Polyimide aerogel fiber as well as preparation method and application thereof

Abstract

The invention discloses a polyimide aerogel fiber as well as a preparation method and application 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 acrylic acid, polyethylene glycol, a photoinitiator and a cationic surfactant into the polyamide acid solution, and mixing to form a spinning solution; step 3, carrying out wet spinning on the spinning solution, and then entering a coagulating bath to form initial gel fibers; step 4, performing ultraviolet light curing on the initial gel fibers to form gel fibers; and 5, carrying out chemical imidization treatment on the gel fiber, then carrying out stretching treatment, and carrying out supercritical CO2 drying after solvent replacement so as to obtain the polyimide aerogel fiber. Under the synergistic effect of multiple components of the spinning solution, the polyimide aerogel fiber is endowed with excellent mechanical properties and high porosity in cooperation with gelation and ultraviolet curing in a coagulating bath, and the polyimide aerogel fiber can be applied to preparation of heat insulation materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a polyimide aerogel fiber and a preparation method and application thereof. Background Art

[0002] Aerogel fiber is a new type of functional fiber for clothing, offering excellent warmth retention, moisture absorption, and breathability. Produced through sol-gel spinning and specialized drying techniques, aerogel fiber has garnered widespread attention for its ultra-low density, high porosity, and excellent thermal insulation properties. It is considered a next-generation thermal fiber and holds significant application prospects in a wide range of fields, including textiles, the environment, and energy.

[0003] Polyimide aerogel fiber has the advantages of good hydrophobicity, good flame retardancy, high elastic modulus, good thermal stability, and light weight. It has good application prospects in aerospace, clothing manufacturing, smart wearable devices, environmental protection and other fields.

[0004] However, aerogel fibers face the challenge of balancing mechanical strength and thermal insulation performance. The porous structure easily leads to insufficient mechanical properties (breaking strength is usually less than 50MPa), while increasing strength through stretching will sacrifice its thermal insulation performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyimide aerogel fiber and a preparation method and application thereof, which can solve the problem of difficulty in balancing mechanical strength and thermal insulation performance in the preparation of aerogel fibers in the prior art.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing polyimide aerogel fiber comprises the following steps:

[0008] Step 1, synthesizing a polyamic acid solution with a solid content of 15-20 wt%;

[0009] Step 2: adding acrylic acid, polyethylene glycol, a photoinitiator and a cationic surfactant to a polyamic acid solution and mixing to form a spinning solution;

[0010] Step 3: After wet spinning, the spinning solution enters a coagulation bath to form a primary gel fiber;

[0011] Step 4: Curing the primary gel fiber with ultraviolet light to form gel fiber;

[0012] Step 5: The gel fiber is subjected to chemical imidization treatment and then stretched, and then the solvent is replaced and supercritical CO2 dried to obtain the polyimide aerogel fiber.

[0013] The spinning solution is primarily composed of polyamic acid, while acrylic acid provides more carboxylic acid crosslinking sites. Prior to photocuring, the added acrylic acid synergistically bonds with the polyamic acid molecular chains to form a three-dimensional network, stabilizing the initial gel fiber structure. The photoinitiator then promotes the crosslinking polymerization of acrylic acid, forming a covalently crosslinked network that enhances the mechanical properties of the gel fiber and stabilizes the porous structure, facilitating subsequent stretching and minimizing the effects of stretching on the fiber's porous structure. Polyethylene glycol (PEG) induces phase separation in the coagulation bath through solvent-nonsolvent exchange, forming pores. Cationic surfactants and negatively charged polyamic acid molecules self-assemble through electrostatic interactions, forming mesopores. Supercritical CO2 drying removes the solvent, resulting in nanoscale micropores. The fiber structure exhibits a multi-level porous structure with high porosity. The polymerization of acrylic acid, the crosslinking of the cationic surfactant and polyamic acid molecular chains, and the stretching process impart high porosity and excellent mechanical properties to the polyimide aerogel fibers.

