Aramid nanofiber aerogel phase change composite material and a preparation method thereof

Abstract

This invention relates to an aramid nanofiber aerogel phase change composite material and its preparation method. The method involves: preparing an aramid nanofiber dispersion using a mixed solution containing dimethyl sulfoxide, an alkali, and isopropanol; casting the aramid nanofiber dispersion into a mold and subjecting it to ultrasonic treatment; then sequentially placing it in a protic acid solution and deionized water for gelation to obtain a wet gel; subjecting the wet gel to solvent replacement, pre-freezing, and vacuum freeze-drying to obtain an aramid nanofiber aerogel; and then vacuum impregnating the aramid nanofiber aerogel in a phase change material solution, followed by pre-freezing and vacuum freeze-drying to obtain the aramid nanofiber aerogel phase change composite material. This invention, through structural design and process control, achieves a synergistic improvement in mechanical reinforcement, efficient heat storage, and thermal insulation performance, resulting in a novel high-strength aerogel phase change composite material that combines energy storage and thermal insulation.

Description

Technical Field

[0001] This invention belongs to the field of aerogel phase change composite material technology, and particularly relates to an aramid nanofiber aerogel phase change composite material and its preparation method. Background Technology

[0002] Aramid nanofiber aerogels possess characteristics such as low density, high porosity, high toughness, and temperature resistance with flame retardancy, showing great potential for future applications in flame-retardant and heat-insulating applications for low-altitude aircraft. However, at present, the pore size of aramid nanofiber aerogels is relatively large, and their thermal insulation performance needs further improvement.

[0003] To improve the thermal insulation performance of aramid nanofiber aerogels, researchers have attempted to enhance the material's insulation properties by controlling the concentration of aramid nanofibers. However, increasing the concentration of the aramid nanofiber solution is limited, and excessively high concentrations are difficult to prepare. Furthermore, researchers have used composite inorganic silica aerogels to improve the material's thermal insulation performance. However, due to the excessively large pore size of the nanofiber aerogel, the introduction of silica aerogels resulted in severe powder shedding. Additionally, the introduction of the inorganic network increased the material's stiffness but decreased its flexibility, still failing to meet application requirements. There is an urgent need to find new design strategies to control the pore size of the nanofibers and the flexibility of the aerogel to improve the material's thermal insulation performance.

[0004] Currently, phase change materials (PCMs) have shown clear application potential in the fields of thermal energy storage and temperature control. PCMs possess latent heat storage properties, enabling them to maintain a constant temperature at a specific phase transition temperature when the ambient temperature changes. Temperature control is achieved through heat exchange during the phase transition process, thus attracting widespread attention. However, PCMs often face problems in practical applications such as leakage, shape instability, and thermal conductivity mismatch. Although porous materials have been extensively studied as carriers, existing carrier materials often struggle to achieve long-term stable encapsulation and efficient thermal management of PCMs while maintaining high porosity and structural strength. Particularly for aramid nanofiber aerogels, how to control their microstructure to meet both high mechanical and thermal insulation requirements while also adapting to the load and leakage prevention issues of PCMs remains a technical problem requiring further exploration.

[0005] In summary, it is essential to provide an aramid nanofiber aerogel phase change composite material and its preparation method. Summary of the Invention

[0006] To address one or more technical problems existing in the prior art, this invention provides an aramid nanofiber aerogel phase change composite material and its preparation method.

[0007] The present invention provides a method for preparing an aramid nanofiber aerogel phase change composite material in a first aspect, the method comprising the following steps: (1) Aramid fibers were prepared into an aramid nanofiber dispersion using a mixed solution containing dimethyl sulfoxide, alkali and isopropanol; (2) The aramid nanofiber dispersion was poured into a mold and ultrasonically treated, and then placed in a protic acid solution and deionized water in sequence to gel, thus obtaining a wet gel. (3) The wet gel was subjected to solvent replacement, pre-freezing and vacuum freeze-drying to obtain aramid nanofiber aerogel; (4) The aramid nanofiber aerogel was placed in a phase change material solution for vacuum impregnation, and then pre-frozen and vacuum freeze-dried to obtain the aramid nanofiber aerogel phase change composite material.

[0008] Preferably, the aramid nanofiber dispersion contains 1-6% by mass of aramid nanofibers and / or alkali; and / or the mixed solution contains 1-6% by mass of isopropanol.

[0009] Preferably, the ultrasonic treatment time is 0.25~0.75h.

[0010] Preferably, the protic acid in the protic acid solution is one or more of formic acid, acetic acid, and HCl; and / or the concentration of the protic acid solution is 20-99 wt%.

[0011] Preferably, the gelation time in the protic acid solution is 10s to 5min; and / or the gelation time in deionized water is 8 to 16h.

[0012] Preferably, the solvent replacement is performed using an aqueous solution of tert-butanol. More preferably, the aqueous solution of tert-butanol is prepared by mixing tert-butanol and deionized water at a volume ratio of 1:(0.8~1.2); and / or the solvent replacement is performed multiple times, preferably 8 to 10 times, with each solvent replacement lasting no less than 8 hours.

