A form-stable wood-based phase change material via double cross-linking esterification after removal of lignin for thermal energy storage

Abstract

This study developed a form-stable wood-based phase change material (FWPCM) via double cross-linking esterification (DCLE) to prevent PCM leakage and volume expansion. The mixture of polyethylene glycol (PEG) as a PCM and 1,2,3,4-butane tetracarboxylic acid (BTCA) as a cross-linking agent was vacuum-impregnated into delignified wood. Lignin removal was carried out using traditional alkali treatment (Na2SO3/NaOH) and deep eutectic solvent (DES) treatment, with the former removing most lignin and hemicellulose from the wood. The comparison revealed that DES-delignified wood (DW) avoids chemical hydrolysis of cellulose, effectively preserving the lignocellulosic skeleton. The exposed hydroxyl groups in cellulose promoted DCLE, which was confirmed by FTIR and XPS. A small amount of BTCA was added to create ester bonds with cellulose to stabilize PEG in the DW, resulting in the FWPCM that demonstrated excellent leakage resistance and a higher encapsulation rate of 84.75 %. The phase change exhibited a maximum enthalpy of 150.1 J·g-1 at 58.5 °C. FWPCM showed anisotropic heat transfer characteristic (radial 0.14 W/(m·K), longitudinal 0.19 W/(m·K)), high thermal stability (283 °C), and excellent cycling durability (200 cycles). This study provides a reliable, cost-effective and eco-friendly thermal energy storage material for building energy conservation.