Circular Economy For Plastics Research Articles

The role of chemical and solvent-based recycling within a sustainable circular economy for plastics

Chemical and solvent-based recycling of plastic waste may help overcome some of the challenges faced by predominantly applied mechanical recycling techniques. This study quantifies the environmental impacts of chemical and solvent-based recycling as a function of varying process parameters and product composition using life cycle assessment. Furthermore, potential benefits and impacts on a system level are determined. To that end, a high-resolution material flow analysis is conducted for the reference system of Switzerland, covering all main plastic types and applications. In a scenario for the year 2040, we employ environmentally beneficial mechanical recycling where possible and convey suitable remaining waste streams to chemical or solvent-based recycling processes. Applying chemical or solvent-based recycling as a complement to maximum mechanical recycling, instead of thermal treatment with energy recovery, may achieve a reduction in the climate change impact of the system ranging from less than 10 % to almost 40 %. For achieving high environmental benefits, proper process choice and configuration are crucial. Dissolution or depolymerization provide higher benefits relative to other chemical recycling processes, but can only treat certain waste streams and require prior sorting into plastic types. Pyrolysis and gasification appeared to only have the ability to achieve substantial benefits over incineration if their output products can substitute high-impact chemicals and provided that efficient heat transfer and recovery is warranted when implemented on a large scale. As industrial-scale plants for chemical or solvent-based plastic recycling are still lacking, the upscaling potential and the environmental benefits achievable in practice are highly uncertain today.

Structure-Property Relationship and Multiple Processing Studies of Novel Bio-Based Thermoplastic Polyurethane Elastomers.

Currently, the growing demand for polymeric materials has led to an increased need to develop effective recycling methods. This study focuses on the multiple processing of bio-based thermoplastic polyurethane elastomers (bio-TPUs) as a sustainable approach for polymeric waste management through mechanical recycling. The main objective is to investigate the influence of two reprocessing cycles on selected properties of bio-TPUs. Two series of bio-based TPUs were synthesized via a solvent-free two-step method with the use of hexamethylene diisocyanate or hexamethylene diisocyanate/partially bio-based diisocyanate mixtures, bio-based poly(triamethylene ether) glycol, and bio-based 1,3 propanediol. Both the raw bio-TPUs and those subjected to two reprocessing cycles were examined with respect to their chemical, physical, thermal, thermomechanical, and mechanical properties. The conducted research revealed that reprocessing led to changes in the phase separation between the hard and soft segments, thereby affecting the bio-TPUs' properties. Both series of materials showed similar chemical structures regardless of reprocessing (slight changes were observed in the range of carbonyl peak). The thermal properties of TPUs exhibited slight differences after each reprocessing cycle, but generally, the non-processed and reprocessed bio-TPUs were thermally stable up to about 300 °C. However, significant differences were observed in their mechanical properties. The tensile strength increased to 34% for the twice-reprocessed bio-TPUs, while the elongation at break increased by ca. 200%. On the other hand, the processing cycles resulted in a decrease in the hardness of both bio-TPU series (ca. 3-4 °ShA). As a result, the prepared bio-TPUs exhibited characteristics that were closer to those of the sustainable materials model, promoting the circular economy of plastics, with environmental benefits arising from their recyclability and their high content of bio-based monomers (78.4-78.8 wt.%).

Valorization of PE plastic waste into lipid cells through tandem catalytic pyrolysis and biological conversion

Worldwide plastic pollution challenges the existing recycling technologies. Upcycling approaches that can convert plastic waste into value-added products are necessary for the creation of a circular plastics economy. This study demonstrated a process concept to convert Polyethylene (PE) waste into microbial lipid through tandem catalytic pyrolysis and biological conversion by oleaginous yeast Yarrowia lipolytica. PE waste was catalytically pyrolyzed into small molecular hydrocarbons, which were further digested by oleaginous microorganism to accumulate lipid. Through catalyst selection, fermentation intensification, and strain adaptive evolution, a lipid production of 122 mg/L was obtained using pyrolysis oil as sole carbon source. Through the whole process, approximate 15 % of PE was converted into lipid cells. This upcycling process was evaluated through carbon footprint analysis. Cell production, lipid content, and electricity consumption are the main factors influencing the process carbon emission. Sensitivity analysis showed that a carbon reduction can be achieved with the improvement of these parameters. This tandem process establishes a sustainable strategy for the conversion of plastic waste into value-added products.

