Mechanistic insights on the laccase-catalysed modification of technical lignins. A new solution for an old issue

A strategy to understand the chemistry of the changes occurring on kraft and Organosolv lignins during their laccase-catalysed oxidation has been devised in this work. This approach has been based on two steps: (a) fractionation, and (b) enzymatic oxidation. The laccase-oxidised technical lignins as well as their low molecular weight compounds (LMWC) derivatives have been fully characterised via 31P NMR, GPC, and GC-MS. From one side, LMWC formation has been rationalised. From the other side, the variation in the molecular weight of lignins after the enzymatic treatment coupled with the decrease in the content of the various hydroxylated moieties has suggested polymerising/depolymerising activity for the enzyme depending on the nature of the treated substrate. For both technical lignins a more recalcitrant fraction to the action of laccase has been identified, and the overall chemical transformations occurring during the laccase-catalysed have been identified.