The future of plastics may lie in a durable, glassy supramolecular polymer capable of dissolving in saltwater, breaking down into metabolizable components.
The slow degradation of plastic materials released into the environment – whether through recycling and disposal processes, maritime transport losses, tyre wear, washing synthetic textiles, or human negligence – plays a significant role in the creation of microplastics. These pollutants require urgent global intervention as they lead to widespread contamination of terrestrial and marine ecosystems, profoundly affecting human, animal, and plant life.
According to the National Geographic Society, it may take hundreds or even thousands of years for global plastic waste to decompose completely. During this period, as plastics interact with soil and water, they absorb pesticides, chemical pollutants, heavy metals, and antibiotic residues. Microplastics, in turn, act as carriers for these substances, spreading them widely, even infiltrating the food chain [source: Effects of microplastics on the terrestrial environment: A critical review – Environmental Research, 2022].
The global scientific community has long sought alternatives to conventional plastics: plant-based, sustainable, and biodegradable materials. However, a major challenge persists: achieving perfect and complete biodegradability in compliance with current regulations.
Many bio-based plastics available today – commonly known as “bioplastics” – offer a reduced carbon footprint compared to petroleum-derived plastics. Yet, they are not water-soluble, leaving room for innovation and improvement in this vital field.
TAKEAWAYS
Bio-based but not biodegradable: the case of polylactic acid bioplastic
First of all, it is worth mentioning that one of the main regulatory references concerning the requirements for a plastic material to be classified as “biodegradable” is UNI EN ISO 14855-1:2013, which establishes the European standards for determining the «final aerobic biodegradability of plastic materials under controlled composting conditions», specifically requiring 90% decomposition within at least six months.
Other European standards include EN 13432:2000, which pertains to compostable plastics for packaging, and UNI EN 14995:2007 for other types of plastic products. These standards also require passing biodegradability tests (90% within six months) and disintegration tests, which mandate that 90% of the material be reduced to fragments smaller than 2 millimetres within three months.
Regarding the timeframes for biodegradability and disintegration of compostable plastic materials, a study published in PLOS One (Not so biodegradable: Polylactic acid and cellulose/plastic blend textiles lack fast biodegradation in marine waters, May 2023) is highly critical of materials marketed as “biodegradable” that require highly specific conditions, achievable only in industrial environments with extremely high temperatures, for rapid biodegradation.
This is the case for the widely used bioplastic polylactic acid (PLA), derived from naturally occurring sugars in maize and sugar beet. The study tested the biodegradability of PLA in marine waters and found that it failed to degrade within 428 days, far exceeding the timelines set by these standards.
A more recent study (Rapid biodegradation of microplastics generated from bio-based thermoplastic polyurethane, Scientific Reports, 12 March 2024) notes that for biodegradation to occur and be completed, the chemical structure of the plastic compound must include chemically accessible bonds that enzymes from environmental microorganisms (bacteria and fungi) can act upon. These enzymatic processes break down plastics into natural substances such as water, carbon dioxide, or mineral salts.
Supramolecular plastics: durable and fully disintegrable
A practical solution to the challenge of achieving complete disintegration of plastic materials in seawater comes from scientists at the University of Tokyo and the RIKEN Center for Emergent Matter Science in Wako, Japan.
The focus of their recent study, titled “Mechanically strong yet metabolizable supramolecular plastics by desalting upon phase separation” (Science, 21 November 2024), is on “supramolecular plastics” developed in their laboratory.
The researchers explain that «these new plastics were created by combining two entirely non-toxic ionic monomers that form cross-linked salt bridges. These structures give the material both strength and flexibility. In the initial tests, one of the monomers used was a common food additive – sodium hexametaphosphate – while the other was one of several guanidinium-based ionic monomers».
The standout feature of supramolecular plastics lies in the chemical structure of the two ionic monomers, which can be entirely metabolized by bacteria, ensuring total biodegradability in water.
Specifically, in the resulting material, the cross-linked salt bridges formed by the two monomers are irreversible unless exposed to electrolytes, such as those found in seawater. The team’s key breakthrough was the creation of “selectively” irreversible cross-linked salt bridges, which simultaneously provide strength and solubility. Let’s explore how this balance is achieved.
