AMORPHOUS ORIENTATION OF POLY(ETHYLENE-TEREPHTHALATE) BY X-RAY-DIFFRACTION IN COMBINATION WITH FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

Drawing of poly(ethylene terephthalate) (PET) films was performed from the amorphous state using different drawing rates at a temperature of 80 degrees C. The crystallinity of the films was determined by thermal analysis and orientation of the different phases by specular reflection Fourier transform infra-red (FTi.r.) spectroscopy and wide-angle X-ray diffraction. The FTi.r. spectroscopic and X-ray results showed a significant orientation of the different molecular species (trans- and gauche-conformers and crystalline phase), particularly for draw ratios (lambda) greater than 3. Determination of the amorphous orientation from X-ray diffraction of the amorphous phase of PET is shown to be possible. A combination of the FTi.r. results with those obtained for the X-ray orientation of the crystalline phase allowed an independent determination of the amorphous orientation. A good agreement was observed with the corrected X-ray amorphous orientation results for draw ratios greater than 3. Below this draw ratio, low orientation and crystallinity, combined with the inherent limitation of the X-ray technique and crystal imperfections, induced large discrepancies between the two results. It is also shown that the trans-conformer orientation increases steadily with draw ratio from the onset of draw and saturates rapidly, whereas that of the gauche conformer is negligible for all draw ratios.