Self-repairing hydrated salt phase change microcapsule as well as preparation method and application thereof

Abstract

The invention provides a self-repairing hydrated salt phase change microcapsule as well as a preparation method and application thereof, and belongs to the field of phase change materials. The preparation method comprises the following steps: preparing a hydrated salt phase change material and sorbitol into eutectic melt by adopting a melting method; strontium carbonate, sorbitol grafted nano titanium dioxide, SiO2-coated silicone rubber microspheres, hollow Al2O3 microspheres, tannic acid microcapsules, alpha-zirconium phosphate, melamine polyphosphate, diethyl aluminum hypophosphite, carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheets and hydrophilic fumed silica are added into the eutectic melt, and blending is performed to obtain a core material; The preparation method comprises the following steps: adding strontium carbonate, sorbitol grafted nano titanium dioxide, SiO2-coated silicone rubber microspheres, hollow Al2O3 microspheres, tannic acid microcapsules, alpha-zirconium phosphate, melamine polyphosphate, diethyl aluminum hypophosphite, carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheets and hydrophilic fumed silica into the eutectic melt; bio-based polyurethane-polyurea is used as a shell material, the core material is coated in the shell to prepare the microcapsule, and the temperature of the coating operation is not higher than the phase change temperature of the hydrated salt phase change material; the surface is coated with a super-hydrophobic coating. According to the invention, a solid filler system is constructed, and a low-temperature preparation process is combined, so that the phase-change microcapsule with high performance, high reliability and high safety is developed.

Description

Technical Field

[0001] This invention belongs to the field of phase change materials technology, and specifically relates to a self-healing hydrated salt phase change microcapsule, its preparation method, and its application. Background Technology

[0002] Phase change materials (PCMs) are substances that change their state of matter and provide latent heat while maintaining a constant temperature. The process of changing physical properties is called a phase change process, and PCMs absorb or release a large amount of latent heat. Hydrated salt PCMs are a class of crystalline compounds formed by the combination of inorganic salts and water molecules. They store and release thermal energy through hydration-dehydration or solid-liquid phase change processes. They are characterized by high latent heat of phase change, low cost, and good thermal conductivity, making them suitable for medium- and low-temperature thermal storage applications, such as building energy conservation and industrial waste heat recovery.

[0003] However, existing hydrated salt phase change materials (such as sodium acetate trihydrate) suffer from severe overcooling (requiring the addition of nucleating agents), poor cycle reliability (phase separation and leakage), and low thermal conductivity. To address these issues, current research involves adding nucleating agents, thickeners, and other additives to hydrated salt phase change materials and then encapsulating them in microcapsules to form phase change microcapsules. However, traditional methods for preparing high-temperature hydrated salt microcapsules have the following drawbacks: (1) Physically mixed nucleating agents are unevenly dispersed and prone to sedimentation and failure, and traditional nucleating agents (such as borax) are toxic; (2) High-temperature polymerization or post-processing processes can easily cause hydrated salt phase change materials such as sodium acetate trihydrate to lose their water of crystallization, resulting in irreversible performance degradation; (3) Adding a large amount of filler to improve thermal conductivity will significantly reduce the phase change enthalpy of the material; (4) There is a lack of consideration for the safety of the material throughout its entire life cycle, such as the potential ion leaching risk of strontium-based nucleating agents and the environmental risks of perfluorinated coatings. Therefore, developing a phase change microcapsule that combines high performance, high reliability, high safety, and suitable manufacturing process has become a pressing technical challenge in this field. Summary of the Invention

[0004] Therefore, the present invention aims to provide a self-healing hydrated salt phase change microcapsule, its preparation method and application, in order to solve at least one technical problem in the background art.

[0005] This invention is implemented as follows:

[0006] The first aspect of this invention provides a method for preparing self-healing hydrated salt phase change microcapsules, the method comprising the following steps:

[0007] Eutectic melt was prepared by a melting method using hydrated salt phase change materials and sorbitol as raw materials.

[0008] A composite nucleating agent, a self-healing system, an ion fixation agent, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system are added to the eutectic melt and blended to obtain a core material;

[0009] Microcapsules were prepared by encapsulating the core material in a shell using bio-based polyurethane-polyurea as the shell material. The encapsulation temperature was not higher than the phase change temperature of the hydrated salt phase change material.

[0010] A superhydrophobic coating is coated on the surface of the microcapsules to form self-healing hydrated salt phase change microcapsules.

[0011] The composite nucleating agent includes strontium carbonate and sorbitol-grafted nano-titanium dioxide;

[0012] The self-healing system includes SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules;

[0013] The ion fixative is α-zirconium phosphate;

[0014] The halogen-free flame retardant system includes melamine polyphosphate and aluminum diethylphosphite;

[0015] The core-shell thermal conductivity enhancement system includes carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica.

