Lignin-Acrylic Acid Copolymer as an Effective Emulsifier for Oil-Water Emulsion

Oil-water emulsions constitute essential components in a wide range of industries. Despite their extensive use in emulsion systems, synthetic emulsifiers are often associated with environmental concerns and high costs. In this study, lignin-a by-product of the pulping industry-was polymerized with acrylic acid and employed as an emulsifier in a xylene-water system to address this challenge. When testing two lignin-acrylic acid copolymers, the results confirmed that the one possessing a higher molecular weight (7.99 × 10⁵ g/mol) and charge density (4.7 mmol/g) (KL-AA-10) generated xylene-water emulsions with improved stability, and higher viscosity and viscoelastic moduli. These observations were consistent with the greater adsorption of this polymer, relative to the counterparts with a lower molecular weight and charge density at the xylene-water interface, as monitored using a Quartz Crystal Microbalance. The adsorption of KL-AA-10 resulted in the formation of smaller emulsion droplets (D50 = 0.6 µm) within the system, as evidenced by confocal microscopy analysis. This study underscores the potential of lignin as a renewable emulsifier for diverse applications.