Characterisation of laccase-mediated lignin polymerisation: implications for molecular weight, thermal stability, and electrical properties

Kraft lignin was oligomerised using a bulk laccase solution in varying amounts of buffer and ethanol solvents. The activity of laccase and kinetic parameters was analysed by adjusting the buffer pH and ethanol:buffer ratio. The qualitative weighted average molecular weight (Mw) distribution showed significant variation when ethanol (40:60) solvent was used. GPC analysis confirmed the presence of fractions with higher molecular weight, where the Mw after 30 min was 7859, compared to 90 min in the buffer medium, where Mw was only 1779. These condensed units exhibited lower antioxidant values, characteristic of a polymerisation reaction.