Recycled Plastic Research Articles

Chemically recyclable polyvinyl chloride-like plastics

Polyvinyl chloride (PVC) is the world’s third-most widely manufactured thermoplastic, but has the lowest recycling rate. The development of PVC-like plastics that can be depolymerized back to monomer contributes to a circular plastic economy, but has not been accessed. Here, we develop a series of chemically recyclable plastics from the reversible copolymerization of cyclic anhydride with chloral. The copolymerization is highly efficient through the anionic or cationic mechanism under mild conditions, yielding polyesters with tunable structure and properties from multiple commercial monomers. Notably, these polyesters manifest mechanical properties comparable to PVC and polystyrene. Meanwhile, such polyesters are flame-retardant like PVC due to high chloride content. Of significance, these polyesters can be depolymerized back to starting monomers at high temperatures owing to the reversibility of the copolymerization, leading to a circular economy. Overall, the readily available monomers, simple synthesis, advantageous performance, and practical recyclability make the polymers promising for applications.

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.

Efficient polycarbonate plastic upcycling into jet fuel cycloalkanes over a bifunctional MoCo/NiC hetero-catalyst

While there are significant economic benefits associated with plastic recycling, the practical options for treating plastic waste remain relatively limited. This study introduces a novel bimetallic MOF-derived catalyst designed specifically for upcycling polycarbonate plastic into cycloalkanes within jet fuel range. By incorporating dual metals (MoCo) onto the MOF framework, the catalyst creates single metal sites and constructs heterojunctions. Characterizations revealed that the bifunctional catalyst can chemically adsorb phenolic compounds on a highly synergistic heterogeneous surface and lower the energy barrier of hydrodeoxygenation. Integrating the catalyst into a tandem reactor facilitates the conversion of PC plastics into jet-fuels. Achieving an average cycloalkane yield of 84.5% underscores the catalyst’s potential for deep hydrodeoxygenation of actual plastic waste. Furthermore, using waste CDs as feedstock, the cycloalkanes yield remains consistent even after three regeneration cycles, demonstrating the catalyst’s stability. In the low-carbon future, this high hydrodeoxygenation performance catalyst can be applied in chemical upcycling for pursuing a circular plastic economy.

Evaluating fresh and hardened properties of mortar composite with different types of modified polyethylene terephthalate (PET) materials as additives: Modification effects, surface properties, shape factors

Plastic disposal has become a challenge due to its challenging degradability, and plastics recycling is one of the ideal methods. The utilization of recycled plastic in building materials has been widely researched as a possible way to store plastics permanently. An investigation on the modification and incorporation of polyethylene terephthalates (PET) on fresh and hardened properties of mortar composites (MCs) is performed in the study. The work provides understanding of the synergistic effects of plastic modification methods with different types of PET additives on MC properties and to explain behavior of modified PET in mortar composites. Modification methods include microwave radiation, chemicals oxidation and alkaline hydrolysis. These methods are applied on three types of structural PET materials (hard particles, hard strips and soft yarns). The properties of 0.5%–3% PET added MCs include workability, compressive strength (CS), flexural strength (FS) and toughness are determined. At 28 days, 3% hydrolysis-treated PET yarns significantly increased FS by 69.6% and improved toughness by almost 15 times while CS with 3% PET particles modified by microwave radiation and chemicals oxidation were comparable to the control.

Enhancement of liquid/gas production during co-pyrolysis of vacuum residue and plastics due to synergistic interactions

Vacuum residue (VR) was copyrolysed with polyethylene (PE) or polystyrene (PS) in a batch reactor to investigate the corresponding synergistic pyrolytic interactions. The synergistic interactions between VR and plastic pyrolysates enhanced liquid and gas production while reducing coke formation, as compared with VR-only and plastic-only pyrolysis. The pyrolysis of 9:1 w/w VR: PE3M (PE with Mw = 3 MDa) and 9:1 w/w VR/PS350K (PS with Mw ≈ 350 kDa) mixtures produced oil in yields of 28.6 and 38.4 wt%, respectively, which exceeded those expected in the absence of synergistic interactions 1.12- and 1.29-fold, respectively. The corresponding coke yields were ~ 0.9 times lower than those expected in the absence of synergistic interactions. Moreover, copyrolysis synergistically increased the yields of oil-phase paraffins and olefins while decreasing that of aromatic compounds and was therefore concluded to enable effective VR utilisation and plastic recycling by enhancing liquid and gas production.

Waste Plastic to Roads - HDPE-modified Bitumen and PET Plastic Fibres for Road Maintenance in South Africa: A Review.

