Effect of High Temperature on the Change in Color, Dimensional Stability and Mechanical Properties of Spruce Wood

Abstract

In this study the effect of high temperature on mechanical properties, dimensional stability and color of spruce was investigated. Wood specimens conditioned at different relative humidities (50, 65, 80 and 95%) were subjected to heat treatment at 200°C for 2, 4, 8, 10 and 24 h and at 100, 150 and 200°C for 24 h. Color changes were measured in the Minolta Croma-Meter CR-300 color system. Bending strength and modulus of elasticity were determined according to DIN 52186. The results show that heat treatment mainly resulted in a darkening of wood tissues, improvement of the dimensional stability of wood and reduction of its mechanical properties. The darkening accelerated generally when treatment temperature exceeded approximately 200°C. Most of the darkening occurred within the first 4 h of exposure. For the specimens heated to high temperatures, the average decrease in bending strength was about 44-50%, while modulus of elasticity was reduced by only 4-9%. We found that treatment time and temperature were more important than relative humidity regarding the color responses. Strong correlations between total color difference and both modulus of elasticity and bending strength were found. Thus, the color parameters can be estimated quantitatively and used as a prediction of wood strength. KeywordsColor Heat treatment Spruce Bending strength Modulus of elasticity Swelling Moisture content Relative humidity Brought to you by |

Effect of oil impregnation on water repellency, dimensional stability and mold susceptibility of thermally modified European aspen and downy birch wood

“…When wood absorbs moisture from its surroundings, water molecules are inserted between and within the wood polymers (cellulose, hemicelluloses and lignin) forming hydrogen bonds, which causes the wood to swell. During the thermal modification process, degradation of hemicelluloses, modification of lignin, redistribution of extractives, cellulose higher crystallinity content and the reduction of hydrophilic -OH groups in the cell wall result in a significant reduction in the amount of water absorption [7,26]. However, the water repellent properties of TM wood could be further improved after oil impregnation during the post-treatment of the modification process.…”

“…Thermal treatment decreases the number of accessible -OH groups, resulting in a reduced water adsorption and an increase in the dimensional stability [6,7].…”

Alteração da cor da madeira de teca por tratamento térmico

“…De acordo com vários autores (Sundqvist & Morén, 2002;Bekhta & Niemz, 2003;Sehlstedt-Persson, 2005;Esteves et al, 2008), a alteração da cor original da madeira após o tratamento térmico pode ser causada por: 1) formação de produtos oxidativos (por exemplo, quinonas) e produtos da degradação das hemiceluloses e da lignina, os quais migram às superfícies da madeira; 2) remoção ou migração dos extrativos e compostos nutritivos, tais como açúcares de baixo peso molecular e aminoácidos, em direção às superfícies da madeira; 3) aumento no teor de lignina.…”

“…532 Floresta e Ambiente 2014; 21(4):521-534 Lopes JO, Garcia RA, Latorraca JVF, Nascimento AM (Tjeerdsma et al, 1998;Mitsui et al, 2001;Bekhta & Niemz, 2003 O comportamento diferenciado na alteração da cor da madeira de cerne e alburno de teca, após a aplicação dos tratamentos térmicos, pode ser explicado pelos diferentes teores e/ou natureza química de cada tipo de madeira. Os resultados de variação de cor encontrados para a madeira de cerne de teca podem se assemelhar ao resultado obtido por Gouveia (2008) para a espécie de louro-vermelho, cuja madeira também é escura, sendo classificada no grupo das madeiras marrons, tal como o cerne da teca.…”

Comparative analysis of thermally modified and native spruce loaded perpendicular to the grain

“…This process modifies certain structural, mechanical, physical, and chemical wood properties (Boonstra and Tjeerdsma 2006;Windeisen et al 2007), resulting in increased dimensional stability (Popper et al 2005) and durable resistance to fungi and microorganisms (Boonstra et al 2007;Weiland and Guyonnet 2003) on the one hand, and discolouration (Bekhta and Niemz 2003), strength loss (Borrega and Kärenlampi 2008) and a significant odour (Peters et al 2008), on the other hand.…”