Abstract: Based on evaluation of chemical structures of three typical urea-formaldehyde(UF)resins by ¹³C NMR, the techniques of torsion braid analysis (TBA) and differential scanning calorimetry (DSC) were applied, respectively, in order to analyze dynamic viscoelasticity and curing characteristics of these UF resins in different curing systems. UF resins from different formulations have quite different chemical structures, in which the modifier, melamine, was well copolymerized with urea. The relative rigidity of UF resins without curing agent was kept almost consistent during heating-up, then decreased quickly when temperature reached 128℃,which indicated that no crosslinking reaction occurred, and exhibited only the thermoplasticity of the resin. When temperature was higher than 135℃, crosslinking started. The curing mechanisms of UF resins in different curing systems were different from each other. UF resin without modifier started its curing reaction at lower temperature and gave off more heat during the more violent reaction. Curing of both UF resins modified by melamine or modifier M gave off less heat and proceeded more stably.

Key words: urea-formaldehyde resin, low-formaldehyde-emission, curing mechanism, torsion braid analysis, differential scanning calorimetry