Post-consumer Polyethylene Terephthalate Research Articles

Neutral Hydrolysis of Post-Consumer Polyethylene Terephthalate Waste in Different Phases

Post-consumer polyethylene terephthalate (PET) was hydrolyzed in pure water over a wide range of temperatures (190–400 °C) and pressures (1–35 MPa) to produce terephthalic acid (TPA). Solid or molten PET was subjected to water as a saturated vapor, superheated vapor, saturated liquid, compressed liquid, and supercritical fluid. The highest TPA yields were observed for the hydrolysis of molten PET in saturated liquid water. Isothermal and non-isothermal hydrolysis of PET was also explored. Rapidly heating the reactor contents at about 5–10 °C/s (“fast” hydrolysis) led to high TPA yields, as did isothermal PET hydrolysis, but within 1 min instead of 30 min. Notably, these conditions resulted in the lowest environmental energy impact metric observed to date for uncatalyzed hydrolysis.

Development of composites based on a blend of recycled HDPE/post-consumer PET and bentonite clay

The recycling process is the best way to manage waste polymers. From an economic standpoint, more investigation is needed of the whole recycling process to enhance the competitiveness in these systems. A first step is improved interaction and interfacial adhesion of blends. Polyethylene (PE) and polyethylene terephthalate (PET) are incompatible polymers, so their blends in general have poor properties. Compatibilization is thus a necessary step to obtain blends with good mechanical and barrier properties. In this work, blends of recycled (high density polyethylene) (HDPE) and post-consumer PET, with organophilic bentonite clay acting as compatibilization agent at the interface of the two polymers, were obtained. The proportions of HDPE/PET/bentonite (0, 5, 10 and 15% weight percentage of bentonite) were processed by extrusion. The processed materials were characterized regarding density (ASTM D792-13), melt flow index (MFI, ASTM D1238-13), hardness (ASTM D2240–10), infrared absorption spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results indicated the occurrence of some compatibilization.

Preparation and Characterization of Novel Membrane from Waste Polyethylene terephthalate and Bio-based Polymer

A large amount of post-consumer Polyethylene terephthalate (PET) bottle waste could be recycled for downstream products. In this work, used PET bottles were utilized as a raw material to develop environmentally-friendly ultrafiltration membranes by phase inversion technique. Poly(ethylene-2,5-furandicarboxylate) (PEF), prepared from a sustainable bio-based monomer, 2,5-furandicarboxylic acid (FDCA), was blended into rPET matrix to improve the mechanical properties of the membrane. Ethanol was also used as a non-solvent in a coagulation bath and polyethylene glycol (PEG) with a molecular weight of 400 Da was added as a hydrophilic additive. The effects of PEF and PEG incorporation to waste PET-based membranes have been thoroughly studied. The morphology of obtained membrane was investigated using Scanning Electron Microscopy (SEM). The membrane’s permeation and resistance were tested using a pressure-driven dead-end membrane module. The result revealed that adding PEF increased the roughness of the membrane surface, which lowered the flux recovery ratio and rejection performance. However, the filtration performance and the membrane resistance could be improved by adjusting the content of the PEG additive.

Microwave-assisted depolymerization of PET over heterogeneous catalysts

The accumulation of plastic waste in the environment is rising and poses a significant environmental and health threat. Polyethylene terephthalate (PET), used mainly in single-use plastic bottles, accounts for a substantial fraction of this waste. The currently employed recycling strategies are inadequate to deal with the global plastic waste problem. PET glycolysis is a promising depolymerization method but has mainly been conducted using homogeneous catalysts; developing active and sustainable catalysts, and more energy-efficient processes remain challenges. Here, we implement microwave heating in PET glycolysis and identify ZnO as an excellent heterogeneous catalyst. We demonstrate the influence of ZnO's particle size and facet and hydrogen bonding on its activity. Finally, we demonstrate excellent performance for real-world post-consumer PET waste deconstruction with rapid depolymerization into bis(2-hydroxyethyl) terephthalate (BHET), achieving > 95% yields in less than 10 min. Cradle-to-gate life cycle assessment also indicates that BHET produced by ZnO-catalyzed glycolysis has lower global warming potential than the petrochemical-based production and homogeneously-catalyzed glycolysis.

