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Plastic trash: New technique may make compostable

Science desk || shiningbd

Published: 12:44, 22 April 2021  
Plastic trash: New technique may make compostable

In experiments, enzyme-laced plastic film (left) broke down after three days in compost (right). After two weeks, it disintegrated entirely.

A pinch of polymer-munching enzymes could make biodegradable plastic packaging and forks truly compostable.

With moderate heat, enzyme-laced films of the plastic disintegrated in standard compost or plain tap water within days to weeks, Ting Xu and her colleagues report April 21 in Nature.

“Biodegradability does not equal compostability,” says Xu, a polymer scientist at the University of California, Berkeley and Lawrence Berkeley National Laboratory. She often finds bits of biodegradable plastic in the compost she picks up for her parents’ garden.

Most biodegradable plastics go to landfills, where the conditions aren’t right for them to break down, so they degrade no faster than normal plastics.

Embedding polymer-chomping enzymes in biodegradable plastic should accelerate decomposition. But that process often inadvertently forms potentially harmful microplastics, which are showing up in ecosystems across the globe (SN: 11/20/20).

The enzymes clump together and randomly snip plastics’ molecular chains, leading to an incomplete breakdown. “It’s worse than if you don’t degrade them in the first place,” Xu says.

Her team added individual enzymes into two biodegradable plastics, including polylactic acid, commonly used in food packaging.

They inserted the enzymes along with another ingredient, a degradable additive Xu previously developed, which ensured the enzymes didn’t clump together and didn’t fall apart.

The solitary enzymes grabbed the ends of the plastics’ molecular chains and ate as though they were slurping spaghetti, severing every chain link and preventing microplastic formation.

Shiningbd/Mb