CRYSTALLINITY VIS-A-VIS 2-PHASE MODELS OF ORIENTED POLYMERS - INFERENCES FROM AN EXPERIMENTAL-STUDY OF POLY(ETHYLENE-TEREPHTHALATE)

Extensive measurements with poly(ethylene terephthalate) fibers of a b road range of orientational and crystalline order have been made and a nalyzed vis-a-vis two-phase (crystalline and noncrystalline) descripti ons of solid polymer morphologies. The results show that no two fundam entally different methods provide the same estimates, or consistently even the same trends, of phase composition over a broad range of order . Modifications of the simple two-phase model by incorporating order-d ependence of characteristic parameters, such as noncrystalline density , still lead to unsatisfactory results. No meaningful relationship has been found between such parameters and measures of order, such as cal culated birefringence, the noncrystalline phase. However, because of t he simplicity of two-phase models and the absence of any objective fra mework for correlating properties with measures of order with three or more phase compositions, continued use of two-phase models, with cogn izance of their inherent limitations, is recommended in seeking direct ions for process and product development. (C) 1997 John Wiley & Sons, Inc.