Challenges in Recycling of Multi-Material Composites: History
View Latest Version
Please note this is an old version of this entry, which may differ significantly from the current revision.
Contributor:
Kinga Korniejenko
,
Barbara Kozub
,
Agnieszka Bąk
,
Ponnambalam Balamurugan
,
Marimuthu Uthayakumar
,
Gabriel Furtos

Transformation of waste into resources is an important part of the circular economy. The recovery of materials in the most effective way is crucial for sustainable development. Composite materials offer great opportunities for product development and high performance in use, but their position in a circular economy system remains challenging, especially in terms of material recovery.

  • circular economy
  • composite recycling
  • multilateral composite
  • used tyre
  • wind turbine blade
  • solar panel

1. Introduction

Nowadays, the circular economy (CE) is considered a key economic model for many European countries. It was introduced as an economy action plan by the European Commission in 2015 and quickly became a leading initiative [1][2]. However, the concept itself dates to 1966 [3][4]. This model helps to meet the challenge of sustainable development; achieve resource-efficiency; stimulate Europe’s boosted global competitiveness, especially through proportion eco-innovation; and generate new jobs [4][5]. One of the areas where new jobs are created is material reusing and recycling.
The concept of the circular economy is based on new approaches to manufacturing and using the goods. In the traditional, so-called linear economy, the following steps are generally implemented: development, consumption (introduction products to the market, growth, maturity, decline), and disposal of materials/products [6][7]. In the circular approach, linear thinking is transformed into loops. The important factor is reusing and recovering materials and products and consequently reducing environmental impact on the environment. For that, additional steps such as waste prevention and management must be added to traditional linear schemes [2]. The transformation of the linear model to circular approaches helps to achieve global sustainability and to minimalise the pressure on natural resources [1][6]. It also helps to create green growth, especially through complementary activities, including eco-innovation and resource efficiency [1][8].
The shift toward a circular economy, promoting the elimination of waste and the continual safe use of natural resources, is required. Material efficiency is a key element of the circular economy to address the challenges of reducing the impacts on the environment and resource deficiency [1][9]. The improvement of material circularity is a basic concept for the circular economy. Reintroduction of the flow of materials should include their economic, environmental, and social effects [1][5][10]. The important element in this case is also the redesign of materials throughout the product life cycle [6][7][11]. The products should be designed by building a closed-loop process and decreasing resource use. At the same time, the persistent use of resources through recycling and reuse instead of landfilling should be promoted [6][10][11].
Nowadays, waste generation is a serious problem [1]. Waste management has become a series of challenges around the world, including reducing the carbon footprint and reducing carbon emissions [10][12]. It is also directly related to soil, water, and air pollution [1][8]. The large amount of waste is mainly related to increased consumption, which in turn is directly related to the growth of the world’s population and the linear industrialisation system characterised by a low level of material efficiency [10][13]. The global economy is still under transformation into a circular system. To accelerate this process, technology development as well as educational activities are needed. The important element during education is to stress that the benefits of these changes are not only for the environment, but also for the economy and society [5][10]. One of the most important targets is reducing the consumption of natural resources [10][14]. It is strictly connected with the economic benefit associated with the reduction of cost of the virgin materials and also the decrease in the cost of energy. Due to material recovery, resources can be used many times, and new industries are created that also provide benefits to society. Reduced costs also arise from environmental legislation, taxes, and insurance [5]. This process also helps to build a local community [5]. It is worth stressing that this kind of benefit is usually more evident in countries subjected to rapid industrialization and poor environmental regulations [3][15].

