阅读说明：本技术 双层脲醛壳相变微胶囊及其制备方法和应用 (Double-layer urea-formaldehyde shell phase-change microcapsule and preparation method and application thereof ) 是由 杨晶磊 孙赛玲 安金亮 于 2021-09-17 设计创作，主要内容包括：本发明提供一种双层脲醛壳相变微胶囊及其制备方法和应用,涉及相变微胶囊技术领域。本发明的双层脲醛壳相变微胶囊,由内至外依次包括芯材、内层壁材和外层壁材,所述芯材为相变材料,所述内层壁材和外层壁材均为脲醛树脂。本发明的双层脲醛壳相变微胶囊具有高热稳定性和高潜热优点。本发明通过两步加入PUF预聚液,并控制和调整反应过程中的pH值,制得具有双层脲醛壳的相变微胶囊,微胶囊具有高热稳定性和高潜热的优点,而且胶囊间分散性好,胶囊的包覆率高。(The invention provides a double-layer urea formaldehyde shell phase change microcapsule and a preparation method and application thereof, and relates to the technical field of phase change microcapsules. The double-layer urea-formaldehyde shell phase-change microcapsule comprises a core material, an inner-layer wall material and an outer-layer wall material from inside to outside in sequence, wherein the core material is a phase-change material, and the inner-layer wall material and the outer-layer wall material are both urea-formaldehyde resin. The double-layer urea-formaldehyde shell phase change microcapsule has the advantages of high thermal stability and high latent heat. According to the invention, PUF pre-polymerization liquid is added in two steps, and the pH value in the reaction process is controlled and adjusted, so that the phase change microcapsule with the double-layer urea formaldehyde shell is prepared.)

1. The double-layer urea-formaldehyde shell phase-change microcapsule is characterized by sequentially comprising a core material, an inner-layer wall material and an outer-layer wall material from inside to outside, wherein the core material is a phase-change material, and the inner-layer wall material and the outer-layer wall material are both urea-formaldehyde resin.

2. The dual-layer urea-formaldehyde shell phase-change microcapsule of claim 1, wherein the phase-change material is selected from the group consisting of: alkane phase change materials, fatty acid phase change materials, fatty alcohol phase change materials and fatty acid ester phase change materials.

3. The dual-layer urea-formaldehyde shell phase-change microcapsule of claim 2, wherein the phase-change material is selected from the group consisting of: paraffin, octadecane and tetradecanol.

4. A method for preparing the double-layer urea-formaldehyde shell phase-change microcapsule according to any one of claims 1 to 3, which comprises the following steps:

preparing an aqueous phase: mixing an emulsifier, water and polyhydric phenol to obtain a water phase;

preparing an oil phase: heating to melt the organic phase-change material to obtain an oil phase;

preparing PUF prepolymer solution: preparing an inner PUF (physical unclonable function) pre-polymerization solution and an outer PUF pre-polymerization solution by taking urea and formaldehyde as raw materials;

preparing an emulsion: adding the oil phase into the water phase, and carrying out an emulsification reaction to obtain an oil-in-water phase-change emulsion;

primary coating: mixing the oil-in-water phase-change emulsion and the inner-layer PUF prepolymer solution, adjusting the pH value to 3.2-3.6 by using a pH regulator, carrying out polycondensation reaction, adjusting the pH value to 2.6-2.9, and continuing the polycondensation reaction to form an inner-layer wall material on the outer surface of the core material;

secondary coating: and adding the polyphenol and the outer PUF pre-polymerization solution into the solution subjected to primary coating, adjusting the pH value to 3.2-3.6, performing polycondensation reaction, adjusting the pH value to 2.6-2.9, and continuing the polycondensation reaction to form an outer-layer wall material on the outer surface of the inner-layer wall material, thereby obtaining the double-layer urea-formaldehyde shell phase-change microcapsule.

5. The method according to claim 4, wherein the emulsifier is selected from the group consisting of: one or more of ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, arabic gum, polyvinyl alcohol, alkylphenol polyoxyethylene, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide and sorbitan fatty acid ester;

the polyhydric phenol is selected from: one or more of resorcinol, hydroquinone, catechol, pyrogallol, phloroglucinol, catechol, and dopamine.

6. The production method according to claim 4, wherein the pH adjuster is an acid and/or a base; the acid is selected from: hydrochloric acid, nitric acid, sulfuric acid, citric acid, acetic acid, formic acid; the base is selected from: sodium hydroxide, potassium hydroxide, triethanolamine and sodium carbonate.

