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

Epoxies are important thermoset materials with a broadrange ofapplications. They are nominally homogeneous, have high strength andstiffness, but are brittle. In this work, we develop heterogeneousepoxies via additive printing with the goal of improvingductility, without compromising the strength and stiffness. To thisend, we develop a reactive inkjet printing technology in which theresin and hardener components are printed successively using multinozzleprintheads and which provides control of the local stoichiometricratio. This allows creating epoxies with both in-plane and out-of-planelocal compositional and mechanical heterogeneity. We print and testheterogeneous materials with several microstructural designs and demonstratesignificant improvement of ductility, with retention of strength andstiffness. Furthermore, the properties of printed nominally homogeneoussamples are close to isotropic and identical to those of the castmaterial of the same composition. The technology developed makes useof commercially available inks (resin and hardener); it is fully automatedand provides sufficient flexibility and productivity to print complexmacroscopic samples with 50 & mu;m resolution of microstructuralcomposition control.