Recycling materials, such as plastics and metals, is an attractive, but challenging path toward sustainable material manufacture. Now, researchers have made a discovery that may have far-reaching implications in material manufacture by positioning carbon nanotube (CNT) fibers as a sustainable alternative to metals, polymers and much larger carbon fibers.
Researchers at Rice University (Houston, Tex.; www.rice.edu) have demonstrated that CNT fibers can be recycled without structural or property losses, and more readily than some more-difficult-to-recycle materials.
“Recycling has long been a challenge in the materials industry — metals recycling is often inefficient and energy intensive, polymers tend to lose their properties after reprocessing and carbon fibers cannot be recycled at all, only downcycled by chopping them up into short pieces,” said Matteo Pasquali, director of Rice’s Carbon Hub (carbonhub.rice.edu) and the A.J. Hartsook Professor of Chemical and Biomolecular Engineering, Materials Science and NanoEngineering and Chemistry. “We expected that recycling would be difficult and would lead to significant loss of properties. Surprisingly, we found that carbon nanotube fibers far exceed the recyclability potential of existing engineered materials, offering a solution to a major environmental issue.”
In this research, solution-spun CNT fibers were created by dissolving fiber-grade commercial CNTs in chlorosulfonic acid. To simulate recycling of a variety of materials, fibers made from different types of CNTs produced by different manufacturers were initially processed into separate single-source virgin fibers, then recycled by combining them and mixing in chlorosulfonic acid. Surprisingly, mixing the two fibers led to complete redissolution and no sign of separation of the two source materials into different liquid phases. This redissolved material was spun into a mixed-source recycled fiber that retained the same structure and alignment of the virgin fiber. Some materials degrade in quality during recycling, but the CNT fibers retained 100% of their original properties after recycling.
“The ability to fully recycle CNT fibers has broad implications for industries like aerospace, automotive and electronics,” said Michelle Durán-Chaves, a graduate student in chemistry. “We hope this could pave the way for fully recyclable composites in aircraft, vehicles, civil infrastructures and more, ultimately reducing environmental impacts across a wide range of sectors.”
This research is part of the broader program of the Carbon Hub, a Rice-led initiative developing a zero-emissions future, where advanced carbon materials and clean hydrogen are co-produced efficiently and sustainably from hydrocarbons. The work was published in the journal Carbon, and was supported by the Department of Energy’s Advanced Research Project Agency, the Air Force Office of Scientific Research, the Robert A. Welch Foundation, the National Science Foundation, the Novo Nordisk Foundation CO2 Research Center, the Ken Kennedy Institute Graduate Fellowship from Schlumberger and Rice and a Riki Kobayashi Fellowship from Rice’s chemical and biomolecular engineering department.