[0016] Preferably, the weight percentage of the raw materials in the core material of the self-healing hydrated salt phase change microcapsule is as follows:

[0017] Hydrated salt phase change materials: 67%~69%;

[0018] Sorbitol 17%~19%;

[0019] Strontium carbonate 3%~4%;

[0020] Sorbitol grafted onto nano-titanium dioxide at 1%~2%;

[0021] SiO2@silicone rubber microspheres 1%~2%;

[0022] Hollow Al2O3 microspheres: 0.4%~0.6%;

[0023] Tannic acid microcapsules 1.5%~2%;

[0024] Zirconium α-phosphate 0.2%~0.4%;

[0025] Melamine polyphosphate 2%~3%;

[0026] Diethylaluminum hypophosphite 0.7%~0.9%;

[0027] Carboxylated multi-walled carbon nanotubes: 0.5%~1.5%;

[0028] Polydopamine-modified boron nitride nanosheets, 0.5%~1.5%;

[0029] Hydrophilic fumed silica 0.05%~0.15%;

[0030] The hydrated salt phase change material is selected from at least one of sodium acetate trihydrate, sodium sulfate decahydrate, disodium hydrogen phosphate dodecahydrate, and calcium chloride hexahydrate;

[0031] The shell material of the self-healing hydrated salt phase change microcapsule, after curing, is 1wt% to 1.5wt% of the core material.

[0032] Preferably, the method of encapsulating the core material in the shell is selected from any one or more of the following: microfluidic method, sol-gel method, spray drying method, complex coagulation method, in-situ polymerization method, and interfacial polymerization method.

[0033] Preferably, the preparation method includes the following steps:

[0034] S1, hydrated salt phase change material and sorbitol are melt-blended in a vacuum environment at 55℃~58℃ to obtain a eutectic melt;

[0035] S2, a composite nucleating agent, a self-healing system, an ion fixative, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system are blended at room temperature in a high-speed mixer to obtain a solid filler; the solid filler is added to the eutectic melt and mixed uniformly by low-speed stirring to obtain a slurry; the slurry is added to an emulsifier aqueous solution at 5℃~10℃ and homogenized at 5000rpm~6000rpm for 2min~3min to form an emulsion-like core material;

[0036] S3, the temperature of the emulsion-like core material is maintained at 25℃~30℃, a bio-based polyurethane-polyurea prepolymer solution is added, after stirring and adsorption, an aqueous chain extender solution is added dropwise, and the reaction is carried out for 12h~20h to complete the polymerization. After washing and drying, microcapsules are obtained.

[0037] S4 uses a low-temperature plasma polymerization method to coat the surface of microcapsules with a SiOxCyHz superhydrophobic coating to form self-healing hydrated salt phase change microcapsules, where x, y, and z are the atomic ratios of O, C, and H elements, respectively.

[0038] Preferably, S4 specifically comprises:

[0039] The microcapsules prepared by S3 were placed in a low-temperature plasma chemical vapor deposition apparatus, and a reaction was carried out using hexamethyldisiloxane and oxygen as precursors at a temperature of <60°C to form a SiOxCyHz superhydrophobic coating on the surface of the microcapsules.

[0040] Preferably, the chain extender in step S3 is ethylenediamine;

[0041] The preparation steps of the bio-based polyurethane-polyurea prepolymer solution in step S3 are as follows:

[0042] Bio-based polyetheramine and HDI trimer were placed in a reactor and reacted at 50℃~55℃ under nitrogen atmosphere for 3h~4h. After the reaction was completed, the reaction product was diluted with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of 50%~60%.

[0043] The molar ratio of isocyanate groups in the HDI trimer to amino groups in the bio-based polyetheramine is 2.0~2.2.

[0044] Preferably, the preparation steps of the sorbitol-grafted nano-titanium dioxide are as follows:

[0045] A hydroxyl group was reacted with the surface of nano-titanium dioxide using a silane coupling agent to obtain aminopropyl-modified nano-titanium dioxide; this nano-titanium dioxide was then mixed with D-sorbitol and reacted in N,N-dimethylformamide (DMF) solvent under the action of a catalyst. After washing and drying, the sorbitol-grafted nano-titanium dioxide was obtained.

[0046] Preferably, the preparation steps of the polydopamine-modified boron nitride nanosheets are as follows:

[0047] Boron nitride nanosheets were ultrasonically exfoliated in a trihydroxyaminomethane-hydrochloric acid (Tris) buffer solution at room temperature. After centrifugation, the upper suspension rich in boron nitride nanosheets was collected. In an open container, dopamine hydrochloride was added dropwise to the suspension and continuously mechanically stirred at room temperature. The dopamine hydrochloride underwent oxidative self-polymerization on the surface of the boron nitride nanosheets to form a polydopamine coating, thus obtaining polydopamine-modified boron nitride nanosheets.

[0048] The second aspect of the present invention provides a self-healing hydrated salt phase change microcapsule prepared by the above-mentioned method.

[0049] The third aspect of this invention provides the application of the above-mentioned self-healing hydrated salt phase change microcapsule as a temperature regulating material in the fields of building materials, new energy, electronic equipment, power batteries, or medical cold chain.

[0050] Compared with the prior art, the beneficial effects of the present invention include:

[0051] 1. This invention constructs an innovative solid filler system consisting of a composite nucleating agent, a self-healing system, an ion immobilizer, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system. Combined with a low-temperature preparation process, it develops a phase change microcapsule that balances high performance, high reliability, and high safety.

[0052] 2. Regarding the composition of solid fillers, this invention adopts a core-shell synergistic nucleation system of "strontium carbonate + sorbitol grafted TiO2", which effectively suppresses overcooling through lattice matching and interfacial hydrogen bonding; it introduces a multi-mode self-healing system of "physical (microspheres) + chemical (hydrogen bonding) + shape memory" to overcome the cycle life problem; it constructs a multi-dimensional thermally conductive network of "carbon nanotubes + boron nitride nanosheets" to achieve high thermal conductivity with low addition amount; it adopts an α-zirconium phosphate chemical chelation and halogen-free flame retardant system, and replaces the traditional perfluorinated coating with a low-temperature plasma polymerization coating to achieve comprehensive safety and environmental protection.

