Novel phase separation method for the microencapsulation of oxalic acid dihydrate/boric acid eutectic system in a hybrid polymer shell for thermal energy storage

In this study, an oxalic acid dihydrate/boric acid eutectic system (OA-PCM) was used as a phase change material (PCM), and a novel, simple, and eco-friendly phase separation method was developed to microencapsulate the OA-PCM by inducing the coacervation of ethyl cellulose (EC) and acrylonitrile-butadiene-styrene (ABS) to form a hybrid shell with the addition of polydimethylsiloxane at ambient temperature. A series of microencapsulated PCMs (MEPCMs) were prepared using three types of EC, different EC:ABS ratios, and different core/shell ratios. Various characterization techniques were used to evaluate the chemical structure, crystal structure, micromorphology, encapsulation ratio, and thermal properties of the MEPCMs. The results indicated that the MEPCM obtained at an EC:ABS:OA-PCM ratio of 1:1:2 (MEPCM-1:1:2) exhibited an optimal performance with a phase change enthalpy of 178.4 J/g and phase change temperature of 77.9 °C. In addition, the OA-PCM was validated to be successfully encapsulated in the hybrid shell, and the resultant MEPCM-1:1:2 had a uniform particle size, quasi-spherical shape, core-shell structure, and complete hybrid shell. This work proves that the microencapsulation of an OA-based PCM is promising, and the developed novel method also provides a reference for the microencapsulation of other water-soluble PCMs. [Display omitted] •A novel PCM based on oxalic acid dihydrate is microencapsulated for TES.•Microencapsulation is achieved by a simple and eco-friendly phase separation process.•An effective hybrid shell composed of EC and ABS is obtained.•Superior phase change enthalpy (178.4 J/g) is achieved.