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

Abstract

The application provides a self-repairing hydrated salt phase change microcapsule and a preparation method and application thereof, and belongs to the field of phase change materials. The preparation method comprises the following steps: preparing a eutectic melt of a hydrated salt phase change material and sorbitol by using a melting method; adding strontium carbonate, sorbitol grafted nano titanium dioxide, SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, tannic acid microcapsules, alpha-zirconium phosphate, melamine polyphosphate, aluminum diethyl phosphinate, carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheet and hydrophilic fumed silica into the eutectic melt to obtain a core material; using bio-based polyurethane-polyurea as a shell material, coating the core material in the shell to obtain the microcapsule, and the temperature of the coating operation is not higher than the phase change temperature of the hydrated salt phase change material; and coating an ultrahydrophobic coating on the surface. The application constructs a solid filler system, combines a low-temperature preparation process, and develops the phase change microcapsule with high performance, high reliability and high safety.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of phase change materials, and particularly relates to a self-repairing hydrated salt phase change microcapsule and a preparation method and application thereof. BACKGROUND

[0002] A phase change material refers to a substance that changes the state of matter without changing the temperature and can provide latent heat; the process of changing physical properties is called a phase change process, and a phase change material will absorb or release a large amount of latent heat. A hydrated salt phase change material is a kind of crystal compound formed by combining inorganic salts and water molecules, and realizes the storage and release of heat energy through the hydration-dehydration or solid-liquid phase change process; the hydrated salt phase change material has the characteristics of high phase change latent heat, low cost and good thermal conductivity, and is suitable for medium and low temperature heat storage applications, such as building energy saving, industrial waste heat recovery and the like.

[0003] However, the existing hydrated salt phase change materials (such as sodium acetate trihydrate) have serious supercooling phenomenon (a nucleating agent needs to be added), poor cycle reliability (phase separation and leakage), and low thermal conductivity. In order to solve the above problems, the existing research adds nucleating agents, thickening agents and other additives to the hydrated salt phase change material, and then encapsulates the hydrated salt phase change material in a microcapsule to form a phase change microcapsule. However, the preparation method of the traditional high-temperature hydrated salt microcapsule has the following defects: (1) the physical mixing of the nucleating agent is not uniform and is easy to settle and fail, and the traditional nucleating agent (such as borax) has toxicity; (2) the high-temperature polymerization or post-processing process is easy to cause the hydrated salt phase change material such as sodium acetate trihydrate to lose crystal water, resulting in irreversible performance degradation; (3) a large amount of fillers are added to improve the thermal conductivity, which will significantly reduce the phase change enthalpy of the material; (4) there is a lack of consideration of the safety of the material throughout the life cycle, such as the potential ion leaching risk of strontium nucleating agent and the environmental risk of perfluorinated coating. Therefore, it has become a technical problem to be solved in the field to develop a phase change microcapsule with high performance, high reliability, high safety and suitable process. SUMMARY

[0004] In view of this, the present application aims to provide a self-repairing hydrated salt phase change microcapsule and a preparation method and application thereof, and to solve at least one technical problem in the background art.

[0005] The present application is implemented as follows:

[0006] The first aspect of the present application provides a preparation method of a self-repairing hydrated salt phase change microcapsule, which comprises the following steps:

[0007] Preparation of a eutectic melt based on a melting method using hydrated salt phase change materials and sorbitol as raw materials;

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

[0009] The microcapsule is prepared by coating the core material in the shell with the bio-based polyurethane-polyurea as the shell material, and the temperature of the coating operation is not higher than the phase change temperature of the hydrated salt phase change material;

[0010] The self-repairing hydrated salt phase change microcapsule is formed by coating an ultrahydrophobic coating on the surface of the microcapsule;

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

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

[0013] The ion fixing agent is α-zirconium phosphate;

[0014] The halogen-free flame retardant system comprises melamine polyphosphate and aluminum diethyl phosphinate;

[0015] The core-shell heat conduction enhancement system comprises 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-repairing hydrated salt phase change microcapsule is as follows:

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

[0018] Sorbitol 17%~19%;

[0019] Strontium carbonate 3%~4%;

[0020] Sorbitol grafted nano titanium dioxide 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] α-Zirconium phosphate 0.2%~0.4%;

[0025] Melamine polyphosphate 2%~3%;

[0026] Aluminum diethyl phosphinate 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, calcium chloride hexahydrate;

[0031] the shell material in the self-repairing hydrated salt phase change microcapsule is 1wt%~1.5wt% of the core material after solidification.

