Scientists develop method to separate multi-layer plastics

New solvent-free recycling technology aims to separate mixed plastic packaging, targeting a waste stream that currently ends up in landfills or incinerators. Researchers in Singapore have developed a process called depolymerisation-induced polymer separation, or DIPS. This method uses a continuous twin-screw reactive extrusion system to break down specific plastics without applying heat or using chemical solvents. The team from Nanyang Technological University believes the technique could unlock significant economic value from materials that are otherwise difficult to process.

Tackling multi-layer plastics

Multi-layer plastic packaging is common for snacks, instant noodles, and other food products because the layers provide durability and barrier protection. However, these materials are notoriously difficult to recycle because they consist of multiple plastics bonded together. As global plastic production is projected to reach 736 million tonnes by 2040, finding viable solutions for this waste becomes more urgent.

The DIPS process involves reacting polyethylene terephthalate (PET) with glycerol at room temperature. This chemical reaction breaks the PET down into smaller molecules, which alters its physical properties and allows it to separate naturally from the polypropylene (PP) layers. Unlike many chemical recycling technologies that require harsh conditions or solvents, this method relies on extrusion equipment commonly found in the plastics industry.

Lab tests showed that the recovered PP retained up to 90% of its original tensile strength under optimal conditions. That performance is close to virgin-grade material, suggesting the process could produce a high-quality output for industrial use. The team also successfully tested the technology on post-industrial multi-layer packaging waste.

Scaling the solution

One of the biggest hurdles in plastic recycling today is the lack of a viable way to deal with mixed plastics. The researchers argue that their approach could be adapted for other mixed plastic combinations in the future. If multi-layer plastic waste could be recycled efficiently at scale, it could unlock more than EUR 215 billion in annual economic value, based on the team’s estimates.

The recovered PET fraction cannot currently return directly into packaging applications. However, researchers say it could be used in specialty materials or converted into chemical building blocks for new products. This distinction between the two materials creates a clear path for each stream to be utilized differently rather than being lumped together in a generic waste stream.

Commercial deployment could be achievable without major infrastructure changes since the process relies on extrusion equipment already in use. The team is now seeking industry partners to validate the technology under larger-scale operating conditions. The work has been published in Industrial & Engineering Chemistry Research.