Impact of Trace Contaminants on Mechanically Recycled Polyethylene Terephthalate

Polyethylene terephthalate (PET), a material widely used in packaging, offers excellent mechanical, optical, and barrier properties, and is inherently recyclable. In 2024, the global PET market was valued at approximately USD 39 billion, with packaging applications accounting for nearly 82 percent of the total market. With a projected annual growth rate between 6 -9 percent, it is expected to reach USD 50 billion by 2030. However, despite its recyclability, only about 30 percent of PET is currently recycled in the United States, mainly due to limited recycling infrastructure and the challenges posed by trace contaminants in mechanical recycling processes. Among the various trace contaminants, packaging labels made from crystallizable PET, caps composed of density polyethylene (HDPE), and polyvinyl chloride (PVC) from bottles overlooked by automatic sorting systems pose significant challenges to the mechanical recycling of PET. Despite pre-sorting efforts, small fractions of these contaminants remain in the recycled PET stream due to their similar densities and indistinct appearance. This leads to degradation during reprocessing, adversely affecting the molecular weight, thermal stability, mechanical strength, and appearance of recycled PET (rPET). In this study, HDPE, crystallizable PET labels, and PVC were intentionally introduced as contaminants into virgin PET and subjected to multiple extrusion cycles to simulate mechanical recycling. The impact of these contaminants on the thermal, mechanical, and optical properties of rPET was systematically evaluated. The findings provide valuable insight into PET's degradation behavior in the presence of these contaminants and offer guidance for establishing contamination tolerance threshold during recycling at industrial scale.