X‐ray diffraction orientation studies on blown polyethylene films. II. Measurements on films from a commercial blowing unit

Abstract

AbstractX‐Ray diffraction pole figure measurements have been made on a series of films, blown under various conditions from three high‐density polyethylenes. The results are interpreted in terms of two distinct types of orientation. The first, and probably the more normal, is the result of the type of stress crystallization process described by Keller and Machin and has the a and c axes inclined at an angle to the plane of the film. The second type of orientation is crystallographically analogous to that found in cold drawn polyethylene in having the c‐axis distribution substantially along the machine direction. This is termed high‐stress orientation. The type of orientation obtained is dependent both on the blowing conditions and the particular polyethylene. With an experimental Rigidex grade and with Shell LPPE 040 there are always substantially amounts of the conventional low‐stress orientation although certain combinations of machine conditions predispose towards the high‐stress form. This latter type forms readily in the case of Hostalen GM 9955F over a rather wide range of machine conditions and appears to be favored by slower cooling conditions.