Kinetic Investigation for Chemical Depolymerization of Post-Consumer PET Waste Using Sodium Ethoxide

Reaction kinetics provides significant insights into the reaction rate and mechanism to control a chemical reaction. In the present work, the detailed kinetics of glycolytic depolymerization of post-consumer polyethylene terephthalate (PET) waste in the presence of sodium ethoxide (EtONa) was investigated. The glycolysis experiments were conducted in a batch reactor over a temperature range of 160 to 197 °C. The confirmation of the product, the bis(2-hydroxyethyl)terephthalate monomer, was carried out using nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, differential scanning calorimetry, and X-ray diffraction techniques. Investigations on the influence of particle size and temperature showed that conversion increased with a decrease in particle size and increasing temperature. Equilibrium conversions were found at different temperatures, and a van ’t Hoff plot was used to confirm that the depolymerization reaction is endothermic. Gibbs’ free energy was used to calculate the ceiling temperature (TC = 156 °C). Three kinetic models were tested for their applicability. It was found that the EtONa-catalyzed glycolysis of PET follows a first-order reversible reaction kinetic model at higher temperatures (170–197 °C). However, a heterogeneous shrinking core mechanism was applicable in a lower temperature range (160–170 °C). The kinetic evaluation revealed that the PET glycolysis reaction consists of heterogeneous and homogeneous mechanisms depending upon the depolymerization stages at various temperatures.

Optimization and Kinetic Evaluation for Glycolytic Depolymerization of Post-Consumer PET Waste with Sodium Methoxide.

Glycolysis of post-consumer polyethylene terephthalate (PET) waste is a promising chemical recycling technique, back to the monomer, bis(2-hydroxyethyl) terephthalate (BHET). This work presents sodium methoxide (MeONa) as a low-cost catalyst for this purpose. BHET product was confirmed by gas chromatography-mass spectrometry (GCMS), Nuclear Magnetic Resonance (NMR) Spectroscopy, melting point, and Differential Scanning Calorimetry (DSC). It was shown, not surprisingly, that PET conversion increases with the glycolysis temperature. At a fixed temperature of 190 °C, the response surface methodology (RSM) based on the Box-Behnken design was applied. Four independent factors, namely the molar ratio of PET: MeONa (50-150), the molar ratio of ethylene glycol to PET (EG: PET) (3-7), the reaction time (2-6 h), and the particle size (0.25-1 mm) were studied. Based on the experimental results, regression models as a function of significant process factors were obtained and evaluated by analysis of variance (ANOVA), to predict the depolymerization performance of MeONa in terms of PET conversion. Coefficient of determination, R2 of 95% indicated the adequacy for predicted model. Afterward, the regression model was validated and optimized within the design space with a prediction of 87% PET conversion at the optimum conditions demonstrating a deviation of less than 5% from predicted response. A van 't Hoff plot confirmed the endothermic nature of the depolymerization reaction. The ceiling temperature (TC = 160 °C) was calculated from Gibbs' free energy. A kinetic study for the depolymerization reaction was performed and the activation energy for MeONa was estimated from the Arrhenius plot (EA = 130 kJ/mol). The catalytic depolymerization efficiency of MeONa was compared under similar conditions with widely studied zinc acetate and cobalt acetate. This study shows that MeONa's performance, as a glycolysis catalyst is promising; in addition, it is much cheaper and environmentally more benign than heavy metal salts. These findings make a valuable contribution towards the chemical recycling of post-consumer PET waste to meet future recycling demands of a circular economy.

The Influence of Potassium Salts Phase Stabilizers and Binder Matrix on the Properties of Novel Composite Rocket Propellants Based on Ammonium Nitrate.

