Modified Calcium Chloride Hexahydrate Lotus Root Starch/Expanded Graphite Shape-Stabilized Composite Phase Change Materials: Enhanced Heat Storage, Improved Heat Transfer, and Suppressed Supercooling Behavior

Abstract

As one of the biological viscosity agents, lotus root starch (LRS) contains many hydrophilic groups with high water retention capacity. In this study, shape-stabilized composite phase change materials (PCMs) with LRS-modified calcium chloride hexahydrate (CCH) as a phase change material and expanded graphite (EG) as the supporting material were prepared by the vacuum impregnation method. The results showed that when 2 wt % LRS was added, the melting enthalpy of CCH-LRS2.0/EG reached 168.5 J/g, which was 13.3% more than that of CCH/EG. DFT calculation results showed that there were more hydroxyl groups in the molecular structure of CCH and the starch chain segment, which were easy to form hydrogen bonds. When hydrogen bonds were formed, they enhanced the water holding capacity and thermal properties. By adding 1.5 wt % SrCl2·6H2O (SCH) and 2.0 wt % LRS, the supercooling degree decreased to 2.4 °C, and the phase separation was restrained. The thermal conductivity of CCH-LRS2.0-SCH1.5/EG reached 3.030 W/(m·K), which was nearly 2.95 times that of CCH. After 100 cycles, the melting enthalpy of the CCH-LRS2.0-SCH1.5/EG composite PCM only decreased 3.3%. The shape-stabilized composite phase change material has a good application prospect in heat storage.