Microstructure and performance evolution of poly (l-lactic acid) during physical aging: Determinable role of molding...

As one of the biodegradable materials, poly (L-lactic acid) (PLLA) attracts much attention and acquires fast development since it is crucial for alleviating the issue of microplastic pollution. During processing and service, polymers usually experience the physical aging process, leading to the microstructure and performance evolution. Such scenario is especially obvious for PLLA. However, the mechanisms involved remain unclear. Here, the relationship between ductility and relaxation behavior of PLLA during physical aging is investigated. The ductility is greatly dependent upon the molding method, and the quenched samples show higher tensile ductility compared with cold-pressed samples. The cohesional entanglement gradually forms with aging time, and it is closely related to molding methods. The cohesional entanglement has no impact on the α-relaxation process, nevertheless, it greatly restricts the β-relaxation of PLLA. The decrease in the mobility of molecular chains makes it unable to effectively absorb energy when subjected to external forces. Furthermore, physical aging is an irreversible process while quenching treatment can retard the physical aging behavior of PLLA for a certain period. This work provides new insight on the microstructure and performance evolution mechanisms of PLLA during physical aging, which can guide the microstructure design of PLLA-based articles with promising performances.