Characterization of technical lignins by NMR spectroscopy: optimization of functional group analysis by 31P NMR spectroscopy

Abstract

Abstract31P nuclear magnetic resonance (NMR) based on the derivatization reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane is a common approach for the hydroxyl group determination of lignins, but the results are sometimes less reproducible compared to other methods. In the present work, common pitfalls in31P NMR analysis of kraft lignin (KL) and lignosulfonates (LS) are addressed and the results are compared to those obtained by1H NMR spectroscopy. Several experimental parameters are revisited in terms of the reliability of the obtained data, such as the choice of relaxation delay, internal standards, and the best solution technique for the31P NMR analysis of LS. For the first time,31P NMR data of LS are presented based on a new dissolution protocol. The analytical data of a set of lignins consisting of three KLs, one LS, and one milled wood lignin are presented based on the optimized31P NMR approach.