Polyester Plastics Research Articles

Electrochemical Upgrading of Waste Polylactic Acid Plastic for the Coproduction of C2 Chemicals and Green Hydrogen

Tandem alkali-catalyzed hydrolysis and alkaline electrolysis have gradually become appealing avenues for the reformation of polyester plastics into high-value-added chemicals and green hydrogen with remarkable environmental and economic benefits. In this study, an electrochemical upcycling strategy was developed for the electrocatalytic oxidation of polylactic acid (PLA) hydrolysate into valued C2 chemicals (i.e., acetate) and hydrogen fuel using N, P-doped CuOx nanowires (NW) supported on nickel foam (NF) as the electrocatalyst. This 3D well-integrated catalyst was easily prepared from a Cu(OH)2 NW/NF precursor with Saccharomycetes as a green and safe P and N source. The electrocatalyst can efficiently catalyze the lactate monomer derived from the hydrolysis of PLA waste to acetate with high selectivity and exhibits a lower onset potential for the lactate oxidation reaction (LOR) than for water oxidation, saving 224 mV to deliver a current density of 30 mA/cm2. The experimental results reveal that the plausible pathway of the LOR on these CuOx NW involves oxidation and subsequent decarboxylation. Divalent copper species have been verified to be active sites for LOR via in situ Raman spectroscopy.

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.

Task-Specific Deep Eutectic Solvent for Efficient Dissolution and Further Accelerating Alkaline Hydrolysis of Polyesters Into Their Monomers.

Polyester plastics have brought great convenience to modern society. However, the continuous accumulation of their production increasingly threatens human health. Polyethylene terephthalate (PET) is one of the largest type of polyester plastics and its recycling is a major challenge. In this work, deep eutectic solvent (DES) composed of thenyl alcohol and choline chloride (ChCl) was designed for efficient dissolution of PET at 165 °C for 20 min, and further accelerating complete alkaline hydrolysis of PET into its monomer terephthalic acid (TPA) and ethylene glycol (EG) with a high TPA monomer yield (98.2 %) in 25 min at 100 °C. Moreover, the designed DES is also efficient for dissolution and alkaline hydrolysis of other polyester plastics, including poly(trimethylene terephthalate) (PTT) and poly(ethylene furanoate) (PEF) into their monomers. This work provides a feasible and sustainable solution for the recycling of polyester wastes.

Evaluation of char properties from co-pyrolysis of biomass/plastics: effect of different types of plastics

Co-pyrolysis of biomass/plastics is a viable method to obtain high-quality carbon materials. The synergistic effect in the char production process of co-pyrolysis of biomass/plastics affects the properties of the obtained char. However, the synergistic effect research on the char production process of co-pyrolysis of biomass/plastics is facing challenges owing to highly varying composition of different plastics. In this study, the synergistic effect during co-pyrolysis of bamboo (BM) and plastics (polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polycarbonate (PC), and polybutylene terephthalate (PBT)) was investigated. TG results showed that PP, PS, PET, and PBT promoted the release of biomass volatiles and increased co-pyrolysis char yield. Notably, the O-aromatic structure in PC underwent cleavage and deoxygenation reactions, inhibiting the production of co-pyrolysis char during co-pyrolysis process. Char yield from co-pyrolysis process decreased from 24.80% for bamboo pyrolysis to 15.74% for co-pyrolysis of bamboo/PC. The results of physicochemical tests on char samples indicated that the addition of polyhydrocarbon plastics (PP and PS) increased H/C ratio, O/C ratio, heating value and oxidative reactivity of the char compared to bamboo char due to the vapor deposition of hydrocarbons derived from thermal decomposition of plastics on the biomass char. While, co-pyrolysis of biomass and polyester plastics (PET, PC, PBT) improved the pore structure of char and increased oxygen content.

Enhanced degradation of polyethylene terephthalate (PET) microplastics by an engineered Stenotrophomonas pavanii in the presence of biofilm

