Modification of Hardwood Veneers by Heat Treatment for Enhanced Colors

Abstract

This research involved the most widely used wood-species of veneers in Hungary (oak, ash, beech, cherry, and maple). The resulting changes in color produced at treatment temperatures between 80 and 200 °C in different treatment times were evaluated using the CIELab color stimulus evaluation system. For higher temperature treatments, a tight functional relationship was observed between the treatment time and the difference in color stimulus. Heat treatments within a temperature range above 160 °C produced visually perceptible results, while color change resulting from heat treatments at lower temperatures was almost imperceptible. For higher temperature treatment a tight functional relationship was observed between the difference in color stimulus and treatment time (r 2 >min. 0.84). Different tree species produced different extents of change in hue depending on the treatment parameters. Among the color components, the perceptible discoloration was mostly produced by the change in the lightness factor (L*). As the treatment temperature rose, the change in the red (a*) and yellow (b*) components was less significant regardless of the species.

Changes in Colour, Strength and Chemical Properties of Oil Heat Treated 18-Years Old Planted Acacia mangium

“…The chemical composition of wood was highly correlated with the lightness of wood especially hemicellulose where decreases in lightness primarily caused by degradation of hemicellulose particularly pentosans (Bekhta & Niemz, 2003;Huang et al, 2012). Moya et al (2012) and Feher et al, (2014) stated a relation between lightness and extractive content in wood. Todorovic et al, (2012) also suggest that MOR correlated with lightness in wood.…”

“…Lignin is related to the red colour in the wood (Aksoy et al, 2011;Feher et al, 2014). While, yellow related with the photochemistry of chemical composition in cell wall including cellulose and hemicellulose, and wherein lignin was caused by lignin parts with quinonoid and stilbene structure (Sundqvist, 2004;Feher et al, 2014).…”

“…It also caused by the organometallic complex in extractive (Sundqvist, 2004). Besides that, greyish appearances in wood are caused by cellulose and hemicellulose (Forsman, 2008;Feher et al, 2014).…”

“…The negative value indicates the decreases in lightness after oil-heat treatment (Mononen et al, 2002;Feher et al, 2014). This resulting from decrement in certain chemical component especially hemicelluloses and lignin (Bekhta & Niemz, 2003;Huang et al, 2012;Razak et al, 2012).…”

“…It is also related to the greater amounts of Brauns' lignin and proanthocyanidins and extractives content of wood (Feher et al, 2014). The yellowish colour was caused by low molecular weight phenolic substances and is tightly connected to the chemical component of cell wall which are cellulose, hemicelluloses and lignin (Chen et al, 2012;Feher et al, 2014). Whereas, the blue colour is a sign of stain where it is due to the photo-oxidation of lignin and extractives with the production of coloured quinine component (Izyan et al, 2010).…”