Studies on the stretching of polypropylene film. II. Polyaxial stretching

Polypropylene film was stretched polyaxially at 100–160°C., and the orientation behavior was studied by means of optical and x-ray method. The molecular chains oriented progressively to the film surface with an increase in stretching area v_A in the range 1–16, and the (040) selective uniplanar orientation developed at the extreme stretching. The plot of orientation versus v_A was less steep when the stretching was carried out at higher temperature, but the final degree of orientation was independent of the temperature, because the final v_A increased with temperature. At 160°C. premelting occured to such a degree that the high stretching and, consequently, the high orientation could not be obtained. The orientation of the amorphous chains was always behind that of the crystalline region. In the initial stage the polyaxial stretching was not as effective in attaining high biaxial orientation as the two-step biaxial stretching, but the final orientation was the same in both types of stretching because v_A reached a value of 16 in the polyaxial stretching while it was only 2 in biaxial stretching.