(173c) Direct Ink Write of High Solid Suspensions: Considerations in Particle Type and Binder Properties

Construction, energetics, and regenerative medicine are several fields which rely on processing of suspensions with high content of solid particles (> 60 vol%). New processing methods for these areas, such as direct ink write (DIW) 3D printing, have enabled greater part complexity, reduced material waste, and improved safety during manufacturing. However, maximizing solid content presents processing difficulties due to the limited amount of binder in these suspensions, namely high viscosities, poor print resolution, and heterogeneous particle distributions. Despite these complications, for systems with particle diameters on the order of 10² μm, binder effects become more pronounced due to larger interstitial spaces between particles, but these effects remain poorly understood. Providing insights into the complex binder-particle and particle-particle interactions that occur at this scale is crucial for the development of successful DIW formulations. Here, we investigate the dual effects of particle type as well as binder factors in two different solidification mechanisms: solvent evaporation and UV cure. Using rheological tests, we characterize the viscoelastic response of these inks to applied stress mimicking the extrusion process. We use oscillatory time and 3 Interval Thixotropy experiments to analyze solidification post-printing as well as structure breakdown during shear followed by regeneration. We also visualize the microstructure prior to printing and after curing through scanning electron microscopy. For particles, we test spherical SiO₂, non-uniform SiO₂, and non-uniform basaltic soil particles. Binder factors of interest are surface tension of solvents and molecular weight and glass transition temperature of polymers. Fundamental understanding of the interplay between these components during 3D printing will enable a high level of customization of DIW inks for successful processing, enabling precise geometries tailored for novel buildings, safer energetics, or personalized medical devices.