Surface Fractal Dimensionality and Hygroscopicity for Heated Wood

Abstract

The relationship between hygroscopicity and the microsurface of heated wood was examined using the fractal surface dimensionality. The hygroscopicity of heated wood decreased with the increase in heating temperature to 250°C, and then decreased again above 350°C after increasing up to 350°C. This change corresponded to chemical changes in the wood, especially a reduction in hydroxyl groups, up to 250°C, and to the temperature dependence of the fractal dimensionality calculated from nitrogen gas adsorption above 250°C. The fractal dimensionality increased gradually from 100 to 250°C, followed by a rapid increase above 250°C with a peak at 350°C, and leveled off above 400°C. From the results, it is concluded that hygroscopicity of heated wood changes at 250°C and that it is dependent upon the chemical properties of wood below 250°C and upon the surface complexity above 250°C.

Effect of Heat Treament on the Physical and Mechanical Properties of Compression and Opposite Wood of Black Pine

“…The hemicelluloses degrade first (between 160 and 260 °C) due to their low molecular weight and their branching structure (Fengel and Wegener, 1984). Heat treatment decreases the equilibrium moisture content of wood (Nakano and Miyazaki 2003;Ates et al 2009;Wang and Cooper 2005;Metsa-Kortelainen et al 2006), improves its dimensional stability (Yildiz 2002;Bekhta and Niemz 2003;Gonzalez-Pena et al 2004;Wang and Cooper 2005), but decreases mechanical properties Kim et al 1998;Kubojima et al 2000;Bengtsson et al 2002;Bekhta and Niemz 2003;Shi et al 2007). Although wettability decreases (Petrissans et al 2003;Follrich et al 2006;Hakkou et al 2005), the gluing process can be adapted for treated wood (Militz 2002).…”

Improvement of Dimensional Stability of Acacia mangium Wood by Heat Treatment: A Case Study of Vietnam

“…In addition, a very important component with the most hydrophilic ability in the wood, the free hydroxyl (-OH) groups, they are normally placed in the structure of cellulose and hemicellulose, during the heat treatment process, due to thermal release process, the hydrolysis reaction and the formation of cross-linking make the contents of hemicellulose and cellulose in the amorphous region decrease, resulting in a reduction of the number of free hydroxyl groups, therefore, the water uptake of the wood decreased, the water repellent efficiency increased. The reduction in the content of hydroxyl (-OH) groups in the heat treated wood has been demonstrated in many studies (Nakano and Miyazaki 2003) (Fig. 5).…”

“…Hygroscopic property of wood after the heat treatment is closely related to changes in the chemical composition of wood, especially hemicelluloses and crystallization in wood. Water absorption of the wood after the heat treatment is reduced because a large number of hydroxyl groups (-OH) of the carbon-hydrogen compounds decreas (Nakano and Miyazaki 2003). Tuong and Li (2011) examine the change of chemical structure and some properties of Acacia hybrid wood after the heat treatment processes in an N2 gas protection environment with a treated temperature of from 210 o C to 230 o C, the results showed that, after the heat treatment, a certain amount of hydroxyl groups in the Acacia hybrid is decreased, along with the reduction of hygroscopic property and the improvement of dimensional stability of the wood.…”

Water absorption thermodynamics in single wood pellets modelled by multivariate near-infrared spectroscopy

“…Such surfaces of intact wood have fractal dimensions ranging between 2 and 3 (Fan et al 1999;Liu and Furuno 2001;Nakano and Miyazaki 2003) and they form absorption sites for water. Such surfaces of intact wood have fractal dimensions ranging between 2 and 3 (Fan et al 1999;Liu and Furuno 2001;Nakano and Miyazaki 2003) and they form absorption sites for water.…”

“…Differential heat of sorption in the wood-water system has been studied by calorimetry (e.g., Kelsey and Clarke 1956), by the isosteric method based on the Clausius-Clapeyron equation and sorption isotherms (Stamm 1964;Hartley and Avramidis 1993;Yasuda et al 1995), and by the fractal-geometry method (Jaroniec 1990;Fan et al 1999;Nakano and Miyazaki 2003;Cao and Kamdem 2004). To better understand the term differential heat (-DH), one might say that the adsorption of the first gram of water vapour in a large quantity of wood at 0% water content, i.e., vapour adsorbed in infinitesimal amounts by oven-dry wood, produces ca.…”