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Open Access item 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

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, Ángel T.
Keywords:Lignin structure, 2D NMR, HSQC, HMBC, HSQC-TOCSY, Analytical pyrolysis, Infrared spectroscopy, Eucalyptus globulus, Kraft pulping, Totalli chlorine free bleaching, Paper pulp residual lignin
Issue Date:2007
Publisher:American Chemical Society
Citation:Journal of Agriculture and Food Chemistry 55:3477-3490 (2007)
Abstract:Chemical 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
Description:Centro 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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