This review article provides a comprehensive analysis of the transformative potential of waste plastic in South Africa, with a specific focus on high-density polyethylene-modified bitumen and polyethylene terephthalate plastic fibres asphalt. The review encompasses a wide range of topics, including the environmental and socio-economic impacts of plastic waste, the current state of plastic waste management practices in South Africa, and the potential use of waste plastic in road construction. The aim is to critically evaluate the compatibility of recycled waste plastics as bitumen modifiers and fibre to enhance road performance. Additionally, it explores the challenges and opportunities associated with the incorporation of waste plastic in road construction, shedding light on the environmental, economic and technological aspects. The review also emphasizes the need for targeted interventions and collaborative efforts from the South African government and industry stakeholders to address plastic waste management challenges and promote sustainable infrastructure development. Overall, this review provides valuable insights into the transformative potential of waste plastic in South African road maintenance and offers a roadmap for future research and initiatives in this critical area of sustainable development.

Implementation of a Practical Environmental Sustainable Design Project in Interior Architectural Education: A Case Study at the University of Jordan

Objectives: The purpose of this study is to discuss the implementing of a practical project as a new learning methodology to help students develop expertise in the functional, aesthetic, and creative aspects of environmental design. Methods: The research is qualitative in design and based on a case-study approach, in which sixty-three environmental practical projects were explored. The examined design projects were conducted by interior design students at the department of visual arts of the University of Jordan as part of an environmental design course during three semesters in 2022. Results: Nine themes emerged from the study, which were interpreted based on the selecting and processing of materials (either recycled or adapted from the local environment). These materials comprised recycled plastic, recycled paper, recycled metal, recycled wood, recycled glass, recycled threads, resin, ceramic, and plants. The study also found that working with and processing local or recycled materials in practical projects within the study curriculum helped students acquire skills and gain confidence in relation to environmental practice, and increased their awareness of the different usages of materials and their advantages from both a functional and aesthetic perspective. Conclusions: The significance of the study lies in its adoption of a practical approach as a new active learning methodology within art and design educational programmes to meet the current educational standards stipulated by the Ministry of Higher Education and Scientific Research in Jordan. Real-world projects foster students’ development of critical creativity to achieve the ultimate principles of environmental design and prepare them to deal with real challenges within the professional job market.

Mechanical and physical properties of eco-friendly recycled plastic concrete (RPC)

In this research, an Eco-friendly Recycled Plastic Concrete (RPC) having good workability, low density, thermal isolation characteristics, and can be used in structural applications has been engineered. One reference mixture in addition to nine RPC mixtures were studied, where the plastic granules were used as a partial replacement of sand and/or gravel by volume. The studied parameters were the replacement ratios of fine and coarse aggregates by plastic granules; the replacement ratios were: 1) 100, 80, and 60 % from sand; 2) 50, 40, and 30 % from gravel; and 3) 100, 80, and 60 % from sand simultaneous with 30 % from gravel. The effect of incorporating plastic on the physical, mechanical, and thermal properties of the newly developed RPC mixtures have been investigated experimentally via thirty concrete standard cubes (150 × 150 × 150 mm), thirty concrete standard cylinders (150 × 300 mm), and 30 S-shape prisms. A statistical analysis on the test results was carried out using commercial software to determine the optimum proportions of the studied RPC mixtures. The criteria were to maximize the required strengths and to minimize the required density and thermal conductivity. The conducted optimum sand/gravel replacement ratios were 30 % for sand and 80 % for gravel, which were similar to the replacement ratios of Mixture 8 in the current research. This optimum mixture has a unit weight of 1900 kg/m3 and a compressive strength of 27.7 MPa, which were found to meet the limits of structural light weight concrete according to ACI 213R-14 and supports both structural and environmental benefits.

Effect of the shifting from multi-layer systems towards recyclable mono-material packaging solutions on the shelf-life of portioned semi-hard cheese

Packaging with recyclable plastic films could be an interesting alternative solution to extend shelf-life of portioned cheese. Two multi-layer materials of different types of one polymer (MonoMAP1 and MonoMAP2) with different barrier properties (O2: 13 and 20 cm3(STP)/(m2 × 24 h), 0 % RH; CO2: 65 and 92 cm3(STP)/(m2 × 24 h), 0 % RH) and coupled with modified atmosphere (MAP) were considered. Their performances in affecting cheese stability were compared to those of conventional multi-layer solutions under-vacuum (MultiVAC) and MAP (MultiMAP). Microbiological and physicochemical quality indicators were considered for a shelf-life study. In MonoMAP2, the initial loss of carbon dioxide and concomitant permeation of oxygen into the pack caused an earlier proliferation of molds with values of 4.7 log cfu g−1, leading to its inapplicability. In the other packaged samples, the development of rancid volatile compounds resulted the more sensitive quality indicator to be used for shelf-life assessment, with a critical threshold perceived by panelists around 520 mg/kg. Cheese packaged in MonoMAP1 showed a shelf-life associated to rancidity development of about one third lower than that of MultiVAC and MultiMAP ones.

