Eyong wood (Eribroma oblonga), a good candidate for hydrothermal treatment: Optimization of its physical and colorometric properties under the determinant pH effect

Study evaluates the impact of hydrothermal treatment on Eyong wood (Eribroma oblonga) at 145 °C, 160 °C, and 180 °C, focusing on its colorimetric, physical, and chemical properties. Treatment resulted to a progressive darkening (ΔE* = 17.72 ± 2.70 at 180 °C) with a decrease in brightness (L*), increased red hues (a*), decreased yellow hues (b*), a lower hue angle (h), and a decline in pH, enhancing its aesthetic appeal. Physically, reduced equilibrium moisture content (13.57 % to 7.40 %), volume shrinkage (10.45 % to 7.04 %), density (698.97 to 646.76 kg/m³), and water absorption (20.36 ± 2.43 % to 16.64 ± 1.14 %) improved dimensional stability. Chemically, lignin content increased (9.21 % to 13.01 %), while hemicelluloses decreased (44.84 % to 41.80 %), as confirmed by ¹³C NMR. Compared to dry heat, chemical, silicone oil, and saturated steam treatments, hydrothermal treatment enhanced moisture resistance and durability, making it a promising method for outdoor applications where the structure is subject to color variations. Further research should optimize mechanical and biological resistance.