Nanomaterial scientists have developed a simple process that uses graphene and carbon nanotubes to both strengthen and provide electrical conductivity to new composite materials. The discovery has a wide-range of applications, especially in the manufacture of electronics, and is likely to attract the attention of raw material developers and epoxy producers everywhere.
As the research team from Rice University and Beihang Universitymake clear in their findings, published in the journal ACS Nano, there are many limitations with many current technology. “Conductive epoxy composites are of great interest due to their applications in electronics. They are usually made by mixing powdered conductive fillers with epoxy. However, the conductivity of the composite is limited by the low filler content because increasing filler content causes processing difficulties and reduces the mechanical properties of the epoxy host.”
Additionally, when manufacturers add fillers of metal or carbon to make epoxies electrically conductive, they also compromise toughness and durability, complicate the production process, and add weight.
The use of graphene and carbon nanotubes as a raw material solves these problems.
Previous research has involved injecting epoxy resin into 3-D scaffolds such as graphene aerogels and foams. This inspired Principle Investigator, Prof. James Tour, together with Rice materials scientists Pulickel Ajayan, Rouzbeh Shahsavari and Jun Lou and Yan Zhao of Beihang University in Beijing, to create a new epoxy with graphene and carbon nanotubes feedstock.
The result was a much-improved conductive composite that requires a relatively simple four step production process.
As the online scientific journal Phys.org, explains, “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 structure."
The use of graphene in the foam gave the composite a seven-fold increase in compressive strength with only a minute increase in weight. This is due to the marginal increase in density the foam has, even though it makes up only 32% of the new material.
The epoxy maintained an electrical conductivity of about 14 Siemens (a measure of conductivity, or inverse ohms) per centimetre, which will aid its use in the manufacture of electrical equipment.
However, the team further developed the epoxy by adding carbon nanotubes to giving even greater strength and conductivity. As the industry journal Manufacturing.net, reports, “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 centimetre, far greater than nearly all of the scaffold-based epoxy composites reported to date.”
The next step in the discovery is to evaluate the costs and practicalities of using the process in manufacturing. However, Tour is confident that the procedure is upscalable, stating that, “One just needs a furnace large enough to produce the ultimate part. But that is done all the time to make large metal parts by cold-pressing and then heating them.”
Like many other nanotube materials, the improved properties of the composite over earlier epoxies gives this new raw material a great many potential uses. It could replace current carbon-composite resins, be used to pre-impregnate or reinforce fabric, has possible uses in the space, automobile, and aviation industries, or could be used in high-performance products such as sports equipment.
With industrial manufacturers and raw material suppliers constantly adapting carbon nanotubes and graphene for ever more diverse uses, raw material sourcing has never been so small.
Photo credit: Phys.org, Manufacturing.net, ACSNano, & Hollandshielding