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

Abstract

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

Polypropylene Filled With Glass Spheres in Extrusion‐Based Additive Manufacturing: Effect of Filler Size and Printing Chamber Temperature

“…As the investigated composites of the present work are based on the optimized composition of ref. , all the composites show a homogeneous filler distribution, as highlighted for all fillers (Figure b‐d) by white circles for reasons of clarity. This enables a constant printing flow rate over time and does not lead to blocked nozzles.…”

“…Prior to the investigations on printed parts, the morphology and the tensile tests of the filaments ( Figure ) were investigated in order to verify whether the FFF process requirements are met . The matrices of all the filled materials investigated (Figure b–d) exhibit a similar morphology compared to that of neat PP (Figure a).…”

“…All composites ( Table 1 ) were processed by mixing the materials for 30 min at 200 °C in a lab kneader (Polylab Rheomix 3000, Thermo Fisher Scientific Inc., Germany) equipped with two counter‐rotating roller blades at a rotation of 60 rpm. A constant glass filler content of 30 vol% was investigated in order to reduce the warpage of the printed composites in a most promising manner . For all the filled compounds, PP was melted for 2 min.…”

“…Polypropylene (PP), for example, is a promising material for FFF due to its high impact strength, chemical resistance, moisture stability, and low cost . However, little research has been conducted on the main drawback connected with the 3D printing of PP, which is the fact that PP parts are prone to dimensional inaccuracies, in particular to warpage . These are facilitated by the introduction of orientations during printing and the material's high crystallinity .…”

“…One possible approach to further improve the yield stress and simultaneously optimize the warpage behavior of the most promising compound of ref. is to use selected size fractions of the fillers. The effect of different filler sizes on the warpage and the mechanical properties has not yet been investigated for optimized 3D‐printed PP composites in detail, although smaller fillers promise a better shrinkage and warpage reduction .…”