Laser Light and X-Ray Diffraction Studies of Oriented Isotactic Polypropylene (iPP) Prepared by Temperature Slope Crystallization

Isotactic polypropylene (iPP),film was melt-crystallized in a temperature gradient. The ipp film showed well oriented alpha- and beta-crystalline textures along the gradient. The crystalline structure, phase transition boundary and lamellar twisting were examined by X-ray diffraction and laser light diffraction (LLD). On the alpha-beta boundary, LLD shows a sharp streak perpendicular to the boundary, where the a-axis of the beta-crystal is oriented perpendicular to the temperature gradient. Apart from the boundary, the a-axis of the beta-crystal becomes parallel to the gradient. The beta-crystal shows lamellar twisting with a pitch of 200 mu m at room temperature. When heated the beta-crystal, the lamellar distance of 295 angstrom at room temperature decreases to 285 angstrom at 80-100 degrees C and then increases to more than 300 angstrom above 120 degrees C. During the heating, the value of the twist period increases from 200 to 210 mu m at 90-100 degrees C, and then to above 224 mu m at 140 degrees C. The increase of the twist period is related to the increasing crystalline thickness of the beta-lamellae.