Polyethylene terephthalate (PET) microplastics pose significant environmental and human health risks due to their resistance to degradation and accumulation in ecosystems. In this study, we engineered Stenotrophomonas pavanii JWG-G1, a robust biofilm-forming bacterium, to overexpress the PET hydrolase (DuraPETase) for PET microplastics degradation at ambient temperature. Nine endogenous PET hydrolases were identified through genome sequencing of S. pavanii, and were successfully expressed in Escherichia coli BL21(DE3). Among them, hydrolase Est_B achieved 100% degradation of bis(2-hydroxyethyl) terephthalate (BHET) at an initial concentration of 0.23 mg/mL at 30 °C within 4 h, identifying it as a novel BHETase. However, the PET degradation performance of all endogenous PET hydrolases was inferior to that of DuraPETase. The engineered strain overexpressing DuraPETase demonstrated a significant enhancement in PET degradation, achieving a 38.04 μM total product release of high-crystallinity PET microplastics after 30 days at 30 °C. The degradation extent was greater than that of low biofilm-forming engineered strains, attributing to the aggregation of DuraPETase on the PET surface in the presence of biofilm. Additionally, this engineered strain also maintained PET degradation activity across various water environments and demonstrated effectiveness in degrading other polyester plastics. This is the first report demonstrating that an engineered strain of Stenotrophomonas species is capable of simultaneously secreting exogenous hydrolase and degrading polyester microplastics, representing a novel approach in the development of engineered bacteria with potential applications in bioreactor systems and environmental remediation.

Fully biobased poly(butylene furanoate) copolyesters from renewable 2,3-butanediol: Much more than just strengthening and toughening

Making full use of renewable biomass resources to develop biobased polyester plastics with balanced performance is an important part of achieving a low-carbon circular economy. As a representative variety of biobased furan polyesters, the insufficient mechanical properties limit the application of poly(butylene furanoate) (PBF) toward sustainable film materials. This study proposes a trade-off strategy by inserting the rigid biobased 2,3-butanediol (2,3-BDO) unit into the PBF molecular chain. The results show that inserting a small amount of 2,3-BDO can simultaneously realize the strengthening and toughening of PBF. When the content of 2,3-BDO reaches only 4 mol%, the copolymer possesses the tensile strength of 67.0 MPa with the elongation at break of 556.2 %. More appealingly, the crystallizability and barrier properties of copolymers can still be maintained to a certain extent. In general, by inserting a small amount of rigid 2,3-BDO unit, the fully biobased copolyesters can achieve a good balance in terms of crystallization, mechanical, and barrier properties, guaranteeing them to meet the requirements where high strength and toughness are needed.

Selective hydrophilization based on alkaline-catalyzed alcoholysis: An approach to enhance the flotation of waste polyesters

Polyester plastics, constituting a substantial segment of the global plastic market, offer considerable potential market for the polyesters recycling. This study proposed an efficient separation technology for waste polyesters through flotation assisted by alkaline-catalyzed alcoholysis modification. The alkaline-catalyzed alcoholysis modification facilitates the selective hydrophilization of waste polyesters, regulating their float-sink behavior in flotation. According to the polyester floatability, the hydrophilicity of the modified polyesters is in order of PA6 > PET ≈ PU > PC > PMMA. Due to the different C–O and C–N bond strength, the modification selectively induced alcoholysis on the polyesters surface, enhancing their hydrophilicity by increasing the number of rough structure and hydrophilic functional groups on surfaces rather than introducing heteroatoms. The sinking products in flotation, including polyamide 6 (PA6), polyethylene terephthalate (PET), and polyurethane (PU), could be separated from the floating products, such as polycarbonate (PC), and polymethyl methacrylate (PMMA). The binary separation was achieved under optimum conditions. The recovery and purity of PA6, PET, and PU could reach 100.0 % and 100.0 %, 100.0 % and 85.7 %, 79.9 % and 83.1 %, respectively. Consequently, the heterogeneous alcoholysis reactivity contributes to the selective hydrophilization of waste polyesters. This study established a hydrophilicity order of modified polyesters, and promoted flotation separation of waste polyesters.

Ultrathin Porous Carbon Nitride Anchored with Pt Nanoclusters for Synergistic Enhancement of Hydrogen Production in Alkaline Photocatalytic Polyester Reforming.

Photocatalytic reforming (PR) of polyester waste, fueled by renewable sources like solar energy, offers a sustainable method for producing clean H2 and valuable by-products under mild conditions. The design of high-performance photocatalyst plays a pivotal role in determining the efficacy of an alkaline polyester PR system, influencing H2 generation activity and selectivity. Here, ultrathin porous carbon nitride nanosheets (UP-CN) loaded with Pt nanoclusters (Pt NCs, average diameter of 1.7nm) with uniform Pt NCs distribution are introduced. The resulting Pt NCs/UP-CN catalyst can accelerate charge and mass transfer while providing additional active sites, achieving superior H2 generation rates of 11.69mmol gcat -1 h-1 and 2923mmol gPt -1 h-1 under AM 1.5 light, which nine times higher than that of Pt nanoparticles-bulk graphitic carbon nitride composite (1.29mmol gcat -1 h-1 and 258mmol gPt -1 h-1) as counterpart. This performance also surpasses that of previously reported carbon nitride-based and TiO2-based photocatalysts. Moreover, the density functional theory calculations reveal a significant reduction in the energy barrier for the water dissociation step (H2O + * → *H + OH) at the interface between UP-CN and anchored Pt NCs, showcasing the synergistic effect between Pt NCs and UP-CN. This catalytic system also exhibits universality across various polyester plastics.

