Researchers from the National Agency for Advanced Research (Riken) and the University of Tokyo have successfully created a supramolecular material that behaves like petroleum-based plastic, but decomposes when exposed to salt. In the laboratory, the plastic fragment disappears in a salt solution for about an hour.
Without stirring, the material will dissolve on its own in eight and a half hours. Mr. Takuzo Aida, Director of the Center for Emerging Materials Science (at Riken), said that in soil with a certain salt content, a 5cm square piece of plastic will decompose in about 200 hours.
According to the United Nations Environment Programme (UNEP), global plastic pollution will triple by 2040, with 23-37 million tonnes of plastic waste entering the ocean each year. Scientists around the world are racing to develop solutions to the growing plastic waste crisis. Plastic waste is also the main theme of this year’s World Environment Day (June 5), aiming to raise awareness among governments, businesses and people.
Seawater-soluble plastics could be a potential solution to protect oceans and wildlife from the problem of “white pollution”.
The ingredients of this material include sodium hexametaphosphate 6 – NaPO3 (an emulsifier, a popular food additive used in canned milk, ice cream, sauces) and guanidinium ion-based monomers – used in fertilizers and soil conditioners. The above compound forms tightly linked “salt bridges”. These bonds act as “locks,” giving the material the strength and flexibility of petroleum-based plastics, but are easily reversed when exposed to salt.
After decomposition, the new plastic only contains nitrogen and phosphorus, which can be metabolized by bacteria or absorbed by plants. Therefore, this material does not create microplastics that are harmful to aquatic life or enter the food chain.
However, the team also warned that this would require careful post-consumer management of the new material to avoid “eutrophication”, which overloads coastal ecosystems and disrupts ecosystems. The best approach would be to recycle the material in a controlled seawater facility. This way, the raw material could be recovered to produce the supramolecular plastic again, Mr. Aida said.
Although no details on commercialization plans have been released, the project leader said their research has attracted interest, including from many in the packaging sector.
Biodegradable plastics are being touted as an alternative to plastics. However, Mr. Aida said the speed and conditions of their degradation are major challenges. For example, polylactic acid (PLA), a bioplastic, takes a long time to degrade in soil and is insoluble in water. As a result, they remain intact when washed into the ocean. Over time, their structure gradually breaks down into microplastics that cannot be broken down by bacteria, fungi and enzymes.
In addition to developing alternatives to fossil fuel-based plastics, Aida recommends that governments, industries and researchers take decisive action to accelerate the transition. Otherwise, the world’s plastic production and corresponding carbon emissions could double by 2050.
“Children cannot choose the planet they will live on. It is the job of scientists to ensure that future generations inherit the best environment,” Aida said.