Orientation of carbon nanotubes in polypropylene melt

The correlation between shear stress and the orientation of single-walled carbon nanotubes (SWCNTs) in an SWCNT/polypropylene composite during the melt process was investigated. Highly oriented composite fibers were produced by extruding the polypropylene melt using a capillary rheometer. The experimental range of shear rates covered those of common polymer melt-shaping processes. The effect of functionalization of the SWCNTs on orientation was also investigated. Polarized Raman spectroscopy was used to analyze the orientation of the SWCNTs. A high degree of SWCNT orientation was observed under high shear stress, and the functionalized SWCNTs induced a higher degree of orientation than did pristine SWCNTs. The existence of a critical shear stress was observed for the orientation of the SWCNTs, and their orientation was found to occur more efficiently above this critical shear stress. The crystallization temperature and heat of fusion were characterized using a differential scanning calorimeter, and both parameters were observed to increase with the incorporation of SWCNTs.