Chemical upcycling of poly(bisphenol A carbonate) via sequential diamino-/methanolysis: A phosgeneless one-pot route to dimethyl dicarbamate esters

Waste poly(bisphenol A carbonate) (PC) is a potential source of harmful bisphenol A (BPA). In this study a new approach aiming to chemically valorize hazardous PC wastes is described. A one-pot process has been developed that allows to recover BPA from PC used as "phosgene equivalent" for the synthesis of dimethyl dicarbamates MeO2CNH-R-NHCO2Me. Dicarbamate esters are industrially relevant precursors of non-isocyanate polyurethanes and polyureas. The devised process is conducted stepwisely. PC is first depolymerized by reaction with basic diamines H2NRNH2 (1,6-diaminohexane (3a); 4,7,10-trioxa-1,13-tridecanediamine (4a); meta-xylylenediamine (5a); para-xylylenediamine (6a)) into BPA and oligourethanes H[-OArO(O)CNHRNHC(O)-]nOArOH (Ar = 4,4'-C6H4C(Me)2C6H4-) that, in a subsequent step, are one-pot converted into MeO2CNH-R-NHCO2Me and more BPA by transurethanization with methanol. Both the steps proceed under mild conditions and do not require any auxiliary catalyst. The process allows to recover BPA in high yield and, as an additional outstanding advantage, offers a new solution to the synthesis of MeO2CNH-R-NHCO2Me dicarbamates without using poisonous phosgene, traditionally used to this purpose. Aromatic diamines are much less reactive than aliphatic ones. Under conditions comparable with those used for 3a-6a, 4,4'-diaminodiphenylmethane reacted with PC under the assistance of a base catalyst (DBU; NaOH) to give polyurea [-NHRNHCO-]n as major product.

Facile Depolymerization of Thermally Stable Polyetherethersulfone and Polyetheretherketone Using Hydroquinone and Bases

Super engineering plastics such as polyetheretherketone (PEEK) and polyetherethersulfone (PEES) exhibit thermal stability, chemical resistance, and mechanical strength. Such characteristics are attributed to their robust chemical structures composed of stable aryl ethers. These features make chemical recycling difficult. This is because it is necessary to overcome through the stability of the material and then precisely cleave the stable bonds. This study demonstrates the depolymerization of PEES and PEEK by hydroquinone in the presence of sodium hydroxide in 1,3-dimethyl-2-imidazolidinone (DMI) solvent at 150 °C. This method effectively provides monomeric products, diphenylsulfone and benzophenone having two 4-hydroxyphenoxy groups at both para positions. DMI solvent was the crucial factor for this transformation, since it enhanced the reactivity of hydroquinone to cleave the aryl ether bonds.

Compact Disc-Derived Nanocarbon-Supported Catalysts with Extreme Catalytic Activity

Advanced carbon-metal hybrid materials with controllable electronic and optical properties, as well as chemical reactivities, have attracted significant attention for emerging applications, including energy conversion and storage, catalysis and environmental protection. However, the commercialization of these materials is hampered by several vital problems, including energy-intensive synthesis and expensive chemicals, and inefficient control of their structures and properties. Herein, we report the simple and controllable engineering of nanocarbon-metal self-assembled silver nanocatalysts (SSNs) derived from polycarbonate (PC)-based optical discs using microplasmas under ambient conditions. The plasma-engineered catalysts exhibited controlled properties including surface functionalities, hydrophilicities, Ag+/Ag0 metallic states, and Ag loading. The synthesized catalysts leverage localized surface plasmon resonance (LSPR) properties, enabling enhanced catalytic activity for the rapid reduction of carcinogenic 4-nitrophenol (4-NP) to the valuable pharmaceutical intermediate 4-aminophenol (4-AP), achieving a high reaction rate constant of 0.2 ± 0.0 s-1 and completing the reduction in just 30 s. Demonstrating robust performance, the SSNs maintained up to 90% conversion efficiency after ten recycling cycles, underscoring their stability and reusability. This work not only presents an effective approach to upcycling optical disc waste, but also highlights the potential of plasma-engineered nanocatalysts in environmental remediation, offering a low-energy solution for high-efficiency pollutant reduction.

Potassium Carbonate as a Low-Cost and Highly Active Solid Base Catalyst for Low-Temperature Methanolysis of Polycarbonate

As the demand for polycarbonate (PC) plastic increases over the years, the development of a chemical recycling system to produce virgin-like-quality monomers is indispensable not only to attain completely sustainable cycles but also to contribute to the decrease in global plastic pollution. Herein, potassium carbonate (K2CO3) was used as a low-cost, readily available, and highly active solid base catalyst for low-temperature PC methanolysis in the presence of THF as a solvent, producing highly pure and crystalline bisphenol A (BPA) and with a catalytic performance higher than group IIA metal oxides (MgO, CaO, and SrO) and some group IA metal carbonates (NaHCO3, KHCO3, and Na2CO3). THF was the best solvent in aiding the reaction owing to it having a similar polar parameter (δp) to that of PC according to Hansen solubility parameters. By the reaction over the catalyst, 100% PC conversion, 97% BPA yield, and 86% dimethyl carbonate yield were achieved within just 20 min at 60 °C. The catalyst possessed an apparent activation energy (Ea) of 52.3 kJ mol-1, which is the lowest value so far for heterogeneous catalysts, while the mechanistic study revealed that the reaction proceeded via the methoxide pathway. The reusability test demonstrated that the catalyst was reusable at least four times. Furthermore, this catalytic system was successfully applied to actual post-consumer PC wastes and polyesters, including polyethylene terephthalate (PET) and polylactic acid (PLA).

