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Open Access item Structural modification of eucalypt pulp lignin in a totally chlorine free bleaching sequence including a laccase-mediator stage

Authors:Ibarra, David
Chávez Uribe, María Isabel
Rencoret, Jorge
Río Andrade, José Carlos del
Gutiérrez Suárez, Ana
Romero Sánchez, Javier
Camarero, Susana
Martínez Hernández, María Jesús
Jiménez-Barbero, Jesús
Martínez Ferrer, Ángel Tomás
Keywords:2D-NMR, Enzymes, Eucalyptus globulus, FTIR, HMBC, HSQC, Laccase-mediator system, Paper pulp, Py-GC/MS, TCF bleaching
Issue Date:2007
Citation:Holzforschung 61(6): 634-646 (2007)
Abstract:Modification of eucalypt pulp residual lignin in a totally chlorine free (TCF) bleaching sequence including a laccase-mediator stage, in combination with previous oxygen delignification and subsequent peroxide bleaching, was investigated and compared with a chemical TCF sequence. The enzymatic treatment resulted in a strong oxidative modification, as shown by lignin unit 13C2,6-1H2,6 correlations in HSQC 2D-NMR spectra and presence of oxidized pyrolysis markers. The frequency of inter-unit linkages in residual lignin was also modified, as shown by different side-chain 13C-1H correlations. Moreover, H2,6 correlations with side-chain carbons in HMBC spectra revealed the presence of Cα keto and carboxyl groups in lignin from the oxygen-delignified and especially from the enzymatically-treated pulp, together with normal (Cα-hydroxylated) lignin units. Moreover, the results obtained showed that most of this oxidatively-altered lignin is removed under the alkaline conditions used in the peroxide stage. In this way, the pulp kappa number decreased, and the final residual lignin was more structurally-related to that found before the oxidative stages (although with lower content of resinol structures, and higher presence of aryl-aryl ether structures and carboxyl-bearing terminal units). However, the action of hydrogen peroxide is required to attain the high brightness, over 91% ISO, found in final pulp after the enzyme-containing TCF sequence.
URI:http://hdl.handle.net/10261/3303
ISSN:0018-3830
E-ISSNmetadata.dc.identifier.doi = DOI:1437-434X
???metadata.dc.identifier.doi???:http://dx.doi.org/10.1515/HF.2007.096
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