The effects of orientation and crystallinity on the solvent-induced crystallization of poly(ethylene terephthalate). I. Sorption- and diffusion-related phenomena

Abstract

This series of reports summarizes the results of an experimental research program designed to establish the effects of preexisting orientation and crystallinity on solvent-induced crystallization of poly(ethylene terephthalate) films. Dimethylformamide was used as a model for a strongly interacting solvent. Special emphasis has been given to the kinetics of crystallization and diffusion, the morphological and structural modifications, and the accompanying changes in physical properties. This article deals with solvent sorption and desorption. Solvent diffusion and the extent of crystallization decreased with increasing orientation and crystallinity in the starting films, with crystallinity being more important. Despite the semicrystalline morphology, the overall diffusion behavior was found to be Fickian, allowing the calculation of pseudodiffusion coefficients which were dependent on both the draw ratio and the treatment temperature. Solvent treatments at elevated temperatures involved a dual input of thermal and chemical energy, which caused the films to behave differently above and below the glass transition temperature. Solvent desorption and reversible swelling were also found to be dependent on preexisting structure and treatment conditions.