Millimeter-scale flexible phase change microsphere and preparation method thereof

Abstract

The invention relates to the technical field of phase-change materials, and provides a millimeter-scale flexible phase-change microsphere and a preparation method thereof, the particle size range of the phase-change microsphere is 1-5mm, and the phase-change microsphere has flexibility; the preparation method comprises the following steps: dissolving the emulsifier in water to prepare a water phase; the preparation method comprises the following steps: forming an emulsion from a phase change material, an acrylate monomer and an acrylate cross-linking agent through emulsification; adding a water-phase initiator and an oil-phase initiator into the emulsion; after the reaction is finished, filtering a product by using a filter screen, collecting filter residues, and performing vacuum drying; the obtained millimeter-scale microspheres have the characteristics of large particle size and flexibility, can be integrated in intelligent textiles and building thermal management systems, and have the advantage of large size, so that the packaging complexity is reduced, the interface thermal resistance is reduced, and the energy regulation and control efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of phase change materials, and more specifically, to a millimeter-scale flexible phase change microsphere and a preparation method thereof. Background Art

[0002] Phase change materials achieve energy storage and release through their characteristics during the phase transition process and maintain the stability of their own temperature, thereby achieving the purpose of energy conservation and temperature control. By encapsulating phase change materials using microsphere technology, the volume expansion during phase change can be effectively suppressed, and the direct contact between the phase change material and the external environment can be blocked, thereby retaining its original physical properties and significantly improving the stability and durability of the phase change material. Therefore, microsphere phase change materials have higher stability and a wider range of application scenarios compared to pure phase change materials, and can be widely used in fields such as solar energy utilization, energy-saving building materials, functional textiles, and electricity.

[0003] Currently, methods for preparing phase change microspheres include interfacial polymerization, emulsion polymerization, suspension polymerization, etc. However, limited by existing technologies, most of the prepared phase change microspheres are concentrated in the micron level, with a wide particle size distribution, complex preparation processes, and it is difficult to meet the requirements of large-scale industrial production. These factors severely restrict the preparation efficiency of high-quality and highly consistent microspheres, and further limit the popularization and use of phase change microspheres in practical applications.

[0004] For phase change microspheres, the smaller their size, the higher the mass ratio of the shell material in the microspheres. To effectively improve the energy storage density of phase change microspheres, increasing their size to the millimeter level is a feasible strategy. More importantly, millimeter-scale phase change microspheres have significant application value in specific fields. For example, they can be used in the field of thermal management clothing (such as medical protective clothing or extreme environment clothing) and the field of building thermal management (such as thermal regulation systems embedded under the floor or in the wall), thereby achieving efficient energy storage and release and meeting the temperature control requirements in different scenarios.

[0005] In the prior art, the preparation method of millimeter-scale microspheres is mainly the coagulation bath method, but this method has the following technical limitations: the mechanical strength of the obtained microspheres is low, and it is difficult to meet the application requirements under complex working conditions; the selection range of the shell material is limited, and the diversity of material properties cannot be fully utilized; the preparation efficiency is low, and it is difficult to achieve large-scale production. In addition, most microspheres in the prior art adopt a core-shell structure design, which limits the flexible characteristics of the microspheres and makes them significantly insufficient in flexible application scenarios. Therefore, there is an urgent need for a preparation method of millimeter-scale phase change microspheres with a simple preparation process, a wide selection range of shell materials, a significantly improved preparation efficiency, and the obtained microspheres having flexible characteristics. Summary of the Invention

[0006] The object of the present invention is to provide a millimeter-scale flexible phase change microsphere and a preparation method thereof. The method uses the macromolecular self-assembly technology to gradually reorganize small microspheres into millimeter-scale microspheres. At the same time, by combining the synergistic effect of interfacial polymerization and in-situ polymerization, the macromolecular chains formed by the polymerization of acrylate monomers are used to disrupt the continuity of the crystallization of the phase change material, thereby realizing the preparation of millimeter-scale phase change flexible microspheres, which have large particle size and flexibility, and the preparation process is simple, fast, low-cost and highly safe.

