Commercial applications continuous fibers

Because of their unique blend of properties, composites reinforced with high performance carbon fibers find use in many structural applications. However, it is possible to produce carbon fibers with very different properties, depending on the precursor used and processing conditions employed. Commercially, continuous high performance carbon fibers currently are formed from two precursor fibers, polyacrylonitrile (PAN) and mesophase pitch. The PAN-based carbon fiber dominates the ultra-high strength, high temperature fiber market (and represents about 90% of the total carbon fiber production), while the mesophase pitch fibers can achieve stiffnesses and thermal conductivities unsurpassed by any other continuous fiber. This chapter compares the processes, structures, and properties of these two classes of fibers. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

The configuration of a CVD system may adopt numerous forms depending on the particular application. For example, continuous fiber-coating systems are inappropriate to the demands of the microelectronics device field, yet each relies on indispensable CVD steps for major commercial success. The overall CVD system can be segmented into three general components reactant input, reaction zone, and the reaction coproduct removal system. 

Carbon fibers continue to be the main reinforcement materials in advanced composites (qv). The ability to manipulate their physical, chemical, electrical, and thermal properties makes carbon fibers suitable across a wide range of commercial applications, including military [aircraft and missiles (1)], structural [concrete reinforcement (2,3) and automobile body panels], sports equipment (golf... 

The first carbonization of cellulose-based fibers dates back to Thomas Edison, who carbonized a natural cellulose filament for use as an incandescent lamp filament. In the mid-1950s, the Carbon Wool Corporation introduced the first commercial carbonized rayon fibers (79). PAN- and pitch-based carbon fibers have replaced rayon-based fibers in most high performance applications however, they continue to find use as ablative materials in missile nosecones and heat shielding (16). Additionally, the combination of low cost, ease of handling, and high natural porosity makes rayon an attractive precursor for activated carbon fibers (see CELLULOSE Fibers, Regenerated). 

Despite the continned commercial dominance of pitch- and PAN-based fibers, the carbon fiber field is continuously changing. Significant cnrrent research is focused on the production of carbon nanotnbes. Other researchers continue to enhance the nnderstanding of the processes and mechanisms governing the fiber production today. As researchers are better able to imderstand and manipulate fiber microstructures, the commercial applications for carbon fibers will continue to expand. 

The industrial challenge ahead will be to define and develop applications which take advantage of the unique properties of aromatic thermotropic polyesters. Already, commercial demand is growing in the fiber optic, chemical process, electrical/electronic, automotive and houseware markets, and new areas of potential application continue to emerge. 

French, J.D., Weitz, G.E., Luke, J.E., Cass, R.B., Jadidian, B., Bhargava, P., Safari, A., 1997. Production of continuous piezoelectric ceramic fibers for smart materials and active control devices. In Paper Presented to the Proceedings of the SPIE 3044, Smart Structures and Materials 1997 Industrial and Commercial Applications of Smart Structures Technologies, May 23, 1997. 

The most widely used and least expensive polymer resins are the polyesters and vinyl esters. These matrix materials are used primarily for glass fiber-reinforced composites. A large number of resin formulations provide a wide range of properties for these polymers. The epoxies are more expensive and, in addition to commercial applications, are also used extensively in PMCs for aerospace applications they have better mechanical properties and resistance to moisture than the polyesters and vinyl resins. For high-temperature applications, polyimide resins are employed their continuous-use, upper-temperature limit is approximately 230°C (450 F). Finally, high-temperature thermoplastic resins offer the potential to be used in future aerospace applications such materials include polyetheretherketone (PEEK), poly(phenylene sulfide) (PPS), and polyetherimide (PEI). 

Initial applications of molecular composites are expected to be in the aerospace area. Matrix materials based on molecular composites which are reinforced with carbon fiber are expected to be a key area of interest. The use of a molecular composite as a matrix for advanced composites should provide a significant increase in the modulus and strength over that obtainable with conventional thermoplastics and thermosets. Electronic applications are another area where molecular composite commercialization should continue to emerge. 

The facile formation of ceramic materials from molecules has undoubtedly been one of the si ificant contributions made by chemistry to materials science (7). However, it is desirable not only to produce the ceramic per se but also to do so in a specific form, for example a fiber. Therefore, one of the key requirements for any ceramic precursor should be its processability. For this reason, there has been continued research effort aimed at the design of precursors with physical properties suitable for processing prior to pyrolysis. Two examples with sigr cant commercial application are polyacrylonitrile and polyorganosilanes, both of which may be spun into fibers, and upon pyrolysis allow for the manufacture of carbon-graphite (2) and silicon carbide (5) fibers, respectively. Despite much effort, the extension of this polymer-type precursor strategy to other ceramic systems has only met with limited success. 

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