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

Authors: Kelly M. Brinsko, M.S., Sebastian B. Sparenga, M.S., Meggan B. King, B.Sc.

Abstract:

Synthetic fibers derived from naturally derived biological polymers are used in textiles and clothing. Such fibers are referred to as Manufactured Fibers of Natural Origin, or MFNOs.

These fibers include viscose rayon, azlon, and polylactic acid (PLA), among others. With the production of manufactured fibers of natural origin increasing in recent years, these 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.

This study investigated the effects of such degradation on three types of MFNOs: viscose rayon, azlon, and PLA. These fibers, often proclaimed by manufacturers as being biodegradable, were expected to show the most change compared to synthetic fibers, such as polyester or nylon.

Fabric swatches representing each fiber type were exposed to freshwater, saltwater, heat, cold, ultraviolet light, and composter conditions and assessed every six to eight weeks for two years for changes in optical properties, infrared spectra, solubility, and melting-point behavior.

The study found that except for complete degradation, no significant changes were observed in the optical properties, infrared spectra, solubility, or melting points of any of the fibers in any of the environments for the duration of the experiment.

Morphological changes, however, were observed in two PLA swatches and two viscose swatches exposed to UV light, as well as one azlon fabric submerged in either freshwater or saltwater. All viscose swatches in the composter and water environments eventually deteriorated completely.

These results indicate that forensic fiber comparison can be conducted on such fibers exposed to different environments, while highlighting possible explanations for some observed morphological differences.

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