Composite shell phase-change microcapsule, phase-change aerogel composite thermal insulation material and preparation method of composite shell phase-change microcapsule and phase-change aerogel composite thermal insulation material

Abstract

The invention provides a composite shell phase change microcapsule, a phase change aerogel composite thermal insulation material and a preparation method thereof.The preparation method of the composite shell phase change microcapsule comprises the following steps that a phase change core material is heated to be molten and then stirred and ultrasonically mixed with an organic solvent containing a composite emulsifier to be uniform, and water-in-oil emulsion is obtained; adding the composite shell layer precursor solution into the water-in-oil emulsion, adjusting the pH value to carry out hydrolysis reaction, and then adjusting the pH value to carry out polycondensation reaction to obtain a core-shell structure microcapsule suspension; wherein a solute in the composite shell layer precursor solution comprises a silicon source and an inorganic reinforcing phase; and sequentially aging, washing and drying the core-shell structure microcapsule suspension to obtain the composite shell phase change microcapsule. After the composite shell layer phase change microcapsule is subjected to 50 times of severe phase change circulation, the leakage rate can be reduced to 2.2% or below, the phase change latent heat retention rate reaches up to 95% or above, and the composite shell layer phase change microcapsule shows excellent anti-leakage performance, circulation stability and wide temperature range applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a composite shell layer phase change microcapsule, a phase change aerogel composite thermal insulation material and a preparation method thereof. BACKGROUND

[0002] The phase change aerogel (PCM@Aerogel) is a composite functional material formed by loading a phase change material (PCM) on an aerogel matrix, which has two core characteristics: first, the nano-porous structure (pore size 20-50 nm) of the aerogel makes the thermal conductivity as low as 0.012-0.024 W / (m·K), which is much better than traditional thermal insulation materials (rock wool 0.04 W / (m·K), polyurethane foam 0.025 W / (m·K)); second, the solid-liquid phase change characteristics of PCM can realize heat storage and release, such as PEG-4000 phase change latent heat ≥200 J / g, Na2SO4-K2SO4 phase change latent heat ≥250 J / g, which solves the limitation of traditional aerogels that only insulate but do not regulate temperature, and realizes the self-adaptive function of passive insulation and active temperature regulation. Inorganic temperature-resistant fibers (such as glass fiber, basalt fiber) as the base material, with temperature resistance ≥500℃, excellent mechanical properties, and aging corrosion resistance, effectively enhance the toughness of the aerogel, and adapt to various forms such as film and fiber mat, meeting the needs of different high-temperature insulation scenes such as battery packs and pipelines.

[0003] In the prior art, a physical blending method is usually used to directly composite the phase change material with the aerogel matrix. However, this method has the following defects: first, due to poor interface compatibility between PCM and aerogel and lack of effective limited encapsulation structure, liquid PCM is easy to migrate and seep out of the nano-pores when phase change occurs, resulting in high cycle leakage rate and serious decay of heat storage performance; second, the interface bonding force between inorganic fibers and aerogel matrix is weak, and the composite material is easy to delaminate and fail when stressed; in addition, the high-temperature stability of the material system is insufficient, making it difficult to adapt to wide temperature range application requirements; finally, the whole preparation process is complex, resulting in high industrialization cost, which restricts its large-scale application.

[0004] Therefore, it is urgent to provide a composite shell layer phase change microcapsule, a phase change aerogel composite thermal insulation material and a preparation method thereof. SUMMARY

[0005] The present application provides a composite shell layer phase change microcapsule, a phase change aerogel composite thermal insulation material and a preparation method thereof, which can solve the problems of poor interface compatibility between the existing phase change material and the aerogel, and the weak interface bonding force between the inorganic fibers and the aerogel matrix of the phase change aerogel thermal insulation material prepared based thereon, and the difficulty in adapting to wide temperature range application requirements.

[0006] In a first aspect, the present application provides a preparation method of a composite shell layer phase change microcapsule, which comprises the following steps: (1) heating the phase change core material to melt, then stirring and ultrasonic mixing with the organic solvent containing the composite emulsifier to obtain a water-in-oil emulsion; (2) adding a composite shell precursor solution to the water-in-oil emulsion and adjusting the pH value to perform a hydrolysis reaction, then adjusting the pH value to perform a polycondensation reaction, to obtain a core-shell structure microcapsule suspension; wherein the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase; (3) after the core-shell structure microcapsule suspension is sequentially subjected to aging, washing and drying, a composite shell phase change microcapsule is obtained.

[0007] Preferably, in step (1), the phase change core material is at least one of PEG-2000, PEG-4000, PEG-6000, lauric acid, capric acid, sodium sulfate, potassium sulfate, lithium carbonate, sodium carbonate, sodium nitrate or stearic acid.

[0008] Preferably, the composite emulsifier is Span-80 and Tween-60 with a mass ratio of (2-3):1, and the organic solvent is cyclohexane.

[0009] More preferably, the content of the composite emulsifier is 1-1.5wt% of the content of the phase change core material, and the mass ratio of the phase change core material to the organic solvent is 1:(2-3).

[0010] Preferably, in step (2), the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase, and the solvent is ethanol; wherein the silicon source is tetraethyl orthosilicate, and the inorganic reinforcing phase is at least one of ZrO2 nanoparticles or Al2O3 nanoparticles.

[0011] Preferably, in the composite shell precursor solution, the mass concentration of the silicon source is 180-220g / L, and the inorganic reinforcing phase accounts for 3-8wt% of the total amount of the composite shell precursor solution.

[0012] More preferably, the mass ratio of the composite shell precursor solution to the phase change core material is (1.2-2):1.

[0013] Preferably, in step (2), the pH value of the hydrolysis reaction is 1.5-2.0, the temperature is 40-50℃, and the time is 1-2h.

[0014] Preferably, the pH value of the polycondensation reaction is 3.0-3.5, the temperature is 40-50℃, and the time is 1.5-2.5h.

[0015] Preferably, in step (3), the temperature of the aging is 65-75℃, and the time is 5-7h.

[0016] Preferably, before the drying, a step of surface modification with a silane coupling agent solution is further included; wherein the mass concentration of the silane coupling agent solution is 3-5 wt%.

[0017] In a second aspect, the embodiments of the present application further provide a composite shell phase change microcapsule prepared by the preparation method of any one of the first aspect; wherein the composite shell phase change microcapsule has the following characteristics: The particle size is 1-5 μm, the shell coating rate is ≥ 92%, the leakage rate after 50 phase change cycles is ≤ 2.2%, the phase change latent heat retention rate is ≥ 95%, and the shell structure integrity at 900℃ is ≥ 95%.

[0018] In a third aspect, the embodiments of the present application further provide a method for preparing a phase change aerogel composite thermal insulation material based on the composite shell phase change microcapsule of the second aspect; the method comprises the following steps: Step S1: uniformly mixing the composite shell phase change microcapsule, a ternary matrix sol and a cellulose nanofiber suspension to obtain a ternary nano-enhanced phase change sol; wherein the ternary matrix sol is obtained by mixing tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, a phase change promoter and water; Step S2: gradient vacuum pressure impregnation of the modified inorganic fiber substrate with the ternary nano-enhanced phase change sol to obtain a fiber-sol composite; wherein the modified inorganic fiber substrate is obtained by sequentially modifying the inorganic fiber substrate by plasma etching and chemical modifier soaking; Step S3: adding an ice crystal directing agent to the fiber-sol composite for directional freezing, and then sequentially performing vacuum freeze drying, solvent gradient replacement and secondary drying to obtain the phase change aerogel composite thermal insulation material.

[0019] Preferably, in step S1, the mass concentration of tetraethyl orthosilicate in the ternary matrix sol is 180-220 g / L; the ZrO2 nanoparticles account for 2-3 wt% of the total amount of the ternary matrix sol, and the Al2O3 nanoparticles account for 3-5 wt% of the total amount of the ternary matrix sol.

[0020] Preferably, the phase change promoter is obtained by mixing graphene quantum dots and carbon nanotubes; wherein the mass ratio of graphene quantum dots to carbon nanotubes is preferably 3: (6-8).

[0021] More preferably, the phase change promoter is 0.1-0.3% of the total amount of the ternary matrix sol.

