Critical advances and future opportunities in upcycling commodity polymers

Polystyrene nanoplastics reshape the peatland plants (Sphagnum) bacteriome under simulated wet-deposition pathway: Insights into unequal impact of ecological niches

Nanoplastics (NPs) enter peatlands through atmospheric deposition, yet their effects on Sphagnum bacterial communities (SBCs) and plant-self remain unknown. We hypothesize that NPs alter the composition, structure, and co-occurrence pattern of epiphytes (Epi) and endophytes (En), thereby differentially affecting the growth and physiological performance of Sphagnum. The 30-day simulated wet deposition experiment was conducted to test this. Here, polystyrene NPs reduced the α-diversity of SBCs, unevenly reshaped the structure of Epi and En. Mfuzz clustering was used to reveal the co-abundance behavior of SBCs, and the null model found SBCs relied on stochastic assembly, formed stable Epi molecular ecological network (MEN) and connected En MEN. NPs disrupted symbiosis of SBCs, with high-abundance phyla reductions impacting MENs and low-abundance phyla affecting the inter-domain ecological network (IDEN) between Epi and En. Increasingly positive NPs (from carboxyl-modified to unmodified, and then to amino-modified NPs) further decreased SBCs abundance. Key clusters of Proteobacteria (Pro.), with α-Pro. and γ-Pro. as module hubs of MENs, and β-Pro. as a network hub in the IDEN, could reflect these changes. Additionally, NPs lowered plant spread area (P < 0.05) and chlorophyll content (P < 0.01), but the reduction in biomass was not significant. Structural equation modeling showed reduced SBCs α-diversity alleviated the NPs phytotoxicity (up to 33.31 % offset), as genetic analysis revealed that methane oxidation, carbon fixation, and trace element metabolism may upregulate plant nutrient supply. Our findings offer critical insights into NPs deposition risks in remote areas and highlight the responses of plant-bacteriome symbiosis.

Influence of different food matrices on the abundance, characterization, migration kinetics and hazards of microplastics released from plastic packaging (PP and PET)

The effect of food matrix on the release of microplastics from plastic packaging was investigated by treating plastic samples with various food simulants. MPs were released during simulated conditions, and their main source was the separation of plastic samples subjected to ageing. Acidic high oil simulants resulted in the greatest abundance of MPs (1311.33 ± 262.22 and 1414.00 ± 214.52 items/piece). Dual constant kinetic model and Elovich kinetic model described the process well (R2 > 0.9019), indicating the release rate of MPs was mainly controlled by characteristics of plastics and environment. Characterization showed the morphology of plastics became rougher, carbonyl index increased, crystalline shapes changed and proportion of O increased. The release mechanism was deduced to be deterioration of the plastic by oxidative reactions. Finally, hazard assessment methodologies were developed, the results showed these MPs are hazardous to humans. It is hoped that this study will draw more attention to the harmful effects of MPs.

Two Swords Combined: The organic-inorganic hybridized PdMn bimetallenes for waste plastic upgrading

The electroreforming of ethylene glycol (EG) derived from polyethylene terephthalate (PET) to prepare rewarding chemicals is an ideal solution to solve serious plastic pollution. A wet chemical method is used to synthesize organic-inorganic hybridized PdMn bimetallenes (PdMn O-BMs) catalyst. The PdMn O-BMs catalyst have a rich curled structure of nanosheets. The structural regulation of organic-inorganic hybrid significantly affects the adsorption energy of the reaction intermediates, thus improving the catalytic activity of the catalyst. PdMn O-BMs demonstrated superior performance compared to PdMn bimetallenes in the PET hydrolysate. This unique organic-inorganic hybrid nanostructure can effectively convert PET-derived EG into high-value products, such as glycolic acid (GA) and formate. This research not only unfolds a prospective strategy for the catalysts modified by organic ligand, but also brings about a new opportunity for the transformation of PET derivatives into high-value products.

Shell-like Ni(OH)2 loaded with Pd nanoparticle catalyst mediated efficient electrocatalytic upcycling of polyethylene terephthalate plastics to glycolic acid

Electrochemical techniques offer a promising approach to achieving plastic waste recycling, particularly to address plastic pollution problems. In this study, we developed a novel Pd/Ni(OH)2/NF electrocatalyst. with efficient interfacial electron transfer capability in the conversion of ethylene glycol (EG) to high-value-added glycolic acid (GA) from the hydrolyzed product of polyethylene terephthalate (PET) plastics. This Pd/Ni(OH)2/NF electrocatalyst demonstrated low overpotentials of 0.53 V and 0.79 V vs. RHE and achieved current densities of 10 mA cm-2 and 100 mA cm-2, respectively. Notably, Pd/Ni(OH)2/NF electrocatalyst can efficiently produce value-added glycolic acid over a wide potential range (0.9 V-1.3 V), with a maximum Faraday efficiency rate of 94.2 %. The low overpotential and high efficiency of Pd/Ni(OH)2/NF is attributed to the strong electronic interaction at the Pd/Ni(OH)2 interface, which enhances the catalytic conversion of the ethylene glycol. Density functional theory (DFT) calculations provide further theoretical insights into the transformation mechanisms. Additionally, the catalyst demonstrated stable electrocatalytic performance for 100 h in an anion-exchange membrane (AEM) flow reactor at a current density of 100 mA cm-2. This study presents a novel electrocatalyst and viable electrochemical pathway for upgrading PET plastic waste into valuable products.

Sustainable, tough, and water-resistant cellulose-based straws via hierarchical fiber networks and Fe3+ cross-linking

The wide use of plastic straws has posed a persistent environmental challenge, which promotes the development of sustainable alternatives. In this work, inspired by the hierarchical structures of natural materials, we reported a facile approach to prepare straws with high toughness and good water resistance from microscale and nanoscale cellulose fibers. Pulp fibers from rice stalk were treated to prepare cellulose microfibers (CMF) and cellulose nanofibers (CNF), which were hybridized to form a film and roll up for straws. The straws prepared from both micro- and nano- fibers in ratio of 2:3 (CMF:CNF) show the best overall performance in terms of tensile strength (104.5 MPa), toughness (12.6 MJ/m3) and elongation at break (17.0 %). Besides, the straws further cross-linked with Fe3+ to enhance the network bindings between hierarchical cellulose fibers and effectively improve the water resistance. The ionic cross-linking treatment with 50 mM Fe3+ for 2 h resulted in the straws with a water contact angle of ∼126°. The obtained straws can completely disintegrate in natural soil within 45 days. These cellulose-based straws are fully in line with the concept of environmental and ecological sustainability.

Imino-Pyrrole Zn(II) Complexes for the Rapid and Selective Chemical Recycling of Commodity Polymers

Three imino-pyrrole zinc complexes were prepared and applied to the rapid degradation of polylactic acid (PLA) and the depolymerization of bisphenol A polycarbonate (BPA-PC) and polyethylene terephthalate (PET). PLA alcoholysis proceeded rapidly at a range of conditions, including reflux in air. Remarkable activity was demonstrated for the solvent-free methanolysis of PLA at mild conditions with full conversion reached in 11 min at 80 °C. Various conditions were investigated including a range of PLA sources and, importantly, catalyst recycling was demonstrated. The methanolysis of BPA-PC and the glycolysis of PET were achieved, the latter giving full conversion after 1.5 h for all catalysts. The chemical recycling of mixed plastic feedstocks was investigated, including the selective and sequential degradation of a PLA/BPA-PC mixture with a single catalyst and solvent.

