Recent Advances in Waterborne Two-Component Polyurethanes
Actually, there are many alternatives to classical solventborne systems. They are based on waterborne and/or hydrophilic products and are used in wood coatings1, plastic coatings for OEM interior2 and some general industrial applications for metal3. The decision whether to use a solvent- or waterborne system does not only depend on legislation but is influenced by public opinion as well.
When we compare both monomers, differences in their final behavior become evident. HDI is a chain of CH2 groups, which can rotate around the axis of the molecule and will result in a flexible product. The homopolymer has a glass transition temperature of –63 deg C. IPDI, with its cycloaliphatic structure, represents a more rigid form, which results in a glass transition temperature of 105 deg C for the homopolymer. Looking at the standard prepolymer products, we see that the HDI-trimer is a liquid with a viscosity of 600 to 2400 mPa.s at room temperature, whereas the IPDI-trimer is a solid, which is commonly supplied as a solution of 70% solids content in different solvents.