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,P-1096, is substantially smaller than for the 998 cm(-1) band, P-2,P-998. In addition, P-2,P-1096 is not related to the birefringence of the samples, and there is no simple relationship between P-2,P-1096 and P-2,P-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 +/- 4degrees, and the ODF becomes narrower as molecular orientation increases. The 998 cm(-1) band has a tilt angle of approximately 0degrees, 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.