Method for preparing phase change microcapsule based on chitosan and ternary eutectic solvent

Abstract

The invention relates to a method for preparing a phase change microcapsule based on chitosan and a ternary deep eutectic solvent (DES), which specifically comprises the following steps: by taking capric acid, palmitic acid and octadecane as raw materials, adjusting the proportion of the three components to obtain a ternary DES phase change material with higher phase change enthalpy and lower supercooling degree as a core material of the microcapsule; meanwhile, the amphipathicity (hydrophilicity of amino and hydroxyl and lipophilicity of acetyl) emulsification function of the surface of natural renewable chitosan and the characteristic that the surface amino can be subjected to Schiff base reaction with an aldehyde group cross-linking agent are fully utilized, chitosan molecules are anchored to an oil-water interface, a wall material of the phase change microcapsule is constructed, and the phase change microcapsule with the low supercooling degree and the good phase change effect is prepared through an interfacial polymerization method. The chitosan-ternary DES phase change microcapsule has the advantages of being wide in raw material source, green, non-toxic, simple and convenient in preparation process, small in environmental pollution and low in energy consumption.

Description

Technical Field

[0001] The present invention relates to the field of chemical industrial applications, and specifically relates to a method for preparing phase change microcapsules based on chitosan and ternary deep eutectic solvents. Background Art

[0002] Phase change materials (PCMs) refer to materials that can reversibly absorb or release a large amount of heat during phase changes (such as first-order or second-order phase transitions like solid-liquid transitions, gas-liquid transitions, glass transitions, etc.), and the temperature at the phase interface remains almost unchanged. Phase change materials can temporarily store thermal energy and release and utilize it after a certain period. This typical latent heat energy storage method has advantages such as high energy storage density, small volume of system equipment, and good stability. Latent heat (also known as phase change enthalpy, that is, the heat absorbed or released by a unit mass of substance during the phase change process, J / g) is an important indicator for evaluating the performance of PCMs. The higher the latent heat value of the phase change material, the more heat it can absorb or release during the phase change process, and thus it is more effective in energy storage and thermal management.

[0003] Natural hydrophobic deep eutectic solvents (DESs) composed of fatty acids are a type of common phase change materials. These phase change DESs have advantages such as low toxicity, good chemical stability, high latent heat, no corrosion, small phase change volume change, and adjustable phase change temperature. However, there are: ① During the solid-liquid phase change process, the phenomenon of supercooling often occurs, that is, when the temperature is lower than the theoretical crystallization temperature, crystallization still does not occur. In this case, it is necessary to further lower its temperature to complete the phase change heat release process, resulting in an increase in the phase change temperature difference between heat absorption and heat release, and the latent heat released within the theoretical temperature range is not complete, with low energy utilization efficiency; ② Like other solid-liquid phase change materials, during the phase change process from solid to liquid, problems such as liquid leakage will occur. Using microcapsule encapsulation technology can encapsulate the phase change material in the wall layer of the microcapsule, making the phase change occur in a closed space to prevent leakage. However, in most microcapsule encapsulation technologies, petroleum-based emulsifiers are used to improve the embedding rate of the core material and the stability of the microcapsules, resulting in problems such as environmental pollution, difficulty in degradation, and consumption of limited petroleum resources. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of environmentally friendly phase change microcapsules with simple process, adjustable phase change temperature, high phase change enthalpy, and low supercooling degree, so as to solve the problems of high supercooling degree and easy leakage existing in the actual application process of natural hydrophobic fatty acid-based phase change materials.

[0005] Technical solution of the present invention: Octadecane is added to capric acid and palmitic acid as a nucleating agent to provide preferential nucleation sites for capric acid - palmitic acid at a lower temperature, form crystal nuclei of crystallization, and reduce the energy barrier required during the phase change process, thereby suppressing the occurrence of supercooling phenomenon. Through optimized design, an oily ternary deep eutectic solvent (ternary DES) with a low supercooling degree and a high phase change enthalpy value is obtained for use as the core material of the microcapsule. Utilizing the characteristics of chitosan having abundant hydrophilic amino groups, hydroxyl groups, etc. and hydrophobic acetyl groups, its dual functions as an emulsifier and a microcapsule wall material are exerted, and chitosan - ternary DES phase change microcapsules are prepared by the interfacial polymerization method.

