Uniformidade e estabilidade da cor da madeira termorretificada de Tectona grandis L. f.

• Autor(a) principal: Lopes, Juliana de Oliveira
• Data de Publicação: 2012
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRRJ
• Texto Completo: https://tede.ufrrj.br/jspui/handle/jspui/1530
• topic: CIE-L*a*b* system; accelerated aging; photodegradation of wood.; sistema CIE-L*a*b*; envelhecimento acelerado; fotodegrada??o da madeira; Recursos Florestais e Engenharia Florestal

The teak wood (Tectona grandis L. f.) from young plantations (12 years old) has some undesirable characteristics in terms of color uniformity as well as presenting a high proportion of sapwood, which is distinguished from heartwood by the lower durability and light color. In addition, teak wood has color change when exposed to ultraviolet (UV) radiation, which depreciates the product over time. Heat treatments can be applied to change, standardize and stabilise the color of the wood, thus adding more value to the final product. In this context, the objectives of this study were: (1) to determine the effect of spacing between trees on the physical properties (density and moisture content) and the original color of wood, (2) to determine the color change of wood after heat treatments, (3) to evaluate the color uniformity of the wood (pieces containing heartwood and sapwood) after heat treatments and (4) to evaluate the color stability of heat-treated wood after UV radiation in accelerated aging conditions. Nine trees from three different levels of spacing (4 x 2 m, 5 x 2 m and 6 x 2 m) were used, with three trees per spacing. Samples of 150 x 75 x 20 mm were produced and divided into three groups: I: samples with a predominance of heartwood (? 75% heartwood in relation to sapwood), II: samples with 100% of sapwood and III: samples with approximately 50% heartwood and 50% sapwood. The groups I and II were used to determine the physical properties, wood color changes before and after heat treatments and color stability after exposure to UV radiation, whereas those of group III were used to determine the color uniformity after heat treatments. Heat treatments were performed in a laboratorial electric oven from Linn Elektro Therm under two temperatures: 180 and 200?C. Color measurements were performed using the portable spectrophotometer CM 2600d in the CIE-L*a*b* space. The accelerated aging test was performed in a QUV/Spray from Q-Lab chamber. The total cycle of exposure to UV radiation was 168 hours, and color measurements were taken to every 42 hours. The spacing affected the physical properties and the original color of wood. The heat treatment affected more the density of heartwood than sapwood. Heartwood and sapwood presented an average decrease of the 52% in equilibrium moisture content after heat treatments. Heartwood and sapwood had the same lightness pattern at the different spacings. After the heat treatment, wood had a loss of lightness, becoming darker, and this was more pronounced in the treatment at 200?C. Heartwood and sapwood presented different behavior for the coordinates a* and b* depending of spacing, before and after heat treatments. There was a greater formation of red hue and loss on yellow hue of heartwood and sapwood treated at 200?C. Heat treatments caused a higher color change on sapwood than heartwood, which provided greater uniformity to the pieces of wood with heartwood and sapwood. The color of sapwood heat-treated at 180oC woods had higher stability at UV radiation, thus demonstrating the potential of heat treatment to obtain products of higher added value.