(641a) Rheology and Processing of Polymeric Binders for Additive Manufacturing of Dense Pastes

Materials with high particle loadings are important for several applications: in many cases the particles provide the desired functionality and the polymer acts to bind them together into a shape, so maximizing particle content is required. As new processing technologies become more prevalent, such as extrusion-based additive manufacturing, low binder content has introduced challenges, particularly due to the high particle-particle contact areas encountered in highly loaded systems. Understanding how the formulation elements, especially the polymer binder properties, impact the rheological properties and how those translate to processing will enable rapid formulation design and robust processes. We assess different formulations of polymers, in which we suspend model particles at >60 vol%, through rheological characterization to determine formulation parameters resulting in continuous extrusion for direct ink write (DIW) additive manufacturing. Through yield stress and thixotropy testing, as well as through visual comparison, we evaluate ratios of pre-polymer to monomer for photocurable polymers and molecular weight and entanglements for polymer solutions. We also assess shear-induced phase separation in the nozzle as a result of varying the binder formulation and the particle modality. This work will allow us to understand how to design polymer binders for high solids suspensions for direct ink write additive manufacturing to result in homogenous, predictable solid parts for applications ranging from pharmaceuticals to energetic materials to construction on Mars.