Preparation and characterization of a novel low gloss waterborne polyurethane resin

A novel waterborne polyurethane (WPU) resin with low gloss and micro-roughness was synthesized by the prepolymer and self-emulsification method. It was achieved by introducing multi-hydroxyl castor oil and reactive bisphenol A-type epoxy E-44 or E-51 resin to polyurethane prepolymer to form a cross-linking network structural waterborne polyurethane emulsion, which demonstrated the distinctive characteristic of the shear-thinning pseudoplastic fluid with a yield stress. The chemical structures and rough surface morphologies of the WPU films were characterized by FTIR-ATR, LCRS, AFM, SPMS and SEM, respectively. The specular gloss values at 20°, 60° and 85° incident angles were measured, and the values of different kinds of roughness parameters were obtained. The relationship between the gloss and the castor oil content was also discussed in detail. In general, this WPU resin endowed the film with micro-roughness, moderate hardness and good adhesive strength, making it very prospective in substitution for the traditional low gloss coatings.