Abstract
Heat treatment can change wood color without any use of environmentally harmful chemicals, and the efficiency of this process depends on the raw material to be treated. The objective of this study was to evaluate the influence of extractives on the color change of Eucalyptus pellita and Pinus radiata wood during heat treatment. The extractives were extracted in cold water and in dichloromethane as well as totally removed and the wood was treated at 170°C and 200°C for three hours under atmospheric pressure and in presence of air for evaluating the lightness (L*), green-red coordinate (a*), blue-yellow coordinate (b*), color saturation (C) and tonality angle (H) values. Pinus radiata wood was more resistant to discoloration by heat treatment. The removal of total and cold water-soluble extractives before heat treatment changed the L* value of Pinus radiata, a* value of Eucalyptus pellita, and b*, C, and H values of both species. Removal of extractives soluble in dichloromethane did not affect the color of heat treated wood. Thus, understanding the influence of extractives on heat treated wood can allow adapting the raw material to the process for enhancing the applicability of heat treatment for changing wood color.
Highlights
The traditional methods of changing wood color involved use of chemicals, like varnishes and paints, resulting in generation of toluene and xylene (Korkut 2012)
The extractives soluble in dichloromethane were determined according to the American Society for Testing and Materials ASTM D-1108-94 (1994); extractives soluble in cold water according to ASTM D-1110-94 (1994) and the total extractives according to ASTM D-1105-94 (1994)
The proportion of extractives soluble in cold water in E. pellita was higher than in dichloromethane, which represents the pattern for most hardwoods (Moya and Tenorio 2013, Kilic and Niemz 2012), mainly of Eucalyptus species (Morais and Pereira 2012, Zanuncio et al 2014b)
Summary
The traditional methods of changing wood color involved use of chemicals, like varnishes and paints, resulting in generation of toluene and xylene (Korkut 2012). Heat treatment is an environmentally friendly and convenient method for changing the color of wood. This process involves application of heat of 160–230°C on the wood to be treated (Kocaefe et al 2008, Esteves and Pereira 2009, Pétrissans et al 2014). This temperature range degrades the hemicellulose and extractives (Brito et al 2008, Zanuncio et al 2014c). Other factors such as difference between radial and longitudinal section, species and conditions of treatment influences the color of the wood heat treated (Picelli et al 2012, Cademartori et al 2013, Sun et al 2013)
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