Depolymerization of Waste Polycarbonates to Value-Added Products

Additive free aminolysis method developed for the depolymerization/upcycling of polycarbonates. We report here chemical recycling of polycarbonate under ambient conditions to get its monomer bisphenol A, monoaminocarbamate and biscarbamates in 1 : 2 : 1 ratio respectively. By employing the secondary amine as the aminating reagent, facilitates the depolymerization to work under additive/catalyst free conditions. The developed method deals with depolymerization of waste polycarbonates and works even with late-stage amine derivatives such as amoxapine and desloratadine which are drugs molecules known to treat neurotic disorders and allergies respectively. The reaction can be scaled up and works with similar efficacy which depicts the efficiency of the depolymerization of wasteend-of-life polycarbonate plastic waste. The biscarbamate and bisphenol-A was further subjected for the post functionalization to obtain amides and phenol in good yields.

A strategic recovery of value-added monomer from polycarbonate waste through catalytic pyrolysis on ultra-high porous MgO

The huge generation of plastic waste has become significant environmental problem. For environmentally sustainable plastic waste management, thermochemical recycling of widely used plastic waste such as polyethylene, polypropylene, polystyrene, and polyethylene terephthalate have vigorously studied. However, development of proper recycling process for other types of plastic waste is required. In this study, a thermo-catalytic treatment was applied for recovery of value-added monomers and gaseous products from polycarbonate (PC). The systematic study investigating the relationships between pyrolysis conditions (temperature, atmospheric gas, the presence of catalyst) and yield of value-added products was performed. To make the thermochemical process environmentally benign and more efficient, carbon dioxide (CO2) was used as an atmospheric gas in comparing to inert gas (N2). When CO2 was introduced, the yield of PC monomer, bisphenol A (BPA), was nearly doubled at 600 °C. At higher temperature, BPA yield decreased with the increased yield of gaseous products. Because CO2 was the major gaseous product, BPA recovery from the PC pyrolysis was the useful approach in PC disposal practice. To improve BPA yield from PC pyrolysis, two MgO catalysts were utilized (medium porosity MgO-1 and ultrahigh porosity MgO-2). Catalytic pyrolysis under CO2 environment increased BPA yield from 12.8 (pyrolysis without catalyst under N2) to 25.6 (MgO-1) and 30.5 wt% (MgO-2) at 600 °C. High porosity MgO catalyst was more effective in BPA production, and the catalyst deactivation was not shown for 4 consecutive reactions. This study informs that MgO catalyst and CO2 flow gas more than doubled the BPA yield from pyrolysis of PC in reference to conventional pyrolysis system (non-catalytic under N2).

Selectively self-recyclable, highly transparent and fire-safe polycarbonate plastic enabled by thermally responsive phosphonium-phosphate

Both the circular economy and fire-safety of polymer plastics have become a global consensus. Herein, an integrated strategy for selectively self-recyclable, highly-transparent and fire-safe polycarbonate plastic is proposed by thermally responsive phosphonium-phosphate (DP). During its service life, DP, as a flame-retardant with good compatibility, enables polycarbonate plastic with high transparency in visible light, excellent self-extinguishing and high fire-safety. After consumption, DP, as a catalyst, triggers the selective self-recycling of DP-containing polycarbonate in mixed plastics and even in same-kind polycarbonate plastics without an external catalyst. Importantly, the oxygen-consuming mechanism at high temperature in fire accidents (>350 °C) and the double hydrogen bond catalysis mechanism at a lower temperature (180 °C) of DP are key to the life cycle management of polycarbonate from use-stage to post-consumption. This work inspires a new solution to plastic pollution by designing sustainable plastics that satisfy both service-stage and end-of-life criteria, striving towards a zero-waste circular economy.

The current progress of tandem chemical and biological plastic upcycling

Each year, millions of tons of plastics are produced for use in such applications as packaging, construction, and textiles. While plastic is undeniably useful and convenient, its environmental fate and transport have raised growing concerns about waste and pollution. However, the ease and low cost of producing virgin plastic have so far made conventional plastic recycling economically unattractive. Common contaminants in plastic waste and shortcomings of the recycling processes themselves typically mean that recycled plastic products are of relatively low quality in some cases. The high cost and high energy requirements of typical recycling operations also reduce their economic benefits. In recent years, the bio-upcycling of chemically treated plastic waste has emerged as a promising alternative to conventional plastic recycling. Unlike recycling, bio-upcycling uses relatively mild process conditions to economically transform pretreated plastic waste into value-added products. In this review, we first provide a précis of the general methodology and limits of conventional plastic recycling. Then, we review recent advances in hybrid chemical/biological upcycling methods for different plastics, including polyethylene terephthalate, polyurethane, polyamide, polycarbonate, polyethylene, polypropylene, polystyrene, and polyvinyl chloride. For each kind of plastic, we summarize both the pretreatment methods for making the plastic bio-available and the microbial chassis for degrading or converting the treated plastic waste to value-added products. We also discuss both the limitations of upcycling processes for major plastics and their potential for bio-upcycling.

