in a constant temperature oven for drying to obtain completely dried and broken aramid nanofibers;

[0009] (2) adding completely dried and broken up aramid nanofibers and potassium salt to dimethyl sulfoxide to prepare a 0.5-8 wt% aramid nanofiber dispersion; the aramid nanofiber dispersion is sealed and stored away from light to prevent sedimentation;

[0010] (3) preparing a coagulation bath, adding aluminum chloride hexahydrate to a mixed solution of ethanol and water, stirring, and continuing the reaction for 6 to 10 hours after the aluminum chloride hexahydrate is completely dissolved, then adding a dilute hydrochloric acid solution dropwise, stirring and reacting to obtain an aluminum chloride sol, wherein the mass ratio of the aluminum chloride hexahydrate, ethanol, water, and dilute hydrochloric acid solution is 1:6 to 20:6:2;

[0011] (4) uniformly injecting the aramid nanofiber dispersion into a -20 to -80°C frozen coagulation bath aluminum sol, performing multiphase frozen wet reaction spinning to obtain cryogel fibers, soaking the fibers in the frozen coagulation bath aluminum sol for 20 to 26 hours, and waiting for gel aging to obtain gel-aged cryogel fibers;

[0012] (6) The gel-aged cryogel fibers were repeatedly washed with pure water to obtain wet gel fibers, which were then placed in a displacement solvent for solvent displacement, and then freeze-dried at -50 to -60 °C and 0.03 to 0.06 MPa for 24 to 48 h to finally obtain Al2O3-Aramid hybrid aerogel fibers.

[0013] Furthermore, the potassium salt is powdered potassium hydroxide or potassium tert-butoxide.

[0014] Furthermore, when the mass concentration of the aramid nanofiber dispersion is ≤2wt%, the potassium salt is powdered potassium hydroxide, and the specific preparation method of the aramid nanofiber dispersion is: adding completely dried and broken up aramid nanofibers and powdered potassium hydroxide to dimethyl sulfoxide to obtain a mixed solution, the mass ratio of the aramid nanofibers to potassium hydroxide is 1:1~2, and the mixed solution is vigorously stirred for 7 days under nitrogen protection, the aramid nanofibers gradually dissolve, and the solution changes from colorless to dark red viscous liquid and is sealed and stored away from light, thereby preparing the aramid nanofiber dispersion.

[0015] Furthermore, when the mass concentration of the aramid nanofiber dispersion is greater than 2wt%, the potassium salt is potassium tert-butoxide, and the specific preparation method of the aramid nanofiber dispersion is: adding completely dried and broken up aramid short fibers and potassium tert-butoxide in a mass ratio of 1:1 to 1.5 to dimethyl sulfoxide, stirring evenly, adding a proton additive with the same mass as the aramid short fibers, and continuing to stir under nitrogen protection for 3 to 8 hours until the sample is evenly reacted and dissolved to obtain an aramid nanofiber dispersion.

[0016] Furthermore, the mass ratio of aluminum chloride hexahydrate, ethanol, water and dilute hydrochloric acid solution in step (3) is 1:6 to 14:6:2.

[0017] Furthermore, the proton auxiliary agent is one or more of anhydrous methanol, ethanol, and water.

[0018] Furthermore, the spinning parameters are as follows: when the aramid nanofiber dispersion concentration is ≤2wt%, the extrusion speed is 10-20ml / min, and the spinning needle diameter is 19-22G; when the aramid nanofiber dispersion concentration is greater than 2wt%, the extrusion speed is 2-5mL / min, and the spinning needle diameter is 13-16G. The selection of the extrusion speed and needle diameter depends on the dispersion concentration and the desired fiber diameter, ensuring uniform fiber extrusion and proper precipitation in the coagulation bath.

[0019] Furthermore, the replacement solvent in step (6) includes one or more of water, ethanol, cyclohexane, n-hexane, and 25% tert-butanol aqueous solution.

[0020] Furthermore, the concentration of the dilute hydrochloric acid solution in step (3) is 1 mol / L.

