Electrically conductive fibers

A well known and straightforward way of rendering a conventional, insulating polymer-fiber electrically conductive is to blend a suitable conductive filler, as randomly... 

Electrically Conducting Fibers. FlectricaHy conducting fibers are useful in blends with fibers of other types to achieve antistatic properties in apparel fabrics and carpets. The process developed by Nippon Sanmo Dyeing Co., for example, is reportedly used by Asahi in Casbmilon 2.2 dtex (2 den) staple fibers. Courtaulds claims a flame-resistant electrically conductive fiber produced by reaction with guanadine and treatment with copper sulfide (97). 

Process. Any standard precursor material can be used, but the preferred material is wet spun Courtaulds special acrylic fiber (SAF), oxidized by RK Carbon Fibers Co. to form 6K Panox B oxidized polyacrylonitrile (PAN) fiber (OPF). This OPF is treated ia a nitrogen atmosphere at 450—750°C, preferably 525—595°C, to give fibers having between 69—70% C, 19% N density less than 2.5 g/mL and a specific resistivity under 10 ° ohm-cm. If crimp is desired, the fibers are first knit iato a sock before heat treating and then de-knit. Controlled carbonization of precursor filaments results ia a linear Dow fiber (LDF), whereas controlled carbonization of knit precursor fibers results ia a curly carbonaceous fiber (EDF). At higher carbonizing temperatures of 1000—1400°C the fibers become electrically conductive (22). 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

Excellent insulating properties, along with the abiUty to be stmctural components, make plastics the ideal candidate materials for electrical appHcations. Although generally used as insulators, carbon black or carbon fiber can be added to make plastic materials electrically conductive, thereby expanding their usefulness in the electronics area. 

Since asbestos fibers are all siUcates, they exhibit several other common properties, such as incombustibiUty, thermal stabiUty, resistance to biodegradation, chemical inertia toward most chemicals, and low electrical conductivity. 

Zinc—bromine storage batteries (qv) are under development as load-leveling devices in electric utilities (64). Photovoltaic batteries have been made of selenium or boron doped with bromine. Graphite fibers and certain polymers can be made electrically conductive by being doped with bromine. Bromine is used in quartz—haUde light bulbs. Bromine is used to etch aluminum, copper, and semi-conductors. Bromine and its salts are known to recover gold and other precious metals from their ores. Bromine can be used to desulfurize fine coal (see Coal conversion processes). Table 5 shows estimates of the primary uses of bromine. 

Electrical Hazards. Because carbon fibers are conductive, the airborne filaments can create serious problems shorting out electrical equipment. The best option is to locate sensitive equipment in clean rooms outside of areas where carbon fiber is being processed. If this is not possible, electrical cabinets must be effectively sealed to prevent contact with carbon fibers. A filtered air-positive purge provides additional protection for sensitive equipment. 

Pitch-based fibers generally have higher moduh but lower strengths than theh PAN-based counterparts. The specific properties of the various types of carbon fibers are compared in Figure 4. Pitch-based fibers also have higher electrical conductivity, which can be an important consideration in certain circumstances, for example, for use in electromagnetic inductance (EMI) shielding. 

The electrical conductivity of PET fibers as compared with other main synthetic fibers is relatively low. This explains why PET fibers are often utilized in the manufacture of textiles as electroisolating materials. The value of the electrical resistivity characterizing reciprocal conductivity is of the order 10 (/2 cm). The mechanism of the electrical conductivity of PET fibers is still a matter of controversy. According to results attained [57], there are convincing arguments that in the case of PET objects the electrical conductivity is due to the ionic mechanism. 

The low electrical conductivity of PET fibers depends essentially on their chemical constituency, but also to the same extent on the fiber s fine structure. In one study [58], an attempt was made to elucidate the influence of some basic fine structure parameters on the electrical resistivity of PET fibers. The influence of crystallinity (jc) the average lateral crystallite size (A), the mean long period (L), and the overall orientation function (fo) have been considered. The results obtained are presented in the form of plots in Figs. 9-12. 

Epoxy, polyester, phenolic and other resins are used as coatings and linings with or without reinforcement. Glass fiber, silica, carbon and many other materials can be used as filters or reinforcement to produce materials with specific properties of strength, flexibility, wear resistance and electrical conductivity. 

Reduced Wear Electrical Conductivity Glass fibers Carbon fibers Lubricating additives Carbon fibers Carbon powders Ductility, cost Tensile strength, ductility, cost Ductility, cost Tensile strength, ductility, cost... 

Jana, P.B., Mallick, A.K., and De, S.K., Electrically conductive rubber and plastic composites with carbon particles or conductive fibres, in Short Fiber-Polymer Composites, De, S.K. and White, J.R. (Eds.), Woodhead Publishing, Cambridge, 1996, Chapter 7. 

Biefer, GJ Mason, SG, Electrokinetic Streaming, Viscous Flow and Electrical Conduction in Inter-Fiber Networks, The Pore Orientation Factor, Transactions of the Faraday Society 55, 1239, 1959. 

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