Abstract
Thermal treatment (thermal rectification) is a process in which technological properties of wood are modified using thermal energy, the result of which is often value-added wood. Thermally treated wood takes on similar color shades to tropical woods and offers considerable resistance to destructive microorganisms and climate action, in addition to having high dimensional stability and low hygroscopicity. Wood samples of Eucalyptus grandis were subjected to various thermal treatments, as performed in presence (140ºC; 160ºC; 180ºC) or in absence of oxygen (160ºC; 180ºC; 200ºC) inside a thermal treatment chamber, and then studied as to their chemical characteristics. Increasing the maximum treatment temperatures led to a reduction in the holocellulose content of samples as a result of the degradation and volatilization of hemicelluloses, also leading to an increase in the relative lignin content. Except for glucose, all monosaccharide levels were found to decrease in samples after the thermal treatment at a maximum temperature of 200ºC. The thermal treatment above 160ºC led to increased levels of total extractives in the wood samples, probably ascribed to the emergence of low molecular weight substances as a result of thermal degradation. Overall, it was not possible to clearly determine the effect of presence or absence of oxygen in the air during thermal treatment on the chemical characteristics of the relevant wood samples.
Highlights
Tropical wood species have high economic value in the international market on account of their excellent structural and decorative characteristics, yet the worldwide reserves of tropical wood species are currently in decline
Analysis results regarding total extractives content (% ET) found in wood from Eucalyptus grandis thermally treated at three maximum temperatures in presence or absence of oxygen, and the relevant untreated control samples, are illustrated in Table 1, along with multiple statistical mean comparisons, for all parameters being studied
The holocellulose content decreased and the relative lignin content increased with the rise in maximum temperature during thermal treatment
Summary
Tropical wood species have high economic value in the international market on account of their excellent structural and decorative characteristics, yet the worldwide reserves of tropical wood species are currently in decline. A possible solution to this problem is use of alternative, rapidly growing species of lower economic value originated in reforested areas (native or exotic). Overall, these species have inferior physicomechanical properties and are less resistant to attack by microorganisms. The most commonly used technique to improve resistance to attack by microorganisms is impregnating wood with heavy metals (chromium, copper and arsenic or bromine) or using creosote These preserving products are highly hazardous to the environment as they contaminate both groundwater and the soil, in addition to restricting wood use to more selective applications, such as furniture making. On account of their toxicity, these products have been forbidden in North American and European countries
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