Researchers at Nanyang Technological University (NTU) Singapore have developed a method for recycling mixed plastic packaging without the use of chemical solvents, a long-standing barrier to effective processing of multilayer packaging materials. The work, carried out by a team from NTU’s School of Materials Science and Engineering and the Nanyang Environment and Water Research Institute (NEWRI), has been published in the journal Industrial & Engineering Chemistry Research. The technique, called depolymerization-induced polymer separation (DIPS), selectively breaks down one plastic component in a mixed plastic structure while leaving others intact, enabling clean separation and material recovery.
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The Problem with Mixed Plastic Packaging
Multilayer plastic packaging is designed for performance. The combination of different polymers, each contributing specific properties such as oxygen barrier, moisture resistance, mechanical strength or heat sealability, is what makes flexible food packaging capable of extending shelf life and surviving distribution. But the same properties that make these structures commercially effective make them technically difficult to recycle. Conventional mechanical recycling systems process best when dealing with a single, homogeneous polymer stream. When multiple incompatible polymers are combined, the recyclate is typically degraded, low in value and limited in application, which is why the vast majority of multilayer flexible packaging currently ends up in landfill or incineration rather than back in the supply chain.
The scale of the problem is significant. The OECD estimates that global plastic production could reach 736 million tonnes annually by 2040, increasing pressure on systems that already struggle with simpler, single-material waste streams. Multilayer packaging represents one of the most intractable segments of that challenge.
How DIPS Works
The DIPS method is built around a technique called reactive extrusion, an industrial process in which standard extrusion equipment, used routinely to melt and shape plastics in manufacturing, is repurposed to simultaneously drive a chemical reaction. In the NTU team’s process, mixed plastic packaging containing polyethylene terephthalate (PET) and polypropylene (PP) is fed into the extruder together with glycerol, a low-cost, widely available reagent. The glycerol reacts selectively with the PET component, breaking it down through a glycolysis reaction into smaller oligomeric units. The PP fraction, which does not react with glycerol under the same conditions, remains structurally intact throughout the process and can be recovered as a high-quality material.
The selectivity of the reaction is central to the method’s value. Rather than degrading both polymers simultaneously, as conventional chemical recycling approaches tend to do, DIPS exploits the different chemical reactivity of PET and PP to achieve separation without physically pulling the materials apart beforehand. The entire process runs at atmospheric pressure and without solvents, which eliminates the safety, environmental and cost concerns associated with solvent-based chemical recycling routes.
In laboratory testing, the recovered PP material demonstrated properties consistent with high-quality recycled polymer. This is a meaningful result, given that the quality of recyclate is a key determinant of whether recovered material can re-enter the supply chain at value rather than being downcycled into lower-grade applications.
Relevance to the Packaging Industry
The practical implications of the DIPS method – if validated at scale – are significant for several segments of the packaging industry. Flexible food packaging producers and brand owners working with PET/PP laminate structures have had essentially no viable recycling pathway for these materials. The absence of a workable end-of-life route has complicated the recyclability assessments that producers are increasingly required to carry out.
The OECD has estimated that efficient recycling of mixed plastic waste could unlock more than US$250 billion in annual economic value globally. The gap between that potential and current recycling infrastructure is where technologies like DIPS are attempting to operate.
Stage of Development and Next Steps
The research is currently at laboratory scale. The NTU team has indicated that the next phase involves collaboration with industry partners to validate the DIPS process under scaled-up conditions and the researchers have stated they are open to interest from potential industrial collaborators. The jump from laboratory proof-of-concept to industrial deployment is a substantial one. It involves not only engineering scale-up but also economic modelling of reagent costs, throughput rates, energy consumption and recyclate quality at volumes that are meaningful for commercial collection systems.
The reactive extrusion approach is well-suited to scale-up in principle, since extrusion is already a standard industrial process with a mature equipment base. Whether the selectivity of the glycerol reaction with PET is maintained at higher throughputs and with the variability of real-world post-consumer waste streams, which rarely present as clean binary mixtures, will be a key question for the validation phase.
Conclusion
The DIPS method represents a technically interesting step toward addressing one of the most persistent gaps in plastic recycling infrastructure. The solvent-free, reactive extrusion approach avoids the principal drawbacks of existing chemical recycling routes and the quality of the recovered PP in initial testing is encouraging. The path from laboratory result to industrial reality remains significant and the method’s performance with real post-consumer waste at scale has yet to be demonstrated. The research team’s next steps with industry partners will determine whether DIPS can move from a promising proof-of-concept toward a viable contribution to the multilayer packaging recycling challenge.