High tenacity carbon fibers

Carbon and Graphite Fibers. Carbon and graphite fibers (qv) are valued for their unique combination of extremely high modulus and very low specific gravity. Acrylic precursors are made by standard spinning conditions, except that increased stretch orientation is required to produce precursors with higher tenacity and modulus. The first commercially feasible process was developed at the Royal Aircraft Fstablishment (RAF) in collaboration with the acrylic fiber producer, Courtaulds (88). In the RAF process the acrylic precursor is converted to carbon fiber in a two-step process. The use of PAN as a carbon fiber precursor has been reviewed (89,90). 

Chemically Resistant Fibers. Fibers with exceUent chemical resistance to corrosive and/or chemical warfare agents or extreme pH conditions (eg, very acidic or very alkaline) were initially used for protective clothing. However, appHcations for filtration of gases and Hquids in numerous industrial faciHties are now the more important. For example, PPS is suitable for use in filter fabrics for coal-fired boilers because of its outstanding chemical and heat resistance to acidic flue gases and its exceUent durabUity under these end use conditions. Many high tenacity fibers are also chemically inert or relatively unaffected under a variety of conditions. Aramids, gel spun polyethylene, polypropylene, fluorocarbon, and carbon fibers meet these criteria and have been used or are being considered for appHcations where chemical resistance is important. 

Pyrolysis analogous to polymer carbon formation has also been applied to methylchlorodisilane. This is converted to beta silicon carbide fibers of high tenacity. 

Figure 6.10 Effect of hydrogen chloride vapor on weight loss during pyrolysis of continuous filament high tenacity rayon fiber from Teijin Co. Source Adapted from Shindo A, Nakanishi Y, Soma I, Carbon Fibers from Cellulose Fibers, AppI Polym Symposia, No 9, 271-284, 1969.

From Figure 8.1 [6] it can be seen that in terms of modulus and tenacity (i.e., the tensile strength divided by the linear density) only the more expensive carbon fibers and some even more expensive, relatively new experimental heat-resistant fibers outperform the p-aramides. It is noteworthy that the oriented fibers of ultra-high molecular weight polyethylene (UHMWPE), e.g., Dyneema , a product of DSM, The Netherlands, display tenacities and moduli in the same range as most p-aramids, however without having their excellent thermal and flame-resistance, as well as insolubility in most organic solvents. 

Carbon fibers are used almost exclusively in composites. Two main types are offered one with high strength (1.9-3.9 N tex tenacity, 140 N tex modulus) and one with a high-modulus (2.2 N tex tenacity, 280 N tex modulus). Carbon fiber moduli are much higher than those of aramid and gel-spun polyethylene. 

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