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• Multi-material film (PE-PET) has been tested for chemical recycling through two-stage HTL. • 94% recovery of terephthalic acid from PET achieved after subcritical HTL. • The recovered terephthalic acid may be used for the production of virgin PET polymer. • PE yielded 47 wt.% oil and 29 wt.% light hydrocarbons after supercritical HTL. • Oil and light hydrocarbons have a paraffinic-rich composition suitable for steam cracking. Multi-material layered plastic films are used in the food packaging industry due to their excellent properties; however they cannot be mechanically recycled. In this study, a two-stage hydrothermal liquefaction (HTL) process is proposed and tested for chemical recycling of a two-layer film made of LLDPE-PET. Experimental results showed that after a first subcritical stage at 325 °C, 94% of terephthalic acid (TPA) is recovered from the PET fraction as a solid and 47% of ethylene glycol in the aqueous phase. The unconverted PE was then used as feedstock for a subsequent supercritical HTL stage at 450 °C for 90 min, achieving mass yields of 47% and 29% in a naphtha-gasoline oil and in an alkane-rich gas, respectively. In conclusion, this work proved that a sequential HTL procedure can be used for chemical recycling of multilayer plastics, allowing the recovery of PET monomers to be recycled back to the PET industry and a paraffinic oil and hydrocarbon-rich gas phase that could be used as feedstock for steam cracking to produce virgin materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon capture and utilization are crucial parts of minimizing the negative impacts of climate change caused by CO2 emissions. Furthermore, Polyethylene terephthalate (PET) has emerged as the predominant option for beverage packaging and textile fiber on a global scale. Moreover, CO2 capture and utilization can be a great solution to produce PET feedstocks effectively, such as ethylene glycol (EG), terephthalic acid (TPA), and dimethyl. Several strategies have been used to obtain the raw materials for PET production through CO2 utilization, including EG production from ethylene carbonate, EG production from coal, TPA production from benzene, TPA production from p-xylene, and EG production by the electrochemical process. CO2 utilization is often used for chemical production and recycling. However, there is limited information available regarding CO2 utilization in PET production and recycling. This review presents CO2 utilization for PET raw material supply and recycling from an environmental sustainability standpoint.

Evidence for microbial biodegradation of polyethylene terephthalate (PET) has been reported, but little is known about the PET biodegradation process and molecular mechanism by marine microorganisms. Here, we show the biodegradation of PET by the membrane-anchored PET esterase from the marine bacterium Rhodococcus pyridinivorans P23, elucidate the properties of this enzyme, and propose the PET biodegradation by this strain in biofilm. We identify the PET-degrading enzyme dubbed PET esterase through activity tracking. In addition to depolymerizing PET, it hydrolyzes MHET into TPA under acid conditions. We prove that it is a low and constitutively transcribed, membrane-anchored protein displayed on the cell surface. Furthermore, we also investigate the microbial groups possessing PET esterase coupled with the TPA degradation pathway, mainly in the phyla Proteobacteria and Actinobacteriota. Clarification of the microbial PET biodegradation in the marine environment will contribute to the understanding of bioremediation of marine PET pollution. A PET-degrading bacterium forming biofilms on PET surfaces was isolated from marine deep-sea sediment. The PET esterase localized at the cell surface was constitutively produced and also slowly degrading MHET to TPA under acidic conditions. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) can be recovered as high-purity bis(2-hydroxyethyl terephthalate) (BHET) monomer by glycolysis in the presence of Fe3O4 nanoparticles (NPs). In this study, Fe3O4 NPs of various shapes, sizes, and surface areas were synthesized using different colloidal synthesis methods, and the conversion of PET glycolysis and BHET yield were compared. Spinel ferrite NPs, including Fe3O4, were synthesized using the coprecipitation (CP), thermal decomposition (TD), and the hydrothermal (H) methods. Among the NP catalysts, Fe3O4-CP exhibited the best glycolysis performance with a PET conversion of ∼100% and BHET yield of 93.5% at 195 °C for 2 h owing to its high surface area (146.6 m2 g−1). The larger the surface area and the better the dispersion, the higher the glycolysis activity. The glycolysis performance of the mixed spinel ferrite NPs was similar to that of the Fe3O4 NPs, indicating that replacing Fe2+ in the Fe3O4 NPs with other transition metals, M2+, did not significantly change the glycolysis performance. BHET monomers produced from commercial waste PET bottles in large quantities contained trace amounts of metal contaminants, because PET production uses various metal-based additives and catalysts. Amberlite IRC-120, a cation-exchange resin, effectively removed metal impurities from BHET. This study provides an effective strategy for producing recycled PET (r-PET) by waste PET glycolysis. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is a synthetic polymer in the polyester family. It is widely found in objects used daily, including packaging materials (such as bottles and containers), textiles (such as fibers), and even in the automotive and electronics industries. PET is known for its excellent mechanical properties, chemical resistance, and transparency. However, these features (e.g., high hydrophobicity and high molecular weight) also make PET highly resistant to degradation by wildtype microorganisms or physicochemical methods in nature, contributing to the accumulation of plastic waste in the environment. Therefore, accelerated PET recycling is becoming increasingly urgent to address the global environmental problem caused by plastic wastes and prevent plastic pollution. In addition to traditional physical cycling (e.g., pyrolysis, gasification) and chemical cycling (e.g., chemical depolymerization), biodegradation can be used, which involves breaking down organic materials into simpler compounds by microorganisms or PET-degrading enzymes. Lipases and cutinases are the two classes of enzymes that have been studied extensively for this purpose. Biodegradation of PET is an attractive approach for managing PET waste, as it can help reduce environmental pollution and promote a circular economy. During the past few years, great advances have been accomplished in PET biodegradation. In this review, current knowledge on cutinase-like PET hydrolases (such as TfCut2, Cut190, HiC, and LCC) was described in detail, including the structures, ligand–protein interactions, and rational protein engineering for improved PET-degrading performance. In particular, applications of the engineered catalysts were highlighted, such as improving the PET hydrolytic activity by constructing fusion proteins. The review is expected to provide novel insights for the biodegradation of complex polymers. [ABSTRACT FROM AUTHOR]

