Quantitative determination of isocyanate concentration in crosslinked polyurethane coatings

The influence of relative humidity an the rate of isocyanate functionality depletion at the film-air and film-substrate interfaces of a urethane coating was examined using attenuated total reflectance (ATR) FTIR. The effect of relative humidities (RH) ranging from 0 to 80% on crosslinking reactions was examined. The results indicate that reactions of isocyanate groups with OH functionalities are inversely proportional to the RH. The results are discussed in terms of the reactions which occur between water and isocyanate, as well as the plasticization effects of water and solvent molecules. These studies indicate that the presence of competing reactions within the system may result in various degrees of crosslinking.