Effect of adding curcumin on the characterization of castor oil-based waterborne polyurethane coating

Background: This study investigates the use of curcumin as a hydroxyl chain extender in polyurethane (PU) films, which not only absorbs ultraviolet (UV) light but also acts as a polymeric dye. It evaluates the lightfastness of these films and assesses their potential for wood coating applications. Methods: Curcumin-based waterborne PU (CPU) resins were prepared by the prepolymerization method using EDA (Ethylenediamine)/curcumin molar ratios of 9/1, 8/2, 7/3, 6/4, and 5/5. The CPU film was analyzed for its transparency, thermal stability, mechanical strength, and water absorption characteristics. In particular, the wood coating performance and lightfastness of the CPU resin were investigated. Significant findings: The results indicate that higher curcumin content results in an increased proportion of hard segments and hydrogen bonds within the CPU film. Notably, when the EDA/curcumin molar ratio is set to 8/2, the CPU resin exhibits the highest molecular weight, particle size, and cross-linking density, thereby enhancing its tensile strength, Young's modulus, and storage modulus. The results demonstrate the CPU film's ability to absorb UV light, thereby increasing its resistance to light exposure and causing significant color changes in lightfastness tests. CPU resin holds promise for applications as a lightfast yellow coating and a light-sensitive color change indicator.