[0013] Preferably, in step (3) and / or step (4), the pre-freezing is performed at -50℃ to -70℃ for 6 to 10 hours; and / or in step (3) and / or step (4), the vacuum freeze-drying is performed at a cold trap temperature of -50℃ to -70℃ and a vacuum of 1 to 10 Pa, and the drying procedure of the vacuum freeze-drying is to first dry at a temperature of -10℃ to -30℃ for 20 to 30 hours, and then dry at 10 to 20℃ for 5 to 10 hours.

[0014] Preferably, the vacuum impregnation is carried out under a vacuum of -0.08 to -0.1 MPa, the vacuum impregnation temperature is 30 to 90°C, and the vacuum impregnation time is 4 to 12 hours.

[0015] Preferably, the phase change material solution contains one or more of D-mannitol, erythritol, inositol, sorbitol, xylitol, maltitol, neopentyl glycol, polyethylene glycol, and pentaerythritol; and / or the concentration of the phase change material solution is 1-20 wt%, preferably 10-20 wt%.

[0016] The present invention provides, in a second aspect, an aramid nanofiber aerogel phase change composite material prepared by the preparation method described in the first aspect of the present invention.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention achieves a synergistic improvement in the mechanical and thermal properties of aramid nanofiber aerogel phase change material through a strategy of proton donor regulation and porous framework confinement of the phase change material. By employing a strategy of using proton donors to regulate the reprotonation process of aramid nanofibers, the pore size of the aramid nanofiber aerogel is effectively controlled, forming a grapefruit peel-inspired structure. This structure not only significantly improves the mechanical properties of the material but also provides crucial structural confinement for the loading and leakage prevention of the phase change material. The porous framework, through its precisely regulated pore structure, can effectively adsorb and encapsulate the phase change material, preventing leakage during the phase change process. Furthermore, the optimized pore size and pore distribution, after loading the phase change material, utilize the endothermic / exothermic properties of the phase change material during the phase change process to synergistically construct a multi-scale thermal management system combining dynamic temperature regulation and insulation with the aerogel framework. By confining the intermediate-temperature phase change material within the porous framework of the aramid nanofiber aerogel, the heating rate is slowed down, and the steady-state temperature is reduced. Furthermore, if the structure of the aramid nanofiber aerogel is not properly controlled, the pore structure may be overfilled or destroyed when loaded with phase change materials, thereby weakening the dynamic temperature regulation contribution of the phase change material and potentially reducing the thermal insulation performance of the composite material due to damage to the integrity of the skeleton. Therefore, this invention achieves a synergistic improvement in mechanical reinforcement, dynamic heat storage, and thermal insulation performance through structural design and process control, resulting in a novel high-strength aerogel phase change composite material with both energy storage and thermal insulation functions. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments thereof. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] The present invention provides a method for preparing an aramid nanofiber aerogel phase change composite material in a first aspect, the method comprising the following steps: (1) Aramid fibers are prepared into an aramid nanofiber dispersion using a mixed solution containing dimethyl sulfoxide (DMSO), an alkali, and isopropanol; in this invention, the alkali is, for example, potassium hydroxide and / or sodium hydroxide; preferably, the mixed solution is composed of dimethyl sulfoxide (DMSO), potassium hydroxide, and isopropanol, denoted as a DMSO / KOH / isopropanol mixed solution; in this invention, for example, a certain amount of aramid fibers is weighed and placed in the DMSO / KOH / isopropanol mixed solution, and mechanically stirred until the solution turns dark red to obtain an aramid nanofiber dispersion. In this process, the alkali (e.g., KOH) / DMSO system is used to deprotonate the amide bonds in the aramid molecular chain, thereby making the aramid nanofiber dispersion more aramid. The aramid fibers gradually dissociate into nanoscale fibers and are uniformly dispersed in the mixed solution. Preferably, the selected aramid fibers are chopped fibers with a length of 3-6 mm and a diameter of 10-15 μm. Aramid fibers within this size range can fully dissociate during mechanical stirring and deprotonation, which is beneficial for forming a uniform and stable aramid nanofiber dispersion. The present invention does not specifically limit the conditions of the mechanical stirring, and those skilled in the art can choose conventionally. In the present invention, the speed of the mechanical stirring can be, for example, 800-1000 r / min. In the present invention, for operations without specific temperature limitations, all are carried out at room temperature (e.g., room temperature 15-35°C). (2) The aramid nanofiber dispersion is poured into a mold and subjected to ultrasonic treatment, and then placed in a protic acid solution and deionized water in sequence for gelation to obtain a wet gel. In this invention, the aramid nanofiber dispersion is poured into an open mold (a mold without a top cover), and then the aramid nanofiber dispersion in the mold is subjected to ultrasonic treatment immediately. After ultrasonic treatment, the entire mold is immersed in a protic acid solution in sequence to make the sol surface gel rapidly. After the surface gel is formed, an initial wet gel is obtained. The mold and the initial wet gel are then transferred to deionized water for gelation for 8-16 hours to complete the gelation of the system and obtain the wet gel. This invention does not make a specific limitation on the gelation time in the protic acid solution. Those skilled in the art can choose conventionally, for example, 10s-5min. This invention does not make a specific limitation on the power and frequency conditions of the ultrasonic treatment. Those skilled in the art can choose conventionally, for example, the frequency of the ultrasonic treatment is 20-40kHz, and the power is, for example, 200-400W. (3) The wet gel is subjected to solvent replacement, pre-freezing and vacuum freeze-drying to obtain aramid nanofiber aerogel; In this invention, for example, the wet gel is subjected to multiple solvent replacements, and then pre-freezing and vacuum freeze-drying to obtain high-strength aramid nanofiber aerogel. (4) The aramid nanofiber aerogel is placed in a phase change material solution for vacuum impregnation, and then pre-freezing and vacuum freeze-drying are performed to obtain the aramid nanofiber aerogel phase change composite material; the present invention uses a phase change material with high latent heat characteristics to load the aramid nanofiber aerogel to obtain the aramid nanofiber aerogel phase change composite material.