Synergy between multi-components and Ir dopant in Ir-doped high-entropy alloy nanoparticles for efficient and robust ethylene glycol electro-oxidation at an industrial-level current

Electrochemical oxidation of crude ethylene glycol (EG) to commodity chemicals and H2, powered by renewables energy, is a sustainable and promising strategy for upcycling the end-of-life polyethylene terephthalate (PET) wastes. Pt/Pd group noble metals are deemed as state-of-the-art catalysts for the EG electro-oxidation reaction (EGOR). However, these catalysts suffer from high affinity of the carbonyl intermediates, which consequently results in poisoning of active sites and poor electrochemical stability. Herein, we designed and synthesized small-sized PdPtAuNiCu and Ir-doped PdPtAuNiCu high-entropy alloy nanoparticles (abbreviated as PdPtAuNiCu and Ir-PdPtAuNiCu HEANs, respectively) via a wet chemical method. Benefiting from the multisite synergy and Ir dopant, the as-synthesized Ir-PdPtAuNiCu HEANs achieved selective and robust EGOR to glycolate (GA) in alkaline medium with a high mass activity of 2.41 A mg-1 at 0.724 V versus reversible hydrogen electrode (vs. RHE) and a glycolate Faradaic efficiency (FEGA) of 88.8%. In a home-made membrane-free flow electrolyzer assembled with this bifunctional catalyst [(-)PdPtAuNiCu∥Ir-PdPtAuNiCu(+)], ultra-stable EGOR was realized beyond 1200 h at an industrial-level current density of >300 mA cm-2 under a low voltage of 0.724 V. These findings provide a new paradigm for designing efficient and robust EGOR catalysts that can supersede other electrocatalysts for practical applications.

Fluoropolymer Composites from Partially Perfluoroalkylated Waste Polyethylene

Chemically modified plastics have emerged as practical solutions to plastic waste increases. The inherent novelty of decorating polymer chains with chemical functionality results in distinct properties that expand the available application space. Nevertheless, developing designer materials for specific applications beyond compatibilization or mild property enhancement is difficult due to the synergistic effects of both the polar functionality imparted and the parent materials' intrinsic properties. By incorporating perfluoro-alkyl side-chains onto the backbone of dehydrogenated waste HDPE, unique surface properties intermediate between polytetrafluoroethylene (PTFE, the model fluoropolymer) and HDPE become apparent, while the overall material mechanical and thermal properties result in more LLDPE-like materials. This is demonstrated through moderate decreases in the surface free energy of the perfluoroalkylated polyolefin surface (increase in H2O contact angle of ∼6°) and increased ordering under shear when blended with PTFE nanoparticles where the crossover point occurred at higher strains. Critically, perfluoroalkylated HDPE possesses improved rheological modification properties at elevated temperatures with PTFE nanoparticles, resulting in more thermally robust and stable composite materials.

Bulk Depolymerization of Polystyrene with Comonomer Radical Triggers

This study introduces a novel approach to depolymerize polystyrene in the absence of solvent at significantly reduced temperatures through the incorporation of a thermally labile comonomer. Specifically, we employ N-(methacryloxy)phthalimide (PhthMA) as a comonomer with an activated ester capable of thermally triggered decarboxylation. Thermal treatment enables the generation of backbone radicals that promote β-scission and subsequent unzipping. These polystyrene analogs depolymerize with up to 91% reversion to monomer in under 2 h at temperatures significantly lower than those required for conventional polystyrene. As compared to depolymerization triggered by decarboxylation at the ω-chain end, this pendent-group approach was considerably more efficient. The recovered styrene monomer from the bulk depolymerization of poly(styrene-co-PhthMA) copolymers can undergo direct repolymerization, yielding new styrenic materials. This comonomer strategy extends across various styrenic copolymers, highlighting its potential as a broadly applicable method for initiating depolymerization among vinyl polymer classes.

Crosslinking 1,4-polybutadiene via allylic amination: a new strategy for deconstructable rubbers

As post-consumer rubbers (e.g., car tires) continue to accumulate in landfills and the environment, there is an increasing need for more reprocessible materials. Traditionally, devulcanization of rubbers requires excessive energy and releases toxic byproducts. Accordingly, downcycling (e.g., crumb rubber for asphalt or turf) is the major avenue for end-of-life thermoset elastomers. To enable alternative recycling pathways, herein we propose a two-step procedure to crosslink polybutadiene (PBD) as a substitute for vulcanization, resulting in deconstructable soft materials. First, we utilize the established C-H allylic amination of PBD to access thermoplastic elastomer pre-polymers functionalized with electrophilic hexafluoroisopropyl sulfamate (PBD-HFIPS). Then, PBD-HFIPS alcoholysis with diol crosslinkers yields thermoset specimens with tunable thermal, rheological, and mechanical properties dependent on crosslinker identity and density. Finally, treating these thermosets with a nucleophile cleaves sulfamate crosslinks and regenerates the thermoplastic with no characterizable differences from virgin PBD.

Atomic Cu-O-Zr Sites for Highly Selective Production of p-xylene from Tandem Upcycling of PET and CO2

Exploring an efficient catalytic system for tandem upcycling of CO2 and polyethylene terephthalate (PET) is highly desirable for achieving efficient resource utilization of wastes. However, the high activation energy for C═O bonds (in both PET and CO2) and the difficulty in regulating the reaction pathways restricted PET recovery efficiency. Here, we demonstrated the rational design of a single-atom Cu catalyst for precisely catalyzing the hydrogenation of CO2 to methanol and tandem PET upcycling to ethylene glycol (EG) and p-xylene (PX). In the Cu/UiO-66-NH2-A catalyst, Cu atoms are selectively anchored to the Zr-oxo nodes of UiO-66-NH2 to form Cu-O-Zr sites. The Cu-O-Zr sites can effectively activate both CO2 and H2 by reducing the activation energy and accelerate the transformation of PET to dimethyl terephthalate (DMT), which is further hydro-deoxygenated to yield PX. As a result, 20.4% CO2 conversion was obtained within 36 h, with 89.5% and 92.1% yields of PX and EG, respectively. Rapid and precise hydrogen spillover from Cu atoms to adsorbed reactants/intermediates at the Cu-O-Zr sites also drives the reaction process.

Polyethylene Upcycling to Liquid Alkanes in Molten Salts under Neat and External Hydrogen Source-Free Conditions

Development of facile approaches to convert plastic waste into liquid fuels under neat conditions is highly desired but challenging, particularly without noble metal catalysts and an external hydrogen source. Herein, highly efficient and selective polyethylene-to-gasoline oil (branched C6-C12 alkanes) conversion was achieved under mild conditions (<170 °C) using commercially available AlCl3-containing molten salts as reaction media and to provide catalytic sites (no extra solvents, additives, or hydrogen feeding). The high catalytic efficiency and selectivity was ensured by the abundant active Al sites with strong Lewis acidity (comparable to the Al type in acidic zeolite) and highly ionic nature of the molten salts to stabilize the carbenium intermediates. Dynamic genesis of the Al sites was elucidated via time-resolved Al K-edge soft X-ray and 27Al NMR, confirming the tricoordinated Al3+ as active sites and its coordination with the as-generated alkene/aromatic intermediates. The carbenium formation and polyethylene chain variation was illustrated by inelastic neutron scattering (INS) and an isotope-labeling experiment. Theoretical simulations further demonstrated the successive hydride abstraction, β-scission, isomerization, and internal hydrogen transfer reaction pathway with AlCl3 as active sites. This facile catalytic system can further achieve the conversion of robust, densely assembled, and high molecular weight plastic model compounds to liquid alkane products in the diesel range.