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

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

[0034] S1, melt and blend the hydrated salt phase change material and sorbitol under vacuum environment at 55℃~58℃ to obtain a eutectic melt;

[0035] S2, blend the composite nucleating agent, self-repairing system, ion fixing agent, halogen-free flame retardant system, and core-shell heat conduction enhancement system in a high-speed mixer at room temperature to obtain a solid filler; add the solid filler to the eutectic melt and mix uniformly at low speed to obtain a slurry; add the slurry to an aqueous emulsifier solution at 5℃~10℃, and homogenize at a speed of 5000rpm~6000rpm for 2min~3min to form an emulsion-like core material;

[0036] S3, maintain the temperature of the emulsion-like core material at 25℃~30℃, add a bio-based polyurethane-polyurea prepolymer solution, stir and adsorb, then add an aqueous chain extender solution dropwise, and react for 12h~20h to complete polymerization; wash and dry to obtain microcapsules;

[0037] S4, use a low-temperature plasma polymerization method to coat a SiOxCyHz superhydrophobic coating on the surface of the microcapsules to form self-repairing hydrated salt phase change microcapsules, wherein x, y, and z are the atomic proportions of O element, C element, and H element, respectively.

[0038] Preferably, S4 is specifically:

[0039] Place the microcapsules prepared in S3 in a low-temperature plasma chemical vapor deposition device, use hexamethyldisiloxane and oxygen as precursors, and react at <60℃ 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:

[0042] The bio-based polyether amine and the HDI trimer are placed in a reaction kettle, and reacted for 3-4 hours at a temperature of 50-55 DEG C under the protection of a nitrogen atmosphere; after the reaction is completed, the reaction product is 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 polyether amine is 2.0-2.2.

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

[0045] The hydroxyl groups on the surface of the nano-titanium dioxide are reacted with a silane coupling agent to obtain amino propyl modified nano-titanium dioxide; the nano-titanium dioxide is mixed with D-sorbitol, and reacted in a N,N-dimethylformamide (DMF) solvent under the action of a catalyst; after washing and drying, the sorbitol grafted nano-titanium dioxide is obtained.

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

[0047] The boron nitride nanosheet is ultrasonically exfoliated in a tris-hydroxyl aminomethane-hydrochloric acid (Tris) buffer at room temperature, and the upper layer of the suspension rich in boron nitride nanosheet is collected after centrifugation; dopamine hydrochloride is added dropwise to the suspension in an open container, and continuous mechanical stirring is performed at room temperature; the dopamine hydrochloride is oxidatively polymerized on the surface of the boron nitride nanosheet to form a polydopamine coating, and the polydopamine modified boron nitride nanosheet is obtained.

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

[0049] The third aspect of the present application provides the application of the above-mentioned self-repairing 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 application include:

[0051] 1. The present application constructs an innovative solid filler system of composite nucleating agent + self-repairing system + ion fixing agent + halogen-free flame-retardant system + core-shell heat-conducting enhancement system, and develops a phase change microcapsule with high performance, high reliability and high safety by combining with a low-temperature preparation process.

[0052] 2. On the solid filler component, the application adopts a "strontium carbonate + sorbitol grafted TiO2" core-shell synergistic nucleation system, which effectively suppresses supercooling through lattice matching and interfacial hydrogen bonding; introduces a multi-mode self-repairing system of "physical (microspheres) + chemical (hydrogen bonding) + shape memory" to solve the problem of cycle life; constructs a multi-dimensional heat conduction network of "carbon nanotubes + boron nitride nanosheets" to achieve high thermal conductivity at low addition amount; uses alpha-zirconium phosphate chemical chelation and halogen-free flame retardant system, and replaces traditional perfluorinated coating with low-temperature plasma polymer coating to achieve all-round safety and environmental protection.

[0053] 3. The application adopts a low-temperature preparation process of "under the condition that the phase transition temperature of the hydrated salt phase change material is not higher than the temperature" in the process of coating the shell on the core material, including low-temperature slurry preparation, low-temperature emulsification (utilizing the temperature difference of two phases) and low-temperature interfacial polymerization, which fundamentally eliminates the risk of thermal damage of hydrated salt phase change microcapsules in the preparation process.

[0054] 4. The application prepares a bio-based polyurethane-polyurea shell through in-situ interfacial polymerization reaction, and the strategy of synthesizing prepolymer first and then interfacial chain extension ensures that the reaction mainly occurs at the oil-water interface, which can form a more compact and regular shell structure, significantly improving the encapsulation efficiency and mechanical strength; the application uses bio-based polyether amine as raw material, which meets the green chemistry and sustainable development concept, and is an important part of the "non-toxic" feature of the product.

[0055] 5. The application uses low-temperature plasma technology to achieve excellent coating at <60℃. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 The process flow chart of the preparation method of the self-repairing hydrated salt phase change microcapsule of the application. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical scheme and advantages of the application more clear and explicit, the application will be further described in detail below combined with examples. It should be understood that the specific implementation cases described here are only used to explain the application, and are not used to limit the application. In the following examples, all raw materials can be purchased through commercial channels unless otherwise specified.