[0053] 3. In the process of coating the core material with the shell, the present invention adopts a low-temperature preparation process that is "not higher than the phase change temperature of the hydrated salt phase change material throughout the process". This includes low-temperature slurry preparation, low-temperature emulsification (using the temperature difference between the two phases) and low-temperature interfacial polymerization, which fundamentally eliminates the risk of thermal damage to the hydrated salt phase change microcapsules during the preparation process.

[0054] 4. This invention prepares a bio-based polyurethane-polyurea shell through in-situ interfacial polymerization. The strategy of first synthesizing the prepolymer and then extending the chain at the interface ensures that the reaction mainly occurs at the oil-water interface, which can form a denser and more regular shell structure, significantly improving the encapsulation efficiency and mechanical strength. This invention uses bio-based polyetheramine as raw material, which is in line with the concepts of green chemistry and sustainable development, and is an important component of the product's "non-toxic" characteristics.

[0055] 5. This invention uses low-temperature plasma technology to achieve excellent coatings at temperatures below 60°C. Attached Figure Description

[0056] Figure 1 This is a process flow diagram of the preparation method of the self-healing hydrated salt phase change microcapsules of the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. In the following embodiments, unless otherwise specified, all raw materials are commercially available.

[0058] The self-healing hydrated salt phase change microcapsules consist of a core material and a shell. The core material is encapsulated within the shell, and the cured shell material comprises 1 wt% to 1.5 wt% of the core material. The weight percentages of the raw materials in the core material are as follows: hydrated salt phase change material 67% to 69%; sorbitol 17% to 19%; strontium carbonate 3% to 4%; sorbitol-grafted nano-titanium dioxide 1% to 2%; SiO2@silicone rubber microspheres 1% to 2%; hollow Al2O3 microspheres 0.4% to 0.6%; tannic acid microcapsules 1.5%. %~2%; α-zirconium phosphate 0.2%~0.4%; melamine polyphosphate 2%~3%; diethylaluminum hypophosphite 0.7%~0.9%; carboxylated multi-walled carbon nanotubes 0.5%~1.5%; polydopamine-modified boron nitride nanosheets 0.5%~1.5%; hydrophilic fumed silica 0.05%~0.15%; the hydrated salt phase change material is selected from at least one of sodium acetate trihydrate, sodium sulfate decahydrate, disodium hydrogen phosphate dodecahydrate, and calcium chloride hexahydrate, preferably sodium acetate trihydrate.

[0059] like Figure 1 As shown, a method for preparing self-healing hydrated salt phase change microcapsules includes the following steps S1 to S4.

[0060] S1, Preparation of eutectic melt: Eutectic melt is prepared by melting method using hydrated salt phase change material and sorbitol as raw materials.

[0061] S1 specifically involves melting and blending hydrated salt phase change material and sorbitol under vacuum conditions at 55℃~58℃ to obtain a eutectic melt.

[0062] In this invention, hydrated salt phase change material (preferably sodium acetate trihydrate) is the main phase change agent; sorbitol is used for eutectic modification, thereby fine-tuning the phase change point.

[0063] S2, Preparation of core material precursor: Solid filler is added to the eutectic melt and blended to obtain the core material.

[0064] S2 specifically includes:

[0065] S21, a solid filler is obtained by blending a composite nucleating agent, a self-healing system, an ion fixation agent, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system in a high-speed mixer at room temperature.

[0066] Solid filler is slowly added to the eutectic melt obtained by S22 and S1, and the mixture is stirred at low speed (generally 300 rpm to 500 rpm) to obtain a slurry. During this process, the temperature is ≤58℃.

[0067] S23, add the slurry to an emulsifier aqueous solution at 5℃~10℃, and homogenize at 5000rpm~6000rpm for 2min~3min to form an emulsion-like core material. The temperature of the emulsion is <25℃. Any emulsifier permitted in the art can be used in the emulsifier aqueous solution. In the following example, a 2% PVA aqueous solution is selected, and its amount is 5wt% of the slurry, but it is not limited to this.

[0068] The solid filler includes a composite nucleating agent, a self-healing system, an ion immobilizer, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system. The composite nucleating agent includes strontium carbonate and sorbitol-grafted nano-titanium dioxide; the self-healing system includes SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules; the ion immobilizer is α-zirconium phosphate; the halogen-free flame retardant system includes melamine polyphosphate and diethylaluminum hypophosphite; and the core-shell thermal conductivity enhancement system includes carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica.

