| Abstract | The numerous potential advantages offered by electron beam (EB) curing, including higher curing speed, reduced residual stresses, and potentially lower unit costs have resulted in it becoming a very attractive alternative to conventional autoclave curing processes. In recent years, significant progress has been made in developing high-performance EB-curable epoxy resin systems with potential use in aerospace products. However, the cure mechanisms of the EB-curable resins remain poorly understood, leading to poor control of the curing process. Understanding the effects of temperature and other process parameters during EB curing, and any subsequent processes such as post-cure, is important to achieving good process control and desired mechanical performance. This research focused on development of a semi-empirical cure kinetics model for a proprietary commercial EB-curable epoxy resin, CD02. By employing a simple and fast in situ calorimetry technique in combination with modulated differential scanning calorimetry (MDSC), the cure characteristics of an EB-curable epoxy resin were investigated. It was found that curing of the studied resin was strongly influenced by diffusion limitations at temperatures below its glass transition temperature (Tg). This implies that, contrary to conventional wisdom, EB-cured resins must reach high temperatures to achieve full cure. Resin Tg evolution was tracked using MDSCmeasured specific heat changes during multi-step cure cycles. This approach appeared to give better results than conventional dynamic mechanical analysis (DMA). The developed cure kinetics model was based on a model recently developed at Drexel University for prediction of radiation-induced cationic polymerization rates in simple epoxy systems. The Adam-Gibbs diffusion model was used to describe the strong temperature- and Tgdependent diffusion control mechanism. Due to a lack of understanding of the generation of active centers by heat, the kinetics model only considers active center generation by irradiation and hence can be somewhat inaccurate at elevated temperatures. The current model is the only known cure kinetics model that provides any sort of realistic way to predict the cure rate of a EBirradiated commercial resin system of unknown chemistry. |
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