CN112375545B - Manganese dioxide-melamine formaldehyde resin double-shell composite phase change material and preparation method thereof - Google Patents
Manganese dioxide-melamine formaldehyde resin double-shell composite phase change material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, which is prepared by preparing melamine formaldehyde resin microcapsules by using an oxidation-reduction method and an electrochemical adsorption method, and then constructing MnO on the surfaces of the microcapsules2Nano-layer, forming a double-shell spherical structure. Wherein, the surface of the microcapsule is modified to realize negative charge, and the further construction of MnO is realized through redox reaction2A nanolayer; MnO2The micro-morphology of the nano-layer is formed by the nano-particles and the nano-wires. The preparation method comprises the following steps: 1) pretreating raw materials; 2) preparing microcapsules; 3) MnO2And (4) preparing a shell layer. The photo-thermal conversion efficiency of the material used as a phase-change material is 93-99%; the phase change temperature is 10-29 ℃, and the phase change latent heat is 116-169J/g. The invention has the following advantages: 1. the leakage problem in the phase change process is effectively solved; 2. high light-heat conversion efficiency 3, high phase change latent heat and thermal stability.
Description
Technical Field
The invention relates to the field of phase change energy storage materials, in particular to a manganese dioxide-melamine formaldehyde resin double-shell composite phase change material and a preparation method thereof.
Background
In the current society, the human society is continuously developing and accelerating the degree of global industrialization, the corresponding energy demand is continuously increased, and the global energy is increasingly exhausted. The building energy consumption accounts for a large proportion of the total social energy consumption, and how to reduce the building energy consumption and develop novel building energy-saving materials and technologies becomes a hotspot for the research of modern social scholars. Solar energy is an abundant renewable energy source, and the conversion of solar energy into heat energy is a direct and effective application of solar radiation. However, the solar intermittency in time and space reduces the efficiency of solar thermal energy utilization, and latent heat storage is considered as an effective solution to this problem.
The phase change material is also known as latent heat energy storage material and is known as a low-carbon economy leader in the field of building energy conservation. The phase change material is capable of undergoing a phase change in a specific temperature range and adjusting the ambient temperature by the phase change accompanied by energy conversion. Making phase change materials promising for a number of applications in relation to energy storage. However, in the process of direct use as a phase change material, there are problems of leakage, environmental pollution and the like, which limit the application field, and a better method for solving the problems is to microencapsulate the phase change material. The phase change microcapsule energy storage material (PCM) is a substance capable of storing energy and regulating and controlling temperature by utilizing the heat absorption and release effect of the material in the phase change process, and is popular in the research fields of energy storage such as solar heat storage and energy storage application, air conditioning heating, building energy conservation, temperature regulation clothes and the like. The phase-change microcapsule energy storage material is prepared by microencapsulating a phase-change material, realizing the storage and release of heat by utilizing the reversible phase change of the phase-change material, and can be used in the fields of heat storage and temperature control. However, the microcapsule phase change material has the defect of poor photo-thermal performance in application, so that great waste exists in solar energy utilization. The technical problem in the prior art is how to further improve the photothermal conversion efficiency of the composite phase-change material.
The improvement of the Photothermal Conversion efficiency of the phase change material can be realized by adding a nano material with high Photothermal property into the composite phase change material, for example, a microcapsule based on n-octadecane and poly (melamine-SiC/silicon carbide) shell layer is designed by the prior art Xianfeng Wang et al (Wang, Xianfeng, Li, et al, Fabrication and characterization of poly (melamine-formaldehyde)/silicon carbide hybrid fibrous material with enhanced thermal conductivity and light-heat performance [ J ]. Solar Energy Materials & Solar Cells and International Journal developed photo and thermal Energy Conversion, 2018). The photo-thermal performance of the composite material is improved by adding the SiC nano particles. Wherein, the hybrid microcapsule of 5 percent of nano SiC can keep higher encapsulation efficiency and has good photo-thermal property. Under sunlight, the PCMS undergoes phase change with the increase of time, and the latent heat storage process is driven by solar energy. The photothermal performance is improved, but the conversion efficiency is not high, and the maximum temperature is only 50 ℃.
