Study of Transesterification Reaction in Copolymers of Poly(ethylene terephthalate) and Poly(ethylene furanoate) Using Reactive Extrusion

Abstract

Poly(ethylene terephthalate-co-furanoate) (PETF) copolymers offer a promising route to improve the sustainability and performance of poly(ethylene terephthalate) (PET)-based materials. In this study, PETF copolymers containing 10 and 30 wt % poly(ethylene furanoate) (PEF) were produced via reactive extrusion, where successive extrusion passes promoted transesterification between PET and PEF segments, leading to increased chain randomness. While up to four extrusion passes enhanced randomization, the accompanying thermal exposure caused progressive discoloration, with only modest loss of intrinsic viscosity. The increased randomization associated with transesterification reduced crystallinity and slowed crystallization kinetics. However, subsequent biaxial orientation compensated for these effects, allowing 30% PETF films to retain mechanical strength comparable to PET while exhibiting markedly improved oxygen barrier performance. To promote transesterification without extensive multipass processing, zinc acetate was introduced at 0.05–0.25 wt %, which effectively accelerated randomization. A single catalyzed pass achieved a degree of randomness equivalent to that reached after four uncatalyzed passes, at comparable intrinsic viscosity but with markedly better color, indicating that discoloration during reactive extrusion scales with cumulative thermal exposure rather than with the extent of ester exchange. Addition of a hindered phenolic antioxidant improved color further but at the cost of molecular weight, consistent with the dominant scission pathways during melt processing being nonoxidative. Overall, this work demonstrates how controlling transesterification during reactive extrusion governs copolymer structure and, in turn, processing–property relationships in PETF and identifies catalyst-accelerated randomization as a practical route to achieving the required chain architecture within industrially realistic residence times.