[0058] The self-repairing hydrated salt phase change microcapsule comprises a core material and a shell, the core material is wrapped in the shell, and the shell material is 1wt%-1.5wt% of the core material after solidification; wherein the weight percentage of raw materials in the core material is as follows: 67%-69% of hydrated salt phase change material; 17%-19% of sorbitol; 3%-4% of strontium carbonate; 1%-2% of sorbitol grafted nano titanium dioxide; 1%-2% of SiO2@silicone rubber microspheres; 0.4%-0.6% of hollow Al2O3 microspheres; 1.5%-2% of tannic acid microcapsules; 0.2%-0.4% of alpha-zirconium phosphate; 2%-3% of melamine polyphosphate; 0.7%-0.9% of aluminum diethyl phosphinate; 0.5%-1.5% of carboxylated multi-walled carbon nanotubes; 0.5%-1.5% of polydopamine modified boron nitride nanosheet; 0.05%-0.15% of hydrophilic fumed silica; and 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] As shown in Figure 1 A preparation method of the self-repairing hydrated salt phase change microcapsule comprises the following steps S1-S4.

[0060] S1, preparing a eutectic melt: taking hydrated salt phase change material and sorbitol as raw materials, a eutectic melt is prepared based on a melting method.

[0061] S1 specifically refers to: under the condition of 55-58 DEG C and vacuum environment, the hydrated salt phase change material and sorbitol are melt blended to prepare a eutectic melt.

[0062] In the present application, the hydrated salt phase change material (preferably sodium acetate trihydrate) is the phase change main body; sorbitol is used for eutectic modification, and then the phase change point is fine-tuned.

[0063] S2, preparing a core material precursor: adding solid fillers to the eutectic melt to obtain a core material by blending.

[0064] S2 specifically comprises:

[0065] S21, the composite nucleating agent, self-repairing system, ion fixing agent, halogen-free flame retardant system and core-shell heat conduction enhancement system are blended at room temperature in a high-speed mixer to obtain a solid filler;

[0066] S22, the eutectic melt prepared in S1 is slowly added with the solid filler, and the mixture is uniformly stirred at a low speed (generally 300-500 rpm) to obtain a slurry, and the temperature in the process is ≤58 DEG C;

[0067] S23, add the slurry to an emulsifier aqueous solution at 5-10℃, homogenize at 5000-6000 rpm for 2-3 min to form an emulsion-like core material, the temperature of the emulsion <25℃; the emulsifier aqueous solution can be any emulsifier allowed in the art, the following examples use 2% PVA aqueous solution, the amount is 5wt% of the slurry, but not limited thereto.

[0068] The solid filler includes a composite nucleating agent, a self-repairing system, an ion fixing agent, a halogen-free flame-retardant system, and a core-shell heat-conducting enhancement system. The composite nucleating agent includes strontium carbonate and sorbitol grafted nano titanium dioxide. The self-repairing system includes SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, and tannic acid microcapsules. The ion fixing agent is alpha-zirconium phosphate. The halogen-free flame-retardant system includes melamine polyphosphate and diethyl aluminum phosphinate. The core-shell heat-conducting enhancement system includes carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheets, and hydrophilic fumed silica.

[0069] In the composite nucleating agent, the core-shell synergistic nucleating system composed of strontium carbonate and sorbitol grafted nano titanium dioxide effectively inhibits supercooling through lattice matching and interfacial hydrogen bonding. In specific implementations, strontium carbonate is the core component of the nucleating agent. The mismatch rate between the (101) crystal plane of strontium carbonate (d=3.28 Å) and the (002) crystal plane of sodium acetate trihydrate (d=3.25 Å) is low, effectively playing a nucleating role. Sorbitol in sorbitol grafted nano titanium dioxide is grafted with TiO2 on one end and forms a hydrogen bond with the hydrated salt phase change material on the other end, building an interfacial bridge. Sorbitol grafted nano titanium dioxide can be purchased directly for use or prepared using existing methods. In this invention, sorbitol grafted nano titanium dioxide is self-prepared, and the preparation steps are as follows: 1. Take 10 g of hydrophilic nano TiO2 and disperse it in dilute nitric acid with pH=4. Stir at 60℃ for 2 hours, centrifuge, and wash with water until neutral. Dry at 100℃ under vacuum to obtain activated TiO2; 2. Add 0.2 ml of KH550 silane coupling agent to 10 ml of mixed acid solution containing ethanol / water (9:1) with pH=4.5. Stir for about 30 minutes to obtain a hydrolysis solution; 3. Disperse 1 g of activated TiO2 in 20 ml of ethanol and ultrasonic for 30 minutes. Add the hydrolysis solution of step 2 and reflux at 70℃ under N2 protection for 6 hours. Centrifuge and wash with ethanol for 3 times to obtain amino propyl modified TiO2; 4. Disperse 1 g of amino propyl modified TiO2 and 5 g of D-sorbitol in 50 ml of DMF. Add 0.05 g of 4-dimethylaminopyridine (DMAP) as a catalyst. React at 110℃ under N2 protection for 8 hours; 5. After the reaction is completed, separate by centrifugation, and wash with DMF and ethanol for 3 times in turn. Dry at 60℃ under vacuum for 24 hours to obtain the final product, sorbitol grafted nano titanium dioxide.

