Effect of postcure conditions on the dynamic mechanical behavior of water-based polymer-isocyanate adhesive for wood

To study the effect of postcure conditions on the viscoelastic behavior of water-based polymer isocyanate adhesives for wood (API adhesive), dynamic mechanical analysis (DMA) was performed for a simplified model of API adhesives under various postcure conditions. These conditions were achieved by storing the samples at room temperature or by heating them in an oven. Fourier transform infrared (FT-IR) spectroscopy was performed to test for residual isocyanate groups (NCO) and isocyanate derivatives to elucidate the reaction mechanism under the postcure conditions. DMA revealed that the postcure conditions led to wide variations in the viscoelastic behaviors of API films. FT-IR analysis confirmed the decrease of residual isocyanate during postcure treatments. However, the complete consumption of isocyanate could not be achieved under the postcure conditions. A good correlation was found between the DMA result and the chemical changes in the API samples heated above 140 degrees C. However, no correlation was observed in the case of the samples heated at temperatures less than 140 degrees C. This implies that postcure conditions led to a difference in the reaction chemistry of API.