New process peels apart multi-layer plastics

Researchers in Singapore have developed a solvent-free recycling process that separates mixed plastic packaging. They believe this could unlock value from one of the sector’s most difficult waste streams.

Multi-layer plastic packaging is widely used for snacks, instant noodles and other food products. While these materials offer durability and barrier protection, they are notoriously difficult to recycle because multiple plastics are bonded together.

As a result, much of this material ends up in landfill or incineration. Global plastic production projected to reach 736 million tonnes by 2040 adds pressure to find viable recycling solutions.

Researchers from the Nanyang Technological University, the university’s School of Materials Science and Engineering, and the Nanyang Environment and Water Research Institute (Newri) have developed a process called depolymerisation-induced polymer separation (DIPS).

Avoiding solvents

The DIPS process uses a continuous twin-screw reactive extrusion system to selectively break down one plastic while leaving another intact. Unlike many chemical recycling technologies, the process operates at room temperature and does not require solvents.

In trials involving multi-layer packaging made from polyethylene terephthalate (PET) and polypropylene (PP), the PET reacts with glycerol and breaks down into smaller molecules. This changes its physical properties and allows it to separate naturally from the PP.

‘We’re seeing more mixed plastic packaging used in everyday food products but recycling it safely and efficiently is still a major challenge,’ says Hu Xiao, programme director for sustainable chemistry and materials at Newri.

‘Our team set out to tackle this by developing a practical, scalable way to separate these materials without using harmful solvents.’

Industrial scale in sight

According to the researchers, laboratory testing showed that the recovered PP retained up to 90% of its original tensile strength under optimal conditions. That performance brings it close to virgin-grade material. The team also tested the technology on post-industrial multi-layer packaging waste and reported successful separation results.

The process relies on extrusion equipment common throughout the plastics industry so the researchers believe commercial deployment could be achievable without major infrastructure changes.

‘One of the biggest hurdles in plastic recycling today is the lack of a viable way to deal with mixed plastics,’ says Liang Yen Nan. ‘This project was driven by that challenge and our goal is to help move the industry closer to a solution that works in the real world.’

The recovered PET fraction cannot currently return directly into packaging applications. However, researchers say it could be used in speciality materials or converted into chemical building blocks for new products.

Economic appeal

The researchers argue that the DIPS approach could be adapted for other mixed plastic combinations in 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.

‘Our process attempts to bridge the gap between laboratory research and industrial application,’ says project researcher Kathirvel Periasamy. ‘By simplifying separation and eliminating solvents, we aim to make plastic recycling more economically viable and environmentally sustainable.’

The work has been published in Industrial & Engineering Chemistry Research. The R&D team is now seeking industry partners to validate the technology under larger-scale operating conditions.