Plastic pollution plays land and ocean. Chemists are looking for ways to take plastic molecules apart to make it new, high -quality plastic later. Researchers from TU Eindhoven have deployed a chemical reaction based on light for this more than a hundred years ago.
Unlike other photochemical recycling methods, the plastic molecules with their approach can not only be cut loose but also re -linked with the help of light, they write In the scientific journal Advanced Materials. “That has never been done before,” says Fabian Eisenreich, assistant professor Chemical Engineering and Chemistry at Eindhoven University of Technology and one of the authors of the research. “It makes these plastic molecules completely circular.”
Mechanical recycling
Just like plastic itself, plastic recycling is also there in many shapes and sizes. In practice, mechanical recycling is now used slowly. Large pieces of plastic are sorted by type and cut into chips that can be reused. However, companies that are working on this have had a hard time in recent years, because oil companies are fully committed to the production of plastic, making new plastic cheaper than reused plastic.
Meanwhile, there is a lot of research Place in the direction of chemical recycling. Hereby the long chains of molecules that are plastic consists of – polymers – converted into small molecules – monomeren – that can serve as new building blocks for plastic or other chemical products. High temperatures or light float the chemical reactions for cutting, possibly in combination with a catalyst.
“The advantage of light is that it requires much less energy than heat,” says Eisenreich. “Chemically, there are also important differences. With light, molecules can be selectively tackled. If you heat plastic, up to 500 to 800 degrees, it will also break the polymers, but you will get a complex mix of different molecules instead of targeted monomers of one type.”
Yet with light it is also difficult to get the right building blocks back to make new plastic out of it. “Usually the molecules that remain after photochemical recycling are used in other chemical processes. That is seen as high-quality reuse, but it does not complete the plastic circle.”
Photochemical transformations
That has now succeeded, thanks to a process in two steps. Eisenreich gained the idea for the first part of the approach during the preparation of a college for students. “I looked into old text books about photochemistry and came the Pinacol Coupling-Against reactions. These are extensively studied photochemical transformations that were already discovered in 1900. This creates a stable carbon cabbage binding under the influence of light. I was surprised that I could not find any research that this approach had successfully applied to polymers. An attempt was made in the 70s, but that had ended on nothing. “
Since then there has been a lot of innovation in the field of light. With LED, colored light with a lot of energy is easy to broadcast, which has yielded many new options for photochemistry. Eisenreich and his colleagues decided to try again Pinacol Coupling-To be used for making polymers. With success.
Blue LED light
To close the circle, the polymers made must be selectively cut loose, in monomers with which the Pinacol Coupling-Reaction can take place again. That happens with another chemical process. “In addition to blue LED light, we also use a catalyst, cerium chloride,” says Eisenreich. “Our polymer is only receptive to the light if the catalyst is also present. The molecule then breaks in exactly the right place.”
Eisenreich now wants to make more polymers with his approach. His method cannot be applied to existing plastic. It also offers no solution for problems with collecting and sorting different types of plastic. “We design new polymers that can hopefully ever replace it from today -commonly used plastics such as PP and PE. With the same qualities in terms of use, but made with recycling in mind.”