X‐ray diffraction orientation studies on blown polyethylene films. I. Preliminary measurements

Abstract

AbstractX‐Ray diffraction pole figure measurements have been made on six films blown from high‐density polyethylene. Five were prepared on an experimental unit; the sixth, blown on commercial equipment, had a higher degree of overall orientation thus enabling more extensive results for the a‐, b‐, and c‐axis distributions to be obtained. The results provide information on the orientation present, how it may be related to the stress crystallization process of Keller and Machin, and the dependence of the tear strengths in the machine and transverse directions on the orientation. The typical behavior, with the a and c axes at 90° and both at an angle to the plane of the film, is shown to be the result of a composite process involving several types of stress during the blowing operation and a partial relaxation arising at one or possibly two stages of the process. The predicted relative tear strengths, obtained from the concentration of c axes inclined towards the machine direction, are in line with the experimental values. There is some evidence that transcrystallization in the surface layers of the films may lead to a better balance of the tear strengths in the machine and transverse directions.