Kinetics of non-isothermal cold crystallization of uniaxially oriented poly(ethylene terephthalate)

The non-isothermal equation was extended to describe non-isothermal cold crystallization kinetics of oriented polymers. The validity of the equation was examined by using a DSC crystallization curve of oriented poly(ethylene terephthalate) (PET) fibers with a constant heating rate. The double cold crystallization peaks appeared in the DSC curve. The relative degrees of crystallinity at different temperatures were analyzed by using the equation. The results show that the value of the Avrami exponent near to 1 at lower temperatures implies the bundle-like crystal growth geometry and the value of the Avrami exponent near to, 2, at higher temperatures implies the higher dimension crystal growth geometry. The first crystallization process crystallizes at faster rate than that of the isotropic sample, while the second process crystallizes at slower rate than that of isotropic sample. If a simple single process model was used, the value of the Avrami exponent, 0.77, was obtained. The result shows the simple single process model cannot describe the processes of crystallization of oriented PET fibers satisfactorily.