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Lignin modification during Eucalyptus globulus kraft pulping followed by totally chlorine free bleaching: a two dimensional nuclear magnetic resonance, Fourier transform infrared, and pyrolysis-gas chromatography/mass spectrometry study

AuthorsIbarra, David ; Chávez Uribe, María Isabel; Rencoret, Jorge ; Río Andrade, José Carlos del ; Río Andrade, José Carlos del ; Gutiérrez Suárez, Ana ; Romero Sánchez, Javier; Camarero, Susana ; Martínez, María Jesús ; Jiménez-Barbero, Jesús ; Martínez, Ángel T.
KeywordsLignin structure
Analytical pyrolysis
Infrared spectroscopy
Eucalyptus globulus
Kraft pulping
Totalli chlorine free bleaching
Paper pulp residual lignin
Issue Date2007
PublisherAmerican Chemical Society
CitationJournal of Agriculture and Food Chemistry 55:3477-3490 (2007)
AbstractChemical modification of eucalypt lignin was investigated during kraft pulping and chlorine-free bleaching by comparing milled-wood lignin, kraft lignin, and enzymatic residual lignins. The syringyl-to-guaiacyl ratio (S/G) from analytical pyrolysis slightly changed during pulping and bleaching (S/G 3-4) but was much higher in the kraft lignin. Semiquantitative HSQC NMR showed that the relative amount of β-O-4' (around 80% side-chains) and resinol-type substructures (around 15%) was only slightly modified during pulping and oxygen delignification. Other minor inter-unit linkages and terminal units were also detected. However, a decrease of resinol substructures (to only 6%) was found after alkaline-peroxide bleaching. The relative amount of surviving linkages in the highly-phenolic kraft lignin was dramatically modified, resinols being predominant. Oxygen delignification did not change inter-unit linkages, but an increase of oxidized units was found in the HSQC aromatic region, in agreement with the higher amount of pyrolysis markers with oxidized side-chains. HMBC NMR correlations showed that the oxidized units after oxygen delignification bore conjugated ketone groups, and conjugated carboxyls after peroxide bleaching. Presence of xylan and lignin-carbohydrate linkage signals was shown by the HSQC spectra of pulp lignins
DescriptionCentro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain, Instituto de Química, UNAM, Ciudad Universitaria, Coyoacán, CP 04510, México, DF, Instituto de Recursos Naturales y Agrobiología, CSIC, PO Box 1052, E-41080 Seville, Spain, CIT, ENCE, Ctra. Campañó, Ribeiro Vao, E-36157 Pontevedra, Spain; E-mail address: ATMartinez@cib.csic.es (A.T.Martínez
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