[0022] More preferably, the mass ratio of the ternary matrix sol to the cellulose nanofiber suspension is (6-8):3, and the addition amount of the composite shell phase change microcapsule is 35-45% of the total amount of the ternary nano-enhanced phase change sol.

[0023] Preferably, in step S2, the inorganic fiber substrate is a fiber cloth or a fiber felt; wherein the fiber cloth or the fiber felt is made of at least one of glass fiber, basalt fiber, alumina fiber, silicon carbide fiber, aluminum silicate fiber or mullite fiber.

[0024] Preferably, the gas for plasma etching is argon, the etching power is 100-120 W, and the etching time is 5-6 min. More preferably, the chemical modifier is an ethanol solution of KH-560 grafted maleic anhydride, the mass concentration is 2-3%, the soaking temperature is 50-60℃, and the soaking time is 25-35 min.

[0025] Preferably, in the fiber-sol composite, the loading amount of the ternary nano-reinforced phase change sol is 1.5-2.0 times the mass of the modified inorganic fiber substrate.

[0026] Preferably, in step S3, the ice crystal directing agent is dimethyl sulfoxide, and the addition amount of the ice crystal directing agent is 4-6 wt% of the fiber-sol composite.

[0027] In a fourth aspect, the embodiments of the present application further provide a phase change aerogel composite thermal insulation material, which is prepared by the preparation method of any one of the third aspect. The phase change aerogel composite thermal insulation material has the following characteristics: the thermal conductivity at room temperature is ≤0.025 W / (m·K), the thermal conductivity at 900℃ is ≤0.032 W / (m·K), the compressive strength is 1.1-1.4 MPa, the interfacial shear strength is 3.5-3.9 MPa, the delamination rate after 100 cold and hot cycles from -20℃ to 80℃ is ≤3%, and the hydrophobic angle is 135°-145°.

[0028] Compared with the prior art, the present application has at least the following beneficial effects: (1) In the present application, first, the phase change core material is heated to melt and mixed with an organic solvent containing a composite emulsifier to form a stable water-in-oil (W / O) emulsion template, then a composite shell precursor solution including a silicon source and an inorganic reinforcing phase is mixed with the water-in-oil emulsion, and by stepwise pH control, sufficient hydrolysis and rapid polycondensation reactions are realized at the emulsion interface in sequence, and finally, after aging and drying, a phase change microcapsule with a core-shell structure is obtained; through the compounding of the shell material, the ultimate encapsulation of the phase change core material is realized, and the problems of leakage and performance decay in the long-term cyclic use of phase change materials are completely solved. Specifically, the composite shell takes SiO2 as the main network with low permeability, and by doping nano-particle inorganic reinforcing phase, the porosity of the composite shell can be reduced to below 5%, thereby effectively blocking the migration of phase change materials by virtue of its dense barrier effect, and at the same time, the inorganic reinforcing phase significantly improves the structural stability of the composite shell at high temperature (such as 900℃), inhibits the shrinkage and cracking of the SiO2 network, so that the leakage rate of the final composite shell phase change microcapsule can be reduced to below 2.2% after 50 times of severe phase change cycles, and the phase change latent heat retention rate is as high as 95% or more, showing excellent anti-leakage performance, cycle stability and wide temperature range applicability. (2) In the present application, first, tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, a phase change promoter and water are mixed to obtain a ZrO2-Al2O3-SiO2 ternary matrix sol, the ZrO2-Al2O3-SiO2 ternary system in the sol widens the material application temperature range to -20℃-1200℃ through synergistic effect, and the thermal conductivity remains below 0.032 W / (m·K) at 900℃ high temperature; then, the above sol is mixed with the composite shell phase change microcapsule and cellulose nanofiber suspension, and by constructing a nano-micron multi-level reinforcing network, the compressive strength of the material is improved to 1.1-1.4 MPa, and the porous structure of the matrix provides uniform distribution space for the phase change microcapsule, realizing the intelligent cooperation of heat insulation and temperature regulation. At the same time, by means of plasma etching and chemical modifier soaking treatment of the inorganic fiber substrate, combined with gradient vacuum pressure impregnation process, the interfacial shear strength reaches 3.5-3.9 MPa, and the delamination rate is not more than 3% after 100 times of cold and hot cycles; finally, by introducing an ice crystal directing agent for directional freezing, and through vacuum freeze-drying and other processes, a composite thermal insulation material with excellent mechanical properties, wide temperature range stability and intelligent thermal management function is obtained. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a method for preparing composite shell phase change microcapsules, the method comprising the following steps: (1) The phase change core material is heated to melt and then stirred and ultrasonically mixed with an organic solvent containing a composite emulsifier to obtain a water-in-oil emulsion; (2) Add a composite shell precursor solution to the water-in-oil emulsion and adjust the pH value to carry out a hydrolysis reaction, and then adjust the pH value to carry out a condensation reaction to obtain a core-shell structured microcapsule suspension; wherein, the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase; wherein, the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase; (3) The core-shell structured microcapsule suspension is subjected to aging, washing and drying in sequence to obtain composite shell phase change microcapsules.

[0031] In this embodiment of the invention, the phase change core material is first heated to melt and then mixed with an organic solvent containing a composite emulsifier to form a stable water-in-oil (W / O) emulsion template. Then, a composite shell precursor solution including a silicon source and an inorganic reinforcing phase is mixed with the water-in-oil emulsion. By stepwise pH control, sufficient hydrolysis and rapid polycondensation reactions are carried out sequentially at the emulsion interface. Finally, after aging and drying, phase change microcapsules with a core-shell structure are obtained. Through shell material composite, the ultimate encapsulation of the phase change core material is achieved, completely solving the problems of leakage and performance degradation in the long-term cyclic use of phase change materials. Specifically, the composite shell uses low-permeability SiO2 as the main network and is reinforced by nanoparticles to reduce the porosity of the composite shell to below 5%. This allows it to effectively block the migration of phase change materials through its dense barrier effect. At the same time, the inorganic reinforcement significantly improves the structural stability of the composite shell at high temperatures (such as 900℃) and inhibits the shrinkage and cracking of the SiO2 network. As a result, the leakage rate of the final composite shell phase change microcapsule can be reduced to below 2.2% after 50 severe phase change cycles, and the latent heat retention rate of phase change is as high as 95%, demonstrating excellent anti-leakage performance, cycle stability and wide temperature range applicability.

[0032] According to some preferred embodiments, in step (1), the phase change core material is at least one of PEG-2000, PEG-4000, PEG-6000, lauric acid, decanoic acid, sodium sulfate, potassium sulfate, lithium carbonate, sodium carbonate, sodium nitrate, or stearic acid; the composite emulsifier is Span-80 and Tween-60 in a mass ratio of (2~3):1 (for example, it can be 2:1, 2.5:1 or 3:1); the organic solvent is cyclohexane; the content of the composite emulsifier is 1~1.5wt% of the content of the phase change core material (for example, it can be 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%); and the mass ratio of the phase change core material to the organic solvent is 1:(2~3) (for example, it can be 1:2, 1:2.5 or 1:3).

[0033] According to some preferred embodiments, the stirring rate is 600~800 rpm, the time is 20~30 min; the ultrasonic mixing power is 350~450 W, the ultrasonic mode is intermittent (working for 30 s / stopping for 10 s), and the total ultrasonic time is 20~30 min.

[0034] In this embodiment of the invention, the phase change core material can be precisely selected according to the temperature requirements of the actual application scenario, covering three major types: low temperature (-40~20℃), medium temperature (20~80℃), and high temperature (250~1200℃). The melting temperature is 30℃ to 900℃, and the latent heat of phase change is 180~260 J / g, possessing excellent heat storage and release capabilities. Specifically, to meet the phase change temperature of the low temperature type, the phase change core material can be a PEG-2000 and lauric acid composite system with a mass ratio of (6~7):(3~4) or a PEG-1000 and octanoic acid composite system with a mass ratio of (6~7):(3~4). To meet the phase change temperature of the medium temperature type, the phase change core material can be a PEG-4000 and decanoic acid composite system with a mass ratio of (6~7):(3~4). The phase change material can be a composite system of PEG-4000 and stearic acid with a mass ratio of (6~7):(3~4). To meet the high-temperature phase change temperature requirement, the phase change core material can be a mixed salt of sodium sulfate and potassium sulfate with a mass ratio of (6~7):(3~4), a composite system of PEG-6000 and NaNO3 with a mass ratio of (8~9):(2~3), or a composite system of Li2CO3 and Na2CO3 with a mass ratio of (4~5):(4~5). Simultaneously, by precisely controlling the content ratio of the phase change core material to the composite emulsifier, the emulsion stability and microcapsule encapsulation efficiency can be optimized, thereby further improving the cycle life and thermal management reliability of the phase change material.

