Molecular orientation in differently processed poly(ethylene terephthalate) yarns as studied by C-13 2D CP-MAS NMR

The molecular orientation of a series of differently processed industrial fibers of poly(ethylene terephthalate) (PET) has been investigated by C-13 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.