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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. Single‐stage chemical recycling of plastic waste to yield durable composites via a tandem transesterification‐thiocracking process

   https://doi.org/10.1002/pol.20220686  

   Maladeniya, Charini P. ; Tennyson, Andrew G. ; Smith, Rhett C. ( February 2023 , Journal of Polymer Science)

   Environmental contamination by plastic waste is a growing threat to the environment and human health. Unfortunately, most post‐consumer plastics are still disposed of in landfills, even plastics that could be easily recycled via simple chemical processes. This disconnect between technology and implementation is partly due to the economic barrier posed by multi‐step processes that convert plastic waste into commodity goods. There is an urgent need for green methods to convert plastic waste directly into marketable commodities via simple processes. Herein we report a simple, single‐stage process to chemically recycle poly(ethylene terephthalate) (PET) to yield composites having thermal and mechanical properties that are competitive with commercial structural materials like Portland cement. In this protocol, a mixture of PET and geraniol are heated with elemental sulfur. In this process, transesterification between geraniol and PET with concomitant thiocracking of the PET backbone leads to the formation of a highly‐crosslinked sulfur–PET–geraniol (SPG) network composite. The composite exhibited compressive strength (23.1 MPa) greater than that required for Portland cement to be used in building foundations. This new, single‐stage chemical recycling strategy thus employs a bio‐olefin and waste sulfur to convert PET waste into a durable composite that could serve as a sustainable alternative to traditional cements.

    

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3. C–H Functionalization of Polyolefins to Access Reprocessable Polyolefin Thermosets

   https://doi.org/10.1021/jacs.3c08682  

   Neidhart, Eliza K ; Hua, Mutian ; Peng, Zhengxing ; Kearney, Logan T ; Bhat, Vittal ; Vashahi, Foad ; Alexanian, Erik J ; Sheiko, Sergei S ; Wang, Cheng ; Helms, Brett A ; et al ( December 2023 , Journal of the American Chemical Society)

   Upcycling plastic waste into reprocessable materials with performance-advantaged properties would contribute to the development of a circular plastics economy. Here, we modify branched polyolefins and postconsumer polyethylene through a versatile C−H functionalization approach using thiosulfonates as a privileged radical group transfer functionality. Cross-linking the functionalized polyolefins with polytopic amines provided dynamically cross-linked polyolefin networks enabled by associative bond exchange of diketoenamine functionality. A combination of resonant soft X-ray scattering and grazing incidence X-ray scattering revealed hierarchical phase morphology in which diketoenamine-rich microdomains phase-separate within amorphous regions between polyolefin crystallites. The combination of dynamic covalent cross-links and microphase separation results in useful and improved mechanical properties, including a ∼4.5-fold increase in toughness, a reduction in creep deformation at temperatures relevant to use, and high-temperature structural stability compared to the parent polyolefin. The dynamic nature of diketoenamine cross-links provides stress relaxation at elevated temperatures, which enabled iterative reprocessing of the dynamic covalent polymer network with little cycle-to-cycle property fade. The ability to convert polyolefin waste into a reprocessable thermoformable material with attractive thermomechanical properties provides additional optionality for upcycling to enable future circularity. 

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4. Microbial Consortia and Mixed Plastic Waste: Pangenomic Analysis Reveals Potential for Degradation of Multiple Plastic Types via Previously Identified PET Degrading Bacteria

   https://doi.org/https://doi.org/10.3390/ijms23105612  

   Sabrina Edwards ; Rosa León-Zayas ; Riyaz Ditter ; Helen Laster ; Grace Sheehan ; Oliver Anderson ; Toby Beattie ; Jay L. Mellies ( April 2022 , International journal of molecular sciences)

   The global utilization of single-use, non-biodegradable plastics, such as bottles made of polyethylene terephthalate (PET), has contributed to catastrophic levels of plastic pollution. Fortu- nately, microbial communities are adapting to assimilate plastic waste. Previously, our work showed a full consortium of five bacteria capable of synergistically degrading PET. Using omics approaches, we identified the key genes implicated in PET degradation within the consortium’s pangenome and transcriptome. This analysis led to the discovery of a novel PETase, EstB, which has been observed to hydrolyze the oligomer BHET and the polymer PET. Besides the genes implicated in PET degradation, many other biodegradation genes were discovered. Over 200 plastic and plasticizer degradation-related genes were discovered through the Plastic Microbial Biodegradation Database (PMBD). Diverse carbon source utilization was observed by a microbial community-based assay, which, paired with an abundant number of plastic- and plasticizer-degrading enzymes, indicates a promising possibility for mixed plastic degradation. Using RNAseq differential analysis, several genes were predicted to be involved in PET degradation, including aldehyde dehydrogenases and several classes of hydrolases. Active transcription of PET monomer metabolism was also observed, including the generation of polyhydroxyalkanoate (PHA)/polyhydroxybutyrate (PHB) biopolymers. These results present an exciting opportunity for the bio-recycling of mixed plastic waste with upcycling potential. 

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5. The Effect of Elastomer Content and Annealing on the Physical Properties of Upcycled Polyethylene Terephthalate-Maleated Styrene Ethylene Butylene Styrene Blends for Additive Manufacturing

   https://doi.org/10.3390/ma17246272  

   Bermudez, Diego ; Moreno, Stephanie ; Roberson, David A ( December 2024 , Materials)

   Santagata, Antonio (Ed.)

   In the work presented here, we explore the upcycling of polyethylene terephthalate (PET) that was derived from water bottles. The material was granulated and extruded into a filament compatible with fused filament fabrication (FFF) additive manufacturing platforms. Three iterations of PET combined with a thermoplastic elastomer, styrene ethylene butylene styrene with a maleic anhydride graft (SEBS-g-MA), were made with 5, 10, and 20% by mass elastomer content. The elastomer and specific mass percentages were chosen based on prior successes involving acrylonitrile butadiene styrene (ABS), in which the maleic anhydride graft enabled compatibility between different materials. The rheological properties of PET and the PET/SEBS blends were characterized by the melt flow index and dynamic mechanical analysis. The addition of SEBS-g-MA did not have a significant impact on mechanical properties, as determined by tensile and impact testing, where all test specimens were manufactured by FFF. Delamination of the tensile specimens convoluted the ability to discern differences in the mechanical properties, particularly % elongation. Annealing of the specimens enabled the observation of the effect of elastomer content on the mechanical properties, particularly in the case of impact testing, where the impact strength increased with the increase in SEBS content. However, annealing led to shrinkage of the specimens, detracting from the realized benefits of the thermal process. Scanning electron microscopy of spent tensile specimens revealed that, in the non-annealed condition, SEBS formed nodules that would detach from the PET matrix during the tensile test, indicating that a robust bond was not present. The addition of SEBS-g-MA did allow for shape memory property characterization, where deformation of tensile specimens occurred at room temperature. Specimens from the 20% by mass elastomer content sample group exhibited a shape fixation ratio on the order of 99% and a shape recovery ratio on the order of 80%. This work demonstrates a potential waste reduction strategy to tackle the problem of polymer waste by upcycling discarded plastic into a feedstock material for additive manufacturing with shape memory properties.

    

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