Orientation of isotactic polypropylene filament and its new crystalline structure produced by high stretching

Orientation of crystallites in stretched isotactic polypropylene filaments was examined by x‐ray diffraction. It was found that complete overall orientation parallel to the direction of stretching is obtained at a stretching ratio of 4 to 5. Preferential orientation was observed in the stretching process, that is, the orientation of the 010 plane along the fiber axis was predominant in the initial step of orientation and was complete by 100% stretching. It was found that a new crystal structure was formed on further stretching of completely oriented filaments at or slightly above room temperature. The crystal structure can be transformed to an ordinary stable crystal structure by treating the filaments at 100 to 150°C. for comparatively short time. The crystal structure may be a kind of metastable crystal, with nearly hexagonal projection in the plane perpendicular to the fiber axis.