Synergistic Valorization of Hevea brasiliensis-Derived Spent Mushroom Substrate and Elaeis guineensis Fibers for Energy-Efficient Biocomposite Thermal Insulation Panels

Nature-inspired material design has gained increasing attention in the development of sustainable biocomposites for applications requiring the integration of structural performance and functional efficiency. However, many lignocellulosic composites still depend on synthetic binders and fail to achieve a strong effective interaction between constituents, resulting in suboptimal mechanical integrity and thermal behavior while limiting their environmental advantages. This study aims to develop binderless biocomposite panels from Hevea brasiliensis-derived spent mushroom substrate (SMS) and Elaeis guineensis empty fruit bunch (EFB) fibers, emphasizing the synergistic interaction between components for energy-efficient building applications. Chemical characterization revealed complementary roles, with EFB contributing a high cellulose content (57.60%) for reinforcement and SMS providing a higher lignin content (30.51%) for enhanced rigidity and natural binding. Panels were fabricated via hot pressing at a target density of 0.8 g/cm3 without additives. Mechanical properties were evaluated through specific flexural, tensile, internal bond, and impact testing, while thermal conductivity and thickness swelling were used to assess functional performance. The 60% SMS with 40% EFB composition exhibited optimal performance, achieving a specific flexural strength of 20.26 MPa, a flexural modulus of 1943.76 MPa, tensile strength of 6.12 MPa, an internal bond strength of 2.06 MPa, an impact strength of 15.35 kJ/m2, a thickness swelling of 44.80%, and a thermal conductivity of 0.234 W/m.K. These results demonstrate that the combined effect of SMS and EFB in binderless biocomposites derived from secondary products offers a promising biomimetic pathway for designing recyclable, high-performance materials suitable for sustainable and energy-efficient construction systems.