Orientation and relaxation of orientation of amorphous poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) has been uniaxially stretched at different draw ratios and draw rates above its glass transition temperature, in the 80–105°C temperature range. Molecular orientation and relaxation have been followed by birefringence. A decrease in temperature reduces the mobility of the oriented chains resulting in a slow relaxation while an increase in stretching rate results in higher orientation values and rapid relaxation after the extension. The same relaxation behavior has been observed from birefringence and polarization modulation infrared spectroscopy. Rouse relaxation times have been estimated from rheological master curves and birefringence relaxation data, while retraction and the reptation times have been deduced from the scaling laws proposed by Doi and Edwards.