Recycling Of PET Research Articles

A new mechanism for the kinetics of simultaneous depolymerization reaction inside and outside poly (ethylene terephthalate) particles

The depolymerization and recycling of PET is important for waste reduction, resource efficiency and production cost reduction. However, among the industrialized methods for recycling waste PET, the main challenge applicable to the PET glycolysis strategy is the low efficiency and low purity in recovering polyester, which is mainly due to the imperfections in the reaction kinetics model. In this study, we developed a kinetic model for PET glycolysis at different reaction temperatures by investigating the glycolysis process of PET chips at different reaction temperatures to discover new PET glycol depolymerization mechanisms. It was found that the zinc acetate-catalyzed PET glycolysis followed a first-order reversible kinetic model at higher temperature (206–210 °C). However, at lower temperatures (180 °C–205 °C), the experimental curve of the kinetic model is similar to the theoretical curve of the nucleation-controlled model, and in this temperature range, EG depolymerized PET in a manner that internal and external depolymerization proceeded simultaneously. This finding is expected to guide the establishment of a more efficient PET depolymerization process, which is an important guide for recycling waste PET.

Antioxidant-Containing Polymeric Additives for Improved Mechanical Recycling of PET

Antioxidant-Containing Polymeric Additives for Improved Mechanical Recycling of PET

A High-Throughput Screening Platform for Engineering Poly(ethylene Terephthalate) Hydrolases.

The ability of enzymes to hydrolyze the ubiquitous polyester, poly(ethylene terephthalate) (PET), has enabled the potential for bioindustrial recycling of this waste plastic. To date, many of these PET hydrolases have been engineered for improved catalytic activity and stability, but current screening methods have limitations in screening large libraries, including under high-temperature conditions. Here, we developed a platform that can simultaneously interrogate PET hydrolase libraries of 104-105 variants (per round) for protein solubility, thermostability, and activity via paired, plate-based split green fluorescent protein and model substrate screens. We then applied this platform to improve the performance of a benchmark PET hydrolase, leaf-branch compost cutinase, by directed evolution. Our engineered enzyme exhibited higher catalytic activity relative to the benchmark, LCC-ICCG, on amorphous PET film coupon substrates (∼9.4% crystallinity) in pH-controlled bioreactors at both 65 °C (8.5% higher conversion at 48 h and 38% higher maximum rate, at 2.9% substrate loading) and 68 °C (11.2% higher conversion at 48 h and 43% higher maximum rate, at 16.5% substrate loading), up to 48 h, highlighting the potential of this screening platform to accelerate enzyme development for PET recycling.

Production and changeover control of textile and PET recycling

Circular economies have become a strong candidate for addressing environmental challenges by managing end-of-life products to reduce landfill waste. We herewith focus on the recycling of PET from plastic waste and textiles. This paper focuses on recycling PET from plastic waste and textiles and proposes a model for controlling plant operations, emphasizing Quality-Based Changeovers over cleaning to ensure production continuity. This paper also identifies technological and managerial challenges in PET recycling plants as raised in the related literature, such as the need for technology improvement, more effective collection routes and sorting processes, and devoted managerial strategies. Since a relevant industrial need is to manage the changeovers, we develop a model to control the operative management of the plant and to find the feedstock quality to be processed at a given time for profit maximization. A discrete event simulation model is built to represent the behavior of the system under an approximate state-based control policy, i.e. a two-threshold policy. Numerical results and sensitivity analysis highlight the impact of cleaning costs on system behavior, offering insights into optimal operational conditions.

Zinc {ONO} complexes for the chemical recycling of PET and PLA

Nine {ONO} ligands were prepared and treated with ZnEt2 to form a range of complexes. The resulting complexes were characterised in solution through 1H and 13C{1H} NMR spectroscopy, and in the solid state through single-crystal XRD and elemental analysis. Moderate reactivity towards lactide polymerisation was demonstrated, with hydroxyl complexes reaching high conversion in 1–2 minutes at 300: 1: 1. All complexes successfully degraded PLA to methyl lactate and the effect of reaction time, temperature and catalyst loading was explored. Zn(4)2 successfully produced ethyl and n-butyl lactate and was shown to work in ambient conditions, albeit with reduced yield and selectivity. The production of BHET from waste PET was demonstrated with a selection of the most active catalysts. Zn(4)2 was shown to be capable of sequential PLA/PET degradation and to be tolerant of HDPE/PVC contaminants.

