Preparation and characterization of microencapsulated phase change materials for greenhouse application

Among the phase change material microencapsulation process, In Situ Polymerization, Interfacial Polymerization, and other polymerization method are more commonly used in small scale laboratory chemical preparation. In the process of In Situ Polymerization, wall materials of monomer or prepolymer and the catalyst need soluble in the continuous phase, while Interfacial Polymerization reaction requires two kinds of wall material monomers dissolving in immiscible dispersed phase and a continuous phase respectively. Characteristics of microencapsulated phase change material include its apparent morphology, thermal properties of the core material, particle size distribution, toughness and thickness of wall materials and other factors. Selection of core materials in microencapsulation mainly considers their phase transition temperature and ambient temperature of applications, and the screening of wall materials mainly observed their balling effect, chemical stability, thermal stability and mechanical strength, etc. Latent functionally thermal fluid means when microencapsulated phase change material powder is added in a single-phase heat transfer fluid, a stable suspension of solid-liquid two-phase fluid is made, namely phase-change microcapsule suspension. In order to develop a proper kind of microencapsulated phase change material (MEPCM) which can be applied in greenhouse heat storage, three different kinds of MEPCMs were prepared, with butyl stearate, No. 30 paraffin and their mixture as the core materials respectively, melamine resin and polyurea resin and polymethyl methacrylate (PMMA) as wall materials respectively. The property characterization analysis demonstrated that melamine resin microcapsule performed the best: the particle sac wall was smooth and tight; the particle size distribution was uniform and concentrated at about 1 μm, and the average diameter of microcapsule granules was 75.15 μm; the heat resistant temperature was higher than 100℃, meeting the demands of solar greenhouse application; the thermal gravimetric surplus rate of the microcapsules was more than 50%, far larger than that of the other two kinds of polyurea resin and polymethyl methacrylate microcapsules, namely with relatively higher thermo-stability. Therefore, the melamine resin can be used as suitable wall material of microcapsules for preparing microencapsulated phase change material suspensions which can be utilized as liquid medium for solar heat collection, conveyance and release in greenhouses. © 2016, Chinese Society of Agricultural Machinery. All right reserved.