Mixed Plastic Waste Research Articles

Experimental investigation of products from thermal treatment of real-world mixed single-use and multi-layered waste plastics

The usage and disposal of highly abundant single-use and multilayered plastics contribute to significant ecological problems. The thermochemical recovery of these plastics to useful products and chemicals provides opportunity for positive economic and environmental impacts. Most previous research use idealised and unrepresentative feedstocks. To address this, various mixed waste plastics collected from the rejected fraction of a municipal waste recovery facility in Ghana were pyrolyzed at varying temperatures of 450, 500 and 550 °C and their yields compared. The obtained chemical products were analysed using several different techniques. Energy and carbon balances of the processes were produced using the CHNS and energy content of the oil fraction and the compositional results of the pyrolysis gas fraction, the latter of which was measured by Gas Chromatography Thermal Conductivity Detection (GC-TCD). The oils were further assessed via Gas Chromatography Mass Spectrometry (GC-MS) to identify the available valuable compounds. The formed oil contained approximately 40% light hydrocarbons (C6 – C11), 18% middle hydrocarbons (C11 – C16) and 42% heavy hydrocarbon compounds (C16+). The optimal oil yield of 65.9 ± 0.5% and low heating value of 44.7 ± 0.1 MJ/kg for single-use plastics were recorded at highest heating temperatures of 550 and 500 °C, respectively. The findings provide indication that pyrolysis is a fitting solution for energy recovery from waste plastics.

Polyurethane with β‐Selenocarbonyl Structure Enabling the Combination of Plastic Degradation and Waste Upcycling

AbstractDegradable polymers offer a promising solution to mitigate global plastic pollution, but the degraded products often suffer from diminished value. Upcycling is a more sustainable approach to upgrade polymer waste into value‐added products. Herein, we report a β‐selenocarbonyl‐containing polyurethane (SePU), which can be directly degraded under mild conditions into valuable selenium fertilizers for selenium‐rich vegetable cultivation globally, enabling both plastic degradation and waste upcycling. Under oxidation condition, this polymer can be easily and selectively degraded via selenoxide elimination reaction from mixed plastic waste. The degraded product can serve as effective selenium fertilizers to increase selenium content in radish and pak choi. The SePU exhibits excellent mechanical properties. Additionally, we observed the formation of spherulites‐like selenium particles within the materials during degradation for the first time. Our research offers a successful application of selenoxide elimination reaction in the field of plastic degradation for the first time, endowing plastics with both degradability and high reusable value. This strategy provides a promising solution to reduce pollution and improve economy and sustainability of plastics.

Polyurethane with β-Selenocarbonyl Structure Enabling the Combination of Plastic Degradation and Waste Upcycling.

Degradable polymers offer a promising solution to mitigate global plastic pollution, but the degraded products often suffer from diminished value. Upcycling is a more sustainable approach to upgrade polymer waste into value-added products. Herein, we report a β-selenocarbonyl-containing polyurethane (SePU), which can be directly degraded under mild conditions into valuable selenium fertilizers for selenium-rich vegetable cultivation globally, enabling both plastic degradation and waste upcycling. Under oxidation condition, this polymer can be easily and selectively degraded via selenoxide elimination reaction from mixed plastic waste. The degraded product can serve as effective selenium fertilizers to increase selenium content in radish and pak choi. The SePU exhibits excellent mechanical properties. Additionally, we observed the formation of spherulites-like selenium particles within the materials during degradation for the first time. Our research offers a successful application of selenoxide elimination reaction in the field of plastic degradation for the first time, endowing plastics with both degradability and high reusable value. This strategy provides a promising solution to reduce pollution and improve economy and sustainability of plastics.

Valorization of mixed plastics waste for the synthesis of flexible superhydrophobic films

Superhydrophobic surfaces are typically created by enhancing nanoscale roughness or incorporating anti-wetting additives like silanes, nanoparticles, or fluorinated compounds. Limited by the availability of nano-structured templates, simple fabrication, flexibility of the material, and cost-effectiveness, the quest to synthesize superhydrophobic films remains challenging. Herein, we report the valorizing of mixed plastic waste for the synthesis of flexible superhydrophobic films via open-loop recycling. We focused on improving the nanoscale surface roughness of the material by using a series of steps including selective dissolution, thermally induced phase separation, controlled spin-casting, and annealing. We synthesized a two-layered superhydrophobic film with high surface roughness and sufficient mechanical strength, making it suitable for use as a free-standing material. The contact and sliding angles were found to be 159° and 4°, respectively, with an RMS (root mean square) surface roughness of 228 nm. This approach is demonstrated with mixtures of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), which are among the most abundant components of post-consumer plastic waste. Life cycle assessments show that synthesized superhydrophobic films have lower carbon dioxide emissions and embodied energy than virgin PE and PP derived from petroleum. Our design strategy not only yields a superhydrophobic product but also provides an alternative to plastic waste recycling by bypassing cost-intensive sorting techniques.Graphical

Effect of Surface Hydrophilized Plastic Waste Aggregates Made by Mixing Various Kinds of Plastic on Mechanical Properties of Mortar.

