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30

2023

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08

Do you know the preparation technology of phase change microcapsule materials?

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In the preparation of phase-change microcapsule materials, the main film-forming methods currently used include in-situ polymerization, interface polymerization, emulsion-solvent evaporation, complex condensation, sol-gel and spray drying.

In-situ polymerization method: refers to the encapsulation process, the reactive monomer and catalyst are all added to the core material dispersion medium, the reaction monomer and catalyst are all located in the phase-change material emulsion droplets inside or outside the characteristics. In-situ polymerization requires that the monomers be soluble in the continuous phase of the microcapsule system, while the polymeric monomers are capable of producing insoluble prepolymers of low relative molecular mass. Therefore, the polymerization reaction occurs on the dispersed phase core material. The monomer is polymerized at the beginning of the reaction, and when the polymer size increases, it is deposited on the surface of the core material. As polymerization and cross-linking continue, a solid microcapsule shell is eventually formed that can cover the entire surface of the core material droplets. Polymerization, copolymerization and polycondensation and other polymer reactions are commonly used in in situ polymerization of film-forming methods, the method of commonly used monomers are mainly urea formaldehyde, melamine formaldehyde and its copolymerization modified monomer polymer.

Interfacial polymerization method: At least two monomers are required, and the two monomers must be present in an incompatible phase change material emulsion system. The system can be divided into a continuous phase and a dispersed phase, typically a phase change emulsion is disposed in the dispersed phase. When polymerization occurs, the two monomers move from the dispersed phase and the continuous phase to the interface of the two phases respectively, and then the monomers undergo polymerization to form a polymer film to coat the core material into microcapsules. The main reactions are interfacial addition polymerization and interfacial condensation polymerization, and microcapsules of water-soluble core materials and oil-soluble core materials are applicable. The method has mild conditions, fast speed, and low requirements for monomer purity and raw material ratio, so it is widely used. The main monomers used for interfacial polymerization are diisocyanate, diamine, diphthalide chloride, etc. In recent years, the study of using styrene, divinylbenzene and acrylate as capsule wall materials has gradually increased.

Emulsion-solvent evaporation method: usually in the case of stirring, the oil phase and water phase under the action of surfactants to form a stable emulsion, and then the oil phase solvent through the continuous phase volatilization, the core material and wall material due to different surface tension to form shell/core structure. In this method, the oil phase can be directly dispersed into the water phase for emulsification, or the phase inversion emulsification method can be used. The size of microcapsules can be controlled by high-shear dispersion emulsification machine or ultrasonic cell crusher.

Complex coacervation method: refers to the wall material made of two or more polymer materials with opposite charges, the core material is dispersed in the wall material solution, and under appropriate conditions, the electrostatic interaction between the polymers with opposite charges occurs to form a film. After the interaction of polymer materials with opposite charges, the solubility is reduced and phase separation occurs, and the microcapsules are formed. In this process, the number of charges carried by the two oppositely charged polymer ions should be exactly equal, which can be obtained by adjusting the pH value of the solution. Commonly used reaction substances are gelatin, gum arabic, etc., and in order to enhance the waterproof performance, formaldehyde, glutaraldehyde or tannic acid can also be used for crosslinking. Sol-gel method: first, the precursor is dissolved in the solvent to form a uniform solution, and then the solute and the solvent are hydrolyzed or alcoholysis reaction to form a stable sol; Then add a human phase change core material, so that the sol forms a gel on the surface of the core particles, thus preparing phase change microcapsules coated with the core material, which is a commonly used microcapsule preparation method.

Spray drying method: first, the core material is dispersed in the pre-liquefied wall material solution, and then the mixture is atomized in a high-speed airflow, so that the solvent dissolving the wall material is rapidly evaporated, so that the wall material is solidified and finally the core material is microencapsulated. The spray drying method is most suitable for microencapsulation of lipophilic liquids, and the stronger the hydrophobicity of the core material, the better the embedding effect.

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