Crystallization and orientation of isotactic polypropylene film by stretching

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Abstract
Crystallization and orientation of isotactic polypropylene film by stretching were investigated. The specimen used was a film of thickness 0.03 mm. and had ca. 30% crystallinity in the initial state. It was observed both by x‐ray examination and measurement of density that the crystallization of the stretched film increased proportionally to the stretching ratio. And it was confirmed that a quasi‐crystalline structure was already developed in the low stretching ratio coexisting with the ordinary stable crystalline structures. This quasi‐crystal structure can be easily transformed into the ordinary stable state at above 100°C., as well as the quasi‐crystal structure in melt spinning filament, as described in a previous paper. It was also confirmed that the ordinary stable crystalline part was biaxially oriented by high stretching at room temperature, that is, (110) plane of the crystallite was preferentially oriented perpendicular to the surface plane of the film in the cross section perpendicular to the stretching axis. This phenomenon was elucidated from both the cohesive interactions between lattice planes and the compressive stress in the stretching process.