Model-free kinetic analysis of melamine-formaldehyde resin cure

The curing behaviour of an industrial melamine-formaldehyde (MF) resin with four different commercial curing catalysts was analyzed from thermal studies using differential scanning calorimetry (DSC) and model-free kinetic (MFK) analysis. For the kinetic study, the mathematical approaches developed by Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Vyazovkin were used to calculate curing isotherms. With all kinetic approaches the apparent activation energy, E-a, depended to some extent on the degree of conversion (alpha). Besides being obscured by experimental errors, in some cases higher E-a(alpha) were calculated with higher catalyst concentrations, illustrating that E-a(alpha) may not be the only relevant parameter to compare different resin systems. However, E-a(alpha) was found to be well suited for predicting the isothermal curing behaviour of MF resin. The time required for achieving a certain conversion, alpha, was calculated for different temperatures. By comparing the calculated isotherms to experimental isothermal data obtained at 80, 100, and 120 degrees C it was found that the Vyazovkin approach in its advanced form was best suited to predict the curing kinetics of MF with all catalyst systems tested. By applying DSC-MFK it was possible to detect and characterize the de-blocking behaviour of different catalysts for MF curing. The presented results illustrate that isoconversional methods for kinetic analysis of thermochemical data can be applied to the investigation and optimization of melamine-formaldehyde resins. (C) 2009 Elsevier B.V. All rights reserved.