[0007] The object of the present invention can be achieved by the following technical solutions: A preparation method of millimeter-scale flexible phase change microspheres, comprising the following steps: S1. Dissolve the emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene castor oil, lecithin, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate, and the mass fraction of the emulsifier is 1% to 10% of water; S2. Form an emulsion by emulsifying the phase change material, acrylate monomer and acrylate crosslinking agent, wherein the mass ratio of the phase change material to water is 20-80:100, the mass ratio of the acrylate monomer to the phase change material is 1:1 to 1:5, and the mass ratio of the acrylate crosslinking agent to the acrylate monomer is 1:1 to 1:40; S3. Add an aqueous phase initiator and an oil phase initiator to the emulsion, and carry out a polymerization reaction at 70°C - 100°C for 2h - 4h; S4. After the reaction is completed, filter the product using a 400-mesh filter screen, collect the filter residue and dry it in vacuum at 80°C.

[0008] As a preferred embodiment of the present invention, in step 1, the emulsifier is 6-10 parts of polyvinyl alcohol 1788 and is dispersed in 180-250 parts of water to form an aqueous phase.

[0009] As a preferred embodiment of the present invention, in step 2, the phase change material is one or more of straight-chain alkanes, fatty acids, fatty alcohols with 12-28 carbon atoms, and polyethylene glycol with a molecular weight of 900-2000.

[0010] As a preferred embodiment of the present invention, in step 2, the acrylate monomer is one or more of methoxyethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, methoxyethyl acrylate, dodecyl acrylate, octadecyl acrylate, and polyoxyethylene methyl acrylate of dodecyl.

[0011] As a preferred embodiment of the present invention, in step 2, the acrylate crosslinking agent is one or more of ethylene glycol dimethacrylate, trimethylolpropane triacrylate, epoxy acrylate, polyurethane acrylate, triallyl isocyanurate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

[0012] As a preferred embodiment of the present invention, in step 3, the mass ratio of the aqueous phase initiator to the acrylic monomer is 1:8 to 1:100, and the aqueous phase initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, azodiisobutyramidine hydrochloride, azodiisobimidazoline hydrochloride, azodicyanovaleric acid, and azodiisopropylimidazoline.

[0013] As a preferred embodiment of the present invention, in step 3, the mass ratio of the oil phase initiator to the aqueous phase is 1:1 to 1:5; the oil phase initiator is one or more of azodiisobutyronitrile, azodiisooctanenitrile, benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, and diisopropylbenzene peroxide.

[0014] As a preferred embodiment of the present invention, the polymerization reaction temperature in step 3 is 80°C - 90°C, and the time is 3 h.

[0015] As a preferred embodiment of the present invention, the phase change material is 65 parts of 18 straight-chain alkanes, the acrylate monomer is 10 parts of tetrahydrofuran acrylate, 30 parts of dodecyl acrylate, and 1.2 parts of polyoxyethylene dodecyl methacrylate. The acrylate crosslinking agent is 0.4 - 2 parts of dipentaerythritol hexaacrylate. The above materials and 5 - 20 parts of tackifier are added to the aqueous phase and emulsified for 15 minutes at 2000 rpm to obtain a uniform emulsion.

[0016] The present invention also provides a millimeter-scale flexible phase change microsphere prepared according to the above preparation method. The particle size range of the microsphere is 1 mm - 5 mm and it has flexibility.

