Dielectric properties of plastics

Figure 7. Dielectric properties of plasticized PVC with and without a fumed silica (300 m2/g) as a function of temperature.

With the integration of polar groups during the oxidation processes, the dielectric properties of plastic materials also change. Figure 5.170. Again, an induction period is followed by a reaction period that is characterized by an increase in dielectric loss factor by two powers of ten. This behavior is virtually independent of the test frequency selected [763]. 

Figure 13.19 Map of the dielectric properties of plastics (bulk samples). IMSPS, impact-modified SPS IRGFSPS, ignition-resistant GFSPS. PC polycarbonate PPE poly(phenylene ether) PE polyethylene PAr polyarylate PFS polysulfone.

A number of areas in which plastics are used in electrical and electronic design have been covered there are many more. Examples include fiber optics, computer hardware and software, radomes for radar transmitters, sound transmitters, and appliances. Reviewed were the basic use and behavior for plastics as an insulator or as a dielectric material and applying design parameters. The effect of field intensity, frequency, environmental effects, temperature, and time were reviewed as part of the design process. Several special applications for plastics based on intrinsic properties of plastics materials were also reviewed. 

P.Y.17 may be used for mass coloration and also to print PVC film. For these purposes, P.Y.17 is frequently prepared on a VC/VAc (vinyl chloride/vinyl acetate) mixed polymer basis. Good dispersibility in plastics makes these preparations suitable even for thin films. The dielectrical properties of P.Y.17 allow its application in PVC cable insulations. 

Another important factor in dielectric heating is the depth of penetration of the radiation because an even field distribution in a material is essential for the imiform heating. The properties that most strongly influence the penetration depth are the dielectric properties of the material. These may vary with the free space wavelength and frequency of the propagating wave. For low loss dielectrics such as plastics (e" l) the penetration depth is given approximately by ... 

Figure 18.18 Map of dielectric properties of engineering plastics. Among engineering plastics, SPS (impact modified and GF-reinforced HB and IR grades) has very low dielectric dissipation factor and dielectric constant following those of fluorocarbon polymers. PSF, polysulfone PPE, poly(phenylene ether) PES, poly(ether sulfone) PAr, polyarylate...

As their name implies, plastics are easily deformable and once molten they may be heated not only externally, but also internally, by dissipating friction or dielectric heat. Once the pyrolysis temperature is attained, the melt viscosity starts decreasing rapidly and rising pyrolysis vapour bubbles agitate the mix. Many properties of plastics can be derived using methods used and developed by Van Krevelen [13]. The pyrolyzing plastic s rheology is poorly-documented, however, since the evolution of molecular size and strucmre with time and the effects of extraneous matter are difficult to predict. 

The basic role of gas in the electric properties of plastic foams postulated by Domkin has been confirmed by Giessner in a study on the electric properties of epoxide foams, the cells of which were filled with a electronegative gas, sulfur hexafluoride (SFg). The introduction of SFg results in very good dielectric properties over a wide temperature interval, including high Ebr corona resistance (Fig. 21). Previously, Palmer established that Ebr in the case of SFg is by 3.5 times higher than for air. 

These results reveal that- a plastic foam structure may be considered as a system of thin films and, therefore, support a model of plastic foam morphology namely a matrix system composed of thin polymeric films defining two groups of cells (macro- and microcells). Additional support in favor of this model of plastic foam structure is provided by the studies on the electric properties of plastic foams Among the numerous equations so far advanced for the calculation of the dielectric properties, the expressions which describe the dry foam structure by one of the limiting cases of a matrix system, namely a laminated dielectric structure with layers parallel to the force lines of the electrical field, agree best with the experiments >. 

This additive does not adversely affect the dielectric properties of the base polymer, but merely ensures initiation of the electroless plating process upon exposure of the molded plastic substrate to the plating solutions. 

Pradhan, D.K., R. Choudhary, andB. Samantaray, Studies of dielectric and electrical properties of plasticized polymer nanocomposite electrolytes. Materials Chemistry and Physics, 2009.115(2) 557-561. 

Although instances of lyotropic PLCs predate studies of thermotropic PLCs, as they involved solutions of comparatively esoteric species — virus particles and helical polypeptides — studies of these liquid crystals were isolated to a few laboratories. Nevertheless, observations on these lyotropic PLCs did stimulate the first convincing theoretical rationalizations of spontaneously ordered fluid phases (see below). Much of the early experimental work was devoted to characterizing the texture of polypeptide solutions. (23) The chiral polypeptides (helical rods) generate a cholesteric structure in the solution the cholesteric pitch is strongly dependent on polymer concentration, dielectric properties of the solvent, and polymer molecular weight. Variable pitch (<1 - 100 pm) may be stabilized and locked into the solid state by (for example) evaporating the solvent in the presence of a nonvolatile plasticizer.(24)... 

Mica s main use is in gypsmn, but it is used in the plastics industry to improve the mechanical properties of polyolefins and to modify the dielectric properties of other polymers. Quinto Technology of Canada produces an imusually fine grade of mica that does not have the adverse effect on impact strength often experienced with the coarser flakes. Starting from an ore already finer than most, Quinto uses processing equipment to reduce the flake size still further. It can be used in polyolefins, polyamides, and polyurethanes. 

Quantitatively, lower dissipation factors result in higher-quality, higher-performance electrical or electronic systems, having lower electrical losses. Dissipation factor values have no units because they are mathematical ratios. Low dissipation factor values, desirable for electronic plastics, would be below 0.01 and 0.001. Two other terms for dissipation factor are loss tangent and tan delta. A related term is quality factor or Q factor, which is the reciprocal of the dissipation factor. See also dielectric properties electronic plastic. 

Standard testing of electrical properties of plastics includes dielectric strength, permittivity, dissipation factor, smface and volume resistivity, and arc resistance. Dielectric strength is the maximmn voltage required for breakdown and is determined by one of three techniques short-time, slow-rate or slow-rise, and step-by-step. The two last techniques use data from the short-time test to... 

P. Gruner-Bauer, E. Dormann The dielectric properties of diacetylenes during thermal solid state polymerization. Second International Conference Electrical, Optical and Acoustic Properties of Polymers, Canterbury, UK, (The Plastics and Rubber Instimte, London, UK), 15/1 (1990)... 

Most plastics are dielectrics or insulators (poor conductors of electricity) and resist the flow of a current. This is one of the most useful properties of plastics and makes much of our modern society possible through the use of plastics as wire coatings, switches and other electrical and electronic products. Despite this, dielectric breakdown can occur at sufficiently high voltages to give current transmission and possible mechanical damage to the plastic. 

The structure of the polymer determines if it is polar or non-polar and this determines many of the dielectric properties of the plastic. 

In Table 13.3, the mechanical properties of plastics are listed. SPS has a high melting point almost comparable to those of other plastics. An outstanding feature of SPS is that SPS has the lowest specific gravity and dielectric constant. The disadvantage of SPS is its brittleness the impact resistance is low compared to those of other engineering plastics. 

Effects of Temperature and Frequency. According to the theoretical aspects discussed above, a dielectric-loss peak within the range of temperature and frequency in use might adversely Eiffect the performance of a plastic at high voltage stress or in some electronic applications requiring a high impedance (or Q). The a-c electrical properties of plastics may also indirectly assess mechanical properties. 

---