|Jin, M.; Neuber, C.; Schmidt, H.W.: Tailoring polypropylene for extrusion-based additive manufacturing, Additive Manufacturing, 33, 101101 (1-13) (2020) -- DOI: 10.1016/j.addma.2020.101101|
This paper reports on the optimization of polypropylene (PP) feedstock material towards extrusion-based additive manufacturing. To achieve this, two commercially available grades of polypropylene/ethylene random copolymers (raco PP) were modified, aiming to reduce warp deformation caused by shrinkage and at the same time reduce the anisotropic property by improving the interlayer bonding quality of 3D printed parts processed by fused filament fabrication (FFF). A β-nucleating agent, several amorphous polypropylenes (aPP) and one linear low-density polyethylene (LLDPE) were selected as additive or blending component with the goal to reduce shrinkage. The polypropylene feedstock material optimization was conducted by a combination of a labscale filament rod processing method and utilizing printed square tubes to optimize printing performance. The achieved results demonstrate that the crystallization behavior and E-modulus of polypropylene play significant roles for warp deformation in extrusion-based 3D printed parts. The β-nucleating agent alters the crystallization behavior, even a slightly negative influence on the warp deformation was observed. The investigated polymer blend of raco PP and LLDPE shows no significant contribution to reduce warpage and impairs also the interlayer bonding. The best results were achieved by blending raco PP with selected amorphous PPs. With two aPP grades warp deformation could be drastically reduced. In addition, the interlayer bonding quality is remarkably enhanced in these blends in spite of slight decreases in stiffness and strength. In conclusion, the optimized PP feedstock material features less warp deformation, high stiffness, and most importantly, outstanding interlayer bonding qualities.