[0070] In the self-repairing system, SiO2@silicone rubber microspheres, hollow Al2O3 microspheres and tannic acid microcapsules form a multi-mode self-repairing system of "physical (microspheres) + chemical (hydrogen bond) + shape memory". SiO2@silicone rubber microspheres, hollow Al2O3 microspheres and tannic acid microcapsules can be directly purchased and used, or can be prepared by existing methods such as sol-gel method, emulsion polymerization / interface polymerization, self-assembly or surface modification, and are not specifically limited here. Among them, SiO2@silicone rubber microspheres are a kind of core-shell structure composite material with silica (SiO2) as the core and silicone rubber as the outer layer. SiO2 in SiO2@silicone rubber microspheres enhances mechanical strength, silicone rubber improves flexibility, microspheres as carriers optimize subsequent encapsulation uniformity, silicone rubber softens and flows during phase change, and carries SiO2 to fill macroscopic cracks. SiO2@silicone rubber microspheres are dehumidified before being added (such as 70°C vacuum oven dehumidification for 2h), so that the water content is ≤0.5% and the particle size is 1μm~2μm. The role of hollow Al2O3 microspheres is to replace part of the solid SiO2@silicone rubber microspheres, and the hollow Al2O3 microspheres provide macroscopic repair space while having lower density, further reducing the mass ratio of non-active materials; tannic acid microcapsules are chemical repair agents, which use their own hydrogen bonds to repair, and combine with subsequent topological cross-linked polyurea to form shape memory repair.

[0071] The ion fixative uses α-zirconium phosphate, which inhibits the leaching of strontium ions in the composite nucleating agent, ensures the non-toxicity of the product, and improves the safety of the product;

[0072] In the halogen-free flame-retardant system, melamine polyphosphate has good compatibility with the shell; diethyl aluminum hypophosphite is a high-efficiency phosphorus-based synergist that promotes charring and smoke suppression.

[0073] In the core-shell heat conduction enhancement system, carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheets and hydrophilic fumed silica construct a "carbon nanotube + boron nitride nanosheet" multi-dimensional heat conduction network to achieve high thermal conductivity at low addition amount; carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheets and hydrophilic fumed silica can be directly purchased and used, or can be prepared by existing methods, which are not specifically limited herein. In the following examples, carboxylated multi-walled carbon nanotubes and hydrophilic fumed silica are commercially available, wherein the carboxylated multi-walled carbon nanotubes are NC3100 series carboxylated multi-walled carbon nanotubes produced by Shenzhen Nanogate Co., Ltd. (customized), which uses strong acid oxidation method (such as concentrated nitric acid / concentrated sulfuric acid mixture reflux) to treat original carbon nanotubes to introduce functional groups such as carboxyl groups (-COOH) on the tube wall and port. The hydrophilic fumed silica is hydrophilic FST-200 fumed silica produced by Zhejiang Fuji Group, which is a nanoscale white powder made by hydrolysis of silicon halide (such as silicon tetrachloride) at high temperature in hydrogen oxygen flame, and its surface is rich in silicon hydroxyl groups (-SiOH), which makes it have good hydrophilicity, can be wetted by water and dispersed in water, and forms a three-dimensional network structure through hydrogen bonds, thereby playing a key role in thickening, thixotropy, anti-settling and the like. The polydopamine modified boron nitride nanosheet is self-prepared, and the preparation steps are as follows: 1. 1.0 g of original boron nitride nanosheet (BNNS) powder is added to 500 mL of Tris buffer solution with a concentration of 10 mM and pH=8.5; the mixture is placed in an ice water bath, and an ultrasonic cell disruptor is used for ultrasonic treatment at a power of 600 W for 4 hours (working mode: ultrasonic for 2 seconds, intermittent for 3 seconds) to obtain a well-exfoliated and uniformly dispersed BNNS suspension; the BNNS suspension after ultrasonic treatment is centrifuged at 10000 rpm for 15 minutes to remove the thick layer of unexfoliated precipitate, and the upper layer of the white suspension rich in BNNS is collected for use. 2. The white suspension is transferred to a three-necked flask, and the mechanical stirring is started with a speed of 500 rpm; 0.5 g of dopamine hydrochloride is slowly added to the white suspension, and the stirring is continued at room temperature (25°C) for 24 hours, during which the solution color gradually changes from white to gray-black, indicating that dopamine has undergone oxidative self-polymerization on the surface of BNNS to form a firm polydopamine (PDA) coating, and a PDA-BNNS composite suspension is obtained; 3. After the reaction is completed, the PDA-BNNS composite suspension is repeatedly washed with deionized water (12000 rpm, 20 minutes) until the supernatant becomes colorless and transparent to remove the physically adsorbed impurities, and the washed precipitate is dispersed in deionized water again to form a slurry with a solid content of about 5%; a vacuum freeze-drying technology (-50°C, <10 Pa) is used for 48 hours to obtain fluffy and non-agglomerated polydopamine modified boron nitride nanosheets (i.e. PDA-BNNS).The surface of boron nitride nanosheet (BNNS) is modified, the strong adhesion and rich functional groups of polydopamine (PDA) are utilized to improve the dispersibility and compatibility of BNNS in the polymer matrix, and significantly reduce the interfacial thermal resistance between the matrix and the BNNS, so as to maximize the thermal conductivity of the composite material. The method is carried out in water phase, which is safe, environmentally friendly and efficient. When the modified PDA-BNNS is subsequently compounded with carboxylated multi-walled carbon nanotubes to form a three-dimensional thermal conduction network, the dispersibility and interfacial bonding force of the PDA-BNNS in the shell can be significantly improved, which provides a guarantee for the high thermal conductivity of the final product.

