Heat-conducting microcapsule phase-change composite material and preparation method thereof

Abstract

The invention discloses a heat-conducting microcapsule phase-change composite material and a preparation method thereof. The phase-change composite material is a polymer matrix which is formed by polyethylene glycol polyurethane modified heat-conducting microcapsules and has a three-dimensional heat-conducting network path; the heat-conducting microcapsule is of a core-shell structure, the core is paraffin, and the shell layer is boron nitride and polyurethane; the preparation method of the phase change composite material comprises the following steps: reacting an oil phase formed by a mixed solution of paraffin and a polymer with a water phase containing boron nitride to obtain a microcapsule with a core-shell structure, and then mixing the microcapsule with the polymer, heating and shaping to obtain the phase change composite material. The prepared heat-conducting microcapsule phase change composite material is high in melting enthalpy value and good in heat storage performance, has good heat-conducting performance and mechanical performance, still keeps a low leakage rate at a high temperature, and has a good industrial application prospect.

Description

Technical Field

[0001] The invention relates to a phase change composite material, in particular to a heat conductive microcapsule phase change composite material, and also to a preparation method of the phase change composite material. Background Art

[0002] Fossil fuels such as coal, oil and natural gas are limited, and the large-scale use of non-renewable fossil fuels is the main cause of environmental problems such as air pollution and global warming. Therefore, finding new energy and improving energy efficiency are urgent needs for economic and environmental sustainable development. In energy utilization, the mismatch between energy supply and demand in time and space has caused incredible energy waste. Thermal energy storage technology can ensure energy conservation and timely utilization, effectively solve the mismatch between energy supply and demand in time and space, and reduce the size of production equipment, save space and reduce costs. Latent heat storage materials are called phase change storage materials. This energy storage method has the advantages of high energy storage density, small volume change, small temperature change, and easy operation. It is widely used in solar energy utilization, air conditioning, photovoltaics, textiles, building energy conservation and other fields.

[0003] Paraffin has the advantages of large latent heat, low cost, stability, non-toxicity and non-corrosiveness. It is the most promising phase change material for various latent heat storage technologies. However, paraffin also has the disadvantage of easy leakage during the phase change process, which is a complex problem in the widespread use of paraffin as a phase change material (PCM). Paraffin microencapsulated phase change material (MPCM) is an effective measure to improve the thermal performance, stability and volume change of paraffin phase change. Due to the good sealing and structural flexibility of organic materials, microencapsulated phase change materials with polymer shells have been widely studied and applied. However, most phase change materials currently have the disadvantage of low thermal conductivity and cannot quickly store or release heat. In order to solve this problem, the existing technology is to encapsulate by infusing phase change materials in the heat conductive network, but it still cannot solve the defect of high leakage rate. The microencapsulated phase change material itself has a low thermal conductivity, and the prepared composite material has poor thermal conductivity. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a thermally conductive microcapsule phase change composite material with high melting enthalpy, good heat storage performance, good thermal conductivity and mechanical properties, and also to provide a method for preparing the above phase change composite material.

[0005] Technical solution: The thermally conductive microcapsule phase change composite material of the present invention is a composite material with dual phase change temperatures and a three-dimensional thermal conductive network pathway formed by thermally conductive microcapsules modified with polyethylene glycol polyurethane; after mixing the thermally conductive microcapsules with a polyethylene glycol polyurethane matrix, a thermally conductive microcapsule phase change composite material with dual phase change temperatures is obtained; the thermally conductive microcapsule is a core-shell structure, the core is paraffin, and the shell is boron nitride and polyurethane, and the boron nitride and polyurethane are coated on the outer layer of the paraffin core by emulsion polymerization.

[0006] Wherein, the mass ratio of the polyethylene glycol polyurethane, polyurethane, paraffin wax and boron nitride is: 97-551:15-20:7-9:3.