The surface hydrophilization of mixed plastic waste aggregates (MPAs) was conducted to improve the bond between an MPA and the surrounding cement matrix using two types of coating agents: a silicone amine resin and acrylic binders. The coating agents formed a physical bond with the MPAs, and the results of contact angle measurement also revealed that the surface of MPAs was hydrophilic. The workability of a mortar mix increased by up to 1.47 times with the surface hydrophilization of MPAs. Meanwhile, the compressive and flexural strengths of mortar mixes decreased by 29~43% and 72~86%, respectively, at 28 days with the surface hydrophilization of MPAs. Namely, the surface hydrophilization of MPAs was successively conducted, and the workability of mortar mixes was improved accordingly, but the compressive and flexural strengths of mortar mixes decreased as the physical bond was partially separated from not only the MPA but also the surrounding cement matrix and the surface friction was decreased.

Mechanical Properties of Recycling Mixed Waste Plastic Predicted on Pallet Application Using Finite Element Analysis

The enormous use of plastic in any live sector will impact the waste plastic escalation. Unsorted and uncollected wasted plastic properly leads to the creation of mixed waste plastic in landfills. Therefore, mechanical recycling technology for processing mixed waste plastic into pasta phase has been developed. In this research, four sources of mixed waste plastic were implemented derived from household plastic bags (WPB), waste of plastic sack (WPS), waste of used carton beverage (WPAL) and waste plastic from drum pulper in pulp industry (WPI). Those materials were transformed into specimens through extrusion and compression molding, then tested for investigation the mechanical properties. A comparison of density, tensile strength, and compressive strength from each material was exposed comprehensively. Furthermore, finite element analysis (FEA) was employed to compute the reliability of recycle material properties in the pallet application under the racking condition test following ISO 8611 standard. Surprisingly, it was reported a potential performance with a maximum racking load until 700 kg for pallet product using all variants of mixed waste plastics. The maximum capacity was obtained based on consideration of the FEA result exhibited in tresca or maximum shear stress, total deformation, and factor of safety design.

Divergent methods for polyester and polycarbonate depolymerization with a cobalt catalyst

Catalytic methods for the cyclodepolymerization and solvolysis of polyesters and polycarbonates have been realized with a molecular cobalt catalyst. Nascent strategies to modify these methods for use in mixed plastic waste streams are identified.

Environmental impact of different scenarios for the pyrolysis of contaminated mixed plastic waste

Pyrolysis is environmentally superior to landfilling for the treatment of contaminated mixed plastic waste.

Waste Plastics Chemical Recycling in the Context of Refining and Petrochemical Industries

Rising demand for plastic materials results in increasing volumes of plastic waste generated globally. This poses a question of waste collection and handling of the growing waste volumes. With quality limitations of reuse and mechanical recycling, especially end-of-life mixed plastic waste is mostly landfilled, incinerated or lost to environment. Thermochemical recycling, especially pyrolysis, has been historically explored as an attractive alternative waste processing method with a potential to valorise the plastic waste into energy, fuels and more recently also chemicals and virgin polymers. Thermochemical plastic waste processing and treatment of the intermediates towards the final products have been found to be studied mostly in isolation. Therefore, this study provides a combined view. Updated state of pilot and demonstration projects is reviewed. Typical characteristics of plastic waste pyrolysis products are introduced and the areas of potential impacts on existing plants are highlighted. In order to address the circularity and economic aspect, a summary of recent relevant LCA and business studies is provided, showing common sensitivity factors and main assumptions used therein. Overall, this review summarizes the background behind the recycling of waste plastics and presents it in context of challenges and opportunities of integration with existing refining and petrochemical infrastructure.