[0069] In composite nucleating agents, the core-shell synergistic nucleation system composed of strontium carbonate and sorbitol-grafted nano-titanium dioxide effectively suppresses supercooling through lattice matching and interfacial hydrogen bonding. In specific implementation, strontium carbonate is the core component of the nucleating agent. The mismatch rate between the strontium carbonate (101) crystal plane (d=3.28Å) and the sodium acetate trihydrate (002) crystal plane (d=3.25Å) is low, effectively exerting its nucleation effect. In the sorbitol-grafted nano-titanium dioxide, sorbitol is grafted onto TiO2 at one end and forms hydrogen bonds with the hydrated salt phase change material at the other end, constructing an interfacial bridge. Sorbitol-grafted nano-titanium dioxide can be purchased directly or prepared using existing methods. In this invention, sorbitol-grafted nano-titanium dioxide is prepared in-house. The preparation steps are as follows: 1. Take 10g of hydrophilic nano-TiO2, disperse it in dilute nitric acid at pH=4, stir at 60℃ for 2 hours, centrifuge, wash with water until neutral, and vacuum dry at 100℃ to obtain activated TiO2; 2. Add 0.2ml of KH550 silane coupling agent dropwise to 10ml of a mixed acid solution containing ethanol / water (9:1) at pH=4.5, stir and hydrolyze for about 30 minutes to obtain hydrolysate; 3. Disperse 1g of activated TiO2 in 20ml of ethanol, sonicate for 30 minutes, add the hydrolysate from step 2 dropwise, and reflux at 70℃ under N2 protection for 6 hours; centrifuge, wash with ethanol 3 times to obtain aminopropyl-modified TiO2; 4. Disperse 1g of aminopropyl-modified TiO2 and 5g of D-sorbitol in 50ml 0.05 g of 4-dimethylaminopyridine (DMAP) was added to DMF as a catalyst, and the reaction was carried out at 110 °C under N2 protection for 8 hours. After the reaction was completed, the mixture was centrifuged, washed three times with DMF and ethanol, and dried under vacuum at 60 °C for 24 hours to obtain the final product, sorbitol-grafted nano-titanium dioxide.

[0070] In the self-healing system, SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules constitute a multi-mode self-healing system of "physical (microspheres) + chemical (hydrogen bonding) + shape memory". SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules can all be purchased directly or prepared using existing methods such as sol-gel, emulsion polymerization / interfacial polymerization, self-assembly, or surface modification; no specific limitations are made here. Specifically, SiO2@silicone rubber microspheres are a core-shell composite material with silica (SiO2) as the core and silicone rubber as the outer layer. In SiO2@silicone rubber microspheres, SiO2 enhances mechanical strength, silicone rubber improves flexibility, and the microspheres act as a carrier to optimize the uniformity of subsequent encapsulation. During phase transition, the silicone rubber softens and flows, carrying SiO2 to fill macroscopic cracks. Before addition, the SiO2@silicone rubber microspheres undergo dehumidification treatment (e.g., dehumidification in a 70℃ vacuum oven for 2 hours) to ensure a moisture content ≤0.5% and a particle size of 1μm~2μm. The hollow Al2O3 microspheres serve to partially replace solid SiO2@silicone rubber microspheres. While providing macroscopic repair space, the hollow Al2O3 microspheres have a lower density, further reducing the mass proportion of inactive materials. Tannic acid microcapsules are chemical repair agents that utilize their own hydrogen bonds for repair and combine with subsequent topological cross-linked polyurea to form shape memory repair.

[0071] The ion fixative is α-zirconium phosphate, which inhibits the leaching of strontium ions from the composite nucleating agent, ensuring the product is non-toxic and improving product safety.

[0072] In halogen-free flame retardant systems, melamine polyphosphate exhibits good compatibility with the shell; diethyl aluminum hypophosphite is a highly efficient phosphorus synergist that promotes char formation and suppresses smoke.

[0073] In the core-shell thermal conductivity enhancement system, carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica construct a multi-dimensional thermally conductive network of "carbon nanotubes + boron nitride nanosheets," achieving high thermal conductivity with low addition amounts. All three components—carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica—are commercially available or can be prepared using existing methods; no specific limitations are specified here. In the following examples, both the carboxylated multi-walled carbon nanotubes and the hydrophilic fumed silica are commercially available. Specifically, the carboxylated multi-walled carbon nanotubes are NC3100 series carboxylated multi-walled carbon nanotubes (custom-made) produced by Shenzhen Nanoport Co., Ltd., which are treated with a strong acid oxidation method (such as reflux of a concentrated nitric acid / concentrated sulfuric acid mixture) to introduce functional groups such as carboxyl groups (-COOH) into their walls and ports. The hydrophilic fumed silica is the FST-200 hydrophilic fumed silica produced by Zhejiang Fujit Group. Hydrophilic fumed silica is a nano-sized white powder produced by high-temperature hydrolysis of silicon halides (such as silicon tetrachloride) in an oxyhydrogen flame. Its surface is rich in silanol groups (-SiOH), which give it good hydrophilicity. It can be wetted by water and dispersed in water. It forms a three-dimensional network structure through hydrogen bonds, thus playing a key role in thickening, thixotropy, and anti-settling. The polydopamine-modified boron nitride nanosheets were prepared in-house. The preparation steps were as follows: 1. 1. 1.0 g of raw boron nitride nanosheet (BNNS) powder was added to 500 mL of 10 mM Tris buffer solution with pH=8.5; the mixture was placed in an ice-water bath and sonicated at 600 W for 4 hours using an ultrasonic cell disruptor (working mode: 2 seconds of sonication followed by 3 seconds of intermittent sonication) to obtain a well-exfoliated and uniformly dispersed BNNS suspension; the sonicated BNNS suspension was centrifuged at 10000 rpm for 15 minutes to remove the unexfoliated thick precipitate and collect the upper layer of milky white suspension rich in BNNS for later use. 2. Transfer the obtained milky white suspension to a three-necked flask and turn on the mechanical stirrer at a speed of 500 rpm. Weigh 0.5 g of dopamine hydrochloride and slowly add it to the above milky white suspension. Stir continuously at room temperature (25℃) for 24 hours. During this process, the solution color gradually changes from milky white to grayish black, indicating that dopamine has undergone oxidative self-polymerization on the surface of BNNS, forming a strong polydopamine (PDA) coating, and obtaining a PDA-BNNS composite suspension. 3. After the reaction is completed, repeatedly centrifuge and wash the obtained PDA-BNNS composite suspension with deionized water (12000 rpm, 20 minutes) until the supernatant becomes colorless and transparent to remove physically adsorbed impurities. Redisperse the washed precipitate in deionized water to form a slurry with a solid content of about 5%. Treat with vacuum freeze-drying technology (-50℃, <10Pa) for 48 hours to obtain fluffy, non-agglomerated polydopamine modified boron nitride nanosheets (i.e., PDA-BNNS).Surface modification of boron nitride nanosheets (BNNS) utilizes the strong adhesion and abundant functional groups of polydopamine (PDA) to improve the dispersibility and compatibility of BNNS in a polymer matrix, and significantly reduce the interfacial thermal resistance between BNNS and the matrix, thereby maximizing the thermal conductivity of the composite material. This method is carried out in an aqueous phase, making it safe, environmentally friendly, and efficient. When the modified PDA-BNNS is subsequently compounded with carboxylated multi-walled carbon nanotubes to construct a three-dimensional thermally conductive network, it significantly improves the uniformity of dispersion and interfacial bonding within the shell, ensuring the high thermal conductivity of the final product.

