The viscosity of waterborne polyurethane emulsion has different distribution range, and the viscosity of waterborne polyurethane emulsion has different requirements when applied in different fields. In addition to adjusting the viscosity by adding thickening agents, it can also affect the viscosity of waterborne polyurethane emulsion from the molecular structure, including the content of hydrophilic groups, the solid content of waterborne polyurethane emulsion, and the degree of neutralization.

The content of hydrophilic groups on the structure of waterborne polyurethane affects the size of emulsion particles and its viscosity. In anionic waterborne polyurethane, when the carboxylic acid hydrophilic groups increase, the size of the colloidal particles decreases, the distribution Narrows, and the viscosity of the emulsion increases, because the force between the colloidal particles and water increases. The viscosity of polyurethane emulsion is related to the hydrophilicity of hydrophilic monomer, particle size and size distribution, and particle density in polyurethane emulsion.

The influence of solid content on the viscosity and particle size of waterborne polyurethane is also obvious. When the solid content of waterborne polyurethane is low, the content of hydrophilic monomer is fixed, and when the solid content increases, the number of particles in the emulsion also increases, and the force between the latex particles and water increases, so the viscosity of the emulsion increases. When the solid content of waterborne polyurethane emulsion is too large, the prepolymer is difficult to disperse in water, the size of latex particles becomes larger, the distribution becomes wider, and the viscosity of emulsion becomes smaller.

The degree of neutralization also affects the viscosity of aqueous polyurethane emulsion. During the preparation of waterborne polyurethane, due to the double action of hydrophilic group and neutralizer, the double electric layer effect affects the viscosity change. As the neutralization increases, the viscosity may increase more, so the neutralization should be strictly controlled when preparing waterborne polyurethanes.