Examination of selected synthesis parameters for wood adhesive-type urea-formaldehyde resins by 13C NMR spectroscopy.: III

The varying polymer structures of wood adhesive-type urea-formaldehyde resins resulting from different formaldehyde/first urea (F/U-1) mole ratios used in the first step of resin manufacture were investigated using C-13 NMR. As the F/U-1 mole ratio decreased progressively from 2.40 to 2.10 and to 1.80, the viscosity increase due to polymerization during resin synthesis became faster and resulted in decreasing sidechain branches and increasing free urea amide groups in the resin structure. The resultant UF resins, with the second urea added to an overall F/(U-1 + U-2) of 1.15, showed viscosity decreases when heated with stirring or allowed to stand at room temperature that were also characteristic with the F/U-1 mole ratios used in resin synthesis. The formaldehyde emission levels of particleboards bonded with the freshly made UF resins showed relatively small but similarly characteristic variations. (C) 2001 John Wiley & Sons, Inc.