CO2-Sourced Polymer Dyes for Dual Information Encryption

Large amounts of small molecule dyes leak into the ecosystems annually in harmful and unsustainable ways. Polymer dyes have attracted much attention because of their high migration resistance, excellent stability, and minimized leakage. However, the complex synthesis process, high cost, and poor degradability hinder their widespread application. Herein, green and sustainable polymer dyes are prepared using natural dye quercetin (Qc) and CO2 through a one-step process. The CO2-sourced polymer dyes show strong migration resistance, high stability, and can be degraded on demand. Additionally, the CO2-sourced polymer dyes showed unique responses to Zn2+, leading to significantly enhanced fluorescence, highlighting their potential for information encryption/decryption. The CO2-sourced polymer dyes can solve the environmental hazards caused by small molecule dye leakage and promote the carbon cycle process. Meanwhile, the one-step synthesis process is expected to achieve sustainable and widespread utilization of CO2-sourced polymer dyes.

Demonstrating the Efficacy of Core-Shell Silica Catalyst in Depolymerizing Polycarbonate

Polycarbonate (PC) is a highly versatile plastic material that is extensively utilized across various industries due to its superior properties, including high impact strength and heat resistance. However, its durability presents significant challenges for recycling and waste management. Polycarbonate is a thermoplastic polymer representative of the class of condensation reaction polymers obtained from the reaction of bisphenol A (BPA) and a carbonyl source, such as phosgene or alkyl and aryl carbonate. The recycling processes for PC waste include mechanical recycling, blending with other materials, pyrolysis, and chemical recycling. The latter is based on the cleavage of carbonate units to their corresponding monomers or derivatives through alcoholysis and/or hydrolysis and ammonolysis, normally under basic conditions and without catalysts. This study investigates the efficacy of the use of several heterogeneous catalysts based on silica gel as a robust support, including Sc(III)silicate (thortveitite), which has been previously reported for the preparation of polyesters, core-shell Si-ILs, and core-shell Si-ILs-ZnO, which has never been used before in the depolymerization of polycarbonate, proposing a sustainable and efficient method for recycling this valuable polymer. We chose to explore core-shell catalysts because these catalysts are robust and recyclable, and have been used in very harsh industrial processes. The core-shell silica catalysts used in this study were characterized by XRD; SEM_EDX, FT-IR, and ICP-OES analysis. In our experimental protocol, polycarbonate samples were exposed to the catalyst under controlled conditions (60-150 °C, for 12-24 h) using both oxygen and nitrogen nucleophiles. The depolymerization process was systematically monitored using advanced analytical techniques (GC/MS and GPC chromatography). The experimental results indicated that core-shell silica catalyst exhibits high efficacy, with up to 75% yield for the ammonolysis reaction, producing monomers of high purity. These monomers can be reused for the synthesis of new polycarbonate materials, contributing to a more sustainable approach to polycarbonate recycling.

Feedstock recycling of polycarbonate waste via thermochemical conversion supported by municipal solid waste incinerator bottom ash

The rising demand for plastics has driven up its production, causing severe environmental challenges like CO2 emissions and microplastic pollution. Furthermore, improper disposal of incinerator bottom ash (IBA), a byproduct of municipal solid waste (MSW) treatment, poses additional environmental risks. This study explores a method for recovering non-petroleum-based monomers from plastic products. A smartphone case waste (SCW) is used as feedstock in this study and it is made of polycarbonate (PC), confirmed by thermogravimetric analysis and Fourier transform infrared spectroscopy. The MSW incinerator bottom ash (MSW-IBA) is used as a catalyst for thermochemical conversion of SCW. To determine the optimal pyrolysis conditions for BPA recovery, experiments were conducted under different atmospheres (N₂ and CO₂) and catalyst configurations (in situ and ex situ). The MSW-IBA leads to 127% higher yield of bisphenol A (BPA), the monomer of PC, at 600 °C under a N2 atmosphere, compared to non-catalytic conversion. In situ configuration of the catalyst loading leads to up to 147% higher BPA yield than ex situ configuration. The increased BPA production from SCW is most likely because metal oxides (e.g., CaO) present on the MSW-IBA catalyst promote the cleavage of and C-O bonds, dissociation of CO (or CO2) and hydrogen extraction from C1-C3 hydrocarbons and H2. For the catalytic conversion of SCW under a CO2 atmosphere, CO2 adsorbs onto CaO in the MSW-IBA, decreasing the number of active sites. It deactivates the catalyst, resulting in a lower BPA yield (22.96 wt%) than the BPA yield obtained under the N2 atmosphere (25.86 wt%).

Ultrahigh Heat/Fire-Resistant, Mechanically Robust, and Closed-Loop Chemical Recyclable Polycarbonate Enabled by Facile Bond Dissociation Energy Modulation

Plastics serve as an essential foundation in contemporary society. Nevertheless, meeting the rigorous performance demands in advanced applications and addressing their end-of-life disposal are two critical challenges that persist. Here, an innovative and facile method is introduced for the design and scalable production of polycarbonate, a key engineering plastic, simultaneously achieving high performance and closed-loop chemical recyclability. The bisphenol framework of polycarbonate is strategically adjusted from the low-bond-dissociation-energy bisphenol A to high-bond-dissociation-energy 4,4'-dihydroxydiphenyl, in combination with the incorporation of polysiloxane segments. As expected, the enhanced bond dissociation energy endows the polycarbonate with an extremely high glow-wire flammability index surpassing 1025 °C, a 0.8 mm UL-94 V-0 rating, a high LOI value of 39.2%, and more than 50% reduction of heat and smoke release. Furthermore, the π-π stacking interactions within biphenyl structures resulted in a significant enhancement of mechanical strength by as more as 37.7%, and also played a positive role in achieving a lower dielectric constant. Significantly, the copolymer exhibited outstanding closed-loop chemical recyclability, allowing for facile depolymerization into bisphenol monomers and the repolymerized copolymer retains its high heat and fire resistance. This work provides a novel insight in the design of high-performance and closed-loop chemical recyclable polymeric materials.

