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

The findings indicate that forensic fiber comparison can be conducted on such fibers after their exposure to different environments. Possible explanations are offered for some observed morphological differences. Synthetic fibers derived from natural, biological resources include viscose rayon, azlon, and polylactic acid (PLA). A 2-year study was conducted to document any changes these biologically derived polymers may undergo due to varying environmental conditions. Fabric swatches composed of each fiber type were exposed to freshwater, saltwater, heat, cold, ultraviolet light, and composter conditions. Every 8 weeks the swatches were sub-sampled and analyzed with polarized light microscopy. Morphology and optical properties were recorded, including refractive index, pleochroism, birefringence, extinction characteristics, and sign of elongation. Infrared spectra were collected every 8 weeks. Solubility and melting-point behavior were assessed every 6 months. 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; however, morphological changes were observed in two PLA swatches and two viscose swatches exposed to UV light, along with one azlon fabric submerged in either freshwater or saltwater. All viscose swatches in the composter and water environments eventually deteriorated completely. 17 figures, 4 tables, and 14 references