Cure behaviour of epoxy resin matrices for carbon fibre composites

The cure behaviour of two resin formulations (with high and low curing agen t content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of th is work is to investigate the kinetics of this specific epoxy system in ord er to be able to choose a proper set of processing parameters which will gi ve good composite material properties. The shape of the conversion curves g ives evidence of the differences in the cure kinetics of the two systems. F urthermore, 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 differen ces 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 rea ction 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 primar y amines, different reactions may take place (with secondary amines and hyd roxyl groups), depending on the cure temperature and the resin viscosity. (C) 1999 Society of Chemical Industry.