Decentralized Closed-Loop Additive Manufacturing from Post-Consumer PET Bottles: Mechanical Performance and Interpretable Stress-Response Prediction

Decentralized recycling offers a promising pathway for circular additive manufacturing, yet the physical variability of local waste streams often compromises material reliability. This study evaluates the direct conversion of post-consumer polyethylene terephthalate (PET) bottles into structural feedstock for fused filament fabrication (FFF). Using a custom automated extrusion system, bottles with wall thicknesses of 0.25 mm and 0.475 mm were processed into standard 1.75 mm filament. ASTM D638 Type IV tensile specimens were printed from the recovered material and benchmarked against commercial PLA, ABS, and PETG. Results showed that process stability is highly sensitive to initial bottle geometry; continuous extrusion requires strip widths to be strictly calibrated to the source wall thickness. The optimized recycled PET (rPET) filament demonstrated highly competitive mechanical properties. It achieved an ultimate tensile strength of 45.31 MPa, retaining nearly 98% of PLA’s strength, along with superior elongation at break (8.65%) and toughness (2.23 MJ/m³). The system recorded an average material recovery yield of 53.8%. To address quality-control barriers in distributed manufacturing settings, an interpretable XGBoost regression model was developed using 15,738 continuous tensile-strength data points. The model successfully predicted non-linear stress-response trajectories with a Root Mean Square Error of 0.901 MPa. SHAP analysis confirmed that these predictions were driven by physical load and yield-stress parameters rather than data leakage. By combining geometry-specific extrusion guidelines with data-driven quality assurance, this research outlines a practical method for manufacturing engineering-grade structural components directly from recovered plastics.