Properties of Isocyanate-Reactive Waterborne Polyurethane Adhesives: Effect of Cure Reaction with Various Polyol and Chain Extender Content

Three series of isocyanate-reactive waterborne polyurethane adhesives were prepared with various contents of chain extender (4.25/8.25/12.50 mol %) and polyol (20.75/1.6.75/12.50 mol %). Each series had a fixed amount of excess (residual) NCO group (0.50-2.00 mol %). FTIR and H-1-NMR spectroscopy identified the formation of urea crosslink structure mainly above 80 degrees C of various cure temperatures (20-120 degrees C) with excess diisocyanate. The molecular weight, tensile strength, Young's modulus, and adhesive strength depend on excess NCO content and cure temperature and also varied with polyol and chain extender content. The optimum cure temperature was 100 degrees C for all the samples. The tensile strength, Young's modulus, and adhesive strength increased with increasing cure temperature above 60 degrees C up to the optimum temperature) (100 degrees C) and then almost leveled off. Among all the samples, the maximum values of tensile strength, Young's modulus, and adhesive strength were found with 63.22 wt % polyol, 0.93 wt % chain extender, and 1.50 mol % excess (residual) NCO content at 100 degrees C optimum cure temperature.(C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3767-3773, 2009