Regulating polycrystalline behavior of the β-nucleated isotactic polypropylene/graphene oxide composites by melt memory effect

Balancing the stiffness and toughness is always the goal of high performance general plastics, especially for isotactic polypropylene/graphene oxide (iPP/GO) composites. However, during the crystallization of -nucleated iPP, GO exhibits an -nucleating effect, and its nucleation efficiency (NE) is higher than that of some conventional -nucleating agents (-NAs), thus reducing the formation of -phase and therefore the toughness of the material. In this article, we used the melt memory effect of -nucleated iPP/GO composites to improve the formation of -phase. By adjusting the fusion temperature T-f of -nucleated iPP/GO composites, the amount of ordered structure in composites was controlled. The crystallization behavior and melting behavior of composites were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering. The results showed that when T-f=200 degrees C, no ordered structures survived in the melt, no -phase formed due to the strong -nucleating effect of GO; in the T-f range of 178-168 degrees C, large amount of -phase survived in the composites, which helped to improve the formation of -phase during the subsequent cooling process, and the relative content of -phase even reached the maximum value of 85.8%. The mechanism of melt structure on the polymorphic behavior of the composites were also investigated, and it was found that the ordered structure in the melt evidently enhanced the NE of -crystallization, and overcome the challenge from the -nucleation effect of GO. POLYM. COMPOS., 40:E440-E448, 2019. (c) 2018 Society of Plastics Engineers