Recycled Polyethylene Terephthalate Research Articles

Evaluation of asphalt mixtures modified with polyethylene terephthalate (PET)

Polyethylene terephthalate (PET) waste, ubiquitous in packaging and shipping industries, offers logistical advantages through its lightweight, durable nature, fostering cost-effective transportation. However, concerns over PET’s environmental impact arise from its persistence in ecosystems and contribution to pollution, urging industries to prioritize responsible waste management and recycling strategies. Recognizing the pivotal role of the construction industry, leveraging PET recycling in asphalt mixtures presents an applicable solution to curtail the environmental footprint of PET waste. Roadway asphalt construction, a significant industry, holds substantial potential to integrate PET waste into asphalt, offering a promising avenue for sustainable waste utilization. This research investigates the integration of PET waste into Egyptian asphalt mixtures across nine distinct compositions, varying binder percentages (3.0%, 3.50%, and 4%) and PET ratios (6%, 7%, and 8%). Marshall and Hamburg Wheel Rutting tests were conducted, comparing these formulations against a control mix devoid of PET. Notably, optimal outcomes emerged from the 3% binder with 8% PET combination, exhibiting enhanced mix stability and stiffness while meeting established mix design standards, signifying promising improvements in sustainability without compromising performance metrics.

Recycled PET Fibers with Dopamine Surface Modification for Enhanced Interlayer Adhesion in 3D Printed Concrete.

Three-dimensional printed concrete (3DPC) is increasingly recognized in the construction industry for its high design flexibility and the elimination of conventional formwork. However, weak interlayer adhesion remains a significant challenge. The potential of recycled polyethylene terephthalate (PET) fibers for reinforcing 3DPC is being explored, driven by their environmental sustainability and economic advantages. However, there is an inadequate interfacial adhesion between these recycled fibers and the 3DPC matrix. This study investigated the use of dopamine modification to address this issue and enhance the interlayer adhesion of fiber-reinforced 3DPC. Recycled PET fibers were surface-modified using dopamine treatment, forming a polydopamine (PDA) film that improved surface roughness and hydrophilicity. Both unmodified and modified fibers were incorporated into 3DPC at various volume fractions (0.1%, 0.3%, 0.5%). The effects on interlayer adhesion strength, compressive strength, and flexural strength were systematically evaluated and compared. The results showed that the inclusion of 0.3 vol% dopamine-modified fibers resulted in a 22.5% increase in interlayer adhesion strength compared to the control group, and a 14.8% improvement over unmodified fibers at the same content. Additionally, the compressive strength and flexural strength of 3DPC with 0.3 vol% MPET fibers increased by 22.5% and 27.6%, respectively, compared to the control group. Microstructural analysis using SEM and XRD revealed that the dopamine modification significantly improved the interfacial adhesion between fibers and the concrete matrix, explaining the superior performance of modified fibers. This study demonstrates that recycled PET fibers modified with dopamine can effectively enhance the interlayer adhesion of 3DPC. The findings affirm that surface modification techniques can significantly elevate the utility of recycled PET fibers in 3DPC, contributing to the sustainable advancement of construction materials.

Comparative evaluation of the extracellular production of a polyethylene terephthalate degrading cutinase by Corynebacterium glutamicum and leaky Escherichia coli in batch and fed-batch processes

