Enhanced Energy Storage Properties of Building Insulation Materials via Supplementing with EG/PA Composite Phase-Change Materials

This work investigated the impact of paraffin (PA), expanded graphite (EG), and EG-PA composite phase-change materials (PCMs) on the energy storage characteristics of metakaolin-based building insulation materials. The thermal and mechanical characteristics of EG-PA composite porous geopolymer materials were evaluated through density, thermal conductivity, temperature variation, DSC, SEM-EDS, and compressive strength analyses. The findings revealed that supplementing porous geopolymer with EG-PA composites effectively enhanced its thermal conductivity and the samples with more EG-PA showed a faster heating rate and a slower cooling rate, which demonstrated that incorporating the composite PCM substantially improved the thermal storage efficiency of the porous geopolymer. After foaming, the EG-PA composite capsules are firmly anchored onto the pore walls via nonchemical (physical) bonding. In contrast to the significant deterioration of the final pore structure observed when paraffin is directly incorporated into porous geopolymers, the pore structure remains relatively intact when paraffin is encapsulated within expanded graphite to form EG-PA. This suggests that the flake-like EG-PA particles may impede gas diffusion and suppress bubble coalescence and disproportionation during the foam formation stage. The research concept of in situ embedding highly thermally conductive, stable, and leakage-proof EG-PA into the pore walls of porous geopolymers during the foaming process is feasible, providing a foundational basis for exploring composites integrating carbon-based materials, organic PCMs, and geopolymers.