[0074] In this invention, a combination of chemical chelation of α-zirconium phosphate and a halogen-free flame retardant system is used, and a subsequent low-temperature plasma polymerization coating is used to replace the traditional perfluorinated coating, achieving comprehensive safety and environmental protection.

[0075] S3, Microcapsule preparation: Using bio-based polyurethane-polyurea as the shell material, the core material is encapsulated in the shell to form microcapsules. The encapsulation temperature is not higher than the phase change temperature of the hydrated salt phase change material.

[0076] The process of encapsulating the core material in the wall material can employ any process permitted in the art, such as microfluidics, sol-gel method, spray drying, complex coagulation, in-situ polymerization, interfacial polymerization, etc.; no specific limitation is made here. The following examples illustrate the interfacial polymerization method. The temperature of the emulsion-like core material is maintained at 25°C to 30°C. A bio-based polyurethane-polyurea prepolymer solution is added, stirred and adsorbed, and then an aqueous chain extender solution is added dropwise. The reaction is carried out for 12 to 20 hours to complete the polymerization. After washing and drying, microcapsules are obtained.

[0077] The specific steps of S3 using the interface aggregation method include:

[0078] S31. Bio-based polyetheramine and HDI trimer are placed in a dry reaction vessel equipped with a stirrer, thermometer, and condenser. The molar ratio (R value) of isocyanate groups (-NCO) in the HDI trimer to amino groups (-NH2) in the bio-based polyetheramine is strictly controlled between 2.0 and 2.2 to ensure the formation of a prepolymer with -NCO end groups. The reaction is carried out at 50℃ to 55℃ under nitrogen protection for 3 to 4 hours. After the reaction, the reaction product is diluted with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of approximately 50% to 60%. The solution is then cooled to room temperature, sealed, and stored for later use. The amount of ethyl acetate used is adjusted according to the solid content in the bio-based polyurethane-polyurea prepolymer solution.

[0079] S32, the emulsion-like core material obtained in step S2 is transferred to the polymerization reactor, and the system temperature is maintained at 25℃~30℃; under low speed stirring (200rpm~300rpm), the bio-based polyurethane-polyurea prepolymer solution obtained in S31 is slowly added dropwise. After the addition is complete, stirring is continued at this temperature for 30 minutes~40 minutes to allow the prepolymer molecules to fully migrate and adsorb at the oil-water interface of the emulsion droplets.

[0080] S33, maintaining the temperature at 30.0℃±0.5℃, slowly and uniformly add an aqueous solution of chain extender (1wt%~2wt% ethylenediamine aqueous solution, the amount of which is 0.5wt%~10wt% of the product in S32; in the following examples, an aqueous solution of 1.5wt% ethylenediamine aqueous solution is used, the amount of which is 5wt% of the product in S32, but it is not limited thereto). The amino groups of ethylenediamine diffuse in the aqueous phase to the -NCO end groups of the bio-based polyurethane-polyurea prepolymer at the interface and react rapidly to form urea bonds (-NH-CO-NH-), completing chain extension and cross-linking, forming a tough polyurea shell. After the addition is complete, continue the reaction at this low temperature for 12 hours~20 hours (preferably 18 hours~20 hours) to ensure that the reaction is complete and there are no residual -NCO groups.

[0081] S34. After the reaction is complete, filter and wash with deionized water 3 to 5 times to remove water-soluble byproducts and impurities; finally, dry in a vacuum oven at 35°C for 12 hours to obtain surface-dried microcapsules.

[0082] The maximum temperature throughout the entire process of encapsulating the core material does not exceed 35°C, perfectly avoiding the phase transition temperature (58°C) of sodium acetate trihydrate, thus fundamentally eliminating performance failure caused by thermal degradation. The strategy of first synthesizing the prepolymer and then extending the chain at the interface ensures that the reaction mainly occurs at the oil-water interface, forming a denser and more regular shell structure, significantly improving encapsulation efficiency and mechanical strength. This invention uses bio-based polyetheramine as a raw material, conforming to the concepts of green chemistry and sustainable development, and is an important component of the product's "non-toxic" characteristics.

[0083] S4, Coating preparation: SiOxCyHz superhydrophobic coating was prepared by low-temperature plasma polymerization and encapsulated in microcapsules.