The Use of Artificial Intelligence and Machine Learning in Creating a Roadmap Towards a Circular Economy for Plastics

The Use of Artificial Intelligence and Machine Learning in Creating a Roadmap Towards a Circular Economy for Plastics

Circular plastics technologies: depolymerization of polymers into parent monomers

Abstract While most commodity plastics were not designed to easily depolymerize, some common plastics can be broken down into their parent monomers in the presence of heat, pressure, catalysts, and/or solvent. Here, we provide a high-level overview of the depolymerization technologies that have been studied and/or scaled as promising monomer-loop recycling processes for selective plastic waste streams. Namely, commodity plastics that are considered unzippable/depolymerizable include polyethylene terephthalate, polyamides, polymethyl methacrylate, and polystyrene. Monomer-loop recycling technologies are one of several pathways toward a circular economy for plastics.

Harnessing extremophilic carboxylesterases for applications in polyester depolymerisation and plastic waste recycling.

The steady growth in industrial production of synthetic plastics and their limited recycling have resulted in severe environmental pollution and contribute to global warming and oil depletion. Currently, there is an urgent need to develop efficient plastic recycling technologies to prevent further environmental pollution and recover chemical feedstocks for polymer re-synthesis and upcycling in a circular economy. Enzymatic depolymerization of synthetic polyesters by microbial carboxylesterases provides an attractive addition to existing mechanical and chemical recycling technologies due to enzyme specificity, low energy consumption, and mild reaction conditions. Carboxylesterases constitute a diverse group of serine-dependent hydrolases catalysing the cleavage and formation of ester bonds. However, the stability and hydrolytic activity of identified natural esterases towards synthetic polyesters are usually insufficient for applications in industrial polyester recycling. This necessitates further efforts on the discovery of robust enzymes, as well as protein engineering of natural enzymes for enhanced activity and stability. In this essay, we discuss the current knowledge of microbial carboxylesterases that degrade polyesters (polyesterases) with focus on polyethylene terephthalate (PET), which is one of the five major synthetic polymers. Then, we briefly review the recent progress in the discovery and protein engineering of microbial polyesterases, as well as developing enzyme cocktails and secreted protein expression for applications in the depolymerisation of polyester blends and mixed plastics. Future research aimed at the discovery of novel polyesterases from extreme environments and protein engineering for improved performance will aid developing efficient polyester recycling technologies for the circular plastics economy.

Heterogenous electromediated depolymerization of highly crystalline polyoxymethylene

Post-consumer plastic waste in the environment has driven the scientific community to develop deconstruction methods that yield valued substances from these synthetic macromolecules. Electrocatalysis is a well-established method for achieving challenging transformations in small molecule synthesis. Here we present the first electro-chemical depolymerization of polyoxymethylene—a highly crystalline engineering thermoplastic (Delrin®)—into its repolymerizable monomer, formaldehyde/1,3,5-trioxane, under ambient conditions. We investigate this electrochemical deconstruction by employing solvent screening, cyclic voltammetry, divided cell studies, electrolysis with redox mediators, small molecule model studies, and control experiments. Our findings determine that the reaction proceeds via a heterogeneous electro-mediated acid depolymerization mechanism. The bifunctional role of the co-solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is also revealed. This study demonstrates the potential of electromediated depolymerization serving as an important role in sustainable chemistry by merging the concepts of renewable energy and circular plastic economy.

Overview of factors influencing consumer engagement with plastic recycling

AbstractMany semi‐durable and durable consumer goods are composed of plastic. Yet, plastic pollution is one of the most pressing environmental issues as it harms oceans and marine biodiversity. This state of affairs is worsened because plastic recycling rates remain low. Therefore, one commonly proposed solution is to improve plastic waste management to create a circular plastics economy. However, focusing on recycling management alone overshadows the consumption component and how consumers might contribute to recycling efforts. Although not alone in the overall recycling process, consumers are critical stakeholders in this because through their disposal behavior, they determine the responsible discarding of plastic through recycling. The significance of consumer engagement in driving circularity has been strongly emphasized in extant research and practice. Shifting from a linear plastic economy toward a circular one requires the active contribution of all stakeholders, especially the consumer. Hence, given the centrality of consumers' role, this paper provides an overview of the themes related to consumer engagement with plastic recycling. More specifically, the paper reveals three layers of influence on consumer plastic recycling behavior: (1) macroenvironmental factors, (2) situational factors, and (3) individual factors. This review provides scholars, practitioners, and decision‐makers with better insights into the themes to consider in order to spur consumer engagement in plastic recycling.This article is categorized under: Human and Social Dimensions > Behavioral Science Emerging Technologies > Materials Climate and Environment > Circular Economy

Closed-loop Recycling of Vinylogous Urethane Vitrimers.

