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Abstract
Environmentally degraded fibers could impact multiple aspects of a fiber comparison, considering that collected weathered fabrics/fibers may express an altered chemical structure and/or colorimetric property compared to their unexposed counterparts. Depending on the amount of degradation the evidence has suffered, it could be challenging for forensic scientists to make conclusions from their comparative analyses. Observations presented in this study were orchestrated to test the possible outcomes that sunlight has on fabric-based materials. Photodegradation of fabrics was investigated through the use of an environmental chamber for a duration of six weeks, which would be equivalent to three months of real-world UV exposure. Red and blue fabrics of 100% polyester, nylon, and cotton were tested; purity and identity of each sample were confirmed by polarized light microscopy and Fourier-transform infrared spectroscopy. Colorimetric properties were analyzed through fluorescence microscopy. Accelerated weathering was accomplished in an environmental chamber, fabrics were subjected to repeated cycles—two hours at an irradiance of 0.25 w/m2, two hours at 0.47 w/m2, four hours at 0.68 w/m2, two hours at 0.47 w/m2, and lastly two hours at 0.25 w/m2—of UV light (340nm) for 1,008 hours. Relative humidity (< 25%), air temperature (25°C), and black panel temperature (35°C) were programmed to be held constant for the whole duration of the experiment. All exposed fibers either lost all pigment completely or were a faded variation of the original dyed color. Fluorescence microscopic analysis of the blue and red nylon fibers, as well as the red polyester fibers, all revealed substantially varied results between the UV-degraded and their counterparts. In addition, UV-exposed synthetic fibers were found to be more textured, which could have resulted from a reaction between the light and the particles of TiO2 and polymer. This observation should be further studied. Overall, results presented within this study suggest that the UV-exposed fiber would be assumed as a different fiber when compared to its counterpart. Considering that this study mimicked the methods commonly performed by forensic personnel, this conclusion presents a threat for cases with evidentiary fiber samples from both indoor and outdoor conditions.
Publication Date
2023
Subject Major(s)
Chemistry; Forensic Science
Keywords
polymer photodegradation, accelerated weathering, trace evidence, weathered evidence, fluorescent microscopy
Disciplines
Forensic Science and Technology | Polymer Chemistry
Current Academic Year
Senior
Faculty Advisor/Mentor
Eric Hazelrigg
Rights
© The Author(s)
Recommended Citation
Eames, D.A. Analysis of Fiber UV Degradation Through an Environmental Chamber. Presented at The 2023 Annual Poster Symposium for Undergraduate Research and Creativity, Richmond, Virginia, April 26, 2023.