Low supercooling degree formaldehyde-free phase change microcapsule and preparation method thereof

Abstract

The application belongs to the technical field of phase change microcapsule energy storage materials, and is characterized by using polyurethane urea as a shell material, normal alkane as a core material, and a mixture of crystalline resin and multi-dimensional inorganic nanomaterial as a complex nucleating agent, and using an interfacial polymerization method to obtain low supercooling degree formaldehyde-free phase change microcapsules, wherein the total mass of the nucleating agent accounts for 0.1-0.5% of the mass of the core material. The method is simple and low in cost. The phase change microcapsule material prepared by the method can still maintain a low supercooling degree and does not have a phase separation phenomenon after long-term heat absorption and heat release cycles, is suitable for long-term cold and heat cycles, and has a broad development prospect in the fields of textiles, buildings and industrial waste heat recovery.

Description

Technical Field

[0001] This invention belongs to the field of phase change microcapsule energy storage material technology, specifically relating to a low-supercooling aldehyde-free phase change microcapsule and its preparation method. Background Technology

[0002] Phase change microcapsule materials have broad application prospects in textiles, construction, and industrial waste heat recovery due to their large latent heat value, suitable phase change temperature, and stability. However, supercooling can occur during the heat storage and release process of phase change microcapsule materials, causing the control temperature range of the latent heat storage system to shift, increasing energy consumption and reducing system performance.

[0003] Supercooling refers to the difference between the melting peak and the crystallization peak of a phase change material (PCM). A higher initial crystallization temperature indicates that the PCM is more prone to crystallization at low temperatures. An effective method to reduce supercooling is to add a solid nucleating agent to the PCM before microencapsulation, acting as a seed to catalyze crystal growth. The nucleating agent, as a modifier of the PCM core material, works by providing the necessary crystal nuclei in the molten state. This transforms the PCM core material from homogeneous nucleation to heterogeneous nucleation, accelerating the crystallization rate and thus increasing the initial crystallization temperature, thereby reducing the supercooling of the microcapsules. Adding a nucleating agent before encapsulation is the most effective method for addressing the supercooling problem of microcapsules. Using the method of adding a nucleating agent to reduce the supercooling of PCM has advantages such as low cost, wide applicability, and no need for specific equipment.

[0004] Chinese patent CN105542724A discloses a microcapsule phase change material particle doped with metal nanoparticles and its preparation method. This method involves doping the microcapsule phase change material particle with metal nanoparticles during the preparation process, thereby increasing the particle density, improving thermal conductivity, and reducing supercooling. However, metal nanoparticles are prone to agglomeration, making the phase change process irreversible, leading to phase stratification, uneven dissolution, and a decrease in stability during long-term cycling.

[0005] Chinese patent CN108485608B discloses a method for reducing the supercooling of n-alkane-based energy storage material microcapsules. This method uses a combination of two nucleating agents: a homogeneous nucleating agent composed of compounds of the same class with (n+1) to (n+2) more carbon atoms than the phase change core material, combined with the heterogeneous nucleating effect of nanocellulose crystals. Through the synergistic effect of these two nucleating agents, the supercooling of the n-alkane-based energy storage material microcapsules is significantly reduced. This technology requires a relatively large nucleating agent dosage, with the n-alkane material comprising 1.0–3.0% of the raw material and the nanocellulose crystals comprising 0.4–1.8%. The large amount of nanocellulose added results in a rough microcapsule surface, which can easily lead to core material leakage during long-term cycling.

[0006] Chinese patent CN102391839A discloses an alkane microcapsule for suppressing supercooling phase transition, its preparation method, and its application. The selected nucleating agent and phase change agent are of the same type of compound, are miscible, and can form a gel with the phase change agent. Therefore, the morphology of the microcapsule is not affected by the nucleating agent during formation, resulting in a smooth surface, resistance to aggregation, and good dispersibility. This type of nucleating agent can effectively suppress the supercooling phenomenon of organic alkane microcapsules. However, when the phase change agent completely melts, it becomes a solvent, and the two become completely miscible, resulting in a completely liquid state. The gelation phenomenon disappears, and a high-viscosity substance cannot be rapidly formed during crystallization. The difference in density and fluidity between the two leads to microscopic phase separation, resulting in poor long-term cycling stability. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-supercooling phase change microcapsule and its preparation method. By introducing a mixture of crystalline resin and highly thermally conductive multidimensional inorganic nanomaterials (0-dimensional / 1-dimensional / 2-dimensional) as a composite nucleating agent into the core material, the supercooling of the microcapsule is reduced, while phase separation after multiple thermal cycles is avoided. This improves the thermal conductivity of the microcapsule core material and reduces energy loss.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a low-supercooling, formaldehyde-free phase change microcapsule, using polyurethane urea as the shell material and n-alkane as the core material. A mixture of crystalline resin and multidimensional inorganic nanomaterials is introduced as a compound nucleating agent. The low-supercooling, formaldehyde-free phase change microcapsule is obtained by interfacial polymerization. The total mass of the nucleating agent accounts for 0.1-0.5% of the mass of the core material.

