Study of reaction kinetics of E-beam cured cationic epoxy

An important barrier to the development of E-beam (EB) curing as a technology of choice for manufacturing high-quality composite structures is the currently poor state of understanding of the fundamental chemical processes involved. The development of novel characterization techniques for in-situ monitoring of EB curing, such as near infrared (NIR) spectroscopy and EB calorimetry, have significantly advanced understanding of the process, and have led to the first practical radiation cure kinetics model. However, the current first-generation model does not yet capture all the complexities of the cure process and further refinements are required. In this work, EB calorimetry was used to perform in-situ cure rate measurements during radiation curing of PGE, a simple monofunctional epoxy resin. Cure rate measurements were compared with the predictions of the cure kinetics model and key areas of agreement and disagreement are noted. Characteristic features of the reaction were identified and measured, and analyses were conducted to determine the effects of critical process parameters on cure rates. It is shown that, contrary to the model predictions, reactions occurring during irradiation and when the beam is off exhibit distinctly different behaviors. A parallel activity using NIR to study "interrupted" EB curing of epoxy specimens also found the same beam effect. Future studies will aim at using these two techniques, in combination with simple process models, to continue to evolve an improved understanding of the EB curing process.