[0006] A method for preparing phase change microcapsules based on chitosan and ternary deep eutectic solvent mainly includes the following steps:

[0007] (1) Preparation of ternary DES phase change material: Capric acid, palmitic acid, and octadecane are mixed evenly according to a certain mass ratio and placed in a reaction vessel. Under the water bath condition of 50 - 100 °C, it is kept at a constant temperature and continuously stirred until it all becomes a colorless transparent liquid, thus obtaining a hydrophobic ternary DES phase change material;

[0008] (2) Preparation of chitosan solution: Weigh a certain amount of chitosan powder and place it in a container, add distilled water, stir and mix evenly at room temperature to form a suspension, slowly add a certain amount of acid, and continue to stir evenly to obtain an acidic chitosan solution with a mass concentration of 1 - 3%;

[0009] (3) Preparation of chitosan - ternary DES phase change microcapsule emulsion: Under the water bath condition of 40 - 80 °C, according to a certain mass ratio, add the ternary DES phase change material obtained in step (1) to water, stir and mix evenly at a constant temperature at a specified speed of 1000 - 8000 r / min, slowly dropwise add the chitosan solution obtained in step (2), and emulsify for 30 - 120 min to obtain a chitosan - ternary DES phase change microcapsule emulsion;

[0010] (4) Preparation of chitosan - ternary DES phase change microcapsule powder: Within 1 - 2 h, dropwise add a cross - linker to the phase change microcapsule emulsion obtained in step (3). After sufficient reaction, adjust the pH of the system to 8 - 10 with a sodium hydroxide solution with a concentration of (0.1 - 1.0)%, obtain a suspension, filter the suspension, discard the filtrate, retain the precipitate part, wash the precipitate with distilled water multiple times until the filtrate is neutral, and dry the precipitate to obtain chitosan - ternary DES phase change microcapsule powder.

[0011] The mass ratio in step (1) is the mass ratio of capric acid, palmitic acid, and octadecane, and its range is (33.8 - 16.9):(6.2 - 3.1):(60 - 80);

[0012] The acid used in step (2) may be hydrochloric acid, acetic acid, etc., and the dosage of the acid is controlled at 1% of the mass of the chitosan solution;

[0013] The mass ratio in step (3) is the mass ratio of ternary DES to water, and its range is (4-16):100;

[0014] The crosslinking agent in step (4) may be one of glutaraldehyde, vanillin, formaldehyde, terephthalaldehyde, genipin and tannin, and its dosage is 2.5-10% of the mass of the chitosan powder;

[0015] The way to dry the precipitate in step (4) may be freeze-drying or drying in an oven at 50-80 °C.

[0016] Advantages of the present invention:

[0017] (1) The oily ternary eutectic solvent phase change material prepared by using three raw materials of capric acid, palmitic acid and octadecane in the present invention has the advantages of simple preparation process, mild conditions, low supercooling degree and high phase change enthalpy.

[0018] (2) The present invention makes full use of the amphiphilic (hydrophilicity of amino and hydroxyl groups and lipophilicity of acetyl group) emulsifying function on the surface of natural renewable chitosan as an emulsifier, and at the same time, by virtue of the characteristic that its amino group can react with the aldehyde group of the crosslinking agent to form a Schiff base reaction, the chitosan molecules are anchored at the oil-water interface to construct the wall material of the phase change microcapsule, which has the advantages of wide raw material sources, green and non-toxic, simple preparation process, little environmental pollution and low energy consumption. Description of the drawings

[0019] Figure 1 It is the optical microscope image of the microcapsule emulsion for Example 2. As shown in the figure, the surface of the microcapsule is smooth, evenly dispersed, and there is no obvious adhesion, which proves that the emulsifying effect of chitosan is good; at the same time, there is almost no damage on the surface of the microcapsule, indicating that chitosan has strong sealing performance as the wall material. Detailed implementation manners

[0020] Example 1

[0021] (1) Preparation of ternary DES phase change material: Mix capric acid, palmitic acid and octadecane according to the mass ratio of 33.8:6.2:60, place them in a reaction vessel, and continuously stir at a constant temperature in a water bath at 50 °C until all become colorless transparent liquids, that is, obtain oily ternary DES; the measured melting enthalpy and solidification enthalpy of this DES are 210.8 and 205.4 J / g respectively, and the supercooling degree is 1.8 °C;

[0022] (2) Preparation of chitosan solution: Weigh 0.4 g of chitosan powder and place it in a container. Add 50 ml of distilled water and stir evenly at room temperature to form a suspension. Then slowly add 0.12 g of acetic acid to the suspension and stir evenly to obtain a chitosan solution;

[0023] (3) Preparation of chitosan - ternary DES phase - change microcapsule emulsion: Weigh 4.0 g of the DES prepared in step (1), add it to 50 ml of water, and stir evenly at a constant temperature of 50 °C in a water bath at a rotation speed of 2000 r / min to obtain a mixture. Then slowly drop the chitosan solution obtained in step (2) into the mixture and emulsify for 30 min to obtain a chitosan - ternary DES phase - change microcapsule emulsion;