In order to further improve the photothermal performance of the microcapsule, the metal oxide can be added, but the prior research shows that the nano particles are directly added into the milkThe raw materials are easy to agglomerate during melting, and a good adding effect is difficult to realize. Prior art Diaochun Ma et al (Ma, Diaochun; Liu, Han; Chen, Chen; et al. Synthesis of novel microencapsulated phase change material with SnO2/CNTs shell for solar energy storage and photo-thermal conversion [ J]Materials Research Express, 2019.) paraffin @ SnO was prepared by in situ precipitation and electrostatic ion adsorption using paraffin as the phase change core material and tin dioxide and carbon nanotubes as the composite shell material2a/CNTs composite material. In the article, after the composite material is exposed for 3000s under a simulated light source, 5wt% of paraffin @ SnO2And paraffin @ SnO2The temperature of the/CNTs is 82.5 ℃ and 90.2 ℃, respectively, and absorbed solar radiation can be effectively transferred to the phase-change material for storage. But as can be seen from its photothermographic view, paraffin @ SnO2the/CNTs composite material does not have a phase change platform, and cannot play a role of the phase change material in the composite material, namely the ambient temperature of the material cannot be maintained within a certain range. The enthalpy value of the composite material is also reduced to 86J/g, and 57 percent of phase change energy storage function is lost.
Bin Xu et al (Zhou, ZJ, Zhang, et al. Synthesis of novel microencapsulated phase change materials with hopper and hopper oxide for solar energy storage and photo-thermal conversion [ J ] et al]SOL ENERG MAT SOL C, 2018.) A novel microencapsulated phase change material paraffin @ Cu-Cu is prepared by a hydrothermal method and a redox method2And O. Paraffin @ Cu-Cu2The O phase-change material is compared with the paraffin emulsion, and 4wt% of paraffin @ Cu-Cu is found2After the O composite material is irradiated for 3500s, the temperature of the composite material reaches 92.3 ℃, and the O composite material has better photo-thermal conversion performance, but also has the problem of losing the phase change function.
Therefore, it is desired to invent a phase-change microcapsule material for photo-thermal energy conversion and having a phase-change energy storage function, and the following problems need to be solved:
(1) most microcapsule phase change materials have the defect of poor photo-thermal performance in the application aspect.
(2) The photo-thermal property of the microcapsule can be further effectively improved by adding the metal oxide, but the added nano particles are easy to agglomerate during emulsification, and a better adding effect is difficult to realize.
Disclosure of Invention
The composite phase change material has the characteristics of low light reflection and good heat conductivity, and the final composite phase change material aims to provide a manganese dioxide-melamine formaldehyde resin double-shell composite phase change material and a preparation method thereof and is applied as a phase change heat storage material. The photo-thermal conversion material of the composite phase-change material has the characteristics of specific morphology and stable morphology, and the phase-change material has high phase-change latent heat, proper phase-change temperature, high photo-thermal conversion efficiency, excellent thermal cycle stability and leakage-proof performance.
Based on the above object, the inventors have found that:
manganese dioxide is widely used as a cheap transition metal catalyst, and has the advantages of high speed, high efficiency and the like. The photo-thermal conversion efficiency of the melamine formaldehyde resin double-shell material microcapsule is improved by effectively adding the metal oxide manganese dioxide particles, and the latent heat performance of the microcapsule can be improved.
In the experimental process, the inventor finds that the formation of the second layer of manganese dioxide shell material on the surface of the microcapsule cannot be realized by directly adopting the prior art without any treatment.
The reason for this analysis is: the manganese dioxide cannot be adsorbed on the surface of the microcapsule through chemical action or physical action, so that a shell material is formed.
Aiming at the problems, the inventor adopts an electrochemical adsorption method to solve the problems, and the specific method principle is as follows: modifying the surface of the microcapsule by sodium polystyrene sulfonate to form negative charges; then adding a manganese sulfate solution with positive charges, and realizing that the manganese element is firmly adsorbed on the surface of the microcapsule by the principle of mutual attraction of the positive charges and the negative charges; finally, preparing a manganese dioxide shell material on the surface of the microcapsule in situ through an oxidation-reduction reaction to realize a double-shell structure.
