Polymers electric strength

Geometries for the determination of electric strength (a) Sphere on film (b) sphere recessed into sheet (c) cylinders embedded in plastic and (d) the corresponding Weibull plot of the results of many tests on LDPE at 20°C (from Seanor D. A, Ed., Elearical Properties of Polymers, Academic Press, 1982). 

Dielectric strength (electric strength) n. A measure of the voltage required to puncture an insulating material, expressed in volts per mil of thickness (SI V/rrmi). The voltage is the root-mean-square voltage difference between the two electrodes in contact with opposite surfaces of the specimen at which electrical breakdown occurs under prescribed test conditions. Ku CC, Liepins R (1987) Electrical properties of polymers. Hanser Publishers, New York. Weast RC (ed) (1971) Handbook of chemistry and physics, 52nd edn. The Chemical Rubber Co., Boca Raton, FL. 

Kochetov R, Andritsch T, Morshuis PHF, Smit JJ (2012) Anomalous behaviour of the dielectric spectroscopy response of nanocomposites. IEEE Trans Diel Electr Insnl 19 107-117 Kojima Y, Usuki A, Kawasumi M, Okada A, Fukushima Y, Kurauchi T, Kamigaito O (1993) Mechanical properties of nylon 6-clay hybrid. J Mater Res 8 1185-1189 Kolesov SN (1980) The influence of morphology on the electric strength of polymer insulation. IEEE Trans Electr Insul 15 382-388... 

The most interesting properties of polymers are their high mechanical and electrical strength and low electrical conductivity and acoustic impedance, whereas the ferroelectric ceramics exhibit good dielectric, pyroelectric, and piezoelectric properties (4,8,67]. 

Since oxidation of polyethylene can occur during processing and on exposure to sunlight with resulting loss of mechanical and electrical strength, antioxidants are commonly added to the polymer. Antioxidants are generally hindered phenols such as 4-methyl-2,6-tert-butylphenol (BHT) (II) and octadecyl 3-(3, 5 -di-tm-butyl-4 -hydroxyphenyl)propionate (III). 

Fig. 11. Effect of temperature on electric strength of polymers. A, Polyfvinyl alcohol) B, polyfmethyl methacrylate) C, polyfvinyl chloride-co-vinyl-acetate) D, chlorinated polyethylene E, mica F, polystyrene G, polyethylene and H, polyisobutylene (31).

Electrical Insulation. The substitution of a gas for part of a soHd polymer usuaUy results in large changes in the electrical properties of the resulting material. The dielectric constant, dissipation factor, and dielectric strength are aU generaUy lowered in amounts roughly proportional to the amount of gas in the foam. 

For low frequency electrical insulation appHcations, the dielectric constant of the insulation is ideaUy as low as possible (see Insulation, electrical). The lower the density of the ceUular polymer, the lower the dielectric constant and the better the electrical insulation. Dielectric strength is also reduced at... 

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