Scientists at Nanyang Technological University, Singapore (NTU Singapore), have pioneered a groundbreaking technique to revolutionize the recycling of mixed plastic packaging—a notoriously challenging waste category. This innovation introduces a chemical process that can separate and recover individual plastics from multilayer packaging without the use of harmful solvents, offering a cleaner, safer, and more economically viable pathway to deal with one of the planet’s most persistent environmental problems.

Mixed plastic packaging is ubiquitous in the consumer market, especially in food products like snacks and instant noodles. These multilayered materials combine various polymers, bonded to ensure durability and airtight preservation, but these same properties make them incredibly difficult to recycle. Traditional mechanical recycling methods often degrade the quality of the polymers, resulting in low-value materials frequently destined for landfill or incineration. The global scale of this challenge is immense, with plastic production expected to surge to over 700 million tonnes by 2040, intensifying the urgency for effective recycling innovations.

The team from NTU’s School of Materials Science and Engineering alongside the Nanyang Environment and Water Research Institute (NEWRI), led by Professor Hu Xiao, has developed a technology called depolymerisation-induced polymer separation (DIPS). This sophisticated process selectively targets specific plastic components within mixed packaging, breaking down one polymer chemically while leaving others intact, thus enabling their clean separation and recovery. This nuanced chemical intervention is carried out without introducing solvents, eliminating many environmental and health hazards associated with conventional recycling practices.

At the heart of the DIPS method is reactive extrusion, an industrial process that combines melting, shaping, and chemical reaction stages within a single continuous operation. During this process, poly(ethylene terephthalate) (PET)—commonly used in beverage bottles—is mixed with glycerol, a readily available, nontoxic reagent. The process induces a targeted depolymerization of PET, converting it to smaller molecular units with altered physical and chemical properties. This reaction is finely tuned to maintain the integrity of other plastics like polypropylene (PP), a staple in food packaging.

What makes this technique exceptional is the natural separation that occurs post-depolymerization. The qualitative differences in polarity and viscosity between the chemically altered PET and unaffected PP drive an automatic phase separation, allowing the materials to be isolated without laborious sorting or hazardous chemicals. This solvent-free environment operates at ambient pressure, markedly reducing energy consumption and supporting safer industrial scale-up potential.

Laboratory analysis of the recycled PP material revealed it retained mechanical strengths up to 90% of virgin polypropylene under optimized conditions. This remarkable retention of tensile strength underscores the practical viability of this recycled plastic for high-performance applications, a notable improvement over conventional mechanical recycling, which often results in material downgrading. Besides offering environmental benefits, this enhances the economic value proposition of recycling mixed plastics.

While the PET fraction cannot be directly reprocessed into new packaging materials, its chemical profile post-depolymerization makes it a valuable feedstock for specialty applications. These include precursor materials for high-strength epoxy resins used in advanced composites like wind turbine blades. Furthermore, its chemical groups offer pathways to transform it back into monomers, potentially enabling closed-loop recycling and creating a circular economy for PET-based products.

The potential of the DIPS process extends beyond PET and PP. The principles of selective depolymerization and exploitation of differing material properties signal feasibility for broad applicability across various multilayer plastic combinations prevalent in the packaging industry. This adaptability could dramatically reshape industrial recycling practices, minimizing reliance on sorting and solvent-based treatments.

PhD candidate Kathirvel Periasamy, who contributed significantly to developing the DIPS methodology, highlights that this process aims to bridge the gap between laboratory innovation and industrial application. By integrating separation and depolymerization into a single, streamlined operation, DIPS addresses the economic and environmental challenges hampering widespread adoption of mixed plastic recycling.

The implications of efficiently remediating mixed plastic waste go beyond environmental sustainability—they represent a potential economic boon. It is estimated that unlocking effective recycling solutions for mixed plastics could generate annual economic value exceeding $250 billion globally. This transformative impact could drive market incentives for recycling infrastructure development and elevate the quality standards for recycled materials.

Looking forward, the NTU Singapore team plans collaborative efforts with industrial partners to pilot this technology under scaled-up manufacturing conditions. These partnerships aim to validate the process’s commercial feasibility, operational robustness, and integration with existing recycling systems. The researchers actively invite industry stakeholders interested in advancing sustainable plastic waste management to engage in this next phase.

This innovative approach to depolymerization and polymer separation is poised to be a major step forward in tackling one of the most recalcitrant components of plastic pollution. By eliminating harmful solvents, minimizing energy consumption, and producing high-quality recycled plastics, DIPS aligns technological ingenuity with environmental stewardship, potentially rewriting the narrative around mixed plastic recycling for decades to come.

