Enzymatic plastics depolymerization in moist-solid reaction mixtures

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Due to their durability, low weight, versatility and low production cost, plastics have replaced natural materials in many areas and have become essential to modern technology and society, with the most common plastics including polyethylene, polypropylene, polyethylene terephthalate (PET), polystyrene (PS), polycarbonate (PC), polyvinyl chloride, and polyurethane (PUR). The global production of plastics has continuously soared, reaching 317 M tonnes in 2015. In Canada, <9% of all plastics is recycled and ~75% finds its way in the environment, imperilling both marine and terrestrial ecosystems. Whereas PET - a plastic widely used in packaging, bottles and textile - is one of the rare plastics to be considered recyclable, in reality it is mostlydowncycled for re-use as lower-grade products, e.g. from bottles to carpets, after which it cannot be recycled anymore. Moreover, recycling PET back into food-grade products is challenging, requiring harsh chemicals, elevated temperatures and high pressures.We have invented an environment-friendly process, based on enzymes from nature instead of harsh chemicals, for the breakdown of PET plastics. Several enzymes capable of depolymerizing low crystallinity PET have been reported; however, they are inactive towards highly crystalline forms of PET typically found in consumerproducts. Remarkably, our innovative process is not only more efficient, but also enables the depolymerization of high crystallinity PET. Our technology consists of using enzymes in moist-solid reaction mixtures instead of the typical aqueous solutions or slurries. Because it does not use any harsh chemicals, organic or aqueous solvents, and avoids the need for high temperatures and pressures, our process minimizes the production of waste and energy consumption. Our moist-solid reaction mixtures are easier to handle than viscous solutions or suspensions, and only require gentle, intermittent mechanical mixing. We propose here to optimize our PETdepolymerization process and adapt it to other polyesters, PC, PS and PUR plastics. Importantly, the proposed research will offer a solution for recycling plastic waste directly to new plastics or other commodity chemicals.