7. The method according to claim 4, wherein in the step of preparing the aqueous phase, the mass ratio of the emulsifier, the water and the polyphenol is (0.3-1.5): (50-70): (0.1-0.6), the mixing mode is stirring, the stirring speed is 200-500rpm, the temperature is 40-80 ℃, and after the raw materials are dissolved, the pH value is adjusted to be 3.0-3.6;

in the step of preparing the oil phase, the dosage of the organic phase-change material is 6-10% of the total weight of the water phase;

the preparation of the inner-layer PUF prepolymerization solution specifically comprises the following steps: mixing the following components in a mass ratio of (0.6-1): (1.5-2.6) mixing and dissolving urea and formaldehyde solution, adjusting the pH value to 7.5-9, and reacting at 60-70 ℃ for 30-90 minutes to obtain inner-layer PUF (physically unclosed puffs) prepolymerization solution;

the preparation of the outer-layer PUF prepolymerization solution specifically comprises the following steps: mixing the following components in a mass ratio of (0.8-1): (2-2.6) mixing and dissolving urea and formaldehyde solution, adjusting the pH value to 7.5-9, and reacting at 60-70 ℃ for 30-90 minutes to obtain an outer-layer PUF pre-polymerization solution.

8. The preparation method according to claim 4, wherein the step of preparing the emulsion comprises: adjusting the stirring speed of the water phase to be 500-6000rpm, adding an oil phase and a defoaming agent into the water phase, wherein the addition amount of the defoaming agent is 0-2 wt% of the mass of the organic phase change material, and carrying out an emulsification reaction for 5-20min to obtain an oil-in-water phase change emulsion; the defoaming agent is selected from: n-octyl alcohol, n-butyl alcohol, emulsified silicone oil, a higher alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane.

9. The preparation method according to any one of claims 4 to 8, wherein the primary coating step specifically comprises: adjusting the stirring speed of the oil-in-water phase-change emulsion to be 700rpm at 50-80 ℃, adding an inner-layer PUF pre-polymerization liquid, wherein the dosage of the inner-layer PUF pre-polymerization liquid is 4-7% of the total weight of the oil-in-water phase-change emulsion, adjusting the pH value to be 3.2-3.6 by using a pH regulator, reacting for 30-60 minutes, adjusting the pH value to be 2.6-2.9, and reacting for 120-360 minutes;

the secondary coating step specifically comprises the following steps: adding polyphenol into the solution after primary coating, wherein the dosage of the polyphenol is 50-100% of the weight of the polyphenol in the step of preparing the water phase, adjusting the pH value to be 3.2-3.6, adding an outer layer PUF pre-polymerization liquid, the dosage of the outer layer PUF pre-polymerization liquid is 4-7% of the total weight of the oil-in-water phase-change emulsion, adjusting the pH value to be 3.2-3.6, reacting for 30-60 minutes, adjusting the pH value to be 2.6-2.9, and reacting for 120-360 minutes to obtain the double-layer urea-formaldehyde shell phase-change microcapsule.

10. Use of the double-layer urea-formaldehyde shell phase-change microcapsule according to any one of claims 1 to 3 for preparing temperature-regulating concrete, temperature-regulating fiber or heat-conducting slurry.

Technical Field

The invention relates to the technical field of phase change microcapsules, in particular to a double-layer urea formaldehyde shell phase change microcapsule and a preparation method and application thereof.

Background

Phase Change Materials (PCMs) are materials capable of absorbing and releasing a large amount of latent heat of phase change during phase change, and can be classified into four categories, i.e., solid-solid, solid-gas, liquid-gas, and solid-liquid, according to the phase change mechanism. Among them, solid-liquid phase change materials have been the focus of research in recent years due to their advantages of small volume change before and after phase change, large latent heat of phase change, wide range of phase change temperature, good stability, and low cost. The solid-liquid phase change material is selected from paraffin, fatty acid, fatty alcohol, inorganic hydrated salt, etc. The solid-liquid phase change material also has the defects of volume change, poor solid heat-conducting property, easy leakage of liquid and the like during phase change, and the problem can be solved to a certain extent by encapsulating the phase change material into a microcapsule. The phase-change microcapsule has the functions of energy storage and temperature regulation in the phase-change process, and has wide application in the fields of building energy conservation, textile and clothing, electronic products, aerospace and functional hot fluid.

