Tetradecane modified polystyrene low-temperature phase change microcapsule and preparation method thereof
The leakage and poor thermal conductivity of existing low-temperature phase-change microcapsules prepared by using modified polystyrene and tetradecane and adding modified silica sol to the shell layer is solved. The problem is that higher stability and thermal conductivity are achieved and the application scope is expanded.
Patent Information
- Application Number
- CN202411658249.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-19
- Publication Date
- 2025-02-25
AI Technical Summary
Existing low-temperature phase change microcapsules are prone to leakage during the phase change process and have poor thermal conductivity, and are prone to decomposition during application, affecting the phase change performance.
Modified polystyrene as the shell layer and tetradecane as the core layer, low-temperature phase change microcapsules were prepared by in-situ polymerization, and modified silica sol was added to the shell layer to improve thermal conductivity.
It improves the stability, thermal conductivity and phase transformation performance of low-temperature phase change microcapsules, extends the service life of the equipment, and widens its application scenarios.
Smart Images
Figure CN119499993A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of low-temperature phase-change microcapsules, and in particular to tetradecane@modified polystyrene low-temperature phase-change microcapsules and a preparation method thereof. Background Art
[0002] At present, with the rise of the logistics industry, how to ensure the quality of temperature-sensitive crops such as vegetables, fruits, etc. during storage and transportation is particularly important. Latent heat storage is a storage method that absorbs or releases heat due to changes in the physical state of the material. It has higher energy density and safety, and is more concerned by the industry than thermochemical storage and sensible heat storage. Low-temperature phase change materials (solid-liquid phase change materials) have great application prospects in latent heat storage due to their large heat storage capacity and small phase change volume. However, solid-liquid phase change materials are very easy to leak during the phase change process, have poor thermal conductivity, and are prone to decomposition during the application process, causing local cooling, which greatly affects the phase change performance. Therefore, scholars have improved the phase change performance of low-temperature phase change materials in applications by encapsulating low-temperature phase change materials in shells with smaller diameters to make phase change microcapsules, while also improving the recyclability of phase change materials and the service life of equipment.
[0003] Low-temperature phase change microcapsules are mainly composed of two parts: a phase change material as the core material and a polymer or inorganic substance as the shell layer. Methods for encapsulating low-temperature phase change microcapsules include chemical methods, physical-chemical methods, and physical methods. Studies have confirmed that the phase change performance of low-temperature phase change microcapsules prepared by physical methods is poor, significantly lower than that of chemical methods (such as in-situ polymerization methods). For the core material of low-temperature phase change microcapsules, paraffin-based phase change materials have attracted widespread attention due to their high latent heat of phase change, especially tetradecane, which is widely used in the field of low-temperature cold storage. For shell materials, organic polymers are the first choice, but a single organic material is difficult to provide microcapsules with higher thermal conductivity, resulting in the inability of low-temperature phase change materials to meet the requirements of practical applications.
[0004] Therefore, the development of low-temperature phase change microcapsules with high phase change latent heat, high thermal conductivity and high stability has good application prospects in the field of low-temperature storage. Summary of the invention
[0005] The purpose of the present invention is to provide a tetradecane@modified polystyrene low-temperature phase change microcapsule and a preparation method thereof in view of the deficiencies in the prior art.
[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:
[0007] The present invention provides a method for preparing tetradecane@modified polystyrene low-temperature phase change microcapsules, comprising the following steps:
[0008] (1) mixing styrene, tetradecane, an initiator and a crosslinking agent to obtain an oil phase; mixing water and an emulsifier to obtain an aqueous phase;
[0009] (2) mixing the water phase and the oil phase and emulsifying them to obtain an emulsion;
[0010] (3) reacting the modified silica sol and the emulsion under a nitrogen atmosphere to obtain a reaction emulsion;
[0011] (4) The demulsifier and the reaction emulsion are mixed and then demulsified to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0012] Preferably, in step (1), the mass ratio of styrene, tetradecane, initiator and crosslinking agent is 8-12:8-12:0.05-0.1:0.5-4, and the mass ratio of water and emulsifier is 100:0.4-1.
