Circularity in 3D Printing with Poly(Ethylene Terephthalate Glycol): Copolymer Composition Dependent Degradation During Recycling

Reduced environmental impact is commonly cited as a driver for additive manufacturing, but non-circular end-of-life disposition of the printed materials reduces these advantages. In particular, thermoplastics commonly used in material extrusion additive manufacturing (MEX) are not compatible with most recycling infrastructures; polyethylene terephthalate glycol (PETG) is particularly problematic as it compromises the integrity of polyethylene terephthalate (PET) recycling streams. Thus, circular recycling of PETG within the MEX ecosystem is necessary, but the comonomer, cyclohexane dimethanol (CHDM), content differs across commercial sources. Here, we demonstrate that the reduction in the viscosity of the PETG through multiple cycles of print-test-reprocess to filament (recycling) is dependent on the sourcing but not directly correlated with the CHDM content or molar mass. The elastic modulus and tensile strength of the printed PETG are not significantly impacted by recycling over 5 prints. However, the ductility of the printed PETG decreases after recycling one time for the lowest CHDM content PETG while the ductility first increases and then decreases through multiple reprocess cycles with higher CHDM content in the PETG. These results illustrate circular recycling through MEX may increase the number of cycles possible without significant degradation in part stiffness and strength when compared with mechanical recycling using traditional manufacturing methods.