Bioactive nanocellulose films by incorporation of enzymatically polymerized lignin nanoparticles.

In the search of new bioactive and biobased films, the use of lignin nanoparticles (LNP) and cellulose nanofibers (CNF) has gained potential relevance in the last years. In this context, an enzymatic and environmentally friendly pretreatment with laccases has been proposed in this work to modify the properties of the developed cellulose-lignin nanocomposite films. Thus, the laccase treatment successfully polymerized kraft lignin as indicated by the increase in weight average molecular weight (from 3621 to 5681 Da) and the reduction in phenol content (from 552 to 324 mg GAE/g lignin). Moreover, this polymerization also caused a significant reduction in the size of the resulting LNP (6.8 ± 2.4 nm) compared to those obtained from untreated lignin (62 ± 22 nm). The incorporation of both untreated and treated LNP conferred antioxidant, antibacterial and UV-shielding capabilities to the final LNP-CNF films, observing higher antioxidant and UV-shielding values with polymerized LNP probably due to its tiny size and conjugated functional groups, respectively. Furthermore, films with 5 % LNP also showed better thermal stability, elongation at break, water vapor permeability and transparency, compared to CNF control films.