Monitoring diffusion and reaction rate during film formation of waterborne 2-pack polyurethane coatings

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Concern for the environment has been driving major changes in technology in the coatings industry. To reduce the amount of volatile organic compounds (VOC's) released to the atmosphere, new technology is being developed to replace solvent-based coatings with water-based coatings. The biggest challenges have been in industrial coatings, where polyurethane coatings play a particularly important role, for example in automotive, aerospace, industrial maintenance, and plastic coatings applications. The highest performing polyurethane (PUR) coatings involve "2-pack" (2K) solvent-based formulations in which a polyisocyanate (PIC) and a low molecular weight polyol are packaged separately to avoid the intrinsic reaction of the components. The two components are mixed just prior to use and then they have to be applied to a substrate before the reaction between the components becomes too advanced (the "pot life"). Waterborne (WB) 2K-PUR coatings have been developed as an environmentally friendly alternative to solvent-based polyurethanes, but this technology is much more complex. First, the polyisocyanates have to be dispersed in water, where reaction between the PIC and water can occur in competition with the reaction with the polyol. In addition, the polyol is present as small particles rather than discreet molecules. This has a major effect on the way the PIC and polyol react. While attempts have been made to study reaction rates in WB 2K-PUR systems, almost nothing is known about how the components mix at the molecular level, and how this affects the final performance properties of the coating. In this project, we will use special techniques developed by the Winnik group at the University of Toronto to study the rates at which the polymers in the PIC and in the polyol mix and how this compares to the rates at which the chemical reactions occurs. We will study these processes for a wide range of polyol compositions, and we will work with our partners at BASF to translate this fundamental knowledge into the design of high performing WB 2K-PUR coatings.