BackgroundWith a growing global population, the generation of plastic waste and the depletion of fossil resources are major concerns that need to be addressed by developing sustainable and efficient plastic recycling methods. Biocatalytic recycling is emerging as a promising ecological alternative to conventional processes, particularly in the recycling of polyethylene terephthalate (PET). However, cost-effective production of the involved biocatalyst is essential for the transition of enzymatic PET recycling to a widely used industrial technology. Extracellular enzyme production using established organisms such as Escherichia coli or Corynebacterium glutamicum offers a promising way to reduce downstream processing costs.ResultsIn this study, we compared extracellular recombinant protein production by classical secretion in C. glutamicum and by membrane leakage in E. coli. A superior extracellular release of the cutinase ICCGDAQI was observed with E. coli in batch and fed-batch processes on a litre-scale. This phenomenon in E. coli, in the absence of a signal peptide, might be associated with membrane-destabilizing catalytic properties of the expressed cutinase. Optimisations regarding induction, expression temperature and duration as well as carbon source significantly enhanced extracellular cutinase activity. In particular, in fed-batch cultivation of E. coli at 30 °C with lactose as carbon source and inducer, a remarkable extracellular activity (137 U mL−1) and cutinase titre (660 mg L−1) were achieved after 48 h. Literature values obtained with other secretory organisms, such as Bacillus subtilis or Komagataella phaffii were clearly outperformed. The extracellular ICCGDAQI produced showed high efficacy in the hydrolysis of PET textile fibres, either chromatographically purified or unpurified as culture supernatant. In less than 18 h, 10 g L−1 substrate was hydrolysed using supernatant containing 3 mg cutinase ICCGDAQI at 70 °C, pH 9 with terephthalic acid yields of up to 97.8%.ConclusionExtracellular production can reduce the cost of recombinant proteins by simplifying downstream processing. In the case of the PET-hydrolysing cutinase ICCGDAQI, it was even possible to avoid chromatographic purification and still achieve efficient PET hydrolysis. With such production approaches and their further optimisation, enzymatic recycling of PET can contribute to a more efficient and environmentally friendly solution to the industrial recycling of plastics in the future.

Revealing contaminants in China's recycled PET: Enabling safe food contact applications

The lack of data on chemical contamination in recycled polyethylene terephthalate (rPET) in food contact applications, impedes the legalization of rPET in food contact applications in China. This study offers a comprehensive analysis of contaminants in hot-washed rPET flakes, identifying 1011 compounds. While most substances were detected infrequently, some i.e., bis(2-ethylhexyl) phthalate and mineral oil aromatic hydrocarbons stood out for their relatively high average concentrations. Limonene emerged as the most frequently detected flavorants. Rare genotoxic compounds like safrole and diethyl sulfate were detected at low levels, emphasizing the importance of adopting a conservative evaluation approach. Molecular descriptor analysis guided the proposal of four new surrogates, i.e., dimethyl pentanedioate, 2-tridecanone, bis(2-ethylhexyl) terephthalate, and 2,2-dimethoxy-1,2-diphenylethanone, for challenge tests, aiming to better capture the chemical diversity of rPET contaminants. This research unveils the contamination profile of Chinese rPET and suggests adjustments to evaluation protocols, potentially facilitating its high-value applications and minimizing potential harms.

Abiotic degradation and accelerated ageing of microplastics from biodegradable and recycled materials in artificial seawater

Microplastics (MPs) are considered one of the most widespread pollutants in all ecosystems worldwide. In the environment, MPs can undergo hydrolysis and/or oxidation, resulting in the release of low-molecular weight degradation products, along with additives, and adsorbed organic pollutants. In this study, the morphological, chemical, and thermal changes of microplastics obtained from two biodegradable plastics, polylactic acid and Mater-Bi®, and a recycled plastic, recycled-polyethylene terephthalate, were examined after accelerated ageing under photo-oxidative conditions in synthetic seawater in a Solarbox system, and after thermal treatment in the dark. Thermal properties were studied by thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis-mass spectrometry. Compositions and changes of chemical components of the polymers were evaluated by attenuated total reflection-Fourier transform infrared spectroscopy and pyrolysis-gas chromatography–mass spectrometry. The leachable fractions and degradation products released in synthetic seawater by degraded MPs were characterized by gas chromatography–mass spectrometry. This study allowed us to identify hydrolysis as the main degradation pathway of the polymers under analysis, and to characterize not only the oligomers and degradation products released in the water as a consequence of degradation, but also additives used in plastic item formulations. This study improves our understanding of these polymers' behavior under accelerated ageing conditions.

Impact of Ball Milling on the Microstructure of Polyethylene Terephthalate.

