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

Abstract

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, P2,1096, is substantially smaller than for the 998 cm-1 band, P2,998. In addition, P2,1096 is not related to the birefringence of the samples, and there is no simple relationship between P2,1096 and P2,998. 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 appro...