Laccase-catalyzed oxidative modification of lignosulfonates from acidic sulfite pulping of eucalyptus wood
authors Magina, S; Barros-Timmons, A; Evtuguin, DV
nationality International
journal HOLZFORSCHUNG
author keywords concrete; Eucalyptus globulus; laccase; lignosulfonates; oxidative polymerization; plasticizers; sulfite pulping
keywords RESIDUAL LIGNIN; MODEL COMPOUNDS; POLYMERIZATION; SYSTEMS
abstract Lignosulfonates (LS) from acidic magnesium-based sulfite cooking of Eucalyptus globulus wood were modified via laccase-catalyzed oxidative treatment with the aim to improve their performance as plasticizing additives in concrete formulations. The target parameters were the increment of molecular weight (M-w) and the amount of oxidized groups. The laccase-assisted oxidation under optimized conditions (40 degrees C, pH 4.5, enzyme loads of 83-500 U g(-1) for 90 min) allowed M-w increment up to 11-fold and almost doubled the amount of carbonyl and carboxyl groups without using any mediators. Modified LS maintained their solubility in water and possessed a zeta-potential close to that of initial LS. The characterization of modified LS has been carried out by ultraviolet-visible (UV-Vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and quantitative C-13 nuclear magnetic resonance (NMR) spectroscopy, and the sulfonic and phenolic groups were assessed by conductometric titration. It was concluded that IS polymerization occurred mostly via the formation of new aryl ether bonds (two thirds of the modification) and biphenyl bonds (the remaining third). However, part of the newly formed bonds of unknown origin are temperature labile and cleaved during the concentration of LS at pH 4 and 80 degrees C under vacuum, which led to the reduction of the M-w of the modified lignin to almost one third.
publisher WALTER DE GRUYTER GMBH
issn 0018-3830
year published 2020
volume 74
issue 6
beginning page 589
ending page 596
digital object identifier (doi) 10.1515/hf-2019-0272
web of science category Forestry; Materials Science, Paper & Wood
subject category Forestry; Materials Science
unique article identifier WOS:000541917500006
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journal impact factor 1.826
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