Investigation on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi-walled carbon nanotube composites nucleated with β-nucleating agent

The melt structure of isotactic polypropylene (iPP) nucleated with 1.0 mass% multi-walled carbon nanotubes (CNTs) and 0.05 mass% rare earth beta-phase nucleating agent (WBG-II) was tuned by changing the fusion temperature T (f). In this way, the role of melt structure in the crystallization behavior and polymorphic composition of the sample was studied by calorimetry, X-ray diffraction, and scanning electronic microscopy. In this system, the sample cannot form any beta-phase when T (f) = 200 A degrees C, since the alpha-nucleation efficiency (alpha-NE) of CNTs was obviously higher than the beta-NE of WBG-II. By tuning T (f), the content of ordered structures in iPP melt was controlled and it was found that the polymorphic composition of the sample can be efficiently controlled. When T (f) was in the range of 166-174 A degrees C, an amount of ordered structures survived in iPP melt, resulting in a significant increase of beta-phase proportion; moreover, study on the crystallization behaviors of single CNTs-filled iPP and WBG-II-nucleated iPP (iPP/CNTs and iPP/WBG-II, respectively) revealed that the alpha-NE of iPP/CNTs stayed almost constant as T (f) varies from 200 to 166 A degrees C; meanwhile, the beta-NE of iPP/WBG-II increased gradually. Once T (f) decreased to 174 A degrees C and lower, the NE of iPP/WBG-II became higher than that of iPP/CNTs; meanwhile, WBG-II began to play determining role in the polymorphic composition and enhanced the beta-phase proportion of iPP nucleated with CNTs/WBG-II. The findings of this study brought a new pathway to control the polymorphic composition and mechanical properties of iPP/CNTs composites.