Co-grinding wood fibers and tannins: Surfactant effects on the interactions and properties of functional films for sustainable packaging materials

We report on the combination of cellulose nanofibrils (CNF) and condensed tannins from Acacia mearnsii for the development of hybrid, functional films. The tannins are fractionated and concentrated in polyphenolics that are used to functional components in the hybrid materials. Co-grinding of wood fibers with the tannins in aqueous media allows simultaneous fiber deconstruction and in situ binding of tannins on the freshly exposed cellulosic surfaces. Hence, a tightly-bound bicomponent system is produced, which is otherwise not possible if typical adsorption protocols are followed, mainly due to the extensive hydration typical of CNF. A nonionic surfactant is used to tailor the cellulose-tannin interactions. The proposed strategy not only enables the incorporation of tannins with CNF but endows a high and prolonged antioxidant effect of films formed by filtration. Compared to tannin-free films, those carrying tannins have a considerable higher tensile strength and absorb less water. In addition, they show...