The invention realizes the purpose, and adopts the technical scheme that:
manganese dioxide-melamine formaldehyde resin double-shell composite phase changeThe material is prepared by using a redox method and an electrochemical adsorption method, firstly preparing melamine formaldehyde resin microcapsules, and then constructing MnO on the surfaces of the microcapsules2The nano layer forms a double-shell structure, so that the composite phase-change material has high light-heat conversion efficiency and heat storage performance.
The core material of the microcapsule is n-octadecane;
the microcapsule is a melamine formaldehyde resin microcapsule, the surface of the microcapsule is modified by sodium polystyrene sulfonate and sodium chloride, and the effect is that the sodium polystyrene sulfonate and the sodium chloride make the surface of the microcapsule have negative charges;
the MnO2The nano-layer is prepared from manganese sulfate and potassium permanganate serving as raw materials.
The MnO2The micro-morphology of the nano-layer is formed by the nano-particles and the nano-wires.
A preparation method of a manganese dioxide-melamine formaldehyde resin double-shell composite phase change material comprises the following steps:
step 1) pretreatment of raw materials, wherein the proportion of melamine, formaldehyde and deionized water is 3 g: (5-6) mL: (4-6) mL, uniformly stirring and mixing melamine, formaldehyde and deionized water at normal temperature to obtain a solution A, then dropwise adding a triethanolamine solution with the volume fraction of 50% to adjust the pH value to 9, then carrying out prepolymerization reaction at the reaction temperature of 70 ℃ for 1 h to obtain a prepolymer, and emulsifying the prepolymer under the stirring conditions of the emulsification temperature of 70 ℃, the emulsification time of 2 h and the rotation speed of 2500r/min by taking n-octadecane and styrene maleic anhydride to meet the mass ratio of 1:6, wherein the styrene maleic anhydride is a styrene maleic anhydride solution with the mass fraction of 5%;
step 2) preparing microcapsules, wherein the prepolymer and the emulsion meet the volume ratio of 1: 5, slowly dropping the prepolymer obtained in the step 1 into the emulsion obtained in the step 1 under the stirring conditions that the temperature is 70 ℃ and the rotating speed is 600r/min, adjusting the pH value of the solution to 5.5-6 by using organic citric acid with the mass fraction of 15%, continuously stirring for 6 hours to carry out polymerization reaction, adjusting the pH value of the solution to 8-9 by using triethanolamine with the mass fraction of 50% to finish the polymerization reaction, taking an ethanol aqueous solution with the mass fraction of 30% as a washing solution, washing at the temperature of 40 ℃, washing and soaking for 30s, carrying out suction filtration, washing and drying to obtain the melamine-formaldehyde resin microcapsule;
step 3) MnO2Preparing a shell layer, namely firstly dissolving sodium polystyrene sulfonate and sodium chloride in deionized water according to the mass ratio of 1:15, stirring for 15 minutes to obtain a solution B with negative charges, then adding the melamine formaldehyde resin microcapsules obtained in the step 2 into the solution B according to a certain mass ratio, stirring for 1 hour, carrying out suction filtration, placing a product obtained after suction filtration into deionized water, then adding manganese sulfate with positive charges according to the mass ratio of 4:1 to manganese sulfate to potassium permanganate, wherein the concentration of the potassium permanganate solution is 0.0167g/mL, firstly adding the manganese sulfate with positive charges, stirring for 2 hours, then continuously and slowly dripping the potassium permanganate solution, continuously stirring for 2 hours, finally carrying out suction filtration and drying to obtain MnO (manganese dioxide)2Melamine formaldehyde resin double-shell material microcapsule composite phase change material.
The photo-thermal conversion efficiency of the application of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material as the phase change material is 93-99 percent; the phase change temperature is 10-29 ℃, and the phase change latent heat is 116-169J/g.
The experimental detection result of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material obtained by the invention is as follows:
optical characterization (DC) shows that the conventional direct manganese dioxide adding method cannot realize the synthesis of a manganese dioxide shell layer; namely, the microcapsules are not treated by adding sodium polystyrene sulfonate, sodium chloride, manganese sulfate and potassium permanganate, and the synthesis of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material cannot be realized.