Towards global efforts for efficient and sustainable ways to utilize polyethylene terephthalate (PET)‐based plastic waste, herein we report an integrated process for the complete one‐pot transformation of PET‐based plastic waste for hydrogen gas production in an alkaline aqueous condition over a heterogeneous ruthenium catalyst at low temperature (110‐160 °C). We could achieve complete selectivity with a high yield of H2 gas (∼38,000 mL H2/gPET/gRu) without any traces of CO and CO2 contaminations. Complete depolymerization of different types of PET‐based plastic waste was also achieved with high carbon yield (∼98 %) for disodium terephthalate (Na2TPA, 5.2 mmol/gPET) and sodium formate (SF, 9.6 mmol/gPET), along with H2 gas. Moreover, the developed process is scalable to bulk‐level production of hydrogen gas from PET‐based plastic waste, highlighting the potential application of the developed process. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is a commodity polymer known to globally contaminate marine and terrestrial environments. Today, around 80 bacterial and fungal PET-active enzymes (PETases) are known, originating from four bacterial and two fungal phyla. In contrast, no archaeal enzyme had been identified to degrade PET. Here we report on the structural and biochemical characterization of PET46 (RLI42440.1), an archaeal promiscuous feruloyl esterase exhibiting degradation activity on semi-crystalline PET powder comparable to IsPETase and LCC (wildtypes), and higher activity on bis-, and mono-(2-hydroxyethyl) terephthalate (BHET and MHET). The enzyme, found by a sequence-based metagenome search, is derived from a non-cultivated, deep-sea Candidatus Bathyarchaeota archaeon. Biochemical characterization demonstrated that PET46 is a promiscuous, heat-adapted hydrolase. Its crystal structure was solved at a resolution of 1.71 Å. It shares the core alpha/beta-hydrolase fold with bacterial PETases, but contains a unique lid common in feruloyl esterases, which is involved in substrate binding. Thus, our study widens the currently known diversity of PET-hydrolyzing enzymes, by demonstrating PET depolymerization by a plant cell wall-degrading esterase. Microbial enzymes are capable of degrading certain synthetic polymers, with most polyethylene terephthalate (PET) degrading enzymes known to derive from bacteria or fungi. Here, the authors describe an archaeal originating feruloyl-esterase PET46 enzyme with a flexible lid domain and PET degradation capability. [ABSTRACT FROM AUTHOR]

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Polyethylene terephthalate (PET) is a plastic material that is widely used in beverage bottles, food packaging, and other consumer products, which is highly resistant to biodegradation. In this study, we investigated the effects of two insect gut symbionts, Xanthomonas sp. HY-74 and Bacillus sp. HY-75, during PET biodegradation. Both strains degraded PET-containing agar plates, and the sole nutrition source assay showed that HY-74 had different degradation rates depending on the presence of specific carbon and nitrogen sources, whereas HY-75 exhibited comparable degradation across all tested conditions. The two strains biodegraded the PET film with 1.57 ± 0.21% and 1.42 ± 0.46% weight loss after 6 weeks, respectively. Changes in the morphology and structure of the PET films, such as erosion, scratching, and surface roughening, were determined using scanning electron microscopy (SEM). Further, the two strains biodegraded PET powder, broke it into its degradation products, and changed the surface functional groups. This is the first study to investigate the biodegradation of PET by Hymenoptera gut-derived microbes and offers promising insights into the potential applications of insect gut symbionts in PET waste management. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is used in textile and packaging industries. The main source of PET production is fossil fuels with limited capacity. Also, PET products are single use that transform into high volumes of wastes, causing ecosystem problems. Recycling is proposed to confront this challenge. The four major PET recycling techniques are mechanical, chemical, pyrolysis, and enzymatic. Mechanical, pyrolysis, and enzymatic techniques have constrained capabilities to manage PET waste. Chemical recycling is the potential path to expanding recycling PET waste with possibility of upcycling and addressing dirty waste streams. Several chemical methods are introduced and discussed in literature. The five major chemical recycling techniques are glycolysis, alcoholysis, aminolysis, ammonolysis, and hydrolysis. This review describes PET depolymerization via these techniques and introduces hydrolysis as the one that can depolymerize PET in an organic‐free solvent environment. Hydrolysis tolerates PET mixed wastes streams including copolymers. It helps avoid challenges attributed to using organic solvents in reaction systems. Moreover, hydrolysis produces terephthalic acid, PET monomer, which has recently gained attention as the initiative monomer for PET production. The review focuses on three forms of hydrolysis—alkaline, neutral, and acid, by presenting background studies, issued patents, and recent trends on application of hydrolysis. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the chemical recycling methods of polyethylene terephthalate (PET) described in the scientific literature in recent years. The review focused on methods of chemical recycling of PET including hydrolysis and broadly understood alcoholysis of polymer ester bonds including methanolysis, ethanolysis, glycolysis and reactions with higher alcohols. The depolymerization methods used in the literature are described, with particular emphasis on the use of homogeneous and heterogeneous catalysts and ionic liquids, as well as auxiliary substances such as solvents and cosolvents. Important process parameters such as temperature, reaction time, and pressure are compared. Detailed experimental results are presented focusing on reaction yields to allow for easy comparison of applied catalysts and for determination of the most favorable reaction conditions and methods. [ABSTRACT FROM AUTHOR]

The aim of this review article is to show the most recent research on obtaining waterborne polyurethane (WPU) coatings and adhesives using polyester polyol from polyethylene terephthalate (PET) waste, and describing their properties, in the search for a more sustainable product. WPU is obtained in two stages: (1) PET-based polyester polyol synthesis and (2) WPU synthesis. In the first stage, glycolysis is the most widely used degradation method for PET and zinc acetate catalyst to obtain polyester polyol, resulting in oligoesters. Studies with different degradation agents (propylene glycol, triethylene glycol and polyethylene glycol) of PET were highlighted, resulting in different oligoesters. A trend was observed in polyester polyol from the reaction of the post-consumption PET oligoester of using vegetable oil, particularly castor oil. A promising process was also found to obtain PU from polyester polyol in a single stage with renewable oil, which traditionally involves two stages. In the second stage, the processes using acetone solvent and prepolymer mixture were the most commonly used to prepare WPUs. The different synthesis pathways result in different WPU properties, which consequently serve different markets. It was found that adding polyester polyol to the flexible segment of WPUs (synthesized with PET and vegetable oil) led to a more flexible product, an important quality for coatings and adhesives. The presence of cutting agents, chain extenders and nanoparticles had a positive influence on the thermal stability of WPUs. The thermal degradation temperature of WPUs increased by up to 19 °C when PET oligoesters were used for their synthesis, compared to those synthesized without PET oligoesters. Moreover, the initial WPU degradation temperature can increase by up to 60%, depending on the type of glycol (propylene glycol, triethylene glycol, polyethylene glycol) and the PET/glycol molar ratio used in oligoester synthesis (1:2 or 1:10). [ABSTRACT FROM AUTHOR]

Several hydrolases have been described to degrade polyethylene terephthalate (PET) at moderate temperatures ranging from 25°C to 40°C. These mesophilic PET hydrolases (PETases) are less efficient in degrading this plastic polymer than their thermophilic homologs and have, therefore, been the subject of many protein engineering campaigns. However, enhancing their enzymatic activity through rational design or directed evolution poses a formidable challenge due to the need for exploring a large number of mutations. Additionally, evaluating the improvements in both activity and stability requires screening numerous variants, either individually or using high‐throughput screening methods. Here, we utilize instead the design of chimeras as a protein engineering strategy to increase the activity and stability of Mors1, an Antarctic PETase active at 25°C. First, we obtained the crystal structure of Mors1 at 1.6 Å resolution, which we used as a scaffold for structure‐ and sequence‐based chimeric design. Then, we designed a Mors1 chimera via loop exchange of a highly divergent active site loop from the thermophilic leaf‐branch compost cutinase (LCC) into the equivalent region in Mors1. After restitution of an active site disulfide bond into this chimera, the enzyme exhibited a shift in optimal temperature for activity to 45°C and an increase in fivefold in PET hydrolysis when compared with wild‐type Mors1 at 25°C. Our results serve as a proof of concept of the utility of chimeric design to further improve the activity and stability of PETases active at moderate temperatures. [ABSTRACT FROM AUTHOR]

