Researcher Q&A: Finding Safer, Versatile Plastic Solutions

April 20, 2018
Female researcher holds in front of her a piece of light brown polylactide or biopolymer containing lignin, and she's looking at it.Researcher Stephanie Harris looks at a piece of polylactide or "corn plastic" that contains lignin. The addition of lignin, a natural polymer found in plants, significantly reduces water permeability of the polylactide.

Plastics are versatile, inexpensive, and have become a part daily life. Many everyday items such as bottles, food wrappers, pens, and eating utensils are made of plastic or contain plastic. Unfortunately, after such items are discarded, many of them—or what remains of them—end up in the natural environment where they linger and become harmful to people and wildlife.

Researcher Stephanie Harris is driven to create a more versatile and environmentally friendly plastic. She's exploring biobased, compostable polymers containing lignin with Professor Ulrike Tschirner in the Department of Bioproducts and Biosystems Engineering at the University of Minnesota.

Q: Tell us a little bit about your research and why it’s important.

A: My research is primarily related to the physicochemical properties of biobased polymers containing lignin, which is a natural polymer found in plants. What makes our research unique is that we focus on using only biobased materials and producing polymers that break down into nontoxic products in the environment.

Acknowledging the prevalence and usefulness of plastics, our goal is to synthesize earth-friendly, novel polymers that will degrade in a reasonable amount of time into nontoxic, sustainable products that will do no harm. We saw the need for more versatile plant-based, degradable polymers to address a variety of needs and are working on formulations to meet those needs.

Currently produced biobased, compostable polymers have limitations such as the water vapor permeability of the popular biobased polymer, polylactide or PLA. PLA is commonly referred to as "corn plastic" in the Midwest, named for its starting material, corn starch, in this region.

PLA breaks down in commercial composting sites into carbon dioxide, in a sustainable loop. But, since it is a very polar polymer, it's also very water permeable, which makes it an ineffective plastic for containing liquids, foods containing liquid, or even for storing dry foods in high humidity environments.

Our research focuses on tuning the properties of PLA in order to keep it biobased and degradable to environmentally friendly products while decreasing the rate of hydrolytic degradation and increasing its flexibility.

Q: How are you doing that?

Female researcher holds in front of her, side by side, a piece of light brown polylactide or biopolymer containing lignin and one without lignin that's not light brown, and she's looking at it.

The brown or dark brown color of lignin turns the polylactide light brown as shown on the left piece. On the right is polylactide without lignin, which is translucent.

A: We’ve learned that the addition of lignin has the effect of slowing the rate of degradation while not stopping it and significantly reduces water permeability. We’ve also found that varying the stereochemistry of polylactide and adding other monomers to the synthesis can affect the flexibility and toughness of the polymers.

The methods we use involve a preparation of reactants in a nitrogen environment, eliminating the reverse reaction of the polymer synthesis by removing water from the atmosphere. The polymerization is performed in a silicone oil bath.

Once the polymer is formed, it is dissolved and reprecipitated to remove unreacted substances, and then it’s pressed into films that are used for further testing of properties such as the molecular weight of the polymers, the melting and glass transition temperatures, tensile properties, water vapor transition rates, and hydrolytic degradation rates.

We work with the Minnesota Nano Center, the College of Science and Engineering Characterization Facility, the Department of Food Science and Nutrition, and the Chemistry NMR Lab at the University of Minnesota. I also would like to personally acknowledge the contributions of Dr. Ulrike Tschirner, Dr. Shri Ramaswamy, Dr. Ted Labuza, Dr. Laura Babcock, Dr. Jun Ai, Dr. Letitia Yao, and Dr. William Tze to this project.

Q: What questions or challenges remain for you and other researchers?

A: There is still a lot to discover in terms of how to better synthesize these polymers, what formulations work best for a variety of uses, and how they can be tuned to meet the growing need of a world that does not want to seem to give them up, but needs to find sustainable solutions that protect our environment.

Q: What kind of impact would biobased polymers have on people and the environment?

A: The use of more sustainable polymers will positively affect the health of our air, waters, and landfills. If more of these plastics were used, we could eliminate the use of plastics that harm wildlife and produce toxic compounds due to degradation. There are already many companies working globally to find solutions to these problems, including NatureWorks, which is locally based in the Twin Cities.

Q: What items are made out of polylactide now?

A: PLA has a relatively low glass transition temperature, but it is commonly used to make single use utensils, beverage cups and lids, filament for 3D printers, containers for cold or room temperature storage, and much more as formulations improve.

Q: What drives you to do this research?

A: Because I realize that plastics are very useful and inexpensive—and therefore, not going away—I am passionate about replacing harmful plastics and plastic degradation byproducts by finding safer plastic solutions that will not harm wildlife or produce toxins that would have a negative impact on our precious and fragile world.