According to infrared spectrum (FT-IR) tests, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material obtained by the invention is successfully synthesized.
The Scanning Electron Microscope (SEM) tests show that the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is in a regular spherical shape, and the diameter range is 3-8 nm.
The X-ray diffractometer (XRD) tests show that the diffraction peak of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material prepared by the invention, n-octadecane and MnO2The diffraction peaks of (a) are almost identical.
Differential Scanning Calorimetry (DSC) tests show that the phase change temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is 10-29 ℃, and the phase change latent heat is 116-169J/g.
The thermal cycle stability of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material obtained by the invention is good through 100 DSC cycle tests.
Through the test of a photo-thermal conversion system, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material obtained by the invention has high photo-thermal conversion efficiency which is 93-99%.
Compared with the prior art, the invention has the following advantages:
1. the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material has the advantages that the microstructure is a regular microsphere structure with the average diameter range of 3nm-8nm, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material shows good photo-thermal performance under light radiation, and the photo-thermal conversion efficiency is up to 99%;
2. the preparation method of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material comprises the steps of coating the phase change material in the shell material, so that the problem of leakage of the phase change material in the phase change process can be effectively solved;
3. the preparation principle of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is electrochemical adsorption, so that the high phase change latent heat of the phase change material is effectively kept;
4. the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material obtained by the invention grows manganese dioxide nano particles on the surface of the microcapsule by an oxidation-reduction method to form a shell of the microcapsule, so that the microcapsule obtains higher photo-thermal property;
5. the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material keeps good thermal stability on the basis of obtaining high light thermal efficiency, can keep the characteristics of the phase change material for a long time under the high temperature condition, has small changes of phase change temperature and phase change latent heat, and meets the requirements of practical application.
Therefore, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material provided by the invention is stable in shape, high in phase change latent heat, good in thermal cycle stability, proper in phase change temperature, good in leakage-proof performance, high in photo-thermal conversion efficiency, and wide in application prospect in the field of phase change heat storage.
Drawings
FIG. 1 shows MnO in example 1, example 2, example 3, example 4 and comparative example 22，9wt% MnO2microcapsule , 7wt% MnO2 microcapsule, 5wt% MnO2 microcapsule, 3wt% MnO2Infrared (FT-IR) spectra of microcapsules, blank microcapsules;
FIG. 2 shows MnO in example 1, example 2, example 3, example 4 and comparative example 22，9wt% MnO2microcapsule , 7wt% MnO2 microcapsule, 5wt% MnO2 microcapsule, 3wt% MnO2X-ray diffraction (XRD) patterns of microcapsules, blank microcapsules;
FIG. 3 shows 7wt% MnO in example 12A Scanning Electron Microscope (SEM) image of microcapsule;
FIG. 4 shows MnO in example 1, example 2, example 3, example 4 and comparative example 22，9wt% MnO2microcapsule, 7wt% MnO2 microcapsule, 5wt% MnO2 microcapsule, 3wt% MnO2Differential Scanning Calorimetry (DSC) curve for microcapsule, blank microcapsule;
FIG. 5 shows 7wt% MnO in example 12 Differential Scanning Calorimetry (DSC) cycle plot;
FIG. 6 shows 9wt% MnO in example 1, example 2, example 3, example 4, comparative example 22 microcapsule ,7wt% MnO2 microcapsule, 5wt% MnO2 microcapsule, 3wt% MnO2Photothermographic images of microcapsules, blank microcapsules;
FIG. 7 is a comparison of n-octadecane of example 1 before and after heating;
FIG. 8 is a comparison of blank microcapsule of comparative example 2 before and after heating;
FIG. 9 shows 7wt% MnO in example 12Comparing the heating of the microcapsule with that before and after heating;
FIG. 10 shows MnO prepared in comparative example 12An optical representation of the microcapsules;
FIG. 11 shows the preparation of comparative example 2 without MnO addition2Scanning Electron Microscope (SEM) image of blank microcapsule (g).
