X-ray study on crystalline morphology in iPP/MMT nanocomposite fibers

Nanocomposite fibers based on isotactic polypropylene (iPP) and an organically modified montmorillonite (MMT), Cloisite 15A, were formed from the melt at different take-up velocity. The studies were performed for pure iPP fibers and fibers containing three different concentrations of MMT. The supermolecular structures of the fibers at the crystallographic and lamellar levels were examined by means of X-ray scattering methods (WAXS and SAXS). It was found that the dominant crystal form of iPP is alpha modification. The increase of take-up velocity induces the orientation of iPP crystals parallel to the fiber axis. The cross-hatching crystallization of iPP was also observed in the tested fibers. Only for the gravity spun fibers containing MMT, the beta modification of iPP was observed. Assuming that nucleation does not occur on the surfaces of clay platelets but rather in the interlayers of MMT particles, a probable beta-phase nucleation mechanism has been suggested. This mechanism was confirmed by the isothermal crystallization experiment. During heating, the beta crystalline form transformed into alpha-form. The degree of transformation depended on the annealing temperature. The studies also revealed that lamellar stacks of iPP are perpendicular to the MMT layers surfaces.