The presence of polymeric impurities in recycled polyethylene terephthalate (PET) streams, particularly amorphous copolyesters such as polyethylene terephthalate glycol-modified (PETG) and polycyclohexylenedimethylene terephthalate glycol-modified (PCTG), as well as polycarbonate (PC), represents a critical challenge for high-performance applications involving orientation drawing. In this study, the influence of such components on the orientation behavior and resulting mechanical properties of PET-based blends was systematically investigated. Model blends were prepared using virgin materials and processed into monofilaments via inline melt spinning followed by controlled orientation drawing with draw ratios up to 6.5. The evolution of tensile strength, modulus, elongation at break, density, and thermal shrinkage was analyzed as a function of draw ratio. The results demonstrate that PET-rich systems exhibit superior mechanical performance, which is consistent with the development of strain-induced crystallization during orientation drawing, reflected in increased density and reduced thermal shrinkage at higher draw ratios. In contrast, amorphous copolyesters (PETG, PCTG) suppress crystallization, resulting in limited structural development, lower modulus, and significantly higher thermal shrinkage. Blends containing polycarbonate showed reduced maximum draw ratios and tensile strength, indicating restricted orientation capability, but exhibited comparatively low shrinkage at moderate draw levels. The study establishes clear structure–property relationships linking molecular orientation, crystallization behavior, and macroscopic performance in PET-based blends. The findings highlight that even minor amounts (~10 wt%) of amorphous polyester impurities can significantly alter orientation efficiency and end-use properties, emphasizing the importance of feedstock control in recycling processes targeting high-performance-oriented products such as strapping tapes and monofilaments.
Sova et al. (Mon,) studied this question.