Rheological Assessment of Compatibility and Hydrolytic Degradation of Poly(glycolic Acid)/Poly(butylene succinate) (PGA/PBS) Blends

Reactive compatibilization of PGA/PBS blends via epoxy-functionalized chain extender Joncryl for improving mechanical properties and interfacial adhesion. The incorporation of carbodiimide (CDI) anti-hydrolysis agent has delayed the hydrolytic degradation by scavenging carboxylic acid and water molecules. A four-stage hydrolysis degradation mechanism was identified based on changes in plateau modulus (G N 0 ) and frequency (ω) from the oscillatory shear rheology test, offering a rheological fingerprint of hydrolysis evolution. The rheology-based approach can work as an efficient tool, compared to the conventional techniques (e.g., molecular weight loss, sample weight loss, and mechanical performance), in evaluating the structural integrity of biodegradable polyesters. With the growing applications of biodegradable polyesters in packaging and biomedical devices, the performance enhancement and well-controlled degradation profile are equally important for sustainable polyester product development. Among these biodegradable polymers, poly(glycolic acid) (PGA) stands out as a fully environmentally compostable, high-performance biopolyester with exceptional barrier properties and mechanical strength. However, its rapid hydrolysis rate significantly compromises its stability and service life. This work presents a detailed rheological study to evaluate the hydrolytic degradation of compatibilized poly(glycolic acid)/poly(butylene succinate) (PGA/PBS) blends. Reactive extrusion with epoxy-functionalized Joncryl as the compatibilizer, together with the inclusion of carbodiimide (CDI) as a hydrolysis stabilizer, significantly enhanced the mechanical integrity and hydrolytic resistance of PGA/PBS blends. The hydrolysis degradation profiles of the blends were quantitatively investigated using an intrinsic material parameter G N 0 , i.e., the terminal rubbery plateau modulus of the polymer determined by oscillatory shear rheology. Four distinct hydrolysis stages were identified according to the G N 0 vs. frequency (ω) relationship, which interestingly corresponds to the mechanical degradation results. The rheology method offers a more efficient tool in diagnosing the hydrolysis progression of polymers, compared with conventional methods, such as tracking the molecular weight changes, weight loss, and or mechanical performance over time, thus overcoming sampling challenges and analytical limitations. The phase angle and plateau modulus relationship determined through oscillatory shear measurement can be applied as rheological fingerprints for quantifying the hydrolysis of compatibilized polyester blends.