The environmental impact and availability of ingredients are vital for the new generation of rocket propellants. In this context, several novel composite propellants were prepared based on the "greener" oxidizer phase-stabilized ammonium nitrate (PSAN), a micronized aluminum-magnesium alloy fuel, iron oxide powder burn rate modifier, triethylene glycol dinitrate (TEGDN) energetic plasticizer and a polyurethane (PU) binder. The novelty of this study is brought by the innovative procedure of synthesizing and combining the constituents of these heterogeneous compositions to obtain high-performance "eco-friendly" rocket propellants. The polymorphism shortcomings brought by ammonium nitrate in these energetic formulations have been solved by its co-crystallization with potassium salts (potassium nitrate, potassium chromate, potassium dichromate, potassium sulphate, potassium chlorate and potassium perchlorate). Polyester-polyol blends, resulting from recycled post-consumer polyethylene terephthalate (PET) glycolysis, were utilized for the synthesis of the polyurethane binder, especially designed for this type of application. To adjust the energetic output and tailor the mechanical properties of the propellant, the energetic plasticizer TEGDN was also involved. The performance and safety characteristics of the novel composites were evaluated through various analytical techniques (TGA, DTA, XRD) and specific tests (rate of combustion, heat of combustion, specific volume, chemical stability, sensitivity to thermal, impact and friction stimuli), according to NATO standards, providing promising preliminary results for further ballistics investigations.

Dihydroxy Polyethylene Additives for Compatibilization and Mechanical Recycling of Polyethylene Terephthalate/Polyethylene Mixed Plastic Waste.

Polymer blend compatibilization is an attractive solution for mechanical recycling of mixed plastic waste because it can result in tough blends. In this work, hydroxy-telechelic polyethylene (HOPEOH) reactive additives were used to compatibilize blends of polyethylene terephthalate (PET) and linear low-density polyethylene (LLDPE). HOPEOH additives were synthesized with molar masses of 1-20 kg/mol by ring-opening metathesis polymerization of cyclooctene followed by catalytic hydrogenation. Melt-compounded blends containing 0.5 wt % HOPEOH displayed reduced dispersed phase LLDPE particle sizes with ductilities comparable to virgin PET and almost seven times greater than neat blends, regardless of additive molar mass. In contrast, analogous blends containing monohydroxy PE additives of comparable molar masses did not result in compatibilization even at 2 wt % loading. The results strongly suggest that both hydroxy ends of HOPEOH undergo transesterification reactions during melt mixing with PET to form predominantly PET-PE-PET triblock copolymers at the interface of the dispersed and matrix phases. We hypothesize that the triblock copolymer compatibilizers localized at the interface form trapped entanglements of the PE midblocks with nearby LLDPE homopolymer chains by a hook-and-clasp mechanism. Finally, HOPEOH compounds were able to efficiently compatibilize blends derived solely from postconsumer PET and PE bottles and film, suggesting their industrial applicability.

Accelerated Polyethylene Terephthalate (PET) Enzymatic Degradation by Room Temperature Alkali Pre-treatment for Reduced Polymer Crystallinity.

Polyethylene terephthalate (PET) is the most widely employed plastic for single-use applications. The use of enzymes isolated from microorganisms, such as PETase with the capacity to hydrolyze PET into its monomers, represents a promising method for its sustainable recycling. However, the accessibility of the enzyme to the hydrolysable bonds is an important challenge that needs to be addressed for effective biodegradation of postconsumer PET. Here, we combined an alkali pre-treatment (25 °C) with PETase incubation (30 °C) with post-consumed PET bottles. The pre-treatment modifies the surface of the plastic and decreases its crystallinity enabling the access of the enzyme to the hydrolysable chemical bonds. When the alkali pre-treatment is incorporated into the enzymatic process the degradation yields increase more than one order of magnitude reaching values comparable to those obtained during heating/cooling cycles. Our results show energetic advantages over other reported pre-treatments and open new avenues for sustainable PET recycling.