[0035] According to some preferred embodiments, in step (2), the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase, and the solvent is ethanol; wherein, the silicon source is tetraethyl orthosilicate, and the inorganic reinforcing phase is at least one of ZrO2 nanoparticles or Al2O3 nanoparticles; in the composite shell precursor solution, the mass concentration of the silicon source is 180-220 g / L (for example, it can be 180 g / L, 190 g / L, 200 g / L, 210 g / L or 220 g / L), preferably 200 g / L; the inorganic reinforcing phase accounts for 3-8 wt% of the total amount of the composite shell precursor solution (for example, it can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%); the mass ratio of the composite shell precursor solution to the phase change core material is (1.2-2):1 (for example, it can be 1.2:1, 1.5:1 or 2:1), preferably 1.5:1.

[0036] According to some preferred embodiments, in step (2), the pH value of the mixed solution system is adjusted using a 0.1 mol / L oxalic acid solution, the pH value of the hydrolysis reaction is 1.5~2.0 (e.g., 1.5, 1.8 or 2.0), the temperature is 40~50℃ (e.g., 40℃, 45℃ or 50℃), and the time is 1~2h (e.g., 1h, 1.5h or 2h); the pH value of the mixed solution system is adjusted using 25wt% ammonia water, the pH value of the polycondensation reaction is 3.0~3.5 (e.g., 3.0, 3.2 or 3.5), the temperature is 40~50℃ (e.g., 40℃, 45℃ or 50℃), and the time is 1.5~2.5h (e.g., 1.5h, 2.0h or 2.5h).

[0037] In this embodiment of the invention, after adding the composite shell precursor solution to the water-in-oil emulsion, the pH of the mixed solution system is first adjusted to a strongly acidic environment of 1.5-2.0. This allows the silicon source in the system to be continuously and stably hydrolyzed, generating a large number of highly reactive silanols, laying the foundation for the subsequent condensation reaction to construct a complete three-dimensional network structure. Simultaneously, this acidic environment also facilitates the hydroxylation of the inorganic reinforcing phase surface, enhancing its interaction with silanols and promoting interfacial compatibility. Then, the pH of the mixed solution system is adjusted to a weakly acidic range of 3.0-3.5. Under this range, the condensation reaction rate of the large number of silanols previously generated by hydrolysis is accelerated. They interconnect to form strong Si-O-Si bonds, constructing a three-dimensional silica network framework. Simultaneously, these silanols also condense with the hydroxyl groups on the surface of the uniformly dispersed inorganic reinforcing phase nanoparticles, forming strong Si-O-Zr or Si-O-Al chemical bonds. This condensation reaction preferentially occurs at the droplet interface of the water-in-oil emulsion, thereby efficiently and completely encapsulating the phase change core material to form a continuous, dense, and robust composite shell.

[0038] Furthermore, by precisely designing the equal proportions of silicon source and inorganic reinforcing phase, a synergistic effect can be achieved with pH control. Precisely controlling the concentration of silicon source is beneficial for forming a continuous and complete SiO2 network. If the concentration of silicon source is too low, the shell of the composite shell phase change microcapsule will be too thin and prone to rupture. If the concentration of silicon source is too high, the viscosity of the sol will increase, and agglomeration will easily occur during emulsification. Adding a certain amount of inorganic reinforcing phase can make it uniformly embedded and anchored in the SiO2 network. Through crack deflection, bridging and other mechanisms, the toughness, compressive strength and impact resistance of the composite shell are significantly improved. In this embodiment of the invention, the inorganic reinforcing phase is preferably ZrO2 nanoparticles and Al2O3 nanoparticles. ZrO2 nanoparticles account for 5-8% of the total amount of the composite shell precursor solution, and Al2O3 nanoparticles account for 3-5% of the total amount of the composite shell precursor solution. ZrO2 nanoparticles and Al2O3 nanoparticles can bond with SiO2 to form a ternary composite structure of ZrO2-Al2O3-SiO2. This composite structure can effectively suppress the sintering and phase transformation of pure SiO2 at high temperatures. ZrO2 inhibits crystal transformation, and Al2O3 promotes the formation of mullite phase. Together, they reduce the shell porosity to ≤5%, building a strong barrier against the migration of phase transformation material molecules, thereby reducing the long-term cyclic leakage rate to an extremely low level.

[0039] In summary, stepwise pH control for gradient hydrolysis and condensation reactions ensures the controllable preparation of the composite shell structure. Precise control of each component in the composite shell facilitates the design and optimization of its performance. The two work synergistically to ensure that the final ZrO2-Al2O3-SiO2 composite shell phase change microcapsules possess excellent leak-proof performance, high mechanical strength, wide temperature range stability, and long cycle life.

[0040] According to some preferred embodiments, in step (3), the aging temperature is 65~75℃ (for example, it can be 65℃, 70℃ or 75℃), and the time is 5~7h (for example, it can be 5h, 6h or 7h); before drying, the step of surface modification with a silane coupling agent solution is also included; wherein, the mass concentration of the silane coupling agent solution is 3~5wt% (for example, it can be 3wt%, 4wt% or 5wt%).

[0041] In this embodiment of the invention, the core-shell structured microcapsule suspension obtained after the reaction was subjected to isothermal aging at the aforementioned temperature, followed by centrifugation at 2950~3050 rpm for 10~15 min, and then washed three times with anhydrous ethanol. After each washing, the residual amount of phase change material in the supernatant was no more than 0.05 g / L (detected by UV spectrophotometer). Then, a silane coupling agent solution was added for surface modification. By controlling the concentration of the silane coupling agent solution, its amphiphilic molecular structure constructs molecular bridges between the microcapsules and the aerogel matrix, forming covalent bonds and enhancing interfacial bonding. Simultaneously, it optimizes the dispersibility of the microcapsules, reduces the interfacial gap between the microcapsules and the aerogel matrix, and constructs a dense molecular barrier, thereby significantly inhibiting the migration of the phase change material and minimizing the risk of long-term cyclic leakage. Finally, the microcapsules were vacuum dried at 60~70℃ and a vacuum degree of -0.06~-0.08 MPa for 7~9 h to obtain composite shell phase change microcapsules.

[0042] This invention also provides a composite shell phase change microcapsule, prepared by any of the above-described preparation methods; wherein the composite shell phase change microcapsule has the following characteristics: particle size of 1~5μm, shell coverage rate ≥92%, leakage rate ≤2.2% after 50 phase change cycles, latent heat retention rate of phase change ≥95%, and shell structure integrity ≥95% at 900℃.

[0043] This invention also provides a method for preparing phase change aerogel composite thermal insulation materials based on the above-described composite shell phase change microcapsules, the method comprising the following steps: Step S1: Mix the composite shell phase change microcapsules, ternary matrix sol and cellulose nanofiber suspension to obtain a ternary nano-reinforced phase change sol; wherein the ternary matrix sol is obtained by mixing tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, phase change promoter and water. Step S2: The modified inorganic fiber substrate is impregnated with the ternary nano-reinforced phase change sol under gradient vacuum pressure to obtain a fiber-sol composite; wherein, the modified inorganic fiber substrate is obtained by sequentially modifying the inorganic fiber substrate by plasma etching and chemical modifier immersion. Step S3: Add an ice crystal guiding agent to the fiber-sol composite for directional freezing, followed by vacuum freeze-drying, solvent gradient displacement and secondary drying to obtain the phase change aerogel composite thermal insulation material.