Industrial and Laboratory Technologies for the Chemical Recycling of Plastic Waste

Synthetic polymers play an indispensable role in modern society, finding applications across various sectors ranging from packaging, textiles, and consumer products to construction, electronics, and industrial machinery. Commodity plastics are cheap to produce, widely available, and versatile to meet diverse application needs. As a result, millions of metric tons of plastics are manufactured annually. However, current approaches for the chemical recycling of postconsumer plastic waste, primarily based on pyrolysis, lag in efficiency compared to their production methods. In recent years, significant research has focused on developing milder, economically viable methods for the chemical recycling of commodity plastics, which involves converting plastic waste back into monomers or transforming it into other valuable chemicals. This Perspective examines both industrial and cutting-edge laboratory-scale methods contributing to recent advancements in the field of chemical recycling.

Preparation of Non-Isocyanate Polyurethanes from Mixed Cyclic-Carbonated Compounds: Soybean Oil and CO2-Based Poly(ether carbonate)

This study presents the synthesis and characterization of non-isocyanate polyurethanes (NIPU) derived from the copolymerization of cyclic-carbonated soybean oil (CSBO) and cyclic carbonate (CC)-terminated poly(ether carbonate) (RCC). Using a double-metal cyanide catalyst, poly(ether carbonate) polyol was first synthesized through the copolymerization of carbon dioxide and propylene oxide. The terminal hydroxyl group was then subjected to a substitution reaction with a five-membered CC group using glycerol-1,2-carbonate and oxalyl chloride, yielding RCC. Attempts to prepare NIPU solely using RCC and diamine were unsuccessful, possibly due to the low CC functionality and the aminolysis of RCC's linear carbonate repeating units. However, when combined with CSBO, solid NIPUs were successfully obtained, exhibiting good thermal stability along with enhanced mechanical properties compared to conventional CSBO-based NIPU formulations. Overall, this study underscores the potential of leveraging renewable resources and carbon capture technologies to develop sustainable NIPUs with tailored properties, thereby expanding their range of applications.

Catalytic thiolation-depolymerization-like decomposition of oxyphenylene-type super engineering plastics via selective carbon-oxygen main chain cleavages

As the effective use of carbon resources has become a pressing societal issue, the importance of chemical recycling of plastics has increased. The catalytic chemical decomposition for plastics is a promising approach for creating valuable products under efficient and mild conditions. Although several commodity and engineering plastics have been applied, the decompositions of stable resins composed of strong main chains such as polyamides, thermoset resins, and super engineering plastics are underdeveloped. Especially, super engineering plastics that have high heat resistance, chemical resistance, and low solubility are nearly unexplored. In addition, many super engineering plastics are composed of robust aromatic ethers, which are difficult to cleave. Herein, we report the catalytic depolymerization-like chemical decomposition of oxyphenylene-based super engineering plastics such as polyetheretherketone and polysulfone using thiols via selective carbon-oxygen main chain cleavage to form electron-deficient arenes with sulfur functional groups and bisphenols. The catalyst combination of a bulky phosphazene base P4-tBu with inorganic bases such as tripotassium phosphate enabled smooth decomposition. This method could be utilized with carbon- or glass fiber-enforced polyetheretherketone materials and a consumer resin. The sulfur functional groups in one product could be transformed to amino and sulfonium groups and fluorine by using suitable catalysts.

Solvent-Promoted Catalyst-Free Recycling of Waste Polyester and Polycarbonate Materials

Polymeric materials are indispensable in our daily lives. However, the generation of vast amounts of waste polymers poses significant environmental and ecological challenges. Instead of resorting to landfilling or incineration, strategies for polymer recycling offer a promising approach to mitigate environmental pollution. Pioneering studies have demonstrated the alcoholysis of waste polyesters and polycarbonates; however, these processes typically require the use of catalysts. Moreover, the development of strategies for catalyst removal and recycling is crucial, particularly in some industrial applications. In contrast, we present a catalyst-free method for the alcoholysis of common polyester and polycarbonate materials into small organic molecules. Certain polar organic solvents exhibit remarkable efficiency in polymer degradation under catalyst-free conditions. Employing these polar solvents, both polymer resins and commercially available products could be effectively degraded via alcoholysis. Our design contributes a straightforward route for recycling waste polymeric materials.

Hydroxylation-Depolymerization of Oxyphenylene-Based Super Engineering Plastics To Regenerate Arenols

Super engineering plastics, high-performance thermoplastic resins, show high thermal stability and mechanical strength as well as chemical resistance. On the other hand, chemical recycling for these plastics has not been developed due to their stability. This study describes depolymerization of oxyphenylene super engineering plastics via carbon-oxygen main chain cleaving hydroxylation reaction with an alkali hydroxide nucleophile. This method is conducted with cesium hydroxide as a hydroxy source and calcium hydride as a dehydration agent in 1,3-dimethyl-2-imidazolidinone, which provides hydroxylated monomers effectively. In the case of polysulfone, both 4,4'-sulfonyldiphenol (bisphenol S) and 4,4'-(propane-2,2-diyl)diphenol (bisphenol A) were obtained in high yields. Other super engineering plastics such as polyethersulfone, polyphenylsulfone, and polyetheretherketone were also applicable to this depolymerization.

