Processability of Recycled Polypropylene for More Sustainable Pellet-Based 3D Printing

Abstract:

This study evaluates the processability of recycled polypropylene (rPP) in pellet-based material extrusion (MEX) to support more sustainable additive manufacturing. Virgin polypropylene (PP) and post-consumer rPP obtained from end-of-life woven builder bags were processed in neat form and as PP/rPP blends with increasing recycled content. Melt-flow behavior was characterized using a Technological Melt Flow Index (TMFI), a process-specific metric reflecting the combined effects of temperature and screw rotation. Disk-shaped specimens were printed to assess deposition behavior through the build-up rate (BUR), which integrates shear flow in the extruder and elongational deformation during deposition. TMFI results show that rPP exhibits markedly higher flowability than virgin PP below 200°C, indicating potential for lower-temperature, energy-efficient processing. In contrast, printing experiments reveal that BUR systematically decreases with increasing rPP content. This trend indicates a transition to an elongation-dominated deposition regime, where rPP displays higher resistance to extensional deformation during deposition, resulting in narrower roads and reduced spreading. Regression analysis confirms that BUR is governed primarily by flow-rate setting (F%) and nozzle speed (Sp%), whereas nozzle temperature Te (°C) has only a minor influence within the investigated window. Overall, the results demonstrate the competing rheological effects introduced by recycling and highlight the need for tailored parameter optimization to enable higher rPP incorporation in pellet-based 3D printing.

• Periodical: Key Engineering Materials (Volume 1051)
• Pages: 21-27
• DOI: https://doi.org/10.4028/p-Jy7jtU
• Online since: April 2026
• Authors: Dorna Peymani*, Matteo Strano
• Keywords: Pellet-Based Additive Manufacturing (AM), Polypropylene (PP), Recycled Polypropylene (RPP), Sustainable Manufacturing

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