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Carbon Nanofibers and Tubes
The high cost of the carbon based products (at least 1,000 times that of a conventional filler) means that, even allowing for efficiency improvements and scale reduction as they become more mature, they are only going to be of interest in specialist applications, where cost is not a major factor. As such they will only be briefly discussed here. More details can be found in Iqbal and Goyal (2010).
Conventional carbon fibers are well established as polymer reinforcements. They are produced by heat treatment or controlled pyrolysis of various polymer fiber precursors and have micron sized diameters, outside of the nano range. Vapor growth processes allow much finer fibers with nanosized diameters to be produced.
These are produced by similar vapor growth methods to those used for nanofibers, but the particles are hollow hence the name tubes. The tube walls are composed of rolled up graphene sheets and can exist in two forms, single or multi-walled, and the tubes are closed at the ends.
Two important issues are affecting the development of composite applications. The first is cost and the second is effective dispersion into a polymer matrix. As a result there is little commercialization today, but progress is being continually made and both nanofibers and tubes are expected to play an important role in advanced composites.
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