Catalyst- and Solvent-Free Upcycling of Poly(Ethylene Terephthalate) Waste to Biodegradable Plastics.

Poly(ethylene terephthalate) (PET) is an important polymer with annual output second only to polyethylene. Due to its low biodegradability, a large amount of PET is recycled for sustainable development. However, current strategies for PET recycling are limited by low added value or small product scale. It is urgent to make a breakthrough on the principle of PET macromolecular reaction and efficiently prepare products with high added value and wide applications. Here, the catalyst- and solvent-free synthesis of biodegradable plastics are reported through novel carboxyl-ester transesterification between PET waste and bio-based hydrogenated dimer acid (HDA), which can directly substitute some terephthalic acid (TPA) units in PET chain by HDA unit. This macromolecular reaction can be facilely carried out on current equipment in the polyester industry without any additional catalyst and solvent, thus enabling low-cost and large-scale production. Furthermore, the product semi-bio-based copolyester shows excellent mechanical properties, regulable flexibility and good biodegradability, which is expected to substitute poly(butylene adipate-co-terephthalate) (PBAT) plastic as high value-added biodegradable materials. This work provides an environmental-friendly and economic strategy for the large-scale upcycling of PET waste.

Direct Screening of PET Hydrolase Activity in Culture Medium Based on Turbidity Reduction.

The development of an efficient screening method for the activity of PET-degrading enzymes represents a significant technological advance in the field of enzyme research, with the potential to facilitate the advancement of enzymes for PET recycling. By examining the stable conditions of PET suspension and enzyme production conditions, we developed a method to quantify PET-degrading enzyme activity in E. coli culture medium using turbidity reduction as an indicator. High PET concentration or ionic strength caused aggregation of PET, and the best condition for activity detection was 0.5 mg mL-1 PET in 50 mM sodium phosphate pH 7.0. Preculture of E. coli increased the purity of enzyme secreted in medium. To evaluate the screening method, 720 colonies of the PET2-7M-H229X-F233X mutant library were analyzed and three candidates of high-activity mutants were obtained. The thermostability of the mutants could also be easily measured by measuring the residual activity after heat treatment. The H229T-F233M mutant showed 3.4 times higher degradation rate against PET film than the template enzyme at the initial time. The molecular dynamics simulation implied that the F233M mutation makes space for making an α helix and that the H229T mutation resolved the steric hindrance with Trp199. These mutations were speculated to change the angle of the Trp199 side chain of PET2 to an angle similar to that of the Trp185 of IsPETase, making it suitable for PET binding to the active center. Screening of activity using PET suspensions is compatible with robotic automation and is expected to be useful for validating computationally predicted mutations.

Administrative guidance for the preparation of applications for the authorisation of individual recycling processes to produce recycled plastics materials and articles intended to come into contact with food1

Abstract This document provides guidance to applicants submitting applications for the authorisation of individual recycling processes that use a suitable technology to produce recycled plastic materials and articles intended to come into contact with food, which are to be evaluated by EFSA. Currently post‐consumer mechanical PET recycling is the only suitable technology listed in Annex I to Commission Regulation (EU) 2022/1616 that requires individual authorisation. Consequently, this guidance describes the administrative requirements for the preparation and online submission of the dossier to support applications, submitted to the competent authority of a Member State for a new authorisation or for the modification of an authorisation of an individual recycling process based on post‐consumer mechanical PET recycling as technology. It does not apply to novel technologies developed in accordance with Chapter IV of Commission Regulation (EU) 2022/1616. The Transparency Regulation amended the General Food Law by introducing new provisions in the pre‐submission phase and in the application procedure: general pre‐submission advice, notification of information related to studies commissioned or carried out to support an application, public disclosure of non‐confidential version of all information submitted in support of the application and related confidentiality decision‐making process, public consultation on submitted applications. These new requirements, as implemented by the Practical Arrangements laid down by EFSA, are reflected in this guidance. The guidance describes the procedure and the associated timelines for handling applications on individual recycling processes that use a suitable technology, the different possibilities to interact with EFSA and the support initiatives available from the preparation of the application (pre‐submission phase) to the adoption and publication of EFSA's scientific opinion.

Scientific Guidance on the criteria for the evaluation and on the preparation of applications for the safety assessment of post-consumer mechanical PET recycling processes intended to be used for manufacture of materials and articles in contact with food.

