Recycling Technology Research Articles

Multi-category sorting of plastic waste using Swin Transformer: A vision-based approach

Sorting out plastic waste (PW) from municipal solid waste (MSW) by material type is crucial for reutilization and pollution reduction. However, current automatic separation methods are costly and inefficient, necessitating an advanced sorting process to ensure high feedstock purity. This study introduces a Swin Transformer-based model for effectively detecting PW in real-world MSW streams, leveraging both morphological and material properties. And, a dataset comprising 3560 optical images and infrared spectra data was created to support this task. This vision-based system can localize and classify PW into five categories: polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS). Performance evaluations reveal an accuracy rate of 99.75% and a mean Average Precision (mAP50) exceeding 91%. Compared to popular convolutional neural network (CNN)-based models, this well-trained Swin Transformer-based model offers enhanced convenience and performance in five-category PW detection task, maintaining a mAP50 over 80% in the real-life deployment. The model's effectiveness is further supported by visualization of detection results on MSW streams and principal component analysis of classification scores. These results demonstrate the system's significant effectiveness in both lab-scale and real-life conditions, aligning with global regulations and strategies that promote innovative technologies for plastic recycling, thereby contributing to the development of a sustainable circular economy.

Managing waste packaging for a sustainable future: a strategic and efficiency analysis in the European context

AbstractThe management of package waste has become a critical concern in pursuing sustainable development, particularly within the European context, where environmental regulations and sustainability goals are stringent. This paper presents a comprehensive strategic and efficiency analysis of waste packaging management across Europe, examining current practices, policies, and technological innovations in a sample of countries. The work identifies critical challenges and opportunities in the sector using Data Envelopment Analysis and Multicriteria decision analysis. Our findings reveal significant variations in the efficiency and effectiveness of waste packaging management practices among European countries, influenced by differing policy frameworks, recycling infrastructures, and public awareness levels. Sweden and Luxembourg excel in the sustainable and technical model for recycling, while Austria prevails for recovery in both. The strategic vision suggests an emphasis on green premium, and the most sustainable alternatives are those marked by natural fibres and respect for human conditions. The paper concludes with strategic recommendations for policymakers, industry stakeholders, and communities to enhance waste packaging management efficiency. These include policy harmonisation at the EU level, investment in innovative recycling technologies, and fostering public–private partnerships to drive systemic change. By adopting these strategies, Europe can move closer to achieving its sustainability targets, reducing environmental impact, and promoting a circular economy. So, the implications of this paper are both strategic and political. The former is related to identifying the best strategy related to packaging waste, and the latter is to uniform the efficiency of waste packaging management in Europe.

Effects of Waste Generation on the Load Capacity Factor: A Novel Waste Management Assessment for OECD Countries

ABSTRACTThe increase in global waste generation is an important issue directly addressed in the Sustainable Development Goal (SDG)‐12 and OECD countries produce large amounts of waste. In this context, the study examines the influence of waste generated and recycled on the load capacity factor (biocapacity/ecological footprint) in 28 OECD countries from 2000 to 2021 using novel panel data approaches. The study employs augmented mean group and novel half‐panel jackknife estimation approaches within the Load Capacity Curve (LCC) hypothesis and confirms the LCC for OECD nations. In addition, the long‐term prediction results illustrate that waste generation increases environmental destruction, while waste recycled supports the increase in the load capacity factor. The study recommends policymakers in OECD countries to support economic growth and increase investment in waste recycling technologies to achieve SDG‐12.

Impact of Ball Milling on the Microstructure of Polyethylene Terephthalate.

