Synthesis and characterization of microencapsulated phase change material with phenol-formaldehyde resin shell for thermal energy storage

Microencapsulation technique of phase change materials (phase change materials, PCM) is considered as one of the most prospective and useful methods for thermal energy storage. In this study, a novel type of microcapsule for thermal energy storage based on an n-eicosane core and a phenol-formaldehyde resin shell was fabricated via in-situ polymerization process. The research studied the effects of the emulsification concentration, core/shell mass ratio and agitation speed on the thermal properties and morphology of microcapsules to confirm the optimal reaction conditions. The chemical compositions, surface morphology and thermal properties and stability were characterized by X-ray diffractometer (X-ray diffractometer, XRD), Fourier-transform infrared spectroscopy (Fourier-transform infrared spectroscopy, FTIR), field emission scanning electron microscopy (field emission scanning electron microscopy, FSEM), transmission electron microscopy (transmission electron microscopy, TEM) and differential scanning calorimetry (differential scanning calorimetry, DSC), respectively. The synthesized microcapsules were found to show a relatively spherical shape and a well-defined core-shell structure as well as a compact shell. Furthermore, the results showed that when the emulsification concentration was 1%, the core/shell mass ratio was 3:6.47, the agitation speed is 1000r/min, the highest encapsulation efficiency and energy storage efficiency achieve 84.2% and 83.4%, respectively, meanwhile the melting enthalpy and phase transition temperature of the obtained microcapsules reached as high as 173.83 J g-1 and 36.6 °C. In addition, the microcapsule samples prepared under optimal condition also exhibited an excellent thermal reliability even after 500th thermal cycles.