Plastic pollution has become a primary environmental concern in recent years that affects not only the environment but also wildlife and human health. Developing new, alternative ways to reduce and recycle plastic waste is an important and pressing challenge for industries, given its significant impact on greenhouse gas emissions, resource efficiency improvement, and landfilling reduction. Currently, reuse and mechanical recycling are the most employed routes to exploit post‐consumer plastics, but they have their own limitations. Chemical recycling of plastic is a process that offers a sustainable solution to the growing plastic waste problem. But the depolymerization of condensation polymers poses a lot of challenges in chemical recycling. Ionic liquids (ILs) have recently emerged as depolymerization reagents offering various advancements in polymer recycling and waste management. This review assesses the different recycling conditions using ILs for different condensation polymers such as polyesters, polyamides, polycarbonates, and polyethylene terephthalate. It also explores the possibility of using ionic liquid as a catalyst influencing depolymerization efficiency. This review is intended to build on existing knowledge and inform further research in the area of sustainable polymer recycling. [ABSTRACT FROM AUTHOR]

Poly (ethylene terephthalate)-PET is a thermoplastic polymer that occupies a significant place in the food and medicine market, where PET pellets are used in the manufacturing of packages. One-quality criterium for PET is the control of inorganic contaminants, which is indispensable for quality control and the safety of the final plastic product. The present study proposes a microwave-assisted decomposition methodology using diluted acid mixtures, for better quantification of boron (B), barium (Ba), calcium (Ca), cadmium (Cd), cobalt (Co), magnesium (Mg), sodium (Na), phosphorus (P), and lead (Pb) in pellets of PET resin, purchased in Pernambuco, Brazil, and analyzed by inductively coupled plasma optical emission spectrometry (ICP OES). In order to overcome the difficulties faced in the pellet's decomposition and the detection of the inorganic content by ICP OES, an experimental design was carried out, using the strategy of polar coordinates as a statistical tool for the simultaneous analysis of mixing and processing variables. The following optimal parameters were established after full factorial design: 100 mg of resin and 10 mL of a digesting mixture composed of 40% water, 54% of nitric acid and 6% of sulfuric acid, digestion time of 20 min with heating at 220 ºC. The resins analyzed in this study showed higher levels of Ba (0.79 µg g−1) and Pb (1.64 µg g−1), compared to other studies in the literature. [ABSTRACT FROM AUTHOR]

Poly(ethylene terephthalate) (PET) is one of the most important industrial plastics in the world. The development of technologies for its depolymerization aiming at monomer recycling is of paramount interest and in this context enzyme-catalyzed hydrolysis has been recognized as a promising alternative. In the present study, a screening of 10 commercial enzymes using bis-(hydroxyethyl) terephthalate (BHET) as model substrate revealed Candida antarctica lipase B (CALB) and Humicola insolens cutinase (HiC) as potential biocatalysts. HiC showed limitation for the last reaction step, but CALB completely converted BHET to terephthalic acid (TPA), even at the highest substrate concentration investigated (31 mM). When used for PET hydrolysis, HiC demonstrated better potential, although accumulating considerable amounts of the intermediate mono-(hydroxyethyl) terephthalate (MHET). After evaluation of the effects of PET pretreatment, temperature and enzyme addition strategy, the combination of these two enzymes revealed synergy for a more complete PET depolymerization to TPA (mole fraction up to 0.88) and a 7.7–fold increase in PET to TPA yield was achieved. This finding adds new investigation possibilities for one of the most studied and versatile lipases, CALB. [ABSTRACT FROM AUTHOR]

In this study we investigated the ability of a cutinase from Thermobifida cellulosilytica (Thc_Cut1) to hydrolyze poly (ethylene terephthalate) (PET) moieties in different polymer blends. The composition of various materials including commercial available bottles and packaging was determined using Fourier Transform InfraRed spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). When incubated with PET blended with polyethylene (PE) or polyamide (PA) from packaging and bottles without prior separation, Thc_Cut1 selectively hydrolyzed the PET moieties releasing terephthalic acid (TPA) and mono(2-hydroxyethyl) terephthalate (MHET). Polymer blends were hydrolyzed in an up to 9 times higher extent compared to higher crystalline pure PET. The influence of various parameters like temperature, particle size, crystallinity and product inhibition on hydrolysis of PET moieties by Thc_Cut1 was investigated. The amount of products released was up to 10 times higher when the incubation temperature was increased from 40 °C to 60 °C. The smaller the particle size the higher the hydrolysis rates were. Interestingly, semi-crystalline (24%) PET from bottles was hydrolyzed faster than powder from amorphous PET films (12%). An inhibitory effect of bis(2-hydroxyethyl) terephthalate (BHET) on hydrolysis of PET by Thc_Cut1 was observed. [ABSTRACT FROM AUTHOR]

Ideonella sakaiensis is the bacterium that can survive by degrading polyethylene terephthalate (PET) plastic, and terephthalic acid (TPA) binding protein (Is TBP) is an essential periplasmic protein for uptake of TPA into the cytosol for complete degradation of PET. Here, we demonstrated that Is TBP has remarkably high specificity for TPA among 33 monophenolic compounds and two 1,6-dicarboxylic acids tested. Structural comparisons with 6-carboxylic acid binding protein (Rp AdpC) and TBP from Comamonas sp. E6 (Cs TphC) revealed the key structural features that contribute to high TPA specificity and affinity of Is TBP. We also elucidated the molecular mechanism underlying the conformational change upon TPA binding. In addition, we developed the Is TBP variant with enhanced TPA sensitivity, which can be expanded for the use of TBP as a biosensor for PET degradation. • Investigation of periplasmic terephthalate transport protein in I.sakaiensis (Is TBP). • Characterization of Is TBP with a high affinity for TPA • Determination of conformational change mechanism of TBP • Development of higher TPA sensitivity of TPA binding protein [ABSTRACT FROM AUTHOR]

The high demand for recycled polyethylene terephthalate (rPET) driven by an increase in environmental awareness, the application of more restrictive environmental legislations, together with the large increase in the generation of post-consumer PET plastic waste, has resulted in an urgent need for efficient recycling processes. In this work, alkaline hydrolysis is presented as a promising chemical recycling alternative for PET tray waste. PET depolymerization reactions were carried out under mild conditions (80–100 ºC and atmospheric pressure) using tributylhexadecylphosphonium bromide quaternary salt (TBHDPB) as catalyst. Several operating variables were studied based on PET conversion and terephthalic acid (TPA) yield criteria: (i) catalyst mass ratio of TBHDPB to PET (0–0.2); (ii) particle size (0.5–10 mm); (iii) stirring rate (350–700 rpm); and, (iv) temperature (80–100 °C). A good compromise between PET conversion (99.9%) and TPA yield (93.5%) was established after 4 h of reaction, under the following operating conditions: TBHDPB:PET catalyst ratio, 0.2; 100 °C; particle size, 1–1.4 mm; and, stirring rate, 525 rpm. In addition, the experimental kinetic data correctly fits to the proposed shrinking core model. Activation energy values of 60 and 57.4 kJ mol-1 were established for the non-catalyzed and catalyzed reactions, respectively, which implies that TBHDPB catalyst does not apparently modify the reaction mechanism. [Display omitted] • We prove a potential route for closed-loop recycling of PET tray waste plastic. • Phase transfer catalyst significantly increases the diffusion of the reactants. • 91.2% of PET is successfully depolymerized to the monomer. • Alkaline hydrolysis of PET tray correctly fits to the proposed shrinking core model. • Alkaline hydrolysis shows lower activation energies than glycolysis. [ABSTRACT FROM AUTHOR]