[0020] This invention achieves a synergistic improvement in the mechanical and thermal properties of aramid nanofiber aerogel phase change material through a strategy of proton donor regulation and porous framework confinement of the phase change material. By employing a strategy of using proton donors to regulate the reprotonation process of aramid nanofibers, the pore size of the aramid nanofiber aerogel is effectively controlled, forming a grapefruit peel-inspired structure. This structure not only significantly improves the mechanical properties of the material but also provides crucial structural confinement for the loading and leakage prevention of the phase change material. The porous framework, through its precisely regulated pore structure, can effectively adsorb and encapsulate the phase change material, preventing leakage during the phase change process. Furthermore, the optimized pore size and pore distribution, after loading the phase change material, utilize the endothermic / exothermic properties of the phase change material during the phase change process to synergistically construct a multi-scale thermal management system combining dynamic temperature regulation and insulation with the aerogel framework. By confining the intermediate-temperature phase change material within the porous framework of the aramid nanofiber aerogel, the heating rate is slowed down, and the steady-state temperature is reduced. Furthermore, if the structure of the aramid nanofiber aerogel is not properly controlled, the pore structure may be overfilled or destroyed when loaded with phase change materials, thereby weakening the dynamic temperature regulation contribution of the phase change material and potentially reducing the thermal insulation performance of the composite material due to damage to the integrity of the skeleton. Therefore, this invention achieves a synergistic improvement in mechanical reinforcement, dynamic heat storage, and thermal insulation performance through structural design and process control, resulting in a novel high-strength aerogel phase change composite material with both energy storage and thermal insulation functions.

[0021] In step (2) of this invention, ultrasonic treatment was performed before gelation after casting. This is crucial for obtaining a aramid nanofiber aerogel phase change composite material with uniform structure and excellent performance. This ultrasonic treatment helps to disperse any agglomerates that may exist in the aramid nanofiber dispersion and to redistribute them in a highly uniform manner in three-dimensional space. This results in the formation of an ideal wet gel skeleton with narrow pore size distribution, strong network connection, and uniform overall structure during the subsequent gelation process. This invention found that if this ultrasonic treatment is not performed and gelation is carried out directly, it will lead to uneven fiber dispersion and local agglomeration areas will crosslink too quickly under acid induction to form dense clumps. This structural inhomogeneity will cause a decrease in the mechanical strength and an increase in brittleness of the aerogel on a macroscopic level. On a microscopic level, it will lead to structural defects. Furthermore, the uneven pores will cause uneven distribution of the subsequently loaded phase change material, affecting the dynamic temperature regulation performance and potentially exacerbating the risk of phase change material leakage due to stress concentration during cyclic applications. In addition, the large pore defects that may exist may also weaken the overall thermal insulation effect of the material.

[0022] According to some preferred embodiments, the aramid nanofiber dispersion contains 1-6% (mass percentage) of aramid nanofibers and / or alkali (e.g., 1%, 2%, 3%, 4%, 5%, or 6%). In this invention, it is preferred that the aramid nanofiber dispersion contains 1-6% of aramid nanofibers. If the mass fraction of aramid nanofibers is too low, the aramid gel is too weak, and the nanofiber entanglement is insufficient, which is not conducive to strength improvement. If the mass fraction of aramid nanofibers is too high, the system viscosity is too high, which is also not conducive to the preparation of the aramid nanofiber dispersion.

