Modification of the lignin structure of eucalypt feedstocks during chemical deconstruction by kraft, soda-AQ and soda-O2 processing

The modification of the lignin structure in an eucalypt feedstock after alkaline deconstruction by the kraft, soda-AQ and soda-O2 processes was assessed. For this purpose, the residual lignins isolated from the pulps at kappa levels 50, 35, 20 and 15 were analyzed by different analytical techniques, including 2D-NMR, P-NMR and SEC (size exclusion chromatography). In addition, dissolved lignins precipitated from the black liquors of the kraft and soda-AQ processes at kappa 20 and 15 were also analyzed. The distribution of the different lignin substructures in the residual lignins was similar to that in the native lignin, although with a drastic reduction in their content. This reduction was more evident in pulps with lower kappa number due to the more drastic pulping conditions.