[0044] In this embodiment of the invention, firstly, a ZrO2-Al2O3-SiO2 ternary matrix sol is obtained by mixing tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, a phase change promoter, and water. The ZrO2-Al2O3-SiO2 ternary system in this sol, through synergistic effects, broadens the applicable temperature range of the material to -20℃ to 1200℃, and the thermal conductivity remains below 0.032 W / (m·K) at a high temperature of 900℃. Then, the above sol is mixed with composite shell phase change microcapsules and cellulose nanofiber suspension. By constructing a nano-micro multi-level reinforcement network, the compressive strength of the material is increased to 1.1-1.4 MPa. At the same time, the porous structure of the matrix provides a uniform distribution space for the phase change microcapsules, realizing intelligent synergy of thermal insulation and temperature regulation. Meanwhile, by subjecting the inorganic fiber substrate to plasma etching and chemical modifier impregnation, combined with gradient vacuum pressure impregnation process, the interfacial shear strength reaches 3.5-3.9 MPa, and the delamination rate does not exceed 3% after 100 thermal cycles. Finally, by introducing ice crystal guiding agent for directional freezing and vacuum freeze drying, a composite thermal insulation material with excellent mechanical properties, wide temperature range stability and intelligent thermal management function is obtained.

[0045] According to some preferred embodiments, in step S1, the mass concentration of tetraethyl orthosilicate in the ternary matrix sol is 180-220 g / L (e.g., 180 g / L, 190 g / L, 200 g / L, 210 g / L or 220 g / L); ZrO2 nanoparticles account for 2-3 wt% of the total amount of the ternary matrix sol (e.g., 2 wt%, 2.5 wt% or 3 wt%), and Al2O3 nanoparticles account for 3-5 wt% of the total amount of the ternary matrix sol (e.g., 3 wt%, 4 wt% or 5 wt%).

[0046] In this embodiment of the invention, tetraethyl orthosilicate, ZrO2 nanoparticles, and Al2O3 nanoparticles are mixed with water in a specific ratio. Tetraethyl orthosilicate serves as the primary silicon source, and the amorphous SiO2 network formed after its hydrolysis and condensation forms the main body of the aerogel structure. Controlling its content is beneficial for forming a continuous, complete, and highly porosity framework. Furthermore, by introducing a specific proportion of ZrO2 nanoparticles, they can react with some SiO2 at high temperatures to generate a highly thermally stable mullite crystalline phase in situ, effectively improving the temperature resistance of the aerogel. Further addition of a certain amount of Al2O3 nanoparticles allows ZrO2 and Al2O3 nanoparticles to work together as a hard reinforcing phase, uniformly dispersed within the SiO2 matrix. Through mechanisms such as pinning, crack deflection, and bridging, they effectively resist stress concentration, significantly improving the compressive strength of the aerogel matrix. Simultaneously, ZrO2 and Al2O3 synergistically enable the material to maintain structural stability and ultra-low thermal conductivity in environments up to 1200℃. Ultimately, the prepared aerogel integrates the nanoporous properties of SiO2, the high-temperature phase stability of ZrO2, and the reinforcing effect of Al2O3 into a ternary composite system, achieving a balance between thermal insulation performance and structural stability over an extremely wide temperature range from room temperature to ultra-high temperature.

[0047] According to some preferred embodiments, the phase change promoter is obtained by mixing graphene quantum dots and carbon nanotubes; wherein, the mass ratio of graphene quantum dots to carbon nanotubes is preferably 3:(6~8) (for example, it can be 3:6, 3:7 or 3:8); the phase change promoter is 0.1~0.3% of the total amount of the ternary matrix sol (for example, it can be 0.1%, 0.2% or 0.3%).

[0048] In this embodiment of the invention, adding a certain amount of phase change promoter to the ternary matrix sol can significantly optimize the thermal management performance of the final thermal insulation material. The phase change promoter is preferably a composite system formed by graphene quantum dots and carbon nanotubes. Through their synergistic effect, the two not only enhance the thermal energy storage and release efficiency of the material, but also their unique interface effect is conducive to promoting the uniform distribution of phase change microcapsules in the porous aerogel framework.

[0049] According to some preferred embodiments, cellulose nanofiber (CNF) suspensions are prepared by the following method: chitin powder is successively treated with alkali and adjusted with acid, then mechanically ground and homogenized under high pressure, and a crosslinking agent is added for pre-crosslinking to obtain CNF suspensions; wherein, the alkali treatment is a 5% NaOH solution, the treatment temperature is 75~85℃, and the treatment time is 1.5~2.5h; the acid adjustment is a 0.1mol / L hydrochloric acid solution, and the pH value is adjusted to 2. The temperature range is 0~3.0; the mechanical grinding speed is 2500~3500 rpm, and the time is 1~2 h; the pressure of high-pressure homogenization is 25~35 MPa, and the number of homogenization times is 2~3; the crosslinking agent is 1,2,3,4-butanetetracarboxylic acid, and its dosage is 2~3% of the CNF mass; the pre-crosslinking temperature is 75~85℃, and the pre-crosslinking time is 1.5~2.5 h; finally, the concentration of CNF suspension is 0.7~0.9 wt%, the diameter of CNF is 3nm~10nm, and the aspect ratio is ≥50.

[0050] In this embodiment of the invention, chitin is used as raw material. After alkali treatment and acid adjustment, ultrafine cellulose nanofibers (CNFs) with a diameter of 3-10 nm and an aspect ratio ≥50 are prepared through high-pressure homogenization and a 1,2,3,4-butanetetracarboxylic acid pre-crosslinking process. These CNFs form a stable three-dimensional network structure through 1,2,3,4-butanetetracarboxylic acid crosslinking. When composited with an aerogel matrix, the nanofiber network can effectively penetrate the micron-level pores of the aerogel, synergistically constructing a nano-micron multi-level reinforcement system with the inorganic fiber substrate. This structure, through stress dispersion and interfacial synergy, further enhances the mechanical properties of the composite material, thus exhibiting excellent mechanical reliability and damage resistance in practical applications such as pipe wrapping and building installation.

[0051] According to some preferred embodiments, the mass ratio of the ternary matrix sol to the cellulose nanofiber suspension is (6~8):3 (e.g., 6:3, 7:3 or 8:3), and the amount of composite shell phase change microcapsules added accounts for 35~45% of the total amount of ternary nano-reinforced phase change sol (e.g., 35%, 40% or 45%).

[0052] In this embodiment of the invention, the prepared composite shell phase change microcapsules are added to a ternary matrix sol and mixed evenly, then mixed with a prepared CNF suspension. After high-speed shear dispersion, a nano-reinforced phase change sol is obtained. The high-speed shear dispersion speed is 1000~2000 rpm, and the dispersion time is 10~15 min, ultimately obtaining a uniformly dispersed ternary nano-reinforced phase change sol with suitable viscosity and good stability. By precisely controlling the amount of composite shell phase change microcapsules added, the content of phase change material per unit volume can be effectively controlled, thereby achieving precise design of the total heat storage capacity and phase change temperature of the material. If the amount added is too much, it is easy to cause microcapsule agglomeration, destroying the continuity of the matrix and reducing mechanical properties; while if the amount added is too little, it will weaken the phase change temperature regulation function of the material. Furthermore, by synergistically controlling the ratio of the ternary matrix sol to the CNF suspension, a stable nano-micro multi-level reinforcement network can be constructed. Through the synergistic effect of the two, the composite material has both excellent compressive strength and flexibility. Meanwhile, an appropriate amount of CNF suspension can not only effectively prevent the aggregation of phase change microcapsules as a dispersion medium and ensure their uniform distribution in the matrix, but also form an interpenetrating network with the ternary matrix sol through physical entanglement and chemical bonding, thereby enhancing the stability of the porous structure of the aerogel and improving the dimensional integrity and service life of the material during thermal cycling.

[0053] According to some preferred embodiments, in step S2, the inorganic fiber substrate is fiber cloth or fiber felt; wherein, the fiber cloth or fiber felt is made of at least one of glass fiber, basalt fiber, alumina fiber, silicon carbide fiber, aluminum silicate fiber, or mullite fiber; preferably, the plasma etching gas is argon, the etching power is 100~120W (e.g., 100W, 110W, or 120W), and the time is 5~6min (e.g., 5min, 5.5min, or 6min); more preferably, the chemical modifier is an ethanol solution of KH-560 grafted maleic anhydride, with a mass concentration of 2~3% (e.g., 2%, 2.5%, or 3%), an immersion temperature of 50~60℃ (e.g., 50℃, 55℃, or 60℃), and a time of 25~35min (e.g., 25min, 30min, or 35min).

