Effect of heat treatment intensity on wood chemical composition and decay durability of Pinus patula

Abstract

Heat treatment is an effective method to improve biological resistance of low natural durability wood species. The aim of this study was to enhance the decay resistance of Pinus patula, an African low natural durability softwood species, via wood thermal modification technique. Heat treatment was performed on wood specimens under inert conditions at different heat treatment intensities to reach mass losses of 5, 10 and 15%. Heat treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta. The wood chemical and elemental composition was determined as well as extractives toxicity before and after wood thermal modification to understand the reasons of durability improvement. The treated specimens exhibited a significant increase in their durability against wood decay in line with the severity of the treatment. Wood holocellulose was found to be distinctly more sensitive to the heating process than the lignin constituent. In addition, obvious correlations were observed between weight losses recorded after fungal exposure and both holocellulose decrease and lignin ratio increase. The same correlations were observed with the elemental composition changes allowing using the observed differences for predicting of wood durability conferred by heat treatment. Furthermore, no significant differences were M. Pétrissans · P. Gérardin ( ) observed between the toxicity of Pinus patula wood extractives before and after its thermal modification. Einfluss der Stärke der Wärmebehandlung auf die chemische Zusammensetzung und die Dauerhaftigkeit von Kiefernholz (Pinus patula)Zusammenfassung Wärmebehandlung ist eine effektive Methode zur Verbesserung der biologischen Resistenz von Holzarten mit geringer natürlicher Dauerhaftigkeit. Ziel dieser Studie war es, die Fäuleresistenz von Pinus patula, einer afrikanischen Nadelbaumart mit geringer natürlicher Dauerhaftigkeit, durch eine Wärmebehandlung zu verbessern. Dabei wurden Prüfkörper unter Schutzgas mit unterschiedlicher Intensität wärmebehandelt, um Masseverluste von 5, 10 und 15 % zu erreichen. Die wärmebehandelten Prüfkör-per wurden einem Befall mit dem Braunfäulepilz Poria placenta ausgesetzt. Die chemische und Elementzusammensetzung des Holzes sowie die Extraktstofftoxizität wurden vor und nach der thermischen Behandlung bestimmt, um die Gründe der verbesserten Dauerhaftigkeit herauszufinden. Die Dauerhaftigkeit der behandelten Prüfkörper stieg in Abhängigkeit der Behandlungsintensität signifikant an. Die Holzholocellulose reagierte wesentlich stärker auf die Wär-mebehandlung als das Lignin. Dabei wurden deutliche Korrelationen zwischen dem Masseverlust und dem Holzcelluloserückgang sowie dem Anstieg des Ligninanteils festgestellt. Die gleichen Korrelationen ergaben sich für die Änderung der Elementzusammensetzung, wodurch die Verwendung der beobachteten Unterschiede zur Vorhersage der Dauerhaftigkeit von wärmebehandeltem Holz möglich ist. Des Weiteren ergaben sich keine signifikanten Unterschiede zwischen der Toxizität der Holzextraktstoffe von Pinus ...

Effect of the Brazilian thermal modification process on the chemical composition of Eucalyptus grandis juvenile wood: Part 1: Cell wall polymers and extractives contents

“…This result is in accordance with those of other studies of Eucalyptus species (Brito et al 2008, Esteves, Graça andPereira 2008) and other species (Esteves et al 2011, Hill 2006, Kamdem et al 2002, Mohareb et al 2012.…”

“…It is extensively reported in the literature that the extractives content of thermally modified wood increases compared to untreated wood due to degradation of hemicelluloses and lignin (Esteves et al 2008, Esteves et al 2011, Fengel and Wegener 1989, Hill 2006, Mohareb et al 2012, Stamm 1964, Sundqvist 2004. In this particular situation, as can be seen in Table 1, the increase in the total extractives content of thermally modified wood occurred more by hemicelluloses degradation than by lignin degradation.…”

Degradation Mechanism and Chemical Component Changes in Betula platyphylla Wood by Wood-Rot Fungi

“…For C. versicolor and P. betulinus, the lignin content increased slightly but insignificantly, whereas the holocellulose content decreased. These results are similar to those obtained by Mohareb et al (2012). Notably, the white-rot fungus C. versicolor showed a strong ability to degrade cellulose that is comparable with the ability of the brown-rot fungi such as P. betulinus.…”

Control of wood thermal treatment and its effects on decay resistance: a review

“…This author investigated the effect of thermal treatment temperatures (180, 200, 210, 220 and 240°C) and durations on the conferred durability to different European wood species. For the range of temperatures used, wood chemical composition appeared therefore to be a valuable marker of wood durability due to the strong correlations existing between treatment intensity and decay resistance towards Evolution of lignin and holocellulose contents and their respective chemical structures or chemical compositions are directly correlated to Mass Losses (ML) due to thermal degradation reactions, which are also directly correlated to weight losses due to fungal attack (Mohareb et al 2012). Even if mass losses of wood due to its thermal degradation reactions are not always readily available on industrial processes, it seems possible to easily establish calibration curves for given treatment conditions allowing further correlations between elemental composition, treatment intensity and wood decay resistance (Fig.…”