Toward Circular Polymer Materials and Manufacturing: Dynamic Bonding Strategies for Upcycling Thermoplastics and Thermosets

The global production of plastics has reached unprecedented levels, with <10% being recycled and even fewer recycled more than once. This lack of circularity poses critical environmental threats. However, upcycling-recycling materials while improving their properties and functionality-through dynamic bonding strategies offers a promising approach to enhancing polymer sustainability. Dynamic bonds enable polymeric structures to reconfigure under specific conditions, improving thermal, chemical, and mechanical resilience and controllability while facilitating recyclability. This review specifically takes the viewpoint of upcycling existing thermoplastics and thermosets to develop sustainable dynamic covalent networks (DCNs). Integrating these DCN upcycling strategies into the design of additive manufacturing (AM) feedstocks creates unique benefits compared to traditional polymer systems. This approach is briefly highlighted in extrusion-based and light-based AM, assessing the potential for improved material processability, recyclability, and the creation of high-value customized products. The combination of upcycling technologies and AM techniques presents a significant opportunity to advance sustainability in macromolecular science.

Product Oriented Upcycling of Waste Polyethylene Terephthalate Plastic and Carbon Dioxide via Decoupled Electrolysis

End-of-life plastics and carbon dioxide (CO2) are anthropogenic waste carbon resources; it is imperative to develop efficient technologies to convert them to value-added products. Here we report the upcycling of polyethylene terephthalate (PET) plastic and CO2 toward valuable potassium diformate, terephthalic acid, and H2 fuel via decoupled electrolysis. This product-oriented process is realized by two electrolyzers: (1) a solid-state-electrolyte based CO2 electrolyzer and (2) a solid-polymer-electrolyte-based PET electrolyzer. Using a bismuth-based catalyst, the CO2 electrolyzer showed more than 140 h continuous operation at current of 250 mA, resulting in 850 mL pure HCOOH solution with a concentration of 683 mM. Furthermore, we constructed a solid-polymer-electrolyte electrolyzer with an electrode area of 50 cm2 for the electrooxidation of ethylene glycol to formate, achieving 30 A of current at ~1.9 V cell voltage and 80 % formate Faradaic efficiency. With this electrolyzer, we demonstrated the efficient transformation of PET hydrolysate to a mixture of terephthalate and formate. Additionally, combining CO2 derived HCOOH and PET electrolyte, we obtained recycled terephthalic acid and potassium diformate. This work provides an integrated strategy for the valorization of waste carbon resources with less using external resources.

Electrooxidation of Ethylene Glycol to Glycolic Acid with Pt-Ni(OH)2 Catalysts: High Efficiency and Selectivity for PET Plastics Upgrading

The electroconversion of polyethylene terephthalate (PET) into C2 fine chemicals and hydrogen (H2) presents a promising solution for advancing the circular plastics economy. In this study, we report the electrooxidation of ethylene glycol (EG) to glycolic acid (GA) using a Pt-Ni(OH)2 catalyst, achieving a high Faraday efficiency (>90 %) even at high current densities (250 mA cm-2 at 0.8 V vs. RHE). Notably, this catalyst outperforms most existing Pt-based catalysts in terms of catalytic activity. Experimental analyses reveal that: 1) Ni(OH)2 enhances the adsorption of OH- ions and promotes the rapid generation of *OH active species, which are essential for the efficient oxidation of EG to GA; 2) the oxygenophilic nature of Pt improves EG adsorption, and in synergy with Ni, accelerates the oxidation process. Furthermore, Pt lowers the electrolysis potential, preventing excessive oxidation and ensuring high selectivity for GA. This work offers a promising pathway for the electrooxidation-based upgrading of PET plastics and provides valuable insights for future research in this area.

Full Recovery of Epoxy Resin Wastes into Bisphenol A and Epoxy Monomers via Lewis Acid

Epoxy resins (EPs) are important thermosetting plastics and difficult to recycle because of their stable cross-linked structure. In this study, we report a full recovery strategy for the conversion of EPs into high-value platform compounds, i.e., bisphenol A (BPA) and epoxy monomers such as 4,4'-methylenebis (N,N'-diglycidylaniline) (AG80), which involves the selective breaking of the C(sp3)─O bond using commercially available boron trichloride (BCl3), the reconstruction of the broken C(sp3)─N bond and the cyclization of the hydroxy groups. The yield of BPA is 93 wt% with a purity of 99%, and the yield of AG80 is 96 wt% with an epoxy value of 0.43. 100% recovery of EP elements was achieved theoretically, and the actual mass recovery of the EPs is as high as 91%. Because of its versatility, simplicity of operation, mild reaction conditions, and recyclability of all solvents and by-products, this approach shows the potential in solving the current recycling challenges associated with EP waste.

Repurposing Post-Consumer Polyethylene to Access Cross-Linked Polyethylene with Reprocessability, Recyclability, and Tunable Properties

Polyethylene (PE) is the most widely produced plastic but accumulation and resistance to degradation has significantly contributed to the plastic waste crisis. Upcycling has presented promising solutions to transform PE waste into value-added products. In this study, mixed post-consumer PE was successfully repurposed into reprocessable and chemically recyclable cross-linked polyethylene (XLPE). This process involved converting PE into telechelic oligomers, followed by repolymerization using a hybrid cross-linking system consisting of a dynamic cross-linker 2,4,6-triethoxy-1,3,5-triazine (TETA) and non-dynamic cross-linker tris(6-isocyanatohexyl)isocyanurate (Tri-HDI). In the resulting XLPE, TETA facilitated iterative reprocessing with minimal property degradation across cycles, whereas Tri-HDI helped preserve functional performance throughout service life. Compared to PE, XLPE exhibited enhanced mechanical properties, reduced creep deformation under application-relevant temperatures, and high temperature structural stability. Notably, copolymerizing PE oligomers with commercial macrodiols was employed to create composite XLPEs, enabling tuning material properties. After use, XLPE can be efficiently and selectively depolymerized under mild conditions, even when mixed with commercial insulator cables. This depolymerization allows for the recovery of the constituent building blocks, enabling purification and subsequent repolymerization for reuse. This approach demonstrates the potential of repurposing plastic waste into sustainable materials and fostering the development of a circular economy.

Organocatalytic Condensation Polymerization for Synthesis of High Performance Aliphatic Polycarbonate

Aliphatic polycarbonate (APC) with long alkyl segments has received much attention for its biodegradability and biocompatibility. However, owing to its low molecular weight, it usually exhibits poor mechanical properties limiting its application. Here,a novel two-step condensation polymerization procedure by using an organic catalyst (t-BuP2) to synthesize high molecular weight APC is presented. The introduction of branching and hydrogen bonding in the polymerization would significantly improve its thermal and mechanical properties. The APC exhibits a melt temperature ≈80 °C, tensile strength of 17.7 ± 0.9 MPa, and impressive elongation at a break of 1136 ± 25%. This study provides a facile procedure to synthesize high-performance APC via condensation polymerization.

Polyolefin Recycling with Binary Cobalt-Nickel Nanosheets

The recycling of polyolefin plastics into value-added chemicals has emerged as a new frontier regarding the current environmental concerns. In this work, it is demonstrated that binary cobalt-nickel nanosheets (Co─Ni NSs) can serve as a non-noble catalyst for recycling polyethylene and polypropylene plastics. Detailed analysis implies that the strong synergy between Co and Ni in binary Co─Ni NSs enables the electron transfer from Ni to Co and enhances adsorption abilities to H2 and C─C chain, realizing the cracking of polyethylene plastic to liquid products with a selectivity of 83.3% at a conversion of >98%. Impressively, such a catalyst can realize the successful recycling of commercial polyolefin wastes into value-added products. Given the enhanced stability, high selectivity to liquid products, and low-cost of Co─Ni NSs, this work provides a feasible strategy for recycling polyolefin plastics, which will attract extensive attention in various fields including catalysis, materials, energy, and beyond.

