Green And Environmental Protection: New Recyclable Plastics Can Be Safely Decomposed In Seawater Without Producing Micro Plastic Particles

Artistic effect picture of new plastic. The cross-linked salt bridge visible outside the sea water endows the plastic with structure and strength. In seawater (and in soil, not shown), heavy salt treatment will destroy the salt bridge, prevent the formation of microplastics, and make plastics biodegradable. Source: Institute of Physical Chemistry

Researchers led by Takesan Kueda of the Emerging Material Science Center (CEMS) of the Institute of Physics and Chemistry have created a breakthrough plastic that combines durability and environmental protection. This innovative material is not only as strong as traditional plastics, but also biodegradable, with a unique ability to decompose in seawater. By solving key environmental problems, this kind of plastic is likely to greatly reduce the micro plastic pollution that accumulates in the ocean and soil and eventually enters the food chain. The research results of the research team were published in the journal Science today (November 22).

For many years, people have been working hard to develop sustainable alternatives to traditional plastics, because traditional plastics are non biodegradable and harmful to the environment. Although there are some biodegradable and recyclable options, a major challenge still exists: many of these materials are insoluble in water and cannot be degraded in the marine environment. This limitation makes microplastics – less than 5 Millimeters of tiny debris - persistent in marine ecosystems, endangering aquatic life and entering the food chain, including humans.

In their new research, Aida and his team focused on using supramolecular plastics to solve this problem – supramolecular plastics are polymers that hold structures together through reversible interactions. This new plastic is composed of two ionic monomers, which can form cross-linked salt bridges to provide strength and flexibility. In the initial test, one monomer is a common food additive called sodium hexametaphosphate, and the other is any of several guanidine ion monomers. Both monomers can be metabolized by bacteria, thus ensuring the biodegradability of plastics after being dissolved into components.

Aida said, "The reversibility of bonds in supramolecular plastics has always been considered to make them fragile and unstable, while our new materials are just the opposite. In new materials, the salt bridge structure is irreversible unless exposed to electrolytes such as those in seawater. The key discovery is how these selective irreversible crosslinks are generated. "

The key to manufacturing new plastics is desalination. Re desalting restores the interaction and dissolves the plastic. Source: Institute of Physical Chemistry

As with oil-water mixing, after mixing the two monomers in water, the researchers observed two separated liquids. One liquid is viscous and contains an important cross-linked salt bridge, and the other liquid contains water and salt ions. For example, when sodium hexametaphosphate and alkyl biguanide sulfate are used, the sodium sulfate salt is discharged into the aquifer. The final plastic, alkyl SP ?, is made by drying the residue in the viscous liquid layer.

Facts have proved that "desalination" is a key step; Without desalting, the dried material will become brittle crystals and cannot be used. Re desalting the plastic in salt water will lead to the reversal of the interaction, and the structure of the plastic will become unstable within a few hours. Therefore, after creating a strong and durable plastic that can still be dissolved under certain conditions, the researchers then tested the quality of this plastic.

This new plastic is non-toxic and nonflammable – this means that it does not emit carbon dioxide and can be reshaped at temperatures above 120 ° C like other thermoplastics. By testing different types of guanidine sulfate, the research team can prepare plastics with different hardness and tensile strength, which are comparable or superior to traditional plastics. This means that new plastics can be customized according to needs; Hard scratch resistant plastic, rubber silicone plastic, strong load bearing plastic or low tensile flexible plastic are all possible. The researchers also created marine degradable plastics using polysaccharides that form cross-linked salt bridges with guanidine monomers. These plastics can be used for 3D printing and medical or health-related applications.

Finally, the researchers studied the recyclability and biodegradability of this new plastic. By dissolving the original new plastic in brine, they were able to recover 91% hexametaphosphate and 82% Guanidine powder, which shows that recycling is simple and efficient. In the soil, the new plastic sheet can be completely degraded within 10 days, providing phosphorus and nitrogen similar to fertilizers for the soil.

Aida said, "With this new material, we have created a new plastic family. It is solid, stable, recyclable, and has multiple functions. What's more, it will not produce microplastics."