Coalescence study on polymer blend powders for powder bed fusion based Additive Manufacturing

Powder Bed Fusion (PBF) is an emerging 3-D printing method that can be used to create structures relevant to many industries, including the medical field and aeronautics. To use a polymer in this process, the feedstock pellet must be transformed to a spherical powder that must attain specific physical properties to achieve a uniform print. Poor mechanical properties in the printed parts are an important concern for PBF of polymers. Incomplete coalescence of the powder particles during printing is a significant contributor to this problem since the coalescence process is crucial for the consolidation of the printed parts. There have been different approaches to improve the mechanical properties of the printed part, including printing settings adjustment and employing various types and grades of polymeric materials.  This work hypothesizes that the fabrication of polymer blend powders can be an effective way to modify the PBF printing of polymer powder, including controlling the coalescence of neighboring particles.  This improvement, in turn, may improve the mechanical properties in final printed parts. Thus, we report studies that examine the coalescence of polymer blend powders.  In our blend system of polypropylene (PP) and polycarbonate (PC), the results indicate that the presence of the polycarbonate slows the coalescence process, and that extensional flow becomes less important for the blend coalescence with higher PC loadings. Moreover, the viscosity of the matrix decreases as a function of coalescence time due the phase separation between PP and PC. These outcomes provide a better understanding of the impact of the molecular level structure of polymer powders on particle coalescence in polymer powder blends.