Effect of processing on thermal properties of pentaglycerine-based solid-solid phase change materials

Abstract

Plastic crystals hold great potential for compact and cost-effective thermal energy storage (TES) systems due to their solid-solid transitions, high latent heat, and tunable transition temperatures. However, the impact of processing on their thermal properties remains underexplored. Pentaglycerine (PG)-based composites, suitable for TES applications at 80 °C, doped with two sizes of expanded graphite (EG) are investigated in this work. Effects of pressing and casting and common processing methods are evaluated. A comprehensive analysis of key thermal properties characterizing phase change materials was conducted. Specifically, the research focuses on the evaluation of thermal conductivity in both radial and axial directions, performing a thorough study of latent heats and subcooling using differential scanning calorimetry, conducting in situ characterization through solid-state nuclear magnetic resonance, and assessing solid-solid transition kinetics. This study highlights the significant influence of processing on the thermal properties of organic plastic crystals. Adequate processing enhances the effectiveness of EG in addressing the low thermal conductivity of plastic crystals and preventing latent heat drops associated with nanoconfinement effects. Additionally, notable reductions in subcooling can be achieved in PG-based composites simply through this processing, by reducing grain size and consequently lowering the activation energies in the plastic-to-crystal transitions.