Aging of poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends under different conditions: Environmental concerns on biodegradable plastic

Biodegradable plastics (BPs) have been used to replace conventional plastics owing to their environmental harmless and ease of degradation. However, the aging processes of BPs in different environments remain unclear. In this study, we used poly (lactic acid)/poly (butylene adipate-co-terephthalate) (PLA/PBAT) films as model BPs and investigated the 30-d aging behavior of PLA/PBAT films under four conditions (i.e., air without ultraviolet (UV) irradiation, water without UV irradiation, air with UV irradiation, and water with UV irradiation). Our results showed that the aging of PLA/PBAT films was insignificant in all groups except the water with UV irradiation group. In the physical characterization, the PLA/PBAT films exhibited layered structures in water with UV irradiation condition, and the submicron- and nano-sized particles adhered to the bigger-sized fragments. In the chemical characterization, the carbonyl index (CI) of PLA/PBAT films in water with UV irradiation condition decreased from 3.84 to 1.36, and the oxygen-to-carbon (O/C) ratio reached a maximum of 1.78 at 20 d and declined to 0.49 at 30 d, indicating that the oxygen-containing functional groups underwent bond breaking and showed a rapid aging process. This is mainly attributed to the combined effect of hydrolysis and photolysis increases the contact area of PLA/PBAT films and accelerates the aging process. Furthermore, based on two-dimensional correlation spectroscopy (2D-COS) analysis, we suggest that free radicals generated in water with UV irradiation conditions also accelerate the aging process of PLA/PBAT films. This study explored the aging processes of PLA/PBAT films under different conditions, which could aid in clarifying the environmental behavior and provide further information to assess the potential risks of BPs.