WO2023039972A1 - 双层脲醛壳相变微胶囊及其制备方法和应用 - Google Patents

双层脲醛壳相变微胶囊及其制备方法和应用 Download PDF

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WO2023039972A1
WO2023039972A1 PCT/CN2021/123977 CN2021123977W WO2023039972A1 WO 2023039972 A1 WO2023039972 A1 WO 2023039972A1 CN 2021123977 W CN2021123977 W CN 2021123977W WO 2023039972 A1 WO2023039972 A1 WO 2023039972A1
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phase change
phase
puf
preparation
urea
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French (fr)
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杨晶磊
孙赛玲
安金亮
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广州市香港科大霍英东研究院
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/02—Materials undergoing a change of physical state when used
    • C09K5/06—Materials undergoing a change of physical state when used the change of state being from liquid to solid or vice versa
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/06—Making microcapsules or microballoons by phase separation
    • B01J13/14—Polymerisation; cross-linking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/20—After-treatment of capsule walls, e.g. hardening
    • B01J13/22—Coating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/14—Thermal energy storage

Definitions

  • the invention relates to the technical field of phase-change microcapsules, in particular to a double-layer urea-formaldehyde-shell phase-change microcapsule and its preparation method and application.
  • Phase change materials refer to materials that can absorb and release a large amount of latent heat of phase change during the phase change process.
  • phase change materials can be divided into solid-solid, solid-gas, Liquid-gas, solid-liquid four categories.
  • solid-liquid phase change materials have become a research hotspot in recent years because of their advantages such as small volume change before and after phase transition, large phase transition latent heat, wide phase transition temperature range, good stability, and low price.
  • Commonly used solid-liquid phase change materials include paraffins, fatty acids, fatty alcohols, and inorganic hydrated salts.
  • Solid-liquid phase change materials also have the disadvantages of volume change during phase change, poor thermal conductivity in solid state, and easy leakage in liquid state.
  • Phase change microcapsules have the functions of energy storage and temperature regulation during the phase change process, and are widely used in the fields of building energy conservation, textile and clothing, electronic products, aerospace, and functional thermal fluids.
  • Microencapsulation technology uses polymer materials as film-forming materials (wall materials) to completely cover solids, liquids, or gases (core materials) to form solid tiny particles (microcapsules) with airtight or semipermeable capsules.
  • core materials solid tiny particles
  • Microcapsules with airtight or semipermeable capsules.
  • Phase-change microcapsules adopt microencapsulation technology, use phase-change materials as core materials, and wrap them with inorganic materials or synthetic polymer materials by physical or chemical methods to make microcapsules. Commonly used preparation methods include in-situ polymerization, interfacial polymerization, and suspension polymerization.
  • phase change latent heat of phase change microcapsules is determined by the heat enthalpy of the phase change core material itself and the coating rate of the microcapsules.
  • the ideal phase change core material should meet the requirements of high phase change latent heat, phase change temperature and stable performance as much as possible. , non-toxic, wide range of sources, small degree of subcooling and no phase separation, etc., to achieve the effect of energy storage and utilization, and realize the regulation of temperature.
  • the core materials of commonly used phase change microcapsules include: inorganic hydrated salts, paraffins, fatty acids, fatty alcohols, esters and other single phase change materials, and there are also composite core materials obtained by combining several materials.
  • the wall material of the phase change microcapsule can provide a stable phase change space for the phase change material, which can protect and seal the phase change material.
  • the wall material greatly affects the performance of the microcapsule, and different application fields and environments There are different requirements for wall materials.
  • the corresponding wall material can be preliminarily determined according to the properties of the core material, and many factors need to be considered when selecting, mainly including: the stability and durability of the wall material, the permeability and curing degree of the shell material, and the influence of the external environment.
  • Commonly used wall materials for phase change microcapsules include organic urea-formaldehyde resins, melamine-formaldehyde resins, polyurea, polyethylene, etc., and inorganic types such as SiO 2 , TiO 2 , and CaCO 3 .
  • urea-formaldehyde resin has been widely used in research because of its good sealing performance, simple preparation process, heat resistance and good mechanical properties.
  • phase-change microcapsules prepared by the existing urea-formaldehyde shell microcapsule preparation process have poor high temperature resistance, and there is obvious leakage of the core material within 20 minutes of testing at a high temperature of 100°C, which greatly limits the application range of phase-change microcapsules and length of service.
  • the phase change microcapsules prepared by the existing organic shell often sacrifice heat enthalpy, that is, the amount of wall material is increased during preparation, resulting in a low coating rate of the core material, which affects the phase change. Change the temperature control performance of microcapsules. Therefore, it is necessary to improve the high temperature resistance of urea-formaldehyde shell phase change microcapsules, and develop a phase change microcapsule with excellent thermal stability and high latent heat characteristics.
  • a double-layer urea-formaldehyde shell phase-change microcapsule comprising a core material, an inner layer wall material and an outer layer wall material sequentially from the inside to the outside, the core material is a phase change material, the inner layer wall material and the outer layer wall material Both are urea-formaldehyde resins (PUF).
  • PEF urea-formaldehyde resins
  • the above-mentioned double-layer urea-formaldehyde shell phase-change microcapsules have high thermal stability, and there is still no obvious leakage of the core material after baking at 100°C for more than 6 hours, and also have high heat enthalpy and excellent temperature adjustment performance.
  • 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.
  • the alkane phase change material is preferably C8-C26 straight-chain alkanes
  • the fatty acid phase change material is preferably C8-C20 fatty acid
  • the fatty alcohol phase change material is preferably C8-C26 fatty alcohol
  • the fatty acid ester phase change material is preferably C4- C26 fatty acid esters.
  • the phase change material is selected from the group consisting of paraffin, octadecane, and myristyl alcohol.
