Layer structure by shear-induced crystallization and thermal mechanical properties of injection-molded poly(l-lactide) with nucleating agents

•Layer structure in injection-molded PLLA was formed by shear-induced crystallization.•Nucleating agents coud result in decreased crystallinity of PLLA under thermodynamically favorable conditions.•A thick crystalline layer formed in injection-molded PLLA greatly enhances heat resistance property.

A unique oscillation shear injection molding was utilized to investigate the crystallization of poly (l-lactide) (PLLA) under the coexistence of an intense shear flow and nucleating agents. The crystalline morphology and its distribution of injection-molded PLLA were probed by wide-angle X-ray diffraction, showing that an intense shear flow promotes the crystallization significantly, whereas the nucleation effect by nucleating agents is negligible. Additionally, applying an intense shear flow during injection molding processing at a low mold temperature makes PLLA form a crystalline layer structure, including skin, intermediate and core layers. Meanwhile, nucleating agents were found to play different roles in the crystallization of injection-molded PLLA under different processing conditions. The results of thermal mechanical property and Vicat softening temperature show the injection-molded PLLA sample with a thick crystalline layer structure has a greatly enhanced heat resistance property.

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