Plastics dielectric constant

The ion conductivity of the three PEO/PMMA blend compositions, 25/75, 50/50, and 75/25 studied by us increases with ascending LiClO content due to increasing number of free mobile ions as shown in Figure 28. In addition, blend composition with 75 wt% PEO doped with 0 to 12 wt% LiClO displays comparatively higher a values in the order of 10 S cm than the other two blends. Nevertheless, Tan and Johan, (2011) studied the ion conductivity of PEO/PMMA blend polymer electrolyte found that the composition 20 wt% PEO and 80 wt% PMMA is the most miscible proportion for the blend. Figure 28 depicts that the PEO/PMMA 20/80 blend achieves a maximum ion conductivity of 7 x 10 S cm at 10 wt% LiClO, further enhancement in conductivity can be achieved by the addition of a low molecular weight, low viscosity, and high dielectric constant plasticizer, EC. The incorporation of EC facilitates the dissociation of the... 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

Electrical Properties. CeUular polymers have two important electrical appHcations (22). One takes advantage of the combination of inherent toughness and moisture resistance of polymers along with the decreased dielectric constant and dissipation factor of the foamed state to use ceUular polymers as electrical-wire insulation (97). The other combines the low dissipation factor and the rigidity of plastic foams in the constmction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (213). 

Plastic film Melting point, °C Moisture absorption, % Tensile strength, MPa " Ultimate elongation, % Coefficient of thermal expansion, 10-%K Dissipation factor at 1 kH2 Dielectric constant at 1 kHz Dielectric strength, MV/m Cost factor... 

Dielectric Constant The dielectric constant of material represents its ability to reduce the electric force between two charges separated in space. This propei ty is useful in process control for polymers, ceramic materials, and semiconduc tors. Dielectric constants are measured with respect to vacuum (1.0) typical values range from 2 (benzene) to 33 (methanol) to 80 (water). TEe value for water is higher than for most plastics. A measuring cell is made of glass or some other insulating material and is usually doughnut-shaped, with the cylinders coated with metal, which constitute the plates of the capacitor. 

Dielectric Constant, Power Factor and Structure 111 Table 6.1 Typical electrical properties of some selected plastics materials at 20°C... 

The lowest dielectric constant (1.83-1.93) of any known plastics material. (It is to be noted that this is in spite of the fact that the dielectric constant is more than the square of the refractive index, indicating that polarisations other than electronic polarisations are present—see Section 6.3). 

Where plastics are to be used for electrical applications, then electrical properties as well as mechanical and other properties need to be considered. Whilst properties such as resistivity, power factor and dielectric constant are important, they may not be all-important. For example, although polyamides and many thermosetting plastics may show only moderate values for the above properties, they have frequently been used successfully in low-frequency applications. Perhaps more important for many purposes are the tracking and arcing resistance, which are frequently poor with aromatic polymers. 

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... 

A plasticized electrolyte, usually obtained by the addition of small amounts of a liquid of high dielectric constant to a solving polymer electrolyte in order to enhance its conductivity. 

If the wire is to be used to carry much higher frequency currents, the design problem in geometry and plastic selection becomes more complicated. The dielectric constant and dielectric loss values for the plastics become important in the design. At a frequency of one megahertz the effect of the dielectric on the power transmission behavior of the wire is substantial and, even at frequencies of 10 to 100 kilohertz, the insulation on the wire must be considered in the design as a major electrical element in the circuit. More on the subject of insulation will be following this section. 

Capacitor There are several applications for plastics in electrical devices that use the intrinsic characteristics of the plastics for the effect on the electrical circuit. The most obvious of these is the use of plastics particularly in the form of thin films as the dielectric in capacitors. TP polyester films such as Mylar are especially useful for this type of application because of the high dielectric strength in conjunction with a good dielectric constant. 

Mostly known for plasticizers only (see section 3.1), not for plasticized polymers or commercial polymers. The relative dielectric constant indicates the polarisability of the molecule (s of selected solvents for comparison hexane, 1.9 toluene, 2.4 chloroform, 4.8 ethyl acetate, 6.0 dichloromethane, 9.1 acetone, 20.7 water, 80.2). 

A correlation between the dielectric constant of the plasticizer used in a polymer and its water uptake might be expected. However, according to the table below17 (Table 19), no predictions can be made. 

Plasticizer Lipophilicity of plasticizer (log P) Dielectric constant ofplasticizer Water uptake after one week with PVC/plasticizer = 1 2... 

Dimitrakopoulos, C. D. Purushothaman, S. Kymissis, J. Callegari, A. Shaw, J. M. 1999. Low-voltage organic transistors on plastic comprising high-dielectric constant gate insulators. Science 283 822-824. 

Uses Rubber accelerator solvent in fiber and plastic industry rocket fuels lubricants condensers to increase dielectric constant industrial solvent antioxidant nematocide softener of copolymers research chemical plasticizer in acrylonitrile polymers inhibit nitrification in soil chemical intermediate for 1,1-dimethylhydrazine. 

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. 

Plasticizers include tricresyl phosphate and trixylyl phosphate. Foaming agents can be added in the case of using the polymers for wires, which require low dielectric constant and low dielectric loss tangent, such as communication cables, coaxial cables for computers and high-frequency cables. 

Triboelectrification. In triboelectrification, plastics are brought into repeated contact resulting in a loss or gain electrons depending on the relative dielectric constant of the materials (125). In the case of ABS and HIPS, ABS exhibits the higher dielectric constant. Therefore ABS should become positively charged. Once materials have been... 

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