Chemical composition of thermally modified Eucalyptus grandis and Tectona grandis short rotation wood in closed system

This study investigated the chemical composition of short-rotation Eucalyptus grandis (eucalypt) and Tectona grandis (teak) wood subjected to thermal modification in closed system. Four treatments were evaluated: untreated eucalypt wood (EW), thermally modified eucalypt wood (TMEW), untreated teak wood (TW), and thermally modified teak wood (TMTW). Thermal modification was conducted in closed (pressurized) system using a hygrothermal process at a final temperature of 160 °C. Chemical analyses included the determination of total lignin, hemicelluloses, and extractives (total, cold water, and hot water). Additionally, the solubility of wood was assessed in acetone, chloroform, dichloromethane, and a 1:2 (vol:vol) ethanol-toluene mixture. Thermal modification significantly altered the chemical composition of eucalyptus and teak wood, especially by promoting hemicelluloses degradation (4.9% TMEW and 9.4% TMTW) and an apparent increase in lignin (2.5% TMEW and 2.8% TMTW) and extractives content (16.6% TMEW and 7.2% TMTW), with variations depending on wood species and solvent polarity. Furthermore, changes in peak intensity in the FTIR spectra confirmed hemicellulose degradation in TMEW and TMTW.