  • the present invention also provides a preparation method of double-layer urea-formaldehyde shell phase-change microcapsules, comprising the following steps:
  • Preparation of oil phase heating to melt the organic phase change material to obtain an oil phase;
  • Preparation of PUF prepolymerization solution using urea and formaldehyde as raw materials to prepare inner layer PUF prepolymerization solution and outer layer PUF prepolymerization solution;
  • Preparation of emulsion add the oil phase to the water phase for emulsification reaction to obtain an oil-in-water phase change emulsion;
  • Primary coating mix the oil-in-water phase change emulsion with the inner layer PUF prepolymerization solution, adjust the pH value to 3.2-3.6 with a pH regulator, carry out polycondensation reaction, adjust the pH value to 2.6-2.9, continue the polycondensation reaction, and
  • the outer surface of the core material forms the inner wall material;
  • Secondary coating add polyphenol and outer layer PUF prepolymerization solution to the solution after primary coating, adjust the pH value to 3.2-3.6, carry out polycondensation reaction, adjust the pH value to 2.6-2.9, continue the polycondensation reaction, An outer wall material is formed on the outer surface of the inner wall material to obtain double-layer urea-formaldehyde shell phase-change microcapsules.
  • the PUF pre-polymerization liquid is added in two steps, the coating rate of the core material can reach more than 70%, and the compactness of the shell material is improved at the same time.
  • the formed double-layer shell material has excellent temperature resistance, and the capsule has Good dispersion, no adhesion between capsules.
  • the pH value of the reaction system is controlled at a higher value (3.2-3.6) for a period of time, and at this pH, the PUF pre-polymerization solution is on the surface of the core material.
  • the deposition rate is relatively slow, so that a relatively dense shell can be formed, which prevents the formation of a relatively loose shell at the initial high reaction rate, and at the same time reduces the waste caused by the self-accumulation of the wall material.
  • the PUF prepolymer undergoes a certain degree of polycondensation. Different degrees of oligomers are formed.
  • the wall material After a period of reaction, the wall material is dispersed more uniformly, and the wall material concentration decreases to a certain extent. Then the pH value (2.6-2.9) is lowered, and the oligomers are further polycondensed to form a high degree of polymerization.
  • the deposition rate of the wall material is relatively reasonable, implosion is not easy to occur, and the surface of the PUF shell is relatively smooth.
  • the prepolymerization solution is usually added at one time, which easily leads to the self-accumulation of the PUF prepolymer in the solution, thus affecting the thickness and compactness of the shell material, and the prepared microcapsules are easy to stick and have poor dispersibility, which seriously affects the microcapsules. Effects of capsules used in application substrates.
  • the reaction system is always at a higher pH value (such as about 3.8), the polycondensation reaction of the PUF prepolymerization solution is slow, and the deposition rate of the PUF shell material on the core material or capsule surface is too slow, and the formed capsule shell layer is too thin. Under the action of external force, the capsule shell is easily broken, resulting in poor heat resistance of the microcapsules.
  • the emulsifier is selected from: ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, gum arabic, polyvinyl alcohol, alkylphenol polyoxyethylene ether, lauryl One or more of sodium benzenesulfonate, sodium lauryl sulfate, cetyltrimethylammonium bromide, and sorbitan fatty acid ester.
  • the polyphenol is selected from one or both of resorcinol, hydroquinone, catechol, pyrogallol, phloroglucinol, catechol, and dopamine. more than one species.
  • the pH regulator is acid and/or alkali;
  • the acid is selected from: hydrochloric acid, nitric acid, sulfuric acid, citric acid, acetic acid, formic acid;
  • the alkali is selected from: sodium hydroxide, hydroxide Potassium, Triethanolamine, Sodium Carbonate.
  • the mass ratio of the emulsifier, water, and polyphenol is (0.3-1.5): (50-70): (0.1-0.6), and the mixing method is stirring, The stirring speed is 200-500rpm, the temperature is 40-80°C, and the pH value is adjusted to 3.0-3.6 after the raw materials are dissolved.
  • the amount of the organic phase change material is 6%-10% of the total weight of the water phase.
  • the preparation of the inner layer PUF pre-polymerization solution is specifically: mixing and dissolving urea and formaldehyde solutions with a mass ratio of (0.6-1): (1.5-2.6), adjusting the pH value to 7.5-9, 60- React at 70°C for 30-90 minutes to obtain the inner layer PUF prepolymer solution.
  • the preparation of the outer layer PUF pre-polymerization solution is specifically: mixing and dissolving urea and formaldehyde solutions with a mass ratio of (0.8-1): (2-2.6), adjusting the pH value to 7.5-9, 60- React at 70°C for 30-90 minutes to obtain the outer layer PUF prepolymer solution.
  • the step of preparing the emulsion is as follows: adjust the stirring speed of the water phase to 500-6000rpm, add the oil phase and the defoamer to the water phase, the amount of the defoamer added is the organic phase change material 0wt%-2wt% of the mass, emulsification reaction for 5-20 minutes, to obtain the oil-in-water phase change emulsion.
  • the defoamer is selected from: n-octanol, n-butanol, emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene Alcohol amine ether, polyoxypropylene glyceryl ether, polyoxypropylene polyoxyethylene glyceryl ether, polydimethylsiloxane.
  • the first coating step is as follows: adjust the stirring speed of the oil-in-water phase change emulsion to 200-700rpm, the temperature to 50-80°C, add the inner layer of PUF pre-polymerization liquid, and the inner layer of PUF pre-polymerized
  • the amount of polymer is 4-7% of the total weight of the oil-in-water phase change emulsion
  • the pH value is adjusted to 3.2-3.6 with a pH regulator
  • the reaction is 30-60 minutes
  • the pH value is adjusted to 2.6-2.9
  • the reaction is 120-360 minutes .
  • the secondary coating step is specifically: adding polyphenols to the solution after primary coating, the amount of polyphenols is 50-100% of the weight of polyphenols in the step of preparing the water phase, adjusting The pH value is 3.2-3.6, add the outer layer PUF pre-polymerization liquid, the amount of the outer layer PUF pre-polymerization liquid is 4-7% of the total weight of the oil-in-water phase change emulsion, adjust the pH value to 3.2-3.6, and react 30-60 minutes, adjust the pH value to 2.6-2.9, and react for 120-360 minutes to obtain double-layer urea-formaldehyde shell phase-change microcapsules.
