Performance of Side-Streams from Eucalyptus Processing as Sources of Polysaccharides and Lignins by Kraft Delignification

Abstract

The performance of bark, branches, sawdust, forest biomass, and short-rotation eucalyptus in kraft delignification to produce polysaccharides and lignin is reported and discussed. A positive correlation was found between pulping severity required for delignification and lignin reactivity. Among all, branches feedstock is the best source of polysaccharides due to the high pulp yield (48-54%) with a satisfactory delignification degree. Branches lignin was characterized for the first time, evaluating syringyl/guaiacyl/p-hydoxyphenyl (65:22:13), beta-O-4 units (71/100C(6)) and condensed structures (12%). Kraft lignins (KL) were isolated from black liquors, including industrial one, and analyzed by NMR demonstrating remarkable differences. Among all, bark KL reveals the highest depolymerization (lowest beta-O-4 content, 18/100 C-6) and condensation (50%) as a consequence of higher active alkali required for pulping. Sawdust and branches KLs have similar degree of condensation, but the former revealed slightly less beta-O-4 (25/100 C-6) and more hydroxyl phenolic groups (6.6 mmol/g) than branches KL (28/100C(6), 5.9 mmol/g).