Optimization of Hydrothermal and Oleothermal Treatments for the Resistance of Dabema (Piptadeniastrum africanum) Wood

This study examines the effects of hydrothermal and oleothermal treatments on the physical, mechanical, and colorimetric properties of Dabema wood. Samples were heated at 100, 160, and 220 °C for 2, 3.5, and 5 hours under both processing conditions. The physical properties changed markedly after treatment. The equilibrium moisture content decreased from 13.16% in the untreated wood to 7.50% after hydrothermal treatment at 160 °C for 5 hours, and to 4.80% after oleothermal treatment at 220 °C for 5 hours. Water absorption declined from 78% to 39% and then to 17%. Hydrothermal treatment darkened the wood, whereas oleothermal treatment preserved a lighter color. Mechanical performance improved. The modulus of elasticity (MOE) in compression increased from 33332.76 MPa to 70836.53 MPa after oleothermal treatment at 220 °C for 5 hours. Flexural strength reached 56 to 58 MPa. In tension, the MOE increased from 4271 MPa to 5527 MPa, and the maximum tensile strength reached 88 MPa. PCA and RSM analyses indicate that oleothermal treatment at 160 °C for 3.5 to 5 hours offers the most effective conditions for enhancing stiffness while controlling color variation. Thermogravimetric analyses (TG/DTG) show that hydrothermal treatment promotes hemicellulose degradation, whereas oleothermal treatment stabilizes the cellulose–lignin network. Overall, hydrothermal treatment improves dimensional stability, while oleothermal treatment provides an optimal balance between stiffness and color stability. Deep color differences arise from furanic resin formation in hydrothermal treatment, suppressed by oil in oleothermal processing.