Detection of stress-induced morphological alterations of polyethylene terephthalate by gas permeation

Summary

Films of polyethylene terephthalate drawn near the glass transition temperature show evidence of the development of stress-induced morphological alteration (referred to the amorphous, unoriented form) as deduced from observed initial increases in permeability and decreases in apparent permeation activation energy for oxygen. The respective values of$\bar P$ and$E_{\bar P}$ for the smaller molecule, helium, are less affected over the same range of film elongations. A simple two-group transport model of the polymer microstructure suffices to explain the data and electron micrographs reveal that an unusual type of crystalline phase, apparently the result of stretching nearT _g , is the origin of the low activation energy pathways, leading to the observed diffusional enhancement for oxygen.