[0023] According to some preferred embodiments, the mixed solution contains 1-6% (e.g., 1%, 2%, 3%, 4%, 5%, or 6%) of isopropanol. In this invention, it is preferred to use a mixed solution formed by adding a small amount of isopropanol to dimethyl sulfoxide as a dispersant to disperse aramid fibers. This invention has found that when preparing high-concentration aramid nanofiber dispersions, the system viscosity is high and the preparation time is long. Adding an appropriate amount of isopropanol can utilize its hydroxyl groups to promote more effective dissociation of aramid fibers in a DMSO / KOH environment, thereby accelerating the formation of a uniform aramid nanofiber dispersion. If only dimethyl sulfoxide is used… Aramid fibers have low dissociation efficiency, excessively high dispersion viscosity, and excessively long preparation time, which are not conducive to efficient preparation. If only isopropanol is used, its dissociation ability on aramid fibers is insufficient, and it cannot effectively prepare aramid nanofiber dispersions. In addition, the amount of isopropanol added needs to be controlled within a suitable range. The mass fraction of isopropanol in the mixed solution is preferably 1~6%. If the isopropanol content is too high, it will cause fiber agglomeration in the aramid nanofiber dispersion, affecting the dispersion uniformity and the subsequent formation of the three-dimensional network structure. This will result in coarse aerogel pore structure, deterioration of mechanical properties, and affect its load on phase change materials and the overall performance of composite materials.

[0024] According to some preferred embodiments, the ultrasonic treatment time is 0.25~0.75h (e.g. 0.25, 0.5 or 0.75h).

[0025] According to some preferred embodiments, the protic acid solution contains one or more of formic acid, acetic acid, and HCl; and / or the concentration of the protic acid solution is 20-99 wt% (e.g., 20, 30, 40, 50, 60, 70, 80, 90, or 99 wt%). In this invention, the protic acid solution is an aqueous solution of protic acid, and the concentration refers to the mass percentage of protic acid contained in the protic acid solution being 20-99 wt%.

[0026] According to some preferred embodiments, the gelation time in the protic acid solution is 10s to 5min (e.g., 10s, 60s, 1min, 2min, 3min, 4min or 5min); and / or the gelation time in deionized water is 8 to 16h (e.g., 8, 10, 12, 14 or 16h).

[0027] According to some preferred embodiments, the solvent replacement is performed using a tert-butanol aqueous solution. Preferably, the tert-butanol aqueous solution is prepared by mixing tert-butanol and deionized water at a volume ratio of 1:(0.8~1.2). In this invention, it is preferred that the solvent replacement is performed using a tert-butanol aqueous solution, which is prepared by mixing tert-butanol and deionized water at a volume ratio of 1:(0.8~1.2). Using this tert-butanol aqueous solution for solvent replacement can effectively reduce the surface tension between the solvent and the wet gel skeleton, and effectively inhibit excessive ice crystal growth during the subsequent freeze-drying process, thereby obtaining an aramid nanofiber aerogel structure with smaller pore size and more uniform distribution. In contrast, if only deionized water is used for solvent replacement, the high surface tension of water makes it easy to form large ice crystals during freeze-drying, resulting in aerogels with larger pore sizes and looser structures. If only tert-butanol is used for solvent replacement, the relatively high freezing point of pure tert-butanol makes it easy to crystallize and precipitate at room temperature, making it difficult for the solvent replacement process to proceed uniformly in the liquid phase. At the same time, pure tert-butanol has insufficient affinity for aramid nanofibers, which can easily cause fiber aggregation and shrinkage of the three-dimensional network structure, or even partial collapse of the pores, making it difficult to obtain an aerogel skeleton with a uniform structure and intact pores. Therefore, this invention uses an aqueous solution of tert-butanol for solvent replacement, which utilizes the advantage of tert-butanol in reducing surface tension, and maintains the system's low freezing point and excellent affinity with aramid nanofibers through the presence of water. This is beneficial for obtaining a uniform aramid nanofiber aerogel skeleton with excellent mechanical properties, and also for improving the loading and dynamic temperature regulation performance (thermal storage and temperature regulation performance) of the phase change material; and / or the solvent replacement is performed multiple times, with the number of solvent replacements being 8 to 10 times (e.g., 8, 9, or 10 times), and the time for each solvent replacement is not less than 8 hours.

[0028] According to some preferred embodiments, in step (3) and / or step (4), the pre-freezing is pre-freezing at -50℃ to -70℃ for 6 to 10 hours; and / or in step (3) and / or step (4), the vacuum freeze-drying is carried out at a cold trap temperature of -50℃ to -70℃ and a vacuum of 1 to 10 Pa, and the drying procedure of the vacuum freeze-drying is to first dry at a temperature of -10℃ to -30℃ for 20 to 30 hours, and then dry at 10 to 20℃ for 5 to 10 hours.

[0029] According to some preferred embodiments, in step (3) and / or step (4), the pre-freezing is gradient pre-freezing, which is to first cool down to -20 to -40°C at a cooling rate of 0.1 to 0.5°C / min and pre-freeze for 3 to 5 hours, and then cool down to -50 to -70°C at a cooling rate of 3 to 5°C / min and pre-freeze for 3 to 5 hours.

