Lignin provides structural support, a mechanical barrier against microbial infestation and facilitates movement of water inside plant systems. It is the second most abundant natural polymer in the terrestrial environments and possesses unique routes for the production of bulk and specialty chemicals with aromatic/phenolic skeletons. The commercial applications of lignin are limited and it is often recognized for its negative impact on the biochemical conversion of lignocellulosic biomass to fuels and chemicals. Understanding of the structure of lignin monomers and their interactions among themselves, as well as with carbohydrate polymers in biomass, is vital for the development of innovative biomass deconstruction processes and thereby valorization of all biopolymers of lignocellulosic residues, including lignin. In this paper, we review the major energy crops and their lignin structure, as well as the recent developments in biomass lignin characterization, with special focus on 1D and 2D Nuclear Magnetic Resonance (NMR) techniques.
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