Effect of Wood Ash and Boron Salts on Hygroscopicity of Sawdust Composites Bonded with Wheat Protein

Bio-based wood composites bonded with wheat protein represent a sustainable alternative to conventional formaldehyde-based panels; however, their high moisture sensitivity limits dimensional stability and functional reliability. This study comparatively evaluated the effect of incorporating equivalent low dosages (5 wt.% dry basis) of wood ash and boron salts on the hygroscopic behavior of sawdust composites manufactured under identical formulation and processing conditions. By maintaining constant raw material, adhesive system, and consolidation parameters, the experimental design enabled direct assessment of additive performance within the same lignocellulosic matrix. Hygroscopic response was characterized through short-term water immersion tests, analyzing density, hygroexpansion, and water absorption index. Relative to the unmodified control, both additives produced statistically significant improvements with large effect sizes. Wood ash increased bulk density and markedly reduced water uptake, indicating microstructural modification and partial pore blocking. Boron salts achieved the greatest reduction in hygroexpansion, suggesting chemical stabilization of cell-wall polymers. The results demonstrate that even low mineral additions can substantially modify short-term moisture response without compromising adhesive consolidation. These findings provide controlled comparative evidence supporting the use of low-cost inorganic additives to enhance the dimensional stability of sustainable wood composites intended for interior applications.