  • the present invention also provides an application of the above-mentioned double-layer urea-formaldehyde shell phase-change microcapsules in preparing temperature-regulating concrete, temperature-regulating fibers or heat-conducting slurry.
  • the present invention has the following beneficial effects:
  • the double-layer urea-formaldehyde shell phase change microcapsules of the present invention have high thermal stability, and there is still no obvious core material leakage after baking at 100°C for more than 6 hours, and also have high heat enthalpy, excellent temperature adjustment performance, and can be applied to building materials, textiles Industry, electronic products, aerospace and other industries, in products with high requirements on temperature, energy storage and temperature regulation performance.
  • the PUF pre-polymerization liquid is added in two steps, the coating rate of the core material can reach more than 70%, and the compactness of the shell material is improved at the same time, and the formed double-layer shell material has excellent temperature resistance, and The dispersion of the capsules is good, and there is no adhesion between the capsules.
  • Fig. 1 is the DSC curve chart of phase change paraffin 48PCM in embodiment 1.
  • FIG. 2 is a DSC curve diagram of MEPCMs in Example 1.
  • Fig. 3 is the DSC curve of the high temperature test (100°C-6h) of MEPCMs in Example 1.
  • FIG. 4 is a SEM image ( ⁇ 200) of MEPCMs in Example 1.
  • FIG. 5 is a SEM image ( ⁇ 1300) of MEPCMs in Example 1.
  • Example 6 is an optical diagram of MEPCMs in Example 1.
  • FIG. 7 is an optical diagram of MEPCMs in Example 1 after being baked at 50° C. for 10 minutes.
  • Fig. 8 is the DSC curve chart of octadecane in embodiment 2.
  • Fig. 10 is the DSC curve of the high temperature test (100°C-6h) of MEPCMs in Example 2.
  • Fig. 11 is the DSC curve chart of myristyl alcohol in embodiment 3.
  • Figure 12 is the DSC curve of MEPCMs in Example 3.
  • Figure 13 is the DSC curve of MEPCMs high temperature test (100°C-6h) in Example 3.
  • FIG. 15 is an optical image of the phase-change microcapsules in Comparative Example 1 after being baked at 50° C. for 10 minutes.
  • phase change paraffin wax 48PCM phase transition temperature 48° C.
  • Primary coating adjust the rotating speed to 500rpm and the temperature to 60°C, add the inner layer PUF prepolymerization solution, adjust the pH to 3.2 with NaOH and hydrochloric acid solution, react for 60 minutes, then adjust the pH to 2.9, and react for 120 minutes.
  • the DSC curve of the phase-change paraffin wax 48PCM used in this example is shown in Figure 1, and the DSC curve of the MEPCMs prepared in this example is shown in Figure 2. After the MEPCMs were baked at a high temperature of 100°C for 6 hours, the DSC was tested, and the DSC curve is shown in Figure 1. 3.
  • the SEM images of MEPCMs are shown in Fig. 4 and Fig. 5.
  • the optical diagram of MEPCMs at room temperature is shown in Figure 6, and the optical diagram after being baked at 50°C for 10 minutes is shown in Figure 7.
  • the melting enthalpy ( ⁇ Hm) of the phase change core material is 242.2J/g, and the crystallization enthalpy ( ⁇ Hc) is 238.7J/g;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 171.6J/g g, the crystallization enthalpy ( ⁇ Hc) is 168.0J/g, and the core material coating rate is 70.85%;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 170.1J/g after being tested at a high temperature of 100°C for 6h, and the crystallization enthalpy ( ⁇ Hc) was 168.3J/g, the core material coating rate was 70.23%, and the phase change core material had no obvious leakage, indicating that the prepared MEPCMs had excellent thermal stability, and the core material coating rate was above 70%, and the prepared MEPCMs had High heat enthalpy, excellent thermoregulation performance.
  • Primary coating adjust the rotation speed to 400rpm, the temperature to 50°C, add the inner layer PUF prepolymerization solution, adjust the pH to 3.2 with KOH and hydrochloric acid solution, react for 40 minutes, then adjust the pH to 2.7, and react for 150 minutes.
  • the DSC curve of the phase change material octadecane used in this example is shown in Figure 8, and the DSC curve of the MEPCMs prepared in this example is shown in Figure 9, after the MEPCMs were baked at a high temperature of 100°C for 6 hours, the DSC was tested, and the DSC curve As shown in Figure 10.
  • the melting enthalpy ( ⁇ Hm) of the phase change core material is 259.4J/g, and the crystallization enthalpy ( ⁇ Hc) is 259.5J/g;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 211.7J/g g, the crystallization enthalpy ( ⁇ Hc) is 210.3J/g, and the core material coating rate is 81.6%;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 210.0J/g after being tested at a high temperature of 100°C for 6h, and the crystallization enthalpy ( ⁇ Hc) is 208.8J/g
  • the core material coating rate is 81.0%, and the phase change core material has no obvious leakage, indicating that the prepared MEPCMs have excellent thermal stability.
  • the core material coating rate is above 80%, and the prepared MEPCMs have High heat enthalpy, excellent thermoregulation
  • Primary coating adjust the rotation speed to 550rpm and the temperature to 55°C, add the inner layer PUF prepolymerization solution, adjust the pH to 3.5 with triethanolamine and acetic acid solution, react for 55 minutes, then adjust the pH to 2.8, and react for 120 minutes .
  • the DSC curve of the phase change material myristyl alcohol used in this example is shown in Figure 11, and the DSC curve of the MEPCMs prepared in this example is shown in Figure 12. After the MEPCMs were baked at a high temperature of 100°C for 6 hours, the DSC and DSC curves were tested. As shown in Figure 13.
  • the melting enthalpy ( ⁇ Hm) of the phase change core material is 244.3J/g, and the crystallization enthalpy ( ⁇ Hc) is 242.1J/g;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 182.6J/g g, the crystallization enthalpy ( ⁇ Hc) is 186.6J/g, and the core material coating rate is 74.7%;
  • the melting enthalpy ( ⁇ Hm) of the prepared MEPCMs is 182.5J/g after being tested at a high temperature of 100°C for 6h, and the crystallization enthalpy ( ⁇ Hc) is 186.1J/g,
  • the core material coating rate is 74.7%, and the phase change core material has no obvious leakage, indicating that the prepared MEPCMs have excellent thermal stability, and at the same time the core material coating rate is above 70%, the prepared MEPCMs have High heat enthalpy, excellent thermoregulation performance.