The microencapsulation technique is to completely coat a solid, liquid, or gas (core material) with a polymer material as a film forming material (wall material) to form fine solid particles (microcapsules) having a sealing or semipermeable membrane. The phase-change microcapsules (MEPCMs) are prepared by microencapsulation technology, taking phase-change materials as core materials and wrapping the core materials by inorganic materials or synthetic polymer materials by a physical or chemical method. Common preparation methods include in-situ polymerization, interfacial polymerization, and suspension polymerization.

The phase-change latent heat of the phase-change microcapsule is determined by the enthalpy of the phase-change core material and the coating rate of the microcapsule, and the ideal phase-change core material can meet the conditions of high phase-change latent heat, phase-change temperature meeting the requirement, stable performance, no toxicity, wide source, small supercooling degree, no phase separation and the like as far as possible, thereby achieving the effects of energy storage and utilization and realizing the regulation and control of the temperature. At present, the core materials of the commonly used phase-change microcapsules are: inorganic hydrated salt, paraffin, fatty acid, fatty alcohol, ester and other single phase-change materials, and also a composite core material is obtained by compounding several materials.

The wall material of the phase-change microcapsule can provide a stable phase-change space for the phase-change material, plays a role in protecting and sealing the phase-change material, greatly influences various performances of the microcapsule, and has different requirements on the wall material in different application fields and environments. The corresponding wall material can be preliminarily determined according to the properties of the core material, and various factors need to be considered during selection, which mainly comprise: the stability and durability of the wall material, the permeability and curing degree of the shell material and the influence of the external environment.

Common phase-change microcapsule wall materials comprise organic urea-formaldehyde resin, melamine-formaldehyde resin, polyurea, polyethylene and the like, and inorganic SiO₂、TiO₂、CaCO₃And the like. The urea-formaldehyde resin has good sealing performance, simple preparation process, good heat resistance and good mechanical property, and is widely applied to research.

However, the phase-change microcapsule prepared by the existing preparation process of the urea-formaldehyde shell microcapsule has poor high temperature resistance, and obvious core material leakage exists within 20 minutes of a high-temperature test at 100 ℃, so that the application range and the service time of the phase-change microcapsule are greatly limited. In addition, in order to improve the compactness of a product, the phase-change microcapsule prepared by the conventional organic shell usually sacrifices enthalpy, namely the coating rate of a core material is low due to the increase of the using amount of a wall material during preparation, so that the temperature control performance of the phase-change microcapsule is influenced. Therefore, it is necessary to improve the high temperature resistance of the urea-formaldehyde shell phase-change microcapsule, and develop a phase-change microcapsule having excellent thermal stability and high latent heat property.

Disclosure of Invention

In view of the above, there is a need to provide a double-layer urea-formaldehyde shell phase-change microcapsule, which has the advantages of high thermal stability and high latent heat.

The double-layer urea-formaldehyde shell phase-change microcapsule sequentially comprises a core material, an inner-layer wall material and an outer-layer wall material from inside to outside, wherein the core material is a phase-change material, and the inner-layer wall material and the outer-layer wall material are both urea-formaldehyde resin (PUF).

The double-layer urea-formaldehyde shell phase-change microcapsule has high thermal stability, no obvious core material leakage after being baked for more than 6 hours at 100 ℃, high enthalpy and excellent temperature regulation performance.

In one embodiment, the phase change material is selected from: alkane phase change materials, fatty acid phase change materials, fatty alcohol phase change materials and fatty acid ester phase change materials.

The alkane phase change material is preferably C8-C26 straight-chain alkane, the fatty acid phase change material is preferably C8-C20 fatty acid, the fatty alcohol phase change material is preferably C8-C26 fatty alcohol, and the fatty acid ester phase change material is preferably C4-C26 fatty acid ester.

In one embodiment, the phase change material is selected from: paraffin, octadecane and tetradecanol.

The invention also provides a preparation method of the double-layer urea formaldehyde shell phase change microcapsule, which comprises the following steps:

preparing an aqueous phase: mixing an emulsifier, water and polyhydric phenol to obtain a water phase;

preparing an oil phase: heating to melt the organic phase-change material to obtain an oil phase;

preparing PUF prepolymer solution: preparing an inner PUF (physical unclonable function) pre-polymerization solution and an outer PUF pre-polymerization solution by taking urea and formaldehyde as raw materials;

preparing an emulsion: adding the oil phase into the water phase, and carrying out an emulsification reaction to obtain an oil-in-water phase-change emulsion;

primary coating: mixing the oil-in-water phase-change emulsion and the inner-layer PUF prepolymer solution, adjusting the pH value to 3.2-3.6 by using a pH regulator, carrying out polycondensation reaction, adjusting the pH value to 2.6-2.9, and continuing the polycondensation reaction to form an inner-layer wall material on the outer surface of the core material;

secondary coating: and adding the polyphenol and the outer PUF pre-polymerization solution into the solution subjected to primary coating, adjusting the pH value to 3.2-3.6, performing polycondensation reaction, adjusting the pH value to 2.6-2.9, and continuing the polycondensation reaction to form an outer-layer wall material on the outer surface of the inner-layer wall material, thereby obtaining the double-layer urea-formaldehyde shell phase-change microcapsule.

