BEHAVIOR OF MOLECULAR ORIENTATION AND AMORPHOUS ORIENTATION OF THE BIAXIALLY STRETCHED POLY-(ETHYLENE TEREPHTHALATE) FILMS PREPARED BY DRY-PROCESS

Abstract

The previous reports (parts 10 & 11) in this series discussed the effects of crystal orientation on the mechanical properties of the biaxially stretched poly (ethylene terephthalate) films prepared by dry-process. In this report, our interest is concentrated into the effect of molecular orientation and amorphous chain orientation.The samples, stretching system and conditions used in this study are the same as those in the previous reports. The molecular orientation in these stretched films were followed up by the birefringence measurement and the infrared dichroism measurement. A tilting specimen method was used in the birefringence.The following results were obtained:(1) The molecular orientation in the films uniaxially stretched under free width is uniaxial with cylindrical symmetry around the stretching direction, and the orientation is higher for the crystalline than for the amorphous.(2) In the films uniaxially stretched under constnant width the molecular orientation is roughly biaxial.(3) In the two-way successively biaxially stretched films, the molecular orientation changes during the second-direction stretching. The crystal orientation is higher than that of the amorphous segments. Therefore for poly (ethylene terephthalate) film, it is difficult to make all mechanical properties in balanced state by two-way successive biaxial stretching.(4) In the simultaneously biaxially stretched films, the molecular chain orientation is in balance in the machine and the transverse direction at all stretch ratio, and the orientation is at random in the film plane. And, the molecular chain orients in the same direction to the crystal c-axis. The crystalline and the amorphous chains are randomly oriented in the plane.