Devising energy-efficient strategies for the depolymerization of plastics and the recovery of their structural components in high yield and purity is key to a circular plastics economy. Here, we report a case study in which we demonstrate that vinylogous urethane (VU) vitrimers synthesized from bis-polyethylene glycol acetoacetates (aPEG) and tris(2-aminoethyl)amine can be degraded by water at moderate temperature with almost quantitative recovery (~98%) of aPEG. The rate of depolymerization can be controlled by the temperature, amount of water, molecular weight of aPEG, and composition of the starting material. These last two parameters also allow one to tailor the mechanical properties of the final materials, and this was used to access soft, tough, and brittle vitrimers, respectively. The straightforward preparation and depolymerization of the aPEG-based VU vitrimers are interesting elements for the design of polymer materials with enhanced closed-loop recycling characteristics.

Closed‐Loop Recycling of Vinylogous Urethane Vitrimers

AbstractDevising energy‐efficient strategies for the depolymerization of plastics and the recovery of their structural components in high yield and purity is key to a circular plastics economy. Here, we report a case study in which we demonstrate that vinylogous urethane (VU) vitrimers synthesized from bis‐polyethylene glycol acetoacetates (aPEG) and tris(2‐aminoethyl)amine can be degraded by water at moderate temperature with almost quantitative recovery (≈98 %) of aPEG. The rate of depolymerization can be controlled by the temperature, amount of water, molecular weight of aPEG, and composition of the starting material. These last two parameters also allow one to tailor the mechanical properties of the final materials, and this was used to access soft, tough, and brittle vitrimers, respectively. The straightforward preparation and depolymerization of the aPEG‐based VU vitrimers are interesting elements for the design of polymer materials with enhanced closed‐loop recycling characteristics.

Recycling of Plastics as a Strategy to Reduce Life Cycle GHG Emission, Microplastics and Resource Depletion

Plastic waste is the most challenging type of waste because its generation rate (consumption rate) is high, and the current recycling rate is low. The increase in the production and disposal of plastics has led to significant environmental problems including greenhouse gas (GHG) emissions, microplastic pollution, and resource depletion. The study aimed at quantifying the potential environmental effects reduction achieved by recycling the most widely consumed polymers. One approach to establishing a circular economy for plastics is recycling. Plastic recycling as a strategy to reduce life cycle GHG emissions, microplastic emissions, and resource depletion was investigated. Life cycle assessment methodology was employed, considering cradle-to-gate as a system boundary. The results showed that recycling can significantly reduce life cycle GHG emissions and resource depletion. Replacing the virgin material with recycled material reduces the emission to −67 MtCO2e. Recycling could have saved 56.8 million microplastic emissions per year. However, mechanical recycling, which is commercialised nowadays, contributed to an increase in microplastics as much as 2.4 × 109 million particles per year. Recycling will also save about 50 million tonnes of resources from depletion worldwide by recycling around 20 Mt plastics. However, microplastic emissions reduction in the present scenario of mechanical recycling is not possible unless other mechanisms to capture the emitted microplastics are introduced or other recycling methods, such as chemical recycling, are employed.

Monomer Recycling as Complementary Technology in a Circular Economy

AbstractPlastic waste is one of the major challenges facing modern society. Against the background of climate change and finite fossil resources, the realization of a true circular economy for plastics is imperative. Mechanical recycling processes offer a short‐cut path for the recycling of clean, single material waste while they are not capable to handle mixed material or colored feeds. Complementary technologies are necessary to recover pure monomers, hydrocarbon mixtures or syngas from mixed secondary raw material to continuously close the loop in a circular plastics economy. Using the example of PET, this contribution discusses the benefit of integrating a back‐to‐monomer recycling for closing the loop aiming at a holistically approach integrating technological, ecological and economic aspects.

Analysis of the "circular plastics economy" phenomena and its long-term implications for demand for petroleum market.

