Abstract
Microencapsulation is a viable technique to protect and retain the properties of phase change materials (PCMs) that are used in thermal energy storage (TES) applications. In this study, an organic ester as a phase change material was microencapsulated using melamine–formaldehyde as the shell material. This microencapsulated PCM (MPCM) was examined with cyclic cryogenic treatment and combined cyclic cryogenic heat treatment processes. The surface morphology studies showed that the shell surfaces had no distortions or roughness after cryogenic treatment. The cryogenically conditioned microcapsules exhibited diffraction peak intensity shifts and crystal structure changes. The onset of melting for the nonconditioned and conditioned microcapsules were measured to be 8.56–9.56 °C, respectively. Furthermore, after undergoing the cryogenic and heat treatment processes, the PCM microcapsules had appreciable latent heat capacities of 39.8 kJ/kg and 60.7 kJ/kg, respectively. Additionally, the microcapsules were found to have good chemical stability after the cryogenic treatment. In addition, the cryogenically conditioned microcapsules were found to be thermally stable up to 128.9 °C, whereas the nonconditioned microcapsules were stable up to 101.9 °C. Based on the test results, it is obvious that the cryogenically conditioned microcapsules exhibited good thermal properties and are very desirable for cool thermal energy storage applications.
Highlights
Microencapsulation is a viable technique to protect and retain the properties of phase change materials (PCMs) that are used in thermal energy storage (TES) applications
The surface morphology of the as-prepared microcapsules are shown in Figs. 1a, 2a, and the cryogenically conditioned microcapsules are illustrated in Figs. 1b, 2b
The microcapsules treated under LN2 for 4 h revealed the development of rough shell surfaces, as indicated in Fig. 1b, which was observed to be quite similar to the morphology of other reported cryogenically treated materials[30]
Summary
Microencapsulation is a viable technique to protect and retain the properties of phase change materials (PCMs) that are used in thermal energy storage (TES) applications. Phase change materials are latent TES materials that can store and release heat energy through liquid to solid or solid to liquid phase transitions at near isothermal conditions. The issues of organic PCMs are related to their low thermal conductivity, supercooling degree, low heat transfer rate during freezing and melting, and leakage These limitations have been partially addressed by macro- and microencapsulation techniques[15,16,17,18]. Sari et al.[19] microencapsulated various types of paraffin mixtures into a poly(methyl methacrylate) shell material via emulsion polymerization These microcapsules were tested for 5000 thermal cycles and exhibited thermal reliability and good chemical stability between the core and shell materials. Su et al.[20] microencapsulated the Scientific Reports | (2020) 10:18353
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