[0030] In this invention, the pre-freezing in step (3) and / or step (4) is preferably gradient pre-freezing; this invention finds that the gradient pre-freezing process can more precisely control the growth process of ice crystals, thereby obtaining an aramid nanofiber aerogel skeleton with more uniform pore size distribution, denser structure and better mechanical properties after vacuum freeze-drying; this optimized porous network not only has excellent thermal insulation properties, but also lays a better structural foundation for the efficient and uniform loading of subsequent phase change materials; in step (4), the gradient pre-freezing process is used on the aramid nanofiber aerogel after loading phase change materials, which is also beneficial to prevent leakage of phase change materials. The possible reason is: initially Slow cooling (0.1~0.5℃ / min) induces the solvent in the solution to form a large number of fine and uniform ice crystals, allowing the phase change material to be uniformly dispersed in the aerogel skeleton. Subsequent rapid cooling (3~5℃ / min) inhibits excessive ice crystal growth and avoids the formation of localized phase change material enrichment or large-sized crystalline regions. This uniform and refined distribution not only helps to ensure the overall thermal insulation performance of the material, but also enhances the physical binding and interfacial forces between the phase change material and the aramid nanofiber skeleton, making the phase change material more effectively "anchored" in the porous skeleton. This reduces leakage during repeated use and improves the long-term structural stability and functional reliability of the composite material.

[0031] According to some preferred embodiments, the vacuum impregnation is carried out under a vacuum of -0.08 to -0.1 MPa, the vacuum impregnation temperature is 30 to 90°C (e.g., 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or 90°C), and the vacuum impregnation time is 4 to 12 hours (e.g., 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours).

[0032] According to some preferred embodiments, the phase change material solution contains one or more of D-mannitol, erythritol, inositol, sorbitol, xylitol, maltitol, neopentyl glycol, polyethylene glycol, and pentaerythritol; in this invention, the phase change material solution is, for example, an aqueous solution of the phase change material, composed of the phase change material and water; and / or the concentration of the phase change material solution is 1~20wt% (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20wt%), preferably 10~20wt%, which refers to the mass percentage of the phase change material contained in the phase change material solution.

[0033] In this invention, preferably, the concentration of the phase change material solution is 1~20wt%, more preferably 10~20wt%, and the aforementioned polyol-based phase change materials are selected. This concentration range matches the solubility characteristics of the selected phase change materials and the subsequent vacuum impregnation process, ensuring that the phase change material solution has suitable fluidity and permeability, allowing it to fully penetrate into the nanoscale pore network of the aramid nanofiber aerogel under vacuum conditions, achieving efficient and uniform loading. It also enables the loaded aerogel phase change composite material to have high energy storage density and stable shape support structure during the phase change process. The selected polyol-based phase change materials typically have suitable phase change temperature, high phase change enthalpy, and good chemical stability, and good compatibility with the aramid nanofiber skeleton, which is beneficial for forming a stable composite system. This invention reveals that if the concentration of the phase change material solution is too low, the effective components of the phase change material solution are too few. Even with complete impregnation, the actual loading in the aerogel pores is too low, resulting in a significant deficiency in the phase change energy storage capacity of the final aerogel phase change composite material and limited improvement in dynamic temperature regulation performance. If the concentration is too high, the loading of the phase change material after impregnation will be too high, causing the aramid nanofiber aerogel phase change composite material obtained after freeze-drying to become brittle and significantly reduce its flexibility.

[0034] According to some specific embodiments, the preparation of the aramid nanofiber aerogel phase change composite material includes: ① First, weigh out aramid fibers of the same mass as KOH and place them in a mixed solution of DMSO / KOH / isopropanol. Stir mechanically until the solution turns dark red to obtain an aramid nanofiber dispersion. Preferably, the mass fraction of isopropanol in the mixed solution is 1%~6%. Preferably, the mass fraction of aramid nanofibers in the aramid nanofiber dispersion is 1%~6%.

[0035] ② The above-mentioned aramid nanofiber dispersion is poured into a mold (without a top cover) and ultrasonically treated; preferably, ultrasonic treatment is performed for 0.25h~0.75h; the mold is placed in a protic acid solution to allow the surface of the sol system to rapidly gel, obtaining an initial wet gel; preferably, the concentration of the protic acid solution is 20~99wt%; the protic acid solution can provide more protons to densify the surface of the nanofiber skeleton; then the initial wet gel is placed in a deionized solution to complete the gelation of the system, obtaining a wet gel.

[0036] ③ The above wet gel was placed in an aqueous solution of tert-butanol and subjected to nine solvent replacements, with each solvent replacement lasting no less than 8 hours. After pre-freezing and vacuum freeze-drying, a high-strength aramid nanofiber aerogel was obtained.

[0037] ④ The above-mentioned aramid nanofiber aerogel is placed in an aqueous solution of phase change material and vacuum impregnated; preferably, the vacuum impregnation temperature is 30~90℃ and the time is 4~12h; then, after pre-freezing and vacuum freeze-drying, a high-strength aramid nanofiber aerogel phase change composite material is obtained.

[0038] The present invention provides, in a second aspect, an aramid nanofiber aerogel phase change composite material prepared by the preparation method described in the first aspect of the present invention.