[0021] During the aerogel fiber spinning process, high-speed gelation of the spinning solution is a prerequisite for aerogel fiber production. Synthesizing a spinning solution with a high gelation rate is key to producing aerogel fibers with a core-shell structure. Traditional sol materials suffer from the coexistence of hydrolysis and condensation, resulting in a generally slow gelation rate that cannot meet the requirements of aerogel fiber spinning. Reaction spinning allows the dispersion to gel rapidly through a rapid reaction between the coagulation bath and the spinning solution upon contact with the coagulation bath, significantly shortening the gelation time and facilitating the high-throughput production of aerogel fibers. Simultaneously, freezing the coagulation bath transforms the gel fibers into cryogel fibers, maintaining the fiber shape while allowing for more complete reaction between the aramid nanofiber dispersion and the aluminum sol coagulation bath. At room temperature, the dispersion binds prior to acid protons, resulting in weak intermolecular hydrogen bonding and weak binding to aluminum ions. Temperatures between -20 and -80°C increase the viscosity of the aluminum sol. During the reaction, the more viscous aluminum sol exhibits better adhesion to the aramid nanofiber dispersion and a more complete reaction.

[0022] In view of this, the present invention successfully prepared a highly reactive aramid nanofiber dispersion using aramid nanofibers as raw materials, and successfully prepared an aluminum sol coagulation bath using aluminum chloride hexahydrate as raw materials. The aluminum sol coagulation bath is placed in a refrigerator at -20 to -80°C to supercool the aluminum sol coagulation bath. After the nanofiber dispersion enters the coagulation bath, on the one hand, the nanofiber dispersion is re-protonated and assembled, and the aramid nanowires are destabilized and cross-linked at high speed. On the other hand, the supercooled coagulation bath can rapidly coagulate the aramid spinning solution, ensuring high-speed molding of the gel fiber and effective bonding with the shell. Based on the two-phase gel and freezing reaction, while ensuring high-speed gelation of the spinning solution, a gel fiber with a core-shell structure is formed. Aramid nanofibers are used as "core fibers" and their advantages such as high mechanical strength, high concentration of liquid crystal state and high stretching tolerance are utilized to ensure the weavability of the composite fiber material. The Al2O3 aerogel layer is used as the outer shell layer, giving full play to its ultra-low thermal conductivity and high temperature resistance advantages. Combined with the construction of the above-mentioned freezing-two-phase solution reaction mechanism, the effective generation of Al2O3-Aramid hybrid aerogel fibers is ensured, the skeleton strength of the Al2O3-Aramid hybrid aerogel fibers is effectively improved, and the stability of the structure is ensured. It should be pointed out that the two-phase gel reaction strategy used in the present invention forms a composite gel transition phase at the interface of the Al2O3-Aramid two phases, ensuring a close connection between the core layer and the shell layer, and improving the stability of the core-shell structure Al2O3-Aramid hybrid aerogel fibers.

[0023] The advantages and positive effects of the present invention are:

[0024] The present invention uses aramid nanofiber spinning solution and aluminum sol freezing coagulation bath solution, and combines the freezing spinning strategy to produce two-phase reaction and freezing dual molding during the spinning process to carry out high-speed spinning of aerogel fibers, which significantly reduces the difficulty of synthesizing core-shell structure aerogel fibers and improves the stability of the core-shell structure. The prepared core-shell structure Al2O3-Aramid hybrid aerogel fibers have good mechanical properties and thermal insulation properties. The preparation method of the present invention has good scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a macroscopic photograph of the Al2O3-Aramid aerogel fiber prepared in Example 1;

[0026] Figure 2 This is a SEM image of the Al2O3-Aramid aerogel fiber prepared in Example 1 at a magnification of 1150 times;

[0027] Figure 3 This is a macroscopic photograph of the Al2O3-Aramid aerogel fiber prepared in Example 2;

[0028] Figure 4 This is a 760-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Example 2;

[0029] Figure 5 This is a 330-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Example 3;

[0030] Figure 6 This is a 250-fold magnified SEM image of the Aramid aerogel fiber prepared in Comparative Example 1;

[0031] Figure 7 This is a 190-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 2;

[0032] Figure 8 This is a 410-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 3;

[0033] Figure 9 This is a 215-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 4;

[0034] Figure 10 This is a 295-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 5;

[0035] Figure 11 This is a 280-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 6. DETAILED DESCRIPTION

[0036] In order to better understand the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings. In the case of no conflict, the features in the case can be combined with each other. The raw materials used in the following examples are all commercially available analytically pure raw materials.

