Page 62 - Plastics News May 2018

teChnoLogy

Scientists make strong, super-tough carbon sheets at low temperature

n international research "The trick we use is to stitch together the platelets in
Ateam led by scientists at these sheets using sequentially infiltrated bridging agents
Beihang University in China and that interconnect overlapping neighboring platelets, and
The University of Texas at Dallas convert the oxidized graphene oxide to graphene. The
has developed high-strength, key to this advance is that our bridging agents separately
super-tough sheets of carbon act via formation of covalent chemical bonds and van der
that can be inexpensively Waals bonds." Sheets that incorporated the bridging agents
fabricated at low temperatures. were 4.5 times stronger and 7.9 times tougher than agent-
The team made the sheets by free sheets, said Beihang University PhD student Sijie Wan,
chemically stitching together who is a lead author of the journal article. "Unlike carbon
platelets of graphitic carbon, fiber composites, no polymer matrix is needed," he said.
which is similar to the graphite found in the soft lead of "While sheets of expensive carbon fiber composites can
an ordinary pencil. The fabrication process resulted in a provide a similar strength in all sheet-plane directions,
material whose mechanical properties exceed those of the energy that they can absorb before fracture is about
carbon fiber composites that are currently used in diverse one-third that of our sequentially bridged graphene
commercial products. "These sheets might eventually sheets," Wan said. "Because our sheets are fabricated
replace the expensive carbon fiber composites that at low temperatures, they are low cost. In addition to
are used for everything from aircraft and automobile exhibiting high sheet strength, toughness and fatigue
bodies to windmill blades and sports equipment," said resistance, they have high electrical conductivity and are
Dr. Ray Baughman, the Robert A. Welch Distinguished able to shield against electromagnetic radiation. These
Chair in Chemistry at UT Dallas and director of the properties make these sequentially bridged graphene
Alan G. MacDiarmid NanoTech Institute. Baughman is sheets quite attractive for possible future applications."
a corresponding author of an article describing the Other team members from the NanoTech Institute at UT
material published online this week in the Proceedings Dallas are: Dr. Ali Aliev, and Dr. Shaoli Fang, both research
of the National Academy of Sciences.Today's carbon fiber professors; and Dr. Jiuke Mu, co-first author of the
composites are expensive in part because the carbon study and a postdoctoral researcher. Additional Beihang
fibers are produced at extremely high temperatures, University members are: Dr. Lei Jiang, an academician of
which can exceed 2,500 degrees Celsius (about 4,500 the Chinese Academy of Sciences and a foreign member of
degrees Fahrenheit)."In contrast, our process can the U.S. National Academy of Engineering; and Yuchen Li,
use graphite that is cheaply dug from the ground and
processed at temperatures below 45 degrees Celsius (113
degrees Fahrenheit)," said Dr. Qunfeng Cheng, professor
of chemistry at Beihang University and a corresponding
author. "The strengths of these sheets in all in-plane
directions match that of plied carbon fiber composites,
and they can absorb much higher mechanical energy
before failing than carbon fiber composites. Instead of
mechanically stacking large-area graphene sheets, we
oxidize micron-size graphite platelets so that they can
be dispersed in water, and then filter this dispersion to
inexpensively make sheets of oriented graphene oxide,"
Baughman said. "This process is akin to hand-making sheets an undergraduate student who is also a co-first author of
of paper by filtering a slurry of fibers. "At this stage, the study. Dr. Nicholas Kotov, the Joseph B. and Florence V.
the sheets are neither strong nor tough, meaning they Cejka Professor of Chemical Engineering at the University
cannot absorb much energy before rupturing," he said.
of Michigan in Ann Arbor, also contributed.

Plastics News May 2018 62