In this work cross-linking of nanosized colloidal lignin particles (CLPs) from softwood kraft lignin (LignoboostTM) using high redox potential Trametes hirsuta (ThL) and low redox potential Melanocapus albomyces (MaL) laccase was studied by varying enzyme dosage and incubation time. Oxygen consumption method was used to study reactivity of laccases on CLPs including visual detection of red-brown colour due to oxidation of phenolic groups to quinones. Changes in the zeta potentials towards more negative values verified oxidation of CLP surfaces due to carboxyl group formation. Dynamic light scattering measurements showed clear changes in the profiles of CLP size distributions showing cross-linking of the particles after laccase treatments. Changes in surface morphology of enzymatically cross-linked CLPs was studied by atomic force microscopy (AFM). Redispersion of ThL and MaL treated CLPs in tetrahydrofuran (THF) verified that covalent cross-links were formed in CLPs as nanolignin dispersions were stable in organic solvent even overnight. Finally, potential to exploit ultrasound treatment under alkaline conditions with H2O2 for the decolourization of CLPs dispersions was evaluated. It was concluded that enzymatic cross-linking at optimal pH combined with chemical oxidation is an attractive green methodology to prepare spherical, pale and non-smelling CLPs that are stable in organic solvents. As the scale up of both modification methods is feasible, it is anticipated that in the near future CLPs may be exploited as additives in different bionanomaterial applications varying from techno-chemicals to medical sector.

Enzymatic and chemical modifcation of nanosized colloidal lignin particles

253rd National Meeting (2017)

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