High strength insulating polymeric composite based on recycled/virgin polyethylene terephthalate (PET) reinforced with hydrous magnesium silicate (talc)

In the current work, post-consumer polyethylene terephthalate (PET) bottles were reclaimed and reinforced with hydrous magnesium silicate, Mg3Si4O10(OH)2 commonly known as talc and with virgin PET (VPET) for the development of high strength polymeric composites. The composite sheets were prepared using the thermomechanical melt processing method followed by a thermal press technique. VPET was mixed during melt processing of recycled PET (RPET) in a specific ratio to suppress thermal degradation and hydrolysis of developed composite. Various blends of the composite samples of VPET and RPET (RPETx - VPET1-x) with a fixed ratio of talc were prepared and investigated for their strength, conductivity and micro-properties. 45 μm talc particle in ratio 1 to 4 was used. The effect of the talc addition on mechanical properties of the composites at the sub-micron scale was investigated through nanoindentation with quasi-continuous stiffness mode (QCSM) to analyze the nano-mechanical properties as a function of contact displacement. Surface morphology and composition were studied through scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX), which showed a uniform dispersion of talc particles with no agglomerates on the surface. Compressive strength was determined with the universal testing machine (UTM) that revealed the highest compressive strength of RPET80 – VPET20 blend with a lowest thermal conductivity gradient value of 0.0213 W.m−1 observed, thus making it preferable material for insulation purposes. Load-displacement curves displayed the harder behavior of the composite sheet containing RPET80 – VPET20/talc as it needed 100 μN load to impose a penetration depth of 7.5 μm only. The elastic modulus and hardness of RPET80–VPET20/talc composite was significantly improved as compared to other samples.

Efficient depolymerization of polyethylene terephthalate (PET) and polyethylene furanoate by engineered PET hydrolase Cut190

The enzymatic recycling of polyethylene terephthalate (PET) can be a promising approach to tackle the problem of plastic waste. The thermostability and activity of PET-hydrolyzing enzymes are still insufficient for practical application. Pretreatment of PET waste is needed for bio-recycling. Here, we analyzed the degradation of PET films, packages, and bottles using the newly engineered cutinase Cut190. Using gel permeation chromatography and high-performance liquid chromatography, the degradation of PET films by the Cut190 variant was shown to proceed via a repeating two-step hydrolysis process; initial endo-type scission of a surface polymer chain, followed by exo-type hydrolysis to produce mono/bis(2-hydroxyethyl) terephthalate and terephthalate from the ends of fragmented polymer molecules. Amorphous PET powders were degraded more than twofold higher than amorphous PET film with the same weight. Moreover, homogenization of post-consumer PET products, such as packages and bottles, increased their degradability, indicating the importance of surface area for the enzymatic hydrolysis of PET. In addition, it was required to maintain an alkaline pH to enable continuous enzymatic hydrolysis, by increasing the buffer concentration (HEPES, pH 9.0) depending on the level of the acidic products formed. The cationic surfactant dodecyltrimethylammonium chloride promoted PET degradation via adsorption on the PET surface and binding to the anionic surface of the Cut190 variant. The Cut190 variant also hydrolyzed polyethylene furanoate. Using the best performing Cut190 variant (L136F/Q138A/S226P/R228S/D250C-E296C/Q123H/N202H/K305del/L306del/N307del) and amorphous PET powders, more than 90 mM degradation products were obtained in 3 days and approximately 80 mM in 1 day.Graphical

Valorization and recycling of packaging belts and post-consumer PET bottles in the manufacture of sand concrete

