Temperature-dependent β-crystal growth in isotactic polypropylene with β-nucleating agent after shear flow

In our current work, the effect of the shear temperature on the growth of β-crystal in isotactic polypropylene (iPP) with β-nucleating agent is investigated by means of in situ two-dimensional wide-angle X-ray diffraction (2D-WAXD). At low shear temperatures, the formed shear-induced oriented precursors are hard to relax back to random coiled state due to the weak mobility of molecular chains. Therefore, plenty of oriented α-crystals are induced by shear-induced oriented precursors, while β-crystal is greatly depressed. As the shear temperature increases, oriented β-crystal gradually increases along with the decrease of α-crystal. It is deduced that the shear temperature at which the content of β-crystal increases to the (maximum) value found in quiescent crystallization is almost the same as that at which the accelerating effect of flow on crystallization kinetics is completely erased. Our work manifests its significance in regulating β-crystal and thus in the structure and property manipulation of iPP.