Multi‐modal assessment of recycled polyethylene terephthalate composites in additive manufacturing: The role of carbon fiber

Abstract With the growing interest in sustainable manufacturing, 3D printing with recycled Polyethylene Terephthalate (rPET) offers an innovative approach to upcycling waste. This study explores the potential of combining rPET with milled short carbon fibers and polymer chain extenders to produce high‐performance 3D printing filaments through melt extrusion. Filaments containing 5% and 10% carbon fiber, with and without sizing, along with a polymer chain extender, were investigated to enhance viscosity and material properties of rPET. Thermal analysis techniques evaluated the material's thermal stability and transitions, assessing the degradation temperature and calorimetric properties including glass transition and melting temperatures, while the measured carbon fiber content closely matched the theoretical content. Tensile testing of unidirectionally printed samples showed promising mechanical properties. X‐ray micro‐computed tomography assessed fiber length in extruded filaments, comparing it with the target length set during manufacturing, showing agreement. Scanning electron microscopy examined fracture and side surfaces, revealing governing failure mechanisms and defects, attributed to filament production and composition. This study highlights the synergistic role of carbon fiber sizing and chain extenders in enhancing tensile modulus, while improving overall consistency and quality of extruded filaments. It presents a groundbreaking pathway for sustainable, high‐performance additive manufacturing. Highlights Investigated the synergistic effect of CF sizing and chain extenders in rPET. Melt extrusion achieved 10% CF with excellent fiber alignment and integrity. Additives enhanced thermal stability, crystallization, and adhesion. SEM and Micro‐CT revealed improved fiber‐matrix bonding and fewer defects. Tensile modulus doubled through synergy of CF sizing and chain extenders.