New glassy and metabolizable plastics
Much like what happens when oil is poured into water, the Japanese researchers explain, «after mixing the two monomers in water, the liquids separate: one dense and viscous layer containing cross-linked salt bridges, and another aqueous layer containing salt ions».
At this stage came the scientists’ insight: to “push” the sodium hexametaphosphate (dense and viscous) into the aqueous layer. The final plastic material – alkyl SP₂ – was produced by drying the thick layer of viscous liquid, which was then desalinated to prevent the dried material from becoming a brittle crystal unsuitable for practical use.
The resulting plastic, resembling a glass sheet, was subsequently re-salted by immersing it in saltwater, which caused «a reversal of interactions and the destabilization of the structure within a few hours». It was then tested for its recyclability and biodegradability.
«After dissolving the new plastic in saltwater, we were able to recover 91% of the sodium hexametaphosphate and 82% of the guanidinium as powders, demonstrating that recycling is straightforward and efficient» the researchers note.
Glimpses of Futures
With the introduction of this novel material, the research team from the University of Tokyo and the RIKEN Center for Emergent Matter Science in Wako has laid the foundation for a new class of plastics that are simultaneously durable, soluble, recyclable, carbon-neutral, and – most importantly – non-generative of microplastics.
Let us now attempt to forecast possible future scenarios, using the STEPS matrix to explore the social, technological, economic, political, and sustainability impacts that the evolution of this “new plastic” might bring.
S – SOCIAL: once refined, made more malleable, adapted for all traditional plastic applications (currently reliant on petroleum-derived materials), and subjected to additional tests to ensure complete safety (non-toxicity and non-flammability), these innovative, eco-friendly plastics could herald a global transition from the era of “plastic as a problem” to the era of “plastic as a resource.” The research team notes that, when buried in soil, sheets of the new plastic degrade entirely within just ten days. During this period, early tests have shown that the plastic enriches the soil with phosphorus and nitrogen, acting as a natural fertilizer. This represents nothing short of a revolution.
T – TECHNOLOGICAL: in the future, with the integration of biotechnologies, the plastic material (alkyl SP₂) discovered by the Japanese team could surpass the current range of applications for bioplastics. Presently, these applications include packaging (the largest market segment), waste collection (bags for organic waste), food consumption (films, cutlery, catering supplies), and goods transport (shopping bags and hygienic first-layer food packaging). Moreover, remodelling techniques at temperatures exceeding 120°C will enable this “new” plastic to be customized according to specific usage needs. Its properties could range from hard and durable to silicone-like plastics and flexible, low-resistance variants, significantly broadening its technological versatility.
E – ECONOMIC: economically, the most significant challenge for large-scale production of alkyl SP₂ plastic lies in its manufacturing costs, especially when compared to petroleum-derived plastics, which are generally less expensive than bioplastics. Nonetheless, the production of bioplastics is steadily increasing. According to the 2024 European Bioplastics Report on industry development, bioplastics production is projected to grow from the current 2.47 million tonnes to approximately 5.73 million tonnes by 2029. Packaging leads this growth, accounting for 45% of total production, or 1.12 million tonnes produced in 2024.
P – POLITICAL: in light of the EU’s new packaging regulations (including plastic packaging), approved on 24 April 2024 to make them more sustainable and reduce waste, the development of plastics by the Japanese researchers could offer a strategic solution in the future. These plastics would replace current polluting, microplastic-generating materials with environmentally friendly alternatives that safeguard the health of all organisms on the planet. The new rules, effective 1 January 2030, ban plastic packaging for fruits, vegetables, food, and drinks consumed in bars and restaurants, as well as single-serving portions, small disposable packaging, and ultra-lightweight plastic bags under 15 microns within the EU. Alkyl SP₂-based plastic, being non-toxic, non-polluting, and metabolizable in the environment, aligns perfectly with the EU’s policies.
S – SUSTAINABILITY: the fight against global plastic pollution could gain a powerful new ally in the material developed by the Japanese team. The durability, non-toxicity, zero emissions, biodegradability, solubility, and recyclability of these innovative supramolecular plastics position them as fully aligned with environmental and sustainability goals.vEven if abandoned in the environment, such plastics release nothing incompatible with nature, making them an ideal material for a sustainable future.