[0013] Preferably, the initiator in step (1) is azobisisoheptanenitrile; the crosslinking agent is methyl cellulose and methyl methacrylate, and the mass ratio of methyl cellulose to methyl methacrylate is 1:7-9;
[0014] The emulsifiers are sodium dodecyl sulfate and dodecylphenol polyoxyethylene ether, and the mass ratio of sodium dodecyl sulfate to dodecylphenol polyoxyethylene ether is 0.8-1.2:0.8-1.2.
[0015] Preferably, in step (2), the mass ratio of the water phase to the oil phase is 0.8-1.2:0.8-1.2; the emulsification speed is 5000-15000 rpm, and the emulsification time is 10-20 min.
[0016] Preferably, the mass ratio of the modified silica sol in step (3) to the styrene in step (1) is 1-2:10; the reaction temperature in step (3) is 40-80°C, and the reaction time is 3-7h; the reaction is carried out under stirring at a stirring speed of 300-700rpm.
[0017] Preferably, the method for preparing the modified silica sol in step (3) comprises the following steps:
[0018] 1) reacting tetraethyl silicate, anhydrous ethanol and aqueous ammonia to obtain an intermediate;
[0019] 2) Add the silane coupling agent dropwise to the intermediate to react, thereby obtaining the modified silica sol.
[0020] Preferably, in step 1), the mass ratio of tetraethyl silicate, anhydrous ethanol and aqueous ammonia is 1:5-8:0.1-0.2, and the mass concentration of aqueous ammonia is 1-3%; the reaction temperature is 50-80°C, and the reaction time is 20-40 min.
[0021] Preferably, the mass ratio of the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water in step 1) to the mass ratio of the silane coupling agent in step 2) is 100:1-5, and the silane coupling agent is silane coupling agent KH560 or silane coupling agent KH570; the reaction temperature in step 2) is 50-80°C, and the reaction time is 2-5h; the dripping rate in step 2) is 0.005-0.02g / s.
[0022] Preferably, the demulsifier in step (4) is a sodium chloride solution, and the mass concentration of the sodium chloride solution is 8-12%; the mass ratio of the demulsifier to the reaction emulsion is 1:3-5; the demulsification is carried out during stirring, the stirring speed is 50-80 rpm, and the stirring time is 3-10 min.
[0023] The present invention also provides tetradecane@modified polystyrene low-temperature phase-change microcapsules prepared by the preparation method.
[0024] The beneficial effects of the present invention include the following:
[0025] 1) The low-temperature phase change microcapsules of the present invention have modified polystyrene as the shell layer and tetradecane as the core layer; the modified polystyrene shell layer is an organic-inorganic hybrid shell layer, which has stable physical and chemical properties and excellent film-forming properties, providing higher stability and lower leakage rate for the low-temperature phase change microcapsules, while providing better thermal conductivity, making the application scenarios of the phase change microcapsules more extensive; the phase change temperature of tetradecane is 4.5°C, and it has a high phase change latent heat (212J / g) and cyclic stability. When the ambient temperature is low, the core tetradecane in the phase change microcapsule releases heat to the outside world, and the phase changes from liquid to solid; when the ambient temperature is high, the core tetradecane begins to absorb external heat and melts into a liquid. In the solid-liquid phase change process, due to the volume change caused by the melting-solidification of tetradecane, the shell layer will be subjected to certain thermal stress, but because the modified polystyrene has excellent mechanical stability, the phase change microcapsules will not undergo obvious deformation, thereby reducing the leakage of tetradecane.