The rate response of poly(ethylene terephthalate) (PET)‐hydrolases to increased substrate crystallinity (XC) of PET manifests as a rate‐lowering effect that varies significantly for different enzymes. Herein, we report the influence of XC on the product release rate of six thermostable PET‐hydrolases. All enzyme reactions displayed a distinctive lag phase until measurable product formation occurred. The duration of the lag phase increased with XC. The recently discovered PET‐hydrolase PHL7 worked efficiently on "amorphous" PET disks (XC≈10 %), but this enzyme was extremely sensitive to increased XC, whereas the enzymes LCCICCG, LCC, and DuraPETase had higher tolerance to increases in XC and had activity on PET disks having XC of 24.4 %. Microscopy revealed that the XC‐tolerant hydrolases generated smooth and more uniform substrate surface erosion than PHL7 during reaction. Structural and molecular dynamics analysis of the PET‐hydrolyzing enzymes disclosed that surface electrostatics and enzyme flexibility may account for the observed differences. [ABSTRACT FROM AUTHOR]

A series of polyethylene terephthalate-co-[(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)methyl] butanedioate (PET-co-PEDDP) copolyesters were prepared through the reaction among ethylene glycol (EG), terephthalic acid, and [(6-oxido-6H-dibenz[c,e] oxaphosphorin-6-yl)methyl]butanedioic acid (DDP) through the direct esterification and polycondensation processes. Structure study of the prepared copolyesters using Fourier transform infrared spectroscopy and nuclear magnetic resonance (NMR) indicates polyester production. It is concluded that DDP comonomer incorporated into the polymer chain. Examination of the thermal treatment of all samples detected no phase separation. Melting point linearly decreases with DDP content; the Baur's equation could describe the melting point. Melt crystallization kinetics of all synthesized samples in a wide range of cooling rates were investigated by various kinetics models. Due to secondary crystallization, some simple models such as the Avrami equation could not fit the data very well. The best crystallization kinetics model was the Hay model by taking into consideration the secondary crystallization, which is the main achievement of this research. Furthermore, the effects of comonomer on the thermal degradation of copolyesters were also analyzed using thermal gravimetry analysis. The Coats–Redfern equation was applied to examine the influence of comonomer on thermal degradation. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate hydrolases (PETases) are a newly discovered and industrially important class of enzymes that catalyze the enzymatic degradation of polyethylene terephatalate (PET), one of the most abundant plastics in the world. The greater enzymatic efficiencies of PETases compared to close relatives from the cutinase and lipase families have resulted in increasing research interest. Despite this, further characterization of PETases is essential, particularly regarding their possible activity against other kinds of plastic. In this study, we exploited for the first time the use of the microalgal chloroplast for more sustainable synthesis of a PETase enzyme. A photosynthetic-restoration strategy was used to generate a marker-free transformant line of the green microalga Chlamydomonas reinhardtii in which the PETase from Ideonella sakaiensis was constitutively expressed in the chloroplast. Subsequently, the activity of the PETase against both PET and post-consumer plastics was investigated via atomic force microscopy, revealing evidence of degradation of the plastics. [ABSTRACT FROM AUTHOR]

Enzymatic degradation of poly(ethylene terephthalate) (PET) is becoming a reality because of the identification of novel PET‐hydrolysing enzymes (PHEs) and the engineering of evolved enzyme variants. Here, improved variants of leaf‐branch compost cutinase (LCC), a thermostable enzyme isolated by a metagenomic approach, were generated by a semi‐rational protein engineering approach. Starting from a deleted LCC form lacking the secretion signal (ΔLCC), single and double variants possessing a higher activity on PET were isolated. The single‐point F243T ΔLCC variant partially (~ 67%) depolymerized amorphous PET film producing ~ 21.9 mm of products after 27 h of reaction at 72 °C. The S101N/F243T ΔLCC double variant reached a further increase in activity on PET. Notably, for both single and double variants the highest conversion yield was obtained at 55 °C. Kinetics studies and molecular dynamics simulations support that a slight decreased affinity for PET is responsible for the superior degradation performance of the S101N/F243T variant and that this stems from a slightly higher flexibility of the active site region close to position 243. Furthermore, our findings question the need for a high reaction temperature for PET degradation, at least for LCC: at ≥ 70 °C, the conversion of amorphous PET into a more crystalline polymer, resistant to enzymatic hydrolysis, is favoured. The evolved S101N/F243T ΔLCC variant is able to depolymerize fully 1.3 g of untreated postconsumer PET waste in ≤ 3 days at 55 °C (using 1.25 mg of enzyme only), this making PET enzymatic degradation by engineering LCC a more ecofriendly and sustainable process. [ABSTRACT FROM AUTHOR]

To reduce environmental pollution and reliance on fossil resources, polyethylene terephthalate as the most consumed synthetic polyester needs to be recycled effectively. However, the existing recycling methods cannot process colored or blended polyethylene terephthalate materials for upcycling. Here we report a new efficient method for acetolysis of waste polyethylene terephthalate into terephthalic acid and ethylene glycol diacetate in acetic acid. Since acetic acid can dissolve or decompose other components such as dyes, additives, blends, etc., Terephthalic acid can be crystallized out in a high-purity form. In addition, Ethylene glycol diacetate can be hydrolyzed to ethylene glycol or directly polymerized with terephthalic acid to form polyethylene terephthalate, completing the closed-loop recycling. Life cycle assessment shows that, compared with the existing commercialized chemical recycling methods, acetolysis offers a low-carbon pathway to achieve the full upcycling of waste polyethylene terephthalate. The recycling of polyethylene terephthalate is of utmost importance to reduce environmental pollution and reliance on fossil resources however, the existing methods do not process colored or blended polyethylene terephthalate materials. Here, the authors demonstrate the acetolysis of waste polyethylene terephthalate into terephthalic acid and simultaneous acidic degradation of dyes and additives [ABSTRACT FROM AUTHOR]

Chemical resources and techniques have long been used in the history of bulk polyester production and still dominate today's chemical industry. The sustainable development of the polyester industry demands more renewable resources and environmentally benign polyester products. Accordingly, the rapid development of biotechnology has enabled the production of an extensive range of aliphatic and aromatic polyesters from renewable bio-feedstocks. This review addresses the production of representative commercial polyesters (polyhydroxyalkanoates, polylactic acid, poly ε-caprolactone, polybutylene succinate, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene furandicarboxylate, polypropylene furandicarboxylate, and polybutylene furandicarboxylate) or their monomers (lactic acid, succinic acid, 1,4-butanediol, ethylene glycol, terephthalic acid, 1,3-propanediol, and 2,5-furandicarboxylic acid) from renewable bioresources. In addition, this review summarizes advanced biotechniques in the treatment of polyester wastes, representing the near-term trends and future opportunities for waste-to-value recycling and the remediation of polyester wastes under sustainable models. For future prospects, it is essential to further expand: non-food bioresources, optimize bioprocesses and biotechniques in the preparation of bioderived or biodegradable polyesters with promising: material performance, biodegradability, and low production cost. [ABSTRACT FROM AUTHOR]

