Basic Study on the Discrimination of Poly(Ethylene Terephthalate) Fibres by Polarized Confocal Raman Spectroscopy

In forensics, fibres are usually identified by Fourier transform infrared (FT-IR) spectroscopy. Poly(ethylene terephthalate) (PET) fibres from garments are commonly identified, and it is important to be able to discriminate between PET fibres with different manufacturing histories. However, while FT-IR can be used for PET identification, it cannot be used to fully discriminate between different manufacturing subgroups. In this report, the application of polarized confocal Raman microspectroscopy, with the calculation of polarization ratios, can provide better discrimination of manufacturing subgroups than FT-IR. However, the effects of fibre degree of orientation and crystallinity on Raman results have not been investigated previously. In the present study, the effects of these fibre parameters on Ramanderived polarization ratios were investigated for 21 different PET fibres from four different manufacturers. Among the different Raman bands, the 1614 cm(-1) band provided the best discrimination of the manufacturing subgroups. The 1614 cm(-1) polarization ratio was affected by the fibre degree of orientation but not by the degree of crystallinity. The discriminating power of this method was 83.8 %, and the standard deviation at the 1614 cm(-1) polarization ratio was quite low. Furthermore, polarization ratios, even though the fibres varied in diameter (10-45 mu m), gave similar values calculated utilizing the intensity of the 1614 cm(-1) band. Confocal Raman microspectroscopy can successfully discriminate fibres with different degrees of orientation and crystallinity, and different diameters, when the 1614 cm(-1) band is used to calculate the polarization ratio.