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Carbon Nanotubes Make Aerospace Composites Conductive

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We have all been witness to the proliferation of carbon fiber adding lightweight strength to sporting goods like bicycles and tennis racquets. That application of carbon fiber reinforced polymers (CFRPs) has been no more popular than in the aerospace industry, where every gram counts. 

What many of us may not have understood about CFRPs is something called “polymer sizing.” This is a coating that is applied to the surface of the carbon fibers to make them easier to handle and to improve the adhesion between the fibers and the polymer matrix in which they’re embedded.

Now researchers at the University of Surrey’s Advanced Technology Institute (ATI), the University of Bristol’s Advanced Composite Centre for Innovation and Science (ACCIS), and aerospace company Bombardier have collaborated on the development of a carbon nanotube–enabled material set to replace the polymer sizing.  The reinforced polymers produced with this new material have enhanced electrical and thermal conductivity, opening up new functional possibilities. It will be possible, say the British researchers, to embed gadgets such as sensors and energy harvesters directly into the material.

In research described in the journal Scientific Reports, the researchers were able to grow the carbon nanotubes (CNTs) on the carbon fibers in a chemical vapor deposition (CVD) process.

Professor Ravi Silva, Director of ATI and head of the University of Surrey’s Nanoelectronics Centre (NEC), told IEEE Spectrum: 

We addressed a current challenge with chemical vapor deposition–grown carbon nanotubes on carbon fiber, by utilizing a metallic interlayer, which we have shown in previous work by our group to minimize degradation to the underlying substrate…The low temperature photo-thermal CVD (PT-CVD) growth process we have adopted is highly suited for large area, high quality carbon nanotube growth on temperature sensitive substrates. This means that the substrates do not degrade in the growth of CNT.

While this work does not represent the first time carbon nanotubes have been incorporated into polymer composites, this work does stake claim to being the first to replace polymer sizing.

Silva notes that, even without a polymer sizing layer, the nanotubes improved the mechanical integrity of the carbon fiber fabric. This was remarkable, he says, because carbon fibers without sizing are inherently difficult to manipulate and make process of incorporating them into a composite difficult.

Silva also pointed out that the incorporation of nanotubes within the carbon fiber polymers did not result in high void fractions, and therefore maintained the sheets’ mechanical integrity.

What’s more, the carbon nanotube–modified fiber composites could have electronic gadgets baked right into their structures or be endowed  with self-healing capabilities.

The collaborators in this research, who have jointly protected the intellectual property, say the next challenge for them is to scale the technology for production using a roll-to-roll system.

Silva added: “We have in mind the optimization of growth of CNTs for composite applications, the scale up of the technology and the optimization for the various applications. We are looking to progress the technology in a number of different fields and will be happy to work with partners in agreed fields of research.”



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