ITHACA, N.Y. -Cornell University researchers have developed an inexpensive and potentially scalable approach that uses a commercially available peroxide to bind polyethylene and polypropylene together, thereby creating a more useful, high-quality plastic recycling additive.
The findings were published May 19 in the Journal of the American Chemical Society. The co-lead authors were postdoctoral researcher Moritz Kränzlein and doctoral student Shilin Cui. The project was led by Geoffrey Coates, professor of chemistry and chemical biology.
The key to developing their new polyolefin compatibilizer was to look for existing polymers that, with the right processing, could do the job, rather than creating a new one from scratch. Kränzlein began by experimenting with the materials that were already in the lab, always with a few parameters in mind.
“Every second meeting, when I was giving Geoffrey an update, his first question was, what’s the cost? There was always this line of price per pound that I shouldn’t cross,” Kränzlein said. “We tried to really keep that as a focus of this project. Instead of finding a very elegant or sophisticated solution, we tried to find a real-world solution that works.”
A year and a half – and more than 200 experiments – later, the researchers settled on an organic alkyl peroxide that when heated essentially plucks hydrogen molecules off high-density polyethylene (HDPE) and isotactic polypropylene (iPP) so they can be grafted together and form a copolymer material that can be added to a mechanical recycling process for HDPE and iPP mixtures, restoring their properties.
The copolymer can basically be thought of as “plastic soap,” Kränzlein said. “It took us a very, very long time playing around with all the different tuning points until we finally achieved something that that we were happy with.”
Coates is hopeful that the compatibilizer could also lead to the creation of new polymer alloys that leverage the respective strengths of different waste plastics. There would be no need for giant million-dollar plants. Just take some preexisting polymers and add the compatibilizer.
“You could make a whole kind of pallet of alloys that might have better properties than either one of the pure polymers alone, just like stainless steel,” said Coates, who recently launched a startup that specializes in the compatibilizer technology through Cornell’s Praxis Center for Venture Development. “The dream is, if you can make a really rigid polymer that’s also really tough, then you can make packaging that uses less material, yet has the same sort of properties. That’s one of the other big applications for this technology.”
The research was supported the Gerstner Family Foundation, with additional funding from the U.S. Department of Energy through Ames National Laboratory’s Institute for Cooperative Upcycling of Plastics, an Energy Frontier Research Center.
For additional information, read this Cornell Chronicle story.
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Journal
Journal of the American Chemical Society