[0007] The method for preparing the thermally conductive microcapsule phase change composite material comprises the following steps:

[0008] (1) dissolving polyethylene glycol and isocyanate in an organic solvent for prepolymerization to obtain a polymer mixture A;

[0009] (2) adding paraffin wax to the polymer mixture A, heating and mixing to form an oil phase, and dropping the oil phase into an aqueous solution containing an emulsifier and boron nitride, and obtaining microcapsules after the reaction is complete;

[0010] (3) After mixing the polyol and the polyethylene glycol, adding isocyanate, and performing a prepolymerization reaction at a high temperature to obtain a polymer mixture B;

[0011] (4) Add the microcapsules and catalyst prepared in step (2) to the polymer mixed solution B, stir evenly, pour into a mold and heat to prepare a thermally conductive microcapsule phase change composite material.

[0012] Wherein, in step (1), the molecular weight of the polyethylene glycol is 100 to 300, the isocyanate is hydrogenated isocyanate or toluene diisocyanate, and the organic solvent is acetone.

[0013] Wherein, in step (1), the mass ratio of polyethylene glycol, hydrogenated isocyanate, toluene diisocyanate and acetone is 5-8:6-9:3-5:20; the mass ratio is preferably 7:8:4:20.

[0014] Wherein, in step (1), the reaction temperature is not less than 40°C and the reaction time is not more than 4h.

[0015] Wherein, in step (2), the emulsifier is sodium dodecyl sulfate, the addition amount of which is 1-3% of the mass of the aqueous phase, and the addition amount of boron nitride is 3-9% of the mass of the aqueous phase.

[0016] Wherein, in step (3), the type of polyol is glycerol polyether polyol, preferably glycerol polyether-7, glycerol polyether-12 or glycerol polyether-26, the molecular weight of polyethylene glycol is 4000, and the isocyanate is hydrogenated isocyanate, preferably hydrogenated diphenylmethane diisocyanate.

[0017] Wherein, in step (3), the prepolymerization reaction has a temperature not lower than 80° C. and a reaction time not higher than 4 h.

[0018] Wherein, in step (4), the catalyst is stannous octoate, and the added amount is 0.5 to 1.5% of the mass of glycerol polyether.

[0019] Wherein, in step (4), the heating temperature is not higher than 80° C. and the heating time is not less than 10 h.

[0020] Principle of the invention: The thermally conductive microcapsule phase change composite material of the present invention utilizes a phase change microcapsule foam with a boron nitride-polyurethane-paraffin core-shell structure and thermally conductive properties, and after being compounded with a polymer matrix, a three-dimensional thermal conductive network of boron nitride is constructed through the mutual contact of microcapsules, thereby effectively improving the thermal conductivity of the phase change composite material.

[0021] The preparation method of the present invention first dissolves polyethylene glycol and isocyanate in an organic solvent such as acetone for prepolymerization reaction, melts paraffin wax and can be mutually dissolved with the prepolymer to form an oil phase, and adds the oil phase to a water phase containing an emulsifier and boron nitride to form an "oil-in-water" emulsion; under the lipophilic effect of boron nitride, finally obtains a thermally conductive microcapsule with a boron nitride-polyurethane-paraffin core-shell structure, and boron nitride attached to the surface of the microcapsule can effectively solve the problem of poor thermal conductivity of the phase change material itself. Then, a composite reaction is carried out, and the microcapsules are evenly distributed in the polyethylene glycol polyurethane, and the microcapsules are in contact with each other. At the same time, the boron nitride attached to the surface of the microcapsule is in contact with each other, and a continuous thermal conductive path is formed in the polymer matrix, thereby improving the thermal conductivity of the phase change composite material. Since most polymers have low phase change melting enthalpy values, the phase change heat storage performance of the phase change composite material obtained after compounding with microcapsules will be greatly reduced. The present invention preferably uses polyethylene glycol polyurethane, which has phase change heat storage properties to reduce the adverse effects of the polymer matrix, thereby synergistically increasing the heat storage and thermal conductivity of the thermally conductive microcapsule phase change composite material of the present invention.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The thermally conductive microcapsule phase change composite material of the present invention has a high melting enthalpy value of 75.56 J / g; it has good thermal conductivity, and the thermal conductivity coefficient is as high as 1.201 W·m - 1 K -1 , which is twice that of the existing technology; (2) The preparation method is simple and easy, suitable for large-scale production, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the thermally conductive microcapsules prepared in steps 1 to 2 of Example 3 (magnification is 300 times);

