Volume resistivity of polymers

Electrical Conductivity of Metals Electrical Resistivity of Metals Electrical Resistivity of Alloy Cast Irons Resistivity of Ceramics Volume Resistivity of Glass Volume Resistivity of Polymers... 

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 ... 

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 volume resistivity of the substrate was not an important effect in any of our models. This was a consequence of selecting the substrate material to have a resistivity significantly greater than that of the polymer in all cases. For substrates with resistivities which approached that of the polymer, the model can easily be modified. One would then expect that the substrate current would contribute to the total current by approximately the ratio of the substrate to polymer resistivity. 

The specific volume resistivity/temperature or electrical field-strength relation is measured during what usually are called DC measurements. A specific method was developed to determine the volume resistivity of a polymer as a function of the temperature and/or the electrical field strength [2] without the need to wait until the Ic current component has become zero. This method is schematically given in Figure 5.1. 

The volume resistivity/temperature curve clearly illustrates the strong difference in the temperature dependency of the volume resistivity of a polymer in its glassy phase and in its rubbery phase. The Tg-value, obtained by drawing two tangents near this glass-rubber transition, is determined at 1000/T 3.58 or 6°C. This Tg-value is a real static Tg-value and its hypothetical frequency [f(h)l in the frequency/temperature plane will be lower than the f(h) = lxB-2 to lxE-4 claimed by Phillips [12] for dilatometric experiments. A good fit on the Arrhenius plot was obtained assuming an f(h) of lxE-6 for this Tg-value, see below. 

Carbon black is the most widely used conducting filler in composite industry. Carbon black filled immiscible blends based on polar/polar (65), polar/nonpolar (63,66), nonpolar/nonpolar thermoplastics (67,68), plastic/rubber and rubber/mbber blends (69,70) have already been reported in the literature. The properties of carbon black filled immiscible PP/epoxy were reported recently by Li et al. (60). The blend system was interesting because one of the components is semicrystalline and the other is an amorphous polar material with different percolation thresholds. The volume resistivity of carbon black filled individual polymers is shown in Fig. 21.23. 

Electrical Reoulrements. The pottant should contain no plasticizer because plasticizer can reduce the volume resistivity of a polymer drastically. It reduces the resistivity of PVB by 5 orders of magnitude In some formulations. PVB with 40 dlester plasticizer measures only 10 ohm-cm In laminated form at room temperature whereas It measures 10 ohm-cm with the plasticizer driven out. Volume resistivities of 10 2 ohm-cm or less will conduct small amounts of current fairly readily, albeit slowly. (For example, a resolved 5 line palr/mm charge Image has been observed to blur within the first few seconds when placed on the surface of a film or Immersed In a llould of lO I-IO ohm-cm resistivity. The same Image on or In 101 ohm-cm material will not blur for several hours. On a ohm-cm material an Image will last unblurred from weeks to months.)... 

If the distance between two electrodes is 1 cm and the surface area of each electrode is 1 cm, a unitary volume resistivity of material placed between electrodes is measured in ohms-cm. Table 10.6 compares volume resistivities of some plasticizers and polymers. 

The above data show that mixing a polymer with a plasticizer has only marginal influence on volume resistivity of material. But still plasticizers are used in many applications of polymers in conductive and ferroelectric applications. ... 

Typical volume conductivities of rubbers are around 10 -10 Qcm. The electric conductivity of rubber is caused by the presence of impurities which transfer ions and thus electric current. On transition from glassy to elastic state voltrme resistivity decreases by several orders of magnitude because of an increase in ion mobihty. Also plasticization of mbbers decreases their volume resistivity because of the increased ion mobility. Classification of various rubbers according to their electrical conductivity was published elsewhere. As data in Table 10.6 show, polymers are excellent electrical insulators but they can be modified to become good conductors having volume resistance of 10 Qcm or less. ... 

The ability of a polymer to flow or to oppose an electrical current under the application of an external electric field is known as its electrical property. In a good conductor, electrons or ions are able to flow easily through the material. If the material resists the flow, it is described as an insulator. Most polymers are insulators. The volume resistance of a polymer is the resistance of an electric field (current) between the opposite faces of a unit... 

It can be seen in Table 4.3 that electrical properties cover a wide range and thus the volume resistivity of various polymers is between 2 ohm.cm for epoxy resins to 10 ohm.cm for fluorinated ethylene-propylene copolymer. Similarly, dielectric strength is in the range from 12 mV/m for urea-formaldehyde resins to 55 mV/m for fluorinated ethylene-propylene copolymer and 60 mV/m for PA 12. 

Most commercial polymers may be classified as insulating, having volume resistivities of 10 ohm cm or above. However, their properties are extensively modified by compounding, with fillers having the largest effect on properties. These are discussed in Section 7.6.3.3. 

The effect of fillers on the resistance to change or deterioration in the presence of liquids is quite marked. Fillers influence the degree of swelling by replacement of polymers that swells by filler that does not, resulting in reduced swelling through reduction of the volume fraction of polymer in the compound. Some fillers are obviously not suited to specific applications, e.g., carbonate fillers decompose in the presence of acids. 

Composites of banana, hemp, and agave with high-density polyethylene resin were separately prepared in different ratios 60 40, 55 45, 50 50, and 45 55 (wt/wt). These fibers were also treated with maleic anhydride, and the effect of maleic anhydride on surface resistivity and volume resistivity of wood polymer composites was studied. The surface resistivity decreased with an increase in fiber content in the composites, while volume resistivity increased. The maximum surface resistivity and volume resistivity were observed in the untreated banana fiber composite, while minimum surface resistivity and volume resistivity were found in the maleic anhydride-treated agave fiber composite. The decrement in volume resistivity and surface resistivity was due to the increase in cross-linking between the polymer and fiber by treatment with maleic anhydride. 

Double percolation phenomenon has been reported previously for two phase polymer blends loaded with carbon black (P-77). Very low percolation thresholds were reported when conductive carbon black was preferentially localized at the phase boundary (P). Figure 9 shows the volume resistivity of phase-separated nylon/poly-... 

The excellent electrical conducting properties of metals are well known. Metals have resistivities in the range of 10 ohm cm compared with the resistivities of polymers which are on the order of lO ohmcm. Early studies showed there was a correlation between the electrical resistivity of the composite material and the amount of finely divided metal particles blended into it. More importantly, it was determined that a critical volume fraction of metal was required to make the plastic conductive. This critical volume or concentration is called the percolation threshold. This is the concentration at which each particle in the matrix makes contact with at least two other neighboring particles and creates a three-dimensional network in the matrix. 

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