Composites Go Green Through Recycling
The ever-increasing use of composites in aerospace has given rise to technological advances not only in aerodynamics but in so-called green disciplines. Engineers have studied different processes for decades, and recycled composites from Boeing 787s have already found their way onto recreational products such as kayak paddles. Ultimately, though, Boeing would like to see the high-tech plastic and carbon fiber scrap produced during the manufacture of airplane parts reused in aerospace applications, explained Bill Carberry, Boeing Commercial Airplanes project manager and strategy leader for sustainable materials, airplane environmental performance and product development.
Boeing’s partners in the project–Materials Innovation Technology of Lake City, South Carolina, and Coseley, UK-based ELG-Carbon Fibre–use a process called pyrolysis, whereby heat removes the resin from shredded raw composite material, rendering what Carberry described as a kind of fluffy fiber.
Carberry explained that physical properties of recycled composites limit their use to nonstructural parts. Only new material–made of virgin carbon fiber–is strong enough for fabrication of flight-critical components.
“In other words, you wouldn’t use this stuff in wings or a new fuselage,” said Carberry. “But we’ve been doing a lot of work in interior parts such as brackets–in what we call metal-to-plastic conversion–flanges and items like that.” Virgin carbon fiber, he said, comes in rolls of single strands “thousands of feet” long, while recycled composites made of much shorter strands must undergo a process of realignment.
“I use an analogy of a box of wooden matches, said Carberry. “If you throw a bunch of wooden matches into a box and you reimpregnate them with glue, you’ve got a lot of glue and very few wooden matches. But if you line up those matches, all the energy of those matches going in one direction gives you a lot less room for glue.
“So our target is to have a high carbon density, that is, a high match density and so we’re working on technologies for alignment.”
All the time and effort will eventually yield environmental benefits and, of course, cost savings.
It takes some 5 percent of the energy to produce the same amount of recycled fiber as virgin fiber, said Carberry. “So you’re reducing your carbon footprint by 95 percent if you can find applications that use recycled carbon fiber,” he concluded.