Chemical recycling to unlock circularity of advanced composite materials

First REPOXYBLE workshop: Horizon Europe research in the field is showing the way forward


Sustainability of composite materials: the Horizon Europe investments

Composite materials display enhanced physical and chemical properties, allowing for lightweight tailored physical-chemical properties, thus multi-functional and high performance even in extreme applications. The versatility of these advanced materials finds applications in various sectors, such as energy, food and water, transportation, home & leisure, information and ICT, construction.


They represent a viable alternative to conventional materials, for example integrating a complex set of materials into a lighter, thermally, or electrically conductive composite structure.


Novel composite materials are acknowledged as enabling factors to foster green and digital transitions in the transport sector.

However, a lot has yet to be done to develop more sustainable solutions, reducing impacts related to manufacturing and improved recyclability. Nowadays, most polymer-based composite materials are incinerated or even directly landfilled. For example, an estimated 500,000 tons of fiber reinforced polymer (FRP) composite waste will be generated in Europe in 2025; while the global annual FRP recycling capacity is estimated to be less than 100,000 tons.

Introducing biobased components, developing more efficient processes, exploring reuse and recycling technologies are some of the routes explored by a large research investment composed by a portfolio of over 13 Horizon Europe projects, including REPOXYBLE, that have been presented in the European Commission HE Resilience project cluster day on Efficient, Lightweight, Sustainable Advanced Materials  (6th June, 2024).

Based on the outcomes of this event, on June 7th over 50 experts convened in the REPOXYBLE workshop “Processes and methods for recycling, reuse, and recovery of advanced composite materials in transport”. We report here some highlights from the discussion.


Recycling of composites: Current status

  • Most relevant methods for the recycling of polymeric composites include mechanical and thermal recycling (Technology Readiness Level ≥9) and chemical recycling (TRL ~ 6). Other available methods are electrical and biological recycling, but they still have a low TRL (~ 4).
  • Mechanical and thermal recycling allow for high throughput and have well-established markets for their products (e.g. polymer pellet fillers from shredding, or liquid fuels from pyrolysis). On the other hand, they do not allow to recover each and every different constituent (i.e. monomers, additive, fillers, etc.) from the composites, and do not preserve structural properties and quality of the pristine material.
  • Chemical recycling is an emerging alternative method, whenever the primary interest is to recover each and every material constituent separately while preserving their properties and It is currently characterized by an intermediate TRL, and is mainly carried out through hydrolysis, aminolysis, and supercritical solvolysis. It is the ideal technology option to recover constituents featuring high economical value, such as reinforcing fibres. However, it may also imply the use of hazardous substances, and market for recycled products is not yet well established on a large scale.
  • It is stressed that the quality of the recycled materials is an issue for all recycling technologies and this still undermines the implementation of full closed loop


Research pathways for sustainable composites

  • Two main approaches are explored by current research initiatives to implement sustainability and circularity in the composite materials sector:
    • Develop new or optimized ways to reuse, repair, and recycle existing materials. The aim is to reduce as much as possibly quantities and consequently to avoid landfilling.
    • Development of completely new materials taking into account circularity approaches, in terms of reuse, repair and recyclability (possibly closed loop recyclability), as well as Safe and Sustainable by Design (e.g. safety or biodegradability of raw materials) from the early stages of the development, design and use of the materials (modular design). The aim is to avoid or limit the quantities of landfilled materials as much as possible.
  • A mixed approach is generally implemented depending on type of material and value chain, selecting the most efficient approach amongst reuse, repair and recyclability.