[0074] In the present application, chemical chelation of alpha-zirconium phosphate and halogen-free flame retardant system are combined, and subsequent low temperature plasma polymer coating is used to replace traditional perfluorinated coating, realizing all-round safety and environmental protection.

[0075] S3, preparing microcapsules: using bio-based polyurethane-polyurea as shell material, the core material is coated in the shell to form microcapsules, and the temperature of the coating operation 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 adopt the process allowed in the art, such as microfluidic method, sol-gel method, spray drying method, complex coagulation method, in-situ polymerization method, interfacial polymerization method, etc. The following examples are illustrated by the interfacial polymerization method, the temperature of the emulsion-like core material is maintained at 25-30℃, the bio-based polyurethane-polyurea prepolymer solution is added, stirred and adsorbed, then the chain extender aqueous solution is added dropwise, and the reaction is carried out for 12-20h to complete the polymerization, and then the microcapsules are obtained by washing and drying.

[0077] S3, the steps of using the interfacial polymerization method specifically include:

[0078] S31, the bio-based polyether amine and HDI trimer are placed in a dry reaction kettle, the reaction kettle is provided with a stirrer, a thermometer and a condenser, wherein the molar ratio (R value) of isocyanate group (-NCO) in HDI trimer to amino group (-NH2) in bio-based polyether amine is strictly controlled between 2.0-2.2 to ensure that the prepolymer with terminal group -NCO is generated; the reaction is carried out at 50-55℃ under nitrogen protection for 3-4h, after the reaction is completed, the reaction product is diluted with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of about 50%-60%, and then the temperature is lowered to room temperature for sealing storage, and the amount of ethyl acetate is adjusted according to the solid content of the bio-based polyurethane-polyurea prepolymer solution;

[0079] S32, transfer the emulsion-like core material prepared in step S2 to a polymerization reactor, and maintain the system temperature at 25-30 DEG C; under low-speed stirring (200-300 rpm), slowly drop the bio-based polyurethane-polyurea prepolymer solution prepared in S31, and after the dropping is completed, continue to stir at this temperature for 30-40 minutes to allow the prepolymer molecules to fully migrate and adsorb at the oil-water interface of the emulsion droplets;

[0080] S33, maintain the temperature at 30.0 DEG C + / - 0.5 DEG C, slowly and uniformly drop the chain extender aqueous solution (1-2 wt% ethylenediamine aqueous solution, the amount is 0.5-10 wt% of the product of S32, the following examples select 1.5 wt% ethylenediamine aqueous solution, the amount is 5 wt% of the product of S32, but not limited to this), the amino group of ethylenediamine diffuses to the interface of the bio-based polyurethane-polyurea prepolymer in the aqueous phase, and the -NCO end group rapidly reacts to form a urea bond (-NH-CO-NH-), completing the chain extension and crosslinking, forming a tough polyurea shell, after the dropping is completed, continue to react at this low temperature for 12-20 hours (preferably 18-20 hours) to ensure that the reaction is complete and there is no residual -NCO group;

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

[0082] The highest temperature of the shell covering the core material does not exceed 35 DEG C, perfectly avoiding the phase transition temperature (58 DEG C) of sodium acetate trihydrate, and fundamentally eliminating the performance failure caused by thermal degradation. The strategy of synthesizing a prepolymer first and then interfacial chain extension ensures that the reaction mainly occurs at the oil-water interface, can form a more compact and more regular shell structure, and significantly improves the encapsulation efficiency and mechanical strength; the present application uses bio-based polyether amine as raw material, which meets the green chemistry and sustainable development concept, and is an important part of the "non-toxic" feature of the product.

[0083] S4, preparation of coating: using low-temperature plasma polymerization method to coat SiOxCyHz super-hydrophobic coating on the microcapsules.

[0084] S4 is specifically: placing the microcapsules prepared in S3 in a low-temperature plasma chemical vapor deposition device, using hexamethyldisiloxane and oxygen as precursors, and reacting at <60 DEG C to form a SiOxCyHz super-hydrophobic coating on the surface of the microcapsules, x, y, and z are the atomic proportions of O element, C element, and H element, respectively, and the proportions of these elements are not fixed and can vary according to the process conditions and the amount of gas precursors used.