Performance, Combustion, and Emission analysis of diesel engine fuelled with pyrolysis oil blends and n-propyl alcohol-RSM optimization and ML modelling

This experimental work focuses on testing the diesel engine by the replacement of pyrolysis oil extracted from different waste plastics. The novelty of this work is testing the engine performance, combustion, and emission study with the following proportions D90WPO7NP3, D80WPO15NP5, D70WPO23NP7, WPO100, and D100. The pyrolysis oil is extracted from the mixed waste plastics with calcium bentonite as a catalyst and n-propyl alcohol is used as an additive for better igniting developer. From the results, it is found that the performance parameters such as BTE are found to increase in efficiency by 2.2% for the fuel D90WPO7NP3 and decrease in BSFC by 3.1% for the same fuel compared to pure diesel. It is also noticed that the emission properties such as CO2, CO, HC, and O2 content decreased in the order of 5.49%, and 6.2%. 39.2 and 12.5 % as compared to pure diesel. However, there is a slight increase in emissions of NOX due to the presence of uncontrolled enriched constituents in the pyrolysis oil; the increase in NOx emissions is found to be 16.2% compared to diesel fuel at full load conditions. The ML and RSM techniques using ANOVA techniques are adopted to find the least accuracy of data. This shows that the model fits the data well. The linear regression model explains 93.6% of the variation in BTE during training and has 95.9% prediction power. Linear Regression showed good predictive skills, acquiring a high R2 value of 0.985. It is concluded that pyrolysis oil with n-propyl alcohol as an additive gives a better substitute in the field of automobile applications.

Activated carbon adsorption of heteroatom components from pyrolysis oil for improved chemical recycling

Pyrolysis is a promising technique for managing mixed plastic waste. However, its industrial implementation faces significant challenges due to the presence of heteroatom components in the pyrolysis oil. These impurities are the major hurdle to use these feeds in steam crackers. To address this issue, we evaluated the potential of adsorption on activated carbon as a purification method by measuring the adsorption capacity of nine of the most important heteroatom components in pyrolysis oils. Through single-isotherm experiments and modeling, our aim was to understand the interactions between the adsorbate and the adsorbent as well as the influence of the component-pyrolysis oil interaction. Furthermore, multicomponent isotherm experiments further explored cooperative and competitive interactions among different heteroatom components, providing valuable insights into their behavior in complex systems. Our findings highlight benzoic acid as the most effective adsorbate (qm = 193.4 ± 12.8 mg g−1), while less polar components such as cyclopentanone (qm = 15.9 ± 1.79 mg g−1), hexamethylcyclotrisiloxane (qm = 7.11 ± 1.27 mg g−1), and 1-chloropentane (no detectable removal) pose challenges for pyrolysis oil purification without excessive dosing of the adsorbent, in our case activated carbon. Moreover, multicomponent experiments revealed that pyridine exhibits cooperative adsorption behavior, whereas other components engage in competitive adsorption dynamics. The analysis of six multicomponent models emphasized the importance of considering adsorbate–adsorbate interactions in describing the adsorption behavior in complex mixtures. Models equipped with interaction parameters (correlative model) outperformed those without such parameters (predictive model), as evidenced by higher R2 values (R2 = 0.95–0.99) for the former compared to the latter (R2 = 0.84–0.86).

Study on the kinetics of catalytic pyrolysis of single and mixed waste plastics by spent FCC catalyst

Study on the kinetics of catalytic pyrolysis of single and mixed waste plastics by spent FCC catalyst

Climate footprint assessment of plastic waste pyrolysis and impacts on the Danish waste management system

Increased plastic recycling is necessary to reduce environmental impacts related to manufacturing and end-of-life of plastic products, however, mechanical recycling (MR) – currently the most widespread recycling option for plastic waste – is limited by quality requirements for inputs and reduced quality of outputs. In this study, pyrolysis of plastic waste is assessed against MR, municipal solid waste incineration (MSWI) and fuel substitution through climate footprint assessment (CFA) based on primary data from pyrolysis of plastic waste sourced from Danish waste producers. Results of the CFA are scaled to the Danish plastic waste resource in an impact assessment of current Danish plastic waste management, and scenarios are constructed to assess reductions through utilization of pyrolysis. Results of the CFA show highest benefits utilizing pyrolysis for monomer recovery (−1400 and −4800 kg CO2e per ton polystyrene (PS) and polymethyl methacrylate (PMMA), respectively) and MR for single polymer polyolefins (−1000 kg CO2e per ton PE). The two management options perform similarly with mixed plastic waste (200 kg CO2e per ton plastic waste). MSWI has the highest impact (1600–2200 kg CO2e per ton plastic waste) and should be avoided when alternatives are available. Scaling the results of the CFA to the full Danish plastic waste resource reveals an impact of 0.79 Mt CO2e in year 2020 of current plastic waste management. Utilizing pyrolysis to manage MR residues reduces the system impact by 15%. Greater reductions are possible through increased separation of plastic from residual waste. The best performance is achieved through a combination of MR and pyrolysis.

