Japanese researchers have developed a new durable plastic that will not pollute our oceans. The new material is as strong as conventional plastics but breaks down in seawater without forming "eternal" micro-fragments
A new degradable supramolecular plastic that will no longer pollute the waters of seas and oceans. This is the hope emerging from research conducted at the RIKEN Center for Emergent Matter Science (CEMS) in Japan, where a team of scientists has developed a new polymer as durable as conventional plastics, but capable of dissolving upon contact with seawater. A potentially revolutionary material, it would prevent the formation of marine microplastics by slowly dissolving in saltwater into metabolizable compounds.
Completely “soluble” plastic in the sea
Researchers, led by Takuzo Aida, have sought to create safe and sustainable materials that go beyond current biodegradable plastics—like PLA—that, once in the sea, cannot degrade because they are insoluble in water. The fate of these compounds is to fragment into microplastics, particles smaller than 5 mm capable of harming marine life and ending up in the food chain. The solution? In the Japanese study, researchers tackled this issue with supramolecular plastics, polymers held together by reversible interactions.
How supramolecular plastics work
The new degradable supramolecular plastic is composed of ionic monomers held together by reversible interactions. Specifically, the team created it by combining a common food additive (sodium hexametaphosphate) with a compound based on guanidinium ions, like alkyl diguanidinium sulfate. Both can be easily metabolized by bacteria, ensuring full biodegradability once the plastic dissolves into its components.
But why should the polymer dissolve in water? Thanks to the aforementioned reversible interactions. The monomers, placed in an aqueous solution, form salt-bridged networks by expelling salt. The final plastic is made by simply drying the chain of monomers, resulting in a strong, glassy material that can be thermally reshaped like thermoplastics. However, once it comes into contact with seawater, the special plastic reverses the process: the salt breaks the bridges, and the polymer destabilizes within hours.
“We thought the reversible nature of the bonds in supramolecular plastics would make them weak and unstable,” says Aida. “Our new materials, however, are exactly the opposite […] With this new material, we’ve created a new family of durable, stable, recyclable plastics that perform multiple functions and, importantly, do not generate microplastics.”
New sustainable plastics with zero toxicity
Another feature of the study is that these new plastics are non-toxic, non-flammable, do not emit CO2, and can be reshaped at temperatures above 120°C, like other thermoplastics. Therefore, they can be customized for specific needs. They can be hard and scratch-resistant, or softer, resembling rubber-like silicone, weight-resistant, or flexible with low tensile strength. Such plastics can be used in 3D printing and in medical or healthcare applications.
On the sustainability front, the researchers studied recyclability and biodegradability. After dissolving the new plastic in seawater, they were able to recover 91% of the hexametaphosphate and 82% of the guanidinium as powders, highlighting how easy and efficient recycling is. In soil, sheets of the new supramolecular plastic completely degraded over 10 days, providing phosphorus and nitrogen to the soil, similar to a fertilizer.
The research, Mechanically strong yet metabolizable supramolecular plastics by desalting upon phase separation, was published in Science.
