Environmentally friendly lignin-bonded wood-based composites for thermal energy storage in buildings

This study developed a fully bio-based composite consisting of sodium lignosulfonate, a water-soluble lignin derivative (Lig), wood fibre (WdF), and a phase change material (PCM) for building applications. WdFs formed the structural matrix, methyl palmitate (MeP) provided latent heat storage, and lignin served as a renewable binder and stabilizing agent. The composite was designed to combine effective thermal energy storage and enhanced resistance to biological degradation while maintaining its mechanical and physical integrity. The developed Lig@WdF/MeP board had a low density of approximately 355 kg m −3 and an internal bond strength of 0.037 MPa. DSC analysis revealed a melting temperature of 25.8 °C and a melting enthalpy of 95.9 J g −1 , confirming its suitability for passive thermal regulation. The incorporation of MeP increased the thermal conductivity from 0.091 ± 0.005 W m −1 K −1 for Lig@WdF to 0.118 ± 0.006 W m −1 K −1 for Lig@WdF/MeP. The composite retained 98.9% of its initial melting enthalpy after 500 thermal cycles and exhibited no visible MeP leakage or measurable mass loss. During the heating stage of the thermoregulation test, Lig@WdF/MeP reduced the maximum temperature by approximately 3 °C compared with the reference board. The composite exhibited strong biological resistance across all evaluated organisms. Termite survival decreased markedly from 74.7% in the control specimens to 5.2% in Lig@WdF/MeP. Similarly, all Hylotrupes bajulus larvae introduced into Lig@WdF/MeP specimens were found dead at the end of the test, while radiographic examination revealed an almost complete absence of larval galleries. After eight weeks of mould exposure, Lig@WdF/MeP received a rating of 1, compared with 5 for the control specimens, confirming substantially reduced mould development. These findings demonstrate that Lig@WdF/MeP integrates heat storage, low density, structural integrity, and biological resistance within a single lignin-bonded wood composite, offering a sustainable solution for next-generation, lightweight, non-structural building-envelope components.