Isothermal crystallization kinetics and subsequent melting behavior of β-nucleated isotactic polypropylene/graphene oxide composites with different ordered structure

The effects of ordered structure on isothermal crystallization kinetics and subsequent melting behavior of beta-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 (T-f).The results showed that depending on the variation of crystallization rate, the whole Tf range could be divided into three regions: Region I (T-f > 179 degrees C), Region II ( 170 degrees C <= T-f <= 179 degrees C) and Region III (T-f < 170 degrees C). As T-f 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 beta-phase (beta(c)). In Region II, OSE took place, resulting in evident increase of beta(c') achieving 92.4% at maximum. The variation of the isothermal crystallization temperature (T-iso) had little influence on the T-f range (Region II) of the OSE. The higher T-f in Region II was more favorable for the formation of higher beta(c). The ordered structure was favorable for the improvement of the nucleating efficiency of beta-nucleating agent (beta-NE), and was more effective for the improvement of lower beta-NE. (C) 2018 Society of Chemical Industry