[0039] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments. The present invention may have many other embodiments, and those skilled in the art can make various corresponding changes and modifications based on the present invention without departing from its spirit and essence. However, all such corresponding changes and modifications should fall within the scope of protection of the appended claims. Unless otherwise specified, the experimental methods used in the following embodiments and comparative examples are conventional methods. Unless otherwise specified, the materials used in the following embodiments and comparative examples are commercially available.

[0040] Example 1 (1) Weigh 2g of aramid fiber (the length of aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 2g of alkali (KOH) and 88g of dimethyl sulfoxide (DMSO) evenly.

[0041] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.75h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0042] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0043] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 20wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 70℃ and the vacuum impregnation time is 9h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0044] Example 2 (1) Weigh 1.5g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94.5g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 1.5g of alkali (KOH) and 89g of dimethyl sulfoxide (DMSO) evenly.

[0045] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.5h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0046] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0047] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a D-mannitol aqueous solution with a concentration of 18wt% and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 70℃ and the vacuum impregnation time is 8h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0048] Example 3 (1) Weigh 1g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 95g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 1g of alkali (KOH) and 90g of dimethyl sulfoxide (DMSO) evenly.

[0049] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.25h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0050] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0051] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 15wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 70℃ and the vacuum impregnation time is 7h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0052] Example 4 (1) Weigh 3g of aramid fiber (the length of aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 95g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 2g of isopropanol, 3g of alkali (KOH) and 90g of dimethyl sulfoxide (DMSO) evenly.

[0053] (2) Take 48g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.5h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into an acetic acid aqueous solution with a concentration of 80wt% to allow the sol surface to gel rapidly for 3min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0054] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0055] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 5wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 50℃ and the vacuum impregnation time is 8h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0056] Example 5 (1) Weigh 1.5g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 96.5g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 2g of isopropanol, 1.5g of alkali (KOH) and 93g of dimethyl sulfoxide (DMSO) evenly.

[0057] (2) Take 44g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.75h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into an acetic acid aqueous solution with a concentration of 85wt% to allow the sol surface to gel rapidly for 3min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0058] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0059] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 10wt% xylitol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 70℃ and the vacuum impregnation time is 9h. After impregnation, the aramid nanofiber aerogel impregnated with xylitol aqueous solution is taken out from the xylitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0060] Example 6 (1) Weigh 4g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 93g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 3g of isopropanol, 4g of alkali (KOH) and 86g of dimethyl sulfoxide (DMSO) evenly.

[0061] (2) Take 20g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.25h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 90wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0062] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0063] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 10wt% pentaerythritol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 90℃ and the vacuum impregnation time is 11h. After impregnation, the aramid nanofiber aerogel impregnated with pentaerythritol aqueous solution is taken out from the pentaerythritol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0064] Example 7 (1) Weigh 1.5g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 97.5g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 1g of isopropanol, 1.5g of alkali (KOH) and 95g of dimethyl sulfoxide (DMSO) evenly.

[0065] (2) Take 28g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.25h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 20wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 4min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0066] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0067] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 20wt% polyethylene glycol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 80℃ and the vacuum impregnation time is 10h. After impregnation, the aramid nanofiber aerogel impregnated with the polyethylene glycol aqueous solution is taken out from the polyethylene glycol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0068] Example 8 (1) Weigh 1.5g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 93.5g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 5g of isopropanol, 1.5g of alkali (KOH) and 87g of dimethyl sulfoxide (DMSO) evenly.

[0069] (2) Take 40g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.45h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 30wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 5min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0070] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0071] (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 10wt% erythritol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 80℃ and the vacuum impregnation time is 9h. After impregnation, the aramid nanofiber aerogel impregnated with the erythritol aqueous solution is taken out from the erythritol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0072] Example 9 Example 9 is basically the same as Example 1, except that: (1) Weigh 2g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 10g of isopropanol, 2g of alkali and 82g of dimethyl sulfoxide (DMSO) evenly.

[0073] Example 10 Example 10 is basically the same as Example 1, except that: (1) Weigh 10g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 10g of alkali (KOH) and 80g of dimethyl sulfoxide (DMSO) evenly.

[0074] Example 11 Example 11 is basically the same as Example 1, except that: (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 1 wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09 MPa. The vacuum impregnation temperature is 70°C and the vacuum impregnation time is 9 h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50°C for pre-freezing for 8 h. After pre-freezing, vacuum freeze-drying is carried out under a cold trap temperature of -55°C and a vacuum of 10 Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 h, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 h to obtain the aramid nanofiber aerogel phase change composite material.

[0075] Example 12 Example 12 is basically the same as Example 1, except that: (4) The aramid nanofiber aerogel obtained in step (3) is placed in a 30wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09MPa. The vacuum impregnation temperature is 70℃ and the vacuum impregnation time is 9h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution is taken out from the D-mannitol aqueous solution and then directly placed at -50℃ for pre-freezing for 8h. After pre-freezing, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20℃ for 24h, and then raise the temperature of the freeze dryer shelf to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain the aramid nanofiber aerogel phase change composite material.

