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1. Chlorinated Plastics Offer Unique Opportunities and Challenges in Upcycling

   https://doi.org/10.1002/pi.6621  

   Al Alshaikh, Ali ; Bara, Jason E. ( February 2024 , Polymer International)

   Chlorinated plastics are part of the everyday lives of consumers and producers alike. They can be found in buildings, automobiles, fashion, packaging, and many other places. This prevalence makes them a considerable part of the plastic waste crisis. Interest in “upcycling” (as opposed to recycling) has grown recently to augment the possibilities of managing plastic waste. The advances made in plastic upcycling have focused on polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) while chlorinated plastics, chiefly polyvinyl chloride (PVC), have received much less attention. The release of chlorine‐containing molecules during treatment of chlorinated plastic greatly complicates cross‐method upcycling, or even the treatment of plastic mixes containing chlorinated plastics. This review presents a case for extracting value from chlorinated plastics by highlighting appealing upcycling products made owing to, or despite, the C‐Cl bond via depolymerization, carbonization and modification.

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2. Cascade degradation and upcycling of polystyrene waste to high-value chemicals

   https://doi.org/10.1073/pnas.2203346119  

   Xu, Zhen ; Pan, Fuping ; Sun, Mengqi ; Xu, Jianjun ; Munyaneza, Nuwayo Eric ; Croft, Zacary L. ; Cai, Gangshu ; Liu, Guoliang ( August 2022 , Proceedings of the National Academy of Sciences)

   Plastic waste represents one of the most urgent environmental challenges facing humankind. Upcycling has been proposed to solve the low profitability and high market sensitivity of known recycling methods. Existing upcycling methods operate under energy-intense conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. Herein, we report a tandem degradation-upcycling strategy to exploit high-value chemicals from polystyrene (PS) waste with high selectivity. We first degrade PS waste to aromatics using ultraviolet (UV) light and then valorize the intermediate to diphenylmethane. Low-cost AlCl 3 catalyzes both the reactions of degradation and upcycling at ambient temperatures under atmospheric pressure. The degraded intermediates can advantageously serve as solvents for processing the solid plastic wastes, forming a self-sustainable circuitry. The low-value-input and high-value-output approach is thus substantially more sustainable and economically viable than conventional thermal processes, which operate at high-temperature, high-pressure conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. The cascade strategy is resilient to impurities from plastic waste streams and is generalizable to other high-value chemicals (e.g., benzophenone, 1,2-diphenylethane, and 4-phenyl-4-oxo butyric acid). The upcycling to diphenylmethane was tested at 1-kg laboratory scale and attested by industrial-scale techno-economic analysis, demonstrating sustainability and economic viability without government subsidies or tax credits. 

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3. A Generic Platform for Upcycling Polystyrene to Aryl Ketones and Organosulfur Compounds

   https://doi.org/10.1002/ange.202307042  

   Munyaneza, Nuwayo Eric ; Posada, Carlos ; Xu, Zhen ; De Altin Popiolek, Vincenzo ; Paddock, Griffin ; McKee, Charles ; Liu, Guoliang ( July 2023 , Angewandte Chemie)

   Polystyrene (PS) is one of the least recycled large‐volume commodity plastics due to bulkiness of foam products and associated contaminants. PS recycling is also severely hampered by the lack of financial incentive, limited versatility, and poor selectivity of existing methods. To this end, herein we report a thermochemical recycling strategy of “degradation‐upcycling” to synthesize a library of high‐value aromatic chemicals from PS wastes with high versatility and selectivity. Two cascade reactions are selected to first degrade PS to benzene under mild temperatures, followed by the derivatization thereof utilizing a variety of acyl/alkyl and sulfinyl chloride additives. To demonstrate the versatility, nine ketones and sulfides of cosmetic and pharmaceutical relevance were prepared, including propiophenone, benzophenone, and diphenyl sulfide. The approach is also amenable to sophisticated upcycling reaction designs and can produce desired products stepwise. The facile and versatile approach will provide a scalable and profitable methodology for upcycling PS waste into value‐added chemicals.

    

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4. A Generic Platform for Upcycling Polystyrene to Aryl Ketones and Organosulfur Compounds

   https://doi.org/10.1002/anie.202307042  

   Munyaneza, Nuwayo Eric ; Posada, Carlos ; Xu, Zhen ; De Altin Popiolek, Vincenzo ; Paddock, Griffin ; McKee, Charles ; Liu, Guoliang ( July 2023 , Angewandte Chemie International Edition)

   Polystyrene (PS) is one of the least recycled large‐volume commodity plastics due to bulkiness of foam products and associated contaminants. PS recycling is also severely hampered by the lack of financial incentive, limited versatility, and poor selectivity of existing methods. To this end, herein we report a thermochemical recycling strategy of “degradation‐upcycling” to synthesize a library of high‐value aromatic chemicals from PS wastes with high versatility and selectivity. Two cascade reactions are selected to first degrade PS to benzene under mild temperatures, followed by the derivatization thereof utilizing a variety of acyl/alkyl and sulfinyl chloride additives. To demonstrate the versatility, nine ketones and sulfides of cosmetic and pharmaceutical relevance were prepared, including propiophenone, benzophenone, and diphenyl sulfide. The approach is also amenable to sophisticated upcycling reaction designs and can produce desired products stepwise. The facile and versatile approach will provide a scalable and profitable methodology for upcycling PS waste into value‐added chemicals.

    

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5. Two-step conversion of polyethylene into recombinant proteins using a microbial platform

   https://doi.org/10.1186/s12934-023-02220-0  

   Connor, Alexander ; Lamb, Jessica V. ; Delferro, Massimiliano ; Koffas, Mattheos ; Zha, R. Helen ( October 2023 , Microbial Cell Factories)

   The increasing prevalence of plastic waste combined with the inefficiencies of mechanical recycling has inspired interest in processes that can convert these waste streams into value-added biomaterials. To date, the microbial conversion of plastic substrates into biomaterials has been predominantly limited to polyhydroxyalkanoates production. Expanding the capabilities of these microbial conversion platforms to include a greater diversity of products generated from plastic waste streams can serve to promote the adoption of these technologies at a larger scale and encourage a more sustainable materials economy.

   Herein, we report the development of a new strain ofPseudomonasbacteria capable of converting depolymerized polyethylene into high value bespoke recombinant protein products. Using hexadecane, a proxy for depolymerized polyethylene, as a sole carbon nutrient source, we optimized media compositions that facilitate robust biomass growth above 1 × 10⁹ cfu/ml, with results suggesting the benefits of lower hydrocarbon concentrations and the use of NH₄Cl as a nitrogen source. We genomically integrated recombinant genes for green fluorescent protein and spider dragline-inspired silk protein, and we showed their expression inPseudomonas aeruginosa, reaching titers of approximately 10 mg/L when hexadecane was used as the sole carbon source. Lastly, we demonstrated that chemically depolymerized polyethylene, comprised of a mixture of branched and unbranched alkanes, could be converted into silk protein byPseudomonas aeruginosaat titers of 11.3 ± 1.1 mg/L.

   This work demonstrates a microbial platform for the conversion of a both alkanes and plastic-derived substrates to recombinant, protein-based materials. The findings in this work can serve as a basis for future endeavors seeking to upcycle recalcitrant plastic wastes into value-added recombinant proteins.

    

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