2. Challenges in the Recycling of Multi-Material Composites

Composites are materials made from two or more constituent materials. It is usually a combination of a matrix and a filler or reinforcement [1][11]. The materials involved have different physical and/or chemical properties [11][12]. The characteristic of the composite material is different from that of the individual components [1][11]. The matrix could be a metal, a ceramic, or a polymeric material [11][16]. The composites were identified long ago, but their wide use is connected with the beginning of the XX century and industrialisation process [11]. Today, their application is becoming more and more popular because of their outstanding properties. The industries where composites are most used are aerospace, automotive, marine, and energy production [11][17]. The main reasons for their application are economic benefits, for example, lightweight composites are able to replace the traditional ones in the automotive industry and can consequently reduce fuel consumption and, at the same time, air pollution [11][18]. The research provided by Chu and Majumdar [19] shows that a 10% reduction in the structural weight of a car could lead to a 6–8% reduction in fuel consumption [19]. The other reason for creating composites is their increased durability [11][20]. The circular economy approach is usually applied to composites as long as the integrity of the product is involved [6]. In the integrity of composites, the integrity of the material has some distinct aspects, such as a long useful life of the product and a lifetime extension through maintenance and repair [6][21]. Nowadays, many composites do not have viable economic ways of recycling [22][23]. The main reasons are that recycling processes tend to break down the composite into its constituting materials, thus losing the specific composite material properties, or the recovered materials have significantly worse properties than virgin and could be used only for so-called down-cycling applications [7][11]. Due to this challenge, the composite material requires a new approach to recycling: novel concepts and technologies [11][24][25], including the design of new composites based on the old [26]. The alternative solution could be also in the design of the recyclable composites, including epoxy resin based, but this kind of material is still in the experimental phase [27]. Currently, biodegradable organic polymers still have limited participation in the market, and creating more advanced composites is a great technological challenge. Nowadays, the rapid development of composites’ recycling technologies has led some authors to designate the years 2000–2020s as a composite recycling phase [11]. The main objective of this phase is to change the situation in which most of the composite is buried or incinerated, losing the material in the most effective composites [11]. This approach is coherent with the European Union regulations in this area, including the European Agenda 2030. The circular economy in Europe is one of the key elements in this document. It outlines one of the sustainability goals as increasing waste valuation to 70% by 2020 and developing a circular economy for recycling and reuse.
Today, recycling is a high priority in the world, considering that waste management is supported by the circular economy approach [9]. This approach is based on a waste management hierarchy. This hierarchy is part of the Waste Framework Directive and defines the most effective ways of managing waste [3][5][28]. According to this document, the most effective way is waste prevention, for example, through restricted misuse through anticipation at the source while manufacturing. It is related to the philosophy of zero waste production and, in the case of a large number of products for composites, it is relatively easy to apply [3][5][29]. The next desirable form of waste management is reusing. The product reuse, remanufacturing, or refurbishment is usually more profitable for the environment, because it requires less resources and energy. Very often, it is also more economical than conventional recycling of materials, especially as low-grade raw materials [5][30]. This goal for the composites could be achieved by the long life-time of the products.
The next in the hierarchy are recycling and recovery. The border between recycling and recovery is not always clear, especially when we think about the process of incineration to decompose the waste or using energy [5][28]. Recycling and recovery are both important discussed methods for composite recycling and areas where the most important technologies are being developed. Moreover, a lot of different classifications for recycling methods are used. One of them is divided into three main areas: material recycling (usually crushing, grinding, milling, and/or shredding techniques), thermal recycling (combustion, fluoridised bed, and pyrolysis) and chemical recycling, for example solvolysis by using supercritical water or alcohol or chemical degradation in high concertation acids [11][12][29][31]. The most important advantages and disadvantages for the main recycling areas are summarised in Table 1.
Table 1. Advantages and disadvantages of the main areas of recycling.

