Polymers volume resistivity

Polymer Volume resistivity (fl m) Dielectric strength (kV/cm) (J in sample) Dielectric constant Power factor ... 

Plasticizer Volume resistivity, Qcm Polymer Volume resistivity, 2cm... 

Polymer Volume resistivity (Ohm-cm) Dielectric constant 60 Hz 1M Hz Dissipation factor 60 Hz 1M Hz Dielectric strength (V/mil)... 

Poly(vinyl chloride) has a good resistance to hydrocarbons but some plasticisers, particularly the less polar ones such as dibutyl sebacate, are extracted by materials such as iso-octane. The polymer is also resistant to most aqueous solutions, including those of alkalis and dilute mineral acids. Below the second order transition temperature, poly(vinyl chloride) compounds are reasonably good electrical insulators over a wide range of frequencies but above the second order transition temperature their value as an insulator is limited to low-frequency applications. The more plasticiser present, the lower the volume resistivity. 

PTFE is an outstanding insulator over a wide range of temperature and frequency. The volume resistivity (100s value) exceeds lO Gm and it appears that any current measured is a polarisation current rather than a conduction current. The power factor is negligible in the temperature range -60°C to -i-250°C at frequencies up to lO" Flz. The polymer has a low dielectric constant similarly unaffected by frequency. The only effect of temperature is to alter the density which has been found to influence the dielectric constant according to the relationship... 

Figure 15.10. The dependence of apparent volume resistivity on time of polarisation of acrylic polymer (Perspex). (Reproduced by permission of ICI)...

FIGURE 19.6 Dependency on carbon black loading of perimeter distance between the nearest aggregates obtained from three-dimensional-transmission electron microscopic (3D-TEM) images (dp) and volume resistivity at room temperature (pv). (From Kohjiya, S., Kato, A., Suda, T., Shimanuki, J., and Ikeda, Y., Polymer, 47, 3298, 2006. With permission.)... 

The dielectric constant of a polymer (K) (which we also refer to as relative electric permittivity or electric inductive capacity) is a measure of its interaction with an electrical field in which it is placed. It is inversely related to volume resistivity. The dielectric constant depends strongly on the polarizability of molecules tvithin the polymer. In polymers with negligible dipole moments, the dielectric constant is low and it is essentially independent of temperature and the frequency of an alternating electric field. Polymers with polar constituents have higher dielectric constants. When we place such polymers in an electrical field, their dipoles attempt... 

Surface and volume resistivity measurements have been performed on films of polymer alone and polymer with Al(acac) added. Special care was taken to insure that only films of uniformly high quality were measured. Regardless of the film pretreatment, volume resistivities on two independently cast films of polymer alone fall in the 10- - ohm-cm range. No previously published resistivity is available on this particular polymer although upon surveying several ether polyimides from independent sources we measured similar volume resistivities. 

Incorporation of AlCacac) into the polyimide disappointingly shows no significant reduction in volume resistivity relative to the polymer alone. Replicate measurements (1.59 x 10 and 1.12 x 10 ° ohm-cm) on two independently cast films support this conclusion. Reorientation of the same film in the electrode assembly yielded identical results suggesting uniform behavior throughout the film containing Al(acac),. Similar results were obtained on NiCl bl O filled polyimides. (Table V)... 

The volume resistivity is the electrical resistance of a polymer sample of unit area and unit thickness when electrodes placed on two opposite faces apply an electrical potential across it. The volume resistivity is expressed in ohm.cm. 

In contrast to metals and semiconductors, the valence electrons in polymers are localized in covalent bonds.The small current that flows through polymers upon the application of an electric field arises mainly from structural defects and impurities. Additives, such as fillers, antioxidants, plasticizers, and processing aids of flame retardants, cause an increase of charge carriers, which results in a decrease of their volume resistivity. In radiation cross-linking electrons may produce radiation defects in the material the higher the absorbed dose, the greater the number of defects. As a result, the resistivity of a radiation cross-linked polymer may decrease. Volume resistivities and dielectric constants of some polymers used as insulations are in Table 8.3. It can be seen that the values of dielectric constants of cross-linked polymers are slightly lower than those of polymers not cross-linked. 

The usual standard methods for volume and surface resistivity both use the same test piece and electrode geometry and essentially the same measuring circuit. There are no ISO or IEC methods for rubbers but, where national standards specifically for polymers exist, they are usually adaptations of the IEC Publication 600931 for insulating materials in general. The relevant British Standards for rubbers are BS 903-C12 for surface resistivity and BS 903-C23 for volume resistivity. ASTM has an equivalent to the IEC standard for insulating materials generally, D2574, but no standard specifically for rubbers. 

There are several important electrical properties. Insulation resistance is the resistance of polyurethane to the flow of electricity. The insulation resistance is composed of two main components. The "volume resistivity" is the resistance to flow through the bulk of the material and is a function of the composition of the polymer. The second component is the "surface resistivity,"... 

The conductivity and also the activation energy of the conduction appear to be practically insensitive to crystallinity. Both surface and volume resistivity are important in the application of polymers as insulating materials. 

The conductivity is greatly increased by moisture. An obvious relationship exists between the volume resistivity of pure (and dry) polymers and the dielectric constant, as is shown in Fig. 11.10. Apparently, the volume resistivity (R in Q cm) can be estimated by means of the expression ... 

Figure 12.5. Volume resistivity against filler loading for SBR composites filled with carbon black (CB Ensaco 250G from Timcal) and MWNTs. [Figure 5A is reprinted from L. Bokobza, M. Rahmani, C. Belin, J.-L. Bruneel, N.-E. El Bounia "Blends of carbon blacks and multwall carbon nanotubes as reinforcing fillers for hydrocarbon rubbers", Journal of Polymer Science Part B Polymer Physics, 46,1939, 2008, permission from John Wiley and Sons].

The analysis of van der Pauw can be used for arbitrary electrode arrangements on thin samples of anisotropic materials of any shape and has been widely used in studies of conjugated polymers, where only small and irregular samples are available. Four electrodes are attached, as shown in Fig. 5.19(d). The resistance values Ry and R2 are measured as for the Montgomery method. The volume resistivity is then calculated from these values as... 

The volume resistivity of the solid polymer must be > 10 fl-cm. Since the packaging material will make contact with the metal leads of the microelectronics device, it is essential that the compound have a high-volume resistivity. 

The measurement of many other polymer characteristics are of practical importance. Among these are various electrical properties such as volume resistivity, surface resistivity, dielectric constant, arc resistance, etc. Also, solubility properties, polymer-polymer compatibility [22], chemical resistance, resistance to radiations, etc. are measured on polymers (see e.g. [1]). 

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