Improving Interlayer Adhesion in 3D Printing with Surface Segregating Additives: Improving the Isotropy of Acrylonitrile-Butadiene-Styrene Parts

Printed 3D objects built by fused deposition modeling (FDM) are well-known to exhibit large anisotropic mechanical properties. This anisotropy is due to poor diffusion and entanglement of chains between filaments during the deposition process. A weak interlayer bond is thus formed. To combat anisotropy in FDM printed parts, our group has utilized bimodal blends of a chemically identical low molecular weight surface segregating additive (LMW-SuSA) blended with a bulk, commercially available poly(lactide) (PLA). Drastic improvements to the interlayer adhesion and a reduction in the anisotropic character are realized with the introduction of the LMW-SuSA. To expand our understanding of the mechanism responsible for this improvement, we report the introduction of LMW-SuSAs of miscible styrene-co-acrylonitrile (SAN), poly(methyl methacrylate) (PMMA), and immiscible PLA to ABS and their impact on the mechanical properties of printed FDM parts. Decreases in the anisotropy of mechanical properties of ABS blends containing SAN (8.5k, 33k, and 75k), PMMA (33k, 67k, and 100k), and PLA (33k-3 arm and 220k) are tested. With the addition of 33k PMMA and 33k-3 arm PLA to ABS, the transversely oriented parts maximum stress increases by 40 and 25%, respectively. A significant improvement in isotropy in the modulus is also observed. Interestingly, LMW-SuSAs of SAN do not improve the isotropy of the part. More importantly, experiments utilizing energy dispersive X-ray spectroscopy (EDS) confirm the surface segregation of LMW PMMA and PLA to the interfilament interface, indicating that improvements in layer adhesion are a result of increased diffusion and entanglement of chains across the interlayer interface.