New Bayreuth ERC project: Optimized films from recycled plastic waste reduce energy consumption for cooling

Plastic products are indispensable in many sectors of the economy today – be it food packaging, lightweight construction, or medical technology. Nevertheless, comprehensive recycling and upcycling have not yet become established. As a result, a large proportion of plastic waste is still incinerated or disposed of in the environment. At the same time, about 15 percent of global energy consumption is caused by cooling systems: a share that is expected to increase, primarily due to climate change. However, new technology can counteract this development: passive daytime cooling. It avoids heating by solar radiation and, at the same time, emits ambient heat without the need for an external energy supply.

In the ERC-funded project called "CoolChips", Prof. Dr. Markus Retsch and his Bayreuth postdoc Dr. Qimeng Song are going to develop large-area films from plastic waste, such as potato chip bags. These could be used as advanced materials on roofs, blinds, and awnings, for example, to cool residential or office buildings or even car parks. 

"Passive daytime cooling requires materials with special optical properties: They must not absorb sunlight in the wavelength range between 0.3 and 2.5 micrometers but must scatter or reflect all solar radiation in this wavelength range. In the range between 8 and 12 micrometers, on the other hand, they must emit their thermal energy as efficiently as possible in the direction of space. This is because only light in this narrow window can transmit through the atmosphere and escape into space," says Retsch, who holds a chair in physical chemistry at the University of Bayreuth.

Researchers have already developed numerous materials to explore and demonstrate the potential of passive daytime cooling. Many of them have a metallic back coating. The Bayreuth project builds on the knowledge gained with these materials: Aluminium laminates are commonly used composite materials for food and disposable packaging. They consist of several layers that are impermeable to oxygen and moisture. These metal-containing polymer films are industrially produced in large quantities in the form of small-particle products, such as bags for potato chips. Unfortunately, they pose significant problems for today's standard recycling technologies because aluminium contaminates the recycled polymers. At the same time, however, aluminium laminates contain a layer that reflects sunlight, making them attractive for passive cooling technologies.