[0037] Example 1

[0038] A method for preparing a core-shell structured Al2O3-Aramid hybrid aerogel fiber by freezing coagulation bath spinning comprises the following steps:

[0039] (1) Preparation of aramid nanofiber dispersion: 10 g of 5 mm long aramid short-cut fibers were soaked in 50 g of N-methylpyrrolidone for 12 h, then ultrasonically treated for 30 min to remove impurities and sizing agents from the fiber surface. The fibers were then washed three times with anhydrous ethanol and then with pure water, and then dried in a constant temperature oven at 80 °C for 5 h to obtain completely dried and dispersed aramid nanofibers.

[0040] (2) adding 10.0 g of completely dried and broken up aramid nanofibers and 20.0 g of potassium hydroxide to dimethyl sulfoxide, and stirring the mixture for 7 days under nitrogen protection to prepare a 2.0 wt% aramid nanofiber dispersion;

[0041] (3) Weigh 20 g of aluminum chloride hexahydrate using an electronic balance and add it to a hydroalcoholic solution of 280 g of ethanol and 120 g of water. Stir thoroughly to hydrolyze it. After the aluminum chloride hexahydrate is completely dissolved, add 40 g of 1 mol / L dilute hydrochloric acid to promote hydrolysis and obtain aluminum chloride sol.

[0042] (4) placing the aluminum chloride hexahydrate sol in an ultra-low temperature refrigerator at -80°C to freeze, obtaining a supercooled solidification bath, and extruding the aramid nanofiber dispersion into the supercooled solidification bath through a pump-controlled syringe at an extrusion rate of 10 ml / min. Using a needle with a diameter of 19G, the aramid nanofiber dispersion forms cryogel fibers in the supercooled solidification bath, which are then gelled in the freezing solidification bath for 24 hours, and the gel is aged to obtain gel-aged cryogel fibers;

[0043] (5) The aged cryogel fibers were washed with water and ethanol in sequence to remove residual dimethyl sulfoxide and the coagulation bath, and then transferred to a 25 wt% tert-butyl alcohol aqueous solution for solvent replacement for 48 h, with the replacement solvent being replaced every 12 h. Subsequently, the fibers were placed in an ultra-low temperature freezer at -80 ° C for 24 h and vacuum freeze-dried at 0.05 MPa and -50 ° C for 24 h to obtain Al2O3-Aramid hybrid aerogel fibers with a core-shell structure.

[0044] The macroscopic photograph of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 1 is shown in FIG. Figure 1 As shown in the scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 1, Figure 2 shown.

[0045] Example 2

[0046] A method for preparing a core-shell structured Al2O3-Aramid hybrid aerogel fiber by freezing coagulation bath spinning comprises the following steps:

[0047] (1) The preparation of aramid nanofibers was the same as in Example 1;

[0048] (2) Add 8.0 g of aramid nanofibers and 8.0 g of potassium tert-butoxide to 76 g of refined DMSO and stir rapidly for 10 minutes. Subsequently, add 8.0 g of anhydrous methanol in four batches over 1 hour and continue stirring for 8 hours until the sample is uniform, obtaining an 8 wt% aramid nanofiber dispersion.

[0049] (3) Using an electronic balance, 20 g of aluminum chloride hexahydrate was weighed and added to a hydroalcoholic solution of 280 g and 120 g of water. The mixture was stirred thoroughly to hydrolyze the aluminum chloride hexahydrate. After the aluminum chloride hexahydrate was completely dissolved, 40 g of 1 mol / L dilute hydrochloric acid was added dropwise to promote the hydrolysis and obtain aluminum chloride sol.