The annual production of plastic waste is a serious ecological problem as it causes substantial pollution of the environment. Polyethylene terephthalate, a material usually found in disposable plastic bottles, is one of the most popular material used for packaging in the world. In this paper, it is proposed to recycle polyethylene terephthalate waste bottles into benzene-toluene-xylene fraction using a heterogeneous nickel phosphide catalyst formed in situ during the polyethylene terephthalate recycling process. The catalyst obtained was characterized using powder X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The catalyst was shown to contain a Ni2P phase. Its activity was studied in a temperature range of 250–400 °C and a H2 pressure range of 5–9 MPa. The highest selectivity for benzene-toluene-xylene fraction was 93% at quantitative conversion. [ABSTRACT FROM AUTHOR]

PCL-based biodegradable shape-memory polymers (SMPs) are limited in strength, which restricts their practical applications. In this study, a series of novel SMPs, composed of poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and poly(ε-caprolactone) (PCL), were synthesized and cross-linked using planar (benzene-1,3,5-tricarboxylic acid, BTC) or non-planar (glycerol, GC) cross-linkers via the one-pot method. The influence of different kinds of cross-linkers and hard segments of copolyesters on the thermal properties, crystallization behavior, mechanical properties, shape-memory performance, and degradability was investigated by FT-IR, 1H-NMR, DSC, DMA, TGA, XRD, tensile test, intrinsic viscosity measurement, and in vitro enzymatic degradation test. The results indicate that the tensile strength of the copolyester can be significantly improved from 27.8 to 53.2 MPa by partially replacing PET with PEN while maintaining its shape-memory characteristics. Moreover, a small amount of cross-linking modification leads to higher temperature sensitivity, improved shape recovery rate at third round (Rr(3) = 99.1%), and biodegradability in the cross-linked PET/PEN/PCL shape-memory polymers. By changing the crystallization morphology and cross-linking forms of the material, we have developed a shape-memory polymer with both high strength and a high shape recovery rate, which provides a new strategy for the development of shape-memory materials. [ABSTRACT FROM AUTHOR]

Recovery of terephthalic acid (TPA) from waste polyethylene terephthalate (PET) should overcome the long-existing issues of low operation efficiency or massive wastewater generation during the hydrolysis and subsequent separation process to balance economics and environmental friendliness. Here, a high-concentration ethanol aqueous solution of 90 vol% is developed to achieve high-efficiency hydrolysis of PET by selectively cleaving C-O bonds and spontaneous separation of terephthalate using KOH as catalyst at 80 °C for 60 min. More than 98 % of TPA is recovered. It was attributed to the accelerated diffusion of the solvent in a reflux state due to the pore formation in PET and improved wettability between the solvent and PET. Notably, the terephthalate precipitated automatically from the reaction system due to low solubility in the solvent and separated by simple filtration, which avoids a large amount of waste water and acid in the following neutralization of terephthalate. The high efficiency of recycled reaction solution remained within several successive runs. The hydrolysis system is also applicable for degradation of other polymers containing ester groups and shows combined advantages of simplicity, high efficiency and eco-friendliness. [Display omitted] • Waste PET is rapidly depolymerized into TPA by pore formation. • TPA-2 K is self-separated from reaction system with high yield. • The recycled reaction solution remained high efficiency. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is the most abundantly produced plastic due to its excellent performance, but is also the primary source of poorly degradable plastic pollution. The development of environment-friendly PET biodegradation is attracting increasing interest. The leaf-branch compost cutinase mutant ICCG (F243I/D238C/S283C/Y127G) exhibits the best hydrolytic activity and thermostability of all known PET hydrolases. However, its superior PET degradation is highly dependent on its preparation as a purified enzyme, which critically reduces its industrial utility. Herein, we report the use of rational design and combinatorial mutagenesis to develop a novel ICCG mutant RITK (D53R/R143I/D193T/E208K) that demonstrated excellent whole-cell biocatalytic activity. Whole cells expressing RITK showed an 8.33-fold increase in biocatalytic activity compared to those expressing ICCG. Thermostability was also improved. After reacting at 85 °C for 3 h, purified RITK exhibited a 12.75-fold increase in depolymerization compared to ICCG. These results will greatly enhance the industrial utility of PET hydrolytic enzymes and further the progress of PET recycling. [ABSTRACT FROM AUTHOR]

Enzyme‐based depolymerization is a viable approach for recycling of poly(ethylene terephthalate) (PET). PETase from Ideonella sakaiensis (IsPETase) is capable of PET hydrolysis under mild conditions but suffers from concentration‐dependent inhibition. In this study, this inhibition is found to be dependent on incubation time, the solution conditions, and PET surface area. Furthermore, this inhibition is evident in other mesophilic PET‐degrading enzymes to varying degrees, independent of the level of PET depolymerization activity. The inhibition has no clear structural basis, but moderately thermostable IsPETase variants exhibit reduced inhibition, and the property is completely absent in the highly thermostable HotPETase, previously engineered by directed evolution, which simulations suggest results from reduced flexibility around the active site. This work highlights a limitation in applying natural mesophilic hydrolases for PET hydrolysis and reveals an unexpected positive outcome of engineering these enzymes for enhanced thermostability. [ABSTRACT FROM AUTHOR]

Textile waste usually ends up in landfills and causes environmental pollution. In this study, pretreatment methods for textile recycling, including autoclaving, freezing alkali/urea soaking, and alkaline pretreatment, were applied to textile waste with various cotton/polyester blending ratios. The best condition for enzymatic hydrolysis was a 60/40 textile waste blend of cotton/polyethylene terephthalate (PET) with a reusable chemical pretreatment (15% NaOH) at 121 °C for 15 min. The hydrolysis of pretreated textile waste by cellulase was optimized using response surface methodology (RSM) based on central composite design (CCD). The optimized conditions were 30 FPU/g of enzyme loading and 7% of substrate loading, which resulted in a maximum observed value of hydrolysis yield at 89.7%, corresponding to the predicted value of 87.8% after 96 h of incubation. The findings of this study suggest an optimistic solution for textile waste recycling. [ABSTRACT FROM AUTHOR]

Using enzymes to hydrolyze and recycle poly(ethylene terephthalate) (PET) is an attractive eco-friendly approach to manage the ever-increasing PET wastes, while one major challenge to realize the commercial application of enzyme-based PET degradation is to establish large-scale production methods to produce PET hydrolytic enzyme. To achieve this goal, we exploited the industrial strain Pichia pastoris to express a PET hydrolytic enzyme from Caldimonas taiwanensis termed CtPL-DM. In contrast to the protein expressed in Escherichia coli, CtPL-DM expressed in P. pastoris is inactive in PET degradation. Structural analysis indicates that a putative N-glycosylation site N181 could restrain the conformational change of a substrate-binding Trp and hamper the enzyme action. We thus constructed N181A to remove the N-glycosylation and found that the PET hydrolytic activity of this variant was restored. The performance of N181A was further enhanced via molecular engineering. These results are of valuable in terms of PET hydrolytic enzyme production in industrial strains in the future. [ABSTRACT FROM AUTHOR]