[0014] Furthermore, the mass proportion of the acrylic acid in the spinning solution is 3-5 wt%.

[0015] Furthermore, the polyethylene glycol accounts for 2-4 wt% of the spinning solution. The polyethylene glycol has a long molecular chain structure and can be physically entangled with the polyamic acid molecular chains in the spinning solution. The polyethylene glycol molecular chains are interspersed with the polyamic acid molecular chains, and after removal, uniformly distributed pores are formed in situ.

[0016] Acrylic acid is a small molecule monomer that can be evenly dispersed in the spinning solution system. The carboxyl group of acrylic acid forms a hydrogen bond with the amide group of polyamic acid or the ether bond of polyethylene glycol, which can enhance the interpenetration effect of polyethylene glycol in polyamic acid.

[0017] Furthermore, the photoinitiator is photoinitiator 2959, and its mass fraction in the spinning solution is 0.5-1wt%. The pre-gel fibers formed in the coagulation bath have limited structural stability and are easily broken by direct stretching. Using a photoinitiator to promote acrylic acid polymerization and crosslinking stabilizes the gel fiber structure and facilitates subsequent processing. The in-situ pores created by the polyethylene glycol after the coagulation bath are fixed within the gel skeleton by the photocuring action of the acrylic acid, increasing the fiber's porosity.

[0018] Furthermore, the cationic surfactant is at least one of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide, and the mass proportion of the cationic surfactant in the spinning solution is 0.2-0.6wt%. The hydrophilic head group of the cationic surfactant extends outward in the gel system and generates electrostatic interaction with the carboxyl groups on the polyamic acid chain, which can increase the hydrophobicity of the pre-gel fiber in the coagulation bath. The hydrophobic interaction can guide the aggregation of molecular chains in the fiber, promote physical crosslinking, and inhibit excessive swelling. Due to its amphiphilic nature, the cationic surfactant can serve as a dispersion stabilizer for each component in the spinning solution, ensuring the uniformity and stability of the spinning solution.

[0019] Furthermore, the coagulation bath comprises a polar organic solvent, water and ammonium sulfate, wherein the volume proportion of the polar organic solvent in the coagulation bath is 20-40%, and the mass proportion of the ammonium sulfate is 1-2 wt%;

[0020] The polar organic solvent is one of NMP, DMF and DMAC.

[0021] Ammonium sulfate is acidic when dissolved in water. The slightly acidic coagulation bath can accelerate solvent exchange and utilize the pH sensitivity of acrylic acid to quickly form gel fibers under acidic conditions, thereby promoting rapid fiber molding.

[0022] Furthermore, the power of the UV curing is 15-25 mW / cm 2 , the curing time is 1-5min.

[0023] Furthermore, the steps of the chemical imidization treatment are as follows:

[0024] Prepare a 1:1 volume ratio of acetic anhydride and pyridine. Add triethylamine to the mixture at a concentration of 0.5-2 wt%. Stir and mix, then heat to 60-80°C. Add the gel fiber under constant temperature and allow the imidization reaction to proceed for 5-8 hours. Compared to thermal imidization, chemical imidization better maintains a porous fiber structure. Triethylamine is added to neutralize residual acrylic acid monomer and prevent side reactions.

[0025] Furthermore, the stretching process has a draft ratio of 3-5 times. Conventional gel fibers break when stretched in a gel state due to poor structural stability, making them incapable of continuous stretching. Furthermore, the stretching process affects the porous structure of the fiber. The present invention enhances the mechanical properties of the gel fiber by combining gelation in a coagulation bath with light curing, enabling high-ratio stretching and further improving the mechanical properties of the fiber.

[0026] Furthermore, the steps of solvent replacement are as follows:

[0027] The stretched fibers were placed in ethanol and allowed to stand for 6-8 hours, then transferred to tert-butyl alcohol and allowed to stand for 6-8 hours to replace the residual organic solvent in the fibers with ethanol.

