The Laccase Catalysed Tandem Lignin Depolymerisation/Polymerisation

The development of strategies allowing either the production of high value phenolics, or the isolation of properties‐enhanced materials from technical lignins represents a fundamental step in the industrial upcycling of technical lignins. Both aims are met by the strategy presented in the present work, relying on the coupling of solvent‐based fractionation with the oxidative action of a new type of alkaline‐stable genetically modified bacterial laccase. The described approach succeeded in the tandem, high‐yield and selective isolation of valuable lignin‐monomeric compounds (MCs) and high molecular weight and hydrophobicity‐tailored polymerised materials (PMs) from two technical lignins, namely softwood kraft lignin (SKL), and wheat straw organosolv lignin (WSL). With respect to MCs, higher yields as compared to similar studies (up to 17.2 mg/g) were achieved. PMs from SKL samples where characterised by an almost quadrupled Mw, while in the case of WSL the Mw was approximately doubled. Noteworthy, the reaction conditions were optimized in terms of reaction temperature, time, enzymatic loading, and alkalinity for the selective production of single MCs. Most interestingly, technical lignins as well as their fractions and the PMs deriving from their laccase‐catalysed oxidation showed increased hydrophobicity. The present work describes an innovative approach for the enzymatic valorisation of technical lignins allowing the contemporary isolation of high‐value monomeric compounds and oxidatively functionalized polymerised materials. Particular emphasis is given to the implementation of the selectivity of the depolymerisation against simple phenols (e. g. vanillin), and to the tailoring of the hydrophobicity of the polymerised lignin.