| 簡(jiǎn) 介： |
The flow-induced shish-kebabs of polyolefins have been well demonstrated to be highly beneficial to mechanical strength, toughness, heat resistance, gas barrier, etc. However, it is still a challenge to achieve numerous shish-kebabs of biodegradable poly (L-lactic acid) (PLLA)due to its short chain length and semi-rigid chain backbone compared to polyolefinscl]. In this work, a novel injection molding technology, named oscillation shear injection molding (OSIM) ,was applied to provide an intense shear flow on PLLA melt in cavity, in order to accelerate shear-induced crystallization of PLLA in inj ection molded PLLA and PLLA/ramie fiber bio-composites.Numerous of shish-kebabs of PLLA have been successfully achieved in injection-molded PLLA for the first time[2] , and high resolution scanning electron microscopy reveals a diameter of around 0. 7 ym and a long period of一 20 nm for the shish-kebab superstructure. More interestingly, besides the formation of classic shish-kebabs, shear flow-driven transcrystallinity (TC) on ramie fiber surface and hybrid shish-kebab superstructure induced by ramie nanofibers were directly achieved in PLLA/ramie fiber biocomposites by using OSIM. The relationship between these novel superstructures and mechanical properties was also investigated. The results show that a moderate improvement of the mechanical properties such as the tensile strength and stiffness can be obtained due to the presence of shish kebabs. More intriguingly, with the existence of TC, hybrid shish-kebabs and ramie fibers, a noteworthy promotion in tensile strength, stiffness tensile modulus and Notched impact strength is achieved in the biocomposites, obtaining substantial increase of一22% ,～41% and～120% compared to the neat PLLA sample molded by conventional injection molding, respectively. It is believed that further exploration will provide a rich fundamental understanding in the shear-induced crystallization and morphology manipulation of PLLA, aiming to achieve superior PLLA products in injection molding process.
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