Synthesis and Characterisation of New Water-Based Polyurethane Dispersion via Solvent-Free Prepolymer Mixing Process

Abstract

A new type of water-based polyurethane dispersion (NWPUD) was synthesised from isophorone diisocyanate, polyethylene glycol (Mw = 400 g/mol and 1000 g/mol), dimethylol propionic acid, and 1,4-butanediol using the prepolymer mixing process and without the incorporation of any volatile organic solvent. The hard-/soft-segment molar ratio of NWPUD formulations was varied with higher values (i.e. 5 to 11) allowing excess diisocyanate to reduce the prepolymer viscosity. The formulation using polyethylene glycol 400 g/mol with a hard-/soft-segment molar ratio of 5 failed by solidifying upon dispersion in water. Using polyethylene glycol 1000 g/mol and varying hard segment content, successful NWPUD formulations were obtained, all with pH between 6 and 7. FT-IR spectroscopy was used for the identification of chemical structures and functional groups. The colloidal properties of NWPUD formulations such as particle size, zeta potential, and dispersion stability were investigated to demonstrate feasibility for application in industrial coatings. The size distribution of NWPUD formulations varied from heterogeneous to homogeneous when the hard-/soft-segment molar ratio was increased. It was found that formulations with hard-/soft-segment molar ratio between 7 and 11 exhibited the most desirable dispersion stability within the zeta potential range of -50 to -55 mV.