Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers

Rene Sattler; Rui Zhang; Gaurav Gupta; Mengxue Du; Paul-Maximilian Runge; Holm Altenbach; René Androsch; Mario Beiner

doi:10.1021/acs.macromol.3c01940

Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers

Macromolecules. 2024 Mar 19;57(7):3066-3080. doi: 10.1021/acs.macromol.3c01940. eCollection 2024 Apr 9.

Authors

Rene Sattler^{1

2}, Rui Zhang³, Gaurav Gupta^{1

2}, Mengxue Du³, Paul-Maximilian Runge⁴, Holm Altenbach⁴, René Androsch³, Mario Beiner^{1

2}

Affiliations

¹ Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Walter-Hülse-Str. 1, DE-06120 Halle (Saale), Germany.
² Faculty of Natural Sciences II, Martin-Luther-University Halle-Wittenberg, Heinrich-Damerow-Str. 4, D-06120 Halle (Saale), Germany.
³ Interdisciplinary Center for Transfer-Oriented Research in Natural Sciences, Martin-Luther-University Halle-Wittenberg, Universitätsplatz 10, D-06120 Halle (Saale), Germany.
⁴ Institute of Mechanics, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, D-39106 Magdeburg, Germany.

Abstract

We report the results of a study focusing on the influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D-printed parts made from polyamide 12 (PA12) and poly(lactic acid) (PLA) by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and wide-angle X-ray diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid-solid phase transition between the (pseudo)hexagonal γ phase near room temperature and the monoclinic α' phase above the Brill transition temperature T_B = 140 °C. The influence of the print bed temperature T_b on structure formation, polymorphic state, and degree of crystallinity χ_c of the 3D-printed parts is investigated by height and depth-dependent WAXD scans and compared with that of 3D-printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phases is present in the 3D-printed parts. In the case of PLA, a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χ_c and thus the homogeneity of the 3D-printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC, and FSC measurements with relevant printing times, guidelines for 3D-printed parts with a homogeneous structure are derived.