NMR studies of lignin models, derivatives and bleaching effluents

Abstract

NMR problems related to assignment techniques and relaxation restrict the use of NMR in the structural analysis of lignin. These problems have been addressed in three practical studies in this thesis involving a lignin model trimer and peroxide bleaching effluents from spruce and investigation of correlation times of lignin using NMR relaxation. Complete chemical shift assignments for aliphatic and aromatic protons and carbons of a lignin model trimer were made using one- and two-dimensional NMR experiments. Measurements from experiments using the nuclear Overhauser effect were consistent with conformations of this model compound determined from semi-empirical methods and the published experimental crystal structures of model dimers. Structures present in the peroxide bleaching effluents of spruce ground wood were identified using proton, phosphorus and COSY NMR experiments. Correlation times for acetylated kraft lignin fractions varied between 2.7 x 10' s and 8.1 x 10' s when temperature, molecular weight and concentration were changed. A greater concentration dependence was shown for high mass samples.