Extractive composition and summative chemical analysis of thermally treated eucalypt wood

Abstract

Eucalypt wood (Eucalyptus globulus) was heated in an oven for 2–24 h at 170–200°C and in an autoclave with superheated and saturated steam for 2–12 h at 190–210°C. The chemical composition of untreated wood and thermally treated wood with different mass losses in the range of 1.1–11.9% was studied by summative analysis, and the composition of dichloromethane, ethanol and water extracts was determined by gas chromatography mass spectometry (GC-MS). The hemicelluloses degraded first, mainly regarding the arabinose and xylose moieties. Lignin degraded at a slower rate and cellulose was only slightly affected under severe treatment conditions. The extractive content increased first with heat treatment and decreased later on. Almost all of the original extractives disappeared and new compounds were formed, such as anhydrosugars, mannosan, galactosan, levoglucosan and two C5 anhydrosugars. The most prominent lignin derived compounds were syringaldehyde, syringic acid and sinapaldehyde. The main difference between autoclave and oven treated samples was the appearance of more oxidized extractives for the oven treatment.

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.…”

“…Although the averages of insoluble lignin content did not differ between untreated wood and the treatments at 140 and 160 °C, it is reported in the literature that lignin degradation also occurs at these temperatures (Esteves et al 2008, Esteves et al 2011, Fengel and Wegener 1989, Hill 2006, Sundqvist 2004). So, it is possible that some degradation of lignin occurred in the present study, but at a small level when compared to the degradation of hemicelluloses and the increase in extractives content.…”

“…The thermal modification temperatures used in this work (140, 160 and 180 °C) were not high enough to cause mass loss of cellulose, according to previous information in the literature (Esteves, Graça and Pereira 2008;Esteves, Videira and Pereira 2011;Fengel and Wegener 1989;Sundqvist 2004). Therefore, it is assumed that the process did not cause cellulose degradation, so the difference of holocellulose content among the treatments is believed to be attributed basically to the mass loss of hemicelluloses, which are the most thermally labile compounds of the cell wall structure (Fengel and Wegener 1989, Hill 2006, Stamm 1964, Sundqvist 2004).…”

“…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.…”

“…Some laboratorial scale studies have been performed about thermal modification of eucalyptus wood, mostly Eucalyptus globulus (Esteves et al 2007a, Esteves et al 2007b, Esteves et al 2008 from Portugal, Eucalyptus grandis (Batista and Klitzke 2010, Batista et al 2011, Calonego et al 2010, Moura et al 2012, Pessoa et al 2006, Pincelli et al 2002 and Eucalyptus saligna (Brito et al 2008) from Brazil.…”