NMR studies Part 3: Analysis of lignins from modern kraft pulping technologies

This paper examines the changes in lignin structure of kraft black liquor samples isolated during and at the end of the cook. Employing a common wood source a series of conventional kraft pulps, kappa numbers 28, 18, and 13 and extended modified kraft pulps, at kappa numbers of 29, 18, and 14 were prepared. The kraft lignins were isolated and characterized using C-13 and H-1-NMR methods. These studies confirmed that the pulping procedure influences the structural features of kraft lignins, including the content of phenoxy groups, beta-O-aryl ether linkages, and condensed lignin units.