[0024] (4) Preparation of chitosan - ternary DES phase - change microcapsule powder: Drop 0.1 g of terephthalaldehyde into the emulsion obtained in step (3) within 1 - 2 h. After sufficient reaction, adjust the pH of the system to 8 with a 1.0 wt% sodium hydroxide solution to obtain a suspension. Filter the suspension, discard the filtrate, retain the precipitate part, and wash the precipitate with distilled water multiple times until the filtrate is neutral. Freeze - dry the precipitate to obtain chitosan - ternary DES phase - change microcapsule powder. The measured melting enthalpy and solidification enthalpy of the microcapsule powder are 210.8 and 205.4 J / g respectively, and the supercooling degree is 1.8 °C.

[0025] Example 2

[0026] (1) Preparation of ternary DES phase - change material: Mix capric acid, palmitic acid, and octadecane in a mass ratio of 16.9:3.1:80, place them in a reaction container, and continuously stir at a constant temperature in a 50 °C water bath until all become colorless transparent liquids, that is, obtain an oily ternary DES; The measured melting enthalpy and solidification enthalpy of the ternary DES are 225.1 and 220.4 J / g respectively, and the supercooling degree is 0.9 °C;

[0027] (2) Preparation of chitosan solution: Weigh 0.4 g of chitosan powder and place it in a container. Add 50 ml of distilled water and stir evenly at room temperature to form a suspension. Then slowly add 0.12 g of acetic acid to the suspension and stir evenly to obtain a chitosan solution;

[0028] (3) Preparation of chitosan - ternary DES phase - change microcapsule emulsion: Weigh 4.0 g of the DES prepared in step (1), add it to 50 ml of water, and stir evenly at a constant temperature of 50 °C in a water bath at a rotation speed of 2000 r / min to obtain a mixture. Then slowly drop the chitosan solution obtained in step (2) into the mixture and emulsify for 30 min to obtain a chitosan - ternary DES phase - change microcapsule emulsion;

[0029] (4) Preparation of chitosan - ternary DES phase - change microcapsule powder: Within 1 - 2 h, 0.1 g of terephthalaldehyde was added to the emulsion obtained in step (3). After sufficient reaction, the pH of the system was adjusted to 8 with a 1.0 wt% sodium hydroxide solution to obtain a suspension. The suspension was filtered, the filtrate was discarded, and the precipitate part was retained. The precipitate was washed several times with distilled water until the filtrate was neutral, and then the precipitate was freeze - dried to obtain chitosan - ternary DES phase - change microcapsule powder. The measured melting enthalpy and solidification enthalpy of this microcapsule powder were 207.0 and 203.0 J / g respectively, and the supercooling degree was 0.2 °C.

[0030] Comparative Example 1

[0031] (1) Preparation of binary DES phase - change material: Capric acid and palmitic acid were mixed in a mass ratio of 84.5:15.5 and placed in a reaction vessel. Under the condition of a 50 °C water bath, it was continuously stirred at a constant temperature until it all became a colorless and transparent liquid, that is, an oily binary DES was obtained. The measured melting enthalpy and solidification enthalpy of this binary DES were 128.9 and 129.1 J / g respectively, and the supercooling degree was 5.7 °C;

[0032] (2) Preparation of chitosan solution: 0.4 g of chitosan powder was weighed and placed in a container, 50 ml of distilled water was added, and it was stirred evenly at room temperature to form a suspension. Then, 0.12 g of acetic acid was slowly added to this suspension and stirred evenly to obtain a chitosan solution;

[0033] (3) Preparation of chitosan - binary DES phase - change microcapsule emulsion: 4.0 g of the DES prepared in step (1) was weighed, added to 50 ml of water, and stirred evenly at a constant temperature of 50 °C and a rotation speed of 2000 r / min to obtain a mixture. Then, the chitosan solution obtained in step (2) was slowly added dropwise to this mixture and emulsified for 30 min to obtain a chitosan - binary DES phase - change microcapsule emulsion;

[0034] (4) Preparation of chitosan - binary DES phase - change microcapsule powder: Within 1 - 2 h, 0.1 g of cross - linker was added to the emulsion obtained in step (3). After sufficient reaction, the pH of the system was adjusted to 8 with a 1.0% sodium hydroxide solution to obtain a suspension. The suspension was filtered, the filtrate was discarded, and the precipitate part was retained. The precipitate was washed several times with distilled water until the filtrate was neutral, and then the precipitate was freeze - dried to obtain chitosan - binary DES phase - change microcapsule powder. The measured melting enthalpy and solidification enthalpy of this microcapsule powder were 120.1 and 117.2 J / g respectively, and the supercooling degree was 4.6 °C.

