Effect of the Particle Size in Dispersions on the Properties of Waterborne Polyurethane/Casein Composites

Two kinds of aqueous dispersions were prepared from waterborne polyurethane (WPU) and its prepolymer by mixing (M) and grafting (G) with 10 wt % casein, respectively. The resulting dispersions were characterized by using a rotary viscometer and a particle size distribution meter, indicating that the viscosity, Z average size, and polydispersity of the dispersions increased with an increase of the casein content, and the average particle size of the M dispersions (ca. 30−50 nm) was much lower than that of the G dispersions (ca. 50−150 nm). Polyurethane/casein composite sheets were prepared from the dispersions M and G, coded as sheets M and G, respectively. The structure and properties of the sheets were characterized by using infrared spectroscopy, scanning electron microscopy, ultraviolet spectrophotometry, dynamic mechanical analysis, and tensile testing. The results revealed that the sheets M and G all exhibited a certain degree of miscibility, and their tensile strength was much higher than that of th...