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The complete orientation distribution of the a and b crystallographic directions have been measured for a series of tubular extruded polyethylene films as a function of blow ratio. The use of pole figures as a means of representing orientation is emphasized and it is shown that the usual technique of using flat plate x-ray diffraction photographs can lead to erroneous conclusions. Increasing the blow ratio has a distinctly different effect upon the orientation of high density polyethylene film in comparison with low density polyethylene film. In contrast with previously published information our results clearly indicate that the c axis does not orient preferentially perpendicular to the extrusion direction. In particular, it is shown that one cannot in general deduce the maximum in the orientation distribution of the c axis from qualitative estimates of the a and b axes distributions. The ultimate tensile strength, elongation, modulus and tear strengths of these films were measured and the results correlated with the orientation of the crystallo graphic directions.
Lindenmeyer et al. (Fri,) studied this question.