Additives don’t make plastic break down faster

"The claim is that, with the additives, the plastics will break down to a level in which microorganisms can use the decomposed material as food," says Rafael Auras. "That simply did not happen." (Credit: iStockphoto)

Additives that claim to break down plastic bags and soda bottles simply don’t work in common disposal situations such as landfills or composting, a new study finds.

“Making improper or unsubstantiated claims can produce consumer backlash, fill the environment with unwanted polymer debris, and expose companies to legal penalties,” says Susan Selke, coauthor of the study and packaging professor at Michigan State University.

The results, featured in the current issue of Environmental Science and Technology, are a culmination of a three-year study that focused on five additives and three categories of biodegradation, which cover the majority of methods available on the market today.

The team studied biodegradation with oxygen, such as in composting; biodegradation without oxygen, such as in an anaerobic digester or a landfill; and simply burying plastics. The plastics are polyethylene (i.e., plastic bags) and polyethylene terephthalate (i.e., soda bottles).

“There was no difference between the plastics mixed with the additives we tested and the ones without,” says coauthor Rafael Auras, packaging professor. “The claim is that, with the additives, the plastics will break down to a level in which microorganisms can use the decomposed material as food. That simply did not happen.”

What’s the solution?

William Rathje, the late Arizona paleontologist and founder of the Tucson Garbage Project, revealed that even after years underground, chicken bones still had meat on them, grass was still green, and that even carrots still maintained their orange color.

Since organic materials take so long to decompose, it’s not surprising then that plastics, even with the aid of additives, would take decades or longer to break down, if at all. So, if the additives don’t work, what’s the solution?

“The solution is to not make claims that are untrue,” Selke says. “The proper management of waste plastics is the proper management of waste plastics.”

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And for now, that means not using any of the disposal methods or additives included in the study as feasible options, Selke says.

It’s a growing trend that many US cities and countries have banned or have adopted legislation taxing the retail use of plastic bags, one of the largest sources of polyethylene waste. Plastic manufacturers are also seeking solutions to this problem, Selke says.

“Package-user companies funded this study because they wanted to know if the additives that are being marketed to them work,” she says. “They wanted scientific proof to evaluate the products and disposal approaches that are available to them to break down plastic.”

The university’s Center for Packaging Innovation and Sustainability funded the work.

Source: Michigan State University