Science and Technology of Polyurethane Dispersions, Process and applications
von D. Bhattacharjee, B. Erdem
Aqueous polyurethane dispersions (PUDs) have recently emerged to replace their solvent based counterparts for various applications due to increasing health and environmental issues. These dispersions provide unique physical, chemical and mechanical properties compared to other aqueous polymer dispersions like styrene-butadiene and acrylics. In several cases, they are also blended with other waterborne dispersions to optimise performance with cost. We have developed a differentiated technology and capability to produce solvent-free and high solids (~60 wt%) aqueous PUDs from aromatic isocyanate/polyether and aliphatic isocyanate/polyester prepolymers using a high shear continuous mechanical dispersion process. It was found that the formation and stabilization of submicron size colloidally stable particles in this process could be to a large extent controlled by chemical composition of the PU prepolymer and type and amount of surface active agents. The kinetics of polyurethane and polyurea polymerisation with both aliphatic and aromatic isocyanates was studied. The effect of the time and temperature on the film formation and coalescence of soft and hard PUDs, crosslinking of polyurethanes with organofunctional silanes and incorporation of inorganic fillers were also investigated for various applications. Such detailed understanding allows the design and preparation of polyurethanes for a myriad of applications from well-designed combination of a variety of commercially available raw materials.