08-Sep-2022 - American Chemical Society (ACS)

Shining light on why plastics turn yellow

Insights could help researchers design plastic products that last longer before becoming unsightly or unusable

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. 

Facts, background information, dossiers
More about American Chemical Society
  • News

    How to tell if that plastic bottle or bag has recycled material in it

    To encourage more recycling, the U.K. taxes single-use plastic products containing less than 30% recycled material. But aside from a manufacturer’s word, there isn’t an easy way to verify this composition. Now, researchers reporting in ACS Sustainable Chemistry & Engineering have developed ... more

    Nanoplastics can disrupt human liver, lung cells’ processes in lab experiments

    Although it’s unclear what impact this really has on humans, researchers have now taken a step toward answering that question. In ACS’ Environmental Science & Technology, a team reports laboratory results indicating that tiny plastic particles could enter liver and lung cells and disrupt th ... more

    Detecting nanoplastics in the air

    Large pieces of plastic can break down into nanosized particles that often find their way into the soil and water. Perhaps less well known is that they can also float in the air. It’s unclear how nanoplastics impact human health, but animal studies suggest they’re potentially harmful. As a ... more

  • Videos

    What Makes Rubber Rubbery?

    Reactions is looking at sports science today. Sports balls owe their reliability to an unusual polymer. Learn about the chemistry of rubber the all-star’s best friend! more

    Dragon's Blood Could Save Your Life

    This week Reactions is looking at chemistry in bizarre places that could save your life. The science within the blood of the Komodo dragon or in a horseshoe crab can help with antibiotic resistance. But it doesn't end there, so we're taking a closer look at other wild places in nature that ... more

    Why is Olive Oil Awesome?

    Whether you sop it up with bread or use it to boost your cooking, olive oil is awesome. But a lot of chemistry goes on in that bottle that can make or break a product. Take the “extra virgin” standard: Chemistry tells us that a higher free-fatty-acid content leads to a lower grade, less tas ... more

More about University of Minnesota
  • News

    Energy researchers invent chameleon metal that acts like many others

    A team of energy researchers led by the University of Minnesota Twin Cities have invented a groundbreaking device that electronically converts one metal into behaving like another to use as a catalyst for speeding chemical reactions. The fabricated device, called a “catalytic condenser,” is ... more

    First fully 3D-printed, flexible OLED display

    In a groundbreaking new study, researchers at the University of Minnesota Twin Cities used a customized printer to fully 3D print a flexible organic light-emitting diode (OLED) display. The discovery could result in low-cost OLED displays in the future that could be widely produced using 3D ... more

    Exploding and weeping ceramics

    From coffee cups to bathroom tiles, ceramics are brittle.  Subject to the slightest deformation, they shatter. On the other end of the spectrum of materials, some of the most deformable materials known - that also support large stresses while they deform - are shape memory alloys.  The orig ... more

  • Videos

    New method for making zeolite nanosheets for ultra-selective membranes

    A new method to make zeolite nanosheets leads to high performance membranes for separation and purification processes. Credit: Prashant Kumar and Michael Tsapatsis, University of Minnesota more

    Video of heat transfer at the nanoscale

    This video made with the University of Minnesota ultrafast electron microscope (UEM) shows the initial moments of thermal-energy motion in an imperfect semiconducting material. The video shows nanoscale waves of energy, called phonons, moving at about 6 nanometers (0.000000006 meters) per p ... more