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Tectona grandis is the second most important species for reforestation in Costa Rica, and any improvement in its industrialization process is important, especially the drying process. Lumber obtained from a plantation of 12-year-old T. grandis trees was used to evaluate three drying schedules that include integrated steaming processes to determine the combined effect of the steam-drying system on the dried lumber. The variations in the moisture content (MC) and drying rate (DR) with drying time (DT) both before and after the steaming process were modeled mathematically for boards that have a flat and quarter grain pattern. For both types of boards that were dried with and without steaming, a relationship between MC and DT was observed. There was inflexion at 40%, and two mathematical models were computed. Additionally, the relationship between DR and DT for boards with flat and quarter grain patterns was not affected by the steaming process, and an inflection point was observed at 30 h (40% MC for...

Physical and mechanical properties were evaluated on cross-laminated panels (plywood) fabricated with three plantation species (Cordia alliodora, Gmelina arborea and Vochysia ferruginea) from tropical climates in Costa Rica. The panels were glued with urea-formaldehyde resin modified with nanoclay at four concentrations (0.75, 1.00, 1.50 and 2.00 per cent) and unmodified resin. It was determined that addition of nanoclay to urea-formaldehyde adhesive positively decreased moisture absorption and swelling of the plywood panel with statistical significance. However, nano-modification did not have a significant effect on the density and specific weight of plywood. Nano-modification of urea-formaldehyde resin with nanoclay at 0.75 per cent improved the Module of rupture and Modulus of elasticity in flexure parallel to surface in the three species, also increasing mechanical resistance to strains in parallel tension, shear and compression. By means of electronic microscopy, it was evidenced that the nano-modified adhesive became diffused at the inside of the cellular structure of wood in a better way, allowing for the generation of a transition zone that increased the mechanical properties at the macro level. According to the properties evaluated, it was determined that 0.75 per cent is the optimal percentage to use of nanoclay on urea-formaldehyde resin.

De acuerdo con las normas ASTM D 2395-02 y D 143-94, se determinó la contracción total y normal en dirección radial (CR), tangencial (CT) y volumétrica (CV) y el coeficiente CT/ CR total y normal de Acacia mangium Willd., Tectona grandis L. f. y Terminalia amazonia A. Chev, maderas provenientes de plantación. También se determinaron algunas propiedades físicas como peso específico básico (PEB), PE12% y PEanhidro, densidad verde (DV) y normal (DN), punto de saturación de la fibra (PSF) y contenido de humedad (CH). Algunos criterios de clasificación, propuestos por otros investigadores, se aplicaron para categorizar la estabilidad dimensional y propiedades físicas de estas especies. Se encontró que la CR, CT, CV totales y CTtotal/CRtotal tienen diferencias significativas entre especies, al igual que las propiedades físicas PEB y PSF. El índice CTtotal/CRtotal indicó que T. grandis tiene mejor estabilidad dimensional. La relación lineal (R2= 0.7769) indicó que el PSF es un buen indicador de la magnitud de la CVtotal. Las especies de plantación de este estudio comparadas con las del bosque natural tienen estabilidad dimensional similar pero menor PEB.

In this study, Eucalyptus nitens species was nano-characterized to determine variability in nanomechanical properties within the cellular ultra-structure between the bark and wood fibers. Three factors, including site (2 levels), family (2 levels) and fiber type (bark and wood) were analyzed using three response variables, including the elastic modulus (E), hardness (H) and ductility ratio (E/H) in the middle lamella (ML) and the cell wall within the S2 layer. The results indicated significant differences for E S2 and H S2 when comparing fiber types: E S2≈12.52 GPa and H S2≈0.31 GPa for wood fiber and E S2≈10.81 GPa and H S2≈0.26 GPa for bark fiber. There is not statistically significant difference in ductility ratio (E/H) in S2 and ML between fiber types. These results indicate that bark and wood fibers can be used together or separately in the development of new composite materials and engineering products.