Barriers and opportunities: integrated recycling strategy, closed loop approach and secondary markets

  • Sustainability of composites should address the principle of cost effectiveness. Different Endo-fo-Life (EoL) scenarios including reuse, repair, waste collection strategies, and different recycling technologies (e.g. solvolysis) should be explored and adopted to ensure an effective and cost-sustainable repositioning of the materials within the same or other value chains.
  • The quality of the materials retrieved determines the possibilities of application. However, connecting different value chains is always a big challenge and a typical industrial ecosystem problem.
  • Closed loop recycling is still a challenge for polymer-based composites. Currently, high-quality retrieved constituents, such as carbon fibers in epoxy resin systems, cannot be kept in the loop for sufficient time, while ensuring a sustainable and energy cost-effective approach. Heterogeneity (intrinsic composites property) and lack of industrial-scale recycling routes availability are the main barriers.
  • Chemical recycling is currently the most promising method for the implementation of closed loop recycling in the composites sector (TRL < 6).
  • It has already been proven on the lab scale the effective recovery of the different material constituents, allowing to retrieve reinforcing fibres (e.g. carbon fibres) featuring high quality, compared to virgin fibres. However, depending on the composite material, it may also imply the use of hazardous substances, such as various solvents, and could be energy intensive (e.g. supercritical solvolysis).
  • The most interesting secondary composites applications, in terms of demand and value of the market, include automotive, building and constructions, aerospace, energy and sport equipment However, sector specific technical requirements need to be fulfilled; and material certification could represent a real issue for some application sectors.


Future outlook

  • The economic aspect is one of the most important. Companies need to see the advantage in investing and implementing new technologies and approaches that research projects are developing to address circularity and sustainability in the composite sector.
  • The great challenge related to the circularity is to recover materials in high quality and use them during established production processes, enabling a closed loop approach.
  • Chemical recycling is currently not the state of the art for fibre reinforced composites. Therefore, further research in necessary to optimize and integrate this approach into valuable and circula business models.
  • Recyclability, performance and costs have been set as the top three key priorities to address sustainability of composites by the EU research projects currently working on this.


Research projects shared their experiences at the REPOXYBLE workshop

The REPOXYBLE workshopProcesses and methods for recycling, reuse, and recovery of advanced composite materials in the transport sector” hosted presentations from the following five Horizon Europe Research and Innovation actions in the field: FURHY, r-LightBioCom, FOREST, EuReComp, and Carbo4Power.


Elvira Villaro (AVANZARE, coordinator of the REPOXYBLE project) and Christoph Olscher (BOKU University) provided an insight into the REPOXYBLE project with reference to our approach to sustainability and recycling, and presented our main achievements and next steps.

REPOXYBLE is developing new lightweight, bio-based, sustainable and multifunctional epoxy-based composites for aerospace and automotive applications. Carbon fibres and natural fibres (flax), and different additives (graphene-based materials, metallic nanoparticles), will be embedded in the polymeric matrix to provide  multifunctionalities and improve the energy-saving during the newly developed IR curing process. The final composite will feature thermal management, electrical conductivity and self-structural monitoring properties.

The project will prototype surface panels for the engine gondola and the wing of the hypersonic business jet HYPLANE (by the DAC, Campania Aerospace District, Italy) and the monocoque of a fuel-cell low-weight car powered by hydrogen rather than batteries, emitting water (by Riversimple, UK).


Recyclability has been set as one of the top priorities for the REPOXYBLE product solutions, and considered since the early stages of the material design, from a closed loop perspective. Therefore, the project is working on the development of a Depolymerizable Closed Loop Epoxy (DCLE) system, exploring different approaches of modifying either the hardeners or the monomers, to allow for the depolymerization of the composite  at the end of component service life. This will allow the effective recovery of the building blocks, fibres and additives, as high quality secondary raw materials.

The project is now at mid-term: it has already developed a working prototype of the depolymerizable system, and successfully demonstrated the recovery of building blocks in the lab. The next steps of the project are: (a) optimization of the depolymerization process to achieve the best recovery rate; (b) testing the chemical recycling of the formulated epoxy-system with additives; (c) and the manufacturing of fibres- reinforced matrices (i.e. prepregs).


Luigia Longo (CETMA, coordinator of the FURHY project), presented the FURHY work focused on the Ecodesign of biobased and recyclable composite material for aerospace and automotive applications. FURHY project will develop an optimized bio-based, fast curing, recyclable epoxy resin, filled with expanded graphite, that will provide multifunctional and self-monitoring capability to the final composite material, where up to 80% of the total components in the epoxy resin formulation will come from renewable resources. Materials developed will incorporate both bio-based virgin fibres (hemp) and/or recycled carbon fibres (r-CF), including appropriate fiber coatings to maximize the fiber properties. The project will also develop a new effective out-of-autoclave manufacturing process consisting in prepreg compression molding (PCM), and a new closed-loop recycling technology as well, to provide valuable secondary raw materials having properties similar to the virgin materials.