  • a kind of phase-change microcapsule, its preparation method is basically the same as the preparation method of embodiment 1, difference is step (5) and (6), and step (5) and step (6) are specifically:
  • Step (5) adjust the rotational speed to 500 rpm and the temperature to 60° C., add the inner layer PUF prepolymerization solution, adjust the pH to 3.8 with NaOH and hydrochloric acid solution, and react for 180 minutes.
  • Step (6) Add 0.36g resorcinol, adjust the pH to 3.2 with NaOH and hydrochloric acid solution, then add the outer layer PUF prepolymerization solution, adjust the rotation speed to 500rpm, and the temperature is 60°C, adjust the pH with NaOH and hydrochloric acid solution Adjusted to 3.8, reacted for 240 minutes. The product was washed with water, filtered, and dried naturally to obtain phase change microcapsules (MEPCMs).
  • MEPCMs phase change microcapsules
  • the optical diagram of the phase-change microcapsules of this comparative example at normal temperature is shown in Figure 14, and the optical diagram after being baked at 50°C for 10 minutes is shown in Figure 15. It can be seen from the figure that the phase-change microcapsules were baked at high temperature After baking, the capsule shell is basically broken, and the heat resistance is poor.
  • a kind of phase-change microcapsule, its preparation method is basically the same as the preparation method of embodiment 1, difference is step (5) and (6), and step (5) and step (6) are specifically:
  • Step (5) Adjust the rotation speed to 500 rpm and the temperature to 60° C., add the inner layer PUF prepolymerization liquid, adjust the pH to 2.8 with NaOH and hydrochloric acid solution, and react for 180 minutes.
  • Step (6) Add 0.36g resorcinol, adjust the pH to 3.2 with NaOH and hydrochloric acid solution, then add the outer layer PUF prepolymerization solution, adjust the rotation speed to 500rpm, and the temperature is 60°C, adjust the pH with NaOH and hydrochloric acid solution Adjusted to 2.8, reacted for 240 minutes.
  • the product was washed with water, filtered, and dried naturally to obtain phase change microcapsules (MEPCMs).
  • phase-change microcapsules of this comparative example at room temperature is shown in Figure 16. It can be seen from the figure that the phase-change microcapsules have a rough surface and poor compactness.

Abstract

一种双层脲醛壳相变微胶囊及其制备方法和应用。所述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。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。所述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。