[0017] Advantages of the present invention: Through the synergistic effect of the polymerization of acrylate monomers and crosslinking agents, the present invention forms a flexible macromolecular chain network, which destroys the crystallization continuity of the phase change material and enables the microspheres to have the ability of elastic deformation; compared with the rigid shell layer of the traditional core-shell structure, the microspheres prepared by this method can adapt to repeated bending without breaking; Through the combined design based on emulsifiers and acrylate monomers, the present invention can be adapted to a variety of phase change materials; for example, long-chain acrylate monomers are compatible with non-polar alkanes, and monomers containing ether bonds form a stable interface with polyethylene glycol, breaking through the limitation of the traditional coagulation bath method on the selection of shell materials; The present invention realizes precise control of the size of millimeter-scale microspheres by adjusting the concentration of the aqueous-phase emulsifier, the ratio of the phase-change material to the monomer, and the reaction stirring intensity. Compared with the micron-scale microspheres with a wide distribution in the prior art, this method significantly improves the particle size uniformity and meets the size requirements of different application scenarios. The present invention adopts an aqueous-phase / oil-phase dual initiator system (such as ammonium persulfate + azobisisobutyronitrile) to synergistically trigger the polymerization reaction at 70-100°C, shortening the reaction time to 2-4 hours and significantly improving the monomer conversion efficiency. Combining continuous filtration and vacuum drying processes simplifies the production process and solves the problems of low efficiency and difficulty in large-scale production of the traditional coagulation bath method. In summary, the millimeter-scale size design improves the energy storage density, and its flexible characteristics enable it to be integrated into textiles such as protective clothing or embedded in building walls. Compared with traditional micron-scale microspheres, the millimeter-scale structure is easier to position and encapsulate in the thermal management system, reduces the thermal resistance at the material interface, and improves the energy regulation efficiency. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic diagram of the particle size state prepared by the present invention. Detailed Embodiments

[0020] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following will further elaborate on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0021] The present invention provides: A method for preparing millimeter-scale flexible phase-change microspheres, comprising the following steps: S1. Dissolve the emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene castor oil, lecithin, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate, and the mass fraction of the emulsifier is 1% to 10% of the water. S2. The phase change material, acrylate monomer, and acrylate crosslinking agent are formed into an emulsion through emulsification, where the mass ratio of the phase change material to water is 20 - 80:100, the mass ratio of the acrylate monomer to the phase change material is 1:1 to 1:5, and the mass ratio of the acrylate crosslinking agent to the acrylate monomer is 1:1 to 1:40; S3. An aqueous phase initiator and an oil phase initiator are added to the emulsion, and a polymerization reaction is carried out at 70°C - 100°C for 2h - 4h; S4. After the reaction is completed, the product is filtered using a 400 - mesh filter, and the filter residue is collected and vacuum - dried at 80°C.

[0022] The present invention also provides a millimeter - scale flexible phase change microsphere, which is prepared according to the above - mentioned preparation method. The particle size range of the microsphere is 1mm - 5mm and it has flexibility. Example 1

[0023] (1). Preparation of the aqueous phase of the emulsion: 6 parts of polyvinyl alcohol 1788 are dispersed in 194 parts of water to form a uniform aqueous phase; (2). Preparation of the emulsion: 65 parts of octadecane, 10 parts of tetrahydrofuran acrylate, 30 parts of dodecyl acrylate, 0.4 part of dipentaerythritol hexaacrylate, 5 parts of tackifier, and 1.2 parts of polyoxyethylene methyl acrylate dodecyl are added to the aqueous phase and emulsified at 2000 rpm for 15 minutes to obtain a uniform emulsion; (3). Emulsion reaction: 5 parts of ammonium persulfate and 5 parts of azobisisobutyronitrile are added to the obtained emulsion and stirred thoroughly until uniform, and the emulsion is reacted at 80°C for 3h; (4). Filtration and drying: After the reaction is completed, the product is filtered using a 400 - mesh filter, the filter residue is collected and vacuum - dried at 80°C, and finally a millimeter - scale flexible phase change microsphere is prepared. Example 2

[0024] Differing from Example 1, the tackifier is 10 parts, and a millimeter - scale flexible phase change microsphere is prepared using the same steps as in Example 1. Example 3

[0025] Differing from Example 2, the tackifier is 20 parts, and a millimeter - scale flexible phase change microsphere is prepared using the same steps. Example 4

[0026] Differing from Example 2, dipentaerythritol hexaacrylate is 2 parts, and a millimeter - scale flexible phase change microsphere is prepared using the same steps. Example 5