The valorization of local by-products in the manufacture of a new range of sand concrete and the improvement of their properties, will lead to seek an arrangement between performance and cost in order to achieve a resistant material. Waste recycling affects two very important affect namely the environmental impact and the economic impact. The main objective of our work is to contribute to optimize the formulation of sand concrete as part of the recovery of waste, which is harmful to the environment given its bulky and unattractive nature, it is waste plastic. Most PET bottles become waste after use, causing environmental problems. To solve this problem, a method for recycling PET bottles as fibers to strengthen concrete is proposed. Two types of plastic waste are added to sand concrete; the first concerns the recycling of post-consumer bottles in PET, in the form of polyester fiber supplied by the company RET-PLAST and the second type concerns the packaging belts made of polyethylene terephthalate (PET). The properties in the fresh state (workability and density) and in the hardened state (compressive strength, tensile strength and water absorption) of the various produced concretes are analyzed and compared against their respective controls. From the experimental results, it can be concluded that the reinforcement of the cement matrix with PET fibers with a rate of 1% improves the mechanical properties of sand concrete as well as a remarkable decrease in its water absorption capacity.

Acidic hydrolysis of recycled polyethylene terephthalate plastic for the production of its monomer terephthalic acid

Post-consumer polyethylene terephthalate (PET) plastic bottles, after some pre-processing, were chemically depolymerized for the production of terephthalic acid (TPA), an important monomer of PET resin. The optimized condition of PET hydrolysis was 100°C with 80% v/v aqueous sulfuric acid liquor for 30 min reaction time. The terephthalic acids (TPAs) were filtered out from the reaction mixtures with a sintered glass filter. The viscosity of recycled hydrolysis liquor was measured before it was used in a successive batch of PET depolymerization. The viscosity of hydrolysis liquor increased gradually from 5 mm2/s to 87 mm2/s. TPA yields were obtained from 85.03 ± 0.03% to 99.20 ± 0.06% and the color of TPA changed from bright white to off-white in the final batches. The structure of TPA was confirmed by FTIR, mass analysis, and 1H-NMR spectroscopy. The purity of TPA was found to be 95–98% from the HPLC study via external calibration technique. Thermogravimetric analysis (TGA) determined the thermal degradation patterns of TPAs and residual weights. This experiment reveals that repeated use of sulfuric acid hydrolysis liquor would be a good option for PET depolymerization in terms of resource utilization, TPA quality as well as sustainability.

Effects of reinforcing granular columns with fibres generated from plastic bottle waste

Ordinary and reinforced granular columns were both tested in a laboratory to study the effect of internal reinforcement using plastic fibres that were generated through the recycling of post-consumer polyethylene terephthalate bottles. A series of vertical compression tests was undertaken to understand the impact of varying the moisture content of the silt bed and the fibre concentration. The prepared samples were vertically loaded up to a maximum compression of 50 mm, and the load–vertical deformation characteristics were electronically recorded. Post-testing, the deformation behaviour of the column was physically modelled using a paste of plaster of Paris to obtain the maximum bulging diameter. In general, reinforcing the granular columns enhanced the load-carrying capacity, although the degree of improvement was dependent on the testing conditions. For experiments conducted on the softer silt beds, an increase in fibre content resulted in higher loading strengths. The largest enhancement was recorded in the test with wetter silt and with a fibre concentration of 0.1%. This was equivalent to 3.5 times that which was recorded when an ordinary granular column was installed. In terms of lateral deformation, the smallest bulge was obtained in the test with the wetter silt and a fibre content of 0.025%.

A highly porous MgAl2O4 spinel-supported Mn3O4 as a reusable catalyst for glycolysis of postconsumer PET waste

A porous MgAl2O4 spinel-supported Mn3O4 catalyst, which is an efficient and robust catalyst for polyethylene terephthalate (PET) glycolysis, was synthesized from MgAl-layered double hydroxide (LDH) as a template via thermal and chemical treatment, followed by Mn oxide loading. A mesoporous structure in the MgAl2O4 spinel provided a high surface area (278 m2/g) and defects in which Mn3O4 was highly dispersed and strongly stabilized by the substitution of Al3+ and incorporation of Mn cation into the defects. The strong interaction of Mn oxide and the porous MgAl2O4 spinel support led to a dramatic increase of moderate acidic and basic properties, and to high resistance for Mn leaching during glycolysis. Using the Mn3O4/p-spMgAl800 catalyst, a yield of bis(2-hydroxyethyl) terephthalate > 95 % was achieved within 3 h at 190 °C. Despite eleven recycling times with regeneration, the catalytic activity remained without significant deactivation and was completely recovered after thermal regeneration at 500 °C.

