A COMPARISON BETWEEN PA-FTIR AND FT-RAMAN SPECTROSCOPIES IN THE STRUCTURAL-ANALYSIS OF ANNEALED INJECTED-MOLDED POLY(ETHYLENE-TEREPHTHALATE)

With the introduction of the Fourier, Transform technique in Raman spe ctroscopy (FT-Raman) and the development of new methods in FTIR, such as FTIR with photoacoustic detection (PA-FTIR), vibrational spectrosco py has been launched into a new era of application in polymer chemistr y and physics. This work provides a comparative study between PA-FTIR and FT-Raman techniques in which the potentials and limitations of the se two methods are investigated by following and analyzing structural variations that take place in annealed injected-moulded poly(ethylene terephthalate) (PET). Both spectroscopic techniques appear to be suita ble to detect structural changes that occur in PET submitted to differ ent annealing temperatures. We suggest that these variations are direc tly related to conformational rather than crystallinity changes. The m ain drawbacks of PA-FTIR are the lengthy adquisition time of spectra a nd the photoacoustic saturation that can appear in regions with quite high optical absorption coefficient. Conversely, FT-Raman technique do es not suffer from neither of these problems. However, the sensitivity to structural changes of certain infrared bands seems to be higher th an that of analogous Raman bands and small structural details such as the regularity of chain folding, can only be detected in the infrared spectra.