Diffusion studies of poly(ethylene terephthalate) crystallized by nonreactive liquids and vapors

The diffusion of vapors and liquids which induce crystallization in initially amorphous, unoriented poly(ethylene terephthalate) (PET) films was studied. It was determined that these vapors and liquids penetrate the polymer as distinct fronts, and the kinetics of this penetration and the weight uptake kinetics both follow apparent Fickian behavior. Distinct cavitation advanced into the polymer at the penetrant front–dry polymer interface in certain PET–liquid systems, and phenomenological explanations of its existence and of the general diffusion process observed are offered. Finally, the diffusion of the highly interactive liquids dioxane and methylene chloride into cold‐drawn PET was studied and shown to occur considerably more slowly than does the diffusion of these liquids into unoriented films.