[0054] According to some preferred embodiments, a three-stage gradient vacuum pressure impregnation is preferably adopted; wherein, the vacuum degree of the first stage is -0.09~-0.10MPa, and is maintained for 15~25min; the vacuum degree of the second stage is -0.05~-0.06MPa, and is maintained for 10~15min; and the vacuum degree of the third stage is -0.07~-0.08MPa, and is maintained for 15~20min.

[0055] According to some preferred embodiments, in the fiber-sol composite, the loading of ternary nano-reinforced phase change sol is 1.5 to 2.0 times the mass of the modified inorganic fiber substrate (e.g., 1.5 times, 1.8 times, or 2.0 times).

[0056] In this embodiment of the invention, an inorganic fiber substrate is first subjected to a synergistic surface treatment involving plasma etching and chemical modifier immersion. Plasma etching significantly increases the hydroxyl density on the fiber surface, providing physical anchoring points and a highly active chemical interface for subsequent chemical bonding. Further chemical modifier immersion allows the chemical modifier to react with the plasma-treated active surface, forming a robust covalent bond bridging layer. This transforms the interfacial bonding from physical adsorption to chemical bonding, significantly enhancing the interfacial shear strength. Subsequently, a gradient vacuum pressure impregnation process is used to generate aerogel in situ on the modified inorganic fiber substrate surface. Precise control of vacuum and pressure ensures that the aerogel precursor fully penetrates into the micro-gaps of the fiber network, forming a continuous and complete three-dimensional skeleton in situ, avoiding impregnation defects. Finally, a fiber-interface layer-aerogel composite is constructed at the microscale, enabling the material to maintain ultra-low thermal conductivity while possessing excellent mechanical properties and structural integrity.

[0057] According to some preferred embodiments, in step S3, the ice crystal guiding agent is dimethyl sulfoxide, and the amount of ice crystal guiding agent added is 4~6 wt% of the fiber-sol composite (e.g., 4 wt%, 5 wt%, or 6 wt%); the directional freezing temperature is -20~-30℃ (e.g., -20℃, -25℃, or -30℃), the cooling rate is 1.5~2.5℃ / min (e.g., 1.5℃ / min, 2.0℃ / min, or 2.5℃ / min), and the time is 3~5h (e.g., 3h, 4h, or 5h).

[0058] According to some preferred embodiments, vacuum freeze drying is performed at -65~-75℃, with a vacuum degree of -0.1~-0.2MPa, and a drying time of 24~36h; a gradient replacement is performed sequentially using 50% ethanol solution, pure ethanol, and 50% n-hexane solution or 50% ethanol solution and pure n-hexane solvent, with each solvent soaking time being 1.5~2.5h; the secondary drying temperature is 65~75℃, with a vacuum degree of -0.08~-0.09MPa, and a drying time of 1.5~2.5h.

[0059] Unlike traditional supercritical drying, this invention employs directional freezing by adding an ice crystal guiding agent to the fiber-sol composite, precisely controlling the growth of ice crystals along a specific direction to construct an ordered pore structure. Solvent gradient displacement effectively reduces the damage to the aerogel nanoporous structure caused by capillary forces. This drying method significantly reduces the drying time from the traditional 72 hours to 36 hours, while effectively controlling the material's volume shrinkage and maintaining a high porosity of 97%-98%. This provides a practical and feasible technical path for the large-scale production of phase change aerogel composite thermal insulation materials.

[0060] This invention also provides a phase change aerogel composite thermal insulation material prepared by any of the above-described methods; wherein the phase change aerogel composite thermal insulation material has the following characteristics: Thermal conductivity at room temperature ≤0.025W / (m·K), thermal conductivity at 900℃ ≤0.032W / (m·K), compressive strength 1.1~1.4MPa, interfacial shear strength 3.5~3.9MPa, delamination rate after 100 cycles of thermal cycling from -20℃ to 80℃ ≤3%, hydrophobic angle 135°~145°.

[0061] In summary, the embodiments of this invention achieve effective confinement of phase change materials through composite shell microcapsules, enhance high-temperature stability by using a ternary aerogel matrix, improve mechanical properties by introducing cellulose nanofibers, optimize bonding strength through dual interface modification, and reduce preparation costs through innovative drying processes. As a result, the final composite material possesses the characteristics of wide temperature range adaptive thermal insulation (-20℃ to 1200℃), low leakage, high mechanical strength, and high temperature resistance, and can be widely used in building energy conservation, industrial high-temperature pipelines, new energy vehicle battery packs, aerospace thermal protection, and other scenarios.

[0062] To more clearly illustrate the technical solutions and advantages of the present invention, the following examples provide a detailed description of the glass fiber composite filter material with adjustable pore size, the composite shell phase change microcapsules, the phase change aerogel composite thermal insulation material, and their preparation methods.

[0063] Example 1: (1) The phase change core material (PEG-4000 and decanoic acid in a mass ratio of 6:4) was heated to melt and then stirred with an organic solvent containing a composite emulsifier (the composite emulsifier was Span-80 and Tween-60 in a mass ratio of 3:1, and the organic solvent was cyclohexane) at a stirring rate of 600 rpm for 20 min. Then, ultrasonic emulsification was performed with an ultrasonic power of 400 W for 30 min. The ultrasonic method was intermittent (working for 30 s and stopping for 10 s) to obtain a water-in-oil emulsion. The content of the composite emulsifier was 1 wt% of the phase change core material content, and the mass ratio of the phase change core material to the organic solvent was 1:2. (2) Add a composite shell precursor solution composed of tetraethyl orthosilicate and ZrO2 nanoparticles (the mass concentration of tetraethyl orthosilicate is 200 g / L, the ZrO2 nanoparticles account for 5 wt% of the total amount of the composite shell precursor solution, and the mass ratio of the composite shell precursor solution to the phase change core material is 1.5:1) to the water-in-oil emulsion and adjust the pH value to 1.8 and carry out a hydrolysis reaction at 45°C for 1.5 h. Then, keep the temperature constant and adjust the pH value to 3.2 to carry out a polycondensation reaction for 2.0 h to obtain a core-shell structured microcapsule suspension. (3) The core-shell structured microcapsule suspension was aged at 70℃ for 6 hours, then centrifuged at 3000 rpm for 15 minutes, and washed three times with anhydrous ethanol. Then, a 4 wt% silane coupling agent ethanol solution (KH-570) was added for surface modification. The microcapsules were vacuum dried at 65℃ and -0.08 MPa for 8 hours to obtain composite shell phase change microcapsules with a particle size of 3 μm.

[0064] Step S1: Preparation of ternary matrix sol: At 50°C, tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, and deionized water were mixed, and then a phase change promoter (graphene quantum dots and carbon nanotubes in a mass ratio of 3:7) was added. The mixture was stirred at 400 rpm for 1 hour to obtain a ZrO2-Al2O3-SiO2 ternary matrix sol. In the ternary matrix sol, the mass concentration of tetraethyl orthosilicate was 200 g / L, the ZrO2 nanoparticles accounted for 2 wt% of the total ternary matrix sol, the Al2O3 nanoparticles accounted for 4 wt% of the total ternary matrix sol, and the phase change promoter accounted for 0.2 wt% of the total ternary matrix sol. Preparation of cellulose nanofiber (CNF) suspension: Chitin powder was first treated with a 5% NaOH solution at 80°C for 2 hours. Then, the pH was adjusted to 3.0 with 0.1 mol / L hydrochloric acid. The powder was then mechanically ground at 3000 rpm for 1 hour and homogenized under 30 MPa pressure three times. A crosslinking agent (1,2,3,4-butanetetracarboxylic acid) was added, and pre-crosslinking was performed at 80°C for 2 hours to obtain a CNF suspension with a concentration of 0.8 wt%. The amount of crosslinking agent was 2.5 wt% of the CNF mass. The composite shell phase change microcapsules were added to the above ternary matrix sol and mixed well. Then, the above cellulose nanofiber suspension was added and mixed at 1500 rpm for 10 min to obtain a ternary nano-reinforced phase change sol. The mass ratio of the ternary matrix sol to the cellulose nanofiber suspension was 7:3, and the amount of composite shell phase change microcapsules added accounted for 40% of the total amount of the ternary nano-reinforced phase change sol. Step S2: Inorganic fiber substrate modification: Modify the inorganic fiber substrate (basalt fiber felt, bulk density 0.3 g / cm³). 3The modified inorganic fiber substrate (with a thickness of 5 mm, a temperature resistance of 800℃, and an elongation at break of 4%) was first subjected to Ar plasma etching at 100W for 5 min, then soaked in a 2 wt% chemical modifier (an ethanol solution of KH-560 grafted maleic anhydride) at 50℃ for 30 min, and finally dried at 120℃ for 2 h to obtain the modified inorganic fiber substrate. The modified inorganic fiber substrate was impregnated with a ternary nano-reinforced phase change sol in a three-stage gradient vacuum pressure process to obtain a fiber-sol composite. The first stage used a vacuum of -0.09 MPa for 20 min, the second stage used a vacuum of -0.05 MPa for 10 min, and the third stage used a vacuum of -0.07 MPa for 15 min. The loading of the ternary nano-reinforced phase change sol was 2.0 times the mass of the modified inorganic fiber substrate. Step S3: Add ice crystal guiding agent (dimethyl sulfoxide) to the fiber-sol composite, cool to -20℃ at a cooling rate of 2℃ / min for directional freezing for 4 hours, then freeze-dry in vacuum at -60℃ and -0.1MPa for 36 hours, and sequentially perform gradient replacement with 50% ethanol solution, pure ethanol, 50% n-hexane solution or 50% ethanol solution and pure n-hexane solvent, with each solvent soaking time being 2 hours. Finally, vacuum dry at 60℃ and -0.08MPa for 2 hours to obtain phase change aerogel composite thermal insulation material; wherein, the amount of ice crystal guiding agent added is 5wt% of the fiber-sol composite.