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, which are given by way of examples, but are not intended to limit the present invention.
Example 1
A preparation method of a manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material comprises the following steps:
step 1) pretreating raw materials, weighing 6g of melamine, 10ml of formaldehyde and 10ml of deionized water, uniformly stirring and mixing the melamine, the formaldehyde and the deionized water in a single-neck flask at normal temperature to obtain a solution A, then dropwise adding a triethanolamine solution with a volume fraction of 50% to adjust the pH value to 9, then stirring the solution at 70 ℃ for 1 hour to perform prepolymerization reaction to obtain a prepolymer, and taking 25g of n-octadecane and 7.5 styrene maleic anhydride, wherein the styrene maleic anhydride is firstly prepared into a styrene maleic anhydride solution with a mass fraction of 5%, and emulsifying the solution at a rotating speed of 2500r/min at an emulsifying temperature of 70 for 2 hours to obtain an emulsion;
step 2) preparing microcapsules, namely slowly dripping the prepolymer obtained in the step 1 into the emulsion obtained in the step 1 at the temperature of 70 ℃ and the rotating speed of 600r/min, regulating the pH value of the solution to 5.5-6 by using citric acid with the mass fraction of 15%, continuously stirring for 6 hours to carry out polymerization reaction, regulating the pH value of the solution to 8-9 by using triethanolamine with the mass fraction of 50% to finish the polymerization reaction, then placing the reaction product into an ethanol aqueous solution with the mass fraction of 30%, slightly stirring for 30 seconds at the temperature of 40 ℃, and then carrying out suction filtration, washing and vacuum drying to obtain the melamine-formaldehyde resin microcapsules;
step 3) MnO2Preparing a shell layer, dissolving 0.4g of sodium polystyrene sulfonate and 5.84g of sodium chloride in 200mL of deionized water, stirring for 15 minutes to obtain a solution B, adding 2g of the melamine formaldehyde resin microcapsule obtained in the step 2 into the solution B, stirring for 1 hour, performing suction filtration, placing a product obtained after suction filtration into 125mL of deionized water, adding 0.135g of manganese sulfate, stirring for 2 hours, continuously and slowly dropping 30mL of potassium permanganate solution with the concentration of 0.0167g/mL, continuously stirring for 2 hours, and finally performing suction filtration and drying to obtain MnO2Melamine formaldehyde resin double-shell material microcapsule composite phase change material according to MnO2Is named as 7wt% MnO2 microcapsule。
In order to prove that the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is successfully prepared, an infrared spectrum (FT-IR) test is carried out. As a result, 7wt% MnO in FIG. 12 As shown by a microcapsule curve, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is successfully synthesized, and the spectrum of the composite phase change material is completely composed of the absorption peaks of n-octadecane and manganese dioxide, no new group is generated, and the high phase change latent heat of the n-octadecane is favorably maintained.
In order to prove that the crystal structure of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is not changed, XRD test is carried out. The result is shown in fig. 2, the diffraction peak of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material prepared by the invention has no obvious shift and no new diffraction peak compared with the diffraction peak of the blank sample and the manganese dioxide, and shows that n-octadecane still has good crystallinity in the composite phase change material.
In order to demonstrate the microstructure of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, a Scanning Electron Microscope (SEM) test was performed. The results are shown in FIG. 3, the second inventionThe manganese oxide-melamine formaldehyde resin double-shell composite phase-change material is in a regular spherical shape, the diameter of the manganese oxide-melamine formaldehyde resin double-shell composite phase-change material is 3-8nm, and a large amount of MnO is2The nano particles and the nano wires are coated on the surface of the microcapsule.
In order to prove the phase change performance of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, a Differential Scanning Calorimetry (DSC) test is carried out, and the test conditions are as follows: the nitrogen flow rate is 20 m L/min, and the heating and cooling rates are as follows: 5 ℃/min, and the temperature test range is as follows: -20-80 ℃. The results are shown in FIG. 4, wherein the melting temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material is 29.17 ℃, and the crystallization temperature is 23.26 ℃; the latent heat of phase change was found to be 128.25J/g and 128.74J/g.
