Scientists have developed a groundbreaking chemical process that transforms plastic waste into valuable hydrocarbon building blocks for creating new plastics. This advanced method efficiently processes two major types of consumer plastic waste—polyethylene, commonly found in single-use bags, and polypropylene, used in hard plastics like luggage and microwave dishes. Collectively known as polyolefins, these plastics are effectively broken down, including when mixed together, paving the way for a more sustainable approach to managing plastic waste.

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According to the research team, a circular economy for many disposable plastics could be facilitated by the catalytic process developed at Lawrence Berkeley National Laboratory, which would reduce the amount of fossil fuels needed to produce virgin plastic by converting plastic waste back into the monomers needed to make polymers.

“We have an enormous amount of polyethylene and polypropylene in everyday objects, from lunch bags to laundry soap bottles to milk jugs—so much of what’s around us is made of these polyolefins,” said research leader Professor John Hartwig, of the University of California, Berkeley.

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Through a collaboration between the public sector and academia, Hartwig and his colleagues devised a chemical process that utilized three distinct custom heavy metal catalysts: one was used to introduce a carbon-carbon double bond into the polyethylene polymer, and the other two were used to repeatedly cut off a carbon atom from the chain at this double bond. However, the procedure was challenging to scale up because the catalysts disintegrated during the liquid reaction and were rarely recoverable. 

It was two years before to that. These days, cheaper solid catalysts—such as sodium on alumina and tungsten oxide on silica—are frequently employed in the chemical industry for continuous flow processes that reuse the catalyst, taking the place of the more costly, soluble metal catalysts as part of a new process.

Scientists have been searching for ways to convert polyolefins into something more valuable, like the polymers that help produce new plastics, in order to reduce waste. Polyethylene and polypropylene plastics make up about two-thirds of consumer plastic waste worldwide. About 80% end up in landfills, incinerated, or simply dumped in the street where they degrade into microplastics and eventually enter rivers and oceans. Scaling up continuous flow processes to handle large volumes of material is a necessary prerequisite if this is to be used widely and at scale.

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While many experts are working to rebuild plastics from "the ground up" so they may be reused with ease, Hartwig pointed out that the difficult-to-recycle plastics of today will remain a challenge for decades to come.  He stated, “One can argue that we should use only new circular materials and do away with all polyethylene and polypropylene, but the world's not going to do that for decades and decades. Everyone uses polyolefins because they are inexpensive and have useful properties.”