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Polymeric materials are widely used in every human endeavor (bottles, clothes, containers, toys, tools, etc.) due to their unique properties of chemical and mechanical resistance. They are, however, almost non-biodegradable, and their chemical recycling into monomers is difficult and costly, thereby allowing their accumulation into the environment. This review highlights recent advances in the use of deep eutectic solvents (DESs) as catalysts and/or green solvents in plastics degradation, with the aim of designing greener processes for polymers' chemical recycling, by reusing their monomers. These greener processes, in combination with other catalytic approaches, are aimed at introducing plastics as feedstock into the synthesis of other materials, according to the circular economy principles. [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]

The current society has an increasing demand for poly(ethylene terephthalate) (PET). Due to its high crystallinity and hydrophobicity, PET could be hardly degraded for high-value utilization. Besides, the escalating accumulation of waste PET has also led to significant environmental issues. In this study, a convenient and cost-efficient industrial strategy featuring the integration of glycolysis and enzymatic catalysis has been developed for the selective conversion of PET into terephthalic acid (TPA), which provides a method for colored waste PET degradation. Without the need for complex purifying processes, the products of glycolysis directly initiate the next round of the enzymatic system. Through this system, a total yield of 72.47 % of bis-2-(hydroxyethyl) terephthalate(BHET) and mono-(2-hydroxyethyl) terephthalate(MHET) was produced by glycolysis loading sodium bicarbonate (NaHCO 3) catalyst, and the enzyme system almost completely converted a substrate concentration of 100 g/L within 48 h, producing 50.36 g/L TPA. Besides, the product problem of pink color in the air after acidification caused by cobalt ions was solved by resin adsorption. In general, the glycolysis and enzymatic catalysis system in this study has prospects for commercial application due to its value for colored waste PET recycling, which reduces the environmental burden caused by waste PET. [Display omitted] • A strategy combining chemical and biological degradation of colored waste PET has been established. • The process simplifies complex purification steps and reduces energy consumption. • The enzymatic hydrolysis in this process can reach a high substrate concentration of 100 g/L. • The dual enzyme system can maximize the utilization of glycolysis products. • The whole degradation process was carried out in a bio-friendly reaction. [ABSTRACT FROM AUTHOR]

Hydrolytic depolymerization of polyethylene terephthalate (PET) waste was studied using high pressure autoclave reactor at 240 °C (molten state) and autogenous pressure using excess of water in the presence of a phase transfer catalyst polyethylene glycol (PEG 400) and the product profile was traced at various time intervals. In comparison with zinc acetate (used before), PEG 400 was the best catalyst. Concentration profiles were developed for PET, oligomer and terephthalic acid (TPA) using HPLC. Effect of initial molar ratio of 22–110 mol of water/mol PET on depolymerization was studied by using both HPLC and end group analysis. Initial molar ratio of 55–110 mol of water/mol PET was found to give 99 percent conversion in 30 min at 240 °C. A complete conversion of ester linkages to acid group and the desired product TPA was studied. On the basis of ester linkage, 100% conversion was observed in 10–12 min reaction time. At 30 min additional time, it was found to give 95% yield of TPA. Molar concentration of PEG 400 of 2.0 × 10−5 mol/cm3 was sufficient to give the maximum conversion in breaking of ester linkages. The yield and purity of TPA was found to be 90 and 99.1%, respectively. A new mechanism of solid (polymer)-liquid (melt)-liquid (water) phase transfer catalysis (PTC) for hydrolysis was proposed and validated. A pseudo-first order rate equation was fitted for depolymerization with a rate constant of 1.4 min−1 at 240 °C and apparent activation energy of 34.4 kJ/mol. The rate of hydrolysis is very fast and complete depolymerization takes place within 30 min. This is an excellent example of circular economy and cleaner production from waste plastic. [Display omitted] • Conversion of waste PET by hydrolytic depolymerization in to terephthalic acid and ethylene glycol. • Use of PEG 400 as phase transfer catalyst with new mechanism and kinetic model. • A new method of analysis prosed to confirm products. • Hydrolysis rate enhanced and activation energy declined by use of phase transfer catalyst vis-à-vis previous reports/. • Efficient waste polymer recycling as part of circular economy. [ABSTRACT FROM AUTHOR]

