Motorsport and advanced-engineering company Prodrive recently revealed what it confidently sees as a breakthrough process for recycling carbon fiber. It says the development could lead to a significant increase in use of the material across a much wider spectrum of the automotive industry via a reprocessing chain to manufacture further applications, making it available at lower cost, a hurdle that has generally restricted carbon fiber’s use to high-end vehicles.

The new process could make a significant contribution to enhanced vehicle weight-saving measures, allowing recycled carbon fiber to be repurposed for non-load-bearing components and large bodyshell parts.
A further plus: Prodrive’s recycling process itself brings complementary financial benefits because it does not necessitate use of an autoclave, saving time, energy and cost.

Finding substitute resins
John McQuilliam, Prodrive Composites’ chief engineer, said that any breakthrough in carbon-fiber recycling requires a switch to resins that can be readily melted or chemically separated from the fiber content. He believes that Prodrive is the first company to develop such a process, which it calls P2T (Primary to Tertiary). “In addition to ease of recycling, P2T composites can be processed without the need to heat or pressure during manufacture,” McQuilliam told Automotive Engineering.

Obviating the use of an autoclave enables the scaling-up of production without major investment, he added. It also introduces the feasibility of multiple “lifetimes,” because the material can be repeatedly reused.

The basis of the P2T process is the use of a reactive thermoplastic resin instead of a thermosetting type; a plastic monomer is simply reacted with a catalyst in the presence of the fibers to produce a cured laminate.

The P2T research and development was a joint program between Prodrive and an unnamed automotive OEM that required a high-performance structural material with lower environmental impact than conventional composites—particularly end-of-life disposal and practical recycling.

McQuilliam explained that the challenge facing Prodrive’s team was rooted in the traditional materials used for the resin matrix. These are thermosetting plastics, which once set, cannot be readily separated from the composite fibers. Rolls of ‘pre-preg’ (woven fiber sheets pre-impregnated with resin) are supplied to customers who then cut out 2D profiles and lay them up in molds to produce 3D parts, curing through heating to fix the final shape; thermosetting resins are highly convenient materials to support this supply-chain model.

So Prodrive had to convincingly defy carbon-fiber manufacturing tradition to achieve the required breakthrough, using different resins that led to P2T. The process also delivers benefits beyond end-of-life disposal; he stated that the initial—or primary—components produced by the P2T process use virgin composite fibers, so they have the highest-quality mechanical properties, the equal of conventional thermoset composites and therefore suitable for highly-loaded parts such as suspension wishbones.

Better recycling properties
But with the new P2T-derived material, when the primary part reaches the end of its life, the fibers and much of the resin can be recycled by chemical or thermal depolymerization, yielding the raw carbon-fiber material for a secondary part of slightly lower strength, such as a body panel. When the secondary part reaches the end of its life, it can be chopped and remolded into block material to produce 3D solid components—the tertiary-level parts.

Prodrive said the tertiary parts can themselves be recycled several times, until a point is reached where only the re-melted resin is recovered and the fibers are milled to supply other lower-grade parts.

McQuilliam adds that often, different technical advances may end up competing with one another, but in this case, he believes the P2T process complements other current carbon-fiber manufacturing developments in the industry, such as Tailored Fiber Placement (TFP), which is being adopted by many leading composite producers. “TFP uses fewer fibers from the outset by placing them more optimally than in a simple weave pattern, but it still needs an effective recycling process. We can provide that,” he asserted.

The P2T process currently is operating at pilot scale, but McQuilliam is confident that new applications could be introduced to series production within twelve months: “End-of-life recycling is a hot topic throughout the composites world, affecting several industries. In marine circles for example, old glass fiber boats have so little residual value they are often broken up and sent to landfill. In the future, environmental legislation will mandate a more considered approach across all industries,” he said. Continue reading »