Vinyl polymers with fully degradable carbon backbones enabled by aromatization-driven C-C bond cleavage

Degradation of carbon-backbone polymers, which make up most plastics, remains a formidable challenge owing to strong and inert main-chain C-C bonds. While incorporation of comonomers that generate backbone radicals under certain conditions can induce degradation of the polymer chain, such strategies yield complex oligomer mixtures. Here we report aromatization-driven C-C bond cleavage as a viable and powerful strategy to endow the degradability into carbon backbones using acrylic polymers as a model example. The key to this new strategy is the efficient, living, alternating addition copolymerization of acrylates with simple, commercially available and biorenewable coumarin using a frustrated Lewis pair cooperative catalyst. The resulting acrylic copolymers are strong, transparent thermoplastics with key thermal, optical, mechanical properties comparable or superior to poly(methyl methacrylate). Under strong base, alternating copolymers can completely degrade at room temperature through efficient cleavage of main-chain C-C bonds utilizing aromatization as a thermodynamic driving force, to generate pure, pharmaceutically valuable molecules, thus affording durable, robust yet fully degradable carbon-backbone acrylic polymers.

Peripheral Designed Indigo Bola-Amphiphiles for Supramolecular Assembled Nanoarchitectonics in Aqueous Media

Indigo, an ancient natural dye, featured excellent biodegradability to advance in sustainable polymer. Indigo amphiphiles can pave a way for sustainable supramolecular polymers in aqueous media for potential biomedical functional materials. However, contemporary indigo amphiphiles supramolecular commonly assemble into low aspect ratio nanostructures, which hampers the macroscopic soft scaffolds fabrications and smart functional material applications. In this study, we report a novel peripheral designed indigo bola-amphiphiles (IBAs), which assemble into high aspect ratio supramolecular nanofibers in aqueous media. By employing a shear-flow assembly technique with bio-abundant calcium ions, IBAs assemble across multiple length scales into supramolecular macroscopic scaffolds. The structural characterizations of IBAs macroscopic soft scaffolds show different supramolecular structural packing information by scanning electron microscope and X-ray scattering/diffraction techniques. Our supramolecular nanoarchitectonic approach indicates the feasibility of using IBAs molecular design to construct supramolecular macroscopic materials with higher structural order for the future smart biofunctional materials and sustainable supramolecular polymer under more environmentally friendly conditions.

Photocatalytic Conversion of Polyester-Derived Alcohol into Value-Added Chemicals by Engineering Atomically Dispersed Pd Catalyst

Photoreforming presents a promising strategy for upcycling waste polyester-derived alcohol into valuable chemicals. However, it remains a great challenge due to its low performance and unsatisfactory selectivity toward high-value C2 products. Here, we report the highly efficient and selective conversion of ethylene glycol (EG, a monomer of polyethylene terephthalate (PET)) to glycolaldehyde using atomically dispersed Pd species supported on TiO2 catalyst. A glycolaldehyde production rate of 5072 μmol gcat -1 h-1 with a selectivity of 90.0 % and long-term durability can be achieved. Experimental and theoretical results show that Pd single atoms can enhance the photocatalytic activity by enriching the photogenerated holes, which are the dominant species for the selective oxidation of EG to glycolaldehyde. More importantly, the adsorption of EG molecules on the catalysts is significantly promoted, which is subsequently transformed into RO⋅ radicals, a crucial intermediate in producing glycolaldehyde. Additionally, Pd single atoms on TiO2 enable the reduction of the glycolaldehyde desorption barrier, thereby facilitating high selectivity and inhibiting further oxidation to C1 products. This work provides new insights into the photocatalytic conversion of polyester wastes by atomic engineering.

Machine Learning for Developing Sustainable Polymers

Sustainable polymers from renewable resources have been gaining importance due to their recyclability and reduced environmental impact. However, their development through conventional trial-and-error methods remains inefficient and resource-intensive. Machine learning (ML) has emerged as a powerful tool in polymer science, enabling rapid prediction, and discovery of new chemicals and materials. In this review, we examine emerging trends in ML applications for sustainable polymer development, focusing on catalyst discovery, property optimization, and new polymer design. We analyze unique challenges in applying ML to sustainable polymers and evaluate proposed solutions, providing insights for future development in this rapidly evolving field.

Tandem ADMET and CAMMP to Access Degradable Thermosets and Multiblock Copolymers

The development of degradable polymers and multiblock copolymeric (MBCP) compatibilizers represents an appealing strategy to address ever-growing concerns for treating waste plastics of traditional chemical degradation or mechanical recycling. Although recent advancements in cyclic-acyclic monomers metathesis polymerization (CAMMP) and tandem olefin metathesis polymerization (TOMP) have recently been reported to produce degradable polymers and MBCPs via copolymerization of cyclic monomers with acyclic diene comonomers, there have been no reports of preparing high-performance thermosetting materials and multiblock copolymers within the same polymerization system solely through the selection of cycloolefin monomers. To achieve this objective, a TOMP system has been designed that combines acyclic diene metathesis (ADMET) polymerization of diene comonomers followed by CAMMP with cyclic olefin monomers (dicyclopentadiene DCPD or cyclooctene COE). The selection of different cyclic olefin monomers provided access to degradable cross-linked thermosets and multiblock copolymers. Notably, this one-pot, two-step process is highly efficient and requires the addition of only one metathesis catalyst.

Metal Synergistic Dual Activation Enables Efficient Transesterification by Multinuclear Titanium Catalyst: Recycling and Upcycling of Polyester Waste

Developing highly efficient and selective catalysts for chemical recycling and upcycling of plastic waste is essential for establishing a sustainable plastics economy and reducing environmental impact. Here, we report a novel tetranuclear titanium catalyst that enables highly efficient transesterification reactions of esters and polyesters. Detailed experimental and computational studies have revealed that a bi-titanium framework facilitates a dual activation mechanism, activating both alcohol and ester simultaneously, thereby significantly enhancing the transesterification process. This catalyst demonstrated exceptionally high activity in the methanolysis of poly(ethylene terephthalate) (PET) with an activity up to 1.9 × 107 gPET molTi -1 h-1 at 0.005 mol% catalyst loading, producing polymerizable dimethyl ester and glycol monomers. Additionally, it effectively catalyzed the re-polymerization of the recovered monomers, yielding the original polyester with high molecular weight and thereby achieving an ideal circular economy for commodity polyesters. Furthermore, this catalyst can also be utilized for the efficient upgrading of PET waste via transesterification with 1,4-butanediol, polybutylene adipate, and poly(tetramethyene ether glycol), yielding engineering plastic, biodegradable polyester, and thermoplastic elastomer, respectively.

