Isotactic polypropylene films, which were drawn under necking and afterward annealed at 140°C (named A film) or 157° (named B film) with free ends, were redrawn at angle α=0, 30, 45, 60 and 90° to the first draw direction. The reorientation in these films was studied by measuring the distribution of the refractive indices in the film plane and x-ray diffraction. The main results were as follows.
(1) For A film, the distribution was sharpened and the orientation axis was rotated smoothly toward the redraw direction for any α. But for B film, the distribution became broad till around λ=2, except for α=0° and the orientation axis was rotated slowly toward the redraw direction.
(2) For α=0°, for both films, the crystal orientation was lowered at small draw ratios, while the over all molecular orientation was increased with λ. Therefore the orientation of the amorphous chains may be increased rapidly at first. Particularly, the changes were remarkable for B film.
(3) For α=30, 45 and 60°, both films showed two types of the crystal orientation. For A film, a structure may be produced by the strained tie chains on the process of destruction of the original structure, and this may be oriented readily to the redraw direction, but the transformation do not appear except for A
60, 3. While, for B film, the new structure (Type II) having an opposite orientation from the original structure (Type I) appeared manifestly. It seems that the transformation from Type I to Type II structure is followed by the inclination of the lamellae to the film surface and the destruction of the lamellae to the crystal blocks and then, rotation of the crystal blocks about a- or b-axis. These mechanisms may occur concurrently.
(4) For α=90° (only B film), a new structure may be formed and oriented to the redraw direction in a similar manner as above.
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