Unlocking superior properties in polypropylene/polyethylene terephthalate (PP/PET) blends using an ethylene-butylene-acrylate terpolymer reactive compatibilizer

The increasing global plastic production has created an urgent demand for energy-efficient processes to transform mixed plastic waste into value-added products via upcycling. Compatibilization of polypropylene (PP) and poly(ethylene terephthalate) (PET), two used semi-crystalline polymers in industry, is investigated in this study. We evaluate the effectiveness of an ethylene-butylene-acrylate terpolymer (PTW) at different contents in a 70/30 PP/PET blend, examining the resulting physico-chemical characteristics. Adding PTW as compatibilizer significantly reduces the droplet size in the PP/PET blend, improving rheological and mechanical properties. Remarkably, the blend containing 1.5 % PTW exhibits maximum enhancement in mechanical properties. To understand deeply the chemical compatibilization mechanism, Fourier transform infrared spectroscopy (FTIR-ATR), Atomic Force Microscopy combined with infrared spectroscopy (AFM-IR), and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) techniques were employed. The compatibilizer was located at the interphase, and the chemical reaction using AFM-IR and 1H NMR was tracked. These advanced techniques prove the chemical compatibilization mechanism in PP/PET blends with PTW. These findings contribute to understanding the compatibilization processes, offering valuable guidance for developing efficient upcycling processes for mixed plastic waste.

Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment

Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C1–C4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C1–C4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes.

Exploring the potential of clay catalysts in catalytic pyrolysis of mixed plastic waste for fuel and energy recovery

Developing low-cost and high-activity catalysts is one of the keys to promoting the catalytic pyrolysis of waste plastics to fuels for plastic recycling. This work studied the effect of clay as the catalyst on mixed plastic pyrolysis for fuel and energy recovery. Four kinds of clay, including nanoclay, montmorillonite, kaolin, and hydrotalcite, were used as catalysts for the pyrolysis of mixed plastic consisted of polyethylene terephthalate, polystyrene, polypropylene, low-density polyethylene, and high-density polyethylene. The product yield and distribution varied with different clay in pyrolysis. The highest yield of oil was 71.0 % when using montmorillonite as the catalyst. While the highest contents of gasoline range hydrocarbons and diesel range hydrocarbons in the oil were achieved when using kaolin and nanoclay, respectively as catalysts. For the gas products, the CO, C2H4, C2H6, C3H6, and C4H10 increased with decreased CO2 in the gaseous products when using clay as catalysts. In general, the mild acidity of clay catalyst was essential to improve the oil yields and the proportion of the gasoline or diesel range fuels in the catalytic pyrolysis of mixed plastic waste.

Boosting bacterial nanocellulose production from chemically recycled post-consumer polyethylene terephthalate

The circular economy is emerging with new sustainable solutions to the ever-growing plastic waste challenge, garnering increasing attention. In this study, the possibility to modify expensive Hestrin–Schramm medium (HS) for bacterial nanocellulose (BNC) production and replace significant amounts of glucose with terephthalic acid (TPA) derived after reactive extrusion processing of mixed plastic waste yielding post consumer TPA (pcTPA), was evaluated from laboratory scale to fermentation at pilot scale. Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric Analysis (TGA) were used to assess the structural, thermal, and morphological properties of BNC and its generated derivatives. The study's findings highlight the positive impact of pcTPA on BNC yield, surpassing the performance of conventional TPA. The presence of pcTPA in the medium resulted in a BNC yield of 4.01 g/L in a scale-up step of 100 mL cultivation, while the positive control using glucose resulted in a yield of 3.57 g/L. The efficiency of glucose substitution with pcTPA increased with each scale-up step, ultimately reaching a 320% yield increase in comparison to the positive control. Additionaly, the procedure that enhanced the materials' thermoplasticity in the form of derivatives has been established resulting in the production of BNC laurate and BNC octanoate derivatives with melting temperatures of 270 °C and 280 °C, respectively. Overall, this study investigates the potential of this approach as an important circular economic solution, enabling an increased sustainable perspective for polyethylene terephthalate (PET) circularity and significantly a much needed cost reduction for BNC production with enhanced thermoplasticity.

