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Bucky tube is poised to become a fantastic additive for polymer composites

Bucky tube – an arrangement of 60 carbon atoms in the form of a soccer ball, was discovered accidentally in 1985. Bucky tube has incredible properties like high stiffness due to denseness of its atoms and toughness. An unprecedented combination of stiffness and toughness makes bucky tube by far the strongest known fibers in tension – about 100 times stronger than high-strength steel at one-sixth the weight. Many stiff materials are too brittle to be used. Most materials that are not brittle, such as spider silk, can be stretched about 30% beyond resting length, but are not particularly strong
Bucky tube is also the best known conductor of heat, surpassing diamonds. However, unlike bulk diamond, whose thermal conductivity is the same in all directions, bucky tube conducts heat far better down the tube axis than sideways from tube to tube. Thus, a macroscopic crystal of bucky tube where tubes are packed together (running alongside one another in the same direction), the sides with the tube ends would feel cold to the touch like metal, while the other sides would feel like wood - a good thermal insulator. Where bucky tube really performs, however, is in its’ electrical conductivity. The carbon in the planar graphene sheet is bonded in such a way as to free up one electron per carbon atom to wander around freely, rather than stay near its "home" atom.

These material properties render bucky tube to find application in innumerable future technologies. The mechanical (stiffness, strength, toughness), thermal and electrical properties of pure bucky tube materials enable a whole host of applications including batteries, fuel cells, fibers, cables, pharmaceutics and biomedical materials. Several additional applications could be possible when blended with nano tubes.

Metals will always have an upper hand over plastics in electrical conductivity. Plastics are good electrical insulators – an inherent property that gives rise to many of the most widespread and important uses of plastics. Interestingly, if plastics were to become conductive, they have scope to find applications in a broad range of applications. These application areas include: antistatic, electrostatic dissipative and electromagnetic shielding and absorbing materials. Electromagnetic interference and radiofrequency interference (EMI/RFI) shielding is essential in laptop computers, cell phones, pagers and other portable electronic devices to prevent interference with and from other electronic equipment. Currently, metal that is used in this application is added to the electronic equipment cases, imposing substantial weight and manufacturing expense.
Loading of plastics with conductive materials (the most common filler carbon black relatively inexpensive) also provides conductivity. One drawback of carbon black as conductive filler is the high loading required to provide the desired level of conductivity. Conductivity of a filled insulator, such as a polymer increases with filler loading in a classic S-curve. Upto a critical loading, the bulk conductivity changes little, but increases very rapidly upon adding just a bit more filler. This is because high bulk conductivity requires the presence of many long conductive pathways, which are obtained only when the loading is so high that when randomly distributed, the conductive particles are likely to form long chains. This critical loading threshold is actually many times higher than would be required if somehow these particles could be placed in the optimal positions to form long chains with the minimal loading. Large amount of carbon black is wasted in the redundancy required to build up above the threshold level where these long chains form. The critical loading threshold decreases dramatically as the aspect ratio (length to width) of the filler particles increases. This is because longer particles cover a greater distance of the conductive pathway, whereas carbon black, which is spheroidal, has to form a chain of touching particles to cover the distance that fiber-shaped filler would cover by itself.
When a plastic is loaded with carbon black at upto 50% by volume needed to reach the desired bulk conductivity, except for weight savings, the mechanical properties of the composite are severely reduced. Often it is not usable at all, and typically it is no longer mouldable.

Bucky tube offers a solution. First, Bucky tube has excellent electrical conductivity. Second, Bucky tube has a very high aspect ratio. Individual tubes are about 1 nm in diameter (about half the diameter of DNA, and about 1/10,000th the diameter of graphite fibers), and 100-1000 nm in length. Thus, the aspect ratio of buck tubes is around 100-1000, compared with about 1 for carbon black particles. This reduces the critical loading level significantly. Bucky tube self-assembles into “ropes” of tens to hundreds of aligned tubes, running side by side, branching and recombining. When examined by electron microscopy, it is exceedingly difficult to find the end of any of these ropes. Thus, ropes form naturally occurring very long conductive pathways that can be exploited in making electrically conductive filled composites. Initial indications are that dramatically lower loadings of bucky tube are required to reach a given level of conductivity than for any other conductive filler.

The opportunities for conductive plastics, as well as thermosets filled with buckytubes are abundant. Very low loadings (<0.1%) provide for antistatic and electrostatic dissipative applications. One example is in painting automobile body parts, which are increasingly made of plastics. Another area of application for bucky tube-filled plastics is in EMI/RFI shielding, which has uses in portable electronics, and defense applications. If good attenuation of electromagnetic radiation can be attained at bucky tube loadings on the order of 1% or less, good mechanical stability should be maintained, allowing it to be moulded, broadening their uses. Other defense uses of bucky tube composites are similarly significant such as radar-absorbing or modifying material for aircraft and missiles.

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