[0026] 2) The present invention adopts an in-situ polymerization method to prepare low-temperature phase change microcapsules, which has the advantages of simple preparation method, low cost, high production efficiency, and no need to add other reagents during the process; the addition of silica sol improves the thermal conductivity of the polystyrene shell layer, so that the low-temperature phase change microcapsules have better thermal conductivity in practical applications; the preparation method of the present invention can obtain micron-sized low-temperature phase change microcapsules, and the micron-sized low-temperature phase change microcapsules are easier to be evenly dispersed in the solution to obtain a microcapsule suspension, have a lower degree of supercooling, and broaden the application scenarios of the low-temperature phase change microcapsules. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 This is a scanning electron microscope image of the tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in Example 2;
[0028] Figure 2 This is the infrared spectrum of the tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in Examples 1 to 6. DETAILED DESCRIPTION
[0029] The present invention provides a method for preparing tetradecane@modified polystyrene low-temperature phase change microcapsules, comprising the following steps:
[0030] (1) mixing styrene, tetradecane, an initiator and a crosslinking agent to obtain an oil phase; mixing water and an emulsifier to obtain an aqueous phase;
[0031] (2) mixing the water phase and the oil phase and emulsifying them to obtain an emulsion;
[0032] (3) reacting the modified silica sol and the emulsion under a nitrogen atmosphere to obtain a reaction emulsion;
[0033] (4) The demulsifier and the reaction emulsion are mixed and then demulsified to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0034] In the present invention, the mass ratio of styrene, tetradecane, initiator and cross-linking agent in step (1) is preferably 8-12: 8-12: 0.05-0.1: 0.5-4, more preferably 9-11: 9-11: 0.07-0.09: 0.9-3.1, more preferably 10: 10: 0.08: 1.278-2.48; the mass ratio of water and emulsifier is preferably 100: 0.4-1, more preferably 100: 0.6-0.8, more preferably 100: 0.7.
[0035] In the present invention, the initiator in step (1) is preferably azobisisoheptylnitrile; the cross-linking agent is preferably methyl cellulose and methyl methacrylate, and the mass ratio of methyl cellulose to methyl methacrylate is preferably 1:7-9, more preferably 1:7.5-8.5, and more preferably 1:8;
[0036] The emulsifier is preferably sodium lauryl sulfate and dodecylphenol polyoxyethylene ether, and the mass ratio of sodium lauryl sulfate to dodecylphenol polyoxyethylene ether is preferably 0.8-1.2:0.8-1.2, more preferably 0.9-1.1:0.9-1.1, and more preferably 1:1.
[0037] In the present invention, in step (1), styrene and methyl methacrylate are preferably washed separately to remove the polymerization inhibitor therein; the reagents used for the washing are preferably sodium hydroxide solution and water in sequence, and the number of washings with sodium hydroxide solution is preferably 2 to 4 times, and more preferably 3 times; washing with water is terminated when the washing solution is neutral; the mass concentration of the sodium hydroxide solution is preferably 5 to 15%, and more preferably 10%.
[0038] In the present invention, the mass ratio of the water phase to the oil phase in step (2) is preferably 0.8-1.2:0.8-1.2, more preferably 0.9-1.1:0.9-1.1, and more preferably 1:1; the emulsification speed is preferably 5000-15000 rpm, more preferably 7000-12000 rpm, and more preferably 9000 rpm; the emulsification time is preferably 10-20 min, more preferably 13-18 min, and more preferably 15 min.
[0039] In the present invention, in step (3), the emulsion is preferably stirred first, and then the modified silica sol and the emulsion are reacted; the stirring speed is preferably 300-700 rpm, more preferably 400-600 rpm, and more preferably 500 rpm; the stirring time is preferably 20-40 min, and more preferably 30 min; the temperature of the emulsion during stirring is preferably 40-80°C, more preferably 50-70°C, and more preferably 60°C.