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

A simulation-based techno-economic-safety-social-environmental decision-making framework for prioritizing plastic waste treatment processes

Chemical recycling technologies hold promising potential in converting mixed plastic waste into energy and chemicals. This study proposed a simulation-based quantitative life cycle sustainability assessment framework for the potential plastic waste valorization processes. Sustainability metrics including environment, economy, safety, society, and energy were quantified and comprehensively investigated. Based on the Bayesian best-worst weighting and vector-based ranking methods, the normalized and weighted life cycle sustainability scores were used to prioritize the best process. Gasification-based technology was found superior than incineration-based technology, especially in the economic, techno-energetic, and social aspects. However, incinerated-based process with direct CO2 emissions performed better in the environmental aspects compared with the process integrating with carbon capture and utilization unit. Additional environmental burdens were brought to the system when incorporating the carbon capture and methanol synthesis process. Increased system complexity might bring unexpected environmental burdens, and sometimes even outweighed the benefits. Various weights were assigned to the multi-criteria decision-making model, and the gasification-based process consistently ranked first across all scenarios.

A Room‐Temperature Lithium‐Restocking Strategy for the Direct Reuse of Degraded LiFePO4 Electrodes

The sustainable development of lithium iron phosphate (LFP) batteries calls for efficient recycling technologies for spent LFP (SLFP). Even for the advanced direct material regeneration (DMR) method, multiple steps including separation, regeneration, and electrode refabrication processes are still needed. To circumvent these intricacies, new regeneration methods that allow direct electrode reuse (DER) by rejuvenating SLFP electrodes without damaging its structure are desired. Here, a 0.1 M lithium triethyl borohydride/tetrahydrofuran solution, which has the proper reductive capability to reduce Fe3+ in SLFP to Fe2+ without alloying with the aluminum current collector, is selected as the lithiation/regeneration reagent to restock the Li loss and regenerate SLFP electrodes. By soaking the SLFP electrodes in the lithiation solution, we successfully rejuvenated the crystal structure and electrochemical activity of SLFP electrodes with structural integrity within only 6 minutes at room temperature. When being directly reused, the regenerated LFP electrodes deliver a high specific capacity of 162.6 mAh g‐1 even after being exposed to air for 3 months. The DER strategy presents significant economic and environmental benefits compared with the DMR method. This research provides a timely and innovative solution for recycling spent blade batteries using large‐sized LFP electrodes, boosting the closed‐loop development of LFP batteries.

A Room-Temperature Lithium-Restocking Strategy for the Direct Reuse of Degraded LiFePO4 Electrodes.

The sustainable development of lithium iron phosphate (LFP) batteries calls for efficient recycling technologies for spent LFP (SLFP). Even for the advanced direct material regeneration (DMR) method, multiple steps including separation, regeneration, and electrode refabrication processes are still needed. To circumvent these intricacies, new regeneration methods that allow direct electrode reuse (DER) by rejuvenating SLFP electrodes without damaging its structure are desired. Here, a 0.1 M lithium triethyl borohydride/tetrahydrofuran solution, which has the proper reductive capability to reduce Fe3+ in SLFP to Fe2+ without alloying with the aluminum current collector, is selected as the lithiation/regeneration reagent to restock the Li loss and regenerate SLFP electrodes. By soaking the SLFP electrodes in the lithiation solution, we successfully rejuvenated the crystal structure and electrochemical activity of SLFP electrodes with structural integrity within only 6 minutes at room temperature. When being directly reused, the regenerated LFP electrodes deliver a high specific capacity of 162.6 mAh g-1 even after being exposed to air for 3 months. The DER strategy presents significant economic and environmental benefits compared with the DMR method. This research provides a timely and innovative solution for recycling spent blade batteries using large-sized LFP electrodes, boosting the closed-loop development of LFP batteries.

