NMR studies - Part 5: Nature of residual lignin in kraft pulps

Recent advances in kraft pulping have extended the degree of practical deli gnification while improving selectivity. Despite these improvements, little is known about the nature of the residual lignin in low-kappa-number kraft pulps. This paper examines the structure of residual lignin for seven conv entional kraft pulps (kappa no. 33-13) and six Lo-Solids(R) kraft pulps (ka ppa no. 29-11). The residual lignin in each pulp was isolated and character ized by proton nuclear magnetic resonance (H-1 NMR). The results of these a nalyses demonstrate that the overall structure of residual lignin is influe nced by both the extent of delignification and the nature of the pulping pr ocess.