Polyethylene permittivity

The dielectric constant (permittivity) [Eq. (6.2)], which is related to the polarizability of the polymer, is low for nonpolar molecules such as high-density polyethylene (hdpe), which cannot store much energy, but is relatively high for polar polymers. The dielectric constant increases as the temperature increases but reaches a plateau at relatively high temperatures. 

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... 

Dielectric relaxation relies on the presence of dipoles on the moving part of the molecule in order to couple to the electric field and exhibit a dielectric response. Thus, pure unoxidised polyethylene, being non-polar, exhibits a dielectric constant due to atomic and electronic distortions close to the square of the refractive index, as required by theory. It exhibits no frequency-plane relaxation, and the only changes with temperature are due to density changes and melting. A polar polymer such as PET with main-chain dipoles exhibits a DETA scan very similar to a DMT A scan. Figure 7.30 illustrates this. The dielectric permittivity increases with temperature as the sample becomes more polarisable with increasing temperature. In this sense e and... 

By now, there are papers devoted to the investigation of the temperature dependencies of the permittivity of the nanocomposite materials based on the low-density polyethylene with nanopartides of copper oxide [12,13], zinc oxide [14],... 

Thus, it was established that the nanocomposite materials based on low-density polyethylene with minimum porosity and maximum density are obtained by molding at temperatures 110-120 °C. The results open the way to controlled modification of the parameters of such samples by varying the molding temperature. Properties, which depend on the material porosity, include the permittivity, refractive index, and elastic modulus. 

Figure 7.5 The temperature dependence of the relative permittivity for nanocomposite material based on the matrix of a low

Table 7.2 Values of the relative permittivity measured at the minimum and maximum temperatures in the interval studied for the nanocomposite materials based on low-density polyethylene with various concentrations of the iron nanoparticles.

Thus in the course of the investigations it was shown that for obtaining the nanocomposite samples based on the low-density polyethylene with the minimum porosity or maximum density, one should use the molding temperature which is in the range 110-120 °C. The obtained results also indicate the possibility to change some physical macroscopic parameters (density, permittivity, etc.) by changing the molding temperature. 

The resistivity of the conductor is obtained from the conductor resistance and the cross section of fhe conductor S (pc= dc 2 dc )- Ir general, the resistivity is greater than that of the intrinsic resistivity of the conductor (e.g., copper 1.8 x 10 O-m) because of the gap within the stranded conductor. If fhe resisfivify of fhe metallic sheath is not provided by the manufacturer, it is obtained % the resistance and its cross section in the same manner as the main conductor. The relative permittivities of the main insulator and the corrosion-proof layer are determined by their materials. For example, the relative permittivity of a cross-linked polyethylene (XEPE) is 2.3. The permittivity of fhe corrosion-proof layer is widely ranging. However, the value has no effect on the positive-sequence impedance and admittance of the cable. 

Test Methods for a-c Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulating Materials Test Method for Dissipation Factor and Permittivity Parallel with Laminations of Laminated Sheet and Plate Insulating Materials Test Methods for Relative Permittivity (Dielectric Constant) and Dissipation Factor of Polyethylene hy Liquid Displacement Procedure... 

The electrical testing of polyethylene materials seeks to determine the response of a sample to various types of electric fields. Variables include voltage, current (alternating and direct), contact or noncontact conditions, and various types of surface contamination. Methods of characterizing the electrical properties of polyethylene fall into two general categories those that determine electrical characteristics predictive of end use performance and those that seek to rank materials with respect to one another. The first type is exemplified by the measurement of relative permittivity, the second by the determination of arc resistance. 

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