Curing kinetics of amine and sodium hydroxide catalyzed phenol-formaldehyde resins

The effect of both formaldehyde content and catalyst type used in the synthesis of several resole type phenolic resins has been studied by using differential scanning calorimetry. In this study Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman model-free kinetics are applied in order to correlate the dynamic cure behaviour with the mentioned synthesis variables. Strong upward dependency of activation energy on conversion has been detected in all cases up to a maximum value. Lower the formaldehyde content fewer changes in activation energy have been detected, revealing a more homogeneous polymerization. As formaldehyde content increases, stronger variations of energy values have been observed and the maximum value is shifted to lower conversions. By comparing triethylamine and sodium hydroxide catalysts similar behaviour has been observed, with higher energy values and shifting of the maximum in the latter. Friedman approach has been resulted in more convenient and accurate for the energy values determination and KAS method seems useful for the dynamic cure prediction of that type of thermoset.