Raman microscopy of processed polyethylene particles
Raman microscopy was applied to detect structural change within individual particles of low-density polyethylene following chemical and electrochemical processing steps that aimed to facilitate material decomposition. Probing at a depth of ~20 μm from the surface of the nominally 500 μm diameter particles, changes in vibrational bands sensitive to polyethylene crystallinity were evident following treatments and linked to the release of low molecular weight compounds present as additives and products of electrochemical processing. The rise of Raman scattering intensity in vibrational modes associated with polyethylene chains in a zig-zag (trans) conformation near 1128 cm-1, 1294 cm-1 and 1418 cm-1 signaled chain clustering and development of organized, crystalline-like assemblies. Multivariate statistical methods were adapted to aid in discerning spectral change. Principal component (factor) analysis was applied as a simple, rapid means to detect variation in datasets. Least-squares modeling was used to derive pure component spectra reflecting crystallinity change. The work lays a foundation for the use of confocal Raman microscopy coupled with multivariate statistical analysis techniques for quantitative probing of processed polymers.
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