A novel composite phase change material of high-density polyethylene/D-mannitol/expanded graphite for medium-temperature thermal energy storage: Characterization and thermal properties

As pure phase change materials (PCM) filling in supporting porous material are often unfavorable for thermal energy storage (TES) due to the easy leakage, low thermal conductivity, and reduced overall latent heat, composite phase change materials (CPCMs) receive the increasing attention for the future applications. In this work, a novel medium-temperature CPCM was prepared by the method of melt adsorption-compression molding, which used D-mannitol (DM) as PCM, high-density polyethylene (HDPE) as supporting material, and expanded graphite (EG) as thermal enhancement material. The thermophysical properties of such CPCMs were measured and analyzed to identify the optimal material design. The results showed that the leaking of DM from the HDPE/DM composite can be avoided under the 30 % mass loading of HDPE, showing a better adsorption capacity. Among the prepared examples, the CPCM3 (26.4 % HDPE + 61.6 % DM + 12 % EG) has the highest thermal conductivity of 2.66 W/(m center dot K) which is 6.04 times higher than the pure HDPE/DM composite. The CPCM3 also has other favorable characteristics such as a constant melting temperature of around 163.2 degrees C, high latent heat of 224.1 J/ g, supercooling degree of 37.4 degrees C, and decomposition temperature of 411.3 degrees C. The complex influencing mechanisms were further explored with the help of material microstructure characterization. This study is significant because it provides design guidelines for reliable medium-temperature heat storage materials for advanced renewable energy applications.