Cure behaviour of epoxy resin matrices for carbon fibre composites

The cure behaviour of two resin formulations (with high and low curing agent content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of this work is to investigate the kinetics of this specific epoxy system in order to be able to choose a proper set of processing parameters which will give good composite material properties. The shape of the conversion curves gives evidence of the differences in the cure kinetics of the two systems. Furthermore, the values of the activation energies were determined both for formulation in the conversion range where vitrification occurs, following a phenomenological approach. These values give an indication of the differences in the curing mechanisms, when varying the content of curing agent. In particular, for both systems, the same reaction represents the onset of the cure process, ie the autocatalytic epoxy ring opening through addition reaction to the primary amine. This reaction dominates the entire cure process of the epoxy formulation at high curing agent content. Conversely, in the formulations with a low curing agent content, after depletion of the primary amines, different reactions may take place (with secondary amines and hydroxyl groups), depending on the cure temperature and the resin viscosity. © 1999 Society of Chemical Industry