Additive Printing of Thermally Cured Two-Component Epoxy: A Route to Mesoscale Structuring for Improved Ductility

Epoxies are important thermoset materials with a broad range of applications. They are nominally homogeneous, have high strength and stiffness, but are brittle. In this work, we develop heterogeneous epoxies via additive printing with the goal of improving ductility, without compromising the strength and stiffness. To this end, we develop a reactive inkjet printing technology in which the resin and hardener components are printed successively using multinozzle printheads and which provides control of the local stoichiometric ratio. This allows creating epoxies with both in-plane and out-of-plane local compositional and mechanical heterogeneity. We print and test heterogeneous materials with several microstructural designs and demonstrate significant improvement of ductility, with retention of strength and stiffness. Furthermore, the properties of printed nominally homogeneous samples are close to isotropic and identical to those of the cast material of the same composition. The technology developed makes use of commercially available inks (resin and hardener); it is fully automated and provides sufficient flexibility and productivity to print complex macroscopic samples with 50 μm resolution of microstructural composition control.