Tan 8-measurement

The second point is to compare the appropriateness of PD measurements with that of more conventional loss factor (tan 8) measurements. In general, tan 8 measurements show an integral over the insulating material in its entirety. Deviations from tan 8 due to an insulation impairment restricted to a small (local) area cannot be detected to have been caused by the limited... 

The pneumatic impact strengths of a series of well-character-ized styrene-butadiene triblock copolymers (B/S/B) were measured and compared with torsion pendulum tan 8 measurements. Instead of a linear log-log impact strength-tan 8 correlation, an S-shaped curve was observed. The latter is interpreted in terms of the two-phase structures revealed by electron microscopy. 

A dataset of 206 points, containing the experimental values [14-18,22] of tan 8 measured by dielectric relaxation experiments at room temperature (298 5K) for a large number of polymers, was prepared. The test frequencies in the dataset ranged from 50 Hz to 10 MHz. 

The behavior for 50 Hz to 100 Hz was qualitatively different from the behavior for 1 kHz to 10 MHz. Inclusion of the degrees of freedom defined in Chapter 4 improved the quality of the fit for tan 8 measured at 50 Hz to 100 Hz. The more numerous the degrees of freedom (especially of the side groups) were, the more a polymer was able to dissipate energy in... 

Fig. 163. Storage modulus, G, and loss tangent, tan 8, measured at 1 Hz, vs temperature for a 40% solution of X7G in ra-cresol. Reproduced from Polymer [Ret 420] by the courtesy of the authors and Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington 0X51GB, UK...

The B-series of silica samples were also blended with rubber and the compound formulation is shown in Table 17.6. The uncured gums were then tested according to ISO 5794-2 1998. The uncured samples were tested using a Mooney viscometer and an RPA, which measures the dynamic mechanical properties as the samples cure. Figure 17.7 shows the results of these two tests for the Mooney viscosity at 100°C, storage modulus, loss modulus, and tan 8. 

Figure 6. Plot of tan 8 vs. temperature for plasma-polymerized ethane formed at 0.5 ton, 20 cmsSTP/min, 5 W, and KHz. Film thickness was 820 A. (9) Measured at 1 KHz and (X) measured at 10 KHz.

G is called the loss modulus. It arises from the out-of-phase components of y and T and is associated with viscous energy dissipation, ie, damping. The ratio of G" and G gives another measure of damping, the dissipation factor or loss tangent (often just called tan 8), which is the ratio of energy dissipated to energy stored (eq. 16). 

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described earlier, it can be operated as a forced-vibration instrument. It is fully computerized and automatically determines G y G"y and tan 8 as a function of temperature at low frequencies (10-5 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstructures of polymer blends (285) and latex films (286). 

The Rheometric Scientific RDAII dynamic analyzer is designed for characterization of polymer melts and solids in the form of rectangular bars. It makes computer-controlled measurements of dynamic shear viscosity, elastic modulus, loss modulus, tan 8, and linear thermal expansion coefficient over a temperature range of ambient to 600°C (—150°C optional) at frequencies 10-5 —500 rad/s. It is particularly useful for the characterization of materials that experience considerable changes in properties because of thermal transitions or chemical reactions. 

All three systems give similar tensile strength, elongation, and hardness properties. Hysteresis (heat buildup) measured by tan 8 shows an advantage for conventional and semi-EV systems and imaged fatigue follows the expected pattern. 

The tan 8 peak of a dmta thermogram provides a second measure of... 

The sophisticated oscillating die instruments can continue the measurement of dynamic properties after full cure has been reached. ASTM D6601124 covers measurements both during and after cure. A sealed cavity instrument is specified with amplitude 0.2° during cure and 1 to 100% strain after cure. In addition to the usual cure parameters, the in and out of phase moduli and tan 8 are reported. 

The term tan(8) is referred to as the loss tangent, a measure of the relative magnitude of the viscous to the elastic component, or the relative magnitude of lost to stored energy per cycle deformation. Predominately elastic (solid-like) material has a tan(S) <1 (G > G"), whereas a... 

The tan 8 loss curves obtained at 1 Hz for the PET blends with the DMT and TPDE additives [13] are shown in Fig. 23. In contrast to what happens in the dynamic mechanical experiments, the additives lead to only a small shift of the curves relative to the case of pure PET and to the same peak amplitude as for pure PET. Furthermore, the activation energies derived for the p peak obtained from dielectric measurements are the same as the ones for pure PET (Table 1) and the activation entropies are in the same range (Table 2). 

Figure 6.4 Decrease in the loss factor (tan 8) during cure, for the same epoxy-diamine system as that represented in Fig. 6.3, at different frequencies of the dynamic measurements. T] =70°C. (Matejka, 1991 - Copyright 2001 -Reprinted by permission of Springer-Verlag)... 

---