An infrared spectroscopic study of molecular orientation in heat‐set poly(ethylene terephthalate) yarn using attenuated total reflection technique

The attenuated total reflection (ATR) technique has been used to obtain infrared spectra of heat‐set poly(ethylene terephthalate) (PET) fibers. The trans and gauche content have been estimated from the absorbances of the trans band at 1342 cm −1 , the gauche band at 1370 cm −1 , and the internal standard band at 1410 cm −1 . The trans orientation, as calculated from the dichroic ratios of the absorption bands at 1342, 972 and 846 cm −1 , shows a decreasing trend with an increase in heat‐setting temperature. The overall molecular orientation, as calculated from the absorption bands at 1410 and 875 cm −1 , also decreases slightly with an increase in heat‐setting temperature. The infrared data, in combination with X‐ray data, have been used to calculate the amorphous orientation factor. The ATR technique is shown to give quite representative values of the amorphous orientation factor.