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Pyrograf®-III Carbon Nanofiber
Pyrograf®-III is a patented, very fine, highly graphitic, low cost, tubular carbon nanofiber. Pyrograf®-III is available in two types of fiber with diameters ranging from 70 and 200 nanometers and a length of the as-produced fiber estimated to be 50-200 microns. Therefore, nanofibers are much smaller in diameter than conventional continuous or milled carbon fibers (5-10 microns) but significantly larger than carbon nanotubes (1-10 nanometers). Pyrograf®-III nanofiber is currently offered in two types and in the three grades shown below. The nanofiber is also available in several product forms; powder-like (i.e. debulked), paper, pre-dispersed, and compounded product forms.
|Pyrolytically stripped carbon nanofiber. (Removes polyaromatic hydrocarbons from fiber surface).|
|Carbon nanofiber heat-treated to temperatures of 1500°C, which carbonizes chemically vapor deposited carbon present on the surface of Pyrograf®. This heat treatment produces nanofibers which generally provides the highest electrical conductivity in nanocomposites.|
|Carbon nanofiber heat-treated to temperatures up to 3000°C, which graphitizes chemically vapor deposited carbon present on the surface of Pyrograf®. This high heat treatment creates the most graphitic carbon nanofiber and reduces the iron catalyst content to very low levels.|
PR-19 has an average diameter of about 150 nanometers and has a chemically vapor deposited (CVD) layer of carbon on the surface of the fiber over a graphitic tubular core fiber (catalytic layer) as shown in Figure 1. PR-24 has an average diameter of about 100 nanometers and has a minimal CVD carbon overcoat. Because the fibers are produced in a vapor phase, they generally become entangled during growth, producing a mesh-like configuration. This raw form is then debulked to provide the customer with a product that is uniform in bulk density allowing accurate compounding into final products. Pyrograf®-III is currently available in a debulked form designated as XT. This form has a bulk density of 1-3 lb/ft3.
The micrographs in Figure 2 and Figure 3 represent magnified views of the Pyrograf®-III carbon nanofiber in its final debulked product form. The upper image shows the tight bundles of nanofiber typical of the debulked product that has been produced for many years. This type can be difficult to disperse without damaging the nanofiber. The lower image shows the product form processed with an improved debulking method (designated as XT in the product code) that creates loose structures of the carbon nanofiber bundle. The loose bundle of the “XT” carbon nanofiber requires much less energy to achieve dispersion, thus allowing greater retention of fiber length during processing. The new product has been shown to generate the same electrical conductivity in polymer composites at approximately half the loading of the non-XT nanofiber.
Pyrograf®-III can simultaneously provide enhanced electrical conductivity over a broad range along with mechanical reinforcement of certain matrix materials. Other benefits provided by the nanofiber include improved heat distortion temperatures and increased electromagnetic shielding.