Simultaneous Improvement of Strength and Toughness of Poly(lactic acid) via Multiple Dynamic Pressure

To retain its inherent biodegradability, simultaneously improving the strength and toughness of poly(lactic acid) (PLA) is a significant challenge. In this study, we propose an innovative multiple dynamic pressure (MDP) process that can produce pure PLA with excellent mechanical properties. The MDP process generates a dynamic stretching effect by regulating the application and release of pressure, prompting disordered molecular chains to be arranged regularly along the direction of the dynamic force field. This promoted the formation of more ordered crystal forms (α-form) and strengthened the connection between the crystalline and amorphous regions. Results show that after MDP treatment, the tensile strength and strain at break of MDP-PLA are significantly improved, reaching 91.6 MPa and 80.1% respectively, which are 49.4% higher and 10 times higher than those of the samples before treatment. The mechanical properties of MDP-PLA can be regulated as needed by adjusting the cycle times and peak pressure. In addition, through a systematic study of the structural evolution of MDP-PLA, the performance regulation mechanism of the MDP process was thoroughly investigated, and the internal relationship among the process-structure-performance was clarified. This research not only opens a new technical path for the preparation of high-performance pure PLA but also provides important guidance for the high-performance modification of other semi-crystalline polymers, thus possessing significant scientific and engineering value.