[0084] Specifically, S4 involves placing the microcapsules prepared in S3 into a low-temperature plasma chemical vapor deposition (PSCVD) apparatus, using hexamethyldisiloxane and oxygen as precursors, and reacting at <60°C to form a SiOxCyHz superhydrophobic coating on the surface of the microcapsules. x, y, and z represent the atomic ratios of O, C, and H elements, respectively. These elemental ratios are not fixed and can vary depending on the process conditions and the amount of gaseous precursors used.

[0085] Example 1

[0086] A method for preparing self-healing hydrated salt phase change microcapsules, comprising the following steps:

[0087] S1, under vacuum conditions at 55°C, hydrated salt phase change material (sodium acetate trihydrate) and sorbitol are melt-blended to obtain a eutectic melt;

[0088] S2, strontium carbonate, sorbitol-grafted nano-titanium dioxide, SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, tannic acid microcapsules, α-zirconium phosphate, melamine polyphosphate, diethyl aluminum hypophosphite, carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica were blended in a high-speed mixer at room temperature to obtain a solid filler. The solid filler was slowly added to the eutectic melt and stirred and mixed evenly at 400 rpm and below 58°C to obtain a slurry. The slurry was added to a 2% PVA aqueous solution at 5°C~10°C and homogenized at 6000 rpm for 2.5 min to form an emulsion-like core material. The temperature of the emulsion was <25°C.

[0089] In step S3, bio-based polyetheramine and HDI trimer are placed in a dry reaction vessel equipped with a stirrer, thermometer, and condenser. The molar ratio (R value) of isocyanate groups (-NCO) in the HDI trimer to amino groups (-NH2) in the bio-based polyetheramine is 2.1. The reaction is carried out at 50℃~55℃ under a nitrogen atmosphere for 3.5 hours. After the reaction, the reaction product is diluted with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of approximately 50%~60%. The emulsion-like core material obtained in step S2 is transferred to the polymerization reaction vessel to maintain the volume. The temperature was maintained at 25℃~30℃. A bio-based polyurethane-polyurea prepolymer solution was slowly added dropwise under low-speed stirring at 300 rpm. After the addition was complete, stirring continued at this temperature for 30 minutes to allow the prepolymer molecules to migrate and adsorb fully at the oil-water interface of the droplets, achieving polymerization. The temperature was maintained at 30.0℃±0.5℃, and a 1.5wt% ethylenediamine aqueous solution was slowly and uniformly added dropwise. After the addition was complete, the reaction continued at this low temperature for 20 hours. After the reaction was completed, the mixture was filtered and washed five times with deionized water. Finally, it was dried in a vacuum oven at 35℃ for 12 hours to obtain surface-dried microcapsules.

[0090] S4. The microcapsules prepared in S3 were placed in a low-temperature plasma chemical vapor deposition apparatus. Using hexamethyldisiloxane and oxygen as precursors, discharge deposition was performed at 50°C and 250Pa for 30 minutes to form a SiOxCyHz superhydrophobic coating on the surface of the microcapsules, and finally self-healing hydrated salt phase change microcapsules were obtained.

[0091] The amount (parts by weight) of each raw material in the core material in Example 1 is shown in Table 1. After the shell is cured, it is 1.2 wt% of the core material (i.e., eutectic melt + solid filler).

[0092] Table 1

[0093]

[0094] Example 2

[0095] Example 2 is a method for preparing self-healing hydrated salt phase change microcapsules. The only difference between it and Example 1 is the amount of core material and shell. The specific raw materials of the core material are shown in Table 1. After the shell is cured, it is 1.0 wt% of the core material (i.e., eutectic melt + solid filler).

[0096] Example 3

[0097] Example 3 is a method for preparing self-healing hydrated salt phase change microcapsules. The only difference between it and Example 1 is the amount of core material and shell. The specific raw materials of the core material are shown in Table 1. After the shell is cured, it is 1.4 wt% of the core material (i.e., eutectic melt + solid filler).

[0098] Comparative Example 1

[0099] The only difference between this comparative example and Example 1 is that the sorbitol-grafted nano-titanium dioxide in step S2 is a conventional mixture of sorbitol and nano-titanium dioxide. All other steps and conditions are the same as in Example 1.

[0100] Comparative Example 2

[0101] The only difference between this comparative example and Example 1 is that the self-healing system in step S2 does not contain SiO2@silicone rubber microspheres and tannic acid microcapsules, but only hollow Al2O3 microspheres. All other steps and conditions are the same as in Example 1.

[0102] Comparative Example 3

[0103] The only difference between this comparative example and Example 1 is that in step S2, melamine polyphosphate and aluminum diethylphosphite are replaced with conventional flame retardants, namely microencapsulated red phosphorus, in the halogen-free flame retardant system. All other steps and conditions are the same as in Example 1.

[0104] Comparative Example 4

[0105] The only difference between this comparative example and Example 1 is that in step S2, the carboxylated multi-walled carbon nanotubes and polydopamine-modified boron nitride nanosheets in the core-shell thermal conductivity enhancement system are replaced with aluminum nitride. All other steps and conditions are the same as in Example 1.

[0106] Comparative Example 5

[0107] The only difference between this comparative example and Example 1 is that the temperature of slurry preparation in step S2 is increased to 75°C, while the other steps and conditions are the same as in Example 1.

