Carbon-fiber composites can be recycled into new material that is as strong and lightweight as the originals, according to a team of CU-Boulder researchers.
The researchers, in a paper published online in the journal Advanced Materials, say their new process is energy-efficient and cost-effective, thus addressing traditional barriers to carbon-fiber composites’ wider use in manufacturing.
Wei Zhang, CU-Boulder associate professor of chemistry and biochemistry, calls his team’s carbon-fiber composites “unprecedented.”
The Challenge of Recycling Composites
“One of the major challenges facing conventional network polymers and their composites is waste processing and disposal,” Zhang said in an interview with Environmental Leader. “We have shown that polyimines, due to their malleable capability, are reprocessible simply by heating for multiple cycles of recycling. The knowledge gained in this research will shine light in future rational design of novel malleable, recyclable, repairable and responsive functional composite materials, which are highly promising and will significantly ease environmental concerns associated with conventional network polymers.”
Carbon-fiber composites are used in everything from airplanes and cars to personal electronics and fishing poles. The material, however, is generally not recyclable. The glue that binds the fiber in most carbon-fiber composites can be broken down with expensive, energy-intensive processes that may yield toxic waste. Carbon-fiber composites can also be crushed into a fine powder, but composites made with short fibers are weak. Because of this, millions of pounds of carbon-fiber composites typically end up in landfills.
The CU-Boulder team found a way to recycle carbon-fiber composites simply requires by soaking the composite in an organic solution at room temperature.
“The resin that holds the composite together can be chemically broken down and separated from the fibers, enabling both the fibers and the resin to be re-used to make more composite materials of the same strength,” explains Philip Taynton, who earned his doctorate in Zhang’s laboratory last year and is the lead author of the paper. Taynton, along with Zhang and CU-Boulder alumnus Chris Kaffer, have also founded a startup working to bring the carbon-fiber composite to market.
“In our research, no extra energy was used in the recycling process (other than mild stirring), and no waste was created by the recycling process,” Taynton says. “It is a closed-loop energy efficient cradle-to-cradle recycling solution.”
Benefits to Manufacturing
Taynton says the recycling process and the material could have major implications for manufacturing. Currently it’s common for as much as 50 percent of composite materials to be discarded as scrap during the manufacturing process. “This means that manufacturers could see a financial benefit to recycling on the front end, in addition to the retention of material value at the end of a product’s service life,” he says.
Additionally, the material is more quickly fabricated than most carbon-fiber composites, which can take an hour to cure. The CU-Boulder team’s composites can be formed in 60 seconds.
“The exchangeable nature of the chemical bonds which enables the facile recyclability also leads to additional benefits for manufacturers,” Taynton says. “Single plies or sheets of our malleable composite material can be chemically welded together through simple compression molding. This leads to 60-second cycle times for the manufacture of discreet parts, which is a target which was set by the automotive industry for rapid manufacturing of composite materials.”
The startup is called Mallinda — a composite of the words “malleable” and “industries.” The university and Mallinda have signed an exclusive licensing agreement.
The company’s first marketing target is sports gear such as shin guards. Taynton says Mallinda has been working with a few branded sporting goods companies and will be scaling up its manufacturing process over the next 12 months.
Potential Medical, Trasportation, Military Applications
In addition to sports gear, Taynton says the company’s first commercial material can be used in medical, transportation and military applications, which can also benefit from customizable, lightweight components that can be molded to enable custom fitting and have high impact tolerance.
Future developments will target higher processing temperatures and higher stiffness materials. “This will enable our material’s manufacturing efficiencies to shine and compete directly with incumbent composite materials, especially for emerging markets such as light-weighting portable electronics,” Taynton says.
While Mallinda is not the only company working on recyclable composites — others include Connora Technologies, Adesso Advanced Materials and IBM — the CU-Boulder team brings something different to the discussion,” says Anthony Vicari, the analyst who leads Lux Research’s advanced materials research.
“This particular group seems to be simultaneously claiming recyclability, high strength, fast curing times, and self-healing properties, which is a combination I have not previously seen,” Vicari says. “If those claims hold up, and if the company can certify its materials for use in the relevant applications, then these materials may be widely applicable.”
But, he adds, certification is a high bar, requiring years of testing, so commercial adoption in regulated industries remains more than a decade in the future: “Given that there are already several small and large companies developing recyclable thermoset materials (and likely more to come), the odds of any one startup capturing a significant share of the market are necessarily low.”
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