Inverse Micro Raman spectroscopy (IMRS) was used to investigate the drying behavior and film composition of two-pack (2K) waterborne polyurethanes. The system studied is based on the reaction of an acrylic polyol and hydrophilic polyisocynate and the NCO/OH ratio used is 1.4. The differences in the particle size distribution of the initial emulsions result in differences in the coatings structure that can be detected by IMRS. For the formulation prepared with a polyol with an initial dry content of 42% w/w, large heterogeneities of a size up to 20 μm are observed in the film from the very beginning of drying. It is also found that the higher relative intensity of the NH band coincides with a higher polyilsocyanate content. The 2D map of the film show no indication of high local concentration of polyilsocyanate.
展开▼
