Poly(butylene isophthalate-co-2,5-furandicarboxylate): Toward sustainable and moisture-resistant monolayer food packaging

The development of sustainable, renewable materials for food packaging is driving interest toward bio-based aromatic polyesters with high gas barrier performance. Among these, poly(butylene 2,5-furandicarboxylate) (PBF) has shown promising properties, although further improvements are needed to match the performance of conventional multilayer systems. In this work, a series of random copolymers of PBF and poly(butylene isophthalate) (PBI) were synthesized through a solvent-free two-step melt polycondensation process. The molecular structure and composition of the copolymers were checked by NMR spectroscopy and GPC analysis, while their thermal and structural properties were analyzed using DSC, TGA, and XRD techniques. Tensile tests were used to investigate mechanical performance indicating a high tunability of mechanical properties by changing composition. Gas permeabilities for oxygen and carbon dioxide were measured under both dry and humid conditions to evaluate barrier properties, showing that the barrier performance in dry conditions improved with increasing PBI content, whereas under moist conditions, all samples behaved as excellent barrier when sufficiently amorphous. The effect of crystallinity on gas barrier properties was furtherly investigated by comparing amorphous and semicrystalline samples of the same polymer, indicating a detrimental effect of crystallinity on gas permeability, especially under moist conditions. Overall, the study aims to demonstrate the potential of this copolymer family as high-performing materials for monolayer food packaging, with compositions favoring the best balance between performance and bio-based content depending on the desired application.