abstract
The residual lignin (L-R sample) was isolated from unbleached acid sulphite pulp from Eucalyptus globulus with kappa number 18.2 by acidolysis and structurally characterized by wet chemistry and NMR techniques. The main structural features of L-R were compared with lignin isolated from sulphite spent liquor (L-SSL sample) and dioxane lignin (DL sample) from eucalypt wood. L-R contains less sulphonic groups (4.4%) compared to L-SSL (11.3%), and its molecular weight (2200 Da) is very close to that of DL (2600 Da). A part of sulphonic groups is located at the benzylic carbon in beta-O-4' and beta-5' structures. L-R revealed ca. 20% lower abundance of beta-O-4' structures than DL, but ca. 40% higher abundance of these structures than L-SSL. The degree of condensation of L-R was higher than that of DL but lower than that of L-SSL. The condensed structures in L-R mainly originate from C6-linked syringyl units. The structural peculiarities of L-R consisted of the relatively high proportion of syringyl units compared to DL and the strong structural association with he via benzyl ether linkages. The differences in the structure of residual lignins from eucalypt sulphite and kraft pulps have been discussed.
keywords
STRUCTURAL-CHARACTERIZATION; NMR-SPECTROSCOPY; DELIGNIFICATION; IDENTIFICATION; BEHAVIOR; LIQUORS; WOOD
subject category
Forestry; Materials Science
authors
Magina, S; Marques, AP; Evtuguin, DV
our authors
Dmitry Evtyugin
Associate Professor with Aggregation
Sandra Pereira Magina
Researcheracknowledgements
The authors are grateful to FCT (Portuguese Foundation for Science and Technology) for a PhD grant of A.P. Marques (SFRH/BD/31463/2006) and CICECO for the financing of this work within the scope of the FCT grant PEst-C/QUI/UI0062/2013. The financial and technical support from CAIMA - Cellulose Company S. A. (Portugal) - is gratefully acknowledged.