With its combination of lightness and strength, carbon fiber is being used in a growing range of aerospace and automotive applications. Unfortunately, the weave isn't easily recyclable, unlike more traditional steel or aluminum. A team at Georgia Tech is trying to change that, using a new method to recycle the materials in thermoset carbon fiber.
In spite of all its benefits, carbon fiber is a tricky material to deal with when it's reached the end of its life. Steel and aluminum can be recycled, but the valuable carbon strands locked away in pieces of thermoformed carbon fiber are difficult to get to.
Because the polymer matrix used to hold the carbon fibers is usually crosslinked, it can't simply be melted down or stripped away. That means a lot of carbon fiber pieces are thrown away, which is both an expensive waste and bad for the environment.
The Georgia Tech team focused on a specific type of carbon fiber which gets its shape from vitrimer epoxy. A piece of the material is soaked in alcohol, which slowly dissolves the epoxy binding the carbon strands together. Once the process is complete, the fibers and epoxy can simply be separated and used in new applications.
"Vitrimers contain dynamic bonds that can alternate their structure without losing network integrity under certain conditions," says Kai Yu, postdoctoral researcher in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. "We let alcohol, which has small molecules, to participate in the network of alternating reactions, which effectively dissolved the vitrimer."
Yu also says the simple process is easily scaled up, saying "it's very easy to operate, so there's no limit to the size."
The team says that should the process be adopted, it has the potential to drastically cut the amount of carbon fiber waste produced each year. It certainly looks simpler than the system being used by bike manufacturer Trek, which began a carbon fiber recycling program in 2011 and involves cutting waste material into squares and then heating them in an almost oxygen-free environment to free up the fibers.
The findings are published in the journal Advanced Functional Materials.
Source: Georgia Tech