Analysis of poly(ethylene terephthalate) fibers using polarized Raman microscopy

Polarized Raman microscopy was successfully used to obtain orientation parameters (P₂ and P₄) as well as the Raman tensor forms of several bands of PET fibers. The bands at 1616, 998, 1030 and 1096 cm −1 were analyzed. It was found that the orientation parameter P₂ for the 1616 cm−1 band has a linear relationship with birefringence of the samples, indicating that it provides quantitative orientation information for the average chains of PET fibers. It was found that the Raman tensor ratios of this band vary with morphology. This is in agreement with Lesko et al.'s findings and calls into question the use of Raman tensor values obtained from isotropic samples when obtaining the orientation parameters. The 998 cm−1 band was shown to be a crystal band and the P₂ was found to be consistent to that from Yazdanian's X-ray studies. Additionally, it was found that the Raman tensor does not changing with crystallinity and crystal orientation. It was shown that for the first time both the crystallinity and crystal orientation can be obtained from the 998 cm−1 band. The 1030 cm −1 band, which has been assigned to be a gauche band, was observed to be a pure Gaussian band and it was found that both P₂ and P ₄ are equal to zero. This is the first time that direct evidence has been obtained that shows the gauche orientation is indeed random. The 1096 cm−1 band has been observed to exist in crystallized samples. It was found that P_2,1096 is substantially less than P _2,998, and the maximum value for P_2,1096 is about 0.23 for the samples in this research. All of the P_4,1096 are greater than P_2,1096, which means that the angle of the direction of the third principal component of the Raman tensor with the fiber axis is larger than 63°. In summary, quantitative measures of chain orientation, crystal orientation, gauche orientation, crystallinity, gauche amount as well as Raman tensor forms of various vibrations were obtained via polarized Raman microscopy for PET fibers.