[0108] Comparative Example 6

[0109] The only difference between this comparative example and Example 1 is that the reaction conditions after adding ethylenediamine solution after polymerization in step S3 are adjusted to: heat treatment at 90°C for 2 hours. All other steps and conditions are the same as in Example 1.

[0110] Comparative Example 7

[0111] The only difference between this comparative example and Example 1 is that the α-zirconium phosphate in the solid filler of step S2 is removed; all other steps and conditions are the same as in Example 1.

[0112] Comparative Example 8

[0113] The only difference between this comparative example and Example 1 is that the polydopamine-modified boron nitride nanosheets in the core-shell thermal conductivity enhancement system of step S2 are replaced with unmodified boron nitride nanosheets. All other steps and conditions are the same as in Example 1.

[0114] The phase change microcapsules prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were tested for thermal properties, repair system properties and mechanical properties. The results are shown in Table 2.

[0115] The phase transition enthalpy, phase transition temperature, and supercooling were measured using the DSC method; thermal conductivity was measured using the transient hot disk method; the number of cycles was measured according to the ASTM D7891-2015 test method; compressive strength was measured using the microsphere compression test; toxicity / environmental protection standards included: the EU mandatory standard RoHS (Restriction of Hazardous Substances in Electrical and Electronic Equipment), the EU mandatory regulation REACH (Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals), the US Environmental Protection Agency (EPA) standard test method TCLP (Test Standard No. USEPA 1311) on toxicity characteristics leaching procedures, GB 26572-2025 "Requirements for Restriction of Hazardous Substances in Electrical and Electronic Products", and GB / T39498-2020 "Guidelines for the Control of the Use of Key Chemical Substances in Consumer Products"; fire resistance was tested according to the UL-94 standard; water resistance was tested using the water contact angle test; attenuation rate = 10% attenuation / cycles; particle diameter was tested using a laser particle size analyzer; and appearance color was determined visually.

[0116] Table 2

[0117]

[0118] The phase change microcapsules prepared in Examples 1 to 3 of this invention have the characteristics of high thermal conductivity, high enthalpy, and ultra-long cycle life. They are also safe and environmentally friendly, complying with the EU's restrictions on hazardous substances (RoHS) and the EU's safety control of chemicals (REACH). Furthermore, simulation tests show that they do not leach toxic substances and pollute the environment after disposal (TCLP). They also meet my country's requirements for the prevention and control of hazardous substances and key chemical substances. They can be applied in fields such as building materials, new energy, electronic equipment, power batteries, or medical cold chain.

[0119] The supercooling of Comparative Example 1 (physically mixed TiO2 / sorbitol) was as high as 6.8°C, while that of Example 1 of the present invention was only 1.2°C. This indicates that simple physical mixing cannot achieve the efficient heterogeneous nucleation effect brought about by "interface engineering".

[0120] Comparative Example 2 (without a self-healing system) failed after 5000 cycles and had the lowest compressive strength (12.0 MPa). Example 1, however, exceeded 10000 cycles and exhibited high compressive strength (18.5 MPa). This indicates that the combination of physically repairing microspheres and the chemical repair agent (tannic acid) produced a synergistic effect of "1+1>2," significantly improving the material's durability.

[0121] Comparative Example 3 (using microencapsulated red phosphorus MRP) resulted in a pink product, which failed to meet the color requirements of high-end applications and raised concerns about potential toxicity.

[0122] The thermal conductivity of Comparative Example 4 (using AlN powder) was only 1.2 W / m·K, far lower than that of Example 1 (2.4 W / m·K). This demonstrates that the multidimensional synergistic thermal conductivity network constructed by "CNT (one-dimensional) + BNNS (two-dimensional)" is far superior to traditional particulate fillers in improving thermal conductivity efficiency.

[0123] Comparative Example 5 (slurry prepared at 75℃) suffered water loss from PCM due to high temperature, resulting in a sharp drop in enthalpy to 152J / g and a discrete phase transition temperature, leading to the product's near failure.

[0124] Comparative Example 6 (post-treatment at 90℃) resulted in the destruction of the microcapsule structure, with a cycle life of only 950 cycles.

[0125] The phase change microcapsules prepared in Comparative Examples 5 and 6 have significantly lower performance than those in Example 1. The low-temperature preparation process of this invention, which ensures that the phase change temperature of the phase change material is ≤58°C throughout the process, guarantees high performance and high reliability.

[0126] Comparative Example 7 (without α-zirconium phosphate) exceeded the strontium ion leaching limit in the TCLP test, proving that simple physical encapsulation is not enough to ensure absolute safety. "α-zirconium phosphate chemical chelation" is a necessary technical feature to ensure that the product is non-toxic.

[0127] Compared to the surface modification of boron nitride nanosheets (BNNS) with polydopamine (PDA) in Example 1, the use of unmodified BNNS in Comparative Example 8 directly led to a significant decrease in thermal conductivity and serious damage to mechanical properties and cycle life. This is because unmodified BNNS is prone to agglomeration and has weak bonding with the shell, forming phonon scattering centers and stress concentration points.

