Thermo-physical properties of paraffin/TiO2 and sorbitol/TiO2 nanocomposites for enhanced phase change materials: a study on the stability issue

Recently, the demand for an accurate and precise determination of the properties of phase change materials (PCM) has increased considerably owing to the dependence of various applications based on latent heat storage (LHS). As reported earlier, PCM has a higher latent heat of fusion and is the cheapest material to store thermal energy. Still, it has poor thermal conductivity and less heat storage retentivity. For this reason, there is a significant interest in PCM-nanoparticles composites because the incorporation of nanoparticles can enhance the thermal properties of PCM. In the present work, TiO2 NPs were synthesized and incorporated with paraffin and sorbitol (PCM) by varying their mass concentration (0, 5, 10, and 20%) to study and compare the thermal properties of NCs. Different characterizations such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melting temperature testing of nanocomposites by temperature variation method were studied and analyzed. An appreciable decrement in melting point of 19.19, 27.59, 18.57, and 23.89% from 0 to 20% TiO2 concentrations in paraffin and sorbitol was observed from the temperature variation and DSC results, respectively. TGA/DTG results show minimum wt% loss of 57.76% at 316.24 °C and 90.88% at 317.27 °C calculated for 20 and 10% TiO2 concentrations in sorbitol and paraffin, respectively, which corresponds to the thermal stability of NCs. It was verified by both the methods that melting point decreases linearly with an increase in the concentration of NPs in PCM, which further corresponds to the increment in thermal conductivity and thermal storage capacity. Sorbitol exhibits better stability with TiO2 than paraffin as it consists of low strain, less weight loss, and more thermal compatibility. Uncertainty in the determination of the melting point temperature from temperature variation test method and DSC measurements can mainly be ascribed to the difference in the polarity of paraffin/TiO2 and Sorbitol/TiO2 nanocomposites and on the boundary conditions during heating and cooling which markedly affects the dispersion quality of TiO2 nanoparticles within the PCM (paraffin, sorbitol) matrix and these aspects have been modeled pictorially.