Effects of acid leaching and organic intercalation on the thermophysical properties of paraffin/expanded vermiculite composite phase change materials

In this study, original expanded vermiculite (EVM) was treated by acid leaching and organic intercalation to obtain modified EVM (A-EVM and A-O-EVM). Then, with nano Al ₂O ₃ powder as the thermal conductivity filler, a series of paraffin(P)/EVM-based shape-stable composite phase change materials (P/EVM, P/A-EVM, P/A-O-EVM and P-Al ₂O ₃ /A-O-EVM ss-CPCMs) were prepared by the physical impregnation method. DSC results showed that the latent heat of P/EVM was 109.3 J/g. The three modified EVM-based ss-CPCMs had the higher latent heat (> 130 J/g), indicating that two kinds of modification treatments could significantly enhance the heat storage capacity. Moreover, the crystallization ability of paraffin in P-Al ₂O ₃/A-O-EVM was significantly enhanced (solidification latent heat > melting latent heat, H _S > H _M) compared with the ss-CPCMs (H _S < H _M ) without organic intercalation. It was proved that improving the organic affinity and providing abundant nucleation sites were beneficial to reduce the inhibition effect of EVM matrix on the phase change behavior of paraffin during the solidification process. The results of TGA and thermal conductivity tests exhibited that P-Al ₂O ₃ /A-O-EVM possessed high thermal stability and acceptable thermal conductivity (0.43 W/m·K). The thermal cycling measurement results still showed the satisfactory thermal reliability and chemical stability after 100 melting/freezing cycles. Therefore, P-Al ₂O ₃ /A-O-EVM with good thermophysical properties was a promising energy storage material.