Plastic waste is being stitched back together at the molecular level using “chemical zips”—specially designed molecules that bind different types of plastic into a single, stronger material. This matters because only 10% of plastics are currently recycled. Most are downcycled into lower-quality products until they become worthless. A major barrier is that recycling streams contain mixtures of plastics—such as polyethylene milk cartons with polypropylene lids—that require costly separation. The chemical zip approach avoids that step by chemically linking incompatible plastics into hybrid materials that are stronger than any single component. If successful, this research could transform plastic recycling from a downgrading process into an upcycling one. Instead of producing weaker materials destined for landfill, recyclers could create high-value products with improved strength and durability. This would reduce the need for virgin plastic production from crude oil, cut CO₂ emissions, and help shift the plastics industry from a linear to a circular economy. The work focuses on polyesters such as PLA, whose growing use in consumer goods is contaminating existing recycling streams.
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Plastics have helped to build the modern world, and the current era has been dubbed “The Plastic Age” due to the ubiquity and influence of these materials. Yet plastics are both a friend and foe to the environment. While plastic pollution poses a very real environmental danger, plastics are also powering the green revolution as key components of wind turbine blades, batteries, and lightweight electric vehicles. Plastics have reduced CO2 emissions across Europe by a factor of 5-9, and address the global challenge of food security by reducing food waste by 20%. However, current production methods are unsustainable. Over 99% of plastics are currently produced from crude oil, and by 2050, annual plastic production is predicted to use 20% of global oil reserves and generate twice as much CO2 as the aviation industry. Approximately 60% of the 8300 Mt of plastic produced globally by 2015 has been discarded. Plastic waste is thus an attractive alternative feedstock to help conserve oil stocks and avoid energy intensive cracking processes. Transitioning from a linear plastic production model to a circular economy is of urgent importance, yet this requires innovative scientific technologies. Only 10% of plastics are currently recycled. This is partly because "recycled" materials are generally downcycled, with a reduction in material properties such as strength and flexibility leading to progressively lower value applications until recycling is no longer cost effective. This process is further complicated because plastic products often contain multiple types of plastic, such as polyethylene (PE) milk cartons which have lids and labels made from polypropylene (PP). Recycling feedstocks thus often contain a mixture of different plastics that require intensive separation processes and subsequent recycling as individual components. Creative scientific solutions are crucial to address these problems in order to upcycle plastic waste into useful value-added products. The creation of "chemical zips" has enabled efficient recycling of a combination of PE and PP, avoiding the need for separation of these two materials. The "zip" is a molecule designed with different and alternating "teeth"; one set of teeth interacts with PE while the other set interacts with PP to stitch these two plastics together. Remarkably, the new hybrid plastics produced by combining PE, PP and the "zip" give upcycled materials that are stronger than any of the individual components. While game-changing chemical zips have been developed for PE and PP, analogous systems for polyesters remain underexplored. Developing effective chemical zips for degradable polyesters such as poly(lactic acid) (PLA) is an exciting and important target, as increasing consumer awareness has led to a rapid expansion of the PLA market. Contamination of recycling streams with PLA is problematic, as the current separation technologies are less well developed than for conventional plastics, and this challenge is set to grow. This Future Leaders Fellowship (FLF) programme aims to develop a disruptive technology to repurpose waste plastic, by preparing transformative chemical zips to combine polyesters with other waste plastics to produce hybrid materials with improved properties. Strategies to produce these zips have been developed in the first phase of the FLF. In the renewal phase, these zips will be applied to the combination of polyesters with waste plastics including PE, PP and polystyrene (PS) to create a broad range of desirable, diverse and valuable materials, with important economic, environmental and energy benefits for society.
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