Simultaneous electrochemical detection of dimethyl bisphenol A and bisphenol A using a novel Pt@SWCNTs-MXene-rGO modified screen-printed sensor

Since bisphenol A (BPA) and dimethyl bisphenol A (DM-BPA) are human endocrine disruptors (EDCs) with tiny potential differences (44 mV) and widespread applications, there is a lack of published reports on their simultaneous detection. Therefore, this study reports a novel electrochemical detection system capable of simultaneous direct detection of BPA and DM-BPA using screen-printed carbon electrodes (SPCE) as a sensing platform. To improve the electrochemical performance of the SPCE, the SPCE was modified by using a combination of Pt nanoparticles modified with single-walled carbon nanotubes (Pt@SWCNTs), MXene (Ti₃C₂), and graphene oxide (GO). In addition, the GO in Pt@SWCNTs-MXene-GO was reduced to reduced graphene oxide (rGO) by the action of electric field (-1.2 V), which significantly improved the electrochemical properties of the composites and effectively solved the problem of dispersion of the modified materials on the electrode surface. Under optimal experimental conditions, Pt@SWCNTs-Ti₃C₂-rGO/SPCE exhibited a suitable detection range (0.006-7.4 μmol L^-1) and low detection limits (2.8 and 3 nmol L^-1, S/N = 3) for the simultaneous detection of BPA (0.392 V vs. Ag/AgCl) and DM-BPA (0.436 V vs. Ag/AgCl)). Thus, this study provides new insights into detecting compounds with similar structures and slight potential differences. Finally, the developed sensor's reproducibility, stability, interference resistance and accuracy were demonstrated with satisfactory results.

Global plastic upcycling during and after the COVID-19 pandemic: The status and perspective

Plastic pollution has become one of the most pressing environmental issues worldwide since the vast majority of post-consumer plastics are hard to degrade in the environment. The coronavirus disease (COVID-19) pandemic had disrupted the previous effort of plastic pollution mitigation to a great extent due to the overflow of plastic-based medical waste. In the post-pandemic era, the remaining challenge is how to motivate global action towards a plastic circular economy. The need for one package of sustainable and systematic plastic upcycling approaches has never been greater to address such a challenge. In this review, we summarized the threat of plastic pollution during COVID-19 to public health and ecosystem. In order to solve the aforementioned challenges, we present a shifting concept, regeneration value from plastic waste, that provides four promising pathways to achieve a sustainable circular economy: 1) Increasing reusability and biodegradability of plastics; 2) Transforming plastic waste into high-value products by chemical approaches; 3) The closed-loop recycling can be promoted by biodegradation; 4) Involving renewable energy into plastic upcycling. Additionally, the joint efforts from different social perspectives are also encouraged to create the necessary economic and environmental impetus for a circular economy.

Polycarbonate microplastics induce oxidative stress in anaerobic digestion of waste activated sludge by leaching bisphenol A

Polycarbonate (PC) microplastics are frequently detected in waste activated sludge. However, understanding the potential impact of PC microplastics on biological sludge treatment remains challenging. By tracking the changes in methane production under different concentrations of PC microplastics, a dose-dependent effect of PC microplastics on anaerobic digestion of sludge was observed. PC microplastics at 10-60 particles/g total solids (TS) improved methane production by up to 24.7 ± 0.1 % (at 30 particles/g TS), while 200 particles/g TS PC microplastics reduced methane production by 8.09 ± 0.1 %. Bisphenol A (BPA) leached from 30 particles/g TS PC microplastics (1.26 ± 0.18 mg/L) down-regulated intracellular reactive oxygen species (ROS) production, thereby enhancing enzyme activity, biomass viability, and abundance of methanogenic (Methanobacterium sp. and Methanosarcina sp.), ultimately boosting methane production. Conversely, BPA leached from 200 particles/g TS PC microplastics (4.02 ± 0.15 mg/L) stimulated ROS production, resulting in decreased biomass viability and even apoptosis. Modulation of oxidative stress by leaching monomeric BPA is an underappreciated transformative mechanism for improving the mastery of the potential behavior of microplastics in biological sludge treatment.

Advances in the Synthesis of Chemically Recyclable Polymers

The development of modern society is closely related to polymer materials. However, the accumulation of polymer materials and their evolution in the environment causes not only serious environmental problems, but also waste of resources. Although physical processing can be used to reuse polymers, the properties of the resulting polymers are significantly degraded. Chemically recyclable polymers, a type of polymer that degrades into monomers, can be an effective solution to the degradation of polymer properties caused by physical recycling of polymers. The ideal chemical recycling of polymers, i. e., quantitative conversion of the polymer to monomers at low energy consumption and repolymerization of the formed monomers into polymers with comparable properties to the original, is an attractive research goal. In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the "polymerization-depolymerization" equilibrium and closed-loop recycling under mild conditions. This review will focus on the following aspects of closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymer, illustrate the challenges in this area, and provide an outlook on future directions.

Depolymerization of robust polyetheretherketone to regenerate monomer units using sulfur reagents

Super engineering plastics, high-performance thermoplastic resins such as polyetheretherketone, and polyphenylene sulfide have been utilized in industries, owing to their high thermal stability and mechanical strength. However, their robustness hinders their depolymerization to produce monomers and low-weight molecules. Presently, chemical recycling for most super engineering plastics remains relatively unexplored. Herein, we report the depolymerization of insoluble polyetheretherketone using sulfur nucleophiles via carbon-oxygen bond cleavages to form benzophenone dithiolate and hydroquinone. Treatment with organic halides converted only the former products to afford various dithiofunctionalized benzophenones. The depolymerization proceeded as a solid-liquid reaction in the initial phase. Therefore, this method was not affected by the shape of polyetheretherketone, e.g., pellets or films. Moreover, this depolymerization method was applicable to carbon- or glass fiber-enforced polyetheretherketone material. The depolymerized product, dithiofunctionalized benzophenones, could be converted into diiodobenzophenone, which was applicable to the polymerization.

