Preparation and Performance Analysis of Form-Stable Composite Phase Change Materials with Different EG Particle Sizes and Mass Fractions for Thermal Energy Storage

[Image: see text] The low thermal conductivity and leakage of paraffin (PA) limit its wide application in thermal energy storage. In this study, a series of form-stable composite phase change materials (CPCMs) composed of PA, olefin block copolymer (OBC), and expanded graphite (EG) with different particle sizes (50 mesh, 100 mesh, and 200 mesh) and mass fractions are prepared by melt blending. OBC as a support material could reduce PA leakage during melting, and EG as a thermally conductive filler can improve the thermal performance of PCMs. The microstructure characteristics and chemical and thermal properties of prepared CPCMs are tested and analyzed. The results show that PA/OBC and EG have good compatibility, and there is no chemical reaction with each other to generate new substances. Thermal conductivity can be significantly improved by adding EG, and it is greatly enhanced with the increase in EG particle size at the same EG mass fraction. Simultaneously, the addition of EG increased the melting temperature of CPCMs and decreased the solidification temperature as well; meanwhile, the values of melting temperature and solidification are also reversed for CPCMs compared to PA/OBC. There is an optimal content of EG to balance the thermal conductivity and heat storage capacity for CPCMs. The addition of OBC can provide a stable geometric construction, and the leakage will be further improved with the increase in EG content. Finally, the melting time of CPCMs containing EG-50, EG-100, and EG-200 with 4 wt % EG is shortened by 52.9, 41.1, and 37.5%, respectively, compared with PCMs without EG in the heat storage and release experiments. Also, the CPCMs with EG-50 have better thermal performance compared with the CPCMs of EG-100 and EG-200.