Abstract
Eucalyptus globulus wood originating from plantations in Uruguay was subjected to continuous batch kraft cooking (CBC), applying mill-like conditions. Pulp samples were taken at different stages of CBC cooking being representative for all three cooking phases. The residual lignin was successfully isolated in a reasonable yield by a new method, the dissolved wood lignin (DWL) protocol, which is based on the total dissolution of ball milled wood and pulp samples in dimethylsulfoxide and N-methylimidazole (DMSO/NMI) followed by precipitation in dioxane/ water to separate lignin and carbohydrate fractions. For comparative reasons, the lignin was also isolated by a conventional mild acidolysis (AL) method. Extensive structural lignin characterization using 1D and 2D NMR revealed that the DWL protocol allows the isolation of less altered lignin than the AL method. During bulk and residual delignification, the S/G ratio of lignin remaining in the fibers continuously decreased, while the content of b-O-4 units and phenolic OH groups remained almost unaffected, suggesting that the CBC process permits enhanced delignification efficiency and good bleachability.Download PDF