A New Method for Preparing Low Viscosity and High Solid Content Waterborne Polyurethane—phase Inversion Research

In this study, a new emulsification mixing method was proposed to prepare low-viscosity and high-solid content waterborne polyurethane (WPU-H). The phase inversion of the system was determined by online measurement of the torque of the stirrer and the conductivity of the system, and the particle size distribution, viscosity, solid content and stability of WPU-H were also investigated. The results showed that the prepared WPU-H emulsions had a narrow particle size distribution. As the amount of 2,2-Dimethylolpropionic acid (DMPA) in pre-polymers increased, phase inversion was delayed but the system could be reversed easily, thus resulting in an increase in the viscosity of the system and a decrease in the particle size of latex particles. As the acetone amount and the-NCO/-OH molar ratio increased, phase inversion occurred earlier and the system was reversed more easily, thus resulting in a decrease in the viscosity of the system and a double-peak particle size distribution. WPU-H1-c with a single-peak particle size distribution had a solid content of about 51% and a viscosity of 254.0 mPa s, while WPU-H1-b with a double-peak particle size distribution had a solid content of about 54.5% and a viscosity of 205 mPa s.