[0027] Differing from Example 4, the emulsion is reacted at 90°C for 3h, and a millimeter - scale flexible phase change microsphere is prepared using the same steps. Example 6

[0028] Different from Example 5, the water content in the aqueous phase of the emulsion is 250 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps. Example 7

[0029] Different from Example 6, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion is 10 parts, and the water content is 190 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps. Example 8

[0030] Different from Example 5, the amount of dipentaerythritol hexaacrylate is 1.5 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0031] Comparative Example 1 Different from Example 4, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion is 20 parts, and the water content is 180 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0032] Comparative Example 2 Different from Example 8, the amount of tetrahydrofuran acrylate is 20 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0033] Comparative Example 3 Different from Example 2, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion is 30 parts, the water content is 170 parts, and the emulsion reacts at 90 °C, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0034] Comparative Example 4 Different from Comparative Example 3, the water content in the aqueous phase of the emulsion is 194 parts, and the tackifier is 0 part, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0035] Comparative Example 5 Different from Example 5, the amount of dipentaerythritol hexaacrylate is 20 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0036] Comparative Example 6 Different from Example 2, the content of polyvinyl alcohol 1788 in the aqueous phase of the emulsion is 2 parts, and the water content is 198 parts, and millimeter-sized flexible phase change microspheres are prepared by the same steps.

[0037] For the microspheres prepared in the above examples and comparative examples, an optical microscope was used to test the microsphere size, and the specific test data are shown in the following table: Case Sample Status Size Flexibility Example 1 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Example 2 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Example 3 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Example 4 Particles can be obtained 1.5 to 2 mm Flexible even below the phase transition temperature of eicosane Example 5 Particles can be obtained 1.5 to 2 mm Flexible even below the phase transition temperature of eicosane Example 6 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Example 7 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Example 8 Particles can be obtained 1 to 1.5 mm Flexible even below the phase transition temperature of eicosane Comparative Example 1 Particles can be obtained 0.5 to 1 mm Flexible even below the phase transition temperature of eicosane Comparative Example 2 Particles can be obtained 0.5 to 1 mm Flexible even below the phase transition temperature of eicosane Comparative Example 3 Powder can be obtained <0.5 mm Flexible even below the phase transition temperature of eicosane Comparative Example 4 Particles can be obtained 1 to 1.5 mm Flexible only above the phase transition temperature of eicosane Comparative Example 5 Particles can be obtained 2 to 3 mm Not flexible Comparative Example 6 The emulsion is unstable / / As can be seen from the above table, in Examples 1-8, microspheres with a size ranging from 1 mm to 1.5 mm can be prepared, which are flexible when the temperature is lower than the melting point of octadecane, meeting the requirements; in Comparative Examples 1-3, although they are flexible, the particle size cannot fully meet the requirement of being more than 1 mm, not meeting the requirements; in Comparative Examples 4-5, the particle size reaches the millimeter level, but they are not flexible when the temperature is lower than the melting point of octadecane, not meeting the requirements; in Comparative Example 6, an emulsion cannot be obtained, not meeting the requirements.

[0038] It should be noted that the octadecane recorded in the table is octadecane straight-chain alkane.

[0039] It can be understood that an elastic network is constructed by the copolymerization of acrylate and cross-linking agent to disrupt the crystallization continuity of the phase change material, realizing the flexible anti-bending of the microspheres; an innovative emulsifier / monomer combination design (long-chain acrylate coating alkane, ether bond-containing monomer stabilizing the emulsion interface) breaks through the material compatibility limitations of the coagulation bath method; a three-axis regulation mechanism of the aqueous phase emulsifier concentration, phase change material / monomer ratio, and stirring intensity is established to achieve the precise preparation of millimeter-sized microspheres; a water phase / oil phase dual initiator system (ammonium persulfate + azobisisobutyronitrile) is developed, combined with a temperature-controlled polymerization process at 70-100 °C, the reaction time is shortened to 2-4 hours, and the monomer conversion efficiency reaches 98%. A continuous filtration-drying process is used to achieve large-scale production. The obtained millimeter-sized microspheres have both high energy storage density and flexible characteristics, and can be integrated into intelligent textiles and building thermal management systems. Their large size advantage reduces the packaging complexity, reduces the interfacial thermal resistance, and improves the energy regulation efficiency.

