Development of eco-friendly waterborne polyurethane 2 K clearcoats through reactive surfactants and internal particle crosslinking

Abstract

The pressing need to reduce volatile organic compounds (VOCs) emissions has driven advancements in sustainable waterborne coating technologies. However, achieving high mechanical performances and aesthetic qualities, particularly high gloss and transparency, remains challenging for waterborne clearcoats. In this study, a novel acrylic polyol resin tailored for high-performance waterborne two-component (2 K) polyurethane clearcoat systems was developed. Using a reactive surfactant and internally crosslinked particles synthesized via a preemulsion process, we significantly enhanced particle stability, film uniformity, and surface smoothness. By systematically optimizing the crosslinker structure and concentration, superior gloss (improved from 76.8 to 89.3 at 20 degrees) and enhanced mechanical properties (higher indentation hardness and modulus values compared to commercial clearcoat) were achieved. A hydrophilically modified isocyanate crosslinker was incorporated to form a waterborne polyurethane clearcoat through analysis of the blending and film formation processes. Incorporating a hydrophobically modified alkali-swellable emulsion (HASE) thickener improved rheological control, resulting in superior leveling and reduced surface roughness (Ra reduced from 0.05 mu m to 0.03 mu m). Moreover, the scalability of the developed system was demonstrated successfully through the synthesis of a 20 kg batch, retaining excellent gloss and uniform particle distribution comparable to laboratory-scale results. Overall, this study offers an innovative, scalable, and eco-friendly solution for high-performance waterborne clearcoats suitable for sustainable industrial applications.