New plant-based plastic decomposes in seawater without forming microplastics

Plastic pollution has proven stubbornly resistant to quick fixes.

Even so-called biodegradable plastics often linger in the environment, breaking down into microplastics that spread through ecosystems and bodies alike.

Now, researchers in Japan say they have created a plant-based plastic that sidesteps that trap.

The material stays strong during use, yet breaks down rapidly in natural settings without leaving microscopic debris behind.

The work comes from researchers led by Takuzo Aida at the RIKEN Center for Emergent Matter Science (CEMS).

In a new study, the team describes a plastic made from cellulose, the most abundant organic compound on Earth.

The material combines durability, flexibility, and fast decomposition, pushing biodegradable plastics closer to practical reality.

Microplastics have become a global contaminant. Scientists have detected them in oceans, soils, wildlife, and crops. Studies have also found them in human tissue and blood, where they may cause harm.

Many biodegradable plastics fail to solve the problem.

They degrade slowly in seawater or fragment into microplastics before fully breaking down.

Cellulose-based plastics already exist, but most do not decompose quickly in marine environments.

Others require industrial composting conditions. Aida and his team aimed to design a plastic that responds naturally to seawater without complex processing.

Last year, the group reported a supramolecular plastic that dissolved within hours in salt water.

That material relied on reversible bonds between two polymers. Salt disrupted those bonds, causing rapid breakdown.

However, the earlier version lacked the mechanical strength and manufacturability needed for widespread use.

The new plastic builds on that earlier concept. One polymer comes from carboxymethyl cellulose, a wood-pulp derivative that is already FDA-approved and biodegradable.

The second component proved harder to identify. After extensive testing, the team selected a safe crosslinking agent made from positively charged polyethylene-imine guanidinium ions.

When mixed in room-temperature water, the negatively charged cellulose and positively charged ions attract each other.

That attraction forms a cross-linked network, giving the plastic its strength.

In salt water, those salt bridges break apart, triggering decomposition.

To prevent accidental breakdown, manufacturers can apply a thin protective surface coating.

Early versions suffered from brittleness. The plastic appeared clear, colorless, and extremely hard, but fractured easily.

The researchers addressed this by adding a plasticizer. After testing many options, they found that choline chloride, an FDA-approved food additive, worked best.

By adjusting the amount of choline chloride, the team could fine-tune flexibility.

The plastic can remain rigid and glass-like or stretch up to 130 percent of its original length.

It can also form strong transparent films just 0.07 millimeters thick.

Closer to real use

The improvements mark a shift from theory to application. “While our initial study focused mostly on the conceptual,” explains Aida, “this study shows that our work is now at a more practical stage.”

The new material, called CMCSP, matches the strength of petroleum-based plastics.

Its properties remain adjustable without sacrificing transparency, processability, seawater dissociation, or recyclability.

The team also emphasized scalability.

“Nature produces about one trillion tons of cellulose every year,” says Aida.

“From this abundant natural substance, we have created a flexible yet tough plastic material that safely decomposes in the ocean.”

If adopted widely, the approach could reduce plastic pollution at its source, before it fragments into an invisible global problem.

The study is published in the Journal of the American Chemical Society.