An artist’s rendering of Riken’s new biodegradable plastic. Image: Riken
In a huge step in the fight against microplastics, researchers working at the RIKEN Center for Emergent Matter Science (CEMS) have created a new plastic that breaks down in seawater.
CEMS, Japan’s largest comprehensive research institution, is an international hub for research in physics, biology, medicine, and engineering, among other things.
Microplastics are an enormous problem right now. As the name implies, though, they’re very small — anything less than five millimeters in size — and most of them are floating around in the ocean, so they’re out of sight and out of mind (aside from the fact that they’re proliferating our food chain). That’s why a biodegradable plastic that’s relatively durable could be so important to the world’s environmental health. Despite scientists around the world screaming from the rooftops that something needs to be done, there wasn’t a whole lot being done. Until now.
“A strong, glassy supramolecular polymer has been shown to prevent the formation of marine microplastics by slowly dissolving in salt water into metabolizable compounds,” wrote Phil Szuromi in the summary of a paper published in the journal Science. “(Researchers at CEMS) show that salt bridging between sodium hexametaphosphate or sulfated polysaccharides and guanidinium sulfates expels sodium sulfate to create a cross-linked network that is stable until the electrolytes are added back. The dried material is a moldable and recyclable thermoplastic that can be water stabilized with hydrophobic coatings.”
In layman’s terms, that basically means the researchers combined two ionic monomers – atoms or small molecules that can bond together to form larger organic molecules — that are able to form salt bridges to give them stability and flexibility. The ionic monomers they used can be metabolized by certain bacteria, which lets them biodegrade once they’ve floated around for long enough.
“While the reversible nature of the bonds in supramolecular plastics has been thought to make them weak and unstable, our new materials are just the opposite,” said lead researcher Takuzo Aida. “In the new material, the salt bridge structure is irreversible unless exposed to electrolytes like those found in seawater. The key discovery was how to create these selectively irreversible cross-links.”
The new plastic is both non-toxic and non-flammable, and can be reshaped when heated, just like other thermoplastics. That lends itself to any number of applications, from hard, weight-bearing plastics to thin and flexible ones. They can be 3D printed as well.
According to the study, when the plastic has dissolved in salt water, some 91 percent of one part is recoverable and 82 percent of the other. They basically turn into a powder, which would make recycling it far easier. When left in soil, it degraded completely in 10 days. It also has the added benefit of supplying the soil with phosphorous and nitrogen similar to a fertilizer.
“With this new material,” Aida told SciTechDaily, “we have created a new family of plastics that are strong, stable, recyclable, can serve multiple functions, and importantly, do not generate microplastics.”
