Inspired by the way squid skin changes color, researchers have made a temperature-regulating material for coffee cups, takeout containers, grocery delivery bags, and shipping boxes. The insulating material could provide a new solution for food and beverage packaging that is cheap, recyclable, and sustainable, researchers say in a paper published in the journal Nature Sustainability.
The team’s invention is an advanced take on the metallized plastic films that commonly line packaging materials. Compared to those metallic films, the new one offers a way to control how hot or cold to keep the stuff it encases by using minimal energy. It does that by reflecting more or less heat depending on how much it is stretched. So a coffee cup coated with the tunable material would keep its contents hot but the holders hands cool.
“There is an enormous array of applications for this material,” said University of California, Irvine chemical and biomolecular engineering professor Alon Gorodetsky in a press release. “Think of all the perishable goods that have been delivered to people’s homes during the pandemic. Any package that Amazon or another company sends that needs to be temperature-controlled can use a lining made from our squid-inspired adaptive composite material.”
Gorodetsky and his colleagues looked for inspiration at the common squid. The cephalopod’s skin is embedded with organs called chromatophores, which it expands and contracts to change its appearance.
The researchers decided to mimic this property, but to reflect heat instead of light. They deposited copper layers on a flexible aluminum foil. On top of the copper they grew microscopic pillars also made of copper. Then they sprayed it with multiple layers of a rubbery coating.
The metal structures come apart when the film is stretched, letting some infrared heat escape through the gaps. And they go back together when the film is relaxed, so it reflects and keeps more heat in.
To test the heat regulation the material offers, the team filled coffee in disposable paper cups. By covering them with films that were stretched to different extents, they could control how quickly the coffee would cool. The material worked after repeated stretch-release cycles.
The films should be easy to make and for low cost, the researchers write. The copper and rubber raw materials, for instance, cost a dime per square meter, and should become even cheaper when produced at large scale. And recycling it should be easy by removing the copper with vinegar and then recycling the stretchy rubber coating and aluminum films using known commercial methods.
Source: Badshah, M.A., Leung, E.M., Liu, P. et al. Scalable manufacturing of sustainable packaging materials with tunable thermoregulability. Nat. Sustain., 2022.
Image: Melissa Sung, UCI.
