Permittivity plastics

The insulating property of any insulator will break down in a sufficiently strong electric field. The dielectric strength is defined as the electric strength (V/m) which an insulating material can withstand. For plastics the dielectric strength can vary from 1 to 1000 MV/m. Materials may be compared on the basis of their relative permittivity (or dielectric constant). This is the ratio of the permittivity of the material to the permittivity of a vacuum. The ability of a... 

Figure 9. Propagating brush discharges, (a) Insulating dielectric layer of dielectric permittivity e thickness dlayer, and surface charge ey with conductive backing, (b) Example of improper use of plastic (PVC) pipe where surface charge builds up leading to risk of propagating brush discharge.

Dioctyl sebacate (DOS) with relative permittivity e of 3.9 and 2-nitrophenyl octyl ether (NPOE) with e = 23.9 are the traditionally used sensor membrane plasticizers. The choice of a plasticizer always depends on a sensor application. Thus, NPOE appears to be more beneficial for divalent ions due to its higher polarity, but for some cases its lipophilicity is insufficient. Furthermore, measurements with NPOE-plasticized sensors in undiluted blood are complicated by precipitation of charged species (mainly proteins) on the sensor surface, which leads to significant potential drifts. Although calcium selectivity against sodium and potassium for NPOE-based membranes is better by two orders of magnitude compared to DOS membranes, the latter are recommended for blood measurements as their lower polarity prevents protein deposition [92],... 

With increasing frequency, the permittivity of dielectric decreases. A major factor in the selection of insulation is the ability of the insulation to resist the absorption of moisture. Moisture, of course, can greatly lower resistivity. For wire insulation, synthetic polymers and plastics essentially have replaced the use ol natural rubber. Usually, prior to coaling a wire with a plastic material, (lie wire must he treated to assure good contact and adhesion of the insulating material. Copper wire, for example, is treated with hydrogen fluoride, which creates a coating ol clipper fluoride in the... 

Approximate spectroscopic information can often be surprisingly useful. Perhaps the very simplest approximation of all is to use the index of refraction to estimate the dielectric permittivity of a material that is nearly transparent in the visible region. Then use the ionization potential, often tabulated in handbooks, to create a single absorption frequency. For example, consider several plastics that are nonpolar enough that we even ignore any significant terms from the microwave and IR regions. 

Fig. 22. Plot of relaxed permittivity versus time for a low molecular weight DGEBA resin (EPON 825) cured isothermally with DDS at temperatures between410 K and460 K. Crosses represent experimental data the solid curve represents the model described in the text. (Reprinted from Ref. 71 > with permission of the Society of Plastics Engineers)...

ASTM D 1673-79 (1989) Standard Test Methods for Relative Permittivity and Dissipation Factor of Expcmded Cellular Plastics Used for Electrical Insulation, 5 pp (Conun D-9)... 

Several tests are essential for the evaluation of plastics in electrical applications. These tests include dielectric constant (permittivity ASTM-D150-74), which is the ratio of the capacitance of the polymer compared to air, dielectric strength, and dielectric breakdown voltage (ASTM-D149-75). Dielectric breakdown voltage is... 

Permeability of Thermoplastic Containers to Packaged Reagents or Proprietary Products Oxygen Gas Transmission Rate Through Plastic Film and Sheet using a Coulometric Sensor Water Permeability of Geotextiles by Permittivity Permeability of Leather to Water Vapor... 

In such a study, test panels of window film were mounted on glass plates for accelerated ageing. A small hole was cut in the plastic film and an interdigitated single surface dielectric sensor applied to the exposed surface of the adhesive after chilling the plate in a freezer to aid removal of the backing. Measurements of dielectric loss and permittivity were carried out from 0.1 to 100 kHz in decade steps at ambient temperature before and after 600 and 1200h exposure. 

Polyethylene. A thermoplastic produced by polymerization of ethylene. Polyethylene has the greatest bulk of all plastics in terms of both production and consumption. Several industrial processes are used for the polymerization of ethylene. Characteristics of polyethylenes produced in different ways are similar but not quite identical. All of them are microcrystalline translucent (seemingly transparent in thin layers) thermoplastics with a lower density than that of water, low permittivity and dielectric loss, and high resistance to acids and alkali. The different types of polyethylenes are principally classified by density. Low-density polyethylene (LDPE) has a rather branched carbon chain with repeated — CHg—CHg— monomeric units and a density of 0.918 to 0.935 g/cm, while the almost linear high-density polyethylene (HOPE) has... 

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