G. S. Y. YEH Departments of Chemical Engineering

Part 11 discusses numerous examples of a morphological fibrillar-to-lamellar transformation that has reportedly been observed in stretched polymers upon additional thermal treatment (or TIC). Stretched polymers containing initially a typical fibrillar morphology for either crystallites in cold-drawn polymers, crystallites induced by stretching, or simply non-crystalline fibrils can yield a more or less lamellar mor-phology after the thermally-induced transformation. There is no evidence of extended-chain crystals present in either the original fibrils or the transformed lamellae; however, the ex-tent of the transformation is strongly dictated by the annealing conditions and the stretch ratios, and therefore the local strains on tie molecules between the crystallites. Ofparticular intercxst is the observation of lamellar formation in conjunction with decreasing stress (or increasing length) during TIC unde