The orientation distribution of crystallites in polyethylene terephthalate (PET) fibers is generally determined using approximate methods. In this paper an exact equation, based on the generalized treatment of Wilchinsky, is developed which makes use of the intensity-distribution curves of three equatorial planes to determine Hermans' orientation factor. The orientation factors obtained for a few PET samples using this approach are compared with those obtained by using two approximate methods. It is concluded that for fibers having relatively high orientation. the various approaches give reasonably close values for Hermans' orientation factor.
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