Rapid Curing of Epoxy Resin Using Self-Sustained Frontal Polymerization Towards the Additive Manufacturing of Thermoset Fiber Composites

The demand for lightweight and high-performance thermoset fiber composites, such as the carbon fiber reinforced epoxy resin composites, has been rapidly increasing in a wide variety of industries. However, thermoset composites require cross linking for curing and consolidation, which is time consuming and can often take several hours. Additionally, the associated capital, operation, and maintenance costs are immense. The major challenge in the additive manufacturing and repair of thermoset-matrix fiber composites is an issue with the in-situ curing. To address this challenge, one of the promising solutions is to use the frontal polymerization technique to significantly reduce the curing time, from several hours to only a few seconds, while simultaneously obviating the need for external heating sources. In this work, the frontal polymerization of the epoxy resin, i.e., one of the most used thermoset resins for fiber composites, is investigated. Specifically, the frontal polymerization is initiated by the ultraviolet LED light. Then, with the help of a thermal co-initiator, the exothermic heating released due to the photopolymerization triggers the thermal polymerization, leading to a self-sustained polymerization front to form and propagate through the epoxy resin. Preliminary experimental results on the effect of weight fraction of the thermal co-initiator on the performance of the frontal polymerization of epoxy resin are presented and discussed. Results include the temperature measurements, SEM images showing the surface morphology of the cured epoxy resin specimens, and the tensile properties of the cured epoxy resin. The tensile properties of the epoxy resin specimens cured using the frontal polymerization technique are also compared with those of a conventional thermoset epoxy resin.