In the preparation method, the PUF pre-polymerization liquid is added in two steps, the coating rate of the core material can reach more than 70%, the compactness of the shell material is improved, the formed double-layer shell material has excellent temperature resistance, the dispersity of the capsule is good, and no adhesion exists between the capsules.

According to the preparation method, after the PUF prepolymer solution is added, the pH value of a reaction system is controlled to be a high value (3.2-3.6) and reacts for a period of time, under the pH value, the PUF prepolymer solution is slowly deposited on the surface of a core material, so that a compact shell layer can be formed, the formation of a loose shell layer at an initial high reaction rate is prevented, meanwhile, waste caused by self-polymerization of a wall material is reduced, in the process, the PUF prepolymer is subjected to polycondensation to a certain degree to form oligomers of different degrees, after the reaction for a period of time, the wall material is uniformly dispersed, the wall material concentration is reduced to a certain degree, the pH value (2.6-2.9) is reduced, the oligomers are further subjected to polycondensation to form PUF with a high polymerization degree, the deposition rate of the PUF wall material is reasonable, the PUF is not prone to implosion, and the surface of the PUF shell is relatively smooth.

In the prior art, the pre-polymerization solution is usually added at one time, which easily causes the self-accumulation of the PUF pre-polymer in the solution, thereby affecting the thickness and compactness of the shell material, and the prepared microcapsule is easy to adhere and has poor dispersibility, which seriously affects the use effect of the microcapsule in an application base material.

If the pH value is kept low (for example, about 2.8) at the beginning of the polymerization reaction, since the concentration of the PUF prepolymer is high at the beginning, implosion is likely to occur, the surface of the obtained PUF shell is rough, the capsule compactness is poor, and the core material is likely to leak. If the reaction system is always at a high pH value (such as about 3.8), the polycondensation reaction of the PUF prepolymer is slow, the deposition rate of the PUF shell material on the surface of a core material or a capsule is too slow, the formed capsule shell is too thin, and the capsule shell is easy to break under the action of heat or external force, so that the heat resistance of the microcapsule is poor.

In one embodiment, the emulsifier is selected from: one or more of ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, arabic gum, polyvinyl alcohol, alkylphenol polyoxyethylene, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide and sorbitan fatty acid ester.

In one embodiment, the polyhydric phenol is selected from: one or more of resorcinol, hydroquinone, catechol, pyrogallol, phloroglucinol, catechol, and dopamine.

In one embodiment, the pH adjusting agent is an acid and/or a base; the acid is selected from: hydrochloric acid, nitric acid, sulfuric acid, citric acid, acetic acid, formic acid; the base is selected from: sodium hydroxide, potassium hydroxide, triethanolamine and sodium carbonate.

In one embodiment, in the step of preparing the aqueous phase, the mass ratio of the emulsifier, the water and the polyphenol is (0.3-1.5): (50-70): (0.1-0.6), the mixing mode is stirring, the stirring speed is 200-500rpm, the temperature is 40-80 ℃, and after the raw materials are dissolved, the pH value is adjusted to be 3.0-3.6.

In one embodiment, in the step of preparing the oil phase, the organic phase change material is used in an amount of 6-10% by weight of the total weight of the water phase.

In one embodiment, the preparation of the inner layer PUF prepolymerization solution specifically comprises: mixing the following components in a mass ratio of (0.6-1): (1.5-2.6) mixing and dissolving urea and formaldehyde solution, adjusting the pH value to 7.5-9, and reacting at 60-70 ℃ for 30-90 minutes to obtain inner-layer PUF pre-polymerization solution.

In one embodiment, the preparation of the outer-layer PUF prepolymerization solution specifically comprises: mixing the following components in a mass ratio of (0.8-1): (2-2.6) mixing and dissolving urea and formaldehyde solution, adjusting the pH value to 7.5-9, and reacting at 60-70 ℃ for 30-90 minutes to obtain an outer-layer PUF pre-polymerization solution.

