Magnetic Resonance Studies of Thermally Modified Wood

Abstract

Summary Thermal modification of wood produces a wood material with many interesting properties, such as enhanced dimensional stability, lower equilibrium moisture content and increased biological durability. Changes in the chemical structure of pine (Pinus sylvestris) caused by thermal treatment were investigated by studying various components of wood using 13C CPMAS NMR spectroscopy. Electron spin resonance (ESR) spectroscopy on the same set of samples was used to study the formation and stability of free radicals formed during the treatment. The most remarkable changes revealed by solid state NMR were the increase in relative crystallinity of cellulose and destruction and deacetylation of hemicelluloses. Changes in the lignin fraction were mostly registered as diminishment in the methoxyl content, although the intensity of the aromatic region increased relative to the carbohydrate fraction during the treatment. Increase in the intensities of the ESR signals from thermally treated wood samples proves the formation of stable free radicals. In addition, radical formation is believed to take part in condensation reactions leading to crosslinks within the lignin and possibly between lignin and other wood components. Both of the methods used indicate that the changes are most remarkable when the treatment temperature is over 200°C.

Effect of thermal treatment on the chemical characteristics of wood from Eucalyptus grandis W. Hill ex Maiden under different atmospheric conditions

“…The lignin proportion increased as a function of increasing maximum temperature in the thermal treatment (Table 2, C1; r = 0.3996), confirming findings obtained by Brito et al (2008), Kamdem et al (2002) and Sivonen et al (2002). This result BARRICHELO, 1979).…”

“…There is no evidence in literature of the possibility of cellulose degrading and volatilizing in the range of maximum temperatures being tested (up to 200°C). Hemicelluloses, on the other hand, the constituent parts of which were fully or partially eliminated with thermal treatment (Figure 4), already show volatilization and degradation in the range of temperatures being used (BRITO et al, 2008;CANAS et al, 2007;SIVONEN et al, 2002). Given that cellulose, which remains virtually intact at temperatures below 200°C, is composed of glucose, it is expected that the amount of this monosaccharide also remain intact in the thermally treated samples, which leads to a relative increase in the proportion of this carbohydrate in samples.…”

Influence of production variables and starting material on charcoal stable isotopic and molecular characteristics

“…The conversion of carbohydrates, protein, lipids and lignin to char produces similarities in ultimate structure, for example the characteristic 13 C-CP-SSNMR signal at ~120-130ppm is produced by thermal degradation of both lignin and cellulose (Sivonen et al, 2002;Wikberg and Maunu, 2004;Soares et al, 2001). A higher contribution of C derived from cellulosic structures to the mangrove charcoal developed in the initial stages of production, may therefore explain a lower wood-charcoal δ 13 C offset in this species.…”

Novel hydrophobization of wood by epoxidized linseed oil. Part 1. Process description and anti-swelling efficiency of the treated wood

“…Regarding W TM , it is well known that, during thermal modification, AA liberated from hemicelluloses catalyses carbohydrate cleavage and leads to a reduction in the degree of polymerization of carbohydrates and formation of new ether linkages between lignin at high temperatures (Tjeerdsma et al 1998;Sivonen et al 2002;Nuopponen et al 2004;Tjeerdsma and Militz 2005;Windeisen et al 2009). Thus, the values of ASE′ for TM samples do not reflect the real reactions occurring in the cell wall during thermal modification.…”