Shear-induced stereocomplex cylindrites in polylactic acid racemic blends: Morphology control and interfacial performance

Abstract

Realization of structural manipulation in stereocomplex (sc) polylactic acid holds the key to fully leverage its surpassing performance, such as heat resistance and mechanical properties. In this study, we investigated the evolution of crystalline morphology/structure of equimolar racemic blends under the quantitative shear field modulated by the pulling speed of glass fiber (GF). Shear-induced crystallization proceeded above the melting point of homocrystals, allowing the exclusive formation of sc crystallites. Compared to sparse nuclei dispersed around the static GF with no nucleation activity, numerous oriented sc row-nuclei appeared on the surface of pulled GF. With the rise of shear rate up to 160 s−1, the number of row-nuclei was boosted prominently. As a result, interfacial sc cylindrites were fostered due to the preferential radial growth of lamellae outwards the GF axis. The integrity and contour of sc cylindrites could be regulated by the number of sc precursors and thus shear rate. Attractively, the conspicuous enhancement of interfacial adhesion and solvent resistance was attained by the presence of robust sc cylindrites. As confirmed by the single-fiber pull-out test, interfacial strength of the sheared sample (160 s−1) was over three times as large as that of the quiescent counterpart. Besides, the distortion due to the chloroform attack was significantly retarded for the film containing sc cylindrites in contrast to sc spherulites and homocrystal cylindrites. The current effort offers valuable instruction to fabricate the sc-PLA products with tailored crystalline morphology/structure.