Polyethylene terephthalate (PET) is a semi-crystalline polymer that finds broad use. Consequently, it contributes to the accumulation of plastics in the environment, warranting PET recycling technologies. Ball milling is a commonly used technique for the micronization of plastics before transformation. It has also recently been reported as an efficient mixing strategy for the enzymatic hydrolysis of plastics in moist-solid mixtures. However, the effect of milling on the microstructure of PET has not been systematically investigated. Thus, the primary objective of this study is to characterize the changes to the PET microstructure caused by various ball milling conditions. PET of different forms was examined, including pre- and post-consumer PET, as well as textiles. The material was treated to a range of milling frequencies and duration, before analysis of particle size, crystallinity by differential scanning calorimetry and powder X-ray diffraction, and morphology by scanning electron microscopy. Interestingly, our results suggest the convergence of crystallinity to ~30% within 15 minutes of milling at 30 Hz. These results are consistent with an equilibrium between amorphous and crystalline regions of the polymer being established during ball milling. The combined data constitutes a reference guide for PET milling and recycling research.

Flexible PET/Carbon/NiFe‐LDH Electrode for Oxygen Evolution Reaction in Water‐Splitting

AbstractThe development of low‐cost, readily scalable catalytic systems for green hydrogen production is crucial for diverse research and industrial applications. This work demonstrates the facile coupling of carbon/NiFe‐layered double hydroxide (LDH) onto flexible polyethylene terephthalate (PET) substrates deposited by blade coating and spray coating techniques. These low‐temperature solution processes enable high‐throughput electrode fabrication. The resulting carbon electrode exhibits sheet resistance of 25 Ω sq−1, comparable to other state‐of‐the‐art works, and displays excellent adhesion to the substrate and catalyst layer, thereby ensuring system stability. Remarkably, the developed electrode exhibits high catalytic activity for the oxygen evolution reaction (OER), achieving an overpotential of 215.9 and 267.4 mV at 10 mA cm−2 in rigid and flexible substrates respectively, and maintaining its performance even at 10 mA cm−2 for 24 h. This work highlights the potential of this methodology for producing readily transportable, flexible electrocatalytic systems with exceptional performance and minimal surface treatment of the substrate. Additionally, the use of low‐cost, readily recyclable PET plastic aligns with the principles of circular economy, promoting the integration of this platform into both research and industrial environments.

Kinetic modelling and mechanism elucidation of catalyst-free dimethyl terephthalate hydrolysis process intensification by reactive distillation

Polyethylene terephthalate (PET) is a widely used thermoplastic polymer in the packaging and materials industries, and is predicted to have continuous market growth in the future. Methods such as glycolysis and methanolysis of PET have been identified as promising approaches in sustainable chemical recycling of PET. The latter produces dimethyl terephthalate (DMT), which can be easily hydrolyzed to terephthalic acid (TPA) at elevated temperatures and pressures, and further reused for PET production. The aim of this study was to develop a kinetic model for the hydrolysis of dimethyl terephthalate, using the experimental data. Various reaction conditions (temperature, pressure, time) have been investigated and used to calculate the activation energies and reaction rate constants, while the variation in reactor setup with methanol (MeOH) removal was conducted to show its detrimental effect on the efficiency of the reaction and selectivity towards terephthalic acid. The first reaction step of DMT to monomethyl terephthalate (MMT) is relatively irreversible, while the second reaction step of MMT to TPA ceases, as soon as the equilibrium is reached. Highest yields of TPA (76.7 %) were obtained after 40 min at 265 °C, with MeOH removal, and the activation energy was calculated to be 95 and 64 kJ mol−1 for the first and second hydrolysis reaction step, respectively.

Development of Vertical Farming Systems from Waste Polymers Using Additive Manufacturing Techniques

Driven by population growth, rising living costs, and the urgent need to address climate change, sustainable food production and circular economy principles are becoming increasingly important. Conventional agriculture faces significant challenges, including land scarcity, water shortages, and disrupted supply chains. As a solution, cities are adopting vertical farming to enhance urban food security and promote circularity. This research introduces FLOAT (Farming Lab on a Trough), an innovative vertical farming system made from bio-polymers and recycled polyethylene terephthalate glyco (rPETG) pellets from plastic bottles. FLOAT’s design emphasizes sustainability and closed-loop material usage. The study showcases the versatility of additive manufacturing (AM) in creating complex geometries with fully functional 1:1 prototypes. These prototypes highlight FLOAT’s potential as a scalable and adaptable solution for sustainable food production in urban settings, contributing to improved food security and environmental sustainability. By integrating FLOAT with conventional practices, we aim to exceed Singapore’s 2030 food security targets and achieve lasting urban food resilience. FLOAT aims to scale sustainable food production, fostering community ties with food, and nurturing future responsibility.

