Development of fully bio-based, formaldehyde-free wood-fiber composites with integrated thermal energy storage for building applications

This work introduces a bio-derived, thermally functional wood-fiber (WF) composite designed to act as a passive thermal buffer for buildings rather than a conventional insulation material. The material concept is based on embedding n-octadecane (OCT) as a phase change material (PCM) directly within a corn starch-bonded WF network enhanced with expanded graphite (EG) to improve thermal responsiveness, enabling the composite to store and release thermal energy. The composite contained 40 wt% OCT and 5 wt% EG and exhibited leakage-free behaviour. Morphological and spectroscopic analyses confirm that the OCT is physically retained within the fibrous matrix without chemical degradation, ensuring structural integrity and functional stability. Thermal analyses demonstrate that the composite exhibits a well- defined and repeatable phase change behavior, with a latent heat storage of 94.9 J g⁻¹ at a melting temperature of 26.25 °C. More importantly, laboratory-scale thermoregulation experiments reveal that the composite actively moderates temperature evolution, delaying heat transfer during heating and releasing stored energy during cooling, thereby reducing indoor temperature fluctuations relative to conventional WF composites. By merging renewable lignocellulosic resources with latent heat storage functionality through the use of a starch-based binder, this study demonstrates a new design pathway for fully bio-based and formaldehyde-free wood-based building materials that simultaneously enhance energy efficiency, thermal comfort, and sustainability. The developed composite shows strong potential for use in walls, ceilings, partitions, and insulation panels aimed at reducing building energy demand through passive thermal regulation.