In the context of entry into force of Regulation (EU) 2022/1616, EFSA updated the scientific guidance to assist applicants in the preparation of applications for the authorisation or for the modification of an existing authorisation of a 'post-consumer mechanical PET' recycling process (as defined in Annex I of Regulation (EU) 2022/1616) intended to be used for manufacturing materials and articles intended to come into contact with food. This Guidance describes the evaluation criteria and the scientific evaluation approach that EFSA will apply to assess the decontamination capability of recycling processes, as well as the information required to be included in an application dossier. The principle of the scientific evaluation approach is to apply the decontamination efficiency of a recycling process, obtained from a challenge test with surrogate contaminants, to a reference contamination level for post-consumer PET, set at 3 mg/kg PET for a contaminant resulting from possible misuse. The resulting residual concentration of each surrogate in recycled PET is then compared to a modelled concentration in PET that is calculated using generally recognised conservative migration models, such that the related migration does not give rise to a dietary exposure exceeding 0.0025 μg/kg body weight (bw) per day. This is the lowest threshold for toxicological concern (TTC) value, i.e. for potential genotoxicity, below which the risk to human health would be negligible. The information to be provided in the applications relates to: the recycling process (i.e. collection and pre-processing of the input, decontamination process, post-processing and intended use); the determination of the decontamination efficiency by the challenge test; the self-evaluation of the recycling process. On the basis of the submitted data, EFSA will assess the safety of the mechanical PET recycling process.

An efficient and scalable melt fiber spinning system to improve enzyme-based PET recycling

Chemical recycling technologies based on hydrolase enzymes that can depolymerize PET thermoplastic are emerging, yet these approaches require the polymer to be low crystallinity to achieve high conversion. To prepare the polymer for enzymatic depolymerization, current processes rely on melting and cryomilling PET at depressed temperatures to reduce crystallinity and prevent annealing during micronization; however, these approaches require large capital investment in costly equipment, and are not easily incorporated into intermediate-scale, distributed systems. Here, we describe a melt fiber spinning system that achieves significant reduction in crystallinity for real-world PET feedstocks without the need for any active cooling, and can easily be scaled up or down as needed. Single-use water bottles and drinking cups are tested, where they are extruded, drawn and spooled as thin fibers that cool by passive heat dissipation rapidly enough to quench the polymer to low crystallinity (<10%). Additionally, we estimate the fiber spinning also increases the feedstock surface-area-to-volume ratio by up to 15-fold, which further benefits heterogenous enzyme biocatalysis. In small scale PET hydrolase enzyme incubation tests, fiber spinning increased monomer released from PET by 4-fold for drinking cups and 10-fold for water bottles compared to shredded-only controls. Finally, we also show that this system can scale to >300 gs, with the potential for much larger scales, and allows for >95% depolymerization in a larger 20 liter bioreactor run.

Recycling of Waste Plastic PET on Asphalt Concrete (AC) by Using Application of Response Surface Methodology: Effect of PET on AC Formulated by Duriez Model

The wet recycling process of plastic waste was used to design a composite material (asphalt concrete) following the Duriez method. This process aims to improve the rheological performance of asphalt concrete by transforming PET on powdery and added to bitumen. To attend this objective, Doehlert&amp;apos; surface plane was used to assess how the asphalt rate, the PET rate and size, and then the aggregate rate affected the stability (wet and dry) and, in turn, the immersion/compression strength index (RI/C), the absorption capacity, the compactness as well as the void that could be filled by the 0/10 AC (asphalt concrete). All quadratic multivariate polynomial models with interactions were obtained and validated in order to optimize the responses. Thus, the physical characterization made it possible to obtain an asphalt concrete with good mechanical characteristics. In addition, it was observed that the selected factors had a different impact on the responses, which are: IR/C; the water absorption capacity, compactness and void filled by the binder by significantly increasing or decreasing them in simple, quadratic and interaction contributions. From the multi-response optimization, the objective was to obtain a composite material (Asphalt-PET-Aggregates) with has the best rheological characteristic, resulted in the following compromise: Bitumen rate 7%, PET 6% of asphalt, PET size 0,5mm; Aggregate content 93%. The simulated optimal values yielded the following responses were: 0.77 RI/C, immersion/compressive strength (Y.&amp;lt;SUB&amp;gt;RI/C&amp;lt;/SUB&amp;gt;); 2.9%, absorption capacity (Y.&amp;lt;SUB&amp;gt;WAC&amp;lt;/SUB&amp;gt;); 94%, compactness (Y.&amp;lt;SUB&amp;gt;C&amp;lt;/SUB&amp;gt;); 71% void filled by asphalt (Y.&amp;lt;SUB&amp;gt;VFA&amp;lt;/SUB&amp;gt;)

Optimization of Pressurized Alkaline Hydrolysis for Chemical Recycling of Post-Consumer PET Waste.