Experimental and theoretical insights into bioethanol recovery: Valorizing waste PET bottles for sustainable pervaporation membranes

The use of bioethanol as an alternative source of fuel could solve energy and pollution concerns. However, its conventional recovery procedures make the overall process costly and energy intensive. Membrane-based pervaporation (PV) has gained significant attention in recent years. Most membranes that purify bioethanol are fabricated from conventional fossil-based polymers. This study presents the first work for biofuel separation by valorizing waste polyethylene terephthalate (PET) bottles into PV membranes. The performance of the membrane was characterized in terms of FTIR, XRD, TGA, WCA, SEM, and AFM and tested for a 10 wt% ethanol–water feed mixture at different temperatures. The mild hydrophobic character of PET allowed the PV membrane to achieve a separation factor of 10.45, a total flux of 1.7 kg m−2h−1, and a pervaporation separation index (PSI) of 18.72 at 45 °C. The recycled PET membrane (rPET) has higher mass transfer resistance for water compared to ethanol. The density functional theory (DFT) analysis confirms a stronger affinity of PET membrane towards ethanol than water. The results showed that rPET membranes have competitive performance compared to conventional fossil-based derived membranes. This study explores an energy-environment nexus approach, which could significantly contribute to achieving the key United Nations’ sustainable development goals.

Prototype Pultrusion of Recycled Polyethylene Terephthalate Plastic Bottles into Filament for 3D Eco-Printing: Education for a Sustainable Development Project

Prototype Pultrusion of Recycled Polyethylene Terephthalate Plastic Bottles into Filament for 3D Eco-Printing: Education for a Sustainable Development Project

Candle soot-modified rPET electrospun nanofibrous membrane for separating on-demand oil-water mixture and emulsions

The CS-rPET electrospun nanofibrous membrane is fabricated from recycled polyethylene terephthalate (rPET) through electrospinning and enhanced with candle soot (CS) to separate oil-water mixtures and emulsions when pre-wetted by oil or water. Using rPET polymers and CS waste reduces the environmental impact of plastic bottle waste and improves its value. The CS-rPET electrospun nanofibrous membrane showed excellent separation performance in oil-water mixtures, achieving over 81.18 % and 71.38 % of separation efficiency through 40 separation cycles after pre-wetting by oil and after washing with ethanol and pre-wetting by water, respectively. The membrane maintained high separation performance after being pre-wetted by oil for water-in-oil emulsions with efficiencies above 99 % and flux exceeding 12,200 L m−2 h−1. Similarly, the efficiencies remained above 98 % for oil-in-water emulsions after being pre-wetted by water, with a flux over 8000 L m−2 h−1. Additionally, the CS-rPET electrospun nanofibrous membrane exhibited high separation efficiencies above 97 % and flux over 14,000 L m−2 h−1 after pre-wetting by oil and 7700 L m−2 h−1 after pre-wetting by water in harsh environmental conditions. Its adaptability of switchable wettability on-demand after pre-wetting by oil or water highlights its potential for a wide range of challenging oil-water separation applications. However, multiple separation cycles, separation efficiency and flux were reduced, indicating the necessity to improve the membrane's efficiency and reduce the chance of water accumulation in multicycle separation.

Endothermic–Exothermic Hybrid Foaming of Recycled PET Blends

Over the past decades, the use of polyethylene terephthalate (PET) has seen significant growth, particularly in the packaging industry. However, its long decomposition time poses serious environmental challenges. The aim of this research was to develop a process for the foaming of large quantities of recycled PET (rPET) using endothermic and exothermic foaming agents. Various formulations with different ratios of endothermic and exothermic foaming agents were prepared, as well as their mixtures. The study found that the endothermic–exothermic hybrid foaming process resulted in a finer cell-size distribution and enhanced mechanical properties, making the foams highly suitable for widespread applications. The results support the potential use of exothermic foaming agents as nucleating agents in a hybrid foaming system. In particular, the ratio of 3% endothermic and 1% exothermic foaming agents proved optimal in terms of achieving a balance between porosity and mechanical strength, thereby enabling broad industrial applicability.

