Thermomechanical response of thermoplastic polyurethane used in MEX additive manufacturing over repetitive mechanical recycling courses

Abstract

Sustainability is critical nowadays, with a growing interest in polymers, due to their increasing usage in products. Mechanical recycling of polymers involves grinding/shredding and thermal extrusion of the material. This is a thermomechanical process, which negatively affects the bulk mechanical performance of the polymer and may potentially introduce contamination. This work investigates the response of Thermoplastic Polyurethane (TPU) in material extrusion (MEX) 3D printing, after multiple recycling courses. Each course comprises two thermal cycles, one in the extruder for filament fabrication and a second one in the 3D printer's nozzle, for the manufacturing of the parts, following corresponding standards. The response of the material after up to six repetitions of the process was studied in this work. In each repetition, the effect of the process on the mechanical (tensile, flexural, impact, microhardness, Dynamic Mechanical Analysis), thermal (Thermogravimetric Analysis), morphological (Scanning Electron Microscopy), and structural (Micro X-Ray Computed Tomography Scanning & Analysis) behavior of the material was studied. The results of the study show a reasonable potential for the sustainability of the TPU material, exploiting 3D printing advantages. The highest tensile strength is reported in the sixth repetition of the thermal reprocessing of the material, indicating that TPU mechanical recycling is a viable option.