[0024] Figure 2 The SEM images of the thermally conductive microcapsules prepared in steps 1 to 2 of Example 3 at different magnifications (magnifications are 1250 and 3000 times);

[0025] Figure 3 DSC curves of the thermally conductive microcapsule phase change composite material prepared in Example 3 under different cycles;

[0026] Figure 4 is the leakage rate of the thermally conductive microcapsule phase change composite material prepared in Example 3 at different temperatures;

[0027] Figure 5 The shape retention of the thermally conductive microcapsule phase change composite material and paraffin prepared in Example 3 at different temperatures. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention is further described below in conjunction with the examples. The test materials used in the examples can all be purchased through conventional channels.

[0029] Example 1

[0030] The preparation method of the thermally conductive microcapsule phase change composite material of the present invention is specifically as follows:

[0031] (1) Dissolve 7 g of polyethylene glycol and 12 g of isocyanate in an organic solvent and react at 40°C for 3 h;

[0032] (2) adding 7 g of paraffin wax to the synthesized polymer mixture, raising the temperature to 70° C. to mix and form an oil phase, and slowly dropping it into a solution containing 2 g of an emulsifier and 1 g of boron nitride. After the reaction is complete, microcapsules with a core-shell structure are obtained;

[0033] (3) 10 g of polyol and 1.5 g of isocyanate were mixed and heated at 80 °C for 3 h, 20 g of polyethylene glycol and 1 g of isocyanate were added, and heating was continued for 1 h;

[0034] (4) After 10 g of microcapsules and polymer are uniformly stirred, 0.02 g of stannous octoate is added and poured into a mold and heated at 80° C. for 12 h to obtain the thermally conductive microcapsule phase change composite material of the present invention.

[0035] Example 2

[0036] The preparation method of the thermally conductive microcapsule phase change composite material of the present invention is specifically as follows:

[0037] (1) Dissolve 7 g of polyethylene glycol and 12 g of isocyanate in an organic solvent and react at 40°C for 3 h;

[0038] (2) adding 7 g of paraffin wax to the synthesized polymer mixture, raising the temperature to 70° C. to mix and form an oil phase, and slowly dropping it into a solution containing 2 g of an emulsifier and 2 g of boron nitride. After the reaction is complete, microcapsules with a core-shell structure are obtained;

[0039] (3) 10 g of polyol and 1.5 g of isocyanate were mixed and heated at 80 °C for 3 h, 20 g of polyethylene glycol and 1 g of isocyanate were added, and heating was continued for 1 h;

[0040] (4) After 10 g of microcapsules and polymer are uniformly stirred, 0.02 g of stannous octoate is added and poured into a mold and heated at 80° C. for 12 h to obtain the thermally conductive microcapsule phase change composite material of the present invention.

[0041] Example 3

[0042] The preparation method of the thermally conductive microcapsule phase change composite material of the present invention is specifically as follows:

[0043] (1) Dissolve 7 g of polyethylene glycol and 12 g of isocyanate in an organic solvent and react at 40°C for 3 h;

[0044] (2) adding 7 g of paraffin wax to the synthesized polymer mixture, raising the temperature to 70° C. to mix and form an oil phase, and slowly dropping it into a solution containing 2 g of an emulsifier and 3 g of boron nitride. After the reaction is complete, microcapsules with a core-shell structure are obtained;

[0045] (3) 10 g of polyol and 1.5 g of isocyanate were mixed and heated at 80 °C for 3 h, 20 g of polyethylene glycol and 1 g of isocyanate were added, and heating was continued for 1 h;

[0046] (4) After 10 g of microcapsules and polymer are uniformly stirred, 0.02 g of stannous octoate is added and poured into a mold and heated at 80° C. for 12 h to obtain the thermally conductive microcapsule phase change composite material of the present invention.

