Mechanical Recycling Processes of Polyethylene Terephthalate (PET) in the Framework of Circular Bottle-To-Bottle Manufacturing

The amount of plastic waste released into the environment has prompted the scientific community to seek new strategies to tackle the problem. Among common pollutants, Polyethylene Terephthalate (PET) bottles are leading contributors, accounting for 30%–40% of plastic waste. However, recently, new recycling opportunities have been emerging, with academia and industry increasingly focusing on innovative approaches. One method that has boomed recently is solid-state polycondensation (SSP), a process that, through the re-gradation of recycled polymer, gives PET from bottles a second life, aiming for bottle-to-bottle recycling. This paper aims to characterize a recycled regraded PET sample in comparison with mechanically recycled PET, and to compare it with blends made from virgin and recycled PET bottles (monopolymer blends). This last strategy is commonly used in industry to reduce the environmental impact of plastic materials. All samples were characterized in shear and elongational flow, and tensile properties were measured and correlated with variations in molecular structure and morphology. The results showed that monopolymer blends of virgin and recycled PET exhibited tensile strengths of 39.4, 38.5, and 37.1 MPa and elongation at break of 319%, 310%, and 294%, at 10%, 25%, and 50%, respectively, while the regraded PET by SSP showed a tensile strength of 44.7 MPa and elongation at break of 218%, demonstrating that the monopolymer blend exhibits mechanical performance suitable for bottle production.