Structural changes in lignin of thermally treated eucalyptus wood
authors Louren?o, A; Ara?jo, S; Gominho, J; Pereira, H; Evtuguin, D
nationality International
journal JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY
author keywords Thermal treatment; lignin; solid-state(13)C NMR; analytic pyrolysis; eucalyptus wood
keywords MILD TORREFACTION; HEAT-TREATMENT; STRENGTH LOSS; PYROLYSIS; TRANSFORMATION; CRYSTALLINITY; DISSOCIATION; PERFORMANCE; BIOMASS; MODEL
abstract Changes in the lignin structure of eight eucalypt species (E. botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna,andE. viminalis) upon mild thermal treatment, where the temperature was gradually raised from 160 to 230 degrees C over 3 h, were studied by solid-state carbon nuclear magnetic resonance (C-13 NMR) and after lignin isolation from the wood by acidolysis employing liquid-state 1D and 2D NMR techniques. The molecular weight of the isolated lignins was assessed by size exclusion chromatography (SEC) and their composition by analytic pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). The thermal treatment induced in lignin partial demethylation (up toca.30% from total) and a remarkable reduction in beta-O-4 structures (up toca.60%), in an extent depending on the ratio of syringyl and guaiacyl units of the specific lignins. The lignin molecular weight reduced onlyca.25% under the thermal treatment due to the likely occurrence of condensation reactions by homolytic and heterolytic mechanisms. The noticeable increase in phenylcoumaran (beta-5) and pinoresinol/syringaresinol (beta-beta) structures in lignin after thermal treatment was tentatively explained by their relative thermal resistance and by newly formed structures as the result of radical coupling reactions occurred during homolytic dissociation of the beta-O-4 linkages. Lignins in thermally treated wood contained more than twice phenolic hydroxyls and more aliphatic carboxyl groups than lignins in untreated wood.
publisher TAYLOR & FRANCIS INC
issn 0277-3813
year published 2020
volume 40
issue 4
beginning page 258
ending page 268
digital object identifier (doi) 10.1080/02773813.2020.1769674
web of science category Materials Science, Paper & Wood
subject category Materials Science
unique article identifier WOS:000547126600005
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