[0040] In the present invention, the mass ratio of the modified silica sol in step (3) to the styrene in step (1) is preferably 1-2:10, more preferably 1.2-1.7:10, and more preferably 1.4:10; the temperature of the reaction in step (3) is preferably 40-80°C, more preferably 50-70°C, and more preferably 60°C; the reaction time is preferably 3-7h, more preferably 4-6h, and more preferably 5h; the reaction is preferably carried out under stirring, and the stirring speed is preferably 300-700rpm, more preferably 400-600rpm, and more preferably 500rpm.
[0041] In the present invention, the method for preparing the modified silica sol in step (3) preferably comprises the following steps:
[0042] 1) reacting tetraethyl silicate, anhydrous ethanol and aqueous ammonia to obtain an intermediate;
[0043] 2) Add the silane coupling agent dropwise to the intermediate to react, thereby obtaining the modified silica sol.
[0044] In the present invention, the mass ratio of tetraethyl silicate, anhydrous ethanol and aqueous ammonia in step 1) is preferably 1:5-8:0.1-0.2, and more preferably 1:6-7:0.12-0.15; the mass concentration of aqueous ammonia is preferably 1-3%, more preferably 1.5-2%, and more preferably 1.7%; the reaction temperature is preferably 50-80°C, and more preferably 60-70°C; the reaction time is preferably 20-40min, more preferably 25-35min, and more preferably 30min.
[0045] In the present invention, the mass ratio of the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water in step 1) to the mass ratio of the silane coupling agent in step 2) is preferably 100:1-5, more preferably 100:2-4, and more preferably 100:3; the silane coupling agent is preferably silane coupling agent KH560 or silane coupling agent KH570; the reaction temperature in step 2) is preferably 50-80°C, more preferably 60-70°C; the reaction time is preferably 2-5h, more preferably 3-4h; the dripping rate in step 2) is preferably 0.005-0.02g / s, more preferably 0.01-0.015g / s.
[0046] In the present invention, the demulsifier in step (4) is preferably a sodium chloride solution, and the mass concentration of the sodium chloride solution is preferably 8-12%, more preferably 9-11%, and more preferably 10%; the mass ratio of the demulsifier to the reaction emulsion is preferably 1:3-5, and more preferably 1:4; the demulsification is preferably carried out under stirring, and the stirring speed is preferably 50-80 rpm, and more preferably 60-70 rpm; the stirring time is preferably 3-10 min, and more preferably 4-6 min, and more preferably 5 min.
[0047] In the present invention, after the demulsification in step (4) is completed, a reaction solution is obtained, and anhydrous ethanol is preferably first added to the reaction solution to precipitate, and then suction filtration, washing and drying are performed in sequence to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules; the mass ratio of the anhydrous ethanol to the reaction emulsion is preferably 1:4-7, and more preferably 1:6; the suction filtration is stopped when the liquid is drained; the reagents used for the washing are preferably petroleum ether and water in sequence, and the number of washings with petroleum ether is preferably 2-4 times, and more preferably 3 times; the number of washings with water is preferably 2-4 times, and more preferably 3 times; the drying temperature is preferably 30-50°C, and more preferably 40°C; the drying time is preferably 8-16h, and more preferably 12h.
[0048] The present invention also provides tetradecane@modified polystyrene low-temperature phase-change microcapsules prepared by the preparation method.
[0049] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.
[0050] Example 1
[0051] Tetraethyl silicate and anhydrous ethanol in a mass ratio of 1:6 were placed in a water bath at 60°C and stirred at 30 rpm. Ammonia water (the mass concentration of ammonia water was 1.7%, and the mass ratio of tetraethyl silicate to ammonia water was 1:0.1) was added to the mixture at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted for 30 minutes to obtain an intermediate. Silane coupling agent KH570 (the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water and the mass ratio of silane coupling agent KH570 was 100:3) was added to the intermediate at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted at 60°C for 3 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a modified silica sol.
