Physicomechanical performance of chitosan-coated mycelium composites from birch sanding dust and wheat straw

Industrial and agricultural by-products, birch sanding dust (BSD) and wheat straw (WS), were valorized as substrates for the fabrication of mycelium-based composites (MBCs) using the living mycelium of the basidiomycete Trametes versicolor . The composites were functionalized with a chitosan surface coating in 2- and 4-layer configurations. Microscopy, mechanical properties (compressive and flexural strength), water absorption, hygroscopic behavior, and surface wettability were evaluated. BSD-based composites outperformed WS-based blends in both mechanical properties, exhibiting flexural strength 1.3 – 1.7 × higher and compressive strength 2.1 – 3.4 × higher, depending on the layer configuration. Compressive strength was more strongly affected by density than by chitosan coating. Chitosan functionalization reduced water absorption in WS-based composites by up to 30%. WS-based composites exhibited greater hygroscopic adsorption than BSD-based blends. Chitosan coating maintained moisture adsorption values close to 20% at 90% RH, whereas at 95% RH, moisture uptake increased to 20–46%. For BSD-based specimens, chitosan-coated surfaces reached contact angles below 60° within 30 s, while WS-based composites fell below 40°, indicating a more hydrophilic character of the WS substrate. The novelty of this work lies in demonstrating a practical, scalable coating approach to modestly enhance the durability and moisture resistance of MBCs, thereby supporting their wider application in eco-product design.