STRESS-INDUCED CRYSTALLIZATION OF POLY(ETHYLENE-TEREPHTHALATE)

In the reported experiments, quenched amorphous films of poly(ethylene terephthalate) (PET) were stretched at temperatures less than T//g; changes in density, wide-angle x-ray diffraction, and small-angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide-angle x-ray diffraction and of both V//V and H//V small-angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide-angle x-ray diffraction and small-angle light scattering. A model is proposed to explain the observations. Studies are extended to stretching films of PET above their T//g and observing changes in birefringence, density, wide-angle x-ray diffraction and small-angle light scattering as a function of elongation and stretching temperature. Results are compared with those obtained upon stretching films below T//g.