Scientists adjust ring sizes to control biodegradable plastic durability

Scientists at the University of Osaka have developed a way to control how long biodegradable plastics last by adjusting the size of molecular rings threaded onto their structure. Their findings, published in *ACS Sustainable Chemistry & Engineering*, show that tweaking these rings can simultaneously tune the material’s strength and its ability to break down under enzymes.

The discovery addresses a major challenge in sustainable materials: balancing durability with timely decomposition. Biodegradable plastics often fail in real-world use because they’re either too weak or degrade too slowly. Traditional plastics, by contrast, persist for centuries, piling up in landfills and oceans. This new approach offers a precise method to design materials that stay intact for their intended use—like packaging or medical implants—then break down efficiently once discarded.

In lab tests, the Osaka team found that larger rings made the polymer tougher but slowed its breakdown, while smaller rings did the opposite. This trade-off allows engineers to fine-tune properties for specific applications. For example, a sturdy shopping bag could use larger rings to last through multiple uses, then degrade in months rather than years. The work builds on earlier research into "polyrotaxane" polymers, where ring-like molecules slide along a polymer chain, but this is the first time ring size has been shown to directly control both strength and degradation.

The next step is scaling up the process for industrial use. If successful, it could accelerate the shift away from fossil fuel-based plastics, offering a customizable, eco-friendly alternative. The team is also exploring whether other ring-like molecules could provide even more control over material properties.