In recent years, the issues of polymer pollution and carbon footprints have stirred up an active debate around the future of petrochemical industry, which over the past 50 years has been a significant driver of global oil demand. It is assumed that the transition to a "circular plastic economy" should resolve environmental issues for the industry, simultaneously eliminating its dependence on petroleum feedstock. In this work, the authors attempted to untangle the concept of "circular plastics" and assess its potential impact on the market of liquid hydrocarbons. Even in the Moderate scenario, the "circular plastics economy" does become an important factor in demand for hydrocarbons in petrochemical industry, reducing it by 5-10% of the business-as-usual case by 2050 and greatly slowing down demand growth rates after 2045, and the more drastic scenario even sees hydrocarbon demand peak by 2040. These findings indicate the importance of taking into account "plastics circularity" when making long-term forecasts of global oil market.

Microbial Conversion of Cheese Whey to Polyhydroxybutyrate (PHB) via Statistically Optimized Cultures

The intended circular economy for plastics envisages that they will be partially replaced by bio-based polymers in the future. In this work, the natural polyester polyhydroxybutyrate (PHB) was produced by Azohydromonas lata using cheese whey (CW) as a low-cost substrate. Initially, CW was evaluated as the sole carbon source for PHB production; it was found to be efficient and comparable to PHB production with pure sugars, such as saccharose or glucose, even when mild (with dilute acid) hydrolysis of cheese whey was performed instead of enzymatic hydrolysis. An additional series of experiments was statistically designed using the Taguchi method, and a dual optimization approach was applied to maximize the intracellular biopolymer content (%PHB, selected as a quantitative key performance indicator, KPI) and the weight average molecular weight of PHB (Mw, set as a qualitative KPI). Two different sets of conditions for the values of the selected bioprocess parameters were identified: (1) a carbon-to-nitrogen ratio (C/N) of 10 w/w, a carbon-to-phosphorous ratio (C/P) of 1.9 w/w, a dissolved oxygen concentration (DO) of 20%, and a residence time in the stationary phase (RT) of 1 h, resulting in the maximum %PHB (61.66% w/w), and (2) a C/N of 13.3 w/w, a C/P of 5 w/w, a DO of 20%, and a RT of 1 h, leading to the maximum Mw (900 kDa). A final sensitivity analysis confirmed that DO was the most significant parameter for %PHB, whereas C/N was the most important parameter for Mw.

Epoxy Thermosets Designed for Chemical Recycling.

Epoxy thermosets constitute a significant portion of high-performance plastics, as they possess excellent thermal and mechanical properties that are applicable in a wide range of industries. Nevertheless, traditional epoxy networks show strict limitations regarding chemical recycling due to their covalently crosslinked structures. Although existing methods provide partial solutions for recycling of epoxy networks, it is urgent to develop more effective, sustainable, and permanent strategies that will solve the problem at hand. For this purpose, developing smart monomers with functional groups that enable the synthesis and development of fully recyclable polymers is of great importance. This review highlights recent advancements in chemically recyclable epoxy systems and their potential to support a circular plastic economy. Moreover, we evaluate the practicality of polymer syntheses and recycling techniques, and assess the applicability of these networks in industry.

Overcoming Plastic Pollution: Challenges Faced by Brazilian Policies and Perspectives for Stakeholder Engagement and Global Governance Opportunities

This policy position paper begins with a historical overview of the invention and uses of various plastic types, particularly polyethylene, which has become the most widely used plastic commercially. It highlights the rapid growth of our dependence on plastics and the subsequent mismanagement, which has led to their omnipresent and pervasive presence as pollutants, threatening biodiversity, climate change, ocean health, economic sustainability, and human health. The paper also provides an overview of plastic draft laws proposed by lawmakers at the Brazilian Houses of Representatives, emphasizing the importance of delivering effective policies, setting targets and priorities, and aligning with global trends to address the plastic pollution crisis and transition towards a circular economy. The section on governance opportunities examines a practical recommendation specific to Brazil, and subsequently presents ambitious pathways for global standardization and implementation of Environment and Social Governance (ESG). Additionally, a policy roadmap is suggested to incorporate existing approaches, promising strategies, UN Ocean Decade targets, and address concerns identified during the negotiations among UN Member States for a binding legal agreement by 2024 (Plastic Pollution INC1). In the last section, I present practices for adapting ocean literacy and scientific knowledge for different audiences, such as lawmakers and waste pickers, to support informed decision-making processes. Additionally, I present an overview of the benefits that transitioning to a new plastic economy can bring, ranging from global to local social justice associated with the triple planetary crisis: pollution, climate change, and biodiversity loss. Science diplomacy and stakeholder involvement are strongly recommended to find solutions to the plastic pollution problem and towards transforming the circular plastics economy.