Hybrid Coatings of SiO2–Recycled PET Unsaturated Polyester Resin by Sol-Gel Process

Hybrid coatings of SiO2 and recycled unsaturated polyester resin (R-UPR) from recycled polyethylene-terephthalate (PET) were prepared by the sol-gel process on glass substrates. First, SiO2 was synthesized by the sol-gel process using a tetraethyl orthosilicate (TEOS) solution. Next, bis(2-hydroxypropyl-terephthalate) (BHPT) was synthesized from mechanical and chemical recycling (glycolysis) of post-consumer PET bottles in propylene glycol (PG) using ZnA as catalyst, in a Vessel-type reactor (20–200 °C); maleic anhydride (MA) was added and, following the same procedure, the unsaturated polyester (UP) was synthetized, which was cooled to room temperature. Next, styrene (St) and benzoyl-peroxide (PBO)-initiator were added to obtain R–UPR. TEOS (T) and three hybrid solutions were synthesized, with molar ratios of 0:1:0 (T), 1:2:0.25 (H1), 1:1:0.25 (H2), and 1:0:0.25 (H3) for R–UPR:TEOS:3-trimethoxy-(silyl)-propyl-methacrylate (TMSPM), respectively, with which TC, HC1, HC2, and HC3 coatings were elaborated using the immersion technique and polymerized (120 °C for 24 h). The solutions were characterized by FT–IR and TGA, and the coatings by SEM, nanoindentation, AFM, adhesion, and contact angle. The results showed that SiO2 enhanced mechanical (hardness and Young’s modulus) and thermal properties of the R-UPR. The coatings adhered perfectly to the substrate, with thicknesses of micrometer units and a flat surface; in addition, hydrophilicity decreased as SiO2 decreased.

The Use of Recycled PET for the Synthesis of New Mechanically Improved PVP Composite Nanofibers

Polyethylene terephthalate (PET) waste has become a major challenge for the conservation of the environment due to difficult degradation. For this reason, it is important to develop new recycling strategies for reusing this waste. In this work, the electrospinning technique was used to synthesize composite nanofibers of polyvinylpyrrolidone (PVP), recycling PET (RPET) that was obtained from the chemical recycling of postconsumer PET with glycolysis and styrene (ST) as a crosslinking agent. The polymer solutions were analyzed by viscosity and frequency sweeping, while the composite nanofibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), and nanoindentation to compare their properties. The PVP nanofibers presented an average diameter of 257 nm; the RPET/PVP and RPET/PVP/ST composite nanofibers had average diameters of 361 nm and 394 nm, respectively; and the modulus of elasticity and hardness of the RPET/PVP/ST composite nanofibers were 29 and 20 times larger, respectively, than those of the PVP nanofibers. With the synthesis of these composite nanofibers, a new approach to PET recycling is presented.

Band‐Gap Tuned Dilithium Terephthalate from Environmentally Hazardous Material for Sustainable Lithium Storage Systems with DFT Modelling

