Shape-stable sugarcane bagasse biochar/PEG-1000 composite phase change materials for thermal energy storage: enhanced thermal conductivity, leak resistance, and photothermal conversion.

Biochar is widely available, inexpensive, renewable, and features a porous carbon framework, making it an attractive green additive for improving the overall performance of composite phase change materials. In this study, sugarcane bagasse, an agricultural waste, was used as the precursor to prepare three-dimensional porous Sugarcane bagasse biochar (SBB) through high-temperature carbonisation combined with intermittent ball milling. Polyethylene glycol 1000/sugarcane bagasse biochar (PEG-1000/SBB) composite phase change materials were then fabricated using a melt-ultrasonic method. The results showed that the incorporation of SBB significantly improved the thermal conductivity, shape stability, leak resistance, and light absorption capability of the composites. As the SBB content increased, the overall performance of the composites was progressively enhanced, and Polyethylene Glycol 1000/ Sugarcane Bagasse Biochar Composite with 15 wt% SBB (PEG-SBB-15) exhibited the best overall performance. Its thermal conductivity reached 0.85 W·m-1·K-1, which was 3.54 times that of pure Polyethylene glycol 1000 (PEG-1000) (0.24 W·m-1·K-1), while maintaining a relatively high latent heat storage capacity. In addition, PEG-SBB-15 showed excellent shape stability and effectively suppressed leakage during the phase transition process. After 500 thermal cycles, the composite still retained a stable chemical structure and good heat storage performance, indicating excellent cycling reliability. These results demonstrate that sugarcane bagasse biochar is an effective and sustainable reinforcing phase for PEG-1000 and provides a feasible route for developing low-cost, high-performance composite phase change materials.