Description

双层脲醛壳相变微胶囊及其制备方法和应用 技术领域
本发明涉及相变微胶囊技术领域，特别是涉及一种双层脲醛壳相变微胶囊及其制备方法和应用。
背景技术
相变材料(phase change materials，简称PCMs)，是指在相变过程中能吸收和释放大量相变潜热的材料，根据相变机理，可将相变材料分为固-固、固-气、液-气、固-液四大类。其中，固-液相变材料因具有相变前后体积变化小、相变潜热大、相变温度范围广、稳定性好、价格低廉等优点而成为近年来的研究热点。常用的固-液相变材料有石蜡类、脂肪酸、脂肪醇、无机水合盐类等。固-液相变材料同时也存在相变时体积发生变化、固态导热性能差、液态易泄漏等不足，而将相变材料封装形成微胶囊可在一定程度上解决上述问题。相变微胶囊在相变过程中具有储能和调温的作用，在建筑节能领域、纺织服装领域、电子产品、航空航天领域、功能热流体领域有着广泛的应用。
微胶囊化技术是利用高分子材料作为成膜材料(壁材)，将固体、液体、或者气体(芯材)完全包覆，形成具有密封性或半透性囊膜的固态微小粒子(微胶囊)。相变微胶囊(MEPCMs)釆用微胶囊化技术，以相变材料作为芯材，用无机材料或合成高分子材料以物理或化学方法包裹起来，制成微胶囊。常用的制备方法有原位聚合法、界面聚合法、悬浮聚合法。
相变微胶囊的相变潜热是相变芯材本身的热焓和微胶囊的包覆率决定的，理想的相变芯材应尽可能满足相变潜热高、相变温度符合需求、性能稳定、无毒、来源广泛、过冷度小和无相分离等条件，达到能量存储与利用的效果，实现对温度的调控。目前，常用的相变微胶囊的芯材有：无机水合盐、石蜡类、脂肪酸、脂肪醇、酯类等单一相变材料，也有将几种材料相复合得到复合芯材。
相变微胶囊的壁材能够给相变材料提供一个稳定的相变空间，起到保护和密封相变材料的作用，壁材极大地影响微胶囊的各项性能，且不同的应用领域和环境对壁材有着不同的要求。可根据芯材的性质初步确定相应的壁材，选择时需要考虑多方面因素，主要有：壁材的稳定性和耐用性、壳材的渗透性和固化程度、外界环境的影响。
常用的相变微胶囊壁材包括有机类的脲醛树脂、三聚氰胺-甲醛树脂、聚脲、聚乙烯等，以及无机类的SiO 2、TiO 2、CaCO 3等。其中脲醛树脂因其密封性好，制备过程简便，耐热、力学性能良好，现已被大量应用于研究中。
然而，现有的脲醛壳微胶囊制备工艺制备的相变微胶囊，耐高温性能差，高温100℃测试20分钟以内，就有明显的芯材泄露，这大大限制了相变微胶囊的应用范围和服役时长。此外，现有有机壳制备的相变微胶囊，为提高产品的致密性，往往会牺牲热焓，即在制备时增 加壁材的用量，导致芯材的包覆率较低，从而影响相变微胶囊的控温性能。因此，有必要提高脲醛壳相变微胶囊的耐高温性能，开发一种具有优异的热稳定性，同时兼具高潜热特性的相变微胶囊。
发明内容
基于此，有必要针对上述问题，提供一种双层脲醛壳相变微胶囊，具有高热稳定性和高潜热的优点。
一种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(PUF)。
上述双层脲醛壳相变微胶囊，具有高热稳定性，在100℃下烘烤6h以上依然无明显的芯材泄露，而且还具有高热焓，调温性能优异。
在其中一个实施例中，所述相变材料选自：烷烃类相变材料、脂肪酸类相变材料、脂肪醇类相变材料、脂肪酸酯类相变材料。
烷烃类相变材料优选为C8-C26直链烷烃，脂肪酸类相变材料优选为C8-C20脂肪酸，脂肪醇类相变材料优选为C8-C26脂肪醇，脂肪酸酯类相变材料优选为C4-C26脂肪酸酯。
在其中一个实施例中，所述相变材料选自：石蜡、十八烷、十四醇。
本发明还提供一种双层脲醛壳相变微胶囊的制备方法，包括以下步骤：
制备水相：将乳化剂、水和多元酚混合，得到水相；
制备油相：加热使有机相变材料熔融，得到油相；
制备PUF预聚液：以尿素和甲醛为原料，制备内层PUF预聚液和外层PUF预聚液；
制备乳液：将油相加入水相中，进行乳化反应，得到水包油相变乳液；
一次包覆：将水包油相变乳液和内层PUF预聚液混合，用pH调节剂调节pH值为3.2-3.6，进行缩聚反应，调节pH值为2.6-2.9，继续进行缩聚反应，在芯材外表面形成内层壁材；
二次包覆：向经过一次包覆后的溶液中加入多元酚和外层PUF预聚液，调节pH值为3.2-3.6，进行缩聚反应，调节pH值为2.6-2.9，继续进行缩聚反应，在内层壁材外表面形成外层壁材，得到双层脲醛壳相变微胶囊。
上述制备方法中，分两步加入PUF预聚液，芯材的包覆率可达到70％以上，同时提高壳材的致密性，形成的双层壳材具有优越的耐温性能，而且胶囊的分散性好，胶囊间无粘连。
本发明的制备方法中，在加入PUF预聚液后，先将反应体系的pH值控制在较高的数值(3.2-3.6)反应一段时间，在该pH下，PUF预聚液在芯材表面沉积速率较为缓慢，从而能形成较为致密的壳层，防止初期高反应速率下形成较为松散的壳层，同时降低壁材自聚积导致的浪费，此过程中PUF预聚物发生一定程度的缩聚，形成不同程度的低聚物，在反应一段时间后，壁材分散较为均匀，壁材浓度有一定程度的下降，再降低pH值(2.6-2.9)，低聚物进一步缩聚，形成聚合度高的PUF，壁材的沉积速率较为合理，不易发生爆聚，PUF壳表面也比较光滑。
现有技术中通常将预聚液一次性加入，容易导致PUF预聚物在溶液中自聚积，从而影响 壳材的厚度及致密性，而且制得的微胶囊容易粘连，分散性差，严重影响微胶囊在应用基材中的使用效果。
如果在聚合反应初始就保持在较低的pH值(如2.8左右)，由于初始阶段PUF预聚物浓度较高，容易发生爆聚，得到的PUF壳表面粗糙，导致胶囊致密性差，芯材易泄露。如果反应体系一直处于较高的pH值(如3.8左右)，PUF预聚液缩聚反应慢，PUF壳材在芯材或胶囊表面沉积的速率过慢，形成的胶囊壳层过薄，在受热或外力作用下，胶囊壳易破裂，导致微胶囊耐热性能差。
在其中一个实施例中，所述乳化剂选自：乙烯-马来酸酐共聚物、苯乙烯-马来酸酐共聚物、阿拉伯胶、聚乙烯醇、烷基酚聚氧乙烯醚、十二烷基苯磺酸钠、十二烷基硫酸钠、十六烷基三甲基溴化胺、失水山梨醇脂肪酸酯中的一种或两种以上。
