Determination of the glass transition temperature, Tg

However, care must be exercised in assuming that all chemical reactions behave this way, since the cure of an epoxy resin, for example, will affect the glass transition of the resin as the cross-linking reaction progresses and this causes a loss peak that will be frequency dependent. 

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A method that is frequently used because of its relative simplicity is the determination of the glass-transition temperature Tg of the blend, which can be determined by any of the methods discussed in chapter 7. DSC is often used. 

A further important data point within the initial assessment is the determination of the glass transition temperature (Tg). Different test methods are described in more detail in Section 12.5.2. For the first assessment, one method should be selected. When choosing the method, it is important to make sure that the test procedure is compatible with the material in test... 

The classic method for the experimental determination of the glass transition temperature is dilatometry. Thus, as briefly mentioned in Chapter 1, the temperature dependence of the specific volume is determined by a suitable technique, and the temperature at the change in slope upon cooling is taken as Tg. Such a plot is indicated in Figure 5-1, where it is shown that the Tg is... 

No effects of ion exchange temperature on oy and K,. were observed when this treatment was carried out between 430 and 510°C (Figure 12), which corresponded to a range between 75 and 89% of the glass transition temperature (Tg) of UST porcelain. This temperature (Tg), determined by differential thermal analysis, DTA (404S, Netzsch), at a heating rate of 5°C/min in... 

The strength of polymer-impregnated concrete is determined by the glass transition temperature, Tg, of the polymer. Above the Tg, the reinforcement is lost and the concrete is less resistant to salt penetration. 

As for the variation of the cooling rate, one can try to determine the chain length dependence of the glass transition temperature Tg by looking for the intersection point of the linear extrapolations from the liquid and the glassy region in a plot of the ratio T/Ti versus temperature. The result of this analysis from T, which is presented in Fig. 6.15, yields a linear relationship between the Tg and the inverse chain length as has been claimed by theory" and affirmed in many experiments. ... 

The above are all examples of transitions which are of first order. However, second-order transitions can also be followed and determine the position of the baseline in DSC. This leads to the calculation of heat capacity from DSC measurements and is the basis for the establishment of the glass transition temperature (Tg) in polymers. A further extension based on thermodynamic factors is purity determination based on the lowering of the freezing point caused by the presence of impurities. 

The relative apparent activation energy parameter (Ah/R) can be determined experimentally from the cooling rate (q) dependence of the glass transition temperature (Tg) or from the temperature dependence of the relaxation time as shown in Equation 2 ... 

Differential scanning calorimetry (DSC) is fast, sensitive, simple, and only needs a small amount of a sample, therefore it is widely used to analyze the system. For example, a polyester-based TPU, 892024TPU, made in our lab, was blended with a commercial PVC resin in different ratios. The glass transition temperature (Tg) values of these systems were determined by DSC and the results are shown in Table 1. 

The glass transition temperatures (Tg) of both modified and unmodified PSs were determined by DSC analysis, and thermomechanic analysis was controlled by TMK. The results are given in Table 8. It is seen from Table 8 that the highest glass transition temperature (410 K) was obtained with chlorohydrinated PS and that of the lowest (370 K) with olefinic PS. The lowest glass transition temperature in the alkenylated PS caused to elasticity properties on polybutadien and polyisopren fragments. 

The method (27) can best be explained with reference to Figure 2. After stretching to 10, the force f is measured as a function of time. The strain is kept constant throughout the entire experiment. At a certain time, the sample is quenched to a temperature well below the glass-transition temperature, Tg, and cross-linked. Then the temperature is raised to the relaxation temperature, and the equilibrium force is determined. A direct comparison of the equilibrium force to the non-equilibrium stress-relaxation force can then be made. The experimental set-up is shown in Figure 4. 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

A major peak at 280°C matches exactly the glass transition temperature (Tg) determined by DSC. It corresponds with a drop of several orders of magnitude in Young s modulus,... 

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