Probing the Catalytic Degradation of Unsaturated Polyolefin Materials via Fe-Based Lewis Acids-Initiated Carbonyl-Olefin Metathesis

Degradation and recyclability of polymeric materials, including extensively used polyolefins, are becoming increasingly necessary. Chemically stable saturated polyolefin backbones make their degradation frustratingly challenging. The current effective strategy is to create cleavable defects, e.g., C═C double bonds along the backbone, and subsequently depolymerize them via cross-metathesis reaction with olefins. High-value chemicals or reusable polymeric segments are obtained. This two-step protocol provides operable means for alleviating plastics problems. There are several approaches to introduce unsaturation into a polymer backbone, like dehydrogenation or copolymerization of olefins and conjugated dienes. However, for the second step, to conduct a cross-metathesis reaction, only noble metal catalysts can be used most of the time. Regardless of their limited availability, the fact that these organometallics are unfavorably sensitive to impurities would raise barriers in industrial practices. Herein we employed earth-abundant and inexpensive iron-based Lewis acids to initiate carbonyl-olefin metathesis reactions between ketone/aldehyde reagents and unsaturated polyolefins. After explorations in poly(diene)s and industrial thermoplastic elastomers, we extended this protocol to degrade low-density polyethylene (LDPE). Low-molecular weight PE wax-like products were obtained as useful chemicals. This catalytic degradation system is expected to enable the development of more efficient metathesis strategies to promote degradation of polyolefins and pave sustainable ways for reuse of polymeric materials.

Transformation of Bamboo: From Multiscale Fibers to Robust and Degradable Cellulose-Based Materials for Plastic Substitution

Bamboo is an ideal candidate to replace traditional plastics, reduce environmental pollution, and promote harmony between nature and humanity owing to its rapid growth and renewability. However, achieving arbitrary shape-shifting of bamboo while retaining its high strength and degradability remains challenging. This study uses multiscale interface engineering to transform bamboo into a robust, biodegradable, and moldable bamboo cellulose-based material. First, natural bamboo is deconstructed into cellulose fibers, including macro- and nanofibers. Subsequently, the fibers are constructed into high-performance materials using physical and chemical methods, such as surface charge treatment, ion cross-linking, and dense hydrogen bonding networks. The prepared multiscale bamboo cellulose-based materials exhibit excellent properties, with a high specific strength (≈271.8 kN m kg-1), high impact toughness (≈58 kJ m-2), low thermal expansion coefficient (1.19 × 10-6 K-1), excellent formability and biodegradability, and minimal environmental impacts. These properties are superior to those of current commercial plastics and other biomass-derived structural materials. Furthermore, the mechanical properties of the materials can be customized by adjusting the layup configuration, enabling a transition from anisotropic to isotropic characteristics. This transformation demonstrates the significant potential of bamboo for plastic substitution and advances the development of environmentally friendly materials.

Electrochemical Commodity Polymer Up- and Re-Cycling: Toward Sustainable and Circular Plastic Treatment

The demand for commodity plastics reaches unprecedented dimensions. In contrast to the well-developed plethora of methods for polymer synthesis, sustainable strategies for the end-of-life management of plastics continue to be scarce. While mechanical re-cycling often results in downgraded materials, chemical re-cycling or up-cycling offers tremendous potential for an efficient and green approach, thereby addressing the precarious treatment of post-use plastics within a circular carbon economy. Recently, electrochemistry surfaced as a uniquely powerful tool for polymer up-cycling via polymer functionalization or degradation obtaining either novel polymers with valorized properties or high-value recycled small molecules, respectively. While discussing recent progress in that domain, future perspectives of electrochemical polymer modifications until January 2025 are outlined herein.

Polymer Chain Modification via HAT Chemistry and Its Application in Graft Copolymer Synthesis

Hydrogen atom transfer (HAT) chemistry has emerged as a powerful tool for selective molecular functionalization, with significant applications in the pharmaceutical and agricultural industries. More recently, HAT has been explored in polymer chemistry as a versatile strategy for introducing targeted functional groups onto polymer chains, enabling precise control over properties such as solubility and mechanical strength. This study investigates the use of HAT to synthesize reversible addition-fragmentation chain transfer (RAFT) agents (or chain transfer agents, CTAs) by modifying various substrates, including toluene, ethyl acetate, and dioxane, in the presence of bis(dodecylsulfanylthiocarbonyl) disulfide or bis(3,5-dimethyl-1H-pyrazol-1-ylthiocarbonyl) disulfide. The resulting CTAs were evaluated in both thermal and photoinduced electron transfer (PET)-RAFT polymerization for controlled polymerization of various monomers. This approach was then extended to functionalize polycaprolactone (PCL) and polyvinyl acetate (PVAc), enabling the synthesis of graft copolymers with various vinyl monomers. To promote HAT, a range of photocatalysts, including iron(III) chloride (FeCl3), were investigated, offering advantages over conventional thermal HAT systems. Photocatalysis enables mild and efficient radical generation under light irradiation, providing a cost-effective and environmentally friendly alternative to expensive or toxic metal catalysts.

Multicomponent Polymerizations Provide Sustainable Sulfur (Selenium)-Containing Polyesters

ConspectusWith the rapid development of the polymer industry, the contradiction between synthetic polymers and the sustainable development of human society is becoming more and more prominent. The advancement of degradable plastics greatly contributes to the sustainability of our society. Synthetic polymers containing precisely placed in-chain ester groups are expected to be degradable in a controlled manner. Their potential as environmentally benign plastics is significant. For this purpose, there is a clear need for their improved performance. Incorporating sulfur functional groups into polyesters can improve the diverse crucial properties of their counterparts. However, there is a lack of related high-efficiency polymer synthesis methods.In response to this issue, we designed a series of multicomponent polymerization methods for the synthesis of a library of degradable polyesters with tunable structure and properties. This Account summarizes our recent efforts to discover the polymerization approach. The method uses readily available monomers including diols, diamines, H2O, diacrylates, carbonyl sulfide (COS), cyclic thioanhydrides, CO, and selenium powder. The polymerization is usually carried out under mild conditions: at 60 to 90 °C, for 2 to 12 h, using organobases as the catalysts or catalyst-free. This approach achieves the simultaneous incorporation of in-chain ester and sulfur/selenium functional groups including thiocarbonate, thioether, thioester, thiourethane, and selenoether.The method has a wide monomer scope and yields diverse polymers with tunable structures. The obtained polyesters possess weight-average molecular weights of up to 175.4 kDa. Most of these polyesters are thermally stable, exhibiting decomposition temperatures of >200 °C. Due to the diversity of structure, these polymers demonstrate extensively tunable performance covering crystalline plastics, thermoplastic elastomers, and amorphous plastics. These polymers exhibit a wide range of glass-transition temperatures of -60 to 72 °C and a wide range of melting temperatures of 43 to 274 °C. Notably, the polymers containing long alkyl chains (number of carbon atoms ≥ 9) exhibit polyethylene-like crystallinity and mechanical properties. The in-chain thiourethane or amide groups enable enhanced thermal and mechanical properties due to the incorporation of inter/intramolecular hydrogen bonding. These polymers are also easy to degrade via alkali hydrolysis, alcohol hydrolysis, enzymatic hydrolysis, oxidation, etc. The degradation products often have well-defined structure and value-added properties and can even be directly used for repolymerization to achieve a closed-loop chemical cycle. Overall, the multicomponent polymerization presented in this Account furnishes a facile and versatile synthesis of sustainable polymers with tunable structure and properties.