[0028] The present invention also provides a polyimide aerogel fiber, which is prepared by the above-mentioned preparation method.

[0029] The present invention also provides an application of polyimide aerogel fibers. The polyimide aerogel fibers prepared by the above-mentioned preparation method are used to prepare flexible thermal insulation materials.

[0030] Furthermore, the diameter of the polyimide aerogel fiber is 10-30 μm.

[0031] Beneficial effects of the present invention:

[0032] (1) The present invention adds acrylic acid, polyethylene glycol, a cationic active agent and a photoinitiator to a polyamic acid solution, utilizes the hydrogen bonding cross-linking between acrylic acid and polyamic acid and the polymerization of acrylic acid itself to enhance the mechanical properties of the gel fiber, and further guides the gel molding of the gel fiber and the formation of a porous structure by the interpenetration of the long molecular chain of polyethylene glycol and the hydrophobic effect of the cationic active agent.

[0033] (2) Under the conditions of combining coagulation bath gelation and light curing, the interpenetrating cross-linked network formed in the present invention stabilizes the porous structure of the primary gel fiber when the porous structure has not yet fully shrunk or collapsed, thereby enhancing the mechanical properties of the gel fiber, facilitating subsequent stretching treatment, and avoiding structural collapse during drying, giving the polyimide aerogel fiber excellent mechanical properties and high porosity, which can be used to prepare flexible thermal insulation materials. DETAILED DESCRIPTION

[0034] 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.

[0035] Example 1

[0036] Preparation of polyimide aerogel fibers:

[0037] Step 1: Synthesize polyamic acid solution:

[0038] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0039] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 3wt%, the mass proportion of polyethylene glycol is 2wt%, the mass proportion of photoinitiator 2959 is 0.5wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.2wt%.

[0040] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0041] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0042] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0043] Example 2

[0044] The only difference from Example 1 is that the mass proportion of acrylic acid in the spinning solution is increased from 3 wt % to 4 wt %, and the mass proportion of photoinitiator 2959 is increased from 0.5 wt % to 0.7 wt %.

[0045] Preparation of polyimide aerogel fibers:

[0046] Step 1: Synthesize polyamic acid solution:

[0047] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0048] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 4wt%, the mass proportion of polyethylene glycol is 2wt%, the mass proportion of photoinitiator 2959 is 0.7wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.2wt%.

[0049] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0050] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0051] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0052] Example 3

[0053] The only difference from Example 1 is that the mass proportion of acrylic acid in the spinning solution is increased from 3 wt % to 5 wt %, and the mass proportion of photoinitiator 2959 is increased from 0.5 wt % to 0.8 wt %.

[0054] Preparation of polyimide aerogel fibers:

[0055] Step 1: Synthesize polyamic acid solution:

[0056] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0057] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 5wt%, the mass proportion of polyethylene glycol is 2wt%, the mass proportion of photoinitiator 2959 is 0.8wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.2wt%.

[0058] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0059] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0060] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0061] Example 4

[0062] The only difference from Example 2 is that the mass proportion of polyethylene glycol is adjusted from 2 wt % to 3 wt %.

[0063] Preparation of polyimide aerogel fibers:

[0064] Step 1: Synthesize polyamic acid solution:

[0065] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0066] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 4wt%, the mass proportion of polyethylene glycol is 3wt%, the mass proportion of photoinitiator 2959 is 0.7wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.2wt%.

[0067] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0068] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0069] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0070] Example 5

[0071] The only difference from Example 2 is that the mass proportion of polyethylene glycol is adjusted from 2 wt % to 4 wt %.

[0072] Preparation of polyimide aerogel fibers:

[0073] Step 1: Synthesize polyamic acid solution:

[0074] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0075] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 4wt%, the mass proportion of polyethylene glycol is 4wt%, the mass proportion of photoinitiator 2959 is 0.7wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.2wt%.

