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Most Recent Update on: March 21st, 2025, 03:25 pm
Supramolecular chemistry, often termed as “chemistry beyond the molecule,” emphasizes the exploration of molecular recognition and high-order structures created through noncovalent interactions. It has gained attention recently due to research aimed at addressing the issue of plastic breakdown into microplastics. Supramolecular plastics — polymers whose structures are maintained by reversible interactions — are as durable as conventional plastics and eco-friendly, but their uniqueness lies in their ability to decompose in seawater. Consequently, this new type of plastic is expected to contribute to the reduction of harmful microplastic pollution that accumulates in aquatic environments and soil, ultimately infiltrating the food chain.
Each year, manufacturers worldwide produce plastic resins and fibers at a volume of hundreds of millions of metric tons. Larger plastics never fully disintegrate into their constituent substances; they simply diminish into smaller fragments of plastic. Products made from these materials break down in the environment into progressively smaller pieces that can be ingested or inhaled by humans and animals. These microplastics not only travel from rivers to oceans but also inhabit every ecosystem.
More than 460 million metric tons of plastic are produced annually for various applications. Approximately 20 million metric tons of plastic waste enter the environment each year. This figure is anticipated to rise dramatically by 2040. Plastic pollution affects all terrestrial, freshwater, and marine ecosystems. It is a key contributor to biodiversity loss and ecosystem degradation, as well as a factor influencing climate change.
Conventional plastics are unsustainable and detrimental to the environment. Researchers have been striving to develop safe and sustainable alternatives to traditional plastics. While some recyclable and biodegradable plastics exist, the challenge with current biodegradable options like PLA is that they often find their way into the ocean. Biodegradable plastics fail to decompose because they are water insoluble. As a result, microplastics — plastic pieces smaller than 5 mm — are endangering aquatic organisms and making their way into the food chain, including our own bodies.
The plastic crisis demands urgent action, particularly concerning the end-of-life phase of plastics. The breakdown of plastics through biological processes is vital for ecological health, hence the interest in the feasibility of plastic degradation.
Plastics that can metabolize in oceanic environments are highly sought after for a sustainable future. Metabolism — the biochemical processes that sustain cellular life and energy — plays a crucial role in plastic studies. A November 2024 study demonstrates the feasibility of plastics that are mechanically strong yet metabolizable under biologically relevant conditions due to their dissociative properties with electrolytes. Led by Takuzo Aida at the RIKEN Center for Emergent Matter Science (CEMS), a research team has engineered a robust plastic that will not contribute to microplastic pollution in our oceans.
The RIKEN scientists employed salt-bridging sodium hexametaphosphate combined with di- or tritopic guanidinium sulfate in water, resulting in the formation of a cross-linked supramolecular network that remained stable until electrolytes were replenished. This exceptional stability was attributed to a liquid-liquid phase separation that expels sodium sulfate, produced through salt bridging, into a water-rich phase. The two ionic monomers established cross-linked salt bridges, which provide strength and flexibility.
“While the reversible nature of the bonds in supramolecular plastics has historically been regarded as a liability, our new materials are completely opposite,” lead researcher Aida remarked to Phys.org.
Drying the remaining condensed liquid phase produced glassy plastics that are thermally reshappable, resembling thermoplastics, and usable even in aqueous media with hydrophobic parylene C coating. In initial tests, one of the monomers was a common food additive known as sodium hexametaphosphate, while the other was any of a series of guanidinium ion-based monomers. Both monomers can be metabolized by bacteria, ensuring biodegradability once the plastic is dissolved into its components.
The “desalting” process emerged as a crucial step; without it, the resultant dried material was a fragile crystal, unsuitable for application. Reintroducing salt to the plastic by soaking it in saltwater initiated the interactions to revert, causing the plastic’s structure to destabilize within hours. Thus, having created a strong and durable plastic that can still be dissolved under specific conditions, the researchers proceeded to test the plastic’s quality.
The new plastics are non-toxic and non-flammable, resulting in zero CO2 emissions, and can be reshaped at temperatures exceeding 120°C like other thermoplastics. By experimenting with various guanidinium sulfates, the team successfully produced plastics with different degrees of hardness and tensile strengths, all comparable to or superior than conventional plastics. This implies that the new type of plastic can be tailored to requirements; scratch-resistant hard plastics, rubber silicone-like variants, sturdy weight-bearing plastics, or flexible low-tensile ones are all feasible. The researchers also developed ocean-degradable plastics employing polysaccharides that form cross-linked salt bridges with guanidinium monomers. Plastics of this nature can be utilized in 3D printing as well as medical or health-oriented applications.
Lastly, the researchers explored the new plastic’s recyclability and biodegradability. After dissolving the initial new plastic in saltwater, they managed to recover 91% of the hexametaphosphate and 82% of the guanidinium as powders, signaling that recycling is both straightforward and efficient. In soil, sheets of the new plastic fully degraded within 10 days, enriching the soil with phosphorous and nitrogen akin to fertilizer.
“With this new material, we have established a novel family of plastics that are robust, stable, recyclable, multifunctional, and importantly, do not generate microplastics,” Aida states.
It was determined that this methodology could be extended to polysaccharide-based supramolecular plastics suitable for three-dimensional printing. The experimental results have been published in Science.
Final Thoughts
In another positive development for those concerned about human health and ocean pollution, the SEC supported As You Sow over Pepsi Co regarding a shareholder resolution urging the beverage and food giant to mitigate plastic pollution. The SEC’s decision marks the second plastic pollution-related proposal from As You Sow to overcome a no-action challenge, despite stricter guidance from the new administration.
Pepsi’s proclaimed commitments to sustainable packaging ring hollow when over 18% of its packaging remains in non-recyclable flexible formats, cites As You Sow. Flexible packaging is one of the fastest-growing sectors and a significant contributor to global plastic pollution.
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