The Investigation of Morphological and Mechanical Properties of Polymer-Based Electrospun Nanofiber Coated Polystyrene and Recycled Polyethylene Terephthalate Composite Materials

The Investigation of Morphological and Mechanical Properties of Polymer-Based Electrospun Nanofiber Coated Polystyrene and Recycled Polyethylene Terephthalate Composite Materials

Circular economy solutions for plastic waste: improving rheological properties of recycled polyethylene terephthalate (r-PET) for direct 3D printing

Circular economy solutions for plastic waste: improving rheological properties of recycled polyethylene terephthalate (r-PET) for direct 3D printing

Chemical recycling of polyethylene terephthalate using a micro-sized MgO-incorporated SiO2 catalyst to produce highly pure bis(2-hydroxyethyl) terephthalate in high yield

Chemical recycling is a feasible method for achieving the closed-loop recycling of polyethylene terephthalate (PET). In this strategy, post-consumer PET is depolymerized to bis(2-hydroxyethyl) terephthalate (BHET) via glycolysis, which is then repolymerized to yield recycled PET (rPET). Herein, we introduce an innovative approach for the chemical recycling of PET that focuses on glycolysis facilitated by a microsized MgO-incorporated SiO2 catalyst. This choice of catalyst is groundbreaking owing its superior glycolysis-catalysis efficiency and the ease with which it can be separated from the reaction mixture, thereby addressing the common challenges faced by traditional catalysts during PET depolymerization. By employing a heterogeneous catalyst with significantly larger particles than a conventional catalyst, we not only aimed to simplify the catalyst-removal process, thereby improving BHET purity, but also observed enhanced efficiency during the catalytic reaction that led to a superior yield of the desired product. The catalyst was synthesized using a wet impregnation method and its efficiency was evaluated at various reaction times and dosages, which revealed that the microsized MgO/SiO2 catalyst significantly outperforms traditional catalysts, to deliver a 95.1% yield of BHET with negligible amounts of metal detected in the final product. This study not only demonstrated the potential of microsized catalysts during PET glycolysis, but also contributes to the advancement of sustainable PET-recycling practices. We anticipate that the microsized MgO/SiO2 catalyst is a promising alternative for the industrial upcycling of PET waste.

A Systems Firm-Centered Perspective on the Environmental Assessment of Recyclable PET and Glass Soft Drink Containers

This paper adopts a systems firm-centered perspective on the environmental assessment of recyclable glass and PET soft drink containers. We employ LCA and discrete-event simulation modeling for the environmental assessment of the two soft drinks packaging alternatives in operational terms over the entire supply chain over a period of three years. The assessment is based on real data collected from a large soft drink producer and its suppliers. The research and practice contribution of the paper is twofold: first, it introduces a methodological framework for environmental assessment of companies’ packaging environmental impact under different product and operations strategies; and secondly, it provides a holistic environmental assessment of the two packaging materials (PET and glass) taking into account specific operational issues, such as product mix and recycling and reuse options, as well as activity interdependences and stochasticity. The results of the simulation experiments confirm at the operations system level, for glass, the importance for sustainability, to increase the number of reuse cycles (for the particular case, for significant improvement, seven reuses) and the percentage of used bottles collected for refilling (80% recovery rate), whereas for PET, to increase the percentage of recycled PET in new bottles (towards 30%).

Unraveling the Interplay between Stability and Flexibility in the Design of Polyethylene Terephthalate (PET) Hydrolases.

