Rafael Leite Braz

Tensão de Crescimento no Lenho de Eucalyptus benthamii e sua Relação com Características Dendrométricas em Diferentes Espaçamentos

The aim of this study was to evaluate the influence of planting eucalyptus wood with respect to its dendrometric characteristics and longitudinal residual strain (LRS) of the wood, and the relationships between these variables. The material used was Eucalyptus benthamii at five years of age in 2×3, 3×3, 3×4 and 4×4 m spacing. The projection of the crown was determined by measuring eight spokes with variable angles, and maps of crown distribution and projection were prepared. Measurements of LRS were taken 1.30 m above the ground in the four cardinal directions in living trees, with the aid of strain meters (Growth Strain Gauge) by the CIRAD-Foret method. There was great variability in the results of the growth variables and levels of growth stresses for different spacing. The lowest average values of LRS were observed in the south direction, and increased spacing did not significantly alter the LRS values. Correlations between LRS and growth variables were only found with maximum LRS values ​for each tree.

Evaluation of the quality of particleboard panels manufactured with wood from Sequoia sempervirens and Pinus taeda

This work aimed to evaluate the physical and mechanical properties of particleboard panels manufactured with wood particles from Sequoia sempervirens and Pinus taeda and urea-formaldehyde resin (UF), using different mixing ratios of the two species, namely 100%, 0%, 75%, 50% and 25% of sequoia particles. Properties evaluated included panel density and compaction ratio, water absorption and thickness swelling after 24 hours of immersion, internal bond and static bending (MOE and MOR). The low density of sequoia wood raised the compaction ratio of the panels and helped improve their mechanical properties and dimensional stability. Panels manufactured at the ratios of 100%, 75%, 50% and 25% sequoia to pine provided better results compared to panels manufactured with 100% pine. Results of MOE and MOR under static bending and of internal bond met the minimum requirements of standard EN 312:2003 in all treatments. Results revealed that Sequoia sempervirens has great potential for production of particleboard.

Deformação Residual Longitudinal de Clones de Eucalyptus em Local Sujeito a Ventos

During development and growth of trees, mechanical stresses are generated in order to keep it balanced and upright in response to various environmental factors. These efforts are known as growth stresses and can vary in distribution and intensity across different species of the genus Eucalyptus. Thus, the objective was to evaluate the longitudinal residual strains (LRS) and its correlations with tree growth features, physical and mechanical properties of the Eucalyptus urophylla × Eucalyptus grandis hybrid clones. Trees were 30 and 35 months old, located in forest plantations of Vale do Rio Doce, Minas Gerais, in areas subject to wind action, with damping effect and even the breaking of these trees. The LRS measured with extensometer was on average 0.086mm and when associated with other characteristics of the wood, the correlations were not significant. The growth characteristics of trees, basic density, modulus of elasticity (MOE) and modulus of rupture (MOR), and absorbed work were not enough to explain the LRS behavior.

Relação entre a deformação residual longitudinal com crescimento e propriedades da madeira de espécies de Eucalyptus

This study aimed to assess the relationship of longitudinal residual strain due to growth stresses with tree growth variables and the physical and mechanical properties of wood. The species studied were E. dunnii and E. grandis, both with 40, 52 and 64 months of age and E. saligna with ages 28, 40, 52 months of age for solid wood production. The growth stress levels were measured indirectly through the CIRAD-Forêt method. The physical and mechanical properties of wood were obtained in accordance with the standards of COPANT (1972a). Correlations among longitudinal residual strain with tree growth variables and physical and mechanical properties showed a high dispersion; wood at 52 months of age exhibited a more obvious correlation among investigated variables. Thus, forest breeding programs, associated with increments of new silvicultural practices should be directed to the production of wood with desirable characteristics for obtaining the solid wood with low propensity for growth stress.

Curva Característica de Secagem da Madeira de Tectona grandis e Acacia mangium ao Ar Livre

Air drying is a simple, low-cost alternative that can be used in the pre-drying or definitive drying of several woods. The objective of the present work was to study the behavior of the characteristic air drying curve for Acacia mangium and Tectona grandis lumber. Fifteen-year-old trees of each species were cut into logs of approximately 3 m in length. The logs were sawn using a tangential cut system to obtain 3 cm-thick boards. After the wood pile was mounted for drying, the moisture content of samples was determined, and monitoring occurred through the periodic weighing of the control samples. It was possible to observe that, under the environmental conditions imposed, Acacia mangium boards dried more slowly than Tectona grandis boards. A separate analysis of the drying curve for each species is recommended.

Avaliação Colorimétrica de Aglomerados Produzidos com Partículas de Madeira de Sequoia sempervirens e Pinus taeda Submetidos ao Intemperismo Natural

The aim of this work was to establish the effect of using different amounts of Sequoia sempervirens and Pinus taeda wood particles on the colorimetric properties of particleboard and to evaluate the color change after outdoor weathering for six months. The colorimetric properties were measure according to the CIE-L*a*b* 1976 system. The results indicated a direct relation between the proportion of Sequoia sempervirens wood particles used in the blend and the red pigment values (a*) and an indirect relation with the yellow pigment (b*). Thus the final color of a particleboard can be predicted by controlling the amount of particles from the different species used in particleboard production. However, natural weathering for 4 months is sufficient to decrease a* and b* values and eliminate the color difference between the particleboards.

Dendrometry parameters and mechanical resistance of Eucalyptus clone trees in areas subject to wind

This work was developed in order to evaluate the mechanical breakage of trees and its relation to the dendrometric characteristics, the wood specific gravity and bending (MOE, MOR and work to maximum load) in order to select clones more tolerant to wind action. The mechanical resistance of the trees to break was determined by the simulation of the effect of wind on them, getting the strength to break the trees. Ten clones of Eucalyptus urophylla x Eucalyptus grandis hybrid with 30 and 35 months in forest plantations in the lowlands were evaluated. The average force to break the trees was 79.00 kgf, the average height of 2.99 m. The average wood density was 0.40 g / cm3. MOE, MOR and work to maximum load in static bending tests were equal to 60,965 kgf / cm2, 544 kgf / cm2 and10 J, respectively. The CNB017 showed the best results in the resistance of trees to break test and in the physical and mechanical parameters evaluated, being considered the most suitable clone for the areas subjected to wind breakage of trees.

Avaliação Colorimétrica de Aglomerados Produzidos com Partículas de Madeira de Sequoia sempervirens e Pinus taeda Submetidos ao Intemperismo Natural / Outdoor Weathering Evaluation of Particleboards Manufactured from Sequoia sempervirens and Pinus taeda Wood

The aim of this work was to establish the effect of using different amounts of Sequoia sempervirens and Pinus taeda wood particles on the colorimetric properties of particleboard and to evaluate the color change after outdoor weathering for six months. The colorimetric properties were measure according to the CIE-L*a*b* 1976 system. The results indicated a direct relation between the proportion of Sequoia sempervirens wood particles used in the blend and the red pigment values (a*) and an indirect relation with the yellow pigment (b*). Thus the final color of a particleboard can be predicted by controlling the amount of particles from the different species used in particleboard production. However, natural weathering for 4 months is sufficient to decrease a* and b* values and eliminate the color difference between the particleboards.