FOR IMMEDIATE RELEASE | September 06, 2022

Shining light on why plastics turn yellow

“Could Superficial Chiral Nanostructures Be the Reason Polyethylene Yellows as It Ages?”
ACS Applied Polymer Materials

If you own a retro gaming console or have an old roll of packing tape, you’ve seen how plastics turn yellow as they age. Though the cause of this color change has long been attributed to the formation of molecules that act as dyes — the actual chemical changes that take place remained unexplained. Now, researchers reporting in ACS Applied Polymer Materials have identified surface-based chiral nanostructures as the potential culprit.

Understanding how and why polymers degrade with age is key to designing alternatives that can avoid these pathways, allowing plastic products to have a longer lifespan. For one of the most commonly used plastics, polyethylene, it’s long been suggested that ultraviolet (UV) light — the same light that gives us sunburns — initiates reactions in the backbone of the polymer’s structure that cause the yellow color change. However, though chemical changes to polyethylene’s polymeric backbone have been observed after exposure to UV light, those new structures cannot account for polyethylene’s yellowing. One emerging way to intentionally modify the color and the ways that plastics interact with light is to create nano-sized “supramolecular” structures on their surfaces that impact plastics’ properties in a controllable way. Inspired by these surface-based technologies, Margaret M. Elmer-Dixon, Melissa A. Maurer-Jones and colleagues wanted to see if such nanostructures formed unintentionally by UV light could be the cause of polyethylene yellowing.

The researchers first investigated if potential structures formed on yellowed polyethylene films’ surfaces interacted with circularly polarized light, a type of light whose waves travel with a right- or left-handed rotation. The amount of circularly polarized light absorbed by the film in these experiments changed depending on the film’s orientation, suggesting that the yellowed plastic contains new chemical structures that are chiral, that is, they are directional and aren’t identical to their mirror images. Additional experiments showed that most of the degradation during film yellowing occurred on the surface of the films. The team concluded that chiral chemical structures on the surfaces of the polyethylene films are formed during exposure to UV light and are a potential cause for the yellow color of old plastics. They say that these insights could help researchers design plastic products that last longer before becoming unsightly or unusable.  

The authors acknowledge funding from the University of Minnesota, Duluth, the University of Minnesota McKnight Foundation, and the U.S. Department of Energy. 

###

The American Chemical Society (ACS) is a nonprofit organization founded in 1876 and chartered by the U.S. Congress. ACS is committed to improving all lives through the transforming power of chemistry. Its mission is to advance scientific knowledge, empower a global community and champion scientific integrity, and its vision is a world built on science. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, e-books and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.

Registered journalists can subscribe to the ACS journalist news portal on EurekAlert! to access embargoed and public science press releases. For media inquiries, contact newsroom@acs.org.

Note: ACS does not conduct research but publishes and publicizes peer-reviewed scientific studies.

Media Contact

ACS Newsroom
newsroom@acs.org

###

La sociedad American Chemical Society (ACS) es una organización sin fines de lucro fundada en 1876 y aprobada por el Congreso de los Estados Unidos. La ACS se ha comprometido a mejorar la vida de todas las personas mediante la transformación del poder de la química. Su misión es promover el conocimiento científico, empoderar a la comunidad global y defender la integridad científica, y su visión es un mundo construido basándose en la ciencia. La Sociedad es líder mundial en la promoción de la excelencia en la educación científica y en el acceso a información e investigación relacionadas con la química a través de sus múltiples soluciones de investigación, publicaciones revisadas por expertos, conferencias científicas, libros electrónicos y noticias semanales periódicas de Chemical & Engineering News. Las revistas de la ACS se encuentran entre las más citadas, las más fiables y las más leídas en la literatura científica; sin embargo, la propia ACS no realiza investigación química. Como líder en soluciones de información científica, su división CAS se asocia con innovadores internacionales para acelerar los avances mediante la preservación, la conexión y el análisis de los conocimientos científicos del mundo. Las sedes principales de la ACS se encuentran en Washington, D.C., y Columbus, Ohio.

Los periodistas registrados pueden suscribirse al portal de noticias para periodistas de ACS en EurekAlert! para acceder a comunicados de prensa públicos y retenidos.  Para consultas de los medios, comuníquese con newsroom@acs.org.

Nota: ACS no realiza investigaciones, pero publica y divulga estudios científicos revisados por expertos. 

Media Contact

ACS Newsroom
newsroom@acs.org

A person's hands holding an old clock made of yellowed plastic
Plastics, like what was used for this clock’s face, yellow over time; researchers now might know why this happens for polyethelene.
Credit: Dmitriev Mikhail/Shutterstock.com