In Situ Formation of Soft-Rigid Hybrid Fibers Decorated by Sparse Lamellae of PLLA: Achieving Ductile and Heat-Resistant Materials with High Strength

Constructing an oriented crystalline structure with high crystallinity in poly(L-lactide) (PLLA) is one efficient way to improve its mechanical strength, but flexibility is sacrificed because orderly arrangement restricts molecular mobility seriously. In this work, a unique hierarchical structure of soft-rigid hybrid fibers decorated by sparse lamellae of PLLA is in situ constructed successfully to improve mechanical strength and flexibility simultaneously. Through interfacial stereocomplexation between the PLLA matrix and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-poly(D-lactide) (PHBV-PDLA) copolymers, followed by a strong flow field during the multistage stretching extrusion (MSE), soft-rigid hybrid fibers of PHBV/interfacial stereocomplex crystallites (i-SCs) are formed to not only act as a reinforcement filler but also favor energy-dissipating deformation mechanisms. Moreover, under the coupling effect of hybrid fibers and intense flow field, the sparse PLLA lamella with a stiff shish is obtained. Consequently, nanofibrillar PLLA/PHBV-PDLA composites with a highly oriented structure exhibit high strength (94.1 MPa), considerable ductility (65.7%), and excellent heat resistance (E ' 140 degrees C > 310 MPa), compared to sea-island structured PLLA/PHBV-PDLA composites with an isotropic structure (59.3 MPa, 11.7%, and E ' 140 degrees C > 60 MPa). Furthermore, nanofibrillar PLLA/PHBV-PDLA composites can maintain ductility (57.7%) and strength (98.3 MPa) for 886 days at ambient temperature. The strengthening and toughening mechanisms based on the unique structure are proposed by investigating the microstructural changes before and after a tensile test. This work provides significant guidance for strong, ductile, and heat-resistant PLLA-based materials for durable applications.