DETERMINATION OF CRYSTALLINITY AND MORPHOLOGY OF FIBROUS AND BULK POLY(ETHYLENE-TEREPHTHALATE) BY NEAR-INFRARED DIFFUSE REFLECTANCE SPECTROSCOPY

Diffuse reflectance spectroscopy in the near-infrared (NIR) region (1100-2400 nm) was used to characterize the morphology of fibrous and bulk poly(ethylene terephthalate) (PET). The method of Partial Least-Squares (PLS) was used to correlate NIR spectra of PET yarns with percent crystallinity. Standard error of prediction values for percent crystallinity in PET yarns are in the range of 2-3.5% crystallinity, and depended on the specific NIR spectral region used for analysis. Principal Components Analysis (PCA) was used to study the differences in NIR spectra of bulk PET samples that were crystallized at different temperatures. It was observed that NIR spectroscopy can detect changes in both intermolecular and intramolecular interactions in PET. The observed effect of crystallization temperature on the morphology of bulk PET is very similar to effects observed in earlier IR and thermal analyses. In addition, detection of moisture in bulk PET is demonstrated.