Tan delta

Energy loss under low frequency conditions is often used as a key factor for evaluating elastomer compositions. In this respect, the rolling resistance and skidding properties are usually evaluated by tan delta (tan 8) at 60°C and 0°C, where the 60°C value correlates with low frequency loss and 0°C correlates with skid resistance (high frequency loss). 

Figure 2.4. Dielectric constant and tan delta (average values 0.5 to 1.5GHz) of fluoromethylene cyanate esterresin series.

Table 2.4. Dielectric and Tan Delta Characterization of NCOCH2(CF2) OCNResins...

Figure 1 shows the 11 Hz modulus and loss tangent of monomer I cured for seven days at 280 C. (This was the standard cure cycle adopted during development of these resins). Three relaxation processes are evident as peaks in tan delta ... 

Dynamic mechanical testers apply a small sinusoidal stress or strain to a small sample of the polymer to be examined and measure resonant frequency and damping versus temperature and forced frequency. Instrument software computes dynamic storage modulus (G ), dynamic loss modulus (G") and tan delta or damping factor. Measurements over a wide range of frequency and temperature provide a fingerprint of the polymer with sensitivity highly superior to DSC. 

Cure Kinetics. The cure kinetics of the mixed system to the B-stage were determined by the method outlined by Senich, MacKnight and Schneider (7) for two epoxy resins cured with dicyandianide by dynamic spring analysis (DSA). Senich et al. (7) used the elapsed time to the loss peak maximum of tan delta as a measure of the rate of the reaction at each temperature and for each frequency. The slope of an Arrhenius plot of In (tmax) vs. 1/T was then used to determine the activation energy. 

Post C-Stage Cure (Dynamic). Samples that were C-stage cured at lAO C for 2 hours were scanned in the DMTA as a function of temperature (-100°C to 200 C). Raw data of tan delta and E vs. temperature at 30 Hz for the -5 and +5 wt.% samples is shown in Figure 10. 

Figure 10. Raw data of tan delta and E> vs. temperature for the 5 and, +5 wt.% epoxy/ratios ...

Becanse there are many factors involved in the dynamic mechanical compression of polyolefin foams, the Taguchi method was employed in a Perkin Elmer DM A7 dynamic mechanical analyser to establish a method to improve the measurement process. The signal-to-noise ratio was measured to determine how the variability could be improved. Control and noise factors were evaluated and levels chosen, with details being tabulated. Appendix A describes some of the factors. Tests were conducted on two closed cell foams. NA2006 foam is 48 kg/cu m LDPE and NEE3306 foam is 32 kg/cu m EVA. Different factors were shown to influence results for E and tan delta but an optimum combination is proposed for the simultaneous measurement of both properties. The results were less variable as frequency was increased. Small differences in the dynamic response of different materials should be measurable because of the low variability in the experimental results. 18 refs. 

Yu X, Yi B, Liu F et al. (2008) Prediction of the dielectric dissipation factor tan delta of polymers with an ANN model based on DFT calculation. React Fund Polym 68 1557-1562... 

Fig. 33 Friction coefficient (/ ) as a function of (a) tan delta at 25°C, (b) hardness, and (c) mean agglomerate size. Squares indicate PTFE-EPDM composites containing nonmodified PTFE and circles modified PTFE...

The current method of determining the energy properties of polyurethane is the Dynamic Thermal Mechanical Analyzer (DTMA). This instrument applies a cyclic stress/strain to a sample of polyurethane in a tension, compression, or twisting mode. The frequency of application can be adjusted. The sample is maintained in a temperature-controlled environment. The temperature is ramped up over the desired temperature range. The storage modulus of the polyurethane can be determined over the whole range of temperatures. Another important property closely related to the resilience, namely tan delta (8), can also be obtained. Tan (8) is defined in the simplest terms as the viscous modulus divided by the elastic modulus. 

In practice, a material that is "dead" will store much of the applied energy and has a low resilience and a relatively high tan delta. A material that returns much of the energy has a high resilience and a low tan delta. These properties have an influence on the grades used for shock absorbers, springs, bushes, or wheels. 

---