UV-induced frontal polymerization for optimized in-situ curing of epoxy resin for excellent tensile and flexural properties

UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its fiber composites which features the generation of a self-sustaining front that propagates within the entire material. This is different from using the commercially available UV curable resin which prohibited the curing of thermoset composites with opaque fibers (e.g., carbon fiber) due to the UV light being blocked by the fibers. In this study, we experimentally demonstrate that using the UV-induced frontal polymerization allows us to reduce the curing time of a standard tensile specimen of epoxy resin from traditionally 15 h using the oven curing method to only less than 1.5 min. The frontal polymerized epoxy specimens showed comparable and even superior tensile and flexural properties when compared to the traditional oven cured specimens. Moreover, we experimentally investigated the influence of the weight content of the photoinitiator, the UV light intensity, and the specimen geometry on the characteristics of the frontal polymerization process (i.e., front temperature, front velocity, and degree of cure) and the resulting tensile and flexural properties. The results and discussions are expected to provide guidance in scaling up this UV-induced frontal polymerization technique for the sustainable and additive manufacturing and repair of thermoset resin and its fiber composites.