Obtaining phthalate substituted post-consumer polyethylene terephthalate and its isothermal crystallization

Studies were undertaken to determine the composition of five different types of post-consumer polyethylene terephthalate (PET) feedstreams to ascertain the relative amounts of food containers and non-food containers. Deposit post-consumer PET feedstreams contained ~100% food containers, whereas curbside feedstreams contained from 0.04 to 6% non-food containers. Analysis of the PET containers from the different type feedstreams after the containers were subjected to a commercial PET wash system and after processing with a proprietary decontamination technology was accomplished to determine the levels of compounds in the post-consumer PET after the various stages of processing. Comprehensive thermal desorption/GC/MS, purge and trap GC/MS purge and trap GC quantitation, PET dissolution and extraction GC analysis and PET dissolution HPLC analysis established the types and concentrations of compounds that absorb in the PET from the various types of postconsumer feedstreams. A total of 121 compounds were identified in the five different feedstreams. The concentration of absorbed compounds remaining in the deposit material and the non-food applications material after the commercial wash was 28 and 39mgkg -1 respectively. Analysis of the feedstreams after subjecting the material to a proprietary decontamination process demonstrated the ability of removing all the absorbed compounds to a level below the level of the threshold of regulation. The safety of sourcing of post-consumer PET from food use applications verses non-food use applications of PET has been established.

The selective recycling of mixed plastic waste of polylactic acid and polyethylene terephthalate by control of process conditions

Despite significant methodological and technological advancements in chemical recycling of synthetic polymers, an efficient and quantitative conversion of post-consumer polyethylene terephthalate (PET) into terephthalic acid (TPA) under ambient conditions of temperature and pressure still remains a challenge. In this respect, the application of mechanochemistry and multiple advantages offered by solid-state ball milling and vapor-assisted aging have remained insufficiently explored. To further expand their potential, the implementation of organic solvent-free milling as a superior methodology for successful alkaline depolymerization of waste PET (e. g., bottles and textile) into TPA monomer in near-quantitative yields was reported herein. The solid-state alkaline PET hydrolysis was also shown to proceed in excellent yields under aging conditions in humid environment or in the presence of alcohol vapors. Moreover, the performance of mechanochemical ball milling and aging in the gram-scale depolymerization of PET into TPA was demonstrated.

The large amount of post-consumer polyethylene terephthalate (PET) bottles/containers and post-consumer sachet water nylon currently generated in Lagos State makes imperative the search for alternative procedures for treating, recycling or reuse of these waste materials. This is because they are not biodegradable and constitute environmental and health threat to the survival of man and other living things. The sustainable approach to municipal solid waste management in Nigeria is being considered. This research work aimed at recycling of post-consumer PET bottles/containers and post-consumer sachet water nylon to produce composite materials for engineering applications and wastes storage bag (wastes bin) respectively. Plastic waste, polyethylene terephthalate (PET) bottles/containers and sachet water nylon coming from the dumpsites in Lagos State in Nigeria were collected, separated, washed, recycled, extruded and characterized. The products obtained were subjected to tests to evaluate their mechanical properties using Introns Tester Model 1122. The results showed that the PET/LDPE blend mechanical properties depend on the processing conditions and apparatus. High processing temperature and high residence times strongly enhance the degradation processes and reduce the mechanical properties, in particular the elongation at break. However, by introducing additives, such as antioxidants, inert fillers and impact modifiers, these mechanical properties are improved and approached those products made from of virgin polyethylene terephthalate. For the recycled sachet water nylon, the results also showed that there was mechanical properties deficiency in the use of recycled resins and that this deficiency could be minimized through adequate blending with virgin resins. In general, provided that optimal reprocessing conditions with suitable additives, the mechanical properties of the recycled resins are near to those of virgin resins.

Effect of hydrolysis products on the enzymatic degradation of polyethylene terephthalate nanoparticles by a polyester hydrolase from Thermobifida fusca

Current developments in chemical recycling of post-consumer polyethylene terephthalate wastes for new materials production: A review

A method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)4 and Sb2O3 as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004

Used polyethylene terephthalate bottles (PET) dumped indiscriminately onto bare lands and water bodies constitute an eyesore. This problem is viewed as a serious impediment to the flourishing tourism industry in Mauritius. Currently, over 100 million PET bottles are generated annually and the only fully operational disposal route is through the sole sanitary landfill. There is no formal segregation of waste and therefore used PET bottles are disposed of commingled with domestic waste. Despite a satisfactory waste collection system, a considerable amount of used PET bottles unfortunately end up in water bodies and on bare lands. An appreciable amount of PET bottles is now being collected separately for flake production prior to export to South Africa. This paper investigated the environmental impact of five waste management scenarios (100% landfill; 100% incineration with energy recovery; 50% incineration and 50% landfill; 34% flake production and 66% landfill; 100% flake production) for used PET bottles in Mauritius. Comparison of the five scenarios was based on the life cycle assessment (LCA) methodology described in ISO 14040 and ISO 14044. SimaPro 7.1 software was used to analyse the data. Comparison of the five scenarios showed that the highest environmental impacts occurred when 100% of used PET bottles were sent to the landfill. The comparison also indicated that there were least impacts on the environment when all used PET bottles were incinerated with energy recovery.

