Why Does Plastic Yellow as it Ages?? (2021-11-05)
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Why Does Plastic Yellow as it Ages?? (2021-11-05)
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2021
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Abstract
Many polymers yellow as they age. Polymer aging with resultant chemical
changes to the macromolecule is generally attributed to oxidation
pathways, particularly for polyolefins. Because of the basic subunit nature
of polymers, the chemical byproducts generally have little to no
spectroscopic response in the visible region of the electromagnetic
spectrum, yet we readily perceive old plastics as yellow. In fact, this
discoloration is a hallmark to the integrity of a plastic but there is no
physical explanation that can describe the origin of this yellowing. Here we
show that irradiated blown polyethylene sheets preferentially scatter
circularly polarized light. Because scattering of polarized light only occurs
in the presence of chiral structures, our findings provide evidence of
formation of chiral supramolecular structures responsible for preferential
light scattering, the result of which is the appearance of a yellow/brown tint
as the polymer ages. Further, we demonstrate incident polarization
dependent detection of colored light scattering from irradiated
polyethylene films. Finally, we show that the scattered light is distinctly
different in color. Overall, these results provide evidence that the yellowing
of polyethylene, previously assumed to be caused by polymer backbone
rearrangements, is actually the product of chiral, optically active
nanostructures that form on the plastic's surface due to UV irradiation. To
the best of our knowledge, this is the first explanation for polymer
discoloring that considers the development supramolecular structures of
polymers during aging.
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Friday, November 5, 2021, 3:00 p.m.; Chem 200; Dr. Margaret Elmer-Dixon, Post-doctoral Associate, Department of Physics and Department of Mechanical & Industrial Engineering, University of Minnesota Duluth
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Fall 2021 Seminar Series
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Elmer-Dixon, Margaret; University of Minnesota Duluth. Department of Chemistry and Biochemistry. (2021). Why Does Plastic Yellow as it Ages?? (2021-11-05). Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/227600.
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