[0010] Specifically, the crystalline resin has a melting point of 45–90°C and is added in an amount of 0.05–0.5% of the core material weight.

[0011] Specifically, the crystalline resin is a crystalline polyester resin with a completely symmetrical structure, obtained by reacting a diol with a completely symmetrical structure with a diacid with a completely symmetrical structure.

[0012] More preferably, the diol is ethylene glycol or neopentyl glycol, and the dicarboxylic acid is terephthalic acid or maleic anhydride.

[0013] Specifically, the multidimensional inorganic nanomaterial mixture is a mixture of inorganic nanomaterials with 0-dimensional, 1-dimensional, and 2-dimensional structures, and the amount added is 0.05-0.1% of the core material mass.

[0014] More preferably, the multidimensional inorganic nanomaterial mixture is a mixture of nano-Al2O3, carbon nanotubes and graphene or a mixture of nano-Al2O3, carbon nanotubes and boron nitride nanosheets.

[0015] More preferably, the inorganic nanomaterial has undergone hydrophobic modification.

[0016] Furthermore, the inorganic nanomaterials are modified with octadecyl groups. This hydrophobic modification can improve the compatibility of the multidimensional inorganic nanomaterial mixture with n-alkanes.

[0017] This invention also provides a method for preparing aldehyde-free phase change microcapsules with low supercooling, comprising the following steps:

[0018] 1) Preparation of isocyanate prepolymer: react oligomeric polyols with diisocyanates to obtain a mixture of isocyanate prepolymers;

[0019] 2) Preparation of crystalline resin: Weigh diol and dicarboxylic acid and react them at 200-250℃ for 5-8 hours, then cool to 150-200℃ and keep warm for 2 hours to obtain crystalline resin;

[0020] 3) The nucleating agent, which is a mixture of isocyanate prepolymer, n-alkane, crystalline resin and multidimensional inorganic nanomaterial mixture, is mixed evenly to obtain the oil phase; at the same time, an aqueous solution of emulsifier is prepared to obtain the aqueous phase.

[0021] 4) The oil phase is dispersed in the aqueous phase under high-speed stirring. After emulsification at 40-70℃ for 1-20 min, an amine crosslinking agent is added and kept at this temperature for 0.5-2 hours. Then, the temperature is raised to 90-150℃ and kept at this temperature for 2-7 hours. After filtration, washing, and drying, aldehyde-free phase change microcapsules with low supercooling are obtained.

[0022] Specifically, the diisocyanate is one or more of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and lysine diisocyanate (LDI); the oligomeric polyol is a polyether diol or a polyolefin diol.

[0023] More preferably, the polyether diol is polyoxypropylene diol and the polyolefin diol is hydroxyl-terminated polybutadiene.

[0024] Specifically, the weight ratio of the n-alkane to the isocyanate prepolymer mixture is 1 to 7:1.

[0025] Specifically, the amine crosslinking agent has the general formula (CmNxHyOz)n, where m = 1 to 10, x = 3 to 1, y = 0 to 15, and z = 0 to 5. It is one or more of urea, polyethyleneimine, propylenediamine, n-butylamine, and diethylenetriamine, and the amount added is 5 to 10% of the mass of the isocyanate prepolymer mixture.

