A rheological study of the gelling of UF polycondensates

The gelling process of urea-formaldehyde resins has been investigated by rh eological methods. The gel point values were determined by three methods, a nd compared with those obtained by low resolution impulsional H-1-nuclear m agnetic resonance. The activation energy of the curing process was determin ed and the effect of the molar ratio was investigated. In addition, the cri tical power exponents were calculated and the parameters of the relaxation modulus function were also determined. Equations describing the gel time as a function of degree of conversion and reactants molar ratio are presented . (C) 2000 John Wiley & Sons, Inc.