This case study focuses on replacing heavy metal parts in the railway industry with a lightweight, fire-resistant, and intrinsically recyclable epoxy-vitrimer composite, aiming to improve energy efficiency, safety, and end-of-life circularity.
Challenges
The reference products are structural parts made from steel and aluminium. Their primary sustainability challenge is their weight:
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Environmental Hotspot: For metal parts, the use phase is the dominant environmental hotspot. The high mass requires significant energy to transport over the vehicle's 25-year service life, resulting in substantial greenhouse gas emissions.
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Recycling of Composites: While existing composites are lightweight, they are typically based on thermoset resins, which are non-recyclable and end up in landfills or incineration at their end-of-life.
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Safety Concerns: The railway sector has extremely strict fire, smoke, and toxicity (FST) regulations (EN45545-2). Many conventional composites rely on halogenated flame retardants, which are effective but pose potential health and environmental hazards.
Objectives
The main objective was to design a composite material that is safer, lighter, and fully recyclable. The specific KPIs for the new material were:
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Performance: Achieve mechanical properties suitable for railway applications (Tg > 110°C, Tensile strength > 45 MPa) and comply with FST standard EN45545-2 at hazard level HL2.
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Safety: Replace harmful additives by covalently bonding over 90% of flame retardant moieties into the polymer matrix and reduce the release of IAS by >75%.
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Sustainability: Reduce the weight of a full train car body by at least 30% to lower energy consumption during use.
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Recyclability: Achieve 100% recyclability through vitrimerization, with the recycled epoxy retaining over 90% of its original tensile strength.
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Cost: Ensure the material cost is less than 25% higher than the metal part it replaces.
Our SSRbD Approach & Key Findings
The SURPASS solution is a carbon-fibre reinforced composite based on an epoxy-vitrimer resin. This chemistry allows the thermoset material to be dissolved in a solvent at its end-of-life, enabling the recovery of both the resin and the valuable carbon fibres for reuse.
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Environmental Performance (LCA): The use-phase benefits are significant. Because of their lower weight, the composite parts showed a clear environmental advantage over steel in climate change, resource use, and pollution. However, the manufacturing stage of the composite is a major hotspot, driven almost entirely by the high environmental burden of producing carbon fibre. The chemical recycling process also has a notable impact due to the use of environmentally friendly solvent.
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Economic Viability (LCC): At its current low TRL, the manual lab-scale production process makes labour costs the dominant cost driver. However, a use-phase analysis showed that the lightweight composites offer dramatic operational cost savings over 25 years: 78% less than steel and 35-37% less than aluminium, due to reduced energy consumption.
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Hazard & Release Assessment:
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Hazard: The dynamic AFD hardener that brings the recyclable technology to composite materials poses a toxicity risk that must be considered. Thus, alternatives that address the same recyclable technology should be envisaged for future development.
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Release: The SSRbD materials showed better performance in abrasion tests (less weight loss) compared to the benchmark. Crucially, after ageing, the release of nanoparticles from the reference material was higher than from any of the SSRbD materials, indicating better long-term stability.
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Key Takeaways
This case study perfectly illustrates the importance of a full life-cycle perspective. While the manufacturing of the advanced composite has a high initial environmental impact, the benefits during its long operational life are substantial. The key to unlocking its full sustainability potential lies in scaling up production to reduce costs and, crucially, developing a circular supply chain for carbon fibre.