Method

Advantages

Disadvantages

Material recycling

Lack of use of hazardous substances during the process

Possibility of processing complex composites (without the separation of particular materials)

Usually high energy efficiency

Degradation of material properties

Limited possibilities of processing

Thermal recycling

Lack of use of hazardous substances during the process

Useful for mixed materials

High cost of proper infrastructure

By-products such as environmentally dangerous off-gases

Chemical recycling

The very high holding of material properties

Hazardous materials are used during the process

Problems with scalability of most methods

Chemical recycling is the least eco-friendly method compared to mechanical and thermal recycling
There are mainly two motivations associated with recycling of multi-material composite waste: the cost of virgin materials production (usually the minimum one of the components) and the environmental problems with utilisation products. It is important to emphasise the utilisation of the value embedded in materials in as high value applications as possible in recycling [5]. The best solution is so-called up-cycling—it is usually achieved by application of recycled material in new areas, sometimes as an additive for high-value products such as vehicles or electronic products [31][32]. However, while up-cycling is the optimal way for recycling, the composites are very often down-cycled, because of the low cost types of solutions. One of the examples is the use of milled composites as admixtures for single-use materials such as concrete [23][29][33][34].
The last place on the waste management hierarchy is disposal [3][28]. This method is clearly not in line with a circular economy approach. Unfortunately, landfilling is still the main method of waste material management for multi-material products. This is mainly due to the complex and high cost of the recycling methods for composites. Another difficulty of recycling composites is the large market [29]. Application in many areas caused problems in controlling and regulation of composites recycling in all areas. Moreover, new areas for the multi-material composites are being developed, including the additive manufacturing market, from composite filaments for FFF/FDM printing to composite liquid resin for SLA/DLP/LCD printing. The statistic shows that globally only ca. 1% of composite waste is recycled [29]. At the same time, there is an opportunity for widespread use, thanks to the diversification of the sources for potential recyclers.
The basic problems related to composites are complex processing; contamination of material, including problems with separation from the waste stream; and the inconsistent supply of recyclable composite products, which restricts long-term business. Conventional recycling techniques are generally not efficient and create additional waste during the process, such as liquefied waste (bases, acids, and surfactants), hazardous gases, and solid waste [35][36]. The mentioned problems are taken into account where circular economy strategies for composites are created. The most popular strategies are [17]:
  • Ensuring a long life for products, including their use and reuse through manufacturing high-quality and durable products;
  • Extending the lifetime of the products through maintenance, repair, technical upgrading, etc.;
  • Product recovery (increasing the number of cycles);
  • Structural reuse-retrieving structural elements, preserving the material composition, including reuse of the elements of the product in another context or construction;
  • Recycling-recovery of material, including the close of the materials loop.

3. Development of Composites Recycling

The provided analysis clearly shows that the recycling of the multi-material advanced products is a real challenge. It requires the development of new technologies and the improvement of existing ones. Other important challenges are proper law regulations and building social consciousness about the influence of this waste on the environment and social health. Regulatory issues become more and more important, because the shown product starts to be a problem on a global scale, not only for national or local economies [37].
The main goals for the developing techniques mentioned above are high effectiveness and high quality—producing higher quality recycled materials and improving resource efficiency—and at the same time limiting the influence on the environment. Selected case studies show that there is no single ideal solution, but there are a lot of options for particular areas and products. The technologies presented have different properties, advantages, disadvantages, and technology-readiness levels. Additionally, they are dedicated to different material compositions. However, the differences between them are useful for distinguishing the most effective and help to create benchmarks that can be copied for other types of composites.

