Synthesis and characterization of microencapsulated paraffin with TiO2 shell as thermal energy storage materials

In this study, the microencapsulated phase change material with paraffin as core and inorganic TiO2 shell was successfully synthesized by in situ hydrolysis and polycondensation of tetrabutyl titanate in a nonaqueous oil-in-water emulsion using formamide as aqueous phase. The chemical compositions, crystalline structure, morphology and microstructure of paraffin@TiO2 microcapsules were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal properties and thermal stability of the microcapsules were measured by differential scanning calorimeter (DSC) and thermo-gravimetric analyzer (TGA). FT-IR and XRD results proved that there was no chemical reaction between paraffin core and TiO2 shell material. SEM images indicated that the paraffin@TiO2 microcapsules showed a regular spherical shape with the average diameters of 2–5 µm with a smooth shell. SEM and TEM studies also confirmed the paraffin was fully encapsulated with TiO2. DSC analysis indicated that the microcapsules had similar phase change behaviors as those of pure paraffin. Typical sample froze at 52.24 °C with a latent heat of 110.42 J g−1 and melt at 60.41 °C with a latent heat of 107.54 J g−1, of which the encapsulation ratio achieved to 54.58%. TGA results indicated the thermal stability of paraffin was improved by the protection of TiO2 shell through the encapsulation.