Orientation Distribution Functions Obtained via Polarized Raman Spectroscopy of Poly(ethylene terephthalate) Fibers

Polarized Raman microspectroscopy was used to analyze uniaxially oriented fibers of poly(ethylene terephthalate) (PET). A full analysis of bands at 1616, 998, and 1096 cm -1 is reported for cylindrically symmetric PET fibers. Average orientation and crystal orientation are obtained from the 1616 and 998 cm -1 band, respectively. Although both the 1096 and the 998 cm -1 bands are related to the crystallinity, the second Legendre polynomial of the 1096 cm -1 band, P 2,1096, is substantially smaller than for the 998 cm -1 band, P 2,998 . In addition, P 2,1096 is not related to the birefringence of the samples, and there is no simple relationship between P 2,1096 and P 2,998 . The orientation distribution functions (ODFs) for these vibrations were obtained by assuming a Gaussian distribution with a tilt angle relative to the fiber axis and specific to each vibration. The 1616 cm -1 band has a tilt angle of 23 ± 4°, and the ODF becomes narrower as molecular orientation increases. The 998 cm -1 band has a tilt angle of approximately 0°, and the ODF is always very narrow. On the other hand, the tilt angle of the 1096 cm -1 band increases, and the ODF becomes narrower as the molecular orientation increases. However, because of the large tilt angle, P 2 for this band decreases as the molecular orientation increases .