Globally, an estimated 7.4 billion tons of plastic have accumulated, with projections suggesting this could escalate to 40 billion metric tons by 2050. Unfortunately, only about 10% of this plastic is recycled, due to the lack of sustainable and economical solutions [1]. Alarmingly, over 70% of plastic waste ends up in landfills or oceans where it gradually decomposes into small particles (average diameter less than 5 mm), often referred to as microplastics (MPs). This widespread presence of microplastics poses a significant hazard to global ecosystems and human health. Microplastics can be ingested by organisms through various pathways including consumption of contaminated food, inhalation of polluted air, and dermal contact [2].Polyethylene terephthalate (PET), is the second most abundant plastic produced worldwide due to its extensive use in consumer packaging. Conventional mechanical recycling of PET often leads to the loss of its desirable properties [3]. Therefore, there is significant interest in chemical recycling technologies capable of depolymerizing PET. Through chemical hydrolysis at high temperatures, PET can be broken down into its constituent monomers, terephthalic acid and ethylene glycol. Nonetheless, the subsequent chemical separation of these products, particularly ethylene glycol (EG), presents challenges due to its high boiling point, viscosity, and water solubility, necessitating energy-intensive distillation processes. In response to this challenge, electrochemical methods have gained popularity for oxidizing PET hydrolysates into valuable products such as formic acid and glycolate, thereby offering a more sustainable pathway for upcycling [4]. However, most studies on electrochemical upcycling of PET still utilize a two-stage process. Initially, PET is hydrolyzed in a potassium hydroxide KOH solution at temperatures exceeding 80°C. Subsequently hydrolysate is used as an electrolyte to produce formate at the anode while hydrogen is produced at the cathode.Botte's group is investigating electrochemical approaches to convert plastics into valuable chemicals [5]. An effective enhanced electrocatalytic hydrolysis process for recycling PET waste into value-added chemicals was developed. This novel approach integrates the hydrolysis of PET with the concurrent electrochemical oxidation of ethylene glycol employing transition metals as catalyst and using mid temperature conditions. The effect of different variables on the overall conversion and the product distribution were evaluated. Operating time, voltage and particle size were varied, and the end products were characterized by FTIR, SEM, NMR, and IC. Our studies indicate that the electrochemical approach enhanced PET hydrolysis in comparison to traditional chemical hydrolysis [6] along with the oxidation of ethylene glycol into formic acid/formate in a single process eliminating the need for separate hydrolysis. Optimization of this process could be a sustainable approach for upcycling of PET microplastic into valuable products.[1] Li, M. and S. Zhang, Tandem Chemical Depolymerization and Photoreforming of Waste PET Plastic to High-Value-Added Chemicals. ACS Catal. 2024. 14(5): p. 2949-2958,doi: 10.1021/acscatal.3c05535.[2] E. Bäckström, K. Odelius, and M. Hakkarainen, “Trash to Treasure: Microwave-Assisted Conversion of Polyethylene to Functional Chemicals,” Ind. Eng. Chem. Res., vol. 56, no. 50, pp. 14814–14821, Dec. 2017, doi: 10.1021/acs.iecr.7b04091.[3] R. K. Brizendine et al., “Particle Size Reduction of Poly(ethylene terephthalate) Increases the Rate of Enzymatic Depolymerization But Does Not Increase the Overall Conversion Extent,” ACS Sustain. Chem. Eng., vol. 10, no. 28, pp. 9131–9140, Jul. 2022, doi: 10.1021/acssuschemeng.2c01961.[4] Y. Li, L. Q. Lee, H. Zhao, Y. Zhao, P. Gao, and H. Li, “Alcohol–alkali hydrolysis for high-throughput PET waste electroreforming-assisted green hydrogen generation,” J. Mater. Chem. A, vol. 12, no. 4, pp. 2121–2128, Jan. 2024, doi: 10.1039/D3TA05522A.[5] G. G. Botte, “Processes for electrochemical up-cycling of plastics and systems thereof,” WO2021257972A1, Dec. 23, 2021 Accessed: Jul. 21, 2023. [Online]. Available: https://patents.google.com/patent/WO2021257972A1/en[6] F. Lu and G. G. Botte, “Understanding the Electrochemically Induced Conversion of Urea to Ammonia Using Nickel Based Catalysts,” Electrochimica Acta, vol. 246, pp. 564–571, Aug. 2017, doi: 10.1016/j.electacta.2017.06.055.