Abstract: The main purpose of research in membrane gas separation is to develop membranes with high permeability and selectivity. Historically, the gas separation performance of polymeric membranes has been constrained to an upper performance limit. Hence, different methods have been investigated to prepare membranes that can exceed this limitation including the incorporation of inorganic materials into polymer matrices. Membranes formed by this method are called mixed matrix membranes (MMMs). The major challenge is to prepare a defect-free polymer/inorganic nanoparticles interfaces with enhanced separation performance and mechanical and thermal stability. For this purpose, various types of nanoparticles have been proposed and examined experimentally. This review is especially devoted to summarize the fundamental concepts that have to be considered to prepare various types of MMMs, including considerations for the design novel MMMs that will eventually surpass the Robeson's trade-off upper bound. In addition, it provides the pros and cons of various factors that affect the MMM preparation especially for CO2 separation processes. [Copyright &y& Elsevier]

Chemical depolymerization of poly(ethylene terephthalate) (PET) waste is a possible remedy to huge amount of solid waste generation as it results in degradation products that possess a potential of recyclability. PET bottle waste was depolymerized by aminolysis using diethanolamine. Novel synthesis of N1, N1,N4,N4-tetrakis (2-hydroxyethyl) terephthalamide (THETA) with 73-76% yield and terephthalic acid (TPA) with 78-82% yield was achieved. The purified products were analyzed by FTIR, melting point, DSC, DTG and1H-NMR. THETA has various applications in the synthesis of rigid polyurethane foam, unsaturated polyester resins and also as a cross linking agent/ hardener for epoxy resins. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a broad review on the recent advances in the research and development of biobased plastics and bionanocomposites that are used in various applications such as packaging, durable goods, electronics and biomedical uses. The development of biobased materials is driven by renewability, low carbon footprint and in certain cases biodegradability (compostability) issues and helped them in moving from niche markets to high-volume applications. The inherent drawbacks of some biobased plastics such as the narrow processing window, low heat deflection temperatures, hydrophilicity, poor barrier, and conductivity and inferior biocompatibility can be overcome by bionanocomposites. The first part of the paper reviews the recent advances in the development of biobased and biodegradable materials from renewable resources and their advantages and disadvantages. In the second part, various types of bionanocomposites based on four types of fillers i.e. nanocellulose, carbon nanotubes, nanoclays, and other functional nanofillers are discussed. This review also presents up-to-date progress in this area in terms of processing technologies, product development and applications. [Copyright &y& Elsevier]

Terephthalic acid (TPA) wastewater is traditionally being treated by biological method. This study investigates the degradation of three major toxic target organic species, namely terephthalic acid (TPA), isophthalic acid (IPA), benzoic acid (BA), present in the TPA wastewater, by several advanced oxidation processes. The performance of three main oxidation processes such as photofenton oxidation (UV-H 2 O 2 -Fe), photocatalytic ozonation (UV-O 3 -Fe) and photofenton ozonation (UV-O 3 -H 2 O 2 -Fe) were studied. Studies were conducted with and without dilution of TPA wastewater. Photofenton ozonation was found to be most efficient by achieving almost complete destruction of all the three target organics in less than 30 minutes of reaction. In combining several oxidation processes, a comparative study was also carried out between one step addition of oxidants and stepwise addition. [ABSTRACT FROM AUTHOR]

Terephthalic acid (TPA) is a raw material of polyester fiber and polyethylene terephthalate. When TPA is produced by catalytic air oxidation of p-xylene in the presence of acetic acid solvent, most of produced TPA exists in the form of crystalline suspended solids. A microfiltration process may be used to recover TPA, but the microfilters are subjected to fouling and therefore cleaning-in-place (CIP) regimes need to be developed. In this research, the effects of variations to CIP conditions were investigated on the flux recovery accomplished in a TiO2-sintered stainless steel microfiltration membrane (0.1 μm pore size) fouled with TPA. The extent of flux recovery was estimated as the ratio of the stabilized flux obtained during CIP to the water flux value achieved under corresponding operational conditions. Based upon batch solubility tests, sodium hydroxide (NaOH) was chosen as the major cleaning agent for the present experiment. The extent of flux recovery increased with increasing NaOH concentration over the range of 3–4% (w/v) NaOH, but decreased at NaOH concentrations above 4%. The flux recovery was favored at high cross-flow velocities, high temperatures and low transmembrane pressures. A high temperature run of cleaning did not produce any adverse effects up to 70 °C. The addition of surfactants (SDS and Tween 80) to the caustic cleaning agent led to a significant reduction in cleaning efficiency. [Copyright &y& Elsevier]