Biobased Seawater-Degradable Poly(butylene succinate-l-lactide) Copolyesters: Exploration of Degradation Performance and Degradation Mechanism in Natural Seawater

In view of the problem of marine plastic pollution and oil resource depletion, an innovative attempt was made to obtain biobased seawater-degradable polyesters by installing lactic acid (LA) into the poly(butylene succinate) (PBS) backbone and synthesizing a series of random copolyesters named poly(butylene succinate-l-lactide)s (PBSLs). Herein, biobased LA units are chosen as readily hydrolyzable points according to our theoretical calculation. The obtained PBSL copolyesters preserve the structure of PBS when LA units are inserted into this main chain mostly with a single unit. While maintaining excellent mechanical and thermal properties, PBSL shows notably improved degradation performance during a 440-day long-term test in natural seawater compared to PBS, demonstrating rapid loss of weight and mechanical properties, as well as a decrease in the molecular weight. A highly sensitive system for end-product CO2 detection during the seawater degradation process is designed and applied for the first time under conditions close to the natural seawater environment. A record mineralization rate of 16.2% in seawater after 379 days of degradation is achieved for PBSL30, which proved the occurrence of biodegradation in seawater. This result, combined with the analysis of intermediate products, clearly explained the whole degradation mechanism of PBSLs in seawater.