在其中一个实施例中，所述多元酚选自：间苯二酚、对苯二酚、邻苯二酚、连苯三酚、间苯三酚、儿茶酚、多巴胺中的一种或两种以上。
在其中一个实施例中，所述pH调节剂为酸和/或碱；所述酸选自：盐酸、硝酸、硫酸、柠檬酸、醋酸、甲酸；所述碱选自：氢氧化钠、氢氧化钾、三乙醇胺、碳酸钠。
在其中一个实施例中，所述制备水相步骤中，乳化剂、水、多元酚的质量比为(0.3-1.5)：(50-70)：(0.1-0.6)，混合的方式为搅拌，搅拌转速为200-500rpm，温度为40-80℃，待原料溶解后，调节pH值为3.0-3.6。
在其中一个实施例中，所述制备油相步骤中，有机相变材料的用量为水相总重量的6％-10％。
在其中一个实施例中，制备内层PUF预聚液具体为：将质量比为(0.6-1)：(1.5-2.6)的尿素和甲醛溶液混合溶解，调节pH值为7.5-9，60-70℃反应30-90分钟，得到内层PUF预聚液。
在其中一个实施例中，制备外层PUF预聚液具体为：将质量比为(0.8-1)：(2-2.6)的尿素和甲醛溶液混合溶解，调节pH值为7.5-9，60-70℃反应30-90分钟，得到外层PUF预聚液。
在其中一个实施例中，所述制备乳液步骤具体为：调整水相搅拌转速为500-6000rpm，向水相中加入油相和消泡剂，所述消泡剂的添加量为有机相变材料质量的0wt％-2wt％，乳化反应5-20分钟，得到水包油相变乳液。
在其中一个实施例中，所述消泡剂选自：正辛醇、正丁醇、乳化硅油、高碳醇脂肪酸酯复合物、聚氧乙烯聚氧丙烯季戊四醇醚、聚氧乙烯聚氧丙醇胺醚、聚氧丙烯甘油醚、聚氧丙烯聚氧乙烯甘油醚、聚二甲基硅氧烷。
在其中一个实施例中，所述一次包覆步骤具体为：调整水包油相变乳液的搅拌转速为200-700rpm，温度为50-80℃，加入内层PUF预聚液，内层PUF预聚液的用量为水包油相变乳液总重量的4-7％，用pH调节剂调节pH值为3.2-3.6，反应30-60分钟，调节pH值为2.6-2.9，反应120-360分钟。
在其中一个实施例中，所述二次包覆步骤具体为：向经过一次包覆后的溶液中加入多元 酚，多元酚的用量为制备水相步骤中多元酚重量的50-100％，调节pH值为3.2-3.6，加入外层PUF预聚液，外层PUF预聚液的用量为水包油相变乳液总重量的4-7％，调节pH值为3.2-3.6，反应30-60分钟，调节pH值为2.6-2.9，反应120-360分钟，得到双层脲醛壳相变微胶囊。
本发明还提供一种上述双层脲醛壳相变微胶囊在制备调温混凝土、调温纤维或导热浆料中的应用。
与现有技术相比，本发明具有以下有益效果：
本发明的双层脲醛壳相变微胶囊具有高热稳定性，在100℃下烘烤6h以上依然无明显的芯材泄露，而且还具有高热焓，调温性能优异，可应用于建筑材料、纺织业、电子产品、航空航天等行业，对温度、储能和调温性能要求较高的产品中。
本发明的制备方法中，分两步加入PUF预聚液，芯材的包覆率可达到70％以上，同时提高壳材的致密性，形成的双层壳材具有优越的耐温性能，而且胶囊的分散性好，胶囊间无粘连。
附图说明
图1为实施例1中相变石蜡48PCM的DSC曲线图。
图2为实施例1中MEPCMs的DSC曲线图。
图3为实施例1中MEPCMs高温测试(100℃-6h)的DSC曲线。
图4为实施例1中MEPCMs的SEM图(×200)。
图5为实施例1中MEPCMs的SEM图(×1300)。
图6为实施例1中MEPCMs的光学图。
图7为实施例1中MEPCMs经50℃烘10min后的光学图。
图8为实施例2中十八烷的DSC曲线图。
图9为实施例2中MEPCMs的DSC曲线图。
图10为实施例2中MEPCMs高温测试(100℃-6h)的DSC曲线。
图11为实施例3中十四醇的DSC曲线图。
图12为实施例3中MEPCMs的DSC曲线。
图13为实施例3中MEPCMs高温测试(100℃-6h)的DSC曲线。
图14为对比例1中相变微胶囊的光学图。
图15为对比例1中相变微胶囊经50℃烘10min后的光学图。
图16为对比例2中相变微胶囊的光学图。
具体实施方式
为了便于理解本发明，以下将给出较佳实施例对本发明进行更全面的描述。但是，本发明可以以许多不同的形式来实现，并不限于本文所描述的实施例。相反地，提供这些实施例的目的是使对本发明的公开内容的理解更加透彻全面。
除非另有定义，本文所使用的所有的技术和科学术语与属于本发明的技术领域的技术人员通常理解的含义相同。本文中在本发明的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本发明。
以下实施例和对比例中所用的原料，除非特殊说明，均为市售购得。
实施例1
一、制备双层脲醛壳相变微胶囊。
(1)制备水相：在温度为60℃下，将65g去离子水、0.52g乙烯-马来酸酐共聚物混合，机械搅拌速度500rpm，搅拌混合得到含乳化剂的水溶液，然后加入0.4g的间苯二酚，搅拌溶解后用NaOH和盐酸溶液将pH调至3.5。
(2)制备油相：取5g相变石蜡48PCM(相变温度48℃)，加热至熔融，得到液态芯材(即油相)。
(3)制备PUF预聚液：将1g尿素、2.53g 37％甲醛溶液混合溶解，用NaOH和盐酸溶液将pH调至8.1，70℃反应55分钟，得到内层PUF预聚液。将1g尿素、2.5g 37％甲醛溶液混合溶解，用NaOH和盐酸溶液将pH调至8.5，70℃反应70分钟，得到外层PUF预聚液。
(4)制备乳液：保持水相的温度不变，调整转速为1000rpm，将油相加入到水相中，再加入芯材质量分数0.5wt％的正辛醇，乳化反应10分钟，得到均匀稳定的水包油(O/W)相变乳液。
(5)一次包覆：调整转速为500rpm，温度为60℃，加入内层PUF预聚液，用NaOH和盐酸溶液将pH调为3.2，反应60分钟，再调节pH为2.9，反应120分钟。
