Large format additive manufacturing of polyethylene terephthalate (PET) by material extrusion

Polyethylene terephthalate (PET) is an engineering material widely used in packaging and cosmetics, given its excellent mechanical properties, water resistance and recyclability. PET is typically manufactured by injection blow molding but its use in additive manufacturing (AM) is not spread enough due to its (semi)crystalline behavior, which makes it difficult to process by Material Extrusion (ME) technologies. Alternatively, polyethylene terephthalate glycol copolymer (PETG), a fully amorphous material, is used in these technologies. However, PETG has worse mechanical properties than PET. In this context, this work studies the viability of different commercial PET by ME for Large Format Additive Manufacturing (LFAM). While PET for general purposes (PET1 and PET2) could not be printed, a marketable PET for thick-walled products (PET3) allowed to manufacture different objects by ME-LFAM with good dimensional accuracy. DSC and XRD studies evidenced that its slow crystallizing behavior was key to obtaining a proper flow and a successful printing. Young's modulus and tensile strength of PET3 was significantly higher than those of PETG, both from this work and in previous reports found in the literature, since it remains semicrystalline after printing. This allows expanding the library of materials available for AM, positioning PET as a potential material for those industrial applications where PETG does not meet the necessary mechanical requirements.