Trends fueling the composites recycling movement

Composites recycling emerged in the 1990s, led by carbon fiber’s augmented prevalence in industries like aerospace and automotive. This is a natural progression with all materials use in manufacturing — the ever-increasing volume of composites use, and the knowledge that all products have an end of life (EOL), demand a better understanding of how to recycle them. Today, this has been further compounded in the composites industry by global sustainability efforts.

However, progress in commercializing recycling technologies and building recycling capacity have been slow-going until recently. Additionally, to create true closed-loop circularity for composites waste, multiple challenges are still being addressed, including: difficulty of recycling EOL composites due to their multiple constituents (fiber, matrix, coatings), properly sourcing EOL scrap and reaching consensus on the most “eco-friendly” recycling methods. With approximately 115 kilotons of generated carbon fiber waste (factory and EOL) forecasted by 2030, it’s paramount that the industry ramps up its efforts to achieve standardized processes and robust supply chains in order to mitigate non-environmentally friend methods of recycling, and also ensure the ability to recycle these materials generally. (There are already some EU regulations and proposals in place forbidding landfilling, a traditional way of getting rid of generated waste.)

Recycling — like biomaterials and energy-efficient equipment — is a vital area within the broader topic of sustainability, but it is also highly complex, and there is a wide variety of work underway to turn it into a reality. Some companies are focusing on the development of more optimal methods. Others process and repurpose composites waste into various end products and are actively contributing by growing their capacity. There are also an increasing number of projects demonstrating the manufacture of a recyclable end product, often with closed-loop recycling processes.

While the road to global, large-scale implementation remains long, academia and various industry players have been making strides to research, develop and commercialize waste circularity in a variety of ways. Here, CW has compiled some of these efforts.

Note: A majority of composite recycling initiatives address the recycling of fibers reinforced with a thermoset matrix. Some demonstration examples use thermoplastic matrices as part of their “recyclability” focus, and will be described here; however, this article will primarily cover thermoset composite recycling.

Recycling method landscape

The earliest known disposal methods for composites waste began with incineration and landfilling. Both have been deemed environmentally unfriendly for obvious reasons — incineration leads to the release of greenhouse gas emissions and additional pollutants, while landfilling involves similar hazards, in addition to being a short-term solution for such long-lasting materials. Similar methods combines combustion and incineration, which turns the waste component into heat to be used for energy recovery (electricity), though the incineration aspect still results in pollutants (an ash byproduct).

Another form of combustion is cement kiln coprocessing, which replaces fossil fuels like coal with shredded wind blades or other composite parts in the production of cement. A group of European companies are working to prepare a life cycle assessment (LCA) report exploring the environmental impacts of treating EOL composites via this process, noting that in addition to reducing emissions from cement production, it cuts the need for fossil energy sources and virgin raw materials. The KiMuRa project started in December 2020 points to similar advantages, in an effort to increase industry participation.

Mechanical, thermal and chemical recycling are additional recycling methods that have since emerged and are in different stages of maturation, primarily targeting the treatment of carbon fiber- and glass fiber-reinforced polymer (CFRP and GFRP) to recover fibers. Each option offers its own advantages and disadvantages to composites recycling.

Mechanical recycling

Mechanical recycling involves the physical breakdown of EOL composite parts by cutting, shredding, milling and/or grinding into powders and fibrous recyclates for use as filler, in injection molding, 3D printing or other processes. It is a quick and easy process that can result in “near-perfect outputs” and is far less energy-intensive than chemical recycling. Nor does it typically produce harmful gases like CO₂. Its drawback, however, is seen through reduced material size and integrity, particularly strength and tensile modulus properties, meaning that the material’s second use is usually limited to low-value options like fillers and partial reinforcement.

Fairmat (Paris, France) is a key player in the mechanical recycling of composites,  using cutting technologies (incorporating robotics and machine learning) to turn CFRP waste into CFRP chips composed of 100% high-quality, recycled carbon fiber. This process is said to “preserve the inherent strength, durability and high-performance characteristics of the virgin carbon fiber,” and is suitable for industries like sporting goods, consumer electronics and mobility. The company has already signed several carbon fiber scrap repurposing deals, including with Exel Composites, Hexcel and Dassault Aviation, among others.

Elevated Materials (Gardena, Calif., U.S.) is performing a similar function for Toray Composite Materials America Inc. (Tacoma, Wash., U.S.). A 3-year agreement will see Elevated repurpose Toray’s aerospace scrap prepreg materials, including slit-edge and full-width prepreg sheets. The company mechanically downsizes this scrap (Elevated Materials calls this process “upcycling”) and compression molding into press-cured carbon fiber sheets, plates and blocks, which have applications in applications like sports equipment, manufacturing accessories and drones.

