Search

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 β‐nucleated iPP, GO exhibits an α‐nucleating effect, and its nucleation efficiency (NE) is higher than that of some conventional β‐nucleating agents (β‐NAs), thus reducing the formation of β‐phase and therefore the toughness of the material. In this article, we used the melt memory effect of β‐nucleated iPP/GO composites to improve the formation of β‐phase. By adjusting the fusion temperature Tf of β‐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 Tf = 200°C, no ordered structures survived in the melt, no β‐phase formed due to the strong α‐nucleating effect of GO; in the Tf range of 178–168°C, large amount of β‐phase survived in the composites, which helped to improve the formation of β‐phase during the subsequent cooling process, and the relative content of β‐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 β‐crystallization, and overcome the challenge from the α‐nucleation effect of GO. POLYM. COMPOS., 40:E440–E448, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: The effects of ordered structure on isothermal crystallization kinetics and subsequent melting behavior of β‐nucleated isotactic polypropylene/graphene oxide (iPP/GO) composites were studied using differential scanning calorimetry. The ordered structure status was controlled by tuning the fusion temperature (Tf). The results showed that depending on the variation of crystallization rate, the whole Tf range could be divided into three regions: Region I (Tf > 179 °C), Region II (170 °C ≤ Tf ≤ 179 °C) and Region III (Tf < 170 °C). As Tf decreased from Region I to Region III, the crystallization rate would increase substantially at two transition points, due to the variation of the ordered structure status. Calculation of Avrami exponent n indicated that the ordered structure induced the formation of two‐dimensional growing crystallites rather than three‐dimensional growing crystallites. Moreover, in the case of isothermal crystallization, the ordered structure effect (OSE) can also greatly increase the relative content of β‐phase (βc). In Region II, OSE took place, resulting in evident increase of βc, achieving 92.4% at maximum. The variation of the isothermal crystallization temperature (Tiso) had little influence on the Tf range (Region II) of the OSE. The higher Tf in Region II was more favorable for the formation of higher βc. The ordered structure was favorable for the improvement of the nucleating efficiency of β‐nucleating agent (β‐NE), and was more effective for the improvement of lower β‐NE. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]