The recently discovered metagenomic-derived polyester hydrolase PHL7 is able to efficiently degrade amorphous polyethylene terephthalate (PET) in post-consumer plastic waste. We present the cocrystal structure of this hydrolase with its hydrolysis product terephthalic acid and elucidate the influence of 17 single mutations on the PET-hydrolytic activity and thermal stability of PHL7. The substrate-binding mode of terephthalic acid is similar to that of the thermophilic polyester hydrolase LCC and deviates from the mesophilic IsPETase. The subsite I modifications L93F and Q95Y, derived from LCC, increased the thermal stability, while exchange of H185S, derived from IsPETase, reduced the stability of PHL7. The subsite II residue H130 is suggested to represent an adaptation for high thermal stability, whereas L210 emerged as the main contributor to the observed high PET-hydrolytic activity. Variant L210T showed significantly higher activity, achieving a degradation rate of 20 µm h−1 with amorphous PET films. The authors describe the cocrystal structure of the highly efficient polyethylene terephthalate-degrading hydrolase PHL7 with its product terephthalic acid and elucidate the role of residues in subsites I and II for its thermal stability and of residue L210 for its high activity. [ABSTRACT FROM AUTHOR]

Extensive plastic production has become a serious environmental and health problem due to the lack of efficient treatment of plastic waste. Polyethylene terephthalate (PET) is one of the most used polymers and is accumulating in landfills or elsewhere in nature at alarming rates. In recent years, enzymatic degradation of PET by Ideonella sakaiensis PETase (IsPETase), a cutinase-like enzyme, has emerged as a promising strategy to completely depolymerize this polymer into its building blocks. Here, inspired by the architecture of cutinases and lipases homologous to IsPETase and using 3D structure information of the enzyme, we rationally designed three mutations in IsPETase active site for enhancing its PET-degrading activity. In particular, the S238Y mutant, located nearby the catalytic triad, showed a degradation activity increased by 3.3-fold in comparison to the wild-type enzyme. Importantly, this structural modification favoured the function of the enzyme in breaking down highly crystallized (~31%) PET, which is found in commercial soft drink bottles. In addition, microscopical analysis of enzyme-treated PET samples showed that IsPETase acts better when the smooth surface of highly crystalline PET is altered by mechanical stress. These results represent important progress in the accomplishment of a sustainable and complete degradation of PET pollution. [ABSTRACT FROM AUTHOR]

The rapid global growth of plastic production and waste are harbingers of increasing pollution in terrestrial and marine ecosystems for which safe and effective methods of disposal and degradation must be pursued. In the present study, metabarcoding and culture-based studies have been carried out to provide insights into polyethylene terephthalate (PET) biodegradation potential. Post-consumer PET films and powder were exposed to soil samples obtained from an aged oil bitumen spring site in Southwest Iran. To investigate microbial community composition, metagenome was extracted and hypervariable V3-V4 were sequenced (metabarcoding). Comparison of 16S amplicon metagenomic profiles between samples shows that Bacillus spp. and Halomonas spp. were the most abundant among bacterial genera present in soil samples from the vicinity of the oil seep, while Sphingomonas genus was most frequent in sample C collected from a region ~ 0.5 km distant of the oil seep. In the culture-based approach, Brevibacillus and Pseudomonas spp were isolated and analyzed for PET degradation. Field Emission Scanning Electron Microscope (FE-SEM) analysis shows two isolates had been colonized on PET film surface forming biofilm-like structures. PET degradation components were investigated by Gas Chromatography- Mass Spectrometry (GC-MS) which revealed the presence of aliphatic and aromatic compounds in the bacterial media. In addition, X-Ray diffraction (XRD) analysis showed reduction in crystallinity region peaks after 90 days of incubation with bacteria at 32°C. The diversity of the microbial community and the presence of PET degrading bacteria indicate a potential of the native oil seep-contaminated ecosystem for plastic degradation which is acquired following long-term adaptation to petroleum compounds. [ABSTRACT FROM AUTHOR]

This work is concerned with polyethylene terephthalate (PET) saponification by different potassium compounds in various polyols as well as biodiesel's main by-product, crude glycerol. It was established that reaction conditions (initial PET/K+ molar ratio, reaction time, etc.) could control the molecular weight of obtained oligomeric products. In ethylene glycol, depolymerization proceeds rapidly, and already at 10–30 min, PET is completely dissolved in the reaction mixture with the formation of liquid oligomers. Then, these oligomers react with potassium compounds, and after 200 min of the process, there are only solid, low-molecular-weight products (dipotassium terephthalate, monomers, and dimers). At the same time, PET saponification in pure glycerol is less effective, and solid polyether flakes could not fully decompose even after 200 min of the process. Crude glycerol takes the middle position between pure polyols. Based on the obtained data, an improved kinetic model was developed, and rate constants were estimated. This model takes into account PET saponification by potassium salts as well as direct PET glycolysis. Ethylene glycol is formed in situ by transesterification between fatty acid ethylene glycol esters and glycerol in the case of pure and crude glycerol. [ABSTRACT FROM AUTHOR]

Recovering fluorine from end-of-life products is crucial for the sustainable production and consumption of fluorine-containing compounds because fluorspar, an important natural resource for fluorine, is currently at a supply risk. In this study, we investigated the feasibility of chemically recycling a fluorine-containing photovoltaic (PV) backsheet for fluoropolymer recycling. Herein, a PV backsheet consisting of laminated polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) was treated with different concentrations of sodium hydroxide (NaOH) to hydrolyze the PET layer to water-soluble sodium terephthalate (Na2TP) and to separate pure PVDF layer as a solid material. Optimized alkaline conditions (up to 10 M NaOH at 100 °C for 2 h) were determined, under which 87% of the PET layer could be decomposed without any significant deterioration of the PVDF layer. The hydrolysis kinetics of PET layer in NaOH could be explained by the modified shrinking-core model. Considering that the mass of end-of-life PV panels in Japan is estimated to increase to approximately 280,000 tons per year by 2036, PV backsheets are attractive candidates for fluoropolymer recycling, which can be effectively achieved using chemical recycling approach demonstrated in this study. [ABSTRACT FROM AUTHOR]

The enzymatic degradation of the recalcitrant poly(ethylene terephthalate) (PET) has been an important biotechnological goal. The present review focuses on the state of the art in enzymatic degradation of PET, and the challenges ahead. This review covers (i) enzymes acting on PET, (ii) protein improvements through selection or engineering, (iii) strategies to improve biocatalyst–polymer interaction and monomer yields. Finally, this review discusses critical points on PET degradation, and their related experimental aspects, that include the control of physicochemical parameters. The search for, and engineering of, PET hydrolases, have been widely studied to achieve this, and several examples are discussed here. Many enzymes, from various microbial sources, have been studied and engineered, but recently true PET hydrolases (PETases), active at moderate temperatures, were reported. For a circular economy process, terephtalic acid (TPA) production is critical. Some thermophilic cutinases and engineered PETases have been reported to release terephthalic acid in significant amounts. Some bottlenecks in enzyme performance are discussed, including enzyme activity, thermal stability, substrate accessibility, PET microstructures, high crystallinity, molecular mass, mass transfer, and efficient conversion into reusable fragments. [ABSTRACT FROM AUTHOR]

