Catalytic Chemical Sorting of Intractably Mixed Plastics

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There is an urgent global need to devise better strategies to recycle plastics. It is estimated that a total of 8300 million metric tonnes of plastics have been produced to date yet, incredibly, more than 40 years after the launch of the recycling symbol, less than 10% of waste plastics that have been manufactured are recycled. The rest are either poured into landfill, burned to produce CO2 and other harmful gases or, worst of all, discarded into the environment. Plastics will continue to be critical in addressing the growing demands of our society and to eradicate them as a whole is not a realistic solution. A key challenge therefore is fully and effectively dealing with the waste plastics that we generate. Better end-of-life options for plastic waste are urgently required. A key challenge in plastic recycling is addressing complex plastics wastes, exemplified by multilayer films and blends in which the components cannot be readily separated by mechanical means or in which the specific combinations cause problems in the leading chemical recycling methodologies. WRAP's Plastic Flow 2025 report estimates that, after bottles, film is the next largest consumer plastic packaging format (395kt in 2017) of which just 4% was recycled, making this an important technological target. Hence the development of a technology that can complement existing mechanical and chemical methods would be advantageous in areas where current methods may not be possible to apply - to either help address the most challenging plastic waste streams in their entirety or to provide cleaner, more valuable, waste streams for existing processes.This work proposes to develop 'catalytic chemical sorting'. The different chemistry of different polymer backbones in different plastics means that the reactivity of the specific functional groups can be leveraged to selectively depolymerise one polymer in the presence of another, including from mixtures and blends. Extension of this concept would enable the sequential, selective depolymerisation of complex plastic wastes. In order to achieve this, we will fundamentally advance catalytic systems for depolymerisation using a hybrid computational and experimental approach to identify and develop lead systems that can achieve selectivity and be tolerant of the complexities of real plastic wastes, such as additives, impurities, contaminants and implicit polymer mixtures within the same plastic. This project is focussed on the development of the understanding and fundamental application of catalysis to this challenge, however, given the importance of plastic recycling, the research will be guided by insights from our project partners such that on completion of the project, the scientific approach is suitable for development towards industry-specific challenges using the chemistry and computational tools that have been developed.