(6)二次包覆：加入0.36g间苯二酚，用NaOH和盐酸溶液将pH调至3.2，再加入外层PUF预聚液，转速调整为500rpm，温度为60℃，用NaOH和盐酸溶液将pH调至3.4，反应60分钟后，再调节pH为2.9，反应180分钟。产物用水洗涤，过滤，自然干燥，即得相变微胶囊(MEPCMs)。
二、性能测试。
本实施例所用的相变石蜡48PCM的DSC曲线如图1所示，本实施例制备的MEPCMs的DSC曲线如图2所示，将MEPCMs在高温100℃下烘6h后测试DSC，DSC曲线如图3所示。MEPCMs的SEM图如图4和图5所示。MEPCMs在常温下的光学图如图6所示，经50℃烘10分钟后的光学图如图7所示。
由图1-4可知，相变芯材的熔融热焓(ΔHm)为242.2J/g，结晶热焓(ΔHc)为238.7J/g；制备的MEPCMs的熔融热焓(ΔHm)为171.6J/g，结晶热焓(ΔHc)为168.0J/g，芯材包覆率为70.85％；制备的MEPCMs经100℃高温6h测试后的熔融热焓(ΔHm)为170.1J/g，结晶热焓(ΔHc)为168.3J/g，芯材包覆率为70.23％，相变芯材无明显泄露，说明制备的MEPCMs热稳定性能优异，同时芯材的包覆率在70％以上，制备的MEPCMs具有高热焓，调温性能优异。SEM图表明，制得的MEPCMs分散性好，胶囊间无粘连。光学图表明，制得的MEPCMs表面光滑，经高温烘烤后胶囊壳无破裂现象。
实施例2
一、制备双层脲醛壳相变微胶囊。
(1)制备水相：在温度为50℃下，将150g去离子水、0.9g乙烯-马来酸酐共聚物、0.3g聚乙烯醇混合，机械搅拌速度300rpm，搅拌混合得到含乳化剂的水溶液，然后加入0.7g的对苯二酚，搅拌溶解后用KOH和柠檬酸溶液将pH调至3.2。
(2)制备油相：取10.5g十八烷(相变温度28℃)，加热至熔融，得到液态芯材。
(3)制备PUF预聚液：将1.6g尿素、4.34g 37％甲醛溶液混合溶解，用KOH和柠檬酸溶液将pH调至8.0，65℃反应65分钟，得到内层PUF预聚液。将1.7g尿素、4.8g 37％甲醛溶液混合溶解，用KOH和柠檬酸溶液将PH调至8.3，68℃反应56分钟，得到外层PUF预聚液。
(4)制备乳液：保持水相的温度不变，调整转速为800rpm，将油相加入到水相中，再加入芯材质量分数0.62wt％的正丁醇，乳化反应13分钟，得到均匀稳定的水包油(O/W)相变乳液。
(5)一次包覆：调整转速为400rpm，温度为50℃，加入内层PUF预聚液，用KOH和盐酸溶液将pH调为3.2，反应40分钟，再调节pH为2.7，反应150分钟。
(6)二次包覆：加入0.39g对苯二酚，用KOH和柠檬酸溶液将pH调至3.2，再加入外层PUF预聚液，转速调整为400rpm，温度为50℃，用KOH和柠檬酸溶液将pH调至3.2，反应50分钟后，再调节pH为2.7，反应240分钟。产物用水洗涤，过滤，自然干燥，即得相变微胶囊(MEPCMs)。
二、性能测试。
本实施例所用的相变材料十八烷的DSC曲线如图8所示，本实施例制备的MEPCMs的DSC曲线如图9所示，将MEPCMs在高温100℃下烘6h后测试DSC，DSC曲线如图10所示。
由图8-10可知，相变芯材的熔融热焓(ΔHm)为259.4J/g，结晶热焓(ΔHc)为259.5J/g；制备的MEPCMs的熔融热焓(ΔHm)为211.7J/g，结晶热焓(ΔHc)为210.3J/g，芯材包覆率为81.6％；制备的MEPCMs经100℃高温6h测试后的熔融热焓(ΔHm)为210.0J/g，结晶热焓(ΔHc)为208.8J/g，芯材包覆率为81.0％，相变芯材无明显泄露，说明制备的MEPCMs热稳定性能优异，同时芯材的包覆率在80％以上，制备的MEPCMs具有高热焓，调温性能优异。
实施例3
一、制备双层脲醛壳相变微胶囊。
(1)制备水相：在温度为55℃下，将280g去离子水、2.1g苯乙烯-马来酸酐共聚物、0.56g烷基酚聚氧乙烯醚混合，机械搅拌速度400rpm，搅拌混合得到含乳化剂的水溶液，然后加入1.6g的邻苯二酚，搅拌溶解后用三乙醇胺和醋酸溶液将pH调至3.5。
(2)制备油相：取21g十四醇(相变温度38℃)，加热至熔融，得到液态芯材。
(3)制备PUF预聚液：将3.2g尿素、8.1g 37％甲醛溶液混合溶解，用三乙醇胺和醋酸溶液将pH调至8.5，70℃反应75分钟，得到内层PUF预聚液。将4.0g尿素、10.1g 37％甲醛溶液混合溶解，用三乙醇胺和醋酸溶液将PH调至8.0，69℃反应55分钟，得到外层PUF预聚液。
(4)制备乳液：保持水相的温度不变，调整转速为1500rpm，将油相加入到水相中，再加入芯材质量分数0.75wt％的乳化硅油，乳化反应15分钟，得到均匀稳定的水包油(O/W)相变乳液。
(5)一次包覆：调整转速为550rpm，温度为55℃，加入内层PUF预聚液，用三乙醇胺和醋酸溶液将pH调为3.5，反应55分钟，再调节pH为2.8，反应120分钟。
(6)二次包覆：加入1.1g邻苯二酚，用三乙醇胺和醋酸溶液将pH调至3.2，再加入外层PUF预聚液，转速调整为550rpm，温度为55℃，用三乙醇胺和醋酸溶液将pH调至3.2，反应60分钟后，再调节pH为2.8，反应300分钟。产物用水洗涤，过滤，自然干燥，即得相变微胶囊(MEPCMs)。
二、性能测试。
本实施例所用的相变材料十四醇的DSC曲线如图11所示，本实施例制备的MEPCMs的DSC曲线如图12所示，将MEPCMs在高温100℃下烘6h后测试DSC，DSC曲线如图13所示。
由图11-13可知，相变芯材的熔融热焓(ΔHm)为244.3J/g，结晶热焓(ΔHc)为242.1J/g；制备的MEPCMs的熔融热焓(ΔHm)为182.6J/g，结晶热焓(ΔHc)为186.6J/g，芯材包覆率为74.7％；制备的MEPCMs经100℃高温6h测试后的熔融热焓(ΔHm)为182.5J/g，结晶热焓(ΔHc)为186.1J/g，芯材包覆率为74.7％，相变芯材无明显泄露，说明制备的MEPCMs热稳定性能优异，同时芯材的包覆率在70％以上，制备的MEPCMs具有高热焓，调温性能优异。
对比例1