[0076] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0077] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0078] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0079] Example 6

[0080] The only difference from Example 4 is that the mass proportion of hexadecyltrimethylammonium bromide is increased from 0.2 wt % to 0.5 wt %.

[0081] Preparation of polyimide aerogel fibers:

[0082] Step 1: Synthesize polyamic acid solution:

[0083] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0084] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 4wt%, the mass proportion of polyethylene glycol is 3wt%, the mass proportion of photoinitiator 2959 is 0.7wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.5wt%.

[0085] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0086] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0087] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0088] Example 7

[0089] The only difference from Example 4 is that the mass proportion of cetyltrimethylammonium bromide is increased from 0.2 wt % to 0.6 wt %.

[0090] Preparation of polyimide aerogel fibers:

[0091] Step 1: Synthesize polyamic acid solution:

[0092] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0093] Step 2: Add acrylic acid, polyethylene glycol, photoinitiator 2959, and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the mass proportion of acrylic acid is 4wt%, the mass proportion of polyethylene glycol is 3wt%, the mass proportion of photoinitiator 2959 is 0.7wt%, and the mass proportion of cetyltrimethylammonium bromide is 0.6wt%.

[0094] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0095] Step 4: Expose the pre-gel fiber to UV light for curing, setting the light power to 15mW / cm 2 , the continuous curing time is 1 minute to form gel fiber.

[0096] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the gel fiber under constant temperature and allow imidization to react for 8 hours. The imidized fiber is stretched by drafting rollers at a draw ratio of 3. The stretched fiber is placed in ethanol and allowed to stand for 8 hours. It is then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fiber is dried using supercritical CO2 to obtain polyimide aerogel fiber with a fiber diameter of 10-30 μm.

[0097] Comparative Example 1

[0098] The only difference from Example 1 is that in this comparative example, no acrylic acid and photoinitiator are added to the spinning solution, and the primary gel fiber is not subjected to UV curing treatment.

[0099] Preparation of polyimide aerogel fibers:

[0100] Step 1: Synthesize polyamic acid solution:

[0101] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0102] Step 2: Add polyethylene glycol and cetyltrimethylammonium bromide (CTAB) to the polyamic acid solution and mix to form a spinning solution. In the spinning solution, the weight proportion of polyethylene glycol is 2 wt%, and the weight proportion of cetyltrimethylammonium bromide is 0.2 wt%.

[0103] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0104] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the pregel fibers under constant temperature and allow imidization to react for 8 hours. The imidized fibers are stretched by drafting rollers at a stretching ratio of 3. The stretched fibers are placed in ethanol and allowed to stand for 8 hours. They are then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fibers are dried using supercritical CO2 to obtain polyimide aerogel fibers with a fiber diameter of 10-30 μm.

[0105] Comparative Example 2

[0106] The only difference from Example 1 is that in this comparative example, polyimide aerogel fibers are directly prepared from a polyamic acid solution.

[0107] Preparation of polyimide aerogel fibers:

[0108] Step 1: Synthesize polyamic acid solution:

[0109] N-methylpyrrolidone was added to the flask, and pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) were prepared and added to the flask at a molar ratio of 1:1. The mixture was stirred and reacted at room temperature for 6 hours. After the reaction, a polyamic acid solution with a solid content of 15 wt% was obtained.

[0110] Step 2: Degassing the polyamic acid solution to obtain a spinning solution.

[0111] Step 3: Prepare a coagulation bath by mixing N-methylpyrrolidone and water in a volume ratio of 2:8, adding ammonium sulfate at a mass concentration of 1 wt%, and stirring until the ammonium sulfate is completely dissolved. The spinning solution obtained in Step 2 is placed in a wet spinning machine, and the spinning solution is extruded from the spinneret orifice into the coagulation bath to form a pre-gel fiber.