In one embodiment, the step of preparing the emulsion specifically comprises: adjusting the stirring speed of the water phase to be 500-6000rpm, adding the oil phase and the defoaming agent into the water phase, wherein the addition amount of the defoaming agent is 0-2 wt% of the mass of the organic phase change material, and carrying out an emulsification reaction for 5-20 minutes to obtain the oil-in-water phase change emulsion.

In one embodiment, the defoamer is selected from: n-octyl alcohol, n-butyl alcohol, emulsified silicone oil, a higher alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane.

In one embodiment, the primary coating step specifically includes: adjusting the stirring speed of the oil-in-water phase-change emulsion to be 700rpm at 50-80 ℃, adding the inner-layer PUF pre-polymerization liquid, wherein the dosage of the inner-layer PUF pre-polymerization liquid is 4-7% of the total weight of the oil-in-water phase-change emulsion, adjusting the pH value to be 3.2-3.6 by using a pH regulator, reacting for 30-60 minutes, adjusting the pH value to be 2.6-2.9, and reacting for 120-360 minutes.

In one embodiment, the secondary coating step specifically includes: adding polyphenol into the solution after primary coating, wherein the dosage of the polyphenol is 50-100% of the weight of the polyphenol in the step of preparing the water phase, adjusting the pH value to be 3.2-3.6, adding an outer layer PUF pre-polymerization liquid, the dosage of the outer layer PUF pre-polymerization liquid is 4-7% of the total weight of the oil-in-water phase-change emulsion, adjusting the pH value to be 3.2-3.6, reacting for 30-60 minutes, adjusting the pH value to be 2.6-2.9, and reacting for 120-360 minutes to obtain the double-layer urea-formaldehyde shell phase-change microcapsule.

The invention also provides application of the double-layer urea formaldehyde shell phase change microcapsule in preparation of temperature-adjusting concrete, temperature-adjusting fiber or heat-conducting slurry.

Compared with the prior art, the invention has the following beneficial effects:

the double-layer urea-formaldehyde shell phase-change microcapsule has high thermal stability, has no obvious core material leakage after being baked for more than 6 hours at 100 ℃, has high enthalpy and excellent temperature regulation performance, can be applied to industries such as building materials, textile industry, electronic products, aerospace and the like, and can be applied to products with higher requirements on temperature, energy storage and temperature regulation performance.

In the preparation method, the PUF pre-polymerization solution is added in two steps, the coating rate of the core material can reach more than 70%, the compactness of the shell material is improved, the formed double-layer shell material has excellent temperature resistance, the dispersity of the capsule is good, and the capsule is free of adhesion.

Drawings

FIG. 1 is a DSC plot of a phase change paraffin wax 48PCM of example 1.

FIG. 2 is a DSC plot of the MEPCMs of example 1.

FIG. 3 is a DSC curve of high temperature tests (100 deg.C-6 h) of MEPCMs in example 1.

FIG. 4 is an SEM image (. times.200) of MEPCMs in example 1.

FIG. 5 is an SEM image (magnification. times.1300) of MEPCMs in example 1.

Figure 6 is an optical diagram of the MEPCMs of example 1.

FIG. 7 is an optical image of the MEPCMs of example 1 after baking at 50 deg.C for 10 min.

FIG. 8 is a DSC chart of octadecane in example 2.

Figure 9 is a DSC plot of the MEPCMs of example 2.

FIG. 10 is a DSC curve of high temperature tests (100 deg.C-6 h) of MEPCMs in example 2.

FIG. 11 is a DSC chart of tetradecanol in example 3.

Figure 12 is a DSC curve for the MEPCMs of example 3.

FIG. 13 is a DSC curve of high temperature tests (100 deg.C-6 h) of MEPCMs in example 3.

Fig. 14 is an optical diagram of a phase-change microcapsule in comparative example 1.

FIG. 15 is an optical diagram of the phase-change microcapsule in comparative example 1 after being baked at 50 ℃ for 10 min.

Fig. 16 is an optical diagram of a phase-change microcapsule in comparative example 2.

Detailed Description

To facilitate an understanding of the invention, a more complete description of the invention will be given below in terms of preferred embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The starting materials used in the following examples and comparative examples were commercially available unless otherwise specified.

Example 1

Firstly, preparing a double-layer urea formaldehyde shell phase change microcapsule.