[0047] Example 4

[0048] The preparation method of the thermally conductive microcapsule phase change composite material of the present invention is specifically as follows:

[0049] (1) Dissolve 7 g of polyethylene glycol and 12 g of isocyanate in an organic solvent and react at 40°C for 3 h;

[0050] (2) adding 7 g of paraffin wax to the synthesized polymer mixture, raising the temperature to 70° C. to mix and form an oil phase, and slowly dropping it into a solution containing 2 g of an emulsifier and 1 g of boron nitride. After the reaction is complete, microcapsules with a core-shell structure are obtained;

[0051] (3) 10 g of polyol and 1.5 g of isocyanate were mixed and heated at 80 °C for 3 h, 20 g of polyethylene glycol and 1 g of isocyanate were added, and heating was continued for 1 h;

[0052] (4) After 7.5 g of microcapsules and polymer are uniformly stirred, 0.02 g of stannous octoate is added and poured into a mold and heated at 80° C. for 12 h to obtain the thermally conductive microcapsule phase change composite material of the present invention.

[0053] Comparative Example 1

[0054] A composite material, compared with Example 3, in step (4), after 10g of microcapsules and polymers are uniformly stirred, 0.02g of stannous octoate is added, poured into a mold, and allowed to stand at room temperature to obtain a composite material.

[0055] Comparative Example 2

[0056] A composite material, compared with Example 3, in step (4), after 10g of microcapsules and polymers are uniformly stirred, 0.02g of stannous octoate is added, poured into a mold, and heated at 80°C for 6h to obtain a composite material.

[0057] Comparative Example 3

[0058] A composite material, compared with Example 3, in step (4), after 10g of microcapsules and polymers are uniformly stirred, 0.02g of stannous octoate is added, poured into a mold, and heated at 60°C for 12h to obtain a composite material.

[0059] Comparative Example 4

[0060] A composite material, compared with Example 3, in step (4), after 10 g of microcapsules and polymers are uniformly stirred, no stannous octoate is added, and the mixture is heated at 80° C. for 12 h to obtain a composite material.

[0061] The thermally conductive microcapsule phase change composite material prepared in Example 3 was scanned by an electron microscope. Figure 1 and Figure 2 Shown are SEM images of thermal conductive microcapsules at different magnifications.

[0062] The performance of the materials obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was tested:

[0063] The thermal conductivity of the material was tested by a German NETZSCH laser thermal conductivity tester 467. The heat storage performance of the material was tested using a differential scanning calorimeter from the American PerkinElmer Company. The relevant data are shown in Table 1.

[0064] Table 1. Properties of materials obtained from Examples 1 to 4 and Comparative Examples 1 to 4

[0065]

[0066] It can be concluded from Table 1 that in the synthesis stage of microcapsules, boron nitride is used as a thermal conductive filler. As the content of boron nitride increases, the thermal conductivity of the composite material increases. As the content of microcapsules increases, the phase change enthalpy of the composite material increases, and the heat storage performance of the composite material is improved accordingly. In addition, due to the increase in mutual contact between microcapsules and the increase in heat conduction paths, the heat in the composite material diffuses faster along the heat conduction network through the heat load (phonon). However, when too many microcapsules are added, the matrix will not be able to support it, and the composite material will rupture.

[0067] The thermally conductive phase-change composite material obtained in Example 3 has high thermal conductivity and excellent heat storage performance because the amount of thermally conductive microcapsules added is in a balance between the increase in thermal conductivity and the decrease in heat storage capacity. The addition of thermally conductive microcapsules will improve the thermal conductivity, but due to the presence of materials such as boron nitride that cannot phase change, the overall heat storage performance of the composite material will decrease. The amount of thermally conductive microcapsules added in Example 3 is optimal, so it has multiple excellent properties at the same time, achieving the best synergistic effect.

[0068] Comparative Example 1 failed to solidify to obtain a thermally conductive microcapsule phase change composite material because it was not heated after being poured into the mold. Comparative Example 2 failed to solidify due to a short heating time. Comparative Example 3 was not heated enough and was only partially solidified. Comparative Example 4 did not add a catalyst and ultimately failed to solidify.

[0069] like Figure 3 As shown, the thermally conductive phase change composite material prepared in Example 3 has a long cycle stability. After 100 heating-cooling cycles, its phase change enthalpy remains stable and the leakage rate is low. Since the dual encapsulation technology of microcapsules and polymer matrix composites is used in Example 3, the cycle stability under long-term phase change cycles is guaranteed.