Polyolefin Recyclates for Rigid Packaging Applications: The Influence of Input Stream Composition on Recyclate Quality.

In order to shift to a circular plastics economy, high quality recyclates are required to effectively substitute virgin materials. Current approaches to empirically quantify the substitutability for recyclates are mainly limited by the abundance of virgin material grades along with a lack of adequate application-specific property profiles. In contrast, this work aims for a holistic analysis of the substitution potential of polyolefin recyclates intended for rigid packaging applications. This approach is fundamentally based on the classification of virgin polyolefins into different application-specific sub-groups with defined property windows derived from supplier data sheets, which allows for a generalization within one polymer type without neglecting the various available material grades. Moreover, the findings should provide valuable information for improvements of quality-defining process steps along the value chain of mechanical recycling. Therefore, it is of great importance to correlate the input stream composition of the investigated recyclates with the obtained qualities. The investigation of the substitution potential for selected recyclates clearly highlights the necessity of functional recycling for enhanced quality levels, which especially affects the sorting step in the recycling value chain. This work illustrates that a homogeneous waste stream directly correlates with a high substitution potential. Thus, the development of economically viable sorting strategies which take the functionality of plastic waste products into account must be targeted in future research. Furthermore, the development of detailed application-specific property windows in a joint effort with manufacturers should be pursued, as it allows for a meaningful empirical quantification of the substitutability for recyclates obtained from mechanical recycling.

Plastic Waste Utilization via Chemical Recycling: Approaches, Limitations, and the Challenges Ahead

AbstractChemical recycling offers the opportunity to foster the transition towards a circular economy for plastics as a complementary strategy for mechanical recycling. For the implementation of chemical recycling technologies, there are still significant challenges ahead that – besides the definition of binding legal frameworks – need for intensified research: knowledge‐based methods for both the identification of suitable process technologies considering decentralized waste conditions and the design of conversion steps and downstream processing are strongly needed for process development and process evaluation.

Attitudes towards Plastic Pollution: A Review and Mitigations beyond Circular Economy

Plastic pollution has received unprecedented attention globally, and there are increasing calls to control it. Despite this, the uptrends of plastic consumption and mismanaged plastic waste show little sign of reversal. This review aims to examine the attitudes of various societal groups towards plastics to identify the behavioral barriers to reduce plastic pollution and synthesize effective countermeasures. It achieved the aim through content analysis of the most recent literature related to attitudes and behaviors towards plastic pollution, consumption and management, as well as an important emerging theme on plastics recycling ecosystem and economy. It reveals the general negative attitudes of the participants in the studies reviewed towards plastic pollution and their willing attitude to act against it by supporting campaigns, paying for environmentally friendly alternatives and supporting solution-based interventions from governments including policies, regulations and guidelines. Inconvenience due to limited options for plastic items and habits are two main barriers to behavioral changes. This underscores the crucial roles of governments to tap into these attitudes to lead and intensify plastic pollution control through a multi-pronged approach that facilitates systematic substitution of conventional plastics with environmentally friendly alternatives as well as the stepping-up of the circular plastic economy and industrial symbiosis. This review deems that progressively regulated capping of conventional plastic production and consumption could help the transition, and the public could complement government endeavors through education, mutual influence and awareness-raising which could also be driven by governmental policies and programs.

Deconvoluting the roles of polyolefin branching and unsaturation on depolymerization reactions over acid catalysts

Developing a circular economy for plastics is a societal priority with a range of stakeholders engaged in developing pathways to mechanical and chemical recycling. Acid catalysis has been proposed as an attractive strategy to chemically recycle or upcycle plastic waste. In principle, the energetics that govern polyolefin decomposition reactions over Brønsted acid sites should be the same ones known for alkane cracking. However, the nature of polymers as feedstock imposes new challenges for these well-known processes, e.g., strong mass transfer limitations. To better understand the role of polymer structure and diffusion on cracking rates, the effect of tertiary carbons, chain unsaturation, and catalyst active sites distribution were studied. Our findings confirm that higher concentrations of tertiary carbons will govern decomposition reactions, regardless of diffusion limitations. Also, we unveil that LLDPE reactions mostly take place on the external surface of ZSM-5 crystals while HDPE conversion takes place within the zeolite pores.