Chemical Structure Characterization Methods for Lignin Polymer

Lignin is the second most abundant natural polymer after cellulose in the world; and as a cheap, non-toxic and biodegradable material, it is a good alternative to the petroleum-based polyols. Despite researchers’ efforts to identify the structure of lignin, there are many problems which hinder lignin to be accepted as an appropriate monomer and a competitive alternative to the monomers derived from the crude oil for synthesis of polymers such as polyurethane. One of the major problems related to identification of the lignin structure is lack of well-defined protocols and standard. In this paper, a systematic study has been performed to quantitatively identify the functional groups present in the lignin structure using different techniques such as 1H NMR, 13C NMR, 31P NMR, 19F NMR and UV-VIS spectroscopies and titration. The advantages and limitations of each method havealso been discussed. Moreover, the molecular weight and thermal properties of lignin have been determined by a variety of methods.