[0076] Example 13 Example 13 is basically the same as Example 1, except that: (3) The wet gel obtained in step (2) is solvent-displaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent displacements. The solvent displacement is carried out at room temperature of 25°C and the time for each solvent displacement is 8h. Then, gradient pre-freezing is performed. After the gradient pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24h, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6h to obtain aramid nanofiber aerogel. The gradient pre-freezing is to first cool down to -30°C at a cooling rate of 0.3°C / min and pre-freeze for 3h, and then cool down to -60°C at a cooling rate of 3°C / min and pre-freeze for 5h.

[0077] (4) The aramid nanofiber aerogel obtained in step (3) was placed in a 20 wt% D-mannitol aqueous solution and vacuum impregnated under a vacuum of -0.09 MPa. The vacuum impregnation temperature was 70 °C and the vacuum impregnation time was 9 h. After impregnation, the aramid nanofiber aerogel impregnated with D-mannitol aqueous solution was removed from the D-mannitol aqueous solution and subjected to gradient pre-freezing. After gradient pre-freezing, the aerogel was subjected to a cold trap temperature of -55 °C and a vacuum of 10 Pa. The material is subjected to vacuum freeze drying. The drying procedure is as follows: first, the material is placed in a freeze dryer at a shelf temperature of -20°C for 24 hours; then, the shelf temperature is raised to 10°C at a heating rate of 3°C / min and dried at 10°C for 6 hours to obtain an aramid nanofiber aerogel phase change composite material. The gradient pre-freezing procedure is as follows: first, the material is cooled to -30°C at a cooling rate of 0.3°C / min and pre-frozen for 3 hours; then, the material is cooled to -60°C at a cooling rate of 3°C / min and pre-frozen for 5 hours.

[0078] Comparative Example 1 (1) Weigh 2g of aramid fiber (the length of aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 2g of alkali (KOH) and 88g of dimethyl sulfoxide (DMSO) evenly.

[0079] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.75h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0080] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0081] Comparative Example 2 (1) Weigh 1.5g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 94.5g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 1.5g of alkali (KOH) and 89g of dimethyl sulfoxide (DMSO) evenly.

[0082] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.5h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0083] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1) for 9 solvent replacements. The solvent replacement is carried out at room temperature of 25°C for 8 hours each time. Then it is directly placed at -50°C for 8 hours for pre-freezing. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24 hours, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6 hours to obtain aramid nanofiber aerogel.

[0084] Comparative Example 3 (1) Weigh 1g of aramid fiber (the length of the aramid fiber is 3~6mm and the diameter is 10~15μm) and place it in 95g of mixed solution. Stir mechanically until the solution turns dark red to obtain aramid nanofiber dispersion. The mixed solution is made by mixing 4g of isopropanol, 1g of alkali (KOH) and 90g of dimethyl sulfoxide (DMSO) evenly.

[0085] (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Sonicate for 0.25h. The frequency of the sonication is 40kHz and the power of the sonication is 200W. After sonication, place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2min to obtain an initial wet gel. Then, place the initial wet gel in deionized water for 12h to complete the gelation of the system and obtain a wet gel.

[0086] (3) The wet gel obtained in step (2) is solvent-replaced with tert-butanol aqueous solution (made by mixing tert-butanol and deionized water in a volume ratio of 1:1). The solvent replacement is performed 9 times, and the solvent replacement time is 8h each time. Then it is directly placed at -50℃ for pre-freezing for 8h. After the pre-freezing is completed, vacuum freeze-drying is performed under the conditions of cold trap temperature of -55℃ and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it at the shelf temperature of the freeze dryer at -20℃ for 24h, and then raise the shelf temperature of the freeze dryer to 10℃ at a heating rate of 3℃ / min and dry at 10℃ for 6h to obtain aramid nanofiber aerogel.

[0087] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that: (2) Take 24g of the aramid nanofiber dispersion obtained in step (1) and pour it into a mold (without a top cover). Place the mold containing the aramid nanofiber dispersion into a 95wt% acetic acid aqueous solution to allow the sol surface to gel rapidly for 2 minutes to obtain an initial wet gel. Then, place the initial wet gel into deionized water for 12 hours to complete the gelation of the system and obtain a wet gel.

[0088] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that: (3) The wet gel obtained in step (2) is subjected to solvent replacement with tert-butanol. The solvent replacement is carried out 9 times. The solvent replacement is carried out at 40°C and the time for each solvent replacement is 8h. Then, it is directly placed at -50°C for pre-freezing for 8h. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf at a temperature of -20°C for 24h, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6h to obtain aramid nanofiber aerogel.

[0089] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that: (3) The wet gel obtained in step (2) is solvent replaced with deionized water. The solvent replacement is carried out 9 times. The solvent replacement is carried out at room temperature of 25°C and the time for each solvent replacement is 8h. Then it is directly placed at -50°C for pre-freezing for 8h. After the pre-freezing is completed, vacuum freeze-drying is carried out under the conditions of cold trap temperature of -55°C and vacuum to 10Pa. The drying procedure of the vacuum freeze-drying is to first place it in the freeze dryer shelf temperature of -20°C for 24h, and then raise the temperature of the freeze dryer shelf to 10°C at a heating rate of 3°C / min and dry at 10°C for 6h to obtain aramid nanofiber aerogel.

