Luiz Fernando de Moura

Effect of thermal rectification on colors of Eucalyptus Saligna and Pinus caribaea Woods

Eucalyptus saligna and Pinus caribaea var. hondurensis woods underwent a variety of thermal rectication treatments (from 120oC to 180oC) to evaluate the eect of heating on their colorimetric properties. � e following color parameters were measured: lightness (L), a* coordinate (green-red coordinate), b* coordinate (blue-yellow coordinate), saturation (C), and tonality angle (H). � is study demonstrates that thermal rectication can be regarded as a tool for adding value to wood through color modication by heating. Results also suggest that thermal rectication might be a tool for homogenizing wood tonality and reddish color between species. Both tested species have shown very distinct colorimetric behaviors as a function of thermal treatments. � e conifer was more resistant to thermal darkening than the hardwood while exposed to temperatures below 160 o C. � e green-red coordinate (a*) and the tonality angle (H) tended to be homogenized for both species, as they decreased in eucalyptus, and increased in pinus, as a function of heating. � e eect of wood heating on the blue-yellow coordinate (b*), saturation (C), and tonality angle (H) was likely to be opposite between both tested species.

Effect of thermal treatment on the chemical characteristics of wood from Eucalyptus grandis W. Hill ex Maiden under different atmospheric conditions

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.

Surface roughness of heat treated Eucalyptus grandis wood

This study aimed to evaluate surface roughness of heat treated Eucalyptus grandis wood after peripheral planning and sanding performed in directions to the grain and against the grain. For machining tests, workpieces were collected from two different regions in the radial direction, as follows: internal, nearby the pit; external, nearby the bark. Heat treatment was carried out by heating samples at a maximum temperature of 190oC, with total treatment duration of 390 minutes. Heat treated and control samples underwent peripheral planning and sanding tests. The quality of machined surfaces was assessed by means of roughness average (Ra) measurements across and along the grain orientation. Results indicated significant differences in surface roughness as a function of machining feed direction, sandpaper grit size, and heat treatment. Surface roughness has not shown any difference in the radial direction.

Effect of thermal rectification on machinability of Eucalyptus grandis and Pinus caribaea var. hondurensis woods

Thermally rectified wood acquires colors similar to those observed in tropical woods, improved resistance to fungi and weathering, higher dimensional stability and lower hygroscopicity. Little information is available on the effect of heat treatments on the machining properties of wood. In this work, relatively low-valued woods (Eucalyptus grandis and Pinus caribaea var. hondurensis) underwent a variety of thermal rectification treatments (from 140°C to 200°C), performed in presence or scarcity of oxygen. Heat-treated wood underwent peripheral knife-planing (15°, 20°, and 25° rake angles) and sanding tests (60–80, 80–100, and 100–120 grit). Surface quality was evaluated as a function of the incidence of machining defects and uniformity of texture (planed surfaces), and roughness and wettability (sanded surfaces). Thermally rectified samples provided better surface quality after planing, and increased surface roughness after sanding, compared to control samples. The increment of treatment temperature caused an increase in wetting time, which indicates reduced hygroscopicity.ZusammenfassungDurch thermische Behandlung erlangt Holz eine Farbe ähnlich der von Tropenhölzern, sowie eine verbesserte Pilzresistenz und Wetterbeständigkeit, höhere Dimensionsstabilität und niedrigere Hygroskopizität. Nur wenig ist bekannt über den Einfluss der thermischen Behandlung auf die Bearbeitbarkeit von Holz. In dieser Arbeit wurde Holz relativ geringer Qualität (Eucalyptus grandis und Pinus caribaea var. hondurensis) unterschiedlichen thermischen Behandlungen (von 140°C bis 200°C) unterzogen und zwar sowohl in Gegenwart als auch unter Ausschluss von Sauerstoff. Das thermisch behandelte Holz wurde in Hobelversuchen (15°, 20° und 25° Spanwinkel) und Schleifversuchen (60–80, 80–100 und 100–120 Korngröße) geprüft. Die Oberflächenqualität wurde bezüglich des Auftretens von Bearbeitungsfehlern und gleichmäßiger Oberfläche (gehobelte Oberfläche) sowie Rauhigkeit und Benetzbarkeit (geschliffene Oberfläche) beurteilt. Verglichen mit den Kontrollproben wiesen thermisch behandelte Oberflächen nach dem Hobeln eine bessere Oberflächenqualität und nach dem Schleifen eine erhöhte Oberflächenrauhigkeit auf. Eine Erhöhung der Behandlungstemperatur führte zu einem Anstieg der Benetzungsdauer, was auf eine reduzierte Hygroskopizität hinweist.