Preparation and characterization of capric-palmitic-stearic acid ternary eutectic mixture/expanded vermiculite composites as form-stabilized thermal energy storage materials

Abstract

In this study, a composite of form-stable phase change materials (FSPCMs) were prepared by the incorporation of a eutectic mixture of capric–palmitic–stearic acid (CA–PA–SA) into expanded vermiculite (EV) via vacuum impregnation. In the composites, CA–PA–SA was utilized as a thermal energy storage material, and EV served as the supporting material. X-ray diffraction and Fourier transform infrared spectroscopy results demonstrated that CA–PA–SA and EV in the composites only undergo physical combination, not a chemical reaction. Scanning electron microscopy images indicated that CA–PA–SA is sufficiently absorbed in the expanded vermiculite porous network. According to differential scanning calorimetry results, the 70wt% CA–PA–SA/EV sample melts at 19.3°C with a latent heat of 117.6J/g and solidifies at 17.1°C with a latent heat of 118.3J/g. Thermal cycling measurements indicated that FSPCMs exhibit adequate stability even after being subjected to 200 melting–freezing cycles. Furthermore, the thermal conductivity of the composites increased by approximately 49.58% with the addition of 5wt% of Cu powder. Hence, CA–PA–SA/EV FSPCMs are effective latent heat thermal energy storage building materials.