Strain-induced crystallization II. Subsequent fibrillar-to-lamellar transformation Previously presented at the ACS Symposium on Fiber and Yarn Processing Philadelphia (April 9, 1975)

Abstract

Part II 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 morphology 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 extent 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. Of particular interest is the observation of lamellar formation in conjunction with decreasing stress (or increasing length) during TIG under strain. This is in conflict with the generally expected stress increase if chain folding is presumed to occur during formation of lamellae, Consequently, it leads to the conclusion that lamellae form from prefolded structures during TIC. In the light of this surprising conclusion, available evidence on the presence of structure or non-Gaussian chain segments in the amorphous state is also cited. Included are the most recent neutron scattering results from concentrated solutions of polystyrene.