Interfacial studies of crosslinked urethanes: Part IV. Substrate effect onfilm formation in polyester waterborne polyurethanes

These studies examine the effect of substrate surface tension on crosslinki ng reaction sin water-borne polyurethanes (PUR) applied to tin-plated steel , steel, polypropylene (PP), thermoplastic olefin (TPO), and glass. The res ults show that, relative to tin-plated steel, removal of tin-plating from a steel substrate increases isocyanate (NCO) consumption by 42% near the fil m-substrate (F-S) interface. When PUR is allowed to crosslink on steel, PP, TPO, and glass, the NCO concentration is greater at the film-air (F-A) int erface. Furthermore, crosslinking reactions result in a greater amount of u rea-hydrogen bonded species near the F-S interface for all substrates. Whil e an increase of substrate surface tension decreases the amount of urea-hyd rogen bonded carbonyl groups near the F-S interface, TPO was found to exhib it different behavior due to talc stratification near the surface. In this case, the presence of talc in WB-PUR coatings or thermoplastic substrates d ecreases the amount of hydrogen-bonded species and increases NCO consumptio n.