An improved identification method based on Bayesian regularization optimization for the imbalanced proportion plastics recycling using NIR spectroscopy

An improved identification method based on Bayesian regularization optimization for the imbalanced proportion plastics recycling using NIR spectroscopy

Revisiting the activity of two poly(vinyl chloride)- and polyethylene-degrading enzymes

Biocatalytic degradation of non-hydrolyzable plastics is a rapidly growing field of research, driven by the global accumulation of waste. Enzymes capable of cleaving the carbon-carbon bonds in synthetic polymers are highly sought-after as they may provide tools for environmentally friendly plastic recycling. Despite some reports of oxidative enzymes acting on non-hydrolyzable plastics, including polyethylene or poly(vinyl chloride), the notion that these materials are susceptible to efficient enzymatic degradation remains controversial, partly driven by a general lack of studies independently reproducing previous observations. Here, we attempt to replicate two recent studies reporting that deconstruction of polyethylene and poly(vinyl chloride) can be achieved using an insect hexamerin from Galleria mellonella (so-called “Ceres”) or a bacterial catalase-peroxidase from Klebsiella sp., respectively. Reproducing previously described experiments, we do not observe any activity on plastics using multiple reaction conditions and multiple substrate types. Digging deeper into the discrepancies between the previous data and our observations, we show how and why the original experimental results may have been misinterpreted.

Thermal and catalytic pyrolysis of automotive plastic wastes to diesel range fuel

This study investigated the pyrolysis of automotive plastic wastes (APW) for the production of diesel-grade oil products using a modified calcium bentonite clay catalyst. The research aimed to optimize the process for maximum oil yield and diesel range organics yield. The APW was characterized by its chemical composition and physical properties and the optimal temperature and catalyst amount were determined for maximum oil yield and diesel range hydrocarbons. The results showed that the APW contained mixed Acrylonitrile Butadiene Styrene (ABS), High/Low Density Polyethylene (H/LDPE), Polypropylene (PP), Polystrene (PS) and fiberglass, with a large quantity of volatiles and ash. The average oil yield was higher in the catalytic process compared to that in the thermal process. Generally, higher temperature above 450 °C produced waxy oil, thus lower temperature favoured more Diesel Range Organics (DRO). Both processes yield similar yields of C8–C24 DRO, and in both cases, lower temperature favoured high yield of C8-C24 hydrocarbons. The catalyst significantly increased the yield of oil, but did not significantly increase C8–C24 DRO yield. The optimal conditions for a maximum oil yield of 78.6 % and DRO yield of 79.5 % was a temperature of 416 °C and 24.3 wt% clay. Thus, the modified calcium bentonite clay can be used to improve oil yield from pyrolysis of APW. The oil produced had properties such as calorific value (49.85 MJ/kg), flash point (113 °C) and total aromatics 3.55 area%, similar to those of commercial diesel, and comprised mostly of 2,4-Dimethyl-1-heptene (25.37 ± 2.01 %) of thermal and 2, 4 – Dimethyl – 1 – heptane (23.44 ± 2.42) in the catalytic process. The study suggests further research to explore different catalysts, maximization of both DRO and gasoline range organics, recover energy from residues, and conduct techno-economic assessments for plant-scale operations. Additionally, policies on the management of end-of-life vehicles should include provisions for stripping and segregation of plastic components by accredited providers for the purpose of plastics recycling.

Review of Plastic Waste Recycling: Advances, Challenges, and Future Perspectives

Plastic waste recycling is pivotal for sustainable waste management, offering solutions to mitigate environmental impacts and conserve resources. This thesis reviews technological advancements, challenges, and future prospects in recycling various plastic types. It begins with an overview of plastic pollution’s global impact and the imperative to manage plastic waste responsibly amidst rising production. Recycling processes are explored, detailing collection, sorting, cleaning, and reshaping methods that extend plastic life cycles while reducing energy consumption and greenhouse gas emissions. The review highlights challenges such as plastic type variability, recycling infrastructure limitations, and market demand discrepancies, affecting recycling effectiveness. Technological advances, including mechanical and chemical recycling innovations, are analyzed for their potential to improve plastic recycling rates. Economic and environmental implications underscore the benefits of effective recycling, contributing to a circular economy and minimizing landfill waste. Future directions advocate for enhanced recycling technologies, standardized labeling, and policy interventions like extended producer responsibility schemes. By addressing these facets, stakeholders can collaboratively advance sustainable plastic waste management globally, fostering a future where environmental stewardship aligns with economic viability.

