Loss factor, polymers

Tetralluoroethylene polymer has the lowest coefficient of friction of any solid. It has remarkable chemical resistance and a very low brittleness temperature ( — 100°C). Its dielectric constant and loss factor are low and stable across a broad temperature and frequency range. Its impact strength is high. 

Multiphoton processes are also undoubtedly involved in the photodegradation of polymers in intense laser fields, eg, using excimer lasers (13). Moreover, multiphoton excitation during pumping can become a significant loss factor in operation of dye lasers (26,27). The photochemically reactive species may or may not be capable of absorption of the individual photons which cooperate to produce multiphoton excitation, but must be capable of utilising a quantum of energy equal to that of the combined photons. Multiphoton excitation thus may be viewed as an exception to the Bunsen-Roscoe law. 

FIGURE 7.17 Storage modulus and loss factor—temperature plots of the chameleon arhPIB-h-P(p-MeSt) block copolymer. = precipitated into methanol, = precipitated into acetone. (From Puskas, J.E., Dos Santos, L., and Kaszas, G., J. Polym. Set Chem. A., 44, 6494, 2006. With permission.)... 

FIGURE 28.12 Mechanical loss factor as a function of temperature for the ENR stocks containing various fillers. (From Sihy Varghese, J. and Karger-Kocsis, J., J. Appl. Polym. Sci., 91, 813, 2004.)... 

In order to understand the thermodynamic issues associated with the nanocomposite formation, Vaia et al. have applied the mean-field statistical lattice model and found that conclusions based on the mean field theory agreed nicely with the experimental results [12,13]. The entropy loss associated with confinement of a polymer melt is not prohibited to nanocomposite formation because an entropy gain associated with the layer separation balances the entropy loss of polymer intercalation, resulting in a net entropy change near to zero. Thus, from the theoretical model, the outcome of nanocomposite formation via polymer melt intercalation depends on energetic factors, which may be determined from the surface energies of the polymer and OMLF. 

The electric properties of polymers are also related to their mechanical behavior. The dielectric constant and dielectric loss factor are analogous to the elastic compliance and mechanical loss factor. Electric resistivity is analogous to viscosity. Polar polymers, such as ionomers, possess permanent dipole moments. These polar materials are capable of storing... 

The electrical properties of materials are important for many of the higher technology applications. Measurements can be made using AC and/or DC. The electrical properties are dependent on voltage and frequency. Important electrical properties include dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole moment, electrical resistance, power loss, dissipation factor, and electrical breakdown. Electrical properties are related to polymer structure. Most organic polymers are nonconductors, but some are conductors. 

Fig. 2.22. Dependence of the elastic modulus E and the mechanical loss factor 6 on temperature for various polymers. Curves 1 elastomer (statistical copolymer of ethylene and propylene) curves 2 isotactic polypropylene (semicrystalline)...

The corresponding curves for the mechanical loss factor 6 show the following characteristics The transition to the glassy state for elastomers is seen in curve 1 as a characteristic mechanical absorption . On the other hand, two absorption maxima are visible in the curve for the partially crystalline polymer d2. The first one at 10 °C indicates the glass transition, the second one at about 145 °C is coherent with the crystalline melting point. 

Figure 6.44 Dielectric loss factor as a function of cure time and frequency of the oscillating electric field in a fiber-reinforced polymer. Reprinted, by permission, from P. K. Mallick, Fiber-Reinforced Composites, p. 365. Copyright 1988 by Marcel Dekker, Inc.

The power factor (dissipation factor) is the energy required to rotate the dipoles of a polymer in an applied electrostatic field of increasing frequency (ASTM-D150). The loss factor is equal to the product of the power factor and the dielectric constant of the polymer. 

Two other important electrical properties must be taken into consideration when polymers are used as insulation for a high-voltage power cable or electronic wires. ° These are the dielectric constant and the dielectric loss factor, which characterize the energy dissipation in the insulation, the capacitance, the impedance, and the attenuation. 

Figures 2.37 and 2.38, show the isochronal curves of the permittivity and loss factor for P2NBM and P3M2NBM as a function of temperature at fixed frequencies. A prominent relaxation associated with the dynamic glass transition is observed in both polymers. Clearly the effect of the methyl substitution in position 3 of the norbornyl group is to decrease the temperature of this relaxational process.

The most important dielectric properties are the dielectric constant, e, and the dielectric loss factor, tan 8. These properties are of interest for alternating currents indicates the polarizability in an electric field, and, therefore, it governs the magnitude of the alternating current transmitted through the material when used in a capacitor. For most polymers e is between 2 and 5, but it may reach values up to 10 for filled systems. 

Of more importance is the loss factor, tan 8, denoting the fraction of the transmitted alternating current lost by dissipation in the material. Here large differences occur between polymers, as indicated in Figure 8.10. It appears that polymers with the highest specific resistance also show the lowest dielectric losses. It should be remarked, that the values given are very schematical the losses are strongly dependent on frequency and temperature. 

It is much more attractive to heat the films from the inside, namely by the application of a high-frequency electric field. In this case the clamping device remains cold, and the highest temperature is generated at the surfaces to be welded together. Only polymers with a not too low dielectric loss factor (see 8.2.2) are suitable for this process, such as PVC and PMMA. PE, PP and PS, on the contrary, cannot be welded in this way. 

Polymer Izod impact strength (j/m) 7f> (K) hard ness Ball indentation hardness (107 N/m2) Shore D hardness Friction coefficient (-) resistance (ASTM- D1044) (Taber) (mg/lOOOc) Abrasion loss factor (DIN 53516) (mg) Polymer ref. nr. in figures (cf. Table 13.12) ... 

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