Researchers make bioplastics easier to compost

biodegradable plastic

Researchers from Michigan State University’s School of Packaging have developed a way to make a sustainable alternative to petroleum-based plastics more biodegradable.

A team led by Rafael Auras has made a bio-based polymer blend that’s compostable in both home and industrial settings. The work is published in the journal ACS Sustainable Chemistry & Engineering.

“There is a large issue with waste and especially plastic waste,” said Auras, MSU professor and the Amcor Endowed Chair in Packaging Sustainability.

Less than 10 per cent of plastic waste is recycled in the US. In Australia that figure is about 13 per cent, according to Planet Ark. The bulk of plastic waste ends up as litter, creating economic, environmental and health concerns.

“By developing biodegradable and compostable products, we can divert some of that waste,” Auras said. “We can reduce the amount that goes into a landfill.”

Another bonus is that plastics destined for the compost bin wouldn’t need to be cleaned of food contaminants, which is an obstacle for efficient plastic recycling. Recycling facilities routinely must choose between spending time, water, and energy to clean dirty plastic waste or simply throwing it out.

“Imagine you had a coffee cup or a microwave tray with tomato sauce,” Auras said. “You wouldn’t need to rinse or wash those, you could just compost.”

The team worked with polylactic acid, or PLA, which has been used in packaging for more than a decade, and is derived from plant sugars rather than petroleum.

When managed properly, PLA’s waste byproducts are all natural: water, carbon dioxide and lactic acid. Plus, researchers know that PLA can biodegrade in industrial composters. These composters create conditions, such as higher temperatures, that are more conducive to breaking down bioplastics than home composters.

Although industrial compost settings can get PLA to that point, that doesn’t mean they do it quickly or entirely.

In its experiments, supported by the US Department of Agriculture and MSU AgBioResearch, the team showed that PLA can sit around for 20 days before microbes start digesting it in industrial composting conditions.

To get rid of that lag time and enable the possibility of home composting, Auras and his team integrated a carbohydrate-derived material called thermoplastic starch into PLA. Among other benefits, the starch gives composting’s microbes something they can more easily chow down on while the PLA degrades.

Postdoctoral researcher Anibal Bher had been formulating different PLA-thermoplastic starch blends to observe how they preserved the strength, clarity and other desirable features of regular PLA films.

Working with doctoral student Wanwarang Limsukon, Bher and Mayekar they observed how those different films broke down throughout the composting process when carried out at different conditions.

“Different materials have different ways of undergoing hydrolysis at the beginning of the process and biodegrading at the end,” Limsukon said. “We’re working on tracking the entire pathway.”

Using their expertise and the resources at hand, the researchers have demonstrated that completely compostable bio-based plastic packaging is possible. Yet Auras stressed that this alone won’t be enough to guarantee its commercial adoption.

The challenges there aren’t solely technical. They’re social and behavioral as well.

“There’s not going to be one solution to the entire problem of plastic waste management,” Mayekar said. “What we’ve developed is one approach from the packaging side.”

There’s a public misconception that biodegradable and compostable materials can break down relatively quickly anywhere in the environment.

These materials require certain conditions, such as those found in an active compost, to decompose in a timely fashion. Outside of those, biodegradable plastics that are disposed of in the environment are still just litter.

“If people think we develop something biodegradable so it can be littered, that will make the problem worse,” Auras said. “The technology we develop is meant to be introduced into active waste-management scenarios.”

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