Out-time effects on cure kinetics and viscosity for an out-of-autoclave (OOA) prepreg: Modelling and monitoring

The processing and final part quality of out-of-autoclave (OOA) prepreg composites are strongly influenced by the thermo-chemical and thermo-mechanical properties of the resin. These properties are primarily influenced by the out-time, or room temperature exposure time, of the resin prior to cure, and by the chosen cure cycle. However, both these factors can be difficult to control. Therefore, the capacity to track the resin cure state during processing is highly desirable. In this study, neat resin and prepreg samples are aged from 0 to 7 weeks, and the resin cure kinetics and viscosity are measured using differential scanning calorimetry (DSC) and rheometry, respectively, and used to develop accurate predictive models. The dielectric properties of the resin are measured in situ, and correlations to resin cure kinetics and viscosity are developed. The study quantifies the effects of out-time on cure kinetics and viscosity, and shows that both properties can be predicted and monitored in situ with excellent accuracy.