The accumulation of polyethylene terephthalate (PET), a widely used polyester plastic in packaging and textiles, has led to a global environmental crisis. Biodegradation presents a promising strategy for PET recycling, with PET hydrolases (PETase) undertaking the task at the molecular level. Unfortunately, PETase operates only at ambient temperatures with low efficiency, limiting its industrial application. Current engineering efforts focus on enhancing the thermostability of PETase, but increased stability can reduce the structural dynamics needed for substrate binding, potentially slowing enzymatic activity. To elucidate the balance between stability and flexibility in optimizing PETase catalytic activity, we performed theoretical investigations on both wild-type PETase (WT-PETase) and a thermophilic variant (Thermo-PETase) using molecular dynamics simulations and frustration analysis. Despite being initially designed to stabilize the native structure of the enzyme, our findings reveal that Thermo-PETase exhibits an unprecedented increase in structural flexibility at the PET-binding and catalytic sites, beneficial for substrate recruitment and product release, compared to WT-PETase. Upon PET binding, we observed that the structural dynamics of Thermo-PETase is largely quenched, favoring the proximity between the catalytic residues and the carbonyl of the PET substrate. This may potentially contribute to a higher probability of a catalytic reaction occurring in Thermo-PETase compared to WT-PETase. We suggest that Thermo-PETase can exhibit higher PET-degradation performance than WT-PETase across a broad temperature range by leveraging stability and flexibility at high and low temperatures, respectively. Our findings provide valuable insights into how PETase optimizes its enzymatic performance by balancing stability and flexibility, which may contribute to future PETase design strategies.

Tailoring properties of PET-derived Sn-MOFs through efficiency structure defects using trifluoroacetic acid (TFA) with water-based facile and green synthesis route

BackgroundThe synthesis of Metal-Organic Frameworks (MOFs) is increasingly focused on achieving green and cost-efficient methods while producing high-quality products with abundant active sites. This approach is attracting significant attention from researchers. One promising method, modulated synthesis, stands out for its ability to induce structural defects in MOFs and enhance their active sites. However, the challenges in identifying the optimal conditions for critical factors, particularly the quantitative correlation between the modulator and crucial independent variables influencing MOFs performance, underscore the importance of research work in this field. MethodsThis study synthesized tin-based MOFs (Sn-MOFs) utilizing a linker derived from recycled polyethylene terephthalate (PET) waste. A hydrothermal approach was employed, utilizing water-like solvents and trifluoroacetic acid (TFA) as a modulator to effectively induce structural defects. Response Surface Methodology (RSM) was applied to evaluate the effects and interactions of temperature, reaction time, and TFA concentration on optimizing yield and crystalline index (CI) while simultaneously reducing the residual percentage of 1,4-benzene dicarboxylate (H2BDC) in the Sn-MOFs (DI). Significant findingsThe research revealed that temperature, reaction time, and TFA concentration significantly influenced the performance of Sn-MOFs, highlighting the considerable potential of TFA in creating active sites and enhancing the surface area and pore volume of Sn-MOFs through defect engineering. Optimal synthesis conditions for Sn-MOFs included a temperature of 148℃, a reaction time of 24 h, and a molar ratio of H2BDC/TFA of 1.7, yielding 98.51 ± 1.47 % for yield and 80.21 ± 1.32 % for CI, with no detectable residual H2BDC. The resulting Sn-MOF-150 exhibited characteristics such as high thermal and chemical stability, abundant function groups, and a unique hierarchical nanostructure composed of spherical nanoparticles. These findings further emphasize the efficacy of the synthesis approach for Sn-MOF through critical parameter optimization and defect engineering techniques.

Epoxy asphalt binder reinforced with waste polyethylene terephthalate (PET) for improving toughness

ABSTRACT The instinct brittleness of epoxy resin is one of the challenges to the durability of epoxy asphalt pavements, which may cause various failures, such as cracking, potholes and delamination. To improve the toughness of epoxy asphalts, polymer tougheners have been commonly introduced. On the other hand, the rapid accumulation of unrecycled end-of-life polyethylene terephthalate (PET) waste brings a serious environmental problem. Addressing this, the research aims to explore the use of recycled PET (rPET) as a value-added toughener for epoxy asphalt binders. To obtain this goal, waste PET bottles were cut into flakes and integrated into asphalt binders to prepare rPET modified epoxy asphalt binders. The effect of the rPET content on the phase-separated morphology, rotational viscosity and mechanical and thermal properties of epoxy asphalt binder was studied. Notably, rPET dissolved in the asphalt binder, preventing the occurrence of phase separation in the discontinuous phase of rPET modified epoxy asphalt binders. The addition of rPET increased the viscosity, dynamic modulus and the glass transition temperature (Tg) of epoxy of epoxy asphalt binder. Furthermore, the mechanical properties and low-temperature performance of epoxy asphalt binder were also augmented. Remarkably, with the addition of 3 wt% rPET, the toughness of epoxy asphalt binder increased by 48%.