Effect of contaminants and processing regime on the mechanical properties and moldability of postconsumer polyethylene terephthalate bottles

Off-grade thermoplastic poly(ethylene terephthalate) of industrial manufacturers was partially depolymerized to synthesize poly(ethylene terephthalate) oligomers. Influences of reaction time, ethylene glycol/poly(ethylene terephthalate) molar ratio, catalyst concentrations and particle size of off-grade poly(ethylene terephthalate) on yield of partial glycolysis reaction were investigated based on Box–Behnken's design of experiment. Thermal analyses of glycolyzed products was carried out using differential scanning calorimetry. The optimum samples were also well characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and carbon-13 nuclear magnetic resonance spectroscopy. The optimal conditions to synthesize poly(ethylene terephthalate) oligomer for a 120-min glycolysis reaction time were: using ethylene glycol/poly(ethylene terephthalate) of molar ratio of 2 with no catalyst and using granule-shaped poly(ethylene terephthalate). Then, endcapped poly(ethylene terephthalate) oligomer as a compatiblizer for preparing poly(ethylene terephthalate) nanocomposites was produced via reaction between maleic anhydride/phthalic anhydride composition and optimized poly(ethylene terephthalate) oligomers based on central composite design of experiment. The combination of reaction time of 106 min and phthalic anhydride/maleic anhydride molar ratio of 0.85 gave the best results based on d-spacing and peak intensity of nanocomposite samples. Hence, melt mixing of endcapped poly(ethylene terephthalate) with organoclay produced a good intercalation of layered silicate and good dispersion of clay in endcapped poly(ethylene terephthalate) matrix. Analysis of variance was studied for both glycolyzed products and functionalized poly(ethylene terephthalate) oligomers.

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.

Nearly complete depolymerization of untreated post-consumer plastic with an immobilized and reusable PET hydrolase.

Rationality-informed protein evolution enables enhancement of PET hydrolase activity.

<p indent="0mm">Plastics are ubiquitous in daily life due to their outstanding performance and cost-effectiveness. However, plastics are not without their drawbacks. Plastics are synthesized from fossil resources, and their widespread use accelerates the depletion of non-renewable resources. Additionally, their inherent stability makes them resistant to degradation under natural conditions, and they continuously release microplastics that pose significant harm to living organisms. As a result, plastic consumption and pollution are considered to be a critical environmental crisis that threatens sustainable human development. Against the backdrop of China’s heightened environmental protection efforts and its active promotion of “dual carbon” goals, the resource utilization of plastic waste has become a central societal issue. Polyethylene terephthalate (PET), one of the most widely produced polyester plastics, is extensively used in the manufacture of various everyday products and single-use packaging materials. PET synthesis began in the 1940s and has been used on a large scale for disposable packaging since the 1970s. PET is synthesized through the polycondensation of bis(2-hydroxyethyl) terephthalate (BHET), which can be produced by esterification of terephthalic acid (TPA) with ethylene glycol or from dimethyl terephthalate (DMT) and ethylene glycol. Despite existing initiatives aimed at recycling PET, the current recycling rate remains low. PET recycling is generally classified into primary, secondary, tertiary, and quaternary recycling. Primary and secondary recycling involve physical methods that recover PET waste without altering its chemical structure, for instance, PET waste plastic bottles are melt-spun to make recycled polyester fibers. Tertiary recycling restores the molecular value (chemical recycling), while quaternary recycling creates energy from the waste. With the rise of the circular economy, there has been a marked increase in research on PET recycling technologies, particularly in chemical recycling, which aims to establish a closed-loop system in which discarded PET is reintegrated into production. Chemical depolymerization pathways have been developed, allowing PET waste to be broken down into aromatic monomers and ethylene glycol. Through further purification and polycondensation, recycled PET can be produced from these monomers, thereby enabling closed-loop recycling. The depolymerization processes are typically hydrolysis, methanolysis, and glycolysis. Among them, hydrolysis usually requires the participation of water and the reaction with acidic or alkaline substances. Methanolysis requires an excess of methanol to react with PET. Glycolysis likewise requires the addition of large amounts of additional glycol for the reaction. These chemical depolymerization routes have a common by-product, ethylene glycol. However, due to the high boiling point of ethylene glycol, the chemical depolymerization of PET presents significant challenges in terms of separation and purification. In recent years, new recycling strategies have emerged that combine organic synthesis, electrochemical, and photochemical techniques to enhance the utilization of ethylene glycol including selective oxidation reactions to make carboxylic compounds. These innovative strategies not only preserve the valuable aromatic monomers of PET but also facilitate the recovery of new high-value chemicals. This paper reviews the production and recycling technologies for PET plastics, with a particular focus on the chemical depolymerization pathways involved in PET chemical recycling. It systematically examines the current status of traditional PET chemical depolymerization techniques and new strategies for their further development. Additionally, the paper explores the key challenges, research priorities, and prospects for producing high-value monomers from waste PET. This review offers new perspectives and insights for advancing sustainable development and the circular economy while promoting the importance of the waste plastic recycling industry.