Molecular Orientation in Differently Processed Poly(ethylene terephthalate) Yarns As Studied by 13C 2D CP-MAS NMR

The molecular orientation of a series of differently processed industrial fibers of poly(ethylene terephthalate) (PET) has been investigated by 13 C solid-state rotor-synchronized 2D CP-MAS NMR. 1 In addition to the 〈 P 2 〉 order parameters, higher rank order parameters, 〈 P 4 〉 and 〈 P 6 〉, could also be determined. Significant differences in the order parameters were observed as a function of the processing history. The 〈 P 2 〉 order parameters obtained for the range of PET fibers showed a linear relationship with the optical birefringence data. By making plots of the 〈 P 4 〉/〈 P 2 〉 and 〈 P 6 〉/〈 P 2 〉 ratios corresponding with several types of distributions using a Pearson VII function, the orientation distribution was reconstructed. For the as-spun fibers, relatively high 〈 P 4 〉/〈 P 2 〉 and 〈 P 6 〉/〈 P 2 〉 ratios were obtained which points to a heavily tailed orientation distribution. The order parameters of the drawn PET fibers agree quite well with the pseudoaffine deformation model.