(1) Preparing an aqueous phase: mixing 65g of deionized water and 0.52g of ethylene-maleic anhydride copolymer at the temperature of 60 ℃, stirring and mixing at the mechanical stirring speed of 500rpm to obtain an aqueous solution containing an emulsifier, adding 0.4g of resorcinol, stirring and dissolving, and adjusting the pH to 3.5 by using NaOH and hydrochloric acid solution.

(2) Preparing an oil phase: 5g of phase-change paraffin 48PCM (phase-change temperature of 48 ℃) is taken and heated to be molten to obtain a liquid core material (namely an oil phase).

(3) Preparing PUF prepolymer solution: 1g of urea and 2.53g of 37% formaldehyde solution are mixed and dissolved, the pH value is adjusted to 8.1 by NaOH and hydrochloric acid solution, and the reaction is carried out for 55 minutes at 70 ℃ to obtain inner-layer PUF pre-polymerization solution. 1g of urea and 2.5g of 37% formaldehyde solution are mixed and dissolved, the pH value is adjusted to 8.5 by using NaOH and hydrochloric acid solution, and the reaction is carried out for 70 minutes at 70 ℃ to obtain the outer-layer PUF pre-polymerization solution.

(4) Preparing an emulsion: keeping the temperature of the water phase unchanged, adjusting the rotating speed to 1000rpm, adding the oil phase into the water phase, adding n-octanol with the mass fraction of 0.5 wt% of the core material, and carrying out an emulsification reaction for 10 minutes to obtain a uniform and stable oil-in-water (O/W) phase-change emulsion.

(5) Primary coating: adjusting the rotation speed to 500rpm and the temperature to 60 ℃, adding the inner-layer PUF pre-polymerization solution, adjusting the pH to 3.2 by using NaOH and hydrochloric acid solution, reacting for 60 minutes, adjusting the pH to 2.9 again, and reacting for 120 minutes.

(6) Secondary coating: adding 0.36g of resorcinol, adjusting the pH to 3.2 by using NaOH and hydrochloric acid solution, adding the outer-layer PUF prepolymerization solution, adjusting the rotation speed to 500rpm and the temperature to 60 ℃, adjusting the pH to 3.4 by using NaOH and hydrochloric acid solution, reacting for 60 minutes, adjusting the pH to 2.9, and reacting for 180 minutes. Washing the product with water, filtering, and naturally drying to obtain phase change microcapsules (MEPCMs).

And secondly, testing the performance.

The DSC curve of the phase change paraffin 48PCM used in this example is shown in FIG. 1, the DSC curve of the MEPCMs prepared in this example is shown in FIG. 2, and the DSC curve of the MEPCMs tested after baking at a high temperature of 100 ℃ for 6h is shown in FIG. 3. SEM images of the MEPCMs are shown in fig. 4 and 5. The optical patterns of the MEPCMs at room temperature are shown in FIG. 6, and the optical patterns after baking at 50 ℃ for 10 minutes are shown in FIG. 7.

As can be seen from FIGS. 1 to 4, the phase-change core material had a melting enthalpy (Δ Hm) of 242.2J/g and a crystallization enthalpy (Δ Hc) of 238.7J/g; the prepared MEPCMs have the melting enthalpy (delta Hm) of 171.6J/g, the crystallization enthalpy (delta Hc) of 168.0J/g and the core material coating rate of 70.85%; the melting enthalpy (delta Hm) of the prepared MEPCMs after being tested at the high temperature of 100 ℃ for 6 hours is 170.1J/g, the crystallization enthalpy (delta Hc) is 168.3J/g, the coating rate of the core material is 70.23%, the phase-change core material has no obvious leakage, and the prepared MEPCMs are excellent in thermal stability, the coating rate of the core material is more than 70%, high in enthalpy and excellent in temperature regulation performance. SEM shows that the prepared MEPCMs have good dispersibility and no adhesion among capsules. The optical diagram shows that the prepared MEPCMs have smooth surfaces and no crack phenomenon of capsule shells after being baked at high temperature.

Example 2

Firstly, preparing a double-layer urea formaldehyde shell phase change microcapsule.

(1) Preparing an aqueous phase: at the temperature of 50 ℃, 150g of deionized water, 0.9g of ethylene-maleic anhydride copolymer and 0.3g of polyvinyl alcohol are mixed, the mechanical stirring speed is 300rpm, the mixture is stirred and mixed to obtain an aqueous solution containing an emulsifier, then 0.7g of hydroquinone is added, and after stirring and dissolution, the pH value is adjusted to 3.2 by using KOH and a citric acid solution.