[0026] The melting point of organic crystalline resins is generally between 45℃ and 90℃, and the process is a gradual softening process. The molten phase change core material acts as a solvent for the crystalline resin, allowing the softened resin to be uniformly dispersed in the liquid phase of the core material until the resin is completely melted to form a eutectic with high viscosity. Furthermore, the resin molecules form a three-dimensional network structure through hydrogen bonds, imparting thixotropic properties to the n-alkanes, which can only be disrupted under high shear. When cooled to room temperature, the resin rapidly recrystallizes to a solid state, providing more heterogeneous nucleation sites for the phase change core material, inducing faster crystallization, narrowing the melting range of the microcapsules, and reducing their supercooling. During the crystallization process, the viscosity of the phase change core material increases sharply, preventing phase separation and making it suitable for long-term thermal cycling. Simultaneously, introducing multi-dimensional inorganic nanomaterials (0D / 1D / 2D) into the phase change core material serves multiple purposes. Firstly, it acts as a thickener, enhancing the viscosity of the mixture of organic crystalline resin and the phase change core material. Secondly, it increases the contact area between the nano-inorganic particles and the core material, providing more heterogeneous nucleation sites, inducing crystallization, reducing the supercooling of the microcapsules, preventing phase separation after repeated thermal cycles, and improving the thermal conductivity of the microcapsules. Incorporating crystalline resin and multi-dimensional inorganic nanomaterials (0D / 1D / 2D) into the phase change core material yields microcapsules with low supercooling and good thermal conductivity. This technology requires a relatively small nucleation dose, ranging from 0.1% to 0.5% of the phase change core material.

[0027] Compared with the prior art, the present invention has the following outstanding effects:

[0028] 1) Using polyurethane urea as the shell material of microcapsule-type phase change material and n-alkane as the core material of microcapsule-type phase change material, crystalline resin and multi-dimensional inorganic nanomaterials are introduced, and phase change microcapsules with low supercooling and high thermal conductivity are obtained by interfacial polymerization. The preparation is simple and low cost.

[0029] 2) After long-term heat absorption and heat release cycles, this phase change microcapsule material can still maintain a low degree of supercooling and will not exhibit phase separation. It is suitable for long-term hot and cold cycles and has broad development prospects in textiles, construction and industrial waste heat recovery. Attached Figure Description

[0030] Figure 1 SEM image of the phase change microcapsules prepared in Example 3;

[0031] Figure 2 The DSC curve of the phase change microcapsules prepared in Example 3 after 100 thermal cycles;

[0032] Figure 3 SEM images of the phase change microcapsules prepared for comparison.

[0033] Figure 4The DSC curves of the phase change microcapsules prepared for comparison are shown. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. 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. These all fall within the scope of protection of the present invention.

[0035] Example 1

[0036] 1) Weigh 10g of HDI and 5g of PPG, react at 70℃ for 3 hours to obtain a mixture of isocyanate prepolymers.

[0037] 2) Weigh terephthalic acid and ethylene glycol in a molar ratio of 1:1, stir and heat to 220℃ for 8 hours, then cool to 170℃ and keep warm for 2 hours to obtain crystalline polyester resin.

[0038] 3) Weigh 30g of n-octadecane, 0.06g of crystalline polyester resin, 6g of nano-inorganic particles (Al2O3 0.006g, carbon nanotubes 0.003g, graphene 0.006g) and isocyanate prepolymer mixture, and mix them evenly at 70℃ to obtain the oil phase;

[0039] Meanwhile, prepare the aqueous phase: weigh 2g of sodium salt of styrene-maleic anhydride copolymer into a beaker, add 100g of deionized water, stir to completely dissolve the emulsifier, and obtain the aqueous phase.

[0040] 4) Emulsion formation: After the aqueous phase is kept at 60°C for 10 minutes, the oil phase is added to the aqueous phase and emulsified at 4000 rpm for 20 minutes to form a stable oil-in-water emulsion.

[0041] Microcapsule formation: After emulsification, the rotation speed was reduced to 2000 rpm, 3 g of diethylenetriamine was added, and the mixture was kept at this temperature for 1 hour. Then, the temperature was increased to 80°C, and the reaction was continued for 5 hours to complete the reaction, resulting in a phase change microcapsule emulsion with low supercooling. The microcapsule emulsion was washed, purified, filtered, and dried to obtain a low supercooling phase change microcapsule powder.

[0042] In this embodiment, the aldehyde-free phase change microcapsules have an initial crystallization temperature of 24.98℃, a supercooling of 6.49℃, an enthalpy of 175J / g, and a thermal conductivity of 0.32W / m·K.

[0043] Example 2

[0044] 1) Weigh 11g of IPDI and 4g of PPG2000, react at 90℃ for 3 hours to obtain a mixture of isocyanate prepolymers.

[0045] 2) Weigh out terephthalic acid, maleic anhydride and ethylene glycol in a molar ratio of 0.5:0.5:1, stir and heat to 210℃ for 8 hours, then cool to 170℃ and keep warm for 2 hours to obtain crystalline polyester resin.