Addressing the environmental impact of poly(ethylene terephthalate) (PET) disposal highlights the need for efficient recycling methods. Chemical recycling, specifically alkaline hydrolysis, presents a promising avenue for PET waste management by depolymerizing PET into its constituent monomers. This study focuses on optimizing the pressurized alkaline hydrolysis process for post-consumer PET residues obtained from packaging materials. Post-consumer PET packaging waste was chemically recycled by means of an alkaline hydrolysis reaction in a 2 L pressurized reactor under varying conditions of the NaOH/PET ratio and temperature. The reaction's progress was monitored by sampling the liquid phase hourly over a four-hour period. The obtained products were purified, with a focus on isolating terephthalic acid (TPA). Higher temperatures (150 °C) resulted in superior TPA yields (>95%) compared to lower temperatures (120 °C). The NaOH/PET ratio showed minimal influence on the TPA yield. The optimal conditions (T = 150 °C; NaOH:PET = 2) were identified based on TPA yield and reaction cost considerations. This study demonstrates the feasibility of pressurized alkaline hydrolysis for PET recycling, with optimized conditions yielding high TPA purity and efficiency.

Conversion of Contaminated Post-Consumer Polyethylene Terephthalate into a Thermoset Alkyd Coating Using Biosourced Monomers.

The synthesis of a high-performance oxidative cross-linked thermoset alkyd coating is described that utilizes a novel recycling strategy from contaminated postconsumer waste polyethylene terephthalate (wPET). A single-stage "depolymerization-repolymerization" process has been developed that allows the exploitation of a waste stream from a commercial PET recycling process with 95% efficiency, which, when copolymerized with glycerol and tall oil fatty acid, delivers a sustainable fatty acid-functional polyester suitable for use in thermoset alkyd coatings. Physical drying challenges have been tackled via the development of a convergent polymer formulation strategy from a single source of wPET and the formulation of the resulting fatty acid-functional polymers with commercial alkyd driers, delivering a thermoset alkyd coating suitable for industrial applications.

Integrating glycolysis and enzymatic catalyst to convert waste poly(ethylene terephthalate) into terephthalic acid

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 (NaHCO3) 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.

Overcoming the Limitations of Organocatalyzed Glycolysis of Poly(ethylene terephthalate) to Facilitate the Recycling of Complex Waste Under Mild Conditions.

Although multiple methods have been reported in the literature for the chemical recycling of poly(ethylene terephthalate) (PET), large-scale depolymerization is not yet widely employed. The main reasons for the limited adoption of chemical recycling of PET are the harsh conditions required and the lack of selectivity. In this study, the organocatalytic glycolysis of PET mediated by organic bases at low temperatures is studied, and routes to avoid the deactivation of the catalyst are explored. It is shown that the formation of terephthalic acid by uncontrolled hydrolysis leads to issues which can be resolved using potassium tert-butoxide as a cocatalyst. Finally, complex PET waste obtained from a mechanical recycling plant was depolymerized under optimized conditions, obtaining bis(2-hydroxyethyl) terephthalate yields >90% in less than 15 min at only 100 °C. These results open the way to efficient recycling of PET-enriched waste streams under milder conditions.

Unlocking a Sustainable Future for Plastics: A Chemical-Enzymatic Pathway for Efficient Conversion of Mixed Waste to MHET and Energy-Saving PET Recycling.

The heterogeneous monomers obtained from plastic waste degradation are unfavorable for PET recondensation and high-value derivative synthesis. Herein, we developed an efficient chemical-enzymatic approach to convert mixed plastic wastes into homogeneous mono-2-hydroxyethyl terephthalate (MHET) without downstream purification, benefiting from three discovered BHETases (KbEst, KbHyd, and BrevEst) in nature. Towards the mixed plastic waste, integrating the chemical K2CO3-driven glycolysis process with the BHETase depolymerization technique resulted in an MHET yield of up to 98.26 % in 40 h. Remarkably, BrevEst accomplished the highest BHET hydrolysis (~87 % efficiency in 12 h) for yielding analytical-grade MHET compared to seven state-of-the-art PET hydrolases (18 %-40 %). In an investigation combining quantum theoretical computations and experimental validations, we established a MHET-initiated PET repolymerization pathway. This shortcut approach with MHET promises to strengthen the valorization of mixed plastics, offering a substantially more efficient and energy-saving route for PET recycling.

