Cure kinetics of epoxy formulations of the type used in advanced composites

An analysis of the cure kinetics of three different formulations composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) epoxy resin and diaminodiphenyl sulfone (DDS) was performed. A series of isothermal tests was run, and the experimentally obtained results were checked against the proposed kinetic model. An autocatalyzed mechanism with the overall reaction order of 2 was found to adequately describe the cure kinetics. An increase in reaction rate was observed at higher temperature and higher DDS concentration. For a given formulation, the extent of reaction corresponding to the maximum reaction rate was independent of temperature. A secondary exotherm was detected, particularly in formulations with low DDS concentration, at approximately 40% conversion. At that point, the rate of primary amine–epoxide reaction decreases, and other reactions dominate the curing process. Such a mechanism is likely to cause a formation of an inhomogeneous thermoset morphology.