[0046] 3) Weigh 30g of n-octadecane, 0.1g of crystalline polyester resin, 7g of nano-inorganic particles (Al2O3 0.01g, carbon nanotubes 0.008g, boron nitride nanosheets 0.01g) and isocyanate prepolymer mixture, and mix them evenly at 70℃ to obtain the oil phase;

[0047] Meanwhile, prepare the aqueous phase: weigh 1g of sodium dodecyl sulfonate into a beaker, add 100g of deionized water, stir to dissolve, and obtain the aqueous phase.

[0048] 4) Emulsion formation: After the aqueous phase is kept at 60°C for 10 minutes, the oil phase is added to the aqueous phase and emulsified at 4000 rpm for 20 minutes to form a stable oil-in-water emulsion.

[0049] Microcapsule formation: After emulsification, the rotation speed was reduced to 2000 rpm, and a mixture of 2 g diethylenetriamine and 2 g urea was added. After maintaining the temperature for 1 hour, the temperature was increased to 90°C, and the reaction was continued for 5 hours to complete the reaction, resulting in a phase change microcapsule emulsion with low supercooling. The microcapsule emulsion was washed, purified, filtered, and dried to obtain low supercooling phase change microcapsule powder.

[0050] In this embodiment, the aldehyde-free phase change microcapsules have an initial crystallization temperature of 25.11℃, a supercooling of 5.98℃, an enthalpy of 174J / g, and a thermal conductivity of 0.35W / m·K.

[0051] Example 3

[0052] 1) Weigh 10g of IPDI, 2.5g of PPG2000 and 2.5g of hydroxyl-terminated polybutadiene and react them at 95℃ for 3 hours to obtain a mixture of isocyanate prepolymers.

[0053] 2) Weigh terephthalic acid and neopentyl glycol in a molar ratio of 1:1, stir and heat to 200℃ for 8 hours, then cool to 170℃ and keep warm for 2 hours to obtain crystalline polyester resin.

[0054] 3) Weigh 30g of n-octadecane, 0.15g of crystalline polyester resin, 7g of nano-inorganic particles (0.008g of Al2O3, 0.01g of carbon nanotubes, 0.012g of boron nitride nanosheets) and isocyanate prepolymer mixture, and mix them evenly at 70℃ to obtain the oil phase;

[0055] Meanwhile, prepare the aqueous phase: weigh 1.5g of OP-10 into a beaker, add 100g of deionized water, stir, and obtain the aqueous phase.

[0056] 4) Emulsion formation: After the aqueous phase is kept at 60°C for 10 minutes, the oil phase is added to the aqueous phase and emulsified at 4000 rpm for 20 minutes to form a stable oil-in-water emulsion.

[0057] Microcapsule formation: After emulsification, the rotation speed was reduced to 2000 rpm, and a mixture of 2 g hexamethylenediamine and 2 g diethylenetriamine was added. After maintaining the temperature for 1 hour, the temperature was increased to 90°C, and the reaction was continued for 5 hours to complete the reaction, resulting in a phase change microcapsule emulsion with low supercooling. The microcapsule emulsion was washed, purified, filtered, and dried to obtain low supercooling phase change microcapsule powder.

[0058] The aldehyde-free phase change microcapsules in this embodiment have an initial crystallization temperature of 25.14℃, a supercooling of 5.79℃, an enthalpy of 179J / g, and a thermal conductivity of 0.41W / m·K. The microcapsules have a smooth surface morphology. After 100 cycles of thermal cycling, there were no significant changes in the initial crystallization temperature, supercooling, enthalpy, or peak shape, indicating that the microcapsules have good thermal cycling stability and will not leak or separate during long-term use.

[0059] Comparative Example

[0060] 1) Weigh 10g of IPDI, 2.5g of PPG2000 and 2.5g of hydroxyl-terminated polybutadiene and react them at 95℃ for 3 hours to obtain a mixture of isocyanate prepolymers.

[0061] 2) Weigh 30g of n-octadecane and 7g of isocyanate prepolymer mixture, mix them evenly at 70℃ to obtain the oil phase;

[0062] Meanwhile, prepare the aqueous phase: weigh 1.5g of OP-10 into a beaker, add 100g of deionized water, stir, and obtain the aqueous phase.

[0063] 3) Emulsion formation: After the aqueous phase is kept at 60°C for 10 minutes, the oil phase is added to the aqueous phase and emulsified at 4000 rpm for 20 minutes to form a stable oil-in-water emulsion.

