From Scrap to Spar Where Recycled Carbon Fiber Actually Stands in Aircraft Structures
Boeing and Mitsubishi Chemical Advanced Materials are testing prototype cabin sidewall panels made from pyrolysis-derived recycled carbon fiber under Mitsubishi's KyronTEX material line, while separate simulation research found a scaled-down wing spar built from recycled carbon fiber performed within acceptable stress margins compared to a virgin-fiber equivalent. Recycled carbon fiber remains limited to non-structural or secondary aerospace applications due to unresolved fiber length, alignment, and surface sizing deficiencies, with primary structural qualification requiring years of additional testing and supply chain development.
Recycled carbon fiber is gaining traction in aerospace applications, though its role remains largely in secondary structures. The production of carbon fiber is energy-intensive and costly, with significant waste generated during aerospace-grade composite manufacturing. Historically, much of this waste ended up in landfills due to the lack of commercially viable recycling methods. However, advancements are being made in engineering recycled carbon fiber for aircraft components, albeit primarily for non-structural uses. Research into its application in primary structures is still in early stages.
Two main methods exist for reclaiming carbon fiber from composite waste: pyrolysis and solvolysis. Pyrolysis, the more established method, involves heating composite scrap in an oxygen-free environment to decompose the resin matrix, leaving the carbon fiber intact. This process is energy-efficient but does not recover the resin, thus not achieving closed-loop recycling. Solvolysis, a chemical recycling method using solvents, is less mature but has the potential to recover both the fiber and resin. However, scaling solvolysis to meet aerospace supply chain demands remains unproven commercially.
Both methods can reclaim 90 to 95 percent of carbon fiber from scrap with minimal degradation of fiber properties. However, the quality of recycled fiber differs from virgin fiber. Recycled fibers are typically shorter and randomly oriented, affecting their suitability for primary structural layups. The recycling process can alter surface chemistry, weakening resin bonding in new composites. Research into resizing, a chemical surface treatment to improve resin adhesion, shows promise in restoring some interfacial bond strength, but challenges remain.
A notable example of recycled carbon fiber in aerospace is a collaboration between The Boeing Company and Mitsubishi Chemical Advanced Materials. They are evaluating Mitsubishi Chemical's KyronTEX material, made from CarboNXT recycled carbon fiber, for cabin sidewall panels. These panels are a conservative application due to their lower structural load requirements. The KyronTEX system is a thermoplastic composite using resins like polyphenylene sulfide and polyetherimide. Boeing and Mitsubishi Chemical have produced prototype panels, aiming to demonstrate emissions reductions, though no timeline for production has been set.
Research is also exploring recycled carbon fiber in more demanding roles. A study on a scaled-down aircraft wing spar design found that recycled-fiber spar stress values under lift and drag loading were within acceptable margins, though higher than those of virgin material. This indicates comparable structural viability, not superior performance. The study was conducted on a model rather than a full-size spar, and further testing is needed before recycled-fiber structures can be certified for flight.
Efforts to integrate recycled carbon fiber into aerospace supply chains are ongoing. An aerospace and defense working group, including James Cropper Advanced Materials and Hexcel Corporation, is developing enhanced composites for structural applications. The challenge is not only in materials science but also in establishing a reliable supply chain. Consistent, traceable, certifiable feedstock is necessary for recycled fiber to become a standard material in production.
Life cycle assessments show recycling as environmentally preferable to landfill or incineration for composite waste. However, this does not equate to recycled fiber matching virgin fiber's mechanical performance. The growing demand for carbon fiber in aerospace, wind energy, and automotive markets increases the economic incentive to utilize composite scrap, but it remains an engineering challenge.
The commercial market for recycled carbon fiber reflects both growth and uncertainty, with varying market size estimates. While recycled carbon fiber is not yet ready to replace virgin fiber in primary aerospace structures, its development is progressing incrementally. Challenges such as fiber length and alignment, bonding gaps, supply chain consistency, and certification processes remain. Despite these hurdles, recycled carbon fiber is transitioning from waste to a material of engineering interest.
Source: Carbon Fiber Feed