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Examining the Effects of Environmental Degradation on the Optical Properties of Manufactured Fibers of Natural Origin

With the production of manufactured fibers of natural origin increasing in recent years, products such as azlon and polylactic acid fibers are likely to become more common in regular case work in the forensic science laboratory. However, little is known about the changes occurring in their optical and physical properties as an effect of moisture, sunlight exposure, and exposure to various temperatures. A federally funded research study awarded through the National Institute of Justice investigated the effects of such degradation on the optical properties of selected fibers (polylactic acid, azlon, and rayon). These fibers, which are often proclaimed by manufacturers as being biodegradable (because they are made from naturally occurring proteins, sugars, or cellulose), were expected to show the most change compared to synthetic fibers such as polyester or nylon. Environmental conditions such as exposure to water (saltwater and freshwater), UV light, and hot and cold temperatures were explored while any change in optical properties was documented.

Polarized light microscopy observations, including morphology, pleochroism, refractive index, birefringence, extinction characteristics, sign of elongation, solubility, and thermal behavior were monitored throughout two years of exposure to these conditions. Infrared spectra were also collected at various time intervals to complement light microscopy data. Noticeable changes in optical properties of these types of fibers could prove to be important in a forensic setting, notably in fiber comparison and identification. An outline and strategy for this research project was presented, along with preliminary data and an assessment of the occurrence of such fabrics in consumer textiles.

This project was supported by Award No. 2011-DN-BX-K548, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed are those of McCrone Research Institute and do not necessarily reflect those of the Department of Justice.