Plastic products, like polyethylene terephthalate (used in bottles), are popular because they are flexible, strong, durable, and recyclable. Their convenience is hard to beat. Biodegradable plastics, such as polylactic acid (PLA), were introduced as an alternative.
However, PLA takes too long to break down in the ocean, eventually forming microplastics that bacteria, fungi, or enzymes can’t break down. These microplastics have also been found in human blood and brains.
While the full impact on health and the environment is still unclear, microplastics cause ecosystem problems, such as slowing animal growth, reducing fertility, and leading to organ dysfunction.
RIKEN scientists have developed an innovative plastic that biodegrades in saltwater, addressing the growing issue of ocean microplastic pollution. This material is as strong and lightweight as conventional plastics but offers the added benefits of reducing pollution and cutting greenhouse gas emissions from plastic burning.
The breakthrough results from three decades of work on supramolecular polymers, materials with reversible, weaker bonds. While these bonds allow the polymers to disintegrate under specific conditions, their tendency to break down too easily has historically limited their use.
To overcome this, researchers identified a combination of compounds that create a supramolecular material with both durability and the ability to degrade quickly into safe, non-toxic elements when conditions are right.
A team of researchers discovered that combining sodium hexametaphosphate (a food additive) and guanidinium ion-based monomers (used in fertilizers) forms strong cross-linked bonds called salt bridges. These bridges act as “locks,” providing the material with strength and flexibility.
In their experiment, the team mixed the compounds in water, which unexpectedly separated into two layers—a viscous bottom layer containing the bonded materials and a watery top layer. The viscous layer was extracted and dried to create a plastic-like sheet.
This sheet is as strong as regular plastic but also non-flammable, transparent, and versatile. Remarkably, when soaked in salt water, the sheet degraded back into its raw materials within 8.5 hours. The electrolytes in salt water break the salt bridge “locks,” demonstrating a promising solution for reducing plastic pollution.
The sheet can be made waterproof by applying a hydrophobic coating. Interestingly, the team discovered that even with this coating, the material dissolves as quickly as uncoated sheets when its surface is scratched. This allows salt to penetrate and break down the material effectively, maintaining its biodegradable properties even when waterproofed.
The supramolecular material is biodegradable and leaves behind nitrogen and phosphorus, which microbes can use, and plants can absorb. However, researchers warn that careful management is needed, as too many nutrients could harm coastal ecosystems by causing algal blooms that disrupt entire ecosystems.
Journal Reference
- Cheng, Y., Hirano, E., Wang, H., Kuwayama, M., Meijer, E. W. et al. Mechanically strong yet metabolizable supramolecular plastics by desalting upon phase separation. Science 386, 875-881 (2024). DOI: 10.1126/science.ado1782
Source: Tech Explorist
