Tan delta curve

Figure 2 Storage modulus and tan delta curves [DMTA) for TPS, TPS-10%MF and TPS-18%MF. (Dual cantilever, 1 Hz)...

The temperature range between 80°C and 100°C that has been recommended [28] as safe surface temperatures for wood exposed for long periods is not valid for all adhesive types. Figure 12 shows the thermal behaviour of eleven typical adhesives used in the rehabilitation of timber structures. It can be seen that all adhesives exhibit a pronounced decrease in their stiffness with the increase in temperature. If one considers the temperatures these adhesives will have to withstand in service (usually up to 50°C), a very careful selection of the adhesive is necessary. Thus, the temperature of the adhesive joint in service must be below the safe working temperature precribed by the adhesive manufacturer, which should correspond to 10-20°C below the adhesive glass transition temperature (taken from the peak of the tan delta curve, which is the most prevalent criterion appearing in the literature and the most used by adhesive manufacturers) [29]. 

This information allowed the segmentation of the tan-delta curve of a tread compound run from —100 °C to +100 °C, into zones that characterized the tread compound performance in a tire. The tan-delta value in the region of the compound Tg will define its abrasion characteristics. Ice, snow, and wet traction properties can be predicted by the tan-delta values in the region of —20°C to 0°C, while rolling resistance is determined by tan-delta values in the region of - -60°C (Figure 4.3). 

An example of how polymer microstructure and polymer Tg impact performance is when vinyl-butadiene is increased from 10 to 50% in polybutadiene (Table 4.5) [8]. The glass transition temperature increases from —90 to —60 °C, with a corresponding shift in the tan-delta curve. Traction performance has improved significantly, but tread wear and rolling resistance rating drop. 

Figure 7.4 The storage modulus and tan delta curves of PP matrix and PP/KE biocomposites and nanobiocomposites. I. Na. Sim et al.

The first is a stairstep method where the sample temperature is raised in 5°C increments and allowed to equihhrate at each temperature for 3.5 minutes before performing the measurements. Since the sample thermocouple is typically 1 mm away from the face of the material, and the sample will have some thickness that may vary from 0.5—5 mm, this method is designed to overcome the problems associated with thermal lag between the measured temperature and the actual bulk temperature of the material. However, the method has the disadvantage of only providing a data point every 5°C. This may be adequate for instances where the objective of the test is an approximate storage modulus value, since interpolation is possible for applications where the temperature of interest falls between measurement points. However, for identifying exact transition temperatures, which appear as peaks in the loss modulus and tan delta curves, this method is less satisfactory than a continuous heating method. 

More recently, Class and Chu" extended the use of dynamic mechanical measurements to a systematic study of resin-elastomer blends which revealed the relationship between the structure, concentration and molecular weight of resins and their effect on the viscoelastic properties of elastomers. Dynamic mechanical data typical of that obtained from an elastomer or elastomer-resin blend is shown in Fig. 4. G is the elastic or storage modulus, G" is the viscous or loss modulus, and the ratio of G jG gives the tan 6 curve. The temperature at which the tan 6 curve shows a maximum corresponds to a dynamic glass transition temperature. Class and Chu showed that with these types of measurements, the effect of modifying resins on the viscoelastic properties of elastomers can be readily determined. Resins which are compatible with an elastomer will cause a decrease in the elastic modulus G at room temperature and an increase in the tan delta peak or glass transition temperature. Resins which are incompatible with an elastomer will cause an increase in the elastic modulus G at room temperature and will show two distinct maxima in the tan delta curve. 

DMA and generally Tg is determined as a maximum of tan delta curve and seen as a drop in storage modulus curve. 

TAN DELTA - Lower Curve STORAGE MODULUS - Upper Curve... 

Tan Delta n Mathematically expressed as the loss modulus divided by the storage modulus, the tangent of the phase angle between an applied stress and the strain response in a dynamic experiment. NOTE - Tan delta versus temperature curves are commonly reported in dynamic mechanical analysis (DMA) tests. 

Frequency scans are also useful. These are conducted at several temperatures and then via time-temperature superposition can be extrapolated to very low and high frequencies as was done in Fig. 15.8. This same type of data can be converted to a series of temperature scans at different frequencies as shown in Fig. 15.9. From this curve it can be determined that at a peel rate of about 100/s the adhesive will become zippery and the peel force will drop at room temperature (this occurs at approximately the frequency at which the material becomes glassy at the temperature of the peel test). Another common use of the frequency curve is to look at the ability of the adhesive to damp vibrations at various fi equencies. Tan delta is a direct measure of this capability. 

The glass transition temperature and the modulus of the cured matrix were measmed by dynamic mechanical analysis (DMA) in the single cantilever mode, at a frequency of IHz. DMA runs were reeorded with a DMA 2980 Dynamic Mechanical Analyzer from TA instruments. The glass transition temperature (Tg) was measured at the maximum of the Tan delta (5) curve dedueed from DMA experiments. Storage modulus of the matrix was determined at 40°C. 

Results obtained in thermal analysis tests as yet stated are summarized as follows if a QUANTITATIVE determination is requested it seems that DMA is more reliable than DSC, but when one deals with very high polymerization degrees both techniques give ambiguous results. As expected the Tg s determined by taking the onset of E curve follow the same trend as that determined by the maximum of the tan delta peak. 

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