[0052] The styrene was washed three times with a sodium hydroxide solution having a mass concentration of 10%, and then washed with deionized water until the washing solution was neutral. The above washing steps were repeated for methyl methacrylate.
[0053] 10g of styrene, 10g of tetradecane, 0.08g of azobisisoheptonitrile, 0.8g of methyl methacrylate and 0.1g of methyl cellulose were mixed to obtain an oil phase. 100g of deionized water, 0.3g of sodium dodecyl sulfate and 0.3g of dodecylphenol polyoxyethylene ether were mixed to obtain an aqueous phase. The oil phase and the aqueous phase were mixed in a mass ratio of 1:1, and emulsified on a high-speed homogenizer at a speed of 9000rpm for 15 minutes to obtain an emulsion.
[0054] Under nitrogen atmosphere, the emulsion was stirred at 60° C. and 500 rpm for 30 min. 1.4 g of modified silica sol was added to the emulsion, and the mixture was stirred at 60° C. and 500 rpm for 5 h to obtain a reaction emulsion.
[0055] Sodium chloride solution (the mass concentration of sodium chloride solution is 10%) is added to the reaction emulsion (the mass ratio of sodium chloride solution to reaction emulsion is 1:4) stirred at 70 rpm, and the emulsion is broken at 70 rpm for 5 min to obtain a reaction solution. Anhydrous ethanol (the mass ratio of anhydrous ethanol to reaction emulsion is 1:6) is added to the reaction solution to precipitate the precipitate, and the solid product is obtained by suction filtration until the liquid is drained. The solid product is first washed with petroleum ether 3 times, then washed with deionized water 3 times, and then dried at 40°C for 12 hours to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0056] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC1.
[0057] Example 2
[0058] Tetraethyl silicate and anhydrous ethanol in a mass ratio of 1:6 were placed in a water bath at 60°C and stirred at 30 rpm. Ammonia water (the mass concentration of ammonia water was 1.7%, and the mass ratio of tetraethyl silicate to ammonia water was 1:0.1) was added to the mixture at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted for 30 minutes to obtain an intermediate. Silane coupling agent KH560 (the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water and the mass ratio of silane coupling agent KH560 was 100:3) was added to the intermediate at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted at 60°C for 3 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a modified silica sol.
[0059] The styrene was washed three times with a sodium hydroxide solution having a mass concentration of 10%, and then washed with deionized water until the washing solution was neutral. The above washing steps were repeated for methyl methacrylate.
[0060] 10g of styrene, 10g of tetradecane, 0.08g of azobisisoheptonitrile, 1.136g of methyl methacrylate and 0.142g of methyl cellulose were mixed to obtain an oil phase. 100g of deionized water, 0.3g of sodium dodecyl sulfate and 0.3g of dodecylphenol polyoxyethylene ether were mixed to obtain an aqueous phase. The oil phase and the aqueous phase were mixed at a mass ratio of 1:1, and emulsified on a high-speed homogenizer at a speed of 9000rpm for 15 minutes to obtain an emulsion.
[0061] Under nitrogen atmosphere, the emulsion was stirred at 60° C. and 500 rpm for 30 min. 1.4 g of modified silica sol was added to the emulsion, and the mixture was stirred at 60° C. and 500 rpm for 5 h to obtain a reaction emulsion.
[0062] Sodium chloride solution (the mass concentration of sodium chloride solution is 10%) is added to the reaction emulsion (the mass ratio of sodium chloride solution to reaction emulsion is 1:4) stirred at 70 rpm, and the emulsion is broken at 70 rpm for 5 min to obtain a reaction solution. Anhydrous ethanol (the mass ratio of anhydrous ethanol to reaction emulsion is 1:6) is added to the reaction solution to precipitate the precipitate, and the solid product is obtained by suction filtration until the liquid is drained. The solid product is first washed with petroleum ether 3 times, then washed with deionized water 3 times, and then dried at 40°C for 12 hours to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0063] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC2.
