Epoxy compound gets a graphene bump
November 16, 2018
combined with “ultrastiff” graphene foam invented in the Rice lab of
chemist James Tour is substantially tougher than pure epoxy and far more
conductive than other epoxy composites while retaining the material’s
low density. It could improve upon epoxies in current use that weaken
the material’s structure with the addition of conductive fillers.
The new material is detailed in the American Chemical Society journal
By itself, epoxy is an insulator, and is commonly used in coatings,
adhesives, electronics, industrial tooling and structural composites.
Metal or carbon fillers are often added for applications where
conductivity is desired, like electromagnetic shielding.
Researchers have created an epoxy-graphene
foam compound that is tough and conductive without adding significant
weight. Courtesy of the Rouzbeh Shahsavari Group
But there’s a trade-off: More filler
brings better conductivity at the cost of weight and compressive
strength, and the composite becomes harder to process.
The Rice solution replaces metal or carbon powders with a
three-dimensional foam made of nanoscale sheets of graphene, the
atom-thick form of carbon.
The Tour lab, in collaboration with Rice materials scientists Pulickel
Ajayan, Rouzbeh Shahsavari and Jun Lou and Yan Zhao of Beihang
University in Beijing, took their inspiration from projects to inject
epoxy into 3D scaffolds including graphene aerogels, foams and skeletons
from various processes.
The new scheme makes much stronger scaffolds from polyacrylonitrile
(PAN), a powdered polymer resin they use as a source of carbon, mixed
with nickel powder. In the four-step process, they cold-press the
materials to make them dense, heat them in a furnace to turn the PAN
into graphene, chemically treat the resulting material to remove the
nickel and use a vacuum to pull the epoxy into the now-porous material.
“The graphene foam is a single piece of few-layer graphene,” Tour said.
“Therefore, in reality, the entire foam is one large molecule. When the
epoxy infiltrates the foam and then hardens, any bending in the epoxy in
one place will stress the monolith at many other locations due to the
embedded graphene scaffolding. This ultimately stiffens the entire
The puck-shaped composites with 32 percent foam were marginally denser,
but had an electrical conductivity of about 14 Siemens (a measure of
conductivity, or inverse ohms) per centimeter, according to the
researchers. The foam did not add significant weight to the compound,
but gave it seven times the compressive strength of pure epoxy.
Easy interlocking between the graphene and epoxy helped stabilize the
structure of the graphene as well. “When the epoxy infiltrates the
graphene foam and then hardens, the epoxy is captured in micron-sized
domains of the graphene foam,” Tour said.
The lab upped the ante by mixing multiwalled carbon nanotubes into the
graphene foam. The nanotubes acted as reinforcement bars that bonded
with the graphene and made the composite 1,732 percent stiffer than pure
epoxy and nearly three times as conductive, at about 41 Siemens per
centimeter, far greater than nearly all of the scaffold-based epoxy
composites reported to date, according to the researchers.
Scientists at Rice led the effort to develop the material that, when
combined with carbon nanotubes, is more than 1,700 percent stiffer than
pure epoxy. Courtesy of the Rouzbeh Shahsavari Group
Tour expects the process will scale for industry. “One just needs a
furnace large enough to produce the ultimate part,” he said. “But that
is done all the time to make large metal parts by cold-pressing and then
He said the material could initially replace the carbon-composite resins
used to pre-impregnate and reinforce fabric used in materials from
aerospace structures to tennis rackets.
Rice student Xiao Han, a graduate student at Beihang University, and
Rice graduate student Tuo Wang are co-lead authors of the paper.
Co-authors are Rice alumni Peter Samora Owuor and Jongwon Yoon, graduate
student Sung Hoon Hwang, visiting scholars Chao Wang and Lulu Shen, and
postdoctoral researchers Weipeng Wang and Rodrigo Villegas Salvatierra;
and Junwei Sha of Tianjin University, China.
Ajayan is chair of Rice’s Department of Materials Science and
NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor
in Engineering and a professor of chemistry. Shahsavari is an assistant
professor of civil and environmental engineering and of materials
science and nanoengineering. Lou is a professor of materials science and
nanoengineering. Zhao is a professor at Beihang University. Tour is the
T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer
science and of materials science and nanoengineering at Rice.
The Air Force Office of Scientific Research and the China Scholarship
Council supported the research.