Increased adoption of carbon-fiber-reinforced plastics shines spotlight on recycling technologies

The biggest obstacles standing in the way of ubiquitous use of carbon fiber in carbon-fiber-reinforced plastics (CFRPs) are cost and processing efficiency. Lux Research (Boston), a firm providing strategic advice and intelligence on emerging technologies, has released a report, “Carbon Fiber Composites Market Update,” that addresses these and other issues.

Innovations aimed at reducing carbon-fiber cost and improving composite processing efficiency combined with continued global scale-up are driving increased adoption of CFRPs. As higher volumes enter the market, CFRP recycling is increasingly important not only for environmental and economic benefit, but also to avoid upfront landfill costs and to meet stringent automotive regulations in recyclability.

In 2016, the global CFRP market was greater than 60,000 million tons and is expected to grow to 183,000 million tons, or $35 billion, in 2020. However, only a small amount of the scrap produced per year is recycled, and more than $400 million of CFRP ended up in landfills in 2015.

Mainstream reclamation techniques include a pyrolysis step, which is effective at burning off all forms of resin but often produces char and damaged fiber and is energy- and cost-intensive, and a mechanical recycling step—grinding, chopping or milling, for example—which produces short, chopped fibers unfit for use in structural components. Such drawbacks of incumbent recycling methods present innovation opportunities at each step of the recycling value chain.

First is the source. Thermoset CFRPs retain a permanent solid state and cannot be re-melted or reshaped; however, companies like Adesso Advanced Materials, Connora Technologies and Mallinda are addressing the issue by designing purposely recyclable resins or prepreg material. Addesso has developed an amine-based curing agent that allows for fiber recovery, Connora produces cross-linkers to form reversible bonds, and Mallinda’s resin system enables depolymerization, allowing a cradle-to-cradle lifecycle.

The next step is collecting and separating the material. Although collection, shredding and sorting are common practices in aerospace and automotive, only a small fraction of total scrap material is repurposed. To this end, there is a need for regulatory forces or proposed incentives to increase overall collection efficiency, be it an agreement between partners or government policy, says the report. Additionally, end-of-life (EOL) parts—with varying resins, shapes and material compositions—pose a difficulty in accurate identification and stream sorting. A 3D scan method shows promise but requires further development; in addition, further sorting technologies are needed. Pzartech is one company that has developed recognition technology that enables users to identify mechanical parts using 3D image processing and deep learning.

The third step is reclaiming. Companies using the mainstream pyrolysis and mechanical treatment approach include CFK Valley Stade Recycling, ELG Carbon Fiber, Materials Innovation Technologies, and Procotex, among others. These groups claim to retain a high degree of mechanical properties and create a variety of recycled products such as composite parts, preforms, pellets, chopped CF or milled fibers. Materials Innovation Technologies employs a further step, using either a 3D-engineered preform (3-DEP) or co-DEP process to create complex shapes with specific fiber orientations that can increase load capacity. Despite pyrolysis options, alternative recycling solutions that are scalable, low-cost, non-degrading, non-charring, and can preserve fiber length are in demand. This necessity has spurred the development of different technologies. One that is gaining popularity is a non-destructive solvent approach that does not char nor require mechanical treatment, thereby maintaining fiber length.

Variations of the solvent method are used by Adherent Technologies, East China University, Georgia Institute of Technology, Mallinda, Siemens in conjunction with MAI (Munich-Augsburg-Ingolstadt) Carbon Cluster and Washington State University. This technique involves soaking the CFRP for varying durations at room temperature or with heat; it allows for resin recovery, though not all solvent methods effectively process all resin chemistries.

Alternatively, Novana uses a physical melt extrusion process, which converts immiscible polymer mixtures into fiber-reinforced composites without the need for an initial separation or sorting process. East China University also developed a "sunlight" technique to burn off resin, though its effectiveness is environment-dependent and may be more reliable if integrated with a laser energy source instead. Though reclamation methods are slowly developing and diversifying, a large expanse remains until a scalable, comprehensive method is implemented.

The final step is marketing the reclaimed material. Although the chopped length of recycled CFRP disqualifies it from use in structural applications, Lux Research says that it already sees non-structural components such as cabin sidewalls, vehicle trucks, roofs and rear seats being produced. Nonetheless, recycled CFRP has lower performance characteristics when compared with virgin materials, though innovations in preserving fiber length and aligning fiber orientation may lead to improvements.

“As it stands," the Lux Research report concludes, “there is still no perfect, one-size-fits-all solution to recycling CFRP and, considering its complex nature, there may never be one. But a clear value proposition and market need for recycled materials has spawned an enclave of burgeoning technologies, slowly bringing us closer to a scalable and efficient process. In this growing landscape, CFRP recycling is an area that will see only further demand and readers should monitor or partner with leading developers.”

The full report is available on the Lux Research website.