(270h) Recycled Poly(ethylene terephthalate) / Poly(ethylene terephthalate glycol-modified) Composite Filament for Sustainable Material Extrusion Additive Manufacturing

Growing global concerns about plastic waste and sustainability have ramped up demand for the use of recycled plastics in additive manufacturing. However, the compromised mechanical integrity of 3D-printed parts produced from recycled materials poses a major problem. Specifically, recycled polyethylene terephthalate (rPET) tends to have a loss in mechanical performance after reactive extrusion due to a loss of molecular weight, creating low viscosity and weak melt strength making it difficult for fused deposition modeling (FDM).

To overcome these shortcomings, the present study investigates the creation of a recycled composite filament based on a blend of rPET and poly(ethylene terephthalate glycol-modified) (PETG), filled with biomass-based activated carbon and compatibilized by the chain extender pyromellitic dianhydride (PMDA) compatibilizer to offset degradation and improve interfacial adhesion between the phases of the polymer. Through altering the additive compositions, composite filaments of an even diameter of 1.75 ± 0.05 mm were fabricated using melt extrusion to be used for FDM applications. Reactive melt extrusion was utilized for the processing of the material. Thermal testing and rheological indicated increased crystallinity and thermal stability for the PMDA-modified blends. Mechanical properties were shown to increase tensile strength and modulus significantly, especially in the PETG-rich samples, with more ductility retained. FDM trials evidenced good printability with minimal warpage, stable extrusion flow, and improved layer adhesion.

The synergistic effect of PMDA and activated carbon enhanced both material structure and performance, making it possible to produce strong, printable filaments from recycled and commercial polymers. This research offers a scalable and inexpensive route to the production of mechanically reinforced, functionally graded filaments, beneficial to circular economy initiatives in polymer engineering.

Keywords: Fused deposition modeling, Material extrusion-additive manufacturing, Polymer composites, Reactive extrusion, Recycled Poly(ethylene terephthalate)