[0064] Figure 1 This is a scanning electron microscope image of the tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in Example 2. Figure 1It can be seen that the tetradecane@modified polystyrene low-temperature phase change microcapsules are uniform and complete spherical structures.
[0065] Example 3
[0066] The mass of methyl methacrylate in Example 1 was modified to 1.636 g, the mass of methyl cellulose was modified to 0.204 g, and the rest was the same as in Example 1.
[0067] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC3.
[0068] Example 4
[0069] The mass of methyl methacrylate in Example 2 was modified to 2.204 g, the mass of methyl cellulose was modified to 0.276 g, and the rest was the same as in Example 2.
[0070] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC4.
[0071] Example 5
[0072] The mass of methyl methacrylate in Example 2 was modified to 2.756 g, the mass of methyl cellulose was modified to 0.344 g, and the rest was the same as in Example 2.
[0073] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC5.
[0074] Example 6
[0075] The mass of methyl methacrylate in Example 2 was modified to 3.324 g, the mass of methyl cellulose was modified to 0.416 g, and the rest was the same as in Example 2.
[0076] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC6.
[0077] Figure 2 The infrared spectra of tetradecane@modified polystyrene low temperature phase change microcapsules prepared in Examples 1 to 6 are shown in FIG. Figure 2 It can be seen that tetradecane is successfully encapsulated in the polystyrene shell after silica sol modification.
[0078] Example 7
[0079] Tetraethyl silicate and anhydrous ethanol in a mass ratio of 1:8 were placed in a water bath at 80°C and stirred at 50 rpm. Ammonia water (the mass concentration of ammonia water was 3%, and the mass ratio of tetraethyl silicate to ammonia water was 1:0.15) was added to the mixed solution at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted for 20 minutes to obtain an intermediate. Silane coupling agent KH560 (the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water and the mass ratio of silane coupling agent KH560 was 100:1) was added to the intermediate at a rate of 0.005 g / s. After the addition was completed, the mixture was reacted at 80°C for 2 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a modified silica sol.
[0080] The styrene was washed three times with a sodium hydroxide solution having a mass concentration of 15%, and then washed with deionized water until the washing solution was neutral. The above washing steps were repeated for methyl methacrylate.
[0081] 9 g of styrene, 11 g of tetradecane, 0.1 g of azobisisoheptonitrile, 3.366 g of methyl methacrylate and 0.374 g of methyl cellulose were mixed to obtain an oil phase. 100 g of deionized water, 0.36 g of sodium dodecyl sulfate and 0.44 g of dodecylphenol polyoxyethylene ether were mixed to obtain an aqueous phase. The oil phase and the aqueous phase were mixed at a mass ratio of 0.9:1.1, and emulsified on a high-speed homogenizer at a speed of 12000 rpm for 10 min to obtain an emulsion.
[0082] Under nitrogen atmosphere, the emulsion was stirred at 80° C. and 700 rpm for 20 min. 1.53 g of modified silica sol was added to the emulsion, and the mixture was stirred at 80° C. and 700 rpm for 3 h to obtain a reaction emulsion.
[0083] Sodium chloride solution (the mass concentration of sodium chloride solution is 12%) is added to the reaction emulsion (the mass ratio of sodium chloride solution to reaction emulsion is 1:3) stirred at 50 rpm, and the emulsion is broken at 50 rpm for 10 min to obtain a reaction solution. Anhydrous ethanol (the mass ratio of anhydrous ethanol to reaction emulsion is 1:4) is added to the reaction solution to precipitate the precipitate, and the solid product is obtained by suction filtration until the liquid is drained. The solid product is first washed with petroleum ether 3 times, then washed with deionized water 3 times, and then dried at 50°C for 8 hours to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0084] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC7.