Innovations to overcome the current waste problem caused by single-use plastics in the pursuit of a circular economy

Plastic production continues to increase each year, yet only 9% are successfully recycled. This has impacted natural habitats and ecosystems, due to an uncontrolled amount of waste. The food industry is a major contributor to plastic waste. To counter this problem, the demand for environmentally sustainable alternatives, i.e. bio-based plastics, in the pursuit of a circular economy is increasing. As such, this problem is interconnected and at the resource nexus of particularly, food, material, waste, and ecosystem. This systematic review provides an overview of different innovations regarding materials and additives for bio-based plastics for packaging in the food industry. The paper argues that a majority of materials for bio-based plastics originate from the food industry’s value chain and utilizing these resources is essential to reduce waste and to create more value, essentially addressing the problem with a focus on the resource nexus. Moreover, the importance of developing biodegradable and recyclable plastics to reduce the environmental impact of plastic waste is also highlighted, especially in the context of single-use food packaging. These findings and conclusions cumulated into a framework to differentiate the various materials and classify them regarding their biodegradability properties, origin (plant- or animal-based industry by-products and raw materials) and end-of-life scenarios. This contributes to the academic literature and practice by categorizing different kinds of materials, which might be labelled environmentally sustainable, particularly biodegradable, but which might not always be the case and critically discussing implications of this.

Machine learning based prediction of compressive and flexural strength of recycled plastic waste aggregate concrete

In the last 50 years, the use of plastics has increased significantly due to advances in technology, population growth and increasing needs. However, this trend has led to the accumulation of large amounts of plastic waste. Numerous studies have been conducted on the use of recycled plastic materials in concrete production as a means of recycling and environmental protection. This study aims to predict the 28-day cylinder compressive and flexural strength of concretes using Polyethylene Terephthalate (PET), Phenolic Formaldehyde (PF), Polypropylene (PP), Polycarbonate (PC), Polyvinyl Chloride (PCV), High-Impact Polystyrene (HIPS) and High-Density Polyethylene (HDPE) plastic waste as aggregates. In this scope, a comprehensive database was created using experimental results obtained from the literature. Then, this study used six ML models, including Support Vector Regressor (SVR), Random Forest Regressor (RFR), Gradient Boosting Regressor (GBR), XGBoost Regressor (XGR), LightGBM Regressor (LGR), Bagged Decision Trees Regressor (BDTR), to predict the compressive and flexural strength of recycled plastic waste aggregate concrete (RPWAC). From the experimental database, 253 data points with strength between 6.00–70.05 MPa were identified to estimate the compressive strength (CS) and 175 data points with strength between 1.21–7.96 MPa were identified for flexural strength (FS). Cross-validation was used for six ML models and hyperparameter fine-tuning was performed. The results showed that six different ML models predicted the compressive and flexural strengths of RPWAC with high accuracy. The XGR model predicted CS and FS better than the other five different models with R2 values of 0.931 and 0.999, respectively. The three main properties effecting the CS of RPWAC were plastic waste content, water/cement ratio and concrete specific gravity, while the three main properties affecting the FS of RPWAC were cement specific gravity, plastic waste content and cement CS.

RECYCLING OF PLASTIC WASTE BY THE PYROLYSIS METHOD

Chemical recycling of plastic waste can be a useful complement to mechanical recycling to achieve the required rate of plastics recycling and create a climate-neutral and resource-saving circular economy. Various mixed plastic wastes to be recycled in the future are investigated under fully uniform intermediate pyrolysis conditions characterized by moderate heating rates and pyrolysis temperatures. The distribution of the product and the selected properties of the product are determined, and the mass and energy balance of the process is obtained. Product yield and composition are highly dependent on pyrolyzed residues. All results indicate that pyrolysis is a suitable process for obtaining chemical feedstocks from various complex mixed plastic wastes. The main mass and energy balances for chemical recycling of mixed plastic waste by pyrolysis method were determined. Products for recycling raw materials can be obtained from all investigated plastic waste. Product quality often depends on raw materials. The energy requirement for heating, melting, pyrolysis and evaporation is about 5% of the calorific value of the raw material. It has been demonstrated that 50 to 75% of the raw carbon can be recovered in the condensate and reintroduced into the value chain in the chemical industry.