[0050] (4) The aluminum chloride sol is placed in an ultra-low temperature refrigerator at -80°C and frozen. The aramid nanofiber dispersion is extruded into a supercooled solidification bath by a pump-controlled syringe at an extrusion rate of 3 ml / min. A needle with a diameter of 16G is used. The aramid nanofiber dispersion forms cryogel fibers in the supercooled solidification bath, which are then gelled in the freezing solidification bath for 24 hours. The gel is aged to obtain gel-aged cryogel fibers.

[0051] (5) The aged cryogel fibers were washed with water and ethanol in sequence, and then transferred to a 25 wt% tert-butyl alcohol aqueous solution for solvent replacement for 48 h, with the solvent replaced every 12 h. Subsequently, the fibers were frozen at -80 °C for 24 h and freeze-dried in a vacuum at 0.05 MPa and -50 °C for 24 h. Thus, Al2O3-Aramid hybrid aerogel fibers with a core-shell structure were obtained.

[0052] The macroscopic photograph of Al2O3-Aramid hybrid aerogel fiber prepared in Example 2 is shown in FIG. Figure 3 As shown in the scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 2, Figure 4 shown.

[0053] Example 3

[0054] The only difference from implementation 1 is that in step (4), the aluminum chloride aluminum sol is placed in an ultra-low temperature -40°C refrigerator for freezing.

[0055] The scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 3 is as follows: Figure 5 shown.

[0056] Comparative Example 1

[0057] A method for preparing Aramid aerogel fibers by freezing coagulation bath spinning is the same as that in Example 1, except that the coagulation bath liquid is changed into a mixed solution of ethanol and water in step (3).

[0058] The scanning electron microscope image of the aerogel fiber-based thermal insulation material prepared in Comparative Example 1 is as follows: Figure 6 shown.

[0059] Comparative Example 2

[0060] A method for preparing Al2O3-Aramid hybrid aerogel fibers by wet reactive spinning, the preparation method being the same as that of Example 1, except for steps (4) and (5): placing an aluminum chloride sol at room temperature, and extruding an aramid nanofiber dispersion into a coagulation bath via a pump-controlled syringe at an extrusion rate of 3 ml / min using a 16G diameter needle to obtain wet gel fibers; the wet gel fibers are sequentially washed with water and ethanol, and then transferred to a 25wt% tert-butanol aqueous solution for solvent replacement for 48 hours, with the replacement solvent being replaced every 12 hours. The fibers are then frozen at -80°C for 24 hours and vacuum freeze-dried at 0.05 MPa and -50°C for 24 hours. Thus, Al2O3-Aramid hybrid aerogel fibers with a core-shell structure are obtained.

[0061] The scanning electron microscope image of Al2O3-Aramid hybrid aerogel fiber prepared in Comparative Example 2 is as follows: Figure 7 shown.

[0062] Comparative Example 3

[0063] The only difference from Comparative Example 2 is that in step (4), the aluminum chloride sol is placed at 10°C.

[0064] The scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Comparative Example 3 is as follows: Figure 8 shown.

[0065] Comparative Example 4

[0066] The only difference from Comparative Example 2 is that in step (4), the aluminum chloride sol is placed at 0°C.

[0067] The scanning electron microscope image of Al2O3-Aramid hybrid aerogel fiber prepared in Comparative Example 4 is as follows: Figure 9 shown.

[0068] Comparative Example 5

[0069] The only difference from Example 1 is that in step (4), the aluminum chloride hexahydrate sol is placed in a -10°C refrigerator and frozen.

[0070] The scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Comparative Example 5 is as follows: Figure 10 shown.

[0071] Comparative Example 6

[0072] The only difference from Example 1 is that in step (4), the aluminum chloride hexahydrate sol is placed in a -90°C refrigerator and frozen.

[0073] The scanning electron microscope image of the Al2O3-Aramid hybrid aerogel fiber prepared in Comparative Example 6 is as follows: Figure 11 shown.