Preface: 13th Ranshofener Leichtmetalltage

Abstract What strategies are available to minimize resource consumption in the light metal industry through recycling and energy efficiency? How can lightweight design make mobility more sustainable? And what role will artificial intelligence play in future processes in the metal processing industry? These and other questions are addressed at the 13th Ranshofener Leichtmetalltage 2024, which take place on the 26th–27th of September 2024 at the Hotel Gut Brandlhof in Saalfelden, Austria, and are organized in accordance with the criteria of the Austrian Ecolabel for Green Events. Under the guiding theme of “Light Metals Innovations for Environmental and Economic Sustainability”, this year’s conference offers an exciting program in three sessions “Digitalization in the Context of Circularity”, “Sustainable Process Development” and “Innovative Light Metals and their Characterization”. The focus is on decarbonization and digitalization in process and material development as well as the material characterization of light metals. A balanced spectrum of international presentations from universities, RTOs and industry provides participants with an up-to-date overview of the latest scientific findings and successful light metal applications. The 13th Ranshofener Leichtmetalltage 2024 are thus clearly focused on decarbonization and digitalization – even in times of diverse challenges. The first session, “Digitalization in the Context of Circularity”, highlights best-practice examples from the aluminium industry, the balance between sustainability and performance in metal processing and the implementation of complex geometries using wire-based additive manufacturing. The second session, “Sustainable Process Development”, is dedicated to the decarbonization and reduced material consumption of industrial processes, for example through GigaCasting, or the use of innovative recycling technologies. The third session, “Innovative Light Metals and their Characterization”, addresses forward-looking topics such as the development of special aluminium alloys for additive manufacturing, the use of old car scrap for innovative alloys and the decarbonization of the magnesium industry. The conference proceedings contain scientific contributions to the conference. We would like to thank all the authors for their high-quality work and the participants of the 13th Ranshofener Leichtmetalltage 2024 for their interest. We wish you stimulating reading and creative impulses! List of Scientific committee, Organizing committee are available in this Pdf.

Progress in direct recycling of spent lithium nickel manganese cobalt oxide (NMC) cathodes

With the widespread use of lithium-ion batteries (LIBs) in portable electronics and electric vehicles (EVs), the end-of-life (EOL) LIBs are projected to reach 1336 GWh by 2040 under the sustainable development scenario. Proper recycling is urgently needed to minimize the release of hazardous waste and reduce mining activities by reintroducing critical minerals into the supply chain. Lithium nickel manganese cobalt oxide (LiNixMnyCozO2, NMCs) cathodes have become dominant in the LIB market, especially with the increasing production of EVs, which are also the most valuable components in EOL LIBs. Unlike pyrometallurgical and/or hydrometallurgical methods, which convert spent NMCs into metals or metal compounds, direct recycling technologies aim to maximize the value of spent cathodes by restoring their degraded structure and composition. This review summarizes direct recycling methods for NMC cathodes published in the last decade and provides insights into the challenges and future development of direct recycling techniques.

Corrosion-mediated production of uranium(III) chloride from metallic uranium in molten LiCl–KCl salt contained within a stainless-steel crucible

Uranium (III) chloride (UCl3) is a crucial component of a potent nuclear recycling technology—pyroprocessing—and next-generation molten salt reactors. It is usually synthesized by reacting metallic uranium with chlorinating agents (e.g., CdCl2 and PbCl2) in molten chloride salts. In this study, we report the unexpected formation of UCl3 from metallic simulated fuel (simfuel) immersed in impure molten LiCl–KCl salt (in the presence of a small amount of residual H2O) in a stainless-steel (SS) crucible, without a chlorinating agent. We investigated various factors influencing UCl3 formation, including fuel type (metallic simfuel, pure U, oxide simfuel, or no fuel), crucible material (SS or alumina), salt composition (LiCl–KCl or LiCl), temperature (773 K or 923 K), and contact between fuel and SS crucible. UCl3 only formed when metallic fuels (simfuel or pure U) were immersed in molten salt in the SS crucible, with higher concentrations at elevated temperatures. Oxide fuels did not produce UCl3, nor did contact with the crucible affect formation. Our findings suggest that impurities, particularly moisture in the salt, corroded the SS crucible, releasing iron and chromium chlorides that reacted with metallic U to form UCl3. UCl3 formation was more pronounced in LiCl–KCl than in LiCl, and thermodynamic calculations helped establish the mechanism.