Wetwood is commonly reported in temperate species but not so in tropical species. In an old Gmelina arborea Roxb. plantation, wetwood was identified by a darker colour compared with the rest of heartwood; by a higher moisture content (average 182%); and a lower specific gravity (0.34, compared with 0.38 for sapwood and heartwood). Tangential shrinkage was 3.7%, which was significantly higher than that of heartwood and sapwood. Radial shrinkage was not significantly different between wetwood and sapwood, but it was significantly greater (2.6%) in wetwood than in heartwood (1.8%). Wetwood had a significantly higher pH than normal wood, but ash composition was similar to that of normal wood, with the exception of the amounts of iron and potassium. Wetwood and sapwood were less decay resistant than heartwood. Wetwood required less time than heartwood to reach equilibrium moisture content, but more time than sapwood. The tangential and longitudinal diffusion coefficients of wetwood were significantly higher than those of heartwood and lower than those of sapwood. In the radial direction sapwood showed a faster drying rate than wetwood but there was no significant difference between wetwood and heartwood.

Gmelina arborea is one of the most important species for plantation in tropical areas. However, high variability in final moisture content (MCf) is a problem in the drying process. This study sought to determine the variability in MCf in relation to distance from the pith (DP), and anatomic elements. Boards of 1.2 cm in thickness obtained from bark to the pith from 15-year-old plantation trees were dried in a pilot kiln. Anatomical characteristics, initial moisture content (MCi), and specific gravity (SG) were also determined. Pearson correlation matrix was conducted between MCf and the other variables. DP, fiber length, and ray width were correlated negatively with MCf, while fiber diameter was positively correlated. Other studied anatomical properties showed no statistical correlations. Other wood properties such as SG and MCi showed some influence on MCf. DP can be considered as a good practical predictor for MCf in G. arborea because some wood properties are related to MCf. However, other wood characteristics that are not related with DP also influence MCf, such as the presence of sapwood, MCi variation between and within trees, fiber diameter, and ray width. These results suggest that MCf variation in G. arborea is difficult to determine.

Se estudió la variabilidad en las propiedades morfológicas, físicas y térmicas de la fibra de corteza de Eucalyptus nitens (Deane & Maiden) en veinticuatro árboles procedentes de dos sitios y seis familias; mediante técnicas de microscopía óptica convencional, microscopía electrónica (SEM) y análisis termo-gravimétrico (TGA). Dichas propiedades son determinantes para que una fibra lignocelulósica alcance una posible aplicación industrial como material de refuerzo en una matriz termoplástica. Se detectaron diferencias estadísticas significativas en las propiedades de la fibra al analizar el sitio de procedencia de las muestras, la familia y la altura de fuste. Destacan en los resultados de propiedades físicas el espesor promedio de la capa de corteza (4.4 mm), su peso específico (0.757), sus propiedades morfológicas tales como razón longitud/diámetro de fibra (l f/d f= 69.14) y presencia de fibra (45%) en este material. La estabilidad térmica de esta fibra natural hasta los 200ºC y la baja temperatura de fusión de termoplásticos como el polietileno de alta densidad (HDPE); indican que las fibras de corteza de esta especie son una buena opción para aplicarla como material de refuerzo en matrices termoplásticas.

The color of Tectona grandis wood is an attribute that favors its commercialization, however, wood color from fast-growth plantation trees is clear and lacks uniformity. The aim of this work is to characterize steamed teak wood by means of the Fourier transform infrared spectroscopy (FTIR) and [Formula: see text] color systems. Two moisture conditions (green and 50%) and two grain patterns (flat and quarter) of boards were analyzed through the application of different steaming times (0, 3, 6, 9, 12, 15 and 18[Formula: see text]h). The FTIR results showed that the bands at 1158, 1231, 1373 and 1419[Formula: see text]cm[Formula: see text] did not show any change with steaming, whereas the bands at 1053, 1108, 1453, 1506, 1536, 1558, 1595, 1652, 1683, 1700 and 1733[Formula: see text]cm[Formula: see text] presented a decrease in the intensity with the steaming time. The band at 1318[Formula: see text]cm[Formula: see text] was the only one that increased. Lightness ([Formula: see text]) was the most affected parameter, followed by yellowness ([Formula: see text]), while redness ([Formula: see text]) showed the smallest change. Surface color change ([Formula: see text]) presented the lowest value between 3[Formula: see text]h and 6[Formula: see text]h of steam-drying in the boards with flat grain, whereas for boards with quarter grain, the smallest [Formula: see text] value was obtained after 18[Formula: see text]h of steaming.