Subject of Research:
Not applicable

Article Title:
Depolymerization Induced Polymer Separation: A New Strategy for Continuous and Efficient Separation of PP/PET Multilayer Plastic Packaging Waste

News Publication Date:
16-Mar-2026

Web References:
OECD Policy Scenarios for Eliminating Plastic Pollution by 2040
OECD Global Material Resources Outlook to 2060

References:

1. OECD Policy Scenarios for Eliminating Plastic Pollution by 2040; OECD, 2024.
2. OECD Global Material Resources Outlook to 2060: Economic Drivers and Environmental Consequences; OECD, 2019.

Image Credits:
NTU Singapore

Keywords

Industrial chemistry, Materials processing, Chemical separation, Separation techniques, Sustainable chemistry, Plastic recycling, Polymer science, Depolymerization, Reactive extrusion, Environmental engineering, Circular economy, Mixed plastics

Over 20 million tons of polystyrene plastic are produced annually, yet only a small fraction is recycled worldwide. Current recycling methods consume large amounts of energy and often rely on harsh and toxic chemicals to break the strong molecular chains that make up polystyrene. One possible solution is the use of sulfur, which is an inexpensive byproduct formed when refining crude oil. Its unique chemical structure allows it to break up strong chemical chains in long plastic molecules. Despite its abundance, sulfur has very limited applications, and converting it into more usable forms tends to require a lot of heat, rendering it unused for long periods of time. 

Researchers at the Dalian Institute of Chemical Physics hypothesized that sulfur could help break down polystyrene waste to form more valuable chemicals. To power this reaction, they converted sunlight into heat energy through a process called photothermal conversion. They used this heat to transform polystyrene and sulfur into valuable chemicals like 2,4-diphenylthiophene, or chemical D, and 1,3,5-triphenylbenzene, or chemical T, which are used to make semiconductors and chemical sensors. 

To test this, the team mixed ground polystyrene and sulfur at a molar ratio of 1:0.5 in a glass test tube. They sealed the tube with a balloon and secured it onto an iron stand. Then, they focused sunlight onto the bottom of the tube using a curved mirror. As the mixture heated up, the yellow-white solids gradually melted and transformed into a reddish-black liquid after 2 minutes. After heating, the researchers removed the mirror and allowed the system to cool before collecting the gaseous products from the balloon and dissolving the remaining solids for further purification and analysis. 

The researchers then adjusted the reaction conditions to understand what factors influenced their results. They tested the reaction without sulfur, varied the sulfur ratios from 0.2 to 0.8, and replaced elemental sulfur with other sulfur-containing compounds. They also explored adding known photothermal agents, specifically metal oxide additives, to the mixture. 

To compare the difference between sunlight and artificial light, the researchers repeated the experiment indoors using a 100 Watt LED bulb and monitored temperature changes with a thermal camera. They also ran a control experiment using only polystyrene to check how sulfur affected the yield under LED light. They also tested exposure times from 1 to 6 minutes in 1-minute increments to determine how long it took to achieve the highest yields under LED. The researchers used these tests to identify which conditions were necessary for the reaction to occur and how different factors influenced its outcome.

They found that without sulfur or with alternative sulfur-containing compounds, the reaction did not produce chemical D or T under sunlight. In contrast, reactions that included sulfur successfully produced these target products, with the highest yields of 34% for D and 16% for T at a sulfur ratio of 0.5. When they added metal oxides, the chemical yields decreased to 22% and 12%, respectively, suggesting that these additives interfered with the desired reactions. In addition, when the researchers switched from sunlight to LED, the reaction yields dropped to 26% for D and 13% for T. 

Next, they examined how reaction time influenced product formation. They found that yields increased gradually before reaching the maximum at 4 minutes and leveling off. They also noted that mixtures containing sulfur heated up from room temperature to 320°C (608°F), while the control setup only showed a slight temperature increase. The researchers interpreted these results as confirmation of sulfur’s dual role as a reactant and a light-to-heat converter that enables the conversion of polystyrene to useful chemicals.

Taking it a step further, the researchers tested their method on real-world polystyrene wastes, including food packaging, cup lids, and foamed plastics. They successfully produced chemicals D and T from these materials, demonstrating that their process works beyond laboratory samples.

The team concluded that their study presents a simple, fast, and solvent-free approach to converting 2 abundant waste materials into valuable chemicals using sunlight. By combining polystyrene waste and excess sulfur, the researchers offer a new pathway for sustainable polymer upcycling that uses clean energy and is broadly applicable to everyday plastics.

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