Evaluation of sustainable longan shell biochar energized commercial organic phase change material for low temperature thermal regulation

• 2D Longan shell biochar with high specific surface area was synthesized. • Thermal conductance of octadecane improved by 97.89% with 1.2 wt% of LSB. • PCM-Biochar carbon interaction was discussed with thermophysical analysis. Biochar, lauded for its plentiful raw material availability, compatibility with biological systems, and eco-friendliness, has proven effective in boosting the thermal conductivity of phase change materials (PCMs) and enhancing heat transfer in thermal systems. This paper introduces a distinctive eco-friendly composite PCM with improved thermal conductivity, optical absorbance, and thermal stability, achieved by dispersing laboratory-synthesized longan shell biochar (LSB) using carbonization and melting-mixing methods. LSB microparticles of 0.15–0.16 μm were dispersed at different weight fractions of (0.3; 0.6; 0.9; 1.2 and 1.5 wt%) blended with commercial octadecane to further enhance the optical and thermophysical behavior. The morphological characteristics, microstructure, optical absorbance and transmittance and thermal properties are characterized. Among the analyzed composites, the octadecane + 1.2LSB composite exhibited exceptional chemical compatibility, a significant increase in optical absorbance (from 0.212 to 0.735), and a thermal conductivity enhancement of 97.89% (from 0.142 W/(m⋅K) to 0.281 W/(m⋅K)) compared to octadecane; notably, this composite showed a melting enthalpy of 239 J/g without any compensation. The layered sheet-like 3D morphology of LSB along with the mesoporous and micropore surface features a network of sponge-like texture that facilitates the base for stronger intermolecular interaction with the octadecane matrix. Subsequently, the porous structure also contributes to effectively retaining the incident solar rays that enhance the optical absorbance of the composite. The research findings imply that the engineered composite has substantial promise for use in low temperature thermal regulation, presenting an effective and sustainable solution for energy management.