A super-toughened polyethylene naphthalene (PEN) enabled by polyacrylate elastomer with low crosslink density and reactivity

In elastomer toughening of polyester plastics, both the particle size distribution of the elastomer and the interfacial strength between the elastomer and matrix are key factors for toughness. In this work, bi-functional polyacrylate elastomers with controllable crosslinking density and reactivity were designed for enhancing the toughness of polyethylene naphthalene (PEN) matrix. Firstly, the elastomers with crosslinked structure possess increased melt viscosity and endowed wide particle size distribution, which contribute to the construct of thin matrix ligament and make PEN matrix more susceptible to shear-yield. Secondly, the high interfacial strength between elastomer and matrix can facilitate the transfer of external stress from PEN matrix to the elastomer, protecting the matrix from destroying. The resulted PEN blends exhibit an excellent impact resistance of 45.20 kJ/m2 and a high tensile toughness of 3.586 MJ/m3, which are 21.73 times and 47.81 times higher, respectively, than the virgin PEN. The present work may provide an effective approach for designing polyester blends with enhanced impact resistance and tensile toughness.

Efficient biodegradation of Polyethylene terephthalate (PET) plastic by Gordonia sp. CN2K isolated from plastic contaminated environment

Since we rely entirely on plastics or their products in our daily lives, plastics are the invention of the hour. Polyester plastics, such as Polyethylene Terephthalate (PET), are among the most often used types of plastics. PET plastics have a high ratio of aromatic components, which makes them very resistant to microbial attack and highly persistent. As a result, massive amounts of plastic trash accumulate in the environment, where they eventually transform into microplastic (<5 mm). Rather than macroplastics, microplastics are starting to pose a serious hazard to the environment. It is imperative that these polymer microplastics be broken down. Through the use of enrichment culture, the PET microplastic-degrading bacterium was isolated from solid waste management yards. Bacterial strain was identified as Gordonia sp. CN2K by 16 S rDNA sequence analysis and biochemical characterization. It is able to use polyethylene terephthalate as its only energy and carbon source. In 45 days, 40.43 % of the PET microplastic was degraded. By using mass spectral analysis and HPLC to characterize the metabolites produced during PET breakdown, the degradation of PET is verified. The metabolites identified in the spent medium included dimer compound, bis (2-hydroxyethyl) terephthalate (BHET), mono (2-hydroxyethyl) terephthalate (MHET), and terephthalate. Furthermore, the PET sheet exposed to the culture showed considerable surface alterations in the scanning electron microscope images. This illustrates how new the current work is.

Novel polyurethane-degrading cutinase BaCut1 from Blastobotrys sp. G-9 with potential role in plastic bio-recycling

Environmental pollution caused by plastic waste has become global problem that needs to be considered urgently. In the pursuit of a circular plastic economy, biodegradation provides an attractive strategy for managing plastic wastes, whereas effective plastic-degrading microbes and enzymes are required. In this study, we report that Blastobotrys sp. G-9 isolated from discarded plastic in landfills is capable of depolymerizing polyurethanes (PU) and poly (butylene adipate-co-terephthalate) (PBAT). Strain G-9 degrades up to 60% of PU foam after 21 days of incubation at 28 ℃ by breaking down carbonyl groups via secretory hydrolase as confirmed by structural characterization of plastics and degradation products identification. Within the supernatant of strain G-9, we identify a novel cutinase BaCut1, belonging to the esterase family, that can reproduce the same effect. BaCut1 demonstrates efficient degradation toward commercial polyester plastics PU foam (0.5 mg enzyme/25 mg plastic) and agricultural film PBAT (0.5 mg enzyme/10 mg plastic) with 50% and 18% weight loss at 37 ℃ for 48 h, respectively. BaCut1 hydrolyzes PU into adipic acid as a major end-product with 42.9% recovery via ester bond cleavage, and visible biodegradation is also identified from PBAT, which is a beneficial feature for future recycling economy. Molecular docking, along with products distribution, elucidates a special substrate-binding modes of BaCut1 with plastic substrate analogue. BaCut1-mediated polyester plastic degradation offers an alternative approach for managing PU plastic wastes through possible bio-recycling.

