Reactive Extrusion of Polyethylene Terephthalate/Polyethylene Furanoate Copolyesters: Structure–Property Relationships for Rigid Packaging

Copolymerization of Polyethylene Terephthalate (PET) with biobased Polyethylene 2,5-Furan dicarboxylate (PEF) presents a promising route to enhance material properties and increase biobased content of PET copolyesters used in rigid packaging. Traditionally, in situ polymerization of terephthalic acid (TPA) and ethylene glycol (EG) with 2,5-furandicarboxylic acid (FDCA) (5–20 wt %) yields copolyesters with improved characteristics. In this study, we explore a practical alternative approach: reactive extrusion of PET with 10% PEF using a twin-screw extruder to produce copolyesters comparable to those obtained via in situ polymerization. The optimal processing conditions were identified, and the process-structure–property relationships were investigated by analyzing the thermal, mechanical, barrier, and optical properties for both reactive extruded and in situ polymerized samples. Key structural parameters such as degree of randomness, extent of transesterification, and chain length were assessed using nuclear magnetic resonance (NMR) spectroscopy. The results indicated that an optimal transesterification temperature of 290 °C produced blends with properties closely matching those of in situ polymerized copolyesters. The reactive extrusion approach led to notable improvements in the oxygen barrier performance and mechanical strength, enhancing the suitability for rigid packaging. The material’s enhanced functionality was further validated by successfully injection molding preforms and blow molding them into 2 L bottles, later characterizing the bottle properties. Overall, this work highlights the feasibility of reactive extrusion as a scalable method to produce PET–PEF copolyesters with superior properties, effectively bridging the gap between lab-scale development and industrial-scale production.