PVC Dechlorination for Facilitating Plastic Chemical Recycling: A Systematic Literature Review of Technical Advances, Modeling and Assessment

Polyvinyl chloride (PVC) resins are widely used in modern society due to their acid and alkali resistance, low cost, and strong insulation properties. However, the high chlorine (Cl) content in PVC poses significant challenges for its recycling. This study reviews the treatment processes, model construction, and economic and environmental assessments to construct a methodological framework for the sustainable development of emerging dechlorination technologies. In terms of treatment processes, this study summarizes three types of processes, pretreatment, simultaneous dechlorination during chemical recycling, product purification, and emphasizes the necessity of dechlorination treatment from a systematic perspective. Additionally, the construction of models for dechlorination processes is investigated from the laboratory to the industrial production system to macro-scale material, in order to evaluate the potential inventory data and material metabolism behaviors. This review also summarized the methodology framework of Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA), which can be applied for evaluation of the economic and environmental performance of the dechlorination processes. Overall, this review provides readers with a comprehensive perspective on the state-of-the-art for PVC dechlorination technologies, meanwhile offering sustainable guidance for future research and industrial applications of chemical recycling of PVC waste.

Integrated approach of waste analysis and life cycle assessment for the management of non-recyclable plastics in recycling shops

The unbound usage of plastic products in modern society has brought convenience and poses significant environmental challenges. Recycling Shops (RS) are vital in mitigating plastic waste problems in urban waste management. During the recycling process, RS generates non-recyclable plastics that demand scientific solutions for its management. This study conducted material flow analysis (MFA) to estimate the yearly recycled plastic waste in the RSs of Khulna City. Subsequently, a life cycle assessment (LCA) was performed to explore the suitable management facilities for non-recyclable plastics. The results highlighted the contribution of the informal plastic recycling sector to the city's waste management system by recycling 6324 tons of plastic waste per year. Polypropylene (PP) and Polyethylene (PE) were the most abundant polymers among the recycling plastics in RS. The LCA results revealed that among the five considered cases, Open Burning showed the maximum impact on the environment while Sanitary Landfill exhibited the lowest environmental impact across eighteen impact categories. The sanitary landfilling of non-recyclable plastics was identified as an environmentally friendly approach for managing non-recyclable plastics. This study addressed the urgency for appropriately managing non-recyclable plastics to protect the human and environment from plastic pollution in Bangladesh including recommendations for improving current practices.

Continuous process design of the microwave chemical recycling of waste plastics using microwave-absorbing heating elements

Conventional pyrolysis methods to chemically recycle plastic waste require significant energy input owing to inefficient energy transfer from the heat sources to plastics and the generation of excess CO2. Accordingly, there is an urgent need to develop alternative methods for the chemical recycling of waste plastics to limit global warming. In this study, the use of microwaves (MWs) as an efficient energy source for pyrolysis and chemical recycling. However, because plastic is transparent to MW energy, a method that utilizes carbon materials as MW-absorbing heating elements (MWAHEs) was developed. This method directly converted high-density polyethylene (HDPE) into light chemicals in up to 94% yield with 45% ethylene selectivity. A two-stage pyrolysis system incorporating MWAHE-assisted MW pyrolysis was also developed to produce light chemicals in 95% yield with 49% ethylene selectivity. From a chemical engineering perspective, this two-step pyrolysis system is an efficient and feasible method for producing valuable light olefins. This study also demonstrates that MWAHE assisted MW pyrolysis is effective for the chemical recycling of plastic waste. This study offers potential solutions for the environmental problems posed by plastic waste by developing efficient and scalable methods for its chemical recycling.

Highly degradable bio-based plastic with water-assisted shaping process and exceptional mechanical properties

The fabrication of biodegradable and recyclable bio-based plastic by complexing carboxymethyl cellulose (CMC) and cationic polymeric ionic liquid (PILCl) assisted with KNO3 is offered to utilize plastics sustainably and mitigate serious threats to the environment. The CMC/PIL plastic film, formed via electrostatic interactions, exhibits exceptional mechanical properties that surpass those of most conventional plastics. It demonstrates a tensile strength of approximately 200 MPa and a Young's modulus of around 5.5GPa. Even after recycling and regeneration, they essentially retain the original mechanical characteristics with a tensile strength of about 190 MPa. These CMC/PIL plastic films can be processed into three-dimensional (3D) shapes assisted with water and their fundamental qualities maintain after numerous shaping. Besides, they possess excellent biodegradability and can finish biodegrading in a few hours with cellulase and within a few days when exposed to soil. This innovation provides a fresh and practical way to produce degradable plastics.