Recent advances in lignins: fundamentals and applications

Lignin, one of the most abundant biopolymers on Earth, is a constant object of numerous fundamental and applied studies. Lignin processing is a challenging task of biorefining. Recent publications mainly concern various directions of valorization of technical lignins, as well as applications of lignin in medicine and pharmacology, 3D printing, synthesis of carbon fibres and biofuels. In the field of fundamental research, studies on lignin biosynthesis are of special attention. The review is devoted to the latest advances in the chemistry of lignin. The currently available data on the structure and biosynthesis of lignin are discussed. The trends in lignin valorization, such as pyrolysis and carbonation, production of composites, copolymers and nanoparticles, synthesis of practically valuable low-molecular-weight substances, production of hydro- and aerogels, etc., are analyzed in detail. It is noted that at present, the practical application of lignin is developing in two directions: valorization of technical lignins per se, without prior depolymerization, and valorization via low molecular weight compounds, mainly monomers, formed through lignin degradation by various methods.