Fluorescence Labeling of Technical Lignin for the Study of Phenolic Group Distribution as a Function of the Molecular Weight

A novel analytical approach based on fluorescence labeling was developed in the effort to increase the understanding of phenolic group distribution in technical lignins. Selective derivatization with a fluorophore (dansyl chloride) of lignin phenolic functionalities was quantitatively achieved under mild reaction conditions. Reference acetylated lignin and labeled lignin were analyzed by gel permeation chromatography (GPC) coupled to a UV–vis detector (set at 280 nm) and a fluorescence detector (λ excitation: 390 nm, λ emission: 550 nm) to discern the dansyl-linked phenol response from the lignin aromatic skeleton input. After data elaboration, valuable information about the phenolic group distribution as a function of molecular weight for different technical lignins was gathered. This novel analytical approach is applied to model lignin polymer thermal protection properties, a useful parameter in lignin valorization strategies.