Crystallite orientation in extruded polyethylene film
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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.