Nov. 22 () –
Researchers led by Takuzo Aida in the RIKEN Center for Emerging Matter Science (CEMS) In Japan they have developed a new durable plastic that will not pollute our oceans.
The new material is as strong as conventional plastics and biodegradable, but what makes it special is that it breaks down in seawater. The new plastic is therefore expected to help reduce harmful microplastic pollution that accumulates in oceans and soil and eventually enters the food chain. The experimental findings are published in ‘Science’.
Scientists have been trying to develop safe and sustainable materials that can replace traditional plastics, which are not sustainable and harm the environment. Although there are some recyclable and biodegradable plastics, a big problem remains.. Current biodegradable plastics, such as PLA, often end up in the ocean, where they cannot degrade because they are insoluble in water. As a result, microplastics (pieces of plastic smaller than 5mm) are harming aquatic life and finding their way into the food chain, including our own bodies.
In their new studio, Aida and her team focused on solving this problem with supramolecular plastics, polymers with structures linked by reversible interactions.. The new plastics were made by combining two ionic monomers that form cross-linked salt bridges, providing strength and flexibility. In initial testing, one of the monomers was a common food additive called sodium hexametaphosphate and the other was any of several monomers based on guanidinium ions. Both monomers can be metabolized by bacteria, ensuring biodegradability once the plastic dissolves into its components.
“While the reversible nature of the bonds in supramolecular plastics was thought to make them weak and unstable,” says Aida, “our new materials are exactly the opposite.” In the new material, the salt bridge structure is irreversible unless exposed to electrolytes such as those found in seawater. The key discovery was how to create these selectively irreversible cross-links.
As with oil and water, after mixing the two monomers in water, the researchers observed two separate liquids. One was thick and viscous and contained significant structural cross-linked salt bridges, while the other was watery and contained salt ions. For example, when sodium hexametaphosphate and alkyl diguanidinium sulfate were used, the sodium sulfate salt was expelled into the aqueous layer. The final plastic, alkyl SP2, was obtained by drying what remained in the thick, viscous liquid layer.
“Desalination” turned out to be the critical step; Without it, the resulting dry material was a fragile glass, unfit for use. Resalinizing the plastic by placing it in salt water caused the interactions to reverse and the structure of the plastic to destabilize within hours. Therefore, having created a strong, durable plastic that can still dissolve under certain conditions, the researchers next tested the quality of the plastic.
The new plastics are non-toxic and non-flammable, meaning they do not emit CO2, and can be reshaped at temperatures above 120°C like other thermoplastics. By testing different types of guanidinium sulfates, the team was able to generate plastics that had different hardnesses and tensile strengths, all comparable or better than conventional plastics.
This means that the new type of plastic can be customized according to needs; Scratch-resistant hard plastics, rubber silicone-like plastics, strong weight-bearing plastics or flexible low-tension plastics. The researchers also created ocean-degradable plastics using polysaccharides that form salt bridges cross-linked with guanidinium monomers. Plastics like these can be used in 3D printing, as well as medical or health-related applications.
Finally, the researchers investigated the recyclability and biodegradability of the new plastic. After dissolving the new initial plastic in salt water, they were able to recover 91% of the hexametaphosphate and 82% of the guanidinium in the form of powders, indicating that recycling is easy and efficient. In the soil, the sheets of the new plastic completely degraded over the course of 10 days, supplying the soil with phosphorus and nitrogen similar to a fertilizer.
“With this new material, we have created a new family of plastics that are strong, stable, recyclable, can fulfill multiple functions and, most importantly, do not generate microplastics,” concludes Aida.
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