Directed Liquid-Liquid Phase Separation of Polymer Solutions to Enable New Feedstocks for Additive Manufacturing

Powder Bed Fusion (PBF) is an important process in polymeric additive manufacturing. However, there exist limited polymers available for PBF, where most efforts use nylon. We will discuss ongoing research in our group to understand and control the rational development of scalable processing protocols that use liquid-liquid phase separation (LLPS) to reproducibly fabricate polymer powders that are suitable for powder bed fusion. In this process, the solvent quality of a polymer solution is reduced by a temperature quench or addition of non-solvent, causing the polymer to precipitate via phase separation. This results in the formation of polymer particles suitable for PBF that can be easily recovered, which also enables reclamation and reuse of solvent. Understanding the fundamental driving forces that guide the variation of particle size with polymer solution concentration, polymer crystallinity, solvent type, and quench temperature provides pathways to rationally control the size and manufacturability of the final particles.

This process has been used in our group to create powders that are suitable for PBF from polypropylene and products in the waste stream. The process of powder formation is driven by the phase separation of polymer solutions, which involves spinodal decomposition followed by Ostwald ripening and droplet coalescence. Control of powder formation requires understanding which of these processes regulates final particle size in the precipitation process. We will discuss results that determine the impact of temperature, solution concentration, and molecular weight on formed particle size and offer important fundamental understanding into the phase separation processes that govern particle formation. This in turn offers insight that will enable the rational design of thermodynamic conditions required to create polymer powders that are suitable for powder bed fusion for a broad range of polymers, including from the waste stream, using the LLPS process.