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Phase change materials (PCMs) are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings, waste heat recovery, battery thermal management and so on. Especially inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and non-flammable. However, inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature, liquid phase leakage, large supercooling and severe phase separation in the application process. In this work, sodium acetate trihydrate was selected as the basic inorganic PCM, and a novel shape-stabilized composite phase change material (CPCM) with good thermal properties was prepared by adding various functional additives. At first, the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using acetamide. Then the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized CPCM. The thermophysical properties of the resultant shape-stabilized CPCM were systematically investigated. The microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and analyzed. The experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate trihydrate. The obtained shape-stabilized CPCM modified with additional 18% (mass fraction) acetamide and 12% (mass fraction) expanded graphite exhibited good shape stability and thermophysical characteristics: a low supercooling degree of 1.75°C and an appropriate melting temperature of 40.77°C were obtained; the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K) were also satisfactory. Moreover, after 50 accelerated melting-freezing cycles, the obtained shape-stabilized CPCM represented good thermal reliability.

The form-stable paraffin/high-density polyethylene/expanded graphite/epoxy resin composite phase change materials (CPCMs), exhibiting suitable thermal properties, including low melting temperature, high conductivity and high phase change enthalpy, was developed in this work. Herein, paraffin (PA) was utilized as a core PCM. High-density polyethylene (HDPE) was utilized for the shape stabilization and preventing the PCMs leakage. Expanded graphite (EG) was used to increase its thermal conductivity and act also in the porous supporting material. Epoxy resin (ER) was used to provide flexible encapsulated scaffold morphology and keep a highly tight network structure of the PCMs. However, the physical architecture, the chemical architecture and thermal behavior properties of specimens were investigated by using the spectroscopy and calorimetry techniques. The scanning electron microscope (SEM), X-ray diffraction (XRD) and fourier transform infrared spectrometer FTIR tests have shown good uniformity structure and good compatibility of components. In addition, the thermal conductivity tests revealed that the thermal conductivity of PA, initially 0.31 W/(m·K) improved up to 1.9 times by adding the 6 wt% mass fraction of EG in composite PCMs. Furthermore, the differential scanning calorimeter (DSC) measurements indicated that PA melting enthalpy, initially 231 J/g decreased up to 125 J/g with the increase of the amount of HDPE which was due to the limitation caused by the atomic network constructed by the base material. The thermogravimetric analyzer (TGA) and leakage-proof revealed the enhancement of the degradation of PA with the raise of amount of the HDPE into the CPCMs. Therefore, the proposed form-stable CPCMs are a great candidate for the thermal regulation and thermal energy storage employment.