A major challenge in extrusion‐based additive manufacturing is the lack of commercially available materials compared to those in well‐established processes like injection molding or extrusion. This study aims at expanding the material database by evaluating the feasibility of polypropylene, which is one of the most common and technologically relevant semicrystalline polymers. Expanded‐perlite‐filled polypropylene and ternary blends with amorphous polyolefins are evaluated to establish an understanding of their processability and their printability. A detailed study on the shrinkage behavior, as well as on the thermal, mechanical, morphological, and warpage properties is performed. It is found that smaller sized fillers result in a tremendous warpage and shrinkage reduction and concurrently improved mechanical properties than compounds filled with bigger sized fillers. Based on the optimal properties profile, a ternary blend that can overcome the shrinkage and warpage of printed parts is suggested.

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Polypropylene (PP) parts produced by extrusion‐based additive manufacturing (EB‐AM) suffer from warpage issues due to their high degree of crystallinity and orientations introduced during printing. These issues can be overcome by the addition of spherical fillers. However, the low aspect ratio of the filler and high filling degrees necessary for preventing warpage downgrade the mechanical properties, especially the toughness. This study aims at optimizing a PP‐compound containing spherical glass microspheres for the application in EB‐AM by maximizing the matrix–filler compatibility and therefore the printability, tensile properties and toughness, while still counteracting dimensional inaccuracies. A detailed study on the tensile, fracture, thermal, rheological, and impact properties of various compounds containing different glass types was conducted. It was shown that for EB‐AM applications, PP compounds based on borosilicate glass spheres outperform compounds filled with the conventionally used inorganic soda lime glass. The proposed optimized composite exhibits an exceptional interfacial adhesion between the microspheres and the matrix and a homogeneous filler distribution. It offers an improved processability and tensile properties up to the yield point comparable to those of neat PP. In a concluding impact test on printed composites, the optimized system exhibited impact energies 80% higher than compounds containing the conventionally used glass. POLYM. COMPOS., 40:638–651, 2019. © 2017 Society of Plastics Engineers

Parts produced by extrusion‐based additive manufacturing experience the disadvantage of consisting of many weld‐lines, which consequently downgrade their mechanical properties. This work aims at maximizing the strength of printed parts by considering and improving the intra‐ and inter‐layer cohesion between adjacent strands. Therefore, printed poly(lactic acid) specimens were characterized by means of a particular tensile test setup, and the inter‐layer cohesion of printed specimens was evaluated by means of the double cantilever beam test. A detailed parametric statistical evaluation, which included printing temperatures, layer thicknesses, and layer‐designs, was complemented by the material's viscosity data and the analysis of the specimens' fracture surfaces and cross‐sections. An optimal layer‐design was found to be a key parameter in the optimization of strength with regard to different loading directions. Additionally, the maximization of the cohesion leads to a tremendous improvement in the mechanical performance of the printed parts, resulting in strengths of roughly 90% of those of compression‐molded parts. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45401.

A challenge in extrusion‐based additive manufacturing of polypropylene (PP) filled with spherical particles is the combination of decent processability, excellent warpage control, and the retention of the tensile strength of neat PP. This study addresses this issue by adopting two approaches. Firstly, different size fractions of borosilicate glass spheres incorporated into PP are compared. Secondly, the temperature of the printing chamber (TCh) is varied. The effects of these features on the thermal, crystalline, morphological, tensile, impact, and warpage properties of 3D‐printed parts are examined. Smaller glass spheres (<12 µm) are found to be superior to larger fractions in all investigated aspects. Notably, the corresponding composites show higher tensile strengths than neat PP. An increase in TCh results in a more homogeneous temperature distribution within the printing chamber and promotes annealing during printing. Consequently, the dimensional accuracy of printed parts is improved. Additionally, β‐crystals and larger spherulites are formed at a higher TCh.