Barrier Properties of Biodegradable Aliphatic‐Aromatic Copolyesters (PBXT) Series

AbstractAliphatic‐aromatic biodegradable polyesters, characterized by their exceptional macroscopic properties and significant cost‐effectiveness advantages, have facilitated the development of numerous commercial products. In this study, a series of biodegradable poly(butylene alkylene carboxylate‐co‐terephthalate) (PBXT) copolymers with varying methylene numbers in the alkylene units (0, 2, 4, and 8) were synthesized. These copolymers, namely poly(butylene oxalate‐co‐terephthalate) (PBOT), poly(butylene succinate‐co‐terephthalate) (PBST), poly(butylene adipate‐co‐terephthalate) (PBAT), and poly(butylene sebacate‐co‐terephthalate) (PBSeT), were prepared with nearly identical structural and molar compositions. The objective of this study was to comprehensively examine the impact of alkylene unit length on the barrier properties of the materials, delving into aspects such as crystallinity, free volume, molecular chain mobility, as well as adsorption and diffusion of gases within the materials. The findings indicated a decrease in crystallinity from 17.2% for PBOT to 10.2% for PBSeT as the alkylene chain length increased, while maintaining the same chemical composition. Concurrently, the fractional free volume increased from 0.9% to 2.6%, and the melt flow activation energy decreased from 106.6 kJ/mol to 52.1 kJ/mol. Importantly, theoretical calculations were performed, demonstrating that the predominant site for gas adsorption and diffusion was within the material's free volume. These combined observations indicated a gradual decrease in barrier properties as the number of methylene groups in the length of the alkylene unit increases.This article is protected by copyright. All rights reserved