A feasibility study on the utilization of renewable feedstocks for industrial additive manufacturing using binder jetting

This study investigates the feasibility of using walnut shells, a biogenic industrial waste material, as a renewable powder feedstock for binder jetting additive manufacturing. A systematic process chain was developed, including material comminution, sieving, particle-size adjustment, powder characterization, printing trials, and mechanical evaluation of the manufactured specimens. Initial experiments showed that a bimodal powder mixture (20% fine and 80% coarse particles) with a high coarse-particle fraction caused severe layer delamination and insufficient interlayer bonding. By contrast, a trimodal powder composition (62% fine, 13% medium, and 25% coarse particles) with an increased fine fraction enabled stable printing and improved binder absorption. The printed walnut shell/PVA specimens were characterized by scanning electron microscopy, flexural testing, and compression testing. The results revealed a porous microstructure with limited interfacial adhesion and comparatively low mechanical strength in the green state, restricting the material’s use to low-load, and design-oriented applications. Wax infiltration as a post-processing step improved handling and surface quality, as demonstrated through the fabrication of an eyeglass frame. Overall, the study demonstrates, for the first time, that walnut shell powder can be processed by binder jetting when suitable powder preparation and process control are applied. The findings provide a basis for further development of renewable feedstocks, bio-based binders, and post-processing strategies for sustainable additive manufacturing.