Closed-Loop Recycling of Poly(Imine-Carbonate) Derived from Plastic Waste and Bio-based Resources

Closed-loop recycling of polymers represents the key technology to convert plastic waste in a sustainable fashion. Efficient chemical recycling and upcycling strategies are thus highly sought-after to establish a circular plastic economy. Here, we present the selective chemical depolymerization of polycarbonate by employing a vanillin derivative as bio-based feedstock. The resulting di-vanillin carbonate monomer was used in combination with various amines to construct a library of reprocessable poly(imine-carbonate)s, which show tailor-made thermal and mechanical properties. These novel poly(imine-carbonate)s exhibit excellent recyclability under acidic and energy-efficient conditions. This allows the recovery of monomers in high yields and purity for immediate reuse, even when mixed with various commodity plastics. This work provides exciting new insights in the design of bio-based circular polymers produced by upcycling of plastic waste with minimal environmental impact.

Theoretical Study on the Hydrogenolysis of Polyurethanes to Improve the Catalytic Activities

The metal-catalyzed hydrogenolysis of polymers is important in waste recycling; however, it is limited by the harsh reaction conditions and the low activities of catalysts, especially for earth-abundant metal-based catalysts. Herein, we perform a comprehensive study on the hydrogenolysis of polyurethane model catalyzed by Fe-, Mn-, Ru-, and Ir-^iPrMACHO pincer complexes and propose a cascade mechanism comprising two-level hydrogenolysis and the hydrogenation of formaldehyde. In addition, the substrates and ligands are modulated to improve the activities of chemical recycling to monomer. It is found that the pincer ligands could dissociate from the metal centers at high reaction temperatures and further result in the deactivation of catalysts. The rigid Fe and Mn catalysts with tetradentate cyclic ligands are designed following the guidance, and the computations suggest that those designed catalysts could have high stabilities and activities.

Absorption, distribution, metabolism, excretion and toxicity of microplastics in the human body and health implications

Microplastics (MPs; <5 mm) in the biosphere draws public concern about their potential health impacts. Humans are potentially exposed to MPs via ingestion, inhalation, and dermal contact. Ingestion and inhalation are the two major exposure pathways. An adult may consume approximately 5.1 × 10³ items from table salts and up to 4.1 × 10⁴ items via drinking water annually. Meanwhile, MP inhalation intake ranges from 0.9 × 10⁴ to 7.9 × 10⁴ items per year. The intake of MPs would be further distributed in different tissues and organs of humans depending on their sizes. The excretion has been discussed with the possible clearance ways (e.g., urine and feces). The review summarized the absorption, distribution, metabolic toxicity and excretion of MPs together with the attached chemicals. Moreover, the potential implications on humans are also discussed from in vitro and in vivo studies, and connecting the relationship between the physicochemical properties and the potential risks. This review will contribute to a better understanding of MPs as culprits and/or vectors linking to potential human health hazards, which will help outline the promising areas for further revealing the possible toxicity pathways.

Rapid determination of key impurities in high purity bisphenol A with reversed phase separation and triple quadrupole mass spectrometry

Liquid chromatography with diode array detection (DAD) or ultraviolet spectroscopic (UV) detection as the most important analytical technique for the accurate quantification of impurities in bisphenol compounds normally requires long analysis time for baseline separation of all components as well as highly concentrated sample solutions for the detection of trace levels. To expand the application possibilities to all stages of polymerisation processes, an easy and robust reversed phase separation for 7 known impurities of bisphenol-A (BPA) including 4-isopropenylphenol and its dimeric isomers, o, p-bisphenol-A and trisphenol was established in this work. The method has been validated for the detection with triple quadrupole mass spectrometry (qqqMS) and DAD. In the investigated concentration range 0.5 - 100 mg/kg, the linearity is verified for both detection techniques. The limit of quantification (LOQ) for each impurity is with 0.5 - 1.5 mg/kg for qqqMS and 15 mg/kg for DAD sufficient for the evaluation of BPA as a raw material for polymerisation processes. The separation time for all impurities is 10 min whereas earlier reported methods need a minimum of 25 to 40 min. In addition the necessary sample concentration of BPA could be reduced to 5 mg/mL compared to existing methods where the sample concentration typically is > 50 mg/mL. For all those reasons the validated method can be efficiently applied for frequent process monitoring. Furthermore, 4 additional impurities were detected and identified. Mainly these are reaction products from the isopropenylphenol structure in combination with confirmed impurities as trisphenol or chroman. The quantification of these structures was established with trisphenol as reference and two structures were detected in all BPA qualities of this study in a concentration range from 20 - 400 mg/kg.

Upcycling Compact Discs for Flexible and Stretchable Bioelectronic Applications

Electronic waste is a global issue brought about by the short lifespan of electronics. Viable methods to relieve the inundated disposal system by repurposing the enormous amount of electronic waste remain elusive. Inspired by the need for sustainable solutions, this study resulted in a multifaceted approach to upcycling compact discs. The once-ubiquitous plates can be transformed into stretchable and flexible biosensors. Our experiments and advanced prototypes show that effective, innovative biosensors can be developed at a low-cost. An affordable craft-based mechanical cutter allows pre-determined patterns to be scored on the recycled metal, an essential first step for producing stretchable, wearable electronics. The active metal harvested from the compact discs was inert, cytocompatible, and capable of vital biopotential measurements. Additional studies examined the material’s resistive emittance, temperature sensing, real-time metabolite monitoring performance, and moisture-triggered transience. This sustainable approach for upcycling electronic waste provides an advantageous research-based waste stream that does not require cutting-edge microfabrication facilities, expensive materials, and high-caliber engineering skills.

