Dimensional changes during solvent‐induced crystallization of poly(ethylene terephthalate) films

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Abstract
The sample dimensional changes accompanying diffusion with induced crystallization in amorphous poly(ethylene terephthalate) (PET) films are analyzed. Initially, the film's lateral area remains practically constant, but near the end of the process, it increases rapidly, consistent with non‐Fickian models for diffusion. The ultimate relative thickness increase is about double that for the lateral dimension, implying that plastic deformation in the thickness direction accompanies the sorption. Plots of fractional area increase (ΔA/ΔA∞) vs. fractional weight gain (W/W∞) indicate severe softening of the polymer by the penetrant.