Analysis of NCM concentration and extraction efficiency in the lithium-ion battery extraction process

In recent years, with the increasing popularity of portable electronic devices (PEDs) and electric vehicles (EVs), the demand for lithium-ion batteries (LIBs) has continued to expand; however, the supply of raw materials such as nickel cobalt, and manganese (NCM) is limited, and it is essential to develop efficient recycling technologies. Hydrometallurgical methods, particularly extraction processes, can be used to obtain high-grade recycled LIB products with proper control of the process window. This study focused on the separation of NCM from copper (Cu) and aluminum (Al) by diluting the metal concentrations ([Me]) and adjusting the pH (using NH4OH) during extraction. For metal composition analysis, in addition to using inductively coupled plasma mass spectrometry (ICP-MS), ultraviolet–visible (UV–Vis) spectroscopy and colorimetric analysis were also employed to monitor ion concentrations. The change in solution color is directly related to the nickel (Ni) and cobalt (Co) ion concentrations. Moreover, a continuous shift in the Ni ion absorption spectra at different pH values did not occur for the Co ion absorption spectra. According to the extraction efficiency (EE%) results, the lower [Me] resulted in the higher EE% of NCM. The optimal process window was established within the range of 0.025–0.1 M and pH = 6.5–7.4.

Recycling Technologies for Biopolymers: Current Challenges and Future Directions.

Plastic pollution is a major driver of climate change that is associated with biodiversity loss, greenhouse gas emissions, and negative soil, plant, animal, and human health. One of the solutions that has been proposed and is currently reducing the adverse effects of plastic on the planet is the replacement of synthetic plastics with biopolymers. The biodegradable polymers have been adapted for most of the applications of synthetic plastic. However, their use and disposal present some sustainability challenges. Recycling emerges as an effective way of promoting the sustainability of biopolymer use. In this article, we review recycling as a viable solution to improve the sustainability of biopolymers, emphasizing the current types and technologies employed in biopolymer recycling and the challenges faced in their adoption. Our exploration of the future directions in the conversion of biopolymers into new polymers for reuse establishes a connection between established continuous technological innovation, integration into circular economy models, and the establishment and strengthening of collaborations among key stakeholders in relevant industries as necessary steps for the adoption, full utilization, and improvement of recycling technologies for biopolymers. By connecting these factors, this study lays a foundation for the establishment of a roadmap for improved biopolymer recycling technologies and processes that promote the sustainability of synthetic plastic alternatives.

A sustainable recycling process and its life cycle assessment for valorising post-consumer textile materials for thermal insulation applications.

The textile industry along with construction, electronics and plastic generate huge amounts of waste posing challenges to the adoption of the circular economy. This research presents a sustainable and low-cost recycling technology for conversion of post-consumer textile (denim) wastes to useful insulation materials. To accomplish the objective, nonwoven materials were produced using varying proportions of post-consumer recycled denim (r-denim) fibre and hollow polyester (PET) fibre using different punch densities in the needle punching process. Kowalski, Cornell and Vining mixture design, a special type of design of experiments, was adopted to develop the samples. Developed nonwoven materials were characterised for thermal resistance and tensile properties. The results show that nonwoven materials containing the minimum proportion (20%) of r-denim fibres exhibited the highest thermal resistance (0.131 W-1m2K). However, by adjusting the process parameter of the nonwovens, that is, the punch density, the same thermal resistance (0.131 W-1m2K) is also achieved even with 39% r-denim fibres. Additionally, the nonwovens produced from this blend proportion (r-denim:PET = 39:61) demonstrate a reasonable strength of 2.43 cN/tex. Environmental benefits of the developed r-denim/PET nonwovens have been evaluated by the life cycle assessment approach. Results show that the use of ~40% r-denim fibre has reduced the environmental burden significantly. Therefore, the nonwoven materials produced from post-consumer textile wastes hold tremendous potential as an alternative to synthetic fibres in thermal insulation applications. This recycling approach has immense potential to contribute to the efficient utilisation of post-consumer textile waste materials paving the way for environmental sustainability.

