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

摘要

The varying polymer structures of wood adhesive-type urea—formaldehyde resins resulting from different formaldehyde/first urea (F/U1) mole ratios used in the first step of resin manufacture were investigated using 13C NMR. As the F/U1 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 side-chain branches and increasing free urea amide groups in the resin structure. The resultant UF resins, with the second urea added to an overall F/(U1 + U2) of 1.15, showed viscosity decreases when heated with stirring or allowed to stand at room temperature that were also characteristic with the F/U1 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.