Synthesis of a water polyurethane emulsion with high solid content, low viscosity via core-shell method

In this study, the core-shell method was used to prepare water polyurethane (WPU). First, two different prepolymers were synthesized; one contained a hydrophilic group (prepolymer A), whereas the other one had none (prepolymer B). Then, the two prepolymers were mixed at a certain ratio and emulsified to obtain a WPU emulsion. The effect of hydrophilic group content in prepolymer A on the emulsion properties was investigated and compared with the WPU properties prepared via one-pot method. Transmission electron microscopy analysis showed that latex particles with core-shell structures were formed. Results showed that the WPU particle size distribution was narrow. As the content of hydrophilic groups in prepolymer A increased, the emulsion solid content decreased, and the viscosity increased, which was inconducive for the preparation of a WPU with high solid content and low viscosity. When the prepolymer A/prepolymer B mass ratio was 1.2:1, and the hydrophilic group content in prepolymer A was 3%, a WPU with good stability with the solid content of 55.3% and the viscosity of 187.4 mPa s was prepared via core-shell method.