Interlayer molecular migration and reaction in an epoxy-polyurethane coating system: Implications for the system hardness

• The migration of 1-butanol caused the improper curing an epoxy-PU system. 1-Butanol has a two hundred times higher reaction rate than polyol reactant. 2-Butanol helps to improve hardness development Curing coatings under solvent evaporation-suppressed conditions, can lead trapping solvents and subsequent into mid- or topcoats in multilayer coating Such migrations may have adverse effects on mechanical properties, particular. Using two-layer epoxy-polyurethane (PU) system with strong practical significance for heavy industry, aim present work was quantify migration-reaction phenomenon selected alcohols (co-solvents), map underlying mechanisms. In experimental series undertaken, evaporation measured gravimetrically, urethane group formation quantified by use Fourier-transform infrared spectroscopy (FTIR). Simultaneously, transient followed surface morphology studied three-dimensional profilometer. addition, estimate required time dry-to-handle high-pressure compression measurements were conducted. As expected, due build-up closed exposure chamber, amount residual increased conditions. particular, epoxy primer migrated PU topcoat, where it reacted isocyanate reactants. reduced cross-linking density, as consequence this undesired reaction, simultaneous suppressed evaporation, resulted insufficient despite continuous consumption isocyanates indeed observed. To elucidate mechanisms, kinetic study reactivity crosslinker also conducted, showed orders magnitude reactant system, which explains negative migration. comparison, 2-butanol less reactive towards isocyanates, could substitute 1-butanol, whereby, significantly improved conditions from more eight four days. results provide insight guidelines how optimize formulation obtain adequate