[0065] The phase change aerogel composite thermal insulation material in this embodiment is suitable for building exterior wall insulation (-10-60℃), has adaptive temperature regulation and good mechanical strength, and can resist outdoor hot and cold cycles and rainwater erosion.

[0066] Example 2: (1) The phase change core material (PEG-2000 and lauric acid in a mass ratio of 7:3) was heated to melt and then stirred with an organic solvent containing a composite emulsifier (the composite emulsifier was Span-80 and Tween-60 in a mass ratio of 3:1, and the organic solvent was cyclohexane) at a stirring rate of 700 rpm for 20 min. Then, ultrasonic emulsification was performed at an ultrasonic power of 400 W for 30 min. The ultrasonic method was intermittent (working for 30 s and stopping for 10 s) to obtain a water-in-oil emulsion. The content of the composite emulsifier was 1 wt% of the phase change core material content, and the mass ratio of the phase change core material to the organic solvent was 1:2. (2) Add a composite shell precursor solution composed of tetraethyl orthosilicate and Al2O3 nanoparticles (the mass concentration of tetraethyl orthosilicate is 200 g / L, and the Al2O3 nanoparticles account for 3 wt% of the total amount of the composite shell precursor solution) to the water-in-oil emulsion, adjust the pH value to 1.5, and carry out a hydrolysis reaction at 45°C for 1.5 h. Then, keep the temperature constant, adjust the pH value to 3.0, and carry out a condensation reaction for 2.0 h to obtain a core-shell structured microcapsule suspension. (3) The core-shell structured microcapsule suspension was aged at 70℃ for 6 hours, then centrifuged at 3000 rpm for 15 minutes, and washed three times with anhydrous ethanol. Then, a 4 wt% silane coupling agent ethanol solution (KH-570) was added for surface modification. The microcapsules were vacuum dried at 65℃ and -0.08 MPa for 8 hours to obtain composite shell phase change microcapsules with a particle size of 1 μm.

[0067] Step S1: Preparation of ternary matrix sol: At 50°C, tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, and deionized water were mixed, and then a phase change promoter (graphene quantum dots and carbon nanotubes in a mass ratio of 3:7) was added. The mixture was stirred at 400 rpm for 1 hour to obtain a ZrO2-Al2O3-SiO2 ternary matrix sol. In the ternary matrix sol, the mass concentration of tetraethyl orthosilicate was 200 g / L, the ZrO2 nanoparticles accounted for 2 wt% of the total ternary matrix sol, the Al2O3 nanoparticles accounted for 4 wt% of the total ternary matrix sol, and the phase change promoter accounted for 0.1 wt% of the total ternary matrix sol. Preparation of cellulose nanofiber (CNF) suspension: Chitin powder was first treated with a 5% NaOH solution at 80°C for 2 hours. Then, the pH was adjusted to 3.0 with 0.1 mol / L hydrochloric acid. The powder was then mechanically ground at 3000 rpm for 1 hour and homogenized under 30 MPa pressure three times. A crosslinking agent (1,2,3,4-butanetetracarboxylic acid) was added, and pre-crosslinking was performed at 80°C for 2 hours to obtain a CNF suspension with a concentration of 0.8 wt%. The amount of crosslinking agent was 2.5 wt% of the CNF mass. The composite shell phase change microcapsules were added to the above ternary matrix sol and mixed well. Then, the above cellulose nanofiber suspension was added and mixed at 1500 rpm for 10 min to obtain a ternary nano-reinforced phase change sol. The mass ratio of the ternary matrix sol to the cellulose nanofiber suspension was 7:3, and the amount of composite shell phase change microcapsules added was 40% of the total amount of the ternary nano-reinforced phase change sol. Step S2: Modification of inorganic fiber substrate: Modify the inorganic fiber substrate (alkali-free glass fiber cloth, surface density 200 g / m²). 2The modified inorganic fiber substrate (with a thickness of 0.3 mm, tensile strength of 320 MPa, and temperature resistance of 350 °C) was first subjected to Ar plasma etching at 100 W for 5 min, then soaked in a 2 wt% chemical modifier (an ethanol solution of KH-560 grafted maleic anhydride) at 50 °C for 30 min, and finally dried at 120 °C for 2 h to obtain the modified inorganic fiber substrate. The modified inorganic fiber substrate was impregnated with a ternary nano-reinforced phase change sol in a three-stage gradient vacuum pressure process to obtain a fiber-sol composite. The first stage used a vacuum of -0.09 MPa for 20 min, the second stage used a vacuum of -0.05 MPa for 10 min, and the third stage used a vacuum of -0.07 MPa for 15 min. The loading of the ternary nano-reinforced phase change sol was 2.0 times the mass of the modified inorganic fiber substrate. Step S3: Add ice crystal guiding agent (dimethyl sulfoxide) to the fiber-sol composite, cool to -20℃ at a cooling rate of 2℃ / min for directional freezing for 4 hours, then freeze-dry in vacuum at -60℃ and -0.1MPa for 36 hours, and sequentially perform gradient replacement with 50% ethanol solution, pure ethanol, 50% n-hexane solution or 50% ethanol solution and pure n-hexane solvent, with each solvent soaking time being 2 hours. Finally, vacuum dry at 60℃ and -0.08MPa for 2 hours to obtain phase change aerogel composite thermal insulation material; wherein, the amount of ice crystal guiding agent added is 5wt% of the fiber-sol composite.

[0068] The phase change aerogel composite thermal insulation material in this embodiment is suitable for thermal insulation film (-20-80℃) of new energy vehicle battery packs, and can achieve rapid thermal response to prevent the spread of battery thermal runaway.

[0069] Example 3: (1) The phase change core material (sodium sulfate and potassium sulfate in a mass ratio of 6:4) was heated to melt and then stirred with an organic solvent containing a composite emulsifier (the composite emulsifier was Span-80 and Tween-60 in a mass ratio of 3:1, and the organic solvent was cyclohexane) at a stirring rate of 800 rpm for 20 min. Then, ultrasonic emulsification was performed at an ultrasonic power of 400 W for 30 min. The ultrasonic method was intermittent (working for 30 s and stopping for 10 s) to obtain a water-in-oil emulsion. The content of the composite emulsifier was 1.5 wt% of the phase change core material, and the mass ratio of the phase change core material to the organic solvent was 1:2. (2) Add a composite shell precursor solution consisting of tetraethyl orthosilicate, ZrO2 nanoparticles and Al2O3 nanoparticles to the water-in-oil emulsion (the mass concentration of tetraethyl orthosilicate is 200 g / L, the ZrO2 nanoparticles account for 8 wt% of the total amount of the composite shell precursor solution, and the Al2O3 nanoparticles account for 5 wt% of the total amount of the composite shell precursor solution), adjust the pH value to 2.0, and carry out a hydrolysis reaction at 45℃ for 1.5 h. Then, keep the temperature constant, adjust the pH value to 3.5, and carry out a condensation reaction for 2.0 h to obtain a core-shell structured microcapsule suspension. (3) The core-shell structured microcapsule suspension was aged at 70℃ for 6 hours, then centrifuged at 3000 rpm for 15 minutes, and washed three times with anhydrous ethanol. Then, a 4 wt% silane coupling agent ethanol solution (KH-570) was added for surface modification. The microcapsules were vacuum dried at 65℃ and -0.08 MPa for 8 hours to obtain composite shell phase change microcapsules with a particle size of 3 μm.

