Correlating viscosity and die swell in 3D printing of polyphenylsulfone: A thermo-mechanical optimization modus operandi

Abstract

Additive manufacturing (AM) of polyphenylsulfone (PPSU), an amorphous high-performance polymer (HPP), has shown promise in exhibiting structural integrity for many applications. With thermoplastic material extrusion 3D printing, parts consisting of layered melts exhibited voids, where the adhesion quality and void size depend on the processing parameters implemented during printing. However, the structure-process-property (SPP) relationships between the thermal properties and rheological and mechanical behavior of AM PPSU are poorly understood. In this study, a comprehensive analysis of the thermal, thermo-mechanical, and layer-by-layer build-up of PPSU is investigated and correlated with viscosity and extrudate die swell behavior with void fraction volume as confirmed by high-resolution x-ray computed tomography (XCT). Gas chromatography–mass spectrometry (GC–MS) pyrolysis confirmed PPSU composition and degradation at 480 °C, consistent with thermo-gravimetric analysis TGA. A 141% difference in viscosity was observed when processing temperatures increased from 350 °C to 400 °C. Likewise, extrudate die swell decreased with increasing temperatures, resulting in a 17% difference. Tensile and compressive properties confirmed that higher extruding temperatures resulted in lower porosity and higher mechanical strength. In general, higher extruding temperatures lower the viscosity to allow for stronger cohesion between layers; however, increasing the temperature too high results in a below unity extrudate die swell, reducing mechanical properties. Therefore, to optimize the mechanical integrity of 3D printed amorphous PPSU parts, an increase in the viscosity, near unity of the extrudate die swell, and tempered extrusion temperature are needed.