[0085] Example 8
[0086] Tetraethyl silicate and anhydrous ethanol in a mass ratio of 1:5 were placed in a water bath at 50°C and stirred at 50 rpm. Ammonia water (the mass concentration of ammonia water was 1%, and the mass ratio of tetraethyl silicate to ammonia water was 1:0.1) was added to the mixture at a rate of 0.01 g / s. After the addition was completed, the mixture was reacted for 40 minutes to obtain an intermediate. Silane coupling agent KH560 (the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water and the mass ratio of silane coupling agent KH560 was 100:5) was added to the intermediate at a rate of 0.02 g / s. After the addition was completed, the mixture was reacted at 50°C for 5 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a modified silica sol.
[0087] The styrene was washed three times with a sodium hydroxide solution having a mass concentration of 10%, and then washed with deionized water until the washing solution was neutral. The above washing steps were repeated for methyl methacrylate.
[0088] 11 g of styrene, 9 g of tetradecane, 0.05 g of azobisisoheptonitrile, 1.61 g of methyl methacrylate and 0.23 g of methyl cellulose were mixed to obtain an oil phase. 100 g of deionized water, 0.22 g of sodium dodecyl sulfate and 0.18 g of dodecylphenol polyoxyethylene ether were mixed to obtain an aqueous phase. The oil phase and the aqueous phase were mixed at a mass ratio of 1.1:0.9, and emulsified on a high-speed homogenizer at a speed of 5000 rpm for 20 minutes to obtain an emulsion.
[0089] Under nitrogen atmosphere, the emulsion was stirred at 40° C. and 300 rpm for 20 min. 1.32 g of modified silica sol was added to the emulsion, and the mixture was stirred at 40° C. and 300 rpm for 7 h to obtain a reaction emulsion.
[0090] Sodium chloride solution (the mass concentration of sodium chloride solution is 8%) is added to the reaction emulsion (the mass ratio of sodium chloride solution to reaction emulsion is 1:5) stirred at 80 rpm, and the emulsion is broken at 80 rpm for 3 min to obtain a reaction solution. Anhydrous ethanol (the mass ratio of anhydrous ethanol to reaction emulsion is 1:7) is added to the reaction solution to precipitate the precipitate, and the solid product is obtained by suction filtration until the liquid is drained. The solid product is first washed with petroleum ether 3 times, then washed with deionized water 3 times, and then dried at 30°C for 16 hours to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
[0091] The tetradecane@modified polystyrene low-temperature phase change microcapsules prepared in this example are marked as MC8.
[0092] Comparative Example 1
[0093] The modified silica sol in Example 2 is omitted, and the rest is the same as Example 2.
[0094] The phase change performance of the low-temperature phase change microcapsules of Examples 1 to 8 and Comparative Example 1 was tested respectively. The test results are shown in Table 1.
[0095] The test steps of melting temperature and phase change latent heat are as follows: 5 mg of low-temperature phase change microcapsules are placed in an alumina crucible and tested using a differential scanning calorimeter (MettlerDSC3) under a constant nitrogen flow of 20 mL / min. During the test, the heating rate and cooling rate are both 5°C / min, and the temperature range is -40°C to 40°C. Before the test, indium is used as a reference material to calibrate the differential calorimeter.
[0096] Thermal conductivity is tested according to international standard ISO 22007-2.
[0097] The decomposition temperature of tetradecane in the capsules was used to characterize the thermal stability of the low-temperature phase change microcapsules. The test steps were as follows: 8 mg of the low-temperature phase change microcapsule sample was placed in an alumina crucible and tested using a thermogravimetric analyzer (MettlerToledo) under a constant nitrogen flow of 20 mL / min. During the test, the heating rate and cooling rate were both 5°C / min, and the heating range was 30°C to 600°C.
