Agro-food waste upcycling into mycelium insulation: Linking structure with mechanical and fire performance

This study presents a multiscale investigation of mycelium-based biocomposites produced via solid-state cultivation of Ganoderma lucidum on agro-food sidestreams. Three lignocellulosic residues, wheat bran (in two particle sizes), rice straw, and spent coffee grounds, were selected based on global availability and chemical diversity. The biocomposites were characterized to investigate how substrate composition and mycelial growth influence microstructure and macroscopic performance. Monosaccharide analysis and scanning electron microscopy (SEM) revealed that wheat bran supported enhanced mycelial growth. Fine wheat bran-based composites exhibited compressive strengths up to 449 kPa at 30% strain and tensile moduli of 15 to 25 MPa, significantly higher than expanded polystyrene (EPS), a conventional insulator. All biocomposites showed intrinsic surface hydrophobicity (water contact angles of 106-120°). Thermal analyses, including thermogravimetric analysis (TGA) and hot-plate conductivity measurement, confirmed their suitability as porous insulation. Cone calorimetry demonstrated improved fire safety in wheat bran-based composites, with reduced peak heat release rates (112-115 kW/m 2 ) and better fire performance indices up to 0.15 m 2 ·s/kW. Embodied energy and carbon footprint assessments indicated up to 89% lower energy demand and 72% lower CO 2 emissions compared with EPS. Through multiscale characterization and direct benchmarking, this study shows how substrate selection and fungal-substrate interactions can be utilized to tailor performance. The findings provide insights into converting low-value biomass into scalable, fire-safer, and environmentally responsible insulation materials. • Wheat bran, rice straw, and spent coffee grounds upcycled into mycelium insulation. • Multiscale analysis revealed substrate-dependent structure-performance relations. • Wheat bran enabled dense hyphal network, enhancing strength and fire safety. • Improved mechanical performance and fire safety vs. expanded polystyrene (EPS). • Up to 89 % lower energy demand and 72 % lower CO 2 footprint than EPS.