Electronic waste is a global issue brought about by the short lifespan of electronics. Here, the authors report a process to upcycle compact discs into flexible and stretchable bio-electronics.

Introducing SuFEx click chemistry into aliphatic polycarbonates: a novel toolbox/platform for post-modification as biomaterials

As a biodegradable and biocompatible biomaterial, aliphatic polycarbonates (APCs) have attracted substantial attention in terms of post-polymerization modification (PPM) for functionalization. A strategy for the introduction of sulfur(VI)-fluoride exchange (SuFEx) click chemistry into APCs for PPM is proposed for the first time in this work. 4'-(Fluorosulfonyl)benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (FMC) was designed as a SuFEx clickable cyclic carbonate for APCs via ring-opening polymerization (ROP), and an operational and nontoxic synthetic route was achieved. FMC managed to undergo both ROP and PPM through the SuFEx click chemistry organocatalytically without constraining or antagonizing each other, using 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) as a co-organocatalyst here. Its ROP was systematically investigated, and density functional theory (DFT) calculations were performed to understand the acid-base catalytic mechanism in the anionic ROP. Exploratory investigations into PPM by SuFEx of poly(FMC) were conducted as biomaterials, and the one-pot strategies to achieve both ROP and SuFEx were confirmed.

Versatile Chemical Recycling Strategies: Value-Added Chemicals from Polyester and Polycarbonate Waste

Zn^II -complexes bearing half-salan ligands were exploited in the mild and selective chemical upcycling of various commercial polyesters and polycarbonates. Remarkably, we report the first example of discrete metal-mediated poly(bisphenol A carbonate) (BPA-PC) methanolysis being appreciably active at room temperature. Indeed, Zn(2)₂ and Zn(2)Et achieved complete BPA-PC consumption within 12-18 mins in 2-Me-THF, noting high bisphenol A (BPA) yields (S_BPA =85-91 %) within 2-4 h. Further kinetic analysis found such catalysts to possess k_app values of 0.28±0.040 and 0.47±0.049 min^-1 respectively at 4 wt%, the highest reported to date. A completely circular upcycling approach to plastic waste was demonstrated through the production of several renewable poly(ester-amide)s (PEAs), based on a terephthalamide monomer derived from bottle-grade poly(ethylene terephthalate) (PET), which exhibited excellent thermal properties.

Functional use of CO2 to mitigate the formation of bisphenol A in catalytic pyrolysis of polycarbonate

The growing consumption of plastic materials has increased hazardous threats to all environmental media, since current plastic waste management methods release microplastics and toxic chemicals. As such, massive generation of plastic derived pollutants leads to significant public health and environmental problems. In this work, an environmentally sound method for valorization of plastic waste is suggested. In detail, pyrolysis of polycarbonate-containing plastic waste such as automotive headlight housing (AHH) was carried out using CO₂ as a co-reactant. AHH was chosen as it discharges bisphenol A (BPA) and aromatic compounds. Under CO₂ condition, emissions of BPA and its derivatives were suppressed by 14.5% due to gas phase reactions (GPRs) with CO₂. Nevertheless, reaction kinetics for GPRs was not significant. To impart the GPRs, catalytic pyrolysis was done using Ni and Co-based catalysts. During catalytic pyrolysis, syngas production was more than tenfold up comparing to pyrolysis without catalyst. The expedited GPRs over catalysts resulted in the enhanced syngas formation. Total concentration of the toxic chemicals from CO₂-assisted catalytic pyrolysis of AHH decreased by 86.1% and 66.7% over Ni and Co catalysts, comparing to those from N₂ environment.

On the photopolymerization of mevalonic lactone methacrylate: exposing the potential of an overlooked monomer

This manuscript will exhibit the photopolymerization of mevalonic lactone methacrylate, an overlooked monomer, and how functional polymers with lactone pendant units can be synthesized.

Chemical upcycling ofpolymers

As the production volume of polymers increases, so does the amount of plastic waste. Plastic recycling is one of the concepts to address in this issue. Unfortunately, only a small fraction of plastic waste is recycled. Even with the development of polymers for closed loop recycling that can be in theory reprocessed infinitely the inherent dilemma is that because of collection, cleaning and separation processes the obtained materials simply are not cost competitive with virgin materials. Chemical upcycling, the conversion of polymers to higher valuable products, either polymeric or monomeric, could mitigate this issue. In the following article, we highlight recent examples in this young but fast-growing field. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

Plastic waste, which is one of the major sources of pollution in the landfills and oceans, has raised global concern, primarily due to the huge production rate, high durability, and the lack of utilization of the available waste management techniques. Recycling methods are preferable to reduce the impact of plastic pollution to some extent. However, most of the recycling techniques are associated with different drawbacks, high cost and downgrading of product quality being among the notable ones. The sustainable option here is to upcycle the plastic waste to create high-value materials to compensate for the cost of production. Several upcycling techniques are constantly being investigated and explored, which is currently the only economical option to resolve the plastic waste issue. This Review provides a comprehensive insight on the promising chemical routes available for upcycling of the most widely used plastic and mixed plastic wastes. The challenges inherent to these processes, the recent advances, and the significant role of the science and research community in resolving these issues are further emphasized.