Analysis of Poly(ethylene terephthalate) degradation kinetics of evolved IsPETase variants using a surface crowding model

Poly(ethylene terephthalate) (PET) is a major plastic polymer utilized in the single-use and textile industries. The discovery of PET-degrading enzymes (PETases) has led to an increased interest in the biological recycling of PET in addition to mechanical recycling. IsPETase from Ideonella sakaiensis is a candidate catalyst, but little is understood about its structure-function relationships with regards to PET degradation. To understand the effects of mutations on IsPETase productivity, we develop a directed evolution assay to identify mutations beneficial to PET film degradation at 30ºC. IsPETase also displays enzyme concentration-dependent inhibition effects, and surface crowding has been proposed as a causal phenomenon. Based on total internal reflectance fluorescence microscopy and adsorption experiments, IsPETase is likely experiencing crowded conditions on PET films. Molecular dynamics (MD) simulations of IsPETase variants reveal a decrease in active site flexibility in free enzymes and reduced probability of productive active site formation in substrate-bound enzymes under crowding. Hence, we develop a surface crowding model to analyze the biochemical effects of three hit mutations (T116P, S238N, S290P) that enhanced ambient temperature activity and/or thermostability. We find that T116P decreases susceptibility to crowding, resulting in higher PET degradation product accumulation despite no change in intrinsic catalytic rate. In conclusion, we show that a macromolecular crowding-based biochemical model can be used to analyze the effects of mutations on properties of PETases and that crowding behavior is a major property to be targeted for enzyme engineering for improved PET degradation.

Exploring the potential of Meldrum’s acid-bearing chain extenders for mechanical recycling of PET

Abstract Poly(ethylene terephthalate) (PET) is a widely used thermoplastic polymer with exceptional properties, making it a cornerstone in various industries. However, the extensive global demand for PET, particularly in the packaging sector, has led to significant ecological concerns due to inadequate recycling rates. This paper explores the potential of Meldrum’s acid-based chain extenders as a solution to enhance PET recycling. Initially, 2,2,5-trimethyl-5-(4-vinylbenzyl)-1,3-dioxane-4,6-dione (St-MA) was synthesized, and its homopolymers were produced through free radical polymerization and characterized through 1H NMR, FTIR and TGA analyses. Dynamic interactions between recycled PET (rPET) and the synthesized chain extender (HP) in an extrusion environment was further explored, resulting in higher T g and T c for rPET when 0.5 wt% of HP was added as a reactive chain extender. The chemical tunability of this functional ketene-based chain extender holds promise to enhance PET recycling practices. The continuous evolution of regulatory frameworks and environmental concerns may prompt the exploration of novel approaches, such as tailored Meldrum’s acid-bearing chain extenders, which might have the potential to reduce the ecological consequences associated with post-consumer PET waste.

Superior glycidol-free chain extenders for post-consumer PET bottles and PET thermoform blends

The development of non-toxic, glycidol-free chain extenders is essential for enabling the recycling and reuse of both bottle-grade PET (PET-B) and thermoform PET (PET-T) in the packaging industry without the need for separation, thereby addressing the health concerns associated with commercial glycidol-based extenders. Herein, two novel series of novel glycidol-free chain extenders for bottle-grade recycled polyethylene terephthalate (PET-B) and thermoform-grade PET (PET-T) blends are reported. Blends of PET-B with up to 20 wt% of PET-T were incorporated into novel epoxy acrylate chain extenders with terminal (PEAT-BA) and internal (PEAI-BA) epoxy groups. These chain extenders are glycidol-free and improve the mechanical, rheological, and thermal properties of the PET-B/PET-T blends, offering better performance enhancements than are provided by commercial chain extender Joncryl ADR (J). The results showed significant improvements in intrinsic viscosity and mechanical properties by around 10 and 15 %, respectively, without affecting thermal properties. These findings can play a role in enabling the recycling and re-use of PET-B and PET-T blends without requiring separation while offering glycidol-free solutions.

Molecular and material property variations during the ideal degradation and mechanical recycling of PET

To verify if PET mechanical recycling is feasible, we need to acknowledge chemical and material property variations. This review highlights the relevance of the connectivity of these variations as a function of the number of recycling cycles.