Carbon Nanotubes Reinforce Adhesive

We have reported on how engineers are using carbon nanotubes (CNTs) for everything from designing thermoelectric fabric to developing fault-detecting paint. One of the latest applications of CNTs is as reinforcement of a high-strength adhesive for structural components.

Applied Nanotech has unviled its CNTstix, a two-part epoxy adhesive reinforced with carbon nanotubes. It is aimed at marine, automotive, aerospace, industrial automation, and biomedical equipment applications, especially the repair of carbon or glass composite materials. The adhesive is based on the company's CNT Epoxy, which takes advantage of the mechanical properties of CNTs "while reducing the weight of materials needed for a specified application."

The company used proprietary techniques to disperse CNTs uniformly throughout the new substance "to create significant improvements in strength, toughness, durability, vibration damping and other mechanical properties." Uniform CNT dispersion is difficult to achieve, because van der Waals forces generated by their high surface energy cause the nanotubes to bunch together in ropes or bundles.

Typically, sonication, high shear mixing, stirring, and surfactants have been used in the lab to achieve uniform dispersion, but these techniques are usually not practical in large-scale industrial manufacturing. Applied Nanotech uses a microfluidic processor that generates high shear forces to break up CNT ropes and bundles in the solvent.

The company's proprietary functionalization technology is also responsible for improvements in flexural strength, compression strength, and modulus. When unidirectional carbon fiber-reinforced prepregs were prepared with the functionalization method, they showed an improvement in flexural strength and flexural modulus.

An Applied Nanotech spokesman said in an email that, when CNTstix was tested for strength ratings, the peel and adhesion shear strength were 60 percent higher than those of a leading manufacturer's adhesive. The Akron Rubber Development Laboratory conducted the testing based on the ASTM C961 standard test for cohesive strength and adhesive bonding.

CNTstix works with any composite, fibrous, carbon fiber, or fiber-reinforced materials in the automotive, military/aerospace, shipbuilding, and packaging industries, the spokesman said. The composite assemblies it is used with are primarily mechanically molded.

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