Circular economy solutions for plastic waste: improving rheological properties of recycled polyethylene terephthalate (r-PET) for direct 3D printing

As global plastic production reaches unprecedented levels, the increasing amount of plastic entering our oceans poses serious environmental risks. The Circular Economy (CE) concept plays a key role in this shift, from linear to circular, by promoting waste reduction, improved recycling methods, and innovative technologies that convert waste into value-added products. Among waste polymers, poly (ethylene terephthalate) PET, known for its enhanced properties like chemical resistance and mechanical properties, which is widely used for water bottles and food containers, is a prime candidate for recycling efforts. Taking advantage of 3D printing and recycled PET as a feedstock emerged as one of the potential solutions to reuse waste PET. However, 3D printing recycled PET (r-PET) is challenging due to the deterioration of physical properties after recycling compared to virgin PET, like reduced viscosity and melt strength, as well as chain scission. To address these challenges and direct 3D printing of r-PET, this study, for the first time, modified r-PET using a proprietary additive, to make it compatible with 3D printing and enhance properties. Through analysis of flow behavior and examinations of thermal stability, chemical structures, and mechanical properties, it is found that 0.75% is the optimum amount of additive added to r-PET, which improves the printability of r-PET feedstock. After the addition of 0.75% additive, the complex viscosity of the modified r-PET increased from 200 Pa.s to around 1000 Pa.s, which meets the viscosity requirements for 3D printing. In addition, ultimate tensile strength of modified r-PET reached around 51 MPa which is comparable with commercial filaments like ABS, PETG and PLA. The findings of this study highlight the importance of using modifiers as additives to enhance the properties of recycled waste plastic, rendering them suitable for 3D printing. This facilitates the reprocessing and remanufacturing of new products within the framework of a circular economy with the aid of 3D printing.