The use of melting point and refractive index determination to compare colourless polyester fibres

The incidence of polyesters encountered in forensic fibre examinations continues to increase. To meet different consumer needs such fibres can be subjected to many physical and chemical variations during production. Some of these variations are discussed. Accurate comparison of these fibres presents a particular problem to the forensic scientist. Melting point and refractive index determinations were made on various samples of colourless polyesters provided by different manufacturers to assess the comparative value of such information and to find out the possibility of relating it to modifications of the basic polymer. Melting points alone were found to be of little comparative value, but determination of both refractive indices n_∥ and n_⊥ does allow discrimination between samples. Consideration of both melting point and refractive index together may help to provide an insight into polymer variation, though this remains somewhat speculative.     

Note on fabric marks in motor vehicle collisions

Two cases are described where motor vehicle accidents lead to fabric weave impressions and fibres being transferred to the paintwork of vehicles from the clothes of the victims.     

The kinetics of colour change in textiles and fibres treated with detergent solutions: Part I—Colour perception and fluorescence microscopy analysis

The aim of this study was to assess colour changes that occur in several types of commonly available textiles as a result of the long-term effects of various popularly used laundry detergents. A 14 day experiment was conducted using blue, red and grey/black cotton, wool, acrylic and polyester textiles. Colour changes were evaluated through the visual comparison of the colour of the textile samples against that of the untreated (control) material.The kinetics of the changes in the colour of the fibres were monitored using fluorescence microscopy (UV excitation filter). The conclusions include an assessment of the observed changes from a fibre analysis expert's point of view, as well as that of an average user/consumer of the products involved.     

The dye classification and discrimination of coloured polypropylene fibres

A sequential extraction and classification scheme for dyed polypropylene fibres is presented together with suitable thin-layer chromatography (TLC) systems for separating the extracted dyes.Pigment coloured polypropylene fibres are unaffected by solvents and are therefore characterised by microspectrophotometry.     

The persistence of fibres on skin in an outdoor deposition crime scene scenario

Textile fibres were transferred to a pig skin carcass and their persistence determined at daily intervals for up to a 12 day period during which time the carcass was left outdoors exposed to the prevailing weather conditions and animal activity. In the absence of strong winds and precipitation, the loss of fibres was found to be exponential. Stronger winds and heavier precipitation caused an increase in the rate of loss of fibres. The results of this study showed that the majority of fibres transferred to a body deposited outdoors, can be expected to be lost after the first 2 days, however, none of the experiments performed resulted in a complete loss of fibres, even after 12 days exposure. These persistence characteristics differed from those observed in a similar study using small sections of skin, rather than carcasses.The implications of the results of the present study in relation to the examination of fibre evidence in cases of homicide are discussed.     

A comparison of efficiency of manual and automatic fibres search with the Maxcan fibre finder

The aim of this work was to study the efficiency of automatic fibre searching with the Maxcan fibre finder (Cox Analytical Systems, Sweden) in comparison to manual searching. The influence of some parameters (color, thickness, background noise) on the results of a fibre search was considered. Eighteen experimental tapes with different target fibres and different background noises were prepared in the laboratory. Searching of fibres was performed manually and with the Maxcan fibre finder by different operators from four European laboratories. Two laboratories have the Maxcan fibre finder system and the two instruments were used and compared in this study. The results show that searching with the Maxcan is generally as efficient as manual searching, except for very pale or very dark fibres. Note that the tapes used for these experiments were prepared in laboratory, and are not completely representative of the tape that could be obtained in real cases. To generalize the results obtained, further research on real case samples would be necessary.