This entry is adapted from the peer-reviewed paper 10.3390/jcs5090243

References

  1. Avilés-Palacios, C.; Rodríguez-Olalla, A. The Sustainability of Waste Management Models in Circular Economies. Sustainability 2021, 13, 7105.
  2. EU Commission. Closing the Loop—An EU Action Plan for the Circular Economy. Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions COM. 2015. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52015DC0614 (accessed on 20 June 2021).
  3. Adami, L.; Schiavon, M. From Circular Economy to Circular Ecology: A Review on the Solution of Environmental Problems through Circular Waste Management Approaches. Sustainability 2021, 13, 925.
  4. Blomsma, F.; Brennan, G. The Emergence of Circular Economy: A New Framing Around Prolonging Resource Productivity. J. Ind. Ecol. 2017, 21, 603–614.
  5. Korhonen, J.; Honkasalo, A.; Seppälä, J. Circular Economy: The Concept and its limitations. Ecol. Econ. 2018, 143, 37–46.
  6. Dumée, L.F. Circular Materials and Circular Design—Review on Challenges Towards Sustainable Manufacturing and Recycling. Circ. Econ. Sustain. 2021, 1–15.
  7. Wurster, S. Creating a Circular Economy in the Automotive Industry: The Contribution of Combining Crowdsourcing and Delphi Research. Sustainability 2021, 13, 6762.
  8. Das, S.; Lee, S.-H.; Kumar, P.; Kim, K.-H.; Bhattacharya, S.S. Solid waste management: Scope and the challenge of sustainability. J. Clean. Prod. 2019, 228, 658–678.
  9. Walker, S.; Coleman, N.; Hodgson, P.; Collins, N.; Brimacombe, L. Evaluating the Environmental Dimension of Material Efficiency Strategies Relating to the Circular Economy. Sustainability 2018, 10, 666.
  10. Alhazmi, H.; Shah, S.A.R.; Anwar, M.K.; Raza, A.; Ullah, M.K.; Iqbal, F. Utilization of Polymer Concrete Composites for a Circular Economy: A Comparative Review for Assessment of Recycling and Waste Utilization. Polymers 2021, 13, 2135.
  11. Krauklis, A.E.; Karl, C.W.; Gagani, A.I.; Jørgensen, J.K. Composite Material Recycling Technology—State-of-the-Art and Sustainable Development for the 2020s. J. Compos. Sci. 2021, 5, 28.
  12. Shubham, U.; Suriya, V.K.; Neha, M.; Adarsh, R. Comprehensive study of recycling of thermosetting polymer composites—Driving force, challenges and methods. Compos. Part B Eng. 2021, 207, 108596.
  13. Minelgaite, A.; Liobikiene, G. Waste problem in European Union and its influence on waste management behaviours. Sci. Total Environ. 2019, 667, 86–93.
  14. Hattaf, R.; Aboulayt, A.; Samdi, A.; Lahlou, N.; Ouazzani Touhami, M.; Gomina, M.; Moussa, R. Reusing Geopolymer Waste from Matrices Based on Metakaolin or Fly Ash for the Manufacture of New Binder Geopolymeric Matrices. Sustainability 2021, 13, 8070.
  15. Geng, Y.; Doberstein, B. Developing the Circular Economy in China: Challenges and Opportunities for Achieving ‘Leapfrog Development’. Int. J. Sustain. Dev. World Ecol. 2008, 15, 231–239.
  16. Bazan, P.; Nosal, P.; Wierzbicka-Miernik, A.; Kuciel, S. A novel hybrid composites based on biopolyamide 10.10 with basalt/aramid fibers: Mechanical and thermal investigation. Compos. Part B Eng. 2021, 223, 109125.
  17. Joustra, J.; Flipsen, B.; Balkenende, R. Circular Design of Composite Products: A Framework Based on Insights from Literature and Industry. Sustainability 2021, 13, 7223.
  18. Bachmann, J.; Hidalgo, C.; Bricout, S. Environmental analysis of innovative sustainable composites with potential use in aviation sector—A life cycle assessment review. Sci. China Ser. E Technol. Sci. 2017, 60, 1301–1317.
  19. Chu, S.; Majumdar, A. Opportunities and challenges for a sustainable energy future. Nat. Cell Biol. 2012, 488, 294–303.
