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The urea-formaldehyde (UF) reaction under strong alkaline condition was investigated by using quantitative analysis of 13C NMR. The main reaction products were methylolureas and oligomers linked by ether bonds at the beginning stage. With the reaction undergoing, the methylene linkages began to be formed and become predominant at the end point. The conversion of linear methylene ether bond to methylene linkage was also observed. These features were also observed previously for the reaction under acidic condition. It was found that the cyclic ether structure (uron) is much more stable than the linear ether bond, and its stability is second only to the methylene linkages among all the condensed structures. The formaldehyde was consumed in fast Cannizarro reaction under strong alkaline condition, producing considerable amount of methanol, which is the main negative aspect of this condition. With the exception of the differences caused by Cannizarro reaction, the UF production reactions under alkaline and acidic conditions are similar. The pH did not change the thermodynamic nature of the involved reactions, but only changed the competitive relationships of different reactions in kinetics. [ABSTRACT FROM AUTHOR]

The characteristics of UF resin prepared with concentrated formaldehyde were studied in this paper. With the molar ratio F/U = 1.1, the UF resin prepared with concentrated formaldehyde showed better mechanical properties than that with formalin. The13C-NMR and FTIR results indicated that there were more methylene groups, ether groups and urons in a UF resin system prepared with concentrated formaldehyde than those in a normal UF resin. The differential scanning calorimetry and DMA results showed that the curing temperature of UF resin with concentrated formaldehyde was lower than that of a normal UF resin. UF resin with concentrated formaldehyde showed worse thermal stability and higher thermal decomposition temperature. [ABSTRACT FROM AUTHOR]

To develop a soy-based adhesive with good water resistance, non-toxic melamine–glyoxal resin (MG) prepared in the laboratory was used as a cross-linker of soy-based adhesive. The FT-IR and ESI-MS results showed that there was a reaction between melamine and glyoxal. The resulted –CH–OH– groups could be the possible reactive groups for the cross-linking of soy-based adhesive. The wet shear strength of soy-based plywood indicated that the water resistance of soy adhesive cross-linked by MG improved with respect to that with no cross-linker, although it was not good enough to satisfy the relative standard. With the optimized preparation procedures for plywood, specifically, press temperature 180 °C, press time 3 min and resin loading 280 g m−2, type I soy-based plywood could be prepared with a hybrid cross-linker, namely 12%MG + 2% epoxy resin (EPR). The DSC results showed that the reaction between soy-based adhesive and the hybrid cross-linker MG + EPR was very complex. [ABSTRACT FROM AUTHOR]