Kinetics studies of solvent-induced crystallization of drawn poly(ethylene terephthalate) by the in situ density measurement

The effect of draw ratios on the solvent-induced crystallization (SINC) of poly(ethylene terephthalate) (PET) films was investigated. Dimethyl formamide (DMF) and dioxane were used as strongly interacting solvents. A newly devised in situ density measuring apparatus was applied to directly examine solvent peneration kinetics in PET. In this article, the density of PET films, which had a linear relation with crystallinity, was estimated rather than the degree of crystallinity. The solvent-penetrated PET film was divided into three regions: a surface-cavitated, a crystalline-swollen, and an unpenetrated region, to determine the specific characteristics of the respective regions. It was found that the density in the internal region and the fraction of the surface-cavitated region had a larger dependence on draw ratio than on treatment temperature. Also, the diffusion coefficients for the crystalline swollen region were calculated at various draw ratios and the morphological structure of the PET films was described.