In a breakthrough that could change how the world deals with plastic waste, researchers at Japan’s Riken Centre for Emergent Matter Science, in collaboration with the University of Tokyo, have developed a biodegradable plastic that dissolves in seawater within hours and decomposes in soil within 10 days, without leaving harmful microplastics behind.
As described in the journal Science last year, the material not only vanishes harmlessly; it also enhances soil fertility by releasing nutrients such as phosphorus and nitrogen.
Scientists believe it could become a key player in addressing both marine plastic pollution and soil degradation.
“While the reversible nature of the bonds in supramolecular plastics has been thought to make them weak and unstable,” said Professor Takuzo Aida, who led the research, “our new materials are just the opposite.”
A new kind of plastic
The plastic is made from sodium hexametaphosphate, a food-safe additive, and guanidinium ion-based monomers. These ingredients form strong “salt bridges” that give the material both flexibility and durability.
Depending on how it’s processed, the plastic can be made to mimic the properties of rubber, hard coatings, or structural materials, all without the toxic chemicals or microplastic risk of traditional plastics.
And it’s safe to use. The plastic is non-toxic, non-flammable, and can be reshaped at temperatures above 120 degrees Celsius, much like conventional thermoplastics.
Designed to disappear on purpose
What sets this material apart is its ability to break down under specific environmental conditions. When exposed to seawater, the plastic’s salt bridges dissolve, causing the structure to collapse within hours. In soil, the plastic fully biodegrades in approximately 10 days, enriching the earth rather than polluting it.
“Current biodegradable plastics, like PLA, often don’t degrade in marine environments,” Aida explained. “This new plastic does, and quickly.”
That ability could help reduce the growing threat of microplastics in oceans.
Traditional plastics fragment over time, creating particles smaller than 5mm that are nearly impossible to remove from ecosystems. These microplastics are already showing up in the food chain and even in human bodies.
Built for recycling and the circular economy
The new plastic is also highly recyclable. When dissolved in salt water, researchers recovered 91 per cent of the hexametaphosphate and 82 per cent of the guanidinium components as powders, ready to be reused.
This closed-loop potential fits with circular economy goals, where materials are continually reused rather than discarded. The team even demonstrated that different combinations of the guanidinium components could produce plastics tailored for various uses, from scratch-resistant coatings to flexible silicone-like materials.
“In a world facing both plastic pollution and soil degradation, a material that tackles both at once? That’s something special,” said chef and sustainability advocate Michele Gargiul on her blog, where she praised the innovation.
