Eco-friendly solvent-free waterborne hydroxyacrylate dispersions based on bio-based castor oil hyperbranched polyols for two-component polyurethane coatings with damping performance

An eco-friendly, solvent-free waterborne hydroxyacrylate dispersion was developed using a castor-oil hyperbranched polyester polyol (COHPE) as a reactive diluent, enabling the preparation of two-component waterborne polyurethane (2 K WPU) coatings with intrinsic damping functionality. The COHPE was synthesized via esterification and incorporated into the waterborne hydroxyacrylate system to simultaneously reduce viscosity and enhance processability without the use of volatile organic solvents (VOC). The resulting dispersion (COHPE-WA-30) exhibited excellent colloidal stability and uniform particle sizes, while the cured films demonstrated a break strength of 6.81 MPa, elongation at break of 22.26%, and a static water contact angle of 86.2° ± 0.19°. Dynamic mechanical analysis (DMA) revealed the tan δ value remains greater than 0.3 within the temperature range of 43–101 °C, confirming superior damping performance. Moreover, the solvent-low 2 K WPU coatings achieved excellent adhesion (5B), gloss, and solvent resistance, combined with enhanced thermal stability. This study establishes an environmentally benign and scalable approach for fabricating high-performance 2 K WPU coatings that integrate renewable materials, solvent-low processing, and multifunctional mechanical-damping behavior.