Upcycled PET vitrimer filaments via reactive extrusion for high strength heat resistant and repairable FDM parts

Global plastic waste streams motivate routes that convert polyethylene terephthalate into durable, repairable parts through additive manufacturing. The central question addressed is whether a continuous reactive-extrusion process can transform polyethylene terephthalate flakes into vitrimer filaments that deliver high strength, heat resistance, and repairability with practical energy and cost. Developed a twin-screw reactive-extrusion route that couples grafting and vacuum devolatilization with in-line drawing to 1.75 mm filament, and verified transesterification and imine exchange using infrared spectroscopy, solid-state carbon nuclear magnetic resonance, gel fraction, and Flory–Rehner analysis. Rheology and stress-relaxation defined a topology-freezing window of 120–145 °C and activation energies of 148–190 kJ mol -1 , guiding print settings and post-print repair schedules. Printing at 252–255 °C nozzle, 85 °C bed, and 0.20 mm layers produced consistent deposition; mechanical testing reached tensile strength up to 63 MPa, interlayer shear 28–30 MPa, and heat-deflection temperature of 120–125 °C. Weld repair at 150–180 °C restored about 80% tensile strength, and five melt reprocessings retained about 95% heat-deflection temperature with modest viscosity drift. Microscopy showed wider inter-bead necks and about 1.6% porosity with nano-silica, consistent with tougher interfaces. Process energy use totaled 1.70 kWh kg -1 and modeled cost was $1.69 kg -1 with major contributions from feed at $0.752 and electricity at $0.345. The study demonstrates a scalable pathway to high-strength, heat-resistant, and repairable vitrimer parts from waste polyethylene terephthalate with quantified performance, energy, and cost. • Dual dynamic PET vitrimer via reactive extrusion for direct FDM. • Stable print window: 252-255 °C nozzle, 85 °C bed; 0.20 mm layers. • As-printed strength 63 MPa tensile and 28-30 MPa interlayer shear. • Weld repair at 150 °C for 5 min restores about 80% tensile strength. • Five reprocess cycles retain about 95% HDT and 86% storage modulus.