  20. Rocha, I.; Van Der Meer, F.; Raijmaekers, S.; Lahuerta, F.; Nijssen, R.; Mikkelsen, L.P.; Sluys, L. A combined experimental/numerical investigation on hygrothermal aging of fiber-reinforced composites. Eur. J. Mech. A Solids 2019, 73, 407–419.
  21. Beauson, J.; Brøndsted, P. Wind turbine blades: An End of Life Perspective. In MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology; Ostachowicz, W., McGugan, M., Schröder-Hinrichs, J.U., Luczak, M., Eds.; Springer: Berlin/Heidelberg, Germany, 2016; pp. 421–432. ISBN 9783319390956.
  22. Yang, Y.; Boom, R.; Irion, B.; van Heerden, D.J.; Kuiper, P.; de Wit, H. Recycling of composite materials. Chem. Eng. Process. Process. Intensif. 2012, 51, 53–68.
  23. Oliveux, G.; Dandy, L.O.; Leeke, G.A. Current status of recycling of fibre reinforced polymers: Review of technologies, reuse and resulting properties. Prog. Mater. Sci. 2015, 72, 61–99.
  24. Borjan, D.; Knez, Ž.; Knez, M. Recycling of Carbon Fiber Reinforced Composites—Difficulties and Future Perspectives. Materials 2021, 14, 4191.
  25. Gopalraj, S.K.; Kärki, T. A review on the recycling of waste carbon fbre/glass fbre-reinforced composites: Fbre recovery, properties and life-cycle analysis. SN Appl. Sci. 2020, 2, 433.
  26. La Rosa, A.D.; Greco, S.; Tosto, C.; Cicala, G. LCA and LCC of a chemical recycling process of waste CF-thermoset composites for the production of novel CF-thermoplastic composites. Open loop and closed loop scenarios. J. Clean. Prod. 2021, 304, 127158.
  27. Pastine, S.J. Sustainable by Design: Introducing Recyclable Epoxy Technology. Available online: http://www.temp.speautomotive.com/SPEA_CD/SPEA2013/pdf/TS/TS8.pdf (accessed on 4 September 2021).
  28. European Parliament and the Council. Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on Waste and Repealing Certain Directives (Text with EEA Relevance). 2008. Available online: http://data.europa.eu/eli/dir/2008/98/oj (accessed on 24 June 2021).
  29. Navarro, C.A.; Giffin, C.R.; Zhang, B.; Yu, Z.; Nutt, S.R.; Williams, T.J. A structural chemistry look at composites recycling. Mater. Horiz. 2020, 7, 2479–2486.
  30. Wiśniewska, A.; Hernik, S.; Liber-Kneć, A.; Egner, H. Effective properties of composite material based on total strain energy equivalence. Compos. Part B Eng. 2019, 166, 213–220.
  31. Hopewell, J.; Dvorak, R.; Kosior, E. Plastics recycling: Challenges and opportunities. Philos. Trans. R Soc. B Biol. Sci. 2009, 364, 2115–2126.
  32. Ignatyev, I.A.; Thielemans, W.; Vander Beke, B. Recycling of polymers: A review. ChemSusChem 2014, 7, 1579–1593.
  33. Howarth, J.; Mareddy, S.S.R.; Mativenga, P.T. Energy intensity and environmental analysis of mechanical recycling of carbon fibre composite. J. Clean. Prod. 2014, 81, 46–50.
  34. Katarzyna, B.; Le, C.H.; Louda, P.; Michał, S.; Bakalova, T.; Tadeusz, P.; Prałat, K. The Fabrication of Geopolymer Foam Composites Incorporating Coke Dust Waste. Processes 2020, 8, 1052.
  35. Ma, S.; Webster, D.C. Degradable thermosets based on labile bonds or linkages: A review. Prog. Polym. Sci. 2018, 76, 65–110.
  36. Ilyas, M.; Ahmad, W.; Khan, H.; Yousaf, S.; Khan, K.; Nazir, S. Plastic waste as a significant threat to environment—A systematic literature review. Rev. Environ. Health 2018, 33, 383–406.
  37. Majewski, P.; Al-shammari, W.; Dudley, M.; Jit, J.; Lee, S.H.; Myoung-Kug, K.; Sung-Jim, K. Recycling of solar PV panels-product stewardship and regulatory approaches. Energy Policy 2021, 149, 112062.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.
This entry is offline, you can click here to edit this entry!
Video Production Service
Feedback