Deciphering the Code of Poly(L-lactic acid) Monofilament Achieving Orientation Limit

Understanding the limitations of chain orientation is crucial for designing and controlling the properties of semi-crystalline polymers, providing requisite condition for regulating the materials' end-use application. In this work, ultra-strong and tough Poly(L-lactic acid) (PLLA) monofilament is achieved by an oriented forming strategy. It featured a multilayer coaxial structure composed of nanofibrils, microfibrils, transcrystallinity and spherulites with alternating crystalline and amorphous domains. When the nanofibril is disintegrated to the limitation, it exhibits a remarkable elastic modulus of 13.26 ± 0.62 GPa, an excellent breaking strength of 1.14 ± 0.01 GPa, and an outstanding toughness of 120.42 ± 6.28 MJ·m^-3, surpassing other reported biodegradable fibers. Furthermore, deconstructing the multiscale variation in the monofilament that reaches the limits of chain orientation can clarify the mechanism of the oriented forming process. This work serves as a foundation for decoding the orientation limit and achieving extremely high performance in semi-crystalline polymers.