[0035] Comparative Example 2

[0036] (1) Preparation of liquid octadecane phase change material: Octadecane was placed in a reaction vessel and stirred continuously at a constant temperature in a water bath at 50°C until it completely turned into a colorless transparent liquid, thereby obtaining a liquid phase change material. The melting enthalpy and solidification enthalpy of the phase change material were measured to be 243.0 and 242.7 J / g, respectively, and the supercooling degree was 4.6°C.

[0037] (2) Preparation of chitosan solution: Weigh 0.4 g of chitosan powder and place it in a container, add 50 ml of distilled water, and stir at a uniform speed at room temperature to form a suspension. Then, slowly add 0.12 g of acetic acid to the suspension and stir to obtain a chitosan solution.

[0038] (3) Preparation of chitosan-octadecane phase change microcapsule emulsion: Weigh 4.0 g of the liquid phase change material prepared in step (1), add it to 50 ml of water, stir it in a 50° C. water bath at a constant temperature of 2000 r / min to obtain a mixture, then slowly dropwise add the chitosan solution obtained in step (2) to the mixture, emulsify for 30 min, and obtain chitosan-octadecane phase change microcapsule emulsion;

[0039] (4) Preparation of chitosan-octadecane phase change microcapsule powder: Add 0.1 g of crosslinking agent to the emulsion obtained in step (3) within 1 to 2 hours. After sufficient reaction, adjust the pH of the system to 8 with a 1.0% sodium hydroxide solution to obtain a suspension. Filter the suspension, discard the filtrate, retain the precipitate, and wash the precipitate with distilled water for several times until the filtrate is neutral. Freeze-dry the precipitate to obtain chitosan-octadecane phase change microcapsule powder. The melting enthalpy and solidification enthalpy of the microcapsule powder were measured to be 235.3 and 237.1 J / g, respectively, and the supercooling degree was 4.2°C.

[0040] Comparative Example 3

[0041] (1) Preparation of liquid paraffin phase change material: Paraffin was placed in a reaction vessel and stirred continuously at a constant temperature in a water bath at 50°C until it completely turned into a colorless transparent liquid, thereby obtaining liquid paraffin. The melting enthalpy and solidification enthalpy of the phase change material were measured to be 150.3 and 150.6 J / g, respectively, and the supercooling degree was 2.3°C.

[0042] (2) Preparation of chitosan solution: Weigh 0.4 g of chitosan powder and place it in a container, add 50 ml of distilled water, and stir at a uniform speed at room temperature to form a suspension. Then, slowly add 0.12 g of acetic acid to the suspension and stir to obtain a chitosan solution.

[0043] (3) Preparation of chitosan - paraffin phase change microcapsule emulsion: Weigh 4.0 g of the liquid phase change material prepared in step (1), add it to 50 ml of water, and under a water bath at 50 °C, stir it evenly at a constant speed of 2000 r / min to obtain a mixture. Then, slowly add the chitosan solution obtained in step (2) to this mixture and emulsify it for 30 min to obtain the chitosan - paraffin phase change microcapsule emulsion;

[0044] (4) Preparation of chitosan - paraffin phase change microcapsule powder: Within 1 - 2 h, add 0.1 g of cross - linker to the emulsion obtained in step (3). After sufficient reaction, adjust the pH of the system to 8 with a 1.0% sodium hydroxide solution to obtain a suspension. Filter this suspension, discard the filtrate, retain the precipitate part, and wash this precipitate with distilled water multiple times until the filtrate is neutral. Freeze - dry the precipitate to obtain the chitosan - paraffin phase change microcapsule powder. The measured melting enthalpy and solidification enthalpy of this microcapsule powder are 135.5 and 138.4 J / g respectively, and the supercooling degree is 2.1 °C.

[0045] Table 1 Comparison of thermal property data of phase change materials and microcapsule powders

[0046]

[0047] It can be seen from the data results in Table 1 that:

[0048] (1) Compared with the common phase change materials paraffin and binary DES phase change materials, the melting enthalpy of the ternary DES phase change material in the embodiment of the present invention is significantly increased, and its supercooling degree is relatively low. Especially for Example 2, it is only 0.9 °C. Compared with the phase change material octadecane, although the melting enthalpy is slightly lower, it still significantly has the advantage of low supercooling degree, indicating that the ternary DES phase change material of the present invention can better improve the ability of high supercooling degree, that is, it has a higher energy storage efficiency and a stronger ability to regulate the external temperature.

