Enhancement of Thermo-Physical Properties of Expanded Vermiculite-Based Organic Composite Phase Change Materials for Improving the Thermal Energy Storage Efficiency

[Image: see text] In this work, expanded vermiculite (EVM) was modified by acid leaching with different concentrations (0.01, 0.05, and 0.1 mol/L) of HCl solution to obtain three kinds of acid-modified EVM (AEVM-1, AEVM-2, and AEVM-3, respectively). In the composite, polyethylene glycol (PEG) was served as a phase change material (PCM), while EVM and AEVM were served as supporting matrixes. Then, graphite was served as an additive to enhance thermal conductivity, and a series of shape-stabilized composite PCMs (PEG/EVM, PEG/AEVM-1, PEG/AEVM-2, PEG/AEVM-3, and PEG-C/AEVM-3 ss-CPCMs) were prepared by physical impregnation. The latent heats of PEG/AEVM-3 and PEG-C/AEVM-3 in the melting process were 154.8 and 144.7 J/g, respectively, which increased by 22.7 and 14.7%, respectively, compared with that of PEG/EVM, indicating that acid modification effectively enhanced the heat storage capacity. The thermal conductivity of PEG-C/AEVM-3 was 0.43 W/mK, which was 65.4 and 48.3% higher than that of PEG and PEG/EVM, respectively. The results of Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and the thermal cycle test indicated that PEG-C/AEVM-3 reflected favorable chemical stability, thermal stability, and thermal reliability. Therefore, the prepared PEG-C/AEVM-3 with high latent heat and acceptable thermal conductivity was a promising composite PCM in the field of building energy storage.