一种相变微胶囊，其制备方法与实施例1的制备方法基本相同，区别在于步骤(5)和(6)，步骤(5)和步骤(6)具体为：
步骤(5)：调整转速为500rpm，温度为60℃，加入内层PUF预聚液，用NaOH和盐酸溶液将pH调为3.8，反应180分钟。
步骤(6)：加入0.36g间苯二酚，用NaOH和盐酸溶液将pH调至3.2，再加入外层PUF预聚液，转速调整为500rpm，温度为60℃，用NaOH和盐酸溶液将pH调至3.8，反应240分钟。产物用水洗涤，过滤，自然干燥，即得相变微胶囊(MEPCMs)。
本对比例的相变微胶囊在常温下的光学图如图14所示，经50℃烘10分钟后的光学图如图15所示，从图中可以看出，相变微胶囊经高温烘烤后胶囊壳基本破裂，耐热性能差。
对比例2
一种相变微胶囊，其制备方法与实施例1的制备方法基本相同，区别在于步骤(5)和(6)，步骤(5)和步骤(6)具体为：
步骤(5)：调整转速为500rpm，温度为60℃，加入内层PUF预聚液，用NaOH和盐酸溶液将pH调为2.8，反应180分钟。
步骤(6)：加入0.36g间苯二酚，用NaOH和盐酸溶液将pH调至3.2，再加入外层PUF预聚液，转速调整为500rpm，温度为60℃，用NaOH和盐酸溶液将pH调至2.8，反应240分钟。产物用水洗涤，过滤，自然干燥，即得相变微胶囊(MEPCMs)。
本对比例的相变微胶囊在常温下的光学图如图16所示，从图中可以看出，相变微胶囊表面粗糙，致密性差。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。

Claims (10)

  1. 一种双层脲醛壳相变微胶囊，其特征在于，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。
  2. 根据权利要求1所述的双层脲醛壳相变微胶囊，其特征在于，所述相变材料选自：烷烃类相变材料、脂肪酸类相变材料、脂肪醇类相变材料、脂肪酸酯类相变材料。
  3. 根据权利要求2所述的双层脲醛壳相变微胶囊，其特征在于，所述相变材料选自：石蜡、十八烷、十四醇。
  4. 一种权利要求1-3任一项所述的双层脲醛壳相变微胶囊的制备方法，其特征在于，包括以下步骤：
    制备水相：将乳化剂、水和多元酚混合，得到水相；
    制备油相：加热使有机相变材料熔融，得到油相；
    制备PUF预聚液：以尿素和甲醛为原料，制备内层PUF预聚液和外层PUF预聚液；
    制备乳液：将油相加入水相中，进行乳化反应，得到水包油相变乳液；
    一次包覆：将水包油相变乳液和内层PUF预聚液混合，用pH调节剂调节pH值为3.2-3.6，进行缩聚反应，调节pH值为2.6-2.9，继续进行缩聚反应，在芯材外表面形成内层壁材；
    二次包覆：向经过一次包覆后的溶液中加入多元酚和外层PUF预聚液，调节pH值为3.2-3.6，进行缩聚反应，调节pH值为2.6-2.9，继续进行缩聚反应，在内层壁材外表面形成外层壁材，得到双层脲醛壳相变微胶囊。
  5. 根据权利要求4所述的制备方法，其特征在于，所述乳化剂选自：乙烯-马来酸酐共聚物、苯乙烯-马来酸酐共聚物、阿拉伯胶、聚乙烯醇、烷基酚聚氧乙烯醚、十二烷基苯磺酸钠、十二烷基硫酸钠、十六烷基三甲基溴化胺、失水山梨醇脂肪酸酯中的一种或两种以上；
    所述多元酚选自：间苯二酚、对苯二酚、邻苯二酚、连苯三酚、间苯三酚、儿茶酚、多巴胺中的一种或两种以上。
  6. 根据权利要求4所述的制备方法，其特征在于，所述pH调节剂为酸和/或碱；所述酸选自：盐酸、硝酸、硫酸、柠檬酸、醋酸、甲酸；所述碱选自：氢氧化钠、氢氧化钾、三乙醇胺、碳酸钠。
  7. 根据权利要求4所述的制备方法，其特征在于，所述制备水相步骤中，乳化剂、水、多元酚的质量比为(0.3-1.5)：(50-70)：(0.1-0.6)，混合的方式为搅拌，搅拌转速为200-500rpm，温度为40-80℃，待原料溶解后，调节pH值为3.0-3.6；
    所述制备油相步骤中，有机相变材料的用量为水相总重量的6％-10％；
    制备内层PUF预聚液具体为：将质量比为(0.6-1)：(1.5-2.6)的尿素和甲醛溶液混合 溶解，调节pH值为7.5-9，60-70℃反应30-90分钟，得到内层PUF预聚液；
    制备外层PUF预聚液具体为：将质量比为(0.8-1)：(2-2.6)的尿素和甲醛溶液混合溶解，调节pH值为7.5-9，60-70℃反应30-90分钟，得到外层PUF预聚液。
  8. 根据权利要求4所述的制备方法，其特征在于，所述制备乳液步骤具体为：调整水相搅拌转速为500-6000rpm，向水相中加入油相和消泡剂，所述消泡剂的添加量为有机相变材料质量的0wt％-2wt％，乳化反应5-20min，得到水包油相变乳液；所述消泡剂选自：正辛醇、正丁醇、乳化硅油、高碳醇脂肪酸酯复合物、聚氧乙烯聚氧丙烯季戊四醇醚、聚氧乙烯聚氧丙醇胺醚、聚氧丙烯甘油醚、聚氧丙烯聚氧乙烯甘油醚、聚二甲基硅氧烷。
  9. 根据权利要求4-8任一项所述的制备方法，其特征在于，所述一次包覆步骤具体为：调整水包油相变乳液的搅拌转速为200-700rpm，温度为50-80℃，加入内层PUF预聚液，内层PUF预聚液的用量为水包油相变乳液总重量的4-7％，用pH调节剂调节pH值为3.2-3.6，反应30-60分钟，调节pH值为2.6-2.9，反应120-360分钟；
    所述二次包覆步骤具体为：向经过一次包覆后的溶液中加入多元酚，多元酚的用量为制备水相步骤中多元酚重量的50-100％，调节pH值为3.2-3.6，加入外层PUF预聚液，外层PUF预聚液的用量为水包油相变乳液总重量的4-7％，调节pH值为3.2-3.6，反应30-60分钟，调节pH值为2.6-2.9，反应120-360分钟，得到双层脲醛壳相变微胶囊。
  10. 一种权利要求1-3任一项所述的双层脲醛壳相变微胶囊在制备调温混凝土、调温纤维或导热浆料中的应用。
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