Utilizing Surface Segregating Additives to Improve the Isotropy of Fused Deposition Modeling Products

Reducing the anisotropy of 3D printed parts prepared by fused deposition modeling (FDM) is a major goal for researchers in the 3D printing community. For typical FDM parts, mechanical properties observed of samples printed orthogonal to the print bed (transverse) are significantly weaker than those printed parallel to the bed (longitudinal). These anisotropic properties arise due to limited diffusion and entanglement of chains across the inter-layer interface. Minimizing the anisotropy has been achieved in our group by implementing a process in which bimodal blends comprised of a parent, high molecular weight polymer blended with a chemically identical but low molecular weight (LMW) polymer is utilized. Recently, we have extended this research to include LMW additives with various architectures. For linear and 3-arm star type additives, drastic improvements in the mechanical properties are observed in the transverse orientation; however, not for 4-arm star type additives. To better understand these differences, we compare the effect of additive architecture on the layer adhesion of FDM printed parts and their rheology, from which, we provide crucial insight into the mechanism by which the LMW additives improve the interlayer adhesion.