Catalyzed frontal polymerization-aided 3D printing of epoxy thermosets

Abstract

• Tailoring frontal polymerization of epoxy resin with carbon materials • Revealing the size and geometric effect of carbon materials on the catalyzed frontal polymerization of epoxy resin • New method in lowering frontal temperature while maintaining the frontal polymerization rate • 3D printing of epoxy thermoset with self-propagated in-situ curing Frontal polymerization is a self-propagating exothermic reaction and provides a rapid and energy-efficient way to manufacture thermosets. A critical issue for frontal polymerization is to concurrently maintain a low frontal temperature and a self-sustained frontal propagation, which significantly depends on the frontal velocity. In this work, carbon nanotubes (CNTs), graphene oxide(GO) and discontinuous carbon fibers (d-CFs) were incorporated into epoxy thermosets to tune the frontal polymerization. Their catalytic effects on frontal temperature and frontal velocity were studied. Both CNTs and GO were found to significantly reduce the activation energy of frontal polymerization, whereas d-CFs did not show any obvious effect on the activation energy. The real-time non-destructive characterization showed that 1wt % CNTs incorporation reduced the frontal temperature from 240 to 227°C while the front velocity remained the same (6.5 cm min −1 ), indicating effective decoupling frontal temperature from frontal velocity. The frontal temperature could be further reduced to 220°C or lower at an increasing loading of CNTs while the frontal velocity remained the same. In contrast, 1wt% GO incorporation reduced the frontal temperature from 240 to 220°C, but also decreased the frontal velocity from 6.5 to 5.1 cm min −1 (21.5% reduction). In addition, as-prepared CNTs-incorporated epoxy resins were used in the 3D printing process via frontal polymerization and their printability were demonstrated. This discovery opens a new pathway for additive manufacturing through catalyzed in-situ frontal polymerization.