Sustainable approach to produce 3D-printed continuous carbon fiber composites: “A comparison of virgin and recycled PETG”

The use of recycled polymers in 3D printing technologies has recently become a promising research topic because of the global concerns on plastic waste pollution and an increase in awareness of sustainability and circularity. In order to unlock the potentials of 3D printing beyond prototyping purposes, continuous fiber-embedded fused filament fabrication (FFF) as a process for composite production has gained importance. This study focuses on the potential use of recycled, glycol-modified poly(ethylene terephthalate) (rPETG) as a matrix material in continuous fiber additive manufacturing of composites. First, the characteristics of rPETG were compared with those of non-recycled PETG in terms of molecular weight as well as rheological, thermal, and mechanical properties. Then, rPETG and PETG composites containing 25% continuous carbon filament (CCF) fibers (CCFs) were printed using a co-extrusion-type FFF printer. Their tensile and flexural properties were characterized. It was found that the tensile properties of rPETG-based composites were lower than those of PET-based composites, but their flexural properties were nearly the same. The thermodynamic work of adhesion approach was applied to understand the interfacial interactions between the matrix and CFF. It was found that the thermodynamic adhesion between rPETG/CFF was higher than that of PETG/CFF. Additionally, SEM-SE images obtained from the fracture surfaces of the samples supported the findings by showing that the adhesion between rPETG and CF was superior to that between PETG and CF. Thus, this study demonstrated that recycled PETG can be used as a possible matrix material for 3D-printed CCF composites, thus highlighting the ability of recycled plastics to be converted into circular products with high added value.