CRYSTAL ORIENTATION AND THE CHANGE BY DRAWING IN POLYETHYLENE FILM

Abstract

The dimensional changes of tubular extruded polyethylene films in uniaxial stretching was discussed qualitatively in relation to the initial orientation of the crystalline phase. The orientation behavior is investigated by means of X-ray pole figure technique and biaxial orientation.From the experimental results, it was confirmed that the behavior of transverse-and thicknessanisotropic dimensional decrease of film is mainly related with the initial orientation of the b-axis. That is; if a film in which the b axis major orient parallel to the film normal and is stretched in the machine direction, the a- and c-axes are shifted parallel to the film surface, and a stretched texture occurs as a result of inducing the slip on a (100) plane with the a-axis parallel to the transvease direction of film and the b-axis parallel to the film normal. In this case, the length of the film decreases in the transverse direction than in thickness.In terms of crystal orientation the structure of ordinary extruded film is a combination of two simple types of structure, i. e. the crystallites whose b-axes are major oriented in parallel to the transverse direction of the film and in parallel to the film normal. If the film is stretched in the machine direction, the a-axis rotates around the b-axis, and the a-axes are separated rather definitely into those oriented parallel to the film normal and those oriented parallel to the transverse direction as limiting cases. Then the film deformation proceeds with the (100) [001) slip. The length of film decrease in thickness and transverse direction, and the difference of which depends upon the values of and prior to the deformation: if the value of is substantially larger than that of the decrease in thickness is larger than that in the transverse direction.It is certain that the crystal orientation has some effects on the film deformation, irrespective of high or low-density polyethylene and it is recognized that the film deformation proceeds with the common mechanism in both films.