Saltwater biodegradable plastic developed by RIKEN scientists dissolves completely in seawater after 8.5 hours, offering a promising solution to the global microplastic pollution crisis affecting oceans worldwide.
Scientists at the RIKEN Center for Emergent Matter Science in Japan have developed a saltwater biodegradable plastic that completely dissolves when soaked in seawater. This innovation could help address the growing global crisis of microplastic pollution that now affects every corner of our planet.
Microplastics—plastic fragments smaller than 5mm—have infiltrated remote regions of the deep ocean, the Arctic, and even the air we breathe. These tiny particles are increasingly found in human bodies, particularly the blood and brain. While researchers are still studying their full impact, microplastics are known to cause significant problems in marine and terrestrial ecosystems.
The environmental damage is concerning. Studies show these contaminants slow animal growth, impact fertility, and cause organ dysfunction across various species. As pollution continues to spread, finding solutions has become increasingly urgent.
Takuzo Aida, a materials scientist who heads the Emergent Soft Matter Function Research Group at RIKEN, has worked for three decades on developing supramolecular polymers with unique properties. His team’s new saltwater biodegradable plastic represents a significant breakthrough in this field.
Unlike conventional plastics, which use strong covalent bonds that require extensive energy to break, supramolecular polymers feature weaker, reversible bonds. Aida describes these connections as functioning “like sticky notes that you can attach and peel off.”
This distinctive property allows supramolecular polymers to “self-heal” when broken pieces are pressed back together. They can also be easily recycled using specific solvents to break down the material’s bonds at the molecular level.
“Plastics, especially polyethylene terephthalate, which is used in bottles, are incredibly versatile. They are flexible but strong, durable, and recyclable. It’s hard to beat that convenience,” explains Aida. The challenge was creating an alternative with similar performance that wouldn’t persist in the environment.
Existing biodegradable options have significant limitations. Polylactic acid (PLA), which breaks down in soil, often remains intact in ocean environments because it degrades too slowly. Since materials like PLA aren’t water-soluble, they eventually fragment into microplastics that resist further breakdown by natural processes.
Aida’s team focused on creating a supramolecular material with good mechanical strength that could break down quickly under specific conditions. They aimed to develop molecular bonds that would remain stable until exposed to a particular “key” salt.
After screening various compounds, researchers discovered that combining sodium hexametaphosphate (a common food additive) with guanidinium ion-based monomers (used in fertilizers and soil conditioners) created strong “salt bridges.” These cross-linked bonds functioned as molecular “locks,” providing the material with strength and flexibility.
“Screening molecules can be like looking for a needle in a haystack,” Aida notes. “But we found the combination early on, which made us think, ‘This could actually work’.”
The team produced the saltwater biodegradable plastic by mixing the compounds in water. Surprisingly, the solution separated into a viscous bottom layer containing the salt bridge compounds and a watery top layer. The scientists extracted and dried the bottom layer to create a plastic-like sheet.
The resulting material matched conventional plastics in strength while offering additional benefits. It proved non-flammable, colourless, and transparent, making it highly versatile for various applications.
Most importantly, the sheets degraded completely when soaked in saltwater. The electrolytes in seawater functioned as “keys” that opened the salt bridge “locks” at the molecular level. Testing showed the sheets disintegrated after just 8.5 hours of saltwater exposure.
The researchers also developed a waterproof version with a hydrophobic coating. Even with this protective layer, the saltwater biodegradable plastic dissolved just as quickly when its surface was scratched to allow salt penetration.
Beyond degradability, the material offers additional environmental benefits. When broken down, it leaves behind nitrogen and phosphorus—elements that microbes can metabolize, and plants can absorb.
However, Aida cautions that proper management of these breakdown products is essential. While nitrogen and phosphorus can enrich soil, they could overload coastal ecosystems with nutrients, potentially causing algal blooms that disrupt entire ecosystems.
The ideal approach might involve recycling the saltwater biodegradable plastic in controlled treatment facilities using seawater. This method would allow the recovery of raw materials to produce new supramolecular plastics, creating a sustainable cycle.
Aida emphasizes that developing alternatives to fossil fuel-derived plastics is only part of the solution. Governments, industries, and researchers must act decisively to drive meaningful change in the production and use of materials.
Without more aggressive measures, global plastics production and corresponding carbon emissions could more than double by 2050. The industry’s established infrastructure makes change difficult, but Aida believes a tipping point will come.
“With established infrastructures and factory lines, it’s extremely challenging for the plastics industry to change,” says Aida. “But I believe there will come a tipping point where we have to power through change.”
The development of this saltwater biodegradable plastic provides a promising technology that will be ready when that crucial moment arrives. By offering materials that maintain the convenience of traditional plastics while eliminating their environmental persistence, innovations like this could help transform humans’ relationship with plastic.
