Enzymatically treated lignin as a water-soluble polymer for the stabilization of carbon inks and emulsions

Lignin is an abundant aromatic biopolymer with high potential for sustainable material applications, but its limited water solubility restricts its use as a molecular dispersant or surfactant. Here, we report the use of enzymatically modified kraft lignin, obtained via bilirubin oxidase (BOD) oxidation, as a water-soluble amphiphilic polymer for the stabilization of carbon black dispersions and oil-in-water emulsions. The enzymatic treatment yields a low-sulfur and high molecular weight lignin fraction readily soluble at neutral pH. Interfacial tension measurements demonstrate adsorption at both air–water and oil–water interfaces. Stable carbon black dispersions are obtained over a broad concentration window, with a defined phase boundary controlled by the carbon black/lignin ratio. The dispersions exhibit rheological properties compatible with printing technologies. Dried films display electrical conductivity of 35 S m −1 , confirming the formation of percolated carbon networks. In parallel, the modified lignin stabilizes oil-in-water emulsions with remarkable resistance to thermal aging and centrifugation, outperforming sodium dodecyl sulfate under identical conditions. These results demonstrate that enzymatically treated lignin combines amphiphilicity and colloidal stabilization, providing a sustainable alternative to synthetic surfactants for emulsions and advanced carbon-based formulations.