Carbon Nanotubes Used to Heat and Cure Composite Materials

New technique uses carbon nanotube film to directly heat and cure composite materials removing the need for expensive curing ovens.

Composite materials used in aircraft wings and fuselages are typically manufactured in large, industrial-sized ovens: Multiple polymer layers are blasted with temperatures up to 750 degrees Fahrenheit, and solidified to form a solid, resilient material. Using this approach uses a large amount of energy to heat the oven, the gas around it and finally the actual composite.

Engineers at MIT have now developed a carbon nanotube (CNT) film that can heat and solidify a composite without the need for massive ovens. When connected to an electrical power source, and wrapped over a multilayer polymer composite, the heated film stimulates the polymer to solidify.

The group tested the film on a common carbon fibre material used in aircraft components, and found that the film created a composite as strong as that manufactured in conventional ovens — while using only 1% of the energy.

Brian L. Wardle, an associate professor of aeronautics and astronautics at MIT said;

Typically, if you’re going to cook a fuselage for an Airbus A350 or Boeing 787, you’ve got about a four-story oven that’s tens of millions of dollars in infrastructure that you don’t need. Our technique puts the heat where it is needed, in direct contact with the part being assembled. Think of it as a self-heating pizza. … Instead of an oven, you just plug the pizza into the wall and it cooks itself.

The carbon nanotube film is also incredibly lightweight: After it has fused the underlying polymer layers, the film itself — a fraction of a human hair’s diameter — meshes with the composite, adding negligible weight. The team, including MIT graduate students Jeonyoon Lee and Itai Stein and Seth Kessler of the Metis Design Corporation, has published its results in the journal ACS Applied Materials and Interfaces.

Wardle and his colleagues have experimented with CNT films in recent years, mainly for deicing airplane wings. The team recognised that in addition to their negligible weight, carbon nanotubes heat efficiently when exposed to an electric current.

The research team first developed a technique to create a film of aligned carbon nanotubes composed of tiny tubes of crystalline carbon, standing upright like trees in a forest. The researchers used a rod to roll the “forest” flat, creating a dense film of aligned carbon nanotubes. In experiments, they integrated the film into airplane wings via conventional, oven-based curing methods, showing that when voltage was applied, the film generated heat, preventing ice from forming.

So how hot can you go? In initial experiments, the researchers investigated the film’s potential to fuse two types of aerospace-grade composite typically used in aircraft wings and fuselages. Normally the material, composed of about 16 layers, is solidified, or cross-linked, in a high-temperature industrial oven.

The researchers manufactured a CNT film about the size of a Post-It note, and placed the film over a square of Cycom 5320–1. They connected electrodes to the film, then applied a current to heat both the film and the underlying polymer in the Cycom composite layers.

They then measured the energy required to solidify, or cross-link, the polymer and carbon fibre layers, finding that the CNT film used one-hundredth the electricity required for traditional oven-based methods to cure the composite. Both methods generated composites with similar properties, such as cross-linking density.

The results pushed the group to test the CNT film further: As different composites require different temperatures in order to fuse, the researchers looked to see whether the CNT film could, quite literally, take the heat.

At some point, heaters fry out,, they oxidise, or have different ways in which they fail. What we wanted to see was how hot could this material go.

To do this, they tested the film’s ability to generate higher and higher temperatures, and found it topped out at over 1,000 F. In comparison, some of the highest-temperature aerospace polymers require temperatures up to 750 F in order to solidify.

The team is working with industrial partners to find ways to scale up the technology to manufacture composites large enough to make airplane fuselages and wings. The group’s carbon nanotube film may go toward improving the quality and efficiency of fabrication processes for large composites, such as wings on commercial aircraft. The new technique may also open the door to smaller firms that lack access to large industrial ovens.

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