Optimization of mechanical properties of glass-spheres-filled polypropylene composites for extrusion-based additive manufacturing

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. (c) 2017 Society of Plastics Engineers