Global economies depend on the use of fossil‐fuel‐based polymers with 360–400 million metric tons of synthetic polymers being produced per year. Unfortunately, an estimated 60% of the global production is disposed into the environment. Within this framework, microbiologists have tried to identify plastic‐active enzymes over the past decade. Until now, this research has largely failed to deliver functional biocatalysts acting on the commodity polymers such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), ether‐based polyurethane (PUR), polyamide (PA), polystyrene (PS) and synthetic rubber (SR). However, few enzymes are known to act on low‐density and low‐crystalline (amorphous) polyethylene terephthalate (PET) and ester‐based PUR. These above‐mentioned polymers represent >95% of all synthetic plastics produced. Therefore, the main challenge microbiologists are currently facing is in finding polymer‐active enzymes targeting the majority of fossil‐fuel‐based plastics. However, identifying plastic‐active enzymes either to implement them in biotechnological processes or to understand their potential role in nature is an emerging research field. The application of these enzymes is still in its infancy. Here, we summarize the current knowledge on microbial plastic‐active enzymes, their global distribution and potential impact on plastic degradation in industrial processes and nature. We further outline major challenges in finding novel plastic‐active enzymes, optimizing known ones by synthetic approaches and problems arising through falsely annotated and unfiltered use of database entries. Finally, we highlight potential biotechnological applications and possible re‐ and upcycling concepts using microorganisms. [ABSTRACT FROM AUTHOR]

Oil spills, industrial wastewater, and plastic waste have been widely considered major forces that cause severe impacts on the environment, threatening thousands of living creatures and humans. Hence, this study focused on a facile synthesis route of recycled polyethylene terephthalate aerogels modified with graphene oxide (GO-rPET-A) using poly(vinyl alcohol) as a binder, followed by a freeze-drying technique, to cope with pollutants leakage in wastewater. The prepared GO-rPET-A materials showed ultralow density (0.023–0.027 g/cm3), high porosity (98–99%), and high content of mesoporous structure. The influence of graphene oxide (GO) concentrations on the methylene blue (MB) adsorption performance of GO-rPET-A was then investigated, reaching an adsorption rate of more than 99%. The flux rate of MB on GO-rPET-A was also affected after 10-cycle filtering, which occurred by hydrogen bonds and electrostatic interactions. Moreover, after being coated with polydimethylsiloxane-tetraethyl orthosilicate (PDMS-TEOS), the obtained hydrophobic PDMS-TEOS coated GO-rPET-A materials (H-GO-rPET-A) exhibited water resistant ability with a water contact angle of 146°, compressive stress up to 64 kPa, as well as performed high adsorption capacity (9.87 g/g) and selectivity of coconut oil in water. Finally, adsorption kinetics of GO-rPET-A with MB and H-GO-rPET-A with coconut oil was accessed via the pseudo-first-order and pseudo-second-order models. The innovative strategy of preparing hybrid aerogel from recycled polyethylene terephthalate fibers and GO expands applications in wastewater treatment by utilizing plastic waste. [ABSTRACT FROM AUTHOR]

Poly(ethylene terephthalate) (PET) is a manufactured plastic broadly available, whereas improper disposal of PET waste has become a serious burden on the environment. Leaf-branch compost cutinase (LCC) is one of the most powerful and promising PET hydrolases, and its mutant LCCICCG shows high catalytic activity and excellent thermal stability. However, low binding affinity with PET has been found to dramatically limit its further industrial application. Herein, TrCBM and CfCBM were rationally selected from the CAZy database to construct fusion proteins with LCCICCG, and mechanistic studies revealed that these two domains could bind with PET favorably via polar amino acids. The optimal temperatures of LCCICCG-TrCBM and CfCBM-LCCICCG were measured to be 70 and 80 °C, respectively. Moreover, these two fusion proteins exhibited favorable thermal stability, maintaining 53.1% and 48.8% of initial activity after the incubation at 90 °C for 300 min. Compared with LCCICCG, the binding affinity of LCCICCG-TrCBM and CfCBM-LCCICCG for PET has been improved by 1.4- and 1.3-fold, respectively, and meanwhile their degradation efficiency on PET films was enhanced by 3.7% and 24.2%. Overall, this study demonstrated that the strategy of constructing fusion proteins is practical and prospective to facilitate the enzymatic PET degradation ability. [ABSTRACT FROM AUTHOR]

The direct hydrolysis of waste poly(ethylene terephthalate) (PET) was carried out in a high pressure reactor under microwave heating condition. Microwave irradiation enhanced the diffusion of water into the PET matrix by the effect of the structure relaxation and therefore resultantly the degradation rate of PET became high compared with the state of the conventional heating. The complete degradation of PET by direct hydrolysis was achieved for 30 min at high reaction temperature (223-232 o C) and high pressure (2.3-3.0 MPa) under the microwave heating condition. Although the use of HCl catalyst in the acid hydrolysis of PET decreased the yield of terephthalic acid (TPA) at the low HCl concentration region, the complete degradation of PET could be achieved for 15 min at the HCl concentration of 1.0 wt%. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is a prevalent synthetic polymer that is known to contaminate marine and terrestrial environments. Currently, only a limited number of PET-active microorganisms and enzymes (PETases) are known. This is in part linked to the lack of highly sensitive function-based screening assays for PET-active enzymes. Here, we report on the construction of a fluorescent biosensor based on Comamonas thiooxidans strain S23. C. thiooxidans S23 transports and metabolizes TPA, one of the main breakdown products of PET, using a specific tripartite tricarboxylate transporter (TTT) and various mono- and dioxygenases encoded in its genome in a conserved operon ranging from tphC-tphA1. TphR, an IclR-type transcriptional regulator is found upstream of the tphC-tphA1 cluster where TPA induces transcription of tphC-tphA1 up to 88-fold in exponentially growing cells. In the present study, we show that the C. thiooxidans S23 wild-type strain, carrying the sfGFP gene fused to the tphC promoter, senses TPA at concentrations as low as 10 mM. Moreover, a deletion mutant lacking the catabolic genes involved in TPA degradation thphA2-A1 (ΔtphA2A3BA1) is up to 10,000-fold more sensitive and detects TPA concentrations in the nanomolar range. This is, to our knowledge, the most sensitive reporter strain for TPA and we demonstrate that it can be used for the detection of enzymatic PET breakdown products. [ABSTRACT FROM AUTHOR]