A Greener and More Scalable Synthesis of Biogenic Polydisulfides from Lipoic Acid

Ring-opening polymerization (ROP) of 1,2-dithiolanes form polydisulfides, an emergent class of dynamic covalent polymers. However, both monomer and polymer syntheses typically require anaerobic and moisture-free conditions, often employing hazardous reagents and solvents that limit scalability. Herein, efficient, scalable syntheses for poly(ethyl lipoate) and ethyl lipoate that incorporate Green Chemistry principles are disclosed. The synthesis of ethyl lipoate from lipoic acid on a 100-gram scale (>80% yield) is optimized lowering the E-factor (2.27) by an order of magnitude compared to conventional methods. Diphenyl phosphate, a nonhazardous commercial organic acid, is used to synthesize ultra-high-molecular-weight poly(ethyl lipoate) on a 50-gram scale from cationic ROP (CROP). The polymerizations proceed under ambient atmosphere in low-hazard and renewable solvents, and a mild depolymerization strategy to regenerate the monomer is developed. Due to their extreme molar mass, the materials possess unique mechanical and physical properties. Life cycle assessment (LCA) conducted on synthetic and recycling processes shows that the polydisulfide has competitive environmental impacts comparable to several commodity polymers, despite the latter having an efficiency advantage due to economies of scale. These discoveries establish an economical and scalable closed-loop polymer platform that can be broadly applied to various polydisulfides sourced from 1,2-dithiolanes such as lipoic acid.

Circular 3D printing of high-performance photopolymers through dissociative network design

One approach for closed-loop plastics recycling relies on reverting polymers back into monomers because one can then make new plastics without loss of properties. This depolymerization requirement restricts the molecular design to making polymers with high mechanical performance. We report a three-dimensional (3D) printing chemistry through stepwise photopolymerization by forming dithioacetal bonds. The polymerized network can be transformed back into a photoreactive oligomer by dissociation of the dithioacetal bonds. This network-oligomer transformation is reversible, therefore allowing circular 3D printing using the same material. Our approach offers the flexibility of making modular adjustments in the design of the network backbone of a polymer. This allows access to fully recyclable elastomers, crystalline polymers, and rigid glassy polymers with high mechanical toughness, making them potentially suitable for diverse applications.

Continuous Flow Depolymerization of Polycarbonates and Poly(lactic acid) Promoted by Supported Organocatalysts

Mechanical recycling methods are a simple and effective approach to recycling plastics, but they often result in a direct reduction in the quality of the virgin polymer. Alternatively, chemical recycling of plastic waste provides a closed-loop pathway that could offer a solution to the current end-of-life mismanagement of plastics. However, harsh reaction conditions, scalability, and product purification can limit the applicability of this process on a large scale. Here, an organocatalyzed continuous flow depolymerization strategy is proposed for two soluble, commonly used plastics, poly(lactic acid) (PLA) and bisphenol A polycarbonate (BPA-PC). This process used glycolysis to upcycle PLA to alkyl lactate and BPA-PC to bisphenol A and ethylene carbonate under mild reaction conditions (up to 60 °C). The complete depolymerization of both polymers is initially performed under batch conditions, allowing the solvents and catalysts to be screened. The process is further extended under continuous flow to explore catalyst stability and process scalability. Finally, it is demonstrated that alkyl lactate, bisphenol A and ethylene carbonate can be produced from waste polycarbonate and PLA, thus providing safe and economical access to these species through continuous flow depolymerization of plastic waste.

Ring-Opening Polymerization Enables Access to High-Performance Aliphatic-Aromatic Polyamides with Chemical Recyclability

Although polyamides (PAs) have served as one of the most important engineering thermoplastics, it remains a long-standing challenge for chemical recycling of PAs to monomers. Herein, we report a facile approach to construct a series of benzo-fused caprolactams with various functionalities (BLMR). These BLMR monomers underwent robust and well-controlled ring-opening polymerization to afford P(BLMR) products with high thermal stability, enhanced water resistance, and tunable mechanical properties. Impressively, chemical recycling of P(BLMR) to monomer could be accomplished with excellent efficiency in dilute solution at 100-150 °C with a mixed catalyst of t-BuOK and La[N(SiMe3)2]3, thus establishing a closed-loop circularity. The precise control of the polymerization and the recyclability of these semiaromatic polyamides promote a sustainable circular economy while offering the potential to access high-performance materials with tunable thermal and mechanical properties and enhanced water resistance.

Electromagnetically Heating and Oscillating Liquid Metal for Catalyzing Polyester Depolymerization

Depolymerization and recycling of polyesters have shown great significance to economy, ecology, carbon neutrality and human health. Efficient catalysts for thermolysis depolymerization have long been pursued to achieve rapid depolymerization, high selectivity, and low energy consumption. In this study, it is found that liquid metal (LM) can serve as the efficient self-heater, mechanic disturber and catalyst for thermolysis depolymerization of polyesters under alternating electromagnetic fields. When dissolving different metals (e.g., Sn, Zn, Al, and Mg) into gallium, LMs may provide dynamic interactions between the catalyst and reactants, spontaneous metal enriching, and oxidation within the LM surface layer. Without any conventional heaters and mechanic shakers, polycaprolactone is catalytically depolymerized into ɛ-caprolactone at the rate of ≈700 mg h-1 mL-1 with the selectivity of 95.5%. The high surface tension and high mobility of LM also enable continuous depolymerization at an appropriate feeding speed of polyesters (including polyethylene terephthalate, polyhydroxybutyrate and polylactic acid). Thus, this study may offer an unprecedented "all-in-one" platform of liquid metal for continuous thermolysis depolymerization of polyesters, while without any requirement of external heater, mixer, and catalysts.

Circular Economy and Chemical Conversion for Polyester Wastes

Polyester waste in the environment threatens public health and environmental ecosystems. Chemical recycling of polyester waste offers a dual solution to ensure resource sustainability and ecological restoration. This minireview highlights the traditional recycling methods and novel recycling strategies of polyester plastics. The conventional strategy includes pyrolysis, carbonation, and solvolysis of polyesters for degradation and recycling. Furthermore, the review delves into exploring emerging technologies including hydrogenolysis, electrocatalysis, photothermal, photoreforming, and enzymatic for upcycling polyesters. It emphasizes the selectivity of products during the polyester conversion process and elucidates conversion pathways. More importantly, the separation and purification of the products, the life cycle assessment, and the economic analysis of the overall recycling process are essential for evaluating the environmental and economic viability of chemical recycling of waste polyester plastics. Finally, the review offers perspective into the future challenges and developments of chemical recycling in the polyester economy.

The effect of low-temperature plasma pretreatment on the biodegradability of polyethylene films

With the increasing focus on environmental friendliness and sustainable development, extensive research has been conducted on the biodegradation of plastics. The non-hydrolyzable, highly hydrophobic, and high-molecular-weight properties of polyethylene (PE) pose challenges for cell interaction and biodegradation of PE substrates. To overcome these obstacles, PE films were treated with low-temperature plasma before biodegradation. The morphology, surface chemistry, molecular weight, and weight loss of PE films after plasma treatment and biodegradation were studied. The plasma treatment decreased the surface water contact angle, formed C-O and C = O groups, and decreased the molecular weight of PE films. With the increased pretreatment time, the biodegradation efficiency rose to 2.6% from 0.63% after 20 days of incubation. The mechanism was proposed that the surface oxygen-containing groups formed by plasma treatment can facilitate the bio-accessibility and be further decomposed and utilised by the microbes. This study provided an effective and rapid pretreatment strategy for improving biodegradation of PE.

