Impact of polymer molecular weight on droplet coalescence and the properties of parts printed via powder bed fusion

Understanding and controlling the fundamental processes governing sintering is vital to achieving robust structures by laser powder bed fusion (LPBF) process. In this presentation, we will highlight our studies to understand the role of polymer molecular weight (M_w), and thus zero-shear viscosity, on particle coalescence and the powder bed fusion process. Our group has used thermally induced phase separation (TIPS) to form polypropylene (PP) powders from PP with M_W of 12k, 250k, and 340k, and their 50/50 blends (12k/250k,12k/340k, and 250k/340k). The coalescence behavior of the powders was studied, where the Hopper model provides insight into the molecular-level processes that control the consolidation of particles during sintering. Additionally, analysis of printed parts from these powders shows that the bimodal samples exhibit lower void space, higher crystallinity, and more robust mechanical property than the unimodal counterparts. These results provide molecular-level insight into how control of powder M_w can impact the LPBF process and offer pathways to optimize the macroscopic properties of the printed parts.