[0112] Step 5: Prepare a mixture of acetic anhydride and pyridine in a 1:1 volume ratio. Add triethylamine to the mixture at a concentration of 0.5 wt%. Stir and mix, then heat to 65°C. Add the pregel fibers under constant temperature and allow imidization to react for 8 hours. The imidized fibers are stretched by drafting rollers at a stretching ratio of 3. The stretched fibers are placed in ethanol and allowed to stand for 8 hours. They are then transferred to tert-butyl alcohol and allowed to stand for 8 hours. After solvent replacement, the fibers are dried using supercritical CO2 to obtain polyimide aerogel fibers with a fiber diameter of 10-30 μm.

[0113] The performance of the polyimide aerogel fibers prepared in Examples 1 to 7 and Comparative Examples 1 to 2 was tested, and the results are shown in Table 1:

[0114] Table 1

[0115] project Elongation at break % Porosity% Breaking strength MPa Thermal conductivity W / (m·K) Example 1 21 92 730 0.029 Example 2 26 96 826 0.022 Example 3 27 95 860 0.024 Example 4 25 98 801 0.018 Example 5 22 95 764 0.023 Example 6 29 99 895 0.014 Example 7 28 97 890 0.020 Comparative Example 1 11 87 320 0.036 Comparative Example 2 9 76 283 0.040

[0116] As can be seen from Table 1, the polyimide gel fiber prepared in the embodiment of the present invention is based on the synergistic effect of each component and the process coordination. The primary gel fiber stabilizes the internal pore structure through photocuring and further improves the mechanical properties through the subsequent stretching process. While ensuring that the polyimide aerogel fiber has excellent mechanical properties, the high porosity of the fiber improves its thermal insulation performance.

[0117] 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.

[0118] 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 polyimide aerogel fiber, characterized in that: The following steps are involved: Step 1, synthesizing a polyamic acid solution with a solid content of 15-20 wt%; Step 2: adding acrylic acid, polyethylene glycol, a photoinitiator and a cationic surfactant to a polyamic acid solution and mixing to form a spinning solution; Step 3: After wet spinning, the spinning solution enters a coagulation bath to form a primary gel fiber; Step 4: Curing the primary gel fiber with ultraviolet light to form gel fiber; Step 5: The gel fiber is subjected to chemical imidization treatment and then stretched, and then the solvent is replaced and supercritical CO2 dried to obtain the polyimide aerogel fiber.

2. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The mass percentage of the acrylic acid in the spinning solution is 3-5 wt %.

3. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The mass percentage of the polyethylene glycol in the spinning solution is 2-4 wt%.

4. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The photoinitiator is photoinitiator 2959, and the mass proportion of the photoinitiator in the spinning solution is 0.5-1 wt%.

5. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The cationic surfactant is at least one of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide, and the mass proportion of the cationic surfactant in the spinning solution is 0.2-0.6 wt%.

6. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The coagulation bath comprises a polar organic solvent, water and ammonium sulfate, wherein the volume proportion of the polar organic solvent in the coagulation bath is 20-40%, and the mass proportion of the ammonium sulfate is 1-2 wt%; The polar organic solvent is one of NMP, DMF and DMAC.

7. The method for preparing a polyimide aerogel fiber according to claim 1, wherein: The steps of the solvent replacement are as follows: The stretched fiber is placed in ethanol and allowed to stand for 6-8 hours, and then transferred to tert-butanol and allowed to stand for 6-8 hours.

8. A polyimide aerogel fiber, characterized in that: The polyimide aerogel fiber is prepared by the preparation method according to any one of claims 1 to 8.

9. The polyimide aerogel fiber according to claim 8, characterized in that: The diameter of the polyimide aerogel fiber is 10-30 μm.

10. An application of polyimide aerogel fiber, characterized in that: The polyimide aerogel fiber prepared by the preparation method according to any one of claims 1 to 8 is used to prepare flexible thermal insulation materials.