Due to the frequent use of plastics in daily life, encountering microplastics as pollution and trace evidence in forensic investigations is a common occurrence. Nylons are a plastic class known to be strong and durable, and they are used in a variety of products. Nylon is also a popular choice among 3D printing materials, and its strength and durability lend itself to printing tools like keys and even firearms. The analysis of microplastics typically is performed using any combination of microscopy, infrared spectroscopy, Raman spectroscopy, and mass spectrometry. Nylons are known to have fluorescent impurities created during the polymer’s synthesis and processing, so this work set out to develop a method to analyze nylon microplastics non-destructively using room-temperature fluorescence spectroscopy. By analyzing impurities in the sample, fluorescence spectroscopy can provide additional information about the microplastic’s source that other non-destructive methods do not. Excitation-emission matrices, excitation and emission spectra, and synchronous fluorescence spectra were collected from pellets of four different nylons. Using these spectra, all nylons could be distinguished from one another. A trace evidence simulation was then performed with fragmented pellets and a 3D printed key, and the trace microplastics were shown to have spectra that were consistent with those of the bulk plastic. This method was then improved by applying chemometric algorithms to the fluorescence data. Fluorescence spectra, excitation spectra, and excitation-emission matrices collected from Nylon 6 and Nylon 6/12 were found to be indistinguishable by visual comparison. Using synchronous fluorescence spectra from the two nylons in conjunction with Principal Component Analysis and Common Dimension – Partial Least Squares – Discriminant Analysis, the two nylons could be fully discriminated. Overall, this work presents a powerful new tool to non-destructively analyze nylon microplastics and generate more reliable conclusions about the source of the microplastic than current methods alone.
Dr. Andres Campiglia, Committee Chair.
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