Effect Of High Temperature Heat Treatment On Wood Property Under Pressure And The Application Of Its Condensing

The industrial application of the treatment of wood at high temperature is mainly under the atmospheric pressure. However, the researches of wood treatment under different pressures are retalively scarce. Compared with the traditional technology with high temperature and atmoshperic pressure, the treatment under normal pressure has more advantages on the treatment effiency, product quality and energy comsumption. Nowadays, with the increasingly prominent imbalance between the timber supply and demand from China market, the research on the heat treatment technology of wood only with high temperature is of great significance for providing practial guidance and bringing economic values for the highly efficient and value-added application of fast-growing forest plantations.In this thesis, heat treatment of wood at high temperature under normal pressure was systematically investigated. The lumber of Pinus massoniana was treated under different absolute pressures of O.1MPa,0.2MPa,0.4MPa, and0.6MPa, with different temperatures of140℃,160℃,180℃and200℃, according to different residence times of1l,2h and3h. The study began with the heat treatment facility design, and then discussed the effects of heat treatment conditions on the durability, changes of microstructure and chemical composition of treated wood. Based on the analysis of various condensable fractions collected from the heat treatment of wood under the absolute pressure of0.2MPa, the application of different condensable fractions for promoting the seed germination was preliminarily studied.The main results could be summarized as follows:1. The changes of the microstructure showed that the off rate of pit border was between65%to100%, the off rate of pit membrane was between20%to70%, the deformation rate of aperture was between12.5%to50%. With the increasing temperature and pressure as well as prolonged residence time, the tracheid cell wall became thinner, and the off rate of pit border increased. However, no obvious trends were observed for the off rate of pit membrane and the deformation rate of aperture.2. The derivative spectra of the chemical composition changes and two-dimensional infrared spectroscopy showed that the peak intensity of the hydroxyl group (-OH) and conjugated carbonyl group (C=O) of treated wood decreased when the temperature, pressure and prolonged residence time increased. The changes of hydroxyl group were more obivous.3. The results of durability showed that the weight loss of treated wood ranged from2.91%to36.68%, while untreated wood was51.46%. With the increasing heat treatment temperature, pressure and prolonged residence time, the weight loss decreased. The influential sequence was:temperature> pressure> residence time. A3-D model of the relationship between weight loss and treatment conditions was established. The oriented wood modification equations and images from the heat treatment at high temperature under pressure were derived.4. The analysis of the different condensable fractions collected from the heat treatment of wood under the absolute pressure of0.2MPa indicated that the methylglyoxal. Furfural,2-methyl furan, methyl cyclopentenone,2,3-pentanedione,5-methyl furfural, cresol, guaiacol were the main components of the condensable fractions. With the increasing temperature, the phenolic compounds in the condensable fractions decreased and the organic acids content significantly increased.5. The research on the application of different condensable fractions for promoting the seed germination showed that the condensable fractions collected from the heat treatment of wood at the temperature of180℃to200℃could significantly improve the seed germination of the Proteaceae plant imperial flower (King protea).