Improving the forensic value of textiles and fibres through the holistic detection and analysis of acquired characteristics due to environmental factors

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Fibres are a useful form of trace evidence that allows for a suspect, a crime scene or a victim to be linked, based on the comparison of fibres. Currently, analysis of fibres is based on the comparison of manufactured features such as the fibre type, dye and colour. These features are unable to distinguish fibres that have come from a line of mass-produced items, something which has become increasingly common. The use of acquired characteristics to compare fibres is an area of research that has not been substantially explored. This thesis seeks to explore the use of acquired characteristics, specifically laundry detergents, to aid in the comparison of fibres and improve their evidential value. This study was undertaken by washing textiles in a commercial washing machine, changing variables such as the textile type and colour, detergent brand and number of washes. The analysis of the fibres was split into two categories: fluorescence and composition. Fluorescence analysis included the use of both fluorescence microspectrophotometry and the Video Spectral Comparator to detect optical brighteners in detergent residues on washed samples. Composition analysis was split into chemical (Raman Spectroscopy) and elemental (SEM-EDS and LA-ICP-MS/solution ICP-MS). Comparison of the fluorescence of washed and control textiles showed that the fluorescence of the sample after washing is highly dependent on the textile type, with cotton showing the most fluorescence, while wool and polyester showed little to no fluorescence. Washed cotton samples produced a consistent fluorescence peak which was common for all detergent. This peak could also be seen in control samples that had been exposed to optical brighteners in the manufacturing process. Chemical composition analysis of the samples in the form of Raman spectroscopy showed potential to differentiate between different detergents but was unable to detect detergents on the washed samples. Elemental composition comparison of washed and control samples showed a clear difference in the composition of the two samples, with a consistent trend of elements being removed or added in the washing process. Blind sample pairs of fibres of the same fibre type were compared using fluorescence microspectrophotometry and solution ICP-MS to determine whether they could be excluded as having come from the same source, based on if they had been washed or not. Fluorescence microspectrophotometry was able to reliably distinguish the majority of the samples, while solution ICP-MS revealed that it had limitations when it came to interpretation due to variation in the elemental concentration of fibres from the same source. The results in this thesis show that the combination of fluorescence analysis using fluorescence MSP, and elemental composition analysis using solution ICP-MS allows for cotton and wool fibre textiles, but not polyester fibres, to be distinguished based on whether they have or have not been washed before.
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