Carbon-Nanotube Films: Developments in Manufacturing and Applications August 2015
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In May 2015, researchers from North Carolina State University and the Suzhou Institute of Nano-Tech and Nano-Biotics published their research into novel techniques that enable the preparation of meter-wide arrays of aligned carbon nanotubes (CNTs). The "microcombing" method passes a CNT ribbon between two surgical blades that contain micrometer-scale fissures. These fissures separate and align the individual nanotubes—much as an ordinary comb would. Lightweight films of these aligned CNTs exhibit a tensile strength twice that of an uncombed film (3 gigapascals versus 1.5 gigapascals). The electrical conductivity of the microcombed film is also 80% higher than that of the uncombed film. The researchers state that the technique would be "easy to scale up for large-scale production" and that they are looking for an industrial partner to aid commercialization efforts.
In April 2015, Metis Design Corporation—a spin-out company from the Massachusetts Institute of Technology—published the results of its research into the application of aligned CNT films for out-of-oven laminate-curing processes in the aviation industry. Current processes require autoclaves that are inefficient at delivering heat. Applying a current to a CNT film provides a controllable and efficient source of heat that cures polymers without the need for bulky and expensive ovens. Metis Design claims that its technique provides more uniform properties and can reduce energy use by a factor of 1,000—which could, in turn, reduce "composite acquisition costs by up to 50%." The researchers are now collaborating with industrial partners on scaling up their materials.
A previous Explorer article discusses the use of vertically aligned nanotube arrays—the world's "blackest material"—for optoelectronic-imaging applications. The manufacturing applications that this article highlights have the potential to result in significant energy savings in the aerospace industry. The Metis Design system replaces the need for bulky manufacturing infrastructure. The removal of the geometric constraints dictated by autoclave size and the applicability to a wide range of curable polymers could also provide more freedom of design. However, the Metis Design curing device is in the very early stages of development—covering square centimeters rather than square meters—and, as a result of stringent safety regulations, the aviation sector is notoriously conservative in implementing innovative materials or procedures. The specific advantages of CNT films over other microheaters that do not require such significant levels of development are also unclear.
CNT films for resistive heating and curing applications could exhibit broad applicability across a wide range of manufacturing processes. Such CNT films could potentially also find use—beyond manufacturing—in the electronics industry or in commercial applications such as heated seats in automobiles, deicing or anticondensation mechanisms, or even heated clothing for extreme weather conditions. Across all industries, even small, incremental improvements in energy and cost efficiency—which can scale to significant overall gains—are desirable.