The influence of the ionic concentration, concentration of the polymer, degree of neutralization and chain extension on aqueous polyurethane dispersions prepared by the acetone process

There are many variables in the preparation of aqueous polyurethane (PU) dispersions. Chemical and compositional variables such as carboxylic acid concentration, concentration of the polymer, degree of pre/post-neutralization of the carboxylic acids and chain extension that all impact solution properties such as particle size and viscosity. Another variable is the method by which the dispersion is prepared; two primary methods are currently employed in industrial manufacture, the prepolymer mixing process and the acetone process. This study evaluates the impact of the chemical variables on a given PU dispersion formulation prepared by the acetone process. Changes in carboxylic acid concentration, degree of pre/post-neutralization and chain extension were found to have the expected impacts on dispersion solution properties. Increased ionic concentration, and degree of pre-neutralization led to lower particle size and higher viscosity, increased degree of chain extension led to larger particle size and lower viscosity, increased post-neutralization increased both particle size and viscosity, and increased concentration of the polymer led to a viscosity increase without any change in particle size.