Zwitterionic oligomer-grafted lignin as a multifunctional Pickering stabilizer for waterborne methacrylic coatings with enhanced photo-oxidative durability

Lignin is an attractive renewable candidate for the development of sustainable Pickering stabilizers; however, its practical application is often limited by poor colloidal stability, strong self-association, and limited compatibility with polymer matrices. In this work, a zwitterionic functionalization strategy was developed by grafting poly(3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate) (DMAPS) chains onto Kraft lignin particles through a UV-induced thiol–ene reaction. The surface-modified lignin structures were subsequently employed as Pickering stabilizers in surfactant-free miniemulsion polymerization of methyl methacrylate and butyl methacrylate, yielding stable waterborne latexes and homogeneous composite coatings. Compared with unmodified lignin, the L/DMAPS hybrids improved filler dispersion, enhanced filler–matrix interactions, and promoted the formation of a more integrated microstructure. Accelerated UV-aging studies demonstrated significantly reduced oxidation, smaller changes in surface wettability, and improved resistance to photo-oxidative degradation. The optimal 1:1 L/DMAPS formulation provided the highest photostability, highlighting the synergistic combination of lignin UV-screening capability and zwitterionic surface protection. The zwitterionic modification transformed lignin from a conventional Pickering stabilizer into a multifunctional interfacial component that not only stabilized the miniemulsion but also improved polymer–filler interactions, leading to coatings with enhanced viscoelastic performance (higher storage modulus and Tg), reduced solvent uptake, and superior resistance to photo-oxidative degradation.