Bibliometric Analysis of the Effectiveness of Waste Management and Recycling Programs in the Textile Industry

This bibliometric study provides a comprehensive analysis of the evolution and current trends in waste management and recycling within the textile industry, spanning from 1970 to 2024. Utilizing VOSviewer for keyword co-occurrence analysis, the research highlights a significant shift from basic waste management to advanced, sustainable practices integrated into textile production. The study reveals an increased focus on technologies such as wastewater treatment and recycling innovations, reflecting the industry's response to global sustainability demands. The findings illustrate the interdisciplinary nature of textile waste management research and underscore the importance of technological advancements in promoting environmental sustainability. However, the study also identifies ongoing challenges, including regional disparities in waste management effectiveness and the need for global standards. The study emphasizes the necessity for future research to address these challenges, proposing a continued focus on innovative, adaptable recycling technologies and comprehensive waste management strategies that can be implemented globally.

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.

Reviving Spent NCM Cathodes via Spontaneous Galvanic Corrosion in Ambient Atmospheric Condition

AbstractThe recycling of end‐of‐life Li‐ion batteries (EoL LIBs) is critical for maintaining the sustainable LIB industry. In this study, the compositional restoration method for degraded LiΔNi0.6Co0.2Mn0.2O2 cathode via spontaneous galvanic corrosion, which can be conducted at room temperature, is demonstrated. Achieving the lithiation of spent LiΔNi0.6Co0.2Mn0.2O2 to its pristine state at room temperature requires a strong reducing agent with a redox potential lower than 1.6 V (vs Li/Li+), which is very reactive and expensive. In the designed restoration system, spontaneous restoration can be achieved by using an Aluminum (Al) current collector as a reducing agent which has sufficient reducing power (Al/Al3+, 1.37 V (vs Li/Li+)). Moreover, through a galvanic reaction design that utilizes Li‐ion in the electrolyte of spent LIBs, the additional Li source required to replenish the Li‐deficient NCM is minimized. The galvanic corrosion‐based restoration mechanism is systematically analyzed, and a spent Li0.76Ni0.6Co0.2Mn0.2O2 is successfully restored to its pristine state (Li1.05Ni0.6Co0.2Mn0.2O2). Furthermore, restoration strategies accomplishable in not only the cathode state but also the battery state are presented to ensure applicability in practical recycling processes. The proposed strategy suggests a new insight into the direct cathode recycling technology, possessing economic feasibility, and environmental friendliness.

Comparative environmental and economic assessment of emerging hydrometallurgical recycling technologies for Li-ion battery cathodes

The growing demand for electric vehicles has led to a growing concern for battery recycling, particularly for critical raw materials. However, there is insufficient investigation into the environmental and economic impacts of hydrometallurgical recycling methods. In this study we explored emerging hydrometallurgical technologies in economic and environmental perspective to establish conceptual routes to recover Co, Ni and Mn oxides from waste LiNi0.33Mn0.33Co0.33O2 cathode materials from spent Li-ion batteries. After, life cycle assessment and costing techniques were utilized to compare the environmental and economical performances of each conceptual route. Recovery efficiency of metal oxides through each route was also considered as a key factor. Results suggested that deep eutectic solvent-based leaching produces the highest impact under many impact categories while electrolysis-based leaching showed the least. Under purification technologies assessed, ion-exchange based purification showed significantly lower impact under many categories except stratospheric ozone depletion. Solvent based purification has been identified as the worst technology for purification. Hydroxide based calcination has been identified as the most environmentally sustainable calcination method compared to oxalate calcination. The route consists with inorganic leaching, ion-exchange based purification and hydroxide calcination showed the lowest environmental impact (emission effect at 33.8 kg CO2 eq), with lower economic impact ($ 119) and the highest recovery efficiency (78 %) per 1 kg of cathode active materials. However, using electrolysis-based leaching can slightly increase the impacts with lower recovery efficiency (75 %) and better economic performance ($104/kg of cathode active materials). Terrestrial ecotoxicity was identified to be the most affected impact category for the recovery processes. It is recommended that technologies like deep eutectic solvent-based leaching, solvent extraction and environmentally sustainable technologies like supercritical fluid extraction need further studies prior to industrial applications.