[0070] Step S1: Preparation of ternary matrix sol: At 50°C, tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, and deionized water were mixed, and then a phase change promoter (graphene quantum dots and carbon nanotubes in a mass ratio of 3:7) was added. The mixture was stirred at 400 rpm for 1 hour to obtain a ZrO2-Al2O3-SiO2 ternary matrix sol. In the ternary matrix sol, the mass concentration of tetraethyl orthosilicate was 200 g / L, the ZrO2 nanoparticles accounted for 2 wt% of the total ternary matrix sol, the Al2O3 nanoparticles accounted for 4 wt% of the total ternary matrix sol, and the phase change promoter accounted for 0.2 wt% of the total ternary matrix sol. Preparation of cellulose nanofiber (CNF) suspension: Chitin powder was first treated with a 5% NaOH solution at 80°C for 2 hours. Then, the pH was adjusted to 3.0 with 0.1 mol / L hydrochloric acid. The powder was then mechanically ground at 3000 rpm for 1 hour and homogenized under 30 MPa pressure three times. A crosslinking agent (1,2,3,4-butanetetracarboxylic acid) was added, and pre-crosslinking was performed at 80°C for 2 hours to obtain a CNF suspension with a concentration of 0.8 wt%. The amount of crosslinking agent was 2.5 wt% of the CNF mass. The composite shell phase change microcapsules were added to the above ternary matrix sol and mixed well. Then, the above cellulose nanofiber suspension was added and mixed at 1500 rpm for 10 min to obtain a ternary nano-reinforced phase change sol. The mass ratio of the ternary matrix sol to the cellulose nanofiber suspension was 7:3, and the amount of composite shell phase change microcapsules added was 45% of the total amount of the ternary nano-reinforced phase change sol. Step S2: Modification of inorganic fiber substrate: Modify the inorganic fiber substrate (alumina fiber cloth, surface density 250 g / m²) 2The modified inorganic fiber substrate (with a thickness of 0.5 mm, a temperature resistance of 1200℃, and a tensile strength of 250 MPa) was first subjected to Ar plasma etching at 120 W for 6 min, then soaked in a 3 wt% chemical modifier (an ethanol solution of KH-560 grafted maleic anhydride) at 50℃ for 30 min, and finally dried at 120℃ for 2 h to obtain the modified inorganic fiber substrate. The modified inorganic fiber substrate was impregnated with a ternary nano-reinforced phase change sol in a three-stage gradient vacuum pressure process to obtain a fiber-sol composite. The first stage used a vacuum of -0.09 MPa for 20 min, the second stage used a vacuum of -0.05 MPa for 10 min, and the third stage used a vacuum of -0.07 MPa for 15 min. The loading of the ternary nano-reinforced phase change sol was 2.0 times the mass of the modified inorganic fiber substrate. Step S3: Add ice crystal guiding agent (dimethyl sulfoxide) to the fiber-sol composite, cool to -20℃ at a cooling rate of 2℃ / min for directional freezing for 4 hours, then freeze-dry in vacuum at -60℃ and -0.1MPa for 36 hours, and sequentially perform gradient replacement with 50% ethanol solution, pure ethanol, 50% n-hexane solution or 50% ethanol solution and pure n-hexane solvent, with each solvent soaking time being 2 hours. Finally, vacuum dry at 60℃ and -0.08MPa for 2 hours to obtain phase change aerogel composite thermal insulation material; wherein, the amount of ice crystal guiding agent added is 5wt% of the fiber-sol composite.

[0071] The phase change aerogel composite insulation material in this embodiment is suitable for industrial high-temperature pipeline insulation (300-900℃), and has high temperature resistance, low thermal conductivity, and can resist the impact of pipeline thermal expansion.

[0072] Example 4: Example 4 is basically the same as Example 1, except that: In step (1), the phase change core material is Li2CO3 and Na2CO3 in a mass ratio of 5:5. In step (2), ZrO2 nanoparticles account for 10 wt% of the total amount of the composite shell precursor solution. In step S1, ZrO2 nanoparticles account for 5 wt% of the total ternary matrix sol, Al2O3 nanoparticles account for 5 wt% of the total ternary matrix sol, and the concentration of CNF suspension is 1.2 wt%. In step S2, the inorganic fiber substrate is silicon carbide fiber felt with a SiC content of 90% and a bulk density of 0.4 g / cm³. 3 Thickness 10mm, temperature resistance 1600℃, elongation at break 3%.

[0073] The phase change aerogel composite thermal insulation material in this embodiment is suitable for thermal protection of aerospace equipment (800-1200℃), and can withstand high temperature, low high temperature thermal conductivity, and resist extreme temperature shocks.

[0074] Example 5: Example 5 is basically the same as Example 1, except that: In step (1), the phase change core material is PEG-6000 and NaNO3 in a mass ratio of 8:2. In step (2), ZrO2 nanoparticles account for 6 wt% of the total amount of the composite shell precursor solution. In step S1, ZrO2 nanoparticles account for 2 wt% of the total ternary matrix sol, Al2O3 nanoparticles account for 4 wt% of the total ternary matrix sol, and the CNF suspension concentration is 0.9 wt%. In step S2, the inorganic fiber substrate is aluminosilicate fiber felt with Al2O3 + SiO2 = 98% and a bulk density of 0.35 g / cm³. 3 Thickness 8mm, temperature resistance 1000℃.

[0075] The phase change aerogel composite insulation material in this embodiment is suitable for industrial furnace insulation (200-1000℃), has high mechanical strength, and can withstand furnace vibration and impact.

[0076] Example 6: Example 6 is basically the same as Example 3, except that: In step (1), the phase change core material is sodium sulfate and potassium sulfate in a mass ratio of 7:3. In step (2), in the composite shell precursor solution, ZrO2 nanoparticles account for 8 wt% of the total amount of the composite shell precursor solution, and Al2O3 nanoparticles account for 4 wt% of the total amount of the composite shell precursor solution. In step S1, ZrO2 nanoparticles account for 4 wt% of the total ternary matrix sol, Al2O3 nanoparticles account for 5 wt% of the total ternary matrix sol, and the concentration of CNF suspension is 1.0 wt%. In step S2, the inorganic fiber substrate is mullite fiber cloth with 3Al2O3・2SiO2 = 90% and an areal density of 220 g / m³. 2 Thickness 0.4mm, temperature resistance 1300℃, tensile strength 220MPa.

[0077] The phase change aerogel composite insulation material in this embodiment is suitable for ceramic kiln insulation (600-1300℃), has high temperature resistance and low thermal expansion, and can adapt to the high temperature operating environment of kilns.

[0078] Example 7: Example 7 is basically the same as Example 1, except that: In step (1), the phase change core material is PEG-1000 and octanoic acid in a mass ratio of 6:4. In step (2), Al2O3 nanoparticles account for 3 wt% of the total amount of the composite shell precursor solution. In step S2, the inorganic fiber substrate is ultrafine glass fiber mat with a bulk density of 0.2 g / cm³. 3 Thickness 6mm, temperature resistance 300℃.

[0079] The phase change aerogel composite insulation material in this embodiment is suitable for cold chain logistics insulated boxes (-20-0℃), can provide low-temperature insulation, and has good low-temperature freeze-thaw cycle performance.

[0080] Example 8: Example 8 is basically the same as Example 2, except that: In step (1), the phase change core material is PEG-4000 and stearic acid in a mass ratio of 7:3. In step (2), ZrO2 nanoparticles account for 4 wt% of the total amount of the composite shell precursor solution. In step S1, Al2O3 nanoparticles account for 5 wt% of the total ternary matrix sol, and the concentration of CNF suspension is 0.8 wt%. In step S2, the inorganic fiber substrate is a basalt / glass hybrid fiber cloth, with a basalt:glass ratio of 7:3 and an areal density of 180 g / m³. 2 Thickness 0.2mm, temperature resistance 600℃.

