Evidence of char formation during wood heat treatment by mild pyrolysis

• Published in: Polymer degradation and stability 2007-06, Vol.92 (6), p.997-1002
• Main Authors: Inari, Gildas Nguila, Mounguengui, Steeve, Dumarçay, Stéphane, Pétrissans, Mathieu, Gérardin, Philippe
• Format: Article
• Language: English
• Subjects: 13C NMR; Applied sciences; Char; Chemical and Process Engineering; Engineering Sciences; Exact sciences and technology; Heat treatment; Holocellulose; Lignin; Polymer industry, paints, wood; Properties and testing; Wood; Wood. Paper. Non wovens
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2007.03.003

The behaviour of wood polymers during heat treatment carried out under inert atmosphere at 240 °C has been reinvestigated to understand the important decrease of the O/C ratio observed in a previous study using X-ray photoelectron spectroscopy (XPS). Heat treatment was performed not only on beech sawdust but also on its lignin and holocellulose fractions obtained after acidic hydrolysis of polysaccharides or delignification with sodium chlorite. CP/MAS 13C NMR spectra indicate as previously reported an important degradation of hemicelluloses after thermal treatment. However, assignments of the signals appearing in the range of 125–135 ppm and 35 ppm attributed up to now to thermal crosslinking of lignin and formation of methylene bridges should be reconsidered. Indeed, heat treatment of the holocellulose fraction indicates quite similar signals showing that these latter are not due to lignin modification. According to the literature, these new signals have been attributed to the beginning of char formation. Determination of Klason lignin and HPLC analysis of the sugars contained in the hydrolysate support the hypothesis of formation of carbonaceous materials within the wood structure during heat treatment by mild pyrolysis.