Precursors for carbon fibers

Fibers. The principal type of phenoHc fiber is the novoloid fiber (98). The term novoloid designates a content of at least 85 wt % of a cross-linked novolak. Novoloid fibers are sold under the trademark Kynol, and Nippon Kynol and American Kynol are exclusive Hcensees. Novoloid fibers are made by acid-cataly2ed cross-linking of melt-spun novolak resin to form a fuUy cross-linked amorphous network. The fibers are infusible and insoluble, and possess physical and chemical properties that distinguish them from other fibers. AppHcations include a variety of flame- and chemical-resistant textiles and papers as weU as composites, gaskets, and friction materials. In addition, they are precursors for carbon fibers. 

Textile fibers, precursor for carbon fibers, food containers... 

Carbon fiber electrode - Edison produced the first carbon fibers by carbonization of cotton threads in 1879. Today polyacrylonitrile (as well as Rayon and various other organic precursors) is the most common precursor for carbon fiber formation [i]. Carbonization of polyacrylonitrile is carried out at 1500 °C to give highly electrically conducting fibers with 5-10 pm diameter. Fibers carbonized at up to 2500 °C are more graphitic with a carbon content of >99%. Carbon fiber-based materials have found many applications due to their exceptionally high tensile strength. In electrochemistry carbon fiber -> micro electrodes are very important in analytical detection [ii] and for in vivo electrochemical studies [iii]. Carbon fiber textiles are employed in - carbon felt electrodes. 

Pitch is a "pseudo solution" of a wide variety of different generic classes of hydrocarbons ranging from paraffins at one extreme to very highly aromatic species at the other. By using the Theory of Solubility for Non-Electrolytes, specific fractions can be isolated from a pitch by properly selecting a solvent system and extraction conditions. "Tailored" precursors for carbon fiber and other carbon products, such as carbon/carbon matrices and bulk graphites, can thus be obtained. The technique of extraction, the characteristics of different precursors, and the structure and properties of carbon fiber and composites made from solvent extracted precursors will be discussed. 

Phenolic fibers based on spun and cured novolac resins are infusible. These fibers possess excellent flame and chemical resistance, and they evolve only low smoke or toxic gases. These materials are useful for fire protection suits, insulating gloves, curtains, clothing for foundry workers, and flame resistant papers and felts. Phenolic fibers are rigid and they carbonize in the flame while retaining their form. Therefore, phenohc fibers are useful precursors for carbon fibers [1],... 

There are also large differences in yields the yield of carbon fibers from rayon is between 20 and 25%, from polyacrylonitrile 45 to 50% and from pitch around 75 to 85 %. The high yield from pitch is a fundamental reason for the great efforts which are being made worldwide to bring about wider use of pitch as a precursor for carbon fibers. 

A detailed review of acryhc precursors for carbon fibers is given by Gupta et al [19], some precursor examples are discussed by Rajalingam and Radhakrishnan [20], whilst Bajaj and Roopanwal present an overview of the thermal stabilization of acrylic precursors for the production of carbon fibers [21]. 

The homopolymer PAN is not an easy product to process into carbon fiber, since the initial oxidation stage of the carbon fiber process is a difficult reaction to control due to the sudden and rapid evolution of heat, coupled with a relatively high initiation temperature. This rapid surge of heat can cause chain scission with resultant poor carbon fiber properties. As far as is known, homopolymer PAN has never been exploited as a precursor for carbon fiber manufacture. The exothermic reaction can, however, be adequately controlled by suitable comonomers such as itaconic acid. 

PRECURSORS FOR CARBON FIBER MANUFACTURE AN comonomers + water... 

As continuous fiber is required for use as a precursor for carbon fiber, the additional details for making staple fiber are not considered. The precise technical information for such processes is commercially sensitive and will vary from one firm to another. It is noteworthy that recent technology uses the solubility of cellulose in a 4-methylmorpholine-A-oxide/water mix (VINCEL, LYOCELL in the USA). An outline of a typical viscose process is shown in Figure 4.16. 

Petroleum bitumens have been investigated as precursors for carbon fibers [187,188]. The properties of typical petroleum pitches are given in Table 4.10. 

Gupta AK, Paliwal DK, Bajaj P, Acrylic precursors for carbon fibers, J Macromol Sci Rev Macromol Chem Phys, C31(l), 1-89, 1991. 

A copolymer must have acrylonitrile content greater than 85%, preferably 90-95%. To the author s knowledge, no commercial exploitation has been made of homopolymer PAN as a precursor for carbon fiber manufacture. 

Kiminta [63] investigated the rapid stabilization of acrylic precursors for carbon fibers using NH3. 

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