Khatiwada’s Investigation, Illustration Make Journal Cover

Humans create millions of tons of plastic composites every year, used in everything from food packaging and IV bags to wind turbines and airplane windows. Unfortunately, nearly all these materials are derived from petroleum, contributing to global reliance on fossil fuels and making it more difficult to reach international greenhouse gas reduction goals.

Biobased (biologically derived) plastics can fill many of the same important needs as conventional plastics while helping many industries reduce their carbon footprints. However, it is difficult to predict how these biobased composites will perform in industrial equipment designed for petroleum plastics.

“Melt rheology—studying how a material flows when it’s melted—is the first step to manufacturing polymer composites,” said Aditi Khatiwada, a PhD student in the Department of Chemical and Biomolecular Engineering (CBE). “Adding natural fillers like wood flour (finely-ground sawdust) would make biobased composites stronger, but would also change how a material flows when it’s melted. If a material is too viscous, it could jam the extruder (nozzle).”

Khatiwada, who conducts research in the lab of CBE Assistant Professor Ria Corder, recently spearheaded a comprehensive rheological study of biobased polymer composites. In collaboration with CBE-Oak Ridge National Laboratory (ORNL) Joint Assistant Professor Amber Hubbard, Khatiwada’s team characterized the rheological properties of 16 polymer composite formulations made with biobased materials.

“I think that a lot of people have been focused on manufacturing a particular product, so they jump ahead to the formulation that works best for manufacturing that part,” Corder said. “We chose to take a step back. We want to fundamentally understand what is happening when you mix multiple components together.”

Khatiwada’s results, published in ACS Applied Polymer Materials in March, revealed unexpected benefits from certain mixtures—and the team’s AI-generated art representing those findings was selected for the journal’s cover.

It was a proud moment for Hubbard and Corder’s groups, which have been collaborating since the researchers secured a University of Tennessee-ORNL Innovation Institute (UT-ORII) Science Alliance grant in 2024.

“I’m very grateful to the Science Alliance for investing in this project, and I am so incredibly proud of Aditi and the entire team that worked on it,” Corder said. “We’ve gotten some great results so far, and I’m excited to see where this research goes next.’”

Sixteen Sustainable Plastics

Khatiwada’s study focused on two widely used biobased polymers with mechanical properties similar to those of conventional plastics: PLA, which can be made from crops like corn, and PHB, which is produced through bacterial fermentation.

Hubbard’s lab mixed varying ratios of PLA and PHB, then added varying amounts of wood flour as a strengthening filler. In the end, they created 16 unique composite samples.

Back at the University of Tennessee, Khatiwada and other members of the Corder lab evaluated the samples in multiple ways. They studied how the molten plastics flow during extrusion using a rheometer, which lets researchers take measurements as materials are deformed under shear (twisting or bending). They also performed tensile testing to measure the strength at room temperature as the samples were stretched until they fractured, then used scanning electron microscopy to image the fractured surfaces.

During their first round of rheology testing, the researchers discovered that wood flour particles remain mobile within the cooling plastic longer than expected, leading to inconsistent results. While Khatiwada was briefly concerned that the tests would not be done in time, she and her collaborators were able to develop a more robust experimental protocol and retest the wood flour-containing samples before their deadline.

“It was never discouraging,” Khatiwada said. “You learn when you make mistakes. If we could predict everything before doing research, there would be no fun. When we get a different result, that’s interesting, and it gets more and more interesting as you do the experiments.”

Surprising Results Make Compelling Covers

When Khatiwada’s paper was accepted to Applied Polymer Materials, the research team was invited to submit a cover illustration. They used a generative AI tool to create a digital ‘painting’ of a stylized biobased polymer, with PLA and PHB flowing around particles of wood flour to create a melted composite both stronger and more manufacturing-friendly than its parts.

“It was a challenge to think about how best to visually convey the impact of our work to a broader audience,” Corder said. “Being able to take advantage of some of these developing AI artwork tools—communicating the right science as an input and seeing what it could generate—really challenged us to think about our project in different ways.”

With Khatiwada’s comprehensive tests as a starting point and a new, more effective research protocol, the Corder and Hubbard labs will now investigate how to find the right balance between ease of manufacture and final properties.

“If we want to replace fossil fuel-based plastics with sustainable ones, we need a lot of reliable research data so you can choose the exact formulation to get the properties that you want,” Khatiwada explained. “Applying those findings to real-world industry, we may be able to make biobased polymers even stronger than fossil fuel-based plastics.”

Contact

Izzie Gall (egall4@utk.edu)