原位聚合法制备相变材料微胶囊及其致密性

Preparation and penetrability of microencapsulated phase change materials

采用原位聚合法以三聚氰胺-尿素-甲醛预聚物为壁材,包覆一种相变点为24℃、相变焓为225.5 J/g的有机相变材料,制备一种具有调温储热功能的复合材料。通过改变三聚氰胺和尿素摩尔比对微胶囊壁材渗透性和强度进行研究。相变材料受热时会在微胶囊内部产生较大的蒸汽压使微胶囊壁破裂渗出芯材,采用TGA测定微胶囊热失重温度得到胶囊壁破裂时的温度。采用压力法观察微胶囊受力后的形貌,对其强度进行评价。采用752型紫外分光光度仪对微胶囊壁渗透性进行表征。实验结果表明:微胶囊呈球形,平均粒径小于5μm,固化剂滴加速度为0.8 mL/min时微胶囊形貌最好。当尿素质量为反应总单体质量的20%时,与不加尿素相比,微胶囊热失重温度大约提高30℃,可以承受6.0 MPa压力而不破损,并且渗透性并不增加。

Through the in-situ polymerization method, a kind of phase change materials microcapsule was prepared by using melamine-urea-formaldehyde resin as the shell material and a phase change material as the core, of which the melt point and phase change enthalpy are 24℃ and 225.5 J/g respectively. The penetrability and strength of microcapsule were investigated by altering the mole ratio of urea to melamine. The thermal damage mechanism is that the phase change materials leak out from the microcapsule when they are heated, and the breakage of the shell was due to the thermal expansion of the core and shell materials at high temperature. The damage temperature of the microcapsule shell can be obtained by TGA. The strength of the shell was evaluated through observing the surface change under pressure by mean of scanning electron microscopy. The penetrability of the microcapsule was characterized in ethyl alcohol by mean of 752 spectrophotometer. As a result, the average diameter of the microcapsule is smaller than 5 μm, and the particle size is centralized when the dropping rate of the solidifying solvent is less than 0.8 mL/min. The mass loss temperature of the microcapsule can be further enhanced up to 30℃ while the reaction system contains 20% （mass fraction） urea. The microcapsules do not rupture under a pressure of 6.0 MPa, and the core material leaks out very slowly from the microcapsule in ethyl alcohol.