Preparation And Characterization Of Polyurea Microencapsulated Phase Change Materials Through Interfacial Polymerization

The Polyurea microencapsulated phase change materials(Micro PCMs) for its does not contain formaldehyde and other harmful ingredients obtained more and more attention from the researchers. But the traditional polyurea resin polymerized via aromatic diisocyanate and aliphatic binary primary amine usually have poor thermal stability and compactness, due to the reaction rate between these two kinds of monomers is quite fast and the formed polyurea capsule wall is binary linear structure, make its application limited a lot. In this paper, a series of Micro PCMs with high compactness were prepared by using the reaction rate relatively low aliphatic diisocyanate in preparing process and preparing microcapsule with three-dimensional network structure capsule wall. The surface morphologies, chemical structure, phase change behaviors and thermal stability of the prepared Micro PCMs are investigated by using optical microscope, scanning electron microscopy(SEM), FTIR, differential scanning calorimetry(DSC) and thermo-gravimetric analyzer(TGA).On one hand, styrent-alt- maleic anhydride(SMA) was empolyed as the emulsifier, butyl stearate and polyurea resin polymerized via isophorone diisocyanate(IPDI) and diethylene triamine(DETA) were respectively used as the core material and the shell material in preparing the Micro PCMs. The influence of adding TDI monomer in the reaction system on the surface morphology and thermal stability of the prepared Micro PCMs was discussed. It was concluded that the employment of SMA as emulsifier could significantly decrease microcapsule agglomeration, and good emulsification effect could obtain in a less dosage and shorter time. SEM observation showed t hat the uniform particle size of the Micro PCMs were spherical distribution. Surface dishing phenomenon is serious, the addition of TDI in the react system could improve this phenomenon. DSC analysis showed that the prepared Micro PCMs had a melting temperature of 29.8 ℃ and melting enthalpy of 89.5 J·g﹣1.Thermal storage performance was good. There are double exothermic peak in the DSC cooling for Micro PCMs, the supercooling phenomenon was obvious. TG results showed that when the core and wall quality ratio was 3:1, the heat resistant temperature of the prepared Micro PCMs respectively using IPDI and IPDI/TDI mixture as isocyanate were 207 ℃ and 227 ℃. With the increase of wall and core quality ratio, TDI dosage and the Stirring speed, the thermal stability of microcapsules improved.On the other hand, high compactness Micro PCMs with three-dimensional network structure were prepared by using trifunctional glycerol to modify the polyurea wallmicrocapsules. The influence of the addtion way of glycerol and the quality ratio between glycerol and DETA on the surface morphology and thermal stability of the microcapsules was studied. SEM observation showed that the addition of glycerol could obviously improve the surface dishing of the prepared Micro PCMs, and the higher dosage of the glycerol, the less surface dishing had. The approach of how glycerol was added had a certain influence on the thermal stability of the prepared Micro PCMs. The thermal stability of the microcapsules was higher when DETA and glycerol were added sequentially than that of DETA and glycerol were added simultaneously. TG analysis showed that after adding glycerol the prepared three-dimensional network structure Micro PCMs had good thermal stability and high compactness, its heat resistance temperature improved to 240 ℃ from unmodified’s 227 ℃.