[0070] like Figure 4 As shown, the thermally conductive microcapsule phase change composite material prepared in Example 3 has the advantage of low leakage rate at high temperature, and the leakage rate at 80°C is maintained below 1%. This is because the dual packaging technology of microcapsules and polymer matrix composites is adopted in Example 3 to ensure that the phase change material is difficult to leak at high temperature. At the same time, Figure 4 It is also shown that the thermally conductive microcapsules have good shape retention ability at high temperatures.

[0071] When the phase change composite material cannot maintain its shape after the phase change, the phase change composite material has failed and cannot be used any more, resulting in a waste of materials. Therefore, the shape retention ability at high temperature is also an important indicator of the phase change composite material. Figure 5As shown, the thermally conductive microcapsule phase change composite material prepared in Example 3 and paraffin maintain their shapes at different temperatures. It can be seen that the thermally conductive microcapsule phase change composite material of the present invention still maintains its shape at 60°C and 80°C, while paraffin has melted at 60°C and cannot maintain its shape at 80°C, causing leakage. Therefore, the thermally conductive microcapsule phase change composite material of the present invention has a high melting enthalpy value, good heat storage performance, good thermal conductivity and mechanical properties; and still maintains a low leakage rate at high temperatures, and has good industrial application prospects.

Claims

1. A thermally conductive microcapsule phase change composite material, characterized in that: The phase change composite material is a composite material with dual phase change temperature and a three-dimensional heat conductive network path formed by heat conductive microcapsules modified with polyethylene glycol polyurethane; the heat conductive microcapsules are a core-shell structure, the core is paraffin, and the shell is boron nitride and polyurethane. The boron nitride and polyurethane are coated on the outer layer of the paraffin core by emulsion polymerization.

2. The thermally conductive microcapsule phase change composite material according to claim 1, characterized in that: The mass ratio of the polyethylene glycol polyurethane, polyurethane, paraffin wax and boron nitride is: 97-551:15-20:7-9:

3.

3. A method for preparing the thermally conductive microcapsule phase change composite material according to claim 1, characterized in that: The steps include: (1) dissolving polyethylene glycol and isocyanate in an organic solvent for prepolymerization to obtain a polymer mixture A; (2) adding paraffin wax to the polymer mixture A, heating and mixing to form an oil phase, and dropping the oil phase into an aqueous solution containing an emulsifier and boron nitride, and obtaining microcapsules after the reaction is complete; (3) After mixing the polyol and the polyethylene glycol, adding isocyanate, and performing a prepolymerization reaction at a high temperature to obtain a polymer mixture B; (4) Add the microcapsules and catalyst prepared in step (2) to the polymer mixed solution B, stir evenly, pour into a mold and heat to prepare a thermally conductive microcapsule phase change composite material.

4. The preparation method according to claim 3, characterized in that: In step (1), the molecular weight of the polyethylene glycol is 100 to 300, the isocyanate is hydrogenated isocyanate or toluene diisocyanate, and the organic solvent is acetone.

5. The preparation method according to claim 3, characterized in that: In step (1), the mass ratio of polyethylene glycol, hydrogenated isocyanate, toluene diisocyanate and acetone is 5-8:6-9:3-5:

20.

6. The preparation method according to claim 3, characterized in that: In step (2), the emulsifier is sodium dodecyl sulfate, and the added amount is 1-3% of the mass of the water phase, and the added amount of boron nitride is 3-9% of the mass of the water phase.

7. The preparation method according to claim 3, characterized in that: In step (3), the type of polyol is glycerol polyether polyol, the molecular weight of polyethylene glycol is 4000, and the isocyanate is hydrogenated isocyanate.

8. The preparation method according to claim 3, characterized in that: In step (3), the prepolymerization reaction temperature is not less than 80° C. and the reaction time is not more than 4 hours.

9. The preparation method according to claim 3, characterized in that: In step (4), the catalyst is stannous octoate, and the added amount is 0.5-1.5% of the mass of glycerol polyether.

10. The preparation method according to claim 3, characterized in that: In step (4), the heating temperature is not higher than 80° C. and the heating time is not less than 10 h.

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