(2) Preparing an oil phase: 10.5g of octadecane (phase transition temperature 28 ℃) is taken and heated to be molten, and the liquid core material is obtained.

(3) Preparing PUF prepolymer solution: 1.6g of urea and 4.34g of 37% formaldehyde solution are mixed and dissolved, the pH value is adjusted to 8.0 by using KOH and citric acid solution, and the reaction is carried out for 65 minutes at 65 ℃ to obtain inner-layer PUF pre-polymerization solution. 1.7g of urea and 4.8g of 37% formaldehyde solution are mixed and dissolved, the pH is adjusted to 8.3 by using KOH and citric acid solution, and the mixture is reacted for 56 minutes at 68 ℃ to obtain an outer-layer PUF pre-polymerization solution.

(4) Preparing an emulsion: keeping the temperature of the water phase unchanged, adjusting the rotating speed to 800rpm, adding the oil phase into the water phase, adding n-butanol with the mass fraction of 0.62 wt% of the core material, and carrying out an emulsification reaction for 13 minutes to obtain a uniform and stable oil-in-water (O/W) phase-change emulsion.

(5) Primary coating: adjusting the rotation speed to 400rpm and the temperature to 50 ℃, adding the inner-layer PUF pre-polymerization solution, adjusting the pH to 3.2 by using KOH and hydrochloric acid solution, reacting for 40 minutes, adjusting the pH to 2.7, and reacting for 150 minutes.

(6) Secondary coating: adding 0.39g of hydroquinone, adjusting the pH to 3.2 by using KOH and citric acid solution, adding the outer layer PUF prepolymer solution, adjusting the rotating speed to 400rpm and the temperature to 50 ℃, adjusting the pH to 3.2 by using KOH and citric acid solution, reacting for 50 minutes, adjusting the pH to 2.7, and reacting for 240 minutes. Washing the product with water, filtering, and naturally drying to obtain phase change microcapsules (MEPCMs).

And secondly, testing the performance.

The DSC curve of the phase change material octadecane used in this example is shown in FIG. 8, the DSC curve of the MEPCMs prepared in this example is shown in FIG. 9, and the DSC curve of the MEPCMs tested after baking at 100 ℃ for 6h is shown in FIG. 10.

As can be seen from FIGS. 8 to 10, the phase change core material had a melting enthalpy (Δ Hm) of 259.4J/g and a crystallization enthalpy (Δ Hc) of 259.5J/g; the prepared MEPCMs have the melting enthalpy (delta Hm) of 211.7J/g, the crystallization enthalpy (delta Hc) of 210.3J/g and the core material coating rate of 81.6 percent; the melting enthalpy (delta Hm) of the prepared MEPCMs after being tested at the high temperature of 100 ℃ for 6 hours is 210.0J/g, the crystallization enthalpy (delta Hc) is 208.8J/g, the coating rate of the core material is 81.0%, the phase-change core material has no obvious leakage, and the prepared MEPCMs are excellent in thermal stability, the coating rate of the core material is more than 80%, high in enthalpy and excellent in temperature regulation performance.

Example 3

Firstly, preparing a double-layer urea formaldehyde shell phase change microcapsule.

(1) Preparing an aqueous phase: 280g of deionized water, 2.1g of styrene-maleic anhydride copolymer and 0.56g of alkylphenol polyoxyethylene are mixed at the temperature of 55 ℃, the mechanical stirring speed is 400rpm, the mixture is stirred and mixed to obtain an aqueous solution containing an emulsifier, then 1.6g of catechol is added, the solution is stirred and dissolved, and the pH value is adjusted to 3.5 by using triethanolamine and an acetic acid solution.

(2) Preparing an oil phase: 21g of tetradecanol (phase transition temperature 38 ℃) was taken and heated to be melted to obtain a liquid core material.

(3) Preparing PUF prepolymer solution: mixing and dissolving 3.2g of urea and 8.1g of 37% formaldehyde solution, adjusting the pH to 8.5 by using triethanolamine and acetic acid solution, and reacting at 70 ℃ for 75 minutes to obtain inner-layer PUF (physically unclonable function) prepolymerization solution. Mixing and dissolving 4.0g of urea and 10.1g of 37% formaldehyde solution, adjusting the pH to 8.0 by using triethanolamine and acetic acid solution, and reacting at 69 ℃ for 55 minutes to obtain an outer-layer PUF (physically unclonable function) prepolymerization solution.

