Japanese researchers create eco-friendly plastic that dissolves in saltwater

A groundbreaking type of plastic that remains strong during use but rapidly disintegrates in saltwater was created in Japan.

A team of scientists at Japan’s RIKEN Center for Emergent Matter Science (CEMS) has developed this offering a promising solution to plastic pollution.

Traditional plastics are prized for their durability and resilience, making them indispensable in daily life. However, their long-lasting nature becomes an environmental hazard when discarded, persisting for decades or even centuries. These plastics contribute to ecological damage and pose risks to wildlife and human health through microplastic contamination.

Led by Takuzo Aida, researchers at RIKEN CEMS sought to address this issue by creating a supramolecular plastic - a material whose structure is maintained by reversible interactions. Unlike traditional plastics with robust covalent bonds, these new polymers are designed to break down swiftly when exposed to saltwater, leaving behind harmless compounds.

The innovative plastic is formed by combining two ionic monomers that establish cross-linked salt bridges, providing the material with both strength and flexibility. Initial experiments involved using sodium hexametaphosphate, a common food additive, paired with various guanidinium ion-based monomers. Notably, both monomers are biodegradable, ensuring that the plastic’s components can be metabolised by bacteria after dissolution.

According to Aida, while supramolecular plastics are often criticised for their instability, their new material defies expectations by remaining strong until intentionally broken down. The plastic's structure remains stable until exposed to electrolytes like those found in seawater, triggering its degradation.

During the production process, researchers mixed the two monomers in water, resulting in the formation of two distinct liquids: a thick, viscous layer containing essential salt bridges and a watery layer with expelled salt ions. For instance, when sodium hexametaphosphate was combined with alkyl diguanidinium sulfate, sodium sulfate salt separated into the watery layer. The desired plastic, called alkyl SP2, was obtained by drying the viscous layer.

Crucially, the team discovered that the desalting process was essential. Without removing the salt, the resulting material became a brittle crystal unsuitable for practical use. However, when the plastic was reintroduced to saltwater, its structure quickly deteriorated within hours.