In order to prove the thermal cycle stability of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, 100 DSC cycle performance tests are carried out. As shown in FIG. 5, the phase transition temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material fluctuates little after 100 thermal cycles. The latent heat of phase change of the phase change material after 100 times of circulation is 128.11J/g, the phase change material shows good thermal cycle performance in the phase change process, and the phase change material can be widely applied to the field of heat storage.
In order to prove the photothermal conversion effect of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material, photothermal tests are carried out. The results are shown in FIG. 6:
firstly, a temperature platform appears between 30 ℃ and 40 ℃ in the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, which shows that the composite phase change material has a phase change effect therein and can absorb and release heat, and the curve platform of the black microcapsules is not obvious, so that the black microcapsules have poor light absorption capacity and cannot reach the phase change temperature;
secondly, after simulated sunlight irradiates for 20 minutes, the peak value of the composite phase change material is obviously higher than that of a blank sample, and 7wt% MnO is obtained through calculation2The photothermal conversion efficiency of the microcapsule is 99%, and the composite phase change material has high photothermal conversion efficiency comprehensively.
To prove the double shell of manganese dioxide-melamine formaldehyde resinThe leakage-proof effect of the layer composite phase-change material is tested. Pure n-octadecane, prepared blank sample and 7wt% MnO2Placing the microcapsule sample into a 70 ℃ oven to be kept for 30min, photographing the sample before and after heating, and observing the sample, wherein the experimental result is shown in figure 7, figure 8 and figure 9, and the 7wt% MnO2Placing the microcapsule sample into a 70 ℃ oven for 30min, and observing that no leakage occurs; the blank sample is heated to generate a little leakage; while pure n-octadecane has become liquid by heating. Shows that the composite phase-change material is 7wt% MnO2The microcapsule has better leakage-proof performance after phase change.
To prove whether the second shell layer can be synthesized by conventional methods, i.e. investigation of MnO2The effect of the addition mode on the synthesis of the second shell layer by the composite phase change material is provided in comparative example 1, namely the preparation method in step 3 adopts a conventional method.
Comparative example 1
A method for producing a manganese dioxide-melamine formaldehyde resin material, the steps not specifically described being the same as in example 1, except that: in the step 3, 0.16 g of manganese dioxide is directly added without adding sodium polystyrene sulfonate, sodium chloride, manganese sulfate and potassium permanganate, and the obtained material is named as MnO2And (4) microcapsules.
In order to prove that the manganese dioxide shell layer of the manganese dioxide-melamine formaldehyde resin material cannot be successfully coated, the digital video camera is characterized. As a result, as shown in fig. 10, the manganese dioxide was clearly separated from the microcapsule, and the formation of a second layer of manganese dioxide shell material on the surface of the microcapsule was not achieved.
To study MnO2The effect of the content of (b) on the enthalpy and photothermal effect of the composite phase change material comparative example 2 and examples 2, 3, 4, respectively, are provided without the addition of MnO2And adding MnO of 3%, 5% and 9%2The composite phase change material of (1).
Comparative example 2
A method for preparing a n-octadecane/melamine formaldehyde resin microcapsule composite phase change material, which comprises the following steps that are the same as those in the embodiment 1, except that: said step 3 was not carried out, i.e. the material obtained in step 2, the sample was named Black microcapsules.
In order to demonstrate the microscopic morphological structure of the n-octadecane/melamine formaldehyde resin microcapsule composite phase change material, Scanning Electron Microscope (SEM) tests were performed. As shown in FIG. 11, the n-octadecane/melamine formaldehyde resin microcapsule composite phase change material has a regular spherical shape with a diameter of 3-8 nm.
In order to prove the phase change performance of the octadecane/melamine formaldehyde resin microcapsule composite phase change material, a Differential Scanning Calorimetry (DSC) test is carried out. The results are shown in fig. 4, wherein the melting temperature of the n-octadecane/melamine formaldehyde resin microcapsule composite phase-change material is 29.14 ℃, and the crystallization temperature is 23.10 ℃; the phase change latent heat is measured to be 169.06J/g and 168.55J/g, and the phase change enthalpy value is compared with 7wt% MnO2 The enthalpy of the microcapsule is increased.