Thermal recycling

Heat is the primary constituent to breaking down composite scrap in thermal recycling processes, which currently can be broken down into three submethods — pyrolysis, fluidized bed processes, and combustion and incineration. Material is typically subjected to high temperatures (450–700°C) under controlled conditions, so that everything (the resin) is burned away except for the desired fibers. The fluidized bed process recovers energy in addition to fibers/fillers by decomposing the composite matrix via high-temperature air passed through a bed of silica sand, releasing the fiber and filler particles. Pyrolysis similarly decomposes resins and additives using very high temperatures, and often a variety of heat sources, leaving behind short fibers that can be reclaimed and reused. Moreover, the oil and gas byproducts of this process may also be used as chemical feedstocks.

A business structure developed in 2022 between Teijin Ltd. (Tokyo, Japan) and Fuji Design Co. Ltd. (Tokyo) seeks to incorporate Fuji Design’s low environmental impact “precision pyrolysis” technology to produce high-quality carbon fiber from used CFRP. The method uses controlled heating and cooling to reportedly reclaim higher performance fibers via pyrolysis, and potentially also resins.

Similarly, Thermolysis Co. Ltd. (Taichung City, Taiwan) uses pyrolysis to support large-scale recycled carbon fiber (rCF) production, which is then used to manufacture rCF paper and nonwoven materials (rCF prepregs, intermediate laminates and pipe product lines) and rCF pellets (ideal for injection processes) for customers.

A three-phase project between Veolia Recycling and Recovery for Central & Western France (Veolia RVD Centre-Ouest, Aubervilliers, France) and Composite Recycling SA (Ecublens, Switzerland) will establish, scale and launch operations of large-scale thermolysis-based recycling in western France. Veolia specializes in the collection and treatment of non-hazardous waste while Composite Recycling’s thermolysis turns composite waste into fibers and pyrolysis oil end products.

Adapting recycled CFRP into chopped, nonwoven and 3D preform formats via pyrolysis is a method that Carbon Conversions (Lake City, S.C., U.S.) has pursued for a “zero-waste, closed-loop manufacturing process at commercial scale.” In March 2024, the company launched re-Evo TDR, a 3D printing filament reinforced with recycled carbon fiber (rCF).

Thermal recycling remains an attractive option for retaining the original fiber from EOL waste. Not only does it successfully separate matrix from fiber, but depending on the process, the separated fibers can maintain high mechanical properties. Possible disadvantages include high operational cost from significant energy requirements and risk of fiber surface damage caused by overheating. Moreover, while the recovered fiber is of higher quality than mechanical recycling, its properties are not always on par with virgin materials.

Chemical recycling

Chemical recycling seeks to dissolve the present polymer matrix via acids, bases and/or solvents, often at elevated temperature. The most common methods are solvolysis and hydrolysis; the former presents solvents to depolymerize, while the latter causes resin degradation through the presence of water. Chemical recycling generally retains clean and smooth fibers with maximum mechanical properties and features a high resin decomposition ratio. Its disadvantages include the high cost of chemicals and hazardous residues generated during the process.

Chemolysis is a process that can use enzymes to break down a polymer matrix for reuse. For example, Ascorium (Königswinter, Germany) uses this type of process to recycle its polyurethane (PU) composites, recovering 95% of the polyol reacted with polyisocyanurate for reuse in new PU materials and parts.

Another company targeting composites recyclability by studying matrix recovery is Asahi Kasei (Tokyo, Japan), which has partnered with Microwave Chemical Co. (MWCC, Osaka, Japan) to commercialize a chemical recycling process for depolymerizing polyamide 66 (PA66) using microwave technology. The obtained monomers would then be used to manufacture new PA66. While primarily focused on recycling the polymers initially, partners do aim to eventually recycle polymers with fiber reinforcement.

Founded by boatbuilders in 2023, Resolve Composites (Nova Scotia, Canada) is developing ReceTT. While not a particular chemical recycling method itself, it does support different types of solvolysis treatments. Through testing on a boat bow section, Resolve says using ReceTT achieved complete material recovery and an 89% reduction in solvent use compared to using an immersion tank for a component of the same size and geometry. The company is currently still developing ReceTT for future commercialization.

Under the COMPASS project, FACC AG (Ried im Innkreis, Austria) and 13 European partners will use a novel, data-driven approach to research the re-manufacturing and reshaping of thermoplastic composite components at their EOL. More specifically, the digital platform will aim to capture real-time information about component quality, performance and history to represent a digital twin of the part, while also digitally assessing its re-manufacture from a technical and economic standpoint for customers.

Another project, reFrame, is developing laser-based laying technologies for processing high-performance thermoplastics and recyclates, as well as the use of artificial intelligence for the precise monitoring and optimization of these layup processe to achieve recyclable CFRP aircraft structures, with particular attention given to sandwich construction. Development of sustainable mobility concepts will target applicability in safety-critical aircraft components.

An outlook on composites recycling

According to a recent report released by Stratview Research (Detroit, Mich., U.S.), an increased inclination to recycle and use recycled composite products, further driven by industry and the government, will ensure this emerging market’s continued growth. Coinciding with these developments, market application versatility is expected to increase, and the cost of recycled composite products/materials is expected to drop as recycling volumes increase. This is all to say that, while there are still many challenges ahead, there are just as many new developments and initiatives turning recycling into a reality.