Preparation and characterisation of expanded graphite/paraffin composite phase change materials with enhanced thermal properties

Phase change materials (PCMs) are widely used in thermal management and energy storage applications but are limited by low thermal conductivity. Existing methods for fabricating expanded graphite (EG)/paraffin composites face challenges including complex processing, limited thermal conductivity enhancement, poor uniformity, and low scalability. This study presents a novel fabrication method combining wet powder rolling mixing and vacuum impregnation. Effects of EG content, bulk density, and fillers on thermal conductivity are investigated. Results show that EG/paraffin composites exhibit high uniformity and improved thermal properties. Thermal conductivity increases with EG content in both horizontal (kxy) and vertical (kz) directions, plateauing beyond 9 wt%. Anisotropic behavior is observed, with kxy increasing more significantly than kz, particularly beyond 15 wt%. At 20 wt% EG, kxy and kz reach 5.9 W m−1 K−1 and 4.5 W m−1 K−1, respectively, approximately 30 times higher than that of pure paraffin. Thermal conductivity also increases with bulk density, plateauing beyond 705 kg m−3, with kxy slightly exceeding kz. Adding fillers such as graphene nanoplatelets or boron nitride further enhances thermal conductivity. The composites exhibit robust thermal storage/release capacity and stability. This study offers a scalable, cost-effective approach to produce PCM composites with advanced thermal properties for large-scale applications.