[0081] The phase change aerogel composite insulation material in this embodiment is suitable for heat insulation (0-100℃) of household appliances such as heat pump water heaters and ovens, and can resist temperature fluctuations caused by frequent start-stop of household appliances.

[0082] Example 9: Example 9 is basically the same as Example 1, except that in step (3), the surface was not modified with silane coupling agent solution before drying.

[0083] Example 10: Example 10 is basically the same as Example 1, except that in step S1, no crosslinking agent was added for pre-crosslinking when preparing the cellulose nanofiber suspension.

[0084] Comparative Example 1: Comparative Example 1 is basically the same as Example 1, except that in step (2), an ethanol solution of silicon source precursor (tetraethyl orthosilicate mass concentration of 200 g / L) is added to the water-in-oil emulsion and the pH value is adjusted to 1.8 and hydrolysis reaction is carried out at 45°C for 1.5 h. Then, the temperature is kept constant and the pH value is adjusted to 3.2 and polycondensation reaction is carried out for 2.0 h to obtain a core-shell structured microcapsule suspension.

[0085] Comparative Example 2: Comparative Example 2 is basically the same as Example 1, except that the inorganic fiber substrate was not modified in step S2.

[0086] Comparative Example 3: Comparative Example 3 is basically the same as Example 1, except that: in step S1, no cellulose nanofiber suspension is added.

[0087] The performance of the samples provided in the examples and comparative examples was tested, and the test results are shown in Table 1 below: Thermal conductivity test: refer to GB / T10294-2008; latent heat of phase change test: refer to GB / T2587-2008, DSC method; leakage rate test: gravimetric method, weighing the rate of change of weight after 50 cycles; compressive strength test: refer to GB / T14484-2021; interfacial shear strength test: refer to ASTM D3846-2016; hydrophobicity angle test: refer to GB / T30693-2014, contact angle measuring instrument.

[0088] Table 1 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 composite shell phase change microcapsules, characterized in that, The preparation method includes the following steps: (1) The phase change core material is heated to melt and then stirred and ultrasonically mixed with an organic solvent containing a composite emulsifier to obtain a water-in-oil emulsion; (2) Add a composite shell precursor solution to the water-in-oil emulsion and adjust the pH value to carry out a hydrolysis reaction, and then adjust the pH value to carry out a condensation reaction to obtain a core-shell structured microcapsule suspension; wherein, the solute in the composite shell precursor solution includes a silicon source and an inorganic reinforcing phase; (3) The core-shell structured microcapsule suspension is subjected to aging, washing and drying in sequence to obtain composite shell phase change microcapsules.

2. The preparation method according to claim 1, characterized in that, In step (1), the phase change core material is at least one of PEG-2000, PEG-4000, PEG-6000, lauric acid, decanoic acid, sodium sulfate, potassium sulfate, lithium carbonate, sodium carbonate, sodium nitrate or stearic acid; The composite emulsifier is Span-80 and Tween-60 in a mass ratio of (2~3):1, and the organic solvent is cyclohexane; and / or The content of the composite emulsifier is 1 to 1.5 wt% of the content of the phase change core material, and the mass ratio of the phase change core material to the organic solvent is 1:(2 to 3).

3. The preparation method according to claim 1, characterized in that, In step (2), the solvent of the composite shell precursor solution is ethanol; the silicon source is tetraethyl orthosilicate; and the inorganic reinforcing phase is at least one of ZrO2 nanoparticles or Al2O3 nanoparticles. Preferably, in the composite shell precursor solution, the mass concentration of the silicon source is 180-220 g / L; the inorganic reinforcing phase accounts for 3-8 wt% of the total volume of the composite shell precursor solution. More preferably, the mass ratio of the composite shell precursor solution to the phase change core material is (1.2~2):

1.

4. The preparation method according to claim 1, characterized in that, In step (2), the hydrolysis reaction is carried out at a pH of 1.5 to 2.0, a temperature of 40 to 50°C, and a time of 1 to 2 hours; and / or The condensation reaction is carried out at a pH of 3.0-3.5, a temperature of 40-50℃, and a time of 1.5-2.5h.

5. The preparation method according to claim 1, characterized in that, In step (3), the aging temperature is 65~75℃ and the time is 5~7h; and / or Before drying, the process includes a surface modification step using a silane coupling agent solution; wherein the concentration of the silane coupling agent solution is 3-5 wt%.

6. A composite shell phase change microcapsule, characterized in that, The composite shell phase change microcapsule is prepared by any one of claims 1 to 5; wherein the composite shell phase change microcapsule has the following characteristics: The particle size is 1~5μm, the shell coverage rate is ≥92%, the leakage rate after 50 phase change cycles is ≤2.2%, the latent heat retention rate of phase change is ≥95%, and the shell structure integrity is ≥95% at 900℃.

7. A method for preparing phase change aerogel composite thermal insulation material based on the composite shell phase change microcapsules described in claim 6, characterized in that, The method includes the following steps: Step S1: Mix the composite shell phase change microcapsules, ternary matrix sol and cellulose nanofiber suspension to obtain a ternary nano-reinforced phase change sol; wherein the ternary matrix sol is obtained by mixing tetraethyl orthosilicate, ZrO2 nanoparticles, Al2O3 nanoparticles, phase change promoter and water. Step S2: The modified inorganic fiber substrate is impregnated with the ternary nano-reinforced phase change sol under gradient vacuum pressure to obtain a fiber-sol composite; wherein, the modified inorganic fiber substrate is obtained by sequentially modifying the inorganic fiber substrate by plasma etching and chemical modifier immersion. Step S3: Add an ice crystal guiding agent to the fiber-sol composite for directional freezing, followed by vacuum freeze-drying, solvent gradient displacement and secondary drying to obtain the phase change aerogel composite thermal insulation material.

8. The method according to claim 7, characterized in that, In step S1, the ternary matrix sol contains tetraethyl orthosilicate at a mass concentration of 180-220 g / L; ZrO2 nanoparticles account for 2-3 wt% of the total ternary matrix sol, and Al2O3 nanoparticles account for 3-5 wt% of the total ternary matrix sol. The phase change promoter is obtained by mixing graphene quantum dots and carbon nanotubes; wherein, the preferred mass ratio of graphene quantum dots to carbon nanotubes is 3:(6~8); preferably, the phase change promoter is 0.1~0.3% of the total amount of the ternary matrix sol; More preferably, the mass ratio of the ternary matrix sol to the cellulose nanofiber suspension is (6~8):3, and the amount of composite shell phase change microcapsules added is 35~45% of the total amount of ternary nano-reinforced phase change sol.

9. The method according to claim 7, characterized in that, In step S2, the inorganic fiber substrate is fiber cloth or fiber felt; wherein the fiber cloth or fiber felt is made of at least one of glass fiber, basalt fiber, alumina fiber, silicon carbide fiber, aluminum silicate fiber or mullite fiber. Preferably, the plasma etching gas is argon, the etching power is 100~120W, and the time is 5~6min; More preferably, the chemical modifier is an ethanol solution of KH-560 grafted maleic anhydride, with a mass concentration of 2-3%, an immersion temperature of 50-60°C, and a immersion time of 25-35 min; In the fiber-sol composite, the loading of ternary nano-reinforced phase change sol is 1.5 to 2.0 times the mass of the modified inorganic fiber substrate; and / or In step S3, the ice crystal directing agent is dimethyl sulfoxide, and the amount of ice crystal directing agent added is 4~6 wt% of the fiber-sol composite.

10. A phase change aerogel composite thermal insulation material, characterized in that, The phase change aerogel composite thermal insulation material is prepared by any one of claims 7 to 9; wherein, the phase change aerogel composite thermal insulation material has the following characteristics: Thermal conductivity at room temperature ≤0.025W / (m·K), thermal conductivity at 900℃ ≤0.032W / (m·K), compressive strength 1.1~1.4MPa, interfacial shear strength 3.5~3.9MPa, delamination rate after 100 cycles of thermal cycling from -20℃ to 80℃ ≤3%, hydrophobic angle 135°~145°.

Images