[0090] The thermal insulation and mechanical properties of the materials finally prepared in each embodiment and comparative example of the present invention were tested, and the results are shown in Table 1. It can be seen that the comprehensive performance of the materials prepared in each embodiment of the present invention is much greater than that of the comparative examples. The present invention also tested the leakage prevention performance of the aramid nanofiber aerogel phase change composite materials prepared in each embodiment and comparative example, and the results are shown in Table 1. The leakage prevention performance of the aerogel phase change composite materials was characterized by the high-temperature filter paper / weighing method. The specific test method is as follows: the dry filter paper is pre-weighed (W1), and a certain mass (W) is taken. cThe aerogel phase change composite material sample was placed on it and put into a constant temperature oven 20°C above the melting point of the phase change material. After maintaining the temperature for a specified time (2 hours), it was removed and the filter paper contaminated with exudate was immediately weighed (W2). The leakage rate per unit mass of sample was calculated (the calculation formula is: leakage rate = (W2 - W1) / W). c The leakage rate (×100%) was used to quantitatively measure the material's leak-proof capability. A lower leakage rate indicates a better confinement and encapsulation effect of the aerogel porous framework on the phase change material, and superior shape stability and anti-percolation performance during the phase change process. This invention also tested the dynamic temperature regulation performance of the material. Each material (2 mm thick) was placed on a 300°C constant-temperature hot plate, and the temperature change of the sample's upper surface was continuously recorded using an infrared thermal imager. The time required for the sample's upper surface to heat up to 170°C and the final steady-state temperature were measured. The results are shown in Table 1.

[0091] Table 1: Performance of the Examples and Comparative Examples.

[0092] In Table 1, the symbol " / " indicates that the performance indicator was not tested or does not exist.

[0093] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an aramid nanofiber aerogel phase change composite material, characterized in that, The method includes the following steps: (1) Aramid fibers were prepared into an aramid nanofiber dispersion using a mixed solution containing dimethyl sulfoxide, alkali and isopropanol; (2) The aramid nanofiber dispersion was poured into a mold and ultrasonically treated, and then placed in a protic acid solution and deionized water in sequence to gel, thus obtaining a wet gel. (3) The wet gel was subjected to solvent replacement, pre-freezing and vacuum freeze-drying to obtain aramid nanofiber aerogel; (4) The aramid nanofiber aerogel was placed in a phase change material solution for vacuum impregnation, and then pre-frozen and vacuum freeze-dried to obtain the aramid nanofiber aerogel phase change composite material.

2. The preparation method according to claim 1, characterized in that: The aramid nanofiber dispersion contains aramid nanofibers and / or alkali at a mass fraction of 1-6%; and / or The mixed solution contains 1-6% isopropanol by mass.

3. The preparation method according to claim 1, characterized in that: The ultrasonic treatment time is 0.25~0.75h.

4. The preparation method according to claim 1, characterized in that: The protic acid solution contains one or more of formic acid, acetic acid, and HCl; and / or The concentration of the protic acid solution is 20~99wt%.

5. The preparation method according to claim 1, characterized in that: The gelation time in the protic acid solution is 10 s to 5 min; and / or The gelation time in deionized water is 8-16 hours.

6. The preparation method according to claim 1, characterized in that: The solvent replacement is performed using an aqueous solution of tert-butanol. Preferably, the aqueous solution of tert-butanol is prepared by mixing tert-butanol and deionized water at a volume ratio of 1:(0.8~1.2); and / or The solvent replacement is performed multiple times, preferably 8 to 10 times, with each solvent replacement lasting no less than 8 hours.

7. The preparation method according to claim 1, characterized in that: In step (3) and / or step (4), the pre-freezing is pre-freezing at -50℃ to -70℃ for 6 to 10 hours; and / or In step (3) and / or step (4), the vacuum freeze drying is carried out at a cold trap temperature of -50℃ to -70℃ and a vacuum of 1 to 10 Pa. The drying procedure of the vacuum freeze drying is to first dry at a temperature of -10℃ to -30℃ for 20 to 30 hours, and then dry at 10 to 20℃ for 5 to 10 hours.

8. The preparation method according to claim 1, characterized in that: The vacuum impregnation is carried out under a vacuum of -0.08 to -0.1 MPa, the vacuum impregnation temperature is 30 to 90°C, and the vacuum impregnation time is 4 to 12 hours.

9. The preparation method according to claim 1, characterized in that: The phase change material solution contains one or more of the following: D-mannitol, erythritol, inositol, sorbitol, xylitol, maltitol, neopentyl glycol, polyethylene glycol, and pentaerythritol; and / or The concentration of the phase change material solution is 1~20wt%, preferably 10~20wt%.

10. The aramid nanofiber aerogel phase change composite material prepared by any one of claims 1 to 9.

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