A promising, environmentally friendly replacement for plastics derived from petroleum has been made more biodegradable by researchers from Michigan State University’s renowned School of Packaging.
A group led by Rafael Auras has created a bio-based polymer mixture that can be composted in both residential and commercial settings. The research is published in the ACS Sustainable Chemistry & Engineering journal.
In the U.S. and globally, there is a large issue with waste and especially plastic waste.
Rafael Auras, Professor and Amcor Endowed Chair, Packaging Sustainability, Michigan State University
In the United States, less than 10% of plastic waste is recycled. As a result, most plastic waste is disposed of as trash or litter, raising concerns for the economy, the environment, and even human health.
“By developing biodegradable and compostable products, we can divert some of that waste. We can reduce the amount that goes into a landfill,” Auras notes.
Another benefit is that plastics going into the compost bin will not have to be cleaned of food contaminants, a significant barrier to effective plastic recycling. Recycling facilities frequently have to decide whether to spend the time, water, and energy cleaning dirty plastic waste or throwing it.
Auras adds, “Imagine you had a coffee cup or a microwave tray with tomato sauce. You wouldn’t need to rinse or wash those, you could just compost.”
PLA and a “Sweet Spot” for Starch
In many ways, polylactic acid, also known as PLA, seemed like an obvious choice for the team to work with. It has been utilized in packaging for more than a decade and is made from plant sugars as opposed to petroleum.
When properly managed, PLA’s waste byproducts are all natural: carbon dioxide, water, and lactic acid.
Additionally, researchers are aware that PLA can degrade in industrial composters. Compared to home composters, these composters produce conditions that are more favorable for the breakdown of bioplastics, such as higher temperatures.
However, some people thought it was impossible to make PLA compostable at home.
I remember people laughing at the idea of developing PLA home composting as an option. That’s because microbes can’t attack and consume PLA normally. It has to be broken down to a point where they can utilize it as food.
Pooja Mayekar, Study First Author, Michigan State University
Pooja Mayekar is a doctoral student in Auras’ lab group.
Although industrial composting environments can get PLA to that point, it does not happen quickly or completely.
“In fact, many industrial composters still shy away from accepting bioplastics like PLA,” Auras stated.
The team demonstrated that PLA could stay around for 20 days before microbes initiate digesting it in industrial composting conditions in experiments funded by the US Department of Agriculture and MSU AgBioResearch.
To eliminate the lag time and enable home composting, Auras and his team incorporated a carbohydrate-derived material known as thermoplastic starch into PLA. Among other advantages, the starch provides something for composting microbes to eat while the PLA degrades.
Mayekar explains, “When we talk about the addition of starch, that doesn’t mean we just keep dumping starch in the PLA matrix. This was about trying to find a sweet spot with starch, so the PLA degrades better without compromising its other properties.”
Fortunately, Anibal Bher, a postdoctoral researcher, had been developing various PLA-thermoplastic starch blends to see how they maintained the strength, clarity, and other desirable qualities of conventional PLA films.
Bher and Mayekar were able to observe how those various films decomposed during the composting process when carried out under various conditions while working with doctoral student Wanwarang Limsukon.
Limsukon says, “Different materials have different ways of undergoing hydrolysis at the beginning of the process and biodegrading at the end. We’re working on tracking the entire pathway.”
The group performed these experiments utilizing systems that Auras and other lab members, both past and present, built largely from scratch during his 19 years at MSU. The equipment the investigators have access to outside their own lab in the School of Packaging also makes a difference.
“Working with Dr. Auras, the School of Packaging, MSU—it’s great. Because, at some point, we want to be making actual products. We are using facilities around campus to make materials and test their properties. MSU offers a lot of resources,” Bher adds.
“There’s a reason why this is one of the best schools for packaging,” Mayekar said.
Changing the Conversation
The investigators have shown that compostable bio-based plastic packaging is feasible using their knowledge and available resources. Auras emphasized that this will not be enough to ensure its commercial adoption, though.
There are difficulties that go beyond technical ones. They are also behavioral and social.
“There’s not going to be one solution to the entire problem of plastic waste management. What we’ve developed is one approach from the packaging side,” Mayekar noted.
Aside from Auras’ earlier mention of industrial composters’ skepticism about plastics, there is a widespread public misconception that biodegradable and compostable materials degrade relatively quickly anywhere in the environment.
These materials require specific conditions, such as those discovered in active compost, to decompose in a timely manner. Biodegradable plastics that are discarded in the environment are still considered litter.
Auras explains, “If people think we develop something biodegradable so it can be littered, that will make the problem worse. The technology we develop is meant to be introduced into active waste-management scenarios.”
“We need to be conscious of how we manage waste, especially plastics. Even at home, you’ll need to think about how you’re managing that small composting process,” Bher noted.
“It’s really easy to just blame plastic for its problems, but I think we need to change the conversation about how we manage it,” Mayekar details.
The team’s goal with its work is to educate people and raise awareness about this issue. And they have reason to believe they can influence public opinion. After all, no one is laughing at the possibility of composting PLA at home any longer.
Mayekar, P. C., et al. (2023). Breaking It Down: How Thermoplastic Starch Enhances Poly(lactic acid) Biodegradation in Compost─A Comparative Analysis of Reactive Blends. ACS Sustainable Chemistry & Engineering. doi.org/10.1021/acssuschemeng.3c01676.