A bio-based polypeptide dispersant for improved stability of yellow iron oxide in waterborne coatings

Synthetic iron oxide yellow (IOY) pigment, widely used in paints and coatings, presents dispersion challenges in water-based systems. This study investigates the use of a partially hydrolyzed protein (HP) solution derived from sheep wool as a cost-effective and eco-friendly dispersant for IOY particles in water base pigment concentrate. The dispersion performance of HP was evaluated using zeta potential, TEM, FT-IR spectroscopy, grindometer, spectrophotometer, viscometer, and cryptometer analyses. Results showed that peptides and polypeptides in HP effectively adsorb onto IOY surfaces, providing electrostatic and steric stabilization. FT-IR confirmed chemical interactions between HP and IOY particles. Particle size measurements revealed that IOY pigments in samples 011Y (no dispersant), 045Y (reference dispersant), and 035Y (HP dispersant) had average diameters of 875.2, 852.8, and 841.6 nm, respectively. The HP dispersant exhibited superior dispersion stability and higher color and tint strength with the same opacity than the commercial reference, demonstrating its effectiveness as a sustainable alternative wetting and dispersing agent for iron oxide yellow pigments in water-based coatings. The amphiphilic peptides in HP provide exceptional anti-flocculation performance, forming electrostatic barriers that prevent particle re-agglomeration and maintain colloidal stability through combined charge repulsion and spatial hindrance mechanisms.