Application of solid-state ¹³C NMR spectroscopy and dipolar dephasing technique to determine the extent of condensation in technical lignins

Solid-state ¹³C NMR spectroscopy and dipolar dephasing technique was used to determine the extent of condensation in various technical lignins. The accuracy of dipolar dephasing method was first investigated with the aid of some lignin model compounds and two various methods to determine the degree of condensation were compared. On the basis of the model compound experiments both methods based on dipolar dephasing technique can be applied to investigate the extent of condensation in lignin. The lignin results indicate that technical softwood lignins, as well as enzymatically isolated wood lignin, are more condensed than milled wood lignin, which is generally assumed to represent native lignin. Residual lignins isolated after oxygen delignification and peroxide bleaching stages were found more condensed than residual lignin in unbleached pulps. In studies of the spent liquor lignins of flow-through kraft pulping the extent of condensation was found to increase as the cooking proceeded.