[0128] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing self-healing hydrated salt phase change microcapsules, characterized in that, The preparation method includes the following steps: Eutectic melt was prepared by a melting method using hydrated salt phase change materials and sorbitol as raw materials. A composite nucleating agent, a self-healing system, an ion fixation agent, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system are added to the eutectic melt and blended to obtain a core material; Microcapsules were prepared by encapsulating the core material in a shell using bio-based polyurethane-polyurea as the shell material. The encapsulation temperature was not higher than the phase change temperature of the hydrated salt phase change material. A superhydrophobic coating is coated on the surface of the microcapsules to form self-healing hydrated salt phase change microcapsules. The composite nucleating agent includes strontium carbonate and sorbitol-grafted nano-titanium dioxide; The self-healing system includes SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules; The ion fixative is α-zirconium phosphate; The halogen-free flame retardant system includes melamine polyphosphate and aluminum diethylphosphite; The core-shell thermal conductivity enhancement system includes carboxylated multi-walled carbon nanotubes, polydopamine-modified boron nitride nanosheets, and hydrophilic fumed silica.

2. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 1, characterized in that, The weight percentage of raw materials in the core material of the self-healing hydrated salt phase change microcapsules is as follows: Hydrated salt phase change materials: 67%~69%; Sorbitol 17%~19%; Strontium carbonate 3%~4%; Sorbitol grafted onto nano-titanium dioxide at 1%~2%; SiO2@silicone rubber microspheres 1%~2%; Hollow Al2O3 microspheres: 0.4%~0.6%; Tannic acid microcapsules 1.5%~2%; Zirconium α-phosphate 0.2%~0.4%; Melamine polyphosphate 2%~3%; Diethylaluminum hypophosphite 0.7%~0.9%; Carboxylated multi-walled carbon nanotubes: 0.5%~1.5%; Polydopamine-modified boron nitride nanosheets, 0.5%~1.5%; Hydrophilic fumed silica 0.05%~0.15%; The hydrated salt phase change material is selected from at least one of sodium acetate trihydrate, sodium sulfate decahydrate, disodium hydrogen phosphate dodecahydrate, and calcium chloride hexahydrate; The mass of the shell material in the self-healing hydrated salt phase change microcapsule after curing is 1wt%~1.5wt% of the core material.

3. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 2, characterized in that, The method of encapsulating the core material in the shell is selected from any one or more combinations of microfluidics, sol-gel, spray drying, complex coagulation, in-situ polymerization, and interfacial polymerization.

4. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 3, characterized in that, The preparation method includes the following steps: S1, hydrated salt phase change material and sorbitol are melt-blended in a vacuum environment at 55℃~58℃ to obtain a eutectic melt; S2, a composite nucleating agent, a self-healing system, an ion fixative, a halogen-free flame retardant system, and a core-shell thermal conductivity enhancement system are blended at room temperature in a high-speed mixer to obtain a solid filler; the solid filler is added to the eutectic melt and mixed uniformly by low-speed stirring to obtain a slurry; the slurry is added to an emulsifier aqueous solution at 5℃~10℃ and homogenized at 5000rpm~6000rpm for 2min~3min to form an emulsion-like core material; S3, the temperature of the emulsion-like core material is maintained at 25℃~30℃, a bio-based polyurethane-polyurea prepolymer solution is added, after stirring and adsorption, an aqueous chain extender solution is added dropwise, and the reaction is carried out for 12h~20h to complete the polymerization. After washing and drying, microcapsules are obtained. S4 uses a low-temperature plasma polymerization method to coat the surface of microcapsules with a SiOxCyHz superhydrophobic coating to form self-healing hydrated salt phase change microcapsules, where x, y, and z are the atomic ratios of O, C, and H elements, respectively.

5. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 4, characterized in that, Specifically, S4 is: The microcapsules prepared by S3 were placed in a low-temperature plasma chemical vapor deposition apparatus, and a reaction was carried out using hexamethyldisiloxane and oxygen as precursors at a temperature of <60°C to form a SiOxCyHz superhydrophobic coating on the surface of the microcapsules.

6. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 4, characterized in that, The chain extender in step S3 is ethylenediamine; The preparation steps of the bio-based polyurethane-polyurea prepolymer solution in step S3 are as follows: Bio-based polyetheramine and HDI trimer were placed in a reactor and reacted at 50℃~55℃ under nitrogen atmosphere for 3h~4h. After the reaction was completed, the reaction product was diluted with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of 50%~60%. The molar ratio of isocyanate groups in the HDI trimer to amino groups in the bio-based polyetheramine is 2.0~2.

2.

7. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 1, characterized in that, The preparation steps of the sorbitol-grafted nano-titanium dioxide are as follows: Hydroxylation reaction was carried out on the surface of nano-titanium dioxide using a silane coupling agent to obtain aminopropyl-modified nano-titanium dioxide; it was then mixed with D-sorbitol and reacted in N,N-dimethylformamide solvent under the action of a catalyst. After washing and drying, the sorbitol-grafted nano-titanium dioxide was obtained.

8. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 1, characterized in that, The preparation steps of the polydopamine-modified boron nitride nanosheets are as follows: Boron nitride nanosheets were ultrasonically exfoliated in a trihydroxyaminomethane-hydrochloric acid buffer solution at room temperature. After centrifugation, the upper suspension rich in boron nitride nanosheets was collected. Dopamine hydrochloride was added dropwise to the suspension in an open container and mechanically stirred continuously at room temperature. Dopamine hydrochloride underwent oxidative self-polymerization on the surface of boron nitride nanosheets to form a polydopamine coating, thus obtaining polydopamine-modified boron nitride nanosheets.

9. The self-healing hydrated salt phase change microcapsules prepared by the preparation method of any one of claims 1 to 8.

10. The application of the self-healing hydrated salt phase change microcapsule as described in claim 9 as a temperature-regulating material in the fields of building materials, electronic equipment, new energy, power batteries, or medical cold chain.

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