Carbon Fibers from Phenolic Resins

Micron-sized carbon fibers are synthesized from phenolic resin fibers such as Kynol [27]. The carbon fibers prepared are typically in an activated form, which produces well-developed mesopores for use in applications as high-surface area 

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Liu, C. L., W. S. Dong, G. P. Cao et al. 2008. Some effects of textural properties of carbon fibers from phenolic resins on double-layer capacitance in aprotic electrolyte. Journal of the Electrochemical Society 155 F124-F131. 

Xue, R. et al. 2011. Effect of activation on carbon fibers from phenol formaldehyde resins for electrochemical supercapacitors. Journal of Applied Electrochemistry, 41, 1357-1366. 

Lin, R. Y. and Economy, J., Preparation and properties of activated carbon fibers derived from phenolic resin precursor, Appl. Polym. Symp., 1973, 21, 143 152. 

Oya, A., Yoshida, S., Abe, Y., Iizuka, T. and Makiyama, N., Antibacterial activated carbon fiber derived from phenolic resin containing silver nitrate, Carbon, 1993, 31(1), 71 73. 

The development of ACF and AC cloths is closely related to that of carbon fibers (CFs). This makes that the raw materials used for the preparation of ACFs be, chronologically, the same as for CFs. Thus, in 1966, viscose and acetate cloths were, like for CFs, the first materials used to obtain ACFs [4, 5]. The low yield of the ACFs, and CFs, obtained from the above precursors, oriented the research towards the seek of other raw materials for the preparation of cheaper CFs and ACFs with a higher yield. In this way, ACFs were prepared from 1970 using lignin (with the brand of Kayacarbon ALF), polyvinylchloride [6] (i.e., Saran polymer, already used to obtain ACs) and phenolic precursors [7]. The high yield and the good mechanical properties of the ACFs obtained make these precursors very useful for this application. In fact. Economy and Lin [8] developed ACFs from a phenol formaldehyde precursor, which are commercialized since 1976 under the name of Novolak. In 1980, Kuray Chemical Co. Ltd commercialized ACFs from phenolic resin under the name of Kynol. ... 

Aramid cores are made from paper (typically 1.5 mil in thickness) comprising w-aramid floe and fibrids, similar to the papers used in electrical applications discussed in the previous section. Adhesive node lines are printed on paper sheets that are then stacked, pressed, and heated to cure the adhesive. The resulting block is expanded. The adhesive-free areas form the hexagonal cells of the honeycomb configuration. The core is dipped several times in an epoxy or phenolic resin solution until the desired density and mechanical property levels are reached. The core is then cut into slices of the desired thickness. Face sheets are glued to each side of the core. The most common face sheet today is a composite of carbon fiber and epoxy resin. 

Fibers are also produced from phenolic resins. A novolak with Af 800 g/mol is spun at 200 m/min from a melt at 130°C. The product is subsequently cured with formaldehyde gas at 100-150° C over a period of 6-8 h. The yellowish fiber has an extensibility of 30% and carbonizes in a flame with retention of shape. The fibers are mostly used for noninflammable working clothes. End group acetylation gives white fibers, since quinone methyne formation is not possible [see also Equation (25-17)]. 

Carbon fibers can be produced from a wide variety of precursors in the range from natural materials to various thermoplastic and thermosetting precursors Materials, such as Polyacrylonitrile (PAN), mesophase pitch, petroleum, coal pitches, phenolic resins, polyvinylidene chloride (PVDC), rayon (viscose), etc. [42-43], About 90% of world s total carbon fiber productions are polyacrylonitrile (PAN)-based. To make carbon fibers from PAN precursor, PAN-based fibers are generally subjected to four pyrolysis processes, namely oxidation stabilization, carbonization and graphitiza-tion or activation they will be explained in following sections later [43]. 

One typical example of carbon/carbon composite plates is that made by Oak Ridge National Laboratory (ORNL) in the United States [12]. The composite preform was fabricafed by a slurry-molding process from fhe mixed slurry befween short carbon fibers (graphite fibers were also added in some sample plates) and fhe phenolic resin. The mass rafio between fiber reinforcement and phenolic matrix is 4 3. The phenolic matrix improves the mechanical properties and dimensional stability of the plate. A subsequent vacuum molding process was utilized to fabricate composite plates and fluid fields with relatively high resolution (Figure 5.3, [11]). 

Carbon Composites. Cermet friction materials tend to be heavy, thus making the brake system less energy-efficient. Compared with cermets, carbon (or graphite) is a thermally stable material of low density and reasonably high specific heat. A combination of these properties makes carbon attractive as a brake material and several companies are manufacturing carbon fiber—reinforced carbon-matrix composites, which are used primarily for aircraft brakes and race cars (16). Carbon composites usually consist of three types of carbon carbon in the fibrous form (see Carbon FIBERS), carbon resulting from the controlled pyrolysis of the resin (usually phenolic-based), and carbon from chemical vapor deposition (CVD) filling the pores (16). 

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