Study of hybrid isocyanate and high‐mono‐hydroxymethyl urea content urea‐formaldehyde resins

Abstract

AbstractBased on the difference in the reaction rate of different groups of urea‐formaldehyde resins and isocyanate resins, this study designed two different urea‐formaldehyde resins: a normal urea‐formaldehyde resin (UF) and one with high mono‐hydroxymethylurea content (UF*) to react with polymeric methylene diphenyl diisocyanate (pMDI) resin. The difference in mono‐ and di‐hydroxymethyl urea content between UF and UF* resins was analyzed by nuclear magnetic resonance (NMR) spectroscopy, and results showed that the mono‐hydroxymethyl urea content of the UF* resin was much higher than that of the conventional UF resin. The fourier transform infrared spectrometer (FTIR) analysis of differences between UF* and UF resin showed that the UF* process did not change the main structure of the conventional urea formaldehyde resin. Differential scanning calorimeter (DSC) analysis showed that the curing temperature of the hybrid UF*‐pMDI resin was reduced 27.3°C compared to that of the UF‐pMDI resin. When these hybrid resins were used to bond plywood respectively, test results showed that the UF*‐pMDI resin improved the dry and wet bonding strength by 2.6% and 3.9%, respectively, compared with the UF‐pMDI resin under the condition of hot pressing time (3 min) and temperature (140°C), meeting the requirement of Chinese standard of GB/T 9846–2015 for Class III board. This study provides a new path for further improving the performance and design of hybrid resins based on isocyanate and urea‐formaldehyde resin.