[0074] Evaluation and characterization

[0075] Figure 1 This is a macroscopic photograph of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 1. Figure 2 This is a SEM image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 1 at a magnification of 1150 times. Figure 3 This is a macroscopic photograph of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 2. Figure 4 This is a 760-fold magnified SEM image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 2. Figure 5 This is a 330x magnified SEM image of the Al2O3-Aramid hybrid aerogel fiber prepared in Example 3. It can be seen that the shell and core layers of the core-shell Al2O3-Aramid hybrid aerogel fiber prepared in the present invention are tightly integrated, and the core layer structure is dense and evenly distributed. This stable shell structure gives the Al2O3-Aramid hybrid aerogel fiber excellent mechanical properties, low thermal conductivity, and high temperature resistance.

[0076] Figure 6 This is a 250x magnified SEM image of the Aramid aerogel fiber prepared in Comparative Example 1. It can be seen that a core-shell structure cannot be formed using a conventional coagulation bath; Figure 7 This is a 190x magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 2. The gelation rate using a room-temperature coagulation bath is slower than that using a frozen coagulation bath, and the internal and external bonding is poor, with surface wrinkling and shedding. The frozen coagulation bath achieves high-speed spinning while also achieving good aerogel fiber formation, with the inner and outer layers tightly bonded together by intermolecular forces. The core-shell Al2O3-Aramid hybrid aerogel fiber exhibits better high-temperature resistance than Aramid aerogel fibers. The addition of the alumina component improves the high-temperature resistance of the fiber's outer layer, thereby enhancing the overall high-temperature resistance of the fiber and broadening its application in extreme high-temperature environments.

[0077] Figure 8 This is a 410-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 3. Figure 9 This is a 215-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 4; Figure 10 This is a 295-fold magnified SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 5. Figure 11The SEM image of the Al2O3-Aramid aerogel fiber prepared in Comparative Example 6, magnified at 280°, shows that as the coagulation bath temperature gradually decreases from 10°C, 0°C, and -10°C, the bonding between the core layer and the shell layer becomes better and better. The core-shell fibers prepared at low temperatures have a more stable and complete structure than those at room temperature, but the overall structure is not as good as the shell structure of the examples. The core-shell aerogel fibers prepared at -90°C have a tight bond between the outer shell and the inner core, but the interior has collapsed. This is because the freezing coagulation bath with an excessively low temperature is not conducive to the formation of a porous network structure in the inner core layer.

[0078] The fiber's tensile strength at break was tested using an Instron universal testing machine, with a 1 cm specimen length and a tensile rate of 1 mm / min. The maximum tensile strength at break was measured. Thermal conductivity was measured using an insulation material thermal conductivity tester. The data are shown in Table 1.

[0079] Table 1

[0080] name Mechanical properties (MPa) <![CDATA[Thermal conductivity (W·m -1 ·K -1 )]]> Example 1 4.0 0.032 Example 2 4.2 0.030 Example 3 4.1 0.033 Comparative Example 1 3.2 0.038 Comparative Example 2 3.3 0.038 Comparative Example 3 3.5 0.037 Comparative Example 4 3.6 0.037 Comparative Example 5 3.5 0.038 Comparative Example 6 3.6 0.039

[0081] As can be seen from Table 1, the mechanical properties of the aerogel fibers prepared in the examples are higher than those of the aerogel fibers prepared in the comparative examples. This is because the sol-gel process is the result of the combined action of the dual mechanisms of coagulation bath and freezing. When the spinning solution is squeezed into the freezing coagulation bath, a more ordered directional structure will be formed under low temperature conditions of -20 to -80°C, thereby improving the mechanical and physical properties of the aerogel fibers. The thermal conductivity of the examples is lower than that of the comparative examples. This is because the addition of the low thermal conductivity alumina aerogel layer in the outer shell and the formation of a composite gel transition phase at the interface between the Al2O3-Aramid two phases ensure a close connection between the core layer and the shell layer, making the structure more stable and ensuring that the Al2O3-Aramid aerogel fibers have a lower thermal conductivity and better thermal insulation effect. At the same time, due to the difference in coagulation bath temperature, the degree of bonding between the inner core and the outer shell of the aerogel fibers is different, and the thermal conductivity is slightly different, but the overall fluctuation is not large.