[0040] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more; it should be understood that the terms "open hole", "upper", "lower", "thickness", "top", "middle", "length", "inner", "perimeter", etc. indicating the orientation or position relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention.

[0041] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing millimeter-scale flexible phase-change microspheres, characterized in that: The following steps are involved: S1. dissolving an emulsifier in water to prepare an aqueous phase, wherein the emulsifier is selected from one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyoxyethylene fatty alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene castor oil, lecithin, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate, and the mass fraction of the emulsifier is 1% to 10% of water; S2. The phase change material, the acrylate monomer and the acrylate crosslinker are emulsified to form an emulsion, wherein the mass ratio of the phase change material to water is 20-80:100, the mass ratio of the acrylate monomer to the phase change material is 1:1 to 1:5, and the mass ratio of the acrylate crosslinker to the acrylate monomer is 1:1 to 1:40; S3. Adding the aqueous phase initiator and the oil phase initiator to the emulsion, and carrying out the polymerization reaction at 70°C-100°C for 2h-4h; S4. After the reaction is completed, the product is filtered using a 400-mesh filter, and the filter residue is collected and dried in a vacuum at 80°C.

2. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: In the step 1, the emulsifier is 6-10 parts of polyvinyl alcohol 1788 and is dispersed in 180-250 parts of water to form an aqueous phase.

3. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: In step 2, the phase change material is one or more of straight-chain alkanes with 12-28 carbon atoms, fatty acids, fatty alcohols, and polyethylene glycols with a molecular weight of 900-2000.

4. The millimeter-level flexible phase-change microsphere and preparation method according to claim 1, characterized in that: In the step 2, the acrylate monomer is one or more of methoxyethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofuran acrylate, methoxyethyl acrylate, dodecyl acrylate, octadecyl acrylate, and behenyl polyoxyethylene methacrylate.

5. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: In step 2, the acrylate crosslinking agent is one or more of ethylene glycol dimethacrylate, trimethylolpropane triacrylate, epoxy acrylate, polyurethane acrylate, triallyl isocyanurate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

6. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: In the step 3, the mass ratio of the water phase initiator to the acrylic acid monomer is 1:8 to 1:100, and the water phase initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobiscyanovaleric acid, and azobisisopropylimidazoline.

7. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: In step 3, the mass ratio of the oil phase initiator to the water phase is 1:1 to 1:5; the oil phase initiator is one or more of azobisisobutyronitrile, azobisisoheptylnitrile, dibenzoyl peroxide, dodecyl peroxide, di-tert-butyl peroxide, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, and diisopropylbenzene peroxide.

8. The method for preparing millimeter-scale flexible phase-change microspheres according to claim 1, characterized in that: The polymerization reaction temperature in step 3 is 80° C.-90° C. and the reaction time is 3 hours.

9. A method for preparing millimeter-scale flexible phase-change microspheres according to any one of claims 3 to 5, characterized in that: The phase change material is 65 parts of 18 straight-chain alkane, the acrylate monomer is 10 parts of tetrahydrofuran acrylate, 30 parts of lauryl acrylate, and 1.2 parts of dodecyl polyoxyethylene methacrylate, and the acrylate crosslinker is 0.4-2 parts of dipentaerythritol hexaacrylate. The above materials and 5-20 parts of tackifier are added to the water phase, emulsified at 2000 rpm for 15 minutes to obtain a uniform emulsion.

10. A millimeter-scale flexible phase-change microsphere, characterized in that: The microspheres are prepared according to the preparation method according to any one of claims 1 to 8, wherein the particle size of the microspheres is in the range of 1 mm to 5 mm and the microspheres are flexible.

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