Preparation, properties and application of waterborne hydroxyl-functional polyurethane/acrylic emulsions in two-component coatings

A serious of waterborne hydroxyl-functional polyurethane/acrylic (PUA) emulsions for two-component coatings was prepared by copolymerizing different weight ratios of hydroxyethyl acrylate (HEA)/butyl acrylate (BA) with methyl methacrylate and acrylic-terminated polyurethane dispersion via an emulsion process. The results showed that increasing the weight ratio of HEA/BA led to a decrease in the average particle sizes and a narrowing in the particle size distribution, but an increase in the viscosity of their emulsions. Meanwhile, their films showed increased thermal resistance, adhesion on substrate, tensile strength, and hardness, but decreased water resistance and enhanced wettability. When the emulsions were applied in two-component coatings, their water resistance was greatly improved and the wettability was reduced; in addition, their glass transition temperature, thermal stability, adhesion on substrate, tensile strength, and hardness were further increased. It was suggested that hydroxyl groups of PUA can not only engage in the intramolecular and/or intermolecular hydrogen bonding, but also form covalently crosslinked networks with polyisocyanate in their films.