In order to prove the photothermal conversion effect of the n-octadecane/melamine formaldehyde resin microcapsule composite phase change material, photothermal tests are carried out, and the photothermal conversion efficiency of black microcapsule is 74% through calculation. As shown in FIG. 6, compared with example 1, MnO was not present2The photothermal effect is greatly reduced.
Example 2
The preparation method of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is the same as the preparation method of the embodiment 1 in the steps which are not particularly described, and the difference is that: the mass of the manganese sulfate in the step 3 is 0.065g, the volume of the potassium permanganate in the step 3 is 15mL, and the obtained sample is named as 3wt% MnO2 microcapsule。
In order to prove the phase change performance of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, a Differential Scanning Calorimetry (DSC) test is carried out. The results are shown in FIG. 4, the melting temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material is 29.70 ℃, and the crystallization temperature is 23.50 ℃; the latent heat of phase change was found to be 152.71J/g and 151.74J/g.
In order to prove the photo-thermal conversion effect of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change materialPhoto-thermal testing was performed to calculate 3wt% MnO2The photothermal conversion efficiency was 93%. As shown in FIG. 6, the results were compared with those of example 1 with MnO2The photothermal effect is reduced to some extent.
Example 3
The preparation method of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is the same as the preparation method of the embodiment 1 in the steps which are not particularly described, and the difference is that: the mass of the manganese sulfate in the step 3 is 0.10g, the volume of the potassium permanganate in the step 3 is 25mL, and the obtained sample is named as 5wt% MnO2 microcapsule。
In order to prove the phase change performance of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, a Differential Scanning Calorimetry (DSC) test is carried out. The results are shown in FIG. 4, wherein the melting temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material is 29.64 ℃, and the crystallization temperature is 23.61 ℃; the latent heat of phase change was found to be 142.13J/g and 141.44J/g.
In order to prove the photothermal conversion effect of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material, photothermal test is carried out, and 5wt% MnO is obtained through calculation2 The photothermal conversion efficiency of the microcapsule is 95%. As shown in FIG. 6, the results were compared with those of example 1 with MnO2The photothermal effect is reduced to some extent.
Example 4
The preparation method of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is the same as the preparation method of the embodiment 1 in the steps which are not particularly described, and the difference is that: the mass of the manganese sulfate in the step 3 is 0.211g, the volume of the potassium permanganate in the step 3 is 50mL, and the obtained sample is named as 9wt% MnO2 microcapsule。
In order to prove the phase change performance of the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material, a Differential Scanning Calorimetry (DSC) test is carried out. The results are shown in FIG. 4, wherein the melting temperature of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material is 29.56 ℃, and the crystallization temperature is 23.33 ℃; the latent heat of phase change was found to be 116.63J/g and 116.56J/g.
In order to prove the photothermal conversion effect of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material, photothermal test is carried out, and 9wt% MnO is obtained through calculation2 The photothermal conversion efficiency of the microcapsule was 97%. As shown in FIG. 6, the results were compared with those of example 1 with MnO2Increase in the amount of the compound, the photothermal effect thereof is somewhat reduced;
combining the experimental results of examples 1-4 and comparative examples 1-2, the following conclusions can be drawn:
1、MnO2the content of the manganese dioxide-melamine formaldehyde resin is within the range of 3-9%, the manganese dioxide-melamine formaldehyde resin double-shell composite phase change material can be realized, and the anti-leakage effect is achieved;
2. the DSC results show that due to MnO2The content is increased, so that the enthalpy value of the composite material integrally shows a rising trend;
3. the photothermal effect test result shows that the manganese dioxide nanoparticles have the phenomena of light absorption performance and light reflection of n-octadecane, so that the manganese dioxide nanoparticles are subjected to MnO (manganese dioxide)2The relative content of the n-octadecane is increased, namely the content of the n-octadecane is reduced, and the photothermal effect of the composite material shows an upward trend.
Combining properties, MnO2Is 7%, i.e., the sample is designated as 7wt% MnO2 And microcapsule is the best condition of performance.
