Whenever Rock West Composites fills an order for carbon fiber fabric or prepregs, they know full well that a certain percentage of that material will end up as waste. That is the nature of carbon fiber fabrication. Thanks to manual layup methods that require laying fabric inside a mold before curing, there is almost always waste involved. It would be nice if that waste could be effectively recycled.
Waste is a big problem throughout the composites industry. Aerospace companies, which are among the most prolific consumers of carbon fiber, generate waste just like the smaller fabricators who purchase from Rock West. And that says nothing of those carbon fiber products that reach end-of-life. They become waste as well.
The big challenge in recycling carbon fiber waste is finding a way to separate the fibers from the polymer they are embedded in. This is easier said than done. Currently, there are three ways to do it: mechanical, chemical, and thermal.
1. Mechanical Recycling
Recycling carbon fiber mechanically is a matter of putting waste materials through a shredder. Like a wood chipper reduces large branches to small chips, a shredder reduces large pieces of carbon fiber waste to much smaller pieces. How small depends on the eventual use of the recycled product.
Mechanical recycling is effective to a certain degree. The rendered material can be utilized in a hot mold-injecting environment. It can also be compressed in sheets that can be used for future manual layups. The one caveat here is that the new parts made from mechanically recycled carbon fiber will not have the same structural integrity as virgin carbon fiber. It cannot be used to make things like jetliner fuselage panels.
2. Chemical Recycling
Applying certain kinds of solvents to carbon fiber waste can separate fibers from polymer by slowly breaking down and dissolving that polymer. The resulting material consists of tiny carbon fibers coated with a residue that must subsequently be cleaned off.
Like mechanical recycling, this method for reclaiming carbon fiber does reduce the structural integrity of those fibers. However, because the fibers have not been altered through mechanical means, they can be realigned somewhat. That makes finished products a bit stronger than those made of mechanically recycled material. They are still not as strong as virgin carbon fiber though.
3. Thermal Recycling
Thermal recycling is the most expensive and damaging way to recycle carbon fiber waste. It involves heating up waste products to temperatures high enough to completely melt the polymer so it can be separated out. It takes almost as much heat energy to do this as it does to cure virgin fibers in epoxy resin.
The resulting fibers have to be cleaned. This adds to the time and expense of recycling. Finished fibers can be combined with virgin fibers, compressed into a fabric or mat, or used in an injection molding process.
Reducing the Cost of Carbon Fiber
The one thing all of these recycling methods have in common is their goal: to reduce the cost of carbon fiber on the open market. The fact is that virgin carbon fiber will always be in demand for those applications that require maximum strength and rigidity. But there are other applications in which strength and rigidity requirements are not as stringent.
Recycled carbon fiber is ideal for those applications because it can be produced at a lower cost. The net effect is more affordable carbon fiber and less waste going into landfills. It sounds like the perfect combination for a world that relies more heavily on composites than ever before.