From Polyester Plastics to Diverse Monomers via Low-Energy Upcycling.

Polyester plastics, constituting over 10% of the total plastic production, are widely used in packaging, fiber, single-use beverage bottles, etc. However, their current depolymerization processes face challenges such as non-broad spectrum recyclability, lack of diversified high-value-added depolymerization products, and crucially high energy consumption. Herein, an efficient strategy is developed for dismantling the compact structure of polyester plastics to achieve diverse monomer recovery. Polyester plastics undergo swelling and decrystallization with a low depolymerization energy barrier via synergistic effects of polyfluorine/hydrogen bonding, which is further demonstrated via density functional theory calculations. The swelling process is elucidated through scanning electron microscopy analysis. Obvious destruction of the crystalline region is demonstrated through X-ray crystal diffractometry curves. PET undergoes different aminolysis efficiently, yielding nine corresponding high-value-added monomers via low-energy upcycling. Furthermore, four types of polyester plastics and five types of blended polyester plastics are closed-loop recycled, affording diverse monomers with exceeding 90% yields. Kilogram-scale depolymerization of real polyethylene terephthalate (PET) waste plastics is successfully achieved with a 96% yield.

Characterization and engineering of plastic-degrading polyesterases jmPE13 and jmPE14 from Pseudomonas bacterium.

Polyester plastics are widely used in daily life, but also cause a large amount of waste. Degradation by microbial enzymes is the most promising way for the biobased upcycling of the wastes. However, there is still a shortage of high-performance enzymes, and more efficient polyester hydrolases need to be developed. Here we identified two polyester hydrolases, jmPE13 and jmPE14, from a previously isolated strain Pseudomonas sp. JM16B3. The proteins were recombinantly expressed and purified in E. coli, and their enzymatic properties were characterized. JmPE13 and jmPE14 showed hydrolytic activity towards polyethylene terephthalate (PET) and Poly (butylene adipate-co-terephthalate) (PBAT) at medium temperatures. The enzyme activity and stability of jmPE13 were further improved to 3- and 1.5-fold, respectively, by rational design. The results of our research can be helpful for further engineering of more efficient polyester plastic hydrolases and their industrial applications.

Catalytic depolymerization of polyester plastics toward closed-loop recycling and upcycling

Catalytic depolymerization of polyester plastics toward closed-loop recycling and upcycling

Preparation of Block Copolymers by a Sequential Transesterification Strategy: A Feasible Route for Upcycling End-of-Life Polyester Plastics to Elastomers

Preparation of Block Copolymers by a Sequential Transesterification Strategy: A Feasible Route for Upcycling End-of-Life Polyester Plastics to Elastomers

Medium entropy metal oxide induced *OH species targeted transfer strategy for efficient polyethylene terephthalate plastic recycling

Increasing plastic waste is environmentally and biologically detrimental, and converting plastic waste into value-added chemicals and fuels by electrocatalytic methods is recognized as an up-cycling process that facilitates resource utilization. Here, we report a generalized medium entropy metal oxide Ni0.5Ce0.5Co2O4 induced *OH species targeted transfer strategy to selectively electrocatalytic upgrade various polyester plastics into value-added chemicals under alkaline conditions. Polyethylene terephthalate (PET) was upgraded to potassium diformate with high Faraday efficiency (95 %) and selectivity (>91 %) at a high current density of 343 mA cm−2, generating both terephthalic acid and hydrogen. The synergistic interplay between Ni and Ce in Ni0.5Ce0.5Co2O4 facilitates the adsorption of ethylene glycol molecules and hydroxide ions, prompting the directionally oriented hydroxyl (*OH) to partake in the oxidation of ethylene glycol, thereby fostering the oxidation of hydrolyzed PET products. This work not only develops an excellent electrocatalyst for the upcycling of various polyester plastics but also guides the design of medium entropy metal oxides as electrocatalysts.

Determination of plastic polyester oligomers in real samples and their bioeffects.

Plastics are ubiquitously, becoming part of our everyday life. Recently, the issue of human exposure to micro- and nanoplastic particles and potentially resulting toxicological consequences has been broached, triggered by the discovery of microplastics in foodstuff and dietary exposure via contaminated food and beverages. Within this EU-FORA fellowship project, a determination and quantification of plastic polyester plastics oligomers in food samples was performed to assess exposure at these categories of 'nanoplastics', evaluating them as potential contaminants or as indicators and marker compounds of the exposure to specific nanoplastics/microplastics from polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). UHPLC-TOF-MS/MS analysis has been set-up for 10 PET and PBT oligomers and analysis has been performed in foods and drinks. Moreover, the project focused also on the effects of these oligomers in in vitro and ex vivo experiments. These data would be combined with EFSA Comprehensive Food Consumption Database, for the exposure and risk assessment of these 'Nanoplastics'.

