Strong Shear Flow-Driven Simultaneous Formation of Classic Shish-Kebab, Hybrid Shish-Kebab, and Transcrystallinity in Poly(lactic acid)/Natural Fiber Biocomposites

A strong continuous shear flow was imposed on the melt of ramie fiber reinforced poly(lactic acid) (PLA) biocomposites during practical processing. Classic shishkebabs and typical transcrystallinity were simultaneously formed in the sheared PLA/ramie fiber samples, which were closely related to formation of row-nuclei induced by the strong shear flow that was further amplified by incorporated natural fibers. Interestingly, some nano-sized ultrafine ramie fibers tended to absorb and stabilize the as-formed row-nuclei, which subsequently grew into the unexpected hybrid shishkebabs. We proposed that the formation of hybrid shishkebabs underwent the process of "capturing extended chain bundles for hybrid shishes" with the applied shear flow acting as the driving force. Further attempts were made to understand their contribution to the mechanical performances. With the existence of transcrystallinity, PLA/fiber interfacial adhesion was considerably enhanced. Meanwhile, positive reinforcing and toughening effects could originate from the shish-kebabs and hybrid shish-kebabs with extended chain bundles. Consequently, a noteworthy enhancement in tensile strength, tensile modulus, storage modulus, and impact toughness was achieved in the modified biocomposites, obtaining a substantial increase of 14.0%, 8.4%, 23.4%, and 90.4%, respectfully, compared to the control biocomposite. These results clearly demonstrated that the precisely controlled interfacial crystalline structures under industrial conditions of processing are highly beneficial to the mechanical performances.