[0049] (2) Compared with the microcapsule powders with common phase change materials paraffin and binary DES as the core materials and chitosan as the wall material, the melting enthalpy of the chitosan - ternary DES microcapsule powder of the present invention is significantly increased and the supercooling degree is significantly reduced. Especially for Example 2, the increases in its melting enthalpy are 52.8% and 72.4% respectively, and the decreases in the supercooling degree are 90.4% and 95.6% respectively. Compared with the microcapsule powder with octadecane as the core material and chitosan as the wall material, the melting enthalpy of the chitosan - ternary DES microcapsule powder of the present invention has a slight decrease, but the supercooling degree is significantly reduced. Especially for Example 2, the decrease reaches 95.2%, proving that the chitosan - ternary DES microcapsule powder of the present invention has a higher phase change enthalpy value and a lower supercooling degree, and its heat storage capacity and temperature regulation ability are stronger.

[0050] (3) After conducting 100 thermal cycle tests on the chitosan - ternary DES microcapsule powder in Example 2 at a temperature range of -10 - 60°C for its usage scenarios, it was found that there was no significant change in the phase transition temperature range of the microcapsules. At the same time, the melting enthalpy and solidification enthalpy values remained at 95.21% and 97.68% of the original values respectively, proving that the microcapsules in Example 2 of the present invention are well - encapsulated and can be reused multiple times.

Claims

1. A method for preparing phase change microcapsules based on chitosan and a ternary deep eutectic solvent (DES), mainly comprising the following steps: (1) Preparation of ternary DES phase change material: Decanoic acid, palmitic acid and octadecane are mixed uniformly in a certain mass ratio and placed in a reaction container. The mixture is kept constant temperature in a water bath at 50 to 100° C. and stirred continuously until the mixture becomes a colorless transparent liquid, thereby obtaining a hydrophobic ternary DES phase change material. (2) Preparation of chitosan solution: Weigh a certain amount of chitosan powder and place it in a container, add distilled water, and stir at a constant speed at room temperature to mix uniformly to form a suspension, slowly add a certain amount of acid, and continue to stir uniformly to obtain an acidic chitosan solution with a mass concentration of 1-3%; (3) Preparation of chitosan-ternary DES phase change microcapsule emulsion: under a water bath condition of 40-80° C., the ternary DES phase change material obtained in step (1) is added into water according to a certain mass ratio, stirred uniformly at a constant temperature at a stirring speed of 1000-8000 r / min, and the chitosan solution obtained in step (2) is slowly added dropwise, and emulsified for 30-120 min to obtain a chitosan-ternary DES phase change microcapsule emulsion; (4) Preparation of chitosan-ternary DES phase change microcapsule powder: within 1 to 2 hours, add a crosslinking agent to the phase change microcapsule emulsion obtained in step (3). After sufficient reaction, adjust the pH of the system to 8 to 10 with a sodium hydroxide solution having a concentration of (0.1 to 1.0)% to obtain a suspension. Filter the suspension, discard the filtrate, retain the precipitate, wash the precipitate with distilled water for multiple times until the filtrate is neutral, and dry the precipitate to obtain chitosan-ternary DES phase change microcapsule powder.

2. The method for preparing phase change microcapsules based on chitosan and a ternary deep eutectic solvent according to claim 1, characterized in that: The mass ratio in step (1) is the mass ratio of decanoic acid, palmitic acid and octadecane, and its range is (33.8-16.9): (6.2-3.1): (60-80).

3. The method for preparing phase change microcapsules based on chitosan and a ternary deep eutectic solvent according to claim 1, characterized in that: The acid used in step (2) can be hydrochloric acid, acetic acid, etc., and the amount of the acid is controlled to be 1% of the mass of the chitosan solution.

4. The method for preparing phase change microcapsules based on chitosan and a ternary deep eutectic solvent according to claim 1, characterized in that: The mass ratio in step (3) is the mass ratio of DES to water, and its range is (4-16):

100.

5. The method for preparing phase change microcapsules based on chitosan and ternary deep eutectic solvent according to claim 1, characterized in that: The cross-linking agent in step (4) can be one of glutaraldehyde, vanillin, formaldehyde, terephthalaldehyde, genipin and tannin, and its usage is 2.5-10% of the mass of chitosan powder.

6. The method for preparing phase change microcapsules based on chitosan and ternary deep eutectic solvent according to claim 1, characterized in that: The drying conditions in step (4) can be freeze drying or 50-80° C. oven drying.

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