Recent advances in recycling and upcycling of hazardous plastic waste: A review

Plastic is a widely used material across various industries, including construction, packaging, healthcare, and automotive, among others. Global plastic production was estimated at 311 million tonnes in 2014 and is expected to double within two decades, continuing to rise towards 2050. As plastic pollution poses significant environmental and health risks, effective recycling and upcycling strategies are crucial for sustainable waste management. This paper explores the impact of plastic waste on public health and ecosystems, reviews chemical, mechanical, and biological recycling methods, and examines upcycling approaches. It also addresses key challenges such as limitations in chemical upcycling, scaling up carbonization, and inefficiencies in sorting and processing for mechanical recycling. Additionally, recent innovations-including enzymatic depolymerization for PET recycling, upcycling plastic waste into advanced carbon materials like graphene and carbon nanotubes, photochemical and photocatalytic upcycling, PVC recycling via Cl-transfer systems, and advancements in mechanical recycling for multi-layer plastics-are discussed to highlight emerging solutions in plastic waste management. By addressing these challenges and gaps, this paper provides valuable insights into advancing plastic waste management through innovative recycling and upcycling technologies, paving the way for more sustainable and environmentally friendly solutions to combat global plastic pollution.

Stereochemistry-Tuned Hydrogen-Bonding Synergistic Covalent Adaptable Networks: Towards Recycled Elastomers with Excellent Creep-Resistant Performance

Covalent adaptable networks (CANs) offer innovative solutions for the reprocessing and recycling of thermoset polymers. However, achieving a balance between easy reprocessing and creep resistance remains a challenge. This study focuses on designing and synthesizing polyurethane (PU) materials with tailored properties by manipulating the stereochemistry of diamine chain extenders. By employing cis- and trans-configurations of diamine extenders, we developed a series of PU materials with varying mechanical properties and creep resistance. The trans-configured materials (R,R-DAC-PU or S,S-DAC-PU) exhibited superior creep resistance and mechanical strength due to dense hydrogen bonding networks. The cis-configured materials (Cis-DAC-PU) exhibited enhanced processability and elasticity. Under 0.1 MPa stress, R,R-DAC-PU showed a mere 3.5 % strain change at 170 °C over 60 minutes, highlighting its superior creep resistance. Both configurations can be recycled via urea bond exchange reactions using hot pressing or solvothermal methods. Density Functional Theory (DFT) calculations indicate that both the (R,R-DCA-UB-U)2 and (S,S-DCA-UB-U)2 segments form six hydrogen bonds with shorter bond lengths, leading to stronger hydrogen-bonding interactions. Conversely, the (Cis-DCA-UB-U)2 segment forms four hydrogen bonds with longer bond lengths, resulting in weaker interactions. This work highlights the critical role of stereochemistry in designing high-performance, recyclable polymer materials with tailored properties.

Upcycling Polynorbornene Derivatives into Chemically Recyclable Multiblock Linear and Thermoset Plastics

Synthetic polymers have found widespread use, but their ineffective end-of-life treatment is causing a significant environmental and human health crisis. Here, we demonstrate the upcycling of polynorbornene derivatives (pNBEs) through their deconstruction into distinct oligomeric buildings blocks that can be repolymerized into chemically recyclable pNBEs-like multiblock polymers via dehydrogenative polymerization. The resulting materials exhibit diverse mechanical properties, while integrating high melting temperatures (Tm as high as 133 °C). Notably, this method could also enable the selective deconstruction of permanently cross-linked polydicyclopentadiene (pDCPD) thermosets into telechelic-OH functionalized oligomers, overcoming the significant challenges posed by their robust network structure in recycling and degradation. The resulting pDCPD oligomers can subsequently be repolymerized with macrodiols to create multiblock thermosets with tunable mechanical properties, including Young's modulus and tensile elongation. After use, upcycled plastics could be effectively deconstructed back to the oligomers for recovery and repolymerization. Overall, this work establishes an approach that can be utilized to upcycle pNBEs into previously inaccessible multiblock thermosets and thermoplastics with full recyclability, and may be generalizable to a range of polymers to shift their end-of-life waste disposal toward sustainable recovery and reuse.

Selective Degradation of Polyethylene Terephthalate Plastic Waste Using Iron Salt Photocatalysts

Plastic pollution poses a significant challenge to environmental conservation. Efficient recycling of plastic is a key strategy to address this issue. Polyethylene terephthalate (PET), commonly found in plastic bottles, represents a substantial portion of plastic waste. Consequently, the efficient degradation and recycling of PET is crucial for the sustainable development of society. However, the implementation of methods for PET depolymerization and recycling typically necessitates alkaline/acidic pre-treatment and significant energy input for heating. Here, we propose a gentle, and highly efficient photocatalysis approach for selectively degrading PET plastic waste into terephthalic acid (TPA) in high yield (up to 99 %) using cost-effective iron salts. Notably, this method achieved excellent selectivity with high TON and TOF values, applying oxygen or air as environmentally friendly oxidants. In addition, the solvent can be recycled without compromising the TPA yield, and large-scale reactions can be performed smoothly.

Catalytic closed-loop recycling of polyethylene-like materials produced by acceptorless dehydrogenative polymerization of bio-derived diols

Petroleum-derived polyolefins exhibit diverse properties and are the most important and largest volume class of plastics. However, polyolefins are difficult to efficiently recycle or break down and are now a persistent global contaminant. Broadly replacing polyolefins with bio-derived and degradable polyethylene-like materials is an important yet challenging endeavour towards sustainable plastics. Here we report a solution for circular bio-based polyethylene-like materials synthesized by acceptorless dehydrogenative polymerization from linear and branched diols and their catalytic closed-loop recycling. The polymerization and depolymerization processes utilize earth-abundant manganese complexes as catalysts. These materials exhibit a wide range of mechanical properties, encompassing thermoplastics to plastomers to elastomers. The branched diols, produced through a thiol-ene click reaction, can be polymerized to plastics with significantly enhanced tensile properties, toughness and adhesive properties. These materials could be depolymerized back to monomers through hydrogenation and were separatable with a monomer recovery of up to 99%, unaffected by the presence of dyes and additives. Overall, this system establishes a route to more sustainable plastics.

Sustainable Strategies for Converting Organic, Electronic, and Plastic Waste From Municipal Solid Waste Into Functional Materials

The valorization of municipal solid waste permits to obtain sustainable functional materials. As the urban population burgeons, so does the volume of discarded waste, presenting both a challenge and an opportunity. Harnessing the materials and the latent energy within this solid waste not only addresses the issue of disposal but also contributes to the innovation of functional materials with applications in the energy, electronics, and environment sectors. In this perspective, technologies for converting, after sorting, municipal solid waste into valuable metals, chemicals, and fuels are critically analyzed. Innovative approaches to convert organic waste into functional carbon materials and to create, from plastic and electronic wastes, metal-organic frameworks for energy conversion, storage, and CO2 adsorption and conversion are proposed. Green hydrometallurgy routes that permit the recovery of precious metals avoiding noble metals' oxidative leaching, thus avoiding their downcycling, are also highlighted. The reclaimed precious metals hold promise for use in optoelectronic devices.

Highly adaptable oxidative upcycling of polyolefins to multifunctional chemicals containing oxygen and nitrogen

Highly adaptable upcycling of waste polyolefins was demonstrated to obtain high-value nitro-containing polycarboxylic acids in high carbon yields. This method is applicable to a wide range of polyolefins, mixed PP/PE in any ratio, as well as actual polyolefin products and their mixtures. Moreover, the obtained products are homogenized with similarity in molecular weight and functional groups, enabling direct reutilization as fine chemicals or feedstocks for preparation of recyclable high-performance/functional materials. This work provided a new universal and efficient upcycling strategy for waste polyolefins, which may reshape the model of waste plastics recycling, while providing alternative functional chemicals and materials to achieve sustainable development.

