Tackling Waste Polystyrene with Sunlight

InfoMetricsFiguresRef. ACS Central ScienceASAPArticle This publication is Open Access under the license indicated. Learn More CiteCitationCitation and abstractCitation and referencesMore citation options ShareShare onFacebookX (Twitter)WeChatLinkedInRedditEmailJump toExpandCollapse First ReactionsJanuary 2, 2025Tackling Waste Polystyrene with SunlightClick to copy article linkArticle link copied!Light-to-heat conversion by carbon black enables local heating and depolymerization of polystyrene to its monomer.Hyun Suk WangHyun Suk WangLaboratory of Polymeric Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5 8093, Zurich, SwitzerlandMore by Hyun Suk Wanghttps://orcid.org/0000-0002-2515-3906Athina Anastasaki*Athina AnastasakiLaboratory of Polymeric Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5 8093, Zurich, Switzerland*Email: [email protected]More by Athina Anastasakihttps://orcid.org/0000-0002-6615-1026Open PDFACS Central ScienceCite this: ACS Cent. Sci. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://pubs.acs.org/doi/10.1021/acscentsci.4c02187https://doi.org/10.1021/acscentsci.4c02187Published January 2, 2025 Publication History Published online 2 January 2025newsPublished 2025 by American Chemical Society. This publication is licensed under CC-BY 4.0 . License Summary*You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:Creative Commons (CC): This is a Creative Commons license.Attribution (BY): Credit must be given to the creator.View full license*DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. This publication is licensed underCC-BY 4.0 . License Summary*You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator.View full license *DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. License Summary*You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator. View full license *DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. License Summary*You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below: Creative Commons (CC): This is a Creative Commons license. Attribution (BY): Credit must be given to the creator. View full license *DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. ACS PublicationsPublished 2025 by American Chemical SocietySubjectswhat are subjectsArticle subjects are automatically applied from the ACS Subject Taxonomy and describe the scientific concepts and themes of the article.DepolymerizationPlasticsRecyclingStyrenesWastesYou would not want to touch the surface of a black car on a sunny summer day─it is scorching! This is because of a phenomenon called "photothermal conversion," or a light-to-heat conversion of black pigments on the car surface. In this issue of ACS Central Science, Stache and co-workers exploit this very phenomenon to chemically recycle polystyrene (PS) to its monomer, styrene, using an inexpensive and ubiquitous material─carbon black. (1)PS, widely recognized for its use in packaging and disposable products, presents a significant environmental challenge due to its low recycling rates and accumulation in landfills. Although mechanical recycling methods exist, they are limited by the inevitable degradation of material properties with each cycle. Chemical recycling via depolymerization, (2,3) which reverts PS back into styrene monomers, offers the potential for infinite recycling but is typically constrained by high energy demands, requiring temperatures typically in excess of 400 °C. (4) Furthermore, bulk heating of PS leads to an uncontrolled flux of reactive intermediates, leading to undesirable byproducts. Photochemical methods for PS conversion have also been limited, as they often produce non-monomeric products (e.g., benzoic acid) due to the thermodynamic challenges of styrene depropagation. (5)The authors present a remarkably simple approach that addresses these limitations by leveraging carbon black as a photothermal conversion agent. Their method achieves efficient depolymerization of PS under visible light irradiation, creating localized thermal hotspots while maintaining subpyrolytic bulk temperatures (Figure 1). Carbon black (CB) is a cost-effective pigment widely used in commercial products, such as coffee cup lids. However, its near-zero recycling rate makes it an environmental burden. Stache and colleagues have repurposed this ubiquitous material, utilizing its high photothermal conversion efficiency (i.e., low fluorescence quantum yield) that drives the depolymerization of PS. As a proof of concept, the authors synthesized PS particles embedded with varying amounts of CB via emulsion polymerization to maximize physical contact between the polymer and the photothermal agent. Upon irradiating these PS-CB composites with white LEDs, a maximum styrene yield of 57% was achieved after 30 min. Remarkably, the bulk temperature during the reaction remained below 150 °C, as measured with a thermocouple, despite the purely thermal nature of the process. This efficiency of depolymerization at low bulk temperatures is noteworthy, particularly when compared to conventional pyrolysis methods. Other products of the reaction, including trimers, dimers, toluene, and α-methylstyrene, accounted for approximately 30% of the total small-molecule products. Furthermore, CB could be reused for multiple depolymerization cycles, highlighting the robustness of the methodology.Figure 1Figure 1. Depolymerization of polystyrene (co)polymers using carbon black as photothermal conversion agents, as developed by Stache and co-workers. (1) Copyright 2024. The Authors. Published by American Chemical Society.High Resolution ImageDownload MS PowerPoint SlideThe authors present a remarkably simple approach that addresses these limitations by leveraging carbon black as a photothermal conversion agent.The versatility of the CB-based depolymerization process was demonstrated through its application to various styrene-based copolymers containing comonomers with notoriously high ceiling temperatures (i.e., with low propensity for depropagation). Copolymers incorporating methyl acrylate, acrylonitrile, and isoprene were successfully depolymerized to regenerate both styrene and the comonomers, with only a minor reduction in overall conversion efficiency.The methodology was further validated with postconsumer plastics. Black PS products, such as foam trays, food containers, and coffee cup lids─materials that already contain carbon black─were effectively depolymerized (Figure 2). Even white and clear PS plastics could be depolymerized after the addition of CB. Importantly, the reaction was robust against common food contaminants, such as soy sauce and sugar, maintaining high yields despite their presence. Additionally, mixed plastic waste streams containing as little as 10% by weight black PS foam achieved comparable yields. This suggested that black plastic contamination in waste streams could even be beneficial in enhancing recycling. In a demonstration of the process's sustainability, the authors used sunlight instead of LEDs as the energy source. By focusing natural sunlight onto black PS foam using a Fresnel lens, they achieved an impressive styrene yield of 80%. Although the contribution of direct thermal effects from the concentrated sunlight is unclear, direct photolysis of the PS backbone by high-energy rays (λ < 300 nm) can be ruled out as the lens was made of plastic.Figure 2Figure 2. Depolymerization of commercial polystyrene products using either already-present black pigments or additional carbon black.High Resolution ImageDownload MS PowerPoint SlideThis suggested that black plastic contamination in waste streams could even be beneficial in enhancing recycling.The work by the Stache team represents a significant advancement in chemical recycling, and the next step could potentially involve scaling the technology for industrial applications. Light penetration through carbon-black-filled plastics is inherently limited, necessitating the development of specialized reactor designs or extended reaction times to ensure consistent processing. Nevertheless, the simplicity and effectiveness of this method, coupled with its compatibility with current waste streams, position it as a promising candidate for future recycling technologies. By addressing technical challenges, this approach could pave the way for scalable, energy-efficient chemical recycling solutions.The simplicity and effectiveness of this method, coupled with its compatibility with current waste streams, position it as a promising candidate for future recycling technologies.Author InformationClick to copy section linkSection link copied!Corresponding AuthorAthina Anastasaki - Laboratory of Polymeric Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5 8093, Zurich, Switzerland; https://orcid.org/0000-0002-6615-1026; Email: [email protected]AuthorHyun Suk Wang - Laboratory of Polymeric Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5 8093, Zurich, Switzerland; https://orcid.org/0000-0002-2515-3906ReferencesClick to copy section linkSection link copied! This article references 5 other publications. 1Oh, S.; Jiang, H.; Kugelmass, L. H.; Stache, E. E. Recycling of Post-Consumer Waste Polystyrene Using Commercial Plastic Additives. ACS Cent. Sci. 2024, DOI: 10.1021/acscentsci.4c01317 Google ScholarThere is no corresponding record for this reference.2Coates, G. W.; Getzler, Y. D. J. N. R. M. Chemical recycling to monomer for an ideal, circular polymer economy. Nat. Rev. Mater. 2020, 5 (7), 501– 516, DOI: 10.1038/s41578-020-0190-4 Google Scholar2Chemical recycling to monomer for an ideal, circular polymer economyCoates, Geoffrey W.; Getzler, Yutan D. Y. L.Nature Reviews Materials (2020), 5 (7), 501-516CODEN: NRMADL; ISSN:2058-8437. (Nature Research) Abstr.: The majority of post-consumer plastic waste is not recycled. Impediments to the recycling of commodity polymers include sepn., impurities and degrdn. of the macromol. structures, all of which can neg. affect the properties of recycled materials. An attractive alternative is to transform polymers back into monomers and purify them for repolymn. - a form of chem. recycling we term chem. recycling to monomer (CRM). Material recycled in this way exhibits no loss in properties, creating an ideal, circular polymer economy. This Review presents our vision for realizing a circular polymer economy based on CRM. We examine the energetics of polymn. and other challenges in developing practical and scalable CRM processes. We briefly review attempts to achieve CRM with commodity polymers, including through polyolefin thermolysis and nylon 6 ring-closing depolymn., and closely examine the recent flourishing of CRM with new-to-the-world polymers. The benefits of heterocycle ring-opening polymn. are discussed in terms of synthetic control and kinetically accessible polymer-backbone functionality. Common chem. and structural characteristics of CRM-compatible ring-opening-polymn. monomers are identified, and the properties, benefits and liabilities of these recyclable polymers are discussed. We conclude with our perspective on the ideals and opportunities for the field. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntVOmt7Y%253D&md5=ce62cb9ab02615ebcde8b8dd674aa2523Lohmann, V.; Jones, G. R.; Truong, N. P.; Anastasaki, A. The thermodynamics and kinetics of depolymerization: what makes vinyl monomer regeneration feasible?. Chem. Sci. 2024, 15 (3), 832– 853, DOI: 10.1039/D3SC05143A Google ScholarThere is no corresponding record for this reference.4Lu, C.; Xiao, H.; Chen, X. Simple pyrolysis of polystyrene into valuable chemicals. e-Polym. 2021, 21 (1), 428– 432, DOI: 10.1515/epoly-2021-0037 Google ScholarThere is no corresponding record for this reference.5Parkatzidis, K.; Wang, H. S.; Anastasaki, A. Photocatalytic Upcycling and Depolymerization of Vinyl Polymers. Angew. Chem., Int. Ed. 2024, 63 (19), e202402436 DOI: 10.1002/anie.202402436 Google ScholarThere is no corresponding record for this reference.Cited By Click to copy section linkSection link copied!This article has not yet been cited by other publications.Download PDFFiguresReferences Get e-AlertsGet e-AlertsACS Central ScienceCite this: ACS Cent. Sci. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://doi.org/10.1021/acscentsci.4c02187Published January 2, 2025 Publication History Published online 2 January 2025Published 2025 by American Chemical Society. This publication is licensed under CC-BY 4.0 . License Summary*You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:Creative Commons (CC): This is a Creative Commons license.Attribution (BY): Credit must be given to the creator.View full license*DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. Article Views-Altmetric-Citations-Learn about these metrics closeArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.Recommended Articles FiguresReferencesAbstractHigh Resolution ImageDownload MS PowerPoint SlideFigure 1Figure 1. Depolymerization of polystyrene (co)polymers using carbon black as photothermal conversion agents, as developed by Stache and co-workers. (1) Copyright 2024. The Authors. Published by American Chemical Society.High Resolution ImageDownload MS PowerPoint SlideFigure 2Figure 2. Depolymerization of commercial polystyrene products using either already-present black pigments or additional carbon black.High Resolution ImageDownload MS PowerPoint SlideReferences This article references 5 other publications. 1Oh, S.; Jiang, H.; Kugelmass, L. H.; Stache, E. E. Recycling of Post-Consumer Waste Polystyrene Using Commercial Plastic Additives. ACS Cent. Sci. 2024, DOI: 10.1021/acscentsci.4c01317 There is no corresponding record for this reference.2Coates, G. W.; Getzler, Y. D. J. N. R. M. Chemical recycling to monomer for an ideal, circular polymer economy. Nat. Rev. Mater. 2020, 5 (7), 501– 516, DOI: 10.1038/s41578-020-0190-4 2Chemical recycling to monomer for an ideal, circular polymer economyCoates, Geoffrey W.; Getzler, Yutan D. Y. L.Nature Reviews Materials (2020), 5 (7), 501-516CODEN: NRMADL; ISSN:2058-8437. (Nature Research) Abstr.: The majority of post-consumer plastic waste is not recycled. Impediments to the recycling of commodity polymers include sepn., impurities and degrdn. of the macromol. structures, all of which can neg. affect the properties of recycled materials. An attractive alternative is to transform polymers back into monomers and purify them for repolymn. - a form of chem. recycling we term chem. recycling to monomer (CRM). Material recycled in this way exhibits no loss in properties, creating an ideal, circular polymer economy. This Review presents our vision for realizing a circular polymer economy based on CRM. We examine the energetics of polymn. and other challenges in developing practical and scalable CRM processes. We briefly review attempts to achieve CRM with commodity polymers, including through polyolefin thermolysis and nylon 6 ring-closing depolymn., and closely examine the recent flourishing of CRM with new-to-the-world polymers. The benefits of heterocycle ring-opening polymn. are discussed in terms of synthetic control and kinetically accessible polymer-backbone functionality. Common chem. and structural characteristics of CRM-compatible ring-opening-polymn. monomers are identified, and the properties, benefits and liabilities of these recyclable polymers are discussed. We conclude with our perspective on the ideals and opportunities for the field. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntVOmt7Y%253D&md5=ce62cb9ab02615ebcde8b8dd674aa2523Lohmann, V.; Jones, G. R.; Truong, N. P.; Anastasaki, A. The thermodynamics and kinetics of depolymerization: what makes vinyl monomer regeneration feasible?. Chem. Sci. 2024, 15 (3), 832– 853, DOI: 10.1039/D3SC05143A There is no corresponding record for this reference.4Lu, C.; Xiao, H.; Chen, X. Simple pyrolysis of polystyrene into valuable chemicals. e-Polym. 2021, 21 (1), 428– 432, DOI: 10.1515/epoly-2021-0037 There is no corresponding record for this reference.5Parkatzidis, K.; Wang, H. S.; Anastasaki, A. Photocatalytic Upcycling and Depolymerization of Vinyl Polymers. Angew. Chem., Int. Ed. 2024, 63 (19), e202402436 DOI: 10.1002/anie.202402436 There is no corresponding record for this reference.