[0085] Example 1

[0086] A preparation method of self-repairing hydrated salt phase change microcapsules, comprising the following steps:

[0087] S1, melt and blend hydrated salt phase change material (sodium acetate trihydrate) and sorbitol under vacuum environment at 55℃ to obtain eutectic melt;

[0088] S2, blend strontium carbonate, sorbitol, grafted nano titanium dioxide, SiO2@silicone rubber microspheres, hollow Al2O3 microspheres, tannin acid microcapsules, alpha-zirconium phosphate, melamine polyphosphate, aluminum diethyl phosphinate, carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheet and hydrophilic fumed silica in a high-speed mixer at room temperature to obtain solid fillers; slowly add the solid fillers into the eutectic melt, and stir uniformly at a speed of 400 rpm and a temperature below 58℃ to obtain slurry; add the slurry into 2% PVA aqueous solution at 5℃-10℃, and homogenize at a speed of 6000 rpm for 2.5 min to form emulsion-like core material, and the temperature of the emulsion is <25℃;

[0089] S3, place bio-based polyetheramine and HDI trimer in a dry reaction kettle equipped with a stirrer, a thermometer and a condenser tube, wherein the molar ratio (R value) of isocyanate group (-NCO) in the HDI trimer to amino group (-NH2) in the bio-based polyetheramine is 2.1; react at a temperature of 50℃-55℃ in a nitrogen atmosphere for 3.5 h; after the reaction is completed, dilute the reaction product with ethyl acetate to obtain a bio-based polyurethane-polyurea prepolymer solution with a solid content of about 50%-60%; transfer the emulsion-like core material prepared in step S2 into a polymerization reaction kettle, and maintain the system temperature at 25℃-30℃; slowly and dropwise add the bio-based polyurethane-polyurea prepolymer solution under low-speed stirring at 300 rpm; after the dropwise addition is completed, continue to stir at this temperature for 30 min to allow the prepolymer molecules to fully migrate and adsorb at the oil-water interface of the emulsion droplets to achieve polymerization; maintain the temperature at 30.0℃±0.5℃, and slowly and uniformly dropwise add 1.5 wt% ethylenediamine aqueous solution; after the dropwise addition is completed, continue to react at this low temperature for 20 h; after the reaction is completed, filter and wash with deionized water for 5 times; and finally dry in a vacuum oven at 35℃ for 12 h to obtain microcapsules with dry surface;

[0090] S4, place the microcapsules prepared in S3 into a low-temperature plasma chemical vapor deposition device, and use hexamethyldisiloxane and oxygen as precursors to discharge and deposit at 50℃ and 250 Pa for 30 min to form a SiOxCyHz super-hydrophobic coating on the surface of the microcapsules, thereby finally obtaining self-repairing hydrated salt phase change microcapsules.

[0091] The amounts (weight parts) of the core material raw materials in this embodiment 1 are shown in Table 1, and the shell after curing is 1.2 wt% of the core material (i.e. eutectic melt + solid fillers).

[0092] Table 1

[0093]

[0094] Example 2

[0095] This example 2 is a preparation method of self-repairing hydrated salt phase change microcapsules, which is only different from example 1 in the amount of core material and shell, and the specific core material of each raw material is shown in table 1, and the shell is 1.0wt% of the core material (i.e. eutectic melt + solid filler) after solidification.

[0096] Example 3

[0097] This example 3 is a preparation method of self-repairing hydrated salt phase change microcapsules, which is only different from example 1 in the amount of core material and shell, and the specific core material of each raw material is shown in table 1, and the shell is 1.4wt% of the core material (i.e. eutectic melt + solid filler) after solidification.

[0098] Comparative example 1

[0099] This comparative example is only different from example 1 in that the sorbitol grafted nano titanium dioxide in the composite nucleating agent of step S2 adopts the conventional mixture of sorbitol + nano titanium dioxide, and other steps and conditions are consistent with example 1.

[0100] Comparative example 2

[0101] This comparative example is only different from example 1 in that no SiO2@silicone rubber microspheres and tannin acid microcapsules are added in the self-repairing system of step S2, only containing hollow Al2O3 microspheres, and other steps and conditions are consistent with example 1.

[0102] Comparative example 3

[0103] This comparative example is only different from example 1 in that melamine polyphosphate and aluminum diethyl phosphite in the halogen-free flame retardant system of step S2 are replaced by conventional flame retardant, i.e. microencapsulated red phosphorus, and other steps and conditions are consistent with example 1.

[0104] Comparative example 4

[0105] This comparative example is only different from example 1 in that carboxylated multi-walled carbon nanotubes and polydopamine modified boron nitride nanosheet in the core-shell heat conduction enhancement system of step S2 are replaced by aluminum nitride, and other steps and conditions are consistent with example 1.

[0106] Comparative example 5

[0107] This comparative example is only different from example 1 in that the temperature of slurry preparation in step S2 is increased to 75℃, and other steps and conditions are consistent with example 1.

[0108] Comparative Example 6

[0109] The difference between this comparative example and Example 1 is only that the reaction condition after adding the ethylenediamine solution after the polymerization in step S3 is adjusted to heat treatment at 90℃ for 2 hours, and other steps and conditions are consistent with Example 1.

[0110] Comparative Example 7

[0111] The difference between this comparative example and Example 1 is only that the α-zirconium phosphate in the solid filler in step S2 is deleted, and other steps and conditions are consistent with Example 1.

[0112] Comparative Example 8

[0113] The difference between this comparative example and Example 1 is only that the polydopamine modified boron nitride nanosheet in the core-shell heat conduction enhancement system in step S2 is replaced by an unmodified boron nitride nanosheet, and other steps and conditions are consistent with Example 1.

