Incorporating Steric Hindrance into the Additive Design Enables a Robust Formulation of Alumina Ink for Extrusion-based 3D Printing

The capabilities of additive manufacturing for fabrication of complex and thin-walled ceramic-based objects are restricted by the availability of ceramics inks. Formulations of current ink systems strictly depend on using a high content of organic additives (5-30 wt %). The high amounts of additives affect uniformity and dimensional accuracy of the final object. Here, we designed a single additive that enables printing of high aspect ratio and thin-walled structures (height/width = 58) from an ink of alumina nanoparticles that comprises very low organic content (i.e., 1.25 wt % of nanoparticles mass). In addition to the generally exploited electrostatic effect, this additive has purpose-driven tailoring to harness steric hindrance to control the viscoelastic response of ceramic suspensions and realize an optimum ink for extrusion-based 3D printing. We pursued a stepwise approach in developing such an additive through synthesis of series of copolymers with backbone monomers of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid and side chains of poly(ethylene glycol). When the optimized additive is used, the suspension attains similar to 80 wt % solid loading-99% of the theoretical limit calculated by the Krieger-Dougherty equation. The shrinkage and deflection of the printed patterns as well as compactness and sinter-ability of dried structures are monitored. The printed structures did not experience any deformation or deflection during printing and reached 68% of theoretical density (TD: 3.98 g/cm(3)) after drying. This compactness allowed sintering at lower temperatures and improved dimensional control of the final product. Our approach to formulate ceramic inks enables the embodiment of fully aqueous systems with the utmost material content and has the potential to expand the limited portfolio of ceramic inks.