Chemical Upcycling of Waste Poly(bisphenol A carbonate) to 1,4,2-Dioxazol-5-ones and One-Pot C-H Amidation

Chemical upcycling of poly(bisphenol A carbonate) (PC) was achieved in this study with hydroxamic acid nucleophiles, giving rise to synthetically valuable 1,4,2-dioxazol-5-ones and bisphenol A. Using 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD), non-green carbodiimidazole or phosgene carbonylation agents used in conventional dioxazolone synthesis were successfully replaced with PC, and environmentally harmful bisphenol A was simultaneously recovered. Assorted hydroxamic acids exhibited good-to-excellent efficiencies and green chemical features, promising broad synthetic application scope. In addition, a green aryl amide synthesis process was developed, involving one-pot depolymerization from polycarbonate to dioxazolone followed by rhodium-catalyzed C-H amidation, including gram-scale examples with used compact discs.

Biodegradation of bisphenol-A polycarbonate plastic by Pseudoxanthomonas sp. strain NyZ600

Bisphenol-A polycarbonate (PC) is a widely used engineering thermoplastic and its release has caused damage to the ecosystem. Microbial degradation of plastic represents a sustainable approach for PC reduction. In this study, a bacterial strain designated Pseudoxanthomonas sp. strain NyZ600 capable of degrading PC was isolated from activated sludge by using diphenyl carbonate as a surrogate substrate. Within a 30-day period of incubating with strain NyZ600, PC films were analyzed with atomic force microscopy, scanning electron microscope, water contact angle, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, differential scan calorimeter and thermogravimetric analysis technique. The analyses results indicated that the treated PC films were bio-deteriorated and formed some "corrosion pits" on the PC film surface. In addition, strain NyZ600 performed broad depolymerization of PC indicated by the reduction of Mn from 23.55 to 16.75 kDa and Mw from 45.67 to 31.97 kDa and two degradation products bisphenol A and 4-cumylphenol (the two monomers of PC) were also found, which established that PC were biodegraded by strain NyZ600. Combing all above results, it is clear that the strain NyZ600 can degrade PC which provides a unique example for bacterial degradation of PC and a feasibility for the removal of PC waste.

Valorisation of plastic waste via metal-catalysed depolymerisation

Metal-catalysed depolymerisation of plastics to reusable building blocks, including monomers, oligomers or added-value chemicals, is an attractive tool for the recycling and valorisation of these materials. The present manuscript shortly reviews the most significant contributions that appeared in the field within the period January 2010–January 2020 describing selective depolymerisation methods of plastics. Achievements are broken down according to the plastic material, namely polyolefins, polyesters, polycarbonates and polyamides. The focus is on recent advancements targeting sustainable and environmentally friendly processes. Biocatalytic or unselective processes, acid–base treatments as well as the production of fuels are not discussed, nor are the methods for the further upgrade of the depolymerisation products.

Advances, Challenges, and Opportunities of Poly(γ-butyrolactone)-Based Recyclable Polymers

The discovery and prosperous growth of synthetic polymers have presented both significant advantages and daunting challenges in the last century. To address the issues of environmental pollution and fossil consumption, recyclable, degradable, and/or biobased polymers have been given much attention in the polymer science community. This viewpoint focuses on the emerging fully chemical recyclable poly(γ-butyrolactone)-based polymers. The breakthrough from nonpolymerizable to efficient polymerization is highlighted by the benefits of the development of a series of catalysis for ring-opening polymerization of γ-butyrolactone. Subsequently, the design of γ-butyrolactone derivatives and synthesis of more recyclable polymers are summarized together with the discussions about the structure and property relationship. Finally, the remaining challenges and promising opportunities are suggested in order to provide insights into the further direction for sustainable polymers.

Chemical recycling of poly-(bisphenol A carbonate) by diaminolysis: A new carbon-saving synthetic entry into non-isocyanate polyureas (NIPUreas)

The present study describes an unprecedented approach to valorize potentially hazardous poly-(bisphenol A carbonate) (PC) wastes. In THF, under non-severe conditions (120 °C), the reaction of PC with long-chain diamines H₂NRNH₂ (2 equivalents) provided a tool to regenerate the monomer bisphenol A (BPA; 83-95%, isolated) and repurpose waste PC into [-NHRNHCO-]_n polyureas (PUs; 78-99%, isolated) through a non-isocyanate route. Basic diamines (1,6-diaminohexane, 4,7,10-trioxa-1,13-tridecanediamine, meta-xylylenediamine, para-xylylenediamine) reacted with PC without any auxiliary catalyst; less reactive aromatic diamines (4,4'-diaminodiphenylmethane, 2,4-diaminotoluene) required the assistance of a base catalyst (1,8-diazabicyclo[5.4.0]undec-7-ene, NaOH). The formation of [-NHRNHCO-]_n goes through a carbamation step affording BPA and carbamate intermediates H[-OArOC(O)NHRNHC(O)-]_nOArOH (Ar=4,4'-C₆H₄C(Me)₂C₆H₄-) that, in a subsequent step, convert into [-NHRNHCO-]_n and more BPA. All the PUs were characterized in the solid state by CP/MAS ¹³C NMR (δ(CO) = 152-161 ppm) and IR spectroscopy. The positions of ν(N-H) and ν(CO) absorptions are typical of "hydrogen-bonded ordered" bands suggesting the presence of H-bonded groups in network structures characterized by some degree of order or regularity. DSC and TGA analyses showed that the PUs are thermally stable (T_d,5%: 212-270 °C) and suitable for being processed since their degradation begins at temperatures about 100 °C higher than their T_g or T_m.