Olive Pomace as a Reinforcing Agent in PETG Filaments for 3D Printing in the Context of Circular Economy.

3D printing is increasingly present in many industrial applications, where petroleum-based polyethylene terephthalate glycol (PETG) is gaining importance. This is due to both its mechanical properties and ease of printing. In this context, with the aim of reducing the presence of plastics during the manufacturing process, the addition of olive pomace (OP) as an additive is proposed. OP is a residue from the olive oil industry that represents an environmental challenge, due to its high content of organic matter and phytotoxic compounds. To optimize the fabrication and further analysis of 3D printing filaments composed of a mixture of PETG and OP, a design of experiment (DoE) was used. To gain knowledge about the relationship between mechanical properties of different OP/PETG blends, OP particle size as filler, and extrusion number to produce the optimal filament, analysis of variance (ANOVA) besides response surface methodology (RSM) was applied. Additionally, thermogravimetric (TGA), differential scanning calorimetry (DSC), infrared (IR) spectroscopy analysis, and scanning electron microscope (SEM) of the new composite material blends were carried out. Subsequently, different OP/PETG filaments were produced via material extrusion additive manufacturing. This study revealed that the addition of 8% (v/v), < 100 µm OP particle size, fabricated using a double extrusion process, to PETG composites exhibited significantly enhanced mechanical properties. In particular, the incorporation of OP filler resulted in a remarkable increase in yield strength (35%), tensile strength (8.4%), and Young's modulus (27%). Furthermore, slight improvement in ductility, evidenced by an increase in elongation at yield (4.18%) and at break (5.16%), demonstrates the potential of OP as a valuable and sustainable reinforcement material for PETG composites. These findings pave the way for the development of high-performance environmentally friendly materials derived from residues, in the context of circular economies, for applications that require stiffer, stronger, and more tenacious material than straight PETG.