A comparative study of recycled PET, PETG, and virgin opaque PET for material extrusion

Abstract

Additive manufacturing using material extrusion (MEX) is a widely used technology that facilitates the creation of durable, lightweight, and stable components for various applications. Polyethylene terephtalate (PET), the most used plastic for bottles, cannot be printed due to inadequate rheological properties. This study aims to characterize recycled PET (PETr) to identify the optimal parameters and conditions necessary for this polymer to compete effectively with conventional thermoplastic filaments used in 3D printing. A comparative study is conducted between PETr, virgin opaque PET (PETo) to assess PETr’s performance against virgin opaque PET, and PETG (polyethylene terephthalate glycol), one of the most used materials in MEX. This work is part of a larger project whose ultimate goal is to modify PETr to achieve rheological properties similar to PETG. Materials undergo different transformations through extrusion, drying, and thermocompression, followed by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and rheological testing to assess thermal and mechanical properties. Initial DSC results indicate that PETr and PETo are semi-crystalline, melting at approximately 238°C-257°C, while PETG is amorphous. TGA results show a degradation temperature of 443°C – 451°C. Rheological tests reveal a Newtonian plateau whatever the temperature for PETG in the frequency range, whereas the viscosity of recycled PET and opaque PET exhibit a significant change in viscosity curves with temperature. Findings suggest that recycled PET is currently not a viable option, the polymer must be formulated to adjust it thermal and rheological properties to be considered as a competitive option for 3D printing applications, aligning environmental benefits with the mechanical standards of commercial filaments.