In this research, a calcium-terephthalate metal-organic framework ([Ca(BDC) (H2O)3]) was synthesized by a new high yield solvothermal method as an efficient adsorbent. Terephthalate ligand recovered from polyethylene terephthalate (PET) waste was used as a precursor in the synthesis process. The adsorption ability of this compound to remove copper(II) from aqueous solutions was investigated. Experimental designs involving Plackett-Burman and Doehlert designs were used for the optimization of the adsorption process. Plackett-Burman design was used for screening the effective factors such as pH, adsorbent dosage, and initial concentration of Cu(II). Running Doehlert design (DD) as an optimization approach led to find a model for relation between response and effective factors and maximized uptake capacity (q) of Cu(II) (q = 351.3 mgg-1) under optimum conditions (pH = 5, adsorbent dosage = 1.50 mg and initial concentration of Cu(II) = 150 mgL-1). Infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and field-emission scanning electron microscopy (FESEM) analyses were applied to investigate the chemical and crystal structure of [Ca(BDC)(H2O)3]. Furthermore, kinetics, isotherms, thermodynamics, and desorption studies are complementary divisions of this research. [ABSTRACT FROM AUTHOR]

Currently, the metal-organic framework (MOF) is a promising candidate for flame-retardant polymers. In this study, a Fe-based MOF, MIL-88B(Fe), was introduced to polyethylene terephthalate (PET) and 3-hydroxyphenylphosphinyl-propanoic acid copolymer (P-PET) to reduce the fire hazard involved in using PET. The limiting oxygen indexes (LOIs) of MIL-PET and MIL-P-PET improved by 27% and 30%, respectively. The UL-94 level achieved for MIL-P-PET was V-0 rating. The thermal degradation and carbonization mechanisms of MIL-PET and MIL-P-PET were systematically investigated through thermogravimetric analysis coupled with a Fourier transform infrared spectroscopy (TG-IR), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), X-ray photoelectron spectroscopy (XPS), and Raman spectrum combined with quantum chemical molecular dynamics simulation. With the addition of MIL-88B(Fe), high graphitization and a hard flammability char residual were generated. Compared with neat PET, the ferric ions efficiently catalyzed the homolytic cleavage and dehydrogenation of PET to produce a large amount of CO2 and terephthalic acid for MIL-PET in gas phase. Rough and hierarchical char residual with ferric oxide was also generated when temperatures exceeded 600 °C. However, the carbonization process was inhibited due to the coordinated complex between phosphorus and ferric ions in MIL-P-PET, invaliding the decarboxylation and generating more benzoic acid and its precursor, which led to heavy smoke. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is one of the most widely used food contact materials due to its excellent mechanical properties and recyclability. Migration of substances from PET and assessment of compliance are usually determined by experimental testing, which can be challenging depending on the migrants of interest. Low concentrations and missing reference standards, among other factors, have led to inadequate investigation of the migration potential of PET oligomers. Migration modeling can overcome such limitations and is therefore a suitable starting point for exposure and risk assessment. In this study, the activation energy-based (EA) model and the AP model were used to systematically evaluate the migration potential of 52 PET oligomers for 12 different application scenarios. Modeling parameters and conditions were evaluated to investigate their impact and relevance on the assessment of realistic exposures. Obtained results were compared with safety thresholds known from the concept of toxicological thresholds of concern. This allowed the evaluation and identification of oligomers and/or applications where migration or exposure levels may be associated with a potential risk because they exceed these safety thresholds. Overall, this study demonstrated that migration modeling can be a high-throughput, fast, flexible, and suitable approach for comprehensive exposure assessment. [ABSTRACT FROM AUTHOR]

Enzymatic deconstruction of poly(ethylene terephthalate) (PET) is under intense investigation, given the ability of hydrolase enzymes to depolymerize PET to its constituent monomers near the polymer glass transition temperature. To date, reported PET hydrolases have been sourced from a relatively narrow sequence space. Here, we identify additional PET-active biocatalysts from natural diversity by using bioinformatics and machine learning to mine 74 putative thermotolerant PET hydrolases. We successfully express, purify, and assay 51 enzymes from seven distinct phylogenetic groups; observing PET hydrolysis activity on amorphous PET film from 37 enzymes in reactions spanning pH from 4.5–9.0 and temperatures from 30–70 °C. We conduct PET hydrolysis time-course reactions with the best-performing enzymes, where we observe differences in substrate selectivity as function of PET morphology. We employed X-ray crystallography and AlphaFold to examine the enzyme architectures of all 74 candidates, revealing protein folds and accessory domains not previously associated with PET deconstruction. Overall, this study expands the number and diversity of thermotolerant scaffolds for enzymatic PET deconstruction. Enzymes have potential for recycling plastics such as PET, a polyester used in textiles and single-use packaging. Here, the authors identify and characterize additional PET-active biocatalysts and expand the number and diversity of thermotolerant scaffolds for enzymatic PET deconstruction. [ABSTRACT FROM AUTHOR]

The accumulation of macro-, micro- and nano-plastic wastes in the environment is a major global concern, as these materials are resilient to degradation processes. However, microorganisms have evolved their own biological means to metabolize these petroleum-derived polymers, e.g., Ideonella sakaiensis has recently been found to be capable of utilizing polyethylene terephthalate (PET) as its sole carbon source. This study aims to prove its potential capacity to biodegrade two commercial PET materials, obtained from food packaging containers. Plastic pieces of different crystallinity were simultaneously introduced to Ideonella sakaiensis during a seven-week lasting investigation. Loss in weight, appearance of plastics, as well as growth of Ideonella sakaiensis—through quantitative real-time PCR—were determined. Both plastics were found enzymatically attacked in a two-stage degradation process, reaching biodegradation capacities of up to 96%. Interestingly, the transparent, high crystallinity PET was almost fully degraded first, followed by the colored low-crystallinity PET. Results of quantitative real-time PCR-based gene copy numbers were found in line with experimental results, thus underlining its potential of this method to be applied in future studies with Ideonella sakaiensis. [ABSTRACT FROM AUTHOR]

Plastic pollution is a global concern due to the long half-life and high resistance of many synthetic plastics to natural biodegradation. Therefore, great effort is required to avoid littering. However, the challenge of managing the ever-increasing quantities of plastic waste is daunting. The biodegradation of synthetic plastics, such as polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyurethane (PUR) by microorganisms is either slow or under investigation as to whether it occurs at all in different environmental niches (e.g., soil, aquatic systems). There is an urgent need to complement the existing knowledge on the biodegradation and biotransformation of synthetic plastics to enable effective bioremediation strategies to mitigate the effects of environmental plastic contamination. Therefore, the aim of this review is to highlight current fundamental and applied research regarding the most promising biodegradation processes for synthetic plastics, the synthesis and applications of the most effective plastic-degrading enzymes, successful biotechnological strategies to improve degradation, such as enzyme engineering and novel reactor designs, and plastic waste bioconversion into value-added products. In addition, this review is intended to depict indications for techno-economic analyses toward the valorization of plastic biodegradation processes and the environmental impacts of synthetic plastic biodegradation. Combining strategies, such as enzymatic plastic degradation followed by microbial biotransformation with the broad array of available pretreatment methods and abiotic factors, can contribute, under confined conditions, to the end-of-life utilization of plastics, consequently leading to more efficient biorecycling processes, and hence, to a circular plastic economy. [ABSTRACT FROM AUTHOR]

Enzymes sequestered from microbes have demonstrated the ability to readily digest amorphous regions of polyethylene terephthalate (PET) in ambient conditions. Although nascent, enzymatic depolymerization can soon vie for commercialization and provide monomeric feedstock at rates comparable to petrochemical feedstock for repolymerization, achieving the coveted goal of cradle‐to‐cradle recycling. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]