Abstract
The effect of thermal treatments on physical and mechanical properties of rose gum and Sydney blue gum wood was evaluated. Wood samples were thermally modified in a combination: pre-treatment in an autoclave (127°C - 1h) and treatment in an oven (180-240°C - 4h); and only treatment in an oven at 180-240°C for 4h. Chemical changes in the structure of woods were evaluated through infrared spectroscopy. Evaluation of physical properties was performed through mass loss, specific gravity, equilibrium moisture content and dimensional stability tests. Surface changes were analyzed through apparent contact angle technique and static bending tests were carried out to evaluate the mechanical behavior. Use of pre-treatment in autoclave affected the properties analyzed, however oven, resulted in the highest changes on wood from both species. Chemical changes were related to the degradation of hemicelluloses. Moreover, a significant decrease of hygroscopicity and mechanical strength of thermally modified woods was observed, while specific gravity did not significantly change for either of the species studied. The best results of decrease of wettability were found in low temperatures, while dimensional stability increased as a function of temperature of exposure in oven. The highest loss of mechanical strength was observed at 240°C for both species.
Highlights
Over the years, many processes have been developed in order to protect wood against xylophages agents, mainly treatments of impregnation with chemical products
The high changes as a function of temperature of treatment were found in the peaks related to the hemicelluloses, mainly at 1731 cm-1, which is typical in unconjugated ketone and carboxyl acids present in lignin and hemicelluloses (Colom et al 2003)
According to Fengel and Wegener (2003), when wood is exposed to high temperatures, the polysaccharides content significantly decrease because have more sensible reactivity than the cellulose
Summary
Many processes have been developed in order to protect wood against xylophages agents, mainly treatments of impregnation with chemical products. Thermal treatment promotes changes in the physical properties of wood, especially as swelling and shrinkage, equilibrium moisture content, weathering resistance, color and mass loss. In this context, physical changes of thermally modified woods are highly dependent on the conditions of treatments (Hill 2006, Korkut et al 2008). Thermal treatments modifying the wood’s wettability, which is directly related to the chemical changes on wood structure, especially to the degradation of the hemicelluloses
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