Claims (7)
1. A preparation method of a manganese dioxide-melamine formaldehyde resin double-shell composite phase change material is characterized by comprising the following steps:
step 1) pretreating raw materials, namely, using melamine, formaldehyde and deionized water to meet a certain proportion, uniformly stirring and mixing the melamine, the formaldehyde and the deionized water at normal temperature to obtain a solution A, then dropwise adding a triethanolamine solution with the volume fraction of 50% to adjust the pH value to 9, then carrying out prepolymerization reaction under a certain condition to obtain a prepolymer, and using n-octadecane and styrene maleic anhydride to meet a certain mass ratio, and emulsifying under a certain condition to obtain an emulsion;
step 2) preparing microcapsules, namely slowly dripping the prepolymer obtained in the step 1 into the emulsion obtained in the step 1 under a certain condition by using the prepolymer and the emulsion to meet a certain volume ratio, regulating the pH value of the solution to 5.5-6 by using organic citric acid with the mass fraction of 15%, continuously stirring for a certain time to carry out polymerization reaction, regulating the pH value of the solution to 8-9 by using triethanolamine with the mass fraction of 50% to finish the polymerization reaction, and then carrying out suction filtration, washing and drying on a reaction product to obtain the melamine-formaldehyde resin microcapsules;
step 3) MnO2Preparing a shell layer, firstly dissolving sodium polystyrene sulfonate and sodium chloride in deionized water according to a certain mass ratio, stirring for 15 minutes to obtain a solution B with negative charges, then adding the melamine formaldehyde resin microcapsule obtained in the step 2 into the solution B according to the certain mass ratio, stirring for 1 hour, carrying out suction filtration, placing a product obtained after suction filtration into the deionized water, adding manganese sulfate with positive charges according to a certain mass ratio of manganese sulfate and potassium permanganate, stirring for 2 hours, then continuously and slowly dripping a potassium permanganate solution, continuously stirring for 2 hours, and finally carrying out suction filtration and drying to obtain the manganese dioxide-melamine formaldehyde resin double-shell layer composite phase change material.
2. The method of claim 1, wherein: in the step 1, the melamine, the formaldehyde and the deionized water meet the requirement that the ratio is 3 g: (5-6) mL: (4-6) mL, wherein the prepolymerization reaction condition in the step 1 is that the reaction temperature is 70 ℃, the reaction time is 1 h, the mass ratio of the n-octadecane to the styrene maleic anhydride in the step is 1:6, wherein the styrene maleic anhydride is a styrene maleic anhydride solution with the mass fraction of 5%, and the emulsification condition in the step 1 is that the emulsification temperature is 70 ℃, the emulsification time is 2 h, and the rotation speed is 2500 r/min.
3. The method of claim 1, wherein: the volume ratio of the prepolymer to the emulsion in the step 2 is 1: and 5, slowly dripping the prepolymer in the step 2 into the emulsion under the stirring condition that the temperature is 70 ℃ and the rotating speed is 600r/min, adjusting the pH value, and then continuing stirring, namely, the polymerization reaction time is 6 hours, wherein the suction filtration and washing conditions in the step 2 are that an ethanol water solution with the mass fraction of 30% is used as a washing solution, the washing temperature is 40 ℃, and the washing and soaking time is 30 seconds.
4. The method of claim 1, wherein: the mass ratio of the sodium polystyrene sulfonate in the step 3 to the sodium chloride is 1:15, the mass ratio of the manganese sulfate to the potassium permanganate in the step 3 is 4:1, and the concentration of the potassium permanganate solution is 0.0167 g/mL.
5. The method of claim 1, wherein: MnO of manganese dioxide-melamine formaldehyde resin double-shell composite phase change material2The micro-morphology of the nano-layer is formed by the nano-particles and the nano-wires.
6. The application of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material obtained by the preparation method according to claim 1 as a phase-change material is characterized in that: the light-heat conversion efficiency is 93-99%.
7. The application of the manganese dioxide-melamine formaldehyde resin double-shell composite phase-change material obtained by the preparation method according to claim 1 as a phase-change material is characterized in that: the phase change temperature is 10-29 ℃, and the phase change latent heat is 116-169J/g.
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