Refined Industrial Tannins via Sequential Fractionation: Exploiting Well-Defined Molecular Structures for Controlled Performance in Pickering Emulsions Costabilized with Chitin Nanofibrils

Tannins from Acacia mearnsii (black wattle) are one of the few industrially available sources of nonlignin polyphenols. The intrinsic chemical heterogeneity and high dispersity of industrial tannins complicate their use in applications where the reactivity or colloidal interactions need to be precisely controlled. Here, we employ a solubility-centered sequential fractionation to obtain homogeneous tannin fractions with a dispersity index lower than 2. The well-defined and homogeneous fractions were characterized using NMR and MALDI-TOF and were used to prepare Pickering emulsions by costabilization with chitin nanofibrils. We demonstrate that the emulsion droplet size and associated properties can be tuned by using tannin fractions of varied molar mass, which is a result of fine control over the tannin-chitin complexation interactions at the oil-water interface. In addition to enhancing emulsion stability, the addition of tannin to chitin-stabilized Pickering emulsions has proven to be a viable strategy for engineering the emulsion's viscoelastic properties, as well as introducing antioxidative properties. Overall, we demonstrate a facile method to finely control the properties of industrial tannins and enable their customization to allow their utilization in high-performance multiphase systems.