Improved lignin properties and reactivity by modifications in the autohydrolysis process of aspen wood

Autohydrolysis of aspen wood breaks down lignin beta-O-4 linkages via both acidolysis and homolytical cleavage. A simultaneous repolymerization by lignin-lignin condensation is the major reason for the low degree of delignification and the poor lignin reactivity. Modification of the autohydrolysis reaction by the addition of either NaOH or 2-naphthol changes the mechanism such that less acidolysis and fewer lignin-lignin condensation reactions take place, and an almost complete delignification can be achieved. The resulting isolated lignins have a low M., a light color and still contain some of the native beta-O-4 linkages. Lignin from autohydrolysis in the presence of NaOH possesses more carboxylic acid groups, while the addition of 2-naphthol results in a lignin with a large amount of phenolic hydroxyl groups and incorporated naphthalene rings. These types of change are beneficial since the lignin structure becomes much more homogeneous with a greater potential for further upgrading and use. (c) 2007 Elsevier B.V. All rights reserved.