AbstractIn the fast‐developing world, people must migrate to hybrid electric vehicles with a high energy density of lithium‐ion batteries to reduce air and sound pollution primarily. Herein, acid hydrolysis is used to depolymerize vest post‐consumer polyethylene terephthalate (PET) bottles, resulting in pure terephthalic acid (TPA). It was used in an acid‐base reaction to produce the dilithium terephthalate (Li2TP). By using1H,13CNMR, and FTIR spectroscopy, the obtained TPA and its salt Li2TP are thoroughly studied. In terms of electrochemical properties, TPA has a restricted reversible capacity of 102 mAh g−1with dramatic fading and a coulombic efficiency of 98.2 % over the 50th cycle at 1 C. The resulting Li2TP, displays a three‐fold higher reversible capacity of 295 mAh g−1, with 99.8 % capacity retention and stable cycling at a similar rate over the 50th cycle. Moreover, computationally found that the charged state of Li2TP has a highly unstable structure due to a high steric hindrance and strong similar charge repulsion between lithium ions and it shows bandgap energy 0.2318 eV with four ionic bonds (1.7748 Å) and two new metallic bonds (3.2114 Å), which is 22 times smaller than TPA. Furthermore, Li2TP has a lower dielectric constant/loss and higher dipole movement than TPA, with values of 1.32E+04/1.24E+03, and 5.93E+03 respectively, and it improves Li‐ion transportation of Li2TP in organic electrolytes.

Ultrafast 99% Polyethylene terephthalate depolymerization into value added monomers using sequential glycolysis-hydrolysis under microwave irradiation

Effective and efficient hybrid depolymerisation technologies are emerging as high potential sustainable routes with considerable benefits over conventional recycling methods for the achievement of circular economies for plastics. Herein, combined green and fast glycolysis-hydrolysis depolymerization of polyethylene terephthalate (PET) was carried out under microwave irradiation (MW) with excellent efficiencies. In MW assisted glycolysis of PET, the catalytic activity of two deep eutectic solvents (DES) based on (choline chloride-urea (DES 1)) and (choline chloride-thiourea (DES 2)) was evaluated and compared. Optimised glycolysis conditions were determined using Box Behnken Design (BBD) to attain maximum weight loss of PET, low crystallinity and increased carbonyl index of residual PET. DES volume of 4 mL, 5.5–6 mL of ethylene glycol, and 0.5 min MW irradiation time resulted in a prominent rise in PET weight loss and carbonyl index of residual PET. DES 2 showed an improved catalytic activity than that of DES 1 which is associated to its stronger interaction with EG and PET polymer chains during the course of the reaction. Residual PET obtained post glycolysis reaction was further depolymerized using MW assisted hydrolysis in the presence of weakly basic Na2CO3 and EG. Within 3-minute, the proposed sequential depolymerization technologies facilitated ≈99% conversion of PET to terephthalic acid (TPA), monohydroxyethyl terephthalate (MHET), and bis (2-hydroxyethyl) terephthalate (BHET) monomers produced at a yield of 62.79–80.66%, 17.22–34.79% and 0.54–0.59% respectively. Application on post-consumer PET sample also revealed very satisfactory results with 96.77–98.25% PET conversion and 60.98–78.10% yield of TPA.

Enzymatic Degradation of Polyethylene Terephthalate Plastics by Bacterial Curli Display PETase

The extensive production and use of polyethylene terephthalate (PET) have generated an enormous amount of plastic waste, which potentially threatens the environment and humans. Enzyme biocatalysis is a promising green chemistry alternative, relative to the conventional fossil-derived production process, to achieve plastic waste treatment and recycling. In this work, we created a biocatalyst, BIND-PETase, by genetically engineering the curli of an Escherichia coli cell with a functional PETase enzyme for biocatalytic degradation of PET plastics. BIND-PETase could degrade PET to generate degradation products at the concentration level of greater than 3000 μM under various reaction conditions. The effects of key reaction parameters, including pH, temperature, plastic substrate mass load, and surfactant addition were characterized. BIND-PETase was reusable for PET degradation and remained stable with no significant enzyme activity loss when stored at both 4 °C and room temperature for 30 days (Student’s t test, p > 0.05). Notably, BIND-PETase could enable the degradation of PET microplastics in wastewater effluent matrix. Moreover, BIND-PETase could depolymerize highly crystalline postconsumer PET waste materials under ambient conditions with degradation efficiency of 9.1% in 7 days. This study provides a new horizon for developing environmentally friendly biocatalytic approaches to solve the plastic degradation and recycling challenge.