[0082] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structure Al2O3-Aramid hybrid aerogel fiber by freezing coagulation bath spinning, characterized in that: The steps include: (1) Add 2-8 mm aramid short fibers to N-methylpyrrolidone and soak for 10-14 hours, ultrasonically treat for 20-40 minutes, then wash with anhydrous ethanol and pure water in sequence and place in a constant temperature oven for drying to obtain completely dried and broken aramid nanofibers; (2) adding completely dried and broken up aramid nanofibers and potassium salt to dimethyl sulfoxide to prepare a 0.5-8 wt% aramid nanofiber dispersion; (3) adding aluminum chloride hexahydrate to a mixed solution of ethanol and water, stirring, and continuing the reaction for 6 to 10 hours after the aluminum chloride hexahydrate is completely dissolved, then adding a dilute hydrochloric acid solution dropwise, stirring and reacting to obtain an aluminum chloride sol, wherein the mass ratio of the aluminum chloride hexahydrate, ethanol, water, and dilute hydrochloric acid solution is 1:6 to 20:6:2; (4) uniformly injecting the aramid nanofiber dispersion into a -20 to -80°C frozen coagulation bath aluminum sol, performing multiphase frozen wet reaction spinning to obtain cryogel fibers, soaking the fibers in the frozen coagulation bath aluminum sol for 20 to 26 hours, and waiting for gel aging to obtain gel-aged cryogel fibers; (5) The gel-aged cryogel fibers were repeatedly washed with water and ethanol, then placed in a replacement solvent for solvent replacement, and then placed in an ultra-low temperature refrigerator at -80°C for 8 to 24 hours of freezing treatment, and then freeze-dried at -40 to -60°C and 0.05 MPa for 24 to 48 hours to finally obtain Al2O3-Aramid hybrid aerogel fibers.

2. The preparation method according to claim 1, characterized in that The potassium salt is powdered potassium hydroxide or potassium tert-butoxide.

3. The preparation method according to claim 2, characterized in that When the mass concentration of the aramid nanofiber dispersion is ≤2wt%, the potassium salt is powdered potassium hydroxide. The specific preparation method of the aramid nanofiber dispersion is: adding completely dried and broken up aramid nanofibers and powdered potassium hydroxide to dimethyl sulfoxide to obtain a mixed solution, wherein the mass ratio of the aramid nanofibers to the potassium hydroxide is 1:1-2, and the mixed solution is vigorously stirred for 5-8 days under nitrogen protection, the aramid nanofibers gradually dissolve, and the solution changes from colorless to dark red viscous liquid and is sealed and stored away from light, thereby preparing the aramid nanofiber dispersion.

4. The preparation method according to claim 2, characterized in that When the mass concentration of the aramid nanofiber dispersion is greater than 2wt%, the potassium salt is potassium tert-butoxide. The specific preparation method of the aramid nanofiber dispersion is: adding completely dried and broken up aramid short fibers and potassium tert-butoxide in a mass ratio of 1:1 to 1.5 to dimethyl sulfoxide, stirring, adding a proton additive with the same mass as the aramid short fibers, and continuing to stir under nitrogen protection for 3 to 8 hours until the sample is evenly reacted and dissolved, thereby obtaining the aramid nanofiber dispersion.

5. The preparation method according to claim 1, characterized in that The mass ratio of aluminum chloride hexahydrate, ethanol, water and dilute hydrochloric acid solution in step (3) is 1:6 to 14:6:

2.

6. The preparation method according to claim 4, characterized in that The proton auxiliary agent is one or more of anhydrous methanol, ethanol and water.

7. The preparation method according to claim 1, characterized in that Among the spinning parameters, when the mass concentration of the aramid nanofiber dispersion is ≤2wt%, the extrusion speed is 10-20ml / min, and the spinning needle diameter is 19-22G; when the mass concentration of the aramid nanofiber dispersion is >2wt%, the extrusion speed is 2-5mL / min, and the spinning needle size is 13-16G.

8. The preparation method according to claim 1, characterized in that The replacement solvent in step (6) includes one or more of water, ethanol, cyclohexane, n-hexane, and 25% tert-butanol aqueous solution.

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