In a world overwhelmed by plastic waste, researchers led by Takuzo Aida at the RIKEN Center for Emergent Matter Science (CEMS) have developed a durable plastic that does not contribute to microplastic pollution in our oceans. This new material is as strong as conventional plastics and biodegradable, but its unique characteristic is that it breaks down in seawater [1].
Scientists worldwide have been trying to develop safe and sustainable materials that can replace traditional plastics, which are non-sustainable and harm the environment. This recent article explores developments in combating microplastics in the fashion textile industry.
While some recyclable and biodegradable plastics exist, one big problem remains. Current biodegradable plastics like Polylactic acid, also known as PLA, often find their way into the ocean. PLA and other industrial bioplastics have been found to contain as many as 20,000 chemical features, indicating a broad range of chemical additives, many of which are identical to those added to conventional plastics [2].
Fortunately, in CEMS’s new study, Aida and his team focused on solving this problem with supramolecular plastics – polymers with structures held together by reversible interactions [1].
Figure 1: Ko Phi Phi Don, Thailand. [3]
How Have the New Plastics Been Made?
The new plastics are created by combining two ionic monomers, forming cross-linked salt bridges, providing strength and flexibility. In initial tests, one of the monomers used was sodium hexametaphosphate, a common food additive, while the other was one of several guanidinium ion-based monomers. Bacteria can metabolise both monomers, ensuring the plastic is biodegradable once it breaks down into its components.
“While the reversible nature of the bonds in supramolecular plastics has been thought to make them weak and unstable,” says Aida, “our new materials are just the opposite.” In the new material, the structure of the salt bridges is irreversible unless exposed to electrolytes, such as those found in seawater. The key discovery was how to create these selectively irreversible cross-links [1].
Much like when mixing oil into water, the researchers found that mixing the two monomers in water created two layers: a thick, viscous one with structural cross-linked salt bridges and a watery layer containing salt ions. For instance, combining sodium hexametaphosphate and alkyl diguanidinium sulphate expelled sodium sulphate into the watery layer. The plastic, known as alkyl SP2, was formed by drying the thick layer.
A crucial step was “desalting,” which prevented the dried material from becoming a brittle crystal. Resalting the plastic in salt water destabilised its structure within hours.
This new plastic is:
- non-toxic,
- non-flammable,
- and can be reshaped above 120°C.
The researchers created plastics with varying hardnesses and strengths suitable for different applications, including ocean-degradable options for 3D printing and medical use.
Moreover, they tested recyclability. Dissolving the plastic in salt water allowed them to recover 91% of hexametaphosphate and 82% of guanidinium, indicating efficient recycling. The plastic also fully degraded in soil within 10 days, releasing nutrients like phosphorus and nitrogen.
“With this new material, we have created a family of plastics that are strong, stable, recyclable, multifunctional, and do not generate microplastics,” says Aida [1].
Study Limitations
The materials demonstrated sensitivity to water, especially salt water. While this sensitivity can aid in environmental degradation, it may restrict specific applications. To mitigate this issue, the researchers applied protective coatings such as parylene C. However, the study has not included long-term durability testing under various environmental conditions or fully explored considerations for scaling up manufacturing [4].
Conclusion and Key Insights
This research presents a new method for creating sustainable plastics that effectively balance durability and environmental biodegradability. Unlike traditional plastics, which only break down into microplastics, these new materials can completely dissolve in salt water. This marks a significant advancement in the effort to combat marine plastic pollution. The successful incorporation of biological materials, such as chondroitin sulphate, suggests strong potential for further development using other natural polymers. Additionally, these materials can be reshaped with heat and are recyclable, offering practical manufacturing and waste management advantages at the end of their life cycle [4].
About Pager Power
Pager Power undertakes technical assessments for developers of renewable energy projects and tall buildings worldwide. For more information about what we do, please get in touch.
References:
[1] RIKEN CEMS Press Release – Bye-bye microplastics: new plastic is recyclable and fully ocean-degradable. Accessed on 27/12/24. Available at: https://www.riken.jp/en/news_pubs/research_news/pr/2024/20241122_1/index.html#:~:text=Researchers%20led%20by%20Takuzo%20Aida,it%20breaks%20down%20in%20seawater
[2] Plastic Pollution Coalition. The Hidden Costs of Top-Selling PLA Bioplastic. Accessed on 27/12/24. Available at: https://www.plasticpollutioncoalition.org/blog/2024/2/29/the-hidden-costs-of-top-selling-pla#:~:text=PLA%20does%20not%20biodegrade%20at,contaminate%20food%20and%20water%20sources.
[3] Jonny Clow. Ko Phi Phi Don, Thailand. Accessed on 27/12/24. Available from Unsplash on: https://unsplash.com/photos/green-boat-on-beach-during-sunset-bl5T3frR9pc
[4] StudyFinds. Microplastics crisis solved? Scientists create plastic that vanishes in seawater. Accessed on 27/12/24. Available at: https://studyfinds.org/plastic-vanishes-in-seawater/
