Differential thermal analysis glass transition temperature determined using

The measurements of Young s modulus in dependence of the temperature (dynamic-mechanical measurements, see Sect. 2.3.5.2) and the differential thermal analysis (DTA or DSC) are the most frequently used methods for determination of the glass transition temperature. In Table 2.10 are listed and values for several amorphous and crystalline polymers. 

In DSC the measured energy differential corresponds to the heat content (enthalpy) or the specific heat of the sample. DSC is often used in conjunction with TA to determine if a reaction is endothermic, such as melting, vaporization and sublimation, or exothermic, such as oxidative degradation. It is also used to determine the glass transition temperature of polymers. Liquids and solids can be analyzed by both methods of thermal analysis. The sample size is usually limited to 10-20 mg. 

Many relatively slow or static methods have been used to measure Tg. These include techniques for determining the density or specific volume of the polymer as a function of temperature (cf. Fig. 11-1) as well as measurements of refractive index, elastic modulus, and other properties. Differential thermal analysis and differential scanning calorimetry are widely used for this purpose at present, with simple extrapolative eorrections for the effects of heating or cording rates on the observed values of Tg. These two methods reflect the changes in specific heat of the polymer at the glass-to-rubber transition. Dynamic mechanical measurements, which are described in Section 11.5, are also widely employed for locating Tg. 

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

Differential thermal analysis was used to delineate the glass forming regions in the Ge-Te system (Takamori et al (1970)) and the Ge-Te-As system (Savage (1971)). Myers and Felty (1967) and de Neufville (1972) have thermally determined the composition dependence of the glass transition temperature for several multicomponent chalcogenide glasses, from which they have obtained information on the chemistry and structure of these materials. 

Differential thermal analysis is widely used for determining exotherm and endotherm of reactive substances. It can also be used for determining transition temperatures, such as the glass transition temperature and the melt temperature of polymers (ASTM D3418). ASTM D472 provides directions for reporting thermoanalytical data. 

In addition to DSC, other instruments, such as differential thermal analysis (DTA) and electrical resistance analysis (ER), are also commonly used in determining the thermophysical properties of a lyophilized formulation, such as the glass transition temperature (T, the collapse temperature, etc. One of the examples using DTA and ER has been recently reported by... 

The more common techniques used to analyze thermosets and composites are thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which can determine the thermal properties and also the best conditions for application of the materials. These techniques can be apphed to polymers to determine their specific heat, degree of polymerization, flanunability, degradation, cure, glass transition temperature (Tg), and other characteristics. Analysis of composites should consider the behavior of each component, including the matrix, reinforcement, plasticizers and fire retardants. 

---