[0064] Microcapsule formation: After emulsification, the rotation speed was reduced to 2000 rpm, and a mixture of 2 g hexamethylenediamine and 2 g diethylenetriamine was added. After maintaining the temperature for 1 hour, the temperature was increased to 90°C, and the reaction was continued for 5 hours to complete the reaction, resulting in a phase change microcapsule emulsion with low supercooling. The microcapsule emulsion was washed, purified, filtered, and dried to obtain aldehyde-free phase change microcapsule powder.

[0065] The aldehyde-free phase change microcapsules in this comparative example had an initial crystallization temperature of 20.70℃, a supercooling of 12.07℃, an enthalpy of 178 J / g, and a thermal conductivity of 0.025 W / m·K.

Claims

1. A low-supercooling, aldehyde-free phase change microcapsule, characterized in that: Polyurethane urea is used as the shell material, and n-alkane is used as the core. The material is prepared by introducing a mixture of crystalline resin and multidimensional inorganic nanomaterials as a composite nucleating agent, and obtaining low-supercooling aldehyde-free phase change microcapsules by interfacial polymerization. The total mass of the nucleating agent accounts for 0.1 to 0.5% of the core material mass.

2. The low-supercooling aldehyde-free phase change microcapsule according to claim 1, characterized in that: The crystalline resin has a melting point of 45~90℃ and is added at a rate of 0.05~0.5% of the core material weight.

3. The low-supercooling aldehyde-free phase change microcapsule according to claim 1, characterized in that: The crystalline resin is a crystalline polyester resin with a completely symmetrical structure, obtained by reacting a diol with a completely symmetrical structure with a diacid with a completely symmetrical structure.

4. The low-supercooling, aldehyde-free phase change microcapsule according to claim 1, characterized in that: The multidimensional inorganic nanomaterial mixture is a mixture of inorganic nanomaterials with 0-dimensional, 1-dimensional, and 2-dimensional structures, and the amount added is 0.05~0.1% of the core material mass.

5. The low-supercooling, aldehyde-free phase change microcapsule according to claim 4, characterized in that: The multidimensional inorganic nanomaterial mixture is a mixture of nano-Al2O3, carbon nanotubes and graphene, or a mixture of nano-Al2O3, carbon nanotubes and boron nitride nanosheets.

6. A method for preparing low-supercooling aldehyde-free phase change microcapsules according to any one of claims 1 to 5, characterized in that: Includes the following steps: 1) Preparation of isocyanate prepolymer: react oligomeric polyols with diisocyanates to obtain a mixture of isocyanate prepolymers; 2) Preparation of crystalline resin: Weigh diol and dicarboxylic acid and react them at 200-250℃ for 5-8 hours, then cool to 150-200℃ and keep warm for 2 hours to obtain crystalline resin; 3) The nucleating agent, which is a mixture of isocyanate prepolymer, n-alkane, crystalline resin and multidimensional inorganic nanomaterial mixture, is mixed evenly to obtain the oil phase; at the same time, an aqueous solution of emulsifier is prepared to obtain the aqueous phase. 4) The oil phase is dispersed in the aqueous phase under high-speed stirring. After emulsification at 40-70℃ for 1-20 min, an amine crosslinking agent is added and kept at this temperature for 0.5-2 hours. Then, the temperature is raised to 90-150℃ and kept at this temperature for 2-7 hours. After filtration, washing, and drying, aldehyde-free phase change microcapsules with low supercooling are obtained.

7. The method for preparing low-supercooling aldehyde-free phase change microcapsules according to claim 6, characterized in that: The diisocyanate is one or more of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and lysine diisocyanate (LDI); the oligomeric polyol is a polyether diol or a polyolefin diol.

8. The method for preparing low-supercooling aldehyde-free phase change microcapsules according to claim 7, characterized in that: The polyether diol is polyoxypropylene diol, and the polyolefin diol is hydroxyl-terminated polybutadiene.

9. The method for preparing low-supercooling aldehyde-free phase change microcapsules according to claim 6, characterized in that: The weight ratio of the n-alkane to isocyanate prepolymer mixture is 1 to 7:

1.

10. The method for preparing low-supercooling aldehyde-free phase change microcapsules according to claim 6, characterized in that: The amine crosslinking agent has the general formula (CmNxHyOz)n, where m = 1 to 10, x = 3 to 1, y = 0 to 15, and z = 0 to 5. It is one or more of urea, polyethyleneimine, propylenediamine, n-butylamine, and diethylenetriamine, and the amount added is 5 to 10% of the mass of the isocyanate prepolymer mixture.

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