Bio-plastics Not so Good at Biodegrading: Ohio State Study

Fred Michel (left) and Eddie Gómez in the laboratory. (Photo by Ken Chamberlain)
  • Researchers find some "green" plastics may not be better for the environment than petroleum-based plastics.

WOOSTER, Ohio -- Ohio State University researchers have found that most bio-plastics or "green" plastics currently available in the market do not biodegrade within the time period used in standard solid-waste management processes and do not meet industry standards for compostability.

"Most people don't think about the end-of-life cycle of bio-plastics and assume that because these products are called 'green,' they are automatically better for the environment," said Fred Michel, a biosystems engineer with the university's College of Food, Agricultural, and Environmental Sciences (CFAES).

"However, this study shows that some bio-based plastics currently available in the market actually biodegrade poorly. And in some cases, bio-plastics can be worse for the environment than fossil fuel-based plastics when taking into account inputs needed to grow crops from which these products are made, land and water use, and the greenhouse gases released from these plastics when they do break down."

The study -- conducted by Michel and Eddie Gómez, a recent Ohio State Ph.D. graduate -- was published in the December issue of the journal Polymer Degradation and Stability.

The researchers studied a wide range of materials to compare their biodegradability: bio-based plastics made from crops such as corn, natural fiber composites (such as coconut fiber), and conventional (petroleum-based) plastics amended with additives that are meant to help them break down.

As controls, they used conventional polypropylene plastic (which is known to not biodegrade) and cellulose paper, which fully biodegrades.

These materials were tested in three different environments: compost (115 days), anaerobic digestion (50 days), and soil (660 days).

Results indicate that only one of the bio-plastics included in the study -- a PHA (polyhydroxyalkanoate) plastic made via sugar fermentation -- biodegraded to significant extents in all three environments. Additionally, the conventional plastics treated with commercial additives showed almost no degradation, despite claims to the contrary made by the manufacturers of such products.

Gómez said this study shows more research is needed about the life-cycle behavior of "green" plastics before claims can be made about their biodegradability and potential environmental benefits.

"It surprised me that most of the materials cannot be certified as compostable and that the additives don't really work as advertised, and yet they are in the market right now," said Gómez, who worked under Michel's supervision.

"The main point here is that we don't know what is behind these materials, and research needs to be conducted before they go out in the market making different claims. Consumers don't usually have access to information about these materials."

Currently, the only entity that can certify whether a material is compostable is the Biodegradable Products Institute (BPI), a not-for-profit organization that sets science-based standards for compostable materials biodegrading in large composting facilities.

Plastics have become a major component of municipal solid waste and pose a growing environmental pollution problem, especially as large amounts of these materials end up in landfills or are released into the environment. According to data from the U.S. Environmental Protection Agency, only 8 percent of the 31 million tons of plastic waste generated annually in the U.S. is recycled.

Michel and Gómez said there are many misconceptions about the nature of both conventional and bio-based plastics that need to be clarified, so consumers and industries that use these products can make more informed decisions.

"There are some petroleum-based plastics that are biodegradable, while there are bio-plastics that are not," said Michel, an associate professor in the Department of Food, Agricultural and Biological Engineering. "Biodegradability is not necessarily dependent on the source of the plastic, but rather on the building block used to make the plastic."

For example, most plastics are made from polyethylene or polypropylene derived from crude oil and natural gas, and will not biodegrade. Polyethylene also can be synthesized from renewable resources such as sugar cane ethanol, but the plastics made from this building block are still not biodegradable even though they came from a plant.

On the other hand, plastics made from polylactic acid (PLA) are biodegradable. PLA can be produced both through the fermentation of starch crops and from fossil fuels.

"When it comes to biodegradability, talking about fossil fuel-based versus bio-based plastics does not make much sense," Michel said. "Instead, we need to classify plastics into four categories, which are outlined in our study: conventional plastic, bio-based plastic, biodegradable plastic, and biodegradable bio-based plastic."

Finally, Michel and Gómez said several factors need to be taken into consideration before knowing whether one type of plastic is better than another in terms of its impact on the environment.

"When landfilled, conventional plastics do not further contribute to climate change because the carbon contained in them stays right in the landfill," Michel said. "Also, if these plastics are recycled and less energy goes into recycling them than into making them in the first place, then they contribute even less fossil carbon dioxide to the environment.

"In these cases, conventional plastics may have less of an impact on greenhouse-gas emissions than plastics designed to biodegrade. Biodegradable plastics, made from either fossil fuels or crops, will release carbon and potentially methane into the atmosphere as they biodegrade -- especially if these plastics end up in a landfill."

Still, Michel said, biodegradable bio-based plastics can have a positive impact on the environment, especially when considering the problems caused by plastic pollution on a global scale.

"Inadvertently released conventional plastics have polluted nearly every natural habitat and environment in the world, and plastic pollution is a daunting crisis for marine environments," he said.

"Additionally, the 'cradle-to-grave' use of materials is unsustainable and is rapidly depleting natural resources. Ideally these materials would be bio-based and compostable so that they can be recycled and used to enrich soils for crop production, or would biodegrade when released into the environment."

Michel is based on the Wooster campus of the Ohio Agricultural Research and Development Center, which is the research arm of CFAES.



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Fred Michel