BEHAVIOR OF MOLECULAR ORIENTATION, NONCRYSTALLINE ORIENTATION AND THE MECHANICAL PROPERTIES OF THE. BIAXIALLY STRETCHED POLYPROPYLENE FILMS PREPARED BY DRY-PROCESS
The previous report (part 5) in this series has shown the effects of crystalline orientation on the mechanical properties of the biaxially stretched polypropylene films prepared by dry-process, and successively this report shows the effects of molecular orientation and noncrystalline chain orientation. In this study the samples, stretching system and stretching conditions are also the same as those described in the previous reports. The behaviors of molecular orientation in these stretched
... were followed up by the birefringence measurement and the infrared dichroism. In the birefringence measurement a tilting specimen-method was used. The following results were obtcined : (1) The molecular orientation in the films uniaxially stretched under free width is uniaxial with cylindrical symmetry around the stretching direction, and the crystalline orientation improves preferably to the amorphous. (2) In the films uniaxially stretched under constant width, however, the molecular orientation is roughly biaxial. The orientation of amorphous region gives rise to the characteristic elongation to beak the films. (3) In the two-way successively biaxially stretched films, the molecular orientation changes during the second-direction stretching. The crystalline orientation is better than that of the amorphous segments. Therfore, for the crystalline polymer films as polypropylene, it is difficult to make all mechanical properties in balanced state by two-way successive biaxial stretching. (4) In the simultaneously biaxially stretched polypropylene films, the molecular chain orientation is in balance in the machine and the transverse direction at all stretch ratio, and the planar orientation distributed at random is resulted. And, the molecular chain orients in the same direction to the crystal c-axis. The mechanical properties of the films have no directional specificity. This phenomenon is veryfied from the fact that the crystalline and the amorphous chains, are randomly oriented in the plane.