Could Superficial Chiral Nanostructures Be the Reason Polyethylene Yellows as It Ages?

Margaret M. Elmer-Dixon, Liam P Fawcett, Brian R. Hinderliter, Melissa A. Maurer-Jones

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Understanding the degradation of plastics, some of the most widely used materials on Earth, is crucial in a broad range of fields from materials design to environmental monitoring. Many polymers yellow as they age, but there is no chemical explanation that can describe the origin of this yellowing for polyolefins specifically. Here, we show that irradiated blown polyethylene sheets preferentially scatter circularly polarized light. Because scattering of circularly 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 that may be the underpinnings for the perceived yellow/brown tint as polyethylene ages. Further, we demonstrate incident polarization-dependent detection of colored light scattering from irradiated polyethylene films and 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 structures 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 provides evidence for the development of supramolecular structures of polymers during aging. Because of this, our findings provide an alternative direction in plastic degradation research for understanding the chemical and structural changes. Findings presented here shift our understanding about materials degradation and can inform our future materials designs and recovery.

Original languageEnglish (US)
Pages (from-to)6458-6465
Number of pages8
JournalACS Applied Polymer Materials
Volume4
Issue number9
DOIs
StatePublished - Sep 9 2022

Bibliographical note

Funding Information:
The authors acknowledge Emma Sorensen for her help with collecting bulk crystallinity measurements and Adam Finke for providing aged PE samples that were used initially in the testing. Further, the authors would like to thank the UMD Department of Chemistry and Biochemistry for use of their CD spectrophotometer and FTIR. UMD provided funding for this work both to L.P.F. from the Department of Chemistry and Biochemistry at UMD in the form of a teaching assistantship and M.A.M.-J. as part of her startup funds. M.M.E.-D. was supported by the University of Minnesota McKnight Foundation in an award to B.R.H. DOE (NEUP DE-NE0008540) awarded to B.R.H. and M.A.M.-J. additionally supported this work.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

Keywords

  • accelerated aging
  • chiral nanostructures
  • photochemistry
  • plastic degradation
  • scattering
  • yellowing

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