Non-destructive fibre analysis of blended clothing for forensic applications

Abstract

In recent years, global market demands for blended fibres are booming due to their cost-effectiveness and enhanced properties. Therefore, the usage of blended fibres is high and thus there are greater chances of encountering fibre blends at crime scene in forensic cases such as assault and hit-and-run. Fibre analysts have often relied on analytical techniques developed for single fibres to identify fibre blends. This study was therefore conducted to characterize binary-blended samples using light microscopy and infrared spectroscopy as well as to evaluate the effectiveness of these techniques on analyzing fibre mixture. In this study, 5 reference fibre samples and 25 clothing samples were subjected to physical examination, followed by examination with stereomicroscope, polarizing and fluorescence microscopes as well as attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Stereomicroscopy was found to provide preliminary screening by furnishing information regarding the weave or knit pattern and twist direction of yarns. Polarized light microscopy was found to be effective in detecting fibre blends and examining optical properties, delustrant levels and fibre diameters but it could not confirm the generic classes of man-made fibres. Fluorescence microscopy allowed fibre discrimination by comparing fluorescence activity. ATR-FTIR was superior in determining types of polymeric man-made fibres compared to polarizing microscope. However, it was found that the infrared spectra needed to be obtained from several areas of a fabric in order to discover the presence of fibre mixtures. In most of the blended samples, correlation of more than 80% was achieved by comparing the blended fibres with combined spectra of individual fibres. In conclusion, non-destructive techniques of microscopy using 3 types of microscope (stereo, polarizing and fluorescence) followed by infrared spectroscopy (ATR-FTIR) are recommended to be used for characterizing fibre blends effectively.