(4) Preparing an emulsion: keeping the temperature of the water phase unchanged, adjusting the rotating speed to 1500rpm, adding the oil phase into the water phase, adding emulsified silicone oil with the mass fraction of the core material of 0.75 wt%, and carrying out an emulsification reaction for 15 minutes to obtain a uniform and stable oil-in-water (O/W) phase-change emulsion.

(5) Primary coating: adjusting the rotation speed to 550rpm and the temperature to 55 ℃, adding the inner-layer PUF pre-polymerization solution, adjusting the pH to 3.5 by using triethanolamine and an acetic acid solution, reacting for 55 minutes, adjusting the pH to 2.8, and reacting for 120 minutes.

(6) Secondary coating: adding 1.1g of catechol, adjusting the pH value to 3.2 by using a triethanolamine and acetic acid solution, adding an outer layer PUF prepolymer solution, adjusting the rotation speed to 550rpm and the temperature to 55 ℃, adjusting the pH value to 3.2 by using the triethanolamine and the acetic acid solution, reacting for 60 minutes, adjusting the pH value to 2.8, and reacting for 300 minutes. Washing the product with water, filtering, and naturally drying to obtain phase change microcapsules (MEPCMs).

And secondly, testing the performance.

The DSC curve of the phase change material tetradecanol used in this example is shown in FIG. 11, the DSC curve of the MEPCMs prepared in this example is shown in FIG. 12, and the DSC curve of the MEPCMs tested after baking at 100 deg.C for 6h is shown in FIG. 13.

As can be seen from FIGS. 11-13, the phase-change core material had a melting enthalpy (Δ Hm) of 244.3J/g and a crystallization enthalpy (Δ Hc) of 242.1J/g; the prepared MEPCMs have the melting enthalpy (delta Hm) of 182.6J/g, the crystallization enthalpy (delta Hc) of 186.6J/g and the core material coating rate of 74.7 percent; the melting enthalpy (delta Hm) of the prepared MEPCMs after being tested at the high temperature of 100 ℃ for 6 hours is 182.5J/g, the crystallization enthalpy (delta Hc) is 186.1J/g, the coating rate of the core material is 74.7%, the phase-change core material has no obvious leakage, and the prepared MEPCMs are excellent in thermal stability, the coating rate of the core material is more than 70%, high in enthalpy and excellent in temperature regulation performance.

Comparative example 1

A phase change microcapsule, which is prepared in substantially the same manner as in example 1 except for the steps (5) and (6), wherein the steps (5) and (6) are specifically:

and (5): regulating the rotation speed to 500rpm and the temperature to 60 ℃, adding the inner-layer PUF pre-polymerization solution, regulating the pH to 3.8 by using NaOH and hydrochloric acid solution, and reacting for 180 minutes.

And (6): adding 0.36g of resorcinol, adjusting the pH to 3.2 by using NaOH and hydrochloric acid solution, adding the outer-layer PUF prepolymerization solution, adjusting the rotation speed to 500rpm and the temperature to 60 ℃, adjusting the pH to 3.8 by using NaOH and hydrochloric acid solution, and reacting for 240 minutes. Washing the product with water, filtering, and naturally drying to obtain phase change microcapsules (MEPCMs).

An optical diagram of the phase-change microcapsule of the present comparative example at normal temperature is shown in fig. 14, and an optical diagram of the phase-change microcapsule after being baked at 50 ℃ for 10 minutes is shown in fig. 15, and it can be seen from the diagrams that the capsule shell is basically broken after the phase-change microcapsule is baked at high temperature, and the heat resistance is poor.

Comparative example 2

A phase change microcapsule, which is prepared in substantially the same manner as in example 1 except for the steps (5) and (6), wherein the steps (5) and (6) are specifically:

and (5): regulating the rotation speed to 500rpm and the temperature to 60 ℃, adding the inner-layer PUF pre-polymerization solution, regulating the pH to 2.8 by using NaOH and hydrochloric acid solution, and reacting for 180 minutes.

And (6): adding 0.36g of resorcinol, adjusting the pH to 3.2 by using NaOH and hydrochloric acid solution, adding the outer-layer PUF prepolymerization solution, adjusting the rotation speed to 500rpm and the temperature to 60 ℃, adjusting the pH to 2.8 by using NaOH and hydrochloric acid solution, and reacting for 240 minutes. Washing the product with water, filtering, and naturally drying to obtain phase change microcapsules (MEPCMs).

The optical diagram of the phase-change microcapsule of this comparative example at room temperature is shown in fig. 16, and it can be seen from the diagram that the phase-change microcapsule has a rough surface and is less dense.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.