[0098] Table 1 Phase change performance test results of low temperature phase change microcapsules
[0099]
[0100]
[0101] It can be seen from Table 1 that the low-temperature phase change microcapsules of the present invention using polyethylene modified by silica sol as the shell layer and tetradecane as the core layer have a lower melting temperature and a higher latent heat of phase change; at the same time, the polyethylene modified by silica sol is used as the shell layer, which provides a higher thermal conductivity for the low-temperature phase change microcapsules; the modified shell layer is an organic-inorganic composite material with better thermal stability, thereby ensuring that the low-temperature phase change microcapsules do not experience performance degradation in a higher temperature range.
[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A method for preparing tetradecane@modified polystyrene low-temperature phase change microcapsules, characterized in that: The following steps are included: (1) mixing styrene, tetradecane, an initiator and a crosslinking agent to obtain an oil phase; mixing water and an emulsifier to obtain an aqueous phase; (2) mixing the water phase and the oil phase and emulsifying them to obtain an emulsion; (3) reacting the modified silica sol and the emulsion under a nitrogen atmosphere to obtain a reaction emulsion; (4) The demulsifier and the reaction emulsion are mixed and then demulsified to obtain tetradecane@modified polystyrene low-temperature phase change microcapsules.
2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of styrene, tetradecane, initiator and crosslinking agent is 8-12:8-12:0.05-0.1:0.5-4, and the mass ratio of water and emulsifier is 100:0.4-1.
3. The preparation method according to claim 1 or 2, characterized in that: The initiator in step (1) is azobisisoheptanenitrile; the crosslinking agent is methyl cellulose and methyl methacrylate, and the mass ratio of methyl cellulose to methyl methacrylate is 1:7-9; The emulsifiers are sodium dodecyl sulfate and dodecylphenol polyoxyethylene ether, and the mass ratio of sodium dodecyl sulfate to dodecylphenol polyoxyethylene ether is 0.8-1.2:0.8-1.
2.
4. The preparation method according to claim 3, characterized in that: In step (2), the mass ratio of the water phase to the oil phase is 0.8-1.2:0.8-1.2; the emulsification speed is 5000-15000 rpm, and the emulsification time is 10-20 min.
5. The preparation method according to claim 4, characterized in that: The mass ratio of the modified silica sol in step (3) to the styrene in step (1) is 1-2:10; the reaction temperature in step (3) is 40-80°C, and the reaction time is 3-7h; the reaction is carried out under stirring, and the stirring speed is 300-700rpm.
6. The preparation method according to claim 4 or 5, characterized in that: The preparation method of the modified silica sol in step (3) comprises the following steps: 1) reacting tetraethyl silicate, anhydrous ethanol and aqueous ammonia to obtain an intermediate; 2) Add the silane coupling agent dropwise to the intermediate to react, thereby obtaining the modified silica sol.
7. The preparation method according to claim 6, characterized in that: Step 1) The mass ratio of tetraethyl silicate, anhydrous ethanol and ammonia water is 1:5-8:0.1-0.2, and the mass concentration of ammonia water is 1-3%; the reaction temperature is 50-80°C, and the reaction time is 20-40 minutes.
8. The preparation method according to claim 7, characterized in that: The mass ratio of the total mass of tetraethyl silicate, anhydrous ethanol and ammonia water in step 1) to the mass ratio of the silane coupling agent in step 2) is 100:1-5, and the silane coupling agent is silane coupling agent KH560 or silane coupling agent KH570; the reaction temperature in step 2) is 50-80°C, and the reaction time is 2-5h; the dripping rate in step 2) is 0.005-0.02g / s.
9. The preparation method according to claim 8, characterized in that: The demulsifier in step (4) is a sodium chloride solution with a mass concentration of 8 to 12%; the mass ratio of the demulsifier to the reaction emulsion is 1:3 to 5; the demulsification is carried out during stirring with a stirring speed of 50 to 80 rpm and a stirring time of 3 to 10 min.
10. Tetradecane@modified polystyrene low-temperature phase change microcapsules prepared by the preparation method according to any one of claims 1 to 9.