Thermal performances of stearic acid/sepiolite composite form-stable phase change materials with improved thermal conductivity for thermal energy storage

To improve leak-proof performance of phase change materials (PCMs), hydrochloric acid-modified sepiolite (SEP) was used to encapsulate stearic acid (SA), and expanded graphite (EG) was employed as fillers to improve thermal conductivity. A series of form-stable PCMs SA/SEP and SA/SEP/EG were prepared by a combination method of direct impregnation and dry pressing with leakage tests being performed. Their crystalline structure, chemical compatibility, microstructure, latent heat, thermal stability and thermal conductivity were characterized by XRD, FT-IR, SEM, DSC, TG and thermal conductivity analysis, respectively. The leakage tests proved that the loaded mass fraction of SA in the SEP/EG could attain to 60%. The DSC experimental results showed that the composite SA60%/SEP/EG (15%) had a relative large melting latent heat of 113.7 J g−1. The thermal conductivity analysis demonstrated that the enhanced ratio of thermal conductivity in SA60%/SEP/EG (15%) was about 9 times to that of SA35%/SEP. In addition, the XRD, FT-IR, SEM and TG results indicated that the as-prepared composites were obtained by a physical mixing process with well chemical compatibility and thermal durability. Compared with the previous studies, the shape-stable SA60%/SEP/EG (15%) holds some competitive advantages.