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

[0115] Among them, the phase change enthalpy value, phase change temperature and supercooling degree are measured by DSC method; the thermal conductivity is measured by transient plane heat source method (Hot Disk); the cycle number is measured according to ASTM D7891-2015 test method; the compressive strength is measured by microsphere compression test; the test standards for toxicity / environmental protection include: EU mandatory standard RoHS of “Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment”, EU mandatory regulation REACH of “Regulation on Chemical Registration, Evaluation, Authorization and Restriction”, and standard test method TCLP (test standard number USEPA 1311) of “Toxicity Characteristic Leaching Procedure” formulated by U.S. Environmental Protection Agency (EPA), GB 26572-2025 “Requirements for Restriction of Hazardous Substances in Electrical and Electronic Products”, and GB / T 39498-2020 “Guidelines for the Use of Key Chemical Substances in Consumer Products”, the fire resistance is tested according to UL-94 standard; the water resistance is tested by water contact angle; the attenuation rate = 10% attenuation / number; the particle diameter is tested by laser particle size analyzer; the appearance color is visually observed.

[0116] Table 2

[0117]

[0118] The phase change microcapsules prepared in Embodiment 1 to Embodiment 3 have the characteristics of high thermal conductivity, high enthalpy, super long cycle life and the like, are safe and environmentally friendly, meet the requirements of the European Union on the limitation of harmful substances (RoHS), meet the safety control of the European Union on chemicals (REACH), and after being discarded, through simulation tests, it is shown that the phase change microcapsules will not seep out toxic substances to pollute the environment (TCLP), and meet the requirements of China on the prevention and control of harmful substances and key chemicals, and can be applied in the fields of building materials, new energy, electronic equipment, power batteries or medical cold chain and the like.

[0119] The supercooling degree of Comparative Example 1 (physical mixing of TiO2 / sorbitol) is as high as 6.8℃, while that of Embodiment 1 of the present application is only 1.2℃. This shows that simple physical mixing cannot achieve the high-efficiency heterogeneous nucleation effect brought by the “interface engineering”.

[0120] Comparative Example 2 (without a self-repairing system) fails after 5000 cycles, and has the lowest compressive strength (12.0MPa). Embodiment 1 cycles more than 10000 times and has a high compressive strength (18.5MPa). This shows that the compounding of physical repair microspheres and chemical repair agents (tannic acid) produces a “1+1>2” synergistic effect, which significantly improves the durability of the material.

[0121] Comparative Example 3 (using microcapsule red phosphorus MRP) causes the product to be pink, which cannot meet the color requirements of high-end applications, and there are potential toxicity concerns.

[0122] The thermal conductivity of Comparative Example 4 (using AlN powder) is only 1.2W / m·K, which is much lower than that of Embodiment 1 (2.4W / m·K). This proves that the multi-dimensional synergistic thermal conduction network constructed by “CNT (one-dimensional) + BNNS (two-dimensional)” is much better than traditional granular fillers in improving thermal conduction efficiency.

[0123] Comparative Example 5 (preparing slurry at 75℃) causes the PCM to lose water due to high temperature, resulting in a sharp drop in enthalpy to 152J / g, and the phase change temperature is discrete, and the product is basically invalid.

[0124] Comparative Example 6 (post-processing at 90℃) causes the microcapsule structure to be damaged, and the cycle life is only 950 times.

[0125] The performance of the phase change microcapsules prepared in Comparative Example 5 and Comparative Example 6 is obviously lower than that of Embodiment 1, and the low-temperature preparation process of the present application “the whole process is ≤ the phase change temperature of the phase change material (58℃)”, which ensures high performance and high reliability.

[0126] Comparative Example 7 (without α-zirconium phosphate) has an excessive strontium ion leaching in the TCLP test, which proves that simple physical packaging is not absolutely safe, and “α-zirconium phosphate chemical chelation” is a necessary technical feature to ensure the non-toxicity of the product.

[0127] Compared with the surface modification of polydopamine (PDA) on boron nitride nanosheets (BNNS) in embodiment 1, the unmodified BNNS directly leads to a significant decrease in thermal conductivity, a serious damage to mechanical properties and cycle life in comparative example 8, because the unmodified BNNS is easy to agglomerate and weakly combined with the shell, forming a phonon scattering center and a stress concentration point.

