The ordered structure of partially melted isotactic polypropylene (iPP) was investigated using polarized optical microscopy (POM) and small-/wide-angle X-ray scattering (SAXS/WAXS) measurements. The crystalline morphology was first examined by means of pulling a glass fiber through the iPP melt, which was generated by partially melting a preformed spherulite. The results from the POM experiments indicated that, even at a minimal pulling rate, the surviving ordered structure could also relocate along the direction of fiber pulling and grow into cylindrites eventually. In addition, during the quiescent crystallization from the partially melted sample, which had the same thermal history of fiber-pulling experiments, the obvious memory effect of melt was also observed from the results of X-ray experiments. Moreover, the SAXS profile derived from the partially melted iPP at 170 °C was fitted by the theory of scattering amplitude with the cylindrical form factor. The fit result implied that the surviving ordered structure is of cylindrical nanocrystals with a diameter D ≈ 30 ± 3 nm and height h ≈ 45 ± 3 nm, which can significantly influence the crystallization morphology and kinetics during the subsequent crystallization process.
Keywords: crystallization; isotactic polypropylene; ordered structure; partial melting.