Three-stage pyrolysis–steam reforming–water gas shift processing of household, commercial and industrial waste plastics for hydrogen production

Five common single plastics and nine different household, commercial and industrial waste plastics were processed using a three-stage (i) pyrolysis, (ii) catalytic steam reforming and (iii) water gas shift reaction system to produce hydrogen. Pyrolysis of plastics produces a range of different hydrocarbon species which are subsequently catalytically steam reformed to produce H2 and CO and then undergo water gas shift reaction to produce further H2. The process mimics the commercial process for hydrogen production from natural gas. Processing of the single polyalkene plastics (high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP)) produced similar H2 yields between 115 mmol and 120 mmol per gram plastic. Even though PS produced an aromatic product slate from the pyrolysis stage, further stages of reforming and water gas shift reaction produced a gas yield and composition similar to that of the polyalkene plastics (115 mmol H2 per gram plastic). PET gave significantly lower H2 yield (41 mmol per gram plastic) due to the formation of mainly CO, CO2 and organic acids from the pyrolysis stage which were not conducive to further reforming and water gas shift reaction. A mixture of the single plastics typical of that found in municipal solid waste produced a H2 yield of 102 mmol per gram plastic. Knowing the gas yields and composition from the single plastics enabled an estimation of the yields from a simulated waste plastic mixture and a ‘real-world’ waste plastic mixture to be determined. The different household, commercial and industrial waste plastic mixtures produced H2 yields between 70 mmol and 107 mmol per gram plastic. The H2 yield and gas composition from the single waste plastics gave an indication of the type of plastics in the mixed waste plastic samples.Graphical abstract

Polychlorinated biphenyls in bovine milk from a typical informal electronic waste recycling and related source regions in southern India before and after the COVID-19 pandemic outbreak

For more than a decade, Chennai city in southern India has been evidenced with informal electronic waste (e-waste) recycling and open burning practices as the potential sources for polychlorinated biphenyls (PCBs). PCBs can bioaccumulate in livestock particularly cows grazing on the contaminated soil. The outbreak of the COVID-19 pandemic led to additional challenges associated with waste management practices. Hence this study aims to elucidate twenty-five PCB congeners in bovine milk from the previously reported PCB source regions in Chennai and the suburbs before and after about three years of the pandemic outbreak along electronic waste recycling (EWR), open burning dumps (OBD), and residential (RES) transects. The geomean concentration of Ʃ25PCBs in ng/g lipid weight (lw) followed a decreasing trend of EWR (13 ng/g lw) > OBD (8 ng/g lw) > RES (4 ng/g lw). Over 80 % of PCBs stemmed from EWR and OBD transects before and after the pandemic. However, a significant surge in the level of PCB-52 was observed in the OBD transect after the pandemic outbreak. Most toxic PCB congeners, PCB-126 and -169 were significant contributors to TEQs in EWR and OBD transects and can be reasoned with the burning of waste materials and mixed plastics in these transects. The highest average daily dose (ADD) exposure risk was for children from EWR and was significantly higher (p < 0.05) than other transects. Mean ADD-induced TEQ (6.6 pg TEQ/kg-bw/day) from the cows grazing around Kodungaiyur dumpsite slightly exceeded the EU guideline of 5.5 pg TEQ/kg-bw/day after the outbreak of the pandemic due to PCB-126. However, none of the samples exceeded the US FDA (1.5μg/g milk fat) recommendation limits for PCBs in milk fat. Prolonged exposure to such persistent organic pollutants interlinked with the burning of mixed waste in the open dumps can be a public health concern.

Integrating PET chemical recycling with pyrolysis of mixed plastic waste via pressureless alkaline depolymerization in a hydrocarbon solvent

This study presents a proof of concept for a technology train that integrates polyethylene terephthalate (PET) recovery from mixed plastic waste and plastic pyrolysis. PET is depolymerized into terephthalic acid (TPA) by hydrolysis using a low volatility oil as medium, which enables (i) low-pressure operation, and (ii) a selective separation and recovery of TPA from the product mix by a simple process of filtration, washing, and precipitation. Full PET conversion and high TPA recovery (>98 %) were achieved at 260 °C.This technology train is demonstrated to be effective for processing mixed waste streams, leading to higher yield and quality of liquid product from thermal pyrolysis when compared with feedstock that has not been pre-treated. Further, the technology could be readily integrated with a plastics pyrolysis process, whereby a by-product from the pyrolysis could be used as the low-volatility oil.