Dynamic mechanical analysis study of the curing of phenol-formaldehyde novolac resins

The curing reaction of typical commercial phenol-formaldehyde novolac resins with hexamethylentetraamine (HMTA) was followed by dynamic mechanical analysis. The evolution of the rheological parameters, such as storage modulus G ', loss modulus G ", and tan delta (G " /G '), as a function of time, for samples of the phenolic resins on cloth, was recorded. The curing reaction, leading to the formation of a crosslinked structure, is described by a third-order phenomenological equation. This equation takes into account a self-acceleration effect, as a consequence not only of the chemical reaction of crosslinking after the gel point but of phase segregation as well. This rheokinetic model of the curing of phenolic novolac resins permits the determination of the numerical values of the kinetic equation constants. The influence of the composition, structure, and physical treatment on the curing kinetics of the novolac resins is evaluated. (C) 2001 John Wiley & Sons, Inc.