UC Berkeley Chemists Can Now Vaporize Plastic Waste Into Molecular Building Blocks

Chemists at UC Berkeley said they have created a new laboratory process that could represent a major step forward in recycling plastic products — from single-use bags commonly found in grocery stores to the harder materials like toys, yogurt tubs, coffee pods and luggage.

Currently, recycling facilities often mix up plastic waste and melt it to develop new products. Mechanical recycling, as the process is known, can generate playscapes for children’s parks, decking furniture and other low-value products.

However, the Berkeley research team’s method, published Thursday in the journal Science, breaks the plastics down much further to the level of essentially molecular puzzle pieces, which can be reconstructed into new plastics.

That means a sandwich bag could be recycled into a new sandwich bag, a soiled milk jug into a fresh milk jug, Berkeley chemist John Hartwig, who led the research team, explained to KQED.

With mechanical recycling, “if you mix the sandwich bag and the milk jug together and then try to remake an object from that, you can’t make a very good milk jug and you can’t make a very good sandwich bag,” he said.

“We’re trying to bring the plastics back to the chemicals from which they’re made in the first place,” Hartwig said.

The researchers use a catalyst, a component of a chemical reaction that makes it go faster, to vaporize both polyethylene and polypropylene plastics — two of the largest volumes of plastics in existence — transforming the solid waste into gases.

The polymers are reduced to their chemical precursors, which can then be reconstructed. In a press release, the university said the process brings “a circular economy for plastics one step closer to reality.”

“It’s like taking a pearl necklace, breaking it in the middle so that the pearls can fall out,” Hartwig said. “You can take the pearls one by one; go make the same pearl necklace or a shorter one or a longer one.”

About two-thirds of the world’s plastic waste is made from polyethylene and polypropylene materials, and 80% of it is either incinerated or ends up as litter in the street, floating in the ocean or tossed into a landfill. The rest is recycled.

These types of plastics mixed together in the waste stream are hard to separate using robots and other methods. But Hartwig’s team found their process can break polyethylene and polypropylene materials down even when they are mixed, which alleviates the burden of separating them.

Government and industry are scrambling to stem the growing amount of plastic waste that ends up as trash and pollution. Scientists estimate about 8 million metric tons enter the world’s oceans each year, which is “the equivalent of dumping a garbage truck of plastic waste into the ocean every minute,” according to a report from researchers working with the National Academies of Sciences, Engineering, and Medicine.

Plastic waste floats on the surface of the sea, throughout its vast water column and is stored deep in its sediment. Researchers have found it in the Great Lakes, Lake Tahoe and other freshwater ecosystems, and increasingly in the foods and beverages consumed by humans.

According to research from UC Santa Barbara, published in 2017, half of all the plastic that ever existed was produced within the prior 13 years.

Though Hartwig’s team found success in the lab, they had to refine the work for it to become industrially feasible, a distance that he described as the “so-called valley of death” for new scientific achievements. His team is pursuing federal grants and discussions with industrial partners.

The business case is not yet clear. Transforming a used yogurt container into a new yogurt container, while valuable for the environment, generates a commodity chemical that’s already available to companies at a very low cost. To make this process economically feasible might require a new plastic tax or similar legislation.

The research advances an early achievement from the Berkeley team, in which they successfully used an expensive heavy metal catalyst in a similar process. While interesting, that was largely an academic exercise.

With this new study, Hartwig’s team replaced the metal catalyst with a more practical solution: sodium and tungsten. “These are elements that are widely available, inexpensive, and already used commercially,” he said.