Electrical resistance fibers

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). 

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. 

The high electrical resistivity of asbestos fibers is weU-known, and has been widely exploited in electrical insulation appHcations. In general, the resistivity of chrysotile is lower than that of the amphiboles, particularly in high humidity environments (because of the availabiHty of soluble ions). For example, the electrical resistivity of chrysotile decreases from 1 to 2100 MQ/cm in a dry environment to values of 0.01 to 0.4 MQ/cm at 91% relative humidity. Amphiboles, on the other hand, exhibit resistivity between 8,000 and 900,000 MQ/cm. 

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. 

Figure 10 Electrical resistivity of PET fiber versus birefringence of the fiber.

Metal Metal, ceramic, carbon, glass fibers Elevated temperature strength Electrical resistance Thermal stability... 

Electrical Carbon fibers Ductility, Ductility, Resistivities of 1 to... 

Changes in electrical resistivity (V3) and mechanical properties (V3, V4) of graphite fibers upon nitration have been studied. Increases in elastic modulus, and decreases in tensile strengths, have been related to removal of boundary dislocations by the intercalation process proposed elsewhere iN4). 

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and use. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

Similarly, by directly measuring changes in electrical resistance during mechanical deformation it is possible to monitor crack propagation in hierarchical composites with non-conductive fibers and CNTs dispersed in the matrix [48]. Figure 8.7(b) shows... 

Fig. 8.7 Examples of hierarchical composites where the presence of CNTs is used for SHM. (a) Damage detection through thermal imaging of resistively-heated CNTs in an alumina composite [47] and (b) detection of crack propagation by monitoring electrical resistance (normalized by specimen length) in a CNT/glass fiber/epoxy composite [48], With kind permission from IOP (2011) and Wiley (2006).

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