Reactive binder-jet 3D printing process for green strength enhancement

In this study, a reactive binder jetting process is developed to provide a simple manufacturing process for 3D objects. A multiple-jetting method is first developed to deliver sodium alginate (SA) together with calcium ions using separate nozzles to create hydrogel patterns on a gypsum powder bed. The printed green specimen shows reasonable mechanical strength for sample transfer but exhibits low water resistance. To further improve the mechanical strength, trivalent or tetravalent cationic ions are used to produce highly crosslinked alginate hydrogels with high viscosity. Among these cationic solutions, the specimen printed with tetravalent Zr4+ ink shows the best flexural strength of 8.7 MPa. The green specimen also possesses good abrasive resistance, with a pencil hardness of 6H and a Shore D hardness of 43.5 HD, surpassing that of commercial chalk (1H and 30 HD). Moreover, the printed sample shows great water resistance and remains intact without deformation during ultrasonication for four hours. Finally, the SA/Zr4+ ink combination can be used with regular color inks to print full-color 3D gypsum samples with excellent color accuracy, structural details, and good water resistance.