This study was aimed at evaluating the effect of thermal treatment on the physical and mechanical properties of Eucalyptus grandis wood. Boards were taken from 5.9-year-old E. grandis trees. The boards were thermally modified at temperatures up to 220°C in the Laboratory of Wood Drying and Preservation from UNESP, Botucatu, SP, in Brazil. The results indicated that the thermal modification caused significant decreases of up to: (1) 49.3% and 10.5% in the equilibrium moisture content and in the density of wood, respectively; (2) 53.3% in the volumetric swelling;(3) 52.3% in the modulus of rupture at static bending, without changes in the compressive strength parallel to grain and the respective modulus of elasticity; and (4) 20.7% in the Janka hardness. It was found that the specific gravity and compression parallel to the grain test were not the most suitable ones for evaluating the quality of thermally modified wood. Physikalische und mechanische Eigenschaften von thermisch modifiziertem E. grandis HolzZusammenfassung Ziel dieser Studie war es, den Einfluss einer thermischen Behandlung auf die physikalischen und mechanischen Eigenschaften von Eucalyptus grandis Holz zu untersuchen. Aus 5,9-Jahre alten E. grandis Bäumen wurden Bretter eingeschnitten und im Trocknungslabor der UN-ESP in Botucatu, SP, in Brasilien bei Temperaturen bis zu 220°C thermisch modifiziert. Die thermische Modifikation führte zu folgenden Ergebnissen: Rückgang der (1) Gleichgewichtsfeuchte um bis zu 49,3 % und der Dichte um bis zu 10,5 %, (2) der Volumenquellung um bis zu 53,3 %, (3) der statischen Biegefestigkeit um bis zu 52,3 % und (4) der Janka-Härte um bis zu 20,7 %. Die Druckfestigkeit in Faserrichtung sowie der entsprechende Elastizitätsmodul än-derten sich nicht. Es zeigte sich, dass die Rohdichte und die Druckfestigkeit in Faserrichtung zur Bestimmung der Qualität von thermisch modifiziertem Holz nicht gut geeignet sind.

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The objective of this study was to evaluate the effect of thermal treatment on the biological resistance of Eucalyptus grandis wood to the decay fungus Picnoporus sanguineus. Boards from 5 years and 11 months old E. grandis trees, taken from the stock possessed by the Duratex-SA company, were thermally-modified at 140 degrees C, 160 degrees C, 180 degrees C, 200 degrees C and 220 degrees C in the Laboratory of Wood Drying and Preservation from UNESP, Botucatu, SP, Brazil. Samples of each treatment were treated according to ASTM D-2017 (1994). The experiment tested the accelerated decay caused by the decay fungus P. sanguineus on a system of soil-block wood. The results of thermal treatment showed that an increase of temperature of 180-220 degrees C caused reductions of between 15.7% and 82.4% in the weight loss in the samples from E. grandis incubated with P. sanguineus.

In this study the effect of thermal treatment on the equilibrium moisture content, chemical composition and biological resistance to decay fungi of juvenile and mature Hevea brasiliensis wood (rubber wood) was evaluated. Samples were taken from a 53-year-old rubber wood plantation located in Tabapuã, Sao Paulo, Brazil. The samples were thermally-modified at 180°C, 200°C and 220°C. Results indicate that the thermal modification caused: (1) a significant increase in the extractive content and proportional increase in the lignin content at 220°C; (2) a significant decrease in the equilibrium moisture content, holocelluloses, arabinose, galactose and xylose content, but no change in glucose content; and (3) a significant increase in wood decay resistance against both Pycnoporus sanguineus (L.) Murrill and Gloeophyllum trabeum (Pers.) Murrill decay fungi. The greatest decay resistance was achieved from treatment at 220°C which resulted in a change in wood decay resistance class from moderately resistant to resistant. Finally, this study also demonstrated that the influence of thermal treatment in mature wood was lower than in juvenile wood.

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This study aimed to evaluate the effect of thermal treatment on the physical properties of juvenile and mature woods of Eucalyptus grandis. Boards were taken from 30-year-old E. grandis trees. The boards were thermally modified at 180 °C in the Laboratory of Wood Drying and Preservation at UNESP, Botucatu, Sao Paulo state, Brazil. The results showed that thermal modification caused: (1) decrease of 6.8% in the density at 0% equilibrium moisture content of mature wood; (2) significant decreases of 14.7% and 35.6% in the maximum volumetric swellings of juvenile and mature woods, respectively; (3) significant decreases of 13.7% and 21.3% in the equilibrium moisture content of juvenile and mature woods, respectively. The influence of thermal modification in juvenile wood was lower than in mature wood and caused greater uniformity in the physical variations between these types of wood in E. grandis.

The present study is aimed at evaluating the anatomical characteristics of Eucalyptus grandis wood and the transition age between the juvenile and mature woods. Four trees of 23-year-old E. grandis were used. The juvenile, transition and mature wood zones were found by fiber length measurement from the pith to the bark. Samples were taken from juvenile wood, transition wood and mature wood and the anatomical properties of the wood were determined. The results showed that: (1) the fiber length, cell wall thickness, slenderness ratio, cell wall fraction and tangential vessel diameter increase from pith to bark; (2) fibers, axial parenchyma, ray parenchyma cells and vessels are equally distributed from pith to bark; (3) the transition zone between juvenile and mature wood occurs between the age of 8 and 13 years.

The objective of this study was to evaluate the effect of log steaming and of the diametrical position of boards on the timber quality of Eucalyptus grandis. Logs with diameters between 20 and 25 cm, between 25 and 30 cm and between 30 and 35 cm were studied. Half of logs were kept in its original condition, and the other half was steamed at 90 degrees C for 20 h. Later, the logs were cut into flat saw boards, and defects due to growth stress relief were measured. The results show that: (1) boards from control logs show different magnitudes of cracking according to the diameter of the log and the diametrical position of the board; (2) boards from logs with diameters between 30 and 35 cm and those from next to the pith develop larger cracks; and (3) boards from steamed logs show a reduction in the magnitude of cracking and a homogenous distribution of this defect relative to diametrical position within the log.