[0128] The above-described embodiments only express several embodiments of the present application, which are described in a more specific and detailed manner, but should not be understood as a limitation on the scope of the patent of the present application. It should be noted that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing self-repairing hydrated salt phase change microcapsules, characterized in that, The preparation method comprises the following steps: The preparation method comprises the following steps: The eutectic melt is prepared based on a melting method with hydrated salt phase change materials and sorbitol as raw materials; The composite nucleating agent, self-repairing system, ion fixing agent, halogen-free flame-retardant system, core-shell heat-conducting enhancement system are added into the eutectic melt to obtain the core material by blending; The core material is coated in the shell with bio-based polyurethane-polyurea as shell material to obtain the microcapsule, and the temperature of the coating operation is not higher than the phase change temperature of the hydrated salt phase change material; An ultrahydrophobic coating is coated on the surface of the microcapsule to form the self-repairing hydrated salt phase change microcapsule; The composite nucleating agent comprises strontium carbonate and sorbitol grafted nano titanium dioxide; The self-repairing system comprises SiO2@silicone rubber microspheres, hollow Al2O3 microspheres and tannic acid microcapsule; The ion fixing agent is alpha-zirconium phosphate; The halogen-free flame-retardant system comprises melamine polyphosphate and aluminum diethyl phosphinate; 2. The method of claim 1, wherein the self-repairing hydrated salt phase change microcapsules are prepared by the steps of: The core-shell heat-conducting enhancement system comprises carboxylated multi-walled carbon nanotubes, polydopamine modified boron nitride nanosheet and hydrophilic fumed silica. The weight percentage of the raw materials in the core material of the self-repairing hydrated salt phase change microcapsule is as follows: Hydrated salt phase change material 67%~69%; Sorbitol 17%~19%; Strontium carbonate 3%~4%; Sorbitol grafted nano titanium dioxide 1%~2%; SiO2@silicone rubber microspheres 1%~2%; Hollow Al2O3 microspheres 0.4%~0.6%; Tannic acid microcapsule 1.5%~2%; Alpha-zirconium phosphate 0.2%~0.4%; Melamine polyphosphate 2%~3%; Aluminum diethyl phosphinate 0.7%~0.9%; Carboxylated multi-walled carbon nanotubes 0.5%~1.5%; Polydopamine modified boron nitride nanosheet 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; 3. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 2, characterized in that, The mass of the shell material after curing in the self-repairing hydrated salt phase change microcapsule is 1wt%~1.5wt% of the core material.

4. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 3, characterized in that, The method for coating the core material in the shell is selected from any one or a combination of microfluidic method, sol-gel method, spray drying method, complex coagulation method, in-situ polymerization method and interfacial polymerization method. The preparation method comprises the following steps: S1, under the vacuum environment at 55℃~58℃, the hydrated salt phase change material and sorbitol are melt blended to obtain the eutectic melt; S2, the composite nucleating agent, self-repairing system, ion fixing agent, halogen-free flame-retardant system and core-shell heat-conducting enhancement system are blended at room temperature in a high-speed mixer to obtain solid fillers; the solid fillers are added into the eutectic melt, and the mixture is uniformly stirred at low speed to obtain slurry, which is added into an emulsifier aqueous solution at 5℃~10℃, and homogenized at a speed of 5000rpm~6000rpm for 2min~3min to form the core material in the form of emulsion; S3, the temperature of the core material in the form of emulsion is maintained at 25℃~30℃, and the bio-based polyurethane-polyurea prepolymer solution is added, and after stirring and adsorption, the chain extender aqueous solution is added dropwise, and the polymerization is completed after reaction for 12h~20h, and the microcapsule is obtained after washing and drying; S4, a low-temperature plasma polymerization method is used to coat a SiOxCyHz super-hydrophobic coating on the surface of the microcapsule, forming a self-repairing hydration salt phase change microcapsule, x, y, and z are the atomic proportions of O element, C element, and H element, respectively.

5. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 4, characterized in that, The S4 is specifically: The microcapsule prepared in S3 is placed in a low-temperature plasma chemical vapor deposition device, hexamethyldisiloxane and oxygen are used as precursors, and a SiOxCyHz super-hydrophobic coating is formed on the surface of the microcapsule under the condition of <60℃.

6. The method of claim 4, wherein the self-repairing hydrated salt phase change microcapsules are prepared by the steps of: The chain extender in step S3 is ethylenediamine; The preparation step of the bio-based polyurethane-polyurea prepolymer solution in step S3 is: The bio-based polyetheramine and HDI trimer are placed in a reaction kettle, and the reaction is carried out under the protection of nitrogen atmosphere at a temperature of 50℃-55℃ for 3h-4h. After the reaction is completed, the reaction product is 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 step of the sorbitol grafted nano-titanium dioxide is: The hydroxylation reaction of silane coupling agent with the surface of nano-titanium dioxide is carried out to obtain amino propyl modified nano-titanium dioxide. Then it is 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 is obtained.

8. The method for preparing a self-healing hydrated salt phase change microcapsule according to claim 1, characterized in that, The preparation step of the polydopamine modified boron nitride nanosheet is: The boron nitride nanosheet is ultrasonically exfoliated in a trihydroxy aminomethane-hydrochloric acid buffer at room temperature, and the upper layer of the suspension rich in boron nitride nanosheet is collected after centrifugation. In an open container, dopamine hydrochloride is added dropwise to the suspension, and mechanical stirring is continuously carried out at room temperature. Oxidative self-polymerization of dopamine hydrochloride occurs on the surface of the boron nitride nanosheet, forming a polydopamine coating, and obtaining a polydopamine modified boron nitride nanosheet.

9. A self-repairing hydration salt phase change microcapsule prepared by the method of any one of claims 1 to 8.

10. The use of a self-repairing hydration salt phase change microcapsule according to 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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