Fernando Cepero Mejias (Coventry University) presented r-LightBioCom circularity and recyclability innovations. The r-LightBioCom project is developing new advanced bio-based and high-performance thermosets with inherent recyclability properties for automotive, aeronautical and infrastructure sectors. Both recycled fibres (r-CF, r-GF, r-Aramid) and natural fibres (basalt, flax, hemp) will be used to manufacture new sustainable textiles. Energy efficiency in manufacturing technologies will be implemented through RTM combined with frontal photopolymerization technologies, or vacuum infusion coupled with microwaves, focusing on small area of the resin to enable fast curing. The project will use a combination of mechanical and chemical recycling technologies, to recover the fibres from the composite matrix. Information related to the production cost, structural integrity and environmental impact of the project solutions will feed into the development of a Coupled Ecological Optimization (CEO) Framework.


Rocío Ruiz Gallardo (AIMPLAS, coordinator of the FOREST project) provided an overview on FOREST approach to the development of advanced lightweight materials for energy-efficient structures for the bus transport, aeronautic and automotive sectors, based on three main routes: reduction, recovery, reshape. The project will develop biobased thermoplastics and thermosets, reinforced with recycled carbon fibres recovered from aerospace and automotive waste. Biobased and carbon-based additives will be also included to enable fire-retardant and EMI-shielding properties. Manufacturing of the different components will rely on energy-efficient Out-of-Autoclave processes, such as pultrusion, compression molding, and stamping overmolding. Concerning the recycling process for carbon fibres, the project already successfully obtained non-woven 100% recycled carbon fibre (rCF) mat, and is working on recovery of continuous rCF for pultrusion thermoplastic UD-tape.


Dionisis Semitekolos (National Technical University of Athens – R-NanoLab, coordinator of the EuReComp project), presented the EuReComp approach and results based on the 6R strategy to promote in particular reuse, repair and recycling of EoL composites from aircraft and energy industries. EoL fiber reinforced composites from windmill, aircraft and automotive industries are collected, dismantled, separated and destinated for different routes, depending on their structural integrity, fiber content and type: materials containing glass-fibres typically undergo repair and reuse processing, to produce demo cases; while materials containing carbon fibres are instead processed via chemical recycling using solvolysis (Sub-& supercritical H20, Chemical-assisted,  Plasma-enhanced). Depending on the type of carbon fiber recovered (continuous CFs, CFs fabric patches, chopped CFs), different manufacturing technologies are used (filament winding, compression molding, 3D printing, vacuum infusion) to produce new demo cases, e.g. an automotive shaft, a formula seat, a steering wheel and container pontoon.


Tatjana Kosanovic Milickovic (National Technical University of Athens – R-NanoLab, coordinator of the Carbo4Power project) presented the Carbo4Power project results on the development of a new generation of lightweight, high-strength, durable structures for offshore windmill and tidal turbine rotor blades. The project developed dynamic thermosets based on 3R resins (reprocessable, repairable and recyclable) and explored the possibilities offered by nano-engineering on the different material components (e.g. epoxy, fibres, coatings). Nano-engineered hybrid (multi)materials and their intelligent architectures will provide different ad hoc functionalities to the turbine blades (e.g. enhanced mechanical properties, lightning and erosion protection, self-healing, anti-/de-icing), increasing their operational performance and durability, while reducing the cost of energy production, maintenance and their environmental impact. As well, recycling of blade materials will be optimized thanks to the advanced functionalities of 3R resins and adhesives with debonding on demand properties.


The REPOXYBLE workshop have seen the participation of more than 50 representatives from academia and industry, experts in the field of chemical systems, novel technologies, and production, recycling and recovery of high-value composite constituents.


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