Environmentally ion-dissociable high-performance supramolecular polyelectrolyte plastics

Robust and stiff polymeric materials usually rely on dense covalent crosslinking, which endows them with excellent properties such as high durability and outstanding thermal stability. However, because of the strong covalent bonds within the network, these polymeric materials are not easily degraded or recycled, giving rise to uncontrolled accumulation of end-of-life plastics in seawater or soil. Here, we present a general strategy to fabricate high-performance supramolecular polyelectrolyte plastics with environmentally ion-dissociable properties in a facile manner. By combining dynamic supramolecular hydrogen bonding and multiple electrostatic crosslinking with hydrophobic interactions, the resulting stable supramolecular polyelectrolyte plastic possesses a tensile strength of 93.6 ± 3.3 MPa and a Young's modulus of 2.3 ± 0.3 GPa, outperforming most of the commercial plastics. More importantly, the unique supramolecular dynamic network structures endow the polyelectrolyte plastics with excellent remoldability, good recyclability, and efficient dissociation in seawater and soil under ambient conditions. The simple fabrication strategy developed herein for robust sustainable polyelectrolyte plastics appears to be applicable to other bio-sourced and synthetic polyelectrolytes. This work provides a practical way for fabricating sustainable high-performance plastics by elegantly designing the supramolecular networks of polyelectrolytes.

Focal Point Association of Core-Crystalline Micelles with an Amphiphilic Corona Block

We report the preparation of star-like supermicelles by the secondary association of triblock comicelles or scarf-like micelles driven by a change in solvency. These building blocks were synthesized by seeded growth in which crystallites of a triblock terpolymer, either PFS27-b-PTDMA81-b-POEGMA45 (to form triblock comicelles) or PFS66-b-PTDMA81-b-POEGMA45 (to form scarf-like micelles), served as seeds for crystallization-driven self-assembly (CDSA). PFS-b-PTDMA unimers were added in the seeded growth step. The corona-forming block PTDMA-POEGMA is amphiphilic and sensitive to polarity changes of the solvents. We sought solvents in which the upper critical solution temperature (UCST, TUCST) of POEGMA was slightly above room temperature (RT). Examples included 1-decanol and 1-decanol/decane mixtures. Seeded growth proceeded normally in solvents above the UCST of POEGMA. When the solution temperature was lowered below TUCST, or when the triblock comicelles or scarf-like micelles were transferred to a solvent (e.g., 1-decanol) below its TUCST, the center blocks associated to form star-like supermicelles. The addition of small amounts of THF to the medium to increase the solvency for POEGMA led to dissociation of the supermicelles. Transfer of the triblock comicelles to 1-pentanol at RT, below the UCST of PTDMA, also led to controlled secondary association to form supermicelles with a different morphology. Seeded growth with PFS25-b-PDMAEMA184 unimers led to supermicelles in which the poly(dimethylaminoethyl methacrylate) corona chains could serve as carriers for gold nanoparticles (AuNPs). These AuNP@supermicelle complexes could serve as recoverable catalysts, for example to catalyze the condensation polymerization of bis(dimethylsilyl)benzene and pentanediol. They were highly active catalysts and showed excellent mechanical robustness for recovery and reuse.

Toward a Circular Economy of Heteroatom Containing Plastics: A Focus on Heterogeneous Catalysis in Recycling

Plastics play a vital role in modern society, but their accumulation in landfills and the environment presents significant risks to ecosystems and human health. In addition, the discarding of plastic waste constitutes to a loss of valuable material. While the usual mechanical recycling method often results in reduced material quality, chemical recycling offers exciting opportunities to valorize plastic waste into compounds of interest. Its versatility leans on the broad horizon of chemical reactions applicable, such as hydrogenolysis, hydrolysis, alcoholysis, or aminolysis. The development of heterogeneous and supported organocatalysts has enormous potential to enhance the economic and industrial viability of these technologies, reducing the cost of the process and mitigating its global environmental impact. This review summarizes the challenges and opportunities of chemically recycling heteroatom-containing plastics through heterogeneous catalysis, covering widely used plastics such as polyesters (notably PET and PLA), BPA-polycarbonate (BPA-PC), polyurethane (PU), polyamide (PA), and polyether. It examines the potential and limitations of various solid catalysts, including clays, zeolites, and metal-organic frameworks as well as supported organocatalysts and immobilized enzymes (heterogeneous biocatalysts), for reactions that facilitate the recovery of high-value products. By reintroducing these high-value products into the economy as precursors, this approach supports a more sustainable lifecycle for plastics, aligning with the principles of a circular economy.

Recycling Polyester and Polycarbonate Plastics with Carbocation Lewis Acidic Organocatalysts

The effective management of plastic waste is critical for environmental sustainability. This work explores the use of carbocation catalysts for the recycling of common polyesters and polycarbonates through alcoholysis. We demonstrate complete depolymerization of end-of-life materials and investigate the relationship between the catalytic reactivity and the structural features of the carbocation compounds, including the cations and their counteranions. Carbocations function as Lewis acids, facilitating the interaction with carbonyls in polymer chains. Moreover, our approach enables the hierarchical degradation of the polyester blends. This research not only elucidates the catalytic role of carbocations in the alcoholysis of these polymers, but also establishes a metal-free process for the efficient recycling of waste plastics.

Upcycling waste commodity polymers into high-performance polyarylate materials with direct utilization of capping agent impurities

Commodity polymers are ubiquitous in our society, having replaced many inorganic and metal-based materials due to their versatile properties. However, their functionality heavily relies on the addition of various components known as additives, making it challenging to recycle the polymer fraction of plastic materials effectively. Thus, it is crucial to develop efficient chemical recovery strategies for commodity polymers and additives to facilitate the direct utilization of recovered monomers and additives without additional purification. Here, we develop a strategy for co-upcycling two types of waste commodity polymers, polycarbonate, and polyethylene terephthalate into polyarylate, a high-performance transparent engineering plastic. By incorporating a highly active metal-free ionic liquids catalyst for methanolysis and a two-stage interface polymerization technique with variable temperature control, we successfully prepare polyacrylate film materials from real end-of-life plastics with direct utilization of capping agent impurities in recovered monomers. These materials exhibit excellent thermal performance (Tg = 192.8 °C), transmittance (reach up to 86.73%), and flame-retardant properties (V-0, UL-94), equivalent to those of commercial polyarylate (U-100, about $10000/ton), and could be further easily close-loop recycled. Demonstrated in kilogram-scale experiments and life cycle assessments, this approach offers a low-carbon, environmentally friendly, and economically feasible pathway for upcycling waste commodity polymers.

Strong and tough bioplastics prepared by in-situ polymerization of ε-caprolactone-oligomers in lignocellulosic nanofiber network

Cellulose biocomposites have emerged as attractive alternatives to fossil-based plastics because of their excellent renewability and biodegradability; however, their water resistance and mechanical properties remain challenging. Herein, a cellulose- containing bioplastic with high a reinforcement content, water stability, and toughness is reported. Lignin-containing cellulose nanofibers (LCNF) were prepared by pretreating eucalyptus wood powder with a deep eutectic solvent and high-pressure homogenization. Then, the pre-synthesized ε-caprolactone oligomers were in-situ polymerized in LCNF. The interaction of LCNF with ε-caprolactone-oligomers in the LCNF-crosslinked polycaprolactone (LCNF-PCL) bioplastic resulted in excellent mechanical properties (tensile strength: 76.59 MPa; toughness: 9.82 MJ m-3). The LCNF-PCL bioplastic also demonstrated excellent water stability (wet tensile strength: 34.21 MPa; water absorption: <5 %), thermal stability, and UV protection. This approach may provide a potential method for utilizing lignocellulosic resources to develop environmentally friendly bioplastics with good toughness and water stability.