Rapid marine degradable poly(butylene oxalate) by introducing promotion building blocks

The design and development of high-performance marine-degradable plastics have long been considered a superior strategy to address marine plastic pollution. To achieve a balance between rapid marine degradability and high performance of polyester plastics, this work designed two series of poly(butylene oxalate) (PBOx) copolymers with intrinsic hydrolysis ability using poly(ethylene oxalate) (PEOx) and poly(glycolic acid) (PGA) as promotion building blocks. The synthesis process, crystallization properties, barrier performance, and mechanical properties of copolymers were comparatively investigated. Additionally, the marine degradability of copolymers received specific focus. The theoretical calculation demonstrated that the introduction of promotion blocks reduced the hydrolysis energy barrier of the copolymers. In general, the results revealed the advantages of PBEOx copolymer in satisfying practicality and better regulating marine degradability. The high gas barrier performance, suitable thermal properties, tunable mechanical properties, and rapid marine degradability endow the copolymer as a promising candidate toward sustainable and marine-degradable plastics.

Solar-driven hydrogen evolution in alkaline seawater over earth-abundant g-C3N4/CuFeO2 heterojunction photocatalyst using microplastic as a feedstock

Production of sustainable H2 fuel by photoreforming plastic waste is an emerging novel approach to tackling environmental pollution and energy shortage. We developed a n-p heterojunction g-C3N4/CuFeO2 photocatalyst made of only earth-abundant elements using a simple and scalable process. The heterostructure effectively suppresses the charge recombination, which is evident from a significant reduction in the emission of photoluminescence in g-C3N4/CuFeO2 compared to that of g-C3N4. g-C3N4/CuFeO2 exhibits promising performance in photoreforming various kinds of polyester plastics. Notably, g-C3N4/CuFeO2 outperforms g-C3N4 and CuFeO2, showing more than 60-fold and 100-fold enhanced activity for H2 evolution by photoreforming hydrolyzed polyester microfiber, respectively. On the other hand, the nuclear magnetic resonance study suggests formate is the main oxidizing organic product. Interestingly, g-C3N4/CuFeO2 can also perform photoreforming using non-pretreated plastics in alkaline solutions. g-C3N4/CuFeO2 maintains 84 % of activity toward H2 evolution by replacing pretreated poly(butylene succinate) solution with non-pretreated poly(butylene succinate) as the feedstock. Given the freshwater resource shortage, seawater, the most abundant on Earth, also served as the water resource under investigation. g-C3N4/CuFeO2 photocatalyst preserves its almost intact photocatalytic activity by replacing pure water with 25 % content seawater, although a decrease in activity is observed in higher seawater content. Activities for H2 evolution of 241 ± 6.2 μmol h−1 gcat−1 and 150 ± 8.2 μmol h−1gcat−1 were achieved by photoreforming hydrolyzed polyester microfiber over g-C3N4/CuFeO2 in 25 % and 100 % seawater content, respectively. This study demonstrates that non-toxic and noble-metal-free g-C3N4/CuFeO2 serves as an efficient and well environmentally adaptive photocatalyst for plastic reforming.

Chemoenzymatic Photoreforming: A Sustainable Approach for Solar Fuel Generation from Plastic Feedstocks.

Plastic upcycling through catalytic transformations is an attractive concept to valorize waste, but the clean and energy-efficient production of high-value products from plastics remains challenging. Here, we introduce chemoenzymatic photoreforming as a process coupling enzymatic pretreatment and solar-driven reforming of polyester plastics under mild temperatures and pH to produce clean H2 and value-added chemicals. Chemoenzymatic photoreforming demonstrates versatility in upcycling polyester films and nanoplastics to produce H2 at high yields reaching ∼103-104 μmol gsub-1 and activities at >500 μmol gcat-1 h-1. Enzyme-treated plastics were also used as electron donors for photocatalytic CO2-to-syngas conversion with a phosphonated cobalt bis(terpyridine) catalyst immobilized on TiO2 nanoparticles (TiO2|CotpyP). Finally, techno-economic analyses reveal that the chemoenzymatic photoreforming approach has the potential to drastically reduce H2 production costs to levels comparable to market prices of H2 produced from fossil fuels while maintaining low CO2-equivalent emissions.