Plastic-Degrading Enzymes from Marine Microorganisms and Their Potential Value in Recycling Technologies.

Since the 2005 discovery of the first enzyme capable of depolymerizing polyethylene terephthalate (PET), an aromatic polyester once thought to be enzymatically inert, extensive research has been undertaken to identify and engineer new biocatalysts for plastic degradation. This effort was directed toward developing efficient enzymatic recycling technologies that could overcome the limitations of mechanical and chemical methods. These enzymes are versatile molecules obtained from microorganisms living in various environments, including soil, compost, surface seawater, and extreme habitats such as hot springs, hydrothermal vents, deep-sea regions, and Antarctic seawater. Among various plastics, PET and polylactic acid (PLA) have been the primary focus of enzymatic depolymerization research, greatly enhancing our knowledge of enzymes that degrade these specific polymers. They often display unique catalytic properties that reflect their particular ecological niches. This review explores recent advancements in marine-derived enzymes that can depolymerize synthetic plastic polymers, emphasizing their structural and functional features that influence the efficiency of these catalysts in biorecycling processes. Current status and future perspectives of enzymatic plastic depolymerization are also discussed, with a focus on the underexplored marine enzymatic resources.

Surface Catalytic Repair for the Efficient Regeneration of Spent Layered Oxide Cathodes.

Direct recycling is considered to be the next-generation recycling technology for spent lithium-ion batteries due to its potential economic benefits and environmental friendliness. For the spent layered oxide cathode materials, an irreversible phase transition to a rock-salt structure near the particle surface impedes the reintercalation of lithium ions, thereby hindering the lithium compensation process from fully restoring composition defects and repairing failed structures. We introduced a transition-metal hydroxide precursor, utilizing its surface catalytic activity produced during annealing to convert the rock-salt structure into a layered structure that provides fast migration pathways for lithium ions. The material repair and synthesis processes share the same heating program, enabling the spent cathode and added precursor to undergo a topological transformation to form the targeted layered oxide. This regenerated material exhibits a performance superior to that of commercial cathodes and maintains 88.4% of its initial capacity after 1000 cycles in a 1.3 Ah pouch cell. Techno-economic analysis highlights the environmental and economic advantages of surface catalytic repair over pyrometallurgical and hydrometallurgical methods, indicating its potential for practical application.

Enhancing flame retardancy in 3D printed polyamide composites using directionally arranged recycled carbon fiber

Combining recycled carbon fiber (rCF) and 3D printing technology has shown great potential for fabricating functional prototypes and production parts used in the aerospace and automotive industries. However, it is still a challenge to design flame-retardant 3D printed parts with high mechanical properties and flame-retardant rating. In the work, a flame-retardant polyamide (PA)-based composite for material extrusion 3D printing was prepared by utilization of rCF, polyhedral oligomeric silsesquioxanes (POSS), and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene (DOPO)-based flame retardant. The 3D-printed composites have high thermal stability, mechanical properties, and excellent flame retardancy with a V-0 rating. With the benefits of material extrusion 3D printing, directionally arranged rCF in 3D printed composites could effectively inhibit the fire spread, extend the time to ignition (TTI), reduce the total heat release (THR) and total smoke release (TSR) of 3D printed composites. The directional flame-retardant mechanism is mainly the thermal conductivity mechanism of the condensed phase and the promotion of stable ordered carbon layer formation. It provides a promising path for designing high-performance flame-retardant materials.