Effect of mechanical recycling on the rheological and mechanical properties of bio-based and bio-degradable polybutylene succinate

In this study, the effect of mechanical recycling on the molecular, rheological and mechanical properties of poly(butylene succinate) (PBS) was thoroughly investigated via closed loop extrusion. Molecular characterization techniques, such as size exclusion chromatography (SEC) and Fourier transform infrared spectroscopy (FTIR), as well as oscillatory shear rheology were used to monitor the changes associated with reprocessing. Tensile tests were also performed to quantify the evolution of mechanical properties, such as Young's modulus (E), ultimate tensile strength (σult) and elongation at break (εb). The FTIR results showed significant changes of the hydroxyl groups in recycled PBS (rPBS). SEC confirmed a sudden molecular weight (Mw) drop by about 67 % and increased polydispersity with number of recycling loops (total extrusion time). On the other hand, the rheological properties, such as zero-shear viscosity (η0), storage moduli (G'), loss moduli (G'') and longest relaxation time (τ), were significantly changed with increasing screw rotating speed (shear stresses) and extrusion (residence) time. These results highlight the importance of controlling the mechanical recycling conditions for rPBS to ensure suitable rheological and mechanical properties after mechanical recycling, as well as the need of chain extender to preserve material properties and resources.