Strengthening soy for better bioplastics

Soy proteins are used in plant-based natural polymers meant to eventually supplant plastic materials. But to compete with the petrochemical-based products, such polymers need to be stronger and less brittle.

Researchers at Washington University in St. Louis have developed a method to do that, explained in a study published in the journal Polymer Composites. Marcus Foston, a professor of energy, environmental and chemical engineering at the McKelvey School of Engineering, led the research. Foston, who is also director of the Synthetic Biology Manufacturing of Advanced Materials Research Center, studies how to repurpose biomass waste into useful chemicals and materials.

One such example of biomass waste is cellulose, the most abundant natural polymer on Earth. Researchers can yield cellulose nanocrystals from microfibrils of many plant sources and those nanocrystals make good scaffolding for bioplastic materials, but they could be better.

In this study, the team found they could further strengthen the nanocomposite properties of this material by modifying the surface interactions of the nanocrystals. Using a surface coating of polydopamine, a molecule inspired from the sticky adhesive proteins in mussels, the team was able to increase the nanocomposites' tensile strength and flexibility by more than 300%.

The work serves as a proof of concept that naturally derived materials like cellulose and soy protein can be optimized to better compete with conventional plastics.