Valorisation of industrial waste wood in mycelium-based biocomposites for thermal insulation: A hygrothermal and microstructural analysis

The construction sector faces the dual challenges of reducing embodied carbon and managing millions of tonnes of waste wood currently lost to incineration. While mycelium-based biocomposites (MBBs) have emerged as a promising bio-based insulation class, their hygrothermal characterisation when produced from recycled - rather than virgin agricultural - substrates remains critically underexplored. This study addresses this gap by evaluating the engineering viability of manufacturing MBBs using Ganoderma sessile grown on recycled wood substrate for thermal insulation applications. Four replicate panels (approximately 485 × 485 × 185 mm) were fabricated using industrial waste wood particles, with material properties characterised via elemental analysis, scanning electron microscopy (SEM), X-ray computed tomography (CT), and steady-state thermal conductivity testing according to ISO 8302. Elemental analysis revealed a carbon-to-nitrogen (C/N) ratio of 54.8, confirming a nutrient-limited environment suitable for fungal colonisation. The resulting biocomposite panels exhibited an average bulk density of 157.4 kg·m⁻³ and achieved a thermal conductivity of 0.055 ± 0.001 W·m⁻¹ ·K⁻¹ with a water vapour diffusion resistance factor µ = 2.0 ± 0.6. Dimensional stability analysis indicated anisotropic behaviour, with significantly lower shrinkage in the horizontal plane (3.15%) compared to the thickness direction (8.5%). Scanning electron microscopy revealed differential hyphal colonisation across panel height, with denser mycelium networks at surfaces than in the centre. Computed tomography enabled visualisation of inorganic contaminants within the composite, demonstrating its utility as a quality-control tool. These findings demonstrate that recycled wood-based MBBs offer a competitive, circular alternative to conventional insulation, effectively bridging waste valorisation with energy-efficient building envelope design. To the authors’ knowledge, this is the first study to provide a comprehensive hygrothermal dataset - combining thermal conductivity, water vapour diffusion resistance, and sorption isotherm data - for MBBs derived specifically from recycled industrial waste wood, addressing a critical gap in the literature on sustainable bio-based insulation materials.